CLS_ResearchReport_2014_WEB

Canadian Light Source Inc.
Research Report2014
www.lightsource.ca

Canadian Light Source Research Report 2014
Editor: Victoria Martinez
ISBN 978-0-9783761-5-4
© 2014 Canadian Light Source Inc. All rights reserved.
Canadian Light Source, Inc.
44 Innovation Boulevard
Saskatoon, SK, Canada S7N 2V3
Telephone: +1-306-657-3500
Fax: +1-306-657-3535
E-mail: cls@lightsource.ca
www.lightsource.ca
Layout and Cover Design: Reach Communications

2 0 1 4 r e s e a r c h R e p o r t 1
Table of Contents
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Message from the CEO . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2014 Year in Review Timeline . . . . . . . . . . . . . . . . . . . . . 4
Chemical & Materials
1 Impact of the selenolate ligand on the bonding
properties of Au25 nanoclusters . . . . . . . . . . . . . . . . . . 8
2 Aluminum-phosphate binder formation in zeolites
as probed with X-ray absorption microscopy . . . . . . . . .11
3 The metallic nature of epitaxial silicene
monolayers on Ag(111) . . . . . . . . . . . . . . . . . . . . . . .14
4 Sudden reversal in the pressure dependence
of Tc in the iron-based superconductor CsFe2As2:
A possible link between inelastic scattering
and pairing symmetry . . . . . . . . . . . . . . . . . . . . . . . 17
5 Pursuit of quantum monodromy in the far-infrared
and mid-infrared spectra of NCNCS using
synchrotron radiation . . . . . . . . . . . . . . . . . . . . . . . .20
Instrumentation Techniques
1 Development of a bent Laue beam-expanding
double-crystal monochromator for biomedical
X-ray imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Life Sciences
1 Crystal structures of wild type and disease
mutant forms of the ryanodine receptor
SPRY2 domain . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2 Modification and periplasmic translocation
of the biofilm exopolysaccharide
poly-β-1,6-N-acetyl-D-glucosamine . . . . . . . . . . . . . 29
Earth Environmental
1 Arsenic speciation in newberyite (MgHPO4•3H2O)
determined by synchrotron X-ray absorption
and electron paramagnetic resonance
spectroscopies: Implications for the fate
of arsenic in green fertilizers . . . . . . . . . . . . . . . . . . 32
2 Nitrogen input quality changes the biochemical
composition of soil organic matter stabilized
in the fine fraction: a long-term study . . . . . . . . . . . . 35
CLS Innovations
Industrial Science Update . . . . . . . . . . . . . . . . . . . . . . . 38
Saving lives with light: The Medical Isotopes Project . . . . . . 40
Students On the Beamline . . . . . . . . . . . . . . . . . . . . . . . 42
Bancroft Award Winner:
Riccardo Comin’s High-Tc Superconductivity Insight . . . . . . . 44
Beamlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Photon Port Allocation . . . . . . . . . . . . . . . . . . . . . . . . . 48
Facts and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2014 Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
50 Years of Accelerator Science . . . . . . . . . . . . . . . . . . . 61

C a n a d i a n L i g h t S o u r c e2
Acknowledgements
Funding Partners
The Canadian Light Source thanks all of our funding partners for their commitment to the advancement of science
and technology.
Canadian User universities
Operating
Capital
RMC CMR

Message from the CEO
This year’s Research Report showcases the depth and breadth
of scientific exploration and discovery taking place at the CLS.
Included are 10 of this year’s most significant and exciting
publications spanning a range of areas. In health sciences there
have been breakthroughs in the investigation of genetic heart
conditions and bacterial biofilms. There have been exciting
new results in materials science involving 2-dimensional silicon,
high temperature superconductors and gold nanoparticles.
New discoveries about arsenic in green fertilizers and nitrogen
in soils show the growth of work in the environmental sector.
These results, along with chemical studies of novel catalysts and
the fundamental behaviour of large organic molecules, make
it clear that the CLS continues to grow scientifically. Significant
technical innovation continues with enhancement of our imaging
capabilities, and in a world first the CLS has developed a beam
expander that turns short beamlines into virtual long ones.
Of course, a report like this one cannot include every 2014
science highlight. After all, over 250 publications using CLS data
came out this year alone. A more detailed overview of these
stories can be found on our website. These include studies of
embryonic teeth, African sleeping sickness and cystic fibrosis;
investigations of innovative materials such as graphene,
nanogold and carbon nanotubes; a unique study of a Siberian
Bronze Age skull; and a celebration of the 500th protein structure
deposited into the Protein Data Bank from the CMCF beamlines.
Great science breeds ideas, innovations and unanticipated
impacts. Within these pages, you will also find updates from
two of our landmark innovations in synchrotron science: the
world-leading industrial science program, and the Medical
Isotope Project (MIP). Working with customers in the mining, oil
and gas, pharmaceutical, and aerospace sectors, we have made
advancements in tracking environmental effects, innovative and
efficient methods for oil extraction, and providing essential data
for products and drug development.
The MIP facility commenced production in November 2014. It is
the world’s first electron linear accelerator facility dedicated to
the production of medical radioisotopes. Mo-99, the precursor to
the important medical isotope Tc-99m, is now being shipped to
the Prairie Isotope Production Enterprise.
None of this would be possible without the commitment of our
partners and the passion of our community, our employees and
our users.
As we turn the corner into a new decade of science, we are
reconnecting with our local communities, reengaging our
users, renewing our commitment to our vision and mission,
and refocusing our operations to ensure maximum impact and
output. Together with our funding partners, users, customers and
local communities, we will ensure a very bright future for all.
2015 will be an even bigger, brighter and better year!
Rob Lamb
CEO
2 0 1 4 r e s e a r c h R e p o r t 3

An exhibit of stunning
imagery from CMCF is featured
at the Saskatoon Mendel
Art Gallery LUGO 2014, in
conjunction with the United
Nations Educational, Scientific
and Cultural Organization
(UNESCO) launch ofTheYear of
Crystallography.
The CLS welcomes Huan-
hua Wang from the
Institute of High Energy
Physics at the Chinese
Academy of Sciences for
a six-month visit.Wang
brings many years of
experience as a research scientist developing
and operating beamlines at the Beijing
Synchrotron Radiation Facility. During his
visit he will participate in beamline capability
development on theVESPERS beamline.
The CLS is a key partner in the Consortium
for Research and Innovation in Aerospace
in Quebec’s (CRIAQ) 100th project, entitled
Additive ManufacturingTechnologies
for Aerospace Components, which aims
to generate knowledge about design,
transformation and high-strength aluminum
alloy properties for additive manufacturing of
aerospace components.
The CLS says farewell to Josef
Hormes (right) who served as
executive director for five and a half
years. Dr. Hormes leaves to pursue
his research interests and to spend
more time with family, splitting
his time between Germany and
Louisiana. Mark de Jong (left), CLS
director of accelerators, assumes
the role of acting executive director.
SGM Beamline Scientist Tom Regier
(left) is named one of CBC Saskatchewan’s
Future 40. UnderTom’s leadership, his
beamline has been one of the most
successful at the CLS and is recognized as
one of the best in the world.
The Honourable Rob Norris,
Saskatchewan Advanced Education
Ministerand the Government of
Saskatchewan announce continued
investment in health and life science
research, with direct benefits to the
research capabilities of the BioXAS
beamline.
University of Saskatchewan graduate student Michael
Greschner joins the CLS in the area of condensed matter
physics. Michael completed his undergraduate courses at
Queen’s University and the University ofVictoria and originally
hails from New Brunswick.
Rajivsingh (Kiran) Mundboth begins his work as a
postdoctoral fellow onVESPERS to study enhanced X-ray
micro-diffraction capabilities. He obtained his PhD degree from
Université Joseph Fourier in Grenoble, France and previously
worked at Diamond Light Source as a Research Associate in
the Optics Group. Kiran recently relocated to Saskatoon from
Mauritius.
Adam Gillespie joins the CLS as a research
associate in soil chemistry with SGM, with
a focus on developing and applying XANES
for the characterization of soil samples.
Adam completed his PhD at the University
of Saskatchewan and has been working in
Ottawa for Agriculture and Agri-Food Canada
as an NSERCVisiting Fellow.
University of Saskatchewan graduate
student Samira Sumaila joins the CLS
in green mining. Samira obtained her
degree in Environmental Science in Ghana
before starting her Master’s degree in
Urban Environmental Engineering at École
Centrale de Nantes in France.
The Honourable Michelle Rempel,
Minister of State responsible forWestern
Economic Diversification Canada, visits
the CLS January 15 to learn more about
synchrotron research and the ongoing
Medical Isotope Project.
JANUARY FEBRUARY MARCH
2014 Timeline
Research associate Adam Leontowich works to
implement the detailed design of a new cryo-
cooled scanning transmission X-ray microscope
(STXM) for the SM beamline upgrade project.
This microscope will allow CLS users to study a
wider range of materials, especially biological,
medical and other soft matter through
spectromicroscopy and spectro-tomography
techniques on cryogenically cooled samples.
Year in Review

The 2013 G. Michael Bancroft PhDThesis Award,
for the strongest published PhD work using CLS
data, presented to University of British Columbia
student Riccardo Comin. Comin uses the REIXS
beamline to study correlated oxide materials and
high-temperature superconductors.
Kee Eun Lee joins the
SXRMB beamline team
where she develops
new synchrotron
techniques related to
the characterization of
nanostructured catalysts
under in situ conditions. Kee Eun held a
postdoctoral position at the Department of
Chemistry at the University of Saskatchewan
prior to joining the CLS at the beginning of
March. Kee Eun obtained her PhD in materials
engineering at McGill University and her MSc.
in inorganic chemistry at Sogang University in
Seoul, Korea.
Theory Day, April 11, is a chance for staff and
users to showcase innovative techniques and
new research, like the work presented by HXMA
beamline scientist, Ning Chen.
On June 3, the CLS signs a
memorandum of understanding with
Mitacs, a national, not-for-profit
organization that brings together
academia, industry and the public
sector to develop cutting edge tools
and technologies vital to Canada’s knowledge-based economy.
The Application of Synchrotron Imaging for
Crop ImprovementWorkshop, held in Saskatoon
June 10-12, explores the application of
synchrotron light to imaging plants to support
the selection and development of superior crop
lines.The workshop looks at ways plants can be
structurally and functionally imaged, in vivo to in situ, and applying
this information to aid in the development and selection of higher
yielding crop varieties.
The CLS community thanks Dr. Walter
Davidson, Chair of the Board of
Directors, 2010-2014, for his service
and dedication to promoting scientific
research in Canada.
A beautiful sculpture by renowned artist and University of
Saskatchewan Professor Emeritus Eli Bornstein is reinstalled on the
CLS grounds.This work was designed so its appearance would change
in response to daily shifts in sunlight and shadow, as well as seasonal
variations.
The CLS is welcomes Peter Blanchard,
industrial science research associate. Peter
joins the CLS after returning to Canada from
Australia where he held a postdoctoral research
associate position at the University of Sydney.
Peter obtained his PhD in chemistry from the
University of Alberta and did his undergraduate studies at Memorial
University in Newfoundland. In addition to supporting industrial
research clients, Peter will be working on a collaborative project with
Andrew Grosvenor from the University of Saskatchewan and AREVA
Resources Canada Inc. to improve understanding of the long term
disposal of mill tailings, important in future mine site reclamation.
CLS Annual Users’Meeting takes place May 1-2
on the University of Saskatchewan campus with
keynote speaker Adam Hitchcock, professor of
materials research at McMaster University.
Toby Bond joins the CLS as
the new industrial science
associate.Toby obtained his
chemistry degree from the
University of Saskatchewan
before heading off to
Dalhousie University for his
MSc.Toby returned to Saskatoon in October 2012
and was working as an Analytical Chemist for
the Saskatchewan Isotope Laboratory before
joining the CLS.
Saroj Kumar joins the
CLS as theTHRUST Mid-IR
Postdoctoral Fellow. Saroj
joined the Mid-IR team from
the Laboratory for Structure
and Function of Biological
Membranes where he was
a Postdoctoral Fellow at the Université Libre de
Bruxelles in Brussels, Belgium.
The 2014 User Advisory Committee User Support
Award is given to BMIT Staff Scientist George
Belev (right).
Installation and
testing begins
on the new
QMSC beamline
monochromator.
APRIL JUNEMAY
2 0 1 4 r e s e a r c h R e p o r t
T I M E L I N E
5

JULY AUGUST SEPTEMBER
The new Chair andVice Chair for the User's Advisory Committee
(2014-15) are, respectively, Andrew Grosvenor (University
of Saskatchewan, right) and Jeff Warner (Cameco Corp., not
pictured). Both terms begin Sept. 1. Rob Scott (University of
Saskatchewan), Robert McKellar (National Research Council),
and Aimy Bazylak (University ofToronto) have been elected
to the UAC to serve three-year terms beginning in September.
Mercedes Martinson (U of S) has been elected as a student
member, serving a two-year term.The following regular
members' terms ended August 2014: Ken Burch (Boston
College), Kirk Michaelian (Natural Resources Canada), and
Jennifer van Wijngaarden (University of Manitoba).The UAC
and CLS thank these individuals for their service to the user
community and their work on behalf of the facility.
Jarvis Stobbs joins the
experimental facilities
division as a science
associate, experimental
floor. Jarvis relocated
to Saskatoon from
Estevan, SK, where he
was completing a work term for his chemical
technology diploma at the Boundary Dam
power station.
Our new BMIT ID line during testing.The
glowing window show the X-ray beam passing
through a carbon window to remove soft
X-rays.
Robert Lamb joins the CLS as the new CEO and
executive director. Rob has been a light source
user in Europe, the U.S. and Asia for over 25
years. He was also the founding director of the
Australian Light Source. Educated at Melbourne
and Cambridge Universities, Rob has held academic
appointments in England, Germany, the United
States, Hong Kong and Australia, as well as senior
administrative positions in both university and
government.
The CLS is honoured to host former Saskatchewan
Premier Lorne Calvert and former Canadian
Prime Minister Paul Martin, with CEO Robert
Lamb and Saskatchewan MLA Rob Norris.
The CLS is on display at Nuit Blanche Saskatoon
Sept. 27. Using images and sound recording from
several beamlines, the installation shows the
audience some of the outstanding research at
the CLS.
Saskatchewan Advanced Education Minister, the
Honourable Kevin Doherty, holds a medical isotope
sample cartridge during a visit to the CLS.
2014 TimelineYear in Review

R e s e a r c h H i g h l i g h t s
OCTOBER DECEMBERNOVEMBER
T i m e l i n e
On Oct. 18 the CLS opened its doors to the public
to showcase health research using synchrotron
technology.The event was hosted by the CIHR-
THUST program at the University of Saskatchewan
and was supported by CLS staff and scientists.
In order to work
together and coordinate
our efforts as a facility,
the energy storage
working group was
formed to encourage
inter-beamline discussion and collaboration in
this area.Their inaugural meeting was held on
Nov. 14 and was attended by 15 participants
from all around the CLS.
BioXAS beamteam leaders Graham George, U of S Professor
and Canada Research Chair in X-ray Absorption Spectroscopy
and Ingrid Pickering, University of Saskatchewan Professor,
and Canada Research Chair in Molecular Environmental Science,
announce the first data collected on the beamline, Dec. 19.
Scott Rosendahl joins
the CLS as the Mid-IR staff
scientist. Scott is a familiar
face around the CLS, having
assisted the Mid-IR beamline
as a technical assistant for the
past four years while working
towards his PhD. In 2013, he received his PhD in
chemistry from the University of Saskatchewan.
MP Kelly Block and the Honourable Jeremy
Harrison, Saskatchewan Minister for Innovation,
join CLS scientists to announce the first shipment
of medical isotopes produced in its dedicated linear
accelerator Nov. 14.The Medical Isotope Project
(MIP) facility at the CLS is the first of its kind in
the world, relying on powerful X-rays to produce
isotopes, unlike traditional nuclear reactor-based
methods. Natural Resources Canada’s Isotope
Technology Acceleration Program (ITAP ) and the
Government of Saskatchewan funded the project.
NSERC President
Mario Pinto (r)
arriving safe and
sound Nov. 28.,
despite the weather,
to meet with CEO
Rob Lamb.
The CLS celebrates the 10-year anniversary of the
official grand opening (Oct. 22, 2004). After five
and a half years of construction and $174-million
invested, the switch was flipped and science in
Canada would never be the same again.
CMCF announces the successful solution of 500
protein structures using the CLS.The 3-dimensional
structures of proteins can be determined using
powerful synchrotron X-ray light, and these structure
models are deposited in the Protein Data Bank—a
worldwide repository describing and showcasing
proteins and other biological macromolecules.
Many of these structures have been critical to the
publication of 286 peer-reviewed journal articles.
The undulator for our new QMSC photoemission beamline moves
into the magnet mapping room where the machine will be
calibrated before being moved into the storage ring.
2 0 1 4 r e s e a r c h R e p o r t 7

PRINCIPAL CONTACT:
PengZhang
AssociateProfessor
DepartmentofChemistryandthe
SchoolofBiomedicalEngineering
DalhousieUniversity
peng.zhang@dal.ca
902-494-3323
Journal/Principal
publication:
JournalofPhysicalChemistryC,
August212014,Issue37,Volume
118,pp.21730-21737.DOI:dx.doi.
org/10.1021/jp508419p
Authors:
DanielM.Chevrier
DepartmentofChemistry
DalhousieUniversity
XiangmingMeng
AnhuiUniversity
Dr.QingTang
UniversityofCaliforniaRiverside
Dr.De-enJiang
UniversityofCaliforniaRiverside
Dr.ManzhouZhu
AnhuiUniversity
Dr.AmaresChatt
DalhousieUniversity
Dr.PengZhang
DepartmentofChemistryandthe
SchoolofBiomedicalEngineering
DalhousieUniversity
Impact of the selenolate ligand on the
bonding properties of Au25 nanoclusters
Introduction
Research on thiolate-protected gold nanoclusters
(thiolate-Au NCs) has made a profound
impact on our understanding of thiolate-Au
nanomaterial structure and properties [1, 2].
Since the determination of its total structure [3,
4], the Au25(SR)18 NC has served as an excellent
model system to elucidate more refined details on
luminescence [5], heteroatom doping [6, 7], and
catalytic activity [8, 9]. Continuing to correlate such
properties with the total structure of Au25(SR)18
NCs is an important steppingstone for exposing
the potential thiolate-Au NCs hold for applications
in such areas as catalysis and biomedical-related
technologies.Atomically precise selenolate-
protected gold nanoclusters (selenolate-Au NCs
or Aun(SeR)m) have recently surfaced in this field
of Au NC research. Earlier studies have pursued
selenium-based ligands for the protection of larger
Au NPs to improve the stability or to investigate the
surface structure of selenolate-Au nanomaterials
[10-12]. In particular, the Au-Se bond is expected
to be more covalent in nature than the Au-S bond
because of the larger covalent radius of Se and
the almost identical electronegativities of Se and
Au. Exchanging the thiolate ligands for selenolate
ligands could therefore enhance the stability of Au
NCs.
Science
Phenylethanethiolate-protected Au25
(Au25(SC2H4Ph)18) and benzeneselenolate-
protected Au25 (Au25(SePh)18) NCs studied herein
were synthesized according to a modified Brust
two-phase method and a previously published
ligand-exchange protocol, respectively [13]. Both
Au25(SeR)18 and Au25(SR)18 were synthesized in the
anionic state (counterion: [N(C8H17)4]+
) and were
thoroughly characterized to confirm the chemical
composition [13].Au L3- and Se K-edge X-ray
absorption spectroscopy (XAS) measurements were
collected in transmission mode at the PNC/XSD
beamline of the Advanced Photon Source (Argonne
National Laboratory,Argonne, IL, USA) using a
Si(111) monochromator and a rhodium mirror.
Powdered samples of Au25(SR)18 and Au25(SeR)18
were packed into kapton film pouches, sealed,
and folded until an ample absorption edge jump
(Δµ0~0.5) was obtained. Multiple measurements
were collected for each XAS experiment to ensure
reproducibility of fine structure oscillations.Au
foil or Se mesh reference materials were measured
simultaneously with the Au25 NC sample for
calibration of the absorption edge energy (11.919
and 12.658 keV for Au and Se, respectively).
Measurements were conducted at 300 K under
ambient conditions and at 50 K using a helium-
cooled cryostat chamber.
Figure 1 (a) displays the Au L3-edge EXAFS
oscillations at 50 K in k-space for Au25(SeR)18 along
with Au25(SR)18 for direct comparison of the Au
local structure. By comparing the k-space spectra,
it is evident that exchanging the thiolate for the
selenolate ligand dramatically changes fine structure
oscillations in the early k-space region (2-6 Å−1
) due
to Au−Se bonding. The late k-space oscillations (8-
13 Å−1
) also increase in intensity, possibly from more
tightly ordered Au−Au bonding. For the Fourier
transform (FT) to radial space (R-space) (shown in
Figure 1 (b)), a k-space region from 3-13 Å−1
was
used for both samples to allow the incorporation
of multiple scattering shells with enough spatial
resolution to distinguish different Au−Au scattering
paths (ΔR=~0.2 Å, the approximate difference
between core and surface Au−Au bond lengths).
A detailed multishell Au L3-edge EXAFS fitting
analysis was conducted following a similar data
treatment protocol to our previous work on
phenylethanethiolate-protected Au19(SR)13 and
Au25(SR)18 NCs [14, 15]. Four scattering shells
were used to fit Au L3-edge EXAFS along with two
shells to fit the Se K-edge EXAFS. Together, this
offers a site-specific investigation of Se−C,Au−Se
(from both edges),Au−Au core (Au−Au1),Au−Au
surface (Au−Au2), and Au−Au aurophilic (Au−Au3)
environments.
Discussion
The effect of temperature on the ligand shell of
Au25(SeR)18 NCs was first investigated from the Se
K-edge perspective. EXAFS fitting of the R-space
spectrum, as shown in Figure 1 (d), indicates the
Se−Au bonding at 300 K is almost identical to 50
K. Se−C bonding, on the other hand, increases in
length by 0.08 Å, from 1.87(3) to 1.95(2)Å, when
1 Chemical AND Materials science

2 0 1 4 r e s e a r c h R e p o r t 9
the temperature rises to 300 K (depicted in
Figure 2). Lengthening of the Se−C bond
at higher temperature could be related to
a previous stability study on Au25(SeR)18
NCs that found Se−C bonds to be weaker
than S−C bonds under high temperature
treatment [16].
Multishell EXAFS fitting of the Au L3-edge
spectra (Figure 1 (c)) indicates a very small
decrease in Au−Se bonding (similar to Se
K-edge results) at the higher temperature.
A dramatic thermal contraction of all three
Au−Au shells is observed (plotted in Figure
2), where Au–Au1 decreases from 2.775(9)
Å to 2.70(1)Å, Au–Au2 from 2.98(1)Å to
2.87(2)Å, and Au–Au3 from 3.60(3)Å to
3.45(4)Å. This is contrary to our previous
EXAFS temperature-dependent study on
Au25(SR)18 NCs15
(and reproduced with
the Au25(SR)18 sample in this work), where
Au-thiolate and Au−Au core interactions
slightly increase with temperature and
aurophilic interactions remain similar
in average distance. We hypothesize that
since the average Au–Se bond length
does not decrease at the higher measured
temperature, contraction of aurophilic
bonding on the surface must originate
from a change in the Ausurface–Se–Austaple
bond angle to bring staple and surface Au
atoms closer together, accounting for the
decrease found in the Au−Au3 distance.
To confirm this hypothesis of aurophilic-
induced thermal contraction, we performed
first-principles molecular dynamics
(MD) simulation based on DFT (details
reported in original publication). Starting
with the DFT-optimized structure of the
Au25(SePh)18 NC (that is at 0 K) shown in
Figure 3, we heated up the cluster to 300
K in the MD simulation to investigate our
proposed mechanism of negative thermal
expansion. Figure 3 displays the isolated
dimeric staple unit and surface environment
of Au25(SePh)18 from optimized DFT
structures at each temperature along with
the average bond angles for each structure.
Consistent with our proposal, the angle
between Ausurface–Se–Austaple (indicated as
(i)) becomes more acute at 300 K by ca.
7° and is as small as 70.4° (smallest angle
for 0 K was found to be 78.1°).Along with
this, the Austaple–Se–Austaple angle (indicated as
(ii)) becomes more obtuse at 300 K by ca. 2°
which helps to bring the staple Au closer to
the Au13 surface.
Figure 1. Au L3-edge (a) k-space spectra and (b) FT R-space spectra of Au25(SR)18 and Au25(SeR)18 NCs
measured at 50 K. (c) Au L3-edge and (d) Se K-edge multi-shell EXAFS fit of Au25(SeR)18 NCs at different
temperatures.
Figure 2. Temperature-dependent plots of (a) Au25(SeR)18 site-specific bond distances (models and
circled regions correspond to the bond type).

Conclusion
To summarize, selenolate-protected Au25
NCs were studied with a detailed site-
specific, multishell EXAFS analysis from
both Au and Se perspectives at varied
temperatures. Significantly longer aurophilic
interactions from staple Au to surface Au
sites were identified for Au25(SeR)18 which
become shorter with increasing temperature,
inducing a contraction of the entire Au−Au
framework in Au25. Temperature-dependent
structural changes were also observable
from Au and Se electronic properties
(details reported in original publication),
providing further evidence of the Au−Au
framework contraction. These experimental
findings are consistent with results from
MD-DFT structural modeling and ab initio
simulations of X-ray spectra. This work
brings to light the remarkable bonding
behaviour of Au25 nanoclusters induced
by the selenolate ligand and implies that
the selenolate-protected Au NCs behave
differently from their thiolate counterparts
in the context of aurophilic bonding.
References
[1] Jin, R. Quantum sized, thiolate-protected gold
nanoclusters. (2010). Nanoscale 2, 343-362.
[2] Jiang, D. (2013). The expanding universe of thiolated
gold nanoclusters and beyond. Nanoscale 5, 7149-7160.
[3] Heaven, M. W.; Dass, A.; White, P. S.; Holt, K. M.;
Murray, R. W. (2008). Crystal structure of the gold
nanoparticle [N(C8H17)4][Au25(SCH2CH2Ph)18]. J. Am.
Chem. Soc. 130, 3754-3755.
[4] Zhu, M.; Aikens, C. M.; Hollander, F. J.; Schatz, G. C.;
Jin, R. (2008). Correlating the crystal structure of a thiol-
protected Au25 cluster and optical properties. J. Am.
Chem. Soc. 130, 5883-5885.
[5] Wu, Z.; Jin, R.(2010). On the ligand’s role in the
fluorescence of gold nanoclusters. Nano Lett. 10, 2568-
2573.
[6] Kumara, C.; Aikens, C. M.; Dass, A. (2014). X-ray
crystal structure and theoretical analysis of Au25-
xAgx(SCH2CH2Ph)18- alloy. J. Phys. Chem. Lett. 5, 461-
466.
[7] Gottlieb, E.; Qian, H.; Jin, R. (2013). Atomic-level
alloying and de-alloying in doped gold nanoparticles.
Chemistry. 19, 4238-4243.
[8] Zhu, Y.; Qian, H.; Jin, R. (2011). Catalysis
opportunities of atomically precise gold nanoclusters.
J. Mater. Chem. 21, 6793-6799.
[9] Shivhare, A.; Ambrose, S. J.; Zhang, H.; Purves, R.
W.; Scott, R. W. J. (2013). Stable and Recyclable Au25
Clusters for the Reduction of 4-Nitrophenol. Chem.
Commun. (Camb). 49, 276-278.
[10] Yee, C. K.; Ulman, A.; Ruiz, J. D.; Parikh, A.; White, H.;
Rafailovich, (2013). M. Alkyl selenide- and alkyl thiolate-
functionalized gold nanoparticles: Chain packing and
bond nature. Langmuir. 19, 9450-9458.
[11] Zelakiewicz, B. S.; Yonezawa, T.; Tong, Y. (2004).
Observation of selenium-77 nuclear magnetic
resonance in octaneselenol-protected gold
nanoparticles. J. Am. Chem. Soc. 126, 8112-8113.
[12] Li, Y.; Zaluzhna, O.; Xu, B.; Gao, Y.; (2011). Modest,
J. M.; Tong, Y. J. Mechanistic insights into the Brust-
Schiffrin two-phase synthesis of organo-chalcogenate-
protected metal Nanoparticles. J. Am. Chem. Soc. 133,
2092-2095.
[13] Meng, X.; Xu, Q.; Wang, S.; Zhu, M. (2012). Ligand-
exchange synthesis of selenophenolate-capped Au25
nanoclusters. Nanoscale. 4, 4161-4165.
(14) Chevrier, D. M.; Macdonald, M. A.; Chatt, A.; Zhang,
P.; Wu, Z.; Jin, R. (2012). Sensitivity of Structural and
Electronic Properties of Gold−Thiolate Nanoclusters to
the Atomic Composition : A Comparative X-ray Study
of Au19(SR)13 and Au25(SR)18. J. Phys. Chem. C. 116,
25137-25142.
Figure 3. MD-DFT simulated structure of the Au25(SePh)18 NC. A typical structural change of the dimeric motif in the Au25(SePh)18 NC
from 0 K (after DFT geometry optimization) (bottom left) to 300 K (after heating up in DFT-based MD simulation) (bottom right) with
average bond angles.
(15) Macdonald, M. A.; Chevrier, D. M.; Zhang, P.;
Qian, H.; Jin, R. (2011). The Structure and Bonding of
Au25(SR)18 Nanoclusters from EXAFS: The Interplay of
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15282-15287.
(16) Kurashige, W.; Yamaguchi, M.; Nobusada, K.;
Negishi, Y. (2012). Ligand-Induced Stability of Gold
Nanoclusters: Thiolate versus Selenolate. J. Phys. Chem.
Lett. 3, 2649-2652.
Acknowledgements
P.Z. acknowledges funding support from Dalhousie
University and NSERC in the form of discovery
grants. PNC/XSD facilities at the Advanced Photon
Source (APS) (Argonne National Laboratory) and
research at these facilities are supported by the U.S.
Department of Energy − Basic Energy Sciences, a Major
Resources Support grant from NSERC, the University
of Washington, the CLS and the APS. Use of the APS
and Office of Science User Facility operated for the U.S.
Department of Energy Office of Science by Argonne
National Laboratory, was supported by the U.S. DOE
under Contract No. DE-AC02-06CH11357. The authors
are thankful for the technical assistance provided by Dr.
Robert Gordon at PNC/XSD facilities. D.J. would like to
acknowledge the DFT-MD simulation support by the
University of California, Riverside Startup Fund.
Beamline information
Au L3-edge and Se K-edge XAFS data were collected in
transmission mode using gas ionization chambers at
PNC/XSD facilities (Sector 20-BM), Advanced Photon
Source, Argonne National Laboratory, IL, USA.

2 0 1 4 r e s e a r c h R e p o r t 11
PRINCIPAL CONTACT:
Prof.Dr.Ir.BertM.Weckhuysen
InorganicChemistryand
CatalysisGroup
UtrechtUniversity
b.m.weckhuysen@uu.nl
+3130-253-4328
Journal/Principal
publication:
JournaloftheAmericanChemical
Society,November21,2014,Issue51,
Volume136,pp.17774-17787.DOI:
10.1021/ja508545m
Authors:
HendrikE.vanderBij1
DimitrijeCicmil1
JianWang2
FlorianMeirer1
FrankM.F.deGroot1
BertM.Weckhuysen1
1
InorganicChemistryand
CatalysisGroup
UtrechtUniversity
2
CanadianLightSource
Aluminum-phosphate binder formation in
zeolites as probed with X-ray absorption
microscopy
Introduction
Catalysis performed over the crystalline
microporous alumino-silicates known as zeolites is
of enormous importance to the oil and gas industry,
as their use saves billions of dollars in process and
energy costs [1]. Due to their wide and valuable
application range in catalytic cracking and potential
use in catalytic fast pyrolysis of biomass, (bio-)
alcohol dehydration and (bio-) alcohol conversion
to hydrocarbons, there is a great academic interest
in zeolites as heterogeneous catalysts [2-5].As
was recently pointed out in two reviews, academic
research has focused mainly on the performance of
pure zeolite materials. However, the application of
binders and matrices used in industrially relevant
catalyst bodies to increase mechanical strength and
attrition resistance also exert huge influences on
performance [6,7].
One such interaction between binder and zeolite is
with the addition of aluminum-phosphate (AlPO4).
Especially in the field of catalytic hydrocarbon
cracking, the addition of AlPO4 to zeolites, often in
combination with a zeolite phosphatation step, leads
to an enhanced light olefin selectivity, hydrothermal
stabilization, improved mechanical strength,
and attrition resistance [8-12]. Furthermore,
it has been shown that AlPO4 can form from
a zeolite’s own aluminum supply by applying
a dealumination and subsequent phosphorus
modification (phosphatation) step [13-17]. By
combining chemical imaging at the SM beamline
at the CLS with bulk characterization techniques,
it was possible to study the formation of an AlPO4
phase in three different industrially relevant zeolites
(H-USY, H-mordenite and H-ferrierite). X-ray
tomography was used to visualize, for the first time,
a 3-dimensional nanoscale chemical reconstruction
of the AlPO4 phase in a single H-mordenite
aggregate.
Science
An amorphous AlPO4 phase was synthesized in
H-mordenite by applying a pre-steam treatment,
followed by the addition of phosphoric acid. In situ
Scanning Transmission X-ray Microscopy (STXM)
was then carried out to follow the crystallization of
the AlPO4 phase during heating (Figure 1) using the
peak at 1570.4 eV in the recorded X-ray absorption
near edge structure (XANES) as an indicator for the
annealing of the amorphous AlPO4 into the more
crystalline AlPO4 structures. The 2-dimensional
chemical maps also suggest that the AlPO4 is
present on the external surface of the zeolite
indicated by the fact that the concentrations of Si
(gray intensities) and Al (coloured intensities) show
no significant spatial correlation. This observation
was further studied by soft X-ray tomography,
visualizing morphology and chemical nature of a
single zeolite particle (Figure 2). The results revealed
that the particle (AlPO4/Mordenite) consists of an
aggregate of smaller crystals and contains specific
islands with high concentrations of phosphorus and
aluminum. Statistical analysis of the tomography
data confirmed the 2-D STXM results, indicating
that the islands are indeed located on the external
surface of the zeolite material. Inside the aggregate,
phosphorus and aluminum are also present, but at
lower concentrations. Furthermore, two distinct
types of Al K-edge XANES were observed: type 1
represents the aluminum found in AlPO4/Mordenite
after crystallization (highly crystalline AlPO4) and
type 2 the one before crystallization (amorphous
AlPO4), as shown in Figure 1.While Al of type
1 is more dominant in the high aluminum, high
phosphorus regions at the external surface, type 2 is
found in the medium aluminum, low phosphorus
regions inside the denser parts of the zeolite.
Highly crystalline AlPO4 was also detected at high
concentrations for zeolite H-Y, while the AlPO4
phase was not observed in the zeolitic interior
of this sample, indicated by the XANES, which
resembled that of aluminum-silicates and not that
of AlPO4 structures. Finally, crystalline AlPO4 was
not detected in H-ferrierite.
Discussion
During thermal or hydrothermal treatment of the
amorphous AlPO4 phase (Al-O-P)n linkages anneal,
which leads to the crystallization of the amorphous
AlPO4 phase. In order for the AlPO4 phase to
grow as 3-D crystal structures, sufficient space is
needed. Therefore, it is assumed that if AlPO4 is
located inside the zeolite micropores crystallization
is inhibited, leading to the higher concentration

of amorphous AlPO4 found inside the
zeolite H-mordenite. Such an effect was not
observed for zeolite H-USY, as the AlPO4
phase was found exclusively outside of the
crystal for the samples under study.
The results reported by Corma and
co-workers are in agreement with this
observation, as they showed by 27
Al MAS
NMR that the spectroscopic signals for
amorphous AlPO4 were almost eliminated
after the crystallization of the AlPO4 phase
in H-USY [13]. It is postulated that the
pore dimensionality of the framework plays
a role: the 1-dimensional pore structure
of zeolite H-mordenite is prone to pore-
blockage, causing parts of the AlPO4 phase
to be trapped inside the channel system
and therefore hindering subsequent
crystallization. In the 3-D channel system
of zeolite H-Y, these constrains are not as
dominant resulting in a stronger segregation
between (i) AlPO4 outside the zeolite and
(ii) framework aluminum inside the zeolite.
However, further studies will be necessary to
fully substantiate these claims.
In the case of H-ferrierite, due to the
inaccessible nature of the extra-framework
aluminum species, the formation of a
crystalline AlPO4 phase is unlikely to take
place. Phosphoric acid readily reacts with
extra-framework aluminum, and it has been
suggested that extra-framework aluminum
species in H-ferrierite are trapped in the
structure; these species are therefore not
available to react and an AlPO4 phase cannot
form [18].
Conclusion
A detailed study has been performed
on the formation of an aluminum-
phosphate (AlPO4) binder from the
framework aluminum supply of three
industrially relevant zeolites, namely
H-USY, H-mordenite and H-ferrierite.
The amorphous AlPO4 phase was found
to consist of four-, and six-coordinated
aluminum connected to PO4- units. The
majority of the amorphous AlPO4 phase
was heterogeneously distributed on the
external zeolitic surface, while only small
concentrations were detected in the zeolitic
interior. During a subsequent thermal or
hydrothermal treatment the amorphous
AlPO4 phase crystallizes into AlPO4 with no
observable migration during crystallization.
The formation of an AlPO4 binder by using
part of the framework aluminum supply
is an interesting method for multiple
Figure 1. In situ crystallization of the aluminum-phosphate (AlPO4) phase within H-mordenite monitored by
Scanning Transmission X-ray Microscopy (STXM). Chemical maps of sample AlPO/Mordenite (a and d) before
and (b and c) after heating at 400 °C. Greyscale masks are constructed from the Si map and indicate the particle
area. Brighter regions have a higher optical density. The colored Al K-edge XANES in (e) and (f) correspond to the
coloured masks in (a) and (b). (c-d) Mask of the highest phosphorus optical density.
Figure 2. (a) 3-D representation of a steamed, phosphated, and subsequently post-steamed H-mordenite
aggregate, AlPO4, reconstructed from the soft X-ray tomography data. Voxel size is 63x63x63 nm3
. Grey colored
voxels correspond to data collected at an energy measured before the aluminum K-edge (1555 eV) and relates
to the particle density. Blue-coloured voxels represent the aluminum distribution and green colored voxels the
phosphorus distribution. Low intensity voxels are not shown. The average Al K-edge XANES is shown in black,
and was obtained by 2-D STXM of the particle. It should be noted that voxels do not contain a full Al K-edge
XANES. Tomography data was collected only at 1555 eV (particle density), 1565 eV (peak A) and at 1570.4 (peak
B). The ratios between the recorded peak A and peak B intensities were used to identify corresponding Al phases
(Type 1 and Type 2). The blue box highlights a high aluminum and high phosphorus island on the surface with
corresponding Al K-edge XANES, while the red box highlights aluminum present in the crystal interior. (b, c)
Statistical analysis of the voxel data, showing correlations of aluminum, phosphorus and particle densities. It can
be observed that there are regions that contain high phosphorus, high aluminum and high Type 1 aluminum and
regions that contain low phosphorus, medium aluminum and high Type 2 aluminum.

2 0 1 4 r e s e a r c h R e p o r t 13
reasons. First, it requires zeolites with high
aluminum content, which are cheaper
and more environmentally friendly to
produce, since the use of organic templates
is not required [19-20]. Second, the pre-
dealumination step leads to the formation of
mesopores, creating a hierarchical material,
facilitating access to reactant and product
molecules during catalysis [21, 22].And
third, a thorough understanding of the
formation of AlPO4 from extra-framework
aluminum should allow one to form AlPO4
species inside the zeolite channel/cage
system, altering its shape-selective effects
[23].
As this is, to our best knowledge, one of
the few works that explores the creation
of a zeolite binder material made from
components of the zeolite itself, it is too
premature to present a fully unified view
on AlPO4 formation in zeolite materials.
However, we do hope that this work may
stimulate future characterization studies that
further explore these promising avenues.
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properties for methanol to propylene (MTP) reaction.
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Martineztriguero, L. J. (1994). Orthophosphoric acid
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[14] Costa, A. F., Cerqueira, H. S., Ferreira, J. M. M.,
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X., ... Liu, Z. (2004). Solid-state MAS NMR studies
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[17] van der Bij, H. E., Aramburo, L. R., Arstad, B.,
Dynes, J. J., Wang, J., Weckhuysen, B. M. (2014).
Phosphatation of Zeolite H-ZSM-5: A Combined
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15(2), 283-292.
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(2009). Al-rich zeolite beta by seeding in the absence
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S., Molenbroek, A. M., Sarro, P. M., Zandbergen, H. W.
(2008). Atomic-scale electron microscopy at ambient
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J. C., Pianetta, P. (2012). TXM-Wizard: a program for
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Acknowledgements
Joris Goetze, Mustafa Al Samarai and Ramon Oord of
Utrecht University are kindly thanked for their help
during the STXM measurements. Prof. Dr. Henny
Zandbergen and Dr. Meng-Yue Wu from TU Delft are
thanked for supplying a MEMS in situ nanoreactor.
N2-physisorption measurements were performed at
Utrecht University by Arjan den Otter, Nazila Masoud
and Dr. Ying Wei.
STXM experiments were performed at the Canadian
Light Source (CLS) Beamline 10ID-1. Samples were
dispersed in H2O and a droplet was placed on a silicon
nitride window. After drying in air the sample was
placed in the STXM chamber, which was subsequently
evacuated to 10-1 mbar. A polarized X-ray beam was
obtained using a 1.6 m long, 75 mm period Apple II
undulator. The X-ray beam was focused to ~30 nm
spot size on the sample plane using a Fresnel zone
plate (ZP). The beam from the ZP passed through a
molybdenum-based order-sorting aperture (OSA),
with a 50 µm pinhole. The OSA allowed only first-order
ZP diffracted light to pass. Spectral image sequences
(stacks) are measured by recording images over a
range of photon energies. After aligning the image
sequence, spectra of the whole or a subregion were
extracted for comparison. For the in-situ measurements
a micro-electromechanical system (MEMS) designed
nanoreactor was used [24]. All STXM data analysis
was performed using aXis2000 [25]. Sinograms and
binslices were constructed and reconstructed using
the TXM-Wizard software [26] and using the iterative
Algebraic Reconstruction Technique (iART) algorithm.
The 3-dimensional data was analyzed using Avizo 8.0
and MATLAB.

PRINCIPAL CONTACT:
NeilJohnson,B.Sc.
Ph.D.Candidate
DepartmentofPhysicsand
EngineeringPhysics
UniversityofSaskatchewan
johnson.neil@usask.ca
306-966-6380
Journal/Principal
publication:
AdvancedFunctionalMaterials,
Issue33,Volume24,September2,
2014,pp.5253-5259.DOI:10.1002/
adfm.201400769
Authors:
NeilW.Johnson,Dr.IsraelPerez,Dr.
DavidMuir,Prof.AlexanderMoewes
DepartmentofPhysicsand
EngineeringPhysics
Dr.DavidMuir
CanadianLightSource
Dr.PatrickVogt
TechnischeUniversitätBerlin
Dr.AndreaResta,Prof.GuyLeLay
Aix-MarseilleUniversity
Dr.AndreaResta
SOLEILSynchrotron
Dr.PaolaDePadova
ConsiglioNazionaledellaRicerche-ISM
Prof.ErnstZ.Kurmaev
M.N.MikheevInstituteofMetal
Physics
UralFederalUniversity
The metallic nature of epitaxial silicene
monolayers on Ag(111)
Introduction
Silicene is the silicon-based cousin to the
2-dimensional“wonder material”graphene.When
it is freestanding, it is expected to possess many
of the characteristics that make graphene such an
attractive candidate material for next-generation
electronic devices. However, freestanding silicene
is yet to be observed.Atom-thick honeycomb
silicon sheets have been grown on the surface of
extremely flat silver crystals through physical vapour
deposition [1], but whether these sheets are of any
practical use was matter of significant debate.While
some experiments indicated that these epitaxial
silicene sheets were metallic [2], others reported
observing the hallmarks of a“Dirac cone”in the
electronic structure [3], a feature that is associated
with the exciting electronic characteristics of
graphene.
One of the main reasons for the disagreement over
the true electronic nature of epitaxial silicene sheets
was that no“element-specific”measurements had
been performed on the material. That is, the existing
experimental studies did not distinguish between
electrons belonging to the silicene sheet and those
belonging to the underlying silver substrate, leading
to multiple interpretations of the data.
Science
Using the X-ray emission spectroscopy (XES)
endstation of the REIXS beamline, we performed Si
L2,3-edge soft X-ray emission and Si 2p absorption
spectroscopy—XES and X-ray absorption
spectroscopy (XAS), respectively—on monolayer
epitaxial silicene samples. These samples were
grown at the CLS using the thin-film deposition
chamber located just outside the REIXS hutch.
This chamber is outfitted with LEED, RHEED and
a quartz crystal growth monitor for characterizing
deposition rates and sample quality.
As silicene is extremely oxygen-sensitive, once the
samples were grown in ultra-high vacuum they
had to be transferred from the deposition chamber
to the XES endstation without breaking vacuum.
This was accomplished with the use of a custom
vacuum transfer cart, which prevented the samples
from seeing more than 10-7
Torr of pressure from
the moment of deposition all the way through to
measurement.
XES and XAS serve as element- and orbital-specific
probes of the occupied valence and unoccupied
conduction states, respectively.At the Si L2,3
emission and 2p absorption edge, we primarily
measure Si states with s and d character, according
to the dipole selection rules.While it may have been
preferable to attempt to probe the Si p states using
Si K XES and Si 1s XAS, the penetration depth of
the required photons would be far too large to be
sensitive to a single layer of Si atoms.
To complement these measurements, we also
performed full-potential density functional
theory (DFT) calculations using the WIEN2k
program suite. Our calculations allowed us to
evaluate structural models of epitaxial silicene
monolayers on the Ag(111) surface, to calculate the
electronic structures of these monolayers and to
simulate the results of our soft X-ray spectroscopy
measurements.
Discussion
Our DFT calculations predicted a wide variety of
stable structures for epitaxial silicene monolayers.
However, for each of these structures we calculated
very similar electronic characteristics. Namely, they
were found to be metallic and exhibited significant
interaction with the underlying substrate. Silver was
initially chosen as a growth platform for silicene
because it was expected to have minimal interaction
with the sheets, but our calculations showed that
this was not the case for any of the monolayers we
considered.
XES and XAS measurements supported the
conclusions of our DFT calculations. The overlap
between the measured valence and conduction
states were found to be consistent with metallic
silicon, and the good general agreement
between calculated and measured spectra
validated our structural models and electronic
structure calculations. These measurements also
demonstrated how extremely oxygen-sensitive
silicene really is, as the emission spectra began to
show SiO2-like features after 15 minutes of beam
exposure at 10-9
Torr.Whatever little residual oxygen
remained in the measurement chamber after it was
flushed with dry nitrogen gas and pumped down
to ultra-high vacuum (UHV) conditions was still
enough to somewhat oxidize the monolayer.

2 0 1 4 r e s e a r c h R e p o r t 15
Conclusion
Our soft X-ray study of epitaxial silicene
monolayers on the Ag(111) surface
confirmed that they are indeed metallic and
interact significantly with their substrates.
As such, they are not suitable candidates
for 2-D electronic applications.We also
showed that these samples have a strong
tendency to oxidize, even doing so under
UHV conditions. This would suggest that
any useful silicene device would have to
be passivated by some form of chemical
modification in order to prevent oxidation,
which would inevitably change its electronic
properties.
There are still a large number of promising
avenues to explore in silicene research.
Alternate, non-metallic growth substrates
have been proposed [4], silicene multilayers
[5] and nanoribbons [6] on silver substrates
are yet to be fully understood, and
functionalization and chemical modification
of silicene monolayers may lead to oxidation
resistance and weakened interaction with
growth substrates [8].
Recently, the first silicene-based transistor
was created [8]. The silicene monolayer
used in this device was initially derived from
physical vapour deposition on Ag(111),
much like the process we used to obtain
Figure 1. (a) The structure of low-
buckled freestanding silicene. Note
the sublattice inversion symmetry
of the upper and lower layers. The
relaxed structures of (b) (3 × 3)/(4
× 4) and c-e) (√7 × √7)/(√13 × √13)
epitaxial silicene. (3 × 3)/(4 × 4)
silicene has 18 Si atoms per unit cell
for a coverage ratio of 1.125 Si:Ag,
while the (√7 × √7)/(√13 × √13)
silicene structures contain 14 Si sites
per unit cell for a coverage ratio of
1.077 Si:Ag. Visualization provided
by the VESTA software package.
Figure 2. (a) Theoretical XES and XAS
spectra obtained from the calculated
Si pDOS for epitaxial and freestanding
silicene. The Fermi energy is marked
by a dashed vertical line. Calculated
XAS spectra including a Si 2p core-hole
are indicated by a dashed line. (b) XES
and XAS measurements of epitaxial
silicene and Si references (a sputtered
crystalline Si wafer in fuchsia and an
amorphous SiO2 crystal (XES) and
native SiO2 oxide on a Si wafer (XAS) in
black). Dotted lines indicate peaks in
the XES spectrum and the calculated or
measured features they are attributed
to. The overlaps of the measured and
calculated XES and XAS spectra, which
are used as a metric for the degree
to which the substances are metallic,
are shown in the rightmost panels,
magnified 2× vertically and on an
enlarged horizontal range.

our epitaxial monolayers.While the device’s
performance was not up to the standards of
bulk silicon or graphene-based transistors
and it oxidized in a matter of minutes, this
achievement represents an important first
step toward silicene-based electronics.
References
[1] Vogt, P., De Padova, P., Quaresima, C., Avila, J.,
Frantzeskakis, E., Asensio, M. C., ... Le Lay, G. (2012).
Silicene: compelling experimental evidence for
graphenelike two-dimensional silicon. Physical review
letters, 108(15), 155501.
[2] Tsoutsou, D., Xenogiannopoulou, E., Golias, E., Tsipas,
P., Dimoulas, A. (2013). Evidence for hybrid surface
metallic band in (4× 4) silicene on Ag (111). Applied
Physics Letters, 103(23), 231604.
[3] Huang, S., Kang, W., Yang, L. (2013). Electronic
structure and quasiparticle bandgap of silicene
structures. Applied Physics Letters, 102(13), 133106.
[4Kaloni, T. P., Schreckenbach, G., Freund, M. S. (2014).
Large Enhancement and Tunable Band Gap in Silicene
by Small Organic Molecule Adsorption. The Journal of
Physical Chemistry C, 118(40), 23361-23367.
[5] Vogt, P., Capiod, P., Berthe, M., Resta, A., De Padova,
P., Bruhn, T., ... Grandidier, B. (2014). Synthesis and
electrical conductivity of multilayer silicene. Applied
Physics Letters, 104(2), 021602.
[6] De Padova, P., Quaresima, C., Ottaviani, C.,
Sheverdyaeva, P. M., Moras, P., Carbone, C., ... Le Lay, G.
(2010). Evidence of graphene-like electronic signature
in silicene nanoribbons. Applied Physics Letters, 96(26),
261905.
[7] Huang, B., Xiang, H. J., Wei, S. H. (2013). Chemical
Functionalization of Silicene: Spontaneous Structural
Transition and Exotic Electronic Properties. Physical
review letters, 111(14), 145502.
[8] Tao, L., Cinquanta, E., Chiappe, D., Grazianetti, C.,
Fanciulli, M., Dubey, M., ... Akinwande, D. (2015).
Silicene field-effect transistors operating at room
temperature. Nature nanotechnology, 10(3), 227-231.
Acknowledgements
The authors gratefully acknowledge financial support
from the Natural Sciences and Engineering Research
Council of Canada (NSERC) and the Canada Research
Chair Program, the“2D-NANOLATTICES”project of
the Future and Emerging Technologies (FET) program
within the 7th framework program for research of the
European Commission under FET Grant No. 270749, the
Deutsche Forschungsgemeinschaft (DFG) under Grant
No. VO1261/3–1, support from CONACYT Mexico under
grant 186142, and the Russian Foundation for Basic
Research (Projects 14–02–00006). Calculations used
Compute Canada's WestGrid HPC consortium.
We used the XES endstation of the REIXS beamline
(10-ID2). Our measurements consisted of Si 2p XAS
in TEY-mode and Si L2,3 XES (non-resonant) using a
microchannel plate detector.
Figure 3. (a) High-resolution STM topograph (6×6
nm, Ubias=-1.12 V, I = 0.65 nA) of the (4×4) silicene
monolayer. Clearly visible is the“flowerlike”
pattern that results from the upward displacement
of 6 of the 18 Si atoms in the honeycomb
structure. (b) STM topograph (21.6×21.6 nm, Ubias
= -1.20 V, I = 1.08 nA) of “(√13×√13)”silicene. STM
topographs were obtained under UHV conditions
( 2×10-10
Torr).

2 0 1 4 r e s e a r c h R e p o r t 17
PRINCIPAL CONTACT:
Dr.FazelFallahTafti
Post-DoctoralFellow
PrincetonUniversity
ftafti@princeton.edu
Journal/Principal
publication:
PhysicalReviewB,Issue13,Volume
89,pp.134502.DOI:10.1103/
PhysRevB.89.134502
Authors:
F.F.Tafti1,*
J.P.Clancy2
M.Lapointe-Major1
C.Collignon1
S.Faucher1
J.A.Sears2
A.Juneau-Fecteau1
N.Doiron-Leyraud1
A.F.Wang3
X.-G.Luo3
X.H.Chen3
S.Desgreniers4
Young-JuneKim2
LouisTaillefer1,5,†
1
DépartementdephysiqueRQMP
UniversitédeSherbrooke
2
DepartmentofPhysics
UniversityofToronto
3
HefeiNationalLaboratoryfor
PhysicalSciencesatMicroscaleand
DepartmentofPhysics
UniversityofScienceand
TechnologyofChina
4
FacultyofScience
UniversityofOttawa
5
CanadianInstitutefor
AdvancedResearch
Sudden reversal in the pressure dependence
ofTc in the iron-based superconductor
CsFe2As2: A possible link between inelastic
scattering and pairing symmetry
Introduction
Few superconductors can host more than one
pairing state. Such superconductors bring the
possibility of a transition from one pairing
symmetry to another in the same material: an
extremely rare event of fundamental importance,
since the transition temperature can respond
differently to tuning parameters in different pairing
states. The multi-band nature of superconductivity
in iron-based superconductors brings these
materials one step closer to the possibility of hosting
more than one pairing symmetry. However, to tune
the same material from one pairing state to another,
it should also allow for near degeneracy between
different pairing states. Several theoretical proposals
suggested such an intriguing possibility in the over-
electron-doped chalchogenides, but in 2013 we
discovered this rare transition in over-hole-doped
pnictide KFe2As2 by observing a sudden reversal in
the pressure dependence of Tc in this material [1]. In
the present work, we report our finding of the same
phenomenon in another system CsFe2A2 shown
in Figure 1. This finding establishes the change of
pairing symmetry as a common trend amongst
over-hole-doped iron-pnictides. This time we try
to push our understanding of the parameters that
control this transition by comparing CsFe2A2 and
KFe2As2.
Our work encompasses a thorough investigation
of lattice parameters of KFe2As2 under pressure up
to 60 kbar via high pressure X-ray measurements
as well as resistivity and Hall measurements under
pressure on both CsFe2A2 and KFe2As2 up to 18
and 25 kbar, respectively.We show that lattice
parameters and disorder do not play a role in
controlling the critical pressure Pc where Tc reversal
occurs. By analyzing the response of resistivity to
pressure we find a link between inelastic scattering
processes encoded in the resistivity data and the Tc
reversal.
Science
Several studies on the Ba1−xKxFe2As2 series suggest
that lattice parameters, in particular the As-Fe-
As bond angle, control Tc [2-4]. To explore this
hypothesis, we measured the lattice parameters of
KFe2As2 as a function of pressure up to 60 kbar in
order to find out how much pressure is required
to tune the lattice parameters of CsFe2As2 so they
match those of KFe2As2. Cs has a larger atomic size
than K; hence one can view CsFe2As2 as a negative-
pressure version of KFe2As2. The four panels of
Figure 2 show the pressure variation of the lattice
constants a and c, the unit cell volume (V = a2
c),
and the intraplanar As-Fe-As bond angle (α) in
KFe2As2. The red horizontal line in each panel marks
the value of the corresponding lattice parameter in
CsFe2As2. In order to tune a, c, V, and α in KFe2As2
to match the corresponding values in CsFe2As2, a
negative pressure of approximately -10, -75, -30,
and -30 kbar is required, respectively.Adding
these numbers to the critical pressure for KFe2As2
(Pc=17.5 kbar), we would naively estimate that the
critical pressure in CsFe2As2 should be Pc+30 kbar
or higher.
We find instead that Pc=14 kbar, showing that other
factors are involved in controlling Pc. It is possible
that the lower Pc in CsFe2As2 could be due to the
fact that Tc itself is lower than in KFe2As2 at zero
pressure, i.e., that the low-pressure phase is weaker
in CsFe2As2. One hypothesis for the lower Tc in
CsFe2As2 is a higher level of disorder. To test this
idea, we studied the pressure dependence of Tc in
a less pure KFe2As2 sample. Figure 1 compares the
T–P phase diagram in three samples: (1) a high-
purity KFe2As2 sample, with ρ0=0.2µΩcm; (2)
a less pure KFe2As2 sample, with ρ0=1.3µΩcm,
measured here; (3) a CsFe2As2 sample with
ρ0=1.5 µΩcm. Different disorder levels in our
samples are due to growth conditions, not deliberate
chemical substitution or impurity inclusions.
First, we observe that a six-fold increase of ρ0 has
negligible impact on Pc in KFe2As2. Second, we
observe that Pc is 4 kbar smaller in CsFe2As2 than
in KFe2As2, for samples of comparable ρ0. These
observations rule out the idea that disorder could
be responsible for the lower value of Pc in CsFe2As2
compared to KFe2As2.

Figure 1. Pressure dependence of Tc in three samples: pure KFe2As2 (black circles), less pure KFe2As2 (gray circles),
and CsFe2As2 (sample 2, red circles). Even though the Tc values for the two KFe2As2 samples are different due
to different disorder levels, measured by their different residual resistivity ρ0, the critical pressure is the same
(Pc=17.5kbar). This shows that the effect of disorder on Pc in KFe2As2 is negligible. For comparable ρ0, the critical
pressure in CsFe2As2 , Pc=14 kbar, is clearly smaller than in KFe2As2.
Figure 2. Structural parameters of KFe2As2 as a function of pressure, up to 60 kbar: (a) lattice constant a; (b)
lattice constant c; (c) unit cell volume V=a2
c; (d) the intraplanar As-Fe-As bond angle α as defined in the inset.
Experimental errors on lattice parameters are smaller than symbol dimensions. The black dotted line in panels
(a), (b), and (c) is a fit to the standard Murnaghan equation of state extended smoothly to negative pressures. The
black dotted line in panel (d) is a third-order power-law fit. In each panel, the horizontal red line marks the lattice
parameter of CsFe2As2, and the vertical red line gives the negative pressure required for the lattice parameter of
KFe2As2 to reach the value in CsFe2As2.
Discussion
In a recent theoretical work by Fernandes
and Millis, it is demonstrated that different
pairing interactions in 122 systems can
favour different pairing symmetries [5].
In their model, SDW-type magnetic
fluctuations with wave vector (π, 0) favour
s± pairing, whereas Neel-type fluctuations,
with wave vector (π, π), strongly suppress
the s± state and favour d-wave pairing.A
gradual increase in the (π, π) fluctuations
eventually causes a phase transition from an
s± superconducting state to a d-wave state,
producing a V-shaped Tc vs. P curve [5]. In
KFe2As2 and CsFe2As2, it is conceivable that
two such competing interactions are at play,
with pressure tilting the balance in favour
of one versus the other.We explore such
a scenario by looking at how the inelastic
scattering evolves with pressure, measured
via the inelastic resistivity, defined as ρ(T )−
ρ0, where ρ0 is the residual resistivity.
Figure 3(a) shows raw resistivity data from
the KFe2As2 sample with ρ0=1.3µΩcm
below 30 K. To extract ρ(T )−ρ0 at each
pressure, we make a cut through each curve
at T=20 K and subtract from it the residual
resistivity ρ0 that comes from a power-law fit
ρ=ρ0+AT n to each curve. ρ0 is determined
by disorder level and does not change as a
function of pressure. The resulting ρ(T=20
K)−ρ0 values for this sample are then plotted
as a function of normalized pressure P/Pc
in Figure 3(b). Through a similar process
we extract the pressure dependence of ρ(20
K)−ρ0 in CsFe2As2 and the purer KFe2As2
sample with ρ0 =0.2µΩcm in Figures 3(c)
and (d). In all three samples, at P/Pc 1,
the inelastic resistivity varies linearly with
pressure. As P drops below Pc, the inelastic
resistivity in (K,Cs)Fe2As2 shows a clear rise
below their respective Pc, over and above the
linear regime. Figure 3 therefore suggests
a connection between the transition in
the pressure dependence of Tc and the
appearance of an additional inelastic
scattering process.
Conclusion
In summary, we discovered a pressure-
induced reversal in the dependence of the
transition temperature Tc on pressure in
the iron-based superconductor CsFe2As2,
similar to our previous finding in KFe2As2.
We interpret the Tc reversal at the critical
pressure Pc as a transition from one pairing
state to another. The fact that Pc is smaller
in CsFe2As2 than in KFe2As2, even though all
lattice parameters would suggest otherwise,
shows that structural parameters alone
do not control Pc. We also demonstrate

2 0 1 4 r e s e a r c h R e p o r t 19
Figure 3. (a) Resistivity data for the KFe2As2 sample with ρ0=1.3 μΩcm at five selected pressures. The black
vertical arrow shows a cut through each curve at T=20 K and the dashed line is a power-law fit to the curve at
P=23.8 kbar from 5 to 15 K that is used to extract the residual resistivity ρ0. Inelastic resistivity, defined as ρ(T=20
K)−ρ0, is plotted vs. P/Pc in (b) the less pure KFe2As2 sample, (c) the purer KFe2As2 sample, and (d) CsFe2As2, where
Pc=17.5 kbar for KFe2As2 and Pc=14 kbar for CsFe2As2. In panels (b), (c), and (d) the dashed black line is a linear fit
to the data above P/Pc=1.
that disorder has negligible effect on Pc.
Our study of the pressure dependence of
resistivity in CsFe2As2 and KFe2As2 reveals
a possible link between Tc and inelastic
scattering. Our proposal is that the high-
pressure phase in both materials is an s±
state that changes sign between Γ-centered
pockets. As the pressure is lowered, the
large-Q inelastic scattering processes that
favour d-wave pairing in pure KFe2As2 and
CsFe2As2 grow until at a critical pressure
Pc they cause a transition from one
superconducting state to another, with a
change of pairing symmetry from s wave to
d wave. The experimental evidence for this is
the fact that below Pc the inelastic resistivity,
measured as the difference ρ(20 K)−ρ0,
deviates upwards from its linear pressure
dependence at high pressure.
References
[1] Tafti, F. F., Juneau-Fecteau, A., Delage, M. E., de
Cotret, S. R., Reid, J. P., Wang, A. F., ... Taillefer, L.
(2013). Sudden reversal in the pressure dependence
of Tc in the iron-based superconductor KFe2As2. Nature
Physics,9(6), 349-352.
[2] Rotter, M., Pangerl, M., Tegel, M., Johrendt, D.
(2008). Superconductivity and crystal structures
of (Ba1− xKx) Fe2As2 (x= 0–1). Angewandte Chemie
[3] Kimber, S. A., Kreyssig, A., Zhang, Y. Z., Jeschke, H.
O., Valentí, R., Yokaichiya, F., ... Argyriou, D. N. (2009).
Similarities between structural distortions under
pressure and chemical doping in superconducting
BaFe2As2. Nature Materials, 8(6), 471-475.
[4] Chu, J. H., Analytis, J. G., Kucharczyk, C., Fisher, I.
R. (2009). Determination of the phase diagram of the
electron-doped superconductor Ba (Fe 1− x Co x) 2 As
2. Physical Review B, 79(1), 014506.
[5] Fernandes, R. M., Millis, A. J. (2013). Suppression of
superconductivity by Neel-type magnetic fluctuations
in the iron pnictides. Physical review letters,110(11),
117004.
Acknowledgements
We thank A.V. Chubukov, R.M. Fernandes, and A.
J. Millis for helpful discussions, and S. Fortier for
his assistance with the experiments. The work at
Sherbrooke was supported by the Canadian Institute
for Advanced Research and a Canada Research Chair
and it was funded by NSERC, FRQNT, and CFI. Work
done in China was supported by the National Natural
Science Foundation of China (Grant No. 11190021), the
Strategic Priority Research Program (B) of the Chinese
Academy of Sciences, and the National Basic Research
Program of China. Research at the University of Toronto
was supported by the NSERC, CFI, Ontario Ministry of
Research and Innovation, and Canada Research Chair
program.
High-pressure X-ray experiments were performed on
polycrystalline powder specimens of KFe2As2 up to 60
kbar with the HXMA beam line at the Canadian Light
Source, using a diamond anvil cell with silicon oil as
the pressure medium. Pressure was tuned blue with
a precision of 2 kbar using the R1 fluorescent line of
a ruby chip placed inside the sample space. XRD data
were collected using angle-dispersive techniques,
employing high-energy X-rays (Ei=24.35 keV) and
aMar345 image plate detector. Structural parameters
were extracted from full profile Rietveld refinements
using GSAS software.

PRINCIPAL CONTACT:
DennisTokaryk
Professor
DepartmentofPhysics
UniversityofNewBrunswick
dtokaryk@unb.ca
5064587933
Journal/Principal
publication:
PhysicalChemistryChemicalPhysics,
2014,Issue33,Volume16,pp.17373-
17407.DOI:10.1039/c4cp01443j
Authors:
ManfredWinnewisser1
BrendaP.Winnewisser1
FrankC.DeLucia1
DennisW.Tokaryk2
StephenC.Ross2
BrantE.Billinghurst3
1
DepartmentofPhysics
TheOhioStateUniversity
2
DepartmentofPhysicsandCentrefor
Laser,Atomic,andMolecularSciences
UniversityofNewBrunswick
3
CanadianLightSource
Pursuit of quantum monodromy in the far-
infrared and mid-infrared spectra of NCNCS
using synchrotron radiation
Introduction
Quantum monodromy has a dramatic and defining
impact on all those physical properties of chain
molecules that depend on a large-amplitude
bending coordinate, including in particular the
distribution of the ro-vibrational energy levels.As
revealed by its pure rotational (a-type) spectrum
[1], cyanogen iso-thiocyanate, NCNCS (Figure 1
illustrates its structure), is a particularly illuminating
exemplar of quantum monodromy: it clearly shows
the distinctive monodromy-induced dislocation
of the ro-vibrational energy level pattern for
its low-lying bending mode labelled ν7. This
dislocation centers on a lattice defect in the energy
vs. momentum map of the ro-vibrational levels at
the top of the barrier to linearity, and represents
an example of an excited state quantum phase
transition [2, 3].
The large amplitude ro-vibrational dynamics
of the low-lying bending mode in NCNCS is
intimately linked to the topology of the surfaces
of constant energy in the four-dimensional phase
space associated with motion constrained by
the potential function. Monodromy resulting
from the champagne-bottle bending potential
[4] is strongly imprinted on the wavefunctions
and patterns of energy levels associated with
this mode. Generalized-SemiRigid-Bender
(GSRB) Hamiltonian calculations show that all
important physical quantities, including effective
rotational constants, ro-vibrational energies,
and the expectation values of the electric dipole
moment components, show the effects of quantum
monodromy [1].
Before conducting our experiments at the CLS, data
were limited to pure-rotational ΔJ=+1 transitions
within a selection of ν7 bending vibrational levels.
We have now obtained high-resolution far-infrared
spectra of transitions between the large-amplitude
ν7 bending vibrations, and to several mid-infrared
levels. Initial analyses of the data demonstrate the
accuracy of the previous GSRB calculations, and
provide a direct measurement of the energy level
positions plotted on the energy-momentum map
shown in Figure 4.
Science
Cyanogen iso-thiocyanate, NCNCS, is the best
model system found so far for a molecule that
clearly exhibits a distinctive monodromy-induced
dislocation in the energy level pattern. The large-
amplitude ν7 bending mode of NCNCS, which has
a bent equilibrium structure (see Figure 1), can
be studied from the ground state to levels above
the barrier to linearity, with very little interference
from other vibrational excitations [1, 5-7]. The
connection between the bending motion of NCNCS
and the champagne bottle potential function can be
understood by considering the schematic potential
shown on the left-hand side of Figure 1. There
the radial coordinate can represent the ν7 bending
motion of the molecule with the origin (where
the hump of the potential lies) corresponding to
the linear configuration. For NCNCS the angular
coordinate in this schematic figure then represents
rotational motion around the long-axis (a-or
z-axis) of the molecule. It is the nature of the
coupling between these two motions that leads to
monodromy in NCNCS.
The large amplitude of the ν7 (CNC bending)
vibration means that the inverse moments of inertia
of the molecule cannot be treated as constants
during this motion, which is why the ν7 vibrational
mode cannot be separated from the rotational
motion [1]. It is because of this that we have used
the GSRB to model the ν7 bending + rotational
energy levels of NCNCS, and to calculate the
intensities of the transitions in the ν7 sequence.
Ab initio calculations of the transition moments
in NCNCS [5] indicated that the ν7 band we were
seeking was one of the weakest fundamental
transitions in the molecule. Nonetheless, over
four two- to three-week campaigns at the CLS,
we learned how to synthesize S(CN)2 under the
constraints of working in a remote lab (the CLS wet
labs), and how to effectively pyrolyze this precursor
to form the more stable isomer NCNCS. In the end,
we successfully acquired the far-infrared bending-
mode spectra of both NCNCS (see Figure 2) and
S(CN)2 between 60-200 cm-1
at high resolution
using the synchrotron radiation. The data permitted
an interesting comparison between the rather rigid
bent molecule S(CN)2 [8, 9] and the much floppier
isomer NCNCS.

2 0 1 4 r e s e a r c h R e p o r t 21
Discussion
The GSRB calculations (Figure 3), based on
the calculated dipole moment [5], indicated
that both b-type and a-type transitions
would be observed in the spectrum of the
ν7 band sequence in NCNCS. This would
be desirable, since the a-type transitions
connect points on the energy-momentum
map with the same rotational quantum
number Ka but with different vibrational
quantum number (vertical transitions
on the map shown in Figure 4), while the
b-type transitions connect points with a
change of both a rotational quantum and a
vibrational quantum (diagonal transitions
(not shown) in Figure 4). However, a
comparison of Figures 2 and 3 clearly shows
that only a-type transitions were observed in
our data. A similar situation was previously
reported in the pure rotational spectra, for
which both a- and b-type transitions were
predicted to occur, but in which only the
a-type transitions have so far been identified
[1]. The transitions assigned at the time
of publishing the paper that is the subject
of this report are shown as vertical purple
arrows in Figure 4. These transitions allow
us to determine for the first time absolute
intervals between some vibrational levels,
provided that they share a common angular
momentum Ka.
To find the absolute energy of all levels
relative to the lowest possible level, b-type
transitions with ΔKa=±1 must be observed
and assigned. While neither the pure-
rotational nor the far-infrared spectra
appear suitable for this purpose, a mid-
infrared band that we observed near 1185
cm-1
shows evidence of both a- and b-type
transitions. Analysis of this spectrum could
allow us to determine the relative energy
between vertical stacks of levels shown in
Figure 1. The concept of monodromy (Greek for“once around”) for the dynamics of a particle in a potential energy function shaped like the bottom part of a champagne bottle
was introduced by Larry Bates [10] in 1991. This potential energy function is circularly symmetric with two conserved physical quantities: energy and angular momentum.
The left-hand panel of this figure shows a schematic champagne bottle potential energy function for the quasi-linear in-plane bending mode of NCNCS. The large-amplitude
coordinate ρ is defined on the molecular structure in the right-hand panel. The critical point of the potential function is indicated together with the topologies of phase-space
surfaces of constant energy above and below this point [5]. The equilibrium structure of NCNCS from ab initio calculations with CCSD(T)/cc-pV5Z level of theory is given in the
right-hand panel [5].
Figure 2. The experimentally-observed spectrum of the ν7 band sequence, taken in absorption against the
continuum provided by synchrotron radiation from the Canadian Light Source. 121 mTorr of NCNCS was admitted
into the 2 m-long sample cell, through which the synchrotron light passed 36 times.
Figure 4, thereby completing the energy-
momentum map. Further, perturbations
between levels within the ν7 sequence,
observed in the original pure-rotational
spectrum, can be used to corroborate
intervals obtained via the 1185 cm-1
band,
and to determine intervals that this band
may not provide.
Conclusion
Our investigation of the effects of quantum
monodromy on the spectrum of NCNCS
is nearly complete.We have found that this
elusive species is more stable than its isomer
S(CN)2, in agreement with our recent ab
initio calculation which has it more stable
by about 50 kJ mol−1
[9], and that we can
produce it reliably and consistently in the
requisite quantities at the CLS. Further,
we have found that it exhibits remarkable
chemical and kinetic stability in a 2 m-long
stainless steel White cell if the cell is cooled
below 0°C. In addition to acquiring spectra
of several higher-frequency small-amplitude
vibrational modes in NCNCS, we have
attained our main goal of observing the
large-amplitude far-infrared bending mode
ν7 and its associated sequence bands through
its ro-vibrational spectrum near 80 cm−1
.
However, the question remains: where
are the b-type rotational or ro-vibrational
transitions (Figure 2)? Perhaps they are
considerably weaker than predicted, and the
signal-to-noise ratio of our data is not yet
sufficient to reveal them. It is important to
note that the intensities calculated using the
GSRB rely on the ab initio dipole moment
functions as described in [1].Any inaccuracy
in those results will be reflected here.
Our GSRB calculations concerning energy
levels, line positions, wave functions,
expectation values of dipole moment
components and line intensities together

with initial results presented in this work
indicate that the unusual structure of the
large-amplitude bending fundamental band
system of NCNCS is a very specific signature
of monodromy. Such signatures must
appear in the spectrum of any molecule that
is excited above its barrier to linearity.
References
[1] Winnewisser, B. P., Winnewisser, M., Medvedev, I. R.,
De Lucia, F. C., Ross, S. C., Koput, J. (2010). Analysis
of the FASSST rotational spectrum of NCNCS in view
of quantum monodromy. Physical Chemistry Chemical
Physics,12(29), 8158-8189.
[2] Larese, D., Iachello, F. (2011). A study of quantum
phase transitions and quantum monodromy in the
bending motion of non-rigid molecules. Journal of
Molecular Structure, 1006(1), 611-628.
[3] Larese, D., Pérez-Bernal, F., Iachello, F. (2013).
Signatures of quantum phase transitions and excited
state quantum phase transitions in the vibrational
bending dynamics of triatomic molecules. Journal of
Molecular Structure, 1051, 310-327.
[4] Bates, L. M. (1991). Monodromy in the champagne
bottle. Zeitschrift für angewandte Mathematik und Physik
ZAMP, 42(6), 837-847.
[5] Winnewisser, B. P., Winnewisser, M., Medvedev, I. R.,
Behnke, M., De Lucia, F. C., Ross, S. C., Koput, J. (2005).
Experimental confirmation of quantum monodromy:
The millimeter wave spectrum of cyanogen
isothiocyanate NCNCS. Physical review letters, 95(24),
243002.
[6] Winnewisser, M., Winnewisser, B. P., Medvedev, I.
R., De Lucia, F. C., Ross, S. C., Bates, L. M. (2006). The
hidden kernel of molecular quasi-linearity: quantum
monodromy. Journal of molecular structure, 798(1), 1-26.
[7] King, M. A., Kroto, H. W., Landsberg, B. M. (1985).
Microwave spectrum of the quasilinear molecule,
cyanogen isothiocyanate (NCNCS). Journal of Molecular
Spectroscopy, 113(1), 1-20.
[8] Kisiel, Z., Dorosh, O., Winnewisser, M., Behnke, M.,
Medvedev, I. R., De Lucia, F. C. (2007). Comprehensive
analysis of the FASSST rotational spectrum of S(CN)2.
Journal of Molecular Spectroscopy, 246(1), 39-56.
[9] Kisiel, Z., Winnewisser, M., Winnewisser, B. P., De
Lucia, F. C., Tokaryk, D. W., Billinghurst, B. E. (2013).
Far-Infrared Spectrum of S(CN)2 Measured with
Synchrotron Radiation: Global Analysis of the Available
High-Resolution Spectroscopic Data. The Journal of
Physical Chemistry A, 117(50), 13815-13824.
Acknowledgements
The experimental work of The Ohio State University
team was supported by the Army Research Office,
NSF, and NASA. B. Billinghurst would like to thank all
of his colleagues at the Canadian Light Source for
their advice particularly Dr. J. C. Bergstrom for endless
discussions about the physics of synchrotrons. Damien
Forthomme and Colin Sonnichsen are thanked for
their help with the initial experiments. Dr. Sylvestre
Twagirayezu is recognized and thanked for all his help
in setting up the chemical laboratory in May 2013.
DWT acknowledges financial support from the Natural
Sciences and Engineering Research Council of Canada
(NSERC). SCR would like to thank Dr. K. M. T. Yamada for
many helpful discussions with regard to the calculation
of intensities. The authors thank Professor Zbigniew
Kisiel for critically reading the manuscript.
Beamline Information
Far-Infrared Beamline 02B1-1 using the IFS 125HR
Bruker Fourier transform spectrometer.
Figure 3. The top panel shows all predicted a-type parallel sub-bands for the CNC in-plane large amplitude bending
mode ν7 for NCNCS. The middle panel displays all predicted b-type perpendicular sub-bands including Δvb=0, 1, 2, 3
transitions. In the bottom panel the superposition of all a-type and b-type transitions displays the entire hybrid band
system of the large-amplitude bending mode ν7 for a limited range of J and Ka values. This means an enormous number
of weak THz- and/or FIR ro-vibrational transitions if we include the fully extended P-, Q- and R-branches in a spectral
range of roughly 130 cm-1
centered around 100 cm-1
. This hybrid band system has a calculated total band intensity of
only 4 km mol-1
.
Figure 4. Excerpt of the energy-momentum map for J=Ka with the 7 assigned sub-bands of the ν7 large amplitude
in-plane bending mode of NCNCS for Ka=0 and vb=1 0, 2 1, 3 2; for Ka=1 and vb=1 0, 2 1, 3 2; for Ka=2
and vb=1 0. As of this writing 48 Loomis–Wood strands have been identified, allowing us to start building a fully
experimental version of the ro-vibration energy-momentum map.

2 0 1 4 r e s e a r c h R e p o r t 23
PRINCIPAL CONTACT:
MercedesMartinson
PhDCandidateinPhysics
EngineeringPhysics
mercedes.m@usask.ca
Journal/Principal
publication:
JournalofSynchrotronRadiation,
Volume21,2014,pp.479-483.DOI:
10.1107/S1600577514003014
Authors:
MercedesMartinson1
NazaninSamadi2
GeorgeBelev3
BasseyBassey1
RobLewis4
GurpreetAulakh5
DeanChapman1
1
PhysicsandEngineeringPhysics
2
BiomedicalEngineering
3
BiomedicalImagingand
TherapyBeamlines
CanadianLightSource
4
MedicalImaging
5
AnatomyandCellBiology
Development of a bent Laue beam-
expanding double-crystal monochromator
for biomedical X-ray imaging
Introduction
Biomedical X-ray imaging techniques using
synchrotron light sources has been well established
[1-7]. Biomedical beamlines are in use around the
world for a variety of imaging techniques including
in-line phase contrast and micro-CT.At the CLS
in Saskatoon, two biomedical beamlines have been
commissioned.While both of these beamlines offer
high flux, they suffer the drawback of small beam
heights. BMIT-BM produces a maximum beam
height of approximately 7 mm at the 23 m source-
to-sample distance; BMIT-ID produces a maximum
beam height of 11 mm at the 55 m source-to-
sample distance.As a result, most samples must be
scanned vertically through the beam to image the
entire region of interest.
Vertical scanning poses severe limitations in two
major areas. CT scans must be made in small
vertical sections, and consecutive sections require
enough overlap to reliably stitch the projections
together, so regions of the subject are imaged
repeatedly, a time-consuming process. In addition
to longer scan times, the resulting vertical sections
must then be stitched together during processing,
which increases both processing time and likelihood
of error.
The second, and more important, limitation is in
dynamic imaging [8]. Many important physiological
processes can only be understood by capturing
movies of live systems. Examples include coronary
angiography and functional lung imaging [9-13].
Scanning subjects using synchrotron beam makes it
impossible to capture entire processes in one shot,
which represents a major limitation for cutting-edge
studies into physiological processes.
Science
When a crystal wafer is cylindrically bent with the
concave side facing the source, the diffracted beam
will diverge with a virtual focus on the incident
side of the crystal. Two such crystals placed in a
non-dispersive divergent geometry [14] (Figure 1)
produce a beam with a vertical height proportional
to the distance between the second crystal and the
virtual focal point of the first crystal. The bending
radius of the second crystal must be such that its
focal point is the same as that of the first crystal in
order to allow maximum reflection from the planes
in the second crystal.
The focal point of a crystal is a function of bending
radius, asymmetry and Bragg angles (χ and θΒ,
respectively). The relationships between focal
points, fij, and bending radii, ρi, are given below.
cos(χ – θΒ)
–
cos(χ + θΒ)
=
2 (1)
f11 f12 ρ1
cos(χ + θΒ)
–
cos(χ – θΒ)
=
2 (2)
f21 f22 ρ2
The expansion factor is determined by the ratio
of bending radii. For the preliminary attempt, the
following parameters were chosen: bending radius
of first crystal: ρ1=1 m (f12= -0.5 m), bending radius
of second crystal: ρ2=3 m (f21= 1.5 m), distance
between crystals: Δf =1 m.
A preliminary experiment was performed using
(1,1,1) silicon crystal wafers with a (1,1,1)-type
reflection such that χ=19.47°. The beam size and
shape were imaged on burn paper at three locations.
Expansion was calculated as the ratio between the
diffracted and incident beam.
Discussion
The beam was expanded vertically to a maximum
height 7.7x larger than the incident beam. The
beam quality was evaluated using both absorption
and phase-based imaging modalities.Absorption
imaging tests were conducted for both projection
and CT imaging. Flat-dark corrected images were
devoid of artefacts, despite a visible line of lower
intensity due to another competing reflection
diffracting away intensity.
The expanded beam was used to capture live animal
dynamic images using the flat panel detector
running at 30 frames per second. This setup allowed
an entire adult mouse to be imaged laterally in a
single shot (Figure 2).
1 Instrumentation Techniques
~
~

Flux was measured at 20.0 keV as
confirmed by the absorption K-edge using
a molybdenum filter. The measured flux
was calculated to be 1.2×107
ph/s·mm2
·mA
without a filter. This would produce a
surface dose of 2 mGy/s·mA. In contrast,
the beamline’s Bragg double crystal
monochromator produced a flux of 5.7×106
ph/s·mm2
·mA under the same conditions.
A knife-edge placed horizontally in the
expanded beam (Figure 3) revealed
significant vertical blurring, which increased
with the distance between the edge and
detector. The blurring was not present in
the horizontal direction, as a knife-edge
placed vertically produced a sharp image at
all distances. These results indicate that the
X-rays exiting the second crystal are parallel
horizontally but not vertically. The vertical
beam divergence can be explained by
diffraction occurring in-depth within both
crystals producing a polychromatic focus
and allowing multiple rays to exit the same
point in the second crystal but at different
angles.
Conclusion
The expanded beam was capable of
completely filling the high-resolution
(8.75 µm) Hamamatsu detector (FOV
31.08 mmH x 23.31 mmV) regularly used
for micro-CT. This expansion would allow
objects up to about 21 mm in height to be
imaged in a single rotation, rather than the
vertical scanning method traditionally used
at BMIT. This improvement would reduce
scan times by as much as 85%.
This proof-of-principle study was made
to determine whether a bent Laue beam
expander could be developed for biomedical
imaging applications. Beam expansion
was successfully performed under a variety
of conditions with expansions ranging
from 2x to 7.7x (Table 1). The measured
flux per unit area was comparable to
that available with the flat Bragg double
crystal monochromator currently used
in the beamline. The increase in total
photon count while expanding the beam
size is made possible by the enhanced
bandwidth of the bent Laue double crystal
monochromator.
Some initial experiments were performed to
demonstrate the viability and usefulness of
the method. Problems that were identified
include beam divergence after the second
crystal as well as non-uniformity of the
beam. The latter problem will be addressed
by better control over the crystal and
bending process but the beam divergence
effect will require further study.
Table 1: Summary of expansion results and energy parameters.
Attempt Incident
height
(mm)
Diffracted
height
(mm)
Expansion
factor
Silicon
Wafer
Reflection
type
Bragg
angle
Energy
(keV)
Proof-of-principle 2.5 9.0 3.6 (1,1,1) (1,1,1) 3.42° 33.16
Target of 3x 2.1 4.2 2.0 (5,1,1) (2,2,0) 6.56° 28.3
Target of 5x 2.9 15.0 5.2 (5,1,1) (2,2,0) 6.56° 28.3
Target of 7x 3.0 23.0 7.7 (5,1,1) (2,2,0) 6.56° 28.3
µCT imaging 4.0 28.0 7.0 (1,1,1) (1,1,1) 6.56° 17.3
Dynamic imaging 6.5 40 6.2 (1,1,1) (1,1,1) 6.31° 18.0
Flux 0.54 3.8 7.0 (1,1,1) (1,1,1) 5.67° 20.0
Figure 1. Schematic of the crystal geometry and orientation, ray-tracing diagrams and focal lengths.

2 0 1 4 r e s e a r c h R e p o r t 25
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Figure 2. Flat-dark-corrected frame from a movie of a live mouse captured with a 200 mm flat-panel detector
(Hamamatsu C9252DK-14) at 30 frames/s. The movie is available online in the supporting information. The vertical
line on the right is an artefact of the detector, not the beam.
Figure 3. Vertical and horizontal knife-edge placed at (a) 140 mm and (b) 5135 mm sample-detector distance.
Acknowledgements:
The authors wish to acknowledge Melanie van der
Loop for overseeing the live animal imaging test.
Mercedes Martinson, Nazanin Samadi, Bassey Bassey,
and Gurpreet Aulakh are Fellows, and Dean Chapman
and Rob Lewis are Mentors in the Canadian Institutes
of Health Research Training grant in Health Research
Using Synchrotron Techniques (CIHR-THRUST). This
work is supported in part by a Discovery Grant from the
Natural Sciences and Engineering Research Council of
Canada (NSERC) and Canada Research Chair.
Beamline information:
BMIT-BM beamline.

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