THIS IS A PRESENTATION ON TRANSMISSION ELECTRON MICROSCOPY .(APART FROM DIFFERENT BOOKS,I HAVE ALSO TAKEN INFORMATION FROM DIFFERENT WEBSITES & PRESENTATIONS AVAILABLE IN NET ..

1. TRANSMISSION ELECTRON MICROSCOPy (TEM) BY SUTAPA SAHA msc. Inorganic chemistry 2008-2010 university of delhi

2. OUTLINE

3. INTRODUCTION IN 1931,WHILE CONDUCTING RESEARCH FOR HIS MASTERS AT THE TECHNICAL COLLEGE OF BERLIN,ERNST RUSKA & MAX KNOLL DESIGNED THE FIRST TEM ERNST RUSKA MAX KNOLL SPECIMEN MUST BE ULTRATHIN

4. SIMPLE DIAGRAM TO SHOW THE DIFFERENCE BETWEEN SLIDE PROJECTOR & TEM

5. DIAGRAM TO REPRESENT TEM’S WORKING Virtual Source First Condenser Lens Second Condenser Lens Condenser Aperture Sample Objective Lens Objective Aperture Selected Area Aperture First Intermediate Lens Second Intermediate Lens Projector Lens Main Screen (Phosphor)

6. 1. HIGH TENSION CABLE DIFFERENT COMPONENTS OF TEM 2. ELECTRON EMITTER 3. STEPPER MOTORS FOR CENTERING THE ELECTRON BEAM 8. PROJECTOR LENS 9. OPTICAL LENS 4. CONDENSER 5. APERTURE CONTROLS 10. FLUORESCENT SCREEN 6. SPECIMEN HOLDER 7. OBJECTIVE LENS 11. VACUUM PUMP LEADS 12. GONIOMETER 13. VACUUM AND MAGNIFICATION CONTROL 14. FOCUSING CONTROL

7. SOME TYPICAL TEMs

8. ELECTRICAL CONNECTION OF THE GUN

9. IN CASE OF (TE) ACCORDING TO RICHARDSON’S LAW WHERE, Jc=CURRENT DENSITY(Am-2 ) k =1.38 ×10 -23 J K-1 (BOLTZMANN’S CONSTANT) TC=CATHODE TEMPERATURE A≈ 12×10⁵ AK-2m-2 Øw =WORK FUNCTION IN CASE OF (FE) ACCORDING TO FOWLER NORDHEIM FORMULA WHERE, E= ELECTRIC FIELD REST OF THE TERMS BEAR MEANING AS USUAL. Jc = k1 |E|2/øw exp(-k2 øw3/2/|E|) Jc = ATc2 exp(-øw/ kTc)

10. Condenser lenses ALIGNMENT IT CONTROLS HOW STRONGLY THE BEAM IS FOCUSED ( CONDENSED) ONTO THE SAMPLE.IT DETERMINES THE SIZE OF THE SPOT THAT STRIKES THE SAMPLE

11. CONDENSER LENSES CONTINUED CHANGING THE STRENGTH OF THE TWO LENSES WE CAN CHANGE THE POSITION OF THE FOCUS

12. HERE WE SEEM TO HAVE BROKEN A RULE, IN THIS DIAGRAM. WE HAVE BENT THE RAYS IN FREE SPACE AT THE PLANES, WHERE THEY REACH FOCUS ACCORDING TO THE PREVIOUS DIAGRAM. SURELY BEAMS JUST CAN’TBEND, WITHOUT HAVING A LENS OR DEFLECTION COIL. TRUE. IN FACT, WHAT WE ARE DOING IS CHANGING OUR ATTENTION FROM ONE SET OF BEAMS THAT PASS THROUGH THE FIRST LENS, TO A 2ND SET OF BEAMS THAT PASS THROUGH THE 2ND LENS. CONDENSER LENSES CONTINUED AS WE CHANGE THE EXCITATION OF THE TWO LENSES,THE MAGNIFICATION OF THE IMAGE CHANGES.THIS WAY ADJUSTING THE EXCITATION OF THE TWO LENSES WE CAN VARY THE SPOT SIZE.

13. RESOLUTION IS LIMITED BY LENS ABERRATION Spherical Aberration Marginal Focus Axial Focus Optic Axis Disc of minimum confusion Chromatic Aberration Lens Focus A Focus B Point is imaged as disc SPHERICAL ABERRATION IS CAUSED BY THE LENS FIELD ACTING INHOMOGENOUSLY ON THE OFF AXIS RAYS. Optic Axis Disc of minimum confusion Lens CHROMATIC ABERRATION IS CAUSED BY THE VARIATION OF THE ELECTRON ENERGY & THUS ELECTRON ARE NOT MONOCHROMATIC

14. ASTIGMATISM CORRECTION OF ASTIGMATISM ASTIGMATISM MEANS THAT THE STRENGTH OF THE LENS IS DIFFERENT IN TWO DIFFERENT DIRECTIONS.THAT MEANS THERE ARE NOW TWO FOCUS POINTS. ASTIGMATISM CAN BE COMPENSATED FOR BY PLACING A SIMPLE STIGMATOR IN THE POLEPIECE BORE OF THE LENS. STIGMATOR WORK BY ADDING A SMALL QUADRUPOLE DISTORTION TO THE LENSES. y x Line focus in y direction Line focus in x direction IN ORDER TO COPE WITH EVERY POSSIBLE ORIENTATION OF ASTIGMATISM,WE NEED TWO SETS OF QUADRUPOLES MOUNTED AT 45⁰ DEGREES TO ONE ANOTHER. THE OVAL IS MEANT TO REPRESENT A PERSPECTIVE VIEW OF THE TOP OF THE LENS.

15. SPHERICAL ABERRATION CAN BE COMPENSATED FOR BY A COMBINATION OF MAGNETIC QUARDRUPOLE & CORRECTION OF SPHERICAL & CHROMATIC ABERRATION OCTOPOLE LENSES, WHEREAS ACOMBINATION OF ELECTROSTATIC & MAGNETIC QUADRUPOLES IS NECESSARY FOR THE CHROMATIC ABERRATION. IN BF ONLY THE TRANSMITTED PRIMARY BEAM IS ALLOWED TO PASS OBJECTIVE APERTURE TO FORM IMAGES IN DF ONLY DIFFRACTED BEAMS ARE ALLOWED TO PASS THE APERTURE

16. SAMPLE MUST BE THIN ENOUGH,SHOULD BE OF THE ORDER OF 100-200 nm, SO THAT IT CAN TRANSMIT AN ELECTRON BEAM PREPARATION OF SAMPLE THE THINNER THE SAMPLE,LESS IS THE SCATTERING OF THE ELECTRON BEAM AND BETTER THE IMAGE & ANALYTICAL RESOLUTION. IN CASE OF MATERIALS OF SMALL DIMENSION LIKE POWDERS OR NANOTUBES,A DILUTE SAMPLE CONTAINING THE SPECIMEN IS DEPOSITED ONTO SUPPORT GRID OR FILMS. IN CASE OF METALS & SEMICONDUCTORS DIFFERENT TECHNIQUES LIKE ELECTROPOLISHING,CHEMICAL ETCHING ARE USED. IN CASE OF BIOLOGICAL SAMPLES DIAMOND KNIFE OR ULTRAMICROTOME IS USED TO CUT THIN SECTIONS. SOMETIME TO INCREASE THE CONTRAST & TO ISOLATE A CERTAIN AREA OF INTEREST STAINING METHOD IS USED. MORE RECENTLY FOCUSSED ION BEAM METHOD HAVE BEEN USED TO PREPARE SAMPLES.THIS TECHNIQUE MAKES IT POSSIBLE TO MILL VERY THIN MEMBRANES FROM A SPECIFIC AREA OF INTEREST IN A SAMPLE LIKE SEMICONDUCTOR OR METAL GRID IS A SIEVE WOVEN FROM A THIN METAL WIRE,USUALLY NICKEL OR COPPER GRIDS OF 3 mm DIAMETER ARE COMMERCIALLY AVAILABLE WITH DIFFERENT MESH SIZES(GENERALLY OF 100-200 µm SIZE)

17. CONVENTIONAL TEM TYPES OF TEM HIGH RESOLUTION TEM ANALYTICAL TEM HIGH VOLTAGE TEM

18. THANK YOU