The document discusses transmission electron microscopy (TEM), detailing its historical development, key components, and operational principles. It covers the adjustments of condenser lenses, resolution limitations due to aberrations, and sample preparation techniques for effective imaging. Additionally, it mentions various types of TEM and the importance of using ultrathin samples for optimal results.

1. TRANSMISSION ELECTRON MICROSCOPy(TEM) BYSUTAPA SAHAmsc. Inorganic chemistry2008-2010university of delhi

2. OUTLINE

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

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

5. DIAGRAM TO REPRESENT TEM’S WORKINGVirtual SourceFirst Condenser LensSecond Condenser LensCondenser Aperture SampleObjective LensObjective Aperture Selected Area Aperture First Intermediate LensSecond Intermediate LensProjector LensMain Screen (Phosphor)

6. 1. HIGH TENSION CABLEDIFFERENT COMPONENTS OF TEM2. ELECTRON EMITTER3. STEPPER MOTORS FOR CENTERING THE ELECTRON BEAM8. PROJECTOR LENS9. OPTICAL LENS4. CONDENSER5. APERTURE CONTROLS10. FLUORESCENT SCREEN6. SPECIMEN HOLDER7. OBJECTIVE LENS11. VACUUM PUMP LEADS12. GONIOMETER13. VACUUM AND MAGNIFICATION CONTROL14. FOCUSING CONTROL

7. SOME TYPICAL TEMs

8. ELECTRICAL CONNECTION OF THE GUN

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

10. Condenser lensesALIGNMENTIT 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 CONTINUEDCHANGING 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 ABERRATIONSpherical AberrationMarginal Focus Axial FocusOptic AxisDisc of minimum confusionChromatic AberrationLens Focus A Focus BPoint is imaged as discSPHERICAL ABERRATION IS CAUSED BY THE LENS FIELD ACTING INHOMOGENOUSLY ON THE OFF AXIS RAYS.Optic AxisDisc of minimum confusionLensCHROMATIC ABERRATION IS CAUSED BY THE VARIATION OF THE ELECTRON ENERGY & THUS ELECTRON ARE NOT MONOCHROMATIC

14. ASTIGMATISMCORRECTION OF ASTIGMATISMASTIGMATISM 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.yxLine focus in y directionLine focus in x directionIN 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 ABERRATIONOCTOPOLE 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 IMAGESIN 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 BEAMPREPARATION OF SAMPLETHE 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 METALGRID 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 TEMHIGH RESOLUTION TEMANALYTICAL TEMHIGH VOLTAGE TEM

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