1 Introduction - Electron Microscopy and Diffraction

Do Minh Nghiep  Materials Science Center 

Electron Microscopy and Diffraction 1. Introduction

Contact 





Lecturer: Đỗ Minh Nghi ệ p Tel. 38691332 e-mail: n hie mail.hut.edu.vn Class time: Mon 14:50-17:20 Class room: D6-106

01/01/2009

Handouts-MSE4346 -K51 KHVL

2

ourse ou comes 









n erstan ng o mage orma on elect el ectrom romagn agneti eticc le lense nses. s.

y g ass an

. Understanding of the construction of various types of  electron microscopes, the function of the various parts and methods of image formation. Understanding of methods of  sample preparation for  . Ability to utilize EDS and WDS results for  elemental  microchemical) analysis. ( microchemical)

01/01/2009

Handouts-MSE4346 -K51 KHVL

3

on en • • • • • • • • 01/01/2009

Introduction to to EM EM Electron optics Elec El ectr tron on so sour urce ce an and d vac vacuu uum m sys syste tem m Elec El ectr tron on-m -mat atte terr inter interac acttio ion n SE M TEM Electron diffraction EDS and WDS Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

4

Lab works 1. Preparation of an alloy specimen to observe its microstructure by SEM 2. Determination and imaging of chemical composition of the alloy specimen by SEM and EDS . repara on o an spec men o mage its microstructure and to analyze ED pattern 01/01/2009

Handouts-MSE4346 -K51 KHVL

5

ea ng 



Textbook: Handouts References:

1. D. B. Williams and C. B. Carter, Transmission electron microscopy , Books 1 to 4, Plenum Press, 1996 Electron ron micro microscopy scopy of thin crystals; Huntington, N. Y., R. 2. P. Hirsch, et al.; Elect . . ., 3. Elizabeth M. Slayter, Henry S. Slayter; Lig Light ht and ele electro ctron n mic microsc roscopy  opy ; Cam Ca mbr brid idge ge (E (Eng ngllan and) d),, Ne New w Yor ork, k, Ca Cam mbr brid idge ge Un Uniive vers rsit ityy Pr Pres ess, s, 19 1992 92 . form fo rmat atio ion n an and d mi micr croa oana naly lysi sis; s; Be Berl rlin in,, Ne New w Yo York rk,, Sp Spri ring nger er-V -Ver erla lag, g, 19 1993 93 5. John M. Cowley; Diffraction physics; Amsterdam, New York: North-Holland Pub. Co., New York: Sole distributors for the U.S.A. and Canada, Elsevier  NorthNor th-Hol Hollan land, d, 198 1981 1 01/01/2009

Handouts-MSE4346 -K51 KHVL

6

ra ng The weighting factors used to determine t e na gra e:

 

01/01/2009

Lab work and reports: Mid-term test and final exam:

Handouts-MSE4346 -K51 KHVL

20 % 70 %

7



Week 1 Week 2 Week 3 Week 4

Why elect electron ron micros microscope cope - a brief histo history ry Electron sources, Vacuum Electron optics, Electromagnetic lenses, Resolution limits Electron beam -specimen interactions



Week 5

Mid-term test 

Week 6

SEM: Scanning system, Detectors, SE image, Backscattered image, Resolution , , Diffraction, Phase) Microprobe analysis: Detection systems (EDS, WDS), Qualitative and quantitative analysis













Week 8



Week 9

Practical lab for SEM, EDS 



Week 10

Electron diffraction, Diffraction patterns



Week 11

Practical lab for TEM, ED



Week 12

Final exam

01/01/2009

Handouts-MSE4346 -K51 KHVL

8

Introduction • a er a s c arac er zza a on • H History istory • W Why hy EM EM ? • • O Overview verview of of SEM SEM and and TEM TEM TE 01/01/2009

Handouts-MSE4346 -K51 KHVL

9

characterization mean? 

Character: a sum of qualities that make a person / thing different from others



Characterize: to indicate / describe / investigate / express the character  of a person / thing (action)



Mater Ma terial ials s cha charac racter teriza izatio tion: n: internal nal micr microstru ostructure cture of an engineering materials - in specifying the inter including the chemistry, the crystallography, the structural morphology  engineerin eering g prope properties rties of materials, and reflects the need to - in terms of  engin know the physical, chemical and mechanical properties of the materials before we can design an engineering system or manufacture its components 01/01/2009

Handouts-MSE4346 -K51 KHVL

10

characterization is important?

It is believed that optimization of material properties through control of  . 01/01/2009

Handouts-MSE4346 -K51 KHVL

11

structure and properties • • At Atom omic ic le leve vel:l: Ph Phys ysic icss and and Che Chemi mist stry ry • Mi Micr cros osco copi picc leve level:l: Che Chemi mist stry ry and and Mat Mater eria ials ls Sci Sci.. . • Ma Macr cros osco copi picc leve level:l: Mec Mecha hani nica call and and Mate Materi rial alss Eng. Eng. 01/01/2009

Handouts-MSE4346 -K51 KHVL

12

of materials 





01/01/2009

Mechanical properties em ca proper es Physical properties - Th Ther erma mall prop proper erty ty - Op Optitica call prop proper erty ty - El Elec ectr tric ical al pr prop oper erty ty - Ma Magn gnet etic ic pr prop oper erty ty Handouts-MSE4346 -K51 KHVL

13

Equipments analysis molecular levels)

01/01/2009

Handouts-MSE4346 -K51 KHVL

14

Equipments analysis levels)

01/01/2009

Handouts-MSE4346 -K51 KHVL

15

Histor

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

16

Optica Opti call/l/liigh ghtt micr cros osco cope pe (OM) M):: visible light limits magnification of max 1000-2000X and resolution of 0,2 mm. Electron microscope (EM) is deve de velo lope ped d fo forr ov over erco comi ming ng th thes ese e lilimi mita tatition ons. s. 

1932 - 1938:

- The first TEM (1932, idea of EM, Max Knoll and Ernst Ruska, Germany) - The first SEM (1 (193 938, 8, la late ter  r STEM STEM - TEM with scanning coil, Knoll and , 

1940 19 40 -1 -195 952 2:

- The first SEM for thick sample (1942, Zworykin et al., RCA a ora or or es . . , re reso u on mm. - The first Fie ielld Em Emiiss ssio ion n el elec ectr tron on so sour urce ce (1942, FE Gun) - The SEM with resolution of 50 nm (1952, Oatley and McMullan, ng an 01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

17



1959-1967:

- SEM with stereoscan (Wells) - Performance of  SE detector  (1960, Everhart and Thornley) - The first co comm mmer erci cial al EM (1965) - Electron-channeling contrast for crystal orientatitio ons (1967) [Oatley (1982), J. Appl. Phys. 53, R1]

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

18

1932 theory of EM 1986 Nobel Prize winners 01/01/2009

Antonie van Leeuwenhoek, th .,

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

19

James Hillier 

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

20

1938 - First SEM is produced produced 01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

EM 1940 21

The prototype of the first Stereoscan supplied by the Company to the duPont duPo nt Com Company pany,, U.S.A. (Stewart and

McMullan’s original microscope

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

22

Wh EM ?

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

23

e n on 





Microscope - A device with a lens or series of lenses

that enlarge (magnify) the appearance of an object . Image - Perception of an object using your eyes ( vision). One can sense an object without vision (touch, etc..). Requ Re quir ires es vi visi sibl ble e liligh ght. t. Lens - A lens is an optical component  which is used to . glas assy sy ma mate teri rial  al , whereas non-uniform made of a gl electromagnetic electromagne tic fields are used as lens for electrons.

01/01/2009

Handouts-MSE4346 -K51 KHVL

24



Ma nification - The ratio between ima e size to the obje ob ject ct si size ze. Can be varied by changing the distance

between the object and the final lens (of the eye) or by . 

Wavelength - Distance between peaks of the waveform.

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

25



Resolution

- RP is the the sma smalle llest st points at which two or more objects can be distin dis tin uis uished hed as se ara arate te. - Res Resolu olutio tion n is is the ability of  a lens to distinguish at infinity, when they are viewed in the image plane. 01/01/2009

Handouts-MSE4346 -K51 KHVL

26

’

RP ≈ (1/2)λ 

In 1870, Ernst Abbe (1840-1905) de deri rive ved d ma math them emat atic ical al expression for resolution of microscope: Res Resolu olutio tion n is 

limited to

≈  0.5

the wavelength of illuminating source.

,

RP = ---------------NA = n.sin  n - ind index ex of refr refract action ion

α  - half angl angle e of illum illuminati ination on .

increasing the half angle of illumination, b) in incr cre eas asin ing g th the e re reffra ract ctiv ive e index of the lens by using Crown glass, and c) decreasing the . 01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

27



Increase sin α  decr cr.. wo work rkin in dista tan nce incr cr.. si size of of th the le lens :



Increase refractive index n (oil refractive index is higher than air)

01/01/2009

Handouts-MSE4346 -K51 KHVL

28

Replacing visible light by electron beam

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

29

01/01/2009

Handouts-MSE4346 -K51 KHVL

30

e sma est stance etw twe een two po nts t at can e resolved by 

uman eye:

. - . mm



Light microscope:

0.2 μm



SEM:

1-2 nm



TEM:

2Å

This high resolution is achieved by TEM thanks to the use of a high energy electron beam (small wavelength). 01/01/2009

Handouts-MSE4346 -K51 KHVL

31

ew ng op ons Instrument

Magnification

Resolution [µm]

Sample environment

ye Magnifying glass Optical microscope

TEM

01/01/2009

r 

Sample thickness

c

2-10

15-100

Air 

Thick

200-1300

0.2

Air or Oil

Thick

-

.

acuum

103-1.5X106

0.00014

Vacuum

Handouts-MSE4346 -K51 KHVL

c Thin

32

Electron-- d Electron dual ual (wave(wave-particle) (w -particle) character: Light particles - M Matter atter waves waves wa Hermann Busch (1924): Axial magnetic fields refract electrons

Planckk constant constant (6.624 X 10-27 erg/s erg/s)) h - Planc v - ele  p = mv : momentum) electr ctron on vel veloci ocity ty ( p V - acc accele elerat rating ing vol voltag tage e mo - res restt elec electro tron n mass mass - re a v s c e ec ron mass

01/01/2009

.

x

-

gram =

Handouts-MSE4346 -K51 KHVL

o pro on 33

e

≈ 



ro g e re at ons p 1/2

Resolution limit of light microscope: - can ec ecrease o nm - n.sinα  is limited to ≈ 1.6 - Thu Thuss the the ma maxim ximum um res resol oluti ution on is abo about ut 200 nm Cannot go beyond this even with better optics. Solution ? Use illumination of  shorter wavelength

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

34

eso u on o m croscopes 

Resolution of electron microscope:

- λ can decrease to ≈ 10-3 nm - n.sinα  is very small, because n ≈ 1 and α  ≈ 0.1 radians , of 0.0389 Å and a theoretical resolution of 0.0195 Å ! - But in pra practi ctice ce most most TEM TEMss will will on only ly hav have e an actual  resolution 2.4 Å at 100 kV

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

35

refraction/bending

on a ray of illumination entering a medium of differing density causing . In the vacuum environment of  an electron microsco e the index of refraction is 1.0 and therefore NA depends solely on the half   angle α  of ilillu lumi mina natition on.. 

In electron microscopy the refractive index cannot exceed . , e a ang e s very sma , and thus the only thing that can be adjusted is decreasing the 

Refractive index: n = tan i/tan r 01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

36

en ng y enses Conver Conv ergi ging ng (c (con onve vex/ x/po posi siti tive ve)) le lens ns:: bends rays toward the axis. It has a positive focal length. Forms a real  inverted image of an object placed to the left of the first focal point and an erect virtual image of an object placed between the first focal point and the lens. 

Diverging (concave/negative) lens : bends away ay fr from om th the e ax axis is. It has a the light rays aw negative focal length. An object placed 

in an erect virtual image. It is not possible to construct a negative magnetic lens although neg ne gat ativ ive e ele lect ctro rost stat atiic le lens nses es ca can n be ma made de.. 01/01/2009

Handouts-MSE4346 -K51 KHVL

37

Glass lenses (curved glass or mirror) for visible light  concave convex

Electromagnetic lenses (solenoid/coil) for  (electron, protons, positrons) 01/01/2009

Handouts-MSE4346 -K51 KHVL

38

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

39

Equipments for structural analysis m croscop c eve s

01/01/2009

Handouts-MSE4346 -K51 KHVL

40



Scan Sc Scanning anni ning ng El Elec ectr tron on M Micr Mi iccros ro osco sccope op pes es - SEM Versions: Environmental (ESEM) / Low Voltage (LV LVS SEM) /

ar e ressure Field Emission (FE FESEM) SEM)

eva e

ressure

,

-



Versions: High Resolution (HR HRT TEM), Scanning- (STEM),

Field Emission (FE FET TEM), Energy Filtering (EF EFTEM) TEM) 

Anal An Analytical alyt ytic ical al El Elec ectr tron on M Micr Mi iccros ro osco sccope op pe e - AE M Versions: SE SEMM-ED EDS/ S/WD WDS, S, ST STEM EM-E -EDS DS-E -EEL ELS S

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

41

Overview of EMs

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

42

nnin El r n Microscope - SEM 



SEM is an instrument using electron light to image and control the material sample in very fine scale. What is imaged and controlled: controlled :  – Surfa Surface ce topogr topography aphy (SE: micro microstru structure cture roug roughnes hness) s)  – , and size)  – Com Compos positi ition on con contra trast st (BS (BSE) E)  – Elem Elementa entall composi composition tion (EDS/ (EDS/WDS: WDS: qual qualitati itative ve and and quantitative analysis)  –

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

43



The

SEM

is

a

distinctly

image formation than is an optical microscope and a TEM. In the SEM, the probe examines the object one spot at  a time, then gives out an array n o e resu s rom many ma ny sp spot ots. s. 

The optical microscope, (also TEM) conversely, takes the signals from simultaneouslyexamined spots, and gives em ac a a once. 

01/01/2009

Handouts-MSE4346 -K51 KHVL

44

01/01/2009

Handouts-MSE4346 -K51 KHVL

45

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

46

Construction of SEM

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

47

Construction of SEM

JEOL SEM 6335F 01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

48

unc ons o 

ma n par s

Electr Elec tron on gu gun n (fi (filam lament ent/ca /catho thode, de, Weh Wehnel neltt cylinder, anode): gen genera eratin ting/ g/ emi emitti tting  ng  electron beam





Lens system (condense and objective lenses): focusing/linking electron beam Scanning coil: scanning electron beam over specimen surface



coll llec ecti ting ng ele lect ctro rons ns an and/  d/  Detectors:: co Detectors  x-rays



Mearurement system (Cathode Ray Tube-CRT, electronic devices): data amplifying, acquisition and processing  01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

49



ormat on o acce erate e ectron eam towar   specimen by a positive voltage (kV)









01/01/2009

narrow beam with electromagnetic lenses and metallic meta llic diap diaphrag hragms/a ms/apertu pertures res Focusing and scanning electron beam into specimen surface through electromagnetic lenses and scannin coil Beam-specimen interaction Data ac acqu quis isititio ion n an and d im imag agin ing g Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

50

In environmental SEM 

Ionizing of rest gas to eliminate electric charge on , - A low low vac acu uum is us used ed avaiable - Hy Hydr drat ated ed spe speci cime mens ns are are all allow owed ed - Che Chemic mical al comp composi ositio tion n is ana analyz lyzed ed for for only only specimen (without coating)

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

51

econ ary

(BSI) 

Compositional contrast



Transmitted Transm itted Electron Imaging (TEI) 

Internal ultrastructure



01/01/2009

Sca cann nniin nnin in El Ele ect ctro ron n Microscope (SEM)

Energy-Dispersive X-ray Spectrometry (EDS)

ec ron mag ng (SEI)

Surface topography, ,

Electron Backscattered Diffraction (EBSD) 

Crystallographic info

Elemental composition, mapping and linescans Handouts-MSE4346 -K51 KHVL

52



ros strengt s : - Hig Higher her reso resolut lution ion and and dept depth h of fie field ld than than that that of OM OM (the (the surf surface ace of  - Allows Allows for dir direct ect obs observ ervati ation on of sur surfac face e morp morphol hology ogy - InIn-sit situ u envir environm onment ental al studi studies es are are possi possible ble (e.g (e.g.. catal catalyst ystss in an atmosphere) - Mi Micr croa oana naly lysi siss (com (compo posi sitition on of of sma smallll are areas as)) - Typ Typica ically lly a low powe powerr techni technique que,, so orga organic nic mat materi erial al can can be be studie studied d - Ver Veryy good good at at looki looking ng at an aver average age of of sizes sizes and arra arrange ngemen ments ts in in a - Easy Easy op oper erat atio ion n and and ma main inte tena nanc nce e - Neg Neglig ligibl ible e damage damage of spec specime imen n (throu (through gh coat coating ing,, heati heating ng duri during ng radiation

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

53

Pros and cons of SEM 

Cons (weaknesses/limitations) (weaknesses/limitations):: -

01/01/2009

Specim Spec imen enss mus mustt be be sui suita tabl ble e in in vac vacuu uum m False/ Fal se/art artifi ificia ciall out output putss thr throug ough h sam sample ple pre prepar parati ation on Coat Co atin ing g nonnon-co cond nduc uctitive ve sam sampl ples es is is req requi uire red d The Th e cry cryst stal allilini nity ty ca cann nnot ot be de dete term rmin ined ed Resolu Res olutio tion n is often often not suf suffic ficien ientt to tel telll all all of the the surf surface ace fea featur tures es Scanni Sca nning ng proc process ess is slo slow w and and so sam sample ple may mov move e lead leading ing to distorted images

Handouts-MSE4346 -K51 KHVL

54

Transmission Electron Microscope - TEM TEM

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

55

01/01/2009

Handouts-MSE4346 -K51 KHVL

56

01/01/2009

Handouts-MSE4346 -K51 KHVL

57

Electrons path in TEM: condenser lens(es) and aperture → sample → objective lens(es) and aperture → projector  lens es → screen

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

58



TEM is designed to project a onto screen (we see only the shadow of the specimen). It’s thanks to contrast (intensity difference) of  ransm e unsca ere an forward diffracted / scattered beam. 

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

59

-

-

Each particle image represents a 2D projection of the 3D object

A single projection image is plainly insufficient to infer the struct str ucture ure of an ob ect ect.. 01/01/2009

Handouts-MSE4346 -K51 KHVL

60

-

Watch out! A cover slide!

01/01/2009

Handouts-MSE4346 -K51 KHVL

61

High Resolution TEM - HRTEM HRTEM Con Co ntr tra ast in inte tens nsit it di diff ffer ere enc nce e on ima e la lane ne:: 

Mass-thickness contrast (BF imaging)



Diffraction contrast (BF, DF imaging)



Phase contra contrast st / HREM and Moire’ Moire’ fringe fri nges s (HR ima imagin ging) g)

01/01/2009

HREM image

Interference pattern

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

62

comparison of parameters

01/01/2009

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

63

TEM ca abilities Electron Diffraction

BrightBrigh t- and Dark-Fie Dark-Field ld Imaging Imaging mag ng   



Internal ultrastructure Nanostructure dispersion Defect identification

High-Resolution Transmission Transm ission Electron Microscopy (HR-TEM)  

Interface structure Defect structure

Microscope (TEM)

Energy-Dispersive X-ray Spectrometry (EDS)

Crystallographic info

Electron Energy Loss Spectroscopy (EELS)  

Chemical composition Other bonding info

Elemental composition, mapping and linescans 01/01/2009

Handouts-MSE4346 -K51 KHVL

64

- Very hig high h resoluti resolution on is poss possible ible 

Cons - Ex ensive machine for hi h resolution - Extre Extreme me heatin heating g of the sample sample can can destro destroyy it - Only thin sam samples ples can be be studie studied d - Sam Sampl ple e must must be be in a goo good d (10 (10-6 Torr) vacuum

01/01/2009

Handouts-MSE4346 -K51 KHVL

65



SEM High resolution for thick bulk samples: 20-50 Å (most commercial SEM) and < 10 Ao



 



3D-imaging due to large depth of field ma magn ca on ava a e as for light microscope

01/01/2009



TEM High resolution (1,2-1,5 Å) for very thin samples (most commercial TEM) Information about crystal structure (crystal lattice an or en a on, dislocation, twinning,…)

Handouts-MSE4346 Handouts-MSE4346 -K51 KHVL

66