The New TEM facility at LCI, KSU. Min Gao Liquid Crystal Institute Kent State University

Transcription

1 The New TEM facility at LCI, KSU Min Gao Liquid Crystal Institute Kent State University 1

2 Questions to be answered How does TEM work? Why thin specimen? How to prepare one? What is the TEM at LCI like? Functions available and principles? How is the facility running so far? Any exciting results? How to use the TEM lab? 2

3 Facts about the TEM facility at LCI Instruments Specifications Applications 3

4 What we have at LCI FEI Tecnai F20ST-STEM Schottky field mission gun 40 kv-200 kv 0.24 nm point-to-point resolution ±70 tilting angle 0.2 nm spot size Attachments Low-dose mode & tomography EDAX energy dispersive x-ray spectrometer (EDS) Gatan imaging filter (incl. EELS) 4k*4K slow scan CCD Cryo-holder & anti-contaminator Assisting equipments Vitrobot Plasma cleaner Vacuum station 4

5 How good is this microscope? It would be very easy to make an analysis of any complicated chemical substance; all one would have to do would be to look at it and see where the atoms are. I put this out as a challenge: Is there no way to make the electron microscope more powerful? Richard P. Feynman, 1959, There s Plenty of Room at the Bottom 1 Corrected EM Haider (200keV) La in γ-al 2 O 3 in situ -1 Resolution (Ang. ) Electron Microscope Light Microscope Amici Ross Abbe Marton Ruska Dietrich (200keV) Year Borisevich, 2004 Batson et al. Nature 2002 Second best thing after corrected TEM It is the best thing considering Cost of TEM and maintenance Easy to use 85% applications do not need Cs corrector 5

6 General description of the TEM facility at LCI Things making this facility standing out: the optimum integration of some most advanced TEM techniques, for example: cryoem An application-oriented versatile microscope Excellent for materials science/life science/solid state physics/chemistry Current setup: nanomaterials/soft-materials requiring simple sample preparation A heavily computerized TEM with some bugseasy to operate 6

7 Philips and FEI microscopes EM420 CM200 7

8 I've gotta see some atoms, excuse me, --Obama Titan 8

9 How much a TEM cost? $4-5 per ev 200 kev: 1M$ + accessories (easily up to 0.5-1M) extremely stable high-voltage supplies, extremely stable currents to each electromagnetic coil/lens, continuously-pumped high- or ultra-high-vacuum systems, and a cooling water supply circulation through the lenses and pumps. As they are very sensitive to vibration and external magnetic fields, microscopes designed to achieve high resolutions must be housed in stable buildings (sometimes underground) with special services such as magnetic field cancelling systems. There must be some solid reasons that we need such an expensive machine! 9

10 How does TEM work? Importance of thin specimens Electron-material interaction Techniques and Information 10

11 Advantage of thin samples 50 nm Cu, 25 kv, 5 nm probe, 1000 electrons 50 nm Cu, 200 kv, 1 nm probe, 1000 electrons Thin specimen in SEM (Thin specimen in) TEM Where is my surface? Surface damage 11

12 What thin samples do you need? Represent the material you are studying: sometimes the thicker the better Electron transparent: dependent on the accelerating voltage, thickness of the specimen, and atomic number of the specimen. Uniformly thin Stable under the electron beam Conducing and nonmagnetic in the laboratory environment Generally speaking: nm for conventional TEM; 15 nm for high resolution TEM 12

13 How to put the thin samples into the TEM? The general form of a TEM specimen is a 3mm thin disk Supporting grids Put the thin disk into a holder which goes to the TEM sample stage 13

14 How to prepare a thin sample? Bulk materials: Agate Mortar and Pestle Bulk & thin films: Wheel Saw Polishing machine Dimpler Ion milling A lot of techniques have been developed to make TEM specimens 14

15 Focused ion beam: TEM samples Au+Pd coating first Deposition of Pt protection layer View from 52 Start of cutting Under cut

16 Other materials Nanomaterials: Biomaterials Very easy Quite difficult Dispersed on supporting carbon film Vitrobot Ultramicrotomy 16

17 Electron-thin specimen interaction Backscattered Electrons (Rutherford) Incident electron beam (E) Characteristic X- rays EDS Secondary electrons Auger electrons Cathodoluminescence Light E f E f E f E f E E e-h pair EBIC Specimen Large-angle Incoherent elastically scattered electrons (Rutherford) Z-contrast STEM Coherent elastically scattered electrons Diffraction Imaging HRTEM E- E Inelastically scattered electrons Other signals from interaction with many nuclei or electrons: Bremsstrahlung x-ray (EDS), Plasma excitation (EELS) EELS EFTEM 17

18 Instruments (TEM & STEM) Reimer, TEM,

19 Information from a modern TEM Gao et al. PRB, 62, 5413 (2000) In situ Gao et al. APL, 72, 2544 (1998) Gao et al. Unpublished Why TEM? CBED Gao et al. JAP, 80, 4767 (1996) EELS /EDS Gao et al. Z. Metallkd. 93, 438 (2002) O-K 1s 2p O Si Mo Mo/SiO x Gao et al. PRB, 62, 5413 (2000) Gao & Duan, Mater. Trans. JIM, 39, 883, 1998 Si 19

20 Knowing the limitations of TEM Artifacts due to 2-D projections (3D TEM) Interpretation of images Poor Sampling: all TEMs have only examined <1 mm 3 of materials! (First use low resolution but better sampling tools) Electron beam irradiation and contamination (diffraction imaging, low temperature, low dose, cryoem) Sample preparation (low temperature, low-energy low angle ion milling, FIB-site specific, freeze-fracture, vitreous ethane ice) Vacuum environment (environmental EM, in vitro) Not so much about properties (in situ, combination) 20

21 Au+Si+O Si_L C_K O_K What have been done in the test running period at LCI? Service summary Available techniques Representative results 21

22 TEM Startup Holiday Cryo-trial Min in China Service hours FEI Cryo Training Number of samples Weekly service hours and number of samples Total service hours: 186 Cryo: 83 hrs Week Total number of samples: 113

23 Service hours vs groups Soumitra Basu Teaching Laurie Broadwater 6%1% 4% 20% Peter Palffy-Muhoray Songping Huang Mieteck Jaroniec 20% L.C. Chen 4% 8% 30% 4% 3% Quan Li Oleg Lavrentovich Tony Jakli

24 Available TEM techniques Imaging (diffraction contract, high resolution, Z-contrast, energy-filtered) Diffraction (select-area, convergent beam, large angle CBED, nano-area) Spectrometry (EDS, EELS) CryoEM 3D tomography 24

25 Imaging (contrast) Mass and thickness contrast Diffraction contrast Phase contrast (e.g., HRTEM) Z-contrast 25

26 Imaging (LCI)

27 TEM bright field image and STEM Z-contrast (dark field) image Sample from Prof. Peter Palffy-Muhoray s group

28 HRTEM Sample from Prof. Peter Palffy- Muhoray s group

29 HRTEM of quantum dots Sample from Prof. LC Chien s group

30 Diffraction Sample from Dr. Quan Li s group 30

31 An nteresting sample C SiO x Au Sample from Prof. Peter Palffy-Muhoray s group

32 EDS spectral imaging Au O Si Au+Si+O Si_L C_K O_K Sample from Prof. Peter Palffy-Muhoray s group

33 Cryo-Vitrobot Controlled environment: temperature (4-60 C) and humidity (room cond. 100%) designed for bio and liquid A small droplet of liquid is applied to pre-treated carbon film Two filter papers are used to blot the liquid and leave a thin layer of liquid (e.g., 100 nm thick, adjustable blot force, time and repetition). Shoot the sample into coolant (ethane) and freeze it at very high speed.

34 First bio-sample Laurie Broadwater, Chemistry

35 A thermotropic sample Sample from Prof. LC Chien s group

36 A lyotropic sample Sample from Prof. Oleg Lavrentovich s group

37 Resolution beyond freeze fracture Very challenging: <10 e/nm 2 Sample from Prof. Jakli s group

38 Diffraction in Liquid Crystals Larger area Sample from Prof. Jakli s group

39 3D tomography A video taken by Dr. Lee Pullan (FEI) during the cryoem training 39

40 Plan for the next step Soon be running regularly Rules and operation procedures Usage rates (machine use, staff service) and billing Self-user Training: Single operator MG + several self-users Right now: 1-on-1 based on research needs Later: a TEM course including lab training if allowed Web page of the facility 40

41 How to use the facility more efficiently Highly efficient, professional, yet friendly service The TEM will be aligned by the staff routinely, so you do not need to be an expert in TEM Know your sample as well as possible If you don t know TEM so well, have an in-depth discussion with the staff before scheduling your experiment Have a student with good experimental skills and a lot of patience Analyze your data immediately Introduce more outside users to keep the rates low Acknowledge the facility properly Pay your bill in time 41

42 Questions being answered How does TEM work? Why thin specimen? How to prepare one? What is the TEM at LCI like? Functions available and principles? How is the facility running so far? Any exciting results? How to use the TEM lab? 42