1. Nanoscale Science and Technology II. Tools and Processing Techniques
M. Meyyappan
Director, Center for Nanotechnology
NASA Ames Research Center
Moffett Field, CA
web:
Guest Lecturer: Dr. Geetha Dholakia
Nanoscale Imaging Tools

2. Overview of microscopy
Optical Microscope
Electron Microscopes
Transmission electron microscope
Scanning electron microscope
Scanning probe microscopes
Scanning tunneling microscope
Atomic force microscope
NOTE: This talk has been put together from material available in books, various websites, and from data obtained by NASA nanotech group. I have given acknowledgements where ever possible.

3. Image construction for a simple biconvex lens
OPTICAL MICROSCOPES
Image construction for a simple biconvex lens

4. Important parameters Magnification: Image size/Object size
Resolution: Minimum distance between two objects that can still be distinguished by the microscope.

5. Schematic of a simple optical microscope
Total visual magnification
MOBJ X MEYE

6. Rayleigh criterion for resolution Δx ~ 0.2μ;
Please check the first web site to watch a Java Applet on the dependence of Rayleigh criterion on  of incident radiation and on the numerical aperture.

7. THE ELECTRON MICROSCOPES
de Broglie : λ = h / mv
λ: wavelength associated with the particle
h: Plank’s constant ^-34 J.s;
mv: momentum of the particle
m_e: ^-31 kg; e ^-19 coloumb
P.E eV = mv2/2 => λ = 12.3/VÅ
V of 60kV, λ= 0.05 Å => Δx ~ 2.5 Å
Microscopes using electrons as illuminating radiation
TEM & SEM

9. Transformers: 20-100 kV; Vacuum pumps: 10-6 – 10-10 Torr
Components of the TEM
Electron Gun: Filament, Anode/Cathode
Condenser lens system and its apertures
Specimen chamber
Objective lens and apertures
Projective lens system and apertures
Correctional facilities (Chromatic, Spherical, Astigmatism)
Desk consol with CRTs and camera
Transformers: kV; Vacuum pumps: 10-6 – Torr

10. Schematic of E Gun & EM lens
Magnification: 10,000 – 100,000; Resolution: 1 nm-0.2 nm

11. TEM IMAGES
; com ;

12. Schematic of SEM
Physics dept, Chalmers university teaching material

14. Electron scattering from specimen
Resolution depends on spot size
Typically a few nanometers
Topographic scan range: order of mm X mm
X rays: elemental analysis

15. Some SEM images CNT in an array Blood platelet Dia: 7
CNT: NASA nanotech group; Blood cell: www. uq.edu. au

16. Scanning probe microscopy
1982 Binning & Rohrer, IBM Zurich.
STM, AFM & Family.
Resolution:
Height: 0.01nm, XY: 0.1nm
Local tip-sample interaction: Tunneling (electronic structure), Van der Waal’s force, Electric/Magnetic fields.
Advantages: atomic resolution, non destructive imaging, UHV, ambient/liquids, temperatures.
Diverse fields: materials science, biology, chemistry, tribology.

17. Scanning tunneling microscope
I  e-2d
I: Tunneling current;  (decay const.) =  2m/ h
d: tip-sample distance
; spm.aif.ncsu.edu

18. Operational modes and requirements
Vibration isolation: 0.001nm
Reliable tip - sample positioning
Electrical and acoustic noise isolation
Stability against thermal drift
Good tips
STM Mechanical stability
Topography (conducting surfaces and biological samples).
ST Spectroscopy (from IV obtain the DOS).
STP(spatial variation of potential in a current carrying film).
BEEM (Interfacial properties, Schottky barriers).

19. Electronics Current to voltage converter: Gain 108-1010 Bias Circuit
Feedback Electronics: Error amplifier, PID controller, few filters.
Scan Electronics: +X -X +Y -Y ramp signals (generated by the DA card).
HV Circuit amplifies the scan voltages and the feedback signal to ± 100 V from ± 10 V.
Data acquisition and image display

20. STM Images HOPG: ambient Si(7X7): UHV Courtesy: RHK Tech.
Physics dept, IISc, India
Si(7X7): UHV
Courtesy: RHK Tech.

21. Nasa nano group

22. Courtesy: Eigler, IBM Almaden
More pictures
2.6 nm X 2.6 nm self assembled organic film. Molecular resolution.
NASA nano group
Quantum corral
Fe on Cu(111)
Courtesy: Eigler, IBM Almaden

23. Scanning tunneling spectroscopy
dI/dV  DOS of sample
J.C. Davis Group, Berkeley.
Effect of Zn impurity on a
high Tc superconductor
T: 250mK.

24. Scanning tunneling potentiometry
Platinum film
Physics dept, IISc, India

25. ATOMIC FORCE MICROSCOPE;

26. AFM modes of operation Contact mode Non-contact mode
Force: nano newtons
Non-contact mode
Force: femto newtons
Freq. of oscillation 100kHz
Intermittent contact
Image any type of sample.
Park Scientific handbook

27. AFM Images
Mica: digital instruments; Grating:

28. Acronyms galore! MFM: Magnetic force microscopy
EFM: Electrostatic force microscopy
TSM: Thermal scanning microscopy
NSOM: Near field scanning optical microscope

29. Top-Down vs. Bottom-Up Techniques
• Top-down techniques take a bulk material, machine it, modify it into the desired shape and product
- classic example is manufacturing of integrated circuits
using a sequence of steps sush as crystal growth, lithography, deposition, etching, CMP, ion implantation… 
(Fundamentals of Microfabrication: The Science of Miniaturization, Marc J. Madou, CRC Press, 2002) 
• Bottom-up techniques build something from basic materials
- assembling from the atoms/molecules up
- not completely proven in manufacturing yet
Examples:
Self-assembly
Sol-gel technology
Deposition (old but is used to obtain nanotubes, nanowires, nanoscale films…)
Manipulators (AFM, STM,….)
3-D printers (

30. Deposition Techniques
Inorganic Materials
Organic Materials
• Physical
• Chemical (CVD)
• Plasma deposition
• Molecular beam epitaxy
(can be physical or chemical)
• Laser ablation
• Sol-gel processing
Thermal evaporation
• Spin coating
• Dip coating
• Self-assembling
monolayers
Sputtering

31. Physical Deposition Approaches
• Thermal evaporation
- Old technique for thin film dep.
- Sublimation of a heated material onto a substrate in a vacuum
chamber
- Molecular flux = N0 exp
= activation energy
- heat sources for evaporation (resistance, e-beam, rf, laser)
• Sputtering
- The material to be deposited is in the form of a disk (target)
- The target, biased negatively, is bombarded by positive ions
(inert gas ions such as Ar+) in a high vacuum chamber
- The ejected target atoms are directed toward the substrate
where they are deposited.

32. Sol-gel Process Sequence

33. Sol-gel Technology
• Versatile process for making ceramic and glass materials (powders, coatings, fibers… variety of forms).
• Involves converting from a liquid ‘solution’ to a solid ‘gel’
• Start with inorganic metal salts or metal alkoxides (called precursors); series of hydrolysis and polymerization reactions to prepare a colloidal suspension (sol).
• Next step involves an effort to get the desirable form
- thin film by spin or dip coating
- casting into a mold
• Further drying/heat treatment, wet gel is converted into desirable final product
• Aerogel: highly porous, low density material obtained by removing the liquid in a wet gel under supercritical conditions

34. Sol-gel Technology (cont.)
• Ceramic fibers can be drawn from the gel by adjusting the viscosity
• Powders can be made by precipitation, or spray pyrolysis
• Examples
- Piezoelectric materials such as lead-zircomium-titanate (PZT)
- Thick films consisting of nano TiO2 particles for solar cells
- Optical fibers
- Anti-reflection coatings (automotive)
- Aerogels as filler layer to replace air in double-pane structures

35. 3D Printing • Check http://www.mit.edu/tdp/www
• Solid freeform fabrication, currently working only at sub-mm level, is amenable for nanoscale prototyping
• Works by building parts in layers. Starts with a CAD model for the structure
• Each layer begins with a thin distribution of powder spread over the surface of a powder bed
• Technology similar to ink-jet printing
• A binder material selectively joins particles where the object formation is desired
• A piston is lowered that leads to spreading the next layer
• Layer-by-layer process is repeated
• Final heat treatment removes unbound powder
• Allows control of composition, microstructure, surface structure