III. TOOLS

1
Introduction to Nanotechnology
III. TOOLS M. Meyyappan Director, Center for
Nanotechnology NASA Ames Research Center Moffett
Field, CA 94035 email mmeyyappan_at_mail.arc.nasa.
gov web http//www.ipt.arc.nasa.gov Guest
Lecturer Dr. Geetha R. 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

3
Optical Microscopes

• Image construction for a simple biconvex lens

4
Schematic of a Simple Optical Microscope
Important parameters Magnification Image
size/Object size Resolution Minimum distance
between two objects that can still be
distinguished by the microscope.

• Total visual magnification
• MOBJ X MEYE

www.microscopy.fsu.edu
5
Rayleigh Criterion for Resolution
?x 0.2µ

• www.microscopy.fsu.edu www.imb-jena.de
• 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.

6
The Electron Microscopes

• Use the wave nature of an elecron for imaging
• de Broglie ? h / mv
• ? wavelength associated with the particle
• h Planks constant 6.63 x 10-34 J.s
• mv momentum of the particle
• me 9.1 x 10-31 kg e 1.6 x 10-19 coloumb
• P.E eV mv2/2 gt ? 12.3/?VÅ
• V of 60kV, ? 0.05 Å gt ?x 2.5 Å
• Thus higher resolution than the optical
  microscope is attainable
• Microscopes using electrons as illuminating
  radiation
• TEM SEM

7
TEM
8
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 20-100 kV Vacuum pumps 10-6
  10-10 Torr

9
Schematic of E Gun EM lens

• Magnification 10,000 100,000 Resolution 1
  nm-0.2 nm
• www.udel.edu

10
TEM Images
www.udel.edu www.nano-lab. com www.thermo.com
11
Schematic of SEM
Physics dept, Chalmers university teaching
material
12
SEM
13
Electron Scattering from Specimen
www.unl.edu

• Resolution depends on spot size
• Typically a few nanometers
• Topographic scan range order of mm X mm
• X rays elemental analysis

14
Some SEM Images
CNT in an array
Blood platelet Dia 7?
CNT NASA nanotech group Blood cell www.
uq.edu. au
15
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 Waals force,
  Electric/Magnetic fields.
• Advantages atomic resolution, non destructive
  imaging, UHV, ambient/liquids, temperatures.
• Diverse fields materials science, biology,
  chemistry, tribology.

www.spm.phy.bris.ac.uk
16
Scanning Tunneling Microscope
I ? e-2?d

• I Tunneling current ? (decay const.) ? 2m?/
  h
• d tip-sample distance
• www.mpi-halle.mpg.de spm.aif.ncsu.edu

17
STM 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).

18
STM 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

19
STM Images
HOPG in ambient Geetha Ramaswamy, Thesis (1999),
Physics Dept, I.I.Sc., India
Si(7X7) UHV Courtesy RHK Tech.
20
More Pictures

• Molecular resolution image of a self assembled
  monolayer (SAM).
• Geetha R Dholakia, W. Fan, M. Meyyappan,
  Appl. Phys. A, 80 1215 (2005).
• Quantum corral Fe on Cu(111)
• Courtesy Eigler, IBM Almaden

21
Scanning Tunneling Spectroscopy

• STM can also be used to obtain electronic data
  about the sample
• dI/dV ? DOS of sample
• For Eg Effect of Zn impurity on a high Tc
  superconductor
• T 250mK.
• (J.C. Davis Group, Cornell)

22
Scanning Tunneling Potentiometry
STM can also be used as a local probe of
potential and electric field Geetha Ramaswamy
and A.K. Raychaudhuri, A.P.L. Vol. 75, p. 1982,
1999.
Top Topography potential distribution in the
nanoscale in a platinum film. Bottom left
Electric field near a grain boundary triple point
(TP above).
23
Atomic Force Microscope

• www.fys.kuleuven.ac.be www.chem.sci.gu.edu.au

24
AFM Modes of Operation

• 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
25
AFM Images
Mica digital instruments Grating
www.eng.yale.edu
26
Acronyms Galore !

• Based on the force or physical quantity used to
  acquire the image, a number of scanning probe
  microscope techniques are available
• MFM Magnetic force microscopy
• EFM Electrostatic force microscopy
• TSM Thermal scanning microscopy
• NSOM Near field scanning optical microscope