NANO SCALE IMAGING

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NANO SCALE IMAGING Cheng-Lin Zheng Project
Advisors Katharine Dovidenko, Vincent
LaBella  School of Nanosciences and
Nanoengineering UAlbany Institute for
Materials, University at Albany - SUNY Academic
Advisor Palmyra Catravas, Union College
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Outline

• Introduction on carbon nanotubes (CNT)
• Two nano-scale characterization Methods Focused
  Ion Beam Microscopy and Scanning Tunneling
  Microscopy
• Images Taken with Focused Ion Beam Microscope and
  Scanning Tunneling Microscope
• Discussion

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Introduction

• What are carbon nanotubes (CNT)?
• Visualized as 2-D graphite sheets rolled into
  tubes
• Carbon atoms in hexagonal array
• Electrical and mechanical properties determined
  by atomic arrangement, diameter and length of CNT
• SWCNTs and MWCNTs
• Properties of CNT
• Mechanical properties extremely strong
• High thermal stability and conductivity
• Can be either semiconductor or metallic
• Some issues
• Indirect measurement of CNTs
• Uncertainty in data obtained from indirect
  measurement
• Project goal
• Compare advantages and trade-offs of two
  nano-scale characterization methods Focused Ion
  Beam Microscopy and Scanning Tunneling Microscopy

CNT
(b) Carbon Nano Tubes of FIB
(a) Graphite Sheet Image of STM
Reference (a) STM image taken by Autumn
Carlsen, (c) and (d) Simulated
images, E. T. Thorstenson, Z. Ren, T-W. Chou,
Composites Science and Technology 61 (2001)
1899-1912
(d) Simulated CNT Image
(c) Simulated Graphite Sheet Image
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Focused Ion Beam Microscope (FIB)

• Main components
• source of ions (Ga-ion, 30kV)
• ion optics column
• sample stage
• secondary electron detector
• gas injection systems
• Secondary electrons emitted from the sample are
  collected to form the image.
• Applications
• Surface imaging
• Material modification sputtering, etching and
  deposition
• Implantation
• Cross sectioning

From FEI FIB200 Manual
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Images of a Sample Containing Carbon-nanotubes
Taken with FIB Microscope under Various
Magnifications
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Images of a Sample Containing Carbon-nanotubesTak
en with FIB Microscope Comparison under
Different Ion Beam Currents
4 pA Ga ion beam current
350 pA Ga ion beam current
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Cross-sectional Images of CNT Taken with FIB
(part I) Process of Cross-Sectioning CNT and
Images of CNT with Pt Deposition
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Cross-sectional Images of CNT Taken with FIB
(part II) Images of Milling and Final Cross
Section of CNT

• Process of Cross Sectioning CNT
• Locate CNT with distinct feature
• Pt deposition to protection CNT (11pA-150pA)
• Milling (1000pA)
• Clean cross-section milling(11pA-70pA)

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Scanning Tunneling Microscope

• Components (constant current mode)
• Sample
• Sharp tip
• Mechanism to control the location of tip in the
  plane parallel to sample surface
• Feed back loop to control the height of the tip
  above the sample
• Keep constant tunneling current by adjusting the
  height of tip at each measurement point. The
  current-distance relationship is exponential I
  ?exp(-Vz)
• Applications
• Atomic structure
• Topography
• Measure conductivity

www.fkp.uni-erlangen.de/methoden/stmtutor/stmtech.
html
www.tmmicro.com/spmguide/1-1-0.htm
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STM Images of Graphite Sheet
STM Images of Graphite
RMS roughness 0.223 nm
RMS roughness 0.311 nm
17-20-31
By Autumn Carlsen
17-20-31
17-20-31
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Discussion

• FIB and STM are complementary
• FIB measures length and diameter of CNTs
• STM helps to view the atomic structure of CNTs
  by imaging graphite sheets.

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Thanks to

• Professor Dovidenko, Professor LaBella, School of
  NanoSciences and NanoEngineering, University at
  Albany, SUNY
• Professor Catravas, Electrical Engineering
  Department, Union College
• Mel Stinzianni and Autumn Carlsen, School of
  NanoSciences and NanoEngineering, University at
  Albany, SUNY
• Dean Balmer and Ted Balmer, Union College