In-situ Controlled Growth of Carbon Nanotubes by Local Synthesis

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In-situ Controlled Growth of Carbon Nanotubesby
Local Synthesis

• Researchers Takeshi Kawano and Michael Cho
• Advisor Professor Liwei Lin
• Berkeley Sensor Actuator Center
• kawano_at_me.berkeley.edu

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Outline

• Background
• Motivation
• Experimental procedure
• In-situ monitoring of CNT connection
• Self-assembled single CNT
• CNT/Si junction and contact resistance
• Electrical properties of Si/CNT/Si system
• Carbon nanotube-based nanoprobe electrode
• Summary

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Background Carbon nanotube
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Motivation

• CMOS integration of nano structures
• (carbon nanotubes (CNTs))
• Local and selective synthesis
• using silicon microstructures (MEMS)
• Device applications to nano sensors and
• nano electronics

1. In-situ controlled growth of CNT
2. Assembly of single CNT
3. CNT/silicon contact discussed

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Experimental Procedure
Local synthesis of CNT
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In-Situ Monitoring of CNT Connection
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I-V Curves of Silicon/CNT/Silicon System
2.5 MW
Nanotube Diameter 50nm Length 10.3mm
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Carbon Nanotube-based Nanoprobe Electrode
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Background Nanoprobe for cell/neuron
Microprobe devices for neuronal tissue
From J. Donoghue, Nature Neuroscience, 5, pp1085
(2002)
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Motivation

• Carbon nanotube based nanoprobe electrode
• Low invasive Intracellular probe for potential
  recording
• Intracellular probe for chemical detector

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Biocompatible Insulator for CNT Parylene-C

• Parylene-C Properties Characteristics
• CVD(chemical vapor deposition) at Room temp.
• High electrical resistivity (1016 W-cm)
• Biocompatible material
• Conformal fashion and pinhole free

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Process Sequence
Process sequence
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TEM Image of CNT Probe
TEM image of a single CNT Outside 50-nm-thick
Parylene-C. Inside 10-nm-diameter CNT
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Future Work

• In-situ Controlled Growth of Carbon Nanotubes by
  Local Synthesis
• Contact issue ( metal contact with tungsten,
  gold electrode)
• More real-time growth measurements
• Investigation of the IC-compatibility
• Carbon Nanotube-based Nanoprobe Electrode
• Impedance measurement of CNT probe
• Penetration into cells (first with Onion cells)
• Recording of biological signal from cell/neuron

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Summary

• In-situ Controlled Growth of Carbon Nanotubes by
  Local Synthesis
• In-situ controlled synthesis of CNT using MEMS
  structures
• Bias 2 5 V, gaps between Si structures 5
  10 mm (E-field 0.2 1 V/mm)
• Instant of the CNT connection monitored
  (growth time is 8 50 seconds)
• Single CNT connection controlled by the
  in-situ monitoring system
• Electrical properties of Si/CNT/Si system and
  CNT/Si junction
• CNT/Si contact resistance discussed with
  metal/Si junction model
• Overall resistance of the single CNT is 2.5 MW
• Carbon Nanotube-based Nanoprobe Electrode
• Device concept proposed
• Carbon nanotube electrode for intracellular
  recording
• Low-invasive probe and low-damage to
  cell/neuron
• Fabrication and experimental results
• Parylene-C deposited (50100nm-thick), CNT tip
  exposed, I-V measured

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Background Carbon nanotube
CNT probe in chemistry and biology
M. Lieber Gr., Nature, 394, 2 (1998).

• chemically modified nanotube tips
• detecting specific chemical and biological
  groups.

Silicon MOS-compatibility
Gas detection sensor
Y. Tseng, et al., Nano Letters, 4, 1 (2004).
NASA

• SWNTs between two electrodes
• Interaction between gas molecules and CNT.
• Electrical signal observation, such as I or V.
• Tested gases NO2 , NH3 , etc.

• SWNT
• poly-Si inter connection
• 875?C CVD

http//www.nasa.gov/centers/ames/research/technolo
gy-onepagers/gas_detection.html
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I-V Curves of Silicon/CNT/Silicon System
Properties of CNT
Properties of CNT
Number of CNTs Diameter Length Overall
resistance
9 50 ? 3 nm 8.8 mm (Average) 480 kW
Number of CNTs Diameter Length Overall
resistance
1 50 nm 10.3 mm 2.5 MW
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Future Work

• In-situ Controlled Growth of Carbon Nanotubes by
  Local Synthesis
• Contact issue ( metal contact with tungsten,
  gold electrode)
• More real-time growth measurements
• Investigation of the IC-compatibility
• Carbon Nanotube-based Nanoprobe Electrode
• Impedance measurement of CNT probe
• Penetration into cells (first with Onion cells)
• Recording of biological signal from cell/neuron

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Self-Assembled Single CNTs
Synthesis parameters
Gaps Bias V1 Bias V2
8 mm 7.5 V 2.5 V
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CNT-Silicon Heterojunction
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Electrical Properties of CNT Probe
I-V measurement (a) Setup for the measurement (Au
electrode) (b) SEM image of CNT (d) I-V curves of
CNT (CNT 22mm-length and 30nm-diameter)
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Acknowledgements
I would like to thank Lei Luo, Sha Li, Brian
Sosnowchik for their insightful discussions,
especially Brians contribution for the I-V
measurement and voltage acquisition interface,
and other Lab mates. And I would like to thank
staff at the EML (Electron Microscopy Laboratory)
at UC Berkeley, for their TEM work.