©2006 university of california prepublication data march 2006 in-situ controlled growth of carbon...
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©2006 University of California Prepublication Data March 2006
In-situ Controlled Growth of Carbon Nanotubesby Local Synthesis
Researchers Takeshi Kawano and Michael ChoAdvisor Professor Liwei Lin
Berkeley Sensor & Actuator Center
kawano@me.berkeley.edu
©2006 University of California Prepublication Data March 2006
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
©2006 University of California Prepublication Data March 2006
Background – Carbon nanotube –
CNT-based nanomotor
A. Zettl Gr., Nature, 424, 408 (2003)
IC integrated CNT
H. Dai Gr., Nano Letters, 4, 1 (2004)
CNT-based bio-probe
M. Lieber Gr., Nature, 394, 52 (1998).
Nanotube oscillator
P. L. EcEuen Gr., Nature, 431, 284 (2004).
©2006 University of California Prepublication Data March 2006
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 CNT3. CNT/silicon contact discussed
©2006 University of California Prepublication Data March 2006
Experimental Procedure
Electric field assisted synthesis
Gaps between Si structures
Bias between Si (V2 )
Electric field (V2 / gaps)
5 ~ 10 m 2 ~ 5 V
0.2 ~ 1 V/m
Temperature
C2H2/Ar gasSynthesis pressure
850 ~ 900C 60 / 55 sccm
250 Torr
Local synthesis of CNT
©2006 University of California Prepublication Data March 2006
In-Situ Monitoring of CNT Connection
RV
VVVR
R
V
R
VVVI
OutT
OutCNT
Out
CNT
Out
)(
)(
21
21
©2006 University of California Prepublication Data March 2006
I-V Curves of Silicon/CNT/Silicon System
2.5 M
Nanotube Diameter 50nm Length 10.3m
©2006 University of California Prepublication Data March 2006
Carbon Nanotube-based Nanoprobe Electrode
Outline
Background – Nanoprobe for cell/neuron –
Motivation
Biocompatible insulator for CNT
Process sequence
Images of CNT probes
Electrical properties of CNT probe
©2006 University of California Prepublication Data March 2006
Background – Nanoprobe for cell/neuron –
AFM with NanoneedleI. Obataya, C. Nakamura, S. HanN. Nakamura, J. Miyake, Nano Letters, 5, 1 (2005).
Multi-functional ProbeS. Nagasawa, H. Arai, R. Kanzaki, I. Shimoyama,Proc. of Transducers’05, 1230 (2005).
Microprobe devices for neuronal tissue
From J. Donoghue, Nature Neuroscience, 5, pp1085 (2002)
DiameterNeural Activity Extracellular IntracellularFrequency
5 ~ 10 m
100 V100 mV
DC10 kHz
Properties of Neuron
©2006 University of California Prepublication Data March 2006
Motivation Carbon nanotube based nanoprobe electrode Low invasive Intracellular probe for potential recording Intracellular probe for chemical detector
©2006 University of California Prepublication Data March 2006
Biocompatible Insulator for CNT– Parylene-C –
CNT encapsulated with Parylene TEM image (50nm-thick Parylene)
Parylene-C Properties & Characteristics CVD(chemical vapor deposition) at Room temp.
High electrical resistivity (~1016 -cm)
Biocompatible material
Conformal fashion and pinhole free
©2006 University of California Prepublication Data March 2006
Process Sequence
Process sequence
SEM images(a) As-grown single CNT between silicon structures(b) After Parylene deposition, (c) After tip expose(d) Close-up view of the exposed tip in (c)
©2006 University of California Prepublication Data March 2006
TEM Image of CNT Probe
TEM image of a single CNT
Outside: 50-nm-thick Parylene-C. Inside: 10-nm-diameter CNT
©2006 University of California Prepublication Data March 2006
Layout of MEMS structure for CNT probe
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
©2006 University of California Prepublication Data March 2006
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 m (E-field 0.2 ~ 1 V/m) 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 M
“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 (50~100nm-thick), CNT tip exposed, I-V measured
©2006 University of California Prepublication Data March 2006
©2006 University of California Prepublication Data March 2006
Background – Carbon nanotube –CNT probe in chemistry and biologyM. Lieber Gr., Nature, 394, 2 (1998).
chemically modified nanotube tips detecting specific chemical and biological groups.
SWNT poly-Si inter connection 875C CVD
Silicon MOS-compatibilityY. Tseng, et al., Nano Letters, 4, 1 (2004).
Gas detection sensorNASA SWNTs between two electrodes
Interaction between gas molecules and CNT. Electrical signal observation, such as I or V.Tested gases: NO2 , NH3 , etc.
http://www.nasa.gov/centers/ames/research/technology-onepagers/gas_detection.html
©2006 University of California Prepublication Data March 2006
I-V Curves of Silicon/CNT/Silicon System
Number of CNTsDiameterLength Overall resistance
Properties of CNT
950 3 nm
8.8 m (Average)480 k
Number of CNTsDiameterLength Overall resistance
Properties of CNT
150 nm
10.3 m2.5 M
©2006 University of California Prepublication Data March 2006
Layout of MEMS structure for CNT probe
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
©2006 University of California Prepublication Data March 2006
Self-Assembled Single CNTs(a) (b)
(c) (d)
Synthesis parameters
Gaps
Bias V1
Bias V2
8 m 7.5 V2.5 V
©2006 University of California Prepublication Data March 2006
CNT-Silicon Heterojunction
CNT : Work function of CNT
Si: Electron affinity of silicon
Eg-Si : Band gap of silicon
Ei -EF : Fermi level for silicon
Bp: Barrier height
Bp = ( S
+ Eg-Si ) - CNT
= 0.37~0.67 eV
CNT: multiwall CNT (root and tip growth)Si: p+type, conc. 1019/cm3
Contact resistanceSpecific contact resistivity C : 10-5~10-4 -cm2 [1]
Barrier height Bp : 0.4 eV
Concentration of Silicon:1019 /cm3(p-type)
Contact area A : 2 10 -11 cm2
Diameter of CNT : 50nm
Contact resistance = 0.5 ~ 5M
AR C
Contact
[1] K. K. Ng and R. Liu, IEEE Trans. ED, 37, 1535 (1990)
©2006 University of California Prepublication Data March 2006
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: 22m-length and 30nm-diameter)
©2006 University of California Prepublication Data March 2006
I would like to thank Lei Luo, Sha Li, Brian Sosnowchik for their
insightful discussions, especially Brian’s 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.
Acknowledgements
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