1. ©2006 University of California Prepublication Data March 2006 In-situ Controlled Growth of Carbon Nanotubes by Local Synthesis Researchers Takeshi Kawano and Michael Cho Advisor Professor Liwei Lin Berkeley Sensor & Actuator Center kawano@me.berkeley.edu

2. ©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

3. ©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).

4. ©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 CNT 3.CNT/silicon contact discussed

5. ©2006 University of California Prepublication Data March 2006 Experimental Procedure Electric field assisted synthesis Gaps between Si structures Bias between Si (V 2 ) Electric field (V 2 / gaps) 5 ~ 10  m 2 ~ 5 V 0.2 ~ 1 V/  m Temperature C 2 H 2 /Ar gas Synthesis pressure 850 ~ 900  C 60 / 55 sccm 250 Torr Local synthesis of CNT

6. ©2006 University of California Prepublication Data March 2006 In-Situ Monitoring of CNT Connection

7. ©2006 University of California Prepublication Data March 2006 I-V Curves of Silicon/CNT/Silicon System 2.5 M  Nanotube Diameter 50nm Length 10.3  m

8. ©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

9. ©2006 University of California Prepublication Data March 2006 Background – Nanoprobe for cell/neuron – AFM with Nanoneedle I. Obataya, C. Nakamura, S. Han N. Nakamura, J. Miyake, Nano Letters, 5, 1 (2005). Multi-functional Probe S. 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) Diameter Neural Activity Extracellular Intracellular Frequency 5 ~ 10  m 100  V 100 mV DC  10 kHz Properties of Neuron

10. ©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

11. ©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 (~10 16  -cm)  Biocompatible material  Conformal fashion and pinhole free

12. ©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)

13. ©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

14. ©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

15. ©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

16. ©2006 University of California Prepublication Data March 2006

17. 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.  SWNT  poly-Si inter connection  875  C CVD Silicon MOS-compatibility Y. Tseng, et al., Nano Letters, 4, 1 (2004). Gas detection sensor NASA  SWNTs between two electrodes  Interaction between gas molecules and CNT.  Electrical signal observation, such as I or V.  Tested gases: NO 2, NH 3, etc. http://www.nasa.gov/centers/ames/research/techno logy-onepagers/gas_detection.html

18. ©2006 University of California Prepublication Data March 2006 I-V Curves of Silicon/CNT/Silicon System Number of CNTs Diameter Length Overall resistance Properties of CNT 9 50  3 nm 8.8  m (Average) 480 k  Number of CNTs Diameter Length Overall resistance Properties of CNT 1 50 nm 10.3  m 2.5 M 

19. ©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

20. ©2006 University of California Prepublication Data March 2006 Self-Assembled Single CNTs (a) (b) (c) (d) Synthesis parameters Gaps Bias V 1 Bias V 2 8  m 7.5 V 2.5 V

21. ©2006 University of California Prepublication Data March 2006 CNT-Silicon Heterojunction  CNT : Work function of CNT  Si : Electron affinity of silicon E g-Si : Band gap of silicon E i -E F : Fermi level for silicon  Bp : Barrier height  Bp = (  S + E g-Si ) -  CNT = 0.37~0.67 eV CNT: multiwall CNT (root and tip growth) Si: p + type, conc. 10 19 /cm 3 Contact resistance Specific contact resistivity  C : 10 -5 ~10 -4  -cm 2 [1]  Barrier height  Bp : 0.4 eV  Concentration of Silicon:10 19 /cm 3 (p-type) Contact area A : 2  10 -11 cm 2  Diameter of CNT : 50nm Contact resistance = 0.5 ~ 5M  [1] K. K. Ng and R. Liu, IEEE Trans. ED, 37, 1535 (1990)

22. ©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: 22  m-length and 30nm-diameter)

23. ©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