Nano-Lithography

Objective: In this study we demonstrate a method to synthesize CNT with a single chirality (metallic or semi-conducting type). We also demonstrate that we can synthesize CNT with high number (spatial) density and with precisely defined location for the growth of CNT.

Problem Definition: Microelectronic applications require precise location and chirality of synthesized CNTs with high spatial density. Conventional CVD synthesis techniques typically yield mixtures of CNTs (semi-conducting and metallic types) that grow at random locations - which makes it very costly for incorporation in nano-electronic circuitry. This technique obviates two significant hurdles that prevent the exploitation of CNTs in nano-electronics.

General Procedure: Dip Pen Nanolithography (DPN) techniques were used to deposit metal catalysts at precisely defined locations and pattern precisely defined sizes on a variety of substrates such as gold, silicon, silicon nitride, etc. (Fig. 1). DPN process enabled precise control of the composition of the deposited catalyst (Fig. 2). After deposition of catalysts, a low temperature Chemical Vapor Depisition (CVD) process was used to synthesize CNT. Various known catalysts (e.g., Pd, Pt, Rh, Ni, Co, and Fe) were deposited using DPN. Characterization studies before and after CVD synthesis of CNT showed that the CNT were of uniform diameter with a very narrow range of variability (less than 1 nm). Characterization studies include: LFM, XPS, XRD, STS, micro-Raman spectroscopy, TEM, and SEM).

Conclusion and Future Direction: Since the diameter of nanotube controls the chirality - the chirality of the CNT was precisely defined using this technique and resulted in high purity of synthesized CNT. The diameter of the CNT measured by TEM was found to be consistent with the micro-Raman Spectroscopy measurements. Hence, the results showed that CNT samples of a single chirality can be obtained using this technique. The results indicate that the chirality of the synthesized CNT can be controlled by changing the synthesis conditions (e.g., size of the catalyst patterns, composition of the catalysts, temperature of CVD, gas flow rates, etc.). We are currently fabricating a MEMS platform (called ‘PIMTEM’) to optimize the metal deposition procedure and the synthesis conditions using different materials.

Graduate Students: Hongjoo Yang and Nicholas Niedbalski

Former Graduate Students: Seokwon Kang, David Huitink Rohit V. Gargate,
and Alberto Rival Cardona

Undergraduate Student: Jim Koss

Collaborator: Dr. Saion K. Sinha, University of New Haven.

Project funded by: SPAWAR and DARPA

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