Diamond films grown by microwave Plasma enhanced chemical vapor deposition (PECVD) from an Ar-CH4 mixture can have grain sizes in the range of 2-5 nm. These ultrananocrystalline diamond films retain most of the surface and bulk properties of crystalline diamond. Using microfabrication techniques, UNCD is deposited in the pyramidal shaped pits of silicon wafer to produce very sharp UNCD AFM probes. A silicon oxide layer is grown as an intermediate step before UNCD deposition to enhance the sharpness of pyramidal pits formed.

UNCD can also be doped with nitrogen during growth to enhance its electrical conductivity. Gas mixture with 10% nitrogen can produce UNCD with a conductivity of ~30/ohm*cm, which is then used to microfabricate conductive AFM probes. UNCD probes have very high wear resistance and very high melting point, which makes them more robust as compared to conductive AFM probes made by metallic coatings.

Various conductive AFM experiments have been done using these probes. A contact resistance of ~6.25 kohm has been measured. These probes were also used to generate conductive potential maps of gold films deposited on silicon substrates.

In order to conduct potentiometry experiments, Pt wires were deposited between gold electrodes using e-beam deposition. A potential difference was applied across the electrodes and a conduction map was obtained using conductive UNCD probes. It was observed from the potential map that the wire was short-circuited at some places, which could not be observed in topographical map.

Personnel

• H.D. Espinosa (PI)
• R. Agrawal (Graduate Student)
• B. Peng (Graduate Student)

Collaborators

• M. Hersam (Materials Sciences and Engineering, NU)
• O. Auciello (Argonne National Lab)
• J. Carlisle (Argonne National Lab)
• N. Moldovan (Diamond Technologies)

Selected Publications

• H.D. Espinosa, N. Moldovan, K.-H. Kim, "Novel AFM Nano Probes." Applied Scanning Probe Methods, Vol. 5: Scanning Probe Microscopy Techniques. Edited by B. Bhushan, H. Fuchs, and S. Kawata. Springer-Verlag, Heidelberg, to be published in 2007.

• K.-H. Kim, N. Moldovan, C. Ke, H.D. Espinosa, X. Xiao, J.A. Carlisle, and O. Auciello. "Novel Ultrananocrystalline Diamond Probes for High- Resolution Low-Wear Nanolithographic Techniques," Small, Vol. 1, No. 8-9, p. 866-874, 2005.

• H.D. Espinosa, B.Peng, N. Moldovan, T.A. Friedmann, X. Xiao, D.C. Mancini, O. Auciello, J. Carlisle, C.A. Zorman, and M. Merhegany. "Elasticity, Strength and Toughness of Single Crystal Silicon Carbide, Ultrananocrystalline Diamond, and Hydrogen-free Tetrahedral Amorphous Carbon." Applied Physics Letters, Vol. 89, No. 7, Art. No. 073111, 2006.

Patents

• H.D. Espinosa and N. Moldovan, "Atomic Force Microscopy (AFM) Chip for Conductive Contact Mode Techniques Made of Nanocrystalline Diamond Thin Films - Design and Fabrication." NU Disclosure No. 25075 (provisional patent application filed in 2006).