Hydrogenated Diamond Surfaces Studied by Atomic and Kelvin Force Microscopy

Dr. Bohuslav Rezek

Abstract

High conductivity and negative electron affinity of hydrogen terminated diamond surfaces are features which attract a lot of attention because of their potential for application in devices. [1] Understanding and exploitation of these features has been a subject of many research efforts. [2,3]

In this contribution we employ atomic force (AFM) and Kelvin force microscopies (KFM) to characterize and modify both morphologic and electronic properties of hydrogenated (100) diamond surfaces with high lateral resolution. We discuss thoroughly origin of the AFM and KFM contrast and deduce values of local surface work function and Fermi level.

KFM is used to obtain information on electronic properties of diamond surfaces. On a hydrogen terminated surface KFM shows bright contrast in comparison to oxygen terminated surroundings. Using gold and aluminum pads as a reference, work function of 4.9 eV and Fermi level 0.7 eV deep in the valence band are determined. Illumination of the sample results in a shift of Fermi level by as much as 0.2 eV, in agreement with an increase in conductivity.

AFM is applied not only to characterize surface morphology but also to locally control surface termination of diamond surfaces with resolution of ~ 10 nm using negatively biased AFM cantilevers. While in some reports [3] an accompanying growth on the surface is observed in our case nanoscale patterns are scribed into the diamond surface, down to a depth of 3 nm. We discuss our observation that the pattern profile apparently changes from depth to height when measured by non-contact AFM. By current-voltage measurements and scanning electron microscopy we show that the inscribed patterns exhibit electronic properties different from the hydrogenated rest of the surface, namely lower conductivity and higher electron affinity.

[1] H. Okushi, Diam. Relat. Mater. 10 (2001) 281.

[2] F. Maier, M. Riedel, B. Mantel, J. Ristein, and L. Ley , Phys. Rev. B 85 (2000) 3472.

[3] M. Tachiki, T. Fukuda, K. Sugata, H. Seo, H. Umezawa, and H. Kawarada, Jap. J. Appl. Phys. 39 (2000) 4631.