The effect of grain boundaries and adsorbates on the electrical properties of hydrogenated ultra nano crystalline diamond

• Published in: Diamond and related materials Vol. 18; no. 9; pp. 1118 - 1122
• Main Authors: Gan, L., Bolker, A., Saguy, C., Kalish, R., Tan, D.L., Tay, B.K., Gruen, D., Bruno, P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.2009; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Diffusion; interface formation; Electrical conductivity; Electrical properties of specific thin films; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Exact sciences and technology; H and H 2O adsorbents; Physics; Solid surfaces and solid-solid interfaces; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Temperature dependent; Thin film structure and morphology; Ultrananodiamond; Electrical conductivity; H and H 2O adsorbents; Ultrananodiamond; Temperature dependent; Grain boundaries; Temperature dependence; H and H; Crystal defects; Reversible processes; Electrical properties; Adsorbates; O adsorbents; Carbon; Heat treatments; Adsorbents; Dangling bonds; Irreversible processes; Ultrananocrystalline diamond; Monocrystals; Humidity; Diffusion
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2009.02.023

The results of a comprehensive study on the temperature dependence of the electrical properties of hydrogenated and air exposed undoped UNCD layers following heating/cooling cycles are presented. The results clearly show that, in contrast to hydrogenated and air exposed single crystal type IIa diamond, which exhibits a clear highly conductive p-type surface layer, the electrical properties of hydrogen and H 2O exposure of UNCD are determined by the properties of the entire layer. The changes in the electrical conductivity of UNCD as a result of heating are governed by two different processes: (i) Loss of water from the external surface that takes place at about 150 °C. This process is reversible, reviving the electrical properties upon exposure to humidity, just like in single crystalline diamond.(ii) Modification of the inter-grain material, which occurs at higher temperatures possibly due to H diffusion and passivation of some dangling bonds in the inter-grain material. This increases the resistivity in an irreversible manner. The conduction mechanism in the inter-grain material is characterized by variable range hopping in band tails thus indirectly proving that the material between the grains is some kind of amorphous carbon.