Microscopic Electrical Conductivity of Nanodiamonds after Thermal and Plasma Treatments
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Microscopic Electrical Conductivity of Nanodiamonds after Thermal and Plasma Treatments Jan Čermák1, Halyna Kozak1, Štěpán Stehlík1, Vladimír Švrček2, Vincent Pichot3, Denis Spitzer3, Alexander Kromka1 and Bohuslav Rezek1,4 1
Institute of Physics ASCR, Cukrovarnická 10, 16200 Prague 6, Czech Republic. Research Center for Photovoltaics, AIST, Tsukuba, 305-8568, Japan 3 Nanomatériaux pour les Systèmes Sous Sollicitations Extremes (NS3E), UMR 3208 ISL/CNRS/Unistra, Institut franco-allemand de recherches de Saint-Louis (ISL), 5, rue du Général Cassagnou, 68300 Saint-Louis, France 4 Faculty of Electrical Engineering, Czech Technical University, Technická 10, 16627 Prague 6, Czech Republic. 2
ABSTRACT Atomic force microscopy (AFM) is used to measure local electrical conductivity of HPHT nanodiamonds (NDs) dispersed on Au substrate in the as-received state and after thermal or plasma treatments. Oxygen-treated NDs are highly electrically resistive, whereas on hydrogentreated NDs electric current around -200 pA at -2 V is detected. The as-received NDs as well as NDs after an underwater radio-frequency (RF) plasma or laser irradiation (LI) treatments contain both electrically conductive (two types: highly and weakly conductive) and highly resistive particles. The higher conductivity is attributed to H-terminated (RF) or graphitized (LI) NDs. The lower conductivity is attributed to NDs with hydrogenated amorphous carbon shell. INTRODUCTION Diamond particles with sizes below 100 nm, so-called nanodiamonds (NDs), represent a novel carbon-based nanomaterial with features that are considered promising for applications ranging from biomedicine to energy conversion and spintronics [1–4]. NDs structural, chemical, optical as well as electronic properties play significant role in these applications. The properties and related functions of NDs can be adjusted by modification of surface termination, i.e. of the surface chemical moieties. Modification of NDs surface is commonly achieved by a thermal or plasma treatment in specific gases where hydrogen, oxygen, or ambient air are the most common ones [5,6]. Recent experiments indicated that thermal and plasma treatments have a more complex effect on NDs compared to bulk diamond [7,8]. For instance, graphitization during vacuum annealing is observed at much lower temperatures on NDs than on bulk diamond [7]. This can be attributed to nanoscale dimensions, structural defects and to commonly present carbon shell of the NDs, be they of detonation or HPHT (high-pressure high-temperature) origin. Properties of NDs are typically studied by various spectroscopic methods (infrared spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, dynamic light scattering, etc.) and conductivity measurements [9]. However, these methods characterize NDs as an ensemble and thus provide averaged properties. Scanning probe methods are able to resolve data related to individual nanoparticles [10]. By surface potential measurements (KPFM) in
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