Abstract

Over the last two decades the diamond with the unique combination of its extreme properties has provoked widespread scientific interest and stimulated a variety of technological applications. Besides to be the hardest and the best conductor of heat among the known materials, it has also got a very high chemical inertness and resistance to the high energy particles/radiation. Nowadays, the synthetic diamond is produced from two of the earth's most common materials: graphite or methane, by utilizing the HPHT (High Pressure 5-15 GPa, High Temperature 1500-3500 °C) technique, that imitates the formation conditions of natural diamond or the CVD (Chemical Vapor Deposition) technique, respectively. The advantage of CVD technique is the low values of the pressure and temperature below the atmospheric pressure and 1200 °C, respectively. The CVD process as its name implies, involves a gas-phase chemical reaction occurring above a solid surface, which causes direct deposition of diamond film onto the surface from activated carbon radicals (CH3, CH2, CH, C, C2) of methane. Gas phase activation can be achieved by several different routes like:i) combustion flame (oxyacetylene or plasma thorces); ii) thermal (hot filament CVD);iii) plasma (DC, RF, microwave, etc).The CVD technique assisted by microwave plasma is the most used and the most investigated. The involved processes are complex (dissociation, excitation, ionization and so on of CH4 and H2 gases) and can occur in different types of reactors: NIRIM, ASTEX e Bell Jar.In the present contribution, polycrystalline diamond films have been produced from CH4-H2 plasmas in a MWPECVD (Micro-Wave Plasma Enhanced CVD) apparatus including an ASTEX-type reactor. Generally the CH4-H2 plasmas are "black boxes" that can be highlighted by a parametric study and diagnostic techniques: of the plasma phase by the OES (Optical Emission Spectroscopy) and of the plasma-surface interface by PI (Pyrometric Interferometry). This last allows to monitor in-situ, in continuous and in real time the deposition rate and the temperature. The following MWPECVD process parameters have been studied: the power (1000-1800 Watt), the gas mixture composition (CH4 percentage 0.5-2%), the substrate temperature (740-950 °C) and the pressure (96-133 hPa). The films have been deposited on pieces of polished p-doped silicon (100) substrates, 500 ?m thick and with an area 2.6x2.6 cm2. Prior to the deposition the Si substrates have ultrasonically been treated ex-situ for one hour in an ethanol suspension of diamond powder (40-60 µm). Such treatment is aimed at the increase of the nucleation density to promote the deposition process. The chemical composition, structure and morphology of the obtained material have been characterized using the following techniques: Raman spectroscopy, XRD (X-ray diffraction) and SEM (Scanning Electron Microscopy).In particular, the influence of the different process parameters on the deposition rate,

Autore Pugliese

• Cicala Grazia

Tutti gli autori

• G. Cicala; M. A. Nitti

Titolo volume/Rivista

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Anno di pubblicazione

2011

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