Search

Presents information relating to the development of the bias enhanced nucleation (BEN) step in connection with the case of the synthesis of diamond films by the microwave plasma assisted chemical vapor deposition technique (MPCVD). Occurrence of treatment; What the scratching pretreatment leads to; Conducing of the different observations.

Abstract: Silicon substrates are often used to synthesize polycrystalline diamond films by microwave plasma assisted chemical vapour deposition technique (MPCVD). In the case of highly oriented diamond films, several steps are employed to carefully prepare the silicon surface (pre-treatment steps), to nucleate diamond crystals (nucleation step) and to thick the film (growth step). In this study, we characterize {100} silicon substrates and diamond released from its silicon substrate by electronic microscopies (TEM and SEM), by Atomic Force Microscopy (AFM) and by X-ray photoelectron spectroscopy (XPS), to follow the substrate transformations after each step, particularly the formation and the evolution of the silicon carbide and to characterise the diamond films grown on the carburised silicon. We show that according to the experimental conditions and the level of surface/gas contamination by carbon and silicon species, isolated islands or continuous β-SiC compound are formed over the silicon surface and can generate defects such as voids or strip structures that influence the subsequent diamond nucleation and growth. [Copyright &y& Elsevier]

Abstract: In the case of diamond deposit obtained by microwave plasma assisted chemical vapour deposition technique (MPCVD) where the bias enhanced nucleation (BEN) was used to initiate diamond islands on silicon substrate, we simultaneously studied nucleation parameters such as crystal density and epitaxial ratio according to main synthesis conditions. These ones were relative to in situ pretreatment steps occurring before diamond growth, i.e. plasma etching and bias sequences. The nucleation parameters were studied by the high resolution SEM associated to image analysis techniques on homogeneous 1 cm2 samples. We observed that hydrogen etching duration clearly modified the epitaxial ratio without any change on the crystal density. So an optimal epitaxial ratio was reached for a moderate hydrogen etching while crystal density remained quite constant. The bias step was analysed in terms of duration and electrical behaviour (voltage and intensity) in relation to the plasma density that we were able to modify by physically confining the discharge. Bias duration clearly modified crystal density and epitaxial ratio. In later case, we observed a short optimal duration (between 30–90 s) for a 120 V bias voltage depending on the etching. We showed too that for a given bias duration the epitaxial ratio was all the more high as the voltage is low. The study of crystal density in relation to electrical characteristics of bias step showed that the more important parameter for nucleation is the electrical charge density (including intensity and time) and not the voltage, since nucleation density of 108 cm−2 can be maintained for voltage close to 35 and 50 V respectively if the plasma power density during the bias is higher or if the BEN duration is longer. [Copyright &y& Elsevier]

Isolated diamond crystals have been deposited on silicon by the microwave plasma assisted chemical vapor deposition technique using the bias-enhanced nucleation step. The true epitaxial ratio, defined as the number of epitaxied crystals to the total crystal number before coalescence, has been calculated by high-resolution scanning electron microscopy coupled to image analysis software. This ratio is correlated to the conditions of the etching step which precedes the bias step. This investigation allows us to determine the better conditions to obtain homogeneous epitaxied deposit with an optimum epitaxial ratio in the absence of a preceding carburization step, and to propose a qualitative explanation about the effect of the etching step on the silicon substrate. [Copyright &y& Elsevier]

Abstract: Amorphous hydrogenated carbon (a-C:H), Si-containing a-C:H and a-C:H/Si-containing a-C:H multilayered films have been deposited by low frequency plasma enhanced chemical vapour deposition (LF-PECVD) from cyclohexane and/or tetramethylsilane gas mixtures. Structural and mechanical properties of single layers have been first studied in relation with the working pressure, the gas mixture and especially the plasma power. By optimising these parameters, a-C:H films reveal very interesting mechanical and tribological properties (hardness of 23 GPa, friction coefficient of about 0.04 and wear rate of 1.50 10−7 mm3 N−1 m−1 (under air, against Al2O3, with Hertz pressure of 0.65 GPa)) with compressive residual stress values about −1 GPa. Inversely, Si-containing a-C:H films offer a wider range of mechanical behaviour (7–20 GPa for the hardness and 50–170 GPa for the Young modulus) while preserving lower residual stress values (−0.5 GPa). Then, previous results have been exploited to study a-C:H/Si-containing a-C:H multilayered coatings. Transmission Electron Microscopy, nanoindentation, stress measurements and ball-on-disk tribometer were used to characterize these multilayered films. First results show the possibility to obtain from precursor gas inlet modulation thick multilayered coatings (∼10 µm) with period thicknesses down to 15 nm. Period thickness has no influence on hardness, Young modulus and residual stress within the investigated domain. However, friction coefficient and wear resistance are improved by decreasing the period or by optimising the properties of the Si-containing layer. [Copyright &y& Elsevier]

Abstract: Orientation imaging techniques based on electron backscattering diffraction (EBSD) and convergent beam electron diffraction (CBED) pattern acquisition carried out respectively in the scanning electron microscope (SEM) and in the transmission electron microscope (TEM) were used to characterise the orientation of crystals in two highly oriented diamond (HOD) films with different thicknesses. The substrate surface modification has been also investigated by EBSD. The films were synthesised on Si(100) in a microwave plasma chemical vapor deposition (MPCVD) reactor where nucleation is initiated via an in situ pretreatment consisting in a carburization step followed by a bias enhanced nucleation (BEN). For the thin film EBSD allowed to highlight the presence of alpha-SiC on the silicon substrate as well as to evaluate their epitaxial relationship. The TEM-based system allowed to obtain more accurate misorientation data of the fine grained diamond structure corresponding to the first stages of growth. For the thicker film, EBSD was used to determine the mosaicity at the surface. [Copyright &y& Elsevier]

Highly oriented diamond (HOD) films were deposited on Si (0 0 1) substrates by the microwave plasma assisted chemical vapor deposition technique using the bias enhanced nucleation (BEN) step. The formation of HOD films is often linked to the presence of few parts per million of nitrogen which stabilizes the texture but deteriorates the chemical quality of the film. In this study, we show that carbon monoxide can be used without nitrogen addition to conserve the 〈0 0 1〉 texture and to promote the {1 0 0} facet extension on the top of the diamond film. After a nucleation step carried out by the BEN technique, and after a subsequent growth time limited to 30 min in a CH4/H2 gas mixture avoiding the coalescence step, HOD films were synthesized using CH4/H2, CO/H2 and N2/CH4/H2 gas mixtures for a growth time fixed to 10–14 h. The effect of carbon monoxide or nitrogen on the morphologies and the texture of the diamond films is discussed from the results of scanning electron microscopy and the texture measurements performed by X-ray diffraction. [Copyright &y& Elsevier]

Sm0.5Ca0.5MnO3 thermochromic thin films were synthesized using dc reactive magnetron co-sputtering and subsequent annealing in air. The film structure was studied by x-ray diffraction analysis. To validate the thermochromic potentiality of Sm0.5Ca0.5MnO3, electrical resistivity and infrared transmittance spectra were recorded for temperatures ranging from 77 K to 420 K. The temperature dependence of the optical band gap was estimated in the near infrared range. Upon heating, the optical transmission decreases in the infrared domain showing a thermochromic effect over a wide wavelength range at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous hydrogenated carbon (a-C:H) and Silicon doped a-C:H (Si-DLC) and a-C:H/Si-DLC multilayered films were deposited by low frequency plasma enhanced chemical vapour deposition (LF PECVD). Influences of plasma power and substrate temperature were first investigated on structural and mechanical properties of a-C:H films elaborated from cyclohexane–hydrogen mixtures. The hybridation ratio, Csp2/Csp3, was evaluated by means of Raman spectroscopy and High Resolution Solid-State Nuclear Magnetic Resonance (SSNMR). Stress measurements were realised by the substrate bending method. Nanoindentation and ball on disk tribometer were used in order to determine nanohardness, Young modulus and friction behaviours respectively. Si-DLC films were then elaborated by incorporating tetramethylsilane in the previous gas mixtures. Those layers revealed a significantly reduced stress level comparing to a-C:H films without a dramatic loss of mechanical properties. Finally a-C:H and Si-DLC layers were associated to elaborate a multilayered system which presents mechanical and tribological properties equivalent to an a-C:H monolayer properties while maintaining a lower residual stress level. [Copyright &y& Elsevier]