Amorphous SixC1 Research Articles

Simulations of structures of amorphous SixC1−x films

Amorphous SixC1−x films possess the potential to improve wear performance in humid atmospheres and at higher temperatures. But some experimental work on the films showed that silicon contents greatly influenced their microstructures and mechanical properties. Therefore, simulations of molecular dynamics were carried out to predict structures of the SixC1−x films at different silicon contents. The results show that the sp3/sp2 ratio of all the films increases, but the stiffness of the films is decreasing with an increase in silicon contents. Moreover, silicon atoms are almost surrounded by carbon atoms, which is in agreement with the experiments.

Growth of amorphous SixC1−x thin films using a methane–silane high energy ion beam

Abstract Amorphous Si x C 1− x films, with x ranging from 0.30 to 0.70, were grown by high-energy ion beam deposition starting from a methane–silane gas mixture. XPS analysis of the samples shows that it is possible to incorporate silicon to the amorphous carbon matrix giving an Si/C ratio depending on the methane–silane gas mixture. Raman spectra of the thermally annealed films indicate that the silicon incorporation in a-C films increases their thermal stability. There is no evidence of a complete graphitization up to 900°C, while in a-C samples graphitization occurs at about 500°C. This result shows that thermal stability is a function of the film composition.

Anomalous photoluminescence from 3C-SiC grown on Si(111) by rapid thermal chemical vapor deposition

Single crystal 3C-SiC epitaxial films are grown on Si(111) surfaces using tetramethylsilane by rapid thermal chemical vapor deposition. Strong blue/green photoluminescence (PL) was observed at room temperature from the free films of SiC prepared by etching the Si substrate. The main PL peak energy varies from 2.1 to 2.4 eV with full widths at half-maximum between 450 and 500 meV, depending on the growth condition, excitation wavelength and excitation light intensity. A weak peak at 3.0 eV also appeared. The infrared (IR) spectra of free films of SiC exhibit modes associated with CH and OH groups. We also compared PL characteristics of free films of SiC with those from porous SiC produced by anodization of SiC/Si to determine the origin of the PL. Porous SiC shows a PL peak centered at 1.9 eV, different from those in SiC. From the analysis of the IR spectra and scanning electron microscopic images, we tentatively suggest that the origin of the PL from free films of SiC might be associated with an OH group adsorbed on defects or some localized states as is the case for an amorphous SixC1−x alloy.

An XAFS study of the poly-carbosilane conversion to SixC1−x

Abstract The pyrolysis process from polycarbosilane (PCS) to SixC1−x has been followed up to 1473 K mainly by means of Si K X-ray absorption fine structure spectroscopy and solid state 29Si nuclear magnetic resonance. The structural conversion from the starting PCS to the resulting amorphous SixC1−x phase has been discussed from the obtained X-ray absorption near edge structure and 29Si magic-angle spinning nuclear magnetic resonance results. The silicon environment of the original and pyrolyzed PCS samples has been studied by extended X-ray absorption fine structure results.

LOW FREQUENCY GLOW DISCHARGE HYDROGENATED AMORPHOUS SILICON CARBIDE FILMS

ABSTRACT Hydrogenated amorphous SixC1−x:H films with various compositions were prepared by low frequency (110 kHz) glow discharge decomposition of a silane and methane mixture diluted by helium. The deposition rate, the composition, the structure and the refractive index of the films were studied using SEM, AES and IB analyses. Only the deposition rate was found to be influenced by the position of the silicon substrate in the reactor. From infrared analyses we estimate that the structure of the films is a tetrahedral network where carbon atoms are randomly replaced by silicon atoms and where only one single hydrogen is bound to silicon. The rather dense and inorganic character of these films is confirmed by the high values of their refractive index ranging from 2.1 for x=0 to 3.4 for x=1.

Phonon density of states of amorphous SixC1− x

The phonon density of states (PDOS) of amorphous silicon carbide ( a- Si x C 1− x ) has been computed for compositions with x = 0.47, 0.5, 0.57, 0.69 and 0.80 based on an angular force model, in which only nearest-neighbour interactions are considered. The significance of the computed phonon density of states to the interpretation of Raman and infrared spectra of a- Si x C 1− x is discussed.

The Local Atomic Arrangement in Amorphous Sixc1−x:H By Electron Energy Loss Spectroscopy and Electron Diffraction

ABSTRACTWe have used electron energy loss spectroscopy (EELS) and electron diffraction to study the local atomic arrangement in amorphous SixC1−x:H in the composition range 0.37 < × < 1. In the thin films, which were pre-pared by radio-frequency glow discharge from a mixture of methane and sil-ane, the π at the K-edge of C does not show up even for the highest C-content, i.e., Si0.37C0.63, consistent with fourfold coordinated C in the whole composition range studied. Also the electron diffraction results suggest a tetrahedral network. Models where the minority element is sur-rounded by four atoms of the majority element, fit the experimental data better than models based on a random distribution of Si and C on the tetra-hedral network.

Chemical bonding states in the amorphous SixC1–x: H system studied by X-ray photoemission spectroscopy and infrared absorption spectra

Abstract XPS studies and infrared absorption measurements of the reactively sputtered (RS) amorphous SixC1–x: H alloy system have been made. The binding energy of the Si 2p core electrons decreases monotonically as the alloy composition x increases while the corresponding line-width remains almost constant. On the other hand, a curve of the C 1s core electron binding energy versus x has a kink at around x = 0·5∼0·6. Infrared absorption spectra reveal the existence of C–H, Si–H, Si–C bonds in the films. These results are discussed in terms of chemical bonding states.

Compositional and structural properties of amorphous SixC1−x : H alloys prepared by reactive sputtering

Amorphous SixC1−x : H alloys are prepared by simultaneous rf reactive sputtering of silicon and graphite in a H2-Ar gas mixture. Silicon, carbon, and hydrogen contents are measured for the entire range of x by electron spectroscopy for chemical analysis (ESCA), Rutherford-backscattering method, and thermal evolution of hydrogen. Evolution temperature dependence of the number of evolved hydrogen atoms is measured. The hydrogen-evolution behavior and the optical gap are x dependent. These phenomena are discussed in the light of chemical-bonding states.

Photoluminescence in the amorphous system SixC1−x

We report the observation of visible photoluminescence in the amorphous SixC1−x(H) alloy system. The spectrum consists of two bands one of which shifts linearly with x. For x=0.4 the principle luminescence maximum lies at 2.1 eV.