Nanocrystalline silicon carbide ͑SiC͒ thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (T d) ranging from 80 to 575°C and different gas flow ratios ͑GFRs͒. While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of T d , GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope ͑HRTEM͒, micro-Raman, Fourier transform infrared ͑FTIR͒ and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300°C. The degree of crystallization increases with increasing T d and the crystalline fraction (f c) is 65%Ϯ2.2% at 575°C. The f c is the highest for the films deposited with hydrogen dilution in comparison with the films deposited with argon and helium at the same T d. The Raman spectra also confirm the occurrence of crystallization in these films. The HRTEM measurements confirm the existence of nanocrystallites in the amorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are in reasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractive index ͑n͒ with T d is found to be quite consistent with the structural evolution of these films. The films deposited with high dilution of H 2 have large band gap (E g) and these values vary from 2.6 to 4.47 eV as T d is increased from 80 to 575°C. The size dependent shift in the E g value has also been investigated using effective mass approximation. Thus, the observed large band gap is attributed to the presence of nanocrystallites in the films.

Low-k films with k of 2.5–2.9 were deposited under different conditions of pressures and temperatures using a plasma-enhanced chemical vapor deposition (PECVD) system. These films were prepared using a new liquid precursor, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) and H2 carrier gas. The rf power was kept as low as possible to maintain the original ring structure in the films. The as-deposited films were annealed and the dielectric and optical properties were investigated. Identification of the absorption bands in the IR spectra for as-deposited films reveals a broadband around 950–1200 cm−1 arising from the Si–O stretching mode of the ring (1065 cm−1) and chain structure (1000 cm−1), respectively; a band at 750–900 cm−1 due to Si–O bending (790 cm−1); Si–CH3 rocking mode (760 cm−1); a sharp band centered at 1260 cm−1 due to a Si–CH3 bending mode; and a broadband at 2800–3000 cm−1 due to the CH group. A comparison of the IR spectra of the PECVD film and TVTMCTS liquid reveals that vinyl vibrations (Si–CH=CH2) at 960, 1410, and 3030–3095 cm−1 for CH2 and at 1598 cm−1 for C=C present in the liquid were not detected in the CVD films. Hence C=C bonds were broken in the plasma polymerization process. As the pressure and the deposition temperature (TD) increased, the intensity of the Si–O vibration arising from the ring structure increased and decreased, respectively. Thus by tuning the pressure and TD we can control the structure of the film. There is a good correlation found between the Si–CH3 and Si–O ring intensities and k values; the increasing Si–CH3 and Si–O ring is accompanied by decreasing k. The films were thermally stable up to 400 °C annealing temperature.

Room-temperature 1535-nm-band photoluminescence in ~126 nm silica films (6 at. % doping), produced by spin-coating an Er 2 O 3 and tetraethylorthosilicate sol-gel formulation on silicon substrates, was studied as a function of vacuum furnace annealing (500 to 1050 C). Emission is strongly enhanced for annealing near 850 C, which is shown by modeling the temperature dependence as arising from thermally-activated removal of hydroxyl ions. Suitability of such a process for silicon-based applications is discussed. PACS Numbers: 78.20.Ek,

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In this study, we analyzed the concentrations of accumulation and coarse modes measured during November 2013-July 2017 at an urban background site in Amman, Jordan. The concentrations showed distinct seasonal variations with high concentrations with a monthly average higher than 100 cm −3 and 1.5 cm −3 , respectively, for accumulation and coarse modes during the winter and low concentrations with a monthly average less than 40 cm −3 and 1-1.5 cm −3 , respectively, for accumulation and coarse modes during the summer. Sand and dust storms (SDS) affected the coarse mode during the early spring whereas local dust resuspension affected them during the autumn. The gravimetric analysis confirmed the seasonal variation of the calculated particulate mass concentration but suggested that the assumption of spherical particles and unit density is not always proper. The ATR-FTIR analysis of selected filters revealed that aerosols in the background atmosphere of Amman are a mixture of locally emitted (fossil fuel combustion) and local/regional dust. Based on the 24-h average of the calculated PM 10 , the pollution standard index (PSI) revealed that about 81% of the days were either good or moderate air quality conditions. About 71% of the days were below the 24-h PM 10 limit value according to the Jordanian air quality standards (120 μg m −3).

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We present a supercritical CO 2 (SCCO 2 ) process for the preparation of nanoporous organosilicate thin films for ultralow dielectric constant materials. The porous structure was generated by SCCO 2 extraction of a sacrificial poly(propylene glycol) (PPG) from a nanohybrid film, where the nanoscopic domains of PPG porogen are entrapped within the crosslinked poly(methylsilsesquioxane) (PMSSQ) matrix. As a comparison, porous structures generated by both the usual thermal decomposition (at approximately 450°C) and by a SCCO 2 process for 25 and 55 wt% porogen loadings were evaluated. It is found that the SCCO 2 process is effective in removing the porogen phase at relatively low temperatures (<200°C) through diffusion of the supercritical fluid into the phase-separated nanohybrids and selective extraction of the porogen phase. Pore morphologies generated from the two methods are compared from representative three-dimensional (3D) images built from small-angle x-ray scattering (SAXS) data.

Photoluminescence is observed at room temperature from phonon-assisted band-to-band emission in Si (1.067 eV peak) using unpatterned bulk p-type silicon wafer samples that were spin-coated with Er-doped (6 at. %) silica-gel films (0.13 m) and vacuum annealed; the strongest emission was obtained at ~700 C. Comparative study of annealing behavior indicates two-orders of magnitude efficiency enhancement. Emission from Er +3 ions in the silica film is used to gauge relative emission strengths. Mechanisms for inducing emission from silicon utilizing stresses in sol-gel-films are discussed. Graphical Abstract