Effect of silane flow rate on structural,electrical and optical properties of silicon thin films grown by VHF PECVD technique

Hydrogenated silicon thin films deposited by VHF PECVD process for various silane flow rates have been investigated. The silane flow rate was varied from 5 sccm to 30 sccm, maintaining all other parameters constant. The electrical, structural and optical properties of these films were systematically studied as a function of silane flow rate. These films were characterized by Raman spectroscopy, Scanning Electron Microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and UV–visible (UV–Vis) spectroscopy. Different crystalline volume fraction (22%–60%) and band gap (∼1.58 eV–∼1.96 eV) were achieved for silicon thin films by varying the silane concentration. A transition from amorphous to nanocrystalline silicon has been confirmed by Raman and FTIR analysis. The film grown at this transition region shows the high conductivity in the order of 10⁻⁴ Ω⁻¹ cm⁻¹.     

Effects of oxygen percentage on the growth of copper oxide thin films by reactive radio frequency sputtering

Copper oxide thin films were deposited onto glass substrates by reactive radio frequency magnetron sputtering at various oxygen percentage flow rates R(O₂). X-ray diffraction analysis revealed that nanocrystallite copper oxide thin films with cubic, tetragonal, and monoclinic structure were formed at R(O₂) values of 10%, 20%, and ≥30%, respectively. Energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy were used to verify the copper oxides phases. With increased R(O₂), the root mean square surface roughness of the deposited films decreased from 4.82 nm to 1.78 nm. Moreover, both the band gap type and value changed with increased R(O₂). For R(O₂) at 20%, single phase tetragonal Cu₄O₃ thin film with a direct band gap of 2.20 eV was formed. For R(O₂) ≥ 30%, single phase monoclinic CuO thin films with an indirect band gap of 1.20 eV–1.25 eV were formed. In addition, conductive copper oxide thin films tended to form for R(O₂) < 30%, whereas insulator oxide thin films tended to form for R(O₂) ≥ 30%. Through this study, the crystallization behavior, the band gap, and the resistivity properties of the deposited copper oxide thin films as a function of the R(O₂) were obtained.     

Optical properties change in amorphous (As2S3)0.87Sb0.13 thin films by photo and thermal induced process

Exposure with above band gap light and thermal annealing at a temperature near to glass transition temperature, of thermally evaporated amorphous (As₂S₃)_0.87Sb_0.13 thin films of 1 μm thickness, were found to be accompanied by structural effects, which in turn, lead to changes in the optical properties. The optical properties of thin films induced by illumination and annealing were studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Photo darkening or photo bleaching was observed in the film depending upon the conditions of the light exposure or annealing. These changes of the optical properties are assigned to the change of homopolar bond densities.     

Studies of surface and interface phonon polariton characteristics of wurtzite ZnO thin film on wurtzite 6H-SiC substrate by p-polarized infrared attenuated total reflection spectroscopy

The surface and interface phonon polariton characteristics of a wurtzite ZnO thin film grown on a wurtzite 6H-SiC substrate are investigated by p-polarized infrared attenuated total reflection spectroscopy. Two absorption dips corresponding to the leaky surface phonon polariton (SPP) mode of ZnO and the interface phonon polariton (IPP) mode of ZnO/6H-SiC are clearly observed at 558 and 916 cm^− 1, respectively. The observations are in good agreement with the results determined from the theoretical surface polariton dispersion curve simulated by means of an anisotropy model. Finally, the effects of the ZnO thin film thickness on the SPP and IPP modes are deduced from the theoretical calculations.     

The effect of the presence of Ag nanoparticles on the photocatalytic degradation of oxalic acid adsorbed on TiO2 nanoparticles monitored by ATR-FTIR

Photocatalytic degradation of oxalic acid adsorbed on the Ag/P25 TiO₂ composite nanoparticle films were investigated using ATR-FTIR technique under UV irradiation. Ag/P25 TiO₂ composite nanoparticle films with various Ag content were tested. Topography and chemical structure/composition of the composite nanoparticle films were analyzed by AFM and XPS respectively. It was found that in the degradation reaction of the oxalic acid, the presence of only 2% Ag nanoparticles leads to six times more oxalic acid degradation compared to that degraded in the presence of pure P25 TiO₂ nanoparticles. The degradation rate of the oxalic acid is three times higher in the case of Ag/TiO₂ composite nanoparticle film than in the case of pure TiO₂ nanoparticles. It was observed that both the rate of oxalic acid degradation and the degraded amount of the oxalic acid were significantly affected by Ag incorporation.     

The formation of a SiOx interfacial layer on low-k SiOCH materials fabricated in ULSI application

The characterizations of SiOCH films using oxygen plasma treatment depends linearly on the O₂/CO flow rate ratio. According to the results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses, it was found that the carbon composition decreases with increasing O₂/CO flow rate ratio, because more carbon in the Si–O–C and Si–CH₃ bonds on the film surface would be converted by oxygen radicals. It was believed that the oxygen plasma could oxidize the SiOCH films and form a SiO_x interfacial capping layer without much porosity. Moreover, the result of FTIR analysis revealed that there was no water absorbed on the film. A SiO₂-like capping layer formed at the SiOCH film by the O₂/CO flow rate ratio of 0.75 had nearly the same dielectric properties from the result of capacitance–voltage (C–V) measurement in our research.     

Effects of hydrogen dilution on CNx film properties deposited using rf PECVD from a mixture of ethane,nitrogen and hydrogen

Carbon nitride (CN_x) thin films were deposited using radio frequency plasma enhanced chemical vapor deposition (rf PECVD) from a mixture of ethane (C₂H₆), nitrogen (N₂) and hydrogen (H₂) gases. The C₂H₆ and N₂ flow rates were kept constant, while the H₂ flow rate was varied. The effects of hydrogen dilution on the growth rate and structural properties of the films were studied. It was found that a significant increase in the films growth rate was observed with the introduction of H₂ at as low as 25 standard cubic centimeters per minute (sccm). A set of CN_x films deposited from C₂H₆:N₂ mixture without any inclusions of H₂ were also presented in this work as a reference to compare the differences between those two sets and to understand the roles of H₂ to the films properties. At highest H₂ flow rate, the structure of the films changed from polymeric to graphitic and the quenching of PL was observed. Furthermore, higher N incorporation with lower E_g was obtained for these films compared to those of C₂H₆:N₂ films. The change in the structure of the films corresponds to changes in their chemical bonding. As N incorporation increased, the porosity of the films increases and thus affects the disorder in the film structures.     

Silicon-carbon-oxynitrides grown by plasma-enhanced chemical vapor deposition technique

In this paper we report some preliminary results about the growth at low temperature (493 K) of hydrogenated silicon-carbon-oxygen-nitrogen amorphous thin-film alloys (a-SiC_xO_yN_z:H) by means of capacitively-coupled radio-frequency (13.56 MHz) plasma-enhanced chemical vapor deposition using a mixtures of silane (SiH₄), propane (C₃H₈), nitrous oxide (N₂O) and ammonia (NH₃) precursor gases. Thin films of a-SiC_xO_yN_z:H were grown at different deposition conditions, obtaining growth speeds varying from 0.22 to 0.44 nm/s. The films were characterized by means of Fourier transform infra-red spectroscopy in order to investigate the internal bonding structure, by UV-VIS transmittance spectroscopy to check the optical properties and by mechanical profilometry to measure the film thickness and estimate the growth rate. The comparison of structural and optical properties of samples grown with and without NH₃ presence in the gas mixture showed that the ammonia addition allows a better control of nitrogen incorporation in the film structure, while increasing film transparency and reducing the growth rate.     

The effect of the magnetron sputtering gun size on the characteristics of the plasma and CNx film deposition

To investigate the effect of the gun size on plasma and carbon nitride film deposition characteristics in RF magnetron sputtering system, we performed the RF sputtering deposition with different gun sizes and targets (50.8 mm and 76.2 mm in diameter). The result shows that there are remarkable different results between two magnetron sputtering guns: in plasma measurement result, the 50.8 mm gun made a column-like discharge from the target to substrate where the deposition takes place, but the 76.2 mm gun made a small volume discharge confined nearby the target, in FTIR spectra and hardness test result, the CN_x films deposited by the 50.8 mm gun contained more sp³ CN bonds, and less hydrogenated bonds and better nano-hardness, compared with those by the 76.2 mm gun. This result is ascribed to the fact that the magnetic field configuration evolution, especially the null point difference, with varying gun size can influence the plasma structure and film property changes.     

Fourier transform infrared spectroscopy characterization of AlN thin films grown on sacrificial silicon oxide layers via metal organic vapor phase epitaxy

Aluminum nitride (AlN) films were grown using metal organic vapor phase epitaxy techniques on Si (111) substrates patterned with silicon oxide (SiO_x) stripes and the vibrational properties of these films were investigated by Fourier transform infrared (FTIR) techniques. The grown films contained a predominantly wurtzite AlN phase. The AlN film on SiO_x was prone to corrosion when subjected to wet etching in buffered hydrofluoric acid solution thereby changing the material properties of the AlN film on SiO_x. The change in the material properties of the AlN films on SiO_x can be gauged from the decrease in the relative integrated areas under the A1 (TO) and E1 (TO) modes of the AlN film. The analysis shows that FTIR is a viable tool for investigating the material properties of AlN thin film structures with lateral dimensions as low as 100 μm.     

Structural and optical properties of high refractive indices lead vanadate thin films

Glasses with the chemical formula xWO₃–50PbO–(50 − x)V₂O₅, (0 ≤ x ≤ 10 mol%) were prepared by the usual melt quenching technique. FTIR analysis revealed that, the incorporation of WO₃ into the lead-vanadate network increases the number of bridging oxygens, and replaces low-coordinated structural units such as PbO₄, and VO₄ with higher coordinated structural units WO₆ and VO₅ which increases the number of bonds and the average cross-link density. Thin films of these glasses onto quartz substrates have been obtained by thermal evaporation technique. Based only on the measured transmittance spectra in the wavelength range 200–2500 nm, both the film thickness and the complex index of refraction have been calculated precisely. The absorption edge was shifted toward the long wavelength side (i.e. red shift of the optical band gap) as the WO₃ content increases. The dispersion of the refractive index was discussed in terms of the single oscillator model. The allowed non-direct transitions successfully describe the absorption mechanism in these films. Based on generalized Miller's rule, the third-order non-linear optical susceptibility χ⁽³⁾ has been investigated. The obtained values of χ⁽³⁾ values are rather large, indicating that the films under study are interesting materials for non-linear optical devices.     

Chemical analysis of NiAlFe thin films sputter deposited onto sapphire substrates

NiAlFe thin films were prepared onto sapphire single crystals by physical vapour deposition (PVD) and these were analysed by X-ray photoelectron spectroscopy (XPS) in combination with argon ion etching to determine the composition depth profile and interfacial characteristics of the samples. Non-linear least square fitting (NLLSF) analysis of the data was required due to the conflict of several peaks of interest. XPS depth profiles show that, for non-annealed NiAlFe–Al₂O₃, the interface is sharp and oxygen diffusion occurs at different annealing temperatures. Ni remains chemically unaffected by the presence of oxygen while the formation of aluminium oxide compounds occur. Two iron species are present in the film thickness where the low binding energy component is attributed to Fe–Fe or Fe–Al interactions and the higher one to the NiAlFe compound. The reduction-dissolution of the sapphire substrate leads to depletion of oxygen in the sapphire surface layer and the formation of alumina at the NiAlFe–Al₂O₃ interface. Within the film, aluminium and nickel are present as an intermetallic compound. Annealing of the samples induces surface oxidation and the subsequent formation of an Al₂O₃ layer. This type of interphase morphology should lead to optimal fibre/matrix (F–M) adhesion, and therefore optimal load transfer between the matrix and reinforcement.     

Acrylamide assisted polymeric citrate route for the synthesis of nanocrystalline ZrO2 powder

Nanocrystalline ZrO₂ powders have been prepared using acrylamide assisted polymeric citrate combustion (autoignition) route. Process parameters (i.e., total metal ions to citric acid ratio) were varied for the formation of polymeric resin in order to obtain the final product with desired properties (organic free, smaller crystallite size, etc.). The effect of three different citric acid amounts in the formation of nanocrystalline ZrO₂ powder was investigated using FTIR, XRD, TG/DTA and SEM-EDS, respectively, to identify the structural coordination, phase, thermal behavior and microstructure of the polymeric intermediates as well as the final ZrO₂ powders. Organic free ZrO₂ powder with two different phases of metastable t-ZrO₂ and m-ZrO₂ were prepared by calcining the polymeric intermediates at 600 °C. The lowest crystallite was found to be 18 and 16 nm, respectively, for the t-ZrO₂ and m-ZrO₂ phases prepared with total metal ions to citric acid ratio of 1:3.     

Uniform α-Fe2O3 nanotubes fabricated for adsorption and photocatalytic oxidation of naphthalene

Uniform α-Fe₂O₃ nanotubes with small aspect ratio were successfully fabricated by a hydrothermal method. In situ Fourier-transform infrared spectroscopy was used to study the mechanistic details of adsorption and photocatalytic oxidation of naphthalene over theα-Fe₂O₃ nanotubes. A possible degradation mechanism of naphthalene was proposed.     

Electrical characterization of amorphous silicon carbide thin films deposited via polymeric source chemical vapor deposition

Polymeric source chemical vapor deposition (PS-CVD) was used to synthesize amorphous silicon carbide (a-SiC) thin films. The PS-CVD process was conducted at temperatures between 750 and 1000 °C. The substrates used were silicon single crystal wafers of p-type and n-type, and thermally grown silicon dioxide substrates. The chemical and electrical properties of the films were studied by various techniques, including Fourier transform infrared spectroscopy, elastic recoil detection (ERD), and capacitance-voltage technique. A correlation was observed between the average concentration of oxygen in the films and the deposition temperature, linking a low oxygen concentration to a high deposition temperature. However, the concentration of oxygen in the films deposited at the same temperature is independent of the substrate. The thin films deposited at low temperature showed insulating behaviour, while the semiconducting behaviour is obtained at high deposition temperatures. Ohmic contacts were obtained on the deposited semiconductor thin film by evaporating nickel contacts, followed by annealing of the sample at 800 °C for 2 min.     

Novel one-component polymeric benzophenone photoinitiator containing poly (ethylene glycol) as hydrogen donor

Benzophenone (BP) is a common initiator which is often used in the UV-curing production and related fields. However, the shortcomings such as toxicity, odor, and migration always limit the development of the traditional BP photoinitiator. Polymeric benzophenone photoinitiator (PEG-BP) was synthesized basing on polyethylene glycol (PEG), succinic anhydride, 4-hydroxybenzophenone and epichlorohydrin. The structure of PEG-BP was characterized by IR and ¹H NMR. The radiation absorption of PEG-BP was detected by UV spectrophotometer with the maximum absorption wavelength at 283 nm in acetonitrile solvent, undergone significant redshift corresponding to small molecule photoinitiator BP, thus enhanced the photosensitive efficiency of UV-curing system in the long wavelength region. Besides, PEG-BP has better water solubility than BP, thus could be used in both oil and aqueous solution. The obvious advantage of this initiator was the elimination of amine based hydrogen donors and to provide alternative hydrogen donors with easily availability and non-toxicity. The effects of molecular weights of PEG-BP, photoinitiator concentration, UV-radiation intensity and different monomers on photopolymerization kinetics were investigated in detail. The synthesized polymeric photoinitiators are attractive to be used as type II photoinitiators.     

Synthesis of carbon nitride powder by selective etching of TiC0.3N0.7 in chlorine-containing atmosphere at moderate temperature

We reported the synthesis of carbon nitride powder by extracting titanium from single inorganic precursor TiC_0.3N_0.7 in chlorine-containing atmosphere at ambient pressure and temperature not exceeding 500 °C. The TiC_0.3N_0.7 crystalline structure acted as a template, supplying active carbon and nitrogen atoms for carbon nitride when it was destroyed in chlorination. X-ray diffraction data showed that the obtained carbon nitride powders were amorphous, which was in good agreement with transmission electron microscope analysis. The composition and structure of carbon nitride powders were analyzed by employing Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Results indicated that disorder structure was most likely for the carbon nitride powders and the N content depended greatly on the chlorination temperature. Thermal analysis in flowing N₂ indicated that the mass loss started from 300 °C and the complete decomposition occurred at around 650 °C, confirming the low thermal stability of the carbon nitride material.     

Investigation of kinetics and morphology development for polyurethane-urea extended by DMTDA

The relationship between the reactions kinetics and morphology development during the polyurethaneurea (PUU) curing process has been investigated simultaneously by in situ Fourier transform infrared spectroscopy (FTIR). The data of the FTIR spectra showed that with the increase of conversion, the absorbance of NH bands increases and its band sites shifts to lower wavenumbers; the absorbance of free urethane carbonyl kept nearly constant at low conversion, and then decreased much because of the interaction of the formed urea links, and then changed little at high conversion owing to the diffuse control. The band sites of hydrogen bonded urea carbonyl similarly shifted to lower wavenumbers and the absorbance of the hydrogen bonded urea carbonyl, associated with the phase separation of hard segments, became stronger with buildup of hydrogen bond between urea links. The carbonyl bands available during curing process were further assigned. Both interactions, such as hydrogenised effect and phase separation, played a major role in the matrix formation of the PUU polymer.     

Study of a new resin-based composites containing hydroxyapatite filler using Raman and infrared spectroscopy

The degree of conversion of polymeric matrix in hydroxyapatite-containing dental fillings by Raman and infrared spectroscopy has been determined. Resin-based dental composites are one of the most popular filling materials used in dentistry. These light-cured materials are characterized by the value of the degree of conversion, which depends on curing time and influences the quality of obtained dental filling. Distribution of the filler into polymeric matrix, which has a significant impact on the properties of the final product, has been determined by Raman mapping. The applied procedure also has allowed to present the changes of the degree of conversion on the examined surfaces. The results of the study demonstrate the versatility of the Raman spectroscopy as the analytical spectroscopic technique for determining chemical properties of dental fillings and providing insight into their organization at the microstructural level. The obtained degree of conversion values have been compared with data for the commercially available dental fillings characterized by other authors.     

Atomic layer deposition of tungsten using sequential surface chemistry with a sacrificial stripping reaction

Tungsten (W) films were grown with atomic layer control using a novel sequence of self-limiting surface reactions. The tungsten film growth was achieved by dividing the binary reaction WF₆+Si₂H₆→W+2SiHF₃+2H₂ into two separate half-reactions. Alternating exposures to WF₆ and Si₂H₆ in an ABAB… sequence produced tungsten deposition at temperatures between 425 and 600 K. The Si₂H₆ reactant served only a sacrificial role to strip fluorine from tungsten without incorporating into the film. FTIR spectroscopic investigations demonstrated that the WF₆ and Si₂H₆ half-reactions were complete and self-limiting at T>400 K. In situ spectroscopic ellipsometry measurements determined a tungsten growth rate of 2.5 Å/AB cycle with WF₆ and Si₂H₆ reactant exposures sufficient for complete half-reactions. The surface topography of the deposited tungsten films was flat indicating smooth film growth. The tungsten films were either amorphous or composed of very small crystalline grains and contained no measurable silicon or fluorine. These results represent the first demonstration of atomic layer deposition of smooth single-element metal films using sequential surface chemistry.