Narrow Results

The electronic structures of L-cysteine adsorbed on Au(111)/Si(111) and surfaces were studied by using X-ray photoelectron spectroscopy (XPS). L-cysteine multilayers on Au(111)/Si(111) and surfaces were prepared under UHV condition. L-cysteine monolayers were obtained by annealing such multilayer sample up to 130°C. In the case of the Au(111)/Si(111) surface, we observed no chemical shift and no change in the peak intensity ratios among C1s, N1s, O1s and S 2p before and after annealing. On the other hand, the component attributed to COOH group in C1s spectra decreased after annealing. In addition, O1s XPS spectra of monolayer on the surface was composed of two distinct peaks, which indicates that there are two kinds of O atoms in different conformations. These observations indicate that the COOH group adsorbs directly to a surface atoms and dissociate by the interaction with the substrate Si(111) trimer atoms.

The effect of various laser processing parameters on the kerf width and cut quality of Si wafer as well as encapsulated Si wafer is investigated. The parameters are then optimized to minimize the heat affect zone and obtain the best possible cut quality. It has been found that oxygen is the most suitable assist gas for laser dicing and that the highest gas pressure may not produce the best cut quality. The effect of laser repetition rate, pump energy, feed rate, and number of passes are also studied. Under optimized parameters, the cut quality of Si wafer using laser dicing is found to be comparable to diamond saw dicing.

Highly (002)-oriented nanocrystalline ZnO thin films were deposited on glass substrates at a substrate temperature of 500°C in air atmosphere by low-cost spray pyrolysis method. Room temperature photoluminescence spectral studies show the presence of near band edge emission and defect level emission (DLE) from the samples. The DLE wavelength is blueshifted about 22 nm and further emission intensity enhancement is observed in (002)-oriented sample as compared to that of wurtzite ZnO phase. The modifications in local defect levels and change in crystalline symmetry are attributed to the blue shift in the DLE region of c-axis oriented sample. The increased emission intensity of (002)-oriented samples is due to improvement in crystalline quality, preferential oriented growth and spherical morphology of nanocrystalline grains.

The critical thickness of structural transition from a tetragonal structure to a normal bulk structure for epitaxial ultrathin films deposited on the metallic and semiconductor substrates is thermodynamically considered. It is found that equilibrium between the elastic energy of the tetrahedral structure and the film–substrate interface energy is present when a critical thickness is reached. The predictions of the critical thickness are in agreement with the experimental results of films.

CdS thin layers of 250 nm thick doped with zero, 0.1, 0.2 and 0.3 weight percents iron were deposited on glass substrates by modified flash evaporation technique in vacuum at the pressure of 5 × 10⁻⁶ mbar. The structure of the films was investigated by X-ray diffractometry. It was revealed that the films had hexagonal structure with (002) preferred orientation. Field emission scanning electron microscopy (FESEM) was employed to study the surface morphology of the prepared samples. It was found from FESEM images that the Fe-doped CdS film showed more surface uniformity. Optical absorption data of the films were used to measure the band gap of the films. It was found that the band gap of the samples decreased upon increasing the Iron concentration. Photoluminescence (PL) spectra of the CdS:Fe thin films were used to study most prominent excitation peaks within the energy range (1.6–2.6 eV). The variation in peak energy was observed upon increasing the Fe content in the films.

This work explores the structural, surface and optical properties of NiO films grown on Si, GaAs, PET and glass substrates. The NiO films were deposited on these substrates under same conditions by using radiofrequency (RF) magnetron sputtering of NiO target at 100${}^{\circ }$C. The structural study by X-ray diffraction (XRD) showed the existence of (200) and (220) oriented NiO peaks on all the substrates. The preferred orientation of NiO films on Si, GaAs and glass was along (200) plane whereas the film grown on PET was observed to be oriented along (220) plane. The crystallite size of NiO on GaAs was the largest among the other substrates. The RMS surface roughness on PET was higher as compared to the other substrates. The band gap of NiO films grown on glass and PET was estimated from UV–Vis transmittance spectroscopy whereas the UV–Vis reflection spectroscopy was carried out to find out the band gap of NiO grown on GaAs and Si substrates. The band gap of NiO on PET was higher than its band gap obtained on other substrates. The results obtained on properties of NiO films on different substrates were correlated with each other.

In order to determine its electronic and chemical properties, the Al₂O₃/p-GaN(0001) interface is studied in situ by the X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). Using physical vapor deposition (PVD) method, the Al₂O₃ film is deposited step by step under ultra-high vacuum (UHV) onto p-GaN(0001) surface covered with residual native Ga oxide. Prior to the first Al₂O₃ layer evaporation, binding energy of the Ga 3$d$ substrate line is equal to 20.5eV. The PVD method of deposition leads to an amorphous Al₂O₃ film formation. For the final 12.0nm thick Al₂O₃ film binding energy of the Al 2$p$ line is set at 76.0eV and for the O 1$s$ line at 532.9eV. The valence band offset (VBO) and the conduction band offset (CBO) of the Al₂O₃/p-GaN(0001) interface are determined to be equal to $-$1.6eV and 1.8eV, respectively.