H. C. Ong

Determination of the optical constants of zinc oxide thin films by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) has been used to determine the complex pseudo dielectric functions, e1(E)+ie2(E), of ZnO films on (0001) Al2O3 substrates over the spectral range of 1.33 and 4.96 eV at room temperature. The SE measurements are carried out with E⊥c at angles of incidence of 60° and 65° with respect to the surface normal. Below the band gap, the refractive index n is found to follow the first order Sellmeir dispersion relationship n2(λ)=1+1.881λ2/(λ2−0.05382). A free excitonic structure located at the band edge of 3.32 eV is clearly observed in the pseudo absorption spectrum. Elliott expression with Lorentzian broadening is used to model the pseudo absorption coefficient above the band edge.

THE EFFECT OF NITROGEN ON PULSED LASER DEPOSITION OF AMORPHOUS SILICON CARBIDE FILMS : PROPERTIES AND STRUCTURE

The influence of nitrogen on amorphous silicon carbide films deposited at room temperature using pulsed laser ablation has been investigated. Depositions were carried out either in ultrahigh vacuum or in a nitrogen ambient ranging from 10 to 100 mT. The mechanical and optical properties, as well as composition and structure of the resulting films, were evaluated using a variety of analytical techniques. Vacuum-deposited films, exhibited high hardness but suffered from high compressive stresses ({approx_gt}1 GPa). At low nitrogen background pressures ({lt}30 mT), films with an optimum balance between hardness ({approximately}16 GPa), adhesion, and intrinsic stress ({lt}220 MPa) were found, making them ideal candidates for protective coating applications. As nitrogen pressure was increased, mechanical performance degraded due to the increasing amount of SiO{sub 2} found in the films as evidenced by spectroscopic ellipsometry, infrared spectroscopy, and Auger electron spectroscopy measurements. The source of oxygen is attributed to residual water vapor present in our vacuum system. Optical emission spectroscopy was used to confirm the presence of Si{endash}O species in the laser-induced plasma plume. {copyright} {ital 1996 Materials Research Society.}

Structural properties of yttria-stabilized zirconia thin films grown by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) thin films grown by pulsed laser deposition method on (0001) sapphire substrates have been studied by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). It was found that the crystal orientation of the YSZ films changes as a function of oxygen pressure during deposition. At low oxygen pressure (50 mTorr), well-defined (111) oriented YSZ films are grown. High oxygen pressure favors the nucleation of (001) oriented YSZ grains. A model to explain the preferred growth direction of (001) YSZ is presented. Utilizing the experimental data, we have developed a two-step process to epitaxially grow high-quality (001) oriented YSZ on (0001) sapphire substrate. {copyright} {ital 1999 Materials Research Society.}

Potassium titanyl phosphate thin films on fused quartz for optical waveguide applications

Thin films of potassium titanyl phosphate (KTiOPO4) for photonic applications have been fabricated on fused quartz substrates by pulsed excimer laser ablation. The textured films were optically uniaxial with the symmetry axis oriented normal to the film surface. The principle component of the second order electric susceptibility was oriented parallel to this symmetry axis and was determined to be about 16 times the magnitude of quartz for the fundamental wavelength of 1.064 μm. This configuration, with the largest nonlinear optical response for polarizations perpendicular to the film surface, is desirable in TM guided wave applications. Planar optical waveguide measurements were performed and the linear waveguide loss was measured. The frequency dependence of χ(2)(ω) was determined and found to be uniform for visible second harmonic wavelengths.

Large second-order optical nonlinearities in pulsed laser ablated silicon carbide thin films

Large second‐order nonlinear optical response has been observed in silicon carbide thin films deposited by pulsed laser ablation on sapphire and fused silica substrates; films on both substrates were uniform and optically transparent but exhibited distinct orientations. The d33 values of the sapphire‐substrate samples were determined to be 10 pm/V.

DEVELOPMENT OF FLAT, SMOOTH (100) FACETED DIAMOND THIN FILMS USING MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

A novel approach has been used to develop (100) faceted diamond films with flat, smooth surfaces. A morphological study of the early stages of growth behavior of (100) homoepitaxial films versus process temperature and methane percentage was carried out using atomic force microscopy. The results showed that spiral growth features and penetration twin density were dominant for growth conditions not well suited for (100) growth. Optimized process parameters were found to proceed via a step mechanism consistent with ledge growth on (2{times}1) reconstructed (100) diamond surfaces. These optimized conditions were then applied to growth of polycrystalline diamond on pretreated silicon susbtrates. A unique octahedral faceted film resulted, indicating strong preference for growth in the {l_angle}100{r_angle} direction. Scanning electron microscopy, x-ray diffraction, and Raman spectroscopy were used to assess film morphology, internal fiber texture, and carbon phase, respectively. A second stage growth step was used to flatten the surface topography to achieve the desired (100) flat tile-like morphology. This smooth (100) surface exhibited enhanced tribological performance compared to a typical randomly textured diamond film. {copyright} {ital 1997 Materials Research Society.}

Synthesis of In2O3 nanowires enhanced by anodic alumina membrane

Large-scale single crystalline In2O3 nanowires were successfully synthesized on anodic alumina membranes by a simple thermal evaporation method at 570°C. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy studies revealed the formation of single crystalline In2O3 nanowires with diameters of 50–100 nm and lengths of up to a few hundreds of micrometers. Cathodeluminescence study revealed existence of oxygen vacancies evidenced by a strong and broad emission at 470 nm with a shoulder at 400 nm. The growth mechanism of the nanostructures is also discussed.