J. R. Blachere

Epitaxial growth of ZnO films on Si substrates using an epitaxial GaN buffer

We report on epitaxial growth of ZnO films on Si(111) substrates using an epitaxial GaN buffer layer. A rf magnetron sputtering process has been developed and utilized in growing epitaxial GaN buffers on Si, and then ZnO films on the GaN-buffered Si substrates. X-ray diffraction analysis shows that both the ZnO and GaN films are of a monocrystalline wurtzite structure with an epitaxial relationship of ZnO[0001]//GaN[0001]//Si[111] along the growth direction and ZnO[112_01]//GaN[112_0]//Si[11_0] along the in-plane direction. The successful growth of epitaxial ZnO/GaN films on Si demonstrates the feasibility and promise of integrating various functional devices on the same substrate.

Growth of highly oriented Pb(Zr, Ti)O3 films on MgO-buffered oxidized Si substrates and its application to ferroelectric nonvolatile memory field-effect transistors

We have grown highly oriented lead zirconate titanate [Pb(Zr, Ti)O3 or PZT] films on oxidized silicon substrates using a thin MgO buffer layer (7–70 nm thick). Ferroelectric nonvolatile memory field-effect transistors (FETs) were successfully fabricated using the metal/PZT/MgO/SiO2/Si structure in conjunction with radio-frequency sputter deposition of PZT and MgO films. The fabricated devices show excellent performance in ferroelectric polarization switching and memory retention. The results indicate that a thin MgO buffer serves well not only as a template layer for the growth of oriented PZT films on amorphous substrates, but also as a diffusion barrier between a ferroelectric and a substrate during device fabrication, protecting the SiO2/Si interface and the FET channel region.

Pedogenic origin of dolomite in a basaltic weathering profile, Kohala peninsula, Hawaii

We document stoichiometric dolomite occurring in a nonsaline Quaternary soil on the Kohala peninsula, northwestern Hawaii. Geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind-blown dust. The strontium isotopic composition of the dolomite (87Sr/87Sr = 0.7045–0.7048) is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater. Infiltration of soil waters with elevated Mg/Ca (>1) derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early-precipitated soil calcite and/or to direct dolomite precipitation in the profile. This demonstrates that well-ordered dolomite can form in a nonmarine environment at temperatures <100 °C without undergoing burial diagenesis.

Lead–zirconate–titanate-based metal/ferroelectric/insulator/semiconductor structure for nonvolatile memories

We have investigated the structural and electrical properties of the metal/ferroelectric/insulator/semiconductor (MFIS) structure that incorporates a MgO/SiO2 insulating buffer between a ferroelectric layer and Si substrate. Highly oriented lead–zirconate–titanate [Pb(Zr,Ti)O3, or PZT] films were grown on the MgO-buffered oxidized silicon substrates with a rf magnetron sputtering technique. The x-ray diffraction and energy-dispersive x-ray spectroscopy analysis results show that a MgO buffer serves well not only as a template layer for growing oriented PZT films on an amorphous surface but also as a diffusion barrier between PZT and Si substrates. The memory window of the MFIS structure was characterized with a capacitance-versus-voltage method. Numerical analyses were also carried out to simulate the MFIS capacitor characteristics. In this simulation, the PZT films were assumed to have a two-layer structure in which the dielectric and ferroelectric properties of an initial layer are significantly weaker ...

Hot corrosion of alumina

The hot corrosion of single crystal and polycrystalline aluminas has been investigated in SO[sub 2]--SO[sub 3]--O[sub 2] environments and in the presence of molten Na[sub 2]SO[sub 4]-based deposits at temperatures of 700 and 1000 [degree]C. The effect of microstructure and impurities on the corrosion has been emphasized. Weight changes and wetting angles were determined, and the evolution of the morphology of the exposed substrates and the reaction products was investigated in detail. The corrosion was small under the conditions of this study and generally increased with the impurity content of the polycrystalline aluminas. Based on the experimental results, particularly those obtained by electron microscopy and microanalysis using the SEM/EPMA (scanning electron microscope--electron probe microanalyzer), mechanisms are proposed for the corrosion of polycrystalline aluminas which emphasize the role of the silicate impurities and the synergy of their corrosion with that of the alumina grains. As a result, the alumina grains were dissolved by acidic fluxing under the acidic and the basic experimental conditions.

Blueshift of surface plasmon resonance spectra in anneal-treated silver nanoslit arrays

Silver nanoslit arrays were anneal treated in vacuum, and the effects on the surface morphology of silver and the surface plasmon resonance characteristics were investigated. Optical transmission through nanoslit arrays shows a distinctive change in the spectral profiles after annealing: A clear blueshift of the transmission peaks and dips (20nm shift for an anneal temperature of 150°C). Scanning electron microscopy reveals a morphological change of silver: Increased grain sizes, and smooth and round surface profiles after the anneal treatment. The observed blueshift of transmission spectra correlates well with the geometrical and dimensional changes of silver islands defined between slits, which are found to alter the surface plasmon resonance conditions involving various mechanisms in different regimes.

Real-time simulation of nucleation and growth of vacuum-evaporated thin metallic films

Abstract A real-time computer simulation of the nucleation and growth of thin films deposited from the vapor phase is presented. The model incorporates material properties of the deposit and substrate and deposition parameters including the incidence rate and substrate temperature. At each selected instant a projection of the simulated film is computer plotted. Samples of simulated silver and gold films deposited onto cleaved NaCl substrate are shown.

Sintering of submicron metallic particles

An approximate analytical solution to the complete sintering of submicron hemispheres under conditions relavant to the preparation of semi-continuous metallic films is derived. The sintering of two spheres controlled by surface diffusion with no grain boundary formation is broken into two distinct parts: sintering with no shrinkage followed by spheroidization. The time for each part is derived and it is found that the time for spheroidization is about 17 times larger than the time of neck growth. The results are generally in agreement with the treatment of some previous investigators. It is shown also that under normal deposition conditions the contribution of the deposition source can be neglected during a sintering event simplifying significantly the simulation.

Temperature dependence of lead loss in r.f. magnetron sputtering of a stoichiometric Pb(Zr,Ti)O3 target

Abstract The temperature dependence of lead loss was studied for r.f. magnetron sputtering of a stoichiometric Pb(Zr,Ti)O 3 target (Zr:Ti ratio of 53:47). Films deposited at 200 °C or below crystallized into perovskite Pb(Zr,Ti)O 3 on receiving an annealing treatment at 600 °C or above. No excess lead was used either during sputtering or during post-deposition annealing. The Pb(Zr,Ti)O 3 films thus prepared are highly ferroelectric with a maximum polarization of 37 μCcm −2 , a remanent polarization of 22 μCcm −2 , and a coercive field of 40 kVcm −1 measured at 50 Hz. This suggests that lead loss during deposition is negligible for deposition temperatures of 200 °C or below. Films deposited at 500 °C were dielectric as-deposited, and became weakly ferroelectric after being annealed at 800 °C for 1 h. X-ray spectroscopy analysis of the film indicates significant loss of lead at 500 °C. Depositions at 600 °C, however, resulted in thermally stable and dielectric ZrTiO 4 films. The structural and dielectric properties of the films remained unchanged even after annealing at 800 °C for 1 h. X-ray spectroscopy analysis indicates that lead was lost completely during sputtering at 600 °C. Utilizing this temperature dependence of lead loss to control the composition of deposited films, a Pb(Zr,Ti)O 3 /ZrTiO 4 heterostructure was also prepared successfully from a single oxide target with a two step, single deposition process.

An algorithm to calculate the contact angle of heterogeneous nucleation

Abstract We developed an algorithm to calculate the contact angle of evaporated silver and gold on alkali halide substrates. The algorithm differs from previous published work in that it uses the single-atom critical nucleus concept.