Carolyn Rubin Aita

THERMODYNAMICS OF TETRAGONAL ZIRCONIA FORMATION IN A NANOLAMINATE FILM

Zirconia–alumina transformation‐toughening nanolaminates were fabricated by reactive sputter deposition. The average crystallite size and volume fraction of each zirconia polymorph were determined by x‐ray diffraction. The volume fraction of tetragonal zirconia, the phase necessary for transformation toughening, was found to strongly depend upon the zirconia layer thickness. An end‐point thermodynamics model involving hemispherical cap zirconia crystallites was developed to explain this phenomenon. In excellent agreement with experimental results, the model predicts that unity volume fraction of tetragonal zirconia is produced in the nanolaminate when the zirconia layer thickness is less than the radius at which a growing zirconia crystallite spontaneously transforms to the monoclinic phase.

Auger electron and x‐ray photoelectron spectroscopy of sputter deposited aluminum nitride

Basal crystallographic orientation and semiamorphous films which are nominally aluminum nitride were grown by reactive sputter deposition on silicon substrates and characterized by x‐ray photoelectron spectroscopy and Auger electron spectroscopy. The binding energy of the aluminum 2p, nitrogen 1s, and oxygen 1s core electrons and the kinetic energy of the aluminum LVV and KLL Auger transitions indicate that all films contain a component which is chemically identifiable as AlN. The films contain oxygen as a major impurity. The difference in the manner in which oxygen is incorporated into the films, determined by these two spectroscopic techniques, is discussed and related to deposition conditions.

Basal orientation aluminum nitride grown at low temperature by rf diode sputtering

Aluminum nitride films with solely a (0001), or basal crystallographic orientation have been grown on single‐crystal silicon and silicon dioxide‐coated silicon at substrate temperatures below 100 °C. The deposition technique used was rf diode sputtering of an aluminum target in argon/nitrogen gas mixtures containing 50–100% nitrogen. Unintentional oxygen doping of the growing films was minimized by a target clean‐up procedure which was monitored by glow discharge mass spectrometry. X‐ray diffraction measurements on the films included relative integrated intensity, peak half width, and precise peak position from which the lattice constant normal to the basal plane was calculated. The preliminary results of a study of the evolution of film crystallography from multiorientation aluminum to single‐orientation aluminum nitride as the sputtering gas nitrogen content is increased are also presented.

Wet oxidation of GeSi at 700 °C

About 500‐nm‐thick films of Ge0.36Si0.64 and Ge0.28Si0.72 grown epitaxially on (100)Si have been oxidized at 700 °C in wet ambient. A uniform GexSi1−xO2 oxide layer forms with a smooth interface between it and the unoxidized GexSi1−x layer below. The composition and structure of that layer remains unchanged as monitored by backscattering spectrometry or cross‐sectional transmission electronic microscopy. The oxide of both samples grows as square root of oxidation duration. The parabolic rate constant increases with the Ge content and is larger than that for wet oxidation of pure Si at the same temperature. The absence of a regime of linear growth at this relatively low temperature indicates a much enhanced linear rate constant.

Tetragonal zirconia growth by nanolaminate formation

Multilayer films of polycrystalline zirconia and amorphous alumina were grown by reactive sputter deposition and characterized using x‐ray diffraction and high resolution electron microscopy. We demonstrate that the layer spacing can be scaled to insure nanosize crystallites in the zirconia layer. The result is that nanolaminates with a high volume fraction of retained tetragonal zirconia are produced, independent of deposition parameters and without the addition of a stabilizing dopant.

Radio frequency sputter deposited boron nitride films

Thin films (∼1 μm) of boron nitride were grown on water‐cooled glass, silicon, and sapphire substrates by reactive sputter deposition from a BN target in Ar, Ar/N2, and N2 discharges. The effect of sputtering gas composition on film chemical and optical behavior is reported and discussed in the present paper. The following changes occurred as the gas N2 content was increased: (1) The concentration of excess boron in the films, relative to an external standard, decreased. (2) Absorption of visible and ultraviolet radiation decreased. (3) The energy band gap increased by >2 eV. Smaller band gap values were correlated with excess boron. (4) The average B–N bond strength and the ordering of B and N atoms to form B–N bonds increased. Near stoichiometric (B/N=1.1–1.4), colorless, wide band gap (5.4–5.6 eV) films were grown in gas containing from 25% to 100% N2.

Near‐band gap optical behavior of sputter deposited α‐ and α+β‐ZrO2 films

The functional dependence of the optical absorption coefficient on photon energy in the 4.9–6.5 eV range was determined for α‐ and α+β‐ZrO2 films grown by reactive sputter deposition on fused silica. Two allowed direct interband transitions in α‐ZrO2 were identified, with energies equal to 5.20 and 5.79 eV. Modification of these transitions in α+β‐ZrO2 is reported.

Sputter deposition of platinum films in argon/oxygen and neon/oxygen discharges

We have investigated the resistivity, crystallography, and chemistry of films sputter deposited from a platinum target in argon and neon discharges containing small amounts of oxygen. The results presented here indicate that the oxidation behavior of platinum is strongly dependent upon the type of rare gas used for the deposition. A comparison of the dependence of platinum‐oxygen bond formation on cathode voltage and deposition rate suggests that oxide formation in the films is controlled by a reaction which occurs at the target surface and is enhanced when neon carrier gas is used. A large increase in resistivity above that of bulk platinum metal is always correlated with platinum‐oxygen bond formation in the film.

The air‐exposed surface of sputter deposited silicon carbide studied by x‐ray photoelectron spectroscopy

X‐ray photoelectron spectroscopy analysis of the air‐exposed surface of sputter deposited amorphous silicon carbide films shows three dominant features: (1) Si–C bonding characteristic of SiC, with Si 2p electron binding energy at 100.4–100.7 eV and C 1s electron binding energy at 282.7–283.2 eV, (2) Si–O bonding characteristic of SiO2, with Si 2p electron binding energy at 102.1–102.5 eV, O 1s electron binding energy at 532.0 eV, and the O 1s‐Si 2p electron binding energy difference equal to 429.5–429.9 eV, and (3) a strong adventitious C signal. The spectral features are consistent with a model for the surface of SiC powder consisting of several monolayers of hydrocarbons over several nm of SiO2 that overlays the bulk SiC. The oxidation behavior of the film surface was found to depend upon the cathode voltage at which the film was deposited.

Transmission electron microscopy study of zirconia–alumina nanolaminates grown by reactive sputter deposition. Part I: zirconia nanocrystallite growth morphology

Abstract Pure zirconia films and zirconia–alumina nanolaminate films grown by reactive sputter deposition are studied by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). The phase composition and morphology associated with zirconia crystallite growth are investigated by examining films containing zirconia layers of varying thickness. These studies, performed at room temperature, suggest that the zirconia crystallites initially grow in the tetragonal phase to a critical size of 6.0±0.2 nm, in agreement with a value of 6.2 nm predicted by end-point thermodynamics. Past the critical size, incorporation of additional zirconia molecules into the zirconia layers is accomplished predominantly by transformation of the growing crystallites to the monoclinic phase, and less frequently by deposition of amorphous zirconia. Transformation to the monoclinic phase is accompanied by a highly faulted intermediary phase. The subsequent growth behavior of monoclinic crystallites is consistent with a three-dimensional interface-controlled, diffusion-limited growth process with a growth exponent between 3 and 4. Nanoindentation measurements of nanolaminates with 5-nm thick zirconia layers give a hardness of ~8 GPa for the upper strata where the morphology of the tetragonal zirconia layers contains an intrinsic roughness. The hardness increases to ~10 GPa closer to the substrate where the laminar morphology is more pronounced. Youngs modulus is between 156 and 195 GPa for these same nanolaminates.