Randal W. Tustison

Epitaxial Fe films on GaAs for hybrid semiconductor‐magnetic memories

The magnetic and structural properties of Fe films deposited by ion‐beam sputtering (IBS) on (100)‐oriented GaAs substrates are described. The films are between 30 and 600 nm thick and are characterized by a coercive field of approximately 3–6 Oe. The saturation magnetization and anisotropy field, inferred from vibrating sample magnetometer measurements agree substantially with the values expected for bulk Fe. Films deposited on the (100) substrate show the expected fourfold (or ‘‘biaxial’’) symmetry with no indication of a uniaxial anisotropy component. These properties make the films ideally suitable for the intended application in a hybrid semiconductor‐magnetic memory, in which two magnetic remanent states with mutually orthogonal magnetization directions interact with an electronic flip‐flop circuit.

Epitaxial Fe films on (100)GaAs substrates by ion beam sputtering

We report the successful growth of single‐crystal Fe films on GaAs substrates in (100) orientation by ion beam sputtering. Magnetic measurements show that the crystalline anisotropy field of these films is substantially the same as that of bulk single crystals.

Magnetic resonance experiments on ion beam sputtered {100} Fe films

Ferromagnetic resonance (FMR) measurements have been performed on single‐crystal Fe films, produced by ion beam sputtering techniques on GaAs substrates. In‐plane FMR results over the frequency range 0.1–20.0 GHz were obtained by a slot line technique. The magnetic parameters deduced from these measurements are comparable to bulk Fe. In‐plane angular variation reveals a negligible uniaxial anisotropy contribution to the magnetic anisotropy energy. Spin‐wave excitations were observed in 9.5‐GHz cavity measurements, and are found to obey the n2 law. The exchange stiffness constant is found to be somewhat larger than seen in other epitaxial Fe films. These results show that epitaxial Fe/GaAs films possessing good magnetic properties may be produced by ion beam sputtering techniques.

Current and Future Development of Calcium Lanthanum Sulfide

Transparent samples of CaLa2S4 have been produced with good optical imaging characteristics and no significant impurity absorption bands between the intrinsic absorption edges. However, the optical transmittance of CaLa2S4 is still not adequate due to scattering and broadband absorption. Processing studies to improve the optical transmittance have concentrated on powder sulfurization, milling, and sintering. The best optical quality samples achieved to date have been fabricated using powder consisting primarily of CaSO4 and La2O2S, milled with burundum media, and sintered at 1150°C. The rain erosion resistance of CaLa2S4 has been shown to be substantially better than that of ZnS.

Optical properties of ALON (aluminum oxynitride)

Aluminum oxynitride or ALON is a transparent polycrystalline ceramic material having high strength (380 MPa) and hardness (1950 kg/mm2). The transmission range of ALON extends from 0.2 micrometer in the UV through the visible to 6.0 micrometer in the infrared. This material is made by conventional powder processing and sintering a powder compact to full density and optical transparency. Powder compacts of near net shape and size are made by conventional dry pressing, by slip casting, and by injection molding methods. This gives the material great latitude in size and shape capabilities not afforded by materials formed by single crystal growth methods. Intrinsic transparency extending from ultraviolet wavelengths (UV) to mid-infrared wavelengths (MID-IR) and low levels of optical scatter have been achieved. In this paper recent measurements of the spectral dependence of forward optical scatter, the spectral emittance from room temperature to 1200 degrees Celsius, and the index of refraction (n) of ALON are presented. Literature values for the changes in refractive index with temperature (dn/dT) are compared.

Magnetron sputtering of Fe onto GaAs substrates: Energetic bombardment effects

Fe films were deposited on (100) GaAs substrates by magnetron sputtering. Bombardment of the films during growth by energetic particles from the plasma had a significant impact on film properties including resistivity, crystallographic orientation, and stress. Preferred orientation of the (200) Fe planes parallel to the substrate surface was observed over a wide range of deposition conditions. The (200) Fe rocking curve widths of these films compare favorably with those of films deposited using molecular beam epitaxy, and the resistivities were comparable to that of bulk Fe. Positions directly in front of the cathode as well as low cathode power appear to favor the formation of (200) Fe texture, however, the rocking curve width and lattice parameter are relatively independent of substrate position and cathode power.

Calcium Lanthanum Sulfide As A Long Wavelength IR Material

Calcium lanthanum sulfide (CLS) is under development as a long wavelength infrared (LWIR) window/dome. A coating has been demonstrated to protect CLS from the effects of high humidity and to increase its resistance to rain drop impact damage. Coated CLS exhibits better impact damage resistance than coated ZnS. Processing studies have focussed on improving the optical quality and fracture strength of CLS. Recent work has also concentrated on materials with a molar composition of 90 La2S3 : 10 CaS.

Deposition and annealing of ion beam sputtered Y‐Ba‐Cu‐O superconducting films

Highly oriented, near‐stoichiometric films of YBa2Cu3O7−δ have been deposited onto (100) MgO, (100) yttria‐stabilized zirconia, and (110) SrTiO3 by ion beam sputtering from a single, off‐stoichiometric target. Their crystal structure and resistance behavior were found to depend on the crystallization temperature of a two‐step post‐deposition anneal, which was varied from 750 to 1000 °C. The highest zero‐resistance temperature (73 K) and degree of preferred orientation was observed for a film which was deposited on (100) MgO and annealed for a short time at 950 °C.

Optical properties of durable oxide coatings for infrared applications

There is a continuing need for durable and protective coatings for long wavelength infrared (LWIR) windows and domes as a result of the environmental and mechanical vulnerability of most LWIS transparent materials. Diamond coatings would be ideal except for the fact that relatively high deposition temperatures are required to deposit films having low optical absorption. Diamond-like carbon films deposited at low temperatures are typically too absorbing or highly stressed. Certain transition metal oxide films can be used successfully for many applications, are very durable and can be deposited by traditional thin film deposition methods. In this study, Y2O3, ZrO2 and HfO2 films are deposited and characterized, in particulara their absorption coefficients as a function of wavelength are derived at wavelengths in the LWIR. Durable oxide coatings are deposited over full-size LWIR windows.

Aluminum oxynitride's resistance to impact and erosion

Aluminum oxynitride (ALON) is a polycrystalline ceramic material useful for windows, domes, and other optical elements. It is transparent in the visible to mid-wavelength infrared. Data is presented on the affects of impacts with sand and water particles on polished surfaces. Velocities up to 690 m/sec were used.