James L. Lamb

Substrate heating rates for planar and cylindrical-post magnetron sputtering sources

Abstract Substrate heating energies per atom deposited are reported for planar magnetron sputtering of aluminum, chromium, nickel, copper, molybdenum, indium, tantalum, tungsten and platinum in argon as well as for aluminum and chromium sputtered in O 2 . Data are also reported for cylindrical magnetron sputtering of niobium, silver, tantalum, tungsten and Pb-Sn in argon as well as for molybdenum sputtered in neon, argon, krypton and xenon. The planar and cylindrical magnetron heating rates were comparable. The heating energies for argon sputtering ranged from 10–15 eV per deposited atom for the light metals to almost 100 eV atom -1 for tantalum and tungsten. The implied reactive sputtering heating energies were about 500 eV molecule -1 for Cr 2 O 3 and 1150 eV molecule -1 for Al 2 O 3 . Special experiments were conducted to examine the contributions to the substrate heating of plasma species and ion neutralization and reflection at the cathode. The data indicate that charged plasma species do not contribute significantly to the heating but that neutralized and reflected ions play a significant role in the planar as well as the cylindrical cases despite the differences in cathode geometry.

High Tc superconducting NbN films deposited at room temperature

Thin films of niobium nitride with superconducting transition temperature (Tc ) of 15.7 K have been deposited on a variety of amorphous as well as crystalline substrates including glass, glazed ceramic, fused quartz, and sapphire, maintained at room temperature, by dc reactive magnetron sputtering in a mixture of Ar and N2 gases. The effects of the deposition conditions, particularly the carrier gas pressure and composition, on the film crystal structure, orientation, and resistivity have been studied in an effort to maximize the superconducting transition temperature. A study of the variation of nitrogen consumption with nitrogen injection pressures for constant background argon pressures is conducted and found to be an absolute indicator of the NbN formation systematics. Initially, the consumption increases linearly with the injection pressure but beyond a certain threshold, it shows a distinct drop. The desired high Tc  NbN with B1 crystal structure is formed in the vicinity of this turning point of th...

Thermal stability studies of sputter-deposited multilayer selective absorber coatings☆

Multilayer sputtered coatings of the Al2O3/M/Al2O3/R type, where M is a semitransparent absorbing layer and R is a low emittance reflecting layer, show promise as selective absorber coatings. In this paper we describe an investigation of the thermal stability of Al2O3/M/Al2O3/R-type coatings with M layers of chromium, nickel, molybdenum, tantalum and a PtAl2O3 cermet, and with Al2O3 layers deposited by both direct r.f. sputtering of alumina and reactive sputtering of aluminum. In order to simplify the thermal stability studies, the substrates were glass plates and the R layers were made of the same metal as the M layers, except in the PtAl2O3 case where the R layers were chromium or platinum. In all cases, proper selection of the coating thicknesses yielded solar absorptances equal to or greater than 0.90 and room temperature emittances of about 0.12 or less. Coatings of the basic M layer, the M layer coated with an Al2O3 layer, and the complete multilayer stack were subjectedj to various thermal tests in air and vacuum over the temperature range from 300 to 700°C with test periods of from 8 to about 1000 h. The diffusion barrier properties of the Al2O3 layers, and therefore the thermal stability of the coatings, depended primarily on the method of deposition of the Al2O3 layers. Thus coatings with reactively sputtered Al2O3 layers underwent absorptance changes in the 300–450°C range in air or vacuum. Coatings with directly r.f.-sputtered Al2O3 layers were stable in air to 500–600°C and in vacuum to at least 650–700°C.

Sputter-deposited Al2O3/Mo/Al2O3 selective absorber coatings

The development of large-area magnetron sputtering sources has made sputtering attractive for selective absorber applications. In this paper we describe an investigation of Al2O3/Mo/Al2O3 (AMA) interference-type selective absorber coatings deposited by cylindrical magnetron sputtering onto low emittance molybdenum-coated glass and stainless steel substrates. Both post and hollow cathode magnetrons were used. The Al2O3 layers were formed by reactive sputtering from aluminum and by r.f. sputtering from alumina targets. The semitransparent molybdenum intermediate layers were deposited with and without oxygen injection. The optical constants for the individual sputtered layers were determined from transmission and reflectance measurements and were used to calculate the influence of these layers on the solar absorptance of the complete AMA coating. The optical properties of the sputtered AMA layers were in reasonable agreement with theory, yielding hemisperical solar absorptances αH of 0.92–0.95 with total hemispherical emittances eH of 0.06–0.10 at 20°C. The highest absorptions and the lowest emittances were obtained for coatings in which the center molybdenum layer had been deposited with oxygen addition. The thermal stabilities of coatings with r.f. sputtered Al2O3 were superior to with reactively sputtered Al2O3. AMA coatings on stainless steel with an Al2O3 diffusion barrier were stable (less than 2% loss in α) at 700°C in vacuum and at 550°C in air. These coatings are therefore attractive for a range of selective absorber applications including high temperature collectors for use between 300 and 600°C.

Sputter-deposited Pt-Al2O3 selective absorber coatings☆

Abstract In this paper we describe an investigation of several configurations of selective absorber coatings which incorporate sputter deposited Pt-Al 2 O 3 cermet layers. The potential application is for medium and high temperature collectors. The coatings were prepared by codeposition using Al 2 O 3 and platinum cylindrical-post magnetron sputtering sources. Three coating configurations were investigated:(1) a Pt-Al 2 O 3 cermet, with a linearly graded platinum content and an Al 2 O 3 antireflection layer, which was deposited onto platinum-coated glass; (2) a Pt-Al 2 O 3 cermet, with a uniform platinum content and an Al 2 O 3 antireflection layer, which was deposited onto platinum-, chromium- and molybdenum-coated glass; (3) an Al 2 O 3 /M/Al 2 O 3 (AMA) type of coating, with an M layer consisting of a uniform Pt-Al 2 O 3 cermet, which was deposited onto platinum-, chromium- and molybdenum-coated glass. Hemispherical absorptances α H greater than 0.9 were obtained for all three configurations. Hemispherical emittances of less than 0.1 at 20 °C were obtained for the graded and AMA configurations. The uniform cermets possessed higher emittances (approximately 0.13). Coatings deposited at 500 °C onto platinum-coated glass appear to be stable (less than 1% loss in α H ) at 600 °C in air. Coatings deposited at lower temperatures (about 150 °C), or onto chromium or molybdenum substrates, were less stable but show promise for many applications in the range 300–500 °C.

Sputter-deposited PtAl2O3 graded cermet selective absorber coatings

Abstract PtAl 2 O 3 cermet selective absorber coatings with graded Pt compositions have been deposited by co-sputtering from Pt and Al 2 O 3 sources. Both direct rf sputtering from an alumina target and reactive sputtering from an aluminum target in an Ar/O 2 working gas, were investigated for depositing the Al 2 O 3 component of the coatings. The substrate were glass and stainless steel plates. Sputtered coatings of Pt, Mo, Cr, Ta, W and ZrB 2 were used as low emittance base layers. Experiments are reported which explored the dependence of the coating optical properties on the cermet layer thickness and Pt content, and on the aluminum oxide antireflection layer thickness. Hemispherical absorptances as high as 0.97, with room temperature emittances in the 0.06 to 0.08 range, have been achieved. The coatings with rf-sputtered Al 2 O 3 , and Pt low emittance base layers, underwent no changes in optical properties after being heated to 600°C in air for as long as 2000 h. These coatings therefore exhibit the same remarkable thermal stability that was originally reported by the Cornell University group for evaporated PtAl 2 O 3 coatings. The coatings with reactive sputtered aluminum oxidem or alternate base layers such as ZrB 2 , exhibited somewhat reduced thermal stability but should be adequate for intermediate temperature applications (up to 400°C in air).

Performance and impedance studies of thin, porous molybdenum and tungsten electrodes for the alkali metal thermoelectric converter

Columnar, porous, magnetron-sputtered molybdenum and tungsten films show optinum performance as AMTEC electrodes at thicknesses less than 1.0 μm when used with molybdenum or nickel current collector grids. Power densities of 0.40 W cm−2 for 0.5 μm molybdenum films at 1200 K and 0.35 W cm−2 for 0.5 μm tungsten films at 1180 K were obtained at electrode maturity after 40–90 h. Sheet resistances of magnetron sputter deposited films on sodium beta″-alumina solid electrolyte (BASE) substrates were found to increase very steeply as thickness is decreased below about 0.3–0.4 μm. The a.c. impedance data for these electrodes have been interpreted in terms of contributions from the bulk BASE and the porous electrode/BASE interface. Voltage profiles of operating electrodes show that the total electrode area, of electrodes with thickness <2.0 μm, is not utilized efficiently unless a fairly fine (∼1×1mm) current collector grid is employed.

Refractory amorphous metallic (W0.6Re0.4)76B24 coatings on steel substrates

Refractory metallic coatings of (W0.6Re0.4)76B24 (WReB) have been deposited onto glass, quartz, and heat-treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As-deposited WReB films are amorphous, as shown by their diffuse x-ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (~1000°C) crystallization temperature. Adhesion strength of these coatings on heat-treated AISI 52100 steel is in excess of ~20, 000 psi and they possess high microhardness (~2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin-on-disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 µm thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel.

Neural network based feed-forward high density associative memory

A novel thin film approach to neural network based high density associative memory is described. The information is stored locally in a memory matrix of passive, nonvolatile, binary connection elements with a potential to achieve a storage density of 109bits/cm2. Microswitches based on memory switching in thin film hydrogenated amorphous silicon, and alternatively in manganese oxide, have been used as programmable read-only memory (PROM) elements. Low energy switching has been ascertained in both these materials. Fabrication and testing of memory matrix is described. High speed associative recall approaching 107bits/sec and high storage capacity in such a connection matrix memory system is also described.

Semiconductor‐metal graded‐index composite thin films for infrared applications

Theoretical/experimental studies have been carried out on germanium:silver (Ge:Ag) graded‐index composite thin films which demonstrate that graded coatings, consisting of varied concentrations of Ag with respect to the Ge film thickness, exhibit different optical properties ranging from selective infrared (IR) reflectance to broadband IR absorptance. The graded coatings have been produced by dc magnetron cosputtering of Ge and Ag and the spectral properties are found to be stable against temperature. The coatings have been applied to an infrared tunnel sensor (micro‐Golay cell) to improve the device performance.