Armond B. Chase

Effect of MgO on the Crystal‐Growth Defects and Optical Absorption of Flux‐Grown In2O3

Crystals of In2O3 grown from a pure flux have inclusions and striations and, because of oxygen deficiency, are nonstoichiometric and almost black. The addition of MgO to the melt produces crystals that have no inclusions or striations, and that have optical properties characteristic of stoichiometric In2O3. Therefore, Mg acts as an efficient compensator of the oxygen deficiency. This paper describes the effect of MgO on the visible optical absorption spectrum and on the crystal defects. One possible model of the role of Mg in compensating In2O3 is discussed briefly.

A further investigation of factors influencing domain configurations in yttrium iron garnet

Abstract The domain patterns exhibited by flux-grown crystals of yttrium iron garnet are described and interpreted in terms of oriented strains resulting from the growth process. Thin sections that are carefully prepared and have as one surface a well-defined growth pyramid show domain patterns consisting of parallel bands when observed by transmitted polarized light. The bands are symmetrically arranged around the growth center responsible for the pyramid to form a system of concentric diamonds. The directions of magnetization within the bands are not parallel to the 〈111〉 easy directions of magnetization in the plane of the sample but rather cross each quadrant formed by the growth pyramid at an angle of about 45°. Surface domain patterns, formed by deposition of colloidal magnetite, are also symmetrical with respect to the growth pyramids and can be correlated with the transmission patterns. Surface tree patterns are observed and interpreted as arrays of compensating domains resulting from the presence of weak magnetic poles on the crystal faces. The effects of annealing and silicon incorporation on the domain patterns of yttrium iron garnet are described and discussed in terms of strain reduction.

Habit changes of Y3Al5O12 and Y3Ga5O12 grown from a PbO-PbF2 flux

Abstract The habit of single crystals of Y 3 Al 5 O 12 and Y 3 Ga 5 O 12 , when grown from a PbO-PbF 2 flux, is dependent on both the PbO-to-PbF 2 ratio and the Y 2 O 3 -to-Al 2 O 3 or -Ga 2 O 3 ration in the melt. Y 3 Ga 5 O 12 crystals have a pure {211} habit when grown from either a Y 2 O 3 or PbO rich melt. The crystals develop small {110} faces when grown from a Ga 2 O 3 or PbF 2 rich melt. Y 3 Al 5 O 12 crystals have a pure {110} when grown from either a PbF 2 or Al 2 O 3 rich melt and develop {211} faces as well in a PbO or Y 2 O 3 rich melt. The crystals incorporate Pb (replacing Y in the lattice) when grown from PbF 2 , Al 2 O 3 or Ga 2 O 3 rich melts. It is believed that the habit variations are caused by changes in either the surface diffusion or step propagation, due to Pb contamination, that favor the development of {110} faces. In addition, the crystal habits of the mixed system Y 3 (Al, Ga) 5 O 12 were studied and found to be directly dependent on the Al 2 O 3 / Ga 2 O 3 melt ratio. This suggests that (for the melt compositions used) the tendencies for Y 3 Al 5 O 12 to have a {110} habit and for Y 3 Ga 5 O 12 to have a {211} habit are essentially the same and that the relative surface energies of the {211} and {110} faces of the solid solution crystals are dependent on the bulk composition of the crystal.

Habit modification of SiO2 doped Y3Al5O12, Y2Fe5O12, and Y3Ga5O12 garnets

Abstract The habits of single crystals of the synthetic garnets, when grown from a SiO2 contaminated PbO-PbF2 flux, are dependent on the concentration of SiO2 in the melt. Y3Ga5O12 and Y3Fe5O12 crystals have a pure {211} habit when grown from an undoped melt. The crystal habit changes smoothly from {211} to {110} to {110} ≅ {100} for Y3Ga5O12, and from {211} to {110} for Y3Fe5O12 with increasing SiO2 in the melt. Y3Al5O12 crystals change from {211} > {110} to {211} or from {110} > {211} to {110} with increasing SiO2 in the melt. The basic habit of Y3Al5O12 garnet is dependent on the bulk composition of the melt. Spectrochemical analysis of SiO2 doped Y3Ga5O12 crystals revealed that up to 1.3wt% Si4+ was incorporated in the crystal and similar amounts in both YIG and YA1G garnets. The total divalent metal ion (Pb2+, Ca2+, and Mg2+) concentration in the crystal charge-compensates for Si4+ to maintain electrical neutrality. Analysis and comparison of the variations in oxygen positions in garnets of various composition indicate a tetrahedral site distortion for doped crystals that leads to surface energy conditions favoring a {110} habit for Si4+ doped crystals of Y3Fe5O12 and Y3Ga5O12. On the other hand, the habit change of Y3Al5O12 is believed to be dependent on a surface-contamination mechanism.

Influence of Crystal Growth on Domain Behavior in Yttrium Iron Garnet

The behavior of magnetic domains in certain sections of single crystal yttrium iron garnet is related to growth history. Discontinuities in domain patterns coincide with lines of intersection of vicinal faces on the growth surfaces of the crystals, and regions delineated by the discontinuities show differences in magnetic behavior. The relationship of these effects to oriented strains resulting from growth processes is considered.

Coordination Chemistry and Kinetics of Preferential Etching on Surfaces of TiO2 (Rutile).

Abstract Fused KHSO 4 can be used as both a polish and a preferential etchant for the {001} surfaces of rutile, depending on the temperature of the system. Polishing occurs at temperatures above 550°C. At temperatures below 550°C, three types of etch pit are observed, two well defined with regular shapes (sides parallel to the and and directions, respectively) and one irregularly shaped. Photochemical deposition of silver [1] onto the crystal surface and subsequent removal (HNO 3 ) prior to etching causes the irregularly shaped pits to be etched more rapidly than in the case of a surface region that was not predeposited. A chemical reaction mechanism is presented to interpret the observed etching behavior. The crystal structure (i.e. the different ionic composition of different crystallographic planes) and surface chemistry of rutile are considered in the formulation of this mechanism. It is suggested that etchant molecules form surface complexes on the TiO 2 (after dehydration of surface OH groups) through coordination of Ti 4+ via terminal and bridged out-of-plane O 2− positions. Evidence is presented to show that the etching rate-determining reaction is the dissolution of these soluble surface complexes. The observed photochemical effects are explained on the basis of the trapping of photogenerated holes or electrons at certain crystal defects.

ETCHING BEHAVIOR OF IN2O3 GROWN FROM PBO-B2O3,

Single crystals of In2O3 grown from a PbO–B2O3 solution are etched by HNO3 or HNO3–HCl solutions. Characteristic etch pits and etch tubes are described. The number of etch pits is found to be related to the growth history of the crystals. The relationship of the etch tubes to crystal growth is discussed.

Extremely Uniform Electrodeposition of Submicron Schottky Contacts.

A plating technique has been developed that yields extremely uniform metal deposits on semiconductor surfaces. This technique utlilizes high‐field pulses which are extremely short in duration. The technique has produced theoretical Schottky barrier diode spreading resistances for contacts with dimensions ranging from 2.5 to 0.12 μm in diameter.

Habit of Fe2O3 grown from Na2B4O7

Abstract Single crystals of hematite (Fe 2 O 3 ) grown from Na 2 B 4 O 7 occur as plates, rods, hoppers, and equidimensional solid crystals. The habit was found to correlate with the growth rate and crystal defects. Plates and rods occured for the highest growth rates used with the plate size controlled by rapid growth perpendicular to the 〈0001〉. The rods are the result of twinning on the {01–12}. The hoppers and solid crystals grow in slow-cooled melts and are typical of crystals grown from high-viscosity melts.

High Field Pulse Plating: Gold on Platinum Electrodes

In this paper a electrodeposition technique, high field pulse plating (HFPP), is explored over a wide range of experimental parameters. The experimental setup is fully described. Results are presented for gold plated onto platinum using pulse widths varying from 100-500 ns, at voltages between 10-40 V, and using repetition rates between 10-100 kHz. A conceptual model is presented for use in understanding trends that are experimentally observed. Scanning electronmicrograph photographs and optical reflectivity results demonstrate that a smoother surface is obtained with the HFPP process compared to dc plating.