Dissolution Potentials And Activation Energies Of InSb Single Crystals

The rest (or corrosion) and dissolution potentials of InSb single crystals in HC1 were determined. There is no potential difference (within error limits) between the inverse {111} faces in pure HC1. A difference of up to 44 mV and more develops as soon as the InSb electrode is anodically dissolved. The potential becomes less noble in the sequence In{111}, {100}, {110}, Sb{111}. The Tafel relationship is observed over three decades of current density. With additions of FeCl3, FeCl2, K3Fe(CN)6, K4Fe(CN)6, H2C4H4O6 to 2N HC1, the anodic potentials of both inverse {111} faces are shifted to more active values; the e\u27H of In{111} is always nobler than that of Sb{111}. There are indications that the various potentials observed are a function of current density within the pores of a protective layer, Sb^OsCU. The apparent activation energy, ca. 20 kcal/mole, of the anodic dissolution reaction is nearly the same on all crystallography planes of InSb. The rate of anodic dissolution of Sb{111} in pure 2N HC1 is 3-7 times larger than that of the inverse face at the same potential. © 1972, by The Electrochemical Society, Inc. All rights reserved

Thermal Expansion Of Tungsten At Low Temperatures

Lattice parameters, thermal expansion coefficients, and Grüneisen parameters of tungsten are determined by an x-ray method in the temperature range of 180-40 K without the use of liquid gases. Lattice parameters are expressed as a function of temperature. Thermal-expansion coefficients decrease with temperature and show no anomaly in contrast to a hypothesis proposed by Featherston and Neighbours. Grüneisen parameters γ are decreasing with temperature in accordance with the theoretical predictions. © 1971 The American Institute of Physics

The Anodic Dissolution Reaction Of InSb: Etch Patterns, Electron Number, Anodic Disintegration, And Film Formation

The etching behavior of the inverse {111} planes of undoped, semiconducting, n-type, InSb single crystals was explored. Depending upon the etchant, including anodic dissolution, various etch patterns were obtained on the inverse planes. In general, the etch pits on the In{111} plane were round, and the face was shiny, whereas the face of the inverse plane was dark and rough. The rates of dissolution in the electrolytes used were very low, especially in absence of oxidizers. The components dissolve as In3+ and Sb3 +. At current densities above 40 or 60 mA cm-2 (on Sb{111} or In{111}), growth of a black, colloidal film of Sb4O5Cl2 containing very fine metallic Sb particles occurs on both planes. The Sb particles result from the partial disintegration of InSb. Upon heating the film in vacuum, recrystallization occurs and the Sb aggregates to form larger particles. An explanation is offered for the different behaviors of the inverse {111} planes. © 1971, by The Electrochemical Society, Inc. All rights reserved

Low Temperature Lattice Parameters And Expansion Coefficients Of AI2Au And LiF Gruneisen Constants Of LiF

There is no difference in the thermal expansion behavior of an intermetallic compound (Al2Au) and of an ionic (LiF), except in the magnitude of the expansion coefficients, which for both compounds upon cooling below 40°K approach zero. The lattice parameters of the two compounds mentioned decrease uniformly and without anomalies with lowering the temperature, approaching a constant value below 40°K. The a–T relationship between 40 and 180° is given in form of equations. A pump working on the Joule‐Thomson principle was used for cooling. The GRÜNEISEN parameter, γ, of LiF between 40 and 180°K is a constant, contrary to theoretical prediction. The values of a, α and γ agree well with previous measurements, where liquid gases were used for cooling and lattice parameter determinations and a dilatometer for expansivity measurements. Copyright © 1972 Verlag GmbH & Co. KGaA, Weinhei

Thermal Expansion Behavior Of Silicon At Low Temperatures

Lattice parameters, thermal expansion coefficients and Grüneisen parameters of silicon are determined by an X-Ray diffraction method in the temperature range of 180-40 K without the use of liquid gases. Thermal expansion of silicon becomes negative below 120 K which is discussed in terms of its lattice vibrations and crystal structure. © 1972

Perfection of the Lattice of Dislocation-Free Silicon, Studied by the Lattice-Constant and Density Method

The lattice-constant and density method revealed that a high-purity silicon crystal free of dislocations has a perfect lattice without an excess of vacant sites or interstitials (n′=8.0000 4) within the limits of error, in agreement with the results obtained with the decoration method. The lattice constant of vacuum heated silicon powder of semiconductor purity was 5.43070±0.00004 A; that of the nonheat-treated powder was 5.43081 A at 25°C. The constants determined from crystal chips by the rotating crystal method were lower: between 5.43028-5.43048 A at 25°C. As the constants of each series of measurements could be reproduced very well (s=±0.00004 A), the lower values suggested the presence of some unknown systematic errors, the magnitude of which is outside the scope of errors due to absorption. The thermal expansion coefficients of all samples between 10°-60°C were (2.6±0.4)×10 -6/°C. The average density of etched crystal chips was 2.3289±0.0001 g/cm 3. The lower density of the nonetched chips indicated the presence of microcracks, removable by etching, within the distorted surface layers. There was no significant difference in density of bars sawed, or of chips broken from the crystal and etched

Anodic Dissolution Of Zinc In Potassium Nitrate

The apparent valence of pure zinc dissolving anodically in 3% KNO3 was determined as a function of current density, temperature, and ultrasonic agitation. The apparent valence of zinc dissolving anodically at 24°C diminishes from 2.01 ± 0.01 at low current densities to 1.86 at about 50 ma and remains fairly constant up to about 80 ma cm−2. This valence is affected to some extent by the preparation, e.g., polishing of the electrode, but is independent of its structure (mono- or polycrystal). Ultrasonic vibrations do not influence the apparent valence at high current densities. In all cases a black film (corrosion product) spalls off the anode but to a larger extent with ultrasonics. The apparent valence decreases with increasing temperature (measurements between 25° and 68°C) and again with increasing current density, and appears to vary as a function of metal history. Fine metallic Zn particles are found in the dark corrosion product. The average size of the particles increases with increasing temperature. On the basis of the above, it is concluded that the normal valency of zinc ions, +2, does not change during anodic dissolution in nitrate solutions, but the apparent valence of less than 2 arises as a consequence of increased local corrosion and of surface disintegration of the anode. Both occur outside the electrical circuit thus accounting for the lower coulombic equivalent. A mechanism for the disintegration phenomenon is presented. © 1967, The Electrochemical Society, Inc. All rights reserved

Current Density-Anodic Potential Curves Of Single Crystal GaAs At Low Currents In KOH

Single p-type, GaAs crystals of high purity, Zn doped, were used to determine whether or not the inverse octahedral {111} faces show potential differences and various rates of anodic dissolution. The Ga{111}, As{111}, {110}, and {100} faces, were polished, etched, and etch-polished with concentrated H2SO4 + H2O2, and immersed in IN KOH. The Ga{111} faces were found to be the most noble with respect to rest and anodic dissolution potentials. The potential difference between the inverse {111} faces was as large as 0.14v for the rest and 0.123v for the dissolution potentials. The 4 anodic polarization curves gave nearly parallel Tafel lines, with a slope of 66.0 ± 1 mv/log i, up to current densities of 0.5 ma/cm2. The rate of anodic dissolution of the As{111} faces was 69 X as high as the inverse Ga{111}. The activation energies of dissolution of all 4 faces were equal within experimental limits: 16.7 ± 0.7 kcal mole−1. It is concluded that the slow step in the dissolution of GaAs is a one electron discharge with subsequent steps leading to the formation of Ga(OH)3 to provide a protective coating not readily soluble in KOH. From this point of view all observed phenomena can be explained in a qualitative manner. © 1968, The Electrochemical Society, Inc. All rights reserved