摘要:

We investigated the halide composition depth profile in micron‐size silver halide microcrystals using x‐ray photoelectron spectroscopy in conjunction with ion etching. Using a double‐jet technique, intentionally mixed halide microcrystals were precipitated such that the thermodynamic equlibrium of the solution‐solid interface was maintained. Microcrystals precipitated using halide‐conversion techniques showed a compositional variation. In bromide‐converted silver chloride microcrystals, after an initial decrease from the surface value, the chloride ion concentration increased smoothly with depth, leveling off (at about 100 nm below the original surface) to a value about 10% higher than in the surface region. X‐ray diffraction patterns from these microcrystals show a skewed line shape for the halide‐converted materials. A graded‐band‐gap model is proposed which may account for the tendency of the halide‐converted crystals to form an internal latent image.

ISSN:0021-8979    

DOI:10.1063/1.322527

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

It has been reported that the tin coverage on a tungsten tip increases the stability of the tip surface at an elevated temperature under an applied external field. In the present work the existence of the covering atoms on the heated tungsten tips was examined by measuring the variation in the field emission current with the reduction of the coverage of adatoms due to the gradual field evaporation. The result indicates that a substantial amount of the adatoms remain on the heated surface and no noticeable amount of the unknown entity contributes to the increased surface stability. The observed field strength required to deform a tin‐covered tungsten tip was found to be two to three times higher than gallium‐covered, indium‐covered, or bare tungsten tips. As a heated field emission cathode the stable tin‐covered tip emitted a high current corresponding to a current density of well above 1×106A/cm2, which is an order of magnitude higher than that obtained for a bare tungsten tip. Occasionally, the covered tip heated above 900 °C exhibited an entirely new cubic structure which would indicate the formation of the presently unknown ordered Sn‐W and In‐W alloys.

ISSN:0021-8979    

DOI:10.1063/1.322528

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A method is developed for quantitatively predicting the chemical composition and thickness distributions of alloy films deposited by decoupled‐plasma multitarget rf sputtering in which the substrates rotate at a variable rate through separate glow discharges. The film thickness distributions deposited from each target are expressed in terms of deposition variables such as applied target voltage, target radius, sputtering pressure, substrate rotation radius, rotation rate, and target‐substrate separation. Predicted films thickness distributions were found to be in agreement with experimental results in which &bgr; backscattering was used to measure the thickness of InSb films deposited on both stationary and rotating substrates. Using deposition parameters determined from the model presented in this paper, single‐phase In1−xGaxSb alloy films were grown whose experimentally determined compositions agreed with predicted values. Intercalated films with layer thicknesses of less than 100 A˚ and films which were chemically graded in the lateral and in‐depth directions were also grown.

ISSN:0021-8979    

DOI:10.1063/1.322529

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Recent experimental data on the influence of additional vacancies and Frenkel pairs upon the stageIErecovery of electron‐irradiated Al and Al‐15 ppm Ag and newly obtained results on the dilute alloy system Al‐ (5–65) ppm Mg are analyzed in terms of the chemical reaction rate theory. The corresponding rate equations are solved numerically yielding the following quantitative results: the capture radius of a vacancy for an Al self‐interstitial,rAlv=2.1a0; the capture radii of an Mg and of an Ag atom, respectively,rMg=0.33rv,rAg=0.6rv; the electrical resistivity of a unit concentration of vacancies, &rgr;v=2.0×10−4&OHgr; cm/unit concentration. The best fit has been obtained with a value ofEm=112 meV for the migration energy of la self‐interstitial and a frequency factor of 3×1014sec−1.

ISSN:0021-8979    

DOI:10.1063/1.322530

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The rate of carbon deposition on 0–1‐&mgr;m diamond seed crystals was investigated in the temperature range 1140–1475 °C, methane partial pressures form 10−3to 44.4 Torr and hydrogen partial pressures from 0 to 16.4 Torr. Two distinct kinetic regimes were found. A relatively rapid initial rate of diamond growth decayed exponentially to a final slow constant rate as graphitic carbon was codeposited and covered the surface. A maximum initial diamond growth rate of 1.06×10−7g cm−2min−1, which corresponded to a nominal linear growth rate of only 0.45 &mgr;m per day, was observed. Dilution of methane with hydrogen decreased the nucleation rate of graphitic carbon relative to that of diamond resulting in a increase in the diamond yield. The activation energy for diamond deposition from pure methane was 55 kcal mole−1. The dependence of the initial rate data on methane partial pressure could be described by a Langmuir‐type equation. The deposits were identified by chemical etching, chemical analysis, density measurements, x‐ray and electron diffraction, transmission electron microscopy, and optical measurements. The crystalline quality of the diamond was not determined and could be highly defective.

ISSN:0021-8979    

DOI:10.1063/1.322531

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Dislocations have been studied in YIG by transmission electron microscopy. Loops are found to have (a/2) ⟨111⟩ Burgers vectors whereas dislocation segments may have (a/2) ⟨111⟩ ora⟨001⟩ ones, the latter resulting from the attractive reaction of dislocations with (a/2) ⟨111⟩ Burgers vectors. Owing to the large unit cell of YIG, experimental imaging conditions prevented from concluding on the possibility of dislocation dissociation.

ISSN:0021-8979    

DOI:10.1063/1.322532

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

In this paper we consider propagation of finite‐amplitude plane waves of uniaxial strain in piezoelectric disks exhibiting fully coupled nonlinear response. In particular, we derive explicit expressions for determination of the electric current in external circuits consisting of resistors, inductors, or capacitors connecting the electrodes on the faces of a disk. The formulation of a specific‐boundary initial‐value problem is discussed and a discussion of how the fully coupled electromechanical problem may be solved numerically is given.

ISSN:0021-8979    

DOI:10.1063/1.322533

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

In this paper we have proposed an extension to the current theory of irreversible thermodynamics by introducing the concept ofinternalforce. Within the resulting new framework we show that the phenomenon of creep enhancement, by neutron irradiation, can be explained physically and can be evaluated quantitatively by theoretical means. It is shown that the essential predictions of the theory agree well with experimental observations in the instance cited.

ISSN:0021-8979    

DOI:10.1063/1.322512

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Atomic ordering in bulk austenitic single‐crystal samples of composition Fe‐31 at.% Ni was investigated using x‐ray and neutron diffraction techniques. Samples were annealed between 450–550 °C for time periods between 1.5 h and 55 days. No superlattice peak was observed in any case providing no evidence of long‐range order in these samples. X‐ray studies on martensitic samples of the same composition revealed a tetragonality of about 0.4% which was increased insignificantly by the ’’ordering’’ heat treatment given to the austenite prior to the martensitic transformation. If martensite tetragonality is linearly related to the difference in the first and second short‐range order parameters of the austenite (as seems likely in this alloy) this observation supports and extends the results of the studies on the austenitic single crystals.

ISSN:0021-8979    

DOI:10.1063/1.322513

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Zircon crystals that have been damaged by a naturally occurring radioactive contaminant, referred to as metamict zircons, have density values ranging from 4.70 to 3.90 g/cm3. The present work is a study of the effect of the damage on the single‐crystal elastic moduli. A systematic and very marked decrease (i.e., up to 69%) of the elastic moduli with density have been observed. All the longitudinal and the shear elastic moduli decrease with radiation damage and approach two common saturation values of 1.5×1012and 0.49×1012dyn/cm2, respectively. Present observation of the elastic moduli of the radiation‐damaged zircon crystals confirms Warren’s theoretical predictions concerning the effect of different pore geometries on the compressibility. Qualitative correlation of the elastic moduli with the structural changes arising from radiation damage in zircon crystals suggests that the marked decrease of the elastic moduli in the radiation‐damaged zircons is caused by the nonspherical defect clusters, microcracks, and pores generated during radiation damage. Thermal annealing, x‐ray diffraction, elastic moduli, and density measurements on the zircon samples confirm the ’’three‐stage’’ process proposed for the metamict transformation of zircons, but the final product of metamictization does not seem to be a mixture of ZrO2and SiO2crystallites.

ISSN:0021-8979    

DOI:10.1063/1.322514

出版商:AIP    

年代:1976

数据来源: AIP