Dependence of the crystallization rate of vacuum-deposited amorphous antimony films on the film thickness

The crystallization rate of vacuum-deposited amorphous antimony (a-Sb) films was investigated as a function of the film thickness d. Experimental plots of the observed growth rate v against d^-1 for systems such as Sb/glass and Sb/Ge show that the relationship between v and d^-1 are convex towards the origin. Such a feature is well interpreted by a model in which

$\text{v=}\text{1}\text{d}\text{∫}\text{d}\text{0}\text{u}\text{d}\text{z}$

where u is the actual growth rate of the crystallite in the a-Sb film and z the distance from the film surface adjacent to the substrate. The quantity u is assumed to vary as follows: u = αzⁿ + u_s when 0 ? z ? d_s0, u = u_i when d_s0 ? z ? d ? d_v0 and u = β(d ? z)ⁿ + u_v, when d ? d_v0 ? z ? d where $\text{α =}\text{(u}{}_{\mathrm{i}}\text{? u}{}_{\mathrm{<mtext>s</mtext>}}\text{)}\text{d}{}_{\mathrm{<mtext>s</mtext><mtext>0</mtext>}}{}^{\mathrm{n}}$, $\text{β =}\text{(u}{}_{\mathrm{i}}\text{? u}{}_{\mathrm{<mtext>v</mtext>}}\text{)}\text{d}{}_{\mathrm{<mtext>v</mtext><mtext>0</mtext>}}{}^{\mathrm{n}}$, d_s0 and d_v0 are thickness of surface regions near the substrate and the vacuum respectively, u_i is the growth rate inside the film, u_s and u_v are the rates at surfaces adjacent to the substrate and the vacuum respectively and n an adjustable numerical parameter. As a typical example, for the Sb/Ge system at 30°C, u_i, u_s and u_v are estimated to be 139 μm s^-1, 25.4 μm s^-1 and 0.2 μm s^-1 respectively and d_s0 and d_v0 to be 133 Å and 143 Å respectively with n = 3.     

New phase with K2NiF4 structure in the LaLiFeO system

The existence has been proved, for the first time, in the LaLiFeO system of the phase (La_1.75Li_.25) (Fe_.5Li_.5)O_4?x with tetragonal symmetry ($\text{a}{}_{\mathrm{o}}\text{=3.765±0.001}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{=12.918±0.01}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}\text{=3.43}$) and K₂NiF₄-type structure.This phase gives probably the first example of lithium distribution in both A and B sites of A₂BO₄-type mixed oxides. The high $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}$ ratio suggests a strong elongation of FeO₆ octahedra induced by a high spin Fe(IV) d⁴ configuration. The results of structural studies and of Mössbauer analysis, confirming the above conclusions, are reported.     

Stationary photoconductivity of mixed Tl1−xAgxInSe2 crystals

Tl_1?xAg_xInSe₂ (x = 0 to 0.03) single crystals of solid solution were grown by Bridgeman-Stockbarger techniques. Photoelectric measurements were taken at 300 and 77 K. With an increase in the value of x, the equilibrium concentration is increased 10 to 100 times. At 77 K a region of impurity photosensitivity has been detected which is bordered by the fundamental absorbtion edge. The photosensitivity ($\text{R}{}_{\mathrm{d}}\text{R}{}_{\mathrm{p}}$) of the solid solution crystals at 77 K increases from 8.2 (x = 0) to 55.2 (x = 0.03) the conclusion is made that when Tl is replaced by Ag then the sensitization of semiconductor.     

Fracture toughness characterization of several aluminum alloys in semi-brittle fracture

A method has recently been developed for determining a nonlinear fracture toughness parameter defined by the relation $\text{G}\text{?}{}_{\mathrm{c}}\text{=}\text{C}\text{?}\text{G}{}_{\mathrm{c}}$ where G_c is the critical elastic strain energy rate as defined by Irwin. The $\text{C}\text{?}$ term is a function of the nonlinearity of the load-displacement test record and has been evaluated using the three parameter Ramberg-Osgood approach, although other curve fitting techniques could be applied as well. The method is quite straightforward and is applicable to plane stress, plane strain and mixed mode testing although only plane stress conditions are considered in this paper. For the case of a linear load-displacement record $\text{C}\text{?}\text{→ 1}$ and $\text{G}\text{?}{}_{\mathrm{c}}$ reduces to the linear elastic result.The toughness parameter $\text{G}\text{?}{}_{\mathrm{c}}$ has been evaluated for a number of high strength aluminum alloys and compared with published G_c values for these materials. The tests were conducted on center-cracked sheets of 2014-T6, 2024-T81, 7075-T6 and 7475-T61 aluminum alloys under conditions of varying specimen geometry and displacement gage length. It was found that the values of $\text{G}\text{?}{}_{\mathrm{c}}$ obtained from displacement readings with a gage length of 2 in. generally agreed with published values of $\text{G}{}_{\mathrm{c}}\text{=}\text{K}{}_{\mathrm{c}}{}^2\text{E}$. The $\text{G}\text{?}{}_{\mathrm{c}}$ values were found to vary inversely with gage length and a/w ratios. The variation in values for $\text{G}\text{?}{}_{\mathrm{c}}$ is of the same order of magnitude as the scatter in published values for G_c. However, $\text{G}\text{?}{}_{\mathrm{c}}$ appears to be less sensitive than G_c to changes in a/w.     

A correlation of critical points

Critical points were correlated for fluids which obey the three-parameter equation of state according to which the compressibility factor, $\text{Z=}\text{P}\text{dRT}$, is given by Z=1 + k_Bδκ (θ, δ), in which κ (θ, δ) is a universal function of reduced temperature, $\text{θ =}\text{T}\text{T}{}_{\mathrm{B}}$, and reduced density, $\text{δ =}\text{d}\text{d}{}_{\mathrm{<mtext>O</mtext>}}$. The three parameters which distinguish one fluid from another are k_B, T_B, and d_O. It is shown that experimental inflection points of the pressure versus density isotherms of gases obeying this equation of state all fall on the same reduced curve of θ versus δ. Critical points also must lie on this curve, at a location dependent on k_B. Critical densities are too uncertain experimentally to permit a definite correlation, but the critical temperatures of sixteen fluids are shown to fall on a common θ_c versus k_B curve with an average deviation of 0.4 degrees. The critical pressures of these same fluids lie within a few tenths of an atmosphere on a common π_c ($\text{π =}\text{P}\text{d}{}_{\mathrm{<mtext>O</mtext>}}\text{RT}{}_{\mathrm{<mtext>B</mtext>}}$) versus k_B line. This correlation of critical points is accomplished using values of the three parameters that had previously been determined by fitting supercritical PVT data to the equation of state.     

On certain properties of CdxHg1−xTe thin solid films (x⩽0.2)

The Hall coefficient R_H, electrical conductivity σ and Hall mobility μ_H have been measured in thinCd_xHg_1?xTe solid films over a range of thickness from 1.0 to 12 μm for x as high as 0.2. The dependences of the electrical properties on temperature and thickness were measured in the temperature range 77–300 K.The temperature and thickness dependences of the mobility are discussed on the basis of the relation $\text{1}\text{μ}{}_{\mathrm{<mtext>H</mtext>}}\text{=}\text{1}\text{μ}{}_{\mathrm{<mtext>b</mtext>}}\text{+F}$ where the first term is due to scattering in the bulk material and F is a term used to account for the (lack of) crystalline structure and the effects of film thickness.     

Models for the effect of chemisorbed gases on the electrical resistance of metal films

Three hypotheses are considered for the proportionate change of resistance $\text{ΔR}\text{R}{}_1$ when a continuous metal film of resistance R₁ adsorbs gas: (a) a loss of metallic properties at the surface; (b) a change in the electron scattering parameter at the surface; and (c) a change in the electron concentration throughout the film. Two models of the film structure are used to compare the predictions of these hypothesis with our experimental data for the systems $\text{O}{}_2\text{Er}$, $\text{CO}\text{Er}$, $\text{CO}\text{Ti}$ and $\text{O}{}_2\text{Ti}$. The flat plate model accounts for neither R₁ nor $\text{ΔR}\text{R}{}_1$. A simple version of the columnar model accounts for $\text{ΔR}\text{R}{}_1$ by either (a) or (b) for the first three systems and by (c) for the fourth, but it does not explain all the properties of the clean films. The linear approximation given by Mola and Heras for the columnar model of Mayadas and Shatzkes accounts satisfactorily for R₁ and $\text{ΔR}\text{R}{}_1$ for $\text{O}{}_2\text{Er}$, $\text{CO}\text{Er}$ and $\text{CO}\text{Ti}$ by increases in the electron scattering coefficient at the grain boundaries. It does not account for $\text{ΔR}\text{R}{}_1$ with $\text{O}{}_2\text{Ti}$ because that system incorporates gas into the metal lattice.     

The SrFeO2.5 | SrFeO3.0 system. Evidence of a new phase Sr4Fe4O11 (SrFeO2.75)

Evidence is presented for a new phase of ideal composition SrFeO_2.75 in the system SrFeO_3?x (0.5 ? x ? 0). Electron diffraction evidence suggests orthorhombic or body-centred tetragonal symmetry with lattice parameters related to the cubic perovskite lattice parameter a_c by $\text{a}\text{? 2√2}\text{a}{}_{\mathrm{c}}$, $\text{b}\text{? 2}\text{a}{}_{\mathrm{c}}$. $\text{c}\text{? 2√2}\text{a}{}_{\mathrm{c}}$. A plausible model for the structure is presented which is related to that of SrFeO_2.5. Powder x-ray diffraction photographs reveal only a simple cubic perovskite cell for SrFeO_2.75, presumably because the ordered domains giving rise to the superstructure observed in electron diffraction are small in extent. At other intermediate compositions slow cooling gives mixtures of the new phase and either SrFeO_2.5 or SrFeO₃. The two-phase regions narrow at high temperatures and thermogravimetric studies at 1 atm pressure of oxygen indicate a single phase between SrFeO_2.5 and SrFeO_2.75 between 500°C and 950°C.     

Analysis of a turbulent boundary layer subjected to a strong adverse pressure gradient

We define two non-dimensional parameters $\text{Λ =}\text{τ}{}_{\mathrm{w}}\text{p}{}_{\mathrm{x}}\text{δ}$ and $\text{R}{}_{\mathrm{p}}\text{=}\text{U}{}_{\mathrm{p}}\text{δ}\text{ν}$ where τ_w is the wall stress, p_x(?0) is the pressure gradient to which the turbulent boundary layer (of thickness δ) is subjected, ν is the kinematic viscosity, $\text{U}{}_{\mathrm{p}}\text{= (}\text{νp}{}_{\mathrm{x}}\text{p}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ is a characteristic velocity and p is the density. The limit corresponding to the strong adverse pressure gradient is formulated as Λ → 0, R_p → ∞, ΛR_p finite. Using appropriate inner and outer asympcotic expansions, both above a wall layer possibly scaling with τ_w and ν, it is found by an application of Millikan's argument that there is an inertial sublayer where the streamwise velocity distribution obeys a half-power law, whose slope depends on Λ, and intercept on ΛR_p. Indeed comparison with available experimental data shows the inner law to be well represented by $\text{u}\text{Up}\text{= (3.5 + 19Λ)(}\text{yU}{}_{\mathrm{p}}\text{ν}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ 2.5ΛR}{}_{\mathrm{p}}$. The outer flow obeys a generalized defect law; use of constant eddy viscosity closure yields results in good agreement with experiment.     

Effet du champ électromagnétique fluctuant sur l'évolution des structures d'une couche métallique trés mince déposée sur substrat amorphe ou cristallin

It is believed that the grains of a thin metallic film are polarized by the electric field of “zero point” electromagnetic oscillations. This polarization causes a bipolar interaction force F which is calculated by using a bipolar approximation which is valid for short intergrain distances l.If the grains are not spherical, the curves F(l) generally exhibit a repulsive maximum between two ranges of the attractive forces. The curves F(a_) indicate the existence of a critical diameter (a_)_c. The grains are fixed by the repulsive forces for $\text{a}{}_{\mathrm{}}\text{? (a}{}_{\mathrm{}}\text{)}{}_{\mathrm{<mtext>c</mtext>}}$. Furthermore, a grain can only grow by the capture of impinging atoms or by the surface diffusion of adatoms.     

Crystal structures and crystal chemistry in the system Na1+xZr2SixP3−xO12

As part of a search for skeleton structures for fast alkali-ion transport, the system Na_1+xZr₂Si_xP_3?xO₁₂ has been prepared, analyzed structurally and ion exchanged reversibly with Li⁺, Ag⁺, and K⁺ ions. Single-crystal x-ray analysis was used to identify the composition NaZr₂P₃O₁₂ and to refine its structure, which has rhombohedral space group R3?c with cell parameters $\text{a}{}_{\mathrm{<mtext>r</mtext>}}\text{= 8.815(1)}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{<mtext>r</mtext>}}\text{= 22.746(7)}\text{A}\text{?}$. A small distortion to monoclinic symmetry occurs in the interval 1.8 ≤x≤ 2.2. The structure for Na₃Zr₂Si₂PO₁₂, proposed from powder data, has space group $\text{C}\text{2}\text{c}$ with $\text{a}{}_{\mathrm{<mtext>m</mtext>}}\text{= 15.586(9)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{<mtext>m</mtext>}}\text{= 9.029(4)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{<mtext>m</mtext>}}\text{= 9.205(5)}\text{A}\text{?}$, and β = 123.70(5)° Both structures contain a rigid, three-dimensional network of PO₄ or (SiO₄) tetrahedra sharing corners with ZrO₆ octahedra and a three-dimensionally linked interstitial space. Of the two distinguishable alkali-ion sites in the rhombohedral structure, one is completely occupied in both end members, the occupancy of the other varies across the system from 0 to 100 percent. Several properties are compared with the fast Na⁺-ion conductor β-alumina.     

G̃c and R-curve fracture toughness values for aluminum alloys under plane stress conditions

The effect of specimen geometry and subcritical crack growth on the nonlinear energy fracture toughness, $\text{G}\text{?}{}_{\mathrm{c}}$, has been examined for thin, center-cracked sheets of 2024-T3 and 7075-T6 aluminum alloys. The procedure followed was to independently vary the specimen length, L, width, w, andd crack length-to-specimen width ratio and to determine the toughness both at the onset of subcritical crack growth and at the initiation of unstable fracture. Comparisons were also made with the R-curve toughness, G_R, evaluated at unstable fracture from which it was found that both $\text{G}\text{?}{}_{\mathrm{c}}$ and G_R displayed the same trend of change with geometrical variables, with $\text{G}\text{?}{}_{\mathrm{c}}$ consistently higher than G_R. When the nonlinear energy fracture toughness was evaluated at the onset of subcritical crack growth, it was found that the geometry dependence essentially disappeared.Scanning electron microscopic examination of some typical fracture surfaces showed that stable crack growth was accompanied by a gradual change of fracture mode from plane strain to plane stress. An analysis of possible errors in the experimental procedure showed that the scatter observed in $\text{G}\text{?}{}_{\mathrm{c}}$ values was not due to experimental errors, but apparently due to inhomogeneities in the materials. Several techniques were also introduced for the purpose of more directly incorporating crack growth into the $\text{G}\text{?}{}_{\mathrm{c}}$ determination, but it was found that they did not cause significant variation in the toughness values.     

Condition for stable growth of branched cracks

In order to clarify the reason why the stable growth of branched cracks occurs in delayed failure, while not in other subcritical crack propagation process such as fatigue, the stress intensity factor after crack branching in delayed failure was dropped to various values, and the propagation behavior of both cracks was investigated.The well balanced growth of branched cracks in delayed failure occurs only when the crack propagation velocity after crack branching belongs to the region II where the crack propagation velocity is constant independently of $\text{K}$. The fatigue cracks at the tips of artificially branched cracks, on the other hand, can not propagate stably, and only either crack propagates preferentially.The exponent in the crack propagation law ($\text{d}\text{a/}\text{d}\text{t =}\text{c}{}_1\text{K}{}^{\mathrm{<mtext>m</mtext>}}\text{or}\text{d}\text{a/}\text{d}\text{N =}\text{c}{}_2\text{(ΔK)}{}^{\mathrm{<mtext>m</mtext>}}$) expresses the degree of unbalance growth of branched cracks. The stable growth of branched cracks occurs only when the crack propagation velocity is constant independently of $\text{K}$ or $\text{ΔK}$, i.e. $\text{m}\text{= 0}$.     

Temperature dependence of the surface diffusion distance of bismuth atoms adsorbed on mica,carbon and silicon monoxide surfaces

The mean distance of surface diffusion of bismuth adatoms on mica, carbon and silicon monoxide surfaces has been determined at different temperatures by measurement of the instantaneous sticking coefficient and the nucleus density.The surface diffusion distance has been found to increase with decreasing temperature in accordance with the formula

$\text{X=}\text{1}\text{2}\text{a}{}_0\text{v}{}_{\mathrm{0d}}\text{v}{}_{\mathrm{0a}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{exp}\text{E}{}_{\mathrm{a}}\text{? E}{}_{\mathrm{d}}\text{2RT}$

at temperatures above 413, 373 and 383 K for mica, carbon and silicon monoxide respectively. Here X is one-half of the diffusion distance, E_a is the adsorption energy, E_d the activation energy for surface diffusion, a₀ the diffusion jump distance and v_0a and v_0d the vibrational frequencies associated with re-evaporation and with surface diffusion respectively. Below these temperatures it has been found that the temperature dependence of the diffusion distance deviates from the above formula; this can be explained by the presence of residual gas molecules adsorbed on the surfaces.From the temperature dependence of the diffusion distance, the respective values of the pre-exponential term $\text{a}{}_0\text{(}\text{v}{}_{\mathrm{0d}}\text{v}{}_{\mathrm{0a}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and the difference of energies E_a?E_d have been estimated as 7.6 Å and 5.8 kcal mol^?1 for mica, 17 Å and 3.2 kcal mol^?1 for carbon and 58 Å and 1.3 kcal mol^?1 for silicon monoxide.     

Disorder saturation in heavy ion implanted semiconductors

Studies of ion implantation induced disorder production in Si, GaAs and InP as a function of heavy ion fluence are examined for similarities. In all cases disorder increases rapidly then reaches a quasi saturation with increasing fluence. The ‘knee’ at which the transition to quasi-saturation occurs is identified, from disorder-depth distribution function measurements, as corresponding to production of a continuous amorphous layer. The thickness of this layer is found, for all three substrates and a range of ion species and energies to be well described by the relations:

$\text{X=X}{}_{\mathrm{d}}\text{+(2.7×0.5)Δ}\text{X}{}_{\mathrm{d}}$

where X_d is the mean damage depth and ΔX_d is the standard deviation of damage profile. This allows reasonable prediction to be made of critical fluences required for initial amorphous layer production.     

The crystal structures of Ba2LaRuO6 and Ca2LaRuO6

Neutron diffraction experiments have been performed to determine the structures of Ba₂LaRuO₆ and Ca₂LaRuO₆. Both are ordered, distorted perovskites. Ba₂LaRuO₆ is monoclinic, space group $\text{P}\text{2}{}_{\mathrm{<mtext>1</mtext>}}\text{n}$ with $\text{a}{}_0\text{=6.0285(7)}\text{A}\text{?}$, $\text{b}{}_0\text{=6.0430(7)}\text{A}\text{?}$, $\text{c}{}_0\text{=8.5409(6)}\text{A}\text{?}$, β=90.44(1)^o. The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca₂LaRuO₆ is triclinic, space group P1 with a₀=5.6179(5), b₀=5.8350(5), c⁰=8.0667(4), α=90.0^o, β=89.76(1)^o, γ=90.0^o. The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.     

The incommensurate solid solution phase Na5−4x Zr1+x(PO4)3:0.04 <x <0.15

The orthophosphate solid solution phase, Na_5?4x Zr_1+x(PO₄)₃:0.04 ? x ? 0.15 has trigonal symmetry with an apparent one dimensional incommensurate superstructure parallel to c_HEX. Using selected area electron diffraction patterns as a guide, an indexing scheme for the powder X-ray data has been devised. The parameter $\text{k = c}{}_{\mathrm{<mtext>supercell</mtext>}}\text{c}{}_{\mathrm{<mtext>subcell</mtext>}}$ varies smoothly with composition from ～ 10.4 at x = 0.04 to ～4.4 at x = 0.11 and is believed to originate in ordering of the extra interstitial Zr⁴⁺ ions. The Na⁺ ion conductivity increases gradually with x and for x = 0.108 varies from ～5×10^?8 ohm^?1 cm^?1 at 25°C to ～1×10^?3 ohm^?1 cm^?1 at 300°C.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.