摘要:

We present a crystallization study of melt‐spun Fe‐Zr metallic glasses. Unlike Cu‐Zr and Ni‐Zr, the immediate crystallization products cannot be understood in terms of the equilibrium crystalline phase diagram: all are metastable or unstable phases. In the composition range Fe25Zr75to Fe33Zr67, there is evidence that explosive crystallization occurs. The behavior of the activation energy with composition suggests there may be a eutectic at the composition Fe37.5Zr62.5.

ISSN:0021-8979    

DOI:10.1063/1.334455

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Gold and iron are known to interact in silicon at temperatures below ∼400 °C to form gold‐iron pairs with band‐gap energy levels ofEv+0.434 eV andEc−0.354 eV. In this work, the details of the formation and dissociation of these pairs were examined and from the equilibrium concentrations a binding energy of 1.22±0.02 eV was deduced. The activation energy of the gold‐iron pair formation process was found to be 0.8 eV; when corrections were made to extract the activation energy for the iron diffusion coefficient from the data, a value of 0.42 eV was obtained. This is substantially smaller than the values of 0.7–0.9 eV obtained from iron precipitation and iron‐boron pairing studies. It was noted during the higher‐temperature dissociation process that there was concurrent precipitation of the iron which caused the dissociation to appear to be a two‐stage process. This precipitation also resulted in substantial irreversibility of successive dissociation and pair formation anneals. Finally, it is pointed out that these low‐temperature instabilities in the concentration of gold and the deep‐level gold‐iron complex are likely to result in device instabilities when gold and iron contamination occur.

ISSN:0021-8979    

DOI:10.1063/1.334456

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Polycrystalline samples of AgGa(Se1−zTez)2alloys were prepared by a melt‐and‐anneal technique, annealing at 650 °C for up to 4 months being required to give good equilibrium conditions. It was confirmed that single phase solid solution occurs at all values ofzand values of lattice parametersa,c, andc/awere determined from Guinier–Haegg powder photographs. Line intensities were obtained from diffractometer measurements and, hence, values of the anion displacementudetermined as a function ofz. Comparison of these experimental data has been made with the expressions proposed by Abrahams and Bernstein and by Jaffe and Zunger. The values ofufrom the former equation show rather poor agreement, particularly at the AgGaSe2end of the composition range. However, the equations of Jaffe and Zunger, used with Phillips radii, give very good agreement for bothuandabut poorer agreement forcandc/a. The optical energy gapE0is found to show a parabolic variation withz. Comparison with seven similar alloy systems shows that theE0versus composition curve is bowed for mixed‐anion alloys but practically linear for mixed‐cation alloys.

ISSN:0021-8979    

DOI:10.1063/1.334457

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Amorphous Si and Ge layers, produced by noble gas (Ar or Xe) implantation of single crystal substrates, have been crystallized in a differential scanning calorimeter (DSC). The MeV implantation energies resulted in amorphous layers of micron thickness whose areal densities were determined using the Rutherford backscattering and channeling of 1‐MeV protons. These techniques allow determination of the amorphous‐crystal interface velocity (which is proportional to the rate of heat evolution &Dgr;H˙ac) and the total enthalpy of crystallization &Dgr;Hac. Amorphous Ge was found to relax continuously to an amorphous state of lower free energy, with a total enthalpy of relaxation of 6.0 kJ/mol before the onset of rapid crystallization. The interface velocity for crystallization on (100) substrates, was found to have an Arrhenius form with an activation energy of 2.17 eV. The value of &Dgr;Hacwas found to be 11.6±0.7 kJ/mol, the same as for samples prepared by deposition. For Si, &Dgr;Hacwas determined to be 11.9±0.7 kJ/mol without any evidence of heat release due to relaxation. The (100) interface velocity was found to have an activation energy of 2.24 eV. The effects of the implant depth profile on the regrowth velocity could also be observed directly in the DSC signal. From the value of &Dgr;Hacand Gibbs free‐energy calculations, the melting temperature of amorphous Si has been determined to beTal=1420 K.

ISSN:0021-8979    

DOI:10.1063/1.334406

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Monte Carlo studies show that an exclusion principle, based upon a minimum allowed O‐O separation in adjacent tetrahedra, drastically restricts the relative orientations such tetrahedra can assume. This ad hoc criterion, with no energy considerations involved, reproduces the experimentally observed Si‐O‐Si angle distribution determined from the structural data of a large number of silicas and silicates. Similar results are obtained when Coulombic or nonbonded energy calculations are used. When extended structures are formed, this steric requirement alone causes additional and severe restrictions on the relative orientations of adjacent tetrahedra. In fact, it is not possible to have completely random orientations of tetrahedra beyond the first neighborhood shell, unless some nonrandomness is introduced to help formation of closed rings. Thus, the completely random continuous network model fails to produce extended structures in vitreous silica and defect models must be introduced to patch up the model. These considerations also apply to GeO2and SiS2structures.

ISSN:0021-8979    

DOI:10.1063/1.334407

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We conducted an experiment to study the growth kintetics of the oxidation‐induced stacking faults (OSF) ofn‐ andp‐type (100) and (111) Si wafers with resistivities of 0.8–15 &OHgr; cm. The OSF size data are as expected for thep‐type (100) and (111) wafers as well as for then‐type (100) wafers. For then‐type (111) 0.8–2 &OHgr; cm wafers, however, no OSF were generated at a temperature higher than ∼1100 °C and those grown at 1050 °C are considerably smaller than expected. This indicates that in then‐type (111) wafers there exists a mechanism that depletes Si self‐interstitials, in addition to the normal mechanism of interstitial injection. Obviously, the effect is dependent on orientation as well as on doping. The same kind of effect was found before via diffusion studies, which, however, did not appear as doping dependent. We propose that this discrepancy is apparently due to the fact that, in one diffusion experiment,p+(111) materials (Ga implanted to a concentration exceeding 1020cm−3) were oxidized.

ISSN:0021-8979    

DOI:10.1063/1.334408

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The redistribution of thep‐type dopant Be during the growth of GaAs and AlGaAs by molecular beam epitaxy has been studied using secondary ion mass spectrometry and capacitance–voltage carrier profiling. An asymmetric redistribution of Be toward the epitaxial layer surface has been observed in GaAs, along with a more symmetric diffusion in AlGaAs. The effects of Be concentration, growth conditions, and Fermi level on Be redistribution have been investigated. The long‐range asymmetric redistribution may be due to Be carried forward with the growth surface, while the more symmetric redistribution observed in AlGaAs is consistent with an interstitial–substitutional model for Be diffusion.

ISSN:0021-8979    

DOI:10.1063/1.334409

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The time‐dependent craze failure process of polymers has been investigated. The process is characterized by several stages: deformation, development of microporosity, craze initiation, craze propagation, craze‐crack transition, and propagation of crack to final fracture. Using Laurent’s series expansion and convolution integral form of material’s constitutive function, a time‐, temperature‐, and stress‐dependent instability criterion for viscoelastic media has been considered. It is found that under a constant load, an incubation time for craze initiation can be obtained. This incubation time goes to zero for sufficiently high values of stress and approaches to infinity for low values of stress. The crazing stress depends linearly on temperature, and decreases as the test temperature increases toward the glass transition temperature. The interrelationship among the applied stress, craze initiation time, and temperature is then established and a fairly general time‐dependent theory on craze or quasifracture initiation in viscoelastic media is formulated.

ISSN:0021-8979    

DOI:10.1063/1.334410

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Young’s modulus was measured by tensile testing on Cu/NiFe thin foils containing short‐wavelength composition modulation of 1.4–10.0 nm. The foils, of 53% Cu/40% Ni‐7% Fe composition, were produced by vapor deposition using a three‐source evaporator. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase (up to 300%) in modulus for two distinct ranges of composition wavelength: 2.1–2.7 and 3.6–4.1 nm. The increase was proportional to the square of the composition amplitude. The stress‐strain curves of the modulated foils displayed a Hookean behavior below 0.2% strain.

ISSN:0021-8979    

DOI:10.1063/1.334411

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The elastic field of a semi‐infinite wedge crack and its interaction with a screw dislocation under mode III loading conditions are examined. The stress field around the wedge crack is expressed in terms of a wedge stress intensity factor. The rate of falloff of the stress field with distance from the crack tip is found to be a function of the wedge angle. The relationship between the stress intensity factors for the wedge and sharp cracks is derived and used to estimate the magnitude of stress relaxation occurring at the crack tip due to crack blunting. The crack extension force for the wedge crack is calculated and is shown to be zero. The modifications in the stress field and the local wedge stress intensity factor due to the presence of the dislocation are calculated. From the image stress on the dislocation, the condition for the emission of dislocations from the wedge crack is obtained in terms of the critical wedge stress intensity factor for dislocation generation. It is found that the emission of dislocations from the crack tip is more difficult when the crack is blunting.

ISSN:0021-8979    

DOI:10.1063/1.334412

出版商:AIP    

年代:1985

数据来源: AIP