摘要:

We measured the dielectric susceptibility and the polarization of three crystals in the system BaxSr1−xTiO3(x=0.39, 0.26, andx=0.24) which exhibit a diffused ferroelectric phase transition. The results are interpreted using an extension of the Devonshire theory to diffused phase transitions. Diffuseness of the phase transition in BST is not caused by crystalline imperfections but is an inherent feature of this transition.

ISSN:0021-8979    

DOI:10.1063/1.323074

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Working with capacitors produced with thin organic layers (orthophenanthroline with three stearic chains) significant variations were observed in parallel conductance and capacitance in the neighborhood of the transition pointT=35 °C. An investigation of conductance properties in alternating current revealed that these layers are the site of ion relaxation phenomena between two equilibrium positions separated by a potential barrier. A sudden drop in activation energy was observed at 35 °C, falling from a valueE1=1.25 eV toE2=0.65 eV. This variation, attributed to a phase change, leads to a rapid increase in capacitance and conductanceGin the neighborhood of 35 °C (&Dgr;G/G≳50%/d °C). The phenomenon is reversible, and the structure oscillates between two stable states, depending on temperature.

ISSN:0021-8979    

DOI:10.1063/1.323075

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The composition and properties of silicon nitride layers deposited by dc reactive sputtering in a mixture of argon and nitrogen slightly contaminated by oxygen traces were studied. Both MeV4He backscattering and direct observation of nuclear reactions on nitrogen and oxygen were used to analyze the deposits. The films appear uniform with depth. Their stoichiometry and the incorporations of oxygen and argon vary with the partial pressurePN2of nitrogen. For small values ofPN2there is a large amount of argon (Ar/Si=11%), while the oxygen amounts are low (O/Si<2%); asPN2increases, an abrupt decrease of argon incorporation (down to Ar/Si 5 2%) is associated with an abrupt increase of oxygen incorporation (up to O/Si=15%). The N/Si ratio increases practically linearly withPN2up to a saturation value of 1.5 corresponding to an excess of nitrogen with respect to stoichiometric Si3N4. Argon incorporation does not seem to have a large effect on properties of the films such as etching rate, resistivity, and thermal stability which appear, on the other hand, strongly dependent on the N/Si and O/Si values. The mechanisms of dc reactive sputtering are discussed in light of the results.

ISSN:0021-8979    

DOI:10.1063/1.323076

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The elastic non‐Coulomb and Coulomb scattering of high‐energy ions is proposed in useful combination of protons with 4–6 MeV and heavy ions (16O,12,13C) with 15–35 MeV as effective quantitative and nondestructive spectroscopy of metal surfaces. This method provides analyzing depths of 1–50 &mgr;, high mass or depth resolutions of 100–1000 A˚, and selective high sensitivity for hydrogen and light elements up to Si. Successful application is demonstrated by examples measuring superconductors and metals of group V and binary A‐15 compounds. The materials of interest for superconducting cavities, tunneling elements, and high field superconductivity like Nb3Sn have been investigated concerning the problems of oxide layers, composition and contamination, thermal treatment, and interfaces.

ISSN:0021-8979    

DOI:10.1063/1.323077

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Van Vechten, using a semi‐empirical theoretical approach, has computed the equilibrium pressures at which various III‐V compounds as well as C, Si, Ge, Sn, and SiC transform to the metallic &bgr;‐tin phase. A characteristic of each of the groups BX, AlX, GaX, and InX, whereXis a specific metalloid (N, P, As, Sb), is that the theoretical transformation pressure decreases as the atomic number of the metal atom B, Al, Ga, and In increases. The calculated values for the sequence BP, AlP, GaP, and InP are 401, 269, 216, and 141 kbar, respectively. Currently published values are available for GaP at 220 and 240 kbar and for InP at 105–115 kbar. In the present experiment, in which a direct simultaneous electric resistance comparison method is used, it is shown that AlP becomes conductive at a pressure equal to or less than ZnS which has been shown to transform at 150 kbar. Note should be made of the fact that the pressure at which we find AlP to be conductive is clearly considerably less (rather than more) than the pressure at which GaP becomes conductive. Direct simultaneous comparison with GaP in our cell also shows this to be the case. The possibility is suggested that the conductive phase of AlP seen here may not have the &bgr;‐tin structure for which Van Vechten’s calculations apply, but instead may have the sodium chloride structure for which his calculations do not apply.

ISSN:0021-8979    

DOI:10.1063/1.323078

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A system of approximate surface wave equations and edge conditions in one scalar variable is derived from Hamilton’s principle for linear piezoelectric media by assuming suitable depth behavior and integrating with respect to depth. The assumed behavior with depth is determined from the known surface‐wave solutions of the three‐dimensional equations for both the plated and unplated substrate. The influence of the inertia, stiffness, and electrical shorting of the film is included in the analysis. The approximate equations are expressed in terms of the known fundamental material constants and no measurement of model parameters is required. Bulk‐wave scattering is not considered. The approximate equations, which admit of a transmission‐line representation, are applied in the analysis of surface‐wave reflection by both uniformly and nonuniformly spaced arrays of reflecting strips plated on various substrates. Among other things, the calculated reflection curves indicate a slight asymmetry for heavier film materials on account of the dispersion caused by the strips. Although this effect has been observed experimentally, it has not been reproduced by other analytical models.

ISSN:0021-8979    

DOI:10.1063/1.323079

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Processes of the phase transformation in nearly stoichiometric niobium nitride, from cubic &dgr;‐NbN to hexagonal &egr;‐NbN, are studied by selected‐area electron diffraction, by using NbNxfilms of the transition state prepared by annealing &dgr;‐NbNxfilms at about 1000 °C in an atmosphere of H2gas. The diffraction patterns taken from the annealed NbNxfilms suggest that the phase transformations (vacancy‐poor‐) &dgr;‐NbNx(cub.) → (N‐vacancy‐) ordered &dgr;‐NbN (tet.)  → ordered &zgr;‐NbN (hex.)  → ordered &ggr;′‐NbN (mon.)  → &dgr;′‐NbN (hex.)  → &egr;‐NbN (hex.) occur. Ordered &dgr;‐NbN, ordered &zgr;‐NbN, ordered &ggr;′‐NbN, and &dgr;′‐NbN are transient phases which occur during the transformation &dgr;‐NbNx → &egr;‐NbN, and the superlattice structures of the three ordered phases are described by the ordering of N vacancies with random Nb vacancies in their fundamental lattices. Mechanisms of the transformations from &dgr;‐NbNxto &egr;‐NbN at about 1000 °C are discussed on the basis of the transient phases observed during the phase transformations.

ISSN:0021-8979    

DOI:10.1063/1.323080

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

An experimental study to determine the orientation of surface structures with respect to atomic‐bond direction is presented. The As‐stabilized (2×4) and C(2×8), and Ga‐stabilized (4×2) and C(8×2) surface structures all have their twofold direction parallel to the plane containing the dangling surface bonds and perpendicular to that of the back bonds.

ISSN:0021-8979    

DOI:10.1063/1.323081

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Measurements have been made on the amount and type of gas species released under x‐ray irradiation from Al2O3and stainless‐steel surfaces in an ultrahigh vacuum environment. These surfaces had not been degassed but had been held more than 24 h at a background pressure of 1×10−9Torr prior to irradiation. The energy spectrum of the x rays was characteristic for a tungsten‐target bremsstrahlung spectrum for electron energies varying from 15 to 50 keV. The predominant gas species observed mass spectrometrically were CO2from Al2O3and O2, CO2, and CO from stainless steel. Mean quantum yields for the release of the species have been determined and are in the range from 3×10−5to 2×10−3molecules per number of photons in the bremsstrahlung spectrum. Mean quantum yields were observed to decrease with increasing mean photon energy. The mean photon energy dependence of the mean quantum yield for gas release was correlated with the photon energy dependence of the photon absorption coefficient of the substrate material. The amount of CO2released was found to be independent of CO partial pressure.

ISSN:0021-8979    

DOI:10.1063/1.323082

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

An x‐ray diffraction technique recently developed by Houska and co‐workers was applied to the problem of measuring interdiffusion at 350 °Cin 3.3 &mgr; Au–60 at.% Pd bimetallic thin films. The technique consists of matching experimental intensity bands to those calculated from assumed concentration profiles. The profiles which gave best fit were then Boltzmann‐Matano analyzed during the first stages of interdiffusion. The later stages were analyzed with the help of a linear diffusion equation applied to a finite slab. Experimentally determined values of D˜ were found to be close to those extrapolated from bulk high‐temperature measurements but far from those obtained from 150 A˚ films.

ISSN:0021-8979    

DOI:10.1063/1.323060

出版商:AIP    

年代:1976

数据来源: AIP