摘要:

The role of CuO in reducing the volume change and altering the transition temperature of structural phase transitions in ammonium nitrate is studied by electron paramagnetic resonance (EPR). At room temperature, two distinct EPR spectra, indicative of two chemical forms of copper were observed in ammonium nitrate heated from the melt containing 5% by weight of CuO and through which NH3gas was bubbled. One spectrum having an orthorhombicgtensor with principle componentsg1= 2.185,g2= 2.109, andg3= 2.055 is assigned to the Cu(NH3)2+4complex. The other spectrum, also having orthorhombic symmetry, withg1= 2.315, andg2= 2.264, is tentatively assigned to a Cu2+ion either interstitial or substitutional in the lattice. Thegvalues of this spectrum were quite sensitive to temperature and change substantially during the structural phase transition at 60 °C. Heating ammonium nitrate to 160 °C for an hour changed the tetramine copper complex into a new spectrum which is identified as the diamine complex of copper. At room temperature this spectrum slowly returned to the tetramine complex. The role of these forms of copper in reducing the volume change associated with the above room‐temperature phase transition is discussed.

ISSN:0021-8979    

DOI:10.1063/1.329898

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A general coupled amplitude equation is developed for surface acoustic waves (SAW) from coupled‐mode theory. The derivation accounts for the surface propagating character and bulk decay pattern of the uncoupled modes. The general equation is applied to interactions arising from the weak nonlinearities of the materials supporting SAW’s. Coupling contants K of the nonlinear interactions are shown to be determined from the nonlinear material constants and normalized particle velocity, electric, and strain fields of the linear normal modes. For conservative coupling, a single coupling constant describes a given three‐wave interaction. For a given mode &agr;, the coupling constant to two other modes (&bgr;,&ggr;) scales as the product of the frequencies of modes &bgr; and &ggr; (&ohgr;&bgr;&ohgr;&ggr;). Theory shows how one‐dimensional single‐nonlinear‐parameter models can approximately account for multiharmonic generation onYZ‐LiNbO3. Applying the theory to experiments on second‐harmonic generation, we find the nonlinear coupling constant forYZ‐LiNbO3is ‖K‖≊1.1×109m/sec2 W1/2at 50 MHz. Similarly for (11¯0)‐(001) Bi12GeO20, we find ‖K‖≊1.4×108m/sec2 W1/2at 50 MHz and ‖K‖≊5.3×108m/sec2 W1/2at 100 MHz. The nonlinear coupling constant units are for interacting field amplitudes normalized to the square root of action density integrated over depth (W sec2/m)1/2.

ISSN:0021-8979    

DOI:10.1063/1.329899

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An experiment was carried out to measure the magnitude of the nonlinear coupling constant for a noncollinear surface‐wave interaction on Y‐cut LiNbO3. the resonant interaction was an upconversion interaction in which two surface acoustic waves with frequencies of 36 and 214 MHz interacted to produce a 250‐MHz wave. The 36‐MHz wave was launched with a phase velocity in theZdirection, and the 214‐MHz wave was launched with its phase velocity 10° off theZdirection. The magnitude of the coupling constant was found to be: (2.8±0.6)×109m/sec2W1/2.

ISSN:0021-8979    

DOI:10.1063/1.329900

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

An atomistic model for the transformation of amorphous (&agr;) to crystalline silicon films while in contact with a crystalline substrate is presented. The atomic structure of the {100}, {110}, and {111} surfaces is examined and related to the observed interface migration rates. The assumption that for an atom to attach successfully to the crystal it must complete at least two undistorted bonds, leads to the prediction that the {100} amorphous/crystalline interface should advance fastest and the {111} slowest. The origin of crystal defects is discussed in terms of the atomistic recrystallization mechanism. Microtwins are found to be a logical consequence of crystallization on the {111} surfaces but are not expected to form on any other interface. Once microtwins are formed they can increase the recrystallization rate of a {111} surface. This phenomenon is both described in the model and experimentally observed.

ISSN:0021-8979    

DOI:10.1063/1.329901

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Low‐pressure chemical vapor‐deposited (LPCVD) silicon nitride films on silicon have been characterized by means of Rutherford backscattering (RBS), Auger electron spectroscopy (AES) combined with ion sputtering, and spectroscopic ellipsometry. It appeared that all LPCVD samples in the examined thickness range of 50 –500 A˚ had an oxygen‐containing layer equivalent to 15–20 A˚ of SiO2at the nitride‐silicon interface. This interfacial layer originates from the native silicon oxide present at the silicon substrate when the deposition of nitride is started. For comparison, oxide‐free silicon substrates were nitrided in ammonia at temperatures between 800–1160 °C. The thermal nitride films were found to be very thin, at the most 30 A˚, even after 5 h of nitridation. Both the LPCVD and thermal nitride films oxidize slightly when transferred into the ambient; a surface layer equivalent to 8 A˚ of SiO2was detected. Auger and RBS results agree very well for all nitride films investigated. It is shown that RBS can be made a very sensitive probe for such thin multilayer structures by performing glancing‐angle scattering experiments under channeling conditions. Spectroscopic ellipsometry proves to be more sensitive to the interface structure than to the surface composition. Although quantitatively deviating results were obtained, in the extremely thin thermal nitrides this optical technique traces chemical intermediates, not perceived with RBS or AES.

ISSN:0021-8979    

DOI:10.1063/1.329902

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Insulating films consisting of both aluminum oxide (Al2O3) and native oxide (Ga‐As‐O) have been grown anodically onp‐ andn‐type GaAs in a dc oxygen plasma. Films were grown at a constant anodization current up to 2000 A˚ in thickness using GaAs wafers precoated with 50 to 150 A˚ of Al. Auger analysis using ion milling for depth profiling revealed Al2O3mixed with native oxide in the upper 1000 A˚ and only native oxide at the GaAs interface. It was found that the presence of the Al2O3did not prevent the buildup of As at the GaAs interface during anodization. The composite films were found to be ohmic with a resistivity of 1015&OHgr;‐cm for electric fields below about 6×105V/cm. The presence of the Al2O3increased the breakdown strength to about 4×106V/cm. An analysis of the capacitance‐voltage characteristics of metal‐oxide‐GaAs devices measured from 100 to 1 MHz showed a typical interface‐state density of 2–6×1012cm−2 eV−1in the lower half of the GaAs band gap. In contrast to earlier reports, the addition of Al2O3to the anodic oxide did not alter the As and Ga distributions in the native oxide adjacent to the GaAs substrate nor did it appreciably improve the electrical properties of the oxide‐GaAs interface.

ISSN:0021-8979    

DOI:10.1063/1.329903

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The microstructure of sputtered thin films of platinum, deposited on glass substrates in the presence of argon, is investigated by x‐ray diffraction. (111) layers tend to align parallel to the substrate surface and the degree of orientation depends on the film thickness, deposition rate, gas pressure, and cathode potential. These parameters can be optimized to give maximum orientation or crystallinity. From an analysis of the breadths of the (111) and (222) reflections by the variance and Fourier (Warren‐Averbach) methods and from peak asymmetries, the domain size, strain, dislocations density, and faulting probability are obtained for as‐prepared and annealed films. It is found that annealing decreases the strain due to dislocation. Large domain sizes with low fault and dislocation densities occur at high deposition rates and low pressures, and structural perfection is greatest when the ratio of the deposition rate to the pressure is in the region of 2000 A˚ min−1Torr−1. It appears that some annealing due to particle bombardment takes place during deposition.

ISSN:0021-8979    

DOI:10.1063/1.329904

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Thermal stability of films of Pd2Si and PdSi formed on ⟨111⟩ Si wafers has been studied by x‐ray diffraction. We observed that Pd2Si transformed to PdSi at temperatures around 810±10 °C and PdSi transformed back to Pd2Si when annealed below that temperature. We conclude that Pd2Si rather than PdSi is the thermodynamically stable phase on Si at low temperatures, contrary to the existing Pd‐Si phase diagram. The conclusion has been confirmed by annealing bulk Pd‐Si diffusion couples at 750 °C to form Pd2Si, then at 850 °C to transform part of the Pd2Si to PdSi, and then returning to 750 °C to convert the PdSi back to Pd2Si and Si. The bulk transformations were measured by x‐ray diffraction and electron microprobe.

ISSN:0021-8979    

DOI:10.1063/1.329905

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The energy shifts of valence and conduction band states in silicon due to the interaction of electrons and holes with ionized donors have been calculated by performing a partial wave analysis. The potential is modeled by the Yukawa form with the screening radius determined self‐consistently by the Friedel sum rule. The results show that this effect is an important part of the optically measured band‐gap narrowing. The variation of the Fermi energy due to this phenomenon is also calculated.

ISSN:0021-8979    

DOI:10.1063/1.329906

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Capacitance‐voltage characteristics of a metal‐oxide‐amorphous silicon structure are analyzed in order to obtain the density of statesN(E) in microwave glow discharge amorphous silicon films. Our measurement and deconvolution techniques reveal some structure in the density of states profile. At the midgapN(E) is found to be lower than 1017cm−3eV−1.

ISSN:0021-8979    

DOI:10.1063/1.329907

出版商:AIP    

年代:1982

数据来源: AIP