摘要:

The amorphization of Ni‐Nb multilayered alloy films by xenon ion irradiation at room temperature and by high‐temperature solid‐state reaction was studied. The composition range favoring amorphization was carefully determined to be 20–85 at. % Ni by energy‐dispersive spectroscopy attached to the transmission electron microscope. A new metastable crystalline phase (MX) of hexagonal structure was formed in Ni75Nb25and Ni70Nb30multilayered films. Interestingly, in the Ni75Nb25multilayered films, with increasing mixing dose an amorphous phase was first formed and then the MX‐phase was observed, while in the Ni70Nb30multilayered films the MX phase was formed at relatively low doses and turned amorphous upon further mixing or 400 °C annealing for 2 h. Besides, annealing of the as‐deposited Ni70Nb30multilayered films at 300 °C for half an hour also resulted in the formation of the MX phase. The thermal stability of the ion‐mixed amorphous alloys was also studied by subsequent annealing. To give semiquantitative interpretation to all the above observations, the Gibbs free‐energy diagram of the system, in which especially the free‐energy curve of the MX phase is added, was constructed on the basis of the model of Nissenetal. [CALPHAD7, 51 (1981)] and the method proposed by Alonso and Simozar [Solid State Commun.46, 765 (1983)]. The explanation based on this diagram is in good agreement with our experimental results.

ISSN:0021-8979    

DOI:10.1063/1.353205

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An analytical model is developed to predict the effective thermal conductivity of multiphase composites reinforced with coated fillers. The coated fillers are modeled as confocal spheroids, thus enabling the simulation of a wide range of reinforcement geometry ranging from thin flake to continuous fiber. The orientation of the coated fillers is described by a density distribution function which can simulate completely random, in‐plane random, and aligned distributions as special cases. The analytical approach appears to be the only one in the literature that renders closed‐form predictions of the effective thermal conductivity of composites with misoriented coated reinforcement and thus recourse to a numerical scheme is not required. The analytical approach is specialized to consider the effects of a thermal resistance at the filler‐matrix interface of a composite. Results of the proposed model are compared with those obtained by self‐consistent and differential estimates [Y. Benveniste and T. Miloh, J. Appl. Phys.69, 1337 (1991)] for the effective thermal conductivity of a composite reinforced by completely random coated short fibers. The proposed model is in close agreement with the other two models for low conductivity coatings, but differs appreciably for high conductivity coatings. Finally, good agreement is shown to exist between analytical predictions and experimental results obtained from the literature for a diamond particle/zinc‐sulfide matrix composite with an interfacial thermal resistance.

ISSN:0021-8979    

DOI:10.1063/1.353206

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Deuterium diffusion profiles in GaAs doped with different acceptors of group II (Mg,Zn,Cd) or group IV (C,Ge) have similar characteristics even though the neutralization of acceptors measured at 300 K is not always efficient. Conductivity and Hall measurements have been used to study the electrical characteristics of hydrogenatedp‐type GaAs epilayers. The temperature dependence of the free‐carrier concentration and hole mobility before and after hydrogenation shows that the neutralization of acceptors by atomic hydrogen leads to the elimination of the shallow acceptor states. Infrared‐absorption lines associated with hydrogen‐acceptor complexes are observed for all acceptors except magnesium. It is established that the microscopic structure of hydrogen‐acceptor complexes depends on the acceptor site in the lattice.

ISSN:0021-8979    

DOI:10.1063/1.353207

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In this work, the refractive index profiles of SiO2/Si3N4/SiO2/silicon (ONO) structures were measured and analyzed by ellipsometry. The ONO structures were obtained by oxidizing the Si3N4/SiO2/silicon structure in a wet O2ambient at the temperature range of 900–1050 °C for different lengths of time. It was found that for a nitride film thickness less than 250 A˚, oxygen not only oxidized the surface, but diffused through the nitride and oxidized the inner surface of the nitride. This result was confirmed by the Auger analysis. The kinetics of the wet O2oxidation of nitride at the above temperature range was linear for an oxidation time of 30–120 min. The activation energy was 2.24 eV.

ISSN:0021-8979    

DOI:10.1063/1.353208

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

InsituSi‐TaSi2composites are studied by synchrotron white beam topography and by double axis diffractometry. These results show that the single crystal Si matrix is of excellent quality: Rocking curve widths are between 40 and 60 s of arc, and the topographs do not exhibit asterism. Diffuse radial streaks in the Laue patterns originate from diffraction by the TaSi2rods in the matrix: TheK‐absorption edge of filters placed in the incident x‐ray beam produces a sharp change in contrast in the streaks, and this is used to determine thedspacings present in the streaks and to show that considerable preferred orientation exists between the TaSi2rods and the Si matrix.

ISSN:0021-8979    

DOI:10.1063/1.354081

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effect of rf power and substrate temperatureTson the optical, electrical, and structural properties ofa‐Si1−xCx:H alloy films deposited in the new hot‐plasma‐box glow‐discharge reactor are reported. The rate of deposition as well as the total fractionxof the carbon incorporated in the alloy films were found to vary in a direct proportion with the rf power, whereas the same parameters displayed an inverse proportionality to the changes inTs. Second, the hydrogen concentration in the alloy films was found to decrease with the increase in substrate temperature while it did not show appreciable variation with the changes in rf power. Next, the structural disorder in the amorphous network was observed to increase rapidly with increase in rf power although a slight improvement was made possible by elevating theTs. The analysis of Raman scattering and optical band‐gap measurements on these alloy films indicates that a large proportion of the Si—C and C—C bond pairs favors the diamondlike (sp3) bonding configuration at low rf power when theTsis high, whereas the graphitelike (sp2) C—C clusters show up only at high rf power values when theTsis low. The efficiency of C incorporation in these alloy films prepared by the present technique appears to be better than its best possible magnitude in the conventional open parallel‐plate glow‐discharge‐deposition systems.

ISSN:0021-8979    

DOI:10.1063/1.353209

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

High‐resolution transmission electron microscopy, electron holography, and high‐spatial‐ resolution (19 A˚) computer‐controlled parallel electron‐energy‐loss spectrometry (PEELS) were used to probe the structure of and chemical profile across two thin silicon oxide‐nitride‐oxide layered structures of nominal widths of 10 A˚‐50 A˚‐10 A˚ and 30 A˚‐50 A˚‐30 A˚. It was found that the individual layers of the stacked structures could be clearly imaged using electron holography, but not with electron microscopy due to the behavior of the microscope transfer function and the shape of the potential profile of the structure. Holography revealed that the layers of the 10 A˚‐50 A˚‐10 A˚ system were in fact 14 A˚‐28 A˚‐18 A˚±5 A˚, and the oxide layer in contact with the substrate (first oxide layer) was discontinuous. PEELS showed that the second oxide layer contained nitrogen, and the nitride layer had a silicon‐to‐nitrogen concentration ratio of 1.0±0.1. The 30 A˚‐50 A˚‐30 A˚ system was in fact 30 A˚‐20 A˚‐40 A˚‐15 A˚±5 A˚. The second oxide layer was SiO1.6±0.2, and nitrogen was found near the film surface which made the structure appear to be four layers. These results show the power of holography in characterizing thin, light‐element, amorphous layers and the importance of computer‐controlled parallel energy‐loss line scans for obtaining analytical information at the highest spatial resolution with minimum dose.

ISSN:0021-8979    

DOI:10.1063/1.353210

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The thermal behavior of Ta/Ge superlattices has been studied using Raman spectroscopy. The high‐frequency Raman spectra, obtained as a function of annealing temperature, reveal no significant change in the superlattice structure up to an anneal temperature of 400 °C. The interlayer diffusion at the Ta/Ge interfaces occurs at 500 °C followed by complete crystallization of the superlattice at 600 °C. Raman scattering from the folded acoustic modes of the superlattices was also employed to study the thermal behavior of superlattices, and the results thus obtained corroborate the above findings.

ISSN:0021-8979    

DOI:10.1063/1.353211

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Using x‐ray diffraction, Rutherford backscattering spectrometry, Auger electron spectroscopy, and scanning electron microscopy, effects of ambient anneal and Pt thickness on the interdiffusion of Pt/Ti bilayers deposited on SiO2/Si and on reactively sputtered TiN/Ti/Si substrates have been investigated. The Pt layer was 2000 or 930 A˚ thick while the Ti thickness was fixed at 1000 A˚. The wafers were annealed in either O2or N2ambients or in N2followed by O2, with temperatures ranging from 600 to 800 °C for 30 min. The anneal ambients and the thickness of Pt relative to the Ti layer had tremendous effects on the interdiffusion processes, the reaction products, and the surface morphology of the multilayer structures. Samples annealed in O2were generally rough, with bumps of the order of 1000 A˚, while those annealed in N2were relatively smooth. With lead zirconium titanate on top, the surface of Pt/Ti electrode annealed in O2at 650 °C was relatively smooth.

ISSN:0021-8979    

DOI:10.1063/1.353212

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The interaction energyEirrIof arrays of dislocations with nonperiodic (or irregular) distribution is calculated. The calculations have been made for uniform‐random and Gaussian distributions of dislocations. The method used is, however, general and can also be applied to any arbitrary or an observed distribution of dislocations. The results for several values of average spacingp¯ and standard deviation &sgr; are given and are compared with the energyEIof periodic arrays with spacingp=p¯. The total energyEirrTof strained layers containing nonperiodic dislocation arrays is also calculated. The results for both 90° and 60° dislocations are given. For sufficiently large numbers of dislocations,EirrIis always larger thanEI. The difference between the energiesEirrIandEIincreases rapidly as the standard deviation &sgr; of the nonperiodic distribution increases. The equilibrium strain relaxation in thick layers and the strain relaxation on annealing the metastable layers are usually calculated by modeling the nonperiodic array as an equivalent periodic array withp=p¯. It is found that this procedure for the calculation of the strain relaxation is not valid.

ISSN:0021-8979    

DOI:10.1063/1.353213

出版商:AIP    

年代:1993

数据来源: AIP