摘要:

Metal coating application onto optical fibers by the freezing technique is accompanied by the emergence of cavities empty of metal, which are situated at regular intervals along the fiber. This article attempts to explain the nature of this phenomenon, which is shown to be inherent in the freezing technique. The regular cavities are due to the instability of the melt flow during the phase transition process at the point of contact of the cool fiber and the melt. Resonance of one of the eigen vibrations of the entrance meniscus with chaotic perturbations of the melt flow accounts for the periodicity of the cavities. The results of the theoretical analysis are confirmed by the experimental data. The conclusions of this analysis allow one to explain the presence of a similar phenomenon in the “spinning” process used for the fabrication of amorphous-alloy thin ribbons. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365267

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The photoelectrochemical properties of ap-type silicon (100) electrode coated with tungsten oxide thin film were investigated as a function of annealing temperature. The variation in the annealing temperature affected the photocurrent of aWO3/p-Sielectrode. A maximum photocurrent was obtained when the 500 ÅWO3thin film coatedp-Si electrode was annealed at 350 °C for 1 h. A further increase in the annealing temperature and film thickness degraded the photocurrent. This can be explained in terms of electrical resistivity, carrier concentration, and depletion layer width. AWO3thin film deposition on thep-Si shifted the flatband potential of thep-Si electrode by 0.3 V in the anodic direction, resulting in an improvement in conversion efficiency. These results are supported by x-ray diffraction, Auger electron spectroscopy, and capacitance measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365268

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of the exposure of underlying dielectric (phophosilicate glass and borophosphosilicate glass) films to a humid air ambient on crystallographic orientations in Al–Si–Cu/Ti/TiN/Ti layered structures has been investigated as a function of the boron content and exposure time of the dielectric films. The Al(111) orientation in the layered structures was found to improve drastically with increasing boron content and exposure time of the dielectric films. The full width at half maximum value of an Al(111) x-ray rocking curve reached less than 1°. It was also found that the Al–Si–Cu surface becomes smoother and the average grain size increases as the Al(111) orientation improves. The improved Al(111) orientation was attributed to the improved Ti(002) orientation of the bottom Ti films. The mechanism of the improved Ti(002) orientation was investigated. It was confirmed that the improved orientation is closely related with the surface concentration of the absorbed water in the dielectric films. Further, it was demonstrated that interconnects fabricated from the improved layered structure have excellent electromigration performance. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365269

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Suspended epitaxial YBaCuO microbolometers were successfully fabricated by two silicon micromachining techniques. The first one used the reactive ion etching (RIE) of Si substrates and the second one the etching of theSiO2layer in separated by implanted oxygen (SIMOX) substrates. This work aims at the modeling and the measurement of the bolometric performances of IR pixels (100×100 &mgr;m2detection area) constituted by suspended bridges in series. The influence of both the dimensions and the thermophysical properties of the materials constituting the membrane is discussed. Thermal conductances and time constants were measured as functions of the length and the width of different suspended bridges fabricated by RIE. Comparison of a “RIE type” bridge with a bridge of same dimensions fabricated from a SIMOX substrate shows that the sensitivity-bandwidth product of the SIMOX bridge is improved by one order of magnitude. All measurements on suspended bridges are consistent with calculations from thermal model. The specific detectivityD*of a 4-&mgr;m-wide suspended meander line, measured at 85 K under irradiation from a blackbody, is2.5×109 cmHz/W,with a thermal time constant of 564 &mgr;s. These performances are among the best reported for YBaCuO microbolometers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365225

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

High performance pseudomorphicInxGa1−xAs/GaAsmodulation doped field effect transistors (MODFETs) grown by metalorganic chemical vapor deposition have been characterized at dc using modulation spectroscopy. A transconductance as high as 175 and 253 mS/mm was obtained at 30&percent; and 40&percent; indium content, respectively. In order to identify the origin of the MODFETs’ features we have performed a self-consistent Schrodinger–Poisson calculation of the subband and intersubband energies. The photoreflectance spectra can be divided into two parts by the photon energy; one belongs to the GaAs bulk transition and the other belongs to theInxGa1−xAs/GaAsquantum well transition including two-dimensional electron gas (2DEG) signals. The built-in electric fields are20.6×104 V/cmand22.6×104 V/cm.From photoreflectance spectra peaks at 1.035 and 1.06 eV show that their energies agree with line shape fitting and 2DEG theory. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365226

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Dynamic random access memory data retention characteristics were investigated as a function of operating voltage. Based on a statistical process, called the trap-level-distribution model, which was proposed in our previous report, we further assumed that the junction leakage current by Shockley–Read–Hall process is enhanced by an electric field through the trap-assisted-tunneling process. We incorporated into the model two processes that cause variation in the electric field at the traps; the variation of electric field itself and the spatial trap distribution. By comparing the Monte Carlo and analytical calculations with the experimental results, we found that the retention time distribution is not only caused by the energy level and spatial distributions of the traps, but by the space-charge-region field distribution among the cells. A possible origin of the field distribution is the variation of dopant profile among the junctions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365227

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The formation of metastableC40–MoSi2andC49–TiSi2during the mechanical alloying of metal/silicon powder mixtures has been investigated by x-ray diffraction. The mechanical alloying of a Si-rich Mo/Si powder mixture results in the formation of bothC11b–MoSi2andC40–MoSi2.TheC40–MoSi2phase is metastable and transforms toC11b–MoSi2after annealing at 850 °C. The mechanical alloying of a stoichiometric Ti/Si powder mixture leads to the incipient formation ofC49–TiSi2and the subsequent polymorphic transformation toC54–TiSi2.The lattice parameters ofC49–TiSi2,as determined from a mechanically alloyed Ti/Si powder sample that has been annealed at 700 °C, are as follows:a0=3.56 Å,b0=13.57 Å,andc0=3.55 Å.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365228

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Observations of the free-surface behavior under shock compression by the gapped-flat mirror method were performed onB4CandSi3N4ceramics to study their shock-yielding properties. Jagged profiles of the moving free-surface in the plastic region, with a special scale of about one mm and a maximum local displacement of a few 10s of &mgr;m, were observed forB4Cpolycrystals. Similar profiles forSi3N4polycrystals were smooth. Such profiles forB4Cpolycrystals were also observed in the elastic region. It is suggested that these observations reflect the heterogeneous nature of shock compression in solids, and further indicate that a macroscopic slip system plays an important role in the elastoplastic transition ofB4Cmaterial under shock compression and decompression. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365229

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The compensation effect, well known in catalytic reactions, is shown to apply equally well to the solid-phase epitaxial (SPE) growth ofSi1−xGexalloys. A linear relationship exists between the logarithm of the pre-exponential factor and the activation energy of the SPE growth rate. This linear relationship, together with the activation energy obtained earlier, enables one to completely describe the growth rate ofSi1−xGexalloys. The effect holds for both strained and unstrained SPE. The model is applicable to other binary alloys. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365230

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Enhancement of the resonant peak current through the ground quantum-well state at room temperature is observed at a low voltage by adding the second quantum-well structure to the AlAs/GaAs (001) double-barrier single quantum-well heterostructure. The peak to valley current ratio increases slightly with the increasing temperature up to room temperature, and shows stable characteristics up to high temperature in this AlAs/GaAs (001) triple barrier heterostructure. The results indicate that the optimum alignment of the Fermi level with the lined-up quantum-well states can greatly improve the resonant peak current in the low voltage range, and therefore device characteristics. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365231

出版商:AIP    

年代:1997

数据来源: AIP