摘要:

In this work, we study the origin of the optical losses in Al‐free InGaAsP/GaAs (&lgr;=0.808 &mgr;m) and InGaAs/GaAs/InGaP (&lgr;=0.980 &mgr;m) lasers. Theoretical modeling and the experimental results indicate that the scattering of the laser beam by refractive index fluctuation in the alloys is the dominant loss in our lasers, and the loss due to the free‐carrier absorption and scattering by interface roughness are negligible. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117751

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A novel micromechanical infrared (IR) radiation sensor has been developed using commercially available piezoresistive microcantilevers. Microcantilevers coated with a heat absorbing layer undergo bending due to the differential stress between the top layer (coating) and the substrate. The bending causes a change in the piezoresistance and is proportional to the amount of heat absorbed. The microcantilever IR sensor exhibits two distinct thermal responses: a fast one (<ms) and a slower one (∼10 ms). A noise equivalent power (at a modulation frequency of 30 Hz) was estimated to be ∼70 nW/Hz1/2. This value can be further reduced by designing microcantilevers with better thermal isolation that can allow microcantilevers to be used as uncooled IR radiation detectors. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117752

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We show that an asymmetrically chirped, single‐section distributed‐feedback (DFB) laser is capable of sustained self‐pulsations at frequencies in excess of 200 GHz. These pulsations arise from mode beating and are absent in uniform or symmetrically chirped DFB lasers. For sufficiently large coupling constants, the pulsation frequency can approach a terahertz. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117753

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The temporal and spectral evolution of soft x‐ray pulses (40–100 A˚) emitted from Al plasma produced by a pair of femtosecond Ti:sapphire laser pulses at normal incidence was studied. Both the soft x‐ray emission and the pulse duration increased with increase in the scale length of the preformed plasma. Prepulse enhanced soft x‐ray emission about 100 times with a pulse duration of 100–130 ps. A spectrally resolved time history revealed that the emission at shorter wavelengths started and decayed relatively more quickly, and emissions at longer wavelengths built up and decayed more slowly. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117754

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Calorimetric measurements and undercooling investigations were performed on the high‐melting, completely miscible binary systems (Co, Ni, Fe)‐Pd. The alloys, characterized by phase diagrams with concavous liquidus and solidus lines, exhibit heat‐of‐fusion values considerably lower than calculated assuming ideal solution behavior. As a consequence, these metallic systems offer the possibility to achieve the hypercooling regime at a reduced extent of undercooling. Investigations on the undercoolability of the liquid alloys indicate the surmounting of the calculated hypercooling limit. Time‐resolved radiation thermometry experimentally proved the appearance of complete isenthalpic solidification. Metallographic investigations of samples solidified from different levels of undercooling revealed the corresponding stages of microstructural evolution. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117755

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The desorption of hydrogen from a novel material, a Ti45Zr38Ni17‐H quasicrystal, was observed using high‐temperature powder x‐ray diffraction, demonstrating the potential utility of Ti‐based quasicrystals in place of crystalline or amorphous hydrides for hydrogen storage applications. The maximum observed change in hydrogen concentration was from 61 at. %, corresponding to a hydrogen‐to‐metal ratio (H/M) of 1.54, at 91 °C to less than 2.5 at. % (H/M=0.025) at 620 °C. The onset temperature of desorption is below 350 °C. Surface oxidation was found to promote the formation of crystalline hydride phases. Highly oxidized samples transformed to a mixture of the C14 Laves and C15 Laves crystalline hydrides, and the Ti2Ni phase. When the oxidation was less severe, a reversible transformation between the quasicrystal and crystalline hydride phases was clearly observed, demonstrating the stability of the Ti45Zr38Ni17quasicrystal at very low hydrogen concentrations, and temperatures as high as 661 °C. This is the first evidence for a stable Ti‐based quasicrystal and for reversible hydrogen storage in a quasicrystalline phase. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117756

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thin films of porous silicon formed by electrochemically etching silicon wafers changed color when exposed to an ambient atmosphere saturated in various organic solvent vapors. The degree of the color change was related to the refractive indices of the solvents. Analysis of the data using a four‐layer optical model indicated that the film refractive index increased up to 15% when solvent molecules replaced air in the pores. Solvent condensing from the saturated atmosphere filled up to 45% of the total void volume. Thermally oxidizing the films to make them hydrophilic resulted in surfaces which changed color upon exposure to water. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116819

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Microstructuring of Si with XeF2can be optimized by increasing the contrast in choosing a wavelength with minimal nonselective etching. The efficiency of selective etching with optimal quality can be increased by factors of 100 and 500 by using wavelengths around 120 and 110 nm, respectively, in comparison to longer wavelengths around 200 nm. The high efficiency of typically 10 removed atoms per photon, the availability of optical materials for imaging and the potentially high spatial resolution at 120 nm compared to the conventional excimer laser andI‐line wavelengths present a perspective for generating line densities required in the Gbit range. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116820

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Nonequilibrium molecular dynamics simulations have been employed to develop a mechanistic model for the development of an out‐of‐plane (fiber) texture in polycrystalline thin films. The depositing atoms preferentially sputter film atoms from grains with high surface energies. As the film grows, an atomic shadowing mechanism leads to the lateral growth of the grains with a height advantage—eventually leading to the occlusion of randomly oriented grains. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116821

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Epitaxial layers of CuInS2are grown on chemically hydrogen terminated Si(111) surfaces with 4° miscut by molecular beam epitaxy. The morphological and structural properties are determined by scanning electron microscopy, transmission electron microscopy, x‐ray diffraction, and texture analysis. The data show growth in the ⟨112⟩ direction and substantial twinning of the 75‐nm‐thick films. High‐resolution cross‐sectional micrographs of the interface indicate semicoherent epitaxial growth via an interfacial indium‐rich secondary phase. The pronounced faceting of the film surface is discussed in relation to twin lamellae. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116822

出版商:AIP    

年代:1996

数据来源: AIP