摘要:

In the soldering reaction at 200 °C between eutectic SnPb and plated Pd/Ni on Cu leadframes, two thicknesses of Pd of 760 and 2500 Å were used. Even very thin Pd can lead to continuous spreading of the solder on the leadframe; no stable wetting angle can be observed. Anisotropic spreading and spike formation were found due to the mechanical effect of rolling of the leadframe, and they are more pronounced in the thinner Pd samples. In the interfacial reaction, we have observed the formation of a ternary Pd–Ni–Sn compound andNi3Sn4.While spalling of the ternary compound occurs, no spalling of theNi3Sn4was found. The latter forms a rather uniform layer consisting of small scallop-type grains. We found that the growth rate ofNi3Sn4is much slower, by a factor of about 10, than that ofCu6Sn5in the reaction between Cu and eutectic SnPb. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120434

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Mass transport caused by buoyancy convection in front of the solid–liquid interface was evaluated in terms of measurements of primary dendritic spacing combining with separation of the effective (or integral) mass transport coefficientDL.It was shown thatDLin normal gravity (1g) condition was 1.64 times as high as that in microgravity (&mgr;g) condition at the cooling rate(v)of 0.056 K/s forPd40Ni40P20alloy. The higherDLvalue is due to the contribution of buoyancy convection on the ground. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119469

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

PolarizedCo Kedge extended x-ray absorption fine structure measurements obtained with electric vector parallel and perpendicular to the film plane indicate differences in Co bonding along these two directions in room-temperature evaporatedCo0.16Pd0.84alloy films. A local modulation of the Co fraction whose amplitudes are 0.05–0.09 exists along the growth direction in the alloy films. Pd underlayer and Pd spacer layers alternated with the alloy layer induce coherency strains resulting in an anisotropic effective strain state. Both anisotropic strain and local compositional modulation are likely to contribute to the perpendicular magnetic anisotropy observed in these alloys. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119470

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An optical spectroscopy, based upon the determination of the difference between the reflectivity forp-polarized light (Rp) and the squared reflectivity fors-polarized light (Rs2) with an angle of incidence of 45°, is proposed to study the interaction of excitons with the surface potential in semiconductors. It is found thatRp−Rs2as a function of the wave frequency is quite sensitive to the form of the surface potential. In addition, the generation of longitudinal modes such as the quantized polarization waves of excitons produces resonant dips well-identified in the new spectrum. On the other hand, the transverse resonances present inRpandRsdisappear in the differenceRp−Rs2.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119471

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The first observation of atomic long range ordering inAlxGa1−xNthin films grown by electron cyclotron resonance assisted molecular beam epitaxy on sapphire and 6H-SiC substrates is reported. The phenomenon was investigated by studying the superlattice peaks (0001), (0003), and (0005) using x-ray diffraction. The relative intensity of these peaks was found to be largest for Al content in the 30&percent;–50&percent; range in qualitative agreement with expectations for an ordered structure of idealAl0.5Ga0.5Nstoichiometry. The average size of the ordered domains in the films was found to be within a factor of 4 of the films’ thicknesses. The degree of ordering depends on the III/V flux ratio and exhibits a weaker dependence on Si doping. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119916

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ultrafast heating of cold holes is investigated in bulk GaAs using a high-sensitivity two-color absorption saturation technique. Measurements performed as a function of the lattice temperature and of the carrier excess energy show that absorption of optical phonons is the main hole heating mechanism for the investigated temperatures in the range 100–300 K. Using a numerical model for carrier dynamics, the optical deformation potential is estimated to bed0∼40 eV.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119472

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this letter, we describe the characteristics of molecular beam epitaxy GaAs/AlGaAs quantum-well infrared photodetectors (QWIP’s) grown on a GaAs substrate, and on a GaAs-on-Si substrate produced by metalorganic chemical-vapor deposition. Important issues for QWIP applications such as dark current, spectral response, and absolute responsivity are studied. We find that compared to a similar detector structure grown on a GaAs substrate, the detector grown on a GaAs-on-Si substrate exhibits similar dark current and absolute responsivity while displaying a small blueshift in the spectral response. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119473

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ferroelectric bismuth-layerSrBi2Ta2O9(SBT)thin films were prepared onPt/Ti/SiO2/Sisubstrate by plasma-enhanced metalorganic chemical vapor deposition. The films were crystallized at temperatures between 500 and 600 °C. The dielectric constant and dissipation factor of SBT films were 320 and 0.04 at an applied frequency of 1 MHz, respectively. The remanent polarization(Pr)and the coercive field(Ec)obtained for a 200 nm thickSr0.9Bi2.3Ta2.0O9films deposited at 550 °C were15 &mgr;C/cm2and 50 kV/cm at an applied voltage of 3 V, respectively. The leakage current density was about5.0×10−8 A/cm2at 300 kV/cm. The films showed fatigue-free characteristics up to1.0×1011switching cycles under 6 V bipolar pulse. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119475

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of hydrogen dilution of up to 54:1(=H2:SiH4)on hydrogenated amorphous silicon germanium (a-SiGe:H) was investigated at a low substrate temperature, while keeping the optical gap(Eopt)constant. It was found that deterioration of the film properties, when substrate temperature decreases, can be compensated by the high hydrogen dilution method. As the substrate temperature decreases from 230 to 180 °C, the high photoconductivity, high photosensitivity, and low silicon dihydride content ofa-SiGe:H can be maintained with a high hydrogen dilution ratio of 54:1, although these properties becomes worse with conventional low hydrogen dilution ratios. Probably, hydrogen radicals substitute for the surface reaction energy lost by decreasing the temperature. Besides,a-SiGe:H films deposited under higher hydrogen dilution have more germanium and less hydrogen content than those of the conventional films, despite having the sameEopt.One possible explanation for whyEoptcan be kept constant is the suppression of the formation of Ge–Ge bonds at the growing surface by the energy supplied by the hydrogen radicals. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119476

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Detailed studies of the often-observed resonance feature near 3.4 eV in the reflectance difference spectrum ofSi/SiO2interfaces and Si surfaces show that the resonance is due to the intrinsic local-field effect, and that its energy position coincides with theE1energy of bulk Si. Using the energy position of the resonance of the pseudomorphically grownSi/CaF2interfaces as a reference point, the strain-induced resonance energy shift of the Si interface layer at severalSi/SiO2interfaces are obtained and the strain in these layers is determined. The results show that the interface layers are highly strained with an equivalent hydrostatic pressure of 0.79 GPa, but still maintain a high degree of order. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119477

出版商:AIP    

年代:1997

数据来源: AIP