摘要:

It has recently been discovered that the pyroelectric and nonlinear optical properties of polyvinylidene fluoride (PVF2) closely resemble those of a ferroelectric. In this work, we investigate more fully the ``ferroelectric'' behavior of PVF2. Measurements of the pyroelectric properties and polarization reversal are described. Commercially available PVF2films have been used for radiation detection at 10.6 &mgr;m with responsivities of 17 V/W and noise equivalent power (NEP) of 15×10−9W/Hz1/2at 100 Hz (0.02‐cm2detector area). Although this NEP is considerably higher than that for other pyroelectric materials, this polymer seems particularly attractive in applications where ultimate detectivity is not required because of the great ease and low cost with which detector films can be constructed in any shape or size.

ISSN:0021-8979    

DOI:10.1063/1.1659927

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The localized‐vibrational‐mode absorption of ion‐implanted Al and P in GaAs is observed. The implants were done at room temperature with a flux of ∼3×1012ion/cm2sec and fluences of 2.0×1016, 2.8×1016, and 3.7×1016/cm2at 1 MeV. The &Dgr;n=1 transition of Al substitutional on the Ga sublattice and P substitutional on the As sublattice are observed, and liquid‐nitrogen‐temperature absorption measurements are made for isochronal anneals from 200 to 900°C. The Al‐implanted GaAs shows an AlGalocal mode near 362 cm−1and GaAs implanted with P shows a band near 355 cm−1similar to melt‐doped crystals, but with increased linewidths. From the integrated absorption, it is estimated that nearly all of the Al and P is AlGaand PAsafter 900°C anneal, and the site symmetry is approximately tetrahedral.

ISSN:0021-8979    

DOI:10.1063/1.1659928

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Localized vibrational modes of boron‐lithium pairs have previously been observed in silicon; the10B(11B) localized mode is split into an axial mode at 584(564) cm−1and a doubly degenerate transverse mode at 681(655) cm−1. In this work the infrared absorption bands of these modes were observed in boron‐doped lithium‐compensated GexSi1−xfor 0≤x≤0.12. The bands were slightly lowered in frequency and asymmetrically broadened by the addition of the germanium. The asymmetric shape results from the superposition of the absorption from boron atoms with different second‐neighbor configurations; the line shape is fit well by a simple model for interactions between the boron and Ge second neighbors and the assumption of random distribution of Ge throughout the crystal. The broadening is attributed primarily to lattice strain, the effect of the mass change being calculated to be far too small, and to modification of the Li&sngbnd;B interaction. It is found that the Li&sngbnd;B pairing distance must be smaller then the previously reported values of 2.4–2.9 Å. New bands at 553 and 651 cm−1, attributed to boron with a Ge first neighbor, are split off from the previously observed boron localized modes in the sample with 12% Ge. These are weaker than would be predicted by a random distribution of Ge, indicating that boron and Ge tend to avoid first‐neighbor pairs, or that the oscillator strength of the boron mode is lessened by a Ge first neighbor.

ISSN:0021-8979    

DOI:10.1063/1.1659929

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements have been made of the infrared absorption of GexSi1−xalloys forx≤0.12 andx≥0.88. The measurements were made in the range 100–700 cm−1at temperatures from 10 to 300°K. In Si‐rich alloys (x≤0.12) absorption bands are seen near 485, 400, and 125 cm−1which are essentially temperature independent, indicating a single‐phonon process. The bands do not correspond well with the predictions of simple models for resonance mode absorption, but are more nearly characteristic of the single‐phonon density of states for Si. In the Ge‐rich alloys (x≥0.88) the Si localized mode is observed as an absorption band at 389 cm−1forx=0.99, increasing to 394 cm−1atx=0.88. The absorption cross section &agr;peak/[Si] is only 4×10−21cm2, smaller by 102−103than observations for other local modes in semiconductors. Two‐phonon absorption bands at about 200 and 290 cm−1in Ge are enhanced by the addition of Si. The over‐all temperature dependence of the absorption strength is large enough that it is not obvious whether the observed enhancement is temperature dependent or is a temperature‐independent absorption, caused by the Si, superposed on a temperature‐dependent background.

ISSN:0021-8979    

DOI:10.1063/1.1659930

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Metastable Fe alloys containing up to 25 at.% Ga, obtained by rapidly quenching from the liquid state, have been studied using the Mo¨ssbauer effect. A least‐squares analysis of the data has allowed identification of individual configurations of atoms surrounding each Fe atom and the comparison of these configurations with various ordered and disordered states. Partial ordering of the BiF3type has been definitely observed at 25 at.% Ga, and the results suggest that is may extend to compositions as low as 20 at.% Ga.

ISSN:0021-8979    

DOI:10.1063/1.1659931

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Expressions for the centroid shift of a diffraction line due to geometrical factors have been deduced for a diffractometer case in which the specimen surface is inclined to the x‐ray beam at an arbitrary angle. Such a geometry is encountered in the determination of residual stress using a diffractometer. The effects of the centroid shift of a diffraction line due to geometrical factors on the stress derived from the diffractometer measurements have been discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659932

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements of ultrasonic attenuation due to the scattering of longitudinal elastic waves from a distribution of cavities in a solid medium are found to be consistent with theoretical predictions. Under certain conditions such measurements can be utilized to nondestructively characterize the size and number density of such a collection of scatterers.

ISSN:0021-8979    

DOI:10.1063/1.1659933

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Short‐duration light pulses accompanied by current pulses have been observed on warming KDP crystals x‐ray irradiated at 77°K. The pulses start a few degrees above the transition temperature (TC=123°K) and continue until about 200°K. The pulses appear only under ambient gas pressures above about 0.1 Torr. Warming of the irradiated crystal to an intermediate temperature betweenTCand 200°K causes only a partial exhaustion of the pulses, and after cooling and reheating pulses appear only above the temperature reached in the former cycle. The pulses originate from discharges into the surrounding atmosphere. A simple model is given to account for the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.1659934

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements of dielectric properties, pyroelectricity, and the electron paramagnetic resonance spectrum of Gd3+as a function of temperature have been used to examine the phase transitions in CsPbCl3. The results indicate the presence of five phase transitions and the loss of a center of symmetry at 194 K. The results together with the apparent order of the transitions, and published data, enable the Landau criterion to be used so that the point group of each phase may be identified. A reasonable choice of space group is also made.

ISSN:0021-8979    

DOI:10.1063/1.1659935

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A computer model was used to calculate the shape and average velocityvof a dislocation acted on by a viscous drag, and moving through a field of point obstacles. As a special case, the operation of a Frank‐Read source was computed also. At sufficiently low velocities (and stress levels), the behavior is governed entirely by the obstacle spacing and strength; conventional tensile testing probably falls in this regime. At sufficiently high velocities (and stress levels), the behavior is governed entirely by the viscous drag; shock deformation falls in this regime. In between lies a wide range in which the two effects superimpose, each contributing measurably to the flow stress. The strain rate sensitivitym= (∂lnv/∂ln&sgr;)T, where &sgr; is the stress, reflects this behavior. At low and high velocities, respectively,mcharacterizes the obstacles and the drag. But in betweenmis characteristic of neither, and in fact reflects the change in the contributions of the two strengthening mechanisms when the applied stress is changed.

ISSN:0021-8979    

DOI:10.1063/1.1659936

出版商:AIP    

年代:1971

数据来源: AIP