摘要:

The adiabatic elastic constants of holmium were determined in the temperature range from 78 to 300 K, using high‐purity single crystals. The constants were obtained from the ultrasonic‐wave velocities (20 MHz) measured by the pulse‐superposition method. The values of the constants at room temperature in units of 1011dyn/cm2arec33=8.015,c44=2.592,c11=7.612,c12=2.600, andc13=2.072. Using these values, the Debye temperature was computed to be 181 K. The sound velocities tend to vary with temperature in an anomalous fashion near the Ne´el temperature(TN=131 K). Attenuation and sound‐velocity measurements nearTNpermit an estimate of the relaxation time for spin fluctuations, which was found to be 3×10−10sec.

ISSN:0021-8979    

DOI:10.1063/1.1661857

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An analysis of acoustic waves in viscoelastic materials reveals that the stress relaxation function for such materials can be evaluated from acoustic dispersion data. In this paper we illustrate this method by evaluating the longitudinal stress relaxation function for the solid polymer, polymethyl methacrylate (PMMA) using previously reported acoustic data. From this result, we deduce the relaxation function appropriate for describing the shock wave response of PMMA by specifying the time‐scale characteristic of plate impact experiments. This relaxation function compares well with the function determined from the experimental observations of steady shock waves in PMMA.

ISSN:0021-8979    

DOI:10.1063/1.1661858

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The specific energy loss of4He ions in silicon has been determined in the energy range 420–2750 keV. Several different methods of determining the specific energy loss were used to check the results. Studies were made of the variation of specific energy loss with silicon density and showed that lower‐density amorphous silicon has relatively higher specific energy losses. Studies were also made of the specific energy loss of4He ions in radiation‐damaged silicon, polycrystalline silicon, and single‐crystal silicon. The values were then used in a thick‐target calculation to generate spectra of4He backscattering from silicon targets. These calculations were compared to experimental spectra over a range of energies and backscattering angles. All calculations were within 2% of the experimental spectra. The ``random'' spectrum from a spinning crystal target was compared to thick‐target calculations and shown to be useful as a normalizing spectrum with an accuracy of ±5%.

ISSN:0021-8979    

DOI:10.1063/1.1661859

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The spectrum functions of the reactant and the product of a second‐order reaction field concentration, for different spectral ranges, have been investigated with the application of Pao's concept of a simple continuous spectral cascading process for the transfer of turbulent kinetic energy, heat, and mass at large wave numbers. This consideration has been made under suitable conditions outlined in this paper.

ISSN:0021-8979    

DOI:10.1063/1.1661860

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Measurements of heat capacity as a function of temperature are used to evaluate the changes in heat content of three deformed polymers during isothermal annealing treatments. The polymers investigated are the same as those used in previous studies of length recovery, viz., amorphous polycarbonate (PC) and semicrystalline polyethylene (PE), and polypropylene (PP). Cold‐drawn PC is characterized by a smaller heat content than the undrawn material, while drawn PE and PP have larger heat contents than their undrawn forms. In all cases, the differences between the original and drawn states are of the order of a few cal gm−1. These differences are observed to anneal out completely in the case of PC heat treated in the vicinity of its glass transition, while only incomplete recovery is observed in the case of PE and PP. Activation‐energy spectra characterizing the recovery process are derived from the variation of heat content with annealing time. The spectra are centered about 22.6 kcal (g atm)−1for PC, about 24.1 kcal(g atm)−1for PE, and about 19.2 kcal(g atm)−1for PP. The spectra characterizing enthalpy recovery are similar to those derived previously from retraction kinetics, and indicate the similarity of relaxation processes involved in the two recovery phenomena.

ISSN:0021-8979    

DOI:10.1063/1.1661862

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The effect of 300‐keV proton bombardment and subsequent annealing on the optical absorption and electrical resistivity of bulkp‐type (p=2×1018and 1.4×1019cm−3) GaAs has been studied. Proton doses were in the range 1013−1017cm−2. It is found that bombardment‐induced optical absorption increases monotonically, but sublinearly, with proton dose. The shape of the optical transmission spectrum indicates that bombardment creates a distribution of energy levels extending into the forbidden gap. Activation energies for annealing of the optical absorption have been determined from isothermal annealing data and range from ∼1.5 to ∼3.4 eV, which indicates that at least two kinds of defects are involved. Current‐voltage measurements show that the average electrical resistivity of the bombarded layers goes through a maximum at ∼2.5×105&OHgr; cm at a proton dose of ∼3×1015cm−2. It is shown that annealing can eliminate the bombardment‐induced optical absorption while still retaining a high electrical resistivity. The optimum annealing time and temperature is a function of the proton dose. From these results a set of useful conditions for the proton‐bombardment fabrication of stripe‐geometry GaAs lasers is determined. Many qualitative similarities exist between the results presented here and those obtained in GaP, which are presented in the following paper.

ISSN:0021-8979    

DOI:10.1063/1.1661863

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The electrical and optical properties of proton‐bombardedp‐ andn‐type liquid‐encapsulated Czochralski‐grown GaP have been investigated as a function of 300‐keV proton dose and subsequent annealing. Proton bombardment of GaP introduced lattice damage into a surface layer equivalent in thickness to the proton penetration range, and resulted in a large increase in the electrical resistivity, as well as an increase in optical absorption of this damaged surface layer. The thickness of the damaged layer increased linearly with proton energy at approximately 1.0 &mgr;/100 keV in the energy range from 100 to 300 keV. Electrical resistivity in bothp‐ andn‐type samples increased with proton dose to a maximum of ∼1014&OHgr; cm at a dose of 4×1014protons/cm2, and then the resistivity decreased with increasing dose. Optical absorption spectra indicated a continuous distribution of energy levels extending into the band gap. The absorption at 6328 Å (visible red) increased monotonically with proton dose from ∼10% and 1014protons/cm2at 300 keV to ∼90% at 1017protons/cm2. Layers approximately 3.0 &mgr; thick have been produced which have high electrical resistivity (> 1010&OHgr;cm) and relatively low optical absorption (< 10%). The activation energies governing the annealing of the optical and electrical defects are in the range from 2 to 4 eV. The existence of large activation energies for the annealing of bombardment‐induced high resistivity implies high stability near room temperature. This stability combined with ease of forming high‐integrity pinhole‐free layers of controlled thickness on GaP substrates suggests useful applications in the GaP device fabrication technology. Many qualitative similarities have been observed between the proton‐bombarded GaP examined here and the bombardedp‐type GaAs discussed in the previous paper.

ISSN:0021-8979    

DOI:10.1063/1.1661864

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The depth distributions of boron atoms and of radiation‐induced defects are measured in the same set of silicon samples implanted with 100‐keV boron ions at room temperature to a dose of 1×1016/cm2, by utilizing the11B(p,&agr;)8Be nuclear reaction and by channeling analysis with 1.5‐MeV He+ions, respectively. Distributions of both boron atoms and the primary defects are asymmetric and significantly deviated from the Gaussian distribution. The width (FWHM) of the damage distribution is about 0.26 &mgr; and is much larger than that of boron distribution which is 0.09 &mgr;. The peak of the primary defect distribution is about 15% shallower than that of the boron distribution. The secondary defects have a Gaussian distribution, the peak depth of which almost coincides with that of boron distribution. The correlation between the electrical and the channeling measurements are also studied, and it is suggested that the secondary defects are strongly associated with boron atoms.

ISSN:0021-8979    

DOI:10.1063/1.1661865

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have measured the stress birefringence in several magnetic garnets (YIG, YbIG, GdTbIG, and CVBIG) and one nonmagnetic garnet (GdGaG). Measurements were made at room temperature by applying both a static uniaxial stress and a saturating magnetic field along ⟨100⟩ and ⟨111⟩ axes. Nonuniformities in the samples and the loading procedure made it valuable to measure the birefringence automatically as a small light spot scanned the crystal. It was found that the photoelastic effect is 2 orders of magnitude too small to account for the linear magnetic birefringence as a birefringence associated with the macroscopic magnetostrictive strain. The stress optical constantB(&Dgr;n/stress) in the magnetic crystals was found to be about −1.8×10−13cm2/dyn for stress along ⟨100⟩, and −3.0×10−13for stress along ⟨111⟩. Diamagnetic GdGaG has values forBof −1.2×10−13and −3.0×10−13, respectively. It seems plausible then that the tensors describing the photoelastic and magneto‐optic effects are not strongly coupled. The dispersion of the stress birefringence is very slight in the range 4000–10 000 cm−1, implying that the photoelastic effect arises from the remote transitions responsible for the refractive index.

ISSN:0021-8979    

DOI:10.1063/1.1661866

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Diode pumping of solid‐state lasers is analyzed. The analysis differs from more conventional analysis by the inclusion of a detailed calculation of the pumping rate and by the use of a Gaussian transverse intensity distribution as well as a circular approximation. Explicit expressions are obtained for the slope efficiency and the threshold. The temperature dependence of both parameters is investigated. Experimental results are obtained with a Nd : YAG diode‐pumped laser. These results are compared with the predictions of the analysis. The experimental results yielded a laser power output of 52 mW in TEM00modes at 269°K.

ISSN:0021-8979    

DOI:10.1063/1.1661867

出版商:AIP    

年代:1973

数据来源: AIP