摘要:

A rotating‐anvil shear press was used to measure the friction coefficient and shear strength of thin layers of copolymers of tetrafluoroethylene with ethylene and hexafluoropropylene at room temperature at pressures up to 5 kbar. The friction coefficient of both copolymers decreased monotonically, approaching a small asymptotic value at high pressure. The shear strength of both materials increased approximately linearly with pressure. The ethylene copolymer exhibited a small discontinuity suggestive of a polymorphic transformation.

ISSN:0021-8979    

DOI:10.1063/1.1662161

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Infrared absorption spectra of five lithium silicate and six potassium silicate glasses of varying composition (20–35 mole% Li2O and 15–40 mole% K2O, respectively) are examined in the range 1500–100 cm−1. The frequencies of the main absorption bands decrease with an increase of alkali‐metal oxide (M2O) content, with the exception of the −960 cm−1shoulder for the lithium silicate glasses. The pressure dependences to[inverted lazy s]40 kbar, of all the main infrared absorption frequencies, which are pressure sensitive, are found to be positive. The values ofd &ngr;i/d Pare higher for potassium silicate glasses than for sodium and lithium silicate glasses. The effects of pressure are found to be opposite to the compositional effects. The Gru¨neisen mode &ggr;'s, &ggr;i, evaluated from the pressure dependence of the infrared absorption frequencies, are apparently related to the polarizing power of the alkali‐metal ion. The results discussed in light of previous high‐pressure infrared absorption studies of fused silica and sodium silicate glasses clearly indicate that &ggr;i, &ggr;th, and &ggr;HTgenerally increase withM2O content in alkali silicate glasses.

ISSN:0021-8979    

DOI:10.1063/1.1662162

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Thermally stimulated current (TSC) was obtained under a small bias voltage from low‐density polyethylene which had been subjected to a high electric field. Two peaks were found at 50 and 85°C with apparent activation energies of 1.2–1.3 eV and 1.4–1.5 eV, respectively. These peaks were attributable to the drift of thermally released carriers under the external bias field. On comparison of the activation energies obtained from the TSC and the isothermal steady‐state conduction currents, the results were explained successfully with a field‐assisted trapping model where a trap is surrounded by a Coulomb repulsive barrier for electron capture.

ISSN:0021-8979    

DOI:10.1063/1.1662163

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Pulsed room‐temperature laser action has been observed in Nd3+: LiYF4at 1053 nm. A threshold of 8 J and a slope efficiency of 0.82% was obtained with a 60% reflectivity output mirror. These results are compared to Nd3+: YAG data taken in the same cavity. Loss coefficients are calculated for each material and are compared.

ISSN:0021-8979    

DOI:10.1063/1.1662164

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Low‐temperature photoluminescence spectra are presented for Si crystals which have been irradiated with high‐energy electrons. Studies of isochronal annealing, stress effects, and the temperature dependences of the luminescence are used to discuss the nature of the luminescent transitions and the properties of defects. Two dominant bands present after room‐temperature anneal of irradiated material are discussed, and correlations of the properties of these bands are made with known Si defects. A band between 0.8 and 1.0 eV has properties which are related to those of the divacancy, and a band between 0.6 and 0.8 eV has properties related to those of the Si‐G15 (K) center. Additional peaks appear in the luminescence after high‐temperature anneal; the influence of impurities and the effects of annealing on these lines are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662165

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Lithium doping has a dramatic effect on the low‐temperature photoluminescence of electron‐irradiated Si. In oxygen‐lean Si with Li doping, a new irradiation‐dependent luminescence band between 0.75 and 1.05 eV is observed, which is dominated by a zero‐phonon peak at 1.045 eV. This band is believed to be due to radiative transitions involving a Li‐modified divacancy. This band is present also in oxygen‐rich, Li‐diffused Si and is accompanied by bands previously related to the si‐G15 (K) center and the divacancy. The intensities of the Li‐modified divacancy and Si‐G15 (K) center bands are relatively weak in the oxygen‐rich material, apparently due to the formation of lithium‐oxygen complexes which reduce the concentration of unassociated interstitial Li and O.

ISSN:0021-8979    

DOI:10.1063/1.1662166

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The normal spectral emissivity of an indirectly heated wafer of single‐crystal NiO has been measured for &lgr; = 0.645 &mgr;m and &lgr; = 0.546 &mgr;m. The NiO was characterized by a room‐temperature resistivity of 7 × 1010&OHgr; cm, and the measurements were made using a thermal equivalent of an electrical potentiometer consisting of an incandescent NiO surface as the ``unknown'', a tantalum blackbody furnace as the ``standard'', and a thermoprobe as a ``comparison device'' with which the surface temperatures of the ``unknown'' and the ``standard'' may be compared. This arrangement is useful for the determination of emissivities of substances which are not readily fashioned into blackbodies. It is found that NiO is a very good emitter having an emissivity which ranges from about 0.94 to 0.90 as the temperature is varied from 1100 to 1500°K; and that the emissivity in the red is almost identical to the emissivity in the green. These results permit the speculation that NiO may well radiate as an almost black graybody over the red‐green range within the temperature interval stated. The effects of the temperature gradients normal to the surface, which occur as a consequence of the indirect method of heating the wafer, have been examined in detail, but the influence of these nonisothermal conditions was found to be negligible when compared to the limits of error except around the highest temperatures used for the measurements in the green. The intrinsic isothermal emissivities of NiO in the red and in the green were found to be &egr;0.645 &mgr;m= − 691 (5) × 10−8T+ 1.001 (7) and &egr;0.546 &mgr;m= − 959 (2) × 10−8T+ 1.033 (1), respectively.

ISSN:0021-8979    

DOI:10.1063/1.1662167

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The expressions for the normal and the directional spectral emissivity of effectively infinite slabs (that is, slabs that are virtually opaque to radiation) of transparent materials in the presence of constant temperature gradients normal to the surface are derived; the results are related to the isothermal emissivities, and conditions are specified under which the effects of the temperature gradient may be neglected. The ambiguity, which rests in the fact that the slab is not at the same temperature throughout, is resolved by defining the emissivities in relation to a comparison blackbody which is at the surface temperature of the slab.

ISSN:0021-8979    

DOI:10.1063/1.1662168

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The initial switch in polycrystalline V2O5specimens (300–400 &mgr; thick) at room temperature is associated with melting caused by power‐induced Joule heating and also with a color change from yellow‐orange to black. The resulting black material exhibits threshold switching. High‐pressure studies show a pressure dependence on threshold power for V2O5, and on threshold field for an amorphous chalcogenide. Low‐temperature studies indicate an increase in turnover power with decreasing temperature for V2O5. High‐temperature studies show that V2O5melts with decreasing resistivity at about 690°C.

ISSN:0021-8979    

DOI:10.1063/1.1662169

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A recent investigation of the binary borosilicate glass system has led to the realization of a useful cladding material for pure fused silica core fiber optical waveguides. The feature which makes the borosilicate glass useful is that its index of refraction is sufficiently less than that of pure fused silica to allow light guidance in silica core‐borosilicate clad fibers. The previous work offered no explanation for the observed but unexpected behavior of the borosilicate refractive index. Continued studies of this glass system have now led to a quantative explanation of the refractive index behavior. Two theoretical approaches are discussed. One is based on the Sellmeier dispersion model and the other on a molar refractivity analysis. The main quantities of interest turn out to be density, composition, structure, and ionicity. An important prediction based on this work is that properly quenched borosilicate glass can have a refractive index even lower than previously observed. This prediction was subsequently confirmed and has the the practical consequence of allowing the waveguide designer greater latitude in his choice of variables. A further observation is that borosilicate glasses exhibit larger ``energy gaps'' than composite glasses such as soda‐lime‐silicates, and may therefore be more desirable from the point of view of absorption loss.

ISSN:0021-8979    

DOI:10.1063/1.1662170

出版商:AIP    

年代:1973

数据来源: AIP