摘要:

The conversion efficiency of ZnS transducers evaporated on a glass substrate for elastic surface waves has been measured as a function of the ZnS film thickness and analyzed by using a simple model. It is found that the thickness dependence of the conversion efficiency is affected by elliptic particle motion at the position of electrodes located at the interface between the ZnS film and the substrate (type I) or at the surface of the ZnS film (type II). Conversion efficiency calculated from the potential induced at the electrodes is in good agreement with the experiments. The analysis shows that the internal impedance of the thin‐film transducer is not simply proportional to &Dgr;vs/vs, where &Dgr;vsis the perturbation in surface‐wave velocity when the electrodes are replaced by a thin‐film perfect conductor. Theory suggests that type I is most efficient when the thickness is about 0.4 times the surface wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1662603

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In an abnormal dc glow discharge sputtering system the current at a constant voltage and pressure is often found to decrease from an initially high value to a steady‐state level as the cathode surface is sputtered. We have investigated the relationship between this decrease in current and the level of cathode surface contamination by periodically analyzing the surface during sputter cleaning using the soft x‐ray appearance potential technique. We find that the excess initial current results from contaminating gas liberated from the chamber wall and cathode surface by the action of the discharge. The rate at which cathode surface contaminants are removed and the residual level that is indicated by the steady‐state discharge current are both strongly dependent on the over‐all cleanliness of the discharge system. With proper attention to cleanliness, however, it is found that the steady‐state discharge current can be used as a process control variable, indicating the attainment of a relatively clean cathode surface.

ISSN:0021-8979    

DOI:10.1063/1.1662604

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Available techniques for the chemical analysis of epitaxial semiconductor films are limited because of typical sample thicknesses of 0.7–10 &mgr;m. The use of glow‐discharge optical spectroscopy was investigated as an analytical technique. GaAs was dc sputtered in Ar and the glow discharge monitored for the electroluminescence associated with one or more target elements. The present detection limit for Sn in GaAs is 3×1016atoms cm−3for a volume sputtering rate of 1.5×10−5cm3/min. The luminescent intensities combined with sputtering rates were used to estimate concentration profiles as a function of depth for GaAs1−xSbxfilms grown on GaAs. Sputtering yields have been measured for GaAs over the range 0.5–3 kV and found to vary with orientation in the following order: (111)As, (111)Ga, (211), and (110).

ISSN:0021-8979    

DOI:10.1063/1.1662605

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A calculation is made of the absorption current, dielectric constant, and dielectric loss expected from electron tunnelling into a single trapping level in a dielectric. Plots are given of current versus time, and of dielectric constant, dielectric loss, and loss tangent against frequency. This model reproduces the approximatet−ndependence of absorption current (t=time, n≃1) and nearly constant tan&dgr; observed experimentally in many insulators. Numerical comparison with experiment shows that this model may apply to the case of high polymers, but is unable to account for the higher absorption currents occurring in oxides and similar inorganic dielectrics.

ISSN:0021-8979    

DOI:10.1063/1.1662606

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The formation of helium blisters on the (111) surface planes of monocrystalline niobium by implantation of 0.5–1.5‐MeV helium ions has been investigated for total doses ranging from 0.1 to 1.0 C/cm2for different target temperatures, angles of incidence of the projectiles, and channeling conditions. The results indicate that the blister shape is strongly dependent on target temperature. At 900 °C and for channeled projectiles, almost all the blisters have a threefold symmetry resembling a ``crow‐foot'' shape. The alignment of the crow‐foot blisters with respect to each other exhibits an asymmetry in that their prongs are aligned along only one set of ⟨112⟩ directions of the host niobium lattice such as [12¯1], and [112¯], and [2¯11] directions and not along the other equivalent set such as the [1¯21], [1¯1¯2], and [21¯1¯] directions. As the target temperature is lowered, the tendency to form dome‐shaped blisters increases; at room temperature only dome‐shaped blisters form. The average blister size appears to increase with decreasing target temperature, with increasing degree of channeling, and with increasing projectile energy; at room temperature the last of these variables is the one with the most pronounced effect on the size. The blister density is more than two orders of magnitude less for channeled projectiles than for unchanneled ones for irradiation at a target temperature of 900 °C. For the unchanneled projectiles, the angle of incidence of the projectiles does not appear to change the morphology of the blisters significantly.

ISSN:0021-8979    

DOI:10.1063/1.1662607

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In order to investigate the role of firing atmosphere on the rate of transformation of a ZnS crystal, crystalline ZnS of hexagonal or cubic form was fired for 0.5–24 h at 800 and 1050 °C in each atmosphere of He, HCl, H2S, H2, O2, and their various mixtures, and the crystal structure of the fired ZnS was analyzed by x‐ray diffraction. At 800 °C, the transformation from hexagonal to cubic form occurred slightly in O2and H2S, markedly in HCl, but hardly at all in He and H2although NaCl was added. At 1050 °C, the transformation from cubic to hexagonal form occurred easily in all atmospheres except H2and notably in HCl. The transformation occurred in H2with added NaCl more easily than in pure HCl. Based on these results, it is concluded that the rate of transformation of a ZnS crystal is influenced both by the formation of defects, which result in the contact reaction between the atmosphere and the surface of the ZnS crystal, and by the bulk diffusion of anions (S2−and O2−).

ISSN:0021-8979    

DOI:10.1063/1.1662608

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A model has been developed to predict the lifetime &tgr;fof integrated circuit metalizations which operate at high dc densitiesJe. Grain‐boundary electromigration, internal heat generation, and current crowding at growing voids dominate the rate processes that lead to failure. Joule heating of the stripe causes an initial temperature rise &Dgr;T0and heat flow into the substrate. If this rise is appreciable an instability exists in the stripe. When vacancies electromigrate down grain boundaries and precipitate on a suitable boundary, forming an elongated void, the electric current will be diverted. This is serious if the crack has a substantial length component perpendicular to the current flow which increases vacancy currents to the crack tip and the local heating. An analytical model considering these effects and the time for a crack to propagate across the stripe width yields a stripe lifetime integral which fits the formPn=(1/2)(1+0.265&ggr;&Dgr;T0). Here &ggr;=&Dgr;H/kT2is the temperature coefficient of the diffusion constant.Pn, the crack width, and the initial electromigration grain boundary flux then largely determine the stripe lifetime. The self‐heating contribution &Dgr;T0is shown to be an important term in the interpretation of accelerated test data and for proper extrapolation to lower temperature‐and‐current stress levels. The stripe temperature coefficient of resistance and melting point are shown to have only secondary effects on lifetime. Lifetimes have aJe−ndependence withnvarying from unity at low &Dgr;T0levels to 15+ for high &Dgr;T0levels and are determined by the stripe and heat‐sink temperatures. For maximum stripe lifetimes, wide stripes with good thermal coupling to the heat sink are desirable.

ISSN:0021-8979    

DOI:10.1063/1.1662609

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The spontaneous electric polarizationPshas been measured for Gd2(MoO4)3over the temperature range from 4.2 °K to the Curie point. Near 4 °K the maximumPsis slightly less than 0.29 &mgr;C/cm2with a very low temperature coefficient. An electric field enforced phase transition from paraelectric to ferroelectric at temperatures just above zero‐fieldTcdemonstrates the first‐order nature of the phase change. Better agreement was found nearTcbetweenPsand the relation (T − T1)1/3than betweenPsand a Landau‐type function.

ISSN:0021-8979    

DOI:10.1063/1.1662610

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The growth process and the microstructure of very thin W films (80–500 Å) deposited by rf sputtering on SiO2and Si substrates have been observed by transmission electron microscopy (TEM). The resistivity and stress in these films have been related to the film microstructure, composition, and to the deposition conditions (substrate bias and rf deposition power). Thin W films deposited on silicon dioxide substrates under zero or positive bias have been found to grow in two distinct growth stages. Stage I corresponds to the formation of a thin continuous film (80–100 Å thick) of &bgr;‐W. The &bgr;‐W phase has the A‐15 crystal structure and has been identified as a faulted W3W compound. A small grain size (50–100 Å) is characteristic of the &bgr;‐W film. Stage II corresponds to the transformation of the &bgr;‐W film into a pure &agr;‐W film with the bcc crystal structure. This thermally activated phase transformation takes place in the temperature range 100–200 °C. It is characterized by the growth of &agr;‐W nuclei until complete coalescence of the &agr;‐W islands; the resulting &agr;‐W film consists of large grains (1500–2500 Å) which are free of dislocations. The end of stage II occurs for a critical film thicknesstcbeyond which the film is a continuous &agr;‐W film. The value oftcis controlled by the rf deposition power and the substrate temperature. On the other hand, films deposited on negatively biased substrates do not contain the &bgr;‐W phase. These films consist of large &agr;‐W grains (1500–2000 Å) with a high dislocation density. The resistivity of thin W films deposited under zero or positive bias is controlled by the amount of &bgr;‐W present in the film. The pure &bgr;‐W films have a high resistivity (100–300 &mgr;&OHgr; cm); after the complete transformation &bgr;‐W→&agr;‐W the large resistivity (30–40 &mgr;&OHgr; cm) of these films is attributed to scattering by impurities. In particular, the lower resistivity of W films deposited under negative bias is related to their lower oxygen content. The sign and magnitude of the stress in these films are also controlled by the film microstructure, It is found that the stress in the films containing the &bgr;‐W phase is always tensile with a &sgr; of (6–12) × 109dyn/cm2. The films consisting of &agr;‐W are always compressively stressed in the range (2–12) × 109dyn/cm2.

ISSN:0021-8979    

DOI:10.1063/1.1662611

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A thin lithium wire was extruded and exploded in vacuum and the resulting plasma was studied during the first 2 &mgr;sec of the discharge. Included in the study were scattering of aQ‐switched ruby laser beam, high‐speed streak photographs showing the laser‐plasma interaction, and time‐resolved emission spectra. The low pressure in the discharge chamber of 5×10−5Torr prevented current shunting and also resulted in a ``clean'' lithium emission spectrum. The electron density calculated from mass conservation and temperature varied from 1017to 1019cm−3as the plasma column oscillated in diameter. These densities matched those obtained from a Fresnel reflection model very well. Broadening or shifting of the scattered light was less than 1 Å and the intensities yielded electron densities from 2×1019to 1022cm−3when interpreted as cooperative electron scattering. The emission spectra from 3500 to 6900 Å showed three Li I, seven Li II, one Li III, and one unidentified line. The spectroscopic temperature obtained from various line ratios averaged about 4 eV, whereas the temperature found from a simple ``snowplow'' model analysis varied from 4 to 25 eV. The electron density measured by Stark broadening of emission lines compared well with the average density obtained through mass conservation.

ISSN:0021-8979    

DOI:10.1063/1.1662612

出版商:AIP    

年代:1973

数据来源: AIP