摘要:

Dielectric properties, lattice‐ and microstructure of ceramic BaTiO3showing grain sizes of 0.3–100 &mgr;m were studied. At grain sizes <10 &mgr;m the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter. The decreasing width of the domains can be theoretically explained by the equilibrium of elastic field energy and domain wall energy. The smaller the grains, the more the dielectric and the elastic constants are determined by the contribution of 90° domain walls. The permittivity below the Curie point shows a pronounced maximum &egr;r≊5000 at grain sizes 0.8–1 &mgr;m. At grain sizes <0.7 &mgr;m the permittivity strongly decreases and the lattice gradually changes from tetragonal to pseudocubic.

ISSN:0021-8979    

DOI:10.1063/1.336051

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Experimental and computational methods are presented for the complete characterization of the thermoluminescence response obtained from thermoluminescent phosphors upon exposure to localized Gaussian laser heating beams. A number of different phosphor configurations are described as examples. These include LiF:Mg,Ti (TLD‐100, Harshaw Chemical Corporation) in form of chips, which are widely used in the dosimetry of ionizing radiation, and thin‐layer dosimeters prepared either as self‐supporting films or powder in a polyimide matrix, or on substrates of LiF single crystals or borosilicate glass. It is demonstrated that all relevant optical and thermal properties of the dosimeters can be determined by these methods and that, based on this knowledge, the expected thermoluminescence response of a given configuration can be simulated as a function of a number of experimental parameters.

ISSN:0021-8979    

DOI:10.1063/1.336052

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Thin films of &agr;‐sulfur were prepared on quartz plates by a high‐vacuum thermal‐evaporation method. In an optical investigation of the thin films at room temperature, a direct allowed transition at 4.43 eV was observed. An indirect allowed transition was also observed with a band gap of 2.61 eV and assisting phonons of 0.11 eV. These observations were supported by reflectivity data obtained by an integrating sphere.

ISSN:0021-8979    

DOI:10.1063/1.336053

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We report the first observation of free exciton transitions (X), as well as donor and acceptor bound exciton transitions (D0X,D+X, andA0X), in the high‐resolution photoluminescence (PL) spectra of high‐quality AlxGa1−xAs layers grown by molecular beam epitaxy (MBE) over the composition range 0.01≤x<0.2. This observation contrasts markedly with several previous investigations of AlxGa1−xAs samples of somewhat higher composition (x>0.2) in which only one or two bound exciton transitions have been reported together with the typically observed carbon free‐to‐bound transitions (e,A0). From a systematic study of MBE growth and PL spectral characterization, we find that both the free and bound exciton transitions of the AlxGa1−xAs layers correlate to their counterparts in high‐purity MBE GaAs layers and that their photon energies increase linearly with increasingxvalue, as expected for these low AlAs mole fraction samples. At compositions as low as 2.1%, and as high as 12.5%, spectral linewidths ofD0Xtransitions were found to be as narrow as 0.3 and 2 meV, respectively, in reasonably good agreement with the recent PL linewidth predictions of Singh and Bajaj which are based on a theory of alloy scattering. These observations confirm the high quality of the lowx‐value AlxGa1−xAs samples which were grown to thicknesses between 1 and 2 &mgr;m at substrate temperatures approaching 700 °C in a MBE system having low background impurity contamination.

ISSN:0021-8979    

DOI:10.1063/1.336054

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The decay of excess carriers induced in a semiconductor sample by a laser pulse is studied. The decay rate is proved to be independent of the spatial dependence of the hole‐electron generation rate provoked by the laser beam. The effect of surface recombination can be minimized by waiting until the response drops to about 1% of its initial value. The accuracy of photoluminescence decay measurements of Auger lifetime is examined in view of this and other criteria developed here.

ISSN:0021-8979    

DOI:10.1063/1.336055

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Properties of rf‐sputtered molybdenum oxide films for electrochromic display devices have been investigated. This report mainly concerns the dependence of the properties on the oxygen concentration in the sputtering atmosphere. The oxide films were prepared by rf sputtering from a compressed powder MoO3target under an operating pressure of 4×10−2Torr using a mixture of Ar‐0.5–50% O2. Electrical resistivity of the films formed increases with increasing oxygen concentration in the sputtering atmosphere and ranges from 2.5×1010to ∼1×1012&OHgr; cm. Spectral transmittance of the films is about 85% in the visible and near‐infrared region. Optical band gap and refractive index of these films are 2.67–2.76 eV and 2.01–2.26, respectively. Electrochemichromic properties of the films were also studied using asymmetric cells, and it was found that a good electrochromic performance was obtained usually by the cells composed of the films with a resistivity of 2.5×1010&OHgr; cm.

ISSN:0021-8979    

DOI:10.1063/1.336307

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We present results of computer simulations of the characteristics of amorphous silicon alloyp‐i‐nsolar cells in both undegraded and degraded conditions for illumination through then+orp+layers. Changes in device performance upon degradation correlate well with realistic changes in the minority carrier diffusion length of the intrinsic layer. The results of our model are in good agreement with experimental data and lead us to conclude that the observed degradation in the electronic properties of amorphous silicon alloys are only consistent with the observed increases in the localized state density if the photoinduced metastable defects have larger capture cross sections than the localized states in as‐deposited material. The analysis of recombination losses shows that upon degradation, primarily because of the decrease in the minority carrier diffusion length, cells illuminated through then+layer exhibit a loss of short‐wavelength response whereas those illuminated through thep+layer exhibit a loss of long‐wavelength response.

ISSN:0021-8979    

DOI:10.1063/1.336056

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We utilized photoluminescence (PL) spectroscopy underinsituconditions to study slow chemical changes on CdSe/polysulfide liquid‐junction solar cells, as a function of aging procedures. The aging conditions were (1) focused light under open‐circuit conditions; (2) focused light under short‐circuit conditions; and (3) total darkness. For the first time we report that cells do age under open‐circuit conditions, and that the decrease in stability and the changes in the PL, with aging time, are similar to those observed for cells which are aged under short‐circuit conditions. At the initial stages of the light‐induced aging processes, changes in the defect concentration in the photoanode were observed. In addition to the CdSe PL there is a broad PL in the spectral range of 1.7 eV (CdSe) up to 2.4 eV (CdS). This PL is identified to be due to the mixed phase compound of CdSe1−xSx. At the final stages of the aging processes characteristic CdS Raman spectra was detected. Such PL and Raman changes were not detected for the cells which were aged under total darkness. Underexsituconditions the envelope of two PL spectra due to CdSe and CdSe1−xSxcompound changes with the excitation light. Variation of efficiency and PL peak intensity with aging time shows a good correlation between PL peak intensity and the efficiency of the cell.

ISSN:0021-8979    

DOI:10.1063/1.336057

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Magnetic characteristics have been investigated for a magnetoresistive thin‐film sensor biased using a permanent magnet thin film. Here, Co‐Pt thin film is applied to the device as a bias film. Such microlithographed Co‐Pt thin films show the same magnetic properties as as‐sputtered films. Biasing strength depends on the permanent magnet film thickness, its composition or magnetic properties, and the biasing angle. The output of the sensor is very high.

ISSN:0021-8979    

DOI:10.1063/1.336058

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Conductivity and magnetic circular dichroism (MCD) in the near infrared are measured inp‐type Ca‐doped yttrium iron garnet films. Two MCD components are known to arise in these films, associated with Ca2+substitution: one peaked at about &lgr;=1.2 &mgr;m, the other one at &lgr;=1.6 &mgr;m. We show that the center responsible for the &lgr;=1.6 &mgr;m component is the only one responsible for the remarkable electrical properties recently reported for these films. The other center provides charge compensation of Ca2+which is uneffective from the point of view of conduction which may be thus considerably enhanced by inhibiting formation of this center.

ISSN:0021-8979    

DOI:10.1063/1.336059

出版商:AIP    

年代:1985

数据来源: AIP