摘要:

Laser‐excited, time‐resolved spectroscopy techniques were used to investigate the characteristics of energy transfer in YVO4:Nd3+crystals. The temperatuare and time dependencies of the energy transfer rates were determined for both host‐sensitized and impurity ion interaction processes. The former process is found to have characteristics consistent with the migration and trapping of localized host excitons whereas the latter process is consistent with multistep energy migration via a two‐phonon‐assisted electric dipole‐dipole interaction mechanism.

ISSN:0021-8979    

DOI:10.1063/1.327950

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We present the results of a theory describing the saturation behavior ofp‐type GaSb, AlAs, AlSb, and InAs for light having a wavelength near 10.6 &mgr;m. The dominant absorption mechanism is direct intervalence band transitions where a free hole in the heavy‐hole band absorbs a photon and makes a transition to the light‐hole band. The decrease in the absorption coefficient with increasing intensity is found to be closely approximated by an inhomogeneously broadened two‐level model, and values of the saturation intensity are reported for each material. We analyze the systematic dependence of the saturation intensity on the material parameters. We also report the temperature dependence of the saturation intensity near room temperature.

ISSN:0021-8979    

DOI:10.1063/1.327951

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Semi‐insulating GaAs materials, undoped or doped with concentration of chromium varying from 6×1015to 4×1017cm−3, have been studied using both Hall effect measurements and optical absorption measurements. It is definitively concluded that compensation comes from the presence of the deep donor EL2 in undoped materials, and from both this deep donor and the deep acceptor related to chromium in Cr‐doped materials. Sets of curves are given which allow the determination ofND‐NA, the concentration of shallow donors and acceptors, knowing the Hall mobility and the Cr concentration in a given sample. Such curves can be a working tool for assessing any piece of semi‐insulating GaAs in a routine way.

ISSN:0021-8979    

DOI:10.1063/1.327952

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A Monte Carlo calculation technique based on both the partial wave expansion method for elastic scattering and Krefting and Reimer’s treatment for inelastic scattering was applied for quantitative study by Auger electron spectroscopy. The theory has described the experiment of energy and angular distributions of backscattered electrons with considerable success. Dependence of the Auger signal generation on primary electron energy was investigated with a scanning Auger electron microscope, and the result was compared with the theory for a number of elements of practical interest. Through this, we have found that the present Monte Carlo approach allows us to evaluate contributions of backscattered electrons to Auger signal generation leading to more comprehensive quantitative AES study.

ISSN:0021-8979    

DOI:10.1063/1.327953

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Sputtering yields for different ions and materials at low ion energies have a similar energy dependence. Due to this similarity, yield data can be characterized by a normalized energy function and two parameters for each ion target combination. One of these parameters is the threshold energy. An energy scaling can be based on this parameter. The other parameter is a multiplication factor. Both parameters depend mainly on the ion and target massM1andM2and on the surface binding energyEB. An analytic expression for the normalized functions and both the parameters is given. This empirical relation also allows an estimate of unknown sputtering data, ifM1,M2, andEBare noted. A physical interpretation of the empirical relation is given for the caseM1≪M2, as in this case special collision processes which dominate the sputtering can be identified.

ISSN:0021-8979    

DOI:10.1063/1.327954

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

It has been observed that the surface temperature obtained during laser heating of lightly damaged material is generally considerably lower than the temperature obtained in heavily damaged material. We develop a model which explains this observation by taking into acount the diffusion of the photoexcited carriers. The time evolution of temperature profiles was calculated for pulsed ruby and Nd : YAG illumination of silicon and ruby illumination of GaAs. The material, optical, and electronic properties were varied, according to the material quality. Surface recombination of the carriers was also taken into account. For the same laser power, the induced temperature was lower and the heating times were longer in good‐quality materials than in heavily damaged materials. This is because of longer carrier difusion lengths in good‐quality material. The effect of the damage on the heating was found to be much more pronounced for Nd : YAG than for ruby irradiation because a larger portion of the ruby laser energy (excess above band gap) is given rapidly to the lattice through quasithermalization inside the semiconductor energy bands. Thermal spikes are formed as the result of the preferential recombination of the carriers at the surface. For a sufficiently fast surface recombination, the temperature profile may develop a secondary maximum in the material interior.

ISSN:0021-8979    

DOI:10.1063/1.327955

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Reflection‐mode quantum efficiencies have been calculated for thep‐InP bias‐assisted photoemitter (TE cathode) and have been found to be consistent with experimental data. The calculations, using Monte Carlo techniques, consider the transport of photogenerated electrons to the surface as well as the transmission of electrons at the surface into vacuum. Dependence of the predicted yield upon bias voltage and doping is discussed. Acceptor doping in the mid 1016/cm3range is indicated as a good choice for a high quantum efficiency photocathode.

ISSN:0021-8979    

DOI:10.1063/1.327956

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Angular distributions of sputtered Si atoms from polycrystalline Si targets were measured for Ar+ions of 3 and 10 keV, at angles of incidence of 0° (normal incidence) and 60°. The results were compared with the theoretical ones obtained from Monte Carlo calculations by Kangetal. Theory describes qualitatively the experimental results fairly well. Some discrepancy between the theoretical and experimental results was, however, found in the preferred ejection angles. The preferred ejection angle of the experimental results for 10 keV at angle of incidence of 60° agrees very well with that suggested by the universal curve of the correlation between the preferred ejection angle and sputtering yield, which has been proposed by Betzetal.

ISSN:0021-8979    

DOI:10.1063/1.327957

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The Auger electron spectrum induced by the impact of 100‐keV Ar+on metallic aluminum is shown to be consistent with the source of Auger electrons being ejected target particles. The principal spectral line has been identified as being due to ejected Al atoms with a single 2pvacancy. Subsidiary peaks are due to ejected atoms and Al+ions with one or two 2pvacancies. The ion‐induced Auger spectrum of silicon is similar. By contrast the spectrum induced by Ar+impact on Be exhibits a rather broad peak characteristic of aK‐shell vacancy and is similar to that induced by the impact of electrons. By considering the lifetime of the BeK‐shell vacancy we conclude that the Auger decay occurs while the Be atoms are either in the solid or interacting with the surface.

ISSN:0021-8979    

DOI:10.1063/1.327958

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The evolution of the electron emission of impregnated cathodes has been measured over many thousands of hours of operation at various temperatures in diodes and traveling‐wave tubes. Certain physical methods were used to investigate the correlation between these results and the mechanisms of cathode operation: X‐ray fluorescence electron microprobe analysis has given a new access to the study of the consumption of the active materials (barium and calcium) at various stages of cathode life. While barium depletes according to thet1/2law, an approximatet1/3law found for calcium could result from a two‐step process in the barium and calcium chemistry. The formation and desorption of synthetized emissive layers on a nonimpregnated porous tungsten plug in a Becker‐type test diode is one way to investigate the properties of emissive surfaces. The behavior of layers synthetized at low temperatures onto active impregnated cathodes suggests a surface equilibrium depending on the chemical nature of the substrate. Emission charts are proposed to compare, over a large range of temperatures, the different types of cathodes, in particular, the characteristics of uncoated and coated ones.

ISSN:0021-8979    

DOI:10.1063/1.327959

出版商:AIP    

年代:1980

数据来源: AIP