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Notes: Spin polarized core level photoemision studies are capable of providing local site specific magnetic information. 3s core level photoemission spectra are characterized by a main peak and satellite whose separation reflects the exchange interaction between the core level and the net spin in the valence bands. However, there is currently considerable disagreement as to whether the splitting between these two peaks may be taken as a measure of the local moment. An alternative approach is to examine the intensities of the different peaks in the spectra. Indeed analysis of the multiplet intensities in the final state suggests that it should be possible to obtain a reasonable measure of the local magnetic moment through measurement of the spin dependent intensities in the multiplet structure. In detailed spin polarized photoemission studies of the 3s core level of Fe and Co films grown on Ag(001) and Cu(001) substrates, respectively, we find that this is indeed the case. This suggests that studies of the spin polarization of the 3s core level photoemission may provide an important new technique for the measurement of magnetic moments in thin films. Lineshape fitting reveals new information about the lifetime of the core holes. Previous studies have suggested that a majority spin core hole will be shorter lived than a minority spin core hole because of the higher density of majority spin electrons in the valence bands. However, our studies indicate that the lifetime is more complicated and that it shows a strong dependence on the LS in the final state. © 1996 American Institute of Physics.

Notes: This article reports the effect of Al doping into MnBiSi films on the structure and magneto-optical properties of the parent. Under suitable Al doping, the x-ray diffraction peaks of (002) and (004) move to a larger 2aitch-theta value related to that of MnBiSi. Moreover, two satellite peaks appear beside the main (002) and (004) peaks of MnBiAlSi. Such structural distortion due to Al doping results in an increased Kerr rotation angle, an effective perpendicular anisotropy constant Ku, as well as improvement of the thermal stability of MnBiSi.

Notes: The effects of Zn ion on magnetic properties Fe3O4 magnetic colloids were investigated in this study. Fe3O4 magnetic colloids were produced by the chemical coprecipitation method, i.e., mixing an acidic solution containing FeCl2⋅4H2O, FeCl3⋅6H2O, ZnCl2⋅4H2O, with a NaOH alkali solution at 70 °C, and then centrifuging them from the mixed solution. Various reaction times, solution pH values, and Zn ion contents were also used. Fe3O4 magnetic fluid was obtained by adding ammonium oleate into the mixed solution, precipitating the colloids from the solution, neutralizing the colloids by hydrochloric acid, and dispersing the colloids in n-hexane. XRD, EDX, TEM, and VSM were used to determine the structure, chemical compositions, particle sizes, and magnetic properties of the colloids and the magnetic fluid. The spinel colloids was easily form at a higher pH value in solutions where the pH value ranged from 7 to 12. Fe3O4 colloids were completely formed within the first minute of mixing and the particle size of Fe3O4 colloids did not increase with time after the first minute.The lattice parameter of Fe3O4 colloids increased linearly with the Zn ion content because the diameter of Zn ion is larger than that of Fe ions. The particle size of Fe3O4 colloids was found to be 10 nm by TEM. For an initially fixed Zn content of 8 wt % in solutions, the Zn content in the Fe3O4 colloids ranged from 3.32 wt % at pH=5 to a maximum value of 7.85 wt % at pH=10. Later, it reduced to 7.51 wt % at pH=12 because Zn ion has the lowest solubility at pH=10. At 8 wt % of zinc ion in the solution, the σs of the Fe3O4 colloid increase sharply from 0 at pH=3 to 92 emu/g at pH=8 and then reach a maximum value of 94 at pH=10. The σs value and Hc value of the Fe3O4 colloid were found significantly improved by adding a suitable amount of Zn ions, e.g., ranging from 70 emu/g and 48 Oe at Zn=0 wt % to a maximum 94 emu/g and 50 Oe at Zn=7.14 wt %. Later they reduced to 70 emu/g and 44 Oe at Zn=12.52 wt % when prepared at pH=10. The σs value of the magnetic fluid was found linearly proportional to the colloid content in the magnetic fluid. For a colloid containing 7.51 wt % of Zn ion, the σs value of the magnetic fluid is 9.8 emu/g at 25 wt % of colloid. © 1996 American Institute of Physics.

Notes: The base-collector junction of GaAs/AlGaAs single heterojunction bipolar transistors has been observed to emit light at avalanche breakdown. The spectral distribution curve exhibits broad peaks at 2.03 and 1.43 eV, with the intensities dependent upon the reverse current. These observations suggest that electrons, excited to the upper conduction band by the field, lose their energy by impact ionizing electron-hole pairs and producing the 2.03 eV light, which corresponds to the threshold energy for electron impact ionization. The band-edge emission is the result of direct-gap free-carrier recombination and self-absorption of the high-energy transition.

Notes: Intersubband transitions in GaAs/GaAlAs multiquantum wells (QW) under hydrostatic pressure have been investigated with photomodulated transmission spectroscopy and free-standing QW samples. In addition to the direct transitions associated with the Γ critical points, several L-related transitions between the L conduction band and the Γ valence band of the GaAlAs barriers and between the L conduction subbands and the Γ valence subbands inside the GaAs quantum wells are observed. The distinct L-related spectral features are a clear indication that photomodulated transmission is particularly useful for enhancement of the weak phonon-assisted indirect transitions. © 1997 American Institute of Physics.

Notes: GaAs-based field-effect transistor structures have been grown on InP substrates with the InGaAs/GaAs strained-layer superlattices and 1.5 μm GaAs layer as the buffer. The low-temperature (4 K) photoluminescence (PL) from this GaAs buffer has been studied for the first time. Among five observable peaks, the excitonic transition at energy 1.513 eV and the impurity associated recombination at energy 1.483 eV have been identified with the aid of reflection, absorption, and temperature and excitation-intensity dependent PL measurements. The peak at 1.504 eV, most probably due to an exciton bound to a defect, is greatly enhanced compared with that of homoepitaxially grown GaAs. The optical results show that GaAs films of good quality can be grown on InP substrate, which is consistent with device results.

Notes: We report for the first time large excitonic absorption at room temperature in AlGaAs/GaAs multiple quantum well structures grown on Si substrates in a p-i-n configuration, using photocurrent measurements. We demonstrate an optical reflection modulator which is based on the quantum-confined Stark effect and exciton broadening with a reverse bias voltage applied across the p-i-n structure. A 7.7% change in the reflectivity of the device with 6 V reverse bias voltage was observed. These results demonstrate clearly that optical device quality AlGaAs/GaAs is obtainable directly on Si substrates which has great implications with regard to the monolithic integration of optical III-V and electronic Si technology.

Notes: The photoreflectance (PR) spectra of bulk AlxGa1−xAs alloys with x≤0.45 were studied. The observed line shapes from different samples suggest that the PR technique is very sensitive to the material quality, surface condition, and the background impurities. The energy gap derived from the PR spectra compared well to that obtained from the absorption spectra. The relationship between the energy gap and the Al mole fraction value x was established through the nuclear resonance reaction analysis. The electric field near the surface was calculated from the periodicity of Franz–Keldysh oscillations observed in many of the samples. From our analysis, we believe that the number of oscillations shown in PR spectra corresponds to sample quality, in general. We also believe that the low-field-like line shape is mainly caused by the fluctuation of Al distribution along the growth direction. An additional feature related to the impurity transition was also observed in the spectra.

Notes: The magnetic field splitting and strain splitting of the emission lines in the 1.5040–1.5110 eV range in GaAs are reported. In the Voigt configuration the lines show doublet splittings in applied magnetic fields. In combined magnetic and strain fields four lines are observed in this configuration. All of the lines show a similar splitting. The splittings agree with what would be expected for shallow donor-acceptor pair centers in a zinc-blende structure.