Search

Multisubband transport of the two-dimensional electron gas (2DEG) in modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures has been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. It is found that the mobility of the 2DEG in the first subband in a triangular quantum well at the heterointerface decreases significantly, while the mobility of the 2DEG in the second subband increases, when the Al[sub 0.22]Ga[sub 0.78]N barrier is partially relaxed. Such behavior of the 2DEG mobility is explained by the nonuniformity of the piezoelectric polarization field at the heterointerface induced by the Al[sub 0.22]Ga[sub 0.78]N relaxation and strong interface scattering. Meanwhile, it is concluded that the scattering from the remote ionized donors is the main mechanism contributing to the quantum scattering time and responsible for the intersubband scattering in the quantum well at the heterointerface. [ABSTRACT FROM AUTHOR]

Discusses a spectroscopic ellipsometry study of cerium dioxide thin films grown on sapphire by radio frequency magnetron sputtering. Examination of the crystallinity, chemical structure and surface morphology of the films through x-ray diffraction, x-ray photoelectron spectroscopy and atomic force microscopy; Analysis of the surface roughness of the crystalline films; Experimental details and result of the study.

Abstract: Strong effects of ferromagnetic layer (FMCo, and Ni80Fe20) on the magnitude and blocking temperature of exchange coupling are observed in antiferromagnetic NiO-based films NiO (5nm)/FM1 (t nm)/FM2 (6-t nm). The existence of interfacial spins configuration in glass-like state and FM anisotropy are proposed to interpret a minimum shown in thermal magnetization curves for films with strong exchange coupling effect. The microstructural change of FM layer and the long-range interaction of exchange bias are taken into account to explain a strong dependence of exchange coupling energy density on the thickness t F of FM layer when t F<5nm. [Copyright &y& Elsevier]

Titanium nitride (TiN) is well known for its excellent conductivity, inertness, and good optical reflectivity at long wavelengths. These properties make it a potential IR-reflective back contact material suitable for ultrathin Cu(In,Ga)Se2 (CIGS) solar cells. Using a pulsed power, 12 cm linear hollow cathode source fitted with Ti targets and with N2 as the reactive gas, TiN films were deposited on Mo-coated glass. The static deposition rate was 50 nm/min for a sputtering power of only 500 W. The high deposition rate indicates the advantage of the reactive environment, hollow cathode sputtering method, i.e., the reactive gas is excluded from the target. Electrical, optical, and physical properties of the films were measured. Resistivities in the range of 50–60 μΩ cm were achieved. Reflectance and x-ray diffraction measurements were conducted, and the effects of deposition parameters such as substrate bias and substrate temperature were studied. The optical emission from N and Ti atoms in the plasma was also studied. CIGS solar cells were successfully fabricated on TiN and a conversion efficiency of 12.3% was achieved. Transparent and moderately conductive TiO2 films doped with Nb were also prepared. The electrical and optical properties of these films are reported, and the reflectance of a-Si solar cells was reduced via incorporation of a TiO2:Nb layer. [ABSTRACT FROM AUTHOR]

Magnetite (Fe3O4) thin films have been grown on ferroelectric BaTiO3 (BTO) single crystal substrates by pulsed laser deposition. Transmission-electron microscope observations demonstrate the orientation relationship between Fe3O4 and BTO as [400]Fe3O4∥[200]BTO and [004]Fe3O4∥[002]BTO. Experimental measurements of magnetization, coercivity and remanent magnetization of the films show abrupt jumps at around phase transition temperatures of BTO and opposite jump signs are observed for the in-plane and out-of-plane measurements. The magnetization jumps can be suppressed by a strong external magnetic field. These results were discussed in terms of the interface strain induced changes of magnetic domain structure in the Fe3O4 film. This work demonstrates the presence of strong magnetoelectric coupling between Fe3O4 and BTO. [ABSTRACT FROM AUTHOR]

Fe3O4/SiO2/Si heterojunction was fabricated by growing Fe3O4 film on an n-typed Si wafer with the native SiO2 buffer layer using the pulsed laser deposition. Transmission electron microcopic study shows the high quality of the heterojunction interfaces and the SiO2 layer is 2.5 nm thick. This junction shows a backward diodelike rectifying behavior and an anomalously giant positive magnetoresistance (MR) for the large reverse bias voltages. The temperature dependence of MR shows a peak around the Verwey transition temperature with a maximum MR of 87% under a -2 V bias voltage. The results were discussed by considering the band structure of the heterojunction and the effect of the reverse bias voltage. [ABSTRACT FROM AUTHOR]

Highly-conductive and crack-free n-Al[SUB0.6]Ga[SUB0.4]N films with thickness up to 1μm were achieved by using high-temperature AlN or AlGaN/AlN superlattice (SL) buffer layers. Room-temperature Hall measurements show the highest electron concentration of 3.5×10[SUP18]cm[SUP-3] with mobility of 25 cm[SUP2]/V s. Electron mobility was increased from 25 to 35 cm[SUP2]/V s by introducing the AlGaN/AlN SL buffer layer. Second ion mass spectroscopy indicates that there is high oxygen doping concentration in the film, and that the film resistivity decreases with increasing oxygen concentration from 1×10[SUP17] to ∼1×10[SUP19]cm[SUP-3]. [ABSTRACT FROM AUTHOR]

Discusses a simple transmission technique for measuring the electrooptic coefficients of poled polymer films. Principle of the method; Determination of the electrooptic coefficient; Use of the method to characterize nonlinear optical polymers; Reliability of the method.

The exchange coupling between PtFe and Fe in PtFe/Fe films with Cr2O3 or Cr2O3/Cu spacer layers is indirect and long range. Microstructures of as-deposited and annealed thin films are studied. Coercivity over 10 kOe is obtained in PtFe/Cr2O3(5 Å)/Fe(25 Å) films but decrease with thicker Cr2O3 spacer layer. Comparably, coercivity can be maintained at about 10 kOe if spacer layer is changed into Cr2O3(x Å)/Cu(5 Å) (5 Å ≤ x ≤ 25 Å). For a fixed total thickness of the spacer layers, the coercivity generally decreases with gradual replacement of Cr2O3 by Cu, indicating the different effects of spacer layers on mediating the exchange coupling between PtFe and Fe. Using Cr2O3 or Cr2O3/Cu as a spacer layer is a promising way for realizing exchange-coupled PtFe/Fe composite films. [ABSTRACT FROM AUTHOR]

Highly (100) oriented Ba[sub 0.9]Sr[sub 0.1]TiO[sub 3]/LaNiO[sub 3] heterostructures have been grown on Si(100) using chemical solution routes. X-ray diffraction analysis shows that Ba[sub 0.9]Sr[sub 0.1]TiO[sub 3] thin films are high (100) orientation (α[sub 100]=0.92). Atomic force microscopy investigation shows that they have large grains about 80-200 nm. A Pt/Ba[sub 0.9]Sr[sub 0.1]TiO[sub 3]/LaNiO[sub 3] capacitor has been fabricated and showed excellent ferroelectricity, the remnant polarization and coercive field are 10.8 μC/cm2 and 96 kV/cm, respectively. The electric field dependence of capacitance measurement shows that the capacitor has large capacitance tuning ([C[sub max]-C[sub min]]/C[sub max]x100%) of 63%. The Ba[sub 0.9]Sr[sub 0.1]TiO[sub 3] thin films have high dielectric constant (ε) of 200 at 1 MHz. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have measured the dependence of the indices of refraction n on alloy composition of Zn[sub 1-x-y]Mg[sub x]Cd[sub y]Se films grown by molecular beam epitaxy on InP substrates for a series of alloy compositions x and y. The compositions of the Zn[sub 1-x-y]Mg[sub x]Cd[sub y]Se thin films were determined by photoluminescence and x-ray diffraction experiments. A prism coupler technique, capable of measuring n with an accuracy of at least 0.1% at discrete wavelengths, was then used to measure n of each of the thin films. In all of the samples, at least three guided modes were observed in the spectrum obtained by the prism coupler method. The accurate values of n obtained by this method show an inverse relationship with respect to their band gaps. In addition, by comparing the n values obtained for the quaternary Zn[sub 1-x-y]Mg[sub x]Cd[sub y]Se alloys with the previously obtained values for the ternary Zn[sub 1-x]Cd[sub x]Se and Zn[sub 1-x]Mg[sub x]Se alloys, it is concluded that n of the quaternary system is almost completely dictated by the content of Mg. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the thickness and refractive index of benzocyclobutene thin films using ellipsometry. Changes in the ellipsometric parameters with temperature; Dependence of temperature sensitivity on film thickness; Impact of thermal sensitivity on wavelength.

The combination of grazing incidence small angle x-ray scattering (GISAXS) and grazing incidence wide angle x-ray scattering (GIWAXS) with optical imaging ellipsometry is presented as an upgrade of the available measurement techniques at the wiggler beamline BW4 of the Hamburger Synchrotronstrahlungslabor. The instrument is introduced with the description of the alignment procedure to assure the measurement of imaging ellipsometry and GISAXS/GIWAXS on the same sample spot. To demonstrate the possibilities of the new instrument examples of morphological investigation on films made of poly(3-hexylthiophene) and [6,6]-phenyl-C61 butyric acid methyl ester as well as textured poly(9,9-dioctylfluorene-alt-benzo-thia-diazole) are shown. [ABSTRACT FROM AUTHOR]

Abstract: In this work, Y2O3:Eu3+ thin film phosphors were prepared by electro-deposition method. The effect of Na+ and K+ ions on the photoluminescence properties of Y2O3:Eu3+ thin film phosphor was studied in details. It was found that the addition of Na+ and K+ ions could improve the photoluminescence intensity by 3 to 4 times. The highly improved photoluminescence intensity may be caused by different factors. The improved crystallinity and the increased optical volume caused by the flux effect of Na+ and K+ ions could be the major reasons for the enhanced photoluminescence intensity. It was also found that the average lifetime of Y2O3:Eu3+ thin film phosphors could be adjusted by the molar amount of Na+ and K+ ions. [Copyright &y& Elsevier]

Abstract: [Nd–Fe–B(x nm)/FeMn(d nm)] n thin films were deposited by magnetron sputtering on Si (100) substrates heated at 650°C. The influence of the composition and thickness of FeMn layer on the structure and magnetic properties of Nd–Fe–B films are investigated. The Nd–Fe–B/FeMn multilayer films present an enhanced coercivity and a reduced saturation magnetization, in comparison with those of a Nd–Fe–B single layer. The coercivity of [Nd–Fe–B(x nm)/FeMn(5nm)] n films increases with increasing the period number of FeMn layer for the same thickness of magnetic layer, while the coercivity in [Nd–Fe–B(50nm)/FeMn(5nm)] n films increases with decreasing the period number of Nd–Fe–B/FeMn bilayers. The coercivity H c of about 17.2kOe is achieved in the Nd–Fe–B(50nm)/FeMn(5nm) film. [Copyright &y& Elsevier]

Magnetite (Fe3O4) thin films have been grown on ferroelectric BaTiO3 (BTO) single crystal substrates by pulsed laser deposition. Transmission-electron microscope observations demonstrate the orientation relationship between Fe3O4 and BTO as [400]Fe3O4∥[200]BTO and [004]Fe3O4∥[002]BTO. Experimental measurements of magnetization, coercivity and remanent magnetization of the films show abrupt jumps at around phase transition temperatures of BTO and opposite jump signs are observed for the in-plane and out-of-plane measurements. The magnetization jumps can be suppressed by a strong external magnetic field. These results were discussed in terms of the interface strain induced changes of magnetic domain structure in the Fe3O4 film. This work demonstrates the presence of strong magnetoelectric coupling between Fe3O4 and BTO. [ABSTRACT FROM AUTHOR]