Materials Science Forum Vols. 449-452

Abstract: With new models of AM1 solar spectra and Si refractive indices in the wavelength range of 0.4
0.97
, effective absorption powers of Si solar cells coated with the single and double AR layers were theoretically calculated for the first time. The SiO2, Si3N4 and SiO2/Si3N4 easily obtainable in the standard Si process were used as the AR layers of Si solar cell. Optimum thicknesses showing the maximum absorption power for AR layers of SiO2, Si3N4 and SiO2/Si3N4 were as follows: d(SiO2)=10001, d(Si3N4)=7001 and d(SiO2/Si3N4) =500 1 /3001 . Effective absorption powers in the solar cells of SiO2-Si, Si3N4-Si and SiO2/Si3N4-Si were 520W/m2, 565W/m2 and 607W/m2 at AM1 in the optimum conditions of AR coating, respectively

Abstract: Hydrogenated amorphous silicon (a-Si:H) has attracted much attention in various electronics applications such as thin films transistors, color sensors, and solar cells[1]. However, many devices made from a-S:H are observed to degrade with time, which is commonly associated with hydrogen related defects [1]. It has been observed that, by increasing the hydrogen dilution in the precursor gas used in the plasma, one can obtain hydrogenated nanocrystalline silicon (nc-Si:H), which contains crystalline grains embedded in an amorphous silicon matrix. These materials can be deposited by plasma enhanced chemical vapor deposition (PECVD) techniques. The presence of nc- Si in a-Si:H changes the optical and electronic properties of the material [2]. Nc-Si:H thin films have exhibited unique and useful characteristics. In particular, nc-Si:H thin films exhibit photoluminescence (PL) and electroluminescence (EL) behavior at room temperature [3]. The dilution of SiH4 with hydrogen has been recognized as an effective method for the transition from the amorphous to the nanocrystalline phase in the nc-Si:H thin films. The presence of hydrogen on the growing surface gives termination of dangling bonds and also an extraction of SiH3 radicals [4]. The supply balance between the hydrogen and SiH3 radicals is a key factor in determining the film structure [4]. The presence of excess hydrogen or hydrogen-bonded Si radicals (SiHn = 1, 2, 3) in the gas mixture passivates the dangling bonds on the growing surface and etches the growing surface. Etching eliminates part of the disordered structure and enhances the crystalline phase because the crystalline structure is the lowest energy configuration. In this paper, we report the study of the effects of the hydrogen species on the nanostructures and optical properties of nc-Si:H thin films prepared by PECVD techniques

Abstract: Two types of the organic light-emitting devices (OLEDs) with different emission structures were prepared using Alq3 (aluminum tris 8-hydroxyquinoline) host material and quinacridone (QD) dopant at the emission layer. One is the OLED device with emission layer consisting of Alq3 host material doped with QD dopant ("codoped OLED"). The another one has a seperated QD dopant film in the Alq3 emission layer ("undoped OLED"). The maximum brightness of the codoped and undoped OLEDs were 3207 cd/m2 and 1570 cd/m2, respectively. The wavelength of the maximum emission peak in the undoped sample was 527 nm and shifted slightly toward longer wavelength with the value of 540 nm for the codoped OLED sample. The maximum luminous efficiency of the undoped OLED was about 1.4 lm/W and increased to 7.0 lm/W for the codoped sample.

Abstract: The adsorptive on pure iron and copper surfaces was investigated with angle resolved X-ray photoelectron spectroscopy (ARXPS) and atomic force microscope (AFM). Organic species and a little amount of water (micro-droplets surrounded with nanometer-scale film-like-domains) were detected on the oxidized and/or hydrated metallic surfaces for both specimens and their minute structures were discussed.

Abstract: Half metallic ferromagnets are candidate materials for novel electronic devices, which can control the spin character of the conducting electrons. Electronic band calculation predicted that Co2MnGe Heusler compounds may has the half metallic band structure. In the present study, structure and magnetic properties have been investigated of the Co2MnGe for bulk and thin films. In the bulk sample, plate defects have been found.

Abstract: Coating of
-Fe2O3 nanoparticles with SiO2 layer by wet chemical synthesis and its applications to protein separation and purification were investigated. The average particle size of
-Fe2O3 core was 20 nm and SiO2 layer thickness was 5 nm. The band of OH- radicals on SiO2 layer was detected between 3600 and 3200 cm-1 in wave numbers, which showed that the surface property of coated nanoparticles was similar to that of conventional fumed silica. Finally, the feasibility of
-Fe2O3/SiO2 nanoparticles for magnetic separation media in various bio processes was discussed in terms of structural and functional properties such as pore structure and magnetic properties.

Abstract: Sm2Fe17Nx compound is a prospective candidate as a material for high performance permanent magnets because of its good intrinsic magnetic properties with a Curie temperature of 747K, a room-temperature anisotropy field of 14T and a room-temperature saturation magnetization of 1.5T. However, Sm2Fe17Nx compound decomposes to
-Fe and Sm nitride above 873K and conventional powder metallurgy processing techniques fail to meet the processing requirements. Shock consolidation is a viable alternative to process this compound. Fully dense Sm2Fe17Nx bulk materials were fabricated by cylindrical explosive consolidation technique using water as a pressure transmitting medium. Explosive consolidation is performed under cold state and fully dense materials can be obtained without any degradation of the characteristics of the powder states. Sound compacts were obtained without any cracks or teas, and the value of (BH)max of Sm2Fe17Nx compact is 23.8 MGOe.

Abstract: We present the ferromagnetism and magnetotransport properties in the (Ga,Mn)N epitaxial films with very low Mn concentrations grown by plasma-enhanced molecular beam epitaxy (PEMBE). The (Ga,Mn)N epitaxial films were found to exhibit ferromagnetic ordering with Curie temperature of 700 K. All the films exhibit n-type characteristics. The negative magnetoresistance was observed below 150 K, and found to gradually increase with decreasing temperature. The ferromagnetism in the (Ga,Mn)N is due to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the localized Mn moments mediated by the electron gas.

Abstract: The magnetic properties were investigated on Co66Fe4B15Si15 amorphous ribbons of annealed at temperature range from 473 K to 773 K in vacuum (A-batch) and open air (B-batch). Static permeability from domain wall motion decreases with annealing temperature both in A- and B-batch sample. The permeability from magnetization rotation increases up to 700 K annealing temperature, but then decreases. The GMI profiles show a symmetric curve in A-batch samples irrespective of annealing temperature. In B-batch samples, symmetric profiles are shown up to 650 K annealing temperature, while they becomes asymmetric for further annealing temperature, due to the exchange bias-field induced by surface crystalline layer.

Abstract: The magnetic properties were investigated on Co66Fe4B15Si15 amorphous ribbons of annealed at temperature range from 473 K to 773 K in vacuum (A-batch) and open air (B-batch). Static permeability from domain wall motion decreases with annealing temperature both in A- and B-batch sample. The permeability from magnetization rotation increases up to 700 K annealing temperature, but then decreases. The GMI profiles show a symmetric curve in A-batch samples irrespective of annealing temperature. In B-batch samples, symmetric profiles are shown up to 650 K annealing temperature, while they becomes asymmetric for further annealing temperature, due to the exchange bias-field induced by surface crystalline layer.