• Korean Journal of Materials Research
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• v.21 no.8
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• pp.439-443
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• 2011

The crystal structure and magnetic properties of a new solid solution type ferrite $(Fe_2O_3)_5-(Al_2O_3)_{3.4}-(Ga_2O_3)_{0.6}-SiO$ were investigated using X-ray diffraction and M$\"{o}$ssbauer spectroscopy. The results of the X-ray diffraction pattern indicated that the crystal structure of the sample appears to be a cubic spinel type structure. The lattice constant (a = 8.317 ${\AA}$) decreases slightly with the substitution of $Ga_2O_3$ even though the ionic radii of the Ga ions are larger than that of the Al ions. The results can be attributed to a higher degree of covalency in the Ga-O bonds than in the Al-O and Fe-O bonds, which can also be explained using the observed M$\"{o}$ssbauer parameters, which are the magnetic hyperfine field, isomer shift, and quadrupole splitting. The drastic change in the magnetic structure according to the Ga ion substitution in the $ (Fe_2O_3)_5(Al_2O_3)_{4-x}(Ga_2O_3)_xSiO$ system and the low temperature variation have been studied through a M$\"{o}$ssbauer spectroscopy. The M$\"{o}$ssbauer spectrum at room temperature shows the superpositions of two Zeeman patterns and a strong doublet. It shows significant departures from the prototypical ferrite and is comparable with the diluted ferrite. The doublet of spectrum at room temperature appears to originate from superparamagnetic clusters and also the asymmetry of the doublet appears to be caused by the preferred orientation of the crystallites. The M$\"{o}$ssbauer spectra below room temperature show various complicated patterns, which can be explained by the freezing of the superparamagnetic clusters. On cooling, the magnetic states of the sample were various and multi critical.

• Journal of the Korean institute of surface engineering
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• v.35 no.1
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• pp.39-46
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• 2002

$Cu_2$$ZnSnS_4$(CZTS) thin film is one of the candidate materials for the solar cell. It has an excellent optical absorption coefficient as well as appropriate 1.4~1.5eV band gap. The purpose of this study is replacing a half of high-cost Indium(In) atoms with low-cost Zinc(Zn) atoms and the other half with low-cost Tin(Sn) atoms in the lattice of CIS. Thin films were deposited on ITO glass substrates using a compact target which were made by $Cu_2$S, ZnS, SnS$_2$ powder at room temperature by rf magnetron sputtering and were annealed in the atmosphere of Ar and $S_2$(g). We investigated potentialities of a low-cost material for the solar cell by measuring of thin film composition, the structure and optical properties. We could get an appropriate $Cu_2$$ZnSnS_4$ composition. Structure was coarsened with increasing temperature and (112), (200), (220), (312) planes appeared to conform to all the reflection Kesterite structure. A (112) preferred orientation was advanced with increasing the annealing temperature as shown in the diffraction peaks of the CIS cells and was available for photovoltaic thin film materials. The band gap increased from 1.51 to 1.8eV as the annealing temperature increased. The optical absorption coefficient of the thin film was about $10^4$$cm^{-1}$.

• Advances in materials Research
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• v.12 no.3
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• pp.179-192
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• 2023

We have studied the structural and optical properties of the non-doped and Co 0.08 at.%, Co 0.02 at.%, and Co 0.11 at.% doped ZnO nanorods (NRs) synthesized using the simple low-temperature chemical bath deposition (CBD) method at 95℃ for 2 hours. The scanning electron microscope (SEM) images confirmed the morphology of the ZnO NRs are affected by Co incorporation. As observed, the Co 0.08 at.% doped ZnO NRs have a larger dimension with an average diameter of 153.4 nm. According to the International Centre for Diffraction Data (ICDD) number #00-036-1451, the x-ray diffraction (XRD) pattern of non-doped and Co-doped ZnO NRs with the preferred orientation of ZnO NRs in the (002) plane possess polycrystalline hexagonal wurtzite structure with the space group P63mc. Optical absorbance indicates the Co 0.08 at.% doped ZnO NRs have stronger and blueshift bandgap energy (3.104 ev). The room temperature photoluminescence (PL) spectra of ZnO NRs exhibited excitonicrelates ultraviolet (UV) and defect-related green band (GB) emissions. By calculating the UV/GB intensity, the Co 0.08 at.% is the proper atomic percentage to have fewer intrinsic defects. We predict that Co-doped ZnO NRs induce a blueshift of near band edge (NBE) emission due to the Burstein-Moss effect. Meanwhile, the redshift of NBE emission is attributed to the modification of the lattice dimensions and exchange energy.

• Transactions on Electrical and Electronic Materials
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• v.1 no.4
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• pp.11-15
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• 2000

This paper presents a process optimization of antireflection (AR) coating on crystalline Si solar cells. Theoretical and experimental investigations were performed on a double-layer AR(DLAR) coating of MgFe$_2$/GeO$_2$. We investigated GeO$_2$ films as an AR layer because they have a proper refractive index of 2.46 and demonstrate the same lattice constant as Si substrate. RF sputter grown GeO$_2$ film showed deposition temperature strong dependence. The GeO$_2$ at 400$\^{C}$ exhibited a strong (111) preferred orientation and the lowest surface roughness of 6.87 $\AA$. Refractive index of MgFe$_2$film was measured as 1.386 for the most of growth temperature. An optimized DLAR coating showed a reflectance as low as 2.04% in the wavelengths ranged from 0.4 ㎛ to 1.1 ㎛. Solar cells with a structure of MgFe$_2$/GeO$_2$/Ag/N$\^$+//p-type Si/P$\^$+//Al were investigated with the without DLAR coatings. We achieved the efficiency of solar cells greater than 15% with 3.12% improvement with DLAR coatings. Further details about MgFe$_2$,GeO$_2$ films, and cell fabrication parameters are presented in this paper.