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In this study, the correlation between the specific growth rate of Phaeodactylum tricornutum and fucoxanthin (fucoxanthin) biosynthesis was investigated both in batch and in semi-continuous cultures. Fucoxanthin content from P. tricornutum biomass showed a positive correlation with specific growth rate during the normal culture period. The maximum yield of fucoxanthin (2.42 mg g−1 dry biomass) was observed at day 5, and the highest specific growth rate (1.91) was observed at day 4, both of which were during the exponential phase. Upon treatment with growth inhibitors (AZD-8055 or norflurazon) during the exponential phase, fucoxanthin content decreased with growth rate in a concentration-dependent manner. In a semi-continuous culture of P. tricornutum with dilution rates from 0.1 to 0.5 day−1, we found a positive correlation between specific growth rate and fucoxanthin biosynthesis in a steady-state condition. Based on the transcriptome analysis results, different metabolic and key regulatory genes were active at different growth phases. Particularly, during the exponential growth phase, various genes related to regulatory mechanisms, such as cell growth and replication, were expressed, whereas in the stationary phase, their expression was reduced. In the fucoxanthin biosynthesis pathway, 1-deoxy-d-erythritol 2,4-cyclodiphosphate synthase (ISPD) and violaxanthin deepoxidase (VDE) genes showed higher expression levels in the exponential phase, thus indicating that they are critical genes for the regulation of fucoxanthin biosynthesis in P. tricornutum. Our results are valuable to our understanding of the basic mechanism of fucoxanthin biosynthesis, thus providing theoretical guidance for the commercial production of fucoxanthin derived from P. tricornutum.

We report high efficiency cell processing technologies for the ultra-thin Si solar cells based on crystalline Si thin foils (below a 50 µm thickness) produced by the proton implant exfoliation (PIE) technique. Shallow textures of submicrometer scale is essential for effective light trapping in crystalline Si thin foil based solar cells. In this study, we report the fabrication process of random Si nanohole arrays of ellipsoids by a facile way using low melting point metal nanoparticles of indium which were vacuum-deposited and dewetted spontaneously at room temperature. Combination of dry and wet etch processes with indium nanoparticles as etch masks enables the fabrication of random Si nanohole arrays of an ellipsoidal shape. The optimized etching processes led to effective light trapping nanostructures comparable to conventional micro-pyramids. We also developed the laser fired contact (LFC) process especially suitable for crystalline Si thin foil based PERC solar cells. The laser processing parameters were optimized to obtain a shallow LFC contact in conjunction with a low contact resistance. Lastly, we applied the random Si nanohole arrays and the LFC process to the crystalline Si thin foils (a 48 µm thickness) produced by the PIE technique and achieved the best efficiency of 17.1% while the planar PERC solar cell without the Si nanohole arrays exhibit 15.6%. Also, we demonstrate the ultra-thin wafer is bendable to have a 16 mm critical bending radius.

Hydroponic plant culturing requires the concentration of nutrients in the supplied solution to be maintained at a constant level. For example, phosphate ion concentration directly affects crop growth, which necessitates the development of convenient and rapid techniques for on-site phosphate quantitation. Herein, we developed a new low-cost colorimetric method of quick on-site phosphate quantitation based on a modification of the conventional molybdenum colorimetric method. Specifically, the nutrient solution treated with ascorbic acid and molybdate was analyzed by colorimetric method after 10 min incubation, and a phosphate quantitation protocol was proposed. To verify this protocol, 50 nutrient solution samples with concentrations of 0–200 ppm were used to develop a model and perform a validation experiment, and the PLSR (Partial Least Squares Regression) and PCR (Principal Component Regression) models were developed and validated using a crossvalidation method and sample transmission spectra. The PLSR model, employing smoothing preprocessing at a 5 nm wavelength spacing, exhibited the best prediction performance and showed an error of ~10% within the measurement range during verification. In addition, an artificial neural network-based model achieved R2=0.93 for the training set and R2=0.86 for the validation set. Finally, we developed convenient-to-use software for phosphate ion quantitation by the presented method and performed a demonstration test.

The production of low potassium vegetables arose out of the dietary needs of patients with renal dysfunction. Attempts have been made to reduce potassium content in vegetables and fruits; however, induced potassium deficiency has often resulted in decreased yields. Here, we investigated a new method of producing low potassium kale and present the characteristics of the resulting produce. By substituting potassium nitrate with calcium nitrate in the nutrient solution 2 weeks before harvesting, the potassium content of kale was reduced by 70% without a deterioration in yield and semblance qualities. Despite no relationships being detected between potassium deficiency and anti-oxidative properties, the total glucosinolate content, an indicator of the anti-cancer effect of cruciferous vegetables, was significantly increased by potassium deficiency in kale. This study demonstrates a novel method of producing low potassium kale for patients with renal failure, without a reduction in yield but with beneficial increase in glucosinolates.

The dried Ganoderma lucidum (GL) has been widely used for its pharmacological properties and bioactive ganoderic acids (GAs). Herein, extraction procedures combining ultra-sonication and heating were optimized using response surface methodology based on four variables (antioxidant activity, anti-diabetic activity, total GAs content, and total polysaccharide content) and principal component analysis. The extraction of freeze-dried GL at temperatures between 64.2 and 70 °C for 1.2 h maximized the antioxidant activity and GA content, whereas the polysaccharide content and anti-diabetic activity were maximized by extraction between 66.8 and 70 °C for more than 2.8 h. Heat-dried GL extracted at 50 °C for 3 h provided the greatest anti-inflammatory activity against HaCaT cells by suppressing the response to inflammation related cytokines at mRNA levels. These results suggest that extraction conditions might be a limiting factor for target-oriented investigations, and optimized extraction methods may improve the potential effect and quality of harvested GL products.

This work was financially supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) (Grant No. 20143030011850), and funded by the Ministry of Trade, Industry and Energy (MOTIE). I. Kim acknowledges KUUC (KIST-UNIST-Ulsan Center for Convergent Materials) for partial financial support.

Texturing of silicon wafers with periodic gratings in submicron scale is one of effective light trapping routes especially for thin crystalline silicon solar cells. The grating can be very effective for trapping of photons near band gap of crystalline silicon when its period is suitably chosen. The asymmetric gratings provide higher light trapping efficiency than symmetric ones because the asymmetric one suppress the escape of internally reflected light in the silicon wafers. In this study, we conceptually show that asymmetric grating can be fabricated by simple stacking of a dielectric layer onto the symmetric silicon grating structures. Optical simulations were performed to calculate optical absorptions in thin crystalline silicon of a 5 μm thickness with symmetric and asymmetric grating structures. We demonstrate that with the asymmetric grating structures combined with highly efficient antireflection coating, optical absorptions in the thin silicon wafers can reach over 97% of the Lambertian absorption limit.

Ginseng is a perennial herb used as valuable traditional medicine for more than three thousand years. Ginsenosides are the major group of pharmacologically active components of ginseng, and they are effective against various diseases. Present study was designed to investigate the impact of foliar silicon sprays on growth characteristics, physiological traits, and pharmaceutical quality of 6-year-old ginseng plants. Three different concentrations i.e. 50 mg/L, 100 mg/L, and 200 mg/L of Si was used as foliar treatment. Compared to control, stem hardness was enhanced up to 54% in 100 mg/L treatment followed by 38% in 50 mg/L and 36% in 200 mg/L. SEM analysis showed that the density of epidermal cells was 21-25% higher in Si-treated plants than that in the control plants. Cuticle thickness was found higher in Si treated plants as compared to control. Overall a total of 25%, 38%, and 54% of cuticle thickness and 43%, 49%, and 63% ginseng roots production was observed in plants treated with Si treatment of 50 mg/L, 100 mg/L, and 200 mg/L, respectively. Results suggest that out of three different concentrations of Si treatments, 200 mg/L found to be most effective in overall higher Si content in leaves with thick cuticle and higher root production, 100 mg/L treatment showed high photosynthesis rate followed by stomatal conductance, chlorophyll content and stem hardness. 50 mg/L was found to be least effective. Out of 12 ginsenosides analyzed in 6-year-old ginseng roots, the most common were AP, Rg1, Rb1, and Re. The content of ginsenosides per gram of ginseng roots did not show any significant differences among treatments, but overall, ginsenosides contents were higher in Si-treated plants because of increased root growth triggered by increased Si level. Our study show that the application of aerial sprays with elevated Si levels increases the growth, promotes the physiological and morphological traits and increases the yield of 6-year-old ginseng plants. In addition, this study implied the importance of Si for commercial production of high-quality ginseng roots.

The optical absorption efficiency (OAE) of thin crystalline Si (c-Si) solar cells was examined by using a direct absorption calculation algorithm based on the three-dimensional modeling and ray-tracing technique. The back contact was assumed to be made of ZnO based oxide layers with different optical constants and metallic electrode, and the front surface was assumed to be Lambertian. Simulation results showed that the insertion of non-absorptive oxide layer between c-Si and Al improved OAE, and that the relative amount of enhancement increased with decreasing refractive index, manifesting the reduction in absorption loss in Al electrode due to the increased total internal reflection. In the case of absorptive oxide layer, although increase in OAE was still attainable when compared with the back contact without oxide, the OAE was subdued significantly due to large absorption loss in oxide layer. The optimal oxide layer thickness was around 200 nm for non-absorptive oxide, and that of absorptive oxide decreased with increasing extinction coefficient. In the case of Ag metal contact, the enhancement of OAE due to the use of oxide layer was much less than the case of Al because of inherent high reflectivity and low absorption loss in Ag layer.

Optical properties, surface plasmon resonance (SPR) response characteristics, and the adhesion properties of the plasmonic stacks with titanium nitride (TiNx) adhesion layers were analyzed and compared with those of the Au single stack and the plasmonic stacks with conventional titanium adhesion layer. All the films were deposited by radio frequency magnetron sputtering. TiNx single layer exhibited higher electrical conductivity and reflectance in long wavelength range than Ti single layer of similar thickness. When compared with the plasmonic stacks with Ti adhesion layer, the plasmonic stacks with TiNx adhesion layer showed higher peak transmittance and less absorption loss in wavelength range longer than 500 nm. Examination of the SPR response curves revealed that much improved SPR characteristics could be attained if conventional Ti adhesion layer were replaced by TiNx layer, and it was attributed to the lower damping of TiNx film than Ti film at corresponding thickness. Also, it was proved that TiNx layer could provide sufficient adhesion strength at the glass/TiNx and TiNx/Au interfaces, which is comparable with that of Ti layer.

Solar cells, especially thin film solar cells, utilize rough surfaces actively in order to improve light trapping efficiency. In this study, we propose a new optical simulation method, which is capable of taking into consideration the realistic surface and interface morphology. The proposed simulation algorithm is based upon a non-sequential ray tracing technique, and direct calculation of the optical absorption energy is performed by separating the light passing through medium into the coherent part and the incoherent part in the course of non-sequential ray tracing throughout the whole region of solar cell structure. It was shown that the new method can give more accurate estimation of the absolute absorption energy in the individual layer when applied for a thin film Si solar cell structure with rough surface of bidirectional scattering distribution function. Furthermore, the proposed algorithm was proved to be very effective in analyzing solar cells with complex geometry like concentrator photovoltaic system, which necessitates the combination of coherent and incoherent calculation.

Al-doped ZnO (AZO) films prepared at different substrate temperature and AZO films with intentional Zn addition (ZAZO) during deposition at elevated substrate temperature were fabricated by radio frequency magnetron sputtering on glass substrate, and the resulting structural, electrical, optical properties together with the etching characteristics and annealing behavior were comparatively examined. AZO films deposited at 150 °C showed the optimum electrical properties and the largest grain size. XPS analysis revealed that AZO films deposited at elevated temperature of 450 °C contained large amount of Al content due to Zn deficiency, and that intentional Zn addition during deposition could compensate the deficiency of Zn to some extent. It was shown that the electrical, optical and structural properties of ZAZO films were almost comparable to those of AZO film deposited at 150 °C, and that ZAZO films had much smaller etching rate together with better stability in severe annealing conditions than AZO films due possibly to formation of dense structure.

Fluorine doped ZnO (FZO) films were deposited on Corning glass by radio frequency (rf) magnetron sputtering of pure ZnO target in CF 4 containing gas mixtures, and the compositional, electrical, optical, and structural properties of the as-grown films as well as the vacuum-annealed films were investigated. The fluorine content in FZO films increased with increasing CF 4 content in sputter gas. FZO films deposited at elevated temperature of 150 °C had considerably lower fluorine content and showed a poorer electrical properties than the films deposited at room temperature. Despite high fluorine contents in the films, for all the FZO films, the carrier concentration remained below 2×10 20 cm −3 , leading to fairly low doping efficiency level. Vacuum-annealing of the FZO films deposited at room temperature resulted in substantial increase of Hall mobilities, reaching as high as 43 cm 2 /Vs. This was attributed partly to the removing of oxygen vacancies and/or the forming chemical bonds with interstitial zinc atoms by fluorine interstitials and partly to the passivation effect of excess fluorine atoms by filling in the dangling bonds at the grain boundaries. For all the films with thickness of around 300 nm, the optical transmissions in visible were higher than 80%, and increased with increasing fluorine content up to 85% for the film with highest fluorine content.

ZnO films co-doped with H and Al (HAZO) were prepared by sputtering ZnO targets containing Al2O3 dcontent of 1 (HA1ZO series) and 2 wt.% (HA2ZO series) on Corning glass (Eagle 2000) at substrate temperature of 150 °C with Ar and H2/Ar gas mixtures. The effects of hydrogen addition to Al-doped ZnO (AZO) films with different Al contents on the electrical, optical and structural properties of the as-grown films as well as the vacuum- and air-annealed films were examined. For the as-deposited films, the free carrier number in both series of HAZO films increased with increasing H2 content in sputter gas. HA2ZO film series prepared from target containing 2 wt.% Al2O3 showed better crystallinity and higher carrier concentration than HA1ZO film series deposited using target containing 1 wt.% Al2O3. The crystallinity and the Hall mobility of HA2ZO film series decreased with increasing H2 content in sputter gas, while those of HA1ZO film series showed a reversed behavior. Although HA2ZO film series yielded lower resistivity than HA1ZO film series due to higher carrier concentrations, the higher figure of merit (expressed as 1 / ρα, where ρ and α represents the resistivity and absorption coefficient, respectively) was observed for HA1ZO film series because of substantially low absorption loss in these films. When annealed in air ambient, HA1ZO film series showed much stronger stability than HA2ZO film series. Vacuum-annealing resulted in drop of the carrier concentrations as well as large shrinkage in lattice constant, which indicated that the hydrogen dopants are in relatively volatile state and can be removed easily from the films upon annealing.

ZnO films with varying fluorine content were prepared on Corning glass by radio frequency magnetron sputtering of ZnO target containing ZnF2 at room temperature, and the compositional, electrical, optical, and structural properties of the as-grown films together with the vacuum-annealed films were investigated. The fluorine content in the fluorine doped ZnO (FZO) films increased almost linearly with increasing ZnF2 content in sputter target, and the highest atomic concentration was 7.3%. Vacuum-annealing caused a slight reduction of fluorine content in the films. The resistivity of the as-grown FZO films deposited showed a typical valley-like behavior with respect to the fluorine content in film, i.e. having minimum resistivity at intermediate fluorine content. Despite high fluorine content in the FZO films, the carrier concentration remained below 1.2 × 1020 cm−3, leading to very low doping efficiency level. Upon vacuum-annealing, the resistivity of FZO films decreased substantially due to increase in both the carrier concentration and the Hall mobility. From the structural analysis made by X-ray diffraction study, it was shown that addition of small amount of fluorine enhanced the crystallinity of FZO films with (002) preferred orientation, and that large amount of fluorine addition yielded disruption of preferred orientation. It was also shown that doping of fluorine rendered a beneficial effect in reducing the absorption loss of ZnO films in visible range, thereby substantially enhancing the figure of merit.

In this study, indium–zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In 2 O 3 –12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In 2 O 3 -oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10 − 4 Ω cm, and the highest mobility value amounting to 47 cm 2 /V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.

A study was made to examine the electromagnetic interference (EMI) shielding effect of multilayered thin films in which indium–zinc oxide (IZO) thin films and Ag or Ag alloy thin films were deposited alternately at room temperature using a RF magnetron sputtering. The optical, electrical and morphological properties of the constituent layers were analyzed using an ultraviolet-visible photospectrometer, a 4-point probe and an atomic force microscopy (AFM), respectively. The EMI shielding effect of the multilayered thin films was also measured using a coaxial transmission line method. A detailed analysis showed that the control of the film morphologies, i.e., the surface roughnesses of the constituent metal layers was essential to an accurate estimate of the electrical and optical properties of multilayered coatings. It was shown that properly designed IZO/Ag alloy multilayered thin films could yield a visible transmission of more than 70%, a sheet resistance of less than 1 Ω/sq., together with an EMI shielding effect larger than 45 dB in the range from 30 to 1000 MHz.

The use of ultrathin c-Si (crystalline silicon) wafers thinner than 20 mu m for solar cells is a very promising approach to realize dramatic reduction in cell cost. However, the ultrathin c-Si requires highly effective light trapping to compensate optical absorption reduction. Conventional texturing in micron scale is hardly applicable to the ultrathin c-Si wafers; thus, nano scale texturing is demanded. In general, nanotexturing is inevitably accompanied by surface area enlargements, which must be minimized in order to suppress surface recombination of minority carriers. In this study, we demonstrate using optical simulations that periodic c-Si nanodisk arrays of short heights less than 200 nm and optimal periods are very useful in terms of light trapping in the ultrathin c-Si wafers while low surface area enlargements are maintained. Double side texturing with the nanodisk arrays leads to over 90% of the Lambertian absorption limit while the surface area enlargement is kept below 1.5. (C) 2014 Optical Society of America

An investigation was conducted on the mechanical properties of compositionally modulated Al/AlN thin films deposited by r.f. magnetron sputtering on Si(100) substrates. The films were made to have modulation periods ranging from 40 to 200 nm. The volume fraction of Al was varied from 0.125 to 0.625 for films with the minimum modulation period of 40 nm, but it was set to 0.5 otherwise. Hardness and adhesion of the deposited films were examined by nanoindentation and scratch test method, respectively. Residual stress of monolithic Al and AlN films with varying thickness and multilayered films was also measured by a conventional beam-bending technique. As compared with a monolithic AlN film, films of various modulation periods with the Al volume fraction of 0.5 were found to have lower hardness. On the other hand, high hardness comparable to and 12% higher than that of monolithic AlN film was registered for films that have the modulation period of 40 nm and the Al volume fraction 0.125 and 0.25, respectively. All the modulated films were found to have critical loads almost twice as high as that of a single AlN film, except the one with the lowest Al volume fraction. From the scratch test, a cohesive failure was observed for films with alternating layers in residual stress state of opposite signs whereas an adhesive failure was noticed otherwise. These observations indicate that a load-carrying capacity of a modulated film depends not only on the modulation period and individual layer thickness but on the residual stress states of alternating layers.

An experiment was conducted to investigate the origin of the nonlinear optical characteristics of crystalline Ge2Sb2Te5 and Ge-doped SbTe thin films which have been demonstrated to have the capability of a superresolution readout. By means of the real-time measurement of the electrical resistance combined with concurrent optical reflectance/transmittance measurement during pulsed laser irradiation of varying power, it was found that the absorption coefficients of these films decrease with increasing laser power, accompanied most probably by an increase in the carrier concentration. This finding may be understood in light of the saturable absorption due to band filling by thermally assisted photoexcited carriers. This has been previously proposed as an important cause of the superresolution effect of PbTe, which belongs to the chalcogenide degenerate semiconductors such as the GeSbTe materials under study.

A nonvolatile memory technology utilizing reversible changes between fcc and hcp crystalline phases is proposed. In this new type of phase-change memory, data are stored in different forms of crystalline phases of (Ge/sub 1/Sb/sub 2/Te/sub 4/)/sub 0.8/(Sn/sub 1/Bi/sub 2/Te/sub 4/)/sub 0.2/ chalcogenide alloy. RESET operation produces the less conductive metastable fcc phase via melt-quenching from the more conductive stable hcp phase and SET operation involves a phase change from fcc directly to hcp. Both RESET and SET operations can be completed as fast as 70 ns with large changes in cell resistance.

We demonstrate the fabrication of shallow Si nanopillar structures at a submicron scale which provides broadband antireflection for crystalline Si (c-Si) solar cells in the wavelength range of 350 nm–1100 nm. The Si random nanopillars were made by reactive ion etch (RIE) processing with thermally dewetted Sn metals as an etch mask. The diameters and coverages of the Si nanopillars were adjusted in a wide range of the nanoscale to microscale by varying the nominal thickness of the Sn metals and subsequent annealing temperatures. The height of the nanopillars was controlled by the RIE process time. The optimal size of the nanopillars, which are 340 nm in diameter and 150 nm in height, leads to the lowest average reflectance of 3.6%. We showed that the power conversion efficiency of the c-Si solar cells could be enhanced with the incorporation of optimally designed Si random nanopillars from 13.3% to 14.0%. The fabrication scheme of the Si nanostructures we propose in this study would be a cost-effective and promising light trapping technique for efficient c-Si solar cells.

An approach is proposed to develop recording materials for high speed phase change optical data storage. It utilizes a thin film alloy mixture between a stoichiometric GeSbTe alloy and an additive ternary telluride alloy. Selection rules for an additive alloy are suggested. For a test, (Ge1Sb2Te4)1−x(Sn1Bi2Te4)x thin films are deposited by co-sputtering and their structural and thermal properties are studied. Ge1Sb2Te4 and Sn1Bi2Te4 are found to form a completely soluble pseudo-binary system, whose crystalline lattice parameters obey Vegard’s rule over the entire range of x (0

The effect of varying microstructures of Mo films on CIGS preferred orientation has been studied by changing Mo working pressure (in sputtering). CIGS I(220)/I(112) and IGS I(300)/I(006) have strong dependencies of the residual stress of Mo closely related to its microstructures: they increases with Mo pressure and then gradually decreases with Mo pressure, as the residual stress does. The trend is exactly opposite to the known effect due to Na. Thus this work shows that Mo microstructure itself can determine IGS and CIGS textures without assistance of other factors such as Na. XRD analysis on selenized Mo and TEM work on IGS/Mo show that MoSe 2 reactivity itself influences the IGS texture more than its orientation. In addition, MoSe 2 reactivity depends on the in-grain density of Mo which is linearly related to the residual stress.

A new approach is proposed to obtain fast crystallizing materials based on a conventional GeSbTe alloy for rewritable phase change optical data storage. By means of co-sputtering, Ge1Sb2Te4alloy was mixed with Sn1Bi2Te4alloy so as to form pseudo-binary alloys (Ge1Sb2Te4)1-x(Sn1Bi2Te4)x (x is a mole fraction). From structural and optical analyses of the co- sputtered and annealed alloy films, the formation of stable crystalline single phases was observed along with a Vegard's law behavior, suggesting a homogeneous mixing of the two alloys. By use of a 4 layered disk with (Ge1Sb2Te4)0.85(Sn1Bi2Te4)0.15 recording layer, a preliminary test of writing and erasing was carried out and the results were compared with the case of the disk with Ge1Sb2Te4recording layer. The (Ge1Sb2Te4)0.85(Sn1Bi2Te4)0.15 recording layer was found to yield markedly higher erasibility, especially with increasing disk linear velocity.

To better understand the role of nitrogen (N) during crystallization of Sb-rich phase change materials, a study was conducted using Sb and Sb70Te30 as host materials of N. Crystallization of the as-sputtered Sb–N films of varying N content was examined to reveal that Sb–N bonds are formed in the as-sputtered states, enhancing amorphous phase stability increasingly with N content. Crystallization appeared to proceed with irreversible dissociation of these bonds to form N2 molecules that may then exist stably during the subsequent memory operations. N2 molecules are considered to play as growth-retarding agents as demonstrated with memory operations of N-doped Sb70Te30.

We investigated the bias polarity dependence of the characteristics of a phase change memory device and found that the device showed higher resistance both at programed and erased states, extended erasing time, and higher threshold voltage (Vth) under negative bias than those under the conventional positive bias. Taking advantage of this dependence, we were able to obtain four highly distinguishable resistance states in such a reproducible manner that may be utilized for a reliable multilevel storage. We explain this polarity dependence in terms of the difference in the density of trap states at the interfaces between the phase change material and electrodes.

A study was made to examine the electrical, compositional, structural and morphological properties of Ag thin films deposited by DC magnetron sputtering in atmosphere with deposition temperature from room temperature to 15 using in-line sputter system. The Ag films deposited at temperature above in oxygen atmosphere gave a similar specific resistivity to and even lower oxygen content than those deposited using pure Ar sputter gas The Ag films deposited with pure Ar gas was mainly composed of crystallites with [111] preferred orientation, while, for those deposited in oxygen atmosphere, more than 50% of the volume was composed of crystallites with [100] orientation. The difference in the micro structure did not cause any difference in the specific resistivity of Ag films. The results showed that the transparent conducting oxide films and the Ag films could be processed sequentially in the same deposition chamber with careful control of deposition temperature, which might result in a cost reduction for constructing the large scale in-line deposition system.

A new approach to determine the optical constants of thin films using a single wavelength light source without measurement of film thickness has been introduced in this paper. From the reflectance and transmittance measured over a range of film thicknesses, the optical constants of as-deposited GeSbTe alloy films at a wavelength of 685 nm as well as the film thickness at each point of measurement have been obtained by use of a nonlinear fitting. A self-consistent validation of the approach is also presented by comparing the optical constants obtained in both cases of film-incidence and substrate-incidence.