Atomistic origins of the phase transition mechanism in Ge2Sb2Te5

Combined static and molecular dynamics first-principles calculations are used to identify a direct structural link between the metastable crystalline and amorphous phases of Ge2Sb2Te5. We find that the phase transition is driven by the displacement of Ge atoms along the rocksalt [111] direction from the stable-octahedron to high-energy-unstable tetrahedron sites close to the intrinsic vacancy regions, which give rise to the formation of local 4-fold coordinated motifs. Our analyses suggest that the high figures of merit of Ge2Sb2Te5 are achieved from the optimal combination of intrinsic vacancies provided by Sb2Te3 and the instability of the tetrahedron sites provided by GeTe

Economical And Systematical Evaluation On Rainfall Harvesting System (Case Study : Rainfall Harvesting System Designed In Taebaek City, Republic Of Korea)

Recently, climate change has caused drought to become more frequent and is becoming one of the serious natural disasters, resulting damages in infrastructure facilities, economy and private property losses etc. Taebaek city of Gangwon-do lies in the northeast Korean Peninsula along the steep mountain slopes, all the way to the sea. Thu, this city exhibit the Marine Climatic Characteristics. During the past 10 years, the average rainfall of Taebaek city is 849.9mm/year, which is less than the average rainfall for the whole country (1,274mm/year). This research is still ongoing. The next assessment will be on the construction cost of rainfall harvesting system (through school types) and the LCC (Life Cycle Cost) of Maintenance Administration. After which, discussion for the impacts Rainfall Harvesting System on the water supply self-sufficiency of Taeback city will be made. Lastly, conclusion on the future economic benefit for Taeback city will be given. ACKNOWLEDGEMENT This research was supported by a grant(12-TI-C01) from Advanced Water Management Research Program funded by Ministry of Land, Infrastructure and Transport of Korean governmen

High quality epitaxial growth of PbTiO3 by molecular beam epitaxy using H2O2 as the oxygen source

Single crystalline PbTiO3films have been epitaxially grown on SrTiO3 (001) substrates by molecular beam epitaxy using H2O2 as the source of active oxygen. The optimum growth conditions have been determined by analyzing a range of growth parameters affecting growth and used to attain single phase and stoichiometric PbTiO3thin films.In situ reflection high-energy electron diffraction pattern indicated the PbTiO3films to be grown under a two-dimensional growth mode. The full width at half maximum of the rocking curve of a relatively thin65nm (001) PbTiO3film is 6.2arcmin which is indicative of high crystal quality. The band gap of PbTiO3, as determined by ellipsometric measurement, is 3.778eV

Spectroscopic ellipsometry and absorption study of Zn1-xMnxO/Al2O3 (0 \u3c= x \u3c= 0.08) thin films

We grow Zn1−xMnxO∕Al2O3 (0⩽x⩽0.08)thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5eV. Using the model of Holden et al. [T. Holden et al., Phys. Rev. B56, 4037 (1997)], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gapenergy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large broadening of both the E0 band gap and its exciton partner E0x peaks even for less than 2% of optically determined Mn composition. In ellipsometric spectra, we also find Mn-related 3eV optical structure. In particular, optical absorption spectra with varying N2 gas flow rate show that the Mn-related peak intensity decreases with increasing N2 flux. The decrease of the 3eV Mn-related peak intensity is attributed to increasing N2 flow rate and Mn–N hybridization

Visible-ultraviolet spectroscopic ellipsometry of lead zirconate titanate thin films

We measured pseudodielectric functions in the visible-ultraviolet spectral range of Pb(ZrxTi1−x)O3 (x=0.2, 0.56, 0.82) (PZT)grown on platinized silicon substrate using the sol-gel method and also on (0001) sapphire using radio frequency sputtering method. Using a parametric optical constant model, we estimated the dielectric functions of the PZTthin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical point model, we determined the parameters of the critical points. In the second derivative spectra, the lowest bandgap energy peak near 4eV is fitted as a double peak for annealedPZTs associated with the perovskite phase. As-grown PZTs have mainly pyrochlore phase and the lowest bandgap is fitted as a single peak. We compared the bandgap energies with literature values

Dielectric functions and critical points of PbTiO3, PbZrO3, and PbZr0.57Ti0.43O3 grown on SrTiO3 substrate

Single crystalline PbTiO3, PbZrO3, and PbZr0.57Ti0.43O3 thin films on SrTiO3 (001) substrates were grown by a combination of molecular beam epitaxy and rf sputtering methods. The authors measured the dielectric functions of the thin films using spectroscopic ellipsometry and determined the interband critical point energies using standard critical point model. They compared the critical point energies to the band structure calculations in the literature. The data suggest that anticrossing behavior occurs between Ea and Eb near Zr=0.17. This phenomenon is attributed to a coupling between X1c and X3c bands caused by intrinsic alloy disorder

An Analysis Of Discharge And Water Level Changes Due To Weir (In The Case Of The Waegwan And Nakdong Station In South Korea)

ABSTRACT Our country, Korea, lacks the per capita water endowment because of the high population density and geographical characteristics. Therefore, The 4 Rivers Project has been promoted since 2009. In order to control effectively drought or floods caused by abnormal climate and strong rainfall in summer, it was done and completed in 2013. The Nakdong River is the longest in the 4 Rivers Project, which it was conducted among the country\u27s major rivers, and a lot of hydraulic structures were installed. we selected Nakdong and Weagwan stations which are located in the Nakdong River. Because the change was smaller there with the inflow of tributaries flow than elsewhere. And many hydraulic structures were installed between Nakdong and Weagwan stations, which used T/M machine to collect real-time data. In this study, we compared and analyzed the flow change of real-time and water level data of prior to weir installation on May, June, July, 2009 and completion of weir installation on May, June, July , 2013. The original purpose of installing the weir is well-kept. After installation of Hydraulic structures(weir), the discharge difference between the Nakdong Station and Weagwan Station was reduced , and both of Nakdong and Weagwan stations are almost maintain a constant value of water level without being affected by rainfall. Also, we could confirm that the maximum water-level variation is decreased after installation of the weir. Based on this, we judged that hydrological effects on drought or floods due to abnormal weather were decreased by the time of weir installation. ACKNOWLEDGEMENT This research was supported by a grant(12-TI-C01) from Advanced Water Management Research Program funded by Ministry of Land, Infrastructure and Transport of Korean governmen

Spectroscopic ellipsometric study of ZnO and Zn1-xMgxO thin films grown on (0001) sapphire substrate

We grew ZnO and Zn1-xMgxO thin films on (0001) sapphire substrates by using metal-organic vapor phase epitaxy and measured the pseudo-dielectric functions using variable-angle spectroscopic ellipsometry. We analyzed the pseudo-dielectric functions by using the multi-layer model. The dielectric functions were fitted by using a Holden model dielectric function. We used anisotropic layer modeling for the ZnO thin film, whereas we adopted the approximation of isotropic layer modeling for the Zn1-xMgxO alloys. We also discuss the Mg composition dependence of the bandgap and the binding energy in Zn1-xMgxO alloys, and consider the valence-band ordering in ZnO thin films.The work of H. Lee was supported in part by the Special Equipment Program of the Korean Basic Science Institute through the Korean Science and Engineering Foundation (KOSEF, R23-2002-000-00006-0). The work of G.-C. Yi was supported by the Advanced Environmental Biotechnology Research Center (No. R11-2003-006)

Efficient Perovskite Light-Emitting Diodes Using Polycrystalline Core-Shell-Mimicked Nanograins

Making small nanograins in polycrystalline organic-inorganic halide perovskite (OIHP) films is critical to improving the luminescent efficiency in perovskite light-emitting diodes (PeLEDs). 3D polycrystalline OIHPs have fundamental limitations related to exciton binding energy and exciton diffusion length. At the same time, passivating the defects at the grain boundaries is also critical when the grain size becomes smaller. Molecular additives can be incorporated to shield the nanograins to suppress defects at grain boundaries; however, unevenly distributed molecular additives can cause imbalanced charge distribution and inefficient local defect passivation in polycrystalline OIHP films. Here, a kinetically controlled polycrystalline organic-shielded nanograin (OSN) film with a uniformly distributed organic semiconducting additive (2,2 ',2 ''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole), TPBI) is developed mimicking core-shell nanoparticles. The OSN film causes improved photophysical and electroluminescent properties with improved light out-coupling by possessing a low refractive index. Finally, highly improved electroluminescent efficiencies of 21.81% ph el(-1) and 87.35 cd A(-1) are achieved with a half-sphere lens and four-time increased half-lifetime in polycrystalline PeLEDs. This strategy to make homogeneous, defect-healed polycrystalline core-shell-mimicked nanograin film with better optical out-coupling will provide a simple and efficient way to make highly efficient perovskite polycrystal films and their optoelectronics devices.

Dielectric functions and electronic band structure of lead zirconate titanate thin films

We measure pseudodielectric functions in the visible-deep ultraviolet spectral range of Pb(ZrxTi1−x)O3 (x=0.2,0.56,0.82) (PZT), Pb0.98Nb0.04 (Zr0.2Ti0.8)0.96O3, Pb0.91La0.09 (Zr0.65Ti0.35)0.98O3, and Pb0.85La0.15Ti0.96O3 films grown on platinized silicon substrates using a sol-gel method and on (0001) sapphire using a radio-frequency sputtering method. Using a parametric optical constant model, we estimate the dielectric functions(ϵ) of the perovskite oxide thin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical-point model, we determine the parameters of the critical points. In the second derivative spectra, the lowest band-gapenergy peak near 4 eVis fitted as a double peak for annealed PZTs due to the perovskite phase. As-grown PZTs have mainly pyrochlore phase and the lowest band-gap peak is fitted as a single peak. We also examine the effect of dopants La and Nb, which substitute at Pb and Zr (Ti) sites, respectively. We found three band gaps Ea(∼3.9eV), Eb (∼4.5eV), and Ec (∼6.5eV) in the order of increasing energy. The Ea and Eb band-gap energies were not sensitive to Zr composition. We discuss the change of critical-point parameters for PZTs in comparison to the band-structure calculations based on local-density approximation. The near constancy of the lowest band-gap energy independent of Zr composition is consistent with the band-structure calculations