bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal and elastic properties of Ge-Sb-Te based phase-change materials
Authors: Zalden P. , Bichara C. , Eijk J. v. , Hermann R. P. , Sergueev I. , Bruns G. , Buller S. , Bensch W. , Matsunaga T. , Yamada N. , Wuttig M. 
Published: September 2011

ABSTRACTPhase-change materials undergo a change in bonding mechanism upon crystallization, which leads to pronounced modifications of the optical properties and is accompanied by an increase in average bond lengths as seen by extended x-ray absorption fine structure (EXAFS), neutron and x-ray diffraction. The reversible transition between a crystalline and an amorphous phase and its related property contrast are already employed in non-volatile data storage devices, such as rewritable optical discs and electronic memories. The crystalline phase of the prototypical material GeSb2Te4 is characterized by resonant bonding and pronounced disorder, which help to understand their optical and electrical properties, respectively. A change in bonding, however, should also affect the thermal properties, which will be addressed in this study. Based on EXAFS data analyses it will be shown that the thermal and static atomic displacements are larger in the meta-stable crystalline state. This indicates that the bonds become softer in the crystalline phase. At the same time, the bulk modulus increases upon crystallization. These observations are confirmed by the measured densities of phonon states (DPS), which reveal a vibrational softening of the optical modes upon crystallization. This demonstrates that the change of bonding upon crystallization in phase-change materials also has a profound impact on the lattice dynamics and the resulting thermal properties.
The modulation of bulk-organic solar cells: the effect of serial and parallel resistances and the relationship with the microscopic morphology
Authors: Trindade A.J. , Santos M.G. , Gomes J. , Pereira L. 
Published: September 2011

ABSTRACTThis work shows the relationship between the morphology (studied by AFM) of an active bulk-heterojunction (BHJ) layer composed by MEH-PPV (poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) and PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and the respective photovoltaic figures of merit. It is observed that the most relevant parameter (influencing the efficiency) is the fill-factor (FF), as both the open circuit voltage and short circuit current are not significantly affected by the microscopic morphology. Different local conformation of the active films can change the FF from near 25% to more than 65%, having a strong impact in the efficiency. These results were modulated by an equivalent circuit. Serial and parallel resistances were related with the physical behavior of the organic cells. These were observed to have a direct relationship with the achieved morphology.
Effect of Vanadium Ions on the Functional Properties of Nanocrystalline Zinc Oxide
Authors: Gálvez Saldaña Marco A. , Perez Oscar Perales , Guinel Maxime J-F 
Published: September 2011

ABSTRACTA systematic study was carried out to determine the effects of composition and grain size on the structural, optical and magnetic properties of pure ZnO and vanadium-doped ZnO nanocrystalline powders and films in the 0.0 at.% V - 6 at.% V range. The powders and films were synthesized via a sol-gel approach, where ethanolamine was used to increase the viscosity of the precursor solutions and promote the adhesion of the films onto quartz substrates. Powder X-ray diffraction confirmed the formation of ZnO (host oxide) after annealing of the precursors in air. The average grain size in the thin films ranged from 11 nm to 23 nm when the samples were annealed in air for one hour between 450ºC and 550ºC. UV-vis and photoluminescence confirmed the formation of the host oxide. Also, the photoluminescence intensity was found to be strongly dependent on the amount vanadium. Furthermore, it was found that the vanadium concentration and the annealing temperature play an important role in the ferromagnetic behavior of the material.
Temperature Dependent Optical Response of Si(100): Theory vs. Experiment
Authors: Shkrebtii A.I. , Heron J. , Cabellos J.L. , Witkowski N. , Pluchery O. , Mendoza B.S. , Borensztein Y. 
Published: September 2011

ABSTRACTWe investigate theoretically and experimentally the temperature-dependent linear optical properties of the clean c(4×2) reconstructed Si(100) surface for a wide range of temperatures. We combine two theoretical formalisms: the first one incorporates the contribution of temperature-dependent atomic motion to the surface optical response and, the second uses a dielectric function layer-by-layer separation method. Using these formalisms, we model temperature-dependent reflectance anisotropy (RA) of this surface for the first time: finite temperature ab-initio Car-Parrinello Molecular Dynamics (CPMD) at different temperatures up to 1000 K provide temperature-dependent atomic structural inputs for optical calculations and subsequent average of dielectric functions. Experimentally, one-domain c(4x2) Si(100) surface was prepared and characterised by Reflectance Anisotropy Spectroscopy (RAS) in a temperature range between 300 K and 800 K. Good agreement between experiment and theory is demonstrated, including a temperature-induced red shift of both the surface and bulk optical peaks. Theoretical results indicate that the temperature-induced modification of the optical response is substantially more pronounced for the surface than for the bulk.
Electron position: jumping in double concentric quantum rings
Authors: Filikhin I. , Matinyan S. , Nimmo J. , Vlahovic B. 
Published: September 2011

ABSTRACTSemiconductor heterostructures as quantum dots or quantum rings (QR) demonstrate discrete atom-like energy level structure. In an atom the position of an electron can be changed by electromagnetic field influence with accompaniment of quantum number change. In present work we show that in the weak coupled Double Concentric Quantum Ring (DCQR), the electron jumping is possible due to tunneling accompanied with level anti-crossing which has a place in a magnetic field. We study DCQR composed of GaAs in an Al0.70Ga0.30As substrate under influence of a magnetic field. In our model the DCQR is considered within three dimensional single sub-band effective mass approach. When a magnetic field is applied in the z direction, perpendicular to the DCQR plane. The results of the numerical calculations for DCQR are presented for DCQRs of different geometry.
Defect-free and Defective Surfaces of the Pyrochlore Oxide La2Zr2O7: A Theoretical Study
Authors: Mantz Yves A. 
Published: September 2011

ABSTRACTIn this work, the low index faces of lanthanum zirconate (La2Zr2O7, LZ) are studied at the level of density-functional theory, representing the first theoretical attempt to characterize the surfaces of a pyrochlore oxide. All possible surface terminations formed by cleaving a perfect crystal are considered, as well as selected defective surfaces. After deriving the expression for the free energy of an LZ surface, surface free energies are computed. The most stable surface terminations are identified, their geometric and electronic structures discussed, and a motivation provided for calculating ratios of certain surface free energies more accurately for comparison to experimental results that will be obtained.
Surface Modification of α-Fe2O3 Nanorod Array Photoanodes for Improved Light-Induced Water Splitting
Authors: Shen Shaohua , Kronawitter Coleman X. , Jiang Jiangang , Guo Liejin , Mao Samuel S. 
Published: September 2011

ABSTRACTα-Fe2O3 nanorod arrays were fabricated by a low-temperature aqueous chemical growth (ACG) technique and followed by an annealing process. For the surface doping of α-Fe2O3 nanorods, β-FeOOH nanorods obtained via ACG were coated with a thin layer of Cr3+ precursor solution by spin coating, and then underwent the annealing treatment in air. Conducting polymer polypyrrole (PPy) decorated α-Fe2O3 nanorods were prepared by electrodeposition method using malic acid contained pyrrole aqueous solution. Primary results showed that the photocurrents of α-Fe2O3 nanorod array photoanodes were greatly enhanced by surface doping of Cr3+, as well as PPy decoration. This might be due to the retarded charge recombination and promoted surface reaction rate of photogenerated holes with water. Further investigation on surface modification of α-Fe2O3 nanorod array photoanodes is currently conducted in our group.
Theoretical investigation of Er-O co-doping in hexagonal GaN
Authors: Sanna Simone , Gerstmann Uwe , Schmidt Wolf Gero 
Published: September 2011

ABSTRACTThe co-doping of hexagonal GaN with Er and O is investigated by means of density functional calculations. Predominantly Er-O defect-pairs characterized by a binding energy around 0.5 eV are formed. Different geometric configurations with various orientations (i.e. axial and basal pairs with C3v or C1h symmetry) are expected with similar formation energies. Independent of the particular configuration, the presence of oxygen does not deeply affect the atomic structure and the electronic charge distribution around the Er centers. The relatively high binding energy suggests that Er-O pairs should survive thermal treatment. An investigation of the binding energy per bond indicates that on the other hand Er-Ox complexes (x=2,3,4) are not likely to be formed (differently from Er-O co-doped Si). Rather, as long as the oxygen fluence does not overtake the Er fluence, different oxygen ions will be bound to different Er-centers.
Dynamics of Water Confined on the Surface of Titania and Cassiterite Nanoparticles
Authors: Ross Nancy L. , Spencer Elinor C. , Levchenko Andrey A. , Kolesnikov Alexander I. , Abernathy Douglas L. , Boerio-Goates Juliana , Woodfield Brian F. , Navrotsky Alexandra , Li Guangshe , Wang Wei , Wesolowski David J. 
Published: September 2011

ABSTRACTWe present low-temperature inelastic neutron scattering spectra collected on two metal oxide nanoparticle systems, isostructural TiO2 rutile and SnO2 cassiterite, between 0-550 meV. Data were collected on samples with varying levels of water coverage, and in the case of SnO2, particles of different sizes. This study provides a comprehensive understanding of the structure and dynamics of the water confined on the surface of these particles. The translational movement of water confined on the surface of these nanoparticles is suppressed relative to that in ice-Ih and water molecules on the surface of rutile nanoparticles are more strongly restrained that molecules residing on the surface of cassiterite nanoparticles. The INS spectra also indicate that the hydrogen bond network within the hydration layers on rutile is more perturbed than for water on cassiterite. This result is indicative of stronger water-surface interactions between water on the rutile nanoparticles than for water confined on the surface of cassiterite nanoparticles. These differences are consistent with the recently reported differences in the surface energy of these two nanoparticle systems.
Influence of Surface Preparation on Scanning Kelvin Probe Microscopy and Electron Backscatter Diffraction Analysis of Cross Sections of CdTe/CdS Solar Cells
Authors: Moutinho H.R. , Dhere R.G. , Jiang C.-S. , Al-Jassim M.M. 
Published: September 2011

ABSTRACTElectron backscatter diffraction (EBSD) provides information on the crystallographic structure of a sample, while scanning Kelvin probe microscopy (SKPM) provides information on its electrical properties. The advantage of these techniques is their high spatial resolution, which cannot be attained with any other techniques. However, because these techniques analyze the top layers of the sample, surface or cross section features directly influence the results of the measurements, and sample preparation is a main step in the analysis.In this work we investigated different methods to prepare cross sections of CdTe/CdS solar cells for EBSD and SKPM analyses. We observed that procedures used to prepare surfaces for EBSD are not suitable to prepare cross sections, and we were able to develop a process using polishing and ion-beam milling. This process resulted in very good results and allowed us to reveal important aspects of the cross section of the CdTe films. For SKPM, polishing and a light ion-beam milling resulted in cross sections that provided good data. We were able to observe the depletion region on the CdTe film and the p-n junction as well as the interdiffusion layer between CdTe and CdS. However, preparing good-quality cross sections for SKPM is not a reproducible process, and artifacts are often observed.
Impact of thickness variation of the ZnO:Al window layer on optoelectronic properties of CIGSSe solar cells
Authors: Keller Jan , Knipper Martin , Parisi Jürgen , Riedel Ingo , Dalibor Thomas , Avellan Alejandro 
Published: September 2011

ABSTRACTWe studied the thickness variation of equally doped ZnO:Al films used as conductive window layer in Cu(In,Ga)(Se,S)2 (CIGSSe) thin film solar cells. The IV-characteristics of solar cells with window layer thickness of d1=200nm exhibit a strong enhancement of the short-circuit current density JSC (ΔJSC = 3mA/cm2) as compared to samples with module-like ZnO:Al-film thickness (d2=1200nm). Accordingly, the quantum efficiency reveals the spectral regimes where the JSC-gain occurs. Moreover, current-voltage measurements reveal that the cells with thicker ZnO:Al exhibit slightly decreased open circuit voltage VOC. This finding can be assigned to a decreased net-doping density NA, which appears to be introduced by additional heat flux during the longer process time required for deposition of thicker ZnO:Al films. However, the improved efficiency of solar cells with thinner window layer comes along with an increase of the series resistance (RS) by almost a factor of 2, which will have consequences for the series connection of elements in a module. XRD-diffractograms and SEM cross-section imaging suggest that the enhanced RS in cells with thin ZnO:Al is not exclusively related to the thickness but is also due to a reduced (002)-texture and an elongated lateral charge carrier pathway.
High Haze and Low Resistive MgO/AZO Bi-layer Transparent Conducting Oxide for Thin Film Solar Cells
Authors: Kang Dong Won , Woo Jong Seok , Choi Sung Hwan , Lee Seung Yoon , Lee Heon Min. , Han Min Koo. 
Published: September 2011

ABSTRACTWe have propsed MgO/AZO bi-layer transparent conducting oxide (TCO) for thin film solar cells. From XRD analysis, it was observed that the full width at half maximum of AZO decreased when it was grown on MgO precursor. The Hall mobility of MgO/AZO bi-layer was 17.5cm2/Vs, whereas that of AZO was 20.8cm2/Vs. These indicated that the crystallinity of AZO decreased by employing MgO precursor. However, the haze (=total diffusive transmittance/total transmittance) characteristics of highly crystalline AZO was significantly improved by MgO precursor. The average haze in the visible region increased from 14.3 to 48.2%, and that in the NIR region increased from 6.3 to 18.9%. The reflectance of microcrystalline silicon solar cell was decreased and external quantum efficiency was significantly improved by applying MgO/AZO bi-layer TCO. The efficiency of microcrystalline silicon solar cell with MgO/AZO bi-layer front TCO was 6.66%, whereas the efficiency of one with AZO single TCO was 5.19%.
Memory Retention Characteristics of Data Storage Area Written in Transition Metal Oxide Films by Using Atomic Force Microscope.
Authors: Kinoshita K. , Yoda T. , Kishida S. 
Published: September 2011

ABSTRACTConductive atomic-force microscopy (C-AFM) writing is attracting attention as a technique for clarifying the switching mechanism of resistive random-access memory (ReRAM) by providing a wide area filled with filaments, which can be regarded as one filament with large radius. We observed a C-AFM writing area of NiO films using SEM, and revealed a correlation between the contrast in a secondary electron image (SEI) and the resistance written by C-AFM. In addition, the dependence of the SEI contrast on the beam accelerating voltage (Vaccel) suggests that the resistance-change effect occurs near the surface of the NiO film. As for the effect of electron irradiation on the C-AFM writing area, it was shown that the resistance change effect was caused by exchanging oxygen with the atmosphere at the surface of the NiO film. This result suggests that the low resistance and high resistance areas are, respectively, p-type Ni1+δO (δ< 0) and insulating (stoichiometric) or n-type Ni1+δO (δ ≥0).
Upconversion In Rare-Earth Ion-Doped NaYF4 Crystals and Nanocolloids
Authors: Patel Darayas N. , Hardy Lauren A. , Smith Tabatha J. , Smith Eva S. , Wright Donald M. 
Published: September 2011

ABSTRACTNano-colloids and nano-crystals doped with ions of rare-earth elements have recently attracted a lot of attention of scientific community. This attention is due to unique physical, chemical and optical properties attributed to nanometer size of the particles. They have great potential of being used in applications spanning from new types of lasers, especially blue and UV lasers, phosphorous display monitors, optical communications, and fluorescence imaging. In this paper we investigate the infrared-to-visible upconversion luminescence in bulk crystals doped with ytterbium and holmium co-doped and ytterbium and thulium co-doped NaYF4 upconversion phosphors. The phosphors were prepared by using simple co-precipitation synthetic method. The initially prepared phosphor has very weak upconversion fluorescence. The fluorescence significantly increased after the phosphor was annealed at a temperature of 600 0C. Nanocolloids of this phosphor were obtained using methanol as solvents and they were utilized as laser filling medium in photonic crystal fibers. Under 980 nm laser excitation very strong upconversion signals were obtained for ytterbium and holmium co-doped phosphor at 541 nm, 646 nm and 751 nm, and 376 nm, 476 nm, 646 nm, 696 nm and 803 nm for ytterbium and thulium co-doped phosphor. The particle sizes of the nanocolloids were analyzed using Atomic Force Microscope. The reported nanocolloids are good candidates for fluorescent biosensing applications and also as a new laser filling medium in fiber lasers.
Fabrication of Silicon on Borosilicate Glass Microarrays for Quantitative Live Cell Imaging
Authors: Martin David T. , Sandoval Sergio , Carter Andy , Rodwell Mark , Smith Stefan , Kummel Andrew C. , Messmer Davorka 
Published: September 2011

ABSTRACTPlanar arrays of microwells were fabricated in Silicon on borosilicate glass (pyrex) substrates in order to facilitate live cell fluorescence imaging experiments for cells sequestered inside their own individual microenvironments for incubation and quantification of single cell seceretions. Two methods of deep silicon etching were compared: cryogenic deep reactive ion etching (DRIE) and time multiplexed DIRE (Bosch Process). A 200um Si wafer was bonded to a 500um pyrex substrate. Cryogenic DRIE allowed for the reliable fabrication of 75-100um deep microwells with 60x60um openings across a 10x10mm substrate while the Bosh Process allowed for etching entirely through the Si layer, producing 200um deep microwells with transparent bottoms and steep sidewalls while maintaining the target 60x60um opening geometry.
Optical and electrical properties of solution processable TiOx thin films for solar cell and sensor applications
Authors: Li Jiguang , Pu Lin , Gupta Mool C. 
Published: September 2011

ABSTRACTRecently, few tens of nanometer thin films of TiOx have been intensively studied in applications for organic solar cells as optical spacers, environmental protection and hole blocking. In this paper we provide initial measurements of optical and electrical properties of TiOx thin films and it’s applications in solar cell and sensor devices. The TiOx material was made through hydrolysis of the precursor synthesized from titanium isopropoxide, 2-methoxyethanol, and ethanolamine. The TiOx thin films of thickness between 20 nm to 120 nm were obtained by spin coating process. The refractive index of TiOx thin films were measured using an ellipsometric technique and an optical reflection method. At room temperature, the refractive index of TiOx thin film was found to be 1.77 at a wavelength of 600 nm. The variation of refractive index under various thermal annealing conditions was also studied. The increase in refractive index with high temperature thermal annealing process was observed, allowing the opportunity to obtain refractive index values between 1.77 and 2.57 at a wavelength 600 nm. The refractive index variation is due to the TiOx phase and density changes under thermal annealing.The electrical resistance was measured by depositing a thin film of TiOx between ITO and Al electrode. The electrical resistivity of TiOx thin film was found to be 1.7×107 Ω.cm as measured by vertical transmission line method. We have also studied the variation of electrical resistivity with temperature. The temperature coefficient of electrical resistance for 60 nm TiOx thin film was demonstrated as - 6×10-3/°C. A linear temperature dependence of resistivity between the temperature values of 20 – 100 °C was observed.The TiOx thin films have been demonstrated as a low cost solution processable antireflection layer for Si solar cells. The results indicate that the TiOx layer can reduce the surface reflection of the silicon as low as commonly used vacuum deposited Si3N4 thin films.
Oxidized Single-Walled Carbon Nanotubes: Removal of Carbonaceous Functionalized Material by Washing with Solvents or Base
Authors: Canto Elisa Del , Flavin Kevin , Movia Dania , Giordani Silvia 
Published: September 2011

ABSTRACTOxidized single-walled carbon nanotubes (SWNTs) have been prepared following a widely reported two-step purification/oxidation procedure in the presence or absence of a treatment with base (NaOH). The oxidized nanotube samples washed with solvents or base appear close to identical with respect to both appearance and properties. Efficient removal of both metal and carbonaceous impurities and introduction of –COOH groups on the nanotube surface have been demonstrated by AFM, Raman and FTIR spectroscopy. Furthermore, persistence of optical properties was confirmed using UV-vis/NIR absorption and NIR photoluminescence spectroscopies.
Analysis on interface layer between Pt electrode and ferroelectric layer of solution-processed PZT capacitor
Authors: Pham Thanh V , Bui Trinh N Q , Phan Tue T , Miyasako Takaaki , Tokumitsu Eisuke , Shimoda Tatsuya 
Published: September 2011

ABSTRACTPt/Pb(Zr0.4Ti0.6)O3 (PZT)/Pt capacitors were prepared by the sol-gel technique and their electric properties were analyzed. The asymmetry of polarization-electric field (P-E) and capacitor-voltage (C-V) curves exhibits existence of an interface layer (dead-layer) between top Pt electrode and PZT thin film. By conducting temperature dependant measurement, the Pt/PZT/Pt capacitor was confirmed to be Schottky emission conduction. In addition, barrier height of PZT contact calculated 0.67eV. On basic a series capacitors model and Schottky contact of Pt/PZT interface, the thickness and the dielectric constant of this dead-layer were estimated to be 6.4 nm and 170, respectively. Moreover, the dielectric constant of 900 was obtained for the real PZT ferroelectric layer. The existence of the dead-layer was also confirmed by the high resolution transmission electron microscopy (HR-TEM) observation and the energy dispersive X-ray (EDX) analysis on PZT ferroelectric layer in the Pt/PZT/Pt structure. Based on EDX analysis result, a 10-nm layer at Pt/PZT contact was suggested to be the dead-layer.