bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time Evolution of Photoconductivity in TiO2 Electrodes Fabricated by a Sol Gel Method
Authors: Xie Zhibin , Burlakov Victor M , Henry Bernard M. , Kirov Kiril R. , Grovenor Christopher R. M. , Assender Hazel E. , Andrew G. , Briggs D. , Kano Mitsuru , Tsukahara Yusuke 
Published: April 2011

ABSTRACTWe report here on the time evolution of photoconductivity under continuous illumination in nanocrystalline TiO2 samples prepared by a sol gel method, and also on the conductivity decay once the illumination is switched off. We observe strong dependence of the photoconductivity on the illumination intensity for both processes. It is found that the conductivity decay after high-intensity illumination is slower than after low-intensity illumination, and we have attempted to explain these experimental results using a model involving hole trapping-detrapping processes.
Quantum Dot-Single Wall Carbon Nanotube Complexes for Polymeric Photovoltaics
Authors: Landi Brian J. , Castro Stephanie L. , Evans Chris M. , Ruf Herbert J. , Bailey Sheila G. , Raffaelle Ryne P. 
Published: April 2011

ABSTRACTThe ability to dissociate the photo-generated excitons and transport the resulting charge carriers are the major impediments in improving the efficiency of polymeric solar cells. In order to simultaneously address both of these issues, we have investigated the use of quantum dotsingle wall carbon nanotube (QD-SWNT) complexes as a suitable nanomaterial dopant in these devices. The formation of CdSe-SWNT complexes occurred through covalent attachment of carboxylic acid-functionalized SWNTs with CdSe-aminoethanethiol (AET) quantum dots. An additional synthetic approach was evaluated using both electrostatic and covalent attachment schemes for CuInS2-mercaptoacetic acid (MA) quantum dots and amine terminated SWNTs. The efficacy of each approach is discussed, including the necessary transmission electron microscopy (TEM) and optical absorption spectroscopy data to probe the interactions between nanomaterials. The potential effects of charge transfer between components may have important implications in the efficiency of these materials for polymeric photovoltaic devices.
High Efficiency P3HT/PCBM Solar Cell
Authors: Inoue Kanzan , Ulbricht Ross , Madakasira Pallavi C. , Zhou Miaoxin , Lee Sergey B. , Ferraris John , Zakhidov Anvar A. 
Published: April 2011

ABSTRACTWe report a nearly twofold increase of short circuit current: from Isc ∼ 10 mA/cm2 to Isc = 16–20 mA/cm2 in P3HT/PCBM solar cells (SC) employing freshly prepared regio-regular poly(3-hexylthiophene) (RR-P3HT) without special purification. The power conversion efficiency is enhanced to η≥ 4% as compared to our best η=3.8% in SC with commercial polymer despite the decreased filling factor (FF= 0.42, as compared to best FF = 0.59). We used our earlier found [1] procedures with optimal post heat treatment temperatures and time for our polymer SC. We also discovered a strong correlation between the device preparation procedures and performance. The optimal phase separation of PCBM and RR-P3HT into a bi-continuous network structure occurs after quite long solution stirring times (enhanced homogenization) and surprisingly very short annealing time at optimal temperature. We also found that the optimal concentration of PCBM in a RR-P3HT matrix is rather low, only c∼35 wt%, contrary to high c∼80 wt% in PPV based SC.
Novel Strategies for the Preparation of TiO2 Nanofibers
Authors: Balkus Kenneth J. , Xiong Chunrong , Macias-Guzman Minedys 
Published: April 2011

ABSTRACTThe various polymorphs of titanium oxide (TiO2) are probably the most widely studied materials for photovoltaic applications. It is well known that composition and particles size can have a profound effect on photoactivity. It is thought that high surface to volume nanostructures such as nanofibers and nanorods may possess the optimal properties. We have developed technology for the preparation of TiO2 nanofibers in a variety of forms including core shell structures, papers and films. The formation of mesoporous TiO2 fibers as spider webs and papers has been achieved by electrostatic deposition. The mesoporous fibers and other forms such as shaped particles and films have been employed as templates to grow TiO2 nanofibers in various configurations. The proposed research below will address the synthesis and characterization of the TiO2 fibers developed by these techniques
Expanded experimental space for luminescence studies of thin film CdS/CdTe solar cells
Authors: Feldman Scott , Ohno Tim , Kaydanov Victor , Collins Reuben 
Published: April 2011

ABSTRACTWe have explored a large range of experimental space for photoluminescence (PL) and electroluminescence (EL) measurements of CdS/CdTe solar cells. This space includes changes in temperature, injection intensity (laser power for PL, current for EL), electrical bias for PL, and laser energy for PL. Measurements were resolved both spectrally and spatially (2D for EL, 1D for PL). Combination of EL and PL measurements revealed that most spatial inhomogeneity was the result of non-uniform current transport rather than local variations in recombination rate. The greatest spectral resolution was obtained with low temperature EL at low injection rates. High injection EL as well as high forward biased PL suppressed band-edge emission at low temperatures. Spectral structure was found to be greater in EL than in PL. These effects likely originated from preferential current transport along grain boundaries and/or certain grains.
Improved Efficiency in Hydrogenated Amorphous Silicon Solar Cells Irradiated by Excimer Laser
Authors: Damitha A. A. , Adikaari T. , Ravi S. , Silva P. , Kearney Michael J. , Shannon John M. 
Published: April 2011

ABSTRACTExcimer laser crystallisation is used to fabricate nanocrystalline thin film silicon Schottky barrier solar cells, in a superstrate configuration with indium tin oxide as the front contact and chromium as the back contact. 150 nm thick intrinsic absorber layers are used for the solar cells, and was crystallised using an excimer laser with different laser energy densities. These layers were characterised using Raman spectroscopy and optical absorption before device fabrication. External quantum efficiencies of the devices were calculated from the spectral response data of the devices. A maximum efficiency of 70 % is observed for low energy irradiation, which is significant for very thin absorber layers. Device operation is discussed with proposed band structures for the devices and supplementary measurements.
Electrospun Poly(vinylidene fluoride)-based Carbon Nanofibers for Hydrogen Storage
Authors: Chung H. J. , Lee D. W. , Jo S. M. , Kim D. Y. , Lee W. S. 
Published: April 2011

ABSTRACTPoly(vinylidene fluoride) (PVdF) fine fiber of 200–300 nm in diameter was prepared through the electrospinning process. Dehydrofluorination of PVdF-based fibers for making infusible fiber was carried out using DBU, and the infusible PVdF-based nanofibers were then carbonized at 900–1800°C. The structural properties and morphologies of the resulting carbon nanofibers were investigated using XRD, Raman IR, SEM, TEM, and surface area & pore analysis. The PVdF-based carbon nanofibers had rough surfaces composed of 20-to 30-nm granular carbons, indicating their high surface area in the range of 400–970 m2/g. They showed amorphous structures. In the case of the highly ehydrofluorinated PVdF fiber, the resulting carbon fiber had a smoother surface, with d002 = 0.34–0.36 nm, and a very low surface area of 16–33 m2/g. The hydrogen storage capacities of the above carbon nano-fibers were measured, using the gravimetric method, by magnetic suspension balance (MSB), at room temperature and at 100 bars. The storage data were obtained after the buoyancy correction. The PVdF-based microporous carbon nanofibers showed a hydrogen storage capacity of 0.04–0.4 wt%. The hydrogen storage capacity depended on the dehydrofluorination of the PVdF nanofiber precursor, and on the carbonization temperatures.
Decomposition Kinetics of Lithium Amide and Its Implications for Hydrogen Storage
Authors: Pinkerton Frederick E. 
Published: April 2011

ABSTRACTKinetics of the lithium amide (LiNH2) decomposition reaction 2 LiNH2 → Li2NH + NH3 were determined using thermogravimetric analysis (TGA). LiNH2 is a primary component of the hydrided state of Li3N- and Li2NH-based storage materials. Its decomposition by ammonia release, and the resulting degradation of hydrogen storage capacity, has important implications for the durability of Li-N-H storage systems. Fine powders of LiNH2 were prepared by ball milling for 20 min. Kinetic parameters were extracted from a set of TGA weight loss curves taken at different heating rates between 1 and 20°C/min, and the activation energy Ea was determined to be 124 kJ/mole. Although decomposition occurs slowly below 300°C, isothermal TGA measurements on Li3N demonstrate that its cumulative effect is large in real Li-N-H systems, where LiNH2-containing hydrided material is held at elevated temperature under dynamic gas flow.
Biaxial strain induced electrical inhomogenities and phase separation in the ferromagnetic metallic phase in thin films of La0.7Ca0.3MnO3: A scanning tunneling potentiometry/spectroscopy study.
Authors: Paranjape Mandar , Mitra J. , Raychaudhuri A. K. , Mathur N. D. , Blamire M. G. 
Published: April 2011

ABSTRACTWe have investigated the effect of biaxial strain on local electrical/electronic properties in thin films of La0.7Ca0.3MnO3 with varying degrees of biaxial strain in them. The local electrical properties were investigated as a function of temperature by scanning tunneling spectroscopy (STS) and scanning tunneling potentiometry (STP), along with the bulk probe like conductance fluctuations.The results indicate a positive correlation between the lattice mismatch biaxial strain and the local electrical/electronic inhomogenities observed in the strained sample. This is plausible since the crystal structure of the manganites interfere rather strongly with the magnetic/electronic degrees of freedom. Thus even a small imbalance (biaxial strain) can induce significant changes in the electrical properties of the system.
Linear measurements of nanomechanical phenomena using small-amplitude AFM
Authors: Hoffmann Peter M. , Patil Shivprasad , Matei George , Tanulku Atay , Grimble Ralph , Özer Özgur , Jeffery Steve , Oral Ahmet , Pethica John 
Published: April 2011

ABSTRACTDynamic Atomic Force Microscopy (AFM) is typically performed at amplitudes that are quite large compared to the measured interaction range. This complicates the data interpretation as measurements become highly non-linear. A new dynamic AFM technique in which ultra-small amplitudes are used (as low as 0.15 Angstrom) is able to linearize measurements of nanomechanical phenomena in ultra-high vacuum (UHV) and in liquids. Using this new technique we have measured single atom bonding, atomic-scale dissipation and molecular ordering in liquid layers, including water.
Atomically Resolved Imaging of Epitaxial CaF2 on Si(111) using Noncontact Atomic Force Microscope
Authors: Seino Yoshihide , Abe Masayuki , Morita Seizo 
Published: April 2011

ABSTRACTEpitaxial calcium fluoride (CaF2) film surfaces grown on Si(111) were imaged with the atomic force microscopy operated in the noncontact mode in ultrahigh vacuum. Our experimental results reproducibly reveal two kind of topographic patterns with the atomic scale contrast. The line profiles obtained from the topographic image exhibit that the change of tip-polarity plays the important role for obtaining two atomic corrugation patterns by considering the interaction between the tip and the two topmost surface atoms. It is similar to the results from the literature obtained on the cleaved CaF2 surface with both positively and negatively terminated tip.
Electrical characterization using Scanning Capacitance Microscopy of the local electronics properties of Ge semiconductor nanostructures.
Authors: Brémond G. , Marchand J. J. , Descamps A. , Budau P. , Bassani F. , Ronda A. , Berbezier I. , Stoïca T. , Vescan L. 
Published: April 2011

ABSTRACTGe nanocrystals embedded in SiO2 via a low temperature thermal oxidation of a Si/Ge/Si stack structure grown by low pressure chemical vapour deposition or by molecular beam epitaxy in localized focalized ion beam nanopatterns are characterized by scanning capacitance microscopy. Local electrical spectroscopy on the Ge structure shows hole or electron charging by the Ge nanocrystal, thanks to the complete electrical isolation induced by the oxidation process. The scanning capacitance microscope allows measuring the discharging kinetics of the electron, giving an order of the retention time value of several hours.
Mapping of local electronic properties in nanostructured CMR thin films by Scanning Tunneling Microscopy (STM) and Local Conductance Map (LCMAP)
Authors: Kar Sohini , Ghosh Barnali , Brar L. K. , Paranjape M A. , Raychaudhuri A. K. 
Published: April 2011

ABSTRACTWe have investigated the local electronic properties and the spatially resolved magnetoresistance of a nanostructured film of a colossal magnetoresistive (CMR) material by local conductance mapping (LCMAP) using a variable temperature Scanning Tunneling Microscope (STM) operating in a magnetic field. The nanostructured thin films (thickness ≈500nm) of the CMR material La0.67Sr0.33MnO3(LSMO) on quartz substrates were prepared using chemical solution deposition (CSD) process. The CSD grown films were imaged by both STM and atomic force microscopy (AFM). Due to the presence of a large number of grain boundaries (GB's), these films show low field magnetoresistance (LFMR) which increases at lower temperatures.The measurement of spatially resolved electronic properties reveal the extent of variation of the density of states (DOS) at and close to the Fermi level (EF) across the grain boundaries and its role in the electrical resistance of the GB. Measurement of the local conductance maps (LCMAP) as a function of magnetic field as well as temperature reveals that the LFMR occurs at the GB. While it was known that LFMR in CMR films originates from the GB, this is the first investigation that maps the local electronic properties at a GB in a magnetic field and traces the origin of LFMR at the GB.
Electrical AFM Measurements for Evaluation of Nitride Erosion in Shallow Trench Isolation Chemical Mechanical Planarization
Authors: Stefanov Yordan , Ruland Tino , Schwalke Udo 
Published: April 2011

ABSTRACTThis article proposes a new application of tunneling current measurements Atomic Force Microscopy (AFM) for evaluation of silicon nitride stop-layer erosion in Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP). Simultaneous topographical and electrical AFM measurements allow a clear identification of ‘open’ silicon surfaces on nanometer scale by enhanced tunneling currents in those areas. The measurement technique is non-destructive and can be successfully implemented for process control.
Near-Field Scanning Optical Microscopy of Phase Separation Effects in Dilute Nitride Alloys.
Authors: Mintairov Alexander , Kosel Thomas , Sun Kai , Ustinov Victor , Merz James 
Published: April 2011

ABSTRACTThe effect of nitrogen composition on structural parameters of intrinsic quantum dots (QDs) has been studied in GaAs1-yNy and InxGa1-xAs1-yNy alloys (y∼0. 015–0.03) using low-temperature near-field scanning optical microscopy (NSOM) combined with magneto-photoluminescence spectroscopy. We used measurements of the diamagnetic shift (magnetic field strength 0–10T), temperature dependent spectra (temperature range 5–300K) and near-field monochromatic images for the estimation of the size, nitrogen excess and density of QDs. The obtained values (size ∼10–30 nm, nitrogen excess ∼0.005 and density ∼100 /μm-3) suggest spontaneous formation (phase separation) of QDs. Strong lateral inhomogeniety of the QD distribution on a micron length scale was observed.
Local electromechanical properties of ferroelectric materials for piezoelectric applications
Authors: Kholkin A. L. , Bdikin I. K. , Shvartsman V. V. , Orlova A. , Kiselev D. , Bogomolov A. A. , Kim S.-H. 
Published: April 2011

ABSTRACTLocal electromechanical characterization is becoming prerequisite for the development of ferroelectric-based piezoelectric devices including multilayer actuators, micromotors, piezoelectric filters and, especially, microelectromechanical systems (MEMS), which combine piezoelectric elements and control electronics on the same chip. In this work, we present the results of local electromechanical characterization of several important ferroelectric materials including Pb(Zr, Ti)O3 (PZT) and (Pb, La)(Zr, Ti)O3 (PLZT) in both thin film and ceramic form. Local piezoelectric hysteresis measurements are performed by the piezoelectric force microscopy (PFM) that detects small electric field-induced deformation on the nanoscale e. g., within the single grain of a polycrystalline material. A number of novel phenomena is observed with increasing dc bias voltage including the jump of ferroelectric domain wall to the grain boundary, the “fingerlike” instability of domain wall, and the local phase transition into ferroelectric phase.
Semiconductor Dopant Profile and Dielectric Characterization with Scanning Capacitance Microscopy
Authors: Kopanski J. J. 
Published: April 2011

ABSTRACTScanning capacitance microscopy (SCM) has been commonly used to image dopant gradients in silicon and other semiconductors. As a mobile, high-resolution (to 10 nm) metal-oxide-semiconductor (MOS) probe, SCM also is a non-destructive, contactless tool with which to examine local variations in dielectric thin film quality and local variations in semiconductor substrate properties. Virtually any measurement that can be made with fabricated metal electrodes can also be made with SCM. Two particular applications being pursued are characterization of high-κ dielectric films on silicon for next generation integrated circuits and characterization of native and deposited insulators on wide bandgap semiconductors.Local differential capacitance (ΔC) versus tip bias (Vdc) measurements can be made with SCM using an ac voltage to generate the differential capacitance signal. These measurements differ from conventional C-V measurements due to the 3-D nature of the scanning capacitance microscope tip and the method used to generate the differential capacitance signal. Theoretical predictions and experimental measurements are made of SCM differential capacitance versus dc bias voltage (ΔC-V) curves for MOS capacitors with various levels of fixed and interface traps. The goal of this work is to determine if quantitative interface trap distributions can be made using SCM and if variations in interface density can be observed near defects or device structures. The response of the SCM MOS capacitance measurement to a local electric field stress and optical pumping from the atomic force microscope (AFM) laser will also be discussed.
The electron microscopy and XRD investigation of structure processes in CMR crystals LaMnO3+δ
Authors: Shekhtman V.Sh. , Sedykh V. , Afonikova N.S. , Dubovitskii A.V. , Kulakov V.I. 
Published: April 2011

ABSTRACTThe specific features of structural transformations in lanthanum manganite are analyzed in terms of the macrosymmetry conservation principle. The possible mechanisms of phase transformations are proposed reasoning from a sequence of structural transitions, including the restoration of a virtual configuration of cubic perovskite with double the lattice parameter. It has been synthesized and investigated three phases Pnma I, Pnma II, R3c. It has been shown by X-ray diffraction analysis and Mössbauer spectroscopy that the transition from the Pnma I to Pnma II phase in LaMnO3+d compound occurs through the intermediate phase Pnma II* virtually by “jump”. The HEED investigations of the synthesized phases have shown that the Pnma I and R3c phases have the expected simple pattern whereas the electron-diffraction pattern of the Pnma II phase strongly differs.
Interactions of Hydrating Tricalcium and Dicalcium Silicate using Time-Resolved Quasielastic Neutron Scattering
Authors: Peterson Vanessa K. , Neumann Dan A. , Livingston Richard A. 
Published: April 2011

ABSTRACTHydrating tricalcium and dicalcium silicate mixtures were studied using time-resolved quasielastic neutron scattering. Application of a hydration model allowed the extraction of several parameters describing the hydration mechanics. The hydration rate during the nucleation and growth period, diffusivity during the diffusion limited regime, and the maximum amount of product able to be formed were not related linearly to the mixture combinations. Addition of dicalcium silicate at approximately 20 wt. % caused a sharp alteration to these parameters, including reduced hydration rate and reaction layer permeability. These two factors lead to the prediction that more reaction products would be ultimately manufactured during the reactions at this composition.
Real-Time XRD Characterization of Growth of Sputtered Tantalum Films
Authors: Lee S. L. , Mueller J. , Windover D. 
Published: April 2011

ABSTRACTAn in-situ DC magnetron sputter deposition system was constructed on the goniometer of an X-ray diffractometer for investigation of thin film nucleation and growth in real time. Tantalum films were deposited on silicon and A723 steel substrates under various deposition conditions. This paper showed: 1) Ta films evolved in single or mixed α-Ta and β-Ta phase on Si and Fe with very different growth characteristics. 2) Crystalline phase was sensitive to deposition mechanics, Ta film changed phase spontaneously without external parameter changes. 3) In pressure range 0.65–13 Pa at 100 watts, phase was not sensitive to pressure variations, but deposition rate and degree of texture decreased at high gas pressure. 4) Depositions using heavier gas showed higher a-Ta concentrations. 5) Reverse sputter cleaning of target and substrate surfaces improved Ta film adhesion.
X-Ray Nanoplasma Instruments and Tools
Authors: Bloom Scott , Rieger Harry , Alwan Jim 
Published: April 2011

ABSTRACTSoft x-rays have wavelengths in the range of 1–15 nm and therefore the diffraction limited spot size of focused x-rays can be as small as 1.22 × the radiation wavelength, or less than 20 nm spot size. Using our pulsed x-ray source and focusing a small collected solid angle of this x-ray radiation to a sample provides enough power to form a very hot plasma that emits a range of radiation from UV through IR that can be collected and analyzed on a conventional optical spectrometer. In addition to diagnostic capabilities the instrument can be also used as a tool to form structures at nanometer scale resolution. Since the plasma is formed by ablating the target material with x-rays the target can be patterned or nanomachined using the plasma itself. It should be possible to pattern nanoscale devices by rastering the material under the nanoplasma. Finally in analogy to plasma assisted CVD processes, organometallic vapors could introduced into the sample chamber such that the nanoplasma locally plates out specific species of metals of other materials on the target at nanoscale sizes for forming devices, circuits, wires, etc. This paper presents a design for a nanoplasma instrument, predicted performance parameters will be presented, and development issues identified and discussed.