bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Effects At Interfaces In Cu (cr, mo, w, ta, re) Multilayers
Authors: Bello A. F. , Van Buuren T. , Klepeis J. E. , Barbee T. W. 
Published: April 2011

ABSTRACTInterfacial electronic effects between Cu and the transition metals Cr, Mo, W, Ta, Re, are investigated by determining the strength of the white line absorption resonances on the L3,2 edges of Cu in Cu5/TM5 multilayers. X-ray absorption (XAS) was performed to study the white lines, which are directly related to the unoccupied states of Cu in the multilayers. The metallic multilayers are 2 nm in period and 200 nm in total thickness. Each period contains 5 monolayers of Cu and 5 monolayers of the transition metal: = 40% of the atoms are at interfaces. These material pairs form ideal structures for the investigation of interfacial electronic effects as they form no compounds and exhibit terminal solid solubility. Only weak white lines are observed on the L3,2 edges of Cu since all the d-orbitals are filled. In the Cu/TM multilayers, however, we observed enhancement of the Cu white lines. We attribute this to the charge transfer from the “interfacial Cu atoms” d-orbital to the transition metal layers. Analysis of the white line enhancement enables calculation of the charge transfer calculation from the Cu to the transition metal. Cu shows a charge transfer of about 0.03 electrons/interfacial Cu atom in Cu/Cr, 0.064 in Cu/Mo, 0.35 in Cu/Ta, 0.17 in Cu/W , and 0.23 in Cu/Re. This charge transfer is consistent with the enhanced absorption energy of Cu on these materials as observed in thermal desorption experiments.
The Chemical Environment Of Er3+ In A-Si:Er:H And A-Si:Er:O:H
Authors: Tessler Leandro R. , Piamonteze Cínthia , Iñguez Ana Carola , Alves M. C. Martins , Tolentino H. 
Published: April 2011

ABSTRACTWe have measured extended x-ray absorption fine structure (EXAFS) of the Er LIII edge in a-Si:Er:O:H with different concentrations of Er and O. The samples were prepared by reactive RF co-sputtering from a silicon target partially covered with metallic erbium platelets. They present the characteristic Er 3+ photoluminescence at 1.54 μm as deposited. The FFT of the Er EXAFS provides two well separated peaks. The characteristics of the first peak resemble those of Er2O3. We associate the first neighbor shell with oxygen atoms, even in non intentionally oxygenated samples. The average coordination and Er-O separation are significantly smaller than in Er2O3. This may be the reason why Er3+ luminescence in a-Si:H presents small temperature quenching. The second shell is interpreted as being composed of silicon atoms.
An Exafs Study of Compositional Homogeneity in Sol-gel Processed Potassium Tantalum Niobates
Authors: Wilkinson A. P. , XU J. , Pattanaik S. 
Published: April 2011

ABSTRACTA series of K(Ta1-x Nbx)O3 solid-solution samples were prepared by direct reaction of oxides and carbonates, a homogeneous sol-gel process, and an inhomogeneous sol-gel process. The inhomogeneous sol-gel samples were prepared by the prehydrolysis of separate KTaO3 and KNbO3 precursor solutions followed by mixing of the resulting sols, drying and calcination. An examination of these samples by EXAFS at the Ta LIII and Nb K-edges, i) illustrated the difficulty of obtaining homogeneous solid solutions via direct reaction of oxides/carbonates, and ii) showed that the homogeneity of a solid-solution could be controlled by varying the hydrolysis procedure used during its sol-gel synthesis.
X-Ray Absorption Spectroscopy Studies of Electrochemically Deposited Thin Oxide Films
Authors: Balasubramanian M. , Melendres C. A. , Mansour A. N. , Mini S. 
Published: April 2011

ABSTRACTWe have utilized “in situ” X-ray Absorption Fine Structure Spectroscopy to investigate the structure and composition of thin oxide films of nickel and iron that have been prepared by electrodeposition on a graphite substrate from aqueous solutions. The films are generally disordered. Structural information has been obtained from the analysis of the data. We also present initial findings on the local structure of heavy metal ions, e.g. Sr and Ce, incorporated into the electrodeposited nickel oxide films. Our results are of importance in a number of technological applications, among them, batteries, fuel cells, electrochromic and ferroelectric materials, corrosion protection, as well as environmental speciation and remediation.
Electronic and Spatial Structure Studies of Cadmium and Zinc Dialkyldithiocarbamate Molecules in Nonaqueous Solutions Used in the Processes Spray Pyrolysis
Authors: Erenburg S. B. , Bausk N. V. , Zemskova S. M. , Tkachev S. V. , Mazalov L. N. 
Published: April 2011

ABSTRACTCdK EXAFS and 113Cd NMR spectra, ZnK EXAFS and XANES spectra were measured for solutions of cadmium and zinc dialkyldithiocarbamates in organic solvents with different donor numbers: tributylphosphine, methylene chloride, benzene, dibutylsulfide, pyridine, dimethylsulfoxide and for some model compounds. The parameters of the local surroundings of the Cd and Zn atoms for complex forms in solutions were determined using EXAFS . Spatial structure models of the complex forms in a metal chelate - nonaqueous solvent system are suggested. It is established that coordination of nitrogen atoms by cadmium atoms in pyridine solutions is realized for both Cd[(C2H5)2NCS2 ]2 and Cd[(n−C4 H9)2NCS2]2. For the tributylphosphine solution of Cd[(n−C4H9) 2NCS2]2 and Zn[(n−C4H9)2NCS2]2, additional coordination of the phosphorus atoms of the solvent molecules by the metal atoms are established.
Structural Changes in Iron(II) Polymeric Complexes upon Thermally and Optically Induced Spin Transition Determined by EXAFS Spectroscopy
Authors: Erenburg S. B. , Bausk N. V. , Lavrenova L. G. , Shvedenkov Yu. G. , Mazalov L. N. 
Published: April 2011

ABSTRACTChanges in the electronic and spatial structure of polymeric Fe(II) complexes with 1,2,4- triazoles and various anions upon spin transition was studied using EXAFS and XANES spectroscopy. Spin transition and structural changes were induced by variations of the anion, dilution with Zn, under heating or the action of light. In all complexes, the spin transition is accompanied by drastic changes in the local environment of Fe atoms. The increase in spin transition temperature for the complexes with variable anions CIO4-, I-, Br-, BF4-, NO3- was found to correlate with changes in the Fe-N distances and changes in bond covalence determined from the chemical shifts in Mössbauer spectra. High spin metastable long life states were detected and studied in the polymeric complex Fe(atrz)3(ClO4)2. It was established that the changes in structure of polymeric complexes upon the transition to a metastable high spin state under the action of light differ from those in the thermally induced spin transition. Such differences are determined by mutual influence of Fe atoms in high spin and low spin states in polymeric chains.
Automated Indexing of Laue Images from Polycrystalline Materials
Authors: Chung Jin-Seok , Ice Gene E. 
Published: April 2011

ABSTRACTThird generation hard x-ray synchrotron sources and new x-ray optics have revolutionized x-ray microbeams. Now intense sub-micron x-ray beams are routinely available for x-ray diffraction measurement. An important application of sub-micron xray beams is analyzing polycrystalline material by measuring the diffraction of individual grains. For these measurements, conventional analysis methods will not work. The most suitable method for microdiffraction on polycrystalline samples is taking broad-bandpass or white-beam Laue images. With this method, the crystal orientation and non-isostatic strain can be measured rapidly without rotation of sample or detector. The essential step is indexing the reflections from more than one grain. An algorithm has recently been developed to index broad bandpass Laue images from multi-grain samples. For a single grain, a unique set of indices is found by comparing measured angles between Laue reflections and angles between possible indices derived from the x-ray energy bandpass and the scattering angle 2 theta. This method has been extended to multigrain diffraction by successively indexing points not recognized in preceding indexing iterations. This automated indexing method can be used in a wide range of applications.
The Mechanism of Twinning in Zincblende Structure Crystals: New Insights on Polarity Effects From a Study of Magnetic Liquid Encapsulated Czochralski Grown Inp Single Crystals
Authors: Dudley M. , Raghothamachar B. , Guo Y. , Huang X. R. , Chung H. , Larson D. J. , Hurle D. T. J. , Bliss D. F. , Prasad V. , Huang Z. 
Published: April 2011

ABSTRACTSynchrotron White Beam X-ray Topography (SWBXT) and synchrotron X-ray anomalous scattering have been employed to determine the polarity of {111} edge facets, anchored to the three phase boundary (TPB) on which twinning is observed to nucleate in Magnetic Liquid Encapsulated Czochralski (MLEC) grown sulfur doped, <001> InP single crystals. Analysis of the results indicates that both the formation of edge facets and the nucleation of twins occur preferentially on {111}P faces. Of the four possible sets of edge facets, belonging to the {111}P form, which are oriented so as to be thermodynamically favored to be anchored to the TPB, two can give rise to a {115} to {111}P external shoulder facet conversion upon twinning, while the other two can give rise to a {114} to {110} conversion. For these cases, twinning is only observed when the {111}P edge facets are anchored to the TPB in a region where the shoulder angle is close to 74.21° or 70.53°, facilitating the production of the {115} and {114} external shoulder facets, respectively, prior to twinning. These observations are discussed in light of calculated surface energies of the various internal and external facets.
Twin and Grain Boundary in InP :A Synchrotron Radiation Study
Authors: Han Yujie , Jiang Jianhua , Wang Zhouguang , Liu Xunlang , Jiao Jinghua , Tian Yulian , Lin Lanying 
Published: April 2011

ABSTRACTExperimentally observed X-ray reflectivity curves show bi-crystal(twin) characteristics. The study revealed that there was defect segregation at the twin boundary. Stress was relaxed at the edge of the boundary. Relaxation of the stress resulted in formation of twin and other defects. As a result of formation of such defects, a defect-free and stress-free zone or low defect density and small stress zone is created around the defects. So a twin model was proposed to explain the experimental results. Stress(mainly thermal stress), chemical stoichiometry deviation and impurities nonhomogeneous distributions are the key factors that cause twins in LEC InP crystal growth. Twins on (111) face in LEC InP crystal were studied. Experimental evidence of above mentioned twin model and suggestions on how to get twin-free LEC InP single crystals will be discussed.
Pulsed Femtosecond Excimer Laser-Induced Chemically Clean Etching of Diamond
Authors: Malshe A.P. , Ozkan A.M. , Railkar T.A. , Molian P.A. , Brown W.D. 
Published: April 2011

AbstractChemically clean etching of thermodynamically metastable diamond using a 500 femtosecond (fs), 248 nm KrF excimer laser is reported. The experimental results, characterized by micro-Raman spectroscopy indicate that unlike nanosecond (ns) pulsed laser processing of diamond, fs laser irradiation of the surface does not generate any graphite or amorphous carbon residues. Microstructural analysis of the fs pulsed laser etched surface indicates streaks.
Crystal Quality and Orientation of Pulsed Laser Deposited Barium Titanate Thin Films
Authors: Gottmann J. , Klotzbücher T. , Vosseler B. , Kreutz E. W. 
Published: April 2011

AbstractKrF excimer laser radiation (λ=248 nm, τ=25 ns) is used for pulsed laser deposition of BaTiO3 thin films on Pt/Ti/Si multilayer substrates. The processing gas atmosphere consists of O2 at typical pressures of p=10-3-5·10-1 mbar. The investigations concentrate on the influence of the substrate temperature and the kinetic energy of the film forming particles on the crystalline structure and orientation of the growing films.X-ray diffraction measurements and polarization dependent micro Raman spectroscopy reveal oriented growth of the films with c-axis orientation normal to the substrate surface and [100] texture if the energy of the particles is > 60 eV, while at lower kinetic energies a [110] or [111] texture with partly a-axis orientation is preferred. The ferroelectricity and the dielectric constant of the films, as determined by polarization versus voltage (P-V) and capacitance versus voltage (C-V) impedance measurements, decreases with increasing kinetic energy of the film forming particles. This decrease of the dielectric properties correlates with the change of the preferred orientation and the crystalline quality of the films.
Preparation and Characterization of (Ba1-xSrx)TiO3 Thin Films for Infrared Detection by Pulsed Iaserdeposion Method
Authors: Kubo R. , Xu H. , Yoshino Y. , Okuyama M. 
Published: April 2011

AbstractBa1-xSrxTiO3 thin films have been deposited on Pt/Ti/SiO2/Si substra by the pulsed ArF laser deposition method. Deposition conditions, such as ambient gas and substrt temperatze, have been optmized to rrxove crystallinepropesty. Fe oelectric p e phasehasbeenobtainod ithe BSTthin filns deposited above 500°C in Q2 gas havingpressure ofabout 13Pa. Using N2O gas instead of O2 gas improved the crystallinity, because highly chemical active oxygen radicals produced due to ultraviolet inadiation of the laser. Doping of Bi ranging around 2% fills of the role of decrease leakage current of BST thin films. Temperature dependence of the dielectric constant (εr) shows a sharp change, peaking aroumd room temperature. The peak point exists below 25°C in the ratio of Ba/Sr=1.1 film, and shills above 50°C in Ba/Sr=5.7 film. When the Ba/Sr ratio is 1.4 the dielectric peak exists near 27°C and is very sharp. The maxinium differentW rate of dielectric constanttversus temperature is the largest in Ba/Sr=1.4 film and is about 100K-1. This value is equivalent to apyroelectric coefficient of 1.8 × 10-7 C/cm2K, which is almost the same as that of LiTaO3 single crystl, a typical pyroelectric material.
Pulsed Laser Deposition of BaxSr1-xTiO3 Thin Films for Frequency Agile Microwave Electronics
Authors: Chang W. , Horwitz J. S. , Pond J. M. , Kirchoefer S. W. , Chrisey D B. 
Published: April 2011

AbstractOriented, single phase thin films (~5000Å thick) of BaxSr1-xTiO3 (BST) have been deposited on to (100) MgO and LaAlO3 (LAO) single crystal substrates using pulsed laser deposition (PLD). A strong correlation is observed between the microstructure of the deposited film and the dielectric tuning and loss at microwave frequencies. Microstructural defects observed in as deposited films include strain, due to film substrate lattice mismatch and oxygen and cation vacancies. Compensation of the ablation target with excess Ba and Sr is observed to increase the dielectric constant and to reduce the dielectric loss. Post-deposition, bomb annealing of films at high temperatures (1250°C) is observed to fill oxygen vacancies and increase grain size. The difference in the dielectric behavior for as-deposited and low temperature annealed BST films on MgO and BST films on LAO is observed and may be attributed to the differences in film stress. A further improvement in the dielectric behavior is observed by the addition of donor/acceptor dopants such as Mn. The data shows that ferroelectric thin films can be used to build tunable microwave circuits that offer significant performance advantages over devices made from conventional semiconducting materials.
Microstructure and Temperature Dependence of Microwave Penetration Depth of Ag-YBa2Cu3O7-δ Thin Films
Authors: Kaur Davinder , Pinto R. 
Published: April 2011

AbstractWe report the measurements of the magnetic penetration depth λ(T) of Ag-doped YBa2Cu3O7-δ (YBCO) thin films in the film thickness range 1500-4000A and temperature range 18-88K. The films are insitu grown by laser ablation on LaAlO3 <100> single crystal substrates. The penetration depth measurements are performed by microstrip resonator technique. A correlation of λ(T) with the film microstructure observed with Atomic Force Microscopy has shown that λ(T) depends critically on the film microstructure. Temperature dependence of λ(T) has also been studied for best quality films.The experimental results are discussed in terms of BCS theory (s-wave pairing) and d-wave Pairing with and without impurity scattering. The results are found to be best fitted to the d-wave model in dirty limit with impurity scattering. Near Tc, we have also compare the (3D) XY critical regime and the Ginzburg-Landau (GL) behaviour.
Amorphous Diamond Films Deposited by Pulsed-Laser Ablation: the Optimum Carbon-Ion Kinetic Energy and Effects of Laser Wavelength
Authors: Lowndes Douglas H. , Merkulov Vladimir I. , Puretzky A. A. , Geohegan D. B. , Jellison G. E. , Rouleau C. M. , Thundat T. 
Published: April 2011

AbstractA systematic study has been made of changes in the bonding and optical properties of hydrogen-free tetrahedral amorphous carbon (ta-C) films, as a function of the kinetic energy of the incident carbon ions measured under film-deposition conditions. Ion probe measurements of the carbon ion kinetic energies produced by ArF and KrF laser ablation of graphite are compared under identical beam-focusing conditions. Much higher C+ kinetic energies are produced by ArF-laser ablation than by KrF for any given fluence and spot size. Electron energy loss spectroscopy and scanning ellipsometry measurements of the sp3 bonding fraction, plasmon energy, and optical properties reveal a well-defined optimum kinetic energy of 90 eV to deposit ta-C films having the largest sp3 fraction and the widest optical (Tauc) energy gap (equivalent to minimum near-gap optical absorption). Tapping-mode atomic force microscope measurements show that films deposited at near-optimum kinetic energy are extremely smooth, with rms roughness of only ~ 1 Å over distances of several hundred nm, and are relatively free of particulates.
Matrix Assisted Pulsed Laser Evaporation (Maple) of Polymeric Materials: Methodology and Mechanistic Studies
Authors: Piqué A. , McGill R. C. R. A. , Chrisey D. B. , Callahan J. , Mlsna T. E. 
Published: April 2011

AbstractA new matrix assisted pulsed laser evaporation (MAPLE) technique has been developed at the Naval Research Laboratory, to deposit superior quality ultra thin, and uniform films for a range of highly functionalized polymeric materials. The MAPLE technique is carried out in a vacuum chamber, and involves directing a pulsed laser beam onto a frozen target, consisting of a polymer dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target, where both solvent and polymer molecules are lifted into the evacuated gas phase. A solvent and polymer plume are generated incident to the substrate being coated. Si(111), and NaCl substrates coated with thin layers of polymer have been examined by a range of techniques including: optical microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy. Under optimum conditions the native polymer was transferred to the substrate without chemical modification as a highly uniform film.The MAPLE technique offers a number of advantages over conventional polymer deposition techniques, including the ability to precisely and accurately coat a relatively large or small targeted area with an ultrathin, and uniform coating with sub monolayer thickness control. Conventional pulsed laser ablation techniques can be utilized for coating a limited number of polymers, but we have found that for highly functionalized materials the native polymer structure is almost completely lost in the process. In contrast, when the MAPLE conditions are optimized the deposition of even highly functionalized polymeric materials proceeds with little effect on the intrinsic polymer structure.
A Comparison of Single-Wall Carbon Nanotube Production Using Continuous Wave and Pulsed Laser Vaporization
Authors: Dillon A.C. , Parilla P.A. , Jones K.M. , Riker G. , Heben M.J. 
Published: April 2011

AbstractWe have produced single-wall carbon nanotubes (SWNTs) by Nd:Yag laser vaporization of porous cobalt-nickel/graphite targets for the first time without applying external heat to the target. Both continuous wave (c.w.) and pulsed laser-techniques were explored. In the pulsed experiments, the energy density per pulse was varied between 0.12 and 0.62 J/cm2 and pulse rates ranged from 24 kHz down to 3 kHz corresponding to average powers of 25.5 to 16 W. Continuous wave experiments were conducted at average powers which corresponded to those measured for each of the pulsed runs. An additional run at 30 W was also performed. A rigorous method developed for the analysis of transmission electron microscopy (TEM) images was used to estimate SWNT content in the laser-generated carbon samples. The pulsed and continuous wave processes both produced a linear increase in SWNT content with increasing average power. These results are not intuitive for the pulsed laser-production since a higher average power corresponds to a lower peak pulse power. In fact, a pulsed run with the maximum pulse energy of 0.62 J/cm2 (3 kHz, 16 W), produced no detectable SWNTs. A maximum SWNT content of 78% was observed for c.w. experiments at a power of 30 W. Additional laser experiments performed on dense cobalt-nickel / graphite targets at room temperature enabled a better understanding of the carbon removal mechanisms for the pulsed versus c.w. processes. Cumulatively, these investigations indicate that high energy laser pulses produce particles from highly porous targets by ablation which are too large to readily be incorporated into growing nanotubes. Successful high-yield production of SWNTs relies upon remaining in a vaporization regime during synthesis.
Use of Matrix Assisted Pulsed Laser Evaporation (Maple) for the Growth of Organic Thin Films
Authors: Piqué A. , Chrisey D.B. , Spargo B.J. , Bucaro M.A. , Vachet R.W. , Callahan J.H. , McGill R.A. , Leonhardt D. , Mlsna T.E. 
Published: April 2011

AbstractA novel variation of conventional pulsed laser deposition, called matrix assisted pulsed laser evaporation, or MAPLE, has been utilized for growing organic thin films. The MAPLE technique is carried out in a vacuum chamber and involves directing a pulsed laser beam) onto a frozen target consisting of an organic compound dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target with both solvent and organic molecules being released into the chamber. The volatile solvent is pumped away, whereas the organic molecules coat the surface of a substrate. Very thin and uniform films (50 to 100 nm) of various organic materials, such as carbohydrates, have been deposited on Si(111) and NaCl substrates. The films prepared using this method have been examined by optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and electrospray mass spectrometry. Careful control of the processing conditions allowed carbohydrates such as sucrose and glucose, in addition to high molecular weight polymers such as dextran, to be transferred to the substrate as uniform films, without significant chemical decomposition. The use of MAPLE films for chemical and biological sensor applications is being investigated and the potential of this technique for producing high quality thin films of other organic compounds will be discussed.