bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-Assembled Organic Monolayer Films on Underpotentially Deposited Metal Layers
Authors: Jennings G. K. , Laibinis P. E.
Published: June 2019

This paper describes a new family of organized molecular assemblies that are produced by the spontaneous adsorption of alkanethiols onto gold surfaces that have been modified by the underpotential deposition of copper or silver. The system has the flexibility associated with the formation of self-assembled monolayers by the adsorption of thiols onto gold with the advantage of improved stability. The use of these systems as modified electrodes is also addressed.
Thin Layer Electrochemical Studies of ZnS, ZnSe, and ZnTe Formation by Electrochemical Atomic Layer Epitaxy (ECALE)
Authors: Colletti Lisa P. , Thomas Sajan , Wilmer Elvin M. , Stickney John L.
Published: June 2019

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Zn, Te, Se, and S on polycrystalline Au substrates have been performed. These studies were initiated to investigate the electrodeposition of ZnTe, ZnSe, and ZnS by electrochemical ALE (ECALE). Zn UPD on Au begins at -0.5 V and results in a coverage of 0.47 monolayer (ML). Te and Se atomic layers were formed using a two step process where bulk chalcogenide was removed by reduction, leaving the atomic layer. The reduction of the last atomic layer of Te or Se was not observed, regardless of how negative the potential was scanned. Sulfur atomic layers were spontaneously deposited below -0.6 V from a sulfide solution. Thermodynamic effects are clearly evident during the first monolayer of deposition. Zinc deposition onto Te, Se, and S coated electrodes occurs at progressively more positive potentials as the stability of the zinc compounds increase.

This initial information was used to develop ECALE cycles for the compounds, and thin-films were formed by repeated application of the cycles. The dependence of the deposit coverage on the deposition potentials was examined and found to display the characteristic “S” curve of a surface limited process. In addition, the dependence of the coverage on the number of ECALE cycles performed was found to be near the ideal 0.5 ML per cycle for ZnSe and ZnS. The ZnTe coverage per cycle was less than expected indicating that further optimization of deposition conditions is needed.
UHV Model Experiments of Electrochemical Etching of GaAs BY H2O/Br2
Authors: Henrion O. , Klein A. , Ettenkofer C. , Jaegermann W.
Published: June 2019

To investigate the initial steps of GaAs etching Br2 and H2O were (co)adsorbed onto the (110) cleavage plane at 100 K and the interaction investigated by SXPS and LEED. H2O is dissociatively adsorbed at low temperatures and leads to Fermi level pinning close to midgap. Br2 leads, depending on coverage, to the formation of bromides of different stoichiometries. During annealing to 290 K the bromides mostly evaporate from the surface (etching). Br2 and H2O coadsorption leads to Ga-oxide remaining on the surface. For the reactive interfaces band bending is not observed. The results of the adsorption experiments are compared to electrochemically prepared surfaces.
Scanning Probe Investigations of Cleaved Heterostructure Layers
Authors: Ebel J. L. , Schlesinger T. E. , Reed M. L.
Published: June 2019

We present differential oxidation rate effects in cleaved heterostructures containing GaAs, AlGaAs, InGaP and InGaAs measured by atomic force microscopy (AFM). AFM images of the cleaved structures are presented, along with step height measurements at the different material interfaces. These height differences are the result of differences in oxidation rates of the heterostructure layers. The method used to extract the small step-height information from the images is also presented. Typical step heights range from about one to twenty angstroms for the structures measured. We have also observed steps which mimic the oxidation steps, but which are not related to the epitaxially grown material structure. However, in these cases images of both sides of the cleaved pieces show inverse (rather than similar) topographies. We also present results of digital etching techniques used to enhance the step heights based on the same differential oxidation mechanism.
Microelectrochemical Characterization and Modification of Semiconductor Surfaces with Polycrystalline Ti/TiO2 as an Example
Authors: Michaelis A. , Kudelka S. , Schultze J. W.
Published: June 2019

Different new micro-methods such as anisotropy micro-ellipsometry (AME), photoresist micro-electrochemistry, micro-photocurrent spectroscopy, and UV-laser scanning were performed simultaneously to characterize and modify heterogeneous semiconducter surfaces. All measurements were carried out on single grains with the Ti/TiO2 system as an example. The crystallographic orientations of the substrate grains were determined in-situ by AME. It is shown that both the electronic and the optical properties of the semiconducting TiO2 films sensitively depend on the substrate texture. Film properties such as layer thickness and defect state concentration vary with the substrate orientation in a systematic manner.

The TiO2 films were modified at high local resolution by means of focused UV-laser illumination. Both a thickening (writing) or thinning (erasing) of the films could be realized depending on the potential applied during the illumination. Therefore, the anodic potential could be used to control the layer thickness and to generate semiconducting structures with thickness gradients.
Kinetic Model for Layer - by - Layer Homoepitaxial Growth
Authors: Trofimov V. I. , Mokerov V. G. , Shumyankov A. G.
Published: June 2019

A new kinetic model for homoepitaxial growth on a singular surface is presented. The model combines the familiar rate equations approach and the concept of a feeding zone that allows connection between the growth processes occuring in neighbouring monolayers. The model involves the irreversible 2D nucleation, growth and coalescence of islands in each growing monolayer and consists of an infinite set of coupled rate equations for the adatom and island densities and coverage in successive monolayers. The temporal evolution of the surface morphology (rms roughness and RHEED intensity) is studied with this model. It is shown that the growth mode is fully determined by a single dimensionless parameter μ = D/J where D and J are the normalized surface diffusion coefficient and deposition flux, respectively. There exist five regions of μ corresponding the different growth regimes varying from smooth 2D layer-by-layer growth at sufficiently high values of μ (>108) to very rough Poisson-like random deposition growth at μ <10−4. The extension of the model to the case of heteroepitaxy is also discussed.
In Situ Investigation of Working Battery Electrodes Using Synchrotron X-Ray Diffraction
Authors: Jisrawi N. M. , Thurston T. R. , Yang X. Q. , Mukerjee S. , McBreen J. , Daroux M. L. , Xing X. K.
Published: June 2019

The results of an in situ investigation of the structural changes that occur during the operation of working battery electrodes using synchrotron radiation are presented. Two types of electrodes were investigated: an AB2-type Laves phase alloy anode with the composition ZrxTi1-xM2 and a proprietary cell based on a LixMn2O4 spinel compound cathode made by Gould electronics. For the Laves phase alloy compositions with x=0.25 and 0.5 and M=V0.5N1.1Mn0.2Fe0.2 were examined. Cells made from two different batches of LixMn2O4 material were investigated. The relationships between battery performance and structural changes will be discussed. In the later case, we also discuss the role of over-discharging on the LixMn2O4 structure and on battery operation.
Electroless Deposition of La1−xSrxMnO3Perovskite Film on Yttria Stabilized Zirconia Substrate
Authors: Sasaki T. , Matsumoto Y.
Published: June 2019

A LaMnO3precursor was electrolessly deposited on a YSZ substrate in a solution containing Mn2+, La3+, an oxidizing agent and some additives. Peroxydisulfate was used as the oxidizing agent. The LaMnO3precursor was an amorphous and hydrous MnO2which contained La3+ions. The incorporation of La3+ions into the precursor oxide film was based on the ion-exchange reaction, where La3+ions in the solution were exchanged for H+ions on the deposited amorphous and hydrous MnO2. A La1-xSrxMnO3precursor was also prepared from the LaMnO3precursor by the ion-exchange reaction of some of the La3+ions in the LaMnO3precursor for Sr2+ions in the solution. (La0.5Sr0.5)0.75MnO3perovskite film was obtained from the precursor films on Pt substrate by heat-treatment at 800 °C.
Electrodeposition for Hi-MEMS with Special Reference to Fabrication of a Magnetic Mini-Motor
Authors: O'Sullivan E. J. , Cooper E. I. , Romankiw L. T. , Horkans J. , Kwietniak K. T.
Published: June 2019

Electrodeposition through photoresist masks is a critical, enabling technology for fabrication of the thick structures (of up to several hundred microns) involved in HI-MEMS. Process integration is an important issue in HI-MEMS. The electrodeposited structure is influenced by the choice of optical or X-ray lithography. Thickness uniformity of the deposit on the wafer scale can be optimized by the use of an auxiliary cathode. On the device or feature scales, thickness uniformity can be improved by the thoughtful design of the pattern to be plated.

A variable reluctance, planar, integrated mini-motor with a 6 mm diameter rotor has been fabricated using lithography, electrodeposition and dielectric planarization processes. The rotors were fabricated separately, released from the substrate, and slipped on the shaft, which was plated up as part of the stator fabrication.
Atomic Force Microscopy Study of Surface Evolution During Electrocrystallization of Zinc-Dion Alloys
Authors: Czerwinski F. , Kondo K. , Szpunar J. A.
Published: June 2019

Zn-Fe alloys, composed of η (h.c.p.) phase, were electrolytically deposited on cold rolled steel substrates from sulfate electrolytes. Deposits, which initially exhibited a morphology of approximately 20 nm thick platelets inclined 10–20 deg to the substrate surface, subsequently evolved either into triangular pyramids or hexagonal columnar crystals depending on the deposition conditions. A combination of X-ray texture measurements and AFM topographical analysis was used to characterize the growth surface of Zn-Fe alloys. For the morphology of hexagonal columnar crystals, the (00·1) basal planes were aligned perpendicular to the growth direction. For the morphology of the triangular pyramids, the (10·0) and (00·1) planes of η phase were tilted to the growth direction and surrounded the growth surface. For both morphologies the micro- and nanosize steps of growth were identified.
Corrosion of Electronic and Magnetic Devices and Materials
Authors: Frankel Gerald S.
Published: June 2019

Corrosion of thin film structures commonly used in electronic and magnetic devices is discussed. Typical failure modes are presented, and galvanic corrosion is discussed in some detail since it is one common problem with such devices. A graphical explanation for the determination of the ohmic potential drop during galvanic corrosion is presented. The corrosion problem of thin film disks is shown to have changed during the past ten years owing to changes in disk structure. The corrosion susceptibility of two antiferromagnetic alloys used for exchange coupling to soft magnetic layers is discussed.
Stm Study of the Influence of Adsorption on Step Dynamics
Authors: Moffat T. P.
Published: June 2019

In situ STM has been used to examine the influence of anion adsorption and metal underpotential deposition on the structure and dynamics of steps on copper surfaces. Chloride is shown to form potential dependent adlayer structures on Cu(100) and Cu(111) which strongly affects the orientation of the surface steps. The adlayer acts as a template guiding step evolution during metal deposition and dissolution. Metal underpotential deposition (upd) exhibits similar effects on step structure. This is demonstrated for Pb upd on Cu(lll). In this instance the Pb monolayer displaces chloride from the surface and leads to a reorientation of the steps and an alteration of the step dynamics.
Structure of Momolayers of Silicotungstate Anions on Ag(111) and Au(111) Electrode Surfaces
Authors: Ge Maohui , Niece Brian K. , Wall Craig G. , Klemperer Walter G. , Gewirth Andrew A.
Published: June 2019

α-Dodecatungstosilicate (α-SiW12O404−) anions form ordered monolayers on Ag(111) and Au(111) surfaces. In-situ STM images reveal that the silicotungstate ion forms a square adlattice with an intermolecule spacing of 10.2 ± 0.5 Å on both Ag and Au surfaces. Additional structures exhibiting either row or rhombic motifs are observed on Au electrodes. The structure of the adlattices can be modeled using a simple model which maximizes the coordination of the silicotungstate ion to the electrode while maintaining van der Waals contacts between terminal oxygens of adjacent silicotungstates.
Millimeter-Submillimeter Vector Measurements in Free Space, and in Resonant Structures. Application to Dielectrics Characterization.
Authors: GOY Philippe , Gross Michel , Caroopen Sylvain , Mallat Juha , Tuovinen Jussi , Maestrini Alain , Annino Guiseppe , Fittipaldi Maria , Martinelli Massimo
Published: June 2019

Usual vector measurements need to compare the signal detected through the Device Under Test DUT, with the signal coming directly from the source. Thanks to a very simple original method developed since 1989, vector detection can also be done with a purely electronic reference. In transmission experiments, there is no need for any directional coupler, and the frequency coverage extends from 8 to 1000 GHz. Quasi-optical propagation is used in the millimeter-submillimeter frequency range. Transmission through dielectric slabs in free space will give an easy measurement of the permittivity. Its real part will be obtained from the phase rotation, and its imaginary part from the amplitude decay. With dielectric coating deposited onto metal, the reflection method is necessary for the characterization. Low-loss materials are characterized with the open cavity perturbation technique. Extremely low loss materials can constitute “whispering gallery” resonators, very easy to excite and characterize.
Millimeter Wave Solid State Devices
Authors: Rosenau Steven A. , Liang Cheng , Zhang Weikang , Deng Bihe , Li Weiying , Chang Chia-Chan , Hsu Pei-Ling , Hsia Richard P. , Jiangs Fan , Domier Calvin W. , Luhmann Neville C.
Published: June 2019

Examples of novel solid state devices are presented, together with descriptions of their applicability to the diagnosis of laboratory, processing and fusion plasmas. GaAs varactor diodes can be arranged in large monolithic grid arrays, forming millimeter wave frequency multiplier based sources and high speed switches, or embedded in transmission lines to provide a true time delay for phased antenna array beam steering. Micro-electromechanical systems (MEMS) switches are exciting new devices with numerous applications, including low loss millimeter wave switches, phase shifters and mechanically tunable structures.
Silicon Wafer Subsurface Characterization with UV/Millimeter-Wave Technique
Authors: Ogita Yoh-Ichiro , Gan-nen Yuichiro
Published: June 2019

In subsurface characterization for Si wafers using a photoconductivity technique with a ultra-violet photoexcitation and millimeter wave reflection, high sensitivity technique for100 GHz was discussed experimentally and theoretically. The technique detected photoconductivity decays measured for p/p+ and n/n+ epitaxial wafers. The epilayer contaminated with Mo and Fe was characterized by the technique. Photoconductivity amplitude (PCA) intensity measured for as-polished Si wafers in commercial use after removing the subsurface by SC1 cleanings well reflected the behavior of removal of slight subsurface damage induced by mirror-polishing. The damage depth was determined to be 21 nm.
Millmeter Wave Aquametry
Authors: Meriakri Viacheslav V.
Published: June 2019

Specific advantage of millimeter (MM) wave aquametry is discussed. MM waves ensure better spatial resolution and better sensitivity to water than microwaves. MM waves are less sensitive to conducting impurities than microwaves, and MM waves can be used for water testing in media that are opaque to optical and infrared radiation. In the paper the water content measurement methods for some liquid and solid-state materials are described. Examples of devices for water control in crude oil, alcohol, powders used in metallurgy, paper, timber are considered. Usually it is possible to measure moisture content in real time (including in flow) with uncertainty less than 0.1%.
Dynamical X-ray diffraction analysis of Solid Phase Epitaxy growth of Si1-yCy heterostructures
Authors: Rodriguez-Viejo J. , el-Felk Zakia
Published: June 2019

The strain and damage produced on Si substrates by high-dose ion implantation of Si and C is investigated after thermal treatments by double and triple crystal X-ray diffraction, high ressolution transmission electron microscopy (HRTEM) and Secondary Ion Mass Spectrometry (SIMS). Si implantation (180 keV, 5×1015 Si at cm−2) at liquid nitrogen temperature forms a buried amorphous layer. Annealing at temperatures close to 650°C results in epitaxial films with significant defect recovery. X-ray rocking curves show the existence of interference fringes on the left hand side of the 004 Si peak indicating the presence of tensile strained Si layers due to the generation of Si interstitials during the implantation process. C implantation, at 60 keV, 7×1015 cm−2 and 450°C, in the preamorphized Si wafers results in the growth of Si1-yCy epitaxial films with a low amount of substitutional carbon (y≍ 0.1%). Rapid thermal annealing at 750°C results in highly defective epitaxial films with a maximum carbon content close to 0.4%.The high density of defects is responsible for the partial strain relaxation observed in those layers. The amount of substitutional Si also decreases drastically with increasing temperature. Profile fitting of rocking curves using dynamical X-ray theory is used to estimate the C concentration and the strain and disorder profiles of the heterostructures.
Silica Nano-particle Filled Poly(ethylene-ran-hexene)/xylene Gels
Authors: Wang Howard , Han Charles C.
Published: June 2019

The effect of silica nano-particle filler on poly(ethylene-co-hexene)/xylene gels has been investigated using mainly small angle neutron scattering and rheological measurements. Both non-filled and filled polymer gels show same characteristics in the structure factor and mechanical properties during melting and gelation. These observations suggest that particle interaction is screened by the absorbed polymers and the effect of the silica filler is mainly softening the gelation transition by introducing defects to the crosslinking microcrystals.
Interaction and Energy Level Alignment at Interfaces between Pentacene and Low Work Function Metals
Authors: Koch N. , Ghijsen J. , Ruiz R. , Pflaum J. , Johnson R. L. , Pireaux J.-J. , Schwartz J. , Kahn A.
Published: June 2019

A number of low workfunction metals (samarium, alkali metals) were deposited onto vacuum sublimed thin films of pentacene. The change in the valence electronic structure of the organic material was studied by in situ ultraviolet photoemission spectroscopy (UPS). Alkali metal intercalation leads to the appearance of a new photoemission feature within the pentacene energy gap, due to a charge transfer from the alkali atoms to the lowest unoccupied molecular orbital (LUMO) of the organic material. The energy spacing between this emission feature and the relaxed highest occupied molecular orbital (HOMO) of the pristine molecule is 1 eV. From X-ray photoemission spectroscopy core level analysis, we estimate a concentration ratio of two alkali metal atoms per pentacene molecule at maximum intercalation level, leading to a complete filling of the LUMO. This is consistent with the results from UPS that the new emission is always observed below the Fermi-level. Samarium is found to exhibit a more subtle interaction with pentacene: the molecular orbitals remain almost unperturbed upon Sm deposition. The resulting energy level alignment at this interface seems to be very favorable for the injection of electrons from Sm into pentacene, as the HOMO-onset is found at 1.8 eV below the metal Fermi edge. This value is close to the 2.2 eV HOMO-LUMO gap of pentacene measured by UPS and inverse photoemission spectroscopy, thus corresponding to a small electron injection barrier.
'The Role of the Grain Boundary on the Resistivity of Pb(Fe1/2Nb1/2)O3 at Room Temperature
Authors: Lee Sang-Bop , Lee Kwang-Ho , Kim Hwan
Published: June 2019

The effect of changing sintering temperature on the grain boundary properties and the room temperature resistivity (ρRT) of Pb(Fe1/2Nb1/2)O3 (PFN) was investigated. Monitering the temperature dependence of resistivity showed that the ρRT's of 1050°C and 1150°C-sintered specimen were 1011ΩEcm and 104ΩEcm respectively, but the resistivity above 300°C became nearly identical. The previous model, that the low resistivity of PFN is due to the electron hopping between Fe2+ and Fe3+ driven by the reduction of PFN, couldn't explain this phenomenon, and the reconsideration of the Fe reduction revealed that the difference of electron concentration between the 1050°C and 1150°C-sintered specimen couldn't exceed one order of magnitude. The role of the grain boundary was introduced in order to account for this phenomenon.
Calculations of Atomic and Electronic Structure for (100) Surfaces of SrTiO3 Perovskite
Authors: Eglitis R. I. , Heifets E. , Kotomin E. A. , Borstel G.
Published: June 2019

We present and discuss main results of the calculations for the surface relaxation and rumpling of SrTiO3 surfaces with TiO2 and SrO terminations using a wide variety of methods of modern computational physics and chemistry, including the shell model (SM) and ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT). The HF and DFT formalisms with different exchange-correlation functionals are implemented into Crystal-98 computer code using a Gaussian-type basis set. We demonstrate that a hybrid B3PW formalism gives the best results for the bulk SrTiO3 properties. Results are compared with previous ab initio plane-wave LDA calculations and LEED experiments. Our calculations demonstrate an increase of the covalency effects between Ti and O atoms near the surface.
Soft-phonon Dynamics in the Isotopically Induced Ferroelectric Phase Transition of Strontium Titanate
Authors: Yagi Toshirou , Kasahara Masaru , Tsujimi Yuhji , Hasebe Hiroki , Yamaguchi Masashi , Wang Ruiping , Itoh Mitsuru
Published: June 2019

Abtract:

The ferroelectric phase transition of SrTi18O3 (STO8), where the quantum paraelectricity is reduced by the exchange of oxygen atoms 16O for its isotope 18O, has been studied by both Brillouin scattering and Raman scattering. The Brillouin spectra of the c44 and c66 modes in the paraelectric-tetragonal phase show anomalous behavior in the temperature region several degrees above TC accompanied by a central peak. The characteristic shape of the central peak indicates a coupling mechanism between the acoustic mode and an overdamped soft polar mode. Though the ferroelectric soft A2u mode is Raman inactive in the paraelectric phase, it has been observed in the x(yz)-x geometry indicating a local symmetry breaking above TC. Existence of the ferroelectric micro region in the temperature range far above TC is confirmed by the broad spectral component. The soft mode dynamics is concluded in the phase transition of STO18. The doublet spectrum is observed without any of considerable change by the isotope exchange.
Superconductivity Near Ferromagnetism in MgCNi3
Authors: Rosner H. , Weht R. , Johannes M. , Pickett W.E. , Tosatti E.
Published: June 2019

Superconductivity and ferromagnetism have been believed to be incompatible over any extended temperature range until certain specific examples - RuSr2GdCu2O8 and UGe2- have arisen in the past 2-3 years. The discovery of superconductivity above 8 K in MgCNi3, which is primarily the ferromagnetic element Ni and is strongly exchange-enhanced, provides a probable new and different example. This compound is shown here to be near ferromagmnetism, requiring only hole-doping by 12% substitution of Mg by Na or Li. This system will provide the means to prode coupling, and possible coexistence, of these two forms of collective behavior without the requirement of pressure.
Lead Stereochemistry in Incommensurate Ferroelectric Perovskites and in Incommensurate Lead Monoxide
Authors: Baldinozzi Gianguido , Raulot Jean-Marc , Seshadri Ram
Published: June 2019

We have performed Rietveld refinements on neutron and synchrotron diffraction patterns and density functional calculations on various ferroelectric lead perovskites and on α lead monoxide (litharge). These structural data have allowed to shed some light on lead stereochemistry in these compounds. In particular, we discuss the changing in the lead behaviour between the paraelectric cubic phases and the low temperature anti or ferroelectric phases in Pb2CoWO6 and Pb2MgTeO6 (both incommensurate), in Pb2MgWO6 (antiferroelectric) and in PbMg1/3Nb2/3O3 (relaxor). The possible phase transition mechanisms are reviewed and the bonds are compared to those in the aperiodic structure of α-lead monoxide.
Aluminum in Magnesium Silicate Perovskite: Synthesis and Energetics of Defect Solid Solutions
Authors: Navrotsky Alexandra , Schoenitz Mirko , Kojitani Hiroshi , Xu Hongwu , Zhang Jianzhong , Weidner Donald J. , Akaogi Masaki , Jeanloz Raymond
Published: June 2019

MgSiO3 - rich perovskite is expected to dominate the Earth's lower mantle (pressures > 25 GPa), with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms: MgA+ SiB = MA + MB and SiB = AlB + 0.5 VO. Phase synthesis studies show that both substitutions do occur, and the nonstoichiometric or defect substitution is prevalent along the MgSiO3 - MgAlO2.5 join. Oxide melt solution calorimetry has been used to compare the energetics of both substitutions. The stoichiometric substitution, represented by the reaction 0.95 MgSiO3 (perovskite) + 0.05 Al2O3 (corundum) = Mg0.95Al0.10Si0.95O3 (perovskite), has an enthalpy of -0.8±2.2 kJ/mol. The nonstoichiometric reaction, 0.90 MgSiO3 (perovskite) + 0.10 MgO (rocksalt) + 0.05 Al2O3 (corundum) = MgSi0.9Al0.1O2.95 (perovskite) has a small positive enthalpy of 8.5±4.6 kJ/mol. The defect substitution is not prohibitive in enthalpy, entropy, or volume, is favored in perovskite coexisting with magnesiowüstite, and may significantly affect the elasticity, rheology and water retention of silicate perovskite in the Earth.
Thermodynamic Properties From Static-Lattice Calculations with Soft Modes
Authors: Ackland Graeme J. , Drummond Neil D.
Published: June 2019

While phase transition pressures and zero temperature thermodynamic properties can be accurately determined from electronic structure calculation, transition temperatures are more problematic because of the need to sample phase space and quantise vibrations. The quasiharmonic method has proved extremely accurate for calculating thermodynamic properties up to 90% of the melting point without explicit phase space sampling for most materials, but has low temperature divergences for soft mode materials such as perovskites. Here we present a modified quasiharmonic method which avoids these difficulties. Using a simple model system, we demonstrate trends of behaviour in both the classical and quantum limits showing the importance of phonon quantisation in soft-mode behavior.
Ultraviolet-Assisted Pulsed Laser Deposition of Barium Strontium Titanate on Si: Characterization of the Interfacial Layer
Authors: Craciun V. , Craciun D. , Bassim N. D. , Howard J. M. , Singh R. K.
Published: June 2019

Barium strontium titanate (BST) thin films were grown directly on Si substrates by the conventional and ultraviolet-assisted pulsed laser deposition techniques. X-ray photoelectron spectroscopy, x-ray diffraction and reflectivity, variable angle spectroscopic ellipsometry, current-voltage, capacitance-voltage, and high-resolution transmission electron microscopy were used to investigate the composition, thickness, and electrical properties of the grown structures. It has been found that at the interface between the Si substrate and the grown dielectric layer, an interfacial layer was always formed. The chemical composition of the layer consisted of SiOx partially mixed with the grown BST, without any evidence of silicate formation.
Particle Size Dependent Magnetoresistance And Magnetothermoelectric Power Of La0.5Pb0.5MnO3 Showing Metal-Insulator Transition
Authors: Banerjee Aritra , Pal S , Chaudhuri B K
Published: June 2019

Particle size dependent transport properties (resistivity and thermopower) of La0.5Pb0.5MnO3 has been investigated both in presence and in absence of magnetic field B=0.0-1.5T (maximum). All the samples show metal-insulator transition (MIT) with a peak at the MIT temperature (Tp). Magnetic field decreases the resistivity with an increase in the peak temperature Tp. Particle size, conductivity and Tp of the sample increase with increasing annealing time. High temperature semiconducting (insulating) part of the resistivity curve is divided into two distinct regimes. Resistivity data for T>qθ/2, can be well fitted with the nearest neighbor small polaron hopping (SPH) model. Polaron hopping energy (WH) decreases with increase of particle size. The lower temperature part (Tp>T>qθ/2) of the semiconducting (insulating) regime is found to follow variable range hopping (VRH) model. With the increase of particle size, the temperature range of validity of the VRH mechanism decreases. The low temperature metallic regime (for T<Tp) of the resistivity (both in absence and in presence of field) data fit well with ρ = ρ0 +ρ2.5 T2.5 and transport mechanism in this region is mainly dominated by magnon-carrier scattering (∼T2.5). Particle size has, however, comparatively little effect on Seebeck coefficient (S). In all the samples with different particle sizes, S changes sign below Tp. In contrast to magnetoresistance, application of magnetic field increases S at low temperature (T<Tp) for these samples. Similar to the resistivity results, thermopower data in the metallic phase (both for B=0.0 and 1.5T) can also be analyzed by considering magnon-scattering term along with an additional spin-wave fluctuation term (∼T4).
Tunability of High-Dielectric-Constant Materials from First Principles
Authors: Rabe K. M.
Published: June 2019

A first-principles method, based on density functional perturbation theory, is presented for computing the leading order tunability of high-dielectric-constant materials.
Ge-rich Si1-XGeX Nanocrystal Formation by the Oxidation of As-Deposited Thin Amorphous Si0.7Ge0.3 Layer
Authors: Yoon Tae-Sik , Kim Ki-Bum
Published: June 2019

Ge-rich Si1-XGeX nanocrystals are formed by the selective oxidation of Si during the dry oxidation of an amorphous Si0.7Ge0.3 layer. The oxidation kinetics of the alloy film shows the activation energies of linear and parabolic rate constants are about 1.35 and 1.02 eV, respectively, based on the model proposed by Deal and Grove. In addition, as a result of the selective oxidation of Si and Ge pile-up during the oxidation process, Ge-rich Si1-XGeX nanocrystals are formed with the size of 5.6 ± 1.7 nm and the spatial density of 3.6×1011/cm2 at 600°C. At higher temperature of 700 and 800°C, the size of nanocrystal is increased to about 20 nm. The nanocrystals formation by oxidation is thought to be due to higher oxidation rate at grain boundary than at bulk grain. Therefore, the dependence of size on temperature is explained with the grain size determined by solid phase crystallization of amorphous film, oxidation rate, and grain growth.
Nanostructured Polymer Brushes With Reversibly Changing Properties
Authors: Usov Denys , Stamm Manfred , Minko Sergiy , Froeck Christian , Scholl Andreas , Müller Marcus
Published: June 2019

We investigated the interplay between different mechanisms of the lateral and vertical segregation in the synthesized via “grafting from” approach symmetric A/B (where A and B are poly(styrene-co-2,3,4,5,6-pentafluorostyrene) and poly(methylmethacrylate), respectively) polymer brushes upon exposure to different solvents. We used X-ray photoemission electron spectroscopy and microscopy (X-PEEM), AFM, water contact angle measurements, and oxygen plasma etching to study morphology of the brushes. The ripple morphology after toluene (nonselective solvent) revealed elongated lamellar-like domains of A and B polymers alternating across the surface. The dimple-A morphology consisting of round clusters of the polymer A was observed after acetone (selective solvent for B). The top layer was enriched with the polymer B showing that the brush underwent both the lateral and vertical phase segregation. A qualitative agreement with predictions of SCF theory was found.
High Strength Nanoscale Al/Al3Sc Multilayers formed by Interface Reaction
Authors: Phillips M.A. , Clemens B.M. , Nix W.D.
Published: June 2019

Polycrystalline Al/Sc multilayer samples are grown via magnetron sputtering. The deposition of Sc onto Al results in significant intermixing between the two components. Substrate curvature, measured in-situ during deposition, reveals behavior similar to that seen in other systems where a slow diffuser is deposited onto a fast diffuser. The multilayer films are further characterized via transmission electron microscopy (TEM), analytical electron microscopy, and X-ray diffraction (XRD), confirming the intermixing and formation of a coherent crystalline phase, likely to be Al3Sc, in the interfacial regions. Nanoindentation hardness tests show that by adding a few percent of Sc to Al films and carefully controlling the location of the Sc, increases in hardness up to 6 times that of a pure Al film can be obtained.
Photoluminescence of Nano-scaled YAG:Ce Phosphor Powders
Authors: Chen In-Gann , Chen Yulin , Hwang Chii-Shyang , Juang F.S. , Chang S.J. , Su Y.K. , Mueller G.O. , Mueller-Mach R.
Published: June 2019

Four series of YAG:Ce phosphor powders were synthesized by solid state, co-precipitation, and sol-gel (with two different growth inhibitors, HMDS and PAA respectively) methods, which results in the average particle sizes of 800, 56, 43, and 32 nm respectively. All the nano-scale YAG powders were heat treated below 1000_. Both TEM and XRD results of these nano-scale YAG powders show high degree of crystalline structure. Photoluminescence (PL) characterization shows that the nano-scale YAG phosphor powders emit a higher intensity of luminescence than that of sub-micro sized samples. The effect of different Ce doping level on the PL of (Y3-xCex)Al5O12 shows a maximum at x ∼ 0.01. The Commissiom International de I.Eclairage (CIE) chromaticity coordinates were determined and show different trends of shifts in the resulting PL spectra. Systematic study of the processing parameters characterized by DTA/TGA, XRD, FTIR, and BET will be discussed in detail in the report.
Growth of GaN Nanorods on (0001) Sapphire Substrates by Hydride Vapor Phase Epitaxy
Authors: Kim Hwa-Mok , Kim Doo Soo , Chang Young Wook , Kim Deuk Young , Kang Tae Won
Published: June 2019

GaN nanorods were grown on (0001) sapphire substrates by hydride vapor phase epitaxy HVPE) through a self-assemble process. The nanorods were grown at high growth rate, with the c-axis maintained perpendicular to the substrate surface. The dependence of rod diameter and density on growth conditions was systematically investigated. The average diameter was minimized to 80-120 nm and the density of the GaN nanorods was 100×1012 rods/m2.
The Local Electronic structure at Grain Boundaries and Hetero- Interfaces in ZnO Thin Films Grown by Laser Deposition.
Authors: Kvit Alexander , Duscher Gerd , Jin Chunming , Narayan Jagdish
Published: June 2019

The structure and chemistry of interfaces and grain boundaries are known to influence the optical and electrical properties of wide-band gap semiconductors structures. ZnO/AlN/Si(100) heterostructures grown by laser deposition were studied by conventional and high-resolution transmission electron microscopy (HRTEM). The local electronic structure of ZnO grain boundaries was investigated by high resolution Z-contrast imaging using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy in a scanning mode. Zcontrast imaging and EELS were performed simultaneously enabling direct correlations between interface chemistry and local structure to be made. ZnO grain boundaries are composed of a periodic array of a basic structural unit. On the basis of the electron energy-loss near-edge structure (ELNES) of zinc and oxygen edges associated with the ZnO- grain boundaries, the corresponding electronic spectrum was discussed.
Investigation of Oxidation Process of Ultrathin Amorphous and/or Nano-Crystalline Silicon Films
Authors: Mu R. , Wu M. , Liu Y.C. , Ueda A. , Henderson D.O. , Hmelo A. B. , Feldman L.C.
Published: June 2019

A series experiments were conducted and reported here on how to employ quartz crystal microbalance (QCM) as a highly mass sensitive sensor to study a-Si film and Si nanocrystals oxidation under ambient oxygen. An experimental calibration procedure has been developed to prevent problems with QCM systems during routine study. With the help of pulsed laser deposition (PLD) technique, one can purposely deposit a thin layer of a heavy element as an insitu calibrant which can be analyzed by RBS quantitatively for QCM. The errors resulted from manufacture's sensor, non-repeatable sensor mounting and handling, temperature cycling history from run to run and so on will be effectively eliminated. Our preliminary results indicate that the oxidation process of a-Si thin films has two stages. A fast oxidation associated with surface and near surface oxidation followed by a slow oxidation. The former is depends on the oxygen vapor pressure in the chamber and the later is oxygen diffusion controlled process.
[ZnSe(dbn)1/2] and [ZnSe(hda)1/2]: Two New Members of Inorganic-Organic Hybrid Semiconductor Nanocomposites Exhibiting A Strong Quantum Confinement Effect
Authors: Huang Xiaoying , Li Jing
Published: June 2019

Two new inorganic-organic hybrid II-VI semiconductor nanostructures have been synthesized by solvothermal reactions. These nanostructures consist of inorganic 2∞[ZnSe] layers and organic bridging diamine molecules as spacers. The crystal structures of [ZnSe(dbn)1/2](1, dbn = 1,4-diaminobutane) and [ZnSe(hda)1/2](2, hda = 1,6-hexanediamine) have been determined by the powder X-ray diffraction method. They are isostructural and crystallize in the orthorhombic crystal system, space group Pbca(No.62), Z = 4. Crystal data for 1: a = 6.646(3), b = 6.473(3), c = 22.31(1) Å, V = 961.2(13) Å3, for 2: a = 6.6252(18), b = 6.4505(17), c = 27.138(7) Å, V = 1159.8(9) Å3. The optical absorption experiments show that both 1 and 2 generate a very large blue shift in the absorption edge (1.5-1.6 eV) due to a strong quantum confinement effect (QCE). Thermogravimetric behavior of both compounds has also been investigated.
Organic Molecules in an Electrical Circuit: An Afm Study of a Negative-Differential-Resistance Molecule
Authors: Ramachandran Ganesh K. , Rawlett Adam M. , Hopson Theresa J. , Nagahara Larry A. , Tsui Raymond K. , Lindsay Stuart M.
Published: June 2019

2,5-di(phenylethynyl)-4‘-4“-dithiolate-1-nitrobenzene has been shown to exhibit negative differential resistance (NDR) and spontaneous switching when inserted into inert molecular monolayers between metal contacts. We have used conducting atomic force microscopy to measure the electronic properties of individual dithiolated molecules 2,5-di(phenylethynyl)-4“ 4‘“dithiolate-1-nitrobenzene and 2,5-di(phenylethynyl)-4“4‘“thioacetyl-benzene inserted into an alkanethiol monolayer and chemically bonded to gold nano-contacts to form a covalentlyconnected molecular circuit (bonded contacts). The data show qualitative agreement with previously published results for similar molecules deposited in a nanopore containing several hundred molecules, allowing us to make the important conclusion that the measured negative differential resistance (NDR) is native to the molecule and not an intermolecular phenomenon.
Deterministic Synthesis of ZnO Nanorods
Authors: Heo Y. W. , Varadarajan V. , Kaufman M. , Kim K. , Ren F. , Fleming P. H. , Norton D. P.
Published: June 2019

The deterministic growth of ZnO nanorods using molecular beam epitaxy is reported. The process is catalyst-driven, as single crystal ZnO nanorod growth is realized via nucleation on Ag islands that are distributed on a SiO2-terminated Si substrate surface. Growth occurs at substrate temperatures on the order of 300-500°C. The nanorods exhibit diameters of 15-40 nm and lengths in excess of 1 μm. Nanorod placement can be predefined via location of metal catalyst islands or particles. This, coupled with the relatively low growth temperatures needed, suggests that ZnO nanorods could be integrated on device platforms for numerous applications, including chemical sensors and nanoelectronics.
Automatic Film Formation System For Ultra-Thin Organic Heterostructure By Mass-Controlled Layer-by-layer Sequential Adsorption Method Within One Nanometer Interface Roughness
Authors: Shiratori Seimei , Ito Takahiro
Published: June 2019

An automatic film formation system using an enhanced mass-controlled layer-by-layer sequential adsorption process was newly developed for the fabrication of ultra-thin organic films formed by various polymers, monomers, and inorganic materials. This technique can be applied to both water solutions and volatile solvents. In this process, a quartz crystal microbalance (QCM) was attached to the arm of a robot and the frequency shifts during the adsorption of the materials were monitored. By feeding back the data acquired by the QCM from the deposition to the dipping time, a high quality self-assembly film was produced. As a result, the interface roughness between the layers can be controlled within one nanometer. The cross-sectional TEM (transmission electron microscopy) observation of the films formed by the conventional time controlled dipping method and the newly established mass-controlled dipping method reveals that the interface of the heterostructure of the latter was much smoother than the former. In addition, this automatic dipping system can be applied not only for polyelectrolytes, but also for inorganic materials.
A Novel Patterning Method for Metal-Organic Precursors on a SiOx/Si Substrate Using a Local Electric Field
Authors: Fudouzi Hiroshi , Kobayashi Mikihiko , Shinya Norio , Chikyow Toyohiro , Ahmet Parhat , Naruke Tamami
Published: June 2019

This paper demonstrates a new technique to form a patterned metal-oxide film on a silicon wafer using a local electric field. The idea of the technique involves using an interaction between metal-organic molecules dissolved in a non-polar solvent and a local electric potential field on a substrate. In this paper, an alkoxide and a metal-organic complex were used as metalorganic precursors. The precursor molecules were selectively deposited at the electrified region of the substrate. The deposited precursor films were heated with an electric furnace to form oxide films. Patterned TiOx and Sr-Ti oxide films were formed on a SiOx/Si substrate. These patterned thin films are potentially applicable to electric and optical devices. We believe that this new technique provides a new bottom-up process of molecular assembly for nanofabrication.
Electrochemical Preparation of Silver Selenide Films and Nanowires from Aqueous Solutions
Authors: Chen Ruizhi , Xu Dongsheng , Zhou Weilie , Tung Le Duc , Spinu Leonard , Guo Guolin
Published: June 2019

Both thin films and nanowires of silver selenide were synthesized by electrodeposition from an aqueous acid electrolyte containing silver ion complexed with SCN- and selenium dioxide at room temperature. Orthorhombic Ag2Se films with Ag slightly in excess were obtained. After annealing in argon atmosphere, the films are highly (002) oriented. A positive transverse magnetoresistance of about 20–25% at T = 5 K, and 10–13% at T = 300 K, in fields of H=50 kOe were observed in the electrodeposited films. Furthermore, silver selenide nanowires were synthesized from the same aqueous system by electrodeposition in porous anodic alumina templates. X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Energy dispersive absorption X-ray (EDAX) characterization results showed that the nanowires are highly crystalline with (002) growth direction after annealing. In addition, the atomic ratio of Ag/Se in the films and the nanowire samples can be controlled from about 3.0 to 2.1 by adjusting the concentration of AgI and SeIV source and the deposition potential.
Ti-Island-Catalyzed Si Nanowire Growth by Gas-Source MBE: Morphology and Twinning
Authors: Tang Qiang , Liu Xian , Kamins Theodore I. , Solomon Glenn S. , Harris James S.
Published: June 2019

Silicon nanowires catalyzed by Ti islands have been grown by molecular beam epitaxy (MBE) using Si2H6 as the gas source and characterized by in situ reflection high-energy electron diffraction (RHEED), scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM). Approximately one monolayer of Ti was deposited on Si(001) wafers, which, during annealing, reacted with silicon and formed TiSi2 islands. After annealing, but before Si growth, the stoichiometric TiSi2 (C49) phase was observed with RHEED.

The silicon nanowires are typically between 20 and 40 nanometers in diameter and several hundred nanometers long. The nanowires changed their growth direction several times during growth, resulting in complex RHEED patterns, which can be matched very well by simulated RHEED patterns calculated assuming that the nanowires change their direction by twinning along (111) planes. RHEED patterns of epitaxial silicon nanowires, first-order twinned nanowires (twinned relative to the substrate orientation), second-order twinned nanowires (twinned relative to the first-order twin), and TiSi2 were observed.
Performance Comparisons of Abrasive Containing and Abrasive Free Slurries for Copper Low-k CMP
Authors: Nguyen John , Martin Gerald , Carpio Ron , Grief Malcolm , Joshi Somit
Published: June 2019

The commercially available abrasive containing slurries for copper CMP have shown some advantages in high removal rates, low friction at low down force, and minimal to no copper residues, regardless of the polisher architecture, either rotary, orbital, or linear polishing. However, the abrasive containing slurries have some disadvantages such as high dishing and erosion with more micro-scratches due to the presence of abrasives. In contrast, the abrasive free polishing slurry has lower removal rate, and seems to be sensitive to polishing architecture, but it has good planarization, low topography, less micro-scratches, and most importantly is insensitive to over-polish.

At this stage, the best results for copper CMP are being achieved by the use of the multi-step and multi-slurry process in which copper is polished first, and barrier layers are polished with a different set of consumables. The intent of this paper is to focus on the first step, the copper removal step, and to compare different approaches for this first step; namely, the use of slurries containing abrasives with slurries that are free of abrasives on the orbital polisher. The combined process with low percent solid and small-sized abrasives for the bulk copper removal step and abrasive free polishing (AFP) slurry for the residual copper removal step on an orbital polisher has produced a very robust process window with excellent results including low topography, low erosion, insensitivity to over-polish and low cost of ownership.