bluuebunny/crossref_metadata_2025_split huggingface dataset:
Suppression of the Relaxor State in Ca-Doped SrTiO3 with Modest Pressure
Authors: Venturini Eugene L. , Samara George A. , Kleemann Wolfgang 
Published: June 2019

AbstractWe report very large changes under modest hydrostatic pressure in the nature of the relaxor ferroelectric (FE) response for a single crystal of SrTiO3 doped with 0.7 mol % CaTiO3. The Ca cation dopants generate polar clusters within the FE soft mode, readily polarized host crystal. At ambient pressure the cluster size increases with decreasing temperature, leading to a dispersive (relaxor) state below ∼18 K. However, the application of modest pressure stiffens the soft mode frequency of the host lattice and reduces cluster growth, thereby decreasing the glass-like transition temperature at roughly –35 K/kbar. Above 0.5 kbar there is no evidence for the relaxor state; rather, a temperature- and frequency-independent dielectric response reflecting quantum paraelectric behavior evolves. These results demonstrate the extreme sensitivity to pressure of relaxors with low transition temperatures, i.e., in the quantum regime where characteristic energies are small.
Roughness of electronic interfaces in Ga As p-n multilayers investigated by cross-sectional scanning tunneling microscopy
Authors: Jäger N. D. , Urban K. , Weber E. R. , Ebert Ph. 
Published: June 2019

AbstractWe investigated the roughness of the electronic interfaces of GaAs p-n multilayers using cross-sectional scanning tunneling microscopy. We demonstrate that these interfaces exhibit a much larger roughness than the underlying essentially perfect ‘metallurgical’ interface, due to the individual long range electrostatic screening fields around each dopant atom near the interface and due to a clustering of dopant atoms. The clustering and the inherently connected local lack of dopant atoms gives rise to charge carrier depletion zones extending locally through entire nominally homogeneously doped layers once the layer thickness is close to the cluster dimensions. Thus, local variations in the dopant atom distribution limit the precision of the spatial and energetic positioning of the Fermi energy in nanoscale semiconductor structures.
Characterization of SiC Implanted with B or Al Using Thermal Admittance Spectroscopy
Authors: Smith S.R. , Capano M.A. , Evwaraye A.O. 
Published: June 2019

AbstractWe have measured the thermal activation energies of electrically active defects in 4H- and 6H-SiC implanted with either Al or B ions, using Thermal Admittance Spectroscopy. The net acceptor concentrations were monitored using room temperature low frequency Capacitance-Voltage measurements. The substrates were n/n+ epilayers. The implantations plus annealing produced p-type layers that were acceptable for characterization. The specimens were annealed in Ar at 1600 ° C, after which Ni Schottky diodes were fabricated on the specimens. Annealing times were 5, 15, 30, and 60 min. In some of the specimens, a shallow level was found that did not correspond to known levels. As the annealing progressed, energy shifts were noted for some of the detected levels. In some specimens, the implanted p-type impurity and the n-type residual dopants in the substrate were simultaneously detected. Measurements of electrically active ptype species were compared to “control” specimens implanted with Ar. From this comparison, we conclude that at least one shallow donor level is introduced into the bandgap by the implantation process, and is not annealed out. The defects associated with the implantation may affect actual device performance of diodes by destabilizing the lattice occupation of the implanted dopant atoms (energy shift with annealing), and act as lifetime killers.
Influences of Lattice Sinks and Defect Interactions on Solutes in Compounds
Authors: Collins Gary S. , Zacate Matthew O. 
Published: June 2019

AbstractA thermodynamic model for the site preference of dilute solutes in ordered compounds was developed recently. The model is extended here in two ways to help interpret experimental results from this laboratory. (1) A preference for solutes to occupy sites in ‘sinks’ such as grain boundaries rather than regular lattice sites is included using a simple model. A wide range of site preference behavior is found; for example, a solute may switch between substitutional and sink sites with changing composition. (2) The effect of an attractive interaction between solute and defect on the site preference is examined. Conditions are established under which a solute can be stabilized by association with a defect on a site where the solute would otherwise not be found.
Photo-induced Dissociation and Optical Cross Section of Si-H and S-H Complexes in GaAs and AlGaAs
Authors: Barbé M. , Bailly F. , Chevallier J. , Silvestre S. , Loridant-Bernard D. , Kurowski L. , Constant E. , Constant M. 
Published: June 2019

AbstractIn GaAs, (Si,H) complexes are efficiently dissociated at 300 K by photons with energies above 3.5 eV. Their optical cross-section is 10-19-10-18 cm2. This dissociation is the result of an electronic excitation of the Si-H bond of the complex from a bonding state to an antibonding state. (Si,H) and (S,H) complexes in AlGaAs alloys are also dissociated under UV illumination with optical cross-sections similar to GaAs. In passivated 2D AlGaAs-GaAs heterostructures, the evolution of the extra sheet carrier concentration at low photon densities presents a loss of free carriers attributed to the filling of surface states. In AlGaAs and in 2D AlGaAs-GaAs heterostructures, the replacement of hydrogen by deuterium in the complexes shows that the (Si,D) and (S,D) complexes are significantly more stable than the (Si,H) and (S,H) complexes as previously found in GaAs:Si,H.
Photoluminescence and Infrared Absorption Study of Isoelectronic Impurity Passivation by Hydrogen
Authors: Capizzi M. , Polimeni A. , Högher von Höghersthal G. Baldassarri , Bissiri M. , Bonapasta A.Amore , Jiang F. , Stavola M. , Fischer M. , Forchel A. , Sou I.K. , Ge W.K. 
Published: June 2019

AbstractThe effects of H irradiation and thermal annealing on the optical properties of (InGa)(AsN) heterostructures have been investigated by photoluminescence (PL) and infrared absorption, as well as by theoretical methods. It has been found that different N clusters contribute to the band gap red-shift reported for (InGa)(AsN) alloys, with a sizable localization of the carrier wavefunctions around N atoms. Infrared absorption measurements indicate that two different NH complexes are formed, whose vibrational frequencies are in good agreement with theoretical estimates. The ability of hydrogen to passivate different isoelectronic impurities is confirmed by PL results in H irradiated Zn(STe).
Field emission characteristics of carbon nanotubes synthesized by C3H4 and NH3 gases
Authors: Jeong Taewon , Han Jae Hee , Yi Whikun , Yu SeGi , Lee Jeonghee , Heo Jungna , Lee Chang Soo , Yoo Ji-Beom , Kim J. M. 
Published: June 2019

AbstractUsing a gas mixture of propyne (C3H4) and ammonia (NH3) as a carbon precursor, we have successfully synthesized multiwalled carbon nanotubes (CNTs) by the direct current (dc) plasma enhanced chemical vapor deposition (PECVD) onto Co-sputtered glass at 550°C. As the flow ratio of NH3 to C3H4 in the mixture gas increased, the crystallinity and alignment of CNTs were improved. In addition, the field emission characteristics of CNTs were also improved. the turn-on voltage became lower, and the current density and the field enhancement factor were more increasing. Raman spectroscopy and scanning electron microscopy were utilized to confirm the effect of the gas flow ratio on CNTs. Therefore, the gas flow ratio was found to be one of important factors to govern the crystalline and field emission characteristics of CNTs. The growth mechanism of CNTs using a C3H4 gas is under investigation with the possibility that three carbon atoms in a C3H4 molecule is converted directly to a hexagon of a CNT by combining two molecules.
Microstructure Studies on Hexagonal Layered Ni-S Nanocrystals
Authors: Sun Xiang-Cheng , Reyes-Gasga J. , Toledo J. A. 
Published: June 2019

AbstractLayered nickel-sulfides (Ni-S) nanocrystals had been successfully prepared by lowtemperature hydrothermal approach. Rietveld X-ray diffraction (XRD) analysis revealed that these layered Ni-S materials have two different hexagonal structure phases, NiS1.03 and NiS, both phases are NiAs-type with space group of P63/mmc. X-ray energy dispersive spectra (XEDS) analysis and TEM observations also confirmed these two nanocrystals of NiS1.03 and NiS. High-resolution transmission electron microscopy (HREM) lattice images indicated moiré fringes with rotational or translational patterns were observed in these layered Ni-S nanophases materials. In particular, it was found that all the simulated HREM images were in good agreement with the observed HREM lattice images. Especially, the simulated SAED patterns obtained from the hexagonal Ni-S crystallographic model showed that the experimental SAED patterns taken along [11.0], [00.1] and [10.0] zone axes presented reflections produced by double diffraction effect.
Manipulations of Nanoparticle Chain Aggregates in Transmission Electron Microscopy
Authors: Suh Yong J. , Prikhodko Sergey V. , Friedlander Sheldon K. 
Published: June 2019

AbstractWe have developed a nanostructure manipulation device (NSMD) to apply tension to a single nanoparticle chain aggregate (NCA) mounted in a transmission electron microscope. The system was used for studying stretching and contraction of carbon chain aggregates. Carbon NCAs generated by laser ablation of a graphite target were stretched and bent using the NSMD. The NCA was stretched up to 310% of its initial length before becoming taut and then breaking. The broken NCA contracted rapidly showing its elastic behavior. The NCA was plastically deformed during stretching through unraveling of kinks along the NCA. However, the unraveling was irreversible so that the chain formed a loop with a big curvature as its two ends were brought closer together.
Morphology and Atomic Structure of Grain Boundaries in GaN Grown by MOVPE
Authors: Takuma Eriko , Ichinose Hideki , Sanorpim Sakuntam , Onabe Kentaro 
Published: June 2019

AbstractThe morphology and the atomic structure of a hexagonal gallium nitride (h-GaN) grain boundary was investigated employing a conventional TEM and an atomic resolution high voltage transmission electron microscope (ARHVTEM).GaN was grown on a patterned GaAs (001) substrate by the metalorganic vaporphase epitaxy (MOVPE) method using selective area growth (SAG) and epitaxial lateral overgrowth (ELO) process. The pattern mask was aligned along [110] direction of the GaAs (001) substrate. Cubic GaN (c-GaN) grew in the window of the patterned substrate. h-GaN was nucleated on the {111} plane of the c-GaN and grew in the lateral direction to fabricate a grain boundary in the halfway between two masks. The resulting symmetric tilt grain boundary was a Σ 9 CSL boundary. The boundary plane was in most cases parallel to the {3308} plane. Structural analysis revealed that the boundaries consist of ordinary 6-memebered rings and some 5-membered and 7-membered rings. Additionally, the expected atomic bonding angle deviates from the experimental findings. The different bonding angle was attributed to contributions of ionic bonding in GaN.
Rolled-up In(Ga)As/GaAs Nanotubes Diameter as a Function of Structural Properties
Authors: Deneke Ch. , Müller C. , Schmidt O.G. 
Published: June 2019

AbstractInherently strained bilayers of In(Ga)As/GaAs, Epitaxially grown on top of an AlAs sacrificial buffer layer roll-up into free-standing nanotubes if they are released from their substrate by selective underetching, Here, we preseant a systematic study of the tube diameter as a function of total bilayer thickness and the ratio between the two layer thinknesses. We show that the diameters of the tubes are well described by a continous mechanical model.
Stamp Deformation During Microcontact Printing
Authors: Jagota Anand , Sharp Kenneth G. , Kristunas David F. 
Published: June 2019

AbstractStamp deformation often produces undesirable effects that limit the practice and precision of micro-contact printing. We have experimentally studied one of the most pervasive consequences of undesired deformation: roof collapse of low-aspect-ratio recesses. Stamp behavior under increasing loads can readily be assessed by mounting stamps on flat glass and viewing stamps from below through an inverted microscope. Dynamic as well as limiting equilibrium behavior can be determined. Features with aspect ratios varying by a factor of ten were examined. We find that roof collapse initiates with the formation of a contact between the roof of the stamp and the substrate. This is followed by rapid growth of the contact region, driven by attractive interfacial forces. Contact growth usually terminates leaving a noncontacting “moat” region. Experimental measurements of the critical stress for roof collapse are in very good agreement with theory.
Nanostructured Carbon Capsules with Hollow Core/Mesoporous Shell Structure
Authors: Yu Jong-Sung , Yoon Suk Bon , Sohn Kwonnam , Kim Jeong Yeon , Hyeon Taeghwan 
Published: June 2019

AbstractCarbon capsules with hollow macroporous core/mesoporous shell were synthesized using sacrificial submicrometer-size solid core/mesoporous shell (SCMS) silica spheres as templates. Size of the hollow macroporous core and thickness of the mesoporous shell can be easily controlled by the choice of silica spheres and the amount of TEOS/C18-TMS mixture, respectively.
Textured Zinc Oxide by Expanding Thermal Plasma CVD: the Effect of Aluminum Doping
Authors: Groenen R. , Kieft E.R. , Linden J.L. , Sanden M.C.M. van de 
Published: June 2019

AbstractAluminum doped ZnO films are deposited on glass substrates at a temperature of 200°C by expanding thermal plasma CVD. Surface texture, morphology and crystal structure have been studied by AFM, SEM and XRD. A rough surface texture, which is essential for application as front electrode in thin film solar cells, is obtained during deposition. The addition of aluminum as a dopant results in distinct differences in film morphology, a transition from large, rounded crystallites to a more pyramid-like structure is observed. The structure of films is hexagonal with a preferred crystal orientation in the faces (002) and (004), indicating that films are oriented with their c-axes perpendicular to the substrate plane. In addition, spectroscopic ellipsometry is used to evaluate optical and electronic film properties. The presence of aluminum donors in doped films is confirmed by a shift in the ZnO band gap energy from 3.32 to 3.65 eV. In combination with reflection and transmission measurements in the visible and NIR ranges, film resistivities have been obtained from the free-carrier absorption. These results are consistent with direct measurements. Resistivities as low as 6.0 10-4 Ωcm have been obtained.
Chemically deposited antimony selenide thin films
Authors: Rodríguez-Lazcano Y. , Peña Y. , Nair M.T. S. , Nair P. K. 
Published: June 2019

AbstractChemical bath deposition of thin films of antimony selenide from aqueous solutions containing complexes of antimony with citrate, tartrate and thiosulfate as ligands and sodium selenosulfate as source of selenide is reported. The films obtained appear amorphous in the as-prepared form and become crystalline upon annealing at 300°C. The X-ray Diffraction (XRD) patterns of the annealed films show peaks attributable to Sb2Se3 and Sb2O3. Electron microprobe analyses have shown that the atomic ratio of Se/Sb is less than 1.5 in these films. The films are photoconductive and exhibit a high resistivity in the dark. Both direct (1.4 eV) and indirect (1.3-1.5 eV) band gaps are observed for the films.
Pattern density effects in fixed abrasive polishing
Authors: Venigalla Rajasekhar , Economikos Laertis , Babu S.V. 
Published: June 2019

AbstractWe investigated pattern density effects during chemical mechanical planarization (CMP) for shallow trench isolation (STI) applications using fixed abrasive pads to better control the fixed abrasive polishing process. We observed that the polishing characteristics of higher pattern density features are strongly dependent on the presence of lower pattern density features on the same die in the wafer. This has been attributed to the aggressive action of lower pattern density features on the fixed abrasive pad which results in a more effective activation of the pad by them. Thus even the 100% pattern density features are initially polished at a very high rate when lower density features are present.
Evolution of Charged Gap Statesin a- Si:H Under Light Exposure
Authors: Zeman M. , Nádaždy V. , Swaaij R.A.C.M.M. van , Durný R. , Metselaar J.W. 
Published: June 2019

AbstractThe charge deep-level transient spectroscopy (Q-DLTS) experiments on undoped hydrogenated amorphous silicon (a-Si:H) demonstrate that during light soaking the states in the upper part of the gap disappear, while additional states around and below midgap are created. Since no direct correlation is observed in light-induced changes of the three groups of states that we identify from the Q-DLTS signal, we believe that we deal with three different types of defects. Positively charged states above midgap are related to a complex formed by a hydrogen molecule and a dangling bond. Negatively charged states below midgap are attributed to floating bonds. Various trends in the evolution of dark conductivity due to light soaking indicate that the kinetics of light-induced changes of the three gap-state components depend on their initial energy distributions and on the spectrum and intensity of light during exposure.
Present Status Of Hot Wire Chemical Vapor Deposition Technology
Authors: Schropp R.E.I. 
Published: June 2019

AbstractIn the last few years, tremendous progress has been made in the field of Hot Wire Chemical Vapor Deposition (HWCVD): (1) It has been shown that there are no fundamental limitations in HWCVD with respect to substrate area. Using a periodic configuration of multiple short wires, good uniformity (± 7.5 %) has been demonstrated by Anelva over an area of 96 cm × 40 cm. (2) High quality microcrystalline Si can be produced. Solar cells in the n-i-p configuration are currently better than those made by PECVD. At Jülich, the efficiency of such cells is 9.4 %, and Utrecht has recently made the first HWCVD multibandgap triple junction solar cells, (3) HWCVD offers the potential of ultra high deposition rates. At NREL, a-Si:H has been deposited at rates in excess of 12 nm/s, and at Utrecht University μc-Si:H rates are in excess of 1 nm/s. (4) Thin film transistors (TFTs) with mobilities in excess of 1 cm2/Vs with an a-Si:H channel have been shown to be stable and μc-Si:H TFTs have been made with mobilities in excess of 40 cm2/Vs. (5) The efficient production of atomic H in HWCVD is beneficial in passivation processes, but it can also be applied in efficient etching processes. (6) Alloys of Si with various functions can be made, such as SiNx for antireflection and passivation coatings. Remarkably, all of the above results have been achieved without detailed knowledge about the primary reactions at the filament, the gas phase reactions, and the reactions with the growing film. The choice of filament material and its operation temperature have a large influence on the production of various reaction species and thus, on the structure of the resulting film. HWCVD is basically an ion-free deposition technique, which is an advantage for many kinds of thin films. HWCVD has also proven its feasibility in polymer deposition and nanotube formation.
Physicochemical Characterization of Porous Silicon Surfaces Etched in Salt Solutions of Varying Compositions and pH
Authors: Rosario-Canales Mariem , Guadalupe Ana R. , Fonseca Luis F. , Resto Oscar 
Published: June 2019

AbstractWe prepared porous silicon (PSi) structures by standard electrochemical processes using aqueous sodium fluoride (NaF) solutions. We report the dependence of the porous structure on the variation of pH and salt concentration of the etching solution, and the applied current density. The PSi structures were characterized by Scanning Electron Microscopy (SEM) and Secondary Ion Mass Spectroscopy (SIMS) to determine the pore size and distribution and the surface chemical composition. Results obtained from SEM show that the PSi grown has two different structures depending on the current density. Low current densities produce a uniform, high-density arrangement of pores while high current densities yield a sponge-like structural network. SIMS results indicate that the porous framework is covered with a silicon oxide layer.
Microcrystalline Silicon Thin Film Growth by Electron Cyclotron Resonance Chemical Vapour Deposition at 80°C for Plastic Application Ian
Authors: Bu Ian Y.Y. , Flewitt A.J. , Robertson J , Milne W.I. 
Published: June 2019

AbstractMicrocrystalline silicon deposited at low temperatures (<150°C) is a candidate material for use as the channel layer in thin film transistors deposited on plastic substrates. This would enable driver electronics to be integrated onto cheap flexible AMLCD panel.In this study microcrystalline silicon was deposited by Electron Cyclotron Resonance Plasma Enhanced chemical Vapour Deposition (ECR-PECVD) at a temperature of 80°C, compatible with most plastic such as PET and PEN. A source gas mixture of SiH4 and H2 was employed. The structural and optical properties of samples deposited under a range of deposition conditions were measured.
Characterization of Nanocrystalline Silicon Film grown by LEPECVD for Photovoltaic Applications
Authors: Bollani M. , Binetti S. , Acciarri M. , Fumagalli L. , Arcari A. , Pizzini S. , Känel H. Von 
Published: June 2019

AbstractThis work deals with the structural properties of nanocrystalline (nc) silicon films for solar cell applications, grown using a new PECVD process based on an arc discharge plasma characterized by low ion energies, called LEPECVD (Low energy PECVD). This process permits to increase the intensity of the plasma discharge in the growth region and thus to achieve higher growth rates while avoiding ion-induced surface damage of films. The structural properties of the LEPECVD grown films were studied as a function of the deposition parameters (substrate temperature, growth rate, hydrogen dilution) by Raman Spectroscopy, SEM, and HRTEM analysis. The results of this work allowed us to identify the process requirements suitable for the growth of nc-grains in an amorphous matrix.
Influence of Substrate Temperature and Hydrogen Dilution Ratio on the Properties of Nanocrystalline Silicon Thin Films Grown by Hot-Wire Chemical Vapor Deposition
Authors: Moutinho H.R. , Jiang C.-S. , Nelson B. , Xu Y. , Perkins J. , To B. , Jones K.M. , Romero M.J. , Al-Jassim M.M. 
Published: June 2019

AbstractWe have studied the influence of substrate temperature and hydrogen dilution ratio on the properties of silicon thin films deposited on single-crystal silicon and glass substrates. We varied the initial substrate temperature from 200° to 400°C and the dilution ratio from 10 to 100. We also studied the effectiveness of the use of a seed layer to increase the crystallinity of the films. The films were analyzed by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and transmission and scanning electron microscopy. We found that as the dilution ratio is increased, the films go from amorphous, to a mixture of amorphous and crystalline, to nanocrystalline. The effect of substrate temperature is to increase the amount of crystallinity in the film for a given dilution ratio. We found that the use of a seed layer has limited effects and is important only for low values of dilution ratio and substrate temperature, when the films have large amounts of the amorphous phase.