bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Atomic-Scale Characterization of Defects on Cleaved Vanadium and Molybdenum Oxide Surfaces Using Stm
Authors: Rohrer Gregory S. , Smith Richard L. 
Published: April 2011

AbstractScanning tunneling microscopy (STM) was used to determine the structure of cleaved, single crystal surfaces of V205, V6013, Mo18052, and Mo8023. Constant current images were recorded in ultrahigh vacuum and in air. By imaging well-defined surfaces that exhibit structural and chemical similarities, and comparing the observations to the known bulk structures, it is possible to establish a reliable interpretation for the contrast in the STM images. A comparison of images from the V6013(001) and the V205(001) surfaces clearly shows that the surface V coordination polyhedra that are capped by vanadyl 0 can be distinguished from those that are not. This allows vacancies in the vanadyl 0 position to be identified on cleaved V205(001) surfaces. Mo18052(100) and Mo8023(010) provide models for two different characteristic types of surface/crystallographic shear (CS) plane intersections. The shear in Mo8023 lies in the (010) surface plane and creates dark contrast along the [001]. The CS planes in Mo18052, on the other hand, have components of shear both in and normal to the (100) surface plane and create white contrast parallel to [010]. These standards for contrast identification can be used to identify defects on inhomogeneous surfaces.
The Influence of Surface Structure on the Interaction of Water with TiO2 (100)
Authors: Henderson Michael A. 
Published: April 2011

AbstractThe influence of surface structure on the interaction of water with TiO2(100) (rutile) was investigated. Two unique surface structures of the (100) crystal face can be prepared by oxidation (the bulk-terminated surface) and by vacuum reduction (the {110}-microfaceted surface). Thermal desorption profiles, which measure of the strength of the adsorbate-surface interaction, indicate that submonolayer coverages of water are more stable on the bulk-terminated surface than on the {110}- microfaceted surface. Also, subtle differences exist in the way water interacts with 2-coordinate 02 sites on these two surfaces. The implications of these results are considered for the acid/base properties of microcrystalline particles.
Photoluminescence Studies of [(CdSe)1(ZnSe)2]9-ZnSeTe Multiple Quantum Wells Under High Pressure
Authors: Wang Z.P. , Liu Z.X. , Han H.X. , Zhang J.Q. , Li G.H. , Peng Z.L. , Yuan S.X. 
Published: April 2011

ABSTRACTWe have performed photoluminescence (PL) measurements at liquid nitrogen temperature under high pressure up to 5.5 GPa and in the temperature range 10-300 K at atmospheric pressure on {(ZnSe)30(ZnSe0.92Te0.08)30(ZnSe)30[(CdSe)1(ZnSe)2]9}x5 multiple quantum wells. The PL peaks, EB, E1 and Ew corresponding to the band edge luminescence in ZnSe barrier layer, the transitions from the first conduction subband to the heavy-hole subband in ZnSe0.92Te0.08 layers and [(CdSe)1(ZnSe)2]9 ultra short period superlattice quantum well (SPSLQW) layers have been observed. Experimental results show that ZnSe0.92Te0.08/ZnSe forms a type-I superlattice (SL) in contrast to the type-II ZnSe/ZnTe SL. The pressure coefficients of the EB, E1 and Ew exciton peaks have been determined as 67, 63 and 56 meV/GPa, respectively. With increasing temperature (or pressure), the E1 peak-intensity drastically decreases which is attributed to the thermal effect (or the appearance of many defects in ZnSe0.92Te0.08 under higher pressure).
Ge Nanocrystals Grown on Si(111) by Molecular Beam Epitaxy with and without CaF2 Buffer Layers
Authors: Deelman Peter W. , Thundat Thomas , Schowalter Leo J. 
Published: April 2011

ABSTRACTThe Stranski-Krastanov growth mode of Ge thin films on Si and the clustering behavior of Ge on calcium fluoride have been exploited to grow self-assembled nanocrystals by molecular beam epitaxy. The growth of the samples was monitored in situ with RHEED, and they were analyzed ex situ with AFM and RBS. For each system (Ge/Si and Ge/CaF2/Si), the dependence of Ge islanding on substrate temperature and on substrate misorientation was studied. When grown on Si(111) at temperatures between 500°C and 700°C, Ge clusters nucleated at step edges on vicinal wafers and nucleated homogeneously on on-axis wafers. Above 600°C, no transition to a spotty RHEED pattern, which would be expected for island growth, was observed for the vicinal samples. Ge grown at 500°C on on-axis Si(111) formed islands with a relatively narrow size distribution, typically 160nm in diameter and 10nm to 20nm in height. When grown on a CaF2 buffer layer, Ge islands nucleated homogeneously at a substrate temperature of 750°C, resulting in randomly distributed, oblate crystallites approximately 100nm to 200nm in diameter. At 650°C and 700°C, although we still observed many randomly distributed, small crystallites, most islands nucleated at step bunches and had a length scale of over 500nm.
Formation of Submicron Single Crystal Particles and Dots by Laser Ablation
Authors: Wu Hong , Vispute R. D. , Narayan J. 
Published: April 2011

ABSTRACTWe have investigated the formation of micron-sized single crystal dots of germanium by pulsed laser ablation. The laser ablation of a Ge target (KrF excimer laser λ=248 nm, pulse rate 10Hz, pulse duration 25x10−9 seconds, and energy 10J /cm2) results in the formation of micron and submicron liquid droplets which are ejected from the target. These droplets can be crystallized into single crystal dots on lattice-matched substrates by rapid liquid-phase recrystallization. We report the details of microstructure as a function of dot size. It is found that under these conditions, below a critical size (about 2μm), the dots are crystalline;above which dots become polycrystalline. We discuss the implications of the results in producing doped and undoped single-crystal quantum dots for device applications.
Semiconductor Nanocrystals formed in SiO2 by Ion Implantation
Authors: Zhu Jane G. , White C. W. , Budai J. D. , Withrow S. P. , Chen Y. 
Published: April 2011

ABSTRACTNanocrystals of group IV (Si, Ge and SiGe), III-V (GaAs), and II-VI (CdSe) semiconductor materials have been fabricated inside SiO2 by ion implantation and subsequent thermal annealing. The microstructure of these nanocrystalline semiconductor materials has been studied by transmission electron microscopy (TEM). The nanocrystals form in near-spherical shape with random crystal orientations in amorphous SiO2 Extensive studies on the nanocrystal size distributions have been carried out for the Ge nanocrystals by changing the implantation doses and the annealing temperatures. Remarkable roughening of the nanocrystals occurs when the annealing temperature is raised over the melting temperature of the implanted semiconductor material. Strong red photoluminescence peaked around 1.67 eV has been achieved in samples with Si nanocrystals in SiO2.
Correlation of Size and Photoluminescence for Ge Nanocrystals in SiO2 Matrices
Authors: Yang C.M , Shcheglov K.V. , Brongersma M.L. , Polman A , Atwater H.A. 
Published: April 2011

ABSTRACTSynthesis and size-dependent photoluminescence has been performed for Ge nanocrystals in SiO2 matrices with average diameters between 2 nm and 9 nm, formed by room temperature ion implantation into SiO2 followed by precipitation during vacuum thermal anneals. Nanocrystal size distributions obtained from electron microscopy data were used in conjunction with a quantum-confined exciton recombination model[l] to generate calculated photoluminescence spectra, which were compared with experimental spectra.
Raman, Absorption, and Photoluminescence Studies of a CdSxSe1−x Semiconductor Doped Color Glass
Authors: Morgan S. H. , Pan Z. , Mu R. , Long B. H. 
Published: April 2011

ABSTRACTA CdSxSe1−x semiconductor doped sodium zinc borosilicate glass has been made and investigated by Raman, linear absorption, and photoluminescence measurements. The glass color changes from colorless through yellow and orange to red after annealing at 625 C with increasing annealing time. The average size of Cd(S,Se) quantum dots in glass has been determined by low-frequency Raman scattering in the order of several nanometers and increases with annealing time. The resonant Raman spectra from colored glasses show the longitudinal optical phonons of CdSe and CdS-like modes in alloy microcrystals, at 204 cm−1 and 284 cm−1, respectively. The stoichiometric composition of CdSxSe1−x nano-particles, x, determined by Raman scattering, is about 0.3. The photoluminescence spectra of colored glass samples show two emission bands, which are attributed to the electron-hole recombination and emission from trap centers of surface states, respectively.
Trap States in Cd(S,Se) Nanocrystals Probed by Photomodulation Spectroscopy
Authors: Stokes Kevin L. , Persans Peter D. 
Published: April 2011

ABSTRACTIntensity, temperature and frequency-dependent photoabsorption spectroscopy are used to probe trap states in CdSo.44Seo.56 nanoparticles in glass. The photoabsorption signal from 6.2 nm radius particles is found to be a combination of two effects: bleaching, due to phase space filling, and an electric-field effect. Frequency-dependent photoabsorption data show that the electric-field effect is caused by a long-lived (r=30 /µs at T=293 K) trap state and that the bleaching occurs on a faster time scale. The trap activation energy obtained from the temperature dependence of the lifetime is 0.23 ±0.06 eV. Only bleaching is observed in the smaller nanocrystallites.
The Formation of Porous Silicon Layers Formed in a Non-Aqueous Electrolyte
Authors: Rieger Melissa M. , Kohl Paul A. 
Published: April 2011

ABSTRACTThe formation of porous silicon layers was examined with respect to crystal orientation and the presence of water. Unlike the etching of (111) silicon in aqueous HF solutions, no pores were formed in HF-MeCN. The etching of (111) silicon in HF-MeCN resulted in the formation of triangular pits defined by the {111} planes. A mechanism for the etching is proposed where steric hindrance of the surface terminated hydrogens induces bond strain and enhances the chemical reactivity. The mechanism also accounts for the formation of pores in (100) silicon, and the formation of a highly branched microporous structure when silicon is etched in an aqueous solution.
Effect of Rapid Thermal Oxidation on Blue and Red Luminescence Bands of Porous Silicon
Authors: Sen S. , Kontkiewicz A. J. , Kontkiewicz A. M. , Nowak G. , Siejka J. , Sakthivel P. , Ahmed K. , Mukherjee P. , Witanachchi S. , Hoff A. M. , Lagowski J. 
Published: April 2011

ABSTRACTPhotoluminescence (PL) of porous silicon after rapid thermal oxidation was studied using excitation energies of 5.0 and 6.4 eV. The emission spectra in both cases are dominated by a broad blue band centered at 430-450 nm and a much weaker red band positioned at 680-720 nm. Using atomic force microscopy (AFM), we have found a correlation between blue PL intensity and increase in feature size caused by progressive oxidation. The blue luminescence, found in porous Si only after oxidation, is identical, with respect to spectrum and fast decay, to that of thermally grown oxide on crystalline Si. Based on these findings, we conclude that the blue luminescence originates from SiO2 rather than from Si nanocrystals embedded in the oxide matrix. The red luminescence, on the contrary, has a different origin. The intensity of red band is a function of oxidation temperature and at RTP above 1050 °C, the red band is completely eliminated. The red luminescence characteristics are discussed in relation to the possible mechanism.
Size, Shape, and Crystallinity of Luminescent Structures in Oxidized Si Nanoclusters and H-Passivated Porous Si
Authors: Schuppler S. , Friedman S. L. , Marcus M. A. , Adler D.L. , Xie Y.-H. , Ross F. M. , Harris T. D. , Brown W.L. , Chabal Y. J. , Szajowski P. J. , Chaban E. E. , Brus L. E. , Citrin P. H. 
Published: April 2011

ABSTRACTNear-edge and extended x-ray absorption fine structure measurements from a wide variety of H-passivated porous Si samples and oxidized Si nanocrystals, combined with electron microscopy, ir-absorption, α-recoil, and luminescence emission data, provide a consistent structural picture of the species responsible for the luminescence observed in these systems. For luminescent porous Si samples peaking in the visible region, i. e., ≤700nm, their mass-weighted-average structures are determined here to be particles–not wires, whose short-range character is crystalline – not amorphous, and whose dimensions – typically <15 Å – are significantly smaller than previously reported or proposed. These results depend only on sample luminescence behavior, not on sample preparation details, and thus have general implications in describing the mechanism responsible for visible luminescence in porous silicon. New results are also presented which demonstrate that the observed luminescence is unrelated to either the photo-oxidized Si species in porous Si or the interfacial suboxide species in the Si nanocrystals.
Simultaneous Detection of Radiative and Non-Radiative Recombination in Porous Silicon
Authors: Grivickas Vytautas , Linnros Jan 
Published: April 2011

ABSTRACTRadiative and non-radiative recombination in porous silicon (PSi) is measured under a wide injection range by detecting of photoluminescence (PL) and free-carrier absorption (FCA) decay. We used 2.34 eV and 140 ns light pulses for carrier excitation in PSi flakes. The excited carriers were probed by focused cw IR light and the carrier concentration was calculated by using the free-carrier absorption cross section of bulk (c-Si). The results demonstrate a scaling between the total PL yield in the S-band, integrated over wavelengths, and the free carrier concentration. At lower injections the observed free carrier and PL decay follow a similar, density-independent stretched-exponential law. At injections approaching 1018 cm−3, a fast recombination component appears reducing the lifetime by a factor of ten. This component is attributed to Auger recombination of separated e-h pairs on a set of Si subclusters.
Electronic and Structural Properties of Si46: A Novel Solid of Silicon Fullerenes
Authors: Saito Susumu , Oshiyama Atsushi 
Published: April 2011

ABSTRACTWe report the electronic structure of the S46 lattice having a just lnm-size unit cell and has been optimized within the density-functional theory. The Si46 lattice studied is the real geometry of Si atoms crystallized with metal atoms, and consists essentially of dodecahedral-cage Si20 fullerenes proposed by us previously. Although all the Si atoms are tetrahedrally coordinated, its electronic structure is found to be considerably different from that of the diamond Si lattice due to the pentagonal Si-Si network. Si46 is an important new Si semiconductor to be synthesized in the future. We also report the electronic structure of Na2Ba6Si46. The material is found to be metallic and the Fermi-level density of states is very high due to the hybridization between Si and Ba states, which should be of essential importance for the superconductivity observed in Na and Ba codoped Si46.
The Thermal Conductivity of Porous Silicon
Authors: Lang W. , Drost A. , Steiner P. , Sandmaier H. 
Published: April 2011

ABSTRACTThe thermal conductivity of porous silicon is measured as prepared and after oxidation. The measurement method uses thermal wave propagation in the porous film. We investigate three types of porous silicon: Nanoporous p-type silicon, nanoporous n-type silicon and mesoporous p+-type silicon. The nanoporous material shows a thermal conductivity in the region of 1.2 W/mK to 1.8 W/mK as prepared and after oxidation. This value is close to silicon oxide. The mesoporous material shows a high thermal conductivity of 80 W/mK as prepared which drops to 2.7 W/mK after oxidation.
Modelling the Multiplicity of Conductance Structures in Clusters of Silicon Quantum Dots
Authors: Boeringer D. W. , Tsu R. 
Published: April 2011

ABSTRACTWe have fabricated diode structures containing clusters of nanoscale silicon particles. The modelling of the observed multiple current steps from resonant tunnelling through the quantum states of these particles is presented. Whenever the applied voltage aligns the Fermi surface of the contact to a discrete state, conduction results. Since the clusters are connected in parallel, successive connections of parallel current paths can cause multiple current steps. These current steps can be drastically amplified by avalanche multiplication when the substrate is deeply depleted. The transport in this regime is quite nonlinear, and cannot be represented by a linear equivalent circuit. Apart from gaining a fundamental understanding of the measured I-V characteristics of our diodes, our results serve to promote new applications for quantum switches.
Porous Silicon Used as an Initiator in Polymerization Reactions
Authors: Heinrich Julie L. , Lee Alice , Sailor Michael J. 
Published: April 2011

ABSTRACTPorous silicon is investigated as an initiator for radical polymerization reactions. Surface radicals and photogenerated e−/h+ pairs in porous silicon can be used to initiate polymerization reactions. Porous silicon wafers were placed in ethanolic solutions of methyl methacrylate, N-vinylcarbazole, acrylonitrile, or styrene and either left in the dark or excited by light. Methyl methacrylate polymerized in the absence of light, presumably via silicon-based radical initiator sites at the porous silicon surface. The N-vinylcarbazole polymerized to a small extent in the dark, and to a much greater extent during white light irradiation of the porous silicon surface. Photopolymerization is thought to occur via excited state hole transfer from the porous silicon to the N-vinylcarbazole monomer. Very little to no polymerization of acrylonitrile or styrene could be detected either in the dark or under illumination.
Electronic Properties of Silicon - M Binary Clusters (M = C & Na)
Authors: Nakajima A. , Nakao K. , Gomei M. , Kishi R. , Iwata S. , Kaya K. 
Published: April 2011

ABSTRACTElectronic properties of silicon-carbon and silicon-sodium binary clusters, produced by laser vaporization, were investigated by photoelectron spectroscopic or photoionization spectroscopic method. The photoelectron spectra of the C1Sim-1- clusters are similar to those of pure Sim- clusters in the peak positions and their envelopes, which is attributed to the similar electronic structure of Si and C atoms, leading to a similar geometry. In contrast, the similarity in the photoelectron spectra is not observed between Cn- and Cn-1Si1 clusters, which is attributed to a change in their geometry; from chain to ring.The ionization energies (Ei) of the SinNam clusters (l≤n≤15) were determined from the threshold energy of their ionization efficiency curves. The clear parallelism between the ionization energy of SinNa and the electron affinity (EA) of Sin is found; there are three local minima at n=4, 7 and 10. This implies the facts that (1) the structure of the SinNa clusters keeps the frame of the corresponding Sin cluster unchanged and that (2) the parentage of singly occupied molecular orbital (SOMO) of SinNa is the LUMO of Sin. Furthermore, the EAs of SinNa (4≤n≤7) were determined from the threshold energy in the photoelectron spectra of SinNa". When the EAs of SinNa are compared with those of Sin, the EAs decrease at n=4-6, but the EA increases at n=7. The results of ab initio calculation show that the Na atom is bound by two Si atoms (bridge site) at n=4-6, whereas it is bound by one Si atom (apex site) at n=7.
Blue and Green Electroluminescence from Porous Materials
Authors: Mimura H. , Matsumoto T. , Kanemitsu Y. 
Published: April 2011

ABSTRACTIn applying porous Si (PS) to color display technology, it is important to fabricate light emitting devices with three primary colors. However, there have been few reports on blue and green electroluminescence (EL), and its mechanism (even the relationship between PL and EL spectra) is unclear. To obtain blue and green EL and to investigate its mechanism, we have formed PS anodized under UV illumination (UV-PS) with green photoluminescence (PL) and porous SiC with blue PL. Consequently, green and blue light emitting devices were successfully fabricated by using these materials. The observed spectra are from 350 to 750 nm with a peak of, 520 nm for ITO / UV-PS junctions and from 300 to 600 nm with a peak of 470 nm for ITO / porous SiC junctions. The EL mechanism is also discussed by reference to experimental results of comparing PL and EL spectra and of investigating the dependence of EL intensity on current.
The Influence of Local Ambient Atmosphere on the Electroluminescent Stability of Porous Silicon Diodes
Authors: Zhang Libing , Coffer Jeffery L. , Gnade Bruce E. , Xu DaXue , Pinizzotto Russell F. 
Published: April 2011

ABSTRACTIn this work, the influence of surrounding ambient atmosphere on the stability of electroluminescent (EL) porous Si (PS) diodes fabricated from anodic oxidation of epitaxially grown p-type layers on n-type Si substrates is investigated. These structures are characterized using photoluminescence (PL), electroluminescence (EL), and infrared (IR) spectrosopies, as well as scanning electron microscopy (SEM). Such structures yield orange emission with maxima near 620 nm upon the application of moderate applied voltages (3-7 V). In strong oxidizing environments, EL intensity degrades completely within 30 minutes; in contrast, the integrated intensity remains essentially unchanged in the same timeframe in the presence of a vigorous flow of inert gases such as nitrogen and argon. Infrared spectroscopic studies strongly suggest that electroluminescence degradation is related to porous silicon surface oxidation.
Stabilization of electroluminescence and photoluminescence of porous n-silicon by chemical oxidation in H2O2
Authors: Kozlowski F. , Wagenseil W. , Steiner P. , Lang W. 
Published: April 2011

ABSTRACTWe have oxidized porous (n-)silicon samples in solutions of H202 and have found that PL can be stabilized at a high level. The PL intensity of as prepared samples (PL quantum efficiencies in the range of 5 %) degrades to about 1/3 of the initial value in some ten minutes (the exact value depends on the experimental conditions). After having treated the samples for about 30 - 45 minutes in hydrogen peroxide it can be observed that bright PL remains stable for hours. These results confirm similar experiments performed with porous silicon made from p-substrates1. While red electroluminescing samples have shown long time stability for about 100 hours2, samples with blue-green electroluminescence have a lifetime of about 20 - 40 minutes. Oxidizing electroluminescent samples as described above results in a stabilization of electroluminescence for more than 7 hours.
Structural, Optical and Electrical Properties of μc-SiC:H Thin Films Deposited by the VHF-GD
Authors: Fluckiger Roger , Meier J. , Shah A. , Pohl J. , Tzolov M. , Carius R. 
Published: April 2011

ABSTRACTIn the present paper the authors present new results on thin (μc-SiC:H films deposited at low temperatures by the Very High Frequency - Glow Discharge technique (VHF-GD) at 70 MHz. The individual effects of each of the deposition parameters (methane and diborane gas phase ratios, input power, deposition temperature and pressure) are investigated with respect to the structural, optical and electrical properties of the films; the goal being the growth of optimised, thin μc-SiC:H layers for use as highly conductive and high gap window layers in solar cells.
Porous Silicon: A Possible Buffer Layer for Diamond Growth on Silicon Substrates
Authors: Liu Zhaohui , Zong B.Q. , Lin Zhangda 
Published: April 2011

ABSTRACTContinuous diamond films have been grown on porous silicon by hot filament chemical vapor deposition. The demonstration of diamond growth on porous silicon seems to suggest that porous silicon can act as a buffer layer for diamond growth on Si substrates, and that the nanoscale structures of porous silicon play an important role in nucleation and growth of diamond.