bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Visible and the Infrared Luminescence Bands as a Tool for Characterization of the Porous Silicon Bandstructure
Authors: Petrova-Koch V. , Muschik T. , Polisski G. , Kovalev D. 
Published: April 2011

ABSTRACTThe visible and the infrared photoluminescence bands in porous Si have been studied at low temperature for two series of samples: one in which the size of the crystallites has been varied and another in which the degree of surface degradation has been changed. It is shown that the relation of the two bands can be explored for characterization of the porous Si bandstructure. The size- and the surface dependence of the valence band and of the conduction band related states is discussed. A model is proposed for explanation.
Investigation of Electronic Properties of Porous Silicon by the Pulsed Surface Photovoltage Technique
Authors: Dittrich Th. , Flietner H. 
Published: April 2011

ABSTRACTElectronic states in por-Si are investigated by the pulsed surface photovoltage technique using the por-Si/c-Si interface as probe. The values of the potentials at the por-Si/n-Si and at the por-Si/p-Si interface are -0.05 V and +0.47 V, respectively. Non-monotonous photovoltage transients related to trapping in por-Si are observed. The traps can be annealed at 150°C and generated in H20 atmosphere.
Porous Silicon as an Ultraviolet Light Source
Authors: Kozlowski F. , Huber B. , Steiner P. , Sandmaier H. , Lang W. 
Published: April 2011

ABSTRACTIn addition to photoluminescence and electroluminescence porous silicon is capable of emitting an ultraviolet line spectrum. This emission can be observed already at ambient conditions. We could identify this line emission as the spectrum of nitrogen. At a pressure of about 10 mbar the UV-intensity exceeds the intensity at ambient pressure about two orders of magnitude. Angular dependent spectroscopy and the light emission behaviour at lowered pressure led us to the conclusion that the silicon structures in the samples behave as sub-micrometer-sized electron guns. Dye covered glass substrates can be excited by the intense UV-light at about 5-20 mbar so that the red and green light of the dyes can easily be recognized under usual laboratory illumination. A luminous density of 240 Cd/m2 and 40 Cd/m2 could be achieved for the green luminescing ZnS:Cu,Al and the red luminescing YVO4:Eu respectively. Continuous UV-light emission could be observed for more than 1.5 hours at 2 mbar.
Visible Electroluminescence from Al-Porous Silicon Reverse Bias Diodes Formed on the Base of Degenerate N-Type Silicon
Authors: Lazarouk S. , Bondarenko V. , Pershukevich P. , La Monica S. , Maiello G. , Ferrari A. 
Published: April 2011

ABSTRACTWe demonstrate current induced visible light emission from Schottky junctions between aluminium electrodes and porous silicon formed by electrochemical etching of degenerate n+ -type silicon. HF concentration and anodizing current were chosen to yield preparation conditions in the transition region between electropolishing and porous silicon formation regimes. The light emitting diodes were formed by magnetron sputtering of aluminum on the porous silicon surface. Visible electroluminescence (EL) was recorded when dc or ac voltages larger than 4 V were applied between the aluminium electrodes. The visible EL appears in the dark, at the edge of the electrodes at a reverse bias of 5-6 V. The intensity of emitted light increases with applied voltage; at applied bias higher than 7 V the light emitted was observable by the naked eye at normal daylight. Compared to forward bias solid state contact porous silicon devices, the structure has an increased stability (after 100 hours of continuous operation under a 7 V reverse bias, no appreciable modification was observed in emission intensity). The main features of this electroluminescence are very similar to the ones observed under avalanche breakdown of silicon p-n junctions.
Optoelectronic Effects in Porous Silicon Related to the Visible Luminescence Mechanism
Authors: Koshida N. , Koyama H. , Ozaki T. , Araki M. , Oguro T. , Mizuno H. 
Published: April 2011

ABSTRACTSome optoelectronic effects in porous Si (PS) have been investigated in relation to the visible luminescence mechanism. As regards photoluminescence (PL), particular emphasis is placed on the relationship between photoconduction (PC) and PL excitation (PLE) spectra, the interaction of external electric field and PL emission, and polarization properties of PL Main subjects of electroluminescence (EL) studies reported here are the dynamic behavior of EL operation and the formation of a large-area contact by a conducting polymer (polypyrrole: PP). The observed experimental results (almost complete coincidence of PC spectra with PLE ones, linear polarization memory of PL definite correlation between the polarization degree and the PL efficiency, and comparable response time of electrical PL quenching and EL to the PL decay time) are consistent with our hypothesis that the major process of PL takes place within Si nanocrystallites. The electrical characterization of light-emitting PS diodes with PP contacts ensures the usefulness of the contact formation by electropolymerization as a technique for uniform and efficient carrier injection into PS.
Luminescence Properties of Silicon Clusters: Chain, Ladder and Cubic Structures
Authors: Kanemitsu Yoshihiko 
Published: April 2011

ABSTRACTWe have studied the luminescence properties of chemically synthesized Si8 clusters and Si-based polymers with different backbone structures. The optical properties of Si8 clusters depend strongly on the shape of clusters. The luminescence properties of the cubic Si8 cluster are different from those of the chain and ladder Si8 clusters. Moreover, the ladder and network Si polymers whose backbones are constructed by the organosilicon units with three Si-Si bonds exhibit broad photoluminescence spectra in the visible region. These luminescence properties are entirely different from those of the chain structure constructed by the organosilicon units having two Si-Si bonds. The unique optical properties of silicon clusters and polymers are discussed.
Luminescence Properties of Silicon Oxynitride Films
Authors: Fischer T. , Muschik T. , Schwarz R. , Kovalev D. , Koch F. 
Published: April 2011

ABSTRACTSilicon oxynitride films, deposited by chemical vapour deposition using a high He dilution are investigated with respect to their photoluminescence properties. At low temperatures the PL spectra, which show broad maxima around 2 eV, consist of two contributions with different decay times: a ns-fast and a ms-slow component, the slow one disappearing above 80 K. To account for these findings and for absorption measurements, a model is proposed to describe the structure of the samples consisting of inclusions of Si rich regions in an a-SiOxNy:H matrix with a common molecular aggregate as luminescence center. The different PL lifetimes supposedly result from different feeding mechanisms. Such a behaviour may be present in oxidized porous Si as well.
Si1−xGexY Alloy Nanocluster Materials Chemical Vapor Deposition of Si2H6Ge2H6 Mixtures in Zeolite Y
Authors: Dag Ömer , Kuperman Alex , Ozin Geoffrey A. 
Published: April 2011

ABSTRACTSi1−xGexY alloy nanocluster materials are synthesized by the chemical vapour deposition of Si2H6/Ge2H6 mixtures within the diamond lattice of 13Å supercages in acid zeolite Y. A multianalytical approach to the study of these Si1−xGexY nanomaterials over the full compositional range 0<x<1 provides information concerning the mode of formation, geometric and electronic structures, trends in the optical properties of the encapsulated alloy nanoclusters.
Control of Grain Size and Texture of Poly-Si with Atomic Hydrogen Under In Situ Ellipsometric Observation
Authors: Nakamura K. , Akasaka T. , He D. , Shimizu I. 
Published: April 2011

ABSTRACTA systematic study was performed to fabricate poly-Si thin films on glass substrates. Amorphous tissues were efficiently removed by forming a textured structure with the aid of atomic hydrogen. According to the real-time observation by spectroscopic ellipsometry(SE), the grain growth was enhanced by permeation of atomic hydrogen into the sub-surface. Hall measurements were made over a rather wide temperature range: 100 K--350 K. A rather high Hall mobility of 20 cm2/Vs or more was obtained at room temperature due to the reduction of amorphous tissues remaining at grain boundaries.
Grain Boundary Location-Controlled Polt-Si Films for Tft Devices Obtained Via Novel Excimer Laser Process
Authors: Kim H. J. , Im James S. 
Published: April 2011

ABSTRACTBased on a previously acquired physical understanding of the excimer-laser-induced crystallization process, we have developed a new crystallization technique that produces controlled microstructures and possesses a wide processing window. A patterned oxide capping layer was used as an antireflective coating to induce complete melting of an Si film under an SiO2 pattern, and partial melting of the Si film in the areas not under the capping layer—allowing controlled super lateral growth to proceed from the incompletely melted portion of the film to the completely melted portion. For the simple stripes used in this investigation, when the width of the completely molten region is less than a critical distance (above which nucleation of solids occurs in the middle of the completely melted regions), the resulting microstructure has large and elongated grains with one precisely located grain boundary running parallel to the stripe In the middle of the oxide capped region.Arrangement of TFT devices on the resulting Grain boundary Location-Controlled (GLC) Si films with one (or zero) grain boundaries located perpendicular to the flow of electrons within the active channel portion of the TFT devices is illustrated. Such devices are expected to possess performance and uniformity characteristics that are superior to currently available poly-Si TFT devices.
Fabrication of Photoluminescent Amorphous Pillar Silicon Structures
Authors: Lazarouk S. , Katsuba S. , Kazuchits N. , De Cesare G. , Monica S.La , Maiello G. , Proverbio E. , Ferrari A. 
Published: April 2011

ABSTRACTFabrication of amorphous pillar silicon structures showing visible photoluminescence (PL) by naked eye is reported. Some attempts involving silicon etching processes were previously performed by other authors, but PL from the resulting pillar structures was never observed.The pillar silicon structures were grown by Plasma Enhanced Chemical Vapour Deposition (PECVD) of hydrogenated amorphous silicon (a-Si:H) over the surface of porous aluminum oxide films, previously formed by anodization process. Alumina pore dimensions varied between 4-200 nm, depending on the parameters of the anodization process. The size of the grown a-Si:H pillars was quite homogeneous and could be tightly controlled by the anodization conditions. Immediately after PECVD process, PL from the pillar structure was very weak and not visible by naked eye, but after a short electrochemical treatment in 1% wt HF at 2 mA/cm2 it became quite bright and visible at normal daylight. A red shift, very similar to the one shown by porous silicon formed on monocrystalline substrates, was observed during samples drying after the electrochemical treatment.
Carrier Confinement Effects in Epitaxial Silicon Quantum Wells Prepared by MOCVD
Authors: Maruska H. Paul , Sudharsanan R. , Bretschneider Eric , Davydov Albert , Yu J.E. , Pathangey Balu , Jones K.S. , Anderson Timothy J. 
Published: April 2011

ABSTRACTSilicon multiquantum wells ranging in width from 3 to 15 nm were deposited on closely lattice-matched ZnS barriers. MOCVD was used to deposit the ZnS films using diethyl zinc and hydrogen sulfide as the precursors; disilane was used to deposit silicon layers at low temperatures. Single and multiple silicon nano-layers were observed by transmission electron microscopy and secondary ion mass spectrometry. Photoluminesence studies revealed emissions peaks which were blue-shifted with respect to the edge emission from bulk silicon substrates. The observation of emission from silicon nanostructures shifted to wavelengths as short as the 800-850 nm range is consistent with the effects of quantum confinement in silicon nanostructures.
The Crystallographic Modeling of C60 Orientations in a Cubic Lattice
Authors: Shekhtman Veniamin Sh. , Dilanyan Ruben A. , Rybchenko Oksana G. 
Published: April 2011

ABSTRACTThe symmetry conditions which rule the matching of a fulleren molecule's main axis in a translational lattice are considered. The full set of orientational states for the structure of fullerene are obtained. The different levels of correlations between symmetry axes of icosahedral molecule and cubic lattice are considered. This result used for analysis of orientational ordering models, including modulation structure and discrete orientational glass.
Molecular Dynamics Simulations of Hypervelocity Buckminsterfullerene Collisions
Authors: Robertson D.H. , Brenner D.W. , White C.T. 
Published: April 2011

ABSTRACTMolecular dynamics simulations of high-energy collisions between various combinations of C60 and C70 fullerenes were performed to calculate the threshold for molecular fusion of these clusters as a function of the center-of-mass collision energy. For collision energies below 90 eV, only non-reacting collisions occurred with no observation of any fusion. However, at higher collision energies molecular fusion of the colliding clusters was observed with the fusion probability approaching 1 by 160 eV collision energy. The non-fusing, rebounding collisions showed deeply inelastic behavior with the loss of translational energy to internal energy varying from 50 to 70 percent.
Search for the Ground State of C60B10
Authors: Esfarjani Keivan , Ohno Kaoru , Kawazoe Yoshiyuki 
Published: April 2011

ABSTRACTRecent experimental discovery of C60B10 has motivated the present search for the possible atomic structures of this system. We have already studied the electronic properties of C58BN within the density functional theory, and are interested in the effects of other substitutions of carbon atoms by boron and nitrogen in fullerenes. In our all-electron calculation, we adopt the mixed-basis approach in which 1s and 2p orbitals in addition to about 3000 plane waves are included. The total energy and the band gap of many possible configurations are calculated in order to predict the most stable structure of this system. The density of states is presented as well for the ground state configuration.
Fullerene Superconductors: Effects of Molecular Orientation and Valence
Authors: Yildirim T. , Barbedette L. , KniaŹ K. , Fischer J. E. , Lin C. L. , Bykovetz N. , Stephens P. W. , Sulewski P. E. , Erwin S. C. 
Published: April 2011

ABSTRACTWe report results of high-resolution x-ray diffraction, dc magnetometry and Raman scattering on the quaternary alkali and ternary mixed alkali-alkaline earth fullerene compounds Na2RbxCs1−x C60 (0 < x < 1) and Rb3−δ BaδC60 (δ ∼ 0.4 and 2.0). These have the same cubic space lattices as K3C60 and Rb3C60 however the former exhibit long-range orientational correlations with Pa3 symmetry and the latter have N > 3 delocalized electrons per molecule. We show that the dependence of Tc on lattice constant is much steeper for the ordered as compared to the merohedrally disordered phases with N = 3, and that within the constraint of cubic symmetry Tc decreases significantly with increasing N > 3, in disagreement with some theoretical predictions.
Medical Applications of Water-Soluble Polyhydroxylated Fullerene Derivatives
Authors: Chiang Long Y. , Lu Fung-Jou , Lin Jaw-Town 
Published: April 2011

ABSTRACTThe promising positive results in reducing superoxide free radicals (O2-.), generated by invitro xanthine and xanthine oxidase, have been demonstrated in the evaluation of potential uses of novel water-soluble [60] fullerenols as free radical scavengers. Observation reveals the inherent application of fullerenols in a wide range of medical and clinical areas as preventive alternatives for a long-term medical treatment.
Metal Film Nucleation and Growth on C60 Interfacial Layers
Authors: Hebard A. F. , Eom C. -B. , Haddon R. C. , Phillips Julia M. , Marshall J. H. 
Published: April 2011

ABSTRACTThe effect that the presence or absence of interfacial C60 layers has on the nucleation and subsequent growth of overlying thin metal films has been studied using in situ resistivity measurements. Comparisons are made for Al and Cu films grown on quartz and yttria stabilized zirconia (YSZ) substrates. Our results indicate that electron donation across M/C60 (M=Al, Cu) interfaces reduces the percolation threshold for conductivity while simultaneously giving rise to an increased resistance in the metal due to electron depletion. Additional physical processes that are taken into account include the effect of different interfacial energies at the M/C60 and M/substrate boundaries and the effect of substrate tunneling between percolating metallic islands during the initial stages of film growth.
Nonlinear Optical and Transport Properties of Fullerene Crystals
Authors: Byrne Hugh J. , Akselrod Lidia , Werner Andreas T. , Maser Wolfgang K. , Kaiser Mathias , RÜhle Wolfgang W. , Roth Siegmar 
Published: April 2011

ABSTRACTPicosecond time resolved photoluminescence and photoconductivity measurements are performed to investigate the influence of high intensity illumination on the properties of Fullerene crystals. A highly nonlinear dependence of both the photoluminescence characteristics and the photoconductive response of the fullerenes is seen and temperature dependent measurements indicate that the nonlinear processes are associated with an insulatormetal-like phase transition in the material, and thus that the electronic properties of the excited state are dramatically altered at high excited state densities. The observed behaviour is compared and contrasted to the changes in the optical properties upon photochemical modification of the pristine material via Raman spectroscopy. Application of a simple phenomenological model to calculate the contribution of intermolecular exchange and correlation energies in the excited state supports the proposal that the observed phenomena originate from a Mott-like phase transition. A further manifestation of this behaviour is the emergence of a broadband electroluminescent emission above a critical injection current density.
Crystalline Boron Carbide Encapsulated Into Carbon Nanoclusters from Arc-Discharge Soot
Authors: Seraphin Supapan , Zhou Dan , Jiao Jun 
Published: April 2011

ABSTRACTUsing a boron-containing composite anode in an arc discharge, we found in the soot on the reactor walls graphitic multiwalled carbon clusters that contained boron carbide crystals, as identified by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and electron diffraction. The encapsulants are compounds of the lightest element that has yet been encapsulated, and the first of the non-metallic. The multiwalled graphitic cages partially encapsulating the boron compounds have rarely been observed in the soot of arc-discharge material produced from anodes not containing boron. We explain this exception by the known tendency of boron to catalyze graphitization.
The Effect of O2 Intercalation on the Rotational Dynamics and the Ordering Transition of C60
Authors: Myers S. A. , Assink R. A. , Schirber J. E. , Loy D. A. 
Published: April 2011

ABSTRACTWe have used 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the structure and rotational dynamics of C60 containing oxygen molecules located in the interstitial sites of the fcc lattice. Under normal conditions, a narrow peak at 143.7 ppm is observed for C60. When exposed to oxygen at moderate pressures, several additional resonances appear in the 13C MAS NMR spectrum. These secondary resonances are shifted downfield from the main peak at 143.7 ppm and are due to the Fermi-contact interaction of the paramagnetic oxygen molecules with the 13C nuclear spins. The presence of oxygen depresses the orientational ordering transition by ca. 20 K as observed by DSC. The spin-lattice relaxation time (T1) of each secondary peak shows a minimum near the ordering transition, indicating that this transition is not dependent on the number of oxygen molecules surrounding an individual C60 molecule. The T1 due to paramagnetic relaxation, normalized by the number of surrounding oxygen molecules, is constant. This observation demonstrates that within a given sample, the dynamics of C60 molecules are independent of the number of surrounding oxygen molecules.
High Yield Conversion of Carbon Nanotubes to Nanostraws at Mild Conditions
Authors: Hwang Kuo Chu 
Published: April 2011

ABSTRACTSeveral oxidants were examined for their abilities in opening carbon nanotube end caps. Up to 91% of carbon nanotubes were found to have at least one open end when treated by 0.2 M KMnO4/ 10% H2SO4 or 0.2 M KMnO4/ 0.2 M CrO3 aqueous solution at 100° C, 90 min. That is, σ82% of carbon nanotubes was converted to “nanostraws”. The morphologies of the processed carbon nanotubes reflect the relative strength of these oxidants. The mechanism of carbon nanotube end cap opening processes will be discussed.
Nuclear Reaction Probe of Oxygen Vacancy Migration in Electrically Fatigued PZT Thin Film Capacitors
Authors: Pfeffer R.L. , Wilber W.D. 
Published: April 2011

ABSTRACTThe migration of oxygen vacancies and their entrapment near film-electrode interfaces has been proposed as a cause of fatigue (i.e., polarization weakening) in ferroelectric thin film capacitors. To test this idea, lead zirconate titanate (PZT) thin films were epitaxially deposited by laser ablation on LaAlO3 substrates with yttrium barium cuprate (YBCO) base electrodes. Thin film capacitors were formed by deposition of noble metal (Pt) cap electrodes; half of them were then electrically fatigued by repeated polarization reversals (108 cycles). The distributions of oxygen in the two halves were then compared by means of accelerator-based nuclear backscattering (using the narrow elastic resonance at 3.045 MeV in the scattering of 4He from 16O) throughout the bulk of the PZT films and especially right under the Pt electrodes. We were unable to detect any difference in the oxygen profiles to within the accuracy of measurement, which was about 1 % of the oxygen concentration. Compositional changes, at least involving oxygen, do not seem to be responsible for the striking electrical alterations seen in fatigued PZT.
Crystallization and Texture of Bi-Containing Layered Perovskite Thin Films
Authors: Chen S-Y. , Du X-F. , Chen I-W. 
Published: April 2011

ABSTRACTCrystallization and texture formation of a number of layered perovskite thin films prepared by the MOD method has been investigated. The crystallization temperature increases with increasing complexity of the structure, rendering it more difficult to obtain c-axis oriented films. Texture formation can be facilitated by the introduction of a seeding layer, such as PbBi2Nb2O9, which has a somewhat lower crystallization temperature, and by multiple coatings, which allow successive crystallization. Grain size is also reduced by the above practice. These results are compared with similar findings in PZT thin films to conclude that texture development in layered perovskites is nucleation controlled.