bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Impact of Fermi Pinning on Thermal Properties of the Instabilities in ZnO TFTs
Authors: Cross R.B.M. , De Souza M. M. 
Published: April 2011

ABSTRACTIn this paper we describe gate bias and temperature induced device instabilities of inverted-staggered ZnO-TFTs. It is shown that low positive and negative gate bias results in the transfer characteristics shifting in a positive and negative direction respectively. It is suggested that this is a consequence of temporary charge trapping at or close to the channel/insulator interface. The degradation of device parameters such as the threshold voltage, subthreshold slope and effective channel mobility is demonstrated at elevated measurement temperatures, suggesting the generation of defects and/or trap states in the interfacial region. In addition, it is postulated from the extracted activation energy of the drain current that the Fermi-level is pinned during the operation of the devices due to the high level of states close to the conduction band edge. These results highlight the relatively ease with which defects could be created at the interface, indicating a high concentration of weak or strained bonds. Both charge trapping and defect creation-induced instabilities appear to be reversible, as all devices regain their original characteristics after a period of relaxation at room temperature.
Multipolar Photonic Interactions between Quantum Dots of Different Sizes
Authors: Matsueda Hideaki 
Published: April 2011

ABSTRACTMultipolar interactions between quantum dots involving real and virtual photons are compared on the basis of our (micro-photoluminescence) spectra of coupled QDs (quantum dots), and suggested as the principle of intra-device, inter-device, and inter-chip interconnections and logical operations, with the device concepts for solid state nanometer networks and a quantum computer.
Optical Properties of Colloidal CdSe/ZnS core/shell Nanocrystals Embedded in a UV Curable Resin
Authors: Joshi Abhishek , Davis Edwin , Narsingi Kaushik , Manasreh Omar , Weaver B. D. 
Published: April 2011

ABSTRACTOptical absorption and photoluminescence techniques were used to investigate the band gap of colloidal CdSe/ZnS core/shell nanocrystals matrixed in a UV curable resin. The band gap was measured for several nanocrystals with size ranging between 1.9 and 4.0 nm. The band gap (Eg) was determined from the first exciton peaks observed in the optical absorption spectra. Both Debye and Einstein temperatures were estimated from fitting the energy band gap vs. temperature using two different empirical expressions.
Optical Properties of Heavily Doped n-type CdSe Quantum Dots for Intersubband Device Applications
Authors: Zhang Shengkun , Zhou Xuecong , Shen Aidong , Wang Wubao , Alfano Robert , Lu Hong , Charles William , Yokomizo I , Tamargo Maria , Franz K , Gmachl C 
Published: April 2011

ABSTRACTIn this research, interband and intersubband optical properties of heavily doped n-type CdSe quantum dots were investigated by temperature dependent photoluminescence (PL) spectroscopy, picosecond time-resolved PL spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Two doped and one undoped CdSe quantum dot samples with multiple QD layers were grown over ZnCdMgSe barrier layers on InP (001) substrate by molecular beam epitaxy. Heavy doping leads to decreasing of activation energy of nonradiative recombination centers, however, does not affect the luminescence efficiency of doped quantum wells. Time resolved PL experiments show that the PL decay times of the doped samples have weak dependence on well width and are much longer than that of the undoped sample. The two doped CdSe QD samples show strong Intersubband IR absorption that peaked at 2.54 μm, 2.69 μm and 3.51 μm. The ISB absorption is found to be strongly polarization dependent due to the large size of the QDs.
Novel Morphologies of InAs Quantum Dot Growth on GaAs Surfaces Containing Nanostructures Formed by Droplet Epitaxy
Authors: Lee Jihoon , Wang Zh. M. , Liang B.L. , Sablon K. , Strom N. W. , Salamo G. J. 
Published: April 2011

ABSTRACTSelf-assembled InAs quantum dot clusters (QDCs) and InGaAs QD molecules (QDMs) have been demonstrated through a growth technique called “droplet epitaxy” by molecular beam epitaxy (MBE). For QDCs, the size and density of QDs can be controlled with variation of InAs monolayer coverages. For QDMs, Ga contribution from GaAs mound with the interaction of InAs deposition resulted in various number of InGaAs QDs per GaAs mound, ranging from 2 to 6 (bi-QDMs to hexa-QDMs) depending on the specific InAs monolayer deposition. High step density on sidewall of GaAs mound and anisotropy of surface diffusion gave a rise to preferential formation of InAs and InGaAs QDs around GaAs mounds. This hybrid growth approach combining droplet epitaxy and typical QD growth is relatively simple and flexible and doesn't require further ex-situ surface preparation. This approach of QD arrangement can find applications in optoelectronics as well as physical study of QD interaction.
Isotropic Lateral Ordering of III-V Quantum Dots Over GaAs (001) By Self-Assembly
Authors: Hussein Mohammad Lutfi , Marega Euclydes , Salamo Gregory 
Published: April 2011

ABSTRACTLateral ordering of InGaAs quantum dots over GaAs (001) has been achieved in earlier reports resembling anisotropic pattern. We present in this letter a method of breaking the anisotropy of ordered QDs by changing the growth environment. We do show experimentally that using As2 molecules instead of As4 as a background flux is effective in controlling the diffusion of Ga adatoms in away to make it possible to produce isotropic ordering of InGaAs QDs over GaAs (001). Our results are consistent with reported experimental and theoretical studies on surface structure and diffusion mechanism over GaAs.
Modeling of Silicon Nanodots Nucleation and Growth Deposited by LPCVD on SiO2 : From Molecule/surface Interactions to Reactor Scale Simulations
Authors: Zahi Ilyes , Vergnes Hugues , Caussat Brigitte , Esteve Alain , Djafari Rouhani Mehdi , Mur Pierre , Blaise Philippe , Scheid Emmanuel 
Published: April 2011

ABSTRACTWe present first results combining models at continuum and atomistic (DFT) levels to improve understanding of key mechanisms involved in silicon nanodots (NDs) synthesis on SiO2 by Low Pressure Chemical Vapor Deposition (LPCVD) from silane SiH4. In particular, by simulating an industrial LPCVD reactor using the CFD code Fluent, we find that the deposition time could be increased and then the reproducibility and uniformity of NDs deposition could be improved when highly diluting silane in a carrier gas. A consequence of this high dilution seems to be that the contribution to deposition of unsaturated species such as silylene SiH2 highly increases. This result is important since our first DFT calculations have shown that silicon chemisorption on silanol Si-OH or siloxane Si-O-Si bonds present on SiO2 substrates could only proceed from silylene (and probably from other unsaturated species). The silane saturated molecule could only contribute to NDs growth, i.e. silicon chemisorption on already deposited silicon bonds. Increasing silylene contribution to deposition in highly diluting silane could then also exalt silicon nucleation on SiO2 substrates and then increase NDs density.
Phonon Overheating in Quantum Dots: Low Electronic Densities
Authors: Král Karel 
Published: April 2011

ABSTRACTThe electronic coupling to the longitudinal optical phonons has been recently used to interpret theoretically the electronic energy relaxation in quantum dots. In this theory the LO phonon modes served as a reservoir, on which the electron executes multiple scattering acts. Quite reasonably such a phonon subsystem is expected to be passive, namely, in a long-time limit of development, the whole system should be able to achieve such a stationary state, in which the statistical distributions of both subsystems, electron and phonons, do not change in time. We remind briefly that the recent approach to the relaxation in quantum dots has led to a non-passivity of such a reservoir. We remind as well the method of a partial elimination of the phonon overheating effect by using the Lang-Firsov transformation. Then we apply such a modified relaxation theory to the electronic relaxation at low electronic densities in quantum dots and come to conclusions concerning the role of e-LO scattering mechanism. We show that the modified theory of relaxation gives a plausible dependence of relaxation rate on temperature of sample. We also come to conclusions that at low levels of electronic excitation of quantum dot sample the electron-LO phonon mechanism can become relatively weak with respect to other relaxation mechanisms not supporting the electronic up-conversion effect.
Self-assembly of Semiconductor Quantum Dots by Droplet Epitaxy
Authors: Koguchi Nobuyuki 
Published: April 2011

ABSTRACTWe have proposed a novel self-assembling growth method, termed Droplet Epitaxy, for the direct formation of QDs without using any lithography in 1990. Compared with the island formation based on the Stranski-Krastanow growth mode, the Droplet Epitaxy is applicable to the formation of quantum dots not only in lattice-mismatched but also in lattice-matched systems such as GaAs/AlGaAs. The process of the Droplet Epitaxy in MBE chamber consists of forming numerous III-column element droplets such as Ga or InGa with homogeneous size of around 10 nm on the substrate surface first by supplying their molecular beams, and then reacting the droplets with As molecular beam to produce GaAs or InGaAs epitaxial microcrystals.
Another advantage of the Droplet Epitaxy is the possibility of the fabrication of QDs structures without wetting layer by cotrolling the stoichiometry of the substrate surface just before the deposition of III-column element droplets.
Also we can control the shape of the QDs structure self-organizingly such as pyramidal shape, single-ring shape and concentric double-ring shape. These ring structures will provide excellent possibilities for the investigation of quantum topological phenomena.
Nanostructuring Rh(110) Surfaces by Ion Etching
Authors: Molle Alessandro , Toma Andrea , Boragno Corrado , Valbusa Ugo , de Mongeot Francesco Buatier 
Published: April 2011

ABSTRACTThe ion irradiation of the Rh(110) surface results in the self-organised formation of various nano-structured morphologies like ripples, mounds, pyramids which have been thoroughly studied as a function of the incidence angle and of the impact energy of the impinging ions. A study of the evolution of the surface ripples at various impact energies above the hot-spot threshold, has been rationalized in terms of a contribution due to an ion-induced surface diffusion mechanism. In the very low ion incidence regime, where the formation of hot spots following ion impact is inhibited, the formation of a rhomboidal pyramid pattern is singled out and attributed to the predominant reorganization of surface adatom and vacancies produced in the topmost surface layers. The metastable rhomboidal pyramid pattern, was recently proven to have extraordinary chemical reactivity since it is endowed with a very high density of undercoordinated step sites runnin along the very open <1-12> azimuthal direction.
Characterization of Medium-range Order in Self-Assembled Organic-inorganic Hybrid by Fluctuation X-ray Microscopy
Authors: Fan Lixin , Paterson David , McNulty Ian , Treacy M. M. J. , Kumar Dushyant , Du Phong , Wiesner Ulrich , Gibson J. Murray 
Published: April 2011

ABSTRACTThe control of formation and ordering of self assembled nanostructures, with medium- to long-range order, is a challenge that limits advances in many fields of nanotechnology. We have developed a technique, which we call fluctuation x-ray microscopy, that offers quantitative insight into medium-range correlations in disordered materials at nanometer- and larger-length scales. We examined the influence of sol-gel process variables on medium range order in PI-b-PEO/ aluminosilicate bulk using this technique. The nano-structuring of inorganic materials was directed by polymer self-assembly. The medium range correlation between the nanostructures in two hybrids was quantitatively examined and compared.
Grain Size Refinement in Cu bottom lead in CPP GMR Stack
Authors: Tadisina Zeenath Reddy , Gupta Subhadra , Papusoi Cristian , Fujiwara Hideo , Morris Robb , Thompson Gregory 
Published: April 2011

ABSTRACTGMR current-in-plane (CIP) spin valves are currently used in production of high density recording heads. For the next generation of heads, with recording densities higher than 100 billion bits per square inch (Gbpsi), confined-current-path (CCP), current- perpendicular-plane (CPP) GMR heads are the subject of intensive study. For the CPP stack, thick (150 nm) Cu leads are required to minimize the potential drop across the leads. This often leads to a rough film surface in the bottom lead which translates up into the GMR stack, thereby reducing the GMR effect because of roughening of the interfaces. Thick bottom leads also have large average grain sizes, leading to an increase in the coercivity of the ferromagnetic layers deposited on top of these leads. In order to decrease the grain size and roughness of the bottom Cu lead, lamination of the thick (150 nm) Cu with Ta interlayers was carried out, keeping the total Cu and Ta thicknesses constant. As the number of Ta-Cu bilayers was increased, the roughness decreased significantly. It was observed that the roughness decreased from over 1 nm for a single bilayer to about 0.3 nm for 10 bilayers. Atomic force microscopy (AFM) was used to determine the roughness of the samples and in-plane grain size. Scanning electron microscopy was used to confirm the in-plane grain size. X-ray diffraction was used to analyze the out-of-plane grain size of the Cu/Ta laminates. Cross-sectional transmission electron microscopy (TEM) was also utilized to analyze the interface quality. An increase in the resistance of the laminated lead was seen with increase in the number of laminations. This undesirable side effect can be minimized by improvement of the base vacuum of the sputter system, deposition at relatively high rates, and reduction of the latency time between successive film depositions. The in-plane film stress was also studied as a function of lamination frequency, and found constant for the same total thickness of Ta and Cu, as expected. The coercivity of Co90Fe10 layers deposited over laminated Cu/Ta leads was seen to decrease with increasing lamination frequency, also as expected. An even stronger effect on the CoFe coercivity was produced by using a 5nm Ta layer to cap the thick Cu lead, yielding significantly lower coercivity
Directed Self-Assembly of Thin Block Copolymer Films under Controlled Atmosphere
Authors: Kim Sangcheol , Briber R. M. , Karim Alamgir , Jones Ronald L. , Kim Ho-Cheol 
Published: April 2011

ABSTRACTWe have developed a simple and fast methodology to control the orientation of cylindrical microdomains in thin block copolymer films under controlled atmosphere conditions. Asymmetric block copolymers of polystyrene and poly(ethylene oxide) (PS-b-PEO) were dissolved in toluene and spin coated with less than one minute exposure to different solvent vapors and controlled humidity. The specific choice of solvents was based on the polymer solubility parameters and the solvent vapor pressure. By controlling the spin coating environment we were able to produce cylinders with orientations ranging from parallel to perpendicular with respect to the substrate. Orientation was apparently controlled by the preferential affinity of the vapor atmosphere. A combinatorial gradient technique was employed to investigate the mechanism of solvent-induced microdomain orientation.
Magnetic Property of á-Fe Nanoparticles Prepared by Solventless Thermal Decomposition Method
Authors: Han Young Chul 
Published: April 2011

ABSTRACTNano sized α-Fe particle was synthesized by modified thermal decomposition method. It resulted in the higher saturation magnetization (Ms) almost equivalent to the value of bulk Fe power (Mbulk = 210 emu/g). To prepare Fe nanoparticles, the Fe2+-(oleate)2 complex was annealed at 400 J in pyrex tube and the prepared Fe3O4 nanoparticle was reduced to Fe crystal structure at 700 J with NaCl under Ar+H2 gas atmosphere and annealed again under high vacuum system of 10−5 torr. The crystallinity and structure of the Fe nanoparticle was investigated by powder X-ray diffraction (XRD). The shape and size was confirmed by transmission electron microscope (TEM) images. The magnetic properties were characterized with coercivity and remanence from hysteresis loop by vibrating sample magnetometer (VSM)
Iron substituted SrRuO3 thin films
Authors: Ullah Aman , Yoo Young Zo , Chmaissem Omar , Kolesnik Stanislaw , Dabrowski Bogdan , Alan Genis 
Published: April 2011

ABSTRACTFe-doped SrRuO3 thin films were grown on SrTiO3 (STO) substrates by using the Pulse Laser Deposition (PLD) method. Fe concentrations in the SrRuO3 thin films ranged from 0 % to 11 % to manifest the effect of Fe doping on their microstructure. Lattice constants of the films did not show obvious changes with the Fe doping whereas surface morphologies drastically changed from stepped to island structure with increasing Fe. X-ray reflectivity revealed that the surface and interfacial roughness decreased with increasing concentration of Fe. Surface roughness of the films was confirmed by atomic force microscopy. Therefore, a precise determination of film roughness as well as its growth mechanism using X-ray and AFM is exploited to correlate the Fe doping with structural disorder.
Continuous Synthesis of Inorganic Magnetic Nanocomposites by Laser Pyrolysis for Biomedical Applications
Authors: Veintemillas Sabino , Bouchet-Fabre Brigitte , Morales Maria Puerto , Leconte Yann , Costo R , Bonville Pierre , Herlin-Boime Nathalie C 
Published: April 2011

ABSTRACTNanocomposite particles made from encapsulation of magnetic nanoparticles in an inorganic matrix have a real interest in biomedicine due to their high resistance against biodegradation compared with nanoparticles encapsulated in an organic matrix and little work has been published concerning such materials. In this work we use the laser pyrolysis method for the preparation of magnetic composites of Fe-based nanoparticles dispersed in silica and carbon. The precursor is an aerosol of a precursor which can be easily used in a safe way. Important advantages of the laser pyrolysis method are the reproducibility, simplicity (one step method) and continuity which allows producing significant amounts of nanoparticles. The short reaction times (ms) involved in the nucleation of the powders insure the nanometric particle size of both the magnetic component and the inorganic matrix.This paper is focused on the synthesis and characterization of the Fe@SiO2 and Fe@C nanopowders generated by laser pyrolysis of ferrocene diluted in toluene and carried to the reaction zone in aerosol form. The silica coating was formed by the addition of tetraethoxysilane (TEOS) to the reactant. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), specific surface area determination (BET) and magnetic measurements. In the case of Fe@SiO2 the process generates rather homogeneous iron/magnetite particles smaller than 10 nm in diameter surrounded by a SiO2 coating of about 20 nm. In the case Fe@C the process generate iron based magnetic nanoparticles of complex composition smaller than 11 nm surrounded by a graphitic carbon layer of 50 nm. Stable aqueous dispersions at physiological pH were produced for both systems by means of strong oxidation in aqueous solutions, which is a very encouraging result for application in the field of living tissues.
Negative Refractive Index of Meta-materials at Optical Frequencies
Authors: Ramakrishna S. Anantha , Chakrabarti Sangeeta 
Published: April 2011

ABSTRACTScaling the performance of metamaterials to obtain negative refractive index at optical frequencies has been of great interest. One of the great barriers to the scaling is that real currents cannot be driven at very high frequencies and one is more dependent on displacement currents to generate negative magnetic permeability. Moreover to keep the dimensions of the metamaterials physically accessible, the structural lengthscales of the metamaterials begin approach the wavelength of the radiation in free space and homogenisation is often questionable. Here we will show that metamaterials such as Split ring resonators in these high frequency limits exhibit complex behaviour. Magnetic activity and Negative refractive index behaviour can, indeed, be obtained at optical frequencies but will need to be interpreted very carefully. The plasmonic nature of the metallic system and excitation needs to be considered in detail.
Negative Index Metamaterials with Deeply Subwavelength Structural Dimensions from Near Infrared to Visible Based on Thin Filmsββ
Authors: Lomakin Vitaliy , Fainman Yeshaiahu , Shvets Gennady 
Published: April 2011

ABSTRACTNovel two and three-dimensional doubly negative metamaterials (DNM), viz. metamaterial with simultaneously negative permittivity, permeability, and index of refraction, are introduced. The metamaterials comprise deeply subwavelength periodic unit cells, can be tuned to operate in the near infra-red and visible spectra, and can be manufactured using standard nanofabrication methods with compatible materials. The DNMs' unit cell comprises an optically thin metal film sandwiched between two thin metal strips or patches residing at a small distance from the film. The cavity formed between the strips or patches supports resonances with magnetic and electric response that can be tuned to exist in overlapping frequency bands thus leading to the DNM operation.
Enhancement of Ferroelectricity and Magnetoelectric Effect of BiFeO3 Thin Films on Membrane Structure
Authors: Nakashima Seiji , Yun Kwi-Young , Nakamura Yoshitaka , Okuyama Masanori 
Published: April 2011

ABSTRACTMultiferroic BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/thick (200 μm) and membrane (15 μm) Si substrate by pulsed laser deposition (PLD) to confirm the influence of stress from substrate. Si membrane was obtained by etching using reactive ion etching (RIE) until thickness is to be 15 μm. The X-ray diffraction peaks of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane substrate slightly shift to lower angles, compared to those on Pt/TiO2/SiO2/Si (200 μm) substrate. Ferroelectric hysteresis loops were also measured at 150 K before and after Si etching by RIE. The BiFeO3 thin film on the Pt/TiO2/SiO2/Si (15 μm) membrane structure shows remanent polarization (Pr) of 95 μC/cm2 for a maximum applied voltage of 18 V, which is larger than Pr = 71 μC/cm2 of BiFeO3 thin film on Pt/TiO2/SiO2/Si (200 μm) substrate at the same measurement conditions. Under magnetic field of 1.1 T, remanent polarization (Pr) of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane structure increased from 95 μC/cm2 to 101 μC/cm2 at 150 K due to stress relaxation of BiFeO3 thin film.