bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Carbon, Silicon, and Boron-nitride Nanostructures via Microwave Plasma Enhanced Chemical Vapor Deposition
Authors: Cui Hongtao , Liu Wei , Stoner Brian R. 
Published: April 2011

AbstractCarbon, silicon nitride and boron nitride nanostructures were synthesized using microwave plasma enhanced chemical vapor deposition. Both scanning and transmission electron microscopies and x-ray diffraction were used to observe the morphology and structures while energy dispersive x-ray was used to determine the composition of the nanostructured materials. Bamboo-like multiwalled carbon nanotube structures were observed while silicon nitride showed novel needle-like solid structures. All materials were deposited using a thin film iron catalyst seeded on either silicon with reactive plasma gases containing either a mixture of methane and ammonia or ammonia. A general discussion of the nucleation and growth mechanisms for the various materials will also be included.
Electron Emission from Pentagons on a Carbon Nanotube Tip Revealed by Field Emission Microscopy
Authors: Hata Koichi , Takakura Akihiro , Saito Yahachi 
Published: April 2011

AbstractField emission of electrons from multiwall carbon nanotubes (MWCNTs) has been investigated by field emission microscopy (FEM) in an ultra-high vacuum chamber. An MWCNT whose tip is capped by curved graphite layers gives a FEM pattern consisting of 6 bright pentagons when the surface of the nanotube tip is clean. Even in the ultra-high vacuum with a base pressure of about 10-10 Torr, residual gas molecules, attracted by polarization forces, adsorb on the nanotube tips. The adsorbed molecules reside preferentially on the pentagonal sites, giving bright spots in the FEM pattern. A flash heating the emitter at about 1300 K allows the molecules to desorb, and the nanotube emitter recovers the original clean surfaces. The adsorption and desorption of gas molecules are responsible for stepwise increases and decreases in the emission current, respectively.
Use of Multi-Walled Carbon Nanotubes for Conductive Probe Scanning Force Microscopy (Cp-SFM)
Authors: Stavens Kevin B. , Andres Ronald P. 
Published: April 2011

AbstractMulti-Walled Carbon Nanotubes (MWNTs) mounted on commercial Scanning Force Microscopy (SFM) cantilevers have proven to be excellent probes for high resolution Tapping Mode-Scanning Force Microscopy (TM-SFM). Because of their robust nature and high electrical conductance, MWNTs are also attractive for use in Conductive Probe-Scanning Force Microscopy (CP-SFM). To be used in this application, however, the MWNT must be mounted via a high conductance contact to a conductive cantilever. A technique has been developed that produces such a contact. First, a MWNT is attached using acrylic adhesive to a commercial SFM cantilever that has been vacuum coated with gold. Then, a cap of gold is deposited over the junction between the MWNT and the SFM cantilever via spatially selective electro-deposition.
Electrochemical Testing of Potential Molecular Devices
Authors: Price David W. , Dirk Shawn M. , Rawlett Adam M. , Chen Jia , Wang W. , Reed Mark A. , Zacarias Angelica G. , Seminario Jorge M. , Tour James M. 
Published: April 2011

AbstractCyclic voltammetry (CV) was used to study the reduction potentials of 2,5-di(ethynylphenyl)-4-nitroaniline and 2,5-di(ethynylphenyl)nitrobenzene. Although no absolute reduction potentials can be used in the correlation between solution (CV) and solid state (nanopore) embodiments, each CV plot showed two reductions. The first and second reduction might correspond to switching events of recently reported molecular electronic devices in a nanopore. Cyclic voltammetry results are also reported for other potential molecular scale electronic devices.
Submicron Patterned Anodic Oxidation of Aluminum Thin Films
Authors: Huang Qiyu , Lye Whye-Kei , Longo David M. , Reed Michael L. 
Published: April 2011

AbstractAlumina formed by the electrochemical anodization of bulk aluminum has a regular porous structure [1]. Sub-100 nm pores with aspect ratios as high as 1000:1 can easily be formed [2] without elaborate processing. Anodization of aluminum thus provides the basis for the inexpensive, high throughput microfabrication of structures with near vertical sidewalls [2]. In this work we explore the patterned anodic oxidation of deposited aluminum thin films, facilitating the integration of this technique with established microfabrication tools. An anodization barrier of polymethylmethacrylate (PMMA) is deposited onto 300 nm thick aluminum films. The barrier film is subsequently patterned and the exposed aluminum anodized in a 10% sulfuric acid solution. Barrier patterning techniques utilized in this study include optical exposure, ion-beam milling and nano-imprint lithography. Sharp edge definition on micron scale patterns has been achieved using optical methods. Extension of this technique to smaller dimensions by ion-beam milling and nano-imprint lithography is presented. We further report on the observation of contrast reversal of anodization with very thin PMMA barriers, which provides a novel means of pattern transfer. Potential applications and challenges will be discussed.
Nanoscale Silicon Microcavity Optical Sensors for Biological Applications
Authors: Chan Selena , Horner Scott R. , Miller Benjamin L. , Fauchet Philippe M. 
Published: April 2011

AbstractThe large surface area of porous silicon provides numerous sites for many potential species to attach, which makes it an ideal host for sensing applications. The average pore size can be easily adjusted to accommodate either small or large molecular species. When porous silicon is fabricated into a structure consisting of two high reflectivity multilayer mirrors separated by an active layer, a microcavity is formed. Multiple narrow and visible luminescence peaks are observed with a full width at half maximum value of 3 nm. The position of these peaks is extremely sensitive to small changes in refractive index, such as that obtained when a biological object is attached to the large internal surface of porous silicon. We demonstrate the usefulness of this microcavity resonator structure as a DNA optical biosensor which displays appropriate sensitivity, selectivity, and response speed. A probing strand of DNA is initially immobilized in the porous silicon matrix, and then subsequently exposed to its sensing complementary DNA strand. Red-shifts in the luminescence spectra are observed and detected for various DNA concentrations. The spectral shifts confirm successful recognition and binding of DNA molecules within the porous structure. Detailed device fabrication procedures and the results of extensive testing will be presented. The detection scheme has also been extended to include the detection of viral DNA, proteins, and potentially bacteria. This work will lead to the development of a “smart bandage”, where the detection of bacteria or viruses can be diagnosed and an antibiotic treatment can be recommended.
Thermal Functionalization of Hydrogen-Terminated Porous Silicon Surfaces with Terminal Alkenes and Aldehydes
Authors: Boukherroub Rabah , Lockwood David J. , Wayner Danial D. M. , Canham Leigh T. 
Published: April 2011

AbstractH-terminated porous silicon (PSi) surfaces were chemically modified with terminal alkenes and aldehydes at high temperature to yield organic monolayers covalently attached to the surface through Si-C and Si-O-C bonds, respectively. Diffuse reflectance infrared Fouriertransform and X-ray photoelectron spectroscopies have been used to characterize the surfaces. Derivatized surfaces retain the PSi photoluminescence. Chemography was used to monitor the chemical changes of the PSi surface when exposed to 100% humidity in air. Organic monolayers linked through Si-C bonds are found to be highly resistant and have shown a better protection of the surface against corrosion compared to surfaces that are linked through Si-O-C bonds. The surface functionalized with ethyl undecylenate exhibits an even higher passivation of the surface through the presence of small amounts of oxide, which are induced by traces of water present in this chemical reagent, along with organic molecules attached to the surface.
Factors affecting Ge nanocrystal size in co-sputtered Ge+SiO2films
Authors: Choi WK , Ng V , Ho YW , Chen TB , Ho V 
Published: April 2011

AbstractThe high resolution transmission electron microscopy and Raman spectroscopy results of germanium nanocrystals embedded in SiO2 synthesized by rapid thermal processing (RTA) have been presented. From the results of samples with different Ge concentrations, it was concluded that there is a narrow window in the Ge concentration that can produce nanocrystals. We also showed that it is possible to vary RTA duration or temperature to produce Ge nanocrystals with varying sizes. Our results therefore suggest that it is possible to utilize (i) annealing duration and; (ii) temperature to tune crystal sizes for optoelectronic applications.
Novel Solid Nano Diamond/Pyrocarbon Semiconductor Materials
Authors: Gordeev Sergey K. , Belobrov Peter I. , Kiselev Nikolay I. , Petrakovskaya Eleonora A. , Ekstrom Thommy C. 
Published: April 2011

AbstractPorous solids made of nano diamonds cemented by pyrocarbon show a semiconductor behavior where the properties are controlled by the factor γ = mass ratio of sp2/sp3 phases. The volume electrical conductivity μ (T) was measured in the temperature range 77 - 290 K as a function of γ. By controlling the ratio γ from 0 to 50 %, the electrical conductivity will change by 12 orders of magnitude. The semiconductor activation energy depends on γ-ratio and has values between 0.03 - 0.3 eV. The variable-range hopping conduction was checked by measuring μ against T and to look for a T1/4 dependence. A positive thermoelectric power showed that NDC was p-semiconductor with a narrow band gap. The paramagnetic nanodiamonds, g = 2.0027(1) and δH = 0.86(2) mT, will still have this property in the NDC material and both the g-value and line width are not dependent on γ-ratio and temperature. The concentration of unpaired electrons is 41019 spin/g that equals to one dangling bond per nanodiamond particle. Absences of magnetoresistance and Hall potential were observed for all NDC materials. This was interpreted as resulting from a Tamm - Lifshitz - Pekar electronic conduction mechanism within onedimensional band of surface states.
Effects of the Substrate Temperature, Annealing Temperature, and Hydrogen Presence During Sputtering on the Luminescence of Eu-Doped Nanocrystalline Si/SiO2
Authors: Nery G. A. , Fonseca L. F. , Liu H. , Resto O. , Weisz S. Z. 
Published: April 2011

AbstractWe synthesized RF co-sputtered Eu2O3, Si and SiO2 on quartz substrates at different temperatures, and with and without the presence of H2 gas during sputtering. The photoluminescence of the samples was measured using both the 514.5nm green line and 457.9nm blue line of an Ar laser. The samples were then annealed, their luminescence remeasured, and the process repeated for a range of temperatures from 470°C to 1084°C. The effects of substrate temperature, presence or absence of H2, annealing, and the use of the green or blue line on the observed luminescence are presented.
Effect of Hydrogen Treatment on High Efficiency Electroluminescence Device Using Silicon Nanocrystals
Authors: Sato K. , Izumi T. , Iwase M. , Show Y. , Nozaki S. , Morisaki H. 
Published: April 2011

AbstractWe have fabricated the electroluminescence (EL) device using silicon (Si) nanocrystals, which were formed on Si substrate by co-sputtering of Si and silicon dioxide (SiO2). By treating with the Si nanocrystals in the hydrofluoric (HF) acid solution, the SiO2 region of the luminous layer reduced, and then, the electrons were efficiently injected in the Si nanocrystals. At the same time, Pb-center (non-radiative recombination center) was decreased by hydrogen termination to the Si-dangling bond in the interface between the Si nanocrystals and the SiO2 layer From these effects of the HF treatment, the high efficiency red light emission with the external quantum efficiency (EQE) of 0.35 % was obtained from the HF treated EL device under the operating voltage of +4.5 V.
Optical and structural analysis of Ge quantum dots embedded in strained Si quantum wells grown on patterned substrates
Authors: Beyer A. , Müller E. , Sigg H. , Stutz S. , David C. , Grützmacher D. , Ensslin K. 
Published: April 2011

AbstractGermanium quantum dots embedded in silicon have been used in the past to improve the opto-electronic properties of Si based materials. The idea is to overcome the limitation of the indirect band gap of Si by a strong localization of the carriers in quantum dots. However, the Ge quantum dots provide a strong carrier confinement only for the holes, the electrons are only weakly confined in the Si. In this study we embedded the Ge quantum dots in strained Si quantum wells grown on relaxed SiGe buffer layers. The strained Si quantum wells provide a confinement of the electrons in the vicinity of the Ge dots.The structures were deposited on planar as well as on patterned substrates by molecular beam epitaxy. The structural and optical properties of the samples were analyzed using high resolution cross sectional transmission electron microscopy (TEM) as well as low temperature photoluminescence. The size of the mesa structures have been used as experimental parameter. Relaxed buffer layers grown on line shaped mesa structures show a strongly reduced dislocation density. Consequently the deep luminescence attributed to dislocations in the buffer layers is strongly reduced and pronounced photoluminescence of the quantum structures grown on top of the buffer layers can be observed.
Photoluminescence from Nanoscale Si in a-SiOxMatrix
Authors: Umezu I. , Yoshida K. , Inada M. , Sugimura A. 
Published: April 2011

AbstractWe prepared a-SiOx (x < 2.0) films by co-sputtering Si and SiO2 targets and found that these films included nano-scaled a-Si regions in a-SiOx matrix. The structure of the films was evaluated by X-ray photoemission spectroscopy (XPS) and infrared absorption. The XPS spectra in the a-SiOx films showed two Si 2p peaks around 99.6 and 104 eV. This indicates that the a-SiOx films were composed of Si and a-SiO2 regions. The optical gap energy of this system rapidly increased when x exceeded 0.7. The rapid increase in the optical gap of this system indicates the formation of nanometer sized Si islands. The photoluminescence (PL) peak energy of this material decreased with increasing temperature above 60 K when x was less than 0.7. On the other hand, when x exceeds 0.7, the PL peak energy increases with temperature above 60 K. The quenching of PL intensity also takes place at 60 K. These results indicate a film structure change at x = 0.7, and recombination path and carrier distribution changes at 60 K. A correlation between film structure and PL properties are discussed. PL properties in this system are explained by superposition of the PL peak from nanoscale Si and a-SiO2 matrix.
Correlation Between Bulk Morphology and Luminescence in Porous Silicon Investigated by Evaporation Induced Pore Collapse
Authors: Sirbuly Donald J. , Mason Michael D , Buratto Steven K. 
Published: April 2011

AbstractWe use a combination of scanning electron microscopy, laser scanning confocal microscopy and luminescence spectroscopy to correlate the emission properties of anodized porous silicon (PS) with film morphology in samples that have undergone evaporation induced collapse of the underlying porous structure. Several PS samples were investigated as a function of the current density (J) and total etch time, while the total charge (Q) injected per unit area (and the total Si removed) was kept constant during etching. From this data two classes of PS samples emerge. Porous silicon samples produced at high current density have a 3-dimensional pore network with a narrow distribution of blue-green emitting chromophores. In contrast, low current density samples form a 2-dimensional pore network normal to the Si substrate with larger chromophores and exhibit broad red luminescence.
Silicon Nanoclusters in Si-SiO2 System
Authors: Espinoza-Beltrán F.J. , Díaz-Flores L.L. , Yáñez-Limón J.M. , Morales-Hernández J. , Rodríguez-Melgarejo F. , Vorobiev Yuri , González-Hernández J. 
Published: April 2011

AbstractLow concentration of Si nanoparticles (n-Si) produced by a ball milling method were introduced into a SiO2 matrix by the sol-gel method. These SiO2 sol-gel suspensions were prepared with high water-TEOS ratios. The samples obtained have high silanol concentration as was proved by infrared spectroscopy. The silanol structures of this samples are resistant for temperature as high as 800°C. Raman scattering measurements showed evidence of a photo-oxidation effect of the nSi particles embedded into the SiO2 matrix with high silanol concentration. The nanometric size of the Si particles was computed from Raman scattering measurements. The photo-oxidation effect was observed as a gradual shifting and broadening of the Raman signal due to the reduction of the particle size from 14 to 7 nm.
Fabrication and Characterization of Cold Electron Emitter Based on Nanocrystalline Silicon Dots
Authors: Nishiguchi K. , Zhao X. , Oda S. 
Published: April 2011

AbstractA cold electron emitter has been made from nanocrystalline silicon (nc-Si) dots. Nc-Si dots are formed in the gas phase by very-high-frequency (VHF) plasma enhanced chemical vapor deposition (CVD). Electrons, accelerated by electric field, are ballistically transported through nc-Si and SiO2, then extracted into vacuum. Electron emission efficiency is optimized through varying nc-Si film thickness, surface roughness, and by short thermal oxidation.
A Significant Change in Refractive Index of Nanocrystalline Porous Silicon Induced by Carrier Injection
Authors: Toriumi Y. , Takahashi M. , Koshida N. 
Published: April 2011

AbstractTo verify the availability of porous silicon (PS) device for application to optical switching, the photonic response of PS for carrier injection has been studied for a microcavity configuration. The observed reflectance spectral shift in the PS microcavity with increasing diode current is analyzedunder the assumption that the refractive index of nanocrystalline silicon is increased by carrier injectionand the subsequent accumulation possibly in localized states. This is consistent with the experimental results obtained from dynamic response measurements: there are fast and slow components in the refractive indexchange. It is also demonstrated that under the pulsed operation, the PS microcavity operates as a current-induced nonlinear optical switching device.
Gas source molecular beam epitaxy of high quality AlGaN on Si and sapphire
Authors: Nikishin S. , Kipshidze G. , Kuryatkov V. , Zubrilov A. , Choi K. , Gherasoiu Íu. , Peralta L. Grave de , Prokofyeva T. , Holtz M. , Asomoza R. , Kudryavtsev Yu. , Temkin H. 
Published: April 2011

ABSTRACTWe report the results of epitaxial growth experiments on AlxGa1−xN (0≤ x ≤ 1) on Si(111) and sapphire substrates aimed at understanding the origin and elimination of cracking. We describe growth procedures resulting in thick layers of AlxGa1−xN, grown by gas source molecular beam epitaxy with ammonia, that are free of cracks. In GaN layers with the thickness of ∼2.5 µm, we find the background electron concentration of (1-2)×1016 cm−3 and mobility of (800±100) cm2/Vs. In AlxGa1−xN (0.2 < x < 0.6) with the film thickness of 0.5-0.7 µm the electron concentration of (2-3)×1016 cm−3 is obtained. Low background concentrations in GaN allow for formation of p-n junctions by doping with Mg. Light emitting diodes with the peak emission at 380 nm have been demonstrated.
Polarity of Hexagonal GaN Grown on GaAs (111)A and (111)B Surfaces by HVPE and Movpe
Authors: Takahashi O. , Namerikawa M. , Tanaka H. , Souda R. , Suemasu T. , Hasegawa F. 
Published: April 2011

Summary:Dependence of hexagonal GaN polarity on the polarity of GaAs (111) substrates was investigated by CAICISS for HVPE and MOVPE. Although polarity of MOVPE GaN followed the polarity of GaAs substrate; Ga polar for (111)A and N polar for (111)B, both layers of HVPE GaN grown on GaAs (111)A & B surfaces were Ga polarity. Crystal quality was better for Ga polarity layers than for N polarity layers for MOVPE. However, Ga polar GaN grown on GaAs (111)B by HVPE had better crystal quality than that on the (111)A. These results can be understood by difference of the buffer layers and difference of growth kinetics between HVPE and MOVPE.
Surface Modification of Cubic Gan Buffer Layer Grown by Metalorganic Vapor Phase Epitaxy
Authors: Nagayama Akira , Katayama Ryuji , Wu Jun , Onabe Kentaro , Sawada Hidetaka , Takuma Eliko , Ichinose Hideki , Shiraki Yasuhiro 
Published: April 2011

ABSTRACTAnisotropic X-Ray diffraction (XRD) and transport properties of cubic GaN grown on GaAs substrates correspond to the features of low-temperature grown GaN (LT-GaN) buffer layer. When the LT-GaN layer is grown on the surface tilted from (001) to [1-10] with annealing in arsenic ambient, the macroscopic step edges along [1-10] direction are modified by either the ambient of thermal annealing, or substrate misorientation. A parallel conduction in GaN, GaAs, and GaN/GaAs hetero-interface was observed by photoconductivity measurements. Transmission electron microscope (TEM) observation shows that self-annihilations for (-111) B stacking faults are preferentially occurred near GaAs interface when GaN film grown on the surface tilted from (001) toward [1-10] (As step edge) is annealed in arsenic ambient. TEM observation also shows that stacking faults and dislocations are preferentially generated near GaN/GaAs interface. It is suggested that anisotropic transport properties correspond to the well-like potential generated by band bending at GaN/GaAs interface. The nearly isotropic mobility of 3,000 cm2/Vsec at 77K is obtained by improving interface property.
Growth Mode and Defects in Aluminum Nitride Sublimated on (0001) 6H-SiC Substrates
Authors: Liu Lianghong , Liu Bei , Shi Ying , Edgar J. H. 
Published: April 2011

ABSTRACTThe effect of substrate preparation on the sublimation growth of AlN on 6H-SiC was investigated at about 1800°C and 400 torr. Short and long-time sublimation growths of AlN indicated that the nucleation, growth mode, and defects formed depended on the substrate surface preparation. Growth on an off-axis 6H-SiC substrate with 6H-SiC epilayer was in the step flow growth mode in contrast to the island growth mode on as-received substrates, while the 2-D growth was achieved on substrates first coated with an AlN epitaxial layer. Cracks due to the lattice and mainly large thermal expansion coefficient mismatch were always observed in the deposited AlN crystal, as characterized by SEM and optical microscopy.
Raman spectroscopy studies in InGaN/GaN wurtzite epitaxial films
Authors: Correia Maria R. , Pereira Sérgio , Monteiro Teresa , Pereira Estela , Alves Eduardo 
Published: April 2011

ABSTRACTIn this work we studied a set of nominally undoped epitaxial InxGa1−xN wurtzite films grown on (0001) sapphire substrates. In order to separate the contribution of the strain and indium content in the phonon mode frequency, indium mole fraction was determined using a strain insensitive method, Rutherford backscattering spectrometry (RBS). Strain was evaluated by comparing the lattice constants measured by X-ray diffraction (XRD) with the relaxed lattice parameters given by Vegard's law. Samples with comparable indium content, but under different states of strain were used as reference. This allowed the behaviour of different Raman shift modes for both, strain and composition to be independently established. We also assess the potentiality of Raman spectroscopy for the evaluation of crystalline quality by comparing the results obtained with the ones provided by other well-established methods such as XRD and RBS.