bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionic Size Limits for A Ions in Brannerite (ATi2O6) and Pyrochlore (CaATi2O7) Titanate Structures ( A = tetravalent rare earths and actinides)
Authors: Vance E. R. , Carter M. L. , Stewart M. W. A. , Day R. A. , Begg B. D. , Ball C. J.
Published: April 2011

The lower limit of the size of the octahedral A4+ ion in the ATi2O6 brannerite structure is just smaller than that of Ce/Pu. Attempts to expand the A ion size beyond that of Th by (a) substituting a Ba ion plus two U5+ ions for three A ions or (b) substituting one Ba plus one hexavalent ion for two A ions did not succeed. Ge, Sn and Zr substitutions in the Ti site of ThTi2O6 do not exceed 0.2 formula unit in ceramic preparations. These and other coupled substitutions in the B site of ThTi2O6 showed that the average B site size could tolerate deviations of < 1%. Ce4+ is unusually stabilised in air atmospheres at temperatures close to the melting point of 1400°C in the A site of brannerite. Lattice parameter data on different endmember ATi2O6 brannerites are given. The lower and upper size limits for the eightfold A ions in the pyrochlore structure are around 0.100 and 0.117 nm respectively. A BaUTi2O7 stoichiometry did not produce a pyrochlore structure, and when fired in either argon or air yielded a mixture of BaUTiO6, whose structure is still uncertain, plus brannerite and rutile.
Microanalysis of Radiation Damage Across a Zoned Zircon Crystal
Authors: Palenik Chris S. , Ewing Rodney C.
Published: April 2011

An oscillatory-zoned single crystal of zircon (ZrSiO4) from Sri Lanka (560 Ma) provides a unique opportunity to study radiation effects over the dose range of 2.1 - 10.6·1015 á-decay events/mg (0.1 - 0.5 dpa). Each zone has a different radiation dose due to variations in the U (0.09 - 0.53 wt %) and Th (0 - 0.11 wt %) content, but all zones share the same thermal history. The zones span a nearly complete range of microstructures from crystalline to aperiodic. Measurements of birefringence show an inverse-linear correlation with dose over the range of doses observed. Micro-Raman spectroscopy results show that a decrease in peak frequency relative to an undamaged zircon, peak broadening and decreases in peak intensity occur with the accumulation of radiation damage.
Protein/Polymer Hybrid Biomimetic Valves
Authors: Ho Dean , Schmidt Jacob J. , Montemagno Carlo D.
Published: April 2011

Membrane channel and pore proteins represent a versatile class of molecules that offer opportunities to serve as engineered nano-valves. We are inserting OmpF, a voltage-gatable pore protein, into planar membranes for applications in microfluidics and sensing. To emulate and improve upon natural membranes, we have selected triblock copolymers containing UV cross-linkable end groups. We are developing a microfabricated version of a conventional black lipid membrane/copolymer characterization apparatus which will enable us to rapidly analyze composite membrane properties as a function of area and applied electrical bias. We show that only slight deviations of conventional planar lipid membrane formation procedures with triblock copolymers are sufficient for polymer monolayer membrane formation. We report the results of the preliminary tests on polymer membrane formation and stability as well as the construction of the microfabricated device.
Biomimetic Poly(L-Lactic Acid) Scaffolds with Interconnected Macropores, Collagen-Like Nano-Scale Fibers, and Bone-Like Apatite
Authors: Chen Victor J. , Ma Peter X.
Published: April 2011

Highly porous nano-fibrous poly(L-lactic acid) (PLLA) scaffolds were prepared and incubated in a simulated body fluid which resulted in thein situformation of partially carbonated bone-like apatite. The macroporous interconnected architecture was created with a three-dimensional mold of thermally-bonded paraffin microspheres. PLLA solution was cast over the paraffin mold and was thermally induced to phase separate to form nano-scale fibers that mimic the fibrous structures of type I collagen. To potentially improve the osteoconductivity of these scaffolds, they were incubated in a buffered simulated body fluid at 37°C for certain periods of time to allow for apatite formation. It was seen that over time, the apatite particles increased in size. In addition, the growth of apatite particles on the nano-fibrous scaffolds was compared with the growth of particles on similar porous PLLA scaffolds with a solid-walled (not nano-fibrous) morphology. It was seen that the initial number of particles per unit area and the overall increase in mass of the scaffolds were significantly higher in the nano-fibrous scaffolds than in the solid-walled scaffolds. These novel scaffolds have well-defined architectures at three different size scales: (i) interconnected spherical pores ∼250–400 m in diameter; (ii) fibrous collagen-like matrix with fibers 50–500 nm in diameter; and (iii) carbonated bone-like apatite particles at the nanometer to micrometer scales; the scaffolds may serve as superior support for bone tissue regeneration.
Deformable interconnects for conformal integrated circuits
Authors: Périchon Lacour Stéphanie , Huang Zhenyu , Suo Zhigang , Wagner Sigurd
Published: April 2011

The electro-mechanical response of thin gold layers evaporated onto silicone substrates is reported. Gold layers are prepared either thin and flat or thin and wavy on the compliant substrate. The electrical resistance of gold/silicone stripes is measured and analyzed during tensile deformation. For a 100-nm thick gold layer evaporated on a 1-mm thick silicone membrane, we have observed electrical continuity up to ∼ 22 % strain. This maximum strain decreases when the gold layer thickness is raised.
Sub-wetting layer continuum states in the self-organized quantum dot samples
Authors: K. Král , P. Zdeněk , Khás Z. , Čerňanský M.
Published: April 2011

In polar semiconductor samples of the self-organized quantum dots, grown by the Stranski-Krastanow growth method, the lowest-energy extended states of the motion of the electronic excitations, are assumed to be the wetting-layer states. The coupling between these extended states and the electronic states localized in the individual quantum dots, may influence the optical spectra of such samples in the sub-wetting layer region of energy. This effect is studied assuming the Fröhlich's coupling between the electrons and the polar optical phonons. The contribution of this interaction to the appearance of the sub-wetting layer continuum in the optical spectra, and to the level broadening of the localized states, pointed out in some experiments, is estimated.
Investigation of the Shape of InGaAs/GaAs Quantum Dots
Authors: Lehman Susan Y. , Roshko Alexana , Mirin Richard P. , Bonevich John E.
Published: April 2011

Three samples of self-assembled In0.44Ga0.56As quantum dots (QDs) grown on (001) GaAs by molecular beam epitaxy (MBE) were studied using atomic force microscopy (AFM) and high-resolution transmission electron microscopy (TEM) in order to characterize the height, faceting, and densities of the QDs. The cross-sectional TEM images show both pyramidal dots and dots with multiple side facets. Multiple faceting has been observed only in dots more than 8.5 nm in height and allows increased dot volume without a substantial increase in base area. Addition of a GaAs capping layer is found to increase the diameter of the QDs from roughly 40 nm to as much as 200 nm. The areal QD density is found to vary up to 50 % over the central 2 cm x 2 cm section of wafer and by as much as 23 % on a length scale of micrometers.
Dislocation-induced spatial alignment of self-assembled InAs/GaAs quantum dots
Authors: Lee H. S. , Lee J. Y. , Kim T. W. , Park Y. J.
Published: April 2011

We have studied the alignment of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy using misfit dislocations generated due to the strained InxGa1-xAs/GaAs superlattice system. Structural characteristics of aligned SAQDs have been investigated by using atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements. AFM and TEM images showed that vertical stacked InAs QD arrays were aligned along <110> direction on the controlled strained layer. The anisotropic alignments along the [110] and [110] directions are closely related with the anisotropy of strain-relief for both directions, which affect the anisotropic diffusivity of indium adatoms on the strained superlattice layer. The strong alignment appears on the highly strained layer. These results indicate that aligned InAs quantum dots formed by changing the periods of strained superlattice hold promise for potential applications in nanoelectronic devices, such as single electron tunneling devices.
Raman spectroscopy of self-assembled InAs quantum dots in wide-bandgap matrices of AlAs and aluminium oxide
Authors: Tenne D. A. , Milekhin A. G. , Bakarov A. K. , Bajutova O. R. , Haisler V. A. , Toropov A. I. , Schulze S. , Zahn D. R. T.
Published: April 2011

Vibrational properties of self-assembled InAs quantum dots (QD’s) embedded in AlAs and aluminium oxide were studied by Raman spectroscopy. The InAs/AlAs QD structures were grown by molecular beam epitaxy on GaAs (001) substrates. The following main features of the phonon spectra of InAs/AlAs QD nanostructures were observed: 1) asymmetric lines of QD LO phonons affected by strain, confinement and size inhomogeneity of QD’s; 2) confined phonons of InAs wetting layer (WL); 3) two bands of interface phonons in the AlAs frequency region, attributed to modes associated with the planar interface WL/AlAs matrix and the three-dimensional QD/matrix interface; 4) doublets of folded acoustic phonons caused by periodicity in the multilayer QD structures. The influence of growth temperature, varied from 420 to 550°C, on the morphology of QD’s was investigated. QD’s grown at 420°C are found to have the smallest size. Increasing the temperature up to 480°C leads to the formation of larger InAs islands and improved size homogeneity. Further temperature elevation (above 500°C) causes partial re-evaporation of InAs leading to a decrease of QD size and density, and, finally, their complete disappearance. InAs QD’s embedded in aluminium oxide were fabricated by selective oxidation of the AlAs matrix in self-assembled InAs/AlAs QD’s. Micro-Raman spectroscopy data show that depending on oxidation conditions (humidity, temperature) InAs QD’s in an oxide matrix can be even more strained than before oxidation, or become fully relaxed. At the boundaries of oxidized/non-oxidized areas the presence of amorphous and crystalline As clusters is evident.
Photoluminescence within Crystalline-Si/SiO2 Single Quantum Wells.
Authors: Lockwood D. J. , Dharma-wardana M. W. C. , Lu Z. H. , Grozea D. H. , Carrier P. , Lewis Laurent J.
Published: April 2011

Ultrathin single quantum wells of crystalline silicon (c-Si) confined by SiO2 have been prepared by chemical and thermal processing of silicon-on-insulator wafers. The photoluminescence (PL) produced by these nanometer-thick single wells contains two bands: one exhibits a peak energy of ∼1.8 eV, while the second increases rapidly in peak energy with decreasing c-Si layer thickness. Comparison with theories based on self-consistent first-principles calculations shows that the increase in PL peak energy of the second band is consistent with that predicted for the c-Si energy gap of such wells. It also agrees with the measured band gap variation. The ∼1.8 eV PL band is attributed to the recombination of electron-hole pairs confined at the c-Si/SiO2 interface.
A New Synthetic Route to Alkyl Terminated Silicon Nanoparticles.
Authors: Pettigrew Katherine A. , Power Philip P. , Kauzlarich Susan M.
Published: April 2011

This paper describes the preparation of alkyl terminated silicon nanoparticles that are air and moisture stable by the oxidation of magnesium silicide with bromine and then the subsequent termination with an alkyl Grignard reagent. The nanoparticles have been characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy.
New Pairs of Inks and Papers for Photolithography, Microcontact Printing, and Scanning Probe Nanolithography
Authors: Porter Lon A. , Choi Hee Cheul , Schmeltzer J. M. , Ribbe Alexander E. , Buriak Jillian M.
Published: April 2011

Currently, there is considerable interest in producing patterned metallic structures with reduced dimensions for use in technologies such as ultra large scale integration (ULSI) device fabrication, nanoelectromechanical systems (NEMS), and arrayed nanosensors, without sacrificing throughput or cost effectiveness. Research in our laboratory has focused on the preparation of precious metal thin films on semiconductor substrates via electroless deposition. This method provides for the facile interfacing of metal nanoparticles with a group (IV) and III-IV compound semiconductor surfaces. Morphologically complex films composed of gold, platinum, and palladium nanoparticles have been prepared as a result of the immersion of germanium and gallium arsenide substrates into dilute, aqueous solutions of tetrachloraurate (III), tetrachloroplatinate (II), and tetrachloropalladate (II), respectively. Continuous metallic films form spontaneously under ambient conditions, in the absence of a fluoride source or an externally applied current. This facile electroless deposition methodology provides an alternative to complex and expensive vacuum methods of metallization, yet allows for the preparation of both thin and thick nanostructured films with control over surface morphology and deposition rate. Furthermore, precious metal films prepared in this way exhibit excellent adhesion to the underlying semiconductor substrate. The resultant films were characterized utilizing scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and scanning probe microscopy (SPM). In order to apply this novel metallization method toward the development of useful technologies, patterning utilizing photolithography, microcontact printing (μCP), and scanning probe nanolithography (SPN) has been demonstrated.
Sol-gel Template Synthesis and Liquid CO2 Developed TiO2/CdS Composite Nanowire Arrays
Authors: Cheng Bin , Murray Clarence W. , Samulski Edward T.
Published: April 2011

TiO2/CdS composite nanowire (∼ 200 nm diameter and ∼ 50 μm length) arrays were successfully prepared by the sol-gel template method. An anticipated good nanowire arrays was obtained by using liquid or supercritical CO2 to develop the target materials in purification process. The morphology, crystallinity, and composition of the product was characterized by SEM, XRD, and EDX.
2D Assemblies of Silicon Nanocrystallites Prepared by sol-gel Method from Triethoxysilane.
Authors: Rouquette Jerôme , Pauthe Monique , Ramonda Michel , Taliercio Thierry , Gil Bernard , O'Donnell Kevin P.
Published: April 2011

The sol-gel route using triethoxysilane as a precursor has been used to prepare films of Si nanocrystallites. These films were deposited on (001)-oriented silicon substrates either by spin coating deposition of a liquid phase that was further heat-treated under static vacuum (dots embedded in silica gel) or by vapour phase from the thermal decomposition under vacuum of the dried gels (uncapped dots). We address the structural characterisation of these samples and we find that a spontaneous orientation of the crystallites is obtained for heating treatment beyond 800°C if the dots are deposited in the vapour phase. The optical properties of dots embedded in silica gel reveal a strong red-orange photoluminescence due to carrier recombination at the dot surface, which is noticeably contaminated by oxygen and hydrogen.
Preparation and Characterization of Fine barium carbonate Particles
Authors: Lihong Su. , Shenru Qiao. , Jun Xiao. , ying Huang. , Aibo Zhang. , qiuyu Zhang.
Published: April 2011

As a starting material to produce BaTiO3 ceramic, BaCO3 fine powders (<1 μm in diameter) are required. In this paper, how to transform 2–3μm length viraulate BaCO3 microlite into 0.2–0.8μm globose particle is discussed. The factors that affect aggregation and dispersion in fine powder are experienced. Special equipment is introduced to this process. The particle diameter is determined by the SEM micrograph. The whole process is a simple method.
Preparation and Photoactive Characterization of Tube-shaped Al-doped ZnO Ceramics.
Authors: Fujishiro Yoshinobu , Awano M. , Kanzaki S.
Published: April 2011

ABSTRUCT:

Tubular Al-doped ZnO particles were prepared by homogeneous precipitation in the mixed solutions of Al(NO3)2, Zn(NO3)2, sodium dodecyl sulfate (SDS) surfactant and urea. At the molar ratio of Metal ions(Mt) : SDS : urea : H2O is 1 : 2 : 20 : 60, tubular products formed by heating at 80°C for 12 h. Plate like ZnO particles were obtained at Mt : SDS : urea : H2O = 1 : 2 : 10 : 60 or 1 : 1 : 20 : 60. The diameter of typical ZnO tube is ca.100 nm, and the length of tube is about 600nm (aspect ratio = 6). The relative surface area of tubular Al-doped ZnO is ca. 40.2 m2/g. The photo-decomposition rate of NO3- ions using tubular Al-doped ZnO particles was higher than standard TiO2 photo-catalysts (P-25) by irradiation >290nm light in 10mM KNO3-10vol%EtOH solutions at 30°C. The obtained materials showed DC conductive properties as compacted substrate by sintered at 400°C.
Electroless Deposition and Patterning of Morphologically Complex Precious Metal Films on Semiconductor Surfaces
Authors: Porter Lon A. , Choi Hee Cheul , Ribbe Alexander E. , Buriak Jillian M.
Published: April 2011

Precious metals are choice materials for a myriad of applications due their high electrical conductivity, resistance to corrosion, and ligand binding specificity. Indispensable in modern electronics fabrication, precious metals also enjoy widespread use as catalysts, support substrates, and sensor elements. Recent progress towards metallization on diminishing size regimes has imposed increasingly stringent demands upon thin film preparation methodologies. Metallization techniques employed in ultra large scale integration (ULSI) device fabrication, nanoelectromechanical systems (NEMS), and arrayed nanosensors will require unparalleled control of surface morphology, deposition rate, and substrate adhesion without sacrificing throughput or cost effectiveness. Furthermore, precious metal films of this type are essential for fundamental investigations aimed at elucidating the intricate nature of interfacial topics ranging from self-assembled monolayers (SAMs) to heterogeneous catalysis. In contrast to complex and expensive vacuum methods of metallization, research in our laboratory has focused on the preparation of precious metal thin films on semiconductor substrates via electroless deposition. Thin and thick films of gold, platinum, and palladium nanoparticles have been prepared as a result of the immersion of germanium and gallium arsenide substrates into dilute, aqueous solutions of tetrachloraurate (III), tetrachloroplatinate (II), and tetrachloropalladate (II), respectively. This methodology yields nanostructured precious metal films with control over surface morphology and deposition rate. Moreover, metal films prepared in this manner exhibit excellent adhesion to the underlying semiconductor substrate. The resultant films were characterized utilizing scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and scanning probe microscopy (SPM). This method provides for the facile interfacing of metal nanostructures with group (IV) and III-IV compound semiconductor surfaces.
Electrophoretic Deposition of CdSe Nanocrystal Films on Conducting Electrodes
Authors: Islam Mohammad A. , Xia Yuqi , Kraines Benjamin J. , Herman Irving P.
Published: April 2011

A dc electric field is used to attract thermally charged CdSe nanocrystals in solution to rapidly form large-area, micron-thick films of equal thickness on both electrodes. A pair of Au-on-Si or conducting ITO-on-glass electrodes was submerged in the nanoparticle solution and a dc voltage was applied in a dark room. Uniform, robust, very smooth, and apparently identical films formed on both electrodes. Photoluminescence and absorption of the films showed that they are indeed made of dense arrays of individual nanocrystals. The deposition implies there are both positively and negatively thermally charged dots in solution. These high quality dense arrays of the nanoparticles could be useful in several applications.
Anisotropy in the Phonon Dispersion Relations of Graphite and Carbon Nanotubes Measured by Raman Spectroscopy
Authors: Samsonidze Georgii G. , Saito Riichiro , Jorio Ado , Souza Filho Antonio G. , Grüneis Alexander , Pimenta Marcos A. , Dresselhaus Gene , Dresselhaus Mildred S.
Published: April 2011

The possible semiconducting device use of single wall carbon nanotubes (SWNTs) requires a technique for the determination of the exact structure of the nanotubes assembled in the device configuration. Raman spectroscopy has been established as a precise and non-destructive tool for the characterization of graphitic nanostructures. Double resonance theory, which is used to explain the dispersive nature of the Raman bands, has attracted much attention for its potential use for the characterization of the electronic and phonon spectra of these nanostructures. Dispersive features in the Raman spectra of low dimensional graphitic materials, such as carbon nanotubes, can be used to measure directly the anisotropy, or the trigonal warping effect, in the phonon dispersion relations about the hexagonal corner of the Brillouin zone (BZ) of graphite.
TEM and PL Study of FeSi2 Precipitates Formed in Si by Iron Implantation Using a Metal Vapor Vacuum Arc Ion Source
Authors: Gao Y. , Cheung W.Y. , Wong S.P. , Shao G. , Homewood K.P.
Published: April 2011

In this work, FeSi2 precipitates were formed in Si by iron implantation using a metal vapor vacuum arc ion source. Transmission electron microscopy (TEM) was used to determine the crystal and defect structures of the implanted samples. It was found that the implantation temperature played an important role on the shape and phase formation of the FeSi2 precipitates, as well as the formation and distribution of the dislocation loops. When implantation was performed at an elevated temperature of about 380°C, there were a lot of dislocation loops formed and only β-FeSi2 precipitates were observed. When implanted at a low temperature of about -100°C followed by a dual step annealing process, the samples were found to be free of dislocation loops, and γ-FeSi2 and β-FeSi2 precipitates coexisting and coherent with the silicon substrate were observed. Photoluminescence (PL) spectra of different line shapes from these implanted samples were observed. By combining the PL and TEM results, the origins of the PL peaks in different samples could be distinguished and identified to be from β-FeSi2 precipitates or from crystal defects in the samples.
Electroluminescent devices based on Er-doped Si nanoclusters
Authors: Priolo F. , Iacona F. , Pacifici D. , Irrera A. , Miritello M. , Franzò G. , Sanfilippo D. , Di G. , Fallica P.G.
Published: April 2011

The electroluminescence (EL) properties of Er-doped Si nanoclusters (nc) embedded in metal-oxide-semiconductor devices are investigated. It is shown that, due to the presence of Si nc dispersed in the SiO2matrix, an efficient carrier injection occurs and Er is excited producing an intense 1.54 μm room temperature luminescence. The EL properties as a function of the current density, temperature and time have been studied in details, elucidating the radiative and non-radiative de-excitation properties of the system. We have also estimated the excitation cross section for Er under electrical pumping finding a value of −1×10 cm. This value is two orders of magnitude higher than the effective excitation cross section of Er ions through Si nc under optical pumping, and quantum efficiencies of ∼1% are obtained at room temperature in these devices. These data will be presented and the impact on future applications discussed.
Resist Requirements and Limitations for Nanoscale Electron-Beam Patterning
Authors: Alexander Liddle J. , Gallatin Gregg M. , Ocola Leonidas E.
Published: April 2011

Electron beam lithography still represents the most effective way to pattern materials at the nanoscale, especially in the case of structures, which are not indefinitely repeating a simple motif. The success of e-beam lithography depends on the availability of suitable resists. There is a substantial variety of resist materials, from PMMA to calixarenes, to choose from to achieve high resolution in electron-beam lithography. However, these materials suffer from the limitation of poor sensitivity and poor contrast.

In both direct-write and projection e-beam systems the maximum beam current for a given resolution is limited by space-charge effects. In order to make the most efficient use of the available current, the resist must be as sensitive as possible. This leads, naturally, to the use of chemically amplified (CA) systems. Unfortunately, in the quest for ever smaller feature sizes and higher throughputs, even chemically amplified materials are limited: ultimately, sensitivity and resolution are not independent. Current resists already operate in the regime of < 1 electron/nm2. In this situation detailed models are the only way to understand material performance and limits.

Resist requirements, including sensitivity, etch selectivity, environmental stability, outgassing, and line-edge roughness as they pertain to, high-voltage (100 kV) direct write and projection electron-beam exposure systems are described. Experimental results obtained on CA resists in the SCALPEL® exposure system are presented and the fundamental sensitivity limits of CA and conventional materials in terms of shot-noise and resolution limits in terms of electron-beam solid interactions are discussed.
New Processing Techniques for the Creation of Micro-Opto-Mechanical Machines and Photonic Devices Embedded in Glass
Authors: Abraham Meg , Fuqua Peter , Taylor David P. , Hansen William W. , Helvajian Henry , Presser Nathan , Livingston Frank , Lumondiere Stephen La
Published: April 2011

The use of lasers to create intricate three-dimensional and buried structures [1] in photostructural glass has been well demonstrated at The Aerospace Corporation over the past four years. In these instances the glass used (Foturan™, made by the Schott Group) forms a silver nucleation sites on exposure to intense UV laser light via a two-photon process. Subsequent annealing causes a localized crystal growth to form a meta-silicate phase which can be etched in dilute hydrofluoric acid at rates of 20 to 50 times that of the unprocessed glass. We are now in the process of experimenting with another formulation of photosensitive glass, also pioneered by Corning Glass Works, that behaves differently during the bake process. In the second case, a photoexposure and bake process creates a silver-halide crystal and forms an adjacent void in the glass. A second photoexposure and bake allows for the migration of more silver into the void creating patterned formations of silver nano-wires [2]. Recent experiments with this type of glass have shown that the manipulation of the size and density of the embedded nano-wires as well as the overall pattern of the clusters can be controlled using direct-write exposure to laser processing.
Optical Nanolithography Using Evanescent Fields
Authors: Blaikie Richard J. , McNab Sharee J. , Alkaisi Maan M.
Published: April 2011

In the optical near field region the well understood resolution limits for projection optical lithography can be overcome. This offers the possibility of performing optical nanolithography without the need to use expensive, deep ultraviolet light sources. For exposures that utilise evanescent fields close to metallic amplitude masks sub-diffraction-limited resolution has been achieved experimentally, and the theoretical resolution limits have been explored using vector electromagnetic near field simulations. Resolution down to 20nm using exposure wavelengths greater than 400nm is predicted. It is also found that the exposure wavelength is of secondary importance in this regime, and that the properties of the mask are much more significant. Scaling to smaller feature sizes requires better resolution and control during mask manufacture, rather than the conventional (and costly) approach of driving the exposure wavelength deeper and deeper into the ultraviolet. Near field interference effects have also been explored, and the characteristics of spatial frequency doubling using Evanescent Interferometric Lithography (EIL) have been determined by simulation. Sub-diffraction-limited resolution can be achieved with increased exposure intensity compared with conventional interferometric lithography. The tradeoff is against the depth of field in the resultant interference pattern. Finally, the use of negative refraction and surface plasmons have been investigated to improve further the resolution in the evanescent near field, and to produce novel, three dimensional near field patterns.
Wet-Process Molecular Planting in A Specific Site on Silicon with Si-C Covalent Bonds
Authors: Tada Hirokazu , Ara Masato , Tanaka Shoji
Published: April 2011

Alkyl monolayers anchored covalently on silicon were prepared through the reaction between 1-alkenes and hydrogen-terminated silicon (111) surfaces. The 2D-patterning of the surface was done by local oxidation with an atomic force microscope (AFM) and 3D-molecular assemblies were fabricated by immobilization of molecules in a specific site of the patterned surface. The surfaces were anodized with a contact-mode AFM by applying a positive bias voltage to the surface with respect to the platinum-coated cantilever under ambient conditions, which resulted in nanometer-scale oxidation of surfaces. The anodized areas were etched and terminated with hydrogen atoms by NH4F solution, in which we could immobilize various molecules having C=C bonds. We put arylamine molecules to which organic dyes such as fluoroscein were anchored. The intensity of luminescence varied depending on dopant concentration of substrates. Luminescence was very weak on highly-doped silicon possibly due to effective energy transfer from dyes to substrates. The method demonstrated is one of the promising ways to fabricate 3D-assemblies of molecular-scale electronic devices with a stable interface on silicon.
FIB-assisted Pt Deposition for Carbon Nanotube Integration and 3-D Nanoengineering
Authors: Dovidenko K. , Rullan J. , Moore R. , Dunn K. A. , Geer R. E. , Heuchling F.
Published: April 2011

In this study, the Focused Ion Beam (FIB) instrument has been used for carbon nanotubes integration and nanoegineering studies. Results of thorough investigation (electrical, structural and chemical) of ultra-thin Pt contact lines and pads fabricated by the FIB, along with evaluation of nanomodification of the carbon nanotubes under the Ga+ ion beam and during Pt deposition are presented. The initial stages of FIB-assisted Pt deposition on multi-wall nanotubes are studied by transmission electron microscopy (TEM). The FIB parameters are optimized to provide non-destructive imaging and controllable Pt deposition with minimal damage on the nanotubes. We have demonstrated effective use of FIB-fabricated Pt pads as means of attaching the nanotubes to the substrate for atomic force and ultrasonic force microscopy studies.
Interband Transitions in GaInNAs/GaAs Single Quantum Wells
Authors: Manasreh M. O. , Friedman D. J. , Ma W. Q. , Workman C. L. , George C. E. , Salamo G. J.
Published: April 2011

Photoluminescence (PL) spectra of interband transitions in GaInNAs/GaAs single quantum wells grown by metalorganic chemical vapor deposition technique on semi-insulating GaAs substrates were measured at 77 K for several samples grown with different In composition and dimethylhydrazine (DMH)/III ratios. The results show that the PL intensity increases as the In mole fraction is increased from 0 to 25%, but the PL intensity is degraded for samples with an In mole fraction of 30% or higher. The peak position energies of the PL spectra were investigated as a function of the DMH/III ratio. Thermal annealing effect induced a blue-shift in the PL spectra peak position energy in samples grown with high DMH/III ratio.
Properties of GaAsSb QW Heterostructures Having Various Barrier Materials Grown by Metalorganic Chemical Vapor Deposition
Authors: Noh Min Soo , Ryou Jae Hyun , Chang Ying-Lan , Weissman Robert , Dupuis Russell D.
Published: April 2011

Pseudomorphic GaAs1-xSbx quantum-well (QW) structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD) have been studied with various barrier materials to investigate the energy band lineup. To determine the band lineup of these structures, we have performed low-temperature current-dependent cathodoluminescence (LT-CL) measurements at 10K. For the structure with GaAs barriers, the data show strong evidence of Type-II staggered band lineup, which means that holes are confined in the valence band heavy-hole level of the GaAs1-xSbx quantum well and electrons are confined in the conduction band of the GaAs barrier.

For the InGaP barriers, however, we observed only one peak that is related to transitions of a Type-I band lineup. From the LT-CL results, we find that the valence-band discontinuity ratio (Qv) between the GaAs0.73Sb0.27 double quantum wells (DQWs) and the GaAs barriers is ∼1.20. Furthermore, to improve the carrier confinement, we propose that InGaP barriers provide a Type-I band lineup with the GaAsSb QW.
Electrical and Optical Properties of Zinc Oxide Thin Films and Heavily Aluminum-doped Zinc Oxide Thin Films Prepared by Molecular Beam Epitaxy
Authors: Ohgaki Takeshi , Kawamura Yuji , Ohashi Naoki , Kakemoto Hirofumi , Wada Satoshi , Adachi Yutaka , Haneda Hajime , Tsurumi Takaaki
Published: April 2011

ZnO (ZO) and Aluminum (Al) doped ZnO (AZO) films were grown on sapphire substrate via oxygen radical assisted molecular beam epitaxy (MBE) technique. The results of XRD measurement and temperature dependent Hall measurement confirmed that the AZO films were typically highly degenerate semiconductor with good crystallinity. The resistivity of these films were closed to the theoretical lower limit. The optical properties of these films were investigated by photoluminescence (PL) spectra and absorption spectra. Strong band-edge emission was observed in the AZO films with good crystallinity in spite of high carrier concentration more than 1020 cm-3. A sift of absorption edge to higher energy side and a gradual increase of the absorption was observed for the AZO film.
A Single Source Approach To Deposition Of Nickel and Palladium Sulfide Thin Films By LP-MOCVD
Authors: Waters J. , O'Brien P. , Park J.H.
Published: April 2011

Compounds of the type M(S2CNRR’)2, M = Ni(II), Pd(II), RR' = Et2, MeEt and MenBu, have been synthesized and used as single-source precursors for the fabrication of NiS and PdS thin films via low-pressure (LP) metal-organic chemical vapour deposition (MOCVD). The phase of nickel sulfide films deposited on glass substrates was found to be NiS1.03 or a mixture of NiS1.03 and NiS, whilst palladium sulfide films were only tetragonal PdS. The films have been characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX).
Passivation of Defects in ZnO by Hydrogen Plasma Irradiation
Authors: Ohashi Naoki , Ishigaki Takamasa , Sekiguchi Takashi , Sakaguchi Isao , Haneda Hajime
Published: April 2011

Hydrogen doping effects on luminescence properties of bulk ZnO samples were examined by using a pulse-modulated plasma irradiation technique. Three kinds of ZnO samples, including both single- and poly-crystals, were employed as specimens. Secondary-ion-mass-spectroscopy analysis revealed that the surface layer to 100 nm was doped with hydrogen after the irradiation and its concentration was in the order of 1017 cm-3. The efficiency of band edge emission was increased by the hydrogenation. However, the degree of the improvements depended on impurity and defect concentration in the original samples.
Design and Fabrication of a VCSEL With Graded Bragg Mirror Interfaces for Operation at 850nm
Authors: Zhang Chichang , Christou Aris
Published: April 2011

Based on the AlxGa1-xAs/GaAs system and with graded Distributed Bragg mirrors (DBRs), a VCSEL for operation at 850–860nm is reported. The graded transition bands inside the DBRs were designed in order to achieve the tradeoff between the number of DBR layers and the low threshold current of the laser. The structure optimized had 39 pairs in the n-DBR stack and a low threshold current of 1.6mA was achieved. The device was fabricated with MBE growth, oxide confinement and RIE for MESA definition. The experimental results and physical characterization of the device are also reported to fully understand the VCSEL performance. The threshold current and other parameters predicted by the simulation are in good agreement with experimental results.
High Gain, Low Threshold Current GaInAsP Based Vcsels for Operation at 1.24UM
Authors: Tan Zhuopeng , Li Yixin , Christou Aris
Published: April 2011

An electrically pumped 1.24um GaxIn1-xAsyP1-y Vertical Cavity Surface Emitting Laser (VCSEL) has been designed and simulated. Threshold gain of 153cm-1 and threshold current of 1.00mA was obtained. The external efficiency predicted is 0.31. Also the optimized design of VCSEL structure is presented in this article. GaInAsP and AlInAs constitute the Distributed Bragg Reflectors (DBRs) multilayer stack. Reflectivity of the top DBRs is 0.97 and reflectivity of the bottom DBRs is 0.9978 and is shown to provide a good resonant cavity and sufficient lasing intensity. Compared with other reported structures, the present VCSEL has a lower threshold current and higher threshold gain.
Trace Water Detection in Phosphine By Cavity Ring-down Spectroscopy
Authors: Lehman Susan Y. , Bertness Kris A. , Hodges Joseph T.
Published: April 2011

We are using cavity ring-down spectroscopy (CRDS) to measure concentrations of water in nitrogen and, for the first time to our knowledge, in phosphine. Water vapor concentrations have been measured in purified and unpurified phosphine, indicating a water mole fraction of (22.0 ± 1.0) x 10-6 in unpurified phosphine. After purification with an in-line, chemically-reactive purifier, the mole fraction of water in phosphine was less than 0.1 × 10-6. Mole fractions as high as (730 ± 60) × 10-6 have been measured in unpurified phosphine, suggesting that the H2O vapor concentration increases substantially with time as the gas is stored in a cylinder. The materials properties of AlInP grown by molecular beam epitaxy (MBE) with CRDS-characterized PH3 were found to be relatively insensitive to water contamination at the 22 mol/mol level.
Stability of Non-Hydrogenated and Hydrogenated P-Channel Polycrystalline Silicon Thin-Film Transistors
Authors: Hastas N. A. , Dimitriadis C. A. , Kamarinos G.
Published: April 2011

The effects of high gate voltage Vg stress on the stability of non-hydrogenated and hydrogenated short p-channel polysilicon thin-film transistors (TFTs) are investigated for operation in the saturation region. The degradation mechanisms were identified from the evolution with stress time of the static device parameters. In non-hydrogenated TFTs, transconductance overshoot and a turnover behavior in the threshold voltage were observed. The results indicate that hot-electron trapping near the drain dominates in the initial stages of stress and channel holes are injected into the gate oxide followed by interface states generation as the stress proceeds further. In hydrogenated TFTs, first an effective shortening of the channel length is observed due to trapping of hot-electrons. As the stress proceeds further, donor-type interface states are generated and the electric field near the drain increases due to built-up of positive charge resulted from trapping of hot-holes in these states.
Graded-Band-Gap Semiconductors: the Possibilities for Improvement of p-n Junction Performance
Authors: Sokolovskii Bogdan , Yasnytskyi Roman
Published: April 2011

The paper theoretically analyzes properties of graded-band-gap (GBG) p-n structures in which band gap linearly enlarges with increasing the distance from the junction metallurgical edge. It is shown that by means of band-gap grading one can significantly reduce the diffusion reverse current caused by carrier thermal generation in the structure base regions and Ohmic contacts. The numerical estimations have been made for the case of p-n junction on the basis of CdHgTe solid solution.
MOCVD Growth and Characterization of GaInNAs/GaAs/InGaAs/GaAs Quantum Well Structures
Authors: El-Emawy Abdel-Rahman A. , Cao Hongjun , Nuntawong Noppadon , Liu Chiyu , Osiński Marek
Published: April 2011

Effects of MOCVD growth parameters on structural and optical properties of double-quantum-well (DQW) structures containing uncoupled GaInNAs/GaAs and InGaAs/GaAs quantum wells have been investigated. By varying growth temperature, growth rate, V/III ratio, and DMHy flow rates, we have achieved a longer-wavelength emission from a GaInNAs well than from an InGaAs well grown in the same structure. GaInNAs/GaAs multiple-quantum-well structures grown under optimum conditions emitted at 1.25 μm.
Nonstoichiometry of Epitaxial FeTiO3+δFilms
Authors: Fujii Tatsuo , Sadai Makoto , Kayano Masakazu , Nakanishi Makoto , Takada Jun
Published: April 2011

Epitaxial thin films of (001)-oriented FeTiO3+δwere prepared on α-Al2O3(001) single crystalline substrates by helicon plasma sputtering technique. The FeTiO3+δfilms had large oxygen nonstoichiometry, which seriously depended on both substrate temperature and oxygen pressure during the sputtering deposition. The valence states of Fe ions in FeTiO3+δchanged monotonically from Fe2+to Fe3+with decreasing the substrate temperature from 900 to 400°C or with increasing the oxygen pressure from 0.9 to 1.8×10-6Pa. The change of Fe valence states from Fe2+to Fe3+induced the magnetic phase transition only for the films prepared at 900°C. The films containing Fe2+were paramagnetic while those with Fe3+were antiferromagnetic at room temperature. The oxygen nonstoichiometry of the FeTiO3+δfilms was probably produced by cation vacancies and disarrangement of Fe3+and Ti4+ions, which randomly occupied both interstitial and substitutional sites of the FeTiO3related structure.
Structural Quality and Electrical Behavior of Epitaxial High-k Y2O3 / Si(001)
Authors: Vellianitis G. , Apostolopoulos G. , Dimoulas A. , Argyropoulos K. , Mereu B. , Scholz R. , Alexe M. , Hooker J. C.
Published: April 2011

Y2O3 thin films were grown directly on Si (001) by MBE and annealed in-situ under UHV at various annealing temperatures. The samples were investigated in-situ by RHEED and ex-situ by HRTEM. A 7 to 15 Å thick non-uniform interfacial amorphous layer is observed in the as-grown sample. After annealing at 490°C under UHV for 30 minutes the amorphous layer is reduced and a sharp Y2O3/Si interface is obtained. At higher annealing temperatures, YSi2 islands start to form at the Y2O3/Si interface. I-V measurements performed on generic MIS structures show that the annealed samples exhibit higher leakage current density than the as-grown sample, due to reduction of the wide band gap interfacial layer. Leakage current densities in annealed samples remain below 1A/cm2, which is acceptable for future high-κ transistor fabrication.
Co-doping Deposition of p-type ZnO Thin Films using KrF Excimer Laser Ablation
Authors: Ebihara Kenji , Ohshima Tamiko , Ikegami Tomoaki , Asumussen Jes , Thareja Raj K.
Published: April 2011

We report on the attempt to fabricate p-type ZnO thin films using various doping techniques based on the pulsed laser deposition (PLD). As an accepter, we have doped the N atom by using high purity nitric monoxide (NO) ambient gas. NO is dissociated into N and O at an energy of 6.5 eV which is lower than at N2 (9.76 eV). Moreover the dissociation reaction of NO is simpler than other nitrogenous gases such as N2O, NO2, and NH3. One of our doping techniques is co-doping of Ga and N atom by ablating ZnO:Ga target in NO gas, and another is the ablation of the metal Zn target in NO gas. Both of Ga and N co-doped ZnO films and N doped ZnO films have c-axis orientation as well as undoped ZnO films. The surfaces of these doped films are rough while the undoped ZnO thin film is very smooth and have hexagonally shaped grains. We found it possible to fabricate the p-type ZnO film by ablating the metal Zn target in NO gas.
Atomic Ordering in Self-assembled Epitaxial II-VI and IV-VI Compound Semiconductor Quantum Dot Systems
Authors: Möck Peter , Pierz Klaus , Topuria Teya , Browning Nigel D. , Wu Huizhen , McCann Patrick J.
Published: April 2011

Transmission electron microcopy (TEM) in both the parallel illumination and scanning probe mode revealed atomically ordered entities within a 5 to 250 nm range in a IV-VI and a II-VI compound semiconductor quantum dot (QD) system. While the II-VI system was a nominal [001] CdSe/(Mn0.1Zn0.9)Se multilayer structure with the QDs embedded, the IV-VI system nominally consisted of [111] PbSe islands. The comparison of photoluminescence (PL) spectra from the CdSe/(Mn0.1Zn0.9)Se structure with those of a reference structure, that was grown to the same nominal specification under otherwise identical conditions except that no Mn was incorporated into the cladding layers, revealed for the former sample two peaks at approximately 2 and 2.1 eV. We tentatively attribute these two PL peaks to two groups of atomically ordered entities.
Thermal characterization and modeling of intermediate phase formation in 20/80 nm and 10/20 nm Cu/Mg multilayers
Authors: González-Silveira M. , Rodríguez-Viejo J. , Clavaguera-Mora M.T.
Published: April 2011

The kinetics of intermediate phase formation in the Cu/Mg multilayer system is analyzed using Differential Scanning Calorimetry. Three main exothermic processes are found during the continuous DSC treatments. The first two, significantly overlapped, are related to the same process, nucleation and growth of the Mg2Cu along the interface. We interpret differences between the Mg/Cu and Cu/Mg interfaces are at the origin of this unexpected behavior. The third exothermic reaction is due to the growth of the Mg2Cu phase perpendicular to the original interface. A kinetic model is developed which yields calorimetric traces in good agreement with the experimental data.
Rate Equation Theory for Island Sizes and Capture Zone Areas in Submonolayer Deposition: Realistic Treatment of Spatial Aspects of Nucleation
Authors: Evans J.W. , Li Maozhi , Bartelt M.C.
Published: April 2011

Extensive information on the distribution of islands formed during submonolayer deposition is provided by the joint probability distribution (JPD) for island sizes, s, and capture zone areas, A. A key ingredient determining the form of the JPD is the impact of each nucleation event on existing capture zone areas. Combining a realistic characterization of such spatial aspects of nucleation with a factorization ansatz for the JPD, we provide a concise rate equation formulation for the variation with island size of both the capture zone area and the island density.
First-principles calculation of the effect of strain on the diffusion of Ge adatoms on Si and Ge (001) surfaces
Authors: van de Walle A. , Asta M. , Voorhees P. W.
Published: April 2011

First-principles calculations are used to calculate the strain dependencies of the binding and diffusion-activation energies for Ge adatoms on both Si(001) and Ge(001) c(4×2) reconstructed surfaces. Our calculations reveal that over the range of strains typically sampled during quantum dot self-assembly (0 to 1% compressive strain) the binding and activation energies on a strained Ge(001) surface increase and decrease, respectively, by 0.21 eV and 0.12 eV. For a growth temperature of 600 °C, these strain-dependencies give rise to a 16-fold increase in adatom density and a 5-fold decrease in adatom diffusivity in the region of compressive strain surrounding a Ge island with a characteristic size of 10 nm lying on top of a Si substrate covered by a Ge wetting layer.