bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of the Post-Closure Safety Case for the Low Level Waste Disposal Site at Drigg, United Kingdom
Authors: Watts Len
Published: April 2011

This paper provides an overview of the development of the post-closure safety case (PCSC) for the solid low level radioactive waste (LLW) disposal site at Drigg. The paper outlines the background to the site, the implementation of a systematic approach to understanding the site and undertaking a post-closure radiological safety assessment (PCRSA), communication activities, key factors in the PCSC and issues to be investigated further in the forward programme.

The Drigg site is the UK's principal near-surface facility for disposal of LLW. Disposals commenced in 1959 to trenches whereas current practice involves disposal to concrete vaults. Disposals are carried out under an authorisation from the UK Environment Agency. Periodically the Environment Agency reviews the authorisation to ensure consistency with current regulatory requirements. British Nuclear Fuels plc (BNFL) will produce an updated PCSC in 2002; in preparation for this, BNFL published in March 2000 a status report on the development of the PCSC.

BNFL and the Environment Agency conduct an information exchange process on the development of the PCSC. This process has led to notable improvements, as well as affording a mechanism for providing clarifications and building confidence in the PCSC. BNFL undertakes other communication activities including scientific publication, conference presentation, participation in international programmes (such as those of the IAEA and NEA) and liaison with local communities. Peer review of the PCSC is also being carried out.

Central to the safety case is a systematic PCRSA, which promotes transparency and traceability and demonstrates a rigorous treatment of relevant uncertainties. The approach aligns with international best practice for near-surface disposal facilities and includes the assessment of features, events and processes and the use of tools such as conceptual model uncertainty forms. This formalisation helps to identify and understand the key factors for the PCSC. Additional qualitative or simple quantitative information is used to augment the PCRSA so as to provide a wider context to inform decision-making.
Magnetic Recording at High Densities on Protein-Derived CoPt Nanoparticles
Authors: Hoinville Jay , Bewick Angus , Gleeson David , Jones Richard , Kasyutich Oksana , Mayes Eric , Nartowski Artur , Warne Barnaby , Wiggins Jason , Wong Kim
Published: April 2011

This paper reports on the progress in developing self organized nanoparticulate arrays for magnetic recording at densities beyond 30 Gbit/cm2 (200 Gbit/in2), and in particular describes the beneficial use of biological templates in developing such arrays. Chemically synthesized, high magnetocrystalline anisotropy magnetic nanoparticles have demonstrated extremely narrow size distributions that are critical in reducing media noise. Due to their monodispersity, they also exhibit emergent self-patterning that could potentially support bit-per-particle densities up to 2–8 Tbit/cm2 (10–50 Tbit/in2).

High anisotropy L10 CoPt precursor grains are prepared within apoferritin from aqueous reactants, with synthesis conditions controlling grain size, structure and composition. Smooth films on glass disk substrates are produced by either spin- or dip-coating from aqueous dispersions of the precursor material. Films are typically annealed at 590 °C for 60 minutes with a 19 kPa (190 mBar) partial pressure of H2 to form the L10 phase.

We report on recently produced films that have demonstrated moderate-density recording using a contact drag tester with commercial, 0.35 μm-wide magnetoresistive (MR) heads. The highest areal density currently achieved for these nanoparticulate films is 0.93 Gbit/cm2 (6.0 Gbit/in2).
Nano-fibrous scaffolding architecture enhances protein adsorption and cell attachment
Authors: Woo Kyung Mi , Chen Victor J. , Ma Peter X.
Published: April 2011

Tissue engineering aims at resolving problems such as donor shortage and immune rejection faced in transplantation. Scaffolds (artificial extracellular matrices) play critical roles in tissue engineering. Recently, we developed nano-fibrous poly(L-lactic acid) (PLLA) scaffolds under the hypothesis that synthetic nano-fibrous scaffolding, mimicking the structure of natural collagen fibers, could create a more favorable microenvironment for cells. This is the first report that the nano-fibrous architecture built in three-dimensional scaffolds improved the features of protein adsorption, which mediates cell interactions with scaffolds. Scaffolds with nano-fibrous pore walls adsorbed 4 times more serum proteins than scaffolds with solid pore walls. More interestingly, the nano-fibrous architecture selectively enhanced protein adsorption including fibronectin and vitronectin, even though both scaffolds were made from the same PLLA material. Furthermore, nano-fibrous scaffolds also allowed more than 1.7 times of osteoblastic cell attachment than scaffolds with “solid” pore walls. These results demonstrate that the biomimetic nano-fibrous architecture serves as superior scaffolding for tissue engineering.
Washing of Electrotextiles
Authors: Slade Jeremiah , Agpaoa-Kraus Marty , Bowman Jeremy , Riecker Andrew , Tiano Tom , Carey Charles , Wilson Patricia
Published: April 2011

The ability to integrate electrical functionality into textile garments is becoming increasingly desired for consumer devices, military applications and for companies with large distributed workforces. This technology has the potential to facilitate the transfer of information and increase efficiency in many arenas. One of the major hurdles that has hindered the wedding of electronics and clothing has been the need to wash the resulting garment. This paper describes a study of the long term effects of washing and dry-cleaning electrotextile elements.
Improving Electrotextile Wearability Using Stiffness Testing Methods
Authors: Slade Jeremiah , Wilson Patricia , Farrell Brian , Teverovsky Justyna , Thomson Douglas , Bowman Jeremy , Agpaoa-Kraus Marty , Horowitz Wendy , Tierney Edward , Offray C. M. , Winterhalter Carole
Published: April 2011

The ability to integrate electrical functionality into textile garments is becoming increasingly desired both on the battlefield and in the work environment. In order to accomplish this, the issue of compatibility of mechanical properties between dissimilar materials needs to be addressed. Textiles are typically selected for comfort while electrical materials are chosen for superior electrical properties with secondary consideration given to properties such as flexibility. As a result many attempts to integrate electrical functionality into textiles result in stiff, unwieldy garments that have difficulty gaining user acceptance.

Part of the electrotextile work done at Foster-Miller has focused on the integration of these dissimilar materials in a manner that does not degrade the wearability of the garment. Our work has included the development of textile cables that carry power and data using both electrical and optical media. In order to assess the wearability of these cables a method was needed of testing their stiffness. Several methods of measuring textile stiffness existed but did not address the many issues and material characteristics unique to conductive textiles.
Low-Voltage Organic Thin Film Transistors on Flexible Plastic Substrates with Anodized Ta2O5 Gate Insulators
Authors: Inoue Youji , Fujisaki Yoshihide , Iino Yoshiki , Kikuchi Hiroshi , Tokito Shizuo , Sato Fumio
Published: April 2011

Organic thin film transistors (OTFTs) that operate at low voltage were fabricated using a tantalum oxide (Ta2O5) gate insulator on plastic substrates. The Ta2O5 insulator was prepared by anodizing a Ta gate electrode. The high dielectric constant of the Ta2O5 enabled the OTFTs to operate at a lower voltage than those of previous devices. The OTFTs exhibited a high field-effect mobility of 0.35 - 0.51 cm2/Vs, and a current on/off ratio of 105-106 at gate voltages of less than 5 V. The threshold voltage of -1.1 V and the subthreshold slope of 0.2 V/decade were the best among those reported to date. We also demonstrated operation of a phosphorescent organic light-emitting device (OLED) with the OTFT operating at a low voltage.
Organic Transistor Sensors and Memory Elements Fabricated Via Solution Deposition
Authors: Katz H. E. , Someya T. , Gelperin A. , Mushrush M. , Facchetti A. , Marks T. J.
Published: April 2011

Thiophene-phenylene oligomer semiconductors (structures below) have many favorable attributes for electronics on flexible and rounded substrates. They are synthesized in 2–3 steps from readily available starting materials and are chemically stable. Their mobilities are typically above 0.01 cm2/Vs and their threshold voltages can be tuned by altering the thiophene-phenylene ratio. Deposition from solution is facile, and cast films with usable mobilities are repeatedly obtained on a variety of surfaces. Higher-order function such as nonvolatile memory and chemical sensitivity have been demonstrated.
Chemically Functional Semiconductor Nanocrystals: Electrochemistry and Self-Assembly on Surfaces
Authors: Hutchins Benjamin M. , Latham Andrew H. , Williams Mary Elizabeth
Published: April 2011

Semiconductor nanocrystals (i.e., Quantum Dots, QDs) exhibit size-dependent emission properties and have synthetically adjustable ligand shells, making them interesting materials for applications ranging from luminescent displays to biomolecular tags. In this paper, the electrochemical properties of two types of nanocrystal are studied with an emphasis on the effect of core/shell vs core structures. The band gap energy of CdSe particles, measured using optical spectroscopy, was shown to increase slightly with the application of a ZnSe shell, as expected based on the increased energy required to transfer an electron through the shell material. The electrochemically determined band gaps are overestimated in the case of CdSe/ZnSe core/shell nanoparticles, reflecting the band gap of the ZnSe shell. Finally, QDs were self-assembled onto gold surfaces by electrostatic and covalent attachment, and their presence confirmed by fluorescence spectroscopy. The high intensity of emitted light shows that the QDs can be self-assembly onto metallic surfaces, without energy transfer quenching of the luminescence.
Size and shape dependent level structure in CdSe quantum rods
Authors: Rothenberg Eli , Mokari Taleb , Banin Uri , Katz David , Wizansky Tommer , Millo Oded
Published: April 2011

Optical spectroscopy and Scanning Tunneling Microscopy are used to study the size and shape dependence of the electronic states in CdSe quantum rods. The quantum rods were grown using colloidal chemistry synthesis methods, with good control over size and size distribution. Samples having average rod dimensions ranging from 10 to 60 nm in length and 3.5 to 7 nm in diameter, with aspect ratios varying between 3 to 12, were investigated. Both optical (at 10 K) and tunneling (at 4.2 K, on single rods) spectra show that the level structure depends primarily on the rod diameter and not on length. With increasing diameter, the band gap and the excited state level spacings shifted to the red. The level structure is assigned using a multi-band effective-mass model, showing relatively good agreement with experiment. We shall also discuss the effect of single electron charging on the tunneling spectra, possibly reflecting the quantum rod level degeneracy.
Transport Properties of Superlattice Nanowires and Their Potential for Thermoelectric Applications
Authors: Lin Yu-Ming , Dresselhaus Mildred S.
Published: April 2011

A theoretical model for the electronic structure and transport properties of superlattice (SL) nanowires is presented, based on the electronic tunneling between quantum dots. Due to the periodic potential perturbation, SL nanowires exhibit unusual features in the electronic density of states that are absent in homogeneous nanowires. Transport property calculations of PbSe/PbS SL nanowires are presented, showing improved thermoelectric performance compared to homogeneous nanowires because of a lower lattice thermal conductivity and an enhanced Seebeck coefficient, indicating that SL nanowires are promising systems for thermoelectric applications.
Carrier Tunneling, Current Instabilities, and Negative Differential Conductivity in Nanocrystalline Silicon – Silicon Dioxide Superlattices
Authors: Kamenev B. V. , Grom G. F. , Lockwood D. J. , McCaffrey J. P. , Laikhtman B. , Tsybeskov L.
Published: April 2011

Low temperature measurements of differential conductivity in nanocrystalline Si – amorphous SiO2 superlattices surprisingly reveal a clear double-peak structure associated with tunneling via levels of light and heavy holes. Numerical simulations show not only detailed agreement with the experiment but also predict that the studied system has no stable solutions for carrier concentration higher than 1017 cm−3. According to this prediction, partial screening of the external electric field generates current instabilities and oscillations, and that is experimentally observed. The developed model also suggests that a more uniform electric field and stabilization of carrier transport at a higher level of carrier density can be achieved under transient carrier injection.
SiC-Like Phase and Room-Temperature Photoluminescence of Low-K SiOCH Films
Authors: Ligatchev V. , Wong Rusli T.K.S. , Liu B. , Ostrikov K.
Published: April 2011

Carbon-doped hydrogenated silicon oxide (SiOCH) low-k films have been prepared using 13.56 MHz discharge in trimethylsilane (3MS) - oxygen gas mixtures at 3, 4, and 5 Torr sustained with RF power densities 1.3 − 2.6 W/cm2. The atomic structure of the SiOCH films appears to be a mixture the amorphous SiO2-like and the partially polycrys-talline SiC-like phases. Results of the infra-red spectroscopy reflect the increment in the volume fraction of the SiC-like phase from 0.22 − 0.28 to 0.36 – 0.39 as the RF power increment.

Steady-state near-UV laser-excited (364 nm wavelength, 40±2 mW) photoluminescence (PL) has been studied at room temperatures in the visible (1.8 eV – 3.1 eV) subrange of photon spectrum. Two main bands of the PL signal (at the photon energies of 2.5 – 2.6 eV and 2.8 − 2.9 eV) are observed. Intensities of the both bands are changed monotonically with RF power, whereas the bandwidth of ∼0.1 eV remains almost invariable. It is likely that the above lines are dumped by the non-radiative recombination involving E1-like centres in the amorphous-nanocrystalline SiC-like phases. Such explanation of the PL intensity dependences on the RF power density is supported by results of experimental studies of defect states spectrum in bandgap of the SiOCH films.
Functionalization of Porous Silicon with Alkenes and Alkynes via Carbocation-Mediated Hydrosilylation
Authors: Schmeltzer J. M. , Porter Lon A. , Stewart Michael P. , López Carmen M. , Buriak Jillian M.
Published: April 2011

Efforts to produce stable, derivatized porous silicon have yielded a number of chemical methods capable of functionalizing this interesting material with organic monolayers. Hydride-terminated porous silicon substrates react with alkenes and alkynes in the presence of dilute triphenylcarbenium salt solutions to respectively produce alkyl- and alkenyl-functionalized materials. Characterization by transmission FTIR and solid-state NMR suggests the formation of highly stable silicon-carbon bonds to yield covalently bound organic moieties. Porous silicon passivated in this fashion exhibits a greater resistance than that of the native material to chemical degradation, indicating that the organic functionalities may serve to sterically shield the nanocrystallites from nucleophiles. Hydrosilylation is proposed to proceed via hydride abstraction from the substrate followed by electrophilic attack by the subsequent species upon the alkene/alkyne, a mechanism previously hypothesized for the formation of stabilized β-silyl carbocations. The reaction is tolerant of a variety of substrate functional groups and native porous silicon surfaces but depends markedly upon the identity of the salt counteranion, among other solution parameters.
Imaging, Structural and Chemical Analysis of Silicon Nanowires
Authors: Barsotti R. J. , Fischer J. E. , Lee C. H. , Mahmood J. , Adu C. K. W. , Eklund P. C.
Published: April 2011

Laser ablation has been used to grow silicon nanowires with an average diameter of 6.7 nm ± 2.7 nm surrounded by an amorphous SiOx sheath of 1–2 nm. This paper reports the imaging, chemical and structural analysis of these wires. Due to the growth temperature and the presence of calcium impurities and trace oxygen, two distinct types of wires are found. They appear to grow by two different processes. One requires a metal catalyst, the other is catalyzed by oxygen.
Nano-Optics of Bismuth Nanowires
Authors: Black M. R. , Hagelstein P. L. , Dresselhaus M. S.
Published: April 2011

The optical absorption from an indirect L-T point valence band transition in bismuth nanowires is simulated based on a surface sensitive term, which is very weak in bulk bismuth, but effectively couples the L and T point bands in bismuth nanowires. The experimental Fourier transform infrared absorption spectra in the energy range 0.08 to 0.5 eV are compared to theoretical simulations for absorption resulting from indirect interband transitions between subbands at the L point valence band to subbands at the T point valence band as the polarization, tellurium doping, and wire diameter are varied. The simulated absorption from this indirect transition reproduces many of the experimentally observed trends and allows us to conclude that the dominant feature in the experimental absorption spectra of Bi nanowires results from an indirect L-T point transition which is enhanced in Bi nanowires.
Particle Production in High Density Silane Plasma
Authors: Shen Z. , Kim T. , Kortshagen U. , McMurry P. H. , Campbell S. A.
Published: April 2011

To understand the mechanisms of nanoparticle formation and its potential applications, we have investigated silicon particles formed in various gasses in an inductive coupled plasma (ICP) system and have measured their structural properties by electron microscopy. Particle generation in pure SiH4 and SiH4/H2 are reported. ICP silane plasmas are shown to be an interesting and versatile source of nanoparticles. Three regimes are mapped out: a regime of no observable particle growth at the lowest pressures, a regime of polydisperse and agglomerated particles at the highest pressures, and a regime yielding highly monodisperse particles at intermediate pressures. Conditions that generate these nonagglomerated, extremely monodisperse silicon particles are emphasized. For H2 dilutions less than 92%, the growth rate is almost independent of H2 partial pressure. Particle growth decreases steadily when the H2 dilution is increased further. TEM images, however, indicate that the addition of hydrogen decreases the particle density. At higher dilution ratios, polycrystalline particles are obtained. Under all other conditions the particles are amorphous. Reasons for this behavior are explored.
Ion Projection Direct-Structuring For Nanotechnology Applications
Authors: Loeschner Hans , Fantner Ernest J. , Korntner Regina , Platzgummer Elmar , Stengl Gerhard , Zeininger Michaela , Baglin J. E. E. , Berger Ruediger , Brünger Wilhelm H. , Dietzel Andreas , Baraton Marie-Isabelle , Merhari Lhadi
Published: April 2011

Large-field ion-optics has been developed for reduction printing. Sub-100nm ion projection direct-structuring (IPDS) of patterned magnetic media discs has been demonstrated, extending over 17mm diameter exposure fields, in a single exposure. First results of IPDS patterning of nanocomposite resist material are presented. Information about a novel 200x reduction projection focused ion multi-beam (PROFIB) tool development is provided. Further IPDS nanotechnology applications are discussed.
Shape Variations and Control in Self-Assembled Metal Nanoclusters
Authors: Zubris M. , Solimando M. , Goldberg E. P. , Reich S. , Tannenbaum R.
Published: April 2011

The selective interaction of metal clusters with various polymers constitutes the basis for the self-assembly approach to the synthesis of organic-inorganic hybrid materials, that leads to the control of particle size, geometry and dispersion gradient. Metal particles were synthesized by the thermal decomposition of an organometallic precursor, in this case, iron pentacarbonyl, in the presence of a polymer matrix. Under the conditions utilized for these reactions, the aggregation of the metallic clusters competed with the interactions between the growing metal fragments and the polymer matrix. The dominance of one reaction route as compared to the other, ultimately determined the equilibrium particle shape, size and distribution for each metal-polymer system. In this work, we attempted to analyze the formation of iron oxide nanoclusters in several structurally-distinct polymers, and developed a general mechanistic view to explain the characteristics of the polymer-metal oxide hybrid materials that were obtained.
Epitaxial Praseodymium Oxide: A New High-K Dielectric
Authors: Osten H. J. , Bugiel E. , Fissel A.
Published: April 2011

We show results for molecular beam epitaxial (MBE) growth of praseodymium oxide on Si. On Si(100) oriented surfaces, crystalline Pr2O3 grows as (110)-domains, with two orthogonal in-plane orientations. Epitaxial overgrowth with Si could not been realized so far. We obtain perfect epitaxial growth of hexagonal Pr2O3 on Si(111). These layers can also be overgrown epitaxially with Si leading to novel tunnel structures. Crystalline Pr2O3 on Si(OOl) is a promising candidate for highly scaled gate insulators, displaying sufficiently high-K value of around 30, ultra-low leakage current density, good reliability, and high electrical breakdown voltage. The Pr2O3/Si(001) interface exhibits the symmetric band alignment, desired for applying such material in both n- and p-type devices. The valence band as well as the conduction band offset to Si is above 1 eV. The electron masses can be assumed to be very heavy in the oxide. This effect together with the suitable band offsets leads to the unusually low leakage currents found experimentally. Finally, the integration of crystalline Pr2O3 high-K gate dielectrics into a conventional CMOS process will be demonstrated.
Z-contrast Imaging and EELS of Dislocation Cores at the Si/GaAs Interface
Authors: Lopatin S. , Duscher G. , Pennycook S. J. , Chisholm M. F.
Published: April 2011

The interface between silicon and epitaxial GaAs thin film grown by metalorganic chemical vapor deposition was studied using atomic-resolution Z-contrast imaging. Z-contrast imaging provides chemical composition information and allows direct interpretation of micrographs. Electron energy loss spectroscopy (EELS) yields correlation between structure and chemistry. Different types of dislocation were identified at the Si/GaAs interface. Atomic structure of non-reconstructed 90° dislocation (exhibiting a dangling bond) is refined by means of computer simulations based on functional density theory. EELS form planar Si/GaAs interface and dislocation cores obtained and analyzed.
Raman Scattering Study for Self-Organized Ge Quantum Dots Formed on Si Substrate
Authors: Yang T. R. , Dvoynenko M. M. , Feng Z. C. , Ferguson I. , Cheng H. H.
Published: April 2011

A Raman scattering study for self-organized Ge dots on Si substrate is presented. Raman signals from the Ge islands and Si substrate have been separated, by means of difference Raman spectroscopy technique. The wetting layer thickness and strain were estimated from the line width and the position of the peak. The estimated wetting layer thickness values are comparative with the Ge dot height obtained from microscopy measurements. As explained, the strain is observed to decrease with an increase of the Ge island height and the wetting layer thickness.
A Boron Doped Amorphous Silicon Thin-Film Bolometer for Long Wavelength Detection
Authors: Heredia-J A. , Torres-J A. , Jaramillo-N A. , De la Hidalga-W F.J. , Landa-V. M.
Published: April 2011

The fabrication of a bolometer for infrared detection using a boron doped amorphous silicon (a-Si-B:H) thin film is presented for the first time. This thin film (170 nm) was deposited on a silicon nitride membrane sustained by a frame made of micromachined crystalline silicon in order to improve the thermal isolation. Electrical connectivity to the element was achieved by means of aluminum contact pads. The resultant figures of merit, measured at room temperature, were: electrical conductivity of 1.513×10-3 (Ω-cm)-1, thermal coefficient of resistance of 3.4 %K-1, and the device is sensitive to temperature variations as small as 20 mK.
The Growth and Characterization of Zinc Oxide Thin Film on Fused Silica and SiO2/Si(100) Substrates
Authors: Jin C. , Tiwari A. , Porter H. , Park M. , Narayan J.
Published: April 2011

ABSTRATCT

In this work, ZnO thin films were grown on amorphous fused silica and pre-oxidized silicon substrates by using pulsed laser deposition technique. X-ray diffraction patterns showed that the films were highly crystalline and c-axis oriented. The surface morphologies of the films were observed by using scanning electron microscope and optical microscope. Free exciton absorption was observed at room temperature for the film grown on fused silica substrate. The strong near-UV luminescence peaked at 380 nm were observed for all the films and was attributed to the phonon-related exciton emission. The effect of oxygen partial pressure on the luminescence intensity is also reported.
Characterization of AlInAsSb and AlGaInAsSb MBE-grown Digital Alloys
Authors: Vaughn Leslie G. , Ralph L. , Xu Huifang , Jiang Yingbing , Lester Luke F.
Published: April 2011

As one of the few Type I band offset, antimony-based material systems available for 3.3 to 4.2 micron mid-infrared multiple quantum well lasers, AlInAsSb alloys have been used as barriers with InAsSb wells. Previously, AlxIn(1-x)AsySb(1-y) quaternary alloys have been grown by MBE as random alloys up to an aluminum fraction, x = 0.10 on GaSb substrates and x = 0.15 on InAs substrates. Random alloy growth of quaternary films with increased aluminum content, although beneficial to the devices, is limited by a miscibility gap. We have used a digital alloy technique to grow stable, single phase, GaSb lattice-matched, optically smooth quaternary alloys for aluminum fractions of 0.05 to 0.5, well into the miscibility gap. DCXRD results show FWHM of 0th order alloy peaks are within 1.5 to 2 times that of the highly crystalline GaSb substrates and have well defined thickness fringes corresponding to the total film thickness and the digital alloy period. TEM images show very well ordered alloys with characteristic ultrathin superlattice structure having smooth interfaces, very little strain and atomic ordering limited to that imposed by the digital alloy technique. Photoluminescence measurements are used to fit a model for bandgap prediction from known alloy compositions. Theoretical studies have predicted that the addition of a fifth element, gallium, may help suppress Auger recombination through its effects on the subband structure. So, gallium is added to the quaternary to produce a quinternary alloy lattice-matched to GaSb. These AlGaInAsSb alloys have DCXRD and TEM results similar to the quaternary. The stable, single-phase growth of these quinternary alloys across the composition range is promising for improving the operating characteristics of mid-IR lasers.
Silicon CMOS BEOL Compatible Optical Waveguide Micro-mirrors
Authors: Ponoth Shom , Agarwal Navnit , Persans Peter , Plawsky Joel
Published: April 2011

Optical waveguides are being explored for on-chip purposes to overcome the speed limitations of electrical interconnects. Passive optical components like waveguides and vertical outcouplers are important components in such schemes. In this study we fabricate planar waveguides with integrated vertical micro-mirrors using standard Back End of the Line silicon (BEOL) CMOS based processes. Around 1.6 μm of a hybrid alkoxy siloxane polymer with a refractive index of ∼ 1.50 at the intended wavelength of 830 nm is used as the core and plasma deposited silicon oxide with a refractive index of ∼ 1.46 is used as the cladding. The angular face in the polymer waveguide that would function as the mirror surface was fabricated by a pattern transfer method which involves transferring the angle in a template to the waveguide using anisotropic reactive ion etching. The sidewall angle realized in a positive resist on patterning was used as the angle template. Exposure and development conditions were adjusted for Shipley® S1813 photoresist to generate a sidewall angle of ∼ 65°. The anisotropic Reactive Ion Etching (RIE) was done using a CF4/O2 plasma chemistry. A gas composition of 50/50 CF4/O2 was chosen in order to minimize the etch related roughness of the polymer and the photoresist. The metallization of the mirror faces was done using a self-aligned maskless technique which ensures metal deposition only on the angular face and also eliminates a lithography step.
Photoluminescence in UHV/CVD tensile-strained Si type-II quantum wells on bulk crystal SiGe substrates
Authors: Sheng S.R. , Rowell N.L. , McAlister S.P.
Published: April 2011

Near band-edge photoluminescence (PL) in high-quality UHV/CVD tensile-strained Si type-II quantum wells (QWs) with varying well width grown on bulk crystal SiGe substrates has been studied. In contrast to the blue-shifts observed in the PL lines of Si1-xGex QWs on Si, the PL lines of Si QWs exhibit red-shifts with increasing excitation density. The PL from the SiGe substrate shows no such shift. The PL red-shifts decrease as the well width decreases, and are essentially independent of temperature up to 15K where a transition from bound exciton emission to higher energy free exciton emission occurs. The rapid thermal annealing (RTA) was found to improve the crystal quality of the samples. RTA enhances the integrated PL intensity, results in narrowing and blue-shifting of PL bands, and reduces the exponent in the excitation power dependence as well as the amount of red-shifting at a given excitation density. Possible mechanisms for the observed shifts to lower energies of the PL lines with excitation density were examined, including band bending, band-filling, and binding of excitons to impurities.
GaSb-based Materials for Mid-infrared Photodiodes Operating in the 0.9–2.55 μm Spectral Range
Authors: Andreev I.A. , Kunitsyna E.V. , Mikhailova M.P. , Yakovlev Yu.P. , Ioffe A.F.
Published: April 2011

The paper discusses some recent developments in the GaSb/GaInAsSb/GaAlAsSb heterostructure epitaxial growth and fabrication of GaInAsSb/GaAlAsSb photodiodes for the 0.9–2.55 μm spectral range.
Intersubband Transitions in InxGa1-xAs/AlGaAs Multiple Quantum Wells for Long Wavelength Infrared Detection
Authors: Workman Clayton L. , Wang Zhiming , Ma Wenquan , George Christi E. , Panneer Selvam R. , Salamo Gregory J. , Zhou Qiaoying , Omar Manasreh M.
Published: April 2011

We report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown InxGa1-xAs/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded InxGa1-xAs buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in InxGa1-xAs wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.
Single Crystal High Frequency Cavity-based EPR Spectroscopy of Single Molecule Magnets
Authors: Hill S. , Edwards R. S. , Jones S. I. , Maccagnano S. , North J. M. , Aliaga N. , Yang E-C. , Dalal N. S. , Christou G. , Hendrickson D. N.
Published: April 2011

We report high frequency electron paramagnetic resonance (EPR) investigations of a series of high spin (total spin up to S = 10) manganese and nickel complexes which have been shown to exhibit single molecule magnetism, including low temperature (below ∼ 1K) hysteresis loops and resonant magnetic quantum tunneling. A cavity perturbation technique enables high sensitivity oriented single crystal EPR measurements spanning a very wide frequency range (16 to 200+ GHz). Fitting of the frequency and field orientation dependence of EPR spectra allows direct determination of the effective spin Hamiltonian parameters. Studies on a range of materials with varying (approximately axial) site symmetries facilitates an assessment of the role of transverse anisotropy (terms in the Hamiltonian that do not commute with ŝz) in the magnetic quantum tunneling phenomenon.
Microstructure and Magnetic Property of L1o CoPt–20 at.% C Magnetic Thin Film
Authors: Oh D. Y. , Park J. K.
Published: April 2011

The CoPt-20at.%C thin films of 20nm thickness were sputter-deposited in the form of CoPt/Cn (n=1: carbon layer thickness=4nm; n=4: each carbon layer thickness=1nm) and were transformation-annealed at 650°C for various times. Carbon was found to dissolve into CoPt lattice and enlarge the c/a ratio of the ordered CoPt lattice. The amount of carbon dissolution increases with the decreasing carbon layer thickness at a given total carbon concentration.

The carbon dissolution larger than a critical amount can lead to a shift of the phase equilibrium of ordering and produce a stable fine two-phase mixture of ordered and disordered phases at the equi-atomic composition of Co:Pt. This results in a fine and uniform stagnant grain structure of about 20nm on annealing at 650°C. The carbon dissolution by increasing the c/a ratio of the ordered CoPt lattice reduces both the saturation magnetization and the magnetocrystalline anisotropy constant of the film and leads to a reduction of coercivity of CoPt films.
Quantum Computing: From Bragg Reflections to Decoherence Estimates
Authors: Pfeifer Peter , Hou Chen
Published: April 2011

We give an exposition of the principles of quantum computing (logic gates, exponential parallelism from polynomial hardware, fast quantum algorithms, quantum error correction, hardware requirements, and experimental milestones). A compact description of the quantum Fourier transform to find the period of a function—the key step in Shor's factoring algorithm—illustrates how parallel state evolution along many classical computational paths produces fast algorithms by constructive interference similar to Bragg reflections in x-ray crystallography. On the hardware side, we present a new method to estimate critical time scales for the operation of a quantum computer. We derive a universal upper bound on the probability of a computation to fail due to decoherence (entanglement of the computer with the environment), as a function of time. The bound is parameter-free, requiring only the interaction between the computer and the environment, and the time-evolving state in the absence of any interaction. For a simple model we find that the bound performs well and decoherence is small when the energy of the computer state is large compared to the interaction energy. This supports a recent estimate of minimum energy requirements for quantum computation.
Hrtem Investigation of Effect of Various Rare Earth Oxide Dopants on Epitaxial Zirconia High-k Gate Dielectrics
Authors: Kiguchi Takanori , Wakiya Naoki , Shinozaki Kazuo , Mzutani Nobuyasu
Published: April 2011

The effects of several rare earth oxide on the capacitance-voltage (C-V) characteristics and the SiO2 interlayer growth of ZrO2 based gate dielectrics were examined. The width of the hysteresis window of La2O3 stabilized ZrO2 (LaSZ) gate dielectric was only 0.2V, on the other hands, that of Sc2O3 stabilized ZrO2 (ScSZ) gate dielectric was 1.4V HRTEM analysis indicated that the growth of SiO2 interlayer of RSZ (R=Sm,Nd,La) gate dielectric was about 1nm, which was less than half of the ScSZ one. These results indicate the advantage of the ZrO2 gate dielectric doped with rare earth oxide composed of larger ionic radius cation.
The Behavior of Cyclic Voltammetry Stripping (CVs) with Tin-Doped Indium Oxide in 0.3M Hydrochloric Acid
Authors: Li K. C. , Huang C. A. , Tu G. C. , Wang W. S.
Published: April 2011

The cyclic voltammetry stripping (CVs) behavior of the tin-doped indium oxide (ITO) on SiO2 in 0.3M HCl is reported. The CVs result showed an obvious reduction-current peak that occurred during the first cathodic potential scanning. Smaller reduction current and more negative potential of the reduction-current peak were also observed for the ITO that was annealed at 500 °C. The result was attributed to the replenished oxygen-deficient site and the oxygen anion density is decreased in the ITO. The present study has proved that CVs is a useful method to differentiate the carrier concentration in ITO film controlled by different pretreatments. Many spherical In-Sn particles were formed on the ITO when the reduction current took place. During precipitation of these spherical particles, the grain boundaries of the ITO were dissolved and the ITO surface nearby the grain boundaries offered a preferred nucleation site for the formation of these spherical In-Sn particles. Based on the microstructure observed and the result derived from the short potential range scanning, the formation mechanism of the spherical particle is proposed.
Step bunching during Si(001) homoepitaxy caused by the surface diffusion anisotropy
Authors: Mysliveček J. , Schelling C. , Schäffler F. , Springholz G. , Šmilauer P. , Krug J. , Voigtländer B.
Published: April 2011

Scanning tunneling microscopy experiments show that the unstable growth morphology observed during molecular beam homoepitaxy on slightly vicinal Si(001) surfaces consists of straight step bunches. The instability occurs under step-flow growth conditions and vanishes both during low-temperature island growth and at high temperatures. An instability with the same characteristics is observed in a 2D Kinetic Monte Carlo model of growth with incorporated Si(001)-like diffusion anisotropy. This provides strong evidence that the diffusion anisotropy destabilizes growth on Si(001) and similar surfaces towards step bunching. This new instability mechanism is operational without any additional step edge barriers.
Facet-Facet Barrier on Surfaces: Proposal and Experimental Validation
Authors: Huang Hanchen , Woo C. H. , Wei H. L. , Liu S. J. , Zhang X. X. , Altman M. , Wang E. G.
Published: April 2011

Surface processing is generally kinetics limited. Migration barriers, both on flat surfaces and near steps, therefore are of crucial importance. In this paper, we describe a kinetic barrier that separates two neighboring facets on surfaces. The contrast of this concept relative to the conventional Ehrlich-Schwoebel barrier is shown through molecular dynamics/statics calculations on copper and aluminum. The effects of this new kinetic barrier are demonstrated through lattice Monte Carlo simulations. The predicted effects are in direct correspondence with validation experiments on copper and silver thin films.
Ab-Initio Theory of Grain-Boundary Segregation in α-Alumina: Energetics, Atomistic and Electronic Structures
Authors: Fabris Stefano , Elsässer Christian
Published: April 2011

The modifications in atomistic structure, chemical bonding, and energetics induced by sub-stitutional cation impurities isolated in bulk and segregated at grain boundaries of α-Al2O3 were investigated by first-principles electronic-structure calculations. The dependency of these modifications on the boundary type, species and concentration of defects, was studied by selecting the following variety of systems: two different twin boundaries (the prismatic Σ3 (1010) and the pyramidal Σ13 (1014) twins), five cation impurities X (X=Ti, Sc, Y, Ca, and La), and two concentration regimes for the segregant (≈ 3 and ≈ 6 atoms/nm2). A partial covalent character is found to be a distinctive feature of the X-O bond in both bulk and interfacial atomic environments, and to drive the structural distortions of the octahedral XO6 clusters. The energetics of segregation reveals a linear relationship between segregation energy and impurity size.
Orientation Dependence of Photochemical Reduction Reactions on SrTiO3 Surfaces
Authors: Giocondi Jennifer L. , Rohrer Gregory S.
Published: April 2011

Polished and annealed surfaces of randomly oriented crystallites were used to study the orientation dependence of the photochemical activity of SrTiO3 surfaces. Silver cations reduced from an aqueous solution produce solid silver metal at the reaction site. The amounts of silver produced by a fixed exposure were used as a relative measure of each grain's activity. The surface structure of the grains was observed using atomic force microscopy and the surface orientation of each grain was determined by electron backscattered diffraction. Surfaces annealed in air for 6h at 1200° C were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. By correlating the orientations of individual grains to the amount of deposited silver, we conclude that surfaces with the complex {100} facet are the most active.
Surface Chemistry of Mesoporous Materials: Effect of Nanopore Confinement
Authors: Wang Yifeng , Bryan Charles , Xu Huifang , Gao Huizhen
Published: April 2011

Acid-base titration and metal sorption experiments were performed on both mesoporous alumina and alumina particles under various ionic strengths. It has been demonstrated that surface chemistry and ion sorption within nanopores can be significantly modified by a nano-scale space confinement. As the pore size is reduced to a few nanometers, the difference between surface acidity constants (ΔpK = pK2 – pK1) decreases, giving rise to a higher surface charge density on a nanopore surface than that on an unconfined solid-solution interface. The change in surface acidity constants results in a shift of ion sorption edges and enhances ion sorption on that nanopore surfaces.
Effect of Si and P on the Formation and Crystallization of Ti25Hf50Ni25 Metallic Glasses
Authors: Huett V. T. , Kelton K. F.
Published: April 2011

Ti255Hf50Ni25 metallic glasses, prepared by rapid quenching, are strongly metastable with a 65°C separation between the glass transition temperature, Tg = 335°C, and the onset temperature for primary crystallization. The deep metastability of the glass is likely due to sluggish nucleation and growth kinetics, limited by the Hf diffusion. The glass crystallizes to a nano-scale microstructure consisting of an icosahedrally symmetric ordered phase. This phase is metastable and transforms to a stable Ti2Ni-type phase with annealing at higher temperatures. The primary crystallization to a metastable icosahedrally-ordered phase suggests that the local structure of the glass contains a high degree of icosahedral short-range order. Here, glass formation and crystallization were studied in alloys containing 2 at.% of Si and P.
Microstructure and mechanical properties of slowly cooled Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 with ductile bcc phase
Authors: Kühn Uta , Eckert Jürgen , Mattern Norbert , Radtke Nicolle , Schultz Ludwig
Published: April 2011

We report about the preparation and properties of a Be-free Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 alloy with a glassy or a nanocrystalline matrix and ductile bcc precipitates, which were developed with the aim to improve the mechanical properties. The samples were prepared in form of rods by injection casting into a copper mold. The phase formation as well as the resulting microstructure and the mechanical properties of the different samples have been investigated upon cooling from the melt at different quenching rates. The formation of the bcc phase embedded in a glassy matrix is strongly governed by the alloy composition and the actual cooling rate during solidification, because the glass forming ability is much lower compared to Zr-based alloys containing Be. Already small reductions in cooling rate lead to precipitation of additional crystalline phases. Compression tests reveal that the in-situ glassmatrix composite undergoes work hardening and plastic deformation prior to failure. Surprisingly, also a nanocrystalline matrix leads to high elastic strain values. These features significantly improve the mechanical behavior of the composites compared to the monolithic glass.
Fragility of Metallic Glass Forming Liquids
Authors: Fan G. J. , Wunderlich R. K. , Fecht H.-J.
Published: April 2011

Based on the available kinetic and thermodynamic data, we compare the kinetic fragility and thermodynamic fragility of different metallic glass forming liquids. The results indicate a correlation between the kinetic and thermodynamic fragility in metallic glass forming liquids, consistent with the energy landscape model which predicts a connection between the kinetic and thermodynamic properties of supercooled liquids. The metal - metalloid glass forming alloys such as PdNiCuP are found to exhibit a distinctively different correlation as compared to early – late transition metal – type metallic glass forming alloys such as ZrTiCuNiBe. For the same thermodynamic fragility the former exhibit a much larger kinetic fragility indicating that the two classes of alloys have a different liquid structure. In addition, the relationship between the kinetic fragility and the Gibbs free energy difference between the undercooled liquid and the crystalline phases has been discussed in both metal metalloid glass forming alloys and early - late transition metal – type metallic glass forming alloys.
Strain Localization in a Molecular-Dynamics Model of a Metallic Glass
Authors: Falk Michael L. , Shi Yunfeng
Published: April 2011

Molecular dynamics simulations of a two-dimensional amorphous solid exhibit strain localization when loaded in uniaxial tension with free boundaries. The degree of localization depends sensitively on the rate of loading and on the existence of surface defects. Regions of both dilation and contraction arise during the shear band slip process. These dilation and contraction events correspond to dynamic free-volume generation and annihilation during shear. Correlations of the dilation and contraction of the material reveal a length scale of 1–4 atomic diameters associated with this physical process. Dilation is observed to result in nanometer scale cavitation.