bluuebunny/crossref_metadata_2025 huggingface dataset:
Water and Gas Movement in Mx80 Bentonite Buffer Clay
Authors: Horseman Stephen T. , Harrington Jon F. , Sellin P.
Published: April 2011

This paper describes a long-term laboratory test designed to examine the sensitivity of gas flow in Mx80 buffer bentonite subject to a constant volume boundary condition. A constant volume and radial flow (CVRF) apparatus was designed to enable gas flow from a centrally located injection filter to be independently monitored at three sink-filter arrays mounted around the circumference of the clay specimen. Axial and radial total stresses and internal porewater pressure were continuously monitored. Gas entry, breakthrough and peak gas pressures were found to be systematically higher under constant volume boundary conditions than under previously reported constant stress and radially-constrained test conditions [6, 9, 10]. The observation that gas pressures are sensitive to test boundary conditions supports the hypothesis that gas entry is accompanied by dilation of the bentonite fabric. Gas penetration of the clay caused a substantial increase in total stress and internal porewater pressure. Abrupt drops in gas pressure, accompanied by similar drops in total stress, were interpreted as fracture propagation events. The outflow of gas was always non-uniformly distributed between the sinks. Furthermore, the distribution of flow between sinks often changed abruptly during the course of an experiment indicating that gas pathways were very unstable. When gas injection stopped, the gas pressure and rate of outflow spontaneously declined with time. Under constant volume conditions, the gas pressure at the asymptote exceeded the internal porewater pressure by an amount equal to the capillary pressure. In constant volume tests on clay with high water saturation, capillary pressure has a value close to the measured swelling pressure of the clay.
The Uptake of Strontium by Calcium Silicate Hydrates under High pH Conditions: An Experimental Approach to Distinguish Adsorption from Co-precipitation Processes
Authors: Tits J. , Wieland E. , Dobler J.-P. , Kunz D.
Published: April 2011

The interaction of Sr(II) with CSH phases has been investigated to distinguish adsorption from co-precipitation processes and to assess the relevance of these processes for performance assessments. Batch-type sorption experiments were carried out to study the adsorption of Sr(II) on synthetic CSH phases at different C:S ratios. Co-precipitation experiments were conducted by precipitating CSH phases in the presence of Sr(II) at two different precipitation rates.

Distribution ratios (Rd) of Sr(II) obtained from the sorption and co-precipitation studies were found to be similar in value. The results indicate that co-precipitation processes do not enhance Sr(II) uptake by CSH compared to adsorption. In both the co-precipitation and adsorption experiments the same sorption sites are accessible to Sr(II). The precipitation rate of the CSH phases has no significant influence on the Rd values.
Low Temperature a-Si:H TFTs with a SiO2 Gate Insulator Deposited by Liquid Phase Deposition
Authors: Cross Richard B. M. , Oxley David P. , Manhas Meenakshi , Narayanan Ekkanath. M. Sankara
Published: April 2011

A systematic study has been made of the influence of the deposition conditions on the properties of SiO2 grown by liquid phase deposition (LPD), and a-Si:H manufactured by plasma enhanced chemical vapour deposition (PECVD) with the novel facility of source-gas heating. It is demonstrated that LPD-SiO2 can be grown at 50°C with good dielectric properties. Material has been produced with a resistivity of 1015 &cm and a dielectric strength of 9 MVcm-1.The oxide was found to have a negative fixed oxide charge of 4 × 1011 cm−2, with a dielectric constant of 3.08 and a refractive index of 1.44. In the case of a-Si:H, pre-heating the source gases has enabled material to be grown at 125°C with a hydrogen content of ∼ 10 at%, with a predominance of monohydride bonding and a photosensitivity of ∼ 104. Inverted-staggered thin film transistors have been fabricated incorporating these films with an On/Off ratio of five orders of magnitude, a sub-threshold slope of 1.3 Vdecade−1 and a field effect mobility of 0.20 cm2V−1s−1
The effect of substrate temperature and interface oxide layer on aluminum induced crystallization of sputtered amorphous silicon
Authors: Hossain Maruf , Abu-Safe Husam , Barghouti Marwan , Naseem Hameed , Brown William D.
Published: April 2011

The effect of substrate temperature and interface oxide layer on aluminum induced crystallization (AIC) of amorphous silicon (a-Si) is investigated. The effect of substrate temperature on the AIC process was studied by changing the deposition temperate of a-Si from 200 to 300°C in a Al/a-Si/glass configuration. To study the effect of interface oxide on AIC, samples with a-Si/Al/glass, a-Si/Al-oxide/Al/glass, and Al/Si-oxide/a-Si/glass configurations were prepared at a fixed substrate temperature. The samples were annealed in the temperature range from 300°C to 525°C for different periods of time. The X-ray diffraction (XRD) patterns confirmed the crystallization of the a-Si films in the various configurations. From the analysis, we report that crystallization of a-Si happen at 350°C annealing temperature in the Al/a-Si/glass configuration. However, with or without the presence of Si-oxide at the interface, crystallization saturated after annealing for 20 minutes at 400°C. On the other hand, when Al-oxide is present at the interface, higher annealing temperatures and longer annealing times are required to saturate the crystallization of a-Si. Environmental Scanning Electron Microscope (ESEM) and Energy Dispersive X-Ray (EDX) mapping were used to study the surface morphology as well as the layer sequence after crystallization. This analysis revealed that Si-Al layer-exchange happens regardless of the deposited film configuration.
The Role of Charged Gap States in Light-Induced Degradation of Single-Junction a-Si:H Solar Cells
Authors: Zeman M. , Nádazdy V. , Metselaar J.W.
Published: April 2011

Computer simulations of single-junction hydrogenated amorphous silicon (a-Si:H) solar cells with different thickness of the intrinsic layer were carried out in order to study the role of charge gap states in their light-induced degradation. It is demonstrated that it is the decrease of positively charged states above midgap, Dh, and the increase of neutral states around midgap,Dz, and negatively charged states below midgap, De in the intrinsic layer that result in a drop of performance of the solar cells due to light soaking. These changes in the gap states are in accordance with our recent experimental results from the charge deep-level transient spectroscopy on undoped a-Si:H. The experimentally observed changes in the dark and illuminated J-V curves and spectral response could not be simulated with the same set of input parameters by only increasing the defect-state density in the intrinsic layer.
The Influence of Light-Soaking and Atmospheric Adsorption on Microcrystalline Silicon Films studied by Coplanar Transient Photoconductivity
Authors: Smirnov V. , Reynolds S. , Finger F. , Main C. , Carius R.
Published: April 2011

A study of the effects of light-soaking and atmospheric adsorption (aging) on the dark- and photo-conductivity of a series of microcrystalline silicon films of varying crystallinity is presented. Light-soaking in vacuum slightly reduces photoconductivity in films close to the amorphous – microcrystalline transition, and there is also a reduction in dark current. Aging increases the dark current, and thus unless due care is taken during light-soaking experiments to eliminate or compensate for aging, the apparent effect of light-soaking may be reduced or even reversed in sign. Transient photocurrent decays confirm the presence of a large density of metastable light-induced defects. A shift in the apparent distribution of defects occurs on prolonged aging, which may be due either to changes in the DOS or a shift in the Fermi level.
Device Characteristics of Ultra-shallow Junctions Formed by fRTP Annealing
Authors: Satta A. , Lindsay R. , Severi S. , Henson K. , Maex K. , McCoy S. , Gelpey J. , Elliott K.
Published: April 2011

The creation of ultra-shallow junction for CMOS devices at the sub-100 nm node is driving significant efforts in developing thermal processing to give rise to high dopant activation in combination with limited diffusion. Flash-assist Rapid Thermal Annealing™ (fRTP™) is a promising new annealing technique, which involves the heating of the bulk of the wafer to an intermediate temperature using rather conventional spike RTP, followed by a short and intense pulse of light localized on the implanted wafer surface.

In this work, we have systematically investigated the junction formation of different implants under fRTP anneals in terms of profile and devices. Co-implanted Ge and F species provide more box-like profiles with improved activation. Although leakage currents are higher for fRTP-annealed junctions than for spike-annealed junctions, appropriate fRTP process parameters and correct process conditions provide a critical tool to control and reduce the leakage current of co-implanted fRTP junctions to acceptable levels. Proper implant and anneal are requested for minimizing pattern effect and improving device performance.
The Role of Stress on the Shape of the Amorphous-Crystalline Interface and Mask-Edge Defect Formation in Ion-Implanted Silicon
Authors: Ross Carrie E. , Jones Kevin S.
Published: April 2011

Stress is known to affect the regrowth velocities during recrystallization of an amorphous layer. This study investigates how the stress from patterned structures alters regrowth and in turn affects defect formation. Prior to patterning, 80Å SiO2 and 1540Å of silicon nitride were deposited on a 200 mm [001] silicon wafer. A 40keV Si+ amorphizing implant at a dose of 1×1015 atoms/cm2 was then performed into the patterned wafer. The regrowth of the amorphous layer along the mask edge was studied by partially recrystallizing the layer for various times at 550°C both with the mask present and after etching off the oxide and nitride pads. A significant number of cross-sectional Transmission Electron Microscopy (TEM) samples were prepared and imaged. It was found that the stress from the patterned structures enhances the vertical and lateral regrowth velocities, as well as alters the shape of the amorphous-crystalline interface during regrowth. Previous studies have shown that uniaxial tensile stress increases the regrowth velocity. Simulations show that the region of interest in these samples is under tensile stresses, suggesting that this type of stress should accelerate the regrowth velocity. In addition dislocation half loops are observed to form along the mask edge for certain structures. The nucleation of these defects is suppressed by the presence of the film. The relationship between the stress from the patterned structures, the regrowth of the amorphous layer, and the formation of dislocation half-loops along the mask edge will be discussed.
Formation and Morphology Evolution of Nickel Germanides on Ge (100) under Rapid Thermal Annealing
Authors: Lee K.Y. , Liew S.L. , Chua S.J. , Chi D.Z. , Sun H.P. , Pan X.Q.
Published: April 2011

Phase formation and interfacial microstructure evolution of nickel germanides formed by rapid thermal annealing in a 15-nm Ni/Ge (100) system have been studied. Coexistence of a NiGe layer and Ni-rich germanide particles was detected at 250°C. Highly textured NiGe film with a smooth interface with Ge was observed. Annealing at higher temperatures resulted in grain growth and severe grooving of the NiGe film at the substrate side, followed by serious agglomeration above 500°C. Fairly low sheet resistance was achieved in 250-500°C where the NiGe film continuity was uninterrupted.
Effects of Alloying on Properties of NiSi for CMOS Applications
Authors: Dal Mark van , Akheyar Amal , Kittl Jorge A. , Chamirian Oxana , Pottera Muriel De , Demeurisse Caroline , Lauwers Anne , Maex Karen
Published: April 2011

Effects of alloying Ni with Pt and Ta on silicide properties for CMOS technology have been studied. It was found that Pt is soluble in NiSi, which is in line with literature, whereas Ta segregates towards the surface during thermal treatment. Additionally, Ta retards NiSi formation at low temperature. Thermal stability of NiSi on Si is improved more efficiently by alloying Ni with Pt compared to Ta. Silicide/diffusion contact resistance is extracted using the Transmission Line Structure. In our experiments, contact resistivity appeared to be virtually unaffected with respect to the alloying element. Thermal stability on narrow poly Si structures was also improved when Ni was alloyed with Pt. Similar leakage currents for Ni and Ni(Pt) silicides on N+ and P+ junctions were obtained. The results presented in this work suggest that Pt is a better candidate as alloying element to improve NiSi thermal stability for CMOS processes than Ta.
Indium in silicon: interactions with native defects and with C impurities
Authors: Alippi P. , Magna A. La , Scalese S. , Privitera V.
Published: April 2011

Equilibrium geometries and formation energies of neutral and charged In complexes with silicon native defects (vacancy (V) and self-interstitials (I)) and with C impurities are investigated within density functional theory, using the Vienna Ab-initio Simulation Package. We determine formation energies and ionization levels of different complexes and discuss the contribution of I and V to indium diffusion. We also identify the In-C defect responsible for the increased electrical activation in In+C-doped silicon samples. The ab initio energetics is then implemented in a continuum diffusion code in order to simulate the diffusion of as-implanted In profiles under different thermal treatments.
Study of BF2 ion implantation into crystalline silicon : Influence of fluorine on boron diffusion
Authors: Ihaddadene-Lecoq Lilya , Marcon Jerome , Ketata Kaouther
Published: April 2011

We have investigated and modeled the diffusion of boron implanted into crystalline silicon in the form of boron difluoride BF2+. Low energy BF2+ 1×1015 cm−2 implantations at 2.0keV were characterized using Secondary Ion Mass Spectrometry (SIMS) in order to measure dopant profiles. RTA was carried out at 950°C, 1000°C, 1050°C and 1100°C during 10s, 20s, 30s and 60s. The results show that concentration profiles for BF2+ implant are shallower than those for a direct B+ ion implantation. This could be attributed to the presence of fluorine which trap interstitial Si so that interstitial silicon supersaturation is low near the surface.
Self-Assembled Monolayers as Model Substrates for Atomic Layer Deposition
Authors: Whelan Caroline M. , Demas Anne-Cécile , Schuhmacher Jörg , Carbonell Laureen , Maex Karen
Published: April 2011

Our understanding of the role of the initial surface on atomic layer deposition (ALD) of Cu diffusion barrier materials is limited by the complexity of the sequential reactions and the heterogeneous nature of typical dielectric substrates. The atomically controlled surface chemistry of self-assembled monolayers (SAMs) provides a means of creating model substrates for ALD. Here we report on ALD of WCxNy films on SAMs derived from bromoundecyltrichlorosilane adsorbed on silicon dioxide. The as-prepared SAM is macroscopically ordered with the expected Br-termination and has a well-defined chemical composition as determined by contact angle measurements and X-ray photoelectron spectroscopy, respectively. Temperature programmed desorption spectroscopy confirms that the SAM is stable to 550°C. It survives multiple cycles of ALD at 300°C as evidenced by the detection of mass fragments characteristic of the alkyl chain and supported by the persistence of a Br 2p peak at 71 eV. X-ray fluorescence, ellipsometry and atomic force microscopy reveal that the underlying SAM influences WCxNy film coverage, thickness, and morphology.
In-situ XPS Study of ALD Ta(N) Barrier Formation on Organosilicate Dielectric Surface
Authors: Liu Junjun , Bao Junjing , Scharnberg Michael , Ho Paul S.
Published: April 2011

Beams of nitrogen and hydrogen radicals were investigated as surface pre-treatment and process enhancement techniques for atomic layer deposition (ALD) of tantalum nitride barrier layer on a dense organosilicate (OSG) low k film. In-situ x-ray photoelectron spectroscopy (XPS) studies of the evolution of the low k surface chemistry revealed an initial transient growth region controlled mainly by the substrate surface chemistry. Pre-treatment of the low k surface with radical beams, particularly with nitrogen radicals, was found to enhance significantly the chemisorption of the TaCl5 precursor on the OSG surfaces. The enhancement was attributed to the dissociation of the weakly bonded methyl groups from the low k surface followed by nitridation with the nitrogen radicals. In the subsequent linear growth region, atomic hydrogen species was able to reduce the chlorine content under appropriate temperature and with sufficient purge. The role of the atomic hydrogen in this process enhancement is discussed.
Barrier Layer Morphological Stability and Adhesion to Porous Low-κ Dielectrics
Authors: Saxena R. , Cho W. , Rodriguez O. , Gill W. N. , Plawsky J. L.
Published: April 2011

Two particularly important reliability issues facing the integration of low- κ dielectric films are the fracture energy of the barrier-dielectric interface and the barrier layer integrity during processing. We have noticed that the compressive stresses in the barrier layers on low- κ dielectrics lead to spontaneous delamination and formation of telephone-cord like morphologies. These morphologies allow the measurement of fracture energy and are advantageous over artificially contrived features to yield realistic debonding parameters. The fracture energy of common barrier films, TaN and Ta, was determined using this method for varying porosity nanoporous silica and MSQ. Detailed characterization of the telephone cord morphology using a combination of Optical Microscopy, SEM and Profilometry was done. The fracture energy for Ta on different low-κ dielectrics was evaluated using a 1-D model for straight buckles. The kinetic coefficient of buckling was also evaluated.
Atomic Layer Deposition of Tantalum Nitride on Organosilicate and Organic Polymerbased Low Dielectric Constant Materials
Authors: Straten Oscar van der , Zhu Yu , Rullan Jonathan , Topol Katarzyna , Dunn Kathleen , Kaloyeros Alain
Published: April 2011

A previously developed metal-organic atomic layer deposition (ALD) tantalum nitride (TaNx) process was employed to investigate the growth of TaNx liners on low dielectric constant (low-k) materials for liner applications in advanced Cu/low-k interconnect metallization schemes. ALD of TaNx was performed at a substrate temperature of 250°C by alternately exposing low-k materials to tertbutylimido-tris(diethylamido)tantalum (TBTDET) and ammonia (NH3), separated by argon purge steps. The dependence of TaNx film thickness on the number of ALD cycles performed on both organosilicate and organic polymer-based low-k materials was determined and compared to baseline growth characteristics of ALD TaNx on SiO2. In order to assess the effect of the deposition of TaNx on surface roughness, atomic force microscopy (AFM) measurements were carried out prior to and after the deposition of TaNx on the low-k materials. The stability of the interface between TaNx and the low-k materials after thermal annealing at 350°C for 30 minutes was studied by examining interfacial roughness profiles using cross-sectional imaging in a high-resolution transmission electron microscope (HR-TEM). The wetting and adhesion properties of Cu/low-k were quantified using a solid-state wetting experimental methodology after integration of ALD TaNx liners with Cu and low-k dielectrics.
Silver Patterning by Reactive Ion Beam Etching for Microelectronics Application
Authors: Gao L. , Gstoettner J. , Emling R. , Wang P. , Hansch W. , Schmitt-Landsiedel D.
Published: April 2011

Dry etching of silver for the metallization in microelectronics is investigated. Etching is performed using an electron-cyclotron-resonance reactive-ion-beam-etching system (ECR-RIBE) in an Ar/CF4 or Ar/CF4/O2 mixture. The etch characteristics are strongly affected by ion energy (beam voltage and microwave energy); the O2 concentration in the reactive mixture has only a small effect. An anisotropic, smooth etch profile and clean surface are obtained. Focused ion beam (FIB) and atomic force microscopy (AFM) have been used to study the etched profile and the roughness, respectively.
Novel Opto-Electronic Braid System with Kumihimo-Structure as a New Concept of Flexible Electronics
Authors: Tanaka Kuniaki , Kuniyoshi Sigekazu
Published: April 2011

Following the new concept proposed as an opto-electronic integrated system with “textile structure”, we propose here another integrated system-concept of flexible electronics based on “braid structure”. The braid integrated system forms electronic equipment constructed by the filamentous body. Opto-electronic integrated circuits are constructed with Kumihimo-structure by weaving more than three threads on which various devices, and components, such as, transistors, photoelectric transducers, contact-electrodes, pads for wiring and other passive components of circuits are mounted periodically.

From the experience of the designing of some basic logic circuits, the Kumihimo-structure weaved by eight-threads of two groups is proposed as a basic structure of the integrated circuit for application to single track braid system. Characteristics and elemental technologies of the braid system are analyzed for the extension of the concept. Application area of the system and requirements for the system are discussed. The braid system is also discussed in flexible electronics concept.
Degradation of MEH-PPV due to Oxygen/Moisture Traps through C-V Analysis and Attenuated Total Reflection IR Spectroscopy
Authors: Khillan R. K. , Su Y. , Varahramyan K.
Published: April 2011

We present the studying of oxygen and moisture traps in MEH-PPV through the MIS Capacitance – Voltage (C-V) analysis, and the Attenuated Total Reflection Infrared (ATR IR) spectroscopy technique. The presence of oxygen studied by ATR IR has also been verified by optical images from high resolution optical microscope. In quasi-static C-V measurements of the MIS (Al/MEH-PPV/p-Si) capacitors made, an extension of the weak inversion region was measured before strong inversion, which becomes more pronounced with aging. This increase in the weak inversion region is attributed to electron trapping by oxygen to form negative ions in the MEH-PPV layer. ATR IR spectroscopy shows the formation of carbonyl peak at 1651 cm−1 with aging, which is due to the presence of oxygen. Both the C-V analysis and Attenuated Total Reflection IR Spectroscopy are powerful tools for investigating the degradation of MEH-PPV polymer.
Large area p-i-n flexible image sensors
Authors: Vieira M. , Louro P. , Fernandes M. , Schwarz R. , Schubert M.
Published: April 2011

Large area p-i-n image sensors deposited on plastic substrates were produced at low temperatures (110 °C) by PE-CVD and compared with similar sensors deposited on glass substrates. The same sensing element structure ZnO:Al/p(SiC:H)/i(Si:H)/n(SiC:H)/Al was used for both devices. In this work the efforts are focused mainly on the optimization of the output characteristics of the sensor when fabricated on plastic substrates. The role of the sensor configuration and readout parameters in the image acquisition process is analyzed. The optical- to-electrical transfer characteristics show a reasonable quantum efficiency under a red light pattern, broad spectral response, and reciprocity between light and image signal.

First results show that the sensors deposited on flexible substrate present smaller light to dark sensitivity than those deposited on glass. In both, the non ohmic behavior of the transparent conductive oxide front contact blocks the carrier collection and leads to a surprising linear dependence of the image signal with the applied voltage.
Resolving Orientation Correlations in Deformation Structures by EBSD
Authors: Pantleon Wolfgang
Published: April 2011

For visualization of orientation inhomogeneities in crystalline material orientation imaging maps are conventionally used, with different colors representing different orientations. Two different approaches are proposed to extract more information from the orientation data on deformation structures gathered by electron back-scattering diffraction. First, a statistical approach is introduced for obtaining the chord length distribution of a grain structure and, secondly, an evaluation scheme is presented to resolve the details of the deformation structure within individual grains.
Ca2RuO4Thin Film Growth by Pulsed Laser Deposition
Authors: Wang Xu , Xin Yan , Lee Hanoh , Stampe Patricia A. , Kennedy Robin J. , Zhou Zhixian , Zheng Jim P.
Published: April 2011

Bulk Ca2RuO4 is an antiferromagnetic Mott insulator with the metal-insulator transition above room temperature, and the Neel temperature at 113 K. There is strong coupling between crystal structures and magnetic, electronic phase transitions in this system. It exhibits high sensitivity to chemical doping and pressure that makes it very interesting material to study. We have epitaxially grown Ca2RuO4 thin films on LaAlO3 substrates by pulsed laser deposition technique. Growth conditions such as substrate temperature and O2 pressure were systematically varied in order to achieve high quality single-phase film. Crystalline quality and orientation of these films were characterized by X-ray diffractometry. Microstructure of the thin films was examined by transmission electron microscopy. The electrical transport properties were also measured and compared with bulk single crystal.
Piezoelectric – Ferromagnetic Interface Engineering for Voltage Driven Coercivity Changes
Authors: Eyckmans Wouter , Borghs Gustaaf , Boeck Jo De
Published: April 2011

Ferromagnetic thin films were combined with piezoelectric substrates with the purpose of obtaining voltage controllable magnetization behavior. The interface between the ferromagnetic and piezoelectric material was examined for optimized voltage controlled magnetic response. Magneto Optic Kerr Effect (MOKE) measurements, supported by atomic force microscopy (AFM), showed the need to polish the piezoelectric substrates to a roughness below 1nm RMS (1*1νm2scan) for a minimum coercivity of 3kA/m. The magnetic anisotropy dependence on deposition, and anneal temperature was determined, and was shown to cause temperature driven coercivity changes up to 45 A/Km. A buffer layer between the piezoelectric substrate and the ferromagnetic thin film doubled the relative importance of the voltage driven magnetic effects.
Zinc oxide nanocluster formation by low energy ion implantation
Authors: Muntele I. , Thevenard P. , Muntele C. , Chhay B. , Ila D.
Published: April 2011

Variable size nanocluster embedded in silicon substrate were obtained by low energy implantation methods. We used optical spectroscopy to measure the optical properties of the implanted samples. The implantation parameters like the ions energy, dose and sputtering rate were calculated with SRIM [13]. Most of the implanted Zn ions (83%) clustered and oxidized during the implantation process, with the remaining 17% being oxidized during annealing in air.
Electrical Properties of ZnO Thin Films Deposited by Pulsed Laser Deposition.
Authors: Heluani S. P. , Simonelli G. , Villafuerte M. , Juarez G. , Tirpak A. , Braunstein G. , Vignolo F.
Published: April 2011

Structural and electronic transport properties of polycrystalline ZnO thin films, prepared by pulsed laser deposition, have been investigated. The films were deposited on glass and Si3N4/Si substrates using O2 and N2 atmospheres. X-ray analysis revealed preferential c-axis orientation perpendicular to the sample substrate. Films deposited under relatively high O2 pressure were highly resistive. However, the conductivity σ increased while the films were irradiated with ultraviolet light, showing an Arrhenius (In σ ∝ T-1) dependence as a function of temperature. The ZnO film deposited in N2 atmosphere exhibited at room temperature a resistivity ∼ 1 Ω cm, and a sheet carrier concentration ∼ 5 1012 cm-2. The variation of the conductivity with temperature, in the range 60 – 150 K, follows a In σ ∝ T-1/4 dependence characteristic of variable range hopping. An analysis of the experimental results of conductivity as a function of temperature, in terms of possible doping effects, as well as conduction mechanisms is presented.
Dispersion Engineering of Three-Dimensional Silicon Photonic Crystals: Fabrication and Applications
Authors: Venkataraman Sriram , Schneider Garrett , Murakowski Janusz , Shi Shouyan , Prather Dennis W.
Published: April 2011

In this paper, we propose the design and fabrication of buried silicon optical interconnect technology, the sub-surface silicon optical bus (S3B). The proposed approach relies on engineering the dispersion properties of embedded silicon three-dimensional photonic crystals to create sub-micron routing channels and control light propagation. Further, we present a method for the fabrication of buried three-dimensional (3D) photonic-crystal structures using conventional planar silicon micromachining. The method utilizes a single planar etch mask coupled with time-multiplexed, sidewall-passivating, deep anisotropic reactive-ion etching, to create an array of spherical voids with three-dimensional symmetry. Preliminary results are presented that demonstrate the feasibility of realizing chip-scale optical interconnects using our proposed approach.
Growth of Nonpolar (1100) Films and Heterostructures by Plasma-Assisted Molecular Beam Epitaxy
Authors: Brandt Oliver , Sun Yue Jun , Ploog Klaus H.
Published: April 2011

We discuss the growth of M-plane GaN films and (In, Ga)N/GaN multiple quantum well (MQW) structures on LiAlO2(100) substrates by plasma-assisted molecular beam epitaxy. The adsorption and desorption kinetics of Ga on M-plane GaN is studied by reflection high-energy electron diffraction, allowing us to identify the optimum growth conditions with regard to surface morphology. Furthermore, we investigate the compositional profile of M-plane (In, Ga)N/GaN MQWs grown under conditions resulting in comparatively abrupt interfaces. The results demonstrate that significant In surface segregation occurs for the case of M-plane (In, Ga)N. The dependence of the transition energies of the M-plane MQWs on the actual well thickness reveals, however, that the structures are indeed free of electrostatic fields along the growth direction.
Dependence of the E2 and A1(LO) modes on InN fraction in InGaN epilayers
Authors: Hernández S. , Cuscó R. , Artús L. , O'Donnell K.P. , Martin R.W. , Watson I.M. , Nanishi Y. , Kurouchi M. , Van der Stricht W.
Published: April 2011

The behavior of the E2 and A1(LO) optical phonons in Inx Ga1-x N has been analyzed by Raman scattering over the whole composition range. The frequencies of the E2 and A1(LO) modes decrease with increasing InN fraction. These modes display a significant broadening for an InN fraction of ≈ 60% and their linewidth decreases towards both ends of the composition range as a consequence of reduced cation disorder. Our results show a one-mode behavior for both E2 and A1(LO) modes of InGaN.
Thermally stable transparent Ru-Si-O Schottky contacts for n-type GaN and AlGaN
Authors: Kaminska E. , Piotrowska A. , Golaszewska K. , Lukasiewicz R. , Szczesny A. , Kowalczyk E. , Jagodzinski P. , Guziewicz M. , Kudla A. , Barcz A. , Jakiela R.
Published: April 2011

We have developed the deposition and studied the electrical characteristics and thermal reliability of Ru-based contacts on n- type GaN as well as on AlGaN/GaN heterostructure. Amorphous, conducting and transparent RuSiO4 contacts with their extremely low reverse currents and thermal stability up to 900°C, show great potential for use as Schottky contacts to n-type GaN and gate electrodes for AlGaN/GaN HEMT in high temperature, high power applications as well as in UV detectors.
Fabrication and characterization of GaN nanopillar arrays
Authors: Wang Y.D. , Tripathy S. , Chua S.J. , Fonstad C.G.
Published: April 2011

Various nanofabrication technologies are currently under investigation to realize fine patterning of III-Nitrides. Dry and wet etching techniques have been explored in the past for the fabrication of GaN-based devices. However, due to etch-induced damage, it is still a major challenge to achieve high-quality GaN-based nanostructures with high aspect ratio. In this study, GaN nanopillars were fabricated by inductively coupled plasma etching (ICP) using anodic aluminium oxide (AAO) as a mask. High-spatial resolution optical techniques were employed to characterize these pillar arrays. The average diameter and length of these pillars are about 60–70 nm and 350–400 nm, respectively. Low temperature micro-photoluminescence spectra show a red shift compared with the spectrum recorded from the as-grown GaN, indicating stress relaxation in these nanopillars. The evidence of good crystalline quality is also confirmed by micro-Raman measurement where red shift of the E2(TO) mode from GaN nanopillars suggest partial relaxation of the compressive strain.
Strong room temperature 510 nm emission from cubic InGaN/GaN multiple quantum wells
Authors: Li S.F. , As D.J. , Lischka K. , Pacheco-Salazar D.G. , Scolfaro L.M.R. , Leite J.R. , Cerdeira F. , Meneses E.A.
Published: April 2011

Cubic InGaN/GaN double heterostructures and multi-quantum-wells have been grown by Molecular Beam Epitaxy on cubic 3C-SiC. We find that the room temperature photoluminescence spectra of our samples has two emission peaks at 2.4 eV and 2.6 e V, respectively. The intensity of the 2.6 eV decreases and that of the 2.4 eV peak increases when the In mol ratio is varied between X = 0.04 and 0.16. However, for all samples the peak energy is far below the bandgap energy measured by photoluminescence excitation spectra, revealing a large Stokes-like shift of the InGaN emission. The temperature variation of the photoluminescence intensity yields an activation energy of 21 meV of the 2.6 eV emission and 67 meV of the 2.4 eV emission, respectively. The room temperature photoluminescence of fully strained multi quantum wells (x = 0.16) is a single line with a peak wavelength at about 510 nm.
X-ray characterization of GaN single crystal layers grown by the ammonothermal technique on HVPE GaN seeds and by the sublimation technique on sapphire seeds
Authors: Raghothamachar Balaji , Dudley Michael , Wang Buguo , Callahan Michael , Bliss David , Konkapaka Phanikumar , Wu Huaqiang , Spencer Michael
Published: April 2011

Single crystal GaN substrates are a more reliable, efficient and low cost alternative to sapphire and SiC substrates that are currently being used for developing nitride based devices such as LEDs, high power FETs and laser diodes. GaN growth by two techniques are investigated here. In ammonothermal growth (analogous to hydrothermal growth which is commonly used for quartz), using potassium and lithium amide as mineralizers and GaN powders and vapor grown polycrystals as nutrients, thick GaN single crystal layers have been grown on both faces of (0001) HVPE GaN seeds in nickel based autoclaves. In GaN sublimation growth, Ga is transported under a temperature gradient in an ammonia atmosphere from a GaN powder source to the sapphire substrate which has a 3–6 micron GaN epilayer deposited on it. Synchrotron white beam x-ray topography (SWBXT) was initially used to image the defect structures in the layers. High resolution x-ray diffraction experiments were also carried out and reciprocal space maps were recorded from the grown GaN layers. Characterization results will be discussed with respect to the growth conditions.
The intrinsic free carrier mobility in AlGaN/GaN quantum wells
Authors: Carosella F. , Germain M. , Farvacque J.-L.
Published: April 2011

The aim of this contribution is to determine theoretically the maximum mobility that can be expected in AlGaN/GaN quantum wells as soon as the free carriers are only submitted to intrinsic scattering mechanisms associated with phonons and the carrier-carrier interaction. In our model, we consider that the carrier-carrier two bodies collisions do not constitute by themselves a relaxation mechanism since they conserve the momentum and the energy of the electron system. Thus, we assume that the free carriers act only through their contribution to the dynamical dielectric response of the material and, at least, through their collective behavior resulting into plasmons which, when damped, constitute now a real relaxation mechanism. The full scattering strength is connected with the imaginary part of the total reversed dielectric function including the lattice and the free carrier contributions. This approach automatically includes the scattering mechanisms associated with hybrid phonon/plasmon particles.
Synthesis of Microcrystalline Silicon Films by Low Energy Electron-Beam-Induced Deposition at Cryogenic Temperature
Authors: Sato Tetsuya , Nakagawa Kiyokazu , Aoki Yutaka , Sato Shouji
Published: April 2011

We have proposed an advanced method for formation of semiconductor thin films at substrates temperatures below 100K. We have synthesized amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) films using low-energy electron-beam-induced-chemical vapor deposition (EBICVD) onto cooled substrates which adsorb source gases (SiH4 or Si2H6) at cryogenic temperature. The temperature dependence on growth rate of the films, hydrogen content and optical constants were investigated. The μc-Si:H could be formed at 40–45 K on SiO2 using He-discharged-EBICVD with SiH4. The crystallinity of silicon was evaluated by Raman scattering spectroscopy and X-ray diffraction.
Si1-xGex Nanocrystals Observed by EFTEM: Influence of the Dry and Wet Oxidation Process
Authors: Cuadras A. , Arbiol J. , Garrido B. , Morante J.R , Rodriguez A. , Rodríguez T.
Published: April 2011

We report about the formation of Si1-xGex nanocrystals (NC) in an oxide matrix after oxidizing a polycrystalline Si0.7Ge0.3 layer in wet and dry conditions. We have characterized the NC by Energy Filtered Transmission Electron Microscopy (EFTEM). EFTEM images analyses show the evolution of the oxidation of polycrystalline Si0.7Ge0.3 layer. We observe that a layer with Ge-rich nanoclusters is formed. For wet oxidations we find Ge-rich Si1-xGex nanocrystals while for dry oxidations Si is oxidized faster and Ge is completely segregated. Results are contrasted with infrared and Raman spectroscopies. In conclusion, wet oxidation seems to be preferable to oxidize polycrystalline Si1-xGex to obtain Ge-rich NC embedded in an oxide matrix, as both Ge and Si are oxidized, in contrast to dry oxidation, where Ge is mainly segregated.
Quasiballistic Electron Emission from Planarized Nanocrystalline-Si Cold Cathode
Authors: Tsuchiya Yoshishige , Nakatsukasa Takuya , Mizuta Hiroshi , Oda Shunri , Kojima Akira , Koshida Nobuyoshi
Published: April 2011

Mechanism of electron transport through planerized nanocrystalline-Si (nc-Si) cold cathode surface emitting devices was investigated. The energy distribution of electrons emitted from nc-Si emitter was obviously not Maxwellian, which was usually obtained at conventional cold cathode devices, but was similar to that from the nanocrystalline porous silicon diode emitter. These results strongly suggest that electrons are emitted quasiballistically from our devices and indicate that the planarized nc-Si layer play an important role in this high efficiency cold cathode emitter.
Surface Nitridation of Amorphous Carbon by Nitrogen Ion Beam Irradiation
Authors: Iwasaki Chihiro , Aono Masami , Kitazawa Nobuaki , Watanabe Yoshihisa
Published: April 2011

Amorphous carbon was irradiated with a nitrogen ion beam and changes in composition and tribological properties after surface nitridation have been studied. The nitrogen ion beam energy was varied from 0.1 to 2.0 keV under the constant ion current density. Composition and chemical bonding states near the surface were analyzed by X-ray photoelectron spectroscopy (XPS). Tribological properties were studied by a pin-on-disk type tribotester. XPS studies show that the nitrogen concentration near the surface increases after nitrogen ion irradiation. The depth profiles of nitrogen in the irradiated specimens display that the nitrogen concentration near the surface is maximized after 0.2 to 0.7 keV ion irradiation. From the pin-on-disk testing, it is found that the friction coefficient of amorphous carbon increases after irradiation by 1.5 keV nitrogen ions, while the friction coefficient does not change drastically after irradiation by 0.2 keV ions.
Simulations of Chemotaxis and Random Motility in Finite Domains
Authors: Jabbarzadeh Ehsan , Abrams Cameron F.
Published: April 2011

Rational design and selection of candidate porous biomaterials to serve as tissue engineering constructs rests on our ability to understand the influence of the porous microarchitecture on the transport of chemical species (e.g., nutrients and signaling compounds), fluid flow, and cellular locomotion and growth. We have begun to study the behavior of chemotactically mobile cells in response to unsteady signaling molecule concentration fields using a computational simulation-based model. The model couples fully time-dependent finite-difference solution of a reaction-diffusion equation for the concentration field of a generic chemoattractant to biased random walks representing individual moving cells. This model is a first step in building a quantitative, pore-level model of mass and cellular transport in porous tissue-engineered constructs. In these proceedings, we focus on our recent findings regarding the influence of flux-reactive boundary conditions in heterogeneous 2D domains on the chemotactic response of otherwise randomly moving cells. In particular, we find that, when cells are forced to “crawl” around obstacles in order to approach a point source of chemoattractant, the reactivity of the obstacle surface with respect to the chemoattractant strongly determines the morphology of the cells' paths of locomotion. Cells crawl along non-reactive surfaces and strongly avoid reactive surfaces, due to the nature of the chemoattractant concentration gradients near the surface. We show further that tuning the reactivity of the surfaces of two obstacles defining a gap can control the passage of cells through the gap. From our work, we infer the importance of a proper treatment of boundary conditions in any future pore-level quantitatve modeling of mass transport and cellular response in porous media.
Nanoscale RGD Peptide Organization Regulates Cell Proliferation and Differentiation
Authors: Hsiong Susan , Yong Lee Kuen , Alsberg Eben , Mooney David
Published: April 2011

RGD (arginine-glycine-aspartic acid) containing peptide sequences, common cell attachment sites present in many extracellular matrix (ECM) proteins, mediate many important cellular processes. The role of nanoscale organization of RGD peptides in the regulation of the adhesion, proliferation and differentiation of both preosteoblasts (MC3T3-E1) and multipotential (D1) cell lines in vitro was investigated in this study. Alginate polymer chains with varying RGD peptide degree of substitution were mixed with unmodified polymer chains at different ratios to allow variation of RGD peptide spacing in the nanometer scale, independently of the overall bulk density of peptides presented from the material. Proliferation of both cell types was observed to be closely correlated to RGD island (defined as a cluster of RGD peptides) spacing, independently of overall bulk ligand density, following cell adhesion to alginate hydrogels. Increased RGD island spacing was observed to promote spreading of MC3T3-E1 cells while simultaneously suppressing their proliferation. However, increased RGD island spacing decreased spreading of D1 cells while also decreasing proliferation. Moreover, differentiation of preosteoblasts was significantly upregulated in response to decreased RGD island spacing, whereas differentiation of multipotential cells was modestly regulated by this variable. These results demonstrate that the nanoscale organization of adhesion ligands may be an important variable in controlling cell phenotype and function. In addition, cellular responses to nanoscale ligand organization differ depending on the cell type, and this may be related to the differentiation stage of the cells.
Real-Time Salmonella Detection Using Lead Zirconate Titanate-Titanium Microcantilevers
Authors: McGovern John-Paul , Shih Wan Y. , Shih Wei-Heng , Sergi Mauro , Chaiken Irwin
Published: April 2011

Current methods for analysis of unknown powders in suspicious packages involve sending samples to laboratory facilities where a variety of time-consuming tests are performed. We have developed and investigated the use of a lead zirconate titanate - titanium (PZT-Ti) microcantilever for in situ detection of the common food- and water-born pathogen, Salmonella typhimurium. Using a bifunctional linking molecule to immobilize antibody on the titanium surface of the microcantilever, we can directly detect salmonella cells in suspensions of differing concentration. This novel surface functionalization technique along with the sub-nanogram sensitivity of the cantilever has allowed for direct quantification of S. typhimurium cells in suspension.
Layer-by-layer printing of cells and its application to tissue engineering
Authors: Kesari Priya , Xu Tao , Boland Thomas
Published: April 2011

Tissues and organs exhibit distinct shapes and functions nurtured by vascular connectivity. In order to mimic and examine these intricate structure-function relationships, it is necessary to develop efficient strategies for assembling tissue-like constructs. Many of the top-down fabrication techniques used to build microelectromechanical systems, including photolithography, are attractive due to the similar feature sizes, but are not suitable for delicate biological systems or aqueous environments. A layer-by layer approach has been proposed by us to pattern functional cell structures in three dimensions. Freeform cell structures are created by the inkjet method, in which cells are entrapped within hydrogels and crosslinked on demand. The cells are viable, functional and show potential for cell maturation as exemplified by the diversion of hematopoietic stem cells into multiple cell types. These results show promise for many tissue engineering applications.
Infrared Emitting Dye and/or Two Photon Excitable Fluorescent Dye Encapsulated in Biodegradable Polymer Nanoparticles for Bioimaging
Authors: Baba Koichi , Ohulchanskyy Tymish Y. , Zheng Qingdong , Lin Tzu-Chau , Bergey Earl J. , Prasad Paras N.
Published: April 2011

Near infrared fluorescent dyes have a significant potential in biological applications. However, many of these organic dyes are hydrophobic and/or their fluorescence is quenched in aqueous media. Nanoparticle technology has been utilized to overcome the hydrophobic property of these dyes, but there remain problems in their fabrication. To overcome these problems, a novel fabrication technique for incorporating hydrophobic dyes in a biodegradable polymer nanoparticle has been developed. An infrared emitting dye (D1) and a two photon excitable fluorescent dye (BT101) were selected as prototypic dyes for incorporation. The D1 nanocrystal dye shows quenched emission in aqueous media. Upon encapsulation in a polymeric nanoparticle, its emission at 1.1 to 1.35 μm was recovered. BT101 dye doped nanoparticles demonstrated significant increase in fluorescent yield in aqueous media as compared to the free dye. In addition, several different sizes of BT101 doped polymer nanoparticles were fabricated (c.a. 35 nm to 100 nm in size). The fluorescence intensity was found to increase with the particle size. The investigation of uptake of BT101 nanocrystal and BT101 doped PLGA nanoparticles by culture cells revealed the importance of polymer coating of dye for efficient cell imaging.