bluuebunny/crossref_metadata_2025 huggingface dataset:
Flexible magnetics on plastic substrates: magnetic lithography, magnetic nanostructures and other applications
Authors: Bandić Z. Z. , Albrecht T.R. , Bonhote C. , Katine J. , Rooks M.
Published: April 2011

Flexible Magneticsencompases the design, fabrication and characterization of magnetic devices and systems built on thin flexible substrates. Although device and system functionality is magnetic in nature, flexible magnetics draws interesting parallels to flexible electronics, especially in the challenge of fabrication on plastic substrates. Some of those challenges include substrate surface quality and maximum processing temperature, tooling issues related to mechanical properties of flexible substrates, adhesion of thin films deposited on plastics, as well as thermal stability of fabricated devices.

One application of flexible magnetics relevant to the information storage industry is magnetic lithography. Magnetic lithography is a process qualitatively analogous to contact optical lithography. Magnetic lithography transfers information from a patterned magnetic mask (analogous to the optical photomask) to magnetic media (analog of the photoresist), and is interesting for applications in rapid, parallel magnetic recording. The magnetic mask consists of patterned magnetically soft material (FeNiCo, FeCo) on a thin flexible plastic substrate, typically Polyethylene Teraphtalate (PET) or polyimide. When uniformly magnetized media is brought into intimate contact with the magnetic mask, an externally applied magnetic field selectively changes the magnetic orientation in the areas not covered with the soft magnetic material. The flexible magnetic mask offers superior compliance to contaminated or nonplanar magnetic media. We discuss nanofabrication challenges of magnetic masks on plastic substrates, including electron beam lithography, electroplating and lift-off processing on the nanometer scale, adhesion of metal thin films on PET and polyimide substrate, and release of plastic films from the rigid substrates used during the processing. We present results on fabricated magnetic masks, and magnetic force microscopy images of the magnetic transition patterns.

Besides fabrication of magnetic nanostructures and devices on plastic substrates, we also present our results on nanoscale patterning of plastic thin film. We will present our results on fabrication of sub-100 nm scale nanochannels in polyimide films, as well as self-assembly of ordered arrays of polyimide nanodots. Nanoscale patterned plastic films are interesting for the potential application in magnetic lithography, as well as for the application in micro- and nanofluidics, due to the mechanical flexibility and biological inertness of plastic materials. We will discuss interesting biosensing systems that may result from the combination of magnetic functionality, electronic control and patterned nanofludic channels on plastic substrates.
Enhancement of the Electrical Properties of ITO Deposited on Polymeric Substrates by Using a ZnO Buffer Layer
Authors: Fortunato E. , Gonçalves A. , Carvalho C. Nunes de , Pimentel A. , Lavareda G. , Marques A. , Martins R.
Published: April 2011

In this paper we present the effect of the insertion of a non-doped nanocrystalline zinc oxide/buffer layer on the electrical, optical and structural properties of indium tin oxide produced at room temperature by radio frequency plasma enhanced reactive thermal evaporation on polymeric substrates. The electrical resistivity of the ITO films is reduced by more than two orders of magnitude (4.5×10−1 to 2.9×10−3 ωcm). From the Hall effect measurements it is observed that the large decrease associated to the electrical resistivity, is due to the increase associated to the Hall mobility. Concerning the optical properties no effect was observed, being the transmittance in the visible and near the infra red region always higher than 80%.
A method for in-situ measurements of the growth in the bulk of deformed single crystals at the 3DXRD microscope
Authors: Schmidt S. , Jensen D. Juul
Published: April 2011

With the Three Dimensional X-ray Diffraction microscope (3DXRD) located at the European Synchrotron Radiation Facility (ESRF) full 3D spatial information of grains in the interior of a sample can be measured non-destructively. In this paper we discuss the possibility of an extension to this scenario, namely in-situ annealing studies, where the 3D spatial grain shape can be monitored as function of time. Consequently, local boundary migration rates can be estimated and compared to the deformed microstructure. Such information may reveal to what extend the deformed microstructure influences the growth of a grain during recrystallization.
The General Synthesis of Nanostructured V/VI Semiconductors
Authors: Christian Paul , O'Brien Paul
Published: April 2011

Semiconductors in the V/VI series have band gaps ranging from 2.2 eV for Sb2S3 to 0.21 eV for Bi2Te3 spanning the range seen from conventional mid to narrow band gap materials to semi-metals. These materials, especially those with narrower band gaps, demonstrate thermo-electric properties and are used in Peltier devices. There are examples in the literature of the synthesis of several of these materials in a nanostructured form, however the reactions often rely on highly toxic reagents, especially in the case of tellurium containing materials. Further more there are no reports of general routes applicable to all three chalcogenides.

In this paper we describe a general method for the synthesis of chalcogenide V/VI nanomaterials by the reaction of acetate salts with the corresponding chalcogenide under reflux conditions in long chain alkyl amines, typically octylamine or dodecylamine. The effect of temperature and capping agent on the morphology of the final product are discussed and in particular the synthesis of Bi2S3 nanorods, Bi2Se3 and Bi2Te3 nanowafers and Sb2Se3 nanowires are described.
Prospect for III-Nitride Heterojunction MOSFET Structures and Devices
Authors: Johnson M. A. L. , Barlage D. W. , Braddock Dave
Published: April 2011

Heterojunction field effect transistors (HFET) for high-frequency and high-power electronics have been an area of active research in recent years as a key enabling technology for applications ranging from wireless communications to power distribution. III-Nitride semiconductors are a leading candidate for fulfilling the material requirements of these devices based on the combination of large bandgap energy, high thermal conductivity, high electron mobility and saturated electron velocity. While III-Nitride HFETs have demonstrated remarkable advances, serious materials related limitations still exist, primarily related to charge states and trapping effects at the semiconductor surface. Several groups have investigated solutions such as the deposition of dielectric passivation layers and asymmetric field-plate gate geometries for controlling the influence of trap states near the metal/semiconductor FET interface. We have demonstrated a metal-oxide semiconductor FET (MOSFET) with a substantially unpinned interface which is capable of establishing substantial charge accumulation under the gate. These III-Nitride MOSFETs may be designed to operate in either depletion mode or enhancement mode. GaN/InGaN heterojunction MOSFETs exhibit enhancement mode peak transconductance at gate voltages Vg>+5V, corresponding to energy greater than the bandgap of the underlying semiconductor which provides strong evidence of an unpinned MOS interface. Additionally III-Nitride MOSFETs eliminate the need for field plate gate structures as the electric field geometry in the gate-drain region changes limiting the tunneling of charge to unfilled surface states. In depletion mode, low-rf dispersion InGaN/GaN MOSFETs exhibit excellent microwave with ft = 8GHz for optically defined gates dimensions.

We review the history of compound semiconductor MOSFET development and overlaying these developments with recent advances in the III-Nitride materials and device research. Differences in chemistry of III-Nitrides relative to all other compound semiconductors and the epitaxial deposition of gate-oxides such as Gadolinium Gallium Oxide (GGO), opens the possibility for dramatically improved devices at microwave and mm-wave frequencies as well as power MOSFET rectifiers. Initial III-Nitride MOSFETs results are presented as well as a quaternary thermodynamic framework for the stability of gate-oxide on nitride semiconductors. We also identify key materials related research challenges expected to impact the ongoing development of III-Nitride MOSFETs.
Properties of Gallium Selenide Doped with Sulfur
Authors: Voevodin Valeriy G. , Bereznaya Svetlana A. , Korotchenko Zoya V. , Morozov Aleksandr N. , Sarkisov Sergey Yu. , Fernelius Nils C. , Goldstein Jonathan T.
Published: April 2011

This paper presents the results of investigations on the influence of sulfur doping on properties of gallium selenide crystals, grown by the Bridgman method from melts with sulfur content of 0.01–3 mass %, using the Hall effect, optical absorption, photoconductivity and microhardness measurements on GaSe: S. The results obtained are explained by assuming the formation of solid solutions of GaSxSe1−x and the presence of the competitive processes of point defects and structural disorder formation.
Nominal PbSe nano-islands on PbTe: grown by MBE, analyzed by AFM and TEM
Authors: Moeck Peter , Kapilashrami Mukes , Rao Arvind , Aldushin Kirill , Lee Jeahuck , Morris James E. , Browning Nigel D. , McCann Patrick J.
Published: April 2011

Nominal PbSe nano-islands were grown in the Stranski-Krastanow mode on (111) oriented PbTe/BaF2 pseudo-substrates by molecular beam epitaxy (MBE). The number density and morphology of these islands were assessed by means of atomic force microscopy (AFM). Transmission electron microscopy (TEM) was employed to determine the strain state and crystallographic structure of these islands. On the basis of both AFM and TEM analyses, we distinguish between different groups of tensibly strained islands. The suggestion is made to use such nano-islands as part of nanometrology standards for scanning probe microscopy.
Effect of GaN Surface Treatment on the Morphological and Optoelectronic Response of Violet Light Emitting Diodes
Authors: Jamil Muhammad , Grandusky James R. , Shahedipour-Sandvik Fatemeh
Published: April 2011

We report on the study of the effect of various surface chemical treatment processes of n-GaN template layers used for subsequent growth of light emitting diode (LED) structures. The treatment procedure included cleaning in organic solvents, organic solvents followed by 5 minutes of HCl, organic solvents and 5 minutes of HCl followed by 2 minutes and finally 10 minutes of HF treatment. Chemical, optical and electrical properties of the surfaces of GaN and InGaN-based LED structures were systematically investigated by x-ray photoemission spectroscopy (XPS), auger electron spectroscopy (AES), atomic force microscopy (AFM), photoluminescence (PL) and electroluminescence (EL) spectroscopy. GaN layers that were grown on the samples treated with HCl and HF showed dramatically different surfaces having high density of 3D structures with high roughness. As measured by AFM, growth of the LED structure on top of the GaN layer continued the 3D-growth mode. LED structures grown on the HCl and HF treated GaN template layers showed minimal to no PL and EL emission and failed after a short period. We suggest a qualitative model of the growth that could potentially explain the underlying phenomena leading to such pronounced changes in the optoelectronic properties and surface conditions of the LED structures due to the treatment of the initial template layers.
Moth-Eye Light-Emitting Diodes
Authors: Kasugai Hideki , Miyake Yasuto , Honshio Akira , Kawashima Takeshi , Iida Kazuyoshi , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu , Kinoshita Hiroyuki , Shiomi Hiromu
Published: April 2011

Nitride-based blue-light-emitting diodes having a moth-eye structure were fabricated on the backside of a 6H-SiC substrate. The light extraction efficiency and the corresponding output power were increased by 3.8 times compared with those of an LED having the conventional structure. The results of theoretical analysis agree with these findings.
Group III nitrides grown on 4H-SiC (3038) substrate by metal-organic vapor phase epitaxy
Authors: Honshio Akira , Kitano Tsukasa , Imura Masataka , Miyake Yasuto , Kasugai Hideki , Iida Kazuyoshi , Kawashima Takeshi , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu , Kinoshita Hiroyuki , Shiomi Hiromu
Published: April 2011

The heteroepitaxial growth of a GaN single crystal by metal-organic vapor phase epitaxy on a 4H-SiC (3038) substrate was demonstrated. The crystallographic orientation of GaN was found to be dependent on growth pressure. When the growth pressure was 1000 hPa, the orientation of the GaN single crystal was consistent with that of the SiC substrate, where the c-plane of the GaN was single crystal tilted 54.7° from the surface plane. Then, we fabricated a violet-light-emitting diode (LED) with a GaInN multiple-quantum-well (QW) active layer grown on the GaN layer, which coherently grew on the 4H-SiC (3038 ) substrate. The blue shift of the peak wavelength with increasing injection current of up to 100 mA was confirmed to be two times smaller than that of a conventional LED on a c-plane sapphire substrate due to a low internal polarization.
High-Frequency Generation in Low-Mobility Superlattices
Authors: Litvinov Vladimir , Manasson Alexander
Published: April 2011

We study the transport properties of miniband electrons in an electromagnetic field as related to the high-frequency generation in a semiconductor superlattice (SL). We study the regimes where the external ac-field is in resonance and out of resonance with the two lowest SL minibands.

In the diffusive quasi-static regime Bloch oscillations and electrical domains do not develop and high-frequency generation may occur as a result of the negative high-harmonic nonlinear conductivity. This regime is different from the frequency conversion in a stable nonlinear media. We point out that AlGaN/GaN material system has a great potential for the high-power SL terahertz (THz) source.
Metalorganic Chemical Vapor Deposition of Non-polar III-Nitride Films over a-plane SiC Substrates
Authors: Li Jiawei , Gong Zheng , Chen Changqing , Adivarahan Vinod , Gaevski Mikhail , Kuokstis Edmundas , Shatalov Maxim , Gao Ying , Zhang Zehong , Arjunan Arul , Sudarshan T. S. , Paul Maruska H. , Yang Jinwei , Asif M.
Published: April 2011

We report progress in growing non-polar a-plane III-nitride films and heterostructures over a-plane 4H-SiC. a-plane SiC is more closely lattice-matched to a-plane GaN than is r-plane sapphire. Consequently, better structural quality a-plane nitride films may result over a-plane SiC substrates. By migration enhanced metalorganic chemical vapor deposition (MEMOCVD), an atomically smooth (1120)AlN layer with RMS roughness of 0.3nm was obtained. From the results of XRD, the structural defects in the AlN layer on SiC substrates were strongly reduced compared to those grown on r-plane sapphire. Also by applying our selective area lateral epitaxy (SALE) growth procedure, we achieved high structural and optical quality a-plane GaN films on 4H-SiC with RMS roughness only 0.4nm. Therefore, non-polar III-nitride films and heterostructures on SiC substrates are promising building blocks for realizing high performance polarization-free devices.
Determination of surface barrier height and surface state density in GaN films grown on sapphire substrates
Authors: Park Seong-Eun , Kopanski Joseph J. , Kang Youn-Seon , Robins Lawrence H. , Shin Hyun-Keel
Published: April 2011

Photoreflectance (PR) modulation spectroscopy was performed to investigate surface properties of GaN films grown on sapphire substrates. From the period of the Franz-Keldysh oscillations, the surface electric field across the GaN space charge region was found to be (197 ± 11) kV/cm, which corresponds to a surface state density of 1.0×1012 cm−2. A surface barrier height of 0.71 eV was determined by fitting the dependence of the PR intensities on pump beam power density. We suggest that a deep level is formed at 2.68 eV above the GaN valence band edge due to the large density of surface states.
Excess Carrier Lifetime Measurements for GaN on Sapphire Substrates with Various Doping Concentrations and Surface Conditions by the Microwave Photoconductivity Decay Method
Authors: Kato Masashi , Watanabe Hideki , Ichimura Masaya , Arai Eisuke
Published: April 2011

We have measured excess carrier lifetimes in GaN with various doping concentrations and surface conditions by the microwave photoconductivity decay method. GaN samples were grown by metalorganic chemical vapor deposition (MOCVD) without intentional doping and with Si doping or Mg doping on a-face sapphire substrates. By using the microwave photoconductivity decay method, we obtained 1/e excess carrier lifetimes of larger than 50 μs for the Si doped and undoped GaN and of less than 10 μs for the Mg doped GaN. We changed surface conditions for the samples by the inductively coupled plasma (ICP) etching and investigated effects of surface conditions on the carrier recombination behavior. The ICP etching has negligible effects on carrier lifetime in the Si doped GaN. On the other hand, in the undoped GaN, the ICP etching lengthened the carrier lifetime compared with the as-grown sample. On the contrary, the ICP etching shortened the carrier lifetime in the Mg doped GaN. The ICP etching seems to form hole traps and recombination centers at GaN surfaces and thus the carrier lifetime became longer in the undoped GaN and shorter in the Mg doped GaN.
Influence of Mis-Orientation of C-plane Sapphire Substrate on the Early Stages of MOCVD Growth of GaN Thin Films
Authors: Kim Seong-woo , Aida Hideo , Suzuki Toshimasa
Published: April 2011

We have studied the early stages of GaN growth to realize the growth mechanism of GaN thin films on mis-oriented sapphire substrates which affects the surface and crystal quality of GaN thin films. As the result, it was found that the larger mis-orientation angle helps the growth of the larger grain of GaN and leads to the earlier shift of growth mode from 3D to 2D. The AFM observation of closed-coalesced GaN thin films revealed the difference in the micro-step structures by the mis-orientation angle of sapphire substrate. The result of x-ray rocking curve as a function of mis-orientation angle well matched with the microstructure of GaN surface, indicating that the larger mis-orientation angle helps the column ordering of GaN crystals.
Mechanisms of Raman Scattering in doped Indium Nitride
Authors: Pinquier Claire , Demangeot François , Frandon Jean , Gaio Miguel , Briot Olivier , Maleyre Bénédicte , Clur-Ruffenach Sandra , Gil Bernard
Published: April 2011

Highly n-doped InN layers are investigated by means of Raman scattering: a strong mode is evidenced near the frequency of the A1(LO) phonon, despite the high conductivity of the films. This observation is interpreted assuming the breakdown of the wave-vector conservation leading to the decoupling of the plasmon from the phonon. The lineshape of the longitudinal optical mode is simulated using the Lindhard-Mermin dielectric function for various light scattering processes: we found that the charge density fluctuation mechanism is dominant, at least in the visible excitation range.
Recombination Mechanism in Short-Wavelength GaN/AlGaN Quantum Wells
Authors: Fuhrmann D. , Retzlaff T. , Rossow U. , Hangleiter A.
Published: April 2011

To date, light emission by AlGaN-based heterostructures and LED's operating in the ultraviolet region is far less efficient than emission from longer wavelength structures based on GaInN. We have realized GaN/AlGaN quantum well structures emitting in the 360–320 nm range with peak room-temperature internal efficiencies reaching more than 20 %. From detailed studies of the temperature and excitation power dependence of the efficiency we find that excitons play a crucial role enhancing radiative recombination in such structures. Except for the peak internal efficiency, which reaches 73 % in GaInN/GaN, the overall behavior in GaN/AlGaN and GaInN/GaN is very similar, suggesting that the main difference is the nonradiative recombination mechanism.
Influence of Substrate Misorientation Angle and Direction in Growth of GaN on Off-axis SiC (0001)
Authors: Suda Jun , Nakano Yuki , Kimoto Tsunenobu
Published: April 2011

Growth of GaN on 4H- or 6H-SiC (0001) Si-face substrates with various misorientation angles and directions is presented. GaN layers were directly grown on the SiC substrates by molecular-beam epitaxy using elemental Ga and rf plasma-excited active nitrogen. First, 4H-SiC (0001) 8°-off toward the [11–20] direction was investigated. Before the growth of GaN, ex-situ high-temperature gas etching was carried out, resulting in a smooth SiC initial surface. However, the surface of the subsequently grown GaN layer has wavy features with peak-to-valley height of 30 nm. Since the direction of the undulations is parallel to the misorientation direction, this feature must originate from the substrate misorientation. Step bunching and large faceting along <01–10> and <10–10> directions occurred during the growth of GaN. Lowering the growth temperature suppresses large faceting, and results in reduction of the peak-to-valley height to 3 nm. However, the surface still has the same undulating features on a smaller length scale. On the other hand such morphology was not observed for GaN grown on (0001) on-axis SiC substrates (misorientation < 0.3°). The influence of the polytype of the SiC substrate and the misorientation angle and direction are also discussed.
Optical activation of Si nanowires using Er-doped sol-gel derived silica
Authors: Suh Kiseok , Park Oun-Ho , Bae Byeong-Soo , Lee Jung-Chul , Choi Heon-Jin , Shin Jung H.
Published: April 2011

Optical activation of Si nanowires (Si-NWs) using sol-gel derived Er-doped silica is investigated. Si-NWs of about 100 nm diameter were grown on Si substrates by the vapor-liquid-solid method using Au catalysts and H2 diluted SiCl4. Afterwards, Er-doped silica sol-gel solution was spin-coated, and annealed at 950 °C in flowing N2/O2 environment. Such Er-doped silica/Si-NWs nanocomposite is found to combine the advantages of crystalline Si and silica to simultaneously achieve both high carrier-mediated excitation efficiency and high Er3+ luminescence efficiency while at the same time providing high areal density of Er3+ and easy current injection, indicating the possibility of developing sol-gel activated Si-NWs as a new material platform for Si-based photonics.
Computer Simulation of Charging and Erasing Transients of a Ge/Si Hetero-nanocrystal-based Flash Memory
Authors: Zhao Dengtao , Zhu Yan , Li Ruigang , Liu Jianlin
Published: April 2011

The transient process of the programming and erasing is very important for a nanocrystal-floating-gate flash memory. In this work, a computer simulation was carried out to investigate the charging, retention and erasing processes of our proposed Ge/Si hetero-nanocrystal floating gate flash memory. The transient gate current, the transient drain current and the average charge in one dot were simulated respectively. Evident hysteresis features can be observed in the transient processes in a voltage-sweeping measurement mode. While measuring the transient process in a constant voltage mode, the time decay of transient current and charge are weakened if Ge is used on the Si dot, indicating a longer retention time for Ge/Si-floating-gate flash memory.
Fabrication and Electrical Characterization of Silicon Nanowire Arrays
Authors: Dilts Sarah M. , Mohmmad Ahmad , Lew Kok-Keong , Redwing Joan M. , Mohney Suzanne E.
Published: April 2011

High density boron-doped silicon nanowire arrays were fabricated within the pores of anodized alumina membranes via vapor-liquid-solid (VLS) growth Anodized alumina membranes with a nominal pore diameter of 200 nm served as templates for the sequential electrodeposition of silver, cobalt, and gold which served as the backside electrical contact, ohmic contact metal and catalyst metal for VLS growth, respectively. Boron-doped silicon nanowires were then synthesized within the pores by VLS growth using silane (SiH4) and trimethylboron (TMB) gas sources. Arrays of Al dots were deposited on the top surface of the membrane after nanowire growth. A series of samples was prepared with different SiNW lengths and boron doping levels. Two point probe measurements were used to measure the I-V characteristics of the silicon nanowire arrays before and after annealing. Nanowire resistivity and contact resistance were determined from plots of resistance versus nanowire length. The resistivity of the SiNW was observed to decrease with the addition of TMB during growth.
Photochemical Deposition of Transparent Low Refractive Index SiO2 Topcoat for Laser Head at Room Temperature
Authors: Tezuka Y. , Murahara M.
Published: April 2011

A transparent, low refractive index SiO 2 film was photo-chemically laminated on a glass slab laser head by the Xe2* excimer lamp in the atmosphere of NF3 and O2 mixed gas at room temperature; which made it possible to inhibit the decrease in the laser output power caused by the evanescent wave leakage.

The transparent SiO2 film of 260nm thickness was laminated on the non-heated substrate by the lamp irradiation for one hour. The hardness of the film before annealing was 3 by Mohs’ Scale of Hardness, and its hardness improved to 5 after annealing at 250 degrees centigrade for one hour. The refractive index of the film was 1.42, being lower than the index of silica glass that is 1.46. Furthermore, the transmittance in the visible region increased by 2% with it s antireflection coating.
Structural Nanocomposite Bonding Reinforced by Graphite Nanofibers with Surface Treatments
Authors: Roy Xu L. , Lukehart Charles M. , Li Lang , Sengupta Sreeparna , Wang Ping
Published: April 2011

Graphitic carbon nanofibers were used to reinforce epoxy resin to form nanocomposite adhesive bonding. GCNFs having a herringbone atomic structure are surface-derivatized with bifunctional hexanediamine linker molecules capable of covalent binding to an epoxy matrix during thermal curing and are cut to smaller dimension using ultrasonication. Good dispersion and polymer wetting of the GCNF component is evident on the nanoscale. Tensile and shear joint strength measurements were conducted for metal-metal and polymer-polymer joints using pure epoxy and nanocomposite bonding. Very little bonding strength increase, or some bonding strength decrease, was measured.
Structural factors determining the nanomechanical performance of transition metal nitride films
Authors: Sarakinos K. , Kassavetis S. , Patsalas P. , Logothetidis S.
Published: April 2011

Chromium nitride (CrN) and Titanium nitride (TiN) thin films were deposited employing unbalanced magnetron sputtering (UBMS) for various values of substrate bias voltage (Vb). The structural characterization of the films in terms of phase identification and the density determination was achieved utilizing X-Ray techniques (XRD and XRR respectively), while the internal stresses were calculated by the change of the substrate's curvature using Stoney's equation. The nanomecahnical properties of the films (hardness and elastic modulus) were investigated using the Nanoindentation (NI) technique in the Continuous Stiffness Measurement (CSM) configuration. According to the NI results the hardness of the films ranges between between 15–25 GPa while the elastic modulus between 180–250 GPa. The analysis revealed that the hardness of the films is maximum when their orientation is pure (either [111] or [100]), while it is minimized under mixed orientation regime. Furthermore, the hardness of the films increases as the internal compressive stresses and the mass density increase. The latter can be validated through the comparison of the results concerning the above films to reported results for TiN films prepared by balanced magnetron sputtering (BMS)
Biocompatibility of CAD/CAM ORMOCER polymer scaffold structures
Authors: Doraiswamy A. , Patz T. , Narayan R. , Chichkov B. , Ovsianikov A. , Houbertz R. , Modi R. , Auyeung R. , Chrisey D. B.
Published: April 2011

A fresh approach with a novel process and a hybrid material is explored for developing designer 3-dimensional functional tissue scaffolds. The process of two photon-induced polymerization generally used for electronic and optical materials is introduced for developing biological scaffolds. Hybrid materials containing organic-inorganic units, ORMOCERs, fabricated with this process are tested for biocompatibility using various cell-types and compared with known standards such as polystyrene and ECM (Extracellular Matrix). Results show good adherence of different cells to these materials, and a growth rate comparable to bioactive materials. Structures with various surface topologies are developed and tested for preferential growth. The study is a first step towards developing bioactive and bioresorbable heterogeneous three-dimensional scaffolds.
Novel Angiogenic Compounds for Targeted Drug Delivery
Authors: Wieghaus Kristen A. , Capitosti Scott M. , Brown Milton L. , Botchwey Edward A.
Published: April 2011

Induction of angiogenesis is necessary for the success of engineered implantable tissues in order to meet oxygen and nutrient requirements of cells during tissue repair. Insufficient vascularization in bone graft reconstruction may impede healing and initiate hypoxic cell death at the interior of the implant. As a result, endogenous growth factors have been studied to enhance angiogenesis during wound repair. However, these peptide-based molecules are highly sensitive to processing that occurs during scaffold biomaterial fabrication and treatment for tissue engineering purposes. We report here the development of new small molecule regulators of angiogenesis that may circumvent the impediments associated with protein-based growth factor delivery. In this study, we report the design and evaluation of SC–3–143 as a regulator of endothelial function. We show that the compound significantly increases the formation of microvascular networks in vitro, and selectively enhances endothelial survivability by reducing endothelial cell death under serum deprived culture conditions.
Preparation of drug delivery biodegradable PLGA nanocomposites and foams by supercritical CO2 expanded ring opening polymerization and by rapid expansion from CHCIF2 supercritical solutions
Authors: Asandei Alexandru D. , Erkey Can , Burgess Diane J. , Saquing Carl , Saha Gobinda , Zolnik Banu S.
Published: April 2011

The synthesis of poly(lactic-co-glycolic acid) (PLGA) by the ring opening copolymerization of D, L-lactide and glycolide was performed at 110 °C to 130 °C using Sn(Oct)2 as catalyst, 1, 10-decanediol as initiator in a supercritical sc-CO2 expanded medium at pressures of up to 3, 500 psi. Due to the limited monomer solubility in sc-CO2 at low temperatures (70 °C), only Mn = 2, 500 is typically obtained. However, molecular weight increases with both temperature and sc-CO2 pressure. Thus, Mn = 13, 000 (PDI = 1.28) was obtained at 110 °C - 130 °C even in the absence of fluorinated surfactants. Biodegradable drug delivery nanocomposites based on dexamethasone and poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) were prepared by the rapid expansion of the corresponding supercritical CHClF2 solutions (110 °C, 200-300 bar) in air (RESS) and in toluene (RESOLV). The RESS process leads to a broad particle size distribution (100-500 nm) while the RESOLV generates a narrower distribution centered around 100 nm and is accompanied by the formation of a few large particles, most likely due to aggregation.
Selective Laser Sintering of Polycaprolactone Bone Tissue Engineering Scaffolds
Authors: Partee Brock , Hollister Scott J. , Das Suman
Published: April 2011

Present tissue engineering practice requires porous, bioresorbable scaffolds to serve as temporary 3D templates to guide cell attachment, differentiation, and proliferation. Recent research suggests that scaffold material and internal architecture significantly influence regenerate tissue structure and function. However, lack of versatile biomaterials processing methods have slowed progress towards fully testing these findings. Our research investigates using selective laser sintering (SLS) to fabricate bone tissue engineering scaffolds. Using SLS, we have fabricated polycaprolactone (PCL) and polycaprolactone/tri-calcium phosphate composite scaffolds. We report on scaffold design and fabrication, mechanical property measurements, and structural characterization via optical microscopy and micro-computed tomography.
Formation of Intermetallic-Ceramic Composites from Nanoreactants in a Self-Sustaining Reaction Regime
Authors: Dargar Shivanee R. , Groven Lori J. , Swiatkiewicz Jacek J. , Puszynski Jan A.
Published: April 2011

Processing of nanoreactant energetic system, Al-TiO2, in the thermal explosion mode of combustion synthesis was investigated. Simultaneous combustion synthesis and densification experiments were carried out in a uniaxial press to obtain homogeneous as well as functionally graded products of the above reactant system. It was demonstrated that TiAl3-Al2O3 composite product synthesized from Al-TiO2 reactant system retained its sub-microstructure despite a short term exposure to higher temperatures. Composite materials with densities of 96–98% of the theoretical densities were obtained. The effect of several key processing parameters such as initial composition of reactants and temperature-pressure conditions on morphology of combustion synthesized product, their phase composition, and residual porosity were investigated. DSC, XRD, SEM, and LIBS analyses were used to characterize both reactants and products.
Sol-gel synthesis of silica–based mesoporous powders
Authors: Armelao Lidia , Bottaro Gregorio , Campostrini Renzo , Gialanella Stefano , Ischia Marco , Poli Fabrizia , Tondello Eugenio
Published: April 2011

Mesoporous silica powders have been synthesized starting from aqueous solutions of Si(OCH2CH3)4 (TEOS) under acidic conditions, using non-ionic alkyl poly(ethylene oxide) oligomer (Brij76) as a structure-directing agent. Template removal was performed by thermal treatment in air as well as by ethanol extraction. The annealing process (400 - 600°C) resulted in more efficient elimination of the organic molecules, thus yielding hexagonal (p6mm) mesopor-ous materials with pore volume and specific surface area ranging between 0.58 – 0.41 cm3/g and 900 – 700 m2/g, respectively. The systems were characterized by X-Ray Diffraction (XRD), N2 BET adsorption, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Particular attention was focused on the evolution of the system mesostructural and porous features as a function of the template removal procedure. The obtained mesoporous networks are suitable as matrices for the development of nanocomposite systems in which the dispersion or the growth of various guest species (clusters, molecules…) can be addressed into the host mesopores.
Dielectric Constant of Barium Titanate Synthesized by Containerless Processing
Authors: Yu Jianding , Paradis Paul-François , Ishikawa Takehiko , Yoda Shinichi
Published: April 2011

Containerless processing is an attractive synthesis technique that permits deep undercooling and provides the possibility to solidify the undercooled liquid into a selected phase, and to synthesize materials with novel properties. Spheroidal BaTiO3samples with a diameter of approximately 2mm were solidified by containerless processing, using an electrostatic levitation apparatus. Single crystal hexagonal BaTiO3and polycrystalline perovskite BaTiO3were successfully synthesized at different undercoolings levels. An oxygen-deficient single crystal of hexagonal BaTiO3obtained with this method, exhibited a giant permittivity higher than 100000, with a loss component tanδof about 0.1 at room temperature. The permittivity showed weak temperature dependence in the 70 K to 300 K range, and a dramatic drop by 2 orders of magnitude below 70 K. In comparison, the polycrystalline perovskite BaTiO3showed a permittivity of 4000 at room temperature.
Ag–B Thin Films Prepared by Magnetron Sputtering
Authors: Metz Oren , Pelleg Joshua , Sinder Misha , Shneck Roni , Sokolovsky Vladimir
Published: April 2011

The discovery of the new superconductor MgB2 with critical temperature of Tc = 39 K stimulated great activity in search for materials with higher Tc. Theoretical works predicted the possibility of obtaining such superconducting materials in other borides also, in particular in AgB2. It was predicted in these works that diborides of metals having the AlB2 type structure, among them AgB2 may have superconductivity with a Tc higher than 39 K. In an early very short report the lattice parameters of AgB2 were evaluated in a synthesized specimen. However, no other indication exists that AgB2 was ever produced. We report the preliminary results of our attempts to prepare AgB2 films.

Thin films of Ag-B were produced by magnetron cosputtering in Ar ambient from two separate targets that of B and Ag on Si (100) substrates. The specimens were subjected to X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photo spectroscopy (XPS), Auger analysis and optical microscope (OM) investigations. Resistivity measurements in a wide temperature range were measured. No superconductivity was yet observed in the range ∼10 – 200. K on the basis of resistivity measurements. Preliminary results indicate that AgB2 might be an unstable phase.
Barium Strontium Titanate Ceramics Prepared by a Reaction-Sintering Process
Authors: Liou Yi-Cheng , Chen Jen-Hsien , Wu Chi-Ting
Published: April 2011

Barium strontium titanate (Ba0.7Sr0.3TiO3, BST) ceramics prepared by a reaction-sintering process were investigated. The mixture of raw materials of stoichiometric Ba0.7Sr0.3TiO3 was pressed and sintered into ceramics without any calcination stage involved. Perovskite BST ceramics were obtained after sintered at 1330–1370°C for 2–6 h. For 6 h soak time, a density value 5.68g/cm3 (99.8% of the theoretic value) was obtained at 1350°C sintering. Grains of sizes between 2μm and 15μm were formed after 1330–1370°C sintering for 2–6 h. A diffused ferroelectric-paraelectric transition was observed in pellets sintered at 1330°C for 2 h and disappeared at a longer soak time or a higher sintering temperature.
Preferential Crystallization of β-FeSi2 from Micro-droplets Generated by Laser Ablation.
Authors: Narazaki Aiko , Sato Tadatake , Kawaguchi Yoshizo , Niino Hiroyuki
Published: April 2011

β-FeSi2 was successfully fabricated at room temperature via the deposition of molten micro-droplets generated by the KrF excimer laser ablation. Only the molten droplets precipitated as the β-FeSi2 crystalline phase on a silicon substrate kept even at room temperature, whereas the rest of film was amorphous. The crystallization behavior of micro-droplets has been discussed in the light of non-equilibrium process due to rapid cooling on the substrate. After the deposition, pulsed laser annealing was also performed in order to improve the crystallinity of the β-FeSi2 microprecipitates-containing film.
Structure-Property Relationships in Tb4PtGa12 and Y4PtGa12
Authors: Williams Willa M. , Lee Han-Oh , Moldovan Monica , Fisk Zachary , Young David P. , Chan Julia Y.
Published: April 2011

Single crystals of Y4PtGa12 have been synthesized and characterized by X-ray diffraction. The compound crystallizes in the cubic Im3m space group with lattice parameters a = 8.530(5) Å. Magnetic property measurements show that Y4PtGa12 does not order magnetically. Structure-property relationships with the isostructural antiferromagnet Tb4PtGa12 are discussed.
Pressure Tuning of Crystalline As2Te3
Authors: Scheidemantel T. J. , Meng J. F. , Badding J. V.
Published: April 2011

We report the pressure dependence of the thermoelectric power of As2Te3. Pressures up to 10 GPa were induced using a Mao-Bell diamond anvil cell. The absolute value of the thermoelectric power dropped from S ≈ 230μV/K at ambient pressure to S ≈ 75 GPa near 5 GPa. At 6 GPa it then increased rapidly to S ≈ 220βV/K. This behavior is indicative of a structural phase transition as suggested by previously published high pressure phase diagrams.
On the Factors Governing the Refractive Indices of Inorganic Materials
Authors: Rocquefelte Xavier , Goubin Fabrice , Jobic Stéphane , Whangbo Myung-Hwan
Published: April 2011

Three key factors influencing the refractive indices of inorganic solid state materials were discussed on the basis of the concept of optical channels and the dielectric functions calculated for two series of closely related oxides. Implications of our observation concerning efficient UV blockers were discussed.
CHEMICAL AND PHYSICAL HARDNESS OF SOLIDS
Authors: Gilman John J.
Published: April 2011

The concept of chemical hardness was originally developed as a measure of the stability of molecules. Its relationship to physical hardness and to solids is demonstrated here. Also, it is shown that shear moduli, and polarizabilitites, as well as band gaps are related to chemical hardness. Finally, evidence is presented that indentation hardness numbers are better measures of critical phase transition compressions than “pressure-cell” data.
Direct Femtosecond Inscription of Fiber Bragg Gratings.
Authors: Martinez Amós , Dubov Michael , Khrushchev Igor Y. , Bennion Ian
Published: April 2011

Direct, point-by-point inscription of fiber Bragg gratings by infrared femtosecond laser is reported. Using this technique, highly reflective gratings can be rapidly inscribed in standard, untreated fiber. Thermal studies demonstrate increased thermal stability compared to the UV-inscribed gratings.
Modifications and Color Markings in Glasses by UV Laser Radiation
Authors: Talkenberg M. , Falkenberg G. , Krauss M. , Kreutz E. W.
Published: April 2011

Rare earth-, transition metal- and metal doped soda lime-, BK7- and photosensitive lithium aluminosilicate glass are irradiated by pulsed UV laser radiation (wavelength λL = 355nm, pulse length tp = 10 to 80 ns) as a function of repetition rate, pulse energy and overlap between successive pulses. The solid state laser radiation is focused into the volume to fluences below the removal-threshold. Depending on the chemical composition, the laser parameters, and the processing variables the laser radiation is absorbed by optically- and photochemically active polyvalent ions with conversion of the optical energy into fluorescence stimulation and ionization as well as color center formation resulting in modifications and/or color markings in the VIS. The absorption and concentration changes of the polyvalent ions are probed by optical spectroscopy and transient absorption spectroscopy. The photochemical and -physical processes such as oxidation and reduction of polyvalent ions and/or color center generation underlying the modifications and color markings are discussed.
Adsorption of DNA onto Charged Spheres
Authors: Hodrien Alison J. , Voice Alison M. , Waigh Thomas A.
Published: April 2011

The complexation behaviour of linear DNA (negatively charged) with surface functionalised sub-micron latex spheres is studied by dynamic light scattering (DLS), small-angle neutron scattering (SANS), small-angle x-ray scattering (SAXS), and micro rheology. The complexes are measured in solution as a function of component concentration (CDNA, CSPH) and added salt concentration (Cs). In the absence of salt, measured radius increases with CDNA (CSPH held constant) up to a plateau value. The presence of salt causes a decrease in the measured complex radius, which may be due either to increased flexibility of the chains allowing them to form a more compact layer on the sphere surface, or dissociation of the two components due to screened electrostatics. More detailed experiments to determine this are underway.
Characterizations of enriched metallic single-walled carbon nanotubes in polymer composite
Authors: Chen Bin , Li Jing , Lu Yijiang , Cinke Martin , Au Dyng , Harmon Julie P. , Muisener Patrici Anne O. , Clayton LaNetra
Published: April 2011

We characterize the electric properties of single-walled carbon nanotube (SWNT) dispersed in the polymethyl methacrylate (PMMA) composites. In the melt-blended sample, the SWNTs – originally semiconducting – became predominantly metallic. The interaction of the PMMA and SWNT is investigated by the polarized Raman studies. The structure changes in the PMMA and SWNT shows that the anisotropic interactions play important role in SWNT electronic density of states (DOS) changes. The increased metallic SWNT percentage is confirmed by the conductivity and dielectric constant measurements of composite and neat PMMA.
Perceptions of Nuclear Wastes across Extreme Time Perspectives
Authors: Drottz‐Sjöberg Britt‐Marie
Published: April 2011

An empirical study, financed by the Swedish Radiation Authority (SSI), on perception of time, time periods, and responsibilities related to the final repository for spent nuclear fuel was conducted in 2002. Citizens of the Oskarshamn and Östhammar municipalities (N=1,501) responded to a postal questionnaire regarding their participation in site‐specific investigations for the building of the Swedish repository, administered by the Swedish Nuclear Fuel and Waste Management Co (SKB). Approximately 41% of the sampled citizens responded to an eight‐page questionnaire, which included tasks of time estimates of specified historic events (e.g., when the first human landed on the moon, the development of Homo sapiens) and possible future events (e.g., a new glacial ice period, a radiation leakage from canisters in the repository). Some questions asked for risk estimations in relation to the repository, i.e., for oneself and for others in the community. Other questions inquired about perceptions of risks and responsibilities related to future generations. SSI was especially interested in the respondents' ratings of the importance of the authority's reviews of SKB's research programs for specified time periods, i.e., during operation, in a thousand years, ten thousand years, hundred thousand years, and up to a million years. The overall results showed rather restricted time horizons among the respondents. Risk estimations relating to nuclear wastes were not extremely high, and as usual the risk to others rated higher than the risk to oneself. Regarding the importance of SSI's review of SKB's research programs, people emphasized the importance of such reviews in the near future in contrast to the distant future, i.e., while under operation and up to 1,000 years, rather than for the longer time periods of relevance for the reviews. People also perceived the consequences to be much more severe in the shorter time perspectives than in the longer ones, given a leakage from the canisters in the repository. The importance of future generations' life situations was reported as high, and perceived to be of greater importance to oneself than to others. The construction of a safe final repository for spent nuclear fuel ranked the highest on a list of topics when respondents indicated the responsibilities of current generations. Ranked second and third were the items “to fight criminality” and “to give children and youth a good education.” The responsibility for depositing spent nuclear fuel in a reassuring manner was mainly attached to the entrepreneur, SKB, closely followed by the authorities (SSI and the Swedish Nuclear Safety Authority, SKI). The discussion focuses on the apparent paradox involving participants rather short time horizons, especially into the future, decreasing risk estimates across long time perspectives, and very high ratings regarding current generations' responsibilities for the life situations of future generations.