bluuebunny/crossref_metadata_2025 huggingface dataset:
Pt/TiO2 Growth Templates for Enhanced PZT films and MEMS Devices
Authors: Potrepka Daniel M. , Fox Glen R. , Sanchez Luz M. , Polcawich Ronald G.
Published: September 2011

The crystallographic texture of lead zirconate titanate (PZT) thin films strongly influences the piezoelectric properties used in MEMS applications. For PZT films poled to saturation, the piezoelectric response is sequentially greater for random, {111}, and {001} texture. Textured growth can be achieved by relying on crystal growth habit and can also be initiated by the use of a seed layer that provides a heteroepitaxial template. Template choice and the process used to form it determine the structural quality and ultimately influence performance and reliability of MEMS PZT devices such as switches, filters, and actuators. This study focuses on how {111}-textured PZT is generated by a combination of crystal habit and templating mechanisms that occur in the PZT/bottom-electrode stack. The sequence begins with {0001}-textured Ti deposited on thermally grown SiO2 on a Si wafer. The Ti is converted to {100}-textured TiO2 (rutile) through thermal oxidation. Then {111}-textured Pt can be grown to act as a template for {111}-textured PZT. The Ti and Pt are deposited by DC magnetron sputtering. The TiO2 and Pt film textures and structure were optimized by variation of sputtering deposition times, temperatures and power levels, and post-deposition anneal conditions. The relationship between Ti, TiO2, and Pt texture and their impact on PZT growth will be presented.
Giant Piezoresistive Variation of Metal Particles Dispersed in PDMS Matrix
Authors: Stassi Stefano , Canavese Giancarlo , Lombardi Mariangela , Guerriero Andrea , Fabrizio Pirri Candido
Published: September 2011

An Investigation of the piezoresistive response of a metal-polymer composite based on nickel conductive filler in a polydimethylsiloxane (PDMS) insulating matrix for tactile sensor application is presented in this paper. Lacking a mechanical deformation, the prepared composites show no electric conductivity, even though the metal particle content is well above the expected percolation threshold. In contrast, when subjected to uniaxial compression, the electric resistance is strongly reduced. A variation of up to nine orders of magnitude was registered. The thickness of the insulating layer between particles decreases when the sample composite is compressed. Therefore, the electric conduction which is related to a tunneling phenomena, increases exponentially. This behavior is further enhanced by the presence of very sharp nanometric spikes on the particles surface which act as field enhancement factors. In the presented work, the piezoresistive behavior of the composite, the stability in time of the resistance value and the response to several cycles of compression and decompression are evaluated on samples with different physical parameters like nickel content, PDMS copolymer/curing agent ratio and thickness.
The Impact of Hands-on Experience in Undergraduate Nanotechnology Education
Authors: Oxenham Joseph A. , Teker Kasif
Published: September 2011

Nanotechnology, a field interested in materials with features smaller than 100 nanometers and possessing novel properties, is a field that is unquestionably in a period of rapid growth. As the limits of existing technologies are pressed, the need arises for faster, better, and stronger materials and devices. Manipulation of matter on the nanoscale is quickly becoming the next frontier of materials and technology. Due to the scale of the phenomena and the exploratory nature of nanoscience and nanotechnology, a high degree of knowledge in many diverse fields is required. This requires a centralized presentation to students in order to best teach them the required knowledge.

In the past, knowledge has mostly been transferred hand-to-hand on an active level. However, in modern education, the classroom and lectures take a more active role. With this rise, the position and focus of hands-on work has diminished [1], while at the same time undergraduates remain isolated from research being conducted at universities [2]. With the broad nature of nanoscience and nanotechnology, it is becoming more important to maximize students’ learning ability in order to train future researchers and workforce. This paper explores the impact of a hands-on research experience in undergraduate nanotechnology education. This experience is presented to show the importance of student involvement on hands-on projects for their learning process.
High Yield Polymer MEMS Process for CMOS/MEMS Integration
Authors: Ray Prasenjit , Seena V. , Apte Prakash R. , Rao Ramgopal
Published: September 2011

MEMS community is increasingly using SU-8 as a structural material because it is self-patternable, compliant and needs a low thermal budget. While the exposed layers act as the structural layers, the unexposed SU-8 layers can act as the sacrificial layers, thus making it similar to a surface micromachining process. A sequence of exposed and unexposed SU-8 layers should lead to the development of a SU-8 based MEMS chip integrated with a pre-processed CMOS wafer. A process consisting of optical lithography to obtain SU-8 structures on a CMOS wafer is described in this paper.
Anti-Tumor Chloroquine-Gold Nanocomposites and their Binding Interaction with Bovine Serum Albumin: Biophysical and Biochemical Aspects of Protein Binding
Authors: Joshi Prachi , Chakraborti Soumyananda , Ramirez-Vick Jaime E. , Ansari Z. A. , Shanker Virendra , Chakrabarti Pinak , Singh Surinder P.
Published: September 2011

We have conjugated chloroquine onto nano-sized, thiol-stabilized gold nanoparticles by using 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) / N-hydroxysulfosuccinimide (NHS) chemistry. The formation of gold nanoparticles was confirmed using optical spectra for characteristic surface plasmon band; the average size of gold nanoparticles was found to be 5-7 nm from electron microscopy measurements. The anti-tumor activity of prepared nanocomposite, vis-à-vis chloroquine itself, had been demonstrated using MCF-7 breast cancer cell line. To determine the binding affinity of gold-chloroquine nanocomposites to transport proteins present in blood serum, we studied the binding interaction of gold-chloroquine to bovine serum albumin (BSA), the most abundant plasma protein. The binding was studied by using isothermal titration calorimetry and fluorescence spectroscopy and was analyzed in terms of binding constant, entropy and enthalpy change. The gold-chloroquine nanocomposites were found to interact efficiently with BSA and fluorescence quenching experiments involving Trp212 suggests that the nanocomposites bind at site I of BSA.
Assembly Strategies for Fully Aligned and Dispersed Morphology Controlled Carbon Nanotube Reinforced Composites Grown in Net-Shape
Authors: Farmer Benjamin L. , Beard Mark A. , Ghita Oana , Allen Robert , Evans Ken E.
Published: September 2011

Long carbon fibre polymer composites represent the state-of-the-art materials technology for high performance weight driven structures, such as airframes. Although a significant amount of optimisation remains to be done to fully exploit the benefits of long fibre composites, these materials are relatively speaking still very crude, when compared to what nature has achieved with wood or bone for example. Nanomaterials, and specifically carbon nanotubes (CNTs), have teased with their spectacular mechanical and physical properties in isolation. These headline properties have prompted much work into the manufacturing of composite materials using CNTs as reinforcements, but thus far, successful exploitation of these impressive properties has been modest. A gap remains before these materials represent a real competition to long carbon fibre composites, even though fairly modest applications such as CNTs as fillers for matrix toughening and imparting electrical functionality are showing some promise. In this paper a critique is made of various reinforcement approaches through the lens of ’nano-augmented, ’nano-engineered’ and ’nano-enabled’ categories as defined by Airbus. These approaches are compared to an analysis of nature’s ’baseline’. A new ’nano-enabled’ strategy for the growth of fully aligned and dispersed bulk CNT composite materials and structures, allowing for simultaneous multi-scalar morphological and topological optimisation, is described. This new strategy, analogous to nature’s approach, consists of the vapour phase growth of aligned forests of carbon nanotubes coupled to the environment of Additive Layer Manufacturing (ALM). Early feasibility results are presented and currently identified challenges to successful scale-up are discussed.
Formation of Micro and Nanostructured Nickel/Silica and Nickel/Metal Composites by Electrodeposition of Mesoporous Silica onto Nickel Foam
Authors: Cordes Nikolaus L. , Bakker Martin G.
Published: September 2011

Extremely high surface area porous electrodes are of interest as current collectors for advanced batteries and as the basis for supercapacitors. For moderate to large scale storage applications a three-dimensional material is needed with porosity at multiple length scales. We are developing a combined bottom up/top down approach to creating such materials by using electrodeposition of mesoporous silica on nickel foam, a commercially available porous conductor widely used as the current collector in various batteries. Electrodeposition produces a conformal coating on the nickel foam. By controlling the electrodeposition time the morphology of the mesoporous silica can be varied from a thin film up to 500 nm thick to a loosely bound agglomeration of mesoporous silica particles capable of completely filling the 0.3-0.5 mm voids of the nickel foam. The internal diameter of the mesopores in the silica can be controlled in the range 2.5-4.8 nm by changing the chain length of the templating surfactant used. Gas adsorption shows surface areas of 400-1600 m2/g of silica deposited, consistent with the assumed structure of the material.
Magnetic refrigeration with GdN by Active Magnetic Refrigerator cycle
Authors: Hirayama Yusuke , Okada Hiroyuki , Nakagawa Takashi , Yamamoto Takao. A. , Kusunose Takafumi , Takenori Numazawa , Mastumoto Koichi , Irie Toshio , Nakamura Eiji
Published: September 2011

A magnetic refrigeration test was performed using a test device filled with spherical GdN material synthesized by the hot isostatic pressing (HIP) method. Refrigeration with an active magnetic regenerator cycle was tested in the temperature range between 48 and 66 K, with the field changing from 1.2 to 3.7 T and 2.0 to 4.0 T at upper and lower sides of the regenerator bed filled with the GdN spheres, respectively. Temperature spans about of 2 K were obtained at both sides, and the total temperature span in each cycle attained about 5 K. The specific heat of the material was measured to calculate the magnetic entropy change ΔS and the adiabatic temperature change ΔT induced by the magnetic field change ΔH. It was suggested that for a given ΔH, larger ΔS and ΔT can be exploited when demagnetized to lower H, especially, to zero field.
Preparation of heteroepitaxial SrRuO3 thin film on Si substrate and microstructure of BaTiO3-NiFe2O4 epitaxial composite thin film deposited on the SrRuO3 bottom electrode using PLD
Authors: Wakiya Naoki , Sakamoto Naonori , Sawamura Shigeki , Fu Desheng , Shinozaki Kazuo , Suzuki Hisao
Published: September 2011

A “0-0 type” multiferroic BaTiO3-NiFe2O4 (BT-NF) composite thin film was prepared on SrRuO3/(La,Sr)MnO3/CeO2/YSZ/Si(001) substrate using pulsed laser deposition (PLD). Epitaxial growth of the film was confirmed using x-ray pole figure measurements. Cross-sectional TEM observations revealed that the crystal structure and morphology of the BT-NF composite thin film depends on the oxygen pressure during deposition. The film deposited at 1.0×10-2 Torr has smaller grains than that deposited at 1.0×10-1 Torr. The magnetic and ferroelectric properties of BT-NF composite thin film were correlated with the microstructure that was controlled by oxygen pressure during deposition. The film deposited at 1.0×10-2 Torr had paramagnetic properties with less polarization than the film deposited at 1.0×10-1 Torr.
Graphene growth on SiC and other substrates using carbon sources
Authors: Mitchel W. C. , Park J. H. , Smith Howard E. , Grazulis L. , Mou S. , Tomich D. , Eyink K. , Elhamri Said
Published: September 2011

Direct deposition of graphene from carbon sources on foreign substrates without the use of metal catalysts is shown to be an effective process with several advantages over other growth techniques. Carbon source molecular beam epitaxy (CMBE) in particular provides an additional control parameter in carbon flux and enables growth on substrates other than SiC, including oxidized Si and sapphire. CMBE using thermally evaporated C60 and a heated graphite filament on SiC is reported here. The graphene films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and Hall effect. Graphene films on Si-face SiC grown using the C60 source have Bernal-like stacking and n-type conduction while those grown using the graphite filament have turbostratic stacking and p-type conduction. The sheet concentration for both n- and p-type doping is linearly dependent on film thickness.
Room Temperature Superparamagnetism observed in Foam-like Carbon Nanomaterials
Authors: Bandow Shunji , Asano Hirohito , Muraki Susumu , Mizuno Takahiro , Jinno Makoto , Iijima Sumio
Published: September 2011

Magnet-attractive carbon nanopowder can be produced by a pulsed Nd:YAG laser (10 Hz) vaporization of pure carbon in a few % of H2 containing Ar gas at 1000°C. On the other hand, magnet-attractive nanopowder cannot be formed when vaporizing in pure Ar. As-grown carbon nanopowder includes a few to ten % of micron sized graphite flakes as the impurity. Removal of such flakes can be achieved by a centrifugal separation and the supernatant is checked by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Magnetization curve at 400 K is easy to saturate at low magnetic field of 10 kG, and no hysteresis is observed. This feature is explained by a superparamagnetism of finely dispersed ferro- or ferri-magnetic nanoparticles. Elementary analyses using electron energy loss spectroscopy (EELS) and atomic absorption spectroscopy (AAS) suggest that the observed strong magnetism should be an intrinsic carbon magnetism.
A fully automated remote controllable microwave-based synthesis setup for colloidal nanoparticles with integrated absorption and photoluminescence online analytics
Authors: Einwächter Simon , Krüger Michael
Published: September 2011

We present a fully automated microwave-based synthesis setup for colloidal nanoparticles. Integrated absorption and photoluminescence online analytics opens the possibility to monitor the growth of various nanoparticles at any stage of the reaction. Spectroscopic investigation within the first seconds of a reaction is accessible opening the possibility to detect potential critical size nuclei as a function of the reaction conditions. Beside the possibility to perform systematic mechanistic studies, this system allows a high degree of synthesis control leading to very good product reproducibility. In conjunction with an automated auto sampler unit systematic multiple reactions can be performed one after each other and compared. The setup is remote-controllable allowing worldwide online control accessibility over the synthesis setup including data processing, visualization and storage. The performance of the setup will be demonstrated by using the synthesis of CdSe nanocrystals as a model system and can be extended to the synthesis of various metallic and semiconducting nanoparticles.
In Vitro Behavior and Design of a New Type Implant with Nanostructured Surface
Authors: Rosca J.C. Mirza , Raducanu D. , Martin D. Gonzalez , Lorente J.A. Garcia , Vasilescu C.
Published: September 2011

This study was aimed to investigate in vitro and in vivo behavior of a Ti6Al7Nb biomaterial with a nanostructured HA-type coating and also the design and realization of a new special knee implant together with a selection of a suitable animal model for preclinical experimentation of the implants.

The metallic material used like substrate alloy for layer deposition was a Ti6Al7Nb alloy obtained by double electron beam melting furnace. In order to obtain a nano-crystalline HA-coating first sodium titanate layer was obtained on the surface and then the implant was immersed in Ringer solution with additional PAW1 biovitroceramic (particles under 20 μm). Different deposition times (5, 10 and 19 days) were employed. Microscopy analysis and corrosion tests of the implants relieves that the nanostructured HA layer after 19 days of immersion shows promising results as regarding the implant employ in preclinical experiments.

After a complex design based on knee bone radiography there has been manufactured two different types of devices for the metallic implants: a metallic plate and a pin. Two plates and two pins were implanted in each animal.

For in vivo experiments the chosen animal model was the mini-pig because of its strong chirurgical resistance and perfect anesthesia toleration. For the testing 10 animals were used for implantation and one for the control. When the plate is implanted the bone has to have a good blood supply after the cut in order to avoid bone to die. All experimented implants were maintained in the animal during six months and periodically inspected. No sign of infection or another problem were observed during this period.
Optical and Spectroscopic Ellipsometric Study of Indium Boron Nitride Sputtered Thin Films with Low Boron Concentration
Authors: Ebdah Mohammad A. , Kordesch Martin E. , Ingram David C. , AlBrithen Hamad , Ibdah Abdel-Rahman A. , Cooper Kevin
Published: September 2011

Amorphous indium boron nitride (a-InBN) thin films were successfully fabricated using radio frequency (RF) magnetron sputtering, and were deposited onto fused silica and c-Si(100) substrates. Sputtering was achieved using a target of polycrystalline B and In species with B/In nominal at.% ratio of 25/75 under the flow of nitrogen. The structure and composition of the films have been investigated by X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. The XRD patterns reveal that the sputtered films are amorphous, and the XPS confirms the presence of boron in the films in addition to an oxide overlayer. The optical absorption of samples grown on silica was obtained using spectrophotometry (SP) technique in the wavelength range (200 - 800) nm. Analysis of the absorption coefficients using the Tauc linear extrapolation gives an optical bandgap of 2.05 eV, indicating a higher bandgap comparing to the measured optical bandgap of a-InN (1.25 eV) due to doping with boron. Films grown on c-Si(100) were characterized by spectroscopic ellipsometry (SE) technique in the wavelength range of (300-1700) nm. The measured ellipsometric spectra are described well by a two-layer model structure, which consists of a transparent layer on top of an absorbing layer. The thicknesses and optical functions of the transparent and absorbing layers were obtained by analyzing the measured ellipsometric spectra, Ψ and Δ within the framework of the Cauchy–Urbach (CU) and Tauc–Lorentz (TL) models, respectively. While the overlayer is completely transparent over the measured range (k(λ) = 0), the absorbing layer underneath it exhibits a clear absorption above its optical bandgap of 2.15 eV, which is in a good agreement with the SP finding. There was an excellent agreement between the bandgap obtained as a fitting parameter from the optical model and that obtained by linear extrapolation using the empirical Tauc and Cody models for amorphous semiconductors.
Plasma-Enhanced Metalorganic Chemical Vapor deposition of Lipon Thin Films
Authors: Meda Lamartine
Published: September 2011

Lithium phosphorus oxynitride (Lipon) thin films have been deposited by a plasmaenhanced metalorganic chemical vapor deposition (PE-MOCVD) method using triethyl phosphate [(CH2CH3)3PO4] and lithium tert-butoxide [(LiOC(CH3)3] precursors. Growth rates were between 100 and 415 Å/min, and thicknesses ranged from 1 to 2.5 μm. X-ray powder diffraction showed that the films were amorphous, and X-ray photoelectron spectroscopy revealed approximately 6.9 at.% carbon in the films. The ionic conductivity of Lipon was measured using electrochemical impedance spectroscopy (EIS) and approximately 1.02 μS/cm was obtained, which is consistent with the ionic conductivity of Lipon deposited by radio frequency magnetron sputtering of Li3PO4 targets. An all-solid-state thin-film lithium microbattery such as Li/Lipon/LiCoO2/Au/substrate was successfully fabricated with Lipon deposited by PE-MOCVD. The battery has a capacity of ca. 22 μAh/cm2μm.
Li motion mechanisms in (Li,Na)3xLa2/3-xTiO3 (x = 0.067 and 0.167) series followed by ND, NMR and Impedance spectroscopy.
Authors: Varez A. , Rivera A. , Bucheli W. , Jimenez R. , Sanz J.
Published: September 2011

The dependence of Li mobility on structure and composition of quenched Li0.5-xNax La0.5TiO3 (0 ≤ x < 0.5) and slowly cooled Li0.2-xNaxLa0.6TiO3 (0 ≤ x < 0.2) perovskite series, has been investigated by means of Neutron Diffraction (ND), Nuclear Magnetic Resonance (NMR) and Impedance Spectroscopy (IS). The first series displays rhombohedral (√2ap, √2ap, 2√3ap; S.G. R-3c) symmetry and vacancies are randomly distributed on A-sites (disordered phases), while Li0.2-xNaxLa0.6TiO3 series, presents orthorhombic unit cells (2ap, 2ap, 2ap; S.G. Cmmm) and the vacancies are preferentially located in alternating layers along the c-axis (ordered phases). In both cases, Li ions are shifted from A sites to a fourfold coordination at unit cell faces of the single cubic perovskite and octahedral are tilted along the rombohedral axis in Li-rich and along b-axis in Li- poor series. By heating the elimination of the octahedral tilting takes place changing the symmetry from rhombohedral to cubic in Li-rich samples, and from orthorhombic to tetragonal in Li-poor samples; however no changes were detected in La-vacancy distributions. For a particular value of sodium content (x=0.3 for Li0.5-xNaxLa0.5TiO3 and x=0.17 for Li0.2-xNaxLa0.6TiO3), the conductivity drops several orders of magnitude indicating that the amount of vacancies approaches the percolation threshold. In the temperature range 77-500 K, conductivity of Na-doped samples displays departures from the Arrhenius behavior, decreasing activation energy from 0.37 to 0.25 eV in disordered samples and from 0.37 to 0.12 eV in ordered ones. The structural sites occupancy has been investigated by ND, while Li mobility was evaluated through NMR and Impedance spectroscopy. The temperature dependence of thermal BLi factors has been related to the increment of conductivity that precede structural transformations, suggesting that Li motion trigger detected transitions in both series.
Reconfigurable Graphene Logic Device Based on Tilted P-N Junctions
Authors: Tanachutiwat Sansiri , Lee Ji Ung , Wang Wei
Published: September 2011

In this paper, we introduce a novel reconfigurable graphene logic based on graphene p-n junctions. In this logic device, switching is accomplished by using co-planar split gates that modulate the properties that are unique to graphene, including ambipolar conduction, electrostatic doping, and angular dependent carrier reflection. In addition, the use of these control gates can dynamically change the operation of the device, leading to reconfigurable multi-functional logic. A device model is derived from carrier transmission probability across the p-n junction for allowing quantitative comparison to CMOS logic. Based on this model, we show that the proposed graphene logic has significant advantages over CMOS gate in terms of area, delay, power, and signal restoration. Furthermore, the device utilizes a large graphene sheet with minimal patterning, allowing feasible integration with CMOS circuits, for potential CMOS-graphene hybrid circuits.
Nb-substituted TiO2 Nanosheet Exfoliated from Layered Titanate for photocatalysis
Authors: Song Haiyan , Sjåstad Anja O. , Norby Poul , Fjellvåg Helmer
Published: September 2011

Photoelectrochemical behavior and Photocatalytic decomposition of Methylene Blue were studied on (Nb,Ti)O2 nanosheets electrode and (Nb,Ti)O2 particles produced from nanosheets, respectively. A detailed characterization of the materials show that Nb-substitution suppresses the transition from anatase to rutile. Depending on the oxygen partial pressure during the transformation, the Nb-substitution into TiO2 provokes different defect situations and also electronic properties. 1% Nb-substitution can drasticly increase the photocurrent and photocatalytic activity of Ti0.9O2 due to the formation of new defects and electron traps that can promote the separation of photoinduced holes and electrons. However, high concentration of electron traps produced by heavy Nb-doping can serve as efficient recombination centers that caused loss of photocatalytic activity of the samples.
On the Sol-gel Synthesis and Characterization of Titanium Oxide Nanoparticles
Authors: Chaudhary Varun , Srivastava Amit K. , Kumar Jitendra
Published: September 2011

TiO2 nanoparticles have been prepared by sol-gel process using titanium isopropoxide as a precursor with ethanol and water as solvents. The synthesis involves gel formation, digestion for 24h, drying at 100oC for 10h, and calcination in air at 500-800oC for 2h. The resulting powder has been studied with respect to phase(s), morphology, optical absorption and photo -luminescence (PL) behaviour. The calcination of dried sol-gel product at 500oC for 2h leads to formation of anatase phase that possesses a tetragonal structure (a = 3.785 Å, c = 9.514 Å, Z = 4), average crystallite size ~ 11 nm and band gap of 3.34 eV. Further, increasing the time (t) of calcination causes crystallite growth that follows the relation d = α – β exp (-t/τ), α = 18.1 nm, β = 9.6 nm and τ = 6.9h. However, calcination of sol-gel product at 800oC for 2h gives rise to a rutile phase (tetragonal a = 4.593Å, c = 2.959Å, Z = 2), average crystallite size ~ 25 nm and band gap of 3.02 eV. The anatase phase exhibits strong PL emission peaks (excitation wavelength 405 nm) at 2.06 and 1.99 eV due to defect levels within the energy band gap. This observation has been attributed to finite size effects occurring in nanoparticles.
Label Free DNA Detection Using Large Area Graphene-Based FET Biosensors
Authors: Guo Shirui , Lin Jian , Penchev Miroslav , Yangel Emre , Ozkan Mihrimah , Ozkan Cengiz S.
Published: September 2011

This work describes the fabrication of highly sensitive graphene-based field effect transistor (FET) biosensors in a cost-effective way and its application in label-free DNA detection. CVD graphene was used to achieve mass production of FET device through photolithography method. Non-covalent functionalization of graphene with 1-Pyrenebutanoic acid succinimidyl ester ensures the high conductivity and sensitivity of the device. The present device could reach the low detection limit as low as 3*10-9 M.
Electrical Properties of Thin Layers Consisting of Surface Functionalized Silicon Nanoparticles
Authors: Nelles Jürgen , Rodríguez Castellón Enrique , Simon Ulrich
Published: September 2011

The present study investigates systematically, how the electrical properties of thin films consisting of silicon nanoparticles are affected by an organic monolayer coating the particles. Therefore, films of as-prepared silicon nanoparticles with a size of about 23 nm as well as freshly etched ones, both terminated with hydrogen, are compared with films of silicon nanoparticles functionalized with different 1-alkenes. It is found that the activation energy of the electron transport through the nanoparticle films scales with the thickness and permittivity of the respective organic monolayer.
Fabrication of Rh-doped TiO2 nanofibers for Visible Light Degradation of Rhodamine B
Authors: Obuya Emilly A. , Harrigan William , O’Brien Tim , Andala Dickson , Mushibe Eliud , Jones Wayne E.
Published: September 2011

The synthesis and application of environmentally benign, efficient and low cost heterogeneous catalysts is increasingly important for affordable and clean chemical technologies. Nanomaterials have been proposed to have new and exciting properties relative to their bulk counterparts due to the quantum level interactions that exist at nanoscale. These materials also offer enormous surface to volume ratios that would be invaluable in heterogeneous catalysis. Recent studies point at titanium dioxide nanomaterials as having strong potential to be applied in heterogeneous photocatalysis for environmental remediation and pollution control. This work reports the use of surface modified anatase TiO2 nanofibers with rhodium (Rh) nanoparticles in the photodegradation of rhodamine B (RH-B), an organic pollutant. The dimensions of TiO2 nanofibers were 150±50 nm in diameter and the size of the Rh nanoparticles was ~5 nm. The Rh-doped TiO2 catalyst exhibited an enhanced photocatalytic activity in photodegradation of rhodamine B under visible light irradiation, with 95 % degradation within 180 minutes reaction time. Undoped TiO2 did not show any notable phocatalytic activity under visible light.
Seeing through Corrosion: Using Micro-focus X-ray Computed Tomography and Neutron Computed Tomography to Digitally “Clean” Ancient Bronze Coins
Authors: Nguyen Hai-Yen , Keating Steven , Bevan George , Gabov Alexander , Daymond Mark , Schillinger Burkhard , Murray Alison
Published: September 2011

Vast numbers of bronze coins have been, and continue to be, excavated from archaeological sites around the Greco-Roman world. While often of little value from a strictly numismatic point of view, these coins provide invaluable data within their respective stratigraphic contexts and are used to date occupational and architectural phases more precisely than by ceramics alone. Unfortunately, the build-up of corrosion and mineralization on these coins during their centuries of burial often obscures their legends. Rather than employing potentially destructive and time-consuming chemical or mechanical cleaning techniques to reveal these features, commercially available Micro-focus X-Ray CT systems are now sufficiently well developed to reveal original surface features and to permit identification by a trained numismatist without any cleaning at all.
THIN FILM SILICON SOLAR CELLS UNDER MODERATE CONCENTRATION
Authors: van Dam L.M. , van Sark W.G.J.H.M. , Schropp R.E.I.
Published: September 2011

There are only very few reports on the effects of concentration in thin film silicon-based solar cells. Due to the presence of midgap states, a fast decline in fill factor was observed in earlier work. However, with the advent of more stable and lower defect density protocrystalline silicon materials as well as high quality micro-/nanocrystalline silicon materials, it is worth revisiting the performance of cells with these absorber layers under moderately concentrated sunlight. We determined the behavior of the external J-V parameters of pre-stabilized substrate-type (n-i-p) amorphous and microcrystalline solar cells under moderate concentrations, between 1 sun and 21 suns, while maintaining the cell temperature at 25oC. It was found that the cell efficiency of both the amorphous and the microcrystalline cells increased with moderate concentration, showing an optimum at approximately 2 suns. Furthermore, the enhancement in efficiency for the microcrystalline cells was larger than for the amorphous cells. We show that the Voc’s up to 0.63 V can be reached in microcrystalline cells while FF’s only decrease by 9%. The effects have also been computed using the device simulator ASA, showing qualitative agreement.
Effect of Dynamic Bias Stress (AC) In Short-Channel (L=1.5μm) p-Type polycrystalline Silicon (poly-Si) Thin Film Transistors (TFTs) on the glass substrate
Authors: Choi Sung-Hwan , Mo Yeon-Gon , Han Min-Koo
Published: September 2011

We have investigated the stability of short channel (1.5μm) p-Type polycrystalline silicon (poly-Si) Thin Film Transistors (TFTs) on the glass substrate under AC bias stress. The variation of threshold voltage in short channel poly-Si TFT was considerably higher than that of long channel poly-Si TFT. Threshold voltage of the short channel TFT was considerably moved to the positive direction during AC bias stress, whereas the threshold voltage of a long channel was rarely moved. The variation of threshold voltage in the short channel p-type TFT under AC bias stess was more compared to that under DC bias stress. The threshold voltage of short channel (L=1.5μm) poly-Si TFT was increased about -7.44V from -0.305V to -7.745V when VGS = 5 (base value) ~ -15V (peak value), VDS = -15V was applied for 3,000 seconds. This positive shift of threshold voltage and significantly degraded s-swing value in the short channel TFT under dynamic stress (AC) may be due to the increase of the stress-induced trap state density at gate insulator / channel interface region.
Mixed phase silicon oxide layers for thin-film silicon solar cells
Authors: Cuony Peter , Alexander Duncan T.L. , Löfgren Linus , Krumrey Michael , Marending Michael , Despeisse Mathieu , Ballif Christophe
Published: September 2011

Lower absorption, lower refractive index and tunable resistance are three advantages of doped silicon oxide containing nanocrystalline silicon grains (nc-SiOx) compared to doped microcrystalline silicon, for the use as p- and n-type layers in thin-film silicon solar cells. In this study we show how optical, electrical and microstructural properties of nc-SiOxlayers depend on precursor gas ratios and we propose a growth model to explain the phase separation in such films into Si-rich and O-rich regions as visualized by energy-filtered transmission electron microscopy.
Room Temperature Fabricated ZnO:Al with Elevated and Unique Light-Trapping Performance
Authors: Johnson E. V. , Charpentier C. , Emeraud T. , Lerat J.F. , Boniface C. , Huet K. , Prod’homme P. , Roca i Cabarrocas P.
Published: September 2011

We present a novel ZnO:Al fabrication process consisting of room-temperature vacuum sputtering followed by an excimer laser annealing (ELA). The ELA treatment improves the optical transmission of the films, and the film resistivities (<1 mΩ·cm) remain stable or improve with increasing laser fluence up to 0.6 J/cm2, as the carrier density increases but the carrier mobility is degraded. This process is followed by a standard dilute HCl chemical texturing step, and produces substrates with suitable texture, conductivity, and transparency properties for thinfilm photovoltaic applications. Substrates resulting from this process display elevated haze levels (80% at 600 nm and 50% at 800 nm) after the wet-chemical etching step. Such substrates have been used to make single junction hydrogenated nanocrystalline silicon solar cells, and an increase in the short-circuit current of up to 2.2 mA/cm2 is observed compared to a substrate deposited by a standard room-temperature sputtering + wet-etch process. This gain is primarily due to increased photo-response in the red due to improved light-scattering, as at wavelengths greater than 600 nm, a gain in photocurrent of up to 1.7 mA/cm2 is observed.
Current Collecting Grids for R2R Processed Organic Solar Cells
Authors: Abbel Robert , van den Boomen Jaquelien , van Lammeren Tim , de Koning Tom , Valeton Josué J. P. , Meinders Erwin R.
Published: September 2011

Exposure to highly focussed flash light (photonic flash sintering) has been developed as a technology to successfully cure printed metal inks on temperature sensitive plastic substrates. In contrast to the traditional approach of thermal oven sintering, conductivities up to 30 % of the value of bulk silver can be achieved within a few seconds without foil deformation. The compatibility of this technology with R2R production has been demonstrated with line speeds up to 5 m/min. As a consequence, our approach is expected to enable the high throughput fabrication of current collecting grids for organic solar cells in order to replace transparent electrodes based on metal oxides such as ITO. Additionally, our new sintering technology has enabled us to process a new generation of conductive inks, based on copper complexes, which cannot be processed by oven sintering.
Effect of Working Distance on Properties of Sputtered Molybdenum Films
Authors: Pethe Shirish A. , Kaul Ashwani , Dhere Neelkanth G.
Published: September 2011

Molybdenum back contact deposition is a bottleneck in high volume manufacturing due to the current state of art where multi layer molybdenum film needs to be deposited to achieve the required properties. In order to understand and solve this problem experiments were carried out. The effect of working distance (distance between the target and the substrate) on film properties was studied and is presented in this work. Earlier work carried out at Florida Solar Energy Center reflected on the effect of the sputtering power and working gas pressure on the film properties. This work is continuation of that effort in understanding effects of various sputtering parameters and determining the possible route to develop single layer molybdenum films with the required properties of near zero stress, low resistivity and good adhesion to substrate.
Transmission electron microscopy of misfit dislocation and strain relaxation in lattice mismatched III-V heterostructures versus substrate surface treatment
Authors: Wang Y. , Ruterana P. , Desplanque L. , El Kazzi S. , Wallart X.
Published: September 2011

High resolution transmission electron microscopy in combination with geometric phase analysis is used to investigate the interface misfit dislocations, strain relaxation, and dislocation core behavior versus the surface treatment of the GaAs for the heteroepitaxial growth of GaSb. It is pointed out that Sb-rich growth initiation promotes the formation of a high quality network of Lomer misfit dislocations that are more efficient for strain relaxation.
Infrared Studies of the (1-x) PbTe – (x) PbSnS2 System
Authors: Hasapis Thomas C. , Girard Steven N. , Hatzikraniotis Euripides , Paraskevopoulos Konstantinos M. , Kanatzidis Mercouri G.
Published: September 2011

In this work we report on the infrared properties of the thermoelectric (1-x)PbTe-xPbSnS2 system with x=0.03, 0.06, 0.11 and 0.33. The results obtained by the analysis of the reflectivity spectra are discussed together with the structural and morphological characteristics obtained by XRD and SEM-EDS measurements. The system was found macroscopically homogeneous for x=0.03 and x=0.06 and phase separated for x=0.11 and x=0.33. The analyzed ~150cm-1 PbS impurity mode demonstrated a composition close to the PbTe0.98S0.02 for the major phase. The incorporation of PbSnS2 causes a reduction in plasma frequency (decrease in carrier frequency concentration) and an increase in carrier mobility.
Optimizing Stressor Film Deposition Sequence in Polish Rate Order for Best Planarization
Authors: Zhang John H , Xiao Changyong , Strane Jay W , Venigalla Rajasekhar , Economikos Laertis , Hall Lindsey , Chen Jie , Stoll Derek C , Wallner Jin , Zhuang Haoren , Ferreira Paul , Kleemeier Walter , Goldberg Cindy , Moon Yongsik , Truong Connie , Sudijono John , Chen Xiaomeng , Sampson Ron
Published: September 2011

Chemical Mechanical Polish (CMP) is one of the key technologies for the development of modern high performance integrated circuits. The requirements for the CMP uniformity get extremely demanding in order to meet the litho requirements for 32nm technology node and beyond. In this paper, two kinds of orders related to the stressor films that affect the CMP uniformity are revealed. The first is the stressor films deposition order according to the CMP polish rate of each stressor film. The second is the stress gradients order that formed inside the films sitting on top of the stressors. Through the optimization of the order, we show successfully removal of couple hundreds angstroms stressor step heights within 300mm wafer range. The method developed here can also find applications in microelectromechanical systems and 3D integration circuits.
Complementary Resistive Switches (CRS): High speed performance for the application in passive nanocrossbar arrays
Authors: Rosezin Roland , Linn Eike , Nielen Lutz , Kügeler Carsten , Bruchhaus Rainer , Waser Rainer
Published: September 2011

In this report, the fabrication and electrical characterization of fully vertically integrated complementary resistive switches (CRS), which consist of two anti-serially connected Cu-SiO2 memristive elements, is presented. The resulting CRS cells are initialized by a simple procedure and show high uniformity of resistance states afterwards. Furthermore, the CRS cells show high switching speeds below 50 ns, making them excellent building blocks for next generation non-volatile memory based on passive nanocrossbar arrays.
Thick Beryllium Coatings by Magnetron Sputtering
Authors: Xu H. , Alford C. , Chason Eric , Detor A. , Fuller T. , Hamza A. , Hayes J. , Moreno K.A. , Nikroo A. , van Buuren T. , Wang M. , Wu J. , Youngblood K.P.
Published: September 2011

Thick (>150 μm) beryllium coatings are studied as an ablator material of interest for fusion fuel capsules for the National Ignition Facility (NIF). As an added complication, the coatings are deposited on mm-scale spherical substrates, as opposed to flats. DC magnetron sputtering is used because of the relative controllability of the processing temperature and energy of the deposits. We used ultra small angle x-ray spectroscopy (USAXS) to characterize the void fraction and distribution along the spherical surface. We investigated the void structure using a combination focused ion beam (FIB) and scanning electron microscope (SEM), along with transmission electron microscopy (TEM). Our results show a few volume percent of voids and a typical void diameter of less than two hundred nanometers. Understanding how the stresses in the deposited material develop with thickness is important so that we can minimize film cracking and delamination. To that end, an in-situ multiple optical beam stress sensor (MOSS) was used to measure the stress behavior of thick Beryllium coatings on flat substrates as the material was being deposited. We will show how the film stress saturates with thickness and changes with pressure.
Multicolor Luminescence from Ca3Y2(SiO4)3:Eu2+,Eu3+ Material
Authors: Dobrowolska Anna , Zych Eugeniusz
Published: September 2011

Ca3Y2(SiO4)3 powder activated with Eu was prepared with ceramic method. Its spectroscopic properties in VUV-UV-Vis region together with structure and morphology were analyzed. Luminescence measurements indicated that Ca3Y2(SiO4)3 prepared in a reducing atmosphere contained both Eu2+ and Eu3+ ions. The excitation could be tuned to generate a complex luminescence consisting of a broad band related to a blue-greenish 5d → 4f emission of Eu2+ and 4f → 4f red luminescence of Eu3+. Their superposition covered the whole visible part of spectrum and appeared almost white among others upon excitation around 390 nm.
Laser-treated Parchment Paper: An Inexpensive Microfluidic Platform
Authors: Chitnis Girish , Ding Zhenwen , Chang Chun-Li , Savran Cagri A. , Ziaie Babak
Published: September 2011

In this paper, we report on a method for fabricating an inexpensive microfluidic platform on parchment paper. Parchment paper was selected for this purpose due to its wide availability for culinary applications and hydrophobic silicone-based surface coating. We were able to selectively modify the surface structure and property (hydrophobic to hydrophilic) using a CO2 laser. The modified surface has highly-porous structure which helps to trap chemical and biological reagents for analysis. The treated surface is stable over time and can be used for aqueous droplet assembly. Finally, we demonstrated the applicability of this platform for performing chemical reaction using luminol-based hemoglobin detection.
Microstructural characterization of GaAs-AlxGa1-xAs core-shell nanowires grown by Au-catalyst assisted MOVPE
Authors: Altamura D. , Miccoli I. , Prete P. , Lovergine N. , Tapfer L.
Published: September 2011

In this work, we report on the microstructural and morphological characterization of III-V semiconductor nanowires (NWs) epitaxially grown on (111)B-GaAs substrates by Au-catalyst assisted metalorganic vapor phase epitaxy. As-grown dense (108-109 cm-2) arrays of few-micron long vertically-aligned (i.e. parallel to the <111> crystallographic axis) GaAs, AlxGa1-xAs and core-shell GaAs-AlxGa1-xAs NWs were investigated, carrying out HRXRD measurements on different (hkl) reflections and by recording reciprocal space maps (RSMs) around the materials (111) reciprocal lattice points (relps). We show that NW diffraction peaks are visible in the RSM by means of characteristic halos. In the case of GaAs NWs, the halo is located at the (111) relp indicating that the NWs are grown along the <111> direction and parallel to the <111> axis of the GaAs substrate. On the contrary, for AlxGa1-xAs NWs or intentional core-shell GaAs-AlxGa1-xAs NWs the halo is displaced (along the momentum transfer normal to the surface, Qz) with respect to the GaAs (111) relp due to the elastic lattice strain associated with the compositional variation, e.g. the Al molar fraction in the AlxGa1-xAs alloy, within the nanostructures.
Co2+ ions-containing ordered silica monoliths: Influence of the copolymer P123/Si and Co2+ ions/Si ratios on the organization of the monoliths
Authors: Delahaye Emilie , Aouadi Merwen , Durand Dominique , Beaunier Patricia , Fornasieri Giulia , Bleuzen Anne
Published: September 2011

Among the different possibilities to control the size, the shape and the spatial organization of nano-objects, one consists in the use of the ordered mesoporosity of silica matrices as nanoreactors for their synthesis. This strategy has been used to elaborate Prussian Blue Analogues (PBA) exhibiting photomagnetic properties. Since the synthesis of these nanocomposites begins with the obtention of mesoporous silica monoliths containing Co2+ ions, we focus in this paper on the effect of the quantity of Co2+ ions and the amount of surfactant on the nanostructuration of these monoliths.
Functional and Functionalized Silicate Materials
Authors: Johnson Brandy J. , Melde Brian J. , Lin Baochuan , Charles Paul T. , Malanoski Anthony P. , Nasir Mansoor
Published: September 2011

Mesoporous organosilicate materials combine tunable binding characteristics, high surface area, and low materials density with an ordered pore network. Surface modifications provide the potential for incorporation of a variety of functional groups. We have taken advantage of these characteristics for the development of a range of materials to be utilized in various applications. In one approach, porphyrins are incorporated into the materials to provide unique catalytic properties. In these materials, the organosilicate scaffold stabilizes the porphyrin catalyst and facilitates interaction of the catalyst and target. Catalysis can be stimulated through exposure to light or application of an electrical current. The selectivity of the materials can be influenced through choice of organic bridging groups in the organosilicate structure and through selection of the porphyrin component. In addition, a type of molecular imprinting can be applied to provide sites on the pore walls that enhance adsorption selectivity for the target. These materials are directed at the development of self-decontaminating surfaces and coatings. Similar materials characteristics have been utilized in the development of solidphase extraction materials for use in the pre-concentration of nitroenergetic targets from ground and surface water samples. These materials are being incorporated into systems for in situ water quality monitoring. Mesoporous organosilicates can also be applied to the encapsulation of proteins and nucleic acids, stabilizing them for wider application of technologies utilizing these reagents. Modifications to the pore surfaces, in this case, are used to incorporate stabilizing agents such as sugars and proteins which should extend shelf-life and reduce storage restrictions.