bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaling of Hafnium-based High-k Dielectrics
Authors: Triyoso Dina H. , Hegde Rama I. , Gregory Rich , Gilmer David C. , Schaeffer James K. , Samavedam Srikanth B. , Kaushik Vidya , Rochat Nevine
Published: April 2011

In this paper, various approaches to extend scalability of Hafnium-based dielectrics are reported. Among the three crystal phases of HfO2 (monoclinic, cubic and tetragonal), the tetragonal phase has been reported to have the highest dielectric constant. Tetragonal phase stabilization by crystallizing the thin HfO2 using a metal capping layer and by adding zirconium is demonstrated. The microstructure, morphology, optical properties and impurities of HfxZr1-xO2 dielectrics (for 0<x<1) are discussed. Subtle but important modification to high-k / Si interface characteristics resulting from addition of Zr into HfO2 is reported. To further boost the dielectric constant of hafnium-based dielectrics, incorporation of TiO2, which has been reported to have high dielectric constant, is explored. HfxZr1-xO2/TiO2 bilayer films were fabricated. 30 Å TiO2 films were deposited on a 5, 8, 12 or 15 Å HfxZr1-xO2 underlayer to determine the minimum thickness needed to maintain good thermal stability with Si substrate. CV and IV results indicated that 12-15 Å is the optimal thickness range for the HfxZr1-xO2 underlayer. A dielectric constant as high as 150 for TiO2 layer is extracted from TiO2 thickness series deposited on12 Å HfxZr1-xO2 underlayer. In addition to increasing the k-value of Hafnium-based dielectrics, it is important that the threshold voltage of these high-k devices is low. Here we report the use of thin Al2O3 capping layers to modulate PMOS threshold voltages. About 100 mV reduction in threshold voltage is achieved by capping HfO2 with a 5Å Al2O3 film. Finally, dielectric scaling by modifying the Si/high-k interfacial layer is attempted. Nitrogen incorporation into HfxZr1-xO2 is shown to be a simple and effective method to lower the capacitance equivalent thickness (CET) of Hafnium-based dielectrics.
Effect of Systematic Changes of Ti and Hf Si-oxynitride Alloys by Nitrogen Incorporation as a Bond Constraint on Electrical and Material Properties
Authors: Lee Sanghyun , Lucovsky Gerry , Fleming L. B. , Luning Jan
Published: April 2011

We have investigated the effect of Si3N4 content in (Ti(Hf)O2)x(Si3N4)y(SiO2)1-x-y pseudo-ternary alloys by tracking systematic changes of electrical properties, including electrically active defects. Results from Soft x-ray photoelectron spectroscopy (SXPS) studies indicate no detectable hole traps for Ti/Hf Si oxynitrides with Si3N4 content >35%; these alloys have equal concentrations of Ti(Hf)O2 and SiO2, ~30-32%, and additionally are stable for annealing in Ar ambients to temperatures of 1100°C. Derivative near edge x-ray absorption spectroscopy (NEXAS) comparisons for the O K1 edges of TiO2 and optimized Ti Si oxynitride alloys provides a significantly reduced average crystal field d-state splitting from 1.9 to 1.6eV, as well as decreased electron trapping, and is correlated with a four-fold coordination of Ti in the Ti Si oxynitride alloys. The flat band voltage shift with varying frequency from 10 kHz to 1MHz in these alloys is less than 12 mV and the compositional dependence of current-voltage characteristics on Si3N4 composition results in the lowest leakage current at a Si3N4 content of ~40 % with the smallest equivalent oxide thickness (EOT) as well. Based on these studies, Transition Metal (TM) Si oxynitride alloys are anticipated to yield EOT <1 nm for scaled CMOS devises.
Influences of Plasma Processed Interface Layers on Germanium MOS Devices with ALD Grown HfO2
Authors: Sugawara Takuya , Sreenivasan Raghavasimhan , Oshima Yasuhiro , McIntyre Paul C.
Published: April 2011

Germanium and hafnium-dioxide (HfO2) stack structures' physical and electrical properties were studied based on the comparison of germanium and silicon based metal-oxide-semiconductor (MOS) capacitors' electrical properties. In germanium MOS capacitor with oxide/oxynitride interface layer, larger negative flat-band-voltage (Vfb) shift compared with silicon based MOS capacitors was observed. Secondary ion mass spectrum (SIMS) characteristics of HfO2-germanium stack structure with germanium oxynitride (GeON) interfacial layer showed germanium out diffusion into HfO2. These results indicate that the germanium out diffusion into HfO2 would be the origin of the germanium originated negative Vfb shift. Using Ta3N5 layer as a germanium passivation layer, reduced Vfb shift and negligible hysteresis were observed. These results suggest that the selection of passivation layer strongly influences the electrical properties of germanium based MOS devices.
Impact of Interfacial Nitridation of HfO2 High-k Gate Dielectric Stack on 4H-SiC
Authors: Mahapatra Rajat , Chakraborty Amit K. , Tappin Peter , Miao Bing , Horsfall Alton B. , Chattopadhyay Sanatan , Wright Nick G. , Coleman Karl S.
Published: April 2011

HfO2 films were grown on SiO2/4H-SiC and SiON/4H-SiC layers by evaporation of metallic Hf in an electron beam deposition system followed by thermal oxidation. X-ray photoelectron spectroscopy confirmed the formation of HfO2 films. There is no evidence of formation of hafnium silicide or carbon pile up at the surface as well as at the interfacial layer. Electrical measurements show the presence of fewer slow traps in the HfO2/SiON gate dielectric stack on 4H-SiC and comparable values of interface state density. The HfO2/SiON stack layer improves leakage current characteristics with a higher breakdown field and has better reliability under electrical stress.
Rashba Spin-Splitting and Spin Currents in GaN Heterojunctions
Authors: Weber Wolfgang , Seidl Simon , Golub Leonid E. , Danilov Sergey N. , Bel'kov Vasily V. , Ivchenko Eugenious L. , Prettl Wilhelm , Kvon Zee Don , Cho Hyun-Ick , Lee Jung-Hee , Ganichev Sergey D.
Published: April 2011

Gallium nitride is a potentially interesting material system for Spintronics since it is expected to become ferromagnetic with a Curie-temperature above room temperature if doped with manganese and long spin relaxation times are detected in this material.
Mobility of Charge Carriers in Dilute Magnetic Semiconductors
Authors: Foygel Michael G. , Niggemann James , Petukhov A. G.
Published: April 2011

We studied electrical transport in dilute magnetic semiconductors, which is determined by scattering of free carriers by localized magnetic moments. In our calculations of the scattering time and the mobility of the majority and minority-spin carriers we took into account both the effects of thermal spin fluctuations and of built-in spatial disorder of the magnetic atoms. These effects are responsible for the magnetic-field dependence of the mobility of the charge carriers. The application of the external magnetic field suppresses the thermodynamic spin fluctuations thus increasing the mobility. Simultaneously, depending on the type of the carriers and on parameters of the impurity potential, scattering by built-in spatial fluctuations of the atomic spins increases or decreases with the magnetic field. The latter effect is due to the change in the magnitude of the random local Zeeman splitting with the magnetic field. We discuss the role of the above effects on mobility and magnetoresistance of semiconductors where magnetic impurities are electrically active or neutral.
Structural Effects of Transition Metal Oxide Calcinations on Wurtzite Type Semiconductors That are Ferromagnetic at Room Temperature
Authors: Moeck Peter , Noice Lori , Li Chunfei , Gupta Amita , Erni Rolf , Browning Nigel D. , Rao K.V.
Published: April 2011

Gallium nitride powders and zinc oxide powders were each calcined with a few weight percent of copper oxide and/or magnesium oxide either in air or N2. Powder X-ray diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy were performed in order to observe calcination induced structural effects on these wurtzite type semiconductors. We note that our earlier magnetic results on Cu doped GaN are qualitatively consistent with recent first principle calculations [Wu et al., Appl. Phys. Lett. 89 (2006) 62505].
Correlations Between Optical Transmission and Magnetic Properties of Doped and Undoped GaMnN
Authors: Mahros Amr M. , Luen M. O. , Emara A. , Berkman E. A. , Arkun F. E. , Zhang X. , Muth J. , El-Masry N. A. , Bedair S. M.
Published: April 2011

Ferromagnetism (FM) in GaMnN was found to be related to the position of the Fermi level relative to the Mn deep-level band. The location of the Fermi level can be altered by doping GaMnN with Si (n-type) and Mg (p-type) dopants, resulting in a ferromagnetic to paramagnetic transformation. We have found that this manipulation of the Fermi level also can affect the optical properties of GaMnN, GaMnN: Mg and GaMnN: Si. The major optical absorption bands were found either to be enhanced or diminished depending on the level and nature of the doping elements. Therefore, a correlation between optical properties and saturation magnetization of GaMnN can be established.
Interface Properties of PrxAl2-xO3 (x = 0 to 2) Dielectrics on TiN Studied by Synchrotron Radiation X-ray Photoelectron Spectroscopy
Authors: Lupina Grzegorz , Schroeder Thomas , Wenger Christian , Dabrowski Jarek , Lippert Gunther , Müssig Hans-Joachim
Published: April 2011

Extending the scalability of deep trench capacitor dynamic random access memories requires introduction of a high-k dielectric-based storage capacitor structure. Pr-enriched Al2O3 dielectrics with TiN electrodes appear as a promising materials system for this application. Electrical measurements performed on this materials combination show, however, that achieving a very low capacitance equivalent thickness and low leakage current requires very careful control of the electrode/dielectric interface properties. In particular, formation of a parasitic interface layer has to be avoided. For this purpose, we carried out a systematic synchrotron radiation x-ray photoelectron spectroscopy study to non-destructively investigate the interface reactivity of the PrxAl2-xO3 (x = 0, 1, 2)dielectrics with TiN metal electrodes. The depth profiling study shows that the TiN substrate is covered with a native TiO2. Additionally, a thin interfacial Ti oxynitride layer is present between these compounds, resulting in a TiN/TiNO/TiO2 materials stack. Molecular beam deposition of Al2O3 onto substrates of this structure leads to a remarkable reduction of the native oxide. In contrast, in the same way deposited PrAlO3 and Pr2O3 dielectrics are significantly less reactive towards TiO2. As a consequence, the native TiON/TiO2 remains the main component of the interface layer in the TiN/PrAlO3 and TiN/Pr2O3 capacitor stacks. Such a configuration poses severe scalability problems to the Pr aluminate dielectrics.
Transport AC Losses of YBCO Coated Conductor Coils
Authors: Grilli Francesco , Ashworth Stephen P.
Published: April 2011

Certain practical applications of YBCO coated conductors (CC) involve superconducting tapes wound in coils. In such a configuration the superconducting tape is arranged as closely packed turns, leading to an increase of the magnetic field generated by the current in the tapes and, consequently, a significant increase in the AC losses, with respect to an ‘isolated’ tape. In order to predict and reduce the refrigeration requirements of applications, it is therefore very important to be able to quantify the magnitude of such AC losses, both experimentally and by means of numerical calculations.
Robust Printing and Dispensing Solutions with Three Sigma Volumetric Control for 21st Century Manufacturing and Packaging
Authors: Li Bo , Clark Patrick Alan , Hail Kenneth
Published: April 2011

The trend for the electronics industry to develop more functional, smarter and more compact devices has stressed the traditional manufacturing and packaging processes including the printing/dispensing technology. The traditional printing technique (e.g. time-pressure needle dispensing, screen printing, pin transfer and jetting) each has their own disadvantages in terms of dimensionality, accuracy, repeatability, flexibility and consistency, which have become the bottle neck of the industry. Enabling tools and technologies are greatly needed for the manufacturing and packaging of highly integrated and complicated parts and assemblies. In this paper, nScrypt will present novel pumping technologies and innovative printing/dispensing solutions for 21st century manufacturing and packaging. nScrypt's novel pump and robust system can dispense with precise volume control for tens of picoliter resolution, accurately place or align within a few microns, conformably print on exaggerated surfaces of tens of centimeters, and are flexible with materials and patterns. Dispensing of micro lines, dots, three-dimensional structures and conformal printing will be presented. This process has a wide range of applications including, but not limited to, conductors, resistors, optics, adhesives, sealants, frit, solders, encapsulates, wire bonding, underfilling, flip-chip bumping and 3-D structures.
Hot Embossing of Electron Beam Generated Structures in Polypropylene
Authors: Leech Patrick W.
Published: April 2011

The hot embossing of electron beam generated structures with linewidths 0.35-3.25 μm has been examined in biaxially-oriented polypropylene (BOPP). The individual test elements consisted of pixels of 30 x 30 μm with a specific configuration of symbols and lettering. The embossing of these features has been performed as a function of temperature (80-140 °C) and applied pressure (2-20 kPa). Significant increases in both embossed depth and sidewall angle was evident over the temperature range 100 to 130 °C with a leveling off at higher temperatures attributed to the onset of a regime of viscous liquid flow. At temperatures within this regime, a critical level of pressure was required to fill the mold features. Accurate embossing of medium and coarse lettering (0.50-0.65 μm linewidth) and geometric symbols (1.25-3.25 μm linewidth) has been demonstrated at a temperature of 130 °C and an applied pressure of 13 kPa. The finest lettering (0.35 μm linewidth) was incompletely embossed under these conditions.
Photoinduced Charge Transfer at Hybrid Semiconductor Interfaces
Authors: Cabanillas-Gonzalez Juan , Egelhaaf Hans Joachim , Lanzani Guglielmo , Brambilla Alberto , Duò Lamberto , Finazzi Marco , Ciccacci Franco
Published: April 2011

We monitor in real time photoinduced charge injection at the interface between a fluorinated copper phthalocyanine layer (CuPcF16) deposited by thermal evaporation on top of a p - doped GaAs (100) wafer. Literature data on the electron affinity of CuPcF16 (5.2 eV respect to vacuum level) combined with photoemission measurements indicates an energy offset of 1.1 eV for the GaAs conduction band respect to the CuPcF16 LUMO level. This suggests that charge transfer at the organic - inorganic interface is feasible. We study bilayers of GaAs and CuPcF16 thin films (25 nm) by pump - probe spectroscopy with 200 fs time resolution. Pump photons at 780 nm excites the CuPcF16 layer whereas probe photons in the visible range, reflected by the GaAs surface, monitor induced changes at the interface. We observe a strong photoinduced absorption band centered around 560 nm which appears during the pulse duration, shows a build-up dynamics and persists beyond 0.2 ns. This band cannot be attributed to single material contribution, as demonstrated by test experiments with single layers. By applying steady state (CW) electromodulated spectroscopy we identify charge state absorption in CuPcF16 in the same spectral region as the photoinduced absorption band. We thus assign our transient dynamics to formation of CuPcF16 ions at the interface, following charge injection. On account of the rapid charge formation we identify this system as a potential candidate for the fabrication of hybrid photodiodes.
Engulfment of Protruding Micro-Nails Fabricated on Chip Surface by Cultured Neurons Improve Their Adhesion to The Electronic Device
Authors: Spira Micha E. , Kamber Dotan , Dormann Ada , Cohen Ariel , Bartic Carmen , Borghs Gustaaf , Shabthai Keren , Langedijk J.P.M. Langedijk , Yitzchaik Shlomo , Shappir Josef.
Published: April 2011

One of the major problems in assembling efficient neuro-electronic hybrids systems is the low electrical coupling between the components. This is mainly due to the low resistance, extracellular cleft formed between the cell's plasma membrane and the substrate to which it adhere. This cleft shunts the current generated by the neuron, or the device and thus reduces the signal to noise ratio. To increase the clefts electrical resistance we fabricated gold micronails that protrude from the transistor gate surface. The micronails were functionalized by phagocytosis facilitating peptides. Cultured neurons readily engulf the functionalized micronails forming tight physical contact between the cells and the surface of the device
Characterization of a Micro Capillary Zone Electrophoresis System With Integrated Amorphous Silicon Based Optical Detectors
Authors: Schöler Lars , Seibel Konstantin , Schäfer Heiko , Püschl René Johannes , Wenclawiak Bernd , Böhm Markus
Published: April 2011

Application specific Lab-on-Microchips (ALMs) making use of the combination of complex microfluidic networks with microelectronic circuits and micro optical components allow the realization of miniaturized application specific biological and chemical processing and analysis devices. Fluorescence sensing is one of the most widely used detection technologies, e.g. for DNA fluorescence labelling in Micro Capillary Electrophoresis (µCE) due to its superior sensitivity and specificity. Unfortunately, commercially available fluorescence sensing systems are physically very large, non portable, expensive and constrain the analysis in portable diagnostic and medical care. Integrated semiconductor optoelectronic devices can provide a portable, parallel and inexpensive solution for on chip fluorescence sensing.

Most µCE applications working in the spectral range of visible light. For the integration of optical detection components a photon energy range of 1.6 eV - 3.1 eV is of interest. The a-Si:H technology accomplished due to the low dark current and high absorption coefficient against to crystalline silicon the requirements in that spectral range. In this paper we combine a:Si-H photo sensors with a fluidic micro system to detect the fluorescence of a rhodamine analyte mixture. The analyte mixture was excited by light with a wavelength in the range of λEx = 450 - 490 nm. The a-Si:H detector reveals a low dark current density on the order of 10-10 A/cm2 and a sufficient dynamic range of ∼100 dB under illumination of ∼1000 lx as a function of bias voltage. The measurement shows that the movement of the rhodamine plug in the microchannel causes a significant rise in the pin-diode photo current, which correlates to the evaluated signal of a microscope image detector. The photo current difference for excitation and additional fluorescence amounts to 2.4 µA.
Development of a Lab-on-a-Chip for the Characterization of Human Cells
Authors: Ertl Peter , Richter Lukas , Mak Andy , Stepper Christoph , Kast Michael , Brückl Hubert
Published: April 2011

Microfabricated biochips are developed to continuously monitor cellular phenotype dynamics in a non-invasive manner. In the presented work we describe the novel combination of contact-less micro-dielectric sensors and microfluidics for quantitative cell analysis. The cell chip consists of a polymeric fluidic (PDMS) system bonded to a glass wafer containing the electrodes while temperature and fluid flow are controlled by external heating and pumping stations. Additionally, the cell chip contains an integrated reference arm providing a low-noise detection environment by eliminating background signals and interferences. The high-density interdigitated capacitors (µIDC) are designed to monitor living cells in a space of approximately 10 nL volume by controlling critical electrode characteristics, such as size, shape and passivation composition as well as thickness. The integrated µIDCs are isolated by a 300 nm multi-passivation layer of defined dielectric property and provide non-invasive, stable, robust and non-drifting measurement conditions. The performance of this detector is evaluated using various bacterial, yeast and mammalian cells.
Polarized Silver Nanoparticles by Ionic Liquid and Its Application to Facilitated Olefin Transport Membranes
Authors: Kang Sang Wook , Char Kookheon , Kang Yong Soo
Published: April 2011

The BMIM+NO3-/Ag metal nanocomposite membranes were utilized for separation of propylene/propane mixtures. The selectivity of propylene/propane and the mixed gas permeance increased to 10 and 1.3 GPU, respectively. It is anticipated that the interactions between NO3- of BMIM+NO3- and the surface of silver nanoparticles causes the Ag surface to be partially positively charged, resulting in the reversible complexation with propylene and consequently facilitated propylene transport. The surface positive charge was confirmed from the increase in the binding energy of the d5/2 orbital of the silver nanoparticles by x-ray photoelectron spectroscopy. It increased from 368.26 for the neat silver nanoparticles to 368.47 eV for BMIM+NO3-/Ag metal composite. The positively charged surface of silver nanoparticles can be utilized as a new durable olefin carrier for facilitated transport.
New Organo-Inorganic Materials for Water Contaminants Remediation
Authors: Ortiz-Polo Araceli , Richards-Uribe Rosa M , Otazo-Sánchez Elena M , Prieto-García Francisco , Hernández-Ávila Juan , Acevedo-Sandoval Otilio , Gordillo-Martínez Alberto
Published: April 2011

Materials with high specific surface areas such as pillared clays and zeolites have been studied and can be used to remediate contaminated water. Chemical functionality or compounds can be anchored or attached to the surface of a low-cost material used as a support matrix. This work studied the suitability of inexpensive natural mineral soils to decontaminate waste water from mine and metallurgic industries. Native mineral soils were also impregnated with commercial 1,3 diphenyltiourea (DFT) to improve retention of heavy metal ions. The natural mineral soils were from Hidalgo State in Mexico: white marble (calcite: CaCO3), volcanic gravels named “red and black tezontles” (anorthite matrix: CaO.Al2O3.(SiO2)2with FexOyand PbxOy), green zeolites (mordenite: Na2CaK2.OAl2O3.10SiO2.7H2O) and kaolin (kaolinite: Al2O3(SiO2)2.H2O). They were ground and sieved. The 50 mesh fraction was studied by Raman and FTIR spectroscopy, X ray powder diffraction and scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX). From these solids new hybrid materials were prepared by impregnation with DFT in ethanolic solutions. Products were characterized and compared with untreated materials. Tezontles, zeolites and kaolinite showed the best impregnation levels. In their surfaces, grown DFT crystals showed different structures. The obtained hybrid solids were tested using several metallic ion solutions: Mn(II), Ni(II), Co(II), Cd(II), Hg(II), Pb(II), Cu(II) and Zn(II). The metallic adducts were analyzed and the adsorption capacity is discussed. The materials showed high remotion percentages for all metal ions and low Hg(II), Pb(II) and Cd(II) final concentrations. They have good potential for use in remediation of contaminated water with highly toxic metal ions. The metallic adducts were characterized by FTIR and Raman spectroscopy, as well as SEM/EDX analysis. However, all of mentioned methods were not useful for detection of impregnated DFT nor adsorbed or coordinated metallic ions on the supporting materials. Only the SEM/EDX method was found to be suitable for analysis.
3D Composites Based on Hydroxyapatite-Chitosan-Polysiloxane as a Biomimetic Scaffold Materials
Authors: Neira-Carrillo Andrónico , Arias José Ignacio , Fernández M. Soledad , Pai Ranjith Krishna , Quilodrán C Claudia , Arias José L
Published: April 2011

Three-dimensional (3D) composites of hydroxyapatite, phosphorylated and/or nonphosphorylated chitosan and sulphonated methylsiloxane polymer (HA/P-CHI: CHI/ S-MSP) were prepared by solid-liquid phase separation and solvent sublimation method. The HA, P-CHI and S-MSP were synthesized by chemical continuous wet-calcination, phosphorylation reaction and hydrosilylation-sulphonation reactions, respectively. 3D composites were analyzed by scanning electron microscopy (SEM). Swelling ability, stability and formation of HA particles on the composites immersed in simulated body fluid (SBF) were analyzed. Osteoblasts showed high viability when cultured on composite scaffolds. 3D composites were not degraded after 8 weeks of subcutaneous implantation in rats.
Design of Functionalized Fe3O4 Nanoparticles for Elaboration of Nanostructured Films with Magnetic Properties
Authors: Daou Toufic Jean , Mammeri Fayna , Buathong Saïwan , Bras Yves Le , Ung Diane , Gallani Jean Louis , Donnio Bertrand , Guillon Daniel , Pourroy Geneviève , Begin-Colin Sylvie
Published: April 2011

There is currently a great interest in the preparation of nanostructured magnetic films possessing well-defined structures and controlled properties. Recent progresses in colloidal nanocrystals synthesis and processing have led to new methods for producing films and superstructures made with these materials. Hybrid films have been prepared by organizing functionalized magnetite nanoparticles in large patterns using the Langmuir Blodgett technique. Magnetite nanoparticles with an average particle diameter of 39nm have been prepared and then coated with amphiphilic molecules. The resulting decorated particles, with a hydrophobic outer layer, have proven suitable for being processed by the LB technique. The microstructure and the compacity of the nanoparticle arrays appear to depend on the nature of the organic moiety used to decorate the nanoparticles (carboxylate or phosphonate end-capped stilbene derivatives).
Titanium Oxo-Clusters: Vesatile Nano-Objects for the Design of Hybrid Compounds
Authors: Rozes Laurence , Cochet Sébastien , Frot Théo , Fornasieri Giulia , Sassoye Capucine , Popall Michael , Sanchez Clément
Published: April 2011

The description of three titanium oxo-clusters and their use as inorganic components of hybrid organic-inorganic materials are reported. The first approach consists to add titanium oxo-clusters, [Ti6O4(C6H5COO)8(OPrn)8], in an ORMOCER⊗ based hybrid medium. Nano-sized titanium oxo-clusters combined with the chemical nature of the components, allow the tuning of the optical properties, especially the refractive index. The second approach consists to associate functionalized titanium oxo-clusters to elaborate hybrid materials with perfectly defined inorganic domains. The more relevant example of titanium oxo-cluster to build hybrid networks from nano-building blocks is the oxo-cluster [Ti16O16(OEt)32]. Indeed, the nature and the number of functional groups at the surface of these metallic oxo-clusters can be tuned in order to generate cross-linking agents of organic polymers. The studies of the structure-property relationships of the resulting nanocomposites have been investigated. Finally the structure of a purely carboxylate oxo-clusters is briefly described. This new family of stable oxo-clusters opens the way for the production of original hybrid compounds.
Mimicking the Nature to Achieve Superhydrophobic Surfaces by Vapor Phase Deposition
Authors: Gupta Sushant , Chakkaravarthi Arul Arjunan , Singh Rajiv , Stevens Nate , Opalko Jeff , Singh Deepika
Published: April 2011

A novel technique was developed to create superhydrophobic polytetrafluoroethylene (PTFE) surface using nanosecond pulse electron deposition (PED) technique. The PTFE or Teflon thin films deposited on silicon substrate showed superhydrophobicity evidenced by the contact angle of 166±2 degrees. The SEM micrographs reveal the clustered growth of the deposited film and two level sub-micron asperities which is corroborated by the AFM. FTIR and contact angle studies were conducted to study the chemical nature and the wetting properties of the films.
Hydroxyapatite Coatings Produced by Right Angle Magnetron Sputtering for Biomedical Applications
Authors: Hong Zhendong , Mello Alexandre , Yoshida Tomohiko , Luan Lan , Stern Paula H. , Rossi Alexandre , Ellis Donald E. , Ketterson John B.
Published: April 2011

Hydroxyapatite coatings have been widely recognized for their biocompatibility and utility in promoting biointegration of implants in both osseous and soft tissue. Conventional sputtering techniques have shown some advantages over the commercially available plasma spraying method; however, the as-sputtered coatings are usually non-stoichiometric and amorphous which can cause some serious problems such as poor adhesion and excessive coating dissolution rate. A versatile right-angle radio frequency magnetron sputtering (RAMS) approach has been developed to deposit HA coatings on various substrates at low power levels. Using this alternative magnetron geometry, as-sputtered HA coatings are nearly stoichiometric, highly crystalline, and strongly bound to the substrate, as evidenced by analyses using x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). In particular, coatings deposited on oriented substrates show a polycrystalline XRD pattern but with some strongly preferred orientations, indicating that HA crystallization is sensitive to the nature of the substrate. Post deposition heat treatment under high temperature does not result in a marked improvement in the degree of crystallinity of the coatings. To study the biocompatibility of these coatings, murine osteoblast cells were seeded onto various substrates. Cell density counts using fluorescence microscopy show that the best osteoblast proliferation is achieved on an HA RAMS-coated titanium substrate. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.
Plasma Deposited Porphyrin/Phthalocyanine Films as Promising Optical Gas Sensing Materials
Authors: Maggioni Gianluigi , Tonezzer Michele , Carturan Sara , Quaranta Alberto , Severova Katerina , Della Mea Gianantonio
Published: April 2011

5,10,15,20 meso-tetraphenyl porphyrin (H2TPP) and copper phthalocyanine (CuPc) films have been deposited by means of a recently developed plasma based technique named glow discharge induced sublimation (GDS). The two macrocycles have been deposited by vacuum evaporation (VE) and H2TPP by spin coating (SPIN) as well for comparison. The physical properties of the films have been characterized by means of scanning electron microscopy (SEM) and nitrogen physisorption measurements. SEM images and physisorption isotherms highlight both the much higher surface roughness and specific surface area of GDS samples with respect to the VE and SPIN ones. Optical sensing measurements, performed in differently concentrated ethyl alcohol atmospheres, highlight that GDS samples yield much higher response intensities than SPIN and VE films, short response times and complete recovery.
Synthesis and Characterization of Electropolymerized Porphyrin Nanofibers
Authors: Walter Michael G. , Wamser Carl C.
Published: April 2011

Electrochemical oxidation of tetrakis-5,10,15,20-(4-aminophenyl)porphyrin (TAPP) on fluorine-doped tin oxide electrodes leads to a conductive polymeric film (poly-TAPP) with a nanostructured fibrous morphology. The nanofiber structure and growth rate are enhanced by the addition of pyridine (5 - 15%) to the dichloromethane electrochemical solution. Electropolymerization in the absence of pyridine leads to a more highly bundled poly-TAPP structure with a spectrum indicative of protonated porphyrin units. Testing of poly-TAPP electrodes in an electrochemical iodide cell and in a 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (PCBM) integrated solid state photovoltaic cell indicates modest photoactivity.
3D Photonic Crystals as Diffractive and Energy Selective Filter for Tandem Thin Film Solar Cells
Authors: Wehrspohn Ralf B. , Bielawny Andreas , Rockstuhl Carsten , Lederer Falk
Published: April 2011

We suggest a photonic structure with energy selective and diffractive properties to be incorporated in thin-film tandem solar cells. Our device enhances the pathway of incident light within a amorphous silicon photovoltaic (PV) top cell in its spectral region of low optical absorption. This leads to an increase in the short-circuit current of the top cell. For a conductive inverted opal structure as intermiediate layer, we numerically determine an current increase of 1.44mA/cm2 for an a-Si:H / c-Si thin-film tandem cell corresponding to an increase in the absolute efficiency from 11.1% to 12.4%.
Bragg Reflector Waveguide and Electro-Optic Modulator Based on Barium Titanate Epitaxial Thin Films
Authors: Liu Zhifu , Lin Pao-Tai , Wessels Bruce W.
Published: April 2011

We report the nanofabrication of Bragg reflector waveguide structure based on barium titanate (BTO) epitaxial thin film grown on MgO substrate and characterized its optical transmission. A low pressure (~1 Torr) nano-lithography was used for the formation of Bragg reflector waveguide structure. We demonstrate that there is sufficient refractive index contrast to form a well-defined stop band by forming gratings in a top strip layer of Si3N4 that was grown on BTO thin film. Simulation of the optical transmission and stop band of TE mode, and electro-optic (EO) modulator tunability are discussed as well. The non-linear photonic crystal waveguides are potentially suitable as tunable optical filters and ultra-wide bandwidth modulators.
Angular Dispersion of Photonic Pseudogap in Opal vs Inverse Opal
Authors: Teh Lay Kuan , Wong Chee Cheong
Published: April 2011

We have recently achieved a non-dispersive, low-order pseudogap in the blue region near the L-point in electrodeposited ZnO inverse opal. This behavior is a consequence of the change in the interconnecting network of interstices from a low dielectric (air) in the opal to a high dielectric one in the inverse opal. To verify this, we present the calculated photonic bands along the LW direction, which corresponds to the angular range explored experimentally by means of angle-resolved spectroscopy. We also studied the dispersion as a function of refractive index contrast (RIC). Further increase of the RIC above the threshold necessary to open up a complete photonic bandgap between the 8th and 9th bands does not have significant effects on improving the non-dispersive characteristic in the pseudogap. The results could be extended to make other inverse photonic structures of different symmetry with non-dispersive bands suitable for the study of optical processes involving low group velocity.
Organic/Inorganic Hybrid Glasses Doped with (Erbium-ions/CdSe) Nanoparticles for Laser Amplifications
Authors: Choi Kyung
Published: April 2011

Hybrid organic/inorganic silicate materials are employed to incorporate rare-earth metal ions for laser amplification applications. Performance of laser amplifiers doped with rare-earth ions significantly relies on glassy hosts. We thus designed and synthesized highly fluorinated glassy hosts doped with biphase of Er3+/CdSe nano-particles. Fluoroalkylene-bridged xerogels containing Er3+-ions show low absorptions at the 1540 nm in this study. The presence of CdSe nano-particles also significantly influences the fluorescence environment of Er3+-ions in the fluorinated glassy matrices.
Fourier Transform Infrared Absorbance and Photoluminescence Spectroscopy Studies of CdSe Colloidal Quantum Dot/Conducting Polymer Nanocomposites for Application to Infrared Photodetectors
Authors: Lantz Kevin R. , Stiff-Roberts Adrienne D.
Published: April 2011

In this paper we investigate the optical properties of four CdSe colloidal quantum dot/conducting polymer nanocomposites deposited on GaAs substrates using photoluminescence and Fourier transform infrared spectroscopy absorbance. The purpose of this investigation is to find an appropriate electron-conducting polymer for use in a photoconductor that utilizes intraband transitions in the conduction band to detect mid- to long-wave-infrared radiation. As a feasibility demonstration, we fabricate a two-terminal photoconductor and characterize its dark current and spectral responsivity (at 125 K), demonstrating intraband peaks at 0.465 and 0.527 eV, which correspond to 2.67 and 2.35μm.
Micromachining for Terahertz Artificial Materials
Authors: Gallant Andrew , Swift G. Peter , Dai De Chang , Kaliteevski Mikhail , Zeze Dagou A , Wood David , Petty Michael C , Brand Stuart , Abram Richard A. , Chamberlain J. Martyn
Published: April 2011

In this paper we report on the development of micromachined filters for operation at terahertz frequencies. SU8, a negative photodefinable epoxy, is used to define arrays of high aspect ratio rods which are subsequently sputter coated in gold to form the filter. We fabricate and test a filter with a fixed period but variable diameter along the length of the array. By moving the array in the terahertz beam we demonstrate the ability to mechanically tune specific filter characteristics from a single device.
Support Controlled Catalytic Chemical Vapor Deposition of Carbon Nanotubes
Authors: Wang Yunyu , Li Bin , Luo Zhiquan , Shi Li , Yao Zhen , Bryan Eugene N , Nemanich Robert J , Ho Paul S
Published: April 2011

Carbon nanotubes (CNTs) have been grown by catalytical chemical vapor deposition (CCVD) with a thin iron layer as the catalyst. High surface tension metal, tantalum (Ta), and low surface tension, SiO2, have been deposited as the supporting layers before depositing the catalysts. SEM, TEM, STEM and EELS have been used to examine the morphology, structure, and chemical profile of iron nanoparticles and CNTs. The results have shown that the catalyst nanoparticle morphologies were distinctly different on two supports. In particular, Fe nanoparticles on SiO2 were found to follow a Vollmer-Weber (VW) growth mode and a Stranski-Krastanov (SK) growth mode on Ta. It was also found that CNT growth varied significantly on two supports in terms of morphology, growth rate and growth mode. Dense CNTs were grown on Ta with fast growth rates (> 1µm/min) and vertical alignment for the iron thicknesses of 1.5-9 nm. In contrast, CNTs grown on SiO2 exhibited a slow growth rate (< 100 nm/min) with all deposited iron thicknesses, indicating a severe catalyst poisoning. The results suggested that the catalyst morphology in combination with the presence of an iron wetting layer contributed to the enhanced CCVD growth of CNTs on Ta.
Growth of Boron Nanowires by Chemical Vapor Deposition
Authors: Guo Li , Singh Raj N.
Published: April 2011

Motivated by the extensive research on carbon nanotubes (CNTs), boron and its related nano-structures have attracted increasing interests for potential applications in nanodevices and nanotechnologies due to their extraordinary properties. B-related nanostructures are successfully grown on various substrates in a CVD process. The boron nanowires have diameters around 50-200 nanometers and lengths up to a few microns. The gas chemistry is monitored by the in-situ mass-spectroscopy, which helps to identify reactive species in the process. Modified vapor-solid growths as well as VLS growth mechanisms are proposed for the growth of these nanostructures. The role of the catalysts in the synthesis is also discussed.
Composition and Strain Dependence of the Piezoelectric Coefficients in Semiconductor Alloys
Authors: Hammerschmidt T. , Migliorato M. A. , Powell D. , Cullis A. G. , Srivastava G. P.
Published: April 2011

We propose a tight-binding model for the polarization that considers direct and dipole contributions and employs microscopic quantities that can be calculated by first-principles methods, e.g. by employing Density Functional Theory (DFT). Applying our model to InxGa1-xAs alloys allows us to settle discrepancies between the values of e14 as obtained from experiments and from linear interpolations between the values of InAs and GaAs. Our calculated piezoelectric coefficient is in very good agreement with photo current measurements of InAs/GaAs(111) quantum well samples.
Direct Assembly of Quantum Confined Nano-Particles
Authors: Pluemel Ingo , Hitzbleck Klemens , Rangelow Ivo W. , Meijer Jan , Wiggers Hartmut
Published: April 2011

Advances in nanoparticle technology enable the production of new types of electronic devices, catalytic systems and complex functional surface coatings. For most of these applications, random deposition or self-assembled arrangement of the particles on surfaces are sufficient. However, an increasing number of potential applications such as single electron transistors and quantum computers require exact placement of single nanoparticles with sub-10 nm resolution and specific size. Till date, techniques that provide an exact online placement of countable and size-selected nanoparticles for functional devices have not been reported. For this purpose a cluster-jet system, based on a gas-phase nanoparticle synthesis source, connected to a focussing collimator system has been developed. The objective of this technique is to assemble countable single nanoparticles with spatial resolution of 10 nm or below onto a pre-structured substrate. In the first stage of this system, nanoparticles in the size regime between 3 and 10 nm are synthesized in a lowpressure microwave plasma reactor. This reactor has the unique advantage of generating particles with defined size distribution, structure, morphology and low degree of agglomeration due to coulomb repulsion during particle formation and growth. Separated single particles are extracted by means of a particle laden molecular beam. A mass filter consisting of a particle mass spectrometer (PMS) coupled to the reactor is used to select nanoparticles of a specific size, according to their mass, charge and kinetic energy. In order to achieve the designated lateral resolution, the particle laden beam will be collimated by electromagnetic lenses and focused onto a pierced AFM-tip. Operation of the focusing mechanism and tip preparation have been successfully performed separatly and are currently being adapted to the use in the cluster-jet system. After completion, this technique is intended to enable the assembly of nanoparticles in almost any desired two-dimensional structure onto a substrate.
Silica Nanoparticles Three Dimensional Assembly: An Integrative Chemistry Approach Toward Designing Opal-Like Silica Foams
Authors: CARN Florent , BACKOV Renal
Published: April 2011

Novel meso-/macroporous SiO2 monoliths have been reached by applying a nanotectonic pathway within a confined geometry, i.e. a non-static air-liquid foam pattering process. Final scaffolds are a very close transcription of the tailored periodic air-liquid foam template while highly ordered close-packed silica colloids are texturing the as-synthesized foam walls. The interconnected nanoparticles and associated void space between adjacent particles allow generating intrinsic mesopores, thereby defining hierarchically organized porous scaffolds. The good control over both the air-liquid foam's water volume fraction and the bubble size allow a rational tuning of the macropore shape (diameter, Plateau border's width). At the nano-scale, heterogeneous textural character is associated with abrupt variation in the film's topology certainly governed by the complex liquid flow present within the foam film. This flow induces a surfactant concentration gradient that causes a sort of marginal regeneration on the side of the film. According to these observations, the heterogeneous character of the film surface revealed by AFM can be interpreted like a direct expression of the liquid flow within the air-liquid foam's film.
Transmission Electron Microscopy Study on the Surface Properties of CNTs and Fullerites Exposed to CF4 Plasma
Authors: Shoda Kaoru , Takeda Seiji
Published: April 2011

Various types of CNTs, i.e. single-wall, double-wall, triple-wall, quadruple-wall and multi-wall carbon nanotubes (CNTs), and fullerites were fluorinated in inductive coupled radio-frequency (RF) CF4 plasma at 13.56 MHz, and their structural and bonding properties were investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). We have discussed the correlation between the number of graphene sheets in a CNT and the stability against the fluorination. TEM and XPS analysis clearly state that increase of the number leads to the gain of fluorinated stability. The fluorination of CNTs is initiated at outer tubes and proceeds to inner tubes with increasing RF power, but fluorination depth is limited to only surface area. The fluorination of fullerites forms amorphous layer at the surface, and increases the depth of the layer with RF power.
Modeling and Simulation of n-Type Carbon Nanotube Field Effect Transistors Using Ca as Contact Electrodes
Authors: Khan Aurangzeb , Shah A. Q.S , Gou Jihua
Published: April 2011

In this research work, a model has been proposed in view of the recent experimental demonstration using Calcium (Ca) as a contact metal to realize the n-type carbon nanotube field effect transistors (CNTFET). In order to fully optimize this proposed device model, effects of different parameters like the work function, oxide thickness, the oxide capacitance and the source velocity limits were studied. Among all the parameters, the work function of the contact metal plays an important role for controlling the flow of carriers through the carbon nanotube channel and to reduce the threshold voltage. A semi-classical simulation of the proposed n-type CNTFET has been performed. Results show an excellent subthreshold swing value of 62.91 mV/decade, close to the International Technology Roadmap for Semiconductor (ITRS) specifications.
Electrical and Thermal Properties of Carbon Nanotube Polymer Composite Films
Authors: Dervishi Enkeleda , Li Zhongrui , Saini Viney , Biris Alexandru R. , Lupu Dan , Trigwell Steve , Biris Alexandru Sorin
Published: April 2011

The electrical and thermal properties of carbon nanotubes (CNT)-polymer nanocomposite materials have been studied. The carbon nanostructures were analyzed by several analytical techniques, including Electronic Microscopy, Raman Spectroscopy, and X-Ray Photoelectron Spectroscopy. Carbon nanotubes were grown by catalytic chemical vapor deposition on metal/metal oxide catalytic systems using acetylene or other hydrocarbons. Raman Spectroscopy was used to analyze the CNT and CNT-polymer nanocomposite materials. The thermal and electrical properties of these CNT-polymer nanocomposite materials depend on the amount of CNTs in the polymer and also on the uniformity of the CNTs dispersed in the polymer. A reduction in electrical resistivity was observed, as the nanotubes' concentration in the polymeric films increased, while optical transparency remained 85 % or higher relative to acrylic films without nanotubes.