bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple Detection of Binding Events Using an Anchoring Transition of Liquid Crystals on the Immobilized oligoDNAs
Authors: Kim Hak-Rin , Choi Min-Geon , Kim Joo-Eun , Choi Eui-Yul , Oh Sang-Wook , Kim Jae-Hoon
Published: April 2011

To detect biological events, biosensors require a transducer part where specific biomolecular binding events at a bioreceptor part is converted to measurable quantitative signals. Currently, most of biosensors adopt a fluorescent or radioactive probing technique as a transducer. However, such approaches require expensive and sophisticated analysis procedures with laboratory-based equipment.

In this work, we propose a novel method for optically detecting hybridization results in a deoxyribonucleic acid (DNA) chip using an anchoring transition of liquid crystal (LC) alignment. To investigate the effects of structural changes of DNA on the LC alignment, we used a functional substrate on which single-stranded oligonucleotide DNA (ssDNA) was selectively immobilized to a Biotin Chip substrate. In our experiment, we used a 19-mer oligoDNA or p53 tumor suppressor as a bioreceptor and its complementary partner oligoDNA as a target material.

Before hybridization, surface nematic LC (NLC) molecules on the immobilized ssDNAs are homeotropically aligned by a steric interaction between the freely penetrated NLC molecules and the ssDNA. After hybridization, the penetration of the NLC molecules is hindered by the double strand DNA (dsDNA) due to their increased packing density. Such an interface condition makes the surface ordering of the NLC molecules very weak, as a result, the NLC in the bulk has a planar inhomogeneous orientation. Although hybridization events of the DNA and the subsequent molecular interaction between the immobilized DNA and the NLC molecules takes place within a layer whose thickness is in the tens of nm, such binding events can be communicated to the NLC bulk beyond a distance of tens of μm though the long-range elastic deformation of the NLC molecules. Thus, the hybridization event is converted to amplified optical signals via birefringent nature of the NLC between crossed polarizers. Our NLC-based DNA chip array showed that the extinction ratio of transmitted light depending on the hybridization results was approximately four, which could be read by the naked eye. Since such anchoring behaviors on the immobilized DNA are very similar to those on the conventional amphiphilic homeotropic surfactant of LCs, it is expected that quantitative analysis of hybridization events can be explored with our simple system.
On the Role of Oxygen Vacancies in the Determination of the Gas-Sensing Properties of Tin-Oxide Nanowires
Authors: Mosca Roberto , Zha Mingzheng , Calestani Davide , Lazzarini Laura , Salviati Giancarlo , Zappettini Andrea , Zanotti Lucio , Comini Elisabetta , Sberveglieri Giorgio
Published: April 2011

SnO2 nanowires have been recently employed in the “gas-sensors” field and excellent results of conductometric and optical tests on SnO2 nanowires-based gas sensors have been reported.

However, the mechanism that controls the gas-sensing effect in metal oxides nanowires is not fully understood yet. Here the authors present the first results of an in-depth study about the influence of post growth treatments on the physical and gas sensing properties of SnO2 nanowires.

In particular, SnO2 nanowires grown by a vapour transport technique were annealed in a oxygen-rich atmosphere and then characterized by different techniques to assess the influence of the treatment on the nanowires properties.

The annealing in oxygen atmosphere is shown to strongly affect the PL and CL spectra, the electrical resistivity as well as the gas sensing properties of the nanowires. The obtained results are consistent with a reduction of the oxygen vacancies concentration induced by the O2 treatment and seem to confirm the role of these defects in affecting the gas response of SnO2 nanowires-based sensors.
A Computational Study on SnO2 Au-Doped Grains: CO Adsorption
Authors: Mazzone Anna
Published: April 2011

In this study an analysis is made of the adsorption properties of nanocrystalline SnO2 containing a metallic dopant. The analysis is based on semi-empirical Hartree-Fock and scattering theories and the structures considered are SnO2 grains with a rutile lattice and a size comparable with the experimental ones. The grains contain rows of gold atoms located on the grain surface or in an endohedral position, in the grain interior, and the adsorbed system is generated by depositing a CO molecule on the grain surface. The calculations illustrate the dependence of the binding energies and ofthe conductance on the grain size, on the location of the metallic additives in both the clean and in the CO-adsorbed grains. New mechanisms of adsorption and of current transport are proposed.
Thermal Stability of Supported Noble Metal Nanoclusters
Authors: Kutluk Galif , Yagi Shinya , Sumida Hirosuke , Namatame Hirofumi , Taniguchi Masaki
Published: April 2011

Highly dispersive and size controlled Pd and Pt nanoclusters have been synthesized by gas condensation and Arc plasma source. The morphology, crystallographic structures, electronic structure and the temperature dependence of chemical states of nanocluster were investigated by using TEM, AFM, EXAFS and XPS, respectively. The results show that non-passivized Pd nanoclusters with the size of 1.5~ 5.7nm are consisted with pure Pd core covered by highly oxidized PdO2 thin layer. The dioxide state PdO2 layers start to converting to Pd at 120°C and vanishing at 180°C in a reduction atmosphere.
Effect of Calcination Temperature on Interface Properties Between In2O3 and Au Electrode in Micro Gap Semiconductor Gas Sensors
Authors: Tamaki Jun , Niimi Jun , Konishi Satoshi
Published: April 2011

The In2O3 thin film nanosensors were fabricated by dropping In(OH)3 sol on nano gap electrode with 0.1-2.5 micron of gap size, dried, and calcined at various temperatures. The grain size of In2O3 and thus the number of In2O3 grains were changed by calcining at 600-850 °C. The size of grain was increased from 15 nm at 600 °C to 55 nm at 850 °C, and thus the number of grains in 0.3 micron gap was decreased from 19 to 5.3. Contrary to the expectation, the small resistance changes to both 1 ppm Cl2 (resistance increase) and 0.5 ppm Cl2 (resistance decrease) were obtained for In2O3 nanosensors calcined at 700-850 °C. These were contributed to the changes in the surface and interface chemical state to suppress the adsorption of or substitution with Cl2 molecule.
Investigation of the humidity effects on SnO2-based sensors in CO detection
Authors: Malagu' Cesare , Benetti Michele , Carotta Maria Cristina , Giberti Alessio , Guidi Vincenzo , Milano Luciano , Martinelli Giuliano
Published: April 2011

An algorithm for compensating water vapor pressure in CO detection is proposed here and tested on SnO2 thick-film gas sensors. For each sensor working at a fixed temperature, the conductance, G, is fitted by an analytical surface, whose expression can be inverted to determine the CO concentration once the water partial pressure is measured. As soon as the rate of water-vapor pressure change is slower than about 300 Pa/min, G is a function of the temperature, water vapor and CO concentration. If quicker water vapor variations occur instead, the sensing film undergoes a non-negligible transitory phenomenon during which G assumes different values even at fixed water vapor pressure and temperature. This phenomenon prevents the compensation from working properly. An explanation of the behavior is offered by the interpretation of kinetics equations at surface.
The Strain Status of the Buried Self-assembled InAs quantum dots using MeV technique
Authors: Wang Hsing-Yeh , Chen C.H. , Niu H. , Wu S.C. , Lee C.P.
Published: April 2011

The strain status of the buried InAs self-assembled quantum dot was comprehended by measurement first time. Results show the in-plane strain is compressive and lattice in the growth direction is lager than the lattice of GaAs. The strain of the sample annealed at 650 degree relaxes in the growth direction. The growth and the lateral direction become relaxed in the sample annealed at 750 degree.
Luminescence properties of newly developed red-emitting phosphors M2Si2O7:Eu3+ (M=La, Y) under UV/VUV excitation
Authors: Zhang Zhiya , Wang Yuhua
Published: April 2011

The red-emitting phosphors of Eu3+ doped M2Si2O7 (M=La, Y) were synthesized by a solid-state reaction method and their luminescence properties in UV-VUV region have been studied. On the excitation spectra, the Eu3+-O2- CT band is of higher intensity for La2Si2O7, while for Y2Si2O7, the absorption around 150nm is much stronger and this can be assigned to the Y3+-O2- CT band in company with the Si-O group absorption. The emission spectra show higher intensity and better color purity for La2Si2O7:Eu3+ under 254nm excitation due to Eu3+ occupying the non-centrosymmetric site. Under 147nm excitation, Y2Si2O7:Eu3+ exhibits stronger emission with purer red, which can be corresponded to the absorption of Y3+-O2- CT in the VUV region.
Selective Area Heteroepitaxy of Nano-AlGaN UV Excitation Sources for Biofluorescence Application
Authors: Jindal Vibhu , Grandusky James , Shahedipour-Sandvik Fatemeh , LeBoeuf Steven , Balch Joleyn , Tolliver Todd
Published: April 2011

We report on the selective area heteroepitaxy and facet evolution of AlGaN nanostructures on GaN/sapphire substrate using various mask materials. We also report on the challenges associated with selection of an appropriate mask material for selective area heteroepitaxy of AlGaN with varying Al composition. The shape and the growth rate of the nanostructures are observed to be greatly affected by the mask material. The evolution of the AlGaN nanostructures and Al incorporation were studied exhaustively as a function of growth parameters; including temperature, pressure, NH3 flow, total alkyl flow and TMAl/(TMAl+TMGa) ratio. The growth rate of nanostructures was reduced drastically when higher Al percentage AlGaN nanostructures were grown. The growth rates were increased for higher Al percentage AlGaN using a surfactant which resulted in a high quality pyramidal structure. As indicated by high resolution x-ray diffraction (XRD) and cathodoluminescence (CL) spectroscopy, composition of Al in the AlGaN nanostructure is significantly different from that of a thin film grown under the same growth conditions.
Area Selective Atomic Layer Deposition by Soft Lithography
Authors: Chen Rong , Porter David W. , Kim Hyoungsub , McIntyre Paul C. , Bent Stacey F.
Published: April 2011

Area selective HfO2 thin film growth through atomic layer deposition (ALD) has been achieved on octadecyltrichlorosilane (ODTS) patterned Si substrates. Patterned hydrophobic self-assembled monolayers (SAMs) were first transferred to Si substrates by micro-contact printing. Using hafnium-tetrachloride or tetrakis(dimethylamido) hafnium(IV) and water as ALD precursors, amorphous HfO2 layers were then grown selectively on the SAM-free regions of the surface where native hydroxyl groups nucleate growth from the vapor phase. The HfO2 pattern was readily observed through scanning electron microscopy and scanning Auger imaging, demonstrating that soft lithography is a simple and promising method to achieve area selective ALD. To evaluate the selectivity, the resolution of the soft lithography based method was compared with that of area selective ALD of HfO2 by selective surface modification of patterned silicon oxide obtained using long-time SAM exposure. It was found that the selective surface modification showed much higher spatial resolution and selectivity, an observation consistent with previous studies indicating that highly ordered and densely packed ODTS films were important to achieve complete deactivation.
Phase Change Materials - From Structures to Kinetics
Authors: Wuttig Matthias , Welnic Wojciech , Detemple Ralf , Dieker Henning , Kalb Johannes , Wamwangi Daniel , Steimer Christoph
Published: April 2011

Phase change materials possess a unique combination of properties which include a pronounced property contrast between the amorphous and crystalline state, i.e. a high electrical and optical contrast. In particular the latter observation is indicative for a considerable structural difference between the amorphous and crystalline state. At the same time the crystallization of the amorphous state proceeds on a fast time scale. This raises the question how structure, properties and kinetics are related in phase change alloys. It will be demonstrated that only a small group of covalent semiconductors with octahedral-like coordination has the required property combination. This is related to their thermodynamic properties which govern the kinetics of crystallization.
Thermal Analysis and Structural Design of Phase Change Random Access Memory
Authors: Zhao Rong , Lim Ler Ming , Shi Luping , Lee Hock Koon , Yang Hongxin , Chong Tow Chong
Published: April 2011

A thermal modeling based on Finite Element Method (FEM) was used to simulate Phase Change Random Access Memory (PCRAM) cells. The factors affecting temperature distribution of a PCRAM cell structure such as geometry, device structure and the properties of the individual materials were investigated. The results of the analysis provided the fundamental design of a novel cell structure which has a better performance and reliability.
Dielectric Constants and Endurance of Chalcogenide Phase-Change Non-Volatile Memory
Authors: Savransky Semyon D. , Prokhorov Eugenio F.
Published: April 2011

Initial attempts to create memory from chalcogenide glasses (g-Ch) had limited success particularly because the first generation of these materials (labeled as CG1) has inferior endurance (about 106SET-RESET cycles). Recent progress in phase-change non-volatile memory (PC-RAM) related to superior properties of Ge2Sb2Te5(GST) alloy [1,2]. The paper answers the vital for PC-RAM development question: “Why is endurance of GST memory cells (about 1011cycles) much higher than of CG1 cells?” We show that superior endurance is related to features of –U centers [3] creation in GST during RESET of PC-RAM cells. The native –U centers exist in g-Ch due to the softness of atomic potentials [3]. They play a significant role in SET process of CG1 and GST [2,4]. The –U centers behavior in GST [5] is different compared with CG1 while other properties (threshold voltage, resistivity, etc.) are basically the same [1-4]. We found that dielectric permittivities e of CG1 and GST are also different.

The e values in Ge-Sb-Te alloys films have been determined from impedance measurements in sandwich samples using method described in [6] and reported in the paper. Amorphous GST has relatively high and distinct static and optical dielectric permittivities eo=16.5 and e'=15.3 to compare with CG1 where e practically independent on frequency. Hence the second term in the effective polarization potential Ep = q^2[(1-1/e')/r + (1/e' - 1/eo)/L] is strong (here r and L are the average atomic radius and interatomic bond distance, q is the electron charge). It allows to screen the Coulomb repulsion at an –U center quite effectively in GST. Therefore polarization helps –U centers creation in amorphous GST and impedes these centers formation in crystalline hexagonal GST films where eo=38 and e'=61. In contrast to CG1 [3], the creation and destruction of –U centers during RESET and SET processes in GST [4] are not accompanied by strong plastic mechanical stresses in a memory cell. This feature (higher barrier between elastic and plastic deformations) predetermines possibility of numerous SET-RESET cycles in this alloy. Therefore, the deformation mechanism of –U centers formation in CG1 leads to inferior endurance while the polarization mechanism of their creation in GST ensures decent endurance. Second factor is hybritization of –U centers with extended states can also play role in good memory alloys. Obtained experimental e values in non-stochiometric films allow to conclude about expected endurance in the framework of the proposed model.
Toward a constructive homogenization theory of composite metamaterials
Authors: Cabuz Alexandru I , Felbacq Didier
Published: April 2011

In the homogenization of composite metamaterials the role played by the relative positions of the wires and resonators is not well understood, though essential. We present an effective medium approach which can systematically account for these effects. It involves independently homogenizing rows of wires and planes of resonators as slabs with negative permittivity and permeability respectively. The metamaterial is then treated as a 1D single negative anisotropic stack. Using this approach we show that it is in principle possible to satisfy the requirements of Pendry's superlens, [mu]=[epsilon]=-1 , up to losses. We propose a class of structure geometries which seems promising for achieving this holy grail of metamaterial science.
Sub-wavelength Imaging through Metallic Nanorod Array
Authors: Ono Atsushi , Kato Jun-ichi , Kawata Satoshi
Published: April 2011

Negative index material is expected to exhibit interesting optical properties. Especially, superlens effect, which is predicted by John B. Pendry in 2000, is very attractive to overcome the diffraction limit in optical imaging [1]. Although there is no negative index material in nature, Pendry numerically suggested that several metals, only dielectric constant is negative at optical frequencies, behave like a superlens under the electrostatic limit and for the p-polarized fields. X. Zhang experimentally demonstrated this superlens effect by constructing nanolithography system with silver thin film in 2005 [2].

In this presentation, we newly propose a sub-wavelength imaging system at optical frequency regime in an array of metallic nanorods [3]. The near-field components of dipole sources were plasmonically transferred through the rod array to reproduce the image of the dipoles in the other side.

We calculated the field distribution at the different planes of imaging process using the finite-difference time-domain (FDTD) algorithm and found that the spatial resolution was 40 nm, which was much beyond the diffraction-limit and was limited by the array pitch. The typical configuration is a hexagonal arrangement with 40 nm periodicity of silver rods of 50 nm height and 20 nm diameter. The image formation highly depends on the coherence and the polarization of the dipole sources, array pitch, and the source-array distance. The principle of our near-field imaging is based on the longitudinal resonance of the localized surface plasmon along a metallic nanorod. The spectral responses of the device are also investigated.
Field-effect Transistors of Tetracene Single Crystal on top of a Flexible Substrate
Authors: Kim Tae-Heon , Lee Joon Ho , Kim Jin heon , Seoul Chang
Published: April 2011

Tetracene single crystals were prepared by the vapor transport method. The polyimide films were used for both substrate and gate dielectric layer. The single-crystal FETs should perform better than thin film transistors. Very thin crystals (~1 μm) were adhered to the substrate by due to electrostatic forces. The mobility of tetracene single-crystal field-effect transistors reaches the room-temperature value of 5×10-4 cm2/Vs.
PPy-coated Electrically Conducting Fabrics with High Strain Sensitivity
Authors: Xue Pu , Tao X.M. , Tsang H.Y. , Leung M.Y
Published: April 2011

This paper studies a flexible strain sensor from PPy-coated fabric prepared by a chemical vapor deposition procedure under low temperature. The mechanisms of its strain sensing behavior were investigated. In-situ tensile tests in a scanning electron microscope (SEM) were conducted for PPy-coated electrically conducting yarns prepared in the same procedure as that for the PPy-coated fabric. The results exhibited the developed PPy-coated fabric possessed the high strain sensitivity and the large workable strain range, which attribute to the high performance of PPy-coated PU fibers and the crack-opening and crack-closing mechanism happened on the surface of PU fibers, as well as the excellent properties of knitted fabric structure.
Optical nano-textile sensors based on the incorporation of semiconducting and metallic nanoparticles into optical fibers
Authors: Dhawan Anuj , Muth John F. , Kekas Dennis J. , Ghosh Tushar K.
Published: April 2011

By incorporating optical fiber based devices into woven and non-woven fabrics, one can distribute these devices across large areas. In this work, novel fiber optic devices with nanofunctionality are developed by incorporating metallic and semiconducting films and nanoparticles inside the optical fibers. This is accomplished by first depositing the material of interest on the tip of the optical fiber, then overcoating the fiber with a protective layer of silicon dioxide before fusing this structure to an optical fiber. This results in a continuous fiber that can be woven, or placed into nonwoven textiles. In this study the incorporation of gold nanoparticles and vanadium oxide compounds into the core of optical fibers and an in-line Fabry-Perot sensor using these techniques are described.
Solvent–Controlled Helicity in Self-Assembling Rosette Nanotubes
Authors: Johnson Ross S , Yamazaki Takeshi , Kovalenko Andriy , Fenniri Hicham
Published: April 2011

A newly designed module was synthesized and found to self-assemble into rosette nanotubes (RN) in both water and methanol. Characterization using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) established the formation of analogous RNs in both solvents. However, the chiroptical outcome of the assemblies, observed by circular dichrosim (CD) spectroscopy, was found to be mirror image based solely on the solvent used. Preliminary molecular modeling studies indicated the formation of M and P helical rosette nanotubes, in agreement with the experimental observations. This work represents the first example of solvent-controlled helicity in a self-assembling supramolecular system.
Self-Assembled Lipid Tubules: Synthesis, Characterization, and Ordered Arrays
Authors: Zhao Yue , Mahajan Nidhi , Fang Jiyu
Published: April 2011

The rolling of lipid bilayer sheets into hollow cylindrical tubules have emerged as a group of interesting supramolecular nanostructures. Here, we image the self-assembled tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphochloline (DC8,9PC) with atomic force microscopy. Nanoscale ripple structures with a periodicity of ~ 200nm in the cylindrical lipid tubules are observed. We develop two simple methods based on microfluidic networks and surface patterning to produce two dimensional ordered arrays of parallel aligned lipid tubules on substrates.
Comparison of Piezoelectric and Carbon Nanotube-Based Actuators
Authors: Golnabi Hossein , Ghorannevis Mahmod , Golnabi Masoud
Published: April 2011

The goal of this study is to compare operation and performance of the piezoelectric and carbon nanotube actuators, by focusing on the conditions that such piezoelectric device can be replaced by carbon nanotube actuators in a near future. For many years piezoelectric (PZT) and electrostrictors devices have been the key elements for the construction of actuator systems such as positioners, miniature ultrasonic motors, and adaptive mechanical motors. However, in recent years major advances and accomplishments have been reported in the field of nanotube materials, which promise a breakthrough in the field of nanosensors and nanoactuators. The aim here is to make a comparison between the PZT- and CNT-based actuator/sensor devices in terms of the actuator materials, designs, and device control techniques. First, a model is established for the operation of a typical PZT actuator and the related electromechanical coupling relations and equations governing the actuation process are described. In the second study actuation behavior of carbon nanotube materials is modeled and the results concerning a similar parameter to that of PZT are reported.
Chromatographic Separation of Single Wall Carbon Nanotubes
Authors: Bauer Barry J. , Bajpai Vardhan , Fagan Jeffrey A. , Becker Matthew L. , Hobbie Erik K.
Published: April 2011

Size exclusion chromatography (SEC) has been used to separate single wall carbon nanotubes (SWNT) dispersed by chemical modification in organic solvents and by DNA in aqueous solution. The chromatographic detection includes size sensitive detectors, multi-angle light scattering (MALS) and intrinsic viscosity (IV), which can provide information on the size and shape of the SEC fractions. The dispersions were also characterized by small angle neutron scattering (SANS) and atomic force microscopy (AFM). Chemical modification was accomplished by covalent attachment of octadecyl amine to acid treated SWNT and by covalent attachment of butyl groups through free radical grafting. Both covalent attachment methods produced dispersions that contained impurities or clusters of SWNT. The DNA dispersions produced the best dispersions, being predominately single nanotubes.
Highly Flexible and Transparent Single Wall Carbon Nanotube Network Gas Sensors Fabricated on PDMS Substrates
Authors: Cho Chi-Won , Lim Chae-Hyun , Woo Chang-Seung , Jeon Hyung-Suk , Park Bonghyun , Ju Heongkyu , Lee Cheol-Jin , Maeng Sunglyul , Kim Ki-Chul , Kim Sang Hyeob , Lee Seung-Beck
Published: April 2011

We report on the basic characteristics and gas sensing operation of density controlled single-walled carbon nanotube (SWCNT) thin films on poly(dimethyl siloxane) (PDMS) substrates The vacuum filteration and PDMS mold transfer method allowed the density of SWCNT distributed to have non-local uniformity. The optical transparency of the SWCNT thin films was inversely proportional to SWCNT density and conductivity. The flexible SWCNT thin film showed high mechanical stability with negligible change in conductance after being bent by 180o. We evaluated its gas sensing operation depending on SWCNT density and bias voltage. It was shown that lower SWCNT density thin films had higher sensitivity to NH3 gas, which may be due to higher exposed surface area for lower density SWCNT thin films. Also, we found that lower bias voltage devices showed faster recovery times. The results show that vacuum filteration and mold transfer method produced flexible SWCNT thin films that have stable mechanical and electrical characteristics and also stable gas sensing capabilities making them applicable to future flexible integrated sensors.
Structure-Based Carbon Nanotube Separations by Ion-Surface Interactions
Authors: Lustig Steven R , Jagota Anand , Khripin Constantine , Zheng Ming
Published: April 2011

Single-stranded DNA wraps helically around individual single walled carbon nanotubes to form a DNA/CNT hybrid, which is both stable and dispersible in aqueous solution. Subjected to ion-exchange chromatography, a hybrid elutes at an ionic strength that depends on the electronic band structure of the core nanotube, thus providing a mechanism for separating nanotubes by chirality. We present experimental data and a theoretical model for this separation process on dielectric substrates that explains all the salient features observed experimentally to date, and provides accurate predictions for critical elution salt concentration. The competition between adsorption on the stationary phase and counterion condensation in the mobile phase is characterized by estimating the difference in free energy between the two states of the hybrid. Parametric study of the DNA wrapping geometry, SWNT dielectric properties, hybrid length and diameter indicates that the elution is most sensitive to the hybrid's effective charge density, primarily governed by the DNA helical pitch. The model correctly predicts hybrids with metallic nanotubes are weaker binding than hybrids with semiconducting nanotubes and larger diameter nanotubes are eluted at later times.
Deformation-induced Transformations of Nanocrystalline Ge-Si Film During Indentation
Authors: Xu Ziwen , Ngan A.H.W. , Huang J.G. , Meng X.K.
Published: April 2011

Thin films of Ge-Si with a duplex nanocrystalline structure were fabricated by magnetron co-sputtering and nanoindentations were made on these films. Transmission electron microscopy and Raman spectroscopy were used to analyze the deformed microstructures in the residual indentations. Amorphization and diamond-cubic (dc) to non-diamond-cubic (non-dc) phase transformation were observed and considered as the major micromechanisms in the deformation of the Ge-Si duplex nanocrystals.
Deformation Mechanisms of Nanocrystalline Hexagonal Close-Packed Metals
Authors: Zheng Guangping
Published: April 2011

Using molecular dynamics simulation of nanocrystalline (nc) samples with grain size of 10 nm, a reverse martensitic transformation from hexagonal close-packed (hcp) to face-centered cubic (fcc) structure is observed in nc-cobalt and nc-zirconium undergoing plastic deformation. In nc-cobalt hcp-to-fcc transformation is prevalent and deformation twinning is rarely observed. The transformation mechanism involves the motion of Shockley partial dislocation 1/3<1100> in every other (0001)hcp /(111)fcc plane. In nc-zirconium the hcp-to-fcc transformation competes with the deformation twinning. From the simulation results, it is suggested that the interaction among partials should be considered to understand the deformation mechanisms of hcp nc metals.
Molecular Dynamics Simulation of the Glass Transition of Ortho-Terphenyl in Bulk and Thin Films
Authors: Ghosh Jayeeta , Faller Roland
Published: April 2011

The glass transition temperature in thin film depends strongly on film thickness and interaction with the substrate and it is normally a priori not clear which way it deviates from the bulk value. This causes new challenge in the technological advancement of smaller and smaller electronic devices. In this study molecular dynamics simulations of a low-molecular weight organic glass former, ortho-terphenyl, are carried out in bulk and freestanding films. The main motivation is to provide insight into the confinement effect without interface interactions. Based on earlier models of ortho-terphenyl we developed an atomistic model for bulk simulations. The model reproduces the literature data from simulations as well as experiments. After characterizing the bulk model we form a freestanding film. This film gives us the opportunity to study the dynamical heterogeneity near the glass transition by in-plane mobility and reorientation dynamics. We also develop a structurally coarse-grained model for this glass former based on our atomistic model to study bigger system for a longer period of time.
Deformation Micromechanics of Carbon-Nanotube/Epoxy Composites
Authors: Young Robert J , Kao Chih-Chuan
Published: April 2011

The micromechanical behavior of randomly-oriented epoxy/SWNT composites has been investigated by using Raman spectroscopy. In particular, the shift of the nanotube Raman G' band with composite strain has been monitored. It has been demontrated that there is a strong interface and good stress transfer between the epoxy matrix and SWNTs up to about 0.4% strain but at higher matrix strains the interface appears to break down. By comparing the data in a cyclic deformation experiment, the detailed behavior of carbon nanotube composites can be determined, such as the efficiency of stress transfer and interface breakdown.
Continuum Modeling of Bilayer Lipid Membranes
Authors: De Vita Raffaella , Hopkinson David , Sundaresan Vishnu B. , Leo Donald J.
Published: April 2011

A continuum model is used for the description of the mechanical response of bilayer lipid membranes (BLMs) subjected to hydrostatic pressure. The model is formulated under the assumption that the BLMs are Smectic A liquid crystals. The mean orientation of the amphiphilic molecules is postulated to be perpendicular to the lipid layers and each layer is idealized as a two dimensional liquid. The permeation process governs the motion of the molecules through the smectic layers. The approach taken in this study is based on the seminal works of Helfrich [1] and de Gennes [2] on Smectic A liquid crystals. The failure process of the BLMs, which is observed in the experimental studies, is considered to be due to extrusion of the BLMs through the pores of the polycarbonate filters.
Molecular-Dynamics Study of the Morphological Evolution of a Metallic Cluster Deposited on a Surface
Authors: Shintani Kazuhito , Terajima K. , Kometani Y.
Published: April 2011

The morphological evolution of a Co cluster deposited on a Cu substrate is investigated by means of molecular-dynamics simulation. The many-body potential based on the second moment approximation of a tight-binding Hamiltonian (TB-SMA) is employed to calculate the interactions between Co and Cu atoms. The results show that the effect of the substrate anisotropy appears in the morphology of a deposited cluster. It is also revealed that the total period of the structural change of such a cluster can be divided into the three stages, viz., (I)change to an epitaxial structure, (II)overspread of diffusing Cu atoms on the cluster, and (III)solid dissolution of Co atoms into the Cu substrate.
Kinematical Analysis of the Evolution of Reflection High Energy Electron Diffraction Patterns of Quantum Dot Heterostructures: Correlation with Strain and Anisotropy
Authors: Feltrin Andrea , Freundlich Alexandre
Published: April 2011

The strain distributions and of reflection high energy electron diffraction (RHEED) patterns of uncapped pyramidal shape InAs Stranski-Krastanov quantum dots fabricated on GaAs(001) substrate are investigated theoretically. The three dimensional strain anisotropy is computed with an atomistic elasticity approach, using inter-atomic Keating potentials and the strain energy is minimized using the conjugate gradient numerical method. RHEED images are predicted in the framework of the kinematical theory, by taking into account the refraction of the electron beam at the quantum dot/vacuum interface. Clear correlation between RHEED image features and quantum dot structural properties is established. The study stresses the potential of RHEED for future experimental real-time (during growth) detections and deciphering of strain anisotropies in quantum dots.
Parallel nano-Differential Scanning Calorimetry: A New Device for Combinatorial Analysis of Complex nano-Scale Material Systems
Authors: McCluskey Patrick James , Vlassak Joost J.
Published: April 2011

A new device is presented for the combinatorial analysis of complex nano-scale material systems. The parallel nano-differential scanning calorimeter (PnDSC) is a micro-machined array of calorimetric cells. This new approach to combinatorial calorimetry should expedite the analysis of nano-scale material thermal properties. A power compensation differential scanning calorimetry measurement, not yet performed on a device of this type, is described. A NiTi specific heat measurement demonstrates the scanning calorimetry capability of the PnDSC.
Mechanical studies of hydrogel encapsulated membranes
Authors: Jeon Tae-Joon , Malmstadt Noah , Schmidt Jacob
Published: April 2011

We have encapsulated lipid bilayer membranes within a polyethylene glycol dimethacrylate hydrogel (PEG-DMA). These hydrogel encapsulated membranes (HEMs) are significantly longer-lived and more mechanically stable than traditional lipid membranes. Over 50 attempts, HEMs usually remained intact for over 48 hours, and some lasted up to 5 days. The electrical characteristics of the HEMs were consistently stable over this period of time. The approximate thickness of the HEM was measured to be 4.7±0.5 nm (n=25), consistent with a lipid bilayer. The resistance of the HEM remained over 10 GΩ over the period of electrical measurement. Simultaneous electrical and optical measurements showed that HEMs have unusual mechanical stability, whereas free-standing lipid membranes are typically susceptible to mechanical perturbation. The HEMs could withstand much greater applied pressures than unsupported membranes. In situ electrical and optical monitoring of the HEMs showed that the gel made intimate contact with the membrane, suggesting that direct mechanical support of the bilayer is the mechanism of membrane stabilization. Single channels of alpha-hemolysin, were incorporated into HEMs and continuously measured for over 4 days. Finally, combination of the HEM with an automated membrane microfluidic formation process is proposed as a prototype platform for high throughput drug screening or small molecule sensing.
Biocompatible Parylene Neurocages for Action Potential Recording and Stimulation
Authors: Tooker Angela , Erickson Jon , Tai Yu-Chong , Pine Jerry
Published: April 2011

Parylene neurocages are biocompatible and very robust, making them ideally suited for studying neural networks. We present a design and fabrication process for building parylene neurocages for in vitro studies of neural networks. The fabrication process, on either silicon or glass substrates, incorporates electrodes into the neurocages to allow for stimulation and recording of action potentials. The resulting neurocages have a long-term cell survival rate of ∼50% and have proven to be 99% effective in trapping neurons.
a-Si:H Electrolyte-Gate Thin Film Devices for Biological Applications
Authors: Goncalves Dina , Prazeres Duarte M.F. , Chu Virginia , Conde Joao P.
Published: April 2011

This paper presents the use of a-Si:H electrolyte-gate thin film transistors (EG-TFTs) for the pH sensing and the detection of DNA and proteins (horseradish peroxidase, HRP). The sensing layer used was SiNx or SiO2. The devices show linear sensitivity to pH above the point of zero charge and respond to the adsorption of oligonuleotides and HRP with typical Langmuir adsorption behavior. DNA immobilization and hybridization detection is demonstrated. Surface control and reproducibility issues are addressed by the measurement of surface contact angles.
Elastic Interconnects for Stretchable Electronic Circuits using MID (Moulded Interconnect Device) Technology
Authors: Brosteaux Dominique , Axisa Fabrice , Vanfleteren Jan , Carchon Nadine , Gonzalez Mario
Published: April 2011

An MID (Moulded Interconnect Device) technology was developed for the production of elastic electronic interconnections. The stretchability is obtained using tortuous horseshoe shaped metallic wiring, embedded in a matrix of PDMS (poly dimethyl siloxane). In this way stretchable interconnects have been realized, consisting of 4 micron thick gold wires, embedded in 250 − 500 μm thick silicone material. . Stretchable interconnections, realised with this technology, have a maximum stretchability above 100%, with a stable resistivity of about 1.5 Ω per running cm for a track width of 100μm. A first simple operating stretchable electronic circuit has been fabricated, consisting of a blue LED driven by stretchable wiring. The technology is under development for use in biomedical applications in the first place, but has potential to be extended for various other applications like smart textiles, robotic skins, etc.
Mechanistic Studies of Hydrogen Release from Solid Amine Borane Materials
Authors: Bowden Mark , Kemmitt Tim , Shaw Wendy , Hess Nancy , Linehan John , Gutowski Maciej , Schmid Benjamin , Autrey Tom
Published: April 2011

Ammonia borane (NH3BH3) is a molecular solid with a high volumetric and gravimetric density of hydrogen. We report room temperature structural data which shows how the freely rotating NH3 and BH3 groups allow a N-H…H-B dihydrogen bond in which hydrogen atoms on adjacent molecules are separated by only 1.90Å. The initial decomposition of ammonia borane at 80-100°C into (NH2BH2)n and H2 has been studied by in-situ nmr spectroscopy and kinetic studies using isotopic substitution. The reaction proceeds by a bimolecular pathway involving a [NH3BH2NH3]+BH4− intermediate with an activation energy of 136kJmol−1.
Quantitative Structure-Uptake Relationship of Metal-Organic Frameworks as Hydrogen Storage Material
Authors: Kim Daejin , Lee Tae Bum , Choi Seung-Hoon , Choi Sang Beom , Yoon Jihye , Kim Jaheon
Published: April 2011

We reported the relationship between the structure of metal-organic frameworks (MOFs) and the capability of hydrogen uptake. The QSPR (quantitative structure-property relationship) method was used to find out the factor which affects the adsorption amount of hydrogen molecule on the MOFs. The derivatives which were substituted by functionalized aromatic rings showed the effect of polarization within the identical topology of the frame and similar lattice constants. And the typical series of MOFs with different topology of the frames were investigated to examine the influence of topological change. For the consideration of saturation of hydrogen adsorption amounts, the result of fitting the adsorption curve with Langmuir-Freundlich equation was used to the QSPR approach additionally. We found out that the polar surface area plays a key role on the adsorption amount of hydrogen molecule into the MOFs and the specific value of electrostatic potential surface was calculated to indicate the interaction between hydrogen molecule and MOF.
Hydrogen Storage in Novel Carbon-Based Nanostructured Materials
Authors: Whitney Erin S. , Curtis Calvin J. , Engtrakul Chaiwat , Davis Mark F. , Su Tining , Parilla Philip A. , Simpson Lin J. , Blackburn Jeffry L. , Zhao Yufeng , Kim Yong-Hyun , Zhang Shengbai B. , Heben Michael J. , Dillon Anne C.
Published: April 2011

Experimental wet chemical approaches to complex an iron atom with two C60 fullerenes, representing a new molecule, dubbed a “bucky dumbbell,” have been demonstrated. The structure of this molecule has been determined by 13C solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). Furthermore, this structure has been shown to have unique binding sites for dihydrogen molecules with the technique of temperature programmed desorption (TPD). The new adsorption sites have binding energies that are stronger than that observed for hydrogen physisorbed on planar graphite, but significantly weaker than a chemical C-H bond. Further development of these molecules could make them ideal candidates for onboard vehicular hydrogen storage.
Recent Progresses on Complex- and Perovskite-Hydrides for Hydrogen Storage
Authors: Orimo Shin-ichi , NAKAMORI Yuko , Ikeda Kazutaka , Li Hai-Wen
Published: April 2011

Recent progresses on two series of light-element hydrides are briefly explained from the viewpoint of 1) prevention/suppression of gas-phase ammonia from mixtures of Mg(NH2)2 and LiH, and also 2) occurrences of reversible dehydriding and rehydriding reactions in NaMgH3.
Boron Doping Effects on the Electro-optical Properties of Zinc Oxide Thin Films Deposited by Low-Pressure Chemical Vapor Deposition Process
Authors: Steinhauser Jerome , Faÿ Sylvie , Schlüchter Romain , Myong Seung Yeop , Vallat Evelyne , Ballif Christophe
Published: April 2011

Boron-doped zinc oxide (ZnO) films deposited by Low-Pressure Chemical Vapor Deposition (LPCVD) technique are used as Transparent Conductive Oxide (TCO) to contact thin-film silicon solar cells. In this paper, the effect of boron introduced as dopant during ZnO formation is studied. These films are highly transparent in the visible range, whereas in the near infrared region their transmittance decreases with the increase of boron content due to free carrier absorption (FCA). A shifting of the fondamental band gap is also observed. The resistivity decreases of about one order of magnitude with the increase of the doping ratio ([B2H6]/[DEZ]) from 0 to 2. This resistivity drop is mainly due to an increase of the free carrier concentration. In low doped samples, Hall mobility increases with grain size, whereas it shows no grain size dependence in highly doped layers. This suggest that the scattering by grain-boundary is the main limiting factor for transport in low doped ZnO samples, whereas in highly doped ZnO films transport is controlled by the ionized impurity scattering within the grains.
Adsorption of Methane on the (100) Surface of MgO: Insight into Surface-Adsorbate and Adsorbate-Adsorbate Interactions from First-Principles Calculations
Authors: Drummond Michael L , Sumpter Bobby G , Shelton William A , Larese John Z
Published: April 2011

First principles calculations using density functional theory (DFT) are reported for two layers of methane adsorbed on the (100) surface of MgO. The lowest energy structure determined has a first layer with C2v methanes adsorbed above magnesium atoms, with hydrogen atoms pointed towards neighboring oxygen atoms, and a rotation of 90° in between each neighboring methane. The second layer methane layer has a similar structure, except the hydrogen atoms are directed towards nearest neighbor magnesium atoms. It is found that the structure of the first layer has a large effect on the relative energies of proposed bilayer structures, as does the calculated separation between the two layers of methane. Competing roles of surface-adsorbate and adsorbate-adsorbate interactions are also discussed.
Effects of Sputtering Power and Annealing Temperature on the Properties of Sc-doped ZnO Thin Films
Authors: Shiao Ming Hua , Jaing Cheng-Chung , Huang Yu-Jia , Su Chien-Ying , Lu Chih-Jung
Published: April 2011

Sc-doped ZnO thin films were deposited on Corning 1737 glasses by using RF magnetron co-sputtering system with Sc2O3 and ZnO targets. Different sputtering powers of Sc2O3 target and post annealing of 550°C for 2 hr were investigated to understand the effect on microstructural, optical and electrical properties of Sc-doped ZnO thin films. From X-ray diffraction (XRD) results, the Sc-doped films have (002) preferred orientation. Cross-sectional scanning electron microscope (SEM) show that the Sc-doped ZnO thin films have columnar structure before and after annealing procedure. Atomic force microscopy (AFM) surface measurement also shows that the surface roughness of the films was smoother when the Sc2O3 sputtering power increased. The optical transmission of as deposited Sc-doped films in the visible region all exceeded 80%, and increased about 3% after samples annealed. Electrical resistivity measurement reveals that the as-deposited Sc-doped ZnO thin films had lowest resistivity of 0.97 Ω cm when the Sc2O3 sputtering power was 125W. After annealing the lowest resistivity decreased to 9.85 × 10−2 Ω cm in which 200W of the Sc2O3 sputtering power was applied.
Orientation Dependence of Strontium-doped Lead Zirconate Titanate (PSZT) Thin Films on RF Magnetron Sputtering Conditions
Authors: Sriram Sharath , Bhaskaran Madhu , Holland Anthony Stephen , Reeves Geoffrey K
Published: April 2011

Studies on strontium-doped lead zirconate titanate (PSZT) have been reported for its high piezoelectric and ferroelectric properties. For PSZT to exhibit pronounced piezoelectric behaviour it must have a crystalline grain structure (perovskite orientation). This paper is a study of the deposition of PSZT thin films by RF magnetron sputtering and the effect of cooling rate, after deposition at temperatures between 500 °C and 700 °C. X-Ray Diffraction (XRD) results are used to show how a cooling rate of 5 °C/min increases the degree of perovskite orientation in sputtered films, when compared to a cooling rate of 15 °C/min. The absence of significant shifts in the positions of diffraction peak patterns in XRD results are used to demonstrate low stress in the deposited films. Atomic Force Microscope (AFM) imaging is used to show the crystalline nature of the PSZT thin films.