bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric Constants and Endurance of Chalcogenide Phase-Change Non-Volatile Memory
Authors: Savransky Semyon D. , Prokhorov Eugenio F. 
Published: April 2011

AbstractInitial 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

AbstractIn 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

AbstractNegative 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

AbstractTetracene 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

AbstractThis 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

AbstractBy 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractSize 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

AbstractWe 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

ABSTRACTSingle-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

ABSTRACTThin 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

ABSTRACTUsing 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTWe 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

ABSTRACTParylene 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.