bluuebunny/crossref_metadata_2025 huggingface dataset:
Large Thermoelectric Voltage in Point Contacts of Ni Ferromagnetic Metals
Authors: Kondo Kenji , Kaiju Hideo , Ishibashi Akira
Published: September 2011

Recently, we have proposed a spin quantum cross structure (SQCS) device toward the realization of novel spintronics devices. In this paper, we have investigated thermoelectric effects in point contacts (PCs) of Ni ferromagnetic metals using SQCS devices, theoretically and experimentally. The calculated results show that the thermoelectric voltage Vq changes from 0.48 mV to 2.12 mV with the temperature difference of PCs increasing from 10 K to 50 K. Also, the magnitude of the theoretical thermoelectric voltage agrees very well with that of the experimental result. PCs of SQCS devices with Ni electrodes can serve as spin dependent thermobatteries.
Dispersion of nanoparticles in media of biological interest
Authors: Carriere Marie , Casanova Axelle , Herlin Boime N.
Published: September 2011

Nanoparticles (NP) are introduced in a growing number of commercial products, including food and beverage, daily use hygiene products such as toothpaste, or orally-administered drugs. To study the possible toxicity of these nanoparticles, a model system is the in vitro response of eukaryotic cells to the presence of NP. However, to understand the observed effects, it is clear that good physical and chemical characterization of NP, and in particular of their dispersion are needed. Indeed, the expected effects should be different if the study is dealing with agglomerates or isolated nanoparticles. For fundamental understanding, it appears important to work with nanoparticles as well dispersed as possible while being in relevant biological condition, i.e. cellular culture cell.

In this context, we have studied the dispersion of a very common industrial titania NP (Degussa P25 produced in ton quantities). When dispersed in water, the suspensions of NP appear stable for weeks.. When transferred in the cell culture medium (DMEM) or if directly dispersed in DMEM, strong evolution of size is seen as well as sedimentation. To address this problem, we have compared different ways, coming from materials science, of dispersing NP in water with the idea to break in a preliminary step some of the necks between nanoparticles. The effect of dry ball milling, liquid ball milling, size of the balls and Ultrasonic dispersion will be compared. The best results were obtained from high power ultrasonic dispersion. To avoid direct aggregation, when going to DMEM, a “surfactant” relevant with biological studies (Foetal Bovine Serum (FBS)) was added in the suspension in order to coat the nanoparticles prior to transfer in DMEM (or other cell media). The result obtained with various surfactants and cell media will be presented. It must be noted that our best results were obtained in the FBS + DMEM medium.
Continuous Tunable Optical Detectors with a-Si:H Bias Sensitive Photodiodes
Authors: Merfort Christian , Seibel Konstantin , Bablich Andreas , Watty Krystian , Boehm Markus
Published: September 2011

Today’s image-based systems in civil security rely on sensors based either on CMOS or CCD technology, and they do not analyze color with sufficient equivalence to the human eye. The main reason for this is that the function of the fundamental color matching curves of the cones in the human eye can hardly be reproduced by technical systems [1]. Common color sensors are optimized for the three-area method in accordance with the standard DIN 5033-6. In civil security applications, for example, color sensors are used to identify the potential danger of whitish powder samples. Colorimetric classification based on the three-area method only provides suboptimal results [2], but not an unequivocal optical description. A series of tests performed at the IMT with more than 30 types of whitish powder samples were carried out with a spectrophotometer. These measurements showed that specimens with similar or different chemical compositions cannot be distinguished by the human eye, using the three-area method, exhibit characteristic differences in the CIE-L*a*b* measurement system under spectral method conditions. Until now, the realization of the spectral method on chip has been impossible with common color sensors. In this paper, we present a-Si:H-based bias-sensitive ni3p photodiodes, which have been fabricated successfully in a low temperature PECVD process. Present research focuses on the optimization of the continuous tunability of a-Si:H multispectral photodiodes, to increase the number of spectral stimulus specifications.
Strain Engineering and Luminescence in Si/SiGe Three Dimensional Nanostructures
Authors: Modi Nikhil , Tsybeskov Leonid , Lockwood David J. , Wu Xiao Z. , Baribeau Jean Marc
Published: September 2011

Strain engineering in composition-controlled Si-Si/Ge nanocluster multilayers with high germanium content (~ 50%) is achieved by varying thicknesses of Si/SiGe layers and studied by low temperature photoluminescence (PL) measurements. The PL spectra show reduction in strained silicon energy bandgap and a splitting presumably associated with partial removal of heavy hole-light hole degeneracy in SiGe valence band. Time-resolved PL measurements performed under different excitation wavelengths show dramatically different PL lifetimes, ranging from ~ 2 μs to 10 ns and an unusually high PL quantum efficiency. The results are explained by using the Si/SiGe interface recombination model, which is supported by ultra-high resolution transmission and analytical electron microscopy measurements.
Organic Biodegradable Aerogels Used in Controlled Drug Release
Authors: Veronovski Anja , Novak Zoran , Željko Knez
Published: September 2011

There are a lot of synthetic polymers which can be used for controlled drug delivery, however they are not easily accepted by the organism. Also incorporation of drugs into carriers runs under difficult conditions. Therefore scientists have been inclined to use natural-origin polymers, such as proteins and polysaccharides. Some of these promising natural polysaccharidic candidates are alginic acid sodium salt, guar gum and chitosan due to their outstanding merits. They are similar to extracellular matrix having high chemical versatility, good biological performance and cell or enzyme-controlled degradability. Many polysaccharidic hydrogels for drug delivery have already been prepared, but one of their weakness is their short life in dry air conditions; thus, special coating materials are being developed for enhancing their life time.

Alginates were used in the present research for synthesis of organic biodegradable gels by sol-gel process, which were further easily converted to aerogels by supercritical drying. They are safe for use, nontoxic, and derived from renewable sources. Aerogels made of alginate are dry and stable materials, which makes them interesting as a substitute to hydrogels. Alginates undergo reversible gelation in aqueous solution through interaction with divalent cations such as Ca2+, which create ionic inter-chain bridges. Two fundamental methods of ionic cross-linking were used to prepare alginate hydrogels: the diffusion method, where spheres are created and the internal setting method resulting in monoliths. After producing the hydrogel, alcogels were formed by solvent exchange using 100% ethanol. Ethanol was later replaced by supercritical CO2 with supercritical drying (100 bar, 35°C). Aerogels made from natural polysaccharides combine both biocharacteristics and aerogel characteristics such as high porosity and specific surface area, which makes them really attractive in drug delivery applications. The aerogels obtained in present research were therefore studied as drug carriers. The effects of the alginate composition and synthesis method on model drug nicotinic acid release were investigated. The results indicated that by using the internal setting cross-linking method for obtaining aerogels nicotinic acid was released in a more controlled manner. That is why further investigation was done on alginate spherical beads for prolonging their drug release. A multi-step sol-gel process was applied to generate complex aerogels with multi-membranes. First ionically cross-linked spherical cores were obtained by dropwise addition of sodium alginate solution into a CaCl2 solution. These cores were further immersed into alginate solution, filtered through a sieve and dropped into a salt solution again. By repeating the above process, different multi-membrane hydrogels were produced and further converted to aerogels. By adding more membranes around core burst drug release was successfully inhibited.
Single Nanoparticle Detection using on-chip Notched Ring Resonator
Authors: Wang S. , Yi Y.
Published: September 2011

A new photonic structure was demonstrated to achieve strong optical coupling between nanoparticle and photonic molecule by utilizing a notched micro ring resonators. By creating a notch in the ring resonator and putting a nanoparticle inside the notch, large spectral shifts and splittings at nm scale can be achieved, compared to only pm scale observed by fiber tip evanescently coupled to the surface of microsphere, thereby significantly lowered the quality factor requirement for single nanoparticle detection. The ability for sorting the type of nanoparticles due to very different mode shift and splitting behavior of dielectric and metallic nanoparticles is also emphasized.
Far Infrared Characterization of Single and Double Walled Carbon Nanotubes
Authors: Chou S. G. , Ahmed Z. , Samsonidze G.G. , Kong J. , Dresselhaus M. S. , Plusquellic D. F.
Published: September 2011

High resolution far infrared absorption measurements were carried out for single walled and double walled carbon nanotubes samples (SWCNT and DWCNT) encased in a polyethylene matrix to investigate the temperature and bundling effects on the low frequency phonons associated with the low frequency circumferential vibrations. At a temperature where kBT is significantly lower than the phonon energy, the broad absorption features as observed at room temperature become well resolved phonon transitions. For a DWCNT sample whose inner tubes have a similar diameter distribution as the SWCNT sample studied, a series of sharp features were observed at room temperature at similar positions as for the SWCNT samples studied. The narrow linewidth is attributed to the fact that the inner tubes are isolated from the polyethylene matrix and the weak inter-tubule interactions. More systematic studies will be required to better understand the effects of inhomogeneous broadening and thermal-excitation on the detailed position and lineshape of the low frequency phonon features in carbon nanotubes.
Light-induced Tuning of Microfiber-knot Resonator Overlaid with Azobenzene-doped Nematic Liquid Crystals
Authors: Hsiao Vincent K.S. , Chen Zhe , Jheng Min-Chi , Li Xiaoqing , Yu Jianhui
Published: September 2011

This paper demonstrates light-induced tuning of optical spectrum from optical microfiber knot resonator overlaid with an azobenzene-doped nematic liquid crystal (azo-doped NLC). The high-quality fiber resonator is made by drawing the single mode fiber to the micro-size diameter and self-twisting the microfiber as a knot shape. During the UV light irradiation the azobenzene molecules perform trans-to-cis photoisomerization which disrupts the NLC orientation. The disrupted NLC changes the effective refractive index within the LC overlaid fiber area and shifts the optical spectrum of microfiber knot resonator. The 0.25 nm spectral shifting of resonance wavelength was observed under the irradiation of 50 mW UV light.
Characterization of Group III-Nitride Based Surface Acoustic Wave Devices for High Temperature Applications
Authors: Justice J. , Rodak L.E. , Narang V. , Lee K. , Hornak L.A. , Korakakis D.
Published: September 2011

In this study, aluminum nitride (AlN) and gallium nitride (GaN) thin films have been grown via metal organic vapor phase epitaxy (MOVPE) on silicon and sapphire substrates. Samples were annealed at temperatures ranging from 450 to 1000 °C in atmosphere. AlN and GaN thin film quality has been characterized before and after annealing using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). Surface acoustic wave (SAW) devices with titanium/platinum interdigital transducers (IDTs) designed to operate at the characteristic frequency and fifth harmonic have been realized using traditional optical photolithographic processes. SAW devices on GaN were thermally cycled from 450 to 850 °C. The S21 scattering parameter of SAW devices was measured before and after thermal cycling by a vector network analyzer (VNA). An approach for the suppression of electromagnetic feedthrough (EF) to improve device performance is discussed. Feasibility of 5th harmonic excitation for GHz operation without sub-micron fabrication is also investigated. SAW devices have also been fabricated on the more traditional SAW substrate, lithium niobate (LiNbO3), and device response was compared with those on AlN and GaN at room temperature.
Nano-scale Creep Compliance of Hybrid Aerogels
Authors: de la Rosa-Fox N. , Morales-Flórez V. , Piñero M. , Esquivias L.
Published: September 2011

The copolymerization between TEOS (tetraethoxysilane) and silane derivatives was promoted by the application of high power ultrasound to the precursor liquid mixtures in the same way as in the classical sol-gel method. The specific organic precursor was selected from the silanol-terminated polymer family with different molecular functionality and the inorganic precursor was from the silicon alkoxide family. Ultrasound, through the acoustic cavitation process, influences the formation of a very fine distribution of silica particles and avoids cyclidation of the polymer, thus favoring copolymerization with the inorganic particles and leading to the formation of a highly porous and rubber-like solid aerogel. Creep compliance curves, corresponding to the time-dependent depth response to a step load, are imprint site dependent, with pore, soft and stiff sites discerned. In all cases, an instantaneous elastic deformation is apparent. For longer test times, depending on the imprint sites, elastic deformation and newtonian flow produce the rise and fall of the creep curve. Linear parts of the curve on a log-log scale indicate potential growth with small exponents for the creep compliance level. Isochrones stress-strain diagrams show a superlinear trend and an increase with time, which reveals the nonlinear viscoelasticity of these hybrid aerogels. The elasto-plastic response to creep can be tuned by the molecular functionality of the different silane derivatives studied.
Stability Investigation of CuInS2 based heavy-metal free nanocrystals
Authors: Xie Chuang , Zhang Yu , Wang Andrew Y. , Yu William W. , Wang Jingkang , Xu Jian
Published: September 2011

In the present work the photostability of high-quality CuInS2 based nanocrystals (Zn-Cu-In-S/ZnSe/ZnS and CuInS2/ZnS core/shell nanocrystals) of different sizes and concentrations were investigated at ambient condition both under UV irradiation and in the darkness. The photostability of commercial CdSe/ZnS core/shell nanocrystals were used as reference to compare to that of CuInS2 based nanocrystals. The half-life times of the CuInS2 base nanocrystals are 2-8 times that of the reference which indicates the CuInS2 base NCs we obtained in the present work are very stable, reliable and competent for the application in biomedical fields.
Efficiency of Cationic Rosette Nanotubes for siRNA Delivery
Authors: Alshamsan Aws , EL Bakkari Mounir , Fenniri Hicham
Published: September 2011

Cationic rosette nanotubes (RNTs) were generated by functionalization of selfcomplementary twin guanine-cytosine (G^C) motifs with up to 15 L-lysine residues (Kn.T, n = 1–15). siRNA binding capacity was determined by gel retardation assay on agarose gel. Up to K5.T, siRNA complexation was a function of oligolysine-chain length and mole ratio of Kn.T. At higher Kn.T, local cationic density employed by supramolecular assembly emerged as a contributor to siRNA complexation. We have shown that no effective siRNA binding was achieved with equivalent mole ratios of corresponding oligolysine peptides (not conjugated to the G∧C motif). With K12.T, siRNA complexation gave spherical structures in the range of 200 nm, which was internalized and retained by human cell lines without noticeable cytotoxicity. In this report, we demonstrate for the first time the capacity of the RNTs as siRNA carriers that can be tailored to achieve maximum siRNA loading efficiency without carrier-associated cell toxicity. We anticipate these cationic RNTs to be effective in the delivery of biologicallyfunctional siRNA.
Synthesis and Control of ZnS Nanodots and Nanorods with Different Crystalline Structure from an Identical Raw Material Solution and the Excitonic UV Emission
Authors: Uehara Masato , Sasaki Satoshi , Nakamura Yusuke , Lee Changi , Nakamura Hiroyuki , Maeda Hideaki
Published: September 2011

We synthesized ZnS nanocrystals from identical raw material solution by the thermal decomposition of an amine complex. The shapes of products were changed by simply varying heating rate. At higher heating rate, we obtained the isotropic zincblende nanocrystals. At the lower heating rate, the nanorods were formed and the length was increased with the decrease of heating rate. The nanorods had wurtzite structure below 175 °C, and consequently transformed to zincblende phase during a temperature rise to 200 °C. These particle shapes and phases were related to the adsorption properties of amine ligands. Additionally, the synthesized ZnS nanodots and nanorods exhibited predominantly band-edge emission in fluorescence spectra.
Defect-Selective Etching of Icosahedral Boron Arsenide (B12As2) Crystals in Molten Potassium Hydroxide
Authors: Whiteley C.E. , Mayo A. , Edgar J.H. , Dudley M. , Zhang Y.
Published: September 2011

The present work reports on the defect-selective etching (DSE) for estimating dislocation densities in icosahedral boron arsenide (B12As2) crystals using molten potassium hydroxide (KOH). DSE takes advantage of the greater reactivity of high-energy sites surrounding a dislocation, compared to the surrounding dislocation-free regions. The etch pits per area are indicative of the defect densities in the crystals, as confirmed by x-ray topography (XRT). Etch pit densities were determined for icosahedral boron arsenide crystals produced from a molten nickel flux as a function of etch time (1-5 minutes) and temperature (400-700°C). The etch pits were predominately triangle shaped, and ranged in size from 5-25μm. The average etch pit density of the triangle and oval etch-pits was on the order of 5x107cm-2 and 3x106cm-2 (respectively), for crystals that were etched for two minutes at 550°C.
Hexagonal Boron Nitride Nanowalls Synthesized by Unbalanced RF Magnetron Sputtering
Authors: BenMoussa Boumédiène , D’Haen Jan , Borschel Christian , Saitner Marc , Soltani Ali , Mortet Vincent , Ronning Carsten , D’Olieslaeger Marc , Boyen Hans-Gerd , Haenen Ken
Published: September 2011

A recurrent problem in the synthesis of hexagonal boron nitride (h-BN) is contamination with oxygen and carbon, leading to possible detrimental effects on optical and electronic properties. Here it is shown that the addition of H2 to the N2/Ar mixture used during the deposition process, clearly suppresses the incorporation of these elements, reducing their combined level below 5 %. The surface morphology, assessed with scanning electron microscopy (SEM), revealed the presence of h-BN nanowalls, i.e. vertically positioned 2D structures consisting out of several h-BN sheets. While Fourier transform infrared (FTIR) spectroscopy revealed the sp2 nature of the bonds, confirming the hexagonal nature of the nanowalls, the quasi-perfect stoichiometry of the material was evidenced by combining energy dispersive X-ray analysis (EDX) and Rutherford backscattering spectroscopy (RBS). The dimensions and density of these walls are clearly film thickness dependent and cross-sectional TEM images confirmed the increasing level of porosity with film thickness. A dense layer of material is present at the substrate-film interface, which gradually evolves into the 2D nanowall structures.
Complete Characterization of Thermoelectric Materials by a Combined van der Pauw Approach and the Effect of Radiation Losses
Authors: de Boor Johannes , Schmidt Volker
Published: September 2011

We have recently presented a novel method for a complete thermoelectric characterization [J. de Boor, V. Schmidt. Adv. Mater. 22:4303, (2010)]. This method is based on the well-known electrical van der Pauw method and allows measurement of the electrical and thermal conductivity, the Seebeck coefficient and the thermoelectric figure of merit. After a short review of this method we will discuss the systematic measurement errors of the method. It turns out that radiative heat loss can affect the thermal conductivity measurement significantly. We will give a simple estimation for the relative error due to radiation losses and discuss error minimizing strategies.
Size Effects in Bi-Sb Solid Solutions Thin Films
Authors: Rogacheva Elena I. , Orlova Dar’ya S. , Dresselhaus Mildred S. , Tang Shuang
Published: September 2011

The room-temperature dependences of the electrical conductivity σ, Seebeck coefficient S, Hall coefficient RH, and the thermoelectric power factor P on the thickness (d=10–300 nm) of the thin films grown on mica substrates by thermal evaporation in vacuum of Bi-Sb solid solutions crystals with 4.5 at.% Sb were obtained. It was established that an increase in d up to ~ 200 nm leads to a change in kinetic coefficients and that in the thickness dependences of the thermoelectric properties, quantum oscillations were observed. It was shown that the monotonic component of the σ(T) dependence can be satisfactorily approximated by theoretical calculations based on the classical Fuchs - Sondheimer theory. The theoretically estimated period of oscillations is in a good agreement with the experimentally observed period.
Construction of Molecular Shuttles Based on Kinesin Motor Proteins and Microtubules
Authors: Oliveira Daniel , Domyoung Kim , Umetsu Mitsuo , Adschiri Tadafumi , Teizer Winfried
Published: September 2011

The intracellular cargo delivery performed by kinesin motor proteins can be biomimetically employed to engineer tailor-made artificial nanotransport systems. Kinesin (expressed on an Escherichia coli system) and microtubules (obtained from the polymerization of tubulin proteins) were prepared and characterized. We report recent results and explore the aim of the construction of biomotor-based NanoElectroMechanical Systems (NEMS) and their potential applications, e.g. as drug delivery systems.
Optimizing Process Variables to Control Fiber Diameter of Electrospun Polycaprolactone Nanofiber Using Factorial Design
Authors: Khan Saida P. , Bhasin Kadambari , Newaz Golam M.
Published: September 2011

In the electrospinning process, fibers ranging from 50 nm to 1000 nm or greater can be produced by applying an electric potential to a polymeric solution [1, 2]. Our group has studied the fabrication of electro-spun Poly-caprolactone (PCL) nanofiber consisting of a range of fiber diameter (nm-um) and pore sizes. PCL is a biocompatible, FDA approved and biodegradable [3, 4] polymer. As a solvent we have used 2,2,2-trifluoroethanol (TFE) for its biocompatibility, conductivity and high dielectric constant. The electrospinning technique consists of a simple setup with a number of variables working in a complex and unpredictable way. The variables affecting fiber diameter are polymer concentration in the solution, flow rate, applied voltage, tip to collector distance, diameter of the needle/capillary, polymer/solvent dielectric constant etc. In our study we have found that concentration of the solution and molecular weight of the polymer are the most important parameters for forming the nanofibers and viscosity is important for the fiber diameter. To optimize so many variables to control the fiber diameter, we have used the factorial design method. The study is important for the fabrication of biomimetic scaffold for vascular implant and tissue engineering application.
Fabrication and Characterization of Two Compliant Electrical Contacts for MEMS: Gallium Microdroplets and Carbon Nanotube Turfs
Authors: Kim Y. , Qiu A. , Reid J. A. , Johnson R.D. , Bahr D. F.
Published: September 2011

Because of their high mechanical compliance and electrical properties, the idea of using Ga and CNTs for micro electrical relay contacts has been investigated to minimize damage from switching and make good electrical contacts. Ga was electroplated into droplets on the order of 50 µm in radius on single crystal Si to create a contact for a switch that can be annealed to recover its original electrical properties after mechanical damage. CNTs were grown on Si substrates, coated with a thin Au layer, and transferred to other Si or Kapton substrates through thermocompression bonding. In the case of the Ga contact, repeated switching led to an increase in the resistance, but the resistance recovered after a thermal reflow process at 120 °C. Longer term and larger area contacts were used to measure the contact behavior under switching conditions of up to 200 A/cm2. At moderate cycling conditions (on the order of 200 cycles) the adhesion began to significantly degrade the switch. The oxidation behavior of the Ga droplets was characterized for thermal reflow, suggesting a passivating 30 nm oxide forms at 100 °C. The oxide formed by the Ga is thin and fragile as demonstrated by its use in a switch. The Ga droplets were examined with electrical contact resistance nanoindentation and the loads at fracture and the onset of electrical contact were identified. CNT turfs were also tested for making patterned electrical contacts; turfs of lateral dimensions similar to the Ga droplets were tested using electrical resistance testing during nanoindentation and as macroscopic contacts, and shown to be able to carry similar current densities. The results will be compared between the two systems, and benefits and challenges of each will be highlighted for creating compliant electrical switches and contacts.
Engaging High School Students in University Research
Authors: Davis Kathleen M. , Muskin Joseph J.
Published: September 2011

The absence of engineering from K-12 curricula and mainstream media often causes students to refer back to historical stereotypes regarding what engineers look like and the type of work they do. Such misconceptions may prevent high school students from pursuing engineering as a field of study and increase the need for engineering educational programs [1]. Nano-Challenge is an outreach program that orients high school students to engineering through a one-year research internship. The program is held at the Center for Nanoscale Chemical, Electrical, Mechanical Manufacturing Systems (Nano-CEMMS) at the University of Illinois at Urbana-Champaign. A major focus of the program is to involve students from groups traditionally underrepresented in STEM fields and inform them about engineering earlier in their careers. An external program evaluation provides anecdotal information about the students’ experiences and gives feedback to inform program improvement.
Fabrication and Characterization of MEMS-Based Structures from a Bio-Inspired, Chemo-Responsive Polymer Nanocomposite
Authors: Hess Allison E. , Zorman Christian A..
Published: September 2011

This paper reports the development of micromachining processes, as well as electrical and mechanical evaluation of a stimuli-responsive, mechanically-dynamic polymer nanocomposite for biomedical microsystems. The nanocomposite, which consists of a cellulose nanofiber network embedded in a poly(vinyl acetate) matrix, was shown to display a switchable stiffness comparable to bulk samples, with a Young’s modulus of 3570 MPa in the dry state, which reduced to ~25 MPa in the wet state, with a stiff-to-flexible transition-time dependent on exposed surface area. Upon immersion in phosphate buffered saline, the ac resistance through the PVAc-TW thickness was found to reduce from 8.04 MΩ to ~17 kΩ. Electrochemical impedance of an Au electrode on PVAc-TW was found to be ~178 kΩ at 1 kHz, and this was found to be stable as the probe shank was flexed to compress the metal, but increased with increasing flex angle when the metal was flexed into a tensile state.
Ga1-xGdxN-Based Spin Polarized Light Emitting Diode
Authors: Jamil Muhammad , Zaidi Tahir , Melton Andrew , Xu Tianming , Ferguson Ian T.
Published: September 2011

In this work, a room temperature spin-polarized LED based on ferromagnetic Ga1-xGdxN is reported. The device was grown by metalorganic chemical vapor deposition (MOCVD) and is the first report of a spin-LED based on Ga1-xGdxN. Electroluminescence from this device had a degree of polarization of 14.6% at 5000 Gauss and retained a degree of polarization of 9.3% after removal of the applied magnetic field. Ga1-xGdxN thin films were grown on 2 μm GaN templates and were co-doped with Si and Mg to achieve n-type and p-type materials. Co-doping of the Ga1-xGdxN films with Si produced conductive n-type material, while co-doping with Mg produced compensated p-type material. Both Si and Mg co-doped films exhibited room temperature ferromagnetism, measured by vibrating sample magnetometry.
Origin of Hysteresis in La0.67Ca0.33MnO3
Authors: Morrison K. , Berenov A. , Cohen LF
Published: September 2011

Hysteresis is unattractive for magnetocaloric applications because it introduces loss in the cooling cycle. It is however usually associated with a first order transition and large entropy change. In this paper we review the sources of hysteresis in magnetocaloric materials and in particular in manganite systems where the nature of the transition in terms of whether it is indeed a first order transition remains elusive.
Tunneling Effects and Electrical Conductivity of CNT Polymer Composites
Authors: Xu S. , Rezvanian O. , Peters K. , Zikry M.A.
Published: September 2011

A three-dimensional (3D) carbon nanotube (CNT) network computational model was developed to investigate the electrical conductivity and current flow in polymer composites with randomly dispersed CNTs. A search algorithm was developed to determine conductive paths for 3D CNT arrangements and to account for electron tunneling effects. Tunneled currents were obtained as a function of tunneling distance and matrix material. Several possible CNT conductive paths were obtained and finite-element representative volume elements (RVEs) were then used to predict current densities in different CNT arrangements. The predictions indicate that random CNT arrangements can be optimized for current transport.
Designed-in Molecular Interactions Lead to Superior Thermo-mechanical Properties in Nanocomposites
Authors: Ozden E. , Atilgan A.R. , Bilge K. , Menceloglu Y.Z. , Atılgan C. , Papila M.
Published: September 2011

The effect of the nanofiller chemistry on the mechanical behaviour of thermoset polymer matrix nanocomposites is investigated. The interaction between a crosslinked polymer resin and the reinforcing nanofibers driven by their chemistry is revealed by molecular dynamics simulations. Specifically, crosslinked network systems of neat epoxy and epoxy-P(St-co-GMA) are modeled to discuss the effect of various molecular interactions as a function of temperature on a molecular basis. At 433K°, incorporation of single molecule of bonded P(St-co-GMA) and nonbonded P(St-co-GMA) lead to increase in Young’s modulus by 10% and 6%, respectively, compared to neat epoxy system.
Structural Characterization of Micron-scaled Reticulated Copper Foams
Authors: Lin Stephanie J , Nadler Jason H.
Published: September 2011

The development of a multifunctional, micron-scaled, reticulated copper foam that reliably exhibits high intrinsic thermal conductivity, efficient capillary fluid and evaporative transport over a wide area presents a unique challenge. In this work, the relationship of critical foam processing variables such as sintering temperature and template size on the pore size distribution and pore neck/body ratio is investigated using image analysis. The resulting fluid permeability values of these foams are estimated by using the Kozeny Carman equation and the porosity, surface area per unit area and tortuosity obtained through image analysis. Estimating the fluid permeability of these foams is useful for predicting the mass and heat transfer within the porous network, and provides a metric for optimizing the foam’s structural characteristics for a particular application.
Thermoelectric properties of Zn-Sn-Sb based alloys
Authors: Ito Motoki , Ohishi Yuji , Muta Hiroaki , Kurosaki Ken , Yamanaka Shinsuke
Published: September 2011

In the Zn-Sn-Sb ternary system, Zn4Sb3, ZnSnSb2, and ZnSb have attracted attentions as advanced thermoelectric materials. Zn-Sn-Sb based alloys with various compositions were fabricated and the thermoelectric properties were investigated. That system is composed by orthorhombic ZnSb phase, tetragonal ZnSnSb2 phase with chalcopyrite structure, and rhombohedral SnSb phase. Large Sn content increases volume fraction of the metallic SnSb phase, which degenerate the powar factor. The ZnSb based alloy shows relatively large Seebeck coefficient. Sn substitution for ZnMxSb1-x significantly enhances the power factor, which indicates that Sn is effective dopant for ZnSb.
Thin film amorphous silicon bulk-mode disk resonators fabricated on glass substrates
Authors: Gualdino A. , Chu V. , Conde J. P.
Published: September 2011

The fabrication and characterization of thin-film silicon bulk resonators processed on glass substrates is described. The microelectromechanical (MEMS) structures consist of surface micromachined disk resonators of phosphorous-doped hydrogenated amorphous silicon (n+-a-Si:H) deposited by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD). The devices are driven into resonance by electrostatic actuation and the vibrational displacement is detected optically. Resonance frequencies up to 30 MHz and quality factors in the 103-104 range in vacuum were measured. A high density of modes that increases with resonator diameter was observed. Membrane-like vibrational modes show good agreement with finite element simulations. The effect of geometrical dimensions of the disks on the resonance frequency was also studied. When operated in air higher harmonic modes show increasing quality factors.
Modeling of the Magnetocaloric Effect in Heusler Ni-Mn-X (X = In, Sn, Sb) Alloys Using Antiferromagnetic Five-State Potts Model with Competing Interactions
Authors: Sokolovskiy Vladimir V. , Buchelnikov Vasiliy D. , Kostromitin Konstantin I. , Taskaev Sergey V. , Entel Peter
Published: September 2011

A simple theoretical five-state Potts model for the investigation of magnetocaloric effect in systems with competing ferromagnetic and antiferromagnetic interactions has been proposed. It is shown that this simple model can be applied to the description of the origin of the negative and positive magnetocaloric effect in systems with competing interactions, for example, Heusler alloys.
Sodium Hydride as Alternative Energy Having Hydrogen Absorption and Hydrogen Generation Functions and Hydrogen Fuel Cycle
Authors: Murahara Masataka , Ohkawara Toshio
Published: September 2011

Hydrogen was converted to such a material as coal or oil with a low specific gravity so that it could be stored for a longer period and transported for a long distance at room temperature and under atmospheric pressure; which is sodium metal or sodium hydride. Sodium metal is produced with molten-salt electrolysis from seawater by wind power and transported to a thermoelectric power station in the consumption place for hydrogen-fueled combustion power generation. Sodium hydroxide, a waste, is re-electrolyzed to produce sodium for hydrogen generation; which constructs a hydrogen fuel cycle. This hydrogen fuel cycle is a clean, environmentally friendly recycle system that never requires repeated supply of raw materials in the same manner as the nuclear fuel cycle. Sodium or sodium hydride is an alternative energy.
A Fully Atomistic Reactive Molecular Dynamics Study on the Formation of Graphane from Graphene Hydrogenated Membranes
Authors: Autreto Pedro A. S. , Flores Marcelo Z. , Legoas Sergio B. , Santos Ricardo P. B. , Galvao Douglas S.
Published: September 2011

Recently, Elias et al. (Science 323, 610 (2009).) reported the experimental realization of the formation of graphane from hydrogenation of graphene membranes under cold plasma exposure. In graphane, the carbon-carbon bonds are in sp3 configuration, as opposed to the sp2 hybridization of graphene, and the C–H bonds exhibit an alternating pattern (up and down with relation to the plane defined by the carbon atoms). In this work we have investigated, using reactive molecular dynamics simulations, the role of H frustration (breaking the H atoms up and down alternating pattern) in graphane-like structures. Our results show that a significant percentage of uncorrelated H frustrated domains are formed in the early stages of the hydrogenation process, leading to membrane shrinkage and extensive membrane corrugations. This might explain the significant broad distribution of values of lattice parameter experimentally observed. For comparison purposes we have also analyzed fluorinated graphane-like structures. Our results show that similarly to H, F atoms also create significant uncorrelated frustrated domains on graphene membranes.
A CMOS Compatible Carbon Nanotube Growth Approach
Authors: Cott Daire , Sugiura Masahito , Chiodarelli Nicolo , Arstila Kai , Vereecken Philipe M. , Vereecke Bart , Van Elshocht Sven , De Gendt Stefan
Published: September 2011

In future technology nodes, 22nm and below, carbon nanotubes (CNTs) may provide a viable alternative to Cu as an interconnect material. CNTs exhibit a current carrying capacity (up to 109 A/cm2), whilst also providing a significantly higher thermal conductivity (SWCNT ~ 5000 WmK) over Copper (106 A/cm2 and ~400WmK). However, exploiting such properties of CNTs in small vias is a challenging endeavor. In reality, to outperform Cu in terms of a reduction in via resistance alone, densities in the order of 1013 CNTs/cm2 are required. At present, conventional thermal CVD of carbon nanotubes is carried out at temperatures far in excess of CMOS temperature limits (400 C). Furthermore, high density CNT bundles are most commonly grown on insulating supports such as Al2O3 and SiO2 as they can effectively stabilize metallic nanoparticles at elevated temperatures but this limits their application in electronic devices. To circumvent these obstacles we employ a remote microwave plasma to grow high density CNTs at a temperature of 400 C on conductive underlayers such as TiN. We identify some critical factors important for high-quality CNTs at low temperatures such as control over the catalyst to underlayer interaction and plasma growth environment while presenting a fully CMOS compatible carbon nanotube synthesis approach
Graphene for Magnetoresistive Junctions
Authors: Inoue J. , Hiraiwa T. , Sato R. , Yamamura A. , Honda S. , Itoh H.
Published: September 2011

Influence of the linear energy-momentum relationship in graphene on conductance and magnetoresistance (MR) in ferromagnetic metal (FM)/graphene/FM lateral junctions is studied in a numerical simulation formulated using the Kubo formula and recursive Green’s function method in a tight-binding model. It is shown that the contribution of electron tunneling through graphene should be considered in the electronic transport in metal/graphene/metal junctions, and that the Dirac point (DP) is effectively shifted by the band mixing between graphene and metal electrodes. It is shown that MR appears due to spin-dependent shift of DP or spin-dependent change in the electronic states at DPs. It is shown that the MR ratio caused by the latter mechanism can be very high when certain transition metal alloys are used for electrodes. These results do not essentially depend on the shape of the junction structure. However, to obtain high MR ratios, the effects of roughness should be small.
Effect of Phosphorus Doping on the Young’s Modulus and Stress of Polysilicon Thin Films
Authors: Bassiachvili Elena , Nieva Patricia
Published: September 2011

On-chip MEMS (Micro Electromechanical Systems) characterization devices have been used to extract the Young’s modulus and average stress of polysilicon doped with phosphorus using thermal diffusion from a spin-on-dopant source. A customized fabrication process was developed and the devices were fabricated and tested. Resonant and static deformation tests were performed using microbridges. Information gathered from these experiments was combined to extract the Young’s modulus and residual stress of the thin film. Several doping concentrations, from undoped to 2.99×1020 phosphorus atoms/cm3 (4.148×10-4 Ω/cm), have been studied and it has been concluded that the Young’s modulus of phosphorus doped polysilicon with a chemical phosphorus concentration of 1.96×1020 atoms/cm3 (4.572×10-4 Ω/cm) increases by approximately 50GPa and the average stress of polysilicon with a phosphorus concentration of 2.99×1020 atoms/cm3 (4.148×10-4 Ω/cm) becomes more tensile by approximately 63 MPa relative to undoped specimens.
Giant Electrocaloric Effect in High-Energy Electron Irradiated P(VDF-TrFE) Copolymers
Authors: Lu S. G. , Li X. Y. , Cheng J. P. , Gorny L. , Zhang Q. M.
Published: September 2011

A direct calorimetry method was developed and used to measure the electrocaloric effect (ECE). A temperature change ΔT of over 20 °C and an entropy change ΔS of over 95 J/(kgK) were procured at 33 °C and 160 MV/m in the high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 68/32 mol% copolymers, which were larger than those of terpolymer blends (ΔT = 9 °C, ΔS=46 J/(kgK) at 180 MV/m and room temperature) and our earlier report on P(VDF-TrFE) 55/45 mol% normal ferroelectric copolymer (12 °C and 55 J/(kgK) at 80 °C). We observed that the β value ((8.7±0.6)×107 JmC-2K-1) in the equation of ΔS=1/2βΔD2 derived from ΔS - ΔD2 relation for irradiated copolymers was larger than that of the terpolymer blends ((5.4±0.5)×107 JmC-2K-1). It was also found that the irradiated copolymer showed a sharp depolarization peak at Td < Tm (maximum permittivity temperature), which is frequency independent, in the dielectric constant - temperature characteristics, a larger depolarization value at Td in the thermally stimulated depolarization current (TSDC) - temperature relationship, and a larger volume strain/longitudinal strain ratio over terpolymer blends. The giant ECE in irradiated copolymer is regarded as due to the greater randomness present in the relaxor state. In irradiated copolymers, the long all-trans chains are broken by the high-energy electrons, which make the small sized all-trans sequences more easily reorient along the electric field, more remarkably affecting the permittivity, TSDC, and volume strain.
Scanning Electron Microscopy and Surface Enhanced Raman Spectroscopy Correlation Studies of Functionalized Composite Organic-Inorganic SERS Nanoparticles on Cancer Cells
Authors: Leen Koh Ai , Sinclair Robert
Published: September 2011

Composite Organic-Inorganic Nanoparticles (COINs) are a novel type of surface-enhanced Raman (SER) scattering nanoparticle formed by aggregating inorganic silver particles in the presence of a chosen organic molecule with a distinct Raman fingerprint. Binding between antibody-functionalized COINs and cells is detected primarily using Raman spectroscopy, which measures spectral shifts of the excitation light due to inelastic scattering. It has been suggested that the amount of antibody-conjugated COINs binding on cells will vary according to the antigen-expression levels in cells and will lead to changes in measured SERS intensities. COINs functionalized with antibodies CD54 and CD8 were conjugated to U937 and SupT1 cancer cells and investigated in this study. SERS intensity measurements were obtained from each of the four sample variants and normalized against control samples comprising non-antibody-functionalized COINs with cells. The amount of COINs binding on cells was determined using scanning electron microscopy (SEM) and correlated with the SER spectroscopy intensity. Although we found a positive correlation between the number of COINs binding to cells and their respective SERS intensity, this relationship is not one-to-one, nor does it appear to be linear. We demonstrated that SEM imaging and SER spectroscopy can complement each other to provide information about COINs binding onto cancer cells.
Novel Computational Approaches to Li Diffusion and Electron Transport for High Capacity Battery Materials
Authors: Leoni Stefano , Seifert Gotthard , Craco Luis , Boulfelfel Salah Eddine
Published: September 2011

The intrinsic channel structure and low volume work makes olivines phosphates (LiMPO4) versatile for Li uptake and release. The understanding of Li cation diffusion/transport mechanisms inside olivines are crucial aspects, which we address using advanced molecular dynamics simulations. Activation energies calculated from DFT concluded 1D diffusion within channels as also indicated by neutron diffraction direct imaging techniques. On explicitly including temperature we find that - besides main conduction paths along the easy channels - distinct, less frequent but relevant diffusion paths exist. We point out that capacity and diffusion/conduction issues must be understood in a much more detail-rich framework, under realistic simulation conditions within finite temperature simulations. For evaluating electrical conductivity, we use advanced DFT methods to correctly capture the insulating states of the charged and discharged olivine materials. Based on the Kubo formalism, reliable conductivity/resistivity curves can be calculated for comparison with experiments and for anticipating properties.
Tracing Reversible and Irreversible Li Insertion in SiCO Ceramics with Modeling and Ab-Initio Simulations
Authors: Kroll Peter
Published: September 2011

We present combined modeling and simulation studies of Li insertion in amorphous SiCO ceramics. Atomistic models of amorphous SiCO with and without so-called “free” carbon have been crafted using a network modeling approach and subsequently relaxed and optimized within density functional theory.

In a first series, Li atoms are randomly inserted to test for sites with high binding energy. We find that Li prefers always bonding to O. The enthalpy of insertion, however, depends strongly on electronic states available in the SiCO host matrix. While Li inserted into insulating SiO2 is an energetically unfavorable process, the enthalpy of insertion in SiCO glass is decreased. Some glassy SiCO models exhibit favorable sites for Li insertion, which share a common motif in their local atomic environment. The presence of “free” carbon in SiCO then promotes Li insertion, because carbon-related structural imperfections give rise for low-lying unfilled electronic states. Consequently, strong and irreversible bonding of Li into SiCO is provided, if bonding of Li-cations in Li-O bonds outweighs the promotion energy for the electron to occupy unfilled electronic states.
Growth of CuO and CuGaO2 Thin Films by Spin-coating Method
Authors: Alias Afishah , Sakamoto Masato , Uesugi Katsuhiro
Published: September 2011

CuO and CuGaO2 thin films have been grown on Si (100) substrates using a sol-gel spincoating method. CuO films were successfully fabricated by the annealing around 700°C. At higher temperatures (>800°C), pyramidal CuO islands with 1~2μm in width and 0.4~0.8μm in height were observed. They arranged structures as a straight line parallel to the <110> and <010> directions, which suggests the self-organized growth of CuO pyramidal islands. Delafossite CuGaO2 films were fabricated as well, using Cu-Ga-O mixed solutions with Ga/(Cu+Ga) atomic ratio of 0.5. These results indicate that Cu-based compounds were fabricated by the sol-gel spincoating method.