bluuebunny/crossref_metadata_2025 huggingface dataset:
Conjugated Polymer Network Ultrathin Films on Metal Interfaces using the Precursor Polymer Approach: Design, Synthesis and In-situ Characterization
Authors: Advincula Rigoberto , Xia Chuanjun , Taranekar Prasad , Onishi Ken , Deng Suxiang , Baba Akira , Knoll Wolfgang
Published: April 2011

We have reported recently a novel method for cross-linking conjugated polymers involving a “precursor polymer” route, where the electrochemical method can be used to prepare ultrathin films on conducting metal and metal oxide surfaces. In this paper, we present the design, synthesis, protocol, and recent results in the application of these thin film materials. An emphasis will be given on how these films are characterized in-situ by a combined surface plasmon spectroscopy (SPS) and electrochemical approach. As a methodology, the concept can be extended to new methods of electrodeposition, patterning, and grafting of conjugated polymers on electrochemically addressable metal surfaces. Compared to spin-cast or electropolymerized monomer films, they are very robust both thermally and mechanically. Other applications of these films to sensors, dielectric materials, non-lithographic patterning, etc. are currently being investigated.
Plastic Deformation of Glassy Polymers: Correlation Between Shear Activation Volume and Entanglement Density
Authors: Ho Janet , Govaert Leon , Utz Marcel
Published: April 2011

The shear activation volumes of miscible polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) (PS-PPO) blends at different PS-PPO ratios were determined experimentally by both plane strain and uniaxial compression at constant strain rates. We find that the same correlation between the shear activation volume and the entanglement density ρe holds for the blend as well as for various pure glassy polymers: . Since the shear activation volume is closely related to the size of the plastic shear zones, this correlation suggests that the cooperativity of the elementary processes of plastic deformation in glassy polymers scales with the entanglement density.
Oriented Growth of Model Molecules of Polyethylene and Poly(tetrafluoroethylene) (n-C44H90 and n-C24F50) and Angle-resolved UPS Study of Their Intramolecular Energy Band Dispersion (E=E(k)) Relation
Authors: Yoshimura Daisuke , Miyamae Takayuki , Hasegawa Sinji , Hosoi Yukinobu , Sakurai Yoko , Yamamoto Masato , Ishii Hisao , Ouchi Yukio , Ueno Nobuo , Seki Kazuhiko
Published: April 2011

We report on the recent progress of our continued effort for the preparation and characterization of well oriented films of tetratetracontane (n-C44H90) and perfluorotetracosane (n-C24F50), which are good model molecules of fundamental polymers, polyethylene (CH2)n and poly(tetrafluoroethylen) (CF2)n, vacuum-deposited on metal surfaces. When the surface of the metal substrate was oxidized, the deposited chain molecules are aligned with their molecular axes vertically standing on the surface, while they lie flat on the surface when atomically clean Cu(100) surface was used. In the case of n-C44H90 on Cu (100), low-energy electron diffraction (LEED) studies revealed that the molecules were also azimuthally aligned with the chain axis almost parallel with the <100> and <010> axis, and infrared reflection-absorption spectroscopy (IR-RAS) enabled detailed studies of the film structure at increasing film thickness._By applying the technique of angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) to these flat-lying molecules, the intramolecular energy-band dispersion relation could be determined, The results agreed well with the results deduced from the previous work using vertically standing molecules assuming an inner potential V0. of –5 eV, confirming the validity of the estimation of V0. Excellent agreement was found between the observed and simulated spectra using the independent-atomic-center (IAC) approximation. Also the value of the vacuum level shift by molecular deposition was deduced for TTC/Cu(100) system to be – 0.3 eV. As for n-C24F50, the E(k) relation deduced in our previous study using vertically standing molecules showed discrepancy with band calculations. The detailed reexamination of the experimental data using IAC calculations for the previous report gave more realistic estimation of V0, and the newly deduced E(k) relation using this data showed good correspondence with theoretical band calculations, thus removing the difficulty in the previous work.
The Benefits of High-K dielectrics for Polymer TFTs
Authors: Raja Munira , Sedghi Naser , Higgins Simon J. , Eccleston W.
Published: April 2011

An increasing range of high-K dielectric is becoming available and it is very worth considering incorporating them into polymer TFTs. One of the benefits is that if metal gates are used then aqueous anodisation provides a very simple approach that is compatible with solution based processing. The details of this process are described. High-K dielectrics reduce threshold voltage and, therefore, increase switching speed. Of particular importance is the problem of bias instability. All the results involve the fractionation and controlled doping of poly-3-hexylthiophene.
The Direct-Write Polymer Field-Effect Transistor
Authors: Sluch M. I. , Taylor R. M. , Church K. H.
Published: April 2011

Field-effect transistors (FET's) have been directly written onto glass and Si substrates. The FET';s use the regioregular conjugated polymer poly(hexylthiophene) as the active semiconductor, with a formed polyurethane insulator layer and drain, source, and gate electrodes written in Ag. The FET's were fabricated solely by direct writing techniques. The low processing temperatures, the elimination of photolithography, and the flexibility of the direct writing process make this technology especially attractive for low-frequency applications.
Microwave Characterization Of Electro-Optic Polymers
Authors: Subramanyam Guru , Mathala Prasanna , Chevalier Christine , Davis Antonio , Yaney Perry , Grote James
Published: April 2011

Electro-optic polymer thin-films were characterized at microwave frequencies, for possible applications in GHz modulators. Single layers of the polymers were spin coated on low loss magnesium oxide substrates for characterizing the polymers at microwave frequencies. Coplanar waveguide test structures were designed for evaluation of the relative dielectric permittivity as well as the loss-tangent of the polymers at microwave frequencies. A conformal mapping technique was used for the extraction of relative dielectric constant of the polymer films based on the microwave scattering parameter measurements. As an example, a DR1-PMMA polymer had a relative dielectric permittivity of 3.01 and a loss-tangent of 0.075 at 8 GHz. The design of the test structures, the procedure for the accurate determination of the dielectric permittivity and the loss-tangent of the polymer films are discussed in this paper.
Direct-Write Polymer Diodes
Authors: Sluch Mikhail I. , Parkhill Robert L. , Taylor Robert M. , Church Kenneth H.
Published: April 2011

Conjugated polymer Schottky diodes have been directly written onto glass and alumina substrates. The rectifying contact was made between the p-type semiconductor poly(3,4-ethylene-dioxythiophene) doped with polystyrene sulfonic acid and Zn. The devices exhibit rectification ratios in the range of 102:1 to 103:1 at biases of ±1 V and ±10 V, respectively. The devices demonstrate rectification at frequencies up to 250 kHz. A full-wave bridge rectifier circuit written onto a glass substrate converts ac to dc up to 250 kHz and ±5 V.
Fabrication and characterization of tunable magnetic nanocomposite materials
Authors: Dikeakos M. , Tung L.D. , Veres T. , Stancu A. , Spinu L. , Normandin F.
Published: April 2011

Ferromagnetic nanocomposites in which magnetic nanoparticles are embedded into a polymeric matrix can replace conventional ferrites in the near future in applications such as: filters, high frequency inductors, chokes, sensors, core-shape and planar transformers, hybrid circuits and transponders. These dense magneto-dielectrics will provide a new approach in the fabrication of soft magnetic materials. In a magnetic/polymeric nanocomposite solid, the resistivity can be drastically increased, leading to significantly reduced eddy-current losses. In addition, the coupling between neighbouring magnetic nanoparticles results in much better soft magnetic properties at high frequencies than those of conventional bulk materials or ferrites. In order to study the influence of dipolar interactions between ferritic nanoparticles, samples of varying ferritic density were prepared. A polymeric binder (pre-swollen in toluene) was added to the nanoparticles, which were then cold-pressed using a standard compaction method. Characterization of the materials was carried out by means of x-ray diffractometry, electron microscopy, magnetometry, and high-frequency complex permeability measurements. Initial results show that tunable static and dynamic magnetic properties of the nanocomposite materials may be achievable.
Comb-Like Polymer Thin Films Prepared by Ionization-Assisted Deposition of Acrylate Compounds
Authors: Usui Hiroaki , Katayama Atsuhiro , Honda Takanobu , Tanaka Kuniaki
Published: April 2011

Alkylacrylate compounds were deposited by the ionization-assisted deposition (IAD) method to form thin films of comb-like polymers having long alkyl side chains on the vinyl polymer backbone. From the source material of n-octadecyl acrylate, polymer thin films having average molecular weight of 6000 were obtained at the polymer yield of 45 to 65%. For the preparation of fluorinated polymer thin films, 1H, 1H, 11H-eicosafluoroundecyl acrylate was used as the source material. Although the conventional evaporation method could not accumulate any films with this material, the IAD was able to produce insoluble thin films that have large contact angle against water droplet. In either material, the polymerization reaction was enhanced with increasing electron emission current for IAD. These results indicate that the IAD enables the preparation of thin polymer coatings that have polyethylene or Teflon-like properties without using the solvents.
A TFT Strategy for Polymer Circuits
Authors: Sedghi Naser , Raja Munira , Lloyd Giles C. R. , Liversedge Iain , Higgins Simon J. , Eccleston Bill
Published: April 2011

Although integrated circuit design principles are well understood, they lead to the possibility of radically new modes of device operation when applied to conjugated polymers. Design for speed is very important, even when this is not a primary requirement for a particular application, since supply voltage can be reduced and with it power dissipation. For all-polymer circuits, on thermally insulating plastic substrates, device operating temperature will also be reduced. This has implications for device stability. There are a number of factors that are important in increasing circuit speed. Reduction of channel length must be accompanied by a reduction of gate overlap capacitance and this makes the conventional versions of bottom gate TFT perform badly. Vertical devices are a particularly attractive proposition providing that off-currents can be maintained at a low level. One approach is to use Schottky barriers as the source and drain. Examples will be explained, as will the very unusual mode of operation of such devices. Optimum load structures will also be defined.
Buckling instabilities of thin cap layers deposited onto low-k dielectric films
Authors: Iacopi F. , Brongersma S.H. , Abell T.J. , Maex K.
Published: April 2011

Compressive stresses in thin capping films deposited onto low-k dielectric substrates are particularly prone to relaxation through buckling. This is due to insufficient cap/low-k film adhesion energy and to the compliance of low dielectric constant films. Low-k dielectric films, especially when porous, have low elastic modulus and demonstrate poor adhesion to other layers.

When adhesion is poor the cap film can locally buckle as if unconstrained. The buckle front can propagate like a crack and lead to complete delamination of the cap layer. If the cap/low-k film adhesive energy is high, wrinkling instabilities can take place under specific conditions determined by the geometry and the mechanical properties of the stack. In this case the dielectric also deforms due to stress relaxation. A theoretical and experimental evaluation of the parameters influencing the occurrence of these instabilities is presented. This study was carried out to explore the application and reliability of low-k materials as dielectrics for advanced interconnects.
Nanoscale Structure/Property Correlation Through Aberration-Corrected Stem And Theory
Authors: Pennycook S.J. , Lupini A. R. , Varela M. , Borisevich A. , Chisholm M. F. , Abe E. , Dellby N. , Krivanek O.L. , Nellist P. D. , Wang L. G. , Buczko R. , Fan X. , Pantelides S. T.
Published: April 2011

The combination of atomic-resolution Z-contrast microscopy, electron energy loss spectroscopy and first-principles theory has proved to be a powerful means for structure property correlations at interfaces and nanostructures. The scanning transmission electron microscope (STEM) now routinely provides atomic-sized electron beams, allowing simultaneous Z-contrast imaging and EELS as shown in Fig. 1. The feasiblity of correcting the inherently large spherical aberration of microscope objective lenses promises to at least double the achievable resolution. The potential benefits for the STEM, however, may turn out to be much greater than those for the conventional TEM because it is very much less sensitive to chromatic instabilities. The 100 kV VG Microscopes HB501UX at Oak Ridge National Laboratory (ORNL) is now fitted with an aberration corrector constructed by Nion Co., which improved its resolution from 2.2 Å (full-width-half-maximum probe intensity) to around 1.3 Å. It is now very comparable in performance to the uncorrected 300 kV HB603U STEM at ORNL which, before correction, also had a directly interpretable resolution of 1.3 Å, although information transfer had been demonstrated down to 0.78 Å8. Initial results after installing an aberration corrector on the 300 kV STEM indicate a resolution of 0.84 Å. The theoretically achievable probe size in the absence of instabilities is predicted to be 0.5 Å.
Application Fields of SEM/SPM Hybridsystems: Nanoscopic EBIC and Near Field CL
Authors: Heiderhoff Ralf , Joachimsthaler Ingo , Balk Ludwig J.
Published: April 2011

SPM/SEM-hybridsystems are more than only a combination of complementary microscopy techniques, because the used probes can simultaneously either be used as sensors, which give access to a vast variety of material properties, or as actuators, which can deliberately modify samples properties. The wide application field as well as flexibility is demonstrated exemplarily on techniques in microanalyses like nano-probing, cathodoluminescence, electron beam induced currents, and thermal analyses. These results provide an interesting perspective with respect to failure analyses and reliability of modern materials and devices.
Study of doping in GaAs layers by local probe techniques: micro-Raman, micro-photoluminescence and cathodoluminescence
Authors: Ardila Angel M. , Martínez O. , Avella M. , Sanz Luis F. , Jiménez J. , Gérard B. , Napierala J. , Gil-Lafon E.
Published: April 2011

The free carrier concentration of GaAs layers grown by MOCVD either on GaAs or Si substrates, by the conformal method in the last case, was obtained from the micro-Raman spectra using the hydrodynamic approach to fit the LO phonon-plasmon coupled Raman modes. The results on homoepitaxial layers were used as a calibration of the fitting method. The measurements in the selectively doped conformal layers were then compared with data obtained by micro-photoluminescence and cathodoluminescence spectroscopy and imaging. The doping data are compared with those deduced from the room temperature micro-photoluminescence and cathodolumiescence spectra.
High spatial resolution ultrafast scanning tunneling microscopy
Authors: Yarotski Dzmitry , Taylor Antoinette J.
Published: April 2011

We demonstrate ultrafast dynamical imaging of surfaces using a scanning tunneling microscope with a low-temperature-grown GaAs tip photoexcited by 100-fs, 800-nm pulses. We detect picosecond transients on a coplanar stripline and demonstrate a temporal resolution (full-width at half maximum) of 1.7 ps. By dynamically imaging the stripline, we demonstrate that the local conductivity in the sample is reflected in the transient correlated current and that 20-nm spatial resolution is achievable for a 2 ps transient, correlated signal. We apply this technique of photoconductively-gated ultrafast scanning tunneling microscopy to study carrier dynamics in InAs/GaAs self-assembled quantum dot samples at T=300 K. The initial carrier relaxation proceeds via Auger carrier capture from the InAs wetting layer (WL) on a timescale of 1–2 ps, followed by recombination of carriers on a 900 ps timescale. Finally, we demonstrate junction-mixing ultrafast STM (JM-USTM) using picosecond voltage pulses propagating on a patterned metal-on-metal (Ti/Pt). Using JM-USTM we have achieved a spatio/temporal resolution of 1 nm/8 ps.
Scanning Tunneling Optical Resonance Microscopy (STORM)
Authors: Raffaelle R.P. , Gennett T. , Lau J. E. , Jenkins P. , Castro S.L. , Tin P. , Wilt D.M. , Pal A.M. , Bailey S.G.
Published: April 2011

The ability to determine the in-situ optoelectronic behavior of semiconductor materials has become especially important as the size of device architectures is reduced and the development of complex microsystems has increased. Scanning Tunneling Optical Resonance Microscopy or STORM has the ability to interrogate the optical bandgap as a function of position within a semiconductor microstructure. This technique uses a tunable solid-state Ti sapphire laser whose output is “chopped” using a spatial light modulator and is coupled by a fiber optic to a scanning tunneling microscope in order to illuminate the tip-sample junction. The photoenhanced portion of the tunneling current is spectroscopically measured using a lock-in technique. The capabilities of this technique were verified using semiconductor microstructure calibration standards that were grown by organometallic vapor phase epitaxy (OMVPE) at the NASA Glenn Research Center. Bandgaps characterized by STORM measurements were found to be in good agreement with the bulk values determined by transmission spectroscopy, photoluminescence, and with the theoretical values that were based on x-ray diffraction results.
Kelvin Probe Microscopy and Cathodoluminescence Microanalysis of the Irradiation Induced Modification of Insulating Materials.
Authors: Stevens-Kalceff Marion A.
Published: April 2011

A combination of Kelvin Probe Microscopy (KPM) and Cathodoluminescence (CL) microanalysis has been used to characterize ultra pure silicon dioxide (SiO2) exposed to electron irradiation in a Scanning Electron Microscope. Charged beam irradiation of poorly conducting materials results in the trapping of charge at pre-existing or irradiation induced defects thereby inducing a localized electric field within the irradiated micro-volume of specimen. The residual surface potentials associated with the localized electric field have been mapped using KPM. Evidence of electro-diffusion and defect micro-segregation in charged beam irradiated SiO2 is observed. The associated mobile defect species are identified using CL microanalysis techniques. The high correlation between KPM and CL images confirms the significant influence of localized potentials on the microstructure of technologically important SiO2.
Nanoindentation: From forces to energies
Authors: Garcia-Manyes Sergi , Gorostiza Pau , Sanz Fausto
Published: April 2011

We have performed nanoindentations using the tip of an AFM cantilever. Experiments have been made on a freshly etched hydrogen terminated Silicon (111) surface, yielding penetrations of less than 1 nm so that the onset of the plastic region(or yield threshold) determination have been carefully investigated. Furthermore, other nanomechanical properties such as hardness have been also investigated. The energy involved in such indentation processes where a nanometric deformation of the surface takes place, has been for the first time calculated by calibration against a non deformable surface, and a correlation with the atomic structure of the indented single crystal is inferred.
FIB-TEM Characterization of Locally Restricted Implantation Damage
Authors: Wanzenboeck Heinz D. , Harasek Stefan , Brezna Wolfgang , Lugstein Alois , Langfischer Helmut , Bertagnolli Emmerich , Grabner Ulf , Hammer Gerold , Pongratz Peter
Published: April 2011

Imaging critical features by using transmission electron microscopy (TEM) or scanning electron microscopy (SEM) provides a versatile approach for nanostructure characterization. The combination of focused ion beam (FIB) technology for exposing defective sites beneath the surface is shown. Reliability testing and defect analysis by localized characterization of multilayered structures is demonstrated. TEM-imaging of a transistor gate with a locally confined radiation damage demonstrates target preparation by FIB yielding high-resolution TEM samples. The TEM imaging requires a longer sample preparation but provides high image quality (TEM). Investigation of materials previously processed with FIB revealed amorphization damage by the high energetic Ga-ion beam. This damage layer with a thickness in the range of 50 to 100 nm was confirmed in simulation. This disadvantageous damage by amorphization originating from FIB preparation of the cross-section could be removed by soft sputtering with a 250 V Ar+ion beam. This combined method using FIB for microsample preparation and TEM for imaging and analysis was proven to be a powerful tool the exploitation of nanostructured devices and for defect analysis on a highly localized scale.
Location of Current Carrying Faults in Integrated Circuits by Magnetic Force Microscopy
Authors: Pu A. , Rahman A. , Thomson D.J. , Bridges G.E.
Published: April 2011

In Integrated Circuits failure analysis excessive power supply current flowing into the IC is often used to indicate the presence of a faulty device. Location of these faulty devices can be problematic as the devices are often buried under several layers of conducting interconnect. By imaging the magnetic field produced by current flowing in an IC a faulty device can be located. In this paper we present experimental results on imaging current-carrying faults on integrated circuits using Magnetic force microscopy. We have experimentally determined that MFM is capable of measuring currents as small as 1 to 10 microampere on ICs in a 30 Hz bandwidth. We have carried out modeling calculations comparing the simulation results with experimental results using realistic MFM tip geometry. From these results we have devised a method to accurately locate the position of the internal current carrying faults from MFM images with micrometer uncertainty.
STM Light Emission from p-type GaAs (110) surface
Authors: Hoshino M. , Yamamoto N.
Published: April 2011

STM stimulated light emissions (STM-LE) from cleaved surfaces of GaAs(110) were investigated using a UHV-STM combined with a light detection system. Clean surfaces of Zn doped GaAs (p=5×1018) were obtained by mechanical cleavage in UHV. Light emission from the cleavage surface showed a single peak in a spectrum, which corresponds to luminescence by the conduction band to acceptor level transition in GaAs. In STM image Zn acceptors show bright tri angular-shaped contrasts, while in photon map they show dark contrasts when taken with a sample bias voltage of 2.0 V and 2.2 V at 80K. This contrast can be explained from the local band bending due to the charging effect or strain effect of the Zn acceptor.
Casimir Forces Between Nanoparticles and Substrates
Authors: Román-Velázquez C. E. , Noguez Cecilia , Villarreal C. , Esquivel-Sirvent R.
Published: April 2011

We study the Casimir force between a nanoparticle and a substrate using a spectral representation formalism. We consider the interaction of metal nanoparticles with different substrates within the dipolar approximation. The force is calculated as a function of the distance between the particles and the substrate. The particles are made of gold or potassium spheres, and the substrate is titanium dioxide, sapphire or a perfect conductor.
Tunneling Spectroscopy of short atomic chains.
Authors: Stein Jeremy , Zypman Fredy R.
Published: April 2011

In this paper we present results on transmission-energy and current-voltage curves for a Scanning Tunneling Microscopy probe in the presence of an atomic chain, operating in spectroscopy mode. We compare the results with independently calculated density of sates. Finally, we propose algorithms to process this experimental information to obtain chemical specificity and position of impurities in the chain.
Influence of Substrate on In-Plane Electrical Conduction of CuPc Nano-Crystals
Authors: Nakamura Masakazu , Watanabe Masatoshi , Maruyama Tsuyoshi , Iizuka Masaaki , Kudo Kazuhiro
Published: April 2011

We have investigated the conductivity variation of copper phthalocyanine nano-crystals deposited on SiO2 and mica. The density of surface hydroxyl group on SiO2 was estimated to be more than 10 times larger than that on mica by X-ray photoelectron spectroscopy. The grown crystals on both substrates were categorized to be a-axis orientation of α–form. Conductance-distance (G-d) measurements for various crystalline grains having different heights have been carried out with current imaging using atomic force microscope. The obtained conductivity vs. crystal height plot indicates that lower height crystals have higher conductivities on both surfaces. Besides, the lower height crystals on SiO2 have higher conductivity than those on mica. These results suggest that the electrons in the bottommost molecular layer are transferred to the electrophilic functional groups on the substrate surface. Such a phenomenon at organic semiconductor/insulator interface is reported for the first time.
Damping and Stiffness Enhancement in Composite Systems with Carbon Nanotubes Films
Authors: Lass E. A. , Koratkar N. A. , Ajayan P. M. , Wei B. Q. , Keblinski P.
Published: April 2011

Structural damping is an essential design parameter for many engineering applications. We demonstrate here the potential for the use of multi-walled carbon nanotube films in structural systems where vibrational energy dissipation is important. These films can provide a light weight, minimally intrusive alternative to conventional damping materials such as visco-elastic polymers. In addition, because of their multifaceted properties, damping materials utilizing carbon nanotubes are expected to be superior to traditional materials and may enhance the performance of the system by increasing structural stiffness and thermal stability.
Radiolytic Synthesis of Bimetallic Nanoparticles with High Aspect Ratio
Authors: Doudna C. M. , Bertino M. F. , Pillalamarri S. , Blum F. D. , Tokuhiro A. T. , Chattopadhyay S. , Terry J.
Published: April 2011

We present a technique to synthesize high aspect ratio metallic nanostructures based on the radiolysis method. In our experiments, we use gamma rays to irradiate aqueous solutions containing Ag and Pt ions and a water-soluble polymer. The aspect ratio of the nanoparticles is controlled by varying the radiation dose rate, the type of polymer, and the type of counter ions. Transmission electron microscopy shows that wire-like structures composed of grains with a face centered cubic (fcc) structure can be formed with a length of up to 3.5μm and typical diameters between 5 and 12nm. X-Ray absorption spectroscopy shows that Ag and Pt do not form an alloy, but remain segregated.
Preferred Orientation in Fibers of Hipco Single Wall Carbon Nanotubes from Diffuse X-Ray Scattering
Authors: Zhou W. , Winey K. I. , Fischer J. E. , Ramesh S. , Saini R. K. , Ericson L. M. , Davis V. A. , Pasquali M. , Hauge R. H. , Smalley R. E.
Published: April 2011

Neat Fibers of HiPco single wall carbon nanotubes extruded from strong acid suspensions exhibit preferred orientation along fiber axes. We characterize the extrusion-induced alignment using x-ray fiber diagrams and polarized Raman scattering, using a model which allows for some fraction of the sample to remain completely unaligned. We show that both x-ray and Raman data are required for a complete texture analysis of SWNT fibers.
Polymer-Attached Functional Inorganic-Organic Hybrid Nano-composite Aerogels
Authors: Liu Xipeng , Wang Mingzhe , Risen William M.
Published: April 2011

ABSTACT

Novel materials in which modified inorganic-organic hybrid silica aerogels are attached to polymer chains have been synthesized. The aerogels are based on chitosan, a bioderived polymer from chitin, and they contain silica. The first stage of the modifications includes attachment of isocyanate, amine onto the chitosan chains embedded within the aerogel. These groups are employed in the second stage to develop the reactions required to “string” aerogel particles along functionalized linear polymers or to employ these polymers to crosslink the composite aerogels. The initial chitosan-silica aerogel particles have an ultimate size of about 2nm, and their functionally modified forms were reacted at sizes up to 1 m. These aerogels can take up and hold dyes and water-soluble drugs. The chemistry to synthesize polyamino-siloxane based aerogel composite was discussed. In addition, two approaches to synthesize PHEMA aerogel hybrid were studied.
Plasticity in Nanomaterials
Authors: Zhan Guo-Dong , Kuntz Joshua D. , Wan Julin , Mukherjee Amiya K.
Published: April 2011

There have been many predictions of the reinforcing effects of carbon nanotubes in various composite matrices but large improvements in properties have not yet been convincingly demonstrated. In the present study, we have successfully realized this possibility in reinforcing nanocrystalline alumina. Fully dense single-wall carbon nanotubes (SWCN)/Al2O3 nanocomposites with nanocrystalline alumina matrix have been fabricated at sintering temperatures as low as 1150°C by spark-plasma-sintering (SPS). A fracture toughness of 9.7 MPam1/2, nearly three times that of pure nanocrystalline alumina, has been achieved in the 10 vol.% SWCN/Al2O3 nanocomposite. Moreover, high-strain-rate superplasticity has been achieved in Al2O3/ZrO2/MgAl2O4 nanocomposite with truly nanocrystalline grain size of 100 nm. Compression superplastic tests were conducted in the temperature range of 1300–1450°C at strain rates 10-3-10-1 s-1. The results generated a stress exponent of ∼ 2 and an activation energy of ∼ 620 kJ/mol.
Coating of Ultrathin Polymer Films on Carbon Nanotubes by a Plasma Treatment
Authors: He Peng , Lian Jie , Shi Donglu , Wang Lumin , Mast David , van Ooij Wim J. , Schulz Mark
Published: April 2011

Ultrathin polymer films have been deposited on both single- and multi-wall carbon nanotubes using a plasma polymerization treatment. HRTEM experiments showed that an extremely thin film of the pyrrole layer (2–7 nm) was uniformly deposited on the surfaces of the nanotubes including inner wall surfaces of the multi-wall nanotubes. Time-of-Flight Secondary ion mass spectroscopy (TOFSIMS) experiments confirmed the nanosurface deposition of polymer thin films on the nanotubes. The deposition mechanisms and the effects of plasma treatment parameters are discussed.
Arc Plasma Synthesis of Nanostructured Fe Powder
Authors: Lee Gil-Geun , Kim Sung-Duck
Published: April 2011

To investigate the effect of the parameters of the arc plasma process on the characteristics of the iron nano powder, the hydrogen volume fraction in the powder synthesis atmosphere was changed from 10% to 50%. The particle size, phase structure and magnetism of the synthesized iron powder were studied using the FE-TEM, XRD and a vibration magnetometer at room temperature. The particle size increased simultaneously with the increase in the hydrogen volume fraction, and the particle size ranged from about 20nm to 100nm with the change of the hydrogen volume fraction increasing from 10% to 50%. The synthesized iron powder particle had a shell-core structure composed of the crystalline a-Fe in the core and the crystalline Fe3O4 in the shell. The iron nano powder synthesized under the high hydrogen volume fraction condition had a higher saturation magnetism and lower coercive force than the values of the one synthesized under the low hydrogen volume fraction condition.
Characterization of Nanoparticle Films and Structures Produced by Hypersonic Plasma Particle Deposition
Authors: Perrey Christopher R. , Thompson Ryan , Barry Carter C. , Gidwani Ashok , Mukherjee Rajesh , Renault Thierry , McMurry P. H. , Heberlein J. V. R. , Girshick S. L.
Published: April 2011

There is great potential for the use of nanostructures in numerous applications. Investigation of nanoparticle films and structures is an important area of research for the production of nanoengineered devices. However, for these devices to become a reality, a production method that can yield high-rate synthesis of nanostructured powders is necessary. The hypersonic plasma particle deposition (HPPD) process has been shown to be capable of such high-rate production of nanoparticle films and structures. Versatile in its ability to manufacture nanoparticles of different chemistries HPPD also has the capability of in situ particle consolidation and assembly. In this study, chemically diverse films and structures have been produced by HPPD on a variety of substrates. Using novel specimen preparation techniques, these nanoparticles have been characterized by TEM. Fundamental issues of importance have been investigated for both the nanoparticle structure and the constituent nanoparticles. These issues include nanoparticle crystallinity and defect structure. The chemical homogeneity and structural characteristics of the deposition are also investigated. This application of microscopy to aid process development has resulted in insights into the nanoparticle formation process and the dynamics of the HPPD process.
Mechanical and Thermoviscoelastic Behavior of Clay/Epoxy Nanocomposites
Authors: Abot Jandro L. , Yasmin Asma , Daniel Isaac M.
Published: April 2011

The study of organic-inorganic nanocomposites has become relevant in recent years since these materials exhibit synergistic properties derived from the two components. Thermosetting polymers like epoxies that have high mechanical properties provide a baseline for further improvement with the addition of nanoclay particles. These nanocomposites can be used as the matrix of a fiber reinforced composite and lead to higher matrix dominated mechanical properties including elastic modulus, strength and fracture toughness. This study concentrates on the mechanical and thermoviscoelastic properties in the glassy regime of nanocomposites prepared by direct mixing. The elastic modulus of the nanocomposites was found to improve with respect to the pure epoxy modulus at the expense of both tensile strength and ductility regardless of clay content. The glass transition temperature was also found to decrease as well. The morphology of the nanocomposites was studied and correlated with the aforementioned properties.
Preparation and Characterization of Alumina based TiNn and SiCn Composites
Authors: Carlsson Mats , Johnsson Mats , Pohl Annika
Published: April 2011

Ceramic composites containing 2 and 5vol. % of nanosized commercially available TiN and SiC particles in alumina were prepared via a water based slurry processing route followed by spark plasma sintering (SPS) at 75 MPa in the temperature range 1200–1600°C. Some of the samples could be fully densified by use of SPS already after five minutes at 1200°C and 75 MPa. The aim was to control the alumina grain growth and thus obtain different nano-structure types. The microstructures have been correlated to some mechanical properties; e.g. hardness and fracture toughness.
Structure and elastic properties of immiscible LDPE-PP blends: dependence on composition
Authors: Petronyuk Julia S. , Priadilova Olga V. , Levin Vadim M. , Ledneva Olga A. , Popov Anatolii A.
Published: April 2011

Local elastic properties and microstructural features of low-density polyethylene-polypropylene (LDPE-PP) blends have been studied by microacoustical technique, differential scanning calorimetry and infrared spectroscopy. Focused ultrasonic beam of acoustic microscope has been employed to measure elastic wave velocities, bulk and shear elastic moduli and Poisson ratio. The experiments show that the mechanical properties of immiscible LDPE-PP blends are non-additivily changeable in relation to ones of primary gomopolymers. Maximum of the moduli values is achieved with small addition of LDPE to PP. Additional drawing of bipolymer shows essential increasing of orientation ability for PP chains in 5/95 – 10/90 % LDPE-PP compositions. DSC curves show no significant deviations in melting temperature and crystallinity degree for different compositions of PP and LDPE phases. Internal microstructure has been imaged for the blends by acoustic microscopy technique. It allows revealing dispersivity of components over the blend body.
The Development of Alternative Molds for Micromolding
Authors: Garino Terry , Cesarano Joseph , Morales Alfredo
Published: April 2011

Micromolding is a recently developed technique for fabricating parts in the millimeter size range with minimum features and dimensional tolerances less than 10 μm. This degree of precision is achieved by fabricating a master using the LiGA process. The molds made from the master are then filled with powder of the desired material to form parts that are then released from the mold and sintered to high density. Currently, molds are made of either poly(methyl)methacrylate (PMMA) or poly(dimethylsiloxane) (silicone rubber, PDMS). The PMMA molds must be dissolved to release the parts using a solvent that limits the choice of binder used to hold together the powder in the part. The PDMS molds are soft and therefore not suitable for lapping the parts prior to removal from the mold. Recently, two new types of molds materials have been investigated that can be removed utilizing a phase change, either melting or sublimation. The development of these new mold materials, which allow a wider choice of binders, will be described.
A Chemical Sensor Using Neurons and a 3-D Micro-fluidic Chip
Authors: McNally H. , Kufluoglu H. , Akin D. , Grimmer J. , Walker J. , Shi R. , Borgens R. , Bashir R.
Published: April 2011

In recent years, there has been a merger of microelectronics and biological sciences to develop integrated nano and micro-scale biosensors or biochips. The implementation of portable, rapid and economic methods for detecting different biological species on a chip will benefit from the development of electronic means for the analysis of cells. Neurons are very attractive as chemical sensors due to their sensitivity to specific toxins and their unique electrical properties. The use of closed well micro-fluidic devices for the growth of neurons has not been explored extensively. In this work, we will describe surface preparation techniques to enhance the neuronal cell viability and growth on microfabricated surfaces. We have fabricated micro-fluidic bio-chips for the trapping of neurons and to examine their growth. Neural cells are maintained in a chamber on the chip with fresh nutrient media continuously flowing through the chamber. The temporal viability of the neural cells within the chip will be reported. The long-term goals of the project include electrically measuring the viability of the cells inside the micro-fluidic chambers.
Strain Gradient Effect in Cone Indentation
Authors: DiCarlo Anthony A. , Yang Henry T. Y. , Chandrasekar Srinivasan
Published: April 2011

A size effect is known to exist in the strength and hardness of metals at small length scales. For example, the hardness of a pyramid indentation at the macro-scale is constant and typically independent of indentation size due to the self-similar feature of the indentation. But, at the meso-scale, this hardness has been observed to increase with decreasing indentation size. This increase has been attributed to the influence of strain gradient on the flow stress. At this point, the contribution of a rotational gradient to the hardness is unclear.

This study investigates the sensitivity of the hardness to rotational strain gradients through a Cosserat continuum. Finite element simulation of cone indentation is employed to conduct this investigation. The effect of varying indentation strain fields is modeled using indentation with cones of varying angles. The results demonstrate the role of rotational gradients in indentation.
<0001> channeling stopping power of MeV He+ ions in 4H- and 6H-SiC.
Authors: Nipoti Roberta , Letertre Fabrice
Published: April 2011

4H-SiC and 6H-SiC thin films as top surface layers of SiCOI wafers and Rutherford Back Scattering experiments with He+ ions in the energy range 0.9 – 2.2 MeV were used for measuring the He+ ions <0001> channeling stopping power with respect to the SiC random one. The film thicknesses were in the range 270–360 nm. The ratio between axial and random stopping power values decreased for increasing energy values and was higher for the 6H polytype with respect to the 4H one, i.e. it ranged from 0.85 to 0.72 for the former and from 0.80 to 0.66 for the latter.
Radial distribution functions of amorphous silicon carbide
Authors: Ishimaru Manabu , Bae In-Tae , Hirotsu Yoshihiko
Published: April 2011

Atomistic structures of amorphous silicon carbide generated by energetic particles were examined by electron diffraction techniques in combination with imaging plates. Atomic pair distribution functions revealed that not only heteronuclear (silicon-carbon) bonds but also homonuclear (silicon-silicon and carbon-carbon) bonds exist in the first coordination shell of amorphous silicon carbide induced by ion- or electron-beam-irradiation. Structural changes from amorphous silicon carbide to amorphous silicon were observed under the electron irradiation.
Four Current Examples of Characterization of Silicon Carbide
Authors: Bai S. , Ke Yue , Shishkin Y. , Shigiltchoff O. , Devaty R. P. , Choyke W. J. , Strauch D. , Stojetz B. , Dorner B. , Hobgood D. , Serrano J. , Cardona M. , Nagasawa H. , Kimoto T. , Porter L. M.
Published: April 2011

A description is given of the profiling of CVD grown 3C SiC on undulant (001) Si using low temperature photoluminescence (LTPL). Inelastic neutron scattering (INS) and X-ray Raman scattering (XRS) are compared for acoustical modes of 4H SiC. Schottky barrier heights are obtained for 4H and 6H SiC on different crystal faces using three different measuring techniques. Scanning electron microscopy (SEM) is used to display a variety of porous SiC morphologies achieved in n-type and p-type SiC.

This paper is intended to be the introduction to the “CHARACTERIZATION” section of this volume. To serve this purpose we illustrate the subject matter with new results using four distinct experimental techniques.
Hall Scattering Factor of Holes and Shallow Defect Centers in Aluminum-doped SiC
Authors: Pensl Gerhard , Ciobanu Florin , Krieger Michael , Laube Michael , Reshanov Sergey , Schmid Frank , Wagner Günter , Nagasawa Hiroyuki , Schöner Adolf
Published: April 2011

The Hall scattering factor of holes rH,h(T) in 4H- and 6H-SiC is determined by comparing the temperature-dependent free hole concentration p(1/T) obtained from Hall effect and from the neutrality equation with defect parameters, which are independently determined by SIMS and C-V measurements. rH,h(T) strongly deviates from 1 and assumes values between 1.4 and 0.5 at temperatures ranging from 100K to 800K. rH,h(T) is identical for 4H-and 6H-SiC within the measurement uncertainty. Al-doped SiC epilayers of the 3C-, 4H- and 6H-polytype were investigated with admittance spectroscopy and DLTS prior to and subsequent to processing steps. Depending on the SiC polytype, a different number of shallow acceptors is observed, which are thermally stable up to high temperatures (1700°C).
Experimental Studies and Thermodynamic Modeling of the Interaction of O2 with SiC
Authors: Song Y. , Smith F. W.
Published: April 2011

We report on experimental studies and thermodynamic modeling of the reaction of O2 with the 4H- and 6H-SiC surfaces at high temperatures. This reaction leads to the growth of passivating SiO2 layers at high O2 pressures, etching of the surfaces at lower pressures, and enhancements of the surface segregation of carbon at still lower pressures. A pressure-temperature phase diagram for the oxidation of SiC is presented. Evidence for the thermal decomposition of the SiO2 layer on SiC is also presented.
SiC BJT's for High Power Switching and RF Applications
Authors: Agarwal Anant , Ryu Sei-Hyung , Capell Craig , Richmond James , Palmour John W. , Phan Binh , Stambaugh Jerry , Bartlow Howard , Brewer Ken
Published: April 2011

In this paper, high performance, high voltage NPN bipolar junction transistors in 4H-SiC are presented for applications in low frequency (< 5 MHz) power conversion systems as well as in RF (425 MHz) power amplifiers. The power BJTs for low frequency switching applications were designed to block 1300 V and showed a specific on-resistance of 8.0 mohm-cm2, which outperforms all SiC power switching devices ever reported. Moreover, these transistors show a positive temperature coefficient in the on-resistance and a negative temperature coefficient in the current gain, which enable easy paralleling of the devices. In addition, RF BJTs were designed, fabricated and tested for operation at UHF frequencies. The common emitter breakdown voltage was in excess of 500 V consistent with the 5 micron collector thickness. For VCC = 20 V, fT peaked at about 1.5 GHz. A single cell was measured in common emitter mode with a collector supply voltage of 80 V in class AB at 425 MHz. A 100 μs pulse width with 10% duty cycle was used. A maximum output power of 50 W for a single cell was achieved. The peak large signal power gain was 9.6 dB. The collector efficiency at the power output of 50 W was 51% with a power gain of 9.3 dB. This represents the first demonstration of a SiC RF BJT.
Fabrication and Measurement of 4H-Silicon Carbide Avalanche Photodiodes
Authors: Burr Kent , Sandvik Peter , Arthur Stephen , Brown Dale , Matocha Kevin
Published: April 2011

Avalanche photodiodes (APDs) that are sensitive in the ultraviolet (UV) from approximately 250 – 350 nm have been fabricated from 4H-SiC. The SiC APDs, which use hole-initiated avalanche multiplication, were produced using n-type SiC epitaxial layers grown on a p-type substrate. In order to achieve avalanche breakdown in the bulk of the material, a dry ion-based etching technique was used to form sloped sidewalls on the devices. The devices had an area of approximately 1 mm2, and they had maximum breakdown voltages of approximately 500 V. The APDs had a positive temperature coefficient for avalanche breakdown voltage and showed excellent stability for multiplication factors in excess of several hundred. Dark current, photo responsivity, and multiplication measurements from room temperature to 150°C will be presented. The dark noise performance of the APDs has also been characterized using a standard nuclear spectroscopy system consisting of a charge sensitive preamplifier, a shaping amplifier, and a multichannel analyzer. The input equivalent dark noise charge and excess noise factor for the dark current was measured over a range of shaping times, temperatures, and bias voltages. The noise performance of SiC APDs in applications such as gamma ray or x-ray spectroscopy will be highly dependent on the achievement of low bulk leakage current at the operating point. Here, an ionization coefficient ratio (k=α/β) of 0.078 was found.