bluuebunny/crossref_metadata_2025 huggingface dataset:
Thickness Dependence of Leakage Current Behavior in Epitaxial (Ba,Sr)TiO3 Thin Films
Authors: Ahn Kun Ho , Kim Sang Sub , Baik Sunggi
Published: April 2011

Thickness dependence of leakage current behaviors was investigated in epitaxial (Ba0.5Sr0.5)TiO3 thin films with different thicknesses of 55 - 225 nm prepared on Pt(001)/MgO(001) substrates by a radio-frequency magnetron sputtering technique. Below a certain critical film thickness (≤ 55 nm), the Schottky emission is a ruling leakage conduction mechanism over a wide electric field range. In contrast, in thicker films (> 55 nm), the Schottky emission still operates at low electric fields, however at high electric fields the Fowler-Nordheim (F-N) tunneling dominates. The transition film thickness appears to be associated with overlapping of the depletion layers formed at the top and bottom electrode interfaces.
Synthesis and Ferroelectric Properties of Sr- and Nb-codoped Bi4−xSrxTi3−xNbxO12 Thin Films by Sol-Gel Method
Authors: Matsuda Hirofumi , Iijima Takashi , Uchida Hiroshi , Okada Isao , Watanabe Takayuki , Funakubo Hiroshi
Published: April 2011

Ferroelectric Bi4Ti3O12 (BIT) thin films were modified by the substitution of Sr2+ ions for Bi3+ ions and of Nb5+ for Ti4+ (codoping) by spin-coating and decomposition of chemical solutions of metal-alkoxide materials (the nominal compositions of Bi4−xSrxTi3−xNbxO12 where x=0.0, 0.5, 1.0, 1.5). Single-phase thin films were crystallized above 550°C with BIT-type structure. The ferroelectric properties were found, though, with the values of Pr=10 μC/cm2 Ec=100 kV/cm, εr=300, and tanδ<5 % for Bi3.5Sr0.5Ti2.5Nb0.5O12 (x=0.5) annealed at 650 °C. Perhaps due to the lowering of the Curie temperature with increasing x, the maximum value of δr increased.
Simulation of the Variability in Next-Generation Microelectronic Capacitors with Polycrystalline Dielectrics
Authors: Cousins Jesse L. , Kotecki David E.
Published: April 2011

Monte Carlo simulations of capacitors with polycrystalline (Bax, Sr1−x)TiO3 (BST) dielectrics were performed. The variation in capacitors due to the polycrystalline microstructure of the dielectric was investigated, as well as the effects of varying the distribution of crystal sizes. When a lognormal probability density function (pdf) was used to approximate the crystal area pdf and the average number of crystals per capacitor was near 100, it was found that the minimum capacitance value was nearly independent of the standard deviation of crystal area distribution. Both the mean and maximum capacitance values were found to increase as the width of the standard deviation increased.
High Temperature Dielectric Properties of Sol-Gel Derived Thick PZT thin Films with Different Zr/Ti Atom Ratios
Authors: Cheng Jinrong , Zhu Wenyi , Li Nan , Cross L.Eric
Published: April 2011

PZT thin films of different thicknesses and Zr/Ti ratios of 60/40, 52/48 and 45/55 were coated onto platinized silicon substrates by using 2 methoxyethanol (2-MOE) based sol-gel spinon technique and crystallized with a rapid thermal annealing (RTA) process. XRD analysis revealed that thin PZT films exhibit random texture, while the thicker ones exhibit (100) texture, which was independent of composition. Dielectric constants and dissipation factors of PZT thin films were measured at elevated temperatures and as a function of frequency. For films with a thickness of ∼ 4 μm, the Curie points are at 350, 375 and 422°C for Zr/Ti ratios of 60/40, 52/48 and 45/55, respectively. All these films exhibit a high remnant polarization. A remnant polarization of 35 μC/cm2 had been achieved for the 60/40 films. No enhancement of the dielectric constant was observed in films with a composition close to MPB. The higher dielectric constant observed in films with the highest Zr content was explained by the concept of domain engineering.
Structure and Morphology of Epitaxially Intergrown (100)- and (116)-Oriented SrBi2Ta2O9 Ferroelectric Thin Films on SrLaGaO4(110) Substrates
Authors: Lee H. N. , Zakharov D. N. , Reiche P. , Uecker R. , Hesse D.
Published: April 2011

SrBi2Ta2O9 (SBT) epitaxial thin films having a mix of (100) and (116) orientations have been grown on SrLaGaO4(110) by pulsed laser deposition. X-ray diffraction θ2 θ and pole figure scans, and cross-sectional transmission electron microscopy (TEM) analyses revealed the presence of two epitaxial orientations, SBT(100) ∥ SLG(110); SBT[001] ∥ SLG[001] and SBT(116) ∥ SLG(110); SBT [110] ∥ SLG[001]. By calculating the integrated intensity of certain x-ray diffraction peaks, it was established that the crystallinity and the in-plane orientation of the (100) and (116) orientation are best at a substrate temperature of 775 °C and 788 °C, respectively, and that the volume fraction of the (100) orientation at about 770 °C reached about 60%. By scanning force microscopy and cross-sectional TEM investigations we found that the a-axisoriented grains are rounded and protrude out due to the rapid growth along the [110] direction, leading to a distinct difference of the surface morphology between (100)- and (116)-oriented grains.
Lead telluride-based far-infrared photodetectors – a promising alternative to doped Si and Ge
Authors: Dolzhenko Dmitriy , Ivanchik Ivan , Khokhlov Dmitriy
Published: April 2011

Doping of the lead telluride and related alloys with the group III impurities results in appearance of unique physical features of the material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. We review physical principles of operation of the photodetecting devices based on the group III-doped IV-VI including possibilities of fast quenching of the persistent photoresponse, construction of a focal-plane array, new readout technique, and others. Comparison of performance of the state of the art Ge(Ga) and Si(Sb) photodetectors with their lead telluride-based analogs shows that the responsivity of PbSnTe(In) photodetectors is by several orders of magnitude higher. High photoresponse is detected at the wavelength 116 micrometers in PbSnTe(In), and it is possible that the photoconductivity spectrum covers all the submillimeter wavelength range.
Hole concentration vs. Mn fraction in a diluted (Ga,Mn)As ferromagnetic semiconductor
Authors: Santos Raimundo R. dos , Oliveira L. E. , Castro J. d'Albuquerque e
Published: April 2011

The dependence of the hole density on that of Mn sites in Ga1−xMnxAs is studied within a mean-field approach to the hole-mediated ferromagnetism in III-V Mn-based semiconductor compounds. We parametrize the hole concentration, p, as a function of the fraction of Mn sites, x, in terms of the product m* (Jpd)2 (where m* is the hole effective mass and Jpd is the Kondo-like hole/local-moment coupling), and the critical temperature Tc. By fitting m* (Jpd)2 to experimental data for Tc(x), we establish the dependence of p on x, which is interpreted in terms of a reentrant metal-insulator transition taking place in the hole gas.
Thin Films of Antimony-Tin Oxide as Counter-Electrodes for Proton Working Electrochromic Devices
Authors: Naghavi N. , Marcel C. , Dupont L. , Rougier A. , Tarascon J-M.
Published: April 2011

We report here on thin films proton-working electrochromic devices based on the wellknown tungsten oxide as the coloring electrode, and Antimony Tin Oxide (ATO) as the ionstorage counter-electrode. We show that films deposited by Pulsed Laser Deposition (PLD) technique have an apparent Sb solubility up to 70 at %, and exhibit unusual electrochromic properties. Through potentiostatic tests we'll demonstrate that depending on the composition which influences film morphology, the Sn-Sb-O films could either present a faradic or a capacitive-like behavior, associated to a color or a neutral switching over a wide range of potentials, respectively. The structural properties of ATO films are characterized by X-ray diffraction and transmission electron microscopy (TEM). Electrochromic behavior is studied by means of cyclic voltamperometry coupled with ex situ optical transmittance measurements in the visible range. The maximum proton-storage capacity is observed for ATO films containing 40–50 at % Sb, while being quasi-neutral when switching over a wide range of potentials. These compositions are finally retained for the assembly of our WO3/proton-electrolyte/ATO devices, whose performances are reported.
Quantitative Secondary Ion Mass Spectrometry (SIMS) of III-V Materials
Authors: Lierde P. Van , Tian C. , Rothman B. , Hockett R. A.
Published: April 2011

Secondary ion mass spectrometry (SIMS) provides direct methods to characterize the chemical composition of III-V materials at major, minor and trace level concentrations as a function of layer depth. SIMS employs keV primary ions to sputter the surface and sensitive mass spectrometry techniques to mass analyze and detect sputtered secondary ions which are characteristic of the sample composition. In-depth compositional analysis of these materials by SIMS relies on a number of its unique features including: (1) keV primary ion sputtering yielding nanometer depth resolutions, (2) the use of MCs+ detection techniques for quantifying major and minor constituents, and (3) ion implant standards for quantifying trace constituents like dopants and impurities. Nanometer depth resolution in SIMS sputtering provides accurate detection of diffusion of dopants, impurities and major constituents. MCs+ refers to the detection of “molecular” ions of an element (M) and the Cs+ primary beam. MCs+ minimizes SIMS matrix effects in analysis for major and minor constituents, thus providing good quantification. This paper presents a SIMS study of AlxGa1−xAs structures with three different x values. MCs+ (M=Al or Ga) data are presented for the accurate determination of major and minor components. Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD) data were crosscorrelated with the MCs+ results. Three specimens with different x values were ion implanted with H, C, O, Mg, Si, Zn and Se to study quantification of trace levels. SIMS data acquired on a double focusing instrument (CAMECA IMS-4f) and a quadrupole instrument (PHI ADEPT 1010) are also compared. Lastly, we discuss our efforts to improve the analysis precision for pand n-type dopants in AlGaAs which currently is ± 3% (1 sigma).
Passive components on AlN for application in AlGaN/GaN power amplifiers
Authors: Jacobs B. , Straaten B. Van , Kramer M. , Karouta F. , Hek P. De , Suijker E. , Dijk R. Van
Published: April 2011

We have investigated Coplanar Waveguide (CPW) elements on AlN for use in future AlGaN/GaN based power amplifiers. This technology becomes crucial if a via-hole technology is not available. Lines, discontinuities, metal-insulator-metal (MIM) capacitors and resistors were measured and modelled. These elements are embedded between two adaptors for RF probing. A technique was developed to de-embed the adaptors from the overall measurement and hence correctly determine the properties of the element itself. Measurements on elements containing multiple ports with right angles can best be carried out using standard calibration techniques followed by carefully reorienting the probes. It is shown that for accurate design of matching networks operating at 10 GHz each element has to be carefully modelled. The method presented in this paper can be a useful contribution tackling some of the problems related to the design of these networks.
Palladium and Aluminum Gate Metals/Aluminum Nitride/Silicon Balanced Capacitors for Selective Hydrogen Sensing
Authors: Prakasam H. E. , Serina F. , Huang C. , Auner G. W. , Rimai L. , Ng S. , Naik R.
Published: April 2011

An alternate array of Pd/AlN/Si and Al/AlN/Si metal-insulator-semiconductor (MIS) devices has been developed using plasma source molecular beam epitaxy (PSMBE) method for deposition of AlN on Si and magnetron sputtering for deposition of Pd and Al electrodes (via mask) on AlN. Both devices show essentially identical capacitance (C) versus voltage (V) characteristics of the typical MIS capacitor. However, the C-V characteristic of a Pd-device shows a clear shift in the presence hydrogen, while that of an Al-device shows no shift. These sensors were characterized using C(V) and C(time) measurements under varying hydrogen concentration. The effects of oxygen and hydrocarbon gases on the sensors were also studied. The Pd-device responds selectively to hydrogen. These results suggest the possibility of fabricating a balanced sensor structure, which might have significant practical importance, as it would cancel all thermal and material sources of drift in the electrical component of the sensor response.
Apriori Process-Property Relationships of GaN Epitaxial Growth in Ga/N/H/C/O Systems
Authors: Loukeris Constantine , Khan Shumaila , Takoudis Christos G.
Published: April 2011

A comprehensive thermodynamic analysis has been performed for the Ga/N/H/C/O system. Apriori process-property relationships of the metal organic chemical vapor deposition (MOCVD) of Gallium Nitride (GaN) are thus obtained. The parameter space for pure GaN growth is studied for system water vapor levels of 0.1 ppb – 10 ppm, system pressure between 10-6- 106 Torr, N/Ga feed ratios of 1 - 100,000, C/Ga feed ratios of 0 – 100, and H2/Ga feed ratios of 100 – 10,000. Higher growth temperatures for pure GaN are predicted at high operating pressures (for pressures greater than 0.1 Torr), low C/Ga feed ratios, high carrier gas flow rates, and mostly at low N/Ga feed ratios. Because relative C/Ga, N/Ga and H2/Ga feed ratios have been considered, the predictions in this study are applicable to any multiple and single precursor systems. Such analyses can be easily extended to the molecular beam epitaxy of GaN, when the feed ratio C/Ga = 0. Experimental data reported on the growth of GaN are found to be in good agreement with our theoretical predictions, for many systems that have included different source species.
Double pendeo-epitaxial growth of GaN films with low density of threading dislocation
Authors: Hong Y. K. , Jung H. S. , Hong C-H. , Kim M.H. , Leem S-J.
Published: April 2011

A double pendeo-epitaxy technique for growing uniformly GaN films with low defect density over the entire surface of a substrate has been achieved by metalorganic chemical vapor deposition(MOCVD). The structural properties of the first pendeo-epitaxial layers were optimized with the ratio of the lateral to the vertical growth rate, which is strongly affected by the growth temperature and the TMGa flow rate. The second pendeo-epitaxial growth was performed on the first regrown layers after removing a high defective region originating from underlying GaN seed layer. From the analysis of atomic force microscopy(AFM) images, the termination of surface steps by threading dislocations were not observed at the second regrown GaN layers. This result implies that a very low density of threading dislocation exists on the GaN surface. Cathodoluminescence(CL) results showed a strong band-edge emission from the all regrown regions.
Effect of Additional HCl on the Surface Morphology of High Quality GaN on Sapphire by HVPE
Authors: Xiu X.Q. , Zhang R. , Lu D.Q. , Gu L. , Shen B. , Shi Y. , Zheng Y.D.
Published: April 2011

The effect of introduction of additional HCl on the surface morphology and structural properties of hydride vapor phase epitaxy grown GaN during growth is investigated, and high quality GaN with smooth surface on sapphire is obtained by adding the additional HCl into the HVPE reactor. The result is attributed to the control of polarity of GaN films during growth. The additional HCl altered the equilibrium at the GaN growth front, and the reversible reaction decreased the nucleation density or growth rate. Further, lower growth rate promote the surface diffusion and the coalescence over (0001) plane. Additional HCl may improve the surface morphology by suppressing the (000-1) polarity growth in the initial stage of the growth.
Growth of GaN:Sb MBE-Layers
Authors: Cristea P. , Ebling D.G. , Benz K.W.
Published: April 2011

The single crystalline growth of the GaNxSb1-x system is difficult due to the miscibility gap expected for nearly the whole composition range under thermodynamic equilibrium conditions. The gap is determined by the differences of the atomic radii and of the electro negativities for N and Sb. To overcome this problem crystal growth has to be performed under non-equilibrium conditions with kinetically controlled growth, as it is observed for molecular beam epitaxy (MBE) growth. A single crystalline MBE-growth within the miscibility gap has been demonstrated already in the GaAsxN1-x system exhibiting a similar large miscibility gap. GaN:Sb-layers were grown on Si(111)-substrates by MBE using NH3 as a N-source and solid element sources for Ga and Sb. The parameter window for growth was limited due to side reactions like the decomposition of NH3, the desorption of (at high temperature volatile) compounds like Sb and GaSb or the reaction of Sb with NH3. The composition of the layers was analyzed by XRD and RBS. Antimony bulk concentrations of up to 1.6 % could be obtained in GaN. Optical characterization of the samples was performed by CL-measurements and indicate Sb-induced transitions in the 2.2 eV and 1.42 eV range.
Prepare of ZnAl2O4/-Al2O3 complex substrates and growth of GaN films
Authors: Bi Z.X. , Zhang R. , Li W. P. , Wang X.S. , Gu S.L. , Shen B. , Shi Y. , Liu Z.G. , Zheng Y.D.
Published: April 2011

With the solid phase reaction between the ZnO film and -Al2O3 substrate, the ZnAl2O4/-Al2O3 complex substrate have been prepared. GaN films were then directly grown on this new kind of substrate using light-radiation heating low-pressure metalorganic chemical vapor deposition (LRH-LP-MOCVD) without any nitride buffer layer. The structure and surface morphology of the ZnAl2O4/-Al2O3 substrates and GaN epilayers have been characterized by employing X-ray diffraction (XRD) and scanning electron microscope (SEM). The result show that as the thickness of ZnAl2O4 layer is increased, the film changes from a (111)-oriented single crystal to a poly-crystal, together with the surface morphology transforms from uniform islandsa a to the bulgy-line structure, leading to GaN films grown on ZnAl2O4/ -Al2O3 substrates varying from c-axis oriented single-crystal to poly-crystal.
In-Situ Rheed Observation of Mocvd-Gan Film Growth
Authors: Sumiya Masatomo , Ogusu Noritaka , Osada Kouhei , Fuke Shunro
Published: April 2011

We developed the MOCVD apparatus equipped with RHEED system, which enable us to observe in-situ and real time RHEED for GaN film growth in ~100mTorr of pressure. We attempted to grow GaN film with this MOCVD chamber in 100mTorr. The in-situ RHEED was subsequently observed along the film deposition process in order to understand both the role of buffer layer and the mechanism of GaN film growth by MOCVD on highly lattice-mismatched substrate like sapphire. The results indicate that oxygen removed from the sapphire surface was observed during its cleaning in H2 flow at 1100°C. The dependence of re-crystallization and evaporation of the buffer layer on the annealing ambient was also detected. Although the nitrogen was slightly deficient, HT-GaN film with smooth surface was obtained in 100mTorr by adding H2 gas and reducing total flow rate. In preliminary deposition, the RHEED oscillation-like was observed in MOCVD-GaN growth. Thus, our developing deposition system has a potential to understand the growth mechanism with atomic level.
Modification of Stress in CVD Tungsten Silicide (Polycide) Film by SiO2Capping
Authors: Pelleg Joshua , Elish E.
Published: April 2011

Stresses in chemical vapor deposited polycide tungsten silicide (poly-Si/WSi2) wereevaluated at each stage of fabrication. The individual layers of the Si/SiO2/Poly-Si/WSi2/Poly-Si multilayer structure were deposited sequentially on separate wafers and subjected to x-ray diffraction analysis in the as deposited and annealed conditions to determine the changes in strain occurring in WSi2. Samples cut from wafers containing all the layers were capped with a 25nm thermal oxide and the strain in the WSi2film was also analyzed by XRD. The change in strain of the WSi2layer, following each step of the fabrication process, was evaluated by the lattice parameter variation of the c axis. The layers of the multilayered film affect the stress in the WSi2. A poly-Si layer on top of WSi2reduces its stress, since it introduces a compressive component, which further decreases upon annealing. It also maintains a Si supply at the poly- Si/SiO2interface, thus, eliminating Si outdiffusion during heat treatment in an oxygen containingambient. Capping the system by a thin oxide layer modifies the stress pattern of the WSi2, which becomes compressive.
Mechanical Properties and Stresses in Thin Gold Films on a Silicon Substrate
Authors: Xie Changjin , Emery Richard D. , Yang Seung-Yong , Tong Wei
Published: April 2011

Thin gold films with a thickness of 2mm were deposited on a silicon substrate by electron-beam evaporation. The material microstructure and internal stresses of the as-deposited gold films were characterized by scanning ion microscopy, orientation imaging microscopy, and X-ray diffraction. Microtensile tests of free-standing gold film samples were carried out to establish their intrinsic mechanical properties (in connection with a finite element analysis using crystal plasticity). Nanoindentation tests of the thin gold films attached to the silicon substrate were also carried out. Finite element analyses incorporating the crystal plasticity model were used to evaluate the effects of thin film textures, constraints due to the elastic substrate, and internal stresses on the plastic deformation behavior of the thin gold films under indentation at a direction normal to the film surfaces. Results of the combined experimental and numerical investigation indicate that the internal stresses have a strong effect on the uniaxial compression stress-strain behavior of the gold films and it may contribute to the relatively large hardness numbers obtained from the nanoindentation tests.
Constitutive Response of Passivated Copper Films: Experiments and Analyses
Authors: Shen Y.-L. , Ramamurty U.
Published: April 2011

The constitutive behavior of passivated copper films is studied. Stresses in copper films of thickness ranging from 1000 nm to 40 nm, passivated with silicon oxide on a quartz or silicon substrate, were measured using the curvature method. The thermal cycling spans a temperature range from - 196 to 600°C. It is seen that the strong relaxation at high temperatures normally found in unpassivated films is nonexistent for passivated films. The copper film did not show any rate-dependent effect over a range of heating/cooling rate from 5 to 25°C/min. Further analyses showed that significant strain hardening exists during the course of thermal loading. In particular, the measured stress- temperature response can only be fitted with a kinematic hardening model, if a simple constitutive law within the continuum plasticity framework is to be used. The analytic procedures for extracting the film properties are presented. Implications to stress modeling of copper interconnects in actual devices are discussed.
Real-Time in Situ Imaging of the Delamination of thin Ta Films on Si(100) Substrates Via a Synchrotron Radiation Technique
Authors: French B. L. , Bilello J. C.
Published: April 2011

The thermal stress-induced delamination of 500nm polycrystalline Ta coatings on Si(100) substrates was studied via a recently developed real-time in situ imaging technique. This method used white beam synchrotron (on SSRL station 2-2) Laue transmission diffraction topography coupled with simultaneous direct radiography to record the thermomechanical failure modes of the Ta films as a function of temperature. The observations were made using a novel experimental apparatus, consisting of a 600°C hot stage and a portable CCD x-ray imaging/storage system with ~20m m resolution. The system is capable of recording 30 images/sec; hence, at moderate strain rates not only was the morphology of failure evident, but detailed study of the dynamics of delamination was also possible. The mode of failure and the adhesion strength are correlated with the physiochemical nature of the coating-substrate interface, and also with the degree of in-plane/out-of-plane texture of the Ta films. These observations should be capable of extension to the study of a variety of adhesion and cyclic failure issues in thin coatings.
Atomic Force Microscopy and Transmission Electron Microscopy Study of Self-Organized Ordering in Vertically Aligned PbSe Quantum Dot Superlattices
Authors: Raab A. , Springholz G. , Lechner R. T. , Vavra I. , Kang H. H. , Salamanca-Riba L.
Published: April 2011

Self-organized lateral ordering is studied for PbSe/Pb1-xEuxTe quantum dot superlattices as a function of spacer thickness using atomic force microscopy and transmission electron microscopy. It is found that a pronounced hexagonal lateral ordering tendency exist not only for fcc-stacked superlattices but also for those with vertical dot alignment. For the latter case, a best in-plane ordering is observed for Pb1-xEuxTe spacer thicknesses around 160 Å. This is accompanied by a pronounced narrowing of the size distribution to values as low as ±8%. The resulting in-plane dot separations and dot densities are tunable by changes in spacer thickness. Similar marked changes are also found for PbSe dot shape as well as the dot sizes. This provides additional means for the tuning of the optical and electronic properties of the dots.
The influence of many body interactions in the stress-velocity relation of a single dislocation in a 2D lattice
Authors: Robles M. , Mustonen V. , Kaski K. , Patriarca M.
Published: April 2011

The stress-velocity relation of a single dislocation moving in a 2-D lattice has been studied using interactive molecular dynamic simulations. A hybrid interatomic model potential which couples Lennard-Jones(LJ) potential and the Embedded Atom Model (EAM) potential, is used to include radial and many body interactions. Both parts are assembled by a parameter so that the potential can be changed to describe a pure radial interaction to a strong many body interaction in a continuous way. Setting up a constant-stress scenario, the movement of a single dislocation is tracked from zero velocity state, up to a terminal velocity state. The external stress vs. terminal velocity curves have been obtained in the subsonic regime for different values of the coupling parameter. Non-linear relations are found velocity regime 0.1ct to 0.6ct, where Ct is the transverse speed of sound. Results have been analyzed using an augmented Peierls model to seek the connection between atomic scale, continuum variables and the limiting speed of dislocations
Materials Characterization and Device Performance of a CMR-Ferroelectric Heterostructure
Authors: Surthi S. R. , Kotru S. , Pandey R. K.
Published: April 2011

Abstract:The films of colossal magnetoresistive La0.67Ca0.33MnO3 (LCMO) and ferroelectric SbSI were grown by pulsed laser deposition method for fabricating their heterostructures. By varying the processing conditions during film growth and controlling subsequently the annealing conditions, the resistivity transport properties of the LCMO films could be greatly modified. Preliminary tests on the ferroelectric field effect transistor (FeFET) based on LCMO-SbSI heterostructure showed that the device behaves like a nonvolatile memory element. The FeFET showed a maximum channel modulation of ∼10% at room temperature, and the switching voltage was less than 2 V.
Determination of Total Energy Tight Binding Parameters from First Principles Calculations Using Adaptive Simulated Annealing
Authors: Froseth Anders G. , Derlet Peter , Hoier Ragnvald
Published: April 2011

Empirical Total Energy Tight Binding (TETB) has proven to be a fast and accurate method for calculating materials properties for various system, including bulk, surface and amorphous structures. The determination of the tight binding parameters from first-principles results is a multivariate, non-linear optimization problem with multiple local minima. Simulated annealing is an optimization method which is flexible and “guaranteed” to find a global minimum, opposed to classical methods like non-linear least squares algorithms. As an example results are presented for a nonorthogonal s,p parameterization for Silicon based on the NRL tight binding formalism.
Salt-Induced Block Copolymer Micelles as Nanoreactors for the Formation of CdS Nanoparticles
Authors: Zhao Hanying , Douglas Elliot P.
Published: April 2011

A novel preparation method of CdS nanoparticles in the core or corona of micelles is presented. Poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) and cadmium ions form aggregates of single micelles, called compound micelles, upon addition of the cadmium acetate salt into a solution of the block copolymer in tetrahydrofuran. The growth of CdS nanoparticles is confined to the core of single micelles after introduction of hydrogen sulfide gas into the solution. UV-visible spectroscopy, fluorescence spectroscopy, and transmission electron microscopy were employed to characterize the prepared core-embedded CdS nanoparticles. Corona-embedded CdS nanoparticles were prepared by dropping the core-embedded CdS nanoparticles into water with a low pH value. The location change of the CdS nanoparticles was accompanied by a structural change of the micelles, a change from compound micelles to single micelles. In a single micelle, CdS nanoparticles distribute randomly in the corona. The size of the nanoparticles increases slightly after the transition.
Nanostructuring of Multilayers by a Thermally Driven Self Assembling Process
Authors: Herweg C. , Dreyer S. , Troche P. , Hoffmann J. , Sievers S. , Lang C. , Freyhardt H. C.
Published: April 2011

Multilayers consisting of two immiscible components (e.g. Fe/Ag Fe/Au or Ni/NiO) could by transformed by an annealing process into a nanostructured system of non statistically distributed nearly spherical particles in a surrounding matrix of the complementary component. The non statistical arrangement of the particles and the dynamics of the disintegration process strongly depend on the initial interface energy, i.e. the local interface curvature and the local interfacial stress. Detailed microstructure investigations of the different systems are used to interpret the measured transport properties.
Hydrogen Storage Capacity Improvement of Nanostructured Materials
Authors: Lawrence Jeremy , Xu Gu
Published: April 2011

Safe, lightweight, and cost-effective materials are required to practically store hydrogen for use in portable fuel cell applications. Compressed hydrogen and on-board hydrocarbon reforming present certain advantages, but their limitations must ultimately render them insufficient. Storage in hydrides and adsorption systems show promise in models and experimentation, but a practical medium remains unavailable. To study hydrogen storage properties a new volumetric testing apparatus was designed and constructed. Adsorption conditions are evaluated up to pressures exceeding 250 bar and a broad range of temperatures. RF sputtering was used to introduce metals to carbon nanotubes with the aim to enhance hydrogen storage. Here we show a significant improvement in the gravimetric storage density over that of as-prepared single-wall nanotube samples that may be due to the unique interface introduced.
Preparation and Characterization of Nanostructured Particulate Catalytic Materials
Authors: Tong Baiyun , Siriwardane Upali , Naidu Seetala V. , Murty Akundi N. , Zhong Zhenchen
Published: April 2011

Laser Induced Solution Deposition (LISD) is essentially a laser chemical processing with similar mechanism of the counterpart – laser chemical vapor deposition (LCVD). It is a novel method for synthesizing nanocsale particles or thin films with the combined advantages of laser chemical vapor deposition and electroless chemical deposition in solution (electrolyte). It is simple and efficient, and it can produce high quality nanoparticles or patterned uniform thin films. In this paper the nanostructured Co/CoOx particles have been fabricated by LISD technique. We have characterized the deposited materials by using scanning electron microscope (SEM), the high-resolution transmission electron microscope (HRTEM) and X-ray diffraction technique (XRD). We have found that the sizes of the deposited particles are smaller than 5 nm uniformly suspended in the solution used in the LISD deposition, and the sizes are smaller than 500 nm on the silicon substrates inserted in the deposited solution. The results by energy dispersive X-ray analysis (EDX) have indicated that there are Co peaks and O peaks, which meant there were oxygen contamination or the deposited products were cobalt oxide rather than pure cobalt nanoparticles. The X-ray diffraction has shown that we have obtained pure Co nanoparticles in some cases but we have obtained cobalt oxides in other cases, which mainly depended on the experimental conditions such as the selection of solvents and solutes as well as the selection of the lasers including the wavelength and the power of the laser beams. The studies of the magnetic properties, catalytic properties as well as their relationship of pure cobalt nanoparticles and cobalt oxide nanoparticles are in good progress and we will publish the useful results elsewhere.
Pressure Isotherms of Hydrogen Adsorption in Carbon Nanostructures
Authors: Chen Xiaohong , Dettlaff-Weglikowska Urszula , Haluska Miroslav , Hulman Martin , Roth Siegmar , Hirscher Michael , Becher Marion
Published: April 2011

The hydrogen adsorption capacity of various carbon nanostructures including single-wall carbon nanotubes, graphitic nanofibers, activated carbon, and graphite has been measured as a function of pressure and temperature. Our results show that at room temperature and a pressure of 80 bar the hydrogen storage capacity is less than 1 wt.% for all samples. Upon cooling, the capacity of hydrogen adsorption increases with decreasing temperature and the highest value was observed to be 2.9 wt. % at 50 bar and 77 K. The correlation between hydrogen storage capacity and specific surface area is discussed.
Reductive Photopatterning of Phenylene-Vinylene-Based Polymers
Authors: Kavc T. , Langer G. , Kern W. , Ruplitsch A. , Mahler K. , Stelzer F. , Hayn G. , Saf R. , List E.J.W. , Zojer E. , Ahmed M. T. , Pogantsch A. , Iskra K.F. , Neger T. , Hörhold H.-H. , Tillmann H. , Kranzelbinder G. , Toussaere E. , Jakopic G.
Published: April 2011

Photochemical methods were developed to obtain a variation of the refractive index in aromatic polymer surfaces and a change in the photoluminescence characteristics of phenylene-vinylene-based polymers. Films of aromatic polymers, among them polystyrene (PS), poly(2-vinylnaphthalene) (PVN) and derivatives of poly(-phenylene-vinylene) (PPV) were UV irradiated in the presence of gaseous hydrazine (N2H4). The photoreaction led to a strongreduction of the refractive index of the polymers due to a hydrogenation of the aromatic units. In the case of PPV, we observed reductive photobleaching. This new technique was employed to produce photogenerated patterns in PPV. The results are compared to oxidative bleaching.
3D Periodic Arrays of Nanoparticles Inside Mesoporous Silica Films
Authors: Besson Sophie , Gacoin Thierry , Jacquiod Catherine , Ricolleau Christian , Boilot Jean-Pierre
Published: April 2011

CdS nanoparticles were grown inside a 3D hexagonal porous silica film. The film pore size and organization allowed the perfect control of particle repartition and size (3.5 nm), leading to a 3D nanocrystal array inside the silica matrix. The method was extended to another silica porous structure with larger pores, which allowed to obtain larger particles (5.8 nm). This process was then successfully generalized to other metal sulfides.
Flexible Plastic Liquid Crystal Displays
Authors: West John L. , Novotny Greg R. , Fisch Michael R. , Heineman David
Published: April 2011

Flexible plastic liquid crystal displays (LCDs) offer a number of advantages over traditional glass displays. Roll-to-roll manufacturing of such displays makes possible large size, inexpensive displays. While this type of manufacturing is still in the future, here we report solutions of some of the pressing problems needed to achieve this goal. We utilize liquid crystal effects that do not require polarizers and can therefore utilize commercially available, birefringent substrates such as polyesters and polyethylene terephthalate. We achieve excellent optical and mechanical performance of these flexible displays, even when bent, by creating polymer networks and polymer walls that adhere the front and back substrates and maintain uniform spacing between the substrates. Roll-to-roll processing of flexible plastic displays also requires that the photolithographic techniques used to pattern the electrodes on the current glass LCD’s be replaced by printing techniques and the development of techniques to rapidly etch unwanted electrode material. We must also develop and optimize techniques for rapidly forming polymer walls. Here we report methods of patterning ITO electrodes on flexible plastic substrates using conventional wax transfer printing techniques and rapid etching and cleaning techniques. We also report experiments that elucidate the basic science of rapidly forming polymer walls. We combine these new achievements and understanding and demonstrate their utility by fabricating a flexible plastic LCD using techniques compatible with roll-to-roll manufacturing. Finally, we discuss the critical issues that must be addressed if flexible plastic LCD’s are to reach their full potential.
Optical Rheology of New Liquid Crystalline Thermosets (LCTs): Influence of Shear on Disclination Texture
Authors: Qin Haihu , Mather Patrick T.
Published: April 2011

Liquid crystalline thermosets (LCTs) have been under intensive study because of their outstanding mechanical performance and low viscosity during processing. We have successfully synthesized four kinds of nematic bismaleimide thermosets that differ in the nature of a pendant group substitution and that feature a thermally stable nematic phase. Importantly, the pendant groups were found to be efficient in depressing the melting point to a level that allows for flow and cure at reasonably low temperatures. By blending two particular monomers with monofunctional maleimide that we synthesized, N-(4-hydroxyphenyl) maleimide (HPMI), the melting point is depressed and the curing process is postponed to higher temperatures. Such a blend has a processing window amenable to much-needed thermal and rheological characterization, particularly the evolution of disclination density during shear flow as cure progresses. Our previous work on disclination density measurements during shear flow has revealed particular scaling of dimensionless disclination density with dimensionless shear rate. The influence of shearing on the disclination density, flow patterns, and molecular orientation though gelation of thermosetting liquid crystals remains unexplored. In this presentation, we will follow a description of material synthesis with a report on the results of optical rheology experiments applied to the ternary blends containing HPMI and two bismaleimide monomers, detailing the influence of shear on disclination density though gelation.
Permeability of A Liquid Crystalline Epoxy
Authors: Feng Jianxun , Douglas Elliot P.
Published: April 2011

This paper presents a comparison of moisture permeation in liquid crystalline and conventional epoxy systems. The permeability is obtained using a dynamic method. It is found that both epoxy systems exhibit Fickian behavior. The liquid crystalline epoxy network exhibits higher barrier properties for moisture transport than the conventional epoxy network. The efficient chain packing within the smectic mesophase of the liquid crystalline thermoset (LCT) is suggested as the main factor for this difference. The stoichiometry has a large effect on the moisture permeation. The diffusion coefficient decreases monotonically with increasing amine/epoxide functional ratio. The permeability (P) and solubility coefficient (S) reach a minimum at a functional ratio of one. The mechanism of the permeation is described in terms of the two-phase morphology present and hydrogen bonding between absorbed water and the network.
Nanocharacterization of Surface and Interface of Different Epoxy Networks
Authors: Gu X. , Raghavan D. , Ho D.L. , Sung L. , VanLandingham M.R. , Nguyen T.
Published: April 2011

The effect of network changes on the surface and interface properties of amine-cured epoxy has been investigated. Samples of different crosslinked epoxies are prepared by mixing stoichiometrically pure diglycidyl ether of bisphenol A (n=0.03) with different ratios of 1,3-bis(aminomethyl)cyclohexane (terafunctional amine) and cyclohexylmethylamine (difunctional amine). All samples are cured in CO2-free air. Both the film surface in contact with air and that in contact with the silicon substrate (the interface) are analyzed using atomic force microscopy (AFM) and nanoindentation. Small angle neutron scattering (SANS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurements, are used to assist in the interpretation of AFM results. Substantial morphological and mechanical differences are observed between the surface and the interface for different crosslinked epoxies. The findings have strong implications on the wettablity, adhesion, and durability of amine-cured epoxies.
A Broad Perspective on the Dynamics of Highly Confined Polymer Films
Authors: Soles Christopher L. , Douglas Jack F. , Wu Wen-Li , Peng Huagen , Gidley David W.
Published: April 2011

The manner in which the dynamics of a polymer are affected by thin film confinement is of technological significance, impacting thin film applications such as lubricants, adhesives, and chemically amplified photoresists. In this manuscript we use specular X-ray reflectivity (SXR), beam positron annihilation lifetime spectroscopy (PALS), and incoherent neutron scattering (INS) to study the influence of thin film confinement on the apparent glass transition temperature Tg and the thermal expansion coefficients of thin polycarbonate (PC) films. Both the SXR and PALS indicate a significant suppression of Tg when the film thickness becomes less than 200 Å. However, the INS measurements suggest an increase in the apparent Tg below this same length scale. These disparate estimates of the thin film Tg seem to indicate that each technique is sensitive to slightly different aspects of the glass formation process. However, all three agree that thin film confinement results in reduced thermal motion, regardless of the precise temperature that is ‘designated' as the thin film Tg.
Analysis of Radiation Damage in Lysozyme Crystals with High Resolution Triple Axis X-Ray Diffraction
Authors: Matyi Richard J. , Volz Heather M.
Published: April 2011

High resolution triple axis X-ray diffraction has been used to monitor the effects of X-ray radiation damage in hen egg white lysozyme crystals. At long irradiation the expected decrease in peak intensity and increase in the angular extent of the peak breadth was seen. In contrast, both the intesi-ties and peak breadths exhibited more complex behavior during the initial stages of irradiation. Possible reasons for these observations are discussed.
Deformation Mechanisms in Natural Polymer Fibers and Composites
Authors: Young Robert J. , Eichhorn Stephen J. , Sirichaisit J. , Brookes Victoria L.
Published: April 2011

The molecular deformation of both silkworm (Bombyx mori) and spider dragline (Nephila edulis) silks has been studied using a combination of mechanical testing and Raman spectroscopy. It was found that both materials have well-defined Raman spectra and that some of the bands in the spectra shift to lower wavenumber under the action of tensile stress or strain. The band shift was linearly dependent upon stress for both types of silk fiber for the 1085/1095 cm-1 band. This observation provides a unique insight into the effect of tensile deformation upon molecular structure and the relationship between structure and mechanical properties. The measurement of micromechanical deformation within samples of wood, flax and hemp fibers using Raman spectroscopy is also reported. Upon tensile deformation of the samples it was found that the characteristic Raman peak for cellulose, located at 1095 cm-1, shifted towards a lower wavenumber, indicating that the polymer chains within the cellulose were also being deformed. The magnitude of the shift with strain was found to be similar for all samples. No shift occurred of the peak that is characteristic of the non-load-bearing lignin (1600 cm-1) in the wood samples due to its amorphous structure. The similarities between the Raman band shifts in silk and cellulose are discussed.
Near-Field Scanning Optical Images of Bacteria
Authors: Paula Ana M. de , Toledo Juliana A. , Silva Haroldo B. , Weber Gerald
Published: April 2011

Near field scanning optical microscopy (NSOM) and spectroscopy techniques were used to study the shape and the cell membrane details in bacteria. We present transmission and topo-graphic images for the bacteriaPseudomonas aeruginosausing the Aurora NSOM from ThermoMicroscopes. TheP. aeruginosahas been widely studied due to its clinical importance in many infectious diseases. The samples were stained by the Gram method and we measured the absorption of laser light at 488 nm by the dye (Safranin) fixed at the bacteria membrane. To obtain good images we had to improve the sample preparation in order to obtain isolated bacteria at the microscope slab. This was achieved using individual colonies, from a dry growth procedure, diluted in physiologic solution. Comparison of the topographic and transmission images give information on the shape and details of the absorption of the laser light by the cell membrane. The results show patterns that depend on the thickness and shape of the membrane, thus revealing details of the cell membrane with nanometer resolution. These results could be an important tool for instance in studies of the effects of antibiotics on the cell membrane.
Controlling Material Properties of Ionically Cross-Linked Alginate Hydrogels by Varying Molecular Weight Distribution
Authors: Kong Hyun-Joon , Mooney David J.
Published: April 2011

The mechanical properties of alginate hydrogels are critical to their successful use in tissue engineering. We hypothesized that combining alginates of differing molecular weights would allow one to readily control and decouple the viscosity of the pre-gel solution from the post-gel stiffness. To test this, binary hydrogels were prepared by incorporating low molecular weight (MW) alginate (Mn ~ 3.3 x 104 g/mol) into 1 %(w/w) alginate solutions composed of high MW alginate (Mn ~ 2.2 x 105 g/mol). The addition of low MW alginate had minimal effects on the solution viscosity, allowing high solids loading in the solution while maintaining a workable solution. However, the increased mass loading resulted in much higher stiffness gels following ionic cross-linking with calcium. These data may be interpreted in relation to the microstructure of the solution versus hydrogel.