bluuebunny/crossref_metadata_2025 huggingface dataset:
Spontaneous Imbibition of Liquids into Nanopores
Authors: Huber Patrick , Knorr Klaus , Kityk Andriy V.
Published: April 2011

We present measurements on the spontaneous imbibition of water, a linear hydrocarbon (n-C16H34) and a liquid crystal (8OCB) into the pore space of monolithic, nanoporous Vycor glass (mean pore radius 5nm). Measurements of the mass uptake as a function of time, m(t), are in good agreement with the Lucas-Washburn - prediction typical of imbibition of liquids into porous hosts. The relative capillary rise velocities scale as expected from the bulk fluid parameters.
In situ SAXS/WAXS of Zeolite Microwave Hydrothermal Synthesis
Authors: Tompsett Geoff A. , Panzarella Bernard , Conner W. Curt , Jones Keith W
Published: April 2011

The microwave hydrothermal synthesis of silicalite zeolite was monitored in situ using small and wide angle X-ray scattering (SAXS and WAXS). A custom-built waveguide reactor provided the microwave heating at 2.45 GHz frequency. Microwave power up to 300 W was supplied by a SAIREM generator via a coax connection. A sample port in the waveguide section allowed a thin-walled glass sample vessel to be held in the microwave field. The sample vial was sealed with a fiber optic temperature probe used for monitoring the temperature. Silicalite zeolite precursor solutions were heated temperatures between 100 and 130°C for up to 120 minutes. The SAXS or WAXS patterns were simultaneously scanned during the reaction under microwaves via X-ray beam through slots in the side of the waveguide. The progress of silicalite zeolite formation was followed and the analysis of SAXS patterns showed the primary particles of 2 nm shifted to aggregates of 5.8 nm in diameter, in 120 minutes at 130°C.
pH Effect on the Optical Properties of Peroxo-Titanium Complex
Authors: Cai Ruxiong , Itoh Kiminori , Sun Changqing
Published: April 2011

Interesting optical properties of peroxo-titanium hydrogen peroxide complex against pH changes were studied for the first time using an analytical UV-VIS spectrophotometer. A freshly prepared peroxo titanium complex with pH value of 2.21 exhibited an orange color. This color changed to light orange, cloudy yellow, and then translucent pale-yellow as its pH value increased to 3.9, 5.8 and 6.7 or above. UV-VIS spectra show that the fresh complex had an absorption band rising at wavelength around 400 nm to higher energy, but had no maximum peak. A new absorption peak appears at 245nm for the cloudy yellow samples. This is similar to that of colloidal TiO2, which suggests that TiO2 particles might form upon increasing pH value to or above 5.80. The formation of TiO2 particles was accelerated in the pH value range from 6 to 9, but not in the acidic environment. In H2SO4 acidified environment, the color turned red-orange instead, and a strong absorption at 397nm was observed only at pH =0.99. Based on the experimental observations, a model for the color-forming species and possible applications by using the techniques generated from the present study were proposed.
Alkanethiol Mediated Release of Surface Bound Nanoparticles Fabricated by Nanosphere Lithography
Authors: Zhao Jing , Haes Amanda J , Zhang Xiaoyu , Zou Shengli , Hicks Erin M , Schatz George C , Van Duyne Richard P
Published: April 2011

This work presents an innovative approach to produce monodisperse solution-phase triangular silver nanoparticles with well-controlled geometry. Ag nanotriangles are fabricated by nanosphere lithography (NSL), functionalized with alkanethiol molecules and then released from the substrate into solution. The resulting single isolated nanoparticles are subsequently asymmetrically functionalized with alkanedithiol molecules to form dimer pairs. The optical properties of the Ag nanoparticles have been measured using UV-Vis spectroscopy while their structural properties have been characterized using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Theoretical calculations based on Mie theory and the Discrete Dipole Approximation (DDA) method have been done to interpret the optical properties of the released Ag nanoparticles.
Dominant Factor of Squareness in P-E Hsyteresis Loops of MOCVD-PZT Films
Authors: Funakubo Hiroshi , Sumi Akihiro , Morioka Hitoshi , Okamoto Shoji , Yokoyama Shintaro
Published: April 2011

The effects of P-E properties of epitaxially grown rhombohedral Pb(Zr,Ti)O3 film on the film thickness and temperature were systematically investigated. (100)-oriented rhombohedral Pb(Zr0.65Ti0.35)O3 films with 50 - 3200 nm in thickness were grown on (100)cSrRuO3//(100)SrTiO3 substrates by metalorganic chemical vapor deposition (MOCVD). The ratio of the remanent polarization (Pr) to saturation polarization (Psat), the Pr/Psat ratio, at room temperature decreased with decreasing the film thickness. Moreover, the Pr/Psat ratio at 10 K of 180-nm-thick films was smaller than that of 3200-nm-thick film and dropped at lower temperature with increasing the film thickness. These results suggest that the small Pr/Psat ratio of thin film at room temperature is originated to both of small Pr/Psat ratio even at 10K and their drop starting at lower temperature when the temperature increased.
Evaluation of Pb Precursors for Liquid Injection Atomic Layer Deposition of Pb(ZrxTi1-x)O3 Thin Films
Authors: Watanabe Takayuki , Hoffmann-Eifert Susanne , Hwang Cheol Seong , Waser Rainer
Published: April 2011

Pb(DPM)2 and Pb(TMOD)2 dissolved in ethylcyclohexane were evaluated as precursors for future atomic layer deposition (ALD) of Pb(Zr,Ti)O3 films. PbO films were deposited by a liquid injection atomic layer deposition on Pt-covered Si substrates at different deposition temperature and precursor volume per cycle. Pb(DPM)2 and Pb(TMOD)2 started thermal decomposition at deposition temperature of around 270°C and 320°C, respectively. Against increasing Pb(DPM)2 injection at 240°C, the deposition rate of PbO films saturated at around 1 Å/cycle, but kept increasing at 300°C, which is above the thermal decomposition temperature. The deposition rate of PbO films at 240°C dropped to a constant value with enough purge time after precursor injection and reactant supply. A saturated deposition rate of PbO films was also observed for Pb(TMOD)2 below the thermal decomposition temperature. However, the saturation behavior observed for Pb(TMOD)2 was slower and the saturated growth rate was higher comparing to Pb(DPM)2. In addition, the film thickness of the PbO films had an apparent gradient over the substrates. These results indicate that Pb(DPM)2 shows more reactive and stable chemisorption comparing to Pb(TMOD)2 for the self-limiting growth rate.
New method of ferroelectric thin film characterization using a polarization instability invoked by a voltage cycling
Authors: Yamada Yuki , Shuto Susumu , Kunishima Iwao
Published: April 2011

The polarization change invoked by bipolar pulse cycling stress (voltage cycling) was investigated in detail for a Pt/PZT/Pt ferroelectric capacitor. The remnant polarization increased after voltage cycling, then, it decreased during storage and approached to the initial value. The estimated activation energy of the decay of the gained-polarization during the storage was 0.52eV. This value suggests that the valence change between Ti3+ and Ti4+ is the key of this phenomenon. The model where Ti-related defects pin the polarization was introduced to explain the result. Based on the findings and the model, a combination of voltage cycling and storage is useful to characterize internal defects. We propose this characterization method, named voltage cycling method, as an effective way to analyze internal defects in a ferroelectric capacitor.
Fabrication of Transparent Ferroelectric-Gate Thin Film Transistors with Nonvolatile Memory Operation
Authors: Tokumitsu Eisuke , Senoo Masaru , Shin Etsu
Published: April 2011

We demonstrate transparent thin film transistors (TFTs) with nonvolatile memory operation using Bi4-xLaxTi3O12 (BLT) as a gate insulator and indium tin oxide (ITO) as a channel. ITO is also used for the gate, source and drain electrodes. Drain current-drain voltage (ID-VD) characteristics of transparent ITO/BLT ferroelectric-gate TFTs exhibit excellent n-channel transistor operations. On current of 0.35 mA was obtained when the applied gate voltage is 6V. On the other hand, the off current of the device is as low as 10-10A, which indicates that the ITO channel is sufficiently depleted by the ferroelectric polarization. In addition, drain current-gate voltage (ID-VG) characteristics demonstrate clear counterclockwise hysteresis loop due to the ferroelectric gate insulator. Optical transmittance of the fabricated device is greater than 60% including the quartz substrate.
Local ferroelectric switching properties in BiFeO3microstructures and their piezomagnetic response
Authors: Harnagea Catalin , Cojocaru Cristian Victor , Pignolet Alain
Published: April 2011

We report here the successful fabrication of BiFeO3(BFO) isolated micron-sized structures by pulsed laser deposition. The islands have a relatively constant aspect ratio (height/lateral size) of 0.1-0.3. We present their local ferroelectric characterization, using piezoresponse force microscopy (PFM), showing that the micron-sized BFO islands exhibit a strong piezoresponse and have ferroelectric domains with lateral sizes down to the 100 nm range. We also present here the first results ofMagnetostriction Force Microscopyexperiments performed on these structures. On ferromagnetic samples this method reveals a piezomagnetic or magnetostriction contrast, associated with magnetic domains. In our case, we show that the contrast can be associated to the magnetoelectric effect.
Characterization of Semi-insulating SiC
Authors: Son Nguyen Tien , Carlsson Patrick , Magnusson Björn , Janzén Erik
Published: April 2011

Electron paramagnetic resonance was used to study defects in high-purity semi-insulating (HPSI) substrates grown by high-temperature chemical vapor deposition and physical vapor transport. Deep level defects associated to different thermal activation energies of the resistivity ranging from ~0.6 eV to ~1.6 eV in HPSI substrates are identified and their roles in carrier compensation processes are discussed. Based on the results obtained in HPSI materials, we discuss the carrier compensation processes in vanadium-doped SI SiC substrates and different activation energies in the material.
Time-Dependent Bias Stress-Induced Instability of SiC MOS Devices
Authors: Lelis Aivars , Habersat Daniel , Olaniran Fatimat , Simons Brian , McGarrity James , McLean F. Barry , Goldsman Neil
Published: April 2011

We have observed a gate-bias stress induced instability in both the threshold voltage of SiC MOSFETs and the flatband voltage of SiC MOS capacitors. The magnitude of this bias stress-induced instability generally increases linearly with log time, with no saturation of the effect observed, even out to 100,000 seconds. The magnitude also increases with increasing gate field. A positive gate-bias stress causes a positive shift and a negative gate-bias stress causes a negative shift, consistent with electron tunneling into or out of oxide traps near the SiC / SiO2 interface as opposed to mobile ions drifting across the gate oxide. The effect is repeatable.
Kinetics of the Nucleation and Growth of Helium Bubbles in bcc Iron
Authors: Deo Chaitanya Suresh , Srivilliputhur Srinivasan G. , Baskes Michael , Maloy Stuart , James Michael , Okuniewski Maria , Stubbins James
Published: April 2011

Microstructural defects are introduced in materials upon irradiation with energetic particles. These defects can cause degradation of mechanical properties and contribute to material failure. Transmuted helium in irradiated stainless steels exerts deleterious effects on material properties. We have performed kinetic Monte Carlo (kMC) simulations of point defect diffusion and clustering in bcc alpha iron. The model includes helium and vacancy diffusion and spontaneous clustering and dissociation of the point defects from the clusters. We employ the kMC simulations to investigate the time evolution of the point defect configuration leading to defect clustering and bubble formation. The concentration of embryonic point defect clusters is determined as a function of the simulation time.
Effect of Pressure on Electronic Structure of Pb1−xSnxTe Alloys Doped with Gallium
Authors: Skipetrov Evgeny Pavlovich , Golubev Alexander , Dmitriev Nikolay , Slyn'ko Vasily
Published: April 2011

The galvanomagnetic effects in the n-Pb1−xSnxTe:Ga (x=0.09-0.21) alloys at the temperatures 4.2≤T≤300 K and under hydrostatic compression up to 16 kbar have been investigated. It is shown that in all samples and in the whole investigated pressure range temperature dependencies of resistivity and Hall coefficient have a “metallic” character, indicating stabilization of Fermi level by the impurity resonant level. Using the experimental data in the frame of two-band dispersion law the dependencies of the free electron concentration and the Fermi level position upon temperature, matrix composition and pressure were calculated. The temperature, composition and pressure coefficients of gallium resonant level movement were obtained and the electronic structure under varying the alloy composition and under pressure were built.
Developing Biosensors for Monitoring Orthopedic Tissue Growth
Authors: Sirivisoot Sirinrath , Yao Chang , Xiao Xingcheng , Sheldon Brian W. , Webster Thomas J.
Published: April 2011

The objective of this in vitro present study was to create a biosensor which can monitor in situ orthopedic tissue growth juxtaposed to a newly implanted orthopedic material. This biosensor has unique properties including the ability to sense, detect, and control bone regrowth. Such a biosensor is useful not only in regenerating tissue necessary for orthopedic implant success, but also to aid in informing an orthopedic surgeon whether sufficient new bone growth occurred. If the sensor determines that insufficient new bone growth occurred, the sensor can also act in an intelligent manner to release bone growth factors to increase bone formation. The primary biomaterial in this biosensor is anodized Ti, developed by chemical etching and passivation treatments. Carbon nanotubes (CNTs), because of their electrical and mechanical properties, are essential to consider when designing such biosensors since they will be used to apply and measure conductivity changes as new bone grows next to the implant. For this, parallel multiwall CNTs were grown from the pores of the anodized Ti by a chemical vapor deposition process. Lastly, these sensors will be composed of a conductive, biodegradable, polymer layer that degrades when bone grows and, consequently, undergoes a change in conductivity that can be measured by the CNTs grown out of the anodized Ti. This conductive, biodegradable polymer consists of polypyrrole (which is conductive) and poly-lactic-co-glycolic acid (which is biodegradable). Preliminaryin vitroresults suggest that osteoblast functions (specifically alkaline phosphatase activity and calcium deposition) on CNTs grown on anodized Ti are significantly enhanced when compared to anodized Ti and currently-used Ti; thus, it is anticipated that bone growth could be enhanced on these novel biomaterial sensors.
Theoretical Study of Si-Rich Transition-Metal Silicides with Double-Graphene-Like Structures
Authors: Miyazaki Takehide , Kanayama Toshihiko
Published: April 2011

We propose a novel form of graphene-like Si nanostructure based on ab initio total-energy calculation and geometry optimization, (MSi12)n, with M being transition metal atom. It has a three-layer structure, where the two layers of Si atoms in graphene-like positions sandwich another layer of transition metal atoms. The electronic structure may become semiconducting or metallic, depending on the choice of M and arrangement of Si atoms. This hypothetical material can be regarded as a Si-rich phase of transition metal silicide. A potential impact of our finding in forthcoming ultra-scaled Si technology is also discussed.
Nanoscale Transistors: Physics and Materials
Authors: Lundstrom Mark S. , Cantley Kurtis D. , Pal Himadri S.
Published: April 2011

We analyze a modern-day 65nm MOSFET technology to determine its electrical characteristics and intrinsic ballistic efficiency. Using that information, we then predict the performance of similar devices comprised of different materials, such as high-k gate dielectrics and III-V channel materials. The effects of series resistance are considered. Comparisons are made between the performance of these hypothetical devices and future generations of devices from the ITRS roadmap, including double-gate MOSFETs. We conclude that a Si channel device with a high-k gate dielectric and metal gate will outperform III-V channel materials for conventional CMOS applications, but will still not suffice in achieving long-term ITRS goals.
Nucleation Process During Excimer Laser Annealing of Amorphous Silicon Thin Films on Glass: A Molecular-dynamics Study
Authors: Munetoh Shinji , Mitani Takanori , Kuranaga Takahide , Motooka Teruaki
Published: April 2011

We have performed molecular-dynamics simulations of heating, melting and recrystallization processes in amorphous silicon (a-Si) thin films deposited on glass during excimer laser annealing. By partially heating the a-Si surface region with 2 nm depth and removing thermal energy from the bottom of the glass substrate, a steady-state temperature profile was obtained in the a-Si layer with the thickness of 15 nm and only the surface region was melted. It was found that nucleation predominantly occurred in the a-Si region as judged by the coordination numbers and diffusion constants of atoms in the region. The results suggest that nucleation occurs in unmelted residual a-Si region during the laser irradiation and then crystal growth proceeds toward liquid Si region under the near-complete melting condition.
Band-Gap Modulation and Kohn Anomalies in Two-Dimensional Graphite and Single-Wall Carbon Nanotubes
Authors: Samsonidze Georgii , Barros Eduardo B. , Son Hyungbin , Saito Riichiro , Dresselhaus Gene , Dresselhaus Mildred S.
Published: April 2011

The electron-phonon coupling in two-dimensional graphite (graphene sheet) and metallic single-wall carbon nanotubes (SWNTs) is analyzed. In the graphene sheet the G-band phonon mode induces oscillations of the Fermi points, while the G′-band phonon mode opens a dynamical (oscillating with the phonon frequency) band gap, and accordingly, both phonon modes exhibit Kohn anomalies. Similarly, truly metallic armchair SWNTs undergo Peierls transitions driven by the G−- and G′-band phonon modes both of which open a dynamical band gap. In addition, the dynamical band gap induces a non-linear dependence of the phonon frequencies on the doping level and gives rise to strong anharmonic effects in the graphene sheet and metallic SWNTs.
FET Properties of Surface Silylated Single Wall Carbon Nanotubes
Authors: Kumashiro Ryotaro , Hiroshiba Nobuya , Ohashi Hirotaka , Akasaka Takeshi , Maeda Yutaka , Suzuki Shinzo , Achiba Yohji , Hatakeyama Rikizo , Tanigaki Katsumi
Published: April 2011

Single wall carbon nanotubes (SWNTs) having semiconducting properties are promising as electronic materials for nano-scale devices in the future, and the electrical properties of SWNTs are of significantly fundamental and practical interests. It is well known that the field effect transistors (FETs) fabricated using semiconducting SWNTs show high performance in terms of the mobility. However, carriers in pristine SWNTs are mostly holes and, therefore, SWNTs -FETs usually show p-type properties. As for SWNTs, chemical carrier doping has been reported so far for controlling carrier concentration like graphite intercalations. Two major techniques in SWNTs are generally possible; one is endohedral doping and the other is the exohedral chemical modifications. It has been exemplified that doping with alkali metals can introduce electron carriers into SWNTs. Furthermore, the electrical transport properties of SWNTs were reported to be controlled by the endohedral insertion of organic molecules inside the SWNTs. A similar carrier doping could exohedrally be possible when the SWNTs surface is chemically modified. With such chemical modifications, the charge transfer from the substituent groups to SWNTs will be expected and this could modify the electronic states of SWNTs. We reported the FET properties of individual SWNTs exohedrally modified by Si-containing organic moieties, and demonstrated that p-type nanotubes can be converted to n-type ones. However, because of ununiformity of the surface-chemical modifications of SWNTs, the true effects of the exohedral modifications on FET properties were extremely difficult to be evaluated. In this meeting, we will present comparison of the FET properties of the exohedrally silylated SWNTs between separated individual and spread-sheet samples. For evaluating the FET properties, the chemically modified SWNTs have been dispersed on a FET substrate, and the measurements have been carried out at ambient temperature using a conventional method for a separated SWNTs and a spread-sheet SWNTs film. As a reference, the experiments were also made in the same manner on chemically non-modified CNTs. From the experimental results, it will be demonstrated that an n-type property can be enhanced by the exohedral modifications both in the case of the spread-sheet samples and in the case of the individual ones. We will discuss the effects of surface silylation on the electronic states of these SWNTs.
Dependence of the Raman Spectrum of Silicon Nanowires on the Wire Environment
Authors: Scheel Harald M. , Reich S. , Thomsen C.
Published: April 2011

The large surface to volume ratio in nanometer sized wire structures cause a strong dependence of the optical Raman mode on the thermal conductivity of a surrounding medium. On the basis of optical measurements on silicon nanowires as a function of excitation laser power we explain the very large red-shifted Raman spectra observed already for moderate laser powers. This thermal effect is enhanced by a silicon oxide sheath, rendering a reduced thermal contact of the wires to the substrate. The intrinsic redshift due to spatial confinement in silicon nanowires is found to be smaller than 2 cm−1.
Elastic Properties of Normal and Binormal Helical Nanowires
Authors: da Fonseca Alexandre Fontes , Malta C P , Galvão Douglas S
Published: April 2011

A helical nanowire can be defined as being a nanoscopic rod whose axis follows a helical curve in space. In the case of a nanowire with asymmetric cross section, the helical nanostructure can be classified as normal or binormal helix, according to the orientation of the cross section with respect to the helical axis of the structure. In this work, we present a simple model to study the elastic properties of a helical nanowire with asymmetric cross section. We use the framework of the Kirchhoff rod model to obtain an expression relating the Hooke's constant, h, of normal and binormal nanohelices to their geometric features. We also obtain the Young's modulus values. These relations can be used by experimentalists to evaluate the elastic properties of helical nanostructures. We showed that the Hooke's constant of a normal nanohelix is higher than that of a binormal one. We illustrate our results using experimentally obtained nanohelices reported in the literature.
Fabrication and Characterization of Nickel Nanowire Polymer Composites
Authors: Denver Heather , Hong Jeongmin , Borca-Tasciuc Diana-Andra
Published: April 2011

Magnetic polymers are multi-functional composites emerging as a new category of smart materials. This work focuses on fabrication and characterization of magnetic polymer nanocomposites based on polydimethylsiloxane (PDMS) elastomer matrix. The magnetic fillers are commercially available Ni nanoparticles and respectively in-house fabricated Ni nanowires. Synthesis of Ni nanowires is achieved by electroless deposition inside nanoporous anodic alumina templates. After template removal, the nanowires are coated with 1-Octodecanethiol surfactant and mixed with PDMS using a FlackTek SpeedMixer™. In parallel, nanoparticles are mixed with PDMS, without undergoing surfactant coating. Both composites are evaluated by scanning electron microscope (SEM) to determine dispersion uniformity. Mechanical properties are resolved by tensile tests performed by an instron. Preliminary results suggest that surfactant addition enhances dispersion, while mechanical properties of the composites for up to 5 vol. % of added nickel remain close to that of the polymer matrix without filler.
The Molecular Structures and Properties of Novel Eu(III) Complexes with Asymmetric Bis-phosphine Oxides
Authors: Iwanaga Hiroki , Aiga Fumihiko , Amano Akio
Published: April 2011

Several novel Eu(III) complexes with asymmetric bis-phosphine oxide- ligands were synthesized. The relation between molecular structures of bis-phosphine- oxide ligands and properties of Eu(III) complexes was investigated and some interesting results were obtained. Solubility of Eu(III) complexes in fluorinated medium and silicone oil were strongly dependent on the length of alkyl chain (n) binding two phosphine oxide- parts. Also, the thermal properties of Eu(III) complexes were correlated to the solubility. Eu(III) complex 6(n=3), which has phenyl and n-octyl groups as the substituents of a bis-phosphine oxide- ligand, was found to be highly soluble and have large fluorescence intensity.
Single Molecule Studies of a 2,7-Bis-(Phenylethenyl)fluorenone: Implications for Green-Emission Bands in Fluorene-Based OLEDs
Authors: Odoi Michael Y , Hammer Nathan I , Rathnayake Hemali , Lahti Paul M , Barnes Michael D
Published: April 2011

The color purity of blue polyfluorene fluorescence emission is often adversely contaminated by green emission bands. The origin of this green emission has been attributed to various factors including on-chain oxidation of fluorene leading to monomeric fluorenone emission and inter/intra-chain interaction between segments of fluorenone units leading to excimer formation on the polyfluorene backbone. We report here emission properties at the bulk and single molecule level of a molecular fluorene derivative and compare them to those of its oxidative fluorenone derivative. Whereas the bulk fluorescence emission of 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethyl-9H-fluorene (OFPV) exhibits a blue to blue-green emission at about 480 nm, 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethyl-9H-fluorenone (OFOPV) shows red luminescence with a peak centered at about 630 nm. However, the peak position for OFOPV shifts to higher energies (∼540 nm) upon dilution or dispersion in polymer matrices like PMMA or Zeonex. Single molecule measurements of OFOPV show fluorescence spectra dominated by peaks around 540 nm, with a small minority at longer wavelengths that are attributed to emission from dimers or higher aggregates. This distribution indicates that monomeric emission of OFOPV is green, consistent with green emission bands seen in polyfluorenes.
Photoluminescence and Electroluminescence in Combination of Rare-Earth Metal Complexes and Phosphorescent Molecules
Authors: Kin Zenken , Hino Yuichi , Kajii Hirotake , Hasegawa Yasuchika , Kawai Tsuyoshi , Ohmori Yutaka
Published: April 2011

We investigated luminescent properties of rare-earth metal complexes and phosphor-rescent molecules doped in a conducting polymer. Electroluminescent (EL) properties in combination of red emissive europium complex of tris(di-benzoylmethane)-mono(4,7-diphenyl-phenanthroline) europium (III) (Eu(dbm)3phen) and blue phosphorescent molecule of bis[(4,6-difluoro-phenyl)-pyridinato-N,C2'] (picolinate) iridium (III) (FIrpic) doped in poly(N-vinyl-carbazole) (PVK) and a new rare-earth complex tris(hexafluoroacethylacetonato) (phenan-throline) samarium(III) [Sm(hfa)3(phen)2] have been investigated as an EL emitter. White EL has been obtained from mixed layer of Eu(dbm)3phen and FIrpic, and EL from Sm complex has been obtained. Energy transfer and the emission mechanisms have been discussed.
Improvement of Short Channel Mobility and Operational Stability of Pentacene Bottom-Contact Transistors with a Sulfuric Acid and Hydrogen Peroxide Mixture (SPM) Treatment of Au Electrodes
Authors: Kawakami Haruo , Maeda Takahiko , Kato Hisato
Published: April 2011

We report a reduction in the contact resistance between pentacene and Au source/drain electrodes of organic field effect transistors (OFETs) with bottom-contact structure. By immersing the Au electrodes in a sulfuric acid and hydrogen peroxide mixture (SPM), the injection barrier between the Au electrodes and pentacene was lowered by approximately 0.2 eV and the contact resistance significantly decreased. The fabricated bottom-contact OFETs revealed a field-effect mobility of more than 0.66 cm2/Vs at a channel length ranging from 3 to 30 μm, which is comparable to that of top-contact OFETs with a 50 μm channel length. The transfer characteristics of the OFET with the SPM treatment were stable even after 44days storage in air under room illumination without any passivation. Moreover, the drain current reduction due to threshold voltage (Vth) shift under continuous application of gate voltage quickly recovered toward the original value with unloading of gate voltage.
Structure and Morphology of Tetracene Thin Films on Hydrogen-Terminated Si(001)
Authors: Qin X. R. , Tersigni A. , Shi J. , Jiang D. T.
Published: April 2011

Scanning tunneling microscopy (STM), atomic force microscopy (AFM) and near-edge x-ray absorption fine structure (NEXAFS) have been used to study the structure of tetracene films on hydrogen-passivated Si(001). A distinct growth morphology change that occurs around a few monolayers of film thickness was characterized. This coverage-dependent film structural phase transition leads to a molecularly ordered film structure commensurate with the crystalline substrate.
Effects of Environment on Modlus of Low-k Porous Films Used in Back End of Line
Authors: Simonyi Eva E , Dimitrakopoulos Christos D , Lane Michael , Liniger Eric , Volksen Willi
Published: April 2011

Reliability is an important requirement for the newly developed porous low-k ILD materials that are being introduced into (BEOL). Dependence of Young's moduli, as measured by nanoindentation technique, on the environment [such as high relative humidity, water immersion and recovery] is presented along with FT-IR spectra for a number of films with different k values. Effect of the moduli changes on cracking behavior is also discussed.
Dielectrophoresis-Based Assembly and High-Frequency Characterization of Carbon Nanotube Bundles
Authors: Woodson Michael , Tselev Alexander , Liu Jie
Published: April 2011

As the size of integrated circuit elements decreases, the properties of carbon nanotubes (CNTs) become increasingly attractive for interconnect applications. To be used by industry, full characterization of the electronic properties of CNT aggregates is essential.

Dielectrophoresis from CNTs suspended in liquid has been demonstrated as a simple route to bundles of aligned parallel nanotubes. We describe a method by which circuits including such bundles may be fabricated, and provide some high-frequency measurements of their electrical properties. The contributions of the contacts can be separated from those of the bundle itself.
Porosity and its Effect on Barrier Performance of Thin Electroless Cobalt Alloy Caps
Authors: Chen Qingyun , Liu Jun , Walker Elizabeth , Hurtubise Richard , Stritch Daniel , Lin Xuan
Published: April 2011

Pinhole densities of electroless cobalt alloy films on copper substrate are characterized using optical and electrochemical methods. The impact of pits or pinholes on deposit film barrier property is discussed. The improved film barrier property is shown by reduction of pits formation through deposition process optimization.
Copper Chemical Vapor Deposition using a Novel Cu(II) Precursor for Contact Via Filling Process
Authors: Zama Hideaki , Nishimura Yuuji , Yago Michiyo , Watanabe Mikio
Published: April 2011

Chemical vapor deposition (CVD) of copper using both a novel Cu(II) β-diketonate source and hydrogen reduction process was studied to fill contact vias with the smallest diameter in the 32nm and more advanced generation chip. Pure Cu films were grown under the condition with the product of hydrogen partial pressure and H2/Cu source molar ratio being over 1,000,000. We succeeded in filling the 40-nm-diameter contact vias by optimizing the growth condition of the Cu-CVD in both substrate temperatures and reaction pressures.
A Trial for Micro-Scale Evaluation of Adhesion Strength around Cu Metallization Systems
Authors: Kamiya Shoji , Arakawa Hitoshi , Shimomura Hiroshi , Omiya Masaki
Published: April 2011

Adhesion strength of the interface between Cu film and SiCN cap layer for IC metallization system was evaluated by a technique developed by the authors. In this technique, microscopic specimens with the in-plane dimension less than 10 μm were fabricated by focused ion beam system and loaded directly by a sharp diamond stylus with submicron tip radius. By comparing the crack extension behavior with the three-dimensional numerical simulation, the interface adhesion energy was evaluated to be 5 J/m2. The same interface was subjected also to the four-point bending experiment, which is widely applied to interface adhesion measurement. The evaluation results by the two techniques agreed reasonably well with each other.
Silicon Nanocluster Formation by a Pulse-type Gas Feeding Technique in the LPCVD System for the Nonvolatile Memory Applications
Authors: Kim Kyoungmin , Kim Eunkyeom , Bae Myeongwook , Son Daeho , Lee Juhyung , Han Moonsup , Sok Junghyun , Park Kyoungwan
Published: April 2011

We developed a pulse-type gas-feeding technique in low pressure chemical vapor deposition system in order to grow Si nanoclusters with high density and uniform size. The maximum density and average size of the Si nanoclusters were 7 × 1011/cm2 and 7 nm, respectively. Floating gate memory devices containing the storage node of the Si nanoclusters were fabricated. The memory window was 4.5 V when the writing and erasing voltages were +14 V and −18 V, respectively. The writing and erasing times were measured to be 1 ms and 200 ms, respectively. The retention time of Si nanocluster nonvolatile memory was estimated about 10 years.
Deposition Of Uniform Size Metallic Nanoparticles For Use In Non Volatile Memories
Authors: Verrelli Emanuele , Tsoukalas Dimitris , Giannakopoulos Konstantinos , Ioannou Dimitris
Published: April 2011

In this work we investigate the non-volatile memory behavior of Ni nanoparticles embedded within an insulating matrix. Nickel nanoparticles are deposited at room temperature by a new high-vacuum technique over a 4 nm tunneling thermal SiO2 layer followed by the deposition of HfO2 as a control insulator. Memory windows of ∼1.5V are observed in MOS capacitors at gate pulse voltages of 8V. Charge retention for write and erase state clearly indicate long time charge storage behavior.
A Comparison of N+ type and P+ type Polysilicon Gate in High Speed Non-Volatile Memories
Authors: Kim Moon Kyung , Chae SooDoo , Kim Chung Woo , Lee Jo-won , Tiwari Sandip
Published: April 2011

The polarity of gates and the threshold voltages are primary parameters that determine the electric fields in the gate stack region of non-volatile memories. This field is central to programming, retention and the other characteristics of the devices. We have investigated the effect of the gate polysilicon polarity, experimentally, for silicon-oxide-nitride-oxide-silicon (SONOS) memory devices on silicon-on-insulator (SOI) wafers. An ultra-thin oxide-nitride-oxide (ONO) film with high trap density and strong localization of the trapping provides the scalability and retention in our structures. The effect of ONO film, grown and deposited and of doping was simulated and characterized. Retention is affected by the electric field between the control gate and the storage node. Our experiments and simulations verify the consequences of different polarity of control gates through the change in electric field that they cause in retention and erase times for n+ and p+ polysilicon gate SONOS memories is verified through the characteristic energies of the processes.
Nonvolatile Resistive Switching Devices Based on Nanoscale Metal/Amorphous Silicon/Crystalline Silicon Junctions
Authors: Jo Sung Hyun , Lu Wei
Published: April 2011

M/a-Si:H/c-Si based nonvolatile resistive switching devices with active areas down to 50 nm×50 nm have been fabricated and explored. Close to 100% device yield was achieved without necessity of high voltage forming process. Both rectifying switching and non-rectifying switching were demonstrated in a controllable fashion. The potential for this structure as nanoscale nonvolatile memory devices was investigated in terms of scalability, retention time, endurance and switching speed. The device showed switching speed faster than 5 ns, endurance cycles more than 106 and retention time longer than 150 days without any degradation of stored data. The devices exhibit improved resistance switching ratio when scaled down.
Reversible Multi-level Resistance Switching of Ag-La0.7Ca0.3MnO3-Pt Heterostructures
Authors: Shang Dashan , Chen Lidong , Wang Qun , Wu Zihua , Zhang Wenqing , Li Xiaomin
Published: April 2011

Resistance random access memory (RRAM) has attracted intense attention in recent years for the potential application as nonvolatile memory. One of the tempting properties of RRAM is the multi-level memory, in which several resistance states can be obtained and each of them can be used to save information. In this paper, the electric-pulse-induced multi-level resistance switching of the Ag-La0.7Ca03MnO3-Pt heterostructures was studied. The multi-level resistance switching (MLRS) was observed in the switching from high to low resistance state (HRS→LRS) by applying electric pulse with various pulse voltages. The threshold pulse voltages of MLRS are related to the initial resistance values as well as the switching directions. On the other hand, the resistance switching behavior from low to high resistance states (LRS→HRS) shows unobvious MLRS. MLRS was explained by the parallel effect of multi-filament forming/rupture in the Ag/La0.7Ca0.3MnO3 interface layer. The present results suggest a possible application of Ag-La0.7Ca03MnO3-Pt heterostructures as multi-level memory devices.
Surface Morphologies and Optical Properties of Homoepitaxial ZnO Grown by Close-Spaced Chemical Vapor Transport
Authors: Abe Koji , Tokuda Tetsuya , Banno Yuta , Eryu Osamu
Published: April 2011

Chemical vapor transport (CVT) using carbon as a transporting agent is studied for homoepitaxial growth on O-polar ZnO substrates. To increase growth rate at high temperatures, we keep a substrate close to ZnO source powder. Surface smoothness and crystal quality of epilayers are remarkably improved by increasing a substrate temperature. Smooth surfaces are observed on the epilayer grown at substrate temperatures above 920°C.
Photocurrent Spectral Distribution and Relaxation in CdS/CdTe Heterojunctions
Authors: Vatavu Sergiu A. , Gasin Petru A. , Ferekides Chris S. , Caraman Iuliana M.
Published: April 2011

Photocurrent spectral distribution and relaxation in CdS/CdTe heterojunctions Sergiu Vatavu, Petru Gasin, Iuliana Caraman. Thin film CdS/CdTe solar cells have proved their importance in use as solar energy converters achieving 16.5 % efficiency. Thin film CdS/CdTe heterojunctions have been deposited by close spaced sublimation method (CSS), onto SnO2 covered glass plates (2õ2 cm2). The thickness of CdS and CdTe thin films was 0.3-1.6 m and 2.3-6.6 m respectively. For to enhance CdS/CdTe heterojunctions photoelectrical parameters and photosensitivity, the deposition procedure was followed by annealing in presence of CdCl2 at 420C for 15-60 min. Ni has been used as back contact to CdTe. After annealing, the photoelectrical parameters at 100 mW/ñm2 are: Uoc=0.73 V, Isc=21.7 mA/cm2, ff=0.43.

The analysis of the photosensitivity for samples with different thicknesses of the component layers in the 78-293K temperature range showed, that the increase of the photoconductivity for photon energies ħw>1.9 eV is determined by the generation-recombination processes in CdSxTe1-x interface layer, and in the 1.42 eV-1.85 eV region, by light absorption mechanism in CdTe.

At direct biases of the CdS/CdTe heterojunctions (2Uoc), the photocurrent spectral distribution is determined by the generation-recombination processes in CdS layer. The annealing of the heterojunction in presence of CdCl2 results in photocurrent increase more than one order of magnitude. CdS/CdTe at reverse biases, having a constant sensitivity in visible and near infrared spectral region, can be used in photometry as radiation detector.

The analysis of the absorption spectra and the photocurrent spectral distribution at direct biases resulted in determination of the holes mean free path in CdTe layer, being equal to 1.05 mm.

The ratio of the ambipolar diffusion coefficient and surface recombination velocity for CdS/CdTe interface is 0.3 m and the diffusion length is 0.6 m at 78K. The same parameters for Ni/CdTe interface are: 0.025 m and 0.05 m respectively.

The phococurrent relaxation curves have been studied for illumination throught both sides of the heterojunctions at different biases, temperatures and wavelength, determining different penetration depths and materials excitation. Nonequilibrium charge carriers lifetime has been determined. The thermal annealing of the CdS/CdTe heterojunctions in presence of CdCl2 determine the nonequilibrium charghe carrier lifetime increase by more than one order of magnitude from 22 s up to 280 s.
Study of Recombination in Cu(In,Ga)Se2 Solar Cells by Time-Resolved Photoluminescence
Authors: Shirakata Sho , Nakada Tokio
Published: April 2011

Time-resolved PL (TR-PL) measurements have been carried out on Cu(In1-x,Gax)Se2 (CIGS) thin films and solar cells to study the recombination of photo-generated minority carriers . Room temperature PL of both CIGS thin films and solar cells exhibited band-to-band transition for alloy composition x of 0-0.4, and PL decay curves have been utilized as a measure of carrier lifetime. The solar cell fabrication leads to the enhancement of band-to-band PL intensity, reduction of defect-related PL, and increase of PL decay time. It is noted that the increase in PL decay time has been observed in CIGS films after CBD-CdS deposition. Solar cells with high conversion efficiency are characterized by both high PL intensity and long PL decay time. The PL decay curve of CIGS solar cell is studied in terms of the alloy composition x. For small x, PL decay times of CIGS solar cells are almost independent of the emission photon energy. For large x, PL decay time depended on PL emission energy. he result suggests the change of the recombination mechanism in the CIGS solar cells with the change in the alloy composition x.
TEM study of Locations of Cu in CdTe Solar Cells
Authors: Yan Yanfa , Jones Kim , Zhou Jie , Wu Xuanzhi , Al-Jassim Mowafak
Published: April 2011

Using scanning transmission electron microscopy and nanoprobe X-ray energy-dispersive spectroscopy, we studied the locations of Cu in CdTe solar cells and test interfaces with intentionally introduced Cu sources. We found three primary locations of Cu: 1) back-contact region, 2) CdTe layer, and 3) CdTe/CdS junction areas. In the back-contact region, Cu diffused from back-contact can convert the Te-rich layer into Cu-Te compounds. In the CdTe layer, a higher concentration of Cu is found to distribute along grain boundaries, but not in twin boundaries and stacking faults. In the CdTe/CdS junction area, Cu is found uniformly in the CdS layer. However, significant segregation of Cu into CdS/TCO interfaces is also found.
Mechanical Properties of Indium Tin Oxide on Polyethylene Napthalate Substrate
Authors: Bhagat Shekhar , Zoo Y. , Han H. , Lewis J. , Grego S. , Lee K. , Iyer S. , Alford T. L.
Published: April 2011

This work investigates the mechanical properties of ITO on PEN substrates as a function of processing conditions, including rf power, substrate temperature, and substrate treatment. The best mechanical performance is obtained from high substrate temperature and low rf power. Plasma treatment gases also influence mechanical properties, with mixture of nitrogen and hydrogen gases producing the best results. This work provides an initial understanding of the impact of sputter process conditions on film's mechanical performance.
CdS/CdTe Solar Cells Made by High-Rate Magnetron Sputtering
Authors: Plotnikov Victor , Compaan Alvin
Published: April 2011

The dependence of deposition rate of CdTe film on deposition pressure and RF power has been studied. The optimum argon pressure was found to be 5 mTorr while the growth rate as a function of power is slightly superlinear. A deposition rate of 140 nm/min has been achieved which is five times faster than for our conventional deposition conditions. Films were characterized by means of X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). Pressure has been found to have a greater effect on film morphology than magnetron sputter power. Working devices have been made with 2-micron layers of CdTe deposited at different powers and 10 mTorr of argon pressure. The effect of different temperatures of CdCl2 post-deposition treatment on cell performance was studied. Efficiency of 11.8% with a 2-micron CdTe layer deposited at 133 nm/min was achieved.
The Phase Boundary Between β-Si3N4 and γ-Si3N4 at Elevated Temperatures and Pressures
Authors: Togo Atsuchi , Kroll Peter
Published: April 2011

The phase boundary between β-Si3N4 and γ-Si3N4 is investigated at high-pressure and high-temperature using first-principles lattice dynamics calculations within the quasi-harmonic approximation. We find a positive slope of the phase boundary. It turns out that the thermal expansion of the spinel-type γ-phase is larger than that of the phenacite-type β-phase. On the other side, pressure affects more the volume of β-Si3N4 than of γ-Si3N4, reflected in the higher bulk modulus of γ-Si3N4. The origin of the different temperature behavior of these phases, consequently, goes along with a larger volume dependence of the zero point energy in γ-Si3N4 in comparison to β-Si3N4.
Photoelectrochemical Etching of GaN Thin Films With Varying Carrier Concentrations
Authors: Leach Jacob H. , Özgür Ümit , Morkoç Hadis
Published: April 2011

The evolution of the surface morphology of unintentionally doped and Si-doped GaN samples subjected to photoelectrochemical (PEC) etching in the carrier-limited regime in aqueous KOH is reported. It was found that a nanoporous structure precedes whisker formation in samples in which high densities of whiskers ultimately form. Increasing the light intensity accelerated the rate of change of the surface morphology, but increasing the molarity of the KOH had no effect on the etching. Applying biases to the samples during etching also accelerated or decelerated the rates of change of the surface morphology. Thus, the surface morphology in the carrier-limited regime tends to only depend on parameters of the starting layers, as well as how much etching in total has occurred. The identification of variations in surface morphology at different times during PEC etching of GaN may have utility in that assorted nanopatterning of the GaN surface can be intentionally achieved in a controllable, large-scale, and inexpensive manner.
Pigment Analysis of Two Thai Banner Paintings
Authors: Giaccai Jennifer
Published: April 2011

The pigments used in two Thai banner paintings (phra bot) were examined using X-ray fluorescence (XRF), Fourier transform infrared microscopy (FTIR) and polarized light microscopy (PLM). The two paintings examined dated from the late 18th and the late 19th century. The paintings examined follow the trends observed on Thai wall paintings and manuscripts from the same time periods. Pigments identified include vermilion, iron oxide earths, red lead, lead white (hydrocerrusite), calcium carbonate, kaolin, Prussian blue, gamboge, artificial ultramarine, copper citrate and a copper-arsenic green.