bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Director Fluctuations in Confined Liquid Crystals
Authors: Basu Sarmistha , Arroyo Edwin , Aliev Fouad
Published: April 2011

Dynamic light scattering was applied to study the influence of randomness, boundary conditions (planar-axial and homeotropic-radial) and layer thickness (at nanoscale) of 5CB and 8CB confined to cylindrical pores and filled with Aerosil particles on relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first process is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation process (with slower relaxation time than the first one) is most likely due to the fluctuations in layers nearest the wall surface. The separation between the first and the second (slow) processes is clearer for thinner layers and the amplitude of the slow process is greater for thinner layers. This suggests that the slow process is surface related relaxation. The mode due to relaxation of fluctuations of director orientation in the vicinity of the surface of Aerosil particles was observed in filled liquid crystals as well.
The Encounter Probability for Random Walkers in a Confined Space
Authors: Lavine James P.
Published: April 2011

Particles diffusing in a confined space should encounter one another with a probability that depends on the size and dimension of the space. The present work uses pairs of random walkers on a lattice to investigate the encounter probability in one, two, and three spatial dimensions. There is an initial rapid decay of the survival-time distribution that is followed by an exponential decay in time. The characteristic time for this latter decay is strongly dependent on the model space size and scales as a power law in the size. The exponent of the power law depends on the number of spatial dimensions. For a fixed L, the exponential tail of the survival-time distribution has a similar slope when the initial separation of the two walkers is varied. The spacing between the exponential decay curves scales with the initial separation in 1-D, but not in 2-D or 3-D. In addition, the mapping of two random walkers to an equivalent single walker is explored.
Site-specific Labeling of Active Proteins with Gold Nanoparticles
Authors: Aubin-Tam Marie-Eve , Hamad-Schifferli Kimberly
Published: April 2011

Covalent conjugation of nanoparticles to proteins is challenging as proteins have numerous residues to which the nanoparticle can non-specifically adsorb. This is problematic as non-specific adsorption is known to denature the protein, altering its structure and thus compromising protein activity. We study site specific gold nanoparticle labeling of two enzymes, Ribonuclease S and Cytochrome c, with the goal of understanding conditions that minimize non-specific adsorption and optimize protein structure and activity. Ribonuclease S is a two-piece protein made of S-peptide and S-protein. 3nm gold nanoparticle is attached to a mutated cysteine residue on the S-peptide. The altered enzymatic activity of gold labeled Ribonuclease S is determined using RNA substrate with a fluorophore-quencher couple. Cytochrome c is linked to 1.5nm nanoparticles with ligands having neutral, negatively, or positively charged endgroups, through covalent attachment of gold with a specific surface cysteine residue. The labeled protein is characterized by circular dichroism spectroscopy and UV-visible absorption. For both proteins, agarose gel electrophoresis was used to determine optimal reaction stoichiometry and also probe non-specific adsorption between the nanoparticle and protein.
The Aspect Ratio Dependence of the Fluorescence of Gold Nanorods: An Experimental and Theoretical Study
Authors: Eustis Susie , El-Sayed Mostafa A.
Published: April 2011

Experimental observations and theoretical treatments are carried out for the band shape and relative intensity of the emission from gold nanorods of various aspect ratios in the range between 2.6 (1.5 theory) and 6.3 (9 theory). The calculation of the fluorescence spectra requires knowledge of the nanorod size distribution, the enhancement factors and the shape of the un-enhanced fluorescence spectrum. The comparison between the observed and calculated fluorescence band shapes is found to be good. The calculated changes in the relative intensities with aspect ratios are found to be much greater than that observed experimentally. This is due to the fact that for the observed emission of all the rods studied, nonradiative processes dominate the relaxation mechanism of the excited state, a fact that was not included in the theoretical treatments. Experimental results and theoretical treatments will be presented.
A Computational Study on CO Adsorption onto SnO2 Small Grains
Authors: Mazzone Anna M. , Morandi V.
Published: April 2011

The focus of this study is on the adsorption properties of the nanocrystalline materials and SnO2 has been chosen as the appropriate example. Therefore model structures consisting on SnO2 grains with a rutile lattice and a size comparable with the experimental ones have been considered and the adsorbed system is generated by depositing a CO molecule above a tin or oxygen atom on the grain surface. The calculations, based on semi-empirical Hartree-Fock and scattering theories, illustrate the dependence of the binding and adsorption energies of grains on their size and shape and show the effects of these energies on the grain conductance.
Iron Oxide Composite Nanoparticles and Sensing Properties
Authors: Wang Lingyan , Shi Xiajing , Mahs Sakienah , Choi Jeongku , Sarup Karan , Wang Guannan Roger , Luo Jin , Lu Susan , Zhong Chuan-Jian
Published: April 2011

This paper reports findings of an investigation of the synthesis of monolayer-capped iron oxide and core (iron oxide)-shell (gold) nanocomposite and their assembly towards thin films as sensing materials. Pre-synthesized and size-defined iron oxide nanoparticles were used as seeding materials for the reduction of gold precursors, which was shown to be effective for coating the iron oxide cores with gold shells (Fe oxide@Au). The unique aspect of our synthesis is the formation of Fe oxide@Au core-shell nanoparticles with controllable surface properties. By controlling the reaction temperatures and manipulating the capping agent properties and solution compositions, the size, shape, composition, and monodispersity can be tailored. The core-shell nanoparticles were shown to form molecularly-mediated thin film assemblies using molecular mediators. The sensing properties of the nanostructures on piezoelectric devices were examined for the detection of volatile organic compounds. The preliminary results have provided important insights into the design of core-shell nanocomposites as sensing materials.
Analytical TEM Observation of Gold Nano-Particles on Cerium Oxide
Authors: Akita Tomoki , Tanaka Koji , Kohyama Masanori , Haruta Masatake
Published: April 2011

The structure of Au nano-particles supported on CeO2 was investigated by using an analytical transmission electron microscope (TEM). The shape change of Au particles was observed during TEM observation, such as shrinking down to a mono-atomic layer on the CeO2 substrate. The electron beam irradiation experiment revealed that the shape change of Au particles is concerning with the oxidation state or the density of oxygen vacancies of CeO2 substrate where the rapid desorption and adsorption of oxygen occurs. It was also found that the reduction by strong electron beam irradiation and subsequent oxidation generate the decoration of Au particles by cerium oxide.
Electrosynthesis of Magnetostrictive Nanosensor Array
Authors: Li Suiqiong , Orona Lisa , Fu Liling , Cheng Z.-Y.
Published: April 2011

Magnetostrictive nanobars as sensor platform were induced. Based on the resonance behavior of strips made from thin films, it is identified that the amorphous Fe-B alloy is a good candidate for fabricating high performance sensor platform. The fabrication process of amorphous Fe-B nanobars using electrochemical deposition is reported. The magnetization hysteresis loop of Fe-B nanobars with the diameters of 50, 100 and 200 nm, respectively, was characterized. It is found that, for all nanobars, the coercive field measured along length direction is smaller than the coercive field measured perpendicular to length direction. The physics behind the phenomena is discussed.
Preparation and Characterization of Thin Films by Pulsed Laser Deposition for NOx gas Sensor
Authors: Bhuiyan Md. Mosharraf Hossain , Ueda Tsuyoshi , Shinguu Hiroshi , Ikegami Tomoaki , Ebihara Kenji
Published: April 2011

Gas sensors based on WO3 thin films doped with platinum (Pt) or palladium (Pd) were prepared by KrF excimer pulsed laser deposition method combined with dc sputtering. The films were deposited on silicon, quartz and Al2O3 sensor substrate with Pt interdigital electrodes at various substrate temperatures from 300°C to 500 °C, and oxygen pressures from 100 mTorr to 300 m Torr, respectively during the deposition. The morphology and structure of the films were examined by AFM and XRD. The sensor property of the WO3−x thin films was measured by the two terminal resistance method at operating temperatures of 25 °C to 400 °C. The sensitivity of the WO3 thin film gas sensors with doping (platinum or palladium) was found to be higher than that of undoped WO3 thin films gas sensors. The sensitivity of the pt doped WO3 films to different concentration of NO gas was examined and the sensitivity was found to be increased with increasing NO gas concentration.
Effect of Diameter on Longitudinal Displacement in Disk Shape 10-μm-thick Lead Zirconate Titanate Films
Authors: Iijima Takashi , Osone Satoko , Shimojo Yoshiro , Okino Hirotake , Yamamoto Takashi
Published: April 2011

Micro-machined piezoelectric film devices are usually fabricated onto substrates, so that the displacement response of the film is clamped with the substrate. To investigate the longitudinal displacement behavior of 10-μm-thick lead zirconate titanate (PZT) films deposited onto Si substrates, disk shape structures with diameters of 20 to 80-μm were fabricated by an reactive ion etching (RIE) process. The polarization-field (P-E) hysteresis curves did not show a remarkable difference with decreasing the PZT disk diameter. On the other hand, unipolar driven longitudinal displacement increased, and the amount of the displacement was saturated at a diameter of 30 and 20 μm. The AFM measured longitudinal piezoelectric constants, AFM d33, were estimated in the case of before poling and after poling at 100V for 10 min. The AFM d33 for the before and after poling process were 65 and 94 pm/V for 80-μm-diameter film disk, and 153 and 315 pm/V for 20-μm-diameter film disk, respectively. The value of poled AFM d33 for 20-μm-diameter film disk was comparable to bulk PZT ceramics. These results suggest that the decrease of the disk diameter reduces the Si substrate bending related with the clamping effect between the film and substrate, and facilitates domain reorientation in the poling process. It seems that the actual piezoelectric constant of films can be estimated from the longitudinal displacement when the ratio of the PZT disk diameter, d, to the PZT film thickness, t, shows d/t < 3 for 10-μm-thick PZT films.
Effect of PLT Buffer Layers on the PZT Thin Films for Scaling-Down Ferroelectric Materials
Authors: Dong Hua Li , Lee Eun Sun , Chung Hyun Woo , Ahn Byung Du , Lee Sang Yeol
Published: April 2011

The Hysteresis characteristics of below 400 nm- thick Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Pt (111) /Ti/SiO2/Si substrates have showed very poor with remanent polarization of 1∼3 μC/cm2 in our previous research. To study the further scaling-down, we introduced the method of our previous research that the (Pb0.72La0.28)Ti0.94O3 (PLT) buffer layers play an important role in enhancing the ferroelectric properties of the PZT thin films. As a result, the remanent polarization of 300 nm-thick PZT thin films with the 10 nm-thick PLT buffer layers have showed 32 μC/cm2 at applied voltage of 8 V and 24 μC/cm2 at applied voltage of 5 V. Inserted the PLT seed layers between the PZT thin films and substrate, the hysteresis characteristics of PZT thin films were improved a lot. The dielectric and leakage current properties of PZT thin films were also investigated.
Observation of Domain Switching in Fatigued Epitaxial Pb(Zr,Ti)O3 Thin Films
Authors: Kim Yong Kwan , Yokoyama Shintaro , Ueno Risako , Morioka Hitoshi , Sakata Osami , Kimura Shigeru , Saito Keisuke , Funakubo Hiroshi
Published: April 2011

We performed x-ray diffraction measurements by using highly brilliant synchrotron radiation on epitaxial Pb(Zr0.35Ti0.65)O3 film capacitor structures. Small regions of 300-nm-thick epitaxial Pb(Zr,Ti)O3 thin films with Pt and SrRuO3 top electrodes were measured after applying various numbers of switching cycles of the electric field. Epitaxial Pb(Zr,Ti)O3 thin films were prepared on epitaxial (100)cSrRuO3/(100)SrTiO3 substrates by pulsed-metalorganic chemical vapor deposition. The volume faction of c-domain and remanent polarization was plotted against the number of switching cycles. In the both capacitors, the Vc increased as the switching cycle increased independent of fatigue behavior.
Morphology Control, Dopant Incorporation, and Selective Epitaxial Growth of 4H-SiC at Low Temperatures Using CH3Cl Growth Precursor
Authors: Koshka Yaroslav , Krishnan Bharat , Lin Huang-De , Melnychuk Galyna
Published: April 2011

Low-temperature homoepitaxial growth of 4H-SiC using halo-carbon precursors was further investigated to address the problems limiting increase of the growth rate of the defect-free epilayers at growth temperatures below 1300°C. Enhanced etching of Si clusters in the gas phase was achieved by adding HCl during the low-temperature growth. The effective Si/C ratio above the growth surface was increased as a result of reduced depletion of silicon vapor species by cluster condensation, which resulted in drastically improved epilayer morphology and significant increase of the growth rate. An intentional insitu nitrogen doping of epitaxial layers during 1300°C growth on Si and C faces revealed more than an order of magnitude higher nitrogen donor incorporation in the C-face epitaxial layers. Finally, a feasibility of selective epitaxial growth using low-temperature masking materials such as SiO2 was demonstrated.
High-Resolution X-ray Topography of Dislocations in 4H-SiC Epilayers
Authors: Kamata Isaho , Tsuchida Hidekazu , Vetter William M , Dudley Michael
Published: April 2011

Silicon carbide (SiC) substrates and epilayers contain many crystal defects, such as micropipes, screw dislocations, threading edge dislocations (TEDs), basal plane dislocations (BPDs) and stacking faults. To investigate these defects, synchrotron radiation topography is frequently carried out. When the monochromatic synchrotron X-ray topography is taken by the grazing-incidence reflection geometry using 11-28 reflection, screw dislocations, TEDs and BPDs are simultaneously seen and shown as different topographic images [1]. Many studies of dislocations were reported using 11-28 reflections in 4H-SiC [1,2]. Topographic images of the dislocations have been analyzed by the ray-tracing method of computer simulation [3]. However, experimental images of dislocations were not fully matched to the fine structure of simulation images, because of a lack of resolution in recording media: conventional films and nuclear emulsion plates [3]. This time, we report obtaining high-resolution topographic images using a new recording medium, and compare results between the experiment and the computer simulation. Synchrotron topography in 11-28 reflection was carried out at SPring8 applying holography films as high-resolution recording media. The TED images are distinguished as four types, which have ribbon-like features with different rotating angles, through the use of the films. The four different TED images agree well with the computer simulated images which have been reported by Vetter et.al. taking into account of the different Burgers vector directions [3]. By comparing the three topographic images taken at g=-12-18, 11-28 and 2-1-18, we confirmed experimentally that the four types of TED images originated from the difference of Burgers vector directions. We also investigated high-resolution topographic images of elementary screw dislocations, micropipes, and BPDs in 4H-SiC epilayers. The experimental image of screw dislocation fairly matched with simulated image. The fine features in the experimental topographic images of micropipes and BPDs are also compared with the simulated images in detail. [1] T. Ohno, H. Yamaguchi, S. Kuroda, K. Kojima, T. Suzuki, K. Arai: J. cryst. Growth. Vol. 260 (2004) 209. [2] H. Tsuchida, T. Miyanagi, I. Kamata, T. Nakamura, R. Ishii, K. Nakayama and Y.Sugawara: Jpn. J. Appl. Phys. Vol. 25, (2005), L806-808. [3] W. Vetter, H. Tsuchida, I. Kamata, M. Dudley: J. Appl. Cryst. Vol. 38, (2005), 442-447.
The Formation Mechanism of Carrot Defects in SiC Epifilms
Authors: Chen Hui , Wang Guan , Chen Yi , Jia Xiaoting , Bai Jie , Dudley Michael
Published: April 2011

Carrot-like defects in a 7 off-cut (from [0001] toward <1-210> direction) 4H-SiC wafer with a 36μm thick 4H-SiC epilayer have been investigated using Nomarski optical microscopy, synchrotron white beam x-ray topography (SWBXT), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray topographs confirm that threading screw dislocations are often associated with the carrots. Cross-sectional TEM observation confirms that a prismatic stacking fault exists below the carrot. This fault was found to show contrast in all observed diffraction geometries except for g=0004. A model for the mechanism of formation of this type of defect during epitaxial growth is proposed.
Deep Levels in As-Grown and Electron-Irradiated P-type 4H-SiC
Authors: Danno Katsunori , Kimoto Tsunenobu
Published: April 2011

Deep levels in as-grown and electron-irradiated p-type 4H-SiC have been investigated by deep level transient spectroscopy (DLTS). Three hole traps, namely HK2, HK3, and HK4, could be detected in the temperature range from 350K to 700K. Activation energies of the hole traps were estimated to be 0.84 eV for HK2, 1.27 eV for HK3, and 1.44 eV for HK4 from the Arrhenius plot of emission-time constants assuming temperature-independent capture cross section. By double-correlated DLTS (DDLTS), they were revealed to be donor-like (+/0) traps. The concentrations of HK3 and HK4 centers were clearly increased by low-energy (116 keV) electron irradiation. Based on thermal stability of the HK3 and HK4 centers up to 1350°C and the dependence of HK4 concentration on the electron fluence, they may originate from a complex including defect(s) caused by carbon displacement.
Advances in 4H-SiC Homoepitaxy for Production and Development of Power Devices
Authors: Thomas Bernd , Hecht Christian , Stein René , Friedrichs Peter
Published: April 2011

In this paper we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system. This equipment exhibits a capacity of 7x3” wafers per run and can be upgraded to a 6x4” setup. Characteristics of epilayers and reproducibility of the proc-esses are reported. Furthermore, we show recent results of p-type SiC homoepitaxial growth on 3” 4° off-oriented substrates using a single-wafer hot-wall CVD. The dependence of layer prop-erties on growth parameters, doping and thickness uniformity as well as doping memory effects are discussed. For the characterization of epitaxially grown pn-junctions first research grade pin-diodes were fabricated. The p-type emitters were either deposited in the same growth run to-gether with the n-type buffer and drift layers (continuous growth) or the n- and p-layers were grown in two different growth runs (separate growth).
Degradation of Current Gain in SiC BJTs
Authors: Agarwal Anant , Krishnaswami Sumi , Richmond James , Capell Craig , Ryu Sei-Hyung , Palmour John , Jones Kenneth , Scozzie Charles
Published: April 2011

The reduction in the current gain of SiC BJTs has been observed after operating the devices for as little as 15 minutes. It is accompanied by an increase in the on-resistance of the BJT. The origin of the current gain degradation in the BJTs is investigated. Two possible mechanisms, which may be simultaneously present in the device, are thought to be responsible: (a) increase in the surface recombination particularly in the region between the emitter and the base implant, and (b) bulk recombination in the base due to the generation and growth of stacking faults. Initial observation reveals the presence of stacking fault in the base-emitter region when the device is forward-biased. At the same time, minimizing the effect of recombination from the surface using improved passivation helped in the suppression of the current gain degradation in SiC BJTs.
DNA-Templated Assembly of Conducting Gold Nanowires
Authors: Satti Amro , Aherne Damian , Barrett Claire , Floyd Liam , Quinn Aidan , Redmond Gareth , Fitzmaurice Donald
Published: April 2011

The use of DNA to template the assembly of gold nanowires from gold nanoparticles is reported. Double-stranded calf thymus DNA, was deposited on a polystyrene-coated silicon wafer substrate. The substrate was then exposed to an aqueous dispersion of positively charged gold nanoparticles (~ 4 nm diameter), which adsorbed at the negatively charged DNA template. The adsorbed nanoparticles were then enlarged and enjoined by electroless deposition leading to formation of continuous nanowires of 85 nm average diameter. Gold electrodes were then overlaid on individual nanowires using conventional lithographic techniques. Two-terminal current-voltage measurements were employed to characterize the electrical characteristics of single nanowires. The nanowires exhibit resistivity values < 6 × 10-7 Ωm. These and related findings have implications for the design and assembly of next generation electronic devices.
Understanding and Control of Lateral Contraction in Stamping Lithography
Authors: Li Zheng , Tan Li , Liu Gang-yu
Published: April 2011

Thin film contraction under external mechanical stress can be used to miniaturize size and increase density of patterned features on top. Nonlinear Finite Element Analysis is used to provide guidance on this contraction process. It was found that the substrate contraction causes stress accumulation along interfaces between protruded features and substrate. These stress accumulation complexes the control of profile changes on patterned features and suggest a design of patterned features arranged beyond a critical distance to avoid cross-interference.
Controlling Length of Gold Nanorods and Monitoring Their Growth Mechanism Using X-ray Absorption Spectroscopy
Authors: Liu Ru-Shi , Chen H. M. , Hu S. F.
Published: April 2011

A new approach to fabricate long length of gold nanorods by controlling the volume of growth solution will be reported. The shape evolutions ranging from fusiform nanoparticles to 1-D rods was observed. Increasing the addition of growth solution can control the length of nanorods. The length of rods can be extended to 2 £gm, and nanorods with aspect ratios of up to ~ 70 could be obtained. Moreover, X-ray absorption spectroscopy (XAS) is applied herein to elucidate the growth mechanism of gold nanorods. The gold ions were directly reduced to gold atoms by ascorbic acid during the reaction, and then gold atoms were deposited on the surface of gold seeds that were introduced into the reaction. Extended X-ray absorption fine structure (EXAFS) confirmed the growth of gold and the environment around Au atoms over the reaction. The XAS are expected to have wide applications in the growth of gold and other related materials.
Experimental and Ab-initio Investigations of Osmium Diboride
Authors: Hebbache M. M. , Stuparevic L. , Zivkovic D. , Zemzemi M.
Published: April 2011

More than half a century after their discovery, almost nothing is known about the physical properties of osmium borides, thought their structures have been clearly identified in the early sixties. We re-examined the phase diagram of the binary system osmium-boron and confirm the existence of two hexagonal phases, OsB1.1, Os2B3 and an orthorhombic phase, OsB2. Our microhardness measurements show that the synthesized OsB2 is extremely hard. In addition, first-principles calculations have been conducted to investigate its physical properties. It is shown that OsB2 is also a low compressibility material. Most of the transition metal borides have already found applications as in protective armor, nuclear reactors, reinforcement, etc. OsB2 can be used in applications like hard coating.
Photolithographic Process Based on High Contrast Acrylate Photoresist for Multi-Protein Patterning
Authors: Chatzichristidi Margarita , Petrou Panagiota S. , Douvas Antonios M. , Diakoumakos Constantinos D. , Raptis Ioannis , Misiakos Konstantinos , Kakabakos Sotirios S. , Argitis Panagiotis
Published: April 2011

Continuing the effort of our group for biocompatible, photoresist-based lithographic processes, high contrast near UV photoresists are presented along with a novel multi-step lithographic scheme. The proposed lithographic scheme is based on successive lithographic steps (exposure at 310 nm) on the same substrate for the patterning of different proteins. The photoresists are based on (meth)acrylate tetrapolymers and a near UV sensitive sulfonium salt as photoacid generator and can be processed under mild baking and development conditions allowing patterning of proteins without denaturation and loss of their molecular recognition capability. Protein patterning in successive lithographic steps down to 2μm has been achieved. Sub-1μm patterning structures have been also obtained. Lithographic results were evaluated with SEM and fluorescence microscopy, after the recognition of the patterned biomolecules by their fluorescently labeled counterparts.
Spin Relaxation in SiGe Islands
Authors: Malissa Hans , Jantsch Wolfgang , Chen Gang , Lichtenberger Herbert , Fromherz Thomas , Schäffler Friedrich , Bauer Günther , Tyryshkin Alexei , Lyon Stephen , Wilamowski Zbyslaw
Published: April 2011

We present our work on the spin relaxation of electrons confined in SiGe islands. Ge islands are grown on unstructured and structured Si(100) substrates by MBE, and lead to strain in the Si layer that is deposited on top. These quantum dot structures are investigated by photoluminescence and electron spin resonance (ESR) experiments, the latter both in continuous wave and pulsed mode. We observe a g-factor and an ESR line width that correspond to Si conduction band electrons with additional inhomogeneous broadening.
The Role of Local Fields in the Optical Properties of Silicon Nanocrystals
Authors: Trani Fabio , Ninno Domenico , Cantele Giovanni , Iadonisi Giuseppe
Published: April 2011

In this paper we discuss the role of local fields in the optical properties of silicon nanocrystals. Using a semiempirical tight binding approach, local field effects are included into the linear response theory, going beyond the standard independent particle approximation. The results show that local field effects give an important contribution to the optical properties of silicon nanocrystals, leading to a strong suppression of the absorption in the visible spectral range. This effect is attributed to the classical surface polarization contribution. A comparison between the atomistic tight binding approach and a classical dielectric model shows that the dielectric model gives reasonable results not only for large, but even for small silicon nanocrystals.
Multi-mode Mid-IR Silicon Raman Amplifiers
Authors: Jalali Bahram , Raghunathan Varun , Rice Robert R
Published: April 2011

This paper discusses the prospects of silicon as a Mid-wave Infra-red Raman crystal. As a specific example of novel devices that can be realized, we introduce the concept of multi-mode silicon Raman amplifiers and their application in infrared image pre-amplification. The same technology also has application in incoherent beam combining.
Carbon Nanotubes as Potential Cold Cathodes for Vacuum Microelectronic Applications
Authors: Gupta Sanju
Published: April 2011

Materials science is playing a dramatic role in discovering new materials with tailored physical properties. Cold cathodes/field emitters are one of the examples. Electron field emitting materials are of vital importance for a variety of vacuum microelectronic devices including field emission displays for flat panel displays, electron microscopes, X-ray generators, and vacuum lamps. This is the driving force to investigate the advanced nanostructured carbons as cold cathodes as one of the potential candidates. Recently, they are also being proposed for thermionic power generators. The rationale is that reducing one or more dimensions of a system below some critical length changes the systems' physical properties, where carbon nanotubes (CNTs) in the class of carbon nanostructures serve as a model example. In this paper, synthesis and characterization of vertically aligned multiwall and single-/double-wall carbon nanotube films using a microwave plasma-assisted chemical vapor deposition technique for vacuum microelectronics is presented. Recent advances in their synthesis, processing, and characterization indicate that the above mentioned potential is slowly being realized. Experiments showed that by continuous reduction in the thickness of the catalyst film produces hollow concentric tubes in contrast to bamboo-like multiwalled tubes with larger thickness. To assess the electron field emission properties, besides the traditional field emission (I-V) properties, temperature dependent field electron emission microscopy (T-FEEM) enabling real-time imaging of electron emission providing information on emission site density, temporal variation of the emission intensity, and insight into the role of adsorbates from nanotube films will be discussed. Physics based models (such as negative or low electron affinity, geometric enhancement, surface dipole, tunneling due to adsorbates, structure modification due to doping etc.) will be described to support the experimental observations in addition to weak thermionic field emission contribution. These findings provided a great insight into the field emission mechanism and a contrasting comparison between small and large diameter carbon nanotubes.
Chemically Modified Multiwalled Carbon Nanotubes as an Additive for Supercapacitorsβ
Authors: Kim Yong-Jung , Abe Yusuke , Yanagiura Takashi , Kitani Masaaki , Kodama Tsuyoshi , Higuchi Keita , Endo Morinobu
Published: April 2011

The incorporation of chemically modified multi-walled carbon nanotubes (MWNTs) have demonstrated, as an additive material to enhance the electrical conductivity, into the electrode gives rise to a highly improved rate capability of a super-capacitor. The preferential attack of potassium hydroxide on less disordered carbon results in the formation of high-performance MWNTs with increased surface area, electrical conductivity and sustained long tube morphology, simultaneously. It is envisaged that newly developed functional MWNTs will be utilized in various electrochemical systems, where high current is critically required.
Patterning Scheme Based on Photoacid Induced Spectral Changes for Single Layer, Patterned Full Color Light Emitting Diodes
Authors: Vasilopoulou Maria , Pistolis Giorgos , Botsialas Athanasios , Stathopoulos Nikos , Rangoussi Maria , Argitis Panagiotis
Published: April 2011

Photochemically induced emission tuning (PIET) for the definition of different color emitting areas in a single conducting polymeric layer is demonstrated. The commercially available poly(9-vinylcarbazole) (PVK), well known as a hole transporting layer in OLEDs technology, was used. The three primary colors emitting areas in a single layer of PVK film were defined using a suitable green emitter 1-[4-(dimethylamino)phenyl]-6-phenylhexa-1,3,5,-triene (DMA-DPH) along with the red emitter (4-dimethylamino-4'-nitrostilbene) (DANS). The selected emitters were dispersed in the PVK films in the presence of a photoacid generator (PAG). Various onium salts were tested as photoacid generators in order to select those, which could cause effectivily the photoinduced protonation and emission tuning of the probes molecules. Through proton induced bleaching of the red emitter and proton induced spectral shift of the green one, the definition of all three primary color emitting areas was possible. In this way the unexposed areas of the film remain red, the areas exposed with the intermediate dose become green and the fully exposed areas emit blue color. Intermediate colors and white light can also be obtained.
The Impact of Capping on the Mobility and Thermal Stability of Organic Thin Film Transistors
Authors: Meyer Stephan , Sellner Stefan , Schreiber Frank , Dosch Helmut , Ulbricht Gerhard , Fischer Matthias , Gompf Bruno , Pflaum Jens
Published: April 2011

We performed temperature-dependent studies on pentacene thin film transistors (TFTs) with and without encapsulation. The capping layer is realized either by a sputtering layer of aluminum oxide (AlOx.) or, alternatively, by a polymeric layer of poly-para-xylylene (PPX). A field-effect can be demonstrated for both capping materials up to temperatures of about 140 – 170 °C, which is about 50 °C above the desorption point of uncapped pentacene thin films on SiO2 substrates. Complementary studies by thermal desorption spectroscopy and temperature dependent x-ray diffraction show that the organic layer remains crystalline on the substrate far above the electrical breakdown temperature of the encapsulated device.
Surface Modifications using Thiol Self-Assembled Monolayers on Au Electrodes in Organic Field Effect Transistors
Authors: Hiroshiba Nobuya , Kumashiro Ryotaro , Komatsu Naoya , Suto Yusuke , Ishii Hisao , Takaishi Shinya , Yamashita Masahiro , Tsukagoshi Kazuhiro , Tanigaki Katsumi
Published: April 2011

The influences of self-assembled-monolayers (SAMs) modifications on the gold electrodes in organic field effect transistors are studied using benzen-thiols (BzTs) having amino (NH2), nitro (NO2) and methyl (CH3) substituents and pentacene as an organic semiconductor. The field effect transistor (FET) characteristics are found to be very sensitive to the preparation condition of the SAMs modified surfaces. This can be rationalized in terms of the barriers against carrier injections made by SAMs and this situation can be monitored using a surface contact-angle method. The enhancement in the field effect mobilities μ is observed when the SAMs modifications to the electrodes are applied, and this could be caused by the higher efficiency of carrier injection attained by the hole transfer from SAMs to pentacene molecules.
Formation of Porous Organosilicate Glasses Produced by PECVD and UV Treatment
Authors: O'Neill Mark L. , Du Lin-Shu , McDaniel Paula L. , Peterson Brian K. , Weigel Scott J. , Haas Mary K. , Vrtis Raymond N. , Sinatore Dino , Bitner Mark D. , Theodorou Kathleen E. , O'Neill Mark L.
Published: April 2011

The deposition and post-treatment processes involved in the production of porous organosilicate glasses (OSGs) by plasma-enhanced chemical vapor deposition (PECVD) with ultraviolet light (UV) treatment are investigated through the use of a deuterated organic porogen precursor using infrared spectroscopy and solid-state nuclear magnetic resonance spectroscopy. Infrared analysis provides evidence for hydrogen-deuterium scrambling between the chemical species during the deposition process, which is exacerbated by the UV treatment process. Analysis of 13C cross-polarized magic angle spinning (CP-MAS) NMR suggests that the porogen exists in domains relatively isolated from the network, in agreement with short UV treatment time morphological data that indicates the pore size is relatively constant from the early stages of UV treatment process. The chemical and morphological information provides further support for a deposition controlled morphology and has implications towards enhanced chemical processing of porous organosilicate glass (OSG) films for back-end-of-line integrated circuit manufacturing.
Electrochemical Corrosion Inhibition System for Photoresist Stripper for New Copper FPD Manufacturing
Authors: Inaoka Seiji , Kim Sang In
Published: April 2011

Development of photoresist stripper with copper compatibility is challenging as conventional corrosion inhibitors do not protect the metal as expected. Copper corrosion inhibition mechanism of newly developed photoresist stripper is proposed that significantly reduces copper corrosion with small amount of corrosion inhibitor.
Laser-Induced Microstructural Modification of Polycrystalline Cu and Ag Films Encapsulated in SiO2
Authors: Zhong Rong , Wiezorek Jorg M.K. , Leonard John P.
Published: April 2011

Excimer-laser-induced rapid lateral solidification was used to produce large grain microstructures in copper and silver thin films. These were multilayer thin film structures consisting of sputter deposited copper and silver thin films encapsulated by silica (SiO2/metal/SiO2/Si substrate). In this process, a single excimer laser pulse and projection imaging optics were used to melt a 60 micron wide line in the metal film. The resolidification of the melted lines is found to occur laterally in the plane of the film, resulting in grains greater than 20 um in length and 1 um wide. Electron diffraction analysis allowed identification of a strong <001> texture in the growth direction along the major axis of the elongated grains as well as similar texture parallel to the film surface. Various dislocation and faulted defect structures are identified and examined in the context of the rapid solidification and potential application to interconnects.
Low Temperature Direct Metal Bonding by Self Assembled Monolayers
Authors: Ang Xiaofang , Chin Li Cheong , Zhang Guo Ge , Wei Jun , Chen Zhong , Wong Chee Cheong
Published: April 2011

Elevated bonding temperature for interconnection deteriorates the reliability of both the device and the interconnect; hence the imperative for developing low temperature bonding methods. This study investigates the feasibility of using self-assembled monolayers (SAMs) to assist direct gold-gold bonding. This involves a simple molecular self-assembly process whereby a monolayer of alkyl chains with a sulfur end group is attached to the gold surface prior to thermocompression bonding. Using this method, we have achieved gold to gold bonding at a bonding temperature below 100°C, a significant reduction compared to the conventional bonding temperatures of above 150 °C. We attribute this temperature reduction to two properties of SAMs - (1) surface passivation of the Au surface that precludes adsorption of surface contaminants, and (2) The easy displacement of SAMs through thermal desorption just before bonding occurs. This SAMs-assisted bonding mechanism is supported by X-ray photoelectron spectroscopy (XPS) and surface plasmon resonance (SPR) results.
Charging Model of a Si Nanocrystal-based Floating Gate in a Quantum Flash Memory
Authors: Leriche Bertrand , Leroy Yann , Cordan Anne-Sophie
Published: April 2011

We propose a theoretical study for charging the floating gate composed of Si nanocrystals (NCs), in a non-volatile flash memory. Only a few electrons tunnel from the channel of a metal-oxide-semiconductor transistor into the two-dimensional array of nanocrystals.

Our model is based on the geometrical and physical properties of the device, in order to take the dispersion of the relevant parameters into account: NC radii, inter-NC distances, tunnel oxide and gate oxide thicknesses. The energy subbands of the channel are explicitly included, together with the doping density.

This three-dimensional model of electron tunneling into a NC is numerically solved through a two-dimensional finite element approach, which allows extensive numerical experimentations.

The tunneling times to charge a single NC or the whole NC floating gate are evaluated in a finer detail, and the influence of the dispersion of the relevant parameters is discussed.

Such a study may help the experimentalists to build efficient quantum flash memories.
No Interfacial Layer for PEDOT Electrodes on PVDF: Characterization of Reactions at the Interface P(VDF/TrFE)/Al and P(VDF/TrFE)/PEDOT:PSS
Authors: Mueller Klaus , Mandal Dipanka , Schmeisser Dieter
Published: April 2011

With photoelectron spectroscopy, we study the interface chemistry of the copolymer poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) and different electrode materials. We compare the interfaces aluminum/P(VDF-TrFE) and PEDOT:PSS/P(VDF-TrFE). PEDOT:PSS is a conductive polymer (Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)). The data sug-gest that we have an interface layer for electrodes, made of aluminum. An interface reaction occurs in both cases: for aluminum as top and as bottom electrode. In contrast, the organic PE-DOT:PSS electrode shows no chemical interaction with the P(VDF-TrFE) polymer. The much lower reactivity of organic electrodes, compared to aluminum, gives a direct hint to im-proved functional properties of thin organic ferroelectric films.
Study of Band Alignment at CBD-CdS/Cu(In1-xGax)Se2 (x = 0.2 - 1.0) Interfaces by Photoemission and Inverse Photoemission Spectroscopy
Authors: Teshima Shimpei , Kashiwabara Hirotake , Masamoto Keimei , Kikunaga Kazuya , Takeshita Kazunori , Okuda Tetsuji , Sakurai Keiichiro , Ishizuka Shogo , Yamada Akimasa , Matsubara Koji , Niki Shigeru , Yoshimura Yukio , Terada Norio
Published: April 2011

Dependence of band alignments at interfaces between CdS by chemical bath deposition and Cu(In1-xGax)Se2 by conventional 3-stage co-evaporation on Ga substitution ratio x from 0.2 to 1.0 has been systematically studied by means of photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES). For the specimens of the In-rich CIGS, conduction band minimum (CBM) by CIGS was lower than that of CdS. Conduction band offset of them was positive about +0.3 ~ +0.4 eV. Almost flat conduction band alignment was realized at x = 0.4 ~ 0.5. On the other hand, at the interfaces over the Ga-rich CIGS, CBM of CIGS was higher than that of CdS, and CBO became negative. The present study reveals that the decrease of CBO with a rise of x presents over the wide rage of x, which results in the sign change of CBO around 0.4 ~ 0.45. In the Ga-rich interfaces, the minimum of band gap energy, which corresponded to energy spacing between CBM of CdS and valence band maximum of CIGS, was almost identical against the change of band gap energy of CIGS. Additionally, local accumulation of oxygen related impurities was observed at the Ga-rich samples, which might cause the local rise of band edges in central region of the interface.
Metastable Defect Distributions in CIGS Solar Cells and Their Impact on Device Efficiency
Authors: Igalson Malgorzata
Published: April 2011

Metastabilities in the electrical characteristics of CIGS devices are commonly observed phenomena originating from persistent changes of shallow and deep levels distributions within the absorber. We examine characteristic changes induced by voltage bias and light together with their relaxation behavior and interpret them as the consequences of a negative-U type of centers predicted by theoretical calculations of Lany and Zunger. It is shown how the properties of these centers justify a model of p+ layer explaining specific features of light and dark current-voltage characteristics. The discussion showing the impact of various charge distributions on carrier transport is presented. The arguments are provided, that centers responsible for metastable effects are also to blame for majority of photovoltaic losses exhibited in various devices.
Variable Light Soaking Effect of Cu(In,Ga)Se2 Solar Cells with Conduction Band Offset Control of Window/Cu(In,Ga)Se2 Layers
Authors: Minemoto Takashi , Hashimoto Yasuhiro , Satoh Takuya , Negami Takayuki , Takakura Hideyuki
Published: April 2011

The impact of the conduction band offset (CBO) between window/Cu(In,Ga)Se2 (CIGS) layers on the light soaking (LS) effect in CIGS solar cells has been studied with continuous CBO control using a (Zn,Mg)O (ZMO) window layer. Two types of CIGS solar cells with different window/buffer/absorber layers configurations were fabricated, i.e., ZMO/CIGS (without buffer layer) and ZMO/CdS/CIGS structures. The CBO values between ZMO and CIGS layers were controlled to -0.15~0.25 eV. Plus and minus signs of CBO indicate the conduction band minimums of ZMO above and below that of CIGS, respectively. Current-voltage (J-V) characteristics of the solar cells with different LS durations revealed that a positive CBO value higher than 0.16 eV induces J-V curve distortion, i.e., LS effect, and all the J-V characteristics stabilized in 30 min. The degrees of the LS effect were dominated by the CBO value between ZMO and CIGS layers in the both structure regardless of the existence of CdS buffer layers. These results indicate that the LS effect is dominated by the highest barrier for photo-generated electrons in the conduction band diagram, i.e., the CBO between ZMO and CIGS layers, and quantitatively the LS effect emerges the CBO value higher than 0.16 eV.
Highly Arsenic Doped CdTe Layers for the Back Contacts of CdTe Solar Cells
Authors: Barrioz Vincent , Proskuryakov Yuri Y. , Jones Eurig W. , Major Jon D. , Irvine Stuart J.C. , Durose Ken , Lamb Dan A.
Published: April 2011

In an effort to overcome the lack of a suitable metal as an ohmic back contact for CdTe solar cells, a study was carried out on the potential for using a highly arsenic (As) doped CdTe layer with metallization. The deposition of full CdTe/CdS devices, including the highly doped CdTe:As and the CdCl2 treatment, were carried out by metal organic chemical vapour deposition (MOCVD), in an all-in-one process with no etching being necessary. They were characterized and compared to control devices prepared using conventional bromine-methanol back contact etching. SIMS and C-V profiling results indicated that arsenic concentrations of up to 1.5 × 1019 at·cm-3 were incorporated in the CdTe. Current-voltage (J-V) characteristics showed strong improvements, particularly in the open-circuit voltage (Voc) and series resistance (Rs): With a 250 nm thick doped layer, the series resistance was reduced from 9.8 Ω·cm2 to 1.6 Ω·cm2 for a contact area of 0.25 cm2; the J-V curves displayed no rollover, while the Voc increased by up to 70 mV (~ 12 % rise). Preliminary XRD data show that there may be an As2Te3 layer at the CdTe surface which could be contributing to the low barrier height of this contact.
Cu(In,Ga)Se2 Prepared from Electrodeposited CuGaSe2/CuInSe2 Bilayer for Solar Cell Applications
Authors: Oda Yusuke , Minemoto Takashi , Takakura Hideyuki , Hamakawa Yoshihiro
Published: April 2011

We report the preparation of Cu(In,Ga)Se2 (CIGS) thin-films using the electrodeposited (ED) CuGaSe2 (CGS)/CuInSe2 (CIS) bilayers. CGS/CIS bilayers were prepared on soda-lime glass /Mo substrates to realize the controlled Ga/(Ga+In) ratios and smooth layers of CIGS thin-films. It was found that the composition and morphology of CGS films was highly dependent on the composition of the bath. Crack-free and morphological CGS thin-films were obtained by the addition of supporting electrolyte and brightener. For the morphology and the crystallization of the ED-CIGS films, the best electric charges of CGS and CIS films were 1.0 C and 6.0 C respectively and the films were annealed at 600 oC for 60 min. However, the interface of the ED-CGS/CIS film had some voids and interdiffusions of Ga and In did not take place by annealing. The CIGS solar cell using ED-CGS/CIS films as an absorber exhibited diode behavior.