bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoplastic Acrylic Lacquer as a Base for Hot Embossing
Authors: Leech P. W. , Lee Robert A.
Published: April 2011

We report the novel use of thermoplastic acrylic lacquer (automotive paint) in the hot embossing of nanoscale structures. Replicas of grating arrays have been produced in coatings of acrylic lacquer using a standard embossing process. The master dies for the experiments comprised grating arrays fabricated by electron beam lithography. Grating patterns with a pitch of 0.7-1.3 μm were configured to produce diffractive images over an area of ~25 × 25 mm. The embossing experiments used a replicated Ni shim as a die and were performed at 100-150 °C and 80 kN force. A temperature above the reflow range for the lacquer, T = 120-150° C, was required in order to achieve a uniform impression across the embossed area of ~80 × 80 mm. The diffractive grating patterns which were embossed into acrylic lacquer have shown optical effects suitable as a security feature including image switching and color movement.
A Novel Design Toward Understanding and Characterizing Transport Behavior of Composite Mesoporous Silica Thin Films
Authors: Chen Zhu , Adams David P , Vasile Michael J , Liu Nanguo , Jiang Yingbing , Xomeritakes George , Brinker C. Jeffrey
Published: April 2011

Research in synthetic materials with controlled transport properties has been inspired by the exquisite selectivity exhibited by natural transmembrane proteins such as ion channels (for selectively transporting ions like sodium and potassium, etc) and aquaporins (for conducting high fluxes of water and excluding ions). In this poster we focus on the transport behavior of highly ordered mesoporous silica thin films synthesized by evaporation induced silica/surfactant self-assembly (EISA). This process allows us to integrate the nanostructures into electronic and fluidic systems by simple coating or spraying procedures, facilitating the characterization of their transport behaviors. Also, the nanocomposite architecture made by this process gives precisely defined pore size, orientation and surface chemistry, allowing tailoring of the motion of molecules and ions transported across the nanochannels. To approach our final goal of understanding and characterizing the transport behavior of our materials, we designed our experiments into three steps: first, we employed focused ion beam (FIB) lithography to drill a single sub-100-nm pore on a substrate support, providing a platform enabling the characterization of trans-membrane behavior of ions/molecules. Second, we developed two EISA approaches to form cubic thin film silica mesophases spanning the FIB-drilled pore. In one approach, we adapted our aerosol-assisted EISA where fusion of liquid crystalline aerosol droplets creates a thin membrane spanning the substrate pore. In the other approach, we modified our synthetic protocol to form ultra thin (20-nm) spanning films by spin-coating. Films with pore sizes ranging from 2nm to 7nm and surface chemistries including –OH, -COOH and –NH2 terminated pore surfaces were prepared in this fashion and integrated to the FIB-drilled single pore substrate support with uniformity to allow tailoring of the motion of ions and molecules. Third, we designed an electrochemical cell in which the FIB-drilled substrates are integrated to enable the measurements of ion fluxes using standard “patch-clamp” instruments. Experiments are conducted to demonstrate the transport characteristics of our materials by measuring transmembrane ion fluxes when specific molecules such as DNA are applied, a method relevant to low cost DNA sequencing. Also, by chemically or physically blocking all but one or several membrane pores, we are attempting to measure ion and water transport in individual synthetic nanopores and compare results with natural ion and water channels.
Control over Pore Positions in Anodised Aluminium Oxide Films via Scratching the Surface of Pure Aluminium
Authors: LeClere Darren , Derby Brian , Thompson George E.
Published: April 2011

Anodised aluminium oxide films have several applications in nanotechnology due to the ability to control the dimensions and ordering of the pores. Several techniques have been developed which allow for accurate control over the ordering of pore arrays. Examples of such techniques are the “Two-Step” method, and embossing with optical gratings or micro-machined Si templates. It will be demonstrated that it is possible to control the position of the pores using a nanoindenting device that has scratched the aluminium surface before anodising. The interpore distances accomplished via this technique were 200nm and 400nm by anodising in 0.3M (COOH)2 at 80V and 0.1M H3PO4 at 160V respectively. Hexagonal and square arrays were created by scratching the aluminium with a series of crosshatched lines.
Spatially Resolved MicroDiffraction Analysis of the Plastic Deformation in the Shock Recovered Al Single Crystaltal
Authors: Barabash Rozaliya , Ice G. E. , Liu W. , Belak J. , Kumar M.
Published: April 2011

A spatially resolved diffraction method with a sub micrometer-diameter beam and 3D differential aperture technique together with MD simulations, SEM and OIM analysis are applied to understand the arrangements of voids, geometrically necessary dislocations and strain gradient distribution in samples of Al (123) single crystal shocked to incipient spallation fracture. We describe how geometrically necessary dislocations and effective strain gradient alter white beam Laue patterns of the shocked materials. We show how to quantitatively determine the orientation and density of geometrically necessary dislocations in the shock recovered Al samples being initially oriented for single slip.
Local Electron Beam Induced Reduction and Crystallization in Electrochemically Deposited Amorphous TiO2 Films
Authors: Kern Philippe , Michler Johann
Published: April 2011

Contrary to crystalline titanium oxide (TiO2), electrochemically deposited amorphous thin TiO2 films are found significantly more sensitive towards electron beam (e-beam) exposure. E-beam irradiation experiments were performed under scanning electron microscope conditions at 20 keV with well controlled beam current (IP), current density and exposure dose. As shown by atomic force microscopy and Micro-Raman spectroscopy, even moderate e-beam exposure immediately leads to oxide reduction due to electron stimulated oxygen desorption, while exposure with IP>1 micro-A and J>1 A/cm2 triggers localized crystallization into anatase phase already after seconds of irradiation. The mechanisms for oxide reduction and beam heating induced crystallization are discussed, and a temperature estimation in the beam center indicates that crystallization occurs at less than 150 °C. The well-defined volume loss upon oxygen desorption is shown to be attractive for precise topographical surface patterning, while the triggering local structural changes within a semi-conductive amorphous matrix opens interesting possibilities for tailoring of its local electrical or catalytic properties.
Epitaxial Growth and Luminescence Characterization of Si-based Double Heterostructures Light-emitting Diodes with Iron Disilicide Active Region
Authors: Suemasu Takashi , Li Cheng , Sunohara Tsuyoshi , Ugajin Yuta , Kobayashi Ken'ichi , Murase Shigemitsu , Hasegawa Fumio
Published: April 2011

We have epitaxially grown Si/β-FeSi2/Si (SFS) structures with β-FeSi2 particles or β-FeSi2 continuous films on Si substrates by molecular beam epitaxy (MBE), and observed 1.6 μm electroluminescence (EL) at room temperature (RT). The EL intensity increases with increasing the number of β-FeSi2 layers. The origin of the luminescence was discussed using time-resolved photoluminescence (PL) measurements. It was found that the luminescence originated from two sources, one with a short decay time (τ∼10 ns) and the other with a long decay time (τ∼100 ns). The short decay time was due to carrier recombination in β-FeSi2, whereas the long decay time was due probably to a defect-related D1 line in Si.
Piezoresistance in Strained Silicon and Strained Silicon Germanium
Authors: Richter Jacob , Arnoldus M. B. , Hansen J. Lundsgaard , Larsen A. Nylandsted , Hansen O. , Thomsen E. V.
Published: April 2011

This paper presents experimental results of the piezoresistance in p-type tensile strained silicon and compressive strained silicon germanium grown by molecular beam epitaxy (MBE) on (001) silicon substrates. The piezoresistance decreases in a tensile strained layer and increases in a compressive strained layer when compared to the unstrained material. The results show that one can tune the piezoresistance by tuning the strain in the piezoresistor and thus tailor the performance of the device. The obtained results show an increase in the piezoresistance effect of 35% in compressive strained silicon germanium and a decrease in the piezoresistance effect in tensile strained silicon of 24%. Furthermore, the results show that the piezoresistance of a tensile strained silicon crystal has a smaller temperature dependency compared to that of unstrained silicon. The piezoresistance effect decreases by 7% in tensile strained silicon compared to the piezoresistance effect decrease in silicon of 18% when changing the temperature from 30°C to 80°C.
SOI-Based Silicon Quantum Dots Contacted by Self-Aligned Nano-Electrodes
Authors: Wolf Conrad R. , Ladenburger Andreas , Enchelmaier Rainer , Thonke Klaus , Sauer Rolf
Published: April 2011

In this paper we present a novel approach to fabricate single-electron devices utilizing different self-organization and self-alignment effects. Silicon quantum dots (QDs) are obtained employing reactive ion etching (RIE) into a silicon-on-insulator (SOI) substrate with a self-assembled etch mask. Electrodes with nanometer separation are fabricated and aligned to the QDs by means of a controlled electromigration process. The tunneling rates of the devices are defined by the native oxide covering the silicon QDs and can be adjusted by self-limiting thermal oxidation. The devices show clear Coulomb blockade behavior as well as Coulomb staircase features. In some samples also a gate influence is present giving rise to Coulomb diamonds in the differential conductance diagram.
Growth of Gallium Nitride Nanowires and Nanospirals
Authors: Koley Goutam , Cai Zhihua
Published: April 2011

GaN nanostructure synthesis was done in a quartz tube furnace using ammonia and liquid Ga as precursors, and hydrogen as the carrier gas. Ni nanoparticles formed due to annealing, has been used as the catalyst layer, facilitating vapor-liquid-solid growth of the nanostructures. The growth process resulted in the formation of two types of structures, straight nanowires, and irregular growth sometimes resulting in nanospirals. Growth using uniform distribution of catalyst over the entire surface resulted in growth of straight nanowires, while growth performed on catalyst patterned surface resulted in growth of nanospirals. The diameter of the nanowires varied from 20 – 100 nm, while for spirals the cross-sectional diameters were found to be in the range of 100 nm – 1 micron, and spiral diameters in the range of several microns. Using the present growth system and gas flow set-up, it was possible to synthesize ultra-long nanowires and spirals, with overall lengths exceeding 70 microns. The regular straight nanowires were found to have a smooth circular cross-section, while the irregular wires and nanospirals were found to have a very rough surface with approximate hexagonal or triangular cross-sections. Some of the spirals changed into straight nanowires with uniform triangular cross-sections. While more investigations are required to fully establish their structures, based on preliminary characterization and past studies, we conclude that the nanowires with circular cross-sections grow along the c-direction [0001], while the spirals and consequent triangular cross-section nanowires grow along one of the non-polar directions. The formation of spirals themselves may be related to the polarization properties of GaN, similar to those predicted for ZnO nanosprings and nanoribbons.
Improved Stability of Solid State Light Emitting Electrochemical Cells Consisting of Ruthenium and Iridium Complexes
Authors: Bolink Henk Jan , Cappelli Luca , Coronado Eugenio , Costa Rubén D. , Graetzel Michael , Nazeeruddin MdK , Viruela Pedro M , Ortí Enrique
Published: April 2011

Two charged organometallic complexes containing bulky hydrophobic ligands based on ruthenium (II) and iridium (III) were synthesized and their performance in solid state light emitting electrochemical cells is described. The complexes were chosen as due to their large ligands a diminished susceptibility towards the formation of destructive complexes during device operation is expected. The LEC device performances reveal the longest living devices reported so far under dc bias. Quantum chemical calculations confirm that the major effect of the bulky diphenylphenanthroline ligands is of steric origin and not related with changes in the molecular electronic structure of the complexes.
Waveguiding, Microcavity Effects and Optically Pumped Lasing in Single Melt Processed Polyfluorene Nanowires
Authors: O'Carroll Deirdre , Redmond Gareth
Published: April 2011

The synthesis of poly(9,9-dioctylfluorene) conjugated polymer nanowires using the method of melt-assisted wetting of nanoporous alumina membrane templates is reported. Polymer nanowires exhibiting blue photoluminescence emission with diameters of approx. 300 nm are obtained. Absorption and photoluminescence spectra of nanowire mats indicate that the nanowires consist of the semi-crystalline form of the polymer. Single wires exhibit active waveguide behavior whereby excited luminescence propagates towards and out-couples at the tips of the nanowires. Spectra of out-coupled emission exhibit multiple modes with mode spacing corresponding to longitudinal Fabry-Pérot cavities of equivalent lengths to those of the nanowires. Above a threshold incident pump energy spectral collapse to a single blue shifted peak with instrument limited line width occurs characteristic of single mode lasing.
Soft Lithography Fabrication of Fully Flexible and Transparent all Organic FETs for Large Area Applications
Authors: Cosseddu Piero , Orgiu Emanuele , Bonfiglio Annalisa
Published: April 2011

Fully flexible and transparent all organic field effect transistors were fabricated by means of an innovative and inexpensive technique. A 1.8μm thick polyethylenetetherephtalate sheet, Mylar® (Du Pont), was used as gate dielectric and at the same time as mechanical support for the whole structure. We used pentacene, deposited by thermal sublimation, as semiconducting layer, whereas poly(ethylene-dioxythiophene)/polystyrene sulfonate (PEDOT/PSS) was used for the realization of the electrodes. Gate electrodes were realized by spin coating, while source and drain electrodes were patterned by micro-contact printing. We fabricated typical p-type field effect transistors, with mobilities up to 2 × 10−1cm2/Vs and Ion/Ioff up to 105, in a very simple and inexpensive way. It is worth to note that this technique allows the realization of bottom contact and top contact transistors. We realized both bottom contact and top contact devices on the same substrate and with the same active layer and we investigated how the structure itself and the active layer morphology influence the electrical properties in terms of hole mobility, Series Contact Resistance and parasitic capacitance effects. The comparison between top-contact and bottom-contact devices shows interesting marked differences that can be mainly attributed to a different PEDOT:PSS/semiconductor interface quality, influencing the most meaningful parameters. The flexibility of the obtained structure and the easy scalability of the technological process, suitable for roll to roll mass production processes, open the way for economic production of high-resolution organic devices
Electronic Structure of Defects in Fcc-C22
Authors: Domingos Helder Sousa
Published: April 2011

Classical and ab-initio calculations were carried out on bulk defects and surfaces of the carbon allotrope Fcc-C22. The results revealed a number of possible defects with spin polarization and one with antiferromagnetic character. The surfaces were shown to be able to host magnetic polarization. Extrinsic light dopants (H and N) were shown to introduce spin polarization for small dopant concentration and to metallize the systems for large concentrations.
Spin Injection and Spin Dynamics at CuPC/GaAs(100) Interface
Authors: Ding Huanjun , Gao Yongli , Sanchez-Albaneda Marina , Wüstenberg Jan-Peter , Cinchetti Mirko , Andreyev Oleksiy , Bauer Michael , Aeschlimann Martin
Published: April 2011

Spin injection from GaAs(100) to organic semiconductor copper phthalocyanine (CuPc) has been investigated experimentally with spin-resolved two-photon photoemission (SR-2PPE) spectroscopy. With SR-2PPE, the dynamics of both electron and spin relaxation have been studied with femtosecond time resolution. The spin-polarized electrons are originally generated in GaAs through optical pumping and injected into CuPc. We observed an enhancement in spin polarization at the interface after initial CuPc deposition. This demonstrates that interface spin scattering is insignificant, which is similar to our previous result of spin injection at CuPc/Co interface. The spin polarization dropped when the CuPc film became thick, an effect attributed to bulk attenuation in CuPc. The lifetime of the unoccupied orbits in CuPC was also studied with red-blue excitation of photon energy 1.56 eV and 3.12 eV, respectively. There was a strong asymmetry in the time-resolved spectra, and an unexpected long lifetime when the lower unoccupied orbital was excited. A simple explanation of this phenomenon will be discussed.
Sol-Gel Process Derived Superhydrophobic Silica Thin Films for Antistiction of MEMS Devices
Authors: Wong ChingPing , Zhu Lingbo , Hess Dennis W , Wong C. P.
Published: April 2011

Based on the theory of superhydrophobicity for low surface energy coatings, we describe a superhydrophobic antistiction silica coating for MEMS devices. The process uses a novel sol-gel process sequence with a eutectic liquid as a templating agent. The eutectic liquid displays negligible vapor pressure and very low melting point (12°C at ambient conditions) to reduce solvent loss during the high speed spincoating process. After a fluoroalkyl silane treatment, superhydrophobicity is achieved on the as-prepared silica thin film. The solvent can be extracted after the gelation and aging processes. Spin speed effect, eutectic liquid:TEOS ratio in the solution were studied in order to optimize the surface roughness to ensure excellent super-hydrophobicity. Comparison of the silica thin films with silicon pillar surfaces showed that superhydrophobicity for the traditional sol-gel derived silica films demonstrated significant improvement, especially under humid conditions. The AFM force curve obtained with a tipless probe showed that the interaction force is greatly reduced on a rough silica superhydrophobic surface. This result offers great potential to reduce stiction failures in MEMS devices.
Smooth Ag Film Deposited Using e-beam Evaporated Ge as an Intermediate Layer for Applications in Nanoscale Devices and Optical Superlens
Authors: Vj Logeeswaran , Kobayashi Nobuhiko P. , Wu Wei , Islam M.Saif , Xuanlai Fang Nicholas , Wang Shih Yuan , Williams R. Stanley
Published: April 2011

In this paper, we highlight a new method to obtain smoother silver (Ag) film characterized by much smaller average RMS surface roughness of ∼0.7nm, peak-to-valley separation of ∼4nm and grain-size distribution ~15nm as compared to conventionally obtainable Ag film characterized by RMS surface roughness of ∼10nm, peak-to-valley separation of ∼20nm and grain-size distribution of ∼100nm. Thin Ag films of ∼15nm (optically thin) were deposited on double-polished borosilicate glass and silicon (100) substrates with 2nm Germanium (Ge) intermediate layers. An optically thick Ag film of 60nm was also prepared with 2nm Ge. The Germanium thicknesses were also varied and similar surface morphology improvements are observable on all the samples. The AFM image analysis shows that having the evaporated Ge intermediate layer drastically changes the Ag surface morphology, namely, the surface roughness, peak-to-valley and grain size distribution. Our smooth Ag results are very promising for applications in molecular electronics interconnect, optical metamaterials, plasmonic superlens and nanophotonics.
Assembly of Fine-Pitch Carbon Nanotube Bundles for Electrical Interconnect Applications
Authors: Zhu Lingbo , Hess Dennis W , Wong ChingPing
Published: April 2011

Carbon nanotubes (CNTs) have been proposed as electrical interconnects, due to their excellent properties. However, the current nanotube growth techniques suffer from several drawbacks. One of the main challenges for applying CNTs to the circuitry is the high growth temperature (>600°C). Such temperatures are incompatible with microelectronic processes. The other issue is the poor adhesion between CNTs and the substrates, which will result in long term reliability issues and high contact resistance. To overcome these disadvantages, we have successfully demonstrated a methodology that we term “CNT transfer technology”. The distinctive CNT-transfer-technology features are separation of CNT growth and CNT device assembly at solder reflow temperature. In this paper, we combined our expertise in growth of well-aligned open-ended CNT bundles with the CNT transfer process to assemble CNT bundles for fine-pitch interconnects applications. To demonstrate the feasibility of transfer process to assemble the fine-pitch CNT bundles, the CNT bundles with diameter, aspect-ratio and pitch of 25 μm, 4, and 80 μm, respectively, were assembled on the copper substrates. The measured resistivity of the long CNTs is ∼2.3×10−4 Ω-cm. The CNT-solder alloy interfaces were observed by the SEM. The results indicated that molten SnPb solder form strong mechanical bonding with open-ended CNTs, suggesting the superior CNT/solder interfacial properties by solder reflow process.
Making Plastic Remember: Electrically Rewritable Polymer Memory Devices
Authors: Prime Dominic , Paul Shashi
Published: April 2011

Organic based electronic memory devices are currently receiving an unprecedented amount attention as possible alternatives for conventional semiconductor memories, due to their simple device structures, ease of fabrication, compatibility with flexible substrates and low cost. Polymer memory devices (PMDs) based on active layers containing gold nanoparticles (Q-Au) with 8-hydroxyquinoline (8HQ) will be presented in this report. Memory performance attributes will also be presented, which are less reported in the literature, but still essential for the realisation of viable organic memory technologies.
Dielectric Characteristics of Donor Doped Nonlead Ba(Cu1/3Nb2/3)O3 Perovskite Material Synthesized by Microwave-assisted Citrate-nitrate Sol-gel Route
Authors: Manavbasi Alp , LaCombe Jeffrey C
Published: April 2011

Nonlead perovskite type, Ba(Cu1/3Nb2/3−xWx)O3 (x = 0, 0.025), ferroelectric ceramic powders (BCN) were prepared by the microwave-assisted citrate-nitrate sol-gel technique. The gel was formed from a stable and homogeneous sol prepared by mixing stable solutions of barium- and copper-nitrate, tungsten citrate, and peroxo-citrato-niobium precursors. Microwave irradiation of the gel resulted in a dark, fluffy precursor material after auto-combustion. Calcination of the as-combusted samples produces a single phase with tetragonal splitting in X-Ray diffraction patterns. The crystallite size of the synthesized samples was found to be 41 nm. Particle morphology and the size of nanocrystalline powders were characterized by scanning electron microscopy and photon correlation spectroscopy, respectively. Electrical and dielectric properties of sintered samples were investigated by impedance spectroscopy. The isothermal ac measurements were performed from room temperature, up to 600 °C for W6+ doped and undoped BCN samples.
HfOx Thin Films for Resistive Memory Device by Use of Atomic Layer Deposition
Authors: Chen Pang Shiu , Lee Heng-Yuan , Wang Ching-Chiun , Tsai Ming-Jinn , Liu Kou-Chen
Published: April 2011

The materials properties and resistance switching characteristics of hafnium oxide-based binary oxide were investigated for next generation memory device application. A nonstoichometric hafnium oxide (HfOx) film with a mixture structure of monoclinic and tetragonal phase and some metallic Hf-Hf bonds on TiN/Si were prepared by atomic layer chemical vapor deposition (ALCVD). Resistance random access memory devices consisting of Pt/HfOx/TiN/Si with low power operation (< 0.4 mW) and reset current (< 100 mA) were fabricated. The resistance ratio of high resistance state to low resistance state maintains 100∼1000 and after 1000 cycles of repetitively switching. A 1-nm-thick Al2O3 film in the interface between top electrode and HfOx films, the Pt/Al2O3/HfOx/TiN/Si memory devices were found that soft-error of set and reset process often occurred. Interface states in the anode side play an important role in maintaining a stable resistive switching for HfOx-based memory devices.
Preparation of Ge2Sb2Te5 Thin Film for Phase Change Random Access Memory by Magnetron Sputtering on Small Hole Patterns
Authors: Kikuchi Shin , Nishioka Yutaka , Kimura Isao , Jimbo Takehito , Ueda Masahisa , Kokaze Yutaka , Suu Koukou
Published: April 2011

Phase Change Random Access Memory [PRAM] is one of the candidates for next generation memory due to its non-volatility, high speed, high density and compatibility with Si-based semiconductor process. Ge2Sb2Te5 [GST] thin film, an active layer in this device, is utilized because it has the well-known property of rapid crystallization without phase separation in erasable compact discs industry.

In order to integrate PRAM to beyond 512Mbit, a high writing current and degradation of cell transition at small cell size become a problem. To resolve these problem, Confined Cell structure PRAM was suggested. However, it was difficult to fill GST layer in a small hole with a conventional sputtering tool because a big overhang occurred.

In this work, we prepared GST films on the small hole patterned wafer by a new concept sputtering tool which designed developed a new concept sputtering tool. The structure of GST film was observed with cross section SEM and the film composition was measured with XRF.

It was observed an overhang was suppressed and a GST film was filled in a small hole with a new concept tool. In addition, the uniformity of the GST film composition was good at less than 1% in 200mm φ substrate.
The effect of Porosity of Metal Zinc Films on the Formation of ZnO Prepared by Thermal Oxidation
Authors: Chao Liang-chiun , Liau Chung-chi
Published: April 2011

ZnO thin films have been prepared by thermal oxidation of metal zinc films with different porosity. High and low porosity metal zinc films are prepared by DC magnetron sputtering and capillaritron ion beam sputtering, respectively. Near bandgap UV emission of ZnO thin films prepared from thermal oxidation of the low porosity film exhibit a maximum PL intensity after thermal oxidation at 410°C, while ZnO films prepared by thermal oxidation of the high porosity films exhibit a maximum PL intensity at oxidation temperature of 900°C. SEM micrographs indicate that ZnO prepared by thermal oxidation of low porosity films have a smooth surface morphology after thermal oxidation at 410°C, while ZnO prepared by thermal oxidation of high porosity zinc films exhibit a grain size of ∼ 800 nm after thermal oxidation at 1000°C.
Cu-doped ZnSe Film with Stoichiometric Composition Deposited at Room Temperature using Compound Sources
Authors: Orita Masahiro , Narushima Takashi , Yanagita Hiroaki
Published: April 2011

Stoichiometric Cu-doped ZnSe crystalline films were prepared on glass substrates from ZnSe and Cu2Se powders using the evaporation method without intentional heating. Post-annealing treatment at 400°C in a vacuum improved the crystallinity, and no secondary phase was observed using X-ray diffraction for a film with a Cu concentration of Cu/(Zn + Cu) = 0.10, which had a conductivity of 28 Scm-1 and good transparency at green and red wavelengths. The thermal probe test indicated p-type carrier polarity, and the effects of annealing were confirmed by irradiating the as-deposited films with a YAG laser (ë = 355 nm). Possibility of producing transparent p-type conducting films on polymer substrates is demonstrated.
Characterization of CdS/CdTe Solar Cells Fabricated by Different Processes
Authors: Tamara Potlog , Khrypunov G. , Kaelin M. , Zogg H. , Tiwari A. N.
Published: April 2011

This paper analyses the photovoltaic parameters of the most promising CdS/CdTe solar cells for large application prepared by close space sublimation (CSS) and high vacuum evaporation (HVE). CdS/CdTe solar cells that have an efficiency of~10 % have been studied by current-voltage, capacitance-voltage and quantum efficiency measurements. The current-voltage characteristics show that the addition of small amounts of Cu or Te to back contacts by thermal evaporation improves contact properties by p+-doping the CdTe surface and creating a pseudo-ohmic contact. The cell deposited by CSS seriously suffers in FF compared to the cells prepared by HVE. For both types of the cells above mentioned measurements reveal that the efficiency of CdS/CdTe solar cells fabricated by CSS is limited by a light-dependent shunt resistance and by a high series resistance, but concerning of the cells fabricated by HVE - by the formation of a thick layer of CdS1-xTex at the interface.
Polarized Luminescence of Defects in CuGaSe2
Authors: Siebentritt Susanne , Augustin Sven , Papathanasiou Niklas , Hebert Damon , Rockett Angus , Bläsing Jürgen , Lux-Steiner Martha Ch
Published: April 2011

The linear polarisation of luminescence light allows conclusions on the symmetry of defects in semiconductors with non-cubic symmetry, like chalcopyrites, for which three shallow acceptors have been identified by photoluminescence. The polarisation dependent photoluminescence allows to determine the symmetry of the defects relative to the c-axis of the crystal. A simple geometrical model implies that chalcogen sites show a predominant direction perpendicular to the c-axis, while metal sites show a predominant direction parallel to the c-axis. Since all three shallow acceptors show polarization parallel to the c-axis, it can be concluded that they are situated on a metal site
Characterization of Local Electrical Property of Coincidence Site Lattice Boundary in Location-controlled Silicon Islands by Scanning Probe Microscopy
Authors: Matsuki Nobuyuki , Ishihara R. , Baiano A. , Hiroshima Y. , Inoue S. , Beenakker C.I.M.
Published: April 2011

Local electrical property of coincidence site lattice boundaries (CSLBs) in location-controlled silicon islands, which are fabricated using micro-Czochralski process (grain filter), was characterized by scanning spreading resistance microscopy (SSRM) and scanning spreading resistance microscopy (SCM). Some CSLBs found in a silicon island are analyzed as Sigma 3 and Sigma 9 by electron back scattering diffraction pattern. These CSLBs are determined as {111}Sigma 3 and {221}Sigma 9 by referring to previous observation results made by transmission electron microscopy. {111}Sigma3 CSLBs shows no activity for SCM or SSRM; this is consistent with previous prediction that {111}Sigma 3 CSLB is not electrical active. We verified a capability of SCM and SSRM for characterizing local electrical property of coincidence site lattice boundary in silicon.
Structural Analysis in Low-V-defect Blue and Green GaInN/GaN Light Emitting Diodes
Authors: Zhu Mingwei , Detchprohm Theeradetch , Xia Yong , Zhao Wei , Li Yufeng , Senawiratne Jayantha , You Shi , Liu Lianghong , Preble Edward A. , Hanser Drew , Wetzel Christian
Published: April 2011

In this study, we characterized the structural defects in blue and green GaInN/GaN LEDs grown on c-plane bulk GaN and sapphire substrates. Low density large V-defects with diameters around 600 nm were found in the blue LEDs on bulk GaN. They were initiated by edge-type threading dislocations (TDs) around the homoepitaxial growth interface. On the other hand, a high density 7×109 cm−2 of smaller V-defects with sidewalls on {1101} facets was observed in the active region of green LEDs on sapphire. Their diameter ranges from 150 to 200 nm. Misfit dislocations (MDs) generated in the quantum wells are found to initiate these V-defects. With optimizing the epitaxial growth conditions, the generation of MDs and their smaller V-defects was largely suppressed. As a result, the light output power improved by one order of magnitude. For green LEDs on bulk GaN, another unique type of defect was found in the active region: an inclined dislocation pair (IDP). In it a pair of dislocations propagate at a tilt angle of 18 to 23° from the [0001] growth direction towards <1100>. This defect seems to be a path of strain relief in the high indium composition quantum wells.
Mn- and Fe- doped GaN for spintronic applications
Authors: Malguth Enno , Hoffmann Axel , Werner Stefan , Kane Matthew H. , Ferguson Ian T.
Published: April 2011

In the context of ferromagnetic spin-coupling in dilute magnetic semiconductors, we present optical investigations on Mg co-doped GaMnN and Fe doped GaN. A complex luminescence feature occurring in Mg co-doped GaMnN around 1 eV was previously attributed to the internal 4T2(F)—4T1(F) transition of Mn4+ involved in different complexes. Selective excitation studies indicate the presence of at least three different complexes. Photoluminescence excitation spectra suggest that the internal Mn3+ transition may represent an excitation mechanism. Magneto photoluminescence spectra indicate equal g values for the ground and excited state. Low temperature infrared absorption spectra of Fe doped GaN allow to unambiguously establish the electronic structure of the Fe2+ center in GaN. Our results suggest that the Fe2+(5T2) state is stabilized against Jahn-Teller coupling by the reduced site-symmetry of the hexagonal lattice.
Two-Dimensional Growth Mode and Reduction of Dislocation Density in Nitride Layers
Authors: Pakula Krzysztof , Baranowski Jacek M. , Borysiuk Jolanta
Published: April 2011

Heteroepitaxial two-dimensional (2D) and three-dimensional (3D) MOVPE growth of nitride layers on sapphire substrates using low temperature (LT) AlN nucleation layer are discussed. It is shown by Atomic Force Microscopy and Transmission Electron Microscopy that the 2D or 3D growth mode of successive AlGaN layers depends predominantly on the growth conditions of the underneath LT AlN nucleation layer.

Modifications of growth conditions of LT AlN nucleation layer in respect of the growth in the conventional way, leads to a drastic change in properties of the successively grown at high temperature AlGaN layer. Main modification is connected with a drastic reduction of the growth rate of LT AlN nucleation layer at higher rector pressure. In this case the growth at high temperature starts evenly on the whole surface, retaining atomic flatness, and occurs in the 2D mode. Therefore, it is possible to grow even a very thin, continuous AlGaN layers directly on top of LT nucleation layer.

The 2D growth mode leads to significant change in extended defect distribution. Edge dislocation density being close to 1010 cm−2, results in the effective relaxation of the internal stress. On the other hand mix dislocations density are close to 108 cm−2. All observed mix dislocations occur in pairs with dislocations with opposite sign. This suggests that all mix dislocations originate from dislocation half-loops. Both types of dislocations, edge and half loops can be effectively reduce in-situ, during the growth using annealing in the presence of silane. This process and precise control of the growth conditions leads to decreasing of mix dislocations density to 2·106 cm−2 and edge dislocations density to 5·108 cm−2.

The newly developed two-dimensional growth mode of nitride layer opens up a new way to reduce strain, decrease density of dislocations and improvement of crystallographic properties.
Phase Transitions in Silicon-Carbon-Nitride Compounds
Authors: Kroll Peter , Gracia Jose , Riedel Ralf
Published: April 2011

The crystal structures of α-Si(NCN)2 and Si2N2(NCN) undergo phase transformations upon compression. A new modification of HP-Si(NCN)2 exhibits all Si atoms in octahedral coordination to N and may be achievable below 30 GPa. In Si2N2(NCN) we find partial increase of coordination for Si, C, and N atoms at about 60 GPa. In both cases, the carbodiimide moiety is the source for the internal reaction that lead to compactification of the structure at elevated pressures. We present 29Si NMR chemical shifts that may help to identify the new coordination environments.
Nitridoaluminosilicate CaAlSiN3 and its Derivatives - Theory and Experiment
Authors: Mikami Masayoshi , Watanabe Hiromu , Uheda Kyota , Kijima Naoto
Published: April 2011

Nitridoaluminosilicate MAlSiN3(M: alkaline-earth element) and its derivatives have attracted more and more attention owing to the fact that the material doped with rare-earth element has intense body color and exhibit efficient luminescence under InGaN diode irradiation. In particular, red phosphor, Eu-doped CaAlSiN3 (CASN), has good thermal property of luminescence and sufficient chemical durability for white LED use. Still, for the lineup of various kinds of white color, it is hoped to tune the red luminescence with other physical/chemical properties kept as possible. Thus the derivatives with different chemical compositions have been intensively explored so far. For the feasibility of such chemical composition change, it is necessary to understand its atomic/electronic structure of the unique crystal, which is a distorted AlN-based wurtzite superstructure (Cmc21, No.36) with Al and Si disordered on 8b site and Ca occupying 4a site. Recently, we have performed first-principles band calculation of CASN and clarified the origin of the Al/Si disorder configuration as well as the feasibility of the virtual crystal approximation of heterovalent cations (Al/Si) for the reproducibility of atomic/electronic structure of CASN.[1] As a natural extension of this study, we have investigated some CASN-derivatives to confirm/predict the crystal structure. The VCA allows us to model the superstructure with various chemical compositions quite easily. In this work, we will present two examples of solid-solution, (Ca,Sr)AlSiN3 and CaAlSiN3-Si2N2O. The agreement between experiment and theory appears quite satisfactory. It is emphasized that the crystal structure of SrAlSiN3 has been successfully predicted by first-principles calculation prior to experimental result. The collaboration of experiment and theory promises us ‘gcrystal-engineering’ to develop new nitrides/oxynitrides effectively and efficiently.
The Reduction Welding Technique Used in Pre-Columbian Times: Evidences from a Silver Ring from Incallajta, Bolivia, Studied by Microscopy, SEM-EDX and PIXE
Authors: Montes Luis Torres , Ruvalcaba Jose Luis , Mendoza Anaya Demetrio , Muñoz Collazo Maria de los Angeles , Franco Velázquez Francisca , Sandoval Pérez Francisco
Published: April 2011

A pre-Columbian silver ring from Incallajta, Bolivia, recovered from an archaeological excavation is composed of a thin sheet of silver bent to form the ring. Two small wires in the shape of the infinity sign are joined to the surface of the ring. Four green stone beads were laid inside the four cavities formed by the wires. Energy dispersive spectroscopy (EDX) and Particle Induced X-rays Emission (PIXE) analyses of the beads proved that they were turquoise. Examination with a stereoscopic binocular microscope indicated that the two wires could have been soldered to the ring by reduction welding, because copper corrosion products were found in the interface of the welding, similar to those seen on two modern silver objects from Indonesia, decorated with granulation. Since reduction welding is a technique not reported before in pre-Columbian metallurgy, further analyses were carried out to prove that it was used here. Thus, the ring was analyzed with Scanning Electron Microscopy (SEM-EDX) and external beam PIXE, showing with certainty that the copper content in the area of the welding was higher than in any other part of the ring, with increasing copper amounts towards the center of the weld.
Trace Element Indicators of Fabrication Technology for Coral Red and Black Gloss Decoration on Greek Attic Pottery
Authors: Walton Marc , Trentelman Karen
Published: April 2011

Laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) was used to study the trace element chemistry of coral red and black gloss slip decoration on Greek Attic pottery (6th century BC). The distribution of trace elements in the body fabric and glaze slips were found to be correlated suggesting the raw materials came from a single source. Furthermore, the so-called high calcium and magnesium (HCM) coral red was found to be a less refined material than black gloss, with trace element characteristics suggestive of a carbonate phase in the raw material. This carbonate component may have imparted refractory properties to the HCM coral red slip material during the three-stage oxidative-reductive-oxidative firing used to produce Attic pottery, allowing it to remain porous and re-oxidize during the final firing step, thus creating its final red color. The so-called low calcium and magnesium (LCM) coral red, on the other hand, was found to be more refined than the HCM coral red slip which suggests that two separate firings would have been needed to produce the red color of this material.
A Ceramic Plaque Representing a Part of the Moses Panel by Lorenzo Ghiberti in the East Baptistery Doors (Florence, Italy)
Authors: Vandiver Pamela B.
Published: April 2011

A ceramic plaque was studied that depicts the figurative part of the lower half of the Moses Panel from the gilt bronze doors that Lorenzo Ghiberti and his workshop installed on the east side of the San Giovanni Baptistery in Florence, Italy. The doors were completed in 1452, and thermoluminescence dating of two areas of the ceramic relief panel gave a broad, but consistent fifteenth century date. No differences were found in the composition, microstructure or phase assemblage of the two stylistically distinct parts of the ceramic panel. Microscopy and radiography were used to reconstruct the forming methods and sequence of steps in manufacture and restoration.
Novel Self-Complimentary Tricyclic Heterocycles: Expanding the Chemistry of Self-Assembled Rosette Nanotubes
Authors: Borzsonyi Gabor , Myles Andrew J. , Johnson Ross , Cho Jae-Young , Yamazaki Takeshi , Kovalenko Andriy , Fenniri Hicham
Published: April 2011

In an effort to increase the internal and external diameter of the RNT's, tricyclic GΛC base derivatives (XGΛC) have been synthesized and characterized. Hierchichal self-assembly results in formation of RNT's with an increased diameter, as evidenced by AFM and TEM measurements. Progress on the derivitization and characterization of the XGΛC RNT's will be presented.
A Tight-Binding Hamiltonian for Band Structure and Carrier Transport in Graphene Nanoribbons
Authors: Finkenstadt Daniel , Pennington Gary , Mehl Michael J
Published: April 2011

To understand nanoribbons of graphene, we developed an ab initio parametrized fit to Carbon and Hydrogen chemical data, out to arbitrary neighbor interactions, including relaxations. Our computed band structure confirms the well-known three-family behavior of armchair bangaps but also predicts a similar familial behavior for conductance in nanoribbon transistors. The Boltzmann carrier transport simulations from calculated phonon spectra show, over a range of temperatures, the familial conductance behavior. Both the peak field-effect mobility and the "on" conductance increase with ribbon width, the later being proportional to the width and inversely proportional to the lattice temperature. We will also discuss phonon-limited scattering of charge carriers in graphene.
Metal-Semiconductor-Metal (MSM) Photodetectors Based on Single-walled Carbon Nanotube Film-GaAs Schottky Contacts
Authors: Johnson Jason L. , Behnam Ashkan , Choi Yongho , Noriega Leila , Ertosun Gunhan , Wu Zhuangchun , Rinzler Andrew G. , Kapur Pawan , Saraswat Krishna C. , Ural Ant
Published: April 2011

We experimentally study the dark and photocurrent in metal-semiconductor-metal (MSM) photodetectors based on single-walled carbon nanotube film Schottky contacts on GaAs. We find that above ∼260°K, thermionic emission of electrons with a barrier height of ∼0.54 eV is the dominant dark current transport mechanism. Furthermore, MSM devices with CNT film electrodes exhibit a higher photocurrent-to-dark current ratio while maintaining a comparable responsivity relative to control devices. This work demonstrates that nanotube films can be integrated as Schottky electrodes in conventional semiconductor optoelectronic devices.
Integrated GaN/AlGaN/GaN HEMTs with Preciously Controlled Resistance on Silicon Substrate Fabricated by Ion Implantation
Authors: Nomoto Kazuki , Ohsawa Tomo , Satoh Masataka , Nakamura Tohru
Published: April 2011

Multiple ion-implanted GaN/AlGaN/GaN high electron-mobility transistors (HEMTs) and preciously controlled ion-implanted resistors integrated on silicon substrate are reported. Using ion implantation into source/drain (S/D) regions, the performances were significantly improved. On-resistance reduced from 10.3 to 3.5 Ω•mm. Saturation drain current and maximum transconductance increased from 390 to 650 mA/mm and from 130 to 230 mS/mm. Measured transfer curve shows that I/O gain of 4.5 can be obtained at Vdd = 10 V.
The Influence of Growth Temperature on Oxygen Concentration in GaN Buffer Layer
Authors: Dumiszewska Ewa , Strupinski Wlodek , Caban Piotr , Wesolowski Marek , Lenkiewicz Dariusz , Jakiela Rafal , Pagowska Karolina , Turos Andrzej , Zdunek Krzysztof
Published: April 2011

The influence of growth temperature on oxygen incorporation into GaN epitaxial layers was studied. GaN layers deposited at low temperatures were characterized by much higher oxygen concentration than those deposited at high temperature typically used for epitaxial growth. GaN buffer layers (HT GaN) about 1 μm thick were deposited on GaN nucleation layers (NL) with various thicknesses. The influence of NL thickness on crystalline quality and oxygen concentration of HT GaN layers were studied using RBS and SIMS. With increasing thickness of NL the crystalline quality of GaN buffer layers deteriorates and the oxygen concentration increases. It was observed that oxygen atoms incorporated at low temperature in NL diffuse into GaN buffer layer during high temperature growth as a consequence GaN NL is the source for unintentional oxygen doping.
Imaging and Elemental Analysis of Polymer/Fullerene Nanocomposite Memory Devices
Authors: Laiho Ari , Baral Jayanta K. , Majumdar Himadri S. , Tobjörk Daniel , Ruokolainen Janne , Österbacka Ronald , Ikkala Olli
Published: April 2011

In this report we study the morphology and chemical composition of a nanocomposite memory device where the active device layer is sandwiched between two aluminum electrodes and consists of a nanocomposite of polystyrene (PS) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The morphology of the active layer is imaged both in plan-view and cross-sectional view by using transmission electron microscopy (TEM). We introduce two techniques to prepare the cross-sections from the active layer, namely, a conventional technique based on microtoming and secondly nanostructural processing with focused ion beam (FIB). Based on the morphology studies we deduce that within the used concentrations the PCBM forms spherical nanoscale clusters within the continuous PS matrix. The chemical composition of the device is determined by using X-ray photoelectron spectroscopy (XPS) and it shows that the thermal evaporation of the aluminum electrodes does not lead to observable inclusion of the aluminum into the active material layer.