bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Spectroellipsometric Characterization of Y2O3-stabilized ZrO2-Au Nanocomposite Films for Smart Sensor Applications
Authors: Sirinakis George , Sun Richard , Siddique Rezina , Efstathiadis Harry , Carpenter Michael A. , Kaloyeros Alain E.
Published: April 2011

Noble metal nanoparticles exhibit significant potential in all-optical, smart-sensing applications due to their unique optical properties. In particular, gold (Au) nanoparticles exhibit a strong surface plasmon resonance (SPR) band, the spectral position and shape of which depends on the size, shape, and density of the nanoparticles and the physical and chemical properties of surrounding environment. Embedding the nanoparticles in an yttria-stabilized zirconia (YSZ) matrix is believed to expand their range of operation to temperatures above 500 °C. YSZ is a material that has been proven suitable for optical applications due to its high refractive index, low absorption coefficient and high transparency in the visible and infrared regions. Thus, its use as a base platform for nanocomposite thin films is expected to provide significant benefits in the development of harsh environment multifunctional sensors.

In this work YSZ-Au nanocomposite films were synthesized from a YSZ and a Au target by the radio frequency magnetron co-sputtering technique in combination with a post-deposition annealing treatment in an argon atmosphere, with the annealing temperature being varied from 500–1000 °C in steps of 100 °C. The microstructure and the optical properties of the resulting films were characterized by x-ray diffraction spectroscopy, scanning electron microscopy and spectroscopic ellipsometry. Results on the effect of the Au particle size on the real and the imaginary part of the refractive index of the nanostructured composites are presented. Future smart sensor systems utilizing these multifunctional material sets for harsh environment sensing applications will likewise be outlined.
AC Loss Modeling in Ba0.5Sr0.5TiO3 Using Dielectric Relaxation
Authors: Pervez Nadia K. , Lu Jiwei , Stemmer Susanne , York Robert A.
Published: April 2011

In universal relaxation, a material's complex dielectric susceptibility follows a fractional power law f1-n where 0 < n < 1 over multiple decades of frequency. In a variety of materials, including Ba0.5Sr0.5Ti03, dielectric relaxation has been observed to follow this universal relaxation model with values of n close to 1. In this work we have shown that the universal relaxation model can be used to calculate dielectric loss even when n is very close to 1. Our calculated Q-factors agree with measured values at 1 MHz; this agreement suggests that this technique may be used for higher frequencies where network analyzer measurements and electrode parasitics complicate Q-factor determination.
RF Magnetron Sputtered Ba0.96Ca0.04Ti0.84Zr0.16O3 Thin Films for High Frequency Applications
Authors: Mahmud Ali , Kalkur T. S. , Cramer N.
Published: April 2011

Perovskite ferroelectric thin films in the paraelectric state exhibit outstanding dielectric properties, even at high frequencies (>1 GHz). The tunable dielectric constant of ferroelectric thin films can be used to design frequency and phase agile components. High dielectric constant thin film ferroelectric materials in the paraelectric state have received enormous attention due to their feasibility in applications such as decoupling capacitors and tunable microwave capacitors; the latter application has been fueled by the recent explosion in wireless and satellite communications. This paper reportsBa0.96Ca 0.04Ti0.84Zr0.16O3 (BCTZ) thin films that were deposited on Pt electrodes using radio frequency magnetron sputtering at a low (450 °C) substrate temperature. Sputtered thin film BCTZ at low substrate temperature is compatible with conventional integrated circuit technology. The structural characterization of the deposited films was performed by x-ray diffraction. The electrical characterization of the films was achieved by capacitance-voltage, current-voltage, and S-parameter (via vector network analyzer) measurements. In addition, the effect of post annealing on the deposited films was investigated. A detailed understanding of both their processing and material properties is discussed for successful implementation in high frequency applications.
An Application of a Low-Loss MOD-Made BST Film Developed Especially with PLD Initial Nucleation Layer to a 20 GHz Tunable Phase Shifter
Authors: Noda Minoru , Popovici Daniel , Okuyama Masanori , Sasaki Yoshinobu , Komaru Makio
Published: April 2011

Barium Strontium Titanate (BST) thin films have been deposited on (100)-oriented MgO substrate by combining preparation of initial layer by Pulsed Laser Deposition and main layer by Metal-Organic-Decomposition method. Films with an initial layer of 20, 30 and 40 nm thickness and final thickness of 400, 650 and 800 nm have been obtained. Physical and dielectric properties of the BST thin films have been characterized from the viewpoint of frequency-agile micro and millimeter wave circuit applications. The results reveal that Ba0.6Sr0.4TiO3 thin films have a good crystallinity with characteristic orientation that is affected by the deposition conditions of the initial layer. Interdigital capacitor with a gap of 10 μm has been characterized and the dielectric loss and tunability are as low as 0.002 to 0.004 and 12%, respectively, at frequency of 1 MHz for the applied voltage from -/+40V to +/-40V. At microwave frequencies, classical coplanar waveguide lines formed on BST/(100)MgO were investigated. A differential phase shift of 18 degree was obtained at 20 GHz with insertion loss of about −2 dB at 60 V for Au/Cr interconnection. Finally, a 3-stage LC-ladder-type phase shifter with variable capacitors of BST thin film has been fabricated considering the experimental results obtained for the coplanar waveguide lines and a maximum phase shift of 40 degrees is obtained at 20 GHz at 60 V.
Integrating Ba1-xSrxTiO3 Thin Films with Large Area, Affordable, Industry Standard Substrates for Microwave Applications
Authors: Nothwanga W. D. , Cole M. W. , Joshi P. C. , Hirsch S. , Ngo E. , Hubbard C. , Demaree J. D.
Published: April 2011

The US Army is actively pursuing technologies to enable transformation goals of a lighter, faster, more potent force via affordable, electronically scanned phased array antennas (ESA's) that will provide the means for achieving a high data rate with beyond-line-of-sight, mobile communications. In order to transition this technology to Army applications, it is important that the cost of each device be decreased from current technology. Traditionally, paraelectric, active thin films of magnesium doped barium strontium titanate, have been deposited on expensive ceramic (MgO, LaAlO3, SrTiO3, Al2O3) substrates, and compositionally designed for tunable microwave applications. By integrating an active, thin film material with a large area, low cost, microwave friendly substrate, the cost could be significantly reduced. While Si is not a suitable substrate for microwave applications, a low cost, microwave friendly, buffer layer on silicon would be.

A high performance Ta2O5 thin film, passive, buffer layer on Si substrates has been successfully designed, fabricated, characterized, and optimized via metalorganic solution decomposition technique. The optimized Ta2O5 based thin film exhibited suitable microwave material properties, including an enhanced dielectric constant (εr = 45.6), low dielectric loss (tan δ=0.006), low leakage current, high film resistivity (ρ=1012 Ω-cm at E=1 MV/cm), excellent temperature stability (temperature coefficient of capacitance of 52 ppm/°C), and outstanding bias stability of capacitance (∼1.41% at 1 MV/cm). The permittivity and dissipation factor, also of extreme importance, exhibited minimal dielectric dispersion with frequency. The dielectric passive buffer layer film was typified by a uniform dense microstructure with minimal defects, and a smooth, nano-scale fine grain, crack and pinhole free surface morphology. At elevated processing temperature, there was negligible elemental interdiffusion at the interface between the substrate and buffer layer as verified by Rutherford Backscatter Spectroscopy and Auger Spectroscopy, ensuring long-term reliability of the heterostructure.

By developing a passive, thin film material that is microwave friendly, we have demonstrated the direct integration of paraelectric active thin films with silicon substrates. This should allow phase shifter materials technology to be implemented across a wide spectrum of Army and commercial applications, specifically, affordable, mobile phased array antenna systems for a variety of DoD applications.
Y-Doping Effects on the Dielectric Behavior of RF-Sputtered BST Thin Films
Authors: Wang Ruey-Ven , McIntyre Paul C. , Baniecki John D. , Nomura Kenji , Shioga Takeshi , Kurihara Kazuaki
Published: April 2011

High dielectric constant, perovskite-structure materials, such as barium strontium titanate (BST), have been widely investigated for use in GHz LSI decoupling capacitor applications. In addition to modifying deposition process parameters, such as increasing deposition temperature, doping may be a viable way to increase permittivity and tunability in BST thin films without increasing the thermal budget. In this research, the effects of Y dopants on the dielectric behavior of RF-sputtered BST thin films have been systematically investigated. The BST thin films were deposited using ceramic targets with different compositions of yttrium oxide dopant. With Y-doping concentration of ∼ 1.3 at.%, the permittivity at around zero electrical fields can be increased by more than 70% compared to nominally undoped BST thin films produced under the same deposition conditions. Based on x-ray diffraction strain analysis and inductively-coupled plasma composition measurements, the correlations among the dopant composition, BST film elastic strain and dielectric behavior have been systematically studied.
Improvement of Adhesion and Microwave Transmission Characteristics of Indium Bump by Silver Coating for Low Temperature Flip-Chip Applications
Authors: Chu Kun-Mo , Choi Jung-Hwan , Lee Jung-Sub , Cho Han Seo , Park Seong-Ook , Park Hyo-Hoon , Jeon Duk Young
Published: April 2011

We have conducted low-temperature flip-chip bonding for both optical interconnect and microwave applications. Flip-chip bonding of vertical-cavity surface-emitting laser (VCSEL) arrays was performed on a fused silica substrate that provides propagation paths of laser beams and also supports a polymeric waveguide. To avoid thermal damage of the polymeric waveguide during the flip-chip bonding, indium bumps were used and the bonding condition of the flip-chip was determined as a heating temperature of 150 °C and a pressure of 500 gf. Experimentally, a thin silver (Ag) layer coated on the indium bump was very effective to enhance the adhesion strength between the indium bump and the VCSEL chip pads. In addition, the microwave characteristic of coplanar waveguide (CPW) package was slightly improved by the Ag coating.
Embedding Ceramic Thick-Film Capacitors into Printed Wiring Boards
Authors: Borland William , Doyle Marc , Dellis Lynne , Renovales Olga
Published: April 2011

Embedding passives into printed wiring boards have numerous advantages that show up in different segments of the market. For example, the ability to locate decoupling capacitors within a couple hundred microns of semiconductor I/Os greatly improves response time and signal integrity leading to product performance improvements. One crucial need, however, is high capacitance density. High capacitance density can only be readily achieved by ceramic technology. Therefore, the focus of this work has been the development of ceramic thick-film capacitor technology that can be used to bury high capacitance density components within an organic substrate. This allows high value decoupling capacitors to be buried for chip packaging or related applications in spaces available within any layer of the substrate.

The dielectric paste is based on doped barium titanate composition and works together with a cofired copper electrode paste. The capacitor system is designed to be screen printed on copper foil in the locations desired in the circuit and fired in nitrogen at 900°C to form the ceramic components. Following this, the foil is laminated, component face down, to the organic laminate using standard prepreg and the inner layer etched to reveal the components in an organic matrix. The system has a dielectric constant of approximately 3000 and achieves a capacitance density of ∼1.5 nF/mm2. In the following sections, issues that we encountered when making embedded capacitors with this first generation system are presented.
Ion Track Enabled High Aspect Ratio Flexible PCB Via Technology
Authors: Lindeberg Mikael , Yousef Hanna , Öjefors Erik , Rydberg Anders , Hjort Klas
Published: April 2011

By combining ion track technology with ordinary low-resolution printed circuitboard lithography it is possible at low cost to create high aspect ratios via connectors, as solid plugs or consisting of bundles of sub-micron connector wires at a small total cross-section.

Ion track enabled microwave circuits in flexible printed circuit boards are suggested to be used in applications like inductors, ferromagnetic resonance microwave filters, circulators and magnetoresistive sensors. In this paper we demonstrate this technology with integrated printed circuitboard devices in two different flexible polyimide-based foils (Espandex and Kapton HN), using the ultra-high-density vias and the sub-micron wires.
Observation of Enhanced Faraday Effect in Garnet-Based Magnetophotonic Crystals
Authors: Fedyanin A. A. , Kobayashi D. , Nishimura K. , Uchida H. , Inoue M. , Aktsipetrov O. A.
Published: April 2011

The fabrication of one-dimensional magnetophotonic crystals (MPC) composed from Bi-substituted yttrium-iron-garnet films separated by the silicon oxide layers is presented. The enhancement of the Faraday rotation angle is observed at the spectral regions of the photonic band gap edges. The effective Faraday rotation achieves the values up to 1.5 degrees per micron at 1100-nm-wavelength.
Photonic Crystal Ridge Waveguides on Magnetic Garnet Films
Authors: Li R. , Huang X. , Levy M. , Yang H. C.
Published: April 2011

This paper discusses the fabrication and testing of on-chip photonic crystals in ferrite waveguides. Photonic bandgap engineering can produce Faraday rotators with highly enhanced polarization rotation for ultra-small integrated optical isolators. The main challenges to such devices are the elimination of linear birefringence and the fabrication of planar photonic bandgap nanostructures. These challenges are addressed in the present article. In particular, we demonstrate the presence of stopbands and resonant polarization response in single-defect magneto-optic photonic crystal ridge waveguides.
YIG Thin Film-Based Two-Dimensional Magnonic and Magneto-Photonic Crystals
Authors: Nikitov S.A. , Tsai C.S. , Gulyaev Yu.V. , Filimonov Yu.A. , Volkov A.I. , Vysotskii S.L. , Tailhades Ph.
Published: April 2011

A new type of photonic crystals entitled “magnonic crystals (MC)” that exhibit forbidden gaps in the microwave spectrum of magnetostatic spin waves (MSW) are reported. The topography of the MCs that consist of two-dimensional (2-D) etched holes periodic structure in yttrium iron garnet films was studied by atomic force and magnetic force magnetometry. The propagation characteristics of spin waves in such 2-D MCs was measured and analyzed.
Effective energy landscapes for mobile ions in solid electrolytes
Authors: Adams Stefan
Published: April 2011

Bond valence mismatch landscapes may serve as simple models of the effective energy landscapes for mobile ions in solid electrolytes. Thereby they provide a tool to identify the ion transport mechanism and allow to predict the activation energy of the ionic conduction. Accounting for the mass dependence of the conversion from the BV mismatch into an activation energy scale yields a correlation that holds for different types of mobile cations. While in most cases the analysis of bond valence mismatch landscapes is consistent with the ion transport mechanism derived from experimental or other computational evidence, the presumed prototype of trivalent cation conductors Sc2(WO4)3 is discussed as an example, where the BV analysis of transport pathways suggests that the interpretation of previous experimental investigations has to be reconsidered. Both bond valence calculations and molecular dynamics simulations suggests that the most probable mobile species in stoichiometric Sc2(WO4)3 is neither Sc3+ nor individual O2- but the complex divalent anion WO42-.
Structure and Electrochemical Performances of the Li1+x(Ni0.425Mn0.425Co0.15)1−xO2 Materials
Authors: Tran N. , Croguennec L. , Weill F. , Jordy C. , Biensan P. , Delmas C.
Published: April 2011

Layered Li1+x(Ni0.425Mn0.425Co0.15)1−xO2 materials (x = 0 and 0.12) have been prepared by a coprecipitation method. The substitution of × Li+ ions for × metal ions in the transition metal layers leads to an increase in the average transition metal oxidation state for charge compensation, which was found to be due to the oxidation of Ni2+ ions into Ni3+ ions. The refinement in the R-3m space group of the X-ray diffraction data has shown an increasing lamellar character for the structure of these materials, with increasing overlithiation. Electron diffraction has revealed the presence of a √3.ahex. × √3.ahex. superstructure due to a cationic ordering in the transition metal layers, those being packed with faults along the chex.-axis. From an electrochemical point of view, the reversible capacity in the 2–4.3V decreased with overlithiation, in agreement with a decreasing amount of exchangeable electrons.
Solution Synthesis and Electrochemical Properties of V2O5 Nanostructures
Authors: Takahashi Katsunori , Wang Ying , Lee Kyoungho , Cao Guozhong
Published: April 2011

We have prepared Ni-V2O5·nH2O core-shell nanocable arrays for Li+ intercalation applications. Ni-V2O5·nH2O nanocables were prepared via formation of Ni nanorod arrays through the template based electrochemical deposition, followed by coating of V2O5·nH2O on Ni nanorods through electrophoretic deposition. Transmission electron microscopy (TEM) micrograph clearly shows the Ni core was covered completely by a V2O5·nH2O shell. Electrochemical analysis demonstrates that in a current density of 1.6 A/g, the Li+ intercalation capacity of Ni-V2O5·nH2O nanocable array is approximately 10 times higher than that of single-crystal V2O5 nanorod array and 20 times higher than that of sol-gel-derived V2O5 film. Both energy density and power density of such nanocable-array electrodes are higher than the V2O5 film electrode by at least one order of magnitude. Such significant improvement in electrochemical performance is due to the large surface area and short diffusion path offered by the nanostructured V2O5·nH2O.
Oxide Ion Conduction in Oxygen Rich Doped Ba2In2O5+δBrownmillerite
Authors: Rolle Aurélie , Giridharan Nambi V. , Roussel Pascal , Abraham Francis , Vannier Rose-Noëlle
Published: April 2011

In order to stabilize the fast oxide ion conducting properties of the high temperature form of Ba2In2O5at lower temperature, oxygen rich doped Ba2In2O5+δbrownmillerite were prepared by partial substitution of Ba and In with higher valence cation. Vanadium, niobium, tantalum, molybdenum and tungsten were introduced on indium site and bismuth on barium site. Solid solutions were evidenced in all the cases. They were characterized by high temperature X-ray diffraction and impedance spectroscopy. A neutron diffraction study was carried out and allowed to extract preferential oxygen pathways in these materials.
Electrochemical and electrical properties of. Nb- and/or C-containing LiFePO4 composites
Authors: Delacourt C. , Wurm C. , Laffont L. , Sauvage F. , Leriche J.-B. , Bouchet R. , Morcrette M. , Tarascon J-M. , Masquelier C.
Published: April 2011

LiFePO4-based powders prepared through various synthesis conditions are presented. Depending on whether the precursors contain carbon or not, LiFePO4-based composites obtained contain significant amounts of carbon as well. We did not succeed in doping LiFePO4 with Nb and produced, instead, crystalline β-NbOPO4 and/or an amorphous (Nb, Fe, C, O, P) matrix around LiFePO4 particles. The total electrical conductivity is of ∼10−9 S.cm−1 at 25°C with an activation energy of ca. 0.65 eV for pure LiFePO4 and LiFePO4/β-NbOPO4 composite. C-containing LiFePO4 samples, including those that had been tentatively doped with Nb, are much more conductive (up to 1.6.10−1 S.cm−1) with an activation energy ΔE ∼ 0.08 eV.
The kinetic and thermodynamic analysis of Li+ in multi-walled carbon nanotubes
Authors: Lin Kezhi , Xu Yanhui , Wang Xiaolin
Published: April 2011

The multi-walled carbon nanotubes (MWNTs) prepared by CVD were used in electrochemical intercalation reaction with Li+. The results of the first several charge-discharge cycles showed that the reversible capacity of the MWNTs was larger than the theoretical capacity of graphitized carbon. The equivalent circuit of the Li+ intercalated into the MWNTs was simulated The diffusion coefficient calculated based on the results of the impedance was in the range between 1 ∼ 4×10−10 cm2s−1. The diffusion coefficient calculated based on the technique of the chronoamperometery was 3.5×10−10 cm2s−1. The diffusion coefficients of the Li+ reacted with MWNTs was in the range of that of the most carbon materials. Using EMF method the partial molar entropy (ΔSx) and partial molar enthalpy (ΔHx) of the Li+ intercalated into the MWNTs were calculated as a function of × in Lix C6 at different temperatures. The values of ΔSx were in the range of 150 ∼ 550 J mol-1K-1. The values of ΔHx at 35 °C were in the range of 40∼110 kJ mol−1. Both of the ΔSx and ΔHx were lower and the changes were smaller than the values of some other carbonaceous materials. By analyzing the results conclusion is obtained that Li+ exist in MWNTs with different types which include adsorption and intercalation types.
Preparation of La1.61GeO5-δ Based Oxide Ion Conducting Film by Pulsed Laser Deposition Method and its Application for SOFC
Authors: Ishihara Tatsumi , Yan Jingwang
Published: April 2011

La1.61GeO5 thin film was fabricated on porous NiO-Ce0.80Sm0.20O2-δ (SDC) substrates by pulsed laser deposition (PLD) under various deposition conditions and the deposition parameters were optimized for obtaining the dense La1.61GeO5-δ film for the electrolyte of SOFC. It has been found that the high substrate temperature and the low oxygen pressure in chamber are suitable for obtaining the dense La1.61GeO5-δ thin film on porous NiO-SDC anode substrate. Since the as-deposited film is amorphous state, post-anneal treatment is essential for obtaining the crystalline La1.61GeO5-δ film. Under the optimized deposition condition, a dense and La1.61GeO5-δ thin film with a thickness of 3 μm can be successfully obtained. The obtained La1.61GeO5-δ film exhibits the electromotive force, which is slightly smaller that that of the theoretical open circuit potential. The power generation property of the cell using the obtained La1.61GeO5-δ film was studied and it was found that the maximum output density of a SOFC single cell using a La1.61GeO5-δ thin film deposited on a porous NiO-SDC substrate reached to 1948.2 mW/cm2 at 1173 K and 424.4 mW/cm2 at 873 K.
Application of CuBr Ion Conductor Thin-Films for Ammonia Gas Detection
Authors: Lauque Pascal , Bendahan Marc , Seguin Jean Luc , Knauth Philippe
Published: April 2011

CuBr films are used to design an ammonia gas microsensor operating at ambient temperature, with high sensitivity and much improved selectivity in comparison with usual conductometric microsensors. The specific detection mechanism relies on adsorption of ammonia molecules and interactions with mobile Cu+ ions in the ionic conductor film. The CuBr films can be prepared by r.f. sputtering, but more simply and cost efficiently by chemical reaction of copper metal with bromine ions. Photolithographic techniques are applied to miniaturize the sensor.
Effect of Anodization Bath Chemistry on Photochemical Water Splitting Using Titania Nanotubes
Authors: Mor Gopal K. , Varghese Oomman K. , Paulose Maggie , Shankar Karthik , Grimes Craig A.
Published: April 2011

In this study highly-ordered titania nanotube arrays of variable wall-thickness and length are used to photocleave water under ultraviolet irradiation. We demonstrate that the wall thickness, and length, of the nanotubes can be controlled via anodization bath composition and temperature. The nanotube length and wall thickness are key parameters influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For 22 nm inner-pore diameter nanotube-arrays 6 μm in length, with 9 nm wall thickness, upon 320–400 nm illumination at an intensity of 100 mW/cm2, hydrogen gas was generated at the power-time normalized rate of 51 mL/hr•W at an overall conversion efficiency of 12.5%. To the best of our knowledge, this hydrogen generation rate is the highest reported for a titania-based photoelectrochemical cell.
Nanoporous Si – Organic Composite Photovoltaics
Authors: Levitsky I. A. , Euler W. B. , Tokranova N. , Xu B. , Castracane J.
Published: April 2011

We report novel composite photovoltaics fabricated from nanoporous Si filled with Copper Phthalocyanine (CuPC) and its derivatives, including discotic liquid crystal CuPC. Porous n-type Si (PSi) was prepared electrochemically (pore size 10–20 nm) and filled with CuPC solution by impregnation under pressure or spin casting (liquid crystal CuPC) onto a porous surface followed by heating to the temperature of the mesophase transition. For porous layer with the thickness more than 1500–2000 nm, the conversion efficiency was up to 3% under a tungsten lamp with solar filters (30 mW/cm2). The porous structure and pore filling were examined by SEM and XPS techniques. Photocurrent spectra of the CuPC-PSi cell demonstrate two bands that correspond to the absorbance of the protonated form of CuPC. A comparative analysis between CuPC and liquid crystal CuPC has been made and conclusions about possible mechanisms of charge transfer and transport are drawn. The solar cell optimization is discussed as well.
Polymer solar cells: screen-printing as a novel deposition technique
Authors: Aernouts Tom , Vanlaeke Peter , Poortmans Jef , Heremans Paul
Published: April 2011

Screen-printing is studied as deposition technique for conjugated material based layers. Photovoltaics based on the principle of bulk donor-acceptor heterojunction are tested using a blend of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1, 4-phenylene vinylene) (MEH-PPV) mixed with the C60-derivative (6, 6)-phenyl C61-butyric acid methyl ester (PCBM). First, different solution concentrations of the donor MEH-PPV material and of the blend are subjected to rheology measurements. Addition of the acceptor (PCBM) to a donor material based solution induces a decrease of the solution viscosity. However, the overall flow behaviour of the blend remains similar to that of the MEH-PPV based solution. Secondly, it is shown that specific printer settings have to be used to obtain active layers that are suitable for opto-electronic applications. Finally, devices with an overall energy conversion efficiency of 1.25% under standardized simulated solar illumination (AM1.5G; 100mW/cm2) have been obtained showing that screen-printing can be a suitable technique for the deposition of the active layer of polymer solar cells.
Controlling Organization in Photovoltaic Diodes from Discotic Liquid Crystals via Anode Surface Energy Alteration
Authors: Schmidtke Johanna P. , Müllen Klaus , Friend Richard H.
Published: April 2011

We report the control of molecular ordering of discotic liquid crystals in thin, blended films used in photovoltaic diodes. The external quantum efficiency (EQE%) of photovoltaic diodes incorporating a crystalline hexabenzocoronene (HBC) derivative is improved by lowering the surface energy of the transparent anode surface with a short alkyl chain. Upon increasing the length of the functionalizing group on the anode, we find that the relative efficiency of the HBC component in the blend improves. Evidence of changed film morphology is also presented.
Preparation of CuInGaSe2 Absorber Layer by Nanoparticles-Based Spray Deposition
Authors: Kim Ki-Hyun , Chun Young-Gab , Park Byung-Ok , Yoon Kyung-Hoon
Published: April 2011

CIGS nanoparticles for the CIGS absorber layer have been synthesized by low temperature colloidal routes. The CIGS absorber layers for solar cells have been prepared by spray deposition of CIGS nanoparticle precursors (∼20 nm) in glove box under inert atmosphere. An automatic air atomizing nozzle spray system with computer controlled X-Y step motor system was used to spray. The nanoparticle precursor CIGS film was deposited onto molybdenum-coated soda-lime glass substrates (2.5 cm × 5.0 cm) heated to 160°C. The film thickness in the range of 2 μm ± 0.3 μm was attained by spraying of 3 mM colloidal over an area of 12.5 cm2. The coalescence between particles was observed in the CIGS absorber layer under post-treatment of over 550 °C. This is related to the reactive sintering among the nanoparticles to reduce surface energy of the particles. The CuxSe thin film, formed on Mo film by evaporation, improved adhesion between CIGS and Mo layers and enhanced the coalescence of the particles in the CIGS layer. These are closely related to the fluxing of Cu2Se phase which has relatively low melting temperature. The CdS buffer layer was deposited on the CIGS/Mo/soda-lime glass substrate by chemical bath deposition. The CIGS nanoparticles-based absorber layers were characterized by using energy dispersive spectroscopy (EDS), x-ray diffraction (XRD) and high-resolution scanning electron microscopy (HRSEM).
Efficient Bulk Heterojunction Photovoltaic Cells using Sublimable Transition Metal Complex as Photosensitizers
Authors: Wong Hei Ling , Man Kitty Ka Yan , Chan Wai Kin , Kwong Chung Yin , Djurišić Aleksandra B.
Published: April 2011

Multilayer bulk heterojunction photovoltaic cells using chlorotricarbonyl rhenium (I) bis(phenylimino)acenaphthene (Re-DIAN) complex as photosensitizer were studied. The complex is sublimable, has lower band gap, good thermal stability and good processibility. It has broad absorption in UV-visible region. Therefore, Re-DIAN exhibits good photosensitising property for photovoltaic cells. Multilayer bulk heterojunction photovoltaic cells with simple structures were fabricated base on Re-DIAN complex. The active layer consists of a blend of Re-DIAN and fullerene that were co-deposited in the same layer by vacuum deposition. The photovoltaic properties of the devices were studied by irradiaton under AM1.5 simulated solar light. The effects of changing the co-deposition film thickness, amount of Re-DIAN photosensitizer, and hole transporting materials were studied.
Bath pH Dependence on the Structural and Optical Properties of Chemical Bath Deposited CdS Thin Films
Authors: Ketipearachchi Udaya S. , Lane David W. , Rogers Keith D. , Painter Jonathan D. , Cousins Michael A.
Published: April 2011

High quality CdS thin films made with ultrasonic agitation during chemical bath deposition were investigated. The change in band gap and variation of atomic stacking during the film growth was observed as a function of bath pH. The band gap of as-deposited thin films of CdS was found to be between 2.26 eV and 2.50 eV, the highest being observed when the pH was 9.0. The transition from cubic (β-CdS) to hexagonal (a-CdS) was observed with decreasing pH. The lattice parameters of CdCl2 treated CdS were found to be a = 0.414 nm and c = 0.672 nm. Calculations based on the Sherrer formula showed significant grain growth after annealing with CdCl2. No apparent effect of ultrasonication on crystalline structure of CdS was seen in this method, although ultrasonication was noted to produce films with a higher quality optical surface. A maximum bath temperature was fixed at 70°C in order to suppress the rate of homogeneous reaction and minimise the evaporation of ammonia from the chemical bath.
The Band Offsets of Isomeric Boron Carbide Overlayers
Authors: Caruso A. N. , Lunca-Popa P. , Losovyj Y. B. , Gunn A. S. , Brand J. I.
Published: April 2011

Semiconducting boron carbide overlayers, formed from the decomposition of orthocarborane and metacarborane have been studied by angle resolved photoemission. The incurrence of surface photovoltage and the photovoltaic process, from the photoemission experiment, reveal band offsets in the orthocarborane multilayer configurations that are invereted relative to single layer configurations. Defect induced gap states which trap charge at the heterostructure interface is used as one explanation of these results. The role of defects is also used to help illuminate why opposite semiconducting type materials are formed from the decomposition of isomer carborane molecules.
Synthesis and Characterization of Cux(In, Ga)ySez Nanoparticles by Colloidal Route
Authors: Kim Ki-Hyun , Chun Young-Gab , Park Byung-Ok , Yoon Kyung-Hoon
Published: April 2011

The quarternary CIGS nanoparticles for absorber layer of solar cells have been synthesized with various mole ratios by colloidal route. The CIGS nanoparticles were prepared by reacting CuI, InI3, GaI3 in pyridine with Na2Se in methanol at 0°C under inert atmosphere. For Cu0.9In0.8Ga0.3Se2 and Cu0.9In0.7Ga0.4Se2 stoichiometric ratios, tube-type nanofibers were obtained with the widths in the range of 20–50 nm and lengths of 0.1–3 μm from reaction at 0°C for 20 min. For Cu1.1In0.68Ga0.23Se1.91, and Cu0.9In0.68Ga0.23Se1.91 ratios, spherical nanoparticles were obtained from the same reaction condition. As compared to particles from Cu0.9In0.68Ga0.23Se1.91 ratio, more uniform and smaller nanoparticles with diameter in the range of 5–20 nm were obtained from the Cu1.1In0.68Ga0.23Se1.91 stoichiometric ratio. The morphology change of the CIGS particles seems to be closely related to the ratio of Cu/(In, Ga).
1MeV electron irradiation effects of GaAs/Si solar cells
Authors: Chandrasekaran N. , Soga T. , Inuzuka Y. , Imaizumi M. , Taguchi H. , Jimbo T.
Published: April 2011

The characteristics of 1 MeV electron irradiated GaAs solar cells grown on GaAs and Si substrates are studied under dark and AM 0 conditions. The short circuit currents (Isc) for GaAs/GaAs cell and GaAs/Si cell have been decreased at higher fluences. The degradation rate of Voc and Pmax for GaAs/Si is slower than that of GaAs/GaAs at the fluence 1×1016 cm−2. This is due to the high radiation resistance of saturation current. It has been due to slow generation of arsnic vacancies related defect (VAs) in the GaAs/Si solar cell, which is determined by photoluminescence analyses and deep level transient spectroscopy.
Scanning Tunneling Luminescence of Semiconductors
Authors: Romero M. J.
Published: April 2011

We review scanning tunneling luminescence (STL) – a photon emission spectroscopy based on scanning tunneling microscopy (STM) – and report on its application to photovoltaics. As part of this exploratory research, we have investigated CuInSe2 thin films, solar cells based on quantum dots, and dilute nitride compounds. STL is very attractive because it is capable of nanometer resolution, which is being demanded by the spectacular advancement of nanoscience and nanotechnology. In addition, STM offers both unipolar and bipolar excitation of the luminescence and, consequently, the transport and recombination of electrons and holes can be investigated independently.
Hydrogen Absorption and Desorption by Magnesium-Based Nano-Composite Materials
Authors: Kojima Yoshitsugu , Kawai Yasuaki , Haga Tetsuya
Published: April 2011

MgH2 was mechanically milled with nano-Ni (nano-Ni/Al2O3/C) and Ni catalysts (Ni), yielding Mg-based nano-composite materials. X-ray and TEM measurements revealed that nano-Ni particles, which are 6–20 nm size, were dispersed in the MgH2 matrix. The nano-composite material with nano-Ni/Al2O3/C showed excellent properties as compared to that with Ni, a ball-milled MgH2 and the mixture of MgH2 and nano-Ni/Al2O3/C in terms of the H2 desorption and absorption. The nano-composite material with nano-Ni/Al2O3/C desorbed H2 of 4.9–5.8 wt% at 423–473 K, while the mixture could not desorb H2 at the temperature. The H2 absorption capacity at 9 MPa and room temperature in 6 hr. increased from below 0.1 wt% for the mixture to 5.0 wt % for the nano-composite material, approaching a maximum of 6.5 wt% in 70 hr. The catalyst activity was improved with decreasing Ni size. The improved kinetics is indicated by the small activation barrier, the short diffusion path length and the high driving force.
NMR and X-ray Diffraction Studies of Phases in the Destabilized LiH-Si System
Authors: Bowman R. C. , Hwang S.-J. , Ahn C. C. , Vajo J. J.
Published: April 2011

Hydrogen absorption and desorption isotherms have been measured on ballmilled mixtures of LiH+Si powders to evaluate the thermodynamic parameters of these reversible reactions. The phase compositions at the various stages of reaction have been examined by Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) of the 7Li, 1H, and 29Si nuclei and powder x-ray diffraction (XRD). The initial mixtures of LiH and Si were found to convert into known Li-Si silicide intermetallics (i.e., Li12Si7, Li7Si3, and Li13Si4) as well as providing evidence for a previously unknown ternary Li-Si-H phase as hydrogen was first desorbed and then absorbed. While the absorption reactions are reversible over portions of the Li-Si-H composition range, incomplete recovery of the original LiH + Si phases was also observed under some test conditions.
Archaeological Copper Smelting at Itziparátzico, Michoacan, Mexico
Authors: Maldonado Blanca E. , Rehren Thilo , Howell Paul R.
Published: April 2011

Mesoamerican copper metallurgy emerged in West Mexico sometime between A.D. 600 and 800. Over a period of approximately 900 years a wide variety of artifacts, typically decorations and other valuable non-utilitarian goods, were produced. By A.D. 1450, the Tarascan kingdom in the state of Michoacan had become the most important center of pre-Hispanic metalworking. Metallurgy played a significant role in the structure of political and economic power in the Tarascan Empire. Metal adornments used as insignia of social status and public ritual became even more associated with political power. While metal was used for an array of goods, virtually nothing is known about the manufacture and the organization of production of this material. Archaeological research at the site of Itziparátzico, near the modern Tarascan community of Santa Clara del Cobre, has recently located potential production areas where concentrations of smelting slag were recorded.

The smelting of ores is almost invariably related to the formation of slags, which form from the various impurities introduced into the smelting process, such as gangue minerals, furnace wall material, and fuel ash. Slag analysis thus has the potential for revealing important information about metallurgical technology. Copper smelting slag recovered from the excavations at Itziparátzico has been analyzed for microstructure and compositional properties using light microscopy, x-ray fluorescence spectrometry (XRF), and scanning electron microscopy with energy-dispersive x-ray spectrometry (SEM/EDS). Preliminary results indicate a smelting technology that used sulfidic ores and highly efficient furnaces. While further archaeological investigations are required to precisely date these activities, this technological information is important for establishing the context and scale of production of copper at the site.
Quantitative and Nanoscale Surface Potential Tracking of Ionic and Organic Adsorbates at sub-Monolayer Coverage
Authors: Eng L. M. , Loppacher Ch. , Zerweck U.
Published: April 2011

We use an improved setup for deducing quantitative surface potential values by means of frequency modulated Kelvin-probe force microscopy (FM-KPFM). This method is sensitive to the electrostatic force gradient rather than the absolute force probed in KPFM so far, and therefore provides both a higher lateral resolution and quantitative values. Furthermore, FM-KPFM allows using cantilevers with high spring constants which even favors both the stability and increased topographic resolution. Here, we apply FM-KPFM to deduce interfacial electrical properties of the sub-monolayer coverage of three adsorbates on metal substrates: lithium chloride films, Copper-porphyrines, and C60 molecules.
A Near-Field Microwave Probe for Quantitative Characterization of Dielectric Thin Films
Authors: Talanov Vladimir V. , Moreland Robert L. , Scherz André , Ming Bin , Schwartz Andrew R.
Published: April 2011

We have developed a novel scanning near-field microwave probe capable of precise quantitative measurements of dielectric constant of thin dielectric films. The technique is noncontact and has a few-micron sampling spot-size. For dielectric films with k<7 and thickness down to 200 nm the probe provides precision and accuracy better than 1% and 5%, respectively. The probe is based on a balanced parallel-plate microwave transmission line operating at 4 GHz. Unlike the apertureless STM- or AFM-based schemes that have been previously employed, our “apertured” approach allows for truly quantitative measurements on a few-micron length scale with result that is insensitive to the material property outside this probing volume.

We will present quantitative measurements on a variety of so-called low-k dielectric films, which are of great interest to the semiconductor industry as replacements for SiO2 in interconnect wiring. When the probe is placed in close proximity to the film under test its fringe capacitance is governed by the sample permittivity, the tip geometry, and the tip-sample separation. We measure this capacitance with a resolution down to 30 zF using a microwave resonator. Extraction of the film dielectric constant is based on an original approach providing for removal of the substrate contribution. Bulk Si and a set of variable thickness thermal oxide films are employed to calibrate the probe. There is no need to know the absolute value of the tip-sample separation for either measurement or calibration procedures; this separation must only be kept nominally the same for both measurements, which is achieved by a virtually material independent shear-force distance control.
Development of an Ultra-High Vacuum Scanning Nonlinear Dielectric Microscope and Near Atomic-Scale Observation of Ferroelectric Material Surfaces
Authors: Odagawa Hiroyuki , Cho Yasuo
Published: April 2011

This paper describes a newly developed ultra-high vacuum type scanning nonlinear dielectric microscope (UHV-SNDM) and the results from a ferroelectric LiTaO3 single crystal measured by the UHV-SNDM. In a cleaved (012) surface of LiTaO3 crystal, we can clearly observe a striped pattern with a period of about 0.3 nm and a granular pattern approximately corresponding to the sub-lattice period. From this image, we confirmed that the SNDM can be applied to lattice-level measurement in ferroelectric insulator materials.
High-Resolution Photochemical Reaction Using Triplet-Sensitizer Probes
Authors: Miki Hideki , Otomo Akira , Mashiko Shinro
Published: April 2011

We propose molecular-scale photochemical-reaction control using triplet-triplet (T-T) energy transfer from a donor molecule attached on a probe to an acceptor on an insulator surface. In this work, we studied the feasibility of photochemical reactions on a substrate surface using a triplet sensitizer probe. We observed an efficient T-T energy transfer from Michler's ketone on the substrate to an acceptor molecule, cinnamoyl group, on the other substrate facing it. Approximately a quarter of the cinnamoyl groups were dimerized by triplet sensitization. We used a cone-shaped dendron molecule to avoid sensitizer self-quenching caused by the triplet energy migration within the probe surface. We then confirmed efficient site separation of the cone's focal point by measuring the absorption and fluorescent properties of the rhodamine B attached to the focal point. The generation-three dendrons provide enough distance between the functional sites on the probe to reduce singlet energy transfer and it should control triplet energy migration.
Electronic Properties of Modified Surfaces Using Contact and Non-Contact Scanning Probe Microscopy Techniques and SECM.
Authors: Neufeld Aaron K , O'Mullane Anthony , Bond Alan M
Published: April 2011

Electrochemical experiments with tetracyanoquinodimethane (TCNQ) modified electrodes in contact with aqueous copper containing electrolytes leads to the incorporation and expulsion of copper ions. This process occurs concomitantly with nucleation and growth processes and significant crystal fragmentation to produce particles with dimensions of the order of 10's of nanometres. During reduction of TCNQ and intercalation of copper ions, different phases of the semiconducting compound CuTCNQ are formed.[1,2] The preparation of both conducting and insulating substrates coated with electroactive TCNQ and CuTCNQ particles of variable size have been made by dip and spin coating procedures. Results suggest that the phase and hence electronic properties of CuTCNQ is dependent on the size of particles that decorate the electrode surface. Combining atomic force microscope (AFM) based methods that interrogate the morphological and electronic properties of nanometre sized particles with use of a scanning electrochemical microscope (SECM) is a new advance in materials characterisation that has proved highly valuable in understanding the highly complex behaviour of these semi-conducting particles.
Apertureless head: a multipurpose tool really combining atomic force microscopy with powerful means for optical investigations.
Authors: Gavrilyuk Vasily V. , Saunin Serguey A. , Zhizhimontov Vladimir V. , Baukov Victor V.
Published: April 2011

An original instrument intended to integrate the advantages of scanning probe, near and far field optical microscopy is presented. The device named Apertureless Head was specially designed to be incorporated to Ntegra scanning probe laboratory, the powerful analytical instrumentation in the nanotechnology field produced by NT-MDT Company, Russia. The device is supposed to be a powerful tool for high resolution analysis in different fields of investigations such as material sciences (optical and optoelectronic, magnetic, semi- and superconducting materials), polymers and biological sciences (structural biology, molecular and cell biology, microbiology, etc.). Probe tip plane light distributions are calculated and different light propagation schemes are discussed.
Simulations of the electrostatic potential in a thin silicon specimen containing a p-n junction
Authors: Somodi P.K. , Dunin-Borkowski R.E. , Twitchett A.C. , Barnes C.H.W. , Midgley P.A.
Published: April 2011

The measurement of potentials associated with dopant atoms in semiconductors at nanometer spatial resolution using off-axis electron holography is known to be affected by the presence of the surfaces of thin specimens. In particular, the potential across a p-n junction is often found to be lower than would be expected from predicted properties of bulk devices. Here we present simulations of two-dimensional potential profiles within a thin (<1 µm) parallel-sided specimen containing a p-n junction. We find that the potential across the p-n junction is always smaller, when projected through the specimen, than would be expected from the properties of the bulk material. Crucially, the step in potential across the junction is independent of the value of the potential on the surface of the specimen for high dopant concentrations (>1017 cm−3). The simulations are compared with experimental data. Although they can account for some of the reduction in the observed potential, they do not fully explain the experimental results.