bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Limitations of Materials for Steel Foil Based Flexible Electronics
Authors: Kuo Po-Chin , Chouvardas Vasilios G. , Spirko Jeff A. , Hatalis Konstantinos M. , Hatalis Miltiadis K.
Published: April 2011

Thin steel foils have been successfully demonstrated as outstanding substrate materials for flexible electronics because of their high mechanical strength, flexibility, light weight and thermal stability. This work investigates mechanical limitations of thin film materials on steel foil substrates. We characterize a three layer structure consisting of 100μgm thick stainless steel foil as the substrate, followed by 1μgm thick spin-on-glass passivation layer and 0.3μgm thick patterned aluminum interconnect layer on top with varying widths between 10- 35μgm by means of a bending experiment. A collapsing radius test method was adopted for the bending experiment and an elliptical curve fit was used to facilitate the strain measurement. The failure strain of aluminum interconnect layer was detected by monitoring the continuity of the test circuit during the experiment. The corresponding results reveal that the passivation layer cracked at a tensile strain of 0.46% and delaminated at a compressive strain of 0.68%. The metal interconnect layer ruptured at a tension strain of 1.26% and delaminated from substrate at a compressive strain of 1.22% due to the delamination of the passivation layer underneath. We determined that the failure of the aluminum interconnect under tension was due to localized elongation caused by cracking of the passivation layer underneath and concluded that a wider interconnect could withstand a larger strain. The stainless steel foil plastically deformed at a relatively small strain of 0.13%; thus, the use of stainless steel with reversible bending capability for flexible electronics is mostly limited by the minimum elastic bending radius of the steel substrate. The flexibility of steel foil based devices can be effectively improved by decreasing the substrate thickness.
Flipchip Bonding of Si Chip on Flexible PEN Foil using Novel Electronic 100 μm Pitch Fan-out Circuitry
Authors: Brand Jeroen van den , Veninga Erik , Kusters Roel , Podprocky Tomas , Dietzel Andreas
Published: April 2011

A novel, cost effective technology to manufacture high density embedded electronic circuitry is demonstrated. The process consists of laser photoablation of the circuitry into a substrate through a mask and subsequent filling using a polymer thick film paste. Because the volume of the substrate is used it is possible to make thick and thereby highly conductive lines using low cost materials and processes. The process is demonstrated for a fan out circuitry in 100 µm thick polyethylene naphthalate (PEN). The fan out circuitry has linewidths of 50 µm and line spacings of 100 µm. The usability of the circuitry is demonstrated by the successful flipchip bonding of a thinned Si daisy chain dummy chip with 176 IO's.
Principal Pilot Line Manufacturing Challenges and Solutions in Direct Fabrication of a-Si:H TFT Arrays on Flexible Substrates
Authors: O¡¯Rourke Shawn M. , Loy Douglas E. , Moyer Curt , Ageno Scott K. , O'Brien Barry P. , Bawolek Edward J. , Bottesch Dirk , Marrs Michael , Dailey Jeff , Cordova Rita , Trujillo Jovan , Kaminski Jann , Allee David R. , Venugopal Sameer , Raupp Gregory B.
Published: April 2011

Principal challenges to direct fabrication of high performance a-Si:H transistor arrays on flexible substrates include automated handling through bonding-debonding processes, substrate-compatible low temperature fabrication processes, management of dimensional instability of plastic substrates, and planarization and management of CTE mismatch for stainless steel foils. In collaboration with our industrial and academic partners, we have developed viable solutions to address these challenges, as described in this paper.
TiO2 Surface State Control for Dye Sensitized Solar Cells with High Efficiency and the Solidification -Fabrication of Charge Carrier Path
Authors: Inakazu Fumi , Ogomi Yuhei , Noma Yusuke , Fujita Yoshihisa , Kono Mitsuru , Yamaguchi Yoshihiro , Kashiwa Yohie , Kogo Takeshi , Hayase Shuzi
Published: April 2011

Improvement of photovoltaic performance for dye sensitized solar cells (DSC) is discussed in terms of electron-path and ion-path. In order to make electron path, we focused on passivation of TiO2 surface states which are observed by thermally stimulated current (TSC). The TiO2 surface was well-passivated with dye molecules under pressurized CO2 atmosphere. It was found that DSC cells prepared by a CO2 process (Cell-CO2) had higher efficiency than those prepared by a conventional dipping process (Cell-DIP) and the higher efficiency was associated with low TiO2-surface state, high electron diffusion coefficient and long electron life time in TiO2 for the Cell-CO2. In addition, dye-staining under pressurized CO2 atmosphere had advantages over a conventional dipping process on rapid dye-uptake and less dye aggregation. In order to fabricate ion-path in solidified electrolyte, we focused on surface modification of nano-materials. Surface of nano-materials such as TiO2-nanoparticles and porous alumina films were modified with imidazolium iodide moieties consisting of long alkyl chains which render surface-molecules self-organized. Redox-species are concentrated on the self-organized molecules and make ion-path. We propose quasi-solid electrolyte system consisting of two layers having different charge carrier concentration to keep high photoconversion efficiencies even after solidification.
Synthetic approaches to study aggregation of tripodal linkers on semiconductor surfaces
Authors: Taratula Olena , Thyagarajan Sujatha , Galoppini Elena
Published: April 2011

Two tripod-shaped adamantane derivatives carrying a pyrene chromophore and three carboxylic acid binding groups, and varying in footprint size (∼ 0.7 and 2.7 nm2), were synthesized as models to study how the footprint size can influence the aggregation of organic dyes bound to ZrO2 thin films. Synthetic approaches and binding properties of large footprint tripodal linkers are discussed.
Polaron Pair Dissociation and Polaron Recombination in Polymer: Fullerene Solar Cells
Authors: Deibel Carsten , Baumann Andreas , Lorrmann Jens , Dyakonov Vladimir
Published: April 2011

In polymer:fullerene solar cells, the field-dependent photocurrent is due to a combination of polaron pair dissociation, competing with monomolecular recombination, and bimolecular recombination. We compare of the experimental photocurrent of P3HT:PCBM bulk heterojunction solar cells to Monte Carlo simulations of bilayer and bulk heterojunction devices. The shape of the photocurrent can be reproduced, the high quantum yield, however, cannot be explained with help of the simulations. In order to analyse the dominant experimental recombination mechanism, we apply the photo-CELIV technique. Our data can be fitted with bimolecular recombination, but only if a reduced Langevin recombination factor is assumed. Thermalisation is accounted for by measuring the time-dependent charge carrier mobility.
Analysis of Strain Compensation in Quantum Dot Embedded GaAs Solar Cells
Authors: Bailey Christopher , Cress Cory , Raffaelle Ryne , Hubbard Seth , Maurer William , Wilt David , Bailey Sheila
Published: April 2011

The effects of strain within stacked layers of InAs quantum dots (QDs) were investigated. InAs QD test structures with and without strain compensation (SC) were analyzed using atomic force microscopy, transmission electron microscopy, and X-ray diffraction. The affects of strain compensation on test structure morphology and on GaAs-based QD solar cell performance was studied as a function of the thickness of the SC layer. X-ray diffraction analysis of the QD embedded test structures reveals a relationship between the SC thickness and the observed crystalline quality. Air mass zero illuminated current vs. voltage data and spectral responsivity measurements were used for the solar cell comparison. When SC is employed, QD insertion shows a lower open circuit voltage, in reference to a baseline device without QDs, but leads to an enhancement in the short circuit current of the device.
Copper Phthalocyanine Nanowire Based Solar Cells
Authors: Singh Vijay , Rajaputra Suresh , Phok Sovannary , Chintakula Goutham , Sagi Gayatri
Published: April 2011

Photovoltaic devices based on organic semiconductors are of interest because of their potential as flexible, lightweight and inexpensive devices. One of the promising devices, involves the heterojunction between copper phthalocyanine (CuPc) and 3,4,9,10-perylenetetracarboxylic bis-benz-imidazole (PTCBI). Earlier, we reported, the highest Voc (1.125V) in a single organic heterojunction solar cell in an ITO/PEDOT:PSS/CuPc/PTCBI/Al structure. Results were interpreted in terms of a modified CuPc-Al Schottky diode for this thin PTCBI layer case and a CuPc-PTCBI heterojunction for the thick PTCBI case. We also reported the device characteristics of Copper phthalocyanine (CuPc)/Aluminum (Al) Schottky diode solar cells. Here, open circuit voltages (Voc) increased from 220 mV at 15 nm to 907 mV at 140 nm. Analysis of the current-voltage characteristics indicated that tunneling and interface recombination mechanisms are important components of the current transport at the CuPc/Al junction. With the objective of higher short circuit current densities in mind, we have extended our earlier work on organic semiconductors to nanowire based designs. In this paper, we report the fabrication, materials and electrical characterization of CuPc nanowire based solar cells in AAO templates by electro-deposition. The CuPc nanowires were electrochemically deposited into the AAO templates using CHCl3 (Chloroform) containing 10-4 M CuPc with 0.5 ml of CF3COOH (Trifluoro acetic acid). The nanowires were characterized by XRD, UV-Vis absorption spectroscopy, electron microscopy and electrical measurements. CuPc nanowires were also electrodeposited onto ITO/glass substrates and compared with templated nanowires for their structural, optical and electrical properties. Effect of the PEDOT: PSS buffer layer on the nanowire based device characteristics was also investigated.
Hierarchical Assembly of 2D Nanostructures of Relevance for Organic Solar Cell Design
Authors: O'Donnell Sarah , Buettner Michael , Reinke Petra
Published: April 2011

The first step in synthesizing a model film morphology via a surface-driven hierarchical assembly process is presented. The goal of the hierarchical assembly is the control of the morphology of complex molecular layers for the investigation of fundamental processes in organic solar cells. Using a focused ion beam (FIB) with Ga+ ions at 30 keV, the surface of highly oriented pyrolitic graphite (HOPG) is patterned with an array of local amorphous carbon ellipsoid spots (ACES), which provide preferential nucleation lines at their perimeter, and thus are instrumental in the control of fullerene island growth. On the undamaged surface regions outside the ACES pattern the fullerene island growth is unperturbed, and presents the well-known combination of round and fractal island shapes. The fullerene deposition at the periphery of the ACES pattern, which is characterized by single ion impact defects, results in stunted, smaller and irregular islands. Inside the ACES array, the C60 island growth is controlled by the shape of the ACES and is constrained to lobes which form around each ACES spot. The array and C60 lobe morphology and geometry are characterized and a subsequent understanding of the C60 diffusion fields and nucleation lines within the array is discussed.
Doped Silicon Nanoparticles Synthesized by Nonthermal Plasma
Authors: Pi Xiaodong , Anthony Rebecca , Campbell Stephen , Kortshagen Uwe
Published: April 2011

Silicon nanoparticles (Si-NPs) < 6 nm have been doped with B and P in nonthermal plasma. The doping efficiency of B is smaller than that of P, consistent with the theoretically predicted larger formation energy of B than P. The effect of doping on the oxidation-induced changes in light emission from Si-NPs is different between B and P. It appears that P is at or near the surface of Si-NPs, and that B is well incorporated inside Si-NPs. Inks based on doped Si-NPs are produced by attaching alkyl ligands to the surface of Si-NPs and dispersing them in organic solvents.
Concentrational restrictions for race track memories based on permalloy
Authors: Weinberger Peter
Published: April 2011

In using the fully relativistic versions of the Screened Korringa-Kohn-Rostoker method and of the Kubo-Greenwod equation domain wall resistivities at the equilibrium domain wall width are calculated for NicFe1-c. It is found that in comparison to the corresponding "bulk" case only between about 0.6¡Ü c<1 the anisotropic magnetoresistance is reduced in the presence of a domain wall sufficiently enough in order to be of practical use for potential race track memories. Around 80% Ni this reduction amount to remarkable 16%!
Magneto-transport Properties of Gd-doped In2O3 Thin Films
Authors: Gupta Ram , Brown D. , Ghosh K. , Mishra S. R. , Kahol P. K.
Published: April 2011

Dilute Magnetic Semiconductors (DMS) are a rare group of promising materials that utilize both the electronic charge - a characteristic of semiconductor materials - and the electronic spin - a characteristic of magnetic materials. Oxide based DMS show promise of ferromagnetism (FM) at room temperature. It has been found that doping metal oxides such as ZnO, TiO2, and In2O3 with magnetic ions such as Fe, Co, Mn, and Cr produces DMS, which exhibit FM above room temperature. In2O3, a transparent opto-electronic material, is an interesting prospect for spintronics due to a unique combination of magnetic, electrical, and optical properties. High quality thin films of rare earth magnetic gadolinium (Gd) doped oxide-based DMS materials have been grown by pulsed laser deposition (PLD) technique on various substrates such as single crystal of sapphire (001) and quartz under suitable growth conditions of substrate temperature and oxygen pressure in the PLD chamber. The effect of rare earth magnetic doping on the structural and electro - magnetic properties of these films has been studied using Raman Spectroscopy, X-Ray Diffraction, Scanning Electron Microscopy, and Magneto - Transport. An X- ray diffraction study reveals that these films are single phase and highly oriented. Characteristic Raman peaks typical of indium oxide are observed at 496 and 627 cm−1. We have observed high magnetoresistance (∼18 %) at a relatively small field of 1.3 Tesla for the films with 10 % gadolinium. A detailed study of temperature and magnetic field dependent resistivity, magnetoresistance, and Hall Effect will be presented.
Magnetic Properties of Nd-Fe-B-M (M=Si, C) Bulk Nanocomposite Magnets Prepared by the Spark Plasma Sintering Method
Authors: Fukuzaki Tomokazu , Tanaka Keisuke , Nishimoto Kazue , Muro Yuji , Nishio Keishi , Tamura Ryuji
Published: April 2011

We have prepared Nd2Fe14B/Fe3B bulk nanocomposite magnets at the compositions of Nd4Fe77.5B18.5-xMx (M=Si, C) by substitution of other elements M for B. For the sample substituted with 1 at.%Si and sintered at 600 oC, the coercivity exhibits the highest value of 227 kA/m. It has also been found that the grain sizes of the Nd2Fe14B and the Fe3B phases depend on the ramp-up time and the reduction of the grain size leads to an increase of the coercivity. On the other hand, the samples substituted with C exhibit soft magnetic behaviors, which is attributed to the suppression of the precipitation of the Nd2Fe14B hard magnetic phase.
Anomalous magnetic ordering transition and induced Raman scattering in BiFeO3 thin films
Authors: Singh Manoj K , Prellier W , Jang H M , Katiyar Ram S
Published: April 2011

Low temperature magnetic properties and Raman spectrum of highly (111)-oriented rhombohedral BiFeO3 (BFO) thin films epitaxially grown on (111) SrTiO3 substrates by pulsed laser deposition have been studied. Zero field cooled (ZFC) and field cooled (FC) magnetization curves display divergence at characteristic temperature Tirr (H), which are magnetic field dependent, suggesting a spin-glass like behavior of the film. The change in magnetic ordering results in anomalous phonon behavior such as the extraordinary enhancement and appearance of new Raman modes due to Brillouin zone folding below ∼200 K.
Engineered Biferroic 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3/La0.6Sr0.4MnO3 Epitaxial Superlattices
Authors: Roy Chaudhuri Ayan , Krupanidhi S.B.
Published: April 2011

Symmetric and asymmetric superlattices (SLs) composed of ferromagnetic La0.6Sr0.4MnO3 (LSMO) and ferroelectric 0.7Pb(Mg1/3Nb2/3)O3 – 0.3PbTiO3 (PMN-PT) with different periodicities have been fabricated on LaNiO3 (LNO) coated LaAlO3 (100) (LAO) substrates by pulsed laser ablation deposition. Structural, ferromagnetic and ferroelectric properties have been studied for all the SLs. All the heterostructures exhibited good ferromagnetic response over a wide range of temperatures (10K – 300K), whereas only the asymmetric SLs exhibited reasonably good ferroelectric behaviour. Ferromagnetic and ferroelectric hysteresis loops observed in the asymmetric SLs confirmed their biferroic nature. Studies were conducted towards understanding the influence of LSMO layers on the electrical responses of the heterostructures. Absence of ferroelectricity in the symmetric SL structures has been attributed to their high leakage characteristics. Strong influence of an applied magnetic field of 1.2T was observed on the ferroelectric properties of the asymmetric SLs. The effect of magnetic field on the ferroelectric properties of the SLs indicated possibility of strong interfacial effect.
PMN-PT Single Crystal Piezo-Electric Acoustic Sensor
Authors: Lee Sung Q , Kim Hye Jin , Lee Sang Kyun , Lee Jae Woo , Park Kang Ho
Published: April 2011

The MEMS (micro-electro-mechanical systems) microphone enables the manufacturing of small mechanical components on the surface of a silicon wafer. The MEMS microphones are less susceptible to vibration because of the smaller diaphragm mass and an excellent candidate for chip-scale packaging. In this paper, we present a piezoelectric MEMS microphone based on (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystal diaphragm. The PMN-PT materials exhibit extremely high piezoelectric coefficients and other desirable properties for an acoustic sensor. The piezoelectric-based microphone can offer the ability to passively sense without the power requirements. In particular, this paper introduces the design of a PMN-PT single crystal diaphragm with interdigitated electrode. We were able to fabricate miniaturized PMN-PT single crystal diaphragms. The fabricated sensor exhibits the sensitivity of 1.5mV/Pa. This implies that the PMN-PT thin film microphone has a potential of excellent acoustic characteristics.
Deposition Rate Effect on Critical Thickness of BaTiO3Epitaxial Thin Film Grown on SrTiO3(001)
Authors: Kawai Masanori , Kan Daisuke , Isojima Seiichi , Kurata Hiroki , Isoda Seiji , Kimura Shigeru , Sakata Osami , Shimakawa Yuichi
Published: April 2011

BaTiO3/SrTiO3(001) epitaxial thin films were prepared at various growth rates by pulsed laser deposition, and their heterostructures were evaluated by synchrotron x-ray diffraction measurements and cross-sectional scanning transmission electron microscopy observations. In a film grown at a low deposition rate (0.01 nm/s), misfit dislocations are found near the interface and a fully relaxed BaTiO3thin film grows epitaxially on the substrate. On the other hand, a film grown at a high deposition rate (0.04 nm/s) consists of strained and relaxed BaTiO3lattices. Our results showed that the critical thickness of BaTiO3/SrTiO3(001) epitaxial thin films can be controlled by the deposition rate and that the critical thickness increases with increasing the deposition rate, and by adjusting the deposition rate we were able to prepare epitaxial thin films consisting of fully strained BaTiO3, partially strained BaTiO3or fully relaxed BaTiO3. We have also achieved the growth controlling of BaTiO3thin films on SrTiO3(001) substrates with SrRuO3bottom electrode layer.
Phase Transition and Dielectric Tunability of Chemical Solution Deposited (Pb0.35Sr0.65)(Zr0.5Ti0.5)O3 Thin Films on Pt/ZrO2/SiO2/Si Substrates
Authors: Karan Naba K , Perez Marilin , Saavedra Jose , Pradhan Dillip K , Thomas Reji , Katiyar Ram S
Published: April 2011

(Pb0.35Sr0.65)(Zr0.5Ti0.5)O3 thin films were grown on Pt/ZrO2/SiO2/Si substrates by chemical solution deposition. As-deposited (pyrolysed at 500°C) films were amorphous and single phase films were obtained at temperature as low as 550°C with a 30 nm SrTiO3 seed layer. Dielectric constant and loss tangent at room temperature were 210 and 0.022, respectively at 100 kHz for the film annealed at 700°C. Frequency dispersion of the dielectric properties was low. The phase transition temperature (ferroelectric to paraelectric) was well below the room temperature and was around 220 K. The room temperature tunability and the k-factor at 500 kV/cm was around 45% and 16, respectively.
Synthesis and Characterization of Pb(Fe1/2Ta1/2)O3
Authors: Martinez Ricardo , Palai R. , Katiyar R.S.
Published: April 2011

Lead iron tantalate Pb(Fe1/2Ta1/2)O3 (PFT) is a compound derived of general formula Pb(BIxBII1-x)O3 wherein x=1/2. In this work synthesis, sintering processes, dielectric, electrical, magnetic measurement, and Raman spectroscopy properties of PFT ceramics are described. The dielectric properties of PFT showed typical relaxor behaviors. We saw that ferroelectric and magnetic orders coexist in PFT at room temperature.
Synthesis, characterization and growth mechanism of ZnO/TiO2 nanohybrid arrays
Authors: Chun Cheng , Ning Wang
Published: April 2011

In this paper, we demonstrate a simple method to synthesize ZnO/TiO2 nanohybrid structure arrays based on the site-specific deposition of titanium oxide on ZnO nanorods under the hydrothermal condition. We have found that the polarity of the ZnO (0001) surface plays an important role in the formation of the nanohybrid structures. Each ZnO nanorod is assembled with one TiO2 particle only at the (0001) end surface. High-resolution transmission electron microscopy study shows that the TiO2 particles that are connected to ZnO nanorods are amorphous. By annealing at different temperatures, these particles can be transformed to nanocrystals of the anatase and rutile phases, which have a particular relationship with the orientation of ZnO nanorods and good interface structures. This work provides a rational approach to the assembly of complex nanohybrids using the intrinsic properties of ZnO nanocrystals.
Visible Luminescence Related to Defects in ZnO
Authors: Reshchikov Michael A. , Nemeth B. , Nause J. , Xie J. , Hertog B. , Osinsky A. , Avrutin V. , Izyumskaya N. , Shimada R. , Morkoc H.
Published: April 2011

We studied several photoluminescence (PL) bands in undoped, Li-, Ga-, and N-doped high-quality ZnO bulk crystals and thin films grown by molecular beam epitaxy (MBE). By analyzing PL in a wide range of excitation power densities, sample temperature, and decay time after a laser pulse, we distinguished and analyzed more than 10 broad bands with unique luminescence properties. Among these bands, only the Cu-related green band with a characteristic fine structure and the Li-related orange band were well-studied and reliably identified in the past.
Hydrogen Migration in Single Crystalline ZnO
Authors: Johansen Klaus Magnus Håland , Christensen Jens Sherman , Monakhov Edouard V. , Kuznetsov Andrej Yu. , Svensson Bengt Gunnar
Published: April 2011

Hydrogen has been proposed as one of the contributors to the native n-type doping in as-grown Zinc Oxide and can also be used as an active (intentional) n-type dopant. In this work we have employed Secondary Ion Mass Spectrometry (SIMS) to study deuterium diffusion profiles in single crystalline ZnO. The samples used are hydrothermally grown, high-resistive (10 kΩ cm) monocrystalline ZnO implanted with deuterium to a dose of 1×1015 cm−2 yielding a peak concentration of approximately 5 × 1018 cm−3 at a depth of 2.2 µm. Diffusion profiles have been studied after 30 minutes isochronal heat treatments from 100ºC up to 400ºC in steps of 50ºC. The observed redistribution can be explained by employing a diffusion model which includes trapping of 2H by Li-impurities and an activation energy of 0.85 eV is extracted for the diffusion of 2H.
Hydrothermally Grown Single-Crystalline Zinc Oxide; Characterization and Modification
Authors: Svensson Bengt Gunnar , Børseth Thomas Moe , Johansen Klaus Magnus , Maqsood Tariq , Schifano Ramon , Grossner Ulrike , Christensen Jens S. , Vines Lasse , Klason Peter , Zhao Qing X. , Willander Magnus , Tuomisto Filip , Skorupa Wolfgang , Monakhov Edouard V. , Kuznetsov Andrej Yu.
Published: April 2011

An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ∼800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10−1 Ωcm is obtained and the Li content is reduced from above 1017 cm−3 to the mid 1015 cm−3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting improvement of the n-type conductivity. However, these clusters have a limited stability and start to dissociate already after 1h at 900 °C, accompanied by a decrease in the conductivity. For topic (ii), n-type doping by hydrogen implantation is shown to enhance the conductivity by about 5 orders of magnitude already in the as-implanted state. Despite substantial loss of hydrogen, the conductivity remains stable, or even increases, after annealing up to ≥600 °C, and necessary conditions for doping by hydrogen are discussed. In (iii), the origin of the commonly observed deep band emission from monocrystalline zinc oxide is investigated using a concept of annealing as-grown samples in different atmospheres. A strong influence by the atmosphere and temperature is observed and the results can be interpreted in terms of dominant effects on the emission by vacancy-related defects.
Application of ZnO to Passivate the GaN-based Device Structures
Authors: Kaminska Eliana , Piotrowska Anna , di Forte Poisson Marie-Antoinette , Delage Sylvain , Lahreche Hacene , Kwietniewski Norbert , Pasternak Iwona , Kruszka Renata , Guziewicz Marek , Boguslawski Piotr , Dynowska Elzbieta , Borysiewicz Michal
Published: April 2011

The fabrication of high-resistivity ZnO-based thin films lattice-matched to AlGaN/GaN structures has been developed. It relies on low-temperature reactive sputter deposition of ZnO:Sb from ZnSb target. Taking into account the hygroscopic nature of ZnO surface, an additional coating by Si3N4 films is applied to ensure the humidity protecition. The developped passivation suppresses leakage currents in Schottky diods, and substantially improves output characteristics of AlGaN/GaN HEMT.
Luminescence of Er-doped ZnO Films: Effects of Thermal Annealing and Doping Concentration
Authors: Pan Zhengda , Morgan S H , Ueda A , Aga R , Steigerwald A , Mu R
Published: April 2011

Photoluminescence (PL) of erbium-doped zinc oxide films with nano-sized grains was studied. The films were grown on silicon (100) and fused silica substrates using e-beam evaporation. The evaporating targets used were sintered pellets of ZnO and Er2O3 mixtures with two different Er concentrations. The films were subsequently annealed at 700 °C in air for an hour. PL was measured at two excitation wavelengths, 325 and 488 nm. The 325 nm is used for exciting the host semiconductor ZnO and 488 nm is used for directly exciting Er3+ ions in the ZnO host. Strong Er3+ luminescence of 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions was observed from annealed film with 4.0 % Er2O3 concentration using either 325 or 488 nm excitation. With 325 nm excitation, the Er3+ luminescence observed is attributed to energy transfer from the excitons in ZnO host to the Er3+ ions doped. The effective energy transfer from ZnO host to the doped Er3+ ions is an essential property for the realization of actual current-injection opto-electronic devices operating at wavelengths of Er3+ emission, for example, at 1.54 μm for the erbium-doped fiber amplifier (EDFA). Our PL results indicate that thermal annealing plays an important role for optically activating the doped Er3+ ions in ZnO nano-crystalline grains of the film.
Blue and Yellow Luminescence in ZnO Films Grown by Peroxide MBE
Authors: Avrutin Vitaliy , Reshchikov Mikhail A. , Izyumskaya Natalia , Shimada Ryoko , Morkoç Hadis
Published: April 2011

We observed strong shifts of the blue and yellow luminescence bands with variation of excitation intensity in ZnO films grown on sapphire by MBE using hydrogen peroxide as a source of reactive oxygen. The blue band, having a maximum in the range from 2.85 to 3.15 eV in different samples and different excitation intensities at 10 K, is attributed to diagonal transitions from the conduction band (or shallow donors) to the valence band in realm of potential fluctuations caused by random distribution of charged point defects in a compensated semiconductor. The yellow band is related to an unidentified deep acceptor.
Valence Band Structure of ZnO and MgxZn1−xO
Authors: Schmidt-Grund R. , Sturm C. , Schubert M. , Rheinländer B. , Faltermeier D. , Hochmuth H. , Rahm A. , Bläsing J. , Bundesmann C. , Zúñiga-Pérez J. , Chavdarov T. , Lorenz M. , Grundmann M.
Published: April 2011

We present an attempt to clarify the valence band order of ZnO and MgxZn1−xO films grown by pulsed laser deposition (PLD) on sapphire substrates. We derive the dependence of spin orbit interaction (Δso) and crystal field interaction (Δcf) on the temperature, strain and cation replacement (Zn with Mg) and compared this with theoretical predictions. The strain was varied by using different orientated sapphire substrates (c-, r-, and m-plane orientations) and by varying the film thicknesses. All these investigations support the conclusion that the symmetry order of the valence band is Γ7-Γ9-Γ7 for ZnO and MgxZn1−xO for x ≤ 0.55.
In-situ AFM study of the crystallization and pH-dependent stability of ZnO(0001)-Zn surfaces
Authors: Valtiner Markus , Grundmeier Guido
Published: April 2011

Polar ZnO(0001)-Zn surfaces can be prepared as very well defined and single crystalline surfaces by hydroxide stabilization simply by introducing hydroxides via a wet chemical cleaning step. Within this proceeding we present an in-situ AFM imaging of the crystallization process. The pH dependent stability of the resulting hydroxide-stabilized surfaces was further investigated by means of an ex-situ LEED approach. These investigations show, that it is possible to obtain high quality single crystalline ZnO(0001)-Zn surfaces in a simple way. Moreover, these surfaces turned out to be very stable within a wide range of pH values between 11 and 3 of NaClO4 based 1mM electrolyte solutions.
Effects of Nanometer-Scale Surface Roughness and Applied Load on the Bond Strength and Contact Resistance of Cu-Cu Bonded 3D ICs
Authors: Leong Hoi Liong , Gan Chee Lip , Thompson Carl V. , Pey Kin Leong , Li Hongyu
Published: April 2011

The effects of total surface roughness of Cu bond layers and applied load during bonding on the bond strength and the contact resistance of the bonded interface were studied for three-dimensional (3D) devices. The 3D structures were fabricated by thermocompression bonding of two wafers, each fabricated with a Cu damascene process. The average bond strength of the samples was found to increase with increasing load, and with decreasing roughness. On the other hand, the average contact resistance increased as the total surface roughness of the bonded interface increased, as well as when the applied load decreased. The increase in bond strength (and also the dicing yield) is related to a smaller true contact area, which can be estimated using a model based on contact mechanics theory. The theory takes into account the roughness of the bonded surface, the applied load during bonding and the nominal bond area. A contact resistance model can also be used to estimate the contact resistance of bonded interfaces based on their true contact area. However, within each set of measurements, a significant spread about the average value of bond strength and contact resistance was observed, suggesting issues of contact and bonding non-uniformity of the wafers. Nonetheless, the contact resistance values given by the model were in good agreement with the minimum values observed in experiments, which may represent the ideal cases of bonding of rough surfaces. Our results show that the impact of surface roughness and applied load on the contact resistance of Cu-Cu thermocompression bonds can be quantified experimentally, and understood in the context of established theory for contact mechanics.
ALD of Lanthanum Aluminate Using Lanthanum Formamidinate Precursor
Authors: Li Huazhi , Shenai Deodatta Vinayak , Pugh Ralph , Kim Jiyoung
Published: April 2011

The physical and electrical characteristics of La2O3 and LaAlO3 films, deposited by atomic layer deposition (ALD) and using a new La formamidinate precursor (La-FAMD), were investigated. The La-FAMD precursor has superior thermal stability and is also the most volatile La source available today. The vapor pressure of La-FAMD, maintained at 100 ºC, is approximately 60 times higher than the commercial available source La-THD (THD = tetramethylheptanedionato).
Computational Models for Crystal Growth of Radiation Detector Materials: Growth of CZT by the EDG Method
Authors: Derby Jeffrey J. , Gasperino David
Published: April 2011

Crystals are the central materials element of most gamma radiation detection systems, yet there remains surprisingly little fundamental understanding about how these crystals grow, how growth conditions affect crystal properties, and, ultimately, how detector performance is affected. Without this understanding, the prospect for significant materials improvement, i.e., growing larger crystals with superior quality and at a lower cost, remains a difficult and expensive exercise involving exhaustive trial-and-error experimentation in the laboratory. Thus, the overall goal of this research is to develop and apply computational modeling to better understand the processes used to grow bulk crystals employed in radiation detectors. Specifically, the work discussed here aims at understanding the growth of cadmium zinc telluride (CZT), a material of long interest to the detector community. We consider the growth of CZT via gradient freeze processes in electrodynamic multizone furnaces and show how crucible mounting and design are predicted to affect conditions for crystal growth.
Recent Advances in Ceramic Scintillators
Authors: Van Loef Edgar , Wang Yimin , Glodo Jarek , Brecher Charles , Lempicki Alex , Shah Kanai S
Published: April 2011

A review is presented of recent ceramic scintillator R&D. Attention is focussed on Ce doped gamma-ray scintillators for medical imaging applications. Ceramic scintillators discussed in detail include SrHfO3:Ce and Lu2Hf2O7:Ce. These materials combine a high density and high atomic number with fast emission and a good light yield and may find practical application in medical imaging modalities such as Positron Emission Tomography and Computed Tomography.
Passivation of Semiconductor Surfaces for Improved Radiation Detectors: X-Ray Photoemission Analysis
Authors: Nelson Art J , Conway A M , Reinhardt C E , Ferreira J L , Nikolic R J , Payne S A
Published: April 2011

Surface passivation of device-grade radiation detector materials was investigated using x-ray photoelectron spectroscopy in combination with transport property measurements before and after various chemical treatments. Specifically Br-MeOH (2% Br), KOH with NH4F/H2O2 and NH4OH solutions were used to etch, reduce and oxidize the surface of Cd(1-x)ZnxTe semiconductor crystals. Scanning electron microscopy was used to evaluate the resultant microscopic surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and core lines were used to evaluate the surface chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics measured. The measurements were correlated to understand the effect of interface chemistry on the electronic structure at these interfaces with the goal of optimizing the Schottky barrier height for improved radiation detector devices.
Surface behavior of heterosubstrates during BEN-MPCVD: a key for diamond heteroepitaxy
Authors: Arnault Jean-Charles , SAADA Samuel , DELCLOS Sophie , INTISO Luciana , PECORARO Stéphane , BERGONZO Philippe
Published: April 2011

The chemical stability of three heterosubstrates (Si, 3C-SiC and iridium) has been studied using the same MPCVD reactor during the successive steps of BEN process. An in situ sequential approach allows a monitoring of the chemical modifications induced by interactions between plasma and surfaces. Contrary to silicon, 3C-SiC and iridium underwent weak surface evolutions during BEN. This leads to favourable conditions for the interface formation in agreement with the better Highly Oriented Diamond films reported in the literature. A short description of the nucleation pathways identified for each heterosubstrate is also presented.
Diamond Amplified Photocathodes
Authors: Smedley John , Ben-Zvi Ilan , Bohon Jen , Chang Xiangyun , Grover Ranjan , Isakovic Abdel , Rao Triveni , Wu Qiong
Published: April 2011

High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator.

The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.
Phosphorus Doped Diamond Electron Emitter Devices
Authors: Tatsumi Natsuo , Ueda Akihiko , Tanizaki Keisuke , Nishibayashi Yoshiki , Imai Takahiro
Published: April 2011

The n-type diamond is known to have high electron emission properties. However, device fabrication on n-type phosphorus doped diamond had 2 difficulties. First, because highly phosphorus doped n-type diamond layer can be grown only on very small (111) diamond substrate, fabrication of highly homogeneous 3 dimensional device such as gate electrode was very difficult. Second problem was that the resistivity of n-type diamond was still over 100 Ω cm and too high for high current electron emission devices. To solve these problems, we developed a new large size composite wafer in which (111) single crystal diamond was buried in polycrystal diamond and a new electrode coated emitter tip structure for conduction support only whose apex was exposed from the electrode. N-type phosphorus doped diamond was grown on the 15 mm composite diamond wafer with high PH3/CH4 concentration of 20% and highly doped active layer was grown on the embedded (111) single crystal. Sharp emitter tip arrays were fabricated by etching the n-type diamond. Electrodes were coated on these tips and exposed area of diamond was less than 200 nm from the apex of the tip. Gate electrodes were fabricated for each emitter tips. Electron emission of these devices were measured in the vacuum of 10−7 Pa. The threshold voltage of the n-type diamond device was 60 V which was lower than 100 V of the p-type diamond device. The threshold voltage of n-type diamond with and without electrode coatings did not changed. This means that electrode coating did not affect the emission properties and electrons were emitted from the diamond surface. The emission current was enhanced by 2 orders by the electrode coatings and total emission current from 1 mm2 reached 1103 mA. This high emission current electron source enables applications to microwave tubes, electron beam processing and integrated micro vacuum devices.
CVD Diamond Applications as TL Radiation Dosimeters
Authors: Pedroza-Montero M. , Melendrez R , Chernov V , Pedroza-Montero M. , Gastelum S , Cruz-Zaragoza E
Published: April 2011

The extraordinary characteristics of chemically vapor deposited (CVD) diamond such as tissue equivalence, radiation hardness, and lack of solubility in water; makes CVD diamond a very promising material for radiation dosimetry applications. Recent investigations have shown that CVD techniques allowed the growing of good quality diamond films in a diversity of substrates to be used in the form of ionization chambers, thermoluminescence (TL) detectors and dosimeters. In the present work, we report on the TL properties of MWCVD diamond exposed to gamma radiation in the 0.05 -1.0 kGy dose range and 43.5 and 81.11 Gy min−1 dose rates. The CVD diamond displays a linear dose behavior and 5% TL cycle reproducibility, without requiring any annealing or thermal treatment before using it as TL dosimeter. In spite of the significant results, some problems remain and a lot of research work is necessary to improve the synthetic material characteristics to optimize the TL/OSL radiation dosimeter properties.
HIGH-SURFACE-AREA BIOCARBONS FOR REVERSIBLE ON-BOARD STORAGE OF NATURAL GAS AND HYDROGEN
Authors: Pfeifer Peter , Burress Jacob W. , Wood Mikael B. , Lapilli Cintia M. , Barker Sarah A. , Pobst Jeffrey S. , Cepel Raina J. , Wexler Carlos , Shah Parag S. , Gordon Michael J. , Suppes Galen J. , Buckley S. Philip , Radke Darren J. , Ilavsky Jan , Dillon Anne C. , Parilla Philip A. , Benham Michael , Roth Michael W.
Published: April 2011

An overview is given of the development of advanced nanoporous carbons as storage ma-terials for natural gas (methane) and molecular hydrogen in on-board fuel tanks for next-generation clean automobiles. The carbons are produced in a multi-step process from corncob, have surface areas of up to 3500 m2/g, porosities of up to 0.8, and reversibly store, by physisorp-tion, record amounts of methane and hydrogen. Current best gravimetric and volumetric storage capacities are: 250 g CH4/kg carbon and 130 g CH4/liter carbon (199 V/V) at 35 bar and 293 K; and 80 g H2/kg carbon and 47 g H2/liter carbon at 47 bar and 77 K. This is the first time the DOE methane storage target of 180 V/V at 35 bar and ambient temperature has been reached and exceeded. The hydrogen values compare favorably with the 2010 DOE gravimetric and volu-metric targets for hydrogen. A prototype adsorbed natural gas (ANG) tank, loaded with carbon monoliths produced accordingly and currently undergoing a road test in Kansas City, is de-scribed. A preliminary analysis of the surface and pore structure is given that may shed light on the mechanisms leading to the extraordinary storage capacities of these materials. The analysis includes pore-size distributions from nitrogen adsorption isotherms; spatial organization of pores across the entire solid from small-angle x-ray scattering (SAXS); pore entrances from scanning electron microscopy (SEM) and transmission electron microscopy (TEM); H2 binding energies from temperature-programmed desorption (TPD); and analysis of surface defects from Raman spectra. For future materials, expected to have higher H2 binding energies via appropriate sur-face functionalization, preliminary projections of H2 storage capacities based on molecular dy-namics simulations of adsorption of H2 on graphite, are reported.
Hydrogen Adsorption in MOF-74 Studied by Inelastic Neutron Scattering
Authors: Liu Yun , Brown Craig M. , Neumann Dan A. , Kabbour Houria , Ahn Channing C.
Published: April 2011

Adsorption of hydrogen and the occupancy of different binding sites as a function of hydrogen loading in MOF-74 are studied using inelastic neutron scattering (INS). Hydrogen molecules are observed to fully occupy the strongest binding site before populating other adsorption sites. The comparison of the INS spectra at 4 K and 60 K indicates that hydrogen adsorbed at the strongest binding site is strongly bound and localized. We also show that when two hydrogen molecules are adsorbed into a single, attractive potential well, the shortest inter-H2 distance is about 3 Å, consistent with our previous observation of inter-H2 distance when adsorbed in two neighboring potential wells.
Evolution of Crystal Orientation in Obliquely Deposited Magnesium Nanostructures for Hydrogen Storage Applications
Authors: Cansizoglu Mehmet F. , Watanabe Fumiya , Wang Pei-I , Karabacak Tansel
Published: April 2011

Crystal orientation (texture) is an important parameter in the hydrogen absorption and desorption properties of various materials. In this study, we investigate the formation of magnesium nanorod arrays with crystal orientations that are not normally observed in conventional Mg thin films. Mg nanorods are produced using an oblique angle deposition technique through a physical self-assembly process. In this study sputtering and thermal evaporation systems are utilized for the growth of Mg nanorods and thin films on silicon wafer pieces. We present a detailed X-ray diffraction and scanning electron microscopy analysis. It is discussed that under oblique incidence, evolution of crystal orientations with lower adatom mobility are promoted due to the shadowing effect.
Mechanisms for the Variation of Electrical Resistivity of Palladium Films in Hydridation-dehydridation Processes
Authors: Tang Yu Ming , Chan Yiu Bun , Ong Chung Wo
Published: April 2011

Hydridation of palladium (Pd) is accompanied by a substantial volume expansion. The electrical resistivity (ρ) would rise because the volume fraction of the hydride phase increases. However, if the material structure is porous/defective, hydridation induced volume expansion may lead to the closing of some pores/defects to result in a drop of ρ. We verified that a magnetron sputtered Pd film deposited at a higher argon ambient pressure (ϕ) was more defective, such that the contribution from the latter mechanism was stronger with increasing ϕ, and reached a maximum level for a film deposited at a ϕ of 6 mTorr. However, the film structure was weaker and unstable during the switching cycles, such that the magnitude of the change of ρ was found to increase successively with increasing number of switching cycles. The performances of ρ during initial soaking in H2 and subsequent hydridation and dehydridation switching cycles were different. The observed results are presented and discussed in this paper.
Oxidation Behavior of Zr-Nb Alloys at 973-1273 K in Air
Authors: Arima Tatsumi , Miyata Kensaku , Idemitsu Kazuya , Inagaki Yaohiro
Published: April 2011

Oxidation behaviors of Zr-Nb alloys were investigated under the condition of high temperatures and dry air.