bluuebunny/crossref_metadata_2025 huggingface dataset:
Perspectives on an Advanced Hydrogen Storage System: Platinum-Carbon Nanotube Nanocomposite Materials
Authors: Zacharia Renju , Rather Sami-ullah , Hwang Sang Woon , Manuel Stephan Arul , Nahm Kee Suk
Published: April 2011

Transition-metal functionalized-carbon nanotubes (CNTs) represent an important genre of hydrogen storage systems that exhibit superior storage capacity and improved storage kinetics when compared with the pristine CNTs. Here, we compare the reversible gravimetric hydrogen storage capacity of platinum-functionalized CNTs with that of pristine tubes, both measured at 300 K and an equilibrium hydrogen pressure of 1.67 MPa. The maximum reversible hydrogen storage capacity exhibited by the nano-composite material is found to be 3.2 ± 0.1 wt%, which is a nearly 50 % enhancement when compared with that of the pristine tubes. The enhanced hydrogen storage capacity of functionalized CNTs is attributed to the spill-over phenomena as suggested by the estimated storage capacity of Pt phase. The hydrogen storage in Pt nanoparticles modeled using the atomic magic number calculation and Pt hydride stoichiometry of PtH4 also suggests that nearly 15 closed shells of Pt atoms reversibly adsorb and spill hydrogen on to CNT binding sites.
Structural, Magnetic and Electrochemical Properties of the Spinel LiMn2-yCoyO4 Nanosized Powders
Authors: Amdouni Nourredine , Gendron François , Mauger Alain , Julien Christian M
Published: April 2011

We present the synthesis, structure, magnetic properties and electrode behaviour of LiMn2-yCoyO4 (0≤y≤0) spinel oxides prepared by the wet-chemitry via the carboxylic acid route. LiMn2-yCoyO4 samples crystallise with the cubic spinel-like structure (Fd3m S.G.). Optical spectra indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Co,Mn)-O bonds. Magnetic susceptibility and electron spin resonance measurements show the compositional dependence of the magnetic parameters, i.e. Curie temperature, Curie-Weiss constant and Néel temperature, when Mn is substituted by Co. The overall electrochemical capacity of LiMn2-yCoyO4 oxides have been reduced due to the 3d6 metal substitution, however, a more stable charge-discharge cycling performances have been observed when electrodes are charged up to 4.3 V as compared to the performance of the native oxide.
Solid Oxide Fuel Cells in Unmanned Undersea Vehicle Applications
Authors: Carreiro Louis George , Burke A. Alan
Published: April 2011

The Navy is currently investigating solid oxide fuel cells (SOFCs) for the propulsion of unmanned undersea vehicles (UUVs). SOFCs are being targeted because of their potential to carry out extended missions, which are not possible using current battery technology. In addition, they offer the advantages of being able to utilize energy-dense hydrocarbon fuels and are self-sustaining while supplying heat to reforming processes.

The SOFC system evaluated in this study consisted of a Ni-YSZ-based, 6-cell stack with anode supported cells close-coupled with a micro-channel steam reformer. Various reformate gas compositions, steam to carbon ratios and flow rates were tested to gather a range of data under the expected operating conditions of UUVs. The system was operated for more than 70 hours consuming approximately 0.5 to 0.7 ml/min of fuel and producing about 100 to 230 watts of power. The integrated stack and reformer displayed stable performance with a fuel utilization of 80% and an efficiency of 50% at maximum power output.
Semi-Transparent Amorphous Silicon Solar Cells on Inexpensive Plastic Substrates
Authors: Matulionis Ilvydas , Hu Jian , Stavrides Alex , Call Nathan , Kunrath Augusto , Madan Arun
Published: April 2011

We report a monolithic series connected semi-transparent (transmission > 40%) amorphous silicon (a-Si:H) solar cell panel (substrate area 30cm × 40cm), which has an i-layer thickness <2000Å and an active area efficiency, η ∼ 3%. We also report on all laser scribed, series connected mini-modules with an aperture area η > 3% constructed on inexpensive plastic substrates.
Activated Carbons for High Power Energy Storage: Below the Surface of Non-Faradaic Reactions
Authors: Barpanda Prabeer , Amatucci Glenn G
Published: April 2011

The effect of iodine doping on the electrochemical performance of activated carbons for non-aqueous symmetric and asymmetric hybrid supercapacitors was investigated. The incorporation of iodine via high energy mechanical milling techniques significantly modified the physical and electrochemical properties of activated carbon precursors. The increasing amount of iodine into carbons leads to a unique combination of lower surface area coupled with higher volumetric and gravimetric electrochemical capacitance. Iodine modification of the carbon resulted in a 100% increase in volumetric capacitance. This improvement was a result of improved non-faradaic capacitance and the development of faradaic capacity.
Improving Polymer Based Photovoltaic Devices by Reducing the Voltage Loss at the Donor-Acceptor Interface
Authors: Moet Date J. D. , Slooff Lenneke H. , Kroon Jan M. , Chevtchenko Svetlana S. , Loos Joachim , Koetse Marc M. , Sweelssen Jorgen , Veenstra Sjoerd C.
Published: April 2011

This paper discusses the characterization and optimization of organic solar cells based on a bulk heterojunction consisting of an alternating copolymer, containing a fluorene and a benzathiadiazole unit with two neighboring thiophene rings, and a fullerene derivative (PCBM). The resulting power conversion efficiency amounts 3.9±0.2 % (AM1.5, 100 mW/cm2) and these polymer solar cells are therefore considered auspicious for further research.
The Effect of Excess Carbon on the Crystallographic, Microstructural, and Mechanical Properties of CVD Silicon Carbide Fibers
Authors: Marzik James V , Croft William J. , Staples Richard J. , MoberlyChan Warren J.
Published: April 2011

Silicon carbide (SiC) fibers made by chemical vapor deposition (CVD) are of interest for organic, ceramic, and metal matrix composite materials due their high strength, high elastic modulus, and retention of mechanical properties at elevated processing and operating temperatures. The properties of SCS-6™ silicon carbide fibers, which are made by a commercial process and consist largely of stoichiometric SiC, were compared with an experimental carbon-rich CVD SiC fiber, to which excess carbon was added during the CVD process. The concentration, homogeneity, and distribution of carbon were measured using energy dispersive x-ray spectroscopy (SEM/EDS). The effect of excess carbon on the tensile strength, elastic modulus, and the crystallographic and microstructural properties of CVD silicon carbide fibers was investigated using tensile testing, x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
Metastable Defects in Tritiated Amorphous Silicon
Authors: Ju Tong , Whitaker Janica , Zukotynski Stefan , Kherani Nazir , Taylor P. Craig , Stradins Paul
Published: April 2011

The appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to 3He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half âlife of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 1016 to 1017 /cm3 , which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value of 3x1019/cm3 after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2x1020/cm3). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200°C, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150°C, has been isothermally annealing at 300 K for several months. The defects remain well above their saturation value at 300 K, and the shape of decay suggests some interaction between the defects.
Effects of Nitrogen Addition on the Properties of a-SiCN:H Films Using Hexamethyldisilazane
Authors: Limmanee Amornrat , Otsubo Michio , Sugiura Tsutomu , Sato Takehiko , Miyajima Shinsuke , Yamada Akira , Konagai Makoto
Published: April 2011

We deposited a-SiCN:H films by HWCVD using a gas mixture of hexamethyldisilazane, H2 and N2, and fabricated cast polycrystalline silicon solar cells with the a-SiCN:H passivation and anti-reflection layer. N2 addition led to the reduction of the refractive index of the a-SiCN:H films due to the increase in nitrogen concentration of the films. This improved performance of the antireflection layer. The advantage of adding N2 to the process was demonstrated by the improvement in short circuit current (JSC) and efficiency of cast polycrystalline silicon solar cells. At present, the efficiency of cast polycrystalline silicon solar cell using a-SiCN:H film as a passivation layer reached 14.2%.
Crystalline Silicon Surface Passivation by Pecv-Deposited Hydrogenated Amorphous Silicon Oxide Films [a-SiOx:H]
Authors: Mueller Thomas , Duengen Wolfgang , Job Reinhart , Scherff Maximilian , Fahrner Wolfgang
Published: April 2011

In the research field of crystalline silicon (c-Si) solar cells, electronic surface passivation has been recognized as a crucial step to achieve high conversion efficiencies. The main issue of this article is to analyze the surface passivation properties of both, n-type and p-type crystalline silicon wafers by hydrogenated amorphous silicon sub oxide [a-SiOx:H] films the for use in hetero-junction (a-Si/c-Si) solar cells. A window layer is obtained with a certain fraction of oxygen in the a-SiOx:H layers.

The a-SiOx:H films were deposited by decomposition of silane, carbon dioxide and hydrogen as source gases using plasma enhanced chemical vapor deposition (PECVD). Films with varying deposition parameters such as gas flow ratio (oxygen fraction) and plasma frequency (13.56, 70.0 and 110.0 MHz) are compared.

To determine the passivation quality of the a-SiOx:H films, microwave-detected photo conductance decay (µ-PCD) provides a contactless measurement of the effective recombination lifetime of free carriers. The film compositions and also the changes in the microscopic structure of the amorphous network upon thermal annealing are studied using Raman spectroscopy and optical profiling techniques.

The Raman spectra reveal the generation of Si-(OH)x and Si-O-Si bonds after thermal annealing in the layers, leading to a higher effective lifetime, as it reduces the defect absorption of the sub oxides.

For n-type FZ material, lifetime values as high as 1650 µs are obtained, resulting in a surface recombination velocity Seff < 9.5 cm/s.
Characterization of Silicon Carbide Thin Films Obtained Via Sublimation of a Solid Polymer Source Using Polymer-Source CVD Process
Authors: Oulachgar El Hassane , Aktik Cetin , Dostie Starr , Gujrathi Subhash , Scarlete Mihai
Published: April 2011

Silicon carbide thin films have been deposited via sublimation of a solid organosilane polymer source using atmospheric pressure chemical vapour deposition process (PS-CVD). The advantages of this new process include high deposition rate, compatibility with batch process, hazard-free working environment and low deposition cost. The silicon carbide (SiC) thin films obtained through this process exhibit a highly uniform film thickness, highly conformal coating, and very high chemical resistance to acids and alkalis solutions. These proven characteristics make the SiC thin films obtained by PSCVD process very attractive as a structural material for micro-electro-mechanical systems (MEMS) and as a coating film in a wide range of other applications. These SiC thin films are also expected to be attractive as a semiconductor material provided that the defects and oxygen contamination can be reduced and efficiently controlled. In this work we have investigated the chemical, structural, electrical and optical properties of these films, using elastic recoil detection (ERD), Fourier transform infrared (FTIR) spectroscopy, photospectroscopy, ellipsometry, and capacitance-voltage measurements.
ESR Study of Crystallization of Hydrogenated Amorphous Silicon Thin Films
Authors: Su Tining , Ju Tong , Taylor P. Craig , Stradins Pauls , Xu Yueqin , Hasoon Falah , Wang Qi , Harrison Walter A.
Published: April 2011

Solid-phase crystallization and the subsequent re-hydrogenation of the amorphous silicon thin films provides a low cost approach for thin-film crystalline Si:H-based photovoltaic devices. During the hydrogen effusion, significant lattice reconstruction occurs, as hydrogen is driven out of the film, accompanied by creation and migration of a large number of dangling bonds. We used electron-spin-resonance (ESR) to study evolution of the local order surrounding these dangling bonds during crystallization. When samples made by both plasma enhanced chemical vapor deposition (PECVD) and the and hot wire CVD (HWCVD) are heated to 560°C, hydrogen effuses within 30 min, giving rise to H-effused defect densities of about 5x1018 cm-3. Further heating at 560°C results in crystallizati°n in the HWCVD sample after about 200 min. On the other hand, PECVD samples crystallize only when heated up to 580°C, and then only after much longer times (Dt ~ 1300 min) [1,2]. ESR defects in both samples persist at the 5x1018 cm-3 level as long as the sample remains amorphous during the grain nucleation period. As the crystallites appear, the defect densities gradually decrease and saturate at about 3x1017 cm-3 as the crystallization is completed, both in HWCVD and PECVD samples.

In the H-effused states before crystallization, the ESR signals for both the HWCVD and PECVD samples show significant exchange-narrowing, suggesting that the defects are probably clustered. As the sample crystallizes, the defect clustering largely disappears, yet the line-widths in fully crystallized films are somewhat narrower than those in typical micro-crystalline silicon thin films as reported earlier [3]. This difference is probably due the specific structures of the grain boundaries in the present study. The effect of re-hydrogenation on both the H-effused amorphous and crystallized states will be discussed.
Relation between Electronic Properties and Density of Crystalline Agglomerates in Microcrystalline Silicon
Authors: Bronsveld Paula C.P. , Verkerk Arjan , Mates Tomas , Fejfar Antonin , Rath Jatindra K. , Schropp Ruud E.I.
Published: April 2011

A series of silicon thin films was made by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at substrate temperatures below 100 °C at different hydrogen to silane dilution ratios. The electronic properties of these layers were studied as a function of the surface crystalline fraction as determined accurately from a combination of microscope images at different length scales (gathered by using different types of microscopes). The results show that the electrical conductivity increases monotonously as a function of crystalline surface coverage and no discontinuity is observed at the percolation threshold. An increase in conductivity of four orders of magnitude for layers with a high crystalline content is observed after annealing at temperatures up to 170 °C. Combined with the information that oxygen is incorporated at Si-H surface bond sites, this suggests that doping of the intergrain boundaries by oxygen might be dominantly responsible for the electronic properties of mixed phase silicon.
Flexible a-Si:H-based Image Sensors Fabricated by Digital Lithography
Authors: Wong William S. , Ng TseNga , Chabinyc Michael L. , Lujan Rene A. , Apte Raj B. , Sambandan Sanjiv , Limb Scott , Street Robert A.
Published: April 2011

Amorphous silicon-based x-ray image sensor arrays were fabricated on poly-ethylene naphthalate substrates at process temperatures below 180°C. Patterning of the thin-film transistor backplane was accomplished using ink-jet printed etch masks. The sensor devices were found to be comparable to high-temperature processed devices. The integration of the sensor stack, TFT array and PEN substrate resulted in a flexible x-ray image sensor with 180×180 pixels with 75 dpi resolution.
Transient Current Behavior of Vertically Integrated Amorphous Silicon Diodes
Authors: Choong Gregory , Wyrsch Nicolas , Ballif Christophe , Kaufmann Rolf , Lustenberger Felix
Published: April 2011

Monolithic image sensors based on Thin Film on CMOS (TFC) Technology are becoming more and more attractive as an alternative solution to conventional active pixel sensors (APS). Imager with high sensitivity, high dynamic coupled with low dark current values (10-100 pA/cm2 @ 104 V/cm) have been developed. However, issues such as light-induced degradation and image lag hinder the commercial development of a-Si:H based image sensors. The problem of image lag is caused by residual current due to the release of trapped charges after the switch off of the illumination.

In this paper, we present a comprehensive study of the transient behavior of the photocurrent in a-Si:H photodiodes deposited on glass, as well as in corresponding diodes implemented in a TFC image sensor when illumination is switched off or periodically varied. The influence of the pixel architecture for two different cases is also analyzed: One setup reproduces the typical 3 transisor APS pixel architecture behavior, in which the bias voltage of the diode varies with the photogenerated charge while the second setup keeps a constant bias voltage applied to the diode by using a charge integrator.

The influence of the light-induced defect creation on the performance of the sensors is also presented and discussed.
Resistive Losses at c-Si/a-Si:H/ZnO Contacts for Heterojunction Solar Cells
Authors: Einsele Florian , Rostan Phillip Johannes , Rau Uwe
Published: April 2011

We study resistive losses at (p)c-Si/(p)Si:H/(n)ZnO heterojunction back contacts for high efficiency silicon solar cells. We find that a low tunnelling resistance for the (p)a-Si:H/(n)ZnO part of the junction requires deposition of Si:H with a high hydrogen dilution RH > 40 resulting in a highly doped μc-Si:H layer. Such a μc-Si:H layer if deposited directly on a Si wafer yields a surface recombination velocity of S  180 cm/s. Using the same layer as part of a (p)c-Si/(p)Si:H/(n)ZnO back contact in a solar cell results in an open circuit voltage Voc = 640 mV and a fill factor FF = 80 %. Insertion of an (i)a-Si-layer between the μc-Si:H and the wafer leads to a further decrease of S and, for the solar cells to an increase of VOC. However, if the thickness of this intrinsic layer exceeds a threshold of 3 nm, resistive losses lead to a degradation of the fill factor of the solar cells. These resistive losses result from a valence band offset δEV between a-Si:H and c-Si of about 600 meV. The fill factor losses overcompensate the VOC gain such that there is no benefit of the (i)a-Si:H interlayer for the overall solar cell performance when using an (i)a-Si:H/(p)uc-Si:H double layer.
Photocurrent Profile in a-SiC:H Monolithic Tandem Pinpin and Pinip Photodiodes
Authors: Fantoni Alessandro , Vieira Manuela , Vygranenko Yuri
Published: April 2011

We present in this paper results about the analysis of photocurrent and spectral response in a-SiC:H/ a-Si:H pinpin and pinip structures. Our experiments and analysis reveal the photocurrent profile to have a strong nonlinear dependence on the externally applied bias and on the light absorption profile, i.e. on the incident light wavelength and intensity. Our interpretation points out the cause of such effect to a self biasing of the junctions under certain unbalanced light generation of carriers and to an asymmetric reaction of the internal electric fields to the externally imposed bias. The possibility to relate such a behavior to the light intensity and wavelength indicates realistic hypothesis of using these structures and this effect for color recognition sensors.

We present results about the experimental characterization of the structures and numerical simulations obtained with the program ASCA. Considerations about electrical field profiles and inversion layers will be taken into account to explain the optical and voltage bias dependence of the spectral response. Our results show that in both structures the application of an external electrical bias (forward or reverse) mainly influences the field distribution within the less photo excited sub-cell.
Temperature Dependence of Leakage Current in Segmented a-Si:H n-i-p Photodiodes
Authors: Chang Jeff Hsin , Chuang Tsu Chiang , Vygranenko Yuri , Striakhilev Denis , Kim Kyung Ho , Nathan Arokia , Heiler Gregory , Tredwell Timothy
Published: April 2011

Hydrogenated amorphous silicon (a-Si:H) n-i-p photodiodes may be used as the pixel sensor element in large-area array imagers for medical diagnostics applications. The dark current level is an important parameter that dictates the performances of these types of pixelated imaging devices. Through measurements performed at different ambient temperatures, the leakage current components of segmented a-Si:H n-i-p photodiodes were extracted and analyzed. It was found that the central component of the reverse current depends exponentially on bias and temperature. The activation energy of this component is independent of bias. The peripheral component of reverse current exhibits linear bias dependence at temperatures up to 50°C, while the contribution of this component diminishes at high temperatures. The dependence of dark current components on bias and temperature could be described by compact analytical equations. The model of forward and reverse dark current characteristics in temperature range was implemented in Verilog-A hardware description language.
Structural Analysis of Nanocrystalline Silicon Prepared by Hot-wire Chemical Vapor Deposition on Polymer Substrates
Authors: Adachi Michael Musashi , Taghibakhsh Farhad , Kavanagh Karen L. , Karim Karim S.
Published: April 2011

Nanocrystalline silicon (nc-Si:H) films were deposited by hot-wire chemical vapor deposition (HWCVD) directly onto Corning glass and polyimide (Kapton E) substrates. The effect of silane concentration (in hydrogen carrier gas) on film crystallinity and conductivity were studied for a constant substrate growth temperature of 220°C. Raman spectroscopy, X-ray diffraction and cross-sectional transmission electron microscopy (XTEM) showed that nc-Si:H (grain-size 20-65 nm) was observed for silane concentrations below 5.8 %. Similar to previous reports, closer inspection using XTEM found that there was an initial growth of an amorphous interfacial layer which then crystallized into a randomly-oriented polycrystalline material after 10 - 100 nm of growth.. However, unlike previous reports, there was no detectable difference in the structure or conductivity for films grown on the two types of substrates. In both cases, the dark conductivity decreased with increasing silane concentration while the photo-conductivity was uniform for all films at values between 2 and 4×10-5 S/cm.
Manipulating the Hydrogen-Bonding Configuration in ETP-CVD a-Si:H
Authors: Wank Michael , van Swaaij R. A. C. M. M. , van de Sanden M. C. M.
Published: April 2011

The effect of ion bombardment on the relationship between the critical hydrogen concentration and the reactor pressure has been investigated for hydrogenated amorphous silicon (a-Si:H) deposited with the expanding thermal plasma-CVD (ETP-CVD) method. By changing the reactor pressure the ionic cluster formation in the plasma can be varied. It is observed that the decrease of the critical hydrogen concentration with increasing reactor pressure can not be compensated by ion bombardment at 14V biasing. Biasing with 20V however increases the critical hydrogen concentration nearly up to the value obtained at low pressures. This indicates that the incorporation of ionic cluster formed at elevated reactor pressures can be reduced by substrate biasing, possibly due to break-up upon impact on the substrate surface or due to processes occurring in the secondary plasma close to the substrate.
Materials Optimization for Silicon Heterojunction Solar Cells Using Spectroscopic Ellipsometry
Authors: Levi Dean , Iwanizcko Eugene , Johnston Steve , Wang Qi , Branz Howard M
Published: April 2011

Our research team has used hot wire chemical vapor deposition (HWCVD) to fabricate silicon heterojunction (SHJ) solar cells on p-type FZ silicon substrates with efficiencies as high as 18.2%. The best cells are deposited on anisotropically-textured (100) silicon substrates where an etching process creates pyramidal facets with (111) crystal faces. Texturing increases Jsc through enhanced light trapping, yet our highest Voc devices are deposited on un-textured (100) substrates. One of the key factors in maximizing the efficiency of our SHJ devices is the process of optimization of the material properties of the 3 - 5 nm thick hydrogenated amorphous silicon (a-Si:H) layers used to create the junction and back contact in these cells. Such optimization is technically challenging because of the difficulty in measuring the properties of extremely thin layers. This difficulty is compounded by the fact that the properties of such amorphous layers are substrate- and thickness-dependent. In this study, we have utilized spectroscopic ellipsometry (SE) and photoconductivity decay to conclude that a-Si:H films grown on (111) substrates are substantially similar to films grown on (100) substrates. In addition, analysis of the substrate temperature dependence of surface roughness evolution reveals a substrate-independent mechanism of surface smoothening with an activation energy of 0.28 eV. Analysis of the substrate temperature dependence of surface passivation reveals a passivation mechanism with an activation energy of 0.63 eV.
Surface Chemical Characteristics of CMP Polyurethane Pads
Authors: Xiang Hongqi , Prasad Abaneshwar , Remsen Edward E.
Published: April 2011

Attenuated total reflection FT-IR spectroscopy coupled with a hydrogen-deuterium exchange technique is employed to investigate the surface chemistry of two polishing pads, a thermoplastic polyurethane (TPU) pad and a commercial cast urethane (PU) pad. A time/temperature-dependent reduction of nitrogen-hydrogen stretching modes (νN-H) was observed when the pads were immersed in deuterium oxide (D2O). Compared to TPU pads, the PU pads showed an ambiguous correlation between dependence of the band intensity changes and D2O-immersion time/temperature. For both types of pads, a sharp decrease in νN-H band intensity and an unexpected rebound in νN-H band intensity were observed within 24 hrs after immersing the pads in D2O. However, a comparable rebound in νN-H band intensity was not observed for conditioned TPU pad samples. This phenomenon is proposed to be due to a rearrangement of polar groups at the pad surface when the pad is immersed in water, which may influence pad performance on the asperity level.
Spectroscopic and Topographic Investigations of Nanoparticle Abrasive retention in Polyurethane CMP Pads for Cu CMP
Authors: Ul-hasan Iftikhar , Geer Robert
Published: April 2011

A spectroscopic and topographic investigation of abrasive nanoparticle retention in polyurethane chemical mechanical planarization (CMP) pads has been carried out as a function of ex situ pad conditioning parameters for Cu CMP. X-ray photoelectron spectroscopy (XPS) and scanning electron microscope energy dispersive spectroscopy (SEM-EDS) were utilized to quantitatively characterize the presence of alumina nanoabrasive in the pad following Cu CMP. As expected, conditioning did not modify the overall pad morphology but did increase local asperity roughness with increasing conditioner downforce. As expected, the magnitude of the conditioner downforce reduced the overall average alumina nanoabrasive retention, albeit weakly, as determined via XPS. However, local EDS analysis revealed that increased downforce does significantly reduce nanoabrasive retention at pad asperities. In contrast, increased downforce increased the amount of nanoabrasive present in the polyurethane pad surface pores. Moreover, overall conditioning time was shown to be a more dominant parameter compared to conditioner downforce regarding removal of abrasive particles from both pad asperities and pores.
Newly Developed Abrasive-free Copper CMP Slurry Based on Electrochemical Analysis
Authors: Amanokura Jin , Mabuchi Katsumi , Sakurada Takafumi , Nomura Yutaka , Habiro Masanobu , Akahoshi Haruo
Published: April 2011

In order to reduce microscratches and obtain minimized dishing and erosion, we have developed new abrasive-free Cu CMP slurries. During the development of these slurries, some electrochemical examination was performed. The most effective knowledge was obtained through the analysis using rotary Cu disk electrode under pressure. On the basis of these studies, new abrasive-free Cu CMP slurries with a high removal rate and excellent planarity were designed and developed. The mechanism of reducing dishing and erosion was also discussed.
Experimental Investigation and Numerical Simulation of Pad Stain Formation during Copper CMP
Authors: Lee Hyosang , Zhuang Yun , Borucki Leonard , O'Moore Fergal , Joh Sooyun , Philipossian Ara
Published: April 2011

Experiments and simulations were performed to investigate the characteristics of staining on pad surface. Experiments were performed on a table-top axisymmetric polishing system, consisting of a 12-inch non-rotating platen and a 4-inch rotating wafer carrier having the same center axis. Results showed that the stain deposited on each land area was found to be darker in the direction of wafer rotation and in the radial direction, suggesting that staining agent was produced by mechanical action during polishing and was advected downstream by the slurry flow. Generally, staining increased with polishing pressure, wafer rotation rate and polishing time. The simulated slurry velocity showed shear flow on the land areas and wafer-driven circulation in the grooves. Thermal model simulation showed 12 degree temperature rise on the reaction at the surface of wafer.
Contact Model for a Pad Asperity and a Wafer Surface in the Presence of Abrasive Particles for Chemical Mechanical Polishing
Authors: Bozkaya Dincer , Muftu Sinan
Published: April 2011

A contact model for a single spherical (pad) asperity and a flat (wafer) surface, with an interface filled with spherical (abrasive) particles is introduced. Finite element method is used to determine the deformation characteristics of a single spherical abrasive indenting a hyper-elastic pad material. The asperities in Greenwood and Tripp (GT) model, which is widely used for the contact of rough spheres, are replaced with the spherical particles. Relations are developed to predict pad-to-particle-to-wafer contact in two distinct regimes, where a) pad and the wafer are separated by the particle; and b) all three bodies come in contact simultaneously. The results of the model show that the abrasive particles in the (pad) asperity-wafer interface causes the contact to be distributed over an area larger than that predicted by the Hertz model, while the maximum contact pressure becomes relatively lower. The fraction of the load carried by pad-to-wafer and pad-to-abrasive-to-wafer varies along the contact interface of the pad asperity and wafer.
Single Asperity Tribochemical Wear of Silicon by Atomic Force Microscopy
Authors: Katsuki Futoshi
Published: April 2011

We report measurements of single asperity wear on oxidized silicon surface in aqueous KOH using atomic force microscopy (AFM), where the single crystal silicon tip was used both to tribologically load and image the surface. AFM was also operating in the lateral (frictional) force mode (LFM) to investigate the pH dependence of kinetic friction between the tip and the SiO2 surface. We found that the Si tip wear amount strongly depended on the solution pH value and was at a maximum at around pH 10. It was also found that the Si removal volume in moles was approximately equal to that of SiO2 irrespective of the solution pH value. This equality implies that the formation of the Si-O-Si bridge between one Si atom of the tip and one SiO2 molecule of the specimen at the wear interface, followed by the oxidation of the Si surface, finally the bond rupture by the tip movement, the dimeric silica (OH) 3Si-O-Si(OH) 3, including the Si-O-Si bridge is dissolved in the KOH solution. It was also found the frictional force is highly sensitive to the pH values of the solution and peaked at around pH 10. These results indicate that the interfacial reaction would be affected by the frictional force between the Si tip and the SiO2 surface, due to an increased liquid temperature and a compressive stress in Si and SiO2 networks. Strong influence is observed by the pH of the ambient solution confirming the important role of the OH- in the wear mechanism. We present a microscopic removal mechanism which is determined by an interplay of the diffusion of water in Si and SiO2.
Towards a Quantitative Description of Pattern-dependent Planarization with Ceria Slurries
Authors: Rzehak Roland , Vogel Thomas
Published: April 2011

Slurries with ceria abrasives are nowadays widely used for high-end applications like STI. Concerning the pattern dependence of planarization, such slurries exhibit a much more complex behavior than conventional silica-based slurries. The situation is complicated by the fact that depending on often unknown factors like the manufacture of the ceria abrasives and additionally present additives the observed phenomena are also quite diverse. As a consequence, quantitative models are lacking and predictions of post CMP topography that could be used e.g. to derive design rules or optimize dummy fill are not available.

We here present detailed experimental results on one specific slurry system with ceria abrasives that behaves very different from conventional silica-based slurries. Possible causes for this peculiar behavior are discussed to the extent that a statement about their relevance can be made.
Ultra Thin Cu film Fabrication by Supercritical Fluid Deposition for ULSI Metallization
Authors: Momose Takeshi , Sugiyama Masakazu , Shimogaki Yukihiro
Published: April 2011

Initial nucleation and succeeding coalescence in supercritical fluid deposition (SCFD) of Cu was studied in situ by using our devised monitoring technique, i.e. surface reflectivity measurement of visible white light. Fabrication of 10nm-thick smooth and continuous Cu film required by ULSI metallization, was succeeded. Complete filling without any seems and voids into various via patterns of 50 - 200 nm in diameter and 1 μm in depth was also achieved, which was revealed through angled polishing of patterned substrate.
Development of Simple Electrolytes for the Electrodeposition of Pb-Free, Sn-Based Alloy Solder Films
Authors: Han Chunfen , Liu Qi , Ivey Douglas G.
Published: April 2011

A simple, cyanide-free, slightly acidic, chloride-based solution has been developed for the electrodeposition of Sn-0.7wt%Cu solder films. The solution contains only one additive (tri-ammonium citrate) other than the metal salts and is stable for more than 36 days. The optimum citrate concentration is 0.30 mol/L for 0.22 mol/L of SnCl2•2H2O. The addition of 0.003 mol/L of CuCl2•2H2O to this solution can produce near eutectic (Sn-0.7 wt% Cu) deposits, on Au, Ni or Cu substrates, at current densities of 10-12.5 mA/cm2. Plating rates are in the 20-27.5 μm/hr range at room temperature. Copper is evenly distributed (~0.7wt%Cu) through most of the thickness, with slightly higher Cu levels at the solder/Ni interface. After solder reflow at 260°C, two phases are present, Sn plus either Cu6Sn5 for Cu substrates or (Cu,Ni)6Sn5 for Ni substrates.
Hydrogen-induced Nitrogen Passivation in Dilute Nitrides: A Novel Approach to Defect Engineering
Authors: Trotta Rinaldo , Polimeni Antonio , Felici Marco , Pettinari Giorgio , Capizzi Mario , Frova Andrea , Salviati Giancarlo , Lazzarini Laura , Armani Nicola , Mariucci Luigi , Bais Giorgio , Martelli Faustino , Rubini Silvia
Published: April 2011

The capability of hydrogen to passivate nitrogen in dilute nitrides is exploited to in-plane engineer the electronic properties of Ga(AsN)/GaAs heterostructures. Two methods are presented: i) by deposition of hydrogen-opaque metallic masks on Ga(AsN) and subsequent hydrogen irradiation, we artificially create zones of the crystal having the band gap of untreated Ga(AsN) surrounded by GaAs-like barriers; ii) by employing an intense (∼100 nA) and narrow (∼100 nm) beam of electrons, we dissociate the complexes formed by N and H in a spatially delimited part of a hydrogenated Ga(AsN) sample. As a consequence, in the spatial regions irradiated by the electron beam, hydrogenated Ga(AsN) recovers the smaller energy gap it had before hydrogen implantation.
Formation of Hydrogen Related Defects and Nano-Voids in Plasma Hydrogenated ZnO
Authors: Job Reinhart
Published: April 2011

Using μ-Raman spectroscopy (μRS) and cathodoluminescence (CL) analyses, the impact of hydrogen plasma treatments on sintered zinc oxide (ZnO) samples was studied. 1 hour H-plasma treatments (150 W, 13.56 MHz) were applied at substrate temperatures between 250 °C and 500 °C. μRS and CL analyses show that plasma hydrogenation causes significant defects in ZnO samples; i) non-specified defect species are established with a maximal density upon H-plasma exposure at 350 °C substrate temperature, and ii) the formation of oxygen vacancies (VO) can be traced. Moreover, μRS reveals vibration modes of H2 molecules trapped in nano-voids. The experimental results indicate that those nano-voids are created by a coalescence of the VO defects.
The Dynamic Ultrasound Influence on the Diffusion and Drift of the Charge Carriers in Silicon p-n Structures
Authors: Burbelo Roman M. , Olikh Oleg Y. , Hinders Mark K.
Published: April 2011

Nowadays much attention is given to the ultrasound influence on electrophysical properties and defective structure of semiconductors and semiconductor structures [1,2]. In particular, a big interest is caused by the processes which take place in the material under non-equilibrium conditions, caused by the acoustic vibration [2]. This paper is devoted to the study of the ultrasonic waves dynamic influence (in situ) on the processes of the charge transport in a silicon solar sell.

The silicon structures with p-n-transition received by phosphorus ions implantation in a surface layer of Si:B plate have been chosen as the research objects. Transition is located at 0,5 microns depth from surface, n-layer electron concentration is 1019 cm−3, hole concentration is 1.3×1015 cm−3. The specified structures I-V characteristics are measured under ultrasonic fluctuations excitation conditions. The researches were carried out both without external illumination as well as under external illumination. In the latter case, additional carriers photogeneration occurred both at the p-n-transition region and at the p-area depth. Longitudinal acoustic waves were excited in structures with help of LiNbO3 transducer; the ultrasound frequency is 4.1 and 13.6 MHz; the acoustic power is up to 3 W/cm2.

It is revealed, that the changes of diffusion parameters take place at the non-equilibrium conditions caused by ultrasonic lading. These changes are shown in photocurrent rising. Photocurrent increase reached up to 15 %, which corresponds to 2 times diffusion length increasing approximately. Also the essential (up to 40 %) acoustostimulated decreasing of the p-n-transition saturation current is revealed. The characteristic time of the observable effects is level with tens minutes. It is established, that dependence of the dynamic changes on ultrasound power is nonlinear. It is shown, that efficiency of an acoustostimulated influences raises with an ultrasound frequency.

The analysis has shown that observable effects are connected with non-equilibrium processes of defects ionization and reorientation at an acoustic field. It specifies an opportunity of a dynamic management of a charge carriers distribution processes in semiconductor structures by ultrasonic waves.
Deuterium Out-Diffusion Kinetics in Magnesium-Doped GaN
Authors: Chevallier Jacques , Jomard François , Nickel Norbert H. , de Mierry Philippe , Chenot Sébastien , Cordier Yvon , di Forte-Poisson Marie-Antoinette , Delage Sylvain
Published: April 2011

A series of isothermal annealing experiments have been performed in the range 790–920°C under N2 flow in order to study the deuterium out-diffusion kinetics of Mg-doped GaN grown on sapphire under deuterated ammonia. The deuterium concentration was measured by SIMS analysis before and after each annealing step. The kinetics closely follow a first-order law. The activation energy related to the deuterium out-diffusion process is 3.1 eV. In addition, deuterium effusion measurements were performed measuring the molecular HD flux while the specimens were annealed in ultra high vacuum with a linear heating rate. In contrast to SIMS, this method detects the species that migrated out of the sample. Effusion peaks of the HD flux at 360 and 490°C are attributed to the fragmentation of adsorbed CHxDy complexes. The molecular HD flux starts increasing at 800°C which is the onset of the GaN decomposition and has its maximum at 920°C. This HD flux is accompanied by the desorption of H and D containing radicals and molecules desorbing above 900°C.
Modeling of Cu Surface Precipitation and Out-Diffusion from Silicon Wafers
Authors: Guo Hsiu-Wu , Dunham Scott T.
Published: April 2011

Copper is one of the most concerned contaminants for silicon process, due to its detrimental effects on device performance if present in active regions. Gettering of Cu by changing the surface conditions at the wafer surface is commonly used. Acceleration of Cu out-diffusion and surface precipitation was observed with changes of the surface potential, which could be altered by both existing Cu precipitates and organics at the surface. In this work, physically based models are developed to describe the Cu evolution at the wafer surface including the dependence of surface potential. These models are verified by comparison to the experiment measurements from Ohkubo et al. [Jpn. J. Appl. Phys. 1 44, 3793 (2005)].
Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-treatment
Authors: Gu Qilin , Ling Chi-Chung , Cheung Chor-Keung , Luo Jiaming , Chen Xudong , Djurisic Aleksandra , Brauer Gerhard , Anwand Wolfgang , Skorupa Wolfgang , Reuther Helfried , Ong Hock-Chun
Published: April 2011

Au contacts were fabricated on pressurized melted grown n-type ZnO single crystal samples pre-treated with boiling organic solvent and hydrogen peroxide. Contacts fabricated without any pre-treatment and with boiling organic solvent pre-treatment were found to have ohmic behavior. For the samples pre-treated with hydrogen peroxide, the Au contacts were found to have rectifying property. Systematic investigation was performed to study the dependence of the Schottky barrier height and the reverse bias leakage current on the temperature and the duration of the pre-treatment. Positron annihilation spectroscopy (PAS), X-ray photoemission (XPS) and scanning electron microscope (SEM) were also used to understand how the vacancy type defect, contamination and surface morphology would influence the electrical property of the fabricated contacts.
Interaction between Recombination Enhanced Dislocation Glide Process Activated Basal Stacking Faults and Threading Dislocations in 4H-Silicon Carbide Epitaxial Layers
Authors: Chen Yi , Dudley Michael , Liu Kendrick X , Stahlbush Robert E
Published: April 2011

Electron-hole recombination enhanced glide of Shockley partial dislocations bounding expanding stacking faults and their interactions with threading dislocations in 4H silicon carbide epitaxial layers have been studied using synchrotron white beam X-ray topography and in situ electroluminescence. The mobile silicon-core Shockley partial dislocations bounding the stacking faults are able to cut through threading edge dislocations leaving no trailing dislocation segments in their wake. However, when the Shockley partial dislocations interact with threading screw dislocations, trailing 30o partial dislocation dipoles are initially deposited in their wake due to the pinning effect of the threading screw dislocations. These dipoles spontaneously snap into their screw orientation, regardless the normally immobile carbon-core Shockley partial dislocation components in the dipoles. They subsequently cross slip and annihilate, leaving a prismatic stacking fault in (2-1-10) plane with the displacement vector 1/3[01-10].
XPS and STM Studies on Initial Oxidation of Si(110)-16x2
Authors: Suemitsu Maki , Togashi Hideaki , Kato Atsushi , Takahashi Yuya , Konno Atsushi , Yamamoto Yoshihisa , Teraoka Yuden , Yoshigoe Akitaka , Asaoka Hidehito
Published: April 2011

The initial oxidation of Si(110)-16×2 clean surface has been investigated by using real-time synchrotron-radiation photoemission spectroscopy and scanning tunneling microscopy. The Si(110) initial oxidation is characterized by its unique rapid oxidation right after the introduction of oxygen molecules, which is most likely attributed to the preferential reactions at the pentagon pairs of the 16×2 reconstruction.
Structural and Electronic Properties of Oxygen Vacancies in Monoclinic HfO2
Authors: Broqvist Peter , Pasquarello Alfredo
Published: April 2011

We study structural and electronic properties of the oxygen vacancy in monoclinic HfO2 for five different charge states. We use a hybrid density functional to accurately reproduce the experimental band gap. To compare with measured defect levels, we determine total-energy differences appropriate to the considered experiments. Our results show that the oxygen vacancy can consistently account for the defect levels observed in optical absorption, direct electron injection, and trap-assisted conduction experiments.