bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-aligned Process for SiC Power Devices
Authors: Borsa Tomoko , Van Zeghbroeck Bart
Published: August 2010

Silicon carbide is a semiconductor with desirable material properties, such as a wide bandgap and high thermal conductivity. It is an excellent material for constructing power switching devices operating in harsh environments where conventional semiconductors cannot adequately perform. One example of such a power device is a bipolar junction transistor (BJT). While the potential of the SiC BJT is recognized, appropriate techniques for producing devices is lacking due to its difficulty.

For example, in order to achieve a high voltage 4H-SiC BJT switch with nanosecond switching time, the device must have a low base resistance. The simulation results indicate that for an emitter width of 2.0 μm and a base width of 1.2 μm the distance between the two should be 0.4 μm or less to meet the requirement for base resistance. To produce the above-described geometries and spacing, it is desirable to construct the device in a self-aligned manner. Self-alignment in this context means that the relative spacing of features of the device, such as contacts, is automatically controlled by the processing sequence and process parameters, rather than by the careful alignment prior to exposure of a photo sensitive layer. For this purpose, we developed a novel self-aligned process for SiC BJT devices, that enables the fabrication of the design with high yield, as standard silicon self-aligned technique are not applicable.

The newly developed process starts with the deposition of the emitter contact metal, which provides the metal mask for the etching of the emitter ridges. Next, the wafer is planarized with photoresist and etched, so that only the emitter contacts are exposed. Electroless plating is then used to enlarge the contacts, and after removal of the resist, the plating provides an overhang, suitable for lift-off of the base contact metal. After the base contact metal deposition, the structure is planarized and etched, this time with a silicon dioxide layer, again exposing the plated emitter contacts and the lift-off step is the wet etching of the plated metal. The emitters are then all connected with a blanket wiring level, which also forms the base contact pad. This process is simpler and more robust than the process we developed to date. The main difference is the inclusion of a sacrificial lift-off overhang, created by electroless plating. It enables a well controlled overhang independent of steepness of the SiC ridge profile and the height of the emitter mesa. We successfully fabricated the overhang structure on 4H-SiC substrates.

In conclusion, we report the demonstration of a new self-aligned process, which provides a self-aligned emitter contact, a self-aligned base contact and eliminates the need for via holes smaller than the emitter stripe widths. We consider this new process a major improvement over existing processes to fabricate SiC BJT devices.
Ohmic Contacts to Wurtzite Silicon Carbide Using Polarization Technology
Authors: Praharaj Choudhury Jayant
Published: August 2010

We present theoretical calculations for ohmic contact technology to wurtzite Silicon Carbide using thin Indium Gallium Nitride and Aluminium Indium Nitride cap layers. Spontaneous and piezoelectric polarization in Indium Gallium Nitride and Aluminium Indium Nitride cap layers gives rise to bound interface sheet charge density of the order of 1013 electrons per cm2, and built-in electric fields of the order of MV per cm. For Si-face p-type SiC, the large compressive strain in very thin InGaN and AlInN cap layers results in negative sheet charge densities and much lower tunneling widths for holes compared to bulk contacts. For C-face p-type SiC, pseudomorphic nitride layers yield no benefit over bulk contacts since positive interface sheet charge densities repel holes and give higher contact resistances. However, thick, relaxed cap layers lead to spontaneous polarization-based negative charge densities that attract holes, leading to lower contact resistances. The contributions of the heavy, light and split-off band holes to the total tunneling flux is taken into account in our calculations. All tunneling probabilities are calculated within the Wentzels-Kramers-Brillouin approximation. The presence of the appropriate cap layers leads to several orders of magnitude improvement in tunneling transmission probabilities, and in many cases, makes ohmic technology to SiC feasible. While the major difficulties are encountered for contacts to p-type SiC, the effect of cap-based polarization technology on contacts to n-type layers is also discussed in this paper. Our calculations have relevance to contact technology for bipolar devices built from wide band-gap wurtzite semiconductors like heterojunction bipolar transistors, light-emitting diodes and lasers.
Near-interface Traps in n-type SiO2/SiC MOS Capacitors from Energy-resolved CCDLTS
Authors: Basile Alberto F , Dhar Sarit , Rozen John , Chen Xudong , Williams John , Feldman Leonard C. , Mooney Patricia M.
Published: August 2010

Silicon Carbide (SiC) Metal-Oxide-Semiconductor (MOS) capacitors, having different nitridation times, were characterized by means of Constant Capacitance Deep Level Transient Spectroscopy (CCDLTS). Electron emission was investigated with respect to the temperature dependence of emission rates and the amplitude of the signal as a function of the filling voltage. The comparison between the emission activation energies of the dominant CCDLTS peaks and the filling voltages, led to the conclusion that the dominant trapping behavior originates in the Silicon-dioxide (SiO2) layer. Moreover, a model of electron capture via tunneling can explain the dependence of the CCDLTS signal on increasing filling voltage.
Manufacturable 300mm Wafer Thinning for 3D Interconnect Applications
Authors: Qureshi Jamal , Caramto Raymond , Olson Stephen , Mase Jerry , Ito Toshihiro , Yamamoto Eiichi
Published: August 2010

3D interconnect wafer-to-wafer or die-to-wafer integration requires a wafer thinning operation to expose copper (Cu)-filled through-silicon vias (TSVs) from the backside of the wafer. The wafer thinning flow uses edge trim, backgrind, backpolish, and chemical mechanical polishing (CMP). This paper presents an overview of the wafer grinding process. We have demonstrated the capability to edge-trim and backgrind 300 mm TSV and non-TSV wafers down to 30 microns (μm) while bonded to a handle wafer. TSV wafers were further processed on a CMP tool to remove the last few microns of Si, exposing the Cu-filled TSVs. Metrology techniques were used to inspect and measure the wafer edge trim and final thinned wafer thickness. The quality of the thinned wafer was characterized by atomic force microscopy (AFM) to observe surface roughness and by transmission electron microscopy (TEM) to quantify crystalline damage below the surface of the thinned wafer. Further characterization included measuring wafer thickness, total thickness variation (TTV), bow, and warp. Exposed TSVs were characterized by laser microscope to measure the height of Cu protrusions. These critical elements of a manufacturing-worthy 300 mm wafer thinning process for 3D are discussed.
Design, Characteristics and Performance of Diamond Pad Conditioners
Authors: Pysher Douglas J. , Goers Brian , Zabasajja John
Published: August 2010

A wide range of diamond pad conditioner (disk) designs have been characterized and key performance metrics have been collected. Relationships between design characteristics including diamond size and shape, spatial density, and tip height distribution and polishing pad wear rates and pad surface textures have been established for a variety of pads.

Estimation of the depth-of-penetration of working diamonds, from used disk analyses, allows meaningful topographic assessments of alternative conditioner designs and predictions of relative performance. An example of an improved conditioner that illustrates this design methodology is given.

Conditioner aggressiveness and its decay in various slurries have been measured to assess disk lifetime in Chemical Mechanical Planarization (CMP) processes environments. Key factors affecting disk lifetime are discussed and an improved-lifetime conditioner for use in aggressive slurries will be reviewed.
Characterization of Large Particles in Fumed Silica Based CMP Slurry
Authors: Rader W. Scott , Holt Timothy , Tamai Kazusei
Published: August 2010

Large particles in fumed silica dispersions were characterized by sedimentation, light scattering techniques, Transmission Electron Microscopy (TEM), and lacunarity. Applying centrifugation to fumed silica dispersions generated differences in sedimentation rates of large particles. The sedimentation rates of the large particles were affected by morphological differences and the particles remaining in the supernatant displayed buoyant behavior. The large particle morphology varied from branch like aggregates containing large primary particles to particles comprised of highly coalesced, tightly packed small primary particles. The results indicate the presence of different types of large particles in fumed silica dispersions to which conventional large particle characterization is unable to distinguish.
C2H4-Based Plasma-Assisted CD Shrink and Contact Patterning for RRAM Application
Authors: Milenin Alexey , Lisoni Judit , Jossart Nico , Jurczak Malgorzata , Struyf Herbert , Shamiryan Denis , Brouri Mohand , Boullart Werner
Published: August 2010

Critical dimension (CD) shrink and patterning of contact features via plasma etching were studied for typical resistive random access memory (RRAM) stacks. These consist of SiO2 and Si3N4 (total thickness of 65 80 nm) with NiO or pure Ni at the bottom. First, the contact patterning of RRAM stacks was investigated for 90 nm contacts. Thus, a standard high power contact etch recipe was shown to give rise to resist strip challenges due to the incorporation of sputtered Ni in the resist film. Therefore, a low-sputter-yield contact etch recipe based on a CF4/H2/Ar gas chemistry was introduced. The ion sputter efficiency of the recipe was estimated from a blanket SiO2 sputter-yield experiment in Ar plasma for the same recipe settings: this yielded values close to the Ni sputter-yield threshold. Second, plasma-assisted CD shrink was studied in combination with the newly developed patterning scheme to get the contact CD well below the initial 90-nm litho print size. It was shown that a low contact etch power regime could also provide a larger window for contact CD shrink using a C2H4-based chemistry: e.g. the demonstrated CD shrink from 90 nm down to sub-40 nm was shown to be extremely challenging in the case of a high power regime due to polymer instability enhanced with the resulting thickness increase. Perhaps, the relaxation of the polymer film stress, which was measured to be in the range of 1200-1500 MPa, is more easily triggered at higher power settings, which leads to polymer blistering. Finally, the optimization of the plasma-assisted CD shrink step in combination with the low-sputter-yield contact etch recipe was demonstrated to be able to provide CDs as small as 27 nm. The demonstrated approach shows that plasma-assisted CD shrink can provide a robust test vehicle for research programs that require the patterning of small features in the sub-40-nm CD range.
Barrier Metal Ions Drift into Porous Low k Dielectrics under Bias-Temperature stress
Authors: He Ming , Ou Ya , Wang Pei-I , Vanamurthy Lakshmanan H , Bakhru Hassaram , Lu Toh-Ming
Published: August 2010

Ta family has been used as barrier to prevent Cu diffusion into interlayer dielectric in IC applications. Recent experiments demonstrated a more severe flatband voltage shift (ΔVFB) occurred for Ta/porous low k dielectrics/Si capacitors compared to that of Cu/porous low k dielectrics/Si capacitors after a moderate bias temperature stress (BTS). The flatband voltage shift under BTS was interpreted as the penetration of Ta ions into porous low k dielectrics. However, this interpretation has been under debate. In this paper, by using Secondary Ion Mass Spectrometry (SIMS) backside sputter depth profile technique, we report a direct evidence of Ta ions inside porous methyl silsesquioxane (MSQ) in a Ta/MSQ/Si structure after BTS.
An Optimized 300mm BCB Wafer Bonding Process for 3D Integration
Authors: Singh Pratibha , Hudnall John , Qureshi Jamal , Kamineni Vimal Kumar , Taylor Chris , Rudack Andy , Diebold Alain , Arkalgud Sitaram
Published: August 2010

Wafer bonding using benzocyclobutene (BCB) has been discussed in the past for three-dimensional (3D) integration. This paper reports the development and characterization of a manufacturable BCB bonding process for 300 mm wafers using standard 300 mm tools. A systematic optimization approach has been developed to characterize the bulk properties of the BCB film that can be applied to various integration schemes. We specifically discuss one such application—handle wafer bonding. BCB bonding for a range of cross-linking levels has been investigated. The cross-linking level of BCB before bonding is determined using an infrared (IR) variable angle spectroscopic ellipsometer (VASE) technique. The impact of the BCB film preparation and bonding condition on bond quality is characterized using scanning acoustic microscopy (SAM) , IR microscopy, a razor blade test, and four-point bend methods. Based on the results, an optimum cross-linking level for BCB film before bonding was determined for 300 mm wafers to obtain void-free and dendrite-free bonds. Wafers bonded using the optimized BCB process conditions have successfully sustained backgrinding, dry thinning, and standard BEOL metallization steps.
Structural, Magnetic and Magneto-tranport Properties of Reactive-sputtered Fe3O4 Thin Films
Authors: Wang Xinghua , Goolaup Sarjoosing , Ren Peng , Lew Wen Siang
Published: August 2010

Thin films of magnetite (Fe3O4) are grown on a single-crystal Si/SiO2 (100) substrate with native oxide using DC reactive sputtering technique at room tempreture (RT) and 300C. The x-ray diffraction(XRD) result shows the thermal energy during deposition enhances the crystallization of the Fe3O4 and x-ray photoelectron spectroscopy confirms the film deposited at 300C is single-phase Fe3O4 while the film deposited at RT is mostly ν-Fe2O3. The electrical measurements show that the resistivity of the Fe3O4 film increases exponentially with decreasing temperature, and exhibit a sharp metal-insulator transition at around 100 K, indicating the Verwey transition feature. The saturation magnetization Ms of Fe3O4 film measured by vibrating sample measurement (VSM) at RT was found to be 445 emu/cm3.
Direct Synthesis of L10-Phase Nanostructured CoPt Using Dense Plasma Focus Device Operating in Non-optimized Focus Mode
Authors: Pan Zhenying , Rawat Rajdeep Singh , Lin Jiaji , Karamat Shumaila , Lee Paul Choon Keat , Springham Stuart Victor , Tan Augustine Tuck Lee
Published: August 2010

A direct synthesis of (001) oriented nanostructured CoPt thin films has been successfully achieved using a 880 J pulsed Dense Plasma Focus (DPF) device operating in a non-optimized focus mode with a low charging voltage of about 8 kV. The (001) oriented fct structured L10 phase nanostructured CoPt thin films have been synthesized directly in as-deposited sample, as verified by XRD results, without any post deposition annealing. The SEM imaging results show that nanostructured CoPt were achieved in non-optimized focus mode with agglomerate/particle size ranging from 10 to 55 nm. Furthermore, the VSM analysis shows that the as-deposited samples in non-optimized focus mode have higher coercivity (due to direct L10 phase) as compared the annealed sample and the as-deposited sample of optimized focus mode operation.
Memory Effect in Simple Cu Nanogap Junction
Authors: Suga Hiroshi , Horikawa Masayo , Miyazak Hisao , Odaka Shunsuke , Tsukagoshi Kazuhito , Shimizu Tetsuo , Naitoh Yasuhisa
Published: August 2010

We have investigated the resistance switching effect in Cu nanogap junction. Nanogap structures were created by means of electromigration and their electrical properties were measured in a high vacuum chamber. The measured current-voltage characteristics exhibited a clear negative resistance and memory effect with a large on-off ratio of over 105. The estimation from I-V curves indicates that the resistance switching was caused by the gap size change, which implies that the nanogap switching (NGS) effect also occurs in Cu electrodes, a popular wiring material in an integrated circuit.
Crystallization behavior of Ge1Cu2Te3 amorphous film
Authors: Sutou Yuji , Kamada Toshiya , Saito Yuta , Sumiya Masashi , Koike Junichi
Published: August 2010

The electrical resistance on the crystallization process of sputtered-deposited Ge1Cu2Te3 film was investigated by two-point probe method. It was found that the amorphous Ge1Cu2Te3 film crystallizes into a single Ge1Cu2Te3 phase with a chalcopyrite structure, which leads to a large resistance drop. The crystallization temperature of the Ge1Cu2Te3 amorphous film was about 250 °C, which is about 70 °C higher than the conventional Ge2Sb2Te5 amorphous film. The activation energy for the crystallization of the Ge1Cu2Te3 amorphous film was higher than that of the Ge2Sb2Te5 amorphous film. The Ge1Cu2Te3 compound with a low melting point can be expected to be suitable as the phase change material for PCRAM.
Tuneable CMOS and Current Mirror Circuit with Double-gate Screen Grid Field Effect Transistors
Authors: Shadrokh Yasaman , Fobelets Kristel , Velazquez-Perez Enrique
Published: August 2010

The multiple-gate aspect of the Screen Grid Field Effect Transistor (SGrFET) increases functionality and reduces component count of circuits. An independently-driven gate SGrFET is used to control the switching voltage as well as the gain factor of an inverter. The multi-gate configuration of the SGrFET allows a decrease in output conductance without an increase of transistors count. This leads to a reduction in fabrication complexity, chip area and parasitics. In addition, a simple SGrFETs-based current mirror circuit is proposed with gain factor control.
Tuning the Magnetic Domain Structure of Spin-polarized Complex Oxide Nanostructures
Authors: Bettinger Joanna Strongson , Chopdekar Rajesh V. , Mesler Brooke , Chain Douglas , Doran Andrew , Anderson Erik , Scholl Andreas , Suzuki Yuri
Published: August 2010

To successfully incorporate the highly spin-polarized material La0.7Sr0.3MnO3 (LSMO) into spin-based electronic devices it is essential to be able to control and tune the magnetic domain structure. In this work, we geometrically confine epitaxial thin films of LSMO into hexagons to examine the effect of magnetostatic and magnetic anisotropy energies on the domain formation. We find through careful choice of hexagon aspect ratio, crystalline direction, and substrate orientation, we can tune the magnetic domain formation to be single, two, six (flux closure), or other domain configurations.
Synthesis and Thermal Stability of HfO2 Nanoparticles
Authors: Chaubey Girija Shankar , Yao Yuan , Makongo Mangan Julien Pierre Amelie , Sahoo Pranati , Poudeu Pierre F. P. , Wiley John
Published: August 2010

A simple method is reported for the synthesis of monodispersed HfO2 nanoparticles by the ammonia catalyzed hydrolysis and condensation of hafnium (IV) tert-butoxide in the presence of surfactants at room temperature. Transmission electron microscopy shows faceted nanoparticles with an average diameter of 3-4 nm. As-synthesized nanoparticles are amorphous in nature and crystallize upon moderate heat treatment. The HfO2 nanoparticles have a narrow size distribution, large specific surface area and good thermal stability. Specific surface area was about 239 m2/g on as-prepared nanoparticle samples while those annealed at 500 °C have specific surface area of 221 m2/g indicating that there was no significant increase in particle size. This result was further confirmed by TEM images of nanoparticles annealed at 300 °C and 500 °C. X-ray diffraction studies of the crystallized nanoparticles revealed that HfO2 nanoparticles were monoclinic in structure. The synthetic procedure used in this work can be readily modified for large scale production of monodispersed HfO2 nanoparticles.
Emission Inhomogeneity in InAs Quantum Dot DWELL Structures
Authors: Vivas Hernández Alejandro , Polupan Gerorgiy , Velazquez Eric , Guerrero Moreno Ingri J. , Scherbyna L.
Published: August 2010

The photoluminescence spectra and its homogeneity for InAs quantum dots (QDs) embedded into In0.15Ga0.85As/GaAs quantum well (QW) structures with QDs grown at different temperatures (470-535°C) have been investigated at 300 K. Photoluminescence (PL) spectra along the scanning line crossed the wafers were measured at 300 K in a set of points on the QD structures under the excitation of the 804 nm line of a solid state IR laser at an excitation power density of 100 W/cm2. In QD structures with InAs QDs grown at 470°C the low integrated PL intensity, the high dispersion of QD sizes in ensemble and, as a result, the large value of FWHM (50-70meV), but the low dispersion of QD ensemble parameters along the line crossed the structures have been detected. In QD structures grown at high temperatures 490-535 °C the high integrated PL intensity, the low dispersion of QD sizes in ensemble and, as a result, less values of FWHM, but the essential dispersion of QD ensemble parameters along the line crossed the structures have been revealed. The reasons of these types of PL nonhomogeneity have been discussed.
Why Structure Matters – Controlling the Properties of Nanoparticle Hybrid Materials
Authors: Choi Jihoon , Dong Hongchen , Matyjaszewski Kris , Bockstaller Michael R
Published: August 2010

The complementary physical properties of the distinct constituents render polymer-grafted nanocrystals (PGNPs) intriguing materials systems in which property characteristics can be tuned over a wide range from hard particulate to soft polymer-type. Here we demonstrate that dependent on the molecular weight and the graft density of the grafted polymer chains, three characteristic regimes of PGNPs are observed: (1) hard-sphere type colloidal crystalline with the formation of cracks driven by short-range interactions, (2) plastic mesocrystalline with the crazing behaviors by chain entanglement, or (3) disordered structure with soft-polymer type interactions. In addition to controlling the mechanical properties of PGNPs, grafted chains can have a key role in mediating their gradual transformation into more ordered microstructures from nanoparticles with energetically unfavorable property (i.e., activation barrier for crystallization induced by polydisperse nanoparticles [1, 2]).
Novel Pre-oxidation Patterning on Thin Aluminium Film Generating Ordered Nanopores through Anodization
Authors: Fois Giovanni , Bolger Ciara Therese , Holmes Justin D , Cross Graham
Published: August 2010

Anodic Aluminum Oxide (AAO) is widely employed as a template for fabrication of nanowires and nanotubes due to its ability to generate self organized (SO), well ordered pore structures. We have developed a new aluminum pre-patterning technique to create well ordered nanopore arrays on thin films deposited on silicon substrates. We form patterns of thicker oxide on the surface via local oxidation process using a conducting Atomic Force Microscope (AFM) tip working in contact mode. Pores are forced to nucleate between the pre-oxidized regions during the anodization process. The relation between applied voltage and ordered interpore distance has been found to be linear for these supported thin films. However, the pore spacing is highly reduced compared to free standing foils. A new empiric law has been confirmed for a wide range of voltages, solution concentrations and different electrolytes, including oxalic and phosphoric acid. Our results show that pre-oxidation patterning is an alternative technique to achieve an ordered nanoporous template through the anodization process.
Nano Heterojunctions of Cadmium Sulfide and Cadmium Telluride for Photoelectrocemical Cell Applications
Authors: Demirci Sankir Nurdan , Dogan Bahadir , Parlak Mehmet , Kucukyavuz Zuhal
Published: August 2010

This study presents a very cost effective template-based electrochemical technique to synthesize the nano heterojunctions of cadmium sulfide (CdS) and cadmium telluride (CdTe). SEM analysis revealed that the average length of CdS nanowires varied from 500 nm to 4 μm depending on the deposition time and voltage. Also, average diameter of the CdS nanowires ranged between 100 and 200 nm. The structures of CdS nanowires have been confirmed by XRD and EDX analysis. Photoelectrochemical performances of CdS nanowires revealed that there is a dramatic change in the photoelectrochemical performances with the change in deposition time and voltage. The maximum fill factor (FF) and power efficiency (η) of the CdS nanowires has been calculated as 45 % and 1.36 %, respectively. After the optimization of the CdS nanowire deposition conditions based on the PEC performance, CdTe nanostructures have been deposited on CdS nanowires at various deposition time. SEM analysis showed that CdTe nanostructures have a tendency to grow as nanoclusters. It was observed that the density and the average diameter of the clusters was a strong function of the deposition time. The average diameter of the CdTe nanoclusters after 9-hour deposition reached about 260 nm. The successful heterojunction of CdS nanowires with CdTe nanoclusters have been observed in the SEM analysis. It has been concluded that the PEC performances of the CdS nanowires improved significantly after CdTe deposition. The maximum η, obtained in this study is about 8.04 %. This is one of the highest efficiencies reported in the literature for the nanowire array photoelectrochemical cells.
Magnetization Reversal in NiFe Nano-triangles
Authors: Wang Xinghua , Goolaup Sarjoosing , Cong Chunxiao , Lew wensiang
Published: August 2010

We have fabricated sub-100 nm triangles NiFe triangle arrays using NSL and the MOKE measurement and micromagnetic simulations were carried out to investigate the reversal mechanism of the arrays. Enhancement of coercivity compared to the thin film was observed in all the three arrays but in different degree from the MOKE measurement. With the increase of the lateral size of the triangle, the effect of the coercivity enhancing decreases. Micromagnetic simulation shows that instead of domain wall nucleation and annihilation in the thin film, the reversal mechanism of the 45 and 80 nm triangles is dominated by the coherent rotation. While in the 100 nm triangle, the magnetic reversal takes place via forming and reversing a V like sate.
Evolution, Activity, and Lifetime of Alumina-supported Fe Catalyst During Super Growth of Single-walled Carbon Nanotube Carpets: Influence of the Type of Alumina
Authors: Amama Placidus , Pint Cary , Kim Seung Min , Eyink Kurt , Stach Eric , Hauge Robert , Maruyama Benji
Published: August 2010

The influence of the type of alumina used as catalyst support on the evolution, activity, and lifetime of the catalyst during water-assisted CVD growth (or ‘supergrowth') of single-walled carbon nanotube (SWNT) carpets has been studied. The catalyst consisted of a thin Fe film supported on alumina films deposited by different methods: atomic layer deposition (ALD), e-beam, and magnetron sputtering. In order to fully understand the influence of the type of alumina on SWNT carpet growth, crystalline alumina (c-cut sapphire) and annealed alumina deposited by e-beam were also used as catalyst supports. The activity and lifetime of Fe catalyst during SWNT carpet growth showed a strong dependence on the type of alumina used as support. Fe supported on sputtered alumina (sputtered/Fe) showed the highest catalytic activity and lifetime, which was closely followed by e-beam/Fe while Fe supported on sapphire (sapphire/Fe) showed the least catalytic activity and lifetime. AFM, XPS depth profile, variable angle spectroscopic ellipsometry (VASE) studies revealed that the catalyst evolution and the porosity of the different alumina supports correlate with the lifetime and activity of the catalysts.
Electrically conductive composites via infiltration of single-walled carbon nanotube-based aerogels
Authors: Worsley Marcus A , Kuntz Joshua D. , Kucheyev Sergei , Hamza Alex V , Satcher Joe H , Baumann Theodore F
Published: August 2010

Many challenges remain in the effort to realize the exceptional properties of carbon nanotubes (CNT) in composite materials. Here, we report on electrically conductive composites fabricated via infiltration of CNT-based aerogels. The ultra low-density, high conductivity, and extraordinary robustness of the CNT aerogels make them ideal scaffolds around which to create conductive composites. Infiltrating the aerogels with various insulating materials (e.g. epoxy and silica) resulted in composites with electrical conductivities over 1 Scm-1 with as little as 1 vol% nanotube content. The electrical conductivity observed in the composites was remarkably close to that of the CNT scaffold in all cases.
Realization of Highly Controllable Electrolysis Process by Application of Carbon NanoTubes in Field Effect Transistors
Authors: Naghsh Nilchi Jalal , Mohajerzadeh Shamsoddin
Published: August 2010

We have proposed, fabricated and tested a novel structure of Field-Effect Transistor (FET) combined with carbon nanotubes (CNT) to control the process of electrolysis. Our proposed device includes a conventional n-channel MOSFET, with a selective growth of carbon nanotubes in its drain region. MOSFET is made according to standard NMOS fabrication flow chart utilizing the advantage of a self-aligned process. The CNT growth is carried out in plasma and at a high temperature environment, so a thick layer of chromium (200nm) was deposited on the whole structure as a passivating layer to overcome MOSFET degradation caused by dopant escape. Afterward we deposited and patterned a thin layer of nickel (10nm) as the catalyst of CNT growth. The CNTs are grown in a DC-PECVD system. Following this step, we etched away the chromium layer completely. After the growth, the transistors needed an annealing treatment in Argon chamber at 500°C for 5 hours to retrieve their electrical behavior. We believe this happens because the atomic hydrogen can pass through the chromium layer and passivate the impurities and annealing in Argon chamber give them enough energy to leave the silicon.

In this structure, the CNT collection is used as one-side electrode of electrolysis and the MOSFET acts as the current controller. We tested the structure to electrolyze a one molar mixture of water and salt and observed well-controlled current-voltage characteristics.
Vertical Aligned CNT Growth on Metals for Direct Use With Electrical Conductance
Authors: Kim Jin-Ju , Lee Byeong-Joo , Jeong Goo-Hwan
Published: August 2010

We present growth of vertically aligned carbon nanotube (VCNT) on metal substrates such as Cu foils, Inconel 600 and stainless steel (SUS316L) using thermal chemical vapor deposition (TCVD) in order to get a low contact resistance at interface between CNT and substrates for future applications. The temperature range for VCNT growth was 700-775 °C and mixtures of acetylene, argon and hydrogen were used as processing gas. The tube length was controlled by growth time and temperature. Finally, we successfully grew the VCNT on Cu foils over 1 cm2 and confirmed the excellent electrical conductance which can be directly used as anodic electrode in lithium ion battery. On the other hand, the growth of VCNT on Inconel 600 or SUS316L sheets was carried out as purchased. These tubes are expected to be useful for field emission devices.
Low-temperature Wet Chemical Deposition of Ultra-thin ZnS/ZnO Bilayers on Plastic Substrates for Applications of Photovoltaic Devices
Authors: Louh Rong-Fuh , Wu William , Liu Jean , Tsai Irene
Published: August 2010

The ultra-thin II-VI semiconductor ZnS/ZnO bilayers (< 50 nm thickness for each layer) can be easily formed on the plastic substrates at 70˜80°C for 20 min. By low temperature wet chemical synthesis techniques, namely chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR). The specific microstructure of such ZnS/ZnO bilayers including film thickness, particle size and morphology, is also modified and obtained in accordance with processing parameters. Along with thin film quality and morphology, the transmittance and reflectance of ZnS/ZnO layers can be measured by field emission SEM and UV-Vis spectroscopy. Besides the bilayer of ZnS (˜35 nm thick)/ZnO (˜50 nm thick) film with uniform thickness was successfully deposited on the optical grade PET substrates, a well-distributed layer of ZnO nanoparticles with ˜100 nm size on the top of ZnS (35 nm thick) film was also attempted. The average transmittance of these bilayer samples can reach greater 85%. Our future goal is to employ such ZnS/ZnO bilayer structure on potential organic substrates to be associated with flexible photovoltaic devices to meet desired cost-effectiveness requirements.
TiO2/Dye/Electrolyte Interface Engineering by Atomic Layer Deposited Ultra Thin SiO2 for Improved Dye Sensitized Solar Cell Performance
Authors: Shanmugam Mariyappan , Bills Braden , Farrokh Baroughi Mahdi
Published: August 2010

The short circuit density (JSC) and open circuit voltage (VOC) of dye sensitized solar cells (DSSCs) were improved from 9.8 to 17.8 mA/cm2 and 728 to 743 mV by depositing an ultra thin SiO2 layer on mesoporous TiO2 using Atomic Layer Deposition (ALD) method. X ray photoelectron spectroscopy confirmed the growth of SiO2 on mesoporous TiO2 surface. It was also observed that the enhancement in DSSC performance highly depends on the thickness of the ALD grown SiO2 layers on mesoporous TiO2. Compared to the reference DSSC which used untreated TiO2, incorporation of 5 ALD cycles (about 5 atomic layers) of SiO2 on mesoporous TiO2 resulted in 80 % enhancement (E) in the photoconversion efficiency from 4 to 7.2%. It is believed that the deposition of the ultra thin SiO2 film on mesoporous TiO2 modifies the density and activity of the surface states and an optimized layer thickness (5 cycles) leads to significant improvement in the DSSC performance. The enhanced photovoltaic performance was confirmed by dark and illuminated I-V and external quantum efficiency (EQE) measurements.
Phonon density of states of model ferroelectrics
Authors: Choudhury Narayani , Kolesnikov Alexander I , Schober Helmut , Walter Eric J , Johnson Mark , Abernathy Douglas , Lucas Matthew S
Published: August 2010

First principles density functional calculations and inelastic neutron scattering measurements have been used to study the variations of the phonon density of states of PbTiO3 and SrTiO3 as a function of temperature. The phonon spectra of the quantum paraelectric SrTiO3 is found to be fundamentally distinct from those of ferroelectric PbTiO3 and BaTiO3. SrTiO3 has a large 70-90 meV phonon band-gap in both the low temperature antiferrodistortive tetragonal phase and in the high temperature cubic phase.

Key bonding changes in these perovskites lead to spectacular differences in their observed phonon density of states.
Ex-situ and in-situ Neutron Radiography Investigations of the Hydrogen Uptake of Nuclear Fuel Cladding Materials During Steam Oxidation at 1000°C and Above
Authors: Grosse Mirco , van den Berg Marius , Lehmann Eberhard Helmar , Schillinger Burkhard
Published: August 2010

Neutron radiography is a powerful tool for the investigation of the hydrogen uptake of zirconium alloys. It is fast, fully quantitative, non-destructive and provides a spatial resolution of 30 μm. The non-destructive character of neutron radiography provides the possibility of in-situ investigations. The paper describes the calibration of the method and delivers results of ex-situ measurements of the hydrogen concentration distribution after steam oxidation, as well as in-situ experiments of hydrogen diffusion in β-Zr and in-situ investigations of the hydrogen uptake during steam oxidation.
Real-time and Direct Observation of Hydrogen Absorption Dynamics for Pd Nanoparticles
Authors: Matsumura Daiju , Okajima Yuka , Nishihata Yasuo , Mizuki Jun'ichiro
Published: August 2010

Dynamic local structural change of Pd nanoparticles on alumina surface during hydrogen absorption process was directly observed by x-ray absorption fine structure spectroscopy with dispersive mode. Main four parameters of x-ray absorption spectroscopy were determined even in the case of 50 Hz observation. It is clearly revealed that Pd nanoparticles directly change to the hydride phase in 50 ms at 200 kPa of hydrogen pressure. Although large lattice expansion was observed, significant structural distortion was not investigated in the results of the change of Debye-Waller factor.
Organic Heterojunctions for Photovoltaic Applications: C60 Growth on Pentacene
Authors: Cantrell Rebecca Ann , Clancy Paulette
Published: August 2010

Using atomic-scale Molecular Dynamics (MD) and energy minimization techniques in conjunction with semi-empirical MM3 potential energy functions, we consider the adsorption of a C60 molecule on a series of hypothetical pentacene structures that vary only in the tilt of the angle that the short axis of the pentacene molecules makes with the underlying surface (the long axis lying essentially flat, as on a metal substrate). Important relationships were discovered between the angle adopted by the short axis of pentacene on the surface, φ1, and the adsorption and diffusion characteristics of C60. Static energy calculations show that there is a transition of the deepest energy minima from between the pentacene rows at low values of φ1 to within the rows at high values of φ1, where φ1 is the angle the pentacene short axis makes with the surface. MD confirms this trend by the predominant residence locations at the extreme φ1 values. Furthermore, MD results suggest that the C60 traverses the pentacene surface in the east-west direction for lower φ1 values (φ1 ≤ 40°) and in the north-south direction for higher φ1 values (φ1 ≥ 70°). Taking both static and dynamic results together, the most favorable tilt angles for mono-directional nanowire growth should occur between 70° and 80° off-normal.
Steam and Air Oxidation Behavior of Nuclear Fuel Claddings at Severe Accident Conditions
Authors: Große Mirco , Steinbrück Martin , Stuckert Juri
Published: August 2010

The oxidation behavior of zirconium alloys used as materials for nuclear fuel rod claddings is investigated in the temperature range between 973 and 1673 K in steam and air atmosphere. Parabolic kinetics was found for all materials, atmospheres and temperatures, at least at beginning of the reactions. The temperature dependence of the reaction rate is of Arrhenius type. The parameters of the Arrhenius functions are determined and given for steam oxidation. Due to the formation of a large amount of cracks an acceleration of the reactions can occur. Reasons of the crack formations are phase transformations in the oxide layer known as the breakaway effect and, in case of air atmosphere, local oxygen starvation conditions resulting in reactions with nitrogen. The paper gives a short overview of the relevant mechanisms and processes.
Evolution of Static Physical Properties in Plutonium by Self-irradiation Damage
Authors: Chung Brandon W , Lema Kenneth , Hiromoto David
Published: August 2010

The alpha-decay of plutonium leads to the age-related change in physical properties. This paper presents updated results of age-related effects on enriched and reference alloys measured from immersion density, dilatometry, and mechanical tests. After nearly 100 equivalent years of aging, both the immersion density and dilatometry show that the enriched alloys are decreasing in density by less than 0.002% per year and now exhibit a near linear density decrease, without void swelling. The tensile tests show that the aging process increases the strength of plutonium alloys, followed by possible saturation past 70 equivalent years of age. The ultimate goal of this work is to develop capabilities to predict physical properties changed by aging effects.
The pressure-temperature phase diagram of URu2Si2 under hydrostatic conditions
Authors: Butch Nicholas Patrick , Jeffries Jason R. , Evans William J. , Chi Song Xue J. , Leao Juscelino B. , Lynn Jeffrey W , Sinogeikin Stanislav V. , Hamlin James J. , Zocco Diego A. , Maple M. Brian
Published: August 2010

The pressure dependence of the hidden order phase of the heavy fermion superconductor URu2Si2 has been a subject of intense research since shortly after the discovery of the compound decades ago. Applied pressure increases the critical temperature of the paramagnetic / hidden order transition and brings about a transition to long-range antiferromagnetism. The reported pressures and temperatures of these phase boundaries vary between studies: 4 – 7 kbar at low temperature and 12 – 15 kbar at high temperature. We review experimental evidence that the measured values of pressure and temperature are very sensitive to the chosen pressure transmitting medium. Recent x-ray diffraction measurements suggest that the relative position of the silicon atom in the unit cell is changing as a function of pressure. Recent neutron diffraction measurements show that the zero-temperature limit of the hidden order / antiferromagnetic transition occurs at pressures greater than 7.5 kbar.
Fuel Cycle Research and Development Program, Used Fuel Disposition Campaign Objective, Mission, Plans, and Activity Status
Authors: Nutt William Mark , Peters Mark , Swift Peter , McMahon Kevin , Sorenson Ken , Schwab Patrick
Published: August 2010

The safe management and disposition of used nuclear fuel and/or high level nuclear waste is a fundamental aspect of the nuclear fuel cycle. The United States currently utilizes a once-through fuel cycle where used nuclear fuel is stored on-site in either wet pools or in dry storage systems with ultimate disposal in a deep mined geologic repository envisioned. However, a decision not to use the proposed Yucca Mountain Repository will result in longer interim storage at reactor sites than previously planned. In addition, alternatives to the once-through fuel cycle are being considered and a variety of options are being explored under the U.S. Department of Energy's Fuel Cycle Research and Development Program.

These two factors lead to the need to develop a credible strategy for managing radioactive wastes from any future nuclear fuel cycle in order to provide acceptable disposition pathways for all wastes regardless of transmutation system technology, fuel reprocessing scheme(s), and/or the selected fuel cycle. These disposition paths will involve both the storing of radioactive material for some period of time and the ultimate disposal of radioactive waste.

To address the challenges associated with waste management, the DOE Office of Nuclear Energy established the Used Fuel Disposition Campaign within its Fuel Cycle Research and Development Program in the summer of 2009. The mission of the Used Fuel Disposition Campaign is to identify alternatives and conduct scientific research and technology development to enable storage and disposal of used nuclear fuel and wastes generated by existing and future nuclear fuel cycles. The near-and long-term objectives of the Fuel Cycle Research and Development Program and it's Used Fuel Disposition Campaign are presented.
Structural and Crystallization Study of a Simplified Aluminoborosilicate Nuclear Glass Containing Rare-earths: Effect of ZrO2 Concentration
Authors: Caurant Daniel , Quintas Arnaud , Majerus Odile , Loiseau Pascal , Charpentier Thibault , Vermaut Philippe , Dussossoy Jean-Luc
Published: August 2010

Zirconium is an abundant element in nuclear wastes. In this paper, we present structural and crystallization results for a simplified glass composition belonging to the SiO2-Al2O3-B2O3-Na2O-CaO-ZrO2-RE2O3 system (RE = Nd or La) developed to immobilize highly concentrated waste solutions. The effect of varying ZrO2 content on the structure and the crystallization tendency of this glass was studied using a multi-spectroscopic approach. Zr was shown to be located in six-fold coordinated sites whose charge compensation seems preferentially insured by Na+ cations. Whereas a significant decrease of the proportion of BO4 units was observed with ZrO2 content, no effect was detected on the environment of AlO4 units. However, a significant structural evolution of the silicate network occurred due to the formation of Si-O-Zr bonds. Whatever ZrO2 concentration, the crystallization of only a rare earth silicate apatite phase was observed during either slow cooling from the melt or isothermal heat treatment. Whereas nucleation mainly occurred from the surface of the glass without ZrO2, the introduction of zirconium induced apatite crystallization in the bulk. It is proposed that this nucleating effect of ZrO2 is mainly due to changes induced in the neighborhood of Nd3+ cations in glass structure.
New Lanthanide Oxalato-nitrates Crystallized From Acidic Solutions
Authors: Tamain Christelle , Rivenet Murielle , Arab-Chapelet Bénédicte , Grandjean Stéphane , Abraham Francis
Published: August 2010

To identify the various oxalates and oxalato-nitrates likely to form during the nuclear fuel reprocessing we study crystallization of such compounds by various methods (slow diffusion, hydrothermal syntheses, in situ oxalate syntheses …), in different conditions and in presence of monovalent ions. In a first stage, lanthanides are used as surrogates of the actinides (III) radioactive elements. This communication reviews various lanthanides (III) compounds obtained by crystallization from nitric acid solution containing hydrazinium ions. Diethyl oxalate was used as a precursor for oxalate ions. A careful adjustment of the experimental conditions allowed us to synthesize single crystals of nitrates, oxalato-nitrates and oxalates with various ligand/Ln(III) ratio and containing nitrates as ligands or as counter ions. In all the compounds hydrazinium ions are present as counter ions. The crystal growth method is described and the crystal structures, determined by X-ray diffraction from single crystals, are discussed in terms of metal-oxalate frameworks.