bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer Simulation of Compressive Failure in Silica Aerogels
Authors: Good Brian S.
Published: April 2011

Historically, the low thermal conductivity of silica aerogels has made them of interest to the aerospace community for applications such as cryotank insulation. However, recent advances in the application of conformal polymer coatings to these gels have made them significantly stronger, and potentially useful as lightweight structural materials. In this work, we perform multiscale computer simulations to investigate the compressive strength and failure behavior of silica aerogels.

The gels' nanostructure is simulated via the diffusion limited cluster aggregation (DLCA) process, which produces fractal aggregates that are structurally similar to experimentally observed gels. The largest distinct feature of the clusters is the so-called secondary particle, typically tens of nm in diameter, which is composed of primary particles of amorphous silica an order of magnitude smaller. The secondary particles are connected by amorphous silica bridges that are typically smaller in diameter than the particles they connect.

We investigate compressive failure via the application of a uniaxial compressive strain to the DLCA clusters. In computing the energetics of the compression, the detailed structure of the secondary particles is ignored, and the interaction among secondary particles is described by a Morse pair potential parameterized such that the potential range is much smaller than the secondary particle size; an angular potential contribution is included in some of the simulations as well. The Morse and angular parameters are obtained by atomistic simulation of models of the interparticle bridges, with the compressive and bending behavior of these bridges modeled via molecular statics. We consider the energetics of compression and compressive failure, and compare qualitative features of low-and high-density gel failure.
A light scattering study of interactions of oppositely charged proteins in solution
Authors: Ramasamy Perumal Radha , Elmaghrabi Raafat , Halada Gary , Rafailovich Miriam
Published: April 2011

In experiments involving electrophoresis of proteins in gels, it was observed that the mobility of FITC tagged albumin (FITC albumin) was greater than that of TRITC tagged albumin (TRITC albumin). To further understand the effects of tagging proteins with fluorescent dyes, interactions of anionic proteins FITC albumin and untagged bovine serum albumin (BSA), with cationic protein ploy-L-lysine was studied using dynamical light scattering. It was found that aggregates formed by the interaction of FITC albumin with poly-L-lysine were larger than those formed by the interaction between poly-L-lysine and BSA. Using zeta potential measurements it was observed that irrespective of the fluorescent tags attached to them, the zeta potential values of cationic proteins changed from negative to positive with increasing amounts of poly-L-lysine. It was also observed that addition of small amounts of poly-L-lysine to solutions containing FITC albumin decreased the zeta potential drastically. To explain this data, we are proposing a model that suggests that low concentrations of poly-L-lysine serve as scaffold - like structures on which several FITC albumin molecules anchor. We conclude that FITC appears to change the surface charge of albumin significantly and thereby influencing its behavior in solution and its interaction with cationic poly-L-lysine.
Stronger and Longer Synthetic Collagen
Authors: Raines Ronald T.
Published: April 2011

Collagen is the most abundant protein in the human proteome. The post-translational modification of collagen by the enzyme prolyl 4-hydroxylase increases markedly the conformational stability of the collagen triple helix. We have discovered that a previously unappreciated force—stereoelectronic effects—is responsible for this increased stability. By exploiting these stereoelectronic effects (e.g., the gauche effect and n→π* interaction) and reciprocal steric effects, we have created synthetic collagen of unprecedented stability. We have also used the molecular self-assembly of triple-helical fragments to create synthetic collagen of unprecedented length. These synthetic collagens have numerous applications in biotechnology and biomedicine.
A Bacterium's Sense of “Touch”
Authors: Yongsunthon Ruchirej , Lower Brian H. , Fowler Vance G. , Alexander Emily , Lower Steven K.
Published: April 2011

The sheer number of bacteria living on solid surfaces makes a compelling argument for the existence of surface sensing mechanisms. However, surface sensing abilities have not been widely studied in bacteria, because such abilities are not macroscopically observable in attached organisms with limited mobility. We report experimental evidence that attachedStaphylococcus aureuscells recognize the steep gradient near their substrate interface and localize substrate-specific biomolecules toward that region. We present Atomic Force Microscopy-based affinity maps which reflect the cells' biochemical sensory response to the substrate and provide a unique view of regions indicating specific binding activity and bond resilience.
Analysis of Human Spleen Contamination
Authors: Kopani Martin , Weis Martin , Dekan Julius , Jakubovsky Jan , Miglierini Marcel
Published: April 2011

We identified both crystalline and amorphous phase of human spleen particles. The silicon particles in the spleen were 10-30 μm large. Silicon, silicon-aluminium and silicon-calcium particles by EDX were found. We assume that the silicon must enter the organism from the external environment and the presence of silicon in the human spleen is consequence of the cleaning function of human spleen.

Mössbauer spectroscopy of studied tissues revealed different phase of iron oxide in the human spleen. On the ground of this consideration we can claim all samples of investigated tissues exhibit presence of two different paramagnetic iron phases, both based on three-valent (Fe3+) atoms. Consequently only 4 different iron-oxides correspond with experimental results. Multielemental composition of iron particles was found by EDX analysis. We suppose that pH and time are significant factors influence biomineralization of iron in the human spleen.
Radiochemical Synthesis of Au/Iron-oxide Composite Nanoparticles Using PEG
Authors: Seino Satoshi , Kinoshita Takuya , Iida Juinichi , Shibata Yujin , Nakagawa Takashi , Ueno Koji , Yamamoto Takao A
Published: April 2011

Composite nanoparticles consisting of gold and iron-oxide were radiochemically synthesized in aqueous solution systems by using polyethylene glycols. The gold particles with average diameter of 3 nm were firmly immobilized on the surface of the support iron-oxide nanoparticles. The composite nanoparticles specifically adsorbed sulfur-containing amino acids by a Au-S bonding.
Encapsulation of Neural Cells in Nano-Featured Polymer Scaffolds through Co-axial Electrospinning
Authors: Pareta Rajesh A , Webster Thomas J
Published: April 2011

Encapsulation of PC12 cells (neural cell model) in alginate hydrogels with a protective coating of poly(lactic-co-glycolic acid) (PLGA) was achieved in the present study using co-axial electrospinning. Co-axial electrospinning consists of two concentric capillaries compared to only one capillary in conventional electrospinning. This allows for the processing of two liquid solutions simultaneously. Neural cells suspended in hydrogels were injected in the inner capillary, while the carbon nanotubes (added for conductivity) suspended in PLGA were injected in the outer capillary at controlled flow rates. On the application of a high voltage, a compound jet formed at the capillary exits and resulted in a co-electrospun fiber of nerve cells encapsulated in PLGA with carbon nanotubes. Carbon nanotubes were included to make the outer shell conductive to stimulate the PC12 cells. In this study, the voltage varied from 0 to 15 kV and various flow rates were tested to achieve a stable cone-jet mode in electrospinning. The cell density in the media varied from 0.5 to5 million cells/ml and the polymer solution (PLGA) concentration varied from 1 to 10 mg/ml. This resulted in a three dimensional conductive scaffold with nano-features (due to carbon nanotubes) on the polymer surface, which were collected on the grounded substrate. PC12 cells were found to be viable inside microspheres after 3 days. The size of the microspheres was quite uniform and less than 200 μm. This technique may be very useful for the development of cell encapsulated scaffolds which mimic natural body tissue organization for tissue engineering applications such as nervous system regeneration.
Conducting Polymer-based Aptamer Biosensor for in situ Monitoring of Cytokine
Authors: Liao Wei , Randall Bradly , Alba Nicolas , Cui Xinyan Tracy
Published: April 2011

Neural prostheses often suffer from undesired chronic inflammatory tissue response. Therefore; a sensitive and real-time biosensor for inflammatory cytokine detection would provide invaluable information toward solving this problem. Such a biosensor based on an aptamer probe doped in polypyrrole and subsequent electrochemical impedance spectroscopy (EIS) has been developed. PDGF, an important inflammatory cytokine, has been successfully measured in both offline EIS characterization and real-time impedance monitoring. For in situ detection of PDGF, the best sensitivity of 10 ng/ml has been achieved.
Evolution of Film Crystalline Structure During the Ultrafast Deposition of Crystalline Si Films
Authors: Jia Haijun , Kuraseko Hiroshi , Fujiwara Hiroyuki , Kondo Michio
Published: April 2011

By using a high density microwave plasma source, an ultrafast deposition rate over 1000 nm/s has been achieved for polycrystalline silicon (poly-Si) film deposition. We find that crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Systematic study of the deposition process has been performed as a function of the deposition duration. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.
Improved Passivation of a-Si:H / c-Si Interfaces Through Film Restructuring
Authors: Burrows Michael Zanoni , Das U. K. , Bowden S. , Hegedus S. S. , Opila R. L. , Birkmire R. W.
Published: April 2011

The as-deposited passivation quality of amorphous silicon films on crystalline silicon surfaces is dependent on deposition conditions and resulting hydrogen bonding structure. However the initial surface passivation can be significantly improved by low temperature post-deposition anneal. For example an improvement in effective lifetime from 780 μsec as-deposited to 2080 μsec post-anneal is reported in the present work. This work probes the hydrogen bonding environment using monolayer resolution Brewster angle transmission Fourier transform infrared spectroscopy of 100 Å thick films. It is found that there is significant restructuring at the a-Si:H / c-Si interface upon annealing and a gain of mono-hydride bonding at the c-Si surface is detected. Calculations show an additional 3.56 − 4.50 × 1014 cm−2 mono-hydride bonding at c-Si surface due to annealing. The estimation of the surface hydride oscillator strength in transmission mode is reported for the first time to be 7.2 × 10−18 cm on Si (100) surface and 7.5 × 10−18 cm on Si (111).
Probing Carrier Depletions on Grain Boundaries in Polycrystalline Si Thin Films by Scanning Capacitance Microscopy
Authors: Jiang Chunsheng , Moutinho H.R. , To B. , Dippo P. , Romero M.J. , Al-Jassim M.M.
Published: April 2011

Grain boundaries (GBs) in polycrystalline Si thin-film solar cells are believed to limit the photovoltaic efficiencies. In this paper, we report on a nanometer-resolution measurement of the carrier depletion at the GBs, using scanning capacitance microscopy (SCM). The SCM images exhibit the following features: (1) Carrier concentrations are lower at locations around the GBs than on center regions of the grains; (2) The depletion width at the GBs varies considerably, between 0 and 100 nm, depending on individual GBs; (3) Intra-grain carrier depletion was also observed at point and line defects; and (4) The faceted features that were observed on the topography of the as-grown film surface appeared on the SCM images even after the film surface was polished flat. The direct measurement of the carrier depletion on the GBs demonstrates that the GBs in Si thin films indeed create charged gap states. The nonuniformity of the carrier depletions suggests that the gap states depend on specific GB structures, which should relate directly to the grain orientations and grain facets adjacent to the GB. The depletion around the intragrain defects indicates that the defects are charged and can be recombination centers, and thus, harmful to device performance. This paper reports the first step of our studies toward understanding the relationships between the electronic and structural properties on specific GBs.
Nanostructures with Group IV Nanocrystals Obtained by LPCVD and Thermal Annealing of SiGeO Layers
Authors: Morana Bruno , Rodríguez Andrés , Sangrador Jesús , Rodríguez Tomás , Martínez Óscar , Jiménez Juan , Kling Andreas
Published: April 2011

Nanocrystals embedded in an oxide matrix have been fabricated by annealing SiGeO films deposited by LPCVD. The composition of the oxide layers and its evolution after annealing as well as the presence and nature of nanocrystals in the films have been studied by several experimental techniques. The results are analyzed and discussed in terms of the main deposition parameters and the annealing temperature.
Micro Crystalline Silicon TFT by the Metal Capped Diode Laser Thermal Annealing Method
Authors: Arai Toshiaki , Morosawa Narihiro , Inagaki Yoshio , Tatsuki Koichi , Urabe Tetsuo
Published: April 2011

A novel crystallization method for silicon based thin film transistor (TFT) is proposed for the fabrication of high performance large size flat panel displays. In spite of using almost the same TFT fabrication process as that of hydrogenated amorphous silicon (a-Si:H) TFT, the proposed metal capped laser thermal annealing method realizes the formation of uniform and dense micro crystalline silicon (μc-Si), and provides mobility of 3.1 cm2/V•s, threshold voltage (ΔVth) of 2.3 V, and sub threshold slope (S) of 0.93 V/decade. Moreover, proposed stacked n+ amorphous silicon structure realizes extremely low off-current maintaining high on-current. As the reliability of TFT, a threshold voltage sift (ΔVth) under the high current bias stress test (BTS) condition was investigated, and realized the assumed ΔVth of +1.77 V after 100,000 hours stress of 10 μA and 50°C. This value is 2 orders smaller than that of a-Si:H TFT and only three times larger than that of low temperature poly silicon (LTPS) TFT.

We believe that our μc-Si TFT technology is the suitable solution for the high quality, large size flat panel display mass-production.
Micro Photovoltaic Modules for Micro Systems
Authors: Wyrsch Nicolas , Dunand Sylavain , Ballif Christophe
Published: April 2011

Amorphous silicon based solar modules are very attractive for the powering of various microsystems for both indoor and outdoor applications. This technology offers a lot of flexibility in terms of module design, output voltage, shape, size, choice of substrates and offers also the possibility to embed sensors such as photodiodes. This paper focuses on the development of micro-solar modules with area ≤0.15 cm2. Several micro-modules with output voltage of up to 60 V (form 0.1 cm2) were designed and fabricated. The performance limitation introduced by the segment monolithic interconnection and the design of the latter is presented and discussed. An example of a micro-module with a total size of 3.9×3.9 mm2 developed for a micro-robot with dual voltage outputs and embedded photodiodes is also presented.
Quality and Growth Rate of Hot-wire Chemical Vapor Deposition Epitaxial Si Layers
Authors: Teplin Charles W , Martin Ina T. , Jones Kim M. , Young David , Romero Manuel J. , Reedy Robert C. , Branz Howard M. , Stradins Paul
Published: April 2011

Fast epitaxial growth of several microns thick Si at glass-compatible temperatures by the hot-wire CVD technique is investigated, for film Si photovoltaic and other applications. Growth temperature determines the growth phase (epitaxial or disordered) and affects the growth rate, possibly due to the different hydrogen coverage. Stable epitaxy proceeds robustly in several different growth chemistry regimes at substrate temperatures above 600°C. The resulting films exhibit low defect concentrations and high carrier mobilities.
Influence of the Structural Properties of Microcrystalline Silicon on the Performance of High Mobility Thin-Film Transistors
Authors: Chan Kah Yoong , Knipp Dietmar , Carius Reinhard , Stiebig Helmut
Published: April 2011

The influence of the crystalline volume fraction of hydrogenated microcrystalline silicon (mc-Si:H) on the performance of thin-film transistors (TFTs) processed at temperatures below 180 °C was investigated. TFTs employing mc-Si:H channel material prepared near the transition to amorphous growth exhibit the highest electron charge carrier mobilities exceeding 50 cm2/Vs. The influence of the crystalline volume fraction of the intrinsic mc-Si:H material on the transistor parameters like the charge carrier mobility and the contact resistance will be discussed.
Mechanical Properties and Reliability of Amorphous vs. Polycrystalline Silicon Thin Films
Authors: Gaspar Joao , Paul Oliver , Chu Virginia , Conde Joao Pedro
Published: April 2011

This paper presents the mechanical characterization of both elastic and fracture properties of thin silicon films from the load-deflection response of membranes, also known as the bulge test. Properties extracted include the plane-strain modulus, prestress, fracture strength and Weibull modulus. Diaphragms made of low-temperature, hydrogenated amorphous and nanocrystalline silicon films (a-Si:H and nc-Si:H, respectively) deposited by plasma enhanced chemical vapor deposition (PECVD) and, for comparison, membranes composed of high-temperature polycrystalline silicon (poly-Si) deposited by low pressure chemical vapor deposition (LPCVD) have been fabricated and characterized. The structures are bulged until failure occurs. From the stress profiles in the diaphragms at fracture, the brittle material strength is analyzed using Weibull statistics. The bulge setup is fully automated for the sequential measurement of several membranes on a substrate realizing the high-throughput acquisition of data under well controlled conditions. A comprehensive study of the mechanical properties of low-temperature silicon films as a function of deposition parameters, namely substrate temperature, RF power, hydrogen dilution and doping, is presented.
Temperature and humidity effects on the stability of on-plastic a-Si:H thin film transistors with various conduction channel layer thicknesses
Authors: Chen Jian Z , Cheng I-Chun
Published: April 2011

Stability is an important issue for the application of TFTs. In this paper, we present the effects of humidity and temperature on the stability of inverted-staggered back-channel-cut a-Si:H TFTs with various conduction channel layer thickness. We evaluated the stability of on-plastic TFTs of different conduction layer thicknesses made at a process temperature of 150°C on 51-μm thick Kapton polyimide foil substrates.. With conduction channel layer thickness of 50nm, humidity reversibly varies the characteristics of TFTs, but TFTs of conduction layer thickness greater than 100 nm is pretty immune to the humidity change. The temperature dependent stability and characteristics of TFTs were analyzed from 20°C to 60°C. Rising temperature from 20°C to 56°C, the threshold voltage (Vt) drops about 2 volts; on-off current ratio decreases by one order of magnitude mainly due to thermally excited carriers in the off-region.
Noise in Different Micro-bolometer Configurations with Silicon-Germanium Thermo-sensing Layer
Authors: Kosarev Andrey , Kosarev Andrey , Torres Alfonso J , Cosme Ismael
Published: April 2011

A recent interest in thermal detectors is due to plasma deposited materials with large temperature coefficient of resistance (TCR) and micro-machining technology for thermal isolation. Both are compatible with dominating Si CMOS technology that makes it possible developing device-on-chip configurations. In our previous works we have reported on the study of fabrication and characterization of single cell micro-bolometers based on silicon-germanium thermo-sensing films deposited by low frequency plasma [1-3]. Noise measurements are very important part of device characterization, which have been poorly reported in literature. Models proposed by present time for noise description in non-crystalline samples (either in films or in device structures) are still debated and no one can be considered as the only accepted. The goal of this work is to study experimentally noise spectral density in several configurations of micro-bolometers with silicon-germanium (a-SixGey:H) as thermo-sensing films. We studied four configurations: planar structure with a) a-SixGey, y=0.5, b) a-SixGeyBz:H, x=0.5, y=0.45 and z=0.05 ; c) x=0.5, y=0.5, z=0 and d)sandwich structure with x=0.5, y=0.5. These samples were characterized by SIMS (composition), FTIR (H-bonding and H content), conductivity measurements (σ(T), activation energy, TCR), current-voltage characteristics in dark and under illumination (responsivity). Noise spectral density (NSD) versus frequency S(f) was studied in the range of frequency f=1 to f=103 Hz under IR illumination modulated with this frequency and constant bias. The measurements were performed in vacuum chamber with P=10 mTorr. Generally S(f) dependence demonstrated three regions separated by two corner frequencies: fc1 and fc2: 1) f ≤ fc1 S1 α f -γ γ =0.15 to 0.5, 2) fc1 ≤ f ≤ fc2, S2 α f-γ γ = 0.7 to 1.34 and 3) f ≥ fc2 S3 const (f). Different samples studied showed different values of fc1, fc2 γ and S3. These noise characteristics observed experimentally are analyzed in comparison with data reported in literature and possible mechanisms for noise in the frequency regions studied are discussed.
Aligned-Crystalline Si Films on Glass
Authors: Findikoglu Alp T. , Ugurlu Ozan , Holesinger Terry G.
Published: April 2011

We report structural and electronic properties of Aligned-Crystalline Si (ACSi) films on glass substrates. These films show enhanced majority carrier mobilities and minority carrier lifetimes with increasing crystallinity, i.e., with improving alignment and connectivity of the grains. A 0.4-μm-thick ACSi film with a total grain mosaic spread of 4.2° showed Hall mobility of 47 cm2/V.s for a p-type doping concentration of 1.9×1018 cm−3. A prototype n+/p/p+–type diode fabricated using a 4.2-μm-thick ACSi film showed minority carrier lifetime of ∼3.5 μs and estimated diffusion length of ∼30 μm in the p layer with a doping concentration of 5×1016 cm−3.
Links Between Etching Grooves Of Partial Dislocations And Their Characteristics Determined By TEM In 4H SiC
Authors: Ayoub Jean-Pierre , Texier Michael , Regula Gabrielle , Pichaud Bernard , Lancin Maryse
Published: April 2011

We introduce defects into (1120) oriented highly N-doped 4H-SiC by surface scratching, bending and annealing in the brittle regime. Emerging defects at the sample surface are revealed by chemical etching of the deformed samples. The etch patterns are constituted of straight bulges and grooves exhibiting various topographical features. These etch figures correspond to the emergence of double stacking faults dragged by a pair of partial dislocations. In this paper, we discuss the links between the etch figure characteristics and the defect nature. Results obtained by optical and atomic force microscopy are completed by structural analysis of defects performed by transmission electron microscopy. Mobility of partial dislocations in 4H-SiC is discussed and correlated to their core composition and to the effect of the applied mechanical stress.
Influence of Growth Conditions and Substrate Properties on Formation of Interfacial Dislocations and Dislocation Half-loop Arrays in 4H-SiC(0001) and (000-1) Epitaxy
Authors: Tsuchida Hidekazu , Kamata Isaho , Kojima Kazutoshi , Momose Kenji , Odawara Michiya , Takahashi Tetsuo , Ishida Yuuki , Matsuzawa Keiichi
Published: April 2011

Formation of interfacial dislocations (IDs) and dislocation half-loop arrays (HLAs) and their appearance in 4H-SiC epi-wafers are investigated by X-ray topography and KOH etching analysis. Synchrotron reflection X-ray topography demonstrates the ability to image IDs and HLAs simultaneously and reveal their densities as well as spatial distributions in the epi-wafers. The vertical location of IDs in the epi-wafer is also examined by this technique. The influence of wafer warp, in-situ H2 etching prior to epitaxial growth, substrate off-angle as well as the growth face (Si-face and C-face) on the densities and spatial distributions of IDs and HLAs are discussed.
Stress Mapping of SiC Wafers by Synchrotron White Beam X-ray Reticulography
Authors: Zhang Ning , Chen Yi , Sanchez Edward , MacMillan Michael F. , Dudley Michael
Published: April 2011

Synchrotron white beam x-ray reticulography was used to quantitatively map the residual stress/strain in SiC wafers. The basic principle of our study is that there exists a relationship between the stress state in a crystal and the local lattice plane orientation and that this relationship can be exploited in order to determine the full strain tensor as a function of position inside the crystal. The theoretical background of the stress mapping using synchrotron white beam x-ray reticulography is introduced and it is based on the change of plane normal of the lattice plane due to the distortion associated with the residual strain. The stress mapping of a crystal region from a commercial 4H silicon carbide wafer has been studied using this technique and the results are discussed. This technique can in principle be used in any single crystal material.
Degradation of Majority Carrier Conductions and Blocking Capabilities in 4H-SiC High Voltage Devices due to Basal Plane Dislocations
Authors: Ryu Sei-Hyung , Zhang Qingchun , Fatima Husna , Haney Sarah , Stahlbush Robert , Agarwal Anant
Published: April 2011

This paper presents the effect of recombination-induced stacking faults on the drift based forward conduction and leakage currents of high voltage 4H-SiC power devices. To show the effects, 10 kV 4H-SiC MPS (Merged PiN Schottky) diodes have been fabricated on a standard wafer and a low BPD (Basal Plane Dislocation) wafer, and their IV characteristics were evaluated before and after a forward bias stress, which resulted in minority carrier recombination and conductivity modulation in the drift epilayer of the diodes. After the stressing, the diode fabricated on standard wafer showed a significant increase in forward voltage drop, as well as a marked increase in leakage current, which were due to induction of stacking faults. The diode on the low BPD wafer showed very little change after the stress because the induction of stacking faults was minimized. Similar results were also observed on a 10 kV 4H-SiC DMOSFET. The results suggest that recombination-induced stacking faults are detrimental to all device types, and injection of minority carriers in majority carrier devices should be avoided at all times.
Surfaces and Interfaces for Controlled Defect Engineering
Authors: Seebauer Edmund G.
Published: April 2011

The behavior of point defects within silicon can be changed significantly by controlling the chemical state at the surface. In ultrashallow junction applications for integrated circuits, such effects can be exploited to reduce transient enhanced diffusion, increase dopant activation, and reduce end-of-range damage.
Scanning Spreading Resistance Microscopy For 3D-Carrier Profiling in FinFET-based Structures
Authors: Mody Jay , Eyben Pierre , Polspoel Wouter , Jurczak Malgorzata , Vandervorst Wilfried
Published: April 2011

Junction formation in FinFET-based 3D-devices is a challenging problem as one targets a complete conformal doping of the source/drain regions in order to produce equal gate-profile overlaps (and thus transistor behavior) on all sides of the fins. Due to the lack of predictive modeling for several of the doping strategies explored (plasma immersion, cluster implants, vapor phase deposition, etc…) it becomes difficult to correctly predict the performance of the devices and hence, accurate 3D-doping profile determination is desired. Although several dopant/carrier profiling methods exist with excellent one- or two-dimensional resolution and properties, there is an urgent need to extend these towards a quantitative three-dimensional geometry. In this work, we use scanning spreading resistance microscopy (SSRM) with dedicated FinFET test structure to obtain three-dimensional information from successive two-dimensional scanning spreading resistance maps. We also assess the validity of our methodology by comparing various sections along the fins which represent the variability due to the processing and measurement procedure.
Investigation of Platinum Silicide Schottky Barrier Height Modulation using a Dopant Segregation Approach
Authors: Breil Nicolas , Halimaoui Aomar , Dubois Emmanuel , Lampin Evelyne , Larrieu Guilhem , Godet Ludovic , Papasouliotis George , Skotnicki Thomas
Published: April 2011

The role of the dopant activation on the segregation efficiency during the formation of platinum silicide (PtSi) is investigated in this paper. Using an implant before silicidation technique, we first demonstrate an important Schottky Barrier Height (SBH) modulation for As and B segregation. In the case of As, we highlight that an activation of the dopants before the silcidation does not impact the SBH modulation. On the contrary, an important impact of the dopant crystalline position is evidenced for Boron. Also, a comparison of conventional implant versus a PLAsma Doping (PLAD) highlights the suitability of the latter implantation tool for the SBH modulation. Those results are interpreted on the basis of SIMS depth profiling.
Infrared Semiconductor Laser Annealing Used for Formation of Shallow Junction
Authors: Sameshima Toshiyuki , Mizutani Yuta , Sano Naoki , Naito Masao
Published: April 2011

We report continuous-wave (CW) infrared-semiconductor laser annealing of silicon implanted with boron atoms with assistance of diamond-like carbon (DLC) films as optical absorption layer in order to form shallow junctions. BF2 ions were implanted at 10 keV at doses of 1.5×1015 cm−2 thorough an 8-nm thick SiO2 layer. The effective boron dose implanted into silicon was 7.5c1015 cm−2 a half of the implantation dose. The initial boron distribution had a peak concentration of 6×1020 cm−3 at the silicon surface and a concentration of 1×1019 cm−3 at a depth of 27 nm. The samples were coated with 200-nm-thick DLC films. The samples were annealed by irradiation with a 940 nm continuous wave laser at 80 kW/cm2 with a beam diameter of 180 μm for 2.6 ms. Heat flow analysis estimated that the sample surface was heated to 1350°C for 1.5 ms by laser annealing. Laser annealing markedly reduced the sheet resistance to 531 Ω/sq. Boron atoms were almost completely activated with a carrier density close to the effective boron dose of 7.5×1014 cm−2. The in-depth profile of boron concentration hardly changed within 3 nm for laser annealing for 2.6 ms. The intermediate SiO2 layer effectively blocked carbon incorporation to a level below 1017 cm−3. These results show that the present laser annealing method is suitable to form shallow junction of a high dopant activation ratio. We will report low energy implantation of boron-cluster ions followed by the present infrared-semiconductor laser annealing in order to form a shallow junction with a depth less than 15 nm.
Optimization of Stressor Layers Created by ClusterCarbon™ Implantation
Authors: Sekar Karuppanan , Krull Wade A , Horsky Thomas N
Published: April 2011

Si:C layers are interesting candidates as stressor layers for NMOS transistors. Growth of such a Si:C layer has been realized by an expensive epitaxial growth process for devices to produce tensile strain in the channel, leading to enhanced mobility and device performance. Use of a monomer carbon ion implant in conjunction with a Ge pre-amorphizing implant (Ge-PAI) in Si is an alternative, lower cost approach to obtaining such SiC layers. This approach has not yielded desired device performance owing to low carbon substitutionality [C]sub, and also the presence of end-of-range (EOR) defects and large leakage currents due to the Ge-PAI implant. In this study we will show the formation of a Si:C layer using a ClusterCarbon approach that creates self-amorphization in Si thus avoiding an extra Ge-PAI implant step. We show that more than 2% substitutional carbon can be realized by using solid-phase-epitaxial-regrowth (SPER) and millisecond anneal. Si:C layers are characterized by using High Resolution X-ray Diffraction (HRXRD) and SIMS techniques.
Atomistic Simulation and Subsequent Optimization of Boron USJ Using Pre-Amorphization and High Ramp Rates Annealing
Authors: Singer Julien , Wacquant François , Villanueva Davy , Salvetti Frédéric , Laviron Cyrille , Cueto Olga , Rivallin Pierrette , Jaraíz Martín , Poncet Alain
Published: April 2011

This study presents the use of atomistic process simulations to optimize p+/n ultra-shallow junctions fabrication process. We first bring to the fore that a high injection of interstitials close to the boron profile decreases the sensibility of boron diffusion to thermal budget. Preamorphization of the substrate is thus necessary to decrease boron diffusion by thermal budget reduction, the latter being obtained by the use of the thermal conduction tool (Levitor) instead of the classical lamp-type rapid thermal annealing. At the same time we show that the use of Levitor does not enhance boron activation, the substrate being preamorphize or not. So Levitor anneal can improve sheet resistance/junction depth trade-off only with preamorphization implant. Experiments are performed that confirm the predictions of our simulations. Further discussions explain activation path of boron during temperature cycle, as a function of amorphous depth, and for both lamp-type and Levitor anneal.
Concentration-Dependence of Self-Interstitial and Boron Diffusion in Silicon
Authors: Windl Wolfgang
Published: April 2011

In this paper, we discuss the accuracy of ab-initio calculations for self-interstitial and boron dif-fusion in silicon in light of recent experimental data by de Salvador et al. and Bracht et al. Map-ping the experimental data onto the activation energy vs. Fermi level representation commonly used to display ab-initio results, we show that the experimental results are consistent with each other. While the theoretical LDA value for the boron activation energy as a function of the Fermi level agrees well with experiment, we find for the self-interstitial in line with other calculations an underestimation of the experimental values, despite using total-energy corrections.
Effects of Oxygen on the Microstructures, Crystallization, Thermal and Electrical Properties of Tellurium Doped GeSb9 Films
Authors: Shih Hsiang-Wen , Perng Yu-Hsung , Chou Lih-Hsin
Published: April 2011

Tellurium and oxygen co-doped GeSb9 films (denoted as GeSb9-Te/O) with fixed Te concentration for phase change random access memory (PRAM) are investigated. The crystallization temperatures increased from 169°C to 201°C and the crystallization activation energy decreased from 5.53 eV to 2.89 eV as the oxygen concentration increased from 0 at.% to 17.3 at.%. The structures of crystalline GeSb9-Te/O films annealed at 250°C are identified as Sb rhombohedral structure with oxygen concentration less than 18 at.%, and the lattice parameter increased from 4.48 Å to 4.52 Å as the oxygen concentration increased from 0 at.% to 17.3 at.%. The grain size became smaller after oxygen doping. For films with oxygen concentration below 6 at.% and annealed at 250°C, only some of Ge form germanium suboxide GeOx, others remain metallic state. In films with oxygen concentration 28.1 at.% and annealed at 250°C, the GeO2 bond and Sb2O3 bond co-existed. The resistivity of amorphous phase (or crystalline phase) increases from 5.17 Ω-cm to 24.81 Ω-cm (or 1.12×10−4 Ω-cm to 1.05×10−3 Ω-cm), about 4.8 times (or about 9.4 times) as oxygen concentration increases from 0 at.% to 17.3 at.%. The film properties show beneficial in PRAM application.
Characterization of Thermally Evaporated Ag-Ge-S Thin Films
Authors: Wang Fei , Dunn William Porter , Jain Mukul , De Leo Carter , Vicker Nicholas , Savage Richard , Jin Xiaomin , Mamedov Sergey , Boolchand Punit
Published: April 2011

Thin films of ternary (GeS3)1−xAgx glasses (x=0.1 and 0.2) are studied in this work. Thin films are fabricated in a vacuum thermal evaporator at 3 different evaporation angles (0°, 30° and 45°). All thin film samples are examined in Raman spectroscopy. Raman results of both normally and obliquely deposited thin film samples reveal Ge-S CS modes (∼340cm−1) , Ge-S ES (∼360cm−1) modes, and thiogermanate modes Q1∼Q3 (390cm−1∼437cm−1). In addition, sharp peaks due to sulfur rings (S8) are observed at 218cm−1 and 470cm−1. Raman line-shapes of thin films are qualitatively consistent with their corresponding bulk glasses. However, the sharp peaks due to sulfur rings were not observed in bulk glasses. By comparing CS modes of thin films of three angles, we observe that normally deposited (0 degree) thin film shows a red-shift in center and a broadening in width. The film thickness of normally deposited films are significantly smaller comparing with that of corresponding obliquely deposited films.
Thermally-Stable High Effective Work Function TaCN and Ta2N Films for pMOS Metal Gate Applications
Authors: Adelmann Christoph , Lehnen P. , Ragnarsson L.-Å. , Conard T. , Franquet A. , Chang V. S. , Rohr E. , Meersschaut J. , Boissière O. , Lohe C. , Schram T. , Van Elshocht S. , De Gendt S.
Published: April 2011

TaCN-based metal films were grown by metal-organic chemical-vapor deposition (MOCVD) and atomic vapor-deposition (AVD). Thermal decomposition at 500ºC leads to com-positions of approximately Ta0.50C0.4N0.1 (“TaCN”), whereas a reactive process using NH3 leads to the formation of Ta0.65C0.1N0.25 (“Ta2N”) films. All films are nearly amorphous as grown and recrystallize only weakly after spike annealing at 1050°C. The thermal stability of TaCN/HfSiO4 and Ta2N/HfSiO4 stacks during spike annealing at 1050°C was studied and Si and Hf outdiffusion into TaCN or Ta2N was observed. The effective work functions of TaCN and Ta2N on HfSiO4 were found to be as high as 4.9 eV after high thermal budget. It is demonstrated that the effective work function can be further increased to 5.1 eV after high thermal budget by the insertion of a thin Al2O3 capping layer between HfSiO4 and the metal films.
Electrical Properties of Thermally Grown HfO2 and HfO2/TiO2/HfO2 MIM Capacitors fabricated on SiO2/Si Substrate and HfO2 MIM Capacitors Fabricated on Sapphire
Authors: Miao Bing , Mahapatra Rajat , Wright Nick , Horsfall Alton
Published: April 2011

The scaling of contemporary metal-insulator-metal (MIM) capacitors requires oxides of higher dielectric constant (>10), such as hafnium oxide (∼18) and titanium oxide (∼40). Intensive research of these oxides and oxide stacks is needed to develop them into high quality electronic materials for their application as capacitors in high temperature environments. High-k dielectrics such as HfO2 and HfO2/TiO2/HfO2 have been grown by thermal oxidation to fabricate MIM capacitors on SiO2/Si substrates and on sapphire substrates also. The thermally grown Al/HfO2/TiO2/HfO2/Pt/Ti/SiO2/Si MIM capacitor is reported here for the first time. The MIM capacitor using HfO2/TiO2/HfO2 dielectric film shows a similar frequency dependence using HfO2 dielectric on a SiO2/Si substrate, whilst its voltage linearity coefficients, leakage current and temperature coefficient are higher than the capacitor employing HfO2 dielectric. The MIM capacitor with HfO2 dielectric fabricated on sapphire substrate shows the strongest frequency dependence, voltage linearity coefficient and temperature dependence which is related to the surface roughness of substrate. The high capacitance density of these capacitors, ranging from 5.21 fF/µm2, meets the ITRS requirements for analog capacitor up to 2012. The MIM capacitor using 30nm HfO2 dielectric film illustrates highest capacitance density, 5.21 fF/µm2, a VCC of 236 ppm/V2, a temperature coefficient of 290 ppm/ºC, measured up to 300 ºC, and leakage current density which is 1.3 × 10−7 A/cm2 at 1V.
Study of Coercivity-enhanced Ruthenium-doped La0.67Sr0.33MnO3 Thin Films for Pseudo Spin Valve Devices
Authors: Chan Yuk Kwan , Cheng Wang Fai , Lau Hon Kit , Leung Chi Wah
Published: April 2011

This investigation focused on the study of La0.67Sr0.33MnO3 (LSMO) thin films with 5 atomic percent Ru-doping (LSMRO). Specifically, we fabricated epitaxial LSMO and LSMRO thin films on LaAlO3 (LAO) (001) substrates by pulsed laser deposition. Resistance- temperature measurement results showed that the Curie temperature (Tc) of LSMRO thin film deposited under an oxygen ambient pressure of 150 mTorr at 830 °C was above room temperature. Hysteresis measurements and anisotropic magnetoresistance (AMR) results confirmed that coercivity of the optimized LSMRO films, as compared with that of LSMO films, can be greatly increased at low temperatures. The study successfully demonstrated the coercivity enhancement effect of Ru-doping on LSMO thin films deposited on LAO substrates.
Effect of the Surface Structure of Thin Layers on Their Reactivity
Authors: Dultsev Fedor
Published: April 2011

Changes of the electron properties of surface atoms of silicon dioxide film caused by the adsorption of donor-type gas-phase molecules (H2O, O2, NH3, HF) were modeled with the help of semiempirical methods and molecular mechanics. It was shown that the adsorption capacity and reactivity of the layers depend on the Si-O-Si bond angle. The results of calculations are in good agreement with the experimental data and confirm our hypothesis concerning the rearrangement of the surface layer stimulated by the adsorbed molecule.
CuxO/CeO2 Nanocomposites: Synthesis and Reactivity with NO
Authors: Scopel Federico , Galenda Alessandro , Natile Marta Maria , Glisenti Antonella
Published: April 2011

CuxO/CeO2 nanocomposite powders were prepared by wet impregnation of nanosized ceria powder (Cu/Ce nominal atomic ratio from 0.05 to 0.5). XP analysis reveals the presence of Cu2O in the samples with lower Cu/Ce atomic ratio whereas CuO is prevalent in the samples richer in copper. The surface Cu/Ce atomic ratio obtained from XPS data is always higher than the nominal one suggesting the surface segregation of copper. A plateau value (0.9-1.0) is reached for the samples with a nominal Cu/Ce atomic ratio of 0.2 suggesting an island growing mechanism.

The nanocomposite samples and the supporting ceria were exposed to a NO+CO mixture (2% CO, 2% NO, 96% He) and the reactivity was investigated by means of DRIFT spectroscopy and QMS. At 523 K (i.e. the temperature at which the nanocatalysts activity is higher) the capability for NO reduction increases with increasing the Cu/Ce atomic ratio.
Bonding Structure of Ultrathin Oxides on Si(110) Surface
Authors: Yamamoto Yoshihisa , Togashi Hideaki , Kato Atsushi , Suemitsu Maki , Narita Yuzuru , Teraoka Yuden , Yoshigoe Akitaka
Published: April 2011

The thermal oxidation kinetics of Si(110) surface up to oxide layer thickness of 1 ML has been investigated by real-time monitoring of chemical shifted in the Si 2p core-level photoemission using synchrotron radiation. The uptake profiles of every Si oxidation states (Sin+: n = 1 − 4) indicate that the top surface Si(110) oxidation proceeds through a two-step oxidation pathway via Si2+ state, just like the Si(001) surface. In contrast to the Si(001) oxidation, however, Si3+ state is always more abundant than Si4+ state during oxidation. This is related to occurrence of imperfect oxidation of this surface, most probably due to accumulation of compressive strain during oxidation.
Phase Stability of 10mol%Sc2O3-1mol%CeO2-ZrO2 Ceramics
Authors: Yarmolenko Sergey , Fialkova Svitlana , Pai Devdas M. , Sankar Jag
Published: April 2011

Scandia-doped zirconia is a very promising material for solid oxide fuel cells due to its high oxygen conductivity in the 700-850°C temperature range. 10 mol% Sc2O3 - 1 mol% CeO2 - ZrO2 ceramics were sintered at temperatures 1100-1600°C using different heating rates and dwell times. Ceramics sintered at temperatures higher 1300°C were found to exist in cubic phase at room temperature and exhibit slow phase transformation from cubic (c) to rhombohedral (beta) phase between 330 and 400°C. Analysis of c-β phase transition efficiency in the ceramics shows a strong correlation between the transition rate and sintering temperature. Kinetics of phase transitions were studied by high temperature X-ray diffractometry (HTXRD) and differential scanning calorimetry methods. The reversible c-β phase transition was found to have very wide hysteresis (45-70°C), which depends on sintering temperature and density. Coefficients of thermal expansion of c- and β-phases were calculated from temperature dependence of lattice parameters obtained by HTXRD in the temperature range of 25-800°C. Microstructural changes on the surface of the cubic phase due to c-β phase transition studied by SEM and AFM.
Preparation of Long Lasting Phosphor by New Method
Authors: Jin Hu , Xiaoqin Zhu , Donghua Chen , Kaijun Wan , Yuzhong Guo
Published: April 2011

The composite powder of Al(OH)3 and Sr(OH)2, was obtained by means of the hydrolysis of the activated Al-Sr alloy powder in pure water. As a precursor, it could be used to prepare long after phosphor Eu, Dy co-doped SrAl2O4 by the modified solid state reaction at 1300°C. The components and microstructure of the composite powder were investigated by XRD, SEM and EDS techniques, and the luminescent characteristics and the afterglow properties of the long afterglow material were also measured at the same time. The experimental results showed that, the distribution of the two elements Al and Sr was uniform in the microstructure of the composite powder, and the contacting surfaces between the solid reactants were increased effectively at high temperature, and the diffusive paths were abbreviated. Therefore, the reaction velocity was increased, the sinter temperature descended and the luminescent properties enhanced.
Synthesis and characterization of colloidal titania nanoparticles
Authors: Díaz-Fonseca Ana-Lilia , Cheang-Wong Juan-Carlos
Published: April 2011

Spherical submicrometer-sized titanium dioxide (TiO2 or titania) particles were prepared by the sol-gel method from hydrolysis and condensation of titanium alkoxide using different basic catalysts in ethanol/acetonitrile at different annealing temperatures. A systematic study was performed in order to determine the effect on the particle size and shape of the different reagents. Subsequently, they were deposited onto silicon wafers, in order to form a monolayer of TiO2 monodisperse particles. The titania particles were characterized by scanning electron microscopy to determine size and shape, and by X-ray diffraction to find their crystal structure.