bluuebunny/crossref_metadata_2025 huggingface dataset:
Free Recovery Effects of Shape-Memory Polymers for Cardiovascular Stents
Authors: Yakacki Christopher Michael , Shandas Robin , Lanning Craig , Gall Ken
Published: April 2011

The shape-memory effect was examined in polymer stents intended for cardiovascular applications. Four polymer networks were synthesized from poly(ethylene glycol) dimethacrylate and tert-butyl acrylate with 10 wt% and 20 wt% crosslinker, and with glass transition temperatures (Tg) of 52°C and 55°C. Solid and 50% porous stents were manufactured and tested for free strain recoverability at temperatures at or just above 37°C. Stents with lower glass transition temperatures and a higher degree of crosslinking recovered faster than their counterparts. Lower deformation (packaging) temperatures and higher recovery temperatures induce more rapid recovery. The presence of geometrical features, such as pores, initiated recovery sooner, but had negligible influence on overall recovery.
Nanoparticle Ring Structures based on Protein Assemblies
Authors: Behrens Silke , Habicht Wilhelm , Wagner Kerstin , Unger Eberhard
Published: April 2011

The bottom-up wet-chemical synthesis of inorganic materials provides tools for generating nanostructures from particles to one-dimensional structures, but these conventional chemical techniques usually offer little control over the deposition of metals or metal particles into nanosized ring structures although interesting properties and applications, e.g., Aharonov-Bohm rings are expected. Our results provide a straightforward and rapid wet-chemical synthesis to ring-like metal particle arrays. Applying appropriate conditions, tubulin dimers, proteins of 4-5 nm diameter and a length of 8 nm, self-assemble by specific recognitions capabilities into defined superstructures. Ca2+ ions, e.g., direct the assembly of tubulin into 50 nm sized, ring-like structures. In our approach, these ring-like protein assemblies serve as a functionalized scaffold where the metal particles are generated in situ and deposited into spiral-shaped particle arrays, reflecting the arrangement of the protein subunits within the assembly. The resulting size and crystalline structure of the materials were examined using transmission electron microscopy and scanning force microscopy.
Millimeter-scale surface nano-structuring using focused ion beam milling
Authors: Dovidenko Katharine , Potyrailo Radislav A. , Le Tarte Laurie A.
Published: April 2011

New patterning schemes for a variety of applications including sensors and photonics are explored. We present here a comprehensive study of using focused ion beam (FIB) milling to modify surfaces over millimeter-scale areas with nano-patterns of dimensions down to 30 nm. A typical example of a pattern is 40 nm diameter × 40 nm depth wells with a 200 nm pitch. Typical sample materials are metals, but polymer patterning is possible. We have also evaluated the surface of the patterned materials to ensure there are no negative effects of these patterning schemes on the future device performance.
Effects of Dielectrophoretic Parameters on Fabrication and Electronic Properties of Single-Walled Carbon Nanotube Devices
Authors: Dong Lifeng , Youkey Steven , Bush Jocelyn , Lo Jennifer , Jiao Jun , Dubin Valery M , Chebiam Ramanan V
Published: April 2011

We recently developed a novel floating-potential dielectrophoretic method to selectively position individual single-walled carbon nanotubes between two floating electrodes while the bundles of nanotubes and impurities were attracted into the region between two control electrodes. In this study, we investigated effects of several process parameters including electric field distribution, electric field frequency, and solution media in order to understand the physical mechanisms of this dielectrophoretic process and to improve its efficiency. Results showed that both the magnitude and the direction of electrical force applied onto the nanotubes can be tailored by changing these process parameters. It was found that a 1 wt% sodium dodecyl sulfate in deionized water is an efficient solution for separating bundles of nanotubes into individual nanotubes and aligning individual nanotubes with a clean surface between two electrical contacts in comparison to N,N-dimethylformamide, 1,2-dichloroethane, 1,2-dichlorobenzene, 1,1-dichloromethane, ethanol, and isopropanol solutions. The fabricated carbon nanotube devices exhibit electronic properties comparable to nanotube transistors and interconnects fabricated by other methods.
How to realize ultimate spatial and temporal resolutions by laser-combined scanning tunneling microscopy?
Authors: Shigekawa Hidemi , Takeuchi Osamu , Aoyama Masahiro , Terada Yasuhiko , Kondo Hiroyuki , Oigawa Haruhiro
Published: April 2011

By combining scanning tunneling microscopy (STM) and the optical pump-probe technique using a femtosecond pulse laser, we have developed a new microscopy, shaken pulse-pair-excited STM (SPPX-STM), that enables us to observe the dynamics of electronic structures with the ultimate spatial and temporal resolutions.
Rolling behavior of cylindrical micro-object analyzed by finite element method
Authors: Ochiai Toshihiro , Saito Shigeki , Takahashi Kunio
Published: April 2011

Analyzing the rolling behavior of micro-object is necessary for the realization of the micro-manipulation technique by mechanical-method. Thus in this paper, we obtain the rolling resistance of an isotropic elastic cylindrical micro-object in adhesive contact to a rigid surface.

In order to estimate the rolling resistance, we assume this adhesive contact to be the plane strain problem, and calculate the total energy of this system as the numerical function of the contact area using finite element method (FEM). The total energy of this system is defined as the sum of the next three terms: the elastic energy of the cylindrical micro-object, the interface energy within the contact area, and the mechanical potential energy that depends on the external moment applied to the cylindrical micro-object. A careful consideration of the energy balance of the system clarifies that the rolling resistance has the value of 0.1 [10-12Nm] for the polystyrene (where a work of adhesion = 0.1[N/m]) cylindrical micro-object with the radius and thickness. Hence, we establish the procedure of the calculation for the rolling resistance of the micro-object based on the principle of the energy balance by finite element method.
Nanocones- a different form of carbon with unique properties
Authors: Heiberg-Andersen Henning , Helgesen Geir , Knudsen Kenneth , Pinheiro Jean Patrick , Svåsand Eldrid , Skjeltorp Arne
Published: April 2011

It is possible to make perfect conical carbon nanostructures fundamentally different from the other nanocarbon materials, notably buckyballs and nanotubes. Carbon cones are realized in five distinctly different forms. They consist of curved graphite sheets formed as open cones with one to five carbon pentagons at the tip with successively smaller cone angles, respectively. The nucleation and physics of nanocones has been relatively little explored until now. We present here the key facts and latest results on this “5’th form of carbon”.
NiSi Nanowires and Nanobridges Formed by Metal-Induced Growth
Authors: Kim Joondong , Lee Dongho , Anderson Wayne A
Published: April 2011

Nickel monosilicide (NiSi) nanowires (NWs) were fabricated by metal-induced growth at 575 °C. The solid-state reaction of Ni and Si provides linear grown NWs. The parallel grown NW forms a nanobridge (NB) across a trench, patterned with a simple optical lithography and metal lift-off method. The Ni pads gave a good Ohmic contact without affecting the I-V transport characteristics through a NB. The metallic NB, 2.73 µm in length and 50 nm in diameter, gave a low resistance of 148 . The self-assembled nanobridge can be applied to form nanocontacts at relatively low temperatures. The MIG NB is a promising 1 dimensional nanoscale building block to satisfy the need of ‘self and direct’ assembled ‘bottom-up’ fabrication concepts.
Atomistic Study of the Mechanical Properties of One-Dimensional Nanomaterials
Authors: Shintani Kazuhito , Kameoka Shunji , Sato Shuhei , Kometani Yusuke
Published: April 2011

The mechanical properties of Au nanowires under a uniaxial load are investigated by molecular-dynamics simulation. The modified embedded-atom method (MEAM) potential is employed to calculate the interactions between Au atoms. Ten kinds of model nanowires with different cross-sections and axis directions are prepaired. The structural dependence and size effect of the Young’s moduli of Au nanowires are discussed.
Selective Chemical Vapor Growth of Carbon Nanotubes for Application of Electronic-Measuring Nano-Probes
Authors: Okuyama Hiroki , Iwata Nobuyuki , Yamamoto Hiroshi
Published: April 2011

Selectively grown carbon nanotubes (CNTs) and/or vertically aligned CNTs (VACNTs) on patterned metal electrodes have been prepared for applications to a novel electronic-measuring nano-probe. We propose newly a position-controlling method of CNTs by controlling not only a position of catalysts but also the thickness of metal underlayers for the catalysts. The selective growth of CNTs was achieved at edges of the metal pattern by thermal chemical vapor deposition. The width of selectively grown CNTs was minimized, about 2.6 µm. The width was about 80 times as small as that of the metal pattern. VACNTs were synthesized by a plasma enhanced CVD method in which the high electric field in a cathode dark space was applied to the substrates. The VACNTs grew up, however, all over the metal pattern.
Formation of Large Bulk [(Fe0.5Co0.5)0.75B0.20Si0.05]96Nb4 Glassy Alloy by Flux Melting and Water Quenching
Authors: Bitoh Teruo , Makino Akihiro , Inoue Akihisa , Greer A. Lindsay
Published: April 2011

The large bulk glassy [(Fe0.5Co0.5)0.75B0.20Si0.05]96Nb4 alloy specimens with the diameters up to 7.7 mm have been prepared by water quenching the melt immersed in the molten flux of B2O3. The maximum diameter of the obtained specimens is approximately 1.5 times as large as the pre-vious result for copper mold casting should be cooled at the higher rate than the of water quenching. The flux melting improves the glass-forming ability by the elimination of oxides and other inclusion in the molten metal which act as heterogeneous nucleation sites for crystallization.
Multi-paradigm multi-scale modeling of dynamical crack propagation in silicon using the ReaxFF reactive force field
Authors: Buehler Markus J. , van Duin Adri C.T. , Goddard III William A.
Published: April 2011

We report a study of dynamic cracking in a silicon single crystal in which the ReaxFF reactive force field is used for ∼3,000 atoms near the crack tip while the other 100,000 atoms of the model system are described with a simple nonreactive force field. The ReaxFF is completely derived from quantum mechanical calculations of simple silicon systems without any empirical parameters. Our results reproduce experimental observations of fracture in silicon including details of crack dynamics for loading in the [110] orientations, such as dynamical instabilities with increasing crack velocity. We also observe formation of secondary microcracks ahead of the moving mother crack. We conclude with a study of Si(bulk)-O2 systems, showing that Si becomes more brittle in oxygen environments, as known from experiment.
Deviation of the mechanical response of Wall-patterned (001) GaAs Surface: a central-plastic-zone criterion
Authors: Le Bourhis Eric , Patriarche G.
Published: April 2011

Wall-patterned GaAs surfaces have been elaborated by photolithography and dry etching. Different surfaces were produced in order to change the aspect ratio of the walls formed at the substrate surface. The mechanical behaviour of individual walls was investigated by nanoindentation and the responses were compared to that of a standard bulk reference (flat surface). Deviation from the bulk response is detected in a load range of 0.1-25 mN depending on the aspect ratio of the walls. A central-plastic-zone criterion is proposed in view of TEM images of indented walls and allows predicting the response deviation of a given wall knowing its width. The application of substrate patterning for optoelectronic devices is proposed in the perspective of eliminating residual dislocations appearing in mismatched structures.
Solution-Processed ZnO Nanowire Network Thin Film Transistors for Transparent Electronics
Authors: Bakhishev Teymur , Volkman Steven , Subramanian Vivek
Published: April 2011

We describe a process to grow ZnO nanowires in aqueous solution of Hexamine and Zinc Nitrate to obtain a network of nanowires 0.5-1.5μm long. The growth was initiated on ZnO nanoparticles spun-cast onto thermal SiO2. We demonstrate bottom-gate FET structures formed using these nanowire networks as channel layers with gold (Au) and aluminum (Al) source/drain pads. Resulting transistors are well-behaved with on-off ratios >104 and mobility >10-2 cm2/V-s, calculated without accounting for actual surface coverage of nanowires. Actual nanowire mobility is therefore substantially higher, attesting to the potential for this technique as a method for realizing low-cost, high-brightness displays.
In Situ HREM Observation of Phase Transformation Process in FePt and FePtCu Nanoparticles
Authors: Nakanishi Masatoshi , Furusawa Gen-ichi , Waki Kokichi , Hattori Yasushi , Kamino Takeo , Sasaki Katsuhiro , Kuroda Kotaro , Saka Hiroyasu
Published: April 2011

The processes of phase transformation in individual nanoparticles of FePt and FePtCu synthesized by the reverse micelle method, which are chemically homogeneous and monodisperse, have been investigated by an in-situ HREM observation in a FE-TEM. Polycrystalline FePt particles, initially of chemically disordered face-centered cubic phase (A1) were reconstructed into A1 single crystals between 25 °C and 650 °C, followed by phase transformation from A1 to chemically ordered face-centered tetragonal phase (L10) which began between 650 °C and 680 °C. The coalescence began concurrently with phase transformation, i. e., between 650 °C and 680 °C. They turned to be a round-shaped L10 particle between 680 °C and 720 °C. The single crystal formation, the phase transformation from A1 to L10, the coalescence and the round-shaped particle formation were also observed in the FePtCu nanoparticles. The temperatures of single crystal formation, phase transformation (and coalescence) and round-shaped particle formation of the FePtCu nanoparticles were between 25 °C and 500 °C, between 550 °C and 600 °C and between 600 °C and 650 °C, respectively. These temperatures were substantially lower than those for the FePt nanoparticles.
In-situ Microscopic Study of Cu Intragranular Electromigration
Authors: Chen Kuan-Chia , Liao Chien-Neng , Wu Wen-Wei , Chen Lih-Juann
Published: April 2011

Electromigration (EM) in unpassivated copper lines at room temperature has been investigated in ultra-high vacuum by in-situ transmission electron microscopy (TEM). The electric current induced atomic migration in a (211)-oriented Cu grain has been successfully recorded in real-time video. The atomic image of the (211) grain was found to vanish directionally when applying an electric current density of 2 × 106 A/cm2 through the Cu line. The results suggested that the combination of {111} planes and <110> directions to be the easiest EM path in crystalline copper. By performing selective area diffraction (SAD) analysis on a single Cu grain with (111) crystal orientation, some unusual electron diffraction patterns appeared after passing an electric current through the Cu line. It is believed that the EM-induced Cu twinning may be held responsible for the unique diffraction patterns
Carbon Nanotube Growth from Nanoscale Clusters Formed by Ion Implantation
Authors: Choi Yongho , Oakley Jennifer Sippel , Rinzler Andrew , Ural Ant
Published: April 2011

We have demonstrated that iron ions implanted into silicon dioxide thin films form nanoscale clusters which can act as catalyst for carbon nanotube growth. We have implanted iron ions with an energy of 60 keV and three different doses (1014, 1015, and 1016 cm-2) into silicon dioxide thin films thermally grown on silicon substrates. We then used chemical vapor deposition (CVD) to grow carbon nanotubes on these ion implanted substrates with methane as the precursor gas. We studied the effect of ion implantation dose on the structural properties of the nanoscale clusters, as well as the carbon nanotubes nucleated from these clusters. The nanoscale clusters and grown nanotubes were characterized by Atomic Force Microscopy and Raman spectroscopy. The electrical characteristics of the as-grown nanotubes were also characterized. We found that growth of low density, horizontal, and small diameter carbon nanotubes on silicon dioxide is possible using this nucleation technique.
Enhanced Biocompatibility of GPC by Ion Implantation and Deposition
Authors: Zimmerman Robert Lee , Gürhan Ismet , Muntele Claudiu I. , Ila Daryush , Özdal-Kurt Feyzan , Sen B. H.
Published: April 2011

Biocompatible Glassy Polymeric Carbon (GPC) is used for artificial heart valves and in other biomedical applications. Although it is ideally suited for implants in the blood stream, tissue that normally forms around the moving parts of a GPC heart valve sometimes loses adhesion and creates embolisms downstream. Here we compare silver ion implantation and silver deposition, each of which strongly inhibits cell attachment on GPC. Inhibition of cell adhesion is a desirable improvement to current GPC cardiac implants. In vitro biocompatibility tests have been carried out with model cell lines to demonstrate that traces of silver can favorably influence the surface of GPC for biomedical applications.
The Design, Implementation and Assessment of an On-Line, Open-Book Quizzing Environment for an Introductory Materials Science Course.
Authors: Locklin Ralph H , Howell Paul R
Published: April 2011

The authors have developed, implemented and assessed an on-line, open-book quizzing environment for the introductory materials science course, “Materials In Today’s World”. The course is offered as an E-Education course and students may complete the course from anywhere that permits access to our course management system, ANGEL. For reasons that were both pragmatic and philosophical, we decided that the exams/quizzes would not be proctored, they would be delivered wholly on-line, and would be open-book.

In the current paper, we will present and justify our philosophy, of on-line, open-book quizzes: the rich feedback, which is a feature or our quizzing system, QuestionMark Perception, is used both as a teaching tool, and as a means to refine the quiz database. We have replaced the original “high-stakes” midterm and final exam, with a series of lower-stakes, weekly quizzes, which are generated from a large question database. Student response to the quizzing environment is generally very positive.
The Molecule, The Monomer and Materials Science: A Preliminary Report
Authors: Howell Paul
Published: April 2011

There would appear to be a large disconnect between the content of a typical high school chemistry course, and an introductory, college materials science course. For example, A National Science Foundation report notes that,

“the historic bias of chemistry curricula towards small molecule chemistry, generally in the gaseous and liquid states, is out of touch with current opportunities for chemists in research, education and technology”.

In contrast, the typical introductory college materials science course concentrates almost exclusively on the solid state, and a discussion of “small molecular” materials is virtually absent.

In the present contribution, it will be shown how the “molecule” forms part of a hierarchical series of structures, from the sub-atomic to the macroscopic. It will also be argued that the molecule is but a sub-set of a localized grouping of atoms, which is best described by the term “monomer”.

Based on a strict definition of the molecule and monomer, a complete hierarchical scheme for the structure of materials is developed, which should be applicable to both a high school chemistry course, and an introductory materials science course.
Thin Films of GeC Deposited Using a Unique Hollow Cathode Sputtering Technique
Authors: Huguenin-Love James L. , Soukup Rodney J. , Ianno Natale J. , Schrader Jason S. , Dalal Vikram L.
Published: April 2011

Experimental results on thin films of the new material GexC1-x, deposited by a unique dual plasma hollow cathode sputtering technique are presented here. The (Ge, C) system is extremely promising since the addition of C to Ge has reduced the lattice dimensions enough to allow a lattice match to silicon, while increasing the bandgap close to that of c-Si. The sputtering is accomplished by igniting a dc plasma of the Ar and H2 gases which are fed through Ge and C nozzles, cylindrical tubes 30 mm in length with an 8 mm O.D. and a 3 mm I.D.

The basic material, optical, and structural properties were analyzed. Film characterization was performed using Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Auger electron spectroscopy. Additional measurements such as Tauc bandgap, conductivity as a function of temperature and light intensity, and film uniformity have been made. The film properties from a variety of deposition conditions are discussed. The measurements made indicate that the films can be grown so that the C enters the material at lattice sites. In addition, the GexC1-x films absorb photons much more efficiently than either c-Si or c-Ge.

Initial results on Al doped films are presented.
Incubation Layer-Free Nanocrystalline-Si Thin Film Fabricated by ICP-CVD at 150°C for Flexible Electronics
Authors: Han Sang-Myeon , Cha Young-Kwan , Park Joong-Hyun , Park Sang-Geun , Park YoungSoo , Han Min-Koo
Published: April 2011

The nc-Si films where the troublesome incubation layer was almost eliminated were deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) under various dilution conditions. The nc-Si films were analyzed with cross-sectional high resolution transmission electron microscopy (HR-TEM) images. It was verified that the Si crystalline components formed and grew from the surface of buffer layer. The grain size of 20~50nm was measured. The absence of incubation layer in nc-Si film may be attributed mainly to ICP-CVD which generates remote plasma of high density, the role of hydrogen, and the dilution effect on the growth of crystalline. Our experimental results show that incubation-free nc-Si film deposited by ICP-CVD may be suitable for the active layer of bottom gate nc-Si TFTs as well as top gate nc-Si TFTs.
Effects of HWCVD-deposited Seed Layers on Hydrogenated Microcrystalline Silicon Films on Glass Substrates
Authors: Adachi Michael Musashi , Tse Wing Fai Lydia , Cluff Garnet , Kavanagh Karen L. , Karim Karim S.
Published: April 2011

Microcrystalline silicon was deposited by hot-wire chemical vapor deposition (HWCVD) using a graphite filament with and without a thin 50 nm microcrystalline silicon seed layer. Increasing silane concentration diluted in H2 led to a decrease in crystalline fraction as well in a decrease in dark conductivity and photo-conductivity. In addition, films deposited with a seed layer were found to have higher dark conductivity and photo-conductivity than those without a seed layer but deposited at slower growth rates. However, Raman spectroscopy showed that use of a seed layer resulted in only a small increase in crystalline fraction at the surface of the films which had thicknesses between 250-400nm. TEM measurements confirmed the crystalline nature of deposited films showing average grain sizes of 25 nm.
Experimental Studies of Photoluminescence in Mn-Ion Implanted Silicon Rich Oxide Thin Film
Authors: Pan Wei , Dunn R.G. , Carroll M.S. , Wang Y.Q.
Published: April 2011

In this paper, we wish to report our preliminary experimental results from the photoluminescence (PL) studies in a Mn-ion implanted silicon-rich oxide (SRO) thin film. At 4 K, a broad PL peak, centered at ~ 1.2 eV, was observed. It is blue-shifted from the Si substrate peak at ~ 1.1 eV. The temperature (T) dependence of PL was carried out at zero magnetic (B) field and B = 0.5 Tesla, respectively, and showed quantitatively different behaviors. At B = 0, the PL intensity increases very slowly at low temperatures and reaches a maximal value at ~ 40 K. It then decreases as T is further increased. At B = 0.5 Tesla, the peak temperature (Tpeak), whether the intensity is maximal, moves to ~ 80-100 K, and the decreasing rate beyond Tpeak is much smaller than that at B = 0. We speculate that these two different behaviors might reveal, possibly, a ferromagnetic ordering in Mn-ion doped silicon nanocrystals.
The Investigation of High Performance TFT by Thin Beam Directional X-stallization Method
Authors: Chao Chihwei , Peng Jiatien , Cheng CW , Chen Chunghung , Turk Brandon A. , Burfeindt Bernd
Published: April 2011

Thin-beam directional X'tallization (TDX) is a low-temperature-substrate compatible crystallization method that can form directionally solidified poly-si films directly on glass substrates. Without using a mask, extremely long uniformly-spaced poly-Si grains can be formed by TDX. In this paper, we have investigated the influence of laser energy and scan pitch on the properties of the resulting poly-Si films. Grain size and surface morphology of TDX-processed poly-Si films were observed by SEM and AFM. The AFM results demonstrate that, due to the lateral growth phenomenon, TDX poly-Si films are much smoother than films produced by the current industry standard method, Excimer Laser Annealing (ELA). The breakdown of the TDX method is also discussed in this paper. When the laser scan pitch is larger than the lateral growth length that is characteristic of a given poly-Si film and beam property combination, a discontinuous poly-Si film is formed with vertical protrusions and grain boundaries occurring perpendicular to the scan direction. Poly-Si films with vertical protrusions and grain boundaries perpendicular to the direction of current flow will degrade the resulting thin-film transistor (TFT) performance.
Backplane Requirements for Active Matrix Organic Light Emitting Diode Displays
Authors: Nathan Arokia , Striakhilev Denis , Chaji Reza , Ashtiani Shahin , Lee Czang-Ho , Sazonov Andrei , Robertson John , Milne William
Published: April 2011

Organic light emitting diode (OLED) displays are a serious competitor to liquid crystal displays in view of their superior picture quality, higher contrast, faster on/off response, thinner profile, and high power efficiency. For large area and/or high-resolution applications, an active matrix OLED (AMOLED) addressing scheme is vital. The active matrix backplane can be made with amorphous silicon (a-Si), polysilicon, or organic technology, all of which suffer from threshold voltage shift and/or mismatch problems, causing temporal or spatial variations in the OLED brightness. In addition, the efficiency of the OLED itself degrades over time. Despite these shortcomings, there has been considerable progress in development of AMOLED displays using circuit solutions engineered to provide stable and uniform brightness. Indeed the design of AMOLED pixel circuits, particularly in low-mobility TFT technologies such as a-Si, is challenging due to the stringent requirements of timing, current matching, and low voltage operation. While circuit solutions are necessary, they are not sufficient. Process improvements to enhance TFT performance are becoming inevitable. This paper will review pertinent material requirements of AMOLED backplanes along with design considerations that address pixel architecture, contact resistance, and more importantly, the threshold voltage stability and associated gate overdrive voltage. In particular, we address the question of whether conventional PECVD can be deployed for high mobility and high stability TFTs, and if micro-/nano-crystalline silicon could provide the solution.
Effect of Light Illumination on Threshold Voltage and Sub-threshold Slope of Amorphous Silicon Thin Film Transistors
Authors: Jiao Lihong , Wronski Christopher R. , Jackson Thomas N.
Published: April 2011

In this study the light induced defect state creation under 1 sun illumination is investigated through changes in sub-threshold slope, Δ, and threshold voltage, VT, in a-Si:H TFT structures. Threshold voltage changes can be due to either charge trapping or defect state creation near the interface of gate insulator and a-Si:H active layer. By incorporating high quality thermal silicon dioxide in the a-Si:H TFT, the charge trapping effects have been minimized and the changes in threshold voltage can be attributed to induced defect states in the a-Si:H. Since the sub-threshold current is closely related to the band gap defect states, both VT and Δ can be used as a new probe to study the light induced defect creation in the a-Si:H. The information obtained about the nature of gap defect states from the analysis of changes in VT and Δ under light illumination is presented. The results obtained show that under 1 sun illumination there are very fast increases (within 10 seconds) in VT with subsequent slow increases and no observable changes in Δ, similar to those observed in the light induced photoconductivity changes in a-Si:H thin films. The increase in VT under the initial light illumination are associated with the Fermi level in a-Si:H active layers moving downward and causing band bending near the interface region of the gate insulator and a-Si:H active layer. Results are also presented on changes in VT under gate-bias stressing. Comparisons are then made between the results obtained under 1 sun light illumination and those under gate-bias stressing. The information obtained in this study about the nature of the gap defect states derived from characterization of the sub-threshold regimes is discussed.
Metal-Induced Nickel Silicide Nanowire Growth Mechanism in the Solid State Reaction
Authors: Kim Joondong , Bae Jong-Uk , Anderson Wayne A. , Kim Hyun-Mi , Kim Ki-Bum
Published: April 2011

A unique nanowire growth was accomplished at 575 oC by the metal-induced growth (MIG). That is a spontaneous reaction between metal and Si. The deposited metal worked as a catalyst layer to grow nanowire in the solid-state. Various metals (Ni, Co, and Pd) were used in MIG nanowire fabrication and Ni-induced case was successful in demonstrating that metal species should be a dominant mover in nanowire growth. Transmission electron microscopy investigation was performed to observe the nanowire growth direction. The Ni to Si composition was studied by energy dispersive spectroscopy showing the Ni diffusion inside the nanowire as well as the Ni silicide layer. The practical application MIG nanowire was proven by fabricating nanoscale contacts.
Local Current Flow in Mixed-Phase Silicon Solar Cells and Correlation to Light-Induced Open-Circuit Voltage Enhancement
Authors: Yan Baojie , Jiang C.-S. , Moutinho H. R. , Al-Jassim M. M. , Yang Jeffrey , Guha Subhendu
Published: April 2011

We use conductive atomic force microscopy (C-AFM) to measure the local current flow in the mixed-phase hydrogenated silicon n-i-p solar cell structure without the top ITO contact. The forward biased C-AFM images reveal that for the fully amorphous region the current is very low on the entire surface. However, high current spikes appear in the mixed-phase region, where the current spikes are correlated to the formation of nanocrystallite aggregations with a diameter of ~500 nm. Furthermore, the density of the current spikes increases from the mixed-phase to the substantially nanocrystalline regions. The nanocrystallite aggregation supports our previously proposed parallel-connected two-diode model for Voc drops with crystalline volume fraction and light-induced Voc increase in the mixed-phase solar cells. Adding a 50-nm thick a-Si:H buffer layer between the p and i layers significantly reduces the magnitude of the high current spikes, even the top morphology appears unaffected. This result is also consistent with the previously proposed two-diode model for explaining the carrier transport in the mixed-phase solar cells.
Production Technologies of Film Solar Cell
Authors: Takano Akihiro , Tabuchi Katsuya , Uno Masayoshi , Tanda Masayuki , Wada Takehito , Shimosawa Makoto , Sakakibara Yasushi , Kiyofuji Shinji , Nishihara Hironori , Enomoto Hirofumi , Kamoshita Tomoyoshi
Published: April 2011

Light-weight, large-area and flexible solar cells and modules were developed. Roll-to-roll processes including an improved film deposition process named “Stepping-roll process” are used to fabricate large-area hydrogenated amorphous silicon-based solar cells in succession on plastic film substrates. A unique device having through-hole contacts was developed and applied to simplify the production processes and to generate high voltage using connection in series. Production technologies, such as (1) light-weight and large area module fabrication, (2) plasma condition controlled chemical vapor deposition, (3) low substrate temperature selective reactive sputtering, and (4) large-area uniform transparent conductive oxide film deposition are reviewed.
Highly Efficient Microcrystalline Silicon Solar Cells Deposited from a Pure SiH4 Flow
Authors: van den Donker Menno , Rech B. , Schmitz R. , Klomfass J. , Dingemans G. , Finger F. , Houben L. , Kessels W.M.M. , van de Sanden M.C.M.
Published: April 2011

The effect of conventional process parameters on the deposition of μc-Si:H solar cells is reviewed. Then, an approach to solar cell optimization is presented in which hidden, internal parameters are adjusted rather than conventional, external process parameters. The investigation focuses on deposition at low H2 dilution ratio and low total gas flow. A hidden parameter is identified through time resolved optical emission spectroscopy on SiH emission: Transient depletion of the SiH4 source gas leads to uncontrolled deposition conditions during the first 90 s after plasma ignition. There hardly is any effect on plasma properties and deposited film properties for the remainder of deposition after the transient depletion phase. As demonstrator a 9.5 % efficient single junction μc-Si:H solar cell was deposited from a pure SiH4 flow. A reinterpretation of the role of H2 dilution is discussed.
Ge out-diffusion and its Effect on Electrical Properties in s-Si/SiGe Devices
Authors: Uppal Suresh , Kanoun Mehdi , Chattopadhyay Sanatan , Agaiby Rimoon , Olsen Sarah H. , Bull Steve J. , O'Neill Anthony
Published: April 2011

In this paper we report on the quantification of Ge diffusion in strained Si/SiGe (s-Si/SiGe) structures for different Ge content in the SiGe virtual substrate. Using TCAD tools, the diffusivity has been calculated by varying pre-exponential factor and activation energy for Ge diffusion in s-Si and SiGe layers separately and obtaining a fit to the SIMS profiles. We observe an exponential and a linear dependence of pre-factor and activation energy for Ge diffusion in s-Si and SiGe, respectively, which is in agreement with literature. As a result of diffusion, the carrier confinement in thin strained layer reduces and the mobility is affected. Using C-V measurements on MOS capacitors fabricated along with devices, a shift in the flat band voltage has been observed and is attributed to a change in the interface trapped and fixed oxide charge. We observe a stronger effect of the variation of strained layer thickness than Ge content on the change in the flatband voltage. This observation is consistent with an exponential increase in Ge arriving at the interface with decrease in strained layer thickness.
Interaction Between Low Temperatures Spacers and Source Drain Extensions and Pockets for Both NMOS and PMOS of the 65 nm Node Technology
Authors: Cagnat Nathalie , Laviron Cyrille , Mathiot Daniel , Morin Pierre , Salvetti Frédéric , Villanueva Davy , Juhel Marc , Hopstaken Marco , Wacquant François
Published: April 2011

During the MOS transistors fabrication process, the source-drain extension areas are directly in contact with the oxide liner of the spacers stack. In previous works [1, 2, 3] it has been established that boron can diffuse from the source-drain extensions into the spacer oxide liner during the subsequent annealing steps, and that the amount of boron loss depends on the hydrogen content in the oxide, because it enhances B diffusivity in SiO2.

In order to characterize and quantify the above phenomena, we performed test experiments on full sheet samples, which mimic either BF2 source-drain extensions over arsenic pockets implants, or BF2 pockets under arsenic or phosphorus source-drain extensions implants. Following the corresponding implants, the wafers were covered with different spacer stacks (oxide + nitride) deposited either by LPCVD, or PECVD. After appropriate activation annealing steps, SIMS measurements were used to characterize the profiles of the various dopants, and the corresponding dose loss was evaluated for each species.

Our experimental results clearly evidence that LPCVD or PECVD spacer stacks have no influence on the arsenic profiles. On the other hand, phosphorus and boron profiles are affected. For boron profiles, each spacer type has a different influence. It is also shown that boron out-diffuses not only from the B doped source-drain extension in direct contact with the oxide layer, but also from the "buried" B pockets lying under n-doped source drain extension areas. All these results are discussed in term of the possible relevant mechanism.
The Behavior of Ion Implanted Silicon During Ultra-High Temperature Annealing
Authors: Jain Amitabh
Published: April 2011

Ultra-high temperature annealing is emerging as a promising technique for annealing ion implanted layers with a view to maximizing electrical activation while minimizing dopant diffusion. In order to ensure successful implementation, several materials-related problems have been under study. Since the time scale of the process is short, diffusion in the amorphous phase may dominate the final profile. In general, the residual disorder after anneal can be higher than with current anneal processes. However, the short time scale of the process curtails the opportunity for movement of dislocations into regions where the electrical behavior of a device would be affected. An additional effect of the limited time scale is the ability of silicon to plasto-elastically support the high strain-rates that may arise during the anneal.
Electrical Characterization of Residual Implantation-Induced Defects in the Vicinity of Laser-Annealed Implanted Ultrashallow Junctions
Authors: Gonda V. , Liu S. , Scholtes T.L.M. , Nanver L.K.
Published: April 2011

Ultrashallow junctions (USJ) were created by tilted 5 keV As+ implantation to a dose of 3x1015 cm−2 followed by excimer laser annealing (ELA). Sheet resistance and capacitances were measured in the background layer below the USJ. Results showed that sheet resistance was dependent on the laser energies in the close vicinity of these diodes. Doping profiles extracted from the capacitances indicated electrical deactivation here caused by the residual implantation defects. The extent and location of the residual damage is shown to be strongly dependent on the implantation dose and tilt angles, and also influenced by the laser annealing.
Modeling and Experiments of Boron Diffusion During Sub-Millisecond Non-Melt Laser Annealing in Silicon
Authors: Noda Taiji , Felch Susan , Parihar Vijay , Vrancken Christa , Janssens Tom , Bender Hugo , Vandervorst Wilfried
Published: April 2011

Boron diffusion and defect evolution during sub-millisecond (ms) laser annealing with partial SPER are investigated using secondary ion mass spectrometry and transmission electron microscopy. Boron diffusivity enhancement in amorphous-Si is observed during partial SPER at 550 °C. It is shown that boron diffusion during the laser annealing process is a 2-step diffusion (SPER + Laser). The depth of the amorphous layer affects the dopant activation behavior. During sub-ms laser annealing, end-of-range defects are formed and show an evolution behavior. {311} defects cannot completely transfer to dislocation loops after 1300 °C laser annealing. It is considered that the thermal budget of sub-ms laser is too small for full defect evolution. Atomistic diffusion modeling using a kinetic Monte Carlo method can explain the defect behavior during laser annealing.
Nano-Scale MOSFET Devices Fabricated Using a Novel Carbon-Nanotube-based Lithography
Authors: Derakhshandeh Jaber , Abdi Yaser , Mohajerzadeh Shams , Beikahmadi Mohammad , Behnam Ashkan , Arzi Ezatollah , Robertson Michael D. , Bennett C. J.
Published: April 2011

PECVD-grown carbon nanotubes on (100) silicon substrates have been studied and exploited for electron emission applications. The growth of CNT's is achieved by a mixture of hydrogen and acetylene gases in a CVD reactor and a 2-5nm thick nickel is used as the seed for the growth. The presence of DC-plasma yields a vertical growth and allows deposition at temperatures below 650°C. The grown nano-tubes are encapsulated by means of an insulating TiO2 layer, leading to beam-shape emission of electrons from the cathode towards the opposite anode electrode. The electron emission occurs using an anode-cathode voltage of 100 V with ability of direct writing on a photo-resist coated substrates. Straight lines with widths between 50 and 200nm have been successfully drawn. Scanning electron and transmission electron microscopy have been used to investigate the quality and fineness of the results. This technique has been applied on P-type (100) silicon substrates for the formation of the gate region of N-MOSFET devices, showing a drive current of 310μA/μm and Cox of 0.7μF/cm2.
Electron Thermal Transport Properties of a Quantum Dot
Authors: Zianni Xanthippi
Published: April 2011

The electron thermal conductance of a dot has been calculated within a linear response theory in the regime of weak coupling with two electrode leads. Coulomb oscillations are found. We discuss the effect of the interplay between the charging energy, the thermal energy and the confinement in the behavior of the electron thermal conductance.
Diffraction from Periodic Arrays of Oxide-Filled Trenches in Silicon: Investigation of Local Strains
Authors: Eberlein Michel , ESCOUBAS Stephanie , GAILHANOU Marc , THOMAS Olivier , ROHR Pascal , COPPARD Romain
Published: April 2011

The experimental evaluation of stresses at the nanometer scale is a real challenge. We propose an innovative use of High Resolution X-Ray Diffraction to measure local strains induced in silicon by periodic arrays. This technique is non-destructive and allows for the measurement of periodic strain fields in monocrystalline silicon, created in particular by Shallow Trench Isolation process. A 0.58μm-period array of trenches filled with SiO2 gives rise to satellites in reciprocal space maps around the Si substrate peak. The intensity and envelope of these satellites depend on the local strain. The experimental reciprocal space maps are compared to those computed using the kinematical theory from the elastic displacement field calculated with finite element modelling. This technique allows us to study the generation of strain during the main steps of the STI process. During the process, after trenches get filled with oxide and top layers removed, a second diffraction peak appears with a lower intensity than the substrate one. Thanks to finite element modelling, we validate that this peak is caused by an almost constant strain in the silicon active areas. Typical values of strains after trench filling are -1.68*10-3 along × and 1.56*10-3 along z where × and z refer to transverse and perpendicular directions.
Morphological and Structural Evolution of an Ultra-low-k Dielectric During the Porogen Removal
Authors: Rebiscoul Diane , Trouvé Héléne , Remiat Bruno , Clerc Laurence , Louis Didier , Passemard Gerard
Published: April 2011

The use of porous ultra-low-k materials between interconnections for sub 45nm technologies has introduced some barrier diffusion and mechanical problems. In order to avoid the problems caused by the porosity, a hybrid dense material (porogen and matrix) can be used in an alternate integration scheme. In this approach, the porogen is removed after CMP steps by a thermal cure or UV assisted thermal cure. In this work, we have first characterized the impact of the temperature and the duration of the thermal cure on the material. The crosslinking degree increases and the porogen amount decreases with increasing cure temperature. The most important impact of the curing duration happens between 350°C and 400°C. The increase of the curing duration leads to an increase of the porogen loss and a decrease of the refractive index. Secondly, in order to assess the structure of the layer as a function of the depth, the material was etched in a 0.05% HF solution and then characterized. According to the temperature and duration of the cure, the etch-rate can vary as a function of the material depth. This variation is related to a complex gradient inside the material.
Methodology to Determine the Toughness of a Brittle Thin Film by Nanoindentation
Authors: Brillet-Rouxel Helene , Verdier Marc , Dupeux Michel , Braccini Muriel , Orain Stéphane
Published: April 2011

Nanoindentation is the most convenient local technique for measuring elastic modulus, hardness, and fracture toughness of dielectric thin films. This approach is applied to bulk silicon and dielectric thin films (porous and non-porous) on silicon substrate. Reproducible stable cracks are generated from the edges of a cube corner indentor. The validity of theoretical model of use to estimate the toughness from cracks length has been checked on these reference cases. To calculate the toughness of thin film on Si substrate, we first established the loading range in which the cracks only affect the thin film without substrate damage. Several corrective terms have been introduced to the classical toughness estimation formula to take into account the proximity of the film/substrate interface and the residual stress pre-existing in the film. This approach is discussed by comparing experimental results obtained including these improvements to literature results.
Low-k Dielectric Obtained by Noble Gas Implantation in Silicon Oxide
Authors: Assaf Hanan , Ntsoenzok E. , Ruault M-O. , Ashok S.
Published: April 2011

Thermally-grown 220nm-thick silicon oxide layers were implanted at room temperature with 300keV Xe at doses ranging from 0.5 to 5x1016Xe/cm2. As-implanted samples exhibit bubbles in silicon oxide for all doses. Annealing at T≤400°C results in the disappearance of bubbles from SiO2 layer for the dose of 1x1016Xe/cm2. But for the higher doses of 3.5 and 5x1016Xe/cm2, the bubbles are very stable and remain in the sample even after very high thermal annealing. Capacitance measurements show a strong decrease in the dielectric constant k of the implanted SiO2 sample from 4 (reference sample) to 1.5.