bluuebunny/crossref_metadata_2025 huggingface dataset:
Integration of Top-Down and Bottom-Up Nanofabrication Schemes
Authors: Maury Pascale , Crespo-Biel Olga , Peter Maria , Reinhoudt David N. , Huskens Jurriaan
Published: April 2011

The fabrication of 3D nanostructures, which have tunable, sub-100 nm dimensions in all three directions, is a key issue of nanotechnology. Here we describe the integration of top-down nanoimprint lithography (NIL) and bottom-up layer-by-layer (LBL) assembly for the preparation of 3D hybrid nanostructures. NIL provided down to sub-100 nm poly(methylmethacrylate) (PMMA) structures. These were employed to fabricate patterned self-assembled monolayers of cyclodextrin (CD) host molecules on silicon oxide . The consecutive LBL assembly with adamantyl guest-functionalized dendrimers and CD-modified gold nanoparticles resulted in patterned multilayer structures with thicknesses of 3-30 nm. The x,y control by NIL and the z control by LBL assembly ultimately allowed the fabrication of circular structures with a radius of 25 nm and a thickness of 20 nm. The integration of the two methods has thus yielded a versatile 3D nanofabrication methodology comprising of 10-40 process steps.
LaB6 nanowires and their field emission properties
Authors: Zhang Han , Tang Jie , Zhang Qi , Zhao Gongpu , Yang Guang , Zhang Jian , Zhou Otto , Qin Luchang
Published: April 2011

For field-induced electron emission, the two factors that enable a high emission current density at low applied voltages are (a) low work function of the emitter and (b) sharpness of the emitter tip. We have developed and applied a chemical vapor deposition method to synthesize single-crystalline LaB6 nanowires for applications as point electron emitters. The crystallographic orientation of the grown nanowires can be controlled by the catalysts used in synthesis and their typical diameter is ranged from below 20 nm to over 100 nm. The nanowires’ tip is either hemispherical or flat top with rectangular cross-section depending on the catalyst being utilized. The field emission properties have also been measured from the single nanowire emitters and the results are discussed for applications as point electron sources used in high performance electron optical instruments such as the transmission and scanning electron microscopes.
Hierarchical Design of Metal Oxide Multi-Dimensional Arrays from Solutions
Authors: Vayssieres Lionel
Published: April 2011

The hierarchical design of well-defined and highly oriented two- and three-dimensional arrays of conventional semiconductor nanomaterials and their large scale manufacturing at low cost remain a crucial challenge to unfold the very promising future of nanodevices. In addition to economical manufacturing of nanostructured semiconductors, better fundamental knowledge of their electronic structure, physical, interfacial and structural properties and stability, is required to fully exploit their fascinating potentials. To combine such essential requirements, the predictive creation of structurally well-defined and well-ordered functional and multi-functional materials is essential. As an attempt to achieve such ambitious goals, a novel strategy to thin film metal oxide semiconductor nanotechnology processing has been developed and investigated. A thermodynamic growth control concept based on the chemical and electrostatic minimization of the surface energy as well as a thin film growth technique have been developed. Such original approach allows the generation of nanomaterials with novel and functional morphologies. Advanced metal oxide nanostructures consisting of oriented multi-dimensional arrays featuring building blocks of controlled morphologies, sizes, aspect ratios and orientations at nano-, meso-, and microscale are genuinely fabricated directly onto various substrates of large physical areas without template, surfactant, undercoating or applied field from the hydrolysis-condensation of aqueous metal salts solutions at mild temperatures (below 100°C). A survey of the innovative advances in the fabrication of highly oriented and functional nanostructure arrays of transition and post-transition metal oxides are presented as well as one-dimensional confinement effects in purpose-built bundled iron oxide quantum rods.
Micro- and Nanostructure Evolution with Exploding Wires
Authors: NLN Vandana , Sen P.
Published: April 2011

We present an experimental evidence of concentric ring pattern formation in a metal. They form during a single electro-explosion event in a needle-plate configuration. By measuring the dynamic progression of current during the explosion, we discuss evolution of these ring structures. Atomic force microscopy provides details of nanostructures that constitute these rings. From fluctuations in the plasma current recorded during the process, micro and nanostructure evolution is seen to be a self-organization process.
Submicron/nano Grained Stainless Steel with Superior Mechanical Properties
Authors: Rajasekhara Shreyas , Somani M. C. , Koljonen M. , Karjalainen L. P. , Kyröläinen A. , Ferreira P. J.
Published: April 2011

Metastable austenitic stainless steels may transform to martensite when subjected to cold rolling. Upon subsequent annealing the martensite reverts back to ultra-fine grained austenite. Based on this concept, nano/submicron austenitic grains have been produced in a 63% cold rolled commercial AISI 301LN subjected to annealing treatments at 600°C, 800°C and 1000°C for 1, 10 and 100 seconds.

Transmission Electron Microscopy (TEM) observations show the formation of equiaxed austenitic grains as small as ∼ 200nm in samples annealed at 800°C, and a dramatic increase in grain size as the annealing temperature and duration is increased. Additional tensile tests indicate that samples annealed at 800°C for 1 second exhibit a yield strength of ∼ 740 MPa and an total elongation of ∼ 45%. This combination of strength and ductility is excellent exceeding those of conventionally annealed steels (σy=350 MPa; Ductility ∼ 40%) or cold-rolled steels (σy=650 MPa; Ductility ∼ 30%).

Finally, a correlation between the observed grain sizes and mechanical properties, in particular the yield strength, is obtained. Preliminary analysis indicates that the Hall-Petch equation can satisfactorily relate the observed yield strength with corresponding grain sizes.
Molecular Dynamics Study of the Effect of Dopant Atoms on Grain Boundary Sliding
Authors: Millett Paul Christopher , Selvam R. Panneer , Saxena Ashok
Published: April 2011

Molecular dynamics simulations are used to study grain boundary sliding in pure and doped Cu bicrystals using both Lennard-Jones and Embedded-Atom Method potentials. Two tilt [100] grain boundaries are considered: the coincident site lattice Σ5 interface and a random high angle interface. Shear stress between 0.69 GPa and 1.61 GPa was applied to the bicrystals for a duration of 10 ps at ambient temperature (300K) and high temperature (800K). For the pure bicrystals, the sliding of the Σ5 interface with respect to the random interface was lower at 800K and higher at 300K. For the doped bicrystals, interstitial dopant atoms and substitutional dopant atoms with larger atomic radius were effective in retarding grain boundary sliding. These simulations will aid further work to determine how segregated dopant atoms alter the tensile properties of nanocrystalline metals.
Densification of Monosdisperse Iron Nanoparticles from a Colloidal Dispersion at Moderate Heating Rates and Temperatures
Authors: Crane Nathan B , Sachs Emanuel , Allen Samuel M
Published: April 2011

This work reports on the densification of iron nanoparticles heated at moderate rates without applied pressure as observed by TEM imaging, gas adsorption pore size measurement, and X-ray diffraction. Despite a low packing density, the small pore size is amenable to significant densification by pressureless sintering. Carbon residues from the stabilizing ligands affect both the composition and processing of the particles. This approach is amenable to deposition on non-planar or fragile substrates. Additionally, large areas can be processed in parallel.
Experimental Observations of Cylindrical Indentation of a Metallic Glass
Authors: Bastawros Ashraf , Biner S.B. , Bastawros Ashraf
Published: April 2011

In this study, the deformation behavior of a metallic glass under a cylindrical indenter is elucidated with in situ observations. The experimental observations for various indenter radii provide information on both macroscopic and microscopic details of the deformation. The deformation zones developed under indenters with different radii were found to be self-similar, in agreement with the predictions of the cavity expansion model. It will be shown that, the evolution of shear bands under the indenter resembles the solutions obtained from the slip line analysis. Finally, full field strain measurements can provide the detailed information regarding the temporal and the spatial evolution of the shear bands during the course of deformation.
Effects of Glass-Forming Metallic Film on the Fatigue Behavior of C-2000 Ni-Based Alloy
Authors: Liu F. X. , Chiang C. L. , Chu J. P. , Gao Y. F. , Liaw P. K.
Published: April 2011

Glass-forming Zr47Cu31Al13Ni9 (in atomic percent) films of various thicknesses were deposited on the C-2000 Ni-based alloy substrate by magnetron sputtering. Four-point-bending fatigue tests were conducted on the above system with the coated surface on the tensile side. It has been found that both fatigue life and fatigue-endurance limit can be considerably improved, while the degree of fatigue resistance enhancement depends on the maximum applied stress and the film thickness. Mechanisms of fatigue-resistance enhancements of the coated Ni-based alloy are discussed from the following aspects: reduction of surface roughness by the thin-film coating, good adhesion between thin film and substrate, development of residual compressive stress, and excellent ductility of glass-forming thin film (which would be otherwise brittle in bulk form). Of particular interest, we examine the interaction of substrate slip bands and the thin film ductile property, which would delay fatigue crack initiation process and thus extend the fatigue life.
Accelerated sintering of SiC Nanopowder with Stacking Disorder-Order Transformation
Authors: Shirai Kenshiro , Yamamoto Takeshi A , Ohyanagi Manshi , Munir Zuhair A
Published: April 2011

Consolidation of SiC nanopowder with stacking disordered structure was accelerated by milling with the AlN as the additive. SiC powders without the additive was sintered at 1900°C to a density of 99%. The grain size of the sintered material was approximately 500 nm. On the other hand, with AlN as additive, the sintering temperature to reach a density of 98% was reduced to 1700°C by the addition of 1.0 mol% AlN. The grain size of this material was less than 100 nm. The effect of AlN addition on SiC sintering with disorder-order transformation was evaluated by shrinkage profile, XRD analysis, and TEM observation.
High-Strain-Rate Dynamic Mechanical Properties of a W-Reinforced Zr-Based Bulk Metallic Glass Composite
Authors: Martin Morgana , Thadhani Naresh N. , Kecskes Laszlo J. , Dowding Robert J.
Published: April 2011

The structural/mechanical behavior of zirconium-based (Vitreloy106) bulk metallic glass reinforced with tungsten particles is evaluated using elastic and plastic property measurements via static and dynamic compression tests performed on rod shaped samples. Anvil-on-rod impact tests combined with high-speed digital photography and velocity interferometry are used to obtain qualitative and quantitative information about the transient deformation and failure response of the composites. The deformation and failure mechanisms of recovered impacted specimens are also characterized and correlated with their structure and tungsten phase distribution. The results of these experiments and initial attempts at validating constitutive equations based on homogeneous/inhomogeneous plastic/viscous flow in glassy and glassy-crystalline composites will be presented.
Insight into the Deformation Mechanisms under a Sharp Contact Loading in Glass by Atomic Force Microscopy
Authors: Rouxel Tanguy , Yoshida Satoshi , Shang Haixia , Sangleboeuf Jean-Christophe
Published: April 2011

The response of a material to a sharp contact loading, as in the case of Vickers indentation for instance, provides a unique insight into the material constitutive law, including elastic and irreversible deformation parameters as well. However, under such peculiar thermodynamical and mechanical conditions (the mean contact pressure on the contact area reaches values typically higher than 1 GPa, corresponding to the hardness of the material) the deformation processes are complex and the matter located just beneath and around the contact area may experience some structural changes and behave in a way different to the expected - or known - macroscopic behaviour. It is showed in this study by means of detailed topological investigations of the residual indentations by Atomic Force Microscopy (AFM) that the elastic recovery typically represents 50 to 70 % of the indentation volume at maximum load and that the densification contribution may reach 90 % of the residual deformation volume. Besides, most glasses exhibit indentation-creep phenomena, which become significant over time scale of few minutes because of a pronounced shear-thinning behavior..
The Fabrication and Characterization of Amorphous Indium Zinc Oxide (In2O3:10wt%ZnO) based Thin Film Transistors
Authors: Yaglioglu Burag , Yeom Hyo-Young , Beresford Roderic , Paine David
Published: April 2011

Thin film transistors were fabricated using amorphous IZO (In2O3-10wt%ZnO) with low carrier concentration (∼3×1017/cm3) for the channel material and a-IZO with high carrier concentration (∼2×1020/cm3) for source-drain metallization. The performance of a-IZO channel materials processed entirely at room temperature was established using a simple gate-down thin film transistor device. The TFT test structures were fabricated on p-type Si substrates with a thermally grown SiO2 gate oxide. The channel and metallization layers were sputter deposited from a commercially available IZO target at room temperature in a gas atmosphere containing 10 vol.% and 0 vol.% oxygen, respectively. The TFT devices are depletion mode n-channel devices with a high saturation mobility (∼20cm2/Vs) and high on/off ratio (∼108) and, as such, appear to be well suited for active matrix TFT applications.
Micro-patterned NiFeMo Magnetoimpedance Multilayer for Magnetic Sensor Application
Authors: Lee Duhyun , Jeong G.H. , Kim J.H. , Kim Y.S. , Suh S.J.
Published: April 2011

As an alternative to the magnetoimpedance (MI) devices made from amorphous ribbon or wire, this study proposed a thin film type MI device composed with Ag conductive core and soft ferromagnetic NiFeMo sandwich layers. Obtained optimum sandwich structure was Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm/ Ag 900 nm/ Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm, and the width of Ag as 20 µm and the width of NiFeMo as 100 µm. It was patterned by using photolithography and lift-off process. The sandwich structure showed the maximum MI ratio about 40% at the 15 MHz. The impedance change was linear and nearly reversible at the external magnetic field region below the anisotropy field.
On the Mechanism of Resistive Switching in MIM Capacitors – An Approach with In-situ TEM Experiments
Authors: Schroeder Herbert
Published: April 2011

In this contribution an in-situ TEM experiment is suggested to observe the microstructure of a metal/oxide insulator/metal (MIM) capacitor structure during resistive switching due to an applied external voltage or current. The motivation for such an experiment is the fact that there is a large pool on the resistive switching data in the literature, but there is no agreement on the mechanism, which in part is due to missing microstructural observations of the effects. For such an experiment a special TEM sample holder has been developed allowing controlled in-situ application of temperature (RT to 300°C) with a heating stage and of voltage (current) as a part of a 4-terminal resistance measurement set-up. This is combined with a special TEM sample preparation method, the “window”-technique, so that no thinning of the MIM thin film structure is necessary at all (which is an advantage as the oxides are known to be very sensitive to damage introduced by methods such as ion-milling). Special electrode configurations have been designed to allow nearly undisturbed TEM observation of the switching insulator. Identical samples will also be investigated ex-situ in conventional switching experiments to identify the influence of the special TEM environment (high vacuum, irradiation with energetic electrons).
Nucleation and Growth of Defects in He irradiated Fe using Rate Theory and Kinetic Monte Carlo Methods
Authors: Ortiz Christophe Juan , Caturla Maria Jose , Fu Chu Chun , Willaime Francois
Published: April 2011

He desorption in Fe was studied using rate theory and kinetic Monte Carlo models. A good fit to experimental observations was obtained with a migration energy of 1.1 eV and a formation energy of 1.6 eV for the single vacancy. These results could be explained by the presence of traps/impurities in experiments. Simulations show that the release of He during annealing is mainly due to the dissociative mechanism (Frank-Turnbull) and the release of Hei from He-V clusters.
Ion-Induced Surface Modification of EUV and VUV Plasma-Facing Collector Mirrors
Authors: Allain Jean Paul , Hassanein Ahmed , Nieto Martin , Titov Vladimir , Plotkin Perry , Hinson Edward , Rokusek Daniel , Chrobak Christopher , Hendricks Matthew , Klimowych William
Published: April 2011

Generation of extreme ultraviolet (EUV) light for nanolithography requires the use of hot, dense plasmas. Gas discharge produced plasma (GDPP) and laser produced plasma (LPP) are the primary configurations used to generate these plasmas. Both GDPP and LPP collector mirror systems face serious issues regarding lifetime and EUV light reflectivity performance. For both configurations debris, fast ions, fast neutrals, and condensable EUV radiator fuels (Li, Sn) interact with nearby collector mirrors. Sn, in particular is used due to its high conversion efficiency in the 13.5-nm in-band spectrum. In addition to debris, collector mirrors are exposed to impurities (H,C,O,N), off-band radiation (depositing heat) and highly-charged ions leading to their degradation and consequently limiting 13.5 nm light reflection intensity.

This work presents results of Ru and Rh-based collector optics irradiated by Sn ions between at 1.3 keV and exposed to Sn thermal atoms at room temperature. In-situ metrology monitors the effects of ion implantation on ion-induced erosion and EUV reflectivity changes using low-energy ion scattering spectroscopy and X-ray photoelectron spectroscopy. Results find that Sn implants at the first few monolayers leading to a mixed layer at the surface. Sn thermal atoms deposit on top of the mirror surface leading to 10-20% loss of collector mirror EUV light reflectivity.
A short review and Present Status of ZnO Nanoparticle Formation by Ion Implantation Combined with Thermal Oxidation
Authors: Amekura Hiroshi , Plaksin Oleg A , Umeda Naoki , Takeda Yoshihiko , Kishimoto Naoki , Buchal Christoph
Published: April 2011

Recently many groups have started studies of formation of zinc-oxide (ZnO) nanoparticle (NP) in transparent insulators, such as silica glass, sapphire, etc, using ion implantation techniques. In the early half of this article, we shortly review recent activities of ZnO NP formation using ion implantation combined with thermal oxidation. Some groups succeeded but the others did not. Even if they succeeded in the formation of ZnO nanostructures, one reported that they were in the shape of thin film and another reported the NP form. Based on our recent experimental results, we point out the importance of the oxidation temperature and the peculiar shapes and depth profiles of ZnO formed.
Investigation of effects of ion beam irradiation on properties of magnesium oxide films
Authors: Morimoto Yasuhiko , Tanaka Yoshikazu , Ide-Ektessabi Ari
Published: April 2011

Magnesium oxide (MgO) film is commonly used as protecting layer for alternative current plasma display panels (AC-PDPs). Low energy ion induced secondary electron emission coefficient (γ) is one of the important factors to improve performance of AC-PDPs. The aim of this study is to prepare MgO films with high γ using ion beam assisted deposition (IBAD). The film composition, density, and crystal orientation were also investigated. The results suggest that MgO films with high γ can be obtained using IBAD. On the other hand, as the assisted ion beam energy increased to more than 500eV during deposition, (200)-oriented film with low γ grew preferentially and then the γ decreased.
Teaching What You Can’t See: Museum Exhibits as a Bridge to Learning Materials Science
Authors: Castellini Olivia , Holladay Carie E. , Theim Terra , Walejko Gina K. , Zenner Greta M. , Krajniak Paul , Crone Wendy C.
Published: April 2011

The use of exhibits in informal science education venues such as science centers and museums is an integral part of engaging students in science, encouraging them to take science courses in school, and motivating them to pursue science and engineering careers. Through an Internships in Public Science Education Program funded by the National Science Foundation and in partnership with the education efforts of the Materials Research Science and Engineering Center (MRSEC) and the Discovery World Museum of Science, Economics and Technology, we have built and tested interactive components for museum exhibits on advanced materials science and nanotechnology concepts. Our front-end assessment revealed a gap in scientific understanding about objects smaller than can be seen by the naked eye. Facts learned through standard teaching methods were easily recalled, but in-depth, conceptual knowledge and application of those facts are lacking in both children and adults. We designed interactive exhibits to specifically address this disconnect in comprehension. By inviting the learner to actively participate in an interactive exhibit activity, he or she is able to develop a deeper understanding of advanced materials concepts that are difficult to teach with textbooks alone. Formative assessment of our exhibit prototypes show that students and adults not only participate in the interactive exhibit activity, but are able to learn and apply the concepts contained within them.
Materials Engineering Education in Two New Engineering Degree Programs at the Centre for Photovoltaic Engineering
Authors: Corkish Richard Paul , Wenham S. R. , Cotter J. , Sproul A. B. , Aberle A. G. , Bruce A. , Green M. A.
Published: April 2011

The establishment, in 2000 and 2003, of new degree programs in Photovoltaics and Solar Energy Engineering and Renewable Energy Engineering at the Centre for Photovoltaic Engineering at the University of New South Wales, Sydney was in response to predictions, now being fulfilled, of dramatic global market and employment growth. They were developed by the well established photovoltaics research group at UNSW that has produced many important advances, including two commercially important solar cell technologies. Materials-related education in these programs are mainly focussed on the photovoltaic aspects, including study of the fundamental optical, electronic, phononic and excitonic properties of silicon, crystal structure, semiconductor properties, doping and contacts. Cell manufacturing is taught in detail, including by the use of an interactivevirtual production line. Practical projects, taking advantage of a large and active research group, are one of the most important and effective educational tools in both these programs. The Centre also administers postgraduate coursework and research programs.
Crystal Structure Visualizations in Three Dimensions with Database Support
Authors: Moeck Peter , Čertík O. , Upreti G. , Garrick W. , Fraundorf P.
Published: April 2011

Crystallographic databases for inorganic materials that are freely accessible over the internet are reviewed. The Nano-Crystallography Database project is described. Instructions are given on how to visualize in three dimensions the atomic arrangements of the several thousand entries of the Crystallography Open Database.
Women in Materials: a Collaborative Effort between Simmons College and the Cornell Center for Materials Research
Authors: Goldberg Velda , Malliaras George G. , Schember Helene , Kaplan Michael , Soltzberg Leonard , Gurney Richard W. , Johnson Patrick
Published: April 2011

The Women in Materials (WIM) program, supported by the National Science Foundation, is a collaboration between Simmons College, a predominately undergraduate women’s college, and the Cornell Center for Materials Research (CCMR). For the past four years, this program has provided unusual curricular and research opportunities for undergraduate women at Simmons College. This program demonstrates a successful model for enhancing undergraduate science and technology preparation through collaboration between primarily undergraduate institutions (PUIs) and NSF-supported Materials Research Science and Engineering Centers.
Non-Traditional Assessments for New Learning Approaches: Competency Evaluation in Project-Based Introductory Materials Science
Authors: Stolk Jonathan , Krumholz Steven , Somerville Mark
Published: April 2011

Over the last twenty years, NSF and the engineering community have called for systemic changes in engineering education, including an emphasis on contextual understanding; increased teaming skills, including collaborative, active learning; and an improved capacity for life-long, self-directed learning. In addition, ABET has called for engineering graduates that demonstrate an ability to apply science and engineering, and ABET requires assessment processes designed to measure student achievement of learning outcomes. Olin College has responded to these calls for change by embracing new learning approaches and assessment techniques, and by developing project-based courses that encourage experiential understanding of content and aid the development of life-long learning skills. To address the assessment needs of new pedagogical approaches, Olin recently instituted a competency based assessment system to accompany the traditional course grading system already in place. The thread of competency assessments provides grading coherency for both faculty and students, and it provides students with valuable information concerning their development of nontraditional skills that they could use to identify shortcomings and further their learning. In this paper, we describe the new pedagogical approaches in Olin's introductory materials science course, and we explain our implementation of the competency assessment system to measure student attainment of both materials science knowledge and broader skills such as teaming, communication, and experimental inquiry.
The Effect of Oxygen Contamination on the Electronic Properties of Hot-Wire CVD Amorphous Silicon Germanium Alloys
Authors: Datta Shouvik , Cohen J. David , Golledge Steve L. , Xu Yueqin , Mahan A. H. , Doyle James R. , Branz Howard M.
Published: April 2011

A series of four a Si,Ge:H alloy samples with Ge fractions near 30 at.% were deposited by hot-wire CVD (HWCVD) using a Ta filament maintained at 1800oC. During film growth, the level of oxygen contamination was varied from less than 1019 cm−3 to roughly 5 × 1020 cm−3 using a controlled air-leak. The electronic properties of these films were then characterized using transient photocapacitance (TPC) and transient photocurrent (TPI) spectroscopy, as well as the drive-level capacitance profiling (DLCP) techniques. We observed an unexpected systematic improvement of the electronic properties of these HWCVD a Si,Ge:H with increasing oxygen impurity level, which was reflected by a decrease in the deduced Urbach energies. Comparing these with films co-deposited on stainless-steel versus p+ c-Si substrates, we found significantly better electronic properties in the latter case. Comparisons of the TPC and TPI spectra indicated a very high level of hole collection, consistent with these narrow bandtail distributions.
Phononic Amorphous Silicon: Theory, Material, and Devices
Authors: Chawda Samrat , Mawyin Jose , Mahan Harv , Fortmann Charles , Halada Gary
Published: April 2011

The field of phononic-engineered amorphous silicon is introduced. Specifically the construction of devices and waveguides for information conveyance and manipulation via phonons are considered. Typically the phononic properties of a given material are immutable and the phonons have such a limited diffusion length (nanometers) as to be unsuitable for engineering purposes. Crystalline silicon on the other hand has a reasonably large thermal conductivity and phonon diffusion length at sufficiently low temperatures. Phonon diffusion lengths can measure up to centimeters (e.g., crystalline SiO2) at temperature less than 10K but drop to sub microns at room temperature. Amorphous silicon, owing to the inherent scattering structures and owing to localization (of at least some phonon bands), has an anomalously large phonon lifetime [1]. This lifetime maybe indicative of a large phonon diffusion length and/or a fast phonon hop rate from one domain to the next and/or an indication that more than the typical three phonons (umklapp process) are involved in phonon scattering (e.g., see [1]&[2]). Techniques involving small-scaled devices and phonon bands to control umklapp phonon-phonon scattering are described. The potential to exploit inherent amorphous silicon structure as well as the engineering (post film deposition) of di-hydride distributions to induce phonon forbidden bands for significantly reduced multi-phonon scattering is explored. The indirect optical band gap of small domain (and possibly amorphous) silicon [3] provides the physical basis for the transduction of phonon and optical energies. Experimental methods for the post-deposition introduction of phonon scattering structure, the transduction of phononic information to optical information, and experimental approaches including the use of micro-Raman to probe phonon spectra and transport are described. The prospects of a fully integrated phononic, photonic, electronic amorphous silicon technology have been described.
Quantization of crack speeds in dynamic fracture of silicon: Multiparadigm ReaxFF modeling
Authors: Tang Harvey , Rye Janet , Buehler Markus J. , van Duin Adri , 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 about 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. This model has been successfully used to study crack dynamics in silicon, capable of reproducing key experimental results such as orientation dependence of crack dynamics (Buehler et al., Phys. Rev. Lett., 2006). In this article, we focus on crack speeds as a function of loading and crack propagation mechanisms. We find that the steady state crack speed does not increase continuously with applied load, but instead jumps to a finite value immediately after the critical load, followed by a regime of slow increase. Our results quantitatively reproduce experimental observations of crack speeds during fracture in silicon along the (111) planes, confirming the existence of lattice trapping effects. We observe similar effects in the (110) crack direction.
The Influence of Deposition Conditions on the Electronic Properties of a-Si:H Prepared in Expanding Thermal Plasma
Authors: Brinza Monica , Adriaenssens Guy J.
Published: April 2011

A number of a-Si:H samples prepared in an expanding thermal plasma under varying conditions were examined by means of time-of-flight transient photocurrent measurements. A high deposition temperature allows high deposition rates while achieving high hole mobility and mobility-lifetime product. Lower hole mobility but higher μτ product result from slower deposition at lower temperature. Electron μτ products are uncharacteristically low for all samples due to pronounced deep trapping. RF biasing of the substrate does not improve the results.
The Influence of the Hot Wire Temperature on the Crystallization of μc-Si:H Films Prepared by Hot Wire-Assisted-ECR-CVD
Authors: Li Ying , Li Zhi zhong , Chen Guang hua , Kumeda Minoru
Published: April 2011

We have constructed a hot wire assisted ECR-CVD system to prepare a-Si:H and μc-Si:H films. The effect of hot wire temperature on crystallization of a-Si:H films is studied in the films prepared by these system. The crystalline fraction and crystalline grain size are analyzed by Raman scattering. The hydrogen content and the bonding scheme of hydrogen were measured by Fourier transform infrared (FTIR) spectroscopy. At low hot wire temperature, about 20 at.% hydrogen is included in the film. With increasing the hot wire temperature, the total content of the hydrogen, SiH2 and SiH decrease and the microcrystalline phase appears. It is found from the ratio of the crystalline TO peak to the total area of the TO peak of the Raman scattering spectra that the volume fraction of the crystalline phase increases with increasing the hot wire temperature. The crystalline peak has a tendency to shift toward the higher wavenumber with increasing the hot wire temperature, suggesting that the grain size increases with increasing the hot wire temperature.
Role of Surface on the Persistent Photoconductivity in Porous Silicon and Boron Doped a-Si:H
Authors: Agarwal S. C. , Kumar Abhishek , Mandal N P
Published: April 2011

The effect of ambient conditions on light soaking (LS) in porous silicon (PS) sample is studied. In vacuum LS on porous silicon increases dark current (DC) while in presence of water vapor it decreases DC. Interestingly, LS gives a higher DC in vacuum as well as in presence of water vapor for boron doped hydrogenated amorphous silicon a-Si:H(B) samples. A thin layer of polystyrene polymer almost eliminates the light induced degradation of porous silicon (PS) layers but can do so only to a smaller extent in a-Si:H(B). This shows that the effect of LS in PS is different than the effect of LS in a-Si:H(B) and that the surface plays a more important role in PS than in a-Si:H.
Blue Light Emission from PECVD Deposited Nanostructured SiC
Authors: Ivashchenko Liudmyla , Vasin Andriy , Ivashchenko Volodymyr , Ushakov Mykola , Rusavsky Andriy
Published: April 2011

Experimental data on the room temperature blue light emission from nanocrystalline silicon carbide (nc-SiC) films are presented. The silicon carbide films were deposited on silicon substrates with a plasma enhanced chemical vapor deposition (PECVD) reactor from methyltrichlorosilane at substrate temperature in the range of 200-350°C. The film deposited at 350°C is nanostructured and X-ray diffraction proves the presence of the 3C-SiC crystallites. Infrared absorption spectroscopy in the region of Si-C, C-H, C-O, Si-H and Si-O bonds show the corresponding absorption bands. X-ray photoelectron spectroscopy studies confirm this bond picture. Photoluminescence was measured at 77 and 300 K. The bright blue emission has a double-peak structure at 415 and 437 nm. To clarify the origin of such an emission, tight binding molecular dynamics (TB-MD) simulations of several SiC and Si nanoclusters were carried out. Based on the temperature dependence of the photoluminescence and on the simulation data, a possible model of radiative recombination in nc-SiC films was proposed. According to this model, the emission bands at 415 and 437 nm are assigned to band-to-band and band-to-tail recombination in the nanocrystallite core. The recombination at band tails of the interface and Si-C-O-H amorphous tissue gives rise to a shoulder around 470 nm.
Novel Semiconducting Phase of Amorphous Carbon Nickel Composite Films
Authors: Bhattacharyya Somnath , Henley S. J. , Blanchard N. P. , Silva S. R. P.
Published: April 2011

A homogeneously mixed phase of carbon and 10% nickel yielding amorphous carbon-nickel composite (a-C-Ni) films is prepared by an excimer UV pulsed laser ablation. Conductivity study of these films shows a nearly activated conduction. Also a saturation of conductivity below a temperature of 25 K explains the presence of an additional density of states at the Fermi level in these samples. Our experiments demonstrate a very different behaviour of electronic properties of these novel materials compared to undoped diamond-like carbon (DLC) films, which was directly confirmed using valence band spectroscopy.
The Crystallization Mechanism of Poly-Si Thin Film Using High-power Nd:YAG Laser with Gaussian Beam Profile
Authors: Zan Hsiao Wen , Huang Chang Yu , Saito Kazuya , Tamagawa Kouichi , Chen Jack , Wu Tung Jung
Published: April 2011

This paper studies the poly-Si crystallization mechanism under the high power (200 W) Nd:YAG solid state pulsed laser annealing system. It is found that the Gaussian-distributed laser beam profile successfully produce large super lateral growth process window. The devices in the SLG process window exhibit field-effect mobility around 250 cm2/V.s and the threshold voltage lower than 1 V. The influence of a-Si film thickness and the laser scan pitch on the process window is also carefully investigated.
Roughness, impurities and strain in low-temperature epitaxial silicon films grown by tantalum filament hot-wire chemical vapor deposition
Authors: Teplin Charles W. , Page Matthew , Iwaniczko Eugene , Jones Kim M. , Ready Robert M. , To Bobby M. , Moutinho Helio M. , Wang Qi M. , Branz Howard M.
Published: April 2011

We grow epitaxial silicon films onto (100) silicon wafers from pure silane by hot-wire chemical vapor deposition (HWCVD). The films grow epitaxially for a thickness hepi before a Si:H cones nucleate and expand. We study the dependence of hepi on growth rate and the differences between Ta and W filaments. The surface morphology of thin but completely epitaxial films are studied in order to correlate the surface roughness during growth with the eventual epitaxial breakdown thickness. Surface roughness, strain and H at the wafer/film interface are not likely to cause the observed breakdown.
Amorphous Silicon 2-TFT Pixel Circuits on Stainless Steel Foils
Authors: Kattamis Alex Z , Cheng I-Chun , Hong Yongtaek , Wagner Sigurd
Published: April 2011

We have fabricated pixel circuits consisting of two bottom-gate staggered source-drain amorphous silicon thin-film transistors (a-Si:H TFTs) on flexible stainless steel foils. Stainless steel is attractive because it allows for high processing temperatures of >300°C and is a perfect barrier to oxygen and moisture. Our steel foils were 75m thick, with a peak-to-peak surface roughness of >1.2m. This rough, as-rolled, conductive surface needed a thick planarization and passivation (electrical isolation) layer. The surface was planarized with 1.6m of spin-on-glass, which reduced the roughness to ~0.3m peak-to-peak. A passivation layer of 0.6m of SiNx deposited by plasma-enhanced chemical vapor deposition was used to reduce leakage currents and capacitive coupling to the substrate. The 92m × 369m voltage-programmed pixel circuits employ a switching (Sw) TFT (W/L=50/5m), a driver (Dr) TFT (W/L=200/5m), and a 2pF storage capacitor between the gate and source of the Dr TFT. With a supply voltage of VDD=20V and a drive bias of 20V the circuits deliver 26A of current. The vertical stripe pixels were integrated into 48 × (4) × 48 arrays and passivated with SiNx. Anode metal of Al-1% Si was also deposited, preparing the displays for subsequent OLED fabrication. Pixel circuits with this performance can drive top-emitting organic light emitting diodes (OLEDs) and therefore can be used in backplanes for flexible, high-resolution, active-matrix OLED displays.
Band Gap Engineering and Electrical Field Tailoring for Voltage Controlled Spectral Sensitivity
Authors: Vieira Manuela , Louro P. , Fantoni A. , Fernandes M. , Lavareda G. , Carvalho C.N.
Published: April 2011

Stacked ITO/(a-SiC:H)pinpi /(a-Si:H)i'sn/ITO color sensitive detectors are analyzed using the laser scanned photodiode technique. Results show that band gap engineering together with the laser scanned photodiode technique allows a voltage controlled shift of the collection regions, allowing color discrimination at readout voltage that cancels the self-bias effect induced by the steady state illumination, across the back diode. The threshold voltage between green and red discrimination depends on the thickness ratio between a-Si:H (-i')/a-SiCH (-i) layers. As this ratio increases the self-reverse effect due to the front absorption will be balanced by the decrease of the self-forward effect due to the back absorption shifting the threshold voltage to lower reverse bias. The various design parameters and the optical readout process trade-offs are discussed and supported by a 2D numerical simulation. A self-bias model is proposed to explain the voltage controlled spectral sensitivity.
Self-aligned Thin Film Transistor Fabrication with an Ultra Low Temperature Polycrystalline Silicon Process on a Benzocyclobutene Planarized Stainless Steel Foil Substrate
Authors: Moon Jaehyun , Park Dong-Jin , Chung Choong-Heui , Kim Yong-Hae , Yun Sun Jin , Lim Jung Wook , Lee Jin Ho
Published: April 2011

Compared to plastic, from the view point of ultra low temperature poly-Si (ULTPS) processes for realizing flexible active matrix organic light emitting diode (AM-OLED) display, SSF offers high thermal resistance and chemical stability, and lithography stability. As SSF is stiffer than plastic film, SSF is expected to reduce stress which originates from difference in coefficient of thermal expansion. However, SSF substrate itself also bears surface roughness problem, which necessitates an appropriate planarization step. Also to fully integrate both the drive circuits and the pixel thin-film transistor(TFT)s in a monolithic complementary metal-oxide-semiconductor (CMOS) technology high mobility is required, calling for poly-Si usage.

We will deal with the planarization process, and then address various processing issues. Especially, we will demonstrate our successful SLS of Si on SSF substrates. Finally we show the device performances. All fabrication temperatures were kept below 200 oC to meet a ULTPS process.

Due to the rolling process for manufacturing foils, the SSF surface is rough. We have measured average roughness of 500 nm, respectively. With benzocyclobutene (BCB), we have successfully planarized the surface with average roughness was less than 0.5 nm.

Our TFT's active layer was obtained by laser crystallizing amorphous Si (a-Si) films. To obtain a high quality gate dielectric film, we formed a SiO2 film using an O2 plasma treatment on the surface of the poly-Si film and then deposited Al2O3 film by plasma enhanced atomic layer deposition. Then gate metal was deposited and patterned. Source and drain regions were p+ doped by ion implantation to form a self-aligned gate structure. We have used SiNx film as interlayer dielectrics.

Briefly we discuss a practical approach for realizing SLS on a SiO2 buffer. The Si-on-SiO2 layer stacking is energetically unstable. Should have not controlled the heat during laser crystallization, liquid Si would recede to expose the SiO2 layer. Dewetting is suppressed by adjusting the buffer density, and densifying the a-Si film. To implement the SLS, we have optimally conjugated the densities of the buffer film and the a-Si film to produce Si grains with sizes of ~6 ¥ìm on a BCB planarized SSF.

Our p-channel TFT transfer performance exhibits a field effect mobility (¥ì) of 95 cm2/Vs, a threshold voltage (Vt) of -3 V and a sub-threshold swing(S-S) of 0.5 V/dec.. The off-current level is ~ 10 pA at drain voltage (Vd) of -1V and the Ion/Ioff is 106 . Especially our stable Vt consents to the electrical stability for driving displays. This feature might be attributed to the improved interface between the active layer and the gate dielectrics by plasma oxidation.
Application of Thin-Film Amorphous Silicon to Chemical Imaging
Authors: Yoshinobu Tatsuo , Moritz Werner , Finger Friedhelm , Schoening Michael J.
Published: April 2011

A thin-film amorphous silicon (a-Si) deposited on a glass substrate was employed as a semiconductor material for the chemical imaging sensor, which can visualize the distribution of ion concentration in a solution. The sensing properties and the spatial resolution of the a-Si sensors were investigated. Nearly-Nernstian pH sensitivities and submicron resolution were demonstrated, which suggests the superior performance of the chemical imaging sensor based on thin-film a-Si.
Performance of Thin-film a-Si:H Microresonators in Dissipative Media
Authors: Adrega Teresa , Prazeres D. M.F. , Chu V. , Conde J.P.
Published: April 2011

The resonance of electrostatically actuated thin-film a-Si:H microbridges immersed in de-ionized water is detected and characterized. When the operating medium changes from vacuum to air, a small decrease of 5% of the resonance frequency occurs and the quality factor decreases from approximately 1000 to 100. The operation of the microresonators in deionized water produces a 60% shift in resonance frequency to lower values and the quality factor decreases to 10. Appropriate actuation conditions at resonance in water are used to avoid electrolysis and electrode field screening. The detection of the resonance frequency of a microbridge operating in solutions with high conductivities, up to 8 mS/cm, and viscosities up to 0.2 Pa.s is demonstrated.
Low Temperature Poly-Si Sputtering Deposition Through Metal-induced Crystallization and its Application
Authors: Guo Hsiu-Wu , Shih Chen-Luen , Ketterl Joe , Dunham Scott
Published: April 2011

Growth of Si thin films via metal-induced crystallization (MIC) has been demonstrated by several research groups. This process lowers the crystallization temperature compared to standard solid phase crystallization (SPC). Ni is the metal that is most often adopted for this purpose. In this work, a 20-50nm Ni layer was deposited by DC magnetron sputtering onto a 500nm SiO2 layer grown on silicon wafers, followed by Si deposition at 500°C without breaking vacuum. X-ray diffraction (XRD) results and cross-sectional transmission electron microscopy (XTEM) confirmed the formation of poly-Si in a columnar structure with grain sizes in the 100-300nm range. XTEM and XPS show that nickel silicide was formed at the Si-Ni interface. We find that doping type and concentration do not have a significant impact on the grain structure. SIMS reveals no significant loss or redistribution in doping concentration during sputtering.
Fabrication of Location-Controlled Silicon Crystal Grains by Combining Excimer Laser Irradiation with Nanometer-sized A-Si
Authors: Tsai Chun-Chien , Chang Ting-Kuo , Chen Hsiu-Hsin , Chen Bo-Ting , Cheng Huang-Chung
Published: April 2011

In this paper, location-controlled Silicon crystal grains are fabricated by a novel excimer laser crystallization method. An array of 1.8-μm-sized disk-liked grains are formed by this method, and the high-performance n-channel LTPS TFTs with field-effect-mobility reaching 308 cm2/Vs can be fabricated owing to the artificially-controlled lateral grain growth. This position-manipulated Silicon grains are essential to high performance and good uniformity thin film transistors.