bluuebunny/crossref_metadata_2025 huggingface dataset:
Is Transition Metal Incorporated ZnO an Intrinsic Ferromagnetic Semiconductor?
Authors: Bhatti Kanwal P , Chaudhary Sujeet , Pandya Dinesh K , Kashyap Subhash C
Published: April 2011

Studies on Mn, Ni and Co doped ZnO systems have revealed that the RTFM present in these systems can be both intrinsic and extrinsic depending on the choice of TM ion incorporated, technique of preparation and post-synthesis processing. Choice of such a technique that ensures better homogeneity and incorporation of TM ions in the ZnO host, leads to the occurrence of intrinsic, stable and robust RTFM. The air ambient processing eliminates the chances of any metallic cluster inclusions, and instead such TM oxide phases are formed that are non-ferromagnetic. However, post synthesis processing like vacuum annealing of ZnO:Co samples under some situations can give rise to occurrence of extrinsic RTFM. But, this can be overcome by certain additional processing step. ZnO:Co samples with intrinsic RTFM, stable upto 900°C annealing with Curie temperatures in excess of 450°C have successfully been prepared.
Transparent Oxide Semiconductors Obtained by PLD
Authors: Vila Anna , Olziersky Antonis , Font Joaquim , Andreu Teresa , Koep Erik , Morante Juan Ramon
Published: April 2011

In this work we studied metaloxide films such as ZnO, In2O3-ZnO, In2O3-ZnO-ZrO2 and Ga2O3-In2O3-ZnO deposited by pulsed laser deposition on fused silica substrates at room temperature. Optical transmission measurements in the ultra violet – visible region showed that oxygen-rich atmospheres during deposition help to obtain more transparent films in the optical region while improving overall UV absorption transition related to the band gap. Less resistive films are produced in oxygen-rich atmospheres but an increase of oxygen pressure leads to higher resistivity films.
X-ray Absorption Spectroscopy Investigation of Different Crystallographic Structures of Cobalt Nanoparticles
Authors: Palshin Vadim , DeSilva Rohini , Kumar Challa SSR
Published: April 2011

The ultimate goal of nanotechnology is to design successful syntheses to produce nanomaterials with required properties. The properties of nanoparticles mainly depend on their size, shape and crystal structure, hence control over these factors is a major issue in this field. In this study, Co nanoparticles with four different crystallographic structures (hcp, fcc, bcc and epsilon) have been wet-chemically synthesized by varying precursors and surfactants in the reaction. Co K-edge absorption spectra were collected in transmission mode at the XMP beamline at the Center for Advanced Microstructures and Devices (CAMD). The X-ray Absorption Near Edge Structure (XANES) and Fourier Transformed Extended X-ray Absorption Fine Structure (FT EXAFS) spectra were analyzed using the “fingerprint method”, i.e. by comparing them with either standard compounds or with the simulated spectra that were calculated using the FEFF8 code. EXAFS spectra were also analyzed by fitting them with relevant crystallographic models in r-space including higher coordination shells using the IFEFFIT analysis program. All four crystal structure types were conclusively determined by using this approach.
A Modified Chemical Route for Synthesis of Zirconia Thin Films Having Tunable Porosity
Authors: Kumar Manish , Reddy G. B.
Published: April 2011

A new chemical synthesis route is reported for deposition of zirconia thin films having adjustable porosity with average pore size in nanometer range. Deposition method is simply a sol-gel dip coating in which HCl is used as catalyst. TEM and FTIR studies of deposited films show porous microstructure, which depends critically on ageing of sol used. The shift in binding energy of Zr 3d5/2 (at 182.4 eV) attributes the formation of zirconia. Optical results show high transmittance (> 80%) in VIS-NIR region and effective refractive indices values (neff) tend to decrease for films prepared with higher aged sol. Porosity enhancement from 15-52% is observed by neff comparing with refractive index of non porous films (nz).
Structural and Luminescence Properties of Nanocrystalline Eu3+-doped Gd2O3
Authors: Jauregui Segundo , Perales-Perez Oscar , Vasquez Omar , Jia W. , Tomar M. S. , Fachini Esteban
Published: April 2011

The present work addresses the synthesis and characterization of red emitting Gd2-xEuxO3 nanocrystalline phosphors by a modified sol-gel based method. The effects of the annealing temperature and atomic fraction of Eu3+ ions, ‘x’, on the structural and luminescence properties of the produced oxides have been systematically investigated. X-ray diffraction analyses revealed that crystalline cubic-Gd2O3 host structure was obtained when the intermediates (x=0.01-0.30) were annealed at different temperatures in air. Photoluminescence spectra of doped Gd2O3 powders showed all transitions of Eu3+ species, being the 5D0→7F2 transition the most intense. On a common sample-weight basis, the highest photoluminescence intensity was obtained at ‘x’ = 0.15. The energy transfer from host to dopant was verified for all evaluated ‘x’ values, which suggest the actual incorporation of Eu species into the Gd-oxide lattice. It was also found that the photoluminescence intensity was strongly dependent on the annealing temperature and dopant concentration.
Infrared detector activities at NASA Langley Research Center
Authors: Abedin M. Nurul , Refaat Tamer F , Sulima Oleg V , Amzajerdian Farzin
Published: April 2011

Infrared detector development and characterization at NASA Langley Research Center will be reviewed. These detectors were intended for ground, airborne, and space borne remote sensing applications. Discussion will be focused on recently developed single-element infrared detector and future development of near-infrared focal plane arrays (FPA). The FPA will be applied to next generation space-based instruments. These activities are based on phototransistor and avalanche photodiode technologies, which offer high internal gain and relatively low noise-equivalent-power. These novel devices will improve the sensitivity of active remote sensing instruments while eliminating the need for a high power laser transmitter.
Role of Lidar Technology in Future NASA Space Missions
Authors: Amzajerdian Farzin
Published: April 2011

The past success of lidar instruments in space combined with potentials of laser remote sensing techniques in improving measurements traditionally performed by other instrument technologies and in enabling new measurements have expanded the role of lidar technology in future NASA missions. Compared with passive optical and active radar/microwave instruments, lidar systems produce substantially more accurate and precise data without reliance on natural light sources and with much greater spatial resolution. NASA pursues lidar technology not only as science instruments, providing atmospherics and surface topography data of Earth and other solar system bodies, but also as viable guidance and navigation sensors for space vehicles. This paper summarizes the current NASA lidar missions and describes the lidar systems being considered for deployment in space in the near future.
All Fiber Coherent Doppler LIDAR for Wind Sensing
Authors: Ando Toshiyuki , Kameyama Shumpei , Asaka Kimio , Hirano Yoshihito , Tanaka Hisamichi , Inokuchi Hamaki
Published: April 2011

An 1.5 micron pulsed Coherent Doppler LIDAR system using all fiber optical components has attracted attention for remote wind sensing application because of its eye-safety, reliability and easy deployment. We report on our key technologies such as fiber based MOPA (Master Oscillator Power Amplification) transmitter, high peak power optical amplification and a real-time signal processing. Some performance results and applications are also provided.
Development of Low-Cost Multi-Watt Yellow Lasers Using InGaAs/GaAs Vertical External-Cavity Surface-Emitting Lasers
Authors: Fallahi Mahmoud , Fan Li , Hessenius Chris , hader Jorg , Li Hongbo , Moloney Jerome , Stolz Wolfgang , Koch Stephan , Murray James
Published: April 2011

We demonstrate a highly strained InGaAs/GaAs VECSEL operating at 1173 nm with more than 8.5 W output power and tunable over 40 nm. High-efficiency yellow-orange emission is then achieved by intra-cavity frequency doubling. Over 5 W of CW output power in the 585-589 nm spectral regions is achieved. This compact low-cost high-power yellow-orange laser provides an innovative alternative for sodium guidestar lasers or other medical / communication applications.
Quantum Design of Active Semiconductor Materials for Targeted Wavelengths
Authors: Moloney Jerome , Hader Joerg , Koch Stephan W.
Published: April 2011

Performance metrics of every class of semiconductor amplifier or laser system depend critically on semiconductor QW optical properties such as photoluminescence (PL), gain and recombination losses (radiative and nonradiative). Current practice in amplifier or laser design assumes phenomenological parameterized models for these critical optical properties and has to rely on experimental measurement to extract model fit parameters. In this tutorial, I will present an overview of a powerful and sophisticated first-principles quantum design approach that allows one to extract these critical optical properties without relying on prior experimental measurement. It will be shown that an end device L-I characteristic can be predicted with the only input being intrinsic background losses, extracted from cut-back experiments. We will show that textbook and literature models of semiconductor amplifiers and lasers are seriously flawed.
The Effect of Plasma Treatment on the SiO2 film fabricated without Substrate Heating for Flexible Electronics
Authors: Kim Sun-Jae , Han Sang-Myeon , Kuk Seung-Hee , Kang Dong-Won , Han Min-Koo
Published: April 2011

Silicon dioxide (SiO2) films were deposited on crystalline silicon substrate by inductively coupled plasma chemical vapor deposition (ICP-CVD). In this paper, various process parameter-gas flow rate, ICP RF power, Process pressure were discussed for the investigation of refractive index. And some properties of the SiO2 film are investigated. Since there was no external substrate heating during the deposition, the SiO2 film showed poor electrical characteristics, such as shifted flat-band voltage and high effective charge density. We have proposed He plasma pre-treatment in order to reduce the interface fixed charge and some post-treatment. Our experimental results shows that He plasma pre-treatment supply thermal energy for decomposition of reactant gas and to remove effective charges. Hydrogen post-treatment also enhances electrical characteristics. We measured the effect of the plasma treatment using FT-IR spectrum and C-V characteristics.
Self-formation of Ti-rich Layers at Cu(Ti)/low-k Interfaces
Authors: Kohama Kazuyuki , Ito Kazuhiro , Tsukimoto Susumu , Mori Kenichi , Maekawa Kazuyoshi , Murakami Masanori
Published: April 2011

In our previous studies, thin Ti-rich diffusion barrier layers were found to be formed at the interface between Cu(Ti) films and SiO2/Si substrates after annealing at elevated temperatures. This technique was called “self-formation of the diffusion barrier,” which is attractive for fabrication of ultra-large scale integrated (ULSI) interconnects. In the present study, we investigated the applicability of this technique to Cu(Ti) alloy films which were deposited on the four low dielectric constant (low-k) dielectric layers which are potential dielectric layers of future ULSI-Si devices. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) films. It was concluded that the Ti-rich interface layers were formed in all the Cu(Ti)/dielectric-layer samples. The primary factor to control composition of the self-formed Ti-rich interface layers was the C concentration in the dielectric layers rather than the formation enthalpy of the Ti compounds (TiC and TiSi). Crystalline TiC was formed on the dielectric layers with a C concentration higher than 17 at.%.
Al Diffusion in Polycrystalline Cu
Authors: Gstrein Florian , Kennel Harold , Budrevich Andre , Miner Barbara , Plombon John , Andideh Ebrahim
Published: April 2011

The diffusion of aluminum (Al) from a source sandwiched between polycrystalline copper (Cu) thin films was investigated as a function of time and temperature through secondary ion mass spectroscopy (SIMS) and continuum simulations. Extracted diffusion coefficients for the bulk were in line with literature values. In order to simulate the experimentally derived diffusion profiles at temperatures where bulk diffusion is not the dominant diffusion mechanism (room temperature to 350 °C), it was necessary to explicitly include the re-distribution of Al as a result of Cu grain growth during anneal. Aluminum has the tendency to segregate to the Cu/liner and Cu/etch stop (ES) interface. The tendency of Al to segregate to the liner is ten times stronger for ruthenium (Ru) than for tantalum (Ta). In 100 nm wide dual damascene structures lined with Ru, this segregation behavior was responsible for the Al depletion in bulk Cu and for the Al depletion at the Cu/ES interface.
In-situ early stage electromigration study in Al line using synchrotron polychromatic X-ray microdiffraction
Authors: Chen Kai , Tamura N. , Tu K. N.
Published: April 2011

Electromigration is a phenomenon that has attracted much attention in the semiconductor industry because of its deleterious effects on electronic devices (such as interconnects) as they become smaller and current density passing through them increases. However, the effect of the electric current on the microstructure of interconnect lines during the very early stage of electromigration is not well documented. In the present report, we used synchrotron radiation based polychromatic X-ray microdiffraction for the in-situ study of the electromigration induced plasticity effects on individual grains of an Al (Cu) interconnect test structure. Dislocation slips which are activated by the electric current stressing are analyzed by the shape change of the diffraction peaks. The study shows polygonization of the grains due to the rearrangement of geometrically necessary dislocations (GND) in the direction of the current. Consequences of these findings are discussed.
Sacrificial Passivation of Nanoscale Metal Powders for Transient Liquid Phase Bonding
Authors: Bosco Nick , Manhat Beth , Janczak-Rusch Jolanta
Published: April 2011

Differential scanning calorimetry (DSC) was used to evaluate the extent of liquid phase formation in particle compacts (compressed dry powders) comprised of organically capped nano-scale Ag particles and Sn. The Ag nanoparticles employed where synthesized with various organic molecules and procedures to produce particles with a range of capping thicknesses and decomposition temperatures (Td), as measured by thermogravimetric analysis (TGA). A baseline sample containing commercially available un-capped micrometer scale Ag was also investigated for comparison. Results indicate that all of the Sn initially present formed a liquid phase when heated through its melting point when combined with Ag particles exhibiting a comparatively thick cap of low Td. Slightly smaller fractions of Sn liquid were obtained when the Ag's cap was thin and of a high Td while particles with thin-low Td caps exhibited the highest levels of Sn consumption and similar to that observed with the un-capped micron-scale Ag particles. The reduction in the amount of Sn liquid formed is attributed to solid state reaction between the Ag and Sn particles resulting in the formation of a more refractory phase. The extent of the subsequent liquid phase reaction was also evaluated and is demonstrated to not necessarily be adversely effected by the presence of the organics. The significance of this work is the demonstration that organic molecules may be employed to prevent solid state reaction in particle compacts at elevated temperatures, yet allow the subsequent liquid phase reaction proceed uninhibited.
Modelling and Characterization of Ultrasonic Consolidation Process of Aluminium Alloys
Authors: Ghassemieh Elaheh , Ghassemieh Elaheh
Published: April 2011

Ultrasonic consolidation process is a rapid manufacturing process used to join thin layers of metal at low temperatures and low energy consumption. In this work, finite element method has been used to simulate the ultrasonic consolidation of Aluminium alloys 6061 (AA-6061) and 3003 (AA-3003). A thermomechanical material model has been developed in the framework of continuum cyclic plasticity theory which takes into account both volume (acoustic softening) and surface (thermal softening due to friction) effects. A friction model based on experimental studies has been developed, which takes into account the dependence of coefficient of friction upon contact pressure, amount of slip, temperature and number of cycles. Using the developed material and friction model ultrasonic consolidation process has been simulated for various combinations of process parameters involved. Experimental observations are explained on the basis of the results obtained in the present study. The current research provides the opportunity to explain the differences of the behaviour of AA-6061 and AA-3003 during the ultrasonic consolidation process. Finally, trends of the experimentally measured fracture energies of the bonded specimen are compared to the predicted friction work at the weld interface resulted from the simulation at similar process condition. Similarity of the trends indicates the validity of the developed model in its predictive capability of the process.
Numerical Analysis of Packaging-Induced Failures in Cu/Low-k Interconnects
Authors: Karmarkar Aditya Pradeep , Xu Xiaopeng , Lin Xiao , Rollins Greg , Moroz Victor , Lin Xi-Wei
Published: April 2011

With decreasing feature sizes for every technology node, multi-level metallization schemes that employ copper interconnects and low-k dielectrics are required to achieve the requisite circuit performance. Here, the effects of the mechanical stresses originating from the packaging process on Cu/Low-k interconnects are assessed. The impact of package defects on interconnect reliability is also analyzed. It is seen that the package reliability varies with underfill mechanical properties. The packaging process introduces global level stresses that propagate to the local, i.e. interconnect, level. Moreover, the package defects also have an adverse impact on the mechanical stresses in the metallization structure. The package defects alter the mechanical stresses in the metal lines and affect the reliability. The complex interaction between packaging process induced stresses, package level defects and mechanical properties of various materials is analyzed in order to create robust interconnect designs.
Organization of Magnetic/Noble Metal Heterostructures by an Applied External Magnetic Field
Authors: Pazos-Pérez Nicolás , Baranov Dmitry , Hilgendorff Michael , Pérez-Juste Jorge , Liz-Marzán Luis. M. , Giersig Michael
Published: April 2011

This paper describes the synthesis of binary nanoparticles consisting of a noble metal and a magnetic component. These heterostructures were produced by a seeded-growth approach in aqueous solution. FePt nanoparticles, as the magnetic component, were first synthesized in an organic medium, subsequently transferred into water, and finally used as seeds for the growth of the noble metal Au. This procedure results in FePt-Au heterostructures. Moreover, the synthesized heterodimers were organized into mesoscopic lines under the influence of an externally applied magnetic field. The produced heterostructures were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and UV-vis spectroscopy.
Nanoscale Characterization of Metal/Semiconductor Nanocables
Authors: Vidu Ruxandra , McCandless Brian E , Berkheimer Jeff , Duval David J , Stroeve Pieter
Published: April 2011

Comprehensive characterization at nanoscale is needed to create novel nanostructures for high efficiency solar cells. To produce consistent results, wide-ranging characterization procedures for integrated nanostructures have been developed. Characterization of a novel nanowire, nanotube and nanocable system includes: chemical, electrochemical, structural, optical and electrical characterization of nanostructures in relation with growth conditions. We present here results on Au and CdTe/Au system that help understanding how surface composition and properties are modified in this system. New challenges in structural characterization were also identified and improved sample preparation techniques were developed.
Synthesis of GaN Nanostructures at Low Temperatures by Chemical Vapor Deposition
Authors: Chow Christopher Y. , Raghothamachar Balaji , Carvajal Joan J. , Chen Hui , Dudley Michael
Published: April 2011

In this study, we report on the synthesis of gallium nitride (GaN) nanopowders on boron nitride (BN) substrates both with and without the use of metal catalyst by chemical vapor deposition (CVD). The synthesis process is based on the reaction between gallium (Ga) atoms from the decomposition of gallium acetylacetonate and ammonia (NH3) gas molecules. Using this process, gallium nitride (GaN) nanopowders have been synthesized at temperatures as low as 400°C, lower than previously reported. The grown nanopowders were characterized by SEM, EDX and TEM. Analysis reveals that higher yields were obtained by treating the BN substrates with Ni catalyst. Experiments to study the effect of growth conditions on the morphology of the nanopowders and analyze the growth mechanism are ongoing.
Proper Combination of Catalyst Materials and Ethanol for High Yield in CVD Growth of Carbon Nanotubes
Authors: Maeda Fumihiko , Kobayashi Yoshihiro
Published: April 2011

Carbon nanotubes (CNTs) were grown by using a combination of ethanol and metallic Fe, which was not exposed to air before the growth. CNTs were also grown using intentionally oxidized Fe. The reaction products by these growths were analyzed by in situ photoelectron spectroscopy. We found that the oxidized Fe partially remained and did not completely reduce, resulting in low CNT yields. At higher growth temperature, oxide formation was found even when metallic Fe was used. These oxides induced a lowering of the decomposition efficiency of ethanol, resulting in difficulty of CNT growth by the combination of pure ethanol and Fe.
Influences of Hydrogen Gas on Carbon Nanotube Growth
Authors: Ohashi Fumitaka , Chen Guan Yow , Stolojan Vlad , Silva S. Ravi P.
Published: April 2011

For practical deployment of carbon nanotubes, an understanding of their growth mechanism is required in order to obtain better control over their crystallinity, chirality and other structural properties. In this study, we focus on the influences of gas species on carbon nanotube synthesis using thermal chemical vapour deposition. The influence of methane, hydrogen, and helium gases was investigated from the viewpoint of gas chemistry in relation to the nanotube structural change, by varying the growth pressure, the gas-flow ratio and the growth temperature. Simple changes in the hydrogen gas concentration during different growth stages have been found to induce surprising changes to the nanotube formation. The structure of the tubular carbon growth changed from amorphous to graphitic as the growth temperature and the concentration of hydrogen in the initial periods of growth decreases. The excess hydrogen tends to give rise to poor crystalline carbon nanofibres but has the effect of increasing the yields. Hydrogen gas is typically used in reducing metal catalyst particles during the pre-treatment and the carbon nanotube growth periods. We show that while hydrogen species can improve yield, it can also result in the degradation of the nanotube's crystallinity. The use of hydrogen in the growth process is one of the key parameters for enhanced control of carbon nanotube/nanofibre growth and their resulting crystallinity.
Vertically Aligned Carbon Nanotubes Formed Using dc PECVD as Switching Elements for Extreme Environment Space Electronics
Authors: Kaul Anupama B , Kowalczyk Robert , Megerian Krikor , Allmen Paul von , Baron Richard L
Published: April 2011

Vertically aligned carbon nanotube (CNT) nano-electro-mechanical (NEM) switches are currently being investigated for their application in radiation-hard, high temperature space electronics. Carbon nanotubes are attractive for switching applications since electrostatically-actuated CNT switches have low actuation voltages and power requirements, while allowing GHz switching speeds that stem from the inherently high elastic modulus and low mass of the CNT. Our NEM structure consists of CNTs that are grown using dc plasma-enhanced (PE) chemical-vapor-deposition (CVD) for forming vertically aligned, rigid tubes. A gas mixture of acetylene and ammonia were used for tube growth at a total pressure of a few Torr and temperatures up to 700 °C. We have formed arrays of single, vertically aligned tubes directly on Si, which was enabled by this first report of an optical lithography approach used to generate isolated tubes compared to e-beam lithography that is conventionally used. Vertical NEM switch devices were formed where single, vertically aligned tubes were seen within deep trenches, in close proximity to conducting electrodes.
Towards Development and Characterization of Ionic Junction via Microcontact Printing
Authors: Yadav Yamini , Prasad Shalini
Published: April 2011

The paper presents an evaluation of the feasibility of developing ionic surfactant coated single walled carbon nanotube (SWCNTs) (P-N) junction clusters via microcontact printing using intrinsic semi conducting SWCNTs. These SWCNTs are doped with anionic and cationic surfactant molecules respectively, thereby altering the Fermi energy levels of and its electrical properties. Two types of surfactants were used for doping the SWCNTs to develop extrinsically doped P and N type SWCNTs. Sodium dodecyl sulfate (SDS) having Na+ positive ionic charge (anions) and Cetyl trimethylammonium bromide (CTAB), having Br- negative ionic charge (cations) on its hydrophilic ends have been used to generate anionic SWCNTs (P type) and cationic SWCNTs( N- type respectively.
Using, dual level patterning process, these extrinsically doped anionic and cationic semiconducting SWCNTs clusters are alternatively symmetrically patterned in a parallel array to form crossbar P-N junctions onto a standard microfabricated platform using flexible polymeric poly-dimethylsiloxane (PDMS) stamps. Ink-based transfer of the nanomaterial from the relief structures achieves parallel alignment of SWCNTs clusters. The electrical device characterization is achieved by measuring I-V characteristics from the base micro fabricated platform.
Functionality of the nanodevice is demonstrated by studying the rectifying current – voltage (I-V) characteristics that shows promise towards the formation of a junction diode array, which can be used for integrating complex logic devices for high-end applications such as memory module and addressable logic. Lastly, we believe that the chemical modulation method and microcontact printing techniques will have a wide scope for development of nanomaterial-based devices.
Understanding Degradation of Doped Electroluminescent ZnS Phosphors
Authors: Jiang Yu , Stanley Jacob , Ruhlen Laurel , France Chris , Willey John , Bezryadina Anna , Bridges Frank , Carter Sue
Published: April 2011

We have shown recently that the degradation of AC electroluminescence (EL) in ZnS:Cu,Cl and similar phosphors can be significantly reversed by a short anneal near 200°C. To better understand the degradation/rejuvenation processes, we investigated EL degradation and rejuvenation under different conditions. To probe for changes in the local atomic structure about the Cu sites, we collected Extended X-ray Absorption Fine Structure (EXAFS) data at the Cu K-edge EXAFS data for several as-made, thermally degraded (240°C anneal), and EL degraded powders.
Accelerated Molecular Dynamics Simulation of AFM Experiments Using the Bond-Boost Method
Authors: Kim Woo Kyun , Falk Michael L.
Published: April 2011

Accelerated molecular dynamics (MD) simulations of recent Atomic Force Microscope (AFM) experiments on oxidized silicon surfaces demonstrate a nontrivial dependence of frictional force on sliding velocity as well as temperature. By implementing hyper dynamics (HD) via the bond-boost method these simulations achieve sliding velocities in the range of real experimental values. Moreover, an analysis of the effects of temperature and sliding velocity on friction provide evidence for a systematic deviation from the modified Tomlinson model. We hypothesize regarding the origin of these deviations, and use the simulations to analyze the atomic processes that accompany sliding.
Solid Lubrication with Carbon Onions at High Temperature in Vacuum
Authors: Hirata Atsushi , Saito Shinji
Published: April 2011

Solid lubricant properties of carbon onions prepared from diamond nanoparticles through a heat treatment at 1700°C have been examined at high temperatures up to 300°C in air and vacuum. Sliding friction between a silicon disk on which carbon onions were dispersed and a stainless steel ball was measured by means of ball-on-disk type friction testing. Friction coefficients in vacuum decreased with temperatures and became stable above 100°C for longer service lives. On the contrary to this, friction coefficients in air increased with temperatures despite Raman spectroscopic analysis showed that the structure of carbon onions were stable in dry air up to 300°C.
Micromachined Lateral Force Sensors for Characterization of Microscale Surface Forces During Chemical Mechanical Polishing
Authors: Gauthier Douglas , Mueller Andrew , White Robert David , Manno Vincent , Rogers Chris , Hooper Donald , Anjur Sriram , Moinpour Mansour
Published: April 2011

Micromachined structures with diameters ranging from 50 — 100 μm have been applied to the measurement of the microscale shearing forces present at the wafer-pad interface during chemical mechanical polishing (CMP). The structures are 80 μm high poly-dimethyl-siloxane posts with bending stiffnesses ranging from 1.6 to 14 μN/μm. The structures were polished using a stiff, ungrooved pad and 3 wt% fumed silica slurry at relative velocities of approximately 0.5 m/s and downforces of approximately 1 psi. Observed lateral forces on the structures were on the order of 5–500 μN, and highly variable in time.
Mechanics of a Novel Shear-activated Microfiber Array Adhesive
Authors: Majidi Carmel , Fearing Ronald S
Published: April 2011

Elastic rod theory and principles of contact mechanics motivate the development of a novel, shear-activated, microfiber array adhesive. Unlike with conventional Pressure Sensitive Adhesives (PSAs), the microfiber array and backing are composed entirely of a stiff, glassy polymer (polypropylene, elastic modulus E = 1 GPa) and an externally applied shear load is required to achieve contact with a substrate. Previously, results from a Shear Power Test on glass indicated a maximum interfacial shear strength of 10 kPa over 4 sq. cm, a factor of 1000 greater than with a smooth polypropylene sheet of similar thickness. Here we present a theoretical model that describes the mechanism for shear-activated adhesion and predicts a shear strength of 27 kPa, on the order of the experimental measurement.
Mechanical Characterization of High Aspect Ratio Silicon Nanolines
Authors: Huang Huai , Huang Huai , Zhao Qiu , Luo Zhiquan , Im Jang-Hi , Ho Paul S , Kang Min Kyoo , Huang Rui , Cresswell Michael W
Published: April 2011

In this study, we performed nanoindentation experiments on two sets of silicon nanolines (SiNLs) of widths 24 nm and 90 nm, respectively, to investigate the mechanical behavior of silicon structures at tens of nanometer scale. The high height-to-width aspect ratio (∼15) SiNLs were fabricated by an anisotropic wet etching (AWE) method, having straight and nearly atomically flat sidewalls. In the test, buckling instability was observed at a critical load, which was fully recoverable upon unloading. It was found that friction at the contact between the indenter and SiNLs played an important role in the buckling response. Based on a finite element model (FEM), the friction coefficient was estimated to be in a range of 0.02 to 0.05. The strain to failure was estimated to range from 3.8% for 90 nm lines to 7.5% for 24 nm lines.
The Growth and Mechanical Properties of Gold Nanowires
Authors: Dou Rui , Derby Brian
Published: April 2011

We have measured the yield strength of gold nanowire forests with mean diameter 30, 60 and 70 nm fabricated by electro-deposition into porous alumina templates. All nanowire sizes showed yield strengths much greater than expected from polycrystalline gold specimens with the 30 nm specimens having a yield stress in excess of 1.4 GPa. We found no significant work hardening at plastic strains up to 30%. The strength of the nanowires as a function of wire diameter follows the same trend as has been reported for the compression strength of larger gold pillars reported in the literature. TEM observations of deformed wires are consistent with mechanisms of dislocation induced deformation.
Growth and Optical Properties of SnO2 Ultra-Small Nanorods by the Novel Micelle Techniques
Authors: Rath Satchidananda , Nozaki Shinji , Ono Hiroshi , Uchida Kazuo , Khojima Satoshi
Published: April 2011

Tin-dioxide (SnO2) ultra-small nanorods (UNR) have been successfully synthesized using the novel micellar technique. From transmission electron microscopy, the average diameter and length of the UNRs are estimated to be 1.3 nm and 5.0 nm, respectively. The crystal structure of the SnO2 UNRs was found to be tetragonal from the glazing incidence x-ray diffraction. The optical band gap estimated from the absorption spectrum is blue-shifted by 1 eV from that of bulk (3.64 eV). The photoluminescence spectrum shows two groups of peaks each with several fine peaks, one in the wavelength range of 270 – 370 nm and the other in the range of 380 – 500 nm which are due to the strong quantum confinement effect.
Engineering the shape of Zinc Oxide crystals via sonochemical or hydrothermal solution-based methods
Authors: Palumbo Marco , Henley Simon J. , Lutz Thierry , Stolojan Vlad , Cox David , Silva S. Ravi P.
Published: April 2011

Recent results in the use of Zinc Oxide (ZnO) nano/submicron crystals in fields as diverse as sensors, UV lasers, solar cells, piezoelectric nanogenerators and light emitting devices have reinvigorated the interest of the scientific community in this material. To fully exploit the wide range of properties offered by ZnO, a good understanding of the crystal growth mechanism and related defects chemistry is necessary. However, a full picture of the interrelation between defects, processing and properties has not yet been completed, especially for the ZnO nanostructures that are now being synthesized. Furthermore, achieving good control in the shape of the crystal is also a very desirable feature based on the strong correlation there is between shape and properties in nanoscale materials. In this paper, the synthesis of ZnO nanostructures via two alternative aqueous solution methods - sonochemical and hydrothermal - will be presented, together with the influence that the addition of citric anions or variations in the concentration of the initial reactants have on the ZnO crystals shape. Foreseen applications might be in the field of sensors, transparent conductors and large area electronics possibly via ink-jet printing techniques or self-assembly methods.
Effect of interfacial strain on shape and composition of MOCVD grown III-Nitride nanostructures
Authors: Jindal Vibhu , Grandusky James , Tripathi Neeraj , Tungare Mihir , Shahedipour-Sandvik Fatemeh
Published: April 2011

It is determined that the interfacial strain due to lattice mismatch between the substrate (template) and the overgrown nanostructure has substantial influence on the final morphology and faceting of nanostructures. AlGaN and GaN nanostructures were grown on different substrates/templates, namely Sapphire, AlN/Sapphire, Al0.5Ga0.5N/Sapphire and GaN/Sapphire, where interfacial strain for overgrown nanostructures changes from compressive to tensile respectively. GaN nanostructures grown by metalorganic chemical vapor deposition (MOCVD) using identical growth parameters exhibit pyramidal morphologies under low or no mismatch strain, while highly strained structures with compressive strain evolve into prismatic shapes when grown in the c-crystallographic direction. In addition, it is shown that interfacial strain also affects the growth rate and alloy composition of ternary AlGaN nanostructures produced under identical conditions on different templates/substrates. AlGaN nanostructures grown under compressive strain show higher vertical and lower lateral growth rates when compared to those under tensile strain. Scanning electron microscopy, transmission electron microscopy and cathodoluminescene were used to characterize growth rates, shape and composition of the nanostructures. Observed variation in morphologies, growth rates and compositions are explained in terms of the strain dependency of adatom diffusion barriers on strained surfaces and Ehrlich-Schwoebel barriers across different crystallographic planes. Density functional (DFT) calculations were performed to determine the dependency of adatom diffusion on strained GaN and AlN surfaces.
Photoelectron- and Thermionic- Emission Microscopy of Barium/Scandium Thin Films on Tungsten
Authors: Vaughn Joel M. , Kordesch Martin
Published: April 2011

Commercial scandium oxide doped thermionic cathodes have demonstrated current densities over 100 A/cm2. In order to understand the effect of Sc- and Ba- oxides on the emissivity of these cathodes we have imaged thin films of scandium oxide and barium oxide on tungsten foils using photoelectron emission microscopy and thermionic emission microscopy. Arrays of 100 um × 100 um squares of scandium and 25 um × 25 um squares of barium, 200 nm thick, were sputter deposited onto 50 um thick sheets of tungsten foil. Imaging squares of different sizes gives an unequivocal identification of each material and a completely consistent comparison of each material and cathode structure under identical conditions in one image.

The metal squares oxidize in air before imaging. Each sample was heated in situ in a Bauer-Telieps style LEEM/PEEM used primarily in the ThEEM mode. The barium oxide squares emit below 875 K, and diffuse over the scandium below 875 K. Thermionic emission from scandium oxide squares is observed at temperatures significantly larger than 875 K. Failure of the barium oxide film cathode is through barium desorption. AES spectra show that the Sc does not desorb.

While the origin of reduced emission temperature is commonly believed to be a result of a low work function monolayer of Ba and Sc oxides, in our study, the benefits of a combined Ba/Sc cathode are present in a thick (multi-layer), layered structure of barium oxide on top of a thick scandium oxide layer.
Mirror Electron Microscopy for Inspection of Flat Surfaces
Authors: Hasegawa Masaki , Shimakura Tomokazu
Published: April 2011

We have developed a mirror electron microscope (MEM) for inspecting fine processed flat surfaces. This apparatus can detect nanometer-sized particles and scratches on very flat surfaces. Its sensitivity for electric charge distribution is useful for detecting failures in microdevice patterns. In observation of an insulator surface with the MEM, complex features caused by small amount of charge distribution were observed in the images. We believe that the MEM can provide different methods for characterization of electrical behavior on insulator surfaces.
Exploration of the Ultimate Patterning Potential Achievable with Focused Ion Beams
Authors: Gierak Jacques , Bourhis Eric , Mailly Dominique , Patriarche Gilles , Madouri Ali , Jede Ralf , Bauerdick Sven , bruchhaus lars , Hawkes Peter , Biance Anne-Laure , Schiedt Birgitta , Auvray Loïc , Bardotti Laurent , Prevel Brigitte , Mélinon Pascal , Perez Alain , Ferré Jacques , Jamet Jean Pierre , Mougin Alexandra , Chappert Claude , Mathet Véronique , Aigouy Lionel , Robert-Philip Isabelle , Sagnes Isabelle , Braive Rémy , Beveratos Alexios , Abram Izo
Published: April 2011

Decisive advances in the fields of nanosciences and nanotechnologies are intimately related to the development of new instruments and of related writing schemes and methodologies. Therefore we have recently proposed exploitation of the nano-structuring potential of a highly Focused Ion Beam as a tool, to overcome intrinsic limitations of current nano-fabrication techniques and to allow innovative patterning schemes urgently needed in many nanoscience challenges. In this work, we will first detail a very high resolution FIB instrument we have developed specifically to meet these nano-fabrication requirements. Then we will introduce and illustrate some advanced FIB processing schemes. These patterning schemes are (i) Ultra thin membranes as an ideal template for FIB nanoprocessing. (ii) Local defect injection for magnetic thin film direct patterning. (iii) Functionalization of graphite substrates to prepare 2D-organized arrays of clusters. (iv) FIB engineering of the optical properties of microcavities.
Comparing the Role of Dislocations during Plastic Deformation of Nanocrystalline Nickel and Coarse-Grained Nickel during Cold Rolling
Authors: Kulovits Andreas , Mao Scott M , Wiezorek Jorg M
Published: April 2011

We investigated plastic deformation of fully dense electrodeposited nanocrystalline (NC) Ni with an average grain size of 30-40nm. We studied the microstructural evolution during cold rolling of NC Ni to a reduction in thickness up to 76% (true strain equivalent ∼1.42). We determined changes in texture, grain morphology, grain boundary character and grain sizes as a function of cold rolling strain, using X-ray diffraction and transmission electron microscopy TEM. We compared our results of the NC Ni with our own results for cold rolled coarse grained (CG) Ni. Differences and similarities in deformation behavior are discussed with respect to well documented findings in the literature.
Numerical Simulation of Twin-Twin Interaction in Magnetic Shape-Memory Alloys
Authors: Chmielus Markus , Carpenter David , Geleynse Alan , Hagler Michael , Schneider Rainer , Müllner Peter
Published: April 2011

Twin boundary motion is the mechanism that drives the plastic deformation in magnetic shape memory alloys (MSMAs), and is largely dependent on the twin microstructure of the MSMA. The twin microstructure is established during the martensitic transformation, and can be influenced through thermo-magneto-mechanical training. For self-accommodated and ineffectively trained martensite, twin thickness and magnetic-field-induced strain (MFIS) are very small. For effectively trained crystals, a single crystallographic domain may comprise the entire sample and MFIS reaches the theoretical limit. In this paper, a numerical simulation is presented describing the twin microstructures and twin boundary motion of self-accommodated martensite using disclinations and disconnections (twinning dislocations). Disclinations are line defects such as dislocations, however with a rotational displacement field. A quadrupole solution was chosen to approximate the defect structure where two quadrupoles represent an elementary twin double layer unit. In the simulation, the twin boundary was inclined to the twinning plane which required the introduction of twinning disconnections, which are line defects with a stress field similar to dislocations. The shear stress - shear strain properties of self-accommodated martensite were analyzed numerically for different initial configurations of the twin boundary (i.e. for different initial positions of the disconnections). The shear stress - shear strain curve was found to be sensitive to the initial configuration of disconnections. If the disconnections are very close to boundaries of hierarchically higher twins – such as is the case for self-accommodated martensite, there is a threshold stress for twin-boundary motion. If the disconnections are spread out along the twin boundary, twinning occurs at much lower stress.
Very Low-Temperature, Gram-Scale Synthesis of Monodisperse BaTiO3 Nanocrystals via an Interfacial Hydrolysis Reaction
Authors: Morse Daniel E. , Brutchey Richard L.
Published: April 2011

A vapor diffusion sol-gel method is reviewed for the preparation of high-quality BaTiO3 nanocrystals on the gram scale at very low temperatures. The synthesis is based on the kinetically controlled introduction of water into a solution of the bimetallic alkoxide, BaTi(O2C4H9)6, where slow hydrolysis then occurs at the vapor-solution interface followed by nucleation and nanocrystal growth at 16 °C. The resulting 6-nm, quasi-spherical nanocrystals are both monodisperse (without stabilizing agents or size selecting purification) and highly crystalline (without any post-synthesis heat treatment), and are isolated in yields near 100%. Based on new permittivity and calorimetry data, the crystal structure of the nanocrystals is most likely in the paraelectric cubic phase (space group Pm3m) at room temperature, which corroborates previous diffraction data. It was also demonstrated that the BaTiO3 nanocrystals can be doped with trivalent lanthanum cations using the same low-temperature vapor diffusion sol-gel method to yield donor-doped Ba1−xLaxTiO3, which exhibits a considerable PTCR effect.
Fabrication of Hollow Anatase Structure by Using Sea Wool Sponges
Authors: Kwong Fung-luen , Ng Dickon H. L.
Published: April 2011

Highly porous carbon-doped anatase was produced by a simple and time-saving method. The product was prepared by using sea wool sponges and a titanium-contained organic solution. The intermediate product was pyrolyzed sponges coated with amorphous anatase. When further annealed, the final product was an entirely carbon – anatase product with the original structure of sea wool sponges. The struts in the carbon – anatase product were hollow with wall thickness less than 300 nm. Cathodoluminescence measurement showed that this C-TiO2 product was sensitive to visible light.
Synthesis of Biomorphic Silicon Carbide from Wood
Authors: Li Kwok Cheung , Ng Dickon H. L.
Published: April 2011

We have successfully produced biomorphic SiC ceramics from silica-infiltrated wood samples of balsa (Ochroma pyramidale) and flame tree (Delonix regia). This conversion of wood sample to a structure of SiC was performed by a sol-gel technique and a carbothermal reduction process. The biomorphic products were confirmed containing β-SiC and their structures were replica of the original structures of the raw wood samples. The biomorphic products from the denser flame tree (C-SiC) had higher specific strength than that from the biomorphic product from balsa (SiC).
Bio-Inspired Nano-Composite Fabrication on Etched Human Enamel Surface
Authors: Fan Yuwei , Sun Zhi , Moradian-Oldak Janet
Published: April 2011

Because of its significant potential in controlling key steps of apatite mineralization, recombinant amelogenin has been applied in different in vitro systems for the synthesis of uniquely ordered composite material similar to enamel. Here we summarize the results of a series of experiments, in which mineral deposition took place on the exposed surface of enamel from extracted human third molars soaked in calcium phosphate solution, in the presence of amelogenin and fluoride. Analysis of crystal size and morphology revealed that in the presence of both amelogenin (50-100 μg/mL) and fluoride (1 ppm), bundles of oriented rod- like fluoridated apatite crystals were formed creating a dense coating on the enamel substrate. Such organized bundles were not formed at low concentrations of rP172 (< 30 μg/mL). Preparation of such ordered nanocomposites provides a promising approach for development of new generation of dental restorative materials with improved esthetic and mechanical properties.