bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopant segregation to {311} defects during low temperature annealing
Authors: Taniguchi Kenji , Saito Tomoya , Xia Jianxin , Kim Ryangsu , Aoki Takenori , Kobayashi Hiroyuki , Kamakura Yoshinari
Published: April 2011

Boron segregation to {311} defects and transient enhanced diffusion (TED) of boron atoms during thermal annealing were investigated in detail using implanted superlattice and Si bulk wafers. We observed that (1)boron atoms segregate to {311} defects during low temperature annealing, (2){311} defects were formed in the area where the self-interstitial concentration exceeds 3×1017cm3, (3)free self-interstitials in the region beyond the implanted range causes initial rapid enhanced diffusion prior to the onset of normal TED.
In-Situ Photoexcitation-Induced Suppression of Point Defect Generation in Ion Implanted Silicon
Authors: Cho C. R. , Yarykin N. , Rozgonyi G. A. , Zuhr R. A.
Published: April 2011

The formation of vacancy-related defects in n-type silicon has been studied immediately after implantation of He, Si, or Ge ions at 85 K using in-situ DLTS. A-center concentrations in He-implanted samples reach a maximum immediately after implantation, whereas, with Si or Ge ion implanted samples they continuously increase during subsequent anneals. It is proposed that defect clusters, which emit vacancies during anneals, are generated in the collision cascades of Si or Ge ions. An illumination-induced suppression of A-center formation is seen immediately after implantation of He ions at 85 K. This effect is also observed with Si or Ge ions, but only after annealing. The suppression of vacancy complex formation via photoexcitation is believed to occur due to an enhanced recombination of defects during ion implantation, and results in reduced number of vacancies remaining in the defect clusters. In p-type silicon, a reduction in K-center formation and an enhanced migration of defects are concurrently observed in the illuminated sample implanted with Si ions. These observations are consistent with a model where the injection of excess carriers modifies the defect charge state and impacts their diffusion.
Diffusion Mechanisms in Sige Alloys
Authors: Willoughby Arthur F.W. , Bonar Janet M. , Paine Andrew D.N.
Published: April 2011

Interest in diffusion processes in SiGe alloys arises from their potential in HBT's, HFET's, and optoelectronics devices, where migration over distances as small as a few nanometres can be significant. Successful modelling of these processes requires a much improved understanding of the mechanisms of self- and dopant diffusion in the alloy, although recent progress has been made. It is the purpose of this review to set this in the context of diffusion processes in elemental silicon and germanium, and to identify how this can help to elucidate behaviour in the alloy. Firstly, self diffusion processes are reviewed, from general agreement that self-diffusion in germanium is dominated by neutral and acceptor vacancies, to the position in silicon which is still uncertain. Germanium diffusion in silicon, however, appears to be via both vacancy and interstitial processes, and in the bulk alloy there is evidence for a change in dominant mechanism at around 35 percent germanium. Next, a review of dopant diffusion begins with Sb, which appears to diffuse in germanium by a mechanism similar to self-diffusion, and in silicon via monovacancies also, from marker layer evidence. In SiGe, the effects of composition and strain in epitaxial layers on Si substrates are also consistent with diffusion via vacancies, but questions still remain on the role of charged defects. The use of Sb to monitor vacancy effects such as grown-in defects by low temperature MBE, are discussed. Lastly, progress in assessing the role of vacancies and interstitials in the diffusion of boron is reviewed, which is dominated by interstitials in silicon-rich alloys, but appears to change to domination by vacancies at around 40 percent germanium, although studies in pure germanium are greatly needed.
Shallow Boron Implant Activation
Authors: Fiory A. T. , Bourdelle K. K. , Agarwal A. , Gossmann H.-J. , Rafferty C. S.
Published: April 2011

Boron was implanted into n-type Si at energies from 500 eV to 1 keV and doses near 1 E14 cm-2and 1E51 cm−2. Electrical activation was achieved by rapid thermal annealing (RTA) in nominally pure N−2and 0.1% 02 with the fastest available heating rates of up to 150 °C/s, cooling rates up to 80 °C/s, and included “spike” anneals with minimum dwell time at peak temperature. Measurements of sheet resistance, Hall coefficient, and secondary ion mass spectroscopy profiling were used to determine dopant activation and diffusion. Surface oxidation was studied by film thickness ellipsometry. Analyses of electrical transport measurements are used to relate junction depths to sheet resistance and their dependence on annealing temperature and time. For spike annealing, junction leakage and adequate activation limits the minimum practical temperature while diffusion limits the maximum practical temperature for formation of shallow junctions.
Defects and Diffusion in Silicon: An Overview
Authors: Cowern N.E.B. , Mannino G. , Stolk P.A. , Theunissen M.J.J.
Published: April 2011

At the current pace of semiconductor technology development, transistor dimensions in advanced IC products will approach the range of a few tens of nanometers within the next decade. This presents a major challenge for our understanding of defects and diffusion in these tiny devices during processing. In response, an almost explosive growth in research on process physics has taken place at universities, national institutes and industry research labs worldwide. The central issue is the phenomenon of nonequilibrium diffusion driven by processing steps such as oxide growth, high concentration gradients of impurities, and annealing of damage caused by ion implantation. Nonequilibrium diffusion arises from perturbations to the natural thermal equilibrium concentrations of point defects - interstitial atoms and vacancies - in the silicon crystal. This paper gives a snapshot of our current understanding of the atomic-scale interactions between point defects and impurity atoms, extended defects and interfaces, as revealed by recent experimental and theoretical studies. The paper emphasizes the important role played by defect cluster ripening during transient enhanced diffusion and dopant activation.
Real-Time Monitoring by Spectroscopic Ellipsometry and Desorption Mass Spectroscopy During Molecular Beam Epitaxy of AlGaAs/GaAs at High Substrate Temperatures
Authors: Taferner W. T. , Mahalingam K. , Dorsey D. L. , Eyink K. G.
Published: April 2011

A series of AlGaAs/GaAs depositions were monitored in-situ by spectroscopic ellipsometry and desorption mass spectroscopy, under various substrate temperatures (890 K - 990 K) where non-unity sticking conditions occur. An upper bound on the temperature where AlGaAs/GaAs heterostructures may be grown was determined. Ex-situ cross-sectional transmission electron microscopy verified that the AlGaAs/GaAs layer thicknesses grown by molecular beam epitaxy were accurately determined by spectroscopic ellipsometry at these elevated temperatures. The substrate temperature dependence on Ga desorption rates was consistent with Monte Carlo simulation where desorption from both physisorbed and chemisorbed states were included.
Combined Spectroscopic Ellipsometry and Ion Beam Surface Analysis for In-Situ Real-Time Characterization of Complex Oxide Film Growth
Authors: Mueller A.H. , Gao Y. , Irene E.A. , Auciello O. , Krauss A.R. , Schultz J.A.
Published: April 2011

In-situ real time characterization of chemically and structurally complex thin films is becoming important as complex materials are finding more applications in electronic devices. To this end, a unique thin film growth and deposition system was constructed combining a multi-target sputter deposition system with spectroscopic ellipsometry and time-of-flight ion scattering and recoil spectroscopy. This system is demonstrated with studies on YBa2Cu3O7−δand BaSrTiO3 films.
In Situ Growth Studies of Artificial Layered (BA,SR,CA)CUO2 on Quasi-Ideal SrTiO3 Substrates by High Pressure Rheed
Authors: Koster Gertjan , Rijnders Guus J.H.M. , Blank Dave H.A. , Rogalla Horst
Published: April 2011

The layered structure of oxides, like the high-T, cuprates, has been topic of research for some years now. The possibility to control thin film deposition on an atomic level has made fabrication of artificial structures and junctions accessible by depositing atomic layers or molecular blocks sequentially. Perfectly smooth substrate surfaces are hereby a prerequisite.

Using Pulsed Laser Deposition (PLD), different perovskite oxide materials have been deposited on SrTiO3 substrates. With in situ high pressure Reflection High Energy Electron Diffraction we studied growth at different temperatures and oxygen pressures. Ex situ XRD and AFM have been used to study the morphology after deposition.

Here we applied a new approach in obtaining layer-by-layer growth implied by the way of depositing the material, almost regardless of the deposition conditions. By alternating intervals of high supersaturation depositing one unit cell layer with intervals of lower supersaturation, one is able to force a layer-by-layer growth mode, which is in principle only feasible with PLD. We applied this technique to fabricate the layered infinite structure (Ba,Sr,Ca)CuO2 with artificial layered modulation, which have been characterized by XRD and AFM.
Role of Microscopic Stress Fluctuations in Glass Transition and Glass Formation
Authors: Egami T. , Vitek V.
Published: April 2011

Although the structure of liquids and glasses may appear highly disordered, the atomic motions in these phases are rather strongly correlated. Such a correlation, however, cannot be readily described by a pair density function, and higher order correlation functions are necessary. We suggest that the microscopic stresses defined at each atom are quite useful in describing such high order correlations. We discuss how the concept of the microscopic stress fluctuation helps to describe and understand the glass transition and glass formation phenomena. In a molecular dynamics study the local shear stresses were found to become orientationally correlated below a transition temperature, Ts, which is close to the melting temperature. Below Ts the viscosity shows a rapid increase and transverse phonons become more stable. Thus Ts could be viewed as a dynamical glass transition temperature. The conventional glass transition can be described in terms of the elastic percolation of the orientationally correlated regions. On the other hand, the microscopic stresses in the crystalline solid solutions define the topological stability limit of the crystalline phase, and predict the minimum solute concentration to form stable amorphous alloys.
Velocity and Orientation Dependence of Solute Trapping
Authors: Aziz M. J. , Tsao J. Y. , Thompson M. O. , Peercy P. S. , White C. W.
Published: April 2011

The fraction of impurity atoms in the liquid at the solid-liquid interface that join the crystal, known as the segregation coefficient k, during rapid crystal growth is known to deviate away from the equilibrium value towards unity as the interface speed v increases. Several plausible models have been proposed that account qualitatively for this behavior with different functional forms of k(v). We report measurements of the segregation behavior during rapid solidification following pulsed laser melting of Bi-implanted Si. The velocity dependence and the orientation dependence of the segregation coefficient of Bi in Si has been determined to sufficient accuracy to allow us to distinguish between models. Implications for the mechanism of solute trapping are discussed.
Inter-Sub-Level Spectroscopy of P-Type Modulation-Doped Ge Quantum Dots
Authors: Liu J. L. , Wu W. G. , Jin G. , Luo Y. H. , Thomas S. G. , Lu Y. , Wang K. L.
Published: April 2011

Inter-sub-level transitions in p-type modulation-doped Ge quantum dots are observed. The structure is grown by molecular beam epitaxy and consists of 30 periods of Ge quantum dots separated by 6 nm boron-doped Si layers. An absorption peak in the mid-infrared range is observed at room temperature by Fourier transform infrared spectroscopy, and is attributed to the transition between the first two heavy hole states of the Ge quantum dots. This study suggests the possible use of modulation-doped Ge quantum dots for improved infrared detector application.
Structure of InAs Quantum Dots in Si Matrix Investigated by High Resolution Electron Microscopy
Authors: Zakharov N. D. , Werner P. , Ustinov V. M. , Kovsh A.R. , Cirlin G. E. , Smolski O.V. , Denisov D.V. , Alferov Zh. I. , Ledentsov N. N. , Heitz R. , Bimberg D.
Published: April 2011

Quantum dot structures containing 2 and 7 layers of small coherent InAs clusters embedded into a Si single crystal matrix were grown by MBE. The structure of these clusters was investigated by high resolution transmission electron microscopy. The crystallographic quality of the structure severely depends on the substrate temperature, growth sequence, and the geometrical parameters of the sample. The investigation demonstrates that Si can incorporate a limited volume of InAs in a form of small coherent clusters about 3 nm in diameter. If the deposited InAs layer exceeds a critical thickness, large dislocated InAs precipitates are formed during Si overgrowth accumulating the excess of InAs.
Spontaneous Self-Embedding of Three-Dimensional SiGe Islands
Authors: Mateeva E. , Sutter P. , Lagally M. G.
Published: April 2011

It is shown that. under appropriate conditions, high-Ge-concentration coherent 3D SiGe islands grown on Si(100) self-embed in a matrix of low-Ge-concentration alloy. The process may be more generally useful for preserving the shape of self-assembled “quantum dot” islands during embedding in a matrix material.
Dynamics of the Growth of InAs Quantum Dots on GaAs(001) Substrates
Authors: Westwood D.I. , Brown I.H. , Linsell D.N.J. , Matthai C.C.
Published: April 2011

Standard rate equation models of island formation in the InAs/GaAs(001) system have been reassessed in terms of new experimental evidence from real time in-situ reflectance anisotropy spectroscopy (RAS) measurements. These measurements have revealed the behaviour and role of the wetting layer in the modified Stranski-Krastanov growth mode during molecular beam epitaxial growth showing that it can continue to significantly increase in thickness following the onset of islanding. The presence of two dimensional (2D) islands, which act as precursors to three dimensional (3D) islands (the quantum dots) in conventional models, does in principle allow an extension of the “wetting layer”. However, it has been found necessary to extend the standard model to include extra terms that allow material to be incorporated into (and detach from) the wetting layer and which cannot convert to 3D islands. With this improved model, it is found possible to achieve agreement with the RAS measurements.
Doping and Oxidation Effects in Raman Spectra of Manganites
Authors: Podobedov V. B. , Weber A. , Dezanneau G. , Pignard S. , Kreizel J. , Vincent H.
Published: April 2011

Raman scattering from LayRxMnO3-δ compounds (single crystals, ceramics, films) was studied as a function of kind (R) and amount (x) of dopant as well as of oxygen deficit (δ). For x = 0.1 to 0.55, a nearly linear Raman shift of the Ag mode from 240 to 125 cm−1 was observed in Srdoped compounds. While the intensity of disorder-induced Raman bands was found to be sensitive to the oxygen content, the symmetry allowed related Raman modes exhibit the changes in the frequency. As an indication of deposition conditions, lowering of a symmetry of the film structures with respect to single crystals and ceramics was detected. We discuss the physical nature of the observed effects and show how Raman data can be used for the optical characterization of manganite samples.
Liquid Compounds for CVD of Alkaline Earth Metals
Authors: Gordon Roy G. , Barry Seán T. , Liu Xinye , Teff Daniel J.
Published: April 2011

The first room-temperature liquid compounds useful for the CVD of alkaline earth metalcontaining oxides were prepared by reacting metal (Mg, Ca, Sr, and Ba) beta-diketonates with novel polyamine ligands. The compounds are monomeric and can be completely flash-vaporized without leaving any non-volatile residue detectable at the parts-per-million level. A stable, solvent-free liquid mixture was formed by mixing new liquid barium, strontium and titanium compounds. CVD experiments using direct liquid injection of this liquid mixture deposited films of barium strontium titanate. This approach should also be applicable to the deposition of many other multicomponent oxides containing alkaline earth metals: ferroelectrics (strontium bismuth tantalate), metallic conductors (strontium vanadium oxide, lanthanum strontium cobalt oxide), phosphors (calcium tungstate), non-linear optical materials (beta-barium borate), magnetic oxides (barium ferrite), colossal magnetoresistive materials (lanthanum strontium manganese oxide), high Tc superconductors (yttrium barium copper oxide, bismuth calcium strontium copper oxide) and microwave dielectrics (barium magnesium tantalate).
Factors Controlling Transport Properties of Interfaces in High-Tc Superconductors
Authors: Hilgenkamp H. , Schulz R. R. , Schneider C. W. , Goetz B. , Schmehl A. , Bielefeldt H. , Mannhart J.
Published: April 2011

A comprehensive understanding of the transport properties of interfaces in high-Tc cuprates been obtained by considering their microstructure, the possibility of bending of the electronic
band structure in these materials, and the predominant dx2-y2 -symmetry of the order parameter in most high-Tc cuprates. These factors are of central importance for the critical current density and the normal state resistivity of grain boundaries and their dependencies on boundary misorientation and on applied magnetic and electrical fields. In addition, some of these factors play an important role for the transport properties of other interfaces involving high-Tc superconductors, such as superconductors-normal metal contacts.

Based on the improved understanding of the mechanisms controlling interface transport properties, we have been able to meet a long-standing challenge in high-Tc superconductivity and have increased the critical current densities of grain boundaries by large factors, using appropriate doping.
Optical Properties of AlGaAsSb, AlGalnP, AlGaInAs, and GaInAsP for Optoelectronic Applications
Authors: Linnik M. , Christou A.
Published: April 2011

The authors present calculations of quaternary III–V semiconductor alloy optical properties and the comparison of the theoretical data with available experimental results for AlGaAsSb, AlGaInP, AlGaInAs, and GaInAsP alloys. The investigation includes material's energy bandgap and refractive index calculations as a function of the incident wavelength in the transparent region, as well as the composition of the alloy. Optimization of the quaternary alloy refractive indices was obtained from a semi-empirical dielectric function calculations based on the interband transition contributions.
A Three-Dimensional Computer Model for Simulation of Light-Trapping Effects in Porous Silicon
Authors: Charbel Peter T. , Zheng Jim P.
Published: April 2011

It has been demonstrated that porous silicon can be used to enhance the sensitivity, spectral bandwidth, and light acceptance angle of photodiodes. In an attempt to better understand light trapping effects in porous silicon, a three-dimensional model was used to approximate the surface geometry of porous silicon. It was found that the main contributing factor to the observed high efficiencies is the shape of the pores. The general shape resembles cylindrical shaped sections, whose radii are in the micron range. The results of the computer simulation were compared to actual experimental results where porous silicon was tested under variable conditions of lighting and porosity. The comparison shows that the simulation gives a good approximation of the behavior of porous silicon. Although the simulation does not perfectly match experimental values, it does provide the insight that the surface geometry of porous silicon is the main contributing factor to its efficiency in trapping light.
First-Principles Study of Optical Excitations in Alpha Quartz
Authors: Chang Eric K. , Rohlfing Michael , Louie Steven G.
Published: April 2011

The properties of silicon dioxide have been studied extensively over the years. However, there still remain major unanswered questions regarding the nature of the optical spectrum and the role of excitonic effects in this technologically important material. In this work, we present an ab initio study of the optical absorption spectrum of alpha-quartz, using a newly developed first-principles method which includes self-energy and electron-hole interaction effects. The quasiparticle band structure is computed within the GW approximation to obtain a quantitative description of the single-particle excitations. The Bethe-Salpeter equation for the electron-hole excitations is solved to obtain the optical spectrum and to understand the spatial extent and physical properties of the excitons. The theoretical absorption spectrum is found to be in excellent agreement with the measured spectrum. We show that excitonic effects are crucial in the frequency range up to 5 eV above the absorption threshold.
Influence of The Alloy Composition on The Thermodynamic Parameters of Nucleation and Growth of SiGe
Authors: Olivares J. , Rodríguez A. , Sangrador J. , Rodríguez T. , Martín P. , Jiménez J. , Ballesteros C. , Castro M.
Published: April 2011

The influence of the germanium fraction on the parameters of the solid phase crystallization of amorphous silicon-germanium has been studied. Layers of different compositions were deposited by LPCVD at 450 °C and crystallized at 525, 550, 575 and 600 °C. The crystalline fraction was determined as a function of the annealing time for each germanium fraction and temperature. The incubation and the characteristic crystallization times were obtained by fitting the crystalline fraction to Avrami's model. The values of the diffusion activation energy were obtained for different compositions. The dependence of the nucleation rate and the growth velocity on the germanium fraction and the temperature was studied. The three parameters decrease as the Ge fraction increases; though the stronger dependence corresponds to the nucleation rate. The dependences on the composition and the temperature were analyzed in the frame of a conventional nucleation and growth model and their relationship with the corresponding free energies was discussed.
Transitory Metastable Phases in Refractory Metals-Based Systems Solidified by Drop-Tube Processing: A First-Principles Approach
Authors: Berne C. , Pasturel A. , Sluiter M. , Vinet B.
Published: April 2011

The solidification path of highly undercooled refractory metals and their alloys solidified in a ultra high vacuum drop-tube is shown to involve transitory metastable phases. First-principles calculations of structural stability are used to determine the possibility of obtaining metastable phases in these systems, with a view to relate this metastability with the site occupation in the σ phase in the case of the ReTa system.
Premonitory Martensitic Surface Relief Via Novel X-Ray Diffuse and Laser Light Reflectivity from The (001)-Surface of A Ni63Al37Single Crystal
Authors: Klemradt U. , Aspelmeyer M. , Abe H. , Wood L.T. , Moss S.C. , Dimasi E. , Peisl J.
Published: April 2011

Both x-ray diffuse reflectivity and laser light scattering have been used to investigate the temperature-dependent surface behavior of a Ni63Al37single crystal on different length scales. In-situ experiments were performed above the conventional martensitic start temperature Ms to search for premartensitic phenomena. X-ray experiments showed the presence of a surface precursor with second-order (continuous) character several 10 K above Ms. This premonitory effect corresponds to a height-height-correlation function which changes on the nanometer scale as the martensitic transformation is approached. At the martensitic transformation, the surface morphology changed from nanoscopic roughness to macroscopic relief within a temperature interval of less than 1 K via intermediate stages. Laser light scattering was employed to study time-dependent aspects of the athermal martensitic transformation above Ms. The occurrence of a martensitic transformation on isothermal holding after a certain incubation period was observed in Ni-Al for the first time. The measured incubation times increased by four orders of magnitude within a temperature interval of 0.5 K.
Particle Coarsening in Multiphase Ternary Systems
Authors: Holmes W.C. , Hoyt J.J.
Published: April 2011

Particle Coarsening in ternary, multiphase -multicomponent, systems is quite different than its binary counterpart in that the presence of one phase can affect the coarsening behavior of another. We have shown by analytic analysis and numerical simulation that the interaction between two coexisting phases depends on: solution thermodynamics, diffusivities, and equilibrium concentration differences between matrix and precipitate phases. Therefore, different ternary systems create different cross phase interactions which affect coarsening behavior. For example, spatial correlations between the two coarsening phases are a strong function of this interaction and can lead to spatial ordering between the two phases. Also, specific ternary systems can produce kinetic instabilities and pattern formation.
A Raman Study of a Metastable Crystalline State in Amorphous SiGe Layers Under cw Laser Illumination: Influence of the Temperature
Authors: Martin P. , Olivares J. , Rodriguez A. , Sangrador J. , Jinenez J. , Rodriguez T.
Published: April 2011

A metastable crystalline state was observed in amorphous SiGe/Si layers under illumination with a cw laser beam (514.5 nm) with power density below the crystallization threshold. The observation of this state was temperature dependent and it was reversible. The structural properties of this metastable crystallization were studied by Raman spectroscopy.
A Comparison Between the Calculated and Experimental Effects of Enhanced Precursor Translational Kinetic Energy on SiC Growth on Si(100) and Si(L11) from Hexamethyldisilane
Authors: Beck D. W. , Li Q. , Kordesch M. E.
Published: April 2011

Silicon Carbide thin films were grown on Si(100) and (111) substrates at 1050EC using a pulsed supersonic beam of hexamethyldisilane (HMDS) in hydrogen. X-ray diffraction analysis shows that these films contain only the 3C cubic polytype, determined mainly by the SiC(111) diffraction peak at 22 = 35.6E, the SiC(200) peak at 22 = 41.4E and the SiC(220) peak at 22 = 60.OE.

The angle of incidence of the HMDS/hydrogen beam could be varied through an angle of 0 to 90E without displacing the specimen from the focal point of the beam. On the Si(100) surface, the film growth texture was monitored by measuring the ratio of the SiC(111) to (200) diffraction peak intensity for beam incidence angles of 0, 30, 45 and 60E. On Si(111). The SiC(111)/(220) ratio was monitored. An 8-fold increase in the incident translational kinetic energy of the precursor molecules can be achieved at the highest glancing angle. In general, the effects of enhanced translational kinetic energy on SiC film growth were insignificant, in agreement with calculations of the sticking probability for SiC homoepitaxial growth with seeded beams on SiC [1]. Further examination of the films with SEM and AFM revealed the growth of epitaxial islands at low coverages, and the process of island coalescence.
In Situ Observation of Melting and Solidification
Authors: Saka H. , Arai S. , Muto S. , Miyai H. , Tsukimoto S.
Published: April 2011

Melting and solidification of metallic materials have been observed directly using an in-situ heating experiment in an electron microscope. In pure Al melting initiates at the surface, while in a eutectic alloy melting initiates preferentially at eutectic interfaces and grain boundaries. The atomic structure of a solidliquid interface was identified by comparing an experimental image with computed ones.
Experimental Methods and Data Analysis for Fluctuation Microscopy
Authors: Voyles P. M. , Treacy M. M. J. , Gibson J. M. , Jin H-C. , Abelson J. R.
Published: April 2011

We have developed a new electron microscopy technique called fluctuation microscopy which is sensitive to medium-range order in disordered materials. The technique relies on quantitative statistical analysis of low-resolution dark-field electron micrographs. Extracting useful information from such micrographs involves correcting for the effects of the imaging system, incoherent image contrast caused by large scale structure in the sample, and the effects of the foil thickness.
The Atomic Structure of Mosaïc Grain Boundary Dislocations in GaN Epitaxial Layers
Authors: Potin V. , Nouet G. , Ruterana P. , Pond R.C.
Published: April 2011

The studied GaN layers are made of mosaYc grains rotated around the c-axis by angles in the range 0-25°. Using high-resolution electron microscopy, anisotropic elasticity calculations and image simulation, we have analyzed the atomic structure of the edge threading dislocations. Here, we present an analysis of the Σ = 7 boundary using circuit mapping in order to define the Burgers vectors of the primary and secondary dislocations. The atomic structure of the primary ones was found to exhibit 5/7 and 8 atom cycles.
Energy Dispersive X-ray Spectrometry With the Transition Edge Sensor Microcalorimeter: A Revolutionary Advance in Materials Microanalysis
Authors: Newbury Dale , Wollman David , Irwin Kent , Hilton Gene , Martinis John
Published: April 2011

The NIST microcalorimeter energy dispersive x-ray spectrometer provides important advances in x-ray spectrometry. The high spectral resolution, approaching 2 eV for photon energies below 2 keV, the wide photon energy coverage, 250 eV to 10 keV, and the energy dispersive operation enable a wide range of materials characterization problems to be addressed. This performance is especially critical to high spatial resolution, low-voltage x-ray microanalysis performed with the field-emission gun scanning electron microscope.
Isomeric Higher and Smaller Fullerenes: A Profound Enthalpy/Entropy Interplay
Authors: Zhao X. , Slanina Z. , Ōsawa E.
Published: April 2011

Computations of isomeric fullerenes are performed at semiempirical and ab initio quantum-chemical levels: C36, C72, C88. C36 fullerenes and quasi-fullerenes are computed at the SAM1 level, and then at the B3LYP/6-31G* level. Altogether 598 cages are considered. The SAM1 method is also applied to C72, i.e., the solitary isolated-pentagon-rule (IPR) structure and several non-IPR isomers. Finally, the complete set of thirty five topologically different IPR isomers of C88 is computed. In all the cases, energetics is combined with entropy contributions based on the harmonic-oscillator and rigid-rotator model. Considerable temperature effects on the relative stabilities in the systems are found. Relationships to available observed data are discussed throughout and a good agreement is found.
Formation of Nanotube-Based Quantum Dots With Strain and Addimers
Authors: Orlikowski D. , Nardelli M. Buongiorno , Bernholc J. , Roland C.
Published: April 2011

We present the results of a large-scale molecular dynamics investigation of addimers on strained carbon nanotubes. We find that addimers induce a new set of transformations that lead to the formation of extended defects that are actually short segments of tubes of altered helicity. As these defects wrap themselves about the circumference of the nanotube, this suggests that the combination of addimers and strain may well lead to the formation of nanotube-based quantum dots. The formation of these quantum dots is most favorable for the (n.O) zigzag tubes. For these tubes, addimers induce plastic transformations in tubes that normally display brittle behavior.
Partial Carbonization of Aromatic Polyimide Films
Authors: Doyama M. , Ichida A. , Inoue Y. , Kogure Y. , Nozaki T. , Yamada S.
Published: April 2011

Aromatic polyimide films are partially carbonized between 700°C and 1000°C. Electrical conductivity and Hall coeficient have been measured. Electrical conductivity is higher at higher measuring temperatures. The electrical conductivity σ can be expressed as σ= σ0exp (–E /kT), where k is the Boltzman constant. T is the absolute temperature. E depends upon the carborized temperature. The experimental data show the Hall coefficient RH is negative, and this implies the carriers are negatively charged, i.e. electrons. The specimens are n-type semiconductors. The carrier density η can be expressed by η= A1 exp (–E1/κT) and carrier mobility μ can be expressed by μ = A1exp ( E2/κT). E, E1andE2 depend upon the carbonized temperature
Properties of Ion Beam Deposited Tetrahedral Fluorinated Amorphous Carbon Films (ta-C:F)
Authors: Ronning C. , Merk R. , Feldermann H. , Harbsmeier F. , Hofsäss H.
Published: April 2011

We have studied the growth and the properties of ta-C:F films prepared by the deposition of mass separated 12C+ and 19F+ ions as a function of the F concentration CF. The films are always strongly F-deficient due to the formation of volatile CFx, molecules during the deposition process. CF ≈ 25 at.% is obtained for an ion charge ratio of C+:F+ = 1:1. The mass density strongly decreases from 2.9 g/cm3 for ta-C to 1.1 g/cm3 for films with CF ≈ 23 at.%, whereas the electron density related plasmon energy only varies slightly between 31.8 eV and 29 eV. Therefore, films with small CF have both a high mass and high electron density resulting in diamond-like properties. The discrepancy between low mass density and high electron density for films with large cF can be explained by voids. The thickness and composition of films with CF below 20 at.% remains unchanged for vacuum annealing to temperatures of 600 °C for 10 minutes. Loss of F was observed for films with cF above 20 at.%. The compressive film stress decreases with increasing CF, and is further reduced by annealing.
Fluorine Incorporation Into Hard Amorphous Hydrogenated Carbon Films Deposited by PECVD
Authors: Freire F. L. , Jacobsohn L. G. , Franceschini D. F.
Published: April 2011

The incorporation of fluorine into amorphous hydrogenated carbon films deposited by the plasma enhanced chemical vapor deposition technique (PECVD) was investigated. Different mixtures of CH4 and CF4 were employed as the plasma atmosphere, with the partial pressure of CF4 ranging from 0 to 100 %. For all depositions, the self-bias was kept at –350 V. In the case of atmospheres richer than ∼80 % of CF4, no film deposition but substrate erosion was observed. The composition of the films was determined by Ion Beam Analysis (IBA), revealing that fluorine is incorporated into the amorphous network by replacing hydrogen. Infrared (IR) transmission measurements confirmed these results. It was also found that the incorporation of fluorine has the effect of reducing both the internal stress and hardness due to atomic density reduction.
Effect of Argon Addition on Nitrogen Containing Carbon Films Prepared by Hot Carbon Filament CVD
Authors: Watanabe Yoshihisa , Ohnita Shinobu , Kitazawa Nobuaki , Nakamura Yoshikazu
Published: April 2011

Nitrogen containing amorphous carbon (a-CNx) films were prepared on silicon single crystal substrates by heating a carbon filament in low pressure nitrogen atmosphere and the effects of argon addition to nitrogen atmosphere were studied by changing the argon fraction under the total pressure of 100 Pa. The growth rate of the films is found to decrease with increasing the argon fraction. x-ray photoelectron spectroscopy shows that the films are composed of carbon and nitrogen and the optimal fraction of argon addition is observed for increasing the nitrogen concentration. Observations by atomic force microscopy reveal that the film surfaces are covered with particle-like features and the size of the features decreases drastically by argon addition. It is concluded that argon addition to the reactant gas is effective in synthesizing a-CNx films with the smooth surface and high nitrogen concentration
A Surface Diffusion Model for Nanotube Growth
Authors: Louchev Oleg A. , Sato Yoichiro
Published: April 2011

The problem of nanotube growth macrokinetics is viewed within the framework of the continuum surface diffusion equation combined with step-flow growth kinetics. The differences in incorporation rates of adatoms approaching the growth steps from “upper” or lower" terraces are taken into account. These differences can lead to the onset of surface island nucleation in front of a propagating step. This effect is able to cause formation of defects in the growing layer and even to inhibit stable step-flow modes of nanotube growth. The segregation effect of a second phase (BN) in front of the propagating of C layer step is considered, suggesting that it may cause increase in BN concentration and nucleation of islands leading to BN inclusions in C layers or the propagation of a BN layer over C layer.
Comparative Study of Solvent Effect on the Electrochemical Deposition of Polythiophene and Polybithiophene
Authors: Wong T. K. S. , Hu X.
Published: April 2011

Thin films of polythiophene and polybithiophene have been deposited by electrochemical polymerization onto indium tin oxide substrates using two different aprotic organic solvents: acetonitrile and benzonitrile. It was observed that when benzonitrile is used as supporting solvent, the initial deposit is always discontinuous and uniform thin layers could not be obtained. When acetonitrile is the solvent, the deposited layer is continuous. However, both the optical and mechanical properties of the polymer film are inferior. The difference is especially pronounced for thiophene monomers. Characterization results suggest a greater degree of polymerization in benzonitrile solvent.
Electron Irradiated p(VDF-TrFE) Copolymers for Use in Naval Transducer Applications
Authors: Ramotowski T. , Hamilton K. , Kavarnos G. , Zhang Q. , Bharti V.
Published: April 2011

Recently, it was discovered that the transduction / strain capability of p(VDF-TrFE) copolymers can be enhanced by more than an order of magnitude by irradiating the copolymer with large doses (40–300 Mrads) of β-particles (1–3 MeV electrons). The goal of this project is to understand how irradiation improves the electromechanical properties of p(VDF-TrFE) copolymers while simultaneously identifying the secondary effects of the irradiation process on the material (not critical to the electromechanical properties) and attempting to separate the two contributions. It has been found that β-irradiation affects the material profoundly in several different manners. Reduction in the melt temperature, degree of crystallinity, and the resulting crystal quality have been observed for increasing doses of β-particles. Similar results have been observed for the Curie transition, especially in the energy associated with, and the breadth otf the transition. In addition, thermogravimetric analysis indicates that irradiation causes both chain scission and network polymer formation. Solid-state NMR results are discussed in reference to postulated dehalogenation, dehydrohalogenation, and olefinic bond formation activities.
A Discussion of Flow Mechanisms in Superplastic Yttria-Stabilized Tetragonal Zirconia
Authors: Berbon Min Z. , Langdon Terence G.
Published: April 2011

Flow data are reported for a superplastic yttria-stabilized tetragonal zirconia containing 3 mol % of Y2O3 (termed 3Y-TZP). The data are analyzed using a model for interface-controlled diffusion creep and the results are compared with published data for other samples of 3Y-TZP.
Grain Boundary Engineering of Highly Deformable Ceramics
Authors: Mecartney Martha L.
Published: April 2011

Highly deformable ceramics can be created with the addition of intergranular silicate phases. These amorphous intergranular phases can assist in superplastic deformation by relieving stress concentrations and minimizing grain growth if the appropriate intergranular compositions are selected. Examples from 3Y-TZP and 8Y-CSZ ceramics are discussed. The grain boundary chemistry is analyzed by high resolution analytical TEM is found to have a strong influence on the cohesion of the grains both at high temperature and at room temperature. Intergranular phases with a high ionic character and containing large ions with a relatively weak bond strength appear to cause premature failure. In contrast, intergranular phases with a high degree of covalent character and similar or smaller ions than the ceramic and a high ionic bond strength are the best for grain boundary adhesion and prevention of both cavitation at high temperatures and intergranular fracture at room temperature.
Application of Piezoelectric Materials for Use as Actuators and Sensors in Hard Disk Drive Suspension Assemblies
Authors: Heffelfinger J. R. , Boismier D. A.
Published: April 2011

Suspension assemblies, the mechanical arm that supports the read/write head in a Hard Disk Drive (HDD), are incorporating piezoelectric motors for dual-stage actuation. With high displacements and high Curie Temperatures, lead zirconium titanate (PZT) is the preferred piezoelectric material for this application. In this study, commercially available PZT is studied for critical material properties that include strength, aging and particulate generation. An average PZT strength of 111.7 MPa and a Weibull parameter (m) of 12.18 was measured for the material. Aging rates of the dielectric constant vary between 1.9 to 3.2 % per time decade depending on the test condition. The attachment of PZT motors to the suspension assembly provides a method of sensing suspension resonance, shock and temperature fluctuations. Fast Fourier Transform (FFT) analysis of voltage generation of the PZT during drive operation identified a frequency of 6509 Hz that is within 0.2% of the measured resonance frequency of the suspension. The PZT generated several volts for shock events between 500 to 2000 G's of the suspension. Implications of the material parameters and potential sensing capabilities of the PZT are discussed.
Doping Effects in Pb(Mg1/3Nb2/3)O3-PbTiO3 Ceramics for High Power Transduction Applications
Authors: Chen Yun-Han , Hirose Senji , Viehland Dwight , Uchinol Kenji
Published: April 2011

Piezoelectric ceramics are potential high-power electro-acoustic sources, and have been studied for many years. However, when these devices are driven under high level vibration, the electromechanical characteristics depart significantly due to the loss and nonlinear behavior in terms of elastic and dielectric properties. In this paper, we present results concerning the development of modified Pb(Mgl/3Nb2/3)O3-PbTiO3 (PMN-PT) ceramics for high-power application. We have focused efforts on base PMN-PT compositions close to the morphotropic phase boundary. Different mono-doping have been studied to understand the doping effects on the properties of PMN-PT ceramics and, moreover, to improve the properties for the high-power application. Of all the substitutents investigated in this study, Mn-doping was found the only one to improve the properties of PMN-PT significantly for high-power application by reducing the total loss (including mechanical loss as well as the dielectric loss), yet keeping the coupling factor constant. This work is supported by Office of Naval Research.
De-Icing Layers of Interdigitated Microelectrodes
Authors: Courville Zoe , Petrenko V.F.
Published: April 2011

We report development of special active coatings that are capable of de-icing various solid surfaces vulnerable to icing such as airplane wings, helicopter blades, road signs, superstructures, hulls of ships, etc. The coating consists of a thin web of metal interdigitated microelectrodes formed using photolithography. The electrodes are made of very thin copper on a thin and flexible Kapton substrate. After etching, the electrodes were electroplated with Au to increase their resistance to electro-corrosion. The de-icing action of the coating is based on the phenomenon of ice electrolysis. Namely, when ice forms over the electrodes, a small DC bias of 5 V to 30V is applied to the electrodes to generate a DC current through the ice. The ice adjacent to the electrodes is then decomposed into gaseous hydrogen (on the cathode) and gaseous oxygen (on the anode) thus eliminating bonding between the ice and the metal. Moreover, gas bubbles rapidly growing on the interface spread as interfacial cracks thus breaking the ice. We present a theory of such active grids and describe their preparation procedure. Results of mechanical and electrical tests will be shown
Dynamics of MEMS Microengines Using Optoelectronic Laser Interferometry
Authors: Brown G. C. , Pryputniewicz R. J. , De Boer M. P. , Smith Norman
Published: April 2011

We have developed an optoelectronic laser interferometry microscope (OLIM) methodology for rapid characterization of MEMS' motion dynamics. In this study, electrostatic comb drive actuated microengines comprised of a 64 μm diameter drive gear and a 300 μm output gear (load gear) were characterized dynamically. Two different input signals were used: 1) a four-step square wave input and 2) an optimized input signal calculated from an analytical model. Out-ofplane motion on rotating microgears was measured as a function of the input signals. The outof-plane motions for the drive during the four-step input ranged from zero to ±462 nm and from zero to ±514 nm for the drive and output gears, respectively. For the optimum input, the out-ofplane motions ranged from zero to ±1030 nm for the drive gear. However, for the output gear the tilt magnitudes were nearly constant at ±514 rum, and were independent of angular position. The more constant out-of-plane motions of the load gear for the optimized signal are due to improved kinematics and kinetics leading to more continuous rather than impulsive forces (e. g., frictional, inertial) acting on the output gear.
Torsional Micromirror Array Design for Optical Binary Switching and Amplitude Modulation Applications
Authors: Kolesar E.S. , Allen P.B. , Boydston N.C. , Howard J.T. , Ko S.Y. , Wilken J.W.
Published: April 2011

A torsional micromirror was designed and fabricated using a three-level, polysilicon, surface micromachined, microelectromechanical systems (MEMS) process. The torsional micromirrors have highly-reflective, gold-coated polysilicon optical surfaces. Electrostatically induced in-plane and outof-plane vertical deflections on the order of 2.75 νm were achieved. The modeling phase focused on the microdynamical behavior of the torsional micromirror. The IntelliCAD® finite element analysis program was used to generate a plot of the micromirror's deflection (d) versus applied direct current voltage (V). The data was least-squares fitted to the well-established V μ d3/2 relationship. A resonant frequency analysis predicted an approximate switching speed of 6 νsec. The relative reliability (number of operational cycles) of the torsional micromirror design was measured to exceed 2 million flexure events. The potential for using torsional micromirrors as binary optical switches and amplitude modulators is addressed.