bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Carbon-Nitrogen Films with a Broad Beam RF Ion Source
Authors: Ingram David C. , Lanter William C. , DeJoseph Charles A. , Kayani Asghar
Published: April 2011

With the lack of suitable native oxides, gallium nitride based semiconductor devices will need other materials for dielectric, insulating and passivating layers in a variety of device applications. A carbon-nitrogen film is a possible candidate for this application. Insulating films can be made of this material with a variety of techniques. Ion beam techniques are a well accepted way to demonstrate the existence of a material with certain properties and a way to establish the range of those properties in the material. Ion beam assisted deposition has been used in this work to fabricate materials with various stoichiometries in order to determine the range of properties available for this material.

Thin films containing predominantly carbon and nitrogen have been grown using a mixture of methane and nitrogen from a 20 cm rf ion source. The stoichiometry of the films has been measured with Rutherford Backscattering Spectroscopy (RBS), and Elastic Recoil Spectroscopy (ERS). The effect of nitrogen-to-methane ratio, ion energy, and RF power on the film composition, properties, and growth rate is reported together with an analysis of the anticipated growth mechanics.
Microstructure of ELO-GaN Layers Grown by Hydride Vapor Phase Epitaxy
Authors: Gradecak Silvija , Wagner Volker , Ilegems Marc , Bobard Fabienne , Stadelmann Pierre
Published: April 2011

Electron microscopy techniques are applied to investigate structural properties of GaN layers selectively grown by hydride vapor phase epitaxy on crystalline and amorphous GaN seed layers deposited on (0001)Al2O3 substrates. Optimalization of the growth conditions lead to a reduction both of the stacking fault concentration and c-axis tilting in the laterally grown regions. During the lateral growth threading dislocations from the seed layer bend from vertical direction of propagation. Bending behavior depends on the type of the dislocation and on the shape of the GaN film in the initial stage of the growth. Optical properties of laterally grown regions are correlated with the high point-defect incorporation that is revealed by high-resolution electron microscopy.
Effect of High Temperature Single and Multiple AlN Intermediate Layers on N-polar and Ga-polar GaN Grown by Molecular Beam Epitaxy
Authors: Fedler F. , Stemmer J. , Hauenstein R. J. , Rotter T. , Sanchez A. M. , Ponce A. , Molina S. I. , Mistele D. , Klausing H. , Semchinova O. , Aderhold J. , Graul J.
Published: April 2011

Wurtzite GaN samples containing one, three and five 4nm thick high temperature (HT) AlN Interlayers (IL) have been grown on (0001) sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). N-polar as well as Ga-polar thin films have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), and electrical measurements.

All samples under consideration show excellent AFM rms surface roughness below 1nm. Previously, we published a reduction of the threading dislocation (TD) density by a factor of seven due to the introduction of one AlN-IL. When introducing multiple AlN-IL a reduction by a factor of 5.2 is achieved.

Hall measurements show a rise in electron mobility due to possible 2DEG formation at the interface between GaN and the AlN-ILs. Significant growth mode differences between Ga-polar and N-polar samples result in drastically higher electron mobility values for N-polar material. For N-polar samples the exceptional mobility increase from 68 (no AlN-IL) to 707 cm2/Vs (one AlN-IL) as well as the extremely low intrinsic carrier density of 1 x 1017 cm-3 prove the applicability of AlN barriers in inverted FET devices.
Formation of GaN Self-Organized Nanotips by Nanomasking Effect
Authors: Yoshida Harumasa , Urushido Tatsuhiro , Miyake Hideto , Hiramtsu Kazumasa
Published: April 2011

We have successfully fabricated self-organized GaN nanotips by reactive ion etching using chlorine plasma, and have revealed the formation mechanism. Nanotips with a high density and a high aspect ratio have been formed after the etching. We deduce from X-ray photoelectron spectroscopy (XPS) analysis that the nanotip formation is attributed to nanometer-scale masks of SiO2 on GaN. The structures calculated by Monte Carlo simulation of our formation mechanism are very similar to the experimental nanotip structures.
Photoluminescence study of deep-level defects in undoped GaN
Authors: Reshchikov M. A. , Morkoç H. , Park S. S. , Lee K. Y.
Published: April 2011

We studied photoluminescence (PL) and PL excitation (PLE) spectra in a large number of undoped GaN layers grown on sapphire by molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE). The HVPE-grown GaN layers with thickness of ~200 m m were separated from the sapphire substrate by laser lift-off and represented bulk freestanding templates of very high quality. Identical position and shape of the YL band were reproduced in many samples grown by MBE and MOCVD: maximum at ~2.23 eV and full width at half maximum (FWHM) of about 460 meV at room temperature. However, in some samples the band maximum was observed at about 2.0 eV. The freestanding templates reveal a broad band (FWHM=530-680 meV) whose position depends on excitation energy and intensity, varying from 2.22 eV to 2.47 eV. PLE spectra taken from various samples represented a broad band with apparent maximum at about 3.3 eV. For below-gap excitation, the intensity of the YL band was independent of temperature except for the one in the freestanding template. The latter was temperature independent above 60 K, however at lower temperatures the PL intensity decreased by 5 times. An activation energy of 15 meV has been determined that is related to a barrier in the adiabatic potential in the excited state of the defect.
Exciton Spectra of AlN Epitaxial Films
Authors: Onuma T. , Chichibu S. F. , Sota T. , Asai K. , Sumiya S. , Shibata T. , Tanaka M.
Published: April 2011

Excitonic resonance energies in a C-plane AlN epilayer on the (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy were determined as a function of temperature by means of optical reflectance (OR) and cathodoluminescence (CL) measurements. The OR spectra exhibited distinct reflectance anomalies at the photon energies just above the multiple internal reflection fringes, and the spectral lineshape was fitted considering A (???u7v7c) and BC (???9v,???17v7c) exciton transitions. The energies of them at 0 K were obtained to be 6.211 and 6.266 eV, giving the crystal field splitting (Δcr) of approximately 55 meV. The AlNfilm exhibited an excitonic emission even at 300 K, which is due to the small Bohr radius of excitons and large longitudinal optical phonon energies. The Einstein characteristic temperature Q E was estimated to be 580 K.
Growth of AlN bulk crystals from the vapor phase
Authors: Schlesser Raoul , Dalmau Rafael , Yakimova Rositza , Sitar Zlatko
Published: April 2011

AlN single crystals were grown by two different vapor phase processes: by vaporization of metallic Al in a nitrogen atmosphere, or by sublimation of an AlN source. Growth experiments were carried out under quasi-stagnant flow conditions, with typical flow rates of 100 sccm at reactor pressures ranging from 300 to 700 Torr. Growth temperatures ranged from 1800 to 2300°C. In Al vaporization experiments, the crystal shape and fastest growth direction was found to strongly depend on the growth temperature: at relatively low temperatures (1800-1900°C) long needles were grown, temperatures around 1900-2000°C yielded twinned platelets, while c-platelets were formed at temperatures above 2100°C. These c-plates grew at a rate of 5 mm/hr in the c-plane. When using AlN as a source material, growth rates were considerably slower, however, long-term stability of the Al flux was greatly improved. Seeded growth was demonstrated under these conditions. All grown single crystals were transparent and virtually colorless. Analytical results indicated very high crystalline quality and dislocation densities lower than 104cm-3.
Properties of 2D and 3D Dielectric Structures Fabricated by Electrochemical Dissolution of III-V Compounds
Authors: Tiginyanu I.M. , Langa S. , Christophersen M. , Carstensen J. , Sergentu V. , Foca E. , Rios O. , Föll H.
Published: April 2011

Porous layers and membranes representing 2D and 3D dielectric structures were fabricated on different III-V compounds (GaAs, InP, GaP) by electrochemical etching techniques. Nonlithographically fabricated ordered nanopore arrays in InP are reported for the first time. We show that the reflectance from nanostructured InP is lower than that from bulk InP in the spectral interval 1.5-2.2 eV. The artificial anisotropy induced by nanotexturization was studied in porous GaP membranes and the refractive indices for ordinary and extraordinary beams were evaluated.
Transmission Characterization of Drilled Alternating-Layer Three-Dimensional Photonic Crystals
Authors: Kuramochi Eiichi , Notomi Masaya , Yokohama Itaru , Takahashi Jun-ichi , Takahashi Chiharu , Kawashima Takayuki , Kawakami Shojiro
Published: April 2011

We propose a new three-dimensional photonic crystal structure or drilled alternating-layer photonic crystal (DALPC), which can be fabricated by a combination of the deposition of alternating layers of dielectric films and one-time dry etching. Our band calculation predicts that the DALPC has a photonic band gap (PBG) in all directions. We fabricated a Si/SiO2 DALPC by electron beam lithography, bias sputtering, and fluoride-gas electron cyclotron resonance etching. We measured the light transmission of the DALPC sample in both the in-plane and vertical directions. We observed a transmission minimum around the 1.4-µm-wavelength for all measured directions and TE/TM polarizations, which demonstrated a potential of the DALPC as a three-dimensional PBG material.
Interference lithography for 3D photonic band gap crystal layer by layer fabrication.
Authors: Feigel A , Kotler Z. , Sfez B. , Arsh A. , Klebanov M. , Lyubin V.
Published: April 2011

We present fabrication of 3D photonic band gap woodpile crystals from photosensitive chalcogenide glass with the help of interference lithography and layer by layer construction. The alignment method is described, which is scalable to extremely small feature sizes required for photonic crystals in the visible region.
Selective Deposition of Two-Dimensional Colloidal Arrays on Patterned Polyelectrolyte Multilayer Templates
Authors: Zheng Haipeng , Lee Ilsoon , Rubner Michael F. , Hammond Paula T.
Published: April 2011

A new method for the patterning of colloidal particles on polymer templates is presented. A polyelectrolyte multilayer film is deposited onto a chemically patterned monolayer surface, which is further used as a functional template to direct the deposition of charged particles through electrostatic and secondary interactions. After modified by an opposite charged surfactant, the particles change their deposition selectivity from the polyelectrolyte surface to a neutral ethylene glycol monolayer surface. Based on the different selectivity, we have first demonstrated a new approach to direct two component colloidal arrays onto a patterned polyelectrolyte multilayer template.
Direction Dependent Grain-Interaction Models for the Diffraction Stress Analysis of Thin Films
Authors: Welzel Udo , Leoni Matteo , Mittemeijer Eric J.
Published: April 2011

The well-known grain-interaction models for the description of the macroscopic elastic behaviour of polycrystalline specimens, for example the models due to Voigt and Reuss, may be applied to bulk specimens, but they are generally not suitable for thin films because they imply macroscopic elastic isotropy of the body. A thin film is usually at most transversely elastically isotropic, even in the absence of texture. A recently elaborated, alternative model for grain-interaction in thin films, adopting grain-interaction assumptions first given by Vook and Witt (J. Appl. Phys. 7, 2169 (1965)), is able to predict the transversely isotropic elastic behaviour. Although this model is more appropriate for thin films than traditional models, it still imposes extreme grain-interaction assumptions, which are in general not compatible with the true elastic behaviour of real specimens. In this paper a more general approach to grain-interaction in thin films is proposed.
Adaptive Protocol for Robust Estimates of Coatings Properties by Nanoindentation
Authors: Jennett Nigel M. , Bushby Andrew J.
Published: April 2011

The determination of the elastic modulus and hardness of a wide range of coating systems has been studied recently in the EC project INDICOAT. This paper describes a protocol for determining the coating properties, which has been developed and tested in that project. The procedure contains simple to implement strategies to evaluate the response of the coating and design a suitable series of indentation experiments that enable a reasonable estimation of ‘coating-only’ properties. The protocol directs how the experimental design adapts the experimental parameters to each sample. An adaptive protocol is essential to cope adequately with the different indentation responses. Indentation response depends, for example, on coating thickness and the relative properties of coating and substrate and creep response. The protocol also has to adapt itself so that it can reliably target the range of indentation depth with respect to the coating thickness necessary to obtain the coating properties from the composite indentation response. Results presented show that the parameters and approach for measurement of hard coatings are very different to those required for soft or ductile coatings. The systems studied are DLC on tool steel, Au on Ni, aluminium oxide on Ni and aluminium on optical glass (BK7).
Nanoindentation and Magneto-Optical Study of Oxidized Co Thin Films
Authors: Mishra S. R. , Rho J. , Sherfy G. , Roy M. , Buckner T.
Published: April 2011

We have studied the mechanical and magneto-optical properties of postdeposition oxidized Co thin films. Oxidization process leads to the formation of double-layered structure of cobalt oxide on top of metallic cobalt. The nanoindentation measurements show decrease in hardness and Young's modulus at low annealing temperature and are related to increasing porosity of the film. The magneto-optical Kerr effect (MOKE) reveals dependence of the MOKE spectra on annealing temperature. The increased coercivity of the annealed films has been observed by MOKE and is related to the structure of the film.
Nanoindentation and Nanowear Studies of Sputter-Deposited Ultrathin Tin Oxide Films on Glass Substrates
Authors: Wang J. G. , Stahley M. E. , Pantano C. G. , Yang D. H. , Anderson T. , Kuhn L.
Published: April 2011

Tin oxide thin films on glass are used in a variety of applications ranging from transparent conductors to coupling layers to wear resistant coatings. The mechanical properties and wear resistance are crucial to most applications of tin oxide films. In the present study, ultrathin tin oxide films were sputter-deposited on the two different glass substrates. Nanoindentation, nanoscratch and nanowear experiments were performed on the tin oxide films with different thickness using a Hysitron TriboScope at different loads. Hardness and Young's modulus of elasticity were determined from the depth sensing load-displacement data. A lower friction coefficient was observed on the thinner film using the ramping load scratch test. Critical loads were determined by the ramping load scratch test and multi-slide nanowear tests on the tin oxide film deposited on the alkali contained commercial float glass (LOF-P16) glass. Discussion on the effect of surface chemistry on the mechanical properties was made.
Infrared Photoelastic Study of Thin-Film-Edge-Induced Stresses in Silicon Substrates
Authors: Peng H. J. , Wong S.P. , Zhao Shounan
Published: April 2011

The stress distribution in silicon substrates under a silicon dioxide thin film edge, long oxide thin film stripes and long oxide window structures have been studied using the infrared photoelastic (IRPE) method. The experimental IRPE stress fringe patterns were compared with the simulated patterns based on an analytic solution we obtained recently for the stress distribution under a thin film edge in isotropic substrates. Dependence of the stress distribution in these structures on the geometrical parameters such as the stripe width, window width, and substrate thickness were also studied. The implication of a slight discrepancy between the experimental and simulated IRPE patterns on the singular behavior of stress field in the substrate at the film edge and the concentrated force assumption are discussed.
Residual Stress Measurement in a Pt-Aluminide Bond Coat
Authors: Watanabe Makoto , Mumm Daniel R. , Chiras Stefanie , Evans Anthony G.
Published: April 2011

The residual stress induced in a Pt-aluminide bond coat formed on a single-crystal superalloy has been measured. The stresses arise because of the thermal expansion misfit with the substrate on cooling from the manufacturing temperature. Since the lattice parameters are unknown, the interpretation of diffraction measurements is problematic, and the “wafer” curvature method has been applied. This method required that the substrate thickness be systematically reduced by mechanical thinning. It was also required that curvature measurements be made with the bond coat present as well as after it had been removed by thinning. This approach revealed that the bond coat is in residual tension, 140MPa, consistent with its thermal expansion coefficient, relative to that for the substrate.
Mechanical Properties and Porosity of Organo-Silicate Glass (OSG) Low-k Dielectric Films
Authors: Vella J. B. , Xie Q. , Edwards N. V. , Kulik J. , Junker K. H.
Published: April 2011

Low-k material integration issues that plague the microelectronics industry include the compromise in mechanical properties that one incurs in abandoning fully dense silica dieletrics. Typical elastic moduli of OSG low-k dieletric films are 2-10 GPa with corresponding hardnesses of 0.5 to 1.5 GPa. In the present study, the hardness and elastic modulus properties measured by nanoindentation of porous silica based low-k films are correlated with in initial estimates of density using a novel technique of spectroscopic ellispsometry. Transmission electron microscopy and X-ray photoelectron spectroscopy show the structural and chemical similarity of the films. Nanoindentation and spectroscopic ellipsometry results reflect significant deviations in material behavior from that expected from a simple model of silica (SiO2) with included voids or porosity, suggesting that the methyl groups are actively participating in the mechanical and optical properties of the material.
Viscous Creep in Metallic Wires at Elevated Temperatures and Low Stresses.
Authors: Fiala Jaroslav , Kloc Lubos , Sklenicka Vaclav
Published: April 2011

Viscous creep behaviour of several metals and alloys was investigated at the temperatures close to one half of the absolute melting point and at very low stresses using the technique of helicoid specimens. Due to extremely high sensitivity the technique represents a unique tool for measurement of very low creep strains in reasonable time. Helicoid spring specimens were made of wires of either circular or square cross section. The stress distribution along the wire radius (caused by shear stress loading) and threshold stresses were taken into account, as well as the influence of the surface layer loaded by maximum stress.

The experimental results were interpreted as Coble diffusional creep and/or Harper-Dorn dislocation creep. Some data are in a very good agreement with Coble theory especially those obtained on some fine grained materials. For the coarse grained materials is this dependence replaced by large data scattering. Some authors dispute about the role or even the very existence of diffusional creep and offer other explanations. There are many theories trying to describe Harper-Dorn creep mechanism, but none of them is capable to explain all observed properties.

The observed effects which cannot be explained by the current theories are discussed (large scatter of creep rates obtained for coarse grain materials, creep rates much higher than those predicted by the diffusional creep theory in some materials, transition stage duration independent of stress but dependent on temperature.

Despite the problems in theoretical description, the experiment shows clearly that the viscous creep regime must be considered as an important behaviour of structural materials at conditions of engineering practice.
A Study on the Behavior of Water Absorption of SiOf Thin Films Deposited by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition Method
Authors: Kim S. P. , Choi S. K. , Park Youngsoo , Chung Ilsub
Published: April 2011

Fluorinated silicon oxide (SiOF) films were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECRPECVD). The behavior of residual stress w as studied with water absorption. SiOF film showed compressive stress after deposition. The compressive stress increased after the exposure to room air. Fourier transformed infrared (FTI R) spectroscopy analysis was carried after the water absorption. However, the change of chemical bonding structure was not observed during the water absorption in this study. After the exposu re to room air, the films were kept in dry air. The residual stress returns to the initial value after 1 week. Considering the results of the residual stress and FTIR analysis, it is supposed that the water absorption in this study occurs entirely by physical adsorption of H2O molecules to Si-F bonds on the surface.
A New Force-Displacement Model for Continuous Indentation of Bilayer Materials
Authors: Nayebi A. , El Abdi R. , Mauvoisin G. , Bartier O.
Published: April 2011

A new relationship between indentation load and depth in relation to flow stress and strain hardening exponents of film and substrate of bilayers is given. The comparison between the numerical results and those experimentally obtained from known materials, confirms the interest of the proposed model for film characterization of these materials.
Metal Adhesion to <100> Si Substrates with Varying Surface Conditions
Authors: Barbosa Nicholas , Ridley Rodney S. , Strate Christopher H. , Dwyer Robert S. , Grebs Thomas , Vinci Richard P.
Published: April 2011

Adhesion in multi-layer thin film structures was measured using the four-point bend technique. The investigation primarily focused on layers found in the backside metalization processes of Power MOSFETs (typically in a DMOSFET or U-MOSFET structure). Variation in metal layer and substrate condition produced changes in the adhesion behavior of the systems of interest. Pt, Cu, and Ti metals were applied to Si and SiO2 surfaces with various roughnesses in order to establish the relative contributions of surface chemistry and roughness variation. G values ranging from 2 – 100 J/m2 were measured and it was found that variation in surface chemistry has a larger impact than roughness on the adhesion strength of the systems investigated. The four-point bend adhesion test was determined to be adequate for the measurement of weak to intermediate adhesion of metals on Si wafers with RMS roughness values on the order of the metal film thickness.
Fracture Behavior of Micro-Sized Specimens Prepared From an Amorphous Alloy Thin Film at Ambient and Elevated Temperatures
Authors: Takashima K. , Tarumi R. , Higo Y.
Published: April 2011

Fracture behavior of micro-sized cantilever beam type specimens prepared from an electroless deposited Ni-P amorphous alloy thin film has been investigated at ambient and elevated temperatures. Cantilever beam type specimens with dimensions of 10 x 12 x 50 μm3were prepared from an electroless deposited Ni-P amorphous alloy thin film and notches were introduced by focused ion beam machining. Fatigue pre-cracks were introduced ahead of the notches. The introduction of fatigue pre-crack and fracture toughness tests were carried out using a mechanical testing machine for micro-sized specimens. The temperature of the specimen was controlled from room temperature to 473 K using a newly developed heating system. Compared with room temperature, fracture toughness increased approximately 40 % at 373 K but decreased 19 % at 473 K. The increase of fracture toughness at 373 K is considered to be related with the formation of nano-sized crystals and the decrease of fracture toughness at 473 K is considered to be due to the growth of crystals. It is required to consider the fracture behavior obtained in this investigation when designing actual MEMS devices using electroless deposited amorphous films.
In-Situ Mechanical Characterization of a Freestanding 100 Nanometer Thick Aluminum Film in SEM Using MEMS Sensors
Authors: Haque Aman , Saif Taher
Published: April 2011

We present the uniaxial stress-strain response of a freestanding 100 nanometer thick 99.99% pure sputtered Aluminum film with grain size about 60 nanometers, tested in-situ inside a SEM chamber. The specimen is cofabricated with MEMS force and displacement sensors to minimize the experimental setup size, allowing both quantitative and in-situ tests to be performed in SEM and TEM chambers. The experimental results strongly suggest that at this size scale, a) Elastic modulus remains same as the bulk Aluminum, b) Yielding starts at about 625 MPa, and c) Strain hardening effect is absent, which indirectly suggests the deformation at this size scale is not dislocation mechanism based.
Spontaneous Pattern Formation from Focused and Unfocused Ion Beam Irradiation
Authors: Cuenat Alexandre , Aziz Michael J.
Published: April 2011

We study the formation and self-organization of “ripples” and “dots” spontaneously appearing during uniform irradiation of Si, Ge, and GaSb with energetic ion beams. Features have been produced both with sub-keV unfocused Ar+ ions and with a 30 keV Ga+ Focused Ion Beam. We follow the evolution of features from small amplitude to “nanospikes” with increasing ion dose. It appears that the edge of the sputtered region influences the patterns formed, an effect that may make it possible to guide the self-organization by the imposition of lateral boundary conditions on the sputter instability.
Strain Relaxation of He+ Implanted, Pseudomorphic Si1−xGex Layers on Si(100)
Authors: Holländer B. , Mantl S. , Lenk St. , Trinkaus H. , Kirch D. , Luysberg M. , Hackbarth Th. , Herzog H.-J. , Fichtner P.F.P.
Published: April 2011

Strain relaxed Si1−xGex buffer layers are of great importance as virtual substrates for Si1−xGex/Si quantum well structures and devices. We apply He+ ion implantation and subsequent annealing on pseudomorphic, MBE-grown Si1−xGex/Si(100) heterostructures with an implantation depth of about 100 nm below the Si1−xGex/Si interface. A narrow defect band is generated inducing the formation of strain relieving misfit dislocations during subsequent thermal annealing. Efficient strain relaxation was demonstrated for Si1−xGex layers with Ge fractions up to 30 at. %. The variation of the implantation dose and the annealing conditions changes the dislocation configuration and the He bubble structure. At a dose of 2×1016 cm−2 a high degree of relaxation is accompanied by a low density of threading dislocations of about 107 cm−2 for a Ge content of 30%. An additional increase of the Ge content can be achieved by annealing in oxygen. The oxidation of Si1−xGex leads to the formation of SiO2 while the Ge atoms are rejected from the oxide leading to a pile-up of Ge below the oxidation front. The heterostructures were analyzed using X-ray diffraction, Rutherford backscattering/channeling spectrometry and transmission electron microscopy.
Effects of misfit strain on properties of ZnO films grown by pulsed laser deposition
Authors: Park M.C. , Yoon W.H. , Lee D.H. , Myoung J.M. , Bae S.H. , Lee S.Y. , Yun I.
Published: April 2011

A series of ZnO films with various thicknesses were prepared on (0001) sapphire substrate by pulsed laser deposition (PLD). Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis were utilized to investigate the effects of misfit strain on the surface morphology and the crystallinity. The electrical and optical properties of the films were also investigated as a function of the film thickness. It was found that the crystalline quality, electrical and optical properties of the films depended on the film thickness and were improved with increasing the film thickness. This is attributed to the fact that the films thinner than 400 nm are under the severe misfit strain, which decreases as the film thickness increases further.
Intermixing in Ge/Si(001) Islands: Elemental Content and Structure
Authors: Eshed A. , Zhu J. , Yan J. , Beserman R. , Weiss A. H.
Published: April 2011

We have investigated the shapes, thickness, density, composition, and quality of Ge/Si(001) islands grown by solid source molecular beam epitaxy in ultra high vacuum conditions. Nano crystals were formed by means of the Stranski-Krastanow “self assembly” growth mechanism. 5 nm of Ge were deposited on Si(001) substrates, at 500 °C, with deposition rate of 0.5 nm/min. Atomic force microscope measurements reveal islands of various sizes, ranging from 60 nm to 700 nm in diameter. Islands' density found to be correlated with their sizes, with denser areas containing mostly islands of the smaller sizes. Micro Raman spectroscopy, with probing spot of about 0.7 µm diameter, has been used to study the composition, thickness and crystalline quality of the islands. Data were taken at various points on the sample distinguishing between various islands' types. Combined analysis of Raman spectra and the micrographs reveal low amount of alloying (less than 30%) in all types of islands, with the larger islands showing the more amount of intermixing. High crystalline quality of the layers within the islands suggests negligible amount of dislocations.
Low Energy Plasma Enhanced Chemical Vapour Deposition - Plasma Enhanced Deposition of Epitaxial Si and Sige
Authors: Rosenblad Carsten , Kummera Matthias , Deller Hans-Rudolf , Graf Thomas , Dommann Alex , Hackbarth Thomas , Höck Georg , Müller Elisabeth , von Känel Hans
Published: April 2011

Low energy plasma enhanced chemical vapour deposition (LEPECVD) is a deposition technique developed for the epitaxy of Si and SiGe at ultra-high deposition rates. Due to a high current plasma discharge composed of low energy particles, a high plasma enhancement can be obtained without any accompanying plasma induced damage of the wafer surface. The most important application of LEPECVD so far is for compositionally graded relaxed SiGe buffer layers. Such relaxed buffer layers are demonstrated with end composition up to pure Ge and with a growth time below 1 hour. A p-type hetero-MOSFET formed in a SiGe channel compressively strained to a Si0.5Ge0.5 relaxed buffer layer, is demonstrated as one example where the high growth rates of LEPECVD allows the synthesis of devices which cannot be produced with an acceptable throughput with conventional deposition methods. The room temperature effective hole mobility of 760 cm2/Vs obtained on such devices demonstrates a high structural and electrical quality of the LEPECVD material.
Shape Transition in Self-Organized InAs/InP Nanostructures
Authors: Gutiérrez H.R. , Cotta M.A. , Carvalho M.M.G. de
Published: April 2011

In this letter we report the transition from self-assembled InAs quantum-wires to quantumdots grown on (100) InP substrates. This transition is obtained when the wires are annealed at the growth temperature. Our results suggest that the quantum-wires are a metastable shape originated from the anisotropic diffusion over the InP buffer layer during the formation of the first InAs monolayer. The wires evolve to a more stable shape (dot) during the annealing. The driving force for the transition is associated with variations in the elastic energy and hence in the chemical potential produced by height fluctuations along the wire. The regions along the wires with no height variations are more stable allowing the formation of complex, self-assembled nanostructures such as dots interconnected by wires.
Morphology of Self-Assembled InAs Quantum Dots on GaAs(001)
Authors: Arciprete F. , Patella F. , Fanfoni M. , Nufris S. , Placidi E. , Schiumarini D. , Balzarotti A.
Published: April 2011

We have followed by Atomic Force Microscopy (AFM) the epitaxial growth of InAs on GaAs(001) starting from the initial formation of a strained two-dimensional wetting layer up to the self-assembled nucleation and growth of 3D nanoparticles. In this work we underline many aspects of the morphology of this system, which substantiate the role either of kinetics on thermodynamics in the process of growth as well as the role of surface instabilities in controlling lateral ordering of the nanoaggregates.
Island and pit formation during growth and annealing of InGaAs/GaAs films
Authors: Riposan A. , Martin G.K.M. , Bouville M. , Falk M. L. , Millunchick J. Mirecki
Published: April 2011

The surface morphology near the onset of 3D roughening of In0.27Ga0.73As/GaAs films was investigated for films both immediately after growth and after annealing. As expected, 3D island nucleation coincides with the onset of strain relaxation at a critical thickness hc. As strain relaxation continues, pits form adjacent to 3D islands. The onset of the pit formation depends on the growth conditions, including the growth temperature and As overpressure, and the areal coverage of 3D islands. On average, pits form only after the area coverage of islands reaches ~50%. The islands and pits coalesce into ripple arrays as the film thickness increases. Films below and above the critical thickness for 3D roughening were annealed to study the stability of islands and pits. For films with thicknesses below hc, initially smooth surfaces evolve into islanded morphologies upon annealing. For films grown above hc which have both islands and pits on the surface, both islands and pits grow and coalesce during annealing. These results suggest that pit formation is favored, but it requires a minimum island coverage and/or wetting layer thickness in order to nucleate.
Atomic Self-ordering in Heteroepitaxially Grown Semiconductor Quantum Dots due to Relaxation of External Lattice Mismatch Strains
Authors: Möck Peter , Topuria Teya , Browning Nigel D. , Nicholas Robin J. , Booker Roger G.
Published: April 2011

Thermodynamic arguments are presented for the formation of atomic order in heteroepitaxially grown semiconductor quantum dots. From thermodynamics several significant properties of these systems can be derived, such as an enhanced critical temperature of the disorder-order transition, the possible co-existence of differently ordered domains of varying size and orientation, the possible existence of structures that have not been observed before in semiconductors, the occurrence of atomic order over time, and the occurrence of short range order when the growth proceeds at low temperatures. Transmission electron microscopy results support these predictions. Finally, we speculate on the cause for the observed increase in life time of (In,Ga)As/GaAs quantum dot lasers [H-Y. Liu et al., Appl. Phys. Lett. 79, 2868 (2001)].
Strain Accommodation and Relaxation Mechanisms in Epitaxially Grown Manganites
Authors: Casanove Marie-José , Baulès Pierre , Roucau Christian , Magnoux David , Bobo Jean-François , Bibes Manuel , Balcells Lluis , Fontcuberta Josep
Published: April 2011

Epitaxial growth of La1-x(SrorCa)xMnO3 manganites (LSMO or LCMO) has been successfully achieved on SrTiO3 (001) and MgO(001) substrates. We report the influence of the deposition conditions, in particular growth rate, annealing and nature of the substrate, on the state of strain in the manganite layers. Fully strained layers are reported at very slow growth rate on SrTiO3 substrates while misfit dislocations are clearly observed in layers grown on MgO and alsoin layers grown on SrTiO3, after annealing at high temperature. Besides, evidence is given for a rhombohedral (respectively orthorhombic) distortion relaxation in LSMO (respectively LCMO) layers. The microstructure of the manganite layers is analyzed taking into account their non-isomorphic growth on the cubic substrates.
Rapid Prototyping of Plastic Micro Devices by Excimerlaser Ablation
Authors: Klotzbuecher Thomas , Mirtaheri Peyman , Braune Torsten
Published: April 2011

Nowadays the application of micro devices in many fields like e.g. in the life sciences, chemistry and also optics strongly grows in importance. Micro structures often allow efficient processes with low resource consumption and the possibility of high integration. Typical examples are micro and nano titer plates for chemical screening or DNA chips for sequencing, micro mixers and reaction systems for synthesis on demand or micro optical elements like couplers for optical data transmission. Especially plastics are well suited for the cost effective large number fabrication, using high precision mould inserts with injection moulding or hot embossing. Since the micro devices become more and more complex (keywords: lab on a chip and micro total analysis systems, μ-TAS) the fabrication of mould inserts will be more expensive and time consuming. This is the reason why often methods of rapid prototyping are required for design qualification and functionality test purposes during the development. It will be demonstrated that Excimerlaser ablation is a well suited method for rapid prototyping of quasi-three-dimensional micro structures. Almost all polymers can be ablated by the UV laser radiation with very high accuracy, using mask projection techniques. Therefore, the choice of a suited polymer with adapted material properties like for e.g. chemical resistance, optical surface quality or bio-compatibility allows one to account for the requirements of the corresponding application. Moreover, the prototypes can easily be transformed into mould inserts for large number fabrication, using the Laser-LIGA technique. The corresponding technologies will be explained and demonstrated with the aid of several examples, especially taking into account the material aspects.
Laser Direct Writing of Hydrous Ruthenium Dioxide Micro-Pseudocapacitors
Authors: Arnold Craig B. , Wartena Ryan C. , Pratap Bhanu , Swider-Lyons Karen E. , Piqué Alberto
Published: April 2011

We are using a laser engineering approach to develop and optimize hydrous ruthenium dioxide (RuOxHyor RuO2·0.5 H2O) pseudocapacitors. We employ a novel laser forward transfer process, Matrix Assisted Pulsed Laser Evaporation Direct Write (MAPLE-DW), in combination with UV laser machining, to fabricate mesoscale pseudocapacitors and microbatteries under ambient temperature and atmospheric conditions. Thin films with the desired high surface area morphology are obtained without compromising their electrochemical performance. The highest capacitance structures are achieved by depositing mixtures of sulfuric acid with the RuO2·0.5 H2O electrode material. Our pseudocapacitors exhibit linear discharge behavior and their properties scale proportionately when assembled in parallel and series configurations.
Aerosol-Based Direct-Write of Biological Materials for Biomedical Applications
Authors: Marquez Gregory J. , Renn Michael J. , Miller W. Doyle
Published: April 2011

Applying life sciences and engineering principles to the study of cells and engineered tissue has resulted in various successes. These endeavors are poised towards development of functional neo-organs used as native tissue substitutes. Concurrent with this goal, research arenas are directed in the general areas of biocompatible polymer scaffolds, biomimmetic extracellular matrices, control of stem cell differentiation, biomolecule signaling, and directed material delivery. Optomec Inc. is developing an aerosol-based direct-write process for deposition of biological materials into three dimensional, micron-scale patterns. The process uses pneumatic atomization to produce aerosol droplets of proteinacious colloidal dispersions and whole cell suspensions. The droplets are entrained in an air stream and deposited with a proprietary deposition tool. The biological materials can be seeded into three dimensional polymer scaffolds and various substrate surfaces. Optomec's direct write process has applicability to the additive fabrication of engineered tissue. Other applications of the direct write tool include rapid prototyping of analytical biosensors, hybrid BioMEMS, and bio-chip microarray devices.
Analysis of Ion Implantation Damage in Silicon Wafers by a Contactless Microwave Diagnostic
Authors: Ahrenkiel Richard K. , Lojek B.
Published: April 2011

Rapid thermal annealing (RTA) of lattice damage created by heavy ion implantation damage is required to maintain the integrity of semiconductor material used for submicron-integrated circuit devices. A quick, efficient, and contactless diagnostic of the implantation damage is highly desirable in both research and production environments. A contactless measurement technique has been recently applied to this problem that uses a deeply penetrating low-frequency microwave probe frequency operating at 420 MHz. Here, we will demonstrate the use of this high frequency resonance-coupled photoconductive decay (RCPCD) technique, which, when combined with a tunable optical excitation source, enables us to map the radiation damage in boron and arsenic-implanted silicon wafers. We quantify the damage by mapping the minority-carrier lifetime as a function of optical penetration depth. In this work, we quickly and efficiently compared the effectiveness of various RTA processes by the RCPCD diagnostic.
AC Conductivity Based Microstructural Characterization of Yttria Stabilized Zirconia
Authors: Sauti G. , McLachlan D.S.
Published: April 2011

AC conductivity experiments, or Impedance Spectroscopy, at temperatures between 100 and 400°C, made on 8 mole % Yttria Stabilized Zirconia (8YSZ) with different grain sizes, are presented. The results are analyzed using Effective Media Theories, the Brick Layer Model and percolation theory. The results obtained are satisfactory, only if the measured frequency dependant complex conductivity parameters of the grains are inserted in the equations.
Combinatorial optimization of atomically controlled growth for oxide films by the carrousel type laser molecular beam epitaxy
Authors: Takahashi R. , Matsumoto Y. , Koinuma H. , Lippmaa M. , Kawasaki M.
Published: April 2011

A new combinatorial pulsed laser deposition system has been developed for rapid optimization of epitaxial growth process by using a carrousel type masking plate. Under in-situ monitoring of growing surface with reflection high energy electron diffraction, eight films with different compositions or preparation parameters can be fabricated on a single substrate. By using this system, we have succeeded in the one lot optimization of YBa2Cu3O7-d(YBCO), PrGaO3, SrO and BaO film growths on the B-site (TiO2) terminated SrTiO3(001) substrates. Key results from these experiments include the high sensitivity of YBCO film crystallinity to the laser focusing as well as of growth behavior of epitaxial SrO and BaO films to the crystal habit with the underlying atomic layers.
Characterization of Magnetic and Dielectric Properties on Y-Type Magnetoplumbite Epitaxial thin Films for High Frequency Application
Authors: Ueno K. , Ohkubo I. , Matsumoto Y. , Okazaki N. , Hasegawa T. , Itaka K. , Koinuma H.
Published: April 2011

Magnetic films for miniaturization of planar inductors operating at GHz frequencies require high resistivity and high ferro-magnetic resonance frequency. Y type magnetoplumbite Ba2Co2Fe12O22(Co2Y) is a candidate material to meet such requirements because it has about 10 &m resistivity and resonance frequency higher than 2 GHz. Recently we succeeded in the fabrication of Co2Y epitaxial thin film on MgAl2O4 substrate by combinatorial pulsed laser deposition technique [3]. Here, we report on the magnetic and dielectric properties of this film. The DC resistivity of the film was 7.5 &m. The dielectric constant at 1.25 GHz was measured by a microwave microscope to be 11.0. An easy axis coercive force and saturation magnetization were about 145 Oe and 2000 Gauss respectively, being close to those of bulk sample. Furthermore, the magnetic micro domain structures of Co2Y epitaxial thin films were observed by a scanning SQUID microscope.
Scanning Electron-Beam Dielectric Microscopy for the Temperature Coefficient Distribution of Dielectric Materials
Authors: Cho Yasuo
Published: April 2011

Studies on scanning electron-beam dielectric microscopy (SEDM) are reported. This microscopy technique is used for determining the temperature coefficient distribution of dielectric materials using an electron-beam as a heat source instead of a light beam as in photothermal dielectric microscopy. This microscopy technique, which has the ability to simultaneously observe SEM images and the material composition by EPMA, has a resolution better than that of photothermal dielectric microscopy. To demonstrate the usefulness of this technique, the two-dimensional image of a two-phase composite ceramic composed of TiO2 and Bi2Ti4O11 is measured. To shorten a measurement time, a new type of SEDM for measuring the real time transient response caused by a single pulsed electron-beam is also successfully developed. Finally, a quantitative measurement method of temperature coefficient is also developed.
Electrostatic Dispensing of Dry Dielectric Materials
Authors: Tupper Malinda M. , Chopinaud Marjorie E. , Ogawa Takamichi , Cima Michael J.
Published: April 2011

Dispensing micron-scale dielectric materials can be achieved through the use of dielectrophoresis. Electrodes are designed to create a nonuniform electric field. This method is expected to be applicable for transfer of a wide range of dielectric powders as well as small, shaped components. Small, 150 μm diameter silica spheres, as well as sodium fluorescein powder have been dispensed by this method. Selecting the appropriate electrode geometry and electric field intensity controls the amount collected. As little as 1.0 μg of sodium fluorescein powder, and as much as 16 mg of silica beads have been collected, and repeatability within 10 % of the total amount dispensed has been achieved.
Rapid and Quantitative Determination of Crystallization Tendency of Zinc Tellurite Glass Melt by Using Temperature-Gradient Furnace
Authors: Todoroki Shin-ichi , Matsumoto Takehisa , Inoue Satoru
Published: April 2011

Quantitative thermal stability test of glass materials against crystallization is accelerated through a vertical temperature-gradient furnace. In the furnace, zinc tellurite glass melt is sucked into a 75cm-long glass capillary tube (ID 1.5 × OD 8 mmø) and the tube is kept inside to be annealed under a temperature gradient of 300~800°C/50cm. The time to precipitate is determined to make a set of T-T-T (Time-Temperature-Transform) diagrams for different composition and thermal hysteresis. Crystallization is not observed for 65TeO2-35ZnO and 70TeO2-30ZnO (mol%) super-cooled glass melt after 4000s annealing but their stability decreased if the melts were once quenched to below their glass transition temperature before the annealing.