bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship Between Thermally Activated Atomic Diffusion Processes in Co-Cu Nanoscale Granular Films and Electric/Magnetic Properties
Authors: Spizzo F. , Ronconi F. , Vavassori P. , Bordin G. , Bisero D. , Pareti L. , Turilli G.
Published: April 2011

Co-Cu multilayer granular films deposited onto Si substrates have been submitted to thermal treatments in scanning mode. Their magnetisation and resistance have been studied after applying two different heating rates. The comparison between the experimental data measured before and after the treatment points out that the effect of the annealings depends strongly on the heating rate used. We also present XPS data collected as a function of depth to show how the different heating rate modify the composition and chemical environment produced by thermal treatments.
Understanding the Second Harmonic Generation of Light from Nanometal Composites
Authors: Sandrock M. L. , Foss Colby A.
Published: April 2011

We have synthesized two sets of nanometal composites of different metal concentrations via electrodeposition of gold into porous aluminum oxide membranes Within each set, both centrosymmetric and non-centrosymmetric particles were produced whose linear and nonlinear optical effects were investigated.

Because our method of template synthesis allows for the close examination of our composite materials in terms of shape, size. and symmetry, we can interpret the SHG response in terms of differences in local field enhancements of magnetic dipole and quadrupole modes.
Screen-Printed Dye-Sensitized Large Area Nanocrystalline Solar Cell
Authors: Gupta T.K. , Cirignano L.J. , Shah K.S. , Moy L.P. , Kelly D.J. , Squillante M.R. , Entine G. , Smestad G.P.
Published: April 2011

The fabrication and testing of screen printed dye-sensitized large solar cell (15 cm × 15 cm) based on nanocrystalline TiO2 is described. It is the largest photo-electrochemical (PEC) cell that is based on the dye sensitization of thin (8-18 μm) films of TiO2 nanoparticles in contact with a non-aqueous liquid electrolyte. The cell has the potential to be a low cost, commercial, environmentally friendly, photovoltaic option. Surface as well as electrical characterization, of the nanostructured PEC cells have been performed. The efficiency of these large commercial cells are compared to the laboratory-made small PEC cells. Key words: Photoelectrochemical, solar cells, nanocrystalline, dye-sensitized
Intercluster Interaction of TiO2 Nanoclusters Using Variable-Charge Interatomic Potentials
Authors: Ogata Shuji , Iyetomi Hiroshi , Tsuruta Kenji , Shimojo Fuyuki , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: April 2011

A new interatomic potential has been developed for molecular-dynamics simulations of TiO2 based on the formalism of Streitz and Mintmire [J. Adhesion Sci. Technol. 8, 853 (1994)], in which atomic charges vary dynamically according to the generalized electronegativity-equalization principle. The present potential reproduces various quantities of rutile crystal including vibrational density of states, static dielectric constants, melting temperature, elastic moduli, and surface relaxation. Calculated cohesive-energy and dielectric constants for anatase crystal agree well with experimental data. The potential is applied to TiO2 nanoclusters (size 60-80Å) for both anatase and rutile phases to analyze their equilibrium configuration and spacecharge distribution. Stable double-charge layer is found in the surface region of a spherical nanocluster for both rutile and anatase, resulting in enhanced Coulomb-repulsion between the nanoclusters at close proximity.
First Observation of Atomic Long Range Ordering in Metal-Oxide Based ZnMgO Wide Bandgap Heterostructures
Authors: Vispute R. D. , Choopun S. , Li Y. H. , Chalk D. M. , Ogale S. B. , Sharma R. P. , Venkatesan T. , Iliadis A.
Published: April 2011

We report the first observation of atomic long range ordering in the metal-oxide based wide bandgap (3.68 eV) ZnMgO alloy semiconductor thin films grown on sapphire (0001) by pulsed laser deposition. The ZnMgO system has the hexagonal wurtzite structure. The atomic ordering was deduced from the observations of forbidden x-ray diffraction peaks in the wurtzite structure. We show that under optimum thin film growth conditions, Zn and Mg preferentially occupy hcp sublattice. The relative intensity of the superlattice peak was largest for the Mg content in the range of 10%, which is about 50% of the solubility of Mg in ZnO. The observation of long range order in ZnMgO alloy semiconductor is quite important in the context of understanding issues related to the growth kinetics, surface reconstruction, and phase stability of metal-oxide based heterostructures and devices.
Correlation of Ingap(001) Surface Structure During Growth and CuptB-Type Bulk Ordering
Authors: Zorn M. , Kurpas P. , Bhattacharya A. , Weyers M. , Zettler J.-T. , Richter W.
Published: April 2011

The mechanism causing the CuPtB-type ordering of InGaP grown lattice matched to GaAs was investigated by in-situ reflectance anisotropy spectroscopy (RAS/RDS). Experiments were performed during InGaP growth in metal-organic vapour phase epitaxy (MOVPE). From the experiments it can be concluded that bulk ordering only occurs when InGaP growth is performed under phosphorus-rich (2×1)-like surface conditions. Bulk ordering completely disappears under growth conditions which cause a less-phosphorus-rich (2×4)-like surface dimer configuration.
High Resolution Analysis of Embedded Quantum Dots
Authors: Harvey A. J. , Davock H. J. , Goodhew P. J.
Published: April 2011

A key piece of information in the understanding of quantum dot behaviour is the composition of the dot after any capping and/or annealing processes. It is important to know the composition and uniformity of the dots after they have been embedded in a semiconducting matrix, which usually contains one or more of the elements in the dot. This is a classically difficult analytical problem for any TEM technique. This problem has been approached by developing a model of the interaction between the electron probe and any dot/wettinglayer/matrix configuration. This model predicts the shape of an analytical line scan for any particular configuration and includes the effect of beam broadening on the analysis of dots at different depths within the thin section. The results are compared with STEM analyses of InAs dots in a GaAs matrix.
Inas Nanostructures in a Silicon Matrix: Growth and Properties
Authors: Cirlin G. E. , Egorov V. A. , Petrov V. N. , Golubok A. O. , Komyak N. I. , Polyakov N. K. , Samsonenko Yu. B. , Denisov D. V. , Volovik B. V. , Ustinov V. M. , Alferov Zh. I. , Ledentsov N. N. , Heitz R. , Bimberg D. , Zakharov N. D. , Werner P. , Gösele U.
Published: April 2011

Under certain growth conditions InAs/Si heteroepitaxial growth proceeds via Stranski-Krastanow or Volmer-Weber growth modes depending on the growth parameters. Critical thickness at which three dimensional InAs islands start to appear at the Si(100) surface is within the range of 0.7 - 4.0 monolayers (substrate temperature range is 350°C - 430 °C). Their size depends critically on the growth conditions and is between 5 nm and 80 nm (uncapped islands). Critical lateral size of the coherent (Si capped) dislocation-free island is equal to 2 - 5 nm depending on the island height. Islands having larger size are dislocated. Optical properties of InAs nanoscale islands capped with Si reveal a luminescence band in the 1.3 μm region.
Mbe Growth, Structural and Optical Characterization of Inas/Ingaaias Self-Organized Quantum Dots
Authors: Ustinov V. M. , Zhukov A. E. , Kovsh A. R. , Maleev N. A. , Mikhrin S. S. , Musikhin Y. G. , Tsatsul'nikov A. F. , Volovik B. V. , Bedarev D. A. , Maximov M. V. , Livshits D. A. , Bert N. A. , Kop'ev P. S. , Alferov Zh. I. , Ledentsov N. N. , Bimberg D.
Published: April 2011

InAs quantum dots (QD) have been shown to extend the optical emission range for III-V heterostructures pseudomorphically grown on GaAs substrates. One of the ways to achieve 1.3 micron emission from the InAs QDs is to overgrow them with an In-containing alloy layer. In the present work we study structural and optical properties of InAs/In(Ga,Al)As QD structures grown by MBE on GaAs substrates using transmission electron microscopy (TEM), photoluminescence (PL), and electroluminescence (EL). We show that the main reason for the increase in the PL wavelength is the phase separation of the In(Ga,Al)As alloy stimulated by the InAs islands and the effective matrix bandgap plays a minor role. As the result of the local composition modulation, the effective volume of a QD is increased due to the enhancement of In concentration in the vicinity of the InAs island. We study how the effective thickness of InAs and InGaAs affect the crystal perfection and PL peak energy. Using the AlGaAs as a matrix also led to the noticeable red shift of the quantum dot PL line as compared to the GaAs matrix. Possible reasons for this unexpected phenomenon are discussed. Characteristics of the GaAs-based vertical cavity surface emitting structures and high power CW RT edge-emitting lasers for the 1.3 micron range using these QDs are be presented.
Growth Temperature Dependence of Size Distribution of Selfassembled Inas Quantum Dots on Gaas(001): From Diffusion- to Strain-Limited Growth
Authors: Yuan J. , Lian G. D. , Li Z. Y. , Ritchie D. A. , Thompson R. M. , Shields A. J. , Farrer I. , Brown L. M.
Published: April 2011

We have investigated the molecular beam epitaxy (MBE) growth of buried InAs quantum dots on GaAs (001) surface, as a function of deposition temperature, by transmission electron microscopy (TEM) and photoluminescence (PL). We found that the dot growth at low temperature is controlled by diffusion-limited aggregation. As the growth temperature increases, this growth mode is modified by misfit strain, resulting in a narrowing of the size distribution. However, we did not find any evidence for a thermodynamically optimized size. In addition, we found that the optical properties of the quantum dots does not correlate directly with the geometric size of the quantum dots, indicating a complex internal structure for quantum dots grown at high growth temperature.
Photoreflectance Investigation of Inas/Gaas Self-Assembled Quantum Dots Grown by Almbe
Authors: Geddol M. , Ferrinm R. , Guizzetti G. , Patrini M. , Franchi S. , Frigeri P.
Published: April 2011

Photoreflectance measurements have been performed in the 0.8–1.5 eV photon energy range and at temperatures from 80 to 300 K on stacked layers of InAs/GaAs self-assembled quantum dots (QDs) grown by Atomic-Layer Molecular Beam Epitaxy. The spectral features due to the QD optical response were analyzed by using lineshape models characteristic of modulation spectroscopy of confined systems. The dependence of the ground state transition energy on the number of stacked QD layers is investigated and it is shown that Coulomb interaction can account for the observed different behavior of the ensemble optical response of QD families characterized by different morphologies and coexisting in the same sample.
Soft X-Rays for Deep Sub-100 Nm Lithography, with and Without Masks
Authors: Smith Henry I. , Carter D. J. D. , Ferrera J. , Gil D. , Goodberlet J. , Hastings J. T. , Lim M. H. , Meinhold M. , Menon R. , Moon E. E. , Ross C. A. , Savas T. , Walsh M. , Zhang F.
Published: April 2011

The development of micro- and nanofabrication, their applications, and their dependent industries has progressed to a point where a bifurcation of technology development will likely occur. On the one hand, the semiconductor industry (at least in the USA) has decided to develop EUV and SCALPEL to meet its future needs. Even if the semiconductor industry is successful in this (which is by no means certain) such tools will not be useful in most other segments of industry and research that will employ nanolithography. As examples, MEMS, integrated optics, biological research, magnetic information storage, quantum-effect research, and multiple applications not yet envisioned will not employ the lithography tools of the semiconductor industry, either because they are too expensive, insufficiently flexible, or lacking in accuracy and spatial-phase coherence. Of course, direct-write electron-beam lithography can meet many of these non-semiconductor-industry needs, but in other cases a technique of higher throughput or broader process-latitude is necessary. Our experience at MIT in applying low-cost proximity x-ray nanolithography to a wide variety of applications leads us to conclude that this technology can provide an alternative path of a bifurcation. A new projection lithography technique, zone-plate-array lithography (ZPAL), does not require a mask, can operate from UV to EUV to x-rays, and has the potential to reach the limits of the lithographic process.
Polymer-Inorganic High Contrast and High Sensitivity Resists for Nanolithography
Authors: Wu Hengpeng , Wang Jianzhao , Gonsalves Kenneth E.
Published: April 2011

Polyhedral oligosilsesquioxane methacrylate (POSSMA)/methyl methacrylate(MMA)/tert-butyl methacrylate(TBMA)/tert-butyl acrylate(TBA) copolymers were synthesized by solution polymerization. Their preliminary lithography-related properties were studied. It is shown that the mass ratio of MMA/POSSMA=85.8/14.2 leads to an X-ray resist with a high contrast of 23.5 without sacrificing the sensitivity(1350 mJ/cm2) which remains comparable to that of standard PMMA. By careful manipulation of components and compositions, this generic type of polymer could potentially be utilized as a DUV or e-beam resist as well.
Resist Materials Providing Small Line-Edge Roughness
Authors: Namatsu Hideo , Yamaguchi Toru , Kurihara Kenji
Published: April 2011

Our research focuses on the line-edge roughness of resist patterns and how to reduce it in order to establish nanolithography as a practical tool. Commercially available e-beam resists exhibit a line-edge roughness of 3 nm (σ) or more. It is caused mainly by polymer aggregates in the resist. During development, they are extracted through dissolution of the surrounding polymer matrix. That is, the aggregates themselves dissolve more slowly than the surrounding matrix; and those that remain embedded in the resist produce line-edge roughness. To reduce the roughness, the effect of the aggregates must be suppressed. One way of doing this is to use a resist containing small aggregates. A good candidate is hydrogen silsesquioxane, which has a three-dimensional framework. Another way is to use a resist in which the aggregates are linked together, which makes them difficult to extract during development. A good example is an acrylate-type resist with a cross-linker mixed in.
Lithographic Materials Technologies: 193 nm Imaging and Beyond
Authors: Reichmanis Elsa , Nalamasu Omkaram , Houlihan Francis M. , Gabor Allen H. , Neisser Mark O. , Bowden Murrae J.
Published: April 2011

Advances in microlithographic resist materials have been a key enabler of the unabated productivity gains in the electronics industry and are continuing to help push the ultimate limits of optical lithography. The challenges posed by the introduction of new optical lithography technologies that use smaller wavelengths have been successfully met by the materials community through the design of chemically amplified resist technologies and 193 nm resist materials based on aliphatic polymers and dissolution inhibitors. With continued advances in resist materials, exposure systems and resolution enhancement and mask technologies, optical lithography will be capable of patterning ≤ 0.1 μm design rule devices in future fabs.
A kinetic Monte Carlo Model of Silicon CVD Growth from a Mixed H2/siH4 Gas Source
Authors: Fearn M. , Sayed M. , Jefferson J. H. , Robbins D. J.
Published: April 2011

We report the development of an atomistic scale Kinetic Monte Carlo model of silicon CVD growth. By employing a variable time step algorithm, simulations have been performed over a range of time scales, enabling direct comparison with experimental data. The validity of using the kinetic theory of gases for evaluating steady state incoming particle fluxes within the model is demonstrated by comparison with computational fluid dynamics simulations. The model is applied to study hydrogen desorption rates from Si(001) and the dependence of silicon growth rate on substrate temperature, with results found to be in good agreement with experimental data. An experimentally observed decrease of growth rate with increasing H2 partial pressure is also reproduced by the model and shown to be caused by a decrease in silane adsorption on a hydrogen-rich surface.
Molecular Dynamics Simulations of Solid Phase Epitaxy of Si:Growth Mechanism and Defect Formation
Authors: Motooka T. , Munetoh S. , Nisihira K. , Moriguchi K. , Shintani A.
Published: April 2011

We have investigated crystal growth and defect formation processes during solid phase epitaxy (SPE) of Si in the [001] direction based on molecular dynamics (MD) simulations using the Tersoff potential. From the Arrhenius plot of the growth rates obtained by MD simulations, we have found that the activation energy of SPE at lower temperatures is in good agreement with the experimental value, approximately 2.7 eV, while it becomes lower at higher temperatures. This can be attributed to the difference in the amorphous/crystalline (a/c) interface structure. In the low temperature region, the a/c interface is essentially (001) and the rate-limiting step is two-dimensional nucleation on the (001) a/c interface. On the other hand, the a/c interface becomes rough due to (111) facets formation in the high temperature region and the rate-limiting step is presumably a diffusion process of Si to be trapped at the kink sites associated with these facets. Defect formation is found to be initiated by 5-membered rings created at the a/c interface. These mismatched configurations at the interface give rise to (111) stacking faults during further SPE growth.
Multimillion-Atom Simulations of Atomic-Level Surface Stresses and Pressure Distribution on InAs/GaAs Mesas
Authors: Su Xiaotao , Kalia Rajiv K. , Madhukar Anupam , Nakano Aiichiro , Vashishta Priya
Published: April 2011

Large-scale molecular dynamics simulations are performed to investigate the atomiclevel stresses on InAs/GaAs mesas. The simulations are based on an interatomic-potential scheme for InAs/GaAs systems which depends on the local chemical composition. Multiresolution techniques are used to speed up the simulations. InAs/GaAs square mesas with { 101 }-type sidewalls are studied. The atomic-level pressure distribution and surface atomic stresses on the sidewalls with 12, 10, 8 and 6 monolayers of InAs overlayers have been calculated.
Nanostructure Fabrication Using Electron Beam
Authors: Matsui Shinji
Published: April 2011

Nanofabrication strategies developed by using electron beam (EB) are described. Ten-nm structures of organic positive and negative resist patterns have been achieved by using a commercially available EB lithography system. As one of the applications of EB nanolithography to nanodevices, an electrically variable shallow junction MOSFET (EJ-MOS) is described. As a novel approach, material-wave nanotechnology using de Broglie wave has been developed. Line and dot patterns with 100-nm periodicity were exposed on a PMMA resist by EB holography with a thermal field-emitter gun and an electron biprism. This technique allows us to produce nanoscale periodic patterns. Furthermore, the possibility of nanostructure fabrication by atomic-beam holography has been demonstrated by using a laser-trap technique and a computer-generated hologram made by EB lithography.
The Novel Technique of Nanometer-Size Fabrication by Using Conventional Photolithography
Authors: Hashioka Shingi , Matsumura Hideki
Published: April 2011

A novel method to prepare nanometer-size patterns by using currently available massproduction technology is proposed. In this study, a contact pattern-mask with nanometersize slit is fabricated by combination of photolithography and anodic oxidation of metal. The slit width of the pattern-mask can be controlled in the order of nano-meters by anodic voltage during oxidation of side-wall of the metal. 10nm width trench is formed in Si substrate by using such nanometer slit-mask. It is suggested that the technique can be utilized as fabrication process of the nano-scale devices.
Fabrication of Isolated Nanoparticle Circuitry Via Lensless Optical Tweezing (“L. O. T. s”)
Authors: Dearing M. T. , Spalding G. C.
Published: April 2011

We propose a novel method for trapping a nanometer-scale particle into a stable structure useful for a variety of interesting electrical measurements. The particle to be trapped can be dielectric or metallic, magnetic or non-magnetic. Our methodology was developed, in part, to ensure the absence of extraneous nanoparticles in the region of the device under test; it also allows a possible feedback mechanism to indicate when a nanoparticle has been successfully trapped. In particular, we irradiate a substrate containing a tiny etch-pit hole. On the transmission side of the substrate, the diffracted or evanescent optical fields should contain large enough gradients to localize a nanoparticle to the region of the hole.
Molecular Scale Electronics. Critical Nanolithography Issues of Synthesis and Addressing
Authors: Huang S. , Mickelson E. T. , Rawlett A. M. , Asplund C. L. , Cassell A. M. , Kozaki M. , Burgin T. P. , Jones l. , Tour J. M. , Myrick M. L. , Van Patten P. G. , Chen J. , Zhou C.-W. , Muller C. J. , Deshpande M. R. , Reed M. A. , Bumm L. A. , Cygan M. T. , Dunbar T. D. , Weiss P. S. , Allara D. L.
Published: April 2011

As we rapidly approach the point at which solid-state electronic devices cease to be made any smaller, molecular scale electronics offers, perhaps, the best chance for a continued miniaturization of computational devices. We must, however, completely re-think our approach to lithography. Presented in this paper are our solution-phase and solid-support based syntheses of molecular wires of precise length and dimensions, and our methods of addressing these wires via molecular “alligator clips” to gold and platinum electrodes of macroscale dimensions.
Resist Materials and Nanolithography
Authors: Dobisz Elizabeth A.
Published: April 2011

The work focuses on lithographic processes and materials for sub-50 nm lithography. Lithographic results of polymethyl methacrylates of molecular weights of 50,000, 100,000, 496,000, and 950, 000 are compared. It was found that the molecular weight and developer concentration do not affect smallest linewidth, within experimental error. However, the molecular weight does affect the line-to-line resolution in dense gratings of 40–60 nm in contrast and developer induced swelling. 40 nm period gratings are shown. The work next examines the use of chemically amplified resists for nanofabrication, with a focus on SAL-601. Sub-50 nm lines are defined with latitude of an order of magnitude in dose and a factor of two in post exposure bake time. The results are modeled with a diffusion reaction kinetic model and an approach to optimize resolution and reproducibility is presented. Challenges to attaining the ultimate resolution and line-to-line resolution in polymeric resists include contrast, mechanical stability, swelling, and adhesion. Metal binding self assembled monolayers (SAMs) are presented a class of resists, that circumvent the latter three complications. Work at the Naval Research Laboratory on SAM resists is outlined.
Liquid Phase Diffusion Bonding for Thermoelectric Material Pb-Sn-Te
Authors: Shinohara Y. , Hashimoto M. , Imai Y. , Isoda Y. , Nishida I. A.
Published: April 2011

Liquid phase diffusion bonding was applied to the development of the joined thermoelectric material Pb-Sn-Te, which was expected to be superior to the monolithic Pb-Sn-Te. A Sn sheet 50μm thick was used for the inserted material. The sheet was sandwiched between Pb-Sn-Te segments with different hole concentrations, and subsequently the bonding was performed under 2MPa at 700K for 15min in Ar. The Sn sheet was changed to a SnTe interfacial layer of less than 10μm in thickness. The interfacial layer showed high toughness, and good ohmic and thermal contact up to 550K. Liquid phase diffusion bonding was an excellent technique for joining of thermoelectric material Pb-Sn-Te.
Optimisation of Adhesion at Transition Metal-Oxide Interfaces by Processing at Well-Chosen Oxygen Activity
Authors: Backhaus-Ricoult M.
Published: April 2011

Transition metal-oxide interfaces suffer within their thermodynamic stability range Gibbs' adsorption and show important changes in chemical composition with oxygen activity. As a consequence, specific free interfacial energy and adhesion energy also vary with oxygen activity. Adhesion at a given non-reactive transition metal-oxide interface can then be optimised by establishing the proper oxygen activity during processing or by a post-treatment at the interface.

In the present work, the approach of Gibbs' adsorption is extended to crystalline, anisotropic (special) transition metal-oxide interfaces. It is demonstrated that interfacial energy varies with oxygen activity. The variation in energy is studied for different adsorption energies, temperatures and interfacial planes.
Annealing Effects on Interfacial Fracture of Gold-Chromium Films in Hybrid Microcircuits
Authors: Moody N. R. , Adams D. P. , Volinsky A. A. , Kriese M. D. , Gerberich W. W.
Published: April 2011

In this study, stressed overlayers and nanoindentation were used to study the effect of elevated temperature on the resistance to interfacial fracture of gold-chromium films in hybrid microcircuits. The samples were prepared by sputter deposition of gold films and chromium adhesive layers onto sapphire substrates. Some films were left in the as-deposited condition for testing. Others were annealed until either most or all the chromium adhesive layer had diffused from the substrate interface. Stressed overlayers and nanoindentation were then used to drive interfacial delamination and blister formation. From these blisters, interfacial fracture energies were determined using mechanics-based models modified for multilayer film effects. The results clearly showed that the chromium interlayers increased interfacial fracture energy. However, they showed an even greater increase in fracture energy after diffusion had reduced the continuous chromium adhesion layer to a solid solution of gold and chromium, suggesting two different mechanisms act to control resistance to interfacial fracture in these films.
Interface Properties of Ceramic Composites at High Temperature
Authors: Zhou X.-F. , Marston C. , Nutt S. R.
Published: April 2011

For high-temperature performance of ceramic composites, interfaces are designed to provide toughness through debonding while resisting thermal oxidation in aggressive environments. Thus, the evaluation of interfacial properties at high temperatures is of critical importance. In recent work at USC, interfacial properties were measured at high temperatures by single fiber pushout tests. Six advanced ceramic composites were selected to perform pushout testing at 20–1000°C. Variation in interface designs and effects of thermal history were evaluated with respect to interface failure strength. At higher temperatures, the average interfacial bond strength was often higher. SEM observations were correlated with pushout measurements to evaluate the interfacial behavior.
Effect of Self-Assembling Monolayers (SAMs) on Ice Adhesion to Metals
Authors: Peng S. L. , Petrenko V. F. , Arakawa M.
Published: April 2011

In this research we used an original method to study the role of hydrogen bonding in ice adhesion and to minimize the effect of this mechanism on ice adhesion. We coated metals (Au and Pt) with a mono-molecular layer of specific organic molecules that had either strong hydrophobic properties (CH3(CH2)11SH) or strong hydrophilic properties (OH(CH2)11SH). To determine the contribution of hydrogen bonding to ice adhesion, self-assembling monolayers (SAMs) of varying degrees of hydrophobicity/hydrophilicity were created by mixing the hydrophobic and hydrophilic components. All of the SAMs were composed of similar molecules that differed only in their outermost groups, OH- and CH3-. Thus, when the SAMs were grown on the same substrate (almost atomically smooth metal coatings), any differences in their adhesion to ice were due to differences in the hydrogen bonding between the ice and SAMs. The SAMs structure and quality were examined with scanning force microscopy (SFM) and the degree of the SAM's hydrophobicity/hydrophilicity was characterized by the contact angle of water on the monolayers. We then froze water on the SAMs and measured the shear strength of the ice/SAM/metal interfaces. Possible damage to the interfaces was examined with SFM after the ice had melted. We found a good correlation between the contact angle of water and the ice adhesion strength and determined the fraction of ice adhesion caused by hydrogen bonding.
Ultrathin Alumina Films on Metallic Substrates: Structure and Metal Adsorption
Authors: Jennison Dwight R. , Bogicevic Alexander
Published: April 2011

First principles density functional calculations are used to study the structure and properties of ultrathin films of alumina on Al(111) and Ru(0001) substrates. We focus on ∼5 Å two O-layer films, naturally produced by oxidizing NiAl, Ni3Al, and Al deposited on Ru(0001). The interface consists of chemisorbed l×1 oxygen on the underlying metal [1], with a nearly coplanar layer of Al2O3 above. The lowest energy structure of the Al-sublattice is found to consist of zig-zag rows of octahedral and tetrahedral Al ions, resembling the bulk κ-phase. Eleven different adsorbed metals, spanning the periodic table, have been studied [2]. At low coverage the bond is purely ionic; at high coverage most metals bind principally by polarization. Contrary to speculations, isolated vacancies are found on MgO(100) not to directly promote metal nucleation [3], and we suggest this behavior is general. However, ad-OH is found not only to promote island nucleation, but can also, in high concentrations, produce wetting of alumina by Cu [4].
Wetting Transitions of Grain Boundaries
Authors: Blendell John
Published: April 2011

It has been shown that the concepts used to determine the equilibrium shape of crystals can be extended to determine the conditions under which grain boundaries will be fully wetted, partially wetted, or not wetted by a second phase. Recent experimental observations on the equilibrated morphologies of solid or fluid wetting phases along grain boundaries, reveal features that are predicted, and in some cases required, by this construction. Theory distinguishes between cases where surfaces are smoothly curved or where there are facets, edges and corners. In the latter case the conventional comparison of the energy of the original grain boundary with the sum of the surface energy of the two surfaces of the wetting layer leads to erroneous predictions. The correct predictions are obtained by comparing the Wulff shape of the grain boundary (the interfacial energy minimizing shape for a fixed volume of material) with a carefully defined sum of Wulff shapes of the surfaces of the wetting layer. Where orientations that are wetted join with those that are not, there is almost always an abrupt change of orientation. Faceting on two hierarchical levels can occur. Microscopic morphology changes along macroscopically curved surfaces follow well defined rules predicted by theory. The analogy between the thermodynamics of interface faceting and phase transformations allows the well known concepts of phase equilibria to be used to understand the predicted structures. The predictions of the model will be used to identify the nature of the faceting observed in alumina in the presence of a second phase.
Enhancing Oxidation Performance by Control of Interfacial Segregation and Microstructural Design
Authors: Alexander Kathleen B. , Pint Bruce A. , Tortorelli Peter F.
Published: April 2011

Thermally-grown oxide scales on high temperature alloys can provide oxidation protection if they are slow-growing, dense and adherent to the substrate. The factors affecting the integrity of the metal/oxide interface during dynamic oxidation processes are complex and include interfacial segregation, interface morphology, near-interface substrate properties, as well as the development of stresses in the growing oxide scale. Minor additions of reactive elements (RE) to the base metal have been shown to improve the oxidation performance of many high temperature materials. Studies on a variety of alloys have shown that the presence of reactive elements in the alloy affects segregation processes at both the metal/oxide and oxide/oxide interfaces. Whereas segregation to the metal/oxide interface can affect the scale adherence, segregation to the oxide/oxide interfaces in RE-containing systems has been proposed to result in changes in transport mechanisms as well as changes in the scale microstructure itself. High spatial resolution analytical electron microscopy techniques have been used to provide information on the microstructure and microchemistry of the scale and the metal/oxide and oxide/oxide interfaces. In general, in systems which exhibit improved oxidation performance, a consistent set of interfacial segregation phenomena and microstructural features were observed. Examples will be shown from a variety of nickel- and iron-based alumina formers. These kinds of studies, combined with traditional scanning electron microscopy studies of oxide scales can lead to the development of a more complete link between RE doping, interfacial segregation, interfacial/scale microstructure, and oxidation performance.
Ab-Initio Study of the Local Bonding at Metal-Ceramic Heterophase Boundaries
Authors: Köstlmeier S. , Elsässer C.
Published: April 2011

The adhesion geometries of the (100) heterophase boundaries between the metals Al or Ag and spinel (MgAl2O4) were determined by density-functional calculations employing a mixed-basis pseudopotential method. The results compare well with high-resolution transmission-electronmicroscopy studies which were carried out in parallel. An analysis of the calculated electronic structures shows that the strong adhesion of Al on spinel is mediated by directional bonding. The comparatively weak interaction of spinel with Ag is dominated by polarization effects which can be classified as originating from an image-charge interaction. Additionally, the effects of changes in stoichiometry and of segregated substitutional atoms at the interface were analyzed in terms of the excess of the corresponding component at the interface. The implications for the geometric structure and the related mechanical properties at the metal-ceramic junctions are discussed.
Molecular Simulations of Tilted Chain Crystal - Amorphous Interfaces in Polymers
Authors: Gautam S. , Balijepalli S. , Rutledge G. C.
Published: April 2011

Semi-crystalline polymeric materials exhibit metastable interfaces which must simultaneously feature molecular connectivity through chain bonding and disorder across the interface. To address this, off lattice molecular simulations have been constructed to capture the structure and properties of crystal-amorphous interfaces in polyethylene with freely rotating chains. Monte-Carlo simulations were performed on systems having {001 }, {201} and {502} interfaces (polymer chains tilted to the lamella normal by 0°, 34.4° and 41° respectively.)

Results of the simulations reveal changes in interfacial structure with variation in the chain-tilt angle. The degree of tight folding decreases with increasing tilt, from predominantly [110] loops in the {001} interface to [200] and [310] loops on the other interfaces. The topology shifts towards an increase in loosely folded loops along with longer bridges and tails. The results also compare well with a Gaussian chain length distribution model. The {201} interface exhibits the lowest interfacial energy, in apparent agreement with experimental data.
Atmoic-Scale Control of Oxide Substrate Surface/Termination and Novel Heteroepitaxial Growth
Authors: Yoshimoto Mamoru , Mizuno Keisuke , Miyahara Takafumi
Published: April 2011

Atomic-scale surface/termination of single-crystal oxide substrates were examined by coaxial impact collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). CAICISS enabled us to determine the terminating atomic species and their arrangements of single crystal oxide substrates and epitaxial oxide films. Through thermal-annealing of the single crystal oxide substrates, atomically flat terrace and stepped structures were developed on the surface. The molecular layer-by-layer growth was verified by in situ monitoring of reflection high energy electron diffraction (RHEED) intensity oscillation. The atomic-scale substrate engineering made it possible to attain the novel heteroepitaxial growth such as step-decoration epitaxy resulting in the nanowire structures and diamond epitaxy on the ultrasmooth sapphire substrate. The diamond films could be grown epitaxially only on the atomically flat sapphire substrates by pulsed laser ablation of graphite. The novel application of the ultrasmooth sapphire substrate to the AFM observation stage for DNA molecules was also presented.
Si/SiC UHV Direct Wafer Bonded Interface Structure
Authors: Kim M.J. , Xu Hong , Liu R.-J. , Cox M.J. , Carpenter R.W.
Published: April 2011

Planar (001)Si/(0001) Si-terminated 6H-SiC interfaces were synthesized by UHV diffusion bonding of cleaned, on-axis and vicinal wafers at 1100°C for 5 hours, at MPa pressure. The interfaces were crystalline up to their defining plane, without nanospectroscopically detectable impurities. The crack opening tests showed the interfaces were stronger than the Si substrates. Oxygen on the substrate surfaces resulted in silicon carbide on insulator (SiCOI) interface formation.
Low-Pressure Chemical Vapor Deposition of Borosilicate Glasses and their Application to Wafer Bonding
Authors: Hansen Darren M. , Moran Peter D. , Kuech T. F.
Published: April 2011

The essential features of the deposition process and the film properties of borosilicate glasses are presented here as an alternative to pure SiO2in wafer bonding and compliant substrates. While the deposition of SiO2 is a well-studied system, the deposition of boron-doped films is less understood. The deposition rate of the SiO2 mole fraction in the films was accelerated by the presence of trimethylborate and oxygen and this is associated with an increased adsorption of the tetraethylorthosilicate related precursor in the presence of boranols. Typical deposition conditions result in borosilicate glass films with an r.m.s. roughness of ∼0.5 nm as measured by atomic force microscopy. Annealing the films at temperatures above 550°C reduces the film roughness via glass reflow. Room temperature bonding of these films was achieved after a 250 WO2 plasma surface treatment. Fourier-transform infrared investigations of the bonded interface revealed the importance of the role of surface OH and H2O groups in the bonding of these films.
The Effect of Stress in the PdGe Mediated Solid Phase Epitaxial Growth of Ge on GaAs
Authors: Radulescu Fabian , McCarthy John M.
Published: April 2011

The residual stress and the microstructure associated with it were studied in connection with the Pd-Ge ohmic contact formation on GaAs. Evaporated Pd (20 nm) / Ge (150 nm) / Pd (50 nm) thin film stacks on GaAs were annealed at various temperatures and the resulting microstructures were investigated by transmission electron microscopy (TEM). Micro-cantilever beam structures were fabricated with a focused ion beam (FIB) workstation and the residual stress present was calculated from the deflection magnitude. It was found that Ge solid phase epitaxial (SPE) growth on GaAs is associated with a stress relaxation of the thin film system. A new model that suggests the tensile stress induced by the intermediate layer may play an important role in the SPE growth mechanism is proposed. Other cases of solid phase heteroepitaxial growth with an intermediate medium, such as Ge/Au/Si, Co/Ti/Si (the TIME method) and Co/SiOx/Si (the OME method) are discussed in light of this newly proposed model. Also, the possibility of using controlled stress to engineer new methods for growing SPE based heterostructures will be presented.
MBE Growth and Ultrahigh Temperature Processing of High-Quality AlN Films
Authors: Fan Z.Y. , Rong G. , Newman N. , Smith David J. , Chandrasekhar D.
Published: April 2011

Molecular beam epitaxial growth of AlN on sapphire and 6H-SiC has been performed utilizing mono-energetic activated nitrogen ion beams (2-80 eV kinetic energies). The growth temperature of AlN in MBE is found to be limited by the sticking coefficient of incident reactants. The combination of elevated growth temperatures (1050-1150°C), high kinetic-energy reactive nitrogen (>40 eV) and post-growth thermal processing (1150-1350°C) produces high-quality AlN thin-f ilms with narrow rocking curve widths (<2 arcmin) and low dislocation densities (<∼3×108cm−2). In contrast, the use of in-situ step anneals during synthesis did not achieve similar quality materials.
The Use of AlN Interlayers to Improve GaN Growth on A-Plane Sapphire
Authors: Koleske D.D. , Twigg M.E. , Wickenden A.E. , Henry R.L. , Gorman R.J. , Freitas J.A. , Fatemi M.
Published: April 2011

The lack of a suitable, lattice matched substrate for the growth of the group III nitrides typically restricts GaN film growth to substrates such as sapphire or SiC, despite the large lattice and thermal mismatch. With the use of AlN or GaN nucleation layers (NL), GaN films of sufficient quality have been produced for blue LEDs. However, for laser and large-area microwave device applications, the large number of dislocations (> 108 cm−2) limit device performance, and techniques are desired to reduce dislocation density during the growth process. Here, we demonstrate how low temperature AlN interlayers (IL) sandwiched between high temperature (HT) GaN layers can be used to improve the electrical, optical, and structural properties of Si doped GaN films. A nearly two-fold increase in mobility is observed in Si doped GaN grown using 5 AlN IL compared to GaN grown on a single AlN NL. For GaN films grown on multiple AlN IL, cross-sectional transmission electron microscopy images reveal a significant reduction in the screw dislocation density and photoluminescence spectra reveal a reduction in yellow band intensity. An analysis of the electrical data based on a single donor/single acceptor model suggests that the improved electron mobility is the result of a reduced acceptor concentration in the top GaN film. The reduction in the calculated acceptor concentration may be associated with the reduction of the screw dislocation density.
Photoluminescence and Photoluminescence Excitation Mechanisms for Porous Silicon and Silicon Oxynitride
Authors: Liu Xingsheng , Calata Jesus Noel , Liang Houyun , Shi Wangzhou , Lin Xuanyin , Lin Kuixun , Qin G. G.
Published: April 2011

Through a comparative study of the light emission and light excitation property of porous silicon (PS) and Si oxide, photoluminescence (PL) and photoluminescence excitation (PLE) mechanisms for blue-light-emitting PS are analyzed. Strong blue light (445nm) and ultraviolet light (365nm) emission from silicon-rich silicon oxynitride films at room temperature were observed. An analysis of the PL and PLE spectra of PS and Si oxide indicated that for blue-light emission from PS, there are two types of photoexcitation processes: photo-excitation occurring in nanometer Si particles (NSP's) and in the Si oxide layers covering NSPs, and radiative recombination of electron-hole pairs taking place in luminescence centers (LCs) located on the interfaces between NSP's and Si oxide and those inside Si oxide layers. The PL spectra of silicon-rich silicon oxynitride films implies that the PL originated from some LCs in SiOx and SiOxNy:H, while PLE spectra indicates that photoexcitation occurs in NSPs, SiOx and SiOxNy:H. The 365 nm band is attributed to the former two photoexcitation processes and the 445 nm one to the third process. As such, the quantum confinement/luminescence center model appears to be a satisfactory model in explaining the experimental results.
Study of Raman Scattering on InP/InGaAs/InP HEMTs
Authors: Radhakrishnan K. , Patrick T.H.K. , Zheng H.Q. , Yoon S.F.
Published: April 2011

Raman scattering studies have been recently used to relate the strain in the semiconductor layer structure with the line shape of allowed modes. It can yield important information about the nature of the solid on a scale of the order of a few lattice constants. It can also provide an evaluation on the carrier concentration in the channel layer of high electron mobility transistors (HEMTs). In this investigation, Raman scattering was used to study the effect of varying the In mole fraction (x) from 0.53 to 0.81 in the InxGa1−xAs channel layer of InGaAs/InP heterostructures. The effect of varying the doping concentration in the donor layer from 6×1017/cm3 to 2.5×1018/cm3, and the effect of varying the In0.75Ga0.25As channel thickness from 140 Å to 260 Å are also reported.

A two-mode Raman characteristic for all InxGa1−xAs/InP HEMTs is clearly seen, with the two LO modes (InAs-like LO and GaAs-like LO) located at 229cm−1 and 268.6cm−1, respectively. At a Raman frequency of 347cm−1, a small peak is observed due to InP LO mode. As the In composition increases from 0.53 to 0.81, the InAs-like LO mode peak intensity increases while that of GaAs-like LO mode decreases. The peak intensity ratio of InAs-like LO mode and GaAs-like LO mode increases from 0.78 to 1.10. By increasing the doping concentration in the donor layer (ND), there is also an increase in the carrier concentration in the InGaAs channel assuming that the donors are fully ionised. The coupled mode between the InGaAs longitudinal optical phonons and electrons in the InGaAs channel shifts continuously to a low wave number with the increasing ND in the InP donor layer. The increase in the lnGaAs channel thickness from 140Å to 260Å causes the InAs-like LO mode peak to shift to a lower wave number from 235.5 to 228.5cm−1. There is no change in the GaAs-like LO peak position located at 268.4cm−1.
Microstructural Characterization of Antimonide Based III-V Compounds and their Effect On Electro-Optical Properties of Substrate Materials and Devices
Authors: Dutta P.S. , Gutmann R.J. , Charache G.W. , Wang C.A.
Published: April 2011

This paper presents some of the widely used characterization tools for antimonide based III-V compounds, focusing on characterization of defects that limit device operation. The effect of microstructure on the electro-optical properties of GaSb and GaInAsSb important in devices is emphasized.
Cathodoluminescence from Inx Ga1−x as Layers Grown on GaAs Using a Transmission Electron Microscope
Authors: Yamamoto N. , Mita T. , Heun S. , Franciosi A. , Bonard J.-M.
Published: April 2011

InxGa1−xAs epilayers grown on GaAs(100) were studied by cathodoluminescence (CL) spectroscopy and imaging technique with 0.8 nm spectral resolution, using a transmission electron microscope. Linear features appear in the monochromatic CL image taken by the emission from the InxGa1−x.As layers, and do not appear in those from the GaAs layers. There is no direct correlation between the dark-line contrast in the panchromatic CL image (due to misfit dislocations) and the strong line contrast in the monochromatic CL images of the InxGa1−xAs layers. A peak wavelength shift in the CL spectrum was observed as the electron probe was moved across the linear features. The linear features also appear in a thin sample where the misfit dislocations are removed by ion milling, which clearly reveals that the strong line contrast is not directly due to the misfit dislocation. From those results the linear features in the monochromatic CL image are considered to be due to compositional fluctuations of the In concentration in the InxGa1−xAs layer.