bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatially Resolved Photoluminescence in Spontaneously-ordered GaInP2
Authors: Smith S. , Mascarenhas A. , Olson J. M. , Kazmerski L. L.
Published: April 2011

The low-temperature (5K) photoluminescence (PL) of partially-ordered GaInP2 is spatially resolved using high-resolution (from ˜ 0.2μm-0.7μm) scanning optical microscopy, revealing the spatial variation in band gap energy and the spatial origin of the ordering-induced low-energy emission and the associated ‘quantum-dot-like’ narrow spikes which appear when examining areas smaller, or of comparable size, than a single ordered domain. The large number of spectra taken within a micronsized area allow a detailed look at the statistical variation in band-gap energy and lineshape. A systematic study of a series of samples where the order parameter varies from η ˜ 0 to 0.45 shows that for the most highly-ordered samples, the statisitical distribution of excitonic energy and linewidth show evidence of exciton localization, which is also clearly seen by examining the spatial maps of the excitornic energy and linewidth extracted from the measured spectra.
Electronic and Optical Properties of Orientational Superlattices in Gainp Alloys
Authors: Zhang Yong , Fluegel B. , Ahrenkiel S. P. , Friedman D. J. , Geisz J. F. , Olson J. M. , Mascarenhas A.
Published: April 2011

We demonstrate the formation, and the electronic and optical properties of a novel type of semiconductor superlattice in spontaneously ordered GaInP alloys. The most frequently observed ordered structure in MOCVD grown GaInP has CuPt symmetry where the ordering directions occur in the two [111]B directions, corresponding to two distinct ordered variants. A new type of superlattice, termed an orientational superlattice, emerges as the ordered domains are stacked in a sequence whereby the ordering direction switches alternatively from the [111] direction in one domain to the [111] direction in the next domain. The novelty of this type of superlattice lies in that there is neither a band-gap nor an effective mass discontinuity along the superlattice axis. When the GaInP epilayer is grown on an exact (001) or [111]A tilt GaAs substrate, the two ordered variants are equally favorable. Thus, ordered domain twins appear in ordered GaInP epilayers. We present a comparitive study between the single-variant ordered structure and the double-variant ordered superlattice structure, using TEM and time-resolved differential absorption. We show that for a same order parameter, the band-gap of an orientational superlattice is higher than that of a single-variant ordered structure, and the in-plane optical anisotropy between the [110] and [110]B directions is greatly enhanced due to the superlattice effect. The experimental results are explained in terms of the band structure of the orientational superlattice.
Finite Carrier Confinement and Biexcitonic Complexes in Self-Assembled Inas Quantum Dots
Authors: Jaeger A. , Mankad T. , Schoenfeld W. V. , Lundstrom T. , Petroff P. M.
Published: April 2011

The luminescence properties of a single lnAs self-assembled quantum dot (QD) are studied by confocal scanning optical microscopy at low temperature. The observation of single QDs has been accomplished by epitaxial growth of QDs samples with low QD density (less than one QD per μm2) required by the diffraction limited spatial resolution of the microscope. In thick QDs with large confinement energies biexciton binding energies of up to 5.0 meV are found, while in thin and more weakly confined QDs the electron wavefunction penetrates into the surrounding barriers causing reduced biexciton binding energies of less than 2.0 meV. This result can be understood in terms of theoretical calculations of biexcitonic complexes in QDs with finite potential barriers.
Quenching Effects in Scanning Tunneling Microscopy Studies of Epitaxial Growth
Authors: Bell G. R.
Published: April 2011

The experimental aspects of rapid-quench scanning tunneling microscopy are discussed. In particular, the effects of sample quenching are investigated in atomic-scale studies of the molecular beam epitaxial growth of GaAs. Implications for the study of the heteroepitaxial system InAs-GaAs are discussed.
Tem Investigation of Self-Organized Pbse Quantum Dots as a Function of Spacer Layer Thickness and Growth Temperature
Authors: Kang H. H. , Salamanca-Riba L. , Pinczolits M. , Springholz G. , Holy V. , Bauer G.
Published: April 2011

The study of the morphology, lateral and vertical correlation of self-organized PbSe quantum dots in Pb1−xEux Te is presented. The samples consist of quantum dot superlattices of n periods of (PbSe/Pb1−xEux Te) grown on PbTe/(111) BaF2 by the S-K mode using MBE. The Pb1−xEux Te spacer thickness was varied from 34.3nm to 312nm and the growth temperature was varied between 335°C and 380°C. Our TEM results show very good lateral and vertical correlation of the dots. The dots form an array with either a/b/c/a/b/c/... or a/a/a/... vertical stacking sequence along the [111] growth direction. The stacking sequence is accurately controlled by the thickness of the Pb1−xEux Te spacer layer thickness and the growth temperature. The best a/b/c/... spatial correlation was obtained for temperatures around 380°C and spacer thickness of ˜40nm. The dots are highly strained and form triangular pyramids with (111) bases and (100) facets as observed by AFM. The shape of the dots also varied with the Pb1−xEux Te spacer thickness. An analysis of the spatial correlation of the dots' size and shape with respect to spacer thickness and growth temperature is presented.
Gate Technology Issues for Silicon Mos Nanotransistors
Authors: Tennant D. M , Timp G. L. , Ocola L. E. , Green M. , Sorsch T. , Komblit A. , Klemens F. , Kleiman R. , Muller D. A. , Kim Y. , Timp W.
Published: April 2011

This article reviews technology issues in scaling conventional planar transistors to a physical gate length of 30nm that are expected to produce an effective channel length of 10 nm. Gate fabrication features direct write e-beam lithography to form a ring structure capable of exploring the practical limits of gate processing while requiring only a single level of lithography. Other processing elements include ultra-thin gate dielectric formation (∼ 0.6nm); highly selective transformer coupled plasma (TCP) etching; and low energy ion implantation. DC electrical results obtained for high performance n-MOS and p-MOS type nanotransistors made using this process are discussed as are simulations of sub-threshold currents for n-MOS transistors with physical gate lengths down to 26nm
Spm Based Lithography for Nanometer Scale Electrodes Fabrication
Authors: Notargiacomo A. , Giovine E. , Cianci E. , Foglietti V. , Evangelisti F.
Published: April 2011

Scanning probe assisted nanolithography is a very attractive technique in terms of low-cost, patterning resolution and positioning accuracy. Our approach makes use of a commercial atomic force microscope and silicon probes to build simple nanostructures, such as metal electrode pairs, for application in novel quantum devices.

Sub-100 nm patterning was successfully performed using three different techniques: direct material removal, scanning probe assisted mask patterning and local oxidation.
The Mechanism of Mixed-Mode Phase Transformations
Authors: Pond R. C. , Shang P. , Cheng T. T. , Aindow M.
Published: April 2011

The topological theory of interfacial defects and the associated flux analysis are reviewed. It is shown that the shears and diffusive fluxes associated with the motion of disconnections can be determined directly from their crystallographic characteristics, and that the effects of changes in chemical composition, interfacial misfit and ordering can be incorporated into the analysis. The special conditions are identified for which there is conservation of atomic sites during the motion of disconnections. It is shown that, under these circumstances, disconnection motion may result in mixed-mode displacive-diffusive transformations whereby diffusion is required for the transformation to proceed but the interfaces exhibit crystallographic characteristics which one would normally associate with a martensitic transformation. It is shown that the growth of γ lamellae in TiAl-based alloys is an example of such a mixed-mode transformation.
Biaxial Zero Creep Measurements of Interface Energies in Ni/Ag Multilayers
Authors: Lewis A. C. , Mann A. B. , Josell D. , Tapson J. , Weihs T. P.
Published: April 2011

Biaxial zero creep experiments were performed on Ni/Ag multilayer films on sapphire substrates. The equilibrium curvature was measured using a scanning laser and position sensitive photodetector. The experiments were designed to measure the free energy of Ni/Ag interfaces and to investigate their effect on the structural stability of multilayered materials. For the Ni/Ag multilayers studied, significant plastic straining occurs at temperatures above 400°C, enabling the growth stresses and thermal stresses in the multilayers to decay to zero. After a long time at elevated temperatures, the equilibrium curvature is reached for the film/substrate couple. This curvature is determined by the number and the energy of the Ni/Ag interfaces. Using this equilibrium technique, a free energy of 0.44 ± 0.03 N/m was measured for Ni/Ag interfaces at an equilibrium temperature of 550°C.
The Critical Stress for Transmission of a Dislocation Across an Interface: Results From Peierls and Embedded Atom Models
Authors: Anderson P. M. , Rao S. , Cheng Y. , Hazzledine P. M.
Published: April 2011

A continuum Peierls model of a screw dislocation being pushed through an interface and an atomistic EAM study of dislocation transmission across a [0 0 1] Al-Ni interface suggest that core spreading into the interface and misfit dislocations in the interface are both potent effects that can significantly increase barrier strength of interfaces.
Thermodynamics and Kinetics of Interfacial Decohesion
Authors: Mishin Y. , McMahon C. J. , Bassani J. L. , Sofronis P.
Published: April 2011

Thermodynamic and kinetic aspects of interfacial decohesion are analyzed for a uniform separation along an interface subjected to a uniform tensile stress normal to the interface. During the separation process, an embrittling impurity can penetrate into the interface and reduce its cohesive strength. Rice(1976) and Hirth and Rice (1980) analyzed this process in great detail, and in particular considered two limiting cases: slow separation (constant chemical potential of the impurity) and fast separation (constant impurity concentration). Our work extends their analysis to intermediate, time-dependent situations, which correspond to the problem at hand. A phenomenological model is introduced to describe the free energy of the interfacial “solid solution”, stress-separation curves as functions of the impurity concentration, and kinetics of separation. The observed separation kinetics, as well as the work of decohesion, cohesive strength and other interfacial properties, depend on the interrelation between the strain rate and the impurity diffusion rate. An equation of stress-driven diffusion along the interface is derived, and the origin of the stress effect on diffusion is analyzed.
Structural Design of the Geometrical Shape of Interfaces in Bonded Dissimilar Materials Based on Theoretical Elastic Analysis
Authors: Tateno Masayoshi , Fukuzawa Yasushi , Nagasawa Shigeru , Sakuta Hiroshi
Published: April 2011

In order to evaluate the practical strength of a joint and its fracture mode, it is important to find the stress distribution near the edge of the interface by analyses of strength and fracture. The index of stress singularity based on theoretical analysis is a useful tool to indicate the stress distribution.

In this paper, investigations on the evaluation of the practical strength of bonded dissimilar materials based on the stress singularity are carried out. The secant stiffness module, which was used for plastics analysis, was applied to the evaluation of thermal elastoplastic behavior near the interface. Spherical conditions of the interface shape were used for the evaluation of stress behavior and the experiment of bonding strength. The relationship between the index of stress singularity, λ, and the practical strength of the bonded TiB2-Ni system was investigated by comparing theoretical λ, which was determined by substituting the secant stiffness module into Bogy's eigenequation, with the practical strength in the edge angle of the interface between 60° and 90° The correlation factor of the relationship between λ and the practical bonding strength of the TiB2-Ni system was found positive. These results show that the structural design of a geometrical interface which is getting a higher strength joint based on the index of stress singularity is verified experimentally.
Interfacial Engineering in Nanocomposites
Authors: Cantor Brian
Published: April 2011

This paper will present details of interfacial design, structure and properties in a variety of different nanocomposites. The materials discussed include co-sputtered nanoscale Ag/SiO2 and Ag/Si thin films which exhibit novel optoelectronic behaviour, and melt spun nanoscale Pb/Al and Sn/Al sheets which exhibit novel mechanical behaviour. The relationships between processing, structure and properties are discussed for these unusual materials systems.
Z-Contrast STEM Imaging and Ab-Initio Calculations of Grain Boundaries in SrTiO3
Authors: Kim Miyoung , Browning Nigel D. , Pennycook Stephen J. , Sohlberg Karl , Pantelides Sokrates T.
Published: April 2011

The understanding of electrical properties of grain boundaries in perovskites is essential for their application to capacitors, varistors and positive-temperature coefficient resistors. The origin of the electrical activity is generally attributed to the existence of charged defects in grain boundaries, usually assumed to be impurities, which set up a double Schottky barrier as they are screened by dopants in the adjacent bulk crystal. Microscopic understanding of the origin of the grain boundary charge, however, has not been achieved. It is not known yet if the charged grain boundary states are an intrinsic property of a stoichiometric grain boundary, arise from nonstoichiometry, or are caused by impurities. Here, the relation between atomic structure and electronic properties is studied by combining experiment with ab-initio calculations. The starting structures for theoretical calculations were obtained from Z-contrast images combined with electron energy loss spectroscopy to resolve the dislocation core structures comprising the boundary. Dislocation core reconstructions are typical of all grain boundaries so far observed in this material. They avoid like-ion repulsion, and provide alternative sites for cation occupation in the grain boundaries. Optimized atomic positions are found by total energy calculations. Calculated differences in vacancy formation energies between the grain boundaries and the bulk suggest that vacancy segregation can account for the postulated grain boundary charge.
Influence of the Interfacial Properties on the Microstructural Development and Properties of Silicon Nitride Ceramics
Authors: Hoffmann M. J. , Gu H. , Cannon R. M.
Published: April 2011

The influence of the sintering additive system on the grain growth anisotropy of silicon nitride has been studied in the two supersaturated oxynitride glass systems M-Si-Al-O-N (where M = Yb, Gd, Nd, La, and Y) and M-Si-Mg-O-N (where M = Lu, Sm, La, Sc and Y). The glasses contained a low volume fraction of grains and offer the possibility to study grain growth without impingement. Both systems show an increase of the aspect ratio with an increasing cation radius of the rare earth elements. The aspect ratios for the Sc- and Y-based glasses are higher than expected from the ionic radius.

Analytical transmission electron microscopy of the bulk glass and grain boundary film between flocculated particles reveals a difference in chemical composition. The larger rare earth cations are enriched in the film and the smaller ones are depleted compared to the bulk composition. The enrichment of the larger cations can be considered as an adsorption layer which reduces the growth rate of the prism planes. Glass systems with smaller cations (Yb, Gd) reveal a pronounced growth of the prism planes and sialon is formed in the outer region of the grains. The interfacial strength which determines the fracture toughness increases with a decreasing cation radius, but the effect is mainly attributed to the sialon formation rather than by the cation itself.
Interfacial Reactions in Ti-6Al-4V with Laser-Embedded SiC Particles and the Origin of Intergranular Corrosion Susceptibility of an Al-Mg Alloy
Authors: Kooi B. J. , De Hosson J.Th.M.
Published: April 2011

In the first part of the paper the microstructure of Ti-6Al-4V with laser embedded SiC particles is explained. The interfacial reaction between Ti and SiC is responsible for the largely improved wear resistance of the Ti alloy. In the second part the phase responsible for the intergranular corrosion susceptibility of an Al-Mg alloy when annealed above 65 °C is identified and possible mechanisms to solve this interfacial problem are proposed.
Epitaxial Realignment of In-Situ Doped Polycrystalline Silicon for Advanced BiCMOS Technologies
Authors: Chang K. , Thomas S.G. , Lee T-C. , Gregory R.B. , O'meara D. , Noering K. , Kirchgessner J. , Fresquet G. , Parker J. , TILLACK B.
Published: April 2011

Industrial feasibility of an in-situ-doped (ISD) polycrystalline Si process using chemical vapor deposition for advanced BiCMOS technologies is presented. ISD As-doped amorphous and polycrystalline Si layers have been deposited on Si substrates at 610°C and 660°C, respectively, with the deposition rate varying from 120 to 128Å /minute. Samples are compared on the basis of having been subjected to a substrate preclean prior to deposition using an HF solution and an in-situ H2 bake. TEM micrographs reveal the presence of a thin (10-15 Å) native oxide at the deposited layer/substrate interface for samples not precleaned. This is confirmed for both the amorphous and polycrystalline Si depositions. However, for the 610°C-deposited samples given the substrate preclean, a polycrystalline structure with partial epitaxial layer growth is observed. Twins and stacking faults are found at the poly Si/single crystal Si interface, causing interfacial roughness. Post-deposition annealing of the Si films typically generates grain growth, but RBS-channeling characterization of the annealed Si provides evidence of some recrystallization, the extent of which is affected by the original growth condition. Analysis shows that the amorphous deposition at 610°C results in a mixture of epitaxial and polycrystalline Si. Epitaxial realignment of the polycrystalline Si film by post deposition annealing can result in significantly improved device performance.
Ni-Induced Selective Nucleation and Solid Phase Epitaxy of Large-Grained Poly-Si on Glass
Authors: Puglisi Rosaria A. , Tanabe Hiroshi , Chen Claudine M. , Atwater Harry A. , Rimini Emanuele
Published: April 2011

We investigated the formation of large-grain polycrystalline silicon films on glass substrates for application in low-cost thin film crystalline silicon solar cells. Since use of glass substrates constrains process temperatures, our approach to form large-grain polycrystalline silicon templates is selective nucleation and solid phase epitaxy (SNSPE). In this process, selective crystallization of an initially amorphous silicon film, at lithographically predetermined sites, enables grain sizes larger than those observed via random crystallization. Selective heterogeneous nucleation centers were created on undoped, 75 nm thick, amorphous silicon films, by masked implantation of Ni islands, followed by annealing at temperatures below 600 °. At this temperature, the Ni precipitates into NiSi2 particles that catalyze the transition from the amorphous to the crystalline Si phase. Seeded crystallization begins at the metal islands and continues via lateral solid phase epitaxy (SPE), thus obtaining crystallized regions of several tens of square microns in one hour. We have studied the dependence of the crystallization rate on the Ni-implanted dose in the seed, in the 5×1015/cm3 - 1016/cm3range. The large grained polycrystalline Si films were then used as a substrate for molecular beam epitaxy (MBE) depositions of 1 [.proportional]m thick Si layers. Transmission electron microscopy (TEM) analysis showed a strong correlation between the substrate morphology and the deposited layer. The layer presented a large grain morphology, with sizes of about 4 [.proportional]m.
Strain Modification of Epitaxial SrRuO3 Films Using Structural Transitions of Ferroelectric BaTiO3 Substrate
Authors: Lee M. K. , Nath T. K. , Eom C. B. , Smoak M. C. , Tsui F.
Published: April 2011

Electrical conduction and magnetic behavior of ferromagnetic SrRuO3 (bulk Tc= 160 K) were tuned systematically using the structural transitions of ferroelectric BaTiO3 as the growth template. Abrupt resistivity changes of SrRuO3 were observed at the structural transition temperatures of the BaTiO3substrate. The observed effect appears to originate from the lattice changes of BaTiO3 (cubic to tetragonal at 393K, tetragonal to orthorhombic at 278K, and orthorhombic to rhombohedral at 183K) induced by an expansion of spontaneous polarization axis. The observed phenomenon will be very useful for the fabrication of novel perovskite oxide devices.
Study of the Radiative and Non-Radiative Recombination Processes at Dislocations in Silicon by Photoluminescence and LBIC Measurements
Authors: Pizzini S. , Binetti S. , Acciarri M. , Casati M.
Published: April 2011

It is well known that the sharp, room temperature luminescence emission at 1.54 μm from dislocated silicon has set off a great interest for this material in view of its applications in the third window of optical telecommunications. For this reason the dislocation related luminescence in silicon addressed recently a number of investigation aimed at understanding the mechanism of light emission. The problem is still unsolved as most of the experiments done gave contradictory answers to the main questions open, which concern the intrinsic or extrinsic nature of dislocation luminescence and the effect on it of reconstruction, interaction or passivation processes, possibly assisted by metallic or non-metallic impurities.

In order to go more insight on the problem, we started a systematic work on CZ silicon, aimed at understanding the properties of dislocation luminescence. The identification of the energy levels involved in the different dislocation PL bands has been obtained.
Photoreflectance Near-Field Scanning Optical Microscopy
Authors: Paulson Charles , Hawkins Brian , Sun Jingxi , Ellis Arthur B. , Mccaughan Leon , Kuech T. F.
Published: April 2011

A novel Near-field Scanning Optical Microscopy (NSOM) technique is used to obtain simultaneous topology, photoluminescence and photoreflectance (PR) spectra. PR spectra from GaAs surfaces were obtained and the local electric fields were calculated. Sub-wavelength resolution is expected for this technique and achieved for PL and topology measurements. Photovoltages, resulting from the high intensity of light at the NSOM tip, can limit the spatial resolution of the electric field determination.
Optical and Microstructural Characterization of Nanocrystalline Silicon Superlattices
Authors: Tsybeskov L. , Grom G. F. , Krishnan R. , Fauchet P. M. , McCaffrey J. P. , Baribeau J.-M. , Sproule G. I. , Lockwood D. J. , Timoshenko V. , Diener J. , Heckler H. , Kovalev D. , Koch F. , Blanton T. N.
Published: April 2011

We present optical and microstructural characterization of nanocrystalline silicon superlattices (nc-Si SLs). Our samples have better than 5 % Si nanocrystal size distribution and a long range order along the direction of growth provided by periodically alternating layers of Si nanocrystals and SiO2. Flat and chemically abrupt nc-Si/SiO2 interfaces with a roughness of < 4Å are confirmed by transmission electron microscopy (TEM), Auger elemental microanalysis, X-ray small angle reflection, and low-frequency Raman scattering. Photoluminescence (PL) in our structures has been studied in details including time-resolved and steady-state PL spectroscopy in a wide range of temperature, excitation wavelength and power. Resonantly excited PL spectra show phonon steps proving that the PL originates in Si nanocrystals. Electrical measurements show signature of phonon-assisted tunneling proving low defect density nc-Si/SiO2 interface.
Optical Properties of Pseudomorphic SnXGe1−x Alloys
Authors: Ragan Regina , Atwater Harry A.
Published: April 2011

SnxGe1−x alloys are grown coherent on Ge(001) substrates by conventional molecular beam epitaxy. The lattice mismatch between SnxGe1−x and Ge produces a biaxial compression of the alloy in the plane of the substrate and a uniaxial elongation in the growth direction. The change of Eg resulting from the biaxial compression is modeled with deformation potential theory for coherent SnxGe1−x on Ge(001) and coherent SnxGe1−x on Ge(111). For SnxGe1−x on Ge(001), the decrease in the energy band gap due to strain is small, 16 meV for x = 0.10, and Γ7 and L6 shift uniformly. In the case of SnxGe1−x on Ge(111), Γ7 and L6 do not shift uniformly; a large uniaxial splitting occurs at L6, 200 meV for x = 0.10. Another interesting result of a uniaxial strain along [111] is the absence of a direct to indirect energy band gap transition for x < 0.30. Fourier transform infrared spectroscopy transmission measurements of coherent SnxGe1−x on Ge(001) confirm the strain-induced change in the energy band gap is a small effect.
Micro-Raman Characterization of Unusual Defect Structure in Arsenic-Implanted Silicon
Authors: Tuschel David D. , Lavine James P.
Published: April 2011

Raman spectroscopy has often been used to study the damage to semiconductors induced by ion implantation. Off-axis, macro-Raman spectra reveal extensive damage to the silicon lattice, consistent with many literature reports. However, when the same samples were analyzed in the backscattering mode by micro-Raman spectroscopy, evidence was found for orientational dependent lattice damage and an unusual defect structure. P/O micro-Raman spectra reveal the spatially-varying appearance of a band between 505 and 510 cm−1 always accompanied by that of the silicon optical mode at 520 cm−1.
Studies Of Photoreflectance in Cd1−x MnxTe/Cd1−yMnyTe Superlattices
Authors: Chen Chenjia , Wang Xuezhong , Li Haitao , Liang Xiaogan , Chai Guangyu , Ning Zheng , Wang Xun
Published: April 2011

Photoreflectance spectroscopy has been peformed on a series of Cd1−xMnxTe/Cd1−yMnyTe superlattices. Samples were grown on (001) GaAs substrates by molecular-beam epitaxy with different barriers (x=0.3 to 0.8) and wells (y=0 to 0.01). After taking into consideration the strain-induced and quantum confinement effects, the exciton transition energies of the heavy and light holes can be determined using envelope-function calculations. The calculations are in good agreement with the photoreflectance measurement results. These results show that photoreflectance is a powerful probe for the study of quantized state structures in superlattices.
Determination of Optical Properties of Fluorocarbon Polymer Thin Films by a Variable Angle Spectroscopic Ellipsometry
Authors: Lee Kang-Kuk , Park Jin-Goo , Shin Hyung-Jae
Published: April 2011

Optical properties of vapor phase (VP) deposited and spin-coated fluorocarbon (FC) thin films on silicon substrates, such as refractive index, extinction coefficient and film thickness were characterized by a variable angle spectroscopic ellipsometry (VASE) in the range of 300–800 nm. A Lorentz model allows us to simulate the optical constants of the FC films with a minimum number of parameters while maintaining Kramers-Kronig (KK) consistency between the real and imaginary parts of the optical constants. FC films are nearly transparent over the visible spectrum, so it is possible to assume k (extinction coefficient) = 0 over part of the visible spectrum in a Cauchy model. To accurately simulate the obtained ellipsometric spectra, we performed a regression analysis in two steps assuming a three-phase and a four-phase model. The regression analysis was performed using the three-phase model and a best-fit mean-squared error (MSE) value of 1.717 (VP deposited FC film, Lorentz model) was obtained. However, the four-phase model was used to improve the best-fit result of 0.531 (VP deposited FC film, Lorentz model). The surface roughness layer was assumed to be a mixture of FC films and voids under the Bruggeman effective medium approximation (EMA). We found that the best-fit MSE was reduced when surface roughness was included.
Optical Properties and Defect Structure of MOVPE InGaN Films
Authors: Cremades A. , Albrecht M. , Ulloa J. M. , Piqueras J. , Strunk H. P. , Hanser D. , Davis R. F.
Published: April 2011

A series of 100 nm thick InGaN films with In content up to 14% has been grown by MOVPE on SiC substrates. Optical characterization was carried out by means of reflectance spectrometry, photoluminescence and cathodoluminescence. Optical properties of the samples have been correlated with the microstructural properties measured by atomic force microscopy, transmission electron microscopy and X-ray diffraction data. Results indicate a dependence of the optical properties on the In content in the sample, as well as on the residual stress in the films induced by Indium incorporation. Part of the strain is reduced elastically by formation of pinholes which reach the InGaN/GaN interface, where first misfit dislocations are observed to form. Our results show that luminescence is directly correlated with the strain distribution in the layers. Pinholes are observed to act as nonradiative recombination sites for carriers, while strain relaxation around pinholes may enhance luminescence emission. We discuss the influence of strain with respect to In incorporation, the appearance of piezoelectric fields and effects due to strain induced band bending.
Diamond In-Line Monitors for Synchrotron Experiments
Authors: Bergonzo P. , Tromson D. , Brambilla A. , Mer C. , Guizard B. , Foulon F.
Published: April 2011

Diamond polycrystalline films have been synthesised using the Chemical Vapour Deposition (CVD) technique in order to fabricate new types of photo-detectors for the characterisation of x-ray light sources as encountered in synchrotron experiments. Since diamond exhibits a low absorption to low energy x-ray photons, these devices allow beam position monitoring with very little beam attenuation at photon energies as low as 2 keV. We present here diamond based new devices for four different applications, including (i) semitransparent beam intensity and (ii) position monitors with high position resolution (< 2 µm), (iii) beam profile monitors with 20 µm pitch resolution, and (iv) ultra-fast diamond detectors (response time < 100 ps) that enable the intensity and temporal monitoring of fast x-ray pulses. These devices can be used for in-line characterisation of synchrotron beam line experiments for permanent in-situ monitoring of beam instabilities during experiments as well as for synchrotron machine diagnostics.
Resonant x-ray Scattering From the Surface of a Dilute Liquid Hg–Au Alloy
Authors: DiMasi E. , Tostmann H. , Ocko B. M. , Huber P. , Shpyrko O. G. , Pershan P. S. , Deutsch M. , Berman L. E.
Published: April 2011

We present the first resonant x-ray reflectivity measurements from a liquid surface. The surface structure of the liquid Hg-Au alloy system just beyond the solubility limit of 0.14at% Au in Hg had previously been shown to exhibit a unique surface phase characterized by a low-density surface region with a complicated temperature dependence. In this paper we present reflectivity measurements near the Au LIII edge, for 0.2at% Au in Hg at room temperature. The data are consistent with a concentration of Au in the surface region that can be no larger than about 30at%. These results rule out previous suggestions that pure Au layers segregate at the alloy surface.
3-D Measurement of Deformation Microstructure in Al(0.2%)Mg Using Submicron Resolution White x-ray Microbeams
Authors: Larson B.C. , Tamura N. , Chung J.-S. , Ice G.E. , Budai J. D. , Tischler J. Z. , Yang W. , Weiland H. , Lowe W.P.
Published: April 2011

We have used submicron-resolution white x-ray microbeanis on the MHATT-CAT beamline 7-ID at the Advanced Photon Source to develop techniques for three-dimensional investigation of the deformation microstructure in a 20% plane strain compressed Al(0.2%)Mg tri-crystal. Kirkpatrick-Baez mirrors were used to focus white radiation from an undulator to a 0.7 × 0.7 μm2 beam that was scanned over bi- and tri-crystal regions near the triple-junction of the tricrystal. Depth resolution along the x-ray microbeam of less than 5 microns was achieved by triangulation to the diffraction source point using images taken at a series of CCD distances from the microbeam. Computer indexing of the deformation cell structure in the bi-crystal region provided orientations of individual subgrains to ∼0.01°, making possible detailed measurements of the rotation axes between individual cells.
Synchrotron Radiation X-ray Microdiffraction Study of Cu Interconnects
Authors: Zhang X. , Solak H. , Cerrina F. , Lai B. , Cai Z. , Ilinski P. , Legnini D. , Rodrigues W.
Published: April 2011

We have used synchrotron radiation x-ray microdiffraction to study the microstructure and strain variation of copper interconnects. Different types of local microstructures have been found in different samples. Our data show that the Ti adhesion layer has a dramatic effect on Cu microstructure. On site electromigration test has been conducted and strain profile along the same interconnect line was measured before and after this electrical stressing. Cu fluorescence scan was used to find the mass variations along the line. Voids and hillocks can be clearly identified in this scan. x-ray micro-diffraction was used to measure the strain change around the interesting regions.
Surface Interactions of Actinide Ions with Geologic Materials Studied by XAFS
Authors: Sylwester E. R. , Hudson E. A. , Allen P. G.
Published: April 2011

We have investigated the interaction of the actinyl ion, , with silica, alumina, and montmorillonite surfaces under ambient atmosphere and aqueous conditions using x-ray Absorption Fine Structure (XAFS) Spectroscopy. In acid solution (pH ∼ 3.5), the uranyl ion shows a strong interaction with the silica and alumina surfaces, and a relatively weak association with the montmorillonite surface. The extent of direct surface interaction is determined by comparing structural distortions in the equatorial bonding environment of the uranyl ion relative to the structure of a “free” uranyl aquo complex. Based on this formalism, surface complexation on silica and alumina occurs through an inner-sphere mechanism with surface oxygen atoms binding directly to the equatorial region of the uranyl ion. In contrast, sorption on montmorillonite occurs by an outer sphere mechanism in which the uranyl ion retains the simple aquo complex structure and binds to the surface via ion-exchange. In near-neutral solutions (pH ∼ 6), sorption on all of the materials is dominated by an inner-sphere mechanism. The formation of surface oligomeric species is also observed on silica and alumina.
Infrared Evaluation of Heat Generation During the Cyclic Deformation of a Cellular Al Alloy
Authors: Rabiei A. , Hutchinson J. W. , Evans A. G.
Published: April 2011

Heat generation from a notch during the compression-compression fatigue of a cellular Al alloy has been measured and compared with a model. The measurements indicate that heat is generated because of hysteresis occurring in narrow cyclic plastic zones outside the notch. This process continues until the notch closes. At closure, a brief period of heat generation arises because of friction along the notch faces. A plasticity model based on the Dugdale zone is shown to provide a reasonably accurate characterization of the heat generated, with the proviso that an “ineffective” zone be transposed onto the notch tip. It is found that the temperatures generated are too small to cause fatigue by thermal softening. A fatigue mechanism based on either geometric softening of the cells or crack growth in the cell walls is implied.
In Situ Observation of Oxidization Process at the Most Upper Surfaces by x-ray Surface Propagation Waves
Authors: Horiuchi Toshihisa , Ishida Kenji , Matsushige Kazumi
Published: April 2011

The characteristics and applicable studies of the x rays scattered and propagating near the most upper surface of the substrate under the total reflection condition are described. Since the peak energy of the x rays gives direct information on the electron density of the surface materials, some experiments have been first conducted to confirm this. Then, an in-situ observation of oxidization processes for evaporated Cu films has been also conducted under a UV irradiation and an acid vapor exposure, revealing that there exist several oxidizing stages in time variations, namely a slight increase in the electron density at the initial stage, subsequently an abrupt decrease, and then steady value suggesting the sealing-off mechanism in the oxidization phenomena.
Dual Band Infrared Thermography as a NDT Tool for the Characterization of the Building Materials and Conservation Performance in Historic Structures
Authors: Moropoulou A. , Avdelidis N.P. , Koui M. , Kanellopoulos N.K.
Published: April 2011

Infrared thermography is a non-destructive investigation technique, which is largely used because of the outstanding advantages that it is capable to provide in a variety of applications and especially for conservation purposes of historic monuments, where destructive sectioning is prohibited. In the present work, dual band infrared thermography (3–5.4 μm and 8–12 μpm) is used, to evaluate the humidity distribution by capillary rise in reference samples of porous materials in lab, in order to validate the examination of real scale material systems in situ. The combined study of vapor/moisture transport in prototypes simulating porous materials under controlled environmental conditions (Relative Humidity 60–80% & Temperature 25–40°C), provides interpretation tools to the investigation by IR Thermography of transport phenomena occurring at the masonry. The cross-investigation of consolidated porous stones and of repair mortars, in lab and in situ on historic monuments in Greece, permits to evaluate the performance of conservation materials, regarding their compatibility to the porous building stones on historic masonries. It is deduced that Infrared Thermography by recording thermal maps of the real surfaces under study provides information on the differential behavior of the various materials on the masonry scale regarding the water impregnation and evaporation phenomena, which control the weathering effects in porous media. Hence, infrared thermography might be used as a nondestructive technique to evaluate on a micro and macro scale the performance of conservation interventions and materials, in compatibility to the original materials on the level of the structures.
Method and Instrumentation for Nondestructive Characterization of Surface Area and Pore Size Distribution of Thin Films in Their Deposited State
Authors: Boltz E. S. , Spooner Y. H. , Albanna S. G. , Taylor D. J. , Stallings A. R. , Abeyta J. P.
Published: April 2011

TPL has developed a method and instrumentation system for characterizing the surface area and pore size distribution of a thin-film or coating in its as-deposited state. Errors associated with destructive removal of the film are avoided and small sample sizes can be utilized with high-fidelity results.
X-ray Microtomography of Fatigue Crack Closure as a Function of Applied Load In Al-Li 2090 T8E41 Samples
Authors: Morano R. , Stock S.R. , Davis G.R. , Elliott J.C.
Published: April 2011

Crack closure is held to be responsible for very low fatigue crack growth rates in many alloys such as Al-Li 2090 T8E41, and early crack face contact during unloading or prolonged contact during loading seems to reduce the driving “force” for crack extension. High resolution x-ray computed tomography (i.e., microtomography) allows one to image the entire volumes of samples and to quantify opening as a function of applied load over the entire crack surface. Crack closure results are reported for a fatigue crack grown under load ratio R=0.1 in a compact tension sample of Al-Li 2090 T8E41; the crack was free to choose its path unconstrained by side-grooves which are normally used to suppress crack deflection. The inter-relationship between crack path, crack face contact and applied load level are discussed.
Nondestructive Evaluation of Fatigue in Titanium Alloys
Authors: Rösner H. , Meyendorf N. , Sathish S. , Matikas T.E.
Published: April 2011

Dissipated heat has been measured by thermographic technique during fatigue experiments on Ti-6AI-4V. Surface temperature of the specimen was found sensitive to the amount of fatigue damage accumulated in the material. An increased heat dissipation due to fatigue can be related to continuous change in the microstructure (increased dislocation density, stacking faults etc.) of the material. A method based on passive thermography can be proposed to monitor damage accumulation in Ti-6Al-4V due to cyclic loading.
Real-Time Monitoring of Acoustic Linear and Nonlinear Behavior of Titanium Alloys During Cyclic Loading
Authors: Frouin J. , Maurer J. , Sathish S. , Eylon D. , Na J.K. , Matikas T.E.
Published: April 2011

Variation in acoustic nonlinearity has been monitored in real time during fatigue, on four dogbone specimens of Ti-6A1-4V, under low cycle fatigue conditions, from the virgin state all the way to fracture. The results of these experiments show that the acoustic nonlinearity undergoes large changes during the fatigue and follows a similar trend for the material under given fatigue test conditions. Transmission electron microscopic (TEM) examination of the samples with similar composition fatigued to different stages indicates a gradual change in the microstructure and dislocation density, which correlates with the changes in acoustic nonlinearity.
Evaluation of the Degradation Dynamics of Thin Silicon Dioxide Films Using Model-Independent Procedures
Authors: Rodríguez R. , Nafría M. , Miranda E. , Suñé J. , Aymerich X.
Published: April 2011

The degradation and breakdown of thin silicon dioxide films has been analysed using a two-step stress method. This procedure allows the evaluation of the degradation induced by the electrical stress without any assumption about the microscopic nature of the degradation process. The method has been used to analyse and compare the degradation dynamics when constant-voltage (CVS) and constant-current stresses (CCS) are applied to the oxide. Moreover, it is shown that in the case of CVS, the fitting of the I-t characteristics can provide quantitative information about the degradation (degradation rate) and breakdown (mean-time-to-breakdown), without taking into account any degradation model.
Correlation Between Development of Leakage Current and Hydrogen Ionization in Ultrathin Silicon Dioxide Layers
Authors: Afanas'ev V. V. , Stesmans A.
Published: April 2011

The generation of leakage current across 3-6-nm thick thermal oxides on (100)Si under electrical stress or irradiation with 10-eV photons is compared with the radiation-induced defect generation in 35-66-nm thick SiO2 layers. The degradation of both ultrathin and conventional oxides appears correlated with the concentration of atomic hydrogen in the layer. Both the leakage currents and the irradiation-induced defects were found to have two components: one thermally unstable that correlates with the H-induced donor states, and another related to the permanent oxide network damage ascribed to H-assisted Si-O bond break. As both degradation processes involve a proton formed in the oxide, we suggest that H ionization either by electron emission or by trapping a hole triggers oxide degradation.
Initial Oxynitridation of a Si(001)-2×1 Surface by NO
Authors: Miyata Noriyuki , Watanabe Heiji , Ichikawa Masakazu
Published: April 2011

We have investigated the initial oxynitridation of an atomically flat Si(001)-2×l surface by NO. We found that appropriate oxynitridation conditions, in which oxide decomposition does not occur, are required to suppress the roughness of the NO-reacted Si surface. Under these conditions, we investigated the growth behavior and chemical structure. The first oxynitridation, in which NO reacts with the first Si layer on the Si(001)-2×l surface, takes place in a layer-bylayer manner caused by two-dimensional nucleation. However, further oxynitridation for the second Si layer proceeds in a three-dimensional manner in which the atomic-scale roughness at the oxynitride/Si interface increases. In addition, under our oxynitridation conditions, N is incorporated as N ≡ Si3, even though the oxynitride is ultrathin.
Paramagnetic Defects Related to Positive Charges in Silicon Oxynitride Films
Authors: Miura Y. , Fujieda S. , Hasegawa E.
Published: April 2011

Electron spin resonance (ESR) spectroscopy is used to explore the origin of positive charges in silicon oxynitride thin films formed in a N2O ambient. A new type of paramagnetic center in as-grown oxynitrides appeared as a single peak in the ESR spectrum with a zero crossing g value of 2.0006. This value suggests that the paramragnetic center is a kind of E' center. We investigated the quantitative behavior of the positive charge center and the paramagnetic center through the density changes induced by vacuum ultraviolet irradiation and hydrogen annealing. Based on the similar behavior of both types of center, we argue that the paramagnetic centers can account for a significant part of the positive charges specific to oxynitrides. Since the spin density increased with the oxynitridation temperature, the paramagnetic center is closely related to nitrogen incorporation processes.
Dynamics of Silicon Oxidation
Authors: Stoneham A. M. , Szymanski M. A. , Shluger A. L.
Published: April 2011

The rate-determining process in dry oxidation of silicon for thicker oxides (say above 10 nm) is probably the interstitial diffusion of oxygen molecules. For thinner oxides (a few nm), this simple picture is inadequate. The Deal-Grove model of oxidation kinetics fails. Oxide usually grows by an essentially layer-by-layer process, with growth at terraces, not steps, and perhaps oscillatory roughening. Isotope experiments show that interstitial and network oxygens exchange close to the Si/oxide interface and close to the oxide/gas interface. These results imply limiting mechanisms other than diffusion, probably involving charged oxygen species. We have made Density Functional (DFT) Generalised Gradient Approximation (GGA) calculations for a range of neutral and charged oxygen species to assess relative stabilities, diffusion mechanisms, and propensity for isotope exchange. These results identify acceptable mechanisms. We have also used Monte-Carlo methods to examine the consequences of the image interaction bias, and also the effects of the charge transfer processes (like tunnelling) by which charged species form. We comment on implications for oxide quality, especially on the relationship between growth processes and the charge and energy localisation components of breakdown.