bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoluminescence Characteristics of HF-Treated Silicon Nanocrystals
Authors: Nozaki S. , Sato S. , Ono H. , Morisaki H.
Published: April 2011

Si nanocrystals were deposited in a helium atmosphere by the gas-evaporation technique. Their average size is 3.5 nm, much smaller than those of the Si nanocrystals deposited in an argon atmosphere. The PL spectra of the as-deposited and the HF-treated Si nanocrystals were compared. A great increase in the PL intensity of the HF-treated Si nanocrystals is attributed to the hydrogen passivation of Si surface dangling bonds. A good correlation between the amount of Si-O bonds and the PL intensity suggests that the oxygen-passivation of dangling bonds is required for the red-band PL. The PL spectra of the HF-treated Si nanocrystals resemble those of porous Si and clearly indicate that the HF-treated Si nanocrystals well simulate the porous Si.
Visible Luminescence in Si/SiO2 Superlattices
Authors: Lockwood D. J. , Baribeau J.-M. , Grant P. D. , Labbé H. J. , Lu Z. H. , Stapledon J. , Sullivan B. T.
Published: April 2011

Amorphous Si/SiO2 superlattices with periodicities from 2 to 5 nm have been grown on (100) Si wafers by several different techniques: molecular beam epitaxy, magnetron sputtering, and plasma enhanced chemical vapor deposition (PECVD). With the first two methods little or no hydrogen was incorporated during growth and visible photoluminescence (PL) was obtained at wavelengths from 520 to 800 nm. The shift in the PL peak position with Si layer thickness is consistent with quantum confined emission. Annealing the sputtered superlattices at temperatures up to 1100°C produced a very bright red PL that is similar in intensity to that found in porous Si. The PL was also considerably enhanced by deposition on aluminum-coated glass substrates. For large numbers of periods (e.g., 425) the PL was strongly modulated in intensity owing to optical interference within the superlattice. Similar quantum-confined PL was also observed in the PECVD grown superlattices, where the amorphous Si layers were heavily hydrogenated. The blue-red cathodoluminescence observed from sputtered superlattices is due primarily to defects in the SiO2 layers.
Possible Mechanism of the 30–100 Picoseconds Fast and Efficient Photoluminescence From nc-Si/a-SiO2Doped with Transition Metals
Authors: Veprek S. , Wirschem Th. , Dian J. , Perná S. , Merica R. , Veprek-Heijman M. G. J. , Perina V. , Fuss M. , Lin X.
Published: April 2011

The nc-Si/a-SiO2composite thin films doped with tungsten show very fast and efficient photoluminescence (PL). In order to obtain insight into the PL mechanism we have performed a comparative study with other metals. The results lend support to the suggested mechanism which includes the photogeneration of charge carriers due to efficient absorption of the excitation UV light in the silicon nanocrystals followed by energy transfer to the Wn+radiative center from which the light emission occurs.
Growth of Germanium on Porous Silicon (001)
Authors: Thompson W. H. , Yamani Z. , Nayfeh H. M. , Hasan M.-A. , Greene J. E. , Nayfeh M. H.
Published: April 2011

The surface morphology of Ge grown on Si (001) and porous Si(001) by molecular beam epitaxy at 380 °C is examined using atomic force microscopy (AFM). For layer thicknesses of 30 nm, the surface shows islanding while still maintaining some of the underlying roughness of the surface of porous Si. For thicknesses in the 100 nm range, the surface roughness is not visible, but the islanding persists. Unlike the case of silicon where islands tend to merge and nearly disappear as the thickness of the deposited layer rises, we observe on the porous layer the persistence of the islands with no merging even for macroscopic thicknesses as large as 0.73 microns.
The Fabrication of Semiconductor Nanostructure Arrays on a Silicon Substrate Using an Anodized Aluminum Template
Authors: McGinnis S. P. , Cleary J. N. , Das B.
Published: April 2011

We have developed a nanogrowth technology for the fabrication of periodic arrays of semiconductor nanostructures on silicon that is currently being investigated for silicon based x-ray detectors. The semiconductor nanostructures are formed by chemical synthesis in pores of a template created by the anodization of aluminum on a silicon substrate. The use of the silicon substrate allows greater control over the aluminum thin film properties, better in situ monitoring of the pore formation process, and the direct integration of nanostructure arrays with conventional silicon technology.
Electronic Structure of O-D Exciton Ground State in CdSe Nanocrystals
Authors: Chamarro M. , Dib M. , Gourdon C. , Lavallard P. , Lublinskaya O. , Ekimov A. I.
Published: April 2011

We present results on photoluminescence excitation spectra (PLE) of wurtzite CdSe nanocrystals (NCs) embedded in a glass with effective radii in the range 15–35 Å. Information on the near band-gap absorption of an assembly of NCs is obtained by selecting a narrow energy range in the inhomogeneously broadened photoluminescence band. The size and shape dependence of the lowest exciton states are calculated for slightly non-spherical wurtzite NCs. The experimental results are in good agreement with the theoretical predictions when both shape and size dispersions are taken into account.
Formation of Buried Porous Silicon Structure by Hydrogen Plasma Immersion Ion Implantation
Authors: Fan Z. , Chu Paul K. , Lu X. , Iyer S. S. K. , Cheung N. W.
Published: April 2011

Plasma Immersion Ion Implantation (PIII) excels in several areas over conventional ion implantation, for example, higher dose, shorter implantation time, and lower overall cost. The technique can be used to fabricate buried porous silicon. In our experiment, hydrogen is implanted into Si by PIII at 5–30kV to form underlying porous silicon (PS) which emits light at an energy higher than the Si bandgap. The optical properties of the PS samples as measured by photoluminescence are quite good. The PHI technique therefore offers an alternative means to fabricate buried porous silicon structures which can potentially be used to fabricate optoelectronic devices in silicon.
Atomic and Electronic Properties of Small Hydrogenated Silicon Clusters: Si6H2m and Si6H+2m+1
Authors: Miyazaki Takehide , Stich Ivan , Uda Tsuyoshi , Terakura Kiyoyuki
Published: April 2011

The atomic and electronic structures of Si6H2m and Si6H+2m+1 clusters have been investigated in the framework of density-functional theory. For both neutral and ionized clusters we found the structure to belong to one of four distinct structural families. A molecular-orbital picture of hydrogenation is presented. From the calculated formation energies of these clusters, we infer the relative stability of the different structural families discussed.
Anisotropy of the Porous Silicon Photoluminescence
Authors: Polisski G. , Averboukh B. , Kovalev D. , Koch F.
Published: April 2011

Polarization memory effect in the porous Si photoluminescence is studied. The anisotropy of the linear polarization degree is found in the samples etched with polarized light-assistance. The effect is explained by the anisotropie in plane distribution of the elongated Si crystallites. Under resonant optical excitation four-fold anisotropy of the photoluminescence polarization, linked to the crystalline axes of the bulk Si substrate, is observed.
Integrating Bipolar Junction Transistors with Silicon-Based Light-Emitting Devices
Authors: Hirschman K. D. , Tsybeskov L. , Duttagupta S. P. , Fauchet P. M.
Published: April 2011

Silicon-based optoelectronic devices enable the realization of optoelectronic systems that are compatible with integrated circuit manufacturing technology. This work reports on silicon-based visible light-emitting devices (LEDs) that have been successfully integrated into a standard bipolar fabrication sequence. The basic LED structure consists of a 0.5–1.0μm thick silicon-rich silicon oxide (SRSO) active light-emitting layer formed on a p-type silicon wafer by partial oxidation of porous silicon (PSi), with an n+ doped polysilicon cathode. The LEDs exhibit bright electroluminescence (EL) with a spectral peak between 1.75 and 1.90e. The LEDs are connected in a common-emitter configuration to integrated vertical pnp bipolar driver transistors. This is the first demonstration of an all-silicon visible light emitter / bipolar transistor optoelectronic integrated circuit. The LED device fabrication, process integration, and optoelectronic device characteristics are discussed.
Optical and Electrical Properties of Undoped Microcrystalline Silicon Deposited by the VHF-GD with Different Dilutions of Silane in Hydrogen
Authors: Beck N. , Orres P. , Fric J. , Remeš Z. , Poruba A. , Stuchlíková HA , Fejfar A. , Wyrsch N. , Vaněček M. , Kočka J. , Shah A.
Published: April 2011

We show that the optical and electrical properties of microcrystalline silicon (μc-Si:H) deposited by the VHF-GD technique at 110 MHz can considerably be tuned by changing the dilution ratio of silane to hydrogen.

With increasing silane dilution we observe enhanced optical absorption for energies below 2 eV due to the transition of the material from amorphous / microcrystalline mixture to a pure microcrystalline phase. Simultaneously, the light scattering and the defect absorption increases. Strong dilution also promotes the incorporation of impurities into the material, leading to a pronounced extrinsic behaviour as seen from the decrease of the activiation energy of the electrical conductivity.

The electrical properties were investigated in the dark by the Time of Flight technique. We measured drift mobilities at room temperature which slightly increase with dilution, reaching values of 3 cm2/Vs for electrons and 1.2 cm2/Vs for holes. The ratio between electron and hole drift mobilities is found to be around 2 for all samples studied, similar to that of crystalline silicon.

Furthermore, post-transient Time of Flight measurements revealed detrimental electron deep traps in low dilution material.
Enlarged Parameter Space by Use of VHF-GD for Deposition of Thin
 Type μc-Si:H Films
Authors: Torres P. , Meier J. , Flückiger R. , Keppner H. , Shah A.
Published: April 2011

In this paper new results on thin p - type μc-Si:H films deposited at low temperatures of 170 °C by the Very High Frequency - Glow Discharge technique (VHF-GD) are presented. The “tolerated” amount of diborane added in the gas phase ratio as well as the influence of three different plasma excitation frequencies (70, 100 and 130 MHz) in obtaining high electrical conductivity are investigated. The goal is to optimise very thin (< 400 Å) and hence optically transparent films by maintaining high conductivities for the application as window layers of solar cells.
Influence of hydrogen incorporation into Silicon on the room-temperature photoluminescence
Authors: Rappich J. , Dittrich Th. , Timoshenko Y. , Beckers I. , Fuhs W.
Published: April 2011

We investigated the possibility to use the photoluminescence (PL) emission at room temperature for the characterization of grain boundary and surface passivation of μc-Si and single crystalline silicon. The PL-spectra of c-Si and μc-Si taken at 300 K consist of an emission band around 1.1 and 1 eV, respectively. Measuring the PL intensity we study the influence of electrochemical and plasma passivation by hydrogen. We compare the behavior of the films to that of Si crystals. In this case the PL intensity is high for a well H-terminated c-Si surface and decreases during cathodic polarization (hydrogen evolution) which points to the formation of additional non-radiative recombination centers. Whereas the PL intensity of the as prepared μc-Si films is unchanged, that of the annealed films increases during hydrogen evolution indicating the electrochemical passivation of defects on grain boundaries.
Pulsed ESR Study of the Conduction Electron Spin Center in μc-Si:H
Authors: Zhou Jiang-Huai , Yamasaki Satoshi , Isoya Junichi , Ikuta Kazuyuki , Kondo Michio , Matsuda Akihisa , Tanaka Kazunobu
Published: April 2011

The spin-lattice relaxation times (T1) of conduction electron (CE) and dangling bond (DB) centers in μc-Si:H have been directly measured using the 3-pulse inversion recovery method. For both CE and DB, the inversion recovery curve follows a stretched exponential form. T1 of DB is about twice the T1 of CE, however the temperature dependence of T1 seems to be the same for both CE and DB and can be approximated by T−4 While the DB echo decay is modulated by both 29Si and 1H nuclei, we found no modulation of the CE echo decay by the H nucleus, indicating that CE centers are located in H-depleted phases in μc-Si:H. The modulation results are direct evidence that CE centers are located in the crystalline grains and DB centers in the amorphous phases.
The Effect of Film Thickness and Pulse Duration Variation in Excimer Laser Crystallization of Thin Si Films
Authors: Leonard J. P. , Bessette M. A. , Gupta V. V. , Im James S.
Published: April 2011

Recognizing that the processing window in conventional excimer laser crystallization corresponds mainly to the partial melting regime, and that this can be properly simulated using a one-dimensional model, we investigate numerically the melting and solidification of thin silicon films on SiO2. Here a portion of the silicon film is melted and subsequent vertical solidification is initiated from the lower interface bounding the unmelted region. Upper and lower energy density limits for this regime are calculated for crystal silicon films of thickness 10 to 300 nm, and for pulse duration ranging from 10 to 200 ns. These calculations show that increasing pulse duration requires proportionally more incident energy density to partially melt the film, while decreasing film thickness reduces the range of energy densities over which partial melting can occur. The results are explained in terms of characteristic thermal diffusion distances and the enthalpy change associated with melting. In view of the results we discuss optimization of the conventional excimer laser crystallization and the avoidance of complete melting during the process.
Crystallization of Si(1-yCy Films by Excimer Laser Annealing: Characterization of the Microstructure of the Films
Authors: Boher P. , Stehle M. , Stehle J. L. , Fogarassy E. , Grob J. J. , Grob A. , Muller D.
Published: April 2011

Epitaxial Si(1-y)Cy substitutional alloy layers are prepared on monocrystalline silicon substrates by carbon multiple energy ion implantation followed by XeCl excimer laser annealing on large surfaces. Structural analysis of the films before and after laser annealing are made very precisely using spectroscopie ellipsometry (SE), x-ray diffraction (XRD) and Rutherford backscattering (RBS) techniques. We show that annealing energy densities higher than 2J/cm2 result in monocrystalline epitaxial layers with low quantity of defects. The lattice contraction due to the carbon inclusion increases with the implanted C concentration up to about 1.1%. For higher values a more complex behaviour is observed with partial (or total) relaxation of the layer and/or carbide formation‥
Surface Melting of Particles: Predicting Spherule Size in Vapor-Phase Nanometer Particle Formation
Authors: Xing Y. , Rosner D. E.
Published: April 2011

There is still no reliable method to predict the all-important size of the ‘primary’ spherules found in combustion-synthesized particulate products. Toward this end, we introduce surface melting concepts in developing a coagulation-coalescence model for nanoparticles in the low temperature regions of diffusion flames. The associated surface self-diffusivity, which controls the rate of spherule sintering at temperatures well below the equilibrium melting point, is therefore modified to include an important size effect. This formulation is used to calculate the sintering rate of two adjacent particles in a flame coagulation environment corresponding to a condensed phase volume fraction of Ca. 10−1 ppm. Predicted spherule sizes show encouraging agreement with our experimental data for ca. 10 nm diameter Al2O3 particles synthesized on the fuel side of a laminar CH4/O2 diffusion flame seeded with Al(CH3)3 (TMA)[1].
Synthesis and Characterization of Small Grain Sized Molybdenum Nitride Films
Authors: Roberson S. L. , Finello D. , Davis R. F.
Published: April 2011

Polycrystalline, small grain sized, 15 μm thick MoxN (x=1 or 2) films, void of detectable concentrations of molybdenum oxides, have been prepared on 50 μm thick nitrided Ti substrates via conversion of precursor MoO3 films in a programmed reaction with NH3. The latter films were produced via liquid spray pyrolysis of an MoCl5/methanol mixture in air at 500° C. The reaction of MoO3 films with NH3 resulted in a two-phase MoxN mixture consisting of γ-Mo2N and δ-MoN. The change in density of MoO3(ρ=4.69 g/cm3) to γ-MoN (ρ=9.50 g/cm3) and δ-MoN (ρ=9.05 g/cm3) produced grains with a calculated average size of 10 nm without losing adherence to the substrate. The composition of the MoxN films was determined by X-ray diffraction (XRD) and Auger electron spectroscopy (AES) to be ∼ 60% γ-Mo2N and 40% δ-MoN. The results of scanning electron microscopy (SEM) showed the surface morphology of the MoxN films to be highly porous.
Electrical/Dielectric Properties of Nanocrystalline Cerium Oxide
Authors: Hwang Jin-Ha , Mason Thomas O. , Garboczi Edward J.
Published: April 2011

Electrical/dielectric properties of nanocrystalline cerium oxide have been studied using impedance spectroscopy, thermopower, and DC 4-point conductivity. The combined techniques identified the effect of poor electroding on impedance spectra. Incomplete contact between the specimen and the electrode induces an additional arc in the impedance spectra. The additional high resistance feature results from the geometric constriction of current flow at the specimen/electrode interface and can be misinterpreted as a grain boundary response. The defect chemistry, nonstoichiometry, and transport properties were investigated in nanoscale ceria and compared with those of microcrystalline material.
Cluster Formation by Laser Ablation of Zeolites
Authors: Komiyama Hiroshi T. , Harano Azuchi , Okubo Tatsuya , Sadakata Masayoshi
Published: April 2011

Several kinds of zeolites, crystal-SiO2 (α-quartz), arnorphous-SiO2 (quartz glass and ultrafine particles) and α-Al2O3, were ablated by an Nd:YAG laser. Generated positive ions from the targets were measured by TOF-MS (time-of-flight mass spectrometry). In the TOF mass spectra of ablated zeolites, TOx (x=0–2, T = tetrahedral atom, e.g., Si, Al), T2Ox (x=1) and T3Ox (x=4,5) were observed up to m/z=170 (m = mass, z = plus charge of clusters). In the spectra due to the oc-quartz, quartz glass and an α-Al2O3 plate, smaller species, T+, TO+ and TO2+, were mainly detected. These results demonstrate that the clusters from zeolites reflect the characters of the mother structure.
Plasticity and Interfacial Dislocation Structures in Ti-Al
Authors: Parrini L. , Heinrich H. , Kostorz G.
Published: April 2011

The alloy Ti-48.6Al-l.9Cr-l.9Nb-IB with an equiaxed γ microstructure, obtained by heat treatment at 1200°C for 4 h, and with a lamellar mi ero structure, obtained by heat treatment at 1380°C for 1 h, is characterized by compression tests and transmission electron microscopy. A lower activity of superdislocations and a more frequent pinning of ordinary dislocations are detected in the lamellar Ti-Al specimens in comparison with the non-lamellar ones during deformation at room temperature. The activity of superdislocations and the pinning of ordinary dislocations are responsible for the differences in yield stress and brittleness between lamellar and non-lamellar Ti-Al. A very high density of ordinary interfacial dislocations is found in the lamellar structure. These influence the activity of superdislocations and the pinning of ordinary dislocations. At high temperature a change in the deformation mechanism occurs. Above the brittle-to-ductile transition, the material is remarkably softer and the mechanical properties are insensitive to the presence of the lamellar interfaces.
Static and Dynamic Strain Aging in Two-Phase γ-Titanium Aluminides
Authors: Christoph U. , Appel F. , Wagner R.
Published: April 2011

Deformation of two-phase titanium aluminides exhibits discontinuous yielding and a negative strain rate sensitivity over the temperature range 450–750 K. These phenomena are usually associated with the Portevin-LeChatelier effect which is due to the dynamic interaction of diffusing defects with the dislocations. The resulting glide resistance was investigated by static strain aging. The experiments involve the prestraining of samples followed by aging under a relaxing load for certain periods of time. Reloading of the samples resulted in distinct yield points. The investigations were performed on two-phase γ-titanium aluminides having different compositions and microstructures which are currently being considered for technical applications. Accordingly, dislocation locking occurs with fast kinetics which is characterized by a low activation energy. The experimental results will be discussed with respect to the nature of the diffusional mechanism and possible implication on the mechanical properties of the materials.
Strength, Thermal Defects, and Solid Solution Hardening in Nickel-Containing B2 Iron Aluminides
Authors: Schneibel J. H. , Munroe P. R. , PIKE L. M.
Published: April 2011

Nickel-containing ternary iron aluminides with an aluminum concentration of 45 at. % were investigated with respect to room temperature strength, equilibrium vacancy concentration, and the kinetics of vacancy removal. As compared to binary iron aluminides with the same Al concentration, nickel additions reduce the thermal equilibrium vacancy concentration at 1273 K, whereas they increase this concentration at 973 K. Furthermore, at low temperatures such as 673 K, nickel additions increase dramatically the time needed to reach vacancy equilibrium. During prolonged annealing at 673 K, the density of <001> dislocations in Fe-45Al-3Ni (at. %) increased by an order of magnitude. This suggests that dislocations act as sinks for vacancies. At the same time, the number density of small (20–50 nm) voids decreased, indicating that they were not stable in the absence of substantial vacancy supersaturations. Our findings show also that the solid solution strengthening of iron aluminides due to Ni is much weaker than previously thought.
Preparation, Deformation and Fracture of Stoichiometric NiAl Single Crystals
Authors: Löser W. , Köthe A. , Vaerst G. , Güth A.
Published: April 2011

A modified Bridgman method involving vacuum treatment prior to the growth process was developed for preparation of high-accuracy stoichiometric NiAl crystals. Single crystals with stoichiometry deviations < 0.2 wt.% Ni characterized by residual resistance ratios R298K/R4.2K > 4 have been prepared. An improved gravimetric analysis ensured the best accuracy among the various wet chemical analysis methods tested and a total error less than 0.1 at.% for Ni determination in NiAl. The stoichiometric NiAl single crystals exhibit high compressive strain in <123> crystallographic axis of the order of 20 % in the as-grown state and 40 % after annealing 1 h at 1073 K. The critical resolved shear stress was reduced from 104 MPa to 45 MPa by annealing. In 3-point bend tests tensile strains to failure up to 10 % have been achieved. Microscopic oxide inclusions near the sample surface were identified as the cause of crack initiation in bent samples.
Atomistic Simulations of Ti Additions to NiAl
Authors: Bozzolo Guillermo , Noebe Ronald D. , Garg Anita , Ferrante John , Amador Carlos
Published: April 2011

The development of more efficient engines and power plants for future supersonic transports depend on the advancement of new high-temperature materials with temperature capabilities exceeding those of Ni-based superalloys. Having theoretical modelling techniques to aid in the design of these alloys would greatly facilitate this development. The present paper discusses a successful attempt to correlate theoretical predictions of alloy properties with experimental confirmation for ternary NiAl-Ti alloys. The B.F.S. (Bozzolo- Ferrante-Smith) method for alloys is used to predict the solubility limit and site preference energies for Ti additions of 1 to 25 at. % to NiAl. The results show the solubility limit to be around 5 % Ti, above which the formation of Heusler precipitates is favored. These results were confirmed by transmission electron microscopy performed on a series of NiAl-Ti alloys.
Investigation of Superplastic Behavior of NiAI and Ni3Al Duplex Alloy
Authors: Zhenyun Liu , Dongliang Lin , Lin T. L. , Yuefeng Gu , Aidang Shan
Published: April 2011

The superplastic behavior of a NiAI and Ni3Al duplex alloy was investigated. It was found that the alloy exhibits superplastic behavior over a narrow temperature range, from 975 °C to 1025°C at the strain rate of 1.52 × 10-4 s-1. A maximum tensile elongation of 149% was obtained at 1000°C with the strain rate sensitivity up to 0.375. The superplastic deformation of the duplex alloy can be approximately described by an empirical equation of the form: ε = Ao2.67 exp(-303,000 / RT). Optical microstructure and TEM observation show that the superplastic behavior mechanism of the investigated alloy is a process of continuous recovery and recrystallization during deformation.
An Analysis of The Slip of Screw Dislocations in Ll2 Alloys
Authors: Veyssière Patrick , Lem
Published: April 2011

The annihilation of dislocations by cross-slip is studied by numerical simulation of infinitely long dissociated screw dislocations, allowed to move in an elastically anisotropie crystal. The external load is along [123] and cross-slip is permitted both on the octahedral and on the cube plane. The latter, together with cube slip, is thermally activated. Anisotropie elasticity modifies the properties of cross-slip significantly. Under the conditions of the simulations, the processes of APB jumps (APBJs) and repeated APB jumps (RAPBJs) can be largely promoted by interactions with other dislocations, while it is much less likely to occur at an isolated dislocation submitted to the same applied stress. The encounter of dislocations of opposite signs produces dipoles which may or may not tend to annihilate by cross-slip. APB tubes may form upon annihilation under certain circumstances again largely controlled by elastic anisotropy.
Phase Relation and Microstructure of NbCr2 Laves Intermetallics in Ternary Nb-Cr-X Alloy Systems
Authors: Yoshida M. , Takasugi T.
Published: April 2011

The isothermal phase diagrams of ternary alloy systems Nb-Cr-V and Nb-Cr-Mo are determined by metallography, X-ray diffraction (XRD) and transmission electron microscopy (TEM) equipped with energy dispersive X-ray (EDX). In two alloy systems, the C15 NbCr2 Laves phases are equilibrated directly with bcc solid solution without forming any intermediate phases. Relatively large amount of ternary elements V and Mo are soluble in the C15 NbCr2 Laves phases. It is shown that the C15 Laves phases extend along directions so that V occupies Cr site while Mo occupies Nb site. Also, characteristic structure containing micro twins and stacking faults is observed in the C15 Laves phase alloyed with Mo. Bcc phase has a wider solid solution range in the X(=V and Mo)-rich side than the Nb-rich and Cr-rich sides. A variety of duplex microstructures are observed depending on alloy system and alloy composition.
Modification of Interfacial Properties of Polymer Blends with Diblock Copolymer
Authors: Kim S. , Han C. C.
Published: April 2011

The effect of diblock copolymer on the phase-separation process of polymer blends has been investigated by using light scattering and optical microscopic observations. To quench the system into the two phase region, a shear-jump technique is employed instead of the conventional temperature-jump technique. The samples studied are blends of low-molecular-weight polystyrene and polybutadiene with and without added styrene-butadiene block copolymer as a compatibilizer. It was observed that the addition of diblock copolymers could accelerate the phase separation kinetics depending on the shear history. As the concentration of diblock copolymer increases, the distribution of domain sizes becomes narrower and the growth rate slows down. The extent of slowing-down depends on the molecular weight and concentration of the copolymer. The time dependence of domain growth is clearly observed with optical microscopy.
Analysis of Gold Hoard from Late Roman/Early Byzantine Period Found in Jordan
Authors: Williams W.S. , Flanagan J. W.
Published: April 2011

Thirty-four gold solidi coins and two pairs of gold/jewel earrings were discovered at an archaeological site in Jordan, Tell Nimrin. The coins have stamped images of six late Roman/early Byzantine emperors who reigned from 346 AD to 518 AD. These objects were analyzed by X-ray radiography, SEM/EDS and density measurements to find the gold content for comparison with other coins ofthat period to support their authenticity and to see whether debasement of coinage had occurred. The average surface gold content was found by EDS to be 98.1 wt %--typical of the period--but the bulk content calculated from density values was 1 to 3 wt % lower. The reason offered is that when a molten gold-copper or gold-silver alloy solidifies, the region in contact with the blank coin mold freezes first and is gold-enriched. Small “silvery” specks were observed on the obverse (”heads”) side of several coins and found by EDS to be Os-Ir-Ru alloys, which come from placer mining and indicate that the gold also came from placer mining.
Long-Distance Obsidian Trade in Indonesia
Authors: Tykot Robert H. , Chia Stephen
Published: April 2011

Long-distance trade in obsidian from sources in the southwest Pacific has been well-documented for the Lapita culture complex, beginning about 1600 BC. Analyses of obsidian artifacts from recent excavations at Bukit Tengkorak in southeastern Sabah (Borneo, Malaysia) indicate the use of obsidian from multiple sources in Melanesia as early as the 5th millennium BC. The archaeological presence of obsidian, up to more than 3500 km from its source, is the surviving evidence of what was almost certainly the longest Neolithic trade route in the world. In addition, these results indicate that long-distance trade networks existed in Indonesia at least 2500 years prior to the Lapita culture, and strengthen hypotheses of its origins in southeast Asia.
The Alteration and Natural Consolidation Effects of a Ceramic Vessel in Archaeological Excavation From San Lorenzo Tenochtitlán, Veracruz, Mexico
Authors: Guevara M.E. , Lopez M. , Cruz-Lara A. , Cyphers A. , Gama J.E.
Published: April 2011

A study of a ceramic vessel from San Lorenzo Tenochtitlán, Veracruz, México (Early Formative 1550–900 b.C.) was developed using three selected analytical methods: Petrographic thin section, X-ray Diffraction and Scanning Electron Microscopy. The results suggested, that the soil weathering processes on the ceramic vessel generated phenomenons, such as an increase in porosity, a decrease in bulk-density and loss in structural stability.

On the other hand, the presence of amorphous materials (SiO2, FeO3) in the soil, interacted with the ceramic giving it a natural consolidation. The consequences of our study are discussed in detail.
Socioeconomic Implications of Prehistoric Textile Production in the Eastern Woodlands
Authors: Jakes K.A. , Ericksen A.G.
Published: April 2011

Quantitative measures of time and effort as well as assessment of the knowledge base required in each level of textile manufacture (i.e., plant collecting, fiber processing, yarn and fabric formation) result in cost estimates that indicate differences between simply structured materials and complexly structured elaborate materials. These measures were applied to two textiles from a Wilbanks phase (A.D. 950 to 1440) [1] burial of a high status individual from Mound C at Etowah, Georgia [2]. Socioeconomic implications inferred from the resulting analyses include the proposal of craft specialization in the production of complex textiles and of the significance of these complex textiles to Mississippian chiefdoms.
An Organic Colorant used in Painted Ancient Maya Architectural Sculpture at Nakbe, Peten, Guatemala
Authors: Hansen Eric F. , Wallert Arie , Derrick Michele
Published: April 2011

The ancient Lowland Maya are generally considered to have used a limited number of inorganic colorants in their polychrome reliefs due to the lack or inaccessibility of mineral resources, especially during the Late Preclassic period (300 B.C. – 300 A.D.). A notable exception is the manufacture of a blue pigment from indigo and specific types of clay, known as Maya blue, from the Classic Period (300 – 900 A.D.) through Colonial times. Another exception is a recently analyzed cream (or reddish-yellow) colored paint found on exceptionally large architectural polychrome stuccoed sculpture dating to the early Late Preclassic at the site of Nakbe, Petén, Guatemala. The cream paint layer exhibits a dramatic peach-colored fluorescence upon exposure to ultraviolet light. An organic material, extracted with organic solvents from the acid hydrolyzed lime-based plaster surface, was characterized by means of visible light microspectroscopy, FT-IR microspectroscopy and three-dimensional fluorescence spectroscopy. Analysis of the spectra obtained from the cream colorant and comparison with spectra of reference organic materials suggests that anthraquinone derivatives may be responsible for the color, and that these compounds are similar to some of those present in organic red dyes. The cream paint was applied as a single layer with good hiding power overlying the stucco ground. The cream paint is of the same thickness (averaging 15 microns) as the only other paint present on the sculpture, a red paint pigmented with red iron oxide. The presence of organic colorants on exposed architectural features raises particular preservation problems in relation to the increased possibility and rate of deterioration due to environmental exposure of this type of organic colorant in comparison with most inorganic colorants.
Atomic Oxygen Treatment Technique for Removal of Smoke Damage From Paintings
Authors: Rutledge S.K. , Banks B.A.
Published: April 2011

Soot deposits that can accumulate on surfaces of a painting during a fire can be difficult to clean from some types of paintings without damaging the underlying paint layers. A non-contact technique has been developed which can remove the soot by allowing a gas containing atomic oxygen to flow over the surface and chemically react with the soot to form carbon monoxide and carbon dioxide. The reaction is limited to the surface, so the underlying paint is not touched. The process can be controlled so that the cleaning can be stopped once the paint surface is reached. This paper describes the smoke exposure and cleaning of untreated canvas, acrylic gesso, and sections of an oil painting using this technique. The samples were characterized by optical microscopy and reflectance spectroscopy.
Electron Microscopy Studies of the High Temperature Oxidation Behavior of NiAl
Authors: Yang J. C. , Schumann E. , Levin I. , Muellejans H. , Ruhle M.
Published: April 2011

The transient oxidation stage of single crystal (001)NiAl was investigated using scanning electron microscopy, transmission electron microscopy, electron diffraction, high resolution electron microscopy and electron energy loss spectroscopy (EELS). (001)NiAl was oxidized in air at 950°C in order to produce transient forms of alumina on the surface. After oxidation, an oxide scale with plate-like surface morphology formed. We found that the main transient alumina polymorph is γ-Al2O3. The platelets which formed on the surface of the oxide are most likely α-A12O3, not θ-Al2O3. Randomly-oriented α-Al2O3grains were observed at the oxide/metal interface. The NiAl/γ-Al2O3interfaces were examined with EELS. From the changes observed in the electron energy loss spectra, the interfacial terminating plane is determined. Lattice matching arguments are given to explain why these terminating planes are energetically favorable.
STM Study of a Defect-Related Si(001)-c(4×4) Surface
Authors: Yoshimura Masamichi , Ueda Kazuyuki
Published: April 2011

We demonstrate scanning tunneling microscopy studies of a Si(001)-c(4×4) structure which consists of a considerable number of dimer vacancies (missing dimers). Two different preparation methods are examined; one is hydrogen desorption and another is a special annealing and cooling process without hydrogen. The STM images reveal that atomic structure of the c(4×4) prepared without hydrogen is quite different from that prepared with hydrogen and is well described by the missing dimer model. A moiré-like pattern is observed on the c(4×4) surface prepared by hydrogen with an increase in the tip-sample distance, which suggests that the atoms lying in the subsurface should be considered for the precise description of the c(4×4) structure.
The Effect of Strain Relaxation Mechanisms on the Electrical Properties of Epitaxial CaF2/Si(111) Heterostructures
Authors: Schowalter L. J. , Kim B. M. , Thundat T. G. , Ventrice Carl A. , LaBella V. P.
Published: April 2011

A new technique for growth of exactly two monolayers of CaF2 on Si(111) substrates is demonstrated. This technique takes advantage of the tendency of CaF2 to form thick islands at Si step edges on vicinal substrates once a two-monolayer thick wetting layer is deposited. A comparison of I-V characteristics for epitaxial CaF2 layers grown on on-axis versus off-axis substrates demonstrates the advantages of this technique. In addition, preliminary results for electron tunneling through the CaF2 structure is shown using the ballistic electron emission microscopy (BEEM) technique.
Quantitative Eels Profiling of Planar Faults in CaTiO3 Perovskite Approaching Atomic Resolution: A Comparison With Z-Contrast Imaging
Authors: Gu Hui , Čeh Miran
Published: April 2011

Using EELS profiling, CaO planar faults of 1.36 nm spacing in CaTiO3 are resolved. Effective probe size was measured as 1.3 nm by quantitative analysis of EELS profiles, which is remarkably larger than 0.5 nm resolution for Z-contrast in similar conditions. Delocalization in EELS is the origin for this discrepancy, and strong elastic scattering near zone axis plays an important role in the quantification of profiles. Suitable spectrum subtraction successfully separates ELNES signal from the fault in one atomic distance with rock-salt structure. ELNES profiles for different local structures are also achieved. These examples demonstrate that EELS analysis can be performed reliably approaching atomic level, beyond the limit of probe size.
Mismatch and Misalignment at Interfaces Between Ag and Mn3O4 Studied With Hrtem
Authors: Kooi B. J. , Groen H. B. , De Hosson J.Th.M.
Published: April 2011

Internal oxidation of Ag-3at.%Mn resulted in Mn3O4 precipitates with a “parallel” topotaxy with the metal matrix and an octahedron shape due to {111} facets. Due to the tetragonali ty of Mn3O4, only a few planes and directions of Ag and Mn3O4 can be actual parallel. The precipitates exhibited a preference to align {111} planes parallel with the matrix for one pair of facets and then for another pair a tilt of 7.6° occurs which is relieved by ledges in Ag. The dislocation structure at these parallel and tilted {111} interfaces, originating from a 1-dimensional mismatch and including phenomena such as stand-off and dissociation of dislocations, was scrutinized.
Atomic-Force Microscopy of Gold Nanocrystallites on Smooth and Stepped Strontium Titanate Surfaces
Authors: Hamilton J. D. , Pap Anton Akis M. R. , Haglund R. F. , Godbole M. , Lowndes D. H.
Published: April 2011

We have studied the nucleation and growth of Au nanocrystallites with dimensions of tens of nanometers on strontium titanate surfaces using an atomic force microscope. Strontium titanate ablated from a pressed pellet target by a KrF laser was deposited on both planar and offcut strontium titanate substrates. In a separate step, submonolayer quantities of gold were deposited, also by pulsed laser deposition, on the strontium titanate. The surfaces were then scanned by an atomic-force microscope to determine the effects of surface defects (such as steps and kinks on offcut surfaces), substrate temperature, and gold ablation yield on the nucleation, growth and size distribution of the nanocrystallites. The competition between diffusion and nucleation on planar vs stepped surfaces was particularly apparent in the AFM images. These results suggest several ways in which lateral decoration of the strontium titanate by the gold nanocrystallites can be achieved, an important step toward designer nonlinear photonic materials.
Effect of Atomic Bonding on Defect Production in Collision Cascades
Authors: Nordlund K. , Averback R. S. , Diaz de la Rubia T.
Published: April 2011

We study the mechanisms of damage production during ion irradiation using molecular dynamics simulations of 400 eV -10 keV collision cascades in four different materials. The materials Al, Si, Cu and Ge are contrasted to each other with respect to the mass, melting temperature and crystal structure. The results show that the crystal structure clearly has the strongest effect on the nature of the damage produced, and elucidate how the open crystal structure affects the nature of defects produced in silicon.
The effect of the extra ion on residual damage in MeV implanted Si
Authors: Libertino S. , Benton J. L. , Coffa S. , Jacobson D. C. , Eaglesham D. J. , Poate J. M. , Lavalle M. , Fuochi P. G.
Published: April 2011

We have investigated the defect structure of ion-implanted and electron irradiated crystalline Si using deep level transient spectroscopy measurements to characterize both vacancy-(V) and interstitial- (I) type defects and to monitor their evolution upon annealing at temperatures ≤ 600 °C. It is found that only 4% of the Frenkel pairs generated by the energetic particles escape direct recombination and are stored into an equal number of room temperature stable V- and I-type defect complexes. No difference is found in the defect structure and annealing kinetics of ion implanted (1.2 MeV Si to fluences between 1×109 to 1010/cm2) and electron irradiated (9.2 MeV to fluences between 1 and 3×1015/cm2) samples in spite of the fact that denser collision cascades are produced by the ions. Annealing treatments result in a concomitant reduction in the concentration of I and V-type defects, demonstrating that defect recombination occurs preferentially in the bulk and not at the sample surface. Finally, at temperature above 300 °C, when most of the vacancy-type defects have been recombined, a residual concentration of I-type defects is found in ion implanted samples. This interstitial excess, not detected in electron irradiated samples, provides a direct evidence of the imbalance between I and V concentration produced by the extra incorporated ion.
Characterization of interstitial defect clusters in ion-implanted Si
Authors: Benton J. L. , Libertino S. , Coffa S. , Eaglesham D. J.
Published: April 2011

We have investigated the properties of Si interstitial clusters in ion implanted crystalline Si. Deep Level Transient Spectroscopy measurements have been used to characterize the residual damage in Si samples implanted with Si ions at fluence in the range 1×109-1×1012/cm2 and annealed at temperatures of 100–700 °C. We have found that, in the fluence and annealing temperature range where extended defects are not formed, the residual damage is dominated by Si interstitial clusters which introduce deep levels at Ev+0.36 eV and at Ev+O-53 eV. By using Si substrates with a different impurity and dopant content, we have found that C, O and B play a role in determining the defect growth kinetics but are not the main constituents of these clusters. We estimate that 40 to 125 Si self intersti-tials are stored in these clusters and believe that they are the main source of Si self-inter-stitials in transient enhanced diffusion phenomena occurring in the absence of {311} or extended defects.
Interatomic Potential for Condensed Phases and Bulk Defects in Silicon
Authors: Justo J. F. , Bazant M. Z. , Kaxiras E. , Bulatov V. V. , Yip S.
Published: April 2011

We present a new empirical potential for silicon which is a considerable improvement over existing models in describing structures away from equilibrium, such as bulk defects. The interatomic interaction is described by two- and three-body terms using theoretically motivated functional forms which emphasize chemical and physical trends. The numerical parameters in the functional forms are obtained by fitting to several ab initio calculations, which include bulk phases and defect structures. The model is tested to core properties of partial dislocations in the glide set {111}, which are not included in the database, and gives results in very good agreement with ab initio calculations. This is the only known potential capable of describing the structure of both the 30°- and 90°-partial dislocations.
Fick's Law and Transient Diffusion of Boron in Silicon
Authors: Wu David T.
Published: April 2011

The phenomenon of transient diffusion of boron in crystalline silicon is considered. The local equilibrium assumption from the law of mass action is not used in order to estimate the length of the transient regime. For an interstitial diffuser such as boron, the pair of diffusion equations, one each for the mobile and the immobile species, can be interpreted as a generalized Fick's Law in the total concentration with a position- and time-dependent diffusion coefficient whose concentration-weighted average, called the global diffusion coefficient, has an analytic solution for an appropriately defined time-lag. At 850°C for boron, the transient in the global diffusion coefficient is negligible, showing that the local equilibrium assumption is justified. An estimate is given for conditions under which local equilibrium may not be valid.
Point and Extended Defect Interactions in Silicon
Authors: Law M. E. , Earles S. K.
Published: April 2011

Transient Enhanced Diffusion (TED) is one of the biggest modeling challenges present in predicting scaled technologies. Damage from implantation of dopant ions changes the diffusivities of the dopants and precipitates to form complex extended defects. Developing a quantitative model for the defect behavior during short time, low temperature anneals is a key to explaining TED. The surface can play a defining role in the removal of point defects from the bulk, but there is a lot of controversy over the role and strength of the surface sink for point defects. The controversy will be reviewed, and new experimental results will be presented that investigate the role of the surface on TED.
Simple Computer Modeling of the Grain Microstructure of Al-4wt%Cu Interconnection Lines
Authors: Low K.S. , Bull S.J. , O'Neill A.G.
Published: April 2011

A simple computer model is proposed to simulate the microstructural evolution of Al-4wt%Cu lines. The model includes the coarsening and pinning of Al2Cu precipitates which occur during normal grain growth. This model is used to explore how Cu-rich precipitates evolve during normal grain growth, and how they affect the evolution of grain structure from polycrystalline to bamboo.