bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Diffusion and Nucleation Processes in Thin Film Formation: The Case of Ag/Si(111)
Authors: Venables J. A. , Doust T. , Kariotis R.
Published: March 2011

Surface diffusion and crystal growth processes have been studied in the Stranski-Krastanov growth system Ag/Si(111), using several UHV-SEM techniques. By depositing Ag at various rates 0.2 ≤ R ≤ 1.4 ML-min−1 through a mask of holes, surface diffusion of Ag over the intermediate layer has been observed, in competition with re-evaporation at high, and nucleation at low substrate temperatures, in the range 620 < T < 850K. The Si(111) √3Ag intermediate layer has been visualized using biassed secondary electron imaging. The surface diffusion and nucleation processes observed have been analyzed in terms of kinetic models. Comparison with experiment yields values for the adsorption, diffusion and binding (Ea′ Ed and Eb) energies of Ag on the intermediate layer. These values are approximately Ea = 2.45 ± 0.1 eV, Ed 0.35 ± 0.05 eV and Eb = 0.10 ± 0.03 eV, where the uncertainties result at least as much from lack of knowledge of pre-exponential factors in the models as in the accuracy of the experiments.
The Effect of Surface Structure on the Epitaxial Growth of Si on CoSi2(111)
Authors: Tung R. T. , Hellman F.
Published: March 2011

Two distinctively different structures were found on CoSi2(111), the CoSi2-C and the CoSi2-S, which correspond to, respectively, an essentially bulk-terminated surface and one which consists of an additional Si double layer. Details of the two structures suggest new growth techniques for Si epitaxy. Single crystal Si layers with either identical orientation as the silicide or a 180°-rotated orientation can be fabricated by use of carefully designed Si templates.
Molecular Dynamics Studies of the Adatom Induced Rearrangement of the Silicon {100} Surface
Authors: Brenner Donald W. , Garrison Barbara J.
Published: March 2011

A molecular dynamics simulation of the silicon adatom induced rearrangement of the silicon {100} symmetric dimer reconstructed surface has been performed. Surface diffusion is proposed to play a critical role in the reordering of this surface which leads to good epitaxy while it plays much less of a role in the reordering induced by an amorphous overlayer. These results are used to provide atomic-scale models which are consistent with high-energy ion channeling/blocking and LEED studies by Gossman and Feldman of the initial stages of silicon growth on this surface.
Role of Surface Reconstruction and External Ion Beam in the Growth Kinetics of III-V Molecular Beam Epitaxy
Authors: Ogale S. B. , Thomsen M. , Madhukar A.
Published: March 2011

Computer simulations of III-V molecular beam epitaxy (MBE) show that surface reconstruction induced modulation of kinetic rates could give rise to ordering in alloys. Results are also presented for the possible influence of an external ion beam in achieving low temperature epitaxy as well as smoother growth front under usual conditions.
Method for the Reduction of Photothermal Deflection Spectroscopy Data Taken on Amorphous Silicon (a-Si:H)
Authors: Wiedeman S. , Bennett M. S. , Newton J. L.
Published: March 2011

Photothermal deflection spectroscopy (PDS) is a sensitive method used to measure weak optical absorption of sub-bandgap radiation. A method utilizing Fourier transformation is presented which allows removal of optical interference effects and noise which is typically present in PDS data taken on a-Si:H, yet leaves the underlying PDS spectra undistorted. The method greatly facilitates comparison of PDS spectra taken on different samples, and simplifies further analysis. Examples using a-Si samples produced under different deposition conditions are presented to demonstrate the utility of the method.
Porous Morphology and Oxidation Kinetics in a-Si:H RF Sputtered by He/H2
Authors: Shinar J. , Shinar R. , Mitra S. , Albers M. L. , Shanks H. R. , Moustakas T. D.
Published: March 2011

a-Si:H films rf sputtered in 10 mT He and 0.5 mT H2, in contrast to those prepared in Ar/H2 or Xe/H2, exhibit port depositional oxidation when sputtered at power levels of 0.55 – 3.3 W/cm2 (100 – 600W). SEM measurements show that the morphology of the films evolves from a cracked, microcrystalline, glassy one at higher rf power levels to a porous one at low power levels. This trend is also correlated with a sharply increasing density of Si-H2 dihydride bonds at decreasing rf levels. Auger depth profiles of the oxygen concentration in the films agree with a diffusion controlled process of a source solute of O2 molecules into a semi-infinite solid solvent. Yet IR absorption measurements indicate that the oxygen is confined to the internal surfaces of the microvoids. The diffusion constant is a very sensitive functi n of the sputtering conditions. At low rf power levels, it is as low as 10−16 – 10−1 cm2 /sec at room temperature, but increases to ∼10−13 at 250 – 350°C.These results are discussed in terms of a porous network of microvoids, through which the O2 “squeezes” into the film.
Identification of Chemical Growth Mechanisms in Amorphous Semiconductors
Authors: Reimer Jeffrey A. , Mccarthy Michael J. , Gleason Karen K. , Morrison Philip W.
Published: March 2011

Experimental and computational results for three classes of experiments are reported. NMR measurements of phosphorus in amorphous hydrogenated silicon indicate that bonding rearrangements in bulk films are possible. Monte Carlo simulations of film growth demonstrate that surface diffusion is the dominant physical phenomenon responsible for the bulk hydrogen content of a-Si:H films. Finally, the gas phase chemistry of silane, as elucidated by our new “diesel” reactor, is considerably more complicated than many authors assume in models for thin films grown from silane.
Growth of Amorphous and Crystalline Silicon by HR-CVD (Hydrogen Radical Enhanced CVD)
Authors: Shibata N. , Fukuda K. , Ohtoshi H. , Hanna J. , Oda S. , Shimizu I.
Published: March 2011

Systematic studies have been made on preparation of Si thin films from SiF4 under control over the flow of atomic hydrogens. The gas phase reactions taking place in the mixture of fragments (SiFn) resulting from plasma-induced dissociation and atomic hydrogens were widely investigated by a mass spectroscopy. Chemically active species,i.e., SiF2H and SiH2F were found as those related to the growth of films. The growth in the vicinity of substrates involves either endothermic or radical-enhanced reaction for the propagation of the three dimensional Si networks, accompaning release of terminators such as H and F. Accordingly, Si thin films with structures from amorphous to crystalline were obtained by controlling the flow of atomic hydrogen. A marked improvement in the hole-transport was established in the Si films containing hydrogen less than 5–6 at % due to the reduction in the tail states near the valence band.
Thermal Equilibration and Growth of Doped Amorphous Silicon
Authors: Kakalios J. , Street R. A. , Tsai C. C. , Weisfield R.
Published: March 2011

The relation between the thermal equilibration of the defect structure in n-type doped hydrogenated amorphous silicon (a-Si:H) and the deposition conditions has been investigated. When the deposition rate is increased by raising the rf power the equilibration time constants become longer, though the thermal equilibrium processes are qualitatively similar to those in samples grown under optimal conditions. Models relating the slower equilibration rate to the deposition-induced microstructure are explored.
Influence of Plasma Excitation Frequency on Deposition Rate and on Film Properties for Hydrogenated Amorphous Silicon
Authors: Curtins H. , Wyrsch N. , Favre M. , Prasad K. , Brechet M. , Shah A. V.
Published: March 2011

The preparation of hydrogenated amorphous silicon by the radio-frequency (RF) glow discharge technique is shown to be strongly dependent on the plasma excitation frequency. We have investigated the influence of this parameter on the deposition rate, on the hydrogen content and on the opto-electronic properties of the amorphous silicon films, over the range 25 to 150 MHz. A large variation of the deposition rate is observed, while most of the material properties remain practically unchanged. The results should be of considerable interest for mass production of low-cost amorphous silicon thin film devices.
Preparation and Properties of Hydrogenated Amorphous Silicon Produced by Plasma-Enhanced Chemical Vapor Decomposition of Silane
Authors: Tokuda K. L. , Adler D. , Reif R.
Published: March 2011

We have investigated the properties of several hydrogenated amorphous silicon (a-Si:H) films prepared by the plasma-enhanced chemical vapor decomposition (PECVD) of silane. This reactor is singular because it operates at pressures as low as 10 mTorr and uses infrared lamps to heat the growth environment. Structural characterization showed that all the samples were amorphous. Most films had hydrogen concentrations about 5%, optical gaps near 1.6 eV, and neutral dangling-bond concentrations of the order of 5 × 1016 Cm−3. Electrical activation energies were typically in the range 0.5 – 0.6 eV and the photoconductivity under ∼100 mW/cm2 white light was 10−4 (Ω-cm)−1. The dark conductivity was near 10−8(Ω-cm)−1. No significant change in dark conductivity or photoconductivity occurred after several hours of exposure to light.
High Quality Amorphous Silicon Prepared by Catalytic Chemical Vapor Deposition (CTL-CVD) Method
Authors: Matsumura Hideki
Published: March 2011

A new method of producing high quality hydrogenated amorphous silicon (a-Si:H) and its compound films is presented. An SiH4 and H2 gas mixture is decomposed without using any plasmas or photochemical excitation, but using only thermal and catalytic reactions between deposition gas and a heated tungsten catalyzer. Photoconductivity of a-Si:H films produced by, this method reaches 10−3 (Ωcm)−1 and photosensitivity exceeds 105 for illumination of AM-1 light of 100 mW/cm2, highly efficient boron- or phosphorus-doping into the films is achieved, and also the optical band gap of the films is easily controlled without apparent degradation of the properties by adding GeH4 gas to the deposition gas.
Interaction of Reactive Species Obtained by G-D Silane Decomposition with Si(111) and a-Si:H Surfaces
Authors: Cruz S. A. , Mendez-Rosales V. M.
Published: March 2011

We calculate the average surface potential barrier for incorporation of H, Si, SiHb (n=1–4) into films of a-Si:H as well as crystalline Si(111) surfaces. In the first case a local amorphous configuration for the surface is employed through a representative cluster(Si29 H1 0 ) forming 5, 6, 7 Si atom rings. For the crystalline surface, several layers of Si atoms are considered. Pairwise superposition of combined Morse and Thomas-Fermi-Moliére interatomic potentials is assumed for the total interaction between the incoming species and the surface.
Photoluminescence in Hydrogenated Silicon-Germanium Alloys
Authors: Ranganathan R. , Gal M. , Viner J. M. , Taylor P. C.
Published: March 2011

Results of a detailed study of photoluminescence (PL) in the a-Si1−xGex:H system are presented. Many samples exhibit a low energy “tail” to the PL efficiency which is of constant magnitude independent of x. There is a departure from this behavior when a low energy PL peak near 0.8–0.9 eV is present. The position of the low energy PL peak is independent of Ge concentration. It has been suggested that this PL transition is from an electron in the conduction band tail into a silicon dangling bond state. As Ge is added to a-Si:H it is the edge of the conduction band which decreases in energy while the valence band remains relatively constant in energy. It is therefore unlikely that the low energy PL is due to a transition from the conduction band into a silicon dangling bond state because the energy of the silicon dangling bond with respect to the valence band is probably essentially independent of Ge content. If the PL which peaks near 0.8 eV results from a transition which involves a silicon dangling bond, then the transition may be from the dangling bond to the valence band.
Electronic States in Amorphous Solids, Liquids, and Alloys
Authors: Bar-Yam Y. , Adler D. , Joannopoulos J. D.
Published: March 2011

We describe elements of a thermodynamical ensemble theory of electronic states in a variety of disordered systems. Equilibrium energies and kinetics of phase space exploration combine to determiine the ensembles describing disordered systems. Electronic properties are then related to structural energies. This relationship serves to determine the distribution of electronic states present in real materials. Thus we obtain directly electronic properties without a need for detailed microscopic information about the diverse systems. Applications range from the Urbach edge to defect properties providing a unified understanding.
High-Quality a-Si-Based Alloys : a-SiGe Films Fabricated in a Super Chamber and Superlattice Structure a-Si Films Prepared by a Photo-CVD Method
Authors: Tsuda Shinya , Haku Hisao , Tarui Hisaki , Matsuyama Takao , Sayama Katsunobu , Nakashima Yukio , Nakano Shoichi , Ohnishi Michitoshi , Kuwano Yukinori
Published: March 2011

In order to improve the conversion efficiency of a-Si solar cells, high-quality a-Si based alloys of both narrow handgap and wide bandgap were studied.

Concerning the narrow bandgap material, we found a particular dependence of film qualities on substrate temperature. In addition, high-quality a-SiGe:H films were obtained by using a super chamber (separated ultra-high vacuum reaction chamber).

As for the high-quality wide bandgap material, a-Si/a-SiC superlattice structure films fabricated by a photo-CVD method were studied for the first time. From the analysis of their properties, we found that the superlattice structure p-layer was an active layer for photovoltaic effect. A conversion efficiency of 11.2% has been obtained for a pin a-Si solar cell whose player was of the superlattice structure.
Carbon Local Bonding Configurations in Amorphous Hydrogenated Silicon-Carbon Alloys
Authors: Petrich Mark A. , Reimer Jeffrey A.
Published: March 2011

We present the results of a carbon-13 nuclear magnetic resonance (NMR) study of well-characterized thin films of amorphous hydrogenated silicon carbide. The NMR data detail the distribution of carbon local bonding configurations in films which have carbon-to-silicon ratios less than one. In particular, we show data which clearly identify and quantify non-hydrogenated sp2, or unsaturated, carbon bonding environments.
Temperature Dependence of Optical Properties and Minority Carrier Diffusion Length in a-SiGe:H,F
Authors: Schwarz R. , Dietrich K. , Goedecker S. , Kolodzey J. , Slobodin D. , Wagner S.
Published: March 2011

We report the temperature dependence of several optical parameters of thin films of hydrogenated and fluorinated amorphous silicon alloys (a-SiGe:H,F) between 5 and 95 °C. The absorption coefficient near the optical band gap Eg increases with temperature. From this increase we calculate a temperature coefficient for Eg of −4.5×10−4 eV/K, which is essentially independent of band gap The concomittant change of index of refraction n was determined in the near infrared region from the interference pattern in the reflection spectra. The temperature coefficient dn/n/dT is 0.9×10−4 K−1 for un-alloyed a-Si:H,F and increases with increasing Ge atomic fraction. The changes of Eg and n with temperature are consistent with a simple quantummechanical description of the complex dielectric constant. We also report the temperature dependence of the minority carrier diffusion length in a-SiGe:H,F.
Electronic Transport Properties of a-Si:H,F/a-Si,Ge:H,F Superlattices
Authors: Conde J. P. , Aljishi S. , Shen D. S. , Chu V. , Smith Z E. , Wagner S.
Published: March 2011

We study the dark conductivity σd, dark conductivity activation energy Ea and photoconductivity σph of a-Si:H,F/a-Si,Ge:H,F superlattices both perpendicular and parallel to the plane of the layers. In parallel transport, both the σph and σd are dominated by the alloy layer characteristics with the superposition of carrier confinement quantum effects. In perpendicular transport, the σd shows an interplay of quantum mechanical tunneling through the barriers and of classical thermal emission over the barrier layer and the σph is controlled by the decreasing absorption by the silicon barrier layer as the optical gap Eopt of the structure decreases.

We also found that the multilayer structure allows to grow lower gap a-Si,Ge:H,F alloys than achievable under the same deposition conditions for bulk materials. This stabilizing effect allowed us to study low-gap superlattice structures and extract information about these very low gap (<1.2 eV) a- Si,Ge:H,F alloys.
High Conductive a-Si:H/a-SiC:H:F Super Lattice Prepared by a Chemically Controlled Method
Authors: Koinuma H. , Kawasaki M. , Fueki K.
Published: March 2011

Amorphous super lattices composed of a-Si:H and a-SiC:H:F layers were continuously prepared from a gas miture of CF4 and either SiH4 or Si2 H6 by the pulsed plasma and photo (PP&P) CVD method. The method utilizes the difference in photochemical reactivity of the source gases for the formation of layered structure. The layered films prepared by using Si2H6 as silicon source under the condition that they had optical gaps up to 2.0 eV were found to show photoconductivities higher not only than those of a-SiC:H:F films prepared from the same gas mixture by the continuous plasma and photo hybrid CVD but also than those of a-Si:H films by the photo CVD. From the comparison of optical and electrical properties of super lattices prepared, the photoconductivity of the films is suggested to be primarily dependent on the quality of barrier layer rather than on the quality of well layer.
The Characteristics of Amorphous Silicon TFT and its Application in Liquid Crystal Display
Authors: Chikamura T. , Hotta S. , Nagata S.
Published: March 2011

An amorphous silicon TFT particularly suited for the full color liquid crystal display driver has been developed and reported here. Various fundamental factors involved in the a-Si TFT, such as the effects of structure, materials, and the method of fabrications were reviewed and investigated in terms of the field effect mobility, the threshold voltage and the reliabilities. An inverted-staggered TFT structure was employed for the purpose wherein the interface states between two layers was successfully lowered by employing the successive deposition procedures of SiNx gate insulator on the a-Si layer. Proper ohmic contacts and the blocking of hole injections were accomplished by forming a n+ layer between the a-Si layer and the source/drain metal electrodes which consists of a double layer of Al/MoSi2 in order to prevent the aluminum diffusion into the a-Si layer during the 300°C heat treatment at the succeeding fabrication processes. The degradation of display images due to the high intensity backlights was minimized by employing a light shielding layer and by making the thickness of a-Si layer 200 Å against the direct sunlight of up to 100,000 luxes. Stable actual performances of TFT for more than 4000 hours at 80 °C were confirmed. The development of a color LCD TV driven by this TFT is also reported.
Large Scale and Large Area Amorphous Silicon Thin Film Transistor Arrays for Active Matrix Liquid Crystal Displays
Authors: Miki H. , Kawamoto S. , Horikawa T. , Maejima T. , Sakamoto H. , Hayama M. , Onishi Y.
Published: March 2011

The preparation and properties of hydrogenated amorphous silicon thin film transistor arrays for active matrix liquid crystal displays are reported. The effect of amorphous silicon film preparation conditions on the field effect mobility of thin film transistors was investigated. The dry etching rate of silicon nitride film was studied.The thin film transistor arrays have 408 ˜ 640 transistors on the first version and 450 ˜ 640 ˜ 3 transistors on the second version. The liquid crystal panel fabricated using the first version arrays showed good characteristics.
States in the Gap of Doped and Undoped a-Si:H Studied by Photomodulation Spectroscopy
Authors: Zhou T. X. , Vardeny Z. , Tauc J.
Published: March 2011

The steady state photomodulation spectrum, its temperature and excitation intensity dependences have been studied in phosphorous doped and undoped a-Si:H. The spectra are analyzed in terms of photocarriers trapped in band-tail states and dangling bonds (DB) defects in undoped samples and impurities and charged DB states introduced by doping in P-doped samples. In undoped a-Si:H we found that the two DB energy levels D± are symmetrically located about midgap with an effective correlation energy Ueff of 0.6±0.2eV. In P-doped a-Si:H D− is pushed toward midgap by about 0.25 eV and Ueff = 0.4±0. 2 eV.
Deep States in a-Si:H - Changes with Doping and Applied Stress.
Authors: Kočka J. , Vanéček M.
Published: March 2011

Recent Constant Photocurrent Method (CPM) results and a new model of a-Si:H density of states are briefly reviewed. The small but systematic changes of subgap absorption (α) with the applied external stress have been found. When light-soaking is done under the applied stress the strong increase of α is observed. The μτ (mobility-lifetime) versus α duality is demonstrated. The increase of the dangling bond density, combined with the change of its charge state, is used for the explanation of duality. The light induced creation of dangling bond-impurity intimate pairs is speculated to be the driving force for the Fermi level shift.
Time-of-Flight Measurements in a-Si:H Between Room Temperature and 130° C°
Authors: Shen D. S. , Aljishi S. , Smith Z E. , Conde J. P. , Chu V. , Wagner S.
Published: March 2011

The drift mobility μd and the mobility-lifetime product μτ in undoped a-Si:H have been studied up to 130°C. The electron μde is temperature-activated with Eae = 0.13 to 0.16 eV. The electron (μτ)e increases with temperature T. For hole transport, we observe the transition from dispersive to non-dispersive transport with increasing T. The hole μdh is ∼ 1/100 of μde, and is activated with Eah = 0.34 to 0.48eV. The hole (μτ)h does not change much with T. A computer simulation demonstrates the high sensitivity of μd to the band tail width.
Crystal Structure Refinements of Rhombohedral Symmetry Materials Containing Boron-Rich Icosahedra
Authors: Morosin B. , Aselage T. L. , Feigelson R. S.
Published: March 2011

The crystal structures of several icosahedral boron-containing compounds have been refined using MoKα intensity data. Preparation of crystals differs from previous procedures, with boron carbide grown from molten copper and boron arsenide by arsenic vapor transport. The structures consist of icosahedral units bonded together with direct B-B bonds as well as other linkage units (B-C-B and As-As chains).
Rapid Isothermal Annealing of N-Implanted 6H-SiC Layers Used for Fabrication of p-n Photodiodes
Authors: Pensl Gerhard , Helbig Reinhard , Zhang Hong , Ziegler Gonther , Lanig Peter
Published: March 2011

Ion implantation of 14N and Rapid Isothermal Annealing (RIA) were employed to achieve n-type doping in epitaxial-grown 6H-SiC layers. The electrical properties of the implanted films were investigated by Hall effect measurements in order to optimize the annealing parameters. In comparison with standard furnace annealing (1470°C/7min), the annealing parameters for the RIA process could be considerably reduced (1050°C/4min). Based on planar technique, implanted p-n junctions were fabricated. The temperature dependence of I-V characteristics and of the quantum efficiency of photodiodes were studied. The maximum of the quantum efficiency at γ=330 nm reaches values of 35% at 400°C.
Electrical Properties of 3C-SiC and its application to FET
Authors: Yoshida S. , Endo K. , Sakuma E. , Misawa S. , Okumura H. , Daimon H. , Muneyama E. , Yamanaka M.
Published: March 2011

Electrical and luminescent properties of nondoped, and N-doped n-type 3C-SiC layers epitaxially grown on Si(100) by chemical vapor deposition were studied. Nondoped n-type epilayers with carrier concentration of 1×1016cm−3 and the Hall mobility of 750cm2/Vs at room temperature have the activation energy of donors, Ed=2OmeV, which is different from that of the donors in the N-doped layers. The photoluminescence spectra of nondoped layers are different from those of N-doped ones. These results suggest that the donors in the unintentionally doped n-type 3C-SiC are not due to N impurities. 45–70 % of N-donors in the N-doped epilayers are compensated.

Schottky-barrier and MOS-type field-effect transistors have been fabricated from 3C-SiC. The transistor operations of MESFETs and MOSFETs were studied at elevated temperatures up to 440°C. Transconductances of 1.7mS/mm and 0.15mS/mm for MESFET and 0.8 and 0.05mS/mm for MOSFET at room temperature and 440°C, respectively, were obtained. The drain currentvoltage characteristics of both the FETs at room temperature did not change in the least after heating up to 440°C in the air.
AES Studies of the M/SiC Interface with Metal Carbide Formers
Authors: Zeller M. V. , Bellina J. , Saha N. , Filar J. , Hargraeves J. , Will H.
Published: March 2011

After Nichrome, Ni, Cr, and Au/Ta films are deposited onto single crystals of cubic SiC, their reactivities at the metal-semiconductor interface are studied by Auger Electron Spectroscopy. For all metals except Ni, metal carbides are detected at the interfaces. Initially these carbides tend to promote adhesion and limit the reaction with the substrate. Annealing at or above 450°C causes Ni to diffuse into the SiC and the Ta and Cr films to migrate through the capping material and away from the SiC, thereby delaminating. Development of the secondary phases at interface severely complicates the interpretation of the depth profiling data and with the uniformity of the contact film. These phases seem to be initiated at SiC defect sites where the reaction kinetics are considerably different and may be minimized with improved SiC substrates.
Predictions on the Physical Properties of Amorphous Carbon-Tin Semiconducting Alloys I Structure and Optical Properties
Authors: Mpawenayo Prosper
Published: March 2011

The theory developed by Coulson, Rushbrooke and Longuet-Higgins (CRLH) on the electron-charge density and the atom-bond polarisability in hetero-atom conjugated systems is used to show that n-electron charge transfer by Sn substitutional incorporation in aC:H would promote the tetrahedral structure. An agreement with Phillips stability criterion is found.
The effective medium theory is then applied for predictions on the dielectric properties of narrow optical band-gap (0,6–1,5 eV) C-Sn alloys. It is suggested that the incorporation of electronegativeelements (F, Cl) would reduce the high sub-bandgap absorption.
Effect of High Temperature Annealing on the Thermoelectric Properties of GaP Doped SiGe
Authors: Vandersande Jan W. , Wood Charles , Draper Susan
Published: March 2011

Silicon-germanium alloys doped with GaP are used for thermoelectric energy conversion in the temperature range 300°C - 1000°C. The conversion efficiency depends on Z - S2/ρΛ, a material's parameter (the figure of merit), where S is the Seebeck coefficient, ρ is the electrical resistivity and Λ is the thermal conductivity. The annealing of several samples in the temperature range of 1100°C - 1300°C resulted in the power factor P (=S2/ρ) increasing with increased annealing temperature. This increase in P was due to a decrease in ρ which was not completely offset by a drop in S2 suggesting that other changes besides that in the carrier concentration took place. SEM and EDX analysis of the samples indicated the formation of a Ca- P-Ge rich phase as a result of the annealing. It is speculated that this phase is associated with the improved properties. Several reasons which could account for the improvement in the Power factor of annealed GaP doped SiGe are given.
The Effect of Sm, Eu and Yb on the Thermoelectric Properties of Th3P4,-Type Lanthanum Sulfide
Authors: Nakahara J. F. , Beaudry B. J. , Gschneidner K. A. , Takeshita T. , Laboratory Ames
Published: March 2011

The Th3P4-type lanthanum sulfides are n-type semiconductors and a continuous series of solid solutions is found between the compositions of La3S4 and La2S3. These materials are attractive for use in high temperature thermoelectric applications because of their high melting points, low thermal conductivities and their inherent ability to vary the electron concentration from a maximum of 6.02 × 1021 cm−3 for La3S4 to zero for La2S3 (i.e., self-doping). In this study, La3S4 compounds in which trivalent La has been partially substituted by divalent Sm, Eu or Yb (La3−xMxS4 , x = 0.1 to 0.9) have been prepared by the pressure assisted reaction sintering method and were found to have the Th3P4 structure. The thermoelectric properties (Seebeck coefficient and electrical resistivity) were measured as a function of temperature and the optimum composition was found for x between 0.2 and 0.3 in which the electrical power factor was a maximum at 1000°C.
Effect of the Microstructure on the Thermoelectric Properties of Polycrystalline Lanthanum Chalcogenides
Authors: Lockwood A. , Wood C. , Vandersande J. , Zoltan A. , Parker J. , Danielson L. , Alexander M. , Whittenberger D.
Published: March 2011

Small amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline γ-La3-xX4 (X-S, Te; 0<x<l/3). Microscopic examination by SEM of hot pressed La3–xTe4 samples has revealed from 1–5 vol. % of La202Te, an amount which is not detected by x-ray powder diffraction measurements. This amount of La202Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10% to 75% below the electron concentration calculated for single phase La3–xTe4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.
Refractory Films from Spin-Cast Polyacrylonitrile
Authors: Renschler C. L. , Sylwester A. P.
Published: March 2011

Polyacrylonitrile (PAN) films have been spin-cast and pyrolyzed to produce thin (500–1500 Å) carbon films. These films have higher electrical conductivities than carbon films produced by other methods at similar temperatures. The conductivity can be varied by at least four orders of magnitude by changing the pyrolysis temperature. UV, IR, and Raman spectroscopies were used to investigate the chemical structure of the films during different stages of processing.
Stable Positions of a Metal Ion Relative to an Icosahedral Borane
Authors: Beckel C. L. , Howard I. A.
Published: March 2011

We have considered a series of conformations of the neutral complex [Mg+B12H12] including those in which the Mg is internal to the icosahedral B12 cage. Self-consistent molecular-orbital calculations to determine the total cluster energy have been carried out as the Mg atom is moved from the center of the borane to a position 10Å from the center (outside the borane cage). Two energy minima are found as a function of position. One is outside the borane cage. at 3.0–3.5Å from the center; the second is at the center of the borane cage. The central minimum is the deeper of the two if Mg 3d orbitals are included in the basis set.

Many atoms have a low ionization energy and are, as ions, of appropriate “size” to fit inside a B12 cage. Incorporation of such ions into B12 cages in solids may offer significant flexibility in the development of refractory semiconductors and thermoelectrics.
Thermal Properties of Boron-Rich Borides
Authors: Fischer H. E. , Swartz E. T. , Türkes P. R. H. , Pohl R. O.
Published: March 2011

The specific heats of β-B and of B4C have been reviewed, and measurements of a different sample of B4C have been carried out below 80 K. A specific heat anomaly observed previously in boron carbides has been shown to be extrinsic in origin. The thermal conductivity of B1−x Cx, for x < 0.20, between 0.2 and 2000 K has also been reviewed, and recent measurements have been added. The magnitude and temperature dependence of the conductivity are somewhat similar to what is expected for amorphous boron, except for the characteristic plateau which is not clearly discernible. A possible explanation for the strong phonon scattering is discussed.
Thermal Conductivity of Boron Carbides
Authors: Moss Marvin
Published: March 2011

The thermal conductivity, k, of boron carbides of various B/C ratios, two modes of preparation – hot pressed and carbothermic, and two isotopic variants of boron – 11B and normal boron 10.81B, was measured from 300 to 1023 K. The density and composition of the samples were reflected in the magnitude and temperature dependence of k, and were investigated further with scanning electron microscopy, Rutherford backscattering spectroscopy, and Raman spectroscopy. While lower than theoretical density in B4C reduces k, the characteristic monotonic decline of k with increasing temperature is retained. This k-vs.-T behavior distinguishes B4C from material with larger B/C ratios for which the temperature dependence is essentially nil.
Laser Induced Fluorescence and Optical Emission Studies of Fluorocarbon Plasmas
Authors: Booth J. P. , Hancock C. , Perry N. D. , Blaikleye D. C. W. , Cairns J. A. , Smailes R.
Published: March 2011

Laser induced fluorescence of CF2 has been observed in plasmas of CF4 and its mixtures with O2 and H2. Surface removal rates of the radical in pure CF4 were measured by observing the decay of the radical when the plasma is switched off. The reduction in CF2 concentration, and the increase in F atom concentrations (the latter measured by optical emission spectroscopy) on the addition of O2 is reproduced by a model of the plasma in which gas phase chemical reactions play a dominant role. The increase in CF2 concentration on the addition of H2 to a CF4 plasma is shown to be due to a reduction in the surface removal rate.
Plasma Diagnostics for a Low-Pressure Plasma Spray Deposition System
Authors: Weissman Suzanne H. , Smith Mark F. , Chambers William B.
Published: March 2011

Plasma temperatures and spray particle velocities were measured in a low pressure plasma spray system. Plasma temperatures of 6,540–9,050 K were calculated from argon atomic emission spectra by the Boltzmann slope method. Peak particle velocities up to 365 m/s were measured with a laser velocimeter for 44 pm Al2O3, spray powder. Measured particle velocity distributions show a strong dependence on process chamber pressure over the range of 50–600 Torr.
Large Area Electron Beam Enhanced Reactive Etching of SiO2
Authors: Boyer P. Kirk , Verhey Tim , Rocca Jorge J.
Published: March 2011

A large area (2.8 cm2) electron beam source has been developed, characterized, and applied to anisotropic etching of SiO2 masked with photoresist. This beam operates at high pressures (up to 100 mTorr), in reactive gases, and at more than 10 mA/cm2. Beam current can be controlled in several ways independently from beam energy. The 100 – 900 eV low energy beam propagates with collimation through several cm of reactive gas, and is believed to minimize space charge defocusing by collisionally ionizing the working gas.
Mechanism of the Slow-Down of the Silicon Etch Rate by a Fluorocarbon Overlayer in CF4/H2 Reactive Ion Etching of Silicon
Authors: Oehrlein Gottlieb S. , Robey Steve W. , Jaso Mark A.
Published: March 2011

We have utilized an ultrahigh vacuum surface analysis system interfaced via a load-lock to a flexible diode dry etching apparatus to study vacuum transferred CF4/H2 reactive ion etched silicon surfaces by X-ray photoemission spectroscopy (XPS). From the observation and analysis of silicon-fluorine bonding underneath the fluorocarbon film and the dependence of the abundance of fluorosilyl species on the thickness of the fluorocarbon overlayer, the role of the fluorocarbon film in the slow-down of the Si etch rate has been elucidated: The role of the fluorocarbon film is to “protect” the Si surface from attack of fluorine, rather than prevent the escape of SiF4 etch product.
High Quality Deposition of SiO2 Downstream from a Microwave Discharge
Authors: Robinson B. , Hoh P. D. , Madakson P. , Nguyen T. N. , Shivashankar S. A.
Published: March 2011

High quality stoichiometric silicon dioxide films have been deposited on silicon substrates at low pressure(1.0Torr) and low temperatures(≤ 350C) downstream and at a right angle to a microwave discharge. The deposition was accomplished by injecting 2% SiH4 in helium downstream of a N20 microwave generated discharge. Infrared spectroscopic analysis has determined that no detectable SiH, SiOH, Si-H2o or SiN chemical complexes were present in any films deposited at temperatures above 250C. Rutherford Backscattering and Forward Scattering Detection Spectroscopy were used to determine the elemental composition and hydrogen concentration in the films, respectively. The thick films were found to be stoichiometric with no detectable elemental impurities. The measured hydrogen concentration in the thin films was comparable to that measured in thermally grown Si0 2 of approximately the same thickness. The quality of the thin oxides(<30nm) has been determined by fabricating MOS devices from the Si-Si0 2 system.
Plasma Deposited Ni-Al-Mo Metal-Metal Composites
Authors: Jackson M. R. , Siemers P. A.
Published: March 2011

Six different composite microstructures were produced by low pressure plasma deposition of γ/γ'-α Ni-Al-Mo materials. Interlaminate spacing, volume fraction of α Mo, and continuity of the laminate structure were varied. Thermal expansion behavior (25–1250°C), density, and room temperature elastic modulus were correlated with volume fraction of α Mo. Tensile ductility (25–960°C) was correlated with both volume fraction and distribution of the α Mo phase, while yield strength was nearly insensitive to composite structure. Composite strengths were greater than were the unreinforced matrix strengths.
Estimation of Ion Impact Energies and Electrode Self-Bias Voltage in Capacitive RF Discharges
Authors: Savas S. E.
Published: March 2011

The dependences of the electrode self-bias voltage and the ratio of ion energies on electrode area ratio are calculated for a model of capacitively coupled rf discharges. It is assumed that concentric spherical elecrodes with fluid-like radial ion flow adequately models the ion motion, that sheath impedances are dominant, and that ionization processes in the glow are due to ohmically heated electrons. Results show that the ratio of ion energies impacting the smaller electrode to those on the larger depends on the ratio of electrode areas in a more complex manner than a power law.The reason for this is that sheath impedances are more resistive or capacitive at different times in the rf cycle. The self-bias ratio is found to depend relatively little on the ionization model or the pressure but differs substantially from the “power law” result. The agreement of measurements with the model is fairly good.
Reduction of Selected Metal Oxides in a Thermal Plasma Produced by a Nontransferred ARC Torch
Authors: Detering Brent A. , Batdorf James A. , Wai Chien M.
Published: March 2011

Plasma flow field temperatures are determined in a nontransferred arc plasma using emission spectroscopy. This technique is then utilized to identify thermal decomposition and reduction products produced in the plasma plume when metal oxide particles are injected into the plasma arc. The processed particles are then studied using AAS, SEM, EDS and XRD to characterize the chemical changes that have occurred in the particles. A Fourier transform method is used to study changes in particle morphology.
The Effects of Gas Composition and Pressure on RF Plasma Sintering of MgO
Authors: Kong Peter C. , Lau Y. C. , Pfender E.
Published: March 2011

Rapid densification of MgO in an rf plasma without sintering aids is demonstrated. The sintered densities of MgO are sensitive to the plasma composition and gas pressure. In general, specimens are sintered to higher densities in Ar/O2 and Ar/H2O plasmas than in pure Ar plasmas. This may be explained by the effects of plasma enthalpy and surface recombination of charged particles and of atomic species. Analyses show that the evolution of the microstructures of the sintered specimens remains similar, regardless of the plasma conditions. No substantial grain growth is observed.
A Method for Non-Intrusively Determining ion Impact Current Density and Energy Distribution in Capacitively Coupled RF Plasmas
Authors: Savas S. E.
Published: March 2011

The dependence of ion current density on the sheath voltage and thickness, and ion energy distributions as functions of the pressure and sheath voltage amplitude have been calculated using a self-consistent computer code, ISHEATH. The current density is found to obey an approximate power law dependence on the amplitude of the sheath voltage, Vs, and the sheath thickness, d, and, when charge exchange collisions are considered, on the collision parameter α ΞNgas · σcx ·d. The ion energy distribution (IED) is found to mainly depend on α: for α ≃l there is only a slight (≃10%) change from the collisionless case; for a ≤ 10 the IED is peaked at an energy which is much less than the time-average sheath potential.
Bambusicaliscelis, a New Bamboo-Feeding Planthopper Genus of Caliscelini (Hemiptera: Fulgoroidea: Caliscelidae: Caliscelinae), with Descriptions of Two New Species and Their Fifth-Instar Nymphs from Southwestern China
Authors: Chen Xiang-Sheng , Zhang Zheng-Guang
Published: March 2011

Bambusicaliscelis Chen & Zhang gen. nov. (Hemiptera: Fulgoroidea: Caliscelidae: Caliscelinae: Caliscelini) is established to accommodate two new species, Bambusicaliscelis fanjingensis Chen & Zhang, sp. nov. (type species, Guizhou, southwestern China) and B. dentis Chen & Zhang, sp. nov. (Guizhou, southwestern China). Members of the new genus are known to feed exclusively on bamboo (Poaceae: Bambusoideae) and represent the first record of bamboo-feeding planthopper Caliscelidae in China. The main morphological features, male genitalia, and the fifthinstar nymphs of two new species are described and illustrated. In addition, photographs and a key for identifying the adults and fifth-instar nymphs of the genus Bambusicaliscelis are provided. The importance of those groups as a pest on bamboo is discussed briefly. Biological notes and a discussion of those groups' distribution are given.
Seasonal Abundance of the Nearctic Gall MidgeObolodiplosis robiniaein Italy and the Impact of Its AntagonistPlatygaster robiniaeon Pest Populations
Authors: Duso C , Boaria A , Surian L , Buhl P N
Published: March 2011

The Nearctic gall midge Obolodiplosis robiniae (Haldeman, 1847) (Diptera Cecidomyiidae) infesting black locusts, Robinia pseudoacacia L. (Fabaceae), was detected in Asia in 2002 and in Europe (first in Italy) in 2003. Its distribution in Europe has expanded dramatically, probably favored by extensive distribution of its host plant along the main routes. The results of a 3-yr study on the seasonal abundance of O. robiniae in northern Italy are reported here. O. robiniae can develop three to four generations per year by exploiting plants of different ages and vigor. Overwintering takes place as diapausing larvae and adults emerge in spring. Two generations are completed on mature plants where populations decline in summer. Two additional generations can develop on root suckers from midsummer onward. Pest population densities reach their highest levels in late spring. Gall midge larvae were attacked by various predators, but parasitism by the platygastrid Platygaster robiniae Buhl & Duso was particularly significant. The impact of parasitism by P. robiniae is indicated as a key factor in reducing O. robiniae population densities.
Tachinid (Diptera: Tachinidae) Parasitoid Diversity and Temporal Abundance at a Single Site in the Northeastern United States
Authors: Inclan Diego J , Stireman John O
Published: March 2011

Although tachinids are one of the most diverse families of Diptera and represent the largest group of nonhymenopteran parasitoids, their local diversity and distribution patterns of most species in the family are poorly known. In this study, 2 yr of samples from a Malaise trap were used to analyze the local richness and temporal distribution of a tachinid community in southwestern Ohio. In total, 883 tachinid specimens were collected, consisting of 117 species belonging to 69 genera. The majority of the specimens were collected in fall, followed by summer and spring, with 67, 22, and 11%, respectively. Estimated rarefaction curves indicate a predicted species richness of 217 species and suggest that we have sampled only a fraction of the diversity of Tachinidae occurring at this particular site. The species recorded in this study represent 16 and 19% of the species that are likely to occur in the northeastern United States and Ohio, respectively. In North America, there have been few, if any, previous attempts to quantify the diversity of tachinids on a local scale. Our results provide a baseline for understanding the temporal and spatial diversity of these ecologically and agronomically important parasitoids.
To Forage or Not: Responses of Bees to the Presence of Other Bees on Flowers
Authors: Yokoi Tomoyuki , Fujisaki Kenji
Published: March 2011

Information on responses of flower-foraging bees to the presence of other visitors simultaneously using the same resource is essential in further understanding bee decision-making processes during the collection of floral rewards. An individual must evaluate the relative costs of exploiting an occupied resource versus moving on to another resource. We investigated responses of foraging individuals to the presence of conspecifics or heterospecifics in three field experiments with solitary and social bees visiting flowers of wild strawberry, Rubus hirsutus Thunb. (Rosaceae). The proportion of Micrandrena spp. that occupied flowers after meeting other foragers was significantly lower than the proportions of Osmia orientalis Benoist and Apis mellifera L. Moreover, the avoidance response of Micrandrena spp. when approaching dead bees (“artificial” visitors) was stronger than that of the other bee species. We also placed an artificial visitor on flowers and observed subsequent responses of natural visitors. The responses of foraging bees to the presence of other visitors varies among species; O. orientalis more frequently visited flowers on which dead Micrandrena spp. were placed than flowers on which dead bees of other species were deployed. Both A. mellifera and Micrandrena spp. avoided flowers on which any other bees were set. We propose that O. orientalis makes decisions on whether to visit an occupied flower after discriminating between flower occupant species by body size.
Characterization of a New Odorant Binding Protein Gene in Gustatory Organs ofManduca sextaLarvae (Lepidoptera: Sphingidae)
Authors: Campo Marta L Del , Palmer Samantha , Caillaud Marina
Published: March 2011

Taste plays an essential role in the identification of adequate food sources by insects, including lepidopterans. Characterizing genes that are important to successful transduction of tastants in insects leads to understanding of how tastants can regulate insect behavior. One class of proteins, odorant binding proteins (OBPs), have been shown to play a role in olfactory chemotransduction, but their role in taste transduction has been less clear, especially in immature stages of insects. Taste has been shown to be central in host preference by the larva of the tobacco hornworm, Manduca sexta (L.) (Lepidoptera: Sphingidae), and its preferred host plants in the family Solanaceae. We report the discovery of a new OBP gene, Mad10, expressed in the gustatory sensilla styloconica of M. sexta larvae. This is the first time that the expression of an OBP is found in the sensilla styloconica of any lepidopteran.