bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Flame Grown Diamond Films by Luminescence and EPR
Authors: Pereira L. , Pereira E. , Tavares C. , Neto M. , Creades A. , Piqueras J. , Jimenez J. , Martin P. 
Published: April 2011

ABSTRACTFlame grown diamond films, depending on the growth conditions may present various amounts of diamond like carbon (DLC) besides the diamond phase. A correlation of the morphology with the secondary electron emission, cathodoluminescence, photoluminescence, EPR and Raman data is presented for samples grown using in different ratios of oxygen and acetylene.
Visible Light Emission in Silicon-Interface Adsorbed Gas Superlattices
Authors: Tsu Raphael , Morais Jonder , Bowhill Amanda 
Published: April 2011

ABSTRACTHaving an indirect fundamental bandgap, unlike III-V or II-VI compound semiconductors, silicon has not played a role in optoelectronic applications such as injection lasers and light emitting diodes. In an attempt to introduce a sufficient quantum size effect, we present the experimental results on a new type of silicon based superlattices consisting of alternating layers of silicon and monolayers of adsorbed gases, Si/IAG multilayers (Si/Interface Adsorbed Gas), constructed by repeated interruptions of silicon deposition with adsorbed gases of oxygen and hydrogen. Fairly strong visible luminescence has been observed.
Surface Structure of Tetrahedral-Coordinated Amorphous Diamond-Like Carbon Films Grown by Pulsed Laser Deposition
Authors: Mercer T. W. , DiNardo N. J. , Martinez-Miranda L. J. , Fang F. , Friedmann T. A. , Sullivan J. P. , Siegal M. P. 
Published: April 2011

ABSTRACTThe structure and composition of tetrahedral-coordinated amorphous diamondlike carbon films (a-tC) grown by pulsed laser deposition (PLD) of graphite has been studied with atomic force microscopy (AFM). The nanometer-scale surface structure has been studied as a function of growth parameters (e.g., laser energy density and film thickness) using contact-mode and tapping-mode AFM. Although the surfaces were found to be generally smooth, they exhibited reproducible structural features on several size scales which correlate with the variation of laser energy and the effects of excited ion etching.
Laser Doping and Crystallization of Amorphous Silicon Thin Films
Authors: Boyce J. B. , Anderson G. B. , Carey P. G. , Fork D. K. , Johnson R. I. , Mei P. , Ready S. E. , Smith P. M. 
Published: April 2011

ABSTRACTFast-pulse laser crystallization of amorphous silicon thin films on non-crystalline substrates provides a low-temperature process for generating polycrystalline silicon. This process can be augmented by including laser doping to reduce the number of process steps in the fabrication of thin-film polysilicon devices. We have studied the simultaneous laser crystallization and laser doping process, starting with amorphous silicon on fused silica substrates and using the gas immersion technique for the doping. n-type and p-type doping employed PF5 and BF3 gases, respectively. Films were characterized both structurally and electrically. The grain size increases with increasing laser energy density as the film becomes fully melted and reaches a peak value, similar to laser crystallization without doping. The dopant concentration increases with the number of laser shots and, with 100 shots, achieves a high dose with a low sheet resistance below 1000 ohms/square, appropriate for devices. The dopant profile extends to a depth comparable to the melt depth, beyond which it falls off to the background level. Therefore, the doping depth and concentration can be controlled with the laser parameters.
Improved SiCr Resistor Performance by Means of Rapid Thermal Processing
Authors: Maghsoudnia Pirouz 
Published: April 2011

ABSTRACTNew and improved processes for fabrication of SiCr thin film resistors are desirable to achieve precision circuits. Two major draw backs to conventional single target sputtered SiCr resistors are high temperature coefficient of resistance (TCR) and low sheet rho (ρ□). Depositing a very thin film to achieve a higher ρ□, generally degrades the film stability, TCR and manufacturability. Annealing the film at higher temperatures by means of hot air, does increase the film sheet rho but the anneal temperature is limited to below 500°C to avoid film decomposition.A new method of increasing the sheet rho of SiCr films has been established where the deposited film with a ρ□ of 400Ω/□ is annealed to 1400Ω/□. Silicon substrates with thermally grown oxide were deposited with SiCr using rf sputtering. The wafers were ran through a single wafer rapid thermal processor with the chamber filled with dry nitrogen. Anneal temperatures were varied and it was found that the highest sheet rho was obtained at a temperature of 650°C and anneal time of 60 seconds. Resistors were manufactured using the annealed film and electrical characteristics of the resistors evaluated. When compared to hot air annealed SiCr resistors, the RTA SiCr resistors showed improved stability, TCR and sheet rho performance.
Characterization of High Ge Content SiGe Heterostructures and Graded Alloy Layers Using Spectroscopic Ellipsometry
Authors: Heyd A. R. , Alterovitz S. A. , Croke E. T. 
Published: April 2011

ABSTRACTSixGe1–x heterostructures on Si substrates have been widely studied due to the maturity of Si technology. However, work on SixGe1–x heterostructures on Ge substrates has not received much attention. A SixGe1–x: layer on a Si substrate is under compressive strain while SixGe1–x on Ge is under tensile strain; thus the critical points will behave differently. In order to accurately characterize high Ge content SixGe1–x layers the energy shift algorithm, which is used to calculate alloy compositions, has been modified. These results have been used along with variable angle spectroscopic ellipsometry (VASE) measurements to characterize SixGe1–x/Ge superlattices grown on Ge substrates. The results are found to agree closely with high resolution x-ray diffraction measurements made on the same samples.The modified energy shift algorithm also allows the VASE analysis to be upgraded in order to characterize linearly graded layers. In this work VASE has been used to characterize graded SixGe1–x layers in terms of the total thickness, and the start and end alloy composition. Results are presented for a 1 µm SixGe1–x layer linearly graded in the range 0.5 ≤ x ≤ 1.0.
Structure, Stability and Properties of Covalent C34, C20, and C22 Crystals
Authors: Benedek G. , Colombo L. , Corona B. , Galvani E. , Sanguinetti S. , Serra S. 
Published: April 2011

ABSTRACTTopological arguments indicate that an infinite number of covalent carbon crystals may exist with either diamond-like (sp3), graphitic-like (sp2)- or mixed (sp3/sp2) bonding structure. We investigate the structural, elastic and electronic properties of three prototypical structure: C34, C20 and C22, respectively. All of them form a face-centered cubic lattice. Their properties have been calculated by both Montecarlo and molecular dynamics simulations based on the Tersoff potential. Both the sp3-bonded C34 and the sp2-bonded C20 are found to have a cohesive energy per atom very close to that of diamond. A comparison of elastic and electronic properties to those ones of diamond and graphite are also presented and discussed.
Reaction Chamber and Cathode Configurations in Arc Production of Fullerenes
Authors: Pasqualini E. , Podesta C. , GarcÍa A. , Rafael A. , Dengra S. , Paulozzi M. 
Published: April 2011

ABSTRACTThe reaction chamber in the arc production of fullerenes was redesigned with a nozzle surrounding the decomposition zone to allow for clean collection of soot in a filtering cartridge. Quantitative analysis in the region of 300–430 nm in UV-visible spectra permits determination of the abundance of C60 and C70 in the soot. Calibrated curves of absorptivity for both pure fullerenes were employed. In equivalent conditions of current and pressure, electrographites of different origins have different decomposition rates and yields. A mechanism to interpret the cathodic deposit formation is proposed. Decomposition inside a closed cathodic cylinder yields 100% deposit.
Effect of He Pressure on the Superconducting Transition Temperatures of Na2CsC60 and (NH3)4Na2CsC60
Authors: Schirber J.E , Bayless W.R. , Rosseinsky M.J. , Zhou O. , Fleming R.M. , Murphy D. , Fischer J.E. 
Published: April 2011

ABSTRACTThe Na based mixed alkali doped C60 superconductors show anomalous behavior with respect to the “universal” superconducting transition temperature Tc vs lattice constant ao relation followed by most of the fcc A3C60 superconductors. We have measured dTc/dP for Na2CsC60 and (NH3)4Na2CsC60 using solid He as the pressure medium to ∼ 6 kbar finding dTc/dP equal to −0.88±(0.01) K/kbar and −1.0(±0.1) K/kbar for Na2CsC60 and Na2(NH3)4C60 respectively. Our value for Na2CsC60 differs markedly from that obtained by Mizuki et al of about −1.3 K/kbar. However, using N2 or Ar, we obtain values for dTc/dP in substantial agreement with Mizuki et al who used fluorinert to generate their pressure. This work emphasizes the need for compressibility measurements with the same pressure medium in the appropriate temperature range so that meaningful comparisons can be made between various pressure measurements and models which are based on lattice spacing.
Higher Fullerenes: Structure and Properties
Authors: Achiba Yohji , Kikuchi Koichi , Aihara Yuichi , Wakabayashi Tomonari , Miyake Yoko , Kainosho Masatsume 
Published: April 2011

ABSTRACTThe structures of higher fullerenes are described based on 13C NMR measurements of isolated and purified samples. The most interesting aspect deduced from the present structural work on the higher fullerenes up to C90 is that among 19 kinds of fullerenes with different sizes and isomers, 18 fullerenes commonly have at least one C2 symmetry axis in their molecular frame. Only one exception is C90 fullerene with a C1 symmetry. The spectral feature of UV/Visible absorption obtained for the HPLC-isolated C120 fullerene gives, on the other hand, a strong indication that the numbers of co-existing isomer of very large fullerenes are extremely limited, probably one or two. Considering the huge numbers of IPR-(isolated pentagon rule) satisfying isomer of C120 (10,774), these experimental evidences may suggest the presence of very strong selectivity for the formation of stable higher fullerenes, which, in turn, is closely associated with the unknown growth process of a fullerene cage network.
Hreels Studies of KxC60 Thin Films
Authors: Lopinski G.P. , Mitch M.G. , Chase S.J. , Lannin J.S. 
Published: April 2011

ABSTRACTHigh resolution electron energy loss spectroscopy has been used to investigate the vibrational and electronic excitations of single-phase, crystalline AxC60 films. Substantial changes in intramolecular mode frequencies and intensities with alkali concentration arise from charge transfer effects as well as free carrier screening. For x=4, splitting of the t1u band is observed, resulting in an insulating phase with an estimated gap of 0.3-0.4eV. Screening in the x=3 phase results in enhanced surface sensitivity and deviations from bulk stoichiometry at the surface of metallic films are observed.
Structure Sequence and Physical Properties of Rubidium Fulleride C70Rbx
Authors: Kobayashi Mototada , Fukuda Masao , Akahama Yuichi , Kawamura Haruki , Saito Yahachi , Shinohara Hisanori 
Published: April 2011

ABSTRACTA structure sequence of doped fcc, bct, bcc and Rb-saturated fcc phases was observed in C70Rbx with increasing Rb concentration using x-ray-diffraction measurements. The composition of the Rb-saturated phase was estimated to be C70Rb9.4±0.4 from a weight measurement. A model for the structure of C70Rb9 is proposed. Superconductivity in each phase was checked using ac magnetic-susceptibility measurements. All these phases were nonsuperconducting down to 1.3 K.
Polyhydroxylated C60 as an Hypercross-Linking Agent
Authors: Chiang Long Y. , Wang Lee Y. , Wu Rong-Shen , Hsieh Kuo-Huang 
Published: April 2011

ABSTRACTPolyhydroxylated fullerene derivatives (fullerenols) were utilized as an efficient hypercross-linking agent for the synthesis of elastic poly(tetramethylene oxide)-based polyurethane networks with excellent thermal mechanical properties. Polyhydroxylated fullerenes were synthesized from the hydrolysis of polycyclosulfated fullerene derivatives in the presence of water at 85-90 °C or in aqueous NaOH solution at ambient temperature.
Characterization of Ferromagnetic Nanoparticles Produced by A Carbon Arc
Authors: Brunsman E. M. , Anna S. , Majetich S. A. , Mchenry M. E. 
Published: April 2011

ABSTRACTThe effect of increasing metal fraction on carbon arc nanoparticle production is examined for 10–50 weight percent cobalt starting materials. With 500 Torr of helium buffer gas, the carbon arc process yields carbon-coated FCC Co nanoparticles of similar sizes throughout this range. The saturation magnetization is believed to scale linearly with the relative abundance of Co. The variation in the coercivity with abundance is small compared to the dramatic changes which can arise from changes in the size of fine particles. The approach to magnetic saturation is more rapid in high abundance samples. This is attributed to interparticle interactions which align the easy axes when the nanoparticles crystallize within interconnected carbon shells. The switching field distribution as a function of Co abundance arises from both rotational barriers and from barriers due to the particle size distribution.
Functionalization of C60 by Cycloaddition Reactions
Authors: Wilson Stephen R. , Cao Jingrong , Lug Qingyi , Wu Yunhui , Kaprinidas Nikolaos , Lem George , Saunders Martin , Jimenez-Vasquez Hugo A. , Schuster David I. 
Published: April 2011

ABSTRACTFunctionalization of C60 has been achieved by [2+2] photocycloaddition reactions of enones and [2+4] cycloaddition reactions of dienes, the course of these reactions can be followed using electrospray mass spectrometry using a special tagging reagent. Using tagged C60 it was shown that cis and trans cycloadducts are formed from ketones such as 3-methylcyclohexenone. We have also employed the new technique of 3He NMR spectrometry. 3He is an NMR-active nucleus. Fullerenes containing an endohedral 3He atom can be examined by NMR to obtain structural information and potentially determine isomer distributions. Examples, of helium spectra of fullerene hydrides are presented.
Morphology of Nanoparticles and Fullerene Blacks Produced in A Carbon Arc
Authors: Scott John Henry J. , Majetich S. A. , Derrington S. 
Published: April 2011

ABSTRACTUsing X-ray powder diffraction and transmission electron microscopy we examine the morphology and crystallographic structure of carbon-coated nanoparticles produced in a modified Huffman-Kratschmer carbon arc process. Graphite rods containing Ho were consumed in the arc and soots sampled from both the reactor walls and the inner core of the cathode deposit are compared. The inner core soot displays increased crystallinity and less amorphous carbon than wall-deposited soot, and nanoparticles in the inner core have more graphitic layers in the encapsulating shells, more gaps between the carbon coating and the core, and exhibit a greater degree of facetting than particles harvested from the reactor walls. These differences are interpreted as manifestations of the high temperature post-formation environment of the inner core of the cathode deposit.
Low Temperature Internal Friction of thin Fullerene Films
Authors: White B. E. , Freund J. E. , Topp K. A. , Pohl R. O. 
Published: April 2011

ABSTRACTThe lattice vibrations of crystalline solids are generally described by traveling elastic waves. However, the vibrations of fullerene solids are expected to be quite different from typical crystalline solids because of the large molecular mass. In fact, based on measurements of thermal conductivity and specific heat, it appears that the vibrations of compacted fullerene solids are best described as localized. Only below a few Kelvin has evidence for elastic waves been found in these solids where they exist along with the localized tunneling states that are characteristic of amorphous solids. In order to verify the existence of these tunneling defects, the low temperature internal friction of thin fullerene films deposited on a silicon substrate has been measured. Fullerene films were prepared under a variety of conditions with substrate temperatures ranging from 300 K to 500 K. Film grain sizes were characterized using atomic force microscopy, as well as, scanning tunneling microscopy. Grain sizes were found to range between 100 nm and 400 nm. We find that while localized tunneling defects appear to be present in these films, they do not appear to be intrinsic to the fullerene solid. Instead, the tunneling states may be the result of residual disorder that is present in the grain boundaries of the solids.
13C Isotopic Effect on the Raman Spectrum and Structure of C60 Fullerene
Authors: Huong Pham V. , JÉrÔme Denis , Auban-Senzier Pascale , Bernier Patrick 
Published: April 2011

ABSTRACTThe Raman spectrum of 13C enriched C60 samples is recorded and analyzed in comparison with that of undoped 12C60. Comparison with the isotopic effect in diamond and in other infinite solid networks is also made.A frequency shift depending on the amount of 13C is observed for the C=C stretching vibration, without any splitting. This effect is unusual and is a proof that the C=C is not localized and its double bond character is not isolated but strongly coupled with other bonds in the cage. If the CC bond was independent as in small or non-spherical molecules such as organic compounds, an isotopic effect of Δv ≃ 30 cm-1 for 12C=13C and Δv ≃ 60 cm−1 for 13C=13C could be expected and a splitting could appear in the case of uncompleted 13C substitution and variable relative intensities could be observed. It is not the case of 13C60.In isotopic C60, all C=C vibrations in the spherical network are stronglycoupled ; an average isotopic mass must be considered for the randomly distributed isotopic atoms in the material to interpret the experimental result. C60 has thus more solid than molecule behavior.
Micro-Ftir and Theoretical Study of C60 Single-Crystal Vibrational Modes
Authors: Guizzetti G. , Marabelli F. , Patrini M. , Manfredini M. , Milani P. , Benedek G. , Sanguinetti S. 
Published: April 2011

ABSTRACTReflectance (R) and trasmittance (T) of C60 single-crystals have been measured in the 400-5000 cm-1 range, at room temperature, by using micro-Fourier transform IR spectroscopy. The frequencies of the peaks, appearing in both R and T spectra, are compared with the IR active ones calculated for the simple cubic structure with the bond charge model. It appears that all modes which are expected from symmetry arguments to give a dipole activity are actually observed and the corresponding frequencies are in good agreement with the experimental findings.
Laser and oxygen induced damage of C60 single crystal observed by scanning electron microscopy
Authors: Milani P. , Manfredini M. 
Published: April 2011

ABSTRACTModifications induced by laser heating of C60 single crystal are examined by scanning electron microscopy (SEM). The fullerite surface is etched in the presence of oxygen, whereas no substantial change is observed under inert atmosphere. The formation of three dimensional micro-structures is observed depending on laser annealing conditions. Energy dispersive X-ray (EDX) spectroscopy shows that oxygen concentration substantially increases in the irradiated regions.
13C NMR Study of Oxygen Intercalation in C60
Authors: Bernier P. , Luk'yanchuk I. , Belahmer Z. , Ribet M. , Firlej L. 
Published: April 2011

ABSTRACTHigh resolution 13C NMR has been used to investigate the properties of solid C60 after intercalation of molecular oxygen, which does not induce charge transfer with the host molecules. We show that, via the magnetic characteristics of the intercalant, information can be gained on its position and movement in the structure. In particular, molecular oxygen is found to occupy the middle of the octahedral site in the fcc structure of solid C60.
Neutron Scattering Studies of C61H2
Authors: Neumann D. A. , Fischer J. E. , Copley J. R. D. , Heiney P. A. , Rush J. J. , Strongin R. M. , Brard L. , Smith Amos B. 
Published: April 2011

ABSTRACTWe report neutron diffraction measurements of orientational ordering, and inelastic neutron scattering measurements of the inter- and intra-molecular excitations, for the 6:5 annulene isomer (C3 symmetry) of C61H2. We confirm previous x-ray measurements[1] which have shown that above 290K this isomer has an fcc structure, with the molecules orientationally disordered such that the methylene groups preferentially occupy “octahedral” sites. Below 290K, the diffraction pattern can be indexed on a simple cubic lattice, in direct analogy with the orientational ordering transition of C60. The observed low energy dynamics reflect this behavior. A peak corresponding to molecular librations is observed below the transition, at ∼2.5meV, while above the transition the peak collapses into a quasielastic line characteristic of rotational diffusion. The intramolecular spectra show several pronounced peaks. The assignments of these modes are discussed.
Thermal Conductivity of C60 Under High Pressure
Authors: Andersson O. , Soldatov A. , Sundqvist B. 
Published: April 2011

ABSTRACTWe have measured the thermal conductivity λ of highly pure polycrystalline C60 in the range 50 to 300 K under pressures up to 1 GPa. The results are discussed in terms of the lattice structure and dynamics. In particular, we discuss the phase diagram as delineated by anomalies observed in λ and cp at the f c.c.-to-s.c. transition at 260 K and the glass transition at Tg = 90 K, and also the effect on λ of the orientational motion in the s.c. phase. The results are found to be compatible with p-T phase diagram recently suggested by us.
Thermophysical Properties of C70 Up to 1 GPa
Authors: Lundin A. , Soldatov A. , Sundqvist B. 
Published: April 2011

ABSTRACTWe have measured the thermal conductivity λ and the compressibility of highly pure C70 in the range 90 to 450 K under pressures up to 1.2 GPa. Our results for the thermal conductivity indicate molecular rotation in C70 above 280 K at zero pressure. The phase boundary for the rotationally disordered phase has an approximate slope dT/dp = 75 K GPa−1. The bulk modulus B increases linearly with increasing p above 0.1 GPa, with an extrapolated zero pressure value at 296 K of B(0) = 8.3 GPa. Unexpected anomalies are found in both B and λ near 100 MPa, and we tentatively suggest that orientational ordering is responsible.
Diffusion Separation of Fullerenes in Solution
Authors: Eletskii Alexander V. , Okun Michael V. , Stepanov Eugene V. 
Published: April 2011

ABSTRACTThe diffusion of fullerenes in solution is studied taking into account the recently established fact of the formation of clusters containing some number of aggregated fullerene molecules. Based on a droplet model of a cluster, the distribution function of fullerene clusters by size is obtained for various concentrations of solution. It is shown that dissolved fullerene is present mainly in the form of clusters at saturation conditions, but the contribution of clusters decreases as concentration drops down. Since the diffusion mobility of clusters is much less than that of molecules, it leads to the dependence of an effective diffusion coefficient on concentration, which is computed for the case of fullerene C60. The feasibility of the use of this dependence as a basis for a diffusion method of the separation and enrichment of the fullerene extract with a small addition of higher fullerenes is analyzed. Possible schemes for enrichment are discussed.