87,060 research outputs found
Field emission studies on swift heavy ion irradiated tetrahedral amorphous carbon
No full textWe investigate the feasibility of electrically structuring flat films by swift heavy ion irradiation to create durable field emitters. Using mass separated ion beam deposition amorphous carbon films, doped with H and F to influence sp(3)-fraction and dielectric properties, were grown on highly conducting Si substrates. After deposition, the films were irradiated with 350 MeV Au-197 ions creating embedded graphitic channels along their trajectories with diameters only a few nanometers. Those channels were examined using an atomic force microscope (AFM) with a conducting cantilever by applying a bias voltage to the substrate. The channels exhibit conductivities several orders of magnitude higher than the host matrix. Field emission was observed for the F doped samples, and field emission current characteristic and turn-on fields of 30 V/mum were measured. Using field emission energy distribution (FEED) analysis defect states at or near the Fermi level of the track could be identified as the emission source. Computer calculations were performed to approximate the geometric field enhancement of the ion tracks, which was found to be largely reduced by dielectric screening of the amorphous carbon host matrix. (C) 2003 Elsevier B.V. All rights reserved
Magnetoelectronic properties of Gd-implanted tetrahedral amorphous carbon
No full textThe structural, electronic, magnetic, and magnetoelectronic properties of tetrahedral amorphous carbon (ta-C) thin films doped with gadolinium via ion implantation (ta-C(1-x) :Gd(x), x = 0.02 similar to 0.20) have been studied, both as prepared and after annealing, with Xe-implanted samples as control samples. Gd implantation causes significant increases in electrical conductivity, showing that Gd adds carriers as in other rare earth-semiconductor systems. Gd also provides a large local moment from its half-filled f shell. Carrier-mediated Gd-Gd interactions are strong but very frustrated, causing a spin-glass state < 10 K for higher x. An enormous negative magnetoresistance (about - 10(3) at 3 K in a 70-kOe field for x = 0.088) is observed at low T (< 30 K), an indication of carrier-moment interactions that cause magnetic disorder-induced localization and consequent magnetic field-induced delocalization as Gd moments align with the magnetic field. Gd implantation causes substantial changes in Raman intensity, associated with conversion of C-C bonds into Raman inactive bonds, which induce further graphitization after annealing. The changing nature of the C-C bonding with increasing x or with annealing causes the electrical transport properties to depend on Gd concentration x with a nonmonotonic dependence. Systematic but nonmonotonic trends are seen on comparing the magnetic and magnetotransport properties of Gd-doped a-C, a-Si, and a-Ge matrices, suggesting that electron concentration and band gap play separate important roles
Ion implantation into gallium nitride
No full textThis comprehensive review is concerned with studies regarding ion implanted gallium nitride (GaN) and focuses on the improvements made in recent years. It is divided into three sections: (i) structural properties, (ii) optical properties and (iii) electrical properties. The first section includes X-ray diffraction (XRD), transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS), Rutherford Backscattering (RBS), emission channeling (EC) and perturbed yy-angular correlation (PAC) measurements on GaN implanted with different ions and doses at different temperatures as a function of annealing temperature. The structural changes upon implantation and the respective recovery upon annealing will be discussed. Several standard and new annealing procedures will be presented and discussed. The second section describes mainly photoluminescence (PL) studies, however, the results will be discussed with respect to Raman and ellipsometry studies performed by other groups. We will show that the PL-signal is very sensitive to the processes occurring during implantation and annealing. The results of Hall and C-V measurements on implanted GaN are presented in Section 3. We show and discuss the difficulties in achieving electrical activation. However, optical and electrical properties are both a result of the structural changes upon implantation and annealing. Each section will be critically discussed with respect to the existing literature, and the main conclusions are drawn from the interplay of the results obtained from the different techniques used/reviewed. (C) 2001 Elsevier Science B.V. All rights reserved
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
Self-organized formation of layered carbon-copper nanocomposite films by ion deposition
No full textThe quasi-simultaneous deposition of low energy-mass-selected C+ and metal(+) ions leads to the formation of metal-carbon nanocomposites. In the case of C+ and Cu+ deposition, a homogeneous distribution of small copper clusters in an amorphous carbon matrix is expected. However, at a certain C+/Cu+ fluence ratio and energy range, alternately metal-rich and metal-deficient layers in an amorphous carbon matrix with periods in the nm range develop have been observed. The metal-rich layers consist of densely distributed crystalline Cu particles while the metal-deficient layers are amorphous and contain only few and small Cu clusters. The formation of multilayers can be described by an interplay of sputtering, surface segregation, ion induced diffusion, and the stability of small clusters against ion bombardment. This formation has been investigated for the a-C:Cu system with respect to the ion energy and the C+/Cu+ fluence ratio. The sputter coefficient S-M = r(f)S(CCu) + S-CuCu is the parameter to switch between layer growth (S-M 1). (C) 2009 Elsevier B.V. All rights reserved
Morphological change of carbon surfaces by sputter erosion
No full textIn order to study the allotropic effect on ripple formation on carbon surfaces induced by sputter erosion, three types of carbon materials, highly oriented pyrolytic graphite (HOPG), single crystalline diamond and tetrahedral amorphous carbon (ta-C) films, were irradiated with 5-keV Xe+ at an incident angle of 30 degrees. The irradiation fluence was 2 x 10(17) cm(-2) for all irradiations. No ripples were formed on diamond and ta-C surfaces, while ripples with a wavelength of similar to 100 nm occurred on HOPG. Electron energy loss spectroscopy revealed that the surfaces of all carbon materials became amorphous with similar densities upon irradiation. Therefore, the presented results clearly show that rippling depends on the nature of the underlying carbon materials. (c) 2006 Elsevier B.V. All rights reserved
Morphology of Si surfaces sputter-eroded by low-energy Xe-ions at glancing incident angle
No full textSputter erosion of Si generates nanoscale ripple patterns which are stable at ambient conditions and which may serve as an experimental test of ripple formation theories. Up to now, almost all studies on ripple formation of Si-surface have been carried Out with large ion-fluence (varying from 10(17) ions/cm(2) to 10(22) ions/cm(2)) and shown the ripple-pattern orientated in the direction perpendicular to the ion-beam. The present reports on the evolution of Si surfaces after low-energy (5 keV) Xe(+) ion irradiation at room temperature with low ion-fluences of 1 X 10(14) -3 x 10(17) ions /cm(2) at glancing incident angles theta up to 85 degrees. The purpose is to focus on the critical angle 0, of the ripple rotation from perpendicular to parallel orientation to the ion beam. It is found that the nanometer ripple formations occurred for theta > 70 degrees with an orientation perpendicular (for 80 degrees > theta >= 70 degrees) or parallel (for theta>80 degrees) to the ion-beam direction. At the critical angle theta(c) = 80 degrees ion-bombardment produced two-dimensional nanopatterns with tile-like laminas. The size of the laminas increase by raising the ion-fluences. The surface roughness obeys an exponential function (omega similar to exp (R(k) . Phi) for ion-fluences Phi < 1.5 x 10(16) ions/cm(2), while for larger ion-fluences the roughness nearly reaches saturation and only increases slowly according to a power law function omega similar to Phi(beta) with beta approximate to 0.34. (C) 2009 Elsevier B.V. All rights reserved
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
John F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
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