Tuning the electronic structure of graphene by ion irradiation

Mechanically exfoliated graphene layers deposited on SiO2 substrate were irradiated with Ar+ ions in order to experimentally study the effect of atomic scale defects and disorder on the low-energy electronic structure of graphene. The irradiated samples were investigated by scanning tunneling microscopy and spectroscopy measurements, which reveal that defect sites, besides acting as scattering centers for electrons through local modification of the on-site potential, also induce disorder in the hopping amplitudes. The most important consequence of the induced disorder is the substantial reduction in the Fermi velocity, revealed by bias-dependent imaging of electron-density oscillations observed near defect sites

Thickness Dependent Growth of Epitaxial Iron Silicide Nanoobjects on Si (001)

Strain-induced, self-assembled iron silicide nanostructures were grown on Si(001) substrate by conventional Fe evaporation and subsequent annealing. The initial Fe thickness was in the 0.1-6.0 nm range and the annealing temperature was 850 °C. The formed phases and structures were characterized by reflection high energy electron diffraction, and scanning electron microscopy. The electrical characteristics were investigated by I-V and C-V measurements, and by DLTS. The samples show silicide nanostructure formation in the whole thickness range. The shape of the nanostructures varied from rod like to triangular and quadratic depending on the initial Fe thickness. The size distribution of the formed iron silicide nanoobjects was not homogeneous, but they were oriented in square directions on Si(001). Higher thickness resulted in increased particles size. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3518

Saccharothrix sp. PAL54, a new chloramphenicol-producing strain isolated from a Saharan soil

An actinomycete strain designated PAL54, producing an antibacterial substance, was isolated from a Saharan soil in Ghardaïa, Algeria. Morphological and chemical studies indicated that this strain belonged to the genus Saccharothrix. Analysis of the 16S rDNA sequence showed a similarity level ranging between 96.9 and 99.2% within Saccharothrix species, with S. longispora DSM 43749T, the most closely related. DNA–DNA hybridization confirmed that strain PAL54 belonged to Saccharothrix longispora. It showed very strong activity against pathogenic Gram-positive and Gram-negative bacteria responsible for nosocomial infections and resistant to multiple antibiotics. Strain PAL54 secreted the antibiotic optimally during mid-stationary and decline phases of growth. One antibacterial compound was isolated from the culture broth and purified by HPLC. The active compound was elucidated by uv-visible and NMR spectroscopy and by mass spectrometry. The results showed that this compound was a D(-)-threo chloramphenicol. This is the first report of chloramphenicol production by a Saccharothrix species

The Antiviral Antibiotic Feglymycin First Direct Methods Solution of a 1000Plus Equal Atom Structure

The double helical structure adopted by the antiviral peptide feglymycin see picture is reminiscent of that of gramicidin, but feglymycin is more likely to function as an ion carrier than as a membrane channel. With more than 1000 unique atoms this is the largest equal atom crystal structure solved by ab initio direct method

Dipolar random field Ising model: an application to garnet films

The dipolar-random field Ising model (DRFIM) recently introduced displays a behaviour that can be connected to the magnetization of bidimensional magnetic media. Epitaxial magnetic garnet films seem to be the ideal test material for such a model. In this work the results of the measurements performed on garnet samples are presented, as well as the comparisons with simulation results obtained by the DRFIM. The results prove that a variety of hysteresis loops are well described by the DRFIM. This capability does not derive from the fine tuning of a great number of parameters, but by the interplay of exchange and dipolar interactions.Comment: HTML paper, GIF images. To appear on Phys.Rev.B (Brief Reports). Application of the model published on Phys.Rev.B 59 (1999) 985, cond-mat/990707

Polarized light microscopy of chemical-vapor-deposition-grown graphene on copper

Linearly polarized light microscopy (PM) revealed that graphene grown by chemical vapor deposition (CVD) on stepped Cu substrate may appear colored. The coloration is associated with the coupling of the light of 450-600 nm into propagating mode in the graphene layer when the electric vector (E →) of polarized light is parallel with the step edges and with the scattering when the E → is normal to the step edges. PM is an inexpensive, fast, and contamination free method to efficiently visualize graphene and to map the step structure of Cu substrates used for large area CVD growth of graphene. © 2012 American Institute of Physics