Interactions of ions with graphene

We evaluate the stopping and image forces on a charged particle moving parallel to a single sheet of graphene supported by an insulating substrate under the gating conditions. The forces are presented as functions of the particle speed and the particle distance for a broad range of charge-carrier densities in graphene. We also consider the effects of a finite gap between graphene and a supporting substrate, as well as the effects of a finite damping rate that is included through the use of Mermins procedure. The damping rate is estimated from a tentative comparison of the Mermin loss function with a high-resolution reflection electron energy loss spectroscopy experiment.25th Summer School and International Symposium on the Physics of Ionized Gases - SPIG 2010, Aug 30-Sep 03, 2010, Donji Milanovac, Serbi

Annealing effects on the properties of TiN thin films

The structure, absorption coefficient and electrical resistivity studies on TiN thin films are presented. The film of thickness 240 nm was grown on Si (100) substrate by DC reactive sputtering at an average deposition rate of similar to 8 nm/min. After deposition the samples were annealed for 1 h at 600 degrees C and 2 h at 700 degrees C in nitrogen ambient and vacuum furnace, respectively. Structural characterizations were performed by Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties were investigated by spectroscopic ellipsometry while a four point probe was used for electrical characterization. It was found that the post-deposition annealing of the films did not cause any variation in stoichiometry, but strongly affects the structural parameters such as lattice constant, micro-strain and grain size. The observed increase in the grain size after annealing leads to significantly lower value of the coefficient of absorption. These changes could be directly correlated with variation of electrical properties of TiN thin films

Argon Irradiation Effects on the Structural and Optical Properties of Reactively Sputtered CrN Films

The present study deals with CrN films irradiated at room temperature (RT) with 200 keV Ar+ ions. The CrN layers were deposited by d.c. reactive sputtering on Si (100) wafers, at nitrogen partial pressure of 5x10(-4) mbar, to a total thickness of 280 nm. The substrates were held at 150 degrees C during deposition. After deposition the CrN layers were irradiated with 200 keV Ar+ ions to the fluences of 5x10(15) - 2x10(16) ions/cm(2). Structural characterization was performed with Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM) and X-ray diffraction (XRD). Spectroscopic ellipsometry measurements were carried out in order to study optical properties of the samples. The irradiations caused the microstructrual changes in CrN layers, but no amorphization even at the highest argon fluence of 2x10(16) ions/cm(2). Observed changes in microstructure were correlated with the variation in optical parameters. It was found that both refractive index and extinction coefficient are strongly dependent on the defect concentration in CrN layers

Non-isothermal dehydration of equilibrium swollen radiolytically sinthesized Fe3O4 – PVA ferrogel nanocomposite

In this study, the Fe3O4 - PVA ferrogel nanocomposite was synthesized by gamma irradiation. Obtained ferrogel had greater swelling capacity and activation energy of dehydratation as measured by thermogravimetric analysis under non-isothermal conditionsPhysical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Ion-beam irradiation effects on reactively sputtered CrN layers

This paper presents a study of microstructural changes induced in CrN layers by irradiation with 120 keV argon ions. The layers were deposited on (100) Si wafers, at different nitrogen partial pressures (2×10^-4, 3.5×10^-4 and 5×10^-4 mbar), to a total thickness of 260–280 nm. During deposition the substrates were held at 150°C. After deposition the samples were irradiated with argon ions to the fluences of 1×10^15 and 1×10^16 ions/cm2, under the vacuum of 7×10^-6 mbar. Characterisation of the samples structure and morphology were performed by X-ray diffraction (XRD) analysis and cross-sectional transmission electron microscopy (XTEM), and the concentration profiles were determined by Rutheford backscattering (RBS) spectrometry. It was found that the layer composition strongly depends on the nitrogen partial pressure during deposition. A pure stoichiometric CrN phase was achieved for the highest nitrogen partial pressure (5×10^-4 mbar). Argon ions irradiation induces microstructural changes in the CrN layers such as variation of the lattice constants, micro-strain and mean grain size.Paper presented at 4th Serbian Conference on Electron Microscopy, Belgrade, Serbia, 201

The calcification of collagen by HAP functionalized carbon materials

Bone is composed of two phases. The organic phase is made of collagen fibrils assembled in broad fibers acting as a template for mineralization. The mineral phase comprises hydroxyapatite (HAP) crystals grown between and inside the collagen fibers. We have developed a material using functionalized carbon nanotubes, carbon fibers and glasy carbon as scaffold to initiate in vitro mineralization. Mentioned carbon materials are functionalized with carboxylic groups prior to decorating. All samples were dispersed in ultra-pure water and incubated for 2 weeks in a synthetic body fluid with dispersed HAP, in order to induce the calcification of the functionalized carbon materials. Atomic force microscopy (AFM) and transmision electron microscopy (TEM) showed that Ca2+ and PO4 3- ions were deposited as round-shaped nodules. Raman spectroscopic studies confirmed the HAP formation, and image analysis made on TEM pictures showed that HAP were packed around and inside the carbon materials together. All three types of investigated carbon materials leading to successful calcification of collagen. This suggests that it takes the presence of carbon materials to prevent it from calcification of collagen, independent of the structures of the material

Energy loss and deflection of fast ions moving parallel to the graphene sheet

We investigate the interactions of fast ions with graphene, describing the excitations of the electron gas in graphene by a two-dimensional hydrodynamic model. By linearizing the hydrodynamic equations, we derive general expressions for the induced potential, the stopping force and the image force for an ion moving parallel to the graphene sheet. Moreover, the Barkas effect on the stopping force and the analogous corrections to the induced potential and the image force are evaluated within the second-order perturbation approach to the hydrodynamic equations. The numerical results of the linear and nonlinear theories are obtained showing the influence of the ion position and its velocity on the stopping force and the image force.YUCOMAT 2007 : 9th Annual Conference YUCOMAT 2007 : Programme and the book of abstracts; September 10-14, 2007; Herceg Novi, Montenegr

Interactions of Fast Ions with Graphene

In this work, we study the interactions of fast ions with graphene describing the excitations of the electron gas in graphene by a two-dimensional (2D) hydrodynamic model (one-fluid and two-fluid model). The two-fluid model reproduces qualitatively the split of plasmon dispersions into the low-frequency pi-electron branch and the high-frequency sigma+pi-electron branch. We calculate the stopping force and the image force on an ion moving parallel to a single sheet of graphene. Numerical results show that the presence of the low-energy, quasiacoustic plasmon in the two-fluid model gives rise to resonant features at low velocities around its acoustic speed, which are not seen in the one-fluid model. The two models give virtually indistinguishable results for both forces at high speeds. Marked differences between the two models in the values of image forces at low speeds can be seen. Numerical results show that the magnitudes of both the stopping and image forces exhibit typical resonance-shaped velocity dependencies, with the peak positions moving to higher velocities for higher distances and with the overall magnitudes decreasing sharply with increasing distances. The second order corrections are found to be small, as expected for fast ions outside the electron gas, but their relative magnitudes should be easily discernible in experiments on ion grazing scattering from graphene. One notices effects which are similar to those obtained earlier for proton channeling in carbon nanotubes.7th Seminar of Young Researchers, Dec 22-24, 2008, Belgrade, Serbi

Structural changes induced by argon ion irradiation in TiN thin films

In this work, the effects of 120 keV Ar+ ion implantation on the structural properties of TiN thin films were investigated. TiN layers were deposited by d.c. reactive sputtering on Si(100) wafers at room temperature or at 150°C. The thickness of TiN layers was ~240 nm. After deposition the samples were irradiated with 120 keV argon ions to the fluencies of 1×10^15 and 1×10^16 ions/cm2. Structural characterisation was performed with Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM), grazing angle X-ray diffraction (XRD) and atomic force microscopy (AFM). It was found that the argon ion irradiation induced the changes in the lattice constant, mean grain size, micro-strain and surface morphology of the TiN layers. The observed micro-structural changes are due to the formation of the high density damage region in the TiN thin film structure.Paper presented at 4th Serbian Conference on Electron Microscopy, Belgrade, Serbia, 201

Structural, optical and electrical properties of reactively sputtered CrxNy films: Nitrogen influence on the phase formation

The properties of various CrxNy films grown by direct current (DC) reactive sputtering process with different values of nitrogen partial pressures (0, 2x10(-4), 3.5x10(-4) and 5x10(-4) mbar) were studied. The structural analysis of the samples was performed by using X-ray diffraction and transmission electron microscopy (TEM), while an elemental analysis was realized by means of Rutherford backscattering spectrometry. By varying nitrogen partial pressure the pure Cr layer, mixture of Cr, Cr-2 N and CrN phases, or single-phase CrN was produced. TEM analysis showed that at pN(2) = 2x10(-4) mbar the layer has dense microstructure. On the other hand, the layer deposited at the highest nitrogen partial pressure exhibits pronounced columnar structure. The optical properties of CrxNy films were evaluated from spectroscopic ellipsometry data by the Drude or combined Drude and Tauc-Lorentz model. It was found that both refractive index and extinction coefficient are strongly dependent on the dominant phase formation (Cr, Cr-2 N, CrN) during the deposition process. Finally, the electrical studies indicated the metallic character of Cr-2 N phase and semiconducting behaviour of CrN