1,720,964 research outputs found
Self-organized nanoscale multilayer growth in hyperthermal ion deposition
No full textIn the course of thin film growth by co-deposition of low energy mass selected carbon and metal (Au or Fe) ions, an effect of self-organization was found. Although carbon and metal ions were deposited quasi-simultaneously, a multilayer film structure of alternately metal-rich and metal-deficient layers was grown. The period of these layers is of the order of a few nanometers (similar to6-20 nm), and the metal-rich layers consist of metallic nanocrystals. The multilayer formation process is discussed in comparison with earlier studies on C-Cu and C-Ag films with respect to the structural properties of small clusters of the different metals, the influence of sputtering yields, and the deposition parameters. For a variety of compound thin film materials we expect a multilayer structure to develop during simultaneous sputter deposition or ion beam deposition of the components. The suppositions for this scenario are: (a) the deposited elements are immiscible or there are immiscible phases of a compound material, (b) the sputtering yields of the film components imposed by the impinging species are in an appropriate range, and (c) one compound segregates at the surface
Changes in the electronic structure of gold particles upon thiol adsorption as a function of the mean particle size
No full textWe studied the interaction of adsorbed thiol molecules with gold nanoparticles as a function of the mean particle size. The results obtained from MXPS (monochromated X-Ray Photoelectron Spectroscopy) measurements showed that attachment of the thiol sulfur headgroup onto the cluster surface leads to a positive binding energy shift in the Au 4f core-level. The absence of line width broadening upon adsorption indicates that these changes affect the whole particle and not only the particle surface, where the actual Au-S bond is located. The positive binding energy shift depends on the cluster size and increases with decreasing diameter. A maximum shift of 0.41 eV could be measured for the smallest particles (similar to 1 nm). The valence band exhibited positive binding energy shifts similar to the Au 4f core-levels, but smaller in absolute values. Changes in the valence band shape were interpreted as re-hybridization of Au 5d electrons due to the creation of Au-S bonds. Furthermore, we observed a disappearance of the Fermi edge upon thiol adsorption, which we attribute to a sulfur-induced metal-insulator-transition of the gold cluster. (c) 2005 Elsevier B.V. All rights reserved
Synthesis of Au-C-60 cluster materials
No full textWe have investigated the formation of Au clusters in a C-60 fullerene matrix (binary cluster material) with the aim to produce densely packed arrays of ultrasmall Au clusters with sizes below 4 nm. We achieved the formation of a binary cluster material by co-deposition of Au and C-60, and no segregation of the gold was observed. The Au concentration throughout the film was observed with Rutherford backscattering spectroscopy and reflects the deposition rates measured for the single particle fluxes. It was determined by high-resolution TEM that the films show a narrow size distribution of the Au clusters. The size ranges from 1.6 to about 3.8 nm, and the size distribution is determined by the Au concentration. For low Au concentrations of less than 5 atom %, the maximum of the size distribution was positioned at about 2 nm with a full width at half-maximum of 0.5 nm. The gold appears to have a strong influence on the growth mechanism of the films, as evidenced by a dramatic reduction in the mean roughness of the films with increasing Au content, which was observed with atomic force microscopy. For high gold concentrations, the surface roughness decreases to less than half the radius of a C-60 molecule. The competition between surface and volume cluster growth and the role of the Au cluster-fullerene interaction in the film growth are discussed
Ion beam synthesis of diamond-like carbon thin films containing copper nanocrystals
No full textAmorphous carbon thin films containing 0-50 at. % Cu have been grown by mass selected ion beam deposition in order to synthesize isolated Cu nanoparticles within a diamond-like matrix. Raman spectroscopy and x-ray photoelectron spectroscopy show that the sp(3) content of the matrix decreases with increasing Cu content. Simultaneously, the mean particle size of the embedded Cu nanocrystals increases, as x-ray diffraction and transmission electron microscopy analysis reveal. There is apparently no dependence of the matrix structure on the Cu+ ion energy, while the Cu content is strongly influenced by this deposition parameter. (C) 2003 American Institute of Physics
Comparative study of self-assembling of multilayers using reactive sputter deposition and mass selective ion beam deposition
No full textWhile experimenting with the growth of metal-containing amorphous carbon (a-c:Me) thin films using two different growth processes, self-assembled multilayered structures were observed. One of the processes is a reactive magnetron sputter deposition process. The other process is a mass selective ion beam deposition process. Despite of the differences in the growth method and the growth condition, self-assembled multilayered thin films, consisting of alternating dark layer and bright layer, were obtained in both processes. Based on the consideration of energy for atomic diffusion in the thin Films, the growth mechanism is discussed. (c) 2008 Elsevier B.V. All rights reserved
Ion energy thresholds and stability of cubic boron nitride
No full textBoron nitride (BN) film growth of mass selected B and N ion deposition has been investigated in a wide range of ion energies. We observed an ion energy window for the cubic BN (c-BN) growth between 75 eV and at least 15/20 keV. The observed low energy threshold for the growth of c-BN is lower than the c-BN nucleation threshold and fits well to the cylindrical spike model. On the high-energy side, c-BN growth was achieved using 15 keV nitrogen and 20 keV boron ions. Additionally, we studied the stability of c-BN under ion irradiation. These studies showed that cubic boron nitride is extremely stable under ion irradiation. It remains stable under nitrogen and argon ion irradiation with energies between 10 and 30 keV up to fluences approximately 10(17) cm(-2). However, if the c-BN/t-BN interface is irradiated, a complete transition to sp(2)-bonded BN already occurs at a low ion fluence of 10(16) cm(-2). (C) 2003 Elsevier Science B.V. All rights reserved
Luminescence centres in silica nanowires
No full textThree broad cathodoluminescence bands centred at similar to 2.02 eV ( red), similar to 2.78 eV ( blue), and similar to 3.45 eV ( ultraviolet) have been observed from silica nanowires synthesized by thermal evaporation at high temperature. The luminescence intensities of both the red and ultraviolet bands decrease upon electron-beam irradiation, while the intensity of the blue band increases with both irradiation time and specimen temperature. The red, blue, and ultraviolet bands are identified as radiative transitions involving the following centres: nonbridging oxygen hole centres, oxygen-deficient centres, and peroxy linkage. The varying time- and temperature-dependent luminescence intensities can be explained by the mutual transformation of these defects, which is driven by the irradiation- and heat-induced migration and desorption of radiolytic oxygen
Self-organized nanoscale multilayer growth during the deposition of hyperthermal species
No full textThe quasi-simultaneous deposition of low energy-mass-selected C+ and either Au+ or Fe+ ions resulted in the formation of alternately metal-rich and metal-deficient layers in an amorphous carbon matrix with periods in the nrn range. The metal-rich layers consist of densely distributed crystalline particles while the metal-deficient layers are amorphous or contain only smaller numbers of crystalline clusters. A similar structure was found in films grown by reactive dc-magnetron sputtering of Cu, Pt, and Ni targets in an Ar/CH4 plasma. The multilayer formation can be described by an interplay of sputtering, surface segregation, ion induced diffusion, and the stability of small clusters against ion bombardment
Self-assembled nano-scale multilayer formation using physical vapor deposition methods
No full textSelf-assembled alternating carbon and metal layers have been produced by concurrent deposition of carbon and metal atoms using both dc reactive sputter deposition and mass selected ion beam deposition. High-resolution transmission electron micrographs clearly show the alternating metal-rich and -deficient layers with periodicities in the nanometer scale. The appearance of a multilayer structure and its periodicity strongly depend on the deposition parameters, i.e. the metal species, the provided stoichiometry and the ion energy. Here, we discuss the similarities and differences of the parameters used in both physical vapor deposition methods on the impact on the multilayer structures. (c) 2005 Elsevier B.V. All rights reserved
Nucleation mechanism of the seed of tetrapod ZnO nanostructures
No full textTetrapod zinc oxide (T-ZnO) nanorods have been synthesized by evaporation and recondensation of metallic Zn under ambient conditions. The total sizes of the T-ZnO nanostructures range from 300 nm to 15 mu m with leg diameters of about 30 to 650 nm, depending on the deposition temperature. A detailed high-resolution electron microscopy analysis showed that the center core of T-ZnO nanorods consists of four hexagonal grains with a twinlike relation. The nucleation and growth mechanism has been generated on the basis of energy considerations during a phase transition from a fullerenelike ZnO cluster to a nanometer-sized tetrahedron, which is directly visible in our high-resolution transmission electron microscopy investigations. (c) 2005 American Institute of Physics
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