Cu nanocomposite films grown by ion beam cosputtering in the temperature range from room temperature (RT) to 500 °C are investigated. Soft X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) have been used to determine electronic structure of the occupied and unoccupied electronic states of the coexisting carbon and transition metal (TM) constituents. The results from the spectroscopy are supplemented by the film composition data and TM inclusion phase structural information obtained by elastic recoil detection analysis and X-ray diffraction, respectively. The TM(2p) XAS shows that V (Cu) is in carbidic (metallic) state over the whole temperature range, while Co shows a transition from a carbidic toward a metallic state when the growth temperature increases from RT to 500 °C. The C(1s) XAS demonstrates that the increase in the growth temperature favors the formation of graphite-like structures in carbon films. On the other hand, the TM metal incorporation strongly promotes the sp 3 admixture in the surrounding carbon phase which manifests itself through a significant increase in the intensity of a feature in the C(1s) XAS spectra positioned at ∼291 eV resulting from 1s f σ* transitions. In addition, the codeposition of TM atoms with carbon enhances the formation of carbon structures with the prominent peak between π* and σ* regions in the C(1s) XAS spectra positioned at ∼288.5 eV. The effect is independent of the TM tendency to form carbides or TM state (carbidic metallic) while its magnitude increases concomitantly with the TM content and decreases when the crystallinity degree of the inclusion phase increases. The results are discussed on the basis of the nanoparticle imposed curvature on the surrounding carbon network and interactions at the atomic level at the C-TM interfaces.
Interdependence between stress, preferred orientation, and surface morphology of nanocrystalline TiN thin films deposited by dual ion beam sputteringThe influence of transition metal (TM ¼ V,Co,Cu) type on the bulk diffusion induced structural changes in carbon:TM nanocomposite films is investigated. The TMs have been incorporated into the carbon matrix via ion beam co-sputtering, and subsequently the films have been vacuum annealed in the temperature range of 300 -700 C. The structure of both the dispersed metal rich and the carbon matrix phases has been determined by a combination of elastic recoil detection analysis, x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The as-grown films consist of carbidic (V and Co) and metallic (Cu) nanoparticles dispersed in the carbon matrix. Thermal annealing induces surface segregation of Co and Cu starting at ! 500 C, preceded by the carbide-metal transformation of Co-carbide nanoparticles at $ 300 C. No considerable morphological changes occur in C:V films. In contrast to the surface diffusion dominated regime where all the metals enhance the six-fold ring clustering of C, in the bulk diffusion controlled regime only Co acts as a catalyst for the carbon graphitization. These results are consistent with the metal-induced crystallization mechanism in the C:Co films. The results are discussed on the basis of the metal-carbide phase stability, carbon solubility in metals or their carbides, and interface species.
The influence of transition metals (TM) type on the encapsulating carbon (C) medium during the growth of C:TM (TM = V, Co and Cu) composite films with a metal content of ∼30 at.‐% grown by ion beam co‐sputtering in the temperature range of RT‐500 °C is investigated by means of X‐ray diffraction, transmission electron microscopy and Raman spectroscopy. The nanostructure of both C:TM nanocomposite constituents is strongly affected by the TM type and the growth temperature. The nanoparticle size, shape, and phase depend on these parameters. Raman spectroscopy shows that all three metals enhance six‐fold ring clustering of the carbon phase independent of the nanoparticle type, size, shape and phase, and the effect is most pronounced at lower temperatures.
Encapsulated nanoparticles formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices or as large scale templates for nanowire fabrication. In this study, substrate type influence on the morphology of encapsulated metal nanoparticles in C:Ni films grown by ion beam cosputtering is investigated. C:Ni (∼15 atom %) nanocomposite thin films (∼50-70 nm thick) were grown at 400 °C on amorphous SiO 2 and Nb 2 O 5 , polycrystalline TiN, and single crystalline MgO (001) substrates. Combined diagnostics using transmission electron microscopy, grazing incidence smallangle X-ray scattering, and superconducting quantum interference device magnetometry demonstrate that all the films exhibit metallic nanoparticles elongated along the film growth direction, while the substrate material strongly influences their morphology even far away from the film/substrate interface despite the fact that repeated nucleation occurs in all the films. The mean nanoparticle diameter is strongly substrate dependent and ranges from ∼2 to ∼18 nm in the sequence SiO 2 < MgO < Nb 2 O 5 < TiN. In addition, the substrate type influences strongly the vertical film constituent distribution, resulting in a homogeneous metal constituent distribution for the films grown on the SiO 2 and MgO substrates while causing the metal segregation at the film surface for the films grown on the Nb 2 O 5 and TiN substrates. The results strongly suggest that the metal diffusivity, not that of carbon, is the limiting factor determining the film structure. The results are consistent with the nucleation and growth mechanism, with the repeated nucleation events being correlated with the preceding film morphology, rather than that of spinodal decomposition. Furthermore, the findings suggest that a controlled growth of encapsulated nanoparticles may be achieved with an ordinary cosputtering technique by changing the substrate type or state or by applying a variety of prepatterning recipes.
The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investigated. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range from 200 to 500°C. Two major effects are reported: (i) a large anomalous Hall effect amounting to 2 lX cm, and (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves coincide with the rescaled magnetization curves, a finding that is consistent with spin-dependent transport. These findings suggest that C:Co nanocomposites are promising candidates for carbon-based Hall sensors and spintronic devices.
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