Abstract
Germanium (Ge)-carbon (C) core-shell nanowires (NWs), 15 - 80 nm thick and <1 μm long, were grown using continuous-wave laser vaporization of Ge-graphite composite targets in high pressure (0.1 - 0.9 MPa) Ar gas. The NW core was crystalline Ge and the shell was amorphous C. The fraction of the NWs in deposits was changed significantly by the Ge content in the targets and had a maximum at the Ge content of 40 atomic %. With increasing Ar pressure, thicker NWs were grown. A strong correlation was evident between the two diameters of the NW and nanoparticle (NP) attached with the tip of the NW. The growth of the NWs can be explained by the formation of Ge-C liquid-like molten NPs having a specific range of size and composition and precipitation of Ge and C followed by phase separation.
Highlights
One-dimensional semiconductor nanowires (NWs) have attracted much interest due to their size effects and novel properties
We have succeeded in forming some one-dimensional nanostructures, such as carbon nanotubes (CNTs) filled with Cu [11] or SiC [12] and amorphous silicon oxide (SiOx) NWs [13] using continuous wave (CW) laser vaporization in high-pressure (0.1 - 0.9 MPa) Ar gas without the addition of other metal catalysts
A simple method of forming Ge-C core-shell NWs was presented by means of CW laser irradiation onto Ge-graphite targets in the presence of high-pressure Ar gas
Summary
One-dimensional semiconductor nanowires (NWs) have attracted much interest due to their size effects and novel properties. Since the oxide exhibited poor chemical stability [3], some methods including coating by organic monolayers [4] and encapsulation by carbon (C) [5] [6] [7] were studied to prevent the oxidation of Ge NWs. More recently, Ge NWs have gained attention in the research and development of lithium-ion secondary batteries having an alternative anode material of graphite [8]. We have succeeded in forming some one-dimensional nanostructures, such as carbon nanotubes (CNTs) filled with Cu [11] or SiC [12] and amorphous silicon oxide (SiOx) NWs [13] using continuous wave (CW) laser vaporization in high-pressure (0.1 - 0.9 MPa) Ar gas without the addition of other metal catalysts. Unlike the syntheses of Ge-C NWs using arc discharge [15] or pyrolysis [5], our composite NWs are completely filled with Ge and hollow C structures are not presented, NPs are formed as by-products
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