Liquid Ga droplets play a double role in the self-catalyzed growth of GaAs nanowires on Si(111) substrates covered with a native SiO x layer: they induce the formation of nanosized holes in SiO x and then drive the uniaxial nanowire growth directly onto the underlying Si. The independent control of the two mechanisms is a prerequisite for mastering the growth of nanowires, but it is challenging in a conventional growth procedure where they both take place under the same droplets. To that end, we have developed an in situ procedure where the Ga droplets used for the formation of SiO x holes are removed before new Ga droplets drive the growth of GaAs nanowires. In that way, it was possible to study the interaction between Ga droplets and SiO x , to create holes in SiO x with controlled number density and size, and, finally, to grow GaAs nanowires only within those holes. Our results show unprecedented control of the nanowire nucleation with unique possibilities: (1) deliberate control of the number density of nanowires within 3 orders of magnitude (106–109 cm–2) without patterning the substrate and without changing the growth conditions, (2) highly synchronous nucleation events and, thus, exceptionally narrow nanowire length distributions (standard deviation <1% for 3 μm long nanowires), (3) high yield of vertical nanowires up to 80% (against GaAs islands), (4) highly reproducible results, and (5) independent control of the nanowire diameter from the number density. We anticipate that our methodology could be also exploited for different materials or other types of nanostructures.

The article discusses the structure and properties of noncrystalline carbon films synthesized by ion-plasma sputtering of a graphite target in an argon atmosphere at direct current. Analysis of the molecular structure of carbon films was performed using Raman spectroscopy and dependence of the structure of synthesized films on the synthesis temperature and substrate material was revealed. Besides the main G peak possesses the values in a broad frequency range from 1500 to 1575 cm À1 . The evolution of molecular structure peculiarities of synthesized carbon films depending on the synthesis conditions was clearly shown using the numerical methods of the Raman spectra decomposition. Studies of the optical spectra showed that the band gap of synthesized films varies from 0.78 to 1.67 eV and with increasing optical band gap, the value of G peak position decreases under laser excitation of 2.62 and 1.96 eV.

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