Synthesis of few-layered graphene nanoballs with copper cores using solid carbon source.

We report the fabrication of graphene-encapsulated nanoballs with copper nanoparticle (Cu NP) cores whose size range from 40 nm to 1 µm using a solid carbon source of poly(methyl methacrylate) (PMMA). The Cu NPs were prone to agglomerate during the annealing process at high temperatures of 800 to 900 °C when gas carbon source such as methane was used for the growth of graphene. On the contrary, the morphologies of the Cu NPs were unchanged during the growth of graphene at the same temperature range when PMMA coating was used. The solid source of PMMA was first converted to amorphous carbon layers through a pyrolysis process at the temperature regime of 400 °C, which prevented the Cu NPs from agglomeration, and they were converted to few-layered graphene (FLG) at the elevated temperatures. Raman and transmission electron microscope analyses confirmed the synthesis of FLG with thickness of approximately 3 nm directly on the surface of the Cu NPs. X-ray diffraction and X-ray photoelectron spectroscopy analyses, along with electrical resistance measurement according to temperature changes showed that the FLG-encapsulated Cu NPs were highly resistant to oxidation even after exposure to severe oxidation conditions.

Direct gravure printing of silicon nanowires using entropic attraction forces.

The development of a method for large-scale printing of nanowire (NW) arrays onto a desired substrate is crucial for fabricating high-performance NW-based electronics. Here, the alignment of highly ordered and dense silicon (Si) NW arrays at anisotropically etched micro-engraved structures is demonstrated using a simple evaporation process. During evaporation, entropic attraction combined with the internal flow of the NW solution induced the alignment of NWs at the corners of pre-defined structures, and the assembly characteristics of the NWs were highly dependent on the polarity of the NW solutions. After complete evaporation, the aligned NW arrays are subsequently transferred onto a flexible substrate with 95% selectivity using a direct gravure printing technique. As a proof-of-concept, flexible back-gated NW field-effect transistors (FETs) are fabricated. The fabricated FETs have an effective hole mobility of 17.1 cm(2) ·V(-1) ·s(-1) and an on/off ratio of ~2.6 × 10(5) .