Large-area, freestanding, single-layer graphene-gold: a hybrid plasmonic nanostructure.

Graphene-based plasmonic devices have recently drawn great attention. However, practical limitations in fabrication and device architectures prevent studies from being carried out on the intrinsic properties of graphene and their change by plasmonic structures. The influence of a quasi-infinite object (i.e., the substrate) on graphene, being a single sheet of carbon atoms, and the plasmonic device is overwhelming. To address this and put the intrinsic properties of the graphene-plasmonic nanostructures in focus, we fabricate large-area, freestanding, single-layer graphene-gold (LFG-Au) sandwich structures and Au nanoparticle decorated graphene (formed via thermal treatment) hybrid plasmonic nanostructures. We observed two distinct plasmonic enhancement routes of graphene unique to each structure via surface-enhanced Raman spectroscopy. The localized electronic structure variation in the LFG due to graphene-Au interaction at the nanoscale is mapped using scanning transmission X-ray microscopy. The measurements show an optical density of ∼0.007, which is the smallest experimentally determined for single-layer graphene thus far. Our results on freestanding graphene-Au plasmonic structures provide great insight for the rational design and future fabrication of graphene plasmonic hybrid nanostructures.

Atmospheric-pressure plasma-enhanced chemical vapor deposition of a-SiCN:H films: role of precursors on the film growth and properties.

Atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) using Surfx Atomflow(TM) 250D APPJ was utilized to synthesize amorphous silicon carbonitride coatings using tetramethyldisilizane (TMDZ) and hexamethyldisilizane (HMDZ) as the single source precursors. The effect of precursor chemistry and substrate temperature (T(s)) on the properties of a-SiCN:H films were evaluated, while nitrogen was used as the reactive gas. Surface morphology of the films was evaluated using atomic force microscopy (AFM); chemical properties were determined using Fourier transform infrared spectroscopy (FTIR); thickness and optical properties were determined using spectroscopic ellipsometry and mechanical properties were determined using nanoindentation. In general, films deposited at substrate temperature (T(s)) < 200 °C contained organic moieties, while the films deposited at T(s) > 200 °C depicted strong Si-N and Si-CN absorption. Refractive indices (n) of the thin films showed values between 1.5 and 2.0, depending on the deposition parameters. Mechanical properties of the films determined using nanoindentation revealed that these films have hardness between 0.5 GPa and 15 GPa, depending on the T(s) value. AFM evaluation of the films showed high roughness (R(a)) values of 2-3 nm for the films grown at low T(s) (<250 °C) while the films grown at T(s) ≥ 300 °C exhibited atomically smooth surface with R(a) of ~0.5 nm. Based on the gas-phase (plasma) chemistry, precursor chemistry and the other experimental observations, a possible growth model that prevails in the AP-PECVD of a-SiCN:H thin films is proposed.

Solution-based synthesis of crystalline silicon from liquid silane through laser and chemical annealing.

We report a solution process for the synthesis of crystalline silicon from the liquid silane precursor cyclohexasilane (Si(6)H(12)). Polysilane films were crystallized through thermal and laser annealing, with plasma hydrogenation at atmospheric pressure generating further structural changes in the films. The evolution from amorphous to microcrystalline is characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and impedance spectroscopy. A four-decade enhancement in the electrical conductivity is attributed to a disorder-order transition in a bonded Si network. Our results demonstrate a potentially attractive approach that employs a solution process coupled with ambient postprocessing to produce crystalline silicon thin films.