We have used pulsed laser deposition to fabricate graphene on catalytic nickel thin film at reduced temperature of 650 °C. Non-destructive micro-Raman spectroscopic study on our samples, measuring 1x1 cm2 each, has revealed few-layer graphene formation. Bi-, tri-, and few-layer graphene growth has been verified by High Resolution Transmission Electron Microscopy. Our experimental results imply that the number of graphene layers formation relies on film thickness ratios of C to Ni, which can be well controlled by varying the laser ablation time. This simple and low temperature synthesizing method is excellent for graphene based nanotechnology research and device fabrication
Surface plasmon tuning via thermally induced refractive index changes in ferroelectrics is investigated. Epitaxial (Ba 0.7 Sr 0.3 )TiO 3 (BST) thin films were deposited on MgO (001) substrates by pulsed laser deposition. The refractive index of BST thin films measured by the prism-coupling technique was found to increase from 2.3932 (TE)/1.9945 (TM) at room temperature to 2.3949 (TE)/1.9965 (TM) at 66°C. Then 30-nm-Ag gratings with periodicity 750 nm and width 300 nm were fabricated on BST by soft ultraviolet nanoimprint lithography and subsequent lift-off process. The reflection spectra from 500 to 1000 nm with incident angle from 5°to 60°were measured at room temperature and 66°C, with a collimated and p-polarized light incident perpendicularly to the grating direction. Several modes were observed from the spectra. At 66°C, a red shift of a dip at about 850 nm by 2 nm was obtained at an incident angle of 15°. Calculations confirmed that the observed modes belong to the (−1), (2), (−2) and (3) surface plasmon modes from the Ag and BST interfaces and localized mode; the red shift by thermal tuning is also confirmed. The results indicate the feasibility of active modulation in surface plasmon resonance in solid-state structures.
High quality polycrystalline silicon (poly-Si) thin film solar cell was successfully fabricated on soda-lime glass substrates by electron beam (Ebeam) evaporation at low processing temperature. The initial poly-Si seed layer (p+-type 0.5 μm thick) was grown via the aluminum induced crystallization (AIC) method at 450 °C. Prominent interdiffusion and Si crystallization have been observed. X-ray diffraction (XRD) shows that (111) is the dominating crystalline orientation. Post annealing at 450 °C for six hours has produced densely packed Si grains with dimension of more than 10 μm in the plane of the film. Non-destructive Raman spectroscopy reveals the remarkable crystalline improvement for samples after thermal treatment. After removing the top diffused Al by chemical means, an absorber layer (p-type) of 0.9 μm thick was subsequently deposited onto the seed layer by Ebeam evaporation at 500 °C. Transmission electron microscopy (TEM) confirmed good homo-epitaxial growth. Without breaking the high vacuum, an n-type amorphous Si (a-Si) layer (0.7 μm thick) was coated onto the absorber layer to form p-n junction. The corresponding I-V characteristics suggest that our low temperature processing technique is applicable for production of poly-Si thin film solar cell on low cost substrates.
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