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a b s t r a c t Keywords:Zinc oxide thin film Sol-gel preparation Annealing X-ray diffraction Atomic force microscopy Optical properties This investigation deals with the effect of annealing temperature on the structural, topographical and optical properties of Zinc Oxide thin films prepared by sol-gel method. The structural properties were studied using X-ray diffraction and the recorded patterns indicated that all the films had a preferred orientation along (002) plane and the crystallinity along with the grain size were augmented with annealing temperature. The topographical modification of the films due to heat treatment was probed by atomic force microscopy which revealed that annealing roughened the surface of the film. The optical properties were examined by a UVvisible spectrophotometer which exhibited that maximum transmittance reached nearly 90% and it diminished with increasing annealing temperature.

A comparative study of the physical properties of undoped Zinc Oxide (ZnO) and Al doped Zinc Oxide (AZO) thin films were performed as a function of annealing temperature. The structural properties were analyzed using X-ray diffraction and the recorded patterns indicated that the crystallinity of the films always enhanced with increasing annealing temperature while it degrades with Al doping. The topographical modification of the films due to heat treatment was examined by atomic force microscopy which revealed that annealing roughened the surface of all the films; however the AZO films always exhibited smoother morphology than ZnO. Study of optical properties by UV-Visible spectrophotometer demonstrated that the transmittance was gradually diminished with rise in annealing temperature. In addition, a notable increase in the optical bandgap was also observed for the AZO films.

a b s t r a c tSince last decade, graphene has materialized itself as one of the phenomenal materials to modern researchers because of its remarkable thermal, optical, electronic, and mechanical properties. Graphene holds enormous potentials for lab on chip (LOC) devices and can provide diverse fabrication routes and structural features due to their special electronic and electrochemical properties. A LOC device can manipulate fluids using microchannels and chamber structures, to accomplish fast, highly sensitive and inexpensive analysis with high yield. Hence, the graphene based LOC devices can constitute a wellcontrolled microenvironment for both advanced chemical/biological evaluation and low-cost point-ofcare analysis etc. This review critically debates the graphene as a prime candidate for microfluidic devices and their future applicability towards various practical applications. Finally, the opportunities and challenges for the future of graphene with respect to their commercial challenges and sustainability perspectives are discussed.

The effect of Fe and Ni catalysts on the synthesis of carbon nanotubes (CNTs) using atmospheric pressure chemical vapor deposition (APCVD) was investigated. Field emission scanning electron microscopy (FESEM) analysis suggests that the samples grow through a tip growth mechanism. High-resolution transmission electron microscopy (HRTEM) measurements show multiwalled carbon nanotubes (MWCNTs) with bamboo structure for Ni catalyst while iron filled straight tubes were obtained with the Fe catalyst. The X-ray diffraction (XRD) pattern indicates that nanotubes are graphitic in nature and there is no trace of carbide phases in both the cases. Low frequency Raman analysis of the bamboo-like and filled CNTs confirms the presence of radial breathing modes (RBM). The degree of graphitization of CNTs synthesized from Fe catalyst is higher than that from Ni catalyst as demonstrated by the high frequency Raman analysis. Simple models for the growth of bamboo-like and tubular catalyst filled nanotubes are proposed.

Thin films of magnesium doped zinc oxide (MZO) were synthesized using sol-gel method and annealed at different temperatures under ambient condition. The morphological properties of the post annealed MZO films were investigated using X-ray diffraction (XRD) while atomic force microscopy (AFM) was employed to probe the topographical alteration of the films. The optical properties of the post annealed MZO films were examined by UV-Visible spectroscopy and the Tauc method was used to estimate the optical band gap. The studies revealed that, with the rise of annealing temperature the crystallinity and the surface roughness of the MZO films were increased whereas the optical transmittance and the energy bandgap were decreased.

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Cubic silicon carbide (beta-SiC)/SiO2 nanowires with uniform and knotted-core structures have been synthesized on nickel-coated Si(111) substrates at 1150 degrees C by using hexamethyldisilane (HMDS) as the source material in a hot wall atmospheric pressure chemical vapor deposition (APCVD) system. The nanowires consist of a single crystalline beta-SiC core wrapped with an amorphous SiO2 shell. The as-prepared SiC nanowires and the deposited Ni films were characterized by field emission scanning electron microscopy, X-ray diffraction, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, micro-Raman spectroscopy, infrared spectroscopy and atomic force microscopy. The results show that the nanowires are random in direction and have diameter ranges from 25 nm to 70 nm. The core of the nanowires has a cubic zinc blend structure and a high density of planar defects is often found. The twin plane defects are suspected to be the main reason for the formation of the knotted-core SiC nanowires. A possible growth mechanism based on vapor-liquid-solid (VLS) by base growth technique is proposed.