We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemically synthesis and interconnecting sheets.

We report a new synthesis process of colloidal indium (In) doped zinc oxide (ZIO) nanocrystals by a hot injection technique. By fine tuning the synthesis we reached the same nucleation temperature for indium oxide and zinc oxide which helped us to study a dopant precursor dependent In incorporation into the ZnO matrix by using different In sources. The dopant induced shape evolution changes the hexagonal pyramid structured ZnO to a platelet like structure upon 8% In doping. The introduction of trivalent In(3+) into the ZnO lattice and consequent substitution of divalent Zn(2+) generates free electrons in the conduction band which produces a plasmonic resonance in the infrared region. The electron concentration controls plasmon frequency as well as the band gap of host ZnO. The variation of the band gap and the modification of the conduction band have been explained by the Burstein-Moss effect and Mie's theory respectively. The In dopant changes the defect chemistry of pure ZnO nanocrystals which has been studied by photoluminescence and other spectroscopic measurements. The nanocrystals are highly stable in the organic medium and can be deposited as a crack free thin film on different substrates. Careful ligand exchange and thermal annealing of the spin cast film lead to a good conductive film (720 Ω per square to 120 Ω per square) with stable inherent plasmonic absorption in the infrared and 90% transmittance in the visible region. A temperature induced metal-semiconductor transition was found for doped ZnO nanocrystals. The transition temperature shifts to a lower temperature with increase of the doping concentration.

No abstract

Direct cell translocation of nanomaterials is preferred over the endocytotic uptake for various subcellular targeting applications that can bypass the lysosomal trafficking/degradation. Although arginine-rich cell-penetrating peptides are routinely used for cell transfection of wider range materials from molecule to nanoparticle, the direct cell translocation of nanoparticle is not a routine approach, particularly because of the predominate endocytotic uptake. Here we report arginine-terminated, designed nanoparticle of 15–30 nm hydrodynamic size that enters into cell via direct translocation. We found that direct cell translocation of nanoparticle is very efficient without localization at any specific subcellular compartment for 12–24 h. This study shows that nanomaterial can be chemically designed for direct cell translocation and for cytosolic delivery without any biomembrane-coated endosome that can be employed for subcellular targeting applications.