Direct liquid crystal templating from non-ionic polyoxyethylene surfactants has been utilised to produce well-defined birefringent films of nanostructured cadmium telluride films which displayed good optical properties as evidenced by UV/VIS reflectance spectroscopy.
We present the facile synthesis of crystalline V 2 O 5 nanorods and V 2 O 5 /TiO 2 nanocomposites structures by a carbon nanocage (CNC)-assisted growth process, using vanadium triisopropoxide oxide and titanium isopropoxide precursors in air at 500 C. The diameters of the resultant V 2 O 5 nanorods ranged between $10 and 70 nm, while the crystalline V 2 O 5 /TiO 2 nanocomposite structures adopted a unique morphology, due to both crystallisation and templating processes, with V 2 O 5 adopting small-diameter nanowire and nanorod morphologies surrounded by sub-30 nm TiO 2 nanoparticles. The V 2 O 5 nanorods and V 2 O 5 /TiO 2 nanocomposites were characterised by electron microscopy and X-ray diffraction techniques and subsequently reviewed as positive Li-ion electrodes. The phase-pure V 2 O 5 nanorod structures exhibited appreciable Li + storage properties over the potential range of 2.0-4.0 V vs. Li/Li + , displaying capacities of up to 288 mA h g À1 with appreciable cyclic behaviour at test rates of up to $1 C. The crystalline V 2 O 5 /TiO 2 nanocomposite structures displayed similar Li + storage properties, however, increasing molar fractions of TiO 2 led to a decline in the overall capacity versus the single-phase V 2 O 5 counterparts. Interestingly, the Li + insertion behaviour of the V 2 O 5 /TiO 2 nanocomposite displayed character more-typical of amorphous V 2 O 5 , which was ascribed to a structural buffering effect of the inactive TiO 2 phase.
Growth of periodic nanoporous CdTe and ZnO metamaterials is developed and characterised. We model the induced birefringence and measure the charge transport and density of surface states in the films.Nanostructuring materials to produce metamaterials with novel and optimised functional properties is a new field which is already showing great promise. One powerful technique to create such metamaterials with new properties is to grow through lyotropic liquid crystals phase which act as nano-templates. The first materials produced using a liquid crystal template method were silica films in 1995 [l], which had structures on the scale of -3mn. Since this time much research has been concentrated in this field, yet surprisingly only a few semiconductors have been templated. We present work on the fabrication of the nanostructured semiconductors cadmium telluride and zinc oxide along with characterisation of their nanostructure-induced birefringence along with a theoretical model which fully explains the observed birefringence. We also present the results of photocurrent spectroscopy and electrical impedance measurements which allow us to quantify charge transport within the films and the density and nature of surface statesThe films are produced using electrochemical deposition techniques where a plating solution is mixed with the self-assembled lyotropic liquid crystal, the film is then potentiostatically deposited onto a conductive electrode as shown in figure 1[2]. After the film is deposited the surfactant columns are removed with solvents. The film that is left after growth is a semiconductor film containing a hexagonal array of cylindrical air pores with pore diameters -3nm and a separation of -6nm which have a range of thickness (0.1-Ipm) depending on growth time. Surfactant Semiconductor * l l :G~~~rowth Conductive ___!__ !_20nm _Substrate -20nm Fig. 1. Representation of liquid crystal nano -template at the surface of an electrode. Growth occurs from the aqueous phase surrounding the surfactant columns producing a semiconductor containing a hexagonal array of pores at an angle 0.To determine the existence of nanostructuring we employ two main techniques, low angle x-ray diffraction and transmission electron microscopy [2], both giving information about the pore separation with the latter also giving information about the pore diameter. These nanostructured semiconductor metamaterials have new and enhanced properties, one being their giant form birefringence (-4%), which is purely due to the anisotropic nanostructuring imposed on the film. The birefringence of the CdTe, which in its bulk form is isotropic, is clearly observed using polarised optical microscopy with the images seen directly comparable to those seen in the template mixture alone. To quantify the birefringence the anisotropic spectral dependence of individual domains (up to 0. Imm2) has been determined using normal incidence micro-reflectivity experiments with polarised illumination, unpolarised detection, and rotation of the sample in the azimuthal...
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