LiMn 2 O 4 thin films were deposited by reactive pulsed laser deposition technique and studied the microstructural and electrical properties of the films. The LiMn 2 O 4 thin films deposited in an oxygen partial pressure of 100 mTorr and at a substrate temperature of 573 K from a lithium rich target were found to be nearly stoichiometric. The films exhibited predominantly (111) orientation representing the cubic spinel structure with Fd3m symmetry. The intensity of (111) peak increased and a slight shift in the peak position was observed with the increase of substrate temperature. The lattice parameter increased from 8.117 to 8.2417 Å with the increase of substrate temperature from 573 to 873 K. The electrical conductivity of the films is observed to be a strong function of temperature. The evaluated activation energy for the films deposited at 873 K is 0.64 eV.
LiCoO 2 thin films were prepared by electron beam evaporation technique using LiCoO 2 target with Li/ Co ratio 1.1 in an oxygen partial pressure of 5×10 −4 mbar. The films prepared at substrate temperature T s <573 K were amorphous in nature, and the films prepared at T s >573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature range 673-773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co-e g absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co-t 2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment exhibit (104) out plane texture with large grains.
We report selective optical reflectance in an aluminium (Al) coated flexible carbon nanotube (CNT) thin film over a wide range of wavelengths (500–2500 nm). Selective-wavelength surface is achieved by coating CNT surfaces with Al thin film that presented a maximum optical reflectivity of ∼65% in the infrared region. However, CNT film alone showed a reflectance of 15–20% over a larger range of wavelengths without any structural modification, which has not been realized so far. Moreover, a tailorable reflectance in CNT is shown to be achieved by tuning various parameters, namely, the porosity of the material, angle of an incident light, and refractive index of the materials. Owing to higher infrared reflectivity and thermal diffusivity, Al coated CNT presents a potential for a high efficiency solar collector.
Thin films of LiCo0 2 and LiMn20 4 were prepared by pulsed laser deposition technique. The influence of deposition parameters on the structure and surface morphology of the films were studied. The LiCo0 2 films deposited in oxygen partial pressure of 100 mTorr and at substrate temperature of 300 °C exhibited predominantly (003) orientation of the hexagonal R-3m phase indicating that the growth occurs perpendicularly to the substrate surface with an average grain size of 80 ran. Whereas the films grown at higher substrate temperature were polycrystalline with the growth parallel to the substrate surface. The LiMn 2 0 4 thin films prepared at 300 °C exhibited predominantly (111) orientation indicating cubic spinel structure with Fd3m space group.
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