Structural, optical and electrical properties of electron beam evaporated TiOxNy films as selective solar absorber coatings

Titanium oxinitride (TiOxNy) solar absorber coatings were deposited at different oxygen partial pressures onto Cu, Si and glass substrates using electron beam evaporation technique. XRD diffraction patterns evidenced (111), (200) and (220) orientation of TiNx phase. The preferred orientation of the films changed with oxygen partial pressure. XPS revealed the intensity of both Ti 2P3/2 and Ti 2P1/2 increases as a function of oxygen flow, and also shifted towards higher binding energy, indicating more oxidized state of Ti species than that of TiO2 due to incorporation of nitrogen atoms. Formation of uniformly distributed spherical like particles and an increase in surface roughness of the TiOxNy films were observed as a function of oxygen partial pressure as depicted from SEM and AFM, respectively. Ellipsometric and resistivity measurements showed a shift from metallic to semiconductor behaviour of the TiOxNy films as oxygen flow changed. A solar absorptance value of 0.94 in the solar spectrum region and a low thermal emittance value of 0.05 were achieved for the TiOxNy solar absorber coatings prepared at the oxygen partial pressure of 7.5x10-5 Torr due to both interference and intrinsic absorption. This study confirmed that a single layer of TiOxNy film can be a good candidate as selective solar absorber

Pulsed laser deposited Cr2O3 nanostructured thin film on graphene as anode material for lithium-ion batteries

Pulsed laser deposition technique was used to deposit Cr2O3 nanostructured thin film on a chemical vapour deposited few-layer graphene (FLG) on nickel (Ni) substrate for application as anode material for lithium-ion batteries. The experimental results show that graphene can effectively enhance the electrochemical property of Cr2O3. For Cr2O3 thin film deposited on Ni (Cr2O3/Ni), a discharge capacity of 747.8 mA h g-1 can be delivered during the first lithiation process. After growing Cr2O3 thin film on FLG/Ni, the initial discharge capacity of Cr2O3/FLG/Ni was improved to 1234.5 mA h g-1. The reversible lithium storage capacity of the as-grown material is 692.2 mA h g-1 after 100 cycles, which is much higher than that of Cr2O3/Ni (111.3 mA h g-1). This study reveals the differences between the two material systems and emphasizes the role of the graphene layers in improving the electrochemical stability of the Cr2O3 nanostructured thin film.This work was sponsored within the framework of the UNESCO UNISA Africa Chair in Nanosciences & Nanotechnology and the Nanosciences African Network (NANOAFNET) by the National Research Foundation of South Africa, the African Laser Centre (ALC), the University of South Arica (UNISA) in collaboration with the Vice-Chancellor of the University of Pretoria, the National Research Foundation (NRF) of South Africa, iThemba LABS and the Abdus Salam ICTP-Trieste, Italy.http://www.elsevier.com/locate/jalcom2016-07-31hb2016Physic

Optical response of green synthesized thin Cr2O3 films prepared via drop and spin coatings

This study investigated the impact of optical bandgap energy on the optical constants of Cr2O3 thin films, which were prepared via green synthesis method and deposited using drop and spin-coatings at 600, 800, 1000, and 1200 rpm onto Cu substrates. The deposited Cr2O3 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and UV–VIS-NIR spectroscopy. XRD revealed that the prepared nanocoating surfaces are pure eskolaite Cr2O3 phase. The grain size of the prepared Cr2O3 films decreased from 15 nm to 12 nm for the drop and spin coatings, respectively. The morphology of the drop and spin coated samples showed nanorods, mesospherical, and quasi-spherical shaped nanoparticles, respectively, along with the presence of O and Cr. The bandgap energy increased from 2.35 eV to 2.50 eV, with increasing Spin Coater rotational speeds (RS) from drop to 1200 rpm, respectively. As bandgap energy increase, the carriers' spatial dimension shrinks, resulting in grains smaller than or equal to the exciton's Bohr radius. Thicker film materials tend to have lower bandgap energies due to strain effects, whereas smaller grain sizes tend to have higher bandgap energies. The determined refractive index and extinction coefficient values vary as the bandgap energy varies for all prepared samples. These findings confirmed that differences in bandgap energy affect the refractive index (n) and extinction coefficient (k) of Cr2O3 thin films. These are attributed to quantum confinement, internal scattering, and interference effects of Cr2O3 thin film surfaces

Pulsed laser deposited Cr2O3 nanostructured thin film on graphene as anode material for lithium-ion batteries

Pulsed laser deposition technique was used to deposit Cr2O3 nanostructured thin film on a chemical vapour deposited few-layer graphene (FLG) on nickel (Ni) substrate for application as anode material for lithium-ion batteries. The experimental results show that graphene can effectively enhance the electrochemical property of Cr2O3. For Cr2O3 thin film deposited on Ni (Cr2O3/Ni), a discharge capacity of 747.8 mA h g-1 can be delivered during the first lithiation process. After growing Cr2O3 thin film on FLG/Ni, the initial discharge capacity of Cr2O3/FLG/Ni was improved to 1234.5 mA h g-1. The reversible lithium storage capacity of the as-grown material is 692.2 mA h g-1 after 100 cycles, which is much higher than that of Cr2O3/Ni (111.3 mA h g-1). This study reveals the differences between the two material systems and emphasizes the role of the graphene layers in improving the electrochemical stability of the Cr2O3 nanostructured thin film.This work was sponsored within the framework of the UNESCO UNISA Africa Chair in Nanosciences & Nanotechnology and the Nanosciences African Network (NANOAFNET) by the National Research Foundation of South Africa, the African Laser Centre (ALC), the University of South Arica (UNISA) in collaboration with the Vice-Chancellor of the University of Pretoria, the National Research Foundation (NRF) of South Africa, iThemba LABS and the Abdus Salam ICTP-Trieste, Italy.http://www.elsevier.com/locate/jalcom2016-07-31hb2016Physic