Journal of Nano Research Vol. 2

Abstract: Thermochromic glazing is a type of intelligent glazing; one where the properties of the glazing change according to some external stimulus. More particularly a thermochromic window is a device that changes its transmission and reflectance properties at a critical temperature (Tc). Atthis specific temperature the material undergoes a semi-conductor to metal transition. At temperatures lower than Tc the window lets all of the solar energy that hits it through. At emperatures above Tc the window reflects the infra-red portion of solar energy. In such a way thermochromic windows may help reduce air conditioning and heating costs leading to more energy efficient buildings. This review details the nature of the semi-conductor to metal transition and indicates how substitutional doping within a crystal lattice can be used to manipulate and fine tune the critical temperature. Also detailed is the underlying science and methodologies so far employed in the production of thermochromic thin films.

Abstract: Nanocrystalline vanadium oxide thin films have been deposited by reactive DC magnetron sputtering onto glass substrates under different processing conditions. Structural analysis and phase identification have been carried out by means of X-ray diffractometry (XRD). The surface morphologies of the different films have been examined by both scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD results revealed single and multiple phase oxides such as VO2(B), VO2(M), V2O5, etc. with considerable differences concerning to surface morphologies, as observed by SEM and AFM. The effects the O2/Ar flow ratio, DC current, and working pressure on the phases formed and growth rates is discussed. Moreover, VO2(M) films exhibited different morphologies concerning to grain size and shape as well as dissimilar preference in crystal orientation, as a result of the processing conditions. The optical/thermochromic response of the VO2(M) specimens deposited under different growth rate conditions was evaluated by optical spectrophotometry and related to the respective structural characteristics.

Abstract: Applying a bicolor coherent treatment of a Nd-YAG laser with wavelength 1.32 μm and its second harmonic generation, we have investigated photoinduced SHG in Au nanoparticledeposited ZnO nanocrystallinne (NC) films. We have established that coexistence of the such crystallites gives substantially better results compared to the pure ZnO NC deposited onto the glass substrate. It was shown that the value of the second order susceptibility obtained for the large incident angles of the fundamental and writing beams is equal to about 23 pm/V. The better results are obtained during the phototreatment at temperatures near the 60 oC for the Au doped samples and is almost non-sensitive to temperature for the pure samples. The further increase of the temperature leads to decay of the optical second harmonic generation

Abstract: We are presenting our results based on unsymmetrical zinc phthalocyanine by adopting ‘push-pull’ concept for the nanocrystalline dye-sensitized solar cells. Using this sensitizer in combination with nonvolatile organic-solvent-based electrolytes, we obtained a photovoltaic efficiency of 1.52% under standard global AM 1.5 sunlight and compared the results with volatile organic-solvent based electrolyte. These devices exhibit admirable stability when subjected to continuous thermal stress at 60 oC for 1000 h. The sensitizer is thermally stable up to 150 oC and can be useful for roof top applications.

Abstract: Important new applications are possible today in the fields of energy conversion and storage by the application of thin and nanostructured solid films on surfaces. These special films, or multiple films, will be integral parts of the energy systems in the near future for the production of useful thermal and electrical energy and for energy saving applications, especially in buildings. We review the research in this direction. As we are facing the threats of insufficient energy supply and the greenhouse gas emissions from the intense use of fossil sources, we realize that the impacts as well as the future of the solar energy systems have been greatly underestimated. We review the work on solar thermal systems and energy saving applications. The efficient use of solar thermal technologies is very important for the introduction of a sizeable share of environmentally friendly renewable energy sources. New and nano structured materials along with the design and the geometry of advanced systems, capable of achieving high temperatures, as well as on integrated collection and storage systems have been proposed. Recent progress in high-vacuum technology and new materials had a remarkable effect in thin-film quality and cost. As a result new thermal absorbers have appeared along with new evaluation methods. We also present work on low-e coatings and electrochromic thin films that are very important for thermal energy savings in buildings and increase the efficiency of devices. For the photovoltaic solar energy conversion we present results on thin film solar cells and the efforts on dye sensitized nanostructured and organic solar cells.

Abstract: Nanoscaled gallium-doped ZnO (GZO) thin films, bi-layer Pt/GZO thin films, and tri-layer GZO/Pt/GZO thin films were prepared and their characteristics were investigated. These films were deposited on glass substrates using either rf or dc magnetron sputter deposition. The deposition time and the target-to-substrate distance were varied to obtain different total film thicknesses and layer thicknesses. Effects of total film and layer thicknesses on the optical properties and the electrical properties were studied. Theoretical calculations were performed to discuss effect of the thickness on the optical transmittance of the GZO film. As-deposited GZO films show high electrical resistivity, which was greatly reduced by 2 to 3 orders of magnitude due to the introduction of a surface layer of Pt film. However, the optical transmittance was also reduced. This was improved by using an addition anti-refractive GZO surface layer on the Pt/GZO. A GZO/Pt/GZO film exhibiting visible light transmittance greater than 75% and electrical resistivity in the order of 10-4 ohm-cm was obtained.

Abstract: In this paper the effects of post-deposition annealing followed by hydrogen ionimplantation on the properties of CuIn0.75Ga0.25Se2 thin films have been investigated. The samples were grown by flash evaporation onto glass substrates heated at temperature between room temperature and 200°C. Selected samples were subsequently processed under several sets of conditions, including vacuum, selenium, inert (argon) and forming gas (a 9:1 mixture of N2:H2) followed by hydrogen ion-implantation. A high resolution near-infrared photoacoustic spectrometer of the gas-microphone type was used for room temperature analysis of non-radiative defect levels in the as-grown, annealed and hydrogen implanted thin films. The absorption coefficient has been derived from the PA spectra to determine the gap energy and to establish the activation energies for several defect-related energy levels. The changes observed in the PA spectra following annealing and ionimplantation has been directly correlated with the compositional and structural properties of the samples.

Abstract: Carbon nanotubes (CNTs) were functionalized using a simple method of heat treatment under oxygen atmosphere followed by an immersion in a tin nitrate aqueous solution. And well-dispersed SnOx nanodots were decorated on the surface of CNTs. X-ray photoelectron spectroscopy (XPS) analysis showed that the O/C ratio increases with oxygen-treated time. The distribution of carbon-containing functional groups on the CNTs surface, i.e., C−C, C−O, C=O, O−C=O, and π−π* shake up bonds can be identified and deconvoluted by a symmetrical Gauss function. The contact angle of H2O and CNTs is dependent on O/C ration. The relationships between the fraction of carbon-containing functional groups and various oxygen treatment times are also discussed.

Abstract: Based on the assumption that sp3 hybridization is more stable in bulk silicon, this study is a step forward in understanding the structures and mechanical properties of silicon nanotubes (SiNT). Using the well tested form of Tersoff potential we have calculated cohesive energy and other parameters for SiNT of various diameters and chiralities. Using this potential, the results obtained for bulk silicon are satisfactory, so we expect that the same potential would work well with SiNT as well. We calculated Young’ modulus and shear modulus for SiNT. Young’s modulus lies in the range of 100- 200 GPa which is about 10-20 times lower than CNT and shear modulus lies between 200-300 GPa. This work shall motivate further theoretical and experimental work in the field of nanostructures.

Abstract: Single phase W-type barium hexaferrite nano crystals of radar absorbing material (RAM) i.e., BaMe2Fe16O27 (Me2+=Fe2+) were synthesized by a modified flux method that combines the controlled chemical co-precipitation process for nucleation and complete uniform growth during in-situ annealing with NaCl flux under vacuum furnace. Uniform structure morphological transformation of nano crystals from spherical to prism faces were noticed after annealing with increasing temperatures from 200 to 1200 oC for 4 h in vacuum. XRD results showed the single phase nanocrystals of BaFe18O27 with increasing crystallanity and size from 10 to 90 nm during annealing. FESEM and TEM were used to investigate the systematic growth processes of various morphologies of nano crystals. The effect of such systematic morphological transformation of nanocrystals was observed in dielectric, dynamic magnetic and refection loss (RL) properties in Kuband (12.4 -18.0 GHz). A significant increment from -15.23 dB to -43.65 dB with wide range of bandwidth in RL loss is noticed due to the symmetric morphological growth of single phase nano crystals of RAM during annealing. This process of crystal growth, morphology evolution and RL enhancement with respect to increasing temperature were also explained in terms of ostwald ripening and quantum size effect.