Boron-doped nanocrystalline silicon thin films for solar cells

This article reports on the structural, electronic, and optical properties of boron-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The films were deposited by plasma-enhanced chemical vapour deposition (PECVD) at a substrate temperature of 150 °C. Crystalline volume fraction and dark conductivity of the films were determined as a function of trimethylboron-to-silane flow ratio. Optical constants of doped and undoped nc-Si:H were obtained from transmission and reflection spectra. By employing p⁺ nc-Si:H as a window layer combined with a p′ a-SiC buffer layer, a-Si:H-based p-p′-i-n solar cells on ZnO:Al-coated glass substrates were fabricated. Device characteristics were obtained from current-voltage and spectral-response measurements.     

Morphological and optical properties changes in nanocrystalline Si (nc-Si) deposited on porous aluminum nanostructures by plasma enhanced chemical vapor deposition for Solar energy applications

Photoluminescence (PL) spectroscopy was used to determine the electrical band gap of nanocrystalline silicon (nc-Si) deposited by plasma enhancement chemical vapor deposition (PECVD) on porous alumina structure by fitting the experimental spectra using a model based on the quantum confinement of electrons in Si nanocrystallites having spherical and cylindrical forms. This model permits to correlate the PL spectra to the microstructure of the porous aluminum silicon layer (PASL) structure. The microstructure of aluminum surface layer and nc-Si films was systematically studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD). It was found that the structure of the nanocrystalline silicon layer (NSL) is dependent of the porosity (void) of the porous alumina layer (PAL) substrate. This structure was performed in two steps, namely the PAL substrate was prepared using sulfuric acid solution attack on an Al foil and then the silicon was deposited by plasma enhanced chemical vapor deposition (PECVD) on it. The optical constants (n and k as a function of wavelength) of the deposited films were obtained using variable angle spectroscopic ellipsometry (SE) in the UV-vis-NIR regions. The SE spectrum of the porous aluminum silicon layer (PASL) was modeled as a mixture of void, crystalline silicon and aluminum using the Cauchy model approximation. The specific surface area (SSA) was estimated and was found to decrease linearly when porosity increases. Based on this full characterization, it is demonstrated that the optical characteristics of the films are directly correlated to their micro-structural properties.     

Nanocrystalline Metallosilicate Modified Electrodes for the Simultaneous,Sensitive, and Selective Determination of Riboflavin,Rutin, and Pyridoxine

Nanocrystalline metallosilicate modified glassy carbon electrodes were fabricated for the simultaneous determination of vitamins. Among these, nanocrystalline zirconosilicate exhibited the highest activity with a linear range from 30 nM–500 µM for riboflavin and 120 nM–600 µM for rutin and pyridoxine. Sensitivity values of 2.8, 1.49, and 1.13 µA/µM cm² and lower detection limits of 5 nM, 30 nM, and 30 nM for riboflavin, rutin, and pyridoxine, respectively, were found. The proposed sensor is stable and reproducible (RSD<3.5 %). The analytical performance of this sensor was demonstrated in the pharmaceutical preparations (multivitamin tablets) with satisfactory recovery (97–103 %).     

Preparation of PO4^3-, P2O7^4- Anion-Pillared Nanocrystalline Mg-Al and Zn-Al Layered Double Hydroxides in Microwave Fields

Using nanocrystalline [Mg-Al-CO3] and [Zn-Al-CO3] as precursors, [Mg-Al-PO4],[Zn-Al-PO4], [Mg-Al-P2O7] and [Zn-Al-P2O7] have been successfully synthesized by a direct reaction with the free PO4^3- or P2O7^4- using the microwave techniques and the anion-exchange method. And the samples thus obtained were characterized by TEM, FT-IR and XRD. The results show that the initial interlayer carbonate ions can be completely replaced by the free PO4^3- or P2O7^4- under controlled microwave conditions employed for a short time.     

Influence of environment and grain size on magnetic properties of nanocrystalline Mn–Zn ferrite

Nanocrystalline Mn_1−xZn_xFe₂O₄ (0.2?x?0.9) was prepared by mechanical alloying of the concerned oxide precursors and subsequent annealing in air and Ar atmosphere, respectively. Milling and annealing in air produces Zn-ferrites (ZnFe₂O₄) instead of Mn–Zn ferrites as MnO converts to higher oxides at higher oxygen partial pressure and fails to dissolve in the spinel phase. This is confirmed by careful quantitative X-ray diffraction analysis using Rietvelt profile matching and also by the non-saturating paramagnetic nature of the magnetization response with very low saturation level of these spinels milled and annealed in air. On the other hand, single-phase Mn–Zn ferrite results from the identical precursor oxide blend when milling and annealing are carried out under controlled (Ar) atmosphere. The average grain size of the as-milled and annealed powders, measured by Rietvelt refinement, varies between 6–8 and 14–18 nm, respectively. Further investigations performed with Mn_0.6Zn_0.4Fe₂O₄ reveal that a careful selection of annealing parameters may lead to an early superparamagnetic relaxation. Therefore, the blocking temperature can be significantly reduced through proper heat treatment schedule to ensure superparamagnetism and negligible hysteresis at low temperature.     

Nanocrystalline CaTiO3 prepared by soft-chemical route

Nanocrystalline CaTiO₃ has been synthesized by using soft-chemical route. X-ray diffraction study indicates that as-prepared powders were amorphous in nature and formation of CaTiO₃ phase starts at about 773 K. Phase formation saturates at around 1023 K and it remains orthorhombic up to 1400 K. Microstructure analysis by the Rietveld method revealed that the CaTiO₃ crystal size varies from 22.9 to 49.3 nm, while the annealing temperature varies from 773 to 1023 K. The variation of DC resistivity with temperature in the range 400–560 K shows a polaronic behavior in this system.     

Synthesis of flavanones using nanocrystalline MgO

The design and development of a truly nano heterogeneous catalyst for the Claisen-Schmidt condensation (CSC) of benzaldehydes with 2-hydroxyacetophenone to yield substituted chalcones followed by isomerization to afford flavanones with excellent yields and selectivity is described.     

Role of surface-purity in photocatalytic activity of nanocrystalline anatase–titania processed via polymer-modified sol–gel

Nanocrystalline titania powders have been synthesized via conventional and modified sol–gel using an alkoxide precursor for different R, the ratio of molar concentration of water to that of alkoxide precursor, and calcination temperature. The apparent first-order reaction rate-constant obtained for the powder synthesized via conventional sol–gel is comparable with that of commercial Degussa-P25. Conventional sol–gel has been modified using the hydroxypropyl cellulose polymer to increase the specific surface area of the photocatalyst; and hence, to further enhance its photocatalytic activity. Although higher specific surface area and smaller average nanocrystallite size have been obtained for the powders synthesized via modified sol–gel, they exhibit reduced photocatalytic activity relative to that of powders synthesized via conventional sol–gel. The deactivation of the present photocatalyst has been explained on the basis of reduced surface-purity of the powders after processing via modified sol–gel as induced by the presence of surface-residual organic compounds.     

Phase stability and ionic conductivity in substituted La2W2O9

Different substitutions, i.e. Sr²⁺, Ba²⁺, K⁺, Nb⁵⁺ and V⁵⁺, have been performed in the triclinic α-La₂W₂O₉ structure in order to stabilise the high temperature and better ionic conductor cubic β-phase. This approach has been used to try to obtain a new series of ionic conductors with LAMOX-type structure without molybdenum and presumably better redox stability compared to β-La₂Mo₂O₉. Nanocrystalline materials obtained by a freeze-drying precursor method at 600 °C exhibit mainly the β-La₂W₂O₉ structure, however, the triclinic α-form is stabilised as the firing temperature increases and the crystallite size grows. Only high levels of Ba²⁺ and V⁵⁺ substitutions retained the cubic form at room temperature after firing above 1100 °C. However, these phases are metastable above 700 °C, exhibiting an irreversible transformation to the low temperature triclinic α-phase. The synthesis, structure, phase stability, kinetic of phase transformation and electrical conductivity of these materials have been studied in the present report.     

Spin coating of ZnS nanostructures on filter paper and their characterization

In this paper we have reported spin coating of Cu doped Zinc sulphide nanostructures on filter paper flexible substrates. Zinc chloride and thiourea were used as precursors of zinc and sulphur. The samples were characterized by XRD, FE-SEM, EDAX and UV–visible spectrum studies. All the diffractogram peaks confirm the cubic structure of ZnS with small peak of Cu indicates incorporation of Cu into ZnS lattice. FE-SEM micrographs exhibit fibrous morphologies of ZnS structures on filter paper. Compound structures on flexible substrates show ohmic behavior with conductivity about 3.07×10⁶ (Ωcm)⁻¹ to 4.27×10⁶ (Ωcm)⁻¹. Excellent photoluminescence property doped with copper makes them suitable for flexible opto-electronic devices.