Materials Science Forum Vol. 814

Abstract: Graphene, a single layer of sp²-bonded carbon atoms arranged in a honeycomb lattice, has attracted a plethora of attention because of its remarkable physical, mechanical, electronic and optical properties. This paper reviews recent advances in the preparation methods of graphene. Recently, graphene materials research has reached an unprecedented event, and the graphene preparation method also is endless. A lot of papers have been reported, but not an exhaustive list of various preparation methods and its principles. In this article, based on the previous preparations of graphene, comprehensive fabrication methods were summarized, and then, put forward a new vision and perspectives.

Abstract: Nanostructured ZnO with versatile morphologies has great potential applications in many fields. In this work, ZnO materials with different morphologies were deposited on Zn foils by a simple aqueous solution method, and the shape of ZnO can be controlled by the concentration of Cl ions in the solution. Rods, spheres and platelets were obtained respectively with the concentration of Cl ions increase. The competition between Cl ions and growth units in the solution results the formation of ZnO materials with different morphologies. At the same time, the preferential orientation of the crystal plane is also changed by the concentration of Cl ions. The different morphologies of ZnO grown form this kind of solution method was also explained.

Abstract: Highly ordered TiO₂ nanotube array hasbeen widely used as the dye-sensitized solar cells’ (DSSCs) light anode material forits abilities of inhibiting electronic recombination at the interface and improving the beam transmission of the carrier. The morphology and structure of the nanotube would influence the efficiency of the cell. In thisstudy, TiO₂ nanotubes (caliber ranging from 50 to 150nm, length ranging from 0.9 to 4μm) were prepared by a two-step anodization method and the morphology of nanotubes was regulated bythe parameters such as oxidation voltage and oxidation time. The absorbing capacities of nanotubes were measured by the dye adsorption test and the corresponding photoelectric conversion efficienciesweremeasured too. The results indicated that the conversion efficiency was related to the specific surface area and length of the nanotube. The length of nanotube would increase with theoxidation time within acertain limit.Then thedissolution on the top of TNT would reduce nanotubes’ length and lead to the decrease of the specific area, eventuallyimpairedthe photoelectric conversion.

Abstract: Vanadium-sol modified LiFePO₄ material was prepared by 300 °C calcination in a tube furnace. The modified LiFePO₄ material was characterized by X-ray diffraction, field emission scanning electron microscopy, energy disperse spectroscopy and electrochemical impedance spectroscopy. The results indicated that vanadium-sol modified LiFePO₄ had higher first cycling efficiency, lower impedance and polarization, and better electrochemical properties at high charge/discharge rates.

Abstract: Sensitized TiO₂ nanospheres with uniform diameter of ca. 100 nm were successfully synthesized by a hydrothermal method using urea as templates and subsequently employed as robust visible-light photocatalysts. The photocatalytic activities of the sensitized TiO₂ nanospheres evaluated by photodegrading methyl orange (MO) were recorded, giving the best photocatalytic performance for the sample synthesized at 110°C for 36 h. The photocatalytic mechanisms of the sensitized TiO₂ nanospheres were attributed to the reduction of bandgap energies and the sensitizing effect of melon. The resultant melon acted as a sensitizer to absorb visible light and induced electrons which participated in the photodegradation of MO molecules. The new concept was helpful to guide the synthesis of robust photocatalysts, dye-sensitized solar cells, or hybrid solar cells, and the results suggested that the sensitized TiO₂ nanospheres were very promising for enhancing the visible-light photocatalytic activity of TiO₂ photocatalysts.

Abstract: Cu₂MnSnS₄ thin film was successfully prepared by a sol-gel technique on soda lime glass substrate from metal salts and thiourea. The structural and morphological properties of the fabricated film were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The combination of the X-ray diffraction results and Raman spectroscopy reveal that this obtained layer is composed by Cu₂MnSnS₄ phase and has a stannite structure with preferential orientation along the (112) direction. The scanning electron microscopy and atomic force microscopy results show that the synthesized thin film is smooth and compact without any visible cracks or pores. The band gap of the Cu₂MnSnS₄ thin film is about 1.29 eV determined by the UV-vis-NIR absorption spectra measurement, which indicates it has potential applications in solar cells.

Abstract: Cu₂ZnSnS₄ and Cu₂ZnGeS₄ thin films made from the earth abundant and non-toxic materials are quaternary semiconducting compounds which have received increasing interest for solar cells applications. Cu₂ZnSnS₄ and Cu₂ZnGeS₄ thin films have been synthesized by sulfurization of radio frequency magnetron sputtered precursors. The structural and optical properties of the thin films have been investigated and discussed. The result of X-ray diffraction demonstrates that the Cu₂ZnSnS₄ and Cu₂ZnGeS₄ thin films have kesterite (KS; space group I) crystal structure. An obvious blue shift is observed in the Raman spectra as smaller Ge replaces Sn. It is due to the fact that the radius of Ge cation is smaller than that of Sn cation , which results in the shrink of the lattice. Further transmission spectra demonstrate that the values of band gap for CZTS and CZGS thin films are 1.54 eV and 1.98 eV, respectively.

Abstract: In this study, graphite doped silicon was prepared by mechanical alloying (MA). MA is an effective method to manufacture silicon-carbon composite. The results show that the capacity retention ability of the graphite doped silicon by MA anode is better than silicon. The fellow result shows that Li_aC_b appears at the middle of lithiation process and disappear with the production of Li_xSi_y, Li_xSi_y produce and disappears at the end of lithiation process and beginning of delithiation process respectively. The SEI film enhanced with the increasing amount of lithium and silicon-carbon composite material was severely decomposed with the cycles increase.

Abstract: Nanostructured ZnO films were fabricated by chemical vapor deposition (CVD) method with different Sn source concentrations for ethanol sensing application. It was found that the morphology of the ZnO films were obviously affected by Sn concentration, while no any Sn signals were detected in the films. The response of the nanostructured ZnO films increases with the increase of ethanol concentrations, and the S2 sample displays the highest sensitivity. Thephotoluminescence spectra show that more oxygen vacancies exist in the S2 sample than the other samples, which reveals that oxygen vacancies may play a great role to improve the gas sensing properties of the ZnO films.A possible sensing mechanism was proposed to explain these phenomena.This work provides a very simple and efficient method to prepare ZnO gas sensor, its high response and short recovery time are also a merit for the ZnO films used in gas sensor applications.