Advanced Materials Research Vol. 815

Abstract: The fabrication of large area nanoscale periodic structures on material surfaces for hydrophobicity engineering has been difficult due to the complex processes. Here we propose a two-step fabrication method for periodic nanostructures by combining laser interference lithography (LIL) and reactive ion etching (RIE). Sub-micron periodic nanotip patterns are fabricated in the photoresist by LIL, and then transferred into the silicon substrate using RIE. By measuring the contact angle (CA) of a water droplet on the substrate surface, the wettability of the surface with nanotip structures of various periods is studied. Our experiments show that the nanotip structures fabricated by the combined LIL and RIE process deliver satisfactory hydrophobic tendencies when the periods fall into the submicron scale. When the period of the structure is small enough, the hydrophilicity of the surface can be altered into hydrophobicity. The hydrophobicity achieved by this method is reusable and sustainable with low cost and no composition alteration comparing to chemical methods. The process developed in this work provides potential applications in biosensingand digital fluidics.

Abstract: Core-shell Cu-Au nanoparticles were chemically synthesized through a redox-transmetalation method in reverse microemulsion. The powder X-ray diffraction patterns revealed the presence of crystalline gold and copper and the absence of any copper oxides or other byproducts. The core shell structure could be clearly observed by the transmission electron microscope (TEM). In addition, the Cu cores and the gold shells were further verified by the high-resolution transmission electron microscope (HRTEM). The diameter of the nanoparticles ranged from 15 to 25 nm, with 5-10 nm core diameters and 10-15 nm shell thickness. The UV-visible absorption spectra of these nanoparticles showed a red shift (relative to pure gold nanoparticles), also in agreement with the gold shell morphology.

Abstract: A facile solution-phase process has been demonstrated for the selective preparation of single-crystalline Cu nanospindles and microflowers by reducing Cuprous iodide (CuI) with Sodium ascorbate (VCNa) in the presence of Pluronic F-127(F-127) or cetyltrimethylammonium bromide (CTAB). The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). To study the formation process of Cu nanoparticles, samples obtained at various stages of the growth process were studied by XRD. UV-vis spectra of the Cu nanospindles and microflowers were recorded to investigate their optical properties, which indicated that as-prepared Cu nanostructures exhibited morphology-dependant optical property.

Abstract: The article deals with the peculiarities of creation of effective negative pressure and the increase in the forbidden gap width in PbSe nanolayers. The dielectric state that maybe realized under these conditions and their appropriate doping can be considered as a new resource in lead selenide nanolayers. The increasing of the tangential lattice constant with higher growth temperature and layer growth rate confirms this consideration. When determining the forbidden gap width, the optical transmission spectra were processed by a model of the Fabry-Perot interferometer, and, at high concentration of free current carriers, the absorption on them and their degeneracy were taken into consideration.

Abstract: Organic-LDHs was prepared by three methods including co-precipitation, ionexchange and roast reduction process using Lauryl alcohol phosphoric acid ester potassium (MAPK) asmodifier.Polypropylene (PP)/Organically-modified layered double hydroxides (LDH) was prepared by the melt blending method. The structures and morphologies of composites were characterized by X-ray diffraction and TEM. TGA, cone calorimeter, limiting oxygen index (LOI) and the UL94 protocol were used to characterize the thermal stability and fire properties of composites. The results indicate that MAPK was successfully intercalated into the interlayer of LDHs and MAPK has a different arrangement in the interlayer of organicLDHs for different preparation methods of LDHs. PP/ionexchangeorganicLDHs (PP/ion-o-LDHs) and PP/roast reductionorganicLDHs (PP/ro-o-LDHs) show a better dispersion of LDH in PP than PP/co-precipitationorganicLDHs (PP/co-o-LDHs) composites. Compared to pristine PP, the peak heat release rate of PP/10% co-o-LDHs, PP/10% ion-o-LDHs and PP/10% ro-o-LDHs decreased by 21%, 33% and 30% respectively. The limiting oxygen index increased by 3.7 from 17.2(in PP) to 20.9(in PP/10% ion-o-LDHs). All of the composites could obtain an HB in the UL-94 horizontal burning.

Abstract: In order to improve the aqueous solutions viscosity and flocculation performance of cationic polyacrylamide, organic montmorillonite was added into polymerization system of polyacrylamide, the cationic polyacrylamide/dimethyl diallyl ammonium chloride/organic montmorillonite (CPAM/DMDAAC/MMT) nanocomposite was prepared by aqueous two-phase polymerization method. The influence of organic montmorillonite content, cationic monomer content, polyethylene glycol concentration, monomer concentration on the intrinsic viscosity of the CPAM/DMDAAC/MMT nanocomposite were discussed. The reaction conditions were optimized by orthogonal test. The chemical component and organic montmorillonite shape of the cationic CPAM/DMDAAC/MMT nanocomposite were analyzed by FTIR and XRD respectively. The results show that CPAM/DMDAAC/MMT nanocomposite with high aqueous solutions viscosity and beyond compare flocculation performance has been obtained by aqueous two-phase polymerization method. The CPAM/DMDAAC/MMT nanocomposite has been used very well as a flocculating agent.

Abstract: Scanning probe lithography such as atom force microscopy (AFM) has the highest spatial resolution. SPM etching technique employed conductive SPM probe as cathode and metal or semiconductor surface as anode. This paper reports the construction of nanopatterns by conductive nanoetching method on HDT modified Au (111) surface. With Pt-plated probe tip, nanowires of a minimum width of 176 nm was fabricated. The study shows that AFM lithography could be an alternative technology to e-beam lithography and focused-ion-beam.

Abstract: Bifunctional Ag/AgCl/α-Co (OH)₂ nanocomposite with selective adsorption and visible-light photocatalytic activities was prepared by a facile anion-exchange precipitation method via the reaction of α-Co (OH)₂ and AgNO₃, during which Cl anions in the interlayer of α-Co (OH)₂ are consequently released and reacted with Ag ions to form AgCl on the surface of α-Co (OH)₂ nanosheets. The prepared Ag/AgCl/α-Co (OH)₂ nanocomposite was used to adsorb and photodegrade the organic dyes from water. Results indicated that the nanocomposite not only has highly selective adsorption ability but shows good visible-light photocatalytic abilities to organic dyes.

Abstract: In this work, we demonstrate excellent gas sensors based on single-walled carbon nanotubes (SWNTs)-polypyrrole (PPy) networks for the detection of ammonia (NH₃) gas. The SWNTs networks were deposited on oxidized silicon surface functionalized with 3-aminopropytrimethysilane. The Fe³⁺ ions were easily adsorbed on the surface of SWNTs by ion exchange process. After deposition of PPy molecules on the surface of SWNTs by chemical vapor polymerization process in a sealed container with pyrrole vapors, SWNTs-PPy networks were formed. By the combination of traditional silicon processes, SWNTs-PPy networks-based gas sensors were fabricated at a wafer scale. The sensitive properties of the resultant gas sensors for the detection of NH₃ gas were investigated at room temperature. And the results suggested that the gas sensors based on SWNTs-PPy networks exhibited excellent sensitivity to NH₃ gas. This new method is very simple, which holds great potential in the wide spread practical production.

Abstract: In this research, a sequential sol-thermal route has been used to prepare the SnO₂ nanocolloid, Pt nanoparticles were then deposited on the nanosupport to obtain the Pt-SnO₂/MWCNTs. The electrochemical performances of the catalysts were characterized by cyclic voltammetry and chronoamperometry. The Pt (fcc) crystalline was proved to be form on the surface of carbon nanotubes. The Pt based catalyst modified by tin oxides exhibit a electro-chemical performance for methanol electro-oxidation.