Wurtzite CdS and CdSe nanostructures with complex morphologies such as urchin-like CdS nanoflowers, branched nanowires, and fractal nanotrees can be produced via a facile solvothermal approach in a mixed solution made of diethylenetriamine (DETA) and deionized water (DIW). The morphologies of CdS and CdSe nanocrystals can be easily controlled via tuning the volume ratio of DETA and DIW. Urchin-like CdS nanoflowers made of CdS nanorods are in a form of highly ordered hierarchical structures, while the nanowires are branched nanowires, and the fractal CdS nanotrees are a buildup of branched nanopines. The results demonstrated that solvothermal reaction in a mixed amine/water can access a variety of complex morphologies of semiconductor materials. The photocatalytic activity of CdS particles with different morphologies has been tested by the degradation of acid fuchsine under both UV and visible light, showing that the as-prepared branched CdS nanowires exhibit high photocatalytic activity for degradation of acid fuchsine.

This paper presents a solvothermal strategy for chemical modification of TiO(2) nanoparticles with carboxylic acids. Solvothermal reaction between the TiO(2) nanoparticles and carboxylic acid molecules in an autoclave at 100 degrees C provides carboxylic acid-modified TiO(2) particles with a modification efficiency much higher than the conventional immersion method. TiO(2) nanoparticles were prepared by hydrolysis of titanium isopropoxide in nitric acid solution; the modified nanoparticles were characterized by powder X-ray diffraction pattern, scanning electron microscopy, absorption and Fourier transform infrared spectra, and thermogravimetric analysis. Results show that the binding form of the modifier molecules on TiO(2) surface is in a bidentate chelating mode, the crystalline phase composition and morphological structure of the preformed TiO(2) nanoparticles are not affected by the solvothermal reaction, and the surface coverage of the modifier molecules can be adjusted by the weight ratio of modifier/TiO(2) during feeding. It is evident that the reaction processes in the solvothermal strategy involve the formation of double hydrogen bondings between carboxylic acid molecule and TiO(2) at the same Ti site and the coordination at solvothermal temperature by dehydration from the hydrogen bondings. The solvothermal strategy for modifying TiO(2) nanoparticles is expected to find potential applications in many fields; for example, our results demonstrate that the photovoltaic performance of the TiO(2) nanoparticles can be improved by the solvothermal modification even with an insulating modifier and controlled by the modifier coverage.

[15] provides encouragement that the solution-phase methods of SLS and SFLS will eventually reach their potential as a general strategy for nanowire synthesis of any desired material. Experimental SectionPrecursor Preparation: The precursors (tBu) 3 Ga and As(SiMe 3 ) 3 were prepared by literature methods [16,17]. GaCl 3 was purchased and used as received from STREM. A stock solution of 50 mM (tBu) 3 Ga and As(SiMe 3 ) 3 was prepared in hexane under a nitrogen atmosphere. Dodecanethiol-coated gold nanocrystals 7 nm in diameter were prepared by arrested precipitation as described in the literature [18]. The gold nanocrystals were weighed and dispersed in hexane such that the molar concentration of gold was in a 100:1 precursor/gold ratio in the precursor solution.Nanowire Synthesis: A 1 mL reaction cell was loaded with a Si/SiO 2 deposition substrate then heated to 500 C and pressurized to 7 MPa. The experimental apparatus was similar to that in Hanrath and Korgel modified to include two 200 lL 6-way high-performance liquid chromatography (HPLC) injection loops in series [9]. The loop nearest the reactor was loaded with the gold nanocrystal solution, and the other with the precursor solution. Both solutions were sequentially injected into the reactor at 4.00 mL min ±1 as the pressure was ramped to 37 MPa. The reaction proceeded for 8 min before cooling under air flow and depressurizing back to room temperature and ambient pressure. The nanowire product on the substrate forms a yellow film up to several micrometers thick consisting of a mat of tangled GaAs nanowires.Characterization: The GaAs nanowire product was collected on the Si/SiO 2 substrate and characterized by a field-emission scanning electron microscope (SEM) (LEO 1530) operating between 3 and 8 kV using an in-lens detector. HRTEM and EDS analysis (JEOL 2010F, operating voltage 200 kV, with attached Oxford INCA EDS) were performed on nanowires re-dispersed in hexane and drop cast onto lacey carbon-coated copper grids. XRD of nanowires deposited on quartz slides was obtained using a Phillips vertical scanning diffractometer. XPS (Phi ESCA 5700, with monochromatic Al anode operating at 11.75 eV pass energy) data was obtained from wires drop cast on a gold substrate.Device Fabrication: GaAs nanowire devices were fabricated by orienting the nanowires onto a substrate patterned with gold leads and subsequently making electrical contact with Pt electrodes deposited using a focused ion beam technique. A Raith 50 Electron Beam Lithography Tool in combination with a Standard XL Scanning Microscope was used to pattern a PMMA resist layer on a silicon oxide chip. This pattern was metallized by evaporating 3 nm Cr and 30 nm Au in a Denton DV502 Vacuum Chamber. After the chip was cleaned, the wires were deposited using a method similar to literature but without an applied electric field [19]. Nanowires were suspended in a toluene solution by sonication. A drop of the solution was placed onto a chip that had two leads grounded. The drop was removed by blowing over th...