Chenmin Liu

Facile synthesis of water-soluble, highly fluorescent graphene quantum dots as a robust biological label for stem cells

We present a facile electrochemical method for synthesizing uniform sized graphene quantum dots (GQDs) with a strong yellow emission at 14% quantum yield. This approach has enabled a large-scale production of aqueous GQD solution without the need for polymeric or surfactant stabilizers. The structure and emission mechanism of the GQDs have been studied by combining extensive characterization techniques, rigorous control experiments and theoretical calculations. We further demonstrate the distinctive advantages of such GQDs for direct and efficient stem cell labeling, opening up great opportunities for their bio-medical applications.

Porous nanotubes of Co3O4: Synthesis, characterization, and magnetic properties

Stoichiometric Co3O4 porous nanotubes have been synthesized through a simple modified microemulsion method. The structural and the chemical information of the as-grown nanotubes have been investigated by means of x-ray diffraction, electron microscopy, electron energy loss spectroscopy, and dynamic force microscopy. The results reveal that the as-grown materials are formed by concentric stacking of Co3O4 (111) planes or weaved porous nanotubes with diameters ranging from tens to ∼200nm and sidewall thickness ranging from 2to∼20nm. Magnetic property of the sample demonstrates a magnetic transition temperature at 8.4K, indicating macroscopic quantum confinement effects from the sidewall thickness of the porous nanotube.

Synthesis of angstrom-scale anatase titania atomic wires.

Using a nonhydrolytic solution approach, we demonstrate the bulk synthesis of extremely thin crystalline TiO2 atomic wires in the anatase phase with diameters reaching the atomic limit of a few angstroms (approximately 4-5 A). These nearly monodisperse, atomically thin, and soluble TiO2 wires fill a most important size gap in nanowire fabrication. Preliminary results on photocatalytic activity of the atomic wires are also presented on degradation of methylene blue under visible light. These atomic wires are expected to promote exchanges between theory and experiments in fundamental studies of a one-dimensional (1D) system and provide unique building blocks to construct high-performance devices.

Magnetic nanochains of metal formed by assembly of small nanoparticles

Ni nanochains are synthesized with diameters of 150-250 nm and lengths of 0.5-2 microm by assembly of small nanoparticles, which exhibit a magnetic coercivity over two orders of magnitude larger than that of bulk Ni.

From Nanorods to Atomically Thin Wires of Anatase TiO2: Nonhydrolytic Synthesis and Characterization

A nonhydrolytic two-step chemical process has been developed to synthesize ultrathin, nearly monodisperse TiO(2) (anatase) wires with tunable diameters of 5 nm to approximately 4 A, reaching the atomic length scale. The high-quality anatase titania atomically thin wires can be doped and stabilized with nitrogen species by introducing suitable nitrogen-containing molecules. The ultrathin wires, particularly the atomically thin wires, as well as the precursor, have been thoroughly characterized by an extensive series of structural, spectroscopic, and other techniques. Possible formation mechanisms for the rods and the wires are proposed on the basis of experimental results obtained under varying reaction conditions. Also demonstrated are the pronounced effects of size and N-doping on the electronic, optical, and phononic properties of the anatase titania wires in the smallest size regime.

Seed-mediated growth and properties of copper nanoparticles, nanoparticle 1D arrays and nanorods

Copper nanorods were simply prepared by a method of seed-mediated growth in solution. In this method, poly(N-vinyl-2-pyrrolidone) (PVP) was used as a surface modified reagent as well as a soft template. By adjusting the concentration of copper ion and PVP and the refluxing time, the copper nanoparticles, copper 1D array nanoparticles wrapped in PVP and nanorods were obtained successively. Transmission electron microscopy, ultraviolet-visible spectrum and fluorescence spectroscopy were used to characterize the as-prepared copper nanoparticles and nanorods. X-ray absorption near edge structure (XANES) spectrum was carried out to investigate the microstructure. Obvious UV luminescence was observed for the copper nanorods. The mechanism of the growth process of copper nanomaterials was discussed.

Comparative optical study of colloidal anatase titania nanorods and atomically thin wires.

We present results of a comparative study of colloidal anatase titanium oxide nanorods and extremely thin atomic wires of systematically decreasing (2.6 nm down to 0.5 nm) diameter in terms of their optical absorption as well as steady-state and time-resolved photoluminescence. Steady-state photoluminescence spectra of the titania samples show three well-distinguished spectral components, which are ascribed to excitonic emission (4.26 ± 0.2 eV), as well as radiative recombination of trapped holes with electrons from the conduction band (4.04 ± 0.4 eV) and radiative recombination of trapped electrons with holes in the valence band (3.50 ± 0.2 eV) in nanocrystalline anatase TiO(2). Time-resolved photoluminescence measurements point out the existence of different emissive species responsible for the appearance of high-energetic and low-energetic emission peaks of TiO(2) atomic wires and nanorods.

Electrorheological characterization of ultrathin titanium dioxide nanorods solutions using microfluidics

Electrorheological (ER) effect of ultrathin titanium dioxide (TiO2) nanorods solutions in different solvents was investigated. TiO2 nanorods were synthesized and dispersed in raw suspension, Octadecene (ODE) / Oleylamine (OLAM), and hexane/ OLAM, respectively. Hybrid microfluidics with integrated microelectrodes were successfully fabricated to characterize the ER effect of these minute nanorods solutions. We showed, for the first time, that the TiO2 nanorods in ODE/OLAM have the best ER effect in microchannel without clogging problem. The corresponding viscosities at different electric fields were also calculated.

Synthesis and characterization of angstrom-scale anatase titania atomic wires

We present bulk synthesis of anatase titania atomic wires with uniform diameters of approximately ∼4–5 Å which are as thin as about two to three Ti-O bonds across. The synthesis was realized by a nonhydrolytic approach, which carefully controls the formation of a titanium-containing precursor from the reactions of titanium alkoxide and the subsequent growth of the TiO2 atomic wires with the assistance of surfactants.

A method to identify shallow dopants in semiconductor nanowires

In this paper, an electrical measurement method to identify shallow dopants in lowly doped semiconductor nanowires was suggested. Room temperature electrical measurement indicates that electron concentrations of the n-GaN nanowires are about 5.4×1017cm−3. Temperature-dependent measurement of conductivities of single nanowires in low temperature region gives activation energy of 13.3meV, which is consistent with the reported activation energy of 14meV for Si donor in n-GaN films with donor concentration of 7.4×1017cm−3. Our results confirm that the shallow donors in the as-synthesized GaN nanowires are silicon. We consider such a method may be applicable to other semiconductor nanowires.