Wenwen Zhou

High sensitivity SnO2 single-nanorod sensors for the detection of H2 gas at low temperature

Uniform SnO(2) nanorods were grown by inductively coupled plasma-enhanced chemical vapor deposition without catalysts and additional heating. The SnO(2) nanorods were aligned on a pair of Au/Ti electrodes by the dielectrophoresis method. SnO(2) single-nanorod gas sensors were fabricated by connecting individual SnO(2) nanorods to a pair of Au/Ti electrodes with Pt stripes deposited by a focused ion beam. The sensing properties of the SnO(2) single-nanorod sensor were studied. The SnO(2) single-nanorod sensor could detect 100 ppm H(2) at room temperature with repeated response and showed a large change of resistance, fast response time and good reversibility at an elevated operating temperature of 200 degrees C. The optimal sensing performance of the sensor is achieved at the operating temperature of around 250 degrees C.

Preparation and thermoelectric properties of sulfur doped Ag2Te nanoparticles via solvothermal methods

In this work, n-type Ag(2)Te nanoparticles are prepared by a solvothermal approach with uniform and controllable sizes, e.g. 5-15 nm. The usage of dodecanethiol during the synthesis effectively introduces sulfur doping into the sample, which optimizes the charge carrier concentration of the nanoparticles to >1 × 10(20) cm(-3). This allows us to achieve the desired electrical resistivities of <5 × 10(-6)Ω m. It is demonstrated that Ag(2)Te particles prepared by this solvothermal process can exhibit high ZT values, e.g. 15 nm Ag(2)Te nanoparticles with effective sulphur doping show a maximum ZT value of ~0.62 at 550 K.

Growth of dandelion-shaped CuInSe2 nanostructures by a two-step solvothermal process

CuInSe(2) (CIS) nanodandelion structures were synthesized by a two-step solvothermal approach. First, InSe nanodandelions were prepared by reacting In(acac)(3) with trioctylphosphine-selenide (TOP-Se) in 1-octadecene (ODE) at 170 °C in the presence of oleic acid. These InSe dandelions were composed of polycrystalline nanosheets with thickness < 10 nm. The size of the InSe dandelions could be tuned within the range of 300 nm-2 µm by adjusting the amount of oleic acid added during the synthesis. The InSe dandelion structures were then reacted with Cu(acac)(2) in the second-step solvothermal process in ODE to form CIS nanodandelions. The band gap of the CIS dandelions was determined from ultraviolet (UV) absorption measurements to be ∼ 1.36 eV, and this value did not show any obvious change upon varying the size of the CIS dandelions. Brunauer-Emmett-Teller (BET) measurements showed that the specific surface area of these CIS dandelion structures was 44.80 m(2) g(-1), which was more than five times higher than that of the CIS quantum dots (e.g. 8.22 m(2) g(-1)) prepared by using reported protocols. A fast photoresponsive behavior was demonstrated in a photoswitching device using the 200 nm CIS dandelions as the active materials, which suggested their possible application in optoelectronic devices.

The morphology of Au@MgO nanopeapods

The structure of metal nanoparticles embedded inside dielectric nanowires/nanotubes, namely nanopeapods, has been of increasing interest due to their unusual photoresponse and optical adsorption properties. This paper presents a type of new inorganic nanopeapod: faceted Au nanoparticles inside MgO nanowires. The Au self-assembles into a nanoparticle chain during the vapor-liquid-solid growth of the MgO nanowires for which gold also serves as the catalyst. Surprisingly such a chain can follow the whole axis of the MgO nanowires even if the latter zigzag, provided that the amount of gold is sufficient. It is shown that such Au@MgO nanopeapods form not only under metalorganic chemical vapor deposition conditions (Lai et al 2009 Appl. Phys. Lett. 94 022904), but also under our conventional vapor transport deposition condition. This new nanopeapod material might be a candidate for the study of electronic and/or plasmonic wave transport along nanowires.

Stability studies of CdSe nanocrystals in an aqueous environment

In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH-) while photo-generated holes oxidize CdSe to Cd2+ and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH=10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments (bioimaging and dye-sensitized solar cells).

Sign changes of seebeck coefficients due to extrinsic-to-intrinsic transition for PbTe nanocrystals

Three types of PbTe samples, e.g. nanoparticles, nanowires and bulk ingots, have been prepared. The investigation of the Seebeck coefficient of PbTe nanoparticles and nanowires clearly shows the sign change in the temperature range of 575~650 K, which is not observed for bulk ingots. Unfortunately, this temperature range is within the proposed operation temperature range for thermoelectric devices using PbTe and hence, such a change will affect their proper performance. The observed sign change of Seebeck coefficient is not simply caused by the composition variation at high temperature. It is mainly attributed to the extrinsic-to-intrinsic-semiconductor transition for PbTe nanocrystals due to the competing factors between quantum size effect increasing band gap and self-purification process decreasing their charge carrier concentration, which shift the transition point of nanocrystals to lower range as compare to that of bulk samples. Thus, such phenomenon should be considered carefully in the design of thermoelectric devices using semiconductor nanocrystals, which have attracted much attention recently.