Y. W. Chen

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers composite film electrodes

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers (CNTs-CNFs) composite film electrodes has been demonstrated. The large area CNTs-CNFs film was directly grown on Ni plate by low pressure and low temperature thermal chemical vapor deposition. The CNTs-CNFs electrodes have great advantages such as low cost, easy operation, long-term reproducibility, and integrity of monolithic CNTs-CNFs film and current collector. Batch-mode experiments at low voltage (0.4–2V) were conducted in a continuously recycling system to investigate the electrosorption process. Purification of water with good reproducibility was achieved because of optimal pore size distribution of CNTs-CNFs composite films.

Electrosorption of NaCl Solutions with Carbon Nanotubes and Nanofibers Composite Film Electrodes

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibers (CNTs-CNFs) composite film electrodes has been demonstrated. The low-cost, large area CNTs-CNFs composite film was directly grown on Ni plate by low-pressure, low-temperature thermal chemical vapor deposition. Successful purification of water with good reproducibility by electrosorption of CNTs-CNFs composite films was achieved because of optimal pore size distribution, which leads to lower electrical double-layer overlapping effect. The electrosorption capacity of CNTs-CNFs composite film electrodes was ∼ 15-65 μmol/g and comparable to carbon aerogels. The ion sorption followed a Langmuir isotherm, indicating monolayer adsorption.

Large enhancements of NaYF4:Yb/Er/Gd nanorod upconversion emissions via coupling with localized surface plasmon of Au film

Four-layered plasmonic structures of glass/Au/TiO2/NaYF4:Yb, Er, Gd nanorods were fabricated and tremendous improvement in upconversion luminescence (UCL) was observed under infrared 980 nm excitation. The TiO2 film was used as an oxide spacer. The emission intensity of the upconversion (UC) nanorods was strongly modulated by the thickness of the TiO2 layer. The extent of modulation depended on the separation distance between the Au layer and UC nanorods. A maximum UCL enhancement of 192-fold was observed for one green emission (540 nm) when a 10 nm-thick TiO2 film was used; 150-fold was observed for the other green emission (521 nm) at the same thickness of TiO2; and 105-fold was observed for the red emission (654 nm) when a 7.5 nm-thick TiO2 film was used. Alteration of the radiative decay rate was demonstrated for the first time in measurements of the decay times of UC nanorods positioned at various distances from the Au layer. The light interaction and coupling between metal Au and UC nanorods is numerically studied. The UCL mechanisms of multilayer plasmonic structures are discussed. Experimental results are explained and correspond well with those of theoretical calculations.

Large-scale growth of Cu2ZnSnSe4 and Cu2ZnSnSe4/Cu2ZnSnS4 core/shell nanowires

We present a fast and simple protocol for large-scale preparation of quaternary Cu(2)ZnSnSe(4) (CZTSe), as well as CZTSe/Cu(2)ZnSnS(4) (CZTS) core/shell nanowires using CuSe nanowire bundles as self-sacrificial templates. CuSe nanowire bundles were synthesized by reacting Cu(2 - x)Se nanowire bundles with sodium citrate solution. CZTSe nanowires were prepared by reacting CuSe nanowire bundles with Zn(CH(3)COO)(2) and SnCl(2) in triethylene glycol. X-ray diffraction (XRD) and selected area electron diffraction studies show that stannite CZTSe is formed. The formed CZTSe nanowire bundles have diameters of 200-400 nm and lengths of up to hundreds of micrometers. CZTSe/CZTS nanocable bundles with similar morphologies were grown by the addition of some elemental sulfur to the reaction system for growth of CZTSe bundles. The stannite CZTSe/kesterite CZTS core/shell structure of the grown nanocables was confirmed by XRD and high-resolution transmission electron microscope investigation. The influence of S/Se molar ratio in the reaction system on the crystallographic structures and optical properties of CZTSe/CZTS nanocables was studied. The obtained CZTSe/CZTS core/shell nanocable bundles show broad and enhanced optical absorption over the visible and near-infrared region, which is promising for use in photovoltaic applications.

STUDY OF CHEMICAL BATH DEPOSITION OF ZnS THIN FILMS WITH SUBSTRATE VIBRATION

An improved chemical bath deposition (CBD) technique has been provided to prepare zinc sulfide (ZnS) thin films on glass substrates deposited at 80–82°C using a mixed aqueous solution of zinc sulfate, ammonium sulfate, thiourea, hydrazine hydrate, and ammonia at the alkaline conditions. Both the traditional magnetic agitation and the substrates vibration by hand frequently were done simultaneously during the deposition. The substrates vibration reduced the formation and residence of gas bubbles on the glass substrates during growth and resulted in growth of clean ZnS thin films with high quality. Ammonia and hydrazine hydrate were used as complexing agents. It is found that hydrazine hydrate played an important role in growth of ZnS films. The structure and microstructure of ZnS films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis spectroscopic methods. The XRD showed a hexagonal structure. The formed ZnS films exhibited good optical properties with high transmittance in the visible region and the band gap value was estimated to be 3.5–3.70 eV.

Preparation of carbon nanotube field emission device and its driving circuits

As a new type of flat panel display technology, field emission display (FED) has drawn great interest due to the advantages of high display-quality and low power consumption. In this thesis, diode-type 16 times 16 matrix CNT-FED device was designed and sealed based on screen-printing technology. The device showed a low onset electrical field of 0.75 V/mu m and threshold field of 1.75 V/mu m. With proper driving circuits, the dynamic display of the 16 times 16 matrix CNT-FED device was realized.

Influence Of Cadmium Salts On A Modified Chemical Bath Deposition Of Cadmium Sulfide Thin Films

A simply modified bath deposition technique has been successfully used to deposit uniform CdS thin films using cadmium chloride or cadmium acetate as the cadmium ion source, and thiourea as the sulfur source on glass substrates. Both the traditional magnetic agitation and the frequent substrate vibration by hand were done simultaneously during the deposition. Various properties of the deposited films such as surface morphology, crystallinity, and optical properties were investigated. The CdS films deposited from cadmium acetate show a good crystallinity and exhibit a preferential orientation along the hexagonal (002) direction. Their surface morphologies are more homogeneous with smaller grains than those from cadmium chloride. The CdS films prepared from both cadmium ion sources present a high optical transmission (more than 80%) in the visible range with the band gap value of about 2.4 eV. The substrate vibration reduces the formation and residence of gas bubbles on the glass substrate during growth and resulted in deposition of CdS thin films with high quality. XRD, SEM, and UV–Vis measurements have provided the supported data. The fundamental CBD growth mechanisms involving different cadmium salts are discussed.

Electrosorption of cupric ions from solutions by carbon nanotubes and nanofibres film electrodes grown on graphite substrates

Electrosorption of ions from aqueous solutions with carbon nanotubes and nanofibres (CNTs-CNFs) film electrodes has been demonstrated. The cost-effective, large area CNTs-CNFs film was synthesised on graphite substrate by low pressure and low temperature thermal chemical vapor deposition (CVD). Successful removal of Cu2+ from water by electrosorption of CNTs-CNFs films was achieved. The electrosorption capacity of CNTs-CNFs film electrodes was approximately 30.6~136.2 mumol/g. The ion sorption followed a Langmuir isotherm, indicating monolayer adsorption. The degradation of CNTs-CNFs electrodes for the electrosorption of Cu2+ maybe due to the electrolytic reaction occurred on the surface of the electrodes.

PREPARATION OF INDIUM TIN OXIDE FILMS BY RADIO FREQUENCY MAGNETRON SPUTTERING UNDER LOW VACUUM LEVEL

Indium tin oxide (ITO) thin films were prepared by radio frequency (RF) magnetron sputtering and under a quite low vacuum level of 2.3 × 10-3 Pa. The sputtering was done in an Ar and O2 gas mixture at a temperature of 200°C. A ceramic In2O3:SnO2 target (10 wt% SnO2) was used. The microstructures of the films were investigated by a field emission scanning electron microscope (FESEM) and an X-ray diffractometer (XRD). X-ray photoelectron spectroscopy (XPS) was performed to characterize the composition of the films. ITO films with a high transparency in the visible wavelength range (80–95%) were obtained. The dependency of the electrical, optical and structural properties of ITO films on both the O2 flow ratio (O2/(O2 + Ar)) and the working pressure was investigated. In the case of low working pressure (1 Pa), the more highly transparent and conducting films were produced at the lower O2 flow ratio. High working pressure (2 Pa) gave rise to low quality, low transparency and amorphous films. Under RF sputtering at low vacuum level, the main contribution to the chamber atmosphere is due to water vapor. Oxygen originating from water vapor dissociation induced by plasma plays the same role as an oxygen or water vapor flux usually intentionally introduced in the system in order to have good quality films.

PHOTOLUMINESCENCE PROPERTIES OF Er DOPED INTO C-RICH SiC NANOPARTICLE FILMS

Polycrystalline silicon carbide (P-SiC) films containing SiC nanoparticles and Er were prepared by r.f. reactive magnetron co-sputtering technique with SiC and Er targets on low-temperature silicon (111) and silicon dioxide substrates with the mixed gas of pure argon, methane, and hydrogen. Surface morphology and photoluminescence (PL) properties of them were measured by field-emission scanning electron microscope and Raman spectroscopy. The peak position, intensity, and the full width at half maximum (FWHM) of PL spectra were relevant with Er doping levels and deposition conditions.