Guotao Duan

Violet photoluminescence from shell layer of Zn/ZnO core-shell nanoparticles induced by laser ablation

A strong violet photoluminescence (PL) band at 425nm (2.92eV) was observed from the ZnO shell layer of the Zn∕ZnO core-shell nanoparticles prepared by laser ablation in liquid media. Such violet PL decreases with increase of the shell thickness or annealing temperature, showing good controllability. Based on the electron paramagnetic resonance measurements, the violet emission is attributed to the electronic transition from the defect level, corresponding to high-concentration zinc interstitials, to the valence band. This study is in favor to clarify the defect-related emissions and to extend the optical and electronic applications of nanostructured ZnO.

Two-dimensional hierarchical porous silica film and its tunable superhydrophobicity

Base do na monolayer polystyrene (PS) colloidal crystal, large-scale two-dimensional (2D) hierarchical porous silica (orderly arranged macropores and disordered mesopores in its skeleton) with a high specific surface area was fabricated by the sol–gel technique. Such material has demonstrated superhydrophilicity with a water contact angle (CA) of 5 ◦ and superhydrophobicity with a water CA of 154 ◦ after surface modification with fluoroalkylsilane. More interestingly, the water CA can be increased to 165 ◦ using a heat-deformed PS template, which suggests that the superhydrophobicity can be controlled by the template with different heat-deformed extents. Such silica films have applications in fields of adsorbent, catalytic, chromatographic support, microseparator and microfluid devices. (Some figures in this article are in colour only in the electronic version)

Fabrication of self-standing silver nanoplate arrays by seed-decorated electrochemical route and their structure-induced properties

We present an electrochemical route to synthesize silver nanoplates on seed-decorated Indium tin oxide (ITO) glass substrate. The nanoplates are several tens of to several hundred nanometers in dimension. The density of nanoplates covered on the substrate can be controlled well by adjusting the amounts of seed. All the nanoplates are standing on the substrate uniformly even at very high density. Silver nanoplate arrays displayed an extraordinary superhydrophobicity after chemical modification and can serve as highly active surface-enhanced Raman scattering (SERS) substrates for microdetection. The arrays can also be used as electrodes for electrochemical capacitor with high power density.

A template-free electrochemical deposition route to ZnO nanoneedle arrays and their optical and field emission properties

We report a soft and template-free electrochemical deposition method for preparing wafer-scale ZnO nanoneedle arrays on an oriented gold film coated silicon substrate. It has been shown that the ZnO nanoneedles possess single-crystal wurtzite structure and grow along the c-axis perpendicularly on the substrate. Raman and resonant Raman scattering studies have confirmed that the ZnO nanoneedles are of good crystal quality. The room temperature photoluminescence spectrum of such ZnO nanoneedle arrays exhibits a strong ultraviolet emission but negligible visible emission. The time-resolved photoluminescence spectral analysis discloses the excitonic origin of the ultraviolet emission. The field electron emission study, showing notable emission current in a moderate turn-on field, demonstrates potential applications of such ZnO nanoneedle arrays in field emission display devices. The formation of such a ZnO nanoneedle array is attributed to the formation of {0001}-oriented ZnO nuclei on the oriented gold coated silicon substrate and preferential growth along .

Electrochemically induced flowerlike gold nanoarchitectures and their strong surface-enhanced Raman scattering effect

The authors report the fabrication of gold flowerlike nanoarchitectures (FNs) on indium tin oxide coated glass substrate using a low-cost electrochemical strategy at a proper current density and polyvinylpyrrolidone concentration in electrolyte. The FNs are grown and built with the blocks of two-dimensional flakelike nanostructures. Importantly, such FNs show strong surface-enhanced Raman scattering (SERS) effect associated with their geometries, which is much stronger than that from other particle films. The minimum concentration of detectable rhodamine 6G molecules can be down to 10−12M. These FNs with strong SERS effect could be used in chemical analysis, biosensors, and nanodevices with molecule-level detection.

Morphology evolution and photoluminescence properties of ZnO films electrochemically deposited on conductive glass substrates

The current-dependent morphology evolution and photoluminescence properties of zinc oxide (ZnO) films prepared by electrochemical deposition (ECD) method were studied in this paper. It has been shown that the morphologies of ZnO films vary from porous to dense structure, from pillar crystal array to two-dimensional nanosheet covered film, with increase of deposition currents. Correspondingly, orientation of the film evolves from randomly to highly c-axis oriented structure. Current dependence of morphology is attributed to the ECD current-controlled preferential growth velocity along the c axis. All the ZnO films prepared over a wide current range show strong ultraviolet (UV) emission at room temperature, which also shows deposition current dependence in intensity, together with relatively weak defect-related green emission under UV excitations. Further experiments have revealed that a nonradiative relax process and a radiative electron-hole combination process are involved in this defect-related green em...

Phase Diagram, Design of Monolayer Binary Colloidal Crystals, and Their Fabrication Based on Ethanol-Assisted Self-Assembly at the Air/Water Interface

Flexible structural design and accurate controlled fabrication with structural tunability according to need for binary or multicomponent colloidal crystals have been expected. However, it is still a challenge. In this work, the phase diagram of monolayer binary colloidal crystals (bCCs) is established on the assumption that both large and small polystyrene (PS) colloidal spheres can stay at the air/water interface, and the range diagram for the size ratio and number ratio of small to large colloidal spheres is presented. From this phase diagram, combining the range diagram, we can design and relatively accurately control fabrication of the bCCs with specific structures (or patterns) according to need, including single or mixed patterns with the given relative content. Further, a simple and facile approach is presented to fabricate large-area (more than 10 cm(2)) monolayer bCCs without any surfactants, using differently sized PS spheres, based on ethanol-assisted self-assembly at the air/water interface. bCCs with different patterns and stoichiometries are thus designed from the established phase diagram and then successfully fabricated based on the volume ratios (V(S/L)) of the small to large PS suspensions using the presented colloidal self-assembling method. Interestingly, these monolayer bCCs can be transferred to any desired substrates using water as the medium. This study allows us to design desired patterns of monolayer bCCs and to more accurately control their structures with the used V(S/L).

Hierarchical surface rough ordered Au particle arrays and their surface enhanced Raman scattering

A simple, effective, and low-cost method is presented to fabricate an ordered Au particle array with hierarchical surface roughness on an indium tin oxide substrate based on an ordered alumina through-pore template, induced by solution dipping on colloidal monolayer, using an electrochemical deposition strategy. The array consists of periodically arranged and isolated Au microparticles, which show nanoscaled surface roughness. Importantly, this hierarchically rough particle array exhibits strong surface-enhanced Raman scattering effect using rhodamine 6G as probe molecules, associated with its surface geometry. Such structure could be useful, e.g., in sensors, biotechnology, and nanodevices.

Fabrication of Gold Nanoparticles by Laser Ablation in Liquid and Their Application for Simultaneous Electrochemical Detection of Cd2+, Pb2+, Cu2+, Hg2+

In this paper, we demonstrated the fabrication of high active and high sensitive Au nanoparticles by laser ablation in liquid (LAL) method, and their application in electrochemical detection of heavy metal ions. First, LAL method are used to fabricate Au nanoparticles in water in a clean way. Second, the Au nanoparticles were assembled onto the surface of the glassy carbon (GC) electrode by an electrophoretic deposition method to form an AuNPs/GC electrode for electrochemical characterization and detection. Through differential pulse anodic stripping voltammetry method, it shows that the AuNPs/GC electrode could be used for the simultaneous and selective electrochemical detection of Cd(2+), Pb(2+), Cu(2+), and Hg(2+). By studying the influence of test conditions to optimize the electrochemical detection, we can detect Cd(2+), Pb(2+), Cu(2+), and Hg(2+) simultaneously with a low concentration of 3 × 10(-7) M in the experiments.

Fast-Response, Sensitivitive and Low-Powered Chemosensors by Fusing Nanostructured Porous Thin Film and IDEs-Microheater Chip

The chemiresistive thin film gas sensors with fast response, high sensitivity, low power consumption and mass-produced potency, have been expected for practical application. It requires both sensitive materials, especially exquisite nanomaterials, and efficient substrate chip for heating and electrical addressing. However, it is challenging to achieve repeatable microstructures across the films and low power consumption of substrate chip. Here we presented a new sensor structure via the fusion of metal-oxide nanoporous films and micro-electro-mechanical systems (MEMS)-based sensing chip. An interdigital-electrodes (IDEs) and microheater integrated MEMS structure is designed and employed as substrate chip to in-situ fabricate colloidal monolayer template-induced metal-oxide (egg. SnO2) nanoporous sensing films. This fused sensor demonstrates mW-level low power, ultrafast response (~1 s), and parts-per-billion lever detection for ethanol gas. Due to the controllable template strategy and mass-production potential, such micro/nano fused high-performance gas sensors will be next-generation key miniaturized/integrated devices for advanced practical applications.