Guangqiang Liu

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.

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.

Physical Deposition Improved SERS Stability of Morphology Controlled Periodic Micro/Nanostructured Arrays Based on Colloidal Templates

An effective and inexpensive method is developed to fabricate periodic arrays by sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. By a colloidal template induced precursor solution dipping strategy, different periodic arrays of semi-hollow sphere array, inverse opal with monolayer pore arrays and hole arrays are obtained under different conditions. After magnetron sputtering deposition, their morphologies are changed to novel micro/nanostructured arrays of honeycomb-shaped arrays, hollow cavity arrays, and regular network arrays due to multiple direction deposition of sputtering deposition and shadow effect. After coating a gold thin layer, these periodic micro/nanostructured arrays are used as SERS active substrates and demonstrate a very stable SERS performance compared with periodic arrays achieved by direct colloidal template-induced chemical deposition. Additionally, a honeycomb-shaped array displays better SERS enhancement than that of a hollow cavity array or a regular network array. After optimization of honeycomb-shaped arrays with different periodicities, an array with periodicity of 350 nm demonstrates much stronger SERS enhancement and possesses a low detection limit of 10(-11) M R6G. Such stable SERS performance is useful for practical application in portable Raman detecting devices to detect organic molecules.

Vertically cross-linking silver nanoplate arrays with controllable density based on seed-assisted electrochemical growth and their structurally enhanced SERS activity

A facile seed-assisted electrochemical deposition (ECD) route has been presented to fabricate silver nanoplate arrays at room temperature. The nanoplates are hundreds of nanometres to several micrometres in dimension and tens of nanometres in thickness. All the nanoplates are standing vertically on the indium-tin oxide substrate and cross-linking each other. Importantly, the number density of silver nanoplates in the array can be controlled by the amount of seeds pre-coated on the substrate. Further experiments have demonstrated that electric current density during ECD plays a crucial role in the final morphology of the products. A simple and flexible way is presented to study time-dependent morphological evolution only in one step, based on substrate-moved electrochemical deposition, which has revealed that each nanoplate grows up from individual Ag seeds on the substrate. The formation of nanoplates is attributed to the seed-assisted preferential nucleation and quasi-equilibrium oriented growth. Further studies indicate that such Ag nanostructured arrays can serve as highly active surface-enhanced Raman scattering (SERS) substrates and have very homogeneous SERS activity in whole sample.

Tunable Surface Plasmon Resonance and Strong SERS Performances of Au Opening-Nanoshell Ordered Arrays

Au opening-nanoshell ordered arrays with tunable local surface plasmon resonance (SPR) property have been fabricated based on sputtering deposition onto monolayer colloidal crystal. The changes in local SPR peak for the arrays can be well tuned from visible to near-infrared region with decreasing of the spacing between two neighbor opening-nanoshells. It has been revealed that the changes of SPR peak originate from the electromagnetic coupling between two adjacent Au opening-nanoshells. This study is important to design and fabricate surface-enhanced Raman scattering substrates with high activity and practical application.

General Synthesis of 2D Ordered Hollow Sphere Arrays Based on Nonshadow Deposition Dominated Colloidal Lithography

A general strategy, nonshadow deposition dominated colloidal lithography (NSCL), was proposed for the synthesis of two-dimensional (2D) ordered hollow sphere arrays of conductive materials. Gold, polypyrrole, CdS, and ZnO were taken as model materials to demonstrate the NSCL strategy, and built as 2D hollow sphere arrays successfully. In this strategy, a thin gold coating is first introduced on a polystyrene sphere (PS) colloidal monolayer via ion-sputtering deposition, and a hollow sphere array can thus be obtained by further electrochemical deposition on such a monolayer and by subsequent removal of PSs. The proposed strategy is flexible and facile to control the microstructure and size of the hollow sphere array, and the features are as follows: (i) controllable shell of the hollow sphere from single-layer to multilayer with single or multiple compositions, (ii) tunable morphology from simple structure to hierarchical micro/nanostructure, and (iii) changeable arrangement of hollow spheres from close-packing to non-close-packing. Besides these, the hollow sphere size and the shell thickness can also be controlled by changing the colloidal sphere and deposition time, respectively. Further investigation indicates that the success of NSCL should be owed to a key step, that is, an ion-sputtering induced nonshadow deposition surrounding the whole surfaces of colloidal spheres. This allows an equipotential face and thus homogeneous deposition surrounding the surfaces of PSs in an electrochemical deposition process, and final formation of hollow sphere structure. The 2D ordered hollow sphere arrays with controllable microstructure and size could exhibit importance both in fundamental research and in practical applications.

Trace detection of cyanide based on SERS effect of Ag nanoplate-built hollow microsphere arrays

Trace detection of cyanide is studied based on the Ag nanoplate-built hollow microsphere array and its surface enhanced Raman scattering (SERS) effect. This array was fabricated based on electro-deposition and template method under a low current density. Due to the special structure, such array is a good SERS substrate with high activity and structural stability, and good reproducibility. Such substrate was used for detection of trace amount of kalium cyanide (KCN) in water based on its SERS effect. It has been shown that the detection limit can be down to the level of 0.1 ppb. There exists a good linear double-logarithm relation between the Raman signal and the KCN concentration in water in the range from 0.1 ppb to 1 ppm. In addition, it has been found that the suitable laser power for Raman excitation is crucial to trace detection of KCN molecules. This work is of importance in the practical application in device-design based on the SERS effect of noble metal micro/nano-structured arrays.

CuO–ZnO Micro/Nanoporous Array‐Film‐Based Chemosensors: New Sensing Properties to H2S

CuO-ZnO micro/nanoporous array-films are synthesized by transferring a solution-dipped self-organized colloidal template onto a device substrate and sequent heat treatment. Their morphologies and structures are characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectrum analysis. Based on the sensing measurement, it is found that the CuO-ZnO films prepared with the composition of [Cu(2+)]/[Zn(2+)]=0.005, 0.01, and 0.05 all show a nice sensitivity to 10 ppm H2S. Interestingly, three different zones exist in the patterns of gas responses versus H2S concentrations: a platform zone, a rapidly increasing zone, and a slowly increasing zone. Further experiments show that the hybrid CuO-ZnO porous film sensor exhibits shorter recovery time and better selectivity to H2S gas against other interfering gases at a concentration of 10 ppm. These new sensing properties may be due to a depletion layer induced by p-n junction between p-type CuO and n-type ZnO and high chemical activity of CuO to H2S. This work will provide a new construction route of ZnO-based sensing materials, which can be used as H2S sensors with high performances.

An Invisible Template Method toward Gold Regular Arrays of Nanoflowers by Electrodeposition

A new approach, an invisible template method that is realized through controlling the interface electroconductivity of an electrode surface, is presented to synthesize gold regular arrays of nanoflowers with variable separations through further electrochemical deposition. Using polystyrene monolayer colloidal crystals as the first template, a hexagonally packed 1-hexadecanethiol pattern was self-assembled and used as an invisible template to control the interface electroconductivity. Further electrochemical deposition under appropriate conditions can easily lead to gold regular arrays of nanoflowers. This new approach demonstrates a simple route to the fabrication of novel gold micro/nanostructured arrays that may find applications as SERS active substrates, superhydrophobic materials, and so forth.

Gold quasi rod-shaped nanoparticle-built hierarchically micro nanostructured pore array via clean electrodeposition on a colloidal monolayer and its structurally enhanced SERS performance

This paper presents a clean electrodeposition strategy to fabricate a gold hierarchically micro/nanostructured pore array based on a polystyrene sphere colloidal monolayer. The electrodeposition is carried out in an additive-free HAuCl4 electrolyte to assure a gold structure without surface adsorption of surfactants. By controlling the electrodeposition time, the nano-building blocks in the array can be controlled from quasi spherical nanoparticles to quasi rod-shaped nanostructures. Importantly, the gold quasi rod-shaped nanoparticle-built hierarchically micro/nanostructured pore array shows structurally enhanced surface-enhanced Raman scattering (SERS) performance: high activity, nice uniformity and good stability. Such an array as a SERS active substrate may find important applications in analytical chemistry, electrochemistry, sensors, and so on.