Latticing vertically aligned Ag nanorods to enhance its SERS sensitivity

Vertically aligned silver nanorods were good substrates for surface-enhanced Raman scattering. It was found that by organizing these nanorods into hexagonal lattice with a pattern size of 400 nm, the Raman sensitivity can be further enhanced by several times. It was also found that this enhancement was dependent on the separation distance of the lattice patterns, which reached a maximum at a separation distance of 200 nm. This study provides an alternative idea to further enhance the Raman scattering using nanostructures.     

Near-infrared absorption enhancement in microstructured silicon by Ag film deposition

We investigate the influence of spike-like microstructures formed on the silicon surface via fs-laser scanning with different-size on its near-infrared absorption from 1200 to 2500 nm. Although the infrared absorption of the small size microstructures is obviously lower than the large size, it can be further improved to 90 % by a large amount of random and irregular Ag nano particles from a subsequent deposition of Ag thin film. The origins of absorption enhancement are discussed and theoretically analyzed in detail.     

Spreading characteristics of droplets impact on microstructured surfaces with gradient wettability

Journal of Materials Science - Manipulating droplet motion using gradient wettability surfaces has attracted much attention in recent years. In this paper, four kinds of microstructured surfaces...     

Effect of oblique-angle deposition on early stage of Fe-Si growth

We have investigated the initial stage of Fe growth on an Si substrate during reactive oblique-angle deposition (ROAD) at 470 °C by means of atomic force microscopy, reflection high-energy electron diffraction, and high-resolution Rutherford backscattering spectroscopy. During deposition along the normal direction, many Si atoms are displaced from their lattice positions because of reactions with the deposited Fe. However, for ROAD, the number of displaced Si atoms decreases significantly along with a selective growth of nanoislands with diameters of a few 10 nm. Evidently, the local nucleation processes required for iron silicide formation are modified by the geometrical deposition conditions.     

Cell behaviour on chemically microstructured surfaces

Micropatterned surfaces with different chemical topographies were synthesised in order to investigate the influence of surface chemistry and topography on cell behaviour. The microstructured materials were synthesised by photoimmobilising natural Hyaluronan (Hyal) and its sulphated derivative (HyalS), both adequately functionalised with a photorective moiety, on glass substrates. Four different grating patterns (10, 25, 50 and 100 μm) were used to pattern the hyaluronan. The micropatterned samples were analysed by Secondary Ions Mass Spectrometry, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy to investigate the chemistry and the topography of the surfaces. The spectroscopic and microscopic analysis of the microstructured surfaces revealed that the photoimmobilisation process was successful, demonstrating that the photomask patterns were well reproduced on the sample surface. The influence of chemical topographies on the cell behaviour was then analysed. Human and 3T3 fibroblasts, bovine aortic and human (HGTFN line) endothelial cells were used and their behaviour on the micropatterned surfaces was analysed in terms of adhesion, proliferation, locomotion and orientation. Both chemical and topographical controls were found to be important for cell guidance. By decreasing the stripe dimensions, a more fusiform shape of cell was observed. At the same time, the cell locomotion and orientation parallel to the structure increased. However, differences in cell behaviour were detected according to both cell type and micropattern dimensions.     

Recyclable SERS substrates based on Au-coated ZnO nanorods

Vertically aligned Au-coated ZnO nanorods (Au-ZnO NRs) were investigated as cheap, efficient and recyclable SERS-active substrates. The ZnO NRs were prepared through a simple, low-temperature hydrothermal route and made SERS-active through deposition of gold nanoislands by sputtering at room temperature. Optimized samples were able to detect methylene blue over a wide range of low concentrations (from 1 × 10(-4) to 1 × 10(-12) M), with good reproducibility. The photocatalytic properties of Au-ZnO NRs were exploited to recycle these substrates through UV-assisted cleaning. The experimental results showed that these substrates are characterized by high reproducibility and long shelf life, which make them promising as SERS platforms for multiple detection of different molecular species.     

Effects of sputtering power and pressure on properties of ZnO:Ga thin films prepared by oblique-angle deposition

The effects of power and pressure on radiofrequency (RF) diode sputtering in oblique-angle (80°) deposition arrangement are presented. Oblique-angle sputtering of ZnO:Ga (GZO) thin films resulted in a tilted columnar crystalline structure and inclination of the c-axis by an angle of approximately 9° with respect to the substrate. This improved their structural, electrical and optical properties in comparison with films deposited perpendicularly to the substrate. GZO films sputtered by an RF power of 600 W at room temperature of the substrate in Ar pressure 1.3 Pa showed strong crystalline (002) texture, lowest electrical resistivity 3.4 × 10^− 3 Ωcm, highest electron mobility 10 cm² V^− 1 s^− 1, high electron concentration 1.8 × 10²⁰ cm^− 3 and good optical transparency up to 88%. The small inclination angle of the film structure is caused by the high kinetic energy of sputtered species and additional energetic particle bombardment causes random surface diffusion, which is suppressing the shadow effect produced by oblique-angle sputtering.     

Localized adsorption on heterogeneous surfaces

The general theory of localized adsorption on patchwise heterogeneous surfaces, in both the submonolayer and the multilayer range, is presented in this work.Exact and approximate mathematical methods for finding the binding energy distribution are considered for the Langmuir adsorption isotherm.It is shown that all the methods described (related to the solution of Fredholm integral equations of the first kind) can also be applied to the Brunauer-Emmett-Teller multilayer isotherm through the definition of the “enhanced pressure”.The physical interpretations are applied to the Dubinin-Radushkevich isotherm which consequently must be modified, with respect to the original formulation, in the very low pressure limit and in the multilayer range.     

Facile synthesis of Ag/ZnO nanorods using Ag/C cables as templates and their gas-sensing properties

A solid-state chemical reaction with the assistance of Ag/C nanocables was implemented for the preparation of Ag/ZnO nanorods. This is the first time Ag/ZnO nanorods are fabricated by using Ag/C cables as template. Compared with the traditional organic surfactant, Ag/C cable is a new and effective template to control the shape of precursors in the solid-state reaction under ambient conditions. The results of systematical gas-sensing studies demonstrate that the sensor based on Ag/ZnO nanorod materials has high sensitivity, good selectivity and short response and reversion time to ethanol. It demonstrates that Ag/ZnO nanorods can be used as gas-sensing material.     

微结构表面润湿模式转换的实验研究

采用等离子体刻蚀技术及表面硅烷化处理制备了一组硅基方柱阵列样品,测量了其表面与水的表观接触角,简要分析了表面微结构几何参数对润湿模式转换的影响,探讨了方柱阵列微结构表面发生润湿模式转换的原因.结果表明,微结构表面润湿模式转换受微结构几何参数的影响,原因是微结构几何参数的改变会引起表面上的液滴能量的变化,最终导致液滴的润湿状态发生变化.     

Nanostructured surfaces and assemblies as SERS media

Metallic nanostructures attract much interest as an efficient media for surface-enhanced Raman scattering (SERS). Significant progress has been made on the synthesis of metal nanoparticles with various shapes, composition, and controlled plasmonic properties, all critical for an efficient SERS response. For practical applications, efficient strategies of assembling metal nanoparticles into organized nanostructures are paramount for the fabrication of reproducible, stable, and highly active SERS substrates. Recent progress in the synthesis of novel plasmonic nanoparticles, fabrication of highly ordered one-, two-, and three-dimensional SERS substrates, and some applications of corresponding SERS effects are discussed.     

Two-dimensional gradient Ag nanoparticle assemblies: multiscale fabrication and SERS applications

We report a novel method for fabricating silver nanoparticle assemblies with a featured gradient of spatial organizations. The unique step is to generate a gradient of deposit mass by dynamical deposition on a mask-covered substrate with a collimated cluster beam in oblique incidence. Then such gradient can be translated to the gradients of sizes or number densities of the nanoparticles separately, depending on the nature of the substrate surface. Multiscale gradients are implemented from mesoscopic to macroscopic. One-chip rapid detection of the optimal structure for surface enhanced Raman scattering (SERS) is achieved on the gradient assembly with particle number densities.     

Effect of coupling crater structure and Ag nanoparticles on SERS enhancement

Journal of Materials Science - This study was aimed at enhancing surface plasmon resonance through a combination of Ag nanoparticles (NPs) and an asymmetric crater structure capable of...     

Ag nanoclusters synthesized by successive ionic layer deposition method and their characterization

The possibilities of successive ionic layer deposition technology for synthesizing the Ag nanoclusters and nanolayers were analyzed in present article. It was shown that this technology, based on successive treatments of appropriate substrates in solution of cations and anions, is acceptable for the controllable forming of the Ag nanoparticles at the surface of different substrates. Results related to characterization of the Ag nanoclusters synthesized using Ag(NH₃)₂NO₃ or AgNO₃ precursors were discussed. It was found that the concentration and the size of the Ag nanoparticles deposited on a surface of fused quartz, silica gel, and monocrystalline silicon can be controlled by varying composition and pH of the reagent solutions as well as the number of the deposition cycles. It was established that the size of Ag nanoclusters depending on a synthesis conditions may vary from 1–5 nm to 500 nm. Model explained the growth of Ag clusters during successive ionic layer deposition was discussed as well.     

Neurite outgrowth on microstructured surfaces functionalized by a neural adhesion protein

Designed networks of neurons are potentially very useful to investigate neural activities. Using photolithography microgrooves suited in size for single neurons have been produced on glass chips. Two conducting gold lanes ending in each microgroove allow extracelluar stimulation of the neurons and recording of their activity. A cell adhesive surface was created by functionalization of glass with the adhesion peptide RGDC. In addition, in order to optimize the contact of the neuronal cell membrane to the electrode surface axonin-1, a specific neural adhesion protein was used. A recombinant form of axonin-1 was produced and immobilized in a correct orientation on protected gold surfaces through a C-terminal cysteine residue. Neurite outgrowth of neurons cultured on chips derivatized with RGDC or axonin-1 were compared. The developed materials and methods represent a first step towards establishing designed functionalized glass surfaces for neurophysiological investigations.     

Paper-based SERS swab for rapid trace detection on real-world surfaces

One of the important but often overlooked considerations in the design of surface-enhanced Raman scattering (SERS) substrates for trace detection is the efficiency of sample collection. Conventional designs based on rigid substrates such as silicon, alumina, and glass resist conformal contact with the surface under investigation, making the sample collection inefficient. We demonstrate a novel SERS substrate based on common filter paper adsorbed with gold nanorods, which allows conformal contact with real-world surfaces, thus dramatically enhancing the sample collection efficiency compared to conventional rigid substrates. We demonstrate the detection of trace amounts of analyte (140 pg spread over 4 cm2) by simply swabbing the surface under investigation with the novel SERS substrate. The hierarchical fibrous structure of paper serves as a 3D vasculature for easy uptake and transport of the analytes to the electromagnetic hot spots in the paper. Simple yet highly efficient and cost-effective SERS substrate demonstrated here brings SERS-based trace detection closer to real-world applications.     

Localized adsorption with lateral interactions on patchwise heterogeneous surfaces

The extension of the condensation approximation to patchwise heterogeneous surfaces following the Fowler-Guggenheim adsorption isotherm is considered in this work. We show that the condensation approximation can be applied to the Fowler-Guggenheim isotherm better than to the Langmuir isotherm, and that the approximate distribution function tends to become effective when the absolute temperature tends to zero.     

银纳米颗粒有序阵列光学偏振玻璃特性研究

银纳米椭球微粒有序掺杂的光学偏振玻璃具有光学玻璃的高透过率特性和本征的偏振特性,是综合性能好的光学偏振器件。利用米氏理论和电偶极子理论分析了光入射到椭球形银纳米微粒产生的消光特性和偏振机理;建立椭球形纳米微粒周期阵列分布的光学偏振玻璃模型,采用有限元数值算法模拟计算近红外光入射该模型后的偏振光输出特性。通过优化玻璃内部椭球微粒的几何参数,获得波长在700~1 100nm近红外全波段内的偏振玻璃的透过率达到80%以上,消光比达20dB以上;尤其当波长在740~840nm范围内,透过率高达90%以上,消光比达50dB以上。     

Sputter deposition of ZnO nanorods/thin-film structures on Si

Using a recently developed sputter deposition technique, ZnO deposits were grown at the room temperature on silicon wafers with various kinds of copper surface layers. The copper layers were prepared using sputter deposition, thermal evaporation, or electroless plating technique. It was found that the surface copper prepared using both sputter deposition and thermal evaporation technique grew only ZnO thin films, while the surface copper prepared using sputter deposition technique grew ZnO nanorods/thin-film deposits. The relation between the copper characteristics and the growth of ZnO nanorods/thin-film deposits was investigated. The growth kinetics of the ZnO nanorods/thin film structure is also discussed.