Honghua Zhang

Formation of nanostructured surface layer on AISI 304 stainless steel by means of surface mechanical attrition treatment

A nanostructured surface layer was formed on an AISI 304 stainless steel with low stacking-fault energy by means of the surface mechanical attrition treatment (SMAT). The microstructure of the surface layer of the SMATed sample was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and cross-sectional TEM observation was performed to reveal the deformation-driven grain refinement mechanism for the f.c.c. materials with very low stacking-fault energy during SMAT. The grain refinement process in the surface layer involves formation of planar dislocation arrays and twins in deformed grains, twin-twin intersections leading to grain subdivision and a martensite transformation as well, and formation of randomly orientated refined crystallites. The formation of nanocrystallites in the top surface layer was ascribed to the much large strain and strain rate, as well as the multidirectional repetitive loading

Black Gold: Plasmonic Colloidosomes with Broadband Absorption Self-Assembled from Monodispersed Gold Nanospheres by Using a Reverse Emulsion System†

A facile approach for the fabrication of novel black plasmonic colloidosomes assembled from Au nanospheres is developed by an emulsion-templating strategy. This self-assembly process is based on a new reverse water-in-1-butanol emulsion system, in which the water emulsion droplets can dissolve into 1-butanol (oil) phase at an appropriate rate. These Au colloidosomes possess hexagonal close-packed multilayer shells and show a low reflectivity and intense broadband absorption owing to the strong interparticle plasmonic coupling, which is further investigated by a finite-difference time-domain method. This method is universal and is suitable for self-assembly of different noble-metal nanoparticles into different colloidosomes. These colloidosomes have important applications in photothermal therapy, biosensors, and drug delivery.

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.

Rapid synthesis of monodisperse Au nanospheres through a laser irradiation-induced shape conversion, self-assembly and their electromagnetic coupling SERS enhancement.

We develop a facile and effective strategy to prepare monodispersed Au spherical nanoparticles by two steps. Large-scale monocrystalline Au nanooctahedra with uniform size were synthesized by a polyol-route and subsequently Au nanoparticles were transformed from octahedron to spherical shape in a liquid under ambient atmosphere by non-focused laser irradiation in very short time. High monodipersed, ultra-smooth gold nanospheres can be obtained by simply optimizing the laser fluence and irradiation time. Photothermal melting-evaporation model was employed to get a better understanding of the morphology transformation for the system of nanosecond pulsed-laser excitation. These Au nanoparticles were fabricated into periodic monolayer arrays by self-assembly utilizing their high monodispersity and perfect spherical shape. Importantly, such Au nanospheres arrays demonstrated very good SERS enhancement related to their periodic structure due to existence of many SERS hot spots between neighboring Au nanospheres caused by the electromagnetic coupling in an array. These gold nanospheres and their self-assembled arrays possess distinct physical and chemical properties. It will make them as an excellent and promising candidate for applying in sensing and spectroscopic enhancement, catalysis, energy, and biology.

Optical sensor based on hydrogel films with 2D colloidal arrays attached on both the surfaces: anti-curling performance and enhanced optical diffraction intensity

An interesting strategy to create free standing hydrogel composite films with colloidal monolayers attached on both the surfaces, which could act as visualizing sensors with high diffraction intensity, is developed. Owing to the balanced stress on both the surfaces, the colloidal monolayer–hydrogel composite films overcome the curling problem of traditional hydrogel films loaded with a colloidal monolayer on one side. They also display enhanced diffraction intensity compared to those with the attachment of only a single 2D colloidal monolayer due to a multi-diffraction effect. Such sensing hydrogel composite films with anti-curling performance and enhanced optical diffraction intensity are very helpful to improve their practical applications in visual and quantitative detection. In addition, this strategy is universal and could be suitable for fabricating various functional hydrogel films loaded with different nanosphere arrays for novel optical sensors.

Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks

A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10(-10) M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates.

Functionalized periodic Au@MOFs nanoparticle arrays as biosensors for dual-channel detection through the complementary effect of SPR and diffraction peaks

A facile and low-cost method to prepare periodic Au@metal–organic framework (MOF) (MIL-100(Fe)) nanoparticle arrays was developed. The arrays were fabricated in situ using monolayer colloidal crystals as templates, followed by Au deposition on substrates, and annealing. MIL-100(Fe) coatings were applied on the nanospheres using a simple solvent thermal process. The prepared periodic Au@MIL-100(Fe) nanoparticle (NP) arrays were characterized by two peaks in the visible spectra. The first peak represented the surface plasmon resonance (SPR) of the Au nanospheres, and the other peak, or the diffraction peak, originated from the periodic structure in the NP array. After modification with 3-aminophenylboronic acid hemisulfate (PBA), the Au@MIL-100(Fe) NP arrays exhibited sensitive responses to different glucose concentrations with good selectivity. These responses could be due to the strong interaction between PBA and glucose molecules. The diffraction peak was sensitive at low glucose concentrations (less than 12 mM), whereas the SPR peak rapidly responded at high concentrations. The peaks thus demonstrated satisfactory complementary sensitivity for glucose detection in different concentration regions. These results can be used to develop a dual-channel biosensor. We also created a standard diagram, which can be used to efficiently monitor blood glucose levels. The proposed strategy can be extended to develop different dual-channel sensors using Au@MIL-100(Fe) NP arrays functionalized with different recognition agents.

Influence of strain rate on the orientation dependence of microstructure in nickel single crystals

Abstract The deformation microstructures of nickel single crystals (99.945 wt.%) during dynamic plastic deformation and quasi-static compression to a true strain of 0.20 were comparatively investigated. The deformation microstructures are orientation dependent, forming cell structure, slip plane aligned or not slip plane aligned extended boundaries. It is found that the orientation spread decreases, remains unchanged and becomes enhanced when loading along 〈0 0 1〉, 〈0 1 1〉 and 〈1 1 1〉, respectively, as strain rate increases.