Yuping Ren

Enzyme-free amperometric sensing of hydrogen peroxide and glucose at a hierarchical Cu2O modified electrode

In this paper, an enzyme-free amperometric electrochemical sensor was fabricated by casting Nafion-impregnated Cu(2)O particles onto a glassy carbon electrode. A dual dependence of peak current on sweeping rate, which can be attributed for the accumulation of reaction products, was observed on the sensor. Electrochemical analysis of the particulate Cu(2)O for detecting H(2)O(2) and glucose is described, showing remarkable sensitivity in both cases. The estimated detection limits and sensitivities for H(2)O(2) (0.0039 μM, 52.3 mA mM(-1) cm(-2)) and glucose (47.2 μM, 0.19 mA mM(-1) cm(-2)) suggest that the response for H(2)O(2) detection was much higher than for glucose detection. Electron microscopy observation suggested that the hierarchical structures of Cu(2)O resulting from self-assembly of nanocrystals are responsible for the specific electrochemical properties.

Enhanced photoelectrochemical activity for Cu and Ti doped hematite: The first principles calculations

To improve photoelectrochemical (PEC) activity of hematite, the modification of energy band by doping 3d transition metal ions Cu and Ti into α-Fe2O3 were studied via the first-principles calculations with density function theory (DFT)+U method. The results show that the band gap of hematite is ∼2.1 eV and n-type dopant Ti improves the electric conductivity, confirmed by recent experiments. The p-type dopant Cu enhances the utilization ratio of solar energy, shifts both valance, and conduction band edges to a higher energy level, satisfying hydrogen production in the visible light driven PEC water splitting without voltage bias.

One-step fabrication of sub-10-nm plasmonic nanogaps for reliable SERS sensing of microorganisms

Nanoscale gaps in noble metal films can produce intense electromagnetic enhancement. When Raman-active molecules are positioned in these regions, their surface-enhanced Raman scattering (SERS) signals can be dramatically enhanced. However, the lack of convenient and reliable fabrication methods with ultrasmall nanogaps (<10 nm) severely block the application of SERS. Here, we propose a cost-effective and reproducible technique to fabricate the large-area Ag SERS-active substrates which are full of the high-density, sub-10-nm nanogaps by high pressure sputtering, and the enhancement factor (EF) is testified to improve by 10(3) times compared to the continuous Ag film with a smooth surface (the roughness is 0.5 nm) and without nanogaps. Since there are no chemicals used during fabrication, this substrate has a clean surface, which is crucial for acquiring reliable SERS spectra. This SERS-active substrate has then been applied to identify a series of microorganisms, and excellent, reproducible SERS spectra were obtained. Finally, a set of piecewise-linear equations is provided according to the correlation between SERS intensity and rhodamine 6G (R6G) concentration, and the detection limit is calculated to be 0.2×10(-8)M. These results suggest that the high pressure sputtering is an excellent, reliable technique for fabricating sub-10-nm plasmonic nanogaps, and the SERS-based methodology is very promising for being used in biological sensing field.

Microstructures and tensile properties of as-extruded Mg-Sn binary alloys

Abstract The microstructure and tensile properties of the Mg-1.0%Sn- x Y( x =1.5%, 3.0%, 3.5%, atom fraction) alloys extruded indirectly at 350 °C were investigated by means of optical microscopy, scanning electron microscopy and tensile test. The mean grain sizes of α -Mg matrix in the three extruded alloys are 6, 8 and 12 μm, respectively, slightly increasing with the addition of Y. The relationship between microstructure and strength was discussed in detail. The results show that the addition of Y has little effect on the grain refinement of the as-extruded Mg-Sn based alloys above. The only MgSnY phase is detected in the Mg-Sn-1.5%Y alloy, and the Sn 3 Y 5 phase in the Mg-Sn-3.5%Y alloy, whereas both of them simultaneously exist in the Mg-Sn-3.0%Y alloy. The particle shape of MgSnY and Sn 3 Y 5 phase, inherited from the solidification, has little change before and after hot extrusion. Mg-Sn-3.0%Y alloy has the highest ultimate tensile strength (UTS), 305 MPa, by over 50% compared with that of the other two alloys.

Development of high density magnetic recording media for hard disk drives: materials science issues and challenges

Abstract The tremendous increase in areal density of hard disk drives is mainly ascribed to harmonic development between magnetic recording media and heads in their scaling, especially allowing a commercial transition from the longitudinal to perpendicular recording system. This paper reviews the main features, recent breakthroughs and future potentials of both the longitudinal and the perpendicular media from a viewpoint of materials science. Special attention is firstly paid to the ‘trilemma’ problem for the media, i.e. the compromise among writability, thermal stability and signal to noise ratio (SNR). The evolution of media materials these years are then addressed with emphasis on the thermodynamic origin of magnetically induced phase separation of Co-Cr based alloys, which governs media noise and coercivity, and its applications to the current longitudinal media. The materials challenges for media to achieve 500 Gb in.−2 and above are further predicted from the viewpoints of thermal stability improvement and microstructure control of media materials, and their engineering issues have been discussed for the current Co-Cr based alloys, potential FePt and CoPt ordered, phase separated Co-W based alloys and magnetic rare earth compounds. Finally, the future media approaching 1 Tb in.−2 and beyond are addressed with respect to the principles, progress, engineering challenges and future directions.

Chemical synthesis of faceted α-Fe2O3 single-crystalline nanoparticles and their photocatalytic activity

Faceted hematite nanocrystals have been synthesized via a hydrothermal route and their different morphologies can be tuned by appropriate stabilizer molecules. Detailed observation by high-resolution transmission electron microscopy and atomic force microscopy has revealed many terraces, steps, and kinks on the faceted surface of hematite nanoparticles, and thus, one growth mechanism of the terrace-step-kink model has been suggested to play a major role in determining the equilibrium morphology, together with effect of surface chemistry via the interaction between outer surfaces of iron and oxygen ions and functional groups. The photocatalytic activities were evaluated by decomposing rhodamine B dye. It has been shown that polyhedron hematite particles enclosed by high-index surface planes exhibited higher photoactivity. Density functional theory calculations revealed that the higher photoactivity originates from the more flat band edge in directions normal to the surface planes.

Phase equilibria of Mg-rich corner in Mg−Zn−Al ternary system at 300 °C

Abstract The phase equilibria and compositions in Mg-rich corner at 300 °C were determined in the Mg-Zn-Al ternary system through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). The results show that there exist three three-phase regions consisted of α-Mg+Mg17Al12(γ)+Al5Mg11Zn4(ϕ), α-Mg+Mg32(Al, Zn)49(τ)+Al5Mg11Zn4(ϕ) and α-Mg+MgZn+Mg32(Al, Zn)49(τ), respectively. The intermetallic compounds in equilibrium with α-Mg phase all have large composition ranges, not appear to be linear. At the same time, both zinc and aluminum are soluble in the α-Mg solid solution, with which the compounds are in equilibrium.

A synergistic combination of diatomaceous earth with Au nanoparticles as a periodically ordered, button-like substrate for SERS analysis of the chemical composition of eccrine sweat in latent fingerprints

The artistry and the amazingly beautiful hierarchical three-dimensional (3D) patterning of diatoms make them ideal biological scaffolds. Here, fraction-free and ultra-high-purity diatomaceous earth has been successfully prepared by low speed centrifugation in saturated sucrose solution and calcination at 600 °C for 2 h. The prepared citrate-stabilized 18 ± 2.4 and 32 ± 5.4 nm Au nanoparticles were singly, uniformly and densely self-assembled onto amino-functionalized diatomaceous earth templates following their surface morphologies via electrostatic interactions, during which the control experiment and appropriate parameter exploration were performed. The formed 18 ± 2.4 and 32 ± 5.4 nm Au nanoparticle coated diatomaceous earth fine-grained composite materials were pressed into hard, button-like tablets with a fixed diameter of 13 mm and a thickness of 2 mm, and then the two fabricated types of button-like portable tablets were used for surface-enhanced Raman spectroscopy (SERS) detection, and their enhancement factors (EFs), SERS reproducibility and long-term stability were testified using rhodamine 6G (R6G) as the probe molecule. The button-like portable tablet composed of diatomaceous earth-templated 32 ± 5.4 nm Au nanoparticle arrays had a higher EF and was successfully applied to SERS analysis of the trace chemical composition of eccrine sweat in latent fingerprints. It may reveal the medical condition of an individual by analyzing the obtained SERS spectra, suggesting that the SERS-based methodology, due to its high sensitivity, has a potentially wide range of applications in fields that need trace detection, such as medical diagnostics and forensic investigations. Moreover, the button-like, 3D periodically ordered tablet as a portable SERS substrate composed of a synergistic combination of diatomaceous earth with Au nanoparticles in this work is robust, easy to carry around, and applicable to on-site SERS detection.

Partial phase relationships of Mg-Zn-Ce system at 350 °C

Abstract The alloys were prepared in Mg-rich corner of Mg-Zn-Ce system. Partial phase equilibrium relationships of these alloys at 350 °Cwere identified by using scanning electron microscopy(SEM), electron probe microanalysis(EPMA), X-ray diffraction(XRD) analysis and selected area electron diffraction(SAED) pattern analysis of transmission electron microscopy(TEM). Partial isothermal section of Mg-Zn-Ce system in Mg-rich corner was identified. The results show that there is one ternary compound (T-phase) in Mg-Zn-Ce system. The T-phase is a linear ternary compound in which the content of Ce is about 7.7% (molar fraction); while the content of Zn is changed from 19.3% to 43.6% (molar fraction). The crystal structure of T-phase is C-centered orthorhombic. In addition, one two-phase region of Mg+T-phase and one three-phase region of Mg+T-phase+MgZn(Ce) exist in the Mg-rich corner of Mg-Zn-Ce system at 350 °C.

Thermal Oxidation Preparation of Doped Hematite Thin Films for Photoelectrochemical Water Splitting

Sn- or Ge-doped hematite thin films were fabricated by annealing alloyed films for the purpose of photoelectrochemical (PEC) water splitting. The alloyed films were deposited on FTO glass by magnetron sputtering and their compositions were controlled by the target. The morphology, crystalline structure, optical properties, and photocatalytic activities have been investigated. The SEM observation showed that uniform, large area arrays of nanoflakes formed after thermal oxidation. The incorporation of doping elements into the hematite structure was confirmed by XRD. The photocurrent density-voltage characterization illustrated that the nanoflake films of Sn-doped hematite exhibited high PEC performance and the Sn concentration was optimized about 5%. The doped ions were proposed to occupy the empty octahedral holes and their effect on PEC performance of hematite is smaller than that of tin ions.