Jingyun Huang

3D graphene foams decorated by CuO nanoflowers for ultrasensitive ascorbic acid detection

When the in vitro research works of biosensing begin to mimic in vivo conditions, some certain three-dimensional (3D) structures of biosensors are needed to accommodate biomolecules, bacteria or even cells to resemble the in vivo 3D environment. To meet this end, a novel method of synthesizing CuO nanoflowers on the 3D graphene foam (GF) was first demonstrated. The 3DGF/CuO nanoflowers composite was used as a monolithic free-standing 3D biosensor for electrochemical detection of ascorbic acid (AA). The 3D conductive structure of the GF is favorable for current collection, mass transport and loading bioactive chemicals. And CuO nanoflowers further increase the active surface area and catalyze the redox of AA. Thus, all these features endows 3DGF/CuO composite with outstanding biosensing properties such as an ultrahigh sensitivity of 2.06 mA mM(-1) cm(-2) to AA at 3 s response time.

ZnO p-n homojunctions and ohmic contacts to Al–N-co-doped p-type ZnO

ZnO p-n homojunctions were fabricated on quartz substrates by depositing Al-doped n-type ZnO layer on Al–N-co-doped p-type ZnO layer through reactive magnetron sputtering. In/Zn metal contacts to as-grown ZnO show ohmic behavior, and the ohmic contacts can be improved by annealing in an Ar ambient. The optimal annealing temperatures for Al–N-co-doped ZnO and Al-doped ZnO are 550 °C and 600 °C, respectively. The p-n junction characteristic is confirmed by current-voltage measurements. The turn-on voltage is 2 V, with a low leakage current under reverse bias. Series resistances of the ZnO p-n junctions can be lowered by optimizing the annealing temperature, increasing the grain size of the ZnO, or increasing the hole concentration of the p layer.

Electrostatic Self-Assembly of BiVO4–Reduced Graphene Oxide Nanocomposites for Highly Efficient Visible Light Photocatalytic Activities

It is commonly considered that the morphology and interface of semiconductor-reduced graphene oxide (rGO) composite photocatalysts play a crucial role in determining their photocatalyzing performance. Herein, we report on the design and synthesis of BiVO4-rGO nanocomposites with efficient interfacial contact by self-assembly of positively charged amorphous BiVO4 powders with negatively charged graphene oxide (GO), followed by a one-step GO reduction and BiVO4 crystallization via hydrothermal treatment. The as-prepared BiVO4-rGO nanocomposites exhibit high visible light photocatalytic efficiency for the degradation of model dyes, and are significantly superior to bare crystalline BiVO4 and BiVO4-rGO-U that is hydrothermally synthesized using the mixture of GO nanosheets and BiVO4 powders without modification of surface charge. Using multiple characterization techniques, we found that the enhanced photocatalytic performance of BiVO4-rGO arises from the synergistic effects between the microscopic crystal structure of BiVO4 with smaller particle size and more sufficient interfacial interaction between BiVO4 and graphene sheets, leading to increased photocatalytic reaction sites, extended photoresponding range, enhanced photogenerated charge separation, and transportation efficiency. This work may provide a rational and convenient strategy to construct highly efficient semiconductor-rGO nanocomposite photocatalysts with well-contacted interface toward environmental purification and solar energy conversion.

Deposition and characteristics of CdO films with absolutely (200)-preferred orientation

Abstract CdO crystal thin films with (200)-preferred orientation have been prepared on Si and glass substrates by dc reactive magnetron sputtering method. At an optimum substrate temperature of 375 °C, the film has the best crystal quality. By the electrical and transmittance measurements the film shows large carrier concentration of 2.00×10 20 /cm 3 , Hall mobility of 64 cm 2 /V s, resistivity of 4.87×10 −4 Ω cm and a high average transmittance over 80% in the visible region together with a direct band gap of 2.43 eV. In view of the Burstein–Moss (BM) shift, theoretical calculations show that the film has a direct band gap of 2.17 eV, close to its intrinsic band gap of 2.2 eV. The photoluminescence (PL) measurement shows that the pure CdO film has no luminescence behavior, but it can alloy with ZnO to realize its applications in luminescent devices.

ZnO quantum dots synthesized by a vapor phase transport process

A vapor phase transport growth process has been developed to synthesize ZnO quantum dots (QDs) on Si substrates. The characteristics were investigated for as-prepared ZnO QDs without any additional treatment. The formation of ZnO QDs with 6 nm in height and 15 nm in diameter is confirmed by scanning electron microscope and atomic force microscopy. Room-temperature photoluminescence reveals that the as-prepared ZnO QDs exhibit a predominant ultraviolet emission at 3.32 eV while the low energy defect-related blue-green emission is significantly quenched. The band gap of ZnO QDs is determined to be 3.41 eV, which evidently indicates the quantum confinement effects.

Structural and photoluminescent properties of ternary Zn1-xCdxO crystal films grown on Si(111) substrates

The ternary Zn1-xCdxO (0less than or equal toxless than or equal to0.6) alloying films with highly c-axis orientation have been deposited on Si(111) substrates by direct current reactive magnetron sputtering method. X-ray diffraction measurement indicates that the wurtzite-type structure of ZnO can be stabilized up to nominal Cd content x similar to 0.6 without cubic CdO phase separation. The lattice parameter c of Zn1-xCdxO increases almost linearly from 5.229 Angstrom (x = 0) to 5.247 Angstrom (x = 0.6), indicating that Cd substitution takes place on the Zn lattice sites. The photoluminescence spectra of the Zn1-xCdxO thin films measured at 12 K display a substantial red shift (similar to0.3 eV) in the near-band-edges (NBEs) emission of ZnO: from 3.39 eV of ZnO to 3.00 eV of Zn0.4Cd0.6O. The direct modulation of band gap caused by Zn/Cd substitution is responsible for the red shift effect in NBE emission of ZnO

Controlled synthesis of spinel ZnFe2O4 decorated ZnO heterostructures as peroxidase mimetics for enhanced colorimetric biosensing

Controlled synthesis of spinel ZnFe2O4 nanoparticle-decorated ZnO nanofiber heterostructures was carried out with regularly varied particle sizes and uniform distribution. The obtained heterostructures possessed enhanced intrinsic peroxidase-like activity, and the activities regularly changed as the sizes of ZnFe2O4 nanoparticles varied. The heterostructures were further applied in sensitive colorimetric biosensing of urine glucose.

Calculation of critical layer thickness considering thermal strain in Si1−xGex/Si strained-layer heterostructures

In this article, interactions of thermal strain in growth of Si1−xGex strained-layers on Si are analyzed. A formula of critical layer thickness (hc) is obtained based on energy balance considering thermal strain under the assumption that the screw dislocation energy density equals to the sum of the areal strain energy density and thermal strain energy density. The relationship between the thermal expansion coefficient associated with thermal strain and Ge content x is linear. Our calculated values for hc of Si1−xGex strained layers on Si substrates versus mismatch, considering thermal strain, are better agreement with measurements of hc by People and Bean.

A single mesoporous ZnO/Chitosan hybrid nanostructure for a novel free nanoprobe type biosensor.

A novel method of fabricating a free probe type nanoscale biosensor is first demonstrated. A free probe type biosensor based on a single one-dimensional (1D) mesoporous ZnO/Chitosan inorganic-organic hybrid nanostructure is constructed. The as-prepared biosensor exhibited excellent biosensing performance and was stable in solution due to its inorganic-organic hybrid structure. The special mesoporous nanostructure with protuberances favors enzymes loading and enhances electrical communication efficiency. The feasibility of employing a single 1D nanostructure as a separate free nanoprobe for biosensing is demonstrated. This kind of free probe type biosensor will not only provides a new tool for micro-targets detection in microcell and enzymatic studies, but also has the potential to be inserted into single cell or other microorganism for biological studies.

Enhanced near band edge emission of ZnO via surface plasmon resonance of aluminum nanoparticles

The enhanced near band edge emission from a ZnO thin film and nanorod array by capping aluminum nanoparticles has been studied by photoluminescence spectra. The enhancement is attributed to the resonant coupling between the bandgap transition of the semiconductor and the surface plasmon of metal nanoparticles. It is also found that the Al nanoparticles support the surface plasmon from the deep-UV to the visible region with different annealing temperatures. This cost-effective approach is useful for manufacturing highly efficient optoelectronic devices.