Jianbao Xu

Reduced Graphene Oxide Electrically Contacted Graphene Sensor for Highly Sensitive Nitric Oxide Detection

We develop graphene-based devices fabricated by alternating current dielectrophoresis (ac-DEP) for highly sensitive nitric oxide (NO) gas detection. The novel device comprises the sensitive channels of palladium-decorated reduced graphene oxide (Pd-RGO) and the electrodes covered with chemical vapor deposition (CVD)-grown graphene. The highly sensitive, recoverable, and reliable detection of NO gas ranging from 2 to 420 ppb with response time of several hundred seconds has been achieved at room temperature. The facile and scalable route for high performance suggests a promising application of graphene devices toward the human exhaled NO and environmental pollutant detections.

High-Density Three-Dimension Graphene Macroscopic Objects for High-Capacity Removal of Heavy Metal Ions

The chemical vapor deposition (CVD) fabrication of high-density three-dimension graphene macroscopic objects (3D-GMOs) with a relatively low porosity has not yet been realized, although they are desirable for applications in which high mechanical and electrical properties are required. Here, we explore a method to rapidly prepare the high-density 3D-GMOs using nickel chloride hexahydrate (NiCl2·6H2O) as a catalyst precursor by CVD process at atmospheric pressure. Further, the free-standing 3D-GMOs are employed as electrolytic electrodes to remove various heavy metal ions. The robust 3D structure, high conductivity (~12 S/cm) and large specific surface area (~560 m2/g) enable ultra-high electrical adsorption capacities (Cd2+ ~ 434 mg/g, Pb2+ ~ 882 mg/g, Ni2+ ~ 1,683 mg/g, Cu2+ ~ 3,820 mg/g) from aqueous solutions and fast desorption. The current work has significance in the studies of both the fabrication of high-density 3D-GMOs and the removal of heavy metal ions.

Wide-Range Strain Sensors Based on Highly Transparent and Supremely Stretchable Graphene/Ag-Nanowires Hybrid Structures

The increasing demand of electronic devices for physical motion detection has encouraged the development of highly elastic strain sensors. Especially, to capture wide-range physical movements, supremely stretchable and wide-range strain sensors are required. Here, a novel transparent, bendable, stretchable, and wide-range strain sensor based on a sandwich-like stacked graphene and Ag-nanowires hybrid structures is reported. The hybrid structures on 200% pre-stretched polyacrylate (PAC) are patterned which possess good bendability up to 2 mm radius, impressive stretchability up to 200% and comparatively low sheet resistance ≈200 Ω sq-1 with transparency 85%. Pre-stretched PAC technique enables the sensor to work well at extremely high strains and to sense the multidirectional strains efficiently. The Ag-nanowires pattern on PAC is fabricated via the bubble-template method, by which a uniform distribution of Ag-nanowires is achieved with significant connectivity throughout the surface. This not only decreases the power consumption but also enhances the sensitivity of the strain sensor. The demonstrated strain sensor is capable to sense strains between 5% and 200%, and the response time for this sensation is <1 ms.

Three-Dimensional Incompressible Flow Solution of an Axial Compressor Using Pseudostream-Functions Formulation

Based on considering the characteristic features of the momentum equations and meeting the requirement of the continuity, two pseudostream-functions are introduced. The principal equation of each pseudostream-function only contains the terms of its own second-order partial derivatives and does not include the second-order partial derivatives of another pseudostream-function. So the relation between the two equations are loosed considerablly and both equations may be solved separately. This property is valueful to obtain the convergent solution of flow field easily. The equations of the pseudostream-functions and the corresponding boundary conditions are given. Two incompressible flow examples show that this method may become a powerful tool in the aerothermodynamic analysis and design of a compressor.Copyright

Roles of Oxygen and Hydrogen in Crystal Orientation Transition of Copper Foils for High-Quality Graphene Growth

The high-quality graphene film can be grown on single-crystal Cu substrate by seamlessly stitching the aligned graphene domains. The roles of O2 and H2 have been intensively studied in the graphene growth kinetics, including lowering the nucleation sites and tailoring the domain structures. However, how the O2 and H2 influence Cu orientations during recrystallization prior to growing graphene, still remains unclear. Here we report that the oxidation of Cu surface tends to stabilize the Cu(001) orientation while impedes the evolution of Cu(111) single domain during annealing process. The crystal orientation-controlled synthesis of aligned graphene seeds is further realized on the long-range ordered Cu(111) substrate. With decreasing the thickness of oxide layer on Cu surface by introducing H2, the Cu(001) orientation changes into Cu(111) orientation. Meanwhile, the average domain size of Cu foils is increased from 50 μm to larger than 1000 μm. The density functional theory calculations reveal that the oxygen increases the energy barrier for Cu(111) surface and makes O/Cu(001) more stable than O/Cu(111) structure. Our work can be helpful for revealing the roles of O2 and H2 in controlling the formation of Cu single-crystal substrate as well as in growing high-quality graphene films.

Fast Batch Production of High-Quality Graphene Films in a Sealed Thermal Molecular Movement System

Chemical vapor deposition (CVD) growth of high-quality graphene has emerged as the most promising technique in terms of its integrated manufacturing. However, there lacks a controllable growth method for producing high-quality and a large-quantity graphene films, simultaneously, at a fast growth rate, regardless of roll-to-roll (R2R) or batch-to-batch (B2B) methods. Here, a stationary-atmospheric-pressure CVD (SAPCVD) system based on thermal molecular movement, which enables fast B2B growth of continuous and uniform graphene films on tens of stacked Cu(111) foils, with a growth rate of 1.5 µm s-1 , is demonstrated. The monolayer graphene of batch production is found to nucleate from arrays of well-aligned domains, and the films possess few defects and exhibit high carrier mobility up to 6944 cm2 V-1 s-1 at room temperature. The results indicate that the SAPCVD system combined with single-domain Cu(111) substrates makes it possible to realize fast batch-growth of high-quality graphene films, which opens up enormous opportunities to use this unique 2D material for industrial device applications.

Ultra-broadband graphene-InSb heterojunction photodetector

We demonstrate a room temperature ultra-broadband graphene-InSb heterostructure photodetector. By introducing a thin oxide layer between the P-type graphene film and N-type InSb, the dark current is suppressed sharply. The device can detect light from the visible to far infrared region, exhibiting a high responsivity of ∼70 mA W−1 at a typical wavelength of 1.7 μm. It is worth mentioning that the photodetector has delivered a mid-infrared (MIR) photoresponsivity of ∼42 mA W−1, which also opens a way for MIR communication technology.

Significant enhancement of metal heat dissipation from mechanically exfoliated graphene nanosheets through thermal radiation effect

We demonstrate a facile approach to significantly enhance the heat dissipation potential of conventional aluminum (Al) heat sinks by mechanically coating graphene nanosheets. For Al and graphene-coated Al heat sinks, the change in temperature with change in coating coverage, coating thickness and heat flux are studied. It is found that with the increase in coating coverage from 0 to 100%, the steady-state temperature is decreased by 5 °C at a heat flux of 1.8 W cm-1. By increasing the average thickness of graphene coating from 480 nm to 1900 nm, a remarkable temperature reduction up to 7 °C can be observed. Moreover, with the increase in heat flux from 1.2 W cm-1 to 2.4 W cm-1, the temperature difference between uncoated and graphene-coated samples increases from 1 °C to 6 °C. The thermal analysis and finite element simulation reveal that the thermal radiation plays a key role in enhancing the heat dissipation performance. The effect of heat convection remains weak owing to the low air velocity at surface...

Electron-electron interaction, weak localization and spin valve effect in vertical-transport graphene devices

We fabricated a vertical structure device, in which graphene is sandwiched between two asymmetric ferromagnetic electrodes. The measurements of electron and spin transport were performed across the combined channels containing the vertical and horizontal components. The presence of electron-electron interaction (EEI) was found not only at low temperatures but also at moderate temperatures up to ∼120 K, and EEI dominates over weak localization (WL) with and without applying magnetic fields perpendicular to the sample plane. Moreover, spin valve effect was observed when magnetic filed is swept at the direction parallel to the sample surface. We attribute the EEI and WL surviving at a relatively high temperature to the effective suppress of phonon scattering in the vertical device structure. The findings open a way for studying quantum correlation at relatively high temperature.

A Unified Method for Solving Aerodynamic Cascade Design Problems on an Arbitrary Surface of Revolution

A method for solving various aerodynamic problems of transonic cascade design is developed, in which the coordinates equation is derived directly by inverting the stream function and the principal equation of the stream function. The corresponding “boundary conditions are obtained similarly. The coordinates equation has the same type property as that of the original equation and the only difference for various aerodynamic problems is the change of the boundary conditions on the cascade surfaces. Numerical results show that this unified method offers a useful tool for transonic cascade design.© 1988 ASME