Dayuan Xiong

Sequential coupling transport for the dark current of quantum dots-in-well infrared photodetectors

The dark current characteristics and temperature dependence for quantum dot infrared photodetectors have been investigated by comparing the dark current activation energies between two samples with identical structure of the dots-in-well in nanoscale but different microscale n-i-n environments. A sequential coupling transport mechanism for the dark current between the nanoscale and the microscale processes is proposed. The dark current is determined by the additive mode of two activation energies: Ea,micro from the built-in potential in the microscale and Ea,nano related to the thermally assisted tunneling in nanoscale. The activation energies Ea,micro and Ea,nano decrease exponentially and linearly with increasing applied electric field, respectively.

Preparation of multi-layer graphene on nickel-coated silicon microchannel plates by a hydrothermal carbonization procedure and its improved field emission properties

An emission cell comprising multi-layer graphene (MLG) on nickel-coated silicon microchannel plates (Ni/Si-MCPs) was prepared. The Ni3C film was formed on the Si-MCPs by hydrothermal carburization in a polyol solution containing a small amount of NaAc as the carbon source and thermal annealing was performed to produce the vertically and horizontally aligned multi-layer graphene field-emission cathode on the surface of the Ni/Si-MCPs (MLG-MCPs). The microstructure and surface morphology were investigated and field emission (FE) studies indicated that the MLG-MCPs delivered better FE performance than Ni/Si-MCPs due to characteristics such as sharp edges, large aspect ratio, and the vertically and horizontally aligned and patterned MLG with good electrical conductivity. The turn-on field of the sample annealed at 800 °C was 2.0 V μm−1 at a current density of 10 μA cm−2 and the field emission threshold was 3.2 V μm−1 at 1 mA cm−2. The structure was very stable showing 97.5% retention after continuous operation for over 6 h at 2 × 10−5 Pa, suggesting a promising candidate for FE devices. This would open up possibilities for the next generation FE electron sources from well-aligned macroporous graphene with skeleton and extend their practical applications.

Three-dimensional homo-nanostructured MnO2/nanographene membranes on a macroporous electrically conductive network for high performance supercapacitors

A three-step hydrothermal route was designed to fabricate three-dimensional (3D) homo-nanostructured MnO2 (MnO2–MnO2)/nanographene membranes on a macroporous and electrically conductive network (MECN). The preparation technology, structure and morphology, and electrochemical properties of samples are determined systematically. The nanographene/MECN electrode with more defects as the active surface had been synthesized by hydrothermal carbonization. The in situ growth of δ-MnO2 with a carbon-assisted reaction on the nanographene/MECN was strongly adhered to the substrate. The additional α-MnO2 with a redox reaction enhanced the mass loading of MnO2, developing the specific capacitance of the MnO2–MnO2/nanographene/MECN electrode. The materials are demonstrated as an electrode with a maximum capacitance of 4.5 F cm−2 or 179 F cm−3 (894 F g−1) at 1 mA cm−2 for 1 cm2 samples and retaining over 83% after 20 000 cycles in 1 M Na2SO4. The MnO2–MnO2/nanographene/MECN||AC/Ni-foam supercapacitors with high volumetric energy densities exhibit the ideal performance of a supercapacitor (1 mW h cm−3, 40.3 W h kg−1, at 1000 W kg−1), indicating a promising future for supercapacitors.

Photocurrent spectrum study of a quantum dot single-photon detector based on resonant tunneling effect with near-infrared response

We present the photocurrent spectrum study of a quantum dot (QD) single-photon detector using a reset technique which eliminates the QDs “memory effect.” By applying a proper reset frequency and keeping the detector in linear-response region, the detectors responses to different monochromatic light are resolved which reflects different detection efficiencies. We find the reset photocurrent tails up to 1.3 μm wavelength and near-infrared (∼1100 nm) single-photon sensitivity is demonstrated due to interband transition of electrons in QDs, indicating the device a promising candidate both in quantum information applications and highly sensitive imaging applications operating in relative high temperatures (>80 K).

Three-dimensional tetsubo-like Co(OH)2 nanorods on a macroporous electrically conductive network as an efficient electroactive framework for the hydrogen evolution reaction

Conducting the hydrogen evolution reaction (HER) in an alkaline environment using a non-precious transition metal catalyst with high efficiency is challenging. Here, we report excellent HER activity achieved using three-dimensional (3D) tetsubo-like Co(OH)2 nanorods on a macroporous electrically conductive network (MECN) synthesized by a hydrothermal method. This unique framework comprises three levels of porous structures, including a bottom-ordered MECN substrate, an intermediate layer of vertically porous Co(OH)2 nanowires with a mean diameter of 100 nm and length of about 2 μm, and outmost Co(OH)2 nanosheets (≈20 nm). The 3D array structure with a large aspect ratio provides a large specific surface area and exposes more active sites to catalyze electrochemical reactions at the electrode–electrolyte interface. Compared with Co(OH)2 nanosheets on an MECN and foamy Co(OH)2 on an MECN structure, the synthesized architecture has excellent HER catalytic reactivity, including a low potential of −69.2 mV vs. RHE, a cathodic current density of 10 mA cm−2, a small Tafel slope of 61.9 mV dec−1, a high current density, and robust catalytic stability in 1 M KOH, and is promising in HER applications.

Nitrogen-doped multilayered nanographene derived from Ni3C with efficient electron field emission

Stability and durability are crucial to graphene-based field emitting materials. Although well-aligned N-doped graphene has a large aspect ratio and good electrical conductivity, it suffers from weak adhesion to the substrate, electric field shielding, and Joule heating effect and possible damage and collapse may result in dissatisfied field emission properties. Herein, field emitters based on N-doped multilayered nanographene derived from Ni3C films are demonstrated to have strong adhesion to the substrate and a uniform large-aspect-ratio morphology. Field-emission (FE) measurements, from the channel edges of 250 microns in depth and 1 micron in width covered with N-doped multilayer nanographene, were performed on N-doped multilayered nanographene on Ni/Si-MCPs (N-doped MLG-MCPs), revealing a small turn-on field of 0.5 V μm−1, a low threshold field of 1.1 V μm−1, and a large enhancement factor β of 9012 at a distance of 100 μm. In addition, the current density is 2.85 mA cm−2 and 96.2% retention is observed after operation for 6 h. The performance and stability of N-doped MLG-MCPs are better than those reported previously from doped graphene nanostructures and comparable to those of carbon nanotubes and carbon-based nanocomposites. The materials with a well-aligned nanographene skeleton have great potential as next-generation FE electron sources.

Highly efficient field emission from ZnO nanorods and nanographene hybrids on a macroporous electric conductive network

A hybrid structure comprising zinc oxide (ZnO) nanorods and nanographene on a patterned substrate enhances the field emission properties by reducing the work function, avoiding electrostatic screening, and providing more emitters. A theoretical energy-band model is fabricated to analyze the field emission process of the ZnO nanorods and nanographene hybrids. And the structure is modeled with equipotential lines and simulated by Ansys to present the advantages of the three-dimensional (3D) patterned substrate. After theoretical modeling and simulation, a simple, low-cost, and environmentally friendly method that is suitable for industrial production is developed to fabricate ZnO nanorods and nanographene hybrids on a 3D macroporous electric conductive network (MECN). The nanographene is coated on the MECN by hydrothermal carbonization to circumvent the substrate limitation and ZnO nanorods are prepared on the nanographene/MECN substrate hydrothermally. The ZnO nanorods, ∼600 nm long with a diameter of about 70 nm, in combination with nanographene show sharp edges and an ordered lattice pattern and, therefore, electrons flow from the nanographene to the ZnO nanorods and are emitted more easily. The ZnO nanorods/nanographene/MECN has highly efficient field emission properties such as a low turn-on voltage Eon of 0.5 V μm−1 at a current density of 10 μA cm−2, and a large field enhancement factor β of 25550, as well as excellent sustainability and consequently great potential in displays, lighting, and sensors.

Based simulation of high gain and low breakdown voltage InGaAs/InP avalanche photodiode

The InGaAs/InP avalanche photodiode (APD) of thin heterostructure charge layer has studied. Apsys software is used for simulation. For reducing the dark current and achieving higher avalanche gain, a 30 nm InP charge layer and 100 nm InGaAsP grade charge layer used between 400 nm multiplication and absorption layers. Simulation results demonstrated that the low dark current properties and low breakdown voltage (17.5 V) had achieved. The avalanche gain is 88 at reverse bias voltage 17.2 V, and reached 300 at 17.4 V before break down.

Dumping design of CTIA readout circuit based on a low-dimensional quantum structure photoelectric sensor

A practical equivalent circuit model of the low dimensional photoelectric sensor with quantum dots-quantum well (QDs-QW) hybrid hetero-structure is introduced in this article. This model acts as a signal source for ROIC (readout integrate circuit) simulation. An optimal readout integrated circuit employing capacitor feedback transimpedance amplifier (CTIA) structure is designed for the QDs-QW hybrid hetero-structure photoelectric sensor. Based on the photoelectron storage characteristic of the photoelectric sensor, a dumping structure for CTIA readout integrated circuit is studied. This dumping structure is proposed to release the redundant charge stored by the device for improving the performance of the photoelectric sensor readout.

Preparation of SnO 2 Nanoparticles Doped With Palladium and Graphene and Application for Ethanol Detection

A novel ethanol gas sensor constructed with SnO₂ nanoparticles doped with palladium and graphene is described. By incorporating 0.1 wt% graphene and 3 wt% PdCl₂ into SnO₂, the working temperature of the sensor can be reduced to 40 °C and the response is 4.6. The operation temperature can be decreased to near room temperature due to the increased oxygen adsorption by palladium and the high electron mobility by graphene.