Hollow nanostructures are promising building blocks for electrode scaffolds and catalyst carriers in energy-related systems. In this paper, we report a discovery of hollow TiO2 nanostructure ...evolution in a vapor–solid deposition system. By introducing TiCl4 vapor pulses to ZnO nanowire templates, we obtained TiO2 tubular nanostructures with well-preserved dimensions and morphology. This process involved the cation exchange reaction between TiCl4 vapor and ZnO solid and the diffusion of reactants and products in their vapor or solid phases, which was likely a manifestation of the Kirkendall effect. The characteristic morphologies and the evolution phenomena of the hollow nanostructures from this vapor–solid system were in a good agreement with the Kirkendall effect discovered in solution systems. Complex hollow TiO2 nanostructures were successfully acquired by replicating various ZnO nanomorphologies, suggesting that this unique cation exchange process could also be a versatile tool for nanostructure replication in vapor–solid growth systems. The evolution of TiO2 nanotubes from ZnO NW scaffolds was seamlessly integrated with TiO2 NR branch growth and thus realized a pure TiO2-phased 3D NW architecture. Because of the significantly enlarged surface area and the trace amount of Zn left in the TiO2 crystals, such 3D TiO2 nanoforests demonstrated enhanced photoelectrochemical performance particularly under AM (air mass) 1.5G illumination, offering a new route for hierarchical functional nanomaterial assembly and application.
General strategies are proposed by passivated co-doping in present paper to improve the photocatalytic activity of semiconductors for degradation of environmental pollutants.The ideal band gap of ...semiconductors for enhancement of photocatalytic activity can be lowered to match with visible light absorption and the location of the Conduction Band(CB) should be raised to meet the reducing capacity.Then we apply the strategy to anatase TiO2.It is predicted that nonmetal–metal co-doping TiO2can modify the catalyst band edges by raising the valence band(VB) edge signifcantly and making the CB edge increased 0.24 eV.Therefore,the band gap for co-doping system should be narrowed to about2.72 eV.(N,Ta) is predicted to be the target donor–acceptor combination with the band gap of 2.71 eV,which red-shifts the TiO2absorption edge to 457.6 nm in visible range.The band engineering principle will be ft to other wide-band-gap semiconductors for enhanced photocatalytic activity.
Refrigerant vapor-injection technique has been well justified to improve the performance of systems in refrigeration applications. However, it has not received much attention for air conditioning ...applications, particularly for air conditioning in hot climates and for heat pumping in cold climates. In this study, the performance of an 11
kW R410A heat pump system with a two-stage vapor-injected scroll compressor was experimentally investigated. The vapor-injected scroll compressor was tested with the cycle options of both flash tank and internal heat exchanger configurations. A cooling capacity gain of around 14% with 4% COP improvement at the ambient temperature of 46.1
°C and about 30% heating capacity improvement with 20% COP gain at the ambient temperature of −17.8
°C were found for the vapor-injected R410A heat pump system as compared to the conventional system which has the same compressor displacement volume.
A few‐layer MoS2 photodetector driven by poly(vinylidene fluoride‐trifluoroethylene) ferroelectrics is achieved. The detectivity and responsitivity are up to 2.2 × 1012 Jones and 2570 A W−1, ...respectively, at 635 nm with ZERO gate bias. Eg of MoS2 is tuned by the ultrahigh electrostatic field from the ferroelectric polarization. The photoresponse wavelengths of the photodetector are extended into the near‐infrared (0.85–1.55 μm).
Van der Waals heterostructures based on 2D layered materials have received wide attention for their multiple applications in optoelectronic devices, such as solar cells, light‐emitting devices, and ...photodiodes. In this work, high‐performance photovoltaic photodetectors based on MoTe2/MoS2 vertical heterojunctions are demonstrated by exfoliating‐restacking approach. The fundamental electric properties and band structures of the junction are revealed and analyzed. It is shown that this kind of photodetectors can operate under zero bias with high on/off ratio (>105) and ultralow dark current (≈3 pA). Moreover, a fast response time of 60 µs and high photoresponsivity of 46 mA W−1 are also attained at room temperature. The junctions based on 2D materials are expected to constitute the ultimate functional elements of nanoscale electronic and optoelectronic applications.
High‐performance photovoltaic photodetectors based on MoTe2/MoS2 heterojunction are demonstrated. The photoresponse under different biases is measured and the corresponding light‐induced charge transport is discussed. As a self‐powered photodetector, the vertical 2D p–n junctions achieve fast response and broad detection wavelength range. These outstanding properties indicate that 2D van der Waals junctions possess promising applications in photodetection, on‐chip logic circuits, and related applications.
Doped p–n junctions are fundamental electrical components in modern electronics and optoelectronics. Due to the development of device miniaturization, the emergence of two‐dimensional (2D) materials ...may initiate the next technological leap toward the post‐Moore era owing to their unique structures and physical properties. The purpose of fabricating 2D p–n junctions has fueled many carrier‐type modulation methods, such as electrostatic doping, surface modification, and element intercalation. Here, by using the nonvolatile ferroelectric field polarized in the opposite direction, efficient carrier modulation in ambipolar molybdenum telluride (MoTe2) to form a p–n homojunction at the domain wall is demonstrated. The nonvolatile MoTe2 p–n junction can be converted to n–p, n–n, and p–p configurations by external gate voltage pulses. Both rectifier diodes exhibited excellent rectifying characteristics with a current on/off ratio of 5 × 105. As a photodetector/photovoltaic, the device presents responsivity of 5 A W−1, external quantum efficiency of 40%, specific detectivity of 3 × 1012 Jones, fast response time of 30 µs, and power conversion efficiency of 2.5% without any bias or gate voltages. The MoTe2 p–n junction presents an obvious short‐wavelength infrared photoresponse at room temperature, complementing the current infrared photodetectors with the inadequacies of complementary metal‐oxide‐semiconductor incompatibility and cryogenic operation temperature.
Nonvolatile molybdenum telluride (MoTe2) p–n junctions with high rectification factor of 5 × 105 are demonstrated by ferroelectric domains. Coupling to opposite polarized ferroelectric copolymers, electrons or holes accumulate in the corresponding region of the ambipolar MoTe2 channel, defining a p‐n homojunction at the ferro‐electric domain wall. The p‐n junctions can be used as photodetectors and photovoltaic devices.
Implantable nanogenerators are rapidly advanced recently as a promising concept for harvesting biomechanical energy in vivo. This review article presents an overview of the most current progress of ...implantable piezoelectric nanogenerator (PENG) and triboelectric nanogenerator (TENG) with a focus on materials selection, engineering, and assembly. The evolution of the PENG materials is discussed from ZnO nanostructures, to high-performance ferroelectric perovskites, to flexible piezoelectric polymer mesostructures. Discussion of TENGs is focused on the materials and surface features of friction layers, encapsulation materials, and device integrations. Challenges faced by this promising technology and possible future research directions are also discussed.
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