Local large temperature difference and ultra-wideband photothermoelectric response of the silver nanostructure film/carbon nanotube film heterostructure.

Photothermoelectric materials have important applications in many fields. Here, we joined a silver nanostructure film and a carbon nanotube film by van der Waals force to form a heterojunction, which shows excellent photothermal and photoelectric conversion properties. The local temperature difference and the output photovoltage increase rapidly when the heterojunction is irradiated by lasers with wavelengths ranging from ultraviolet to terahertz. The maximum temperature difference reaches 215.9 K, which is significantly higher than that of other photothermoelectric materials reported in the literature. The photothermal and photoelectric responsivity depend on the wavelength of lasers, which are 175~601 K W-1 and 9.35~40.4 mV W-1, respectively. We demonstrate that light absorption of the carbon nanotube is enhanced by local surface plasmons, and the output photovoltage is dominated by Seebeck effect. The proposed heterostructure can be used as high-efficiency sensitive photothermal materials or as ultra-wideband fast-response photoelectric materials.

Significantly enhanced photoresponse of carbon nanotube films modified with cesium tungsten bronze nanoclusters in the visible to short-wave infrared range.

Carbon nanotube (CNT) films are promising materials for application in ultra-broadband photodetectors because their absorption range covers the entire spectrum from ultraviolet to the terahertz region, and their detection mechanism is the bolometric effect. Because of the different and limited photothermal conversion efficiencies of CNTs with respect to various wavelengths, the response performance of existing photodetector devices is unsatisfactory, particularly in the infrared band. In this paper, we propose for the first time the use of cesium tungsten bronze (Cs x WO3) nanomaterials, which have strong infrared absorption and excellent photothermal conversion properties, to decorate a CNT film for construction of a Cs x WO3-CNT composite film photodetector. When compared with CNT-based film photodetectors, the proposed Cs x WO3-CNT composite film photodetector shows a significantly enhanced broadband photoresponse over the range from visible light (405 nm) to the short-wave infrared (1550 nm) region, with an average increase in responsivity of 400% and an average increase in specific detectivity of 549%. In addition, the Cs x WO3-CNT photodetector shows a fast photoresponse, with a rise time of only 28 ms, which represents a 30% improvement over that of the CNT photodetector. This paper thus provides a new concept for the design of a high-performance broadband photodetector.

High-Responsivity Photodetector Based on a Suspended Monolayer Graphene/RbAg4I5 Composite Nanostructure.

Graphene has excellent electrical, optical, thermal, and mechanical properties that make it an ideal optoelectronic material. However, it still has some problems, such as a very low light absorption rate, which means it cannot meet the application requirements of high-performance optoelectronic devices. Here, we produce a high-responsivity photodetector based on a monolayer graphene/RbAg4I5 composite nanostructure. With the aid of poly(methyl methacrylate), we suspend the monolayer graphene on a hollow carving groove with a width of 100 µm. A RbAg4I5 film evaporated on the back of the graphene causes the composite nanostructure to generate a large photocurrent under periodic illumination. Experimental results show that the dissociation and recombination of ion-electron bound states (IEBSs) are responsible for the excellent photoresponse. The device has very high (>1 A W-1) responsivity in wide-band illumination wavelength from 375 nm to 808 nm, especially at 375 nm, where it shows a responsivity of up to ∼5000 A W-1. We designed the dimensions of the carving groove to allow the light spot to cover the entire groove, and we cut the graphene sheet to match the length of the carving groove. With the structural optimizations, the energy of light can be used more efficiently to dissociate the IEBSs, which greatly improves the photoresponse of optoelectronic devices based on the proposed monolayer graphene/RbAg4I5 composite nanostructure.

Growth mechanism and photoelectric properties of a silver nanowire network prepared by solid state ionics method.

A macroscopic silver nanowire (AgNW) network is grown by solid state ionics method. The ion flow during growth of the AgNW network is controlled by maintaining a current in the order of 10-7 A. Scanning electron microscopy (SEM) analysis reveals that the growth direction of AgNWs in the network is irregular and spread evenly in all directions and the nanowires are 40-160 nm in diameter. The microcosmic mechanism of silver nanostructures grown by the solid state ionics method is established by real time and in situ SEM analysis of the growth process of the AgNW networks. To study the photoelectric properties of the network, a self-supported AgNW network sample (∼1 mm wide and 8 mm long) is irradiated with lasers of different wavelengths of 375, 405, 532, 633, 808, and 1064 nm and 10.6 µm, and changes in the current between the two ends of the sample are recorded. The network displays negative photoconductance effect, and the maximum light responsivity is 43 mA W-1. The network displays light responsivity in the ultraviolet light-to-mid-infrared light region, with response times of tens of milliseconds. These findings indicate that the AgNW network has broad application prospect in ultra-wide spectrum photoelectric detection.

Facile fabrication of eutectic gallium-indium alloy nanostructure and application in photodetection.

Eutectic gallium-indium (EGaIn) alloy is a kind of liquid metal and has attracted much attention due to good properties. In order to satisfy the trend of miniaturization and realize more practical applications, the exploration for preparation method and properties of EGaIn at nanoscale are very important. Here, facile vacuum thermal evaporation method is developed to fabricate EGaIn nanostructures. The EGaIn nanoparticle and nanofilm with naturally formed 5 nm thick oxide layers are well prepared. The oxide film formed on the EGaIn surface is an important factor, making the properties of the nanostructure different from the properties of the bulk. Compared with ignorance of oxide layer in bulk materials, the proportion of oxide layer increases evidently in nanostructures, which produce obvious influence on the electric and optical properties. The rectifying characteristic and optoelectronic performance are experimentally observed. The EGaIn nanostructures can generate evident photocurrent responses with good responsivities (∼1 mA W-1) and response speed (∼1 s) under irradiation of 206 nm, 405 nm, 532 nm, 635 nm, 808 nm, 1064 nm and 10.6 µm lasers. These properties are completely different from the metallic properties of EGaIn bulk material.

Generation of Ultrafine Droplets in Femtoliter Scale from a Large Needle with Diameter of 200 Microns.

Ultrafine droplets play important roles in many fields. Here, we prepare ultrafine droplets with volumes in femtoliter scale by applying an electrostatic field between a needle and substrate. The diameter of liquid is reduced significantly to about 1/50 that of the needle tip. By using some solvents consisting of small molecules, ultrafine droplets eject from the needle tip. The volume of the ultrafine droplets depend on the strength of the electrostatic field and properties of the liquid. Ultrafine droplets containing perovskite quantum dots are also ejected on the substrate by using this jetting method. The ultrafine droplets have great potentials in carrying tiny amount of quantum dots and even molecules for various applications.