CNT array-induced nanobubble assembly,nanodisk fabrication and enhanced spectral detection of CNT bundle density

Alignment,functionalization and detection of carbon nanotube(CNT)bundles are vital processes for utilizing this onedimensional nanomaterial in electronics.Here,we report a polymer-assisted wet shearing method to acquire super-aligned craterpatterned CNT arrays by nanobubble(NB)self-assembly with a"migrate and aggregation"mechanism and use craters to controllably mold even-sized nanodisks periodically along CNT bundles with tunable densities.This green,low-cost method can be extended to diverse substrates and fabricate different nanodisks.As an example,the Ag-nanodisk-patterned CNT arrays are utilized as substrates of surface-enhanced Raman scattering(SERS)for rhodamine 6G(R6G)and methylene blue(MB)in which a linear correlation is found between the SERS intensity and the CNT bundle density due to the periodic distribution of hot spots,enabling a spectral detection of CNT bundles and their densities by conventional dye molecules.Distinguishing from routine morphological characterization,this spectral method possesses an enhanced accuracy and a detection range of 0.1–2μm^(–1),showing its uniqueness in the detection of CNT bundle density since the intensity of traditional spectral merely relates to the quantity of CNTs,exhibiting its potential in future CNT-bundle-based electronics.

Carbon nanotube-polypyrrole core-shell sponge and its application as highly compressible supercapacitor electrode

A carbon nanotube （CNT） sponge contains a three-dimensional conductive nano- tube network, and can be used as a porous electrode for various energy devices. We present here a rational strategy to fabricate a unique CNT@polypyrrole （PPy） core-shell sponge, and demonstrate its application as a highly compressible supercapacitor electrode with high performance. A PPy layer with optimal thickness was coated uniformly on individual CNTs and inter-CNT contact points by electrochemical deposition and crosslinking of pyrrole monomers, resulting in a core-shell configuration. The PPy coating significantly improves specific capacitance of the CNT sponge to above 300 F/g, and simultaneously reinforces the porous structure to achieve better strength and fully elastic structural recovery after compression. The CNT@PPy sponge can sustain 1,000 compression cycles at a strain of 50% while maintaining a stable capacitance （〉 90% of initial value）. Our CNT@PPy core-shell sponges with a highly porous network structure may serve as compressible, robust electrodes for supercapacitors and many other energy devices.

Templated synthesis of Ti02 nanotube macrostructures and their photocatalytic properties

Controlled synthesis of hierarchically assembled titanium dioxide （TiO2） nano- structures is important for practical applications in environmental purification and solar energy conversion. We present here the fabrication of interconnected TiO2 nanotubes as a macroscopic bulk material by using a porous carbon nanotube （CNT） sponge as a template. The basic idea is to uniformly coat an amorphous titania layer onto the CNT surface by the infiltration of a TiO2 precursor into the sponge followed by a subsequent hydrolysis process. After calcination, the CNTs are completely removed and the titania is simultaneously crystallized, which results in a porous macrostructure composed of interconnected anatase TiO2 nanotubes. The TiO2 nanotube macrostructures show comparable photocatalytic activities to commercial products （AEROXIDE TiO2 P25） for the degradation of rhodamine B （RhB）. Moreover, the TiO2 nanotube macrostructures can be settled and separated from water within 12 h after photocatalysis, whereas P25 remains suspended in solution after weeks. Thus the TiO2 nanotube macrostructures offer the advantage of easy catalyst separation and recycle and can be a promising candidate for wastewater treatment.

Direct fabrication of carbon nanotube-graphene hybrid films by a blown bubble method

Hybridization of carbon nanotubes （CNT） with graphene provides a promising means of integrating the attributes of both materials, thereby enabling widespread application. Here, we present a method to directly assemble hybrid CNT- graphene films by a blown bubble method combined with selective substrate annealing. We use polymethylmethacrylate （PMMA） as the polymeric matrix to blow bubbles containing self-assembled multi-walled CNT arrays, and then transform the bubble film into a CNT-graphene hybrid film by thermal annealing on a Cu substrate; PMMA serves as the carbon source for growing single to few-layer graphene among the CNT network until a continuously hybridized structure is formed. Compared to the bare （non-hybridized） CNT networks, the hybrid films exhibit improved electrical conductivity and structural integrity. Our method also enables the fabrication of a multi-walled CNT-Si solar cell, which has high power conversion efficiency, through the assembly of hybrid CNT-graphene structures.

Origin of inhomogeneity in spark plasma sintered bismuth antimony telluride thermoelectric nanocomposites

Anisotropy and inhomogeneity are ubiquitous in spark plasma sintered thermoelectric devices.However,the origin of inhomogeneity in thermoelectric nanocomposites has rarely been investigated so far.Herein,we systematically study the impact of inhomogeneity in spark plasma sintered bismuth antimony telluride(BiSbTe)thermoelectric nanocomposites fabricated from solution-synthesized nanoplates.The figure of merit can reach 1.18,which,however,can be overestimated to 1.88 without considering the inhomogeneity.Our study reveals that the inhomogeneity in thermoelectric properties is attributed to the non-uniformity of porosity,textures and elemental distribution from electron backscatter diffraction and energy-dispersive spectroscopy characterizations.This finding suggests that the optimization of bulk material homogeneity should also be actively pursued in any future thermoelectric material research.

Recent progress in thermoelectric nanocomposites based on solution-synthesized nanoheterostructures

Thermoelectric materials, which can convert waste heat into electricity, have received increasing research interest in recent years. This paper describes the recent progress in thermoelectric nanocomposites based on solution-synthesized nanoheterostructures. We start our discussion with the strategies of improving the power factor of a given material by using nanoheterostructures. Then we discuss the methods of decreasing thermal conductivity. Finally, we highlight a way of decoupling power factor and thermal conductivity, namely, incorporating phase-transition materials into a nanowire heterostructure. We have explored the lead telluride-copper telluride thermoelectric nanowire heterostructure in this work. Future possible ways to improve the figure of merit are discussed at the end of this paper.

Graphene-CdSe Nanobelt Solar Cells with Tunable Configurations

We have combined two planar nanostructures, graphene and CdSe nanobelts, to construct Schottky junction solar cells with open-circuit voltages of about 0.5 V and cell efficiencies on the order of 0.1%. By covering transparent graphene or carbon nanotube （CNT） films on selected positions along macroscopically long CdSe nanobelts, we have demonstrated the fabrication of active solar cells with many different configurations and parallel connections from individual or multiple assembled nanobelts. The graphene-CdSe nanobelt solar cells reported here show a great flexibility in creating diverse device architectures, and might be scaled up for cell integration based on assembled nanobelt arrays and patterned graphene （or CNT） films.

Halide Perovskite Epitaxial Heterostructures

CONSPECTUS:The past decade has witnessed the great success and rapid development of halide perovskite materials in photovoltaics and light-emitting devices,which is due to the inherently high photoluminescence quantum yield,long carrier diffusion length,high light absorption coefficient,great defect tolerance,and remarkable tunability.For example,the record efficiency of perovskite solar cells has ramped up to 25.5%,comparable to single-crystal silicon solar cells.In combination with the facile solution processing,perovskite solar cells have gained tremendous attention and interest from both academia and the photovoltaic market.Moreover,as a newly emerging class of semiconductors with excellent properties and low manufacturing cost,it is also promising and meaningful to explore new applications beyond optoelectronic devices,such as transistors,lasers,and memory devices.To this end,the integration of different halide perovskites into epitaxial heterostructures provides an ideal option.On the other hand,from the perspective of fundamental studies,halide perovskite heterostructures also provide a platform to directly visualize ion migration and to study the charge transfer behavior and anomalous exciton phenomena,etc.The aim of our Account is to summarize the synthetic strategies to achieve halide perovskite epitaxial heterostructures and to highlight the effective routes to stabilize halide perovskites and heterostructures.We focus this Account on two-dimensional(2D)halide perovskites and emphasize the important roles the organic ligands play.Specifically,we discuss our recent findings on the incorporation of conjugated organic ligands into 2D halide perovskites leading to enhanced thermal and environmental stability and suppressed halide interdiffusion in the corresponding heterostructures.Molecular dynamics simulation and low-dose aberration corrected transmission electron microscopy were used as powerful tools to unveil and elucidate the working mechanism of stabilization and anion interdiffusion suppression.Following this strategy,diverse halide perovskite heterostructures between different halides,metals,or organic cations and more complex heterostructures and superlattices can be realized.Due to the reduced ion motion and improved stability,the interface of the heterostructures can be kept quite sharp.In the outlook of this Account,we discuss the challenges and a few promising directions with a special focus on the vertical van der Waals(vdW)heterostructures,which are expected to offer more flexibility in heterostructure integration and more opportunities in studying the charge transfer and carrier interaction along the out-of-plane direction.Moreover,the existence of semiconducting organic ligands provides new insights to tune the carrier and exciton behaviors along both in-plane and out-of-plane directions.

CuI-Si Heterojunction Solar Cells with Carbon Nanotube Films as Flexible Top-Contact Electrodes

We report the fabrication of CuI-Si heterojunction solar cells with carbon nanotubes （CNTs） as a transparent electrode. A flexible CNT network was transferred onto tile top of a polycrystalline CuI layer, making a conformal coating with good contact with the underlying CuI. The solar cells showed power conversion efficiencies in the range of 6% to 10.5%, while the efficiency degradation was less than 10% after the device was stored in air for 8 days. Compared with conventional rigid electrodes such as indium tin oxide （ITO） glass, the flexibility of the CNT films ensures better contact with the active layers and removes the need for press-contact electrodes. Degraded cells can recover their original performance by acid doping of the CNT electrode. Our results suggest that CNT films are suitable electrical contacts for rough materials and structures with an uneven surface.