Inspired by nanoscience and nanoengineering, numerous nanostructured materials developed by multidisciplinary approaches exhibit excellent photoelectronic properties ranging from ultraviolet to ...terahertz frequencies. As a new class of building block, nanoscale elements in terms of quantum dots, nanowires, and nanolayers can be used for fabricating photodetectors with high performance. Moreover, in conjunction with traditional photodetectors, they exhibit appealing performance for practical applications including high density of integration, high sensitivity, fast response, and multifunction. Therefore, with the perspective of photodetectors constructed by diverse low‐dimensional nanostructured materials, recent advances in nanoscale photodetectors are discussed here; meanwhile, challenges and promising future directions in this research field are proposed.
Nanostructured materials with different dimensions, such as nanolayers, nanowires, and quantum dots, exhibit excellent photoelectronic properties for photodetectors ranging from the ultraviolet to terahertz frequencies. Besides excellent performances of high sensitivity and fast response for practical applications, they also exhibit many appealing features like high density of integration and multifunction, in conjunction with traditional photodetectors.
Self‐powered ultraviolet (UV) photodetectors, which have vast applications in the military and for civilian purposes, have become particularly attractive in recent years due to their advantages of ...high sensitivity, ultrasmall size, and low power consumption. In particular, self‐powered UV photodetectors driven by a built‐in electric field cannot only detect UV signals but also be powered by the incident signals instead of external power. In this concept, the key issues and most recent developments on photovoltaic type UV photodetectors driven by p–n homojunction, heterojunction, and Schottky junction are surveyed. This should generate extensive interest in this field and encourage more researchers to engage in and tackle the scientific challenges.
In this Concept, self‐powered UV photodetectors driven by a built‐in electric field are presented, which is extremely important for applications in UV detection. The key issues and developments of photovoltaic‐type UV photodetectors driven by the p–n homojunction, heterojunction, and Schottky junction are surveyed. Additionally, the development tendency of next generation photovoltaic‐type UV is also proposed.
Highly crystallized ZnO–Ga2O3 core–shell heterostructure microwire is synthesized by a simple one‐step chemical vapor deposition method, and constructed into a self‐powered solar‐blind (200–280 nm) ...photodetector with a sharp cutoff wavelength at 266 nm. The device shows an ultrahigh responsivity (9.7 mA W−1) at 251 nm with a high UV/visible rejection ratio (R251 nm/R400 nm) of 6.9 × 102 under zero bias. The self‐powered device has a fast response speed with rise time shorter than 100 µs and decay time of 900 µs, respectively. The ultrahigh responsivity, high UV/visible rejection ratio, and fast response speed make it highly suitable in practical self‐powered solar‐blind detection. Additinoally, this microstructure heterojunction design method would provide a new approach to realize the high‐performance self‐powered photodetectors.
Highly crystallized ZnO–Ga2O3 heterostructure microwire is synthesized using a simple one‐step chemical vapor deposition method and the growth mechanism is discussed. A self‐powered solar‐blind photodetector based on individual ZnO–Ga2O3 heterostructures is demonstrated, and has responsivity as high as 9.7 mA W−1 at the wavelength of 251 nm without any external power source.
Thermal management is critical to the performance, lifetime, and reliability of electronic devices. With the miniaturization, integration and functionalization of electronics and the emergence of new ...applications such as light emitting diodes, thermal dissipation becomes a challenging problem. Addressing this challenge requires the development of novel polymer-based composite materials with enhanced thermal conductivity. In this review, the fundamental design principles of highly thermally conductive composites were discussed. The key factors influencing the thermal conductivity of polymers, such as chain structure, crystallinity, crystal form, orientation of polymer chains, and orientation of ordered domains in both thermoplastics and thermosets were addressed. The properties of thermally conductive fillers (carbon nanotubes, metal particles, and ceramic particles such as boron nitride or aluminum oxide) are summarized at length. The dependence of thermal conductivity of composites on the filler loading, filler aggregate morphology and overall composite structure is also discussed. Special attention is paid to recent advances in controlling the microstructure of polymer composites to achieve high thermal conductivity (novel approaches to control filler orientation, special design of filler agglomerates, formation of continuous filler network by self-assembly process, double percolation approach, etc.). The review also summarizes some emerging applications of thermally conductive polymer composites. Finally, we outline the challenges and outlook for thermally conductive polymer composites.
The core–shell nanoparticle structure, which consists of an inner layer “guest” nanoparticle encapsulated inside another of a different material, is the simplest motif in two-component systems. In ...comparison to the conventional single-component systems, complex systems pose both challenges and opportunities. In this Account, we describe our recent progresses in using core–shell motif for exploring new and sophisticated nanostructures. Our discussion is focused on the mechanistic details, in order to facilitate rational design in future studies. We believe that systematic development of synthetic capability, particularly in complex and multifunctional systems, is of great importance for future applications. A key issue in obtaining core–shell nanostructures is minimizing the core-shell interfacial tension. Typically, one can coat the core with a ligand for better interaction with the shell. By selecting suitable ligands, we have developed general encapsulation methods in three systems. A variety of nanoparticles and nanowires were encapsulated using either amphiphilic block copolymer (polystyrene-block-poly(acrylic acid)), conductive polymer (polyaniline, polypyrrole, or polythiophene), or silica as the shell material. Obvious uses of shells are to stabilize colloidal objects, retain their surface ligands, prevent particle aggregation, or preserve the assembled superstructures. These simple capabilities are essential in our synthesis of surface-enhanced Raman scattering nanoprobes, in assigning the solution state of nanostructures before drying, and in developing purification methods for nano-objects. When it is applied in situ during nanocrystal growth or nanoparticle assembly, the intermediates trapped by shell encapsulation can offer great insights into the mechanistic details. On the other hand, having a shell as a second component provides a window for exploring the core–shell synergistic effects. Hybrid core–shell nanocrystals have interesting effects, for example, in causing the untwisting of nanowires to give double helices. In addition, partial polymer shells can bias nanocrystal growth towards one direction or promote the random growth of Au dendritic structures; contracting polymer shells can compress the embedded nanofilaments (Au nanowires or carbon nanotubes), forcing them to coil into rings. Also, by exploiting the sphere-to-cylinder conversion of block copolymer micelles, the Au nanoparticles pre-embedded in the polymer micelles can be assembled into long chains. Lastly, shells are also very useful for mechanistic studies. We have demonstrated such applications in studying the controlled aggregation of nanoparticles, in probing the diffusion kinetics of model drug molecules from nanocarriers to nanoacceptors, and in measuring the ionic diffusion through polyaniline shells.
One may discover a stone tool by chance but it takes more than luck to make a car or cell phone. With the advance of nanoscience, the synthesis of increasingly sophisticated nanostructures demands a ...rational design and a systems approach. In this Review, we advocate the distinction between thermodynamically and kinetically controlled scenarios, that is, whether a product forms because it is the most stable state or because the pathway leading to it has the lowest energy barrier. Great endeavours have been made to describe the multiple concurrent processes in typical nanosynthesis phenomena, so that the mechanistic proposals in the literature are brought into a common framework for easy contrast and comparison.
Understanding starts with distinction: Distinguishing between the thermodynamically and kinetically controlled scenarios is of critical importance when analyzing the complex phenomena in nanosynthesis, such as the growth of nanoparticles, their aggregation, and the shape evolution of polymer nanostructures. The processes are examined in detail in this Review and the mechanistic proposals are categorized in the common framework of thermodynamics and kinetics.
High-performance solar-blind (200–280 nm) avalanche photodetectors (APDs) were fabricated based on highly crystallized ZnO–Ga2O3 core–shell microwires. The responsivity can reach up to 1.3 × 103 A/W ...under −6 V bias. Moreover, the corresponding detectivity was as high as 9.91 × 1014 cm·Hz1/2/W. The device also showed a fast response, with a rise time shorter than 20 μs and a decay time of 42 μs. The quality of the detectors in solar-blind waveband is comparable to or even higher than that of commercial Si APD (APD120A2 from Thorlabs Inc.), with a responsivity ∼8 A/W, detectivity ∼1012 cm·Hz1/2/W, and response time ∼20 ns. The high performance of this APD make it highly suitable for practical applications as solar-blind photodetectors, and this core–shell microstructure heterojunction design method would provide a new approach for realizing an APD device.
With unique ability to concentrate and manipulate light at nanoscale, surface plasmon resonance technologies create additional opportunities for fabricating superintegration photodetectors with ...desirable functionalities. To gain an insight into the state‐of‐the‐art of plasmonic photodetectors, recent advances in novel devices as well as potential building blocks are presented herein. The article focuses particularly on understanding the enhancement mechanism of different architectures such as nanoparticles, gratings, waveguides, antennas, and microcavities. Meanwhile, challenges and potential design schemes are proposed in this inspiring field.
With a unique ability to concentrate and manipulate light at nanoscale, surface plasmon resonance technologies create additional opportunities for fabricating superintegration photodetectors with desirable functionalities. To gain an insight into the state‐of‐the‐art of plasmonic photodetectors, recent advances in novel devices as well as potential building blocks are presented in this feature article.
Hexagonal Ag nanoplates with long and ultranarrow gaps (about 90 nm in length, 2 nm in width) are synthesized via seed-mediated growth method. By growing around the polymer shell on the seed, the Ag ...domain cannot merge at the meet-up point, leaving a long narrow gap in the resulting plate. These gapped nanoplates exhibit high sensitivity in SERS detection, with limitation of 10–9 M for 2-naphthalenethiol.
•Coal gangue is silicon-aluminium materials, which can be used to prepare geopolymer after high-temperature calcination.•Coal gangue geopolymer has a high early strength, higher than that of OPC.45 ...cement paste specimens.•The generation of the zeolite facies crystallization plays an obvious role on the compressive strength of coal geopolymer.•This paper provides experimental and theoretical basis for the development and wide application of coal gangue cementitious materials.
This paper explores the impacts of sodium hydroxide modulus, alkali lye amount and liquid–solid ratio on the strength and microstructure of coal gangue geopolymer materials, involving a total of five sodium hydroxide moduli, four NH/NS mass ratios and seven liquid–solid ratios. To characterize the morphology and structure of coal gangue geopolymer materials, we carried out XRD, TG-DTG, FT-IR and SEM analysis on the specimens respectively. The results show that NH concentration has no impact on paste fluidity and has significant impact on compressive strength of geopolymers. Both paste fluidity and compressive strength of geopolymers increase with the increase in liquid–solid ratio. However, it should be noted that the compressive strength decreases with the increase in liquid–solid ratio when the liquid–solid ratio is greater than 0.32. The optimal NH/NS mass ratio is 1:1.5 ∼ 1:2. In comparison with P.O42.5 cement specimens, coal gangue geopolymers have higher initial strength and lower 28 d compressive strength. The analytical results of microstructure are consistent with those of compressive strength, which demonstrates that the polymerization products of coal gangue geopolymers are N-A-S-H gels and some other aluminosilicate zeolite crystals.
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