Electrically–transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high–performance electrically-transduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electrically-transduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical pers...

Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials

AlGaN-based materials own direct transition energy bands and wide bandgap and thus can be used in high-efficiency ultraviolet (UV) emitters and detectors. Over the past two decades, AlGaN-based materials and devices experienced rapid development. Deep ultraviolet AlGaN-based light-emitting diodes (LEDs) with improved efficiency of 20.3% (at 275 nm) have been produced. An electron beam (EB)-pumped AlGaN-based UV light source at 238 nm, output power of 100 mW, and power conversion efficiency (PCE) of 40% has also been fabricated. UV stimulated emission from AlGaN multiple-quantum-wells laser diodes (LDs) using electrical pumping at room temperature has also been achieved at a wavelength of 336 nm. Compared with GaN-based blue and green LEDs and LDs, the efficiency of AlGaN-based UV LEDs and LDs is lower. Further optimization and improvements in both structure and fabrication are required to realize high-performance devices. In AlGaN-based UV photodetectors (PDs), gain as high as 104 orders of magnitude has been reported using the separated absorption and multiplication region avalanche photodiode structure but is still far from detecting the weak signal, and thus UV single-photon detectors with high detectivity is challenging. Recently, there has been extensive work in the nonlinear optical properties of AlGaN and AlGaN-based passive devices, such as waveguides and resonators. However, how to minimize the scattering and defect-related absorption needs to be further studied. In this review, first, approaches used to grow an AlGaN epilayer and p-type doping are introduced. Second, progress in AlGaN-based UV LEDs, EB-pumped light sources, LDs, PDs, passive devices, and the nonlinear optical properties are presented. Finally, an overview of potential future trends in AlGaN-based materials and UV devices is given.

AlGaN photonics: recent advances in materials and ultraviolet devices

Single-photon detectors (SPDs) are the most sensitive instruments for light detection. In the near-infrared range, SPDs based on III–V compound semiconductor avalanche photodiodes have been extensively used during the past two decades for diverse applications due to their advantages in practicality including small size, low cost and easy operation. In the past decade, the rapid developments and increasing demands in quantum information science have served as key drivers to improve the device performance of single-photon avalanche diodes and to invent new avalanche quenching techniques. This Review aims to introduce the technology advances of InGaAs/InP single-photon detector systems in the telecom wavelengths and the relevant quantum communication applications, and particularly to highlight recent emerging techniques such as high-frequency gating at GHz rates and free-running operation using negative-feedback avalanche diodes. Future perspectives of both the devices and quenching techniques are summarized. Recent progress in single-photon detectors for quantum communication based on III–V compound semiconductor avalanche photodiodes is reviewed. Specifically, Jun Zhang and Jian-Wei Pan at the University of Science and Technology of China and their colleagues in the USA and Switzerland introduce technological advances for InGaAs/InP single-photon detector systems in the telecommunication band along with their associated applications in quantum communication. III–V single-photon avalanche diodes are the most practical tools available for detecting ultraweak near-infrared light. The scientists overview important parameters for evaluating the performance of detector systems based on single-photon avalanche diodes and describe the experimental characterization of these parameters. They also consider emerging techniques, including high-frequency gating at gigahertz rates and free-running operation using negative-feedback avalanche diodes. Finally, the future prospects of these devices are considered.

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Advances in InGaAs/InP single-photon detector systems for quantum communication

Alternative methods, including green synthetic approaches for the preparation of various types of nanoparticles are important to maintain sustainable development. Extracellular or intracellular extracts of fungi are perfect candidates for the synthesis of metal nanoparticles due to the scalability and cost efficiency of fungal growth even on industrial scale. There are several methods and techniques that use fungi-originated fractions for synthesis of gold nanoparticles. However, there is less knowledge about the drawbacks and limitations of these techniques. Additionally, identification of components that play key roles in the synthesis is challenging. Here we show and compare the results of three different approaches for the synthesis of gold nanoparticles using either the extracellular fraction, the autolysate of the fungi or the intracellular fraction of 29 thermophilic fungi. We observed the formation of nanoparticles with different sizes (ranging between 6 nm and 40 nm) and size distributions (with standard deviations ranging between 30% and 70%) depending on the fungi strain and experimental conditions. We found by using ultracentrifugal filtration technique that the size of reducing agents is less than 3 kDa and the size of molecules that can efficiently stabilize nanoparticles is greater than 3 kDa.

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Green synthesis of gold nanoparticles by thermophilic filamentous fungi

Adsorption of SO2 and NO2 molecule on intrinsic and Pd-doped HfSe2 monolayer: A first-principles study

Searching for suitable materials for NO2 sensing has important scientific significance and application value. First-principles calculations have been performed on the adsorption of NO2 and its various interfering gases on the pristine C3N monolayer (p-C3N) and the B-doped C3N monolayer. The studies on the adsorption stability, geometric structure, charge transfer, and electronic structure indicate that the p-C3N is a promising room-temperature NO2 sensor, with high selectivity and sensitivity, and good reversibility. For the B-doped C3N monolayer, the calculated formation energies suggest that B doping into the C3N lattice is thermodynamically highly favorable. Furthermore, B doping by replacing the N atom in the C3N monolayer should can further improve the sensing selectivity and sensitivity of the C3N monolayer toward NO2. However, it is noted that a large adsorption energy for NO2 indicates that the B-doped C3N monolayer may be reversibly operated above the room temperature. The possible reason for the distinct adsorption behaviors of the various molecules is also provided. Our theoretical studies indicate the great potential of the C3N-based two-dimensional semiconductor as good NO2 gas sensors.

C3N monolayers as promising candidates for NO2 sensors

Gold-nanoparticle-based colorimetric array for detection of dopamine in urine and serum.

An in-situ reduction method has been reported to prepare gold nanoparticles (GNPs) of 40–110 nm by using the green reducing agents of proteins, which are activated by H2O2 and the superoxide anion (
 ). The protein of collagen turns HAuCl4 to the aqueous Au(I) ainions, which are further reduced by other proteins to be highly monodispersed and spherical GNPs of different sizes. The GNPs reduced by different proteins are found to be with the exposed {100} facets, the distinctive UV-vis absorption spectra and various colors (See Fig. 1). By means of extracting the color responses, such as red, green and blue (RGB) alterations, an in-situ reduction method-based multidimensional sensing platform is fabricated in the process of GNPs synthesis. Without further modification of GNPs, nine common proteins are found to be well detected and discriminated at different concentrations. Moreover, this sensing platform also demonstrates great potentials in qualitative and semiquantitative analysis on the individuals of these proteins with high sensitivity. Furthermore, the validation of this multidimensional sensing platform has been carried out by analysis on the spiked proteins in human urine and the target proteins in complex matrix (e.g. lysozyme in human tear).

Protein-directed synthesis of highly monodispersed, spherical gold nanoparticles and their applications in multidimensional sensing

InGaAs/InP-modified uni-traveling carrier photodiodes with cliff layer were designed and fabricated for V-band (50-75 GHz) applications. The devices were flip-chip bonded on AlN submounts for efficient heat dissipation. A high-impedance transmission line was designed to compensate for the parasitic capacitance and enhance the bandwidth. Devices with 3-dB bandwidths of 50 and 65 GHz demonstrated high-output RF power of 20.3 and 15.9 dBm, respectively.

High-Power V-Band InGaAs/InP Photodiodes

In this study, the interaction between gas molecules, including H2O, N2, CO, NO, NO2 and N2O, and a WSe2 monolayer containing an Se vacancy (denoted as VSe) has been theoretically studied. Theoretical results show that H2O and N2 molecules are highly prone to be physisorbed on the VSe surface. The presence of the Se vacancy can significantly enhance the sensing ability of the WSe2 monolayer toward H2O and N2 molecules. In contrast, CO and NO molecules highly prefer to be molecularly chemisorbed on the VSe surface with the non-oxygen atom occupying the Se vacancy site. Furthermore, the exposed O atoms of the molecularly chemisorbed CO or NO can react with additional CO or NO molecules, to produce C-doped or N-doped WSe2 monolayers. The calculated energies suggest that the filling of the CO or NO molecule and the removal of the exposed O atom are both energetically and dynamically favorable. Electronic structure calculations show that the WSe2 monolayers are p-doped by the CO and NO molecules, as well as the C and N atoms. However, only the NO molecule and N atom doped WSe2 monolayers exhibit significantly improved electronic structures compared with VSe. The NO2 and N2O molecules will dissociate directly to form an O-doped WSe2 monolayer, for which the defect levels due to the Se vacancy can be completely removed. The calculated energies suggest that although the dissociation processes for NO2 and N2O molecules are highly exothermic, the N2O dissociation may need to operate at an elevated temperature compared with room temperature, due to its large energy barrier of ∼1 eV.

Zhiwen Lu

Papers

C3N monolayers as promising candidates for NO2 sensors

Gold-nanoparticle-based colorimetric array for detection of dopamine in urine and serum.

Protein-directed synthesis of highly monodispersed, spherical gold nanoparticles and their applications in multidimensional sensing

High-Power V-Band InGaAs/InP Photodiodes

Interaction between H2O, N2, CO, NO, NO2 and N2O molecules and a defective WSe2 monolayer