Photoactive Semiconductor Research Articles

A High‐Detectivity, Fast‐Response, and Radiation‐Resistant TiN/CdZnTe Heterojunction Photodiode

AbstractA novel high‐performance ultraviolet–visible–near‐infrared (300–820 nm) heterojunction photodiode based on radiation‐resistant semiconductor materials is proposed. A titanium nitride (TiN) “window” layer is deposited via magnetron sputtering onto a cadmium zinc telluride (CdZnTe) solid solution single crystal. The TiN/CdZnTe heterojunction photodiodes concurrently reveal an outstanding detectivity, response time, and linear dynamic range outperforming similar heterojunction photodiodes and photodetectors, based on photoactive inorganic compound semiconductor materials. Moreover, the added feature of the proposed heterojunction photodiodes is their excellent radiation resistance, experimentally demonstrated under short impulse proton irradiation (170 keV) with an accumulated fluence of 2 × 1012 proton cm−2. This unusual synergy of high performance and advanced radiation resistance of the TiN/CdZnTe photodiodes provides a unique platform for operation in space or radioactively contaminated environments.

(Invited) Crystal Engineering of Bismuth Vanadate for Enhanced Light-Driven Water Oxidation

Photocatalytic and photoelectrochemical processes employing photoactive semiconductors are two key systems in harvesting sunlight for energy and environmental applications. Strategies have been formulated to improve the properties of the semiconductor for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Understanding of the underlying mechanism for the photoexcited charge transportation in relation to their photoactivities is of fundamental importance for rational design of high-performing photoactive materials, which may serve as a useful guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuels generation. Many photoactive semiconductors, including bismuth vanadate, are having inadequate charge transport properties such as low charge mobility, short lifetime, and slow surface kinetics. Standalone single photoactive semiconductors also faces the challenge of meeting the needs for large redox potentials with a sufficiently narrow bandgap for visible light absorption. Coupling two or more components into a photoactive composite may address some of these drawbacks by utilizing the strengths of the individual semiconductors. In this presentation, the charge transportation behavior of single component photoactive semiconductor based on bismuth vanadate, and the composite materials forming heterojunction with bismuth vanadate, will be examined and discussed (example of modulation of BiVO4 photocatalyst in Figure 1 ).1 Typically, crystal facet engineering, interfacing with non-photoactive secondary component, and narrowing the crystal size into quantum-confinement region, will be the three strategies to be shared with audience during the presentation. Preferential charge migration depending on the crystal facet has been reported in various photocatalysts. These promoted charge migration can be further boosted with spatially deposited cocatalysts on the selective redox sites. The manipulation of crystal facet allows the controlled electron transfer to induce 4-electron process (oxygen evolution) or 2-electron process (hydrogen peroxide evolution) in water oxidation. Nanosizing the bismuth vanadate into <10 nm region with distinctive yet interconnected crystal domains leads to the expansion of band structure. Conduction band of bismuth vanadate was expanded to energetic level capable of reducing proton into H2. The traditional O2-evolving bismuth vanadate is now demonstrating H2-producing properties. Figure 1: Time-resolved microwave conductivity (TRMC) spectroscopy signals measured for BiVO4 and its Power-law decay fittings.Reference1. H. Wu, R. Irani, K. Zhang, L. Jing, H. Dai, H. Y. Chung, F. F. Abdi, Y. H. Ng*, Unveiling Carrier Dynamics in Periodic Porous BiVO4 Photocatalyst for Enhanced Solar Water Splitting. ACS Energy Lett. 2021, 6, 3400-3407. Figure 1

Coupled Electromagnetic and Hydrodynamic Semiconductor Modeling for Terahertz Generation

Terahertz (THz) electrical signal generation from a photoactive semiconductor device illuminated by an optical pulse is modeled and simulated. Hydrodynamic equations in time domain are numerically solved for both electrons and holes using the discontinuous Galerkin time-domain finite element method (DGTD-FEM) for the high-frequency charge transport that occurs in the semiconductor device. The obtained frequency spectra of photocurrent in various semiconductor materials under illumination of an ultrashort light pulse are presented. The inertia effects and ballistic transport of carriers play an important role to determine the frequency response of these materials, and the developed hydrodynamic model (HDM) solver delivers a transport analysis by predicting higher and wideband frequency capabilities for GaAs and Ge detectors over Si-photodetectors.

Nanostructured Electrodes Based on Two-Dimensional SnO2 for Photoelectrochemical Water Splitting

Here we demonstrate the fabrication of two-dimensional SnO2 nanosheet arrays and their use as electrodes for solar water oxidation. These nanosheets deposited on commercial transparent electrodes are used as substrates for the deposition of photoactive semiconductors including BiVO4 and Fe2O3. These composite photoanodes show a marked enhancement in their photoelectrochemical (PEC) performance, including improved light absorption, lower onset potentials, and higher photocurrents. Importantly, SnO2 nanosheets alone have negligible PEC activity, suggesting that their role is purely morphological (enhanced surface area) and electronic (surface passivation, improved charge extraction). Our results provide the foundation for further work on photoanode architectures for efficient water splitting.

Concentrate and degrade PFOA with a photo-regenerable composite of In-doped TNTs@AC

“Concentrate-and-degrade” is an effective strategy to promote mass transfer and degradation of pollutants in photocatalytic systems, yet suitable and cost-effective photocatalysts are required to practice the new concept. In this study, we doped a post-transition metal of Indium (In) on a novel composite adsorptive photocatalyst, activated carbon-supported titanate nanotubes (TNTs@AC), to effectively degrade perfluorooctanoic acid (PFOA). In/TNTs@AC exhibited both excellent PFOA adsorption (>99% in 30 min) and photodegradation (>99% in 4 h) under optimal conditions (25 °C, pH 7, 1 atm, 1 g/L catalyst, 0.1 mg/L PFOA, 254 nm). The heterojunction structure of the composite facilitated a cooperative adsorption mode of PFOA, i.e., binding of the carboxylic head group of PFOA to the metal oxide and attachment of the hydrophobic tail to AC. The resulting side-on adsorption mode facilitates the electron (e‒) transfer from the carboxylic head to the photogenerated hole (h+), which was the major oxidant verified by scavenger tests. Furthermore, the presence of In enables direct electron transfer and facilitates the subsequent stepwise defluorination. Finally, In/TNTs@AC was amenable to repeated uses in four consecutive adsorption-photodegradation runs. The findings showed that adsorptive photocatalysts can be prepared by hybridization of carbon and photoactive semiconductors and the enabled “concentrate-and-degrade” strategy is promising for the removal and degradation of trace levels of PFOA from polluted waters.

Enhancing the Photoelectrochemical Hydrogen Evolution Reaction through Nanoscrolling of Two-Dimensional Material Heterojunctions.

The clean production of hydrogen from water using sunlight has emerged as a sustainable alternative toward large-scale energy generation and storage. However, designing photoactive semiconductors that are suitable for both light harvesting and water splitting is a pivotal challenge. Atomically thin transition metal dichalcogenides (TMD) are considered as promising photocatalysts because of their wide range of available electronic properties and compositional variability. However, trade-offs between carrier transport efficiency, light absorption, and electrochemical reactivity have limited their prospects. We here combine two approaches that synergistically enhance the efficiency of photocarrier generation and electrocatalytic efficiency of two-dimensional (2D) TMDs. The arrangement of monolayer WS2 and MoS2 into a heterojunction and subsequent nanostructuring into a nanoscroll (NS) yields significant modifications of fundamental properties from its constituents. Spectroscopic characterization and ab initio simulation demonstrate the beneficial effects of straining and wall interactions on the band structure of such a heterojunction-NS that enhance the electrochemical reaction rate by an order of magnitude compared to planar heterojunctions. Phototrapping in this NS further increases the light-matter interaction and yields superior photocatalytic performance compared to previously reported 2D material catalysts and is comparable to noble-metal catalyst systems in the photoelectrochemical hydrogen evolution reaction (PEC-HER) process. Our approach highlights the potential of morphologically varied TMD-based catalysts for PEC-HER.

Photoelectrochemical and electrochemical urea oxidation with microwave-assisted synthesized Co-Fe2O3@NiO core–shell nanocomposites

This work reported the electrochemical and photoelectrochemical (PEC) properties of a new photoelectrode based on hematite Co-Fe2O3@NiO, a photoactive semiconductor, was prepared using a process involving a combination of the co-precipitation and microwave-assisted synthesis of Fe2O3, Co-Fe2O3 and Co-Fe2O3@NiO, respectively. The obtained products were characterized by X-Ray powder Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive X-ray analysis (EDX), Ultraviolet–Visible (UV–vis) analysis, Fourier Transform Infrared spectroscopy (FT-IR). X-ray diffraction (XRD) pattern of the sample determined the crystal structure of α-Fe2O3 nanoparticles. The SEM image shows spherical nanoparticles. FTIR spectrospy spectrum confirmed the phase purity and chemical bond for the sample. Optical studies show a variation of band gap from 2.118 to 2.07 eV. The electrochemical and photoelectrochemical (PEC) performance of the films were examined by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The electrochemical oxidation of water achieved by Cobalt-doped Fe2O3@GCE modified electrode exhibited the current density of 21 mA/g at 0.5 V vs. SCE for 5 at% of Co and reveals enhanced specific capacitance of 352.11 F/g. The catalytic performance of urea oxidation was measured by cyclic voltammetry on Co-Fe2O3@NiO nanoparticles modified glassy carbon electrode (GCE) in alkaline medium. The electrode Co-Fe2O3@NiO without annealing showed a peak current density of 1.59 mA/cm2 at 0.1 M urea in 1.0 M NaOH, which was 3.6 fold higher than that of Co-Fe2O3@NiO with annealing. In another part, this work reported the photoelectrochemical (PEC) properties of photoanode prepared by spin coating. The highest photocurrent 0.042 mA/cm2 at 0.5 V Vs SCE was obtained for 5% Co-Fe2O3@NiO while the photocatalytic oxidation of urea.

Multidimensional engineered metasurface for ultrafast terahertz switching at frequency-agile channels

Abstract The ability to actively manipulate free-space optical signals by using tunable metasurfaces is extremely appealing for many device applications. However, integrating photoactive semiconductors into terahertz metamaterials still suffers from a limited functionality. The ultrafast switching in picosecond timescale can only be operated at a single frequency channel. In the hybrid metasurface proposed here, we experimentally demonstrate a dual-optically tunable metaphotonic device for ultrafast terahertz switching at frequency-agile channels. Picosecond ultrafast photoswitching with a 100% modulation depth is realized at a controllable operational frequency of either 0.55 THz or 0.86 THz. The broadband frequency agility and ultrafast amplitude modulation are independently controlled by continuous wave light and femtosecond laser pulse, respectively. The frequency-selective, temporally tunable, and multidimensionally-driven features can empower active metamaterials in advanced multiplexing of information, dual-channel wireless communication, and several other related fields.

Terahertz Reconfigurable Intelligent Surfaces (RISs) for 6G Communication Links.

The forthcoming sixth generation (6G) communication network is envisioned to provide ultra-fast data transmission and ubiquitous wireless connectivity. The terahertz (THz) spectrum, with higher frequency and wider bandwidth, offers great potential for 6G wireless technologies. However, the THz links suffers from high loss and line-of-sight connectivity. To overcome these challenges, a cost-effective method to dynamically optimize the transmission path using reconfigurable intelligent surfaces (RISs) is widely proposed. RIS is constructed by embedding active elements into passive metasurfaces, which is an artificially designed periodic structure. However, the active elements (e.g., PIN diodes) used for 5G RIS are impractical for 6G RIS due to the cutoff frequency limitation and higher loss at THz frequencies. As such, various tuning elements have been explored to fill this THz gap between radio waves and infrared light. The focus of this review is on THz RISs with the potential to assist 6G communication functionalities including pixel-level amplitude modulation and dynamic beam manipulation. By reviewing a wide range of tuning mechanisms, including electronic approaches (complementary metal-oxide-semiconductor (CMOS) transistors, Schottky diodes, high electron mobility transistors (HEMTs), and graphene), optical approaches (photoactive semiconductor materials), phase-change materials (vanadium dioxide, chalcogenides, and liquid crystals), as well as microelectromechanical systems (MEMS), this review summarizes recent developments in THz RISs in support of 6G communication links and discusses future research directions in this field.

A “green” all-organic heterostructure functionalized by self-assembled fullerene small molecule with enhanced photocatalytic activity

Photocatalysis has been reported as a potential water purification technology for combating the pathogenic bacteria and degrading the hazardous chemicals. The photoactive organic semiconductors as the emerging class of an alternative to the traditional developed inorganic semiconductors are being widely pursued due to their tunable structures and low toxicity. Herein, the all-organic [6,6]-phenyl C71 butyric acid methyl ester (PC71BM)/g-C3N4 heterostructure have been created by introducing self-assembled n-type fullerene small molecule to the g-C3N4 surface in situ. The absorption edge of the heterostructures with PC71BM as the photosensitizer extend from 450 to 650 nm. Moreover, the charge separation and transfer efficiencies of the photocatalysts are greatly promoted even with 1.0% amount of PC71BM because of its low reorganization energy and high reduction potential. All of these superiorities endow the heterostructures with over 99.7% antibacterial rates toward E. coli and S. aureus and excellent performance against their biofilms after irradiation for 135 and 180 min, respectively. Additionally, the heterostructures achieve excellent photocatalytic degradation ability for Rhodamine B and tetracycline. Importantly, the in vitro experiments reveal that the as-prepared heterostructures possess satisfactory biocompatibility and their toxicity is negligible. This study provides a new perspective for designing ecofriendly all-organic heterostructures with high photocatalytic activity.

Multidimensional Tungsten Oxides for Efficient Solar Energy Conversion

Dimensionalities of materials have more profound connotations than barely the external morphologies. The mechanical, optical, electrical, and magnetic properties of a certain material can be significantly influenced by the spatial degrees of freedom of interactions/excitons. Herein, how multidimensionalities affect their physicochemical properties from the perspective of photoactive tungsten oxide (WO3) materials, which further influence their performances in solar energy conversion applications are looked at. Benefiting from the fruitful research efforts on WO3‐based photocatalysts and photoelectrodes, the key procedures in photoenergy conversion including light absorption, charge separation, and surface reaction, are discussed to elucidate the unique features, advantages, and challenges of the single‐dimensional WO3 heterostructures. Then the optoelectronic properties and performance of mixed‐dimensional WO3 heterostructures are investigated to show the synergistic effect between the specifically combined dimensionalities. The dynamic behaviors of excitons or charge carriers within the mixed‐dimensional structures and at their interfaces are inspected, with several photophysical or chemical phenomena noted for designing other photoactive metal oxide semiconductors. A bumper harvest of WO3 photovoltaics, photocatalysts, and photoelectrodes beyond dimensionality is on the way, hence, it is an opportune chance to evaluate the progress and foresee future directions in this fast‐moving research field.

ZnO Quantum Dot/MXene Nanoflake Hybrids for Ultraviolet Photodetectors

Efficacious utility of fugacious photons within a limited dimension of photoactive semiconductor thin films provides a facile approach to break through the obstacle for the sensitivity improvement of photodetection. Herein, we demonstrate a facile way to fabricate ZnO quantum dot (QD)/MXene nanoflake photodetectors by uniformly blending various ratios of two-dimensional (2D) Ti3C2Tx nanoflakes into ZnO QD thin films, which can establish a carrier transportation highway and light confinement centers within the photoactive layers. The light absorption of hybrid thin films is obviously enhanced because of the localized surface plasmon resonance effect of MXene nanoflakes, resulting in an expressively enhanced external quantum efficiency by 35 times for the device with 0.1 mg/mL 2D Ti3C2Tx nanoflakes (150.0%) in comparison with that of the pristine photodetector (4.3%). Under 350 nm light illumination (1.72 mW cm–2), the carrier transportation in ZnO thin films is significantly accelerated with the hot electron injection from the high-conductivity 2D Ti3C2Tx nanoflakes and thereby the optimal responsivity of 425 mA/W with an improved response speed at 10 V. Furthermore, ZnO QD/MXene nanoflake photodetectors also exhibit an excellent long-term stability. This work provides an efficient method to fabricate high-performance ZnO UV photoelectric devices in the military and civilian fields at low light intensities.

Photo-assisted self-assembly synthesis of all 2D-layered heterojunction photocatalysts with long-range spatial separation of charge-carriers toward photocatalytic redox reactions

Constructing heterojunction photocatalysts has been proven as an ingenious tactic to adjust the lifetimes of the higher redox-active charge-carriers toward highly-efficient photocatalytic applications. Numerous recent efforts focused on the short-range spatial separation of charge-carriers in the heterojunction photocatalysts. However, engineering a long-range transfer channel in the well-designed heterojunction photocatalyst to further spatially separate the charge-carriers is still a huge challenge. In this contribution, we developed a facile photo-assisted self-assembly strategy to synthesize the all 2D-layered heterojunction photocatalysts of SnS2/RGO/g-C3N4 nanosheets (NSs). During the synthesis process, the precursor of 2D graphene-oxide (GO) NSs was converted into the reduced GO (RGO) NSs by the photoactive semiconductors of 2D SnS2 and g-C3N4 NSs. Meanwhile, the above two 2D semiconductors were simultaneously anchored onto the surface of the RGO NSs. Upon visible-light irradiation of the synthesized SnS2/RGO/g-C3N4 NSs, the 2D RGO component could provide a broad electron-transfer surface for the long-range spatial-separation of charge-carriers in the semiconductor components of the NSs. Thus, this all 2D-layered heterojunction photocatalyst exhibited ∼ 9.2 and ∼ 4.6-fold enhancement on the photocatalytic oxidation degradation of the organic dye, and ∼ 68 and ∼ 3.4-fold enhancement on photocatalytic protons reduction as compared to the pure SnS2 and g-C3N4 NSs, respectively.

Cuprous oxide coated silver/graphitic carbon nitride/cadmium sulfide nanocomposite heterostructure: Specific recognition of carcinoembryonic antigen through sandwich-type mechanism

The development of the effective diagnostic method for the determination of cancer biomarkers is one of the most promising strategies for early clinical diagnosis of cancer. Here, based on the preparation of heterogeneous cuprous oxide coated silver (Ag@Cu2O) nanocomposites/graphitic carbon nitride (g-C3N4)/cadmium sulfide (CdS) nanoarrays structure, a highly sensitive photoelectrochemical (PEC) biosensor for the examination of carcinoembryonic antigen (CEA) has been constructed successfully. The combination of photoactive semiconductor materials g-C3N4 and CdS increases the electron transfer rate between them and enhances their photocurrent response, thus greatly increasing the concentration detection range. At the same time, the specific recognition between antigen and antibody is used to form a sandwich structure secondary antibody (Ab2)/CEA/antibody (Ab1). And because Ag@Cu2O has the function of absorbing light and consuming electron donor. Therefore, the successful measurement of CEA was achieved by labeling Ag@Cu2O on Ab2 and finally immobilizing it on the sensor to correlate the current reduction with the CEA concentration. The sandwich PEC biosensor proposed by this signal amplification strategy under optimal conditions has good analytical performance for CEA, with a wide linear detection range (from 10-5 to 1 ng/mL) and a low detection limit of 0.0011 pg/mL. The PEC biosensor constructed by this method showed high sensitivity, excellent anti-interference ability, favourable repeatability, and good stability.

Epitaxial III-V/Si Vertical Heterostructures with Hybrid 2D-Semimetal/Semiconductor Ambipolar and Photoactive Properties.

Hybrid materials taking advantage of the different physical properties of materials are highly attractive for numerous applications in today's science and technology. Here, it is demonstrated that epitaxial bi‐domain III–V/Si are hybrid structures, composed of bulk photo‐active semiconductors with 2D topological semi‐metallic vertical inclusions, endowed with ambipolar properties. By combining structural, transport, and photoelectrochemical characterizations with first‐principle calculations, it is shown that the bi‐domain III–V/Si materials are able within the same layer to absorb light efficiently, separate laterally the photo‐generated carriers, transfer them to semimetal singularities, and ease extraction of both electrons and holes vertically, leading to efficient carrier collection. Besides, the original topological properties of the 2D semi‐metallic inclusions are also discussed. This comb‐like heterostructure not only merges the superior optical properties of semiconductors with good transport properties of metallic materials, but also combines the high efficiency and tunability afforded by III–V inorganic bulk materials with the flexible management of nano‐scale charge carriers usually offered by blends of organic materials. Physical properties of these novel hybrid heterostructures can be of great interest for energy harvesting, photonic, electronic or computing devices.

Enhanced visible-light photocatalytic bacterial inhibition using recyclable magnetic heterogeneous nanocomposites (Fe3O4@SiO2@Ag2WO4@Ag2S) in core/shell structure

In this work, a novel core/shell heterogeneous nanocomposite photocatalyst (Fe3O4@SiO2@ Ag2WO4@Ag2S) was prepared using multistep methods. Several characterization techniques were conducted to analyze the synthesized core/shell magnetic nanocomposites, such as XRD, FE-SEM, TEM, UV-DRS, and VSM. The photocatalytic bacterial inactivation activity of synthesized photocatalysts (Fe3O4@SiO2@Ag2WO4, Fe3O4@SiO2@Ag2S, Fe3O4@SiO2@Ag2WO4@Ag2S, Ag2WO4, Ag2S) was investigated against Escherichia coli (E. coli) bacterium under a visible light source. The synthesized Fe3O4@SiO2@Ag2WO4@Ag2S showed enhanced photocatalytic inactivation activity (approximately 9.5-log reduction) after 105 min of irradiation time. This result is attributed to increasing the photo-generated electron-hole separation by forming a heterojunction between the two photoactive semiconductors (Ag2WO4 and Ag2S) in one system. The kinetic studies revealed that the Fe3O4@SiO2@Ag2WO4@Ag2S exhibited the best E. coli inactivation activity with a constant rate value (kapp/min−1) of 0.07393 min−1, which is 1.4 and 1.7 times greater than that of pure Ag2S and Ag2WO4, respectively. The effects of different parameters on the photocatalytic microbial inactivation were examined, such as initial microbial concentration, catalyst dose, and pH of the solution. The scavenger studies confirmed the important roles of reactive species (H2O2, •O2–, h+) in the photocatalytic reaction. The photocatalytic mechanism of Fe3O4@SiO2@Ag2WO4@Ag2S was well explained by p-n heterojunction based on DRS analysis and scavenger experiments of reactive species. The stability and recyclability studies proved that the Fe3O4@SiO2@Ag2WO4@Ag2S sample is highly stable and easy to separate by the external magnet, which can be used many times as antibacterial agents without significant losses in their photocatalytic activity.

Near‐Infrared Photoactive Semiconductor Quantum Dots for Solar Cells

AbstractSemiconductor quantum dots (QDs) are nanocrystals whose excitons are bound in 3D space. Owning to their remarkable quantum confinement effect, QDs exhibit a discontinuous electronic energy level structure similar to that of atoms, leading to novel physical, optical, and electrical properties for various optoelectronic device applications including solar cells. Near‐infrared photoactive narrow bandgap (NBG) QDs can maximize the use of solar energy through the quantum size effect, offering a good opportunity for designing highly efficient wide‐spectrum responsive solar cells. This review analyzes the recent research progress of NBG QDs as light absorbing materials in solar cells. The critical elaboration of the latest achievements both in material design and device optimization for NBG QD‐based solar cells (QDSCs), including QD synthesis and film fabrication, design of device configuration, classification of NBG QDs and their photovoltaic performance, strategies for performance improvements is focused upon. The current challenges and perspectives for the further advance of NBG QDSCs are also discussed.

Construction of a dual-functional CuO/BiOCl heterojunction for high-efficiently photoelectrochemical biosensing and photoelectrocatalytic degradation of aflatoxin B1

Aflatoxin B1 (AFB1) exposure often causes serious food safety problems and illnesses in humans and animals even at extremely low content. Therefore, ultrasensitive detection and effective degradation of AFB1 is vitally significant. Photoelectrochemical (PEC) approach has been widely applied in sensing and catalysis fields. For achieving robust PEC performance, exploring highly photoactive semiconductor materials is critical. Herein, we constructed a novel and dual-functional copper oxide/bismuth oxychloride (CuO/BiOCl) composite by in-situ growth of CuO on BiOCl surface. The photo-absorption region of CuO/BiOCl was efficaciously broadened from UV to visible range, making for enhanced light harvest. Meanwhile, the p-n heterostructure in CuO/BiOCl clarified that the formed built-in internal electric field could accelerate band-band transfer of carriers. Driven by this, PEC response of CuO/BiOCl was greatly boosted comparing with that of pure CuO or BiOCl. Further combing with the specific aptamer, a favorable CuO/BiOCl-based PEC biosensor was fabricated for AFB1 detection with ultra-sensitivity (detection limit of 0.07 pg mL−1) and satisfactory recoveries (96.4% ∼ 105.7%) in real maize samples. Subsequently, under light irradiation and suitable bias voltage, a degradation rate of ∼81.3% was facilely attained for 5.0 µg mL−1 AFB1, indicating excellent photoelectrocatalytic activity of CuO/BiOCl material. The catalytic mechanism and the main product of AFB1 degradation were analyzed. Taken together, the heterostructured CuO/BiOCl-based PEC assay provides a potential way for monitoring and controlling the AFB1 contamination in the food security areas.

Signal-off photoelectrochemical aptasensor for kanamycin: Strand displacement reaction combines p-n competition

A“signal-off” photoelectrochemical aptasensor based on p-n type semiconductor competitive quenching effect and strand displacement reaction was constructed for the determination of kanamycin. Au NPs@MgIn2S4-graphene composite was used as n-type photoactive semiconductor material. In the presence of the kanamycin, strand displacement reaction was triggered and the p-type CuInS2 quantum dots labeled aptamer was introduced on the Au NPs@MgIn2S4-graphene surface. The CuInS2 quantum dots can competitive consume the electron donors (AA) and light energy of the PEC system, thus quenched the anodic photocurrent of Au NPs@MgIn2S4-graphene. The photocurrent decreased with the increase of kanamycin concentration. The linear range of kanamycin was 1.0 pM–10 μM, and the detection limit was 1.7 pM. In addition, the method can be used for the determination of kanamycin in milk and honey.

Integrated Tapping Mode Kelvin Probe Force Microscopy with Photoinduced Force Microscopy for Correlative Chemical and Surface Potential Mapping.

Kelvin probe force microscopy (KPFM) is a popular technique for mapping the surface potential at the nanoscale through measurement of the Coulombic force between an atomic force microscopy (AFM) tip and sample. The lateral resolution of conventional KPFM variants is limited to between ≈35 and 100nm in ambient conditions due to the long-range nature of the Coulombic force. In this article, a novel way of generating the Coulombic force in tapping mode KPFM without the need for an external AC driving voltage is presented. A field-effect transistor (FET) is used to directly switch the electrical connectivity of the tip and sample on and off periodically. The resulting Coulomb force induced by Fermi level alignment of the tip and sample results in a detectable change of the cantilever oscillation at the FET-switching frequency. The resulting FET-switched KPFM delivers a spatial resolution of ≈25nm and inherits the high operational speed of the AFM tapping mode. Moreover, the FET-switched KPFM is integrated with photoinduced force microscopy (PiFM), enabling simultaneous acquisitions of high spatial resolution chemical distributions and surface potential maps. The integrated FET-switched KPFM with PiFM is expected to facilitate characterizations of nanoscale electrical properties of photoactive materials, semiconductors, and ferroelectric materials.