Change In Photocurrent Research Articles

Blue-light photoelectrochemical aptasensor for kanamycin based on synergistic strategy by Schottky junction and sensitization

The sensitive, selective, and accurate analysis of kanamycin (KAN), a common aminoglycoside antibiotic, is vital to ensure human health and food safety. Here, a well-designed photoelectrochemical (PEC) KAN aptasensor was proposed based on the synergistic strategy by Schottky junction and sensitization. A Schottky junction of CuO/Pd nanocomposite was used as a PEC substrate to immobilize an aptamer. The Schottky barrier not only provided an electron-transfer irreversible passage from CuO to Pd shell but also generated a local surface plasmon resonance between CuO and Pd shell, thus improving the efficient charge separation and light absorption. Complementary-DNA-functionalized CdS quantum dots (CdS QDs) were introduced onto the surface of CuO/Pd via hybridization of the target aptamer to improve the response of the PEC aptasensor further. When CdS was close to Pd shell, the Fermi energy level of CdS was readjusted under the action of the sensitization. The photogenerated hot electrons on the conduction band of CdS were transferred into Pd by a powerful interfacial electric field. Upon blue-light irradiation, the change of photocurrent depended upon the amount of stored negative charge on the surface of the Pd shell and stored positive charge on the valence band of CdS before and after incubation with KAN. Using the photocurrent change as a response signal for the quantitative detection of KAN, the PEC aptasensor exhibited a low detection limit of 20 pM with a wide linear range of 0.1–500 nM. Thus, the developed PEC aptasensor has great potential for applications in various fields.

Giant Photogalvanic effect in Janus monolayer In2SSe

Linear and circular photogalvanic effects (PGEs) in Janus monolayer In2SSe are investigated by non-equilibrium Green’s function technique and combined density functional theory. Janus monolayer In2SSe is a two-dimensional material having Cs symmetry with a reflective surface normal to the orientations of armchair and zigzag., In both the zigzag and armchair directions, linear and circular photogalvanic effects are induced by this symmetry. Our numerical results show that different from monolayer black phosphorus and antimonene, Janus monolayer In2SSe can generate a large photocurrent when the bandgap energy is surpassed by photon energy in the absence of external bias voltage. The photocurrent changes in perfect cosine form with the polarization angle, which can be attributed to the second-order response of polarized light electric field. There is obvious anisotropy in the zigzag and armchair directions. Under the condition of zero bias voltage, the photocurrent in the armchair direction is more robust, which is 15 times higher than that in the zigzag. All the results indicate that Janus monolayer In2SSe is a more suitable alternate material for solar cells in the range of visible light.

Manipulation of hot electron flow on plasmonic nanodiodes fabricated by nanosphere lithography

Energy conversion to generate hot electrons through the excitation of localized surface plasmon resonance (LSPR) in metallic nanostructures is an emerging strategy in photovoltaics and photocatalytic devices. Important factors for surface plasmon and hot electron generation are the size, shape, and materials of plasmonic metal nanostructures, which affect LSPR excitation, absorbance, and hot electron collection. Here, we fabricated the ordered structure of metal-semiconductor plasmonic nanodiodes using nanosphere lithography and reactive ion etching. Two types of hole-shaped plasmonic nanostructures with the hole diameter of 280 and 115 nm were fabricated on Au/TiO2 Schottky diodes. We show that hot electron flow can be manipulated by changing the size of plasmonic nanostructures on the Schottky diode. We show that the short-circuit photocurrent changes and the incident photon-to-electron conversion efficiency results exhibit the peak shift depending on the structures. These phenomena are explicitly observed with finite difference time domain simulations. The capability of tuning the morphology of plasmonic nanostructure on the Schottky diode can give rise to new possibilities in controlling hot electron generation and developing novel hot-electron-based energy conversion devices.

The Highly Uniform Photoresponsivity from Visible to Near IR Light in Sb2Te3 Flakes.

Broadband photosensors have been widely studied in various kinds of materials. Experimental results have revealed strong wavelength-dependent photoresponses in all previous reports. This limits the potential application of broadband photosensors. Therefore, finding a wavelength-insensitive photosensor is imperative in this application. Photocurrent measurements were performed in Sb2Te3 flakes at various wavelengths ranging from visible to near IR light. The measured photocurrent change was insensitive to wavelengths from 300 to 1000 nm. The observed wavelength response deviation was lower than that in all previous reports. Our results show that the corresponding energies of these photocurrent peaks are consistent with the energy difference of the density of state peaks between conduction and valence bands. This suggests that the observed photocurrent originates from these band structure peak transitions under light illumination. Contrary to the most common explanation that observed broadband photocurrent carrier is mainly from the surface state in low-dimensional materials, our experimental result suggests that bulk state band structure is the main source of the observed photocurrent and dominates the broadband photocurrent.

Colossal switchable photocurrents in topological Janus transition metal dichalcogenides

Nonlinear optical properties, such as bulk photovoltaic effects, possess great potential in energy harvesting, photodetection, rectification, etc. To enable efficient light–current conversion, materials with strong photo-responsivity are highly desirable. In this work, we predict that monolayer Janus transition metal dichalcogenides (JTMDs) in the 1T′ phase possess colossal nonlinear photoconductivity owing to their topological band mixing, strong inversion symmetry breaking, and small electronic bandgap. 1T′ JTMDs have inverted bandgaps on the order of 10 meV and are exceptionally responsive to light in the terahertz (THz) range. By first-principles calculations, we reveal that 1T′ JTMDs possess shift current (SC) conductivity as large as 2300 nm μA V−2, equivalent to a photo-responsivity of 2800 mA/W. The circular current (CC) conductivity of 1T′ JTMDs is as large as ∼104 nm μA V−2. These remarkable photo-responsivities indicate that the 1T′ JTMDs can serve as efficient photodetectors in the THz range. We also find that external stimuli such as the in-plane strain and out-of-plane electric field can induce topological phase transitions in 1T′ JTMDs and that the SC can abruptly flip their directions. The abrupt change of the nonlinear photocurrent can be used to characterize the topological transition and has potential applications in 2D optomechanics and nonlinear optoelectronics.

Integration of Fe3O4 nanospheres and micropyramidal textured silicon wafer with improved photoelectrochemical performance

Silicon (Si)-based composites have attracted extensive attention for photoelectrochemical (PEC) application. Herein, micropyramidal textured Si wafer was constructed by wet chemical etching method. Hydrothermally synthesized Fe3O4 nanospheres were further deposited on the micropyramids by a simple dip-coating approach. The integrated Fe3O4 nanospheres and Si micropyramids (denoted as Fe3O4@SiMPs) revealed 20 times of higher PEC efficiency than planar Si wafer, without obvious photocurrent decay and crystalline structure change during chronoamperometry test. The greatly enhanced PEC performance of Fe3O4@SiMPs is largely attributed to the seamless integration of Si micropyramids and Fe3O4 nanospheres. The micropyramidal textured structure can enhance light absorption by reducing the surface reflectance and enhancing the light trapping effect. The micropyramids and Fe3O4 nanospheres on the surface of planar Si wafer offer more specific surface area for the contact of electrode with electrolyte. The Fe3O4 nanospheres not only protect the micropyramids from corrosion, but also accelerate the PEC kinetics by promoting charge transfer between the electrode and the electrolyte. This study can inspire the optimal design of Si wafer-based nanocomposites as efficient PEC catalysts for overall water splitting.

High-resolution additive direct writing of metal micro/nanostructures by electrohydrodynamic jet printing

Patterned conductive structures have attracted significant attention as important components of printed and flexible micro/nanodevices. However, the fabrication of conductive micro/nanostructures with controlled and well-organized morphologies is a key challenge in the development and application of micro/nanoelectronic devices based on low-dimensional materials. To meet the requirements of depositing conductive structures on specific substrates, electrohydrodynamic jet (E-jet) printing, developed as a simple and effective method for fabricating micro/nanopatterns of polymers, was combined with a conventional wet metal etching process for patterning conductive metals on polymer substrates. Under optimized experimental conditions, we achieved fine straight-line patterns with a line spacing of 1 μm at a nanoscale printing resolution (average line width: 68 nm) and grid patterns with variable spacings and grid line widths, down to size of 871 nm. Furthermore, fully printed graphene photodetectors were obtained through in situ direct writing, and their photoelectric response to a change in photocurrent of 0.22 μA was demonstrated. The results suggest that combining E-jet printing with chemical etching is a promising mask-free approach for producing conductive metal patterns for micro/nanoelectronic devices.

Well-ordered polystyrene colloidal spheres for light addressable potentiometric sensor

Light addressable potentiometric sensor (LAPS) is a flexible addressable potential sensor with many advantages including simple structure, high sensitivity, low manufacturing cost and light addressability. It can help us to achieve a high performance and low cost of LAPS to combine well-ordered polystyrene (PS) colloidal monolayer with fabricating of LAPS. This paper presents an alcohol-assisted interfacial fabrication method for fabricating low-cost, large-scale and well-ordered PS colloidal monolayer for LAPS in a simple laboratory. The effects of dispersants on PS colloidal self-assembly monolayer are investigated. The mechanism of well-ordered PS colloidal monolayer fabricated with methyl alcohol as the dispersant and the mechanism of disordered PS colloidal monolayer fabricated with ethyl alcohol as the dispersant are described in detail. The PS colloidal monolayer as a template, is used in fabrication of honeycomb meshed array working electrode to optimize performance of LAPS. Moreover, it is proved that the area ratio of the honeycomb meshed array to the silicon substrate is a constant which is independent of the diameter of the PS colloidal sphere. LAPS with honeycomb meshed array has an acceptable sensitivity of 53.47 mV/pH and high linearity of 99.8% in the measurement of pH. The change of photocurrent is also compared deeply for optimization. The results show that LAPS with honeycomb meshed array can reduce signal crosstalk between the detection points and improve addressability of LAPS.

Photoelectrochemical immunosensor for methylated RNA detection based on WS2 and poly(U) polymerase–triggered signal amplification

A novel photoelectrochemical immunosensor has beenconstructed for the determination of methylated RNA. MoS2 nanosheets with large specific area were employed as photoactive material, gold nanoparticles were used as signal amplification unit and immobilization matrix of 4-mercaptophenylboronic acid, anti-m6A antibody was adopted as methylated RNA recognition reagent, and poly(U) polymerase-mediated RNA chain extension and Ru(NH3)63+ were used as assisted signal amplification unit. With the sensitization effect of Ru(NH3)63+, the photoactivity of WS2 nanosheets was improved greatly, which also improved the sensitivity. Using visible-light excitation and ascorbic acid as electron donor, the sensitive determination of methylated RNA was achieved by monitoring the photocurrent change with different concentrations of methylated RNA. This photoelectrochemical immunosensor hasa wide linear relationship with methylated RNA concentration from 0.05 to 35nM under optimal experimental conditions. The low detection limit of 14.5pM was realized based on 3σcriterion. In addition tothe good selectivity, this sensor also presents highreproducibility with arelative standard deviation of 1.4% for the photocurrent of seven electrodes. The applicability of the developed method was also investigated by detecting the level of methylated RNA in corn seedling leaves with and without sulfadiazine treatment. Graphical abstract A novel photoelectrochemical immunosensor was developed for methylated RNA detection using the photoactive material of MoS2 and poly(U) polymerase-mediated RNA chain extension.

Direct and Continuous Liquid-Level Sensing Using Gallium Nitride Ultraviolet Photodetectors

A liquid-level sensor using a gallium nitride (GaN) ultraviolet (UV) photodetector was successfully demonstrated. As the liquid level was changed, the intensity of UV light on the GaN surface was varied owing to the refraction of light on the liquid surface. For the fabrication of the liquid-level sensor, facile and rapid manufacturing was employed, involving metal wire bonding on the semiconductor surface. To characterize the fabricated sensor, the water level in the cylinder was measured according to the photocurrent change of the GaN UV photodetector. The responsivity of the liquid-level sensor depended on the diameter of the cylinder, applied voltage, and emission angle of the UV source. In particular, a cylinder diameter of 16 cm and an emission angle of 45° yielded a resolution of 0.05 cm up to the water level of 10 cm. The results of this study confirm the feasibility of liquid-level sensors for continuous and simultaneous liquid-level monitoring in harsh environments, including high-temperature plants, nuclear reactors, and chemical tanks.

Identifying Photoinduced Dipolar Polarization and Orbit–Orbit Interaction between Excitons in Organic–Inorganic Hybrid Perovskites

AbstractPhotoinduced polarization and orbit–orbit interaction are important issues in hybrid perovskites toward developing optoelectronic functionalities. This paper identifies that photoinduced polarization occurs in hybrid perovskites with mixed‐cation methylammonium (MA)/formamidinium (FA) (MAxFA(1−x)PbI3) by measuring bulk polarization at 1 MHz in a magnetic field. Interestingly, when the internal dipole moment is increased upon increasing the MA:FA ratio, the photoinduced dipolar polarization can be substantially enhanced, clarifying the controversial issue of whether photoexcitation can induce a dielectric polarization within dipolar polarization regime in hybrid perovskites. Furthermore, upon increasing photoinduced dipolar polarization, it is found that the intrinsic orbit–orbit interaction between excitons can be increased, revealed by monitoring photocurrent change (ΔJsc) upon switching the photoexcitation between linear and circular polarizations. This presents that organic cations are directly involved in the orbit–orbit interaction within band structures. Clearly, the studies provide an insightful understanding of the dipole moment effects on photoinduced dipolar polarization and orbit–orbit interaction between excitons in hybrid perovskites toward controlling the optoelectronic properties.

Long and Ultrastable All-Inorganic Single-Crystal CsPbBr3Microwires: One-Step Solution In-Plane Self-Assembly at Low Temperature and Application for High-Performance Photodetectors.

As ideal building blocks for optoelectronic devices, one-dimensional (1D) single-crystal perovskite microwires (MWs) have received widespread attention due to their unique physical and chemical properties. Herein, a one-step solution in-plane self-assembly method is proposed to directly grow millimeter-long CsPbBr3 MWs with superior crystal quality at atmospheric environment. This method effectively avoids the use of toxic antisolvents. Furthermore, a MW-based photodetector is successfully fabricated, showing high photoresponsivity (20 A/W) and fast response (less than 0.3 ms). The stability of the photodetector is also confirmed by aging MW in air for 60 days, which shows a negligible change of photocurrent from 1.29 to 1.25 nA (-3 V) under the same experimental conditions. This work provides a low-cost and fast synthesis method for the preparation of single-crystal perovskite MWs and demonstrates their potential application for high-performance and stable photoelectronic device.

Highly sensitive photoelectrochemical biosensor for microRNA159c detection based on a Ti3C2:CdS nanocomposite of breast cancer

Herein, an ultra-sensitive photoelectrochemical biosensor based on Ti3C2:CdS nanocomposite was established for the selective detection of microRNA159c. Ti3C2:CdS nanocomposites were used as optoelectronic materials because Ti3C2:CdS interaction effectively separates photogenerated electrons and holes, and significantly improves the high photoelectric conversion efficiency. Firstly, Ti3C2:CdS nanocomposite was deposited on the surface of the fluorine-doped tin oxide (FTO) electrode. After the chitosan (CS) was dropped, the SH-miRNA were bonded on the electrode surface via the S–Cd bond. Then 6-mercaptohexanol (MCH) blocked the unbound site, the DNA strand was introduced to hybridize with the target SH-miRNA. At this time, the obtained photocurrent gradually decreases. Subsequently, the photosensitizer TMPyP as signal amplification was modified, the photocurrent increased significantly. The target SH-miRNA was detected based upon the photocurrent change originated from quantities change of TMPyP. Working under the best experimental conditions, the sensing platform had good stability, selectivity, and high sensitivity. The detection range for miRNA159c was 1.0 × 10−6-1.0 × 10−13 mol·L-l, and the detection limit was approximately 33 fmol·L-l. The detection of miRNA159c in human serum provided a huge opportunity to explore the relationship between the abundance of this miRNA and the incidence of breast cancer (BC), and to further achieve effective detection of BC.

Scanning Electrochemical Photometric Sensors for Label-Free Single-Cell Imaging and Quantitative Absorption Analysis.

A new photoelectrochemical imaging method termed scanning electrochemical photometric sensor (SEPS) is proposed in this work. It was derived from light-addressable potentiometric sensor (LAPS) and scanning photoinduced impedance microscopy (SPIM) using a front-side laser illumination at a field-effect structure. When the laser beam scans across the sensor substrate, local photocurrent changes at inversion due to the light absorption of analytes can be recorded. It will be shown that SEPS could be used for label-free living cell imaging with micro-resolution as well as real-time quantitative absorption analysis, which would broaden the applications of traditional LAPS/SPIM from potentiometric/impedance measurements to local optical analysis.

Multifunctional KBiFe2O5 thick film: advances in functional properties

This paper presents the preparation of KBiFe2O5 thick film and its optical (bandgap), ferroelectric, and photovoltaic properties. The XRD of KBiFe2O5 film reveals orthorhombic crystal structure. The polarization study with an electric field (P–E) shows unsaturated and leaky nature of the hysteresis loop. The film shows fatigue-free polarization till 107 switching cycles. A weakly ferromagnetic behavior is observed in the KBFO film at room temperature arising from the canting of G-type antiferromagnetic spins. The film shows spin-frozen behavior below 125 K. The bandgap value of KBiFe2O5 film is found to be 1.67 eV, which is appropriate for visible light absorption. The photovoltaic study on KBiFe2O5 film gives Voc = 1.89 V, Jsc = − 3.04 × 104 A/cm2, and photovoltaic efficiency 0.11%. The photo-ferroelectric coupling in KBiFe2O5 film is established from the directional change in photocurrent with the polarization switching under forward and reverse fields and also from the enhancement of polarization under light illumination.

A cardiac troponin I photoelectrochemical immunosensor: nitrogen-doped carbon quantum dots-bismuth oxyiodide-flower-like SnO2.

Anovel photoelectrochemical (PEC) immunosensor for the determination of cardiac troponin I (cTnI) was constructed. The flower-like stannic oxide (SnO2) with large specific surface area was prepared by hydrothermal synthesis. Nitrogen-doped carbon quantum dots (NCQDs) with excellent surface property were used as a sensitizer for SnO2. Bismuth oxyiodide (BiOI) is a narrow band gap (1.83eV) nanomaterial, which was firstly modified on NCQDs-sensitized SnO2 through in situ growth method. After NCQDs with small size and BiOI nanoparticles aresuccessively combined with SnO2, the SnO2/NCQDs/BiOI microflower was obtained, which possessed good photochemical properties. Using visible light as excitation source and ascorbic acid (AA) as electron donor, the ultrasensitive and quantitative determination of cTnI was realized by detecting the changes of photocurrent under different concentrations of cTnI. The PEC immunosensor showed a large-scaled response (0.001-100ngmL-1) and a low detection limit (0.3pgmL-1) under optimisedexperimental conditions. The sensorhas potential clinical value in the prediction and diagnosis of cardiovascular diseases in elderly patients with diabetes. Graphical abstract.

Photocurrent measurements in topological insulator Bi2Se3 nanowires

Circular photogalvanic currents are a promising approach for spin-optoelectronics. To date, such currents have been induced in topological insulator flakes or extended films. It is not clear whether they can be generated in nanodevices. In this paper, we demonstrate the generation of circular photogalvanic currents in Bi2Se3 nanowires. Each nanowire shows topological surface states. Here, we generate and distinguish the different photocurrent contributions via the driving light wave. We separate the circular photogalvanic currents from those due to thermal Seebeck effects through controlling laser light polarization. The results reveal a spin-polarized surface-Dirac electron flow in the nanowires arising from spin-momentum locking and spin–orbit effects. The second photocurrent contribution described in this Letter is caused by the thermal Seebeck effect. By scanning the photocurrent, it can be spatially resolved; upon reversing the gradient direction along the nanowire, the photocurrent changes its sign, and close to the gold contacts, the amplitudes of the different photocurrent contributions are affected by the proximity to the contacts. In the center of the nanowires, where the effects from the gold contact/topological insulator stacks vanish, the spin-polarized current remains constant along the nanowires. This allows the all-optical spin current generation in topological insulator nanowires and hybrid structures on the nanoscale, one goal of spin-orbitronics.

Simulations of Benzene and Hydrogen-Sulfide Gas Detector Based on Single-Walled Carbon Nanotube over Intrinsic 4H-SiC Substrate.

Carbon nanotubes (CNTs)-based sensors have gained significant importance due to their tremendous electrical and physical attributes. CNT-based gas sensors have high sensitivity, stability, and fast response time compared to that of solid-state sensors. On exposure to a large variety of organic and inorganic compounds, the conductivity of CNT changes. This change in electrical conductivity is being used as a detection signal to detect different target molecules. Hydrogen-sulfide and benzene are hazardous gases that can cause serious health issues in humans. Therefore, it is mandatory to detect their presence in industrial and household environments. In this article, we simulated CNT-based benzene and hydrogen-sulfide sensor with a nanoscale semiconductor device simulator—Quantumwise Atomistix Toolkit (ATK). The change in the device density of states, electric current, and photocurrent in the presence of target molecules have been calculated. The change in photocurrent in the presence of target molecules has been proposed as a novel detection mechanism to improve the sensor selectivity and accuracy. This change in photocurrent as well as electric current in the presence of target molecules can be used simultaneously as detection signals. Our intension in the future is to physically fabricate this simulated device and use photocurrent as well as electric current as detection mechanisms.

Electrophysical properties of Pb1−XMnXSe epitaxial films irradiated by γ-quanta

Herein, the effect of γ-quanta on electrophysical and photoelectric properties of p-type Pb1-xMnx Se epitaxial films obtained from the molecular cluster on the glass substrate by the method of condensation has been investigated. It has been established that the acceptor-type local levels with the ionization energy of 0.14 eV and 0.175 eV are generated, when p-type Pb1-xMnx Se (x = 0.01) epitaxial films are irradiated by γ-quanta at D >10 kGy doses. The increase in the photoconductivity in the low temperature range 80-180K is due to the discharge of 0.14eV level, but the decrease in the rate of change of photocurrent in the high temperature range is due to the role of local level with 0.175 eV energy as a recombination center.

Rational design of photoelectrochemical cells towards bias-free water splitting: Thermodynamic and kinetic insights

Photoelectrochemical (PEC) water splitting offers a promising way to produce hydrogen and harvest solar energy, however, its low efficiency has made it less economically attractive than other hydrogen production methods. Herein we present a numerical model of PEC cells considering quasi-fermi level splitting and interfacial kinetics to understand the charge transfer process and explore the approaches to increase the energy conversion efficiency. The non-linear change of photocurrent with light intensity under concentrated illumination is for the first time captured by a model. Based on the model, the operation regions of a PEC cell are mapped. Pathways to further promote the energy efficiency of PEC are proposed from the aspect of kinetics and thermodynamics. A new method that enables a precise evaluation of the theoretical boundaries of energy conversion efficiency of photocatalysts is developed taking into account the thermodynamics barrier.