Optoelectronic Sensors Research Articles

Optoelectronic Characterization of 2D Graphene‐Based Heterostructures: Gr/MoS2 and Gr/WS2

In this research, it is aimed to obtain and to compare the electrical conductivity and the transmittance of two graphene (Gr)‐based heterostructures: Gr/WS2 and Gr/MoS2 on quartz. Raman spectroscopy is used to analyze the quality of the samples before and after the measurements. Terahertz time domain spectroscopy in transmission mode is used as a nondestructive technique to obtain the surface conductivity and the transmittance in the frequency range [0.2, 1.6] THz. The transmittance values obtained for both samples are similar, whereas the surface conductivity of Gr/WS2 is higher than the one of Gr/MoS2 and both are higher than the conductivity values obtained for individual homogeneous layers. Fourier transform infrared spectroscopy and UV–Vis spectroscopies are used to obtain the optical transmittance and to evaluate the behavior of each layer in the frequency ranges [90, 180] and [300, 1200] THz, respectively. In the infrared range, the transmittance of the heterostructures is similar to that of the individual materials, although in the visible range the transmittance is totally dominated by the WS2 and MoS2 layers. These characteristics make these heterostructures good candidates to be used for optoelectronics sensors.

Graphene Hybrid Metasurfaces for Mid-Infrared Molecular Sensors.

We integrated graphene with asymmetric metal metasurfaces and optimised the geometry dependent photoresponse towards optoelectronic molecular sensor devices. Through careful tuning and characterisation, combining finite-difference time-domain simulations, electron-beam lithography-based nanofabrication, and micro-Fourier transform infrared spectroscopy, we achieved precise control over the mid-infrared peak response wavelengths, transmittance, and reflectance. Our methods enabled simple, reproducible and targeted mid-infrared molecular sensing over a wide range of geometrical parameters. With ultimate minimization potential down to atomic thicknesses and a diverse range of complimentary nanomaterial combinations, we anticipate a high impact potential of these technologies for environmental monitoring, threat detection, and point of care diagnostics.

Rapid Vital Sign Extraction for Real-Time Opto-Physiological Monitoring at Varying Physical Activity Intensity Levels

Robustness of physiological parameters obtained from photoplethysmographic (PPG) signals is highly dependent on a signal quality that is often affected by the motion artefacts (MAs) generated during physical activity. This study aims to suppress MAs and obtain reliable physiological readings using the part of the pulsatile signal, captured by a multi-wavelength illumination optoelectronic patch sensor (mOEPS), that minimizes the residual between the measured signal and the motion estimates obtained from an accelerometer. The minimum residual (MR) method requires the simultaneous collection of (1) multiple wavelength data from the mOEPS, and (2) motion reference signals from a triaxial accelerometer attached to the mOEPS. The MR method suppress those frequencies associated with motion in a manner that is easily embedded on a microprocessor. The performance of the method in reducing both in-band and out-of-band frequencies of MAs is evaluated through two protocols with 34 subjects engaged in the study. The MA-suppressed PPG signal, obtained through MR, enables the calculation of the heart rate (HR) with an average absolute error of 1.47 beats/min for the IEEE-SPC datasets, and the calculation of HR and respiration rate (RR) to 1.44 beats/min and 2.85 breaths/min respectively for our in-house datasets. Oxygen saturation (SpO 2) levels calculated from the minimum residual waveform are consistent with the expected values of ≥ 95%. The comparison with the reference HR and RR show errors with an absolute accuracy of and the Pearson correlation ( R) for HR and RR are 0.9976 and 0.9118 respectively. These outcomes demonstrate that MR is capable of effective suppression of MAs for a range of physical activity intensities and to achieve real-time signal processing for wearable health monitoring.

Surface crafting and entrapment of CsPbBr3 perovskite QDs in ZIF-8 for ammonia recognition

The substantial optical features of perovskite quantum dots (PQD) lead to rapid growth in the investigation of their surface and lattice doping for optoelectronic and biochemical sensor advancements. Herein, we have used the surface ligand crafting model of PQD by ammonia and its optimum response to recognise ammonia in the sensing cellulose paper. The PQD with acetyl amine and octanoic acid capped were synthesized and entrapped in zeolites imidazole framework to delay the instant quenching and envisaged response to ammonia with high sensitivity. The hybrid perovskite quantum dots and Zeolite imidazolate framework-8 (PQD@ZIF-8) materials were further immersed in cellulose paper for solid-state sensor fabrication for the detection of ammonia by naked-eye and a Xiaomi Note-5 mobile camera. The ammonia was measured with high sensitivity at ambient conditions, with a detection limit of 16 ppm and a linear detection range of 1 to 500 ppm. This research provides a new platform for designing sensor selectivity and sensitivity, which could be used to further develop fluorescent nanomaterials-based sensors for small molecule detection.

Effect of gadolinium doping on the Structural, magnetic, Electrical, Optical, and elastic properties of magnetite nanoparticles

In the present study, Fe3-xGdxO4 nanoparticles (with × varying from 0 to 0.1) were synthesized using the co-precipitation method. Lattice constant and X-Ray density were determined using X-Ray Diffraction (XRD). Transmission Electron Microscopy (TEM) study revealed the formation of rod-like structures along with round-shaped particles after gadolinium doping. Selected Area Electron Diffraction (SAED) showed good crystallinity of nanoparticles. Elastic constants were calculated using FTIR and XRD data. The study of the vibrating sample magnetometer (VSM) revealed that the saturation magnetization increased with Gd3+ doping from 54.3 emu/g at x = 0.0 to 84.8 emu/g at x = 0.04. Coercivity also increased with Gd3+ doping. The value of resistivity has been observed to be 4.02 × 106 Ohm-cm for undoped samples using Keithley’s two-probe method. The dc resistivity of doped samples has been decreased by two orders of magnitude as comparedto the undoped sample. UV–Vis spectroscopy has been used to calculate the band gaps with the help of Tauc plots. The band gap for the undoped particle is 2.46 eV which decreases with Gd3+ doping till 2.08 eV for x = 0.03. Band gaps are correlated to electrical behavior. Young modulus, Bulk modulus, Rigidity modulus, and Poisson’s ratio were found to enhance with gd doping beyond x = 0.03. The increase of elastic constants with doping indicates the strengthening of interatomic bonding. These nanoparticles could have applications as optoelectronic and magnetoelastic sensors.

Bioinspired In‐Sensor Reservoir Computing for Self‐Adaptive Visual Recognition with Two‐Dimensional Dual‐Mode Phototransistors

AbstractArtificial visual systems that dynamically process spatiotemporal optoelectronic signals under complex real‐life environments bear a wide spectrum of edge applications. Despite significant progress in optoelectronic sensors and neuromorphic computing algorithms, developing visual systems that can adapt to a broad illumination range while retaining high performance, high efficiency, and low training costs remains a challenge. Here, this work reports a bioinspired in‐sensor reservoir computing (RC) for self‐adaptive visual recognition. By leveraging voltage‐tunable photoresponses of the MoS2‐based phototransistor array, the RC system demonstrates both scotopic and photopic adaptation functions and maintains a recognition accuracy of 91%. The horizontal modulation (HM) block enables the reservoir to adapt automatically in real‐time under changing illumination conditions, yielding a 90.64% recognition accuracy (14.21% improvement over conventional RC systems). These results pave the way for the emergence of a reconfigurable in‐sensor RC system with broad applications and enhanced performance for an efficient artificial vision system at the edge.

InGaO3 Nanowire Networks for Deep Ultraviolet Photodetectors

Wide band gap semiconductor nanomaterials have great research prospects in power semiconductor devices, radio frequency devices, optoelectronic sensor devices, and so on. Among them, gallium oxide is considered as the representative material of wide band gap semiconductor nanomaterials as a deep ultraviolet (UV) photoelectric sensing device because of its 4.9 eV band gap width. However, the traditional synthesis of this kind of metal oxide semiconductor nanomaterials by the chemical vapor deposition (CVD) method still has some problems. The experimental process is not easy to achieve due to the high temperature of 960 °C, and the lower photocurrent makes it difficult to read the photoelectric signal for subsequent devices because of the optical response current of the order of nanoampere. In this work, gallium antimonide and indium antimonide were selected as the nutrition reaction materials, while oxygen is used as the oxide materials. InGaO3 nanowire network materials were prepared at a lower temperature of 700 °C and a lower working pressure of 0.2 kPa, the deep UV photoelectric response of the optoelectronic devices was measured, and high performance was obtained at 5 V bias, like at a power of 0.64 μW/cm2, the response is 80.1 A/W, detection is 1.03 × 1014, and the external quantum efficiency is 3.9 × 104. Especially, the photoelectric current 34.1 μA is far larger than that of the level of several nanoampere traditional gallium oxide devices. Its reaction principle is that In and Ga metal nucleate and oxidize on the substrate to form InGaO3 nanowires after antimonide decomposition at 700 °C temperature, which is lower than 960 °C of the traditional CVD reaction method. This mechanism is different from that of traditional graphite and oxide powder reduction, which can save energy. In a word, this research has invented a method for preparing indium doping gallium oxide nanomaterials, which provides a reference for rapid preparation of response materials and low-energy consumption for deep UV photoelectric devices.

Elucidating the effect of Pb and Ba substitution in SrTcO3 for advanced radioactive semiconducting applications

In this work, lead (Pb) and barium (Ba) substitution in SrTcO3 (STO) has been studied in detail using density functional theory. The structural stability was tested using optimization, enthalpy of formation and tolerance factor. The structure of SrTc(1−x)ZxO3 for (Z = Ba and Pb; x = 0, 0.25, 0.50 and 0.75) is found to be thermodynamically stable and thus can be made and studied experimentally, in which 25% Ba is the most stable form with ΔH = − 25.43 eV. In electronic properties, the band analysis is performed using PBE-GGA functional and found to follow the Moss–Burstein shift for the studied compounds, while DOS and contour plots have shown mixed p–d hybridization among the constituent elements, which indicates a mixing of covalent and ionic bond between its content atoms. The magnetic properties revealed the existence of weak ferromagnetism which is found to decrease (6.45, 6.02, 6.00 μB) with the increase of Pb content in STO while it increases to (0.04, 5.24, 6.89 μB) for the Ba substitution. Ba substitution shows good electrical conductivity. The optical analysis has shown a high reflectivity value for visible light (especially for 50% Ba with R(0) = 91.3%) and high conductivity σ(ω) (especially for 50% Ba with 12.6 × 103/Ω cm) value in the UV region which suggests the ability of these materials to be used as optical reflectors to prevent radiations and as non-radioactive photocatalysis and optoelectronic sensors.

Selective colorimetric detection of cysteine based on phenylvinylbisquinoline for its potential implementation in optoelectronic sensors

Selective colorimetric detection of cysteine based on phenylvinylbisquinoline for its potential implementation in optoelectronic sensors

Photoelectric and pyroelectric performance modulated by the in-plane ferroelectric polarization in multi-functional α-In2Se3-based transistor

As a typical two-dimensional van der Waals ferroelectric material, α-In2Se3 has great potential in the applications of optoelectronic devices, memories, sensors, detectors, and synapses. Although it has been proved that α-In2Se3 is with simultaneous intercorrelated in-plane and out-of-plane ferroelectric polarization, the degree-of-freedom of in-plane ferroelectric polarization in the α-In2Se3 and its influence on the other properties have always been neglected because of the difficulties in the characterization and application, comparing with the out-of-plane ferroelectric polarization. Specifically, it has not been revealed the influence mechanism how the in-plane ferroelectric polarization modifies the photodetection performance of the α-In2Se3-based transistor. In this report, the four-terminal transistors based on the multi-layered α-In2Se3 are prepared and used to investigate the in-plane ferroelectric polarization influenced photodetection performance. We have demonstrated that the in-plane ferroelectric polarization may reduce the optical response time of α-In2Se3-based transistors, and the pyroelectric performance induced by the in-plane ferroelectric polarization adds a feature to the α-In2Se3-based transistors. These results promote the four-terminal α-In2Se3-based transistor to be a multi-functional device, which can simultaneously detect the light and its induced temperature variation. Our work may offer an approach to understand the in-plane ferroelectric polarization-modulated multi-functional optoelectronics.

State-of-the-art of polyimide films reinforced with fullerene-design, features and applications

Polyimide belongs to the class of high performance polymers containing imide functionalities in the backbone. Polyimide has wide ranging properties of optical transparency, heat stability, mechanical strength, dimensional stability, thermal conductivity, dielectric properties, etc. Fullerene is a zero dimensional hollow symmetrical nanocarbon, frequently employed as nanofiller in the polymers. Fullerene has been reinforced in the polyimide films to further augment the exclusive features and performance. This state-of-the-art review basically emphases the fundamentals, structure, properties, and applications of polyimide films, especially the films reinforced with fullerene nanofiller. The polyimide/fullerene nanocomposite films have been prepared using facile routes such as solution casting, spin casting, in situ method, and other film forming methods. Fullerene nanofiller has been filled in numerous designed polyimides. Number of experimental and theoretical studies have been performed on the high performance polymer/fullerene nanocomposite films. The structural diversity of the polymer/fullerene nanocomposite films and inimitable characteristics have led to significant applications in the optoelectronic devices, photodetectors, and sensors.

MXene Contact Engineering for Printed Electronics.

MXenes emerging as an amazing class of 2D layered materials, have drawn great attention in the past decade. Recent progress suggest that MXene-based materials have been widely explored as conductive electrodes for printed electronics, including electronic and optoelectronic devices, sensors, and energy storage systems. Here, the critical factors impacting device performance are comprehensively interpreted from the viewpoint of contact engineering, thereby giving a deep understanding of surface microstructures, contact defects, and energy level matching as well as their interaction principles. This review also summarizes the existing challenges of MXene inks and the related printing techniques, aiming at inspiring researchers to develop novel large-area and high-resolution printing integration methods. Moreover, to effectually tune the states of contact interface and meet the urgent demands of printed electronics, the significance of MXene contact engineering in reducing defects, matching energy levels, and regulating performance is highlighted. Finally, the printed electronics constructed by the collaborative combination of the printing process and contact engineering are discussed.

Stereopsis-Inspired 3D Visual Imaging System Based on 2D Ruddlesden-Popper Perovskite.

Stereopsis is of great important functions for humans to perceive and interact with the world. To realize the function of stereoscopic imaging, optoelectronic sensors shall possess good photoresponsive performance, multidirectional sensing, and 3D building capabilities. However, the current imaging sensors are mainly focused on 2D imaging, limiting their practical application scenarios. In this study, a stereopsis-inspired flexible 3D visual imaging system (VIS) based on 2D Ruddlesden-Popper perovskite is demonstrated. The 3D-VIS consists of 800 device units, each of which demonstrates excellent photoresponse performance, mechanical characteristics, and environmental stability. In addition to the capability of detecting 2D reflective images, the 3D-VIS realizes the function of detecting the depth of field and fusing object projections of two directions to invert the 3D image by utilizing voxels to rebuild the spatial structure of the object. In the future, the 3D-VIS will have broad application prospects in medical imaging, virtual reality, industrial automation, and other fields.

Development of a new low-cost computer vision system for human gait analysis: A case study.

Today, human gait analysis is commonly used for clinical diagnosis, rehabilitation and performance improvement in sports. However, although previous research works in the literature address the use of motion capture systems by means of optoelectronic sensors, Inertial Measurement Units (IMUs) and depth cameras, few of them discuss their conception, guidelines and algorithms for measuring and calculating gait metrics. Moreover, commercially available motion capture systems, although efficient, are cost restrictive for most of the low-income institutions. In this research work, a new computer vision-based system (CVS) for gait analysis is developed and proposed. The aim is to close the gap found in the literature about the design and development of such systems by providing the requirements, considerations, algorithms and methodologies used to develop a gait analysis system with acceptable precision and accuracy, and at low cost. For this purpose, a linear computer vision method based on the non-homogeneous solution of the calibration matrix was used. The spatio-temporal and angular gait parameters were implemented in the proposed system, and compared with those reported in the literature. The denoising of the spatial gait trajectories and the strategies to detect gait events, are also presented and discussed. The results have shown that the proposed system is satisfactory for human gait analysis in terms of precision, computational performance and low cost.

Thermally activated upconversion luminescence and ratiometric temperature sensing under 1064 nm/808 nm excitation

In this research, a thermally activated upconversion luminescence (UCL) probe with ratiometric temperature sensing under 1064 nm and 808 nm excitation was designed. Especially, Nd3+, Tm3+ and Ce3+ were doped in rare earth nanoparticles (RENPs) as UCL modulators. By optimizing the elements and ratios, the excitation wavelength is successfully modulated to 1064 nm excitation with UCL intensity enhanced. Additionally, the prepared RENPs have a significant temperature response at 1064 nm excitation and can be used for thermochromic coatings. The intensity ratio of three-photon UCL (1064 nm excitation) to two-photon UCL (808 nm excitation) as an exponential function of temperature can be used as a ratiometric temperature detector. Therefore, this designed thermochromic coatings may enable new applications in optoelectronic device and industrial sensor.

An optoelectronic muscle contraction sensor for prosthetic hand application.

Surface electromyography (sEMG) is considered an established means for controlling prosthetic devices. sEMG suffers from serious issues such as electrical noise, motion artifact, complex acquisition circuitry, and high measuring costs because of which other techniques have gained attention. This work presents a new optoelectronic muscle (OM) sensor setup as an alternative to the EMG sensor for precise measurement of muscle activity. The sensor integrates a near-infrared light-emitting diode and phototransistor pair along with the suitable driver circuitry. The sensor measures skin surface displacement (that occurs during muscle contraction) by detecting backscattered infrared light from skeletal muscle tissue. With an appropriate signal processing scheme, the sensor was able to produce a 0-5V output proportional to the muscular contraction. The developed sensor depicted decent static and dynamic features. In detecting muscle contractions from the forearm muscles of subjects, the sensor showed good similarity with the EMG sensor. In addition, the sensor displayed higher signal-to-noise ratio values and better signal stability than the EMG sensor. Furthermore, the OM sensor setup was utilized to control the rotation of the servomotor using an appropriate control scheme. Hence, the developed sensing system can measure muscle contraction information for controlling assistive devices.

Development of an Optoelectronic Integrated Sensor for a MEMS Mirror-Based Active Structured Light System.

Micro-electro-mechanical system (MEMS) scanning micromirrors are playing an increasingly important role in active structured light systems. However, the initial phase error of the structured light generated by a scanning micromirror seriously affects the accuracy of the corresponding system. This paper reports an optoelectronic integrated sensor with high irradiance responsivity and high linearity that can be used to correct the phase error of the micromirror. The optoelectronic integrated sensor consists of a large-area photodetector (PD) and a receiving circuit, including a post amplifier, an operational amplifier, a bandgap reference, and a reference current circuit. The optoelectronic sensor chip is fabricated in a 180 nm CMOS process. Experimental results show that with a 5 V power supply, the optoelectronic sensor has an irradiance responsivity of 100 mV/(μW/cm2) and a -3 dB bandwidth of 2 kHz. The minimal detectable light power is about 19.4 nW, which satisfies the requirements of many active structured light systems. Through testing, the application of the chip effectively reduces the phase error of the micromirror to 2.5%.

Advances in silicon-based in-sensor computing for neuromorphic vision sensors

With the development of the Internet of Things (IoT), intelligent security systems, assisted driving and artificial intelligence, traditional machine vision sensors no longer meet the needs of low power consumption, high sampling rate, high dynamic range and low data redundancy, therefore, the emergence of new vision sensors is urgently needed. Drawing on the information extraction and encoding methods of biological retinas, in-sensor computing photoelectric detection systems have been developed. It has a more efficient sampling model and data transfer mode than frame-based and separated sensory-computing systems. This paper provides an overview of several major silicon-based in-sensor computing neuromorphic vision sensors. Using bio-vision mechanisms as an entry point, the architecture and working principles of these neuromorphic optoelectronic sensors are focused on, their application scenarios, advantages and limitations are compared, and the challenges and possible directions for development are analysed.

Improved Performance of g-C3N4 for Optoelectronic Detection of NO2 Gas by Coupling Metal-Organic Framework Nanosheets with Coordinatively Unsaturated Ni(II) Sites.

Sensitive and selective optoelectronic detection of NO2 with g-C3N4 (CN) is critical, but it remains challenging to achieve ultralow concentration (ppb-level) detection. Herein, Ni metal-organic frameworks/CN nanosheet heterojunctions were successfully fabricated by the electrostatic induced assembly strategy and then treated by a post-alkali etching process for creating coordinatively unsaturated Ni(II) sites. The optimized heterojunction exhibits a record detection limitation of 1 ppb for NO2, well below that observed on pristine CN, and an outstanding selectivity over other gases, along with long-time stability (120 days) at room temperature. The resulting superior detection performance benefits from the enhanced charge transfer and separation of the closely contacted heterojunction interface and the favorable adsorption of NO2 by unsaturated Ni(II) as selective adsorption sites mainly by means of the time-resolved photoluminescence spectra and in situ X-ray photoelectron spectra. Moreover, the in situ Fourier transform infrared spectra and temperature-programmed desorption disclose that the promotion adsorption of NO2 depends on the strengthened interaction between NO2 and Ni(II) node sites at the aid of OH groups from unsaturated coordination. This work offers a versatile solution to develop promising CN-based optoelectronic sensors at room temperature.

Structural and Optical Characterization of g-C3N4 Nanosheet Integrated PVC/PVP Polymer Nanocomposites.

The present work considers the integration of g-C3N4 nanosheets into PVC/PVP polymer nanocomposites at ratios of 0.0, 0.3, 0.6, and 1.0 wt%. The XRD data scans showed semicrystalline structures for all PVC/PVP/g-C3N4 polymer blend films. The FTIR and Raman measurements revealed intermolecular hydrogen bonding between the g-C3N4 surface and the OH- groups of the PVC/PVP network. ESEM morphology analysis for PVC/PVP/g-C3N4 nanocomposite films displayed homogeneous surface textures. The data of TGA showed improved thermal stability as the decomposition temperature increased from 262 to 276 °C with the content of g-C3N4 (0.0-1.0 wt%). The optical absorbance data for PVC/PVP films improved after the addition of g-C3N4. The optical energy gaps showed compositional dependence on the g-C3N4 content, which changed from 5.23 to 5.34 eV at indirect allowed transitions. The refractive index for these blend films enhanced (1.83-3.96) with the inclusion of g-C3N4. Moreover, the optical susceptibility for these nanocomposite films increased as the content of g-C3N4 changed from 0.0 to 1.0 wt%. Finally, the values of the nonlinear refractive index showed improvement with the increased percentage of g-C3N4. When g-C3N4 was added up to 1.0 wt%, the DC conductivity improved from 4.21 × 10-8 to 1.78 × 10-6 S/cm. The outcomes of this study prove the suitable application of PVC/PVP/g-C3N4 in optoelectronic fiber sensors.