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Schottky-contacted nanosensors have attracted extensive attention due to their high sensitivity and fast response time. In this article, we proved that the construction of Schottky contact by Pt nanoparticles (NPs) decoration can effectively improve the performance of V2O5 nanobelts photodetectors. After modified by Pt NPs, the photocurrent of V2O5 nanobelts is increased by more than two orders of magnitude, and the photoresponse speed is improved by at least three orders of magnitude. Detailed studies have shown that the performance enhancement is attributed to the formation of the Schottky contact at the electrode-semiconductor interface due to the decrease of surface gas adsorption and the increase of V2O5 work function after Pt NPs modification. The strong built-in field in the Schottky barrier region will quickly separate photogenerated carriers, thereby reducing the electron-hole recombination rate, resulting in the fast response time and an increase in the free carrier density. Moreover, it is found that this enhancement effect can be regulated by controlling the pressure to modulating the Schottky barrier height at the interface. Overall, the Pt NPs-modified V2O5 nanobelts photodetector exhibits a broad response spectrum (visible to near infrared), fast rise/fall response time (less than 6.12/6.15 ms), high responsivity (5.6 A/W), and high specific detectivity (6.9 × 108 Jones). This study demonstrates the feasibility of building a Schottky barrier to enhance the photodetection performance, which provides a general and effective strategy towards the construction and its practical application of supersensitive and fast-response nanosensors.

Droplet injection methods are widely used in the applications of microelectronic manufacturing, biological engineering, and 3-D printing. This work presents a new jet dispenser driven by a single piezoelectric stack that enables the capability of drop-on-demand patterning under a high working frequency (500 Hz). Due to the special designs of the jet dispenser, a broad range of liquids, whose viscosities span more than four orders of magnitude (21-665 320 cps), can be jetted. Moreover, a coupled Coulomb damping physical model is proposed, which includes an electromechanical and a dynamic model. Both the Coulomb and the fluid-solid damping are considered in the dynamic model. In order to validate the results obtained by using MATLAB/Simulink, the experiments were carried out. The injection performance of this jet dispenser has been tested by employing a self-made jetting platform. The minimum volume of a jetting droplet is about 14.4 nL with liquid wax. The error of volume uniformity among droplets does not exceed 8%, and the error of angle trajectory is about 0.17°. Furthermore, the versatility of the jet dispenser is demonstrated by printing liquid lubricant, food, glue, silver past, and a ceramic slurry in predefined patterns.

Abstact H2 gas sensors for different applications require various detection ranges, such as 1–100 ppm for exhale breath test and 0–40000 ppm for H2 energy vehicles. Coarse-tuning of the detection range could be realized by the selection of the type of H2 sensors. The fine-tuning of the detection range within one type of H2 sensor, however, is little concerned and reported. Herein, we propose to achieve the fine-tuning of the H2 gas detection range of the AlGaN/GaN HEMT devices by adjusting the Pt gate thickness. Devices with various Pt gate thicknesses of 2, 20, 60, and 100 nm were fabricated and investigated. Results show that the HEMT devices have excellent pinch-off characteristic with an on-to-off ratio of ∼four orders of magnitude. For the 100 nm thick device exposed to 500 ppm H2, ultrafast response time of 1.5 s is observed together with high response. With the decrease of gate thickness, both the response and the response time gradually increase, 1850% and 6 s for the 2 nm thick device. Moreover, both the low limit of detection (LOD) and the saturation cencentration decrease from 1.6 to 0.14 ppm and from 30,000 to 5000 ppm, respectively, with the gate thickness reduced from 100 to 2 nm, revealing that fine-tuning of the detection range could be achieved by adjusting the gate thickness. Finally, the response activation energy is also studied, 15.9, 19.7, and 42.8 kJ/mol for 2, 60, and 100 nm thick devices, respectively.

Resistive switching (RS) has been studied for several applications such as information storage and bio-inspired computing, although reliability issues still prevent their massive use. In this work, we present a novel observation of trapping activity that imposes giant random conductance fluctuations, up to 3 orders of magnitude, resembling RTN in RS devices based on TiO2, HfO2 and hexagonal boron nitride (h-BN) under reading voltages (~ 0.1 V). These events appeared reproducible for all the aforementioned RS device types in sequential measurements and under different bias. This behavior is very beneficial to ensure recognition of the device’s two-state in applications such as stochastic computing integrated circuits (ICs).

In this work, a large-area MoS2/graphene barristor device, with an electrically tunable Schottky barrier height, has been studied for detection of various gaseous analytes. The Schottky barrier height could be modulated by over 0.65 eV, allowing the drain current to be tuned by many orders of magnitude. Using diluted NO2 and NH3 gases as analytes, the performance of the barristor device was compared with individual MoS2 and graphene based planar FETs, where the barristor device outperformed its counterparts in terms of response magnitude and limit of detection. Due to the atomically thin nature of MoS2 and graphene, electric field applied to one material could not be fully screened from the other one, which allowed both materials to act as a composite structure when analyte molecules interacted with the barristor device. This apparently reversed the dopant behavior of NO2 and NH3, while increasing the device sensitivity through subthreshold operation. Both conductance and capacitance based measurements are presented to highlight the charge transfer and barrier height modulation, to support the unique sensing mechanism observed in the 2D barristor device. A lower limit of detection in low ppb is established for NO2 and low ppm for NH3, which could be further tuned by altering gate-drain bias conditions.

Electronic skin (E-skin) based on tactile sensors has great significance in next-generation electronics such as biomedical application and artificial intelligence that requires interaction with humans. To mimic the properties of human skin, high flexibility, excellent sensing capability, and sufficient spatial resolution through high-level sensor integration are required. Here, we report a highly sensitive pressure sensor matrix based on a piezoresistive cellulose/single-walled carbon nanotube-entangled fiber network, which forms its own porous structure enabling a superior pressure sensor with a high sensitivity (9.097 kPa-1), a fast response speed (

The scalable synthesis and transfer of large-area graphene underpins the development of nanoscale photonic devices ideal for new applications in a variety of fields, ranging from biotechnology, to wearable sensors for healthcare and motion detection, to quantum transport, communications, and metrology. We report room-temperature zero-bias thermoelectric photodetectors, based on single- and polycrystal graphene grown by chemical vapor deposition (CVD), tunable over the whole terahertz range (0.1-10 THz) by selecting the resonance of an on-chip patterned nanoantenna. Efficient light detection with noise equivalent powers

As an emerging member of the colloidal semiconductor quantum dot materials family, intraband quantum dots are being extensively studied for thermal infrared sensing applications. High-performance detectors can be realized using a traditional p-n junction device design; however, the heavily doped nature of intraband quantum dots presents a new challenge in realizing diode devices. In this work, we utilize a trait uniquely available in a colloidal quantum dot material system to overcome this challenge: the ability to blend two different types of quantum dots to control the electrical property of the resulting film. We report on the preparation of binary mixture films containing midwavelength infrared Ag2Se intraband quantum dots and the fabrication of p-n heterojunction diodes with strong rectifying characteristics. The peak specific detectivity at 4.5 μm was measured to be 107 Jones at room temperature, which is an orders of magnitude improvement compared to the previous generation of intraband quantum dot detectors.

Coupling a semiconductor with an electrical insulator in a single amphiphilic nanoparticle could open new pathways for manufacturing and assembling organic electronic devices. Here, a poly(3,4-ethylenedioxythiophene)/polyaniline (PEDOT/PANI) bilayer is confined on the surface of one lobe of snowman-type Janus nanoparticles (JNPs), such that one lobe is semiconducting and the other is electrically insulating. The PEDOT/PANI bilayer is constructed in two synthesis steps, by asymmetric modification of the JNPs with PANI followed by PEDOT. The addition of the PEDOT layer onto the PANI-modified JNPs leads to an enhancement in the conductivity of up to 2 orders of magnitude. Further, we demonstrate that JNPs are very versatile supports for semiconducting polymers because by tuning their size and geometry the overall conductivity of the JNP powders can be modulated within several orders of magnitude.

In this work, we study thickness down-scaling as a technique to miniaturize piezoelectric ultrasound transducers while preserving a frequency of operation that falls in the 40–100 kHz range, where airborne ultrasound can propagate over several meters distances and attenuation is $100\,\,\mu \text{m}\,\,\times 100\,\,\mu \text{m}$ . We compare this performance to the sensitivities of ultrasound sensors recently published in literature, showing an increase in Rx sensitivity per unit area between 1 and 2 orders of magnitude. [2021-0094]

In terahertz (THz) technologies, generation and manipulation of THz waves are two key processes usually implemented by different device modules. Integrating THz generation and manipulation into a single compact device will advance the applications of THz technologies in various fields. Here, we demonstrate a hybrid nonlinear plasmonic metasurface incorporating an epsilon-near-zero (ENZ) indium tin oxide (ITO) layer to seamlessly combine efficient generation and manipulation of THz waves across a wide frequency band. The coupling between the plasmonic resonance of the metasurface and the ENZ mode of the ITO thin film enhances the THz conversion efficiency by more than 4 orders of magnitude. Meanwhile, such a hybrid device is capable of shaping the polarization and wavefront of the emitted THz beam via the engineered nonlinear Pancharatnam-Berry (PB) phases of the plasmonic meta-atoms. The presented hybrid nonlinear metasurface opens a new avenue toward miniaturized integrated THz devices and systems with advanced functionalities.

Electronic microdevices of self-bending coronene crystals are developed to reveal an unexplored link between mechanical deformation and crystal function. First, a facile approach towards length/width/curvature-controllable micro-crystals through bottom-up solution crystallization was proposed for high processability and stability. The bending crystal devices show a significant increase beyond seven orders of magnitude in conductivity than the straight ones, providing the first example of deformation-induced function enhancement in crystal materials. Besides, double effects caused by bending, including the change of π electron level as well as the enhancement of carrier mobility, were determined, respectively by the X-ray photoelectric spectroscopy and X-ray crystallography to coexist, contributing to the conductivity improvement. Our findings will promote future creation of flexible organic crystal systems with deformation-enhanced functional features towards customized smart devices.

This paper proposes a new structure named a Side Contact lateral Doping Field Effect Diode (SLFED) to overcome the short channel effects of a regular field effect diode (FED). The fabrication of this new structure is simple that can be fabricated by the standard CMOS process technology, and it offers good electrical characteristics. Furthermore, a comprehensive analysis of FEDs has presented. Our results show that the calculated Ion/Ioff ratio is several orders of magnitude larger than of the regular FED. For simulating the structures, we have applied semiconductor device simulation tools.

Measuring the maximum operating temperature within the channel of ultrawide band-gap transistors is critically important since the temperature dependence of the device reliability sets operational limits such as maximum operational power. Thermoreflectance imaging (TTI) is an optimal choice to measure the junction temperature due to its submicrometer spatial resolution and submicrosecond temporal resolution. Since TTI is an imaging technique, data acquisition is orders of magnitude faster than point measurement techniques such as Raman thermometry. Unfortunately, commercially available LED light sources used in thermoreflectance systems are limited to energies less than ∼3.9 eV, which is below the band gap of many ultrawide band-gap semiconductors (>4.0 eV). Therefore, the semiconductors are transparent to the probing light sources, prohibiting the application of TTI. To address this thermal imaging challenge, we utilize an MoS2 coating as a thermoreflectance enhancement coating that allows for the measurement of the surface temperature of (ultra)wide band-gap materials. The coating consists of a network of MoS2 nanoflakes with the c axis aligned normal to the surface and is easily removable via sonication. The method is validated using electrical and thermal characterization of GaN and AlGaN devices. We demonstrate that this coating does not measurably influence the electrical performance or the measured operating temperature. A maximum temperature rise of 49 K at 0.59 W was measured within the channel of the AlGaN device, which is over double the maximum temperature rise obtained by measuring the thermoreflectance of the gate metal. The importance of accurately measuring the peak operational temperature is discussed in the context of accelerated stress testing.

Ultraviolet photodetectors have several critical applications in communications, early missile launch detection, pollution monitoring, and bacterial fluorescence detection. Wide-bandgap metal oxide semiconductors have proven to be high performance ultraviolet photodetectors with some photoresponsivities reaching several orders of magnitude greater than solid state commercial devices and even photomultiplier tubes. However, analysis and design of metal-oxide photodetectors is complicated by oxygen adsorption and photodesorption at the surface. A limited understanding of this adsorption phenomenon hinders the development of new UV photodetectors. This paper clarifies the adsorption and photodesorption process and makes analysis of metal-oxide photoconductors tractable. Several models of oxygen adsorption, oxygen desorption, and adsorption-controlled conduction from across disciplines are summarized. We discuss each model’s use in their intended context, implications for design, fitting parameters, and limitations. We conclude with an argument that current models are insufficient for describing high-gain metal oxide ultraviolet photodetectors, and we outline the requirements for a new model suitable for high-gain sensors.

Terahertz radiation has become an important diagnostic tool in the development of new technologies. However, the diffraction limit prevents terahertz radiation (λ ≈ 0.01–3 mm) from being focused to the nanometre length scale of modern devices. In response to this challenge, terahertz scanning probe microscopy techniques based on coupling terahertz radiation to subwavelength probes such as sharp tips have been developed. These probes enhance and confine the light, improving the spatial resolution of terahertz experiments by up to six orders of magnitude. In this Review, we survey terahertz scanning probe microscopy techniques that achieve spatial resolution on the scale of micrometres to angstroms, with particular emphasis on their overarching approaches and underlying probing mechanisms. Finally, we forecast the next steps in the field. Recent progress in terahertz scanning probe microscopy is reviewed with an emphasis on techniques that access length scales below 100 nm relevant to material science. An outlook on the future of nanoscale terahertz scanning probe microscopy is also provided.

In this work, a novel triad nanocomposites containing trititanate nanotubes, Ag nanoparticles and dopamine were prepared and the SERS properties were measured experimentally. Control over the size and position of the Ag nanoparticles in the TiNT-dop-Ag system, along with the localised surface plasmon resonance (LSPR) of the Ag particles matching the Raman excitation wavelength, gives a SERS enhancement greater than 6 orders of magnitude. Electromagnetic modelling was used to provide a theoretical basis for these results.

Practical application of surface-enhanced Raman spectroscopy (SERS) is greatly limited by the inaccurate quantitative analyses due to the measuring parameter's fluctuations induced by different operators, different Raman spectrometers, and different test sites and moments, especially during the field tests. Herein, we develop a strategy of quantitative SERS for field detection via designing structurally homogeneous and ordered Ag-coated Si nanocone arrays. Such an array is fabricated as SERS chips by depositing Ag on the template etching-induced Si nanocone array. Taking 4-aminothiophenol as the typical analyte, the influences of fluctuations in measuring parameters (such as defocusing depth and laser powers) on Raman signals are systematically studied, which significantly change SERS measurements. It has been shown that the silicon underneath the Ag coating in the chip can respond to the measuring parameters' fluctuations synchronously with and similar to the analyte adsorbed on the chip surface, and the normalization with Si Raman signals can well eliminate the big fluctuations (up to 1 or 2 orders of magnitude) in measurements, achieving highly reproducible measurements (mostly

Since the first experimental observation of optical Airy beams, various applications ranging from particle and cell micromanipulation to laser micromachining have exploited their non-diffracting and accelerating properties. The later discovery that Airy beams can self-heal after being blocked by an obstacle further proved their robustness to propagate under scattering and disordered environment. Here, we report the generation of Airy beams on an integrated silicon photonic chip and demonstrate that the on-chip 1D Airy beams preserve the same properties as the 2D beams. The 1D meta-optics used to create the Airy beam has the size of only 3 by 16 microns, at least three orders of magnitude smaller than the conventional optic. The on-chip self-healing beams demonstrated here could potentially enable diffraction-free light routing for on-chip optical networks and high-precision micromanipulation of bio-molecules on an integrated photonic chip.

Photonic structures with optical resonances beyond a single controllable mode are strongly desired for enhancing light–matter interactions and bringing about advanced photonic devices. However, the realization of effective multimodal photonic structures has been restricted by the limited tunable range of mode manipulation, the spatial dispersions of electric fields or the polarization-dependent excitations. To overcome these limitations, we create a dual-mode metasurface by integrating the plasmonic surface lattice resonance and the gap plasmonic modes; this metasurface offers a widely tunable spectral range, good overlap in the spatial distribution of electric fields, and polarization independence of excitation light. To show that such dual-mode metasurfaces are versatile platforms for enhancing light–matter interactions, we experimentally demonstrate a significant enhancement of second-harmonic generation using our design, with a conversion efficiency of 1–3 orders of magnitude larger than those previously obtained in plasmonic systems. These results may inspire new designs for functional multimodal photonic structures.

The theoretical Shockley-Queisser limit of photon-electricity conversion in a conventional p-n junction could be potentially overcome by the bulk photovoltaic effect that uniquely occurs in non-centrosymmetric materials. Using strain-gradient engineering, the flexo-photovoltaic effect, that is, the strain-gradient-induced bulk photovoltaic effect, can be activated in centrosymmetric semiconductors, considerably expanding material choices for future sensing and energy applications. Here we report an experimental demonstration of the flexo-photovoltaic effect in an archetypal two-dimensional material, MoS2, by using a strain-gradient engineering approach based on the structural inhomogeneity and phase transition of a hybrid system consisting of MoS2 and VO2. The experimental bulk photovoltaic coefficient in MoS2 is orders of magnitude higher than that in most non-centrosymmetric materials. Our findings unveil the fundamental relation between the flexo-photovoltaic effect and a strain gradient in low-dimensional materials, which could potentially inspire the exploration of new optoelectronic phenomena in strain-gradient-engineered materials.

Optical tweezers enable the manipulation of micro- and nanodielectric particles through entrapment using a tightly focused laser. Generally, optical trapping of submicron size particles requires high-intensity light in the order of MW/cm2. Here, we demonstrate a technique of stable optical trapping of submicron polymeric beads on nanostructured titanium surfaces (black-Ti) without the use of lasers. Fluorescent polystyrene beads with a diameter d = 20-500 nm were successfully trapped on black-Ti by low-intensity focused illumination of incoherent light at λ = 370 m from a Hg lamp. Light intensity was 5.5 W/cm2, corresponding to a reduced light intensity of 6 orders of magnitude. Upon switching off illumination, trapped particles were released from the illuminated area, indicating that trapping was optically driven and reversible. Such trapping behavior was not observed on nonstructured Ti surfaces or on nanostructured silicon surfaces. Thus, the Ti nanostructures were demonstrated to play a key role.

In plasmon-mediated photocatalysis it is of critical importance to differentiate light-induced catalytic reaction rate enhancement channels, which include near-field effects, direct hot carrier injection, and photothermal catalyst heating. In particular, the discrimination of photothermal and hot electron channels is experimentally challenging, and their role is under keen debate. Here we demonstrate using the example of CO oxidation over nanofabricated neat Pd and Au50Pd50 alloy catalysts, how photothermal rate enhancement differs by up to 3 orders of magnitude for the same photon flux, and how this effect is controlled solely by the position of catalyst operation along the light-off curve measured in the dark. This highlights that small fluctuations in reactor temperature or temperature gradients across a sample may dramatically impact global and local photothermal rate enhancement, respectively, and thus control both the balance between different rate enhancement mechanisms and the way strategies to efficiently distinguish between them should be devised.

When scaling the lateral size of a ferroelectric random access memory (FeRAM) device down to the nanometer range, the polarization switching-induced displacement current becomes small and challenging to detect, which greatly limits the storage density of FeRAM. Here, we report the observation of significantly enhanced injection currents, much larger than typical switching currents, induced by polarization switching in BiFeO3 thin films via conductive atomic force microscopy. Interestingly, this injected current can be effectively modulated by applying mechanical force. As the loading force increases from ∼50 to ∼750 nN, the magnitude of the injected current increases and the critical voltage to trigger the current injection decreases. Notably, changing the loading force by an order of magnitude increases the peak current by 2-3 orders of magnitude. The mechanically boosted injected current could be useful for the development of high-density FeRAM devices. The mechanical modulation of the injected current may be attributed to the mechanical force-induced changes in the barrier height and interfacial layer width.

All-dielectric optical metasurfaces are a workhorse in nano-optics, because of both their ability to manipulate light in different degrees of freedom and their excellent performance at light frequency conversion. Here, we demonstrate first-time generation of photon pairs via spontaneous parametric-down conversion in lithium niobate quantum optical metasurfaces with electric and magnetic Mie-like resonances at various wavelengths. By engineering the quantum optical metasurface, we tailor the photon-pair spectrum in a controlled way. Within a narrow bandwidth around the resonance, the rate of pair production is enhanced up to 2 orders of magnitude, compared to an unpatterned film of the same thickness and material. These results enable flat-optics sources of entangled photons - a new promising platform for quantum optics experiments.

The value of the ultimate specific power is determined in capacity electrostatic motors having a metal-thin ferroelectric film with a large specific capacity-nanogap-sliding electrode structure. An estimate is made of the maximum frequency of power conversion in these motors. The value of the ultimate power density previously determined for these designs is used to coin power converters based on these structures exceeding the power of inductive motors by 5 orders of magnitude.

The availability of portable analytical devices for on-site monitoring and rapid detection of analytes of forensic, environmental, and clinical interest is vital. We report the development of a portable device for the detection of biochemiluminescence relying on silicon photomultiplier (SiPM) technology, called LuminoSiPM, which includes a 3D printed sample holder that can be adapted for both liquid samples and paper-based biosensing. We performed a comparison of analytical performance in terms of detectability with a benchtop luminometer, a portable cooled charge-coupled device (CCD sensor), and smartphone-integrated complementary metal oxide semiconductor (CMOS) sensors. As model systems, we used two luciferase/luciferin systems emitting at different wavelengths using purified protein solutions: the green-emitting P. pyralis mutant Ppy-GR-TS (λmax 550 nm) and the blue-emitting NanoLuc (λmax 460 nm). A limit of detection of 9 femtomoles was obtained for NanoLuc luciferase, about 2 and 3 orders of magnitude lower than that obtained with the portable CCD camera and with the smartphone, respectively. A proof-of-principle forensic application of LuminoSiPM is provided, exploiting an origami chemiluminescent paper-based sensor for acetylcholinesterase inhibitors, showing high potential for this portable low-cost device for on-site applications with adequate sensitivity for detecting low light intensities in critical fields.

Here, a novel Au Wedge-enhanced Raman spectroscopy (WERS) substrate is proposed. The electric field enhancement factor and the effective mode field radius with varying geometry parameters are investigated. The proper excitation wavelength 633 nm is obtained. The practical application of WERS substrate is discussed. The Au WERS not only can provide a continuous extremely highly localized electric field as surface-enhanced Raman scattering (SERS) hotspots, but also can offer 10 orders of magnitude of SERS enhancement factor. The corresponding results reveal that WERS substrate will be widely applied in optics, biology, chemistry and other fields.

Electro-optic modulation based on a graphene nanoelectromechanical system (NEMS) with superlubricity is proposed and systematically theoretical investigated. We demonstrate that the superlubricity greatly improve the performance of photoelectric modulators based on graphene NEMS due to its extremely low coefficient of friction. The modulation voltage of graphene NEMS electro-optic modulation with superlubricity can be reduced to 200 mV, which is 1–3 orders of magnitude larger lower than that of the traditional electro-optical modulator, giving rise to a dramatic reduction of the power consumption of the modulator by approximately 3 orders of magnitude. The modulation response speed can reach nanoseconds, which is 4 orders of magnitude higher than the speed of traditional mechanical electro-optic modulation. At the same time, this modulator has a very wide modulation wavelength range and is not sensitive to the angle of incident light. Two-dimensional material devices, incorporated with mechanical modulation and superlubricity, will have important applications in optoelectronics and optical communication.

Radio frequency (RF) microelectromechanical systems (MEMS) based on Al1-xScxN are replacing AlN-based devices because of their higher achievable bandwidths, suitable for the fifth-generation (5G) mobile network. However, overheating of Al1-xScxN film bulk acoustic resonators (FBARs) used in RF MEMS filters limits power handling and thus the phone's ability to operate in an increasingly congested RF environment while maintaining its maximum data transmission rate. In this work, the ramifications of tailoring of the piezoelectric response and microstructure of Al1-xScxN films on the thermal transport have been studied. The thermal conductivity of Al1-xScxN films (3-8 W m-1 K-1) grown by reactive sputter deposition was found to be orders of magnitude lower than that for c-axis-textured AlN films due to alloying effects. The film thickness dependence of the thermal conductivity suggests that higher frequency FBAR structures may suffer from limited power handling due to exacerbated overheating concerns. The reduction of the abnormally oriented grain (AOG) density was found to have a modest effect on the measured thermal conductivity. However, the use of low AOG density films resulted in lower insertion loss and thus less power dissipated within the resonator, which will lead to an overall enhancement of the device thermal performance.

While ionic flow over graphenic structures creates electromotive potential, there is a need to understand the local carrier density induced in graphene without any electrode-induced Fermi-level pinning. Here, we show the electrolyte-flow induced localized doping in graphene via inspecting its Raman phononic energy. Graphene's Fermi energy level has a logarithmic dependence to the flow velocity over 2 orders of magnitude of velocity (∼100 μm s-1 to 10 mm s-1). A theoretical model of the electric double layer (EDL) during ionic transport is used to correlate the Fermi level of graphene with the flow rate and the electronic structure (HOMO-LUMO levels) of the ionic species. This correlation can allow us to use graphene as a reliable, non-invasive, optical flow-sensor, where the flow rates can be measured at high spatial resolution for several lab-on-a-chip applications.

Lisää oa-julkaisu, kun saatavilla. A sensitive photoacoustic detection approach employing a silicon cantilever is investigated for power measurement of electromagnetic radiation. The technique which is actuated by pressure waves generated through radiation-induced heat depicts high sensitivity for a considerably large spectral range from 325 nm to 1523 nm. The implemented method shows linear response in the measurement of radiation power from 15 nW to 6 mW demonstrating a dynamic range of almost six orders of magnitude. A numerical model has been developed to analyze and optimize the measurement sensitivity. The model allows studying different dimensions of the cantilever which is one of the key components of the radiation detection process. The numerical results are in good agreement with experimental results. The electromagnetic power detection technique shows future potential for industrial applications and scientific studies.

Understanding electronic and ionic transport across interfaces is crucial for designing high-performance electric devices. The adjustment of work functions is critical for band alignment at the interfaces of metals and semiconductors. However, the electronic structures at the interfaces of metals and mixed conductors, which conduct both electrons and ions, remain poorly understood. This study reveals that a Schottky barrier is present at the interface of the Nb-doped SrTiO3 metal and a LiCoO2 mixed conductor and that the interfacial resistance can be tuned by inserting an electric dipole layer. The interfacial resistance significantly decreased (by more than 5 orders of magnitude) upon the insertion of a 1 nm thick insulating LaAlO3 layer at the interface. We apply these techniques to solid-state lithium batteries and demonstrate that tuning the electronic energy band alignment by interfacial engineering is applicable to the interfaces of metals and mixed conductors. These results highlight the importance of designing positive electrode and current collector interfaces for solid-state lithium batteries with high power density.

Present GaN technology consists primarily of heteroepitaxial, lateral high electron mobility transistors; however, high-power devices would be much more efficiently manufactured with a vertical geometry due to better blocking voltage scaling. This technology has yet to be realized due to the inconsistency of GaN wafer properties. These inconsistencies can be detected with several long-range, non-destructive techniques including Raman spectroscopy, optical profilometry, and photoluminescence mapping. In particular, Raman spectroscopy is an effective tool for determining the carrier concentration of GaN substrates and whether the wafers are uniform or inhomogeneous. In this work, vertical p-i-n GaN diodes are fabricated using both uniform and inhomogeneous wafers determined by using the A1 Raman peak position to monitor carrier concentration. The inhomogeneous samples have regular patterns of varying conductivity as a result of electron-donating defects brought about by changes in crystal stress. By avoiding these defects, we have found that diode performance improves by increasing the +/− 10 V rectification ratio by up to a factor of 5X and reducing the 200 V reverse bias leakage current by several orders of magnitude. Using the higher quality substrates with uniform electron carrier concentrations can improve the rectification ratio by another order of magnitude.

Dual-color photodetection can increase detection accuracy due to the specific information from different wavelengths. Traditional dual-color detectors are based on double optical modules or photovoltage devices, which suffer from huge system weight or low gain. In this Letter, a novel dual-color photodetector with Ge/Graphene/CdS sandwich profile is proposed. While visible and infrared light is mainly absorbed by the CdS and Ge layers, respectively, photoelectrical signals from two wavelengths both conducted by graphene are extracted on time-sequence with different sampling frequencies. Based on a tailored interface process and epitaxy InGaAs instead of bulk Ge layer, the difference in response speed more than 3 orders of magnitude (76 kHz/14 Hz) was realized. Due to the photogating effect, the high gain was obtained for both wavelengths, and a photoresponse enhancement originated from the overlapping of local photogating field is observed. The device provided a new solution for high-gain and CMOS-compatible dual-color photodetection.

The anisotropic magnetoresistance film is an important core material for developing the magnetic sensors. Here, Ta(5)/MgO(3)/NiFe(10)/MgO(3)/Ta(3) multilayers (in nanometer) were prepared by magnetron sputtering and further applied to construct a sensor element by combining with the Wheatstone bridge. The 1/f noise of the sensor element was greatly reduced by three orders of magnitude after annealing at 400 °C for 7200 s, which was mainly due to the significant microstructural changes during the annealing. However, when the sensor element was applied to detect the magnetic signal of a magnetic code disk with 512 N–S magnetic poles, the output voltage signal of the sensor displayed a large fluctuation of ± 0.05 V. In order to reduce the voltage fluctuation, a magnetic sensor chip by using a parallelly arranged multi-path Wheatstone bridges and auto-gain compensation structure was designed, and magnetic sensor elements and the high-performance computing drive module were prepared. The output voltage fluctuation of the magnetic sensor was reduced by about 90% and approached to ± 0.005 V. These findings provide an important basis for the practical application of NiFe-based magnetic sensing film materials.

Optofluidic biolasers have emerged as promising tools for biomedical analysis due to their strong light-matter interactions and miniaturized size. Recent developments in optofluidic lasers have opened a new Frontier in monitoring biological processes. However, most biolasers require precise recording of the lasing spectrum at the single cavity level, which limits its application in high-throughput applications. Herein, a microdroplet laser array encapsulated with living Escherichia coli was printed on highly reflective mirrors, where laser emission images were employed to reflect the dynamic changes in living organisms. The concept of image-based lasing analysis was proposed by quantifying the integrated pixel intensity of the lasing image from whispering-gallery modes. Finally, dynamic interactions between E. coli and antibiotic drugs were compared under fluorescence and laser emission images. The amplification that occurred during laser generation enabled the quantification of tiny biological changes in the gain medium. Laser imaging presented a significant increase in integrated pixel intensity by 2 orders of magnitude. Our findings demonstrate that image-based lasing analysis is more sensitive to dynamic changes than fluorescence analysis, paving the way for high-throughput on-chip laser analysis of living organisms. Agency for Science, Technology and Research (A*STAR) Nanyang Technological University This research is supported by A*STAR under its AME IRG Grant (project no. A2084c0063). We would like to thank the lab support from Centre of Bio-Devices and Bioinformatics and Internal grant NAP SUG-M4082308.040 from NTU.

We present a machine learning based surrogate modeling method for predicting spatially resolved 3D crystal orientation evolution of polycrystalline materials under uniaxial tensile loading. Our approach is orders of magnitude faster than the existing crystal plasticity methods enabling the simulation of large volumes that would be otherwise computationally prohibitive. This work is a major step beyond existing ML-based modeling results, which have been limited to either 2D structures or only providing average, rather than local 3D full-field predictions. We demonstrate the speed and accuracy of our surrogate model approach on experimentally collected data from a face-centered cubic copper sample undergoing tensile deformation.

Optical tweezers are widely used in materials assembly1, characterization2, biomechanical force sensing3,4 and the in vivo manipulation of cells5 and organs6. The trapping force has primarily been generated through the refractive index mismatch between a trapped object and its surrounding medium. This poses a fundamental challenge for the optical trapping of low-refractive-index nanoscale objects, including nanoparticles and intracellular organelles. Here, we report a technology that employs a resonance effect to enhance the permittivity and polarizability of nanocrystals, leading to enhanced optical trapping forces by orders of magnitude. This effectively bypasses the requirement of refractive index mismatch at the nanoscale. We show that under resonance conditions, highly doping lanthanide ions in NaYF4 nanocrystals makes the real part of the Clausius–Mossotti factor approach its asymptotic limit, thereby achieving a maximum optical trap stiffness of 0.086 pN μm–1 mW–1 for 23.3-nm-radius low-refractive-index (1.46) nanoparticles, that is, more than 30 times stronger than the reported value for gold nanoparticles of the same size. Our results suggest a new potential of lanthanide doping for the optical control of the refractive index of nanomaterials, developing the optical force tag for the intracellular manipulation of organelles and integrating optical tweezers with temperature sensing and laser cooling7 capabilities. The resonance of highly doping lanthanide ions in NaYF4 nanocrystals enhances the permittivity and polarizability of nanocrystals, leading to enhanced optical trapping forces by orders of magnitude, bypassing the trapping requirement of refractive index mismatch.

A two-dimensional (2D) model was developed, for the first time, to describe the characteristics of the micromachined thermal expansion-based angular motion (TEAM) sensor, which has been validated by the experimental results. Scaling analysis on the performance characteristics through the 2D model was conducted to optimize the TEAM sensor’s design in terms of the normalized distances between the microheaters and temperature detectors in $x$ and $y$ directions, the thickness of the thin film, the heater width, the cavity depth, and the heater temperature. Furthermore, the proposed 2D model was normalized by two dimensionless numbers, namely Rayleigh number Ra and Peclet number Pe, with a critical Rayleigh number (Ra $^{\ast }_{\mathrm {c}} =18$ ,000) identified to differentiate linear and nonlinear operation regimes of the TEAM sensor. In particular, our 2D model is much faster than the conventional CFD model by three orders of magnitude (18.91s versus 5.5h), enabling rapid system-level optimization of the critical design parameters. Accordingly, the TEAM sensors with three pairs of platinum thermoresistive temperature sensors were designed and fabricated. The fabricated device demonstrated a normalized sensitivity of $11.8~\mu \text{V}$ /°/s/mW based on the working fluid of air, which was more than three times better than previous thermal angular motion sensors. Thus, with the experimental validation, the proposed 2D model should be a reliable tool to realize the systematical design optimization of TEAM sensors integrated with on-chip microelectronics for future industrial IoT applications. [2020-0355]

A new X-ray absorption spectroscopy (XAS) beamline is currently under construction at a bending magnet of the National Synchrotron Radiation Centre SOLARIS. The front end of this beamline was installed in April 2020. This beamline has a few outstanding characteristic features: The monochromator is a fixed exit beam Lemmonier type monochromator allowing to cover the pursued energy range (1 keV to ~15 keV) with 3 sets of crystals: KAP (100) + multilayer, InSb (111) and Ge (220). The monochromator is a high vacuum system allowing the change of crystals in less than an hour. In order to minimize absorption of photons no windows will be installed in the beamline down to the monochromator, and just one thin polypropylene window will be used for separating the vacuum of the monochromator from the ionization chambers and the sample chamber. A special differential ion pump will be installed to maintain the pressure difference of four orders of magnitude between the storage ring and the monochromator. As SOLARIS is a low energy machine, the beamline can be built without any radiation safety hutches without exceeding the strict low radiation safety levels. The straightforward design of the beamline without additional optical elements, its compact overall dimensions and an easy to handle monochromator make this beamline especially user friendly. In combination with the characteristics of the 1.5 GeV SOLARIS storage ring this beamline will be specifically attractive for the tender X-ray range, i.e. the K-edges of important elements such as P, S, Si, Al and Mg.

This article reports humidity sensors based on hierarchical gallium nitride (GaN) with flower-like microstructures based on a scalable hybrid approach. We have fabricated 3D dandelion flower-like GaN hierarchical microspheres with an ammonothermal- conjugated ammoni- fication method (750-1150 °C) for the humidity sensors. The GaN microspheres are analyzed by scanning electron microscopy, X-ray diffraction, Raman and Fourier-transform spectroscopic methods. It is found that the use of oleylamine in the ammonothermal-ammonification hybrid approach, plays an essential role in the GaN morphology. The GaN sensors are prepared by dip-coating the sensor materials on the interdigitated electrode and their humidity sensing performance have been characterized. The humidity sensing performance is investigated at an applied 1V AC bias, by measuring the impedance and charge transfer resistance as a function of the broad range (10 to 95%) of RH. The GaN sensor exhibits a high response of above four orders of magnitude with excellent linearity and stability within the whole measurement range, while the bare GaN humidity sensors exhibited a low response of less than two orders of magnitude with poor linearity and stability. We have also proposed a possible charge transfer mechanism and studied the influence of the defect degree on the sensing performance of the GaN humidity sensors.

A simple and low-cost fabrication of end-bonded contacts InAsSb NW (nanowire) array detector to weak light is demonstrated in this study. The detector is fabricated using InAsSb NW array grown by molecular beam epitaxy on GaAs substrate. The MIGS (metal-induced gap states) is induced by the end-bonded contact which suppresses the dark current at various temperatures. The existence of the interface dipole due to the interfacial gap states enhances the light excitation around the local field, thus upgrade the photo responsivity and photo detectivity to the weak light. The light intensity of the infrared light source in this report is 14 nW/cm2 which is about 3 to 4 orders of magnitude less than the laser source. The responsivity of the detector has reached 28.57 A/W at room temperature with the light (945 nm) radiation, while the detectivity is 4.81×1011 cm·Hz1/2 W−1. Anomalous temperature-dependent performance emerges at the variable temperature experiments, and we discussed the detailed mechanism behind the non-linear relationship between the photoresponse of the device and temperatures. Besides, the optoelectronic characteristics of the detector clarified that the light trapping effect and photogating effect of the NWs can enhance the photoresponse to the weak light across ultraviolet to near-infrared. These results highlight the feasibility of the InAsSb NW array detector to the infrared weak light without a cooling system.

Easy-to-use and sensitive quantification of biomarkers has a great significance in disease prediction, diagnosis, and monitoring. Here, we report a biosensor for simple and sensitive biomarker detection based on the strong light scattering (brightness) of superradiative plasmonic nanoantennas. This nanoantenna is constructed using antibody-decorated gold nanoparticles (Au NPs) immobilized onto a gold mirror by the target antigen, forming a nanoparticle-on-mirror (NPOM) configuration. The NPOM produces an order of magnitude stronger light scattering in the red region compared with isolated Au NPs on the dielectric substrate, due to the strong near-field coupling of surface plasmons across the gap between the Au NPs and the gold film. The increased brightness allows one to observe the captured Au NPs with the naked eye using a dark-field optical microscope. The particle density of the Au NPs varies linearly with the concentration of the target antigen over a broad dynamic range from 10-3 to 103 ng mL-1. This dynamic range is three orders of magnitude broader than that obtained from the previous work based on a dark-field optical microscope. The limit of detection is 1 pg mL-1 (6.67 fM), which is three orders of magnitude more sensitive than that obtained in the previous work using similar conditions. The uniform spatial distribution of the Au NPs on the gold film was allowed to quantify biomarkers with a relative standard deviation as small as 1-7%. Biosensing using superradiative NPs can lower the detection limit, simplify, and speed up the detection procedure for biomarker detection.

Objective. The article deals with the formation of cost-effective light transistors for creating high-speed energy-efficient computer structures that can solve numerous problems with high speed and accuracy. For this purpose, various types of semiconductor structures are used that can emit and absorb photons for receiving and transmitting digital information.Methods. The use of mirror electrodes allows for repeated re-reflection of the generated photons inside the light transistor to recover all the generated energy into electricity. This increases the energy efficiency of the transistor as a whole and allows implementing computer devices with high efficiency in solving various tasks.Results. Most of the useful energy of the information signal is transferred from one electrode to another, and the movement has a higher speed due to the use of photons, rather than drifting electrons, and this indirectly increases the speed of the light transistor by several orders of magnitude and effectively solves the problem of implementing more powerful and high-speed transistors with greater economic benefits.Conclusion. Prospects for the implementation of high-speed energy-efficient computer structures based on both bipolar transistors and unipolar transistors, as well as thyristors, lasers, and other semiconductor components in light-emitting structures have been developed.

Charged domain walls (CDWs) have attracted considerable attention owing to their tunable properties related to high-density information storage and nanoelectronics devices. The excellent time endurance of conductivity is a pressing need, which is directly related to the domain stability and boundary conditions. In this study, we propose an effective method to promote the permanent formation of charged domain walls aimed with tip-induced electric fields. The permanent domain structures and CDWs are attributed to the robust stimulus with tip dimensions combined with effective screening conditions. This interesting conductivity near the domain walls is three orders of magnitude higher than the domain inner, and exhibits attractive anti-fatigue properties with the value of ∼60 pA for the duration of more than one month. In addition, the tunable mechanism of CDWs in LiNbO3 thin films is related to carrier gathering near the domain walls for the inclined boundary. These inclined head-to-head domain walls exhibit conductive features only along the negative direction, which can be modulated by the application of a sub-coercive voltage. The results demonstrate the stable manipulation of domain reversal and charged domain walls in LiNbO3 thin films, highlighting them as a critical component, especially for multiple-state logic circuits and potential ferroelectric diode applications in non-volatile memories and nanoelectronics devices.

An all-dielectric nanoantenna is expected to greatly boost the nonlinear performance owing to its large mode volume and low material loss. However, it still suffers from the relatively weak near-field enhancement and the inferior far-field directivity. In this work, by successively introducing an upper metal ring and a bottom metal film, the plasmonic resonance and the perfect electric conductor (PEC) mirror effect are employed to significantly enhance and tailor the third harmonic generation (THG) from the high-index silicon nanoantenna. Numerical results show that benefiting from both of these two metal components, not only the THG efficiency is increased by more than 1 and 3.5 orders of magnitude compared with those with only single metal component and without any metal component, respectively, but also an improved radiation directivity can be obtained. The dependences of geometric parameters are discussed as well. This work suggests a route to enhance and manipulate the nonlinear radiation by a hybrid nanoantenna and facilitates its practical applications such as biosensing and nonlinear light sources.

A high-performance Bloch surface wave (BSW) sensor based on the hollow fiber (HF) inner coated with the one-dimensional photonic crystal (1DPC) consisting of TiO2 and SiO2 bilayers is proposed. Performances including sensitivity and figure of merit (FOM) of the sensor are investigated theoretically with the ray transmission model. Several structure parameters such as the center wavelength of 1DPC, the thickness of the cap layer and the bilayer period are optimized to obtain a best performance of the sensor. The results show that the proposed sensor has an ultra-high FOM over 1100 RIU-1, which is approximately two and one orders of magnitude higher than that of the HF surface plasmon resonance (SPR) sensor and HF long-range SPR sensor, respectively. Moreover, the proposed sensor has a much broader practical RI detection range, which makes it more useful in sensing applications. The performance of the proposed sensor applicated in temperature sensing is also estimated to prove its application potential.

Nonlinear diffraction of a plane electromagnetic wave from multilayer nonlinear metasurfaces consisting of double-period lattices of rectangular finite-length graphene ribbons on dielectric spacer layers is investigated in the terahertz (THz) frequency range. An increase in the third-harmonic generation efficiency by several orders of magnitude at the surface plasmon–polariton resonance frequencies is demonstrated. It is demonstrated that the third-harmonic frequency can be controlled by dynamic tuning of chemical potential without changing geometry or dimensions of the graphene metasurface.

With the emergence of stretchable/wearable devices, functions, such as sensing, energy storage/harvesting, and electrical conduction, should ideally be carried out by a single material, while retaining its ability to withstand large elastic deformations, to create compact, functionally-integrated and autonomous systems. A new class of trimodal, stretchable yarn-based transducer formed by coating commercially available Lycra® yarns with PEDOT:PSS is presented. The material developed can sense strain (first mode), and temperature (second mode) and can power itself thermoelectrically (third mode), eliminating the need for an external power-supply. The yarns were extensively characterized and obtained an ultrahigh (gauge factor ∼3.6 × 105, at 10–20% strain) and tunable (up to about 2 orders of magnitude) strain sensitivity together with a very high strain-at-break point (up to ∼1000%). These PEDOT:PSS-Lycra yarns also exhibited stable thermoelectric behavior (Seebeck coefficient of 15 μV K−1), which was exploited both for temperature sensing and self-powering (∼0.5 μW, for a 10-couple module at ΔT ∼ 95 K). The produced material has potential to be interfaced with microcontroller-based systems to create internet-enabled, internet-of-things type devices in a variety of form factors.