Ultrafast Recovery Time Research Articles

Ultrafast and Sensitive Hydrophobic QCM Humidity Sensor by Sulfur Modified Ti3C2Tx MXene

MXenes, 2-D transition metal carbides, nitrides, and carbonitrides, have developed to be attractive nanomaterials for humidity-sensitive materials due to their abundant active sites, tunable surface chemistry, and outstanding stability. Nevertheless, metallic conductivity also makes it hard to extract the signal change from semiconductor resistive gas sensors. Here, we introduce quartz crystal microbalance (QCM) as a humidity sensor platform to collect the signal of MXene mass change directly replacing electronic signal detection. Surface modification was taken place for changing the surface functional groups during hydrofluoric acid (HF) etching for enhancing more humidity sensing performance of Ti3C2Tx MXene. Sulfurized Ti3C2Tx MXene QCM sensors show the highest humidity sensing performance than as-synthesized Ti3C2Tx MXene from 6 Hz/% up to 105 Hz/% with an ultrafast response and recovery time (13/6 s). Also, it was calculated up to 20 times more water absorption ratio compared to mass change of the as-synthesized Ti3C2Tx MXene, showing potential for high-performance and fast humidity sensors.

Ultrafast response of self-powered humidity sensor of flexible graphene oxide film

Next-generation humidity sensor, as one of the smart devices in artificial skin or flexible electronics, will need to be self-powered, flexible, fast and accurately detecting in the microenvironment. Although various flexible humidity sensors have already been demonstrated, most of them rely on large external power sources to operate, and still suffer from slow response, poor selectivity in environmental stimuli, and expensive and complicated procedures. Here, we realize a self-powered humidity sensor with ultrafast response and recovery time of less than 0.3 s by flexible GO film. Importantly, of all state-of-the-art humidity sensors, this is the fastest response for humidity sensor. Moreover, the sensor has a high sensitivity within a wide range of RH from 33% to 98%, and an excellent selective response to humidity under multiple environmental stimuli, due to its moist-induced generator. Theoretical computations reveal that protons generated spontaneously from oxygen-containing groups and water molecules, have a fast diffusion behavior as Grotthuss hopping. In particular, we build four real-time measurement systems capable of respiration monitoring of human, smart leaf surface humidity sensor, and energy harvesting. Our work provides a simple way to fabricate next-generation self-powered sensor using GO film with outstanding humidity sensor performance.

Enhanced selectivity and ultra-fast detection of NO2 gas sensor via Ag modified WO3 nanostructures for gas sensing applications

Recently, nanostructured tungsten oxide-based materials have received much attention in the field of the gas sensor due to their superior size-dependent gas adsorption and catalytic properties. Herewith, we have successfully prepared pure and Ag-doped WO3 nanostructures via a hydrothermal method. The effect of doping (Ag) in WO3 and their gas sensing properties was systematically studied. Interestingly, the Ag-2 sensor revealed the enhanced gas sensing response of 52404% @1000 ppb, which is 5-fold higher than that of the pure WO3 sample at 150 ℃. Moreover, Ag-2 sensor possessed an ultra-fast response and recovery time of 1 s and 3.5 s. Further, as-prepared sensors exhibit excellent selectivity, repeatability, and long-term stability. In addition, the DFT calculations were performed to evaluate the adsorption and charge transfer dynamics of NH3, H2S, and NO2 gas molecules on pure and Ag-doped WO3 surfaces. These results pave the new pathway to developing real-time metal oxide-based gas sensors at lower operating temperatures.

Generation of nanogaps on porous ZnO sheets via Li-ion implantation: NO2 gas sensing with ultrafast recovery time

Nanoscale defect structures on material surfaces introduce diverse chemical physics and have received substantial attention. However, nano structure distortions due to low stability and poor reproducibility have indicated the limitation for further electro-device applications using defect control. In this study, the higher activated electron transfer from the nanogaps (NGs) enhances the sensitivity and accelerated depletion region purifying the porous- ZnO (P-ZnO) sheets for NO2 gas-sensor applications. ∼2.2 nm width of NGs on the (101̅0) orientated P-ZnO sheets and 12% higher surface oxygen vacancies (VO) are formed by using Li-ion implantation via the lithiation process. This intrinsic electron-doped ZnO by NGs shows a reduced work function (φ) and an elevated Fermi level (EF) compared to pristine ZnO. Therefore, the reaction between NO2 gas and ZnO significantly accelerates owing to the activated electron transfer that carries ultrafast recovery time (∼16 s), and a low limit of detection (∼4 ppb) at 150 ℃ are obtained for the NG-P-ZnO sheet-based gas sensor. The generation of NGs on the surface via Li-ion implantation with reliable stability provides a new strategy to improve the electrochemical reactivity of semiconducting metal oxides beyond that obtained using conventional material engineering approaches, such as size, shape, and dimension control.

Single atom modified two-dimensional bismuthenes for toxic gas detection.

Accurate detection of toxic gases at low concentrations is often difficult because they are colorless, odorless, flammable and denser than air. Therefore, it is urgent to develop highly stable and sensitive toxic gas detectors. However, most gas sensors operate at high temperatures, making the detection of toxic gases more challenging. Two-dimensional materials with high specific surface area and abundant modulation methods of properties provide new inspirations for the development of new toxic gas sensing materials. Here, bismuthene, a single element two-dimensional material with high carrier mobility and excellent stability, was used as a substrate material to investigate the effects of anchoring and doping on its gas detection performance by density functional theory (DFT) calculations. It is revealed that the surface structure altered by single metal atoms (Ba, Be, Ca, K, Li, Mg, Na, and Sr) can promote the improvement of gas detection sensitivity. Buckled honeycomb bismuthene (bBi) with the Be atom anchored (A-Be-Bi) show superior sensitivity to H2S, while D-Ca-Bi, D-Li-Bi, D-Mg-Bi and D-Sr-Bi also have relatively high toxic gas detection sensitivity. We further discussed the recovery times of these modified bBis at various temperatures to determine the potential for applications. The ultra-fast recovery time of less than 0.5 seconds demonstrates the potential of these systems at room temperature and can be applied to the manufacture of toxic gas sensors used under practical sensing conditions.

SiO2 Passivated Graphene Saturable Absorber Mirrors for Ultrashort Pulse Generation.

Owing to its broadband absorption, ultrafast recovery time, and excellent saturable absorption feature, graphene has been recognized as one of the best candidates as a high-performance saturable absorber (SA). However, the low absorption efficiency and reduced modulation depth severely limit the application of graphene-based SA in ultrafast fiber lasers. In this paper, a single-layer graphene saturable absorber mirror (SG-SAM) was coated by a quarter-wave SiO2 passivated layer, and a significantly enhanced modulation depth and reduced saturation intensity were obtained simultaneously compared to the SG-SAM without the SiO2 coating layer. In addition, long-term operational stability was found in the device due to the excellent isolation and protection of the graphene absorption layer from the external environment by the SiO2 layer. The high performance of the SAM was further confirmed by the construction of a ring-cavity EDF laser generating mode-locked pulses with a central wavelength of 1563.7 nm, a repetition rate of 34.17 MHz, and a pulse width of 830 fs.

High-sensitive and millisecond-response all-nanofiber-optic humidity sensor using evanescent coupling

The reported humidity sensors usually rely on various sensitive materials to increase the humidity sensitivity, while leading to long response time (1 s ∼10 s). By now, it is still challenging to obtain both high-sensitivity and ultrafast-response (∼tens of ms), i.e., high figure of merit (FOM), for optical humidity sensors. Here, we demonstrate an all-nanofiber-optic strategy to break the limit by using evanescent coupling between a nanofiber (NF) and a substrate without any extra sensitive materials. To implement the sensor, a NF is suspended over a 450 nm deep pit etched in a glass-slide. With increase in the ambient humidity, a thin water film over the NF is formed and strengthens both the evanescent field outside the NF and evanescent coupling into the pit, thus leading to decrease in the transmission of the NF. Experiment shows that the sensor achieved a high sensitivity of − 1.162 dB/%RH in the high RH range of 66.5–83.8%RH with ultrafast response (40 ms) and recovery (100 ms) times. A sensor FOMs, defined as the absolute ratio of sensitivity to response time or recovery time, are also proposed to assess the comprehensive performance of the sensor. The response and recovery FOM of the demonstrated sensor here are up to 29.05 |(dB/%RH)/s| and 11.62 |(dB/%RH)/s|, respectively, which are 2–3 order of magnitude higher than the sensor reported previously. Interestingly, the NF sensor also exhibits a high RH resolution of 0.0189%RH in our experiment. The ultra-high FOMs and flexibility of the sensor allows to easily be integrated with a mask for continuously human fast breath monitoring with a 10 Hz bandwidth. Moreover, our sensor has potential applications in the non-contact switch, noninvasive diagnostic of skin conditions and micron location sensing. The proposed sensing mechanism could provide a novel all-fiber-optic strategy to improve both RH sensitivity and response of the optic humidity sensor simultaneously.

2D Few-Layered PdPS: Toward High-Efficient Self-Powered Broadband Photodetector and Sensors

Photodetectors and sensors have a prominent role in our lives and cover a wide range of applications, including intelligent systems and the detection of harmful and toxic elements. Although there have been several studies in this direction, their practical applications have been hindered by slow response and low responsiveness. To overcome these problems, we have presented here a self-powered (photoelectrochemical, PEC), ultrasensitive, and ultrafast photodetector platform. For this purpose, a novel few-layered palladium-phosphorus-sulfur (PdPS) was fabricated by shear exfoliation for effective photodetection as a practical assessment. The characterization of this self-powered broadband photodetector demonstrated superior responsivity and specific detectivity in the order of 33 mA W-1 and 9.87 × 1010 cm Hz1/2 W-1, respectively. The PEC photodetector also exhibits a broadband photodetection capability ranging from UV to IR spectrum, with the ultrafast response (∼40 ms) and recovery time (∼50 ms). In addition, the novel few-layered PdPS showed superior sensing ability to organic vapors with ultrafast response and a recovery time of less than 1 s. Finally, the photocatalytic activity in the form of hydrogen evolution reaction was explored due to the suitable band alignment and pronounced light absorption capability. The self-powered sensing platforms and superior catalytic activity will pave the way for practical applications in efficient future devices.

Silver Nanoplate Composites as Nonlinear Saturable Absorbers for a Q-Switched Laser

Metal nanomaterials have promising applications in ultrafast photonics due to their broadband operation, large third-order nonlinear susceptibility, and ultrafast recovery time. We realized a Q-switched pulsed erbium-doped fiber laser based on a silver nanoplate polyvinyl alcohol film as a saturable absorber. This film, with a modulation depth of 15.7%, was integrated into a fiber laser by means of a sandwich structure. We obtained Q-switched pulses in the 1.5-μm band, which plays an important role in telecommunications and atmospheric detection. Stable Q-switched pulses were obtained at the pump power of 135 mW, with a single pulse energy of 33.8 nJ, a pulse width of 2.3 μs, a repetition rate of 62.4 kHz, and a signal-to-noise ratio of about 45 dB. When increasing the pump power up to a maximum value of 246 mW, the maximum single pulse energy of 57.8 nJ was achieved. This study first demonstrates the potential of silver nanoplates as saturable absorbers in generating stable laser pulses with high energy.

2D Xenes: Optical and Optoelectronic Properties and Applications in Photonic Devices

AbstractIn recent years, tremendous attention has been paid to the investigation of single‐element 2D materials. These 2D materials mainly consist of elements from group IV and group V such as silicene, phosphorene, and antimonene. Together with other four elements from groups III and VI, they are classified as 2D Xenes and exhibit rich optical and optoelectronic properties such as broadband optical response, strong nonlinearity, ultrafast recovery time, and layer‐dependent bandgap. 2D Xenes can be easily integrated with microfibers and other optical platforms. On the basis of their attracting characteristics, 2D Xenes have been utilized in various functional devices. In this review, the optical and optoelectronic properties of the most intensively studied 2D Xenes are introduced. Their applications in photonic devices including all‐optical modulators, wavelength converters, ultrafast lasers, and photodetectors are explicitly explored. Finally, the challenges and future perspectives of photonic devices based on 2D Xenes are discussed.

Compact breath monitoring based on helical intermediate-period fiber grating

Tiny and soft breath sensors offer unique capabilities in a continuous and long-term recording of vital physiological parameters for human health monitoring. Here, we propose an all fiber-optic breath sensor based on helical intermediate-period fiber grating (E-HIPFG) written in an elliptic core polarization-maintaining fiber. This E-HIPFG-based breath sensor shows ultrafast response time and recovery time, which are 34.46 ms and 41.34 ms, respectively. The response time and recovery time are three orders faster than the corresponding values of conventional optical fiber-based breath sensors with humidity-sensitive material. In addition, this sensor does not combine with any additional coating materials or fiber architectures, increasing the stability in a continuous and long-term detection for breath monitoring. The E-HIPFG sensor is insensitive to external influences, such as temperature, torsion and strain, endowing the possibility of stable detection in the moving body. Particularly, the temperature sensitivity of the sensor is 2.75 pm/°C, which is two orders lower than the corresponding value of previous reports. Due to its considerable stability, quick response, and insensitivity to external influences, the E-HIPFG-based breath sensor offers significant potential for long-term and compact breathing monitoring devices.

On-chip low-loss all-optical MoSe2 modulator.

Monolayer transition metal dichalcogenides (TMDCs), like MoS2, MoSe2, WS2, and WSe2, feature direct bandgaps, strong spin-orbit coupling, and exciton-polariton interactions at the atomic scale, which could be harnessed for efficient light emission, valleytronics, and polaritonic lasing, respectively. Nevertheless, to build next-generation photonic devices that make use of these features, it is first essential to model the all-optical control mechanisms in TMDCs. Herein, a simple model is proposed to quantify the performance of a 35-μm-long Si3N4 waveguide-integrated all-optical MoSe2 modulator. Using this model, a switching energy of 14.6 pJ is obtained for a transverse-magnetic (TM) and transverse-electric (TE) polarized pump signals at λ = 480 nm. Moreover, maximal extinction ratios of 20.6 dB and 20.1 dB are achieved for a TM and TE polarized probe signal, respectively, at λ = 500 nm with an ultra-low insertion loss of <0.3 dB. Moreover, the device operates with an ultrafast recovery time of 50 ps, while maintaining a high extinction ratio for practical applications. These findings facilitate modeling and designing novel TMDC-based photonic devices.

Printed GaAs Microstructures‐Based Flexible High‐Performance Broadband Photodetectors

AbstractNano/microstructures of compound semiconductors such as gallium arsenide (GaAs) demonstrate enormous potential for advanced photonic technologies as they provide realistic means for miniaturization of optoelectronic devices that feature better performance and low power consumption. However, intimately integrating them onto flexible substrates is challenging and restricts their use in the next generation of applications such as wearables and soft robotics. Herein, printed arrays of well‐defined and laterally aligned semi‐insulating (undoped) and doped GaAs microstructures are presented to develop high‐performance flexible broadband photodetectors. The direct roll transfer printed GaAs microstructures‐based photodetectors exhibit excellent performance under ultraviolet and near‐infrared illumination, including ultrafast response (2.5 ms) and recovery (8 ms) times, high responsivity (&gt;104 AW–1), detectivity (&gt;1014 Jones), external quantum efficiency (&gt;106), and photoconductive gain (&gt;104) at low operating voltage of 1 V. The achieved performance is among the best reported for broadband photodetectors but with an added benefit of the developed devices having a flexible form factor. Further, the photodetectors show stable performance under mechanical bending (500 cycles) and twisting loading. The developed materials and manufacturing route can enable high‐speed communications and computation via high‐performance flexible electronics and optoelectronics and transform numerous emerging applications such as wearable systems and internet of things.

Novel two-dimensional semi-metallic NiTe2 based saturable absorber for ultrafast mode-locked fiber laser

Two-dimensional transition metal dichalcogenides (TMDs) have been widely used in ultrafast optics. However, the traditional TMDs such as MoS2 and WS2 have narrow operating band and slow carrier recovery time, limiting their practical application. Among various kinds of TMDs, nickel ditelluride (NiTe2) is a special type-II Dirac semi-metallic TMD material developed recently, showing great potential in ultrafast pulse generation due to its broadband optical response, ultrafast carrier recovery time, strong light-matter interaction and high chemical stability. Nevertheless, there has been no research reported on the NiTe2 based saturable absorber (SA) and its application in the mode-locked laser at the 1.5 and 2 μm regions. In this work, few-layer NiTe2 nanosheets were prepared and SA device was further fabricated by depositing them on a tapered fiber. The saturable absorption property of NiTe2 SA was confirmed by using a balanced twin-detector measurement system. With the use of NiTe2 SA, the Er-doped mode-locked fiber laser with a central wavelength of 1567.3 nm and a pulse width of 1.07 ps was achieved. Moreover, the Tm-doped mode-locked fiber laser with a central wavelength of 1966.08 nm was also obtained based on the NiTe2 SA. These results show that NiTe2 is a promising SA material for ultrafast pulse laser.

Conductometric room temperature ammonia sensor based on porous tin oxide

Metal oxide based chemi-resistive sensors are widely accepted for detection of –pollutants in gaseous or aqueous form due to appealing selectivity and stability. Unfortunately, the high working temperature restrict their utilization in many field. Here, we present the room temperature self-recovered NH3 gas sensor based on porous tin oxide, synthesized by sequential elemental de-alloying technique. Interestingly, sensor is capable to detect the ammonia in wide range of concentration from 1 ppb to 10,000 ppm with fast, stable and reproducible response in fully humid (FH, > 90% relative humidity (RH)) atmosphere. Surprisingly, the sensor is ultra-selective towards ammonia as compared to other analytes like acetone, ethanol, toluene, methanol, chloroform and other gases, present in the atmosphere, in conjunction with long term stability, external stimuli free recovery and ultra-fast recovery time being 1.5 s for a concentration of 1 ppb and 4.5 s in highest concentration of 10,000 ppm. The self-recovery and ultra-fast response is due to its self-power generation capability. Overall, the results advocate the fabrication of porous metal oxide based NH3 sensor with high selectivity, reproducibility, ultra-fast recovery and stimuli free self-recovery for room temperature (RT) operation.

RF Sputtered Nb-Doped MoS2 Thin Film for Effective Detection of NO2 Gas Molecules: Theoretical and Experimental Studies.

Doping plays a significant role in affecting the physical and chemical properties of two-dimensional (2D) dichalcogenide materials. Controllable doping is one of the major factors in the modification of the electronic and mechanical properties of 2D materials. MoS2 2D materials have gained significant attention in gas sensing owing to their high surface-to-volume ratio. However, low response and recovery time hinder their application in practical gas sensors. Herein, we report the enhanced gas response and recovery of Nb-doped MoS2 gas sensor synthesized through physical vapor deposition (PVD) toward NO2 at different temperatures. The electronic states of MoS2 and Nb-doped MOS2 monolayers grown by PVD were analyzed based on their work functions. Doping with Nb increases the work function of MoS2 and its electronic properties. The Nb-doped MoS2 showed an ultrafast response and recovery time of trec = 30/85 s toward 5 ppm of NO2 at their optimal operating temperature (100 °C). The experimental results complement the electron difference density functional theory calculation, showing both physisorption and chemisorption of NO2 gas molecules on niobium substitution doping in MoS2.

Open-Shell Graphene Fragments for Scavenging Hazardous Sulfur Hexafluoride Components with Ultrafast Recovery Time: A First Principles Study

Open-Shell Graphene Fragments for Scavenging Hazardous Sulfur Hexafluoride Components with Ultrafast Recovery Time: A First Principles Study

A UiO-66 3D photonic crystal optical sensor for highly efficient chlorobenzene vapor detection.

Chlorobenzene (C6H5Cl) is a flammable liquid with high vapor activity, which is a severe threat to the environment and human health. Therefore, it is essential to develop a highly efficient sensor to detect C6H5Cl vapor. Herein, we developed a UiO-66 three-dimensional photonic crystal (3D PC) optical sensor and investigated its sensing properties toward the C6H5Cl vapor. The UiO-66 3D PCs optical sensor shows a high sensitivity of C6H5Cl vapor, in the concentrations range of 0-500 ppm, the reflectance intensity response to be 0.06% ppm with a good linear relationship, detection limit can reach 1.64 ppm and the quality factor is 10.8. Additionally, the UiO-66 3D PC optical sensor demonstrated great selectivity with the values of selectivity (S) varying from 2.24 to 10.65 for the C6H5Cl vapor as compared with carbon tetrachloride (CCl4), dichloromethane (CH2Cl2), 1,1,2-trichloroethane (C2H3Cl3), benzene (C6H6), deionized water (H2O), ethanol (C2H5OH) and methyl alcohol (CH3OH) vapors. Moreover, the UiO-66 3D PC optical sensor shows an ultrafast optical response time and recovery times of 0.5 s and 0.45 s with exceptional stability and repeatability to 500 ppm C6H5Cl vapor. These excellent sensing properties are attributed to the efficacy of signal transduction, increased porosity and gas adsorption sites, which are intrinsically endowed by the design of the 3D optical structure. The design and fabrication of this UiO-66 3D PC optical sensor might open up potential applications for the detection of the C6H5Cl vapor.

Near‐Surface Buried Plasmonic Nanoparticles in Glass as Novel Nonlinear Saturable Absorbers for Ultrafast Lasers (Advanced Optical Materials 1/2022)

In article number 2101664, Xiaoli Sun, Yuechen Jia, Feng Chen, and co-workers report on the ultrafast pulse generation using a novel saturable mirror based on BK7 glass wafer with embedded silver nanoparticles. Such saturable absorber mirror possesses the combined advantages of broadband response, cost-effective features of low-dimensional materials, and high stability of commercial semiconductor saturable absorber mirrors. It shows strong nonlinear optical modulation properties and ultrafast recovery time based on localized surface plasmon resonance effect. The laser performance is excellent with the pulse width as short as 324 fs and a maximum output power of 0.48 W.

Near‐Surface Buried Plasmonic Nanoparticles in Glass as Novel Nonlinear Saturable Absorbers for Ultrafast Lasers

AbstractUltrafast lasers play important roles for scientific research and industrial applications. Saturable absorbers serve as crucial components for ultrafast laser generation. For decades, securing saturable absorbers with superior performance is one of the focuses in the field of advanced laser technology. In this work, the authors fabricate a new saturable absorption mirror (SAM) based on BK7 glass wafer, which is with a buried thin‐layer of silver (Ag) nanoparticles (NPs). The embedded Ag NPs‐based SAM (Ag‐NPs‐SAM) possesses excellent saturable absorption features due to the localized surface plasmon resonance (LSPR) effect of Ag NPs, and outstanding environmental stability owing to the protection of insulating dielectrics. In addition, benefiting from the ultrafast recovery time of Ag NPs, a continuous‐wave mode‐locking operation with the embedded Ag‐NPs‐SAM at 1037 nm is achieved in a Yb:KGW solid‐state laser system, obtaining pulses of a duration as short as 324 fs. The authors work offers a new strategy toward broadband response and high‐stability saturable absorbers for developing advanced ultrafast lasers.