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The modulation of the terahertz (THz) wave is fundamental for its applications in next-generation communications, biological imaging, sensing, and so forth. Searching for higher efficient modulation is still in progress, although plenty of materials have been explored for tuning THz wave. In this work, optical-transparent self-assembled MXene films are used to modulate the THz reflection at the SiO2/MXene/air interface based on the impedance matching mechanism. By adjusting the number of stacked MXene layers/concentrations of MXene dispersions, the sheet conductivity of the MXene films will be changed so that the impedance at the SiO2/MXene/air interface can be tuned and lead to a giant modulation of THz reflection. Particularly, we demonstrate that the MXene films have highly efficient THz modulation from antireflection to reflection-enhancing with a relative reflection of 27% and 406%, respectively. This work provides a new pathway for developing the MXene films with the combination of optical-transparency and high smart THz reflection characteristics, and the films can be applied for THz antireflection or reflection-enhancing.

This study aimed to assess the effects of microbial inoculants and growth stage on fermentation quality, microbial community, and

The application of terahertz imaging in biomedical diagnostics is limited by the poor imaging contrast due to the strong absorption of terahertz waves by water molecules in the living body. To resolve this problem, gold nanorods (GNRs) have been considered as a possible contrast agent. However, the conventional preparation of GNRs requires using cetyltrimethylammonium bromide (CTAB) as a stabilizing surfactant, which is toxic to animals at high exposures. In this work, a modified seed-mediated growth method was proposed to synthesize silica-coated GNRs, which exhibited better stability and biocompatibility and the same cellular uptake efficiency as compared to those of uncoated GNRs. Moreover, silica-coated GNRs showed higher photothermal efficiency caused by the localized surface plasmon resonance that increased the terahertz reflection amplitude. In particular, the in vitro terahertz imaging of prostate cancer cells demonstrated noticeably higher contrast when silica-coated GNRs were used as a contrast agent. Hence, this study suggests a stable, biocompatible, and efficient contrast-enhancing agent for terahertz imaging, which can expand the scope of its clinical applications.

In this paper, the defects of TiO

VO2 with reversible semiconductor–metal phase transition properties is particularly available for the application in smart opto-electrical devices. However, there are rare reports on comparing its phase transition properties at different ranges. In this study, the VO2 films are designed with the similar crystalline structure and stoichiometry, but different morphologies by inorganic and organic sol-gel methods, and their phase transition characteristics are compared both at infrared and terahertz range. The results indicate that the VO2 film prepared by inorganic sol-gel method shows more compact nanostructure. It results in larger resistivity change, infrared and terahertz switching ratio in the VO2 film. Moreover, it presents that the phase transition intensity of VO2 film in terahertz range is more sensitive to its microstructure. This work is helpful for understanding the susceptibility of terahertz switching properties of VO2 to its microstructure. And it can provide insights for the applicat...

Integration of vanadium dioxide (VO2) on flexible substrates can realize flexible devices which can modulate the photoelectric response triggered by temperature, electric field, laser, etc. But the preparation of high quality flexible films is still blocked due to the high-temperature condition for VO2 growth. In this paper, a one-step procedure was proposed to prepare VO2 thin films on low-priced natural mica substrate by radio frequency (RF) reactive magnetron sputtering with a pure V target in an atmosphere of Ar/O2 gas mixture. Through optimizing the deposition temperature and thickness systematically, a high performance flexible VO2 film was obtained. It demonstrated large resistance change of around 4.8 orders of magnitude, and giant terahertz (THz) switching ratio of around 86.1% across the phase transition. Moreover, the VO2/Mica flexible film remained stable phase transition characteristic during the bending flexibility measurement. This work provides an alternative way to fabricate flexible VO2 film and makes it a candidate for the applications in flexible oxide electronics.

Vanadium dioxide (VO2) with reversible metal-semiconductor transition is one of the most researched smart materials due to its near room-temperature transition at around 68 °C. Coating VO2 (M) nanoparticles onto substrate is superior to fabrication of VO2 (M) thin films owing to its advantages on large-scale preparation and flexible shaping. In this study, freeze-drying has been applied in a convenient precipitating and following annealing process of fabricating VO2 (M) nanoparticles. More importantly, effects of freeze-drying and pre-freezing temperature on phase composition, size distribution and phase-transition temperature of synthesized particles have been systematically researched by varying the pretreatment conditions. It is observed that the application of freeze-drying is crucial to the formation of pure VO2 (M), meanwhile, phase-transition temperature and size distribution of VO2 (M) nanoparticles can be effectively reduced with lowered pre-freezing temperatures. Besides, the influence of different annealing temperatures on nanocrystallite size has been investigated, and it has been found that both the crystallinity and particle size increased as the annealing temperature was increased. Finally, the as-fabricated VO2 (M) particles were coated onto microscopic glass substrate to characterize mid-infrared modulation performance. The coated film (made from sample pre-frozen at −50 °C) exhibits an excellent mid-infrared transmittance change of 23.3% at a fixed wavelength of 4 μm. This work demonstrates the effect of freeze-drying on the fabrication of VO2 (M) nanoparticles and provides a facile method for large-scale preparation of VO2 (M) nanoparticles.

Dynamic tuning of terahertz (THz) wave has a great potential application as smart THz devices, such as switches, modulators, sensors, and so on. However, the realization of flexible THz modulation with high efficiency is rarely observed, which is nearly absent from the booming development and demands on flexible electronics. Here, we report a flexible THz modulation based on conductive polymer composites composed of thermoplastic polyurethane (TPU) and conductive particles (Ni). By designing the additive content of Ni particles, such a flexible layer exhibits resistivity change of 6-7 orders under tensile strain due to the formation of an electron-transport channel provided by the in situ evolution of the Ni network. It could be used to dynamically control the THz transmission with a giant modulation depth of around 96%, at a high strain operation (up to around 58.5%). Moreover, these characteristics are demonstrated to be available for highly tension sensitive THz spectroscopy and imaging. This work opens up a connection between flexible polymer-based composites and THz dynamic devices. It proposes an unprecedented flexible THz modulation with giant tuning efficiency and provides a scheme for contactless and passive tension sensors.

In this work, the thermal degradation behaviors of two kinds of biomasses (pinewood and rice husk) with powder and pellet under three oxygen concentrations were investigated by a self-designed macro-thermogravimetric analyzer. An obvious hysteresis of thermal degradation of biomass pellets was observed under three conditions. The maximum activation energy of biomass pellets was significantly greater than that of biomass powders, while their average activation energies were almost equal based on distributed activation energy model. For the oxygen-rich combustion, the comprehensive combustion character index of powdered and pelletized biomasses ranged from 3.92 × 10−7 to 5.16 × 10−7%2·min−2·°C−3 and from 1.82 × 10−7 to 1.91 × 10−7%2·min−2·°C−3, respectively. Furthermore, the derived biochar of powdered biomass has a higher caloricity than that of pelletized biomass during combustion by TG-DSC analysis. The performances of thermal degradation observed by macro-thermogravimetric analyzer could factually reveal the influence of mass and heat transfer on the thermochemical conversion of powdered and pelletized biomasses.

Thyroid cancer is the most frequent endocrine tumor with a growing incidence worldwide. However, common diagnostic strategy for thyroid cancer classification is hardly to make a proper diagnosis in some cases. To assist classical approach, this study used metabolomics to screen and validate biomarkers from serum and urinary for papillary thyroid cancer (PTC). Overall, 124 untreated PTC, 76 untreated benign thyroid nodule (BTN), and 116 healthy control (HC) were collected in this study. Thirty-six differential metabolites were screened from non-targeted metabolomics with a discovery sample set in comparison with HC and BTN. Serum β-hydroxybutyrate (BHB), docosahexaenoic acid (DHA), 1-methyladenosine (1-MedA), pregnanediol-3-glucuronide (PdG), urinary nicotinic acid mononucleotide (NAM) and xanthosine (Xan) were validated to be significantly differential by targeted metabolomics in validation set. The logistic regression model incorporating six biomarkers had excellent discrimination from receiver-operating characteristics (ROC) analysis, with area under the receiver-operating characteristic curve (AUC) of 0.943 (95% CI 0.902 to 0.983) and 0.952 (95% CI 0.921 to 0.983) for female alone and female + male samples, respectively. The prediction accuracy and false-negative rate in the real setting of one PTC to ten suspicious nodules were 84.7 and 17.7% with the threshold at probablity of 0.5. Results of a double-blind study for PTC and BTN had true positive value of 100% and true negative value of 91.7%. To conclude, BHB, DHA, 1-MedA, PdG, NAM and Xan are suitable biomarkers for PTC, and logistic regression models with the six biomarkers can be potentially used as clinical diagnosis.

The application of terahertz imaging in biomedical diagnostics is limited by the poor imaging contrast due to the strong absorption of terahertz waves by water molecules in the living body. To resolve this problem, gold nanorods (GNRs) have been considered as a possible contrast agent. However, the conventional preparation of GNRs requires using cetyltrimethylammonium bromide (CTAB) as a stabilizing surfactant, which is toxic to animals at high exposures. In this work, a modified seed-mediated growth method was proposed to synthesize silica-coated GNRs, which exhibited better stability and biocompatibility and the same cellular uptake efficiency as compared to those of uncoated GNRs. Moreover, silica-coated GNRs showed higher photothermal efficiency caused by the localized surface plasmon resonance that increased the terahertz reflection amplitude. In particular, the

Tackling the interfacial loss in emerged perovskite-based solar cells (PSCs) to address synchronously the carrier dynamics and the environmental stability, has been of fundamental and viable importance, while technological hurdles remain in not only creating such interfacial mediator, but the subsequent interfacial embedding in the active layer. This article reports a strategy of interfacial embedding of hydrophobic fluorinated-gold-clusters (FGCs) for highly efficient and stable PSCs. The p-type semiconducting feature enables the FGC efficient interfacial mediator to improve the carrier dynamics by reducing the interfacial carrier transfer barrier and boosting the charge extraction at grain boundaries. The hydrophobic tails of the gold clusters and the hydrogen bonding between fluorine groups and perovskite favor the enhancement of environmental stability. Benefiting from these merits, highly efficient formamidinium lead iodide PSCs (champion efficiency up to 24.02%) with enhanced phase stability under varied relative humidity (RH) from 40% to 95%, as well as highly efficient mixed-cation PSCs with moisture stability (RH of 75%) over 10 000 h are achieved. It is thus inspiring to advance the development of highly efficient and stable PSCs via interfacial embedding laser-generated additives for improved charge transfer/extraction and environmental stability.

In this paper, the defects of TiO2/Ag2O nanoheterojunctions are regulated to evaluate the effect of the interface defects on carrier trapping and recombination dynamics by time-resolved photoluminescence spectroscopy (TRPL) and time-resolved terahertz (THZ) spectroscopy. TRPL spectra reveal that interface defects can act as a recombination center and have an accelerative effect on the recombination process of photogenerated carriers under ultraviolet light. Moreover, THZ spectroscopy results demonstrate that interface defects can effectively trap electrons and expedite the Auger recombination. Furthermore, the influence of interface defects on the photocarrier dynamics of TiO2/Ag2O nanoheterojunctions was comprehensively analyzed, providing a valuable experimental reference for the regulation and application of interface defect-fabricated nanoheterojunctions.

Vanadium dioxide (VO2), with reversible metal–semiconductor transition near room temperature, is a compelling candidate for thermochromic windows. Nanocomposite coatings derived from VO2 nanoparticles are particularly superior to VO2 films due to their advantages in large-scale preparation, flexible shaping, and regulation of optical properties. In this work, we developed a novel method for one-step hydrothermal synthesis of W-doped VO2 (M) nanorods and studied their application in large-scale infrared smart windows. On introducing tartaric acid as a new reductant, VO2 underwent a two-stage phase evolution from the pure phase comprising VO2 (A) nanobelts to VO2 (M) nanorods, instead of the conventional three-stage B–A–M phase evolution during hydrothermal synthesis. This transition is very favorable for the large-scale hydrothermal synthesis of VO2 (M). The phase-transition temperature of VO2 (M) nanoparticles can be regulated systematically by W doping, with a reduction efficiency of about 24.52 °C/atom ...

We present a terahertz (THz) amplitude modulator with near perfect modulation depth based on the impedance matching method during the thermally induced insulator-metal transition (IMT) of VO 2 thin films. It has been observed that the impedance matching-induced THz amplitude modulation was sensitive to the resistance switching characteristics of the VO 2 thin films. With four orders of change in resistance of the properly designed VO 2 films during the IMT, we experimentally achieved a near perfect THz modulator with an intensity modulation depth of 99.7% between the insulator phase of VO 2 and the impedance matching state, and intensity modulation depth of 99.94% between the impedance matching state and the metallic phase of VO 2 . The experimental results were well explained by numerical simulations based on the transfer matrix model.

Pure and Ti-doped vanadium dioxide (VO2) thin films were deposited on muscovite substrates using an inorganic sol–gel method. The crystallinity, stoichiometry, surface morphology and phase transition properties of the films were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope and in situ FTIR measurement, respectively. The results indicated that all the VO2 films exhibited polycrystalline structure, with a (011) preferred orientation. But Ti doping affected the morphology of the films remarkably, which then led to varied phase transition properties. Particularly, the phase transition temperature elevated by increasing the doping concentration of Ti (from 61 °C for pure film to 71.5 °C for the film doped with 2.8 at.% Ti), and the hysteresis loop decreased simultaneously. This study proposed a new method to prepare Ti-doped VO2 film and provided considerable insights for the application of Ti-doped VO2 film due to its unique phase transition properties.

We demonstrate an all optically driven memory device based on vanadium dioxide ( V O 2 ) for terahertz (THz) waves. By easily tuning the power of illuminating light, a V O 2 memory device is coded in reconfigurable and multi-level states, taking advantage of its hysteretic metal-to-insulator phase transition (MIT). Further, writing with intense femtosecond pulses, the memory effects are performed by non-thermal photo-induced MIT, and resultant 2-bit coding with a write time of 22 µs is demonstrated, yielding a dramatically improved write rate compared to existing thermally controlled V O 2 memory device. The proposed all optically driven V O 2 -based memory device paves the way for actively manipulating THz waves within robust reconfigurable high-speed memory functionality.

We experimentally investigated the terahertz (THz) reflection modulation property of tungsten-(W-) doped vanadium dioxide (V1-xWxO2) thin film enabled by impedance matching at the interface, which behaves as a giant modulation within a broadband THz frequency range during insulator-to-metal transition. A systematical theoretical model for impedance matching is also established, which includes three factors: sheet conductivity of V1-xWxO2 thin film, incidence angle of THz wave, and refractive index of substrate. With the modeling, we demonstrated a method to continuously tune the impedance matching at the interface of substrate-V1-xWxO2 thin films-air. Four different conductivities of V1-xWxO2 thin films realized by tuning W-doping densities (x = 0, 0.35%, 0.51%, and 1.06%), three incident angles (35°, 45°, 60°), and three substrates (SiO2, Al2O3, and Si,) with refractive indices of 1.95, 2.7, 3.4 were used in our experiments to validate our proposed model. These results provide a promising route for continuously tuning broadband THz wave modulation with the impedance matching effect at the thin film interface.

We proposed and demonstrated a method to enhance photoresponses in the timescale from nanoseconds to microseconds of an all optically driven VO2-based terahertz (THz) wave modulator by driving the initial VO2 close to percolation threshold (via externally heating the initial VO2 thin film near insulator-to-metal transition temperature). We experimentally realized 10-fold, 3-fold, and 3-fold improvement of photosensitivity, photoresponsivity, and optical modulation bandwidth of the VO2-based THz wave modulator, respectively. Percolation theory, along with the macroscopic conductivity response, was used to explain the mechanism for photomodulation response enhancement. The enhanced photomodulation response is promising especially for optical modulators and photodetectors. This approach is also compatible with other optimization methods and can be further used to enhance other VO2-based optoelectronic devices.

We present a terahertz (THz) amplitude modulation method with near perfect E-field amplitude modulation depths that is based on impedance matching in VO2 thin films during the thermally induced insulator-metal transition (IMT). It was observed that the impedance matching-induced THz amplitude modulation was sensitive to the resistance switching characteristics of the VO2 thin films. By designing the VO2 thin films to have four orders of magnitude of change in resistance during the IMT, we experimentally achieved an E-field amplitude modulation depth of 94.5% (intensity modulation depth of 99.7%) between the insulator phase of VO2 and the impedance matching state, and an E-field amplitude modulation depth of 97.6% (intensity modulation depth of 99.94%) between the impedance matching state and the metallic phase of VO2 at 0.5 THz. The experimental results were consistent with the results of simulations based on the transmission matrix model.