A terahertz meta-sensor array for 2D strain mapping.

Large-scale stretchable strain sensor arrays capable of mapping two-dimensional strain distributions have gained interest for applications as wearable devices and relating to the Internet of Things. However, existing strain sensor arrays are usually unable to achieve accurate directional recognition and experience a trade-off between high sensing resolution and large area detection. Here, based on classical Mie resonance, we report a flexible meta-sensor array that can detect the in-plane direction and magnitude of preloaded strains by referencing a dynamically transmitted terahertz (THz) signal. By building a one-to-one correspondence between the intrinsic electrical/magnetic dipole resonance frequency and the horizontal/perpendicular tension level, arbitrary strain information across the meta-sensor array is accurately detected and quantified using a THz scanning setup. Particularly, with a simple preparation process of micro template-assisted assembly, this meta-sensor array offers ultrahigh sensor density (~11.1 cm-2) and has been seamlessly extended to a record-breaking size (110 × 130 mm2), demonstrating its promise in real-life applications.

Tunable C4-Symmetry-Broken Metasurfaces Based on Phase Transition of Vanadium Dioxide (VO2).

Coupling is a ubiquitous phenomenon observed in various systems, which profoundly alters the original oscillation state of resonant systems and leads to the unique optical properties of metasurfaces. In this study, we introduce a terahertz (THz) tunable coupling metasurface characterized by a four-fold rotation (C4) symmetry-breaking structural array achieved through the incorporation of vanadium dioxide (VO2). This disruption of the C4 symmetry results in dynamically controlled electromagnetic interactions and couplings between excitation modes. The coupling between new resonant modes modifies the peak of electromagnetic-induced transparency (EIT) within the C4 symmetric metasurfaces, simulating the mutual interference process between modes. Additionally, breaking the C4 symmetry enhances the mirror asymmetry, and imparts distinct chiral properties in the far-field during the experimental process. This research demonstrates promising applications in diverse fields, including biological monitoring, light modulation, sensing, and nonlinear enhancement.

VO2 Films Decorated with an MXene Interface for Decreased-Power-Triggered Terahertz Modulation.

VO2, which exhibits semiconductor-metal phase transition characteristics occurring on a picosecond time scale, holds great promise for ultrafast terahertz modulation in next-generation communication. However, as of now, there is no reported prototype for an ultrafast device. The temperature effect has been proposed as one of the major obstacles. Consequently, reducing the excitation threshold for the phase transition would be highly significant. The traditional strategy typically involves chemical doping, but this approach often leads to a decrease in phase transition amplitude and a slower transition speed. In this work, we proposed a design featuring a highly conductive MXene interfacial layer between the VO2 film and the substrate. We demonstrate a significant reduction in the phase transition threshold for both temperature and laser-induced phase transition by adjusting the conductivity of the MXene layers with varying thicknesses. Our observations show that the phase transition temperature can be decreased by 9 °C, while the pump fluence for laser excitation can be reduced by as high as 36%. The ultrafast phase transition process on a picosecond scale, as revealed by the optical-pump terahertz-probe method, suggests that the MXene layers have minimal impact on the phase transition speed. Moreover, the reduced phase transition threshold can remarkably alleviate the photothermal effect and inhibit temperature rise and diffusion in VO2 triggered by laser. This study offers a blueprint for designing VO2/MXene hybrid films with reduced phase transition thresholds. It holds significant potential for the development of low-power, intelligent optical and electrical devices including, but not limited to, terahertz modulators based on phase transition phenomena.

Automatic marker-based alignment method for a nano-resolution full-field transmission X-ray microscope.

Driven by the development of X-ray optics, the spatial resolution of the full-field transmission X-ray microscope (TXM) has reached tens of nanometers and plays an important role in promoting the development of biomedicine and materials science. However, due to the thermal drift and the radial/axial motion error of the rotation stage, TXM computed tomography (CT) data are often associated with random image jitter errors along the horizontal and vertical directions during CT measurement. A nano-resolution 3D structure information reconstruction is almost impossible without a prior appropriate alignment process. To solve this problem, a fully automatic gold particle marker-based alignment approach without human intervention was proposed in this study. It can automatically detect, isolate, and register gold particles for projection image alignment with high efficiency and accuracy, facilitating a high-quality tomographic reconstruction. Simulated and experimental results confirmed the reliability and robustness of this method.

Mesoporous black TiO2 hollow shells with controlled cavity size for enhanced visible light photocatalysis.

Black TiO2 formed by introducing lattice disorder into pristine TiO2 has a narrowed band gap and suppresses the recombination of charge carriers. This provides a potential strategy for visible light photocatalysis. However, the microstructural design of black TiO2 for a higher optimization of visible light is still in high demand. In this work, we proposed the preparation of black TiO2 hollow shells with controllable cavity diameters using silica spheres as templates for the cavities and the NaBH4 reduction method. The decreased cavity size resulted in a hollow shell with an enhanced visible-light absorption and improved photocatalytic performance. Moreover, we demonstrated that this cavity can be combined with gold nanoparticles (AuNPs) to form AuNPs@black TiO2 yolk-shells. The AuNPs provided additional visible light absorption and promoted the separation of photogenerated carriers in the yolk-shell structures. This further improved the photocatalysis, the degradation rate of Cr(VI) can reach 0.066 min-1. Our work evaluated the effect of the cavity size on the photocatalytic performance of hollow and yolk-shell structures and provided concepts for the further enhancement of visible-light photocatalysis.

Impact of the uniaxial strain on terahertz modulation characteristics in flexible epitaxial VO2 film across the phase transition.

Exploring flexible electronics is on the verge of innovative breakthroughs in terahertz (THz) communication technology. Vanadium dioxide (VO2) with insulator-metal transition (IMT) has excellent application potential in various THz smart devices, but the associated THz modulation properties in the flexible state have rarely been reported. Herein, we deposited an epitaxial VO2 film on a flexible mica substrate via pulsed-laser deposition and investigated its THz modulation properties under different uniaxial strains across the phase transition. It was observed that the THz modulation depth increases under compressive strain and decreases under tensile strain. Moreover, the phase-transition threshold depends on the uniaxial strain. Particularly, the rate of the phase transition temperature depends on the uniaxial strain and reaches approximately 6 °C/% in the temperature-induced phase transition. The optical trigger threshold in laser-induced phase transition decreased by 38.9% under compressive strain but increased by 36.7% under tensile strain, compared to the initial state without uniaxial strain. These findings demonstrate the uniaxial strain-induced low-power triggered THz modulation and provide new insights for applying phase transition oxide films in THz flexible electronics.

Stereoselective coronas regulate the fate of chiral gold nanoparticles in vivo.

It is unknown how the identity provided by protein coronas on the surface of chiral nanoparticles determines their blood circulation, distribution, and clearance fates of the nanoparticles in vivo. Here, we attempt to investigate how the mirrored surface of gold nanoparticles with distinct chirality reshapes the coronal composition that mediates their subsequent clearance from blood and biodistribution. We found that chiral gold nanoparticles exhibited surface chirality-specific recognition for the coronal components, including the lipoproteins, complement components, and acute phase proteins, ultimately resulting in distinct cell uptake and tissue accumulation in vivo. We observed that these stereoselective behaviors were correlated to subgroups of the corona composition that could bind to low-density lipoprotein receptors. Therefore, this study reveals how chirality-specific protein compositions selectively recognize and interact with cell receptors for chirality-mediated tissue accumulation. This study will deepen our understanding of how chiral nanoparticles/nanomedicine/nanocarriers interact with biological systems to guide the efficient fabrication of target nanomedicines.

Deep-learning-based ring artifact correction for tomographic reconstruction.

X-ray tomography has been widely used in various research fields thanks to its capability of observing 3D structures with high resolution non-destructively. However, due to the nonlinearity and inconsistency of detector pixels, ring artifacts usually appear in tomographic reconstruction, which may compromise image quality and cause nonuniform bias. This study proposes a new ring artifact correction method based on the residual neural network (ResNet) for X-ray tomography. The artifact correction network uses complementary information of each wavelet coefficient and a residual mechanism of the residual block to obtain high-precision artifacts through low operation costs. In addition, a regularization term is used to accurately extract stripe artifacts in sinograms, so that the network can better preserve image details while accurately separating artifacts. When applied to simulation and experimental data, the proposed method shows a good suppression of ring artifacts. To solve the problem of insufficient training data, ResNet is trained through the transfer learning strategy, which brings advantages of robustness, versatility and low computing cost.

Investigating exceptional points in dark-bright mode-coupled plasmonic systems.

Exceptional points (EPs) of non-Hermitian systems are gaining more and more attention due to their important applications in unidirectional transmitters, sensors, etc. However, theoretical studies on EPs of reflection, transmission, and absorption spectra are less available. In this paper, in the dark-bright mode-coupled plasmonic systems, the variations of EPs of reflection, transmission, and absorption spectra are numerically investigated using temporal coupled-mode theory, and an assumption is given using the representation transformation theory. The intermediate representation (IR) is firstly proposed and related to the reflection spectrum, while the normal representation (NR) is associated with the absorption spectrum. In the region far from EPs, the IR (or NR) describes the reflection (or absorption) spectrum well. Near EPs, modified formulas similar to the representation transformation theory are given. In order to verify the correctness of the assumption, two metasurfaces are designed. And the simulation results are in good agreement with the assumption and it is found in the near-infrared and visible-light band that the absorption loss of the dark mode is linearly related to the EPs of reflection, transmission, and absorption spectra, while the radiation loss of the bright mode is only linearly related to the EPs of the absorption spectrum. These laws can help to manipulate the splitting of spectral lines for reflection, transmission, and absorption by adjusting the radiation loss and absorption loss of bright mode, the absorption loss of dark mode, and the coupling coefficients between two resonant modes. This research provides a guiding scheme for the design of micro and nano photonics devices.

Thermal and mechanical THz modulation of flexible all-dielectric metamaterial.

The implementation of Terahertz (THz) modulation is critical for applications in high-speed wireless communications, security screening and so on. Therefore, it is particularly significant to obtain THz wave modulation devices with stable and flexible performance, easy manipulation of the modulation method, and multi-functionality. Here, we propose a flexible all-dielectric metamaterial by embedding zirconia (ZrO2) microspheres into a vanadium dioxide/polydimethylsiloxane (VO2/PDMS) composite, which can achieve thermal and mechanical tuning of THz wave transmission. When the temperature of the ZrO2/VO2/PDMS metamaterial increases, VO2 changes from the insulating phase to the metallic phase, and the 1st (at 0.304 THz) and 2nd (at 0.414 THz) order magnetic resonances exhibit the tunability of 20 GHz and 15 GHz, respectively. When stretched, the 1st and 2nd order magnetic resonances show the tunability of 12 GHz and 10 GHz, respectively. In the meantime, there are accompanying changes in transmittance at the resonances. The ZrO2/VO2/PDMS all-dielectric metamaterial presented in this work provides an alternative strategy for developing actively tunable, flexible, and versatile THz devices. In addition, it has the merits of simple preparation and low cost, promising large-area and rapid preparation of meta-arrays.

Highly Flexible Ti3C2Tx MXene/Waterborne Polyurethane Membranes for High-Efficiency Terahertz Modulation with Low Insertion Loss.

The dynamic control of terahertz (THz) wave transmission on flexible functional materials is a fundamental building block for wearable electronics and sensors in the THz range. However, achieving high-efficiency THz modulation and low insertion loss is a great challenge while maintaining the excellent flexibility and stretchability of the materials. Herein, we report a Ti3C2Tx MXene/waterborne polyurethane (WPU) membrane prepared by a vacuum-assisted filtration method, which exhibits excellent THz modulation properties across stretching. The hydrophilic Ti3C2Tx MXene and WPU enable the uniform 3D distribution of Ti3C2Tx MXene in the WPU matrix. Particularly, the stretchability with the maximum strain of the membranes can reach 200%, accompanied by dynamic tuning of THz transmittance for more than 90% and an insertion loss as low as -4.87 dB. The giant THz modulation continuously decreases with MXene content per unit area, accompanied by a lower density of the MXene interface and diminished THz absorption during stretching. Such a design opens a pathway for achieving flexible THz modulators with a high modulation depth and low insertion loss, which would be used for THz flexible and wearable devices.

Quantitative Insights into a Plasmonic Ruler Equation from the Perspective of Enhanced Near Field.

The plasmonic shift of resonance wavelength induced by near-field coupling enables one to measure nanoscale distances optically. Empirically, the well-known ruler equation correlating plasmon shift with interparticle spacing was proposed. Though it has been widely used in analyzing simulation and experimental outcomes, little is known about the underlying physical mechanism of the characteristic exponential form of the plasmon ruler equation and the universal decay constant therein. In this work, we attempt to decrypt these from the perspective of plasmon near-field enhancement. Based on an analytical quasi-normal mode formula for plasmon shifts, we proved that the exponential decaying electric field is the critical reason that results in the exponential form of the plasmon ruler equation and quantitatively, we found that the universal decay constant in the plasmon ruler equation actually reflects the range of the enhanced near field. This work hopefully helps to deepen the understanding of the mechanism of light-matter interaction in corresponding plasmonic processes.

Cu/Al2O3 aerogels for high-efficiency and rapid iodide elimination from water.

Cu-based functional materials are excellent candidates for the elimination of iodine anions. However, the low utilization rate of Cu and its unsatisfactory adsorption performance limit its large-scale practical applications. This paper proposes a co-gelation method to obtain Cu/Al2O3 aerogels with a high specific area (537 m2/g). Cu/Al2O3 aerogels have a hierarchical porous structure and contain a high proportion of Cu (20.5 wt%). The high dispersibility of Cu, which is based on an in-situ gel process, provides conditions for the high-efficiency elimination of iodide anions. We conducted adsorption experiments that demonstrated that the fabricated Cu/Al2O3 aerogel had an ultrahigh adsorption capacity (407.6 mg/g) and a fast adsorption equilibrium time (0.5 h) for iodide anions. Additionally, the Cu/Al2O3 aerogel could selectively capture iodine anions even in the presence of high concentrations of competing ions (NO3-, SO42-, and Cl- at 60 mmol/L). Importantly, the aerogel can operate in a wide pH range of 3-11 without causing secondary pollution. This work demonstrates that low-cost Cu/Al2O3 aerogels exhibit great potential for eliminating radioactive iodine anions.

Terahertz switchable VO2-Au hybrid active metasurface holographic encryption.

The combination of metasurface and holographic technology is the most cutting-edge development, but most of the proposed designs are static and do not allow active changes through external stimulation after fabrication, which takes only a limited part of the advantage provided by metasurface. Here, we propose and demonstrate a switchable hybrid active metasurface hologram in the terahertz (THz) regime composed of dynamic pixels (VO2-CSRR) and static pixels (Au-CSRR) based on an intelligent algorithm, which can display some/all information in different temperature ranges. In particular, such performance shows excellent potential in the field of optical communication security, making it a promising candidate. To prove this possibility, we propose a scheme for optical information encryption/decryption and transmission, which takes metasurfaces as carriers of encrypted information and state/polarization/positions as the secret key components. Only when the two matches correctly can we get the hidden real information. The security of our proposed scheme has reached an unprecedented level, providing a new road for communication security.

Feature detection network-based correction method for accurate nano-tomography reconstruction.

Driven by the development of advanced x-ray optics such as Fresnel zone plates, nano-resolution full-field transmission x-ray microscopy (Nano-CT) has become a powerful technique for the non-destructive volumetric inspection of objects and has long been developed at different synchrotron radiation facilities. However, Nano-CT data are often associated with random sample jitter because of the drift or radial/axial error motion of the rotation stage during measurement. Without a proper sample jitter correction process prior to reconstruction, the use of Nano-CT in providing accurate 3D structure information for samples is almost impossible. In this paper, to realize accurate 3D reconstruction for Nano-CT, a correction method based on a feature detection neural network, which can automatically extract target features from a projective image and precisely correct sample jitter errors, is proposed, thereby resulting in high-quality nanoscale 3D reconstruction. Compared with other feature detection methods, even if the target feature is overlapped by other high-density materials or impurities, the proposed Nano-CT correction method still acquires sub-pixel accuracy in geometrical correction and is more suitable for Nano-CT reconstruction because of its universal and faster correction speed. The simulated and experimental datasets demonstrated the reliability and validity of the proposed Nano-CT correction method.

Reconfigurable Optical Physical Unclonable Functions Enabled by VO2 Nanocrystal Films.

Optical physical unclonable function (PUF) is one of the most promising hardware security solutions, which has been proven to be resistant to machine learning attacks. However, the disordered structures of the traditional optical PUFs are usually deterministic once they are manufactured and therefore exhibit fixed challenge-response behaviors. Herein, a reconfigurable PUF (R-PUF) is proposed and demonstrated by using the reversible phase transition behavior of VO2 nanocrystals combined with TiO2 disordered nanoparticles. Both the simulation and experiment results show that the near-infrared laser speckle pattern of the R-PUF can be almost completely altered after the phase transition of VO2 nanocrystals, resulting in a reconfigurable and reproducible optical response. The similarity of the response speckles shows an obvious hysteresis loop during the rise and drop of temperature, providing a simple way to regulate and control the response behaviors of the R-PUF. More importantly, the hysteretic characteristic provides a new dimension to describe the challenge-response behavior of the R-PUF besides the laser speckle, providing an effective way to improve the security and encoding capacity of the optical PUFs. The proposed R-PUF can be employed as a promising security primitive for high robustness and high-security authentication and encryption.

Volatile and Nonvolatile Switching of Phase Change Material Ge2Sb2Te5 Revealed by Time-Resolved Terahertz Spectroscopy.

Phase change materials exhibit unique advantages in reconfigurable photonic devices due to drastic tunability of photoelectric properties. Here, we systematically investigate the thermal equilibrium process and the ultrafast dynamics of Ge2Sb2Te5 (GST) driven by femtosecond (fs) pulses, using time-resolved terahertz spectroscopy. Both fs-pulse-driven crystallization and amorphization are demonstrated, and the threshold of photoinduced crystallization (amorphization) is determined to be 8.4 mJ/cm2 (10.1 mJ/cm2). The ultrafast carrier dynamics reveal that the cumulative photothermal effect plays a crucial role in the ultrafast crystallization, and modulation depth of volatile (nonvolatile) THz has switching limits up to 30% (15%). A distinctive phonon absorption at 1.1 THz is observed, providing fingerprint spectrum evidence of crystalline lattice formation driven by intense fs pulses. Finally, multistate volatile (nonvolatile) THz switching is implemented by tuning optical pump fluence. These results provide insight into the photoinduced phase change of GST and offer benefits for all optical THz functional devices.

THz medical imaging: from in vitro to in vivo.

Terahertz (THz) radiation has attracted considerable attention in medical imaging owing to its nonionizing and spectral fingerprinting characteristics. To date, most studies have focused on in vitro and ex vivo objects with water-removing pretreatment because the water in vivo excessively absorbs the THz waves, which causes deterioration of the image quality. In this review, we discuss how THz medical imaging can be used for a living body. The development of imaging contrast agents has been particularly useful to this end. In addition, we also introduce progress in novel THz imaging methods that could be more suitable for in vivo applications. Based on our discussions, we chart a developmental roadmap to take THz medical imaging from in vitro to in vivo.

Photothermal conversion of Ti2O3 film for tuning terahertz waves.

Dynamic tuning of terahertz (THz) wave is vital for the development of next generation THz devices. Utilization of solar energy for tuning THz waves is a promising, eco-friendly, and sustainable way to expand THz application scenarios. Ti2O3 with an ultranarrow bandgap of 0.1eV exhibits intriguing thermal-induced metal-insulator transition (MIT), and possesses excellent photothermal conversion efficiency. Herein, Ti2O3 film was fabricated by a two-step magnetron sputtering method, and exhibited an excellent photothermal conversion efficiency of 90.45% and demonstrated temperature-dependent THz transmission characteristics with a wideband at 0.1-1 THz. We supposed to combine photothermal conversion characteristics with temperature-dependent THz transmission properties of Ti2O3 film, which could introduce solar light as the energy source for tuning THz waves. Our work will provide new sight for investigating MIT characteristics of Ti2O3 at THz regime and exhibit huge potential in the application of tuning terahertz waves in outdoor scenarios in the future.

Distal pancreatectomy with En bloc celiac axis resection for locally advanced pancreatic body/tail cancer: A systematic review and meta-analysis.

Distal pancreatectomy with En-bloc celiac axis resection (DP-CAR) is a challenging procedure that has yielded certain clinical efficacy in the treatment of locally advanced pancreatic body/tail cancer, especially in patients with invasion of abdominal vessels. However, the clinical efficacy and safety of DP-CAR remain controversial. The study aimed to systematically review efficacy and safety of DP-CAR in the treatment of locally advanced pancreatic body/tail cancer. We systematically searched PubMed, EMBASE, Cochrane Library, and Web of Science databases from inception to 1 October 2020. Two studiers independently accomplished the study selection, data extraction, and quality assessment. Initially, of 1032 studies were searched, among which 11 high quality studies including 1072 patients were finally identified. The pooled results showed that DP-CAR versus Distal pancreatectomy (DP), the rate of R0 resection (RR = 0.76; 95%CI: 0.66 to 0.88; p = 0.0002) and 3-year survival (RR = 0.65; 95%CI: 0.43 to 0.98; p = 0.04) was lower, postoperative mortality (RR = 2.48; 95%CI: 1.02 to 6.03; p = 0.04) was higher, the operation time (MD = 104.67; 95%CI: 84.70 to 124.64; p < 0.001) and hospital stay (MD = 3.94, 95% CI 1.35 to 6.53; p = 0.003) were longer. There was no statistical difference between the DP-CAR and DP group in 1-year, 2-year survival rate (RR = 0.84; 95%CI: 0.57 to 1.23; p = 0.37) (RR = 0.70; 95%CI: 0.45 to 1.10; p = 0.12). In conclusion, compared with DP, DP-CAR has worse efficacy and prognosis survival and is more dangerous, but it can obtain better survival benefit and quality of life than palliative treatment. We suggest that DP-CAR can be carefully attempted for effective margin-negative resection. However, surgeons and patients need to know its potential perioperative risk.