Xiaobo Xing

Non-Kirchhoff states of thermal radiation, which benefit from their nontrivial nonreciprocal emissivity properties, are crucial for addressing pressing challenges such as global climate change, energy crisis, and overheating of electronic devices. However, significant challenges remain in the quest to develop a design paradigm characterized by nonreciprocal switching to facilitate transformative breakthroughs in non-Kirchhoff radiative devices. Here, we develop a temperature-activated switchable nonreciprocal thermal emitter comprising a silicon cylindrical grating array on InAs/VO2 films, which enables switchable nonreciprocal thermal radiation for TE modes at λ = 9.481 µm and θ = ±10°, resulting in a remarkable nonreciprocity of 0.45, a high Q-factor of ≈403 for the emissivity, and a switch ratio of 146. Leveraging magneto-optical quasi-bound states in the continuum coupling and VO2's phase transition, the structure achieves robust control: (i) a nonreciprocal “on” state with enhanced light–matter interactions in VO2's insulating phase, and (ii) a nonreciprocal “off” state with negligible effects in its metallic phase for both TE and TM modes, making it a polarization-selective emitter with switchable nonreciprocal thermal radiation. This work bridges the gap in switchable nonreciprocal thermal radiation research and provides insights into the design of practical nonreciprocal thermal structures, with applications in thermal camouflage, energy conversion, and thermal management.

Microfluidic switches are important operating units in microfluidics that enable controlled fluid flow on the chip, providing more functionality of platform. Most fiber based photofluidic devices mainly modulate temperature gradient and microflow by varying optical power. However, only power regulation limits the diversity of the optical field, which makes it difficult to achieve microfluidic control at different localized regions. Here, optical field of a tilted fiber Bragg grating (TFBG) can be theoretically modulated by the incident light wavelength and direction based on the finite element method. A photothermal vortices based microfluidic switch is built by TFBG with multiple linear heat sources. In the simulation, when the incident light is coupled in the forward or reverse direction of TFBG, the reflected position of the optical field is positively moved along the grating region as the wavelength increases. In the experiment, the opening of the microfluidic at different positions and directions can be clearly observed when the wavelength-matched laser is incident at the TFBG in the forward or reverse direction. It is believed that the microfluidic switch provides ideas for more flexible operation and functional integration for photothermal microfluidic devices in the future.

Quantum dots (QDs) exhibit excellent optical and chemical properties, making them advantageous for fluorescence sensing. However, gas sensor using QDs is often hampered by challenges such as gas diffusion and low concentration. This work describes the development of a nitrogen dioxide (NO₂) fluorescence gas sensor that utilizes a QDs@Aerogels/SM composite nanofilm containing CdTe QDs modified by reduced glutathione (GSH), silica microspheres (SMs), and silica aerogel. The SM and porous aerogels create a uniform porous structure that enhances the distribution of QDs. Compared to the pure QDs film, the QDs@Aerogels/SM composite film exhibits enhanced fluorescence intensity. The porous structure promotes the adsorption of NO₂, which improves the detection sensitivity. The QDs@Aerogels/SM composite film was applied in a portable gas sensor. The sensor demonstrates a good linear response to NO₂ gas in the range of 0–10 ppm, with an ultra-low detection limit of 0.096 ppm and high selectivity. The uniform distribution of aerogel and SM enhances the stability of the composite nanofilm, and the fluorescence of the films remains virtually unchanged over a period of 60 days which ensures its optimal performance over extended periods of use. The fluorescent NO₂ sensor demonstrated selective and sensitive quenching upon exposure to NO₂, making it ideal for environmental monitoring and further applications.

This study explores the potential of MoS₂ monolayers as heavy metal sensors for As, Cd, Hg, and Pb using density functional theory (DFT) and Non-Equilibrium Green’s Function (NEGF) simulations. Our findings reveal that As and Pb adsorption significantly alters the surface structure and electronic properties of MoS₂, introducing impurity levels and reducing the band gap. Conversely, Cd and Hg exhibit weaker interactions with the MoS₂ surface. The MoS₂ monolayer sensors demonstrate exceptional sensitivity for all four target heavy metals, with values reaching 126,452.28% for As, 1862.67% for Cd, 427.71% for Hg, and 83,438.90% for Pb. Additionally, the sensors demonstrate selectivity for As and Pb through distinct response peaks at specific bias voltages. As and Pb adsorption also induces magnetism in the MoS₂ system, potentially enabling magnetic sensing applications. The MoS₂ monolayer’s moderate adsorption energy facilitates rapid sensor recovery at room temperature for As, Hg, and Cd. Notably, Pb recovery time can be significantly reduced at elevated temperatures, highlighting the reusability of the sensor. These results underscore the potential of MoS₂ monolayers as highly sensitive, selective, and regenerable sensors for real-time heavy metal detection.

This study explores the potential of β-SnSe monolayers as a promising material for ozone (O₃) sensing using density functional theory (DFT) combined with the non-equilibrium Green’s function (NEGF) method. The adsorption characteristics of O₃ molecules on the β-SnSe monolayer surface were thoroughly investigated, including adsorption energy, band structure, density of states (DOSs), differential charge density, and Bader charge analysis. Post-adsorption, hybridization energy levels were introduced into the system, leading to a reduced band gap and increased electrical conductivity. A robust charge exchange between O₃ and the β-SnSe monolayer was observed, indicative of chemisorption. Recovery time calculations also revealed that the β-SnSe monolayer could be reused after O₃ adsorption. The sensitivity of the β-SnSe monolayer to O₃ was quantitatively evaluated through current-voltage characteristic simulations, revealing an extraordinary sensitivity of 1817.57% at a bias voltage of 1.2 V. This sensitivity surpasses that of other two-dimensional materials such as graphene oxide. This comprehensive investigation demonstrates the exceptional potential of β-SnSe monolayers as a highly sensitive, recoverable, and environmentally friendly O₃ sensing material.

Optofluidic techniques have evolved as a prospering strategy for microparticle manipulation via fluid. Unfortunately, there is still a lack of manipulation with simple preparation, easy operation, and multifunctional integration. In this Letter, we present an optofluidic device based on a graphite oxide (GO)-coated dual-fiber structure for multifunctional particle manipulation. By changing the optical power and the relative distance of the fibers, the system can excite thermal fluidic vortices with three inter-coupled states, namely uncoupled, partially coupled and completely coupled states, and therefore can realize capture, sorting, and transportation of the target particles. We conduct a numerical analysis of the whole system, and the results are consistent with the experimental phenomena. This versatile device can be utilized to manipulate target particles in complex microscopic material populations with the advantages of flexible operation, user-friendly control, and low cost.

In recent years, gold nanomaterials have become a hot topic in photothermal tumor therapy due to their unique surface plasmon resonance characteristics. The effectiveness of photothermal therapy is highly dependent on the shape and size of gold nanoparticles. In this work, we investigate the photothermal therapeutic effects of four different sizes of gold nanorods (GNRs). The results show that the uptake of short GNRs with aspect ratios 3.3–3.5 by cells is higher than that of GNRs with aspect ratios 4–5.5. Using a laser with single pulse energy as low as 28 pJ laser for 20 s can induce the death of liver cancer cells co-cultured with short GNRs. Long GNRs required twice the energy to achieve the same therapeutic effect. The dual-temperature model is used to simulate the photothermal response of intracellular clusters irradiated by a laser. It is found that small GNRs are easier to compact because of their morphological characteristics, and the electromagnetic coupling between GNRs is better, which increases the internal field enhancement, resulting in higher local temperature. Compared with a single GNR, GNR clusters are less dependent on polarization and wavelength, which is more conducive to the flexible selection of excitation laser sources.

Real-time monitoring of volatile organic compounds (VOCs) is crucial for both industrial production and daily life. However, the non-reactive nature of VOCs and their low concentrations pose a significant challenge for developing sensors. In this study, we investigated the adsorption behaviors of typical VOCs (C₂H₄, C₂H₆, and C₆H₆), on pristine and Pt-decorated SnS monolayers using density functional theory (DFT) calculations. Pristine SnS monolayers have limited charge transfer and long adsorption distances to VOC molecules, resulting in VOC insensitivity. The introduction of Pt atoms promotes charge transfer, creates new energy levels, and increases the overlap of the density of states, thereby enhancing electron excitation and improving gas sensitivity. Pt-decorated SnS monolayers exhibited high sensitivities of 241,921.7%, 35.7%, and 74.3% towards C₂H₄, C₂H₆, and C₆H₆, respectively. These values are 142,306.9, 23.8, and 82.6 times higher than those of pristine SnS monolayers, respectively. Moreover, the moderate adsorption energies of adsorbing C₂H₆ and C₆H₆ molecules ensure that Pt-decorated SnS monolayers possess good reversibility with a short recovery time at 298 K. When heated to 498 K, C₂H₄ molecules desorbs from the surface of Pt-decorated SnS monolayer in 162.33 s. Our results indicate that Pt-decorated SnS monolayers could be superior candidates for sensing VOCs with high selectivity, sensitivity, and reversibility.