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The emission of light from charged particles underlies a wealth of scientific phenomena and technological applications. Classical theory determines the emitted photon energy by assuming an undeflected charged particle trajectory. In 1940, Ginzburg pointed out that this assumption breaks down in quantum electrodynamics, resulting in shifts—known as quantum recoil— in outgoing photon energies from their classically predicted values. Since then, quantum recoil in free-electron light-emission processes, including Cherenkov radiation and Smith–Purcell radiation, has been well-studied in theory, but an experimental demonstration has remained elusive. Here we present an experimental demonstration of quantum recoil, showing that this quantum electrodynamical effect is not only observable at room temperature but also robust in the presence of other electron-scattering mechanisms. By scattering free electrons off the periodic two-dimensional atomic sheets of van der Waals materials in a tabletop platform, we show that the X-ray photon energy is accurately predicted only by quantum recoil theory. We show that quantum recoil can be enormous, to the point that a classically predicted X-ray photon is emitted as an extremely low-energy photon. We envisage quantum recoil as a means of precision control over outgoing photon and electron spectra, and show that quantum recoil can be tailored through a host of parameters: the electron energy, the atomic composition and the tilt angle of the van der Waals material. Our results pave the way to tabletop, room-temperature platforms for harnessing and investigating qua- ntum electrodynamical effects in electron–photon interactions. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Submitted/Accepted version This project was partially supported by the National Research Foundation (Project ID NRF2020-NRF-ISF004-3525) and the Agency for Science, Technology and Research (A*STAR) Science & Engineering Research Council (Grant No. A1984c0043). We acknowledge the Facility for Analysis, Characterisation, Testing and Simulation, Nanyang Technological University, Singapore, for use of their electron microscopy/X-ray facilities. Z.L. acknowledges the support from National Research Foundation, Singapore, under its Competitive Research Programme (CRP) (NRF-CRP22-2019-0007 and NRF-CRP26-2021-0004). This research is also supported by A*STAR under its AME IRG Grant (Project No. A2083c0052). L.J.W. acknowledges the Nanyang Assistant Professorship Start-up Grant.

Nonlinear optical activities (e.g., harmonic generations) in two-dimensional (2D) layered materials have attracted much attention due to the great promise in diverse optoelectronic applications such as nonlinear optical modulators, nonreciprocal optical device, and nonlinear optical imaging. Exploration of nonlinear optical response (e.g., frequency conversion) in the infrared, especially the mid-infrared (MIR) region, is highly desirable for ultrafast MIR laser applications ranging from tunable MIR coherent sources, MIR supercontinuum generation, and MIR frequency-comb-based spectroscopy to high harmonic generation. However, nonlinear optical effects in 2D layered materials under MIR pump are rarely reported, mainly due to the lack of suitable 2D layered materials. Van der Waals layered platinum disulfide (PtS2) with a sizable bandgap from the visible to the infrared region is a promising candidate for realizing MIR nonlinear optical devices. In this work, we investigate the nonlinear optical properties including third-and fifth-harmonic generation (THG and FHG) in thin layered PtS2 under infrared pump (1550-2510 nm). Strikingly, the ultrastrong third-order nonlinear susceptibility χ(3)(-3ω;ω,ω,ω) of thin layered PtS2 in the MIR region was estimated to be over 10-18 m2/V2, which is about one order of that in traditional transition metal chalcogenides. Such excellent performance makes air-stable PtS2 a potential candidate for developing next-generation MIR nonlinear photonic devices. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version This research was also supported partially by National Research Foundation Singapore program (NRFCRP19- 2017-01 and NRF-CRP22-2019-0007) and Ministry of Education Tier 2 program (MOE-T2EP50120-0009), and Singapore A*STAR funding (A18A7b0058 and A2090b0144).

Many applications of photonics require efficient nonlinear optical interactions with low power and small footprints. However, the current needs for long interaction lengths and strong laser sources of nonlinear optical devices make them unsuitable for nanophotonic integrated optics. New materials and devices with stronger nonlinear properties have been developed using various approaches in the past few years. One of the largest nonlinear optical responses reported to date has been realized with engineered intersubband transitions in n-doped multiple quantum wells (MQWs) semiconductors. Here, this work proposes to improve further the nonlinear properties of a MQW heterostructure by tailoring its permittivity to reach near-zero values. Materials with vanishing permittivity, called epsilon-near-zero (ENZ) materials, have exotic nonlinear features which can be explored to achieve this goal. To prove this point, this work makes use of In0.53Ga0.47As/Al0.48In0.52As, designs an ultrathin multilayer structure, and couples the designed structure with metasurfaces. Unprecedented nonlinear efficiency within subwavelength propagation lengths is obtained. Such structure with strong second harmonic generation (SHG) enables efficient frequency conversion, while the tunability offered by the metasurface provides new degrees of freedom to control the amplitude, phase, and polarization of the nonlinear light. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Published version This work was supported by the Singapore Ministry of Education (MOE2018-T2-2-189(S)), A*Star AME IRG Grant (A20E5c0095) and Programmatic Funds (A18A7b0058), and the National Research Foundation Singapore Competitive Research Program (NRF-CRP22-2019-0006 and NRF-CRP23-2019-0007).

All-inorganic metal halide perovskites, such as CsPbX3 (X = Br, Cl, or I), have attracted significant interest for a new generation of integrated, high-performance optoelectronic devices. To realize the full potential of layer-by-layer devices, perovskite crystal thin films are preferred over crystal ingots, considering carrier loss during carrier transport. The space-confined method is a facile way of fabricating perovskite crystal films in a geometrically confined space to break the isotropic growth. Many researchers have reported effective preparation of large-area perovskite films using this method. However, most space-confined methods require growth in a liquid phase (solution), which can cause uncontrollable nucleation, surface traps, and unsatisfactory device performance. In this work, a pure solid-state space-confined strategy to grow CsPbBr3 films for the first time without relying on solution conditions is developed. The regular shapes of CsPbBr3 films prepared by this solid-state space-confined strategy can function as effective multimode and single-mode Fabry–Perot (F–P) microlasers under optical pumping. This work overcomes the challenge that the conventional space-confined method can only be adapted to the liquid phase. It also opens a new approach for making high-quality microlasers, which are significant for photonic integrated circuits and optoelectronic devices. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Submitted/Accepted version The authors acknowl-edge support from A*Star-AME-IRG 192E5012-S, NRF-CRP23-2019-0007,NRF-CRP19-2017-01, and LUX Seed Grant 2021LUX02P01.

2D ferromagnets have garnered considerable attention for their potential applications in spintronics, magnonics, and spin-orbitronics. Chromium tellurides (CrxTey), in particular, have drawn interest due to their exceptional magnetic properties and diverse range of chemical stoichiometries, attributed to the phenomenon of chromium self-intercalation. To provide an in-depth understanding of this complex material class, this review first explains the origin of 2D magnetism using two well-known 2D ferromagnets, CrI3 and Fe3GeTe2, and compares the structures of CrTe2, Cr5Te8, Cr2Te3, and CrTe to clarify the self-intercalation phenomenon. In addition, it summarizes the growth conditions of CrxTey using the chemical vapor deposition approach as well as commonly practiced characterization techniques for 2D ferromagnetism. This review also compares ferromagnetic properties while analyzing how Cr intercalants affect the magnetic. Finally, it suggests that more attention should be focused on this material system to unlock its full practical and academic potential, and proposes directions for future research. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Published version Z.L. acknowledges the support from National Research Foundation, Singapore, under its Competitive Research Program (CRP) (NRF-CRP22-2019-0007 and NRF-CRP22-2019-0004), under its NRF-ISF joint research program (NRF2020-NRF-ISF004-3520). This research is also supported by A*STAR under its AME IRG Grant (Project No. A2083c0052).

Scintillators are materials that emit visible photons when bombarded by high-energy particles (X-ray, γ-ray, electrons, neutrinos, etc.) and are crucial for applications, including X-ray imaging and high-energy particle detection. Here, we show that one-dimensional (1D) photonic crystal (PhC) cavities, added externally to scintillator materials, can be used to tailor the intrinsic emission spectrum of scintillators via the Purcell effect. The emission spectral peaks can be shifted, narrowed, or split, improving the overlap between the scintillator emission spectrum and the quantum efficiency (QE) spectrum of the photodetector. As a result, the overall photodetector signal can be enhanced by over 200%. The use of external PhC cavities especially benefits thick and large-area scintillators, which are needed to stop particles with ultrahigh energy, as in large-area neutrino detectors. Our findings should pave the way to greater versatility and efficiency in the design of scintillators for applications, including X-ray imaging and positron emission tomography. Nanyang Technological University Submitted/Accepted version L.J.W. acknowledges the Nanyang Assistant Professorship Start-up Grant.

Colloidal quantum wells (CQWs) provide an appealing platform to achieve emissive many-body correlations for novel optoelectronic devices, given that they act as hosts for strong carrier Coulomb interactions and present suppressed Auger recombination. However, the demonstrated high-order excitonic emission in CQWs requires ultrafast pumping with high excitation levels and can only be spectrally resolved at the single-particle level under cryogenic conditions. Here, through systematic investigation using static power-dependent emission spectroscopy and transient carrier dynamics, we show that Cu-doped CdSe CQWs exhibit continuous-wave-pumped high-order excitonic emission at room temperature with a large binding energy of ∼64 meV. We attribute this unique behavior to dopant excitons in which the ultralong lifetime and the highly localized wavefunction facilitate the formation of many-body correlations. The spectrally resolved high-order excitonic emission generated at power levels compatible with solar irradiation and electrical injection might pave the way for novel solution-processed solid-state devices. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Published version C.D. is grateful for the financial support from the Ministry of Education, Singapore, under its AcRF Tier 2 grant (MOE-T2EP50121-0012). H.V.D. acknowledges the financial support in part from the Singapore Agency for Science, Technology and Research (A*STAR) MTC program under grant no. M21J9b0085, the Ministry of Education, Singapore, under its Academic Research Fund Tier 1 (MOE-RG62/20), and in part from TUBITAK 119N343, 20AG001, 121N395, and 121C266. H.V.D. also acknowledges support from TUBA and TUBITAK 2247-A National Leader Researchers Program (121C266). M.S. also acknowledges the funding through the Australian Research Council Center of Excellence in Exciton Science (grant no. CE170100026).

Ternary logic has been proven to carry an information ratio 1.58 times that of binary logic and is capable to reduce circuit interconnections and complexity of operations. However, the excessive transistor count of ternary logic gates has impeded their industry applications for decades. With the modulation of the ferroelectric negative capacitance (NC) properties on the channel potential, MOSFETs show many novel features including steep subthreshold swing and non-saturation output characteristics, based on which an ultra-compact ternary inverter can be achieved. Compared with traditional bulk materials, layered 2D materials and 2D ferroelectrics provide a clean interface and better electrostatic control and reliability. Even though ultra-low SS (∼10 mV/dec) has been experimentally demonstrated in ferroelectric-negative capacitance-incorporated 2D semiconductor (NC2D) FETs, the available models are still rare for large-scale circuit simulations. In this study, the superb electrical properties of pure 2D material stack-based NC2D FETs (layered CuInP2S6 adopted as the 2D ferroelectric layer) are investigated through device modeling based on the Landau–Khalatnikov (LK) equations in HSPICE. We managed to realize an ultra-compact ternary inverter with one NC2D-PMOS (WSe2) and one NC2D-NMOS (MoS2) in HSPICE simulations, whose transistor count is significantly reduced compared with other counterparts. We also proposed a novel input waveform scheme to solve the hysteresis problem caused by ferroelectric modulation to avoid logic confusion. Additionally, the power consumption and propagation delay of the NC2D-based ternary inverter are also investigated. This work may provide some insights into the design and applications of ferroelectric-incorporated 2D semiconductor devices. Ministry of Education (MOE) Published version This research work was supported by the Ministry of Education, Singapore, under its MOE Tier 2 project (MOE2019-T2-2-075), Shenzhen Science and Technology Innovation Committee JCYJ20200109115210307, and Guangdong Basic and Applied Basic Research Foundation 2019A1515111142, China.

Creating micro/nanostructures on fibers is beneficial for extending the application range of fiber-based devices. To achieve this using thermal fiber drawing is particularly important for the mass production of longitudinally uniform fibers up to tens of kilometers. However, the current thermal fiber drawing technique can only fabricate one-directional micro/nano-grooves longitudinally due to structure elongation and polymer reflow. Here, we develop a direct imprinting thermal drawing (DITD) technique to achieve arbitrarily designed surface patterns on entire fiber surfaces with high resolution in all directions. Such a thermal imprinting process is simulated and confirmed experimentally. Key process parameters are further examined, showing a process feature size as small as tens of nanometers. Furthermore, nanopatterns are fabricated on fibers as plasmonic metasurfaces, and double-sided patterned fibers are produced to construct self-powered wearable touch sensing fabric, revealing the bright future of the DITD technology in multifunctional fiber-based devices, wearable electronics, and smart textiles., Creating micro/nanostructures on fibers is beneficial to many fiber-based devices, which remains a challenge in large-scale fabrication due to elongation and reflow. Here, the authors demonstrate a method for generating high-resolution, arbitrarily designed surface patterns on fiber during the thermal drawing process.

Practical implementation of porous carbon-based composite phase-change materials (CPCMs) for heat dissipation in high-power-density electronics is usually limited by liquid leakage issues and unsatisfactory thermal conductivity resulting from their relatively low filler fraction and/or existence of interfacial thermal resistance between fillers. Therefore, development of shape-stable CPCMs with high thermal conductivity and large latent heat to avoid overheating of electronics remains challenging. Herein, graphene foams (GFs) with very high densities of up to 204 mg/cm3have been synthesized to act as interconnected porous networks of CPCMs. Notably, the obtained CPCM with a filler loading of 11.1 wt % preserves a high heat capacity (171.8 J/g) with a retention of 84.8% while showing a 22.6-fold enhancement in the thermal conductivity as compared to pure PCM (10.13 vs 0.43 W/m·K). A higher thermal conductivity of 14.29 W/m·K can be achieved by further increasing the filler loading to 17.7 wt %, which outperforms many of the previously reported CPCMs based on the interconnected porous carbon-based frameworks. Owing to the superior interconnected network structure of the dense GFs and the strong interconnection between them and PCM molecules, these CPCMs also exhibit leakage-proof shape stability and excellent thermal reliability (at least 100 cycles). Moreover, a state-of-the-art aluminum (Al) package based on the CPCM (filler loading: 11.1 wt %) possessing weight 60% less than its pure Al panel counterpart has been demonstrated to verify better heat transfer efficiency and more efficient phonon pathways of the CPCM composite than those of the pure PCM, which holds great promise for advanced thermal management of emerging applications in electronics. The authors would like to acknowledge the financial support from Thales.

International audience; It is well understood that nonlinear optical (NLO) phenomena are deeply related to the material’s symmetry. Mathematically, the material symmetry can be described in terms of the nonzero parameters in the nonlinear susceptibility tensors. Generally, more complex structures involve more nonzero parameters in the tensor. The number of parameters increases rapidly if higher NLO orders are considered, complicating the physical analysis. Conventionally, these parameters are obtained via abstract symmetry analysis, e.g., group theory (GT). This work presents a novel theoretical analysis to approach the nonlinear tensor using the simplified bond hyperpolarizability model (SBHM) and compare it with GT. Our analysis is based on a light–matter interaction classical phenomenological physical framework. Rather than just looking at the symmetry of the crystal, the model applies physical considerations requiring fewer independent parameters in the tensor than GT. Such a simplification significantly improves the determination of the surface–bulk SHG contribution factors, which cannot be extracted from the experiment alone. We also show for the case of perovskite that the SHG contribution can be addressed solely from their surface dipoles with only one independent component in the tensor. Therefore, this work may open the path for a similar analysis in other complicated semiconductor surfaces and structures in the future, with potential applications to nanoscale surface characterization and real-time surface deposition monitoring.

Two-dimensional materials that are intrinsically ferromagnetic are crucial for the development of compact spintronic devices. However, most non-layered 2D magnets with a strong ferromagnetic order are difficult to synthesize. Here we show that the flakes of trigonal and monoclinic Cr5Te8 can be grown via a chemical vapour deposition method. Using magneto-optical and magnetotransport measurements, we show that both phases exhibit robust ferromagnetism with strong perpendicular anisotropy at thicknesses of a few nanometres. A high Curie temperature of up to 200 K can be obtained by manipulating the phase structure and thickness. We also observe a colossal anomalous Hall effect in the more structurally distorted monoclinic Cr5Te8, with an anomalous Hall conductivity of 650 Ω−1 cm−1 and anomalous Hall angle of 5%. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version Z.L. acknowledges support from the National Research Foundation Singapore (NRF-CRP22-2019-0007 and NRF-CRP21-2018-0007). This research is also supported by the Ministry of Education, Singapore, under its AcRF Tier 3 Programme ‘Geometrical Quantum Materials’ (MOE2018-T3-1-002), and AcRF Tier 1 RG161/19. W.G. acknowledges support from the National Research Foundation Singapore (NRF-CRP22-2019-0004). J.L. acknowledges support from the National Natural Science Foundation of China (grant no. 11974156); Guangdong International Science Collaboration Project (grant no. 2019A050510001); Guangdong Innovative and Entrepreneurial Research Team Program (grant no. 2019ZT08C044); Shenzhen Science and Technology Program (no. KQTD20190929173815000 and 20200925161102001); the Science, Technology and Innovation Commission of Shenzhen Municipality (no. ZDSYS20190902092905285); and assistance of SUSTech Core Research Facilities, especially technical support from the Pico-Centre that receives support from the Presidential fund and Development and Reform Commission of Shenzhen Municipality. J.Z. acknowledges support from the Beijing Institute of Technology (grant no. 2021CX11013) and National Natural Science Foundation of China (grant no. 62174013).

Pentagonal 2D materials as a new member in the 2D material family have attracted increasing attention due to the exotic physical properties originating from the unique Cairo pentagonal tiling topology. Herein, the penta-PdPS atomic layers as a new air-stable 2D semiconductor with the unique puckered pentagonal low-symmetry structure are successfully exfoliated from bulk crystals grown via chemical vapor transport (CVT). Notably, 2D pentaPdPS exhibits outstanding electronic and optoelectronic performance under 650 nm laser: high electron mobility of ≈208 cm2 V−1 s−1, an ultrahigh on/off ratio of ≈108, a high photoresponsivity of 5.2 × 104 A W−1, a high photogain of 1.0 × 105, an ultrahigh detectivity of 1.0 × 1013 Jones, respectively. Significantly, the exceptional puckered pentagonal atomic structure of 2D PdPS makes it strong in-plane anisotropy in optical, electronic, and optoelectronic properties, demonstrating a sizeable anisotropic ratio of carrier mobility and photocurrent with the value of up to 3.9 and 2.3, respectively. These excellent properties make 2D Cairo Pentagonal PdPS a potential candidate in nanoelectronics, optoelectronics, polarized-nanoelectronics, which will significantly promote the development of 2D materials. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Z.L. acknowledges supports from Singapore National Research Foundation – Competitive Research Program NRF-CRP22-2019-0007 and NRF-CRP21-2018-0007. This research was also supported by A*STAR under its AME IRG Grant (Project No. A2083c0052).

Plasmon antennas allow subwavelength confinement and enhancement of electromagnetic fields at the “hotspot” where the radiation efficiency of emitters can be substantially enhanced. Such enhancement, however, is often polarization dependent. Consequently, the radiation behaviors (e.g., radiation pattern and polarization states) of the emitter placed at the hotspot are also modified significantly. Enhancing the radiation efficiency without altering the original radiation pattern and polarization state of the emitter is highly desired for many sought-after applications involving chiral emitters but remains a challenging task, especially at low frequencies. To this end, spoof-plasmon antennas with fourfold and sixfold rotational symmetries are designed and realized experimentally. These plasmon antennas support polarizationindependent localized plasmon resonances, which can significantly enhance the local density of photonic states at the structural center without changing the polarization state of the emitter. As a typical example, the structure with sixfold rotational symmetry is coupled with a half-wave dipole antenna. The measurement results show that the far-field radiation pattern of the dipole antenna is maintained with the radiation efficiency enhanced by more than 2 orders of magnitude, irrespective of the dipole orientation. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version This work is supported, in part, by the National Science Foundation of China under Grants No. 61871127 and No. U21A20459, the 111 Project under Grant No. 111-2-05, and the Fund for International Cooperation and Exchange of the National Natural Science Foundation of China Grant No. 61761136007. Y.L. received funding from the Singapore Ministry of Education [Grant No. MOE2018-T2-2-189(S)], an A*Star AME IRG grant (Grant No. A20E5c0095) and Programmatic Funds (Grant No. A18A7b0058), and the National Research Foundation Singapore Competitive Research Program (Grants No. NRF220 CRP22-2019-0006 and No. NRF-CRP23-2019-0007).

Flexible electronic devices have been extensively studied for their advantages of distinguished portability, conformal contact characteristics, and human-friendly interfaces compared with conventional bulk Si technology. Flexible electronics can be attached to various surfaces like skin and internal organs for human–machine interaction, which has made significant advances in electronics, medicine, neuromorphic computing, etc. Owing to the innovation and maturation of the thin film preparation process, which have promoted the successful preparation of high-quality flexible ferroelectric films. Herein, the preparation of flexible ferroelectric devices and the progress of their applications in recent years are reviewed. Prevailing methods for preparing flexible ferroelectric films including the van der Waals heteroepitaxy on flexible substrate, delamination of the ferroelectric films on rigid substrate by chemical etching techniques, and direct use of novel 2D ferroelectric materials etc. are summarized. The research progress of flexible ferroelectric devices applied to memories, sensors, photovoltaic devices, and energy harvesters are also be discussed in detail. Moreover, the potential applications of flexible ferroelectric devices in the field of neuromorphic computing are studied, a new trend which contributes to the further development of brain-like chip systems. Finally, the challenges and prospects of flexible ferroelectric devices in the future advanced electronics are briefly proposed. Ministry of Education (MOE) This work was financially supported by the National Natural Science Foundation of China (grant nos. 62004056, 61674050, and 61874158), the Project of Distinguished Young of Hebei Province (grant no. A2018201231), the Support Program for the Top Young Talents of Hebei Province (Grant No. 70280011807), the Hundred Persons Plan of Hebei Province (grant nos. E2018050004 and E2018050003), the Supporting Plan for 100 Excellent Innovative Talents in Colleges and Universities of Hebei Province (grant no. SLRC2019018), Special project of strategic leading science and technology of Chinese Academy of Sciences (grant no. XDB44000000-7), utstanding young scientific research and innovation team of Hebei University (605020521001), Special support funds for national high level talents (041500120001), High-level Talent Research Startup Project of Hebei University (521000981426), Hebei Basic Research Special Key Project (F2021201045), Funded by Science and Technology Project of Hebei Education Department (grant no. QN2020178, QN2021026), the Singapore Ministry of Education, (grant no. AcRF TIER 2-MOE2019-T2-2-075).

This paper reports the fabrication, testing and obtained performance of a plasmonic sensor employing a gold (Au) nanohole array chip coated with tungsten disulphide (WS2), which is then functionalized for the detection of protein-protein interactions. A key novelty is that the WS2 was deposited as a monoatomic layer using a wafer-scale synthesis method that successfully provided a film of both high quality and uniform thickness. The deposited WS2 film was transferred onto a Au nanohole array chip using a novel method and was subsequently functionalized with biotin. The final sensor was tested and it demonstrated efficient real-time and label-free plasmonic detection of biotin-streptavidin coupling. Specifically, compared to a standard (i.e. uncoated) Au nanohole-based sensor, our WS2-coated Au nanohole array boosted the spectral shift of the resonance wavelength by ∼190%, resulting in a 7.64-fold improvement of the limit of detection (LOD). National Research Foundation (NRF) Submitted/Accepted version This work was supported by the Singapore National Research Foundation (NRF) and French National Research Agency (ANR), grant number (NRF2017–ANR002 2DPS).

We proposed and demonstrated mode cleaning in a high-power fiber laser by integrating an anti-resonant hollow-core fiber (AR-HCF) into a multimode laser cavity of an ytterbium (Yb)-doped fiber (YDF). An in-house mode-matched AR-HCF was fusion-spliced to a commercial multimode LMA-YDF, ensuring efficient fundamental mode coupling. The AR-HCF inflicts a high propagation loss selectively on higher-order modes, facilitating fundamental mode operation. Thus, the AR-HCF works as an efficient spatial mode filter embedded in the multimode fiber laser cavity and reinforces preferential amplification of the fundamental mode. Beam quality factor enhancement was achieved from M2 = 2.09 to 1.39 at an output power of 57.7 W (pump-power limited). The beam quality can be further improved by refining the AR-HCF fabrication. The proposed technique has a great potential to be exploited in other multimode fiber laser cavities involving erbium- or thulium-doped fibers and obviates the need for complicated specialty active fiber designs. Compared with the commonly used fiber bending technique, our method can achieve an efficient higher-order mode suppression without inducing mode-field deterioration. National Research Foundation (NRF) Published version National Research Foundation Singapore (QEP-P4).

High Q-factor resonance holds great promise for bio-chemical sensing and enhanced light-matter interaction. However, terahertz (THz) magnetic resonances usually demonstrate low Q-factors, resulting in huge energy radiation loss particularly in high frequency bands. Here, we show that high Q-factor magnetic dipole resonance at THz frequencies can be achieved by exploiting the coherent Fano interactions with strong field enhancements in an array composed of single metallic split-ring resonators, working at Wood-Rayleigh anomalies. It can give rise to ultrahigh Q-factor beyond 104 in the THz regime. Experimentally, the measured Q-factor of dominant magnetic dipole resonance can achieve no less than a level of ∼261 by Lorentzian fitting to the experimental data. In addition, a high Q-factor of the fundamental-order magnetic dipole resonance is demonstrated beyond 30. High-Q magnetic dipole resonance is closely associated with ultralow-damping and negative permeability in the THz band. The measurements of magnetic dipole resonances are in good agreement with the theoretical analyses. Our scheme suggests a feasible route to suppress radiative loss for enhanced THz field-matter interaction. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version The authors acknowledge the funding supported by the Fundamental Research Funds for the Central Universities (Talent startup fund No. AUGA5710012622), the National Natural Science Foundation of China (No. 61377110), the Natural Science Foundation of Heilongjiang Province (No. LH2019F012), and the China Scholarship Council (No. 202006120141). Y.L. and Q.J.W. acknowledge funding support from the Singapore Ministry of Education [No. MOE2018-T2-2-189(S)], the A Star AME IRG Grant (No. A20E5c0095), Programmatic Funds (No. A18A7b0058), and the National Research Foundation Singapore Competitive Research Program (Nos. NRF-CRP22-2019-0006 and NRF-CRP23-2019-0007).

Integrating two-dimensional (2D) transition-metal dichalcogenides (TMDCs) into dielectric plasmonic nanostructures enables the miniaturization of on-chip nanophotonic devices. Here we report on a high-quality light emitter based on the newly designed 2D h-BN/WS2 heterostructure integrated with an array of TiO2 nanostripes. Different from a traditional strongly coupled system such as the TMDCs/metallic plasmonic nanostructure, we first employ dielectric nanocavities and achieve a Purcell enhancement on the nanoscale at room temperature. Furthermore, we demonstrate that the light emission strength can be effectively controlled by tuning the polarization configuration. Such a polarization dependence meanwhile could be proof of the resonant energy transfer theory of dipole-dipole coupling between TMDCs and a dielectric nanostructure. This work gains experimental and simulated insights into modified spontaneous emission with dielectric nanoplasmonic platforms, presenting a promising route toward practical applications of 2D semiconducting photonic emitters on a silica-based chip. National Research Foundation (NRF) Submitted/Accepted version This work was supported by Start-up funds of Wuhan University and Singapore National Research Foundation (NRF) under the Competitive Research Programs (NRFCRP-21-2018-0007).

Two-dimensional (2D) ferromagnets with out-of-plane (OOP) magnetic anisotropy are potential candidates for realizing the next-generation memory devices with ultra-low power consumption and high storage density. However, a scalable approach to synthesize 2D magnets with OOP anisotropy directly on the complimentary metal-oxide semiconductor (CMOS) compatible substrates has not yet been mainly explored, which hinders the practical application of 2D magnets. This work demonstrates a cascaded space confined chemical vapor deposition (CS-CVD) technique to synthesize 2D FexGeTe2 ferromagnets. The weight fraction of iron (Fe) in the precursor controls the phase purity of the as-grown FexGeTe2. As a result, high-quality Fe3GeTe2 and Fe5GeTe2 flakes have been grown selectively using the CS-CVD technique. Curie temperature (TC) of the as-grown FexGeTe2 can be up to ∼ 280 K, nearly room temperature. The thickness and temperature-dependent magnetic studies on the Fe5GeTe2 reveal a 2D Ising to 3D XY behavior. Also, Terahertz spectroscopy experiments on Fe5GeTe2 display the highest conductivity among other FexGeTe2 2D magnets. The results of this work indicate a scalable pathway for the direct growth and integration of 2D ternary magnets on CMOS-based substrates to develop spintronic memory devices. [Figure not available: see fulltext.]. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version This work was supported from National Research Foundation Singapore programme NRF-CRP22-2019-0007, NRF-CRP22- 2019-0004 and NRF-CRP21-2018-0007. This work was also supported by the Ministry of Education, Singapore, under its AcRF Tier 3 Programme ‘Geometrical Quantum Materials’ (MOE2018-T3-1-002), AcRF Tier 2 (MOE2019-T2-2-105) and AcRF Tier 1 RG4/17 and RG7/18. We also thank the funding support from National Research foundation (NRF-CRP22- 2019-0004).

We show the increase of the photoluminescence intensity ratio (PLR) and the emission rate enhancement of perovskite cesium lead bromide (CsPbBr3 ) and formamidinium lead bromide (FAPbBr3 ) nanocrystals (NCs) in the presence of single and double gold layer cavities, which we refer to as Metal-Emitter (ME) and Metal-Emitter-Metal (MEM) nanostructures. Up to 1.9-fold PLRs and up to 5.4-fold emission rate enhancements were obtained for FAPbBr3 NCs confined by double gold layers, which are attributed to plasmonic confinement from the gold layers. The experimentally obtained values are validated by analytical calculations and electromagnetic simulations. Such an effective method of manipulation of the spontaneous emission by simple plasmonic nanostructures can be utilized in sensing and detection applications. Ministry of Education (MOE) Published version This research was funded by Ministry of Education, Singapore, grant nos. MOE2016-T2-1-052 and MOE2019-T1-002-063.

Two-dimensional (2D) hybrid lead bromide perovskites are candidates for high light yield, fast scintillators. In this paper, we discuss the effect of commensurate Lithium (Li)-doping (1 : 1 Li : Pb precursor ratio) on the scintillation properties of two previously reported high light yield 2D-perovskite crystals, PEA2PbBr4 and BA2PbBr4. The effect of Li, e.g. light yield enhancement, is more prominent in PEA2PbBr4 compared to BA2PbBr4. Both perovskite crystals show a broadening of the radioluminescence spectrum and a slightly longer afterglow, with residual scintillation below 2% after 5 s for both materials. The effects of Li on the negative thermal quenching exhibited by the perovskites are also discussed. Li doping increases the light yield of PEA2PbBr4 by 78% and both perovskite materials show an improvement in their energy resolutions, with a record of 7.7% at 662 keV for the Li-doped PEA2PbBr4. Both perovskite crystals also show very fast gamma-ray excited scintillation decays, with average times of 12.9 ns and 8.0 ns for PEA2PbBr4 and BA2PbBr4, respectively. This work shows that Li doping brings a significant improvement of the perovskite performance, making the perovskites more competitive for fast, high light yield applications in the medical, security or industrial sectors. Ministry of Education (MOE) The authors acknowledge financial supports from the Singapore Ministry of Education (MOE2019-T1-002-087) and Thales-CINTRA Funding.

CsPbBr3 quantum dots (QDs) have recently gained much interest due to their excellent optical and scintillation properties and their potential for X-ray imaging applications. In this study, we blended CsPbBr3 QDs with resin at different QD concentrations to achieve thick films and to protect the CsPbBr3 QDs from environmental moisture. Then, their scintillation properties are investigated and compared to the traditional commercial scintillators, CsI:Tl microcolumns, and Gadox layers. The CsPbBr3 QD-resin sheets show a high light yield of up to 21 500 photons/MeV at room temperature and a relatively small variation in light yield across a wide temperature range. In addition, the CsPbBr3 QD-resin sheets feature a small scintillation afterglow. The CsPbBr3 QD-resin sheets show a negligible trap density for the concentration below 50% weight, indicating that traps might arise from the aggregation of the QDs. The CsPbBr3 QD-resin sheets are also very stable at low irradiation intensities and relatively stable at higher intensities, with higher CsPbBr3 QD concentrations being more stable. Gamma-ray-excited-time-resolved emission measurements at 662 keV showed that the CsPbBr3 QD-resin sheets have an average scintillation decay time between 108 and 176 ns, which are still 10 000 and 6000 times faster than CsI:Tl and Gadox, respectively. Imaging tests show that the CsPbBr3 QD-resin sheets have a mean transfer function of 50% at 2 lp/mm and 20% at 4 lp/mm, comparable to that of commercial Gadox layers. This feature makes CsPbBr3 QD-resin sheets a good candidate for the low-cost, flexible X-ray imaging screens and γ-ray applications. Ministry of Education (MOE) The authors acknowledge financial supports from the Singapore Ministry of Education (MOE2019-T1-002-087) and Thales-CINTRA Funding.

The prosperity in portable and wearable electronics has stimulated researchers to develop safe, environmentally friendly, and efficient energy-storage technologies. Increased efforts have recently been made to fabricate high-performance rechargeable aqueous alkaline batteries (RAABs) as the frontrunner to complement and even replace the dominant lithium-ion batteries for large-scale energy storage due to the limited lithium resources and the use of flammable and toxic organic electrolyte. Compared with the conventional planar RAABs, fiber-shaped RAABs (FRAABs) manifest several intriguing features, such as miniaturization, adaptability, and weavability, making them an attractive candidate to power wearable and portable electronics. Herein, an overview of the recent progress in FRAABs by categories of fiber-shaped aqueous rechargeable Zn-based batteries, Fe−Ni batteries, and Bi−Ni batteries, with respect to the active electrode materials, device configurations, and battery properties, is comprehensively presented. Finally, the remaining challenges and possible solutions are emphasized as a useful guide for the further development of FRAABs. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Published version This work was sup-ported by the Singapore Ministry of Education Academic ResearchFund Tier 2 (MOE2019-T2-2-127 and MOE-T2EP50120-0002), A*STARunder AME IRG (A2083c0062), A*STAR under IAF-ICP (I2001E0067(IAF-ICP)-P2.1) and I2001E0067 (Schaeffler) P2.1, the SingaporeMinistry of Education Academic Research Fund Tier 1 (RG90/19 andRG73/19), and the Singapore National Research FoundationCompetitive Research Program (NRF-CRP18-2017-02). This work was alsosupported by Nanyang Technological University.

The well-developed preform-to-fiber thermal drawing technique owns the benefit to maintain the cross-section architecture and obtain an individual micro-scale strand of fiber with the extended length up to thousand meters. In this work, we propose and demonstrate a two-step soluble-core fabrication method by combining such an inherently scalable manufacturing method with simple post-draw processing to explore the low viscosity polymer fibers and the potential of soft fiber electronics. As a result, an ultra-stretchable conductive fiber is achieved, which maintains excellent conductivity even under 1900% strain or 1.5 kg load/impact freefalling from 0.8-m height. Moreover, by combining with triboelectric nanogenerator technique, this fiber acts as a self-powered self-adapting multi-dimensional sensor attached on sports gears to monitor sports performance while bearing sudden impacts. Next, owing to its remarkable waterproof and easy packaging properties, this fiber detector can sense different ion movements in various solutions, revealing the promising applications for large-area undersea detection., Though thermal drawing methods are attractive for fabricating fiber-based sensor devices, existing methods allow limited access to low viscosity and low modulus materials. Here, the authors demonstrate a two-step soluble-core fiber fabrication method with wide applicability to soft polymer materials.

Despite its advantages of scalable process and cost-effectiveness, nanoimprinting faces challenges with imprinting hard materials (e.g., crystalline metals) at low/room temperatures, and with fabricating complex nanostructures rapidly (e.g., heterojunctions of metal and oxide). Herein, we report a room temperature ultrasonic nanoimprinting technique (named nanojackhammer) to address these challenges. Nanojackhammer capitalizes on the concentration of ultrasonic energy flow at nanoscale to shape bulk materials into nanostructures. Working at room temperature, nanojackhammer allows rapid fabrication of complex multi-compositional nanostructures made of virtually all solid materials regardless of their ductility, hardness, reactivity and melting points. Atomistic simulations reveal a unique alternating dislocation generation and recovery mechanism that significantly reduces the imprinting force under ultrasonic cyclic loading. As a proof-of-concept, a metal-oxide-metal plasmonic nanostructure with built-in nanogap is rapidly fabricated and employed for biosensing. As a fast, scalable, and cost-effective nanotechnology, nanojackhammer will enable various unique applications of complex nanostructures in optoelectronics, biosensing, catalysis and beyond., Nanoimprinting faces challenges with imprinting hard materials at low or room temperature, and with fabricating complex nanostructures rapidly. Here, the authors overcome these challenges by a room-temperature ultrasonic nanoimprinting technique that capitalizes on the concentration of ultrasonic energy flow at nanoscale.

We present the synthesis and characterization of gallium nitride (GaN) pine tree-like nanostructures (PTLNs) grown by low-pressure chemical vapor deposition. A high yield of PTLNs is densely arranged with each PTLN having a typical length of 15.46 ± 3.38 μm. From Raman spectroscopy, we observe anE2Hpeak at 570 ± 6 cm-1which is the primary characteristic of wurtzite. X-ray and ultraviolet photoemission spectroscopy reveal that the electronic structures of GaN PTLNs indicate an n-type character, while the work function and valence band maximum are determined to be 3.30 ± 0.05 and 3.85 ± 0.08 eV, respectively. We confirm the electronic nature of our structure from the current-voltage characteristics exhibiting rectifying behavior. Density functional theory calculations of GaN PTLNs modeled by germanium-doped GaN nanowires are consistent with our experimental findings. To summarize, the energy-band diagram is presented for the future of GaN PTLNs in the optoelectronic and sensing applications. Ministry of Education (MOE) This research is supported by the Ministry of Education, Singapore, under its Academic Research Fund Tier 2, grant no. MOE2016-T2-1-052 and Tier 1, grant no. MOE2019-T1-002063. F.A. and H.H. would like to acknowledge Toray Science and Technology Research Grant 2021.

By applying a sudden perturbation to one of the components of a mixture of two quantum fluids, we explore the effect on the motion of the second component on a short time scale. By implementing perturbation theory, we prove that for short times the response of the second component is fixed by the energy weighted moment of the crossed dynamic structure factor (crossed f-sum rule). We also show that by properly monitoring the time duration of the perturbation it is possible to identify peculiar fast spin drag regimes, which are sensitive to the interaction effects in the Hamiltonian. Special focus is given to the case of coherently coupled Bose-Einstein condensates, interacting Bose mixtures exhibiting the Andreev-Bashkin effect, normal Fermi liquids and the polaron problem. The relevant excitations of the system contributing to the spin drag effect are identified and the contribution of the low frequency gapless excitations to the f-sum rule in the density and spin channels is explicitly calculated employing the proper macroscopic dynamic theories. Both spatially periodic and Galilean boost perturbations are considered., Comment: 11 pages, 2 figure

We report the optical and scintillation properties of (C6H5CH2NH3)2SnBr4 with excellent absorption length at 20 keV of 0.016 cm, measured bandgap of 2.51 eV, and photoluminescence lifetime of 1.05 μs. The light yield obtained with the 241Am source is 3600 ± 600 photons per MeV, which is much smaller than the maximum attainable light yield obtained from the bandgap. Temperature dependent radioluminescence measurements confirm the presence of thermal quenching at room temperature with the activation energy and the ratio between the attempt and the radiative transition rates of 61 meV and 129, respectively. Although thermal quenching affects light yield at room temperature, this green light-emitting perovskite opens an avenue for new lead-free scintillating materials. Ministry of Education (MOE) Published version This work is part of the project that has received funding from Universitas Prasetiya Mulya, Indonesia Toray Science Foundation, "Penelitian, Pengabdian Masyarakat, dan Inovasi (PPMI) Institut Teknologi Bandung (ITB) 2021, and Ministry of Education, Singapore (award no. MOE2018-T2-1-088). RL and TL measurements were performed at the National Laboratory for Quantum Technologies (NLTK), Nicolaus Copernicus University and supported by the European Regional Development Fund.

Reducing the lateral scale of two-dimensional (2D) materials to one-dimensional (1D) has attracted substantial research interest not only to achieve competitive electronic applications but also for the exploration of fundamental physical properties. Controllable synthesis of high-quality 1D nanoribbons (NRs) is thus highly desirable and essential for further study. Here, we report the implementation of supervised machine learning (ML) for the chemical vapor deposition (CVD) synthesis of high-quality quasi-1D few-layered WTe2 NRs. Feature importance analysis indicates that H2 gas flow rate has a profound influence on the formation of WTe2, and the source ratio governs the sample morphology. Notably, the growth mechanism of 1T' few-layered WTe2 NRs is further proposed, which provides new insights for the growth of intriguing 2D and 1D tellurides and may inspire the growth strategies for other 1D nanostructures. Our findings suggest the effectiveness and capability of ML in guiding the synthesis of 1D nanostructures, opening up new opportunities for intelligent materials development. Ministry of Education (MOE) The authors gratefully acknowledge financial support by National Key Research and Development Program of China (2020YFB2008501 and 2019YFC1520900), the National Natural Science Foundation of China (61974120, 11904289, 61701402, and 61804125), Key Research and Development Program of Shaanxi Province (2020ZDLGY04-08, 2020GXLH-Z-027, 2021JZ-43), the Key Program for International Science and Technology Cooperation Projects of Shaanxi Province (2018KWZ-08), the Natural Science Foundation of Shaanxi Province (2019JQ-613), the Natural Science Foundation of Ningbo (202003N4003), the Fundamental Research Funds for the Central Universities (3102019PY004, 31020190QD010, and 3102019JC004), and the start-up funds from Northwestern Polytechnical University. The authors also acknowledge the support from Ministry of Education, Singapore, under its AcRF Tier 3 Programme "Geometrical Quantum Materials" (MOE2018-T3-1-002) and AcRF Tier 1 RG161/19.

The development of earth-abundant oxygen reduction reaction (ORR) catalysts with high catalytic activity and good stability for practical metal-air batteries remains an enormous challenge. Herein, a highly efficient and durable ORR catalyst is reported, which consists of atomically dispersed Co single atoms (Co-SAs) in the form of Co-N4 moieties and small Co nanoparticles (Co-SNPs) co-anchored on nitrogen-doped porous carbon nanocage (Co-SAs/SNPs@NC). Benefiting from the synergistic effect of Co-SAs and Co-SNPs as well as the enhanced anticorrosion capability of the carbon matrix brought by its improved graphitization degree, the resultant Co-SAs/SNPs@NC catalyst exhibits outstanding ORR activity and remarkable stability in alkaline media, outperforming Co-SAs-based catalyst (Co-SAs@NC), and benchmark Pt/C catalyst. Density functional theory calculations reveal that the strong interaction between Co-SNPs and Co-N4 sites can increase the valence state of the active Co atoms in Co-SAs/SNPs@NC and moderate the adsorption free energy of ORR intermediates, thus facilitating the reduction of O2. Moreover, the practical zinc-air battery assembled with Co-SAs/SNPs@NC catalyst demonstrates a maximum power density of 223.5 mW cm–2, a high specific capacity of 742 W h kg–1 at 50 mA cm–2 and a superior cycling stability. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) The authors thank Nanyang Technological University, Singapore, for providing financial support. This work was also supported by National Research Foundation–Competitive Research Programs (NRF-CRP22-2019-0007, and NRF-CRP21-2018-0007), and the Singapore Ministry of Education AcRF Tier 2 (MOE2019-T2-2-105) and AcRF Tier 1 (RG7/18 and RG161/19). X.Z. acknowledges the financial supports from the National Natural Science Foundation of China (NSFC): Grant No. 21922507 and 21771079, the Jilin Province Science and Technology Development Plan (No. YDZJ202101ZYTS126), and the Fundamental Research Funds for the Central Universities. Y.L. acknowledges the financial supports from the NSFC (Grant No. 22005116), the International Postdoctoral Exchange Fellowship Program (20190054).

NASICON-structured NaTi2(PO4)3 (NTP) is an attractive anode material for aqueous rechargeable sodium-ion batteries (ARSIBs) thanks to its three-dimensional open framework and appropriate negative voltage window. Nevertheless, the lack of flexible and high-performance binder-free NTP-based anodes remains stumbling blocks to the development of wearable ARSIBs. Herein, hollow-structure NTP evenly encapsulated in cross-linked porous N-doped carbon nanofiber (HNTP@PNC) is prepared through electrospinning technology and subsequent carbonization treatment, directly acting as binder-free anode for flexible ARSIBs. Benefiting from its unique hollow structure, continuous conductive network and favorable synergistic effect, the HNTP@PNC electrode displays as high as of 108.3 mAh g−1 rate capacity at 5.50 A g−1 and an impressive cycling stability of 97.2% capacity retention after 3000 cycles. Further, theoretical calculations reveal that NTP with NC coating significantly enhances electronic conductivity and accelerates Na+ diffusion kinetics. Pairing with potassium zinc hexacyanoferrate free-standing cathode, a prototype quasi-solid-state ARSIB with a high-voltage discharge plateau of 1.6 V is successfully constructed, achieving a high volumetric capacity of 24.5 mAh cm−3 and an admirable energy density of 39.2 mWh cm−3, outperforming most reported flexible aqueous rechargeable energy-storage devices. These exciting results provide valuable intuition into the design of novel binder-free NTP-based anodes for next-generation wearable ARSIBs. Agri-Food and Veterinary Authority of Singapore (AVA) Submitted/Accepted version

Thermally drawn multimaterial fibers have experienced rapid development in the past two decades owing to the high scalability, uniformity, and material and structure compatibility of the thermal drawing technique. This article reviews various multimaterial fibers based on different functional structures and their applications in disparate fields. We start from the functional structures achieved in optical fibers developed in the early stage of thermally drawn fibers. Subsequently, we introduce both typical functional structures and unique structures created in multimaterial fibers for varying applications. Next, we present the early attempts in breaking the axial symmetric structures of thermally drawn fibers for extended functionalities. Additionally, we summarize the current progress on creating surface structures on thermally drawn fibers. Finally, we provide an outlook for this trending topic towards wearable devices and smart textiles. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Published version This work was supported by the Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2019-T2-2-127 and T2EP50120-0005), A∗STAR under AME IRG (A2083c0062), the Singapore Ministry of Education Academic Research Fund Tier 1 (RG90/19 and RG73/19), and the Singapore’s National Research Foundation Competitive Research Program (NRF-CRP18-2017-02). This work was also supported by Nanyang Technological University.

The last decade has witnessed the significant progress of physical fundamental research and great success of practical application in two-dimensional (2D) van der Waals (vdW) materials since the discovery of graphene in 2004. To date, vdW materials is still a vibrant and fast-expanding field, where tremendous reports have been published covering topics from cutting-edge quantum technology to urgent green energy, and so on. Here, we briefly review the emerging hot physical topics and intriguing materials, such as 2D topological materials, piezoelectric materials, ferroelectric materials, magnetic materials and twistronic heterostructures. Then, various vdW material synthetic strategies are discussed in detail, concerning the growth mechanisms, preparation conditions and typical examples. Finally, prospects and further opportunities in the booming field of 2D materials are addressed. Ministry of Education (MOE) National Research Foundation (NRF) Published version This work was supported by the National Research Foundation– Competitive Research Program (NRF-CRP21-2019-0007 and NRF-CRP21-2018-0007); the Singapore Ministry of Education Tier 3 Programme ‘Geometrical Quantum Materials’ (MOE2018-T3-1-002), AcRF Tier 2 (2016-T2-2-153) and AcRF Tier 1 (RG7/18 and RG161/19); the National Key R&D Program of China (2020YFA0309200), the National Natural Science Foundation of China (62074025); the Applied Basic Research Program of Sichuan Province (2020ZYD014 and 2021JDGD0026); the Sichuan Province Key Laboratory of Display Science and Technology and the Postdoctoral Innovative Talent Supporting Program (BX20190060).

Molybdenum disulfide (MoS₂) is one of the compounds discussed nowadays due to its outstanding properties that allowed its usage in different applications. Its band gap and its distinctive structure make it a promising material to substitute graphene and other semiconductor devices. It has different applications in electronics especially sensors like optical sensors, biosensors, electrochemical biosensors that play an important role in the detection of various diseases’ like cancer and Alzheimer. It has a wide range of energy applications in batteries, solar cells, microwave, and Terahertz applications. It is a promising material on a nanoscale level, with favorable characteristics in spintronics and magnetoresistance. In this review, we will discuss MoS₂ properties, structure and synthesis techniques with a focus on its applications and future challenges. Published version This research was funded by United Arab Emirates University UPAR project, grant number 31N393.

The change of the phase of light under the evolution of a nanomaterial with time is a promising new research direction. A phenomenon directly related to the sudden phase change of light is the Goos-Hänchen (G-H) shift, which describes the lateral beam displacement of the reflected light from the interface of two media when the angles of incidence are close to the total internal reflection angle or Brewster angle. Here, an innovative design of lithography-free nanophotonic cavities to realize electrically tunable G-H shifts at the singular phase of light in the visible wavelengths is reported. Reversible electrical tuning of phase and G-H shifts is experimentally demonstrated using a microheater integrated optical cavity consisting of a dielectric film on an absorbing substrate through a Joule heating mechanism. In particular, an enhanced G-H shift of 110 times of the operating wavelength at the Brewster angle of the thin-film cavity is reported. More importantly, electrically tunable G-H shifts are demonstrated by exploiting the significant tunable phase change that occurs at the Brewster angles, due to the small temperature-induced refractive index changes of the dielectric film. Realizing efficient electrically tunable G-H shifts with miniaturized heaters will extend the research scope of the G-H shift phenomenon and its applications. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Accepted version K.V.S. and R.S. acknowledge the funding support from Singapore Ministry of Education (MOE) grant numbers AcRF MOE2016-T3-1-006 and MOE AcRF Tier 1 RG96/19 and Advanced Manufacturing and Engineering (AME) Programmatic grant (A18A5b0056) by Agency for Science, Technology and Research (A*STAR). R.M. and R.S.R. would like to acknowledge the Ministry of Education (MOE) through Tier 2 grants (2019-T2-1-058). In addition, C.M.D. and K.T.Y. acknowledge the funding support from Singapore National Research Foundation (NRF) and French National Research Agency (ANR), grant number (NRF2017-ANR002 2DPS).

Combination of anti-resonant hollow-core fiber (HCF) and semiconductor nanomaterial is an effective strategy to obtain high-performance gas sensors with exceptional sensitivity and low power consumption. However, controlling the semiconductor morphology onto HCF is a major challenge to achieve the desired gas sensor with the enhanced sensitivity. Here, a ZnO-Bi2O3 nanosheets (NSs) heterostructure is grown in situ on the surface of HCF by sol–gel and hydrothermal methods. ZnO-Bi2O3 NSs serving as electron acceptors trap electrons after acetone adsorption and then change the refractive index of the surface of HCF. Benefiting from the unique sheet structure and the synergetic effects for multi-component, the resulting ZnO-Bi2O3 NSs enabled HCF gas sensor exhibits high sensitivity, selectivity, and repeatability for detecting acetone at room temperature, particularly in the low concentration range, with the theoretical limit of detection down to 140 parts-per-billion. Meanwhile, the successful application of the ZnO-Bi2O3 NSs enabled HCF gas sensor to distinguish the exhaled breath from the healthy individuals and simulated diabetic cases is demonstrated, which paves the way to achieve non-invasive, ultra-sensitivity gas sensing at room temperature for the early diagnosis of diabetes. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version This work was supported by the Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2019-T2-2-127 and T2EP50120-0005), A*STAR under AME IRG (A2083c0062), the Singapore Ministry of Education Academic Research Fund Tier 1 (RG90/19 and RG73/19) and the Singapore National Research Foundation Competitive Research Program (NRF-CRP18-2017-02), Guangdong Basic and Applied Basic Research Foundation (2019A1515011762), Shenzhen Science and Technology Innovation Foundation (JCYJ20180305125302333, JCYJ20170818093035338, JCYJ20180305125430954), Shenzhen University Fund (860-000002110229) and Foshan City Education Department Foundation.

Self-assembly of colloidal nanocrystals into ordered superlattices is a powerful approach to enable novel collective properties which are not available in individual colloids. However, to date, it remains a major challenge to develop a practical route to modulate such collective properties for potential photonic applications. Herein, it is shown that the collective emission properties in colloidal quantum well (CQW) superlattices, including emission color and anisotropy, can be effectively modulated in a binary host–guest architecture. The experimental and theoretical results reveal that excitons of the host (i.e., the undoped CQWs) generated by photoexcitation can be controllably harvested by the guest (i.e., the Cu-doped CQWs) for light emission, owing to an exciton hopping assisted exciton trapping process. Such a nano-building block with tunable collective optical properties may enlighten novel colloidal material-based photonic applications, including optical anti-counterfeiting, next-generation liquid crystal displays, and multifunctional biological markers. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version The authors would like to acknowledge the financial support from Singapore National Research Foundation under the program of NRF-NRFI2016-08, the Competitive Research Program NRF-CRP14-2014-03, and the Singapore Ministry of Education AcRF Tier-1 grant (MOE2019-T1-002-087). H.V.D. is also grateful to acknowledge additional financial support from the TUBA.

Despite the tremendous progress of coupling organic electrooxidation with hydrogen generation in a hybrid electrolysis, electroreforming of raw biomass coupled to green hydrogen generation has not been reported yet due to the rigid polymeric structures of raw biomass. Herein, we electrooxidize the most abundant natural amino biopolymer chitin to acetate with over 90% yield in hybrid electrolysis. The overall energy consumption of electrolysis can be reduced by 15% due to the thermodynamically and kinetically more favorable chitin oxidation over water oxidation. In obvious contrast to small organics as the anodic reactant, the abundance of chitin endows the new oxidation reaction excellent scalability. A solar-driven electroreforming of chitin and chitin-containing shrimp shell waste is coupled to safe green hydrogen production thanks to the liquid anodic product and suppression of oxygen evolution. Our work thus demonstrates a scalable and safe process for resource upcycling and green hydrogen production for a sustainable energy future., The scale-up of the coupling of water electroreduction (HER) with organic electrooxidation remains challenging. Here the authors address this challenge by coupling HER with electrooxidation of raw biomass chitin, cogenerating acetate and green hydrogen safely at high current density.

Carbon nanotubes (CNTs) have, over the years, been used in research as a promising material in electronics as a thermal interface material and as interconnects amongst other applications. However, there exist several issues preventing the widespread integration of CNTs onto device applications, e.g., high growth temperature and interfacial resistance. To overcome these issues, a complementary metal oxide semiconductor (CMOS)-compatible CNT array transfer method that electrically connects the CNT arrays to target device substrates was developed. The method separates the CNT growth and preparation steps from the target substrate. Utilizing an alignment tool with the capabilities of thermocompression enables a highly accurate transfer of CNT arrays onto designated areas with desired patterns. With this transfer process as a starting point, improvement pointers are also discussed in this paper to further improve the quality of the transferred CNTs. Ministry of Education (MOE) Published version This research was funded by Singapore MOE Tier 2, MOE2018-T2-2-105 and Excelitas Technologies Singapore (EDB-IPP).

The COVID‐19 virus has been recently identified as a new species of virus that can cause severe infections such as pneumonia. The sudden outbreak of this disease is being considered a pandemic. Given all this, it is essential to develop smart biosensors that can detect pathogens with minimum time delay. Surface plasmon resonance (SPR) biosensors make use of refractive index (RI) changes as the sensing parameter. In this work, based on actual data taken from previous experimental works done on plasmonic detection of viruses, a detailed simulation of the SPR scheme that can be used to detect the COVID‐19 virus is performed and the results are extrapolated from earlier schemes to predict some outcomes of this SPR model. The results indicate that the conventional Kretschmann configuration can have a limit of detection (LOD) of 2E‐05 in terms of RI change and an average sensitivity of 122.4 degRIU−1 at a wavelength of 780 nm., The entire world is fighting a major public health crisis in the form a unique viral disease, caused by a coronavirus that has been named COVID‐19. In this work, a theoretical study of a plasmonic sensing scheme in the form of simulations that can be used to detect the COVID‐19 virus is presented.

Two‐dimensional (2D) materials have great potential in the fields of flexible electronics and photoelectronic devices due to their unique properties derived by special structures. The study of the mechanical properties of 2D materials plays an important role in next‐generation flexible mechanical electronic device applications. Unfortunately, traditional experiment models and measurement methods are not suitable for 2D materials due to their atomically ultrathin thickness, which limits both the theoretical research and practical value of the 2D materials. In this review, we briefly summarize the characterization of mechanical properties of 2D materials by in situ probe nanoindentation experiments, and discuss the effect of thickness, grain boundary, and interlayer interactions. We introduce the strain‐induced effect on electrical properties and optical properties of 2D materials. Then, we generalize the mechanical sensors based on various 2D materials and their future potential applications in flexible and wearable electronic devices. Finally, we discuss the state of the art for the mechanical properties of 2D materials and their opportunities and challenges in both basic research and practical applications. Ministry of Education (MOE) Published version Fundamental Research Funds for the Central Universities, Grant/Award Numbers: 31020190QD010, 3102019PY004, 3102019JC004; Ministry of Education - Singapore, Grant/Award Numbers: MOE2015-T2-2-043, MOE2017-T2-2-136, Tier 1 RG7/18; National Natural Science Foundation of China, Grant/Award Number: 11904289; Natural Science Foundation of Shaanxi Province, Grant/Award Number: 2019JQ- 613; Start-up funds from Northwestern Polytechnical University, Grant/Award Numbers: 19SH020159, 19SH020123

The beautiful interplay between light and matter can give rise to many striking physical phenomena, surface plasmon resonance (SPR) being one of them. Plasmonic immunosensors monitor refractive index changes that occur as a result of specific ligand–analyte or antibody–antigen interactions taking place on the sensor surface. The coronavirus disease (COVID‐19) pandemic has jeopardized the entire world and has resulted in economic slowdown of most countries. In this work, a model of a sandwich plasmonic biosensor that utilizes gold nanorods (Au NRs) for the detection of COVID‐19 SARS‐CoV‐2 spike protein is presented. Simulation results for different prismatic configurations for the basic Kretschmann layout are presented. It is found that a BK7 glass prism‐based SPR sensor has an incremental sensitivity of 111.11 deg RIU−1. Additionally, using Comsol Multiphysics the electric field enhancement observed for various aspect ratios and layouts of Au NRs are discussed in depth., The coronavirus disease (COVID‐19) pandemic has adversely affected the entire world, where apart from stressing the medical fraternity, it has resulted in a major economic slowdown. In this paper, a unique detection scheme for quantifying SARS‐CoV‐2 virus using a plasmonic immunosensor that uses gold nanorods for signal amplification is presented.

Light management through low index medium, such as antireflective coating (ARC) provides practical solution to improve the efficiency of photovoltaics. However, a brute-force development of photonic structure on ARC is not necessarily useful, because of random scattering associated with impediment of light transmission. Here, we leverage the concept of disorder, rather than random, structured on ARC for improving efficiency without modifying original architecture of thin-film photovoltaics. We demonstrate a disordered polymer that leads to a total reflectance of 5% while demonstrating a high transmission of 94% across 300 to 820 nm wavelength. Next, we find that the arrangement of disordered points and line arrays constructing the polymer seems to be the key to control bandwidth performance of the ARC. Finally, we apply this into Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 perovskite, and through experiments with wave-optics and full-device simulation, show a 1.6-fold absorption gain leading to 19.59% power-conversion-efficiency by the disordered ARC. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work is supported by the National Research Foundation, Prime Minister’s Office, Singapore under Energy Research Innovation Program (Grant number, NRF2015EWT-EIRP003-004 and NRF-CRP14-2014-03 and Solar CRP:S18-1176-SCRP), and Ministry of Education (MOE2016‐T2‐1‐052).

Surface Plasmon Resonance (SPR) based biosensors have been around in the scientific community for more than two decades and these have facilitated enormous improvement in the detection of complex biomolecules. Since, sensitivity of these sensors directly affects the ease of detection, our work here focuses on using dielectric nanosheets of Titania and Silica to enhance the sensitivity. The anti-reflective property of these dielectric materials promotes greater interaction between the incident light and the plasmonic metal, resulting in generation of more surface plasmons that promotes greater sensitivity. With 40 nm of gold, 3 layers of Titania (9 nm) and a layer of Silica (3 nm), our simulation results predict a sensitivity of 214 deg/RIU at 532 nm, which is a major improvement when compared to other sensor structures. National Research Foundation (NRF) This work was supported by the Singapore National Research Foundation (NRF) and French National Research Agency (ANR) , grant number (NRF2017–ANR002 2DPS).

Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs., Z.L. gratefully acknowledges funding supports from Ministry of Education (MOE) under AcRF Tier 1 (M4011782.070 RG4/17 and M4011993.070 RG7/18), AcRF Tier 2 (2015-T2-2-007, 2016-T2-1-131, 2016-T2-2-153, and 2017-T2-2-136), AcRF Tier 3 (2018-T3-1-002), National Research Foundation – Competitive Research Program (NRF-CRP21-2018-0092), and A*Star QTE programme. P.T., S.M.S., J.R.M., and J.A. acknowledge funding from Generalitat de Catalunya 2017 SGR 327 and 1246 and the Spanish MINECO coordinated projects between IREC and ICN2 VALPEC (ENE2017-85087-C2-C3). ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2017-0706). IREC and ICN2 are funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science PhD program. S.M.S. acknowledges funding from ‘Programa Internacional de Becas “la Caixa”-Severo Ochoa’. J.R.M. recognizes also its affiliation to University of Barcelona. Part of the electron microscopy aspects of this work were supported by the EPSRC (UK), as the SuperSTEM Laboratory is the EPSRC National Research Facility for Advanced Electron Microscopy. Q.J.W. acknowledges the supports from MOE, Singapore grant (MOE2016-T2-2-159, MOE2016-T2-1-128, and MOE Tier 1 RG164/15) and National Research Foundation, Competitive Research Program (NRF-CRP18-2017-02) and NSFC (61704082) as well as Natural Science Foundation of Jiangsu Province (BK20170851). X.W. and B.K.T. gratefully acknowledge funding support from MOE, Singapore (grant no. MOE2015-T2-2-043). H.Z. acknowledges the supports from MOE under AcRF Tier 2 (MOE2015-T2-2-057; MOE2016-T2-2-103; and MOE2017-T2-1-162), AcRF Tier 1 (2016-T1-002-051; 2017-T1-001-150; and 2017-T1-002-119), Agency for Science, Technology and Research (A*STAR) under its AME IRG (Project No. A1783c0009), and NTU under Start-Up Grant (M4081296.070.500000) in Singapore. The authors would like to acknowledge the Facility for Analysis, Characterization, Testing, and Simulation, Nanyang Technological University, Singapore, for their electron microscopy and X-ray facilities. H.Z. also thanks the support from ITC via Hong Kong Branch of National Precious Metals Material Engineering Research Center, and the Start-Up Grant from City University of Hong Kong. Theory and simulations work at Rice university (Z.H., L.W., and B.I.Y.) was supported by the Office of Naval Research grant N00014-18-1-2182.

In this paper, we report a sensitivity-controllable refractive index (RI) sensor based on a reflective θ-shaped microfiber resonator cooperated with Vernier effect. The θ-shaped microfiber resonator is a reflective all-fiber device with comb spectrum under weak coupling condition. By cascading it with a fiber Fabry-Perot interferometer, Vernier effect is generated to demodulate surrounding RI with enhanced sensitivity. Theoretical analysis reveals that RI sensitivity of the combined structure with Vernier effect is m times higher than the sensitivity of singular θ-shaped microfiber resonator. Moreover, by adjusting cavity length of the θ-shaped microfiber resonator, magnification factor M = (m + 1) can be tuned which enables the RI sensitivity to be controlled. Experimental result demonstrates that the RI sensitivity can be widely tuned from 311.77 nm/RIU (Reflective index unit) to 2460.07 nm/RIU when the cavity length of the θ-shaped microfiber resonator is adjusted from 9.4 mm to 8.7 mm. The θ-shaped microfiber resonator based all-fiber RI sensor featuring controllable sensitivity and compact size can be widely used for chemical and biological detections. The proposed scheme of generating Vernier effect also offers a universal idea to increase measurement sensitivity for optical fiber sensing structures with comb spectrum.

The abundance and corrosion-resistant properties of aluminium, coupled with its compatibility to silicon processing make aluminium an excellent plasmonic material for light–matter interaction in the ultraviolet-visible spectrum. We investigate the interplay of the excitation and emission enhancements of quantum dots coupled with ultra-small aluminium nanoantennae with varying rotational symmetries, where emission enhancements of ∼8 and ∼6 times have been directly measured for gammadion and star-shaped structures. We observed spontaneous emission modification in the Al antenna with a C6 symmetry and deduce a Purcell factor in the range of 68.01 < FP < 118.25 at plasmonic hotspots, corresponding to a modified quantum yield of >89% in the single antenna and near-unity quantum yield at the plasmonic hotspots. This finding brings us a step closer towards the realization of circularly polarized nanoemitters. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) This work is supported by the A*Star (SERC 1720700038 and SERC A1883c0002) and the Ministry of Education (2017-T1- 002-117) Singapore, and the Asian Office of Aerospace Research and Development (FA2386-17-1-0039).

Carbon nanotubes (CNTs) are long considered as a promising material for thermal applications. However, problems such as low volume CNT fraction abhorrent to practical applications have been raising the demand for novel architecture of this material. Here we demonstrate two fabrication methods, in which a self-assembly method for fabricating covalent-bonded CNT network (3D CNT) and another method for covalent-bonded C to CNTs (C@CNT) network, and presented both as a potential method to enhance thermal conductivity of CNT arrays. We utilized pulsed photothermal reflectance technique and using new four-layer heat conduction model based on the transmission-line theory to measure thermal conductivity of the samples. The 3D CNT with thermal conductivity of 21 W mK−1 and C@CNT with thermal conductivity of 26 W mK−1 turn out to be an excellent candidate for thermal interface material as the thermal conductivity increased by 40% and 70% respectively as compared to conventional CNT arrays. The improvement is attributed to the efficient thermal routines constructed between CNTs and secondary CNTs in 3D CNT and between C layer and CNTs in C@CNT. The other factor to improve thermal conductivity of the samples is decreasing air volume fraction in CNT arrays. Our fabrication methods provide a simple method but effective way to fabricate 3D CNT and C@CNT and extend the possibility of CNTs towards TIM application. Ministry of Education (MOE) Published version We thank for the financial support from the Swedish Foundation for Strategic Research (SSF) under contract (No SE13–0061), Swedish National Board for Innovation (Vinnova)Graphene SIO-Agenda Program, Formas program on graphene enhanced composite as well as from the Production Area of Advance at Chalmers University of Technology, Sweden. Thanks are also given to the Ministry of Science and Technology of China with the contract No: 2017YFB040600 for the financial support. This research benefited also from the support of the Ministry of Education (Singapore) under the grant MOE2014-T2-2-105.

Hyperbolic metamaterials (HMMs) have emerged as a burgeoning field of research over the past few years as their dispersion can be easily engineered in different spectral regions using various material combinations. Even though HMMs have comparatively low optical loss due to a single resonance, the noble-metal-based HMMs are limited by their strong energy dissipation in metallic layers at visible frequencies. Here, the fabrication of noble-metal-free reconfigurable HMMs for visible photonic applications is experimentally demonstrated. The low-loss and active HMMs are realized by combining titanium nitride (TiN) and stibnite (Sb₂S₃) as the phase change material. A reconfigurable plasmonic biosensor platform based on active Sb₂S₃–TiN HMMs is proposed, and it is shown that significant improvement in sensitivity is possible for small molecule detection at low concentrations. In addition, a plasmonic apta-biosensor based on a hybrid platform of graphene and Sb₂S₃–TiN HMM is developed and the detection and real-time binding of thrombin concentration as low as 1 × 10⁻¹⁵ m are demonstrated. A biosensor operating in the visible range has several advantages including the availability of sources and detectors in this region, and ease of operation particularly for point-of-care applications. Ministry of Education (MOE) Accepted version The authors (K.V.S. and R.S.) acknowledge Singapore Ministry of Education (MOE) (Grant No. MOE2015-T2-2-103) for funding of this research. S.S. and C.T.L. acknowledge support from the NUS-Biomedical Institute for Global Health Research and Technology. We thank Dr. Giorgio Adamo (CDPT, NTU-Singapore) for his support with SEM imaging.