Search

Phase transitions can occur in certain materials such as transition metal oxides (TMOs) and chalcogenides when there is a change in external conditions such as temperature and pressure. Along with phase transitions in these phase change materials (PCMs) come dramatic contrasts in various physical properties, which can be engineered to manipulate electrons, photons, polaritons, and phonons at the nanoscale, offering new opportunities for reconfigurable, active nanodevices. In this review, we particularly discuss phase-transition-enabled active nanotechnologies in nonvolatile electrical memory, tunable metamaterials, and metasurfaces for manipulation of both free-space photons and in-plane polaritons, and multifunctional emissivity control in the infrared (IR) spectrum. The fundamentals of PCMs are first introduced to explain the origins and principles of phase transitions. Thereafter, we discuss multiphysical nanodevices for electronic, photonic, and thermal management, attesting to the broad applications and exciting promises of PCMs. Emerging trends and valuable applications in all-optical neuromorphic devices, thermal data storage, and encryption are outlined in the end.

On-demand and selective regulation of the radiative cooling (long-wave infrared, LWIR) and solar heat gain (ultraviolet-, visible- and near-IR, UV-vis-NIR) of building facades is a grand challenge but essential to decrease energy usage in buildings. Here, we report a reconfigurable interwoven surface that can dynamically switch the overlapping sequence to achieve spectral selectivity and ultrabroadband modulations for windows, walls/roofs with decent spectral modulations, and energy-saving performance. The result surpasses the best reported passive radiative cooling smart windows with a more than doubled visible transmittance (Tlum = 0.50) and LWIR modulation (ΔϵLWIR = 0.57). Our energy-saving samples outperform the commercial building materials across climate zones 2-6. This design principle is scalable and applicable for diverse materials, interwoven structures, and 2D-3D surfaces, which provide a strategy to give programmable heating/cooling modulations in various applications. Ministry of Education (MOE) National Research Foundation (NRF) The research was supported by the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program and the Singapore-HUJ Alliance for Research and Enterprise (SHARE), Minister of Education (MOE) Academic Research Fund Tier 1 RG103/19 (S), RG86/ 20, and RG71/21, and the Sino-Singapore International Joint Research Institute (SSIJRI). J.Y. would like to thank the National Science Foundation for grant numbers CMMI2005374 and CMMI-2013993.

To investigate the risk factors for residual dizziness (RD) in patients with benign paroxysmal positional vertigo (BPPV) after successful repositioning.Searches were performed in PubMed, Embase, Cochrane library, Web of Science, Chinese National Knowledge Infrastructure, and Sino Med up to March 7, 2021 and references of relevant articles were screened. Data from eligible studies were meta-analyzed using Stata version 16.0 and Review Manager 5.4.In this systematic review and meta-analysis of 4487 patients from 31 studies, the prevalence of RD was 43.0% (95% CI 39.0-48.0%). Age (MD 4.17; 95% CI 2.13-6.21, P = 0.000), female gender (OR = 1.28, 95% CI 1.11-1.47, P = 0.001), secondary BPPV (OR 1.88; 95% CI 1.27-2.77, P = 0.001), a longer duration of BPPV before treatment (MD 3.45; 95% CI 1.87-5.02, P = 0.000), abnormal ocular vestibular evoked myogenic potential (OVEMP, OR 4.34; 95% CI 2.78-6.78, P = 0.000), abnormal cervical vestibular evoked myogenic potential (CVEMP, OR 2.48; 95% CI 1.54-3.99, P = 0.000), higher Dizziness Handicap Index (DHI) score before treatment (MD 10.88; 95% CI 5.96-15.80, P = 0.000), anxiety (OR 9.58; 95% CI 6.32-14.52, P = 0.000), osteopenia (OR = 4.40, 95% CI 2.17-8.96, P = 0.000), onset in winter (OR 7.27; 95% CI 2.38-22.24, P = 0.001) and with a history of BPPV (OR 1.79; 95% CI 1.06-3.04, P = 0.03) are the risk factors for RD in patients with BPPV after successful repositioning. The affected side, location or type of semicircular involvement, hyperlipidemia, diabetes, hypertension, heart disease, migraine, sleep disorders, canalolithiasis/cupulolithiasis, the number of times the canalith repositioning procedures (CRPs) were performed and number of vertigo attacks did not correlate with the occurrence of RD.Despite successful treatment, nearly half of the BPPV patients developed RD. RD seems to be a syndrome caused by multiple factors. The pathogenesis of most factors can be explained by psychological and/or physical disorders. Early recognition of these risk factors contributes to the prevention and treatment of RD.

A physical crosslinked thermochromic smart hydrogel demonstrated easy fabrication, improved anti-freezing and good structural integrity across phase transition, to be used in smart windows, sensing, camouflage, etc.

Epidemiological studies on the effect of organophosphate esters (OPEs) on high blood pressure (BP) among children and adolescents are scant. Therefore, the main objective of the present study was to explore the effect of exposure to OPEs on high BP among children and adolescents. A total of 1340 participants were included in the current analyses. Multivariable logistic regression models were implemented to calculate odds ratios (ORs) and corresponding 95% confidence intervals (CIs) to examine the association between OPE metabolites and high BP. We also assessed the modified effect of sex, age, and overweight/obesity on this association. Furthermore, quantile g-computation (Qgcomp) and Bayesian kernel machine regression (BKMR) were exhibited to analyze the association between multiple OPE metabolite mixtures and high BP. After adjusting for covariates, the highest (vs. lowest) tertiles of bis (1-choloro-2-propyl) phosphate (BCPP), bis-2-chloroethyl phosphate (BCEP), and di-n-butyl phosphate (DBUP) were associated with 1.23 (95% CI: 0.83, 1.83), 1.27 (95% CI: 0.85, 1.92), and 1.01 (95% CI: 0.67, 1.53) odds ratios for high BP, respectively. In the Qgcomp, a quartile increase in OPE metabolite mixtures was weakly associated with an elevated risk of high BP (adjusted OR: 1.06, 95CI%: 0.81, 1.37). The results from BKMR showed a positive trend of association between OPE metabolite mixture on the risk of high BP. In conclusion, our study demonstrated that higher levels of BCPP, BCEP, and DBUP were weakly associated with high BP among US children and adolescents. Moderate evidence suggested OPE metabolite mixtures had positive joint effects on high BP. Consequently, longitudinal studies with repeated measurements are warranted to examine the relationships between multiple OPE metabolites and high blood pressure among children and adolescents.

The rapid development of additive manufacturing has fueled a revolution in various research fields and industrial applications. Among the myriad of advanced 3D printing techniques, two-photon polymerization lithography (TPL) uniquely offers a significant advantage in nanoscale print resolution, and has been widely employed in diverse fields, for example, life sciences, materials sciences, mechanics, and microfluidics. More recently, by virtue of the optical transparency of most of the resins used, TPL is finding new applications in optics and photonics, with nanometer to millimeter feature dimensions. It enables the minimization of optical elements and systems, and exploration of light-matter interactions with new degrees of freedom, never possible before. To review the recent progress in the TPL related optical research, it starts with the fundamentals of TPL and material formulation, then discusses novel fabrication methods, and a wide range of optical applications. These applications notably include diffractive, topological, quantum, and color optics. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of TPL and related potential optical applications.

Building-integrated solar cells not only generate electricity but also impact the envelope thermal characteristics, thus changing the micro-climate of buildings. Therefore, the collective effects of energy conservation and generation on buildings should be considered in one design. In this work, a smart photovoltaic window foil with near-infrared (NIR) modulation and low long-wavelength IR emissivity has been fabricated by combining organic perovskite and inorganic tungsten doped vanadium dioxide nanoparticles (W-VO2 NPs). The W-VO2 offers solar modulation and promotes extraction and transport of photogenerated charges, giving peak power conversion efficiency of 15.4% at 25 ℃ and 16.1% at 45 ℃ and average visible transmission of 25.5%, comparable to the best reported semitransparent perovskite solar cell with an additional favorable NIR modulation of 10.7%. This new strategy to integrate energy-saving functionality into photovoltaic foil initiates a new design rule for smart window development. Ministry of Education (MOE) National Research Foundation (NRF) This work was supported by National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program and Singapore Ministry of Education (MOE) Academic Research Fund Tier 1 RG103/19 and RG86/20. This work was co-financed by National Natural Science Foundation of China (Grant Nos. 51572098 and 51632006), National Basic Research Program of China (Grant No. 2013CB632500), Natural Science Foundation of Hubei Province (Grant No. 2015CFB432), Open Fund of State Key Laboratory of Advanced Techology (No. 2016-KF-5).

Vanadium dioxide (VO2) emerges as an attractive plasmonic material due to its unique reversible thermal-responsive phase transition and the promising application in energy-saving smart windows. Here, by optimizing the geometry of VO2 nano-cylinder arrays, we demonstrate a significant performance enhancement for energy-efficient thermochromic windows. Such a performance enhancement relies on the on-off behavior of plasmonic resonance in the extremely high packing density of VO2 nano-cylinder arrays. Different from the typical plasmonic material, silver, VO2 nano-cylinders are characterized to have strong absorbance in near-infrared spectrum with significantly weaker plasmonic coupling to their neighbors, making them suitable to be arranged with a high packing density. The VO2 nano-cylinder arrays exhibit a 160% luminous transmittance increment, comparing to a flat film with the same solar modulation of ~10%. The work provides a better understanding of the plasmonic behavior on phase-change VO2 and an efficient method to enhance smart window performance. Ministry of Education (MOE) National Research Foundation (NRF) Published version Y. Long thanks to the funding support by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme; Minister of Education Singapore Tier 1 RG86/20 and RG103/19; Singapore International Joint Research Institute.

The incorporation of biomimetic structures in a vanadium dioxide (VO2) coating is believed to be a promising way to enhance its thermochromic performance because biomimetic structures enable tailoring of optical properties. Films based on VO2 with grid structures are attracting increasing interest due to the great potential for structure-induced thermochromic enhancements, mainly including enhanced transmittance, antireflection, increased effective solar modulation volume, and localized surface plasmon resonance. Combining some advanced functions, such as self-cleaning and energy conservation and generation, into one thermochromic smart window device is a highly attractive scientific undertaking. Meanwhile, for energy conservation, to continue the trend of enhancing thermochromic properties, hybridation and active control have so far offered the best results compared with other conventional approaches. In conclusion, compared to planar VO2 films, gridded structures are an efficient method to promote thermochromic performance, demonstrated through methods such as mesh printing, ionic strength–induced electrodeposition, dual-phase transformation, and nanosphere lithography.

Supplemental Document for Manuscript

Plasmonic thermochromic films are promising for smart window applications. Hereby, we develop a flexible plasmonic thermochromic film towards multifunctionality. The double-layer film consists of a bottom layer of W/Mg co-doped vanadium dioxide (VO2) rods in a polyurethane acrylate matrix and a top layer of hollow silica spheres (HSSs). Based on the finite-difference time-domain (FDTD) method, we demonstrate for the first time, a transverse and a longitudinal mode of VO2 localized surface plasmonic resonance (LSPR) in near- and mid-infrared bands, respectively, and only the transverse mode contributes to the solar energy modulation performance. The film shows a luminous transmittance of 46.2%, a solar energy modulation of 10.8%, and a critical transition temperature of 36.9 °C. The HSSs overcoating enhances the surface hydrophilicity and thermal insulation, which give rise to more favored functionalities for windows. Ministry of Education (MOE) National Research Foundation (NRF) Q. Xu, Y. Ke, and C. Feng contribute equally. X. Liu acknowledges the support of the National Natural Science Foundation of China (Grant No. 51776143 and U1830127) and Fundamental Research Funds for the Central Universities (Grant No. 2042018kf0238) . The usage of SEM, TEM, and XPS funded by the Open Subsidies for large-scale Equipment of Wuhan University (Grant No. LF20181061) . Y. Long thanks to the funding support by the National Research Foundation, Prime Minister's Office, Singapore under its Campus for Research Excellence and Tech-nological Enterprise (CREATE) programme, Sino-Singapore Interna-tional Joint Research Institute, and Minister of Education Singapore Tier 1 RG86/20 and RG103/19 for funding support.

Vanadium dioxide (VO2) is a unique active plasmonic material due to its intrinsic metal-insulator transition, remaining less explored. Herein, we pioneer the method to tailor the VO2 surface plasmon by manipulating its atomic defects and establish a universal quantitative understanding based on seven representative defective VO2 systems. The record high tunability is achieved for the localized surface plasmon resonance (LSPR) energy (0.66–1.16 eV) and transition temperature range (40-100 oC). Drude model and density function theory reveal the charge of cations plays a dominant role over the numbers of valence electrons to determine the free electron concentration. We further demonstrate their superior performances in extensive unconventional plasmonic applications including energy-saving smart windows, wearable camouflage devices, and encryption inks. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version Y. Long is thankful for the funding support from the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) programme, Sino-Singapore International Joint Research Institute, and Minister of Education Singapore Tier 1 RG86/20 and RG103/19 for funding support. Z. M. Sun is thankful for the funding support from National Key Research and Development Program of China (Grant No. 2017YFB0701700). Y. Zhong, Y. Liu, and X. Ye were supported by the Indiana University FRSP Grant and IU-MSI STEM Initiative Seed Grant.

Transition metal dichalcogenides (TMDs) show promising electrical and electronic properties and potential catalytic applications in the hydrogen evolution reaction (HER). However, most TMDs suffered from low conductivity and scarcity of active edge sites. Herein, new ternary vanadium-based TMD, VSSe alloy single crystals were synthesized for the first time by agent-assisted chemical vapor transport and used as an excellent HER electrocatalyst due to the pure conductive phase and abundant active sites induced by ternary structures. Different transport agents were employed to tune the interlayer spacing, and it was found that the expansion of the (001) interlayer spacing and the co-existence of V3+ could introduce more S or Se vacancies. The exfoliated VSSe sample exhibits a lower overpotential of −180 mV at a current density of 10 mA cm−2, a Tafel slope of 87 mV dec−1, and better durability, which are comparable to or better than those of most previously reported ternary TMD systems. Consistent with the theoretical calculation results, more defects controlled by the transport agent of VCl3 give an enhanced conductivity and a lower H* adsorption energy, and thereby higher HER performance. By simply varying the transport agents, high-conductivity, high-purity, and high-performance TMDs can be fabricated in one step without the conventional post-treatment.

Rapid development of the thermochromic glazing technique promises next-generation architectural windows with energy-saving characteristics by intelligently regulating indoor solar irradiation via modulating windows’ optical properties in response to the surrounding temperature. Vanadium dioxide (VO2) is a promising material for energy-saving smart windows due to its reversible metal-to-insulator transition near room temperature and accompanying large changes in its optical properties. This review provides a comprehensive overview of the application of VO2 to smart windows with particular emphasis on recent progress from the electronic, atomic, nano, and micron perspectives. The effects of intrinsic atomic defects, elemental doping, and lattice strain on VO2 nanocrystals are examined. Nano- and microscale morphology engineering approaches that aim to enhance the thermochromic performance and impart practical multi-functionalities are summarized. Finally, the challenges and future directions of VO2-based smart windows are elaborated to bridge the gap between the lab research and large-scale practical applications. Vanadium dioxide (VO2) is a promising material for energy-saving smart windows due to its reversible metal-to-insulator transition near room temperature. This thermally induced phase transition is reversible, and it is accompanied by a dramatic change in the optical properties in the near-infrared region from a low-temperature transparent state to a more blocking state at high temperatures, imbuing the VO2-based window with the ability to regulate solar heat flux by responding to temperature automatically. In this review, the progress in VO2-based smart windows is overviewed, from the band structure designing at the electronic and atomic scales to morphology engineering from nano- to microscales. We discuss the effects of intrinsic atomic defects, elemental doping, and lattice strain on the electronic and atomic structures of VO2. Subsequently, nano- and microscale engineering methods to enhance the performance of smart windows are presented, including incorporating particles, tuning the porosity, designing nanocomposites, developing biomimetic patterns, creating grids, and applying multifunctional antireflection coatings. The energy efficiency is also discussed from both simulations and experimental aspects. Lastly, challenges and future directions are discussed. We hope that this work may inspire more innovative progress and accelerate the development of this technique from the lab to industry. VO2 is a promising material for energy-saving smart windows due to its reversible metal-to-insulator transition near room temperature and accompanying large changes in its optical properties. This review provides a comprehensive overview of the application of VO2 to smart windows with particular emphasis on recent progress from the electronic, atomic, nano, and micron perspectives. The challenges and future directions of VO2-based smart windows are elaborated to bridge the gap between the lab research and large-scale practical applications. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Privacy and energy-saving are key functionalities for next-generation smart windows, while to achieve them independently on a window is challenging. Inspired by the cephalopod skin, we have developed a versatile thermo- and mechano-chromic design to overcome such challenge and reveal the mechanism via both experiments and simulations. The design is facile with good scalability, consisted of well-dispersed vanadium dioxide (VO2) nanoparticles (NPs) with temperature-dependent localized surface plasmon resonance (LSPR) in transparent elastomers with dynamic micro wrinkles. While maintaining a fixed solar energy modulation of (ΔTsol), the design can dynamically control visible transmittance (Tvib) from 60% to 17%, adding a new dimension to VO2-based smart windows. We prove that the optical modulation relies on the microtexture-induced broadband diffraction and the plasmon-enhanced near-infrared absorbance of VO2 NPs. We further present a series of modified designs towards additional functionalities. This work opens an avenue for independent dual-mode windows and it may inspire development from fundamental material, optic, and mechanical science to energy-related applications. Accepted version

4D printed objects are 3D printed structures whose shape, property, and functionality are able to self‐transform when exposed to a predetermined stimulus. The emerging field of 4D printing has attracted wide interest from both academia and industry since first introduced in 2013. Stimuli‐responsive hydrogels have become a competitive and versatile group of materials for 4D printed devices due to their good deformability, promising biocompatibility, simple manufacturing, and low cost. This review aims to provide a summary of the current progress of hydrogel‐based 4D printed objects and devices based on their fabrication techniques, materials, and applications. Herein, presented are: the characteristics of different additive manufacturing methods such as direct ink writing, fused deposition modeling, and stereolithography; the properties of various stimuli‐responsive hydrogels such as poly(N ‐isopropylacrylamide) and poly(N ,N ‐dimethylacrylamide), alginate, etc.; and diverse applications of 4D printed hydrogels such as actuators, cellular scaffolds, and drug release devices. Opportunities and challenges for 4D printed hydrogels are discussed and prospects for future development are elaborated. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version Y.L. acknowledges the funding support by the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) programme, Singapore Ministry of Education (MOE) Academic Research Fund Tier one RG103/19, and the Sino-Singapore International Joint Research Institute for the funding support.

Smart windows are promised with a significant contribution to the economization of building energy consumption. Such windows can dynamically modulate the indoor solar irradiation, leading to energy-saving for architectural heating and cooling systems. Development of smart windows can mainly be categorized as electro-, thermo-, and photo-stimulated optical response changes. Among them, thermochromic smart windows that change the optical properties in responsive to the temperature are highly competitive due to the low cost, passivity, and rational stimulus-response. Vanadium dioxide (VO2) is a promising candidate for thermochromic smart window application due to its reversible phase transition near the room temperature, accompanied with huge optical properties change. It can be transparent to the near-infrared solar irradiation at low temperature, while shield it at high temperature. However, challenges remain in VO2-based thermochromic smart windows, including the intrinsic yellow-brown color, the relatively low solar energy modulation (ΔTsol) and visible transmittance (Tlum). This thesis is dedicated to improve these shortages and promote the performance of VO2-based thermochromic smart windows, resulting in three effective methods. The photonic crystals were introduced to improve the undesirable yellow-brown color. The Silica/VO2 (SiO2/VO2) core/shell two-dimensional (2D) photonic crystal is prepared and demonstrated to exhibit static visible light tunability and dynamic near-infrared (NIR)modulation. Three-dimensional finite difference time domain simulations predict that the transmittance can be tuned across the visible spectrum while maintaining good ΔTsol of 11.0% and a Tlum of 49.6%. Though the experimental result is not as prominent, it proves that the color changes of VO2 films are accompanied by NIR modulation, which is aligned with the simulation result. In produced samples, colors beyond the yellow-brown are observed, such as green, blue, and red, demonstrating the effectiveness of photonic crystals for tuning the color of VO2-based smart windows. The localized surface plasmon resonance (LSPR) was introduced to promote the performance of the ΔTsol and the Tlum. The phenomenon is demonstrated in tuning the absorption peak position of VO2 to the region with dense solar energy, which was demonstrated on 2D patterned VO2 nanoparticles. Colloidal lithography method was applied to prepare the 2D patterned VO2-based nanocrystals, resulting in nanonet, nanodome, to nanoparticle arrays. LSPR and their application in thermochromic smart windows. The nanoparticle arrays exhibit tunable LSPR at different temperatures and the LSPR red-shift is observed with the increase of the particle size and the media reflective index. A competitive solar regulation efficiency (ΔTsol = 13.2%) and a transmittance contrast at 2000 nm (ΔTNIR = 44%) can be achieved. Pairing reconfigurable metamaterials with the active LSPR was demonstrated to provide performance. A kirigami-inspired elastomer containing plasmonic vanadium dioxide was developed, exhibiting adaptive, broadband, and high-efficient optical modulation. The geometrical transition and the active LSPR function synergistically by manipulating ultraviolet-visible and near-infrared regions, respectively. A new mechanical-thermal energy-saving smart window was developed adopting such materials exhibits an unprecedented solar energy modulation (ΔTsol = 37.7%). Fully thermal responsiveness is also achieved in such a system. Smart window based on such materials are promised better energy-saving ability than commercialized low-emissivity glasses in cities, such as Hong Kong and Houston. Doctor of Philosophy

Two-dimensional (2D) photonic structures, widely used for generating photonic band gaps (PBG) in a variety of materials, are for the first time integrated with the temperature-dependent phase change of vanadium dioxide (VO2). VO2 possesses thermochromic properties, whose potential remains unrealized due to an undesirable yellow-brown color. Here, a SiO2/VO2 core/shell 2D photonic crystal is demonstrated to exhibit static visible light tunability and dynamic near-infrared (NIR) modulation. Three-dimensional (3D) finite difference time domain (FDTD) simulations predict that the transmittance can be tuned across the visible spectrum, while maintaining good solar regulation efficiency (ΔTsol = 11.0%) and high solar transmittance (Tlum = 49.6%). Experiments show that the color changes of VO2 films are accompanied by NIR modulation. This work presents a novel way to manipulate VO2 photonic structures to modulate light transmission as a function of wavelength at different temperatures.

The VO2-based smart windows can dynamically and reversibly adjust the indoor solar irradiation to reduce the energy consumption for building glasses. The paper reports the first successful preparation of Mg-doped VO2@ZrO2 core-shell nanocrystals with promoted thermochromic performance as well as tunable appearance and wettability. To our knowledge, the achieved combination of Tlum of 52.4% and ∆Tsol of 7.1% is comparable to the best-reported results of VO2-based core-shell rod structures. The thickness of ZrO2 shell is tunable between 3-14 nm, resulting in a slightly hydrophobic surface and a slight color change toward blue-green and brighter produced films. The preparation method based on hydrothermal and UV-curing methods is facile. The work may inspire future development of VO2 synthesis, their structure-property, and the application the thermochromic films for energy-saving purposes in buildings or automobiles. National Research Foundation (NRF) Accepted version Zuohao Wen and Yujie Ke contributed equally to this work. X. Liu acknowledges the study is supported by the financial support of this work by NSAF (Grant No. 51776143. The use of SEM, XPS, TEM, and AFM was funded by the Open Subsidies for large-scale Equipment of Wuhan University (Grant No. LF20181061). Y. Long thanks to the funding support by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme and Sino-Singapore International Joint Research Institute for funding support.

Produced in the process of meat spoilage, ammonia (NH3) is believed to be an important gas, as its concentration is a major indicator for evaluating freshness. A flexible NH3 sensor, based on novel polyaniline/Zn-porphyrin (PANI/Zn-tpps4) composite, was designed via a one-step electrodeposition method where a strong π-π conjugated system formed through the combination of the quinone ring of the PANI molecular chain and sulfate radical of the Zn-tpps4 molecule. The new sensor PANI/Zn-tpps4 film possesses outstanding sensing characteristics in terms of response value,enabling it to perform better than pure PANI film. To further explore the performance of PANI/Zn-tpps4 film, the gas-sensing properties, humidity and endurance tests were fully evaluated at low NH3 concentration. It was concluded that the sensing performance was dramatically improved, because the Zn-tpps4,acting as a “bridge”, facilitated the transfer of electrons from NH3 molecules to PANI molecular chains. It is expected that the PANI/Zn-tpps4 sensor can be attached to deformable packaging membrane to form an ideal device as meat freshness indicator.

The controlled fabrication of micro-/nanostructures has been a long-standing research focus. The surface patterning technique via templates consisted of monolayer nanospheres is well recognized as an efficient, reliable, and inexpensive method to fabricate two-dimensional (2D) structural arrays. Recent developments of 2D patterned nanostructures via this method grow rapidly and bring out diverse configurations, intriguing structure-induced properties, as well as novel functionalities in a broad range of applications. This review systematically summarizes the recent progress in the 2D nanostructures from fabrications to applications. Particular emphasis is put on the rational design of structure-related functionality for different applications. The diverse configurations derived from monolayer colloidal crystal templates are firstly introduced. Then, we classify the applications by discussing how the properties are benefited from the well-controlled nanostructures. We concludes the review by elaborating the promising functionalities in specific applications including sensors, solar cells, light-emitting diodes, field-effect transistors, photocatalysis, surface-enhanced Raman scattering, biological manipulation techniques, smart windows, photodetectors, transparent electronic devices, triboelectric nanogenerators, and so on, followed by perspectives on potential challenges and the future development. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version

Summary Architectural windows that smartly regulate the indoor solar irradiation are promised to economize the building energy consumption. Here, we demonstrate a method for adaptive, broadband, and highly efficient solar modulation for energy-efficient smart windows through active plasmonics in reconfigurable structures. We develop a kirigami-inspired elastomer containing plasmonic vanadium dioxide (VO2) nanoparticles, in which the geometrical transition and the temperature-dependent localized surface plasmon resonance (LSPR) present dominant controls in ultraviolet-visible and near-infrared regions, respectively. The active LSPR control, via stretch-induced local dielectric changes is mitigated on reconfigurable metamaterials because of their unique strain distributions. This method demonstrated a desirable property in energy-efficient smart windows facilitating improved solar energy modulation (37.7%), surpassing the best-reported modulation in passive and transparent VO2 thermochromism systems. This first attempt to integrate the plasmonics and reconfigurable structures may inspire developments in smart windows, building energy economization, as well as fundamental studies of plasmonic controls in metastructures.

Organic–inorganic hybrid perovskites with considerable dielectric differences near the phase transition are potential candidates as phase transition materials (PTMs). However, compared with traditional PTMs, which require multiple switchable channels, the hybrid perovskites so far show only switching behavior in dielectric constants. We herein report a new crystal design strategy and successful synthesis of a two-dimensional perovskite (C6H5C2H4NH3)2MnCl4. In this hybrid perovskite, the manganese chloride octahedron is a crystal field sensitive luminescent molecular system. The distortion level of MnCl64– also depends on temperature during the order–disorder phase transition. Hence, such a manganese octahedron-based perovskite can exhibit switching behaviors in both dielectric and optical properties. We observe a 14% decrease in optical absorption and 1.6 times increase in dielectric constant during the phase transition at 365 K. In addition, the characteristic photoluminescence decreases by 17% in intensity. Such a molecule-based crystal design paves a new way to explore multifunctional PTMs based on organic–inorganic perovskites. MOE (Min. of Education, S’pore) Accepted version

We report a robust methodology for synthesizing monodisperse copper-tin-selenide (CTSe) nanocrystals (NCs) of tunable size, shape, and composition including single-crystalline nanosheets, nanoplates, spheres, and tetrahedra. Both the identity and concentration of the selenium precursor play important roles in determining the morphology and crystal structure of the CTSe NCs. In contrast to previous studies, we demonstrated broad tunability of the Cu to Sn ratio. The size of CTSe NCs continuously decreased with increasing Sn incorporation. Moreover, the near-infrared (NIR) localized surface plasmon resonance (LSPR) in CTSe alloy NCs was tuned over a broad range by varying the Cu:Sn ratio. The LSPR red-shifted and decreased in intensity with increasing Sn content. This indicates that the free charge carrier concentration can be manipulated by varying the cation ratio. The cation deficiency responsible for self-doping in these NCs decreases with increasing Sn content. The resulting CTSe NCs and related materi...

Cation deficient transition metal sulfides have attracted increased attention due to their unique properties that arise from degenerate p-doping, particularly their localized surface plasmon resonance (LSPR) and related optical properties. Here, we present the first study of their electrocatalytic activity. We developed a facile one-pot method to prepare p-doped copper sulfide nanoplates with tunable LSPR at moderate temperature (below 100 °C) without any hot injection or rapid mixing step. The doping level was controlled by varying the concentration of cation precursor (Cu2+) to finely tune the LSPR wavelength without changing the nanoplate size or morphology. Cu2–xS nanoplates with three different doping levels were tested for their electrocatalytic activity for the oxygen reduction reaction (ORR) in alkaline solution. Importantly, increasing the concentration of free holes in Cu2–xS significantly enhanced the ORR catalytic activity. Furthermore, to improve the electrical conductivity, the most heavily ...

The objective of this work is to design and demonstrate multilevel optical switches by combining different phase change materials. Ge2Sb2Te5 and VO2 nanolayer structures were designed to maximize the optical contrast between four different reflective states. These different optical states arise due to the independent structural phase transitions of VO2 and Ge2Sb2Te5 at different temperatures. The transfer matrix method was used to model Fresnel reflection for each structural phase combination and then to optimize the VO2 and Ge2Sb2Te5 layer thicknesses, which were found to be 70 nm and 50 nm. These multilevel optical switching results provide further possibilities to design composite materials for applications in active and programmable photonics. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Published version

Architectural windows that smartly regulate the indoor solar irradiation are promised to economize the building energy consumption. Here we demonstrate a method for adaptive, broadband, and high-efficient solar modulation for energy-efficient smart windows through the active plasmonics in kirigami structures. We develop a kirigami-inspired elastomer containing plasmonic vanadium dioxide (VO2) nanoparticles, in which the geometrical transition and the temperature-dependent localized surface plasmon resonance (LSPR) present dominant controls in ultraviolet-visible and near-infrared regions, respectively. The active LSPR control via stretch-induced local dielectric changes is mitigated on kirigami metamaterials due to their unique strain distributions. This method was demonstrated a decent property in energy-efficient smart windows with a decent solar energy modulation (37.7%), surpassing the best reported passive and transparent VO2 thermochromism systems. This first attempt to integrate the plasmonics and kirigami may inspire developments in smart windows, building energy economization, as well as fundamental studies of plasmonic controls in metastructures.

Wearable and stretchable physical sensors that can conformally contact on the surface of organs or skin provide a new opportunity for human-activity monitoring and personal healthcare. Particularly, various attempts have been made in exploiting wearable and conformal sensors for thermal characterization of human skin. In this respect, skin-mounted thermochromic films show great capabilities in body temperature sensing. Thermochromic temperature sensors are attractive because of their easy signal analysis and optical recording, such as color transition and fluorescence emission change upon thermal stimuli. Here, desirable mechanical properties that match epidermis are obtained by physical crosslinking of polydiacetylene (PDA) and transparent elastomeric polydimethylsiloxane (PDMS) networks. The resulting PDA film displayed thermochromic and thermo- fluorescent transition temperature in the range of 25–85°C, with stretchability up to 300% and a skin-like Young’s modulus of ~230 kPa. This easy signal-handling provides excellent references for further design of convenient noninvasive sensing systems.

Vanadium dioxide (VO2) is one of the most widely studied inorganic phase change material for energy storage and energy conservation applications. Monoclinic VO2 [VO2(M)] changes from semiconducting phase to metallic rutile phase at near room temperature and the resultant abrupt suppressed infrared transmittance at high temperature makes it a potential candidate for thermochromic smart window application to cut the air-condition usage. Meanwhile proper electrical potential, stable structure and good interaction with lithium ions make metastable VO2 [VO2(B)] an attractive material for fabrication of electrodes for batteries and supercapacitors. However, some long-standing issues have plagued its usage. In thermochromic application, high transition temperature (τc), low luminous transmittance (Tlum) and undesirable solar modulation ability (△Tsol) are the key problems, while in energy storage applications, short cycling lifetime and complex three-dimension microstructure are the major challenges. The common methods to produce VO2 polymorph are physical vapour deposition (PVD), chemical vapour deposition (CVD), sol-gel synthesis, and hydrothermal method. CVD is an intensively studied method due to its ability to produce uniform films with precise stoichiometry, phase and morphology control. This paper reviews the various CVD techniques to produce VO2 with controlled phases and the ternary diagram shows the relationship between film stoichiometry and various process conditions. The difference between the various CVD systems are commented and the process window to produce VO2 are tabulated. Some strategies to improve VO2′s performance in both energy conservation and energy storage applications are discussed. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

We demonstrate a new strategy for tuning the size of large-diameter and few-walled nitrogen-doped carbon nanotubes (N-CNTs) from 50 to 150 nm by varying the transition metal (TM = Fe, Co, Ni or Mn) used to catalyze graphitization of dicyandiamide. Fe yielded the largest tubes, followed by Co and Ni, while Mn produced a clot-like carbon morphology. We show that morphology is correlated with electrocatalytic activity for the oxygen reduction reaction (ORR). A clear trend of Fe > Co > Ni > Mn for the ORR catalytic activity was observed, in both alkaline media and more demanding acidic media. The Fe-derived N-CNTs exhibited the highest BET (∼870 m(2) g(-1)) and electrochemically accessible (∼450 m(2) g(-1)) surface areas and, more importantly, the highest concentration of nitrogen incorporated into the carbon planes. Thus, in addition to the intrinsic high activity of Fe-derived catalysts, the high surface area and nitrogen doping contribute to high ORR activity. This work, for the first time, demonstrates size-controlled synthesis of large-diameter N-doped carbon tube electrocatalysts by varying the metal used in N-CNT generation. Electrocatalytic activity of the Fe-derived catalyst is already the best among studied metals, due to the high intrinsic activity of possible Fe-N coordination. This work further provides a promising route to advanced Fe-N-C nonprecious metal catalysts by generating favorable morphology with more active sites and improved mass transfer.

Cryptomelane-type octahedral molecular sieve manganese oxide (OMS-2) possesses high redox potential and has attracted much interest in its application for oxidation arsenite (As(III)) species of arsenic to arsenate (As(V)) to decrease arsenic toxicity and promote total arsenic removal. However, coexisting ions such as As(V) and phosphate are ubiquitous and readily bond to manganese oxide surface, consequently passivating surface active sites of manganese oxide and reducing As(III) oxidation. In this study, we present a novel strategy to significantly promote As(III) oxidation activity of OMS-2 by tuning K

A universal approach to develop various two-dimensional ordered nanostructures, namely nanoparticle, nanonet and nanodome arrays with controllable periodicity, ranging from 100 nm to 1 μm, has been developed in centimeter-scale by nanosphere lithography technique. Hexagonally patterned vanadium dioxide (VO

Two-dimensional (2D) photonic structures, widely used for generating photonic band gaps (PBG) in a variety of materials, are for the first time integrated with the temperature-dependent phase change of vanadium dioxide (VO

Nanosized TiO2 with suitable dimensions has been observed to enhance the functions of bone cells; however, the most effective type of nano-TiO2 remains unknown. The Layer-by-Layer (LBL) self-assembly technique has been wildly used to fabricate multilayer thin films of controlled composition, thickness, and architecture. Therefore, to find an appropriate material for orthopedic surgical usage, this study investigates the cytocompatibility and cell activity (using MC-3T3-E1 cells) of nano-TiO2 thin films fabricated by LBL. Four types of nano-TiO2 thin films were synthesized. Surface roughness w measured by field emission scanning electron microscopy (SEM). Hydrophilicity was measured using the contact angle meter. Cell attachment to the materials was observed using SEM. Fluorescent dyes were used to observe the generation of reactive oxygen species and DNA damage. Apoptosis was measured through lactate dehydrogenase leakage assay. The 2-(4,5-dimethyl-2-thiazol-2-yl)-3,5-diphenyl-2H-tetrazolium (MTT) assay w...

The reversible, ultrafast, and multistimuli responsive phase transition of vanadium dioxide (VO2 ) makes it an intriguing "smart" material. Its crystallographic transition from the monoclinic to tetragonal phases can be triggered by diverse stimuli including optical, thermal, electrical, electrochemical, mechanical, or magnetic perturbations. Consequently, the development of high-performance smart devices based on VO2 grows rapidly. This review systematically summarizes VO2 -based emerging technologies by classifying different stimuli (inputs) with their corresponding responses (outputs) including consideration of the mechanisms at play. The potential applications of such devices are vast and include switches, memories, photodetectors, actuators, smart windows, camouflages, passive radiators, resonators, sensors, field effect transistors, magnetic refrigeration, and oscillators. Finally, the challenges of integrating VO2 into smart devices are discussed and future developments in this area are considered.

Architectural windows that smartly regulate indoor solar radiation by changing their optical transmittance in response to thermostimuli are developed as a promising solution toward reducing the energy consumption of buildings. Recently, energy‐efficient smart window technology has attracted increasing scientific interest, with the exploration of energy‐efficient novel materials as well as integration with practical techniques to generate various desired multifunctionalities. This review systematically summarizes emerging thermoresponsive materials for smart window applications, including hydrogels, ionic liquids, perovskites, metamaterials, and liquid crystals. These are compared with vanadium dioxide (VO2), a conventional and extensively studied material for thermochromic smart window applications. In addition, recent progress on cutting‐edge integrated techniques for smart windows is covered, including electrothermal techniques, self‐cleaning, wettability, and also integration with solar cells for bifunctional energy conservation and generation. Finally, opportunities and challenges relating to thermochromic smart windows and prospects for future development are discussed. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

A printable hybrid hydrogel is fabricated by embedding poly(N‐isopropylacrylamide) (PNIPAm) microparticles within a water‐rich silica‐alumina(Si/Al)‐based gel matrix. The hybrid gel holds water content of up to 70 wt%, due to its unique Si/Al matrix. The hybrid hydrogel can respond to both heat and electrical stimuli, and can be directly printed layer‐by‐layer using a commercial 3‐dimensional printer, without requiring any curing. The hybrid ink is printed onto a transparent, flexible conductive electrode composed of silver nanoparticles and sustains bending angles of up to 180°, which enables patterning of various flexible devices such as smart windows and a 3D optical waveguide valve. NRF (Natl Research Foundation, S’pore) Accepted version