White light-emitting diodes (WLEDs) are the key components in the next-generation lighting and display devices. The inherent toxicity of Cd/Pb-based quantum dots (QDs) limits the further application in WLEDs. Recently, more attention is focused on eco-friendly QDs and their WLEDs, especially the phosphor-free WLEDs based on mono-component, which profits from bias-insensitive color stability. However, the imbalanced carrier distribution between red-green-blue luminescent centers, even the absence of a certain luminescent center, hinders their balanced and stable photoluminescence/electroluminescence (PL/EL). Here, an In3+-doped strategy in Zn-Cu-Ga-S@ZnS QDs is first proposed, and the balanced carrier distribution is realized by non-equivalent substitution and In3+ doping concentration modulation. The alleviation of the green emitter by the In3+-related red emitter and the compensation of blue emitter by the Zn-related electronic states contribute to the balanced red-green-blue emitting with high PL quantum yield (PLQY) of 95.3% and long lifetime (T90) of over 1100 h in atmospheric conditions. Thus, the In3+-doped WLEDs can achieve exceedingly slight proportional variations between red-green-blue EL intensity over time (∆CIE = (0.007, 0.009)), and high champion CRI of 94.9. This study proposes a single-component QD with balanced and stable red-green-blue PL/EL spectrum, meeting the requirements of lighting and display.
Thermoelectric technology has potential for converting waste heat into electricity. Although traditional thermoelectric materials exhibit extremely high thermoelectric performances, their scarcity and toxicity limit their applications. Zinc oxide (ZnO) emerges as a promising alternative owing to its high thermal stability and relatively high Seebeck coefficient, while also being earth-abundant and nontoxic. However, its high thermal conductivity (>40 W m-1K-1) remains a challenge. In this study, we use a multi-step strategy to achieve a significantly high dimensionless figure-of-merit (zT) value of approximately 0.486 at 580 K (estimated value) by interfacing graphene quantum dots with 3D nanostructured ZnO. Here, we show the fabrication of graphene quantum dots interfaced 3D ZnO, yielding the highest zT value ever reported for ZnO counterparts; specifically, our experimental results indicate that the fabricated 3D GQD@ZnO exhibited a significantly low thermal conductivity of 0.785 W m-1K-1 (estimated value) and a remarkably high Seebeck coefficient of - 556 µV K-1 at 580 K.
In the quest for materials sustainability for grid-scale applications, graphene quantum dot (GQD), prepared via eco-efficient processes, is one of the promising graphitic-organic matters that have the potential to provide greener solutions for replacing metal-based battery electrodes. However, the utilization of GQDs as electroactive materials has been limited; their redox behaviors associated with the electronic bandgap property from the sp2 carbon subdomains, surrounded by functional groups, are yet to be understood. Here, the experimental realization of a subdomained GQD-based anode with stable cyclability over 1000 cycles, combined with theoretical calculations, enables a better understanding of the decisive impact of controlled redox site distributions on battery performance. The GQDs are further employed in cathode as a platform for full utilization of inherent electrochemical activity of bio-inspired redox-active organic motifs, phenoxazine. Using the GQD-derived anode and cathode, an all-GQD battery achieves a high energy density of 290 Wh kgcathode -1 (160 Wh kgcathode+anode -1 ), demonstrating an effective way to improve reaction reversibility and energy density of sustainable, metal-free batteries.
NO2 is a major air pollutant that should be monitored due to its harmful effects on the environment and human health. Semiconducting metal oxide-based gas sensors have been widely explored owing to their superior sensitivity towards NO2, but their high operating temperature (>200 °C) and low selectivity still limit their practical use in sensor devices. In this study, we decorated graphene quantum dots (GQDs) with discrete band gaps onto tin oxide nanodomes (GQD@SnO2 nanodomes), enabling room temperature (RT) sensing towards 5 ppm NO2 gas with a noticeable response ((Ra/Rg) - 1 = 4.8), which cannot be matched using pristine SnO2 nanodomes. In addition, the GQD@SnO2 nanodome based gas sensor shows an extremely low detection limit of 1.1 ppb and high selectivity compared to other pollutant gases (H2S, CO, C7H8, NH3, and CH3COCH3). The oxygen functional groups in GQDs specifically enhance NO2 accessibility by increasing the adsorption energy. Strong electron transfer from SnO2 to GQDs widens the electron depletion layer at SnO2, thereby improving the gas response over a broad temperature range (RT-150 °C). This result provides a basic perspective for utilizing zero-dimensional GQDs in high-performance gas sensors operating over a wide range of temperatures.
Graphene quantum dots (GQDs) are nanosized graphene derivatives with unique photoluminescence (PL) properties that have advantages in optoelectronic applications due to their stable blue light emission. However, aggregation-caused quenching (ACQ) of GQDs limits the practical applications on light-emitting diodes. Here, we suppress the ACQ phenomena of GQDs by reducing the size and converting GQDs into aggregation-induced emission (AIE)-active materials. As the size of GQDs is reduced from 5 to 1 nm, their solid-state PL quantum yields (PLQYs) are improved from 0.5 to 2.5%, preventing ACQ. Two different rotor molecules, benzylamine (BA) and 4,4'-(1,2-diphenylethene-1,2-diyl)diphenol (TPE-DOH), are selectively functionalized by substituting carboxylic acid and carbonyl functional groups. All functionalized GQDs show AIE behaviors with significantly enhanced solid-state PLQYs, up to 16.8%. Afterglow measurements and theoretical calculations reveal that selective functionalization hinders inter- and intramolecular charge transfer, which enhances the fluorescence rate of GQDs and corresponding PLQY.
Rapid charging capability is a requisite feature of lithium-ion batteries (LIBs). To overcome the capacity degradation from a steep Li-ion concentration gradient during the fast reaction, electrodes with tailored transport kinetics have been explored by managing the geometries. However, the traditional electrode fabrication process has great challenges in precisely controlling and implementing the desired pore networks and configuration of electrode materials. Herein, we demonstrate a density-graded composite electrode that arises from a three-dimensional current collector in which the porosity gradually decreases to 53.8% along the depth direction. The density-graded electrode effectively reduces energy loss at high charging rates by mitigating polarization. This electrode shows an outstanding capacity of 94.2 mAh g-1 at a fast current density of 59.7 C (20 A g-1), which is much higher than that of an electrode with a nearly constant density gradient (38.0 mAh g-1). Through these in-depth studies on the pore networks and their transport kinetics, we describe the design principle of rational electrode geometries for ultrafast charging LIBs.
Over the past few years, many efforts have been devoted to growing single-crystal graphene due to its great potential in future applications. However, a number of issues remain for single-crystal graphene growth, such as control of nanoscale defects and the substrate-dependent nonuniformity of graphene quality. In this work, we demonstrate a possible route toward single-crystal graphene by combining aligned nucleation of graphene nanograins on Cu/Ni (111) and sequential heat treatment over pregrown graphene grains. By use of a mobile hot-wire CVD system, prealigned grains were stitched into one continuous film with up to â¼97% single-crystal domains, compared to graphene grown on polycrystalline Cu, which was predominantly high-angle tilt boundary (HATB) domains. The single-crystal-like graphene showed remarkably high thermal conductivity and carrier mobility of â¼1349 W/mK at 350 K and â¼33â¯600 (38â¯400) cm2 V-1 s-1 for electrons (holes), respectively, which indicates that the crystallinity is high due to suppression of HATB domains.
The mass production of precise three-dimensional (3D) nanopatterns has long been the ultimate goal of fabrication technology. While interference lithography and proximity-field nanopatterning (PnP) may provide partial solutions, their setup complexity and limited range of realizable structures, respectively, remain the main problems. Here, we tackle these challenges by applying an inverse design to the PnP process. Our inverse design platform based on the adjoint method can efficiently find optimal phase masks for diverse target lattices and motifs. We fabricate a 2D rectangular array of nanochannels, which has not been reported for conventional PnP with normally incident light, as a proof of concept. With further demonstration of material conversion, our work provides versatile platforms for nanomaterial fabrication.
Mechanochromic smart membranes capable of optical modulation have great potential in smart windows, artificial skins, and camouflage. However, the realization of high-contrast optical modulation based on light scattering activated at a low strain remains challenging. Here, we present a strategy for designing mechanochromic scattering membranes by introducing a Young's modulus mismatch between the two interdigitated polydimethylsiloxane phases with weak interfaces in a periodic three-dimensional (3D) structure. The refractive index-matched interfaces of the nanocomposite provide a high optical transparency of 93%. Experimental and computational studies reveal that the 3D heterogeneity facilitates the generation of numerous nanoscale debonds or "nanogaps" at the modulus-mismatching interfaces, enabling incident light scattering under tension. The heterogeneous scatterer delivers both a high transmittance contrast of >50% achieved at 15% strain and a maximum contrast of 82%. When used as a smart window, the membrane demonstrates effective diffusion of transmitting sunlight, leading to moderate indoor illumination by eliminating extremely bright or dark spots. At the other extreme, such a 3D heterogeneous design with strongly bonded interfaces can enhance the coloration sensitivity of mechanophore-dyed nanocomposites. This work presents insights into the design principles of advanced mechanochromic smart membranes.
For the last several years, indoor air quality monitoring has been a significant issue due to the increasing time portion of indoor human activities. Especially, the early detection of volatile organic compounds potentially harmful to the human body by the prolonged exposure is the primary concern for public human health, and such technology is imperatively desired. In this study, highly porous and periodic 3D TiO2 nanostructures are designed and studied for this concern. Specifically, extremely high gas molecule accessibility throughout the whole nanostructures and precisely controlled internecks of 3D TiO2 nanostructures can achieve an unprecedented gas response of 299 to 50 ppm CH3 COCH3 with an extremely fast response time of less than 1s. The systematic approach to utilize the whole inner and outer surfaces of the gas sensing materials and periodically formed internecks to localize the current paths in this study can provide highly promising perspectives to advance the development of chemoresistive gas sensors using metal oxide nanostructures for the Internet of Everything application.
Acetone/analysis , Biosensing Techniques/methods , Titanium/chemistry , Biosensing Techniques/instrumentation , Humans , Nanostructures , Porosity , Surface Properties
Continuous real-time measurement of body temperature using a wearable sensor is an essential part of human health monitoring. Electrospun aligned carbon nanofiber (ACNF) films are employed to assemble flexible temperature sensors. The temperature sensor prepared at a low carbonization temperature of 650 °C yields an outstanding sensitivity of 1.52% °C-1, high accuracy, good linearity, fast response time and excellent long-term durability. Moreover, it exhibits high discriminability towards temperature amidst other unwanted stimuli and maintains its original performance even after repeated stretch/release cycles because of highly-aligned structures. The correlation between the atomic structure and the temperature sensing performance of ACNF sensors is established. Contrary to conventional highly conductive temperature sensors, the ACNF sensor with a low electrical conductivity prepared at a low carbonization temperature ameliorates the temperature sensing performance. This anomaly is explained by (i) the smaller and more disordered sp2 carbon crystallites yielding a high negative temperature coefficient, (ii) a larger number of defects, and (iii) a higher pyridinic-N content generating abundant entrapped and localized electrons which are activated once sufficient thermal energy is available. Flexible ACNF sensor's overall performance is among the best-known carbon material-based flexible temperature sensors, demonstrating potential applications in emerging healthcare and flexible electronics technologies.
Nanofibers , Wearable Electronic Devices , Carbon , Electric Conductivity , Humans , Temperature
Over the years, numerous studies have attempted to develop two-dimensional (2D) materials for improving both the applicability and performance of thermoelectric devices. Among the 2D materials, graphene is one of the promising candidates for thermoelectric materials owing to its extraordinary electrical properties, flexibility, and nontoxicity. However, graphene synthesized through traditional methods suffers from a low Seebeck coefficient and high thermal conductivity, resulting in an extremely low thermoelectric figure of merit (ZT). Here, we present an atomic-scale defect engineering strategy to improve the thermoelectric properties of graphene using embedded high-angle tilt boundary (HATB) domains in graphene films. These HATB domains serve as both energy filtering sites to filter out lower-energy charge carriers and scattering sites for phonons. Compared to the conventionally grown chemical vapor deposited graphene, the graphene with HATB domains shows an improved Seebeck coefficient (50.1 vs 21.1 µV K-1) and reduced thermal conductivity (382 vs 952 W m-1K-1), resulting in a ZT value that is â¼7 times greater at 350 K. This defect engineering strategy is promising not only for graphene-based materials but also for 2D materials, in general, where further research and optimization could overcome the limitations of conventional bulk thermoelectric materials in energy-harvesting systems.
One of the well-known strategies for achieving high-performance light-activated gas sensors is to design a nanostructure for effective surface responses with its geometric advances. However, no study has gone beyond the benefits of the large surface area and provided fundamental strategies to offer a rational structure for increasing their optical and chemical performances. Here, a new class of UV-activated sensing nanoarchitecture made of highly periodic 3D TiO2, which facilitates 55 times enhanced light absorption by confining the incident light in the nanostructure, is prepared as an active gas channel. The key parameters, such as the total 3D TiO2 film and thin-shell thicknesses, are precisely optimized by finite element analysis. Collectively, this fundamental design leads to ultrahigh chemoresistive response to NO2 with a theoretical detection limit of ≈200 ppt. The demonstration of high responses with visible light illumination proposes a future perspective for light-activated gas sensors based on semiconducting oxides.
Nanoarchitected materials are considered as a promising research field, deriving distinctive mechanical properties by combining nanomechanical size effects with conventional structural engineering. Despite the successful demonstration of the superiority and feasibility of nanoarchitected materials, scalable and facile fabrication techniques capable of macroscopically producing such materials at a low cost are required to take advantage of the nanoarchitected materials for specific applications. Unlike conventional techniques, proximity-field nanopatterning (PnP) is capable of simultaneously obtaining high spatial resolution and mass producibility in synthesizing such nanoarchitected materials in the form of an inch-scale film. Herein, we focus on the feasibility of using PnP as a scalable fabrication technique for three-dimensional nanostructures and the superiority of the resultant thin-shell oxide nanoarchitected materials for specific applications, such as lightweight structural materials, mechanically robust nanocomposites, and high-performance piezoelectric materials. This review will discuss and summarize the relevant results obtained for nanoarchitected materials synthesized by PnP and provide suggestions for future research directions for scalable manufacturing and application.
Tungsten trioxide (WO3) is an abundant, versatile oxide that is widely explored for catalysis, sensing, electrochromic devices, and numerous other applications. The exploitation of WO3 in nanosheet form provides potential advantages in many of these fields because the 2D structures have high surface area and preferentially exposed facets. Relative to bulk WO3, nanosheets expose more active sites for surface-sensitive sensing/catalytic reactions, and improve reaction kinetics in cases where ionic diffusion is a limiting factor (e.g. electrochromic or charge storage). Synthesis of high aspect ratio WO3 nanosheets, however, is more challenging than other 2D materials because bulk WO3 is not an intrinsically layered material, making the widely-studied sonication-based exfoliation methods used for other 2D materials not well-suited to WO3. WO3 is also highly complex in terms of how the synthesis method affects the properties of the final material. Depending on the route used and subsequent post-synthesis treatments, a wide variety of different morphologies, phases, exposed facets, and defect structures are created, all of which must be carefully considered for the chosen application. In this review, the recent developments in WO3 nanosheet synthesis and their impact on performance in various applications are summarized and critically analyzed.
Chemical vapor deposition has been highlighted as a promising tool for facile graphene growth in a large area. However, grain boundaries impose detrimental effects on the mechanical strength or electrical mobility of graphene. Here, we demonstrate that high-pressure hydrogen treatment in the preannealing step plays a key role in fast and large grain growth and leads to the successful synthesis of large grain graphene in 10 s. Large single grains with a maximum size of â¼160 µm grow by recrystallization of nanograins, but â¼1% areal coverage of nanograins remains with 28-30° misorientation angles. Our findings will provide insights into mass production of high-quality graphene.
Atomically sharp heterojunctions in lateral two-dimensional heterostructures can provide the narrowest one-dimensional functionalities driven by unusual interfacial electronic states. For instance, the highly controlled growth of patchworks of graphene and hexagonal boron nitride (h-BN) would be a potential platform to explore unknown electronic, thermal, spin or optoelectronic property. However, to date, the possible emergence of physical properties and functionalities monitored by the interfaces between metallic graphene and insulating h-BN remains largely unexplored. Here, we demonstrate a blue emitting atomic-resolved heterojunction between graphene and h-BN. Such emission is tentatively attributed to localized energy states formed at the disordered boundaries of h-BN and graphene. The weak blue emission at the heterojunctions in simple in-plane heterostructures of h-BN and graphene can be enhanced by increasing the density of the interface in graphene quantum dots array embedded in the h-BN monolayer. This work suggests that the narrowest, atomically resolved heterojunctions of in-plane two-dimensional heterostructures provides a future playground for optoelectronics.
The cost-effective direct writing of polymer nanofibers (NFs) has garnered considerable research attention as a compelling one-pot strategy for obtaining key building blocks of electrochemical and optical devices. Among the promising applications, the changes in optical response from external stimuli such as mechanical deformation and changes in the thermal environment are of great significance for emerging applications in smart windows, privacy protection, aesthetics, artificial skin, and camouflage. Herein, we propose a rational design for the mass production of customized NFs through the development of focused electric-field polymer writing (FEPW) coupled with the roll-to-roll technique. As a proof of key applications, we demonstrate multistimuli-responsive (mechano- and thermochromism) membranes with an exceptional production scale (over 300 cm2). Specifically, the membranes consist of periodically aligned ultrathin (â¼60 nm) alumina nanotubes inserted in the elastomers. We performed a two-phase finite element analysis of the unit cells to verify the underlying physics of light scattering at heterogeneous interfaces of the strain-induced air gaps. By adding thermochromic dye during the FEPW, the optical modulation of transmittance change (â¼83% to 37% at visible wavelength) was successfully extended to high-contrast thermal-dependent coloration.
The realization of high-contrast modulation in optically transparent media is of great significance for emerging mechano-responsive smart windows. However, no study has provided fundamental strategies for maximizing light scattering during mechanical deformations. Here, a new type of 3D nanocomposite film consisting of an ultrathin (≈60 nm) Al2O3 nanoshell inserted between the elastomers in a periodic 3D nanonetwork is proposed. Regardless of the stretching direction, numerous light-scattering nanogaps (corresponding to the porosity of up to ≈37.4 vol%) form at the interfaces of Al2O3 and the elastomers under stretching. This results in the gradual modulation of transmission from ≈90% to 16% at visible wavelengths and does not degrade with repeated stretching/releasing over more than 10 000 cycles. The underlying physics is precisely predicted by finite element analysis of the unit cells. As a proof of concept, a mobile-app-enabled smart window device for Internet of Things applications is realized using the proposed 3D nanocomposite with successful expansion to the 3 × 3 in. scale.
Long-lived afterglow emissions, such as room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), are beneficial in the fields of displays, bioimaging, and data security. However, it is challenging to realize a single material that simultaneously exhibits both RTP and TADF properties with their relative strengths varied in a controlled manner. Herein, a new design approach is reported to control singlet-triplet energy splitting (∆EST ) in graphene quantum dots (GQD)/graphene oxide quantum dots (GOQDs) by varying the ratio of oxygenated carbon to sp2 carbon (γOC ). It is demonstrated that ∆EST decreases from 0.365 to 0.123 eV as γOC increases from 4.63% to 59.6%, which in turn induces a dramatic transition from RTP to TADF. Matrix-assisted stabilization of triplet excited states provides ultralong lifetimes to both RTP and TADF. Embedded in boron oxynitride, the low oxidized (4.63%) GQD exhibits an RTP lifetime (τT avg ) of 783 ms, and the highly oxidized (59.6%) GOQD exhibits a TADF lifetime (τDF avg ) of 125 ms. Furthermore, the long-lived RTP and TADF materials enable the first demonstration of anticounterfeiting and multilevel information security using GQD. These results will open up a new approach to the engineering of singlet-triplet splitting in GQD for controlled realization of smart multimodal afterglow materials.
