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This paper proposes for the first time the preparation of a series of amino acid ionic liquids (AAILs) via one-step hydrolysis of cheap lactams for the capture of CO2. The structures of the prepared AAILs are confirmed using NMR, FTIR, and ESIMS, and their physical properties are also determined. It is found that these AAILs are reversible CO2 absorbents with very high absorption capacities (0.15 to 0.18 g·g1 at 313.2 K and 1.0 bar), better than almost all task-specific ionic liquids reported in literatures. The absorption mechanism is also elucidated to be a combination of 1:1 and 2:1 stoichiometric reaction of AAILs with CO2 from NMR, FTIR, reaction equilibrium thermodynamical modelling (RETM) and quantum calculations. The AAILs have the advantages of simple synthesis, high yield, and using available cheap raw materials. It is believed that this kind of AAILs have great potentials to be used as efficient CO2 absorbents.

DNA origami technology has rapidly developed into an ideal means to programmably crystallize nanoparticles. However, most existing DNA origami three-dimensional platforms normally used a single type of DNA origami unit, which greatly limits the types of nanoparticle superlattices that can be synthesized. Here, we report a universal strategy to vastly enrich the library of nanoparticle superlattices, based on multiple-unit (≥4 units) DNA origami platforms, which were constructed by programmably cocrystallizing three different DNA origami octahedral “homologs.” Through selectively inserting nanoparticles into DNA origami monomers, numerous nanoparticle superlattices can be synthesized on the basis of the same platform. In this work, we obtained 85 types of DOF/AuNP (DNA origami frame/gold nanoparticle) superlattices using three different DNA origami platforms as examples. We believe that our strategy can provide possible access to fabricate virtually endless types of nanoparticle superlattices and promote the construction of functional materials with special properties.

The capability to manipulate the size of the electronic band gap is of importance to semiconductor technology. Among these, a wide direct band gap is particularly helpful in optoelectronic devices due to the efficient utilization of blue and ultraviolet light. Here, we reported a paraffin-enabled compressive folding (PCF) strategy to widen the band gap of two-dimensional (2D) materials. Due to the large thermal expansion coefficient of paraffin, folded 2D materials can be achieved via thermal engineering of the paraffin-assisted transfer process. It can controllably introduce 0.2-1.3% compressive strain onto folded structures depending on the temperature differences and transfer the folding product to both rigid and soft substrates. Exemplified by MoS2, its folded multilayers demonstrated blue-shifts at direct gap transition peaks, six times stronger photoluminescence intensity, almost double mobility, and 20 times higher photoresponsivity over unfolded MoS2. This PCF strategy can attain controllable widening band gap of 2D materials, which will open up novel applications in optoelectronics.

Polarity often refers to the charge carrier type of a semiconductor or the charging state of a functional group, generally dominating their functionality and performance. Herein we uncover a spontaneous and stochastic polarity-flipping phenomenon in monolayer WSe2, which randomly switches between the n-type and p-type states and is essentially triggered by fluctuating carrier flows from or to the adjacent WS2 monolayer. We have traced such fluctuating carrier flows by interfacial photocurrent measurements in a zero-bias two-terminal device. Such polarity flipping results in switching between the negative and positive correlations between the emission intensities of WS2 and WSe2 in the heterobilayer, which is further well-controlled by the electrostatic gate-tuning experiments in a capacitor-structure device. Our work not only demonstrates giant and intermittent carrier flows through long-range coupling in 2D heterostructures and a consequent spontaneous polarity flipping phenomenon but also provides a two-emitter system with a switchable correlation sign that could project future applications in optical logic devices.

Low-dimensional hybrid perovskites have demonstrated excellent performance as white-light emitters. The broadband white emission originates from self-trapped excitons (STEs). Since the mechanism of STEs formation in perovskites is still not clear, preparing new low-dimensional white perovskites relies mostly on screening lots of intercalated organic molecules rather than rational design. Here, we report an atom-substituting strategy to trigger STEs formation in layered perovskites. Halogen-substituted phenyl molecules are applied to synthesize perovskite crystals. The halogen-substituents will withdraw electrons from the branched chain (-R-NH3+) of the phenyl molecule. This will result in positive charge accumulation on -R-NH3+, and thus stronger Coulomb force of bond (-R-NH3+)-(PbBr42−), which facilitates excitons self-trapping. Our designed white perovskites exhibit photoluminescence quantum yield of 32%, color-rendering index of near 90 and chromaticity coordinates close to standard white-light. Our joint experiment-theory study provides insights into the STEs formation in perovskites and will benefit tailoring white perovskites with boosting performance., Broad-band emission of self-trapped exciton in low-dimensional perovskite is prospective for white LED, yet rational design new white perovskite remains challenge. Here, the authors develop an atom-substituting strategy to trigger exciton self-tapping in perovskites and reveal the mechanism behind.

The short exciton diffusion length (

The excellent mechanical properties of carbon nanotube (CNT) and low effective modulus of its forest makes CNT forest (CNTF) promising in dry adhesives. However, the low contact efficiency of buckled nanotube segments on the surface of the CNTF weakened its adhesion strength, which is far below the theoretical value. To improve the orientation, density, and arrangement of these nanotube segments, a layer of patterned aluminum was added to the conventional catalyst. Thus, a CNTF with densely-packed, horizontally-aligned surface nanotube segments was obtained. Nanoindentation results showed that the adhesion force of this CNTF could reach up to 13.69 mN under optimized conditions, nearly 5.5 times the best results of similar works. The results of coarse-grained (CG) simulations revealed the lateral stretching of these nanotube segments induced bond energy variation made a major contribution to the superior adhesion performance. The formation mechanism of these surface nanotube segments was also thoroughly analyzed.

The construction of a heterointerface by structure-induced partial phase transformation is an effective strategy to synchronously boost conductivity and regulate the ion diffusion kinetics of TiO2 considered as an anode material for sodium ion batteries. However, construction of a highly conductive heterostructure in well-crystallized TiO2 is still a great challenge. Herein, a structure-induced partial phase transformation method is reported to synthesize hierarchical hollow TiO2/TiN heterostructure fibers (HTTFs) with a high specific surface area for use as an anode. The interfacial effect of the heterostructures for the anode materials could improve charge transfer capability. The improvement of the conductivity is due to the electric field generated inside the nanocrystals, which greatly reduces the ion diffusion resistance of nanocrystals and promotes the interfacial electron transport. Density functional theory calculations and experimental results demonstrate that HTTFs greatly facilitated the mobility of holes and ion diffusion, which result in excellent rate capability (270.9 and 113.1 mA h g−1 at 50 and 10 000 mA g−1, respectively) and excellent cycling stability (132.5 mA h g−1 with an average capacity fading of only 0.002% per cycle at 5000 mA g−1 over 10 000 cycles). Such improvements signify that suitable heterogeneous interface design provides an innovative and versatile approach for achieving advanced battery materials.

Two-dimensional (2D) semiconductors have captured broad interest as light emitters, due to their unique excitonic effects. These layer-blocks can be integrated through van der Waals assembly, i.e., fabricating homo- or heterojunctions, which show novel emission properties caused by interface engineering. In this review, we will first give an overview of the basic strategies that have been employed in interface engineering, including changing components, adjusting interlayer gap, and tuning twist angle. By modifying the interfacial factors, novel emission properties of emerging excitons are unveiled and discussed. Generally, well-tailored interfacial energy transfer and charge transfer within a 2D heterostructure cause static modulation of the brightness of intralayer excitons. As a special case, dynamically correlated dual-color emission in weakly-coupled bilayers will be introduced, which originates from intermittent interlayer charge transfer. For homobilayers and type Ⅱ heterobilayers, interlayer excitons with electrons and holes residing in neighboring layers are another important topic in this review. Moreover, the overlap of two crystal lattices forms moiré patterns with a relatively large period, taking effect on intralayer and interlayer excitons. Particularly, theoretical and experimental progresses on spatially modulated moiré excitons with ultra-sharp linewidth and quantum emission properties will be highlighted. Moiré quantum emitter provides uniform and integratable arrays of single photon emitters that are previously inaccessible, which is essential in quantum many-body simulation and quantum information processing. Benefiting from the optically addressable spin and valley indices, 2D heterostructures have become an indispensable platform for investigating exciton physics, designing and integrating novel concept emitters.

Description, Electronic Raman scattering activates the investigation of d-d excitations and electron-spin coupling in 2D antiferromagnets., Correlated-electron systems have long been an important platform for various interesting phenomena and fundamental questions in condensed matter physics. As a pivotal process in these systems, d-d transitions have been suggested as a key factor toward realizing optical spin control in two-dimensional (2D) magnets. However, it remains unclear how d-d excitations behave in quasi-2D systems with strong electronic correlation and spin-charge coupling. Here, we present a systematic electronic Raman spectroscopy investigation on d-d transitions in a 2D antiferromagnet—NiPS3, from bulk to atomically thin samples. Two electronic Raman modes originating from the scattering of incident photons with d electrons in Ni2+ ions are observed at ~1.0 eV. This electronic process persists down to trilayer flakes and exhibits insensitivity to the spin ordering of NiPS3. Our study demonstrates the utility of electronic Raman scattering in investigating the unique electronic structure and its coupling to magnetism in correlated 2D magnets.

Aqueous rechargeable lithium-ion batteries (ARLIBs) as alternative energy storage devices have attracted tremendous attention because of their low cost and high safety. However, it is still a significant challenge to develop flexible high-performance ARLIBs for powering wearable devices because of the lack of all binder-free electrode materials. In this study, we develop one-step hydro-/solvothermal methods to design binder-free electrodes of LiCoO2 polygonal-sheeted arrays and rugby ball-shaped NaTi2(PO4)3 on carbon nanotube fibers as the cathode (LCO@CNTF) and the anode (NTP@CNTF). Both the electrodes are prepared at low temperatures without an extra calcination process, which is a great improvement for the growth process. The electrodes deliver remarkable capacity and extraordinary rate performance in a saturated Li2SO4 solution. Meanwhile, because of the synergy of LCO@CNTF and NTP@CNTF, an impressive capacity of 45.24 mA h cm-3 and an admirable energy density of 67.86 mW h cm-3 are achieved for the assembled quasi-solid-state fiber-shaped flexible ARLIB (FARLIB), which outperform most reported fiber-shaped aqueous rechargeable batteries. More encouragingly, our FARLIB possesses good flexibility, with a 94.74% capacity retention after bending 3000 times. Thus, this work represents a significant step toward developing FARLIBs and provides a new prospect in the design of wearable energy storage devices.

Low-dimensional organic-inorganic hybrid perovskites have demonstrated excellent performance as efficient white-light emitters. The broadband emission with large Stokes shift originates from self-trapped excitons (STEs). Since the mechanism of STEs formation in perovskites is still not clear, preparation of new low-dimensional white perovskites relies mostly on screening lots of intercalated organic molecules rather than a rational design. Here, we report an atom-substituting strategy to trigger STEs formation in layered perovskites. We applied halogen substituting hydrogen of C-H bond in intercalated organic molecules. The halogen-substituents with high electronegativity will withdraw electrons from the tail -NH3+ in the molecule. This results in a large positive charge accumulation on -NH3+, and thus a stronger attractive Coulomb force in ionic bond NH3+-PbBr3-. This plays an important role in transformation of free excitons (FEs) into STEs. Our designed white perovskites reached a high photoluminescence quantum yield of 32%, high color rendering index of near 90 and excellent Commission International de I’Eclairage coordinates close to the standard white-light (0.33, 0.33). This work provides atomic insights into the STEs formation in low-dimensional perovskites and will benefit tailoring white perovskites with boosting performance.

‘Blinking’, or ‘fluorescence intermittency’, refers to a random switching between ‘ON’ (bright) and ‘OFF’ (dark) states of an emitter; it has been studied widely in zero-dimensional quantum dots1 and molecules2, 3, and scarcely in one-dimensional systems4, 5. A generally accepted mechanism for blinking in quantum dots involves random switching between neutral and charged states6, 7 (or is accompanied by fluctuations in charge-carrier traps8), which substantially alters the dynamics of radiative and non-radiative decay. Here, we uncover a new type of blinking effect in vertically stacked, two-dimensional semiconductor heterostructures9, which consist of two distinct monolayers of transition metal dichalcogenides (TMDs) that are weakly coupled by van der Waals forces. Unlike zero-dimensional or one-dimensional systems, two-dimensional TMD heterostructures show a correlated blinking effect, comprising randomly switching bright, neutral and dark states. Fluorescence cross-correlation spectroscopy analyses show that a bright state occurring in one monolayer will simultaneously lead to a dark state in the other monolayer, owing to an intermittent interlayer carrier-transfer process. Our findings suggest that bilayer van der Waals heterostructures provide unique platforms for the study of charge-transfer dynamics and non-equilibrium-state physics, and could see application as correlated light emitters in quantum technology. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)

Physical Review B, 98 (24), ISSN:1098-0121, ISSN:0163-1829, ISSN:1550-235X, ISSN:0556-2805, ISSN:2469-9969, ISSN:1095-3795, ISSN:2469-9950

Transition metal dichalcogenides have valley degree of freedom, which features optical selection rule and spin-valley locking, making them promising for valleytronics devices and quantum computation. For either application, a long valley polarization lifetime is crucial. Previous results showed that it is around picosecond in monolayer excitons, nanosecond for local excitons and tens of nanosecond for interlayer excitons. Here we show that the dark excitons in two-dimensional heterostructures provide a microsecond valley polarization memory thanks to the magnetic field induced suppression of valley mixing. The lifetime of the dark excitons shows magnetic field and temperature dependence. The long lifetime and valley polarization lifetime of the dark exciton in two-dimensional heterostructures make them promising for long-distance exciton transport and macroscopic quantum state generations., Owing to their valley degree of freedom, atomically thin transition metal dichalcogenides show promise for valleytronics. Here, the authors leverage the dark excitons of two-dimensional van der Waals heterostructures to demonstrate a microsecond valley polarization memory effect.

Modulating second harmonic generation (SHG) by a static electric field through either electric-field-induced SHG or charge-induced SHG has been well documented. Nonetheless, it is essential to develop the ability to dynamically control and manipulate the nonlinear properties, preferably at high speed. Plasmonic hot carriers can be resonantly excited in metal nanoparticles and then injected into semiconductors within 10-100 fs, where they eventually decay on a comparable time scale. This allows one to rapidly manipulate all kinds of characteristics of semiconductors, including their nonlinear properties. Here we demonstrate that plasmonically generated hot electrons can be injected from plasmonic nanostructure into bilayer (2L) tungsten diselenide (WSe

Modulating second harmonic generation (SHG) by a static electric field through either electric-field-induced SHG or charge-induced SHG has been well documented. Nonetheless, it is essential to develop the ability to dynamically control and manipulate the nonlinear properties, preferably at high speed. Plasmonic hot carriers can be resonantly excited in metal nanoparticles and then injected into semiconductors within 10–100 fs, where they eventually decay on a comparable time scale. This allows one to rapidly manipulate all kinds of characteristics of semiconductors, including their nonlinear properties. Here we demonstrate that plasmonically generated hot electrons can be injected from plasmonic nanostructure into bilayer (2L) tungsten diselenide (WSe2), breaking the material inversion symmetry and thus inducing an SHG. With a set of pump–probe experiments we confirm that it is the dynamic separation electric field resulting from the hot carrier injection (rather than a simple optical field enhancement) that is the cause of SHG. Transient absorption measurement further substantiate the plasmonic hot electrons injection and allow us to measure a rise time of ∼120 fs and a fall time of 1.9 ps. Our study creates opportunity for the ultrafast all-optical control of SHG in an all-optical manner that may enable a variety of applications. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Controlling nonlinear light-matter interaction is important from fundamental science point of view as well as a basis for future optoelectronic devices1,2. Recent advances in twodimensional crystals have created opportunities to manipulate nonlinear processes electrically3-8. Here we report a strong second-harmonic generation (SHG) in a 2D WSe2 bilayer crystal caused by a back gate field. This unusual process takes place only when the gate polarity causes charge accumulation rather than depletion. Analysis based on bondcharge model traces the origin of SHG to the non-uniform field distribution within a single monolayer, caused by the accumulated sub-monolayer screening charge in the tungsten plane. We name this phenomenon charge-induced SHG (CHISHG), which is fundamentally different from the field- or current-induced SHG3-11. Our findings provide a potentially valuable technique for understanding and noninvasive probing of charge and current distributions in future low dimensional electronic devices. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Recently, organic-inorganic lead halide perovskites have gained great attention for their breakthrough in photovoltaic and optoelectronics. However, their thermal transport properties that affect the device lifetime and stability are still rarely explored. In this work, the thermal conductivity properties of single crystal CH

Polariton lasing is the coherent emission arising from a macroscopic polariton condensate first proposed in 1996. Over the past two decades, polariton lasing has been demonstrated in a few inorganic and organic semiconductors in both low and room temperatures. Polariton lasing in inorganic materials significantly relies on sophisticated epitaxial growth of crystalline gain medium layers sandwiched by two distributed Bragg reflectors in which combating the built-in strain and mismatched thermal properties is nontrivial. On the other hand, organic active media usually suffer from large threshold density and weak nonlinearity due to the Frenkel exciton nature. Further development of polariton lasing toward technologically significant applications demand more accessible materials, ease of device fabrication, and broadly tunable emission at room temperature. Herein, we report the experimental realization of room-temperature polariton lasing based on an epitaxy-free all-inorganic cesium lead chloride perovskite nanoplatelet microcavity. Polariton lasing is unambiguously evidenced by a superlinear power dependence, macroscopic ground-state occupation, blueshift of the ground-state emission, narrowing of the line width and the buildup of long-range spatial coherence. Our work suggests considerable promise of lead halide perovskites toward large-area, low-cost, high-performance room-temperature polariton devices and coherent light sources extending from the ultraviolet to near-infrared range. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

The gate-tunable phonon properties in bilayer MoS

Recently, organic–inorganic lead halide perovskites have gained great attention for their breakthrough in photovoltaic and optoelectronics. However, their thermal transport properties that affect the device lifetime and stability are still rarely explored. In this work, the thermal conductivity properties of single crystal CH3NH3PbI3 platelets grown by chemical vapor deposition are studied via non-contact micro-photoluminescence (PL) spectroscopy. We developed a measurement methodology and derived expressions suitable for the thermal conductivity extraction for micro-sized perovskites. The room temperature thermal conductivity of ∼0.14 ± 0.02 W m−1 K−1 is extracted from the dependence of the PL peak energy on the excitation laser power. On changing the film thickness from 80 to 400 nm, the thermal conductivity does not show noticeable variations, indicating the minimal substrate effects due to the advantage of the suspended configuration. The ultra-low thermal conductivity of perovskites, especially thin films, suggests their promising applications for thermal isolation, such as thermal insulation and thermo-electricity. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Graphene substrates have recently been found to generate Raman enhancement. Systematic studies using different Raman probes have been implemented, but one of the most commonly used Raman probes, rhodamine 6G (R6G), has yielded controversial results for the enhancement effect on graphene. Indeed, the Raman enhancement factor of R6G induced by graphene has never been measured directly under resonant excitation because of the presence of intense fluorescence backgrounds. In this study, a polarization-difference technique is used to suppress the fluorescence background by subtracting two spectra collected using different excitation laser polarizations. As a result, enhancement factors are obtained ranging between 1.7 and 5.6 for the four Raman modes of R6G at 611, 1,183, 1,361, and 1,647 cm[superscript −1] under resonant excitation by a 514.5 nm laser. By comparing these results with the results obtained under non-resonant excitation (632.8 nm) and pre-resonant excitation (593 nm), the enhancement can be attributed to static chemical enhancement (CHEM) and tuning of the molecular resonance. Density functional theory simulations reveal that the orbital energies and densities for R6G are modified by graphene dots., National Natural Science Foundation (China) (Nos. 21233001, 50972001, and 21129001), China. Ministry of Science and Technology (Nos. 2011YQ0301240201 and 2011CB932601), Beijing Natural Science Foundation (No. 2132056)

Surface enhanced Raman spectroscopy (SERS) can largely boost the Raman signal, and thus broaden the manifold potential applications of SERS. According to the current limitations on generality and efficiency, this work designed and developed a transparent, flexible and freestanding substrate and its preparation, conservation and operation procedures. The substrate consists of a polymer supporter and embedded metal nanostructures, which can be used for direct and on-line measurements of samples in various morphologies and circumstances. The detection limit of a flexible SERS(Ag) substrate is lower than 1 pmol/L.

A simple and environmentally friendly approach for the preparation of graphene nanosheets decorated with silver nanoparticles (Ag NPs) has been developed by gamma irradiation at room temperature. Graphene oxide (GO) and silver ions are simultaneously reduced by the electrons generated from the radiolysis of solvent. The addition of ionic liquid plays an important role in GO reduction by scavenging oxidative radicals generated during irradiation. Besides, the ionic liquid also benefits the dispersion and size distribution of Ag NPs. Raman signals of the obtained Ag-reduced graphene oxide are significantly enhanced, exhibiting obvious surface-enhanced Raman scattering activity.

This paper presents a simple method to solve the P4P problem based on co-planar feature points. By enhancing the geometric constraints of the feature points which attached to the target previously, we obtain the three-dimensional camera coordinates of the feature points in two different formulas. Then the translation vector and three rotation angles describing the relationship between target coordinate system and camera coordinate system are computed using a closed-form solution directly. In order to improve the precision about the extraction of the image center coordinate of the feature point, we use the morphology expansion operation to achieve it. The experimental results and theoretical analysis which were compared with the previous method demonstrate that our method is more fast and effective.

Graphene/hexagonal boron nitride (h-BN) vertical heterostructures have recently revealed unusual physical properties and new phenomena, such as commensurate-incommensurate transition and fractional quantum hall states featured with Hofstadter's butterfly. Graphene-based devices on h-BN substrate also exhibit high performance owing to the atomically flat surface of h-BN and its lack of charged impurities. To have a clean interface between the graphene and h-BN for better device performance, direct growth of large-area graphene/h-BN heterostructures is of great importance. Here we report the direct growth of large-area graphene/h-BN vertical heterostructures by a co-segregation method. By one-step annealing sandwiched growth substrates (Ni(C)/(B, N)-source/Ni) in vacuum, wafer-scale graphene/h-BN films can be directly formed on the metal surface. The as-grown vertically stacked graphene/h-BN structures are demonstrated by various morphology and spectroscopic characterizations. This co-segregation approach opens up a new pathway for large-batch production of graphene/h-BN heterostructures and would also be extended to the synthesis of other van der Waals heterostructures.

Chiral structure determination of single-walled carbon nanotube (SWNT), including its handedness and chiral index (n,m), has been regarded as an intractable issue for both fundamental research and practical application. For a given SWNT, the n and m values can be conveniently deduced if an arbitrary two of its three crucial structural parameters, that is, diameter d, chiral angle θ, and electron transition energy E(ii), are obtained. Here, we have demonstrated a novel approach to derive the (n,m) indices from the θ, d, and E(ii) of SWNTs. Handedness and θ were quickly measured based on the chirality-dependent alignment of SWNTs on graphite surface. By combining their measured d and E(ii), (n,m) indices of SWNTs can be independently and uniquely identified from the (θ,d) or (θ,E(ii)) plots, respectively. This approach offers intense practical merits of high-efficiency, low-cost, and simplicity.

Photoacoustic measurement techniques can be used to determine thermal properties on and below the sample’s surface, thus subsurface thermal inhomogeneities, such as continuous profiles of thermal parameters, become measurable by photoacoustic methods. In this paper, the study is focused on the quantitative characterization of material modifications in subsurface layers of laser-hardened Al alloy samples. The variation of surface temperature is measured by PA technique. Then a new numerical algorithm, carried out by employing the pulsed spectrum technique and the regularization method, is used to reconstruct thermal conductivity depth profiles. The experiment results demonstrate that the experiment and the algorithm are very effective for microstructure depth profile reconstruction by nondestructive method.