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1.
Adv Mater ; 32(28): e2001998, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32500553

##### RESUMO

Compared with thin-film morphology, 1D perovskite structures such as micro/nanowires with fewer grain boundaries and lower defect density are very suitable for high-performance photodetectors with higher stability. Although the stability of perovskite microwire-based photodetectors has been substantially enhanced in comparison with that of photodetectors based on thin-film morphology, practical applications require further improvements to the stability before implementation. In this study, a template-assisted method is developed to prepare methylammonium lead bromide (MAPbBr3 ) micro/nanowire structures, which are encapsulated in situ by a protective hydrophobic molecular layer. The combination of the protective layer, high crystalline quality, and highly ordered microstructures significantly improve the stability of the MAPbBr3 single-crystal microwire arrays. Consequently, these MAPbBr3 single-crystal microwire-array-based photodetectors exhibit significant long-term stability, maintaining 96% of the initial photocurrent after 1 year without further encapsulation. The lifetime of such photodetectors is hence approximately four times longer than that of the most stable previously reported perovskite micro/nanowire-based photodetector; this is thought to be the most stable perovskite photodetector reported thus far. Furthermore, this work should contribute further toward the realization of perovskite 1D structures with long-term stability.

2.
Opt Lett ; 45(9): 2580-2583, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32356821

##### RESUMO

Here a continuous axial-spiral phase microplate (CAsPP), based on combining a logarithmic axicon and a spiral phase plate, was proposed for generating high-quality higher-order Bessel vortex beams. The novel optical component implemented via femtosecond laser direct writing possesses compact geometry and unique optical properties. The CAsPP with a diameter of 80 µm possesses a controllable long focus ranging from 50 to 600 µm and exhibits a good self-healing ability after free transmission of about 45 µm. Unique optical properties were demonstrated in both experiments and simulations, which were well matched to each other. This Letter provides new opportunities for applications in integrated optics, optical trapping, laser machining, and information reconstruction.

3.
Opt Lett ; 45(9): 2684-2687, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32356847

##### RESUMO

We propose a precise diamond micromachining method based on ultraviolet femtosecond laser direct writing and a mixed acid heating chemical treatment. The chemical composition of the attached clusters generated during laser ablation and their effects on morphologies were investigated in experiments. The averaged roughness of pristine and processed regions reduced to 0.64 nm and 9.4 nm from 20.5 nm and 37.4 nm, respectively. With this method, spiral zone plates (SZPs) were inscribed on a high-pressure high-temperature diamond surface as micro-optical vortex generators. The optical performances of the diamond SZPs were characterized in both experiments and simulations, which were very consistent with each other. This chemical auxiliary processing method will contribute greatly to the wide application of integration and miniaturization of diamond surface optical components.

4.
Opt Lett ; 45(10): 2724-2727, 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32412451

##### RESUMO

All-inorganic cubic α-CsPbI3 perovskite for red perovskite light-emitting device (PeLED) applications is suffering from a phase transition. Unstable black α phase tends to transit to yellow Î´ phase under ambient conditions, which results in poor performance of the CsPbI3-based PeLEDs. Partial replacement of iodine anion with a comparatively smaller bromine anion in the perovskite film can effectively adjust the Goldschmidt tolerance factor and stabilize the α-phase. A phase-stable CsPb(Br1-xIx)3 perovskite has been obtained at low annealing temperature of 50°C by tuning the iodine-to-bromine ratios. A PeLED with pure red emission based on the CsPb(Br0.43I0.57)3 perovskite has been demonstrated. The maximum luminance and efficiency were 2200cd/m2 and 0.38 cd/A, respectively. Moreover, the PTAA layer was introduced between the PEDOT:PSS and perovskite film to improve the surface morphologies of perovskite. As a result, red PeLEDs with a maximum luminance of 2765cd/m2 have been achieved.

5.
Artigo em Inglês | MEDLINE | ID: mdl-32401489

##### RESUMO

Solar interfacial evaporation has been recognized as a versatile energy conversion protocol for cutting-edge applications such as water treatment and power generation (e.g., hydro voltaic effect). Recently, to enhance water evaporation rates, water temperature and evaporation area have been considered as essential ingredients, and thus photothermal materials and three-dimensional hierarchical structures have been developed to promote light-to-heat conversion efficiency and enhance interfacial evaporation. However, less attention has been paid to the airflow effect, because the interfacial floatability of photothermal membranes should be considered under air blast. Here, inspired from the stable interfacial floatability of lotus leaves, we report the airflow enhanced solar interfacial evaporation approach using a graphene-based Janus membrane. Laser-induced graphene (LIG) film was treated unilaterally by O2 plasma, forming a LIG/oxidized LIG (LIG-O) Janus membrane with distinct wettability on two sides. Higher water evaporation rate of 1.512 kg m-2 h-1 is achieved. The high solar interfacial evaporation performance can be attributed to the two advantages: (i) the combination of microscale capillary water transporting and nanoscale light trapping; (ii) hydrophobic/hydrophilic Janus membrane for stable interfacial floatability under airflow. Our approach is feasible for developing high-performance solar interfacial evaporation devices for practical clean energy utilization.

6.
J Phys Chem Lett ; : 1483-1489, 2020 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-32017570

##### RESUMO

It is well-established that the electronic states of graphene oxide (GO) consist of sp2 clusters with different sizes and the surrounding sp3 matrix according to recent reports. However, addressing the excitation energy migration/redistribution among those electronic states in GO-based complex systems from spectroscopic experiments is still a challenge. Here, we combine the time-resolved absorption and fluorescence depolarization experiments to reveal the excitation energy migration processes in electronic states in GO. We demonstrate that, in sp3 domains of GO, there are charge-transfer states between sp3-hybridized carbon atoms and the oxygen-containing functional groups, and the energy redistribution and charge migration in sp3 matrix occur on the time scale from subpicoseconds to tens of picoseconds. In contrast, the electronic states of sp2 clusters in GO are rather localized and dominantly contribute to the excitation-wavelength-dependent red fluorescence of GO.

7.
Opt Lett ; 45(3): 636-639, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-32004271

##### RESUMO

We report fabrication of silica convex microlens arrays with controlled shape, size, and curvature by femtosecond laser direct writing. A backside etching in dye solution was utilized for laser machining high-fidelity control of material removal and real-time surface cleaning from ablation debris. Thermal annealing was applied to reduce surface roughness to 3 nm (rms). The good optical performance of the arrays was confirmed by focusing and imaging tests. Complex 3D micro-optical elements over a footprint of $100 \times 100\;\unicode{x00B5}{{\rm m}^2}$100×100µm2 were ablated within 1 h (required for practical applications). A material removal speed of $120\;\unicode{x00B5}{{\rm m}^3}/{\rm s}$120µm3/s ($6 \times {10^5} \;{{\rm nm}^3}/{\rm pulse}$6×105nm3/pulse) was used, which is more than an order of magnitude higher compared to backside etching using a mask projection method. The method is applicable for fabrication of micro-optical components on transparent hard materials.

8.
Opt Lett ; 44(21): 5149-5152, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31674953

##### RESUMO

We demonstrate a versatile method for fast and flexible fabrication of either one or an array of microlenses. Multi-foci axial intensity distribution generated by a phase pattern displayed on a spatial light modulator irradiates silica, causing ablation and its internal modification. The following wet etching step defines the diameter r, while the radius of curvature R (hence, the focal length f) is maintained the same. As a result, the numerical aperture NA=r/f changes from 0.2 to 0.4 for the same pulse energy (but different number of multi-foci) during ablation. An isotropic wet etching of silica becomes highly anisotropic for the initial stages of etching following the irradiated pattern. Subsequent evolution of the shape is governed by an isotropic silica etch and forms a spherical lens. This method can be extended to other materials and geometries of micro-optical elements.

9.
Phys Chem Chem Phys ; 21(44): 24262-24268, 2019 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-31663561

##### RESUMO

Periodical structures induced by pulsed lasers are a unique phenomenon when pulsed lasers irradiate on some material surfaces. These periodical structures with a subwavelength-scale period hold potential in integrated-optics and biomimetic micro-nanodevices for their direct shaping by laser pulses. However, the blurred nature of the laser-induced structuring hinders its further exploration in these application scopes. In this review, the plasmon-mediated structuring targeted on various materials, both organic and inorganic, will be discussed profoundly.

10.
Opt Lett ; 44(19): 4817-4820, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31568450

##### RESUMO

We demonstrate an enhanced efficiency of all-inorganic perovskite light-emitting diodes (PeLEDs) by doping an electron acceptor of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) as a p-type dopant into the hole-transport layer (HTL) of poly-triarylamine (PTAA). The conductivity of the PTAA was improved by the formation of the CT complex through the electron transfer from the PTAA to F4TCNQ. Moreover, the hydrophobic surface of the PTAA leads to an improved surface morphology of the perovskite films compared to that on the conventionally used HTL of PEDOT:PSS. As a result, the maximum luminance and efficiency for the doped PTAA-based PeLEDs are 28020 cd/m2 and 13.5 cd/A, respectively, corresponding to 32.7% and 48% improvement in the efficiency compared to those of the pure PTAA or PEDOT:PSS-based PeLEDs.

11.
Nanoscale ; 11(39): 18272-18281, 2019 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-31570914

##### RESUMO

The detection of the polarization states of light is of great significance for the analysis of biological tissue morphologies, image display systems and sensors. Although organic-inorganic hybrid perovskite crystals have excellent photoelectric properties, which make them very suitable for the preparation of photodetectors, their applications in polarized light detection are hindered by their isotropy and instability. Here, we solved this problem by fabricating a stable 2D layered Ruddlesden-Popper perovskite into anisotropic micro-wire arrays with a template-confined method. Based on this anisotropic structure, a high-performance photodetector with a dark current as low as 10-12 A, high responsivity of 3.5 A W-1, detectivity exceeding 1 × 1015 Jones and a fast response with a rise time of 4.1 ms and a decay time of 3.3 ms was achieved and successfully applied for high-performance polarization detection. More importantly, the device maintained a superior performance even after being exposed to an environment of 60% relative humidity without encapsulation.

12.
Nanoscale ; 11(43): 20614-20619, 2019 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-31641724

##### RESUMO

Moisture-responsive actuators based on graphene oxide (GO) have attracted intensive research interest in recent years. However, current GO actuators suffer from low mechanical strength. Inspired by the robustness of nacre's structure, moisture-responsive actuators with high mechanical strength and self-healing properties were successfully developed based on GO and cellulose fiber (CF) hybrids. The hybrid paper demonstrated significantly improved tensile strength, â¼20 times higher than that of pure GO paper, and self-healing properties. A broken paper can be well cured under moist conditions, and the mechanical properties of the self-healed hybrid paper can still maintain similar tensile strength to the pristine one. After controllable ultraviolet light photoreduction treatment, a hybrid paper with a photoreduction gradient along the normal direction was prepared, which can act as a moisture-responsive actuator. A maximum bending curvature of â¼1.48 cm-1 can be achieved under high relative humidity (RH = 97%). As a proof-of-concept, a butterfly-like actuator that can deform itself with moisture actuation was demonstrated. Our approach may pave a new way for designing robust and self-healable graphene actuators.

13.
Glob Chall ; 3(1): 1800070, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31565357

##### RESUMO

Water is the major natural resource that enables life on our planet. Rapid detection of water pollution that occurs due to both human activity and natural cataclysms is imperative for environmental protection. Analytical chemistry-based techniques are generally not suitable for rapid monitoring because they involve collection of water samples and analysis in a laboratory. Laser-based approaches such as laser-induced breakdown spectroscopy (LIBS) may offer a powerful alternative, yet conventional LIBS relies on the use of tightly focused laser beams, requiring a stable air-water interface in a controlled environment. Reported here is a proof-of-principle, quantitative, simultaneous measurement of several representative heavy-metal contaminants in water, at ppm-level concentrations, using ultraintense femtosecond laser pulses propagating in air in the filamentation regime. This approach is straightforwardly extendable to kilometer-scale standoff distances, under adverse atmospheric conditions and is insensitive to the movements of the water surface due to the topography and water waves.

14.
Nanomaterials (Basel) ; 9(10)2019 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-31623407

##### RESUMO

Birefringence of 3 × 10 - 3 is demonstrated inside cross-sectional regions of 100 µ m, inscribed by axially stretched Bessel-beam-like fs-laser pulses along the c-axis inside sapphire. A high birefringence and retardance of λ / 4 at mid-visible spectral range (green) can be achieved using stretched beams with axial extension of 30-40 µ m. Chosen conditions of laser-writing ensure that there are no formations of self-organized nano-gratings. This method can be adopted for creation of polarization optical elements and fabrication of spatially varying birefringent patterns for optical vortex generation.

15.
ACS Appl Mater Interfaces ; 11(41): 38084-38091, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31547649

##### RESUMO

Versatile electronic skin devices that enable detection of multimodal signals have revealed great potential for human health monitoring. To make a versatile electronic skin, hierarchical micronanostructures are essential to obtain improved sensing performance and multisignal detection capability. However, current strategies for developing a nanostructured electronic skin usually involve complex procedures, harsh experimental conditions, and the use of expensive equipment, which limit its practical applications. In this paper, we reported the fabrication of a multifunctional wearable electronic skin with hierarchical micronanostructures by using natural reed leaves as templates. The capacitive-type electronic skin is fabricated by double-sided coating of Au electrodes on an artificial polydimethylsiloxane reed leaf that is duplicated from natural reed leaves via soft lithography. The electronic skin features a very simple device structure yet high sensing performance. It permits multimodal signal detection, including that of pressure, deformation, and proximity, and can serve as surface-enhanced Raman scattering substrates for the detection of metabolites in sweat because of the formation of plasmonic structures. The versatile electronic skin can be attached to the human skin, and it enables effective monitoring of multiphysiological signals, revealing great potential for cutting-edge applications, such as human health monitoring.

##### Assuntos
Materiais Biomiméticos , Ouro , Nanoestruturas , Folhas de Planta , Dispositivos Eletrônicos Vestíveis , Eletrodos , Humanos
16.
Nanoscale ; 11(41): 19119-19139, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31556427

##### RESUMO

Perovskite quantum dots (QDs) have been hotly pursued in recent decades owing to their quantum confinement effect and defect-tolerant nature. Their unique optical properties, such as high photoluminescence quantum yield (PLQY) approaching unity, narrow emission bandwidth, tunable wavelength spanning the entire visible spectrum, and compatibility with flexible/stretchable electronics, render perovskite QDs promising for next-generation solid lighting sources and information displays. Herein, the advances in perovskite QDs and their applications in LEDs are reviewed. Strategies to fabricate efficient perovskite QDs and device configuration, including material composition design, synthetic methods, surface engineering, and device optimization, are investigated and highlighted. Moreover, the main challenges in perovskite QDs of instability and toxicity (lead-based) are identified, while the solutions undertaken with respect to composition engineering, device encapsulation, and lead-replacement QDs are demonstrated. Meanwhile, perspectives for the further development of perovskite QDs and corresponding LEDs are presented.

17.
ACS Appl Mater Interfaces ; 11(40): 37130-37138, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31500405

##### RESUMO

Bimorph actuators hold great promise for developing soft robots. However, poor interlayer adhesion between different materials always threatens their stability for long-term usage. In this paper, instead of using a bilayer structure, we reported the gradient assembly of graphene oxide (GO) sheets and polymer nanospheres for developing robust moisture and light dual-responsive actuators. The distribution gradient of poly(methyl methacrylate) (PMMA) nanospheres along the normal direction of a GO paper leads to an asymmetric structure. The front side that mainly consists of GO is quite sensitive to water molecules, which swells upon exposure to moisture, whereas the back side that is rich in PMMA nanospheres expands obviously due to the photothermal effect. The distinct properties of the two sides endow the composite paper with moisture and light dual-responsiveness. Moreover, since GO has been used as a host material, the composite paper shows a moisture-triggered self-healing property, which permits front-to-front and front-to-back healing. The self-healed paper can maintain similar responsive property and reasonable mechanical strength to the pristine one. As a proof of concept, a dual-responsive gripper actuator and a scorpion robot have been fabricated for light and moisture cooperative manipulation. The gradient assembly strategy may open up a new way for developing robust multiresponsive actuators beyond bilayer structures.

18.
Front Chem ; 7: 506, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31380350

##### RESUMO

As a typical 2D carbon material, graphene, that possesses outstanding physical/chemical properties, has revealed great potential for developing soft actuators. Especially, the unique properties of graphene, including the excellent light absorption property, softness, and thermal conductivity, play very important roles in the development of light-responsive graphene actuators. At present, various light-driven actuators have been successfully developed based on graphene and its derivatives. In this mini review, we reviewed the recent advances in this field. The unique properties of graphene or graphene-related materials that are of benefit to the development of light-driven actuators have been summarized. Typical smart actuators based on different photothermal/photochemical effects, including photothermal expansion, photothermal desorption, photoisomerization, and photo-triggered shape memory effect, have been introduced. Besides, current challenges, and future perspective have been discussed. The rapid progress of light-responsive actuators based on graphene has greatly stimulated the development of graphene-based soft robotics.

19.
Adv Mater ; 31(32): e1901585, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31197895

##### RESUMO

The strong interaction between graphene oxides (GO) and water molecules has trigged enormous research interest in developing GO-based separation films, sensors, and actuators. However, sophisticated control over the ultrafast water transmission among the GO sheets and the consequent deformation of the entire GO film is still challenging. Inspired from the natural "quantum-tunneling-fluidics-effect," here quantum-confined-superfluidics-enabled moisture actuation of GO paper by introducing periodic gratings unilaterally is reported. The folded GO nanosheets that act as quantum-confined-superfluidics channels can significantly promote water adsorption, enabling controllable and sensitive moisture actuation. Water-adsorption-induced expansion along and against the normal direction of a GO paper is investigated both theoretically and experimentally. Featuring state-of-the-art of ultrafast response (1.24 cm-1 s-1 ), large deformation degree, and complex and predictable deformation, the smart GO papers are used for biomimetic mini-robots including a creeping centipede and a smart leaf that can catch a living ladybug. The reported method is simple and universal for 2D materials, revealing great potential for developing graphene-based smart robots.

20.
Opt Lett ; 44(10): 2454-2457, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-31090705

##### RESUMO

A dry-etching-assisted femtosecond laser lithography technology is proposed to in-site fabricate micro-optical components with an ultra-smooth three-dimensional continuous profile on a non-planar substrate. Owing to the nanometric resolution of femtosecond laser multi-photon polymerization and dry etching, smooth micro-optical components can be realized on hard materials with surface roughness of approximately 1.5 nm. With flexible and arbitrary designability of femtosecond laser lithography, various high-quality micro-optical components are realized on sapphire. These results indicate that dry-etching-assisted femtosecond laser lithography has promising potential for versatile fabrication of arbitrary ultra-smooth micro/nanostructures on hard materials.