Search

Intrinsic silicon (Si) is forbidden for infrared (IR) sensing at the communication wavelength like 1.31 or 1.55 µm due to the well‐known bandgap limitation. In this work, an unexpected physical picture of using argon (Ar) is identified, which is usually inert to the surrounding chemical environment and used as a protective agent in semiconductor processing, to overcome the IR‐sensing‐forbidden problem in Si. Here, it is shown by an analysis of a dynamic secondary ion mass spectrometer that such a Si, when exposed to laser pulse in Ar gas, can contain a very high dose of Ar up to 1020 cm−3 even after 1300 days. First‐principles calculations, molecular dynamics, and Hall effect measurements reveal that, due to both steric and dynamic repulsions by Ar orbitals to Si dangling bonds, the Ar‐filled‐vacancy produces a much wider defect band inside the gap, which is not only responsible for strong infrared absorption, but also causes a significant increase in n‐type conductivity, both in line with experiments. The study proves that originally inert elements in fact can act as active impurities in semiconductors for advanced applications, which updates the current knowledge of defect physics. [ABSTRACT FROM AUTHOR]

We have investigated two-photon polymerization of metal ions doped acrylate monomers and oligomers which is applied for three-dimensional (3D) micro/nano-structure fabrication. Titanium (IV) ions doped urethane acrylate photopolymerizable resins were synthesized, and their optical and polymerization properties were investigated. The resolution of two-photon polymerization for micro/nanofabrication was evaluated. Titanium dioxide (TiO2) nanoparticles were generated in the polymer matrix of micron-sized polymer structures. A 3D diamond photonic crystal structure, which consisted of polymer composite materials of TiO2 nanoparticles, was successfully fabricated by direct laser writing and its photonic bandgap was confirmed. This work would give us a new solution for producing 3D micro/nanodevices of functional polymer composite materials. [Copyright &y& Elsevier]

Two-photon absorption (TPA) has been a useful tool in spectroscopy. With the progress of laser technologies, excitation of various photochemical and physical reactions by two or multiphoton processes becomes essential for advanced microscopic imaging, nano-spectroscopy and laser materials processing. In our research, we use TPA to excite local photopolymerization of resins, by which various photonic and micro-mechanical devices and systems have been produced. In this paper, we will summarize our recent progresses including: improvement of three-dimensional (3D) spatial resolutions and their characterization by an ascending scan method, a strategy of shortening fabrication duration, and a 3D micro-diagnosis technology. [Copyright &y& Elsevier]

Colloidal quantum dots (QDs) have been widely studied in display panels due to their near‐unity fluorescence quantum yield and the ability to tune colors across a wide gamut. However, the challenge persists in creating full‐color QD arrays with the necessary precision for high‐resolution display applications in the next generation. This paper introduces a femtosecond laser‐induced forward transfer (FsLIFT) technology that integrates deposition pattern and alignment in a single transfer step. This development enables the fabrication of high‐resolution full‐color QD films. The ability of FsLIFT to precisely locate red, green, and blue QDs in a designated position allows to obtain arbitrarily shaped full‐color patterns and pixel arrays with a resolution of 1.78 µm. In addition, the potential for optoelectronic devices is ensured by the preserved photophysical properties, high smoothness, and continuity of the transferred QD films. Consequently, the light‐emitting diodes (LEDs) are successfully fabricated based on the transferred QD films. This study expects that the introduced straightforward patterning technology, offering high freedom, precision, and repeatability, will contribute to advancing the development of full‐color high‐resolution displays based on QDs. [ABSTRACT FROM AUTHOR]

The fundamental issues on the smallest possible processing accuracy and the best feasible surface smoothness in pinpoint polymerization-based laser fabrication were experimentally investigated. The lateral spatial resolution is improved from the previously reported value, 120 nm, to around 100 nm by intentionally introducing radical quenchers in the resin. The roughness measured from 10 μm×10 μm surface areas were averaged to 4–11 nm, which is found slightly affected by the laser pulse energy but independent on the scanning pitch when it is smaller than a critical value. The surface quality of this level could fully satisfy the requirement of various photonic elements and devices. [ABSTRACT FROM AUTHOR]

We first analyze why most of the photonic crystals produced by two-photon photopolymerization technique exhibit no photonic band gap effect. And then subdiffraction-limited resolution-enabled finely quantified pixel writing, a scheme that has been used in micromachine fabrication, is adopted as the solution. As a result, higher accuracy in depicting and better reproducibility in both fabrication and photonic band gap effect observation are obtained. More important, the method allows for precise precompensation of the structure shrinkage induced by photochemical reactions of polymerization, which may pave the way to high-fidelity fabrication of polymer photonic and optoelectronic devices that require strictly the structural parameters. [ABSTRACT FROM AUTHOR]

We report two-photon pump lasing action of a photonic crystal laser, which comprises fluorescent dye-doped chiral nematic liquid crystals. The dye absorbs light peaking at 466 nm, while the pumping was conducted at 1000 nm wavelength. Due to redistribution of density of states by a stopping band, a strong single-mode stimulated emission was observed at the band edge wavelength of 608 nm with 1 nm detection-limited linewidth. A comparative study shows that under an identical pumping geometry, the two-photon lasing threshold is only 120 times larger than that for the single-photon excitation, a ratio lower than those generally reported for up-conversion lasing. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report critical roles that are played by laser system parameters in two-photon laser nanofabrication, which are not significant in rapid prototyping at larger scale, including: (i) polarization-induced lateral deshaping of volume elements, voxels, the primitive building block of micronanostructures, and (ii) lateral size reduction of voxels at low numerical aperture lens focusing due to thresholding effect. Also interesting is (iii) simultaneous recording of zeroth- and higher-order diffraction patterns, which was not hindered by the two-order light intensity difference by taking the advantage of the large dynamic exposure time range of general resins, a concept that is proposed in contrast to dynamic power range. [ABSTRACT FROM AUTHOR]

We present a method for fabricating three-dimensional photonic crystal structures by means of an interference pattern of laser beams. Two orthogonal square lattice rod-arrays which compose the wood-pile photonic crystal structure are fabricated by interference of four laser beams into photopolymerizable resin. The lattice constant of the photonic crystal can be selected freely by incident angles of laser beams without any deformations of the lattice symmetry and the lattice elements. The proposed method does not require complicated multiple processes compared with the layer-by-layer fabrication method, and thick wood-pile photonic crystals are immediately produced with high precision. [ABSTRACT FROM AUTHOR]

We used a photopolymer consisting of urethane acrylate monomer and free-radical-type initiators as a media for recording two-photon-excited (TPE) focal spots in three dimensions. Mathematically, the initiator plays a role of "k √" operator, transforming the quadratic light intensity distribution to a linear radical concentration distribution. Then, the monomer acts as a three-dimensional (3D) "film," fixing the focal volume where radical concentration is above a threshold as a voxel. An ascending scan method was utilized to avoid substrate truncation and to achieve isolated complete 3D voxels, from which accurate forms of TPE focus were obtained. The 3D photographing technology led to a clear explanation of the origin of pronounced contradictions in reported spatial resolutions, and would be critical for laser precision microfabrication in various materials. [ABSTRACT FROM AUTHOR]

We report on sub-diffraction-limit (SDL) micro/nanofabrication via two-photon-absorption (TPA) photopolymerization. SDL spatial resolution was found possible in a threshold system, where materials responded to light excitation with a pronounced threshold behavior. The diffraction limit in this case became just a measure of focal spot size, but did not put any actual restraint to voxel dimensions. Experimentally, lateral spatial resolution down to 120 nm was realized by using high numerical-aperture optics. In addition, we proposed a profile scanning method, by which the fabrication efficiency was significantly increased. The TPA processing time, in the example given here, was reduced by 90%. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report in this letter an elastic force analysis of two-photon-polymerized submicron oscillators with spiral radius of 150 nm. A laser trapping force was first utilized to mechanically drive the spring of this small size. An overdamped oscillation was observed, according to which, the spring constant was measured to approximately 10[sup -8] N/m. This value was 5-order smaller than the one calculated using oscillator parameters. Both deviated from a more reliable result, 10[sup -6] N/m, as was estimated from the laser trapping force. The significant discrepancies were attributed to scaling effects and to the difference of condensed states of the polymer related to exposure processes. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the fabrication and characteristics of planar microcavities in a log-pile photonic crystal structure formed using light-induced photopolymerization of resin. A planar defect was introduced into the middle of the log-pile structure as a single layer with every second rod missing. The existence of confined cavity states was confirmed experimentally and by numeric simulations. The cavity resonance found at the midgap wavelength λ[sub M]∼4.0 μm had a quality factor of about 130. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The rapid development of nanotechnology for the last 30 years has enabled a rapid expansion in the applications of functional nanoparticles (NPs) on optoelectronic devices. Especially, NPs are of high significance in organic light‐emitting diodes (OLEDs) as they provide feasible solutions to the enduring challenges related to higher device efficiency. The use of NPs with designed structure and functionality is demonstrated, indicative of their great application potentials in OLEDs. Herein, the recent advances in OLEDs with the utilization of functional NPs are summarized. Starting with a brief overview about the unique properties of NPs, comprehensive roles of NPs in OLEDs, which include improving carrier injection abilities, local surface plasmonic resonance, light scattering, and magnetic field effects, are discussed together with their latest research progresses. Furthermore, one‐component and multicomponent heterostructured NPs with multifunctional capabilities in OLEDs are overviewed. Following the summarization of the roles of NPs in OLEDs and their latest research progress, a brief conclusion and outlook regarding the future research directions of highly efficient OLEDs by incorporation of NPs are provided. [ABSTRACT FROM AUTHOR]

3D printing of inorganic materials with nanoscale resolution offers a different materials processing pathway to explore devices with emergent functionalities. However, existing technologies typically involve photocurable resins that reduce material purity and degrade properties. We develop a general strategy for laser direct printing of inorganic nanomaterials, as exemplified by more than 10 semiconductors, metal oxides, metals, and their mixtures. Colloidal nanocrystals are used as building blocks and photochemically bonded through their native ligands. Without resins, this bonding process produces arbitrary three-dimensional (3D) structures with a large inorganic mass fraction (~90%) and high mechanical strength. The printed materials preserve the intrinsic properties of constituent nanocrystals and create structure-dictated functionalities, such as the broadband chiroptical responses with an anisotropic factor of ~0.24 for semiconducting cadmium chalcogenide nanohelical arrays. [ABSTRACT FROM AUTHOR]

3D laser nanoprinting represents a revolutionary manufacturing approach as it allows maskless fabrication of 3D nanostructures at a resolution beyond the optical diffraction limit. Specifically, it endows the printed structures novel physical, chemical, or mechanical properties not observed at macroscopic scale. However, 3D laser nanoprinting typically relies on the photopolymerization process, indicating its limitation on the printable materials and functionalities. The capability to print diverse functional materials beyond polymer will enable a lot of new device applications in nanophotonics, microelectronics, and so on. One of the strategies is to use the 3D‐printed polymer structures as skeletons for functional material deposition, while another is to mix the functional components with the photocurable molecules and print the nanocomposites. More recently, several laser nanoprinting techniques beyond photopolymerization are also developed. In this review, the cutting‐edge technical innovation is summarized and a couple of examples are highlighted showing exciting applications of the printed structures in magnetic microrobots, photonics, and optoelectronics. Finally, the vision for existing challenges and future development in this field is shared. [ABSTRACT FROM AUTHOR]

Achieving higher brightness of a single-photon emitter (SPE) is central for advanced applications from quantum information processing to quantum sensing. However, most approaches of integrating quantum emitters and photonic resonators require accurately localizing the emitter into a photonic structure, which is a challenge. Here, we report using dielectric microspheres for laser focusing to create SPEs in hexagonal boron nitride and in situ enhance the emission via photonic coupling between the SPE and the dielectric microspheres. The photoluminescence intensity is increased by 2.4-fold, achieving a high brightness SPE with a saturation intensity of up to 19.6 Mcounts s−1. This approach provides a feasible way to generate a high-performance SPE while simultaneously enabling precise coupling of the quantum light source and optical resonators. [ABSTRACT FROM AUTHOR]

The development of dynamic 3D codes is widely studied, especially for smart information protection and advanced dynamic information encryption. However, it is challenging to fabricate information carriers with full color, dynamic properties under external stimuli, and high capacity, which restricts their applications. Here, microsized dynamic full color fluorescent 3D codes are successfully fabricated using the multilayer‐independent femtosecond laser‐induced forward transfer (FsLIFT) technology, which achieves simultaneous high‐resolution transferring and patterning. The combination and excitation of multilayered quantum dots film with different colors and patterns ensure dynamic information transformation of the 3D codes. Due to the high spatial resolution of the FsLIFT, the minimum line width of the patterns can reach 1.78 µm, which ensures a high capacity for encoding. In addition, the decoding process of the microsized dynamic fluorescent 3D codes only requires smartphones, microscope patches, and portable light sources. Finally, the facile fabrication and decoding process as well as the customizable patterning abilities demonstrate the practical application potential for the advanced dynamic coding. [ABSTRACT FROM AUTHOR]

Discusses a study which fabricated a micromachine using two-photon photopolymerization. Significance of micromachines to biotechnology; Implication of the quadratic dependence of two-photon absorption probability on photon fluence density; Information on a micro-oscillator fabricated by exceeding the subdiffraction-limit.

Chemical Marangoni propulsion enables dynamic and untethered motion by generating surface tension gradient through chemical release, thereby having great potential for the development of insect‐scale self‐propelled robots. However, as the release and diffusion of chemical "fuels" are commonly uncontrollable, the Marangoni propulsion is unstable, thereby restricting robotic applications. Herein, the laser fabrication of superhydrophobic swimming robots to develop controllable Marangoni propulsion based on a photothermal composite of graphene and polydimethylsiloxane is reported. By combining the microfluidic channels with photothermal air chambers, a light‐triggered switch that can control the release of chemical "fuels" is proposed. Furthermore, a superhydrophobic surface is fabricated on the swimming robot by laser treatment, which reduced water resistance and promoted propulsion. On‐demand actuation and swimming route planning are realized by programming the alcohol/air segments in the releasing channels, on‐demand actuation and swimming route planning have been realized. As a proof‐of‐concept, a Marangoni swimming robot equipped with a miniature digital camera is used in an actual environment. Therefore, this study is expected to advance the practical applications of the chemical Marangoni effect in swimming robots. [ABSTRACT FROM AUTHOR]

Assembling perovskites into heterojunctions is an effective approach to achieve high‐performance photodetectors. Compared with vertical heterojunctions, in lateral heterojunction‐based photodetectors, the reflection loss is reduced because the active layer is in direct contact with light resulting in higher performance and better stability. However, lateral perovskite–perovskite heterojunctions are difficult to achieve using solution methods because the first formed film is easily dissolved by the solvent of the second precursor. In this study, a two‐step imprinting method is developed to fabricate lateral MAPbI3–MAPbBr3 microwire heterojunctions and realize a high‐performance photodetector with a responsivity and detectivity of 1207 A W−1 and 2.78 × 1013 Jones, respectively. At 0 V bias, the device exhibits a responsivity of up to 233 A W−1, which is more than double the previously reported best results. The high‐quality heterojunction endows the photodetectors with ultra‐high polarization sensitivity (Imax/Imin = 8.2) and long‐term stability, retaining 88.2% of its initial performance even after being exposed to air for 391 d. [ABSTRACT FROM AUTHOR]

2D perovskites have been considered as promising candidates for optoelectronic devices due to their good optical and electronic properties compared to 3D perovskites with significantly higher stability. Considering the commercial applications involving displays, image sensors, and fluorescent anti‐counterfeiting labels, the patterning technique of 2D perovskites is urgently required. However, existing patterning approaches still have challenges in high‐resolution fabrication. Here, a facile femtosecond laser direct writing method to fabricate arbitrarily patterned 2D perovskite films with well‐defined profiles and uniform fluorescence properties is developed. The flexible, fine, and non‐thermal diffused patterning abilities of femtosecond laser facilitate diverse 2D perovskite patterns exhibiting bright emission without any pinholes and cracks, as well as high resolution of approximate 2 µm line width. Based on this efficient patterning technique, this study demonstrates fluorescent anti‐counterfeiting labels (quick response code embedded with microlines) based on 2D perovskite films with high humidity stability, which can be identified from 43% to 96% relative humidity. This high‐resolution, reliable, efficient, and facile patterning technique for 2D perovskites with high humidity stability provides a promising technical route for 2D perovskite‐based optoelectronic applications. [ABSTRACT FROM AUTHOR]

We report in this letter two-photon-absorption photopolymerization using fluorescent dye-doped resin, by which complex fluorescence-active three-dimensional (3D) microstructures were readily produced. Structures were imaged by means of two-photon confocal techniques. The realization of dye-doping photopolymerization would be an important step towards production of photonic-crystal-based high-efficiency polymer optoelectronic devices. Furthermore, we found that the doped dye acted as label molecules to stain solidified structures, which provided an effective two-photon fluorescence technique for internal microdiagnosis of polymerized 3D microstructures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Micro/nano optoelectronic devices based on curved substrates play a significant role in the development of wearable devices, electronic skin, conformal sensors, conformal antennas, and soft robots. However, the current fabrication processes are oriented toward planar micro/nano devices, and the fabrication of such devices on curved substrates is challenging. Herein, a temperature‐gradient‐assisted nanoimprint‐based in situ micro/nano‐crystal growth method is proposed to fabricate high‐quality curved perovskite microwire crystal (MWC) arrays on curved surfaces. Based on this curved perovskite MWC array without bending‐induced defects, high‐performance curved photodetectors (responsivity = 414 A W−1, detectivity = 1.2 × 1014 Jones, and external quantum efficiency over 140 000%) with extraordinary stability (85% of original performance maintained for more than 2 years) are fabricated to realize a curved imaging device. These results provide insights into the application of high‐performance perovskite photodetectors in nonconformal optical systems. [ABSTRACT FROM AUTHOR]

Stretchable organic light‐emitting devices (SOLEDs) based on orderly wrinkles have become a promising candidate for the new‐generation deformable displays because of their high‐optoelectronic performance and stretching stability. However, the complex thin film transfer process to form the wrinkles and the decreased display quality caused by the large‐period wrinkles with a few hundreds of microns are obstacles to their practical applications. Herein, a simple transfer‐free technique is designed to introduce the orderly wrinkles with a much smaller period of 70 µm into the SOLEDs, which is the smallest value reported to date for the orderly wrinkles integrated in the SOLEDs. The small‐period wrinkles are invisible by naked eyes and beneficial to the applications of the SOLEDs in high‐quality stretchable displays. The electroluminescence performance of the SOLED with 20% stretchability are comparable to those of the rigid OLEDs on glass substrates. After 2000 cycles of stretching, the luminance of the device remained at 90% of its initial value. Meantime, the transfer‐free technique is compatible with the flexible encapsulation process. The luminance of the encapsulated SOLEDs exhibit negligible decline after 600‐min continuous operation under ambient condition. This work provides an effective solution for achieving high‐performance SOLEDs by a simple process. [ABSTRACT FROM AUTHOR]

Optical crystals are ideal materials for complex functional and durable optical components, but their good stability and hardness bring about difficulties in high‐precision machining and require surface roughness below λ/10. Femtosecond laser ablation is a widely applicable processing method indifferent to material types, but its 3D fabrication capability is limited by the accumulation of ablated debris and rough ablated surface. This work demonstrates a universal and flexible technology for the fabrication of crystalline micro‐optics with required shape and surface roughness for the most demanding optical phase control. The cavitation‐assisted ablation by a direct laser writing mode is followed by a high‐temperature treatment to remove the rough non‐crystalline layer caused by ablation. The annealing at temperatures below the melting point of the crystal reduces the roughness down to ≈2 nm without changing the structure shape. This virtue of maintaining the designed shape without change, which is impossible during thermal morphing of 3D surfaces of glasses, allows for a previously unavailable flexibility of surface finish for the most demanding optical micro‐optical elements made in this study. This universal technology with nanoscale resolution and free‐form 3D manufacturing capability is applicable for various crystals and provides a new way to fabricate micro‐/integrated‐optics and nonlinear optical elements. [ABSTRACT FROM AUTHOR]

The assembly of colloidal particles into 2D or 3D superstructures is significant as the colloidal assembly exhibits collective behavior beyond the sum of single particles. Technically, colloidal particles can either self‐assemble when thermodynamic equilibrium is reached, or directed into specific assembly under external stimulus, such as electric, magnetic, acoustic, or light field. Specifically, light can be focused locally and manipulated in a precise manner, providing the possibility to tailor the assembly kinetics in different degrees of freedom. The understanding of light–matter interaction during the assembly process is challenging but critical for the design and fabrication of diverse colloidal superstructures. In this review, these particles are treated as artificial atoms at colloidal scale to mimic the organization of matter. From this aspect, the light‐directed assembly process is discussed on the basis of the roles of light, including light‐directed nucleation, diffusion, interparticle bonding, and phase control. Beyond what has been observed at atomic scale, colloidal atoms exhibit diversity in size, shape, and composition, and their bonding force is irrelevant to the electronic state, which enriches the geometric complexity of colloidal matter. Finally, the authors summarize the emerging applications of these colloidal superstructures in nanophotonics, nanocatalysis, and nanomedicine, and outline the major challenge and future development. [ABSTRACT FROM AUTHOR]

Soft robots controlled by different actuation schemes are flourishing owing to the continued development of smart materials. However, most of the existing actuators are powered by a single source with predetermined mechanical properties and motion characteristics. Speed, power, and efficiency of these actuators are thus far inferior to their conventional counter parts. How to preload or alter the internal energy distribution and trigger rapid kinetic energy release combined with re‐programmability is a challenge and corresponding solutions will extend the practical use of soft robotics. Herein, a hybrid magnetically and photothermally responsive actuator with high degrees of freedom by using a coupled‐field manipulation strategy is proposed. As a proof‐of‐concept, a crab robot (CraBot) that contains uniformly distributed superparamagnetic particles and localized light‐responsive joints is produced. The spatial magnetic field exerts force on the robot, leading to real‐time adjustment of energy distribution within the entire robot. Meanwhile, the focused light field enables selective deformation of specific joints, releasing the accumulated energy into kinetic energy of motion for quick actuation. The directional accumulation and addressable release of elastic energy enables the CraBot to walk efficiently with improved power and speed. Such a hybrid‐field manipulation strategy holds great promise for sophisticated actuation of soft robots. [ABSTRACT FROM AUTHOR]

Thin, lightweight micro‐diffractive optical elements (M‐DOEs) are of great significance to integrated optics. However, the narrow working bandwidth of M‐DOEs allows them to operate only at specific wavelengths. Existing solutions require multiple components assembly, which is difficult to implement in an integrated system. Here, a general designing and processing scheme of an optofluidic‐integrated broad‐bandwidth M‐DOE is reported, achieving an average diffraction efficiency of over 84% across the entire visible band (406–824 nm). As a proof‐of‐concept, a wideband operating micro‐diffractive lens and orbital angular momentum beam micro‐generator are demonstrated. This strategy provides a common protocol for various broad‐bandwidth M‐DOEs operating in integrated optical systems. [ABSTRACT FROM AUTHOR]

Comprehensive understanding of the interactions between excited states with spin‐valley polarizations is crucial for the applications of monolayer 2D transition metal dichalcogenides (TMDs) in spin‐valleytronics. Here, by broadband femtosecond transient absorption spectroscopy with circularly polarized pump/probe lights, a systematic investigation on the many‐body interactions of band‐edge valley excitons in monolayer MoS2 is performed, where intravalley coherent coupling processes are directly observed at room temperature. Namely, when the intravalley mixing states in the superposition region of A‐exciton and B‐exciton states are excited, there is an intravalley coherent coupling between A‐exciton and B‐exciton in K valley (or A′‐exciton and B′‐exciton in K′ valley) with an oscillation frequency of ≈7–8 THz, rather than the intervalley excitonic coupling in general. The findings elucidate intravalley mixing and coherent oscillations in valley excitons of monolayer TMDs at room temperature, which can give insight into the many‐body coupling mechanisms of excited valley excitons in 2D TMDs. [ABSTRACT FROM AUTHOR]

Nitrogen-vacancy (NV) color centers in diamonds with narrow optical linewidths are commonly used as solid-state single-photon sources that emit indistinguishable photons. However, NV color centers prepared using ion implantation typically have large optical linewidths of over 100 MHz. Herein, we used the femtosecond laser direct writing (FsLDW) technique to prepare single NV color centers in diamond with a narrow optical linewidth of 13.05 ± 0.2 MHz and a long decoherence time of 445 ± 27.6 μs. In addition, the density functional theory was adopted to establish calculation models and illustrate why single NV color centers prepared by FsLDW have narrower linewidths compared to those of the ion implantation method. Thus, this study provides an effective reference for the preparation of narrow-linewidth single-color centers in diamonds and other wide-gap crystals. [ABSTRACT FROM AUTHOR]

Color centers, optically active defects within solids, are vital for leading quantum information technologies such as quantum computing and quantum sensing. An essential prerequisite for realizing scalable quantum architectures is the ability to create quantum emitters deterministically. In the last decades, significant efforts have been devoted to selectively generating color centers. One of the most used methods is high‐energy ion implantation. However, this method usually causes extended lattice damage along the entire trajectory because of ions bombardment. Moreover, the position depth of color centers is also limited by the ions penetrate length in crystals. The direct laser‐writing (DLW) technique has recently emerged as a powerful tool to create color centers in solid‐state materials. It can define color centers at arbitrary depths inside the substrate and operate at the ambient environment, therefore, providing a feasible 3D fabrication method for integrated quantum photonics. Here, recent advancements of laser writing of color centers in solid‐state materials are reviewed, from bulk crystals, such as diamond and silicon carbide, to nanostructures, involving single‐walled carbon nanotubes, 2D layered materials, and quantum dots. [ABSTRACT FROM AUTHOR]

Photonic spin‐orbit interactions (PSOIs) in nanostructures have attracted much interest in nanophotonics, which provide a new paradigm to enhance light‐matter interactions and engineer the wavefronts of light on demand at the nanoscale. Many striking phenomena and functionalities, such as the photonic (quantum) spin‐Hall effect and the spin‐vortex conversion, have been demonstrated. Besides their underlying physics and manifestations, the experimental probing and imaging of PSOIs are also of great importance and highly demanded in not only the fundamental research but also the development of emerging PSOI technologies. Hence, in this review, the state‐of‐the‐art studies on the experimental observations and detections of PSOIs are systematically reviewed, including both the far‐field and near‐field methods. The respective advantages and difficulties of each method are stated and analyzed. The perspectives in probing PSOIs are also discussed. [ABSTRACT FROM AUTHOR]

Exciton related processes in two-dimensional (2D) transition metal dichalcogenides (TMDCs) play important roles in their optoelectronic applications. In this work, through broadband transient absorption spectroscopy, the electronic band structure evolution, exciton energy shifting dynamics and power-dependence spectral characteristics of WSe2 layers, including monolayer, bilayer, tri-layer and bulk WSe2 under 400 nm and 800 nm excitations are investigated. Particularly, under 400 nm excitation, due to the hot-exciton effect, the A-exciton energy shifting dynamics in WSe2 layers have been analysized in detail, where thicker WSe2 samples possess slower hot-exciton cooling lifetimes, and the exciton recombination approaches are affected by the band structure and interlayer interactions, in comparison with that under 800 nm excitation. The power-dependence spectral evolution in WSe2 layers suggests that the charged states like trions could be facilitated in tri-layer WSe2 (or thicker samples) at the same experimantal conditions. These findings in WSe2 layers could provide a deep insight into the hot-exciton related processes in 2D TMDCs from transient experiments ponit of view. [ABSTRACT FROM AUTHOR]

First-principles calculations reveal a Mexican-hat potential energy surface (PES) for two-dimensional (2D) In2Se3. This unique PES leads to a pseudo-centrosymmetric paraelectric β phase that resolves the current controversy between theory and experiment. We further show that while the α-to-β (ferroelectric-to-paraelectric) phase transition is fast and coherent, assisted by an in-plane shear phonon mode, a random distribution of the atoms in the trough of the PES acts as an entropy barrier against the reverse β-to-α transition. This will be the origin of the speed limitation of current In2Se3 ferroelectric devices. However, if one orders the β phase (due to the formation of in-plane ferroelectric domains), the reverse transition can take place within tens of picoseconds in the presence of a perpendicular electric field. Finally, the Mexican-hat PES is a general feature for the entire family of 2D III2-VI3 materials. Our finding offers a critical physical picture in controlling the ultrafast reversible phase transition in 2D In2Se3 and other III2-VI3 materials, which will benefit their practical industrial development for advanced ferroelectric devices. [ABSTRACT FROM AUTHOR]

Generalization of the concept of band topology from lower-dimensional to higher-dimensional (n > 3) physical systems is expected to introduce new bulk and boundary topological effects. However, theoretically predicted topological singularities in five-dimensional systems—Weyl surfaces and Yang monopoles—have either not been demonstrated in realistic physical systems or are limited to purely synthetic dimensions. We constructed a system possessing Yang monopoles and Weyl surfaces based on metamaterials with engineered electromagnetic properties, leading to the observation of several intriguing bulk and surface phenomena, such as linking of Weyl surfaces and surface Weyl arcs, via selected three-dimensional subspaces. The demonstrated photonic Weyl surfaces and Weyl arcs leverage the concept of higher-dimension topology to control the propagation of electromagnetic waves in artificially engineered photonic media. [ABSTRACT FROM AUTHOR]

Phase change memory (PCM) is an emerging non‐volatile data storage technology concerned by the semiconductor industry. To improve the performances, previous efforts have mainly focused on partially replacing or doping elements in the flagship Ge‐Sb‐Te (GST) alloy based on experimental "trial‐and‐error" methods. Here, the current largest scale PCM materials searching is reported, starting with 124 515 candidate materials, using a rational high‐throughput screening strategy consisting of criteria related to PCM characteristics. In the results, there are 158 candidates screened for PCM materials, of which ≈68% are not employed. By further analyses, including cohesive energy, bond angle analyses, and Born effective charge, there are 52 materials with properties similar to the GST system, including Ge2Bi2Te5, GeAs4Te7, GeAs2Te4, so on and other candidates that have not been reported, such as TlBiTe2, TlSbTe2, CdPb3Se4, etc. Compared with GST, materials with close cohesive energy include AgBiTe2, TlSbTe2, As2Te3, TlBiTe2, etc., indicating possible low power consumption. Through further melt‐quenching molecular dynamic calculation and structural/electronic analyses, Ge2Bi2Te5, CdPb3Se4, MnBi2Te4, and TlBiTe2 are found suitable for optical/electrical PCM applications, which further verifies the effectiveness of this strategy. The present study will accelerate the exploration and development of advanced PCM materials for current and future big‐data applications. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO), which has many oxygen functional groups, is a promising candidate for use in moisture‐responsive sensors and actuators due to the strong water–GO interaction and the ultrafast transport of water molecules within the stacked GO sheets. In the last 5 years, moisture‐responsive actuators based on GO have shown distinct advantages over other stimuli‐responsive materials and devices. Particularly, inspired by nature organisms, various moisture‐enabled soft robots have been successfully developed via rational assembly of the GO‐based actuators. Herein, the milestones in the development of moisture‐responsive soft robots based on GO are summarized. In addition, the working mechanisms, design principles, current achievement, and prospects are also comprehensively reviewed. In particular, the GO‐based soft robots are at the forefront of the advancement of automatable smart devices. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO), which has many oxygen functional groups, is a promising candidate for use in moisture‐responsive sensors and actuators due to the strong water–GO interaction and the ultrafast transport of water molecules within the stacked GO sheets. In the last 5 years, moisture‐responsive actuators based on GO have shown distinct advantages over other stimuli‐responsive materials and devices. Particularly, inspired by nature organisms, various moisture‐enabled soft robots have been successfully developed via rational assembly of the GO‐based actuators. Herein, the milestones in the development of moisture‐responsive soft robots based on GO are summarized. In addition, the working mechanisms, design principles, current achievement, and prospects are also comprehensively reviewed. In particular, the GO‐based soft robots are at the forefront of the advancement of automatable smart devices. [ABSTRACT FROM AUTHOR]

Organic single crystals are highly promising for applications in optoelectronic devices because of their higher mobility and thermal stability than amorphous thin films. Although white organic single crystals have been fabricated by the double-doped method and applied to realize white organic light‐emitting devices (WOLEDs), the unbalanced carrier transport properties of the unipolar crystals severely limit the device performance. Here, ambipolar white organic single crystals are obtained by using mixed p- and n-type molecules as an ambipolar host for the red and green dopants. The white crystal with balanced carrier transport and balanced blue, green, and red emission intensity was applied to the single-crystal WOLEDs. The highest brightness of 1956 cd m−2 and the current efficiency of 1.31 cd A−1 are achieved, which are the best performance of the single-crystal WOLEDs reported to date. A high color rendering index is obtained, which varies between 82 and 87 with increasing driving current. It is expectable that this strategy would support the practical applications of organic single crystal-based OLEDs. [ABSTRACT FROM AUTHOR]

Band renormalization effects play a significant role for two-dimensional (2D) materials in designing a device structure and customizing their optoelectronic performance. However, the intrinsic physical mechanism about the influence of these effects cannot be revealed by general steady-state studies. Here, band renormalization effects in organic superacid treated monolayer MoS2, untreated monolayer MoS2 and few-layer MoS2 are quantitatively analyzed by using broadband femtosecond transient absorption spectroscopy. In comparison with the untreated monolayer, organic superacid treated monolayer MoS2 maintains a direct bandgap structure with two thirds of carriers populated at K valley, even when the initial exciton density is as high as 2.05 × 1014 cm−2 (under 400 nm excitations). While for untreated monolayer and few-layer MoS2, many-particle induced band renormalizations lead to a stronger imbalance for the carrier population between K and Q valleys in k space, and the former experiences a direct-to-indirect bandgap transition when the initial exciton density exceeds 5.0 × 1013 cm−2 (under 400 nm excitations). Those many-particle induced band renormalization processes further suggest a band-structure-controlling method in practical 2D devices. [ABSTRACT FROM AUTHOR]

Direct light‐to‐work conversion enables remote actuation through a non‐contact manner, among which the photothermal Marangoni effect is significant for developing light‐driven robots because of the diversity of applicable photothermal materials and light sources, as well as the high energy conversion efficiency. However, the lack of nanotechnologies that enable flexible integration of advanced photothermal materials with actuators of complex configurations significantly restricts their practical applications. In this paper, laser‐induced graphene (LIG) tape is reported as stick‐on photothermal labels for developing light‐driven actuators based on the Marangoni effect. With the help of direct laser writing technology, graphene patterns with superior photothermal properties are prepared on the PI tape. The patterned LIG tape can be stuck on any desired objects and generates an asymmetric photothermal field under light irradiation, forming a photothermal Marangoni actuator. Additionally, the PI tape with LIG patterns can be folded into 3D origami actuators that permit photothermal Marangoni actuation including both translation and rotation. The graphene‐based photothermal Marangoni actuators feature biocompatibility, which is confirmed by MDA‐MB‐231 cells proliferation experiments. Owing to the excellent photothermal property of LIG patterns, the as‐produced photothermal actuators can be manipulated by a variety of light sources, holding great promise for developing light‐driven soft robots. [ABSTRACT FROM AUTHOR]

Carrier mobility is one of the key issues for applications of organic semiconductors in electronic and optoelectronic devices. Organic single crystals possess much higher carrier mobility compared to amorphous films. However, unipolar properties with unbalanced hole and electron transporting ability have been a bottleneck for the high performance of organic single crystal‐based devices. Here, well‐balanced ambipolar organic single crystals are developed by mixing of n‐ and p‐type molecules with maintained single‐crystalline structures. Carrier mobility of the ambipolar single crystals is manipulated by tuning the mixing ratio, and nearly equal hole and electron mobility can be achieved. Highly efficient single crystal‐based organic light‐emitting devices (OLEDs) are demonstrated by employing the ambipolar crystals as the mixed host for a red emitter pentacene to realize efficient exciton confinement and energy transfer within the emissive layer. As a result, maximum luminance of 5467 cd m−2 and current efficiency of 2.82 cd A−1 are achieved, which represents, to the best of the authors' knowledge, the record performance for the organic single crystal‐based OLEDs to date. The strategy to manipulate the charge‐transport properties of the organic single crystals in this work represents a significant step toward practical applications of the organic single crystals in optoelectronics. [ABSTRACT FROM AUTHOR]

In recent years, orbital angular momentum (OAM) beams and their generation methods have drawn increasing interest. Generating multiple OAMs in a three-dimensional space simply and efficiently is meaningful and challenging. Herein, we proposed an integrated multi-OAM generator based on the independent controlling phase division. Realized through the two-photon additive manufacturing, the device possesses a continuous surface with a diameter of 100 μm. Using the generator, arbitrary OAM modes were demonstrated, including the axial position, the number of topological charges, and the direction of rotation. The unique optical characteristics were mutually verified experimentally and through simulation. Vortex beams carrying multiple OAMs will provide more degrees of freedom to manipulate light for exciting applications such as optical communications, micromanipulation, and quantum optics. [ABSTRACT FROM AUTHOR]

Micro‐ring resonators are widely used in many fields due to their compact structure, high integration, and rich functions. In recent years, perovskite materials have been widely concerned because of their superior properties and various shapes of perovskite‐based optical resonators have been achieved. Despite the excellent photoelectric properties of perovskite materials, it is difficult to realize micro‐ring resonators based on perovskite materials due to its tendency to crystallize into cubic structures. Here, this problem is solved by a microstructure edge‐guided crystallization method to fabricate shape‐designable and size‐tunable methylammonium lead bromide (MAPbBr3) micro‐ring resonator arrays with high performance. [ABSTRACT FROM AUTHOR]

Organic light‐emitting devices on fabrics (Fa‐OLEDs) are outstanding candidates for high‐quality wearable displays. High flexibility and conformality to clothes deformations are required for Fa‐OLEDs to keep wearing comfort during body movement. However, it is a great challenge to realize an ultrathin planarization layer with ultrasmooth surface simultaneously on the rough surface of fabrics for Fa‐OLEDs fabrication. Here, a template‐stripping process is employed to fabricate both ultrathin and ultrasmooth planarization layers for highly flexible and efficient Fa‐OLEDs. The thickness of the planarization layer is as small as 3 µm while its surface roughness is only 0.6 nm. The planarization process is insensitive to the textures and morphology of fabrics. As a result, the Fa‐OLEDs show excellent electroluminescent performance and flexibility. The maximum current efficiency of 78 cd A−1 is comparable with that of the conventional planar devices. The variation of current efficiency is as small as 8% after 1000 times of bending with 1 mm bending radius, which is the best bending stability of the flexible Fa‐OLEDs reported to date. The Fa‐OLEDs are successfully used as conformal wearable displays by sewing on clothes and keep working well with a series of arm movements. [ABSTRACT FROM AUTHOR]

Graphene-based actuators featuring fast and reversible deformation under various external stimuli are promising for soft robotics. However, these bimorph actuators are incapable of complex and programmable 3D deformation, which limits their practical application. Here, inspired from the collective coupling and coordination of living cells, we fabricated a moisture-responsive graphene actuator swarm that has programmable shape-changing capability by programming the SU-8 patterns underneath. To get better control over the deformation, we fabricated SU-8 micropattern arrays with specific geometries and orientations on a continuous graphene oxide film, forming a swarm of bimorph actuators. In this way, predictable and complex deformations, including bending, twisting, coiling, asymmetric bending, 3D folding, and combinations of these, have been achieved due to the collective coupling and coordination of the actuator swarm. This work proposes a new way to program the deformation of bilayer actuators, expanding the capabilities of existing bimorph actuators for applications in various smart devices. [ABSTRACT FROM AUTHOR]

Defects play a central role in controlling the electronic properties of two‐dimensional (2D) materials and realizing the industrialization of 2D electronics. However, the evaluation of charged defects in 2D materials within first‐principles calculation is very challenging and has triggered a recent development of the WLZ (Wang, Li, Zhang) extrapolation method. This method lays the foundation of the theoretical evaluation of energies of charged defects in 2D materials within the first‐principles framework. Herein, the vital role of defects for advancing 2D electronics is discussed, followed by an introduction of the fundamentals of the WLZ extrapolation method. The ionization energies (IEs) obtained by this method for defects in various 2D semiconductors are then reviewed and summarized. Finally, the unique defect physics in 2D dimensions including the dielectric environment effects, defect ionization process, and carrier transport mechanism captured with the WLZ extrapolation method are presented. As an efficient and reasonable evaluation of charged defects in 2D materials for nanoelectronics and other emerging applications, this work can be of benefit to the community. [ABSTRACT FROM AUTHOR]