Femtosecond laser direct writing of functional stimulus-responsive structures and applications

Diverse natural organisms possess stimulus-responsive structures to adapt to the surrounding environment.Inspired by nature,researchers have developed various smart stimulus-responsive structures with adjustable properties and functions to address the demands of ever-changing application environments that are becoming more intricate.Among many fabrication methods for stimulus-responsive structures,femtosecond laser direct writing(FsLDW)has received increasing attention because of its high precision,simplicity,true three-dimensional machining ability,and wide applicability to almost all materials.This paper systematically outlines state-of-the-art research on stimulus-responsive structures prepared by FsLDW.Based on the introduction of femtosecond laser-matter interaction and mainstream FsLDW-based manufacturing strategies,different stimulating factors that can trigger structural responses of prepared intelligent structures,such as magnetic field,light,temperature,pH,and humidity,are emphatically summarized.Various applications of functional structures with stimuli-responsive dynamic behaviors fabricated by FsLDW,as well as the present obstacles and forthcoming development opportunities,are discussed.

Encryption/decryption and microtarget capturing by pH-driven Janus microstructures fabricated by the same femtosecond laser printing parameters

Several natural organism can change shape under external stimuli. These natural phenomena have inspired a vast amount of research on exploration and implementation of reconfigurable shape transformation. The Janus structure is a promising approach to achieve shape transformation based on its heterogeneous chemical or physical properties on opposite sides.However, the heterogeneity is generally realized by multi-step processing, different materials,and/or different processing parameters. Here, we present a simple and flexible method of producing p H-sensitive Janus microactuators from a single material, using the same laser printing parameters. These microactuators exhibit reversible structural deformations with large bending angles of ~31°and fast response(~0.2 s) by changing the p H value of the aqueous environment. Benefited from the high flexibility of the laser printing technique and the spatial arrangements, pillar heights, and bending directions of microactuators are readily controlled,enabling a variety of switchable ordered patterns and complex petal-like structures on flat surfaces and inside microchannels. Finally, we explore the potential applications of this method in information encryption/decryption and microtarget capturing.

Review of photoacoustic imaging for microrobots tracking in vivo [Invited]

Microrobots-assisted drug delivery and surgery have been always in the spotlight and are highly anticipated to solve the challenges of cancer in situ treatment. These versatile small biomedical robots are expected to realize direct access to the tumor or disease site for precise treatment, which requires real-time and high-resolution in vivo tracking as feedback for the microrobots’ actuation and control. Among current biomedical imaging methods, photoacoustic imaging(PAI) is presenting its outstanding performances in the tracking of microrobots in the human body derived from its great advantages of excellent imaging resolution and contrast in deep tissue. In this review, we summarize the PAI techniques, imaging systems, and their biomedical applications in microrobots tracking in vitro and in vivo. From a robotic tracking perspective,we also provide some insight into the future of PAI technology in clinical applications.

Five-wavelength optical-resolution photoacoustic microscopy of blood and lymphatic vessels

Optical-resolution photoacoustic microscopy(OR-PAM)has been developed for anatomical,functional,and molecular imaging but usually requires multiple scanning for different contrasts.We present five-wavelength OR-PAM for simultaneous imaging of hemoglobin concentration,oxygen saturation,blood flow speed,and lymphatic vessels in single raster scanning.We develop a five-wavelength pulsed laser via stimulated Raman scattering.The five pulsed wavelengths,i.e.,532,545,558,570,and 620∕640 nm,are temporally separated by several hundreds of nanoseconds via different optical delays in fiber.Five photoacoustic images at these wavelengths are simultaneously acquired in a single scanning.The 532-and 620∕640-nm wavelengths are used to image the blood vessels and dye-labeled lymphatic vessels.The blood flow speed is measured by a dual-pulse method.The oxygen saturation is calculated and compensated for by the Grüneisen-relaxation effect.In vivo imaging of hemoglobin concentration,oxygen saturation,blood flow speed,and lymphatic vessels is demonstrated in preclinical applications of cancer detection,lymphatic clearance monitoring,and functional brain imaging.

Investigation of β-Ga2O3 films and β-Ga2O3/GaN heterostructures grown by metal organic chemical vapor deposition

In this work,(-201)β-Ga2O3 films are grown on GaN substrate by metal organic chemical vapor deposition(MOCVD).It is revealed that theβ-Ga2O3 film grown on GaN possesses superior crystal quality,material homogeneity and surface morphology than the results of common heteroepitaxialβ-Ga2O3 film based on sapphire substrate.Further,the relevance between the crystal quality of epitaxialβ-Ga2O3 film and theβ-Ga2O3/GaN interface behavior is investigated.Transmission electron microscopy result indicates that the interface atom refactoring phenomenon is beneficial to relieve the mismatch strain and improve the crystal quality of subsequentβ-Ga2O3 film.Moreover,the energy band structure ofβ-Ga2O3/GaN heterostructure grown by MOCVD is investigated by X-ray photoelectron spectroscopy and a large conduction band offset of 0.89 eV is obtained.The results in this work not only convincingly demonstrate the advantages ofβ-Ga2O3 films grown on GaN substrate,but also show the great application potential of MOCVDβ-Ga2O3/GaN heterostructures in microelectronic applications.

基于p-SnO帽层栅的高阈值增强型AlGaN/GaNHEMTs

目前,p-GaN帽层技术是实现增强型GaN基HEMT的主流商用技术,但Mg掺杂难激活以及刻蚀损伤等因素限制了器件性能的进一步提升,因此高性能、低成本的增强型帽层技术具有重要的研究意义.本文采用p型氧化亚锡(p-SnO)代替p-GaN作为栅帽层引入AlGaN/GaN HEMT,并通过Silvaco器件仿真和实验验证两方面系统研究了器件的电学性能.仿真结果显示,通过简单改变p-SnO的厚度(50-200 nm)或掺杂浓度(3×10^(17)-3×10^(18)cm^(-3)),可以实现器件阈值电压在0-10 V范围内连续可调,同时器件的漏极电流密度超过120 mA mm^(-1),栅击穿和器件击穿电压分别达到7.5和2470 V.在此基础上,我们实验制备了基于磁控溅射p-SnO帽层的AlGaN/GaN HEMT,未经优化的器件测得了1 V的阈值电压、4.2 V的栅击穿电压和420 V的器件击穿电压,证实了p-SnO薄膜作为增强型GaN基HEMT栅帽层的应用潜力,为进一步提升增强型AlGaN/GaN HEMT性能,同时降低成本奠定了基础.

Confocal visible/NIR photoacoustic microscopy of tumors with structural, functional, and nanoprobe contrasts

Distinguishing early-stage tumors from normal tissues is of great importance in cancer diagnosis.We report fiberbased confocal visible/near-infrared(NIR)optical-resolution photoacoustic microscopy that can image tumor microvasculature,oxygen saturation,and nanoprobes in a single scanning.We develop a cost-efficient single laser source that provides 532,558,and 1064 nm pulsed light with sub-microseconds wavelength switching time.Via dual-fiber illumination,we can focus the three beams to the same point.The optical and acoustic foci are confocally aligned to optimize the sensitivity.The visible and NIR wavelengths enable simultaneous tumor imaging with three different contrast modes.Results show obvious angiogenesis,significantly elevated oxygen saturation,and accumulated nanoparticles in the tumor regions,which offer comprehensive information to detect the tumor.This approach also allows us to identify feeding and draining vessels of the tumor and thus to determine local oxygen extraction fraction.In the tumor region,the oxygen extraction fraction significantly decreases along with tumor growth,which can also assist in tumor detection and staging.Fiber-based confocal visible/NIR photoacoustic microscopy offers a new tool for early detection of cancer.

Photo-induced anti-Markovnikov hydroalkylation of unactivated alkenes employing a dual-component initiator

Metal-free anti-Markovnikov hydroalkylation of unactivated alkenes with cyanoacetate has been developed,featuring the use of a dual-component initiator containing an organic photocatalyst and a radical precursor.When combined,the two components can undergo visible light-induced singleelectron transfer,and serve as a versatile and effective alkyl radical generator.