Yanlei Hu

Fish scale inspired design of underwater superoleophobic microcone arrays by sucrose solution assisted femtosecond laser irradiation for multifunctional liquid manipulation

The preparation of superhydrophilic/superoleophilic/underwater superoleophobic surfaces is inspired by natural surfaces such as fish scales possessing hierarchical micro/nanostructures. In this paper, we report the assembly of self-organized hierarchical microcone arrays on a nickel surface by sucrose solution-assisted femtosecond laser irradiation. The processed surface is superhydrophilic (13.47°–4.01°), superoleophilic (7.45°–3.73°), and underwater superoleophobic (135.22°–166.16°) which are comparable to those of fish scales. The wettabilities of the processed surfaces are tunable by adjusting the mass ratio of sucrose to water and pulse energy to control the height (1.62–10.34 μm) and size (2.1–2.81 μm) of the microcones. Multifunctional liquid manipulation such as microdroplet transferring, static and dynamic storage, liquid transportation and mixing is demonstrated. Our proposed method features rapidness, simplicity and ease of large-area fabrication, which may find broader applications in many fields such as microfluidic devices, fluid microreactors, biomedicine, biomedical scaffolds, and chemical–biological sensors.

Laser printing hierarchical structures with the aid of controlled capillary-driven self-assembly

Significance We propose a strategy to realize designable hierarchical functional structures via laser printing capillary-assisted self-assembly (LPCS). Ultrafast laser printing is applied for building unit blocks and capillary force is finely tuned as driving force. Diverse structures are successfully fabricated by controlling the spatial arrangements, heights, diameters of pillars, and the evaporation process. The ability of these LPCS structures to selectively trap and release microobjects suggests enormous potential applications in the fields of chemistry, biomedicine, and microfluidic engineering. Capillary force is often regarded as detrimental because it may cause undesired distortion or even destruction to micro/nanostructures during a fabrication process, and thus many efforts have been made to eliminate its negative effects. From a different perspective, capillary force can be artfully used to construct specific complex architectures. Here, we propose a laser printing capillary-assisted self-assembly strategy for fabricating regular periodic structures. Microscale pillars are first produced by localized femtosecond laser polymerization and are subsequently assembled into periodic hierarchical architectures with the assistance of controlled capillary forces in an evaporating liquid. Spatial arrangements, pillar heights, and evaporation processes are readily tuned to achieve designable ordered assemblies with various geometries. Reversibility of the assembly is also revealed by breaking the balance between the intermolecular force and the elastic standing force. We further demonstrate the functionality of the hierarchical structures as a nontrivial tool for the selective trapping and releasing of microparticles, opening up a potential for the development of in situ transportation systems for microobjects.

High-efficiency fabrication of aspheric microlens arrays by holographic femtosecond laser-induced photopolymerization

Manufacture of aspheric microlens has always been technically challenging for conventional approaches due to their complex curved profile and tiny sizes. Two-photon polymerization is capable of producing arbitrary shape with high spatial resolution, apart from the disadvantage of ultra-low rate of yield resulting from point-by-point writing strategy. Here, we report parallel fabrication of aspheric microlens arrays (AMLAs) by taking advantage of holographic femtosecond laser direct-writing. The inherent constraints of the spatial light modulator are taken into consideration for achieving improved intensity uniformity and enhanced diffraction efficiency. Closely-packed AMLAs with designable optical parameters are readily fabricated with excellent optical performance.

Large-area one-step assembly of three-dimensional porous metal micro/nanocages by ethanol-assisted femtosecond laser irradiation for enhanced antireflection and hydrophobicity.

The capability to realize 2D-3D controllable metallic micro/nanostructures is of key importance for various fields such as plasmonics, electronics, bioscience, and chemistry due to unique properties such as electromagnetic field enhancement, catalysis, photoemission, and conductivity. However, most of the present techniques are limited to low-dimension (1D-2D), small area, or single function. Here we report the assembly of self-organized three-dimensional (3D) porous metal micro/nanocages arrays on nickel surface by ethanol-assisted femtosecond laser irradiation. The underlying formation mechanism was investigated by a series of femtosecond laser irradiation under exposure time from 5 to 30 ms. We also demonstrate the ability to control the size of micro/nanocage arrays from 0.8 to 2 μm by different laser pulse energy. This method features rapidness (∼10 min), simplicity (one-step process), and ease of large-area (4 cm(2) or more) fabrication. The 3D cagelike micro/nanostructures exhibit not only improved antireflection from 80% to 7% but also enhanced hydrophobicity from 98.5° to 142° without surface modification. This simple technique for 3D large-area controllable metal microstructures will find great potential applications in optoelectronics, physics, and chemistry.

High efficiency integration of three-dimensional functional microdevices inside a microfluidic chip by using femtosecond laser multifoci parallel microfabrication.

High efficiency fabrication and integration of three-dimension (3D) functional devices in Lab-on-a-chip systems are crucial for microfluidic applications. Here, a spatial light modulator (SLM)-based multifoci parallel femtosecond laser scanning technology was proposed to integrate microstructures inside a given ‘Y’ shape microchannel. The key novelty of our approach lies on rapidly integrating 3D microdevices inside a microchip for the first time, which significantly reduces the fabrication time. The high quality integration of various 2D-3D microstructures was ensured by quantitatively optimizing the experimental conditions including prebaking time, laser power and developing time. To verify the designable and versatile capability of this method for integrating functional 3D microdevices in microchannel, a series of microfilters with adjustable pore sizes from 12.2 μm to 6.7 μm were fabricated to demonstrate selective filtering of the polystyrene (PS) particles and cancer cells with different sizes. The filter can be cleaned by reversing the flow and reused for many times. This technology will advance the fabrication technique of 3D integrated microfluidic and optofluidic chips.

Two-photon polymerization of cylinder microstructures by femtosecond Bessel beams

In this work, we present an approach to modulate femtosecond laser beams into Bessel beams with a spatial light modulator (SLM) for two-photon polymerization applications. Bessel beams with different parameters are generated and annular optical fields are produced at the focal plane of the objective. Uniform cylinder microstructures are fabricated by a single illumination during a few seconds without stage translation. By modulating the holograms encoded on the SLM, the diameters of the fabricated annular structures can be flexibly controlled in a wide range with no need of changing the optical elements and realignment of the optical path.

Multifunctional ultrathin aluminum foil: oil/water separation and particle filtration

We present here a kind of novel multifunctional ultrathin aluminum foil which consists of large-area regular micropore arrays covered with nanostructures. These multiscale micro/nanostructures show underwater superoleophobic ability (contact angle > 150°) and oil/water separation function. The novel foils were realized by one-step femtosecond laser irradiation, which is a simple and promising method for preparing special micro/nanostructures due to its high precision, excellent controllability, one-step processing and compatible with various materials. In addition, the micropore arrayed aluminum foil also shows robust filtering performance for particles with different sizes, exhibiting multifunctional applications. This work provides a new way for the construction of aluminum foil-based micropore arrays which can be applied in high-efficiency oil/water separation, particle sorting, and other broader fields.

Two-photon-induced polarization-multiplexed and multilevel storage in photoisomeric copolymer film

We present a two-photon-induced polarization-multiplexed and multilevel data storage method with a bisazobenzene copolymer film. A polarization-adjustable femtosecond pulsed laser is used as writing beam to induce anisotropy, and the recorded information is retrieved by a CCD sensor from the film with corresponding polarized illumination. It is found that the optical axis of bisazobenzene molecules can be reoriented under two-photon excitation by the polarized femtosecond laser via a photoisomerization process. Polarization-multiplexed and multilevel storage is demonstrated by using this method. The capability to combine both advantages of these distinct techniques makes it a novel approach to obtain higher optical data density.

Biomimetic surfaces with anisotropic sliding wetting by energy-modulation femtosecond laser irradiation for enhanced water collection

Biological rice leaf surfaces show a distinct anisotropic sliding property by means of three-level macrogrooves and micro/nanostructures, and they have many potential applications in biomimetic cell movement control, water transportation, and microfluidic devices. However, fabricating artificial three-level biosurfaces with a controllable anisotropic sliding property by a simple and effective method remains a challenge. Herein, we report a simple method to prepare hierarchical groove structures (macro and micro/nano) on polydimethylsiloxane (PDMS) films using energy-modulation femtosecond laser scanning. The macrogrooves for anisotropic control were realized by larger-energy (>0.40 J cm−2) laser scanning, whereas the micro/nanostructures for superhydrophobic ability were fabricated by small-energy (0.08 J cm−2) laser scanning. The processed surface shows a sliding angle (SA) difference of 6° between the perpendicular and parallel directions, which is comparable to that of the natural rice leaf. To quantitatively investigate the anisotropic wettability, surfaces with a different period (100 to 600 μm) and height (30 to 100 μm) were systematically fabricated by adjusting the scanning space and pulse energy. Finally, the distinct ability of the dynamic water droplet anisotropic sliding and size-constrained fog deposition on the anisotropic biosurfaces was demonstrated. The collection efficiency of water on the anisotropic surface with a rotation of 5 and 10 degrees is four times and eighty times higher than that on an isotropic surface.

A rapid two-photon fabrication of tube array using an annular Fresnel lens

A rapid method of fabricating microscopic tubular structures via two-photon polymerization is presented. Novel Fresnel lens is designed and applied to modulate the light field into a uniform ring pattern with controllable diameters. Comparing with the conventional holographic processing method, Fresnel lens shows higher uniformity and better flexibility, while easier to generate. This versatile method provides a powerful solution to produce tube structure array within several seconds.