Abstract
The advanced direct laser printing of functional devices with tunable effective index is a key research topic in numerous emerging fields, especially in micro-/nano-optics, nanophotonics, and electronics. Photosensitized nanocomposites, consisting of high-index materials (e.g., titanium dioxide, TiO2) embedded in polymer matrix, are emerging as attractive platforms for advanced additive manufacturing. Unfortunately, in the currently applied techniques, the preparation of optically functionalized structures based on these photosensitized nanocomposites is still hampered by many issues like hydrolysis reaction, high-temperature calcinations, and, especially, the complexity of experimental procedures. In this study, we demonstrate a feasible strategy for fabricating micro-/nanostructures with a flexibly manipulated effective refractive index by incorporating TiO2 nanoparticles in the matrix of acrylate resin, i.e., TiO2-based photosensitized nanocomposites. It was found that the effective refractive index of nanocomposite can be easily tuned by altering the concentration of titanium dioxide nanoparticles in the monomer matrix. For TiO2 nanoparticle concentrations up to 30 wt%, the refractive index can be increased over 11.3% (i.e., altering from 1.50 of pure monomer to 1.67 at 532 nm). Based on such a photosensitized nanocomposite, the grating structures defined by femtosecond laser nanoprinting can offer vivid colors, ranging from crimson to magenta, as observed in the dark-field images. The minimum printing width and printing resolution are estimated at around 70 nm and 225 nm, indicating that the proposed strategy may pave the way for the production of versatile, scalable, and functionalized opto-devices with controllable refractive indices.
Highlights
As one of the most common strategies used in additive manufacturing, direct-laser printing (DLP), which employs the two-photon polymerization effect, has emerged as a promising technique for fabricating spatially resolved two-dimensional (2D) or threedimensional (3D) structures [1–5]
For the purpose of embedding the anatase TiO2 nanoparticle into the photoresin homogeneously to generate the photosensitized nanocomposite, the modified TiO2 nanoparticles/ethanol suspension was added into photosensitive resin with vigorous stirring for dispersion and ethanol evaporation, which imparted the photopolymerizable property to the TiO2 nanoparticles
Optical direct fabrications of TiO2-based 3D nano-architectures were achieved in a single attempt, which avoided the influence of the post-heat-treatment
Summary
As one of the most common strategies used in additive manufacturing, direct-laser printing (DLP), which employs the two-photon polymerization effect, has emerged as a promising technique for fabricating spatially resolved two-dimensional (2D) or threedimensional (3D) structures [1–5]. Functional photosensitized nanocomposites incorporating large-index titanium dioxide (TiO2 ) in photoresin matrix are regarded as beneficial material candidates for the fabrication of micro-/nano-architectures with spatially varied optical response (e.g., scattering amplitude, phase, and polarization) in the visible and near-infrared range [16,24]. An effective refractive index of TiO2 -based nanocomposite can be obtained as high as 2.3, close to the value of crystal phase [15], the post-heat-treatment may cause undesired structural shrinking [30] and poor adhesion between the sample and the substrate, which may lead to unwanted optical functionalities. The tuning range of the refractive index still needs to be improved beyond the order of 0.01 in this method
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