Buckling polystyrene beads with light

Synthetic Strategies for Polymer Particles with Surface Concavities

Over the past decade or so, there has been increasing interest in the synthesis of polymer particles with surface concavities, which mainly include golf ball-like, dimpled and surface-wrinkled polymer particles. Such syntheses generally can be classified into direct polymerization and post-treatment on preformed polymer particles. This review aims to provide an overview of the synthetic strategies of such particles. Some selected examples are given to present the formation mechanisms of the surface concavities. The applications and future development of these concave polymer particles are also briefly discussed. This article is protected by copyright. All rights reserved.

Nanofabrication Techniques: Challenges and Future Prospects

Nanofabrication of functional micro/nano-features is becoming increasingly relevant in various electronic, photonic, energy, and biological devices globally. The development of these devices with special characteristics originates from the integration of low-cost and high-quality micro/nano-features into 3D-designs. Great progress has been achieved in recent years for the fabrication of micro/nanostructured based devices by using different imprinting techniques. The key problems are designing techniques/approaches with adequate resolution and consistency with specific materials. By considering optical device fabrication on the large-scale as a context, we discussed the considerations involved in product fabrication processes compatibility, the feature's functionality, and capability of bottom-up and top-down processes. This review summarizes the recent developments in these areas with an emphasis on established techniques for the micro/nano-fabrication of 3-dimensional structured devices on large-scale. Moreover, numerous potential applications and innovative products based on the large-scale are also demonstrated. Finally, prospects, challenges, and future directions for device fabrication are addressed precisely.

Optical-force-directed single-particle-based track etching in polystyrene films

The establishment of optical trapping theory by A Ashkin almost half a century ago led to the trapping and manipulation of micro-/nano-objects and atoms by laser beams, which is now applied in many fields. However, in a complex system where multi-physical effects interact synergistically, light-matter interaction becomes dynamic and complicated and is still poorly understood. Here, by utilising plasmonic heating, nanolithography of polystyrene (PS) films and nanomanipulation of gold nanoparticles are realised. We find that laser power and PS film thickness as well as particle shape strongly affect the etching behaviour of the PS films, which is a synergistic effect of photothermal ablation and optical forces. Theoretical calculations and simulations rationalise the proposed mechanism, which is also verified by experimental observation. This understanding not only sheds light on how the synergistic effect of photo-ablation and optical forces acts on the particles and polymer films, but also provides a guideline for light-directed single-particle-based nanolithography and nanomanipulation.

Plasmon-assisted nanojet lithography

The great barrier of optical diffraction significantly limits the resolution of photolithography and the manipulation of nano-objects by light. Here, through utilizing near-field enhancement and photothermal effects, we demonstrate the nanolithography of polystyrene (PS) films and self-jetting of gold nanoparticles (Au NPs), which happen simultaneously. This nanojet lithography creates subwavelength holes via the single step of laser irradiation. We find that the laser power input strongly affects the etching of PS films, as well as the movement of Au NPs, which is a synergic effect of photoablation (including both photothermal and photochemical aspects) and gas pushing. This facile approach not only generates polymer holes with sizes below the diffraction limit, but also provides an intriguing way to detach and move particles on surfaces via thermal jetting.

Elastic wave propagation in smooth and wrinkled stratified polymer films

Periodic materials with sub-micrometer characteristic length scale can provide means for control of propagation of hypersonic phonons. In addition to propagation stopbands for the acoustic phonons, distinct dispersive modes can reveal specific thermal and mechanical behavior under confinement. Here, we employ both experimental and theoretical methods to characterize the phonon dispersion relation (frequency versus wave vector). We employed Brillouin light scattering (BLS) spectroscopy to record the phonon dispersion in stratified multilayer polymer films. These films consist of 4-128 alternate polycarbonate (PC) and poly (methyl methacrylate) (PMMA) layers along and normal to the periodicity direction. The distinct direction-dependent phonon propagation was theoretically accounted for, by considering the polarization, frequency and intensity of the observed modes in the BLS spectra. Layer-guiding was also supported by the glass transition temperatures of the PC and PMMA layers. The number of phonon dispersion branches increased with the number of layers but only a few branches were observable by BLS. Introduction of an additional in-plane periodicity, through a permanent wrinkling of the smooth PC/PMMA films, had only subtle consequences in the phonon propagation. Using the frequencies of the periodicity induced modes and momentum conservation equation we were able to precisely back calculate the wrinkle periodicity. However, a wrinkling-induced acoustic stopband utilizing flexible layered materials is still a challenge.