| Nanostructured materials are of great differences compared to bulk materials in optical absorption properties, and are of great value in the research and applications of many fields, such as energy, sensing, and novel materials. Owing to the rapid development of nanofabrication and optical investigation technologies, conventional materials show new values at nanoscale. In this thesis, we demonstrate our research work on the optical absorption properties of graphite nanostructures and gold nanoparticles, and the applications based on these materials, including broadband optical absorber and optical controlled micro artificial muscles.Firstly, we find that the graphite material with nanocone structured surface exhibit highly efficient broadband absorption. The nanocone structures provide smooth transition of effective refractive indices between the graphite substrate and the air, and thus guide incoming light into the substrate without strong reflection at the surface. Based on simulation analysis, we show the dependence of the absorption efficiency and the bandwidth of absorption on the structure parameters of the nanocones. Optical absorbers with structure thickness of only 1μm are experimentally fabricated by dry etch process using spin-coated gold nanoparticles. An average reflection level of 5% in the wavelength range of 450-1800nm is obtained.Secondly, we propose a graphite nanowire-nanocone composite structure for ultra-black optical absorber. The graphite nanowires at the top layer of the device, which have subwavelength diameters and low material filling factor, provide nearly perfect refractive index matching at the interface between the device and the air. The graphite nanocones at the bottom layer of the device efficiently absorb the light transmitted through the nanowires. The absorber is fabricated through a mask-free dry etch process, and shows an average total reflectance of only 0.7 ± 0.07% in the wavelength range of 500-1000 nm. Compared to previous ultra-thin carbon nanotube optical absorber, our absorber has half its thickness, and around 1/3 of its total reflectance at 1000 nm wavelength.Thirdly, we demonstrate facile optical manipulation of shape of colloidal microparticles made from liquid crystal elastomers. These particles are infiltrated with gold nanospheres with absorption peak at around 530 nm acting as heat transducers that allow for an efficient localized transfer of heat from a focused infrared 1064 nm laser beam to a submicrometer region within a microparticle. Photothermal control of ordering in the liquid crystal elastomer using scanned beams allows for a robust control of colloidal particles, enabling both reversible and irreversible changes of shape. This non-contact controlled micro artificial muscle can potentially be used in the applications of microfluid channel control. By dispersing these micro artificial muscle particles into liquid crystal hosts, we could investigate their interactions with different host materials. Locomotion is observed in the case of a thermotropic nematic liquid crystal host, and transformations of director structures are observed in the case of a lyotropic cholesteric liquid crystal host. These findings bridge the fields of liquid crystal solids and active colloids, may enable shape-controlled self-assembly of adaptive composites and light-driven micromachines. |
