Antibiotic resistance is a global human health threat, causing routine treatments of bacterial infections to become increasingly difficult. The problem is exacerbated by biofilm formation by ...bacterial pathogens on the surfaces of indwelling medical and dental devices that facilitate high levels of tolerance to antibiotics. The development of new antibacterial nanostructured surfaces shows excellent prospects for application in medicine as next-generation biomaterials. The physico-mechanical interactions between these nanostructured surfaces and bacteria lead to bacterial killing or prevention of bacterial attachment and subsequent biofilm formation, and thus are promising in circumventing bacterial infections. This Review explores the impact of surface roughness on the nanoscale in preventing bacterial colonization of synthetic materials and categorizes the different mechanisms by which various surface nanopatterns exert the necessary physico-mechanical forces on the bacterial cell membrane that will ultimately result in cell death.
Research into the three-dimensional nanostructuring of photopolymers by ultrashort laser pulses has seen immense growth over the last decade. In this paper, we review the basic principles and the ...most important developments and applications of this technology. We discuss the mechanisms the linear and nonlinear light absorption at tight focusing conditions, and we present some typical laser writing conditions with numerical examples. The photochemistry of traditional and novel photopolymers together with strategies for their photosensitization for laser structuring by ultra-short pulses are discussed. We also discuss current and potential future applications in diverse fields such as metamaterials, plasmonics, micro-optics, and biomedical devices and implants.
Nanoscale surface texturing, drilling, cutting, and spatial sculpturing, which are essential for applications, including thin-film solar cells, photonic chips, antireflection, wettability, and ...friction drag reduction, require not only high accuracy in material processing, but also the capability of manufacturing in an atmospheric environment. Widely used focused ion beam (FIB) technology offers nanoscale precision, but is limited by the vacuum-working conditions; therefore, it is not applicable to industrial-scale samples such as ship hulls or biomaterials, e.g., cells and tissues. Here, we report an optical far-field-induced near-field breakdown (O-FIB) approach as an optical version of the conventional FIB technique, which allows direct nanowriting in air. The writing is initiated from nanoholes created by femtosecond-laser-induced multiphoton absorption, and its cutting "knife edge" is sharpened by the far-field-regulated enhancement of the optical near field. A spatial resolution of less than 20 nm (
/40, with
being the light wavelength) is readily achieved. O-FIB is empowered by the utilization of simple polarization control of the incident light to steer the nanogroove writing along the designed pattern. The universality of near-field enhancement and localization makes O-FIB applicable to various materials, and enables a large-area printing mode that is superior to conventional FIB processing.
Processing of materials by ultrashort laser pulses has evolved significantly over the last decade and is starting to reveal its scientific, technological and industrial potential. In ultrafast laser ...manufacturing, optical energy of tightly focused femtosecond or picosecond laser pulses can be delivered to precisely defined positions in the bulk of materials via two-/multi-photon excitation on a timescale much faster than thermal energy exchange between photoexcited electrons and lattice ions. Control of photo-ionization and thermal processes with the highest precision, inducing local photomodification in sub-100-nm-sized regions has been achieved. State-of-the-art ultrashort laser processing techniques exploit high 0.1-1 μm spatial resolution and almost unrestricted three-dimensional structuring capability. Adjustable pulse duration, spatiotemporal chirp, phase front tilt and polarization allow control of photomodification via uniquely wide parameter space. Mature opto-electrical/mechanical technologies have enabled laser processing speeds approaching meters-per-second, leading to a fast lab-to-fab transfer. The key aspects and latest achievements are reviewed with an emphasis on the fundamental relation between spatial resolution and total fabrication throughput. Emerging biomedical applications implementing micrometer feature precision over centimeter-scale scaffolds and photonic wire bonding in telecommunications are highlighted.
We analyze the localized surface plasmon resonance spectra of periodic square lattice arrays of gold nano-disks, and we describe numerically and experimentally the effect of disorder on resonance ...width, spectrum, and EM field enhancement in increasingly randomized patterns. The periodic structure shows a narrower and stronger extinction peak, conversely we observe an increase of up to (1-2)×10(2) times enhancement as the disorder is gradually introduced. This allows for simpler, lower resolution fabrication, cost-effective in light harvesting for solar cell and sensing applications. We show that dipole-dipole interactions contribute to diffract light parallel to the surface as a mean of long-range coupling between the nano-disks.
Thermo-optical properties of the nanodisc and metal hole array plasmonic perfect absorber (PPA) metasurfaces were designed and characterized at mid-infrared wavelengths. Both, radiation emitter and ...detector systems operating in various spectral domains are highly sought after for a diverse range of applications, one example being future sensor networks employed in the internet-of-things. Reciprocity of the absorbance and emittance is shown experimentally, i.e., the PPAs are demonstrated to follow Kirchhoff's law where the patterns exhibiting a strong optical absorption were found to be effective thermal emitters. Hence, the Kirchhoff's law is experimentally validated for the metasurfaces in the IR spectral domain where there is a lack of solutions for spectrally narrow-band emitters. The highest efficiency of radiation-to-heat and heat-to-radiation conversion was obtained for Au-Si-Au composite structures.
Detailed spectral analysis of radiation absorption and scattering behaviors of metasurfaces was carried out via finite-difference time-domain (FDTD) photonic simulations. It revealed that, for ...typical metal-insulator-metal (MIM) nanodisc metasurfaces, absorbance and scattering cross-sections exhibit a ratio of σ
/σ
= 1 at the absorption peak spectral position. This relationship was likewise found to limit the attainable photo-thermal conversion efficiency in experimental and application contexts. By increasing the absorption due to optical materials, such as Cr metal nano-films typically used as an adhesion layer, it is possible to control the total absorption efficiency η = σ
/σ
and to make it the dominant extinction mechanism. This guided the design of MIM metasurfaces tailored for near-perfect-absorption and emission of thermal radiation. We present the fabrication as well as the numerical and experimental spectral characterisation of such optical surfaces.
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