Here, we applied direct laser-induced periodic surface structuring to drive the phase transition of amorphous silicon (a-Si) into nanocrystalline (nc) Si imprinted as regular arrangement of Si ...nanopillars passivated with a SiO
2
layer. By varying the laser beam scanning speed at a fixed pulse energy, we successfully tailored the resulting unique surface morphology of the formed LIPSSs that change from ordered arrangement of conical protrusions to highly uniform surface gratings, where sub-wavelength scale ripples decorate the valleys between near-wavelength scale ridges. Along with the surface morphology, the nc-Si/SiO
2
volume ratio can also be controlled
via
laser processing parameters allowing the tailoring of the optical properties of the produced textured surfaces to achieve anti-reflection performance or partial transmission in the visible spectral range. Diverse hierarchical LIPSSs can be fabricated and replicated over large-scale areas opening a pathway for various applications including optical sensors, nanoscale temperature management, and solar light harvesting. By taking advantage of good wettability, enlarged surface area and remarkable light-trapping characteristics of the produced hierarchical morphologies, we demonstrated the first LIPSS-based surface enhanced fluorescent sensor that allowed the identification of metal cations providing a sub-nM detection limit unachievable by conventional fluorescence measurements in solutions.
Unique hierarchical laser-induced periodic surface structures (LIPSSs) enable the detection of metal ions at sub-nM concentrations
via
surface-enhanced fluorescence.
Gold nanostructures consisting of nanoblocks separated by a few nanometer‐wide gaps were fabricated, and found to exhibit strong photoluminescence due to enhancement of the optical near‐field ...localized in the nanogaps. The fabricated structures demonstrate a nanostructured metallic material capable of efficient photoluminescence, whose efficiency can be adjusted by tailoring the nanogap width.
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•Direct femtosecond laser printing can be used to produce IR resonant nanoantenna arrays.•Resonant wavelength of nanoantenna arrays scales with the plasmon running distance.•Tuning of ...the resonance wavelength is achieved by varying nanoantenna shape and array period.•Femtosecond printing can be used to produce fully alloyed plasmonic nanoantennas.
We report on the application of direct femtosecond laser printing for manufacturing periodic nanoantenna structures with various geometry and period, printed on pure or alloyed noble metal films over a silica substrate. By varying applied pulse energy, we have realised a wide range of possible morphologies, from smooth nano-bumps to protruding nanojets with up to 1 μm height, and finally to through microholes. Using several pulse energy levels, we have printed periodic nanojet arrays with periods from 1.75 to 4 μm, and measured their IR reflection spectra. The resonance frequency and magnitude of the resulting absorbance were found to essentially depend on both the periodicity of the arrays and nanojet geometry. We explain these observations by considering nanojet-assisted plasmon excitation running along the nanojets and along the surface, and found a convincing agreement to the experiments. To this end, we have shown that the reported approach is suitable for designing structures with distinct IR resonances, tunable over a range of at least 2–6 μm. Finally, we have also applied direct laser printing to a variety of noble metal alloys, involving gold, silver and palladium in various combinations and compositions, and showed that nanojets can be reliably printed for such alloys, preserving their chemical composition and its homogeneous volumetric distribution.
Femtosecond laser fabricated surface nanograting structures, referred to as ripples, are proposed as efficient substrates for surface‐enhanced Raman scattering (SERS). Ripple substrates show order of ...magnitude higher sensitivity and superior reproducibility as compared to lithographically made commercial SERS sensing substrates. It is demonstrated that the SERS intensity from ripple substrates scales with the thickness of the Au coating. Ag coating on sapphire ripples showed > 2000 times higher sensitivity as compared to the same coating on the flat sapphire surface. The period, duty cycle and aspect ratio of the ripple textures can be adjusted by laser ablation conditions, which could be used for plasmon resonance tuning.
Femtosecond laser fabricated surface nanograting structures, referred to as ripples, are proposed as efficient substrates for surface‐enhanced Raman scattering (SERS). Ripple substrates show order of magnitude higher sensitivity and superior reproducibility as compared to lithographically made commercial SERS sensing substrates. It is demonstrated that the SERS intensity from ripple substrates scales with the thickness of the Au coating.
We demonstrate the fabrication of plasmonic sensors that comprise gold nanopillar arrays exhibiting high surface areas, and narrow gaps, through self-assembly of amphiphilic diblock copolymer ...micelles on silicon substrates. Silicon nanopillars with high integrity over arbitrary large areas are obtained using copolymer micelles as lithographic templates. The gaps between metal features are controlled by varying the thickness of the evaporated gold. The resulting gold metal nanopillar arrays exhibit an engineered surface topography, together with uniform and controlled separations down to sub-10 nm suitable for highly sensitive detection of molecular analytes by Surface Enhanced Raman Spectroscopy (SERS). The significance of the approach is demonstrated through the control exercised at each step, including template preparation and pattern-transfer steps. The approach is a promising means to address trade-offs between resolutions, throughput, and performance in the fabrication of nanoplasmonic assemblies for sensing applications.
All-dielectric resonant micro- and nano-structures made of high-index dielectrics have recently emerged as a promising surface-enhanced Raman scattering (SERS) platform which can complement or ...potentially replace the metal-based counterparts in routine sensing measurements. These unique structures combine the highly-tunable optical response and high field enhancement with the non-invasiveness, i.e. chemically non-perturbing the analyte, simple chemical modification and recyclability. Meanwhile, commercially competitive fabrication technologies for mass production of such structures are still missing. Here, we attest a chemically inert black silicon (b-Si) substrate consisting of randomly-arranged spiky Mie resonators for a true non-invasive (chemically non-perturbing) SERS identification of the molecular fingerprints at low concentrations. Based on the comparative in situ SERS tracking of the para-aminothiophenol (PATP)-to-4,4'-dimercaptoazobenzene (DMAB) catalytic conversion on the bare and metal-coated b-Si, we justify the applicability of the metal-free b-Si for ultra-sensitive non-invasive SERS detection at a concentration level as low as 10-6 M. We performed supporting finite-difference time-domain (FDTD) calculations to reveal the electromagnetic enhancement provided by an isolated spiky Si resonator in the visible spectral range. Additional comparative SERS studies of the PATP-to-DMAB conversion performed with a chemically active bare black copper oxide (b-CuO) substrate as well as SERS detection of the slow daylight-driven PATP-to-DMAB catalytic conversion in the aqueous methanol solution loaded with colloidal silver nanoparticles (Ag NPs) confirm the non-invasive SERS performance of the all-dielectric crystalline b-Si substrate. A proposed SERS substrate can be fabricated using the easy-to-implement scalable technology of plasma etching amenable on substrate areas over 10 × 10 cm2 making such inexpensive all-dielectric substrates promising for routine SERS applications, where the non-invasiveness is of high importance.
Amorphous regions in sapphire with sub‐micrometer 3D resolution have been produced at the focus of a single femtosecond laser pulse. Crystalline‐ to‐amorphous and amorphous‐to‐polycrystalline ...transitions (crystalline and amorphous regions are marked C and A in the HRTEM image) are induced by single‐ and multi‐pulse irradiation, respectively. The wet‐etching selectivity for the amorphous phase is significantly greater than that for the crystalline phase in aqueous HF.
Confined microexplosion produced by a tightly focused fs-laser pulse inside transparent material proved to be an efficient and inexpensive method for achieving high energy density up to several MJ ...per cm3 in the laboratory table-top experiments. First studies already confirmed the generation of TPa-range pressure, the formation of novel super-dense material phases and revealed an unexpected phenomenon of spatial separation of ions with different masses in hot non-equilibrium plasma of confined microexplosion. In this paper, we show that the intense focused pulse propagation accompanied by a gradual increase of ionization nonlinearity changes the profile and spectrum of the pulse. We demonstrate that the motion of the ionization front in the direction opposite to the pulse propagation reduces the absorbed energy density. The voids in our experiments with fused silica produced by the microexplosion-generated pressure above Young's modulus indicate, however, that laser fluence up to 50 times above the ionization threshold is effectively absorbed in the bulk of the material. The analysis shows that the ion separation is enhanced in the non-ideal plasma of microexplosion. These findings open new avenues for the studies of high-pressure material transformations and warm dense matter conditions by confined microexplosion produced by intense fs-laser.
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