The GHz burst mode femtosecond (fs) laser pulses have attracted considerable attention because they can perform better quality and higher efficiency ablation compared to the conventional irradiation scheme of fs pulses (single-pulse mode). Recently, we have demonstrated that the GHz burst mode fs laser pulses can create two-dimensional (2D) periodic surface structures (LIPSS) on Si surfaces. In this paper, we extend the GHz burst mode fs laser processing to form LIPSS on Ti plates. Our aim was to further investigate the more detailed mechanism and explore practical applications. Although the material characteristics of Ti are significantly different from Si, the GHz burst mode fs laser pulses can also create 2D-LIPSS. Then, mesenchymal stem cells cultured on the formed 2D-LIPSS were found to exhibit different behavior on 1D-LIPSS as compared with bare Ti surfaces.
In the last several years, femtosecond laser processing using GHz burst mode, which consists of the ultrashort laser pulse (intra-pulse) trains with the pulse-to-pulse interval of several hundred ps, has attracted much attention, as it can achieve higher-processing quality with enhanced processing efficiency than the conventional femtosecond laser irradiation scheme (single-pulse mode). However, most of the research using the GHz burst mode was aimed at ablation. In this study, we extend the GHz burst mode femtosecond laser processing to the formation of laser-induced periodic surface structures (LIPSS) to explore the possibility of novel nanostructuring, over the single-pulse mode.
Laser-induced near-field effect concentrates the laser energy to be enhanced on a localized area much smaller than the wavelength for nanoprocessing. Owing to the superhigh fabrication resolution, the laser near-field processing has been used for the surface nanostructuring to create photonic devices. The near-field processing is typically performed by using scanning optical microscope or scanning probe microscope combined with laser, while nano/microspheres provide the unique advantages of maskless, time-saving schemes.
In this paper, laser near-field reduction of metal ions assisted by silica spheres is presented for fabrication of plasmonic superlattices on silicon substrate, which can tune localized surface plasmonic resonance wavelengths from the visible to the near-infrared region by adjustment of the lattice periods. In the laser near-field reduction, the incident laser is tightly focused at the bottom side of the silica sphere to confine the reaction the in near-field.
Trace detection of bio-molecules with large molecular weight using surface-enhanced Raman scattering (SERS) method is still challenging, because the troublesome treatment of SERS substrate using coupling or cross-linking agents is required. In this paper, we apply liquid interface assisted SERS (LI-SERS) method, which provides unique features of collection and self-immobilization of analyte molecules on the SERS substrate, to realize the label-free trace detection of bio-molecules with detection limits of pM ~ fM. Specifically, DNA discrimination and quantitative detection of β-Amyloid (Aβ) in trace-concentration are demonstrated to illustrate the ultrahigh sensitivity and versatility of the LI-SERS method.
We have demonstrated UV laser photo-polymerization of elastic 2D/3D structures using UV-curable Polydimethylsiloxane (PDMS). In this technique, UV curable PDMS was locally polymerized to fabricate 1D and 2D single layer structures, as well as 3D multi-layer structures with resolution in micrometer-scale and structure dimension in millimeter-scale. In addition, a hybrid technique of aerosol jet printing followed by UV-LDW was developed to realize 2D patterning of thinner UV curable PDMS layer on free-form surface without solvents. In addition, 3D micro/nano processing for fabrication of 3D microfluidic surface-enhanced Raman spectroscopy (SERS) sensors will be presented as a subtractive process using photo-sensitive glass.
Hybrid femtosecond laser processing, which consists of femtosecond laser assisted wet etching, selective metallization, and laser induced periodic surface structure (LIPSS) formation, has enabled fabricating three-dimensional microfluidic surface enhanced Raman scattering (SERS) chips for highly sensitive sensing. To investigate the dependence of laser wavelength on the period of LIPSS which strongly affects the sensitivity of SERS substrate, two different wavelengths (515 nm and 1030 nm) of femtosecond laser beams have been employed. We observed the morphology of nanoripple on the metal layers under different laser parameters to optimize laser parameters, resulting in fabrication of homogenous LIPSS. The nanoripple with narrower groove (~40 nm) fabricated by 515 nm femtosecond laser induced stronger Raman scattering to achieve the SERS analytical enhancement factor exceeding 1 × 108. Furthermore, we introduced a novel method termed liquid-interface assisted SERS (LI-SERS) to realize extremely sensitive sensing, which achieved the detection limit of aM with analytical enhancement factor exceeding 1 × 1014 for R6G detection. We found the LI-SERS was able to locally aggregate the analyte molecules by Raman excitation laser irradiation at the interface of air and analyte solution containing the analytes in a microchannel. The aggregation forced the analyte molecules to enter into the “hot-spots” by Marangoni effect, which extraordinarily increased the SERS intensity. Furthermore, we employed LI-SERS to detect DNA bases which realized the DNA discrimination in the microfluidic channel by LI-SERS.
The purpose of this paper is to review laser trimming and precision control of alloy strip resistors, which is extensively applied for electronic vehicles and other power electronics. This mini review especially introduces the laser trimming of background, methodology, mechanism, influencing factor and main problem in details. The existing problems and the future development trend of laser trimming are also discussed.
Heavy metal pollution in developing countries urgently becomes a serious environmental issue due to rapid industrial development. Therefore, to detect the trace of heavy metal ions in water and food is very critical for environmental governance and human health. Surface-enhanced Raman scattering (SERS) based on electromagnetic field extraordinary enhanced in the proximity of metal nanostructures can generate strong Raman scatting, which is an effective method for trace detection. Most of SERS devices have been fabricated on the solid substrate surfaces, while detection of toxic substances in the close environment is much more preferable. In this paper, we propose the novel technique that can create 2D periodic metal (Cu-Ag) nanostructure inside 3D glass microfluidic channel by all-femtosecond-laser-processing. Specifically, after fabrication of 3D glass microfluidic channel by femtosecond laser assisted wet etching, Cu-Ag thin films are formed inside the microfluidic channel by femtosecond laser selective metallization. The thin films are then 2D nanostructured by femtosecond laser induced periodic surface structure (fs-LIPSS) formation. The dimension of nanostructured Cu-Ag film is quarter of laser wavelength. By testing with rhodamine 6G, we demonstrate the fabricated microchips can be used as a sensitive SERS device with an enhancement factor larger than 107 and 8.8% relative standard deviation. Consequently, the Real-time SERS detection in microfluidic chips was successfully demonstrated, which verified capability of the fabricated microchips as an excellent microfluidic SERS platform with ultrasensitive and uniform enhancement.
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