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Control of short-pulsed laser induced periodic surface structures with machining -picosecond laser nanotexturing with magnetic abrasive finishing-
摘要： An active area of research is the altering of surface functions (e.g., wettability and cell adhesion) by controlling fine surface structures such as laser-induced periodic surface structures (LIPSS). It has been found that micrometer-scale grooving (produced, for example, using ultraprecision cutting) followed by short-pulsed laser irradiation can result in efficient LIPSS coverage of a large area. However, micrometer-scale grooves can remain on the surface after short-pulsed laser irradiation. In this paper, to clarify the phenomenon and processing principle of groove-assisted short-pulsed laser irradiation, a finite-difference time-domain simulation is developed and experiments are conducted using 304 stainless steel and nickel-phosphorus (Ni–P) plating layer substrates. The use of magnetic abrasive finishing (MAF) is proposed for fabricating sub-micrometer-deep straight grooves with various peak-to-peak distances (pitch length) prior to the short-pulsed-laser irradiation. The subsequent short-pulsed-laser irradiation produces sub-micrometer-deep straight structures superimposed on the MAF-produced surface. While the pattern and depth of LIPSS are influenced by the groove depth made by MAF prior to the short-pulsed laser irradiation, the pitch length of LIPSS is dependent on the laser wavelength. This demonstrates the ability of MAF to produce grooves that guide the LIPSS and the efficacy of the developed method for fabricating fine LIPSS. The geometry of the sub-micrometer deep grooves—made prior to the short-pulsed laser irradiation—is the dominant factor in determining the pattern and geometry of the LIPSS.
关键词： Straight sub-micrometer groove,Surface roughness,Magnetic abrasive finishing,Short-pulsed laser
更新于2025-09-12 10:27:22
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Holey metasurface prism for the reduction of the dispersion of gap waveguide leaky-wave antennas
摘要： Leaky-wave antennas (LWA) are dispersive, meaning that the direction of maximum radiation is a function of frequency. This behavior, called “beam squinting effect” can be reduced by introducing a dispersive metamaterial prism. In this paper a holey metasurface prism is combined with a leaky-wave antenna in gap waveguide technology. The dispersion characteristics of the hole unit cell are studied in order to achieve the reduction of the main beam steering aiming to ±1o or less variation. A prototype designed at the Ka band is measured and compared with the simulation results.
关键词： groove gap waveguide,leaky-wave antenna,metasurface prism,dispersive radiation pattern
更新于2025-09-12 10:27:22
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Design of a Compact 3D Metal Printed Ka-band Waveguide Polarizer
摘要： This letter presents design, development and characterization of compact wide band 3D printed circular waveguide based polarizer operating in Ka-band (28-34 GHz). The polarizer structure is investigated using fundamental and higher order modes and based on which a simplified equivalent structure is derived giving physical insight into its mechanism of operation. The design consists of a pair of radially opposite grooves inside a circular waveguide and excited using a coaxial probe which makes the design simple and highly compact as compared to other conventional circular polarizers. The design is compared with other existing waveguide based polarizers in terms of electrical and physical parameters. Fabrication is done using high resolution direct metal aluminum 3D metal printing. The measured axial ratio is better than 3 dB over the frequency band. The design simplicity makes it attractive for application in millimeter wave frequencies and beyond.
关键词： polarizers,septum,waveguide,ridge waveguides,groove,Circular polarization
更新于2025-09-11 14:15:04
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DNA binding, prominent photonuclease activity and antibacterial PDT of cobalt(II) complexes of phenanthroline based photosensitizers
摘要： The chemistry of Co(II) complexes showing efficient light induced DNA cleavage activity, binding propensity to calf thymus DNA and antibacterial PDT is summarized in this article. Complexes of formulation [Co(mqt)(B)2]ClO4 1–3 where mqt is 4-methylquinoline-2-thiol and B is N,N-donor heterocyclic base, viz. 1,10-phenanthroline (phen 1), dipyrido[3,2-d:20,30-f]quinoxaline (dpq 2) and dipyrido[3,2-a:20,30-c]phenazine (dppz 3) have been prepared and characterized. The DNA-binding behaviors of these three complexes were explored by absorption spectra, viscosity measurements and thermal denaturation studies. The DNA binding constants for complexes 1, 2 and 3 were determined to be 1.6 (cid:2) 103 M(cid:3)1, 1.1 (cid:2) 104 M(cid:3)1 and 6.4 (cid:2) 104 M(cid:3)1 respectively. The experimental results suggest that these complexes interact with DNA through groove binding mode. The complexes show significant photocleavage of supercoiled (SC) DNA proceeds via a type-II process forming singlet oxygen as the reactive species. Antimicrobial photodynamic therapy was studied using photodynamic antimicrobial chemotherapy (PACT) assay against E. coli and all complexes exhibited significant reduction in bacterial growth on photoirradiation.
关键词： singlet oxygen,photocleavage,photoirradiation,Groove binding
更新于2025-09-11 14:15:04
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Nanoscale groove textured β-Ga <sub/>2</sub> O <sub/>3</sub> by room temperature inverse metal-assisted chemical etching and photodiodes with enhanced responsivity
摘要： β-Ga2O3 is an emerging wide band-gap semiconductor that holds great promise for next generation power electronics and optoelectronics. β-Ga2O3 based ultraviolet photodetectors have been the subject of active research for the last few years. However, no micro and nanostructure surface texturing has been demonstrated for efficient light management in β-Ga2O3 optoelectronic applications yet. We hereby present nanoscale groove textured β-Ga2O3 metal-semiconductor-metal photodiodes, enabled by the unique metal-assisted chemical etching (MacEtch) method at room temperature in liquid. Although the textured surface stoichiometry shows ～10% oxygen deficiency which results in a reduced Schottky barrier height and increased dark current, clear enhancement of the responsivity is demonstrated, compared to the planar untreated surface. The realization of MacEtch’s applicability to β-Ga2O3 opens the door for producing more sophisticated device structures for this material, without resorting to conventional dry etch and potential damage.
关键词： responsivity,β-Ga2O3,nanoscale groove textured,photodiodes,metal-assisted chemical etching
更新于2025-09-10 09:29:36