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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Fabrication of Tuned Lipss-Based Metallic Polarization Gratings
摘要： Surface nanostructuring has received increasing attention in recent years due to the wide range of applications in which it offers advantages. Particularly, Laser-Induced Periodic Surface Structures (LIPSS) have proven useful for surface functionalization [1]. LIPSS are periodic formations generated in most materials when irradiated with linearly polarized radiation. The orientation of these structures is directly linked to the polarization of the incident light, while other parameters of their morphology such as period and depth can be controlled with the number of pulses, fluence, wavelength and pulse duration of the incident light. Due to their periodic nature, LIPSS behave optically as nanogratings [2], which have been largely studied as polarization converters (or Polarization Gratings, PGs). PGs are structures that introduce a phase shift in the incident light, which produces a change in its polarization state [3]. Therefore, PGs have potential applications as reflective waveplates [4], showing advantages over transmission waveplates such as higher damage thresholds and a lower temporal dispersion of the pulse. So far, PGs have been fabricated with methods such as direct laser interference or lithography [5]. The main drawbacks of these methods include limited choice of periods for the generated structures or a complex and environmentally unfriendly fabrication process, which could be overcome by a fabrication method based on LIPSS. In order to fabricate LIPSS-based PGs, stainless steel samples were irradiated with a 800 nm femtosecond Ti:Sapphire laser. The laser was focused onto the surface of the sample through a cylindrical lens with a focal length of 10 cm. The sample was translated perpendicular to the laser beam with a mechanical stage at a constant speed, generating LIPSS in a large area of 5 mm x 5 mm in a few seconds. By varying the fluence of the beam and the speed of the stage, LIPSS with different parameters were fabricated. Topography of the samples were characterized with AFM and SEM (Fig. 1a) microscopes, and polarization conversion and reflectivity were examined with a polarimeter. Results show that a gradual change in LIPSS morphology is associated to a gradual change in the ellipticity of the laser beam (Fig. 1b). It is also observed that LIPSS geometry changes smoothly with processing parameters. Therefore, it is proven that LIPSS-based PGs can be fabricated experimentally, and that the properties of such PGs can be tuned changing the LIPSS geometry, as expected. These results are in good agreement with the performed FDTD simulations for different LIPSS morphologies.
关键词： Surface nanostructuring,Polarization Gratings,LIPSS,Polarization conversion,Femtosecond laser
更新于2025-09-12 10:27:22
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From statistic to deterministic nanostructures in fused silica induced by nanosecond laser radiation
摘要： The production of structures by laser machining below the diffraction limit is still a challenge. However, self-organization processes can be useful. The laser-induced self-organized modification of the shape of photolithographic produced chromium structures on fused silica as well as the structuring of the fused silica surface by nanosecond UV laser radiation was studied, respectively. Low fluence single pulse laser irradiation (? > 300 mJ/cm2) cause the formation from chromium squares to droplets due to the mass transport in the molten chromium film. This process is governed by the instability of the molten metal due to the surface tension driven liquid phase mass transport. For a chromium pattern size similar to the instability length two specific droplet distributions were found which are single droplets with a determined position near the centre of the original pattern or random distributed smaller droplets arranged circularly. Each of the metal patterns can be transferred into the fused silica by a multi-pulse irradiation. The experimental results can be simulated well for low fluences by sequential solving the heat and Navier-Stokes equation.
关键词： fused silica,nanostructuring,nanosecond laser,IPSM-LIFE
更新于2025-09-12 10:27:22
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Influence of processing parameters on characteristics of laser-induced periodic surface structures on steel and titanium
摘要： Laser-induced periodic surface structures (LIPSS) can appear due to interaction between polarized laser pulses and surface. They can be used to improve or change the surface functionality. Here, titanium and steel surfaces were irradiated by linearly polarized, 30-ps-laser pulses (wavelength of λ=1064 nm) and 45-ns-laser pulses (wavelength of λ=1060 nm), respectively. We investigated how pulse fluence, number of pulses, and pre-existing defects influence LIPSS formation and period. The results show that fluences lower than single-pulse fluence threshold for ablation lead to LIPSS with periods within 150-500 nm, while increased fluence results in larger spatial period between 800-1100 nm. A slight change in processing parameters can also result in different topographical and/or chemical characteristics of the top surface layer, making LIPSS undetectable by SEM.
关键词： laser nanostructuring,laser surface engineering,LIPSS,laser processing
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Three-Dimensional Laser Nanostructuring of Optical Crystals: Towards Nanophotonic-Engineered Solid-State-Media
摘要： Nanophotonics, where light control is achieved by means of subwavelength-structured media, are so far mostly fabricated by surface lithographic techniques. Inevitably, this dictates that all nanophotonic elements have planar geometry, and lay at (or close to) the surface of dissimilar material substrates. Planarity is an eminent design restriction against the three-dimensional nature of light propagation, and the use of diverse materials imposes limitations to device robustness against environmental factors, such as temperature changes, vibrations and stress. Regardless of these limitations, two “killer” applications of planar nanophotonics, photonic integrated circuits (PIC) (based on sub-μm waveguides and 2D photonic bandgap crystals) and optical metasurfaces (i.e. wavefront shaping devices based on subwavelength-structured wavelength-thick surfaces) are already revolutionizing the communications and sensing industries. Such devices are typically based on silicon (or silicon nitride) on lower index silicon dioxide, thus providing good compatibility with the semiconductor CMOS industry. Applying surface lithography or other methods to directly nanostructure dielectric optical materials in the three dimensions has however been out of reach, so far. As a result, the general fields of solid-state lasers and crystal optics still have a very weak connection to the field of nanophotonics. In fact, the use of crystals for either laser light generation or non-linear frequency conversion is fundamentally equal today as it was in 1960: a homogenous crystal is put inside an optical setup. We will show that crystals such as yttrium aluminum garnet (YAG) and sapphire can be nanostructured on the three dimensions within their volume, with feature sizes down to the 100 nm level and device footprints on the cm scale. To achieve this, we have discovered the possibility of applying ultrafast femtosecond laser processing followed by chemical etching, to produce three-dimensional nanopore arrays of arbitrary design [1]. We will show the first results and limitations of applying the technique in these two important solid-state crystals, and we will report on the first successful fabrication of YAG nanophotonic engineered crystals, where light confinement at sub-wavelength level allows one to produce novel devices, such as metasurfaces and dispersion engineered optical waveguides, for the first time to our knowledge inside a monolithic crystal. The technique also allows to surpass present limitations in the fabrication of photonic crystal fibers (PCF) which currently need to be made of drawable materials (mainly glass or plastic), and also adds the design flexibility to produce 3D photonic structures which are impossible to produce by the drawing technique.
关键词： Nanophotonic-Engineered Solid-State-Media,Optical Crystals,Three-Dimensional Laser Nanostructuring
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || FIB patterning for position-controlled nanowire growth
摘要： Semiconductor nanowire (NW) based heterostructures are a promising material system for next generation optoelectronic devices, such as flexible solar cells and light emitting diodes [1]. Their reduced contact area and surface strain relaxation allow for epitaxial growth on lattice-mismatched substrates, a key advantage for integration of different III-V semiconductors with existing silicon-based technology. Position-controlled NWs can be grown in ordered arrays on Si to improve uniformity and device integration. This is commonly performed by using a SiO2 thin film as a mask. Patterning of circular holes in the mask (Fig. 1(a)) allows for site-specific NW growth in predefined patterns and positions. To date, this is performed using lithography techniques such as electron beam lithography or nanoimprint lithography [2]. Important processing parameters include oxide thickness, hole diameter and pattern pitch, requiring several steps to be optimized in order to achieve a high yield of uniform NWs [3]. Additionally, the catalytic particle is rarely centered in the hole, leading to undesirable asymmetry in the NW cross-sections [4]. In this work, the parameter space for direct patterning of NW growth substrates by focused ion beam (FIB) is explored (Fig. 1). Self-catalyzed GaAsSb NWs were grown using molecular beam epitaxy (MBE) on a FIB patterned Si(111) substrate with 40 nm thermal oxide, where hole size, dose and Ga-beam overlap were systematically varied (Fig. 1(a-c)). It is expected that a higher degree of flexibility and control can be attained using FIB compared to the conventionally used resist-based patterning techniques. In addition, patterning by FIB leads to Ga implantation in both Si and SiO2, which could positively affect the self-catalyzed NW growth and the properties of the NW-substrate system in a unique way. After MBE growth, three distinct growth regimes can be recognized, present in all arrays (Fig. 1(d-e)): The smallest (10 nm pattern) diameter row features a high yield (≤ 80%) of straight NWs. As the hole diameter increases there is initially a transition to more parasitic crystal growth and finally multiple (2-5) NWs grow within each hole. As the dose increases between arrays in each column, the patterned diameter for these transitions decreases proportionally. The results demonstrate that using FIB the parameter space can be mapped out efficiently within a single growth session and that growth can be tuned between aligned single NWs, 2D parasitic crystals and multiple NWs per hole. Transmission electron microscopy and electrical testing of single NWs directly on the growth substrate [5] will be used to refine the structural analysis and study the electrical properties of these NWs. It is expected that in addition to the flexibility of FIB patterning, III-V NWs grown on FIB-patterned Si will exhibit novel properties due to the implantation of Ga and the altered NW-substrate interface.
关键词： self-catalyzed,nanowires,focused ion beam,nanostructuring,GaAsSb
更新于2025-09-11 14:15:04
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Monitoring of Evolving Laser Induced Periodic Surface Structures
摘要： Laser induced periodic surface structures (LIPSS) are generated on titanium and silicon nitride surfaces by multiple femtosecond laser pulses. An optical imaging system is used to observe the backscattered light during the patterning process. A characteristic fringe pattern in the backscattered light is observed and evidences the surface modification. Experiments are complemented by finite difference time domain numerical simulations which clearly show that the periodic surface modulation leads to characteristic modulations in the coherently scattered light field. It is proposed that these characteristic fringe pattern can be used as a very fast and low-cost monitor of LIPSS formation formation during the manufacturing process.
关键词： material processing,laser nanostructuring,optical properties,laser induced periodic surface structures
更新于2025-09-11 14:15:04
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Carrier Dynamics in SnS<inf>2</inf> Single Crystals and Vertical Nanostructures: Role of Edges
摘要： SnS2 is a member of the van der Waals 2D layered materials family. Its moderate bandgap, environmental stability and high carrier mobility makes it attractive for solar energy conversion application. We explore how nanostructuring SnS2 in the form of vertically-aligned nanoflakes to increase the surface area impacts the lifetime and microscopic conductivity of photoinjected carriers compared to the bulk SnS2. Increased surface area and the presence of edges is beneficial to the efficiency of SnS2 photoanode performance but it comes at a cost of increased carrier trapping at surface and edge states.
关键词： THz spectroscopy,van der Waals materials,SnS2,carrier dynamics,nanostructuring
更新于2025-09-11 14:15:04
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Modification of Glial Attachment by Surface Nanostructuring of SU-8 Thin Films
摘要： Various methods are currently under development to enhance the biocompatibility of neural electrodes and to minimize the reactive gliosis around the implant surface. As cells in their native microenvironment interact with 3D nanoscale topographies of the extracellular matrix, physical modification of implant surfaces may provide an alternative solution to the negative tissue response by imitating the structure of the extracellular matrix, and therefore affecting the attachment and behavior of neurons and glial cells. The attachment of primary mouse astrocytes on nanostructured SU8 polymer surfaces fabricated by e-beam lithography was investigated in our study. We found that attachment of primary mouse astrocytes on silicon-SU8 surfaces is strongly influenced by the surface topography.
关键词： SU-8,cell attachment,nanostructuring,cell-surface interaction
更新于2025-09-10 09:29:36
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STRUCTURING OF DIAMOND FILMS USING MICROSPHERE LITHOGRAPHY
摘要： In this study, the structuring of micro- and nanocrystalline diamond thin films is demonstrated. The diamond films are structured using the technique of microsphere lithography followed by reactive ion etching. Specifically, this paper presents a four-step fabrication process: diamond deposition (microwave plasma assisted chemical vapor deposition), mask preparation (by the standard Langmuir-Blodgett method), mask modification and diamond etching. A self-assembled monolayer of monodisperse polystyrene (PS) microspheres with close-packed ordering is used as the primary template. Then the PS microspheres and the diamond films are processed in capacitively coupled radiofrequency plasma using various plasma chemistries. This fabrication method illustrates the preparation of large arrays of periodic and homogeneous hillock-like structures. The surface morphology of the processed diamond films is characterized by scanning electron microscopy and with the use of an atomic force microscope. The potential applications of these diamond structures in various fields of nanotechnology are also briefly discussed.
关键词： polystyrene microspheres,nanostructuring,scanning electron microscopy,reactive ion etching,diamond thin films
更新于2025-09-09 09:28:46
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Numerical Simulation of Plasmon Excitation in Gold Nanostructure of the Parabolic Nanoantenna Type
摘要： Experimentally obtained nanostructures shaped as a through hole with a particle at the center are considered. Their electrodynamic parameters are studied using numerical simulation methods. It is shown that such structures function similarly to parabolic antennas.
关键词： numerical simulation of electrodynamics,nanostructuring of thin films,parabolic nanoantennas
更新于2025-09-04 15:30:14