Abstract:Laser-induced periodic surface structures (LIPSS) are a universal phenomenon observed in all classes of solid materials, giving rise to a variety of self-assembled subwavelength structures with different symmetries. These promising features have opened new opportunities for laser structuring of materials in a wide range of applications, including plasmonics, nanophotonics, nanoelectronics, sensing and even mechanics. However, there is an ongoing debate about the formation mechanism of LIPSS and the current pic… Show more
“…Although SPPs can theoretically only be coupled and propagate at a dielectric/metal interface, laser-induced free-electron generation in semiconductors and dielectrics turns them transiently into a metal-like state, generating conditions for SPP propagation 12 . Yet, there is still a vivid debate about other mechanisms that contribute to the formation of LIPSS in semiconductors, amongst which optical near- and far-field scattering process have recently been identified 14, 15 .Figure 1Optical micrographs of the Si surface after irradiation with ( a ) N = 10 and ( b ) N = 20 horizontally polarized laser pulses at normal incidence ( θ = 0° ) and F = 270 mJ / cm
2 .
…”
Section: Resultsmentioning
confidence: 99%
“…In the present work, we want to focus on a different aspect and illustrate it with new experimental data. We have used the moving-spot modality of fs microscopy 15 , based on recording time-resolved images while the sample is translated using a step size equal to the fringe period. Laser irradiation was performed at θ = 52° and illumination with a fs probe pulse at θ = 0° (c.f.…”
Periodic structures of alternating amorphous-crystalline fringes have been fabricated in silicon using repetitive femtosecond laser exposure (800 nm wavelength and 120 fs duration). The method is based on the interference of the incident laser light with far- and near-field scattered light, leading to local melting at the interference maxima, as demonstrated by femtosecond microscopy. Exploiting this strategy, lines of highly regular amorphous fringes can be written. The fringes have been characterized in detail using optical microscopy combined modelling, which enables a determination of the three-dimensional shape of individual fringes. 2D micro-Raman spectroscopy reveals that the space between amorphous fringes remains crystalline. We demonstrate that the fringe period can be tuned over a range of 410 nm – 13 µm by changing the angle of incidence and inverting the beam scan direction. Fine control over the lateral dimensions, thickness, surface depression and optical contrast of the fringes is obtained via adjustment of pulse number, fluence and spot size. Large-area, highly homogeneous gratings composed of amorphous fringes with micrometer width and millimeter length can readily be fabricated. The here presented fabrication technique is expected to have applications in the fields of optics, nanoelectronics, and mechatronics and should be applicable to other materials.
“…Although SPPs can theoretically only be coupled and propagate at a dielectric/metal interface, laser-induced free-electron generation in semiconductors and dielectrics turns them transiently into a metal-like state, generating conditions for SPP propagation 12 . Yet, there is still a vivid debate about other mechanisms that contribute to the formation of LIPSS in semiconductors, amongst which optical near- and far-field scattering process have recently been identified 14, 15 .Figure 1Optical micrographs of the Si surface after irradiation with ( a ) N = 10 and ( b ) N = 20 horizontally polarized laser pulses at normal incidence ( θ = 0° ) and F = 270 mJ / cm
2 .
…”
Section: Resultsmentioning
confidence: 99%
“…In the present work, we want to focus on a different aspect and illustrate it with new experimental data. We have used the moving-spot modality of fs microscopy 15 , based on recording time-resolved images while the sample is translated using a step size equal to the fringe period. Laser irradiation was performed at θ = 52° and illumination with a fs probe pulse at θ = 0° (c.f.…”
Periodic structures of alternating amorphous-crystalline fringes have been fabricated in silicon using repetitive femtosecond laser exposure (800 nm wavelength and 120 fs duration). The method is based on the interference of the incident laser light with far- and near-field scattered light, leading to local melting at the interference maxima, as demonstrated by femtosecond microscopy. Exploiting this strategy, lines of highly regular amorphous fringes can be written. The fringes have been characterized in detail using optical microscopy combined modelling, which enables a determination of the three-dimensional shape of individual fringes. 2D micro-Raman spectroscopy reveals that the space between amorphous fringes remains crystalline. We demonstrate that the fringe period can be tuned over a range of 410 nm – 13 µm by changing the angle of incidence and inverting the beam scan direction. Fine control over the lateral dimensions, thickness, surface depression and optical contrast of the fringes is obtained via adjustment of pulse number, fluence and spot size. Large-area, highly homogeneous gratings composed of amorphous fringes with micrometer width and millimeter length can readily be fabricated. The here presented fabrication technique is expected to have applications in the fields of optics, nanoelectronics, and mechatronics and should be applicable to other materials.
“…By contrast, during the interaction of silicon with an ultrafast laser in a nonablation regime, the materials melt locally due to the lattice instability induced by a relatively high density of free electrons that exceeds the threshold of nonthermal melting ( n e,thresh ≈ 10 22 cm −3 ) but is below the ablation threshold of silicon . Following the liquid‐phase rapid solidification, crystalline silicon transforms into the amorphous phase . Over above course, femtosecond laser only causes the local phase change of silicon substrate but removes almost no material (Figure S2, Supporting Information).…”
Periodic surface structures are core components for controlling the dispersion and steering characteristics of light. Here, a mask‐free approach using nonablative femtosecond laser processing is proposed and demonstrated to fabricate extremely long‐range uniform periodic surface structures on silicon with tunable diffraction efficiency. First, a cylindrically focused femtosecond laser scans over silicon substrates to efficiently produce large‐area periodic modified stripes in a nonablation regime. Second, the modified stripes act as fine etch stops to generate the desired structures on sample surfaces during the subsequent chemical etching process. The structures produced by the method achieve optimal long‐range uniformity compared to the reported laser‐induced periodic surface structures, which possess a minimum divergence of structure orientation angles of <5°. In addition, the optical characteristics of the prepared structures are measured experimentally. Distinguishable polychromatic diffraction patterns can be clearly observed by broadband light irradiation. Significantly, the chemical etching process endues the structures with ingenious morphology controllability, so that the diffraction efficiency of the incident light can be flexibly tuned, which exhibits a near‐linear function of the etching duration. Such morphology‐controllable periodic surface structures may facilitate applications in broad fields, such as optical communications and optical sensors.
“…Using nanosecond laser irradiation, Pena et al produced micrometer-sized amorphous humps with a height of a few nanometers 18 . Recently, it has been shown that Laser-Induced Periodic Surface Structures (LIPSS) in form of alternating amorphous and crystalline fringes can be fabricated by scanning the laser beam over the sample surface, employing an adequate choice of spot size, repetition rate and scan velocity 19,20 . In the present work we present a simple strategy to fabricate surface-depressed annular amorphous rings with a central crystalline disk, temporally resolve their formation process, and show how these structures can be scaled and stitched together to form arrays with different symmetries.…”
Abstract:We demonstrate a simple way to fabricate amorphous micro-rings in crystalline silicon using direct laser writing. The method is based on the fact that the phase of a thin surface layer can be changed into the amorphous phase by irradiation with a few ultrashort laser pulses (800 nm wavelength and 100 fs duration). Surface-depressed amorphous rings with a central crystalline disk can be fabricated without the need for beam shaping, featuring attractive optical, topographical, and electrical properties. The underlying formation mechanism and phase change path way have been investigated by means of fs-resolved microscopy, identifying fluence-dependent melting and solidification dynamics of the material as the responsible mechanism. We demonstrate that the lateral dimensions of the rings can be scaled and that the rings can be stitched together, forming extended arrays of structures not limited to annular shapes. This technique and the resulting structures may find applications in a variety of fields in optics, nanoelectronics, and mechatronics.
Text:Silicon is more than just a key material for the electronics industry; it can be considered one of the pillars the industry is built on. Si owes this position essentially to its abundance on earth, its semiconducting properties and the existence of two structurally different solid phases (crystalline and amorphous), having very different physical properties. In this context it is worth noting that the amorphous phase can be formed by a variety of methods, including chemical and physical vapour deposition techniques, ion implantation and melting followed by rapid quenching. While some of the properties of the amorphous phase are known to depend on the preparation method 1 it has to be kept in mind that it is still a tetrahedrally coordinated semiconductor with a coordination number close to four 2 , just as the crystalline phase.Laser processing of Si started immediately after sufficiently intense lasers were available 3 and today applications are countless. The ability of pulsed laser irradiation to melt the crystalline material and induce resolidification either into the crystalline or amorphous phase, depending on the irradiation conditions, has been observed already in 1979 by Liu et al 4 . In fact, the authors proposed this concept for data storage applications due to the optical contrast between the two phases. Several experimental parameters influence the melting and freezing kinetics of the material and thus the final phase obtained, the most important ones being the Appl. Phys. Lett. 110, 211602 (2017); doi: http://dx.doi.org/10.1063/1.4984110 2 laser pulse duration, wavelength and number of irradiation pulses, as well as film thickness and choice of substrate in the case of thin Si films [5][6][7][8][9][10] . Despite this early discovery, most laser-induced phase-change studies in Si focused on transforming large areas, for instance laser-annealing of amorphous Si for fabrication of solar cells 11,12 or OLED displays 13 . Less work has been done to imp...
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