Yasser Fuentes-Edfuf

Fabrication of amorphous micro-ring arrays in crystalline silicon using ultrashort laser pulses

We demonstrate a simple way to fabricate amorphous micro-rings in crystalline silicon using direct laser writing. This 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 pathway 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 such as ...

Coherent scatter-controlled phase-change grating structures in silicon using femtosecond laser pulses

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.

Author Correction: Coherent scatter-controlled phase-change grating structures in silicon using femtosecond laser pulses

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Biomimetic structures on steel via self-organization processes in multiple-scan, fs-laser irradiated surfaces

Weakly focused fs-pulses have the potential to produce nanometer structures that self-organize under certain irradiation conditions [1]. Such structures, known as LIPSS [2] (laser induced periodic surface structures), are potential candidates for mimicking surface textures found in nature, on materials of technological interest. This enables surface functionalization for a variety of applications including wettability, optical response, and wear resistance [3, 4].

Fabrication of amorphous-crystalline micro- and nanostructures in silicon using ultrashort laser pulses

Silicon is one of the key-materials of nowadays technology. This is partly related to its special phase change dynamics characteristics. In particular, upon pulsed laser irradiation, silicon can re-solidify either in the crystalline (c-) or amorphous (a-) phase depending on the local supercooling achieved [1]. This feature has recently been used to produce non-ablative LIPSS (Laser Induced Periodic Surface Structures [2]) in crystalline silicon upon multiple laser pulse exposure. The induced structures consist of a-c-fringes with subwavelength period [3].