Laser-based surface processing is an established way for the maskless generation of surface structures and functionalities on a large variety of materials. Laser-driven periodic surface texturing and structuring of thin films is reported for metallic-, semiconductive-, and polymeric films. Here, we introduce subwavelength surface patterning of metal− organic thin films of [Mo 2 S 4 (S 2 CN n Bu 2 ) 2 ], a MoS 2 precursor. Accurate control of one-and two-dimensional (1D and 2D) periodic patterns is achieved on silicon wafers with a pulsed 532 nm ns laser. With suitable combinations of laser polarization, laser pulse energy, the thickness of the SiO 2 passivation layer, and the MoS 2 precursor's thin film thickness, high-quality 1D and 2D self-organized periodic structures are obtained in virtually unlimited areas. The material redistribution related to the pattern formation is thermally driven at low laser energies. Increasing pulse energies beyond a threshold level, in our experiments a factor of 2, fully converts the precursor to MoS 2 .
ZnO nanostructures, semiconductors with attractive optical properties, are typically grown by thermal chemical vapor deposition for optimal growth control. Their growth is well investigated, but commonly results in the entire substrate being covered with identical ZnO nanostructures. At best a limited, binary growth control is achieved with masks or lithographic processes. We demonstrate nanosecond laser-induced Au catalyst generation on Si(100) wafers, resulting in controlled ZnO nanostructure growth. Scanning electron and atomic force microscopy measurements reveal the laser pulse’s influence on the substrate’s and catalyst’s properties, e.g., nanoparticle size and distribution. The laser-induced formation of a thin SiO2-layer on the catalysts plays a key role in the subsequent ZnO growth mechanism. By tuning the irradiation parameters, the width, density, and morphology of ZnO nanostructures, i.e., nanorods, nanowires, and nanobelts, were controlled. Our method allows for maskless ZnO nanostructure designs locally controlled on Si-wafers.
Upon irradiation of a silicon surface with circularly polarized green nanosecond laser pulses, the formation of linear periodic nanostructures is observed. Due to the lack of inherent directional anisotropy by the laser polarization, no 1D-laser-induced periodic surface structures (LIPSSs) formation is expected. The orientation of the formed surface modulation depends on the laser scan direction. Silicon wafers, which are often used in LIPSS studies, are commonly considered inert substrates. This assumption needs to be reconsidered. Our finding is not explained by the current LIPSS theories.
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