In recent years, self-assembled monolayers (SAMs) have been demonstrated to provide promising new approaches to nonlinear\r\nlaser processing. Most notably, because of their ultrathin nature, indirect excitation mechanisms can be exploited in order to fabricate\r\nsubwavelength structures. In photothermal processing, for example, microfocused lasers are used to locally heat the substrate\r\nsurface and initiate desorption or decomposition of the coating. Because of the strongly temperature-dependent desorption kinetics,\r\nthe overall process is highly nonlinear in the applied laser power. For this reason, subwavelength patterning is feasible employing\r\nordinary continuous-wave lasers. The lateral resolution, generally, depends on both the type of the organic monolayer and the\r\nnature of the substrate. In previous studies we reported on photothermal patterning of distinct types of SAMs on Si supports. In this\r\ncontribution, a systematic study on the impact of the substrate is presented. Alkanethiol SAMs on Au-coated glass and silicon\r\nsubstrates were patterned by using a microfocused laser beam at a wavelength of 532 nm. Temperature calculations and thermokinetic\r\nsimulations were carried out in order to clarify the processes that determine the performance of the patterning technique.\r\nBecause of the strongly temperature-dependent thermal conductivity of Si, surface-temperature profiles on Au/Si substrates are very\r\nnarrow ensuring a particularly high lateral resolution. At a 1/e spot diameter of 2 Ã?µm, fabrication of subwavelength structures with\r\ndiameters of 300ââ?¬â??400 nm is feasible. Rapid heat dissipation, though, requires high laser powers. In contrast, patterning of SAMs on\r\nAu/glass substrates is strongly affected by the largely distinct heat conduction within the Au film and in the glass support. This\r\nresults in broad surface temperature profiles. Hence, minimum structure sizes are larger when compared with respective values on\r\nAu/Si substrates. The required laser powers, though, are more than one order of magnitude lower. Also, the laser power needed for\r\npatterning decreases with decreasing Au layer thickness. These results demonstrate the impact of the substrate on the overall\r\npatterning process and provide new perspectives in photothermal laser patterning of ultrathin organic coatings.
Loading....