We report a decreased surface wettability when polymer films on a glass substrate are treated by ultrafast laser pulses in a back-illumination geometry. We propose that back illumination through the substrate confines chemical changes beneath the surface of polymer films, leaving the surface blistered but chemically intact. To confirm this hypothesis, we measure the phase contrast of the polymer when imaged with a focused ion beam. We observe a void at the polymer-quartz interface that results from the expansion of an ultrafast laser-induced plasma. A modified polymer layer surrounds the void, but otherwise the film seems unmodified. We also use x-ray photoelectron spectroscopy to confirm that there is no chemical change to the surface. When patterned with partially overlapping blisters, our polymer surface shows increased hydrophobicity. The increased hydrophobicity of back-illuminated surfaces can only result from the morphological change. This contrasts with the combined chemical and morphological changes of the polymer surface caused by a front-illumination geometry.

中文翻译：

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背照式超快激光处理聚合物的表面附着力

我们报告了当玻璃基板上的聚合物薄膜通过超快激光脉冲以背照式几何形状处理时，表面可湿性降低。我们建议通过基材的背照光将化学变化限制在聚合物膜表面以下，使表面起泡但化学上完好无损。为了证实这一假设，我们在聚焦离子束成像时测量聚合物的相衬度。我们观察到聚合物-石英界面处的空隙是由超快激光诱导的等离子体的膨胀导致的。改性的聚合物层围绕着空隙，但否则薄膜似乎未改性。我们还使用X射线光电子能谱来确认表面没有化学变化。当用部分重叠的水泡图案化时，我们的聚合物表面显示出增加的疏水性。背照式表面疏水性的提高只能归因于形态变化。这与由前照明几何形状引起的聚合物表面化学和形态的综合变化形成对比。