Rota A, Serpini E, Gazzadi G C, Valeri S
CNR- Istituto di Nanoscienze, Centro S3, Via Campi 213/A, 41125 Modena, Italy.
J Phys Condens Matter. 2016 Apr 6;28(13):134008. doi: 10.1088/0953-8984/28/13/134008. Epub 2016 Mar 2.
Although the importance of morphology on the tribological properties of surfaces has long been proved, an exhaustive understanding of nanopatterning effects is still lacking due to the difficulty in both fabricating 'really nano-' structures and detecting their tribological properties. In the present work we show how the probe-surface contact area can be a critical parameter due to its remarkable local variability, making a correct interpretation of the data very difficult in the case of extremely small nanofeatures. Regular arrays of parallel 1D straight nanoprotrusions were fabricated by means of a low-dose focused ion beam, taking advantage of the amorphization-related swelling effect. The tribological properties of the patterns were detected in the presence of air and in vacuum (dry ambient) by atomic force microscopy. We have introduced a novel procedure and data analysis to reduce the uncertainties related to contact instabilities. The real time estimation of the radius of curvature of the contacting asperity enables us to study the dependence of the tribological properties of the patterns from their geometrical characteristics. The effect of the patterns on both adhesion and the coefficient of friction strongly depends on the contact area, which is linked to the local radius of curvature of the probe. However, a detectable hydrophobic character induced on the hydrophilic native SiO2 has been observed as well. The results suggest a scenario for capillary formation on the patterns.
尽管表面形态对摩擦学性能的重要性早已得到证实，但由于制造“真正的纳米”结构以及检测其摩擦学性能都存在困难，目前仍缺乏对纳米图案化效应的详尽理解。在本工作中，我们表明，由于探针 - 表面接触面积具有显著的局部可变性，它可能是一个关键参数，这使得在存在极小纳米特征的情况下很难对数据进行正确解释。利用与非晶化相关的膨胀效应，通过低剂量聚焦离子束制备了平行的一维直纳米凸起的规则阵列。通过原子力显微镜在空气和真空（干燥环境）中检测图案的摩擦学性能。我们引入了一种新颖的程序和数据分析方法，以减少与接触不稳定性相关的不确定性。对接触微凸体曲率半径的实时估计使我们能够研究图案的摩擦学性能与其几何特征之间的关系。图案对粘附力和摩擦系数的影响强烈依赖于接触面积，而接触面积与探针的局部曲率半径相关。然而，我们也观察到在亲水性原生SiO₂ 上诱导出了可检测到的疏水特性。结果表明了图案上形成毛细管的一种情况。
