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中国物理学会期刊

单晶蓝宝石衬底表面微结构对摩擦性能的影响

Effect of surface microstructure on the frictional properties of single-crystal sapphire substrates

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  • 本文使用一种二维摩擦原子力显微镜方法,在大气环境下研究了无定形氧化硅和单晶蓝宝石两种衬底材料和硅探针之间的摩擦行为。结果表明无定形氧化硅衬底和硅探针之间的摩擦力为各向同性;单晶蓝宝石衬底和硅探针之间摩擦力由一个各向同性摩擦分量和一个周期为90°的各向异性摩擦分量组成,其中90°周期摩擦分量与单晶硅针尖晶格对应。对单晶蓝宝石衬底表面进行变负载测试结果表明,单晶蓝宝石衬底和硅探针之间总摩擦由于表面吸附物的擦除效应,总摩擦力表现为随负载增加先减小后增加,并且其各向同性摩擦分量以及90°周期的各向异性摩擦分量也表现出相同趋势。在对单晶蓝宝石衬底进行热处理后,单晶蓝宝石衬底表面出现台阶微结构,其与硅针尖摩擦中对应出现180°各向异性摩擦分量,证明蓝宝石表面台阶结构对其与硅针尖间的各向异性摩擦性质的直接影响。二维摩擦原子力显微镜(two-dimensional friction-force atomic force microscope (2DFF-AFM))方法为分离表界面不同来源摩擦力提供了有效理论和实践路径。

    In previous studies, conducting in-situ friction measurement by atomic force microscope have remained challenging. Two-dimensional friction-force atomic force microscopy (2DFF-AFM) is a method that enables friction measurements on material surfaces at the two-dimensional scale using atomic force microscopy. By combining the torsional signal of the cantilever with the Z-direction piezoelectric feedback corresponding to the bending signal, this method achieves microscopic friction measurements at arbitrary scanning angles. This study used 2DFF-AFM method to investigate the friction behavior between silicon probes and two different substrates (amorphous silicon oxide and single-crystal sapphire) under atmospheric conditions. The results shows that friction on amorphous silicon oxide is isotropic when measured with a silicon probe. Friction on single-crystal sapphire comprises an isotropic component and an anisotropic component with 90° periodicity which arises from single crystal silicon of tip, the high hardness of sapphire wears through the native oxide layer of the silicon tip, exposing the underlying single-crystal silicon; In addition, under the influence of adsorbates, both the isotropic friction signal and 90° periodic anisotropic friction signal exhibit a non-monotonic trend with increasing load, initially decreasing and subsequently increasing. After thermal treatment of single-crystal sapphire substrates, sub-nanometer steps appeared on the surface, and friction measurements showed that sapphire exhibited a friction signal with a period of 180°. This directly indicates that the step structure on the sapphire surface significantly affects the anisotropic friction behavior. The 2DFF-AFM method provides an effective theoretical and practical approach for separating friction forces from different sources at the interface.

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