Sirghi L, Rossi F
Department of Physics, Alexandru Ioan Cuza University, Boulevard Carol I, no. 11, Iasi 700506, Romania.
Nanotechnology. 2009 Sep 9;20(36):365702. doi: 10.1088/0957-4484/20/36/365702. Epub 2009 Aug 18.
The effect of adhesion on nanoscale indentation experiments makes the interpretation of force-displacement curves acquired in these experiments very difficult. The indentation force results from the addition of adhesive and elastic forces at the indenter-sample contact. The evolution of the two forces during the indentation is determined by the variation of the indenter-sample contact radius. In the present work the variation of contact radius during atomic force microscopy (AFM) indentation of elastic and adhesive samples with conical indenters (AFM tips) is indirectly determined by measurements of the contact dynamic stiffness. For weak sample deformations, the contact radius is determined mainly by the adhesion force and indenter apex radius. For strong sample deformations, the contact radius increases linearly with the increase of the indenter displacement, the slope of this linear dependence being in agreement with Sneddon's theory of indentation (Sneddon 1965 Int. J. Eng. Sci. 3 47). Based on these results, a theoretical expression of indentation force dependence on displacement is found. This expression allows for determination of the thermodynamic work of adhesion at the indenter-sample interface and the sample elasticity modulus.
粘附力对纳米尺度压痕实验的影响使得对这些实验中获得的力-位移曲线的解读非常困难。压痕力是由压头与样品接触处的粘附力和弹力共同作用产生的。在压痕过程中，这两种力的变化由压头与样品接触半径的变化决定。在本研究中，通过测量接触动态刚度间接确定了使用锥形压头（原子力显微镜（AFM）针尖）对弹性和粘附性样品进行AFM压痕时接触半径的变化。对于较弱的样品变形，接触半径主要由粘附力和压头顶端半径决定。对于较强的样品变形，接触半径随压头位移的增加呈线性增加，这种线性关系的斜率与斯奈登压痕理论（斯奈登，1965年，《国际工程科学杂志》，第3卷，第47页）一致。基于这些结果，得出了压痕力与位移关系的理论表达式。该表达式可用于确定压头与样品界面处的粘附热力学功以及样品的弹性模量。
