Joshua Giblin-Burnham, Yousef Javanmardi, Emad Moeendarbary and Bart W. Hoogenboom
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By the analysis of simple surface geometries, the FEM modelling shows how measured mechanical and topographic features in AFM images depend on a combination of tip-sample geometry and indentation of the tip into the sample. Importantly for the interpretation of AFM data, nanoparticles may appear larger or smaller by a factor of two depending on tip size and indentation force; and a higher spatial resolution in AFM images does not necessarily coincide with a more accurate representation of the sample surface. These observations on simple surface geometries also extend to molecular-resolution AFM, as illustrated by comparing FEM results with experimental data acquired on DNA. 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引用次数: 0
摘要
原子力显微镜(AFM)能以纳米分辨率提供样品表面的三维形貌。计算模拟可以帮助解释这种表征,但大多仅限于原子力显微镜探针和样品都很硬且不可压缩的情况。但在许多应用中,样品是软的,因此会因原子力显微镜探针施加的力而变形。在这里,我们使用有限元建模(FEM)来研究测量的原子力显微镜形貌如何与软性和可压缩材料的表面结构相关联。与之前的分析研究一致,AFM 测量的弹性模量通常偏离样品材料的弹性模量。通过对简单表面几何形状的分析,有限元建模显示了原子力显微镜图像中测得的机械和形貌特征如何取决于针尖-样品几何形状和针尖在样品中的压痕组合。对于原子力显微镜数据的解释而言,重要的是,纳米粒子的大小可能会因针尖大小和压入力的不同而增大或缩小两倍;原子力显微镜图像的空间分辨率越高,并不一定就能更准确地反映样品表面。这些对简单表面几何形状的观察结果同样适用于分子分辨率原子力显微镜,将有限元结果与在 DNA 上获得的实验数据进行比较就能说明这一点。总之,有限元结果提供了一个框架,有助于解释原子力显微镜测量的表面形貌和局部力学。
Finite element modelling of atomic force microscopy imaging on deformable surfaces
Atomic force microscopy (AFM) provides a three-dimensional topographic representation of a sample surface, at nanometre resolution. Computational simulations can aid the interpretation of such representations, but have mostly been limited to cases where both the AFM probe and the sample are hard and not compressible. In many applications, however, the sample is soft and therefore deformed due to the force exerted by the AFM tip. Here we use finite element modelling (FEM) to study how the measured AFM topography relates to the surface structures of soft and compressible materials. Consistent with previous analytical studies, the measured elastic modulus in AFM is generally found to deviate from the elastic modulus of the sample material. By the analysis of simple surface geometries, the FEM modelling shows how measured mechanical and topographic features in AFM images depend on a combination of tip-sample geometry and indentation of the tip into the sample. Importantly for the interpretation of AFM data, nanoparticles may appear larger or smaller by a factor of two depending on tip size and indentation force; and a higher spatial resolution in AFM images does not necessarily coincide with a more accurate representation of the sample surface. These observations on simple surface geometries also extend to molecular-resolution AFM, as illustrated by comparing FEM results with experimental data acquired on DNA. Taken together, the FEM results provide a framework that aids the interpretation of surface topography and local mechanics as measured by AFM.
期刊介绍:
Soft Matter is an international journal published by the Royal Society of Chemistry using Engineering-Materials Science: A Synthesis as its research focus. It publishes original research articles, review articles, and synthesis articles related to this field, reporting the latest discoveries in the relevant theoretical, practical, and applied disciplines in a timely manner, and aims to promote the rapid exchange of scientific information in this subject area. The journal is an open access journal. The journal is an open access journal and has not been placed on the alert list in the last three years.