Scott William W, Bhushan Bharat
Nanotribology Laboratory for Information Storage and MEMS/NEMS, Department of Mechanical Engineering, The Ohio State University, 206 West 18th Avenue, Columbus, OH 43210-1107, USA.
Ultramicroscopy. 2003 Oct-Nov;97(1-4):151-69. doi: 10.1016/S0304-3991(03)00040-8.
Phase contrast microscopy, using an atomic force microscope, is used to detect and quantify changes in composition across polymer nanocomposites and molecularly thick lubricated surfaces. The technique takes advantage of the contrast in viscoelastic (viscous energy dissipation) properties of the different materials across the surface. Some materials, especially polymers, are found to display viscoelastic behavior. For such materials, the strain response lags the stress by a phase angle that is characteristic of the material. In tapping (or intermittent contact) mode, phase angle contrast is found to be highly dependent on vibration amplitude and mean tip-to-sample distance (setpoint). Phase angle contrast seems to be a stronger function of viscoelastic properties at relatively high vibration amplitude and low mean tip-to-sample distance. In this regime the effects of sample deformation, and thus viscoelastic properties, are dominant. In these contrast images, low phase angle corresponds to materials with low viscoelastic properties. This technique was used to find fairly reproducible phase angle contrast for polyethylene terephthalate (PET) films with embedded ceramic particles, metal particle (MP) magnetic tape, and Si(100) with a nonuniform Z-15 lubricant film. Very little correlation is found between phase angle images and friction force images for PET films with embedded ceramic particles and MP tape; phase angle images give information that cannot be obtained from topography or friction images. A numerical vibration model verifies that viscoelastic properties are dominant for high vibration amplitude and low mean tip-to-sample distance. For these conditions, the model also verifies that low phase angle corresponds to low viscoelastic properties.
利用原子力显微镜的相衬显微镜技术，用于检测和量化聚合物纳米复合材料及分子级厚度润滑表面的成分变化。该技术利用了表面不同材料的粘弹性（粘性能量耗散）特性的对比度。发现一些材料，尤其是聚合物，表现出粘弹性行为。对于这类材料，应变响应滞后于应力一个该材料特有的相角。在轻敲（或间歇接触）模式下，发现相角对比度高度依赖于振动幅度和平均针尖到样品的距离（设定值）。在相对较高的振动幅度和较低的平均针尖到样品距离下，相角对比度似乎是粘弹性特性的更强函数。在这种情况下，样品变形的影响以及粘弹性特性占主导。在这些对比度图像中，低相角对应于粘弹性特性低的材料。该技术用于在嵌入陶瓷颗粒的聚对苯二甲酸乙二酯（PET）薄膜、金属颗粒（MP）磁带以及具有不均匀Z - 15润滑膜的Si(100)上找到相当可重复的相角对比度。对于嵌入陶瓷颗粒的PET薄膜和MP磁带，在相角图像和摩擦力图像之间几乎没有发现相关性；相角图像提供了从形貌或摩擦力图像中无法获得的信息。一个数值振动模型验证了在高振动幅度和低平均针尖到样品距离下粘弹性特性占主导。对于这些条件，该模型还验证了低相角对应于低粘弹性特性。
