We demonstrate contact-resonance-frequency atomic force microscopy (AFM) techniques to nondestructively image variations in adhesion at a substrate/film interface. Contact-resonance-frequency imaging is a dynamic AFM technique to measure the contact stiffness between the tip and the sample. Although typically used to evaluate local elastic modulus, we show here that the contact stiffness can also be used to assess another mechanical property, namely subsurface adhesion. Images were acquired on a sample containing a 20 nm gold (Au) blanket film on silicon (Si)with a 1 nm patterned interlayer of titanium (Ti). This design produced regions of very weak adhesion (Au/Si interface) and regions of strong adhesion (Au/Ti/Si). Values of the contact stiffness were 5 % lower in the regions of weak adhesion. The observed behavior is consistent with theoretical predictions for layered systems with disbonds. Our results represent progress towards quantitative measurement of adhesion parameters on the nanoscale. Such measurement capabilities have important implications for the successful development of thin-film devices, especially in emerging nanotechnology applications.
Citation: Applied Physics Letters
Pub Type: Journals
atomic force acoustic microscopy (AFAM), contact stiffness, thin films