Transmission Electron Microscope Specimen Preparation Techniques for Studies of Surface Plasmon Resonance Bio-sensing Detectors Based on Nanostructured TiO2 and Au Bilayer Films

Abstract

This work concerns the microstructure of surface plasmon resonance bio sensing detectors that enable label-­‐free detection of small amounts of proteins. The detectors are based on metal multilayer films with nano holes on glass substrates. As proteins bind to the holes small changes are induced in the dielectric, which can be probed using localized surface plasmon resonance (LSPR) spectroscopy. The response to different proteins depends on the fine scale microstructure of the detectors including the structure of the holes and the interfaces between the film layers in the metal and between metal and substrate. Electron energy loss spectroscopy (EELS) in the trans-mission electron microscope (TEM) can provide information about the correlation between plasmon response and the microstructure. The samples need to be thin, i.e. less than 100 nm, in order to be transparent to the electron beam. It is important to image and perform the spectro-scopy of the detector structures using both plan view and cross section specimens. The first type of specimens provides an overview of the sample and information about the fine scale morphology of the small holes. The second type reveals the structure of the different interfaces of the detector multilayers. The TEM specimens need to be representative of the original detectors. The details of the specimen preparation methods are crucial for obtaining high quality specimens suitable for the TEM studies. The preparation parameters depend on the geometry and materials of the detectors. This work concerns the develop-ment of specimen preparation techniques for the surface plasmon resonance bio-­‐sensing detectors. Both plan view and cross section TEM specimens with good quality have been prepared and suitable parameters identified. It has also been shown that it is possible to prepare TEM specimens from regions with individual small holes using a combined focused ion beam (FIB)-­‐ scanning electron microscope (SEM).