| AVS 57th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Friday Sessions |
| Session EL+AS+EM+MS+TF-FrM |
| Session: | Spectroscopic Ellipsometry - Inorganic Thin Films |
| Presenter: | D. Schmidt, University of Nebraska-Lincoln |
| Authors: | D. Schmidt, University of Nebraska-Lincoln K.B. Rodenhausen, University of Nebraska-Lincoln S. Schöche, University of Nebraska-Lincoln T. Hofmann, University of Nebraska-Lincoln E.B. Schubert, University of Nebraska-Lincoln M. Schubert, University of Nebraska-Lincoln |
| Correspondent: | Click to Email |
A new concept of agent-free highly sensitive bio-chemical sensing is presented based on the change of birefringence of sculptured thin films (STFs). A mere intermixture of liquid or gaseous molecules with solid state STFs dramatically changes the overall optical properties of the porous film, which can be easily detected by means of ellipsometry or even the bare eye, i.e. light intensity changes upon interaction.
Previously, we have shown that STF exhibit highly anisotropic optical properties, which differ significantly from their bulk properties. Strong form birefringence and large dichroism can be tailored by appropriate deposition geometries to produce desired optical responses. In order to vary structure spacing (void fraction), and enable growth on defined sites self-assembled large-scale substrate patterning by diblock copolymer nanolithography can be exploited. We have demonstrated that generalized spectroscopic ellipsometry is ideally suited for determining geometrical structure and the anisotropic optical properties of STFs [1-3]. Recently, we have demonstrated that the combination of spectroscopic ellipsometry (SE) with quartz crystal microbalance (QCM) methods provides access to organic thin film thickness and porosity information and can further reveal structural properties of thin organic films [4].
Here we report on the application of STFs for bio-chemical sensing by simultaneous in-situ generalized ellipsometry (GE) and QCM measurements. STFs from different materials were deposited by glancing angle electron beam evaporation on gold-coated quartz crystals. Changes in the resonance frequency of the quartz crystals before and after STF deposition were used to determine the void fraction of the STF and agree well with scanning electron micrograph estimates.
In our in-situ experiments, we observe that the optical response of STFs is very sensitive to the ambient medium. We find that the filling of the STFs void fraction with solvents of different refractive index causes changes in birefringence as well as dichroism of the STFs.
Furthermore, the deposition of cetyltrimethylammonium bromide (CTAB), a well-known detergent molecule, is used here in order to demonstrate the detection of organic molecules. We find that the intriguing optical response of the STFs is changing drastically with the deposition of minute amounts of CTAB.
[1] D. Schmidt et al., Opt. Lett. 34, 992 (2009).
[2] D. Schmidt et al., Appl. Phys. Lett. 94, 011914 (2009).
[3] D. Schmidt et al., J. Appl. Phys. 105, 113508 (2009).
[4] K. B. Rodenhausen et al. (in submission, 2010).