Electrochemical protection of thin film electrodes in solid state nanopores.

Solid state nanopores are a core element of next-generation single molecule tools in the field of nano-biotechnology. Thin film electrodes integrated into a pore can interact with charges and fields within the pore. In order to keep the nanopore open and thus functional electrochemically induced surface alteration of electrode surfaces and bubble formation inside the pore have to be eliminated.

Electrochemical characterization of thin film electrodes toward developing a DNA transistor.

The DNA-Transistor is a device designed to control the translocation of single-stranded DNA through a solid-state nanopore. Functionality of the device is enabled by three electrodes exposed to the DNA-containing electrolyte solution within the pore and the application of a dynamic electrostatic potential well between the electrodes to temporarily trap a DNA molecule. Optimizing the surface chemistry and electrochemical behavior of the device is a necessary (but by no means sufficient) step toward the development of a functional device.

Direct measurement of the counterion distribution within swollen polyelectrolyte films.

The depth profile of the counterion concentration within thin polyelectrolyte films was measured in situ using contrast variant specular neutron reflectivity to characterize the initial swelling stage of the film dissolution. We find substantial counterion depletion near the substrate and enrichment near the periphery of the film extending into the solution. These observations challenge our understanding of the charge distribution in polyelectrolyte films and are important for understanding film dissolution in medical and technological applications.

Interfacial effects on moisture absorption in thin polymer films.

Moisture absorption in model photoresist films of poly(4-hydroxystryene) (PHOSt) and poly(tert-butoxycarboxystyrene) (PBOCSt) supported on silicon wafers was measured by X-ray and neutron reflectivity. The overall thickness change in the films upon moisture exposure was found to be dependent upon the initial film thickness. As the film becomes thinner, the swelling is enhanced.

X-ray absorption spectroscopy to probe surface composition and surface deprotection in photoresist films.

Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) is utilized to provide insight into surface chemical effects in model photoresist films. First, NEXAFS was used to examine the resist/air interface including surface segregation of a photoacid generator (PAG) and the extent of surface deprotection in the film. The concentration of PAG at the resist-air interface was higher than the bulk concentration, which led to a faster deprotection rate at that interface.