Michael John Preiner

Efficient optical coupling into metal-insulator-metal plasmon modes with subwavelength diffraction gratings

We demonstrate efficient optical coupling into metal-insulator-metal (MIM) plasmon modes. Subwavelength grating couplers are used to optically excite the MIM plasmon mode, which is observed with reflection spectroscopy. Coupling efficiencies of up to 28% are measured for insulator thicknesses of 12nm. It is found that the MIM resonance has a significant shift in energy as a function of grating depth. This shift is much larger than that seen from traditional surface plasmon modes. MIM plasmons are promising tools for probing molecular junctions due to strong field confinement and high field intensities within the insulator.

Creating large area molecular electronic junctions using atomic layer deposition

We demonstrate a technique for creating large area, electrically stable molecular junctions. We use atomic layer deposition to create nanometer thick passivating layers of aluminum oxide on top of self-assembled organic monolayers with hydrophilic terminal groups. This layer acts as a protective barrier and allows simple vapor deposition of the top electrode without short circuits or molecular damage. This method allows nonshorting molecular junctions of up to 9mm2 to be easily and reliably fabricated. The effect of passivation on molecular monolayers is studied with Auger and x-ray spectroscopy, while electronic transport measurements confirm molecular tunneling as the transport mechanism for these devices.

Identification and Passivation of Defects in Self-Assembled Monolayers

We demonstrate imaging of nanoscale defects in self-assembled monolayers (SAMs). Atomic layer deposition of aluminum oxide (AlO(x)) onto hydrophobic SAMs is followed by imaging using scanning electron microscopy (SEM). The insulating AlO(x) selectively deposits onto the exposed substrate at defect sites and becomes charged during imaging, providing high contrast even for nanometer scale defects. The deposited AlO(x) also acts as a barrier for electron transfer, thereby simultaneously electrically passivating the defects in the SAM as it labels them.

Interfacial effects in thin films of polymeric semiconductors

The surface onto which polymeric semiconductors are cast from solution plays an important role in determining the electrical transport properties of the polymeric thin film. The authors use synchrotron-based x-ray diffraction to show that even moderate roughness (rms∼5 A) can affect the texture of semicrystalline poly(thiophene) thin films. Moreover, the authors use a novel optical characterization technique (surface plasmon resonance spectroscopy) to characterize the appearance of electronic states in the bandgap of thin films (∼20 nm) of regioregular poly(thiophene). Such states may be due to the heterointerface between the thin Au substrate and the polymer.