(204b) Ald Copper-Palladium Thin Films for Molecular Electronics

Atomic layer deposition (ALD) is a powerful tool for nanoelectronics. In addition to its role for growing ultrathin films in microelectronics, ALD can be used for controlling critical dimensions on the nanometer scale. In this work we present a unique technique for growing monolithic molecular electronic tunnel junctions using ALD. In molecular tunnel junctions, the spacing between the metal electrodes must be small enough to adsorb individual or small groups of molecules, on the order of 1-2 nm. This requirement makes ALD an ideal process to fabricate nanoelectronic devices because it provides subnanometer thickness control. Compared to other molecular electronics devices, ALD grown junctions have a number of advantages including the ability to measure and control the electrode chemical composition and atomic structure. Electrical transport measurements through molecules have established that contact effects are significant, so the ability to tune structure and composition is a considerable advantage. Transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and glancing incidence x-ray diffraction (XRD) were used to investigate the chemical composition and atomic structure of ALD-grown copper films on palladium seed layers after various growth conditions. XPS showed that palladium is present on the surface of the film, regardless of how much copper is deposited, and a pure copper surface is not obtained. This is explained by the miscibility of the two metals and the formation of alloys under growth conditions. It is proposed that the presence of palladium on the surface may promote the growth of copper, and this characteristic may be useful to control copper growth and surface layer composition. In addition, XRD and electron diffraction have been used to characterize the electrode structure. It will be demonstrated that ALD grown molecular tunnel junctions are a promising approach to understanding and engineering molecular electronic devices.