Switching of the Fe Oxida\-tion State in Ferro\-cene-Capped Alkanethiols

Molecular electronics has been a rapidly-growing area, due to the simplicity of building molecular devices by self-assembly and the promise of extremely low power consumption as a result of pushing the size down to a few molecules per device. A self-assembled monolayer (SAM) of ferrocene-capped alkanethiols is produced in two stable oxidation states of Fe (Fe$^{2+}$ and Fe$^{3+})$. The oxidation states of Fe are probed with sub-monolayer sensitivity by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy at the iron L$_{2, 3}$ edges $^{[1]}$. NEXAFS provides a direct method to distinguish between the oxidation states of submonolayer by comparing with the bulk sample spectrum. The native Fe$^{2+}$ layer is converted chemically to Fe$^{3+}$, and the Fe$^{3+}$ layer can be switched back to Fe$^{2+}$ or possibly Fe$^{0}$ by irradiation with soft x-rays. The results have implications on switching mechanisms in molecular electronics. [1] Fan Zheng, V. P\'{e}rez-Dieste, J. L. McChesney, Yan-Yeung Luk, Nicholas L. Abbott, and F. J. Himpsel, Appl. Phys. Lett, to be submitted.