@article{tedesco_rowe_nemanich_2010, title={Titanium silicide islands on atomically clean Si(100): Identifying single electron tunneling effects}, volume={107}, ISSN={["0021-8979"]}, DOI={10.1063/1.3437049}, abstractNote={Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (<2 nm) on atomically clean Si(100) substrates followed by annealing to ∼800 °C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to exhibit single electron tunneling (SET) according to the orthodox model of SET. Some of the islands formed are small enough (diameter <10 nm) to exhibit SET at room temperature and evidence of SET has been identified in some of the I-V curves recorded from these small islands. Those curves are analyzed within the framework of the orthodox model and are found to be consistent with that model, except for slight discrepancies of the shape of the I-V curves at current steps. However, most islands that were expected to exhibit SET did not do so, and the reasons for the absence of observable SET are evaluated. The most likely reasons for the absence of SET are determined to be a wide depletion region in the substrate and Schottky barrier lowering due to Fermi level pinning by surface states of the clean silicon near the islands. The results establish that although the Schottky barrier can act as an effective tunnel junction in a DBTJ structure, the islands may be unreliable in future nanoelectronic devices. Therefore, methods are discussed to improve the reliability of future devices.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tedesco, J. L. and Rowe, J. E. and Nemanich, R. J.}, year={2010}, month={Jun} }
 @article{tedesco_rowe_nemanich_2009, title={Conducting atomic force microscopy studies of nanoscale cobalt silicide Schottky barriers on Si(111) and Si(100)}, volume={105}, ISSN={["0021-8979"]}, DOI={10.1063/1.3100212}, abstractNote={Cobalt silicide (CoSi2) islands have been formed by the deposition of thin films (∼0.1–0.3 nm) of cobalt on clean Si(111) and Si(100) substrates in ultrahigh vacuum (UHV) followed by annealing to ∼880 °C. Conducting atomic force microscopy has been performed on these islands to characterize and measure their current-voltage (I-V) characteristics. Current-voltage curves were analyzed using standard thermionic emission theory to obtain the Schottky barrier heights and ideality factors between the silicide islands and the silicon substrates. Current-voltage measurements were performed ex situ for one set of samples (termed “passivated surfaces”) where the silicon surface surrounding the islands was passivated with a native oxide. Other samples (termed “clean surfaces”) remained in UHV, while I-V curves were recorded. By comparing the barrier heights and ideality factors for islands on passivated surfaces and clean surfaces, the effects of the nonpassivated surfaces on conduction have been studied. The barrier heights measured from CoSi2 islands on clean surfaces are found to be ∼0.2–0.3 eV below barrier heights measured from similar islands on passivated surfaces. The main cause of the reduced Schottky barrier in the clean surface samples is attributed to Fermi level pinning by nonpassivated surface states of the clean silicon surface. However, the measured barrier heights of the islands are equivalent on both clean Si(111) and Si(100) surfaces, suggesting that the nonpassivated surface is influenced by cobalt impurities. Furthermore, the barrier heights of islands on the clean surfaces are lower than what can be explained by Fermi level pinning alone, suggesting the presence of additional reductions in the Schottky barrier heights. These variations are greater than what can be attributed to experimental error, and the additional barrier height lowering is primarily attributed to spreading resistance effects. Schottky barrier inhomogeneity is also identified as a possible cause of the additional barrier height lowering and nonideality in the Schottky contacts. Current-voltage measurements of the clean surface samples were also obtained at several temperatures. The barrier heights were found to decrease, and the ideality factors were found to increase with decreasing temperature. The dependence of the barrier height is attributed to the temperature variation of the Fermi level.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tedesco, J. L. and Rowe, J. E. and Nemanich, R. J.}, year={2009}, month={Apr} }