J. R. Ahn

Chemical phase transitions of the HfO2∕SiON∕Si nanolaminate by high-temperature thermal treatments in NO and O2 ambient

Temperature-dependent chemical phase transitions of the HfO2∕SiON∕Si(100) nanolaminate in O2 and NO ambient have been investigated using high-resolution photoemission spectroscopy. Hf4f, Si2p, O1s, and N1s photoemission spectra were measured after annealing the nanolaminate at a temperature between 750 and 1150°C. These spectra show that the chemical phase transitions of the nanolaminate strongly dependend on the ambient gases. The nanolaminate in an O2 ambient is stable below 750°C but the HfO2 and SiON layers dissociate by producing Hf silicides above 950°C. In contrast, the nanolaminate in NO ambient does not transit into Hf silicides up to 1050°C. Interestingly, the HfO2 and SiON layers transforms into HfOxNy and SiNx layers, respectively, with a high thermal stability, where the HfOxNy layers are a high-k dielectric material and the SiNx layers work as a barrier against both Si and O diffusion

Alkali metal (Li, K) induced reconstructions of the W(001) surface

The adsorption of Li and K atoms on the (001) surface of tungsten is found to exhibit remarkable differences in the surface core-level shifts (SCLS) of the W 4f level and in adsorbate-induced changes of the transition temperature of the substrate surface reconstruction. Density-functional theory calculations suggest that these results reflect mainly the different bonding geometry of the adatoms, and, for example, the adsorption of potassium is largely affected by an adsorbate-induced reconstruction of the substrate (dimerization of W atoms).