The interaction of water and carbon dioxide with nanostructured epitaxial (Ba,Sr)TiO3(001) thin film and bulk single crystal SrTiO3(001) surfaces was studied using x-ray photoemission spectroscopy (XPS), thermal desorption spectroscopy (TDS), and density functional theory (DFT). On both surfaces, XPS and TDS indicate D2O and CO2 chemisorb at room temperature with broad thermal desorption peaks (423–723 K) and a peak desorption temperature near 573 K. A comparison of thermal desorption Redhead activation energies to adsorption energies calculated using DFT indicates that defect surface sites are important for the observed strong adsorbate-surface reactivity. Numerical calculations of the competetive adsorption/desorption equilibria for H2O and CO2 on SrTiO3(001) surfaces show that for typical atmospheric concentrations of 0.038% carbon dioxide and 0.247% water vapor the surfaces are covered to a large extent with both adsorbates. The high desorption temperature indicates that these adsorbates have the potential to impact measurements of the electronic structure of BaTiO3–SrTiO3(001) surfaces exposed to air, or prepared in high vacuum deposition systems, as well as the electrical properties of thin film ATiO3-based devices.
A method for the experimental determination of surface photoemission core-level shifts for 3d transition metals J. Appl. Phys. 98, 014908 (2005); 10.1063/1.1948508 Surface and interface chemical composition of thin epitaxial SrTiO 3 and BaTiO 3 films: Photoemission investigation
The importance of interface and bulk transport mechanisms on the leakage current of high dielectric constant thin film capacitors is examined by deriving an equation for the J–VA characteristic of a capacitor that includes the transport mechanisms of thermionic emission (TE), thermionic field emission (TFE), and carrier drift–diffusion (DD). The current is controlled by the slowest of three effective velocity parameters v1md, vD, and ṽ2dm characterizing electron injection into the dielectric at the cathode by TE and TFE, carrier DD in the film bulk, and electron ejection from the dielectric at the anode by TE and TFE, respectively. The effective velocity parameters are evaluated for a Pt/BST/Pt thin film capacitor that has been exposed to forming gas and it is shown that the dominant transport mechanism is interface limited TFE from the cathode with negligible influence of carrier transport by DD in the film bulk. Implications of these results on existing transport calculations for high dielectric constant thin film capacitors are discussed.
Etching yields of SiO2 have been determined for F+, CFx+ (x=1,2,3) ion irradiation with energy ranging from 250 to 2000 eV using a mass-analyzed ion-beam apparatus that can irradiate a single species ion to sample surfaces under an ultrahigh vacuum condition. The etching yield of CFx+ (x=1,2,3) was enhanced by the chemical effects of the ions, and both carbon and fluorine atoms from the incident ions were significant reactants. For lower energies, the etching yield increased with increasing ion energy. Above 1000 eV, the etching yield was gradually saturated with increasing ion energy. In the low ion energy region, steady etching did not occur, and an amorphous fluorinated carbon (a-C:F) film was deposited on the SiO2 surface. The ion energy region in which a-C:F film deposition occurred decreased with increasing fluorine atoms in incident CFx+ (x=1,2,3) ions.
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