The transport physics of domain wall conductivity in La-doped bismuth ferrite (BiFeO3) has been probed using variable temperature conducting atomic force microscopy and piezoresponse force microscopy in samples with arrays of domain walls in the as-grown state. Nanoscale current measurements are investigated as a function of bias and temperature and are shown to be consistent with distinct electronic properties at the domain walls leading to changes in the observed local conductivity. Our observation is well described within a band picture of the observed electronic conduction. Finally, we demonstrate an additional degree of control of the wall conductivity through chemical doping with oxygen vacancies, thus influencing the local conductive state.
Spectroscopic ellipsometry and atomic force microscopy (AFM) experiments are employed to characterize nanocolloidal gold films, self-assembled at APTES-derivatized Si/SiO2 surfaces. X-ray fluorescence measurements after deposition confirm that AFM provides a representative means to probe the absolute surface coverage. Optical properties of gold nanocrystal assemblies are investigated both ex situ after drying and in situ prior to evaporation of the solvent. Quantitative optical characterization of these highly inhomogeneous systems is not unambiquous. Conventional effective medium approximations are not applicable to these systems. To enable an accurate analysis, extinction measurements on colloidal suspensions are performed. The limited particle size in relation to the electron mean free path leads to a modification of the dielectric function at longer wavelengths. Ellipsometry spectra of the colloidal gold films are analyzed qualitatively using an optical invariant and principal component analyses. Quantitative results are obtained using a theory which treats the nanocrystals as polarizabilities at the Fresnel interface. Above approximately 20%, the coverages determined from optical spectra are in agreement with what is found from AFM images. At lower coverages, the optical results seem to overestimate the actual nanocrystal density. The discrepancies are discussed in terms of image charge effects arising from the proximity of the substrate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.