Coexistence of Two Electronic Nano-Phases on a CH$_{3}$NH$_{3}$PbI$_{3-x}$Cl$_{x}$ Surface Observed in STM Measurements

Scanning tunneling microscopy is utilized to investigate the local density of states of a CH$_{3}$NH$_{3}$PbI$_{3-x}$Clx perovskite in cross-sectional geometry. Two electronic phases, 10$-$20 nm in size, with different electronic properties inside the CH$_{3}$NH$_{3}$PbI$_{3-x}$Cl$_{x}$ perovskite layer are observed by the d$I$/d$V$ mapping and point spectra. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in d$I$/d$V$ mapping at $-$2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in d$I$/d$V)$.$^{1}$ [1] \textit{ACS Appl. Mater. Interfaces},~\textbf{2016},~8~(42), pp 29110--29116