Figure 1
From: Impact of Wide-Ranging Nanoscale Chemistry on Band Structure at Cu(In, Ga)Se2 Grain Boundaries
Change in chemistry from the grain boundary to the grain interior \({({\rm{\Delta }}{\rm{{\rm X}}}}_{BI})\). (a) Side-by-side of TEM images of the specimen before and after atom probe analysis used to identify volume of APT reconstruction. Top (bottom) is a TEM image taken after (before) atom probe analysis. (b) Reconstructed volume capturing a GB. Less than 1% of In (red), Se (blue) and Ga (yellow) ions are shown to give an illustration of the specimen tip shape. An isoconcentration surface of 0.35 at. % K (dark yellow) illustrates segregation to the GB. (c) A cylindrical region of interest, taken from dotted square box in (b), used to enclose the reconstructed ions for chemical analysis. The grain boundary is determined by K segregation, shown in dark yellow. (d) Average composition (at. %) of the first 6 nm (four slices) of both ends of the cylinder was calculated as a grain-interior chemical reference. That value was subtracted from the composition of each slice (1.5 nm thick along the axis of the cylinder), leading to the grain boundary, which resulted in a relative change of chemistry \({({\rm{\Delta }}{\rm{{\rm X}}}}_{BI})\) as a function of distance from the grain boundary. Errors: ± 0.2 at. % Cu, ± 0.1 at. % In, ± 0.3 at. % Se, ± 0.07 at % Ga, 0.04 at. ± % K, and ± 0.03 at. % Na.
