Figure 5

(Color) Number of nonperiodic sites (protrusions of height greater than 0.23 nm) per image, from a series of 142 images, all of the same size (20 × 20 nm). "Spikes" in current that only affect one or two pixels of a single scan line were also omitted. For a surface prepared by aging for 96 h in DDI H₂O (but imaged in air), relatively large numbers of nonperiodic sites were observed in the -800 to -500 mV range but not at other bias voltages (blue squares). For a surface prepared by boiling in nitric acid for 1 h, nonperiodic sites were not observed in any significant numbers (red squares). The data points represent averages for different images; error bars are 2σ values from the variance in numbers of sites for the different images.