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Shape and composition of buried PbSe quantum dots determined by scanning tunneling microscopy
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View: Figures


Image of FIG. 1.
FIG. 1.

STM images of PbSe dots covered with different PbTe cap layer thicknesses of 30, 40, 80, and from (a)–(d), respectively. The highly facetted pyramidal shape of the as grown dots is evidenced by the enlarged three-dimensional image of a single uncapped PbSe dot shown as insert in (a). The insert in (b) shows the zoomed-in image of a single surface depression induced by a buried dot.

Image of FIG. 2.
FIG. 2.

(Color online) STM line profiles measured across the surface depressions above PbSe dots for 40, 60, 80, and cap layer thickness (from left to right). The gray lines represent the profiles over individual dots and the blue line the averaged profile.

Image of FIG. 3.
FIG. 3.

(Color online) Top: (a) schematic illustration of the change in PbSe dot structure induced by PbTe overgrowth. (b) Different possible base geometries of the buried dots: (left) facetted truncated pyramid and (right) round frustum. Bottom: color contour plots of the local surface depression induced by differently shaped dots at PbTe cap thickness. [(c) and (d)] simulation for circular, respectively, triangular dot base and (d) STM measurement (filtered). The color scale spans surface height. The comparison between measurement and calculations shows that the actual PbSe dot shape lies in between the two liming cases, as shown in panel (b).

Image of FIG. 4.
FIG. 4.

(Color online) Calculated surface profiles for different dot shapes (gray lines) plotted in comparison with measured STM profiles (blue lines). [(a) and (b)] Dot with Se concentration and facet angle but varying dot base width for cap thickness of (a) 40 and (b) . (c) Dot with and but varying side wall angle . (d) Dot with constant base width , , and but varying Se concentration . The base shape of the dots was assumed as rounded triangle, as indicated in Fig. 2(b).

Image of FIG. 5.
FIG. 5.

(Color online) (a) Best fit (circles) of the STM profiles (blue lines) for cap thicknesses of 40, 60, 80, and using a single set of parameters for the buried dots of , , , and . (b) Calculated amplitude of the surface depression (open symbols) plotted as a function of cap thickness for different Se concentrations of the dots showing the rapid decay with increasing cap thickness. The measured STM values are plotted as full squares and are in good agreement for .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Shape and composition of buried PbSe quantum dots determined by scanning tunneling microscopy