Experimental setup: (a) GLAD via ion beam assisted sputtering. (b)Target-substrate geometry during the GLAD process with slit aperture 2. The polar angle of the sample holder to the target is kept at 1°. However, the glancing angle ranges between 0° and 18°, because of the broad angular distribution of the sputtered particles.
Cross-plane section symmetries in the honeycomb arrangement.
SEM top-view: temporal evolution of Ge nanocolumns in honeycomb arrangement (p = 803 nm, α = 18°) on NSL-patterned Si (100) substrate.
Cross-plane shape of the temporal evolution of Ge nanocolumns inhoneycomb arrangement. (a) cut 1, p = 803 nm, α = 18° and (b) cut 2, p= 803 nm, α = 38°.
GLAD nanocolumn sample in honeycomb arrangement (p = 803 nm, α = 18°) with eight alternating Si/Ge heterojunction pairs. (a) Cross-plane shape of a single Si/Ge nanocolumn. (b) Cross-plane shape of the interdistance deposits showing the ceasing after four heterojunction pairs.
(Left) Cross-plane shape of Ge nanocolumns in honeycomb arrangement (p = 293 nm, α = 18°). During the early stage of deposition, the initial region is formed. When the equilibrium shape has reached, a columnar region with parallel border planes evolves. On top, a characteristically shaped cap is found resulting from the shadow geometry between next neighbors (sketch on the right).
Axial extents of the initial region and the interdistance deposits with respect to the honeycomb pattern periodicity for different glancing angles.
SEM top view: Equilibrium shape of Ge nanocolumns in honeycomb arrangement with respect to the pattern periodicity p and glancing angle α. The arrows indicate the main incidence directions for the inner plane formation.
Column interspace distance between next neighbors with respect tothe pattern periodicity for different glancing angles. For α = 8°, α = 18°, and α = 38°, the obtained interspace distances are , , and , respectively.
(a) Cap height h and (b) column diameter D with respect to the honeycomb pattern periodicity p for different glancing angles. The data points in (a) are average values of direct measurements from SEM cross-plane images. The lines are linear fits () through the data points. The diameter data points in (b) are directly measured out of SEM in-plane images. The lines are calculated from the porosity with Eq. (1). As a reasonable approximation, the lines can be fitted linearly via . The slope values k and l are summarized in Table I.
Cap structure parameters with respect to glancing angle α and pattern periodicity p. The slopes l and k of the linear dependencies of column diameter D and cap height h on the pattern periodicity were applied to determine the cap aspect ratio h/D for the three glancing angles.
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