Thermal stability of Al nanocluster arrays on Si (111)-7 × 7 surfaces

Abstract

By means of in situ high-temperature scanning tunnelling microscopy (STM), the thermal stability of highly ordered artificial Al nanocluster arrays, so-called two-dimensional nanocluster crystals, on vicinal Si (111)-7 × 7 surfaces has been investigated. It was found that Al nanocluster crystals are stable below 500 °C. Above 500 °C, the Al nanocluster crystal transforms into a surface phase with singular triangle shapes on down-terraces (the down-step side of a terrace). However, on up-terraces (the up-step side of a terrace), Al nanoclusters can move on Si (111)-7 × 7 surfaces over a large distance and the Al nanocluster crystal retracts toward the phase until the bare Si (111)-7 × 7 surface is completely recovered on up-terraces. The thermally activated motion of Al nanoclusters was not observed apparently below 400 °C, though Al nanocluster crystals can be formed even at 200 °C. This indicates that it is atom diffusion, not cluster diffusion, which is responsible for the formation process of metal cluster crystals on Si (111)-7 × 7 surfaces.

Dynamic behavior and phase transition of magic Al clusters on Si(111)-7×7 surfaces

“…2 shows the temperature dependence of the jump frequency with a linear y scale. The identification of ͱ3 ϫ ͱ 3-Al has been done in our previous study 9 and also by others. Notably, it is also above 500°C ͑Ref.…”

“…8 In our previous study, 9 the thermal stability of the Al nanocluster crystal was investigated systematically. 1͒ as well as Al, Ga, In, Ag, Na, Pb, etc.…”

Al nanocluster arrays onSi(111)−7×7surfaces: Formation process and interactions among clusters

“…In our previous studies, 17,18 the dynamic behavior of Al magic clusters on the Si͑111͒-7 ϫ 7 surface at high temperature has been investigated by variable-temperature STM. It was found that fast diffusion of magic Al clusters occurs above 500°C, with an activation energy of 2.0± 0.3 eV, together with the decomposition of the clusters into the ͱ3 ϫ ͱ 3-Al phase.…”

Trimeric precursors in formation of Al magic clusters on a Si(111)-7×7surface

“…Recently, surface-mediated magic clustering was employed as the building blocks for identicalsized nanostructures, and the results demonstrated that the fabrication of artificial cluster crystals is possible. [4][5][6][7][8][9][10][11][12][13][14][15] While the fabrication of precise surface nanostructures has made exciting progress, the formation mechanism for this kind of surface magic cluster is still poorly understood, partly because of the complexity of the process from formation to detection. Recent experiments using a variable-temperature scanning tunneling microscope (STM) have given an unprecedented view of epitaxial nucleation and island growth.…”

“…6,7 Our previous studies reported the thermal stability of Al magic cluster arrays and the interaction between arrays. [13][14][15] It was found that the Al magic cluster arrays are stable up to 500 • C, transforming into a ( √ 3 × √ 3)-Al phase above 500 • C. From the activation energy of the Al magic cluster, it was concluded that Al atoms congregate to form the Al magic cluster arrays through a single-atom diffusion process, rather than through a cluster diffusion process. An attractive interaction was found between the Al magic clusters, which is responsible for the honeycomb structure.…”