Nanoscale Res Lett (2006) 1:11–19 13 Fig. 2 STM image of Ge growth on Si(100) without Xe buffer layer below the critical Ge coverage (~3.0 ML). Inset Ge clusters grown with the same approach the formation of a 2D wetting layer [12]. The inset of Fig. 2 shows a thinner Ge layer (~1.2 ML) on Si [16]. At a Ge coverage slightly above the critical thickness, a strain relieving transition leads to 3D island formation [12]. Figure 3a shows a typical SK Ge-island with a base size of 60 nm, which formed on top of the Ge wetting layer with a Ge coverage of 3.2 ML. It is well known that SK Ge islands-shapes display several forms such as hut, pyramid, and dome depending on growth conditions. The background of the STM data also clearly indicates a Ge wetting layer, which is described as a domain 2 · n structure. Ge nanoclusters grown by the BLAG method show a strikingly different morphology as compared to the SK clusters. Figure 3b shows a STM image of Ge nanoclusters after the deposition of 0.5 ML equivalent of Ge atoms on a 6 ML xenon buffer layer. The image was taken at room temperature after the xenon buffer was removed by sublimation. With such a small amount of deposited Ge, it would not be possible to see any cluster formation in the SK growth regime since 0.5 ML is less than the critical thickness [3, 5, 17]. However, with the BLAG method, the Ge nanoclus- ters clearly appear with an irregular 3D or dome-like shape as shown in Fig. 3b. A pristine Si surface along with two-step edges can be seen in the background of the STM image in Fig. 4a. The equivalent Ge coverage derived from the nanocluster size and density conﬁrms that all Ge adatoms exist in the form of nanoclusters. It proves that the mediation of the Xe buffer pre- vents direct interactions of deposited atoms with the substrate and no strained wetting layer formation Fig. 3 STM images of (a) a typical Ge island grown by SK mode just before involving into the 3D dome shape (Ge ~ 3.2 ML); (b) Ge nanoclusters grown by BLAG with a line proﬁle (Ge ~ 0.5 ML) in-between the nanoclusters. The average width of those nanoclusters is 3 nm, and the average height is 0.6 nm with a narrow size distribution as displayed in Fig. 4b. The nanoclusters are remarkably smaller than SK Ge clusters, which normally have a width of 60–200 nm and a height of 12 nm for pyramid or dome shaped clusters on top of a wetting layer [3]. Even the hut clusters are 20–40 nm laterally and 1–3 nm in height [1, 3]. The cluster density is deduced from Fig. 4a to be about 5 · 1012 cm–2; i.e., more than three orders of magnitude higher than SK dots with a density of 108–109 cm–2 in dome or pyramid shapes, and two orders of magnitude higher than hut clusters [1, 3]. The dimensions of these quasi-0D clusters provide the