The evolution of strained Ge/Si(001) islands during exposure to a Si flux was investigated by scanning tunneling microscopy. Dome islands display appreciable shape changes at Si coverages as low as 0.5 monolayer. With increasing coverage, they transform into [105]-faceted pyramids, and eventually into stepped mounds with steps parallel to the <110> directions. These morphological changes are induced by alloying and represent a complete reversal of those previously observed during Ge island growth. The results are interpreted with a simple model in which the equilibrium shape of an island mainly depends on its volume and composition.

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We report on the fabrication of modulation-doped compressively strained Ge quantum wells by low-energy plasma enhanced chemical vapor deposition. A virtual substrate consisting of a thick linearly graded SiGe buffer layer and a cap layer of constant composition is first grown at a high rate (&gt;5 nm/s). The active layer stack, grown at a reduced rate, contains strain compensating cladding layers with modulation doping above the channel. Mobilities of up to 3000 cm2/V s and 87 000 cm2/V s have been achieved at room temperature and liquid He temperature, respectively.

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Low energy plasma enhanced chemical vapor deposition (LEPECVD) has been applied to the synthesis of Si-modulation doped field effect transistor structures, comprising a SiGe relaxed buffer layer and a modulation doped strained Si channel. A growth rate of at least 5 nm/s for the relaxed SiGe buffer layer is well above that obtainable by any other technique. Due to the low ion energies involved in LEPECVD, ion damage is absent, despite a huge plasma density. The structural quality of the LEPECVD grown SiGe buffer layers is comparable to that of state-of-the-art material. The electronic properties of the material were evaluated by growing modulation doped Si quantum wells on the buffer layers. We obtain a low temperature (2 K) Hall mobility of μH=2.5×104 cm2/Vs for the electrons in the Si channel at an electron sheet density of ns=8.6×1011 cm−2.

This paper contains a detailed study of the flow that the classical Hamiltonian induces in R 4 , Θ 3 representing a convergent power series that begins with a third order term. In particular the existence and stability of periodic orbits is investigated.

An intimate relationship between Moser's regularization [1] and the KS-regularization [3] of the 3-dimensional Kepler problem is established. Explicit formulae linking Moser's and the KS-transformation are obtained in the case of negative as well as in the case of positive energies. As a side result it is shown that the KS-transformation owes its existence to the local isomorphism of SO (2,4) and SU(2,2).

Notation 2.8 (∞ ∃x) means 'for an infinite number of x.' (∞ ∀x) means 'for all but a finite number of x;' equivalently, 'for almost all x.' Notation 2.9 If f and g are two functions then f = * g means that (∞ ∀ x)[f (x) = g(x)]. If a is a constant then λx[a] denotes the constant function that always outputs a. The expression f = * λx[a] means that (∞ ∀x)[f (x) = a].