122 research outputs found
How kinetics drives the two- to three-dimensional transition in semiconductor strained heterostructures: the case of InAs/GaAs(001)
The two- to three-dimensional growth transition in the InAs/GaAs(001)
heterostructure has been investigated by atomic force microscopy. The kinetics
of the density of three dimensional quantum dots evidences two transition
thresholds at 1.45 and 1.59 ML of InAs coverage, corresponding to two separate
families, small and large. Based on the scaling analysis, such families are
characterized by different mechanisms of aggregation, involving the change of
the critical nucleus size. Remarkably, the small ones give rise to a wealth of
"monomers" through the erosion of the step edges, favoring the explosive
nucleation of the large ones.Comment: 10 pages, 3 figures. Submitted to Phys. Rev. Let
Dynamical evolution of Ge quantum dots on Si(111): from island formation to high temperature decay
Heteroepitaxial growth is a process of profound fundamental importance as well as an avenue to realize nanostructures such as Ge/Si quantum dots (QDs), with appealing properties for applications in opto- and nanoelectronics. However, controlling the Ge/Si QD size, shape, and composition remains a major obstacle to their practical implementation. Here, Ge nanostructures on Si(111) were investigated in situ and in real-time by low energy electron microscopy (LEEM), enabling the observation of the transition from wetting layer formation to 3D island growth and decay. The island size, shape, and distribution depend strongly on the growth temperature. As the deposition temperature increases, the islands become larger and sparser, consistent with Brownian nucleation and capture dynamics. At 550 degrees C, two distinct Ge/Si nanostructures are formed with bright and dark appearances that correspond to flat, atoll-like and tall, faceted islands, respectively. During annealing, the faceted islands increase in size at the expense of the flat ones, indicating that the faceted islands are thermodynamically more stable. In contrast, triangular islands with uniform morphology are obtained from deposition at 600 degrees C, suggesting that the growth more closely follows the ideal shape. During annealing, the islands formed at 600 degrees C initially show no change in morphology and size and then rupture simultaneously, signaling a homogeneous chemical potential of the islands. These observations reveal the role of dynamics and energetics in the evolution of Ge/Si QDs, which can serve as a step towards the precise control over the Ge nanostructure size, shape, composition, and distribution on Si(111)
Abrupt changes in the graphene on Ge(001) system at the onset of surface melting
By combining scanning probe microscopy with Raman and x-ray photoelectron
spectroscopies, we investigate the evolution of CVD-grown graphene/Ge(001) as a
function of the deposition temperature in close proximity to the Ge melting
point, highlighting an abrupt change of the graphene's quality, morphology,
electronic properties and growth mode at 930 degrees. We attribute this
discontinuity to the incomplete surface melting of the Ge substrate and show
how incomplete melting explains a variety of diverse and long-debated peculiar
features of the graphene/Ge(001), including the characteristic nanostructuring
of the Ge substrate induced by graphene overgrowth. We find that the
quasi-liquid Ge layer formed close to 930 degrees is fundamental to obtain
high-quality graphene, while a temperature decrease of 10 degrees already
results in a wrinkled and defective graphene film.Comment: in pres
Driving with temperature the synthesis of graphene films on Ge(110)
We systematically investigate the chemical vapor deposition growth of
graphene on Ge(110) as a function of the deposition temperature close to the Ge
melting point. By merging spectroscopic and morphological information, we find
that the quality of graphene films depends critically on the growth temperature
improving significantly by increasing this temperature in the 910-930 {\deg}C
range. We correlate the abrupt improvement of the graphene quality to the
formation of a quasi-liquid Ge surface occurring in the same temperature range,
which determines increased atom diffusivity and sublimation rate. Being
observed for diverse Ge orientations, this process is of general relevance for
graphene synthesis on Ge
Atomic Force Microscopy Study of the Kinetic Roughening in Nanostructured Gold Films on SiO2
Dynamic scaling behavior has been observed during the room-temperature growth of sputtered Au films on SiO2using the atomic force microscopy technique. By the analyses of the dependence of the roughness, σ, of the surface roughness power,P(f), and of the correlation length,ξ, on the film thickness,h, the roughness exponent,α = 0.9 ± 0.1, the growth exponent,β = 0.3 ± 0.1, and the dynamic scaling exponent,z = 3.0 ± 0.1 were independently obtained. These values suggest that the sputtering deposition of Au on SiO2at room temperature belongs to a conservative growth process in which the Au grain boundary diffusion plays a dominant role
Beneficial defects: exploiting the intrinsic polishing-induced wafer roughness for the catalyst-free growth of Ge in-plane nanowires
Sintesi dei lattoni del whisky e del cognac e loro analoghi attraverso metatesi dei sistemi diolefinici e riduzioni diastereoselettive
Kinetics study of the GaP(110)/Cu interface via P L2,3VV Auger line shape and x-ray-photoemission spectroscopies
We have studied the evolution of the GaP(110)/Cu interface as prepared at room-temperature (RT) versus low-temperature (LT100 K) conditions. Electron-excited P L2,3VV and Cu M1VV Auger line shapes and x-ray-excited (h=1253.6 eV) Ga 2p3/2, Ga 3d, P 2p, Cu 2p3/2, and Cu 3p core-level emissions were followed as a function of the Cu coverage (2 up to 80). Regardless of the substrate temperature, substrate disruption is observed at 1 monolayer Cu, with P atoms participating in chemical bonds with deposited Cu. In parallel, the topmost Ga atoms are dislodged from their pristine locations and segregate in a metalliclike environment. These processes persist in the intermediate-coverage range (212 Cu) at both temperatures, being only relatively attenuated at LT. At very high Cu thicknesses, strong chemical intermixing and out-diffusion of substrate-derived species are still observed at RT, while these processes are nearly completely inhibited at LT. © 1990 The American Physical Society
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