Temperature-Dependent Site Control of InAs/GaAs (001) Quantum Dots Using a Scanning Tunneling Microscopy Tip During Growth

Site-controlled InAs nano dots were successfully fabricated by a STMBE system (in situ scanning tunneling microscopy during molecular beam epitaxy growth) at substrate temperatures from 50 to 430°C. After 1.5 ML of the InAs wetting layer (WL) growth by ordinal Stranski–Krastanov dot fabrication procedures, we applied voltage at particular sites on the InAs WL, creating the site where In atoms, which were migrating on the WL, favored to congregate. At 240°C, InAs nano dots (width: 20–40 nm, height: 1.5–2.0 nm) were fabricated. At 430°C, InAs nano dots (width: 16–20 nm, height: 0.75–1.5 nm) were also fabricated. However, these dots were remained at least 40 s and collapsed less than 1000 s. Then, we fabricated InAs nano dots (width: 24–150 nm, height: 2.8–28 nm) at 300°C under In and As4 irradiations. These were not collapsed and considered to high crystalline dots

Гидрогеологические условия участка строительства электростанции (г. Калининград)

Актуальность работы темы исследования заключается в том, что эксплуатация ТЭС связана с использованием ресурсов подземных вод. Цель работы: оценить роль подземных вод на этапе строительства и эксплуатации проектируемых объектов ТЭС.The relevance of the research topic is that the operation of thermal power plants is associated with the use of groundwater resources. Objective: to assess the role of underground water at the stage of construction and operation of the projected TPS facilities

The influence of surface stress on the equilibrium shape of strained quantum dots

The equilibrium shapes of InAs quantum dots (i.e., dislocation-free, strained islands with sizes >= 10,000 atoms) grown on a GaAs (001) substrate are studied using a hybrid approach which combines density functional theory (DFT) calculations of microscopic parameters, surface energies, and surface stresses with elasticity theory for the long-range strain fields and strain relaxations. In particular we report DFT calculations of the surface stresses and analyze the influence of the strain on the surface energies of the various facets of the quantum dot. The surface stresses have been neglected in previous studies. Furthermore, the influence of edge energies on the island shapes is briefly discussed. From the knowledge of the equilibrium shape of these islands, we address the question whether experimentally observed quantum dots correspond to thermal equilibrium structures or if they are a result of the growth kinetics.Comment: 7 pages, 8 figures, submitted to Phys. Rev. B (February 2, 1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

On the development of InAs on GaAs(001) as measured by reflectance anisotropy spectroscopy: continuous and islanded films

Reflectance anisotropy spectroscopy (RAS) has been used to monitor the formation and development of InAs islands grown onto GaAs(001) substrates. It is shown by time resolved measurements that entirely different responses are measured at different photon energies and that these correspond to different aspects of the islanding process. At a photon energy of 2.6 eV RAS is very sensitive to the onset of islanding, whereas the 4.0 eV signal appears to be sensitive to the continuous inter-island film. Using the 4.0 eV signal it was possible to follow the real time development of the islanded surface and to identify that at low growth temperatures, beyond the thickness for islanding, only a small fraction of the incident fluxes are incorporated immediately into the islands

Processes of quantum dot formation in the InAs on GaAs(001) system: A reflectance anisotropy spectroscopy study

Reflectance anisotropy spectroscopy (RAS) has been used to monitor the formation and development of InAs islands grown onto GaAs(001) substrates by molecular beam epitaxy. Time resolved measurements show entirely different responses at different photon energies, corresponding to different aspects of the islanding process. At a photon energy of 2.6 eV RAS is sensitive to the onset of islanding, whereas the 4.0 eV signal appears to be sensitive to the continuous interisland wetting layer. Thus, by using the 4.0 eV signal it is possible to follow the real time development of the islanded surface. In particular, it is found that (1) during growth and immediately beyond the point of islanding, a fixed fraction of the incoming flux is directly transferred to the islands, and this fraction increases with increasing growth temperature up to 100%; (2) as a consequence of this, the wetting layer can increase in thickness beyond the 1.6 monolayers islanding thickness, to at least ∼2 monolayers; (3) the importance of islands acting as sinks for the acquisition of material from the wetting layer is revealed; (4) the dynamic equilibrium set up between the islands and the wetting layer is such that the thickness of the latter increases significantly with sample temperature

Optical monitoring of the development of InAs quantum dots on GaAs(001) by reflectance anisotropy spectroscopy

Reflectance anisotropy spectroscopy (RAS) in combination with reflection high‐energy electron diffraction (RHEED) was used to study in situ the initial steps of molecular beam epitaxial growth of InAs on GaAs(001). Due to the large lattice mismatch InAs is known to grow in Stranski–Krastanov mode leading to the formation of quantum dots after the transition from two‐ to three‐dimensional growth mode. In this article the precise determination of the growth mode transition and the subsequent development of the islands have been of particular interest. During the growth of the two‐dimensional InAs layer, the RHEED‐pattern changed from the c(4×4) of the clean GaAs to a (1×3) surface reconstruction. Accordingly, the RAS‐spectra, taken every 0.2 ML, indicate changes of the As‐dimer configuration. At 1.8 ML (spotty RHEED‐pattern) a saturation of the intensity of the dimer related RAS‐signal around 2.6 eV was found. The relaxation of the InAs layer and the formation of the quantum dots was followed by time‐resolved RAS at 2.6 and 4 eV. It is shown here, that the time constant of this process, the thickness of the InAs wetting layer and the equilibrium morphology of the islands are strongly temperature dependent. The remaining equilibrium InAs wetting layer thickness at the surface was estimated to be about 1 ML (0.8 ML at 625 K and 1.2 ML at 725 K)