51 research outputs found
Resonator fabrication for switchable two-color MIR detectors based on p-type SiGe quantum cascade injectors
No full textThe Delft intense slow positron beam 2D-ACAR facility for analysis of nanocavities and quantum dots
No full textPositron annihilation spectroscopy is a powerful method to study materials containing very small concentrations of atomic defects and embedded quantum dots. Depending on the method of producing positrons, there are bulk spectroscopies using fast positrons and depth profiling spectroscopies using slow positrons. Both types of spectroscopies are available at the Positron Centre Delft of the Interfaculty Reactor Institute and are applied in material science. This thesis describes the construction of and the first results obtained with a unique two-dimensional angular correlation of annihilation radiation (2D-ACAR) setup coupled to the continuous high intensity slow positron beam (POSH). This new setup allows for the first time high-resolution momentum distribution measurements of thin films, multilayers, interfaces and metallic quantum dots. Important new information con- cerning the geometric and electronic structure of these systems can be obtained with this setup. At this moment the facility is the only one of this kind in the world.Interfaculty Reactor Institut
Three-dimensional Ge/SiGe multiple quantum wells deposited on Si(001) and Si(111) patterned substrates
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Heterointegration by molecular beam epitaxy: (In,Ga)As/GaAs quantum wells on GaAs, Ge, Ge/Si and Ge/Si pillars
No full textIn-situ Hydrogen Sorption 2D-ACAR Facility for the Study of Metal Hydrides for Hydrogen Storage
No full textWe developed a dedicated hydrogen sorption setup coupled to a positron 2D-ACAR (two-dimensional Angular Correlation of Annihilation Radiation) setup employing a 22Na-source, which will enable to collect 2D-ACAR momentum distributions in-situ as a function of temperature, hydrogen pressure and hydrogen content. In parallel, a dedicated glovebox was constructed for handling air-sensitive metal and metal hydride samples, with a special entrance for the 2D-ACAR sample insert. The 2D-ACAR setup was tested in first measurements on a Pd0.75Ag0.25 foil and on a ball-milled MgH2 powder in both the hydrogen loaded and desorbed states. The hydrogen loaded Pd0.75Ag0.25Hx sample was kept under a 1 bar hydrogen pressure to prevent partial desorption during measurements at room temperature. The collected 2D-ACAR distributions of Pd0.75Ag0.25 and Pd0.75Ag0.25Hx showed similar features as observed in previous studies. The broadening of the ACAR distributions observed for the Mg to MgH2 metal-insulator transition was compared in a quantitative manner to ab-initio calculations reported in the literature.RST/Radiation, Science and TechnologyApplied Science
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