NanoSystems Seminar Series: 2012 Fall Quarters
October 09, 2012
Seth Coe-Sullivan, PhD
Co-founder and Chief Technology Officer
|Quantum Dots: Nanomaterials for Lighting and Display Applications |
Abstract: Quantum dots (QDs) as downconversion materials have several basic properties that have long made them potentially interesting options for the LED lighting and LCD backlight markets – e.g. they are narrowband emitters with a wide range of color tunability. However, limitations such as stability, high temperature operation, and high flux operation have limited QD applicability, as the cost to benefit ratio or value proposition was not previously compelling enough to drive mainstream product adoption.
Over the past year, significant breakthroughs in stability, efficiency and reliability at higher temperatures, as well as large scale investment in manufacturing capacity have eliminated the main barriers to high volume, mainstream product adoptions of QD materials in display devices. In this presentation, we will update the community on the material performance improvements that have broken through these commercialization barriers, and describe how the materials are transforming a variety of products and product forms.
September 11, 2012
Institut fuer Halbleiter- und Festkoerperphysik
Johannes Kepler Universität
|Si/Ge growth on pre-patterned and high-indexed surfaces: From 1D ripples to 3D domes |
Si-Ge heteroepitaxy has been an essential model system for growth of self-assembled nanostructures by the Stranski-Krastanow mode. A striking feature of these structures is their highly facetted shape  that is governed by the formation of energetically favored facets. Evidently, the different shapes depend not only depend on the Ge coverage and growth condition, but also on the substrate orientation. Therefore, local prepattering as well as control of substrate orientation provides a means for tuning the shapes as well as lateral positions of such nanostructures [2-6].
In this presentation, new results on SiGe growth on patterned and vicinal Si substrates are presented, based on in situ scanning tunneling microscopy studies and theoretical calcula¬tions. By STM the complete surface evolution after individual growth steps is revealed with atomic resolution without breaking UHV conditions . It is demonstrated that the growth evolution on high-indexed surfaces can radically differ from that on the usual Si (001) surface in that due to symmetry breaking 1D nanowires instead of 0D quantum dots are formed. As shown by theoretical calculations, the ripples represent a novel pathway for lowering the total free energy of the system [5,6] and show a reversible behavior during annealing. The in-plane Ge nanowires can be also contacted by electrical leads and quantized transport has been demonstrated . Moreover, by prepattering of the Si substrate, the direction and position of the 1D nanowires can be controlled [8,9].
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