Between Dec 19, 2024 and Jan 2, 2025, datasets can be submitted to DRUM but will not be processed until after the break. Staff will not be available to answer email during this period, and will not be able to provide DOIs until after Jan 2. If you are in need of a DOI during this period, consider Dryad or OpenICPSR. Submission responses to the UDC may also be delayed during this time.

Browsing by Subject "Photoluminescence"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Band-Gap tuning through mechanical semiconductor heterostructures
    (2008-12) Makowski, Jan Dominique
    Band-gap engineering of semiconductor heterostructures has become commonplace for laser diodes and photodetectors. However, the quantum states of these devices are largely fixed during crystal growth. This thesis presents a novel method to control the energy of electron states of surface wells. In essence the method adjusts the thickness of a surface quantum well through controlled interaction with a second well. A cantilever with a quantum heterostructure on its underside collapses on top of an identical heterostructure. The air gap between the well serves as a potential barrier and its width determines the interaction between the wells. At the tip the electron gases of both wells overlap to form a well of their combined width. Along the cantilever, the varying air gap dictates the interaction between the wells. A transition zone forms where the electronic configuration changes from the fully coupled case to the case of two individual wells. After successfully releasing cantilevers, interferometric measurements showed that the shape of the collapsed cantilevers matches with theoretical calculations. Van-der-Waals forces across the 125 nm wide air gap do not affect its shape. An actuator to adjust the well separation is demonstrated. It provides vertical deflections from 17 nm towards to 5 nm away from the surface with atomic resolution. Photoluminescence experiments at 4.2 K investigate the energy of electron states. Quantum coupling is demonstrated in 200 Å wide surface quantum wells. The energy shift of up to 12 meV matches well with theoretical calculations.
  • Thumbnail Image
    Item
    Electrical and optical characterization of colloidal silicon nanocrystals
    (2013-12) Li, Meng
    Colloidal silicon nanocrystals (SiNCs), due to their high photoluminescence efficiency and tunable bandgap, can be used to fabricate highly efficient hybrid nanocrystal-organic light-emitting-devices (NC-OLEDs) that emit in red or near infrared spectrum. Despite reports of outstanding device performance, the underlying mechanism of this high efficiency remains unknown. Consequently, this thesis focuses on studying the electrical and optical properties of SiNCs. The electrical conductivity and mobility of electrons and holes are successfully extracted in order to explain the observed dependence of device efficiency on SiNC surface ligand coverage. Steady-state and transient photoluminescence is also examined to better understand the connection between surface ligand coverage and molecular photophysics. In addition, these measurements are used to better understand the mechanisms for non-radiative exciton decay in SiNCs. This work elucidates the relationship between SiNC properties and device performance, potentially guiding the design of future NC materials for high performance.