The UTC Graduate School is pleased to announce that Mohamed Osman Mohamed Koko will present Master’s research titled, DISCRETE ENERGY SPECTRA AND CHARGE TRANSPORT IN METALLIC QUANTUM-DOT SINGLE-ELECTRON DEVICES on 10/16/2026 at 11:00 in ECS 347. Everyone is invited to attend.
Engineering
Chair: Sharief Babikir
Co-Chair:
Abstract:
When a metallic island in a single-electron device shrinks to a few nanometers, quantum confinement makes its electronic spectrum discrete, and charge transport becomes a resonant process governed jointly by Coulomb blockade and the availability of individual energy levels. This thesis develops a circuit-level modeling framework in which the discrete spectrum of each quantum dot is computed from its physical size and work function rather than imposed, and is then incorporated into a state-based master-equation description of single-electron transport. The spectrum is obtained from a finite spherical potential well. A first-generation model retains only states of zero orbital angular momentum with a fixed level degeneracy; the generalized model computes the bound states for every angular momentum the well supports, using a reformulated eigenvalue condition that is free of poles and exponential factors, so that a single sign-change search returns the complete spectrum. Level degeneracies then follow from the geometry as 2(2l+1), producing shell closings at 2, 8, 18, 20, 34, and 40 electrons, and the tunneling rates are weighted by the occupancy and capacity of each individual level. For a 2.5 nm gold dot, the full spectrum places an l=1 state below the second l=0 state, reducing the first excitation gap from 0.63 eV to 0.22 eV. Applied to single-dot transistors with 2.5 nm and 3.5 nm gold dots, the model yields threshold voltages of 0.356 V and 0.21 V and staircase current–voltage characteristics whose steps are traced to specific changes in the set of active charge states. Applied to a coupled two-dot system with 3.5 nm gold dots, it predicts current peaks at 0.306, 0.755, 0.934, and 1.041 V and shows that, although the number of possible charge states grows rapidly with bias, three states account for 99.92% of the occupation probability at the first peak. The framework relates dot dimensions, capacitances, level availability, and bias conditions directly to the electrical response of coupled single-electron circuits.