Osman Mohamed Koko to Present Engineering Master's Research

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

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.