Optical properties and thermal conductivity of resistive Au nanogranular films
| PhD ceremony: | C. Sibanda |
| When: | October 17, 2025 |
| Start: | 11:00 |
| Supervisors: | prof. P. (Petra) Rudolf, prof. dr. G.W. Bosman, prof. dr. C.M. Steenkamp |
| Where: | Academy building RUG / Student Information & Administration |
| Faculty: | Science and Engineering |
In her thesis, Charmaine Sibanda explores ultrathin gold films made of tiny grains—imagine a golden carpet of sand under a microscope. Using a precise deposition method, these nanogranular films are assembled so that they can switch between different electrical states at room temperature. That switching behavior is exactly what neuromorphic computers need: brain-inspired hardware that learns and recognizes patterns with very low energy use.
Sibanda looked beyond the electrical switching to see how the films handle light and heat. With ultrafast laser pulses, she discovered two new electron “vibration modes” (plasmonic responses) that appear only after the films have been switched, showing that switching also changes the films’ optical properties. Atomic-force microscopy revealed subtle surface rearrangements that go along with this.
Under intense light, the films act like smart optical valves: they transmit proportionally less additional light as brightness increases (saturable absorption) and can even self-focus light slightly. Finally, Sibanda measured how quickly “hot” electrons hand over their energy to the material. The transfer is fast, underscoring that thermal management is key for reliable operation of such switches.
Taken together, these insights show how to fabricate and harness nanogranular gold films in a controlled way, bringing practical, scalable, and energy-efficient building blocks for the intelligent computers of the future closer to reality.