Overcoming challenges in single electron charge detection of nanoscale dipoles

Single-electron transistors (SETs) can serve as electrometers to sense single-electron charge switching in nanoscale objects. A sub-20 nm metal double-dot (DD) structure, separated by a tunnel barrier, essentially functions as a dipole, and SETs have been utilized to detect single-electron switching within these DDs. The sensing of single-electron charge switching within these nanoscale metal DDs mimics single-charge sensing in molecular regimes and charge qubit sensing. In this study, two SET electrometers were employed to sense a single DD structure. The sensing outcomes of both SETs confirmed the detection of electron switching within the DD as well as the detection of the other SETs across the DD. To increase the induced charge in the SET due to electron switching within the DD, the SET electrometer was placed in very close proximity to the DD in one of the designs. This design, however, led to the formation of a metal dot tunnel-coupled to the SET electrometer, effectively functioning as a Single Electron Box and potentially disrupting the charge sensing fidelity of SETs while detecting charge switching in the DD. The impact of a SET tunnel-coupled to a metal dot was further investigated in a separate design. It was also demonstrated how proper design of SETs can incorporate a tunnel-coupled metal dot while maintaining the ability to detect electron switching within DDs with high fidelity simultaneously.