Initiating and Monitoring the Evolution of Single Electrons Within Atom-Defined Structures

Abstract

Using a non-contact atomic force microscope we track and manipulate the position of single electrons confined to atomic structures engineered from silicon dangling bonds (DBs) on the hydrogen terminated silicon surface. By varying the probe-sample separation we mechanically manipulate the equilibrium position of individual surface silicon atoms and use this to directly switch the charge state of individual DBs. Because this mechanism is based on short range interactions and can be performed without applied bias voltage, we maintain both site-specific selectivity and single-electron control. We extract the short range forces involved with this mechanism by subtracting the long range forces acquired on a dimer vacancy site. As a result of relaxation of the silicon lattice to accommodate negatively charged DBs we observe charge configurations of DB structures that remain stable for many seconds at 4.5 K. Subsequently we use charge manipulation to directly prepare the ground state and metastable charge configurations of DB structures composed of up to six atoms.

SiQAD: A Design and Simulation Tool for Atomic Silicon Quantum Dot Circuits

“…One electron is equally shared between the two degenerate inner Si-DBs. This is in agreement with the experimental results of [13], where the middle electron hops between those two Si-DBs.…”

“…2) Simulation Results: The OR gate from [6] and the six Si-DB symmetric structure from [13] have been reproduced and simulated in SiQAD. Fig.…”

“…At each instant in time, a hop from i to j occurs with probability P i→j = ν ij dt. A spatial decay of α = 1 nm −1 was assumed, and λ calibrated to the experimental results with ν 0 and r 0 taken from the combined AFM line scans in [13]. Charge population can be modelled by adding additional channels for hopping to and from the surface Si-DBs.…”

“…Additionally, a six Si-DB symmetric structure from [13] designed to illustrate an observed hopping behavior has also been reproduced in SiQAD as seen in Fig. 3.…”

“…It is observed that over a series of AFM line scans either of the inner Si-DBs tends to be fully occupied, and that state tends to persist over multiple line scans. In [13], this behavior is attributed to stabilization of the charge states by lattice relaxation [14], [15], presenting an additional energetic barrier between the degenerate states. The tip influence and thermal fluctuations likely contribute to overcoming this barrier.…”