Abstract
Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni–Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni–Si clusters. The resonance energy is reproducible and the peak spacing of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I–V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. All of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.
Highlights
A major challenge is scaling this technology toward meaningful quantum computation requiring the entanglement of multiple qubits with coherence times long enough for calculations to occur and simultaneously be measured.[3,4,5,6,7,8,9,10,11,12]
Group IV semiconductors are quite attractive for qubit design because they can provide a spinfree environment, where electron spin coherence times have been measured on the order of seconds.[23,24,25]
A submonolayer of Ni was evaporated onto a Si(111) substrate to observe the initial formation of the atomic Ni–Si clusters, as illustrated in the scanning tunneling microscopy (STM) image of Fig. 1a
Summary
There has been significant progress toward the utilization of an electron’s spin for the development of quantum bits (qubits) poised to revolutionize modern computers, where the orientation of the spin serves as the basis for “0” and “1” logic operations.[1, 2] A major challenge is scaling this technology toward meaningful quantum computation requiring the entanglement of multiple qubits with coherence times long enough for calculations to occur and simultaneously be measured.[3,4,5,6,7,8,9,10,11,12] Not surprisingly, materials are at the heart of this challenge, from the fabrication of the qubits to how the electron or nuclear spin interacts with the host material.[13,14,15,16,17] One of the most advantageous platforms has been developing solid-state qubit architectures using traditional semiconductors, where an entire industrial infrastructure exists and hybridization with conventional technology would be greatly beneficial. Complimentary to STM fabrication of individual quantum structures between electrical contacts, we envision scalability by controlling the density of self-assembled quantum dots over an entire surface. There has been significant research in the area of metal functionalization of silicon surfaces in the context of thin film growth, metal silicides, and the modification of surface reconstructions.[32,33,34,35] Guided by these efforts, we investigated the submonolayer deposition of Ni on Si(111) At these low coverages, the surface reconstruction is modified and two distinct Ni–Si clusters emerge that consist of either a “1 × 1” or “√19” quantum dot structure consisting of an ordered grouping of Ni and Si atoms. This research presents a model system for large-scale distribution of atomic quantum dots for potential qubit design that are tunable between two distinct sizes, with reproducible quantized energy levels, and can be designed to exhibit NDR
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