Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics

We review our recent efforts in building atom-scale quantum-dot cellular automata circuits on a silicon surface. Our building block consists of silicon dangling bond on a H-Si(001) surface, which has been shown to act as a quantum dot. First the fabrication, experimental imaging, and charging character of the dangling bond are discussed. We then show how precise assemblies of such dots can be created to form artificial molecules. Such complex structures can be used as systems with custom optical properties, circuit elements for quantum-dot cellular automata, and quantum computing. Considerations on macro-to-atom connections are discussed.Comment: 28 pages, 19 figure

Field-Directed Sputter Sharpening for Tailored Probe Materials and Atomic-Scale Lithography

Fabrication of ultra-sharp probes is of interest for many applications, including scanned probe microscopy and electron-stimulated patterning of surfaces. These techniques require reproducible ultra-sharp metallic tips, yet the efficient and reproducible fabrication of these consumable items has remained an elusive goal. We describe a novel biased-probe field-directed sputter sharpening technique, applicable to conductive materials, which produces nanometer and sub-nanometer sharp W, Pt-Ir, and W-HfB2 tips able to perform atomic-scale lithography on Si. Compared with traditional probes fabricated by etching or conventional sputter erosion, field-directed sputter sharpened probes have smaller radii and produce lithographic patterns 18 – 26% sharper with atomic-scale lithographic fidelity.Office of Naval Research Grant N00014-06-10120Defense Advanced Research Project Agency and Space and Naval Warfare Center, San Diego contract N66001-08-C-2040National Science Foundation grant CHE 10-38015National Science Foundation grant DMR 10-05715National Science Foundation grant CHE 07-50422published or submitted for publicationis peer reviewe

A Single-Atom Transistor

The ability to control matter at the atomic scale and build devices with atomic precision is central to nanotechnology. The scanning tunneling microscope can manipulate individual atoms and molecules on surfaces, but the manipulation of silicon to make atomic-scale logic circuits has been hampered by the covalent nature of its bonds. Resist-based strategies have allowed the formation of atomic-scale structures on silicon surfaces, but the fabrication of working devices—such as transistors with extremely short gate lengths, spin-based quantum computers and solitary dopant optoelectronic devices—requires the ability to position individual atoms in a silicon crystal with atomic precision. Here, we use a combination of scanning tunnelling microscopy and hydrogen-resist lithography to demonstrate a single-atom transistor in which an individual phosphorus dopant atom has been deterministically placed within an epitaxial silicon device architecture with a spatial accuracy of one lattice site. The transistor operates at liquid helium temperatures, and millikelvin electron transport measurements confirm the presence of discrete quantum levels in the energy spectrum of the phosphorus atom. We find a charging energy that is close to the bulk value, previously only observed by optical spectroscopy