Atom-Scale Ohmmeter

A highly stable scanning tunneling microscope measures the electrical properties of a metal on a scale smaller than individual atoms.

A gentle touch. The needle-like tip of a scanning tunneling microscope (STM) terminates in a single atom that can touch a surface at different locations, such as on top of an atom (left) or in the “hollow” between three atoms (right). A highly stable STM that touches the surface without damaging it can measure the differences in electrical conductance among several different types of sites.

A gentle touch. The needle-like tip of a scanning tunneling microscope (STM) terminates in a single atom that can touch a surface at different locations, such as on top of an atom (left) or in the “hollow” between three atoms (right). A highly stable STM that touches the surface without damaging it can measure the differences in electrical conductance among several different types of sites.

A scanning tunneling microscope (STM) can make an image of individual atoms on a surface or move single atoms around. Now researchers have pushed the device’s precision and used it to measure the differences in electrical conductance between different locations around a single atom on a lead surface. The results could help elucidate the properties of metals and superconductors and might one day find use in nanotechnology fabrication.

An STM brings a needle-like probe—the tip of which is a single atom—extremely close to a sample surface in a vacuum. When voltage is applied, electrons can jump, or “tunnel,” across the gap, and measuring the resulting current while moving the tip across the surface leads to an image. In another STM technique, the probe tip touches the sample, allowing atoms to chemically bond with it. Researchers have used this method, known as point contact, to move atoms around like toy blocks. The point contact technique would also be appropriate for measuring electrical conductance of a material at the atomic scale, to learn how current flows in the quantum regime, where the classical Ohm’s law fails. Continue reading Atom-Scale Ohmmeter

Ohm’s Law Survives to the Atomic Scale

Phosphorus atoms make a tiny wire on silicon - Scanning-tunnelling-microscope image showing a highly conducting wire that is only four atoms wide. (Courtesy: Bent Weber)

B. Weber, S. Mahapatra, H. Ryu, S. Lee, A. Fuhrer, T. C. G. Reusch, D. L. Thompson, W. C. T. Lee, G. Klimeck, L. C. L. Hollenberg, M. Y. Simmons
ABSTRACT –  sciencemag.org
As silicon electronics approaches the atomic scale, interconnects and circuitry become comparable in size to the active device components.
Maintaining low electrical resistivity at this scale is challenging because of the presence of confining surfaces and interfaces.
We report on the fabrication of wires in silicon—only one atom tall and four atoms wide—with exceptionally low resistivity (~0.3 milliohm-centimeters) and the current-carrying capabilities of copper.
By embedding phosphorus atoms within a silicon crystal with an average spacing of less than 1 nanometer, we achieved a diameter-independent resistivity, which demonstrates ohmic scaling to the atomic limit.
Atomistic tight-binding calculations confirm the metallicity of these atomic-scale wires, which pave the way for single-atom device architectures for both classical and quantum information processing….
Read more: physicsworld.com