Research on Friction at a atom scale

Friction is almost everywhere and consumes energy. These articles show us a new prospect.

· REPORT
Tuning friction atom-by-atom in an ion-crystal simulator

Friction between ordered, atomically smooth surfaces at the nanoscale (nanofriction) is often governed by stick-slip processes. To test long-standing atomistic models of such processes, we implemented a synthetic nanofriction interface between a laser-cooled Coulomb crystal of individually addressable ions as the moving object and a periodic light-field potential as the substrate. We show that stick-slip friction can be tuned from maximal to nearly frictionless via arrangement of the ions relative to the substrate. By varying the ion number, we also show that this strong dependence of friction on the structural mismatch, as predicted by many-particle models, already emerges at the level of two or three atoms. This model system enables a microscopic and systematic investigation of friction, potentially even into the quantum many-body regime.

Feed: Science: Current Issue
Posted on: Friday, 5 June 2015 10:00 AM
Author: James Hone
Subject: [Perspective] Slippery when dry

Friction and wear account for massive amounts of wasted energy annually (estimates run in the hundreds of billions of dollars in the United States), in addition to unwanted and even unsafe failures of vehicles, machines, and devices (1). For example, nearly one-third of a vehicle's fuel energy is spent on overcoming engine, transmission, and tire friction (2). Engineers have devised many ways to reduce and control friction and wear, but it remains unknown whether superlubricity—the reduction of friction forces to nearly immeasurable levels—can be achieved with practical materials. On page 1118 of this issue, Berman et al. (3) describe an approach that combines the advantages of two nanomaterials with very different mechanical properties—stiff nanodiamonds and bendable graphene—to achieve apparent superlubricity on the macroscopic scale. Authors: James Hone, Robert W. Carpick


View article...<http://www.sciencemag.org/content/348/6239/1087.abstract?rss=1>
· PERSPECTIVE
PHYSICS
Controlling friction atom by atom
1. Ernst Meyer

Friction is a phenomenon of great technological relevance. The empirical laws of friction date back to the investigations of Leonardo da Vinci (1452 to 1519) and Guillaume Amontons (1663 to 1705). Thus, we have known for a long time that friction is proportional to the force normal to a surface and independent of the geometrical contact area. We also know that friction is one of major sources of energy loss, whereby a large amount of energy is dissipated into heat. In some cases, suitable surface preparation can lead to superlubricity, which corresponds to a state with extremely low frictional forces, where energy dissipation is at a minimum (1). On page 1115 of this issue, Bylinskii et al. (2) describe a cold-atom system that takes us to the ultimate limit of friction. They show that a defined number of ions, from one to six, can be moved across an optical lattice to study the elementary processes of atomic friction. Author: Ernst Meyer


View article...<http://www.sciencemag.org/content/348/6239/1089.abstract?rss=1>
FRICTION
A frigid simulator for friction
1. Jelena Stajic
Friction can be a friend or a foe, depending on whether we are trying to brake on a slippery road or to protect moving parts in industrial equipment. It results from the forces between atoms on the two surfaces in contact, but the details of the process are not well understood. Bylinskii et al. constructed a tunable friction simulator out of a handful of cold trapped ions that move in the potential of an optical lattice (see the Perspective by Meyer). They could vary the friction force experienced by the ions from maximal to nearly zero simply by changing the spatial arrangement of the ion array with respect to the optical lattice.

FRICTION
Slip sliding away
1. Marc S. Lavine
Many applications would benefit from ultralow friction conditions to minimize wear on the moving parts such as in hard drives or engines. On the very small scale, ultralow friction has been observed with graphite as a lubricant. Berman et al. achieved superlubricity using graphene in combination with crystalline diamond nanoparticles and diamondlike carbon (see the Perspective by Hone and Carpick). Simulations showed that sliding of the graphene patches around the tiny nanodiamond particles led to nanoscrolls with reduced contact area that slide easily against the amorphous diamondlike carbon surface.