89 research outputs found
Ballistic nanofriction
Sliding parts in nanosystems such as Nano ElectroMechanical Systems (NEMS)
and nanomotors, increasingly involve large speeds, and rotations as well as
translations of the moving surfaces; yet, the physics of high speed nanoscale
friction is so far unexplored. Here, by simulating the motion of drifting and
of kicked Au clusters on graphite - a workhorse system of experimental
relevance -- we demonstrate and characterize a novel "ballistic" friction
regime at high speed, separate from drift at low speed. The temperature
dependence of the cluster slip distance and time, measuring friction, is
opposite in these two regimes, consistent with theory. Crucial to both regimes
is the interplay of rotations and translations, shown to be correlated in slow
drift but anticorrelated in fast sliding. Despite these differences, we find
the velocity dependence of ballistic friction to be, like drift, viscous
DNA nanomapping using CRISPR-Cas9 as a programmable nanoparticle
Physical mapping of DNA can be used to detect structural variants and for whole-genome haplotype assembly. Here, the authors use CRISPR-Cas9 and high-speed atomic force microscopy to ânanomapâ single molecules of DNA
Metallic, magnetic and molecular nanocontacts
Scanning tunnelling microscopy and break-junction experiments realize metallic and molecular nanocontacts that act as ideal one-dimensional channels between macroscopic electrodes. Emergent nanoscale phenomena typical of these systems encompass structural, mechanical, electronic, transport, and magnetic properties. This Review focuses on the theoretical explanation of some of these properties obtained with the help of first-principles methods. By tracing parallel theoretical and experimental developments from the discovery of nanowire formation and conductance quantization in gold nanowires to recent observations of emergent magnetism and Kondo correlations, we exemplify the main concepts and ingredients needed to bring together ab initio calculations and physical observations. It can be anticipated that diode, sensor, spin-valve and spin-filter functionalities relevant for spintronics and molecular electronics applications will benefit from the physical understanding thus obtained
CORE-LEVEL ELECTRON ELECTRON COINCIDENCE SPECTROSCOPY
Two electronâspectrometer systems designed for electronâelectron coincidence spectroscopy are described. One, based on two hemispherical analyzers and xâray excitation, is especially suited for Augerâphotoelectron coincidence spectroscopy (APECS) of solids and surfaces. The other, using a cylindrical mirror analyzer, a hemispherical analyzer, and electronâbeam excitation is designed for nearâdipole (e,â2e) spectroscopy of gaseous samples. Typical results obtained with these instruments are presented
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