Researchers make first observation of atoms moving inside bulk material

October 13, 2014
Researchers make first observation of atoms moving inside bulk material
Selected frames from a sequence of scanning transmission electron microscope images showing the diffusion pathway of a Ce dopant (the bright atom highlighted with a white arrow) as it moves inside a bulk AlN crystal. The final frame overlays the Ce pathway on the Z-contrast image obtained by averaging each frame. Credit: Oak Ridge National Laboratory

Researchers at the Department of Energy's Oak Ridge National Laboratory have obtained the first direct observations of atomic diffusion inside a bulk material. The research, which could be used to give unprecedented insight into the lifespan and properties of new materials, is published in the journal Physical Review Letters.

"This is the first time that anyone has directly imaged single dopant moving around inside a material," said Rohan Mishra of Vanderbilt University who is also a visiting scientist in ORNL's Materials Science and Technology Division.

Semiconductors, which form the basis of modern electronics, are "doped" by adding a small number of impure atoms to tune their properties for specific applications. The study of the dopant atoms and how they move or "diffuse" inside a host lattice is a fundamental issue in materials research.

Traditionally, diffusion of atoms has been studied through indirect macroscopic methods or through theoretical calculations. Diffusion of single atoms has previously been directly observed only on the surface of materials.

The experiment also allowed the researchers to test a surprising prediction: Theory-based calculations for dopant motion in aluminum nitride predicted faster diffusion for cerium atoms than for . This prediction is surprising as cerium atoms are larger than manganese atoms.

"It's completely counterintuitive that a bigger, heavier atom would move faster than a smaller, lighter atom," said the Material Science and Technology Division's Andrew Lupini, a coauthor of the paper.

In the study, the researchers used a scanning transmission electron microscope to observe the diffusion processes of cerium and manganese . The images they captured showed that the larger cerium atoms readily diffused through the material, while the smaller manganese atoms remained fixed in place.

The team's work could be directly applied in basic material design and technologies such as energy-saving LED lights where dopants can affect color and atom movement can determine the failure modes.

"Diffusion governs how dopants get inside a material and how they move," said Lupini. "Our study gives a strategy for choosing which dopants will lead to a longer device lifetime."

Explore further: Observing the random diffusion of missing atoms in graphene

More information: Physical Review Letters. 06 October 2014, DOI: 10.1103/PhysRevLett.113.155501

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1 / 5 (1) Oct 13, 2014
in a bed of rock rubble, the biggest heaviest rocks ( not the densest) ---will eventually float to the top as a result of constant jostling and energy pertuerbations that allows the smaller rocks to fall through the cracks to settle at the bottom. this is in fact why roman roads were built with smaller crushed rock layers on the bottom and bigger rocks (for walking on) on top, the road settles naturally

of course , this is a newtonian phenomena, but i wonder if something like this isn't analgously happening at the quantum level in the structure of a material.

it's not the larger dopant atoms that move faster than the smaller ones ( when they are compared ) it is that the non dopant crystal material finds it easer to move around the external boundaries of a larger material than a smaller ones. almost as if the boundary layer itself is bigger,and it operates as a crack.

bigger dopants means bigger boundaries means more room for sliding/tunneling activity from the bulk atoms.
1 / 5 (1) Oct 14, 2014
Notice that the Ce atoms move in between the atoms of the AIN crystal in a direct path that is half way between the atoms. The AIN atoms do not appear to be moving, so the question is what is causing the Ce atoms to move. Perhaps it is the light of illumination from the experiment.

It is most likely that the electrons of the atoms are located on the exterior of the AIN atomic surfaces of the picture. This is also true for the Ce atoms. However, these electrons are in motion, so it is most likely a vibration effect of these exterior electrons opposing one another.
1 / 5 (2) Oct 14, 2014
CONGRATS! to the TEAM of DoE Oak Ridge National Laboratory.

"Gases are also not PUSHED heavily by the Force of 'Unified ……' but the piece of
heavy mass experiences more force of Unified ……"

I have already stated above line in my manuscript dated 17th, Aug'2013, submitted to the Journal "General Relativity and Gravitation" under heading "GRAVITY"- a PUSHING FORCE [-a "Layman concept of Unified Dark Energy"]

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