An analogy of a silicon AFM tip sliding over a architecture surface, with a TEM angel of the tip inset. Credit: Felice Macera (Phys.org)—Wear is a actuality of life. As surfaces rub adjoin one another, they breach bottomward and lose their aboriginal shape. With beneath actual to alpha with and functionality that generally depends alarmingly on appearance and apparent structure, abrasion affects nanoscale altar added acerb than it does their macroscale counterparts.
Worse, the mechanisms abaft abrasion processes are bigger accepted for things like car engines than nanotech devices. But now, advisers at the University of Pennsylvania’s School of Engineering and Activated Science accept experimentally approved one of the mechanisms abaft abrasion at the aboriginal scale: the alteration of material, atom by atom, from one apparent to another.
The analysis was conducted by Tevis Jacobs, a doctoral apprentice in the Administration of Abstracts Science and Engineering, and Robert Carpick, administration armchair of Automated Engineering and Activated Mechanics.
Their analysis was appear in the account Attributes Nanotechnology.
On the nanoscale, abrasion is mainly accepted through two processes, breach and artificial deformation. Breach is area ample pieces of a apparent breach off at once, like back the point of a pencil snaps off in the average of a sentence. Artificial anamorphosis is what happens back the apparent changes appearance or compresses afterwards breaking, like back the bend of knife gets addled or bent.
These mechanisms about affect bags or millions of atoms at a time, admitting nanoscale abrasion generally gain through a abundant added bit-by-bit process. Determining the mechanisms abaft this added bit-by-bit action is key to convalescent such devices.
“At the nanoscale, abrasion is a actual cogent problem,” Jacobs says. “Nanotechnology is developing abate and abate genitalia for actual tiny machines. Their acquaintance interfaces abrasion out actual quickly, sometimes actual for hundreds of cycles back they charge to survive for trillions or more.”
One abrasion apparatus that had been accepted for the nanoscale is a action accepted as diminutive attrition. There, atoms from one apparent are transferred to the added apparent via a alternation of alone bond-forming and bond-breaking actinic reactions. Added advisers accept attempted to analysis this action by putting two surfaces in acquaintance and sliding one adjoin the other.
Those antecedent investigations complex Diminutive Force Microscopes. Application an AFM involves boring a actual aciculate tip army on a adjustable axle over a apparent while a laser aimed at the axle absolutely measures how abundant the tip moves. By application the tip as one of the surfaces in a abrasion experiment, advisers can absolutely ascendancy the sliding distance, sliding acceleration and amount in the contact. But the AFM doesn’t anticipate the agreement at all; the aggregate of atoms absent from the tip can alone be accepted or advised afterwards the fact, and the aggressive abrasion mechanisms, breach and artificial anamorphosis can’t be disqualified out.
The Penn team’s advance was to conduct AFM-style abrasion abstracts central of a manual electron microscope, or TEM, which passes a axle of electrons through a sample (in this case, the nanoscale tip) to accomplish an angel of the sample, abstract added than 100,000 times.
By modifying a bartering automated testing apparatus that works central a TEM, the advisers were able to advance a collapsed architecture apparent adjoin the silicon tip of an AFM probe. By putting the probe-cantilever accumulation central the TEM and active the abrasion agreement there, they were able to accompanying admeasurement the ambit the tip slid, the force with which it contacted the architecture and the aggregate of atoms removed in anniversary sliding interval.
“We can watch the accomplished action alive to see what happens while the surfaces are in contact,” Jacobs said. “Then, afterwards anniversary pass, we use the TEM like a camera and booty an alike college deepening account of the tip. We can trace its outline and see how abundant aggregate has been lost, bottomward to as baby as 25 aboveboard nanometers, or about 1250 atoms.
“We are barometer changes in aggregate that are one thousand times abate than can be apparent application added techniques for abrasion detection.”
While this new microscopy adjustment can’t angel alone atoms affective from the silicon tip to the architecture punch, it enabled the advisers to see the diminutive anatomy of the cutting tip able-bodied abundant to aphorism out breach and artificial anamorphosis as the apparatus abaft the tip’s wear. Proving that the silicon atoms from the tip were bonding to the architecture and again blockage abaft complex accumulation the beheld and force abstracts into a algebraic test.
“If diminutive abrasion is what’s happening,” Carpick said, “then the amount at which those bonds are formed and the assurance on acquaintance stress—the force per assemblage area—is absolute science. That agency we can administer actinic kinetics, or acknowledgment amount theory, to the abrasion process.”
Now that they could admeasurement the aggregate of atoms removed, the ambit the tip slid and the force of the acquaintance for anniversary beginning test, the advisers could account the amount at which the silicon-diamond bonds anatomy beneath altered altitude and analyze that to predictions based on acknowledgment amount theory, a approach that is commonly acclimated in chemistry.
“The added force the atoms are under, the added acceptable they are to anatomy a band with an atom on the opposing surface, so the abrasion amount should advance exponentially with added stress,” Jacobs said. “Seeing that in the beginning abstracts was a smoker gun. The trend in the abstracts implies that we can adumbrate the amount of abrasion of the tip, alive alone the accent levels in the contact, as continued as this abrasion apparatus is dominant.”
For now, those predictions can alone be fabricated about the abrasion of silicon on architecture in a vacuum, admitting the alternative of those two abstracts was not accidental. They are accepted in nanoscale accessories and accoutrement for nanomanufacturing.
The algebraic abaft the diminutive abrasion apparatus could eventually be activated in a axiological way.
“The ambition of this access of analysis is to get to the point area you acquaint me the abstracts in contact, and you acquaint me the aeon they are in acquaintance and the stresses activated and I will be able to acquaint you the amount at which atoms will be removed,” Jacobs said.
“With a axiological compassionate of wear, you can cleverly architecture surfaces and accept abstracts to accomplish best abiding devices,” Carpick said.
This fundamental, predicative compassionate of abrasion could awfully advance nanomechanical design, accretion functionality and abbreviating costs.
Explore further: Nanotechnologists anatomy near-frictionless architecture actual
Added information: www.nature.com/nnano/journal/v … /nnano.2012.255.html
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