2

Click here to load reader

Making flawless graphene coatings - Phys.org · Making flawless graphene coatings 29 November 2016 ... the first step towards a production method for making larger, flawless sheets

  • Upload
    dangbao

  • View
    218

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Making flawless graphene coatings - Phys.org · Making flawless graphene coatings 29 November 2016 ... the first step towards a production method for making larger, flawless sheets

Making flawless graphene coatings29 November 2016

Credit: AlexanderAlUS/Wikipedia/CC BY-SA 3.0

Graphene, the ultra-thin wonder material just asingle carbon atom in thickness, holds the promiseof such impressive applications as wear-resistant,friction-free coatings. But first manufacturers haveto be able to produce large sheets of grapheneunder precisely controlled conditions. Dirk vanBaarle studied how graphene grows at atomicscale and what determines the friction with othermaterials.

Predictable quality

An almost perfectly friction-free, wear-resistantcoating in machinery could generate enormoussavings in fuel and maintenance. In the world ofnano-technology such coatings will probably evenhave applications that we are currently not able topredict. In his PhD research Dirk van Baarlestudied a candidate for such coatings: graphene.Van Baarle: "It's quite a challenge to producegraphene of a predictable quality."

Graphene is only super strong if the wire mesh of carbon atoms that make up the material are

perfectly regular in form. But with the presentproduction methods, a sheet of graphene is inpractice almost always made up of a patchwork ofsmall pieces that have been grafted onto oneanother. Van Baarle was able to observe almostper carbon atom live how islands of graphene growtowards one another and how this process isinfluenced by temperature and substrate. This isthe first step towards a production method formaking larger, flawless sheets of graphene.

Chicken wire pattern

Graphene occurs spontaneously when a very cleansurface of iridium comes into contact with ethylene(C2H4, a hydrocarbon) at a temperature of around700 degrees Celsius. The gas moleculesdisintegrate on the hot surface, leaving behind thecarbon atoms, which spontaneously form a networkof linked hexagons, in a chicken wire pattern.

For his research Van Baarle used a unique piece ofequipment in the Huygens-Kamerlingh OnnesLaboratory, the VT-STM (Variable TemperatureScanning Tunneling Microscope). This apparatuscomprises a minuscule stylus with a point that isjust a few atoms thick. It can be used tosystematically scan a surface with such a highdegree of precision (what you are in fact doing ismeasuring the flow of electricity between the stylusand the surface) that even individual atoms can bedistinguished. What makes the Leiden instrumentunique is that it can do this even at high andvariable temperatures.

A remarkable finding is that atomic processes occurnot only in the growing layer of graphene. Inpractice, the surface of the iridium does not matchthe atomic layers in the substrate perfectly. Theiridium forms broad steps on the surface, where thegraphene grows over it. But these steps cancontinue to grow underneath the graphene or canwithdraw as a result of the iridium atoms in thesubstrate realigning themselves. This process, too,has to be closely controlled in order to allow perfectsheets of graphene to form.

1 / 2

Page 2: Making flawless graphene coatings - Phys.org · Making flawless graphene coatings 29 November 2016 ... the first step towards a production method for making larger, flawless sheets

Contact points

In the theoretical part of his research, Van Baarledeveloped a model of how friction occurs at atomiclevel. When two surfaces slide over one another,the actual contact points are only nanometres insize, just a very few atoms. The friction is at itsmaximum when the stiffness of the nano-protrusions is roughly average: not too soft, butalso not too stiff.

Van Baarle: "One of my colleagues is currentlycoating an object with nano-needles using alithography technique (a technique that is also usedfor computer chips). These needles vary instiffness, depending on the direction in which theybend. This means that the friction of the surface isdifferent in different directions." This can be useful,for example, for a coating on a revolving axis, toprevent it moving laterally.

"Internally we are already using graphene coatingsin our equipment to reduce friction without usinglubricants," Van Baarle explains. "It has alreadyresulted in a patent and a start-up, AppliedNanolayers. No wonder our professor, JoostFrenken, has already won a valorisation prize."

Provided by Leiden UniversityAPA citation: Making flawless graphene coatings (2016, November 29) retrieved 26 November 2018from https://phys.org/news/2016-11-flawless-graphene-coatings.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, nopart may be reproduced without the written permission. The content is provided for information purposes only.

Powered by TCPDF (www.tcpdf.org)

2 / 2