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  • Translator: Kuan-Yi Li Reviewer: Robert Tucker

  • Carbon is an essential element of life,

  • and is also one of the most abundant elements on earth.

  • Carbon occupies a place in the second row of the periodic table,

  • right above silicon.

  • A single carbon atom

  • consists of 6 protons, 6 or 7 neutrons, and 6 electrons.

  • A well-known example of carbon is the tip of pencils.

  • The tip of pencils consists of graphite,

  • which refers to a collection of carbon atoms, layers of carbon atoms.

  • Each layer of the carbon atoms

  • forms a honeycomb structure which is called graphene.

  • Although scientists knew

  • that graphene layers are the constituents for graphite,

  • for years they were not sure

  • whether a monolayer of graphene could be isolated in nature.

  • Until 2004, when two British physicists finally demonstrated

  • that a single atomic layer of graphene can be isolated and stabilized in nature.

  • These two physicists,

  • Dr. Novoselov and Dr. Geim of Manchester University,

  • not only demonstrated that graphene can be isolated and stabilized in nature,

  • they also carried out detailed studies of the properties of graphene.

  • They found that graphene exhibited very interesting and unique properties

  • that could be promising for a wide range of applications.

  • Therefore, their research ignited great excitement throughout the world.

  • So, what are the unique properties of graphene that makes it so special?

  • Graphene, actually, is both electrically and thermally highly conductive,

  • so electrons on graphene can move like massless particles

  • ballistically across the surface of graphene without being scattered.

  • Graphene is very thin and optically transparent,

  • so light can penetrate through graphene without being reflected.

  • The edges of graphene also exhibit very interesting properties

  • that can be functionalized for chemical applications.

  • The tiny honeycomb structure of graphene

  • can only allow electrons and protons to penetrate through,

  • so, for this reason, graphene can be used for filtering of chemical elements.

  • Moreover, graphene is mechanically flexible

  • and 200 times stronger than steel.

  • You can imagine, with these unique properties,

  • many applications become possible.

  • For instance, the excellent electrical and thermal conductivity,

  • combining with the optical transparency,

  • make it possible for graphene

  • to be applied to nanoelectronics in integrated circuits,

  • to optoelectronic components

  • like solar cells, light-emitting diodes, lasers and display panels.

  • The flexible and strong mechanical properties of graphene

  • can be used for lightweight, high-strength materials

  • applicable to things such as transportation vehicles, airplanes.

  • The excellent chemical filtering capabilities of graphene

  • makes it possible for graphene to be used in desalination, detoxification,

  • chemical sensing, DNA sequencing and even delivery of medicine.

  • The edges of graphene are very interesting also.

  • In fact, there are two distinctly different types of edges for graphene.

  • One is called the armchair edges, the other is called the zigzag edges.

  • The zigzag edges usually are chemically more reactive

  • and so can be functionalized for all kinds of chemical applications.

  • If you take a piece of graphene and cut it into small stripes,

  • then you have graphene nanoribbons.

  • You can have either armchair or zigzag graphene nanoribbons.

  • All of these nanoribbons have very large edge-to-area ratios,

  • and so they can be very good, very effective,

  • for charging and discharging.

  • For this reason, graphene nanoribbons can be used

  • in supercapacitors, batteries for energy storage.

  • Despite all these wonderful properties of graphene,

  • there are major challenges before we can fully realize the potential of graphene.

  • In particular, we need to develop reliable large-scale production of graphene

  • with high quality and low cost.

  • Currently, there are three typical ways of making graphene.

  • The first one is called mechanical exfoliation from graphite.

  • What it is, is actually involving the use of adhesive tapes,

  • or a Scotch tape that you're familiar with.

  • You take a piece of Scotch tape,

  • press it against graphite, and you peel it off.

  • Then you get tiny flakes of graphite.

  • Then you keep repeating the process

  • until you hopefully get little, little flakes of graphene

  • that can be monolayer or bilayer or multilayers.

  • As you can imagine,

  • this is a method that's labor-intensive and very slow in production.

  • It's not scalable:

  • you have no control of the quality and size of the graphene samples.

  • But this was the initial method used by the two Nobel laureates.

  • A second method is based on chemical reduction,

  • which utilizes very toxic chemicals

  • to oxidize graphite into graphite oxide,

  • and then chemically reduces graphite oxide into tiny flakes of graphene.

  • This method, again, is environmentally unfriendly,

  • and also the produced graphene flakes

  • are uncontrollable in size, number of layers and quality.

  • As a matter of fact,

  • most of these graphene flakes consist of lots and lots of impurities.

  • The third method is called chemical vapor deposition,

  • which involves using multistep, long-term processes

  • of growing graphene on metals such as copper or nickel.

  • The growth process involves very, very high temperature -

  • 1,000 degrees centigrade.

  • Typically, this method can produce

  • sufficiently large areas of graphene sheets,

  • and the quality can be reasonable

  • if you take a lot of time

  • to go through many steps to produce the material.

  • Overall this process is very expensive.

  • The other problem is that it's incompatible

  • with most device fabrications.

  • And so, as you can see,

  • all these three methods are not ideal

  • for fully realizing the potential of graphene.

  • To overcome these problems, we recently developed a new method,

  • which is called plasma-assisted, chemical vapor deposition, or PECVD.

  • This process takes place at room temperature, in a single step,

  • and only takes a few minutes,

  • and there we produce excellent quality of graphene.

  • The idea is the following:

  • We take a piece of copper.

  • The copper surface is very reactive and so usually is covered with oxide.

  • We subject the copper piece to hydrogen plasma

  • and other radicals like cyan.

  • And then once we clean up the surface of copper,

  • try to get rid of all of the copper oxide,

  • we flow methane gas through this highly reactive copper.

  • And so the copper surface will rip apart the chemical bonds

  • between carbon and hydrogen,

  • and then allow carbon to nucleate on the surface of the copper

  • and turn into graphene.

  • And with this approach,

  • we can actually grow very large areas of graphene in a very short time,

  • which is of excellent quality,

  • electrically, structurally and mechanically.

  • And here I just show you an example

  • from the images we took

  • using our scanning tunneling microscope on our PECVD-grown graphene.

  • As you can see,

  • at the small scale, you can visualize the honeycomb structure of carbon.

  • We can also modify our process a little bit

  • so that not only can we grow large sheets of graphene,

  • we can also grow graphene nanoribbons.

  • This little modification involves adding additional precursor molecules

  • so that graphene can also grow vertically

  • on the surface of the copper

  • and turn into graphene nanoribbons.

  • So, overall, using our PECVD method,

  • we effectively turn greenhouse gas - that's methane -

  • into very useful material: graphene and graphene nanoribbons.

  • So, what's new in the future?

  • As you can imagine,

  • at this point, when we have these advances in the graphene production,

  • many things become possible.

  • So here I will give you two examples of our ongoing research

  • to give you a flavor of what can be done.

  • The first example is a little exotic.

  • It's called nanoscale strain engineering of graphene.

  • It's purposed for novel optoelectronic applications.

  • One of the most interesting properties of graphene

  • is that if you distort the structure of graphene at the nanoscale,

  • you can actually fundamentally change the electronic properties of graphene.

  • And so now we have essentially flawless pieces of graphene,

  • I can use nanofabrication technology

  • to build nanostructures wherever I want them to be

  • with whatever shapes I want them to be.

  • Then I can lay a layer of graphene over such nanostructures

  • to produce the distortion that I want,

  • and, therefore, I can get the electronic properties that I want.

  • So, as an example, you see here,

  • a 600x600 nanometer-sized layer of graphene

  • can be put over a tetrahedral-like nanostructure.

  • So, graphene is being distorted,

  • and the consequence of it

  • is that electrons on graphene would see this distortion

  • as if you have very strong, spatially alternating magnetic fields.

  • The magnetic fields are so strong, as you can see here, the picture shows -

  • the blue color indicates negative magnetic fields,

  • red color indicates positive magnetic fields,

  • and they are as high as several hundred teslas,

  • much higher than most fields

  • you can produce in any laboratory on earth.

  • And so, if you design these nanostructures properly,

  • and connect them in a special form,

  • electrons will effectively see these alternating magnetic fields,

  • so that when electrical currents on graphene

  • try to pass through these distortions,

  • they will be effectively accelerated

  • as if they were under strong magnetic fields.

  • This acceleration can cause so-called synchrotron radiation,

  • so that photons can be radiated.

  • So, this is similar to the principle of the free-electron laser,

  • except that I don't have to apply any real magnet field,

  • I just have to do strain engineering.

  • And also, instead of a gigantic lab

  • that's required to make a free-electron laser,

  • I can actually make a tabletop free-electron laser using this concept.

  • This is an ongoing research project.

  • Another very practical example of research that we are pursuing

  • is a new generation of interconnects.

  • As you know,

  • one of the major challenges

  • facing the continuing miniaturization of nanoelectronics in integrated circuits

  • is that the interconnects are also shrinking to a very, very small scale.

  • In current technology, the interconnects are based on copper.

  • When you shrink copper into tiny, tiny lines,

  • you start facing very serious problems,

  • because copper becomes granular and very resistive.

  • And, therefore, if you pass electrical current through these interconnects,

  • you're going to generate lots of heat.

  • Furthermore, copper under heat will diffuse into the underlying silicon,

  • which will further degrade

  • the interconnect characteristics and properties.

  • So, these are major issues the semiconductor industries try to solve.

  • Now imagine, if I can put a barrier layer of graphene

  • between the copper and the underlying substrate silicon,

  • then I can prevent copper from diffusing into the silicon

  • because, as I have told you,

  • only electrons and protons can get through graphene.

  • Furthermore, graphene itself

  • is an excellent electrical and thermal conductor.

  • Therefore, with the presence of graphene,

  • the overall interconnect properties are becoming better

  • both electrically and for thermal dissipation,

  • and so overall it will reduce energy consumption.

  • So, these are just two examples

  • of what we are working on with our new development.

  • In general, we can say

  • that you can consider graphene as the next generation wonder material

  • beyond silicon for science and technology.

  • With the new development of advances in graphene production,

  • and also the ingenuity of researchers all over the world,

  • we can expect graphene to open up new frontiers for science and technology

  • that can brighten our future.

  • I have mentioned these possibilities,

  • including next-generation nanoelectronics,

  • optoelectronics,

  • very strong materials that are flexible and lightweight,

  • renewable energy production and storage,

  • and also for medicine and bioengineering.

  • So, with all of these possibilities and reasons,

  • I daresay that even the sky is not the limit.

  • Thank you.

  • (Applause)

Translator: Kuan-Yi Li Reviewer: Robert Tucker

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TEDx】グラフェン技術で構成された新しい世界|内張イエ|TEDx桃園 (【TEDx】A new world composed of graphene-based technology | Nai-Chang Yeh | TEDxTaoyuan)

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    球菌 に公開 2021 年 01 月 14 日
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