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The Next Wonder Material? Graphene The Next Wonder Material? By Michael Tinnesand here is a new wonder material in town that that is ejected to the surface from deep within SHUTTERSTOCK might change our future. Imagine a coffee the Earth’s interior through volcanic eruptions, cup that streams the day’s headlines in while graphite is a black and lightweight mate- real time. Or a cooking pot that can detect rial extracted from coal. be only a single one-atom thick layer—pure the presence of E. coli bacteria that could In diamond, each carbon atom is connected graphene. make you sick. Or a television screen that to four other carbons. This is a very strong The initial samples of graphene were very Tis as flexible and thin as a piece of paper. All arrangement that makes diamonds one of small—only a couple of square millimeters in of these applications could be a reality if the the hardest known materials. In graphite, size each—but large enough to test. Because wonder material, named graphene, lives up to each atom is linked to three others in layers graphene is only one-atom thick, it is con- its hype. of hexagonal (six-sided) shapes that look like sidered to be a two-dimensional material, the chicken wire (Fig. 2, p. 8). The bonds within first example of such a thing in the real world. Chicken wire made the hexagonal sheets are strong, but each Despite being the thinnest material known of carbon layer is only weakly attracted to the next, to exist, it is also the strongest material ever which allows the layers to slip by one another. tested—100 times stronger than steel. Graphene rocked the world of chemistry in In 2004, Andre Geim and Konstantin Even more amazing: Electrons do not 2004 when scientists discovered that it had Novoselov, two chemists at the University scatter as much when they move as they do remarkable properties: It conducted electricity of Manchester, United Kingdom, used this in other materials, such as silicon. This led better than any other common substance, it property to produce samples of graphene researchers to make graphene-based transis- was the thinnest known material—only one- and discover its remarkable properties. They tors that are twice as fast as traditional silicon atom thick—and it was stronger than steel! transistors, which could make computers run After all, carbon is one of the most com- - S much faster. mon and most familiar of the known chemical TTP://LO H OM/2012/02/ , elements, so scientists were surprised to find C . CE N Flexible solar panels ESS E that this new form of carbon had such amaz- I C Graphene has sparked the interest of ing properties. T IN S S .WORDPR O .JPG L ES E Carbon comes in many crystalline forms, , engineers who are trying to make new, light- IG .FIL -TAP SS CE E N weight, and flexible solar panels IT LA called allotropes, the most well-known being E I H S SC RI that could be used to cover diamond and graphite. Allotropes are differ- CH TIN GRAP ent forms of the same element with different Sticky tape can be used to peel off powdered the outside surface of a bonding arrangements between atoms, result- graphite, leaving a single layer of graphene. building, in addition to the ing in structures that have different chemical used sticky tape to separate the layers of roof—which is already and physical properties. The way atoms are carbon in graphite. To get an idea of how their being used. connected to each other in solid materials has technique worked, think of pressing sticky Graphene is nearly a huge impact on their overall properties. tape onto a piece of graphite and pulling it transparent to light—not A diamond and a piece of coal are so dif- only visible light but also away, leaving the sticky surface covered with CRUNCHWEAR.COM ferent that you would never guess that they graphite flakes. Then, press the sticky tape to are both made of the same element—carbon. Solar panels on these backpacks can charge itself and pull it apart. Repeat, and after a few your mobile phone or iPod. In the future, flexible Diamond is a hard and transparent mineral rounds of this, some flakes on the tape will solar panels may even charge your laptop. 6 ChemMatters, OCTOBER 2012 www.acs.org/chemmatters mation is relayed to a processor inside the device, which determines what kind of action to take. All of this is possible because these devices use screens that have thin and transparent coatings that are conductive and can hold a charge. Most portable devices today have screens that are coated with a conductive layer made of indium tin oxide. But this material is brittle, so it is layered on glass to protect and support it. This leads to thick and inflexible displays. Touch screens made with graphene as their conductive element could be printed on thin plastic instead of glass, so they would be light and flexible, which could make cell phones as thin as a piece of paper and foldable enough to slip into a pocket. Also, because of gra- CS phene’s incredible strength, these cell phones BIONI CH would be nearly unbreakable. Scientists TOU expect that this type of touch screen will be the first graphene product to appear in the other forms of electromagnetic radiation, PCs have touch screens that allow the user to marketplace. including ultraviolet and infrared light. Gra- make selections by touching icons or letters phene absorbs only 2% of the light falling on directly on the display screen. Bionic devices it, whether it is ultraviolet, infrared, or all of The basic idea of how most of these Because graphene is thin and flexible, it the wavelengths in between. Combine this devices work is simple. A layer that stores could be integrated into “bionic” devices that with graphene’s ability to conduct electricity, electrical charge is placed on the glass panel S and you have very efficient, electrical conduc- of the screen. When a user touches the ALLA D AT AT tors that are transparent, thin, flexible, and screen with his or her finger, or with a stylus S A cheap. pen, some of the charge is transferred to the TEX This new type of solar panel is currently user, so the charge on the layer decreases. ITY OF S R This decrease is measured by sensors located E under development and consists of organic NIV U photovoltaic cells sandwiched between sheets at each corner of the screen, and this infor- ANG, H of graphene (Fig. 1). A photovoltaic cell is a I Z ME small device that converts the sun’s energy Nanoscale fibers drawn from into electrictity. multiwalled carbon nanotubes have When a photovoltaic cell is sandwiched strengths comparable to spider silk. When they are stretched, between two sheets of graphene, light Negative contact they increase in width (instead of crosses the sheets of graphene and hits the Current flow getting thinner), so they might be photovoltaic cell. As a result, the photovoltaic used to make artificial muscles in Electrons the future. cell generates electricity, which is carried by the sheets of graphene. Silicon Photon These lightweight and flexible solar panels Electron would be implanted in living tis- could be molded to fit an automo- flow Hole sue. The term “bionic”—a mix bile body or be wrapped around of “biology” and “electronic”— furniture or clothing. When added EZ Positive refers to devices that help or contact to any surface, they could collect RNAND E improve an organ or tissue, such light and produce electricity. ONY F H as artificial hearts or cochlear ANT implants, which assist people Figure 1. Schematic representation of a new type Foldable cell of solar cell that consists of a photovoltaic cell with hearing loss. phones sandwiched between two sheets of graphene. Graphene is resistant to the salty ionic solu- When light crosses the graphene and is absorbed tions inside living tissue, so bionic devices Until recently, most electronic by the silicon, the photons that make up the light made of graphene could have long shelf lives, devices were controlled by pushing excite electrons in the silicon, which migrate to the graphene sheet at the negative contact and perhaps lasting a lifetime. This is in contrast buttons, typing on a keyboard, or using move through the graphene structure toward an to metallic parts that can corrode after a few a mouse. Today, most cell phones and tablet external circuit that produces electricity. ChemMatters, OCTOBER 2012 7 (a) (b) (c) Carbon Oxygen Nitrogen Hydrogen (d) (e) (f) OM C . S OTO H AND P EZ RNAND E ONY F H ANT Figure 2. Atomic structures of six common forms of carbon: (a) coal, (b) graphite, (c) diamond; (d) buckyball; (e) nanotube; and (f) graphene. Photos of pieces of coal, a golf club made with graphite, and a diamond ring are examples of products made with the first three forms of carbon. Products made with buckyballs, nanotubes, and graphene are still under development. years, possibly releasing toxic metals into the Available soon? In another method, the graphite is dis- body. solved in a solvent and then sprayed in thin You may have noticed that the words Also, because graphene conducts electrical layers using inkjet-type printers. The solvent “might” and “could” were used many times in signals, it can be connected with neurons, evaporates, and the graphene remains. this article. That is because there is still a long which also send weak electric signals from But none of these methods has been per- way to go before any of these applications cell to cell.
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