Final Paper.docx

GRAPHENE IMPLEMENTATION INTO CELLULAR SCREENS

Zack Philpot (zlp5@pitt.edu, Budny 4:00), Dan Grzybek (djg63@pitt.edu, Budny 10:00)

Conference Session B2 Paper #4220Dan GryzbekZackary Philpot

University of Pittsburgh, Swanson School of Engineering2014-03-061

6

Abstract--This paper will discuss how graphene improves the flexibility and durability of cell phone screens. Graphene is a single, thin layer of carbon atoms that organize into a hexagonal honeycomb shape [1]. This allotrope of carbon is also the primary backbone of graphite [1]. The carbon to carbon backbone in graphene makes the phone extremely strong while still allowing it to be rather flexible. This causes graphene to be a beneficial material and an intriguing target to companies in the commercial industry. Cellular devices are vital to the average person. In fact, according to Time Magazine, a study by the U.N. shows that more people have access to a cellular device (6 billion) than a working toilet (4.5 billion) [2]. The most common phone in the United States is the iPhone 4S, with 97 million units sold in 2013 alone [3]. However, a recent study discovered that almost a quarter of iPhone users had a cracked screen, an unacceptably high percentage. While cracked screens do not render the phone completely useless, they certainly add undesirable annoyances. [3] It is apparent that the current material used to construct iPhones is not sufficient. A new material must be utilized, and this material is graphene. Graphene has been dubbed the strongest material in the world by researchers at Columbia University [4]. Due to its improved strength, a phone that implemented a graphene-made screen would be virtually indestructible, and would be embraced by cell phone consumers. In our research paper, we will review our data pertaining to the molecular structure of graphene and consider the feasibility of graphene constructed cell phone screens by looking at the trials conducted thus far and their results.

Key Words-- Carbon, Cell Phone, Cell Phone Screen, Flexibility, Graphene, iPhone, Screen Strength,

THE START OF SOMETHING NEW

Graphene is a breakthrough material in the scientific world. It is a chemical marvel with a wide range of favorable characteristics such as high flexibility, strength, hardness, and conductivity. Additionally, graphene is extremely small. These characteristics make graphene a viable material for technologies such as batteries, solar panels, and x-ray devices. However, the most important use of graphene devices is for cell phones, and specifically cell phone screens. The current line of cell phone screens are proven unreliable, with consumers regularly experiencing shattered screens with little force endured by the phone. An alternative is needed for these faulty screens. The solution is graphene. Graphene is a superior alternative to current subpar cellular displays due to its unmatched hardness, strength, conductivity, size, and flexibility.

OVERVIEW OF GRAPHENE

Graphene was discovered on October 22, 2004 by Russian scientists Kostya Novoselov and Andre Geim at the Moscow Physical-Technical University [1]. It is a combination of graphite and the suffix ene which is used to form names of organic compounds where the carbon to carbon group has been attributed the highest priority according to the rules of organic nomenclature. Graphene has had a large history of being misrepresented in the scientific community. However, the IUPAC (International Union of Pure and Applied Chemistry) states: "previously, descriptions such as graphite layers, carbon layers, or carbon sheets have been used for the term graphene... it is incorrect to use for a single layer a term which includes the term graphite, which would imply a three-dimensional structure. The term graphene should be used only when the reactions, structural relations or other properties of individual layers are discussed [1]. Graphene is an allotrope of carbon and has a two-dimensional, crystalline structure. Graphene has a hybridization of sp2. This means that graphene has ones orbital and two p orbitals. By having one s and two p orbitals, graphene is capable of forming up to three bonds at a time. As a result, in graphene, carbon atoms are densely packed in a hexagonal pattern. Graphene is the basic structural element of many other allotropes as well, some of which include carbon nanotubes, graphite, and charcoal. Graphene is extremely strong, light, and flexible. Graphene is also nearly transparent and an excellent conductor of electricity. These characteristics will be expounded on further later in the paper.

IMPORTANCE OF CELLULAR DEVICES As time progresses, cellular devices are becoming increasingly more important in everyday life. A simple walk down most streets will leave the viewer with a sight filled with the effect cell phones have produced. People of all ages can be seen using their cell phones to talk, text, play games, and pass time on a daily basis. Additionally, advanced cellular devices can be used to work on the go, and are a necessity to any business man or woman.

FIGURE 1 [5]

Graph comparing age & country to phone usage

As seen in the diagram above, the younger generations have been largely engulfed while even the older generations have fallen to the enticing benefits gained from owning a cellphone. Cell phones were made even more desirable with the introduction and spark of never before seen smart phones introduced in the early to mid-2000s. The first iPhone (iPhone 2G) was introduced to the United States on January 9, 2007 [6]. While apple brand smart phones are not the only intelligent devices on the market, they are certainly the most popular. Over the past decade, companies, designers, and scientists have been working together in order to create new eye catching cell phone designs backed by desirable performance to ensure attention from their consumers. Updated and more efficient models of cellphones are now released annually.

FIGURE 2 [7]

Graph comparing iPhone units sold over the past years

Looking at apple units alone, monthly sales have increased from a mere .3 million units per month in the days of the first iPhone, to an incredible 47.8 million units per month sold during the release of the 4s model [7]. That is an extremely large increase in popularity and demand. The most common phone in the united states is currently the iPhone 4s, with 97 million units still sold in 2013, in competition with the new model iPhone 5 [8]. As one can see, smartphone popularity has dramatically increased in recent years, and is again becoming an important component of everyday life. A study conducted by the United Nations showed that more people now have access to cellular devices (6 billion) than a working toilet (4.5 billion) [2]. This further supports the claim of how important cell phones have become. With that said, and with the increased value people hold in their electronic companions, the importance of making better and more efficient smartphone models is now at its pinnacle. If companies are able to keep making improvements and beneficial changes to their products, they will increase sales while also satisfying the population of cell phone users. This is where graphene can change the market.

CURRENT SCREEN ISSUES

While the percentage of the humans who own a cell phone or smartphone of some variety is growing, so is the number of broken phones screens. Although companies are making large advancements in areas such as speed, memory capacity, and camera qualities, the device screen seems to not be getting as much attention. Small improvements in screen strength have been implemented into new models, however, users are still subject to the possibility of breaking their phone screens. As common as it is to see multiple people walking down the street using their cell phones, the chances that at least one of them has a cracked screen is also favorable. A study released by Squaretrade, a highly popular warranty agency that offers third party protection plans, revealed that American have spent approximately 5.9 billion dollars on iPhone repairs alone from 2007 to 2012 [9]. That sum is more than twice what Americans spend on toilet paper every year. Squaretrade also claimed that over half, approximately 54%, of iPhones needing repair are due to cracked screens. Anyone using a cell phone with a cracked screen is fully aware of the eyesore it creates.

FIGURE 3 [10]

Before & after picture of a cracked iPhone 4s

As one can see from the photo above, the sleek and visual appearance of the common iPhone is masked by the cracked screen. However, the cracked screen does not only create a destroyed display, it also hampers the performance and response of the screen itself. Parts of the screen become unresponsive to the human touch due to the screen fractures. This then creates an annoying interface filled with difficulties for the owner to use. While someone could easily suggest not dropping the phone in the first place as a solution, life does not always go as planned. Companies need a material that they can implement into their devices that will fix these issues. They need a strong and flexible substance to fill in the gap between current models and durable prototypes. A smartphone filled with all of the electronic internals that make it smart with the addition of an unbreakable screen will be very attractive to many buyers. Company sales will increase along with customer happiness and graphene is the material that can make it happen.

PROPERTIES OF GRAPHENE

As previously mentioned, there are a wide number of characteristics which make graphene an extremely useful material for the construction of cell phone screens. These characteristics include its chemical structure and thermal properties.

CHEMICAL MAKEUP

Graphene is an allotrope of carbon that is arranged in a honeycomb-shaped lattice [1]. The carbon to carbon bonds and the hexagonal shape are shown in the image below.

FIGURE 4 [11]

Molecular structure of graphene

Due to the carbon backbone of graphene, it is exceptionally strong. In fact, according to researchers at Columbia University, graphene is the single strongest material in the world and earns a perfect ten on Mohs hardness scale, a measurement of mineral hardness which characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material [4]. The scale ranges from a minimum value of one to a maximum value of ten. The carbon to carbon backbone of graphene also allows the substance to be almost completely transparent. Not only is graphene incredibly strong and transparent, but it is also thin and flexible. The carbon to carbon bond length in graphene is approximately .142 nanometers, and graphene sheets to form a substance with interplanar spacing of .335 nanometers [12]. This extremely tight spacing between atoms results in a graphene stack that is only a millimeter in thickness. Due to graphenes hexagonal shape, it can also be contorted into a vast array of shapes. Because of the 2-dimensional structure of graphene, it is the only form of carbon in which every atom is in exposure for a chemical reaction. Additionally, carbon atoms at the edge of graphene sheets have special chemical reactivity. This reactivity and structure allows graphene to bond with a wide arrow of substances. From other hydrocarbons to silicon, graphene will have no issue reacting and creating strong bonds. However, with the high reactivity of graphene comes a worry that it will react with compounds naturally found in the air. Thankfully, this is not an issue because graphene sheets can be overlaid in order to create a stronger, more stable product. Another astounding chemical trait of graphene is its ability to self-repair holes between sheets. When exposed to hydrocarbons or other molecules of pure carbon, the atoms of graphene perfectly aligned into their hexagonal shape in order to fix any holes, making graphene an exceedingly resilient material.

THERMAL

In addition to its high reactivity, graphene is also thermodynamically unstable. This issue can be resolved identically to how the issue of high reactivity was solved. More graphene sheets are simply overlaid in order to make the molecule stable. Graphene is also an excellent conductor. In fact, physicists at the University of Maryland have stated that in graphene the intrinsic limit to the mobility, a measure of how well a material conducts electricity, is higher than any other known material at room temperature [13]. This can largely be attributed to the fact that graphene encompasses many characteristics of semiconductors and metals. The most important of these characteristics are variable conductivity, which allows a substance to have an excess of electrons, and light emission, which is when excited electrons relax by producing light instead of heat. In any material, energy caused by the temperature may cause atoms to vibrate. These atoms may collide with electrons, causing electrical resistance. In graphene, these atoms cause a resistivity of one micro Ohm/centimeter at room temperature. This is approximately thirty-five percent less than that of copper, which is the least resistive material known at room temperature. Additionally, the mobility of graphene, which is used to measure how fast electrons move in a substance, is about 200,000 square centimeters per volt second. For comparison, indium antimonide, the highest mobility conventional semiconductor known, has a mobility of 77,000 square centimeters/volt second, which pales in comparison to graphene.

HOW GRAPHENE IS APPLIED TO A SCREEN

The majority of touch screens in the present market use a traditional technology called analog resistive [14]. The ability of electricity to pass through a metal or material is termed its electrical resistance. When a touch screen is pressed, it detects how much the current changes and this is how it registers the users input.

FIGURE 5 [15]

Diagram of an analog touch screen

As seen in the image above, the screen is bookended by a top layer of plastic film and a bottom layer of glass. When an individual presses the screen, it makes contact with the glass layer and completes a circuit. The top and bottom layers are both encompassed with a grid of an electrical conductor. This is where graphene comes into the picture and serves as the electrical conductor needed. Current transparent conductors used consist of silicon or indium tin oxide films. Since graphene is stronger, more flexible, and surpasses the conducting ability of both those materials, it is a much better option. Pressing the touch screen makes the glass touch the graphene film and the voltage of the circuit system is then measured. This causes the X and Y coordinates of the touch position to be calculated based on the amount of resistance at the point of contact [14]. This analog voltage is processed by analog-to-digital converters (ADC) to create a digital signal that the device's controller can use as an input signal from the user [14]. Once the signal is input, it is then passed through the phone and output and displayed on the screen.

GRAPHENE SCREENS VERSUS CURRENT SCREENS

The previously mentioned characteristics of graphene are extremely important in creating effective cell phone screens. Strength, flexibility, and conductivity all play an important role in allowing the screen to function as productively as possible.

STRENGTH

One such important characteristic is the hardness and strength of graphene. As stated in current screen issues, almost a quarter of all iPhone users have experienced an issue with cracked screens [9]. This is an extremely alarming rate that needs to be fixed. Cell phones are important items that are used on a daily basis. Therefore, it is vital that they remain functional. Current cell phone screens are made out of materials such as silicon and gorilla glass [16]. While these substances are, in fact, quite strong, they pale in comparison to graphene. As stated, graphene has a hardness of ten on the Mohs hardness scale. Silicon and gorilla glass, on the other hand, have a hardness of only seven, which is significantly weaker than graphene. This discrepancy in hardness has been displayed through numerous trials. In these trials, it has been discovered that graphene screens are far more resistant than any screens created thus far. During the tests, the screens were put under intense pressure and were dropped from various heights and struck with objects such as hammers and bricks. It was discovered that a force of 20,000 newtons would be needed in order for a pencil to puncture a layer of graphene [16]. This is equivalent to the mass of a large SUV. Another issue with the screens of current phones is the resistivity to constant stress endured by touchscreen phones. The constant stress eventually wears down the display of the phone and leads to various errors and lack of recognition by the screen. This issue can render touch screen cellular devices useless. However, graphene has been proven to endure a conceptually endless amount of stress and will therefore never become subject to such issues. In fact, it is estimated that the average person would have to use a phone regularly for over twenty years in order to wear out a graphene-made screen, which is extremely unlikely.

FLEXIBILITY

The flexibility of graphene is also vital in order to create an effective cellular display. The flexibility of the screen helps to aid in the bend but do not break methodology. This methodology explains that, if a material has good flexibility, the force exerted on a phone when it is dropped or hit will be dispersed along the phone, rather than concentrated on one point [16]. Instead of a force of 1000 newtons being felt at one point on the screen like in most phones, a graphene screen would feel ten newtons across the entire screen, allowing the screen to endure a much larger force. Another importance of flexibility is in the possible creation of bendy phones. These phones, as shown below, have the ability to bend into a complete circle.

FIGURE 6 [17]

Bendy Phone prototypes made with graphene

While this technology is not absolutely vital, it is a very interesting possibility. These flexible screens could improve watching videos and playing games among other positives. One other interesting capability of flexible phones is the ability to vastly improve audio quality in cell phones. By manipulating the phone into an arc, the speakers are able to reverberate off the other sides of the phone, magnifying the sound. Therefore, the decibel level produced by the speakers is greatly increased without any costly additions of improvements being made.

CONDUCTIVITY

Graphenes ability to serve as a good conductor also serves its purpose as a cellular display. As previously mentioned, the mobility of graphene is remarkably high. As stated, the mobility is used to show how quickly electrons move in a substance [13]. It is also used in order to measure the speed at which an electronic device can turn on. A high mobility is extremely advantageous in cell phone screens due to the fact that it allows images to be displayed extremely quickly. With graphene screens, cell phone users do not have to become frustrated about waiting for their touch screen phone to load. Additionally, this high mobility and conductivity of graphene allow information and images to travel seamlessly throughout the circuit board.

AFFORDABILITY

Perhaps graphenes most significant quality as a cellular screen is its affordability. The material currently being used is called indium-tin-oxide [16]. As well as not being as strong or as hard as graphene, not being as flexible as graphene, and not being as conductive as graphene, indium-tin-oxide is also far more expensive. The indium in the material is a very rare metal. As a result of its high demand and low supply, the price of indium has climbed to 720 dollars per kilogram. Graphene, on the other hand, can be constructed for as little as 150 dollars per kilogram. Therefore, graphene has the potential to greatly lower the price of cellular devices.

ISSUES WITH GRAPHENE

With all its phenomenal characteristics, there is one reason that graphene is not the leading material for cell phone screens already. Reproducibility. Currently, there is no method for the mass reproduction of graphene. Present day synthesis methods neither create graphene fast enough nor do they create graphene in the mass quantities that are necessary for large distribution. If companies want to be able to use graphene in their phones, they have to be able to handle the high demand. Graphene was first exfoliated in 2004 by a simple method using adhesive tape. The research team first took a chunk of graphite and mechanically removed a sufficient amount to turn it into a thin pad. They then attached adhesive tape to the sides, and manually removed graphite until only a single isolated sheet of graphene remained [1]. This method is clearly not an appropriate method for the mass production of graphene. Some companies have been researching better ways while still taking the same basic manufacturing approach, that being to isolate the graphene. Some examples of new prototypical processes include acid intercalation, vacuum separation and radio-frequency vapor deposition methods [18]. Chemical vapor deposition (CVD) condenses a volatile substance containing carbon onto a copper surface. The graphene layer that forms can then be peeled off onto another substrate. CVD is frequently used to make other thin-film systems for electronic devices [19]. Acid intercalation, the most popular of the three, involves submerging the graphite in a liquid form acid to cause separation. The resulting intermediate state is then mechanically treated to extract graphene platelets [20]. Platelets can be defined as multiple layers of graphene that measure up to hundreds of nanometers across. This process creates mass volumes of graphene in comparison to previous methods, however the use of acids can lead to the oxidation of the graphene. This then requires another process to unoxidize and produce the final desired graphene [20]. While this method is certainly faster than others, it is still not efficient enough for mass scale production. With more research and time, scientists may discover a better solution so they that can fully utilize the potential graphene brings to the table, but for now, it is still limited by its lack of commercialism.

NO OTHER CHOICE Due to its hardness greater than that of diamond, strength to withstand the force of an SUV, conductivity greater than copper, thickness of less than a millimeter, and flexibility to bend in complete circle, graphene is a perfect material for the construction of cell phone screens. Graphene exceeds the abilities of current materials such as gorilla glass, indium-tin-oxide, and silicon in virtually every facet. Graphene has the capability to greatly enhance cellular devices while even decreasing the marginal cost to construct each unit, making it less expensive for the consumer. If a method to mass produce graphene is developed, it could soon monopolize the cellular display industry.

REFERENCES

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ACKNOWLEDGMENTS

We would like to first and foremost thank Ms. Nicole Faina, for her expert guidance throughout the construction of our paper. We would also like to thank our past chemistry teachers for giving us the knowledge required to write our paper. Finally, we would like to thank the librarians for assisting us in our researching.