Physics and Applications of Graphene - Experiments

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The device acted as a humidity sensor. In a graphene based blood glucose testing product was announced. The toxicity of graphene has been extensively debated in the literature. The most comprehensive review on graphene toxicity published by Lalwani et al. Graphene has a high carrier mobility , and low noise, allowing it to be used as the channel in a field-effect transistor.

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However, modifications eg Graphene nanoribbons have created potential uses in various areas of electronics. Graphene transistors have been built that are chemically controlled, and others that are voltage controlled. Graphene exhibits a pronounced response to perpendicular external electric fields, potentially forming field-effect transistors FET.

In , researchers at MIT Lincoln Lab produced hundreds of transistors on a single chip [39] and in , very high frequency transistors were produced at Hughes Research Laboratories.

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A paper demonstrated a switching effect based on a reversible chemical modification of the graphene layer that gives an on—off ratio of greater than six orders of magnitude. These reversible switches could potentially be employed in nonvolatile memories. In , researchers demonstrated four different types of logic gates , each composed of a single graphene transistor.

Typically, the amplitude of the output signal is about 40 times less than that of the input signal.

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In the same year, tight-binding numerical simulations [48] demonstrated that the band-gap induced in graphene bilayer field effect transistors is not sufficiently large for high-performance transistors for digital applications, but can be sufficient for ultra-low voltage applications, when exploiting a tunnel-FET architecture. In February , researchers announced graphene transistors with an on-off rate of gigahertz, far exceeding the rates of prior attempts, and exceeding the speed of silicon transistors with an equal gate length.

At high temperatures, the quantum Hall effect could be measured in these samples. In June , IBM researchers announced that they had succeeded in creating the first graphene-based integrated circuit, a broadband radio mixer. In November researchers used 3d printing additive manufacturing as a method for fabricating graphene devices. In , researchers demonstrated graphene's high mobility in a detector that allows broad band frequency selectivity ranging from the THz to IR region 0. The device consists of two layers of graphene separated by an insulating layer of boron nitride a few atomic layers thick.

Electrons move through this barrier by quantum tunneling. These new transistors exhibit negative differential conductance , whereby the same electric current flows at two different applied voltages. The negative differential resistance experimentally observed in graphene field-effect transistors of conventional design allows for construction of viable non-Boolean computational architectures with graphene.

The results present a conceptual change in graphene research and indicate an alternative route for graphene's applications in information processing. The researchers first fabricated non-graphene-containing structures—the electrodes and gates—on plastic sheets. Separately, they grew large graphene sheets on metal, then peeled it and edtransfer it to the plastic. Finally, they topped the sheet with a waterproof layer. The devices work after being soaked in water, and are flexible enough to be folded.

In researchers devised a digital switch by perforating a graphene sheet with boron-nitride nanotubes that exhibited a switching ratio of 10 5 at a turn-on voltage of 0.

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Density functional theory suggested that the behavior came from the mismatch of the density of states. An electric field can change trilayer graphene's crystal structure, transforming its behavior from metal-like into semiconductor-like. A sharp metal scanning tunneling microscopy tip was able to move the domain border between the upper and lower graphene configurations. One side of the material behaves as a metal, while the other side behaves as a semiconductor. Trilayer graphene can be stacked in either Bernal or rhombohedral configurations, which can exist in a single flake.

The two domains are separated by a precise boundary at which the middle layer is strained to accommodate the transition from one stacking pattern to the other. Silicon transistors function as either p-type or n-type semiconductors , whereas graphene could operate as both.

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This lowers costs and is more versatile. The technique provides the basis for a field-effect transistor. Scalable manufacturing techniques have yet to be developed. In trilayer graphene, the two stacking configurations exhibit very different electronic properties. The region between them consists of a localized strain soliton where the carbon atoms of one graphene layer shift by the carbon—carbon bond distance. The free-energy difference between the two stacking configurations scales quadratically with electric field, favoring rhombohedral stacking as the electric field increases.

This ability to control the stacking order opens the way to new devices that combine structural and electrical properties. Graphene-based transistors could be much thinner than modern silicon devices, allowing faster and smaller configurations. Graphene's high electrical conductivity and high optical transparency make it a candidate for transparent conducting electrodes, required for such applications as touchscreens , liquid crystal displays , inorganic photovoltaics cells, [66] [67] organic photovoltaic cells , and organic light-emitting diodes.

In particular, graphene's mechanical strength and flexibility are advantageous compared to indium tin oxide , which is brittle. Graphene films may be deposited from solution over large areas. Large-area, continuous, transparent and highly conducting few-layered graphene films were produced by chemical vapor deposition and used as anodes for application in photovoltaic devices.

A power conversion efficiency PCE up to 1. Organic light-emitting diodes OLEDs with graphene anodes have been demonstrated. The device was formed by solution-processed graphene on a quartz substrate. The electronic and optical performance of graphene-based devices are similar to devices made with indium tin oxide.

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A carbon-based device called a light-emitting electrochemical cell LEC was demonstrated with chemically-derived graphene as the cathode and the conductive polymer Poly 3,4-ethylenedioxythiophene PEDOT as the anode. In a prototype graphene-based flexible display was demonstrated. The degree of curvature of the sheets above each cavity defines the color emitted. The device exploits the phenomena known as Newton's rings created by interference between light waves bouncing off the bottom of the cavity and the transparent material.

Potential applications of graphene

Increasing the distance between the silicon and the membrane increased the wavelength of the light. The approach is used in colored e-reader displays and smartwatches, such as the Qualcomm Toq. They use silicon materials instead of graphene. Graphene reduces power requirements. In , researchers built experimental graphene frequency multipliers that take an incoming signal of a certain frequency and output a signal at a multiple of that frequency.

Graphene strongly interacts with photons, with the potential for direct band-gap creation. This is promising for optoelectronic and nanophotonic devices. Light interaction arises due to the Van Hove singularity. Graphene displays different time scales in response to photon interaction, ranging from femtoseconds ultra-fast to picoseconds. Potential uses include transparent films, touch screens and light emitters or as a plasmonic device that confines light and alters wavelengths.

Due to extremely high electron mobility, graphene may be used for production of highly sensitive Hall effect sensors.

Material Question

These sensors are two times better than existing Si based sensors. Their size and edge crystallography govern their electrical, magnetic, optical, and chemical properties. Quantum confinement can be created by changing the width of graphene nanoribbons GNRs at selected points along the ribbon. A semiconducting polymer poly 3-hexylthiophene [84] placed on top of single-layer graphene vertically conducts electric charge better than on a thin layer of silicon.

Graphene may be the most remarkable substance ever discovered. But what’s it for?

In a thin film or on silicon, [84] plate-like crystallites are oriented parallel to the graphene layer. Uses include solar cells.

Large-area graphene created by chemical vapor deposition CVD and layered on a SiO2 substrate, can preserve electron spin over an extended period and communicate it. Spintronics varies electron spin rather than current flow. The spin signal is preserved in graphene channels that are up to 16 micrometers long over a nanosecond.