Graphene

Theoretically, we show that the restriction on the mobility of electrons and holes in grafene (on Si substrate) arises from the charged impurities in the dielectric (SiO2), so now work is to obtain a graph svobodnovisyaschih films, which should increase the mobility of up to 2 x 106 cm2 B-1 c-1. Currently, the maximum mobility is reached 2 x 105 cm2 V-1 c-1, and it was obtained in the sample, suspended above the dielectric layer at a height of 150 nm (part of a dielectric has been removed by using liquid travitelya). A sample with a thickness of one atom is maintained through extensive contacts. To improve the mobility of the sample has been cleaned of impurities on the surface by passing a current that the entire sample was heated to 900 K in high vacuum.

Ideal two-dimensional film in the free state can not be obtained because of its thermodynamic instability. But if the film will be defective or it will be deformed in space (in the third dimension), then the «non-ideal» film can survive without contact with the substrate. In the experiment using a transmission electron microscope showed that the graph, there are free film surface and form a complex wavy shape, with lateral dimensions of the spatial heterogeneities of about 5-10 nm and a height of 1 nm. The article it was shown that it is possible to create free from contact with the substrate film, embodied by two edges, forming thus nanoelektromehanicheskuyu system. In this case, suspended the column can be regarded as a membrane, changing the frequency of mechanical vibrations which is proposed to be used for detecting masses, forces and the charge, which is used as a highly sensitive sensor.

Silicon substrate with a dielectric, on which rests Box, should be highly alloyed, so that it can be used as a shutter, through which you can control the concentration and even change the type of conductivity. Since the graph is semimetals, the application of positive voltage to the gate leads to the electronic conductivity of the graph, and the opposite - if you make a negative voltage, the main carriers are holes, so in principle can not be fully Mass column of vehicles. Note that if the graphite is composed of several tens of layers, the electric field is well shielded, as in metals, a great number of carriers in semimetals.

In the ideal case where there is no alloying and shutter voltage is zero, there should be holders of current (see the density of states) that if you follow the naive opinion, should lead to a lack of conductivity. But as shown by experiments and theoretical work, near dirakovskoy point or point elektroneytralnosti dirakovskih for fermions, there is a finite value of conductivity, while the value of the minimum conductivity depends on the method of calculation. This ideal area not known simply because there is no sufficiently sound samples. In fact, all of the graph are connected to the film substrate, and this leads to the heterogeneity, the capacity fluctuations, which leads to spatial heterogeneity of the type of conductivity of the sample, so even at the point elektroneytralnosti the concentration of carriers in theory no less than 1012 cm-2. Here the contrast to conventional systems with two-dimensional electron or hole gas, as there is no metal-insulator transition.