Large-scale Synthesis And Transfer Of Graphene Films

In 2004, a physical research Group led by Prof. Andre Geim and Dr Kostya Novoselov in the University of Manchester used a very different approach, which seem very na?ve method according to ordinary people approach, to obtain the atomic layer of graphene, thus leading a revolution in this area. They proceed from the three-dimensional graphite, using a method known as micro-mechanical cleavage to obtain the graphene of a single atomic layer thickness. Graphite is a layered material, a series overlapping planar array of two-dimensional graphene crystal, which is the team's starting point. Through this three-dimensional crystals and the top-down approach to avoid the stability of small crystals and other all related issues. In addition, this research team also used the same method to obtain the two-dimensional crystal structure of other materials, including boron nitride, transition metal sulfides, and high-temperature superconductor Bi-Sr-Ca-Cu-O. This shocking discovery sends a very important message, that is, under natural conditions, two-dimensional crystals can indeed exist, and very stable.Surprisingly, this crude method can easily prepare large-scale, high-quality graphene crystal up to 100-micron-sized, which triggered a wave of experimental movement. Furthermore, graphene prepared by this method is of very high quality, which can be easily observed the ballistic conduction and the Quantum Hall Effect, which make this material into electronic applications in the future prospects. For example, it can be used to make ballistic field-effect transistor. Although this method can meet the research needs, it need provide other ways to meet the production needs of graphene according to the industrial production yield.Graphene is a honeycomb carbon atoms arranged in hexagonal shapes, which can also be considered ring hydrogen atoms discovered in 1972 by Pauling. Fullerene is composed of spherical carbon molecules, from the physics point of view, is zero-dimensional material to separate the physical state. Through the introduction of five-membered ring, the fullerene is formed (ie. the introduction of positive curvature defects), and can be considered as wrapped graphene. Carbon nanotubes are graphene with carbon bonds re-connected in a particular direction through the coil. Carbon nanotubes can also be considered as one-dimensional material with six-ring structure. Graphite is known for the invention of a pencil since 1564 as a writing tool, which is a carbon allotrope with three-dimensional, because graphite is graphene stacked to form three-dimensional structure with very weak interlayer van der Waals bonding force. If we introduce some pressure on the graphite in the paper, it will produce independent graphene layers. Although graphene is the mother of all these carbon allotrope, and everyone produces graphene when they are using a pencil, it is isolated only 440 years after the discovery of the first pencil. One of the most important reasons is that nobody really believed that graphene can be stable in Free State, and another important reason is that there are not debris graphene can be found with the any existing testing tools. Graphene, which is found in particular the thickness of the SiO2 surface very occasionally, it can be easily observed by the delicate optical effects produced by conventional optical microscopy. Contrast, even though we can directly prepare graphene, however, to find its location is not so easy.The electronic properties of this new material make it a candidate for the wide range in prospects of future electronics. Under the status technology, the electron mobility with 20,000 cm2/Vs can be easily reached by graphene, which is an order of magnitude higher than modern silicon transistors. With the improvement of the quality of the graphene, this value can also continue to be increased. The ballistic conduction in submicron range can be achieved in graphene, which is goals and dreams for all electronic engineers. Graphene-based field-effect transistor is the best choice with the use of quantum dots and p-n junction in double-layer graphene.Another promising direction is to study the spin-valve device. Since the spin-orbit hybridization and spin polarization in graphene can be ignored in the sub-micron distance, which allows us to observe the spin injection and spin valve effects in this material. Morpurgo and his collaborators form Delft University demonstrated superconductivity in the graphene. As well, the supercurrent can be controlled through the gate voltage, which can be used to make superconducting field-effect transistor.When the applications mentioned become the focus of future research, graphene can be directly applied to certain areas, such as gas sensors. Research group in Manchester demonstrate that an electrons or holes doping of graphene can be produced by gas molecules adsorption in environment. We can detect the tiny specific gas concentration of atmospheric by monitoring the resistance change.The main application obstacle of graphene device is the growth of large-size templates. Recently, the macro-size thin film of graphene crystals is prepared by assembly layers of graphite and graphene through chemical derivative of the graphene oxide. However, the sheet resistance of these films is much larger than the expected values. Here we reported the direct synthesis method of large size graphene through the deposited thin layer of nickel, and proposed two different ways to form thin film patterns and transfer them to arbitary substrate. The films show very low sheet resistance ~280? per square, with 80% optical transparency. At low temperatures, graphene films transferred to the silicon dioxide substrate showed electron mobility is higher than 3,700 cm2V-1 s-1 and a half integer quantum Hall effect, which means that the quality can be compared with mechanical exfoliated graphene. We have proved the application of the outstanding mechanical and electrical properties of graphene for high conductivity and transparent stretchable and foldable electrode.On the other hand, graphene synthesized by copper catalysts under low pressure conditions with the significant advantages of controllability in thickness and quality using the vacuum method, however, it is not conducive to cost and production efficiency. Although the chemical deposition methods are conducive to large-scale production of graphene, inevitably, this method requires a solid base, which can withstand temperatures up to 900 degree conditions and the need for erosion catalytic metal layer, which makes direct restrictions on the production, and, unable to use the low temperature polymer substrate. Therefore, transfer graphene from the mother substrate onto other flexible polymer-based surface can extend very critical step of the application of graphene device. However, due to the size of mother substrate and uniform high temperature in furnace severely restricted the size of transfer graphene. We introduce the method of producing high-quality 3-inch wafer size graphene thin films in external environment and introduce real-time erosion of the metal layer, and the transfer method. This method of large-scale synthesis and large-size transfer realize the possibility of applications of the graphene in chip size electronic devices, and flexible, stretchable device. We also confirmed mass production of field-effect thin film transistor array and the production of strain gauge and show the extraordinary properties. The hole and electron mobility in graphene transistor under -0.75V drain bias are 1100±70 and 550±50cm2 / (Vs), respectively. Strain gauge factor is about 6.1. This method indicates an important milestone in the realization of graphene electronic device, and will promote the applications of graphene films to the field of optoelectronics, flexible, and stretchable devices.