Our scientists have made new progress in graphene research

  Graphene's unique structure contains rich and novel physics, which not only provides an important research platform for basic science, but also shows broad application prospects in the fields of electronics, optoelectronics, and flexible devices.

In order to give full play to the excellent properties of graphene and realize its industrial production and application, it is necessary to find a suitable material preparation method so that the prepared graphene can simultaneously meet the conditions of large area, high quality, and compatibility with existing silicon processes.

Up to now, large-area, high-quality graphene single crystals are usually obtained by epitaxial growth on the surface of transition metals, but the subsequent complex transfer process usually causes the degradation of the graphene quality and the pollution of the interface, thus hindering the graphene in the electron Device applications.

  In recent years, Gao Hongjun, an academician of the Chinese Academy of Sciences and a researcher at the Key Laboratory of Nanophysics and Devices at the Institute of Physics of the Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics, has led a team in the preparation, property control and application of graphene and graphene-like two-dimensional atomic crystal materials. Research and exploration have been carried out in this regard, and a series of research results have been obtained.

In the early research work, the researchers found that the graphene epitaxially grown on the transition metal surface has the advantages of large area, high quality, continuous, and controllable layer number; further developed the heterogeneous element intercalation technology based on this system, The use of this technology can effectively avoid the complicated graphene transfer process, so that large-area, high-quality graphene single crystals can be placed on the heterogeneous element intercalation substrate without damage.

Subsequently, the researchers revealed the universal mechanism of the non-destructive intercalation of graphene; using this intercalation technology, the construction of a graphene/silylene heterojunction that exists stably in the air and the regulation of the electronic structure of graphene have been realized.

  On the basis of the above research, the research team’s postdoctoral fellow Guo Hui, doctoral student Wang Xueyan, and deputy chief engineer Huang Li, etc., through continuous efforts, realized the epitaxial high-quality graphene silicon dioxide insulating intercalation on the metal surface, and constructed in-situ Graphene electronic devices.

The researchers realized the epitaxial growth of centimeter-sized, single-crystal graphene on the surface of Ru(0001); on this basis, they developed a stepwise intercalation technique, which inserted two elements, silicon and oxygen, on the same sample. The silicon dioxide film grows at the interface with the Ru substrate; as the amount of silicon and oxygen intercalation increases, the silicon dioxide at the interface gradually thickens, and its structure changes from crystalline to amorphous; when silicon dioxide When the intercalation film reaches a certain thickness, the graphene is insulated from the metal substrate; using the graphene material on the silica intercalation substrate, the preparation of in-situ non-transferred epitaxial graphene devices can be realized.

The experiment first proved the double-layer structure of thin-layer crystalline silica through cross-sectional scanning transmission electron microscopy, and further combined with scanning tunneling microscopy and Raman spectroscopy, it showed that graphene remained large after silica intercalation. The area is continuous and high-quality; with the increase of the amount of silicon and oxygen intercalation, the thickness of the silicon dioxide at the interface of the scanning transmission electron microscope image display can reach 1.8 nanometers; vertical transport tests and theoretical calculations show that the thick layer is amorphous Silica (1.8 nanometers) intercalation layer greatly limits the electron transport process from graphene to the metal Ru substrate, and realizes the electrical near insulation between graphene and the metal Ru substrate; based on 1.8 nanometer silica intercalation layer The graphene electronic devices were prepared in situ with samples of, and through the transport test under low temperature and strong magnetic field, phenomena such as integer quantum Hall effect and weak delocalization of epitaxial graphene were observed.

These phenomena are derived from the intrinsic properties of graphene's two-dimensional electron gas, which further proves that the intercalation of 1.8nm amorphous silica does not destroy the large-area and high-quality characteristics of graphene, and it effectively isolates graphene from Coupling between metal substrates.

  This research provides a new method for preparing large-area, high-quality graphene single crystals fused with silicon-based technology, and provides a foundation for the application research of graphene materials and devices.

(Our reporter Zhan Yuan, our correspondent Guo Hui)