In situ atomic-scale observation of monolayer graphene growth from SiC

Because of its high compatibility with conventional microfabrication processing technology, epitaxial graphene （EG） grown on SiC shows exceptional promise for graphene-based electronics. However, to date, a detailed understanding of the transformation from three-layer SiC to monolayer graphene is still lacking. Here, we demonstrate the direct atomic-scale observation of EG growth on a SiC （11^-00） surface at 1,000℃ by in situ transmission electron microscopy in combination with ab initio molecular dynamics （AIMD） simulations. Our detailed analysis of the growth dynamics of monolayer graphene reveals that three SiC （11^-00） layers decompose successively to form one graphene layer. Sublimation of the first layer causes the formation of carbon clusters containing short chains and hexagonal rings, which can be considered as the nuclei for graphene growth. Decomposition of the second layer results in the appearance of new chains connecting to the as-formed clusters and the formation of a network with large pores. Finally, the carbon atoms released from the third layer lead to the disappearance of the chains and large pores in the network, resulting in a whole graphene layer. Our study presents a clear picture of the epitaxial growth of the monolayer graphene from SiC and provides valuable information for future developments in SiC-derived EG technology.

Impurity-limited quantum transport variability in magnetic tunnel junctions

We report an extensive first-principles investigation of impurity-induced device-to-device variability of spin-polarized quantum tunneling through Fe/MgO/Fe magnetic tunnel junctions （MTJ）. In particular, we calculated the tunnel magnetoresistance ratio （TMR） and the average values and variances of the currents and spin transfer torque （STT） of an interfacially doped Fe/MgO/Fe MTJ. Further, we predicted that N-doped MgO can improve the performance of a doped Fe/MgO/Fe MTJ. Our first- principles calculations of the fluctuations of the on/off currents and STT provide vital information for future predictions of the long-term reliability of production. spintronic devices, which is imperative for high-volume

The complementary graphene growth and etching revealed by large-scale kinetic Monte Carlo simulation

To fully understand the kinetics of graphene growth,large-scale atomic simulations of graphene islands evolution up to macro sizes(i.e.,graphene islands of a few micrometers or with billions of carbon atoms)during growth and etching is essential,but remains a great challenge.In this paper,we developed a low computational cost large-scale kinetic Monte Carlo(KMC)algorithm,which includes all possible events of carbon attachments and detachments on various edge sites of graphene islands.Such a method allows us to simulate the evolution of graphene islands with sizes up to tens of micrometers during either growth or etching with a single CPU core.With this approach and the carefully fitted parameters,we have reproduced the experimentally observed evolution of graphene islands during both growth or etching on Pt(111)surface,and revealed more atomic details of graphene growth and etching.Based on the atomic simulations,we discovered a complementary relationship of graphene growth and etching—the route of graphene island shape evolution during growth is exactly the same as that of the etching of a hole in graphene and that of graphene island etching is exactly same as that of hole growth.The complementary relation brings us a basic principle to understand the growth and etching of graphene,and other 2D materials from atomic scale to macro size and the KMC algorithm is expected to be further developed into a standard simulation package for investigating the growth mechanism of 2D materials on various substrates.

Impurity-induced formation of bilayered graphene on copper by chemical vapor deposition

High-quality single-layered and bilayered graphene (SLG and BLG) was synthesized on copper foil surfaces by controllable chemical vapor deposition (CVD). Impurity nanoparticles formed on the copper foil surface by hightemperature annealing were found to play a crucial role in the growth of BLG. Analysis of energy-dispersive spectrometry (EDS) data indicated that these nanoparticles consisted of silicon and aluminum. According to the inverted wedding cake model, these nanoparticles served as nucleation centers for BLG growth and the free space between a nanoparticle and graphene served as the center of C injection for the continuous growth of the adlayer beneath the top layer. By combining phase-field theory simulations, we confirmed the mechanism of BLG growth and revealed more details about it in comparison with SLG growth. For the first time, this study led to a complete understanding of the BLG growth mechanism from nucleation to continuous growth in the CVD process, and it has opened a door to the thickness-controllable synthesis of graphene. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.