Graphitic overlayers on metals have commonly been considered as inhibitors for surface reactions due to their chemical inertness and physical blockage of surface active sites. In this work, however, we find that surface reactions, for instance, CO adsorption/desorption and CO oxidation, can take place on Pt(111) surface covered by monolayer graphene sheets. Surface science measurements combined with density functional calculations show that the graphene overlayer weakens the strong interaction between CO and Pt and, consequently, facilitates the CO oxidation with lower apparent activation energy. These results suggest that interfaces between graphitic overlayers and metal surfaces act as 2D confined nanoreactors, in which catalytic reactions are promoted. The finding contrasts with the conventional knowledge that graphitic carbon poisons a catalyst surface but opens up an avenue to enhance catalytic performance through coating of metal catalysts with controlled graphitic covers.arbonaceous deposits such as carbidic carbon and graphitic carbon often form on transition metal (TM) surfaces in catalytic processes involving carbon-containing reactants (1). It has been shown that carbidic species can be involved in some hydrogenation reactions, which are attributed to the observed high reaction activity (2-5). In contrast, graphitic carbon deposited on TM is conventionally considered as catalyst poison due to its chemical inertness and physical blockage of surface active sites (6-8). It has been generally assumed that formation of graphitic carbon on metal catalysts should be avoided before and during catalytic reactions (9, 10). Nevertheless, for decades, extensive research efforts have been made to use surface carbon layers formed on TMs and to understand their role in catalytic reactions (11)(12)(13)(14), which, however, have been impeded by complexity of the ill-defined carbon structures. Graphene, as a simple form of graphitic deposit, has been grown on many late TM surfaces via catalytic cracking of carbon-containing gases (15)(16)(17)(18)(19)(20). Surface science studies on the well-defined graphene/metal surfaces have shown that gaseous molecules such as CO, O 2 , and H 2 O can be readily intercalated under the graphene overlayers (21-27). Defects in graphene including island edges (22,23,(28)(29)(30), domain boundaries (26,31,32), and wrinkles (33) provide channels for molecule diffusion into the graphene/metal interfaces. These new results raise the intriguing possibility that the space between graphene overlayers and metal substrates can act as a 2D container for reactions. The distance between the graphene overlayers and the metal surfaces typically falls in the subnanometer range (19,20), and molecules trapped inside interact directly with both the graphene cover and the metal substrate. Catalytic reactions, if occurring, are strongly confined in the 2D space, and extraordinary catalytic performance may be expected due to the confinement effect. In the present work, graphene/Pt(111) [Gr/Pt(111)] was used ...

Using hybrid functional calculation, we identify the key intrinsic defects in Cu2ZnSnS4 (CZTS), an important earth-abundant solar-cell material. The Sn-on-Zn antisite and the defect complex having three Cu atoms occupying a Sn vacancy are found to be the main deep electron traps. This result explains the optimal growth condition for CZTS, which is Cu-poor and Zn-rich as found in several recent experiments. We show that under the growth condition that minimizes the deep traps, Cu vacancy could contribute the majority of hole carriers, while Cu-on-Zn antisite will become the dominant acceptor if the growth condition favors its formation.

A self-assembled iron(II) phthalocyanine single layer adsorbed on the topological insulator Bi 2 Te 3 was investigated by spin-polarized scanning tunneling microscopy and density functional theory calculations. Although the molecule-substrate interaction is dominated by a relatively weak van der Waals force, the local density of states of Fe was found to strongly depend on the adsorption sites, resulting in a supermolecular lattice. Spin-polarized measurements show that the magnetic moment of iron(II) phthalocyanine persists with an in-plane magnetic easy axis, which was further confirmed by density functional calculations.Macrocyclic phthalocyanine, which can be textured by changing the central atom to a magnetic atom, e.g., Fe, Co, Mn, has been intensively investigated because of its potential applications in reading, storing, and manipulating magnetic information [1]. The study of these magnetic metalphthalocyanines (MMPc) generally involves depositing the molecules on various substrates [2][3][4][5][6][7][8][9][10][11][12], with the magnetic moment of the MMPc strongly depending on the interaction between the molecule and the substrate. On metallic substrates, hybridization with the substrates often leads to a great reduction or even quenching of the magnetic moment [9-12], while on insulating substrates, the magnetic moments of the MMPc are usually preserved [8]. The magnitude as well as the easy direction of the magnetic moment can be influenced by the substrates. Taking iron(II) phthalocyanine (FePc) grown on oxidized Cu (110) [8] as an example, a combined theoretical calculation and inelastic tunneling spectra measurement show that the easy axis changes from in the molecular plane of the free molecule to out of plane on oxidized Cu(110), induced by the strong interaction with the substrate [13].On the other hand, due to the weak molecule-molecule interaction, spontaneous magnetic ordering has not yet been found in molecule films. One way to enhance the moleculemolecule interaction is by utilizing the free electron of the substrates. Experimental results on metallic substrates with surface states, however, have not show any hint of long range ordering. Another attempt at growing manganese phthalocyanine (MnPc) on Bi (110) [14]-a substrate with strong spin-orbit coupling (SOC)-suggests the existence of a strong scattering of surface electrons by the magnetic molecules. Recently, the discovery of a topological insulator (TI) with strong SOC opens a new playground for spintronics [15][16][17][18]. It has been proposed that the magnetic adsorbates on the surface of a TI can be aligned via the topological surface state (TSS) electron forming ferromagnetic ordering [19][20][21] perpendicular to the surface. Provided this unique property of TSS, it would be interesting to study the magnetic anisotropy of * Corresponding author: clgao@sjtu.edu.cn magnetic molecules on a TI surface. Nevertheless, due to technical difficulties, the direct determination of the magnetic easy axis of a single molecule remains an experi...