The two-dimensional boron monolayers were reported to be metallic both in previous theoretical predictions and experimental observations. Unexpectedly, we have first found a family of boron monolayers with the novel semiconducting property as confirmed by the first-principles calculations with the quasi-particle GW approach. We demonstrate that the connected network of hexagonal vacancies dominates the gap opening for both the in-plane s+p and p orbitals, with which various semiconducting boron monolayers are designed to realize the band gap engineering for the potential applications in electronic devices. The semiconducting boron monolayers in our predictions are expected to be synthesized on the proper substrates, due to the similar stabilities to the ones observed experimentally.

Boron (B) sheet has been intently studied and various candidates with vacancies have been proposed by theoretical investigations, including the possible growth on metal surface. However, a recent experiment (Science 350, 1513(Science 350, , 2015 reported that the sheet formed on the Ag (111) surface was a buckled triangular lattice without vacancy. Our calculations combined with High-Throughput screening and the first-principles method demonstrate a novel growth mechanism of boron sheet from clusters, ribbons, to monolayers, where the B-Ag interaction is dominant in the nucleation of boron nanostructures. We have found that the simulated STM image of the sheet with 1/6 vacancies in a stripe pattern is in better agreement with the experimental observation, which is energetically favored during the nucleation and growth.Due to the multi-center bonds, boron nanostructures have shown a striking evolution as thesize increases, which have attracted both theoretical and experimental attentions in the past decades [1][2][3][4] [5,6]have been found to be a triangular lattice with proper vacancies, leading to extensive theoretical searches which focus on the concentration and distribution of vacancies [7][8][9][10][11].The 2D boron structure with non-zero thickness has been predicted to possess a distorted Dirac cone, with great potential of applications similar to graphene and silicene [12].The multi-center bonds highly depend on the atomic coordination, which might induce the dramatic effect on the structural stabilities of boron nanostructures. Theoretical investigations have predicted that possible boron sheets could be synthesized on the metal surface (e.g. Cu, Ag, and Au), indicating that the stable sheet with specific concentration and distribution of vacancies would change with the substrate [13][14][15]. Experimentally, thin boron films were found on the Cu surface with a mixture of boron and boron oxide powders as the boron source, where the monolayer of B 28 comprises of B 12 icosahedrons and B 2 16 dumbbells[ ].Notably, the boron sheet with one atom-thick was experimentally determined on the Ag(111) surface using a solid boron atomic source. This simple boron sheet was suggested to be a buckled triangular lattice with no vacancy [17], which is in contrast to the previous theoretically predicted stable configurations of boron sheet on the Ag(111) surface [15].To give a better understanding of the boron sheet's growth, in this paper we have theoretically investigated the possible B nucleation on the Ag (111) To simulate a deposit of the solid atomic boron source on the Ag(111) surface, we considered the adsorption of boron clusters with increasing sizes. Firstly, a single B atom is found to penetrate the first layer with no barrier with the of 2.02 eV (c.f. Fig. S1) .The B atom is initially located at 2 Å above the Ag(111) surface, and the total energy gradually decreases as the height decrease. The adsorption and penetration is shown with the energy profile with the distance between the B atom and th...

The recent advances in 2D ferromagnets are reviewed, including materials synthesis, ferromagnetism modulation, physical properties, and potential device applications.