We investigate atomic and electronic structures of boron nanotubes (BNTs) by using the density functional theory (DFT). The transport properties of BNTs with different diameters and chiralities are studied by the Keldysh nonequilibrium Green function (NEGF) method. It is found that the cohesive energies and conductances of BNTs decrease as their diameters decrease. It is more diffcult to form (N,0) tubes than (M,M) tubes when the diameters of the two kinds of tubes are comparable. However, the (N,0) tubes have a higher conductance than the (M,M) tubes. When the BNTs are connected to gold electrodes, the coupling between the BNTs and the electrodes will affect the transport properties of tubes significantly.
The atomic and electronic structures of a graphene monolayer on a Ru(0001) surface under compressive strain are investigated by using first-principles calculations.Three models of graphene monolayers with different carbon periodicities due to the lattice mismatch are proposed in the presence and the absence of the Ru(0001) substrate separately.Considering the strain induced by the lattice mismatch,we optimize the atomic structures and investigate the electronic properties of the graphene.Our calculation results show that the graphene layers turn into periodic corrugations and there exist strong chemical bonds in the interface between the graphene N × N superlattice and the substrate.The strain does not induce significant changes in electronic structure.Furthermore,the results calculated in the local density approximation(LDA) are compared with those obtained in the generalized gradient approximation(GGA),showing that the LDA results are more reasonable than the GGA results when only two substrate layers are used in calculation.
Scanning tunnelling microscopy is utilized to investigate the local bias voltage tunnelling dependent transformation between (2×1) and c(4×2) structures on Ge(001) surfaces, which is reversibly observed at room temperature and a critical bias voltage of -0.80 V. Similar transformation is also found on an epitaxial Ge islands but at a slightly different critical bias voltage of -1.00 V. It is found that the interaction between the topmost atoms on the STM tip and the atoms of the dimers, and the pinning effect induced by Sb atoms, the vacancies or the epitaxial clusters, can drive the structural transformation at the critical bias voltage.
Different In/Ge(001) nanostructures have been obtained by annealing the samples at 320 C with different coverages of In.Annealing a sample with a critical coverage of 2.1 monolayer of In,different In/Ge(001) nanostructures can be obtained at different temperatures.It is found that thermal annealing treatments first make In atoms form elongated Ge { 103 }-faceted In-clusters,which will grow wider and longer with increasing temperature,and finally cover the surface completely.
Self-assembly and growth of manganese phthalocyanine (MnPc) molecules on an Au(111) surface is investigated by means of low-temperature scanning tunneling microscopy.At the initial stage,MnPc molecules preferentially occupy the step edges and elbow sites on the Au(111) surface,then they are separately adsorbed on the face-centered cubic and hexagonal closely packed regions due to a long-range repulsive molecule-molecule interaction.After the formation of a closely packed monolayer,molecular islands with second and third layers are observed.
We investigate the electronic structures of one and two monolayer iron phthalocyanine (FePc) molecules on Au(111) surfaces. The first monolayer FePc is lying flat on the Au(111) substrate, and the second monolayer FePc is tilted at～15° relative to the substrate plane along the nearest neighbour [101ˉ] direction with a lobe downward to the central hole of the unit cell in the first layer. The structural information obtained by first-principles calculations is in agreement with the experiment results. Furthermore, it is demonstrated that the electronic structures of FePc molecules in one-monolayer FePc/Au(111) system are perturbed significantly, while the electronic structures of FePc molecules in the second monolayer in two-monolayer FePc/Au(111) system remain almost unchanged due to the screening of the buffer layer on Au(111).
