The first-principles calculation method has been used to obtain electronic and structural properties of few-layer-graphenes (FLG), the layer spacing for N = 2, 3, 4, 5, 6, 7 and 8 AB stacked FLG¡¦s are calculated. It is found that the AB stacking is more favorable than the AA stacking and the layer spacing for the two-layer FLG is only 2.725Å, which is substantially reduced from that of the graphite. The average layer spacing for 3-, 4-, 5-, 6-, 7-, and 8-layer AB stacked FLG¡¦s are 3.389Å, 3.331Å, 3.317Å, 3.192Å, 3.220Å, and 3.220Å, respectively, which show that the average layer spacing approaches the bulk value when the number of layers is increased. For all 2- to 8-layer AB stacked FLG¡¦s energy bands overlap near EF and near K, which show that FLG¡¦s are semi-metallic.

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have attracted increasing interests for (opto)-electronics and spintronics. They generally consist of van der Waals stacked layers and exhibit layer-depended electronic properties. While considerable efforts have been made to regulate the charge transport within a layer, precise control of electronic coupling between layers has not yet been achieved. Herein, we report a strategy to precisely tune interlayer charge transport in 2D c-MOFs via side-chain induced control of the layer spacing. We design hexaiminotriindole ligands allowing programmed functionalization with tailored alkyl chains (HATI_CX, X = 1,3,4; X refers to the carbon numbers of the alkyl chains) for the synthesis of semiconducting Ni3(HATI_CX)2. The layer spacing of these MOFs can be precisely varied from 3.40 to 3.70 Å, leading to widened band gap, suppressed carrier mobilities, and significant improvement of the Seebeck coefficient. With this demonstration, we further achieve a record-high thermoelectric power factor of 68 ± 3 nW m−1 K−2 in Ni3(HATI_C3)2, superior to the reported holes-dominated MOFs.