Institute for Materials Chemistry and Engineering and International Research Center for Molecular Systems, Kyushu University, Nishi-ku, Fukuoka, Japan.
Chemphyschem. 2013 Aug 5;14(11):2470-5. doi: 10.1002/cphc.201300136. Epub 2013 Jun 5.
The conductance through single 7,7,8,8-tetracyanoquinodimethane (TCNQ) connected to gold electrodes is studied with the nonequilibrium Green's function method combined with density functional theory. The aim of the study is to derive the effect of a dicyano anchor group, =C(CN)2, on energy level alignment between the electrode Fermi level and a molecular energy level. The strong electron-withdrawing nature of the dicyano anchor group lowers the LUMO level of TCNQ, resulting in an extremely small energy barrier for electron injection. At zero bias, electron transfer from electrodes easily occurs and, as a consequence, the anion radical state of TCNQ with a magnetic moment is formed. The unpaired electron in the TCNQ anion radical causes an exchange splitting between the spin-α and spin-β transmission spectra, allowing the single TCNQ junction to act as a spin-filtering device.
用非平衡格林函数方法结合密度泛函理论研究了单 7,7,8,8-四氰基对醌二甲烷（TCNQ）与金电极的电导。研究的目的是推导二氰基锚定基团，=C(CN)2，对电极费米能级和分子能级之间能级排列的影响。二氰基锚定基团的强吸电子性质降低了 TCNQ 的最低未占分子轨道（LUMO）能级，导致电子注入的能垒极小。在零偏压下，电子很容易从电极转移，因此形成了具有磁矩的 TCNQ 阴离子自由基。TCNQ 阴离子自由基中的未配对电子在自旋-α和自旋-β传输谱之间引起交换劈裂，使单个 TCNQ 结能够作为自旋过滤器件。
