Nanoscience Centre, University of Cambridge, Cambridge, UK.
Nanotechnology. 2012 Mar 9;23(9):095601. doi: 10.1088/0957-4484/23/9/095601. Epub 2012 Feb 10.
We report selective tunnelling through a nanographene intermolecular tunnel junction achieved via scanning tunnelling microscope tip functionalization with hexa-peri-hexabenzocoronene (HBC) molecules. This leads to an offset in the alignment between the energy levels of the tip and the molecular assembly, resulting in the imaging of a variety of distinct charge density patterns in the HBC assembly, not attainable using a bare metallic tip. Different tunnelling channels can be selected by the application of an electric field in the tunnelling junction, which changes the condition of the HBC on the tip. Density functional theory-based calculations relate the imaged HBC patterns to the calculated molecular orbitals at certain energy levels. These patterns bear a close resemblance to the π-orbital states of the HBC molecule calculated at the relevant energy levels, mainly below the Fermi energy of HBC. This correlation demonstrates the ability of an HBC functionalized tip as regards accessing an energy range that is restricted to the usual operating bias range around the Fermi energy with a normal metallic tip at room temperature. Apart from relating to molecular orbitals, some patterns could also be described in association with the Clar aromatic sextet formula. Our observations may help pave the way towards the possibility of controlling charge transport between organic interfaces.
我们报告了通过扫描隧道显微镜针尖功能化六并苯（HBC）分子实现的纳米石墨烯分子间隧道结的选择性隧穿。这导致针尖和分子组装之间的能级对准发生偏移，从而在 HBC 组装中成像出各种不同的电荷密度图案，而使用裸金属针尖则无法获得这些图案。通过在隧道结中施加电场，可以选择不同的隧道通道，这会改变针尖上 HBC 的状态。基于密度泛函理论的计算将成像的 HBC 图案与在某些能级计算的分子轨道相关联。这些图案与在相关能级下计算的 HBC 分子的π轨道状态非常相似，主要低于 HBC 的费米能。这种相关性表明，与室温下通常操作偏压范围内围绕费米能的普通金属针尖相比，HBC 功能化针尖能够进入受限的能量范围。除了与分子轨道有关外，一些图案还可以与 Clar 芳香六元环公式相关联。我们的观察结果可能有助于为控制有机界面之间的电荷输运铺平道路。
