Samejima Yudai, Kobayashi Naritaka, Nakabayashi Seiichiro
Graduate School of Science and Engineering, Saitama University, Shimo-okubo 255, Sakura-ku, Saitama 338-8570, Japan.
Phys Chem Chem Phys. 2021 Sep 14;23(34):18349-18358. doi: 10.1039/d1cp02371c. Epub 2021 Aug 18.
The stabilization mechanism of the Zn-terminated (Zn-) ZnO(0001) surface in electrolyte solutions has been investigated by using atomic-resolution liquid-environment atomic force microscopy (AFM) and an electrochemical method. The electrochemically measured pH dependence of the flat band potential of the Zn-ZnO(0001) surface indicated the adsorption of OH groups onto the (0001) surface in the wide pH range of 1-13. Atomic-scale AFM images of the Zn-ZnO(0001) surface showed a well-ordered hydroxide superstructure in an alkaline solution but a disordered structure in an acidic solution, which is probably attributed to the rapid diffusion of the adsorbed OH groups. Furthermore, the density of the O-terminated step edge on the Zn-ZnO(0001) surface in an acidic solution was higher than that in an alkaline solution. From these findings, we concluded that the excess positive charges of the Zn-ZnO(0001) surface are compensated by the adsorbed OH groups and the O-terminated step edges. In acidic solutions, a higher density of the O-terminated step edge is required for charge compensation. In addition, it was found that potential-dependent reversible surface reconstruction occurs in the local transition area with disordered step orientation by electrochemical AFM. We concluded that the reconstruction compensates the excess surface charges of the local transition area which are induced and varied by potential-dependent local surface states.
通过使用原子分辨率液体环境原子力显微镜（AFM）和电化学方法，研究了电解质溶液中锌端接（Zn-）的ZnO（0001）表面的稳定机制。电化学测量的Zn-ZnO（0001）表面平带电位的pH依赖性表明，在1-13的宽pH范围内，OH基团吸附在（0001）表面上。Zn-ZnO（0001）表面的原子尺度AFM图像显示，在碱性溶液中存在有序的氢氧化物超结构，而在酸性溶液中则为无序结构，这可能归因于吸附的OH基团的快速扩散。此外，酸性溶液中Zn-ZnO（0001）表面上O端接台阶边缘的密度高于碱性溶液中的密度。基于这些发现，我们得出结论，Zn-ZnO（0001）表面的过量正电荷由吸附的OH基团和O端接台阶边缘补偿。在酸性溶液中，需要更高密度的O端接台阶边缘来进行电荷补偿。此外，通过电化学AFM发现，在具有无序台阶取向的局部过渡区域中发生了电位依赖性可逆表面重构。我们得出结论，这种重构补偿了由电位依赖性局部表面态诱导并变化的局部过渡区域的过量表面电荷。
