我们建议二维(2D)材料的结晶度是实现高效功函数(WF)改性的关键因素。对于低至0.7nm的厚度,结晶2DMoO3单层将衬底WF增强至6.4eV。如此高的WF使2DMoO3成为调整阳极材料性能和未来有机电子器件设计的理想选择。准确评估WF至关重要。我们提供了直接在高度有序的热解石墨上生长的2Dα-MoO3的WF的详细研究,通过开尔文探针力显微镜(KPFM)和紫外光发射光谱(UPS)。这项研究强调了受控环境和所得结晶度对于在MoO3中实现高WF的重要性。UPS被证明适用于确定归因于具有较低WF的衬底上的2D岛的较高WF,然而,只有在足够的覆盖范围的特殊情况下。KPFM仍然是纳米级研究的首选方法,特别是在超高真空条件下进行。我们的实验结果得到静电势的密度泛函理论计算的支持,这表明氧空位导致MoO3单层侧面的WF各向异性。这些对2D-MoO3电子特性的新颖见解有望用于设计具有高WF单层膜的电子器件,保持系统的透明度和灵活性。
We propose that the crystallinity of two-dimensional (
2D) materials is a crucial factor for achieving highly effective work function (WF) modification. A crystalline
2D MoO3 monolayer enhances substrate WF up to 6.4 eV for thicknesses as low as 0.7 nm. Such a high WF makes
2D MoO3 a great candidate for tuning properties of anode materials and for the future design of organic electronic devices, where accurate evaluation of the WF is crucial. We provide a detailed investigation of WF of
2D α-MoO3 directly grown on highly ordered pyrolytic graphite, by means of Kelvin probe force microscopy (KPFM) and ultraviolet photoemission spectroscopy (UPS). This study underlines the importance of a controlled environment and the resulting crystallinity to achieve high WF in MoO3. UPS is proved to be suitable for determining higher WF attributed to
2D islands on a substrate with lower WF, yet only in particular cases of sufficient coverage. KPFM remains a method of choice for nanoscale investigations, especially when conducted under ultrahigh vacuum conditions. Our experimental results are supported by density functional theory calculations of electrostatic potential, which indicate that oxygen vacancies result in anisotropy of WF at the sides of the MoO3 monolayer. These novel insights into the electronic properties of 2D-MoO3 are promising for the design of electronic devices with high WF monolayer films, preserving the transparency and flexibility of the systems.