Synthesis of complex two-dimensional heterostructures with tailored optoelectronic properties

复杂半导体/半导体异质结或金属/半导体杂化结构在光电子学领域具有广泛的应用前景。半导体异质结可以通过在异质界面上分离光生电子-空穴对来用于光伏发电。相反，注入到异质结中的载流子可以在界面区域复合，从而发光。金属/半导体杂化结构非常适合于光催化，例如，通过将半导体材料中光学产生的电子转移到附着的金属颗粒上，可以将质子还原为氢。在这个项目中，将开发各种二维异质和杂化纳米结构的化学合成方法。例如，通过控制一种半导体材料在另一种半导体材料上的外延生长，可以合成SnSe/SnS核/壳纳米片，其中价带边级数可以通过阴离子变化来选择性地调节。此外，阳离子交换反应将用于从CuS纳米片开始合成Janus状CuS/CDS异质纳米片，其中导带能量和电子局域化是通过阳离子梯度来控制的。最后，纳米片边缘金属纳米晶体的定向生长应该会导致杂化结构，其中光生电子定位在边缘金属颗粒中，从而产生特别高效的光催化剂。除了纳米薄片的化学合成外，对其光电性能的研究也是本项目的发展方向。这里的一个重要目标是直接跟踪光生载流子在单个杂化和异质结构中的局域化。中心实验结合了共聚焦激光扫描显微镜和扫描力显微镜，允许在纳米结构的局部照明下对静电力进行空间分辨测量。在非接触异质纳米薄膜上，异质界面的电势分布和光生载流子的再分布将以高的空间分辨率被定量地确定。这里还将开发时间分辨测量，以直接跟踪充电和放电动力学。在电接触纳米片上，额外的扫描光电流测量将与静电原子力测量相结合，以研究电势分布，特别是在接触处。这些实验还将使用来自同步辐射光源的聚焦X射线进行，以显著提高光电流测量的空间分辨率，并将其与多种X射线光谱学方法相结合。

Complex semiconductor/semiconductor heteronanostructures or metal/semiconductor hybrid structures are of great interest for various applications in optoelectronics. Semiconductor heterostructures can be used in photovoltaics by separating photo-generated electron-hole pairs across the hetero-interface. Conversely, charge carriers injected into the heterostructure can recombine in the interface region, emitting light. Metal/semiconductor hybrid structures are ideally suited for photocatalysis, e.g., by transferring electrons optically generated in the semiconductor material to attached metal particles, which can reduce protons to hydrogen. In this project, chemical synthesis methods for various two-dimensional hetero- and hybrid nanostructures will be developed. By controlled epitaxial growth of one semiconductor material onto another, SnSe/SnS core/shell nanosheets are to be synthesized, for example, in which the valence band edge progression can be selectively adjusted via anion variation. Furthermore, cation exchange reactions will be used to synthesize Janus-like CuS/CdS hetero-nanosheets starting from CuS nanosheets, in which the conduction band energy and thus the electron localization is controlled via the cation gradient. Finally, the targeted growth of metal nanocrystals on the edges of the nanosheets should lead to hybrid structures in which the photo-generated electrons are localized in the edge metal particles, resulting in particularly efficient photocatalysts. In addition to the chemical synthesis of the nanosheets, the research of their optoelectronic properties is in the foreground of this project. An important goal here is to directly follow the localization of the photogenerated charge carriers in individual hybrid and heterostructures. The central experiment combines a confocal laser scanning microscope with a scanning force microscope, which allows the spatially resolved measurement of electrostatic forces under local illumination of the nanostructure. On uncontacted hetero-nanosheets, both the potential profile across the heterointerfaces and the redistribution of photogenerated charge carriers will be quantitatively determined with high spatial resolution. Time-resolved measurements will also be developed here to directly follow the charging and discharging dynamics. On electrically contacted nanosheets, additional scanning photocurrent measurements will be combined with the electrostatic atomic force measurements to study the potential profile, especially at the contacts. These experiments will also be performed using focused X-rays from synchrotron radiation sources to significantly increase the spatial resolution of the photocurrent measurements and to combine them with versatile X-ray spectroscopy methods.