Hoff Felix, Kerres Peter, Veslin Timo, Jalil Abdur Rehman, Schmidt Thomas, Ritarossi Simone, Köttgen Jan, Bothe Lucas, Frank Jonathan, Schön Carl-Friedrich, Xu Yazhi, Kim Dasol, Mertens Julian, Mayer Joachim, Mazzarello Riccardo, Wuttig Matthias
Institute of Physics (IA), RWTH Aachen University, Sommerfeldstraße 14, 52074, Aachen, Germany.
Peter Grünberg Institute - JARA-Institute Energy Efficient Information Technology (PGI-10), Wilhelm-Johnen-Straße, 52428, Jülich, Germany.
Adv Mater. 2025 Feb;37(7):e2416938. doi: 10.1002/adma.202416938. Epub 2024 Dec 30.
A systematic study of the impact of film thickness on the properties of thin Bi films is presented. To this end, epitaxial films of high quality have been grown on a Si (111) substrate with thicknesses ranging from 1.9 to 29.9 nm. Broadband optical spectroscopy reveals a notable decline in the optical dielectric constant and the absorption peak height as the film thickness decreases, alongside a shift of the absorption maximum to higher photon energies. Raman and pump-probe spectroscopy show that the phonon mode frequencies increase upon decreasing film thickness, with the in-plane mode frequency rising by 10% from the thickest to the thinnest sample. The X-ray diffraction analysis reveals an increasing Peierls distortion for thinner films, explaining the observed property changes. Quantum chemical bonding analysis and density functional theory calculations show that the properties of thin bismuth are influenced by the interplay between electron localization and delocalization, characteristic of metavalently bonded solids. This study shows that for solids that utilize metavalent bonding, a thickness reduction leads to significant property changes. The effect can even be employed to tailor material properties without the need to change material stoichiometry.
本文对薄膜厚度对铋薄膜性质的影响进行了系统研究。为此，在硅（111）衬底上生长了高质量的外延薄膜，其厚度范围为1.9至29.9纳米。宽带光学光谱显示，随着薄膜厚度的减小，光学介电常数和吸收峰高度显著下降，同时吸收最大值向更高光子能量方向移动。拉曼光谱和泵浦 - 探测光谱表明，薄膜厚度减小时，声子模式频率增加，面内模式频率从最厚样品到最薄样品上升了10%。X射线衍射分析表明，较薄的薄膜具有越来越大的派尔斯畸变，这解释了观察到的性质变化。量子化学键合分析和密度泛函理论计算表明，铋薄膜的性质受电子定域和离域之间相互作用的影响，这是准金属键合固体的特征。这项研究表明，对于利用准金属键合的固体，厚度减小会导致显著的性质变化。这种效应甚至可用于在不改变材料化学计量比的情况下调整材料性质。
