Raman Spectroscopy on Metallic Surfaces

金属表面的拉曼光谱

• 批准号: 525620352
• 负责人: Professor Dr. Norbert Esser
• 金额: --
• 依托单位: Standort Berlin
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/525620352?language=en
• 关键词: Raman; Spectroscopy; Metallic; Surfaces

Raman spectroscopy is a widespread analytical technique in solid state physics, materials science and many other disciplines. Up to date, a vast number of studies deals with Raman spectroscopy of optical phonons of nonmetallic compounds, such as semiconductors, insulators and molecules. On the contrary, very few investigations of metals can be found in the literature. In fact, metals such as Cu, Ag and Au crystallize in a primitive lattice with a single atom basis and do not possess optical phonon modes. In contrast to bulk systems, at surfaces, even metals with a single atom basis may exhibit optical phonons, which should generally be accessible by Raman spectroscopy. Moreover, the cross section for surface phonon scattering can be greatly enhanced using light at resonance with an optical transition involving surface electronic states, as shown by the authors in a recent publication. A combined experimental and theoretical approach shall now elucidate the underlying scattering mechanism and the resonant enhancement on different metals and surface orientations. In addition, we aim to extend the investigations to adsorbates on surfaces the backfolding of surface phonon branches via adsorbate-induced superstructures. Metal atom dopants are used to explore the possibility of localizing the optical resonances in surface metal alloys for possible applications in surface catalysis. In contrast to conventional Raman scattering or Surface Enhanced Raman Scattering (SERS), surface Resonant Raman scattering (SRRS) allows the investigation of atomically flat metal surfaces. The resonant enhancement occurs via surface electronic states rather than local fields or plasmons as in SERS. SRRS thus bears new potential for high-resolution vibrational spectroscopy at metal surfaces. The scattering mechanism in SRRS will be studied experimentally in two complementary setups at the Technical University of Berlin (TUB) and at the Johannes Kepler University in Linz, Austria (JKU). Corresponding atomistic calculations in the framework of the density functional theory (DFT) and more refined approaches are performed at the Justus Liebig University in Giessen (JLU). In a recent common investigation, the three applicants could demonstrate for the first time Raman activity at the Cu(110) surface. In the present proposal, the Raman activity of different metallic surfaces as well as the underlying mechanisms will be investigated. The experiments at JKU will focus on the bare and adsorbate covered Cu(110) surface, whereas dependencies on the optical wavelength on other substrates like Ag and Au will be studied at TUB. The JLU will provide an atomistic description of the investigated systems and their lattice dynamics to elucidate system specific scattering mechanisms. The common effort of the three involved groups allows to explore the potential of the newly discovered properties of metallic surfaces in surface analysis or, e.g., applications in the field of catalysis.

拉曼光谱是一种广泛应用于固体物理、材料科学和许多其他学科的分析技术。迄今为止，大量的研究涉及非金属化合物，如半导体、绝缘体和分子的光学声子的拉曼光谱。相反，在文献中很少能找到对金属的研究。事实上，铜、银和金等金属在单原子基的原始晶格中结晶，不具有光学声子模式。与体系统相比，在表面上，即使是单原子基的金属也可能表现出光学声子，这通常应该可以通过拉曼光谱获得。此外，正如作者在最近发表的一篇文章中所示，表面声子散射的横截面可以通过共振光与涉及表面电子态的光学跃迁来大大增强。实验和理论相结合的方法现在将阐明潜在的散射机制和不同金属和表面取向上的共振增强。此外，我们的目标是将研究扩展到表面上的吸附剂，通过吸附剂诱导的超结构使表面声子分支向后折叠。利用金属原子掺杂剂来探索表面金属合金中光学共振的局域化的可能性，以期在表面催化中应用。与传统的拉曼散射或表面增强拉曼散射（SERS）相比，表面共振拉曼散射（SRRS）允许研究原子平面金属表面。共振增强发生在表面电子态，而不是局部场或等离子体。因此，SRRS在金属表面的高分辨率振动光谱方面具有新的潜力。SRRS中的散射机制将在柏林工业大学（TUB）和奥地利林茨约翰内斯开普勒大学（JKU）的两个互补装置中进行实验研究。在密度泛函理论（DFT）框架下的相应原子计算和更精细的方法在吉森的Justus Liebig大学（JLU）进行。在最近的一项共同研究中，三名申请者首次证明了Cu（110）表面的拉曼活性。在本提案中，将研究不同金属表面的拉曼活性及其潜在的机制。JKU的实验将集中在裸露的和被吸附物覆盖的Cu（110）表面，而在ub将研究其他衬底（如Ag和Au）上对光学波长的依赖性。JLU将提供所研究系统及其晶格动力学的原子描述，以阐明系统特定的散射机制。这三个相关小组的共同努力可以探索新发现的金属表面特性在表面分析中的潜力，例如，在催化领域的应用。