Electron spectroscopy and microscopy

„Microscopic understanding“ of a phenomenon is a syno-
nym for the ability to describe it by first principles....

Electron spectroscopy and microscopy

Research topics

„Microscopic understanding“ of a phenomenon is a synonym for the ability to describe it by first principles. The notion mirrors the outstanding importance of truly microscopic techniques for the investigation of matter. Here we use electron microscopy in various forms to study novel materials and combine it with laterally resolved and integrated spectroscopy. The range of problems that can be addressed comprises e.g. the investigation of the microstructure of solids, their chemical in homogeneities, the characterization (and even manipulation) of nano-objects, down to the direct observation of the atomic arrangement of a material. These information are naturally complemented by electronic structure investigations for which electron spectroscopy is the leading tool. We focus on photoemission and inelastic electron scattering using state-of-the art laboratory equipment. 

Organic semiconductor interfaces

The fundamental properties and the application of organic materials in electronic devices is an issue of intensive research. Potential devices are anticipated to enable flexible, low cost electronics. The importance of interfaces for the device performance cannot be overestimated as they determine charge injection and charge flow in the devices. Here, we investigate particular organic semiconductor interfaces in order to develop a general understanding for those. Recently, we have discovered an organic heterojunction, which is characterized by charge- and spin-transfer between the constituents. Related publication

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Transition metal dichalcogenides

The material class of transition metal dichalcogenides (TMD) comprises a number of fascinating physical phenomena. For instance, various competing ground states – such as superconductivity and charge density waves – can be found in some of its representatives. Moreover, these materials have a two-dimensional crystal structure with weak bonding along the crystal c axis, which is reminiscent of graphene. In this regard, TMD materials are also considered to be representatives for future electronics beyond graphene. We investigate the electronic properties, in particular the dynamic response, which e.g. reveals intriguing dispersion relations for plasmons and excitons in some of these materials.  Related publication

Oxide heterostructures and interfaces

Fascinating and counterintuitive phenomena have beenobserved at the interface of certain complex oxides. The mostimportant is the appearance of metallic conductivity betweentwo firm insulators such as SrTiO3 and LaAlO3 reported by Ohtomo and Hwang in 2004. But also superconductivity and magnetism have been found. We investigate the electronic and chemical structure of these new interfaces which hold prospects for both, fruitful fundamental research and the implementation into devices.  Related publication

Heavy fermion materials

The properties of heavy fermion materials sharply deviatefrom conventional metals, most notably in the occurrenceof very large effective masses at low temperatures. Thisis often accompanied by rich phase diagrams consisting ofmagnetic order and unconventional superconductivity. The electronic structure is determined by a subtle interplay between f-electrons and conduction electrons which can be analyzed by means of electron spectroscopy. Related publication

In-situ transport and field mapping at the nanometer scale

Many solid state phenomena in modern materials are not understood at the microscopic scale. For example, topological effects like Skyrmions have been observed as a lattice-like assembly of structures that are predicted to be spin vortices, the inner structure of these objects is still unknown. Another example is the structural response of new electronic materials and nanostructured devices under working conditions. To this end, new in-situ transmission electron microscopy and holography techniques are developed and applied. Related publication

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