VakuumARPES

Vakuum-ARPES, often written as VakuumARPES in German contexts, is a form of angle-resolved photoemission spectroscopy conducted under ultrahigh vacuum to study the electronic structure of solids. The technique relies on the photoelectric effect: photons illuminate a material surface and photoelectrons are emitted. By measuring the kinetic energy and emission angle of the electrons, one can determine the binding energy and crystal momentum of the electronic states. Because emission is dominated by the near-surface region, Vakuum-ARPES is highly surface-sensitive and is especially useful for studying surfaces, thin films, and two-dimensional materials.

In a typical setup, the sample sits inside an ultrahigh vacuum chamber to maintain a clean surface. A photon source—such as synchrotron radiation, a laboratory UV lamp, or a femtosecond laser—illuminates the surface. An electron analyzer, often a hemispherical spectrometer, records the kinetic energy and emission angle, yielding energy– and momentum-resolved maps. Photon energy, polarization, and detection geometry allow selective probing of electronic states. Resolutions are high, with energy resolutions in the meV range and angular resolutions sufficient to resolve detailed band dispersions; lower photon energies emphasize surface sensitivity, while higher energies can access more bulk information.

Applications include mapping band structures and Fermi surfaces, measuring superconducting gaps, identifying surface states in topological insulators, and characterizing the electronic structure of graphene, oxide interfaces, and other quantum materials. The technique supports spin-resolved measurements and, in time-resolved variants (tr-ARPES), tracking ultrafast dynamics after optical excitation.

Interpretation relies on the spectral function A(k, ω) and matrix-element effects that modulate photoemission intensity. The technique provides momentum-resolved information within the limits of energy-, angular-, and surface-roughness-related resolution, and its conclusions depend on sample quality and calibration. Vakuum-ARPES remains a central tool in condensed-matter physics for directly visualizing electronic structures.