ARPES

Angle-Resolved Photoemission Spectroscopy (abbreviated as ARPES) is a method for studying the dispersion of electronic bands in crystalline solids. Recent scientific and technical advancements in ARPES techniques, such as the use of synchrotron radiation and spin detectors, have made this method the best tool for investigating the electronic structure of valence bands on crystal surfaces and nanostructures. The characteristic features of this measurement method include:

Short mean free path of photoelectrons: Due to the short mean free path, photoelectrons are emitted only from the nearest surface layers. For He1-alpha radiation with photon energy , emission occurs practically from 2-3 atomic monolayers near the surface. Electrons excited inside the crystal recombine and are not emitted. This property makes the method particularly useful for studying the surface band structure and nanostructures but also requires atomically clean surfaces. A very good vacuum is essential, with pressure in range of .
Incomplete information about the photoelectron's momentum: The emitted electrons retain their parallel momentum component in the crystal, while the perpendicular component may not be conserved.
Role of the final state: The photoemission process involves both the initial and final electronic states (with the final state usually unknown), which complicates the interpretation of the measurement data.
The initial state must be occupied: Only bands below the Fermi energy are studied.
Photoelectron background: Photoelectron spectra from electronic band states are obscured by a background of inelastically scattered photoelectrons.

Data processing

We are currently developing a plugin that enables data processing of ARPES results using the PyARPES Python library. It is available on github.

The components of ARPES aparaturs:

ARPES spectrometer
- UV source - helium lamp (UVS-300 Specs, Germany),
- 5-axis sample manipulator (Specs, Germany),
- hemispherical electron energy analyser with MCP - multichannel plate detector (Phoibos 150 Specs, Germany),
- Mott spin detector (Specs).
RHEED technique
- electron gun (homemade),
- fluorescent screen and CCD camera (12 bits).
Sample preparation
- effusion cells with: Au, Ag, Pb, Bi, Sb,
- Si source (sublimating),
- resistive heating of silicon sample up to 1200 °C,
- e-beam heating up to 800 °C,
- liquid nitrogen and liquid helium cooling down to 130 K and 20 K respectively,
- quartz microbalance,
- Auger electron spectroscopy - AES.