Beamline overview

Angle resolved photoelectron spectroscopy (ARPES) is an experimental technique that is widely used to study the occupied electron density of states, and the mapping of valence band structure of solid-state materials. The ARPES beamline (BL-10), which has been commissioned in March 2021, is designed to use the photon energy in the range from 30 eV to 1,000 eV, with a planer undulator as its source. The synchrotron beam is monochromatized using variable line spacing plane grating (VLS-PG) based monochromator. The photoemission experimental station consists of dedicated preparation and analysis chambers. The preparation chamber is equipped with LEED and sample cleaning facilities such as sputtering, annealing (e-beam heating), scraping and cleaving. The analysis chamber is equipped with a 5-axis manipulator, closed cycle refrigerator (CCR), hemispherical electron energy analyser and flood gun. Experiments can be carried out at low temperature down to ~20 K. The beamline is optimised to carryout angle resolved photoelectron spectroscopy measurements, valence band spectroscopy in the angle integrated mode, resonant photoelectron spectroscopy, etc.

The Photograph of Beamline

Beamline parameters & Optical layout

The ARPES beamline (BL-10) uses a plane polarized light emitted by a planar undulator, U2.

Optical layout of the beamline

1. First optical element is a vertically mounted toroidal mirror, M1, which accepts the central cone of ID beam emitted within 1 mrad (H) × 0.4 mrad (V) divergence.
2. The M1 focuses the beam vertically on the entrance slit, and horizontally in front of monochromator.
3. Monochromator is consists of four VLS-PGs (290 l/mm, 770 l/mm, 700 l/mm and 1400 l/mm) and two spherical mirrors(SMs), and is operated in constant included angle mode or Monk-Gillieson configuration.
4. Two SMs provided two different included angles to cover the wide energy range and to reduce the thermal load from undulator on the grating by operating the monochromator in lower and higher energy mode.
5. The last optical element is a horizontally mounted toroidal mirror, M2, which focuses the beam on the sample within the spot size of 300 µm (H) × 100 µm (V).

Experimental station

The experimental station of the beamline comprises of a load lock chamber, a preparation chamber and an analysis chamber. The samples can be transferred between the chambers without breaking vacuum.

The experimental station also has a monochromatized He sources (21.2 eV and 40.8 eV), non-monochromatized twin anode X-ray sources (Al Kα: 1486.5 eV and Mg Kα: 1253.6 eV). Before the commissioning of the beamline in March 2021, these sources were in use for several experiments.

Application Areas

Science Highlights

Fe doping in CoSn found to increase the valence band (VB) width and decreases the Co 2p spin-orbit coupling which indicates the strong hybridization between the Fe and Co valence states.

ARPES studies showed that the magnetic ion doping in the topological insulator Bi₂Se₃ not only opens up the energy gap in surface states but also changes the bulk band structure significantly.

Team members

1. Dr. Tapas Ganguli
2. Dr. Soma Banik
3. Ms. Madhusmita Baral
4. Shri Kiran Baraik
5. Shri Suvankar Paul