Angle Resolved Photoelectron Spectroscopy

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.

Photograph of the Beamline
The Photograph of Beamline

Beamline parameters & Optical layout

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

Planar undulator parameters
Energy Range30 eV to 1000 eV
Periodic Length85.2 mm
Peak Magnetic Field0.86 Tesla
K values6.83 to 1.6
Number of Periods24

Beamline Parameters
Energy Range30 eV – 1000 eV
Resolution35 meV at 90 eV photon energy
Flux (calculated)5×1011 photons/sec/200 mA
Beam Size300 µm (H) × 100 µm (V) approximately
MonochromatorFour VLS –Plane Gratings

Optical layout of the beamline
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.

Experimental station
Analysis chamber
Material of constructionMu metal
Base vacuum7x10-11 mbar
Electron analyserPhoibos 150 HSA
Energy resolution: 2 meV
Angular resolution: 0.1°
Flood gunUpto 10 eV for insulating samples
Sample manipulator5 axis with sample cooling with CCR down to 20 K

Preparation chamber
Base pressure of preparation chamber5x10-11 mbar
In-situ sample preparationAr ion sputtering
Sample heatingUpto 800 K
LEED systemPresent

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

Surface Science Separate bulk and surface sensitive information by tuning the photon energies.
ChemistrySurface composition, surface modification by in-situ sputtering and annealing.
Phase transitionTemperature dependent measurements to determine the electronic structure across the crystallographic or magnetic phase transitions.
Applied researchAnalysis and expertise of various applied problems in surface science.
Basic researchDetermination of density of states, band structure and Fermi surface mapping of novel materials.

1. Influence of Fe doping on the electronic structure of Kagome semimetal CoSn.
Kritika Vijay, Archna Sagdeo, Pragya Tiwari, Mukul Gupta and Soma Banik.
Manuscript submitted to DAE-Solid State Physics Symposium 2021
2. Effect of Mn doping in Bi2Se3 topological insulator: probed by DFT and ARPES.
R. Kumar, Soma Banik, Shashwati Sen, A.K. Yadavand D. Bhattacharyya,
Manuscript submitted to DAE-Solid State Physics Symposium 2021

Science Highlights

Influence of Fe doping on the electronic structure of Kagome semimetal CoSn.
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.

Effect of Mn doping in Bi2Se3 topological insulator: probed by DFT and ARPES.
Science Highlights

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
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