resolved photoemission spectroscopy (ARPES) using laboratory source and
synchrotron radiation source:
Photoelectron spectroscopy using laboratory source (XPS and UPS): The photoelectron spectrometer has a four level UHV chamber with mu-metal shielding. In level A, a load lock system is attached for sample transfer and an indigenously fabricated K-cell is mounted for the growth of metal adlayers. Level B consists of ionization gauge and sputter ion gun. In Level C, dual anode x-ray source, hemispherical electron energy analyzer, Helium lamp, low energy electron diffraction (LEED) is mounted (from Specs GmbH, Germany). Level D consists of ionization gauge and quadrupole mass spectrometer. On top DN150 CF flange a 4-axis manipulator with x, y, z and q degrees of freedom is mounted with sample holder (100K to 1200K). The base pressure of 4 x 10-11 mbar has been achieved. Also I have experience with monochromatic Al Ka x-ray source, manipulator with liquid He cooling, omicron and scienta analyzer, etc.
· Photoelectron spectroscopy using Synchrotron radiation: An undulator based beamline (UE 56/2 PGM 1) with photoelectron spectroscopy (PES) endstation using EA125 analyzer (from Omicron GmbH) at BESSY synchrotron radiation source, Berlin, Germany has been used to perform experiments on Al plasmons, Mn/Al and Al/Mn. High-brilliance radiation is produced by insertion device, a planar elliptical double undulator. The undulator comprises of two identical modules separated by a magnetic chicane. The beamline uses a plane grating monochromator and provides photons in the energy range from 89 eV to 1328 eV using two different gratings (400 and 1200 l/mm). We have used high-density line grating (1200) for our measurements as it provides highest spectral resolution. Base pressure of the experimental chamber was about 5×10−11 mbar.
· Low energy electron diffraction (LEED): LEED have been used to study surface crystallinity of different epitaxial metallic adlayers on metal surfaces, single crystals and rare gas implanted Al (111) surface. Also, ferromagnetic shape memory alloys (Ni-Mn-Ga) have been studied by LEED at room temperature (austenitic phase) and low temperature (martensitic phase).
· Coincidence Electron Spectroscopy: These experiments essentially consisted of e--e- pairs emitted upon impact with electrons and photons. Two electrostatic hemispherical analyzers (200mm, Scienta R4000) with spatially resolving detectors (multi-channel plates (MCP) and resistive anodes) were employed to detect electrons and to record angle-integrated energy spectra. In laboratory, we used electron gun (from Kimball Physics Inc.) to accumulate the e2e measurements on Cu (111) surface. The FWHM of the beam at the sample position was approximately 0.3 mm, which has been estimated from the width of the elastic peak. We have also used this system at UE 56/2 PGM-2 beamline in BESSY, Berlin for Auger photoelectron coincidence and double photoemission (γ2e) measurements on Cu (100) surface by using 125 eV photon energy. The analyzers, sample and excitation source were mounted in a UHV (»5×10-11 mbar) chamber. Conventional coincidence timing electronic were used to distinguish correlated particles emitted during a single process (true coincidences) from those that involve the detection of two unrelated particles produced by separate ionization events and fortuitously arrive together at the detectors (random coincidences). True coincidences are always observed within a time interval given by the experimental time resolution and the random coincidences are randomly distributed in time.
· Auger electron Spectroscopy: Cylindrical mirror analyzer (CMA) has been used to characterize the Co/Ni overlayers on Ag (100) surface.
· Positron Annihilation Spectroscopy (in collaboration with Dr. G. Amarendra, IGCAR, INDIA): Using a magnetically guided positron beam, depth resolved Doppler broadening measurements were carried out on as-implanted and thermally annealed samples. Monoenergetic positrons emitted from tungsten moderator in the energy range of 200 eV to 16 keV were implanted. The mean implantation depth of the positron beam is related to the positron beam energy. The implanted positrons rapidly thermalize, diffuse, and finally annihilate with the electrons in the medium giving rise to Doppler broadened energy spectrum. The measurements have been performed by using an HPGe germanium detector having an energy resolution of 1.5 keV at 662 keV g-ray energy.