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Photo-Emission Electron Microscope Beamline (BL-22)

Photo-Emission Electron Microscope Beamline (BL-22)

Introduction:

The Photo-Emission Electron Microscopy (PEEM) is a non-destructive imaging technique that involves shining linearly or circularly polarised X-rays onto the surface of a sample to provide spectroscopic information on nm scale. This information can be used to study nanostructures significant for sensors, catalysts, magnetic materials and nanoscale devices and phenomena such as nanomagnetism.

Laboratory-based imaging techniques such as STM, AFM and TEM are capable of resolving nanostructures but, (apart from a limited capacity with STM), are unable to provide spectroscopic information. The PEEM can link a structure to its function by providing spectroscopic data on nm scale. The well-defined and variable polarisation state of synchrotron radiation can also provide, via dichroism, a contrast mechanism for imaging different magnetizations in ferromagnetic and antiferromagnetic nanostructures.

The PEEM can be used to study the phenomenon of exchange bias, which has revolutionized the capabilities of magnetic information storage discs, where the underlying physical mechanisms are not well understood. There are also applications in the study of nano-particle catalysis, magnetic domain interactions and the characterization of properties of natural materials, such as chemical composition, local environment and phase identification. The fabrication and modification of novel materials on nm scale is another important area. A schematic diagram of the beamline is shown in Fig.1.


Beamline layout:

schematic layout of the PEEM beamline

Fig. 1. A schematic layout of the PEEM beamline (top view) depicting various optical elements used including, M1-Cylindrical Mirror, M2-Plane mirror, GR-Gratings, DCM-double crystal monochromator , M3-Toroidal mirror, (M4, M5) - K-B pair.

Beamline Specifications:

Source

Bending magnet

Energy Range

10 eV - 8 keV

Pre-Mirror

Cylindrical Collimating mirror M1 (at 18.0 m from the source) with very large radius.

Monochromator

Plane Grating Monochromator (M2 and GR) in low (10 - 2100 eV) energy range and Double Crystal Monochromator made of a pair of Si(111) crystals in (+, -) arrangement at higher energy range (2100 eV – 8000 eV).

Post mirror

Final focusing at the sample will be achieved by using toroidal mirror M3 followed by a pair of Kirkpatrick-Baez (K-B) mirrors M4 & M5.

Spot size @sample position

HFWHM = 0.0273cm,VFWHM = 0.0064cm

Photon flux [ph/s]

~ 1011 ph/sec/0.1% bw

Beam on the target

Focussed

Experimental Station:
The experimental station of the PEEM beamline consists of a photo-emission electron microscope.

Microscope
The microscope will incorporate electron optic system consisting of objective, intermediate, transfer and projection lenses with a high precision sample manipulator. These electrostatic lenses will be operating at high voltages (typically ~20 kV). These will be housed in a UHV compatible chamber. A schematic half plane cross-sectional layout of the PEEM lenses is shown in Fig 2 and enlarged view of the objective and projector lenses are shown in Fig 3.

Detector
The detector for the PEEM beamline will be a slow scan CCD which can provide high spatial resolution images.

Schematic half plane cross-sectional layout of the PEEM lenses.

Fig.2 Schematic half plane cross-sectional layout of the PEEM lenses.

(a)schematic half plane cross-sectional enlarged view of objective (b)schematic half plane cross-sectional enlarged view of projector lenses
Fig.3 A schematic half plane cross-sectional enlarged view of (a) objective and (b) projector lenses.

Present Status:

Presently, the procurement and fabrication of various key components of the beamline are underway.

Contact Number : 244 2522

In-charge:     Shri U. K. Goutam      ukgoutam@rrcat.gov.in

Other contributors:

Dr. S. C. Gadkari

gadkari(at)barc.gov.in

Technical Physics Division
Bhabha Atomic Research Centre,
Mumbai – 400 085.

Shri  M.R. Singh

mrsingh@barc.gov.in

Dr. Jagannath

ssai(at)barc.gov.in

Shri Kaushik Dutta

kdutta(at)barc.gov.in


Last Modification on: July 2016