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Scientific Report 2007-2009
Laboratories and Facilities of the Department of Physics
L12. High Pressure Spectroscopy Lab
The research activity carried out at the High Pressure Spectroscopy
Lab in the last ten years was mainly focused on the
study of strongly correlated electron systems such as functional
oxides for the electronic (manganites, multiferroics materials,
spinels,...), charge density wave low dimensional materials (diand
tri-tellurides), and high T C superconductors (e.g. Mgb 2 and
oxypicnitedes). By combining the in house optical spectroscopy
and the structural characterization (neutron and x-ray diffraction)
carried out at the largest European large scale facilities a
rather comprehensive experimental approach to these complex
materials is obtained. Standard ancillary equipments allow to
perform Raman and Infrared measurements over a wide temperature
range (5-500 K by a Oxford cryostat) and the diamond anvil
cell (DAC) technique is employed to compress the samples under
equilibrium conditions up to very high pressure (40-50 GPa).
Applying pressure help in disentangling the effects of the different
interactions simultaneously at work in correlated materials
and can cause interesting structural and magneto-electric transitions.
In particular, spectacular insulator-to-metal transitions
associated to conductivity jump of several order of magnitude
The micro-Raman LabRAM Infinity spec-
Figure 1:
trometer.
can be induced. Owing to the diamond transparency to the electromagnetic radiation over a wide frequency range, DACs
allow to study condensed matter with several spectroscopic techniques, such as optical spectroscopy, x-ray diffraction and
spectroscopy. The HPS laboratory is equipped with a micro-Raman LabRAM Infinity spectrometer and a Bruker IFS66v
Interferometer for infrared measurements. High pressure optical measurements are carried out in house and experiments
are routinely performed by using also infrared and x-ray from synchrotron sources (mainly at ELETTRA and ESRF).
The LabRAM spectrometer is a high-performance Raman microscope-spectrometer suitable
for solid and fluid samples. The LabRAM is equipped with an He-Ne laser (632.81 nm), a
notch filter and two diffraction gratings (1800 line/mm and 600 line/mm). The LabRAM
incorporates state-of-the-art CCD detection and high efficiency optical construction to provide
fast and reproducible analysis. The LABRam spectrometer works in backscattering geometry,
using a notch filter to reject the elastic contribution. The confocal microscope is equipped
with several high quality objectives with different working distances (from less then 1mm to
very long working distance larger then 20 mm) and magnifications (from 10x to 100x). These
allow to collect Raman spectra from very small portion of the sample: the laser spot on the
sample is on the micron scale and the thickness of the scattering volume along the optical axes
can be reduced to tens of microns or less exploiting the confocality. The very long working
distance allows to collect measurements on the micron scale also on samples pressurized by
Figure 2: Details of the
DAC. A multiline air-cooled 100 mW Ar laser from Melles Griot coupled with an optical fiber
LabRAM spectrometer.
system is also available for Raman measurements. This source can be used also on a second
optical table where the availability of a new Peltier-cooled CCD (Symphony from Horiba),
a Triax Monochromator (Jobin-Yvon), and a remote optical head equipped with interferential and notch filters and high
magnification objective allow for a second conventional Raman setup.
The Bruker IFS66v Fourier Transform Infrared system allows measurements in over
wide frequency range, from the far- to the near-infrared. The instrument can work in
vacuum, with the advantage to avoid the strong absorption components due to water
vapour. It is equipped vith different lamps (globar and Hg), beam-splitters (KBr and
mylar), and detectors. The maximum resolution of the instrument is 0.1 cm −1 . Within
the large sample compartment a focusing optical system (Cassegrain objectives) can
be easily allocated.
Several DACs (commercial from BETSA and DIACELL and home made for specific
application) with different characteristic are available. Simple, efficient and portable
gas-pressurizing systems can be used for the membrane DACs. Sample loading can
be carried out at our laboratory for sample preparation. It is basically equipped with
stereoscopic high-magnification optical microscopes, tools and machinery for handling
very small samples, a micro spark-eroder for preparing gaskets for the DACs.
We finally notice that the availability of a Raman micro-spectrometer in our Lab
Figure 3: IFS66v Interferometer
allowed us to successfully carry out studies in the field of cultural heritage. Collecting Raman spectra from very small
specimen allows us to study stratigraphic layers of polished cross-sections of paintings.
http://www.phys.uniroma1.it/gr/HPS/HPS.htm
Related research activities: C35, C36.
Sapienza Università di Roma 185 Dipartimento di Fisica