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Scientific Report 2007-2009
Laboratories and Facilities of the Department of Physics
L4. LOTUS (LOw Temperature Ultraviolet photoelectron
Spectroscopy) Laboratory
The LOTUS laboratory has been established at the Department of Physics
from year 2000, and it is mainly devoted in experimental researches on surfaces
and nano-structures. The group has contributed for many years to the field
with relevant experiments on the electronic state distribution of low-dimensional
systems by state-of-the-art High-Resolution Angular-Resolved Ultraviolet Photoelectron
Spectroscopy (HR-ARUPS). The research is mainly devoted to the
study of the electronic spectral density of states of low dimensional systems and
nanostructures, with particular attention to the low-binding energy region, close
to the Fermi level. We can determine the most relevant band parameters of the
nanostructures grown in-situ (band dispersion, effective mass, metal-insulator
transition...). The ultra-high-vacuum (UHV) apparatus host also Low-Energy
Electron-Diffraction (LEED), Thermal Desorption Spectrsocopy (TDS), Auger
Electron Spectroscopy (AES) to study the long-range ordering, the energetics,
the growth morphology of in-situ grown organic and inorganic architectures
with specific functionalities. Recently, Organic-Molecular Beam Epitaxy (O- Figure 1: HR-ARUPS system, with
MBE) growth of hybid organic-inorganic ordered systems at the nano-scale
has been performed exploiting self-assembling and template-driven aggregation.
Experiments are also carried out by major synchrotron radiation sources,
mainly for absorption (NEXAFS), photoemission (VUV-XPS), and diffraction
two UHV chambers (preparation chamber,
main chamber), also equipped with LEED,
Auger, O-MBE, ion-gun and ancillary facility
for surface preparation.
(GIXD) characterization of the relevant physical systems preliminary studied
in the laboratory. The main apparatus in the LOTUS laboratory (Fig. 1) contains the HR-ARUPS system, equipped with a
Scienta SES-200 electron analyzer, containing a multi-channelplate (MCD) electron detector, with 0.1 ◦ angular and 4 meV
energy resolution. In Fig. 2-a we show the system performances as determined on the 5p 3/2 -Xe core-level in the gas-phase
(a)
(b)
Figure 2: (a) Measurements in the HR-ARUPS apparatus: (left) Xe-5p 3/2 core-level; (right) Cu(119) surface electronic
band structure. (b) LEED, Auger, XPS system in an UHV chamber also containing TDS, O-MBE sources, and ancillary
facility for surface preparation.
(energy resolution) and on the surface band structure of the vicinal crystalline surface Cu(119) (angular resolution). The
photoemission system is equipped with a high-intensity He discharge source, emitting He I and He II main lines, with 21.218
and 40.814 eV photon energies, respectively. Samples can be inserted by an UHV-transfer chamber; the sample manipulator
can be cooled to liquid He temperature and heated to several hundreds of ◦ C. The UHV chamber hosts all ancillary facility
for sample and surface preparation and cleaning (ion-gun, cleaver, etc.), and is also equipped with a LEED-AES system. In
the UHV system there are O-MBE cells for clean, controlled and slow-rate (