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