Luca Gregoratti

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Recent achievements in characterization of micro
and nanomaterials by scanning photoemission
imaging and spectromicroscopy
Luca Gregoratti
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Schematic view of a synchrotron light facility
Beamlines
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Synchrotron radiation spectral bandwidth
From infrared (0.1 eV) to hard X-rays (100 000
eV)

• Synchrotron light provides
• High brightness
• Tunability
• Polarization
• Time structure

Photons energy (eV) Radiation Processus
lt 0,1 Infrared Molecular Vibrations
lt 1,8 Visible Molecular Excitation
lt 3-6 Ultraviolet Molecular Excitation
gt 100 X-rays (soft to hard) X-ray Absorption Fluorescence Photoemission
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List of Operational Beamlines by Technique
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The Microscopy Section at Elettra
Elettra Synchrotron Light Source laboratory

• ESCAmicroscopy 400-950 eV XPS spectro-microscopy
• SPECTROmicroscopy 20-90 eV XPS, ARUPS
  spectro-microscopy
• NANOspectroscopy LEEM, X-PEEM spectro-microscopy
• TwinMic x-ray transmission and absorption
  spectro-microscopy
• IR infrared spectro-microscopy

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Quantitative analysis
Fine Chemical analysis
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X-ray microscopy method characteristics
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Imaging and spectroscopy from metal adsorbate on
MWCNT array with SPEM (in collaboration with
theory_at_elettra)
In3d5/2
Characterization of MWCNT surface analysis of
C1s photoemission in comparison with clean and
defective HOPG surfaces
CVD forests from Nanolab Inc.
SPEM imaging of temperature evolution of In
deposits on the surface of MWCNT array
A. Barinov et al. PRL submitted (2007)
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Imaging and spectroscopy from single MWCNT with
SPEM
High density
Low density
CVD low density forests from Nanolab Inc.
CVD high density forests from Nanolab Inc.
CNT
SPEM image
SPEM image
20 mm
X-ray beam spot FWHM 200nm
Research Topics
Diameter of each nanotube 90nm ? next 60nm!

• Oxidation of the NT under atomic plasma oxygen
• Ag, Au, Pd adsorbate interaction
• PLD deposition of catalytic nanocluster and
  reaction (PhD project)

10 mm
Need for the APSPEM, higher photon energies
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Mo-S based nanotubes chemical characterization (in
collaboration with J. Kovac JSI)
With SPEM we solved their chemical composition
MoS2-xIy
SEM
SPEM

• Results
• The Mo-S nanotubes contain also I, chemically
  bonded
• S2p reflect inner and outer position of S in
  strongly bent S-Mo-S sheets bonding of outer S
  to I at interstitial position.
• VB spectra show finite DOS at EF, metallic
  behaviour

J. Kovac, A. Zalar, M. Remskar et al, Josef
Stefan Inst., Lubljana-Slovenia
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Compositional and electronic study of TCO nano
and microtubes by Photoelectron Microscopy (in
collaboration with A. Cremades UCM)

• Catalyst free growth of TCO structures
  (SnxOy/InxOy/InxNy,GexOy,etc.)
• D. Alina Magdas et al. APL 88,
  113107 (2006)
• SPEM characterization of morphological complex
  structures difficult with other PEM

Electronic behaviour of a single structure

• Charging due to differences in the electronic
  structure
• Mapping of the charging with the multichannel
  acquisition

SPEM images
DE3eV
Local chemical composition of the structures

• Heterogeneous elemental distribution locally
  defined
• Fine chemical analysis

10 mm
30 mm
Need for higher photon energies
A. Cremades et al. Journal of Nanoscience and
Nanotechnology, submitted
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Degradation of light emitting diodes a SPEM
analysis (in collaboration with P. Melpignano
CRP, R. Zamboni CNR-ISMN)
Clean experiment OLED growth and operated in
the SPEM (UHV ambient) failure due to light
emission
OLED exposed to atmospheric moisture failure due
to light emission
64 mm

• Decomposition
• of ITO

64 mm
In
Al
Dark spot in OLED
Al2p
Al
In
increasing voltage and operating time
P. Melpignano et al. Appl. Phys. Lett. 86, 041105
(2005), S. Gardonio et al.
Org. Electr. 8 (1), 37-43, (2007)
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Photoelectron microscopy study of operating
LSM-YSZ cathode surfaces of SOFC (in
collaboration with M. Backhaus Corning Inc.)
Elemental distribution at electrolyte/LSM
interface
Surface composition change with bias
Strongly constraining experimental setup

• Real samples
• High T 650-700C
• pO21x10-6 mbar
• Applied potentials -2VltUlt2V
• Surface sensitive technique
• High lateral resolution

Need for the APSPEM, Higher photon energies
Observation and explanation of electrochemical
cathode activation

• Strong current increase under negative bias when
  Mn spreads on electrolyte
• Mn2 electrolyte surface enrichment?electrolyte
  surface conductivity ? direct oxygen
  incorporation into electrolyte
• Oxygen incorporation extends under bias from TPB
  to the entire electrolyte surface

M. Backhaus et al. ACERS 2007 Proceedings
submitted
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Material gap from model crystalline materials
to metal nano-particles on metal oxide. In situ
PLD particle deposition
Rh on MgO/W(110) PLD species are highly-defected
due to non-thermic evaporation
Oxidation/reduction reactions
Nanoparticles
lt1 ML
2 ?m
AFM
gt1 ML
SPEM Rh3d maps
Microparticle
SEM
64 mm
2 mm

• The nanoparticles/nanofilm possess different
  oxidation/reduction ability than the
  microparticle
• Reducing rate Micro-part.gt Nano-crystalline film
  gt Nano-particles
• Micro-particles of similar sizes show variation
  in the reactive properties different structure,
  local environ.

P. Dudin et al. in preparation
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Mg epitaxial growth
Oxidation of Mg film
Growth is followed in-situ by LEEM
Ef DOS and Iox/Itot for quantification of the
oxide
Oxygen dose
Mg/W(110) dep. 405 K, 0.1ML/min 11.1eV, 5 mm
Film thickness is measured by quantum
interference contrast
Bulk/surface Mg
Oxide Mg
4 - 7 ML Mg/W(110) 0.1-10.1eV/0.2eV, 5 mm
O2exposure
L. Aballe et al, Phys. Rev. Lett. 93, 196103
(2004)
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Oxidation of Mg film chemical nano-mapping
LEEM reveals morphology atomic thickness
? DOSE OXYGEN ?
oxidation rate depends on thickness!!
L. Aballe et al, Phys. Rev. Lett. 93, 196103
(2004)
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Oxidation of Mg film

• strong variations in the oxidation extent as a
  function of film thickness
• The density of bulk states at EF correlated to
  oxidation extent
• activation barrier depends on thickness easier
  charge transfer to O2 1pg ? dissociative
  adsorption more efficient
• Control on film thickness enables modifying the
  molecule surface interaction

DOS at EF
oxidation extent
L. Aballe et al, Phys. Rev. Lett. 93, 196103
(2004)
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Fluorescence spectromicroscopy

• Extremely high lateral resolution (better than 50
  nm)
• Bulk sensitivity
• Bio- nanosystems, environmental systems

Cr
Ti
Fe
Cr
Fe
2 mm
P. Barbieri et al., Dept. of Chem., Univ.
Trieste, I
h?