MANUEL REIVILAR AND JAMILA ELBEGHDADI

1
MODIFICATION AND FUNCTIONALISATION OF GAAS (100)
SURFACES

• MANUEL REI-VILAR AND JAMILA EL-BEGHDADI
• LADIR-CENTRE NATIONAL DE LA RECHERCHE
  SCIENTIFIQUE
• UNIVERSITÉ DE PIERRE ET MARIE CURIE
• THIAIS PARIS (FRANCE)

2
OUTLINE

• Introduction
• Methodology
• Substrates
• Interface chemistry
• Porphyrines
• Perspectives

3
GOALS

• Development of a new type of hybrid sensor
• Nature of the bond between the molecule and the
  semiconductor surface
• Adsorb porphyrines as the sensoring molecules of
  NO
• How the electric potential changes due to the
  interaction of NO with the porphyrines layer
• How the electric potential change affects the
  charge transport in the semiconductor.

4
OUR TASKS

• Controling surface states of GaAs (100)
• To identify chemical specimens hindering the
  chemisorption
• To treat the substrate before the reaction
• Interface stoichiometry
• Adsorption of new molecular specimens
• Grafting functions
• Porphyrines

5
METHODOLOGY

• Surface vibrational spectroscopy
• Infrared spectroscopy in attenuated total
  reflection and multiple internal reflection
  (ATR-MIR).
• High resolution electron energy loss spectroscopy
  (HREELS).

6
ATR-MIR
 l evanescent wave characteristic length q
incidence angle l - wavelength n1- ATR crystal
index of refraction n2- solution index of
refraction n21 n2/n1
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HREELS
IMPACT MECHANISM
DIPOLE MECHANISM
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SUBSTRATES

• GaAs(100) are very reactive towards the
  environment and therefore chemically unstable!
• Different chemical specimens can be identified
  covering GaAs surfaces and most particularly
• Oxides
• Hydroxyl groups
• Bound water
• Carbonates
• Aliphatic hydrocarbons.

9
Degreasing methods
Trichloroethylene, acetone and ethanol under
ultrasounds constitute a common treatment to
degrease GaAs Surfaces.
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Surface oxides
Gallium and Arsenic can present different valence
states. The presence and the composition of
different GaAs oxides could be identified by XPS.

• Ga2O3
• Ga2O
• GaO4
• GaO6
• Ga (OH)3

• As2O3
• AsO3
• AsO6
• As2O5

• See for instance ( and references herein)
• C.C. Surdu-Bob, S.O. Saied, J.L. Sullivan,
  Applied Surface Science, 183 (2001) 126.
• H.C. Liu, S.H. Tsai, J.W. Hsu, H.C. Shih,
  Material Chemistry and Physics, 61 (1999) 117-213.

11
Oxide layers
ATR
a anodic oxidation b chemical
oxidation Lenczyckiet al. TSF,193/194 (1990) 610
12
Wet-etching methods

• Semiconductor surfaces are spontaneously oxided.
  The native oxide layer can be removed by
  different wet-etching treatments are used with
  gauss surfaces after degreasing
• H2SO4H2O2H2O (81100)
• Br2-Methanol (0.05) followed by KOH
• NH4OHH2O (19)
• HFH2O (40)

13
Wet-etched surfaces

• HREELS spectra of
• GaAs (100) surfaces
• as received
• NH4OH treatment
• HF treatment.

14
HF treatment
Surface phonons of GaAs can be observed. HF
etching reduces drastically the oxide in GaAs
surfaces. Some aliphatic contamination is still
present. See for instance L.H. Dubois and G.P.
Schwartz, Journal of Electron Spectroscopy and
Related Phenomena, 29 (1983) 175.
15
Light Effect
GaAs (100) was purged and then exposed to the
light. The oxidation is strongly accelerated
when the surface was exposed to the light.
D. Gräft, M. Grundner, D. Lüdecke and R. Schultz,
J. Vac. Sci.Technol. A8 (1990) 1955.
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INTERFACE CHEMISTRY

• Functions to test
• Carboxylic acids
• Thiols
• Amines
• Amides
• Phosphonates

17
Benzoic acid/ GaAs (100)

• For both etching treatments
• Chemisorotion takes place
• Benzoate formation
• Coordination complex with Ga1
• Different hydrophilicity.

1 S. Bastide, D. Cahen et al. J. Phys. Cehm. 101
1997 2678.
18
Chemisorption
The difference between u(C-O) and u(CO)
determines the type of the complex formed during
adhesion. In our case, the value of 124 cm-1 is
correlated with a bridging complex.
19
Carboxylic Complexes

• K. Nakamoto, Infraredband Raman Spectra .
• J. E. Tackett, Appl. Spectr. 43 (1989) 483.
• A. Gericke and H. Hubnerfuss, Thin Solid Films
  245 (1994) 74.
• G. Ohe et al. J. Phys. Chem. B 103 (1999) 435.

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PORPHYRINES
\b(\c6(Chloro(protoporphyrinato)ion(III)Ferriproto
porphyrin))
(5,10,15,20-Tetrakis-(4-carboxyphenyl)-21,23H-porp
hyrin COOH)
21
Hemin infrared spectrum
22
Hemin
(Chloro(protoporphyrinato)ion(III)Ferriprotoporphy
rin
HREELS spectra of Hemin on Gaas reveal that the
pyrrolic cycles are preferentially oriented
perpendicular to the substrate.
G. Melki, Biochimie 1971, 53, 875-885.
23
T(pCOOH)
HREELS spectra of T(pCOOH) on Gaas reveal that
the pyrrolic cycles are preferentially oriented
parallel to the substrate.
 
 
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PERSPECTIVES

• Other substrates
• Other molecules
• Other porphyrines