Preparation and characterization of
electrodeposited gold SERS substrates
Pierre Brodard, J. Elias, L. Philippe and J. Michler
ICES 2012 | Porquerolles | 04.10.2012
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Gold flails on transparent conductive oxide
SYNTHESIS
substrate: glass/SnO2:F
bath: KAu(CN)2, pH 7.3, 55°C
gelatin: 2 wt%
3-electrodes
electrochemical cell:
working electrode: TCO
counter electrode: Pt spiral wire
reference electrode: Ag/AgCl
• electrodeposition performed at constant potential: - 0.8 V
• deposition time varied: 2.5 - 50 min
SEM images
(20 min. deposition)
J. Elias, P. Brodard, M. G. C. Vernooij, J. Michler, L. Philippe, Electrochim. Acta 2011 (56) 1485.
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Gold flails on transparent conductive oxide
CHARACTERIZATION
XRD
111
=> preferential orientation
(perpendicular to {111} planes)
=> no other phases or impurities
EDX
=> only Au (structures dispersed on Cu grid)
J. Elias, P. Brodard, M. G. C. Vernooij, J. Michler, L. Philippe, Electrochim. Acta 2011 (56) 1485.
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Gold flails on transparent conductive oxide
CHARACTERIZATION
secondary e- image
EBSD
FIB-cut flail
1. many Au nuclei formed instantaneously: Au(CN)2− + e− → Au + 2CN−
=> gold nanoelectrodes
2. gelatin+ adsorb onto gold surface
=> slow growth rate
3. face-selective adsorption of gelatin
=> {111} facets
J. Elias, P. Brodard, M. G. C. Vernooij, J. Michler, L. Philippe, Electrochim. Acta 2011 (56) 1485.
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Gold flails on transparent conductive oxide
RESULTS
SEM images
J. Elias, P. Brodard, M. G. C. Vernooij, J. Michler, L. Philippe, Electrochim. Acta 2011 (56) 1485.
5
Gold flails on transparent conductive oxide
SERS
• p-mercaptoaniline (pMA = 4-aminobenzenethiol)
• monolayer (100 mM pMA, 3 h, rinsing EtOH)
632.8 nm, 1-2 mW, laser spot ∼1mm, 30 s
cluster of flails  massive SERS
single flail  no SERS
J. Elias, P. Brodard, M. G. C. Vernooij, J. Michler, L. Philippe, Electrochim. Acta 2011 (56) 1485.
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Gold flails on transparent conductive oxide
SERS
SERS effect increases with number of flails !
(tested with pMA and BCB, plateau from about 5 flails, not shown)
SERS intensity (a.u.)
4000
3000
2000
1000
0
0
1
2
3
4
5
# of balls
 SERS effect localized in hot-spots (= contact points)
J. Elias, P. Brodard, M. G. C. Vernooij, J. Michler, L. Philippe, Electrochim. Acta 2011 (56) 1485.
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Gold flails on transparent conductive oxide
SERS
1 600
)
If SERS = contact points, why SERS decreases with size of flails ?
 spikes = NANOSPACERS
J. Elias, P. Brodard, M. G. C. Vernooij, J. Michler, L. Philippe, Electrochim. Acta 2011 (56) 1485.
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Gold thin films with different morphologies
SYNTHESIS
substrate: glass/SnO2:F
bath: KAu(CN)2 + KH2PO4, 55°C
3-electrodes
electrochemical cell:
working electrode: TCO
counter electrode: Pt spiral wire
reference electrode: Ag/AgCl
• electrodeposition performed in potential range: - 0.7 V to -1.2 V
• stirred at 300 rpm during electrodeposition
-0.7 V
-0.8 V
-0.9 V
-1.0 V
-1.1 V
-1.2 V
=> flakes
J. Elias, M. Gisowska, P. Brodard, R. Widmer, Y. de Hazan, T. Graule, J. Michler, L. Philippe, Nanotechnology 2012 (23) 255705.
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Gold thin films with different morphologies
MECHANISM
= inhibition of growth
time evolution:
• direct charge
transfer reaction
• hydrogen
evolution reaction
J. Elias, M. Gisowska, P. Brodard, R. Widmer, Y. de Hazan, T. Graule, J. Michler, L. Philippe, Nanotechnology 2012 (23) 255705.
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Gold thin films with different morphologies
RESULTS
AFM
RMS: roughness
-0.7 V
-0.8 V
-0.9 V
-1.0 V
-1.1 V
-1.2 V
J. Elias, M. Gisowska, P. Brodard, R. Widmer, Y. de Hazan, T. Graule, J. Michler, L. Philippe, Nanotechnology 2012 (23) 255705.
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Gold thin films with different morphologies
SERS
• Brilliant Cresyl Blue (BCB = C17H20N3OCl ∙ ½ ZnCl2)
• drop-coated (10-7 M BCB in EtOH)
632.8 nm, 0.25-0.50 mW, laser spot ∼1mm, 0.1 s
J. Elias, M. Gisowska, P. Brodard, R. Widmer, Y. de Hazan, T. Graule, J. Michler, L. Philippe, Nanotechnology 2012 (23) 255705.
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Gold thin films with different morphologies
SERS
evolution of SERS effect: competition between
- generation of hot-spots (roughness)
- size of nanostructures (voltage)
J. Elias, M. Gisowska, P. Brodard, R. Widmer, Y. de Hazan, T. Graule, J. Michler, L. Philippe, Nanotechnology 2012 (23) 255705.
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Conclusion
 SERS in contact points
 no SERS on single spikes
 gap size control by spike size
 SERS proportional to roughness
 SERS inversely proportional to flakes size
 optimum in SERS effect for one surface
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