Metal and transition metal nanostructures are of great interest due to their applicability in various areas such as catalysis, sensing, and optoelectronics. Here we report the formation of palladium (Pd), platinum (Pt), nickel (Ni), and cobalt (Co) nanostructures by galvanic displacement technique. The synthesis method essentially consists of immersing a silicon (Si) substrate in hydrofluoric (HF) acid for 2 min., followed by immersing the substrate in metal or transition metal precursor solution for 5 min. These steps are repeated several times to obtain the desired density of the nanostructures. A series of experiments was performed to monitor the density and morphology of the synthesized nanostructures, and the results were correlated to the number of times the above steps were repeated. Thus, a good control over the nanostructure density was obtained. Further, we investigated the effect of chemical additives, like sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), on the morphology and density of the nanostructures. The characterization of all the above nanostructures was performed by using scanning electron microscope (SEM), energy dispersive x-ray spectrometer (EDS), and ultraviolet-visible spectrometer (UV-Vis).

1. Step-by-step one-cycle deposition (1x)
Deposition of Metal and Transition Metal Nanostructures by Galvanic Displacement
with Limited Hydrofluoric Acid
Minh Tran1 and Sonal Padalkar1,2
1. Department of Mechanical Engineering, 2. Microelectronics Research Center; Iowa State University, Ames, IA 50011
Motivation
• Deposit nanostructures of Pt, Pd, Ni, and Co on Si substrate
• Study morphology and density of metallic nanostructures
with respect to number of deposition cycles
• Study effect of chemical additives on morphology and
density
• Characterize the metallic nanostructures by EDX and UV-
Vis
Objectives
Experimental Details
Morphology and Density
Optical Analysis
Compositional Analysis
Conclusions
Future Directions
Anodic: Si(s) + 6F-(aq) → SiF6
2-(aq) + 4e-
Cathodic: Mn+(aq) + ne- → M(s)
Immerse in
metallic salt
Etch by 10%
(w/w) HF
Cleave 1.5 x
1.5 cm2 n-
type Si (100)
Clean with
acetone, ethanol,
and DI water
Rinse with
DI water
Dry and store
1x 5x4x2x 1x 5x4x3x2x
4x 1x 4x3x2x
500 nm
Si SiO2 Metallic nanostructure M Metal
500 nm 500 nm
1x 1x
5x3x 1x 5x3x
1x 5x3x 1x 5x3x
1x 5x3x 1x 5x3x
500 nm 500 nm
500 nm 500 nm
Metal and transition metal nanostructures with well-
defined morphologies have been successfully deposited
and characterized on Si.
With limited HF, density of metallic nanostructures can be
controlled by the number of deposition cycles
Chemical additives can have different effects, depending
on the metal.
Study the influence of chemical additives on nanostructure
morphology.
Utilize metallic substrates for SERS based sensing.
Utilize transition metal substrates for catalytic and sensing
applications.
Experimental plan
Iowa State University: College of Engineering
Iowa State University Foundation
This method is appealing
Simple and inexpensive.
Self-limiting.
Substrates with any topography can be used.
Galvanic displacement with limited
hydrofluoric acid (HF)
1x 3x 5x
500
nm
Acknowledgements
1x 5x
500
nm
1x 3x 5x 1x 3x 5x
1x 3x 5x 1x 3x 5x
500 nm
500 nm500 nm
500 nm
Note: Ni and Co have negative standard redox
potentials and required additional steps, which
included adjusting pH to 7.5 prior to, and
heating up to 80oC during deposition
Pt:
Spherical particles with
increasing density as the number
of deposition cycles increases
Evolving from spherical to
flower-like particles as the
number of deposition cycles
increases
Ni:
Small particles with increasing
density as the number of
deposition cycles increases
SDS and CTAB hinder particle growth
Co:
Particles from upper layer
elongate as the number of
deposition cycles increases
SDS – hinders particle growth
CTAB: lower density but larger
nanostructures
SDS – decreasing density
CTAB – increasing density, but quasi-
spherical
1x 3x 5x
1x 1x
1x 1x
3x 5x
1x 3x 5x
1x 3x 5x
5x 5x
5x 5x
Flower-like particles for both SDS
and CTAB
Pd:
500 nm
EDX
UV-Vis Analysis
Pt Pd
Ni Co
Normalized UV-Vis spectra of Pt, Pd, Ni, and Co showing
characteristic peaks and increasing absorption toward shorter
wavelengths
Pt Pd
Ni Co
Element Si Ratio
Pt 1738 121278 1.4%
Ni 4385 151900 2.9%
Co 1854 161400 1.1%
Co
Pt
Pd
Ni
Ni
Pt
1x 3x 5x
1x 1x
1x 3x 5x
5x 5x