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High Resolution Microscopical Analysis of Metallurgical Grade Nanoporous
Silicon Particles
E.G. Chadwick 1,2* , D.A. Tanner 1,2 , S. Beloshapkin 1 , H. Zhang 3 , G. Behan 3
1 Materials & Surface Science Institute, University of Limerick, Ireland
2 Department of Design and Manufacturing Technology, University of Limerick, Ireland
3 School of Physics and CRANN, Trinity College, Dublin, Ireland
Abstract
Porous silicon finds numerous applications in the areas
of bio-technology, drug delivery & energetic materials.
This work studies the structural morphology of
chemically etched porous silicon particles using high
resolution electron microscopy techniques combined
with porisometry type measurements. The surface pore
structure is examined in detail using Scanning Electron
Microscopy and Transmission Electron Microscopy
while the internal pore structure is explored using
Focused Ion Beam milling and Ultramicrotomed crosssections.
1. Introduction
Porous Silicon (PS) is a sponge like structure that is
formed when bulk Silicon (Si) is etched either
chemically or electrochemically in hydrofluoric acid
based solutions [1-4]. Since Canham made the
discovery of its room temperature photoluminescence
[1-3], subsequent research followed focusing on
developing possible PS applications in such areas as
microelectronics, chemical and biological sensors [4].
Mesoporous and nanoporous Si is also currently being
investigated for drug delivery, bioactive and energetic
materials applications [5, 6, 7]. The possible
applications of PS would now seem abundant and
therefore microscopical analysis of the material is
critical to aiding in the development of new PS
applications. Vesta Sciences have recently developed
PS nanosponge particles from metallurgical grade Si
through their own patented chemical etching process
(Irish patent no. IE20060360). The work presented here,
studies the structural morphology of these PS
nanosponge particles using high resolution microscopy
techniques to fully characterise the material. The related
surface pore structure is examined in detail and the
internal pore structure is explored using a combination
of sample-prep methods and FIB milling, SEM, TEM &
Helium Ion Microscopy.
2. Results/Discussion
The results of the etched material indicate a
disordered pore structure with pore diameters ranging
from 10-15nm on particles ranging from 4-6µm. When
particles were viewed in the [100] and [111]
crystallographic directions, the pore size appeared to be
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the same for both directions but are however, larger on
thinner Si structures. Internal pore data indicated pore
depths of up to 500nm on some particles with smaller Si
particles appearing more porous internally compared to
the larger Si particles. All microscopy results were
compared with porisometry type measurements.
Figure 1 SEM image of a Porous Silicon
particle
3. References
[1] Canham, L.T., Silicon quantum wire array fabrication by
electrochemical and chemical dissolution of wafers. Applied
physics lett, 1990. 57: p. 1046.
[2] R. Guerrero-Lemus, F. A. Ben-Hander, J. L. G. Fierro, C.
Hernández-Rodríguez, and A.J.M. Martínez-Duart,
Compositional and photoluminescent properties of anodically
and stain etched porous silicon. phys. stat. sol. (a), 2003. 197:
p. 137-143.
[3] Parkhutik, V., Analysis of Publications on Porous Silicon:
From Photoluminescence to Biology. Journal of Porous
Materials, 2000. 7(1): p. 363-366.
[4] Anglin, E.J., Porous silicon in drug delivery devices and
materials. Advanced Drug Delivery Reviews, 2008. 60(11): p.
1266-1277.
[5] Becker, C.C., Luke, Churaman, Wayne, Characterization
and Improvements to Porous Silicon Processing for
Nanoenergetics. Storming Media-Pentagon Reports, 2008. p.
20.
[6] Plessis, M.d., Integrated Nanoporous Silicon Nanoexplosive
Devices. IEEE, 2007. p. 1574-1579.
[7] Chadwick, E., O. Clarkin, and D. Tanner, Hydroxyapatite
formation on metallurgical grade nanoporous silicon particles.
Journal of Materials Science. 2010. 45(23): p. 6562-6568.