* * * * *
The measurement and control of humidity is an important issue: water molecules
are easily adsorbed on almost any surface, where are present as mono-or
multimolecular layers of molecules. The determination of humidity is thus
imperative for improving the quality of life and enhancing industrial
processes.
Commercial sensors are mostly based on metal oxides, such as Al2O3 and
TiO2. Beyond these materials, advanced ones proposed for humidity sensing
devices have been porous silicon and polymers. The investigation focuses
on the improvement of requirements such as: short response time, high
sensitivity, negligible hysteresis, resistance against contaminants, good
long-term reproducibility and possibly a wide operating range for both
humidity and temperature. These requirements are not all always concurrently
met since they are related to competing physical and chemical processes.
Low cost, easiness of manufacture and small-sized sensors are also required;
so it has become mandatory to identify new materials fulfilling all these
characteristics.
Nanostructured materials [1] may offer new opportunities in this context.
Recently, nanostructured carbon films obtained by Supersonic Cluster Beam
Deposition [2] have been characterized as base material for both gas and
humidity sensors both in resistive and capacitive configuration [3, 4,
5]. At the same time, the investigation of the electrical properties of
Single Walled Carbon Nanotubes (SWNTs) obtained by an all–laser
growth process [6], starting from the deposition of catalyst particles
to the growth of nanotubes, in gas or moisture environments is the aim
of the research program I will perform in the frame of my post doctoral
stage.
Acknowledgments:
We are grateful to Fondazione “Angelo Della Riccia” (http://arturo.fi.infn.it/casalbuoni/dellariccia/)
for partial funding of this project. We also acknowledge NSERC of Canada,
FQRNT (Quebec) and the Canada Research Chairs program.
STM image (180×180 nm2) showing
a straight nanotube that crosses many HOPG planes. Tunneling parameters
are It = 1 nA, Vt = 0.1 V. The inset shows an atomically resolved STM
image (2.5×2.5 nm2) of a surface area of the tube [7].
[1] F. Rosei, Nanostructured surfaces: challenges
and frontiers in nanotechnology, J. Phys. Condens. Matter, 16,
(2004), S1373-S1436.
[2] P. Milani, S. Iannotta, Cluster Beam Synthesis of Nanostructured Materials,
Springer Verlag, Berlin, 1999.
[3] M .Bruzzi, P. Piseri, S. Miglio, G. Bongiorno, E. Barborini, C. Ducati,
J. Robertson , P. Milani, Electrical conduction in nanostructured carbon
and carbon-metal films grown by supersonic cluster beam deposition, Eur.
Phys. J. B, 36 (2003) 3-13.
[4] M. Bruzzi, S. Miglio, M. Scaringella, G. Bongiorno, P. Piseri, A.
Podestà , P. Milani, First study of humidity sensors based on nanostructured
carbon films produced by supersonic cluster beam deposition, Sens.
Actuators, B, Chem. 100 (2004) 173- 176.
[5] S. Miglio, M. Bruzzi, M. Scaringella, D. Menichelli, E. Leandri, A.
Baldi, G. Bongiorno, P. Piseri, P. Milani, Development of humidity sensors
based on nanostructured carbon films, in press on Sens. Actuators,
B, Chem.
[6] M. A. El Khakani and J. H. Yi, The nanostructure and electrical properties
of SWNT bundle networks grown by an ‘all-laser’ process for
nanoelectronic device application, Nanotechnology 15,
(2004), S534-S539.
[7] P. Castrucci, M. Scarselli, M. De Crescenzi, M.A. El Khakani, F. Rosei,
N. Braidy, J.H. Yi, Appl. Phys. Lett. 85, (2004),
3857-3859.
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