Semiconductor nanoparticles and ultrathin layers prepared from Langmuir-Blodgett precursors for quantum device applications

Victor Erokhin1,, Cristina Paternolli2, Sergio Paddeu1, Claudio Nicolini2
 
 1Fondazione El.B.A., Corso Europa 30, Genova, Italy
2Institute of Biophysics, University of Genova, Corso Europa 30, Genova, Italy
 

Langmuir-Blodgett (LB) technique [1] is suitable for the realization of organic structures with molecular resolution, suitable for molecular- and bioelectronics. Exposure of such films to the atmosphere of different gases allows to form inorganic particles of nanometer size in them [2]. This fact enlarge the applicability of the LB technology, as it gives the possibility to include also inorganic structures in molecular systems. It was possible to observe several interesting phenomena, quantum in nature, on these nanoparticles [3,4].

 The particles can be also aggregated into thin layers by selective removal of the organic matrix [5]. The thickness resolution of resultant films was found to be of about one nm.

 Nanoparticles can be used as intermediate granules in single-electron junctions (Fig. 1).

 

 

Figure 1
 
Realization of structures with desirable alternation of different semiconductor and insulator layers can allow to form structures, similar to superlattices, where resonant tunnelling phenomena can be observed (Fig. 2).

 

 

Figure 2
 

The aim of this study is to investigate structure and properties of the nanoparticles, formed in LB precursors, and thin films obtained by their aggregation.

 Particles of different materials, such as CdS, PbS, ZnS, etc. were fabricated. Thin layers were also formed by aggregation of these particles. Complex structures, containing inorganic aggregated layers of different types as well as organic monomer and polymer layers, were also prepared.

 The structure of the systems was studied by X-ray diffraction technique (including that carried out in Synchrotron) and electron microscopy. The rheology of the films was investigated by Brewster angle microscopy.

 Electrical and optical properties of the systems were studied. Electrical conductivity was measured both in the film plane and perpendicular to it. Room temperature single electron conductivity was registered in the circuits with nanoparticles.

 All samples performed a blue shift in the optical absorbance due to small sizes of the particles in the films.

References

 1. G.G. Roberts, Langmuir-Blodgett films, Plenum Press, 1990.

 2. E.S. Smotkin, C. Lee, A.J. Bard, A. Campion, M.A. Fox, T.E. Mallouk, S.I. Webber, and J.M. White, Chem. Phys. Lett., 152, 265 (1988).

 3. P. Facci, V. Erokhin, S. Carrara, and C. Nicolini, Proc. Natl. Acad. Sci. USA, 93, 10556 (1996).

 4. V. Erokhin, S. Carrara, H. Amenitch, S. Bernstorff, and C. Nicolini, Nanotechnology, 9, 158 (1998).

 5. P. Facci, V. Erokhin, A. Tronin, and C. Nicolini, J. Phys. Chem., 98, 13323 (1994).