Nanomaterials with disordered, ramified structure are increasingly being used for applications where low cost and enhanced performance are desired. A particular example is the use in printed electronics of inorganic conducting and semiconducting nanoparticles. The electrical, as well as other physical properties depend on the arrangement and connectivity of the particles in such aggregate systems. Quantification of aggregate structure and development of structure/property relationships is difficult and progress in the application of these materials in electronics has mainly been empirical. In this paper, a scaling model is used to parameterize the structure of printed electronic layers. This model has chiefly been applied to polymers but surprisingly it shows applicability to these nanolayers. Disordered structures of silicon nanoparticles forming aggregates are investigated using small angle x-ray scattering coupled with the scaling model. It is expected that predictions using these structural parameters can be made for electrical properties. The approach may have wide use in understanding and designing nano-aggregates for electronic devices.
The size distribution and morphology of silicon nanoparticles have been studied using small‐angle X‐ray scattering (SAXS) and transmission electron microscopy. Quantitative agreement was established between the results of the two methods. The surface characteristics, as well as the size distribution, were found to be independent of the choice of binder material used to prepare printed layers containing the nanoparticles. Intrinsic silicon nanoparticles, produced by laser pyrolysis of silane, have been shown to have a narrow, effectively monodisperse, size distribution and to be roughly spherical in shape. SAXS measurements indicate that the particles have a regular geometry and a smooth surface. There is, however, a thin disordered region at the surface of the particles. Particles produced by milling of bulk silicon have surface fractal characteristics and a high dispersivity resulting from the milling process, in which the particles become smoother as they are milled to smaller size or for longer periods. The size dispersion, but not the median size, is similarly reduced by milling for longer periods
We demonstrate a fully printed transistor with a planar triode geometry, using nanoparticulate silicon as the semiconductor material, which has a unique mode of operation as an electrically controlled two-way (double throw) switch. A signal applied to the base changes the direction of the current from between the collector and base to between the base and emitter. We further show that the switching characteristic results from the activated charge transport in the semiconductor material, and that it is independent of the dominant carrier type in the semiconductor and the nature of the junction between the semiconductor and the three contacts. The same equivalent circuit, and hence similar device characteristics, can be produced using any other material combination with non-linear current-voltage characteristics, such as a suitable combination of semiconducting and conducting materials, such that a Schottky junction is present at all three contacts. C 2013 Author(s)
In printed electronics the use of semiconducting silicon nanoparticles allows more than the simple printing of conductive materials. It gives the possibility of fabricating robust and inexpensive, active and reactive components like temperature sensors which are shown as an example. In our approach high quality silicon nanoparticles with stable, essentially oxide-free surfaces are used to replace the pigment in water-based graphic inks, which on curing have unique semiconducting properties, arising from the transport of charge through a percolation network of crystalline silicon nanoparticles. In this study scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) were employed to investigate the mesoscale structure of the particle network and, more importantly the structure of the interface between particles. An intimate contact between lattice planes of different particles was observed, without the presence of an intervening oxide layer.
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