Nanoparticles for Multi-Functionalization of Silicon : A Plug and Play Approach

K. Prabhakaran and T. Ogino
Device Physics Laboratory

@Fabrication of nanostructures and their functionalization is essential to realize nanometre sized devices. However, problems with the poor controllability of the size, shape, spatial distribution and the functionality itself have been posing formidable challenges. This underlines the need to develop alternative processes such as self-organization and other nature-driven processes. Here, we demonstrate a novel approach whereby, externally synthesized nanoparticles are introduced on to the silicon wafer which is followed by manipulation of surface chemical bonds to introduce a variety of functionalities. Since the particles are synthesized externally this approach enables better control of various parameters.
@Fe2O3 nanoparticles are introduced onto a device quality silicon wafer from a suspension in ethanol through an ultrasonic bath. The samples are dried and loaded into an ultrahigh vacuum chamber equipped with photoelectron spectrometer for monitoring the nature of the surface species. On annealing the samples, the oxygen atoms change the bonding partner from Fe to Si and desorbs as monoxide. This results in the complete reduction of the iron oxide particles to iron at around 760Ž. These particles impart a soft-ferromagnetic property to silicon as shown in figure 2. On depositing a thin layer of silicon onto this sample, followed by annealing at 550Ž, the sample exhibits light emission property. Figure 3 shows the photoluminescence spectrum obtained from this sample. In summary, we could introduce multiple functionality to silicon by treating it with nanoparticles, followed by manipulating the surface chemical bonds.

[1] T. Ogino et al., Account. Chem. Res. 32 (1999) 447.
[2] K. Prabhakaran et al., Advan. Mater. 13 (2001) 1859.

Fig.1. AFM image of Si sample treated with the particles followed by annealing in UHV. Fe articles of uniform size and shape are observed.
Fig. 2. Magnetization data from the particle treated Si showing hysterersis. Inset shows the variation of coercivity.
Fig. 3. PL spectrum recorded from the particle treated Si exhibiting light emission.

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