A self-assembly technique for high density (∼1 × 10 11 cm -2 ) β-FeSi 2 nanodots epitaxially grown on Si (001) substrates was developed using a codeposition method of Fe and Si on ultrathin SiO 2 films with Si nuclei. Photoabsorption spectra of individual nanodots and their photoabsorption maps at the direct-transition photoabsorption edge were obtained using electric field modulation spectroscopy combined with scanning tunneling microscopy with a nanometer spatial resolution.

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A b s h d .?he X-J model is a strongzoupling Limit of both lhe ~l u r a l tighf binding model d pemvskite supermnductors and lhe Anderson lattice model of heay. fermions. The application of the model lo perowkite supercmductivity is straighttonvard, bur is use to describe heay fermions is more speculative. ?he straighl-line motion of charge carriers in the model is sympathetic to antiferromagnetic mrrelations along the path Lraversed, although Ihe motion destroys the long-range anlifenomagnetic order by =changing the WO sublattices in passing. Antiferromagnetism is desmyed in both lhe square laltice geometry relevant to a CuOz plane and the triangular geometry relevanl to an isolated layer of CeAh. A paramagneuc phase uith shoner range rrrelations than suggested by the Heisenberg model seems prefemd by lhe chargecarrier motion in these two-dimensional fxamples.

We studied the luminescence properties of Si-capped β-FeSi2 nanodots (NDs) epitaxially grown on Si substrates by using photoluminescence (PL) and electroluminescence (EL) spectroscopies. Codepositing Fe and Si on ultrathin SiO2 films induced the self-assembly of epitaxial β-FeSi2 NDs. The PL spectra of the Si/β-FeSi2 NDs/Si structure depended on the crystal orientation of the Si substrate. These structures exhibited a broad PL peak near 0.8 eV on both Si(001) and (111) substrates. The PL intensity depended on the shape of the β-FeSi2 NDs. For the flat NDs, which exhibited higher PL intensity, we also recorded EL spectra. We explained the luminescence properties of these structures by the presence of nanostructured Si offering radiative electronic states in the Si cap layers, generated by nano-stressors for upper Si layer: the strain-relaxed β-FeSi2 NDs.