Luminescent core-shell nanostructures of silicon and silicon oxide: Nanodots and nanorods

Abstract

We report synthesis and luminescent characteristics of core-shell nanostructures of silicon and silicon oxide having two different morphologies—spherical (nanodot) and rodlike (nanorod), prepared by controlled oxidation of mechanically milled crystalline silicon and by exfoliation of the affected layer of porous silicon. Colloidal suspensions of these nanostructures exhibit intense room temperature photoluminescence (PL), detectable with the unaided eye. PL band peak energies of the colloidal suspensions formed from porous silicon are blue shifted by ∼1 eV compared to the as-prepared films on silicon substrate. In addition, PL spectra of all the colloidal suspensions blueshift with increase in excitation energy but the PL peaks of as-prepared porous silicon are independent of excitation. However, shape of the nanocrystals (spherical or rodlike) is found to have little effect on the emission spectra. These observations are explained in terms discretization of phonon density of states and electronic transitions involving surface defect states and quantum confinement induced widened band states.

Amorphous Carbon Dots and their Remarkable Ability to Detect 2,4,6-Trinitrophenol

“…In addition, we believe, discretization of phonon density of states in nanostructures also contributes towards the observed excitation dependence of emission energy. It is well known that in colloidal nanostructures the solid-liquid boundaries act as potential barriers for phonons, resulting in phonon confinement within the nanostructures 69 . The photo-excited carriers in such systems relax by emitting phonons corresponding to some discrete states.…”

Temperature dependent photoluminescence from porous silicon nanostructures: Quantum confinement and oxide related transitions

“…Samples for high resolution transmission electron microscopy (HRTEM) were prepared by exfoliation of the porous layer by passing a high current pulse (J ¼ 2 A/cm 2 ) for a very short time ($1 s) that caused the porous layer to detach from the Si substrate due to the enhanced strain generated. 26 The loosely attached layer was then removed by an appropriately cut scotch tape and the crystallites were suspended in isopropanol. The samples were then drop casted on a carbon coated copper grid after thorough sonication and the images were recorded by a JEOL JEM 3010 operating at 300 kV.…”

Collective charge transport in semiconductor-metal hybrid nanocomposite

“…We see that in this case the current increases $10 6 times following metallic inclusions and exhibits intriguing transport characteristics. Consequently, in addition to the abovementioned applications, this particular system holds promise for development of efficient thermoelectric, utilizing the property of low thermal conductivity due to phonon bottleneck observed in Si QDs, 15 and the high electrical conductivity due to inclusion of Ag NPs as observed in the present study.…”

“…2 The Si QDs used in this study exhibit room temperature photoluminescence (after oxidation and etching), which we have studied and reported earlier, 15 and hence provide access to the region of quantum confinement and unique surface/interface states that rule their properties. 16 However, such ultra-small Si QDs are expected to have low dielectric constant giving rise to an increase in the effective electron-impurity potential and weaker screening in the QDs, 17 which is not desirable for producing a conductive array.…”