Oxidation Induced Giant Modulation in the Luminescence of Colloidal Amorphous Porous Silicon Nanoparticles
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Oxidation Induced Giant Modulation in the Luminescence of Colloidal Amorphous Porous Silicon Nanoparticles Jehad K. El Demellawi1, Dalaver H. Anjum2 and Sahraoui Chaieb1 1 Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, K.S.A. 2 Imaging and Characterization Laboratory, King Abdullah University of Science and Technology, Thuwal, K.S.A. ABSTRACT The emission of crystalline silicon nanoparticles as well as nanowires can be tuned by varying their diameters. The diameter selection is achieved via a difficult chemical procedure that necessitates filtration which cannot be easily scaled up. Herein, we report a novel approach for producing and tuning the emission of freestanding colloidal of amorphous porous silicon nanoparticles (which should not be confused with bulk amorphous silicon nor with porous silicon) via a controlled oxidation without relying on size of nanoparticles. This oxidation increases local strain in the disordered network that causes orbital interactions which modifies the band-gap but a new hybridization. INTRODUCTION Porous silicon (p-Si) has been found to have a gamut of applications, such as light harvesting and detection [1-3], hydrogen generation [4], novel tissue culture substrates [5], fuel cells and batteries [6,7], and bio-sensing [8]. Tuning the emission wavelength of silicon nanostructures, such as nanosilicon, without relying on the expensive size selection, such as in crystalline silicon nanoparticles, is attractive [9]. Quantum confinement (a volume effect due to a particle-in-a-box phenomenon) [10,11], and surface effects (surface defects, dangling bonds or molecular species) are thought to be at the origin of the optical properties of nanosilicon [12,13]. Tuning the emissions continuously remains hard to achieve however. The photoluminescence emission wavelength of crystalline silicon nanoparticles depends on their sizes [9]. Bright tunable colloidal amorphous porous silicon nanostructures, however, have not been reported before. Here, we report a 100 nm tuning in the fluorescence emission of freestanding colloidal amorphous porous silicon nanoparticles through controlled oxidation. We note here that while we achieved a blue-shift via oxidation, silicon nanoparticles red shifted instead when oxidized [10]. High resolution transmission electron microscopy, electron energy loss spectroscopy, Raman, photoluminescence as well as UV-Vis were used to characterize this modulation. A theoretical model for this giant modulation is the subject of a future publication. EXPERIMENTAL DETAILS Freestanding colloidal photoluminescent amorphous porous silicon nanoparticles (apSiNPs) suspensions were prepared through etching cleaved strips of single crystal (100) p-type boron doped silicon wafers (Addison Electronics). The silicon strips were submerged, for 15 hours, in an etching bath composed of 4.7 g Iron (III) Chloride (anhydrous 98%, Alfa Aeser) dissolved in a mixture of 42 ml of hydrofluoric acid (49%, Fluka) and 18 ml of hydrochloric acid
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