Synthesis of colloidal solutions with silicon nanocrystals from porous silicon

Abstract

In this work, we have obtained colloidal solutions of Si nanocrystals (Si-ncs), starting from free-standing porous silicon (PSi) layers. PSi layers were synthesized using a two-electrode Teflon electrochemical cell; the etching solution contained hydrogen peroxide 30%, hydrofluoric acid 40% (HF), and methanol. The anodizing current density was varied to 250 mA cm-2, 1 A cm-2, and 1.2 A cm-2. Thus obtained, PSi was mechanically pulverized in a mortar agate; then, the PSi powders were poured into different solutions to get the final Si-ncs colloidal solutions. The different optical, morphological, and structural characteristics of the colloidal solutions with Si-ncs were measured and studied. These Si-ncs colloidal solutions, measured by photoluminescence (PL), revealed efficient blue-green or violet emission intensities. The results of X-ray diffraction (XRD) indicate that the colloidal solutions are mainly composed of silicon nanocrystallites. The result of UV–vis transmittance indicates that the optical bandgap energies of the colloidal solutions varied from 2.3 to 3.5 eV for colloids prepared in methanol, ethanol, and acetone. The transmission electron microscopy (TEM) images showed the size of the nanocrystals in the colloidal solutions. Fourier transform infrared spectroscopy (FTIR) spectra showed different types of chemical bonds such as Si-O-Si, Si-CH2, and SiH x , as well as some kind of defects.PACS61.46Df.-a; 61.43.Gt; 61.05.cp; 78.55.-m; 81.15.Gh

Silicon Nanocrystals with pH-Sensitive Tunable Light Emission from Violet to Blue-Green

“…Figure 2 b,c present the high-resolution TEM (HRTEM) images of silicon NCs, which display two highly-crystalline silicon NCs, with lattice fringes corresponding to (220) and (311) planes of silicon. As can be seen from Figure 2 e, the sharp XRD line indicates the high crystallization and good monodispersion of silicon NCs, consistent with the HRTEM images, exhibiting typical peaks of silicon nanostructures [ 12 , 44 , 59 , 60 ].…”

“…The research on low-dimensional silicon nanostructures is an active research field, due to the interesting chemical and physical properties [ 1 , 2 , 3 , 4 , 5 ]. Of all the low-dimensional silicon nanomaterials, the silicon NCs with a variety of types, such as porous silicon [ 6 , 7 , 8 ], silicon/SiO 2 , or silicon/silicon nitride nuclear shell nanostructure [ 9 , 10 , 11 ], soluble quantum dots [ 12 , 13 , 14 , 15 , 16 , 17 ], silicon NC-based photonic crystal slabs [ 18 ], silicon NC ultrathin films [ 19 ], etc., have drawn increasing attention. In particular, the silicon NCs with intense light emission take up an important place in a large number of applications, including light-emitting sources [ 18 , 20 , 21 ], sensors [ 22 ], detectors [ 13 , 23 , 24 ], bio-tagging [ 22 , 25 ], bio-imaging [ 21 , 26 ], photovoltaics [ 27 ], optical communication [ 28 ], spintronics devices [ 29 ], etc.…”

Porous Silicon Suspensions and Colloids

“…It is well known that the quantum confinement in silicon nanocrystals results in an increase of their band gap, and it can be easily observed in the light absorption spectra. So, absorbance spectra of PSi and SiNPs, which consist of small silicon nanocrystals, are characterized by the lower absorption coefficient and the shift of the absorption edge, in comparison with c-Si (Lehmann and Gösele 1991;Ma et al 1999;Luna López et al 2014).…”

Sonofragmentation of Ultrathin 1D Nanomaterials

“…[10] Topdown synthesis methods that rely on breaking down bulk materials into smaller fragments can be scalably deployed. [11][12][13][14][15][16][17][18][19][20][21] However, the method struggles with monodispersity and with percent yield for such small NPs. Bottom-up synthesis methods can effectively assemble small molecule precursors into larger units to create small NPs.…”

“…A multitude of methods have been developed to produce such NPs . Top‐down synthesis methods that rely on breaking down bulk materials into smaller fragments can be scalably deployed . However, the method struggles with monodispersity and with percent yield for such small NPs.…”