Silicon monoxide – a convenient precursor for large scale synthesis of near infrared emitting monodisperse silicon nanocrystals

Abstract

While silicon nanocrystals (ncSi) embedded in silicon dioxide thin films have been intensively studied in physics, the potential of batch synthesis of silicon nanocrystals from the solid-state disproportionation of SiO powder has not drawn much attention in chemistry. Herein we describe some remarkable effects observed in the diffraction, microscopy and spectroscopy of SiO powder upon thermal processing in the temperature range 850-1100 °C. Quantum confinement effects and structural changes of the material related to the size of the silicon nanocrystals nucleated and grown in this way were established by Photoluminescence (PL), Raman, FTIR and UV-Visible spectroscopy, PXRD and STEM, pinpointing that the most significant disproportionation transformations happened in the temperature range between 900 and 950 °C. With this know-how a high yield synthesis was developed that produced polydispersions of decyl-capped, hexanesoluble silicon nanocrystals predominantly with near infrared (NIR) PL. Using size-selective precipitation, these polydispersions were separated into monodisperse fractions, which allowed their PL absolute quantum yield (AQY) to be studied as a function of silicon nanocrystal size. This investigation yielded volcano-shaped plots for the AQY confirming the most efficient PL wavelength for ncSi to be located at around 820-830 nm, which corresponded to a size of 3.5-4.0 nm. This work provides opportunities for applications of size-selected near infrared emitting silicon nanocrystals in biomedical imaging and photothermal therapy. While silicon nanocrystals (ncSi) embedded in silicon dioxide thin films have been intensively studied in physics, the potential of batch synthesis of silicon nanocrystals from the solid-state disproportionation of SiO powder has not drawn much attention in chemistry. Herein we describe some remarkable effects observed in the diffraction, microscopy and spectroscopy of SiO powder upon thermal processing in the temperature range 850-1100°C. Quantum confinement effects and structural changes of the material related to the size of the silicon nanocrystals nucleated and grown in this way were established by Photoluminescence (PL), Raman, FTIR and UV-Visible spectroscopy, PXRD and STEM, pinpointing that the most significant disproportionation transformations happened in the temperature range between 900 and 950°C. With this know-how a high yield synthesis was developed that produced polydispersions of decyl-capped, hexane-soluble silicon nanocrystals predominantly with near infrared (NIR) PL. Using sizeselective precipitation, these polydispersions were separated into monodisperse fractions, which allowed their PL absolute quantum yield (AQY) to be studied as a function of silicon nanocrystal size. This investigation yielded volcano-shaped plots for the AQY confirming the most efficient PL wavelength for ncSi to be located at around 820-830 nm, which corresponded to a size of 3.5-4.0 nm. This work provides opportunities for applications of size-selected near infrared emit...

Under what conditions does (SiO)N nucleation occur? A bottom-up kinetic modelling evaluation

“…This assumption is supported by accurate theoretical calculations which show the absence of a barrier for the SiO + SiO → (SiO) 2 and SiO + (SiO) 2 → (SiO) 3 reactions. Although a study by Pimental et al 26 reported a modest barrier for the latter (trimerisation) reaction, we could not verify this result and agree with the conclusion of Avramov et al 21 that a barrier for trimerisation does not exist.…”

“…1 Control of segregation in SiO yields systems of sized controlled quantum+confined nanoparticles of silicon 2 or SiO x 3 embedded in a SiO 2 matrix, which are of great interest for light emission applications (e.g. biomedical imaging).…”

Heterogeneous reduction of carbon dioxide by hydride-terminated silicon nanocrystals

“…Thermal treatment of SiO in a 5% H 2 /Ar environment causes a redox disproportionation reaction in which the formally Si(II) in SiO is simultaneously reduced to Si(0) and oxidized to Si(IV). The so-formed Si(0) undergoes nucleation and growth to form ncSi in a SiO 2 matrix25. The size of the produced ncSi is within the range of 2–7 nm (ref.…”

Synthesis of SiOx Nano-Powders Using a Microwave Plasma Torch at Atmospheric Pressure

“…The XRD pattern of synthesized SiO x -NPs is shown in Figure 3(b), red line, the Si (111, 220) diffraction peak. Further, Sun, W. et al, the commercial SiO precursor, has only two broad humps centered at ~23 and ~51 degrees and was observed in the XRD pattern [17]. In this context, the characteristics of synthesized SiO x -NPs which have a 0.91 x value are very close to the SiO.…”