High-yield green fabrication of colloidal silicon quantum dots by low-temperature thermal cracking of porous silicon

Toshihiro Nakamura,Jun Otsubo,Ze Yuan,Nobuyoshi Koshida

doi:10.1063/5.0014206

Abstract

We developed high-yield green fabrication of colloidal silicon quantum dots (QDs) only by low-temperature treatment of porous silicon (PSi) flakes in a reactive organic solution. Heat treatment at ∼50 °C of the PSi flakes in unsaturated hydrocarbon solution mixed with hydrofluoric acid (HF) yields the organically self-surface-passivated Si QD, which exhibit efficient photoluminescence compared with the conventional PSi. The production yield of Si QDs is enhanced by increasing the heat-treatment temperature and HF concentration, and the best results were obtained at ∼50 °C and 50%, respectively. The dispersibility of the prepared Si QDs in the solvents can be controlled by using appropriate organic function groups. The efficient transformation into Si QDs without waste is based on thermal cracking of weakly interconnected Si cores of PSi. Performing a practical clean process, the present result provides a promising route for overcoming limitations in the conventional colloidal QD preparation methods.

Highlights

Crystalline semiconductor nanoparticles with a diameter range less than that of an exciton Bohr radius called semiconductor quantum dots (QDs) are known to have specific physical properties of a confined electron system
The transmittance electron microscopy (TEM) measurements, shown in Fig. 2, reveal that the fabricated colloids are single crystalline Si nanoparticles with a diameter of 3 nm–10 nm, i.e., Si QDs
Compared to porous silicon (PSi) flakes precipitating on the bottom of the glass tube, the prepared colloidal Si QDs exhibit efficient red PL under UV

Summary

INTRODUCTION

Crystalline semiconductor nanoparticles with a diameter range less than that of an exciton Bohr radius called semiconductor quantum dots (QDs) are known to have specific physical properties of a confined electron system. In top-down processes, the fragmentation of the bulk Si crystal can directly yield the colloidal Si QDs. Various fragmentation techniques were employed such as mechanical ball milling, chemical etching, and pulsed laser irradiation in liquid.. Scitation.org/journal/apm of nanopores, PSi is transformed into colloidal Si QDs with the use of some mild fragmentation treatments such as ultrasonification, mechanical milling, and unfocused pulsed laser irradiation.. Scitation.org/journal/apm of nanopores, PSi is transformed into colloidal Si QDs with the use of some mild fragmentation treatments such as ultrasonification, mechanical milling, and unfocused pulsed laser irradiation.27 In these top-down processes, the crystalline quality of Si QDs can be improved by using integrated circuit grade bulk Si crystals as a starting material. Simple thermal transformation is applied to PSi flakes in an organic solution with a reactive solvent (hydrofluoric acid: HF) at ∼50 ○C to confirm the correlation between in situ surface passivation of Si QDs and their dispersibility in solvents

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS