Abstract
In the past decades, silicon nanocrystals have received vast attention and have been widely studied owing to not only their advantages including nontoxicity, high availability, and abundance but also their unique luminescent properties distinct from bulk silicon. Among the various synthetic methods of silicon nanocrystals, thermal disproportionation of silicon suboxides (often with H as another major composing element) bears the superiorities of unsophisticated equipment requirements, feasible processing conditions, and precise control of nanocrystals size and structure, which guarantee a bright industrial application prospect. In this paper, we summarize the recent progress of thermal disproportionation chemistry for the synthesis of silicon nanocrystals, with the focus on the effects of temperature, Si/O ratio, and the surface groups on the resulting silicon nanocrystals’ structure and their corresponding photoluminescent properties. Moreover, the paradigmatic application scenarios of the photoluminescent silicon nanocrystals synthesized via this method are showcased or envisioned.
Highlights
It has been almost 30 years since the discovery of silicon nanocrystals (SiNCs) (Canham, 1990), which carry unique properties distinct from bulk silicon
As for the heating process of silicon-rich oxide in the form of film, a theory of two thermal disproportionation stages was proposed, namely the precipitation of Si when the temperature was above 500°C and the crystallization of excess Si with the even higher temperature starting from ∼1,000°C (Gan et al, 2011)
As for the relationship between the size and quantum yield (QY), taking the most-studied hydrogen silsesquioxane (HSQ) as an example, it was heated within the temperature range from 1,100 to 1,400 °C in a reducing atmosphere (10% H2 + 90% Ar) to obtain the SiNCs with a wide size distribution from under 3–90 nm, all of which were treated by similar surface passivation (Hessel et al, 2012)
Summary
It has been almost 30 years since the discovery of silicon nanocrystals (SiNCs) (Canham, 1990), which carry unique properties distinct from bulk silicon. Among the many factors that helped to find the PL benchmarks of SiNCs, the preparation or synthetic method plays a primary and pivotal role. Similar to many other widely used nanomaterials, SiNCs can be prepared with versatile methods, and each of them has its own advantages and challenges. Electrochemical etching, one of the earliest methods for preparing SiNCs (Cullis and Canham, 1991), sacrifices the controllability of size to realize simplicity (Heinrich et al, 1992; Bley et al, 1996). Laser ablation faces the challenge of controllability, and the requirement of sophisticated equipment hinders its adoption
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