Organically capped silicon nanocrystals

Comparing different surfaces, a “model” SiNC is that terminated with hydrogen (H-SiNC) as hydrogen termination influences the physical properties of the silicon core the least. H-SiNCs provide full spectral tunability [212], following the quantum confinement model well (see Section 16.1.1). However, the Si-H bond on the highly curved surface of an SiNC is much weaker than that on a planar Si, being oxidatively unstable and very sensitive to water [31,41,59,191]. Halogenated, for example, chlorine-terminated surfaces, on the other hand, exhibit only weak photoluminescence (PL) in addition to being unstable in ambient air [64]. Therefore, hydrogenated and halogenated SiNCs are regarded as reactive platforms or sometimes convenient study models under controlled atmosphere [64,212], whereas oxide-covered and organically terminated SiNCs are stable entities, with deeper understanding of physical properties reached in the former, but much wider versatility in the latter. Naturally, other types of attachment, such as Si-S linkage [221], have also been studied

Silicon quantum dots: surface matters

Silicon quantum dots (SiQDs) hold great promise for many future technologies. Silicon is already at the core of photovoltaics and microelectronics, and SiQDs are capable of efficient light emission and amplification. This is crucial for the development of the next technological frontiers—silicon photonics and optoelectronics. Unlike any other quantum dots (QDs), SiQDs are made of non-toxic and abundant material, offering one of the spectrally broadest emission tunabilities accessible with semiconductor QDs and allowing for tailored radiative rates over many orders of magnitude. This extraordinary flexibility of optical properties is achieved via a combination of the spatial confinement of carriers and the strong influence of surface chemistry. The complex physics of this material, which is still being unraveled, leads to new effects, opening up new opportunities for applications. In this review we summarize the latest progress in this fascinating research field, with special attention given to surface-induced effects, such as the emergence of direct bandgap transitions, and collective effects in densely packed QDs, such as space separated quantum cutting

Time-resolved measurements of optical gain and photoluminescence in silicon nanocrystals

In this paper, we present time-resolved optical gain spectroscopy using a combination of the variable stripe length and the shifting excitation spot techniques under pulsed nanosecond excitation at 355 nm. Optical gain measurements in the temporal detection window of 10 ns width, coincident with the excitation pulse, revealed induced absorption losses, whereas measurements with a different detection gate width and delay in two main photoluminescence components (a fast band at ~430 nm decaying in nanoseconds and a slow band at ~620 nm decaying in microseconds) show a positive optical gain of the order of tens of cm-1