Concerns over possible toxicities of conventional metal-containing quantum dots have inspired growing research interests in colloidal silicon nanocrystals (SiNCs), or silicon quantum dots (SiQDs). This is related to their potential applications in a number of fields such as solar cells, optoelectronic devices and fluorescent bio-labelling agents. The past decade has seen significant progress in the understanding of fundamental physics and surface properties of silicon nanocrystals. Such understanding is based on the advances in the preparation and characterization of surface passivated colloidal silicon nanocrystals. In this critical review, we summarize recent advances in the methods of preparing high quality silicon nanocrystals and strategies for forming self-assembled monolayers (SAMs), with a focus on their bio-applications. We highlight some of the major challenges that remain, as well as lessons learnt when working with silicon nanocrystals (239 references).

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Colloidal silicon quantum dots: from preparation to the modification of self-assembled monolayers (SAMs) for bio-applications

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.

https://iopscience.iop.org/article/10.1088/0953-8984/26/17/173201/pdf

Silicon quantum dots: surface matters

Colloidal nanocrystals are nanometer-sized, solution-grown inorganic particles stabilized by a layer of surfactants attached to their surface. The inorganic cores exhibit useful properties controlled by composition as well as size and shape, while the surfactant coating ensures that these structures are easy to fabricate and process. It is this combination of features that makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. But their full potential can only be exploited if we achieve exquisite control over their composition, size, shape, crystal structure and surface properties. Here we review what is known about nanocrystal growth and outline strategies for controlling it.

Colloidal nanocrystal synthesis and the organic-inorganic interface

White light-emitting diodes (white LEDs) have recently attracted substantial interest owing to their remarkable energy conservation. The evolution of fluorescent nanomaterials with tunable optical properties has provided an opportunity for light source design of white LEDs. However, the stability and performance of fluorescent nanomaterial-derived white LEDs still fail to meet the requirements of practical applications. It is therefore imperative to boost their overall device performance, which depends on not only the exploitation of advanced fluorescent nanomaterials but also the design of a superior light source. In this review, the achievements regarding fluorescent nanomaterials as color converters towards white LEDs are highlighted, including semiconductor nanocrystals or colloidal quantum dots (QDs), carbon-based nanoparticles, silicon QDs, and organic–inorganic fluorescent nanocomposites. The challenges and future perspectives in this research area are also discussed.

Fluorescent nanomaterial-derived white light-emitting diodes: what's going on

https://iopscience.iop.org/article/10.1088/1468-6996/15/1/014207/pdf

Colloidal silicon quantum dots: synthesis and luminescence tuning from the near-UV to the near-IR range

A detailed investigation of the photochemical etching of silicon nanocrystals (Si-NCs) in aqueous hydrofluoric acid (HF) mixtures is described. By increasing the HF concentration and lowering the pH upon addition of hydrochloric acid (HCl), oxide-embedded Si-NCs were rapidly etched, and photoluminescence (PL) from the resulting hydride-terminated Si-NCs tailored from the near-IR to the yellow/green spectral region by irradiating the reaction mixture at the desired PL wavelength. These results are consistent with a hole-driven etching pathway rather than the chemically induced oxidation/etch pathway commonly exploited for Si nanostructures. The relationship among NC size, polydispersity, and PL was investigated using small-angle X-ray scattering. We suggest the defect density of Si-NCs is a crucial parameter for effective size control via photochemical exciton-mediated HF etching. Improved HF etching methods are expected to enable Si-NC applications through the realization of narrow polydispersity and PL b...

Wavelength-Controlled Etching of Silicon Nanocrystals

https://www.spiedigitallibrary.org/journals/Journal-of-Nanophotonics/volume-6/issue-1/060302/Commentary-Silicon-nanocrystals-and-their-role-in-photonics/10.1117/1.JNP.6.060302.pdf

Commentary: Silicon nanocrystals and their role in photonics

Oxide-embedded Silicon nanoparticles (OE-Si-NPs) are of great interest for many applications due to unique size effects observed when their size drops below 5 nm (Silicon’s Bohr exciton radius). Some of the suggested applications require patterning of the nanoparticles in an ordered array. Lithographic methods to pattern Si-NPs are common in the literature, however these methods can be costly, and are not time-efficient. Recently, non-lithographic patterning techniques have become very attractive because they are cost-effective and straightforward. In this proceeding we will demonstrate non-lithographic patterning of OE-Si-NPs characterized via AFM and XPS.

Non-lithographic Patterning of Oxide-Embedded Silicon Nanoparticles

Phase separation is a dynamic process that leads to the formation of biomolecular condensates. These condensates contain proteins with high concentrations of intrinsically disordered regions (IDR), which lack a fixed 3D structure. We aim to control phase separation in human cells using the LOV domain, a protein sensor that homodimerizes under blue light. We hypothesize that extant LOV proteins may show nontrivial association with intrinsically disordered regions, and these proteins with IDR regions may induce phase separation under blue light. To determine IDR percentage, we processed sequences from a database of LOV proteins through an algorithm that provides scores for likely intrinsically disordered amino acids. distribution of these LOV proteins as a function percentage was significantly from that of random sequences. We expressed the highest scoring proteins in human cells and monitored their ability to form condensates under blue light. These novel proteins will provide a new tool for researchers to better understand the phenomenon of phase separation.

José R. Rodríguez Núñez

Papers

Wavelength-Controlled Etching of Silicon Nanocrystals

Commentary: Silicon nanocrystals and their role in photonics

Non-lithographic Patterning of Oxide-Embedded Silicon Nanoparticles

Development of Photoswitchable, Phase Separable Biomaterials