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

A co-modification strategy to improve the electrode performance of SiO-based materials through the use of a carbon coating layer and reduced graphene oxide (RGO) network has been developed. The as-synthesized SiOx/C@RGO nanocomposites showed excellent specific capacity, cycling performance and rate capability when used as an anode in lithium-ion batteries.

A three dimensional SiOx/C@RGO nanocomposite as a high energy anode material for lithium-ion batteries

Scalable synthesis of core-shell structured SiO x /nitrogen-doped carbon composite as a high-performance anode material for lithium-ion batteries

We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiOx, 0<x<2) films by high-vacuum annealing and dry oxidation. The SiOx films were deposited by plasma-enhanced chemical vapor deposition at different nitrous–oxide/silane flow ratios. The physical and optical properties of the SiOx films were studied as a result of high-vacuum annealing and thermal oxidation. X-ray photoelectron spectroscopy (XPS) reveals that the as-deposited films have a random-bonding or continuous-random-network structure with different oxidation states. After annealing at temperatures above 1000 °C, the intermediate Si continuum in XPS spectra (referring to the suboxide) split to Si peaks corresponding to SiO2 and elemental Si. This change indicates the phase separation of the SiOx into more stable SiO2 and Si clusters. Raman, high-resolution transmission electron microscopy and optical absorption confirmed the phase separation and the formation of Si NCs in the films. Th...

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Annealing and oxidation of silicon oxide films prepared by plasma-enhanced chemical vapor deposition

A novel, economical flash heat treatment of the fabricated silicon based electrodes is introduced to boost the performance and cycle capability of Li-ion batteries. The treatment reveals a high mass fraction of Si, improved interfacial contact, synergistic SiO2/C coating, and a conductive cellular network for improved conductivity, as well as flexibility for stress compensation. The enhanced electrodes achieve a first cycle efficiency of ∼84% and a maximum charge capacity of 3525 mA h g(-1), almost 84% of silicon's theoretical maximum. Further, a stable reversible charge capacity of 1150 mA h g(-1) at 1.2 A g(-1) can be achieved over 500 cycles. Thus, the flash heat treatment method introduces a promising avenue for the production of industrially viable, next-generation Li-ion batteries.

Engineered Si electrode nanoarchitecture: a scalable postfabrication treatment for the production of next-generation Li-ion batteries.

Silicon-rich silicon oxide thin films have been prepared by thermal evaporation of silicon monoxide in vacuum. The SiOx film composition (1.1⩽ x ⩽1.7) has been controlled by varying the deposition rate and residual pressure in the chamber. Long time stability of all films has been ensured by a postdeposition annealing at 523 K for 30 min in Ar atmosphere. Some films were further annealed at 973 K and some others at 1303 K. Raman scattering measurements have implied the formation of amorphous silicon nanoparticles in films annealed at 973 K and Si nanocrystals in films annealed at 1303 K. The latter conclusion is strongly supported by high resolution electron microscopy studies which show a high density of Si nanocrystals in these films. Photoluminescence has been observed from both amorphous and crystalline nanoparticles and interpreted in terms of band-to-band recombination in the nanoparticles having average size greater than 2.5 nm and carrier recombination through defect states in smaller nanoparticles.

S. Alexandrova

Papers

Raman scattering and photoluminescence from Si nanoparticles in annealed SiOx thin films