Silicon nanocrystals exhibit size-dependent optical and electronic properties that may be exploited for applications ranging from sensors to photovoltaics. In addition, they can be utilized in biological and environmental systems thanks to the nontoxicity of silicon. Synthesis of silicon nanocrystals has been accomplished using a variety of methods. However, creating near monodisperse systems of high purity has been a challenge. The high temperature processing of hydrogen silsesquioxane method of particle synthesis reproducibly provides pure, near monodisperse particles in scalable quantities. These particles can then be liberated using HF etching and functionalized using a variety of methods. This paper outlines our lab procedures for creating silicon nanocrystals, the various functionalization methods and the most commonly used characterization techniques.

The synthesis of germanium nanocrystals (GeNCs) with well-defined surface chemistry is of considerable interest because of their potential applications in the optoelectronic, battery, and semiconductor industries. Modifying and tailoring GeNC surface chemistry provides an avenue by which reactivity, environmental compatibility (e.g., solubility, resistance to oxidation), and electronic properties may be tailored. Hydride-terminated GeNCs (H-GeNCs) are of particular interest because the reactivity of surface Ge-H bonds toward alkenes and alkynes via hydrogermylation affords the potential for convenient modification; however, these reactions and their scope have not been widely explored. This report describes a straightforward route for preparing a GeNC/GeO composite via disproportionation of heretofore-unexplored Ge(II) oxide-based precursor from which the H-GeNCs were freed by subsequently chemical etching. The H-GeNCs were derivatized using a series of hydrogermylation approaches (i.e., thermally activated, radical-initiated, and borane-catalyzed). The presented findings indicate surface functionalization occurs under all conditions investigated; however the nature of surface species (i.e., monolayers vs multilayers) and surface coverage varies depending upon the conditions employed.

Silicon is recognized as a promising anode material for high-performance lithium ion batteries due to its high theoretical specific capacity and elemental abundance. Challenges related to the low electrical conductivity of Si and large volume changes during the lithiation/delithiation cycles, as well as the low rate of lithium diffusion in silicon anodes, hinder practical applications. To provide fundamental insights into these issues, silicon nanocrystal/graphene aerogel nanocomposites were synthesized by combining undecanoic acid-functionalized silicon nanocrystals of various sizes (SiX-COOH, where X represents the nanocrystal diameter of 3, 5, 8, and 15 nm) with conductive mesoporous graphene aerogels (GAs). The silicon nanocrystals are evenly dispersed throughout the graphene aerogel as shown by energy-dispersive X-ray (EDX) mapping. In terms of electrochemical performance, SiX-COOH/GA nanocomposites demonstrated a clear dependence on the size of the embedded silicon nanocrystals, with the composites comprising the larger silicon nanocrystals showing a higher initial capacity but accompanied by rapid decay of capacity retention over 100 cycles. To study the effect of thermal processing on the electrochemical performance, SiX-COOH/GA nanocomposites were annealed at 600 °C to yield annealed SiX/GA nanocomposites. The annealed nanocomposite composed of the smallest silicon nanocrystals, Si3/GA, exhibits a stable specific capacity of ∼1100 mAh/g and capacity retention of over 90% after 500 cycles when tested at a current density of 400 mA/g.

Germanium dioxide has many applications in the optoelectronics sector and is the subject of substantial research interest. In this contribution we report the preparation of germanium dioxide nanoparticles (NPs) of varied sizes and morphologies using a facile sol-gel methodology that requires no addition of templating agents (e.g., surfactants). Morphological control is achieved by tailoring the reaction mixture water/ethanol ratio, ammonium hydroxide concentration, time, and temperature.

In this work the temperature-dependent photoluminescence of alkyl-capped silicon nanocrystals with mean diameters of between 3a nd 9nmh as been investigated. The nanocrystals were characterizede xtensively by FTIR, TEM, powder XRD, and X-ray photoelectron spectroscopy prior to low-temperature and time-resolved photoluminescence spectroscopy experiments. The photoluminescence (PL) properties were evaluated in the temperature range of 41-300 K. We found that the well-known temperature-de-pendentb lueshift of the PL maximum decreases with increasingn anocrystal diameter and eventually becomes a redshift for nanocrystal diameters larger than 6nm. This implies that the observed shiftsc annotb ee xplained solely by band-gap widening, as is commonlya ssumed. We propose that the luminescence of drop-cast silicon nanocrystals is affectedby particlee nsemble effects,w hich can explain the otherwise surprising temperature dependence of the luminescencepeak.[a] M.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.