The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminesce...

Spectroscopic and Device Aspects of Nanocrystal Quantum Dots

Light emission from silicon based on quantum confinement in nanoscale structures has sparked intense research into this field ever since its discovery about 15 years ago A barrier to the widespread utilization of luminescent silicon nanocrystals in such diverse application areas as optoelectronics, solid-state lighting for general illumination, or fluorescent agents for biological applications has been the lack of a simple, high-yield synthesis approach Here we report a scaleable single-step synthesis process for luminescent silicon nanocrystals based on a low-pressure nonthermal plasma

High-yield plasma synthesis of luminescent silicon nanocrystals.

The Controlled Display of Biomolecules on Nanoparticles: A Challenge Suited to Bioorthogonal Chemistry

We report the bulk preparation of nanocrystalline Si−SiO2 (nc-Si/SiO2) composites via straightforward reductive thermal annealing of a well-defined molecular precursor, hydrogen silsesquioxane. The presented method affords quantitative yields of composite powders in large quantities. Freestanding, hydride-surface-terminated silicon nanocrystals that photoluminesce throughout the visible spectrum are readily liberated from nc-Si/SiO2 composite powders upon etching in ethanol−water solutions of hydrofluoric acid. Composites and freestanding particles were characterized using transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FT−IR), and thermogravimetric analysis (TGA).

Hydrogen Silsesquioxane: A Molecular Precursor for Nanocrystalline Si−SiO2 Composites and Freestanding Hydride-Surface-Terminated Silicon Nanoparticles

▪ Abstract This review focuses on the preparation of capped nanoparticles of inorganic materials, classified by composition. The materials described include elemental metals and metalloids (semiconductors), chalcogenide II–VI and IV–VI semiconductors, III–V semiconductors, and oxides (both of simple- and multitransition metal). Although particular emphasis is placed on methods that yield large volumes of nanoparticles, recent novel methods that may not necessarily be scalable are also reviewed. The review makes apparent the richness of chemistry that has become routine to practitioners in the field; diverse inorganic systems with distinct chemistry require distinct methods of preparation.

Synthesis routes for large volumes of nanoparticles

Alkyl-capped and alkyl/alkoxy-capped silicon nanocrystals have been prepared by the oxidation of magnesium silicide with bromine High-resolution transmission electron microscopy confirmed the crystalline nature of the nanoparticles and provided an average diameter of 45 (20) nm for the alkyl-capped and for the alkyl/alkoxy-capped nanoparticles Energy-dispersive X-ray spectroscopy showed that the nanoparticles are composed of silicon, with no evidence of unreacted bromine FTIR spectra were consistent with alkyl- and alkyl/alkoxy-capped surfaces Fluorescence spectroscopy indicated strong ultraviolet-blue photoluminescence, which was attributed to both quantum confinement and surface termination These nanoparticles displayed long-term stability and no degradation of the photoluminescence was observed for a period of 1 year

Solution Synthesis of Alkyl- and Alkyl/Alkoxy-Capped Silicon Nanoparticles via Oxidation of Mg2Si

We describe the synthesis and characterization of nanocrystalline Si prepared by the initial reaction of the metal silicide, Mg 2 Si, with either SiCl 4 or Br 2 and, subsequently, with LiAlH 4 . These reactions produce Si nanoparticles with surfaces that are covalently terminated with H. The resultant nanoparticles can be suspended in organic solvent and are characterized by Fourier transform infrared (FTIR), UV–vis absorption, and photoluminescence (PL) spectroscopy. This work provides the first direct evidence of hydrogen terminated Si nanoparticles synthesized in solution.

A new synthetic route for the synthesis of hydrogen terminated silicon nanoparticles

Nanometer-sized tin, Sn/R, and Sn/Si−R (R = n-C4H9), core/shell nanoparticles have been prepared by the reaction of SnCl4 or SiCl4 with Mg2Sn in ethylene glycol dimethyl ether (glyme) and subsequently with n-C4H9Li. Sn/SiO2 core/shell nanoparticles are produced from the reaction of Mg2Sn with SiCl4 and subsequent reaction with H2O2. Fourier transform Infrared (FTIR) spectra are consistent with n-butyl surface termination for the n-butyl-capped tin (Sn/n-butyl) and the silicon-n-butyl capped tin (Sn/Si-n-butyl) core/shell nanoparticles. High-resolution transmission electron microscope (HRTEM) confirms that the core part of Sn/n-butyl and Sn/Si- n-butyl nanoparticles is consistent with the tetragonal structure of tin, exhibiting lattice fringes of the {200} crystal plane (2.92 A). The FTIR spectrum of Sn/SiO2 confirms the evidence of silica capping and selected area electron diffraction (SAED) is consistent with an amorphous shell (SiO2) and crystalline Sn core. Solid-state nuclear magnetic resonance (NMR) ...

Synthesis and Characterization of Sn/R, Sn/Si−R, and Sn/SiO2 Core/Shell Nanoparticles

Interest in the synthesis of semiconductor nanoparticles has been generated by their unusual optical and electronic properties arising from quantum confinement effects. We have synthesized silicon and germanium nanoclusters by reacting Zintl phase precursors with either silicon or germanium tetrachloride in various solvents. Strategies have been investigated to stabilize the surface, including reactions with RLi and MgBrR (R = alkyl). This synthetic method produces group IV nanocrystals with passivated surfaces. These nanoparticle emit over a very large range in the visible region. These particles have been characterized using HRTEM, FTIR, UV-Vis, solid state NMR, and fluorescence. The synthesis and characterization of these nanoclusters will be presented.

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Qi Liu

Papers

Solution Synthesis of Alkyl- and Alkyl/Alkoxy-Capped Silicon Nanoparticles via Oxidation of Mg2Si

A new synthetic route for the synthesis of hydrogen terminated silicon nanoparticles

Synthesis and Characterization of Sn/R, Sn/Si−R, and Sn/SiO2 Core/Shell Nanoparticles

The Novel Synthesis of Silicon and Germanium Nanocrystallites