Synthesis Of Semiconductor Quantum Dots Research Articles

A de novo protein catalyzes the synthesis of semiconductor quantum dots

De novo proteins constructed from novel amino acid sequences are distinct from proteins that evolved in nature. Construct K (ConK) is a binary-patterned de novo designed protein that rescues Escherichia coli from otherwise toxic concentrations of copper. ConK was recently found to bind the cofactor PLP (pyridoxal phosphate, the active form of vitamin B6). Here, we show that ConK catalyzes the desulfurization of cysteine to H2S, which can be used to synthesize CdS nanocrystals in solution. The CdS nanocrystals are approximately 3nm, as measured by transmission electron microscope, with optical properties similar to those seen in chemically synthesized quantum dots. The CdS nanocrystals synthesized using ConK have slower growth rates and a different growth mechanism than those synthesized using natural biomineralization pathways. The slower growth rate yields CdS nanocrystals with two desirable properties not observed during biomineralization using natural proteins. First, CdS nanocrystals are predominantly of the zinc blende crystal phase; this is in stark contrast to natural biomineralization routes that produce a mixture of zinc blende and wurtzite phase CdS. Second, in contrast to the growth and eventual precipitation observed in natural biomineralization systems, the CdS nanocrystals produced by ConK stabilize at a final size. Future optimization of CdS nanocrystal growth using ConK-or other de novo proteins-may help to overcome the limits on nanocrystal quality typically observed from natural biomineralization by enabling the synthesis of more stable, high-quality quantum dots at room temperature.

Continuous Flow Aqueous Synthesis of Highly Luminescent AgInS2 and AgInS2/ZnS Quantum Dots

Continuous flow synthesis of semiconductor quantum dots (QDs) holds the promise of being highly reproducible, being scalable, and providing precise control of all reaction parameters. Here, we applied this technique to the aqueous synthesis of the Ag–In–S (AIS) core and AIS/ZnS core/shell QDs and optimized several parameters comprising reaction temperature, pressure, time, nature, and the ratio of precursors. Photoluminescence quantum yield (PLQY) values of 32%/44% (average/best) for the core and 77%/83% for the core/shell system have been obtained in short reaction times (8–15 min). We demonstrate by means of combined structural and optical studies that the high PLQY originates from donor–acceptor pair recombination processes, involving essentially [InAg2+ + 2VAg–] defect complexes whose formation is favored by the large excess of indium used (In:Ag ratio of 4:1), and the low reaction temperature (100–120 °C). The structural disorder is further enhanced during ZnS shell growth, which in addition to surface passivation and removal of nonradiative decay channels leads to the partial diffusion of the added zinc ions into the AIS core and the formation of ZnIn− antisite defects. The presented method provides excellent reproducibility and high scalability, facilitating the large-scale production of highly luminescent AIS/ZnS QDs.

A Facile Fabrication of CdSe/ZnS QDs-Block Copolymer Brushes-Modified Graphene Oxide Nanohybrid with Temperature-Responsive Behavior.

In this paper, we described a straightforward one-step chemical method for the synthesis of semiconductor quantum dots(QDs)—block copolymer brushes functionalized graphene oxide(GO) fluorescence nanohybrids. The azobenzene-terminated block copolymer poly(N-isopropylacrylamid)-b-poly(styrene-co-5-(2-methacryoylethyloxymethyl)-8-quinolinol)(PNIPAM-b-P(St-co-MQ)) was modified on the surface of GO sheets via host–guest interactions between β-cyclodextrin-modified GO and azobenzene moieties, and simultaneously CdSe/ZnS QDs were integrated on the block copolymer brushes through the coordination between 8-hydroxyquinoline units in the polymer brushes and CdSe/ZnS QDs. The resulting fluorescence nanohybrid exhibited dual photoluminescence at 620 nm and 526 nm, respectively, upon excitation at 380 nm and LCST-type thermo-responsive behavior which originated from the change in the PNIPAM conformation in the block copolymer brushes of GO sheets.

Properties of semiconductor GaAs nanoparticles, synthesized by combination of mechanical milling methods and chemical etching

The results of realization of the method for obtaining A3B5 nanoparticles with the help of ball-milling and additional liquid-phase etching of the single-crystal material are presented in the article. The conditions for liquid chemical etching of powders of A3B5-type semiconductors (GaAs), which based on the classical technique for polishing the semiconductor surface with a peroxide-ammonia mixture were studied. The dependence of the etching rate on the time and the use of surfactants (cetyltrimethylammonium bromide) were investigated to control the etch rate and nanoparticle sizes. The size distribution and chemical composition of the obtained nanoparticles were studied using scanning electron microscopy (BSE, EDX). This research has shown that nanoparticles A3B5, obtained by this method, have sizes from 2-5 nm, suitable for the synthesis of semiconductor quantum dots.

Colloidal Synthesis of Semiconductor Quantum Dots toward Large-Scale Production: A Review

The development of green synthetic approaches is one of the key materials challenges in moving toward semiconductor quantum dots (QDs) for large-scale production and commercial applications. This article presents a comprehensive overview on the synthesis of colloidal QDs prepared via chemical approaches in solution phase, with emphasis on green routes which possess the advantages of environment-friendly raw materials, simple operation process, and robust mass-scale production. The approaches for the synthesis of QDs in batch reactors are summarized, including hot-injection organometallic synthesis, noninjection organometallic synthesis, aqueous synthesis and biosynthesis approaches, with some of the concerns on their limitations for scale-up, followed by some continuous synthetic methods aiming for reproducible and large-scale production. Current advances in continuous synthesis of QDs by microfluidic devices, high-gravity reactors, and spray-based techniques are briefly introduced. We also provide some i...

Synthesis of CdS Quantum Dots Using Direct Plasma Injection in Liquid Phase

In this work, we introduce a new method using non-equilibrium atmospheric pressure plasma jet (N-APPJ) for the synthesis of semiconductor quantum dots in liquid media with low power consumption at room temperature. In this method, the solution containing CdSO4, Na2S2O3 and thioglycolic acid (TGA) was treated by N-APPJ. Firstly, the key role of plasma applied voltage on the power consumption and the produced plasma reactive species was considered. We then continue to demonstrate that the optical properties such as absorption and photoluminescence of cadmium sulfide quantum dots (QDs) can carefully be controlled with the plasma parameters. Here, the effects of two major plasma parameters such as the plasma applied voltage and treatment time on the size of CdS QDs were investigated. The size of nanoparticles increases with the increase of the voltage and treatment time. It was also displayed that the change of the concentration of Na2S2O3 and TGA in the solution had no significant effect on the size of QDs in plasma method. Finally, X-ray diffraction, X-ray fluorescence spectrometry and transmission electron microscopy were employed to determine the composition, size and crystallinity of prepared CdS QDs.

A facile and general route for the synthesis of semiconductor quantum dots on reduced graphene oxide sheets

Owing to its unique graphitized basal plane nanostructure and intriguing physicochemical properties, graphene is considered as an ideal support for developing nanocomposites for various applications. In this study, a facile and general method was developed for the first time to synthesize a variety of semiconductor quantum dots (SQDs) supported on reduced graphene oxide (RGO) sheets, including RGO/metal oxide and RGO/metal sulfide nanocomposites. The as-prepared nanocomposites were investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy and transmission electron microscopy. It was found that by using octadecylamine (ODA) as both reductive and dispersing agent, the resulting metal oxide and sulfide SQDs were all homogeneously decorated on the surface of RGO sheets. The optical properties of the as-synthesized RGO/SQDs nanocomposites were studied through ultraviolet-visible and photoluminescence spectroscopy. To demonstrate one potential application, the RGO/NiO nanocomposites were used as electrode materials for electrochemical supercapacitors, which exhibit enhanced capacitive performance and long cycle life. It is expected that our prepared RGO/SQDs nanocomposites could serve as promising candidates for power source, catalysis, optical sensitizer and optoelectronic applications.

Colloidal semiconductor nanocrystals: the aqueous approach

This article summarizes the main achievements and challenges in the field of the aqueous synthesis of semiconductor quantum dots in colloidal solutions. Developments in the last two decades demonstrate the great potential of this approach to synthesize nanocrystalline materials with superior properties such as strong photoluminescence, long time stability and compatibility with biological media, and the variability in assembling and self-assembling into larger structures or on surfaces. Being relatively straightforward, the aqueous approach provides some advantages such as versatility, scalability, environmental friendliness and cost effectiveness, leading in summary to very attractive application perspectives.

Investigation on one-pot hydrothermal synthesis, structural and optical properties of ZnS quantum dots

The advantage of hydrothermal synthesis of semiconductor quantum dots (QDs) over the control of particles size, morphology and stability is reported here. In a typical synthesis procedure, the zinc and sulfur precursor molar ratio of 1:3 was used in an aqueous solution at 150 °C. The cubic phase of ZnS with average particles size of 5 nm was confirmed and estimated from the X-ray diffraction (XRD) analysis. The composition and purity of the sample were analyzed from (energy dispersive-ray analysis) EDAX and (X-ray photoelectron spectroscopy analysis) XPS spectra. The absorption spectrum shows the large shift in the absorption band over 90 nm due to the quantum confinement of carriers. The emission spectrum of quantum dots carry more evidence on the presence of shallow trap, deep trap in the band gap of the material responsible for weak emission in the spectral region of 450–500 nm. High resolution transmission electron microscope and scanning electron microscope studies reveal the structural and morphological features of ZnS with slightly distorted spherical morphology. We found that the coordinating ability of solvent strongly influences the reaction process and morphology of the products.

Microwave mediated synthesis of semiconductor quantum dots

AbstractColloidal quantum dots (QD) have tuneable optoelectronic properties and can be easily handled by simple solution processing techniques, making them very attractive for a wide range of applications. Over the past decade synthesis of morphology controlled high quality (crystalline, monodisperse) colloidal QDs by thermal decomposition of organometallic precursors has matured and is well studied. Recently, synthesis of colloidal QDs by microwave irradiation as heating source is being studied due to the inherently different mechanisms of heat transfer, when compared to solvent convection based heating. Under microwave irradiation, polar precursor molecules directly absorb the microwave energy and heat up more efficiently. Here we report synthesis of colloidal II‐VI semiconductor QDs (CdS, CdSe, CdTe) by microwave irradiation and compare it with conventional synthesis based on convection heating. Our findings show that QD synthesis by microwave heating is more efficient and the chalcogenide precursor strongly absorbs the microwave radiation shortening the reaction time and giving a high reaction yield (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of Extremely Small CdSe and Bright Blue Luminescent CdSe/ZnS Nanoparticles by a Prefocused Hot-Injection Approach

Although cadmium selenide is a well-explored material in aqueous and hot-injection synthesis of semiconductor quantum dots, only a few syntheses are reported for the preparation of extremely small cadmium selenide nanocrystallites. We present a hot-injection approach based on the enhancement of the nucleation rate to make cadmium selenide quantum dots with a diameter tunable between 1.5 and 2.2 nm. Furthermore, we present a procedure on how to coat these particles with zinc sulfide, leading to highly efficient fluorophors in the blue region of the visible spectrum. The work was performed without the use of highly reactive (pyrophoric) precursors and represents a basic concept for the preparation of small nanoparticles in general.

Bandgap Engineering and Doping of ZnO and ZnOS Nanocrystals

An active dopant modulates the property of semiconductor and thereby provides the precise control of device parameters. On the other hand if a dopant is incorporated in 2 to 5 nm size nanocrystal, the luminescent and other properties of the dopant are strongly a ected by the quantum con nement provided by the dielectric boundary of the nanocrystal. The dopant in a nanocrystal, henceforth referred as quantum con ned atom (QCA), generates high luminous e ciency [1{3]. This high e ciency suggests that only a single dopant per nanocrystal was incorporated [4{6] since two or more such dopants per nanocrystal would lead to known phenomena of concentration quenching and drastically reduce the quantum e ciency. Synthesis of semiconductor quantum dots has generated immense research e ort because of their unusual optical properties based on quantum con nement e ects. The breakthrough of incorporating a single Mn2+ activator (dopant) in a nanocrystal was rst demonstrated in II-VI semiconductor ZnS [1]. Two key observations were reported; rst that high luminescent e ciency of Mn2+ emission was achieved in nanocrystals of ZnS in the size range of 2 to 5 nm and second the luminescent life time of the Mn2+ emission was reduced by several orders of magnitude. Several groups later were unable to con rm the life time shortening [7]. The key reason was that both high e ciency and life-time shortening of dopant-based luminescence were a result of quantum con nement imposed on the dopant that modulates the luminescent properties and these properties are observed only in nanocrystals of sizes less than 5 nm that contain a single dopant QCA. Besomes et al. [8] have recently studied the e ect of a

Green Chemistry for Large-Scale Synthesis of Semiconductor Quantum Dots

Large-scale synthesis of semiconductor nanocrystals or quantum dots (QDs) with high concentration and high yield through simultaneously increasing the precursor concentration was introduced. This synthetic route conducted in diesel has produced gram-scale CdSe semiconductor quantum dots (In optimal scale-up synthetic condition, the one-pot yield of QDs is up to 9.6g). The reaction has been conducted in open air and at relatively low temperature at 190-230 degrees C in the absence of expensive organic phosphine ligands, aliphatic amine and octadecene, which is really green chemistry without high energy cost for high temperature reaction and unessential toxic chemicals except for Cd, which is the essential building block for QDs.