Structural investigations into colour-tuneable fluorescent InZnP-based quantum dots from zinc carboxylate and aminophosphine precursors.

Fluorescent InP-based quantum dots have emerged as valuable nanomaterials for display technologies, biological imaging, and optoelectronic applications. The inclusion of zinc can enhance both their emissive and structural properties and reduce interfacial defects with ZnS or CdS shells. However, the sub-particle distribution of zinc and the role this element plays often remains unclear, and it has previously proved challenging to synthesise Zn-alloyed InP-based nanoparticles using aminophosphine precursors. In this report, we describe the synthesis of alloyed InZnP using zinc carboxylates, achieving colour-tuneable fluorescence from the unshelled core materials, followed by a one-pot ZnS or CdS deposition using diethyldithiocarbamate precursors. Structural analysis revealed that the "core/shell" particles synthesised here were more accurately described as homogeneous extended alloys with the constituent shell elements diffusing through the entire core, including full-depth inclusion of zinc.

Scalable Patterning of Encapsulated Black Phosphorus.

Atomically thin black phosphorus (BP) has attracted considerable interest due to its unique properties, such as an infrared band gap that depends on the number of layers and excellent electronic transport characteristics. This material is known to be sensitive to light and oxygen and degrades in air unless protected with an encapsulation barrier, limiting its exploitation in electrical devices. We present a new scalable technique for nanopatterning few layered BP by direct electron beam exposure of encapsulated crystals, achieving a spatial resolution down to 6 nm. By encapsulating the BP with single layer graphene or hexagonal boron nitride (hBN), we show that a focused electron probe can be used to produce controllable local oxidation of BP through nanometre size defects created in the encapsulation layer by the electron impact. We have tested the approach in the scanning transmission electron microscope (STEM) and using industry standard electron beam lithography (EBL). Etched regions of the BP are stabilized by a thin passivation layer and demonstrate typical insulating behavior as measured at 300 and 4.3 K. This new scalable approach to nanopatterning of thin air sensitive crystals has the potential to facilitate their wider use for a variety of sensing and electronics applications.

Black phosphorus with near-superhydrophobic properties and long-term stability in aqueous media.

Black phosphorus is a two-dimensional material that has potential applications in energy storage, high frequency electronics and sensing, yet it suffers from instability in oxygenated and/or aqueous systems. Here we present the use of a polymeric stabilizer which prevents the degradation of nearly 68% of the material in aqueous media over the course of ca. 1 month.

Biosynthesis and Characterization of Copper Nanoparticles Using Shewanella oneidensis: Application for Click Chemistry.

Copper nanoparticles (Cu-NPs) have a wide range of applications as heterogeneous catalysts. In this study, a novel green biosynthesis route for producing Cu-NPs using the metal-reducing bacterium, Shewanella oneidensis is demonstrated. Thin section transmission electron microscopy shows that the Cu-NPs are predominantly intracellular and present in a typical size range of 20-40 nm. Serial block-face scanning electron microscopy demonstrates the Cu-NPs are well-dispersed across the 3D structure of the cells. X-ray absorption near-edge spectroscopy and extended X-ray absorption fine-structure spectroscopy analysis show the nanoparticles are Cu(0), however, atomic resolution images and electron energy loss spectroscopy suggest partial oxidation of the surface layer to Cu2 O upon exposure to air. The catalytic activity of the Cu-NPs is demonstrated in an archetypal "click chemistry" reaction, generating good yields during azide-alkyne cycloadditions, most likely catalyzed by the Cu(I) surface layer of the nanoparticles. Furthermore, cytochrome deletion mutants suggest a novel metal reduction system is involved in enzymatic Cu(II) reduction and Cu-NP synthesis, which is not dependent on the Mtr pathway commonly used to reduce other high oxidation state metals in this bacterium. This work demonstrates a novel, simple, green biosynthesis method for producing efficient copper nanoparticle catalysts.

Nanometer Resolution Elemental Mapping in Graphene-Based TEM Liquid Cells.

We demonstrate a new design of graphene liquid cell consisting of a thin lithographically patterned hexagonal boron nitride crystal encapsulated on both sides with graphene windows. The ultrathin window liquid cells produced have precisely controlled volumes and thicknesses and are robust to repeated vacuum cycling. This technology enables exciting new opportunities for liquid cell studies, providing a reliable platform for high resolution transmission electron microscope imaging and spectral mapping. The presence of water was confirmed using electron energy loss spectroscopy (EELS) via the detection of the oxygen K-edge and measuring the thickness of full and empty cells. We demonstrate the imaging capabilities of these liquid cells by tracking the dynamic motion and interactions of small metal nanoparticles with diameters of 0.5-5 nm. We further present an order of magnitude improvement in the analytical capabilities compared to previous liquid cell data with 1 nm spatial resolution elemental mapping achievable for liquid encapsulated bimetallic nanoparticles using energy dispersive X-ray spectroscopy (EDXS).

Solution processing of two-dimensional black phosphorus.

Phosphorene, or two-dimensional (2D) black phosphorus (BP) was the first synthetic 2D elemental allotrope beyond graphene to be isolated and studied. It is useful due to its high p-type carrier mobility and direct band gap that is tunable in the range ca. 0.3-2 eV thus bridging the energy gap between graphene and transition metal dichalcogenides such as molybdenum disulfide. Beyond the 'Scotch-Tape' method that was used to isolate the first samples of 2D BP for prototype studies, a range of potentially scalable solution processing techniques emerged later that can produce electronics grade material. This feature article focuses on such solution-process routes to 2D BP and highlights challenges in processing the material, mainly caused by its susceptibility to oxidation, as well as illuminating new avenues and opportunities in the area.

Nanostructured Aptamer-Functionalized Black Phosphorus Sensing Platform for Label-Free Detection of Myoglobin, a Cardiovascular Disease Biomarker.

We report the electrochemical detection of the redox active cardiac biomarker myoglobin (Mb) using aptamer-functionalized black phosphorus nanostructured electrodes by measuring direct electron transfer. The as-synthesized few-layer black phosphorus nanosheets have been functionalized with poly-l-lysine (PLL) to facilitate binding with generated anti-Mb DNA aptamers on nanostructured electrodes. This aptasensor platform has a record-low detection limit (∼0.524 pg mL(-1)) and sensitivity (36 µA pg(-1) mL cm(-2)) toward Mb with a dynamic response range from 1 pg mL(-1) to 16 µg mL(-1) for Mb in serum samples. This strategy opens up avenues to bedside technologies for multiplexed diagnosis of cardiovascular diseases in complex human samples.

Energy Dispersive X-ray Tomography for 3D Elemental Mapping of Individual Nanoparticles.

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial resolution, and is even capable of providing atomically resolved elemental maps. In this technique, a highly focused electron beam is incident upon a thin sample and the energy of emitted X-rays is measured in order to determine the atomic species of material within the beam path. This elementally sensitive spectroscopy technique can be extended to three dimensional tomographic imaging by acquiring multiple spectrum images with the sample tilted along an axis perpendicular to the electron beam direction. Elemental distributions within single nanoparticles are often important for determining their optical, catalytic and magnetic properties. Techniques such as X-ray tomography and slice and view energy dispersive X-ray mapping in the scanning electron microscope provide elementally sensitive three dimensional imaging but are typically limited to spatial resolutions of > 20 nm. Atom probe tomography provides near atomic resolution but preparing nanoparticle samples for atom probe analysis is often challenging. Thus, elementally sensitive techniques applied within the scanning transmission electron microscope are uniquely placed to study elemental distributions within nanoparticles of dimensions 10-100 nm. Here, energy dispersive X-ray (EDX) spectroscopy within the STEM is applied to investigate the distribution of elements in single AgAu nanoparticles. The surface segregation of both Ag and Au, at different nanoparticle compositions, has been observed.

Sequential bottom-up and top-down processing for the synthesis of transition metal dichalcogenide nanosheets: the case of rhenium disulfide (ReS2).

Bottom-up (aerosol-assisted chemical vapor deposition, AACVD) and top-down (liquid phase exfoliation, LPE) processing methodologies are used in tandem to produce colloids of few-layer thick rhenium disulfide (ReS2) in N-methyl pyrrolidone. The processing route we use is a potentially robust and scalable pathway to manufacture useful 2D materials.

Controlling Size, Morphology, and Surface Composition of AgAu Nanodendrites in 15 s for Improved Environmental Catalysis under Low Metal Loadings.

In this work, a simple but powerful method for controlling the size and surface morphology of AgAu nanodendrites is presented. Control of the number of Ag nanoparticle seeds is found to provide a fast and effective route by which to manipulate the size and morphology of nanoparticles produced via a combined galvanic replacement and reduction reaction. A lower number of Ag nanoparticle seeds leads to larger nanodendrites with the particles' outer diameter being tunable in the range of 45-148 nm. The size and surface morphology of the nanodendrites was found to directly affect their catalytic activity. Specifically, we report on the activity of these AgAu nanodendrites in catalyzing the gas-phase oxidation of benzene, toluene and o-xylene, which is an important reaction for the removal of these toxic compounds from fuels and for environmental remediation. All produced nanodendrite particles were found to be catalytically active, even at low temperatures and low metal loadings. Surprisingly, the largest nanodendrites provided the greatest percent conversion efficiencies.

Tin(II) Sulfide (SnS) Nanosheets by Liquid-Phase Exfoliation of Herzenbergite: IV-VI Main Group Two-Dimensional Atomic Crystals.

The liquid-phase exfoliation of tin(II) sulfide to produce SnS nanosheets in N-methyl-2-pyrrolidone is reported. The material is characterized by Raman spectroscopy, atomic force microscopy, lattice-resolution scanning transmission electron microscope imaging, and energy dispersive X-ray spectrum imaging. Quantum chemical calculations on the optoelectronic characteristics of bulk and 10-layer down to monolayer SnS have been performed using a quantum chemical density functional tight-binding approach. The optical properties of the SnS and centrifugally fractionated SnS nanosheet dispersions were compared to that predicted by theory. Through centrifugation, bilayer SnS nanosheets can be produced size-selectively. The scalable solution processing of semiconductor SnS nanosheets is the key to their commercial exploitation and is potentially an important step toward the realization of a future electronics industry based on two-dimensional materials.

Surface Segregated AgAu Tadpole-Shaped Nanoparticles Synthesized Via a Single Step Combined Galvanic and Citrate Reduction Reaction.

New AgAu tadpole nanocrystals were synthesized in a one-step reaction involving simultaneous galvanic replacement between Ag nanospheres and AuCl4(-)(aq.) and AuCl4(-)(aq.) reduction to Au in the presence of citrate. The AgAu tadpoles display nodular polycrystalline hollow heads, while their undulating tails are single crystals. The unusual morphology suggests an oriented attachment growth mechanism. Remarkably, a 1 nm thick Ag layer was found to segregate so as to cover the entire surface of the tadpoles. By varying the nature of the seeds (Au NPs), double-headed Au tadpoles could also be obtained. The effect of a number of reaction parameters on product morphology were explored, leading to new insights into the growth mechanisms and surface segregation behavior involved in the synthesis of bimetallic and anisotropic nanomaterials.

Surface properties of nanocrystalline PbS films deposited at the water-oil interface: a study of atmospheric aging.

Nanocrystalline thin films of PbS are obtained in a straightforward reaction by precipitation at the interface between toluene (containing a Pb precursor) and water (containing Na2S). Lead thiobiuret [Pb(SON(CN(i)Pr2)2)2] and lead diethyldithiocarbamate [Pb(S2CNEt2)2] precursors are used. The films are characterized by X-ray diffraction and electron microscopy, revealing typical particle sizes of 10-40 nm and preferred (200) orientation. Synchrotron-excited depth-profiling X-ray photoelectron spectroscopy (XPS) is used to determine the depth-dependent chemical composition as a function of surface aging in air for periods of up to 9 months. The as-synthesized films show a 1:1 Pb/S composition. Initial degradation occurs to form lead hydroxide and small quantities of surface-adsorbed -SH species. A lead-deficient Pb1-xS phase is produced as the aging proceeds. Oxidation of the sulfur occurs later to form sulfite and sulfate products that are highly localized at the surface layers of the nanocrystals. These species show logarithmic growth kinetics, demonstrating that the sulfite/sulfate layer acts to passivate the nanocrystals. Our results demonstrate that the initial reaction of the PbS nanocrystals (forming lead hydroxide) is incongruent. The results are discussed in the context of the use of PbS nanocrystals as light-harvesting elements in next-generation solar technology.

Synthesis of biocompatible Au-ZnTe core-shell nanoparticles.

A novel, solution-based route to biocompatible, cysteine-capped gold-zinc telluride (Au-ZnTe) core-shell nanoparticles with potential in biomedical applications is described. The optical properties of the core-shell nanoparticles show combined beneficial features of the individual parent components. The tunable emission properties of the semiconductor shell render the system useful for imaging and biological labeling applications. Powder X-ray diffraction analysis reveals the particles contain crystalline Au and ZnTe. Transmission electron microscope (TEM) imaging of the particles indicates they are largely spherical with sizes in the order of 2-10 nm. Elemental mapping using X-ray energy dispersive spectroscopy (XEDS) in the scanning transmission electron microscope (STEM) mode supports a core-shell morphology. The biocompatibility and cytotoxicity of the core-shells was investigated on a human pancreas adenocarcinoma (PL45) cell line using the WST-1 cell viability assay. The results showed that the core-shells had no adverse effects on the PL45 cellular proliferation or morphology. TEM imaging of PL45 cell cross sections confirmed the cellular uptake and isolation of the core-shell nanoparticles within the cytoplasm via membrane interactions. The fluorescence properties of the Au-ZnTe core-shell structures within the PL45 cell lines results confirmed their bio-imaging potential. The importance and novelty of this research lies in the combination of gold and zinc telluride used to produce a water soluble, biocompatible nanomaterial which may be exploited for drug delivery applications within the domain of oncology.

Near-unity quantum yields from chloride treated CdTe colloidal quantum dots.

Colloidal quantum dots (CQDs) are promising materials for novel light sources and solar energy conversion. However, trap states associated with the CQD surface can produce non-radiative charge recombination that significantly reduces device performance. Here a facile post-synthetic treatment of CdTe CQDs is demonstrated that uses chloride ions to achieve near-complete suppression of surface trapping, resulting in an increase of photoluminescence (PL) quantum yield (QY) from ca. 5% to up to 97.2 ± 2.5%. The effect of the treatment is characterised by absorption and PL spectroscopy, PL decay, scanning transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. This process also dramatically improves the air-stability of the CQDs: before treatment the PL is largely quenched after 1 hour of air-exposure, whilst the treated samples showed a PL QY of nearly 50% after more than 12 hours.

Production of few-layer phosphorene by liquid exfoliation of black phosphorus.

We report the liquid exfoliation of black phosphorus in N-methyl-2-pyrrolidone to form few-layer phosphorene nanosheets.

Real-time imaging and local elemental analysis of nanostructures in liquids.

A new design of in situ liquid cells is demonstrated, providing the first nanometer resolution elemental mapping of nanostructures in solution. The technique has been applied to investigate dynamic liquid-phase synthesis of core-shell nanostructures and to simultaneously image the compositional distribution for multiple elements within the resulting materials.