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International audience; After the use of nanocrystals as light down-converters, infrared sensing appears to be one of the first market applications where they can be used while being both electrically and optically active. Over recent years, tremendous progress has been achieved, leading to an apparent rise in the technological readiness level (TRL). So far, the efforts have been focused on PbS nanocrystals for operation in the near-infrared. Here, we focus on HgTe since its narrower band gap offers more flexibility to explore the extended shortwave and mid-wave infrared. We report a photoconductive strategy fort the design of short wave infrared focal plane array with enhanced image quality. An important aspect often swept under the rug at an early stage is the material stability. It appears that HgTe remains mostly unaffected by oxidation under air operation. The evaporation of Hg, a potentially dramatic aging process, only occurs at temperatures far beyond the focal plane array's standard working temperature. The main bottleneck appears to be the particle sintering resulting from joule heating of focal plane array. This suggests that a cooling system is required, with a first role of preventing the material from sintering even before targeting dark current reduction.

Although order is a defining characteristic of crystals, disordered structures─especially near interfaces─often govern a material’s performance. For example, the interfaces in batteries, coatings, ...

Among iron oxide phases, magnetite Fe3O4 is often the preferred one for nanotechnological and biomedical applications because of its high saturation magnetization and low toxicity. Although there are several synthetic routes that attempt to reach magnetite nanoparticles NPs , they are usually referred as IONPs iron oxide NPs due to the great difficulty in obtaining the monophasic and stoichiometric Fe3O4 phase. Added to this problem is the common increase of size shape polydispersity when larger NPs D gt; 20 nm are synthesized. An unequivocal correlation between a nanomaterial and its properties can only be achieved by the production of highly homogeneous systems, which, in turn, is only possible by the continuous improvement of synthesis methods. There is no doubt that solving the compositional heterogeneity of IONPs while keeping them monodisperse remains a challenge for synthetic chemistry. Herein, we present a methodical optimization of the iron oleate decomposition method to obtain Fe3O4 single nanocrystals without any trace of secondary phases and with no need of postsynthetic treatment. The average dimension of the NPs, ranging from 20 to 40 nm, has been tailored by adjusting the total volume and the boiling point of the reaction mixture. Mössbauer spectroscopy and DC magnetometry have revealed that the NPs present a perfectly stoichiometric Fe3O4 phase. The high saturation magnetization 93 2 A m2 kg at RT and the extremely sharp Verwey transition at around 120 K shown by these NPs have no precedent. Moreover, the synthesis method has been refined to obtain NPs with octahedral morphology and suitable magnetic anisotropy, which significantly improves the magnetic hyperthemia performance. The heating power of properly PEGylated nano octahedrons has been investigated by AC magnetometry, confirming that the NPs present negligible dipolar interactions, which leads to an outstanding magnetothermal efficiency that does not change when the NPs are dispersed in environments with high viscosity and ionic strength. Additionally, the heat production of the NPs within physiological media has been directly measured by calorimetry under clinically safe conditions, reasserting the excellent adequacy of the system for hyperthermia therapies. To the best of our knowledge, this is the first time that such bulklike magnetite NPs with minimal size shape polydispersity, minor agglomeration, and exceptional heating power are chemically synthesized

We have investigated the transformations of colloidal Pd-Cu and Pt-Cu bimetallic alloy nanocrystals (NCs) supported on γ-Al2O3 when exposed to a sequence of oxidizing and then reducing atmospheres, in both cases at high temperature (350 °C). A combination of in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption spectroscopy was employed to probe the NC surface chemistry and structural/compositional variations in response to the different test conditions. Depending on the type of noble metal in the bimetallic NCs (whether Pd or Pt), different outcomes were observed. The oxidizing treatment on Pd-Cu NCs led to the formation of a PdCuO mixed oxide and PdO along with a minor fraction of CuO x species on the support. The same treatment on Pt-Cu NCs caused a complete dealloying between Pt and Cu, forming separate Pt NCs with a minor fraction of PtO NCs and CuO x species, the latter finely dispersed on the support. The reducing treatment that followed the oxidizing treatment largely restored the Pd-Cu alloy NCs, although with a residual fraction of CuO x species remaining. Similarly, Pt-Cu NCs were partially restored but with a large fraction of CuO x species still located on the support. Our results indicate that the noble metal present in the bimetallic Cu-based alloy NCs has a strong influence on the dealloying/migrations/realloying processes occurring under typical heterogeneous catalytic reactions, elucidating the structural/compositional variations of these NCs depending on the atmospheres to which they are exposed.

International audience

Nanocrystals of doped semiconductors, such as Cu_(2-x)S, hold much promise for near infrared active devices because, unlike in noble metals, their tunable infrared plasmon can exist in nanocrystals with diameters

Chemistry of materials 13(16), 6553 – 6563 (2021). doi:10.1021/acs.chemmater.1c02159, During the self-organization of colloidal semiconductor nanoparticles by solvent evaporation, nanoparticle interactions are substantially determined by the organic ligands covering the inorganic core. However, the influence of the ligand grafting density on the assembly pathway is often not considered in experiments. Here, we carry out an in situ synchrotron small-angle X-ray scattering and X-ray cross-correlation analysis study of the real-time assembly of oleic acid-capped PbS nanocrystals at a low ligand coverage of 2.7 molecules/nm2. With high temporal and spatial resolution, we monitor the transitions from the colloidal suspension through the solvated superlattice states into the final dried superstructure. In a single in situ experiment, we observe a two-dimensional hexagonal, hexagonal close-packed, body-centered cubic, body-centered tetragonal (with different degrees of tetragonal distortion), and face-centered cubic superlattice phases. Our results are compared to the self-organization of PbS nanocrystals with a higher ligand coverage up to 4.5 molecules/nm2, revealing different assembly pathways. This highlights the importance of determining the ligand coverage in assembly experiments to approach a complete understanding of the assembly mechanism as well as to be able to predict and produce the targeted superstructures., Published by American Chemical Society, Washington, DC

Nanocrystal heterostructures are one of the frontline energy materials widely known for enhancing the rate of photocatalysis and tuning optical properties and are also used in photovoltaics. These nanostructures where two crystalline nanomaterials are placed together in a single building block and share lattices are extensively studied for chalcogenide semiconductors and metal oxides but limited for recently emerged perovskite nanocrystals. Due to differences in the crystal bonding nature, interface chemistry, and also the formation mechanism, some constraints are present in designing common reaction pathways for the simultaneous formation of perovskites and chalcogenides or similar nanocrystals sharing common lattice planes. Hence, more fundamental understanding of both nucleation and growth of both materials is required for inducing heteronucleations of one on the surface of another. Literature reports also revealed that epitaxial growth of lead halide perovskites with nonhalide or chalcogenide colloidal 0D nanocrystals could not be established yet. Hence, the field remains challenging, and more investigations on both experimental as well as theoretical studies are timely required. Keeping these in mind, in this perspective the state-of-the-art issues related to the formation of all inorganic halides and nonhalide heterostructures formed with epitaxial relations are discussed. At the beginning, the chemistry of these nanocrystals with similarities and dissimilarities in their nature and examples of different heterostructures are summarized, and then, different synthetic possibilities for overtaking the hurdles and designing such heterostructures are proposed.

Inorganic lead halide perovskite nanocrystals (NCs) are an exciting class of luminescent materials with high defect tolerance and broad spectral tunability, but such NCs are vulnerable to degradati...

Despite significant progress in controlling the synthesis of noble-metal nanocrystals, the purity and uniformity of many products are still plagued by the unwanted nucleation events taking place in...

Shell growth around nanocrystal cores is the most efficient way to passivate their surface in order to improve their stability and optical properties. Due to the different atomic arrangements and c...

While manganese (Mn2+)-doped chalcogenide and perovskite CsPbX3 nanocrystals (NCs) have been extensively investigated, the research of color-tunable dual-emissive Mn2+-incorporated two-dimensional ...

Property of the nanocrystals’ surface structure plays a key role in developing novel nanomaterials with high performance and new functionalities. Conventional methods of nanocrystal surface enginee...

Despite many seeded methods having been achieved to synthesize spherical nanoparticles, the one-pot synthesis of Au nanospheres with perfect morphology is still a challenge due to nanocrystals tend...

Doped metal oxide nanocrystals (NCs) exhibit tunable localized surface plasmon resonances (LSPRs) in the infrared spectral region. Compared to the binary oxides commonly studied, plasmonic NCs deri...

Manipulation of material composition can often induce unprecedented optoelectronic changes in semiconductor nanocrystals (NCs). Here, we demonstrate that bornite-phase copper iron sulfide (Cu5FeS4)...

Colloidal copper phosphide (Cu3–xP) nanocrystals are attractive materials because of their ability to support excess delocalized holes, leading to localized surface plasmon resonance (LSPR) absorpt...

PbS colloidal quantum dots (CQDs) are versatile building blocks for bottom-up fabrication of various optoelectronic devices. The transport properties of thin films of this class of materials depend on the size of the CQDs, their surface ligands, and stoichiometry. The most common synthetic methods yield PbS CQDs with an excess of Pb atoms, which induces n-type transport properties in CQD films. In this work, we developed a new synthesis, which offers S-rich PbS CQDs. Thanks to their sufficient colloidal stability in nonpolar solvents, we established a protocol for the integration of these CQDs into thin field-effect transistors and found strong hole-dominated transport with a hole mobility of about 1 × 10–2 cm2/Vs. Moreover, we were able to enhance the electron mobility for almost two orders of magnitude while keeping the hole mobility nearly the same. This approach allows us to obtain reliably p-doped PbS CQDs, which can be used for the fabrication of various electronic and optoelectronic devices., Chemistry of Materials, 33 (1), ISSN:0897-4756

Inorganic perovskite nanocrystals (NCs) have shown good potential as an emerging semiconducting building block owing to their excellent optoelectronic properties. However, despite extensive studies on their structure-dependent optical properties, they still suffer severely from chemical and phase instabilities in ambient conditions. Here, we report a facile method for the synthesis of mixed halide inorganic perovskite NCs based on recrystallization in an antisolvent mixture in an ambient atmosphere, at room temperature. We introduced an alcohol-derivative solvent, as a secondary antisolvent in the solvent mixture, which crystallizes at room temperature. This mediates and facilitates the perovskite crystallization, leading to a high chemical yield and stability. We demonstrate that this secondary antisolvent establishes intermolecular interactions with lead halide salt, which successfully stabilizes the γ-dark phase of perovskite by encapsulating NCs in a solution and thin film. This allows us to produce concentrated NC solutions with a photoluminescence quantum yield of 70%. Finally, we fabricate CsPbI2Br NCs (optical bandgap 1.88 eV) solar cells, which showed a stabilized photovoltaic performance in ambient conditions, without encapsulation, showing a Voc of 1.32 V.

Plasmonic semiconductor nanocrystals have become an appealing avenue for researching nanoscale plasmonic effects due to their wide spectral range (visible to infrared) and great tunability compared...

Colloid immobilization is an established way to load metal nanocrystals (NCs) onto solid supports to make heterogeneous (photo)catalysts. The use of preformed colloidal NCs enables excellent contro...

Oleylamine (OLA) is a ubiquitous organic ligand used in the synthesis of inorganic nanocrystals (NCs) due to its ability to reduce metal precursors and sterically stabilize NCs. However, attempts t...

Complex, anisotropic nanocrystals made from two or more components are extremely interesting functional materials that can drive directional, light-activated processes like charge separation and ph...

Transition-metal phosphide (TMP) nanostructures have been extensively studied for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, phase-controlled synthesis of collo...

Perovskite nanocrystals (NCs) are promising light-emitting materials for next-generation illuminations and displays. The main challenge for practical applications is to achieve high durability. Her...

Various strategies have been proposed to engineer the band gap of metal halide perovskite nanocrystals (NCs) while preserving their structure and composition and thus ensuring spectral stability of the emission color. An aspect that has only been marginally investigated is how the type of surface passivation influences the structural/color stability of AMX3 perovskite NCs composed of two different M2+ cations. Here, we report the synthesis of blue-emitting Cs-oleate capped CsCdxPb1-xBr3 NCs, which exhibit a cubic perovskite phase containing also Cd-rich domains of Ruddlesden-Popper phases (RP- phases). The RP domains spontaneously transforms into pure orthorhombic perovskite ones upon NC ageing and the emission color of the NCs shifts from blue to green over days. On the other hand, post-synthesis ligand exchange with various Cs-carboxylate or ammonium bromide salts, right after NC synthesis, provides monocrystalline NCs with cubic phase, highlighting the metastability of the RP domains. When the NCs are treated with Cs-carboxylates (including Cs-oleate), most of the Cd2+ ions are expelled from the NCs, the NCs’ phase evolves from cubic to orthorhombic and their emission color changes from blue to green. Instead, when the NCs are coated with ammonium bromides, the loss of Cd2+ ions is suppressed and the NCs tend to retain their blue emission (both in colloidal dispersions and in electroluminescent devices), as well as their cubic phase, over time. The improved compositional and structural stability in these latter cases is ascribed to the saturation of surface vacancies, which may act as channels for the expulsion of Cd2+ ions from the NCs.

Bi3+ and Sb3+ doping (and codoping with lanthanides) in Cs2SnCl6 vacancy ordered perovskites and Cs2MInCl6 (M = Na, K, Ag) double perovskites has been shown to open up new opportunities for solid s...

AgBiS2 nanocrystals (NCs) have emerged as attractive absorbers in eco-friendly photovoltaics because of their nontoxic components and high absorption coefficient. Native long-chain ligands of AgBiS...

Exploring novel photonic materials with efficient nonlinear optical response is of great significance for ultrafast photonics. The effective defect control approach is a promising technique for the...

Plasmonic metal oxide nanocrystals are interesting electrochromic materials because they display high modulation of infrared light, fast switching kinetics, and durability. Nanocrystals facilitate ...

The amine-ligated magic-size nanoclusters [(II-VI)13(n-octylamine)13] (II–VI = CdSe and CdTe) and acids HX (X = OBz, OAc, NO3, Br, and Cl where OBz = benzoate and OAc = acetate) react to afford cry...

Plasmonic band-stop filters with tunable optical absorbance in the near- and mid-IR are important for wireless communications, bioimaging, and filtering applications. However, their design is const...

Two-dimensional (2D) molybdenum disulfide (MoS2) has excellent electrocatalytic behavior for the hydrogen evolution reaction (HER), where the catalysis of 2H phase originates from its edges, defects, and strains. Most synthetic methods to activate the electrochemically inert basal planes with catalytic active metals are completed by sequential steps. However, this is extremely time-consuming and lacks production scalability. Herein, we develop a one-step strategy to achieve efficient electrocatalyst of Pt:MoS2 hybrid utilizing atmospheric pressure chemical vapor deposition synthesis on a conductive glassy carbon (GC) plate that can be directly employed as the working electrode in the HER. The monolayer thickness ensures decreased interlayer electron hopping and increased efficiency of the charge transfer from the electrode. We tune the domain morphology by controlling the precursor flux to enter kinetic or thermodynamic growth regime, delivering dendritic or triangular shape. The materials chemistry undertaken provides fundamental insights into the instability of Pt as metal substitutional dopants in the MoS2 lattice, and instead the stable configuration observed is with Pt as highly dispersed small nanocrystals and single atoms bound to the MoS2 surface. The Pt functionalization at a reduced loading level modulates the favorable HER pathway and triggers synergies in the cocatalyst, which exhibits an onset potential of 48 mV, a Tafel slope of 46 mV dec–1, and an exchange current density of 110 μA cm–2. The enriched edges and defects of dendrite endow it superiority to the triangle, with regard to the density of catalytic sites and synergistic effects along with electrical resistance. These underpin the positive role of a large dendritic MoS2 monolayer as a Pt scaffold in water electrolysis.

EuS and related ferromagnetic semiconductors have long been model materials for spintronic device functionality because of their ability to generate highly spin-polarized electrical currents. Altho...

A wide range of material properties can be accessed by tuning the size and shape of nanocrystals (NCs). Cations incorporated into the crystal lattice of indium oxide (In2O3) NCs as dopants have bee...

International audience; To understand the importance of the particle size on the stabilization of metastable tetragonal ZrO2, ultrafine ZrO2 nanocrystals were synthesized via (i) the precipitation method in supercritical water using nitrate precursors, (ii) the sol–gel method in a supercritical ethanol–water mixture, and (iii) the borderline nonhydrolytic sol–gel route in supercritical ethanol using propoxide precursors. The obtained nanocrystals displayed a variation of the monoclinic versus tetragonal molar fractions from 100 wt % down to ≈10 wt % of monoclinic phase. This variation was concomitant with an overall size decrease of the nanocrystals, ranging from 7 to 2 nm depending on the synthesis procedures. Phase contents were quantified by refinement analysis of X-ray scattering data sets and crosschecked with Raman spectroscopy. Our results suggest that an upper limit of ≈90 wt % of the tetragonal ZrO2 phase is possible, even for ultrafine nanoparticles (2 nm). These findings thus question the existence of any critical size limit below which stabilization of pure t-ZrO2 is attainable at low temperatures.

Metal halide perovskites have attracted substantial interest because of their promising properties for optoelectronic applications. Despite much progress made in the field, the exact growth mechani...

Colloidal halide perovskite nanocrystals (NCs) have the possibility of easy scale-up due to their batch synthesis and have demonstrated excellent optoelectronic properties. In particular, perovskit...

A range of different copper-based sulfide shells, such as CuInS2, CuInZnS2, CuInS2-xSex, and CuInZnS2-xSex, have been grown on CuInSe2 (CISe) nanocrystals (NCs) in order to improve their photolumin...