Design of novel compositionally controlled hybrid and ternary nanostructures

[eng] The size/shape dependent and unique physical and chemical properties presented by nanostructured materials have attracted great attention in several fields such as energy harvesting, optoelectronics and biomedicine, among others. Even though binary semiconductors have been some of the most studied systems until now, ternary and quaternary semiconductors have started to stand out due to the wide variety of compositions and, as a result, of properties they offer. The importance of hybrid nanomaterials is growing as well: the association of more than one material in the same nanostructure usually allows the preservation or even, the enhancement, of the different properties of the preliminary materials and combines them with the new ones originated from the interaction between the two domains. This thesis is focused on the design of novel compositionally controlled hybrid and ternary nanostructures based on low toxic materials. Firstly, a simple procedure at room temperature is reported for the synthesis of hybrid and ternary nanostructures of Ag-Au-Se and Ag-Au-S. The method consists in the reaction between pre-synthesised Ag2Se/Ag2S nanoparticles (NPs) and a Au(III) precursor. The reaction time, the concentration of gold solution, the surfactant nature and the Ag:Au ratio are the four key parameters that allow the control of the final product. Regarding the Ag-Au-Se system, Au-Ag2Se hybrid nanoparticles (HNPs), Au-Ag3AuSe2 HNPs and Ag3AuSe2 NPs were successfully synthesised. In addition, Au-Ag3AuSe2 HNPs were tested as thermoelectric material, obtaining an improved response in comparison with the binary material (Ag2Se). The potential of Ag3AuSe2 NPs as Computed Tomography contrast agents was also tested, obtaining promising results in this field. Concerning to the analogous system with sulphur, the higher miscibility of Au and S offers a more complex ternary diagram, with two ternary materials with different stoichiometries: Ag3AuS2 and AgAuS. A gradual transformation of Ag2S to Au2S was achievable by the proposed method, with the possibility of isolating Au-Ag2S HNPs, Au-Ag3AuS2 HNPs, Au-AgAuS HNPs, Au-Au2S HNPs and hollow Au2S NPs. Secondly, another ternary system was studied: Ag-Cu-S. Even though this system also presents two different ternary materials (Ag3CuS2 and AgCuS), the direct hot injection method proposed here only allows the formation of the AgCuS stoichiometry. Two different mechanisms are reported, depending on the precursor of copper used in the synthesis. The material was thermoelectrically characterized as well, but without showing a proper performance. Thirdly, four novel nanostructures based on Cu-Pt-Se are described. They were synthesised by a reaction at high temperature between pre-synthesised Cu2-xSe NPs and a Pt(II) precursor. The nanomaterials were thoroughly structurally and morphologically characterized to study the impact of the Pt:Cu ratio in the final product. The larger the amount of platinum in the structure, the more efficient diffusion of the element occurs through the Cu-Se lattice, with the consequent and slow spell of selenium until its totality. Finally, hybrophilic hybrid inorganic-organic nanocomposites formed by inorganic NPs (Au, Ag, Ag3AuSe2 i Au@Fe3O4) and a highly fluorescent low molecular weight Au(I) metallogelator are presented. Their coupling is mainly based on aurophilic/metallophilic interactions between atoms in the surface of the NPs and Au(I) atoms from the complex. Additionally, the Ag and Au nanocomposites were characterized by Raman Spectroscopy. It is well known that when a molecule is strongly coupled to a plasmonic nanoparticle, the intensity of the Raman peaks of the molecule are intensified. This phenomenon is known as Surface-Enhanced Raman Spectroscopy (SERS) and could be observed in both materials. In summary, in this thesis five hybrid and ternary nanostructured systems, based on low toxic materials, have been synthesised, characterized and studied, following the aim of investigate alternative materials, which, in a future, could be applied in energy conversion and biomedicine fields.[cat] En els últims anys, els materials ternaris i híbrids han començat a sorgir gràcies al gran ventall de composicions i, per tant, de propietats que ofereixen i que els donen la possibilitat d’aplicar-se en diversos camps, com ara l’emmagatzematge d’energia, l’optoelectrònica o la biomedicina. Aquesta tesis està centrada en el disseny de noves nanoestructures ternàries i híbrides basades en materials amb una toxicitat baixa. En primer lloc, s’ha descrit un procediment simple a temperatura ambient per la síntesi de nanoestructures ternàries i híbrides d’Ag-Au-Se i d’Ag-Au-S que consisteix en la reacció entre nanopartícules d’Ag2Se i Ag2S sintetitzades prèviament i un precursor d’Au(III). El temps de reacció, la concentració del precursor d’or, la naturalesa del tensioactiu i la relació Ag:Au són els quatre paràmetres clau que permeten el control del producte final. Addicionalment, dos compostos del sistema Ag-Au-Se van ser caracteritzats termoelèctricament i com a agents de contrast en tomografia computada. En segon lloc, s’ha estudiat un altre sistema ternari, format per Ag-Cu-S. El mètode d’injecció en calent proposat en aquesta tesi permet la formació del material amb estequiometria AgCuS. El material va ser caracteritzat termoelèctricament, tot i que no mostra resultats satisfactoris degut a la seva baixa conductivitat elèctrica. En tercer lloc, es presenten quatre nanoestructures noves basades en Cu, Pt i Se, sintetitzades mitjançant una reacció a alta temperatura entre NPs de Cu2-xSe sintetitzades prèviament i un precursor de Pt(II). L’impacte de la relació Pt:Cu utilitzada en la síntesi en el producte final va ser estudiada. A mesura que la quantitat de platí augmenta en l’estructura, aquest es va introduint més eficientment en la xarxa cristal·lina del semiconductor de coure i seleni, expulsant gradual i lentament el seleni fins a la totalitat, augmentant així el caràcter metàl·lic de les nanoestructures finals. Finalment, es descriuen uns compostos híbrids hidrofílics, formats a partir de NPs inorgàniques (Au, Ag, Ag3AuSe2 i Au@Fe3O4) i un complex d’Au(I) de baix pes molecular i altament fluorescent. El seu acoblament està basat, essencialment, en interaccions aurofíliques/metal·lofíques entre els àtoms de la superfície de la nanopartícula i els àtoms d’Au(I) del complex

Síntesi de nanoestructures híbrides. Au-semiconductor

Màster en Química de Materials Aplicada, Facultat de Química. Curs: 2012-2013, Tutor: Albert Figuerola SilvestreEn els últims anys el camp de les nanoestructures està esdevenint un dels més estudiats arreu degut a les noves i fascinants propietats que ofereixen aquests materials, diferents de les dels materials bulk anàlegs. Les més destacables són la fluorescència observada en quantum dots (QDs) de materials semiconductors i en nanopartícules (NPs) dopades amb terres rares, les propietats superparamagnètiques que solen presentar per exemple els nanocristalls d'òxid de ferro i les propietats plasmòniques que exhibeixen generalment la majoria de NPs de metalls nobles. A més, aquestes propietats depenen de la mida i la forma de les NPs. Aquest treball es centra en dos d’aquests tipus de materials: QDs de semiconductors i NPs d’or

Hybrid 2D-QD MoS2–PbSe quantum dot broadband photodetectors with high-sensitivity and room-temperature operation at 2.5 µm

Broadband infrared photodetectors have profound importance in diverse applications including security, gas sensing, bioimaging, spectroscopy for food quality, and recycling, just to name a few. Yet, these applications can currently be served by expensive epitaxially grown photodetectors, limiting their market potential and social impact. The use of colloidal quantum dots (CQDs) and 2D materials in a hybrid layout is an attractive alternative to design low-cost complementary metal-oxide-semiconductor (CMOS) compatible infrared photodetectors. However, the spectral sensitivity of these conventional hybrid detectors is restricted to 2.1 µm. Herein, a hybrid structure comprising molybdenum disulfide (MoS2) with lead selenide (PbSe) CQDs is presented to extend their sensitivity further toward the mid-wave infrared, up to 3 µm. A room-temperature responsivity of 137.6 A/W and a detectivity of 7.7 × 10^10 Jones are achieved at 2.55 µm owing to highly efficient photoexcited carrier separation at the interface of MoS2 and PbSe in combination with an oxide coating to reduce dark current; the highest value is yet for a PbSe-based hybrid device. These findings strongly support the successful fabrication of hybrid devices, which may pave the pathway for cost-effective, high-performance, next-generation, novel photodetectors.The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research (grant agreement no. 725165) as well as Graphene Flagship under Grant Agreement Nr. 881603 (Core3). The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO), and the “Fondo Europeo de Desarrollo Regional” (FEDER) through grant TEC2017-88655-R, from the Spanish State Research Agency through the “Severo Ochoa” program for Centers of Excellence in R&D (CEX2019-000910-S), from Fundació Cellex, Fundació Mir-Puig, and from Generalitat de Catalunya through the CERCA program.Peer ReviewedPostprint (author's final draft

Highly water-stable rare ternary Ag-Au-Se nanocomposites as long blood term X-rays computed tomography contrast agents

X-ray computed tomography (CT) is a powerful and widely used medical non-invasive technique that requires intravenously administration of contrast agents to enhance the sensitivity and visualization of soft tissues. In this work, we have developed a novel CT contrast agent based on ternary Ag-Au-Se chalcogenide nanoparticles. A facile and gentle ligand exchange by using a 3 kDa PEGylated ligand with a dithiol dihydrolipoic as an anchor resulted in highly water-soluble and monodisperse nanoparticles. Moreover, the injected PEGylated ternary NPs presented excellent characteristics as a CT contrast agent with high bioavailability, low cytotoxicity and long blood circulation times with slow uptake by the mononuclear phagocyte system, thus being ideal for in vivo imaging

Preparation and antitumoral activity of au-based inorganic-organometallic nanocomposites

The synergy between gelator molecules and nanostructured materials is currently a novel matter of study. The possibility to carefully design the skeleton of the molecular entity as well as the nanostructure's morphological and chemical features offers the possibility to prepare a huge variety of nanocomposites with properties potentially different than just the sum of those of the individual building blocks. Here we describe the synthesis and characterization of nanocomposites made by the unconventional combination of phosphine-Au(I)-alkynyl-based organometallic gelating molecules and plasmonic Au nanoparticles. Our results indicate that the interaction between the two moieties leads to a significant degree of aggregation in both hydrophilic and hydrophobic media, either when using DAPTA or PTA-based organometallic molecules, with the formation of a sponge-like hybrid powder upon solvent evaporation. The biological activity of the nanocomposites was assessed, suggesting the existence of a synergetic effect evidenced by the higher cytotoxicity of the hybrid systems with respect to that of any of their isolated counterparts. These results represent a preliminary proof-of-concept for the exploitation of these novel nanocomposites in the biomedical field

Single-exciton gain and stimulated emission across the infrared telecom band from robust heavily doped PbS colloidal quantum dots

Materials with optical gain in the infrared are of paramount importance for optical communications, medical diagnostics, and silicon photonics. The current technology is based either on costly III-V semiconductors that are not monolithic to silicon CMOS technology or Er-doped fiber technology that does not make use of the full fiber transparency window. Colloidal quantum dots (CQDs) offer a unique opportunity as an optical gain medium in view of their tunable bandgap, solution processability, and CMOS compatibility. The 8-fold degeneracy of infrared CQDs based on Pb-chalcogenides has hindered the demonstration of low-threshold optical gain and lasing, at room temperature. We demonstrate room-temperature, infrared, size-tunable, band-edge stimulated emission with a line width of ~14 meV. Leveraging robust electronic doping and charge-exciton interactions in PbS CQD thin films, we reach a gain threshold at the single exciton regime representing a 4-fold reduction from the theoretical limit of an 8-fold degenerate system, with a net modal gain in excess of 100 cm-1.The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER) through grant TEC2017- 88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA, and from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0522). S.C. acknowledges support from a Marie Curie Standard European Fellowship (NAROBAND, H2020-MSCA-IF-2016-750600). I.R. acknowledges support from the Ministerio de Economiá , Industria y Competitividad of Spain via a Juan de la Cierva fellowship. We are also thankful to Dr. Kaifen Wu for fruitful discussions.Peer ReviewedPostprint (published version

Facile morphology control of gold(0) structures from aurophilic assemblies

Different gold microstructures have been synthesized by using supramolecular gold(I) organometallic compounds as templates and Ag nanoparticles as reducing agent. The use of fibers resulting from supramolecular assemblies of neutral gold(I) compounds, gives rise to the formation of microrods. The use of supramolecular assemblies from ionic molecules results in spherical or square-based prisms gold microstructures, depending on the shape of the supramolecular gold(I) precursor assembly. In addition to temperature and reaction time, the solvent has a strong influence on the formation and morphology of the gold structures. Well-defined star-like morphologies have been obtained in chloroform

Monitoring the insertion of Pt into Cu2−xSe nanocrystals: a combined structural and chemical approach for the analysis of new ternary phases

The tuning of the chemical composition in nanostructures is a key aspect to control for the preparation of new multifunctional and highly performing materials. The modification of Cu2−xSe nanocrystals with Pt could provide a good way to tune both optical and catalytic properties of the structure. Although the heterogeneous nucleation of metallic Pt domains on semiconductor chalcogenides has been frequently reported, the insertion of Pt into chalcogenide materials has not been conceived so far. In this work we have explored the experimental conditions to facilitate and enhance the insertion of Pt into the Cu2−xSe nanocrystalline lattice, forming novel ternary phases that show a high degree of miscibility and compositional variability. Our results show that Pt is mainly found as a pure metal or a CuPt alloy at high Pt loads (Pt : Cu atomic ratio in reaction medium >1). However, two main ternary CuPtSe phases with cubic and monoclinic symmetry can be identified when working at lower Pt : Cu atomic ratios. Their structure and chemical composition have been studied by local STEM-EDS and HRTEM analyses. The samples containing ternary domains have been loaded on graphite-like C3N4 (g-C3N4) semiconductor layers, and the resulting nanocomposite materials have been tested as promising photocatalysts for the production of H2 from aqueous ethanolic solutions

Gradual transformation of Ag2S to Au2S nanoparticles by sequential cation exchange reactions: binary, ternary, and hybrid compositions

Cation exchange reactions have been exploited in the last years as an efficient tool for the controlled chemical modi-fication of pre-made nanocrystals. In this work, the gradual transformation of Ag2S nanocrystals into Au2S analogues is performed by sequential cation exchange reactions that allow for a fine control of the chemical composition, delivering also two intermediate ternary sulfides based exclusively on noble metals. The role of two different surfactants in the reaction medium has been studied: while dodecylamine is favoring the heterogeneous nucleation of metallic Au on the surface of the semiconductor domains in detri-ment of the cation exchange reaction, the use of tetraoctylammonium bromide turns out to be crucial for the enhancement of the exchange in order to reach full cation substitution, if desired. The presence of Br- anions in the reaction medium represents an additional tool to modulate the morphology of the final nanocrystals, being either solid or hollow depending on their concentration. The synthetic protocol has been successfully conducted in both spherical and rod-like nanocrystals with identical results, leading to a wide variety of binary, ternary and/or hybrid nanostructures that have been carefully characterized

Synthesis and thermoelectric properties of noble metal ternary chalcogenide systems of Ag-Au-Se in the forms of alloyed nanoparticles and colloidal nanoheterostructures

The optimization of a material functionality requires both the rational design and precise engineering of its structural and chemical parameters. In this work, we show how colloidal chemistry is an excellent synthetic choice for the synthesis of novel ternary nanostructured chalcogenides, containing exclusively noble metals, with tailored morphology and composition and with potential application in the energy conversion field. Specifically, the Ag-Au-Se system has been explored from a synthetic point of view, leading to a set of Ag2Se-based hybrid and ternary nanoparticles, including the room temperature synthesis of the rare ternary Ag3AuSe2 fischesserite phase. An in-depth structural and chemical charac-terization of all nanomaterials has been performed, which proofed especially useful for unravelling the reaction mecha-nism behind the formation of the ternary phase in solution. The work is complemented with the thermal and electric characterization of a ternary Ag-Au-Se nanocomposite with promising results: we found that the use of the ternary nano-composite represents a clear improvement in terms of thermoelectric energy conversion as compared to a binary Ag-Se nanocomposite analogue