Chemically-Controlled Ultrafast Photothermal Response in Plasmonic Nanostructured Assemblies.

Plasmonic nanoparticles are renowned as efficient heaters due to their capability to resonantly absorb and concentrate electromagnetic radiation, trigger excitation of highly energetic (hot) carriers, and locally convert their excess energy into heat via ultrafast nonradiative relaxation processes. Furthermore, in assembly configurations (i.e.

Anisotropic Assembly of Nanocrystal/Molecular Hierarchical Superlattices Decoding from Tris-Amide Triarylamines Supramolecular Networks.

Directed assembly of nanocrystals from conventional templates suffers from poor control over the periodicity of the nanocrystal assembly, which is largely due to the fact that the template exists prior to the assembly and is not generally adaptive. Herein, small organic molecules (tris-amide triarylamines, TATA) are demonstrated as conceptual templates from self-assembly through noncovalent interactions. The as-formed supramolecular structures with terminated alkyl chains, resembling the structure of as-synthesized nanocrystals capped with alkyl chains, are able to interact with nanocrystals through van der Waals attractive forces, thereby enabling directed assembly of nanocrystals into ordered superlattices.

Discrete Supracrystalline Heterostructures from Integrative Assembly of Nanocrystals and Porous Organic Cages.

Although self-assembly across multiple length scales has been well recognized and intensively investigated in natural biological system, the design of artificial heterostructures enabled by integrative self-assembly is still in its infancy. Here we report a strategy toward the growth of discrete supracrystalline heterostructures from inorganic nanocrystals and porous organic cages (), which in principle relies on the host-guest interactions between alkyl chains coated on nanocrystals and the cavity of cage molecules. Density functional theory calculation indicates that an attractive energy of ∼-2 T is present between an alkyl chain and the cavity of a molecule, which is responsible for the assembly of nanocrystal superlattices on the octahedral crystals.

Light-heat conversion dynamics in highly diversified water-dispersed hydrophobic nanocrystal assemblies.

We investigate, with a combination of ultrafast optical spectroscopy and semiclassical modeling, the photothermal properties of various water-soluble nanocrystal assemblies. Broadband pump-probe experiments with ∼100-fs time resolution in the visible and near infrared reveal a complex scenario for their transient optical response that is dictated by their hybrid composition at the nanoscale, comprising metallic (Au) or semiconducting ([Formula: see text]) nanostructures and a matrix of organic ligands. We track the whole chain of energy flow that starts from light absorption by the individual nanocrystals and subsequent excitation of out-of-equilibrium carriers followed by the electron-phonon equilibration, occurring in a few picoseconds, and then by the heat release to the matrix on the 100-ps timescale.

Influence of Cracks on the Optical Properties of Silver Nanocrystals Supracrystal Films.

Physical properties of nanocrystals self-assembled into 3D superlattices called supracrystals are highly specific with unexpected behavior. The best example to support such a claim was given through STM/STS experiments at low temperature of very thick supracrystals (around 1000 layers) where it was possible to image the surpracrystal surface and study their electronic properties. From previous studies, we know the optical properties of Ag nanocrystals self-assembled in a hexagonal network two-dimensional (2D) or by forming small 3D superlattices (from around 2 to 7 layers) are governed by dipolar interactions.

Au nanocrystal superlattices: nanocrystallinity, vicinal surfaces, and growth processes.

Vicinal Au supracrystal surfaces were prepared from Ausingle single domain nanocrystals (NCs), whereas by replacing Ausingle with their polycrystalline counterparts common low-energy supracrystal surfaces were produced. By analogy to atomic crystalline surfaces, we propose a mechanism to explain the formation of such unexpected supracrystal vicinal surfaces, composed of only Ausingle NCs which are non-compact (bct structure) with a coherent alignment of the atomic planes oriented along the [111] superlattice axis and a slight tilt configuration (8.1°) of NCs.

Coating agent-induced mechanical behavior of 3D self-assembled nanocrystals.

The Young's modulus of three-dimensional self-assembled Ag nanocrystals, as so-called supracrystals, is correlated with the type of coating agent as well as the nanocrystal morphology. The Young's moduli of supracrystals of icosahedral Ag nanocrystals are measured in the range of tens to hundreds of megapascals revealing an extremely soft mechanical behavior. The alkylamine molecules used as coating agents weakly interact with the Ag nanocrystal surface favoring translational and orientational ordering of atomic lattice planes of nanocrystals.

Water-Dispersed Hydrophobic Au Nanocrystal Assemblies with a Plasmon Fingerprint.

Hydrophobic Au nanocrystal assemblies (both ordered and amorphous) were dispersed in aqueous solution via the assistance of lipid vesicles. The intertwine between vesicles and Au assemblies was made possible through a careful selection of the length of alkyl chains on Au nanocrystals. Extinction spectra of Au assemblies showed two peaks that were assigned to a scattering mode that red-shifted with increasing the assembly size and an absorption mode associated with localized surface plasmon that was independent of their size.

Impact of the Metallic Crystalline Structure on the Properties of Nanocrystals and Their Mesoscopic Assemblies.

The spontaneous assembly of uniform-sized globular entities into ordered arrays is a universal phenomenon observed for objects with diameters spanning a broad range of length scales. These extend from the atomic scale (10 cm), through molecular and macromolecular scales with proteins, synthetic low polymers, and colloidal crystals (∼10 cm), to the wavelength of visible light (∼10 cm). The associated concepts of sphere packing have had an influence in diverse fields ranging from pure geometrical analysis to architectural models or ideals.

N-Heterocyclic Carbene Ligands for Au Nanocrystal Stabilization and Three-Dimensional Self-Assembly.

N-Heterocyclic carbenes (NHCs) have emerged as a new class of ligands for materials chemistry that appears particularly relevant for the stabilization and functionalization of metal nanoparticles (NPs). The particular properties and high synthetic flexibility of NHCs make them highly attractive tools for the development of new (nano)materials and the fundamental study of their properties. The relationships between the NHC structure and NP structure/properties, including physical, biological, and self-assembly properties, remain largely unknown.

Encapsulation of Zwitterionic Au Nanocrystals into Liposomes by Reverse Phase Evaporation Method: Influence of the Surface Charge.

Since both liposomes and nanoparticles have shown great potential in application for clinical diagnostics and therapeutics, the perfect combination of the two materials is appealing for further improving the theranostic effect. Therefore, fabrication of liposomes loaded with nanoparticles in a controllable manner is desirable. Detection of various factors affecting encapsulation needs to be assigned.

Supracrystalline Colloidal Eggs: Epitaxial Growth and Freestanding Three-Dimensional Supracrystals in Nanoscaled Colloidosomes.

The concept of template-confined chemical reactions allows the synthesis of complex molecules that would hardly be producible through conventional method. This idea was developed to produce high quality nanocrystals more than 20 years ago. However, template-mediated assembly of colloidal nanocrystals is still at an elementary level, not only because of the limited templates suitable for colloidal assemblies, but also because of the poor control over the assembly of nanocrystals within a confined space.

Dispersion of Hydrophobic Co Supracrystal in Aqueous Solution.

Assembly of nanoparticles into supracrystals provides a class of materials with interesting optical and magnetic properties. However, supracrystals are mostly obtained from hydrophobic particles and therefore cannot be manipulated in aqueous systems, limiting their range of applications. Here, we show that hydrophobic-shaped supracrystals self-assembled from 8.

Superior Oxygen Stability of N-Heterocyclic Carbene-Coated Au Nanocrystals: Comparison with Dodecanethiol.

The stability of Au nanocrystals (NCs) coated with different N-heterocyclic carbenes (NHCs) or dodecanethiol (DDT) to oxygen-based treatments was investigated. A dominant effect of the ligand type was observed with a significantly greater oxygen resistance of NHC-coated Au NCs compared to that of the thiol-based analogues. NHC-coated Au NCs are stable to 10 W oxygen plasma etching for up to 180 s whereas the integrity of DDT-coated Au NCs is strongly affected by the same treatment from 60-80 s.

Ligand Exchange Governs the Crystal Structures in Binary Nanocrystal Superlattices.

The surface chemistry in colloidal nanocrystals on the final crystalline structure of binary superlattices produced by self-assembly of two sets of nanocrystals is hereby demonstrated. By mixing nanocrystals having two different sizes and the same coating agent, oleylamine (OAM), the binary nanocrystal superlattices that are produced, such as NaCl, AlB2, NaZn13, and MgZn2, are well in agreement with the crystalline structures predicted by the hard-sphere model, their formation being purely driven by entropic forces. By opposition, when large and small nanocrystals are coated with two different ligands [OAM and dodecanethiol (DDT), respectively] while keeping all other experimental conditions unchanged, the final binary structures markedly change and various structures with lower packing densities, such as Cu3Au, CaB6, and quasicrystals, are observed.

Nano-contact microscopy of supracrystals.

Background: Highly ordered three-dimensional colloidal crystals (supracrystals) comprised of 7.4 nm diameter Au nanocrystals (with a 5% size dispersion) have been imaged and analysed using a combination of scanning tunnelling microscopy and dynamic force microscopy.

Results: By exploring the evolution of both the force and tunnel current with respect to tip-sample separation, we arrive at the surprising finding that single nanocrystal resolution is readily obtained in tunnelling microscopy images acquired more than 1 nm into the repulsive (i.

Beyond entropy: magnetic forces induce formation of quasicrystalline structure in binary nanocrystal superlattices.

Here, it is shown that binary superlattices of Co/Ag nanocrystals with the same size, surface coating, differing by their type of crystallinity are governed by Co-Co magnetic interactions. By using 9 nm amorphous-phase Co nanocrystals and 4 nm polycrystalline Ag nanocrystals at 25 °C, triangle-shaped NaCl-type binary nanocrystal superlattices are produced driven by the entropic force, maximizing the packing density. By contrast, using ferromagnetic 9 nm single domain (hcp) Co nanocrystals instead of amorphous-phase Co, dodecagonal quasicrystalline order is obtained, together with less-packed phases such as the CoAg13 (NaZn13-type), CoAg (AuCu-type), and CoAg3 (AuCu3-type) structures.

Spontaneous formation of high-index planes in gold single domain nanocrystal superlattices.

Crystals of nanocrystals, also called supracrystals and nanocrystal superlattices, are expected to exhibit specific properties that differ from both the corresponding bulk material and nanosized elementary units. In particular, their surfaces have a great potential as nanoscale interaction plateforms. However, control of the symmetry, compacity, and roughness of their surfaces remains an open question.

Ag nanocrystals: 1. Effect of ligands on plasmonic properties.

Silver nanocrystals (NCs) stabilized using amine-terminated coating agents (oleylamine or dodecylamine), their size ranging between 2 and 12 nm in diameter, are synthesized by hot injection methods. Their dispersion in size is relatively low (typically below 10%) without the need for a postsynthesis size segregation process. The amine-terminated coating agents are replaced by thiol-terminated molecules (dodecanethiol or hexadecanethiol) by ligand exchange, allowing the formation of alkanethiol coated Ag colloids.

How nanocrystallinity and order define the magnetic properties of ε-Co supracrystals.

Single domain cubic ε-Co nanocrystals are synthesized via a high-temperature thermal decomposition of cobalt carbonyl in the presence of oleic acid and trioctylphosphane oxide (TOPO). The ε-Co nanocrystals are characterized by a low size distribution (σ < 7%) and the average diameter is tuned from 7 nm to 9 nm by tailoring the molar ratio of the surfactants oleic acid and TOPO. Moreover, we have demonstrated the self-assembly of ε-Co nanocrystals in highly ordered three-dimensional (3D) face-centered cubic (fcc) structures called supracrystals.

Hierarchy in Au nanocrystal ordering in supracrystals: III. Competition between van der Waals and dynamic processes.

Au nanocrystals coated with thiol derivatives of varying chain sizes ranging from C12 to C16 were produced; two different size nanocrystals have been synthesized (5 and 7 nm in diameter) for each coating agent. All of those specimens are characterized by a low size distribution (below 7%). Those Au nanocrystals were used as building blocks to grow larger self-assembled crystalline structures or supracrystals.

Crystal polymorphism: dependence of oxygen diffusion through 2D ordered Co nanocrystals.

8 nm Co nanoparticles with various crystalline structures called polymorphs were produced using different synthetic procedures, such as using reverse micelles, the thermal decomposition of organometallics approach or the hot injection process. These 8 nm Co nanoparticles differing by their crystalline structures are exposed to oxygen at elevated temperature. The fcc Co polycrystalline nanoparticles produce either Co-CoO yolk-shell or CoO hollow structures whereas amorphous Co nanoparticles produce Co-CoO core-shell nanoparticles.

Hierarchy in Au nanocrystal ordering in a supracrystal: II. Control of interparticle distances.

Au nanocrystals coated with thiol derivatives differing by the length of their alkyl chains are used to build 3D superlattices called supracrystals. In this study, we used two sets of Au nanocrystals differing by their sizes and size distributions. The average sizes are 5 nm (Au5) and 7 nm (Au7).

Assessing the relevance of building block crystallinity for tuning the stiffness of gold nanocrystal superlattices.

We study the influence of the size and nanocrystallinity of dodecanethiol-coated gold nanocrystals (NCs) on the stiffness of 3D self-assembled NC superlattices (called supracrystals). Using single domain and polycrystalline NCs as building blocks for supracrystals, it is shown that the stiffness of supracrystals can be tuned upon change in relative amounts of single and polycrystalline NCs.