We report the synthesis of a new nanocrystal (NC) mesophase through self-assembly of water-soluble NC micelles with soluble silica. The mesophase comprises gold nanocrystals arranged within a silica matrix in a face-centered cubic lattice with cell dimensions that are adjustable through control of the nanocrystal diameter and/or the alkane chain lengths of the primary alkanethiol stabilizing ligands or the surrounding secondary surfactants. Under kinetically controlled silica polymerization conditions, evaporation drives self-assembly of NC micelles into ordered NC/silica thin-film mesophases during spin coating. The intermediate NC micelles are water soluble and of interest for biolabeling. Initial experiments on a metal-insulator-metal capacitor fabricated with an ordered three-dimensional gold nanocrystal/silica array as the "insulator" demonstrated collective Coulomb blockade behavior below 100 kelvin and established the current-voltage scaling relationship for a well-defined three-dimensional array of Coulomb islands.

We have demonstrated pressure-directed assembly for preparation of a new class of chemically and mechanically stable gold nanostructures through high pressure-driven sintering of nanoparticle assemblies at room temperature. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle array can be reversibly manipulated allowing fine-tuning of the interparticle separation distance. In addition, 3D nanostructured gold architecture can be formed through high pressure-induced nanoparticle sintering. This work opens a new pathway for engineering and fabrication of different metal nanostructured architectures.

Owing to their size-and shape-dependent properties, [1][2][3] nanoparticles have been successfully used as functional building blocks to fabricate multidimensional ordered assemblies for the development of "artificial solids" (e.g., metamaterials) with potential applications in nanoelectronic and optical devices. [4][5][6][7][8] Until now, the fabrication of ordered nanoparticle assemblies has relied on specific chemical or physical interparticle interactions, such as van der Waals interactions, [6] dipole-dipole interactions, [9] chemical reactions, [8,10,11] and DNA templating. [5,12,13] Consequently, selfassembly has involved the formation of higher-dimensional nanoparticle architectures from single nanoparticles. Herein, we report that a novel external pressure can be utilized to engineer nanoparticle assembly, to fabricate 1D metallic nanostructures and to form ultrahigh-density ordered 1D nanostructure arrays. Ordered films of spherical gold nanoparticles with a face-centered cubic (fcc) mesophase were compressed with a diamond anvil cell (DAC). In situ highpressure small-angle X-ray scattering (HP SAXS) measurements showed that gradual elevation of the external pressure from ambient pressure to 8.9 GPa caused reversible shrinkage of the dimensions of the lattice unit cell and thus enabled the fine-tuning of interparticle spacing. Pressures between 8.9 and 13 GPa drove the nanoparticles to coalesce to form 1D nanostructures (nanorods or nanowires) and ordered hexagonal arrays of the nanostructures with P6mm symmetry. Dispersion of the ordered arrays in organic solvents resulted in uniform single nanostructures that could reassemble into ordered arrays upon evaporation of the solvent. This simple and efficient method enables the nanoengineering of nanoparticle assemblies for the fabrication of new complex nanoparticle architectures without reliance on specific chemical and physical interactions. [5,[8][9][10][11][12][13] We synthesized spherical gold nanoparticles by using a one-phase method and used dodecanethiol as the capping ligand (see details in the Supporting Information).[14] The gold nanoparticles had an average diameter of 5.2 nm with a standard deviation of 4.2 %. The fcc ordered gold-nanoparticle polymer films were fabricated through a solventevaporation process on silicon wafers. When the ordered nanoparticle film was loaded into the DAC (a schematic illustration of the measurement is shown in Figure S1a of the Supporting Information), [15] it maintained the fcc mesophase, which exhibited a [110] orientation, as revealed by smallangle synchrotron X-ray scattering (SAXS) and microscope measurement. The SAXS pattern and integrated spectrum (see Figure S1b,c in the Supporting Information) collected at ambient pressure indicated a pattern specific to an fcc mesophase with the Fm3 m space group. The unit-cell parameter a fcc was calculated to be 104.0 . Representative SEM images (see Figure S1d,e in the Supporting Information) taken of the surface and cross-section of the gold-nanoparticle film verif...

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Monodisperse fluorescent organic/inorganic composite nanoparticles are synthesized through the spontaneous self-assembly of block copolymer polystyrene-blockpoly(vinylpyridine) and rare-earth ions (europium, terbium, thulium, etc.). Depending on the rare-earth ions selected, tunable light-emission colors, including the primary red, green, and blue, are accomplished. Further, by stoichiometric mixing of the nanoparticles that emit different colors, the full color spectrum can be accessed. Both electron microscopy and spectroscopic characterizations confirm specific interactions of rare-earth and block copolymers. The resulting nanoparticles are monodisperse as characterized by dynamic light scattering. They are very stable and can be dispersed in common solvents, and together with homopolymers, they form ordered arrays and thin films (both supported and free-standing) upon solvent evaporation. The resulting nanoparticle thin films exhibit mechanical flexibility for ease of processing or device integration.

Owing to their size-and shape-dependent properties, [1][2][3] nanoparticles have been successfully used as functional building blocks to fabricate multidimensional ordered assemblies for the development of "artificial solids" (e.g., metamaterials) with potential applications in nanoelectronic and optical devices. [4][5][6][7][8] Until now, the fabrication of ordered nanoparticle assemblies has relied on specific chemical or physical interparticle interactions, such as van der Waals interactions, [6] dipole-dipole interactions, [9] chemical reactions, [8,10,11] and DNA templating. [5,12,13] Consequently, selfassembly has involved the formation of higher-dimensional nanoparticle architectures from single nanoparticles. Herein, we report that a novel external pressure can be utilized to engineer nanoparticle assembly, to fabricate 1D metallic nanostructures and to form ultrahigh-density ordered 1D nanostructure arrays. Ordered films of spherical gold nanoparticles with a face-centered cubic (fcc) mesophase were compressed with a diamond anvil cell (DAC). In situ highpressure small-angle X-ray scattering (HP SAXS) measurements showed that gradual elevation of the external pressure from ambient pressure to 8.9 GPa caused reversible shrinkage of the dimensions of the lattice unit cell and thus enabled the fine-tuning of interparticle spacing. Pressures between 8.9 and 13 GPa drove the nanoparticles to coalesce to form 1D nanostructures (nanorods or nanowires) and ordered hexagonal arrays of the nanostructures with P6mm symmetry. Dispersion of the ordered arrays in organic solvents resulted in uniform single nanostructures that could reassemble into ordered arrays upon evaporation of the solvent. This simple and efficient method enables the nanoengineering of nanoparticle assemblies for the fabrication of new complex nanoparticle architectures without reliance on specific chemical and physical interactions. [5,[8][9][10][11][12][13] We synthesized spherical gold nanoparticles by using a one-phase method and used dodecanethiol as the capping ligand (see details in the Supporting Information). [14] The gold nanoparticles had an average diameter of 5.2 nm with a standard deviation of 4.2 %. The fcc ordered gold-nanoparticle polymer films were fabricated through a solventevaporation process on silicon wafers. When the ordered nanoparticle film was loaded into the DAC (a schematic illustration of the measurement is shown in Figure S1a of the Supporting Information), [15] it maintained the fcc mesophase, which exhibited a [110] orientation, as revealed by smallangle synchrotron X-ray scattering (SAXS) and microscope measurement. The SAXS pattern and integrated spectrum (see Figure S1b,c in the Supporting Information) collected at ambient pressure indicated a pattern specific to an fcc mesophase with the Fm3 m space group. The unit-cell parameter a fcc was calculated to be 104.0 . Representative SEM images (see Figure S1d,e in the Supporting Information) taken of the surface and cross-section of the gold-nanoparticle film veri...

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