Showing papers in "ACS Nano in 2007"

Supramolecular chemistry on water-soluble carbon nanotubes for drug loading and delivery.

Abstract: We show that large surface areas exist for supramolecular chemistry on single-walled carbon nanotubes (SWNTs) prefunctionalized noncovalently or covalently by common surfactant or acid-oxidation routes. Water-soluble SWNTs with poly(ethylene glycol) (PEG) functionalization via these routes allow for surprisingly high degrees of π-stacking of aromatic molecules, including a cancer drug (doxorubicin) with ultrahigh loading capacity, a widely used fluorescence molecule (fluorescein), and combinations of molecules. Binding of molecules to nanotubes and their release can be controlled by varying the pH. The strength of π-stacking of aromatic molecules is dependent on nanotube diameter, leading to a method for controlling the release rate of molecules from SWNTs by using nanotube materials with suitable diameter. This work introduces the concept of “functionalization partitioning” of SWNTs, i.e., imparting multiple chemical species, such as PEG, drugs, and fluorescent tags, with different functionalities onto t...

In vivo imaging of transport and biocompatibility of single silver nanoparticles in early development of zebrafish embryos.

Abstract: Real-time study of the transport and biocompatibility of nanomaterials in early embryonic development at single-nanoparticle resolution can offer new knowledge about the delivery and effects of nanomaterials in vivo and provide new insights into molecular transport mechanisms in developing embryos. In this study, we directly characterized the transport of single silver nanoparticles into an in vivo model system (zebrafish embryos) and investigated their effects on early embryonic development at single-nanoparticle resolution in real time. We designed highly purified and stable (not aggregated and no photodecomposition) nanoparticles and developed single-nanoparticle optics and in vivo assays to enable the study. We found that single Ag nanoparticles (5–46 nm) are transported into and out of embryos through chorion pore canals (CPCs) and exhibit Brownian diffusion (not active transport), with the diffusion coefficient inside the chorionic space (3 × 10−9 cm2/s) ∼26 times lower than that in egg water (7.7 ×...

Silver nanoplates: from biological to biomimetic synthesis.

Abstract: This paper describes the synthesis of single-crystalline Ag nanoplates using the extract of unicellular green alga Chlorella vulgaris at room temperature. Proteins in the extract were involved in the biological synthesis, providing the dual function of Ag ion reduction and shape-controlled synthesis of nanosilver. Hydroxyl groups in Tyr residues and carboxyl groups in Asp and/or Glu residues were further identified as the most active functional groups for Ag ion reduction and for directing the anisotropic growth of Ag nanoplates, respectively. The kinetics of Ag ion reduction in biological systems was discussed and probed by using custom-designed peptides. The results showed the Tyr content (the reduction source) and the content of Ag complexers (the reaction inhibitors, e.g., His and Cys) in the protein molecules as important factors affecting the reduction kinetics. The comprehensive system identification effort has led to the design of a simple bifunctional tripeptide (DDY-OMe) with one Tyr residue as ...

Directed self-assembly of block copolymers for nanolithography: fabrication of isolated features and essential integrated circuit geometries.

Abstract: Self-assembling block copolymers are of interest for nanomanufacturing due to the ability to realize sub-100 nm dimensions, thermodynamic control over the size and uniformity and density of features, and inexpensive processing The insertion point of these materials in the production of integrated circuits, however, is often conceptualized in the short term for niche applications using the dense periodic arrays of spots or lines that characterize bulk block copolymer morphologies, or in the long term for device layouts completely redesigned into periodic arrays Here we show that the domain structure of block copolymers in thin films can be directed to assemble into nearly the complete set of essential dense and isolated patterns as currently defined by the semiconductor industry These results suggest that block copolymer materials, with their intrinsically advantageous self-assembling properties, may be amenable for broad application in advanced lithography, including device layouts used in existing nanomanufacturing processes

Electron Storage in Single Wall Carbon Nanotubes. Fermi Level Equilibration in Semiconductor–SWCNT Suspensions

Abstract: The use of single wall carbon nanotubes (SWCNTs) as conduits for transporting electrons in a photoelectrochemical solar cell and electronic devices requires better understanding of their electron-accepting properties. When in contact with photoirradiated TiO2 nanoparticles, SWCNTs accept and store electrons. The Fermi level equilibration with photoirradiated TiO2 particles indicates storage of up to 1 electron per 32 carbon atoms in the SWCNT. The stored electrons are readily discharged on demand upon addition of electron acceptors such as thiazine and oxazine dyes (reduction potential less negative than that of the SWCNT conduction band) to the TiO2–SWCNT suspension. The stepwise electron transfer from photoirradiated TiO2 nanoparticles → SWCNT → redox couple has enabled us to probe the electron equilibration process and determine the apparent Fermi level of the TiO2–SWCNT system. A positive shift in apparent Fermi level (20–30 mV) indicates the ability of SWCNTs to undergo charge equilibration with phot...

Bifunctional Au-Fe3O4 nanoparticles for protein separation.

Abstract: In this article, we report the synthesis of bifunctional Au-Fe(3)O(4) nanoparticles that are formed by chemical bond linkage. Due to the introduction of Au nanoparticles, the resulting bifunctional Au-Fe(3)O(4) nanoparticles can be easily modified with other functional molecules to realize various nanobiotechnological separations and detections. Here, as an example, we demonstrate that as-prepared Au-Fe(3)O(4) nanoparticles can be modified with nitrilotriacetic acid molecules through Au-S interaction and used to separate proteins simply with the assistance of a magnet. Bradford protein assay and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were performed to examine the validity of the separation procedure, and the phosphate determination method suggested that the as-separated protein maintained catalytic activity. This result shows the efficiency of such a material in protein separation and suggests that its use can be extended to magnetic separation of other biosubstances. Moreover, this synthetic strategy paves the way for facile preparation of diverse bifunctional and even multifunctional nanomaterials.

Gold Nanoparticle-Based Miniaturized Nanomaterial Surface Energy Transfer Probe for Rapid and Ultrasensitive Detection of Mercury in Soil, Water, and Fish

Abstract: Contamination of the environment with mercury has been an important concern throughout the world for decades. Exposure to high Hg levels can be harmful to the brain, heart, kidneys, lungs, and immune system of humans of all ages. Driven by the need to detect trace amounts of mercury in environmental samples, here we present a miniaturized, inexpensive, and battery-operated ultrasensitive gold nanoparticle-based nanomaterial surface energy transfer probe for screening mercury levels in contaminated soil, water, and fish which has excellent sensitivity (2 ppt) and selectivity for Hg(II) over competing analytes, with the largest fluorescence enhancement to date for sensing Hg(II) in environmental samples (1100-fold). The sensitivity of our probe to detect mercury level in soil, water, and fish is about 2–3 orders of magnitude higher than the EPA standard limit. We demonstrate that our probe is suitable to screen the amount of mercury in different fish, shellfish, and water samples from various commercial sou...

Nitrogen- and boron-doped double-walled carbon nanotubes.

Abstract: Double-walled carbon nanotubes (DWNTs) doped with nitrogen and boron have been prepared by the decomposition of a CH4 + Ar mixture along with pyridine (or NH3) and diborane, respectively, over a Mo0.1Fe0.9Mg13O catalyst, prepared by the combustion route. The doped DWNTs bave been characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and Raman spectroscopy. The dopant concentration is around 1 atom % for both boron and nitrogen. The radial breathing modes in the Raman spectra have been employed along with TEM to obtain the inner and outer diameters of the DWNTs. The diameter ranges for the undoped, N-doped (pyridine), N-doped (NH3), and B-doped DWNTs are 0.73–2.20, 0.74–2.30, 0.73–2.32, and 0.74–2.36 nm, respectively, the boron-doped DWNTs giving rise to a high proportion of the large diameter DWNTs. Besides affecting the G-band in the Raman spectra, N- and B-doping affect the proportion of semiconducting nanotubes.

Nitrogen-Mediated Carbon Nanotube Growth: Diameter Reduction, Metallicity, Bundle Dispersability, and Bamboo-like Structure Formation

Abstract: Carbon nanotube growth in the presence of nitrogen has been the subject of much experimental scrutiny, sparking intense debate about the role of nitrogen in the formation of diverse structural features, including shortened length, reduced diameters, and bamboo-like multilayered nanotubules. In this paper, the origin of these features is elucidated using a combination of experimental and theoretical techniques, showing that N acts as a surfactant during growth. N doping enhances the formation of smaller diameter tubes. It can also promote tube closure which includes a relatively large amount of N atoms into the tube lattice, leading to bamboo-like structures. Our findings demonstrate that the mechanism is independent of the tube chirality and suggest a simple procedure for controlling the growth of bamboo-like nanotube morphologies.

A General Approach for DNA Encapsulation in Degradable Polymer Microcapsules

Abstract: We report a general and facile method for the encapsulation of DNA in nanoengineered, degradable polymer microcapsules. Single-stranded (ss), linear double-stranded (ds), and plasmid DNA were encapsulated into disulfide-cross-linked poly(methacrylic acid) (PMA) capsules. The encapsulation procedure involves four steps: adsorption of DNA onto amine-functionalized silica (SiO2+) particles; sequential deposition of thiolated PMA (PMASH) and poly(vinylpyrrolidone) to form multilayers; cross-linking of the thiol groups of the PMASH in the multilayers into disulfide linkages; and removal of the sacrificial SiO2+ particles. Multilayer growth was dependent on the surface coverage of DNA on the SiO2+ particles, with stable capsules formed from particles with up to 50% DNA surface coverage. The encapsulation strategy applies to nucleic acids with varied size and conformation and allows DNA to be concentrated over 100-fold from dilute solutions into monodisperse, uniformly loaded polymer capsules. The capsule loadin...

Multimodal nanoprobes for radionuclide and five-color near-infrared optical lymphatic imaging.

Abstract: No imaging modality is perfect. Each has its own distinct advantages and limitations. The simultaneous use of two or more modalities can help to overcome the limitation of each individual method and increase or improve the information obtained during an examination session. The combined use of Computed Tomography (CT) and Positron Emission Tomography (PET) is a successful example of multi-modal imaging: CT provides high resolution anatomical detail and PET provides functional information 1. Currently they are very few examples of multi-modal imaging probes that can be detected by more than one technique: dual agents for recognition by both radionuclide and optical imaging 2,3, or Magnetic Resonance (MR) and optical imaging 4–8. Furthermore, the conventional imaging methods are generally monochrome and only able to detect one contrast agent at a time, limiting us to single parametric data. Single photon scintigraphy has been shown to have potential for simultaneously detecting two different imaging agents, i.e. technetium-99m and thallium-201, by energy resolution 9. However, in this case, both the spatial and the energy resolutions were poor and did not allow for the reconstruction of a precise image from each agent. Multi-color optical imaging is simple to achieve with the technique of spectrally resolved imaging. Herein, two or more optical agents can be differentiated on the basis of their different emission spectra. Multi-color imaging is already commonplace in microscopic imaging and is beginning to be utilized for in vivo imaging 10–12. However, in vivo imaging is essentially limited to long wavelength dyes that emit in the near-infrared (NIR) range (650–850 nm), in order to maximize depth penetration and limit the autofluorescence, background signal 13. With this in mind we have synthesized multi-modal, multi-color nano-sized imaging probes with nearly identical chemical characteristics. This single injection imaging probe offers the potential for both multi-modal imaging and multi-color resolution.

Imogolite Nanotubes: Stability, Electronic, and Mechanical Properties

Abstract: The aluminosilicate mineral imogolite is composed of single-walled nanotubes with stoichiometry of (HO)(3)Al(2)O(3)SiOH and occurs naturally in soils of volcanic origin. In the present work we study the stability and the electronic and mechanical properties of zigzag and armchair imogolite nanotubes using the density-functional tight-binding method. The (12,0) imogolite tube has the highest stability of all tubes studied here. Uniquely for nanotubes, imogolite has a minimum in the strain energy for the optimum structure. This is in agreement with experimental data, as shown by comparison with the simulated X-ray diffraction spectrum. An analysis of the electronic densities of states shows that all imogolite tubes, independent on their chirality and size, are insulators.

Synthesis and self-assembly of polymer-coated ferromagnetic nanoparticles.

Abstract: We describe the synthesis and characterization of polymer-coated ferromagnetic cobalt nanoparticles (CoNPs). The synthesis of end-functionalized polystyrene surfactants possessing amine, carboxylic acid, or phosphine oxide end-groups was accomplished using atom-transfer radical polymerization. This versatile synthetic method enabled the production of multigram quantities of these polymeric surfactants that stabilized ferromagnetic CoNPs when dispersed in organic media. An in-depth investigation into the synthesis of polystyrene-coated ferromagnetic CoNPs was also conducted using various combinations of these polymeric surfactants in the thermolysis of dicobaltoctacarbonyl (Co2(CO)8). Moreover, the application of a dual-stage thermolysis with Co2(CO)8 allowed for the preparation of large samples (200–820 mg) per batch of well-defined and dispersable ferromagnetic nanoparticles. Characterization of these functionalized nanoparticle materials was then done using transmission electron microscopy, X-ray diffra...

Influence of size, surface, cell line, and kinetic properties on the specific binding of A33 antigen-targeted multilayered particles and capsules to colorectal cancer cells

Abstract: There has been increased interest in the use of polymer capsules formed by the layer-by-layer (LbL) technique as therapeutic carriers to cancer cells due to their versatility and ease of surface modification We have investigated the influence of size, surface properties, cell line, and kinetic parameters such as dosage (particle concentration) and incubation time on the specific binding of humanized A33 monoclonal antibody (huA33 mAb)-coated LbL particles and capsules to colorectal cancer cells HuA33 mAb binds to the A33 antigen present on almost all colorectal cancer cells and has demonstrated great promise in clinical trials as an immunotherapeutic agent for cancer therapy Flow cytometry experiments showed the cell binding specificity of huA33 mAb-coated particles to be size-dependent, with the optimal size for enhanced selectivity at approximately 500 nm The specific binding was improved by increasing the dosage of particles incubated with the cells The level of specific versus nonspecific binding was compared for particles terminated with various polyelectrolytes to examine the surface dependency of antibody attachment and subsequent cell binding ability The specific binding of huA33 mAb-coated particles is also reported for two colorectal cancer cell lines, with an enhanced binding ratio between 4 and 10 obtained for the huA33 mAb-functionalized particles This investigation aims to improve the level of specific targeting of LbL particles, which is important in targeted drug and gene delivery applications

Polymer self-assembly as a novel extension to optical lithography.

Abstract: The extreme technological complexity associated with continued dimensional scaling of the photolithographic patterning process to sub-50 nm dimensions has forced the semiconductor industry to seek increasingly innovative alternative approaches. One unconventional method under preliminary consideration involves using self-assembling block copolymer films as high-resolution patterning materials for defining integrated circuit (IC) elements. While these materials are attractive because of their ability to define nanometer-scale dimensions, their ultimate utility as a viable patterning method remains in question because of issues relating to pattern roughness and defectivity. In this issue, Prof. Paul Nealey and co-workers at the University of Wisconsin present compelling first demonstrations of experimental methods by which polymer self-assembly can generate the pattern elements essential for IC fabrication.

Multiple lipid compartments slow vesicle contents release in lipases and serum.

Abstract: Unilamellar vesicles or "liposomes" are commonly used as simple cell models and as drug delivery vehicles. A major limitation of unilamellar liposomes in these applications has been premature contents release in physiological environments. This premature release is likely due to enzyme degradation or protein insertion into the liposome membrane, which significantly increases the bilayer permeability. Encapsulating unilamellar liposomes within a second bilayer to form multicompartment "vesosomes" extends contents retention by 2 orders of magnitude by preventing enzymes and/or proteins from reaching the interior bilayers. The multicompartment structure of the vesosome can also allow for independent optimization of the interior compartments and exterior bilayer; however, just the bilayer-within-a-bilayer structure of the vesosome is sufficient to increase drug retention from minutes to hours. The vesosome is a better mimic of eukaryotic cell structure and demonstrates the benefits of multiple internal bilayer-enclosed compartments.

The power of the pen: development of massively parallel dip-pen nanolithography.

Abstract: If one had complete control of the architecture of a surface, in terms of composition and physical structure, one could ask and answer some of the most important scientific questions in a wide variety of fields, including surface science, catalysis, and cellular biology. Unfortunately, there are few tools that allow one to tailor surface architecture with such control, and of those that exist, such as electron- and ion-beam lithographies, most are limited in terms of the environment in which they can operate, the materials that can be patterned, cost, and throughput. Toward this end, important new scanning probe technologies have been developed that have impacted fields such as electronics, optics, and medicine.

One-Step Synthesis of Nano–Micro Chestnut TiO2 with Rutile Nanopins on the Microanatase Octahedron

Abstract: The solution synthesis of large single crystals of octahedron-like anatase TiO2 is reported, although this novel result is unexpected in the light of reported theoretical calculations. Moreover, systematic control of the crystal growth of rutile nanopins on the microanatase octahedron single crystal results in a nano-micro chestnut-like TiO2 structure. The control of the formation of rutile nanopins on the large single crystals of anatase in the same solution is an interesting and useful technique, based on thermodynamics and surface chemistry.

Peptide-Modified Optical Filters for Detecting Protease Activity

Abstract: The organic derivatization of silicon-based nanoporous photonic crystals is presented as a method to immobilize peptides for the detection of protease enzymes in solution. A narrow-line-width rugate filter, a one-dimensional photonic crystal, is fabricated that exhibits a high-reflectivity optical resonance that is sensitive to small changes in the refractive index at the pore walls. To immobilize peptide in the pore of the photonic crystal, the hydrogen-terminated silicon surface was first modified with the alkene 10-succinimidyl undecenoate via hydrosilylation. The monolayer with the succinimide ester moiety at the distal end served the dual function of protecting the underlying silicon from oxidation as well as providing a surface suitable for subsequent derivatization with amines. The surface was further modified with 1-aminohexa(ethylene glycol) (EG6) to resist nonspecific adsorption of proteins common in complex biological samples. The distal hydroxyl of the EG6 is activated using the solid-phase co...

Scanning electron microscopy of nanoscale chemical patterns.

Abstract: A series of nanoscale chemical patterning methods based on soft and hybrid nanolithographies have been characterized using scanning electron microscopy with corroborating evidence from scanning tunneling microscopy and lateral force microscopy. We demonstrate and discuss the unique advantages of the scanning electron microscope as an analytical tool to image chemical patterns of molecules highly diluted within a host self-assembled monolayer and to distinguish regions of differential mass coverage in patterned self-assembled monolayers. We show that the relative contrast of self-assembled monolayer patterns in scanning electron micrographs depends on the operating primary electron beam voltage, monolayer composition, and monolayer order, suggesting that secondary electron emission and scattering can be used to elucidate chemical patterns.

Light-Assisted Oxidation of Single-Wall Carbon Nanohorns for Abundant Creation of Oxygenated Groups That Enable Chemical Modifications with Proteins To Enhance Biocompatibility

Abstract: We show that light-assisted oxidation with hydrogen peroxide effectively and rapidly opens holes in carbon nanohorn walls and, more importantly, creates abundant oxygenated groups such as carboxylic groups at the hole edges. These oxygenated groups reacted with the protein bovine serum albumin. The obtained conjugates were highly dispersed in phosphate-buffered saline and were taken up by cultured mammalian cells via an endocytosis pathway.

Metastability of Au-Ge liquid nanocatalysts: Ge vapor-liquid-solid nanowire growth far below the bulk eutectic temperature.

Abstract: The vapor–liquid–solid mechanism of nanowire (NW) growth requires the presence of a liquid at one end of the wire; however, Au-catalyzed Ge nanowire growth by chemical vapor deposition can occur at ∼100 °C below the bulk Au−Ge eutectic. In this paper, we investigate deep sub-eutectic stability of liquid Au−Ge catalysts on Ge NWs quantitatively, both theoretically and experimentally. We construct a binary Au−Ge phase diagram that is valid at the nanoscale and show that equilibrium arguments, based on capillarity, are inconsistent with stabilization of Au−Ge liquid at deep sub-eutectic temperatures, similar to those used in Ge NW growth. Hot-stage electron microscopy and X-ray diffraction are used to test the predictions of nanoscale phase equilibria. In addition to Ge supersaturation of the Au−Ge liquid droplet, which has recently been invoked as an explanation for deep sub-eutectic Ge NW growth, we find evidence of a substantial kinetic barrier to Au solidification during cooling below the nanoscale Au−Ge...

Cobalt Ferrite Nanocrystals: Out-Performing Magnetotactic Bacteria

Abstract: Magnetotactic bacteria produce exquisitely ordered chains of uniform magnetite (Fe(3)O(4)) nanocrystals, and the use of the bacterial mms6 protein allows for the shape-selective synthesis of Fe(3)O(4) nanocrystals. Cobalt ferrite (CoFe(2)O(4)) nanoparticles, on the other hand, are not known to occur in living organisms. Here we report on the use of the recombinant mms6 protein in a templated synthesis of CoFe(2)O(4) nanocrystals in vitro. We have covalently attached the full-length mms6 protein and a synthetic C-terminal domain of mms6 protein to self-assembling polymers in order to template hierarchical CoFe(2)O(4) nanostructures. This new synthesis pathway enables facile room-temperature shape-specific synthesis of complex magnetic crystalline nanomaterials with particle sizes in the range of 40-100 nm that are difficult to produce using conventional techniques.

Precisely Defined Protein-Polymer Conjugates: Construction of Synthetic DNA Binding Domains on Proteins by Using Multivalent Dendrons

Abstract: Nature has evolved proteins and enzymes to carry out a wide range of sophisticated tasks. Proteins modified with functional polymers possess many desirable physical and chemical properties and have applications in nanobiotechnology. Here we describe multivalent Newkome-type polyamine dendrons that function as synthetic DNA binding domains, which can be conjugated with proteins. These polyamine dendrons employ naturally occurring spermine surface groups to bind DNA with high affinity and are attached onto protein surfaces in a site-specific manner to yield well-defined one-to-one protein–polymer conjugates, where the number of dendrons and their attachment site on the protein surface are precisely known. This precise structure is achieved by using N-maleimido-core dendrons that selectively react via 1,4-conjugate addition with a single free thiol group on the protein surface—either Cys-34 of bovine serum albumin (BSA) or a genetically engineered cysteine mutant of Class II hydrophobin (HFBI). This reaction...

Molecular Self-Assembly at Bare Semiconductor Surfaces: Characterization of a Homologous Series of n-Alkanethiolate Monolayers on GaAs(001)

Abstract: Structural trends for a homologous series of n-alkanethiolate self-assembled monolayers (SAMs), CnH2n+1S– with 12 ≤ n ≤ 19, on GaAs(001), studied by a combination of grazing incidence X-ray diffraction and infrared spectroscopy, along with ancillary probes, show an overall decay in organization with decreasing n, with the largest changes occurring below n = 15−16. The long-chain monolayers form a mosaic structure with ≤10 nm domains of molecules organized in an incommensurate pseudo-hcp arrangement with nearest neighbor distances of 4.70 and 5.02 A, a 21.2 A2 area per chain, two chains per subcell in a herringbone packing with a chain tilt angle of 14°, and preferential domain alignment along the substrate [110]([110]) step edge direction. In contrast, for n 16 cases. A 4′-methyl-biphenyl-4-thiolate companion SAM shows evidence for ordered structures but with...

Selection of biomolecules capable of mediating the formation of nanocrystals.

Abstract: Biopolymers in the biosphere are well known to mediate the formation of a wide array of inorganic materials, such as bone, shells, lenses, and magnetic particles to name a few. Recently, in vitro experiments with biopolymers such as peptides, RNA, and DNA have shown that templating by these macromolecules can yield a variety of materials under mild reaction conditions. The primary sequence of the biopolymer can be viewed as a proteomic or genomic signature for the templating of an inorganic material from defined metal precursors and reaction conditions. Together with the rapid advances in inorganic particle synthesis by other combinatorial methods, these bioinspired in vitro materials experiments may provide additional insights into possible inorganic materials yet to be discovered and subsequently synthesized by conventional methods. Some of the concepts important to understanding the crystallization phenomena occurring during biopolymer mediation are discussed. A simple kinetic model is provided in the context of known biopolymer-mediated inorganic crystallizations.

Architecture of Pd-Au bimetallic nanoparticles in sodium bis(2-ethylhexyl)sulfosuccinate reverse micelles as investigated by X-ray absorption spectroscopy.

Abstract: In this study, we demonstrate the unique application of X-ray absorption spectroscopy (XAS) as a fundamental characterization tool to help in designing and controlling the architecture of Pd–Au bimetallic nanoparticles within a water-in-oil microemulsion system of water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane. Structural insights obtained from the in situ XAS measurements recorded at each step during the formation process revealed that Pd–Au bimetallic clusters with various Pd–Au atomic stackings are formed by properly performing hydrazine reduction and redox transmetalation reactions sequentially within water-in-oil microemulsions. A structural model is provided to explain reasonably each reaction step and to give detailed insight into the nucleation and growth mechanism of Pd–Au bimetallic clusters. The combination of in situ XAS analysis at both the Pd K-edge and the Au LIII-edge and UV–vis absorption spectral features confirms that the formation of Pd–Au bimetallic clusters follows a (P...

Fabrication of Complex Metallic Nanostructures by Nanoskiving

Abstract: This paper describes the use of nanoskiving to fabricate complex metallic nanostructures by sectioning polymer slabs containing small, embedded metal structures. This method begins with the deposition of thin metallic films on an epoxy substrate by e-beam evaporation or sputtering. After embedding the thin metallic film in an epoxy matrix, sectioning (in a plane perpendicular or parallel to the metal film) with an ultramicrotome generates sections (which can be as thin as 50 nm) of epoxy containing metallic nanostructures. The cross-sectional dimensions of the metal wires embedded in the resulting thin epoxy sections are controlled by the thickness of the evaporated metal film (which can be as small as 20 nm) and the thickness of the sections cut by the ultramicrotome; this work uses a standard 45° diamond knife and routinely generates slabs 50 nm thick. The embedded nanostructures can be transferred to, and positioned on, planar or curved substrates by manipulating the thin polymer film. Removal of the e...

Controlling nanotube dimensions: correlation between composition, diameter, and internal energy of single-walled mixed oxide nanotubes.

Abstract: Control over the diameter of nanotubes is of significance in manipulating their properties, which depend on their dimensions in addition to their structure and composition. This aspect has remained a challenge in both carbon and inorganic nanotubes, since there is no obvious aspect of the formation mechanism that allows facile control over nanotube curvature. Here we develop and analyze a quantitative correlation between the composition, diameter, and internal energy of a class of single-walled mixed oxide aluminosilicogermanate (AlSiGeOH) nanotubes. A series of synthetic AlSiGeOH nanotubes with varying Si/Ge ratio are characterized by X-ray photoelectron spectroscopy, vibrational spectroscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction to relate their compositions and diameters. We then study these nanotubes computationally by first parametrizing and validating a suitable interatomic potential model, and then using this potential model to investigate the internal energy of the nanotube a...

Enhanced 1520 nm photoluminescence from Er3+ ions in di-erbium-carbide metallofullerenes (Er2C2)@C82 (isomers I, II, and III).

Abstract: Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C82 cage such as Er2@C82 (isomers I, II, and III) and (Er2C2)@C82 (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er2@C82 (I, II, III) and (Er2C2)@C82 (I, II, III) metallofullerenes are characterized by comparison with the UV–vis−NIR absorption spectra of (Y2C2)@C82 (I, II, III), where molecular symmetries of the structures are determined to be Cs, C2v and C3v, respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er3+ ions in Er2@C82 (I, III) and (Er2C2)@C82 (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C82 cage. In particular, the PL intensity of (Er2C2)@C82 (III) has been the strongest among the isomers of Er2@C82 and (Er2C2)@C82. Optical measurements indicate that the PL properties of Er2@C82 (I, II, III) and (Er2C2)@C82 (I, II, III) correlate strongly with the absorbance at...