Search

During atomisation, modified agricultural spray formulations can produce less fine spray (for drift control) or reduce the overall droplet size distribution (for efficacy). Motivated by the technical literature concerning antifoaming agents, emulsions with and without solid particles were studied to examine their effect on atomisation. For emulsions, the effects of oil type, oil droplet diameter, surfactant, and presence of solid particles in the oil phase on the sprayed droplet size distribution were examined. Test formulations were compared with a standard commercial formulation and several commercial low-drift adjuvants. Results indicated that large oil droplets and the presence of solid particles reduced the number of fine droplets produced in multi-phase emulsions.

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for the specific, rapid, and nondestructive detection of small molecules. For detection applications, it is desirable to develop means for synthesizing SERS substrates that provide large and consistent Raman enhancement, are inexpensive and simple to synthesize, and are active for a wide variety of molecules. Here we demonstrate that nanoparticle colloids (ranging in size from 5 to 100 nm) that are purposely aggregated using electrolytes can be stabilized in the solid state using common filter paper. The SERS substrate enhancement factor (EF) is characterized using trans-1,2-bis(4-pyridyl)ethylene, and it is observed that an intermediate aggregation state provides the largest substrate EF of ∼3 × 104. Generalized Mie theory is used to investigate the relationship between nanoparticle aggregation extent, cluster geometry, and plasmonic enhancement. Overall, the electrodynamics simulations are in good agreement with experimental EF values and pro...

The intrinsic properties of nanoparticles are both fundamentally interesting and offer tremendous potential for a variety of applications. However, leveraging their utility is difficult because these properties are often intimately connected to nanoparticle stability in solution. We report that cellulose filter paper is a versatile substrate to capture, stabilize, and manipulate nanoparticles. Once immobilized, we present ensemble averaged extinction spectra and propose that this plasmonic paper is a solid state equivalent to a nanoparticle solution. We also demonstrate that capillary flow within the paper creates concentration gradients of reagents for combinatorial chemical reactions on the immobilized nanoparticles. Importantly, the added stability afforded to the nanoparticles by the paper allows for exposure to chemical environments that would otherwise disrupt a nanoparticle colloid. These new capabilities could enable new architectures in nanoparticle-based sensors and biodiagnostics where many of the previous design limitations are entirely avoided.

The microstructure of heterogeneous nanowires plays a major role in determining their properties. For example, core-shell nanowires composed of optically active p- and n-type semiconductors have photovoltaic properties that are superior to their planar counterparts due to more efficient charge separation owing to the high interfacial surface area and relatively small distance required to separate electron-hole pairs. The limited combined use of polymer, core-shell, and plasmonic compositions in nanostructured materials highlights the lack of versatility in current synthetic techniques and emphasizes the need for new synthetic techniques to address unmet challenges facing the photovoltaic community. Here, we report the electrochemical synthesis of solution dispersible, multi-segmented nanowires in which metallic nanostructures are precisely interfaced with core-shell polymeric and inorganic semiconductor materials with nanometer scale resolution.

In general, there are two approaches to scanning probe lithography differentiated by what is being delivered to the patterned surface. One class of tools, such as nanografting,[1] anodic oxidation,[2] and indenting,[3] deliver different forms of energy to a surface to create desired patterns. The other class of tools, such as dip-pen nanolithography,[4] polymer pen lithography,[5] and hard-tip, soft-spring lithography,[6] often referred to as molecular printing techniques,[7] rely on the direct delivery of materials to a surface. The resolution of all of these tools is determined in part by the diameter of the tip, and therefore, poses the question, is it possible to do scanning probe lithography at a resolution that exceeds such a limitation? Herein, we describe a novel strategy that relies on a scanning probe to generate patterns on a surface by using the tip as a plow to create depressions and adjacent raised ridges on a polymer-coated substrate. Anisotropic etching can be used to expose the entire underlying surface except for the corresponding raised features. Subsequent etching allows one to transfer such patterns into the underlying material. Note that these raised features can have geometries significantly smaller than the tip curvature.

We report a simple and highly efficient method for creating graphene nanostructures with gaps that can be controlled on the sub-10 nm length scale by utilizing etch masks comprised of electrochemically synthesized multisegmented metal nanowires. This method involves depositing striped nanowires with Au and Ni segments on a graphene-coated substrate, chemically etching the Ni segments, and using a reactive ion etch to remove the graphene not protected by the remaining Au segments. Graphene nanoribbons with gaps as small as 6 nm are fabricated and characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The high level of control afforded by electrochemical synthesis of the nanowires allows us to specify the dimensions of the nanoribbon, as well as the number, location, and size of nanogaps within the nanoribbon. In addition, the generality of this technique is demonstrated by creating silicon nanostructures with nanogaps.

We report the synthesis of solution dispersible, one-dimensional metal nanostructure arrays as small as 35 nm in diameter using on-wire lithography, wherein feature thickness and spacing in the arrays is tailorable down to approximately 6 and 1 nm, respectively. Using this unique level of control, we present solution-averaged extinction spectra of 35 nm diameter Au nanorod dimers with varying gap sizes to illustrate the effect of gap size on plasmon coupling between nanorods. Additionally, we demonstrate control over the composition of the arrays with Au, Ni, and Pt segments, representing important advances in controlling the ordering of sub-100 nm nanostructures that are not available with current synthesis or assembly methods.

The extinction spectra of Au nanorods electrochemically synthesized using anodic aluminum oxide templates are reported. Homogeneous suspensions of nanorods with average diameters of 35, 55, 80, and 100 nm and varying lengths were synthesized, and their resultant surface plasmon resonances were probed by experimental and theoretical methods. Experimental extinction spectra of the nanoparticles exhibit good overall agreement with those calculated using the discrete dipole approximation. We determine the dependence of the dipole plasmon wavelength on both rod length and diameter, and we then utilize these results to derive an equation for predicting longitudinal dipole resonance wavelength for nanorod dimensions beyond the quasistatic limit. On average, the equation allows one to predict plasmon resonance maxima within 25 nm of the experimentally measured values. An analysis of factors that are important in determining the plasmon width is also provided. For long rods, the width decreases with increasing length in spite of increased radiative damping due to increased frequency dispersion in the real part of the metal dielectric function.

Nanostructures fabricated by a novel technique, termed On-Wire-Lithography (OWL), can be combined with organic and biological molecules to create systems with emergent and highly functional properties. OWL is a template-based, electrochemical process for forming gapped cylindrical structures on a solid support, with feature sizes (both gap and segment length) that can be controlled on the sub-100 nm length scale. Structures prepared by this method have provided valuable insight into the plasmonic properties of noble metal nanomaterials and have formed the basis for novel molecular electronic, encoding, and biological detection devices.

The dependence of iron oxide nanoparticle formation on the structure and thermal properties of Fe oleate complexes has been studied using FTIR, elemental analysis, X-ray photoelectron spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM. The combination of FTIR, elemental analysis, and DSC allowed us to reveal differences between Fe oleate structures for as-synthesized and postsynthesis treated (drying and extraction with polar solvents) compounds. As-synthesized Fe oleate was found to contain a significant fraction of oleic acid, which works as a modifier altering the decomposition process and as an extra stabilizer during iron oxide nanoparticle formation. The thermal treatment of as-synthesized Fe oleate at 70 °C leads to removal of the crystal hydrate water and dissociation of oleic acid dimers, leading to a more thermally stable iron oleate complex whose final decomposition occurs at about 380 °C. Extraction of...

Scanning probe lithography (SPL) is a promising candidate approach for desktop nanofabrication, but trade-offs in throughput, cost, and resolution have limited its application. The recent development of cantilever-free scanning probe arrays has allowed researchers to define nanoscale patterns in a low-cost and high-resolution format, but with the limitation that these are duplication tools where each probe in the array creates a copy of a single pattern. Here, we report a cantilever-free SPL architecture that can generate 100 nanometer-scale molecular features using a 2D array of independently actuated probes. To physically actuate a probe, local heating is used to thermally expand the elastomeric film beneath a single probe, bringing it into contact with the patterning surface. Not only is this architecture simple and scalable, but it addresses fundamental limitations of 2D SPL by allowing one to compensate for unavoidable imperfections in the system. This cantilever-free dot-matrix nanoprinting will enable the construction of surfaces with chemical functionality that is tuned across the nano- and macroscales.

Crystallization is a fundamental and ubiquitous process much studied over the centuries. But although the crystallization of atoms is fairly well understood, it remains challenging to predict reliably the outcome of molecular crystallization processes that are complicated by various molecular interactions and solvent involvement. This difficulty also applies to nanoparticles: high-quality three-dimensional crystals are mostly produced using drying and sedimentation techniques that are often impossible to rationalize and control to give a desired crystal symmetry, lattice spacing and habit (crystal shape). In principle, DNA-mediated assembly of nanoparticles offers an ideal opportunity for studying nanoparticle crystallization: a well-defined set of rules have been developed to target desired lattice symmetries and lattice constants, and the occurrence of features such as grain boundaries and twinning in DNA superlattices and traditional crystals comprised of molecular or atomic building blocks suggests that similar principles govern their crystallization. But the presence of charged biomolecules, interparticle spacings of tens of nanometres, and the realization so far of only polycrystalline DNA-interconnected nanoparticle superlattices, all suggest that DNA-guided crystallization may differ from traditional crystal growth. Here we show that very slow cooling, over several days, of solutions of complementary-DNA-modified nanoparticles through the melting temperature of the system gives the thermodynamic product with a specific and uniform crystal habit. We find that our nanoparticle assemblies have the Wulff equilibrium crystal structure that is predicted from theoretical considerations and molecular dynamics simulations, thus establishing that DNA hybridization can direct nanoparticle assembly along a pathway that mimics atomic crystallization.

Öz bulunamadı.

We report the synthesis of solution-dispersible, 35 nm diameter gold nanorod dimers with gaps as small as ∼2 nm for surface-enhanced Raman scattering (SERS). Using on-wire lithography (OWL), we prepared tailorable dimers in high yield and high monodispersity (∼96% dimers) that produce both large and reproducible SERS signals with enhancement factors of (6.8 ± 0.7) × 10(8) for single dimers in air and 1.2 × 10(6) for ensemble-averaged solution measurements. Furthermore, we show that these structures, which are the smallest ever made by OWL, can be used to detect molecules on flat surfaces and in aqueous solutions. When combined, these attributes with respect to sensitivity, reproducibility, and tailorability lead to a novel and powerful local amplification system for SERS applications.

We report a simple but efficient method to synthesize carbon nanotube-bridged wires (NBWs) with gaps as small as 5 nm. In this method, we have combined a strategy for assembling carbon nanotubes (CNTs) inside anodized aluminum oxide pores and the on-wire lithography technique to fabricate CNT-bridged wires with gap sizes deliberately tailored over the 5–600 nm range. As a proof-of-concept demonstration of the utility of this architecture, we have prepared NBW-based chemical and biosensors which exhibit higher analyte sensitivity (lower limits of detection) than those based on planar CNT networks. This observation is attributed to a greater surface-to-volume ratio of CNTs in the NBWs than those in the planar CNT devices. Because of the ease of synthesis and high yield of NBWs, this technique may enable the further incorporation of CNT-based architectures into various nanoelectronic and sensor platforms.

Nanoparticles are finding utility in myriad biotechnological applications, including gene regulation, intracellular imaging, and medical diagnostics. Thus, evaluating the biocompatibility of these nanomaterials is imperative. Here we use genome-wide expression profiling to study the biological response of HeLa cells to gold nanoparticles functionalized with nucleic acids. Our study finds that the biological response to gold nanoparticles stabilized by weakly bound surface ligands is significant (cells recognize and react to the presence of the particles), yet when these same nanoparticles are stably functionalized with covalently attached nucleic acids, the cell shows no measurable response. This finding is important for researchers studying and using nanomaterials in biological settings, as it demonstrates how slight changes in surface chemistry and particle stability can lead to significant differences in cellular responses.

Modification of iron oxide nanoparticles (NPs) synthesized by high temperature solvothermal routes is carried out using two silanes: (i) N-(6-aminohexyl)-aminopropyltrimethoxysilane (AHAPS) where only one end of the molecule reacts with the surface Fe–OH groups and (ii) 3-(triethoxysilyl)propylsuccinic anhydride (SSA) where both ends are reactive with Fe–OH. Depending on the NP synthesis protocol, the amount of surface OH groups on the NPs may differ, however, for all the cases presented here, the comparatively low OH group density prevents a high density of AHAPS coverage, yielding NP aggregates instead of single particles in aqueous solutions. Alternatively, use of SSA containing two terminal functionalities, anhydride and siloxy, which are both reactive towards the NP surface, results in the formation of discrete dense polymeric shells, providing stability of individual NPs in water. The mechanism of the SSA shell formation is discussed. The evolution of the chemical transformations leads to shells of different thickness and density, yet this evolution can be halted by hydrolysis, after which the NPs are water soluble, negatively charged and exhibit excellent stability in aqueous media.

Iron oxide nanoparticles (NPs) with diameters of 16.1, 20.5, and 20.8 nm prepared from iron oleate precursors were coated with poly(maleic acid-alt-1-octadecene) (PMAcOD). The coating procedure exploited hydrophobic interactions of octadecene and oleic acid tails while hydrolysis of maleic anhydride moieties allowed the NP hydrophilicity. The PMAcOD nanostructure in water and the PMAcOD-coated NPs were studied using transmission electron microscopy, zeta-potential measurements, small-angle X-ray scattering, and fluorescence measurements. The combination of several techniques suggests that independently of the iron oxide core and oleic acid shell structures, PMAcOD encapsulates NPs, forming stable hydrophilic shells which withstand absorption of hydrophobic molecules, such as pyrene, without shell disintegration. Moreover, the PMAcOD molecules are predominantly attached to a single NP instead of self-assembling into the PMAcOD disklike nanostructures or attachment to several NPs. This leads to highly monodisperse aqueous samples with only a small fraction of NPs forming large aggregates due to cross-linking by the copolymer macromolecules.

The development of a lithographic method that can rapidly define nanoscale features across centimetre-scale surfaces has been a long-standing goal for the nanotechnology community. If such a 'desktop nanofab' could be implemented in a low-cost format, it would bring the possibility of point-of-use nanofabrication for rapidly prototyping diverse functional structures. Here we report the development of a new tool that is capable of writing arbitrary patterns composed of diffraction-unlimited features over square centimetre areas that are in registry with existing patterns and nanostructures. Importantly, this instrument is based on components that are inexpensive compared with the combination of state-of-the-art nanofabrication tools that approach its capabilities. This tool can be used to prototype functional electronic devices in a mask-free fashion in addition to providing a unique platform for performing high-throughput nano- to macroscale photochemistry with relevance to biology and medicine.