Adhesion of chemically and electrostatically bound gold nanoparticles to a self-assembled silane monolayer investigated by atomic force volume spectroscopy

The adhesion of gold nanoparticles either electrostatically or chemically attached to a substrate has been probed using AFM operating in force spectroscopy mode. A monolayer of –NH₂ terminated 3-aminopropyltriethoxysilane or –SH terminated 3-mercaptopropyltrimethoxysilane was self-assembled onto a p-type silicon (100) substrate. Each silane monolayer provided the point of attachment for citrate stabilised gold colloid nanoparticles. In the case of the –NH₂ terminated layer gold colloid assembly was driven by the electrostatic attraction between the negative, citrate-capped, gold nanoparticles and a partially protonated amine layer. In the case of the –SH terminated regions, well-known gold–thiol chemistry was used to chemically attach the nanoparticles. An atomic force microscope tip was chemically modified with 3-mercaptopropyltrimethoxysilane and scanned across each surface, where the cantilever deflection was measured at each x, y pixel of the image to create an array of adhesion force curves. This has allowed an unprecedented nanoscale characterisation of the adhesion force central to two common surface attachment methods of gold colloid nanoparticles, providing useful insights into the stability of nanoscale constructs.     

Harnack Inequalities and Discrete—Continuous Error Estimates for a Chain of Atoms with Two—Body Interactions

We consider deformations in ℝ³ of an infinite linear chain of atoms where each atom interacts with all others through a two-body potential. We compute the effect of an external force applied to the chain. At equilibrium, the positions of the particles satisfy an Euler–Lagrange equation. For large classes of potentials, we prove that every solution is well approximated by the solution of a continuous model when applied forces and displacements of the atoms are small. We establish an error estimate between the discrete and the continuous solution based on a Harnack lemma of independent interest. Finally we apply our results to some Lennard-Jones potentials.     

Surface modification of poly(dimethylsiloxane) for microfluidic assay applications

The surface of a poly(dimethylsiloxane) (PDMS) film was imparted with patterned functionalities at the micron-scale level. Arrays of circles with diameters of 180 and 230 μm were functionalized using plasma oxidation coupled with aluminum deposition, followed by silanization with solutions of 3-aminopropyltrimethoxy silane (3-APTMS) and 3-mercaptopropyltrimethoxy silane (3-MPTMS), to obtain patterned amine and thiol functionalities, respectively. The modification of the samples was confirmed using X-ray photoelectron spectroscopy (XPS), gold nanoparticle adhesion coupled with optical microscopy, as well as by derivatization with fluorescent dyes. To further exploit the novel surface chemistry of the modified PDMS, samples with surface amine functionalities were used to develop a protein assay as well as an array capable of cellular capture and patterning. The modified substrate was shown to successfully selectively immobilize fluorescently labeled immunoglobulin G (IgG) by tethering Protein A to the surface, and, for the cellular arrays, C2C12 rat endothelial cells were captured. Finally, this novel method of patterning chemical functionalities onto PDMS has been incorporated into microfluidic channels. Finally, we demonstrate the in situ chemical modification of the protected PDMS oxidized surface within a microfluidic device. This emphasizes the potential of our method for applications involving micron-scale assays since the aluminum protective layer permits to functionalize the oxidized PDMS surface several weeks after plasma treatment simply after etching away the metallic thin film.     

Design and Synthesis of Highly Photostable Yellow–Green Emitting 1,8-Naphthalimides as Fluorescent Sensors for Metal Cations and Protons

Two highly photostable yellow–green emitting 1,8-naphthalimides 5 and 6, containing both N-linked hindered amine moiety and a secondary or tertiary cation receptor, were synthesized for the first time. Novel compounds were configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (4:1, v/v) solution. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Co²⁺) and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the dye fluorescence intensity. Compound 5, containing secondary amine receptor, displayed a good sensor activity towards metal ions and protons. However the sensor activity of dye 6, containing a tertiary amine receptor and a shorter hydrocarbon spacer, was substantially higher. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Cu²⁺ ions.     

Simultaneously All-Optical Inverted and Noninverted Wavelength Conversion Employing Ultra-Small Silicon-on-Insulator Waveguide

We propose single-to-dual all-optical wavelength conversion based on stimulated Raman effect on silicon waveguides. Simulation results of non-return-to-zero (NRZ) pseudorandom bit sequence (2⁷–1 code) at 10, 50, and 200-Gbit/s rates of conversion in an ultra-small silicon-on-insulator waveguide are presented. The main goal in the proposed scheme is that the converted signal can be obtained simultaneously inverted, at the 1550 nm channel (down-conversion) and non-inverted, at the 1846 nm channel (up-conversion), for original signal fixed at 1686 nm.     

Effect of processing on rheological properties and structure development of EPOXY/MWCNT nanocomposites

Polymer nanocomposites of epoxy resin containing multiwall carbon nanotubes (external diameter ~30 ± 10 nm, approximate length 10–20 μm) are studied using a rheological approach to determine the stage of debundling of the nanofiller in the epoxy matrix and the development of the rheological properties and structure with time. The role of processing for nanotube dispersion and structure formation is also determined by polarized microscopy and Raman spectrometry. Functionalization with amine groups is applied for part of the samples (mixing the nanotubes in amine hardener followed by mixing in appropriate amounts of epoxy resin). Further on the experimental procedure has been optimized and samples within the concentration range from 0 to 1.0 wt% have been prepared by applying high speed mechanical mixing and ultrasonic treatment with power of 250 W. The results show that chemical functionalization with amine groups contributes to significant changes in the rheological properties and hence in the structure of the composites, as proved by Raman and POM results, indicating better deaggregation of the carbon nanotubes in the amine hardener and chemical bonding of the amine groups attached to the functionalized nanotube surface with the epoxy matrix. The evolution of the dynamic viscosity in the process of polymerization reveals some interesting aspects as retarded curing in the viscometer cell, compared to the control sample under the same conditions, prolonged polymerization time owing to the applied shear rates and carbon nanotube content.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Self‐Assembly of Functionalized Gold Nanoparticles with Rigid and Flexible Multifunctional Linkers

The interparticle spacing of carboxyl functionalized gold nanoparticles (Au–COOH) was mediated by rigid cross‐linkers, octa(3‐aminopropyl)octasilsesquioxane (POSS–NH₃ ⁺) and poly(amidoamine) dendrimer terminated with hydroxyl groups (PAMAM–OH), and a flexible polymeric linker, poly(hexanyl viologen) (6‐VP). Regular interparticle spacing was achieved by utilizing POSS–NH₃ ⁺ and PAMAM–OH dendrimer as cross‐linkers, whereas size growth of Au–COOH was observed featuring no interparticle spacing by utilizing 6‐VP as the cross‐linker.     

Functionalization of carbon nanofibers with elastomeric block copolymer using carbodiimide chemistry

Surface functionalization of carbon nanofibers (CNFs) with aminopropyl terminated polydimethylsiloxane [(PDMS-NH₂)] and other organic diamines was achieved using carbodiimide chemistry. The carbodiimide chemistry provides faster reaction rate so that the reaction occurs at lower temperature compared to amidation and acylation-amidation chemistry. CNF functionalized with PDMS-NH₂ fibers were further functionalized with oligomer of polyimide (6FDA-BisP) using imidization reaction. The formation of block copolymer on the surface of CNF is proposed as an effective method to engineer the interphase between the fiber and the polymer, which is essential to modulate and enhance the properties of the nanocomposite. The efficiency of the carbodiimide chemistry to functionalize amine terminated groups on CNF and the functionalization of block copolymer was characterized using thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy.     

Investigation of SRS conversion of XeCl laser emission in lead vapor,methane, and hydrogen

We have thus optimized the conditions for SRS conversion of XeCl-laser emission in lead vapor, methane, and hydrogen. The greatest influence on the conversion efficiency is exerted for an SRS cell with lead by the divergence of the pump radiation, the focusing geometry, and the type of buffer gas. The maximum efficiency with respect to absorbed UV energy was ∼57% when xenon gas was used as the buffer, corresponding to 85% of the photon efficiency. The converted radiation could be continuously tuned in the 457.6–459.3 nm band. Addition of a light gas such as helium or hydrogen to methane raised the efficiency of conversion into Stokes components in methane to ∼24 %.     

Fabrication and characterisation of microscale air bridges in?conductive gallium nitride

Fabrication and electrical characterisation of microscale air bridges consisting of GaN heavily doped with silicon is described. These were made from GaN–AlInN–GaN epitaxial trilayers on sapphire substrates, in which the AlInN was close to the composition lattice matched to GaN at ∼17% InN fraction. The start of the fabrication sequence used inductively coupled plasma etching with chlorine chemistry to define mesas. In situ monitoring by laser reflectometry indicated an AlInN vertical etch rate of 400 nm/minute, ∼70% of the etch rate of GaN. Processing was completed by lateral wet etching of the AlInN in hot nitric acid to leave GaN microbridges supported between anchor posts at both ends. Deposition of Ti–Au contact pads onto the anchor posts allowed study of the electrical characteristics. At low applied voltages, vertical conduction through the undoped AlInN layers was minimal in comparison with the current path through the Si:GaN bridges. Typical structures showed highly linear current-voltage characteristics at low applied voltages, and had resistances of 1050 Ω. The observed resistance values are compared with the predicted value based on materials parameters and an idealised geometry. The microbridges showed damage from Joule heating only at current densities above 2×10⁵ A cm⁻².     

Investigation of aminotrimethoxysilanes and organic acids functionalized surface interactions: Theoretical and atomic force microscopy studies

Silane compounds provide many applications in biotechnology field. Chemically adsorbed silanes with reactive terminal groups are used for fabrication of functional material, which can serve as a model substrate for fundamental studies of different surface interactions or as a platform for further chemical reactions.In this work, silane compounds with amine groups were the area of interest. The studies were focused on investigation of amine group interaction with different acid groups. The interactions were probed using atomic force microscope operating in force spectroscopy mode. An atomic force microscope gold tip, functionalized with thiol compounds, served as acid-terminated surface. Interactions at interfaces between the silane self-assembled monolayer (SAM) and the thiol SAM were measured in liquid environment. The results of the measurements were set against the theoretical studies performed by AM1d and PM5 semi-empirical methods. Moreover, prior to chemical force spectroscopy measurements the silane films coverage quality was studied as well. Fourier transform infrared (FTIR) spectrometer and atomic force microscope served as control equipment.     

Large electrostrictive strain in lead-free Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–KNbO<Subscript>3</Subscript> ceramics

In the present work, (1−x)(0.935Bi_0.5Na_0.5TiO₃–0.065BaTiO₃)–xKNbO₃ (BNT–BT–KN, BNT–BT–100xKN) ceramics with x ranging from 0 to 0.1 were prepared by the conventional ceramic fabrication process. A large electrostrictive coefficient of ∼10⁻² m⁴ C⁻² is obtained with the composition x ranging from 0.02 to 0.1, which is close to the well-known electrostrictive material Pb(Mg_1/3Nb_2/3)O₃. Under an electric field of 4 kV/mm, the electrostrictive strain can reach as high as 0.08%. Besides, the electric field induced strain behavior indicates a temperature independent behavior within the temperature range of 20 to 150°C. The large electrostrictive strain is suggested to be ascribed to the formation of non-polar (NP) phase developed by the KNbO₃ substitution, and the high electrostrictive coefficient of BNT–BT–KN ceramics makes them great candidates to be applied in the new solid-state actuators.     

Subbarrier conversion in 125Te45+

We discuss the process of resonant subbarrier internal conversion of γ rays, where the converted electron is transferred to one of the atomic orbitals. For the first time we study how this process is affected by residual interactions: the splitting of the atomic terms in the total angular momentum of the atom, configuration mixing, and the magnetic interaction between the electrons of the atom. The calculations are done by the relativistic multiconfiguration Dirac-Fock method with allowance for the Breit interaction for the M1 transition with an energy of 35 492 eV in multiply charged ions of ¹²⁵Te. We show that allowing for the residual interaction is obligatory if we want to calculate the conversion rate in the vicinity of a resonance correctly. Zh. éksp. Teor. Fiz. 116, 1565–1574 (November 1999)     

Optical anisotropy as a technique for studying ultrafast phase transformations at solid surfaces

A new technique for testing long-range order in high-absorption anisotropic crystals has been developed using conversion of an incident p-(s-)wave to an s-(p-)wave due to optical anisotropy. The technique yields time-resolved measurements of parameters related to phase transformations in thin (10⁻⁶–10⁻⁵ cm) layers with a high resolution (10⁻¹² s). Using picosecond laser pulses and an “Agat” streak camera, the technique has been applied to an experimental investigation of melting and recrystallization kinetics at zinc and graphite surfaces. It was found that the process of melting takes less than 3 ps and the recrystallization time is about 100 ps. Zh. éksp. Teor. Fiz. 113, 2162–2173 (June 1998)     

Avidin conjugation to up-conversion phosphor NaYF4:Yb3+, Er3+ by the oxidation of the oligosaccharide chains

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. After being functionalized with SiO₂–NH₂ layer, these NaYF₄:Yb³⁺, Er³⁺ nanoparticles can conjugate with activated avidin molecules (activated by the oxidation of the oligosaccharide chain). The as-formed NaYF₄:Yb³⁺, Er³⁺ nanoparticles, NaYF₄:Yb³⁺, Er³⁺ nanoparticles functionalized with amino groups, avidin conjugated amino-functionalized NaYF₄:Yb³⁺, Er³⁺ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), UV/Vis absorption spectra, and up-conversion luminescence spectra, respectively. The biofunctionalization of the NaYF₄:Yb³⁺, Er³⁺ nanoparticles has less effect on their luminescence properties, i.e., they still show the up-conversion emission (from Er³⁺, with ⁴S_3/2 → ⁴I_15/2 at ~540 nm and ⁴F_9/2 → ⁴I_15/2 at ~653 nm), indicative of the great potential for these NaYF₄:Yb³⁺, Er³⁺ nanoparticles to be used as fluorescence probes for biological system.     

Stimulated Raman conversion of radiation from a YAG:Nd laser with wavelengths of 1.319, 1.338, and 1.357 µm in a barium nitrate crystal

We have studied stimulated Raman (SRS) conversion to the first Stokes component of multimode (M₂ = 8) radiation from a YAG:Nd laser with lasing wavelengths of 1.319 μm, 1.338 μm, and 1.357 μm in a barium nitrate crystal. We have obtained pulses of converted radiation with energies up to 120 mJ. We have achieved conversion efficiencies greater than 40% for each of the three Raman laser wavelengths of 1.530 μm, 1.556 μm, and 1.582 μm with divergence of the beams of converted radiation close to the diffraction-limited value (M₂ < 1.5). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 330–334, May–June, 2006.     

Photophysical Properties of Lanthanide Hybrids Covalently Bonded To Functionalized MCM-41 by Modified Aromatic Carboxylic Acids

MCM-41 mesoporous silica has been functionalized with aromatic carboxylic acids salicylic acid (Sal) and 2-hydroxyl-3-methylbenzoic acid (HMBA) through co-condensation approach of tetraethoxysilane (TEOS) in the presence of the cetyltrimethylammonium bromide (CTAB) surfactant as a template. Organic ligands salicylic acid or 2-hydroxyl-3-methylbenzoic acid grafted to the coupling agent 3-(triethoxysilyl)-propyl isocyanate (TEPIC) was used as the precursor for the preparation of an organic–inorganic hybrid materials. Novel organic–inorganic mesoporous luminescent hybrid containing Ln³⁺ (Tb³⁺, Eu³⁺) complexes covalently attached to the functionalized ordered mesoporous MCM-41, which were designated as Ln-Sal-MCM-41 and Ln-HMBA-MCM-41, respectively, were obtained by sol–gel process. The luminescence properties of these resulting materials were characterized in detail, and the results reveal that luminescent mesoporous materials have high surface area, uniformity in the mesopore structure and good crystallinity. Moreover, the mesoporous material covalently bonded Tb³⁺ complex (Tb-Sal-MCM-41 and Tb-HMBA-MCM-41) exhibit the stronger characteristic emission of Tb³⁺ and longer lifetime than the corresponding Eu-containg materials Eu-Sal-MCM-41 and Eu-HMBA-MCM-41 due to the triplet state energy of modified organic ligands Sal-TEPIC and HMBA-TEPIC match with the emissive energy level of Tb³⁺ very well. In addition, the luminescence lifetime and emission quantum efficiency of ⁵D₀ Eu³⁺ excited state also indicates the efficient intramolecular energy transfer process in Tb-SAL-MCM-41 and Tb-HMBA-MCM-41.     

Simulations of multiphase reactive flows in fluidized beds using in situ adaptive tabulation

A novel algorithm, in situ adaptive tabulation (ISAT), has been implemented into a multiphase computational fluid dynamics (CFD) code to treat complex chemistry calculations. In this work, isothermal silane pyrolysis in a fluidized bed reactor is presented to test the feasibility and explore the capabilities of ISAT with a finite-volume two-fluid code (MFIX). Based on the results of simulations, an error tolerance of 10^?5 is found to be satisfactory for maintaining the accuracy for the examples investigated. Due to the rapidly changing time step used in the CFD code, the performance enhancement was found initially to be minimal. However, the performance is significantly improved when ISAT is called using a fixed time step.     

The Magnetisation of Large Atoms¶in Strong Magnetic Fields

In this paper we study the asymptotic form of the magnetisation and current of large atoms in strong constant magnetic fields. We prove that the Magnetic Thomas–Fermi theory gives the right magnetisation/current for magnetic field strengths which satisfy B≤Z ^4/3. Received: 24 April 2000 / Accepted: 21 August 2000