New Quantum Structures

Synthesis of CdSe Quantum Dots in Two Solvents of Different Boiling Points for Polymer Optical Fiber Technology

Polymer materials find many applications in various industries. Efforts are being made to obtain structures with increasingly better properties. It is necessary not only to obtain new materials but also to modify existing structures. Such is the situation with polymer optical fibers. The widespread use of polymer optical fibers is impossible, due to their very high optical losses compared to glass optical fibers. The solution to this problem can be the manufacturing of polymer active optical fibers. Active fibers are the basic components of fiber optic amplifiers and lasers that allow the direct amplification of light inside the fiber. In order for their operation to be the most effective, it is necessary to use dopants. The most commonly used are lanthanide ions isolated from the polymer network, active organic dyes, and quantum dots. These dopants are characterized by very high luminescence and long glow times. Quantum dots of CdSe are made using two organic solvents that differ in boiling points-hexane (a low-boiling solvent with a boiling point of 69 °C) and 1-octadecene (a high-boiling solvent with a boiling point of 315 °C). This work aims to test whether the type of solvent used to obtain quantum dots affects the doping capabilities of polymer structures, from which optical fibers can then be drawn.

Nanomaterials: a membrane-based synthetic approach

Materials with nanoscopic dimensions not only have potential technological applications in areas such as device technology and drug delivery but also are of fundamental interest in that the properties of a material can change in this regime of transition between the bulk and molecular scales. In this article, a relatively new method for preparing nanomaterials, membrane-based synthesis, is reviewed. This method entails synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes used contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. This "template" method has been used to prepare polymers, metals, semiconductors, and other materials on a nanoscopic scale.

Quantum Dots and Their Multimodal Applications: A Review

Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

Structure of YSi(2) nanowires from scanning tunneling spectroscopy and first principles

Exceptionally long and uniform YSi(2) nanowires are formed via self-assembly on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a class of nanowires that violates the "odd multiple" rule. The structure of the thinnest wire in this category is determined by comparing scanning tunneling spectroscopy measurements with the calculated surface density of states of candidate models by means of the Pendry R-factor analysis. The relative stability of the odd and even wire systems is analyzed via first-principles calculations.

Preparation and application of a novel core/shell organic nanoparticle as a fluorescence probe in the selective determination of Cr(VI)

A novel core/shell organic nanoparticles, anthracene/poly-acrylamide (AN/PAM), has been prepared successfully. Based on the fluorescence quenching of AN/PAM nanoparticles by Cr(VI), a method for the selective determination of Cr(VI), without separation of Cr(VI) in water, was developed. Furthermore, the reaction mechanism between nano-AN/PAM and Cr(VI) was also discussed. The synthesis and reaction conditions were investigated in detail. The assay is characterized by short reaction time, very few interference stable fluorescence signals, simple instruments and sensitivity. Under optical experimental conditions, a limit of detection of 0.02 microg/ml was achieved. The calibration curve was linear over the concentration range 0.04-2.00 microg/ml with a correlation coefficient of 0.9924. The proposed method has been applied to the selective quantification of Cr(VI) in synthetic samples and waste-water samples with the satisfactory results.

Preparation of fluorescent polyvinyl alcohol keto-derivatives nanoparticles and selective determination of chromium(VI)

A novel fluorescent polyvinyl alcohol keto-derivatives nanoparticle (PVAK) has been prepared in one-step method. The nanoparticles has excitation and emission maxima at 349 and 462 nm, respectively. Based on the fluorescence quenching of PVAK by Cr(VI), we established a simple and selective fluorimetric method for the determination of Cr(VI) without separation of Cr(III) in water. The reaction conditions between Cr(VI) and PVAK were investigated in detail. Furthermore, the reaction mechanism between PVAK and Cr(VI) was also discussed. Under optimal experimental conditions, a limit of detection of 0.02 microg mL(-1) was achieved. The calibration curve was linear over the concentration range 0.1-13.2 microg mL(-1) with a correlation coefficient of 0.9987. The proposed method has been applied to the selective quantification of Cr(VI) in synthetic samples and waste-water samples with the satisfactory results.

Synthesis, Morphology, and Magnetic Characterization of Iron Oxide Nanowires and Nanotubes

We have explored the synthesis of iron oxide particles, tubes, and fibrils within the pores of nanoporous polycarbonate and alumina membranes. The membranes contain uniformly distributed cylindrical pores with monodispersed diameters (varying between 20 and 200 nm) and thicknesses of 6 and 60 microm, respectively. By hydrolysis and polymerization of iron salts, particles of different sizes and phases were formed in the pores, building iron oxide particle nanowires. Alternatively, by the sol-gel technique, using as reagents metalloorganic compounds, fibrils and tubes of different iron oxide phases were prepared. Structural and morphological investigations performed using scanning electron microscopy and transmission electron microscopy revealed ordered iron oxide particle wires, tubes, and fibrils formed inside the membrane nanopores. Magnetic characterization was accomplished with a vibrating sample magnetometer. Below the blocking temperature (T(B)), the magnetic behavior of the nanowires was governed by dipolar interaction between nearest-neighbor nanoparticles inside the pore, whereas the energy barrier, and therefore the T(B) value, was mainly governed by dipolar interaction between magnetic moments over larger (interpore) distances. As expected, crystalline iron oxide nanotubes exhibited magnetic perpendicular anisotropy due to their magnetocrystalline and shape anisotropy.

Vibron-polaron critical localization in a finite size molecular nanowire

The small polaron theory is applied to describe the vibron dynamics in an adsorbed nanowire with a special emphasis onto finite size effects. It is shown that the finite size of the nanowire discriminates between side molecules and core molecules which experience a different dressing mechanism. Moreover, the inhomogeneous behavior of the polaron hopping constant is established and it is shown that the core hopping constant depends on the lattice size. However, the property of a lattice with translational invariance is recovered when the size of the nanowire is greater than a critical value. Finally, it is pointed out that these features yield the occurrence of high energy localized states in which both the nature and the number are summarized in a phase diagram in terms of the relevant parameters of the problem (small polaron binding energy, temperature, lattice size).

Correlation of stress and structure in a simple fluid confined to a pore with furrowed walls

A Lennard-Jones (12,6) film confined between two furrowed walls was simulated by the grand canonical ensemble Monte Carlo method. The walls are constructed by gouging triangular grooves in planar substrates that are structureless on the molecular scale. The furrows are infinitely long in one transverse direction (y) and of nanoscopic width (s(x)) and depth (D). The furrows in the two walls are maintained parallel and in register. The diagonal components of the stress tensor (T(alphaalpha), alpha=x,y,z) are computed as functions of D and the separation between the substrates (s(z)) at fixed temperature, chemical potential, and s(x). The T(alphaalpha) for the film between the furrowed walls are strongly shifted from their counterparts for the film between flat (i.e., planar) walls. The shifts are rationalized in terms of the structure of the film, which becomes more ordered as the furrows deepen and the packing of film molecules becomes more restricted in the two dimensions normal to the y direction. The results demonstrate the profound impact of the coupling between molecular and nanoscopic scales on the properties of geometrically constrained fluids.

Preparation of immobilized proteins covalently coupled through silane coupling agents to inorganic supports

Enzymes were first immobilized on inorganic supports through silane coupling agents over 25 yr ago. Since that initial report, literally hundreds of laboratories have utilized this methodology for the immobilization of enzymes, antigens, antibodies, receptors, and other high and low mol wt compounds. Today silane coupling is one of the commonly used techniques in the arsenal of the biochemist for the binding of material of all sorts to inorganic surfaces. Inorganic materials come in a variety of shapes, sizes, and characteristics. Today silane coupling is one of the most used coupling methods for the preparation of biosensing devices. Sol-gel entrapped enzymes are also produced by the application of silane technology by the polymerization of the silane to form glass-like materials with entrapped protein. This review will discuss the general preparation and characterization of silane coupled proteins with special emphasis on enzymes and describe in detail the actual methods for the silanization and specific chemical coupling of proteins to the silanized carrier.