Advanced Materials

Light-emitting organic materials continue to assume increasing significance in the field of semiconductor laser research, and the Figure depicts several structures that have been demonstrated using organic semiconductors. This review provides a description of the fundamental aspects of lasers and a historical overview of their development, followed by a discussion of the recent progress in optically pumped lasers, and their implications for laser technology.

Conjugated dendrimers are a promising new class of material for organic LEDs. The authors report here an investigation into a new family of conjugated light-emitting dendrimers based on the phenylenevinylene structure, and the effect of generation number (level of branching) on both the electroluminescence and photophysical properties of the materials. High fluorescence was found for all three of the first, second, and third generation dendrimers, while concentration quenching effects are substantially avoided by the dendritic molecular architecture.

Spatially coupled bipolar electrochemistry(SCBE) is a novel technique for the formation of electrical connections between isolated metal components. When a voltage difference is applied across the platinum electrodes, the components become polarized, and copper electrodissolves from the right copper ring (see Figure), and the ions migrate to the silicon chip, where the copper electroplates in the form of a wire (see Cover).

Alumina molecular sieves with continuously adjustable pore sizes are achieved by use of cationic surfactant-assisted synthesis, a technique which is reported for the first time. The “hydrolysis-retarding” role played by triethanolamine allows control of the competition between aluminum hydrolysis/condensation reactions and organic-inorganic self-assembling processes. This leads to thermally stable mesoporous alumina molecular sieves, whose pore size can then be tuned by the adjustment of the molar ratio of the reactants.

That the Langmuir–Blodgett (LB) techniqueallows molecules to pack and orient in a well-defined fashion along a surface lends it suitability for preparing films of compounds with useful magnetic properties. Here is reported the synthesis of a semi-fluorinated iron complex (see Figure) that is extremely stable in the LB film, and whose spin crossover process was able to be followed with a SQUID susceptometer.

A new approach to sol-gel film formation, involving electrochemical control of the pH near a conductive surface, is described here, in which methyltrimethoxysilane (MeTMOS) is deposited onto indium-tin-oxide and gold surfaces. The method is based on a “two-step” sol-gel preparation procedure in which MeTMOS is first pre-hydrolyzed and then polycondensed. A constant negative potential is applied to the electrode surface, increasing the concentration of hydroxyl ions, which act as a catalyst in the condensation process. This results in greater control over the deposition process and thus over film properties.

Well-ordered arrays of Fe₃O₄ nanoparticleswith a new type of packing have been produced using the Langmuir–Blodgett technique. Depending on the local absorption conditions, both 2D and 1D assemblies of nanoparticles are produced, the latter in the form of single and double chains of equally spaced nanoparticles. The Figure depicts a film of Fe₃O₄ nanoparticles on a stearic acid monolayer.

The use of hydrogen bonds for the induction of liquid-crystalline (LC) order is attractive because the resulting self-assembled materials can potentially behave as dynamic systems. In this communication is reported an accelerated response to an electric field through the gelation of hydrogen-bonded molecular aggregates of an amino acid derivative with non-hydrogen bonded LC molecules. The resulting gels are a new class of materials that combine the properties of gels, which form soft solids, with liquid crystals, which possess molecular dynamics and anisotropy.

The synthesis of mechanically stable mesoporous silicaswith large pores can be achieved by casting the lyotropic phases of amphiphilic block copolymers. Here is presented new non-ionic polymer templates that allow larger pore diameters than previously reported with this procedure. In the Figure is depicted a silica with 63 nm diameter cylindrical pores.

The relationship between particle size and bandgap energyin magnesium-containing quantum dots is reported here for the first time. A reverse micellar process was used in the synthesis of the Cd_1–yMn_yS quantum dots, a procedure whereby the size and composition of the quantum dots can be independently controlled. This allowed detailed investigation of the magnetic interactions between Mn²⁺ ions and the electron bands of CdS, and between Mn²⁺ ions themselves, and of how these interactions vary with the size and composition of the Cd_1–yMn_yS quantum dots.

Thermoelectric materials have the ability to convert heat to electricity and are currently used in Peltier cooling devices. Here is reported the combination of electrodeposition with template synthesis to prepare thermoelectric bismuth telluride nanowires within the pores of an alumina template membrane. The individual nanowires can be isolated by removal of the template membrane (see Figure).

Buckminsterfullerene is a conjugated electron-accepting molecule that has potential use in nonlinear optical applications, while the addition of endohedral lithium should transfer charge to the carbon cage, ultimately providing a low potential energy surface for the motion of the Li atom. These authors present a theoretical and experimental investigation into the second hyperpolarizability of Li@C₆₀, and show that the presence of a Li atom inside a C₆₀ cage increases its second hyperpolarizability by an order of magnitude.

Polymer nanocomposites can exhibit unusual properties, and potential applications include catalyst supports and abrasion-resistant coatings. The copolymerization of 4-vinylpyridine in the presence of ultrafine silica sol is reported here to give rise to stable colloidal dispersions of polymer–silica nanocomposites which display a distinctive “currant bun” morphology (see Figure) in contrast to previously reported “raspberry” morphologies.

The synthesis and processing of ultrathin polymer films by stepwise adsorption from solution has enjoyed rapid developments in recent years, such that multilayer architectures can now be designed with nano-precision, while electrostatic adsorption of oppositely charged polymers has been used to produce optically and electrically functional polymers. The authors present the highlights of these developments in this report, before summarizing their own results from polymerization-induced adsorption of films onto solid surfaces.

The inherent spectral purity of lasers makes them attractive for use in video projection technology. These authors have developed a method based on the image mode laser. The concept is described in detail and recent results are summarized and evaluated using standard monochrome images such as the 300 × 300 pixel image mode laser picture shown in the Figure.