We will describe the first synthesis of ordered mesoporous silica using a fluorinated surfactant template. Nitrogen adsorption, x-ray diffraction and TEM results will be presented that show that at room temperature, we form particles with well-ordered 2D hexagonal pores using a cationic surfactant with a partially fluorinated octyl (C8) tail. The pore diameter determined by the inflection in the nitrogen adsorption isotherm is on the order of 2.6 nm and the pore size distribution is very narrow. Consistent diameters are found with a modified Kelvin equation approach and with nonlocal density functional theory. The same pore size and long-range order are found for a range of surfactant to silica ratios.

Understanding the process of self-organization of Ge nanostructures on Si with controlled size distribution is a key requirement for their application to devices. In this study, we investigate the temporal evolution of self-assembled islands during the low pressure chemical vapour deposition (LPCVD) of Ge on Si at 650°C using high growth rates (6–9 nm/min). The islands were characterized by atomic force microscopy, transmission electron microscopy, Rutherford backscattering spectrometry and micro-Raman spectroscopy. We found that the first nanostructures to assemble were small islands, with a narrow size distribution, typical of the ‘lens-shaped’ structures reported in previous studies. Next to form were a population of larger ‘lens-shaped’ islands with a similar surface density to that of the small islands, but with broad height and width distributions. These islands differ from the pyramid-shaped islands previously reported for a similar size range. On further Ge deposition, the population evolves into one of large square-based truncated pyramids with a very narrow size distribution. Such pyramidal structures were previously reported at smaller sizes. Furthermore, we see no evidence of the multifaceted domes previously reported in this size range. The small ‘lens-shaped’ islands appear to be strained, whilst some of the intermediate-sized islands and all the large truncated pyramids contain misfit strain relaxation induced defects. Additionally, in the both the intermediate size ‘lens-shaped’ islands and in the large size truncated pyramidal islands, there is evidence of Si-Ge strain-induced alloying, more significant in the first than in the latter. Our observation of ‘lens shaped’ islands and truncated pyramids at larger sizes than are normally observed, suggests a kinetically driven process that delays the evolution of energetically favourable island structures until larger island sizes are reached.

We report the effect of strain-induced indium clustering on the emission properties of InGaN/GaN multiple quantum wells grown with high indium composition by MOCVD. Nanosize indium clustering confirmed by high-resolution transmission electron microscopy results in the redshift of the emission peak and the increase of the integrated photoluminescence (PL) intensity. We found that strong carrier localization in indium clustering induces the increases of the activation energy of PL integrated intensity and the temperature independence of PL decay profiles. All these observations suggest structurally and optically that the improved emission properties in the InGaN/GaN multiple quantum well with high indium composition are associated with the localized states in the nano-size indium cluster.

Supercritical fluids exhibit a range of unusual properties that can be exploited for the development of new reactions for material synthesis. These reactions are different from those performed in classical solid-state chemistry. Supercritical fluids are interesting as reaction media for the synthesis of nanostructured materials because fluid properties such as density, viscosity, diffusivity and solubility of reagents can be continuously tuned from gas to liquid with small variations in pressure and temperature. Moreover, supercritical fluid processing offers the possibility of using solvents with low toxicity that result in nanostructured materials free of solvent contamination. The process developed at ICMCB obtains nanostructured materials by chemically transforming a metal precursor inside a supercritical fluid. The synthesis of nanostructured materials such as metals, oxides or nitrides is possible at lower temperatures than the classic solid-state chemistry route. Based on experimental results and simulations, the nanostructured material nature, size and morphology can be continuously adjusted as a function of the operating condutions. Our process provides a great contribution in the development of self-assembled nanostructured materials by controlling the chemical composition, size, morphology and the surface properties of nanobricks.

In this paper, we report a self-assembly of surfactant molecules at the interface of air/hygroscopic quaternary ammonium salts such as tetrabutylammonium acetate (TBAAc), tetrabutylammonium bromide (TBAB), and tetrabutylammonium nitrate (TBAN), where they show different hygroscopicity, TBAAc > TBAB > TBAN. Homogeneously dissolved surfactants rearrange themselves when they contact air due to high moisture adsorption behavior of such organic salts. Highly ordered lamellar phases with different lattice spacings have been observed when surfactants with long alkyl chains were used. Alkylammonium halides form monolayers, while neutral alkylamines forms bilayers based upon basal spacings of their X-ray diffraction patterns. The change in basal spacings in lamellar patterns, the alkyl chain conformation of surfactants, and Hbonding property of neutral amine surfactants are discussed in detail.

A novel synthesis route for mesostructured silica films is reported. Nano-phase transition from lamellar phase of surfactant to hexagonal phase of silica-surfactant nanocomposite was found under vapor infiltration. Vapor infiltration was performed using HCl as catalyst source and tetraethoxysilane (TEOS) as framework source. Highly ordered mesostructured silica films are obtained using alkyltrimethylammonium bromide CnTAB (the carbon number in the alkyl chain; n = 8, 10, 12, 14, 16, 18) as templating agent. The d values of the mesostructured silica films increase with increasing the length of the alkyl chain and are controllable by the synthetic temperature. The vapor infiltration synthesis is a simpler process compared to conventional sol-gel techniques and attractive for mass production of a variety of organic-inorganic composite materials and inorganic porous materials. This novel synthetic method provides opportunities for the creation of new materials technologies.

We apply the elastic-energy-release rate (EERR) to identify the favored location of quantum dot (QD) formation in the presence of a laterally or vertically neighboring grown QD on a linear anisotropic elastic substrate. The EERR is defined as the relaxation energy per unit volume of QD growth. Numerical results for InAs QDs on a GaAs(001) substrate are reported. It is shown that the presence of a laterally neighboring QD inhibits the driving force for the formation of a new QD. In contrast, the presence of a buried (vertically) neighboring QD enhances the driving force for the formation of a new QD at its favorable location.

(Publication of the National Institute of Standards and Technology, an agency of the US Government; not subject to copyright.)

It has been shown recently, that the formation of GeSi quantum dots on Si(001) is strongly affected by the surface properties of the substrate. With an increasing number of missing dimer vacancies the growth mode can even change from a Stranski-Krastanow to a kinetic 3D island growth mode. Here we report on atomically resolved scanning tunneling microscopy images of Si(001) after different preparation procedures, namely the conventional high temperature procedure employed for commercial wafers, and Shiraki-type samples which require only low temperature treatment. The latter method yields an atomically flat Si(001) (2 × 1) surface, however, with a defect (ad- and missing dimers) concentration depending on the respective preparation conditions. Furthermore, repeated flashing occasionally yields a (2 × n) reconstructed surface consisting of well-ordered self-assembled trenches of missing dimers, similar to the ones discussed controversially in the previous literature. From our results we can clearly exclude contaminants to be involved.

The preparation of large scale monolayers of dodecanethiol coated nanoparticles on modified silicon substrates for use in storage media is reported. The formation of nanoparticle monolayers was accomplished by vertically pulling various modified silicon substrates at controlled speeds from nanoparticle solutions. The silicon substrates investigated had silanol and hydrogen terminated surfaces, surfaces chemically modified by (CH3) 3SiNHSi(CH3) 3 and (CH3O) 3Si(CH2)2(CF2) 7CF3 and a silicon substrate coated with amorphous carbon. All of these substrates have different surface polarities and a wide variation in monolayer coverage was obtained. The effect of the substrate pulling speed and solvent were also investigated.

Combinations of meso-, macro- and microporous coatings with a chemical composition of 90%Al2O3-10%SiO2 were elaborated on SiC Hi-Nicalon fibers using the sol-gel process. They were evaluated as porous interphase for the reinforcement of CMC. The mesoporous oxide, in contact with the fiber, allows cracks deviation whereas the macroporous one, in contact with the matrix, avoids the gaseous infiltration of the mesopores during the SiC CVD matrix process. It also prevents from oxygen diffusion during high temperature under air. The characterization of the composites was performed by SEM (scanning electron microscopy), TEM (transmission electron microscopy), X-ray diffraction, and EDS (energy dispersive spectrometry). TEM evidenced the porosity gradient as expected. A tensile test on the composites revealed brittle behavior (fracture) and no fiber debonding was observed.

After the successful synthesis of silver nanoplates with shapes of truncated triangle and disk applying a seed-mediated growth process using cetyltrimethylammonium bromide as a shape controller, we here further report the method for systematic control of the size of silver nanoplate in 2-dimensions. Two ways are found effective in size control: one is through the change of the silver seed amounts, which can produce the nanoplates with the size varying from 210 nm to 40 nm; another is through the mild aging of the as-prepared silver nanoplate solution at a proper temperature, which can fine-tune the shape of the nanoplates, such as from triangle to circle, or from plate to sphere. X-ray and electron diffraction analysis reveal that these nanoplates are single crystals and with their basal plane as (111) planes. The in-plane dipole plasmon band of these nanoplates can thus be manipulated within 900 nm to 400 nm, providing new possibilities for applications in the fields such as infrared absorption, nonlinear optical limiting, and Raman or biochemical diagnosis.

This research investigates the role of the substrate in the synthesis of carbon coils. Coils were produced on tungsten, titanium, and glassy carbon substrates via chemical vapor deposition (CVD) of acetylene (C2H2) on electrochemically deposited nickel at 800°C, but the growth varied among the samples. Coils were also produced on pure nickel by the same CVD method. Using tungsten as a substrate, carbon coils intermixed with thin carbon nanotubes were produced in high-yield from nickel particle clusters. On the titanium substrate, carbon coils were synthesized in small, high-yield patches with few co-produced carbon nanotubes. Synthesis from nickel clusters on glassy carbon usually resulted in amorphous carbon, but sparse, low-yield coil growth was observed. Carbon coils were also synthesized when pure nickel wire was used without a separate substrate. These results indicate the nickel catalyst controls the production of carbon coils, but the substrate has some effect on the yield. Carbon coils synthesized were either microcoils, which have diameters of a few microns, or nanocoils, which have diameters of one or two hundred nanometers.

A periodic mesoporous organosilica (PMO) with cubic Pm3n structure has been prepared from bis(trimethoxysilyl)ethane and cetytriethylammonium chloride. The sample has been heat treated under argon up to 1000°C, and the pyrolysis intermediates were analysed by X-ray diffraction using synchrotron radiation, multinuclear solid state NMR (29Si, 13C and 1H) and N2 adsorption-desorption experiments. The cubic Pm3n structure is retained after pyrolysis at 1000°C. The sample is a SiCO glass with mixed SiCxO4-x units (x = 0, 1, 2) and a very large surface area of 730 m2/g.

The surface of strained InGaAs films on GaAs for selective regrowth of InAs nanostructures is investigated by atomic force microscopy and Rutherford backscattering. Various InxGa1-xAs films were annealed at temperatures between 400°C - 800°C. Significant indium desorption was found to occur at temperatures above 550°C.

An industrially viable production method is a prerequisite for the commercialization of templated mesostructured materials, e.g. as carriers of various functionalities in coatings, in the coatings of ink jet paper and liquid chromatography. A small pilot plant was constructed for the continuous production of well ordered mesostructured materials (>10g/h) that can easily be scaled to an industrial process. The silica colloids have a well controlled internal mesostructure and are spherical with a mean diameter of 1-5μm. The mesoscopic pores in the calcined materials are accessible to relatively large molecules; up to 25 % (by weight) of the cationic dye Janus Green B could be adsorbed from an aqueous solution. We have also demonstrated how optically functional silica colloids could be prepared in a one-pot synthesis by introducing different dyes into the precursor solution.

Formation of lipid based hollow, spherical nanocapsules is reported. N-acylphosphotidylethanolamine (egg) derivatives equipped with divinylbenzoyl functionality in their headgroup region were synthesized to explore their polymerization behavior in vesicles. Polymerizable phospholipids alone produced vesicles as an aqueous dispersion and produced stable nanocapsules upon polymerization at room temperature. These structures survived a redispersed cycle following lyophilization and maintained their structural integrity in non-aqueous solvent.

A new approach to create layer-by-layer assembled multilayer ultrathin films with welldefined micropatterns in a short process time is introduced. To achieve such micropatterns with high line resolution in organic multilayer films, microfluidic channels were combined with the convective self-assembly process employing both hydrogen bonding and electrostatic intermolecular interactions. The channels were initially filled with polymer solution by capillary pressure and the residual solution was then removed by spinning process. The micropatterns with distinct line boundaries were obtained and the small ridges were also observed at the edges of the patterned lines. Spin self-assembled vertical heterostructural multilayer patterning using (PVP/PAA)5 micropatterns, which were prepared with microfluidic channels, as a template was also investigated.

Polyviologens (bipyridinium polymers) are effective catalysts for the polymerisation of silicic acid at room temperature and neutral pH. Variations in the alkylene spacer length and the associated counter ion appear to have little, if any, effect upon the rate of polymerisation as measured by the colorimetric molybdosilicate method. The resultant hybrid materials are amorphous aggregates of roughly spherical particles typically less than 0.1μm in diameter.

Single crystalline In203 nanowires were successful synthesized using a laser ablation method. Extensive material characterization such as X-ray diffraction (XRD) and selected area electron diffraction (SAED) revealed a cubic crystal structure for these nanowires with [110] as the growth direction. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to determine the diameter and length of our nanowires. By using monodispersed gold clusters as the catalyst, these nanowires can be grown with well-defined diameters around 10 nm. Individual In2O3 nanowires have been utilized to construct field effect transistors, which confirmed In2O3 nanowires as n-type semiconductors and exhibited on / off ratios as high as 104 at room temperature. The temperature-dependence of the conductance revealed thermal emission as the dominating transport mechanism. Our work can lead to important applications such as chemical sensing for In2O3 nanowires.