Watching mesoporous metal films grow during templated electrodeposition with in situ SAXS

In this paper, we monitor the real-time growth of mesoporous platinum during electrodeposition using small-angle X-ray scattering (SAXS). Previously, we have demonstrated that platinum films featuring the 'single diamond' (Fd3m) morphology can be produced from 'double diamond' (Pn3m) lipid cubic phase templates; the difference in symmetry provides additional scattering signals unique to the metal. Taking advantage of this, we present simultaneous in situ SAXS/electrochemical measurement as the platinum nanostructures grow within the lipid template. This measurement allows us to correlate the nanostructure appearance with the deposition current density and to monitor the evolution of the orientational and lateral ordering of the lipid and platinum during deposition and after template removal. In other periodic metal nanomaterials deposited within any of the normal topology liquid crystal, mesoporous silica or block copolymer templates previously published, the template and emerging metal have the same symmetry, so such a study has not been possible previously.

3D semiconducting nanostructures via inverse lipid cubic phases

Well-ordered and highly interconnected 3D semiconducting nanostructures of bismuth sulphide were prepared from inverse cubic lipid mesophases. This route offers significant advantages in terms of mild conditions, ease of use and electrode architecture over other routes to nanomaterials synthesis for device applications. The resulting 3D bicontinous nanowire network films exhibited a single diamond topology of symmetry Fd3m (Q₂₂₇) which was verified by Small angle X-ray scattering (SAXS) and Transmission electron microscopy (TEM) and holds great promise for potential applications in optoelectronics, photovoltaics and thermoelectrics.

Facile production of thermoelectric bismuth telluride thick films in the presence of polyvinyl alcohol

Bismuth telluride is currently the best performing thermoelectric material for room temperature operations in commercial thermoelectric devices. We report the reproducible and facile production of 600 micron thick bismuth telluride (Bi2Te3) layers by low cost and room temperature pulsed and potentiostatic electrodeposition from a solution containing bismuth and tellurium dioxide in 2 M nitric acid onto nickel in the presence of polyvinyl alcohol (PVA). This was added to the electrolyte to promote thick layer formation and its effect on the structure, morphology and composition of the electrodeposits was investigated by SEM and EDX. Well adherent, uniform, compact and stoichiometric n-type Bi2Te3 films with a high Seebeck coefficient of up to -200 μV K(-1) and a high electrical conductivity of up to 400 S cm(-1) resulting in a power factor of 1.6 × 10(-3) W m(-1) K(-2) at film growth rates of 100 μm h(-1) for potentiostatic electrodeposition were obtained. The films also exhibited a well defined hexagonal structure as determined by XRD.

Aligned platinum nanowire networks from surface-oriented lipid cubic phase templates

Mesoporous metal structures featuring a bicontinuous cubic morphology have a wide range of potential applications and novel opto-electronic properties, often orientation-dependent. We describe the production of nanostructured metal films 1-2 microns thick featuring 3D-periodic 'single diamond' morphology that show high out-of-plane alignment, with the (111) plane oriented parallel to the substrate. These are produced by electrodeposition of platinum through a lipid cubic phase (Q(II)) template. Further investigation into the mechanism for the orientation revealed the surprising result that the Q(II) template, which is tens of microns thick, is polydomain with no overall orientation. When thicker platinum films are grown, they also show increased orientational disorder. These results suggest that polydomain Q(II) samples display a region of uniaxial orientation at the lipid/substrate interface up to approximately 2.8 ± 0.3 μm away from the solid surface. Our approach gives previously unavailable information on the arrangement of cubic phases at solid interfaces, which is important for many applications of Q(II) phases. Most significantly, we have produced a previously unreported class of oriented nanomaterial, with potential applications including metamaterials and lithographic masks.

Surfactant-mediated electrodeposition of bismuth telluride films and its effect on microstructural properties

We report the synthesis of highly crystallographically textured films of stoichiometric bismuth telluride (Bi(2)Te(3)) in the presence of a surfactant, sodium lignosulfonate (SL), that resulted in the improved alignment of films in the (110) plane and offered good control over the morphology and roughness of the electrodeposited films. SL concentrations in the range 60-80 mg dm(-3) at a deposition potential of -0.1 V vs SCE (saturated calomel electrode) were found to yield the most improved crystallinity and similar or superior thermoelectric properties compared with results reported in the literature.

Triplex-directed recognition of a DNA nanostructure assembled by crossover strand exchange

DNA has been widely exploited for the self-assembly of nanosized objects and arrays that offer the potential to act as scaffolds for the spatial positioning of molecular components with nanometer precision. Methods that allow the targeting of components to specific locations within these structures are therefore highly sought after. Here we report that the triplex approach to DNA recognition, which relies on the specific binding of an oligonucleotide within the major groove of double-helical DNA, can be exploited to recognize specific loci within a DNA double-crossover tile and array, a nanostructure assembled by crossover strand exchange. The oligonucleotide can be targeted to both crossover and non-crossover strands and, surprisingly, across the region spanning the crossover junction itself. Moreover, by attaching biotin to the end of the oligonucleotide, we show that streptavidin molecules can be recruited to precise locations within a DX array, with an average spacing of 31.9 (±1.3) nm. This is a promising approach that could be exploited to introduce other components compatible with oligonucleotide synthesis into the wide variety of DNA nanostructures assembled by crossover strand exchange, such as those generated by DNA origami.

Optimization of the electrodeposition process of high-performance bismuth antimony telluride compounds for thermoelectric applications

High-quality films of bismuth antimony telluride were synthesized by electrodeposition from nitric acid electroplating baths. The influence of a surfactant, sodium ligninsulfonate, on the structure, morphology, stoichiometry, and homogeneity of the deposited films has been investigated. It was found that addition of this particular surfactant significantly improved the microstructural properties as well as homogeneity of the films with a significant improvement in the thermoelectric properties over those deposited in the absence of surfactant. A detailed microprobe analysis of the deposited films yielded a stoichiometric composition of Bi(0.35)Sb(1.33)Te(3) for the films electrodeposited in the absence of surfactant and a stoichiometry of Bi(0.32)Sb(1.33)Te(3) for films deposited in the presence of surfactant.

Loosening the DNA wrapping around single-walled carbon nanotubes by increasing the strand length

In this study, we discuss the influence of DNA strand length on DNA wrapping of single-walled carbon nanotubes under high-shear sonication and find that different strand length results in changed DNA-nanotube interaction, which is sensitively probed by the upshift extent of the Raman radial breathing mode bands of nanotubes due to DNA wrapping. The difference in the interaction between nanotubes and DNA strands of various length results in apparently different degrees of wrapping compactness, revealed by atomic force microscopy observations, and nanotube selectivity in wrapping, indicated by both Raman and photoluminescence spectroscopy results. The above findings can be utilized to precisely control the nanotube diameter distribution and modulate the physicochemical properties of the nanotube wrapped by DNA without any direct functionalization of nanotubes. This finding is of considerable interest from both theoretical and practical standpoints.

High density p-type Bi0.5Sb1.5Te3 nanowires by electrochemical templating through ion-track lithography

High density p-type Bi0.5Sb1.5Te3 nanowire arrays are produced by a combination of electrodeposition and ion-track lithography technology. Initially, the electrodeposition of p-type Bi0.5Sb1.5Te3 films is investigated to find out the optimal conditions for the deposition of nanowires. Polyimide-based Kapton foils are chosen as a polymer for ion track irradiation and nanotemplating Bi0.5Sb1.5Te3 nanowires. The obtained nanowires have average diameters of 80 nm and lengths of 20 microm, which are equivalent to the pore size and thickness of Kapton foils. The nanowires exhibit a preferential orientation along the {110} plane with a composition of 11.26 at.% Bi, 26.23 at.% Sb, and 62.51 at.% Te. Temperature dependence studies of the electrical resistance show the semiconducting nature of the nanowires with a negative temperature coefficient of resistance and band gap energy of 0.089+/-0.006 eV.

Addressable molecular node assembly--high information density DNA nanostructures

The inherent self-assembly properties of DNA make it ideal in nanotechnology. We present a fully addressable DNA nanostructure with the smallest possible unit cell, a hexagon with a side-length of only 3.4 nm.(2,3) Using novel three-way oligonucleotides, where each side has a unique double-stranded DNA sequence that can be assigned a specific address, we will build a non-repetitive two-dimensional grid.

Triplex addressability as a basis for functional DNA nanostructures

Here, we present the formation of a fully addressable DNA nanostructure that shows the potential to be exploited as, for example, an information storage device based on pH-driven triplex strand formation or nanoscale circuits based on electron transfer. The nanostructure is composed of two adjacent hexagonal unit cells (analogous to naphthalene) in which each of the eleven edges has a unique double-stranded DNA sequence, constructed using novel three-way oligonucleotides. This allows each ten base-pair side, just 3.4 nm in length, to be assigned a specific address according to its sequence. Such constructs are therefore an ideal precursor to a nonrepetitive two-dimensional grid on which the "addresses" are located at a precise and known position. Triplex recognition of these addresses could function as a simple yet efficient means of information storage and retrieval. Future applications that may be envisaged include nanoscale circuits as well as subnanometer precision in nanoparticle templating. Characterization of these precursor nanostructures and their reversible targeting by triplex strand formation is shown here using gel electrophoresis, atomic force microscopy, and fluorescence resonance energy transfer (FRET) measurements. The durability of the system to repeated cycling of pH switching is also confirmed by the FRET studies.

Optical properties of mesoporous II–VI semiconductor compound films

Direct liquid crystal templating from non-ionic polyoxyethylene surfactants has been utilised to produce well-defined birefringent films of nanostructured cadmium telluride films which displayed good optical properties as evidenced by UV/VIS reflectance spectroscopy.