Polypyrrole Percolation Network Gas Sensors: Improved Reproducibility through Conductance Monitoring during Polymer Growth.

Conducting-polymer-based electrical percolation networks are promising materials for use in high-sensitivity chemiresistive devices. An ongoing challenge is to create percolation networks that have consistent properties, so that devices based on these materials do not have to be individually calibrated. Here, an in situ conductance technique is used during the electrochemical growth of polypyrrole (PPy) percolation networks.

PEDOT percolation networks for reversible chemiresistive sensing of NO.

Detection of NO plays an important role in various safety applications. However, sensitive and reversible sensing of NO remains a challenge. Here we demonstrate the use of poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer percolation networks for chemiresistive sensing of NO.

ANFO vapour detection with conducting polymer percolation network sensors and GC/MS.

Ammonium nitrate mixed with fuel oil (ANFO) is commonly used in improvised explosive devices (IEDs). The development of ANFO vapour sensors that are small, inexpensive, and easy to use will enable widespread IED detection in the context of security and humanitarian demining. Because of concealment and the low vapour pressures of most explosive materials, achieving sufficiently high sensitivity and low limits of detection are some of the main challenges of explosives vapour detection.

Shapes of epitaxial gold nanocrystals on SrTiO substrates.

Morphological control of gold nanocrystals is important as their catalytic and optical properties are highly shape dependent. In this paper we report the shapes of gold nanocrystals which deviate from the equilibrium Wulff shape due to the influence of the SrTiO3 single crystal substrates. The gold crystals are characterized by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM).

Influence of the support on stabilizing local defects in strained monolayer oxide films.

Two-dimensional materials with a honeycomb lattice, such as graphene and hexagonal boron nitride, often contain local defects in which the hexagonal elements are replaced by four-, five-, seven-, and eight-membered rings. An example is the Stone-Wales (S-W) defect, where a bond rotation causes four hexagons to be transformed into a cluster of two pentagons and two heptagons. A further series of similar defects incorporating divacancies results in larger structures of non-hexagonal elements.

Maximising the resolving power of the scanning tunneling microscope.

The usual way to present images from a scanning tunneling microscope (STM) is to take multiple images of the same area, to then manually select the one that appears to be of the highest quality, and then to discard the other almost identical images. This is in contrast to most other disciplines where the signal to noise ratio (SNR) of a data set is improved by taking repeated measurements and averaging them. Data averaging can be routinely performed for 1D spectra, where their alignment is straightforward.

Magnetic Iron Oxide Nanowires Formed by Reactive Dewetting.

The growth and reactive dewetting of ultrathin films of iron oxides supported on Re(0001) surfaces have been imaged in situ in real time. Initial growth forms a nonmagnetic stable FeO (wüstite like) layer in a commensurate network upon which high aspect ratio nanowires of several microns in length but less than 40 nm in width can be fabricated. The nanowires are closely aligned with the substrate crystallography and imaging by X-ray magnetic circular dichroism shows that each contain a single magnetic domain.

Scanning tunnelling microscopy of epitaxial nanostructures.

Epitaxial nanostructures have generated a great deal of interest because of the applications in catalysis, photonics and nanoelectronics. To study the structure and electronic properties at the nanoscale, scanning tunnelling microscopy (STM) has proven a very effective technique due to its extraordinarily high spatial resolution. Growth modes of epitaxial nanostructures depend predominantly on the surface free energy of the deposited material, and that of the substrate onto which it is deposited, leading to layer-by-layer or island growth modes.

The effect of the size of surface Pd island ensembles on electron transfer of adsorbed perchlorate ions on Au(111).

A progressive increase in the size of Pd ensembles on a mica-supported Au(111) single crystal surface can facilitate electron transfer of perchlorate ions at lower anodic potential in CV curves than pure Au(111) due to a strong ligand effect and Pd-Au neighbouring pairs at edge sites render a higher degree of electron transfer.

Controlled growth of Ni nanocrystals on SrTiO(3) and their application in the catalytic synthesis of carbon nanotubes.

Truncated pyramid-shaped Ni nanocrystals were epitaxially grown on SrTiO(3)(001) surfaces and characterised by scanning tunneling microscopy (STM). These nanocrystals were shown to be catalytically active for the synthesis of carbon nanotubes (CNTs). The narrow size distribution of the Ni nanocrystals results in a similar narrow distribution of CNT diameters.

Formation mechanism for a hybrid supramolecular network involving cooperative interactions.

A novel mechanism of hybrid assembly of molecules on surfaces is proposed stemming from interactions between molecules and on-surface metal atoms which eventually got trapped inside the network pores. Based on state-of-the-art theoretical calculations, we find that the new mechanism relies on formation of molecule-metal atom pairs which, together with molecules themselves, participate in the assembly growth. Most remarkably, the dissociation of pairs is facilitated by a cooperative interaction involving many molecules.

Surface and defect structure of oxide nanowires on SrTiO3.

Processing the SrTiO(3)(001) surface results in the self-assembly of reduced titanate nanowires whose widths are approximately 1 nm. We have imaged these nanowires and their defects at elevated temperatures by atomic resolution scanning tunneling microscopy. The nanowire structure is modeled with density functional theory, and defects observed in the center of the nanowire are determined to be Ti(4)O(3) vacancy clusters.

Synthesis of epitaxial metal oxide nanocrystals via a phase separation approach.

Perovskite phase instability of BiMnO3 has been exploited to synthesize epitaxial metal oxide magnetic nanocrystals. Thin film processing conditions are tuned to promote the breakdown of the perovskite precursor into Bi2O3 matrix and magnetic manganese oxide islands. Subsequent cooling in vacuum ensures complete volatization of the Bi2O3, thus leaving behind an array of self-assembled magnetic Mn3O4 nanostructures.

A homologous series of structures on the surface of SrTiO3(110).

Strontium titanate is seeing increasing interest in fields ranging from thin-film growth to water-splitting catalysis and electronic devices. Although the surface structure and chemistry are of vital importance to many of these applications, theories about the driving forces vary widely. We report here a solution to the 3 x 1 SrTiO(3)(110) surface structure obtained through transmission electron diffraction and direct methods, and confirmed through density functional theory calculations and scanning tunnelling microscopy images and simulations, consisting of rings of six or eight corner-sharing TiO(4) tetrahedra.

Endohedral metallofullerenes in self-assembled monolayers.

A method has been developed for the attachment of a dithiolane group to endohedral metallofullerenes via a 1,3-dipolar cycloaddition reaction. This sulfur-containing functional group serves as an anchor, enabling efficient immobilisation of endohedral fullerenes on Au(111) surfaces at room temperature, directly from the solution phase. The functionalised fullerenes form disordered monolayers that exhibit no long-range ordering, which is attributed to both the strong bonding of the dithiolane anchor to the surface and to the conformational flexibility of the functional group.

Shape transitions of epitaxial islands during strained layer growth: anatase TiO2(001) on SrTiO3(001).

Extended annealing in UHV causes the surface region of SrTiO3(001) to become enriched with TiO2, resulting in the formation of epitaxial islands of anatase TiO2(001). The islands are studied using UHV scanning electron microscopy (SEM), which reveals the changes in morphology during growth induced by misfit strain. Starting from a square island, two types of shape transition are observed.

Temperature-dependent stability of supported five-fold twinned copper nanocrystals.

The temperature-dependent structure transition of supported Cu nanocrystals on SrTiO3(001)-(2 x 1) is investigated by scanning tunneling microscopy (STM). We experimentally determine the phase map of supported Cu icosahedral, decahedral, and truncated octahedral nanocrystal shapes as a function of substrate temperature during Cu deposition. We show that a supported nanocrystal of 8500 atoms at a nucleation temperature of 480 degrees C has the same probability of adopting an icosahedral or octahedral shape.

Grating of single Lu@C(82) molecules using supramolecular network.

A supramolecular grating of single Lu@C(82) molecules was obtained by depositing Lu@C(82) molecules onto a room temperature PTCDI-melamine network.

A chiral pinwheel supramolecular network driven by the assembly of PTCDI and melamine.

The mixing of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine) at room temperature in a ratio of 3 : 4 on Au(111) leads to the formation of a new chiral "pinwheel" structure.

C70 ordering on nanostructured SrTiO3(001).

The nanostructured (7 x 4) surface of SrTiO(3)(001) is used as a template to order C(70) into single-molecule-wide chains and linear islands.

Controlled surface ordering of endohedral fullerenes with a SrTiO(3) template.

The ability to select the way in which atoms and molecules self-organize on a surface is important for synthesizing nanometre scale devices. Here we show how endohedral fullerenes (Er(3)N@C(80)) can be assembled into four distinctive arrangements on a strontium titanate surface template. Each template pattern correlates to a particular reconstruction on n-doped SrTiO(3)(001), made in whole or in part by self-assembled arrays of non-stoichiometric oxide nanostructures.

Structure of vapour deposited adenine on a nanostructured perovskite surface studied by STM.

The structures of vapour deposited layers of adenine on a nanostructured SrTiO3(001) surface have been investigated by scanning tunneling microscopy (STM). The STM images reveal details of self-organization of adenine monolayers in which adsorption is controlled both by substrate nanostructure and by intermolecular H-bonding of adenine molecules. Detailed examination of STM images suggests that at least three different ordering structures are possible and two distinct orientations may exist with opposite chirality.

Template ordered open-grid arrays of paired endohedral fullerenes.

Developing useful molecular systems, such as planar networks for novel molecular electronics, requires the ability to control the way molecules assemble at surfaces. Here we report how an oxide crystal surface can be used as a template to controllably order endohedral fullerenes, Er3N@C80, into two-dimensional (2D) open-grid arrays. The crystal surface is made of highly ordered oxide nanostructures which self-assemble on the surface of SrTiO3(001).

Encapsulated Pd nanocrystals supported by nanoline-structured SrTiO3(001).

Palladium nanocrystals were grown on a nanostructured SrTiO(3)(001) surface and annealed in ultrahigh vacuum at 620 degrees C. This leads to the so-called strong metal-support interaction (SMSI) state, characterized by encapsulation of the metal clusters with an oxide layer. Scanning tunneling microscopy (STM) of the oxide adlayer on the Pd(111) cluster surface reveals two superstructures with different lattice parameters and crystallographic rotations.

Ordering of TiO2-based nanostructures on SrTiO3(001) surfaces.

A class of nanostructured surface phases on SrTiO3(001) is reported and characterized through atomic-resolution scanning tunneling microscopy and Auger electron spectroscopy. These surface phases are created via argon ion sputtering and UHV annealing and form close-packed domains of highly ordered nanostructures. Depending on the type of nanostructures present, the domain ordering exhibit either (6 x 2), (9 x 2), (12 x 2), (6 x 8), or (7 x 4) surface patterning.