James S. Bendall

Uptake of Noncytotoxic Acid-Treated Single-Walled Carbon Nanotubes into the Cytoplasm of Human Macrophage Cells

Water-soluble single-walled nanotubes (SWNTs) are being tested as contrast agents for medical imaging and for the delivery of therapeutically active molecules to target cells. However, before they become used commercially, it will be essential to establish their subcellular distribution and whether they are cytotoxic. Here we characterize uptake of unlabeled, acid-treated, water-soluble SWNTs by human monocyte derived macrophage cells using a combination of Raman spectroscopy and analytical electron microscopy and compare our findings to previous work on unpurified SWNTs. Raman spectroscopy demonstrated that acid-treated SWNTs had a greater number of functional groups on the carbon walls than nontreated SWNT. The acid-treated SWNTs were less aggregated within cells than unpurified SWNTs. Bundles, and also individual acid-treated SWNTs, were found frequently inside lysosomes and also the cytoplasm, where they caused no significant changes in cell viability or structure even after 4 days of exposure.

Novel nonvolatile memory with multibit storage based on a ZnO nanowire transistor.

We demonstrate a room temperature processed ferroelectric (FE) nonvolatile memory based on a ZnO nanowire (NW) FET where the NW channel is coated with FE nanoparticles. A single device exhibits excellent memory characteristics with the large modulation in channel conductance between ON and OFF states exceeding 10(4), a long retention time of over 4 × 10(4) s, and multibit memory storage ability. Our findings provide a viable way to create new functional high-density nonvolatile memory devices compatible with simple processing techniques at low temperature for flexible devices made on plastic substrates.

Carbon nanotube array: A new MIP platform

Here we demonstrate that a free-standing carbon nanotube (CNT) array can be used as a large surface area and high porosity 3D platform for molecular imprinted polymer (MIP), especially for surface imprinting. The thickness of polymer grafted around each CNT can be fine-tuned to imprint different sizes of target molecules, and yet it can be thin enough to expose every imprint site to the target molecules in solution without sacrificing the capacity of binding sites. The performance of this new CNT-MIP architecture was first assessed with a caffeine-imprinted polypyrrole (PPy) coating on two types of CNT arrays: sparse and dense CNTs. Real-time pulsed amperometric detection was used to study the rebinding of the caffeine molecules onto these CNT-MIPPy sensors. The dense CNT-MIPPy sensor presented the highest sensitivity, about 15 times better when compared to the conventional thin film, whereas an improvement of 3.6 times was recorded on the sparse CNT. However, due to the small tube-to-tube spacing in the dense CNT array, electrode fouling was observed during the detection of concentrated caffeine in phosphate buffer solution. A new I-V characterization method using pulsed amperometry was introduced to investigate the electrical characterization of these new devices. The resistance value derived from the I-V plot provides insight into the electrical conductivity of the CNT transducer and also the effective surface area for caffeine imprinting.

An investigation into the growth conditions and defect states of laminar ZnO nanostructures

The variation in morphology of zinc oxide when it crystallises is one of the fascinating aspects of this important semiconductor. Alterations in hydrothermal growth conditions can allow the synthesis of a wide range of shapes and structures, including nanowires and layered structures, formed via a secondary growth regime but, to date, little work has investigated the effect changes in growth conditions can have and their influence on the optical properties. Here, systematic changes in growth conditions and reactants were carried out and the results studied using scanning electron microscopy, X-ray diffraction, optical transmission, cathodoluminescence and Raman spectroscopy and atomic force microscopy. We demonstrate that the choice of the reactants can have a significant effect not just on the morphologies of the structure, but on the fundamental properties of the crystalline state such as alterations into the defect states within the system. Furthermore, secondary growth is shown to be dependent on the underlying primary growth morphology, and general reaction conditions for laminar growth are suggested.

Encapsulated inorganic nanostructures: a route to sizable modulated, noncovalent, on-tube potentials in carbon nanotubes.

The large variety of hybrid carbon nanotube systems synthesized to date (e.g., by encapsulation, wrapping, or stacking) has provided a body of interactions with which to modify the host nanotubes to produce new functionalities and control their behavior. Each, however, has limitations: hybridization can strongly degrade desirable nanotube properties; noncovalent interactions with molecular systems are generally weak; and interlayer interactions in layered nanotubes are strongly dependent upon the precise stacking sequence. Here we show that the electrostatic/polarization interaction provides a generic route to designing unprecedented, sizable and highly modulated (1 eV range), noncovalent on-tube potentials via encapsulation of inorganic partially ionic phases where charge anisotropy is maximized. Focusing on silver iodide (AgI) nanowires inside single-walled carbon nanotubes, we exploit the polymorphism of AgI, which creates a variety of different charge distributions and, consequently, interactions of varying strength and symmetry. Combined ab initio calculations, high-resolution transmission electron microscopy, and scanning tunneling microscopy and spectroscopy are used to demonstrate symmetry breaking of the nanotube wave functions and novel electronic superstructure formation, which we then correlate with the modulated, noncovalent electrostatic/polarization potentials from the AgI filling. These on-tube potentials are markedly stronger than those due to other noncovalent interactions known in carbon nanotube systems and lead to significant redistribution of the wave function around the nanotube, with implications for conceptually new single-nanotube electronic devices and molecular assembly. Principles derived can translate more broadly to relating graphene systems, for designing/controlling potentials and superstructures.

Force and energy dissipation variations in noncontact atomic force spectroscopy of composite carbon nanotube systems

UHV dynamic force and energy dissipation spectroscopy in noncontact atomic force microscopy were used to probe specific interactions with composite systems formed by encapsulating inorganic compounds inside single-walled carbon nanotubes. It is found that forces due to nanoscale van der Waals interaction can be made to decrease by combining an Ag core and a carbon nanotube shell in the silver-filled single-walled carbon nanotube (Ag@SWNT) system. This specific behavior was attributed to a significantly different effective dielectric function compared to the individual constituents, evaluated using a core-shell model. Energy dissipation measurements showed that by filling dissipation increases. Aside from minimized Joule dissipation, such an effect was attributed to two short-range mechanisms due to metal filling: softening of C-C bonds resulting in a more deformable nanotube cage, and an increased mechanical damping of the nanotubes bending oscillation mode. Thus, filled and unfilled nanotubes can be discriminated based on force and dissipation measurements. These findings have two different implications for potential applications: tuning the effective dielectric properties and tuning the interaction force for molecular absorption by appropriately choosing the filling with respect to the nanotube.

Observation of Large-Scale Features on Graphite by Scanning Tunnelling Microscopy

Superlattice structures and rippling fringes were imaged on two separate pieces of graphite (HOPG) by scanning tunnelling microscopy (STM). We observed the corrugation conservation phenomenon on one of the superlattice structures where an overlayer does not attenuate the corrugation amplitude of the superlattice. Such a phenomenon may illustrate an implication that nanoscale defects a few layers underneath the surface may propagate through many layers without decay and form the superlattice structure on the topmost surface. Some rippling fringes with periodicities of 20 nm and 30 nm and corrugations of 0.1 nm and 0.15 nm were observed in the superlattice area and in nearby regions. Such fringes are believed to be due to physical buckling of the surface. The stress required to generate such structures is estimated, and a possible cause is discussed. An equation relating the attenuation factor to the number of overlayers is proposed.

Reducing recombination in ZnO photoanodes for dye sensitised solar cells through simple chemical synthesis

A method has been developed to synthesise zinc oxide nanowire arrays that demonstrate superior device performance compared to conventional ZnO nanowires within dye sensitised solar cells (DSSCs). This simple yet effective methodology has produced nanowires with triple device performance when compared to conventional ZnO nanowire DSSCs. We have fully characterised the morphology and physical properties of these wires and have demonstrated that the device improvements are due to a reduction in the recombination centres associated with the ZnO crystal.

Investigating the Hydrothermal Growth of Zinc Oxide Nanostructures Through Seed Layer Control

Abstract Controlling the growth of ZnO nanostructures for photovoltaic applications will ensure greater device efficiency and parameter control. This paper reports on methods to engineer the morphology and tailor the nanostructure growth direction through the hydrothermal synthesis method. Effective control is achieved through the use of a sputtered zinc layer together with modifications of the growth solution. These nanostructures have been developed with a view to incorporation into excitonic solar cells, and methods to improve surface stability using a fully aqueous synthesis method will be discussed.

Cs corrected STEM EELS: Analysing beam sensitive carbon nanomaterials in cellular structures

Identification of individual single wall nanotubes (SWNTs) within a cellular structure can provide vital information towards understanding the potential mechanisms of uptake, their localisation and whether their structure is transformed within a cell. To be able to image an individual SWNT in such an environment a resolution is required that is not usually appropriate for biological sections. Standard transmission electron microscopy (TEM) techniques such as bright field imaging of these cellular structures result in very weak contrast. Traditionally, researchers have stained the cells with heavy metal stains to enhance the cellular structure, however this can lead to confusion when analysing the samples at high resolution. Subsequently, alternative methods have been investigated to allow high resolution imaging and spectroscopy to identify SWNTs within the cell; here we will concentrate on the sample preparation and experimental methods used to achieve such resolution.