Determination of the lateral size and thickness of solution-processed graphene flakes

We present a method to determine the lateral size distribution of solution–processed graphene via direct image analysis techniques. Initially transmission electron microscopy (TEM) and optical microscopy (OM) were correlated and used to provide a reliable benchmark. A rapid, automated OM method was then developed to obtain the distribution from thousands of flakes, avoiding statistical uncertainties and providing high accuracy. Dynamic light scattering (DLS) was further employed to develop an in-situ method to derive the number particle size distribution (PSD) for a dispersion, with a deviation lower than 22% in the sub-micron regime. Methods for determining flake thickness are also discussed

Helical magnetic structure and the anomalous and topological Hall effects in epitaxial B20 Fe1−y_{1-y}Coy_yGe films

Epitaxial films of the B20-structure alloy Fe$_{1-y}$Co$_y$Ge were grown by molecular beam epitaxy on Si (111) substrates. The magnetization varied smoothly from the bulk-like values of one Bohr magneton per Fe atom for FeGe to zero for non-magnetic CoGe. The chiral lattice structure leads to a Dzyaloshinskii-Moriya interaction (DMI), and the films' helical magnetic ground state was confirmed using polarized neutron reflectometry measurements. The pitch of the spin helix, measured by this method, varies with Co content $y$ and diverges at $y \sim 0.45$. This indicates a zero-crossing of the DMI, which we reproduced in calculations using first principle methods. We also measured the longitudinal and Hall resistivity of our films as a function of magnetic field, temperature, and Co content $y$. The Hall resistivity is expected to contain contributions from the ordinary, anomalous, and topological Hall effects. Both the anomalous and topological Hall resistivities show peaks around $y \sim 0.5$. Our first principles calculations show a peak in the topological Hall constant at this value of $y$, related to the strong spin-polarisation predicted for intermediate values of $y$. Half-metallicity is predicted for $y = 0.6$, consistent with the experimentally observed linear magnetoresistance at this composition. Whilst it is possible to reconcile theory with experiment for the various Hall effects for FeGe, the large topological Hall resistivities for $y \sim 0.5$ are much larger then expected when the very small emergent fields associated with the divergence in the DMI are taken into account

Exploring High Aspect Ratio Gold Nanotubes as Cytosolic Agents: Structural Engineering and Uptake into Mesothelioma Cells.

The generation of effective and safe nanoagents for biological applications requires their physicochemical characteristics to be tunable, and their cellular interactions to be well characterized. Here, the controlled synthesis is developed for preparing high-aspect ratio gold nanotubes (AuNTs) with tailorable wall thickness, microstructure, composition, and optical characteristics. The modulation of optical properties generates AuNTs with strong near infrared absorption. Surface modification enhances dispersibility of AuNTs in aqueous media and results in low cytotoxicity. The uptake and trafficking of these AuNTs by primary mesothelioma cells demonstrate their accumulation in a perinuclear distribution where they are confined initially in membrane-bound vesicles from which they ultimately escape to the cytosol. This represents the first study of the cellular interactions of high-aspect ratio 1D metal nanomaterials and will facilitate the rational design of plasmonic nanoconstructs as cytosolic nanoagents for potential diagnosis and therapeutic applications.BLF-Papworth Fellowship from the British Lung Foundation and the Victor Dahdaleh Foundation

A carbon-nanotube based nano-furnace for in-situ restructuring of a magnetoelectric oxide

We present current-voltage (I-V) characteristics of an individual carbon nanotube (CNT) filled with Cr₂O₃, a multi-functional magnetic oxide relevant to spintronics. We demonstrate that a filled CNT during a two probe I-V scan in suspended geometry, can be used like a nano-furnace for controlled restructuring of the oxide encapsulate. With proper utilization of Joule heating during I-V scans, the encapsulate, initially in the form of a polycrystalline nano-wire, converts to beads, nano-crystals and sheets within the CNT. These morphological phases are formed and preserved by controlling the amplitude, rate and holding time of the bias voltage. The sequential restructuring, observed in real time by Transmission Electron Microscopy (TEM), is also accompanied by a substantial enhancement in the current flowing through the CNT. We further demonstrate that advantageously tailoring the morphology of the encapsulate is linked to this current enhancement and can be a route for heat dissipation in nano devices. Magnetization measurements reveal that Cr₂O₃, a well known antiferromagnetic and magnetoelectric, when confined within CNT, exhibits logarithmic time dependence. This slow magnetization dynamics is associated to a pinning mechanism that points towards the possibility of stress induced moments in this system. These measurements elucidate novel magnetic properties of the encapsulate

Carbon nanotubes produced by the catalytic-CVD method

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Direct visualization of electrical transport-induced alloy formation and composition changes in filled multi-wall carbon nanotubes by in situ scanning transmission electron microscopy

In order to evaluate the applicability of metal-filled carbon nanotubes, it is crucial to understand their behaviour in the presence of electric currents. In this work we exploit the significant advantages of combining in situ experiments with scanning transmission electron microscopy in annular dark-field mode and related analytical techniques to gain further insights into the electrical transport induced transformations in Fe-filled P,N-doped multi-wall carbon nanotubes. With these synergistic analysis techniques, we could monitor in real time the dynamical effects that take place in the carbon nanotubes and their Fe filling as a consequence of the passing of an electric current and subsequent Joule heating. A detailed analysis of the formation, evolution and composition of intermediate phases has been possible employing in situ experiments with transmission electron microscopy, scanning-transmission electron microscopy and analysis techniques. We show that a multistage process occurs in which the Fe filling reacts with nitrogen to form an intermediate alloy phase, which then decomposes. The presence of high concentrations of nitrogen within the inner channel of the tube is found to be crucial to this process

Facile, fast, and inexpensive synthesis of monodisperse amorphous Nickel-Phosphide nanoparticles of predefined size

Monodisperse, size-controlled Ni–P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(II)acetyl-acetonate. The nanoparticles were amorphous, contained 30 at% P and their size was controlled between 7–21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth