approaches to controlling the MIT have been made, for example, by electric field effects [9] and through optical means. [10] Today, RNOs retain a strong focus, with recent work striving to understand their physics. [11][12][13][14][15] The R = La compound is the only RNO that does not have an MIT in bulk; it is metallic and paramagnetic at all temperatures. LaNiO 3 (LNO) may prove an ideal candidate as a base for engineering functional oxide heterostructures. For instance, it was suggested that specially engineered superlattices, based on single unit cells (u.c.) of LNO, may support superconductivity, [16] and it has been shown that this material is orbitally polarizable in specifically designed heterostructures. [17,18] Necessary to fine-tune the functionalities of LNO is a full understanding of the effects of heterostructuring on an atomic level, and the implications that the local structure, at this scale, has on the electronic properties. A close examination of the thin film structure at the boundaries with the substrate and the vacuum, as well as the effects of reducing the dimensionality on coexistence and, ultimately, competition between these local structures, is required.In reducing dimensionality, three conductivity regimes have previously been observed; thicker metallic films, intermediate thicknesses with a resistivity upturn, and insulating films under the ultrathin limit, which can be 3-6 u.c., depending upon the substrate. [19][20][21] In line with this, photoemission studies found drastic changes to the LNO Fermi surface as the thickness approaches a few u.c., indicating that there is a fundamental change in the electronic structure. [22,23] Here we report an intriguing thickness-dependent transport behavior in high-quality LNO films grown on a (001) LaAlO 3 (LAO) substrate, whereby conductivity is enhanced in films of 6-11 u.c. (2.3-4.3 nm). A maximum conductivity is also observed in ab initio calculations (for a thickness of 6-8 u.c.). In agreement with scanning transmission electron microscopy (STEM), the simulations further indicate that there are three characteristic local structures in the depth of the films. A three-element model of parallel conductors reproduces the thickness-dependent transport behavior well, and implies that conductivity enhancement derives from a struggle for dominance between the local structure of the surface and of the heterointerface.Both LNO and LAO are rhombohedral (R-3c) in bulk. LNO (pseudocubic lattice parameter 3.84 Å) deposited on LAO (pseudocubic lattice parameter 3.79 Å) is compressively strained by −1.3%.A marked conductivity enhancement is reported in 6-11 unit cell LaNiO 3 thin films. A maximal conductivity is also observed in ab initio calculations for films of the same thickness. In agreement with results from state of the art scanning transmission electron microscopy, the calculations also reveal a differentiated film structure comprising characteristic surface, interior, and heterointerface structures. Based on this observation, a three-element para...

Homogenous graphitic nanofibres (GNFs) have been synthesised by heat treatment of electrospun polyacrylonitrile in dimethylsulphoxide, offering a new solution route of low toxicity to manufacture sub-60 nm diameter GNFs. Fibre beading resulting from the spinning of low-concentration polymer solutions can be reduced with the addition of surfactant or sodium chloride. Characterisation techniques including X-ray diffraction, scanning-and transmission electron microscopy have been used to quantify the effect of the graphitisation process, by heat treatment up to 3000°C, on the weight, diameter and structural morphology of the nanofibres. The GNFs have an entangled micro-fibril structure with graphitic ordering of up to 40 graphene layers after treatment at 3000°C. There is little difference in the degree of graphitisation of GNFs prepared with a 250°C oxidation step compared with those 1235 445720 prepared without, but oxidised GNFs retain more of their original mass after heating under argon flow.

Collective rotations and tilts of oxygen polyhedra play a crucial role in the physical properties of complex oxides such as magnetism and conductivity. Such rotations can be tuned by preparing thin films in which dimensionality, strain, and interface effects come into play. However, little is known of the tilt and rotational distortions in films a few unit cells thick including the question of if coherent tilt patterns survive at all in this ultrathin limit. Here, a series of films of perovskite LaNiO3 is studied and it is shown that the phonon mode related to oxygen octahedral tilts can be followed by Raman spectroscopy down to a film thickness of three pseudocubic perovskite unit cells (∼1.2 nm). To push the limits of resolution to the ultrathin regime, a statistical analysis method is introduced to separate the Raman signals of the film and substrate. Most interestingly, these analyses reveal a pronounced hardening of the tilt vibrational mode in the thinnest films. A comparison between the experimental results, first principles simulations of the atomic structure, and the standing wave model, which accounts for size effects on the phononic properties, reveals that in the ultrathin regime, the Raman spectra are a hybrid entity of both the bulk and surface phononic behavior. These results showcase Raman spectroscopy as a powerful tool to probe the behavior of perovskite films down to the ultrathin limit.

Modulation of intensity with zero effort (MIEZE) is a neutron resonant spin echo technique which allows to measure the intermediate scattering function S(Q, τ) under depolarizing conditions. Since MIEZE produces a complex four dimensional dataset, we have developed the software package MIEZEPY to reduce the dataset and extract S(Q, τ) in a user friendly manner. This is an essential step in establishing the MIEZE technique and improving user operation. MIEZEPY was written in Python as an open source package and was developed on GitHub. In this paper the framework and implementation of this package as well as the physical and mathematical principles underlying the data reduction procedure will be introduced to lay out the complexity of this task.