Conical nanowires appear to be very versatile nanostructures for fabricating high performance piezoelectric nanodevices, for possible applications in the fields of mechanical sensing, piezotronics or piezo-photo-tronics. The results discussed in the present work are aimed at providing useful guidelines for the design of such devices.

Composite rods consisting of Alumina (Al2O3) and Silicon Carbide whiskers (SiCw) are used to fabricate microwave cooking racks because they effectively act as a microwave intensification system that allows cooking at much faster rates than conventional microwave ovens. The percolation behavior, electrical conductivity and dielectric properties of these materials have been reported previously. However, it has been observed that the electrical response of the extruded bars is a function of the rod length and that long rods show substantially different behavior than thinner disks cut from them. A percolation model has been proposed that describes the effect of the alignment of the semiconducting SiC whiskers and the quality of the interfaces present in the composite rods: SiC-SiC and SiC-Al2O3-SiC for example. This study was undertaken with the goal of testing out whether the response of the individual sections could be used to generate the response of the full length rods and to assess the importance of the homogeneous distribution of the SiC fillers on the resultant impedance response.

Lightweight porous metallic materials are generally created through specialized processing techniques. Their unique structure gives these materials interesting properties which allow them to be used in diverse structural and insulation applications. In particular, highly porous Al structures (Al foams) have been used in aircraft components and sound insulation; however due to the difficulty in processing and random nature of the foams, they are not well understood and thus they have not yet been utilized to their full potential. The objective of this project was to determine whether a relationship exists between the relative density (porous density/bulk density) and the mechanical properties of porous Al structures. For this purpose, a combination of computer simulations and experiments was pursued to better understand possible relationships. A Finite Element Method (FEM)-based software, COMSOL Multiphysics 4.3, was used to model the structure and to simulate the mechanical behavior of porous Al structures under compressive loads ranging from 1-100 MPa. From these simulated structures, the maximum von Mises stress, volumetric strain, and other properties were calculated. These simulation results were compared against data from compression experiments performed using the Instron Universal Testing Machine (IUTM) on porous Al specimens created via a computernumerically-controlled (CNC) mill. CES EduPack software, a materials design program, was also used to estimate the mechanical properties of porous Al and open cell foams for values not available experimentally, and for comparison purposes. This program allowed for accurate prediction of the mechanical properties for a given percent density foam, and also provided a baseline for the solid Al samples tested. The main results from experiments were that the Young’s moduli (E) for porous Al samples (55.8% relative density) were 15.9-16.6 GPa depending on pore diameter, which is in good agreement with the CES EduPack predictions; while the compressive strengths (σ c) were 155-185 MPa, higher than those predicted by CES EduPack. The results from the FEM simulations using 3D models (55.8% relative density) revealed the onset of yielding at 13.5-14.0 MPa, which correlates well with CES EduPack data. Overall results indicated that a combination of experiments and FEM simulations can be used to calculate structure-property relationships and to predict yielding and failure, which may help in the pursuit of simulation-based design of metallic foams. In the future, more robust modeling and simulation techniques will be explored, as well as investigating closed cell Al foams and different porous geometries (nm to micron). This study can help to improve the current methods of characterizing porous materials and enhance knowledge about their properties for alternative energy applications, while promoting their design through integrated approaches.

Hybrid alumina-silicone nanolaminate films were synthesized by plasma enhanced chemical vapor deposition (PECVD) process. PECVD allows digital control over nanolaminate construction, and may be performed at low temperature for compatibility with flexible substrates. These materials are being considered as dielectrics for application such as capacitors in thin film transistors and memory devices. In this work, we present the temperature dependent current versus voltage (I-V) measurements of the nanolaminate dielectrics in the range of 200- 310 K to better asses their potential in these applications. Various models are used to know the different conduction mechanisms contributing to the leakage current in these nanolaminate films. It is observed that space charge limited current (SCLC) mechanism is the dominant conduction process in the high field region whereas Ohmic conduction process is contributing to the leakage current in the low field region. The shallow electron trap level energy (E t ) of 0.16 eV is responsible for SCLC mechanism whereas for Ohmic conduction process the activation energy (E a ) for electrons is about 0.22 eV. An energy band diagram is given to explain the dominance of various conduction mechanisms in different field regions in these nanolaminate films.

The crystallinity of a GaN epitaxial layer on a sapphire substrate after the mechanical ding process was estimated by transmission electron microscopy (TEM) and Raman spectroscopic analysis. TEM observation results showed that, the screw dislocations as a threading dislocation were induced by the mechanical dicing process in the limited area up to approximately 1.2 μm from the dicing-line. On the other hand, the crystal strains were up to approximately 7 μm from the dicing-line edge measured by the Raman spectroscopic analysis. The distance difference between the area of the screw dislocations and of the residual strain is caused by the stress relaxation.

Organic photovoltaic (OPV) devices were fabricated using a novel draw bar premetered coating technique, whereby a meniscus of fluid is dragged across a substrate to leave a trailing wet film. The results showed that coating thickness could be controlled by varying the coating speed, rod diameter, gap height, amount of solution injected, rod diameter, rod composition material and number of layers. Devices on PET with active areas of 10 cm2 and active layer thicknesses ranging from 35 to 475 nm were produced using the technique. Active layers of 160 nm were the optimum of thicknesses trialled, achieving typical best efficiencies around 0.4 %. Devices with films thinner than 90 nm did not function due to short-circuiting. The draw-bar coating method has the advantage of allowing controlled deposition of a wide range of film thicknesses with no solution wastage.

Various nanostructures with high-aspect-ratio formed in a low-resistivity silicon wafer by the nano-processing using a carbon nanotube (CNT) probe of a scanning tunneling microscope (STM) have been investigated. The multi-wall CNT probes were obtained with our original pulling-method from CNT dispersion liquid. Nanostructures of point configurations (pit and mound) and line configurations were obtained at the constant tunneling current of 0.1 nA by controlling the bias voltages up to 10 V, processing times up to 300 s and scanning speeds of probe up to 480 nm/s for a line configuration. The aspect-ratio of the pit configuration fabricated at the bias voltage of 3 V increased about 6 times in proportion to the increase in processing time. Remarkable influence of the bias voltage on the configurations indicated that there exists a threshold bias voltage for the transition from the pit configuration to the mound one between 3 V and 5 V, and the aspect ratio of all nanostructures fabricated by the CNT probe were larger than those by a conventional tungsten probe. Finally, cross-sectional TEM observations were also applied to clarify the difference in the formation mechanisms between the pit configuration and the mound configuration. The TEM image of the pit configuration showed neither dislocations nor remarkable strains existed, but in the case of the mound shape TEM analysis indicated the existence of single crystalline silicon region solidified with atomic defects under the mound configuration. Therefore the drastic change of the configurations was attributed to the changes of the atomic-scale microstructures by applying the bias voltages.

Spheroidal colloidal indium tin oxide (ITO) nanoparticles, about 6 nm in diameter, were synthesized in-house and films were fabricated from them on glass substrates by spin coating. These films had high electrical resistivity due to the presence of organic capping ligands around each nanoparticle. Although high temperature annealing has been shown to reduce film resistivity by over eight orders of magnitude, lower temperature processing is desirable for applications like flexible electronics. Colloidal ITO films were subjected to a series of alternating RIE treatments in oxygen (5 minutes duration per cycle) and in argon (1 minute duration per cycle); and parameters such as gas pressure, RIE power and number of cycles were varied. These RIE treatments were found to reduce the film resistivity significantly. Among the parameters studied, gas pressure during RIE was found to be the most important parameter that determined the effectiveness of the treatment. Residual carbon content variation characterization done by XPS depth profiles also indicated similar trends.

Molecular dynamics simulations are performed to investigate the defect accumulation and microstructure evolution in hcp zirconium (Zr) – a material which is widely used as clad for nuclear fuel. Cascades are generated with a 3 keV primary knock-on atom (PKA) using an embedded atom method (EAM) potential with interactions modified for distances shorter than 0.1 Å. With sequential cascade simulations we show the emergence of stacking faults both in the basal and prism planes, and a Shockley partial dislocation on the basal plane.

Crystal structures of long-period stacking-ordered (LPSO) phases in the Mg-TM (transition-metal)-RE(rare-earth) systems were investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The 18R-type LPSO phase is constructed by stacking 6-layer structural blocks, each of which contains four consecutive close-packed planes enriched with TM and RE atoms. Formation of the TM6RE8 clusters with the L12 type atomic arrangement is commonly observed in both Mg-Al-Gd and Mg-Zn-Y LPSO phases. The difference between the crystal structures of Mg-Al-Gd and Mg-Zn-Y LPSO phases can be interpreted as the difference in the in-plane ordering of the TM6RE8 clusters in the structural block. The Mg-Al-Gd LPSO phase exhibits a long-range in-plane ordering of Gd and Al, which can be described by the periodic arrangement of the Al6Gd8 clusters with the L12 type atomic arrangement on lattice points of a two-dimensional 2 $\sqrt 3 $ a Mg × 2 $\sqrt 3 $ a Mg primitive hexagonal lattice, although the LPSO phase in the Zn/Y-poor Mg-Zn-Y alloys exhibits a shortrange in-plane ordering of the Zn6Y8 clusters.

Direct printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method of producing stable inks for ‘in-situ’ deposition of oxide thin films by inkjet printing. The inks were prepared from metal-acetates solutions and printed on a variety of substrates. The acetate precursors were decomposed into oxide films during the subsequent calcination process to achieve the ‘in-situ’ deposition of the desired oxide films directly on the substrate. By this procedure we have obtained room temperature contamination free ferromagnetic spintronic materials like Fe doped MgO and ZnO films from their acetate(s) solutions. We find that the origin of magnetism in ZnO, MgO and their Fe-doped films to be intrinsic. For a 28 nm thick film of Fe-doped ZnO we observe an enhanced magnetic moment of 16.0 emu/cm3 while it is 5.5 emu/cm3 for the doped MgO film of single pass printed. The origin of magnetism is attributed to cat-ion vacancies. We have also fabricated highly transparent indium tin oxide films with a transparency >95% both in the visible and IR range which is rather unique compared to films grown by any other technique. The films have a nano-porous structure, an added bonus from inkjetting that makes such films advantageous for a broad range of applications.

As an approach to improve the thermoelectric properties of the polycrystalline Ca3Co4O9 misfit-layered oxide, substitutions of Co2+…4+ with the heavier cations Ru3+/4+ and In3+ were tested. Polycrystalline samples Ca3Co4-xRuxO9 and Ca3Co4-xInxO9 (0 < x < 0.21) were prepared via a solid-state-reaction route. For each sample the crystal structure was analyzed and a complete thermoelectric characterization was done within a temperature range of 300 K < T < 1125 K.

Both substitution strategies resulted in a significant decrease of the thermal conductivity (κ). For the In3+-substituted samples the decrease of the Seebeck coefficient (α) balanced the κ reduction so that no overall enhancement of the figure of merit (ZT) was found. The Ru3+/4+ substitution reduced the p-type carrier concentration and thus increases the electrical resistivity (ρ el ), while α became larger at low temperatures. Despite the reduction of the power factor, a small enhancement in ZT was observed in the case of x = 0.1 Ru substitution, due to the strong κ reduction. Considering the observed preferred orientation of the Ru-substituted crystallites, a maximum value of ZT = 0.14 perpendicular to the pressing direction is found at T = 1125 K, indicating that Ru substitution is a promising strategy for a further ZT improvement.

We examined the influence of momentary annealing on the nanoscale surface morphology of NiO(111) epitaxial thin films deposited on atomically stepped sapphire (0001) substrates at room temperature in O2 at 1.3 × 10−3 and 1.3 × 10−6 Pa using a pulsed laser deposition (PLD) technique. The NiO films have atomically flat surfaces (RMS roughness: approximately 0.1–0.2 nm) reflecting the step-and-terrace structures of the substrates, regardless of the O2 deposition pressure. After rapid thermal annealing (RTA) of the NiO(111) epitaxial film deposited at 1.3 × 10−3 Pa O2, a periodic straight nanogroove array related to the atomic steps of the substrate was formed on the film surface for 60 s. In contrast, the fabrication of a transient state in the nanogroove array formation was achieved with RTA of less than 1 s. However, when the O2 atmosphere during PLD was 1.3 × 10−6 Pa, random crystal growth was observed and resulted in a disordered rough surface nanostructure after RTA.

The CdTe photoluminescence spectra of CdTe/CdS/ZnO heterojunctions annealed in the presence of CdCl2 have been analyzed in the 4.7-100K temperature range. The analysis has been performed for laser excitation power between 0.01 mW and 30 mW. The analysis showed that the photoluminescence spectrum in the 1.1-1.6 eV region consists of a defect band (1.437 eV) having complex structure and revealing well contoured LO phonon replicas and bound exciton annihilation in the 1.587-1.593 eV region. The band analysis has been carried out by deconvoluting the spectra. It has been shown that the defect band consists of two elementary bands and their phonon replica. An “unusual” temperature dependence of the defect band has been found.

Complex Metallic Alloys (CMAs) are metallic solids of high structural complexity, consisting of large numbers of atoms in their unit cells. Consequences of this structural complexity are manifold and give rise to a variety of exciting physical properties. The impact that such structural complexity may have on the lattice dynamics will be discussed. The surprising dynamical flexibility of Tsai-type clusters with the symmetry breaking central tetrahedron will be addressed for Zn6Sc, while in the Ba-Ge-Ni clathrate system the dynamics of encaged Ba guest atoms in the surrounding Ge-Ni host framework is analysed with respect to the experimentally evidenced strong reduction of lattice thermal conductivity. For both systems experimental results from neutron scattering are analyzed and interpreted on atomistic scale by means of ab initio and molecular dynamics simulations, resulting in a picture with the respective structural building blocks as the origin of the peculiarities in the dynamics.

In search for non-toxic thermoelectric materials that are stable in air at elevated temperatures, zinc oxide has been shown to be one of only few efficient n-type oxidic materials. Our bottom-up approach starts with very small (<10 nm) Al-doped ZnO nanoparticles prepared from organometallic precursors by chemical vapor synthesis using nominal doping concentrations of 2 at% and 8 at%. In order to obtain bulk nanostructured solids, the powders were compacted in a current-activated pressure-assisted densification process. Rapid thermal annealing was studied systematically as a means of further dopant activation. The thermoelectric properties are evaluated with regard to charge carrier concentration and mobility. A Jonker-type analysis reveals the potential of our approach to achieve high power factors. In the present study, power factors larger than 4×10-4 Wm-1K-2 were measured at temperatures higher than 600 °C.

Here we show that microtubular bundles bend flexibly under a hydrodynamic flow to form teardrop patterns. In a highly concentrated microtubular solution, patterns of same-sized teardrops form according to the maximum critical curvature, which is determined by the specific rigidity of the microtubules. Our understanding is that these micropatterns grow when microtubular bundles with hydrodynamic flow energy are converted into stable teardrop patterns as a higher structure. This conversion is generated by the combined effect of multiple kinds of energy, including heat and hydrodynamic flow, as well as life systems. These self-generating patterns in a spatio-temporal stream are reminiscent of what the artist Edward Munch called a scream of nature. We also envision that microtubular pattering with hierarchical structure will broaden the potential application of these geometrical structures and guide biomimetic material engineering towards areas such as integrated energy conversion, soft material patterning, and living signal transduction.

Multilayer structures of Nb2O5/Ag/Nb2O5 have been deposited onto flexible substrates by sputtering at room temperature to develop indium free composite transparent conductive electrodes. The optical and electrical properties of the multilayers are measured by UV–Visible spectroscopy, Hall measurement and four point probe and the effect of Ag thickness has been studied. The critical thickness of Ag to form a continuous conducting layer is found to be 9.5 nm and the multilayer stack has been optimized to obtain a sheet resistance of 7.2 Ω/sq and an average optical transmittance of 86 % at 550 nm. The Haacke figure of merit (FOM) has been calculated for the films, and the multilayer with 9.5 nm thick Ag layer has the highest FOM with 31.5 x 10-3 Ω/sq, which is one of the best FOM reported till date for room temperature deposition on flexible substrates. The multilayered samples are annealed in vacuum, forming gas, air and O2 environments and the optical and electrical properties are compared against the as-deposited samples.

A multi-scale modeling of electron transport via a metal-semiconductor interface is carried out by coupling ab initio calculations with three-dimensional finite element ensemble Monte Carlo simulations. The results for the Mo/GaAs (001) interface show that variations of the electronic properties with the distance from the interface have a strong impact on the transport characteristics. In particular, the calculated tunneling barrier differs dramatically from that of the ideal Schottky model of an abrupt metal-semiconductor interface. The band gap narrowing near the interface lowers resistivity by more than one order of magnitude: from 2.1×10-8 Ωcm² to 4.7×10-10 Ωcm². The dependence of the electron effective mass from the distance to the interface also plays an important role bringing resistivity to 7.9×10-10 Ωcm².