The electronic properties of carbon nanotubes are quite often drastically affected by the presence of defects that can develop during nanotube growth, processing or characterization too. Some of these defects such as pentagon-heptagon rings, substitutional impurities, vacancies and dislocations are of topological nature, and can sometimes create on-tube intramolecular junctions, as found by previous scanning tunnelling microscopy studies.

Our recent STM experiments reveal for the first time a much more complicated junction structure, a hybrid single-walled carbon nanotube consisting of a distinct coiled structure located between two straight segments, each of different helicity. We characterise the hybrid junction at the atomic level and describe its electronic behaviour that has important implications in the practical design of functional components for nanoelectronic applications.

The detailed structure of nanocrystalline BaTiO3 powder during ball milling has been studied using XRD & TEM. The study illustrates important advances in understanding atomic scale properties of this material. Ferroelectric BaTiO3 powder undergoes phase transformation along the sequence Cubic(Pm3m)-tetragonal(P4mm)-orthohombic (Amm2)-rhombohedral(R3m) structure when pressureless sintered samples are cooled from high temperature to low temperature. The high to low symmetry phases are not related to group subgroup symmetry as transformation is discontinuous and first order in nature and the twin relationship in the low symmetry is forbidden by Landau theory. In case of ball milled BaTiO3 powder a continuous and diffusionless phase transition occur via second order to and from a metastable intermediate phase. In this pathway crystallites in the aggregation are twinned and the twin structure is related to crystal point group m3m which in the present case is illustrated as having 6mm symmetry formed under low driving force. The unit cell evolution due to phase transition and the crystallographic relationship are established. The phase transformation, coalescence and twin structure of thermally annealed BaTiO3 nanocrystals under high vacuum has been investigated using in situ high temperature XRD. The structure analysis is performed with the use of the method of computer modelling of disorder structure and simulation of corresponding diffraction pattern.

Perovskite type oxide thin films have attracted a lot of attention, because they are essential materials which will be used for various electric devices such as ferroelectric random access memory (FeRAM) and tunable filter devices. When the materials are used for such capacitive devices, bottom electrode layers for oxide films are very important, since they significantly affect the crystallinity of the oxide films. Platinum (Pt) is one of the well known bottom electrode materials used for the oxide thin films. Pt provides also better nucleation sites for such perovskite materials due to small lattice misfit. Since dielectric properties of ferroelectric films are originated from the displacement of ions in a crystal along the c-axis direction, c-axis oriented ferroelectric thin films are required to attain better dielectric properties. (100) oriented Pt layers are required to attain c-axis oriented perovskite type ferroelectric films. In our previous report, we succeeded in preparing (100)-oriented Pt thin films with thickness of 20 nm on SiO2/Si substrate at substrate temperature Ts above 400 °C using MgO (100) buffer layers which deposited on Fe (100) seed layers. However, the growth of Pt(111) texture appeared when the thickness was increased from 20 nm to 100 nm, since (100) texture has relatively higher surface energy than (111) closely packed texture for Pt surface. It suggested that surface energy of the films changed during the deposition. In order to keep the surface energy, addition of O2 gas was performed during Pt deposition. Pt thin films with (100) preferred orientation with thickness above 100 nm were deposited on the (100) oriented MgO layer prepared on very thin seed Fe layers deposited on SiO2/Si substrates at Ts of 500 °C by facing-targets sputtering. It was also succeeded to attain (100) oriented perovskite oxide layer when they were deposited on the Pt(100)/Mg(100)/Fe/SiO2/Si underlayer.

We have synthesized type-VIII and type-I Ba8Ga16Sn30 clathrates by using different annealing treatments, confirmed with XRD and electron microprobe measurements. NMR lineshape measurements identified a broad resonance corresponding to first-order-shifted satellites. Simulations for the type I structure based on first principles calculations provided an excellent fit to the data, with the best agreement provided by the calculated lowest-energy configuration, having no Ga-Ga bonds. These results allow us to address local configurations within the random type-I alloy, as well as atomic displacements and bond-length distributions, which we compare to experiment.

Influence of operation factors in diffusion test of compacted bentonite (such as agitation of test solution in the reservoir, feed rate of the test solution and mass transfer resistance in the filter) on the diffusion data was examined by reservoir depletion (RD) test method using Cs+. The influence of these factors on the diffusion data was also analyzed based on the mathematical sorption-diffusion model which considered the feed of test solution and mass transfer resistance in the filter as well. The reservoir depletion data showed some remarkable influences of these operational conditions, especially in the system with low ionic strength. Change in mass transfer resistance at filter-compacted bentonite due to the operational conditions was found to be potential factor which disturb the diffusion data. The influence was reduced in the system with high ionic strength of solution.

Discrete volumes of material in the form of a beam have been isolated from a parent limpet tooth using Focused Ion Beam (FIB) techniques. Mechanical bending tests of individual beams are performed using atomic force microscopy (AFM). The relatively small volumes tested in this beam-bending configuration allow approximation of the limpet tooth structure to a uniaxial short fibre composite. This mechanical testing technique is superior to conventional micro-hardness indentation as a defined stress condition within a locally defined volume is examined. Composite theory is shown to be valid for describing the mechanical properties of limpet teeth at sub-micron lengths scales and used to determine the synergy between the nanomaterial constituents.

When present, uranium is usually an element of importance in a nuclear waste repository. In the Waste Isolation Pilot Plant (WIPP), uranium is present in significant quantities, with about 647 metric tons to be placed in the repository [1]. Therefore, the chemistry of uranium, and especially its solubility, needs to be determined under WIPP-relevant conditions.

Long-term experiments were performed to measure the solubility of uranium (VI) in carbonate-free ERDA-6 brine, a simulated WIPP brine, at pCH+ values between 8 and 12.5. These data, obtained from the over-saturation approach, were the first WIPP repository-relevant data for the VI actinide oxidation state. The solubility trends observed pointed towards low uranium solubility in WIPP brine and a lack of amphotericity. At the expected pCH+ in the WIPP (˜ 9.5), measured uranium solubility approached 10-7 M. The objective of these experiments was to establish a baseline solubility to further investigate the effects of carbonate complexation on uranium solubility in WIPP brines, during the ongoing research program in actinide solubility under WIPP-relevant conditions.

When materials are very thin in one or more dimensions, their equilibrium shapes are often curved/bent. Such shapes commonly represent a compromise between elastic strain energy and other thermodynamic forces (e.g. related to surface stresses, electrostatic interactions, or adsorption). Examples include ZnO and SnO2 nanobelts, silica/carbonate helicoids, and graphene sheets and nanoribbons. Here, we demonstrate that when the equilibrium shape of a nanomaterial is not flat/straight, important fundamental material properties may be orders of magnitude different from their bulk counterparts. We focus here primarily on the graphene edges. Graphene in three dimensions is a codimension c = 1 material; the codimension is c = D – d = 3 – 2 = 1, where D is the dimensionality of the space in which the material is embedded and d is the dimensionality of the object. By contrast, a flat graphene sheet has c = 2 – 2 = 0. We use the REBO-II interatomic potential to calculate the edge orientation dependence of the edge energy and edge stresses of graphene with c = 0 and c = 1. The edge stress for all edge orientations is compressive with c = 0. Both edge energy and stresses are in reasonable agreement with DFT calculations. The compressive edge stresses in c = 0 lead to edge buckling (out-of-the-plane of the graphene sheet) for all edge orientations (c = 1). The edge buckling in c = 1 reduces all edge energies and dramatically reduces all edge stresses to near zero (more than an order of magnitude drop). We also report the effect of codimension on the free energy and entropy of a graphene sheet and the elastic properties of ZnO nanohelices.

SiC single crystals are grown at II-VI by the seeded sublimation technique. The process has been scaled up and optimized to support commercial production of high-quality 100 mm diameter, Semi-Insulating (SI) 6H substrates and 100 mm 4H n+ substrates. The growth process incorporates special elements aimed at achieving uniform sublimation of the source, steady growth rate, uniform doping and reduced presence of background impurities.

Semi-insulating 6H substrates are produced using precise vanadium compensation. Vanadium doping is optimized to yield SI material with very high resistivity and low capacitance.

Crystal quality of the substrates is evaluated using a wide variety of techniques. Specific defects, their interaction and evolution during growth are described with emphasis on micropipes and dislocations. The current quality of the 6H SI and 4H n+ crystals grown at II-VI is summarized.

In this work, the drift of ISFET characteristics due to hydration effect was studied. The ISFETs were fabricated using the standard NMOS process. The AgCl reference electrode was fabricated with the electrolysis method. The ISFET modeling was carried out in MATLAB to study the time variation of surface potential and the drain-source current. In addition, the surface morphology and dielectric constant of silicon dioxide were tested to study the hydration effect in order to eliminate the drift. The dielectric constant of the gate oxide increases exponentially with hydration time. The surface morphology studied with the atomic force microscope (AFM) showed no significant change after immersion in water. It is believed that the main cause of the drift is the hydration effect, which is due to the change in dielectric constant of the sensing material and a small number of surface binding sites that react slowly to a change in pH.

Using different pressures of nitrogen, N-doped ZnO nanorod arrays of various densities have been synthesized on quartz substrates by pulsed laser deposition techniques. The nanorods grow preferentially perpendicular to the quartz surface. X-ray diffraction patterns revealed some degradation of the crystal structure at elevated nitrogen pressures. High concentrations of nitrogen doping in ZnO nanorods were estimated by X-ray photoelectron spectroscopy. Raman scattering spectra confirmed the wurtzite structure of N-doped ZnO nanorods. A prototype sensor based on the N-doped ZnO nanorod arrays demonstrates a linear dependence of the conductivity with operating temperature and pressure of a test gas pollutant.

The present work concerns novel approaches to fabricate silicon-based electrodes. In this study silicon nano-particles are synthesized via two aerosol routes: Laser assisted Chemical Vapour Pyrolysis (LaCVP) and Spark Discharge Generation (SDG). These two techniques allow the generation of uniformly sized particles, with a good control over the composition and the range of sizes. Herein, particles with size ranging from 2 to 70 nm were obtained. Starting from these nano-particles, nano-structured porous thin films are produced either by electrospraying a polymeric solution in which LaCVP-produced particles were previously dispersed, or by inertial impacting the SDG-produced particles directly from gas phase onto a substrate. The Electro- Spray (ES) is used to produce composite films for Li-ion battery applications, whereas the Inertial Impaction (II) is used to produce pure silicon films for other purposes (i.e.: sensors).

Recent years, although silica aerogel is expected to be the material for energy savings, the lack of the strength prevents from commercial usages such as heat-insulating windows. To improve mechanical properties, methyltrimethoxysilane is used as a precursor of aerogels because the network becomes flexible due to the relatively low cross-linking density and to the unreacted methyl groups. Because of the strong hydrophobicity of MTMS-derived condensates, uniform and homogeneous gel networks are hardly attained. In this study, we employed surfactant n-hexadecyltrimethylammonium chloride (CTAC) in starting compositions to control phase separation during a 2-step acid/base sol-gel reaction. By changing the starting composition, properties of aerogels such as bulk density and light transmittance are affected. With increasing amount of CTAC, the gel networks became denser and less transparent. Highly transparent aerogels were obtained when the amount of urea was increased.

The multiple-gate aspect of the Screen Grid Field Effect Transistor (SGrFET) increases functionality and reduces component count of circuits. An independently-driven gate SGrFET is used to control the switching voltage as well as the gain factor of an inverter. The multi-gate configuration of the SGrFET allows a decrease in output conductance without an increase of transistors count. This leads to a reduction in fabrication complexity, chip area and parasitics. In addition, a simple SGrFETs-based current mirror circuit is proposed with gain factor control.

We report room temperature ZT calculations for silicon and indium antimonide nanowires of varying radii. Interestingly, some systems deviate significantly from the anticipated trend of ZT vs. radius. The InSb results are particularly remarkable due to the non-monotonic relationship seen between n-type ZT and wire radius; where typically we expect to see only a decrease with increasing radius, for InSb ZT increases between 20 and 100 nm wire radii. This is thought to be due to the high level of degeneracy of subbands for larger nanowire radii. These results indicate that the monotonic relationship between ZT and wire radius observed under strong confinement conditions cannot be assumed, but must be tested on a case-by-case basis for each materials system.

Comparison of the IR spectra of the Cu-phthalocyanine (CuPc) nanocrystals obtained using surface sensitive attenuated total reflectance (ATR) and bulk sensitive transmittance sample configurations revealed small but measurable changes of some vibrational frequencies of the molecules at the surface of nanocrystals with the outermost part of the surface CuPc molecules being the most affected. These changes are caused by electrostatic interactions between the polar components of the molecules on the surface of nanocrystals and external polar molecular species vicinal to the nanocrystals. The external polar species can be either chemically bonded to the CuPc nanocrystal's surface or they can reside in its vicinity without forming a chemical bond with the nanocrystal. Molecular modeling (DMOL3 - Materials Studio and Gaussian calculations) of the impact of selected external polar species vicinal to a CuPc molecule on the CuPc molecular vibrations confirmed experimentally observed changes in the vibrational frequencies of the selected CuPc molecular bonding configurations and provided detailed information on the forces involved in these interactions. The population of external polar species vicinal to the CuPc surface can be modified by washing the nanocrystals or by introducing polar molecular additives miscible with the CuPc nanocrystals. Reduction in the number of external polar additives was accomplished by either centrifuging the aqueous dispersion of the nanocrystals or by organic solvent-based Soxhlet extraction, while their number was increased by soaking (followed by drying) the nanocrystals in high and low pH aqueous solutions containing SO3- and OH- ions. These quantitative and qualitative modifications of the population of external polar species surrounding CuPc nanocrystals were reflected in the corresponding changes of the selected vibrational frequencies of the CuPc surface molecules providing an effective tool for not only recognizing the molecular species vicinal to a nanocrystal but also quantifying their concentration. Some of these modifications can also be observed with a naked eye in the form of noticeable color changes of the CuPc nancrystalline powder. This is due to the extremely high visible extinction coefficient of the CuPc nanocrystals causing that the impinging light is mostly absorbed/reflected within the surface region of the nanocrystals. Changes of the electronic structure within this region, caused by the interactions with the vicinal polar species, shift the vis absorption/reflection spectra changing the observed color of the nanocrystalline powder. Similar results were obtained for other molecular nanocrystals, including yellow chromophore molecules. Preliminary data indicate that the described analytical method of analyzing the molecular polar species vicinal to a molecular nanocrystal could find variety of applications ranging from molecular device fabrication to pharmaceutical materials.

We present a variation of a standard convective self-assembly technique, where the drying meniscus is restricted by a straight-edge located approximately 100 μm above the substrate adjacent to the drying zone. We find this technique to yield films at roughly twice the growth rate compared to the standard technique. We attribute this to differing local evaporation rates in the two cases. We also investigate how the crystal growth rate depends on ambient relative humidity and find a clear linear dependency, which we attribute to the length of the drying zone being constant over a wide range of humidities.

ZnxCd1-xSe/C core/shellnanocrystals with 31-39 nm diameter semiconductor cores and 11-25 nm-thick carbon shells were synthesized from solid state precursors. Transmission electron microscopy showed striations on a scale of ˜1 – 5 nm in the nanocrystals that are indicative of a composition modulation, and reveal a chemical phase separation and possible spinodal decomposition within the nanocrystals. Such a composition modulation within the ternary nanocrystals represents a rarely reported phenomenon that could lead to additional applications. The optical properties and carrier relaxation kinetics of the nanocrystals were examined with variable excitation cathodoluminescence (CL). As the excitation level is increased, carrier filling in two-dimensional (2D) phase-separated Cd-rich regions leads to a partial saturation of states before the onset of carrier filling in the higher bandgap homogenous Zn0.47Cd0.53Se regions. In order to model the state filling using Fermi-Dirac statistics for non-interacting carriers, a random quantum well model was used to determine the electron and hole eigensates in the Cd-rich regions of the nanocrystals.

Thin titanium films of 200 nm thickness were prepared by physical vapor deposition over conducting glass plates and anodized to form titanium oxide nanostructured film that demonstrates photoactivity under ultraviolet visible (UV-vis) illumination. Absorbance and photoelectrochemical measurements indicate that the anodized and nitrogen annealed films absorb UV-vis (λ = 300 to 800 nm) illumination to produce a current of 2.5 mA at 0 V and 3 mA at +0.4 V versus Ag/AgCl. A photocurrent of 110 μA and an open-circuit photovoltage (VOC) of 300 mV was noted without application of external bias. Long-term stability tests showed that the photocurrent was stable for 2 h under continuous illumination. The titanium oxide prepared from a small fraction of titanium deposited over conducting glass demonstrates almost similar activity compared with titanium oxides prepared on foils. The material offers promising potential in other applications such as environmental remediation and photocatalytic water splitting.

The long-term selenate uptake capacity of leached cement was studied by means of a replenishment batch experiment with cement pore water (CPW) doped with selenate. The corresponding blank experiment (without Se) was also done. The systems were studied for 31 cycles (18-days each cycle) to understand the long-term selenate immobilization in leached cement. Results showed that the retention capacity of leached cement exponentially decreases with cycle evolution. Precipitation of ettringite, identified by SEM and XRD, occurred along the experiments. The characterization of the cement solid phases indicated that selenate was only retained in the precipitated ettringite.

Experimental data have been successfully modeled by assuming that selenate incorporates into the precipitating ettringite. Precipitation of ettringite is controlled by the kinetic dissolution of the initially present monocarboaluminate.