In this work, bare and (Fe3+ and Fe2+)-doped ZnO nanoparticles (NPs) have been synthesized in a polyol medium at 180oC. The synthesis in polyol allows a precise control of doping under size-controlled conditions. The Fe concentration varied in the 0-2 at. % range. As-synthesized samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), Photoluminescence (PL) spectroscopy and Vibrational Sample Magnetometry (VSM). XRD measurements confirmed the formation of well crystallized wurtzite ZnO with absence of secondary phases in bare and doped samples; the average crystallite size was estimated at 8.4 ± 0.3 nm for bare ZnO NPs. Systematic shifts in the main diffraction peaks due to the incorporation of the dopant species were observed in the Fe3+ and Fe2+ doped-ZnO samples. FT-IR analyses evidenced the presence of organic moieties on the surface of the nanoparticles that are associated to the functional groups of polyol by-products; these adsorbed species could explain the observed stability of the NPs when suspended in water. PL measurements (excitation wavelength 345 nm) reveled that a tuning in the emission bands of ZnO NPs can be achieved through doping. VSM measurements evidenced a weak but noticeable ferromagnetic response at room temperature (RT) in doped samples.

Scaling contact lithography (microcontact printing, microflexography, and nanoimprint lithography) to large roll-to-roll platforms will enable high speed, low cost lithographic patterning of surfaces. However, many details of robust implementations at the roll-to-roll scale remain an engineering challenge, including precise regulation of printing pressures and the stamp-substrate interaction. This paper introduces a method for precise control of contact pressure that can accommodate large dimensional variations, i.e. varying stamp and substrate thicknesses. This control algorithm is implemented on a simply supported roll positioning stage. Experimental results for microcontact printing and microflexography are shown both with in situ contact measurements on a pseudo substrate and with 5 um silver nanoparticle prints. Ultimately, this approach enables robust printing despite sensitive stamp patterns and large dimensional variations (> 10 μm) in substrates, stamps, and roll equipment.

Here we study the piezopotential, the carrier concentration, and the stored energies in laterally bent piezo-semiconductive NWs with total-bottom contact. Moreover, we give reasons for the well-known existence of two regions where the piezopotential has an opposite sign in comparison with the rest of the NW. Finally, we provide an upper limit to the static mechanicalto-electrical conversion efficiency by computing the ratio between the total stored electrostatic energy and the total (mechanical and electrostatic) stored energy. Our results can provide guidelines for designing devices based on laterally bent piezoelectric NWs.

The advantage of aluminum powder as a fuel additive in energetic formulation includes its high volumetric combustion enthalpy and relatively low cost. However, the thermodynamically predicted benefits of aluminum combustion are rarely achieved because of extended ignition delays associated with heterogeneous reactions occurring at the alumina surface which surrounds the aluminum particle. In order to fully exploit aluminum’s high reaction energy, this effort focuses on adjusting its combustion dynamics by modifying its surface and structure. The modification is achieved by cryo-milling aluminum with cyclooctane, which is liquid at room temperature, but solid when cooled by liquid nitrogen. The prepared materials consist of micron-sized, equiaxial, mostly Al particles with a small amount of cyclooctane. Aluminum surface in the prepared sample is coated with a cyclooctane-modified layer with properties significantly different from those of regular alumina. Its oxidation kinetics, as observed from thermo-analytical measurements, is different from that of pure aluminum. The powder ignites at substantially reduced temperatures, produces shorter ignition delays, and higher aerosol burn rates compared to a regular spherical Al powder with similar particle sizes.

The crystal structure of a-plane GaN/ZnO heterostructures on r-plane sapphire was investigated by using the XRD and TEM measurment. It was found the formation of (220) ZnGa2O4 and crystal orientation of semipolar (10 $\bar 1$ 3) GaN at GaN/ZnO interface. The epitaxial relation of normal surface direction are the sapphire (1 $\bar 1$ 02) // a-GaN (11 $\bar 2$ 0) and ZnGa2O4 (220) // semi-polar GaN (10 $\bar 1$ $\bar 3$ ). Beside, the emission peak energy of ZnO appears shift about 60 meV in the GaN/ZnO/GaN heterostructures due to the re-crystallization of ZnO layer with Ga or N atom and the formation of the localized state.

We present theoretical calculations of the phonon-drag contribution to the Nernst thermoelectric power S yx in Bismuth nanowires. We investigate the thermopower S yx with diameters L ranging from 22 to 900 nm at low temperatures (0.1 - 4.0 K) and high magnetic fields (up to 16 T). We find that the peak of thermopower S yx around 14.75 T exhibits the size effect in two different ways: for wires with L≥200 nm, the peak height increases with decreasing L; for wires with L<200 nm, on the other hand, the peak height rapidly decreases with decreasing L. The dependence is accounted for by considering the contributions of discrete quantized phonon modes. We also discuss the temperature dependence of S yx .

In-depth materials science course offerings are crucial for training the next generation of researchers in many pure and applied fields. However, translating discoveries from the laboratory into domestic and industrial settings requires contributions from professionals outside of these strictly technical areas. Providing non-major students instruction in core scientific ideas and illustrating the myriad pathways by which these ideas become innovative technologies should be an additional goal of science and engineering programs. “Technologies of the Future” (ToF) is a novel course for non-science/engineering majors in which students participate in team-based laboratory and design projects with modern materials systems. After learning about a phenomenon or physical principle in class, students are given the opportunity to explore it in lab and are tasked with the design of a novel device that incorporates it. Example laboratory topics include superhydrophobic surfaces and dye-sensitized solar cells. In the design phase, instructors act as “consultants”, lending their expertise to students unfamiliar with engineering analysis or ancillary physical concepts. Summative activities are designed to leverage the diverse talents of the interdisciplinary teams of students. The course concepts and activities are designed to prepare students for both a modern workplace that requires innovative thinking and a modern world in which emerging technologies offer solutions to pressing environmental and social problems.

In this study, thermoelectric properties of bulk and epitaxy GaN with various doping concentration are investigated. Seebeck coefficients decreased with the increase of carrier concentration for both bulk and epitaxial GaN samples, and the Seebeck coefficients of epitaxial GaN samples are found to be larger than that of bulk GaN samples in the similar carrier density due to the higher dislocation scattering. For epitaxial samples, a high power factor of 4.72 × 10-4 W/m-K2 is observed. The power factors of the bulk GaN samples are in the range of from 0.315× 10-4W/m-K2 to 0.354× 10-4W/m-K2 due to the low Seebeck coefficients.

Graphene is a two-dimensional (2D) hexagonal array of carbon atoms in sp2-hybridized states. Graphene presents unique and exceptional electronic, thermal and mechanical properties. However, in its pristine state graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Because of this there is a renewed interest in other possible two-dimensional carbon-based structures similar to graphene. Examples of this are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and they can be intrinsically nonzero gap systems. These systems can be easily hydrogenated and the amount of hydrogenation can be used to tune the band gap value. In this work we have investigated, through fully atomistic molecular dynamics simulations with reactive force field (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that depending on whether the atoms are in the benzenoid rings or as part of the acetylenic groups, the rates of hydrogenation are quite distinct and change in time in a very complex pattern. Initially, the most probable sites to be hydrogenated are the carbon atoms forming the triple bonds, as expected. But as the amount of hydrogenation increases in time this changes and then the carbon atoms forming single bonds become the preferential sites. The formation of correlated domains observed in hydrogenated graphene is no longer observed in the case of graphdiynes. We have also carried out ab initio DFT calculations for model structures in order to test the reliability of ReaxFF calculations.

Magnetic properties at nano-scale provide a whole spectrum of new phenomena that can be beneficial for spintronic devices characterized with ultra-short response time, high sensitivity to magnetic field and miniature size. The properties and stability of a magnetic system can be enhanced by creating ordered arrays of ferromagnetic nano-particles. Here we report a considerable reduction of coercitivity for a magnetic array using triangular, square and hexagonal particle arrangement. The reduction of coercitivity can be explained by fine-tuning of dipole-dipole interaction between magnetic particles, which is to large degree influenced by the number of nearest neighbors and distance between the particles.

In this paper, we report new phase of crystalline silicon, quasicrystalline silicon thin-film on glass substrate. The surface topography of these films reveal simultaneous existence of sixfold and fivefold symmetry. We found an array of quasi-unit cell in 2-D that formed quasicrystalline solid. This is first time demonstration of quasicrystalline for single element, silicon (Si). Raman spectra suggests that we found crystalline silicon structure on glass substrate that is not single-crystal silicon (c-Si) but very close to c-Si.

The surface structure of oxide materials may be the limiting factor in controlling switching properties at interfaces. Here we investigate and correlate the surface structure and electronic properties of BaTiO3 substrates. By using low energy electron diffraction and scanning tunneling microscopy we are able to identify surface reconstructions based on annealing treatments. We then investigate the effect of contact size on the transport properties on oxide surfaces utilizing atomic force microscopy. Our results show the critical importance of controlling surface structure to optimize electronic properties at oxide interfaces.

Photocatalytic properties of titanium oxide depend on the material size and shape, which can favour a higher interaction between reactants and catalyst. Most of the studies reported until now, show that reducing size down to the nanoscale increases the photocatalytic efficiency. We demonstrate that a multiscale shape design, integrating surface roughness, particle shape, and material 1D processing and orientation, can favour photocatalytic properties in the solid-gas regime, especially mineralization (conversion into CO2), when the material hierarchical 1D orientation is combined with unidirectional gas flow. Several materials with hierarchical structure were prepared and characterized. They have been tested for the photocatalytic mineralization of gaseous acetone, and compared with commercial catalysts. Our study reveals that a suitable combination of multiscale design can favour high mineralization.

Various metallic structures of complex shape, resembling natural objects such as plants, mushrooms, and seashells, were produced when growing nanowires by means of pulsed current electroplating in porous membranes. These structures occur as the result of nanowires self-assembling (biomimetics) if the electroplating is continued after the nanowires reach the membrane surface. By varying the membrane geometry and the pulsed current parameters, and alternating electroplating from two baths with different electrolytes, various models were fabricated, including a hollow container with wall thickness of 10-30 nm. The possibility of shape regulation for models was demonstrated: in certain conditions, mushroom- and shell-like convex-concave models of the same kind were obtained. The hierarchical structure of models at the nano-, micro- and mesoscopic levels is shown through fragmentation and chemical etching. This biomimetic method suggests an analogy between the shape-forming processes of natural plants and their metallic models. Nanostructured mesoscopic objects of metals (Ag, Pd, Rh, Ni, Bi), alloys (PdNi, PdCo, PbIn) as well as their combinations (PdNi/ Pb, PdNi/ PbIn) were obtained. The technological simplicity of the present method makes it suitable for fabricating nanostructured materials that may be efficient in catalysis, superhydrophobic applications, medical filters, and nanoplasmonics.

In this work, a novel low dielectric constant (low-k) pore sealing approach was engineered by depositing firstly a sub-2 nm SAMs and then a 3 nm TiN barrier film. The low-k film was pretreated by plasma to introduce hydroxyl groups onto the surface, followed by SAMs deposition. Then a TiN film was deposited from tetrakis(dimethylamino)titanium (TDMAT) via ALD as a dielectric barrier. Penetration of Ti atoms into low-k was measured and used to evaluate the sealing ability of SAMs. For the samples covered with SAMs, around 90% reduction of Ti atoms penetration was achieved. The pore radius was reduced to below 0.5 nm after the barrier deposition. The ∆k after pretreatment and after SAMs are 0.1 and 0.16, respectively.

Density functional theory and statistical calculations are combined to address the chemical stability and structure of epoxy functionalizations of single-layer graphene. Our computations show that at oxidation levels of O:C<0.5, the Gibbs free energy of formation per epoxide amounts to about 0.6 eV, and the structure of the epoxy functionalizations presents local order and long-range disorder. The positive energy value indicates that in air at p=1 bar and room temperature, epoxy functionalizations of graphene are unstable and prone to spontaneous reduction. Our calculations show also that formation and release of O2 is a slow process whose kinetics is controlled by large energy barriers, the formation of very stable intermediate species, and unlikely electronic transitions.

We report on the maskless integration of micron-sized GaAs crystals on patterned Si substrates by metal organic vapor phase epitaxy. In order to adapt the mismatch between the lattice parameter and thermal expansion coefficient of GaAs and Si, 2 μm tall Ge crystals were first grown as virtual substrate by low energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs structures grown on top of the Ge crystals at the transition towards full pyramids with energetically stable {111} facets. A substantial release of strain is shown in GaAs crystals with a height of 2 μm and lateral sizes up to 15×15 μm2 by both X-ray diffraction and photoluminescence.

The percolation threshold in a ceramic composite depends on the processing conditions used to fabricate them along with the size and shape of the filler. In this study, borosilicate glass microspheres were used as the matrix material and nanosized antimony tin oxide (ATO) particles were used as the filler. The microsphere/ATO composites were fabricated by hot pressing around the glass transition temperature in order to control the viscosity. The pressure and temperature applied allowed the ATO to be confined to the spaces between certain glass particles, forming percolating networks at low volume fractions of the ATO. The electrical properties were examined using ac impedance spectroscopy. The impedance, electric modulus, and tan δ were studied which allowed for valuable insights in structure-property-processing relationships in these materials, along with determination of the percolation behavior in these composites. This analysis on samples right before percolation indicated that there was a highly resistive component affecting long range conductivity which is likely due to porosity at the triple points while the dielectric response is affected by the clusters of ATO nanoparticles. Based on this, the percolation of ATO should reduce down to lower concentrations if the processing conditions are improved to reduce this porosity and further segregate the ATO.