In this paper we demonstrate that graphene is one of the best materials for new types of terahertz lasers as optical and/or injection pumping of graphene can exhibit negative-dynamic conductivity in the terahertz spectral range. We analyze the formation of nonequilibrium states in optically pumped graphene layers and in forward-biased graphene structures with lateral p-i-n junctions and consider the conditions of population inversion and lasing. The latter provides a significant advantage of the injection pumping in realization of graphene terahertz lasers. We benchmark graphene as a prospective material for injection-type terahertz lasers.

The phase-field crystal (PFC) method has emerged as a promising technique to simulate the evolution of crystalline patterns with atomistic resolution on mesoscopic time scales. We use a 2D PFC model based on Elder et al. [Phy. Rev. B 75, 064107 (2007)] to perform a systematic analysis of a liquid-solid interface for a binary alloy system. We propose the method of determining interfacial energies for a curved liquid-solid interface by stabilizing the circular solid seed in the surrounding liquid phase and the liquid droplet in the solid phase for various seed sizes in a finite system. We also investigate the impact of model parameters on the resulting interface energies. The interface energies are computed with various system sizes in order to study the system size effects. In particular, we compare the simulation results in the form of the interface energy as a function of radius with the existing theories.

The deformation behavior of two of the five Fe-Zn intermetallic phases (Γ, Γ1, δ1k, δ1p and ζ), which are formed in the coating layer of galvannealed steel, has been investigated through uniaxial compression tests for single-phase polycrystalline micropillars. The ζ phase is ductile to some extent while the Γ1 phase is brittle. These results are consistent with the Peierls stress estimated from the crystal structures by assuming the primitive Peierls-Nabarro model.

Light-Emitting Electrochemical Cells (LECs) consist of solution processable ionic light-emitting materials and use air stable electrodes. Their operational mechanism relies on both ionic and electronic conduction. The dynamic behavior is primarily determined by the ionic conductivity. Here, we demonstrate that with increasing temperature the LECs turn-on faster yet without decreasing the efficiency. This is due to the activation energy of ionic transport and the temperature independent photoluminescence quantum yields.

The use of a continuous flow non-thermal plasma reactor for the formation of silicon nanoparticles has attracted great interest because of the advantageous properties of the process [1]. Despite the short residence time in the plasma (around 10 milliseconds), a significant fraction of the precursor, silane, is converted and collected in the form of nanopowder. The structure of the produced powder can be tuned between amorphous and crystalline by adjusting the power of the radio-frequency excitation source, with higher power leading to the formation of crystalline particles. Numerical modeling suggests that higher excitation power results in a higher plasma density, which in turn increases the nanoparticle heating rate due to the interaction between ions, free radicals and the nanopowder suspended in the plasma [2]. While the experimental evidence suggests that plasma heating may be responsible for the formation of crystalline powder, an understanding of the mechanism that leads to the crystallization of the powder while in the plasma is lacking. In this work, we present an experimental investigation on the crystallization kinetic of plasma-produced amorphous powder. Silicon nanoparticles are nucleated and grown using a non-thermal plasma reactor similar to the one described in [1], but operated at low power to give amorphous nanoparticles in a 3-10 nm size range. The particles are then extracted from the reactor using an orifice and aerodynamically dragged into a low pressure reactor placed in a tube furnace capable of reaching temperatures up to 1000°C. Raman and TEM have been used to monitor the crystalline fraction of the material as a function of the residence time and temperature. It is expected that for a residence time in the annealing region of approximately ∼300 milliseconds, a temperature of at least 750 °C is needed to observe the onset of crystallization. A range of crystalline percentages can be observed from 750 °C to 830 °C. A discussion of particle growth and particle interaction, based on experimental evidence, will be presented with its relation to the overall effect on crystallization. Further data analysis allows extrapolating the crystallization rate for the case of this simple, purely thermal system. We conclude that thermal effects alone are not sufficient to explain the formation of crystalline powder in non-thermal plasma reactors.

Technetium-99, a β-emitting radioactive fission product of 235U, formed in nuclear reactors, presents a major challenge to nuclear waste disposal strategies. Its long half-life (2.1 x 105 years) and high solubility under oxic conditions as the pertechnetate anion [Tc(VII)O4] is particularly problematic for long-term disposal of radioactive waste in geological repositories. In this study, we demonstrate a novel technique for quantifying the transport and immobilisation of technetium-99m, a γ-emitting metastable isomer of technetium-99 commonly used in medical imaging. A standard medical gamma camera was used for non-invasive quantitative imaging of technetium-99m during co-advection through quartz sand and various cementitious materials commonly used in nuclear waste disposal strategies. Spatial moments analysis of the resulting 99mTc plume provided information about the relative changes in mass distribution of the radionuclide in the various test materials. 99mTc advected through quartz sand demonstrated typical conservative behaviour, while transport through the cementitious materials produced a significant reduction in radionuclide centre of mass transport velocity over time. Gamma camera imaging has proven an effective tool for helping to understand the factors which control the migration of radionuclides for surface, near-surface and deep geological disposal of nuclear waste.

Metadislocations are highly complex and pivotal defects mediating plastic deformation in complex metallic alloys. Here, we review recent results on the structure of metadislocations in the phases T-Al-Mn-Pd, T-Al-Mn-Fe and o-Al13Co4. In these materials, metadislocation motion is of particular interest as it takes place by pure glide in contrast to most other complex metallic alloys. Recently, novel metadislocations were found in the T-phase [1]. They have Burgers vectors ${\rm{\vec b}} = \pm \tau ^{ - n} c\left( {\matrix{ 0 & 0 & 1 \cr } } \right)$ (n = 2, 3, 4) and are associated to two, four and six planar defects, respectively. The type of planar defect depends on the deformation geometry. Metadislocation glide creates (1 0 0) stacking faults and climb creates (0 0 1) phason planes. Metadislocation glide was observed in the o-Al13Co4 phase, as well [2]. The close structural relation of metadislocations in the phases T-Al-Mn-Pd, T-Al-Mn-Fe, Al13Co4 and ε6-Al-Pd-Mn is discussed.

The present work reports the covalent functionalization of single-walled carbon nanotubes (SWCNTs) by ferrocene derivatives with polyethyleneglycol linkers. A very clean initial sample was chosen to avoid any residual catalyst and carbon impurities. Functionalized SWCNTs (f-CNTs) are deposited on the surface of a glassy carbon electrode (GCE) and this modified electrode is used for oxidizing the cofactor NADH (dihydronicotinamide adenine dinucleotide) in the presence of diaphorase. A clear electrocatalytic effect is evidenced, which can only be attributed to the f-CNTs.

Thin films of nanocrystalline ceria on a Si substrate have been irradiated with 3 MeV Au+ ions to fluences of up to 1x1016 ions cm-2, at temperatures ranging between 160 to 400 K. During the irradiation, a band of contrast is observed to form at the thin film/substrate interface. Analysis by scanning transmission electron microscopy in conjunction with energy dispersive and electron energy loss spectroscopy techniques revealed that this band of contrast was a cerium silicate amorphous phase, with an approximate Ce:Si:O ratio of 1:1:3.

Magnetite (Fe3O4) formation within Magnetospirillum magneticum strain AMB-1 occurs under the influence of the Mms6 protein. It is hypothesised that if key iron binding sites within the C-terminus of the Mms6 protein are substituted for alanine, the protein’s overall iron binding ability is diminished. In this study, an atomistic model of Mms6-driven magnetite formation was developed and the attachment of series amino acid repeats (alanine-alanine, alanine-glutamic acid & glutamic acid-glutamic acid) to the {100} & {111} magnetite surfaces were investigated. Our results suggest the substitution of glutamic acid for alanine residues significantly reduces iron binding affinity of the system, thus confirming the hypothesis. In addition, it is shown that the surface of preferable attachment is the {111} magnetite surface.

We report for the first time the a-Si:H/μc-Si:H/μc-Si:H triple-junction solar cells fabricated on W-textured ZnO having a very high haze value which can improve light scattering effect. For further enhancement of light confinement effects, p-type a-SiOx:H and μc-SiOx:H as wide-gap window-layers, n-type μc-SiOx:H as intermediate layers and a back reflector were employed in these solar cells too. From theoretical analysis, we have found an advantage of a-Si:H/μc-Si:H/μc-Si:H structure for an application to low-concentration photovoltaics. For the fabricated solar cells, a conversion efficiency of 8.86% at 1 sun and and 9.86% under 7.2 suns, and a total photocurrent from each subcell of 24.1 mA/cm2 were achieved although there was still a current mismatch among component subcells.

A system combining photovoltaic (PV) and solar thermal approaches is designed to convert solar energy to electricity with high efficiency across the full solar spectrum. Concentrated solar spectrum is split into two parts: PV and thermal. The PV part of the spectrum is further split into several subbands directed to bandgap appropriate solar cells on an inexpensive Si substrate. Epitaxial Ge on Si is used as a virtual substrate for III-V semiconductor growth. At long and very short wavelengths where PV efficiency is low, solar radiation is directed to a high temperature thermal storage tank for electricity generation using heat engines. The potential of using PV waste heat due to thermalization of high energy photoelectrons for electricity generation is also investigated. Detailed optical and thermal analysis show that with optimized design and neglecting optical component loss, system power conversion efficiency can reach 56%, including more than 16% absolute contribution from thermal storage.

A low thermal budget process for back-end compatible PCMO based RRAM cell is essential for 3D stacked memory. In this paper, we investigate two strategies to engineer low thermal budget processing for bipolar switching - (i) deposition engineering i.e. based on deposition temperature and oxygen partial pressure, (ii) post deposition anneal i.e. based on inert anneal of room temperature deposited PCMO film.. We demonstrate that both deposition and anneal shows a transition temperature above which bipolar switching is realized. Oxygen partial pressure is a key deposition process parameter. As oxygen partial pressure is reduced memory window increases, however beyond an optimal O2 partial pressure, unipolar switching is observed. Inert anneal is more effective in thermal budget reduction as N2/550°C/2min anneal has same memory performance as 650°C/2hour deposition process.

Recent developments on the use of the piezoelectric effect in ZnO nanorod-based p-n junctions for energy harvesting applications are presented. Two types of junctions are used. The first is a hybrid p-n device combining the semiconducting polymer poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) with ZnO nanorods. The second type of junction is an all-inorganic junction between n-type ZnO nanorods and p-type CuSCN. It is shown that both these diodes can be produced on flexible plastic substrates, which generate a voltage output when bent. The voltage output of the ZnO/PEDOT:PSS diodes are measured across a range of resistive loads while bending to find a maximum power point of 12 μWcm-2 at 4 kΩ. It is shown that a voltage output is also generated when this structure is vibrated acoustically. The ZnO/CuSCN diode is sensitized to sunlight with a Ru-based dye to form a photovoltaic device. It is shown that the device efficiency can be increased by application of acoustic vibrations. This is attributed to the electric field generated by the piezoelectric effect in ZnO affecting the charge-carrier recombination at the ZnO surface.

Gold (Au) nanoparticles were synthesized and deposited on the perovskite SrTiO3 (STO) via a one-step solution plasma sputter deposition (SPSD) without any reducing reagents at ambient condition. Good dispersion of the Au nanoparticles deposited on the STO surface was clearly observed. The synthesized Au nanoparticles were well-crystallized with a spherical shape and preferably exhibited multiply twinned structure. An average diameter of Au nanoparicles was estimated to be 6.1 ± 1.4 nm by transmission electron microscopy. Enhanced photocatalytic activity was found for the Au-STO when compared to the pure STO, as investigated from the degradation of methylene blue solution under ultraviolet and visible light irradiation. The SPSD seems to be a rapid and facile approach to prepare the Au nanoparticles supported on the metal oxide for photocatalytic applications.

Visible-light photocatalytic property of TiO2 / WO3 / FTO multi-layer structure was investigated. In this structure, the visible-light absorption takes place in the WO3 layer, and generated electrons and holes diffuse into the FTO and TiO2 layers, respectively. The holes diffused into the valence band of the TiO2 layer produce the hydroxyl radicals due to oxidation of H2O and/or OH− adsorbed on the TiO2 surface. The FTO bottom layer, which acts as a scavenger of electrons, contributes to an effective charge separation. As a result, the visible-light photocatalysis is enhanced in this structure.

The effect of Re addition on microstructure and hardness of the Ni3Al (L12) and Ni3V (D022) dual two-phase intermetallic alloys was investigated as functions of alloying (substituting) method of Re and aging condition (temperature and time). Re was added to the base alloy composition by three methods: Re was substituted for Ni, Al and V, respectively. The Re-added alloys were solution-treated at 1553 K and then aged at lower temperatures of 1123 K-1248 K. Apparent age hardening occurred in the alloy where Re was substituted for Ni while no age hardening was observed in the alloys where Re was substituted for Al or V. In the case of the latter two alloys, the hardness was unchanged or reduced with a progression of aging time. These results were discussed in terms of phase separation and ordering in the channel region, and hardening due to Re-rich phase precipitation.

We report the growth of single crystals by a flux method in ambient pressure and tri-axial orientation under modulated rotation magnetic fields (MRFs) on REBa2Cu4O8 (RE124, RE; rare earth elements) compounds. RE124 crystals were grown for RE = Y, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb through appropriate choice of source compounds. All the obtained RE124 powders were tri-axially aligned in MRF of 10T, whereas magnetization axes depended on the type of RE. Moreover, it was found from the changes in the degrees of c-axis and inplane orientation that tri-axial magnetic anisotropies of RE124 also depended on the type of RE. This indicates that it appropriate choice of RE is important for the fabrication of tri-axial oriented ceramics in lower magnetic field conditions.

The development of a novel multidisciplinary Nanoscience Concentration Certificate Program (NCCP) at University of Texas at Brownsville (UTB) is reported. The NCCP intended to prepare undergraduate students to emerging nanotechnology markets, industry trends, cutting edge research and technology developments. The rationale for the NCCP is to integrate and expand nanotechnology-relevant courses within a comprehensive curriculum. The established certificate program includes the following seven new upper level undergraduate courses: (i) Introduction to Nanoscience, (ii) Engineering of Nanomaterials, (iii) Nanofabrication and Nanoelectronics, (iv) Introduction to Bio-Nanotechnology, (v) Environmental Nanotechnology, (vi) NanoOptics, (vii) Capstone Design. This program is designed to address the needs for a multidisciplinary undergraduate education at the UTB, which extends beyond traditional courses within science and engineering disciplines. The designed courses will expose students to the nanotechnology areas as part of integration of nanoscience in UTB’s undergraduate programs. To complete the NCCP and receive a Certificate in Nanoscience and Nanotechnology, students must complete 12 credit-hours of NCCP courses. Our ultimate goal is to establish and maintain at UTB a practical, modular, scalable, transferrable and implementable educational STEM platform in nano-sciences, engineering and nanotechnology. The goal of this paper is to examine an instructional technique for Introduction to Nanoscience course as an example for promoting student understanding of scientific concepts and explanations by using combines teaching learning activities and research oriented strategies.