Graphene specimens produced by chemical vapor deposition usually show p-type characteristics and significant hysteresis in ambient conditions. Among many methods, current annealing appears to be a better way of cleaning the sample due to the possibility of in-situ annealing in the measurement setup. However, long-time current annealing could increase defects in the underlying substrate. Studying the hysteresis with different anneal currents in a graphene device is, therefore, a topic of interest. In this experimental work, we investigate electron/hole transport in a graphene sample in the form of a Hall bar device with a back gate, where the graphene was prepared using chemical vapor deposition on copper foils. We study the hysteresis before and after current annealing the sample by cooling down to a temperature of 35 Kfrom room temperature with a back-gate bias in a closed cycle refrigerator.

We detail a method to produce graphite materials with a three-dimensional, flexible and porous structure obtained from the exposure to CO2 laser radiation. One of them is Laser Induced Graphene (LIG) grown from an insulating polyimide as raw material, and the other is laser reduced graphene oxide (lrGO), obtained from a graphene oxide (GO) thin film. For both materials, we describe their morphology, crystalline structure and electrical characterizations. These materials have important applications in organic electronics technology.

CVD graphene growth typically uses commercially available cold-rolled copper foils, which includes a rich topography with scratches, dents, pits, and peaks. The graphene grown on this topography, even after annealing the foil, tends to include and reflect these topographic features. Further, the transfer of such CVD graphene to a flat substrate using a polymer transfer method also introduces wrinkles. Here, we examine an electropolishing technique for reducing native foil defects, characterize the resulting foil surface, grow single-crystal graphene on the polished foil, and examine the quality of the graphene for such defects.

We examined the influence of the microwave power on the diagonal resistance in the GaAs/AlGaAs two dimensional electron system (2DES), in order to extract the electron temperature and determine microwave induced heating as a function of the microwave power. The study shows that microwaves produce a small discernable increase in the electron temperature both at null magnetic field and at finite magnetic fields in the GaAs/AlGaAs 2DES. The heating effect at null field appears greater in comparison to the examined finite field interval, although the increase in the electron temperature in the zero-field limit appears smaller than theoretical predictions.

Organic-inorganic hybrid materials have shown a remarkable and rapid development during the past decade because they can be tailored to obtain new device concepts with controlled physical properties. Here, we report on the electronic and magnetic properties of multilayer organic-inorganic hybrid films. Electrical transport properties arising from the π electrons in the organic layer are characteristic of a metallic state at high temperature and evolve into a state described by two-dimensional variable range hopping when temperature decreases below 150 K. The intrinsic electronic behavior of the hybrid films was further studied via the optical properties in the IR range. The optical response confirms the metallic character of the hybrid films. In the second part, the magnetic properties are discussed. A long-range ferromagnetic order with an ordering temperature of ∼ 1 K is revealed in the Gd-based hybrid film. The Cu-based hybrid film, however, shows more extended ferromagnetic exchange interactions than the Gd-based hybrid LB film.

The superconductivity has a long history. One of the most recent discoveries is the superconductivity in the Fe- based family with anti- ferromagnetic state at ambient temperature. In this type of material, the transition to the superconductivity state was found in presence of different dopants. In this report we present the results of calculations of the cluster representing Ba4Fe5As8 in presence of Rh and Pd as dopants. The methodology of Embedded Cluster Method at the MP2 electron correlation level was employed. The population analysis showed two main features: the independence of charge density transfer from the spin density transfer and, the presence of orbitals with electron density but without spin density. The observed properties correspond to the RVB mechanism for the superconductivity transition proposed by Anderson for cuprates. This confirms our conclusions obtained in the same material doped by Co and Ni.

The hot rolling process reduces a slab passing through a series of work-rolls to obtain a strip of target thickness. Developing robust, efficient, and accurate simulation methods improve the process. This research aims to minimize the hot rolling time, bending of work rolls, thermal crown, and wear of work rolls, subject to some process constraints. The problem solution is by using a multi-objective genetic algorithm with four function objectives. The second generation of the Non-dominated Sorting Genetic Algorithm was chosen to solve the problem of this research. A probed constitutive model has been incorporated into the algorithm to compute the flow stress as a function of the chemical composition of steels. The algorithm implemented to minimize the four objectives proposed obtained the optimal schedule and associated makespan.

Atomic scale defects critically limit performance of semiconductor materials. To improve materials, defect effects and defect formation mechanisms must be understood. In this paper, we demonstrate multiple examples where molecular dynamics simulations have effectively addressed these issues that were not well addressed in prior experiments. In the first case, we report our recent progress on modelling graphene growth, where we found that defects in graphene are created around periphery of islands throughout graphene growth, not just in regions where graphene islands impinge as believed previously. In the second case, we report our recent progress on modelling TlBr, where we discovered that under an electric field, edge dislocations in TlBr migrate in both slip and climb directions. The climb motion ejects extensive vacancies that can cause the rapid aging of the material seen in experiments. In the third case, we discovered that the growth of InGaN films on (0001) surfaces suffers from a serious polymorphism problem that creates enormous amounts of defects. Growth on ($11\bar{2}0$) surfaces, on the other hand, results in single crystalline wurtzite films without any of these defects. In the fourth case, we first used simulations to derive dislocation energies that do not possess any noticeable statistical errors, and then used these error-free methods to discover possible misuse of misfit dislocation theory in past thin film studies. Finally, we highlight the significance of molecular dynamics simulations in reducing defects in the design space of nanostructures.

The degradation of organic molecules in an aqueous medium using heterogeneous photocatalysis depends on the chemical composition and concentration of the organic compound, the crystalline and morphological nature of the photocatalyst, the pH of the dye dilution, and the reaction temperature. Since photocatalytic degradation is a process that occurs on the surface of the catalytic material, it is desirable to induce maximum adsorption of the organic compound. One strategy to achieve this is to functionalize the surface of the catalyst to retain the molecule of interest. In this work, we studied the interaction of acid orange 7 (AO7) with commercial TiO2-anatase powder catalyst, and with a catalyst synthesized in house using titanium tetrachloride and ethanolamine (TiO2-et). Our results indicate that there is no adsorption of the AO7 dye on the TiO2-et particles. The infrared spectrum of the TiO2-et particles is presented.

The present work describes a simple method to produce zinc oxide nanoparticles supported in nitrogen-doped reduced graphene oxide, ZnO/N-rGO. The rGO structures were nitrogen-doped using hydrazine as nitrogen source (N-rGO) with the purpose of enhancing the rGO capability to promote the electrons transport along their surface. Thus, ZnO/N-rGO catalytic systems were tested as photocatalyst to degrade methylene blue and lignin molecules under ultraviolet (UV) and visible (Vis) light irradiation. N-doping of rGO was confirmed by X-ray photoelectron spectroscopy (XPS). Photocatalytic degradation studies confirm better performance of the ZnO/N-rGO in comparison to ZnO. The percentage of lignin degradation for the ZnO/N-rGO compound under UV was 59%, while using visible energy it was achieved 46%, in a time of 70 min.

In the present investigation, biocomposites were synthesized from a polymeric alginate matrix in which the carrot residue and a natural bentonite (ANat / Bio) or an iron-modified clinoptilolite-type zeolite (ZFe / Bio) were supported. Their properties were evaluated adsorbents in contact with aqueous solutions of methylene blue (MB). In the first hour of contact, 46% removal was obtained for the ZFe / Bio biocomposite and 60% for the ANat / Bio biocomposite; reaching 100% removal for the ZFe / Bio biocomposite and 98% for the ANat / Bio biocomposite after 24 hours. The biocomposites were characterized by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR).

Nanoparticles of titanium dioxide (TiO2), synthesized by the sonochemical technique, were mixed with different amounts of graphene oxide (GO), obtained by the improved method of Hummer, in order to modify their bandwidth. The TiO2/OG compounds were characterized using different techniques: X-ray Diffraction (XRD), transmission electron microscopy (TEM), Raman and UV-Vis-NIR spectroscopy. TiO2 bandgap decreased, with GO incorporation, from 3.2 to 2.72 eV when GO was present at 20 weigh percentage (TiO2/GO-20%). Photodegradation experiments of methylene blue (MB) were performed with the materials to verify their photocatalytic activity. At 40 minutes, the pure TiO2 degraded 48% of MB, whereas the compound TiO2/GO-20% degraded 88%, showing a good incorporation of both compounds and the improvement of TiO2 photocatalitic properties.

Pt/Ce1-xRuxO2 and Ir/Ce1-xRuxO2 catalysts were prepared through the sol-gel technique, under microwave heating. In a first step, the Ce1-xRuxO2 solid solutions were prepared. Subsequently, an incipient wet impregnation process was carried out to homogeneously achieve the dispersion, either of platinum or iridium nanoparticles. The Pt/Ce1-xRuxO2 and Ir/Ce1-xRuxO2 catalysts were characterized by means of SEM, XRD, XPS, TEM, and specific surface area measurements. Crystal size and shifting into the CeO2 structure were detected after ruthenium doping producing the Ce1-xRuxO2 solid-solutions. Trough XPS technique Pt and Ir nanoparticles were found evenly dispersed in a metallic state. Those features allow us to foresee that, in the near future, these materials could be used efficiently as catalysts for oxidation process.