Carla Patrícia Lacerda Rubinger’s research while affiliated with Federal University of Minas Gerais and other places

O primeiro material bidimensional descoberto foi o grafeno em 2004. A partir de então, estudos foram desenvolvidos com outros materiais e, um dos primeiros semicondutores a ser isolado foi o dissulfeto de molibdênio, o MoS2. Ao contrário do grafeno, o MoS2 tem gap de energia, e na forma de monocamada o gap passa de indireto para direto. Essa mudança resulta em uma fotoluminescência de alto brilho. Devido ao alto desempenho elétrico e óptico, o MoS2 (2D) tem grande potencial de aplicação nos dispositivos eletrônicos e campos fotoeletrônicos. Existem diversas técnicas para produzir este material, e uma delas é através do método de Deposição Química de Vapor (CVD) que consiste na formação de cristais no substrato, pela deposição atômica ou molecular, sendo o sólido oriundo de uma reação química onde os precursores estão na fase de vapor. O objetivo deste trabalho será sintetizar e caracterizar o MoS2 pelo método de CVD, a partir de um sistema de equipamento robusto construídos no laboratório. Para preparar os substratos foram submetidos a um tratamento de ultravioleta para permitir que os materiais depositados resistam ao desgaste por contato. Então construiu-se uma câmara para tratamento por radiação UV/ozônio, e, após a preparação, os substratos foram colocados em um forno com temperatura controlada e com atmosfera inerte. Este forno tubular também foi construído com o intuito da produção do MoS2. Após os ensaios foi possível obter a formação de MoS2 com a caracterização pelo MEV, EDS e DRX para análise e identificação dos materiais formados no substrato.

The syntheses of TiO2 and Pd/TiO2 nanoparticles were carried by hydrolysis of alkoxide precursors using the reverse micelles method using titanium tetrabutoxide and palladium acetylacetonate as precursor metals. The method was modified by precipitation with the addition of n-butanol and then washed with an ethanol/water solution at a ratio of 1:1. Morphological characterization was performed by scanning electron microscopy and structural by X-ray diffraction and spectroscopy of Raman scattering. Electrical characterization was performed by impedance spectroscopy and the optical energy gap was determined from transmittance measurements Tauc plot fittings. The material was characterized by a suspension of spherical nanoparticles on the order of 100 nm confirmed by Scanning electron microscopy analysis. They also presented good ionic conductivity as indicated by impedance spectroscopy. Raman spectroscopy showed a systematic frequency shift to the left together with peak broadening as the amount of palladium incorporated onto TiO2 increases, which is characteristic of mesoscopic grains. X-ray diffractograms were carried with washed and dried powder samples and showed a mixture of anatase and brookite phases, with anatase as the predominant one.

This manuscript presents the study of electronic transport on a set of five multilayer molecular beam epitaxy-grown InAs/GaAs semiconductor samples. We developed an automated switch system to carry out electronic transport measurements of mobility and carrier concentration using the van der Pauw technique. Measurements were carried out as a function of temperature within the range of 260 K to 310 K. To identify which scattering mechanisms most contributed to mobility limitation, It was necessary to use the Self-adaptive Differential Evolution meta-heuristic method. This method allowed the determination of the main scattering mechanisms limiting the electronic mobility and identified as scattering by dislocations and phonons. Dislocations consist of the dominant defects in this lattice mismatch structure. Therefore, to increase carrier mobility, we propose some strategies: a change in the sample growth parameters such as substrate temperature and InAs/GaAs layer thickness. Alternatively, annealing of the samples could also be considered to improve sample mobility.

Herein, we describe the design and synthesis of a suite of molecules based on a benzodithiophene “universal crystal engineering core”. After computationally screening derivatives, a trialkylsilylethyne-based crystal engineering strategy was employed to tailor the crystal packing for use as the active material in an organic field-effect transistor. Electronic structure calculations were undertaken to reveal derivatives that exhibit exceptional potential for high-efficiency hole transport. The promising theoretical properties are reflected in the preliminary device results, with the computationally optimized material showing simple solution processing, enhanced stability, and a maximum hole mobility of 1.6 cm² V⁻¹ s⁻¹.

Solution processing of organic semiconductors offers key advantages, including low-cost and compatibility with large-area flexible substrates. Controlling film crystallization from solution, however, is not trivial. This is particularly important since the device properties are highly dependent on the film microstructure, which, in turn, can vary significantly with processing. In this work, we tuned the small molecule organic semiconductor film microstructure by using a binary solvent consisting of a host solvent and a high-boiling point solvent additive and studied the effect of additive content on charge transport. Spin coated 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene films processed from a mixture of chlorobenzene and dichlorobenzene, in various ratios, were investigated by using Polarized Optical Microscopy, Scanning Electron Microscopy and Atomic Force Microscopy analysis and their electrical properties were evaluated from bottom-contact bottom-gate organic field-effect transistors. We found that the mobility increased by three times for a 8% dichlorobenzene content as a result of reducing the density of the grain boundaries within the device channel.

Composites of polyaniline (PANI) with MCM-41 and SBA-15 ordered mesoporous silicas were prepared by liquid and vapor monomer adsorption methods. Both methods resulted in polymer encapsulation inside the mesopores, but a higher amount was obtained using the vapor adsorption method. Composites presented a semiconductor behavior and the charge transport mechanism was consistent with a hopping process between localized states. Based on the results of one-dimensional variable range hopping (1D-VRH) conduction parameters, the SBA-15 with polyaniline incorporated by vapor adsorption was the more conductive and ordered material.

This work focuses on the synthesis of binary composites of polypyrrole and silver and of ternary composites of polypyrrole, silver and organomontmorillonite performed in the presence of mixtures of two surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), in aqueous media. Polypyrrole-silver composites were obtained easily by the direct oxidation of pyrrole by silver nitrate using surfactant mixture. These samples exhibited polypyrrole doped with dodecylsulfate and nitrate and silver contents varied between 60 and 90 wt.%. The electrical conductivity is highly dependent on SDS/CTAB presence and proportions. NO3⁻ acts as the main dopant in the absence of surfactants and the resistivity reaches the highest for PPy-OMt composites compared to silver-content ones. Besides the dopant effect, the surfactants mixtures have noticeable influence on silver particle size and morphology. In ternary composites the silver nanoparticles were spherically (around 100–200 nm) and well dispersed in the polymeric matrix. Activation energy, density of states and hopping characteristic length were calculated and it was found to be influenced by intercalating doped polypyrrole into the layers of montmorillonite in the presence of the Ag and surfactant. One-dimensional Mott’s variable range hopping process was observed and interpreted in terms of straightening and linearization of the polymer chains.

Comparative and quantitative analysis of white light-emitting diodes and other lamps used for home illumination Abstract. We compared the photometric and radiometric quantities in the visible, ultraviolet, and infrared spectra of white light-emitting diodes (LEDs), incandescent light bulbs and a compact fluorescent lamp used for home illumination. The color-rendering index and efficiency-related quantities were also used as auxiliary tools in this comparison. LEDs have a better performance in all aspects except for the color-rendering index, which is better with an incandescent light bulb. Compact fluorescent lamps presented results that, to our knowledge, do not justify their substitution for the incandescent light bulb. The main contribution of this work is an approach based on fundamental quantities to evaluate LEDs and other light sources. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) [

a b s t r a c t In this work, we have shown the preparation of polyaniline (PANI) and mesoporous ordered silica (SBA-15) composites. PANI/SBA-15 composites with different weight ratios were prepared in order to evaluate the electrical conduction mechanism. The analysis of the differential activation energy was carried out for composites, allowing the classification of the variable range hopping as one dimensional for the composites. The hopping parameter as a function of the sample mass ratio indicates that the insertion of aniline into the mesopores improves its intrinsic conductivity. A fibrilar morphology of the conducting PANI is formed by a controlled amount of the added polymer into SBA-15. It was confirmed by SEM and TEM analysis that the composites prepared with different PANI contents have different morphologies, indicating that the amount of polyaniline is crucial to obtain distinct morphologies. SAXS, NAI, TEM and SEM show that SBA-15 maintains its structure even after the polymerization process and the polymer is dispersed on the inorganic matrix. The parameters determined by the investigation of variable range hopping conduction by the differential activation energy method show that the PANI produced in these composites have higher electrical conductivity than pure PANI, possibly due to the improvement of the interparticle, interchain and intrachain processes for the charge transport, which are intimately related to the polymer morphology, fact coherent with SEM and TEM data.