Adenilson Jose Chiquito

Resumo A pesquisa em Física da Matéria Condensada, especialmente o estudo de nanoestruturas, tem papel de destaque no avanço científico e tecnológico, envolvendo aplicações de fenômenos fundamentais da física. Apesar da intensa produção científica na área, sua presença nas publicações de Ensino de Física ainda é muito reduzida no Brasil. Assim, com o objetivo de contribuir com a contextualização e significação de conteúdos nas aulas de graduação em Física, o presente artigo aborda conceitual e matematicamente fenômenos quânticos em nanoestruturas. São apresentados e discutidos: a localização de fônons em nanofios de germânio, que ocorre como resultado do princípio de incerteza aplicado ao confinamento de fônons nas reduzidas dimensões da nanoestrutura; a alteração das bandas de energia e do gap de nanopartículas de silício, provocado tanto pelo efeito de superposição de funções de onda eletrônicas quanto por estados de superfície e impactando na fotoluminescência; e o transporte de corrente em dispositivos de nanofios de germânio que, devido à presença de estados localizados de energia, inclui o mecanismo de hopping. A forma de abordagem, com finalidade didática e pedagógica, permite tanto a compreensão dos conceitos envolvidos quanto a aproximação entre o laboratório de pesquisa e a sala de aula.

In this work, we investigated how the electrical resistivity of LaNiO₃ thin films deposited on SrLaAlO₄ (100), LaAlO₃ (100), and MgO (100) single-crystal substrates by the pulsed laser deposition (PLD) technique can be controlled by femtosecond laser irradiation. Thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM-EDS), and temperature-dependent electrical resistivity measurements. The XRD data indicated good crystallinity and preferential crystallographic orientation. The electronic transport parameters of irradiated samples showed a remarkable decrease in the electrical resistivity for all studied films, which ranged from 38% to 52% depending on the temperature region considered and the type of substrate used. The results indicate a new and innovative route to decrease the electrical resistivity values in a precise, controlled, and localized manner, which could not be performed directly by well-known growth processes, allowing for direct application in non-volatile-memory electrodes.

In this work, we report the evaluation of a (CuO/WO₃)-CuWO₄ heterostructured system as a methanol and acetone gas sensor in different configurations, contrasted with the pure oxides CuO and WO₃. The samples were synthesized using a modified precipitation route followed by a single thermal treatment step to induce multiphase simultaneous crystallization. The structural characterization by XRD showed that all the materials presented the formation of monoclinic CuO and WO₃ and triclinic CuWO₄. No additional phases were detected in the samples, and a reduction in the crystallite size of the CuO phase after the crystallization in the heterostructured system was observed. FE-SEM analysis made it possible to directly observe the morphology and the structures of the samples at the nanometer scale, showing a heterogeneous grain formation and supporting the formation of a heterostructure. UV-Vis DRS was used to study the optical properties of the materials, and the presence of two optical band gaps was successfully determined, which provides further evidence of heterostructure formation via this modified synthesis route. The variation in the resistance of the materials was observed in the presence of methanol and acetone vapors, where the heterostructure exhibited a substantial change in performance in the configuration with 40% copper precursor (Cu40:W60), the sample that presented the highest response as a sensor against these VOCs. To our knowledge, this is the first time that this system has been reported as a gas sensor, using the multiple configurations of the (CuO/WO₃)-CuWO₄ heterostructured system.

We present a study of an anomalous electrical behavior observed in SnO2 memristor devices based on nanowire networks previously studied by our group. This behavior shows strongly depend on the surface–environment interaction of the nanowires. To enhance/evidence it, we built a device based on a single microwire with higher interaction to ambient air. This device proved to be a memristor in cyclic voltammetry. Based on the literature and voltammetry data, we propose a model to describe that behavior based on the formation/rupture of surface conductive paths formed by water molecules adsorbed in oxygen vacancies and the changes caused by these dynamics in the device's equivalent circuit. We also enhance the behavior in nanowire networks, producing devices with a higher exposure level of the nanowires to the environment. Additionally, these network devices showed potential for application in resistive memories, with an ON/OFF ratio of 22.2 and retention of 1400 s.

Transparent Conductive Oxides (TCOs) have been widely used as sensors for various hazardous gases. Among the most studied TCOs is SnO₂, due to tin being an abundant material in nature, and therefore being accessible for moldable-like nanobelts. Sensors based on SnO₂ nanobelts are generally quantified according to the interaction of the atmosphere with its surface, changing its conductance. The present study reports on the fabrication of a nanobelt-based SnO₂ gas sensor, in which electrical contacts to nanobelts are self-assembled, and thus the sensors do not need any expensive and complicated fabrication processes. The nanobelts were grown using the vapor–solid–liquid (VLS) growth mechanism with gold as the catalytic site. The electrical contacts were defined using testing probes, thus the device is considered ready after the growth process. The sensorial characteristics of the devices were tested for the detection of CO and CO₂ gases at temperatures from 25 to 75 °C, with and without palladium nanoparticle deposition in a wide concentration range of 40–1360 ppm. The results showed an improvement in the relative response, response time, and recovery, both with increasing temperature and with surface decoration using Pd nanoparticles. These features make this class of sensors important candidates for CO and CO₂ detection for human health.

In this work, carrier transport in a gold-seeded zinc diphosphide nanowire fabricated by vapor–liquid–solid and photolithography techniques is investigated in detail. The presence of zinc vacancies and interstitial phosphorus along the nanostructure resulted in defect levels evidenced by photoluminescence transitions observed in the near-infrared spectral range (800–900 nm). The electronic transport measurements by thermally stimulated current identified an activation energy of 80 meV, as well as a defect state with photoluminescence emission at 1.40 eV. The electronic transport in the transient regime was verified for temperatures below 50 K up to room temperature, and the photocurrent relaxation was described by a phenomenological model. We observed a well defined square-wave photoresponse of hundreds of nanoamperes per second during 532 nm light excitation, justifying the potential use of the device as a light sensor. Also, for the first time, ab initio calculations were performed considering defects of a Zn monovacancy close to an interstitial P atom to describe the luminescence transitions. The systematic use of a hybrid functional for these defects allows us to determine the presence of polarons due to the distortion of atomic bonds. Through the electronic property simulations, we corroborated the nature of p-type transport in zinc diphosphide nanowires.

In this paper, we present the development of a volatile organic compounds (VOC) gas sensor based on graphite on a PCB multiplexed interdigitated electrode (IDE) sensor. We report the effects of graphite as a sensing material deposited by spray method and its interaction response to specific gases. In addition, we demonstrate how we designed and manufactured IDE sensors with an integrated heating circuit and thermistor element, as well as the 55μL microchamber, which contributed to the fast detection of gases. All experiments were performed with four IDE sensors to verify the reproducibility and sensitivity of the proposed methodology. Our results highlight that acetone presented the highest detection sensitivity, with an electric current increase of ±100 μA at a 200ppm cycle with a response of 0.92s and full recovery at 2.62 s. Furthermore, the developed sensors were able to detect and distinguish between acetone, methanol, isopropanol, ethanol, and chloroform gases. The sensors exhibited outstanding stability and repeatability when evaluated after six months. The sensors’ operation at 2 V makes it suitable for low-power devices with a high potential to be applied in future commercial room temperature VOC gas sensor devices.

When present in specific amounts in the air, the colorless, odorless, and tasteless gases monoxide and carbon dioxide may either replace oxygen in red blood cells (CO) or increase the respiratory rate causing cardiac arrhythmias (CO2), leading to death. Commercial sensors take around 8 h to detect levels of CO (50 PPM), causing moderate poisoning. SnO2 presents controlled interactions with the atmosphere using conductance and vacancy adjustments to capture electrical properties. However, the selectivity of gas detection by SnO2 can still be improved, thus also increasing the application possibilities. The present study aimed to optimize the sensing of CO and CO2 in SnO2 using palladium functionalization. The vapor-liquid-solid method synthesized a network of SnO2 nanobelts decorated with palladium nanoparticles. The sensitivity of the sensors for CO and CO2 were evaluated, characterizing parameters such as response time, a wide range of CO and CO2 concentrations, and temperature. In the seventh measurement cycle, the sensor response for different concentrations of gases in consecutive cycles showed a sensitivity of up to 125% for CO in 60 s. Furthermore, we observed increased sensor sensitivity with material doping with nanoparticles from 130 ppm to 1360 ppm in 30 seconds to CO. Conclusion: The results provide a better understanding of the sensitivity of SnO2 in palladium-decorated nanoparticles, offering insights for detecting low CO concentrations quickly. The behavior of these doped nanosensors showed us the importance of considering them as a practical possibility for detecting these gases of importance to human health.

Summary: We developed an SnO₂ nanowire network visible-blind ultraviolet (UV) photodetector for applications in fields such as safety systems, exposure control, and decontamination processes, among others