Polypyrrole-Tungsten Oxide Nanocomposite Fabrication through Laser-Based Techniques for an Ammonia Sensor: Achieving Room Temperature Operation.

A highly sensitive ammonia-gas sensor based on a tungsten trioxide and polypyrrole (WO3/PPy) nanocomposite synthesized using pulsed-laser deposition (PLD) and matrix-assisted pulsed-laser evaporation (MAPLE) is presented in this study. The WO3/PPy nanocomposite is prepared through a layer-by-layer alternate deposition of the PPy thin layer on the WO3 mesoporous layer. Extensive characterization using X-ray diffraction, FTIR and Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle are carried out on the as-prepared layers. The gas-sensing properties of the WO3/PPy nanocomposite layers are systematically investigated upon exposure to ammonia gas. The results demonstrate that the WO3/PPy nanocomposite sensor exhibits a lower detection limit, higher response, faster response/recovery time, and exceptional repeatability compared to the pure PPy and WO3 counterparts. The significant improvement in gas-sensing properties observed in the WO3/PPy nanocomposite layer can be attributed to the distinctive interactions occurring at the p-n heterojunction established between the n-type WO3 and p-type PPy. Additionally, the enhanced surface area of the WO3/PPy nanocomposite, achieved through the PLD and MAPLE synthesis techniques, contributes to its exceptional gas-sensing performance.

Nanostructured PbS-Doped Inorganic Film Synthesized by Sol-Gel Route.

IV-VI semiconductor quantum dots embedded into an inorganic matrix represent nanostructured composite materials with potential application in temperature sensor systems. This study explores the optical, structural, and morphological properties of a novel PbS quantum dots (QDs)-doped inorganic thin film belonging to the Al2O3-SiO2-P2O5 system. The film was synthesized by the sol-gel method, spin coating technique, starting from a precursor solution deposited on a glass substrate in a multilayer process, followed by drying of each deposited layer. Crystalline PbS QDs embedded in the inorganic vitreous host matrix formed a nanocomposite material. Specific investigations such as X-ray diffraction (XRD), optical absorbance in the ultraviolet (UV)-visible (Vis)-near infrared (NIR) domain, NIR luminescence, Raman spectroscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX), and atomic force microscopy (AFM) were used to obtain a comprehensive characterization of the deposited film. The dimensions of the PbS nanocrystallite phase were corroborated by XRD, SEM-EDX, and AFM results. The luminescence band from 1400 nm follows the luminescence peak of the precursor solution and that of the dopant solution. The emission of the PbS-doped film in the NIR domain is a premise for potential application in temperature sensing systems.

High-Sensitivity Ammonia Sensors with Carbon Nanowall Active Material via Laser-Induced Transfer.

Ammonia sensors with high sensitivity, reproducible response, and low cost are of paramount importance for medicine, i.e., being a biomarker to diagnose lung and renal conditions, and agriculture, given that fertilizer application and livestock manure account for more than 80% of NH3 emissions. Thus, in this work, we report the fabrication of ultra-sensitive ammonia sensors by a rapid, efficient, and solvent-free laser-based procedure, i.e., laser-induced forward transfer (LIFT). LIFT has been used to transfer carbon nanowalls (CNWs) onto flexible polyimide substrates pre-patterned with metallic electrodes. The feasibility of LIFT is validated by the excellent performance of the laser-printed CNW-based sensors in detecting different concentrations of NH3 in the air, at room temperature. The sensors prepared by LIFT show reversible responses to ammonia when exposed to 20 ppm, whilst at higher NH3 concentrations, the responses are quasi-dosimetric. Furthermore, the laser-printed CNW-based sensors have a detection limit as low as 89 ppb and a response time below 10 min for a 20 ppm exposure. In addition, the laser-printed CNW-based sensors are very robust and can withstand more than 200 bending cycles without loss of performance. This work paves the way for the application and integration of laser-based techniques in device fabrication, overcoming the challenges associated with solvent-assisted chemical functionalization.

Nitrites Detection with Sensors Processed via Matrix-Assisted Pulsed Laser Evaporation.

This work is focused on the application of a laser-based technique, i.e., matrix-assisted pulsed laser evaporation (MAPLE) for the development of electrochemical sensors aimed at the detection of nitrites in water. Commercial carbon-based screen-printed electrodes were modified by MAPLE via the application of a newly developed composite coating with different concentrations of carbon nanotubes (CNTs), chitosan, and iron (II) phthalocyanine (C32H16FeN8). The performance of the newly fabricated composite coatings was evaluated both by investigating the morphology and surface chemistry of the coating, and by determining the electro-catalytic oxidation properties of nitrite with bare and modified commercial carbon-based screen-printed electrode. It was found that the combined effect of CNTs with chitosan and C32H16FeN8 significantly improves the electrochemical response towards the oxidation of nitrite. In addition, the MAPLE modified screen-printed electrodes have a limit of detection of 0.12 µM, which make them extremely useful for the detection of nitrite traces.

Facile Modification of Flexible Electrodes via Laser Transfer.

In this work, we report the modification of commercially available electrochemical electrodes with tin oxide (SnO2) and Pd doped SnO2 (Pd-SnO2) via pulsed laser-induced forward transfer (LIFT). The pulsed light irradiation working as in situ pulsed photo-thermal treatment allows for the transfer of SnO2 and Pd-SnO2 from UV absorbing metal complex precursors onto flexible, commercially available screen-printed electrodes. The laser transfer conditions are optimized and the material transferred under different conditions is evaluated morphologically and chemically, and its functionality is tested against the detection of copper ions. For example, by applying laser fluences in the range 100-250 mJ/cm2, the shape and the size of the transferred features ranges from nano-polyhedrons to near corner-grown cubic Pd-SnO2 or near cubic Pd-SnO2. In addition, the EDX analysis is consistent with the XPS findings, i.e., following laser transfer, Pd amounts lower than 0.5% are present in the Pd-SnO2 pixels. First sensing tests were carried out and the transferred Pd-SnO2 proved to enhance the cathodic peak when exposed to Cu(II) ions. This photo-initiated fabrication technology opens a promising way for the low-cost and high-throughput manufacturing of metal oxides as well as for electrodes for heavy metal ion detection.

Facile Fabrication of Hybrid Carbon Nanotube Sensors by Laser Direct Transfer.

Ammonia is one of the most frequently produced chemicals in the world, and thus, reliable measurements of different NH3 concentrations are critical for a variety of industries, among which are the agricultural and healthcare sectors. The currently available technologies for the detection of NH3 provide accurate identification; however, they are limited by size, portability, and fabrication cost. Therefore, in this work, we report the laser-induced forward transfer (LIFT) of single-walled carbon nanotubes (SWCNTs) decorated with tin oxide nanoparticles (SnO2 NPs), which act as sensitive materials in chemiresistive NH3 sensors. We demonstrate that the LIFT-fabricated sensors can detect NH3 at room temperature and have a response time of 13 s (for 25 ppm NH3). In addition, the laser-fabricated sensors are fully reversible when exposed to multiple cycles of NH3 and have an excellent theoretical limit of detection of 24 ppt.

Laser parallel nanofabrication by single femtosecond pulse near-field ablation using photoresist masks.

A new near-field processing method by femtosecond laser ablation using photoresist enhancing masks is numerically and experimentally investigated. Periodical structures with 2 µm pitch, 1 µm width and 300 nm height, created in polymethyl methacrylate photoresist by e-beam lithography, were used to intensify the incident laser radiation. The near-field distribution and the intensification factor of the optical radiation were computed using the Finite-Difference-Time-Domain numerical simulations. The pattern of the photoresist mask was imprinted on the surface of a silicon wafer. Using a single infrared femtosecond laser pulse, uniform and continuum grooves with the width in the range of 250 nm were obtained on large silicon surface.