Nanocrystalline graphite-based sensors for environmental gas monitoring NCG-SENSOGAS |
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Project title: Nanocrystalline graphite-based sensors for environmental gas monitoring
Acronim: NCG-SENSOGAS
Programme/ Project type: PNCDI IV - Program 5.2. Human Resources, Subprogram 5.2.1.Start in Research Research projects to stimulate young independent teams (TE 2023)
Contract no. 26TE⁄ 2025 (PN-IV-P2-2.1-TE-2023-1419)
Project Duration: 08/01/2025 - 31/12/2026
Project Budget: 499.980,00 lei
Contractor: National Institute of Research and Development in Microtechnologies – IMT Bucharest (www.imt.ro)
Contracting Authority: Executive Agency for Higher Education, Research, Development and Innovation Funding – UEFISCDI (www.uefiscdi.gov.ro)
Project manager: Dr. Angela BARACU (angela.baracu@imt.ro)
Air pollution has been identified as one of the major environmental issues, with a significant impact on human health. Rapid industrial development and the emission of various harmful gases from vehicles have led to the emergence of various diseases. Nitrogen dioxide NO2 is one of the most dangerous air pollutants, released by combustion processes, which causes severe respiratory diseases and contributes to acid rains and ozone formation, increasing smog levels (a global issue, especially in China). An innovative gas sensor based on the integration of nanocrystalline graphite (NCG) with Surface Acoustic Wave (SAW) devices is proposed for the sensitive and selective detection of NO2. The high sensitivity of the sensor will be provided both by using SAW devices, which confine the acoustic energy to the sensing surface, resulting an increased sensitivity to surface perturbation, and by the deposition of NCG sensing films, with vertically arranged walls, which enhance specific surface area, improving the sensor's sensitivity. The sensors' selectivity will be conferred by the graphite nanowalls containing graphitic units with increased surface electron density, which interact with NO2 molecules presenting electron withdrawing effects, for an efficient adsorption on the surface's sensor. The scientific challenges include sensing NCG synthesis, with tailored properties, NCG-SAW sensors development, using a novel approach, and the device's sensing performances evaluation.
The main scope of the project is to develop and validate a sensitive and selective sensor based on SAW devices for the NO2 detection, a harmful air pollutant released by combustion processes. The high sensitivity of the sensor will be provided both from using SAW devices, which have the advantage of acoustic energy confined to the sensing surface, resulting in higher sensitivity to surface perturbation, and by the deposition of nanocrystalline graphite sensing films, with vertically arranged walls, which enhance specific surface area and contribute to an increase in the sensor's sensitivity. The selectivity of the developed sensors will be conferred by the GNW, comprised of graphitic units with increased electron density at the surface level, which can favorably interact with NO2 molecules endowed with electron-withdrawing effects, enabling an efficient adsorption process on the sensor surface.
Stage 1/2025
In this stage, the design of the photolithographic masks and the fabrication of the SAW devices on a quartz substrate were carried out using photolithographic techniques. SAW structures with interdigitated Au transducers having element dimensions of10 µm were obtained, arranged in a delay line configuration, with an operating frequency of approximately 79 MHz.
The NO2 sensitive layers based on nanocrystalline graphite NCG were deposited onto the sensing area of the SAW devices using the PECVD technique. Several recipes were tested, and finally, the resulting films were deposited using the optimized recipe. Three films with different morphologies were chosen for testing, the difference between them consisting in the varying deposition temperature (650°C, 700°C și 750°C). After the deposition of the GNW (Graphite Nanowalls) films, they were configured using mask number 2. The selective etching of the NO2 -sensitive films was performed in an O2 plasma, using a physical mask.
The GNW films were characterized morpho-structurally using the following techniques: SEM, AFM, Raman, and XRD. SEM investigations revealed vertically aligned graphite structures, forming a self-supported network, consisting of graphitic walls with nanometer-scale thicknesses. The thicknesses of the GNW films, deposited at different temperatures, varied in the range of 700-970 nm. AFM characterizations confirmed their unique morphology, characterized by graphene planes oriented perpendicular to the substrate and revealed roughnesses between 76.6-82.3 nm. The largest active area was obtained for the GNW film deposited at a temperature of 650°C. XRD analysis confirmed a similar crystalline structure of graphite for all GNW films, with an average crystallite size of approx. 2.3 nm. The Raman spectra of the carbon films showed signals specific to a graphitic structure, along with bands associated with defects arising in the structure during the deposition process.
The devices were subsequently assembled onto a printed circuit board PCB support (package), made of FR-4 material equipped with two thin metallic layers Cu for establishing the electrical connections between (i) the four terminals (two for each signal port) and (ii) the corresponding pads of the actual SAW sensor structures. Their electrical evaluation was then carried out, considering only the analysis of the scattering parameters S measured with the vector network analyzer (LibreVNA 100kHz - 6GHz USB based full 2-port vector network analyzer)."
Conference