NanoSensing
Nanocomposite semiconductor thin films composed of noble metal nanoparticles dispersed in reactive oxide-metal matrices for applications in gas detectors based on surface plasmon resonance

Challenge

The NanoSensing project aims to develop low-cost gas sensors, based on metal-oxide semiconductor (MOS) structures, containing several types of noble metal (NM) nanoparticles (NPs), with near-single molecule sensitivity with large relevance for several industrial sectors.

Solution

The main objective of NanoSensing was to strengthen research, technological development and innovation.
The research will be focused on noble metal (NM) nanoparticles (NPs) such as Au and Ag, which are oxidation resistant and exhibit uniquely intense LSPR absorption peaks in the visible spectrum. The MOS structures will include oxides such as WO3 Ta2O5, ZnO or SnO2, that show high sensitivity to the upper mentioned gases, which are central concerns not only in automotive industry, but also in several areas of industry and consumer products and health care.

Two complementary methods were tested to produce the nanostructured films:
i) the Co-deposition using a cluster source, for Au or Ag, and reactive sputtering of metal targets in O2 atmosphere, for the matrix;

ii) Co-sputtering using a high-power impulse magnetron sputtering (HIPIMS) source, for the noble metal target, and a conventional/HIPIMS source, for the dielectric matrix (in O2 atmosphere). Fundamental understanding of the LSPR effect and systematization of the consequent sensing ability will be carried out through atomistic calculations, while advanced spectroscopy and microscopy will be used to characterize and materials and their performance so that optimized systems/configurations can be designed and subsequently tested. A proof-of-concept will be implemented and the potential for practical application will be assessed through LSPR sensor prototypes, in particular, for automotive related ones.

Objectives, Activities and Results expected / achieved

Goals Achieved:
This project allowed to produce nanocomposite thin films using different combinations of noble metal nanoparticles (Au, Ag and Au-Ag) and dielectric matrices (TiO2, CuO, Al2O3, AlN and ZnO). The films were prepared by reactive magnetron DC sputtering and post-deposition annealing heat treatment. The films were optimized using different deposition conditions to obtain well-defined LSPR bands in the transmittance spectra. Gold clusters were produced by plasma gas condensation method and studied in detail.

The main results of this project allowed the conclusion that LSPR-based sensor prototypes manifest sensitivity to changes in the refractive index of the environment (inert gases such as He, Ar and N2) and to adsorbed gas molecules (oxidizing, reducing and reactive gases such as O2, H2 and CO, respectively). Therefore, the goal of demonstrating the ability of LSPR thin films to be used in a new generation of optical sensors was achieved. It also resulted in 25 publications in international journals, 31 papers in scientific meetings, of which 23 international and 8 national, 4 PhD and 5 MSc theses.