Enrico Della Gaspera

Electronic Tuning of 2D MoS2 through Surface Functionalization

The electronic properties of thiol-functionalized 2D MoS2 nanosheets are investigated. Shifts in the valence and conduction bands and Fermi levels are observed while bandgaps remain unaffected. These findings allow the tuning of energy barriers between 2D MoS2 and other materials, which can lead to improved control over 2D MoS2 -based electronic and optical devices and catalysts.

Colloidal approach to Au-loaded TiO2 thin films with optimized optical sensing properties

TiO2 and Au nanoparticles are synthesized by the colloidal technique and used for nanocomposite thin film preparation. The effect of thermal treatment and organic template presence is analyzed in order to tailor film microstructure. The Au-TiO2 interfaces as well as the overall porosity of the films are analyzed combining structural and morphological characterization along with spectroscopic ellipsometry and surface plasmon spectroscopy analyses. An efficient surrounding of TiO2 nanoparticles around Au colloids is obtained, leading to an extensive noble metal–metal oxide interface, improving functional properties of the films, while keeping a porous structure. Gas sensing tests are performed on these nanocomposites films: reversible sensing dynamics for CO detection are observed with high sensitivity and a correlation between response and recovery times and microstructure is reported.

Low temperature near infrared plasmonic gas sensing of gallium and aluminum doped zinc oxide thin films from colloidal inks (Presentation Recording)

We obtained Gallium-doped and Aluminum-doped Zinc Oxide nanocrystals by non aqueous colloidal heat-up synthesis. These nanocrystals are transparent in the visible range but exhibit localized surface plasmon resonances (LSPRs) in the near IR range, tunable and shiftable with dopant concentration (up to 20% mol nominal). GZO and AZO inks can be deposited by spin coating, dip coating or spray coating on glass or silicon, leading to uniform and high optical quality thin films. To enhance absorbtion in the infrared region, samples can be annealed in inert or reductant atmosphere (N2/Argon or H2 in Argon) resulting in plasmon intensity enhancement due to oxygen vacancies and conduction band electrons density increment. Then IR plasmon has been exploited for gas sensing application, according to the plasmon shifting for carrier density variations, due to electrons injection or removal by the target gas/sample chemical interactions. To obtain a functional sensor at low temperature, another treatment was investigated, involving surfanctant removal by dipping deposited films in a solution of organic acid, tipically oxalic acid in acetonitrile; such process could pave the way to obtain similar sensors deposited on plastics. Finally, GZO and AZO thin films proved sensibility to H2 and NOx, and in particular circumstances also to CO, from room temperature to 200°C. Sensibility behavior for different dopant concentration and temperture was investigated both in IR plasmon wavelengths (~2400 nm) and zinc oxide band gap (~370 nm). An enhancement in sensitivity to H2 is obtained by adding Pt nanoparticles, exploiting catalytic properties of Platinum for hydrogen splitting.

8.5.5 Au Nanoparticles Dispersed Inside Porous TiO2 Thin Films: High Performance Optical Gas Sensors Through Localized Surface Plasmon Resonance Monitoring

Colloidal solutions of Au and TiO2 nanoparticles are prepared and used as nanocrystal inks for the fabrication of porous thin films to be used as optical gas sensor. The introduction of Au nanoparticles in the TiO2 matrix affects the reactions mechanism improving the sensing process, moreover the Au Surface Plasmon Resonance peak can be used for the realization of a gas sensor with tunable sensitivity. The effect of thermal treatment, Au dimension and concentration is analyzed in order to tailor films microstructure and their sensing properties. The nanocomposites showed reversible change in optical absorption/reflection when exposed to reducing gasses (H2, CO) at 300 °C operative temperature or when exposed to volatile organic compounds (alcohols) at room temperature.