No abstract

carrier generation. [1,2] This has led to sig nificant interest in plasmonic nanostruc tures for photocatalysis, either through local heat generation or as a photo sensitizer. [3,4] Materials in the family of plasmonic transition metal nitrides (e.g., TiN, HfN, NbN, WN) feature high ther momechanical robustness and recently have been proposed for applications requiring extreme operating conditions, such as photothermal catalysis or solar thermophoto voltaics. [5] These materials have high melting points and demonstrate high temperature durability, chemical sta bility, and corrosion resistance, while pre senting an optical response similar to Au or Ag plasmonic nanostructures. [5,6] With a strong response in the visible range, high mechanical hardness, low material cost, [6][7][8][9] and outstanding performance in electro chemical reactions, [10][11][12] the photophysics of these materials requires further research. In the following, we will briefly review the current level of understanding of the photophysics of noble metal plasmonic particles, followed by a discussion on transition metal nitride plasmonic nanoparticles.Light absorption and heat generation by noble metal nano particles can be summarized as follows: first, the local surface plasmon resonance (LSPR) is excited, which lasts several fs and decays by nonradiative dephasing through Landau damp ening (1-100 fs). This process generates hot carriers at regions with high optical absorption (hotspots), the hot carriers subse quently decay by electron-electron scattering (1-100 fs) followed by electron-phonon coupling (0.1-10 ps). Ultimately, phonons dissipate heat to the surroundings (1-10 ns). [4,13,14] There is increasing interest in hot carrier processes, chemical reac tions induced by them, and determining whether the observed changes in chemical reactions are due to lattice heating or hot charge carriers. [15,16] Since elementary chemical transformations typically occur on a 1-100 ps timescale, [17] it is essential to characterize the light induced carrier dynamics and thermal relaxation of plasmonic systems that consist of nonnoble metal materials. Recent studies have shown that in particular hafnium nitride (HfN) performs well at converting light into heat through thermoplas monic relaxation. [18,19] This efficient lightinduced heating likely stems from a less negative real permittivity (ε′) and a higher imaginary permittivity (ε″) of HfN relative to noble metals, leading to a lossy plasmonic response accompanied by lower There is great interest in the development of alternatives to noble metals for plasmonic nanostructures. Transition metal nitrides are promising due to their robust refractory properties. However, the photophysics of these nanostructures, particularly the hot carrier dynamics and photothermal response on ultrafast timescales, are not well understood. This limits their implementation in applications such as photothermal catalysis or solar thermophotovoltaics. In this study, the light-induced relaxation processes in water-dispersed Hf...

Dye-sensitized photoelectrochemical (DSPEC) water splitting is an attractive approach to convert and store solar energy into chemical bonds. However, the solar conversion efficiency of a DSPEC cell is typically low due to a poor performance of the photocathode. Here, we demonstrate that Cu-doping improves the performance of a functionalized NiO-based photocathode significantly. Femtosecond transient absorption experiments show longer-lived photoinduced charge separation for the Cu:NiO-based photocathode relative to the undoped analogue. We present a photophysical model that distinguishes between surface and bulk charge recombination, with the first process (∼10 ps) occurring more than 1 order of magnitude faster than the latter. The longer-lived photoinduced charge separation in the Cu:NiO-based photocathode likely originates from less dominant surface recombination and an increased probability for holes to escape into the bulk and to be transported to the electrical contact of the photocathode. Cu-doping of NiO shows promise to suppress detrimental surface charge recombination and to realize more efficient photocathodes.

No abstract

No abstract

Plasmonic sensitization of semiconductors is an attractive approach to increase light-induced photocatalytic performance; one method is to use plasmonic nanostructures in core@shell geometry. The occurrence and mechanism of synergetic effects in photocatalysis of such geometries are under intense debate and proposed to occur either through light-induced charge transfer (CT) or through thermal effects. This study focuses on the relation between the dimensions of Ag@CeO 2 nanocubes, the wavelength-dependent efficiency, and the mechanism of light-induced direct CT. A 4mercaptobenzoic acid (4-MBA) linker between core and shell acts as a Raman probe for CT. For all Ag@CeO 2 nanocubes, CT increases with decreasing excitation wavelength, with notable increase at and below 514 nm. This is fully explainable by CT from silver to the 4-MBA LUMO, with the increase for excitation wavelengths that exceed the Ag/4-MBA LUMO gap of 2.28 eV (543 nm). A second general trend observed is an increase in CT yield with ceria shell thickness, which is assigned to relaxation of the excited electron further into the ceria conduction band, potentially producing defects.

This goal of thesis is to characterize a plasmonic film suitable for use on an optical fibre. This body of work focuses on the study of a thermal and fluorescent enhancing plasmonic film. This film was used on an optical fibre containing a tilted fibre Bragg grating to allow in situ monitoring of temperature, and the coupling of light into the film for both heat generation (thermoplasmonics) and to stimulate fluorescence on the surface (with fluorescent enhancement). This has involved examining the effect of the surface density of silver nanowires, and the presence of a spacer layer.Calculations of the fluorescent enhancement (EF ~18) as well as the heating efficiency were carried out. This film was identified as strongly scattering light that was in the cladding out of the fibre, as well as acting as a high efficiency heat source (100 ± 20 %.) which allowed for the determination of the melting temperature of the silver nanowires.. ii

Alle rechten voorbehouden. Niets uit deze uitgave mag worden vermenigvuldigd, in enige vorm of op enige wijze, zonder voorafgaande schriftelijke toestemming van de auteur. Chapter 4: Influencing Energy and Charge Transfer Between Plasmonic Nanoparticles and Semiconductors: Au/Ce1-xPrxO2 ______________ 6 Introduction ___________________________________________ 7 Results and Discussion ___________________________________ 8 Experimental methods ___________________________________ 9 References_____________________________________________ Appendix B: Supplementary information _________________________ Section 1: Energy levels of Ce(Pr)Ox ________________________ Section 2: Characterization of Au/CPO. _____________________ Chapter 5: Ultrafast photoinduced heat generation by plasmonic HfN nanoparticles __________________________________________ 1 Introduction __________________________________________ 2 Results and Discussion __________________________________ 3 Conclusions ___________________________________________ 4 Methods _____________________________________________