The visible electromagnetic resonances of Si/SiO2 core–shell nanoparticles are controlled by thermal oxidation. The core–shell nanoparticles comprising silicon and silicon dioxide are fabricated through laser ablation and thermal oxidation. The resonant wavelengths of magnetic and electric dipoles excited in the particles are experimentally demonstrated to be controlled in the visible region by the variation of the core diameter, through thermal oxidation.
We evaluated the properties of hot carrier generation on Au and Ag nanoparticle (NP) 2D arrays by monitoring chemical transformation. The arrays were fabricated by assembling the Au and AgNPs, respectively, with a diameter of ∼30 nm. The plasmon resonance peaks of both the arrays were tuned to around 671 nm, where the intraband transition was the dominant pathway for the surface plasmon excitation since the incident photon energy is below the interband transition threshold for both Au and Ag. Time-resolved surface-enhanced Raman scattering (SERS) spectroscopy was utilized to monitor the changes in the molecular structure sensitively. We selected para-aminothiophenol as the molecule, which was well known to transform to 4,4′-dimercaptoazobenzene (DMAB) by hot carriers generated from the plasmonic excited surface. It was observed that the peak intensity of DMAB increased as the total exposure increased due to the increase in the number of DMAB molecules for both metals, similar to our previous reports. The analysis of the SERS spectra showed that larger laser intensity progressed the transformation more rapidly. The analysis also clarified that the chemical transformation occurs more efficiently on the AgNP array compared to the AuNP array. The superiority in the efficiency for Ag may be derived from contribution of more hot carriers generated in the material with the smaller plasmon damping constant.
The interaction strength of progressively longer oligomers of glycine, (Gly), di-Gly, tri-Gly, and penta-Gly, with a natural pyrite surface was directly measured using the force mode of an atomic force microscope (AFM). In recent years, selective activation of abiotically formed amino acids on mineral surfaces, especially that of pyrite, has been proposed as an important step in many origins of life scenarios. To investigate such notions, we used AFM-based force measurements to probe possible non-covalent interactions between pyrite and amino acids, starting from the simplest amino acid, Gly. Although Gly itself interacted with the pyrite surface only weakly, progressively larger unbinding forces and binding frequencies were obtained using oligomers from di-Gly to penta-Gly. In addition to an expected increase of the configurational entropy and size-dependent van der Waals force, the increasing number of polar peptide bonds, among others, may be responsible for this observation. The effect of chain length was also investigated by performing similar experiments using l-lysine vs. poly-l-lysine (PLL), and l-glutamic acid vs. poly-l-glutamic acid. The results suggest that longer oligomers/polymers of amino acids can be preferentially adsorbed on pyrite surfaces.
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