Abstract
Controlling the size and shape of metallic colloids is crucial for a number of nanotechnological applications ranging from medical diagnosis to electronics. Yet, achieving tunability of morphological changes at the nanoscale is technically difficult and the structural modifications made on nanoparticles generally are irreversible. Here, we present a simple nonchemical method for controlling the size of metallic colloids in a reversible manner. Our strategy consists of applying hydrostatic pressure on a Ca cationic sublattice embedded in the irradiated matrix of CaF2 containing a large concentration of defects. Application of our method to CaF2 along with in situ optical absorption of the Ca plasmon shows that the radii of the Ca nanoparticles can be reduced with an almost constant rate of −1.2 nm/GPa up to a threshold pressure of ∼9.4 GPa. We demonstrate recovery of the original nanoparticles upon decompression of the irradiated matrix. The mechanisms for reversible nanocolloid-size variation are analyzed...
Highlights
Metal nanoparticles (MNP) are the pillar of many technological applications extending from calorimetric sensors and chemical catalysts to in vivo imaging and photothermal therapy[1]
Our method consists of applying hydrostatic pressure on Ca MNP embedded in a dielectric matrix, which are generated by irradiating a crystal; in this way, a large concentration of highly mobile point defects is created
Using in situ optical absorption spectroscopy we determine that the radii of the Ca nanoparticles are reduced at an almost constant rate of −1.2 nm/GPa up to a pressure of ∼ 9.4 GPa, when a structural phase transition occurs in CaF2 (Fig.1) and the MNP vanish
Summary
Metal nanoparticles (MNP) are the pillar of many technological applications extending from calorimetric sensors and chemical catalysts to in vivo imaging and photothermal therapy[1]. An additional correction on the plasmon damping due to the small particle size of the colloids has been taken into account.[22] In the present calculations, the dielectric functions and spherical sizes of metallic Ca nanocolloids were obtained at different pressures by assuming that the pressure dependence of the corresponding dielectric function stems from changes in the electron density, a good approximation within the Drude model; the bulk modulus of CaF2 was employed, as justified previously.
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