Formation of Cr₂N nanoparticles by pulsed laser irradiation of a chromium target immersed in liquid nitrogen

Full text: Chromium nitride nanoparticles with cylindrical shapes having aspect (height-to diameter) ratio with particle size (mean diameter) distribution between 0.8 nm and 30 nm were produced by laser irradiation of a chromium target immersed in liquid nitrogen. The Cr was directly converted to chromium nitride(s) nanoparticles according to selected-area electron diffraction analyses using transmission electron microscopy technique. Crystalline nanoparticles are mostly consisting of Cr₂N without evidence of core-shell structure which is commonly reported together with conversion of Cr₂N to CrN and mixture of chromium oxides. In addition, there is no evidence of oxidation by storage or photodegradation of the nanoparticles in isopropyl alcohol suspensions. The intensity profile of small-angle X-ray scattering indicate that geometrical shape of the nanoparticles are not spherical, but cylindrical with an aspect (height-to diameter) ratio in the proportion 7:10. UV-VIS absorption spectroscopy reveal presence of surface plasmon absorption at ultraviolet region at wavelengths of 350, 372, and 397 nm. First-principles calculations of density of states, dielectric function, and optical conductivity performed within the theoretical framework of density functional theory for Cr₂N with hexagonal structure corroborate the formation of surface plasmons. (author)