A Study of Permalloy (Nickel(81)iron(19)) Nanoparticles as Possible Qubits

Abstract

Permalloy nanoparticles are grown in a custom built inert gas condensation system with magnetron sputtering. By careful control of the processing parameters during nucleation, the nanoparticles can be grown with the desired diameter of 5 nm and a narrow size distribution with a standard deviation of ∼0.5 nm. As a result of the nucleation and growth process, the nanoparticles have a polycrystalline structure. Several heating methods are employed in an attempt to recrystallize the nanoparticles. In the end, ultrafast heating with a femtosecond laser system is used to form single crystal nanoparticles. The wavelength of the laser is strongly absorbed by the metal nanoparticles but not by the supporting substrate (a 50 nm thick S1O2 membrane). The ultra short pulse width of 175 fs also reduces the possibility of heat exchange between the particle and the substrate. This rapid heating causes melting of the particle and upon cooling, a single crystalline structure. These single crystal nanoparticles not only fulfill the requirements of the original project but also provide the first clear evidence that melting of metals can be achieved without significant material loss. Two distinct mechanisms of material loss are identified with separate thresholds.