Electron diffraction study of the formation and growth of clusters in supersonic binary N2-Kr gas jets

TL;DR

This study uses electron diffraction to analyze how clusters form and grow in supersonic N2-Kr gas jets, revealing changes in nucleation mechanisms and phase composition influenced by temperature and krypton concentration.

Contribution

It provides new insights into the nucleation mechanisms and phase changes in N2-Kr clusters, highlighting the effects of temperature and impurity concentration on cluster growth.

Findings

Nucleation mechanism shifts from heterogeneous to homogeneous with temperature increase.

Krypton addition increases the fcc phase fraction at lower temperature.

Higher krypton content suppresses cluster growth due to gas condensation kinetics.

Abstract

An electron diffraction diagnostics of substrate-free clusters formed in N2-Kr binary jets expanding through a supersonic nozzle into vacuum was carried out. Gas mixtures contained 0.5, 1, and 6 mol.% krypton, the measured average sizes of aggregations in the cluster beam varied from 500 to 30,000 molecules per cluster. A change in the nucleation mechanism in the jet from heterogeneous to homogeneous was revealed when the temperature of the gas mixture at the nozzle inlet T0 increased from 100 K to 120 K, which had a profound effect on the sizes, phase composition and component composition of the clusters. It was established that the intensification of cluster growth by inserted krypton nucleation centers at T0 = 100 K occurs through an increase in the fraction of the fcc phase. At T0 = 120 K, the effect of cluster growth suppression by the addition of an impurity with significantly stronger intermolecular forces was revealed for the first time. It is shown that the effect is manifested when the krypton gas content increases to 6 mol.% and is caused by the kinetics of gas condensation in a supersonic jet.