  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.
