10:45 AM - 12:15 PM
[MIS14-P10] Polymorph transition-mediated non-classical nucleation and growth in the colloidal heteroepitaxial growth
Keywords:Colloidal crystals, Epitaxial growth, polymorph transition
Colloidal crystals as a model system have intensively been used to elucidate nucleation mechanisms, for which understanding details of the non-classical nucleation process is critical. We have investigated colloidal heteroepitaxial growth, in which we found that polymorph formation and transitions leads to non-classical nucleation and growth. In the present study, nucleation and growth processes associating with polymorph transition are reported, and discussed how they related to the non-classical nucleation and growth.
Colloidal crystallization is achieved by depletion attraction that is induced by added polymers (sodium polyacrylate). A substrate (different particles from that of epitaxial phase) is formed by convective assembly, by which thin colloidal crystal films are fabricated. Typical particle combination for polymorph formation is 790 and 1000 nm for epitaxial phase and the substrate, respectively. By the same particle, two kinds of crystals with different morphologies and orientation against to the substrate are formed, which is denoted as a- and b-phase.
Stability of those two phases is found to be dependent on depletion attraction force, which is tuned by polymer concentration (Cp). In the low Cp, alpha-phase is more stable than beta-phase, while it is opposite at high Cp. Polymorph transition were observed at low Cp, where unstable b-phase are dissolved and the particles of which are incorporated into the a-phase to grow.
Non-classical nucleation and growth process were revealed by in-situ observations. The alpha-phase cluster transitioned into beta-phase which subsequently grow to nucleation size. Also, non-classical growth manner was observed. As growing beta-phase, neighboring alpha-phase cluster is dissolved and absorbed by beta-phase.The colloidal heteroepitaxy has been found to be a good model system for studying non-classical behaviors in nucleation and growth. We will further quantitatively investigate how polymorph transition affects those behaviors.
Colloidal crystallization is achieved by depletion attraction that is induced by added polymers (sodium polyacrylate). A substrate (different particles from that of epitaxial phase) is formed by convective assembly, by which thin colloidal crystal films are fabricated. Typical particle combination for polymorph formation is 790 and 1000 nm for epitaxial phase and the substrate, respectively. By the same particle, two kinds of crystals with different morphologies and orientation against to the substrate are formed, which is denoted as a- and b-phase.
Stability of those two phases is found to be dependent on depletion attraction force, which is tuned by polymer concentration (Cp). In the low Cp, alpha-phase is more stable than beta-phase, while it is opposite at high Cp. Polymorph transition were observed at low Cp, where unstable b-phase are dissolved and the particles of which are incorporated into the a-phase to grow.
Non-classical nucleation and growth process were revealed by in-situ observations. The alpha-phase cluster transitioned into beta-phase which subsequently grow to nucleation size. Also, non-classical growth manner was observed. As growing beta-phase, neighboring alpha-phase cluster is dissolved and absorbed by beta-phase.The colloidal heteroepitaxy has been found to be a good model system for studying non-classical behaviors in nucleation and growth. We will further quantitatively investigate how polymorph transition affects those behaviors.