5:15 PM - 6:30 PM
[MIS17-P02] Heteroepitaxial growth mechanism in colloidal crystallization
Keywords:Colloidal crystals, Epitaxial growth
Colloidal crystals, periodic arrays of colloidal particles, have been attracting great attention due to their versatile applications such as novel optical devices. Besides, the colloidal crystals have been regarded as a useful model of various phenomena as it displays similar phase transition to the atomic system. Among variable methods to control growth and structure of the colloidal crystals, a colloidal epitaxy that utilizes a patterned substrate is an effective technique. However, the technique has been limited to homoepitaxial growth, where structure and lattice spacing of the substrate and epitaxial phase are similar. In this thesis, colloidal crystals are fabricated with the heteroepitaxial growth, where lattice constant of the substrate and epitaxial layer is different. The mechanism is discussed for the heteroepitaxial growth in colloidal crystallization.
Polystyrene particles of 700 nm was used to grow the epitaxial layers. The particle size of the substrates is ranged from 400 to 1300 nm. The sodium polyacrylate is added to induce depletion attractive interaction, by which colloidal crystallization is achieved. The lattice misfit ratio is defined as the (deq – dsubst)/ deq, where deq is equilibrium particle distance as the particle distance of colloidal crystals formed without the substrate (on cover glass), and dsubst is lattice spacing of the substrate. The heteroepitaxial growth was performed in various lattice misfit ratios.
Three growth modes are recognized in the experiment: Layer-by layer, Layer-plus-island, and Island, which is denoted as FM, SK, and VW mode, respectively, as is the heteroepitaxial growth of atomic system. This has been firstly recognized in the growth of the colloidal crystals. Importantly, SK mode in some growth conditions is transitioned into VW by decomposition of the formed layers, the process of which is uncovered by the in-situ observation.
Contrary to the expectation, growth modes do not show clear correlation with the lattice misfit ratio. We inferred that interaction between epitaxial layer and the substrate influences the epaxial growth. Relative particle interaction between substrate and the epitaxial layer is estimated by the strength of the depletion interaction. Consequently, three growth modes are suitably categorized by using two parameters; the interaction between substrate and epitaxial layers as well as the lattice misfit ratio. The findings in the study will well contribute to rational control of the structure and phase of the colloidal crystals.
Polystyrene particles of 700 nm was used to grow the epitaxial layers. The particle size of the substrates is ranged from 400 to 1300 nm. The sodium polyacrylate is added to induce depletion attractive interaction, by which colloidal crystallization is achieved. The lattice misfit ratio is defined as the (deq – dsubst)/ deq, where deq is equilibrium particle distance as the particle distance of colloidal crystals formed without the substrate (on cover glass), and dsubst is lattice spacing of the substrate. The heteroepitaxial growth was performed in various lattice misfit ratios.
Three growth modes are recognized in the experiment: Layer-by layer, Layer-plus-island, and Island, which is denoted as FM, SK, and VW mode, respectively, as is the heteroepitaxial growth of atomic system. This has been firstly recognized in the growth of the colloidal crystals. Importantly, SK mode in some growth conditions is transitioned into VW by decomposition of the formed layers, the process of which is uncovered by the in-situ observation.
Contrary to the expectation, growth modes do not show clear correlation with the lattice misfit ratio. We inferred that interaction between epitaxial layer and the substrate influences the epaxial growth. Relative particle interaction between substrate and the epitaxial layer is estimated by the strength of the depletion interaction. Consequently, three growth modes are suitably categorized by using two parameters; the interaction between substrate and epitaxial layers as well as the lattice misfit ratio. The findings in the study will well contribute to rational control of the structure and phase of the colloidal crystals.