M.Sc Thesis


M.Sc StudentAnastasia Brif
SubjectLattice Distortions in Semiconductor Crystals Induced by the
Incorporation of Intracrystalline Organic
Molecules
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Pokroy Boaz


Abstract

In nature, organisms are able to produce a wide variety of minerals during the process of biomineralization. The resulting biogenic minerals have been studied extensively for the past decade due to their potential to increase our understanding of crystal formation and engineering new and superior materials. The properties of these distinctive materials have been observed in many areas, such as their unique crystal shapes and morphologies, high fracture resistance, altered optical and magnetic properties, and much more. Many of these properties are due to the presence of intracrystalline organic molecules within the individual crystal structures. The presence of these molecules has been shown to strongly influence crystal microstructure and produce anisotropic lattice distortions. Recently, by applying a bio-inspired approach, it has been shown that similar microstructures and lattice distortions can be achieved in synthetic calcium carbonate crystals grown in the presence of organic molecules. However, no similar approach has been performed on non-calcium carbonate crystals. In this work, we use this bio-inspired approach to modify the crystal properties of functional materials such as semiconductors.

We found that amino acids can get incorporated into the crystal lattice of semiconductors, similar to the process observed for calcium carbonate. Moreover, not only that such incorporation exists; the resulting lattice distortions are accompanied by a band-gap energy shift of the semiconductor host. High-resolution X-ray powder diffraction on synchrotron beamlines was used to study the effects that different amino acids have on the structure and microstructure of the bio-inspired semiconductor/amino acid composites. 

This was achieved by measuring the lattice strain combined with the Rietveld refinement method. We studied the incorporation levels along different crystallographic planes via microstructure analysis (i.e., via line profiling). An analysis of the adherence profile of different amino acids is important for achieving better control over the band-gap value of the semiconductor host. We studied the effects of these intracrystalline amino acids on the band-gap of the semiconductor by spectroscopy method and found a linear correlation between the band-gap shifts and the intracrystalline strain caused by the amino acid incorporation. In addition, the presence of intracrystalline molecules has been shown to strongly influence the microstructure of the crystals and influence the resulting crystal shape.

The results of this study show that incorporated amino acids can lead to pronounced shift in the band-gap of semiconductors. Moreover, we believe that this research may open a new bio-inspired route for tuning the band-gaps of semiconductors.