Crystal growth and characterization: study of polymorphism
Growth of crystals and their morphological and structural characterization is a mandatory step in many fields of science and technology. Present state of the art study of crystal growth is widespread and covers both natural (geology, biomineralization) and artificial systems (semiconductors, sensors, optics, lasers, drugs, plasters).
Growth of crystals involves complex physico-chemical processes whose study allows a better control and optimization of results. Among many phenomena, genesis of polymorphic crystal structures can hamper preparation of crystalline materials. Therefore, the study of thermodynamic and kinetic factors directing growth toward a specific polymorph is of great relevance in academic and applied research. Among the parameters triggering polymorphism are temperature or ambient pressure, impurities/additives active during the nucleation stage (including preformed crystals able to select polymorphs by epitaxy), conformational flexibility, isotopic substitution. All these variables can be exploited as powerful control parameters for reaching the final goal, instead of being a source of unpredictable and irreproducible results.
Research activities involve:
Growth of crystals with solution methods under ambient or solvothermal conditions (e.g. microporous coordination polymers exhibiting zeolite-like behavior or catalitic properties, aminoacids) allows preparation of crystals with size from centimeter to nanometer scale with control of morphology. Crystal of organic materials with medium-high vapor pressure can be grown by sublimation or physical vapor transport.
Study of surface processes during crystal growth in nature, laboratory or manifacturing plants (e.g. setting of cements/plasters in the presence of chemical additives) is directed toward aquisition of physico-chemical data ranging from the mesoscopic scale to molecular dimensions. Characterization of growing crystal surfaces is performed by means of optical microscopy or scanning probe microscopy in controlled environments. In situ visualization of growth with time evolution reveals microtopographic surface features connected to growth mechanisms. The microscopic characterization, possibly supported by single crystal X-ray diffraction analysis, can be integrated with theoretical modelling of crystal morphology through periodic bond chains analysis, where the strength of intermolecular interactions developing within the crystal structure can be exploited to estimate the theoretical equilibrium and growth crystal morphology.
Prof. Massimo Moret
CCC-DXCS Lab – U5 Building, 1st Floor, Room 1060-1061