Tuned synthesis of novel 3D mesoscopic ZnO crystals using buffer layer assisted grown catalysts

In this paper, we demonstrate that vapor-liquid-solid (VLS) mode of growth can be employed to obtain three-dimensional (3D cubes or 2D platelets) mesoscopic structures with unusual morphologies and sizes using buffer layer assisted (BLA) grown catalysts. The unusual structures could not be grown by using normally deposited catalyst. It is demonstrated that the shape and the contact angle of the catalyst are the key parameters to realize such an unusual growth. AFM images of the BLA grown Mn nanoparticles showed small contact area and large contact angle with the substrate. The VLS growth was performed in the ambient and in the presence of a carrier gas. The growth done in the presence of a carrier gas led to creation of oxygen vacancies, which affected the ultimate morphology of the grown structure. It was observed that oxygen deficient environment led to the growth of hierarchical micropellets. On the contrary, the presence of oxygen resulted in the quasi symmetrical growth of micro/nano cubes. Finally, the growth mechanism was explained using thermodynamic approach, considering the interface energies and change in the Gibb's free energy. XRD, Raman and PL characterization techniques were employed and found in good agreement with proposed growth mechanism. Self doping of the Mn catalyst was also observed in cubic structures.