Sequential Synthesis Methodology Yielding Well-Defined Porous 75%SrTiO3/25%NiFe2O4 Nanocomposite.

In this research, we reported on the formation of highly porous foam SrTiO3/NiFe2O4 (100-xSTO/xNFO) heterostructure by joint solid-state and sol-gel auto-combustion techniques. The colloidal assembly process is discussed based on the weight ratio x (x = 0, 25, 50, 75, and 100 wt %) of NiFe2O4 in the 100-xSTO/xNFO system. We proposed a mechanism describing the highly porous framework formation involving the self-assembly of SrTiO3 due to the gelation process of the nickel ferrite. We used a series of spectrophotometric techniques, including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N2 adsorption isotherms method, UV-visible diffuse reflectance spectra (UV-Vis DRS), vibrating sample magnetometer (VSM), and dielectric measurements, to investigate the structural, morphological, optical, magnetic, and dielectric properties of the synthesized samples. As revealed by FE-SEM analysis and textural characteristics, SrTiO3-NiFe2O4 nanocomposite self-assembled into a porous foam with an internally well-defined porous structure. HRTEM characterization certifies the distinctive crystalline phases obtained and reveals that SrTiO3 and NiFe2O4 nanoparticles were closely connected. The specific magnetization, coercivity, and permittivity values are higher in the 75STO/25NFO heterostructure and do not decrease proportionally to the amount of non-magnetic SrTiO3 present in the composition of samples.

Growth of germanium nanowires on silicon(111) substrates by molecular beam epitaxy.

Heteroepitaxial growth of Ge nanowires was carried out on Si(111) substrates by MBE. Au seeds were used as precursor for the VLS growth of the nanowires. Even if the Au droplets do not act as catalyst for the dissociation of gas, they are local preferential areas where the energetic barrier of Ge nucleation is lowered compare to the remaining non activated surface. Two sets of Au seeds were used as precursors for the VLS process. The first set have an average diameter of 125 nm and the second of 25 nm. In-situ RHEED monitoring showed a Au wetting layer between these seeds before the nanowires growth as well as at the end of the Ge nanowires growth. It means that the wetting layer acted as a surfactant from the Si(111) surface to the Ge grown layer between the nanowires. Analysis of SEM images brought the fact that the diffusion of gold from the droplets on the surface and the sidewalls of the nanowires via the Ostwald ripening is a key parameter of the growth of the nanowires.