RESUMO
Ni11As8 crystallites 23-nm thick and 250-700-nm wide in lateral dimension were prepared in alkaline hydrothermal condition. Transmission electron microscope (TEM) images and selected area electron diffraction (SAED) analyses showed that the as-prepared Ni11As8 was single-crystalline nanosheets of [331] orientation. The Ni11As8 exhibited an optical absorption onset of 3.00 eV in the visible spectral regime. Its magnetic measurement indicated a weak magnetic hysteresis and unsaturation magnetization with a magnetic susceptibility of 1.37 x 10(-4) cm3/g (at 15 kOe) at room temperature, the origin of which was discussed and assigned to the effect of surface species containing Ni ions. The extended Hückel tight-binding calculation revealed that bulk Ni11As8 has a 3d-localized narrow band below Fermi level and complicated band structure with small band gap in the first Brillouin zone, which supply clues to explain the observed optical and magnetic properties. The formation mechanism of Ni11As8 was studied and attributed to an alkaline hydrothermal redox route on the basis of the Marsh reaction.
RESUMO
Spherical InAs nanocrystals of 30-50 nm were hydrothermally synthesized at 120 degrees C, which showed a 100 meV-blueshift of band gap absorption and phonon confinement of optical vibration mode. The study of hydrothermal formation mechanism indicated that crystalline InAs could be obtained in an extended pH range (approximately -0.15 to 14).