We review recent experimental studies on light-emitting Si materials, and discuss their hybrid electronic properties between the molecular and solid state limits. Strong visible luminescence from Si nanocrystals has attracted much attention from viewpoints of both fundamental physics and the potential application to optoelectronic devices. Quantum confinement effects as well as surface effects control unique luminescence properties of Si nanostructures.
A characteristic waiting time appears at fixed temperature above Tc or Ms for elements, alloys and polymers, where Tc is the usual first-order phase transition temperature and Ms is the normal martenstic phase transition temperature. This waiting time is called incubation time and related with the nucleation probability derived from a nucleation barrier. That is why nucleation process is regarded as thermal activated process at the non-equilibrium state. In particular, such a long incubation time of In-Tl alloys has a good agreement with experimental results by using Roitburd method. Furthermore, detailed and accurate experiments enable us to be aware that two dimensional growth occurs above Tp, where peculiar temperature, Tp, controls the time development of diffraction patterns and appears above Ms in this system. In contrast to soft phonon model, incubation time is essential property of the first-order phase transition and the key to resolve nucleation and growth process.
Surface vibration of CVD-grown diamond surface is measured by HR-EELS. Hydrogen is adsorbed on the sp3-hybridized carbon. On the (001) 2×1 surface, one C-H stretching vibration appears consistently with the dieter-chain model. On the (111) 1×1 surface, two C-H stretching modes appear, which suggests methyl termination model. But the phonon dispersion in the low energy region is well explained by the monohydride termination model. Uniformity of the surface should be checked to discuss this inconsistency. Hydrogen exchange with the gas-phase and the hydrogen desorption/adsorption processes are also investigated.
Crystal structure, chemical bonding and physical property are discussed for the metal-rich cluster compound Nb6I11-xBrx containing discrete clusters and the layered cluster compound Y2-xMxC2Br2-yIy, focusing on the effect of replacement by other atoms having different mass, size and bonding. Nb6I11-xBrx undergoes a spin cross-over phase transition and with increasing Br content the transition temperature shifts from 274 to 170 K. The highest superconducting transition temperature in the yttrium ethenide halides occurs at a intermediate composition rather than at each end-member.