Controlling the metal nanoclusters with atomic precision is highly difficult and further studies on their transformation reactions are even more challenging. Herein we report the controlled formation of a silver alloy nanocluster [AuAg19{S2P(OnPr)2}12] (1) from an Ag20 template via a galvanic exchange route. X-ray structural analysis reveals that the alloy structure comprises of a gold-centered Ag12 icosahedron, Au@Ag12, capped by seven silver atoms. Interestingly upon reacting with one equiv. of silver(i) salt, (1) can transform into a higher nuclearity nanocluster, [Au@Ag20{S2P(OnPr)2}12]+ (2). The conversion process is studied via ESI mass spectrometry and 31P NMR spectroscopy. This kind of size-structural transformation at the single atom level is quite remarkable. Furthermore, the compositions of all the doped nanoclusters (1, 2) were fully characterized with ESI-MS and EDS. The blue shift depicted in the UV-visible and emission spectra of the doped nanoclusters (1, 2) compared with the precursor, Ag20, demonstrates that the doping atoms have significant effects on the electronic structures.

The growth properties of ␤-SiC on ͑100͒ Si grown by rapid thermal chemical vapor deposition, using a single precursor ͑methylsilane͒ without an initial surface carbonization step, were investigated. An optimun growth temperature at 800°C was found to grow single crystalline materials. A simple Al Schottky barrier fabricated on n-type SiC grown on Si substrates exhibited a ''hard'' reverse breakdown of 13 V with a positive temperature coefficient of 2ϫ10 Ϫ4°CϪ1 up to 120°C, indicating an avalanche mechanism. A Pt Schottky barrier fabricated on n-type SiC grown on tilted Si substrates to improve the surface morphology exhibited a breakdown voltage of 59 V, with a negative temperature coefficient. From the analysis of the electrical field distribution, the breakdown probably occurred at interface defects between SiC and Si, as suggested by Raman spectroscopy. To investigate minority transport behavior, SiC/Si heterojunction bipolar transistors ͑HBTs͒ were fabricated and compared to Si bipolar junction transistors. The collector currents of the SiC/Si HBTs were similar to those of Si control transistors, because both devices had the same base structures. Compared to Si control transistors, the base currents of SiC/Si HBTs increased. It seems that the interface defects between Si and SiC act as recombination centers to deplete back-injected holes, instead of being the barrier to stop hole currents, and thus to increase the base currents of SiC/Si HBTs.

The metal-insulator transition (MIT) is an exceptional test bed for studying strong electron correlations in two dimensions in the presence of disorder. In the present study, it is found that in contrast to previous experiments on lower-mobility samples, in ultra-high mobility SiGe/Si/SiGe quantum wells the critical electron density, nc, of the MIT becomes smaller than the density, nm, where the effective mass at the Fermi level tends to diverge. Near the topological phase transition expected at nm, the metallic temperature dependence of the resistance should be strengthened, which is consistent with the experimental observation of more than an order of magnitude resistance drop with decreasing temperature below ∼ 1 K.

An electron-hole plasma recombination model is used to fit the room-temperature electroluminescence from metal-oxide-silicon tunneling diodes. The relatively narrow line shape in the emission spectra can be understood by the quasi-Fermi level positions of electrons and holes, which both lie in the band gap. This model also gives a narrower band gap than that of bulk silicon. The surface band bending in the Si/oxide interface is responsible for this energy gap reduction.