"Forbidden" transitions between quantum Hall and insulating phases in p-SiGe heterostructures

We show that in dilute metallic p-SiGe heterostructures, magnetic field can cause multiple quantum Hall-insulator-quantum Hall transitions. The insulating states are observed between quantum Hall states with filling factors \nu=1 and 2 and, for the first time, between \nu=2 and 3 and between \nu=4 and 6. The latter are in contradiction with the original global phase diagram for the quantum Hall effect. We suggest that the application of a (perpendicular) magnetic field induces insulating behavior in metallic p-SiGe heterostructures in the same way as in Si MOSFETs. This insulator is then in competition with, and interrupted by, integer quantum Hall states leading to the multiple re-entrant transitions. The phase diagram which accounts for these transition is similar to that previously obtained in Si MOSFETs thus confirming its universal character

Synthesis and dispersion of hydroxyapatite nanopowders

Spherical, rod and fibroid hydroxyapatite [HAp, Ca10(PO4)6(OH)2] nanoparticles were prepared and dispersed in aqueous media. Temperature and solution pH were the key factors to synthesis of different morphology and crystallinity. Processing conditions were selected from ternary diagram of pH, temperature and Ca:P ratio. High hydroxyl ion concentration (12.25≥pH≥10.5) and low temperature (298K) favored isotropic non-confined spherical particles, intermediate concentration (9.5≥pH≥7.75) and low temperature (303K) initiated the anisotropic growth of rod shaped particles but low concentration (7≥pH≥5.25) and high temperature (353K) accelerated one-dimensional fibroid morphology. The dispersed HAp–citrate complex exhibited a constant zeta potential and size distribution for six months. ► Low temperature synthesis of different morphology of crystalline hydroxyapatite nanoparticles and their dispersion. ► Temperature, pH and Ca:P are the key factors to control the morphology. ► Different morphology and purity could be synchronized from representative ternary diagram of process control parameters. ► Homogenous dispersions of HAp nanoparticles exhibited constant zeta potential