The formation and photoluminescence (PL) of InP nanowires grown by metal organic vapour phase epitaxy on InP(111)B substrates, using colloidal gold nanoparticles as catalysts, are investigated. The dependence of the orientation and dimensions of the nanowires on the growth temperature is studied using scanning electron microscopy. Vertically aligned [Formula: see text] oriented nanowires with a mean base diameter in the range 50-150 nm, and a tip diameter of 50 nm, show a PL blue-shift of about 80 meV compared to the substrate. Blue-shift due to quantum confinement is ruled out because of the large diameter of the nanowires. A clear correlation between the orientation of the nanowires on the substrate and the PL peak position is observed. Based on x-ray diffraction and transmission electron microscopy measurements, it is proposed that the as-grown vertically oriented nanowires have crystallized in the wurtzite lattice instead of in the zinc-blende structure, which results in a blue-shifted PL.

The catalyst-free metal organic vapor phase epitaxial growth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowire growth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InP nanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies.

Positron annihilation spectroscopy was used to study GaAsN/GaAs epilayers. GaAsN layers were found to contain Ga vacancies in defect complexes. The density of the vacancy complexes increases rapidly to the order of 10 18 cm Ϫ3 with increasing N composition and decreases after annealing at 700°C. The anticorrelation of the vacancy concentration and the integrated photoluminescence intensity suggests that the Ga vacancy complexes act as nonradiative recombination centers.

A series of fire experiments was performed to study the gas temperature development and charring behaviour of timber construction compartments. The measured gas temperatures were 300-500 C lower than predicted by the parametric temperature-time curves of Eurocode 1 for unprotected and insufficiently protected timber structures. For structures protected with a double layer of gypsum plasterboard, the agreement was better. In all cases, however, the prediction was on the safe side. One protective layer of gypsum plasterboard delayed the onset of charring for 20 min. Using two layers, the delay time was doubled. Reduced charring rates for long exposure times were observed, resulting from the increasingly protective effect of the char layer withtime.

The surface effects in the optical properties of catalyst-free grown InP nanowires are investigated. Both as-grown nanowires and nanowires treated with hydrofluoric acid are studied using low- and room-temperature continuous-wave and time-resolved photoluminescence measurements and transmission electron microscopy. It is shown that the room-temperature photoluminescence intensity is increased by two orders of magnitude after the surface treatment, and that there is also a significant increase in the double-exponential photoluminescence decay time.

We report the fabrication of self-catalysed InP nanowires on (111)B, (111)A, (110), and (001) InP substrates. Indium droplets, deposited in situ using metalorganic vapour phase epitaxy, are used as seeds for nanowire growth. The preferential nanowire growth direction is always on (111)B, (111)A, and (110) oriented substrates. On (111)A substrates some initial growth in the [111]A direction is observed before kinking into one of the available directions. The nanowires are optically active at room temperature. On (001) substrates no nanowire growth off the substrate is observed. However, growth still takes place in the two possible equivalent azimuthal directions.

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