Controlled photoluminescence from self-assembled semiconductor-metal quantum dot hybrid array films

Thin films of hybrid arrays of cadmium selenide quantum dots and polymer grafted gold nanoparticles have been prepared using a BCP template. Controlling the dispersion and location of the respective nanoparticles allows us to tune the exciton-plasmon interaction in such hybrid arrays and hence control their optical properties. The observed photoluminescence of the hybrid array films is interpreted in terms of the dispersion and location of the gold nanoparticles and quantum dots in the block copolymer matrix.

Effect of electric field on ammonium perchlorate decomposition

A novel method of detecting the charge-carrying species in inorganic decomposable salts is described. In ammonium perchlorate it is observed that the charge-carrying species at temperatures 150 and 230°C are oppositely charged; i.e., they are negatively charged (ClO−4 ions) at 230°C and positively charged (H+ or NH+4) at 150°C.

Doping Transition Metal (Mn or Cu) Ions in Semiconductor Nanocrystals

Following growth doping strategy and using dopant oxides nanocrystals as dopant sources, we report here two different transition-metal ions doped in a variety of group II-VI semiconductor nanocrystals. Using manganese oxide and copper oxide nanocrystals as corresponding dopant sources, intense photoluminescence emission over a wide range of wavelength has been observed for different host nanocrystals. Interestingly, this single doping strategy is successful in providing such highly emissive nanocrystals considered here, in contrast with the literature reports that would suggest synthesis strategies to be highly specific to the particular dopant, host, or both. We investigate and discuss the possible mechanism of the doping process, supporting the migration of dopant ions from dopant oxide nanocrystals to host nanocrystals as the most likely scenario.

Effect of GPS on understanding relationship between mobile map and environment : A field experiment

Objectives: GPS technology enables the visualisation of a map reader s location on a mobile map. Earlier research on the cognitive aspects of map reading identified that searching for map-environment points is an essential element for the process of determining one s location on a mobile map. Map-environment points refer to objects that are visualized on the map and are recognizable in the environment. However, because the GPS usually adds only one point to the map that has a relation to the environment, it does not provide a sufficient amount of information for self-location. The aim of the present thesis was to assess the effect of GPS on the cognitive processes involved in determining one s location on a map. Methods: The effect of GPS on self-location was studied in a field experiment. The subjects were shown a target on a mobile map, and they were asked to point in the direction of the target. In order for the map reader to be able to deduce the direction of the target, he/she has to locate himself/herself on the map. During the pointing tasks, the subjects were asked to think aloud. The data from the experiment were used to analyze the effect of the GPS on the time needed to perform the task. The subjects verbal data was used to assess the effect of the GPS on the number of landmark concepts mentioned during a task (landmark concepts are words referring to objects that can be recognized both on the map and in the environment). Results and conclusions: The results from the experiment indicate that the GPS reduces the time needed to locate oneself on a map. The analysis of the verbal data revealed that the GPS reduces the number of landmark concepts in the protocols. The findings suggest that the GPS guides the subject s search for the map-environment points and narrows the area on the map that must be searched for self-location.

Electron spectroscopic investigation of the semiconductor-metal transition in La1-xSrxMnO3

We study the electronic structure of La1-xSrxMnO3+δ, x=0, 0.1, 0.2, 0.3, and 0.4, across the semiconductor-metal transition, using various electron spectroscopy techniques. The negligible intensity seen at EF using ultraviolet photoemission spectroscopy and bremsstrahlung isochromat spectroscopy (BIS) indicate an unusual semiconductor-metal transition observed for x≥0.2, consistent with the resistivity data. The BIS spectra show doped hole states developing about 1.4 eV above EF as a function of x. Auger electron spectroscopy gives an estimate of the intra-atomic Coulomb energy in the O 2p manifold to be about 6.8 eV. The Mn 2p core-level spectrum of LaMnO3, analyzed in terms of a configuration-interaction calculation, gives parameter values of the charge-transfer energy Δ=5.0 eV, the hybridization strength between Mn 3d and O 2p states, t=3.8 eV, and the on-site Coulomb energy in Mn 3d states Udd=4.0 eV, suggesting a mixed character for the ground state of LaMnO3.

A study of the reaction of divalent transition metal chlorides with pyridinium poly(hydrogen fluoride), ppht, and the effect of potassium hydrogen fluoride on fluorination and complexation

Studies of the reaction of metal chlorides, MCl2 (M = Mn, Co, Ni, Cu, Zn) with PPHF at room temperature have shown that Mn, Co and Zn form the corresponding metal fluorides, MF2, while Ni and Cu form their dipyridine metal(II) dichloride complexes. Nickel and copper complexes further undergo fluorination and complexation by potassium hydrogen fluoride in PPHF to form KNiF3 and KCuF3.

Metastable extension of the fluorite phase field in Y2O3---ZrO2 and its effect on grain growth

Pure Y2O3 and Y2O3---ZrO2 solid solutions have been prepared by melt atomization and by pyrolysis of nitrate solutions. Extended solubility is readily achieved in both techniques for the entire composition range investigated: melts with 0–30% ZrO2 and precursors with 0–50% ZrO2. However, solidification of under cooled droplets yields almost exclusively single phase powders with the structure of cubic yttria (D53). In contrast, the pyrolysis route leads to a sequence of metastable microstructures beginning with a nanocrystalline disordered fluorite-based (C1) solid solution. Further heating leads to the evolution of much larger (micron size) flake crystals with a {001} texture, concurrent with partial ordering of the oxygen ions to the sites occupied in the D53 structure. The driving force for ordering and the rate of grain growth decrease with increasing ZrO2 addition. Abrupt heating to high temperatures or electron irradiation can induce ordering without substantial grain growth. There is no significant reduction in porosity during the recrystallization, which with the other observations suggests that grain growth is driven by the free energy available for the ordering transformation from fluorite to the yttria structure. This route offers opportunities for single crystal thin film development at relatively low processing temperatures.

Metastable extension of the fluorite phase field in Y2O3---ZrO2 and its effect on grain growth

Pure Y2O3 and Y2O3-ZrO2 solid solutions have been prepared by melt atomization and by pyrolysis of nitrate solutions. Extended solubility is readily achieved in both techniques for the entire composition range investigated: melts with 0-30% ZrO2 and precursors with 0-50% ZrO2. However, solidification of under cooled droplets yields almost exclusively single phase powders with the structure of cubic yttria (D5(3)). In contrast, the pyrolysis route leads to a sequence of metastable microstructures beginning with a nanocrystalline disordered fluorite-based (C1) solid solution. Further heating leads to the evolution of much larger (micron size) flake crystals with a {001} texture, concurrent with partial ordering of the oxygen ions to the sites occupied in the D5(3) structure. The driving force for ordering and the rate of grain growth decrease with increasing ZrO2 addition. Abrupt heating to high temperatures or electron irradiation can induce ordering without substantial grain growth. There is no significant reduction in porosity during the recrystallization, which with the other observations suggests that grain growth is driven by the free energy available for the ordering transformation from fluorite to the yttria structure. This route offers opportunities for single crystal thin film development at relatively low processing temperatures.

Pulsed laser deposition of strontium titanate thin films for dynamic random access memory applications

Polycrystalline strontium titanate (SrTiO3) films were prepared by a pulsed laser deposition technique on p-type silicon and platinum-coated silicon substrates. The films exhibited good structural and dielectric properties which were sensitive to the processing conditions. The small signal dielectric constant and dissipation factor at a frequency of 100 kHz were about 225 and 0.03 respectively. The capacitance-voltage (C-V) characteristics in metal-insulator-semiconductor structures exhibited anomalous frequency dispersion behavior and a hysteresis effect. The hysteresis in the C-V curve was found to be about 1 V and of a charge injection type. The density of interface states was about 1.79 x 10(12) cm(-2). The charge storage density was found to be 40 fC mu m(-2) at an applied electric field of 200 kV cm(-1). Studies on current-voltage characteristics indicated an ohmic nature at lower voltages and space charge conduction at higher voltages. The films also exhibited excellent time-dependent dielectric breakdown behavior.

Effect of magnetic field on the binding energy of a hydrogenic donor in a vertical bar z vertical bar(2/3) quantum well

We have calculated the binding energy of a hydrogenic donor in a quantum well with potential shape proportional to \z\(2/3) as a function of the width of the quantum well and the barrier height under an applied uniform magnetic field along the a axis. As the well width decreases, the binding energy increases initially up to a critical well width (which is nearly the same for all magnetic fields) at which there is a turnover. The results are qualitatively similar to those of a hydrogenic donor in a rectangular well. We have also calculated [rho(2)](1/2) and [z(2)](1/2) for the donor electron. [rho(2)](1/2) is found to be strongly dependent on the magnetic field for a given well width and weakly dependent on the well width and the barrier height, for a given value of magnetic field [z(2)](1/2) is weakly dependent on the applied magnetic field. The probability of finding the donor electron inside the well shows a rapid decrease as the well width is reduced at nearly the well width at which the binding energy shows a maximum.

Mössbauer effect and electron paramagnetic resonance studies on zinc borate glasses containing transition metal oxides

Studies have been carried out in glasses containing Fe2O3, V2O5, and Fe2O3 + V2O5. Mossbauer studies in the ZnO-B2O3-Fe2O3 system show that iron is present as Fe3+ with tetrahedral coordination and that the isomer shift and the quadrupole splitting decrease with increase of Fe2O3 Content; similarly, the isomer shift and quadrupole splitting are also found to decrease with increasing ZnO. On the other hand, in the Na2O-ZnO-B2O3-Fe2O3 system, the isomer shift increases with Na2O or ZnO while the quadrupole splitting is fairly insensitive. Electron paramagnetic resonance in the ZnO-B2O3-Fe2O3 system shows signals at g = 4.20 and 2.0, whose intensity and linewidth show strong dependence on Fe2O3 content. In the ZnO-B2O3-V2O5 system, electron paramagnetic resonance shows that vanadium is present as the vanadyl complex, and the hyperfine coupling constants, A(parallel-to) and A(perpendicular-to) decrease with increasing V2O5 content; on the other hand, g(parallel-to) decreases and g(perpendicular-to) increases slightly, indicating an increase in tetragonal distortion. Zinc borate glasses containing Fe2O3 + V2O5 do not show the hyperfine structure of V4+ due to the interaction between Fe3+ and V4+