Measurements of atmospheric electricity aloft

Measurements of the electrical characteristics of the atmosphere above the surface have been made for over 200 years, from a variety of different platforms, including kites, balloons, rockets and aircraft. From these measurements, a great deal of information about the electrical characteristics of the atmosphere has been gained, assisting our understanding of the global atmospheric electric circuit, thunderstorm electrification and lightning generation mechanisms, discovery of transient luminous events above thunderstorms, and many other electrical phenomena. This paper surveys the history of atmospheric electrical measurements aloft, from the earliest manned balloon ascents to current day observations with free balloons and aircraft. Measurements of atmospheric electrical parameters in a range of meteorological conditions are described, including clear air conditions, polluted conditions, non-thunderstorm clouds, and thunderstorm clouds, spanning a range of atmospheric conditions, from fair weather, to the most electrically active

EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon

Electron paramagnetic resonance (EPR) measurements have been made of amorphous hydrogenated carbon (a-C:H) films grown by plasma enhanced chemical vapor deposition (PECVD) with negative self-bias voltages Vb in the approximate range 10-540 V. For Vb100 V the linewidth is shown to be dominated by the dipolar interactions and exchange and it decreases as Vb increases; the change is shown to arise primarily from a change in the exchange interaction. Evidence for this comes from measurements which show that the spin-lattice relaxation time appreciably shortens and the spin-spin relaxation time lengthens as the bias voltage is increased. The magnitude and variation with bias of the linewidth are consistent with the EPR signal originating from the π-type radicals. ©2000 The American Physical Society

Purity and solubility of nanotubes in arc discharge carbon powder

We have described a novel experimental technique to separate nanotubes from other unwanted carbon species in arc generated carbon soot. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble while extraneous carbon material formed a sediment at the bottom of the sample bottle. This process was monitored using electron paramagnetic resonance (EPR) which showed that 63% of nanotubes were kept in solution while 98.1% of impurities were rejected. This allowed the calculation of the nanotube content in the carbon soot using EPR and thermo-gravitational analysis (TGA) yielding a purity value of 34% for the soot used in this study. This is compatible with estimates made using electron microscopy

Electron delocalization in amorphous carbon by ion implantation

The electrical properties of amorphous carbon are governed by the high localization of the sp π states, and conventional methods of altering the sp content result in macroscopic graphitization. By using ion beams we have achieved a delocalization of the π states by introducing nanoclustering and hence improving the connectivity between existing clusters, as demonstrated by the increase in the conductivity by two orders of magnitude without modification of the band gap. At higher doses, paramagnetic relaxation-time measurements indicate that exchange effects are present. This unveils the possibility of amorphous carbon-based electronics by tailoring the ion-beam conditions, which we demonstrate in the form of a rectifying device

Purity and solubility of nanotubes in arc discharge carbon powder

We have described a novel experimental technique to separate nanotubes from other unwanted carbon species in arc generated carbon soot. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble while extraneous carbon material formed a sediment at the bottom of the sample bottle. This process was monitored using electron paramagnetic resonance (EPR) which showed that 63% of nanotubes were kept in solution while 98.1% of impurities were rejected. This allowed the calculation of the nanotube content in the carbon soot using EPR and thermo-gravitational analysis (TGA) yielding a purity value of 34% for the soot used in this study. This is compatible with estimates made using electron microscopy

Electron paramagnetic resonance of erbium doped silicon

Electron paramagnetic resonance measurements have been made on samples of float zone silicon, implanted with 10^15 Er/cm2. One sample was coimplanted with oxygen to give an impurity concentration of 10^20 O/cm3 and 10^19 Er/cm3. In this coimplanted sample, sharp lines are observed which are identified as arising from a single spin 1/2 Er3+ center having a g tensor exhibiting monoclinic C1h symmetry. The principal g values and tilt angle are g1=0.80, g2=5.45, g3=12.60, and τ=2.6°. In the absence of O, the sharp lines are not observed. No Er3+ cubic centers were detected in either sample. Possible structures for the center are discusse

Electron paramagnetic resonance and photoluminescence study of Er-impurity complexes in Si

Electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy have been used to examine the structure and optical properties of erbium-impurity complexes formed in float-zone Si by multiple-energy implants at 77 K of Er together with either O or F. After implantation a 2-μm-thick amorphous layer was formed containing an almost uniform concentration of Er (1019/cm3)and O (3×1019/cm3 or 1020/cm3) or F (1020/cm3). Samples were annealed in nitrogen at 450 °C for 30 min (treatment A), treatment A+620 °C for 3 h (treatment B), treatment B+900 °C for 30 s (treatment C) or treatment B+900 °C for 30 min (treatment D). Samples coimplanted to have 3×1019O/cm3 and subject to treatment C show a broad line anisotropic EPR spectrum. These samples have the most intense low-temperature PL spectrum containing several sharp peaks attributed to Er3+ in sites with predominantly cubic Td symmetry. Increasing the O concentration to 1020/cm3 produces sharp line EPR spectra the strongest of which are attributed to two Er3+ centers having monoclinic C1h and trigonal symmetry. The principal g values and tilt angle for the monoclinic centers are g1=0.80, g2=5.45, g3=12.60, τ=57.3°, g∥=0.69, and g⊥=3.24 for the trigonal centers. The low-temperature PL spectrum from this sample showed additional sharp lines but the total intensity is reduced when compared to the sample with 3×1019O/cm3. For the sample containing 1020O/cm3 at least four distinct centers are observed by EPR after treatment B but after treatment D no EPR spectrum is observed. The PL spectra are also observed to change depending on the specific anneal treatment but even after treatment D, Er-related PL is still observed. Samples containing 1020F/cm3 and annealed with either treatment B or C produced an EPR spectrum attributed to Er3+in a site of monoclinic C1h symmetry with g1=1.36, g2=9.65, g3=7.91, and τ=79.1°.Tentative models for the structures of Er-impurity complexes are presented and the relationship between the EPR-active and PL-active centers is discussed