Graphitic Carbon Particles Research Articles

Towards automatic electron tomography

Electron microscope control, that allows the automatic recording of tilt series for the 3D reconstruction of individual objects, has been realized. The experimental set-up includes a 200 kV TEM equipped with a 1K x 1K CCD camera, both controlled externally by a fast dedicated image-processing computer. For the goniometer control an accurate electronic readout of the tilt angle and a board driving the goniometer motor have been installed. For low-dose imaging, three to five different specimen areas are used: one (or two) for the determination of object displacements during tilting, one (or two) for autofocusing, and another one for recording the tilt series to be used for the 3D reconstruction. Tilt series can be recorded with a rather low total dose, the lower limit being set by the requirement that subsequent projection images have to be aligned by means of cross-correlation functions. The method has been tested with graphitized carbon particles on carbon film and with negatively stained proteasomes from the archaebacterium Thermoplasma acidophilum. Some future developments towards fully automatic electron tomography are discussed.

Dust Condensation in the Ejecta of SN 1987A

AbstractAn asymmetry of optical emission lines that appeared in Sept. 1988 is interpreted as evidence of dust condensation within the metal-rich ejecta of SN 1987A. A quantitative analysis of this spectroscopic effect is given and shown to be compatible with the photometric record. Moreover, observational and theoretical estimates of the bolometric light curve come into agreement when the far-IR excess is interpreted as thermal emission by grains in the ejecta. A grain population comprising small silicate grains with an admixture of graphite or amorphous carbon particles is suggested by the data. The relevance of this discovery to suggestions that supernovae are major sources of interstellar dust is briefly discussed.

Role of graphitic carbon particles in radiative transfer in the arctic haze

Large concentrations of combustion-generated graphitic carbon particles have been identified at ground level and at altitude in the Arctic atmosphere. Concentrations of these particles during certain times of year and at certain altitudes are comparable to those in urban centers in the United States. These graphitic particles, which have a structure similar to carbon black, have been identified on a molecular level using Raman spectroscopy at sites in the Alaskan, Canadian, and Norwegian Arctic. The black particles are very effective absorbers of solar radiation and can lead to significant heating effects, depending primarily on their distribution in time and space. Recent measurements from an airplane indicate that high concentrations of graphitic particles occur throughout the Arctic troposphere, and at certain altitudes the concentrations can be significantly higher than at ground level. The implications of these results to radiative transfer will be discussed.

Role of combustion‐generated carbon particles in the absorption of solar radiation in the Arctic haze

We have studied the vertical distributions of combustion‐generated graphitic carbon particles and their associated absorption coefficients in the Arctic. These distributions show substantial concentrations of graphitic particles throughout the Arctic troposphere. Vertical profiles in the Norwegian Arctic can show both a strongly layered structure and an almost uniform distribution. Concentrations of graphitic particles within layers can be as large as those found in typical urban areas in the United States. The absorption optical depths associated with these vertical profiles are large enough to cause a substantial change in the solar radiation balance over a highly reflecting surface.

Combustion-generated carbon particles in the Arctic atmosphere

Recent studies in the Alaskan Arctic1–3 show the presence of substantial concentrations of carbon- and sulphur-containing particles that seem to be characteristic of the Arctic region as a whole4–6. These particles are effective scatterers and absorbers of visible radiation3,7 and appear to be responsible for the phenomenon of Arctic haze first reported by Mitchell8. On the basis of trace element analysis, it has been suggested that these particles originate from anthropogenic sources at mid-latitudes1,4. Direct substantiation of combustion-generated particles in the Arctic atmosphere has been provided by the identification of large concentrations of graphitic carbon particles at the GMCC–NOAA (National Oceanic and Atmospheric Administration) observatory near Barrow, Alaska, using Raman spectroscopy3. We report here on an extension of our studies of carbon particles in the Alaskan Arctic to the Canadian Arctic and the Norwegian Arctic. These studies, using the Raman scattering technique, identify substantial concentrations of graphitic carbon particles at ground-level stations throughout the western Arctic.

Direct observation of the tetrahedral bonding in graphitized carbon black by high resolution electron microscopy

Morphology of extremely small particles of graphitized carbon which were found in amorphous carbon films prepared by vacuum deposition has been studied by high resolution electron microscopy. Morphology of single layers of the graphite-like structure that were occasionally formed inside the particles suggests that the bending of the layers should be caused by the carbon atoms having the tetrahedral bonds. Occurrence of the tetrahedral bonds in the graphitized carbon particles is discussed.