Traceable size measurements of nanoparticles are accomplished by means of a calibrated scanning electron microscope operated in transmission mode (TSEM). An image analysis tool was developed which individually determines the boundary and size of every particle based on modelled TSEM signals obtained by Monte Carlo simulations. The model relies on first-principle electron scattering theory taking into account particle and instrument properties. A series of TSEM images containing thousands of particles can be analysed in automated batch processing to attain a particle size distribution. As examples, nanoparticles of three different material classes (gold, silica, latex) with sizes ranging from about 5 to 60 nm are analysed. An uncertainty analysis reveals expanded measurement uncertainties (95% confidence interval) of the mean diameter in the range of 1 to 3 nm.

A field experiment combined with numerical studies provides a better understanding of the area-averaged evaporation and leads to improved parameterization schemes.

Abstract. The millimeter and sub-millimeter waves have been attracting a lot of attention recently in the cloud remote sensing community. This is largely because of their potential use in measuring cirrus cloud parameters with airborne or space-borne radiometers. In this study, we examine the possibility of using polarization measurements in this frequency range to get information on the microphysical properties of cirrus clouds. By using a simple radiative transfer model, we calculated the brightness temperature differences at the vertical and horizontal polarization channels for the following seven frequencies: 90, 157, 220, 340, 463, 683, and 874 GHz. The ice crystals in cirrus clouds are modeled with nearly spherical particles, circular cylinder, and circular plate, as well as with mixtures of these types. We found that the polarization difference signal shows a unique "resonance" feature with the change of ice particle characteristic size: it has a strong response only in a certain range of ice particle size, beyond that range it approaches zero. The size range where this resonance happens depends to a large extent on particle shape and aspect ratio, but to a much less extent on particle orientation. This resonance feature appears even when ice clouds are composed of a mixture of ice crystals in different shapes, although the magnitude and the position of the resonance peak may change, depending on how the mixture is made. Oriented particles generally show larger polarization difference than randomly oriented ones, and plates have larger polarization difference than cylinders. However, the state of particle orientation has a significantly stronger effect on the polarization difference than the particle shape (cylinder or plate). This makes it difficult to distinguish particle shapes using millimeter and sub-millimeter radiometric measurements, if there is no information available on particle orientations. However, if the state of particle shape mixCorrespondence to: J. Miao (jmiao@uni-bremen.de) ture can be predetermined by other approaches, polarization measurements can help to determine ice particle characteristic size and orientation. This information, in turn, will benefit our retrieval of the ice water path of cirrus clouds.

The fabrication of metallic single-walled carbon nanotube electrodes separated by gaps of typically 20 nm width by electron-beam-induced oxidation is studied within an active device configuration. The tube conductance is measured continuously during the process. The experiment provides a statistical evaluation of gap sizes as well as the electron dose needed for gap formation. Also, the ability to precisely cut many carbon nanotubes in parallel is demonstrated.

The extreme climate conditions and the sparse number of research stations in Antarctica limit the number of meteorological records over this area. Satellite radiometric measurements and ground-based GPS measurements can therefore improve the amount of available water vapour information.Combining the Zenith Total Delay (ZTD) time series from 6 Antarctic GPS stations and surface meteorological data, we have determined Precipitable Water Vapour (PW) variations with a 2-hour temporal resolution for a period of 5 years. Data from the Advanced Microwave Sounding Unit (AMSU-B) on board the NOAA-15 satellite cover most parts of Antarctica but with observations limited to merely few times a day. GPS and AMSU-B data sets are therefore complementary with respect to time and space.We present a cross validation between PW results from the two independent retrieval algorithms using one year data. Additionally, we compare the observed PW from AMSU-B and GPS with the National Centre for Environmental Prediction (NCEP) reanalysis. All three data sets are highly correlated. The mean differences between the three data sets are station dependent and vary from À1.7 to þ1.2 mm. A large part of the bias may result from pressure uncertainties affecting the GPS PW estimates. GPS and AMSU-B as independent data sources are confirmed to be accurate methods for PW estimation for the dry Antarctic atmosphere. PW results from the NCEP analysis corresponds, in general, well to the PW observations at the investigated stations along the Antarctic coast. The results obtained at the station O'Higgins differ from those of the other station. O'Higgins is located at the Antarctic Peninsula and has a more humid environment than the coast of the main Antarctic continent, which may explain the peculiar behaviour of this station.