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One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the α-phase Si(111)√3 × √3R30°-Bi at a low substrate temperature of 200 °C. Si films have been studied in situ by reflection electron energy loss spectroscopy (REELS) and Auger electron spectroscopy, as a function of the electron beam incidence angle α and low-energy electron diffraction (LEED), as well as ex situ by grazing incidence X-ray diffraction (GIXRD). Scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) were also reported. The REELS spectra, taken at the Si K absorption edge (~1.840 KeV), reveal the presence of two distinct loss structures attributed to transitions 1s→π* and 1s→σ* according to their intensity dependence on α, attesting to the sp2-like hybridization of the silicon valence orbitals in both thin and thick Si films. The synthesis of a silicon allotrope on the α-phase of Si(111)√3 × √3R30°-Bi substrate was demonstrated by LEED patterns and GIXRD that discloses the presence of a Si stack of 3.099 (3) Å and a √3 × √3 unit cell of 6.474 Å, typically seen for multilayer silicene. STM and STS measurements corroborated the findings. These measurements provided a platform for the new √3 × √3R30° Si allotrope on a Si(111)√3 × √3 R30°-Bi template, paving the way for realizing topological insulator heterostructures from different two-dimensional materials, Bi and Si.

One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the α-phase Si(111)√3 × √3R30°-Bi at a low substrate temperature of 200 °C. Si films have been studied in situ by reflection electron energy loss spectroscopy (REELS) and Auger electron spectroscopy, as a function of the electron beam incidence angle α and low-energy electron diffraction (LEED), as well as ex situ by grazing incidence X-ray diffraction (GIXRD). Scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) were also reported. The REELS spectra, taken at the Si K absorption edge (~1.840 KeV), reveal the presence of two distinct loss structures attributed to transitions 1

Defects in Two-Dimensional Materials addresses the fundamental physics and chemistry of defects in 2D materials and their effects on physical, electrical and optical properties. The book explores 2D materials such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMD). This knowledge will enable scientists and engineers to tune 2D materials properties to meet specific application requirements. The book reviews the techniques to characterize 2D material defects and compares the defects present in the various 2D materials (e.g. graphene, h-BN, TMDs, phosphorene, silicene, etc.). As two-dimensional materials research and development is a fast-growing field that could lead to many industrial applications, the primary objective of this book is to review, discuss and present opportunities in controlling defects in these materials to improve device performance in general or use the defects in a controlled way for novel applications. The present chapter is focused on "d elemental materials beyond graphene.

Spatial concentrations (or spatial clusters) of moving objects, such as vehicles and humans, is a mobility pattern that is relevant to many applications. Fast detection of this pattern and its evolution, e.g., if the cluster is shrinking or growing, is useful in numerous scenarios, such as detecting the formation of traffic jams or detecting a fast dispersion of people in a music concert. On-Line detection of this pattern is a challenging task because it requires algorithms that are capable of continuously and efficiently processing the high volume of position updates in a timely manner. Currently, the majority of approaches for spatial cluster detection operate in batch mode, where moving objects location updates are recorded during time periods of a certain length and then batch-processed by an external routine, thus delaying the result of the cluster detection until the end of the time period. Further, they extensively use spatial data structures and operators, which can be troublesome to maintain or parallelize in on-line scenarios. To address these issues, in this paper we propose DG2CEP, a parallel algorithm that combines the well-known density-based clustering algorithm DBSCAN with the data stream processing paradigm Complex Event Processing (CEP) to achieve continuous and timely detection of spatial clusters. Our experiments with real-world data streams indicate that DG2CEP is able to detect the formation and dispersion of clusters with small latency while having higher similarity to DBSCAN than batch-based approaches.

Carbon nanostructures are achieved by bio-waste Allium cepa, L., (onion vulgaris) peels through pyrolysis at 900 &deg, C. They contain dispersed elements derived by their bio-precursors, like Mg, Ca, S, Na, K, and Cu. Here, we report the self-assembly of new Cu flower-shaped nanostructures organized as nano-roses. Remarkably, the nano-roses show rolled-up petals of Cu0 with a high chemical stability in air, exhibiting an intrinsic pure Cu crystalline phase. This suggests the exceptional potentiality to synthesize Cu0 nanostructures with novel physical/chemical properties. The size, morphology, and chemical composition were obtained by a combination of high-resolution scanning electron microscopy, energy dispersive X-ray spectroscopy, energy dispersive X-ray diffraction, and Raman spectroscopy.

As the Internet of Things is expanding towards applications in almost any sector of our economy and daily life, so is the demand of employing and integrating devices with actuation capabilities, such as smart bulbs, HVAC,smart locks, industrial machines, robots or drones. Many middleware platforms have been developed in orderto support the development of distributed IoT applications and facilitate the sensors-to-cloud communication andedge processing capabilities, but surprisingly very little has been done to provide middleware-level, support andgeneric mechanisms for discovering the devices and their interfaces, and executing the actuation commands, i.e.transferring them to the device. In this paper, we present a generic support for actuation as an extension ofContextNet, our mobile-cloud middleware for IoMT. We describe the design of the distributed actuation supportand present a proof of working implementation that enables remote control of a Sphero mobile BB-8 toy.

The compelling experimental evidence of multilayer silicene synthesis on one monolayer of silver deposited on a silicon substrate, Si(111)√3 × √3-Ag, used as a template is reported. Auger electron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy/spectroscopy, in situ Raman spectroscopy, and energy-dispersive in-plane X-ray diffraction were applied to achieve the fingerprints of √3 × √3 multilayer silicene. Density functional theory calculations provided the structural models of single, bilayer, and three-layer silicene on the Si(111)√3 × √3-Ag surface. Single-layer silicene retains its free-standing form. The structural models, which are consistent with the experimental findings, feature atomic structure substantially different from that of Si(111).

In this chapter we give an overview on the theoretical and experimental investigations of one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) Si nanoribbons (SiNRs) formed on the anisotropic Ag(110) substrate surface. We start by introducing briefly free-standing silicene, a silicon layer with Si atoms arranged in honeycomb lattice, with hexagonal Si-rings as structural units. These hexagonal Si units are subsequently discussed as possible candidates to explain the atomic arrangement of the experimentally synthesized Si nanoribbons on Ag(110). This interpretation is supported by properties such as the presence of the 1D projection of the π and π* bands, forming the so-called “Dirac cones” at the K points of the Brillouin zone, the sp2-like nature of the Si valence orbitals, and the strong resistance against oxidation. Besides these results, the atomic structure as well as the origin of the electronic properties of these Si nanoribbons are still controversially debated in the literature. We address this discussion in the last part of the chapter before summarizing it.

Unmanned Aerial Vehicles (UAVs) are increasingly used as data collectors for Wireless Sensors Networks (WSN) on the ground. Most current research proposes optimizations for the itinerary creation of a single UAV. Our work, however, proposes a distributed algorithm for collecting WSN data using a dynamic set of UAVs. The algorithm takes into account the fact that UAVs could leave or join the group due to either recharging requirements or malfunctions. In our work we also consider the fact that UAVs only have medium-range communication capabilities (a few meters) in order to deliver collected data. Compared to the computationally costly and non-real-time Traveling Salesman Problem (TSP) approach, our algorithm delivers approximately 13% more efficient sensory visiting at certain scenarios without using the optimized tour.

Unmanned Aerial Vehicle (UAV) are increasingly used as data collectors for Wireless Sensors Networks (WSN) on the ground. Most of current research proposes optimizations for itinerary creation for a single UAV. Contrary to this, our work proposes a distributed algorithm for collecting WSN data using a dynamic set of UAVs, that takes into account that UAVs leave or join the group due to recharging or malfunctions. In our work, we consider that the UAVs only have medium-range communication capability (a few meters) to deliver collected data, similar to the assumptions in related work. Compared to the costly and non-real-time Traveling Salesman Problem (TSP)-approach our algorithm delivers approximately 3% more efficient sensor visiting on certain scenarios without using the optimized tour.

The compelling experimental evidence of multilayer silicene synthesis on one monolayer of silver deposited on a silicon substrate, Si(111)?3 × ?3-Ag, used as a template is reported. Auger electron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy/spectroscopy, in situ Raman spectroscopy, and energy-dispersive in-plane X-ray diffraction were applied to achieve the fingerprints of ?3 × ?3 multilayer silicene. Density functional theory calculations provided the structural models of single, bilayer, and three-layer silicene on the Si(111)?3 × ?3-Ag surface. Single-layer silicene retains its free-standing form. The structural models, which are consistent with the experimental findings, feature atomic structure substantially different from that of Si(111).

Mn0.06Ge0.94 samples have been grown by molecular-beam epitaxy on Ge(001)2 x 1. High-resolution transmission electron microscopy shows the coexistence of an ordered diluted Mn0.06Ge0.94 film and of nanoscopic crystallites, which were identified as Mn5Ge3 by electron diffraction. The magnetic properties of the Mn0.06Ge0.94 samples show a superposition of a paramagnetic behavior, due to the interaction of Mn atoms diluted in the Ge host, and a ferromagnetic behavior attributed to the Mn5Ge3 crystallites dispersed into the films. The Mn L-2.3 X-ray absorption spectra of the Mn0.06Ge0.94 films exhibit a lineshape typical of metallic Mn, with considerably reduced multiplet structure. (C) 2006 Elsevier B.V. All rights reserved.

A new procedure is presented for-determining in situ the solar calibration constant, i.e., the Sun-sky radiometer counts for a direct normal solar flux extrapolated to the top of the atmosphere. The method makes use of a modified version of the Langley plot based on the use of an inversion code of column-integrated aerosol size distribution, and it is ordinarily applied to calibrate Prede Sun-sky radiometers. To analyze how such an in situ method can work accurately, the technique has been applied to a five-month dataset obtained from measurements taken in Rome, Italy, by a Prede Sun-sky radiometer from 22 April to 5 November 2001. The precision of the in situ method has been estimated to within 1-2.5%, depending on the wavelength. © 2004 Optical Society of America.

International audience; Thick epitaxial multilayer silicene films with a root 3 x root 3R(30 degrees) surface structure show only mild surface oxidation after 24 h in air, as measured by Auger electron spectroscopy. X-ray diffraction and Raman spectroscopy measurements performed in air without any protective capping, as well as, for comparison, with a thin Al2O3 cap, showed the (002) reflection and the G, D and 2D Raman structures, which are unique fingerprints of thick multilayer silicene.

The growth of Mn nanostructures on a 1D grating of silicon nano-ribbons is investigated at atomic scale by means of scanning tunneling microscopy, low energy electron diffraction and core level photoelectron spectroscopy. The grating of silicon nano-ribbons represents an atomic scale template that can be used in a surface-driven route to control the combination of Si with Mn in the development of novel materials for spintronics devices. The Mn atoms show a preferential adsorption site on silicon atoms, forming one-dimensional nanostructures. They are parallel oriented with respect to the surface Si array, which probably predetermines the diffusion pathways of the Mn atoms during the process of nanostructure formation. © 2013 IOP Publishing Ltd.

Multilayer silicene, the silicon analogue of multilayer graphene, grown on silver (111) surfaces, possesses a honeycomb (√3 × √3)R30° reconstruction, observed by scanning tunnelling microscopy at room temperature, past the initial formation of the dominant, 3×3 reconstructed, silicene monolayer. For a few layers silicene film we measure by synchrotron radiation photoelectron spectroscopy, a cone-like dispersion at the Brillouin zone centre due to band folding. π* and π states meet at ∼0.25 eV below the Fermi level, providing clear evidence of the presence of gapless Dirac fermions.

Densely packed epitaxial Mn-doped Si(0.3)Ge(0.7) nanodots self-assembled on Si(100) have been obtained. Their structural properties were studied using reflection high-energy electron diffraction, energy dispersive x-ray diffraction, atomic force microscopy, extended x-ray absorption fine structure measurements and high-resolution transmission electron microscopy. Mn(5)Ge(1)Si(2) crystallites embedded in Si(0.3)Ge(0.7) were found. They exhibit a ferromagnetic behaviour with a Curie temperature of about 225 K.

The synthesis of silicene, graphene-like silicon, has generated very strong interest. Here, we reveal the growth of high aspect ratio, perfectly straight, and aligned silicon nanoribbons, exhibiting pyramidal cross section. They are multistacks of silicene and show in angle-resolved photoemission cone-like dispersion of their π and π* bands, at the X[overline] point of their one-dimensional Brillouin zone, with Fermi velocity of ~1.3 × 10(6) m sec(-1), which is very promising for potential applications.

Through this review we can follow the various phases that have led to the discovery of the new allotrope form of silicon: silicene. This is a one-atom thick silicon sheet arranged in a honeycomb lattice, similar to graphene. For silicon, which usually is sp3 hybridized, it represents an unusual and rare structure. First, silicene was theoretically hypothesized and subsequently its structure calculated as a possible candidate for nano-ribbons of Si grown on the anisotropic Ag(110) surface. It was only later, when the physical and chemical properties of this peculiar form of silicon, demonstrating the presence of π and π* bands giving the so-called Dirac cones at the K corners of the Brillouin zone, the sp2-like nature of the valence orbitals of the Si–Si bonds and its strong resistance towards oxygen were reported, that the real existence of silicene became recognized in the scientific community. This review is essentially focused on the experimental work performed on 1D isolated silicene nano-ribbons and their 1D dense array grown on Ag(110) surfaces.

International audience; An investigation of the structural, magnetic and electronic properties of ≈ 3 nm thick Mn5Ge3 films epitaxially grown on a Ge(1 1 1)-c(2 × 8) reconstructed surface is reported. High resolution transmission electron microscopy and selected area electron diffraction give evidence of 2.2% in-plane compressive strain between the Mn5Ge3 film and the Ge substrate. Magnetooptical Kerr effect measurements show that the films are ferromagnetic with a Curie temperature of ≈ 325 K. The analysis of Ge 3d core level photoelectron spectra of the Mn5Ge3 films allows determining an upper limit of 76 meV for the Ge 3d5/2 core-hole lifetime broadening. The Ge 3d3/2 core-hole lifetime broadening is found to be 15 meV larger than that of the Ge 3d5/2 core hole, because of the existence of a Coster–Kronig decay channel due to the metallic character of Mn5Ge3.

Silicene, the new allotropic form of silicon, represents an interesting promise for future new nanostructured materials. Here, we investigate the room temperature oxidation of a one-dimensional grating of silicene nanoribbons grown on a Ag(1 1 0) surface by high-resolution Si 2p core level photoemission spectroscopy and low-energy electron diffraction observations. The oxidation process starts at very high oxygen exposures, about 104 times higher than on the clean Si(1 1 1)7 × 7 surface, which demonstrates the low reactivity of silicene to molecular oxygen. Ar+sputtering produces defects, which enhance the oxidation uptake.

Natural hybrid organic–inorganic photovoltaic devices based on TiO2 have been realized. Chlorophyll A (from anacystis nidulans algae), chlorophyll B (from spinach), carmic acid (from insect Coccus cacti L.), synthetic trans- β -carotene, natural fresh picked Morus nigra, and their mixtures have been used as an organic photo active layer to fabricate photovoltaic prototypes. In order to reduce the charge’s interfacial recombination, different thicknesses (5–45 nm) of Si layers, subsequently oxidized in air, were inserted between the TiO2 and chlorophyll B. Scanning electron microscopy of TiO2 and Si/TiO2 systems shows the coexistence at least of four classes of nanoparticles of 60, 100, 150 and 250 nm in size. Auger electron spectroscopy of the Si L2,3V V transition demonstrates the presence of silica and SiOx suboxides. Photocurrent measurements versus radiation wavelength in the range 300–800 nm exhibit different peaks according to the absorption spectra of the organic molecules. All realized photovoltaic devices are suitable for solar light electric energy conversion. Those made of a blend of all organic molecules achieved higher current and voltage output. The Si/TiO2-based devices containing chlorophyll B exhibited an enhanced photocurrent response with respect to those with TiO2 only.

The problems encountered in the elaboration of measurements of direct and sky diffuse solar irradiance are the following: (1) to carry out the calibration for the direct irradiance, which consists in determining the direct irradiance at the upper limit of the atmosphere; (2) to carry out the calibration for the diffuse irradiance, which consists in determining the solid viewing angle of the sky radiometer; (3) to determine the input parameters, namely, ground albedo, real and imaginary parts of the aerosol refractive index, and aerosol radius range; and (4) to determine from the optical data the columnar aerosol optical depth and volume radius distribution. With experimental data and numerical simulations a procedure is shown that enables one to carry out the two calibrations needed for the sky radiometer, to determine a best estimate of the input parameters, and, finally, to obtain the average features of the atmospheric aerosols. An interesting finding is that inversion of only data of diffuse irradiance yields the same accuracy of result as data of both diffuse and direct irradiance; in this case, only calibration of the solid viewing angle of the sky radiometer is needed, thus shortening the elaboration procedure. Measurements were carried out in the Western Mediterranean Sea (Italy), in Tokyo (Japan), and in Ushuaia (Tierra del Fuego, Argentina); data were elaborated with a new software package, the Skyrad code, based on an efficient radiative transfer scheme. © 1999 Optical Society of America.

Silicon oxide nanowires hold great promise for functional nanoscale electronics. Here, we investigate the oxidation of straight, massively parallel, metallic Si nanowires. We show that the oxidation process starts at the Si NW terminations and develops like a burning match. While the spectroscopic signatures on the virgin, metallic part, are unaltered we identify four new oxidation states on the oxidized part, which show a gap opening, thus revealing the formation of a transverse internal nanojunction.

In the quest of nano-objects for future electronics, silicon nanowires could possibly take over carbon nanotubes. Here we show the growth by self-organization of straight, massively parallel silicon nanowires having a width of 1.6 nm, which are atomically perfect and highly metallic conductors. Surprisingly, these silicon nanowires display a strong symmetry breaking across their widths with two chiral species that self-assemble in large left-handed and right-handed magnetic-like domains.

International audience; We investigated the structural and magnetic properties of MnxGe1−x, with 0.02 ⩽ x ⩽ 0.1. The MnxGe1−x samples were grown on Ge(0 0 1)2 × 1 by molecular beam epitaxy, at a substrate temperature of 520 K. The samples were characterized in situ by reflection high-energy electron diffraction and ex situ by high-resolution transmission electron microscopy, energy dispersive X-ray reflectivity and magneto-optical Kerr effect. From microscopy images we evidenced on all samples the presence of Mn5Ge3 nanocrystallites in addition to the MnxGe1−x diluted magnetic semiconductor with an estimated Mn concentration x ≈ 1.5%. The size and the density of the Mn5Ge3 precipitates were found to increase with increasing the Mn concentration x. Magnetic analysis showed ferromagnetism with a Curie temperature of 280 K for all samples.

International audience; Research on diluted magnetic semiconductors (DMS) has generated great interest for their potential application of semiconductors-based magnetic elements. Ferromagnetic (FM) semiconductors simultaneously exhibit semiconducting properties and spontaneous long-range FM order. The coexistence of these properties in a single material provides fertile ground for both fundamental studies and industrial applications. However, device applications have languished because of low magnetic ordering (Curie) temperature and the inability to incorporate these materials in conventional semiconductor material device. In this context, we have focused our study on structural and magnetic properties of MnxGe1−x DMS layers grown by molecular beam epitaxy on semiconducting Ge(1 1 1) substrate. Mn has been incorporated with increasing concentration from x = 0.02 to 0.1. Their structure has been characterized by transmission electron microscope using both conventional imaging and electronic diffraction. Ge–Mn alloy clusters have been clearly observed for the highest Mn concentration, and alloy phase identified. These observations were completed by classic SQUID magnetometry measurements. We will evidence a critical concentration of Ge above which precipitates of Ge3Mn5 form, enhancing the FM signal in the layer.

We studied morphological and magnetic properties of Ge/MnxGe1-x/Ge(0 0 1)2 x 1, x = 0.02-0.04. Several MnxGe1-x alloys were grown on Ge(0 0 1)2 x I by molecular beam epitaxy, as a function of substrate temperature and Mn concentration. The samples were characterized in situ by RHEED, and ex situ by energy dispersive X-ray reflectivity (EDXR) and magneto-optical Kerr effect, (MOKE). From RHEED analysis we found an optimal growth temperature T-epi = 523 K to achieve 2D epitaxial MnxGe1-x (x = 0.02-0.04) alloy on a Ge(001) substrate. X-ray reflectivity measurements provided: the film roughness, the MnxGe1-x scattering length density, and the average thickness for all samples. MOKE analysis showed ferromagnetism with Curie temperature T-C = 270 K for samples grown at T-epi = 523 K. (c) 2006 Elsevier B.V. All rights reserved.

Structural and magnetic properties of Ge 1-x mn x alloys, epitaxially grown on a Ge(001)2 x 1 surface have been investigated. We prepared Ge 1-x mn x films by MBE as a function of substrate temperature and Mn concentration x. In-situ RHEED was used to monitor the streaks of the Ge 1-x mn x epitaxial films. The optimal temperature, to obtain a very well-ordered epitaxial Ge 1-x mn x alloy, for Mn concentrations of x = 0.02, and x = 0.04, was found to be 525 K. Ex-situ magneto-optical Kerr effect and XMCD at the L 2/3 Mn2p absorption edges on Ge 1-x Mn x films, show isotropic magnetic properties. The Curie temperature of about 270 K was found on most of the ordered samples.

We investigated the electronic structure of ultra thin interface of organic titanium bis-phthalocyanine TiPc 2 deposited on InAs(001)(4 x 2)c-(8 x 2) clean surface, by means of high-resolution core-levels and valence band (VB) photoelectron spectroscopies. In4d, As3d, and Cls core levels were measured for different TiPc 2 thicknesses up to 1 monolayer. Surface core level shifts were found on both In4d andAs3d core levels. These shifts originate from the interaction between 4 x 2-c(8 x 2) InAs reconstruction and organic molecules suggesting the presence of strong bounds. C1 core level exhibits a line shape attributed to the C-C and C-N bonds. The VB spectroscopy shows dramatic changes related to the interaction of the TiPc 2 molecule with the InAs related surface states.

Most inversion algorithms used to retrieve the aerosol characteristics from ground-based solar radiation measurements, assume a vertically homogeneous atmosphere and constant aerosol optical characteristics over the whole air column. This assumption leads to correct results only if the extinction of the solar radiation incident on the earth surface depends on the mean optical characteristics of the entire atmospheric column, rather than on the details of the vertical distribution of air particles. The validity of this simplifying assumption is an issue of a certain importance, which requires a more definite answer based on observational evidence. The aerosol vertical profile is significantly affected by the extent of the atmospheric boundary layer, within which the physical properties of the suspended particulate matter show sharp variations. Therefore, if the above assumption were not correct, one should observe a significant correlation between the retrieved optical characteristics and the thickness of the boundary layer measured on the same site over time. In this paper we limit ourselves to study the possible correlations between the aerosol volume size distributions and the mixing height of the atmospheric boundary layer, in order to ascertain whether there exists any dependence between the volume size distributions and the vertical distribution of the aerosol, in a site where there are strong reasons to believe that most of the existing aerosol is confined below the mixing height level. The investigation is based on a dataset of measurements taken at the Southern Great Plains base station of the ARM Program, located in Oklahoma, USA. Measurements of the columnar aerosol characteristics are taken by means of a Cimel sun-sky radiometer of the Aeronet network, while vertical profiles of pressure and temperature, used for the determination of the height of the boundary layer, are taken by vertical sounding systems. In order to find a possible relationship between the columnar aerosol size distribution and the depth of the boundary layer, a statistical analysis has been carried out on this data. The analysis has not shown any significant correlation between those two parameters. This negative result supports the validity, for the Southern Great Plains site, of the assumption that the radiation incident on the earth surface depends only on the mean optical characteristics of the entire atmospheric column, rather than on the details of the aerosol vertical distribution. © 2003 Elsevier Ltd. All rights reserved.

Measurements of sky radiation concern direct solar flux F and diffuse sky flux E; they are used for deriving optical and physical features of the atmospheric aerosols. Sky radiation is measured by the sky-radiometer (a photometer with interferential filters annexed for the selection of the wavelengths at which to operate) and a pointing system. The wavelengths are usually selected within the main atmospheric windows, in order to reduce the radiative transfer problem to a pure scattering problem; the sky radiometer used in the authors' research program operates at 0.369, 0.500, 0.675, 0.776, 0.862 and 1.048 /spl mu/m. Measurements are usually carried out pointing along a conical surface with the same zenith angle of the Sun, or along a plane with the same azimuthal angle. The two quantities considered in their scheme of data elaboration are the direct solar flux F and the ratio R between the diffuse and the direct flux. The authors propose a procedure of calibration based on experimental data concerning both direct and diffuse radiation. A retrieval of only R data is performed for all the available measurements.

Sequential measurements of direct and diffuse solar radiation for each scattering angle in the visible and near infrared region, were carried out with the ground based sun-sky radiometer Prede, in order to determine directly in situ the instrumental errors. The sensitivity of the code Skyrad 3, produced by T. Nakajima, to the experimental errors has been studied in this work. The uncertainty on the retrieved columnar aerosol volume distribution, aerosol optical thickness, single scattering albedo, and phase function, was obtained for each wavelength. Measurements were taken in two locations with very different atmospheric characteristics: Antarctica and Rome, Italy. The method used for the determination of experimental error showed to give good results, independently of the location. The uncertainties obtained for the quantities retrieved by Skyrad 3, are independent of the atmospheric turbidity and, possibly, they can be assumed as general accuracy levels.

In order to investigate the influence of the atmospheric aerosol on the ultraviolet radiation on earth, the measurement campaign Photochemical Activity and Ultraviolet Radiation (PAUR II) Modulation was carried out in the central Mediterranean Sea during the period May-June 1999. Two sites were chosen for measurements: the island of Crete (Greece), and the island of Lampedusa (Italy). The aerosol features over the Lampedusa island, as well as the dust coming from Sahara desert, were investigated by measurements of direct and diffuse solar irradiance carried out with an aureolemeter. The columnar volume size distributions of the aerosol showed a four-modal shape in a less turbid atmosphere when the aerosol optical depth was less than 0.2 at ?=500nm, and a tri-modal shape in a turbid atmosphere when the aerosol optical depth at the same wavelength was greater than 0.5; the background aerosol turned out to be mainly composed of sea salt. The increase of the aerosol optical depth and of the particles density with radius about 1?m has been found to be strictly related to the passage of Saharan dust in the time periods 14-22 May and 1-3 June, 1999. The columnar volume of particles obtained by the aureolemeter has been compared with the columnar volume of particles retrieved by in situ measurements carried out with a forward scattering spectrometer probe (FSSP) aboard a light aircraft flying over the island. Although the above two techniques refer to aerosol columns of different height and operate with different resolutions, their relevant results are in good agreement, especially during days with lower aerosol content. The two volume radius distributions have been also compared and their behaviours show a satisfactory agreement, mainly for particles with radius greater than 1?m. Copyright © 2001 Elsevier Science Ltd.