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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 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.

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.

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).

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.

The majority of fatal car crashes are caused by reckless driving. With the sophistication of vehicle instrumentation, reckless maneuvers, such as abrupt turns, acceleration, and deceleration, can now be accurately detected by analyzing data related to the driver-vehicle interactions. Such analysis usually requires very specific in-vehicle hardware and infrastructure sensors (e.g. loop detectors and radars), which can be costly. Hence, in this paper, we investigated if off-the-shelf smartphones can be used to online detect and classify the driver’s behavior in near real-time. To do so, we first modeled and performed an intrinsic evaluation to assess the performance of three outlier detection algorithms formulated as a data stream processing network which receives as input and processes data streams of smartphone and vehicle sensors. Next, we implemented a novel scoring mechanism based on online outlier detection to quantitatively evaluate drivers’ maneuvers as either cautious or reckless. Thus, we adapted a data mining mechanism which takes into account a sensor’s data rates and power to determine driver behavior in the scoring process. Finally, as the intrinsic evaluation does not necessarily reveal how well an algorithm will perform in a real-world scenario, we evaluated the algorithm that achieved the best result in a real-world case study to assess drivers’ driving behavior. Our results indicate that the algorithm performs quickly and accurately; the algorithm classifies driver behavior with 95.45% accuracy. Moreover, such results are obtained within 100 milliseconds of processing time on average.

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.

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.

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.

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.

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.

Silicon atoms deposited on Ag(111) produce various single layer silicene sheets with different buckling patterns and periodicities. Low temperature scanning tunneling microscopy reveals that one of the silicene sheets, the hypothetical √7 × √7 silicene structure, on 2√3 × 2√3 Ag(111), is inherently highly defective and displays no long-range order. Moreover, Auger and photoelectron spectroscopy measurements reveal its sudden death, to end, in a dynamic fating process at ∼300 °C. This result clarifies the real nature of the 2√3 × 2√3R(30°) silicene phase and thus helps to understand the diversity of the silicene sheets grown on Ag(111).

We present expressions for the resonant magnetic X-ray scattering (XRMS) by surfaces possessing roughness and analyze both the structural and magnetic roughness of a surface, as well as their correlation. We demonstrate that the leading contribution to the difference (DI) in the diffuse scattering between left- and right-circularly polarized light for a rough surface vanishes unless the structural and magnetic roughnesses are correlated, to leading order in the magnetization. The effects of magnetic domain structure and magnetic dead layers on the surface scattering are also discussed.

We report on the electronic properties of straight, 1.6 nm wide, silicene nanoribbons on Ag(110), arranged in a one-dimensional grating with a pitch of 2 nm, whose high-resolution scanning tunneling microscopy images reveal a honeycomb geometry. Angle-resolved photoemission shows quantum confined electronic states of one-dimensional character. The silicon band dispersion along the direction of the nanoribbons suggests a behavior analogous to the Dirac cones of graphene on different substrates.

Combined experiments on the aerosol properties were carried out with a solar aureolemeter, a Sun photometer, three aerosol cascade impactors, and the satellite advanced very high resolution radiometer data, in Cagliari and Carloforte, southern Sardinia, in May and June 1994. The experimental data of the aureolemeter, which operates in the wavelength range from the UV to the near-IR, are analyzed in this paper. The equivalent refractive index of the aerosol particles and the equivalent ground albedo are derived with the inversion library method. With the equivalent refractive index and the equivalent ground albedo, the optical properties of the aerosols, such as the size distribution, the optical thickness, and the single-scattering phase function are retrieved by an updated code, which employs a radiative intensity transfer algorithm and a nonlinear iterative inversion procedure. The columnar aerosols detected in this region have a trimodal size distribution with the volume mode radii located at about 0.15, 0.5, and 2.0 μm they present the typical maritime aerosol characteristics. The behavior of the aerosol optical thickness is described through its variations in 2 entire days. From this experiment we found that for the measurement of the diffuse solar radiation, three operational wavelengths in the UV, the visible, and the near-IR are sufficient to obtain satisfactory information on the aerosol optical properties in the spectral range covered by these wavelengths.

Dewfall and evapotranspiration have been measured with a weighable lysimeter and computed through the energy balance equation, during day and nighttime; the Kazanskiy-Monin nomograph has been used for parameterizing the air sensible heat flux. The experimental data have been taken on a flat lawn, starting after an irrigation. The results show that the values of the computed mean net water flux are always significant, that is, their signs are always unambiguous. There is a general good agreement between derived and measured water fluxes, and a good coincidence between derived and computed dew onset, dew ending and dew duration.

The latent heat flux has been determined during a fog situation by using a method based on the surface heat balance equation and a parameterization of the sensible heat flux. The computed values of the latent heat flux show that it is connected with changes in fog density.

Measurements of the direct solar and diffuse sky irradiances are used for deriving optical and physical features of the atmospheric aerosols: optical depth, size distribution, and complex refractive index. Sky irradiance is measured by means of a sky-radiometer (aureolemeter), which consists essentially of a photometer with annexed interferential filters for the selection of the wavelengths at which to operate, and a pointing system. The device used in the authors' research program, manufactured by the Japanese Company Prede (Tokyo), operates at the following wavelengths: 0.315, 0.400, 0.500, 0.870, 0.940 and 1.040 /spl mu/m. Measurements are undertaken in the two following different ways. Almucantar: pointing along a conical surface with the same zenith angle of the Sun. Principal plane, the instrument aims the sky along a plane with the same azimuth angle of the Sun. The two quantities considered in their scheme of data elaboration are the direct solar irradiance V and the ratio R between the diffuse and the direct irradiance.