In the smooth-surface limit, the angular distribution of the light scattered from a surface maps the power spectral density of its residual surface roughness. This result is essentially independent of the scattering theory used and the statistical properties of the surface roughness. The power spectral densities of engineering surfaces are generally broad and increase with increasing spatial wavelength. As a result, practical surface finish parameters are not intrinsic properties of the surface, but depend, with varying degrees of sensitivity, on the bandwidth limits inherent in their measurement or dictated by their application. These issues are discussed with reference to two classes of finish parameters: those related to the central moments of the scattering spectrum, and those related to the coefficients in the expansion of the shape of the spectrum in inverse powers of the scattering angle. The significance of "1/02" scattering in this context is emphasized. A shot model of surface roughness is then introduced to gain further insight into the relationship between scattering and surface features. In this model inverse power terms are related to "edge" scattering effects from critical points in various types of elemental microdefects. The relationship between this view and electronic noise is pointed out; in particular, the correspondence between "1/62" scattering and "1 /f" or flicker -noise phenomena.

Recent results on achieving ferromagnetism in transition-metal-doped GaN, AlN and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. There is strong potential for new classes of ultra-low-power, high speed memory, logic and photonic devices based on spintronics. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures and most theories predict that the Curie temperature will be a strong function of bandgap. We discuss the current state-of-the-art in producing room temperature ferromagnetism in GaN-based materials, the origins of the magnetism and its potential applications.

ZnO nanorods with diameters of 15-30 nm were grown on Ag-coated Si substrates by catalyst-driven molecular beam epitaxy and then implanted with Mn ϩ or Co ϩ ions to doses of 1 -5ϫ10 16 cm Ϫ2 . After subsequent annealing at 700°C for 5 min, the structural properties of the nanorods were unaffected, but they exhibited ferromagnetism that persisted to temperatures of 225-300 K. The coercive fields were р100 Oe even at 10 K. The results are similar to those obtained for implantation of Mn ϩ or Co ϩ ions in bulk single-crystal ZnO and indicate promise for nanorods for nanoscale spintronic applications.

The residual surface roughness of diamond-turned optics is expected to contain significant periodic components. The optical properties of such surfaces are explored as a special case of Rayleigh-Rice vector scattering theory applied to periodic roughness with vertical amplitudes much smaller than the wavelength of light. Expressions are given for the interpretation of differential-scatter, total-integrated-scatter, reflectometry, and ellipsometric measurements in the limit of a highly conducting. surface. In general, such measurements give varying degrees of information about the two-dimensional power spectral density of the surface roughness within the nominal range from the wavelength of light to the diameter of the probing beam spot. Such information may be useful for the practical characterization of mirror surfaces.

Direct implantation of Fe, Ni or Mn at doses of 3–5×1016 cm−2 into p-type 6H-SiC substrates was carried out at a sample temperature of ∼350 °C. Subsequent annealing was performed at 700–1000 °C for 5 mins. Residual damage in the form of end-of-range defects and dislocation loops in the region from the surface to a depth of ∼0.20 μm were examined by transmission electron microscopy. To the sensitivity of both x-ray diffraction and selected area diffraction pattern analysis, no secondary phases could be detected. Signatures of ferromagnetism were observed in all the highest dose samples, with apparent Curie temperatures of 50 K (Ni), 250 K (Mn), and 270 K (Fe).

This paper discusses the measurement of the finish of diamondturned surfaces by differential light scattering. Experimental scattering data are analyzed by electromagnetic theory to give the two -dimensional power spectral density of the surface roughness. These spectral densities are direct functional measures of the surface quality, and may be characterized in terms of topographic finish parameters. These parameters can then be used to specify surface finish, to predict scattering under a variety of conditions, and to aid in studies of other functional properties of these surfaces. Scattering spectra are separated into three groups corresponding to three classes of surface roughness: periodic tool marks and one-and two -dimensional random roughness. Periodic tool marks give rise to discrete diffraction lines in the scattering spectrum and are characterized by their surface periods and their Fourier amplitudes. Random one-and two -dimensional roughness give rise to one-and two -dimensional continua underlying the diffraction lines and are characterized by band -limited values of the rms surface heights and slopes, and transverse length parameters. Using HeNe light, vertical roughnesses are measured from a fraction of an Angstrom to several hundred Angstroms, for transverse spatial wavelengths from a fraction of a micron to several hundred microns. We review experimental techniques for making these measurements with emphasis on the scatterometer developed in our laboratory, which uses a fixed source -detector geometry and a rotating sample. Results are illustrated by a number of scattering spectra taken with this instrument. IntroductionThis paper addresses two problems: the measurement of the finish of diamond -turned surfaces by differential light scattering, and the characterization of the results in terms of topographic finish parameters. The background of the method is

The Joule heating effect on graphene electronic properties is investigated by using full-band Monte Carlo electron dynamics and three-dimensional heat transfer simulations self-consistently.A number of technologically important substrate materials are examined: SiO 2 , SiC, hexagonal BN, and diamond. The results illustrate that the choice of substrate has a major impact via the heat conduction and surface polar phonon scattering. Particularly, it is found that the poor thermal conductivity of SiO 2 leads to significant Joule heating and saturation velocity degradation in graphene (characterized by the so-called 1/ √ n decay). Considering the overall characteristics, BN appears to compare favorably against other substrate choices for graphene in electronic applications.

GaGdN layers were grown by gas source molecular beam epitaxy with varying crystal quality and Gd concentrations as set by the Gd cell temperature. Magnetic measurements showed ferromagnetic behavior at room temperature, with the saturation magnetization dependent both on Gd concentration and crystalline quality. The Gd concentration was under the detection limit of secondary ion mass spectrometry, and estimated to be on the order of <1017at.∕cm3. As expected at this low dopant concentration, x-ray diffraction measurements showed the films to be single phase. Gd-doped samples codoped with Si to make them conducting with resistivity of 0.04Ωcm showed similar magnetic properties as Gd-doped films without addition of Si.