Contribution Of Surface Roughness Research Articles

Tungsten sputtering and accumulation of implanted carbon and deuterium by simultaneous bombardment with D and C ions

Sputtering of tungsten by simultaneous incidence of gaseous and non-volatile ions is an important field of research for nuclear fusion with magnetically confined plasmas. In order to investigate the underlying processes in detail, W layers deposited on graphite and Si substrates have been irradiated simultaneously with beams of 12keV C2- and 9keV D3+ ions. The dynamics of W sputtering as well as the accumulation of implanted C and D was studied in-situ by ion beam analysis (IBA) using 2.5MeV 3He+ ions. In this work, particularly the sputter yield of W and the implantation of C and D as a function of the C fraction in the incident flux is discussed. Comparison of experimental data to TRIDYN simulations reveal a strong contribution of surface roughness to W sputtering and C implantation. In comparison to the influence of roughness, the contribution of chemical effects appears negligible.

Relevance of surface roughness to tungsten sputtering and carbon implantation

Tungsten sputtering and carbon layer growth by carbon ion bombardment has been investigated by experiments with thin W layers. Preparation of tungsten layers by magnetron deposition allows one to control the surface roughness by choosing appropriate substrates. The fluence dependent elemental composition of the bombarded surface has been studied in situ with ion beam analysis allowing separate measurements of the areal densities of tungsten and carbon atoms. In contrast to weight-loss measurements, this approach is much less affected by nonuniformities of the incident flux and therefore allows one to determine the dependency of the principal physics processes on input parameters with much higher accuracy. After bombardment, ex situ scanning electron microscopy has been used for the qualitative understanding of the evolution of the surface topography with increasing fluence. The experiments clearly show the influence of surface roughness, leading to increased tungsten sputter yields and strongly reduced carbon implantation rates. Comparison of the experimental results with simulations by the Monte Carlo code TRIDYN has verified the validity of the kinematic description for the interaction of carbon ions with mixed carbon-tungsten surfaces. At the same time, chemical effects, such as carbide formation, can be neglected in comparison with the contribution of surface roughness to the dynamics of sputtering and implantation.

Low friction lubrication between amorphous walls: Unraveling the contributions of surface roughness and in-plane disorder

Using molecular dynamics simulations, we show that dodecane films confined between amorphous surfaces at 300 K retain liquid-like behavior down to film thicknesses of at least 1.8 nm and possibly smaller. This is in stark contrast to the behavior of films confined between crystalline surfaces which show an abrupt transition to a very high viscosity state at a film thickness of 4 nm. We show that it is the small increase in surface roughness in going from crystalline to amorphous walls, rather than the in-plane disorder, that is responsible for disrupting the crystalline bridges found in the crystal-confined films. The main consequences of the in-plane disorder are the removal of the orientational pinning of the local domain alignment and the reduction of the critical thickness at which the transition to film rigidity appears.

Combination of Polarized TIRF and ATR Spectroscopies for Determination of the Second and Fourth Order Parameters of Molecular Orientation in Thin Films and Construction of an Orientation Distribution Based on the Maximum Entropy Method

This article describes two mathematical formalisms for the determination of the second and fourth order parameters of molecular films using optical spectroscopy. Method A uses polarized total internal reflection fluorescence (TIRF) to calculate the second and fourth order parameters, {P2(cos theta)} and {P4(cos theta)}, using an independently determined value for the angle between the absorption and emission dipoles, gamma. Method B uses {P2(cos theta)} obtained from attenuated total reflectance (ATR) data, along with polarized TIRF measurements to calculate {P4(cos theta)} and {cos2 gamma}. The choice of a specific method should rely on experimental considerations. We also present a method to separate the contributions of substrate surface roughness and dipole orientation with respect to the molecular axis from the spectroscopically determined second and fourth order parameters. Finally, a maximum entropy approach for construction of an orientation distribution from order parameters is compared with the commonly used delta and Gaussian distributions.

Analysis of surface roughness and morphology of first-year sea ice melt ponds: implications for microwave scattering

Variations in wind forcing over summer first-year sea ice (FYI) melt ponds occur at hourly to weekly scales and are a significant contributor to microwave backscatter (/spl sigma//spl deg/) variability observed from spaceborne synthetic aperture radar (SAR) platforms (e.g., ENVISAT-ASAR and RADARSAT-1). This variability impairs our ability to use SAR to derive information on summer sea ice thermodynamic state and energy balance parameters such as albedo and melt pond fraction. The surface roughness contribution of FYI melt ponds in the Canadian Arctic Archipelago to like-polarized, C-band /spl sigma//spl deg/ estimates is analyzed through a spectral and statistical analysis of surface wave height profiles for varying wind speeds, upwind fetch lengths, and melt pond depths. A unique derivation of melt pond surface wave height spectra is presented based on digital video of melt pond surface wave trains. Significant scale surface roughness was observed even at wind speeds of 3 m/spl middot/s/sup -1/, resulting in small perturbation model estimates of /spl sigma//spl deg/ (HH) ranging from -5 dB at 20/spl deg/ incidence to -22 dB at 50/spl deg/ incidence. Results from a multivariate linear regression analysis show that 53.5% of observed variance in /spl sigma//spl deg/ (HH or VV) can be explained by wind speed, upwind fetch from melt pond edges, and melt pond depth, with no appreciable difference in the relative contribution of explanatory variables. Modeled omnidirectional /spl sigma//spl deg/ as a function of wind speed and incidence angle for 100-m transects collected throughout the melt pond season act to elaborate the role of fetch and depth, as well as the modulating effect of hummocks, on /spl sigma//spl deg/.

The combined influence of a rough surface and thin fluid film upon the splashing threshold and splash dynamics of a droplet impacting onto them

Surface roughness can have a critical effect upon the splashing threshold and dynamics of a drop impacting on either a dry or rough solid surface or one coated by a thin fluid film. As most coating applications and spray systems quickly evolve to a state where the droplets impinge upon fluid deposited by preceding droplets, the combined contributions of surface roughness and a pre-deposited thin liquid film of comparable thickness upon droplet impingement dynamics are examined. For comparison, we include results for droplets impacting on a smooth, dry surface and a smooth surface wetted by a thin fluid film. The inclusion of surface roughness considerably lowers the splashing threshold and alters the splashing dynamics such that differences in fluid surface tensions between 20.1 and 72.8 dynes/cm or viscosities between 0.4 and 3.3 cP have little effect.

Surface roughness contribution to the adhesion force distribution of salmeterol xinafoate on lactose carriers by atomic force microscopy

Adhesion force distributions of silica spheres (5 and 20 µm) and salmeterol xinafoate (4 µm) particles with inhalation grade lactose surfaces and spin coated lactose films were determined by atomic force microscopy (AFM) to investigate the influence of surface roughness on the force distributions. The roughness of lactose particles and films was determined by both AFM and confocal microscopy (CM); the lactose particles showed RMS Rq values between 0.93 and 2.2 µm. The adhesion force distributions for silica and SX probes were significantly different for the different lactose carriers and broad, e.g., the adhesion force distribution between a 5 µm silica sphere and lactose particles ranged from 5 to 105 nN. This contrasted with distributions on smooth spin coated lactose films (RMS Rq of 0.28nm) which were not significantly different and were narrow, e.g., the adhesion force distribution between a 5 µm silica sphere and spin coated lactose films was between 42 and 68 nN. In addition, no significant difference in adhesion force distribution occurred with silica probe size on the lactose carrier surface. The use of X-ray photoelectron spectroscopic analysis confirmed that the lactose surfaces were free of impurities that might contribute to variation in adhesion. Although the almost atomically flat films showed some adhesion variability, the surface roughness of the lactose particles was a major contributing factor to the broad distributions seen in this study. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association.

Impact of SOI Thickness Fluctuation on Threshold Voltage Variation in Ultra-Thin Body SOI MOSFETs

Threshold voltage variation due to quantum confinement effect in ultra-thin body silicon-on-insulator (SOI) MOSFETs is examined. It is experimentally demonstrated that threshold voltage variation drastically increases when SOI layer is thinned down to 3 nm. A percolation model is used to estimate the contribution of surface roughness to V/sub th/ variation. The method to suppress the threshold voltage variation is also proposed, and around 15% reduction in threshold voltage variation is experimentally demonstrated by applying substrate bias. The reason of the suppression can be explained by quantum confinement effect induced by substrate bias.

Electrical Conduction in Thermally Sprayed Thin Metallic Coatings

ABSTRACTThe in-plane electrical conductivity and the apparent density of air plasma sprayed (APS) molybdenum coatings having thicknesses in the range 30 um to 450 um were measured as a function of coating thickness. Both conductivity and the apparent density were found to increase with thickness until a saturation density (∼ 80% of the bulk density of molybdenum metal) was achieved. Attributing this increase in the apparent density to the increased volume fraction of the metallic component (or decreased porosity volume) in the coatings allows for the treatment of the problem in a framework of percolation theories. In order to eliminate the contribution of surface roughness the results were further analyzed using a two-layer parallel resistor model of the coating. In this model the top layer, which was composed of coating roughness, was assumed to have fixed thickness and conductivity whereas the conductivity of the bottom layer was assumed to vary with thickness (density). A fit to the data obtained from the above model showed that the conductivity of the bottom layer obeys a power law relationship of the type σ α (V –Vc)n throughout the composition range (with n=1.72 and Vc=0.09). These results show that that the coatings behave as a three-dimensional percolation system [1] and also indicate the asymmetric shape of the metallic and insulator regions in the coatings [2].

Laboratory photometry of planetary regolith analogs

Laboratory phase curves of planetary regolith analog materials are presented. A study is made of the effect of compaction of the material on its backscattering properties. Further study is also made of the contribution of material surface roughness on its light scattering. First photometric light backscattering measurements in a microgravity environment are introduced as well as some improvements of the laboratory experiment techniques. The measurements show a strong increase in both reflectance and opposition effect amplitude under compaction. Also a broadening of the opposition effect width is observed. These results are in contrast with some of the previous studies on the subject. The surface roughness of a sample is found to be an important factor in measurements of samples with the same packing density. This should be taken into account in further studies.

Quartz Crystal Microbalance (QCM) in High-Pressure Carbon Dioxide (CO2): Experimental Aspects of QCM Theory and CO2 Adsorption

The quartz crystal microbalance (QCM) technique has been developed into a powerful tool for the study of solid-fluid interfaces. This study focuses on the applications of QCM in high-pressure carbon dioxide (CO2) systems. Frequency responses of six QCM crystals with different electrode materials (silver or gold) and roughness values were determined in helium, nitrogen, and carbon dioxide at 35-40 degrees C and at elevated pressures up to 3200 psi. The goal is to experimentally examine the applicability of the traditional QCM theory in high-pressure systems and determine the adsorption of CO2 on the metal surfaces. A new QCM calculation approach was formulated to consider the surface roughness contribution to the frequency shift. It was found that the frequency-roughness correlation factor, Cr, in the new model was critical to the accurate calculation of mass changes on the crystal surface. Experiments and calculations demonstrated that the adsorption (or condensation) of gaseous and supercritical CO2 onto the silver and gold surfaces was as high as 3.6 microg cm(-2) at 40 degrees C when the CO2 densities are lower than 0.85 g cm(-3). The utilization of QCM crystals with different roughness in determining the adsorption of CO2 is also discussed.

Diffraction correction for precision surface acoustic wave velocity measurements.

Surface wave dispersion measurements can be used to nondestructively characterize shot-peened, laser shock-peened, burnished, and otherwise surface-treated specimens. In recent years, there have been numerous efforts to separate the contribution of surface roughness from those of near-surface material variations, such as residual stress, texture, and increased dislocation density. As the accuracy of the dispersion measurements was gradually increased using state-of-the-art laser-ultrasonic scanning and sophisticated digital signal processing methods, it was recognized that a perceivable dispersive effect, similar to the one found on rough shot-peened specimens, is exhibited by untreated smooth surfaces as well. This dispersion effect is on the order of 0.1%, that is significantly higher than the experimental error associated with the measurements and comparable to the expected velocity change produced by near-surface compressive residual stresses in metals below their yield point. This paper demonstrates that the cause of this apparent dispersion is the diffraction of the surface acoustic wave (SAW) as it travels over the surface of the specimen. The results suggest that a diffraction correction may be introduced to increase the accuracy of surface wave dispersion measurements. A simple diffraction correction model was developed for surface waves and this correction was subsequently validated by laser-interferometric velocity measurements on aluminum specimens.

Group delay and chromatic dispersion of thin-film-based, narrow bandpass filters used in dense wavelength-division-multiplexed systems.

Theoretical analysis is made for thin-film-based, 200- and 100-GHz narrow bandpass filters with respect to the intensity response as well as to the chromatic dispersion. The results indicate that the narrower the passband, the higher the chromatic dispersion. The maximum chromatic dispersion appears at the edges of the 0.5-dB passband, owing to the fast change of the group delay in the region. The deviation of chromatic dispersion induced by manufacturing error is simulated. Effective-medium approximation layers are added to simulate the contribution of surface roughness and the mixture interfaces to the passband ripple as well as the chromatic dispersion. The simulations are compared with the experimental results. The measured chromatic dispersion matches the general trend of the theoretical calculation. The imperfect surface and layer mismatch induce additional ripples across the 0.5-dB passband. The maximum chromatic dispersion within a 0.5-dB passband is 20.7 and 54.9 ps/nm for 200- and 100-GHZ narrow bandpass filters, respectively.

Diffraction correction for precision SAW velocity measurements

Surface acoustic wave (SAW) dispersion measurements can be used to nondestructively characterize shot-peened, laser shock-peened, and other surface-treated specimens. In recent years, there have been numerous efforts to separate the contribution of surface roughness from those of near-surface material variations, such as residual stress, texture, and increased dislocation density. This talk addresses the problem that a perceivable dispersive effect, similar to the one found on rough shot-peened specimens, is exhibited by untreated smooth surfaces as well. The dispersion measurements were performed using laser-ultrasonic scanning combined with special digital signal-processing methods. The observed dispersion effect is on the order of 0.1%, which is comparable to the expected velocity change produced by near-surface compressive residual stresses in metals below their yield strength. The cause of this apparent dispersion is the diffraction of the SAW as it travels over the surface of the specimen. It is demonstrated that a diffraction correction may be introduced to increase the accuracy of surface wave dispersion measurements. A simple diffraction correction model was developed for surface waves; this correction was subsequently validated by laser-interferometric surface wave velocity measurements on 2024-T351 aluminum specimens.

Extending the capabilities of scanning probe microscopy for microroughness analysis in surface engineering

AbstractWe present a method for extending the capabilities of scanning probe microscopy (SPM) methods in surface engineering by specific processing and interpretation of topographic data. The first part of this processing permits SPM measurements of different scan sizes to be combined with other microtopographical techniques. The result is a comprehensive description of the surface microstructure based on power spectral density functions. The second part consists of the extraction of a small set of characteristic parameters that objectively characterize the statistical properties of the surface and separate different roughness contributions. Copyright © 2002 John Wiley & Sons, Ltd.

Surface roughness contribution to the Casimir interaction between an isolated atom and a cavity wall

An approximate perturbative method is developed to calculate the corrections to the Casimir force between an isolated atom and a cavity wall due to surface roughness. The results are obtained up to the fourth order in the relative roughness amplitude. All possible types of surface roughness are considered: large scale, short scale, and intermediate, defined by the ratio of the characteristic lateral length scale of roughness to the atom-wall distance. A continuous transition between the corrections due to different types of roughness is carried out. It is shown that the large-scale roughness can lead to corrections of the order of 70% of the net Casimir force. In the cases of large-scale and intermediate-type roughness the lateral Casimir force comes into play, which leads to moving the atom to the nearest extreme point of the vertical force with subsequent dying out oscillations in its vicinity. Possible role wall roughness can play in some phenomena of cavity electrodynamics is discussed.

Molecular Orientation at Surfaces: Surface Roughness Contributions to Measurements Based on Linear Dichroism

The molecular orientation at surfaces plays a key role in many of the interesting optical properties of organic thin films. Accurate determination of molecular “tilt” angles and the distribution in...

Effects of functional groups and surface roughness on interfacial shear strength in ultrahigh molecular weight polyethylene fiber/polyethylene system

Corona discharge treatment was conducted for ultrahigh molecular weight polyethylene (UHMWPE) fiber. The functional groups and surface roughness of the polyethylene fiber surface were determined by an X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The interfacial shear strength of UHMWPE fiber with HDPE film was determined by microbond pullout method. The interfacial shear strength increased by corona treatment. Then, the effect of the chemical and physical factors on the interfacial shear strength was discussed based on the results of multivariate regression analysis. The results indicated that the contribution of functional groups and surface roughness to the interfacial shear strength was expressed as 50 and 50%, respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 243–249, 1999

Classification of sea ice types in the Ross Sea, Antarctica from SAR and AVHRR imagery

ERS-2 synthetic aperture radar (SAR) and Advanced Very High Resolution Radiometer (AVHRR) imagery are used to examine spectral characteristics of late winter/early spring ice in the Ross Sea, Antarctica. The combined spectral signatures are used to distinguish six ice types: fast ice, new ice, smooth first year ice, rough first year ice, thin new ice/wind roughened open water and glacial ice. The procedure firstly involves 'picking' class boundaries from SAR imagery based on the morphology of a speckle reduced backscatter spectrum. These class boundaries are then used as input to an iterative segmentation procedure that involves the repeated application of a speckle reduction filter to the image. For an image from late September 1996 the segmentation procedure enabled separation of five general ice categories each with a characteristic backscatter range. However because of the combined contributions of ice thickness, surface roughness, salinity and water content to the SAR backscatter, further decision criteria are required to separate some physical ice types unable to be resolved individually using this method. Coincident and co-registered infrared data from the AVHRR sensor are used to extract spectral characteristics for the final ice classes. Using this procedure we were able to distinguish floating glacier ice from thin new ice/wind roughened open water and new ice from nearshore fast ice. These ice types were unable to be separated using SAR backscatter intensity alone. In addition image subtraction was also able to clearly delineate areas of shore fast ice.

Contribution of surface roughness of an isotropic solid to low-temperature surface heat capacity

The effect of roughness of the free surface of a semi-infinite isotropic solid on the low-temperature surface heat capacity is studied. The method of modified Green’s function (as compared with that used by Maradudin, Wallis, and Equiluz (1977) and perturbation theory are used for deriving an analytic expression for the contribution of weak roughness to the low-temperature surface heat capacity, which is a correction to the well-known result obtained by Dupuis, Mazo, and Onsager (1960) for the surface heat capacity of a semi-infinite isotropic solid with a plane free boundary. It is proved that the inclusion of roughness of isotropic crystals with optical surfaces increases the surface heat capacity in a wide temperature range (of the order of several kelvins).