Surface roughness analysis and improvement of PMMA-based microfluidic chip chambers by CO2 laser cutting

For the microfluidic chip, the surface roughness of the chamber sidewall is an important parameter in estimating its quality. In this work, the chambers of the polymethyl methacrylate (PMMA)-based microfluidic chip were fabricated by CO₂ laser cutting, and then the surface roughness of the sections cut using different laser parameters and ambient temperature was studied by a non-contact 3D surface profiler. Our observation shows that the surface roughness results primarily from the residues on the laser-cut edge, which are produced by the bubbles bursting. To reduce the surface roughness of the cut section, a new approach is proposed, that is preheating the PMMA sheet to a suitable ambient temperature during laser processing. The results indicate that at a preheat temperature of 70-90 °C, the surface roughness resulting from the cut would be reduced. In our experiment, the best result was that the arithmetical mean roughness is R_a = 100.86 nm when the PMMA sheet was heated to 85 °C.     

Effects of surface inactivation, high temperature drying and preservative treatment on surface roughness and colour of alder and beech wood

Although extensive research has been conducted in wood surface quality analysis, a unified approach to surface quality characterisation does not exist. Measurements of the variation in surface roughness and surface colour are used widely for the evaluation of wood surface quality. Colour is a basic visual feature for wood and wood-based products. Colour measurement is one of the quality control tests that should be carried out because the colour deviations are spotted easily by the consumers. On the other hand, a common problem faced by plywood manufacturers is panel delamination, for which a major cause is poor quality glue-bonds resulting from rough veneer. Rotary cut veneers with dimensions of 500 mm × 500 mm × 2 mm manufactured from alder (Alnus glutinosa subsp. barbata) and beech (Fagus orientalis Lipsky) logs were used as materials in this study. Veneer sheets were oven-dried in a veneer dryer at 110 °C (normal drying temperature) and 180 °C (high drying temperature) after peeling process. The surfaces of some veneers were then exposed at indoor laboratory conditions to obtain inactive wood surfaces for glue bonds, and some veneers were treated with borax, boric acid and ammonium acetate solutions. After these treatments, surface roughness and colour measurements were made on veneer surfaces. High temperature drying process caused a darkening on the surfaces of alder and beech veneers. Total colour change value (ΔE^*) increased linear with increasing exposure time. Among the treatment solutions, ammonium acetate caused the biggest colour change while treatment with borax caused the lowest changes in ΔE^* values. Considerable changes in surface roughness after preservative treatment did not occur on veneer surfaces. Generally, no clear changes were obtained or the values mean roughness profile (R_a) decreased slightly in R_a values after the natural inactivation process.     

Preparation and in vitro characterization of aerosol-deposited hydroxyapatite coatings with different surface roughnesses

Hydroxyapatite (HA) coatings with different surface roughnesses were deposited on a Ti substrate via aerosol deposition (AD). The effect of the surface roughness on the cellular response to the coating was investigated. The surface roughness was controlled by manipulating the particle size distribution of the raw powder used for deposition and by varying the coating thickness. The coatings obtained from the 1100 °C-heated powder exhibited relatively smooth surfaces, whereas those fabricated using the 1050 °C-heated powder had network-structured rough surfaces with large surface areas and were superior in terms of their adhesion strengths and in vitro cell responses. The surface roughness (R_a) values of the coatings fabricated using the 1050 °C-heated powder increased from approximately 0.65 to 1.03 μm as the coating thickness increased to 10 μm. The coatings with a rough surface had good adhesion to the Ti substrate, exhibiting high adhesion strengths ranging from 37.6 to 29.5 MPa, depending on the coating thickness. The optimum biological performance was observed for the 5 μm-thick HA coating with an intermediate surface roughness value of 0.82 μm.     

Influence of self-affine and mound roughness on the surface impedance and skin depth of conductive materials

In this work, we explore the influence of self-affine and mound surface roughness on the surface impedance and skin depth. For self-affine roughness, the surface impedance and skin depth increases with decreasing the roughness exponent H (for k_Fξ?1 with k_F the Fermi wave-vector), and/or increasing roughness ratio w/ξ, where w is the rms roughness amplitude and ξ the in-plane roughness correlation length. For mound roughness, the surface impedance and skin depth decrease monotonically with increasing average mound separation λ when λ>ζ with ζ the correlation length (assuming k_Fζ?1), while for λ<ζ they are both decreased with increasing λ.     

Influence of surface topography and pore architecture of alkali-treated titanium on in vitro apatite deposition

Alkali-treated titanium surfaces have earlier shown to induce bone-like apatite deposition. In the present study, the effect of surface topography of two-dimensional and pore architecture of three-dimensional alkali-treated titanium substrates on the in vitro bioactivity was investigated. Titanium plates with a surface roughness of R_a = 0.13 μm, 0.56 μm, 0.83 μm, and 3.63 μm were prepared by Al₂O₃ grit-blasting. Simple tetragonal and face-centered Ti6Al4V scaffolds with spatial gaps of 450-1100 μm and 200-700 μm, respectively, were fabricated by a three-dimensional fiber deposition (3DFD) technique. After alkali treatment, the titanium plates with a surface roughness of R_a = 0.56 μm were completely covered with hydroxyapatite globules after 7 days in simulated body fluid (SBF), while the coverage of the samples with other surface roughness values remained incomplete. Similarly, face-centered Ti₆Al₄ scaffolds with spatial gaps of 200-700 μm exhibited a full surface coverage after 21 days in SBF, while simple tetragonal scaffolds with spatial gaps of 450-1100 μm were only covered for 45-65%. This indicates the importance of surface topography and pore architecture for in vitro bioactivity.     

A new method to characterizing surface roughness of TiO2 thin films

Titanium dioxide (TiO₂) thin films have been widely coated in the self-cleaning glass for facade application. The benefit of these glasses is its ability to actively decompose organic compounds with the help of ultraviolet light. Understanding the surface roughness of TiO₂ thin films is important before manufacturing of self-cleaning glasses using TiO₂ thin films because surface roughness of TiO₂ thin films has highly significant influence on the photocatalytic performance. Traditional approach for measuring surface roughness of TiO₂ thin films is atomic force microscopy. The disadvantage of this approach include long lead-time and slow measurement speed. To solve this problem, an optical inspection system for rapidly measuring the surface roughness of TiO₂ thin films is developed in this study. It is found that the incident angle of 60° is a good candidate for measuring surface roughness of TiO₂ thin films and y=90.391x+0.5123 is a trend equation for predicting the surface roughness of TiO₂ thin films. Roughness average (Ra) of TiO₂ thin films (y) can be directly determined from the peak power density (x) using the optical inspection system developed. The results were verified by white-light interferometer. The measurement error rate of the optical inspection system developed can be controlled by about 8.8%. The saving in inspection time of the surface roughness of TiO₂ thin films is up to 83%.     

Fractal analysis and atomic force microscopy measurements of surface roughness for Hastelloy C276 substrates and amorphous alumina buffer layers in coated conductors

In coated conductors, surface roughness of metallic substrates and buffer layers could significantly affect the texture of subsequently deposited buffer layers and the critical current density of superconductor layer. Atomic force microscopy (AFM) is usually utilized to measure surface roughness. However, the roughness values are actually relevant to scan scale. Fractal geometry could be exerted to analyze the scaling performance of surface roughness. In this study, four samples were prepared, which were electro polished Hastelloy C276 substrate, mechanically polished Hastelloy C276 substrate and the amorphous alumina buffer layers deposited on both the substrates by ion beam deposition. The surface roughness, described by root mean squared (RMS) and arithmetic average (R_a) values, was analyzed considering the scan scale of AFM measurements. The surfaces of amorphous alumina layers were found to be fractal in nature because of the scaling performance of roughness, while the surfaces of Hastelloy substrates were not. The flatten modification of AFM images was discussed. And the calculation of surface roughness in smaller parts divided from the whole AFM images was studied, compared with the results of actual AFM measurements of the same scan scales.     

Effect of the surface integral in the torque equation of the electromagnetic angular momentum on the Faraday rotation

A circularly polarized plane wave of infinite transverse extent (δ = ∞) has no spin angular momentum, while a realistic light does carry it. This paradox originates from the presence (δ = ∞) and absence (δ ≈ 0) of the surface integral in the total angular momentum J. The same holds for the torque equation of dJ/dt, so that δ is also connected with the relative Faraday rotation angle Θ_F/θ_F when a radius (a) of a cylindrical medium with optical activity is only a little larger than that (b) of light beam, where Θ_F is the Faraday rotation angle and θ_F is the intrinsic Faraday rotation angle of a medium. It is shown here that it is possible to estimate δ for a realistic light from the drastic variation in Θ_F/θ_F near b/a = 1.     

Compositional origin of surface roughness variations in air-annealed ZnO single crystals

We directly investigated the chemical compositional origin of surface roughness variations in air-annealed ZnO single crystal samples for annealing temperatures up to 1000 °C. Atomic Force Microscopy (AFM) showed temperature-dependent changes in surface roughness and morphology, with a maximum in surface roughness of 2 nm found for samples annealed at 400 °C. The O(1s) line, measured by X-ray Photoelectron Spectroscopy (XPS) showed a maximum for Zn(OH)₂ and a minimum for off-stoichiometric ZnO at 400 °C; while the Zn(2p) peaks show an increase in slope at that temperature. These results indicate that the roughness arises from Zn diffusion and loss of surface oxygen.     

Effect of surface roughness on nucleation and growth of vanadium pentoxide nanowires

The effect of surface roughness on subsequent growth of vanadium pentoxide (V₂O₅) nanowires is examined. With increasing surface roughness, both the number density and aspect ratio of V₂O₅ nanowires increase. Structures and morphology of obtained nanowires were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The nanowires are approximately 40-90 nm in diameter and 2 μm in length. X-ray diffraction (XRD) analysis indicates that the obtained nanowires are orthorhombic structure with (0 0 1) out-of-plane orientation. The luminescence property of V₂O₅ nanowires has been investigated by photoluminescence (PL) at 150 K and 300 K. PL results show intense visible emission, which is attributed to different inter-band transitions between the V 3d and O 2p band. This simple fabrication approach might be useful for fabrication of large area V₂O₅ nanowires arrays with high density.     

Metal insulator transition due to surface roughness scattering in a quantum well

We calculate the critical width a_c for a quantum well structure as function of the two-dimensional electron density. For a > a_c the electron gas has a finite dc conductivity at temperature zero, and for a < a_c the dc conductivity is zero. Homogeneous background doping, remote doping, and surface roughness scattering are considered. Due to surface roughness we find a strong increase of a_c at high electron concentration, in novel contrast to heterostructures. Explicit results are presented for GaAs and InAs quantum wells and compared with experimental results. Experiments are suggested to test the predictions of the localization theory.     

Roughness of pigment coatings and its influence on gloss

A robust method is used for analyzing roughness at a wide range of lateral length scales. The method is based on two-point correlation where both the amplitude and lateral spacing of surface heights are considered when determining the roughness. Atomic force microcopy and confocal optical microscopy images were captured for a set of pigment-coated samples. The effects of sampling interval, image size and filtering on surface roughness were studied. Isotropy and periodicity of roughness were determined by analyzing the angular distribution of the correlation length (T) and the autocorrelation function (ACF). A clear dependence of root mean square (RMS) roughness (σ) on T was established for randomly distributed surfaces. By taking into account the σ-T dependence it was possible to obtain σ for various length scales for each sample and thus attaining the most relevant σ for a certain surface function, which in this study was specular reflection of light (gloss). The roughness analysis showed that a small amount of DPP coating was sufficient to completely cover and change the surface of the substrate, while kaolin coatings gave a different response.     

Effects of thermo-hygro-mechanical densification on the surface characteristics of trembling aspen and hybrid poplar wood veneers

The effect of thermo-hygro-mechanical (THM) densification temperature on the surface color, roughness, wettability, and chemical composition of trembling aspen (Populus tremuloides) and hybrid poplar (Populus maximowiczii × P. balsamifera) veneers was investigated. Veneers were subjected to four THM densification temperatures (160 °C, 180 °C, 200 °C, and 220 °C). Veneer color darkened with increasing THM densification temperature. Surface roughness decreased between 160 °C and 200 °C. Wettability decreased after THM densification, but no significant difference was found between treated specimens. ATR-FTIR and XPS results confirmed that THM densification caused major chemical changes in veneer surfaces, and more pronounced at temperatures higher than 160 °C.     

A surface tension study of liquid threads

According to symmetry of liquid threads, definitions of surface tension in axial direction and angular direction are given. The formulas of surface tension in axial direction γ_z and surface tension in angular direction γ_θ are derived. A scheme to calculate Δγ = γ_z − γ_θ is designed. We investigate seven different systems (the numbers of molecules N are 1600, 2240, 2880,3360,4000,4800 and 5280) by molecular dynamics simulations. For liquid threads, Δγ increases with the decreasing radius of dividing surface. It shows that there exists surface tension anisotropy for liquid threads. The results obtained by molecular dynamics simulations support that surface tension is dependent on the dividing surface curvature.     

Influence of assisted ion energy on surface roughness and mechanical properties of boron carbon nitride films synthesized by DIBSD

The BCN thin films were produced by dual ion beam sputtering deposition (DIBSD). The influence of assisted ion energy on surface roughness and mechanical properties of BCN films were investigated. The surface roughness was determined by atomic force microscopy (AFM) and the mechanical properties of BCN firms were evaluated by nano-indentation in N₂ gas. The composition, structure and chemical bonding of the BCN thin films were analyzed by using energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), laser Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). These films appeared as amorphous structure. As a result, the BCN films with the smoothest surface (R_a = 0.35 nm and R_p-v = 4.4 nm) and the highest nano-hardness of 30.1 GPa and elastic modulus of 232.6 GPa were obtained at 200 eV and 12 mA with N₂:Ar = 1:1, and the chemical composition of this BCN film was 81 at.% B, 14 at.% C and 5 at.% N. Moreover, several bonding states such as B-N, B-C and C-N were observed in BCN thin films.     

Adhesion of elastic films on mound rough surfaces

In this work, we have investigated the adhesive behaviour of elastic films in contact with solid substrates, which are bounded by mound surface roughness. This type of roughness is described by the rms roughness amplitude w, the average mound separation Λ, and the system correlation length ζ. It is shown that both lateral roughness parameters Λ and ζ strongly influence adhesive characteristics. Indeed, with increasing elastic film modulus E, film adhesion is only possible for sufficiently large mound separations Λ. Moreover, the critical elastic modulus E_c (for which spontaneous film decohesion takes place for E>E_c) is shown to increase fast with increasing mound separation Λ when Λ?ζ, while as a function of the system correlation length ζ it increases relatively fast when ζ?Λ.     

In situ ellipsometry of surface layer of non-metallic transparent materials during its finish processing

For modern technology applications it is important to develop non-contact methods of control of the modification of dielectric materials surface layer. The aim of the work is to determine the level of roughness changes in the surface layer of non-metallic material, optical glass BK-7, and to control it by in situ ellipsometry. The probing light spot was formed at a second (lower) reflective surface of the plate being studied during its mechanical processing at direct observation of these changes. The fine mechanical polishing was carried out for 2 hours by using the grinding-polishing machine installed directly on the sample table of ellipsometer LEF-3M. The angle of light incidence was close to 70 degree. The ellipsometric parameters, were determined within the mechanically processed area. For this purpose, the probing light beam passed two times through the sample and then returned to the initial (air) medium, where its polarization state was studied. The polarized beam falls on lower plate surface polished by conventional technology using grinding-polishing CeO₂-based instrument “Aquapol” (grain size 1 micron). The time dependences of the ellipsometric parameters during the surface layer treatment were studied. In these dependences the tendency of changes of ellipsometric parameters indicates the surface roughness enhancement.     

Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

NbN_x films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 °C, on the preferred orientation, phase, and surface properties of NbN_x films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN_x films. For a substrate temperature up to 450 °C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650−850 °C, mix of cubic δ-NbN and hexagonal phases (β-Nb₂N + δ′-NbN) were formed. Films with a mainly β-Nb₂N hexagonal phase were obtained at deposition temperature above 850 °C. The c/a ratio of β-Nb₂N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN_x films increased as the temperature was raised from 450 to 850 °C.     

Effect of surface roughness on the optical constants of bulk polycrystalline gold samples

Four bulk polycrystalline samples of gold were subjected to different polishing treatments using diamond pastes of grain size 10, 6, 3 and 1 μm. The effect of surface roughness on the optical constants n and k is studied by 45° angle-of-incidence ellipsometry at 632.8 nm. Results for n and k are extrapolated to the case of an ideal surface which we believe to be highly representative of gold. Comparison with published results for the optical constants of gold thin films is presented.