Optical Roughness Research Articles

Biaxial stresses, surface roughness and microstructure in evaporated TiO 2 films with different deposition geometries

The residual stresses, surface roughness and microstructure in titanium oxide films prepared by electron-beam evaporation and deposited with different geometries were investigated, with particular focus on the in-plane anisotropy of the biaxial stresses and microstructures. Thin films were deposited with various deposition angles on B270 glass substrates and silicon wafers. Two different types of deposition geometries were studied. The residual stress in the thin films was examined by a phase-shifting Twyman-Green interferometer. The optical constants, biaxial stress and surface roughness were found to be related to the evolution of the anisotropic microstructures in the films. The results revealed that the anisotropic stresses that developed in the evaporated titanium oxide films were dependent upon the deposition geometry and microstructure of the films.

The effect of AlN interlayer thicknesses on scattering processes in lattice-matched AlInN/GaN two-dimensional electron gas heterostructures

The scattering mechanisms governing the transport properties of high mobility AlInN/AlN/GaN two-dimensional electron gas (2DEG) heterostructures with various AIN spacer layer thicknesses from zero to 2 nm were presented. The major scattering processes including acoustic and optical phonons, ionized impurity, interface roughness, dislocation and alloy disorder were applied to the temperature-dependent mobility data. It was found that scattering due mainly to alloy disorder limits the electron mobility for samples having spacer layer thicknesses up to 0.3 nm. On the other hand, alloy scattering is greatly reduced as the AlN spacer layer thickness increases further, and hence the combination of acoustic, optical and interface roughness become operative with different degrees of effectiveness over different temperature ranges. The room-temperature electron mobility was observed to increase gradually as the AlN spacer layer increases. A peak electron mobility of 1630 cm2 V−1 s−1 was realized for the sample consisting of a 1 nm AlN spacer layer. Then, the electron mobility decreased for the sample with 2 nm AlN. Moreover, the measured 2DEG densities were also compared with the theoretical predictions, which include both piezoelectric and spontaneous polarization components existing at AlN/GaN interfaces. The experimental sheet carrier densities for all AlInN/AlN/GaN HEMT structures were found to be in excellent agreement with the theoretical predictions when the parasitic (unintentional) GaN layer deposited between AlN and AlInN was taken into account. From these analyses, 1 nm AlN spacer layer thickness is found to be the optimum thickness required for high electron mobility and hence low sheet resistance once the sheet carrier density is increased to the theoretically expected value for the sample without unintentional GaN layer.

The electrodeposition of highly reflective lead dioxide coatings

In the presence of a suitable surfactant, such as hexadecyltrimethylammonium chloride or bromide, highly reflective and hard lead dioxide coatings with a black appearance can be electrodeposited from methanesulfonic acid media at room temperature (295 K). The reflective PbO 2 coatings are compact, adherent to the (vitreous carbon or carbon-polymer) substrate and can be formed at current densities of 10 to 100 mA cm −2 at a thickness up to several hundred microns. The coatings were characterised by measurement of surface optical reflectance, surface roughness, surface microstructure, phase composition and crystallite size. The reflective PbO 2 films were found to mainly consist of the alpha (orthorhombic) phase with feather-like and orientated microstructures. The crystallite size and surface roughness were in the order of tens of nanometres and their optical reflectance was several orders of magnitude higher than matte coatings produced in the absence of additives.

Synthesis of radio frequency plasma polymerized non-synthetic Terpinen-4-ol thin films

Recent advancements in the area of organic polymer applications demand novel and advanced materials with desirable surface, optical and electrical properties to employ in emerging technologies. This study examines the fabrication and characterization of polymer thin films from non-synthetic Terpinen-4-ol monomer using radio frequency plasma polymerization. The optical properties, thickness and roughness of the thin films were studied in the wavelength range 200–1000 nm using ellipsometry. The polymer thin films of thickness from 100 nm to 1000 nm were fabricated and the films exhibited smooth and defect-free surfaces. At 500 nm wavelength, the refractive index and extinction coefficient were found to be 1.55 and 0.0007 respectively. The energy gap was estimated to be 2.67 eV, the value falling into the semiconducting E g region. The obtained optical and surface properties of Terpinen-4-ol based films substantiate their candidacy as a promising low-cost material with potential applications in electronics, optics, and biomedical industries.

Innovatively Optical Surface Roughness Tester “OpTiSurf”

“OpTiSurf”は，オーストラリアのAmcor Research and Technology社が，Australian Paper社の支援を得て開発したものを，カナダのOpTest社によって測定機として製品化したものである。OpTiSurfは，LEDの光源によって現れたサンプルの陰影を縦60mm×横80mmの面積をCCDカメラで撮影する非接触の光学式平滑度測定機である。その為，短時間で非常に広い範囲を一度に測定することが可能で，単葉シートだけでなく，数メーター程度であればMD方向やCD方向の長尺サンプルも測定が可能である。撮影された画像のうち，コントラストの差が大きな縦32mm×横80mmについて，独自の解析プログラムを用いて解析し0．25～32mmまでの7段階に分類されたサイズ別表面粗さ強度として評価する。空気漏洩（エアリーク）方式ではMD,CD，どちらの方向に対しても同じ測定結果になり，一定の方向に対する変動を判断出来ないが，OpTiSurfでは可能である。この様な解析をすることにより，ワイヤーマークに起因する粗さを分離したり，サンプル表面の微細な粗さが繊維による出っ張りであること等が判明したり，エアリーク式による測定では同じレベルの平滑度を持った紙でもOpTiSurfではそれらのデータに差を見ることができた。OpTiSurfは構造が簡単で故障がし難く，保守管理も容易である。機器の設置も単相100VACの電源だけで稼動し，圧縮空気や操作用のPC等を必要としない。測定で得られた画像データや数値データは内部フラッシュメモリーに自動的に保存され，いつでも呼び出して任意のサンプルと比較することができる。

Comparison of the transport properties of high quality AlGaN/AlN/GaN and AlInN/AlN/GaN two-dimensional electron gas heterostructures

The transport properties of high mobility AlGaN/AlN/GaN and high sheet electron density AlInN/AlN/GaN two-dimensional electron gas (2DEG) heterostructures were studied. The samples were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The room temperature electron mobility was measured as 1700 cm2/V s along with 8.44×1012 cm−2 electron density, which resulted in a two-dimensional sheet resistance of 435 Ω/◻ for the Al0.2Ga0.8N/AlN/GaN heterostructure. The sample designed with an Al0.88In0.12N barrier exhibited very high sheet electron density of 4.23×1013 cm−2 with a corresponding electron mobility of 812 cm2/V s at room temperature. A record two-dimensional sheet resistance of 182 Ω/◻ was obtained in the respective sample. In order to understand the observed transport properties, various scattering mechanisms such as acoustic and optical phonons, interface roughness, and alloy disordering were included in the theoretical model that was applied to the temperature dependent mobility data. It was found that the interface roughness scattering in turn reduces the room temperature mobility of the Al0.88In0.12N/AlN/GaN heterostructure. The observed high 2DEG density was attributed to the larger polarization fields that exist in the sample with an Al0.88In0.12N barrier layer. From these analyses, it can be argued that the AlInN/AlN/GaN high electron mobility transistors (HEMTs), after further optimization of the growth and design parameters, could show better transistor performance compared to AlGaN/AlN/GaN based HEMTs.

A method of optical roughness measurement on ultrafine metal surfaces

In the article, an optical method is described to measure the surface roughness on ultrafine machined metal surfaces. The method is capable for measurement of surface roughness without mechanical contact, and without removing the work piece from the machine. The traditional stylus-type devices require direct physical contact, which leaves scratches on the parts, whereas this optical method leaves the parts untouched. It is important to mention in advance that the characteristic magnitude of the roughness has to be below the wavelength of the applied electromagnetic wave, since this assumption is taken strictly in consideration of our method. If we apply any diode laser which operates in the typical wavelength range of 0.6-1 μ m, in such a case the adequate average roughness is below 0.1 μ m, we may speak in this sense about ultrafine machining.

Transition from Casimir to van der Waals force between macroscopic bodies

The transition of van der Waals to Casimir forces between macroscopic gold surfaces is investigated by atomic force microscopy in the plane-sphere geometry. It was found that the transition appears to take place at separations ∼10% the plasma wavelength λp for evaporated gold surfaces, which compares to theoretical predictions by incorporation of experimental optical data and roughness corrections. Moreover, the force data allow estimation of the Hamaker constant AH in the van der Waals regime, which is in good agreement with the Lifshitz theory predictions (even if roughness corrections are taken into account) and former surface force apparatus measurements.

Influence of the Cross-sectional Geometry on Wettability and Cleanability of Polyester Woven Fabrics

Abstract Filament cross-sections used in textiles and composites are becoming more and more complex. The type of cross-sectional shape impacts filament properties and are therefore, yarn and fabric characteristics. In this paper, the influence of different filament cross-section geometry on fibre properties as well as on fabric surface characteristics was studied. PET (polyethylene terephthalate) filament yarns made from two different cross-sectional shaped filaments, round and cruciform, were manufactured by the melt spinning process. Polyester fabrics were manufactured in a needle band weave machine from these two types of filament yarns. Topographic characteristics of polyester fabrics manufactured were determined by an imaging instrument for optical roughness analysis based on the principle of chromatic aberration. Differences between soiling behaviour, cleanability and wettability of the fabrics were revealed and discussed.

Growth of gold/zinc sulphide multilayer films using layer-by-layer assembly of colloidal nanoparticles

Fabrication of multilayer thin films through layer-by-layer (lbl) deposition of charged nanoparticles on tin-doped indium oxide (ITO) coated and uncoated glass substrates are reported. The thin films were constructed by alternately dipping a substrate into a colloidal suspension of chitosan capped zinc sulphide (ZnS) nanoparticles (∼30 nm) and citrate stabilized colloidal gold (Au) nanoparticles (∼20 nm) leading to electrostatic interactions between the oppositely charged nanoparticle layers. Thin films consisting of up to 200 deposition cycles by multiple dipping have been studied and surface morphology, changes in the optical absorption characteristics, thickness, uniformity, roughness and electrical characteristics are reported. The multilayered assemblies, attached to the surface by strong ionic bonds, were highly stable and could not be removed by moderate scratching. The current–voltage characteristics in the forward and reverse bias conditions demonstrated rectifying behaviors in the onset of conduction voltage which makes these films attractive for future electronic devices.

Sensing of human plasma fibrinogen on polished, chemically etched and carbon treated titanium surfaces by diffractive optical element based sensor

Adsorption of human plasma fibrinogen (HPF) on 6 differently treated titanium samples (polished, polished and etched, and 4 titanium carbide coatings samples produced by using plasma-enhanced chemical vapour deposition (PECVD) method) is investigated by using diffractive optical element (DOE) sensor. Permittivity (susceptibility) change and fluctuation in optical roughness (R(opt)) of treated titanium surface in the presence of background electrolyte without and with HPF molecules are sensed by using DOE sensor and optical ellipsometry. Correlation between transmitted light and thickness of molecule layer was found. The findings allow to sense temporal organization and severity of adsorption of nano-scale HPF molecules on polished, on polished and etched, and on titanium carbide surface.

Influence of random roughness on the Casimir force at small separations

The influence of random surface roughness of Au films on the Casimir force is explored with atomic force microscopy in the plate-sphere geometry. The experimental results are compared to theoretical predictions for separations ranging between 20 and $200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The optical response and roughness of the Au films were measured and used as input in theoretical predictions. It is found that at separations below $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, the roughness effect is manifested through a strong deviation from the normal scaling of the force with separation distance. Moreover, deviations from theoretical predictions based on perturbation theory can be larger than 100%.

Optimization of the parameters for nickel electrowinning using interference microscopy and digital image analysis

Ni electrodeposition experiments at a constant current density 220 A/m2 were performed to determine the optimum concentrations of chloride and an organic additive used for an industrial Ni electrowinning. White light interference microscopy was used to acquire digital images of the morphology of the electrodeposited nickel. The scaling analysis was employed to parameterize the morphological information encoded in the images. The standard deviation of the surface height, δ, the critical scaling length, L c, and the optical roughness, 4δ/L c, were determined as a function of the chloride concentration and the amount of organic additives. These parameters were plotted as a function of the two compositional variables. These three-dimensional plots allowed us to find conditions corresponding to the minimum of 4δ/L c, at which the deposited nickel is well leveled.

Electrical and optical study of ITO films on glass and polymer substrates prepared by DC magnetron sputtering type negative metal ion beam deposition

Transparent, conducting indium tin oxide (ITO) films were deposited without intentional substrate heating on glass and polyethersulfone (PES) substrates by a magnetron sputter type negative metal ion source (MSNIS). The effect of substrate type on optical transmittance, electrical resistivity, surface morphology and roughness of the ITO film was analyzed. ITO/glass substrates show a higher optical transmittance (89%) and lower resistivity (4 × 10 −4 Ω cm) than ITO/PES (78%, 6 × 10 −4 Ω cm). X-ray diffraction (XRD) spectra indicate polycrystalline ITO films deposited on glass and amorphous ITO films on PES. Atomic force microscopy (AFM) images also indicate that ITO/glass has a lower surface roughness than ITO/PES. The values of figure of merit ( T 10/ R sh) for ITO/glass ( ϕ TC = 7.7 × 10 −3 Ω −1) are higher than ITO/PES ( ϕ TC = 1.3 × 10 −3 Ω −1), indicating that ITO/glass achieved the best performance in this study.

Determination of optical constants in the EUV/soft X-ray region using the Luus-Jaakola optimization procedure

A Luus-Jaakola optimization procedure is described that simultaneously determines the optical constants, thickness and root mean square roughness of thin films for reflectance versus angle-of-incidences data measured in the EUV/soft X-ray region. The optimization method is applied to different films at different wavelengths. The results show that the Luus-Jaakola optimization procedure is able to determine the thickness of films and the roughness with an accuracy of less than 7%. The optical constants obtained are also in good agreement with reported values for films having an error of less than 1%.

Structural, morphological and optical properties of thermal annealed TiO thin films

Structural, morphological and optical properties of TiO thin films grown by single source thermal evaporation method were studied. The films were annealed from 300 to 520 °C in air after evaporation. Qualitative film analysis was performed with X-ray diffraction, atomic force microscopy and optical transmittance and reflectance spectra. A correlation was established between the optical properties, surface roughness and growth morphology of the evaporated TiO thin films. The X-ray diffraction spectra indicated the presence of the TiO2 phase for the annealing temperature above 400 °C.

Role of Catalyst on Refractive Index Tunability of Porous Silica Antireflective Coatings by Sol−Gel Technique

Porous silica coatings were prepared by acid- and base-catalyzed sol−gel method. Surface morphology studies by atomic force microscopy showed smooth surface for acid-catalyzed coatings while base catalysis resulted in coarse particle morphology. On increasing the tetraethyl orthosilicate to base molar ratio from 1:1 to 1:3, the mean particle size of the coating shifted from 30 to 100 nm while the pore size varied from 4.7 to 14 nm. Infrared spectral analysis exhibited a change in the ratio of integrated peak intensities of Si−O−Si to Si−OH in acid-and base-catalyzed silica coatings. Textural studies showed an increase in particle size and porosity with base concentration. Optical transmission and surface roughness of base-catalyzed samples were found to be higher than that of acid-catalyzed silica coatings.

Kinetic roughening of amorphous silicon during hot-wire chemical vapor deposition at low temperature

We use postdeposition atomic force microscopy and in situ spectroscopic ellipsometry to analyze the roughening of hydrogenated amorphous silicon films deposited by hot-wire chemical vapor deposition at 150°C. From the atomic force microscopy data, the root-mean-squared roughness w increases with deposition time t as w∝tβ with β=0.37±0.02, and the correlation length ξ increases as ξ∝t1∕z with 1∕z=0.31±0.02. From the height-difference correlation function, we obtain a roughness exponent α=0.87±0.04 and a root-mean-squared local slope δ, which increases as δ∝tκ with κ=0.17±0.03. These measurements are indicative of anomalous growth, which we attribute to geometric shadowing. However, the roughening behavior we observe using atomic force microscopy is not reproduced in the spectroscopic ellipsometry data. This contradicts previous reports which found a linear relationship between the thickness of the optical roughness layer and the root-mean-squared roughness. We discuss the discrepancy between the two techniques in terms of short-range roughness and vector perturbation theory.

Optical monitoring of molecular beam epitaxy growth of AlN∕GaN using single-wavelength laser interferometry: A simple method of tracking real-time changes in growth rate

Real-time in situ optical monitoring of growth rate, refractive index, and layer thickness has been achieved for molecular beam epitaxy growth of AlN∕GaN on GaN templates on Si(111) using laser interferometry at normal incidence. The reflectance data were analyzed using the proprietary (ORS Ltd.) software package R-FIT V2.0, which is capable of real-time fitting of the data to solutions of the equations of thin-film interference, hence yielding optimized values for optical constants (refractive index n, absorption coefficient k), growth rate (and hence film thickness) and surface roughness where appropriate. Changes in optimal fitting during growth are thus able to reveal changes in parameters such as growth rate. The problem of intermittent optical access due to the necessity of using a shutter to minimize view-port deposits was solved in two ways. First data were acquired continuously, only when the shutter was open, (1min in three), leading to widely spaced clusters of several data points. Subsequently...

Backside Etching at the Interface to Diluted Medium with Nanometer Etch Rates

The laser etching using a surface adsorbed layer (LESAL) is a new and promising method for precise etching of transparent materials such as fused silica. The etching process is based on the laser irradiation of the interface between a transparent solid and a diluted (vaporized) backside medium that forms an adsorbed layer. A KrF excimer laser (λ = 248 nm) with pulse duration of 25 ns is employed to study LESAL of fused silica. LESAL by means of toluene as adsorbate features outstanding attributes, e.g., low threshold fluences (< 1 J/cm²), an almost constant etch rate on the order of 1 nm/pulse over a wide fluence region, and very low, nearly optical grade surface roughness (~ 1 nm rms). As LESAL mechanism, the thermal ablation of a modified surface layer is discussed. The modification is caused chiefly by the deposition of decomposition products from organic molecules photolysis. The usage of halogenated adsorbate fluorobenzene (C6H5F), difluorobenzene (C6H4F2), chlorobenzene (C6H5Cl), and dichlorobenzene (C6H4Cl2) as diluted backside media reduces significantly the etching threshold and causes an additional characteristic fluence region with Angstrom/pulse etch rate and homogenous and smooth surface topography. The generation of halogen radicals close to the heated surface due to the decomposition of the solvent seems to be the most probably mechanism for a chemical erosion of the fused silica surface.