Optical Surface Roughness Research Articles

Interferometry with coherent Gaussian illumination for roughness and shape measurement

We describe a method that uses coherent Gaussian illumination for the interferometric measurement of roughness and shape of flat optical surfaces. This method allows varying the size of the area under examination of the surface under test without changing any components in the setup. For this, it is only necessary to adjust the position of one of the illuminating lenses of the system. Once the setup has been assembled, additional optical components are not necessary for examining different object areas; thus, diffraction effects that would be introduced by including additional components are avoided. A calculation of the diffraction due to the propagation of the beams through the system is presented to evaluate the precision of the method. For illustrative purposes the measurement of two different areas of an optical flat using a Michelson-type setup is presented.

Non-Destructive and Non-Contact Determination of Layer Thickness and Thermal Properties of PVD and Sol-Gel Layers by Photothermal Methods

Thin layers in combination with metallic substrates are often used for moulding tools. The layer properties depend on the coating parameters and technology (e. g., sol-gel, PVD, CVD). This paper presents the photothermal measurement of layer thickness and thermal properties of PVD and sol-gel layers which are needed for the development of moulding tools. The influence of optical parameters and surface roughness on the results is discussed.

Effects of Process Parameters on the Coating Properties of APS TiO2ioceramic Coatings

The effects of process parameters on coating formation and coating properties were investigated using a fused and crushed TiO₂ powder by the Taguchi method and L 9 (3⁴) orthogonal array. The Taguchi analysis was conducted through the results of the coating properties affected strongly by plasma spraying parameters and TiO₂ powder was sprayed on Ti-6Al-4V alloy substrate. The coating properties were characterized by thickness, microhardness, porosity and surface roughness using optical microscopy, image analyzer and surface roughness tester respectively. An observed optimum condition of plasma spraying process could be found for potential use as a bioceramic coating.

High Quality Sn-Doped In2O3 Films Grown by Pulsed Laser Deposition for Organic Light-Emitting Diodes

AbstractHigh quality Sn-doped In2O3 (ITO) thin films have been grown by pulsed laser deposition (PLD) on glass, flexible polyethylene terephthalate (PET) and single crystal yttria stabilized zirconia (YSZ) substrates for use in organic light emitting diodes (OLEDs). Critical electrode issues for the OLED are related to the optical transparency, electrical resistivity, work function and surface roughness of the ITO film. Our research has focused on improving the properties of the ITO film to increase the efficiency of the OLED. Films were deposited using a KrF excimer laser (248nm, 30 ns FWHM) at fluences of 2 J/cm2 at substrate temperatures ranging from 1 to 100 mTorr. For ITO films (∼ 100 nm thick) deposited at the optimized conditions, a resistivity of 4.1 × 10-4 Ω-cm, 2.2 × 10-4 Ω-cm, 1.8 × 10-4 Ω-cm was observed on PET, glass and YSZ, respectively. The average film transmission in the visible range (400 - 700 nm) was about 90 % and the film surface roughness was about 0.5 nm for the film grown on glass. The Hall mobility and carrier density for ITO films (300 nm thickness) were observed to be in the range of 28 - 34 cm2/V-s and 1.0 - 1.2 × 1021 cm-3, respectively. We have used the ITO films, deposited by PLD on glass, plastic and single crystal YSZ substrates, as an anode contact in OLEDs. The OLED device performance based on PLD ITO anodes is compared with that of the device fabricated on the commercial ITO anode.

Modelling of high temperature optical constants and surface roughness evolution during MOVPE growth of GaN using in-situ spectral reflectometry

An investigation of in-situ optical monitoring during metalorganic vapour phase epitaxy (MOVPE) growth of GaN is reported. We describe the modelling of experimental optical data to determine the important properties of the GaN films such as the high temperature optical constants, the evolving surface roughness during coalescence and the film growth rate. Real time spectral reflectometry has been implemented as a routine tool for quantitative and qualitative monitoring during GaN MOVPE growth across the wavelength range 300–750 nm. The technique allows rapid material optimisation for device performance and tracking of run to run variation. Two multilayer optical modelling techniques have been investigated to simulate the time-dependent reflectance signatures. A virtual interface method where the simulation must begin after a smooth surface has been achieved, and an enhanced modelling routine, developed in-house, to include the evolving surface roughness during coalescence. It is shown that the high temperature optical constants are in close agreement with the limited published literature values, and the growth rate is consistent with post-growth thickness measurements. Using atomic force microscopy (AFM) and spectroscopic ellipsometry to study the surfaces of interrupted GaN growth runs, we show for the first time that the surface topography of a GaN film during coalescence contains components of both macroscopic and microscopic roughness with respect to the optical monitoring wavelengths. Additionally, we obtain very good agreement between values of RMS roughness determined by in-situ spectral reflectometry and spectroscopic ellipsometry compared with AFM.

High-resolution ellipsometric study of an n-alkane film, dotriacontane, adsorbed on a SiO2 surface

Using high-resolution ellipsometry and stray light intensity measurements, we have investigated during successive heating-cooling cycles the optical thickness and surface roughness of thin dotriacontane (n-C32H66) films adsorbed from a heptane (n-C7H16) solution onto SiO2-coated Si(100) single-crystal substrates. Our results suggest a model of a solid dotriacontane film that has a phase closest to the SiO2 surface in which the long-axis of the molecules is oriented parallel to the interface. Above this “parallel film” phase, a solid monolayer adsorbs in which the molecules are oriented perpendicular to the interface. At still higher coverages and at temperatures below the bulk melting point at Tb=341 K, solid bulk particles coexist on top of the “perpendicular film.” For higher temperatures in the range Tb<T<Ts where Ts=345 K is the wetting temperature of the bulk phase, the coexisting bulk particles melt into droplets; and for T>Ts, a uniformly thick fluid film wets to the parallel film phase. This structure of the alkane/SiO2 interfacial region differs qualitatively from that which occurs in the surface freezing effect at the bulk alkane fluid/vapor interface. In that case, there is again a perpendicular film phase adjacent to the air interface but no parallel film phase intervenes between it and the bulk alkane fluid. Similarities and differences between our model of the alkane/SiO2 interface and one proposed recently will be discussed. Our ellipsometric measurements also show evidence of a crystalline-to-plastic transition in the perpendicular film phase similar to that occurring in the solid bulk particles present at higher coverages. In addition, we have performed high-resolution ellipsometry and stray-light measurements on dotriacontane films deposited from solution onto highly oriented pyrolytic graphite substrates. After film deposition, these substrates proved to be less stable in air than SiO2.

Effect of surface roughness on the optical properties of multilayer polymer films

Results of the influence of the surface roughness on the optical transmittance and on the interference spectral fringes produced by reflection of parallel layers of multilayer polymer films are reported. Samples studied were multilayer materials for graphic arts, obtained by spreading adherent emulsion layers over both sides of a substrate of polyethyleneterephatalate (PET) film with different surface roughness. The range of wavelengths of radiation studied is from 320 to 2500 nm, i.e. covering the ultraviolet and visible (UV–Vis), near-infrared (NIR) and infrared (IR) spectra. Strong correlations between spectral parameters of the optical transmittance and surface roughness were found, showing that these spectroscopical techniques are good complementary ways to study the surface characteristics of these engineering materials.

Real Time Spectroscopic Ellipsometry of Amorphous Silicon Grown at High Deposition Rates by Hot-Wire CVD

AbstractWe use real-time spectroscopic ellipsometry (RTSE) for in-situ characterization of the optical properties and surface roughness (Rs) of hydrogenated amorphous silicon (a-Si:H) grown by hot-wire chemical vapor deposition (HWCVD) with varying deposition rates (5 to 120 Å/s). Early time evolution of the Rs during growth is remarkably similar for all deposition rates. During the first few Ås of growth, there is a sharp increase in Rs as the a-Si:H nucleates in separate islands. This is followed by a reduction of Rs as these areas coalesce into a bulk film, which occurs at an average thickness of 100 Å. After coalescence the Rs rises to a stable value that is dependent upon growth conditions with a general tendency for the Rs to increase with growth rate. However, neither the Rs nor the material electronic properties are unique for a given deposition rate. Films grown under high silane flow and low pressure have a better photoresponse and a lower Rs than films grown at the same deposition rate but with low silane flow and high pressure. We observe a stronger correlation of film properties with Rs than with deposition rate; namely a monotonic decrease in photo-response, and increase in optical gap, with increasing Rs.

Structural and optical properties of silver thin films deposited by RF magnetron sputtering

In this work, we investigate the optical and the structural properties of Ag films by means of spectrophotometric techniques and X-ray diffraction methods in the low- and high-angle regimes. The coatings were grown by radio frequency magnetron sputtering on (100)-oriented silicon substrates. Several sets of samples were produced by varying the sputtering pressure (0.15–0.9 Pa) and changing the sputtering power supply in the range of 25–100 W. In particular, the dependence of the coating optical features, surface roughness, texture and residual stress on the parameter β, proportional to the momentum transferred to the growing film from the energetic particles bombarding it, was pointed out. The results indicate that the Ag films are polycrystalline with a moderate [111] texture and compressive in-plane stress was measured for all the investigated samples. The behavior of the stress with the momentum parameter can be summarized as follows: (i) the compressive stress increases in the range 0<β<300 V 2s/Å; (ii) at β∼400 V 2s/Å it shows a very pronounced maximum; (iii) in the range 400<β<800 V 2s/Å it decreases until reaching a saturation value for β>1000 V 2s/Å.

Study of the growth morphology of TiO 2 thin films by AFM and TEM

High refractive index TiO 2 thin films have been deposited by electron-beam evaporation on Si (111) wafers. The substrate temperature during deposition was maintained at 250°C and the deposition rate was approximately 0.05 nm/s. Qualitative film analysis was performed with atomic force microscopy (AFM) and transmission electron microscopy (TEM). It was noted that surface roughness of the film increases with layer thickness and that the growth morphology is different for the films evaporated under the same conditions. A correlation was established between the optical properties, surface roughness and growth morphology of the evaporated TiO 2 thin films.

Optical surface roughness evaluation of phosphorus-doped polysilicon films

The surface roughness of phosphorus-doped polycrystalline silicon (polysilicon) film is widely believed to be related to its electrical property. In this work, the roughness of polysilicon films prepared in situ under varied processing conditions, is determined using an optical technique that is based on measuring the spectral absorbance of specularly reflected light. The roughness measurements attained are found to follow the logical trend of roughness anticipated from phosphorus-doped polysilicon prepared under controlled variations of temperature, pressure and phospine/silane flow ratio.

In-process monitoring of grinding and polishing of optical surfaces

A new tool with which to monitor the quality (roughness and subsurface damage) of optical surfaces during grinding and polishing, intensity-detecting total internal reflection microscopy (iTIRM), is presented. A general description of the new measurement method is given, followed by a description of the experimental in situ measurement setup. Experimental results of the method are presented that demonstrate that iTIRM can be used either to control the roughness-reduction process during production or to investigate the process itself. The possibility of implementing the method in an optical workshop is discussed.

Optical surface roughness study of starch acetate compacts

Optical surface roughness of starch acetate compacts was investigated by specular reflection of a laser beam as a function of angle of incidence. The intensity data was fitted using the model of Gaussian and Lorentzian curves to solve numerical values for optical surface roughness which was observed to be order of 1 μm with the present samples.

Surface roughness measurement using an optical system

In recent years there have been a number of research studies carried out into optical surface roughness measurement, since the optical method has several advantages over the mechanical measuring system. In the present study, an optical method relying on the reflected beam intensity profile is introduced. An He–Ne laser beam is used to scan the surface and a fibre optic probe is employed to collect the reflected beam from the workpiece surface. The reflected beam intensity distribution is approximated by a Gaussian function. Since the data collection is sampled every 1 ms, a considerable number of profiles corresponding to each point at the workpiece surface are collected. However, for a known surface, there exists a unique average surface roughness value. Therefore, the data collected for each profile should be combined to produce a profile that represents the average surface roughness value for that particular surface. Consequently, the reflected beam intensity profile is processed using two different methods, which are: (i) averaging the data points in the intensity profile before introducing the curve-fitting technique; and (ii) introducing curve fitting to obtain the constants for the Gaussian function for each intensity profile, then averaging the constants over the number of profiles. The surface roughness profiles and average surface roughness value (Ra) is measured initially using a Bendix surface proficoder. The relationship between Ra values and the standard deviation (S.D.) of Gaussian function (SDGF) is developed. The study is extended to include uncertainty analysis and standard estimate of errors in the measurement system. It is found that the first method gives an improved standard estimate of error. Moreover, a linear relationship exists between the Ra values and the SDGF of the reflected beam intensity, the greater are the SDGF values the greater is the surface roughness. However, the measurement is limited to a certain range of Ra values; in this case, the accuracy of the measurement drops considerably as the Ra value increases beyond 1 μm.

Comparative study of the roughness of optical surfaces and thin films by use of x-ray scattering and atomic force microscopy

The surface roughness of polished glass substrates and optical thin-film coatings is studied with atomic force microscopy and x-ray scattering. It is demonstrated that both methods permit the determination of power spectral density functions in a wide range of spatial frequencies. The results are in good quantitative agreement.

Determination of the optical constants of diamond films with a rough growth surface

The determination of the optical constants n and k for polycrystalline diamond films with typical growth surface roughness σ of the order of tens to hundreds of nanometers is both an important and a difficult procedure. A method for determining n, k and σ for rough diamond films is presented here. It is based on theoretical expressions for the optical reflectance R and transmittance T for a free-standing thin film incorporating the effects of surface scattering at one surface. The usefulness and validity of this approach are illustrated using experimental R and T data for diamond films. Simplified expressions for R and T are also presented which are valid when scattering or absorption are sufficiently strong to cause interference effects in the films to be averaged out. Prime novelty: Simple expressions for n, k and σ are presented which will enable researchers to extract this important information about the optical constants and surface roughness of their CVD diamond films.

Improvement of diamond X-ray mask membrane: Optical transmittance, surface roughness and irradiation durability

A viable method for the improvement of the polycrystalline diamond X-ray mask membrane is proposed. The use of an ionized cluster beam yields the smoothest surface. Sol-gel planarization film coating with indium tin oxide is the most effective method for obtaining high optical transmittance without sacrificing high synchrotron irradiation durability.

On simultaneous optical sensing of local curvature and roughness of metal surfaces

A novel sensor array for metal-surface curvature and roughness inspections is investigated. The sensor is based on the use of a computer-generated hologram as an analyser of surface curvature and roughness. The sensor can be exploited to estimate the optical surface roughness of irregularly curved surfaces. A contrast parameter to characterize the optical surface roughness is introduced.

Optical sensing of surface roughness and waviness by a computer-generated hologram

An optical surface roughness and waviness sensor for sufficiently smooth surfaces is introduced. The sensor is based on a computer-generated hologram , which focuses the specular reflectance to desired spots on the focal plane. Computer simulations were made to analyze the system and to compute the calibration curve. Contrast analysis was performed to estimate the average roughness of Gaussian surfaces. Results are compared with data measured form surface roughness standards.

Characterization of Sputtered Cerium Dioxide Thin Films

Thin films of CeO2 deposited by rf magnetron sputtering on sapphire and silicon substrates have been characterized with variable angle spectroscopie ellipsometry, atomic force microscopy (AFM), transmission electron microscopy and x-ray diffraction. A novel multiple model was used successfully for determination of the optical properties and surface roughness of the CeO2films. AFM analysis showed that the CeO2 films have hillock-shaped facet morphology. It was found that the surface roughness of CeO2 increased with film thickness. For films on sapphire substrates, the surface morphology and the crystalline quality were improved by post-annealing, e.g. flat surfaces were obtained after annealing at 1100 °C.