Theoretical and experimental study of photo-modulated reflectivity detections for transparent film/opaque substrate structures

A photo-modulated reflectivity method is used to evaluate thermal properties of bilayered structures composed of transparent films deposited on opaque substrates. In order to calculate the photo-modulated reflectivity variations of the bilayered structures induced by focused modulated laser irradiations, a 3-D theoretical model is presented. Due to the complexity of the 3-D theory, a finite element method is used to simulate the laser-induced temperature fields, thermoelastic displacement fields and dielectric constant variations, and finally the photo-modulated reflectivities. Then a quantitative investigation of the thermal properties of the transparent films deposited on opaque substrates can be performed by the experimental measurements and theoretical simulations. As examples, the thermal conductivities of ZnO and diamond films deposited on silicon substrates are evaluated and discussed. PACS 44.10.+i; 42.55.-f; 51.70.+f; 68.60.-p     

Laser diagnostics of nanoscale dielectric films on transparent substrate by integrating differential reflectivity and ellipsometry

The effect of nanometer dielectric films on the differential reflection characteristics of linearly polarized light from non-absorbing materials is investigated in the long-wavelength approximation. The second-order formulas for changes in the reflectance of s- and p-polarized light caused by ultrathin layer are obtained. A detailed analysis of the influence of ultrathin film to the reflectivity of p-polarized light in the vicinity of the Brewster angle is carried out. The novel methods are developed for determining the thickness and refractive index of uniform (or the average values of refractive index of nonuniform) nanometer-scale films by differential reflectivity and ellipsometric measurements.     

Elastic-plastic analyses on the residual stresses and curvature of the film/substrate bilayer system

During thermal cycling, the residual stresses are often generated in the film/substrate bilayer due to the material mismatch between the substrate and the film. If the thickness of the film is relatively high, the thermal residual stresses in it may be of different signs. When the film is subjected to elastic-plastic deformation, two plastic zones with different thicknesses may be generated in the film at a significantly high temperature difference. In this paper, a theoretical model which reflects the complete history of thermal residual stresses and curvatures in the elastoplastic film/substrate bilayer system is developed. Solutions are derived to estimate the residual stresses and curvature in the film as functions of temperature difference. The case of Al/Si system is used to illustrate the implementation of this model. Results show that the critical temperature difference at which the second plastic zone near the film surface is generated near the Al film surface is dependent on the film thickness. The strain hardening of the film has an obvious influence on the magnitude of residual stresses within the film at high temperature difference.     

Radio-photoluminescence properties of CaF2 transparent and opaque ceramics

Radio-photoluminescence (RPL) phenomenon was observed in CaF₂ transparent and opaque ceramics by X-ray irradiation. The RPL appeared as a formation of photoluminescence (PL) emission bands located around 660 and 720 nm caused by F₂⁺ and (F₂⁺)_A centers, respectively. The RPL signal can be deleted by heating, and reusability was observed over ten experimental cycles. The fading of the RPL signal was confirmed to be ~4% in 10 days. The detectable RPL response of CaF₂ transparent ceramics was as low as 1 mGy, and the dynamic ranges were confirmed over 1–10000 mGy with linear response.     

Characteristics of Scholte wave and film characterization in layered thin film overlying substrate structures

The layered film-substrate structure is widely used in many fields such as microelectronic devices, but the ultrasonic measurement of film material parameters, especially the characterization of shear wave velocity, is a difficult problem. In this paper, the dispersion characteristics of Scholte wave at the liquid-solid interface and the acoustic pressure response generated by a pulse excitation are theoretically analyzed. The results show that the Scholte wave dispersion at the liquid-solid int...     

Characteristics of surface acoustic waves in (1120) ZnO film/R-sapphire substrate structures

surface acoustic wave;;(1120)ZnO films;;R-sapphire;;finite element method     

Stoney formula for piezoelectric film/elastic substrate system

With the trends in miniaturization, and particularly the introduction of micro- and nano-electro-mechanical system,piezoelectric materials used in microelectronic devices are deposited usually in the form of thin film on elastic substrates.In this work, the bending of a bilayer comprising a piezoelectric film deposited on an elastic substrate, due to the mismatch,is investigated. An analytic formula relating the curvature of the bilayer to the mismatch, the electroelastic constants and the film thickness is obtained, and from this formula, a transverse piezoelectric constant d_31 can be estimated. Meanwhile the influence of electromechanical coupling coefficient on the curvature is discussed.     

Characteristics and self-cleaning effect of the transparent super-hydrophobic film having nanofibers array structures

Transparent super-hydrophobic films were fabricated using the PDMS method and silane process, based on anodization in phosphoric acid. Contact angle tests were performed to determine the contact angle of each film according to the anodizing time. Transmittance tests also were performed to obtain the transparency of each TPT (trimethylolpropane propoxylate triacrylate) replica film according to the anodizing time. The contact angle was determined by studying the drop shape, and the transmittance was measured using a UV-spectrometer. The contact angle increases with increasing anodizing time, because increasing pillar length can trap more air between the TPT replica film and a drop of water. The transmittance falls with increasing anodizing time because the increasing pillar length causes a scattering effect. This study shows that the pillar length and transparency are inversely proportional. The TPT replica film having nanofibers array structures was better than other films in aspect of self-cleaning by doing quantitative experimentation.     

Controllable fabrication and characterization of conical nanocarbon structures on polymer substrate for transparent and flexible field emission displays

The direct fabrication of fully transparent conical nanocarbon structures (CNCSs) of controlled nanoscopic dimension on a flexible nafion substrate was achieved, using field electron source, by a novel room temperature ion irradiation technique. By controlling the sizes (below the wavelength of visible light) of the CNCSs, the transparency of the substrate can be tailored satisfactorily. The transparency of the CNCSs was observed to be around 90% in the visible regime depending on the ion irradiation time. Our results suggest that the direct fabrication of well controlled fully transparent CNCSs on any transparent and flexible substrate at room temperature could open a novel route for potential applications in future highly transparent, flexible (bendable), low weight and portable field emission displays (FEDs). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

纳米晶SnO2透明导电薄膜的研制

阐述了金属氧化物透明导电薄膜研究的发展情况及其应用前景。介绍了采用磁控溅射技术,使用混合气体Ar和O     

Evaluation of the substrate effect on indentation behavior of film/substrate system

A method to evaluate the substrate effect quantitatively in film indentation is proposed. For the thin film deposited on the substrate, the power function relationship is used to describe the loading curve of the film indentation behavior. The loading curve exponent of the power function which is the fitting parameter can reflect the substrate effect quantitatively. The finite element method is used to simulate the nanoindentation process of the film/substrate system. The loading curve exponent can be obtained from the simulation results. A substrate effect factor based on the loading curve exponent is defined to characterize the effect of the substrate on film indentation. Meanwhile, the dimensionless function of the loading curve exponent related with the material properties and indentation depth is obtained. The results can be helpful to the measurement of the mechanical properties of thin films by means of nanoindentation.     

Determination of the refractive index and thickness of a transparent film on a transparent substrate from the angles of incidence of zero reflection-induced ellipticity

Linearly polarized light incident on a transparent film coating a transparent substrate remains linearly polarized after reflection only at a set of discrete angles of incidence φ_m (m integer). Measurement of these angles of incidence for zero reflection-induced ellipticity (ZRIE) allows simple, direct and explicit determination of the refractive index and thickness of the film, independent of the substrate refractive index. The latter can be separately and easily determined from the azimuths of the incident and reflected linear vibrations at one of the angles of incidence φ_m or, alternatively, from the angle of refraction of light into the substrate using Snell's law. The proposed technique requires that the thickness of the film exceed one-fourth the wavelength of light in the medium of the film, and that it does not fall in a “higher-order” thickness gap when the ratio of the refractive index of the film to that of the ambient is greater than $\text{2}\text{√3}$.     

The electronic structures of epitaxial CrSi2 film prepared on Si(111) substrate

The valence band (VB) electronic structures of CrSi₂ were studied by synchrotron radiation photoemission. Overall features of the VB photoemission spectra measured at room temperature (RT) and 20 K by using synchrotron radiation (photon energy, hν=20–120 eV) were similar. Two characteristic emissions were observed corresponding to the bonding and the nonbonding Cr-d partial density of states (PDOS) in the CrSi₂. The onset of the VB photoemission measured at 20 K was located at about 0.32 eV below Fermi level, due to the energy band gap of CrSi₂ more than 0.32 eV.     

Enhanced cleaning of photoresist film on a transparent substrate by backward irradiation of a Nd:YAG laser

Laser cleaning of a photoresist (PR) on a glass substrate using ns-pulsed Nd:YAG laser was studied. The direction of the substrate facing the laser beam was varied as a main parameter as well as the power of the laser beam. The backward irradiation (BWI) of the third harmonic beam (355 nm) completely removed 1.2 μm thick PR layer with three pulses at 1.5 J/cm² leaving no residues behind; while the forward irradiation (FWI) at the same condition just partially cleaned it. To investigate the difference of removal mechanisms between irradiation directions, the size distributions of particulates generated during laser cleaning were observed using an optical particle counter. The concentration of micron-sized particulates increased with increasing laser fluence up to 1 J/cm² for FWI and 0.5 J/cm² for BWI and then decreased at higher fluences because the target was a very thin film. The concentration of larger particulates for BWI was much higher than that for FWI implying the difference in removal mechanisms. In consideration of the size characteristics of the particulates and the temperature profiles of the PR layer, the most probable distinct mechanism for the BWI would be a blasting due to high temperature at the PR/glass interface. The particulate number concentration decreased rapidly after the completion of cleaning, suggesting that the measurement of the particulate concentration could detect the progress of the cleaning. Our results demonstrated that the backward irradiation will be useful for the laser cleaning of film-type contaminants on an optically transparent substrate.     

Experimental study of the time-resolved reflectivity of chromium film

The transient time-resolved reflectivity of chromium film is studied by femtosecond pump-probe technique with a 70-fs laser. Experimental results show that the reflectivity change increases with the power of the pump laser. The fast decrease of the reflectivity occurs between 0-200 fs which is mainly due to the electron-electron interaction. Subsequencely, the slower recovery of the reflectivity between 200-900 fs is mainly due to the electron-phonon coupling process. The reflectivity after 900 fs rises little to a near-constant value for the thermal equilibrium of the system. The experimental results can be explained properly with numerical simulation of the two-temperature model. It is helpful for understanding of the electron ultrafast dynamics in chromium film.     

Ellipsometric analyses for an absorbing surface film on an absorbing substrate with or without an intermediate surface layer

Various ellipsometric analyses have been derived to characterize the optical properties of a single-layer or a double-layer surface film overlaid on a substrate material. The general numerical technique is independent of the method (or methods) used in the series of ellipsometric measurements which provide the raw data. The convergence to unambiguously determined values of the unknown parameters is systematically carried out in the numerical search procedure. Selected examples are presented to illustrate the validity of various analyses and the possible usage of these analyses to optimize the experimental conditions and measurement methods.     

透明薄膜的干涉相干峰分离算法

白光干涉技术具有高度唯一性,广泛地被使用在三维表面形貌和台阶高度的测量。但是测量透明薄膜时,薄膜表面和基面都有光线反射与参考光线交汇,在被测表面的同一个位置不同高度两次产生干涉条纹,其干涉相干图中出现两个峰值。通过分析透明薄膜产生的干涉相干图的特点,提出了两种算法用来分离不同表面产生的干涉条纹。理论分析和试验结果表明,利用垂直扫描白光干涉法测量透明薄膜,由峰值分离算法和定位算法分别提取薄膜的上下表面,能够得到透明薄膜的高精度三维形貌和厚度信息。     

A null method for making absolute measurements of the reflectivity of transparent solids with high precision

A null method is described for making absolute measurements of the surface reflectivity of transparent solids with high precision ( ≈ 1 part in 10⁴). The phase sensitivity of a two beam interferometer is used to separate signatures of different order produced by multiple reflections in the air gap of a Fabry-Perot etalon constructed from the specimen. Then, by using two apertures in front of the etalon and two moving mirrors, signatures of different order are brought simultaneously to the output port of the interferometer. A difference signal is produced by subtracting the two signatures either optically or electronically, and the apertures are adjusted to produce a null output. The experimental value of the reflectivity is determined by the ratio of the areas of the two apertures and is independent of the photometric accuracy of the detector. The method should also be suitable for investigating weak structure in the reflectivity of transparent solids at the level of ≈ 10⁻⁵ or less.     

Broadband antireflective structures with hole for highly transparent glasses

Optimal sub-wavelength structures (SWS) with parabolic hole on glass substrate are designed using effective medium theory (EMT), which will reduce the reflectance over wavelength range from 300 to 1200 nm and 0° to 80° angle of incidence. The performance of SWS integrated glass is verified by genetic algorithm. The optimized SWS with the cross-sectional profile of parabolic hole have parameters with ∼120 nm diameter and 300 nm height. The average reflectance over wavelength range from 300 to 1200 nm and 0° to 80° angle of incidence could be reduced to only 0.5% by applying the optimized SWS onto glass.     

Synthesis of transparent BaTiO3 nanoparticle/polymer composite film using DC field

Transparent BaTiO₃ nanoparticle/polymer composite films were synthesized from titanium-organic film and barium ion in aqueous solution under direct current (DC) field. Titanium-organic precursor was synthesized from titanium isopropoxide, acetylacetone and methacrylate derivative. The UV treatment was effective to increase the anti-solubility of the titanium-organic film during DC processing. BaTiO₃ nanoparticles were crystallized in the precursor films on stainless substrates without high temperature process, as low as 40°C. The crystallite size of BaTiO₃ increased with increasing reaction temperature from 40 to 50 °C at 3.0 V/cm. BaTiO₃ nanoparticles also grew in size with increasing reaction time from 15 min to 45 min at 3.0 V/cm and 50 °C. Transparent BaTiO₃ nanoparticle/polymer films were synthesized on stainless substrates at 3.0 V/cm and 50°C for 45 min.