Extinction Coefficient Of Films Research Articles

Dependence of Structural and Optical Performance of Lanthanum Fluoride Antireflective Films on O Impurities

Lanthanum fluoride (LaF3) thin films were deposited on the Ge substrate using the molybdenum boat evaporation method. The effect of films’ oxygen impurity on the infrared optical properties has been investigated for the first time in this report. With the increase in oxygen content in the films, the F content decreases, and the O/F ratio decreases from 0.160 to 0.055. XRD patterns reveal that the presence of O impurity destroys the crystal structure integrity of the LaF3 films and leads to the intensification of infrared absorption. The average transmittance decreases from 58.1% to 52.2%, and the peak transmittance decreases from 59.9% to 54.5%. Additionally, the refractive index and extinction coefficient of LaF3 films with different oxygen content are obtained by fitting the transmittance test data. The results show that the refractive index and extinction coefficient of the films in 8–12 μm increase with the increase in oxygen content, the average refractive index increases from 1.339 to 1.478, and the extinction coefficient increases from 0.001 to 0.030. In this paper, the influence of oxygen impurity in the LaF3 film on its infrared optical properties is revealed, which lays a theoretical foundation for the development of high-performance LaF3 infrared antireflective film.

The free carriers loss, free carriers susceptibility, and optical VEL and SEL functions in ZnO films doped by Cu, Al, and Cu-Al composite nanoparticles

The purpose of this work is to investigate the optical constants of ZnO films doped by Cu, Al, and Cu-Al nanoparticles. The reflectance and the transmittance spectra measurements were applied for calculating these optical constants in the range of 200–2500 nm. It can be seen that ZnO films doped with Al nanoparticles have a maximum value nanoparticles size of about 23.73 nm. With increasing annealing temperature for all wavelength range, due to the improvement of crystalline structure and hence decreasing defects, the extinction coefficient of films decreased. The theoretical extrapolation of e1 versus λ2 at low wavelengths values provides the dielectric constant e∞ and for the ZnO films doped with Cu nanoparticles, it has a maximum value of 4.61. The ZnO films doped by Al nanoparticles have a minimum value of $${\chi }_{c}$$ in all energy range. The dissipation factor tan δ of ZnO films doped by Cu nanoparticles especially in high energy has a maximum value. SEL functions in ZnO films doped by Cu nanoparticles have the maximum value.

PRISA: a user-friendly software for determining refractive index, extinction co-efficient, dispersion energy, band gap, and thickness of semiconductor and dielectric thin films

A user-friendly software PRISA has been developed to determine optical constants (refractive index and extinction co-efficient), dispersion parameters (oscillator energy and dispersion energy), absorption co-efficient, band gap and thickness of semiconductor and dielectric thin films from measured transmission spectrum, only. The thickness, refractive index, and extinction co-efficient of the films have been derived using Envelope method proposed by Swanepoel. The absorption co-efficient in the strong absorption region is calculated using the method proposed by Connel and Lewis. Subsequently, both direct and indirect bandgap of the films is estimated from the absorption co-efficient spectrum using Tauc plot. The software codes are written in Python and the graphical user interface is programmed with tkinter package of Python. It provides convenient input and output of the measured and derived data. The software has a feature to cross check the results by retrieving transmission spectrum using the values of refractive index, extinction co-efficient, and thickness obtained from Envelope method. The performance of the software is verified by analyzing numerically generated transmission spectra of a-Si:H amorphous semiconductor thin films, and experimentally measured transmission spectra of electron beam evaporated HfO2 dielectric thin films as examples. PRISA is found to be much simpler and accurate as compared to the other freely available softwares. To help researchers working on thin films, the software is made freely available at https://www.shuvendujena.tk/download.

Simple method to extract extinction coefficients of films with the resolution of 10-5 using just transmission data and application to intermolecular charge-transfer absorption in an exciplex-forming organic film.

A simple method is presented to determine the thickness, refractive index and extinction coefficient of a film with the resolutions of ±1 nm, ±2 × 10-3, and 6 × 10-5, respectively. The method requires only ultraviolet-visible-near-infrared spectroscopy measurement of the transmittance of films with thicknesses of a few micrometers. A very small extinction coefficient of intermolecular charge transfer (CT) absorption of an exciplex-forming organic film is measured in the sub-bandgap wavelength region. This is to demonstrate that the CT absorption with extinction coefficient in the range of 10-3 to 10-5 can be measured indeed using the method, which is in the same resolution as photothermal deflection spectroscopy and Fourier transform photocurrent spectroscopy. The simplicity and feasibility of the proposed approach is expected to promote active study of intermolecular CT absorption in exciplex-forming films.

A new narrow bandgap polymer as donor material for high performance non-fullerene polymer solar cells

Abstract Polymer solar cells (PSCs) based on narrow bandgap (NBG) photovoltaic materials have attracted significant attention due to their unique applications in semitransparent devices and organic tandem solar cells. In this work, we design and synthesize a new NBG polymer PBTT based on 2-(2-ethylhexyl)-thienyl substituted benzodithiophene (BDT-T) and n-octyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TT) as donor material for the applications in non-fullerene PSCs. Compared with the widely used NBG polymer PTB7-Th, PBTT exhibited higher film extinction coefficient of 9.27 × 10 4 cm−1, higher-lying energy levels, more ordered molecule packing and higher hole mobility of 2.13 × 10 −3 cm2 V−1 s −1. The PSCs based on PBTT: IEICO obtained a power conversion efficiency (PCE) of 9.5% with a Voc of 0.86 V, a Jsc of 17.9 mA cm−2 and a FF of 61.3%, which is significantly enhanced over that (7.3%) of the corresponding devices with PTB7-Th as donor. The significantly improved PCE could be attributed to the higher charge mobility and the improved morphology of the PBTT: IEICO blend film. These results demonstrate that PBTT is a very promising NBG polymer donor material for the applications in non-fullerene PSCs.

Study on characterization method of optical constants of germanium thin films from absorption to transparent region

In this paper, the physical dispersion model of the optical constants of the amorphous germanium thin films was studied. Based on the Cody-Lorentz model, the optical constants of the films are characterized from the visible region to the long-wave infrared region. The optical constants are calculated from the inverse calculation of the reflection spectrum and the transmission spectrum in visible region. The calculated optical constants are extended to the infrared transparent region of the germanium thin films, which is consistent with the actual measurement results. The calculated optical constants are verified by the Cauchy model in the transparent region. According to the properties of band gap and tail width, the physical mechanism why the refractive index and extinction coefficient of films is greater than that of bulk material was determined. The decay rate of the germanium film in the long wave direction is lower than that of the germanium crystal due to the presence of the tail state in the germanium film material. Therefore, the refractive index and extinction coefficient of the film are greater than those of the bulk material.

Room temperature deposition of XRD-amorphous TiO2 thin films: Investigation of device performance as a function of temperature

In this study, TiO2 thin films were fabricated by radio frequency sputtering at room temperature in pure Ar atmosphere starting from a 6 in. TiO2 target. The thickness of the films was controlled by deposition time and the effect of Ar sputtering pressure on the characteristics of TiO2 thin films was evaluated. Surface morphology and optical properties of TiO2 films were investigated using X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and UV–Vis spectrophotometry. Also, the refractive index and extinction coefficient of films were inferred by fitting spectrophotometric data. Schottky diode were fabricated by evaporation of Ni on TiO2 films. Current-voltage (I-V) measurements of Ni/TiO2 films showed that the rectifying properties of the device improves with the increasing of TiO2 film density and thickness. Therefore, the best I-V characteristic of the device was investigated depending on the temperature. Also, Ni/n-TiO2/p-Si/Al devices were fabricated to understand their transport mechanism.

Effect of substrate temperature on the properties of Nb2O5:MoO3 (90:10) thin films prepared by rf magnetron sputtering technique

In this work, the effect of substrate temperature on the structural, optical, vibrational and electrochromic properties of radio frequency (rf) magnetron sputter deposited mixed Nb2O5:MoO3 (90:10) thin films have been studied. X-ray diffraction analysis revealed that all the deposited films belong to amorphous nature. The x-ray photoelectron spectroscopic study confirms the compositional purity and the presence of five-valent niobium (Nb5+) and six-valent molybdenum (Mo6+) in the deposited film. The average optical transmittance of the films varied between 88 and 92%. The refractive index and extinction coefficient of films are found to decrease with increasing substrate temperature. Photoluminescence spectra exhibit three characteristic emission peaks and confirm the better optical quality of the deposited film. The longitudinal and transverse optic modes of Nb–O stretching vibrations were observed from the micro-Raman study. The cyclic voltammograms of Li+ and H+ ions clearly show all the films are having better reversibility and reproducibility in their electrochemical analysis. The maximum coloration efficiency of 51.94 cm2/C was obtained for the mixed Nb2O5:MoO3 (90:10) film.

Effect of substrate temperature on structural and optical properties of nickel tungsten oxide thin films

In this work, we present the substrate temperature induced change in the structural, optical, vibrational and luminescence properties of mixed NiO:WO3 (95:5) thin films deposited on glass substrates by rf magnetron sputtering technique. X-ray diffraction analysis revealed the onset of crystallization of the films occurred at 300 °C. The average optical transmittance of the films varied between 91 and 97 % in the visible region. The refractive index and extinction coefficient of films are found to decrease with increasing substrate temperature. It was observed that the dispersion data obeyed the single oscillator of the Wemple-DiDomenico model, from which the dielectric constants, ratio between free carrier density and free carrier effective mass, plasma frequency, oscillator energy, oscillator strength, and dispersion energy parameters of NiO:WO3 films were calculated and reported for the first time due to variation in substrate temperature during deposition by rf magnetron sputtering. The micro-Raman result shows two broad peaks corresponding to one-phonon LO mode at 570 cm−1 and two-phonon LO mode at 1,100 cm−1 due to the vibrations of Ni–O bonds and the peak found at 870 cm−1 belongs to the W–O mode. Room temperature photoluminescence (RTPL) study exhibits two characteristic emission peaks at 3.32 eV (374 nm) and 2.93 eV (423 nm), which corresponding to the transition of 3d8 Ni2+ ions. We have made an attempt to discuss and correlate these results with the light of possible mechanisms underlying the phenomena.

Structural and optical properties of ZnO thin films prepared by sol–gel method

In this Letter thin films of zinc oxide (ZnO) are prepared by sol–gel method and deposited on glass substrate to evaluate structural and optical properties of the film. The films were grown at different thicknesses in the range of 100–180 nm. The properties of layers were characterised using X-ray diffractometer (XRD), atomic force microscope (AFM) and optical spectrophotometer to evaluate the quality of the thin film for photovoltaic applications. The results from XRD pattern revealed that the grown films exhibit wurtzite structure with (002) preferential plane. The results from AFM data revealed that the films had nano-sized grains with a grain size from∼25 to 60 nm depending on the film thickness. The optical spectrophotometer studies exhibited direct allowed transition with an energy bandgap of 3.12–3.02 eV for films with thicknesses of 100–180 nm, respectively. The refractive index as well as extinction coefficient of films was also measured.

薄膜消光系数对镀膜长周期光纤光栅传输谱的影响

薄膜消光系数对镀膜长周期光纤光栅传输谱的影响

Correlation between optical properties of MBE films of AlN and morphology of their surface

AbstractIn this work we revealed correlation between presence of surface defects and peculiarities in ellipsometric spectra and hence in optical properties of AlN films grown by ammonia MBE technique. We propose to use this fact for the fast and non‐destructive checking of film quality. Principal criterions of AlN films quality was both magnitude of phase deviation in maximum and/or a value of false (effective) absorption in transparency field of AlN calculated in according with our model. Our experiments were based on using of spectroscopic ellipsometry (SE). Atomic force microscopy (AFM) was used for determination of geometric size of overlayer roughness. Quantitative parameter related with surface morphology γs was proposed and influence of surface defects upon phase of light reflected was studied to evaluate surface quality from ellipsometric spectra at once, i.e. without any model calculations. Besides, an impact of surface defects upon film extinction coefficient is demonstrated in case when roughness is not taken into account. This approach could be useful for sorting identical films produced in routine growth procedure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of damage threshold to TiO 2 coatings at different laser wavelength and pulse duration

Laser-induced damages to TiO 2 single layers and TiO 2/SiO 2 high reflectors at laser wavelength of 1064 nm, 800 nm, 532 nm, and pulse width of 12 ns, 220 ps, 50 fs, 8 ns are investigated. All films are prepared by electron beam evaporation. The relations among microstructure, chemical composition, optical properties and laser-induced damage threshold (LIDT), have been researched. The dependence of damage mechanism on laser wavelength and pulse width is discussed. It is found that from 1064 nm to 532 nm, LIDT is mainly absorption related, which is determined by film's extinction coefficient and stoichiometric defects. The rapid decrease of LIDT at 800 nm is due to the pulse width factor. TiO 2 coatings are mainly thermally by damaged at long pulse ( τ ≥ 220 ps). The damage shows ablation feature at 50 fs.

Effects of substrate temperature on nanocrystalline diamond growth: an in-situ optical study using pyrometric interferometry

Pyrometric interferometry technique is carried out using a bichromatic infrared pyrometer in order to in-situ investigate the influence of the surface temperature variations on the properties of nanocrystalline diamond films, elaborated in Ar/H 2/CH 4 microwave discharges for different gas compositions. The analysis of the film/substrate system apparent temperature measured by the pyrometer during the synthesis process indicates that the optical absorption of the growing film increases as the deposition temperature is raised. In particular, this trend is underlined by the increase of the film extinction coefficient derived from the experimental curves that ranges from 0.1–0.2 at low and moderate temperatures to 0.6–0.7 at high temperatures. This suggests that the formation of non-diamond absorbent phases within the film, especially sp 2-hybridized compounds, is enhanced at high temperatures. This phenomenon is confirmed by further ex-situ characterizations giving evidence for a significant increase with surface temperature of the graphitic contents in the films. This demonstrates that the pyrometric interferometry is a powerful technique suitable for in-situ controlling and investigating the nanocrystalline diamond growth process.

Properties of titanium oxide film prepared by reactive cathodic vacuum arc deposition

TiO2 thin films were deposited on a soda-glass substrate as a function of gas pressure (0.1–2.0Pa) using conventional unfiltered vacuum arc deposition (UFA), and also deposited using a macroparticle-filtered arc deposition source (FAD). Crystalline structure, microhardness, elastic modulus, and optical properties (transmittance, reflectance, refractive index, extinction coefficient, absorption coefficient, and optical bandgap) were measured or evaluated. All films deposited on unheated substrates were amorphous, and post-annealed films as well as films deposited with in-situ heating were of the crystalline anatase phase. Similar mechanical and optical properties were obtained for the films deposited by UFA over a wide pressure range (0.1–1.0Pa). After the annealing process, the films became harder, and the extinction coefficient of the film increased. The transmittance and the extinction coefficients of films deposited by FAD were found to be slightly superior to those of films deposited by UFA. The optical bandgap was about 3.25eV for as-deposited amorphous material prepared by both UFA and FAD as well as for in-situ heated anatase film prepared by FAD.

Microstructures and optical properties of sol-gel derived TiO2 anatase thin films

TiO2 anatase thin films on quartz substrates were prepared with sol-gel method. The dry gel films, made by spin coating 10 times, were calcined at various temperatures. From X-ray diffraction analyses, it is found that the anatase to rutile phase transformation temperature of the films is higher than 850°C, the films are preferentially oriented on (0 0 1) plane, i. e.c-axis oriented. The thickness, refractive indexes, absorption coefficients and extinction coefficients of the films were determined from UV-Vis transmission spectra of the films using a UV-Vis spectrophotometer. The thickness of the films is about 570 nm. The refractive indexes, absorption coefficients and the extinction coefficients of the present films are larger than the values of anatase films prepared by sputtering. This indicates that the films made with sol-gel method are very dense.

Combined Spectroscopic Ellipsometry and Voltammetry of Tetradecylmethyl Viologen Films on Gold

Dynamic measurements of changes in composition and conformation during adsorption oftetradecylmethyl viologen (C 14 MV) on a gold electrode were made using spectroscopic ellipsometry. Film thickness measurements indicated that a monolayer is initially formed in which the viologen species is in the upright extended position and that conversion to a tilted conformation occurs during equilibration to the final monolayer film. Subsequent reduction of the film as electrode potential was scanned from -0.2 to -0.9 V resulted in linear growth to a multilayer film in which dications (C 14 MV 2+ ) were reduced to radical (C 14 MV .+ ) and neutral (C 14 MV 0 ) species. A gradual increase of the film charge-to-thickness ratio and of the film index of refraction during reduction indicated densification of the deposit. The pattern in the variation of film extinction coefficient with electrode potential indicated that radical dimers were the dominant species in the potential range corresponding to the first reduction step. During the reverse potential scan, the radical film detached due to faster reoxidation of the layers adjacent to the electrode surface.

Ellipsometric Characterization of Copper Deposits

The growth of copper layers electrodeposited from acidic solutions is investigated by in situ ellipsometry. The effect of nicotinic acid on the properties of the copper deposits is also reported. Refractive indices and extinction coefficients of films formed under diferent conditions were obtained by the use of optical models. The ellipsometric results can be interpreted using an anisotropic single layer model for the copper coatings which is related to the morphology of the deposits. The optical constants are strongly dependent on the deposition potential. The presence of the additive modifies slightly the optical properties of the electrodeposited copper layers.

Optical properties of ion assisted deposited zirconia thin films

The nature of the dependence of refractive index, extinction coefficient, and packing density of zirconia films prepared by ion assisted deposition on the energy and current density of ions has been investigated. A broad beam Kaufman ion source has been used to generate oxygen ions in the energy range 100–700 eV and current densities up to 220 μA/cm2. It has been found that the refractive index increases steadily up to an energy of 500 eV beyond which there is a nominal decrease. The highest index obtained was 2.21 at an energy of 500 eV and a current density of 220 μA/cm2. Similarly, with an increase in the current density the refractive index increases initially and seems to saturate beyond a certain critical value dependent on the ion energy. The extinction coefficient was low up to an energy of 300 eV showing a marked increase thereafter. The extinction coefficient was also found to increase at high ion current densities and energies. A critical ion energy and current density beyond which the refractive index as well as the extinction coefficient of these films start deteriorating has been observed.

Annealing Effect on Mechanical Stress in Reactive Ion-Beam Sputter-Deposited Silicon Nitride Films

Optical properties and mechanical stress of silicon nitride films deposited at room temperature by ion-beam sputtering are studied for various compositions in the range of N/Si=0.6 to N/Si=1.4. The refractive index and mechanical stress are investigated before and after annealing by ellipsometry and the Newton ring method. The silicon-rich film extinction coefficient and stress value decrease after annealing. These property variations are explained by a high structural disorder in films deposited at room temperature which is lowered during annealing. The study of a layer deposited at high temperature (600°C) enables us to check the thermal stress effect in the film. A stress evaluation in the film and at the Si3N4-Si interface shows that sputter-deposited silicon nitride is suitable for the local oxidation of silicon.