Refractive Index Of Thin Films Research Articles

Investigation of Physical Properties of Nanostructured Selenium-Based Compound Semiconductors

The study of physical properties of compound semiconductors plays a vital role in the device fabrication point of view. Different investigations suggest that one can tune these properties by impurity dopants, irradiation techniques, adopting different synthesis techniques, etc. In this study, the physical properties of nanostructured thin films of Se–S compound were tuned by different Hg dopant concentrations. X-ray diffraction spectra clarify the preferred crystallite growth occurs in the cubic phase of the corresponding Bravi’s crystal system. The particle size calculated from Bragg’s reflection spectra by using Scherrer’s analytical formula illustrates an enhancement of crystallite size in highly concentrated Hg-doped sample. Similar consequences are found in surface morphological micrographs. The optical band gap reduced from 1.65[Formula: see text]eV to 1.54[Formula: see text]eV on increasing the doping concentration of Hg, according to the computed optical parameters using optical transmission spectra in the wavelength range 200–1100[Formula: see text]nm. The thin-film refractive index dispersion data fits well in accordance with the single oscillator model. Investigation of electrical properties tells that there is significant improvement in electrical conductivity in highly concentrated Hg-doped samples. Therefore, the apparent tuning as observed in the physical properties of the investigated material may have practical uses in industry for a variety of optoelectronic devices.

Metasurface array for single-shot spectroscopic ellipsometry

Spectroscopic ellipsometry is a potent method that is widely adopted for the measurement of thin film thickness and refractive index. Most conventional ellipsometers utilize mechanically rotating polarizers and grating-based spectrometers for spectropolarimetric detection. Here, we demonstrated a compact metasurface array-based spectroscopic ellipsometry system that allows single-shot spectropolarimetric detection and accurate determination of thin film properties without any mechanical movement. The silicon-based metasurface array with a highly anisotropic and diverse spectral response is combined with iterative optimization to reconstruct the full Stokes polarization spectrum of the light reflected by the thin film with high fidelity. Subsequently, the film thickness and refractive index can be determined by fitting the measurement results to a proper material model with high accuracy. Our approach opens up a new pathway towards a compact and robust spectroscopic ellipsometry system for the high throughput measurement of thin film properties.

A simple new method for retrieving spectral changes of the refractive index of thin films from transmission spectra

A new method for calculating the refractive index spectral behaviour of thin films is presented. The method is based on introducing the idea of the order of appearance technique to accurately find the order of interference and Cauchy fitting parameters of the interference peaks observed in the transmission spectra of the thin film under investigation. A very simple mathematical relationship was found that relates the order of appearance and wavenumber of the interference peaks observed in the transmission spectrum. Fitting the data extracted from the measured transmission spectra to the newly found simple mathematical relation, we can extract the order of interference and Cauchy fitting parameters of the thin film under investigation. In addition, the thickness of the film was extracted and found to agree well with the thickness measured using the spectroscopic ellipsometery technique. The proposed method of calculation was successfully applied to five binary semiconductor samples, which are ZnO, ZnTe, ZnS, ZnSe, and SiO2. A very good agreement was found between the proposed method of calculation and the well-known method presented by Swanepoel. Finally, the effect of surface roughness on the FECO peak wavelength was discussed.

Measurement of the thickness and refractive index of a thin film by analyzing reflected interference fringes.

We propose a novel, to the best of our knowledge, method to estimate the thickness and refractive index of a thin film by analyzing the reflectance as a function of the incidence angle. In most cases, interference fringes cannot be obtained from a film within a practical angular range unless it is much thicker than the wavelength. This problem was solved by adopting a high-index material as the medium of incidence, in which case several cycles of interference fringes were observed within a small range of incidence angles near the critical angle, allowing a fringe analysis. Consequently, the thicknesses, as well as the refractive indices of dielectric thin films, could be estimated. Our proposed method gave uncertainties of 20nm and 0.0004 for the thickness and refractive index measurements, respectively.

Numerical evaluation of an external environment effectiveness to the surface plasmon mode in Au slot waveguide for design the sensor simulation

The effective permittivity of gold thin films with an external thin dielectric layer on the top and core of the slot waveguide was evaluated as an effective compound semi-metal layer of the surface plasmonic polariton slot waveguide that will vary due to some environmental factors. By uses simple parallel and series permittivity of compound material, this value need for the computation of the effective propagating vector βsp. This takes for a sensor model designing which the external environment effectiveness was changed by the surface plasmonic mode in its slot waveguide. So the resonance length and grating period are evaluated for the sensor model in the first. Further, the propagation of the SPP surface wave mode along the interface between the compound cladding and Si dielectric waveguide is computed, while the effective refractive index of the compound cladding of the slot waveguide is increased from 1 − 1.50. The computation results showed that the TM0 mode power transfer and propagation length seem to vary with this effective refractive index of the compound cladding on the surface plasmonic polariton waveguide. The 140 nm gap width and 3.70 mm long waveguide is also simulated by the finite different time domain method in the optiwave program, where the TM0 mode transition output is corrected, while the refractive index of the environment layer is changed. The results of the simulation showed good agreement with the computation in that the TM0 mode depends on the external refractive of index and input wavelength. This result shows that loss peak ships vary with the external refractive index thin film layer and input wavelength. Thus, they seem to be useful for sensor applications such as the solution concentration analytic.

Measuring complex refractive index through deep-learning-enabled optical reflectometry

Optical spectroscopy is indispensable for research and development in nanoscience and nanotechnology, microelectronics, energy, and advanced manufacturing. Advanced optical spectroscopy tools often require both specifically designed high-end instrumentation and intricate data analysis techniques. Beyond the common analytical tools, deep learning methods are well suited for interpreting high-dimensional and complicated spectroscopy data. They offer great opportunities to extract subtle and deep information about optical properties of materials with simpler optical setups, which would otherwise require sophisticated instrumentation. In this work, we propose a computational approach based on a conventional tabletop optical microscope and a deep learning model called ReflectoNet. Without any prior knowledge about the multilayer substrates, ReflectoNet can predict the complex refractive indices of thin films and 2D materials on top of these nontrivial substrates from experimentally measured optical reflectance spectra with high accuracies. This task was not feasible previously with traditional reflectometry or ellipsometry methods. Fundamental physical principles, such as the Kramers–Kronig relations, are spontaneously learned by the model without any further training. This approach enables in-operando optical characterization of functional materials and 2D materials within complex photonic structures or optoelectronic devices.

Thickness and refractive index measurements of a thin-film using an artificial neural network algorithm

Thin-film thickness and refractive index measurements are important for quality control in many high-tech industrial manufacturing processes, such as the semiconductor, display, and battery. Many studies have been carried out to measure the thickness and refractive index of thin-films, and recently studies using an artificial neural network (ANN) algorithm have also been conducted. However, strict evaluations of ANNs were not reported in all previous studies. In this study, a multilayer perceptron type of ANN algorithm for simultaneously analyzing the thickness and refractive index of a thin-film is designed and verified by using four thin-film certified reference materials (CRMs) being traceable to the length standard. According to the number of hidden layers and the number of nodes for each hidden layer, 12 multilayer perceptron type ANN algorithms were designed and trained with a theoretical dataset generated through optics theory based on multiple interferences. Subsequently, the interference spectra measured by the four CRMs were put into the 12 trained ANNs as input, and it was checked whether or not the output values were in good agreement with the corresponding certified values of both the thickness and refractive index. As a result, an ANN algorithm having two hidden layers with 100 nodes was selected as the final algorithm and an uncertainty evaluation was performed. Finally, the combined uncertainties for the thickness and refractive index were estimated to be 2.0 nm and 0.025 at a wavelength of 632.8 nm, respectively, as measured using a spectral reflectometer with the well-trained ANN algorithm.

Determination of optical constants and band gap variation of Zn0.98-xCu0.02MgxO thin films

Cu doped ZnO (ZnCuO) is a very important candidate for electronic applications, since it has been shown that it possesses p–type conductivity. In order to broaden its applications, it is crucial to tune optical and electronic properties. In this study, by doping ZnCuO with magnesium, variation of refractive index, extinction coefficient, and band gap of thin films were investigated. Optical constants were evaluated using a transmittance model which is derived from Fresnel equations. Refractive indices of thin films were expressed as a dispersion relation in a polynomial form, while extinction coefficients were modelled as a convolution by Lorentzian curves. It was observed that magnesium doping decreased the refractive index and also caused a blue shift in absorption edge which is a clear indicator of band gap widening.

The effect of gas composition on the properties of silicon oxynitride thin film prepared by low-pressure inductively coupled Ar/N2 plasma

Silicon nitride (Si3N4) has been widely used in semiconductor devices and applications, including the passivation layer in organic light-emitting diode (OLED). However, it becomes more important to adjust the refractive index value of silicon nitride layers. For example, the refractive index difference between the passivation layer and emission layer is one of the problems degrading OLED performance. Recently, silicon oxynitride (SiOxNy) thin films possessing different refractive indexes have been fabricated by varying their nitrogen and oxygen content. In this work, we control the refractive index of SiOxNy thin film by changing the N2 and Ar flow ratio in 13.56 MHz radio-frequency inductively coupled plasma (RF-ICP). To study the effects of gas composition in the plasma on the properties of thin films, nitrogen atom (N) and nitrogen molecular ion (N2+) density are investigated using actinometry and simulation via the synthetic spectrum method, respectively. We observed that when the gas ratio defined as [N2/(N2+Ar)] increases from 0.1 to 0.9, the density of N2+ increases from 4.76×1015m − 3 to 1.71×1016m − 3 and the refractive index of the thin film increases from 1.54 to 1.57. The results indicate that N2+ plays the important role in changing the properties of thin film during the plasma process.

Optical Studies of Thin Films of Cryocondensed Mixtures of Water and Admixture of Nitrogen and Argon.

The interaction of host molecules with water molecules is of primary importance in astrophysical and atmospheric studies. Water-binding interactions continue to attract a broad interest in various fields, especially those related to the formation of assembly structures. Using the physical vapor deposition (PVD) method and a two-beam interferometer with a wavelength of 406 nm, the refractive indices of thin films of a water and nitrogen (argon) mixture were calculated in the range from 15 to 35 K. The results of temperature transformations of the obtained films from a two-beam interferometer, and thermal desorption characteristics from the temperature of condensation to the temperature of evaporation of water (15-180 K), are presented. The relationship between the signal of the interferometer, the refractive index, and the film thickness during glass transition is demonstrated.

Enhanced photoresponse of PVP:GaSe nanocomposite thin film based photodetectors

Two-dimensional materials have become the focus of attention of researchers in recent years. The demand for two-dimensional materials is increasing day by day, especially with the inadequacy of graphene in optical applications. In this context, the optical and electrical characteristics of the PVP:GaSe thin film nanocomposites were investigated. The surface morphologies of the samples were characterized by SEM, the thin film thicknesses and refractive index parameters were measured by the Ellipsometer method, the structural characteristics were obtained by XRD, and Raman and PL spectroscopy was used to determine the optical characteristics. Critical parameters of Au/PVP:GaSe/n-Si photodetector were calculated under various illumination intensities. It is observed that photodetector with PVP:%5GaSe thin film has the best performance results. According to the experimental results, its responsivity, external quantum efficiency, and detectivity values are 0.485 A W−1, %86, and 1.14 × 107 cm Hz1/2 W−1 respectively.

Transparent, Ultrahigh-Refractive Index Polymer Film (n ∼1.97) with Minimal Birefringence (Δn

High refractive index (RI) thin films are of critical importance for advanced optical devices, and the high refractive index polymers (HRIPs) constitute an interesting class of materials for high RI thin films due to low cost, good processability, light weight, and high flexibility. However, HRIPs have yet to realize their full potential in high RI thin film applications due to their relatively low RI, strong absorption in the blue light region, and limited film formation methods such as rapid vitrification. Herein, we report a development of a new HRIP thin film generated through a one-step vapor-phase process, termed sulfur chemical vapor deposition (sCVD), using elemental sulfur and divinyl benzene. The developed poly(sulfur-co-divinyl benzene) (pSDVB-sCVD) film exhibited RI (measured at 632.8 nm) exceeding 1.97, one of the highest RIs among polymers without metallic elements reported to date. Because the sCVD utilized vaporized sulfur with a unique sulfur-cracking step, formation of long polysulfide chains was suppressed efficiently, while high sulfur content as high as 85 wt % could be achieved with no apparent phase separation. Unlike most of inorganic high RI materials, pSDVB-sCVD was highly transparent in the entire visible range and showed extremely low birefringence of 10 × 10-4. The HRIP thin film with unprecedentedly high RI, together with outstanding transparency and low birefringence, will serve as a key component in a wide range of high-end optical device applications.

Determination of thickness and refractive index of SiO2 thin films using the cross-entropy global optimization method

Silicon dioxide (SiO2) is a material that is abundant in nature and has wide application in semiconductor and insulating devices. In this work, a set of six SiO2 samples were grown on a Sigma-Aldrich Silicon substrate, varying the growth time and temperature. This set of samples were grown using times of 10 and 12h and temperatures of 800, 900, and 1000 ºC, under ambient atmosphere. After film growth, reflectance measurements were performed on the films and the substrate, using the Stellarnet UV-VIS-NIR spectrophotometer between 194 and 1081.5 nm. These measurements were modeled using a global optimization method, called Cross-entropy, together with the Bootstrapping resampling technique, seeking to robustly and statistically determine the thin film refractive index as a function of the wavelength and its thickness. To estimate the refractive index of the SiO2 thin film, the Cauchy model was used. For the substrate, reflectance measurements were used. The method proved to be efficient, presenting thickness values that were validated according to growth parameters and literature data. This method proved to be an important and low-cost tool, compared to traditional methods, to help in the steps of building thin films for semiconductor and insulating devices, thus improving their physical properties and enabling the development of new devices.

Rational design of on-chip gold plasmonic nanoparticles towards ctDNA screening

This paper demonstrates the design, synthesis, simulation, and testing of three distinct geometries of plasmonic gold nanoparticles for on-chip DNA screening towards liquid biopsy. By employing a seed-mediated growth method, we have synthesized gold nanospheres, nanorods, and nanobipyramids. In parallel, we developed numerical simulations to understand the effects of nanoparticle geometry on the resonance features and refractive index sensitivity. Both experimental and simulation results were compared through a series of studies including in-solution and on-chip tests. We have thoroughly characterized the impact of nanoparticle geometry on the sensitivity to circulating tumor DNA, with immediate implications for liquid biopsy. The results agree well with theoretical predictions and simulations, including both bulk refractive index sensitivity and thin film sensitivity. Importantly, this work quantitatively establishes the link between nanoparticle geometry and efficacy in detecting rare circulating biomarkers. The nanobipyramids provided the highest sensitivity, approximately doubling the sensitivity compared to nanorods. To the best of our knowledge this is the first report carrying through geometric effects of simulation to clinically relevant biosensing. We put forth here synthesis and testing of three nanoparticle geometries, and a framework for both experimental and theoretical validation of plasmonic sensitivities towards liquid biopsy.

A sensing approach for manganese ion detection by carbon dots nanocomposite thin film-based surface plasmon resonance sensor

Although plenty of carbon dots have been synthesized by many kinds of synthesis methods, their potential in metal sensing applications is still limited. Herein, the application of carbon dots-cellulose nanocrystals (CDs-CNC) thin film towards manganese ions sensing was demonstrated experimentally using surface plasmon resonance (SPR) sensor. The experimental results showed that the CDs-CNC thin film-based SPR sensor provides the detection of parts per billion concentrations of Mn2+ in an aqueous solution with high sensitivity response of 0.0534° ppb-1. The thickness and refractive index of thin films were then determined by fitting the experimental SPR spectra using the WinSpall simulation program. The proposed CDs-CNC thin film-based SPR sensor exhibit better sensing performance in comparison to the previous film-based sensor, suggesting the suitable technology candidate for environmental monitoring applications.

Stoichiometry dependent changes in the optical properties and nanoscale track formation of PECVD grown a-SiNx:H thin films upon 100 MeV Au8+ ion irradiation

a-SiNx:H thin films of different stoichiometry grown by PECVD were subjected to irradiation by 100 MeV Au8+ ions with various fluences to understand the effect of stoichiometry on properties of thin films upon irradiation. Ellipsometry and UV–Vis study suggest the variation in the refractive index of thin films with fluence. The evolution of Hydrogen due to irradiation is quantified with the help of ERDA. RBS was probed to study the change in thin films' composition upon irradiation, which further helps understand the change in thin films' optical properties. Quenching of photoluminescence in the films with all stoichiometries was also observed due to ion irradiation. X-TEM images show the formation of discontinuous ion tracks of radius 2.5 nm in the film closer to silicon nitride stoichiometry. However, Si rich film does not show the clear formation of tracks. Results are explained in the framework of the Thermal spike mechanism of ion-solid interaction.

Sn-induced changes in the structure and optical properties of amorphous As–Se–Sn thin films for optical devices

The present framework is primarily concerned with the optical properties of As40Se60-xSnx thin films. The bulk form has been synthesized by the melt quenching technique. The thin films have been prepared by thermal evaporation technique. The XRD and the SEM techniques showed the non-crystalline nature of the prepared glasses. The refractive index n, energy gap, energy loss functions and other optical constants have been determined. The findings refer to increase of the refractive index of thin films with the increase of Sn content. The energy gap decreases to 1.4 eV with the increasing of Sn content for the investigated films. Further explanation of the physical characteristics of the investigated films made following the approach of chemical bond. Additionally, the optical dispersion dn/dλ, phase velocity vp and group velocity Ug have been discussed in detail.

Модификация оптических свойств поверхностей методом напыления под скользящими углами

The paper considers the optical properties and structure of thin films of titanium dioxide formed by the glancing angle deposition method. It was show that this method allows the formation of coatings having a significantly lower refractive index than that of the initial material. Thus, the experimentally obtained value of the refractive index of thin films of titanium dioxide was ~1.2, which is almost two times less than that of a polycrystalline material. This allows you to use this method to produce the coatings with a variable refractive index using only one material, changing the geometry of the deposition process only.

High transmission from 2D periodic plasmonic finite arrays with sub-20 nm gaps realized with Ga focused ion beam milling

Fabricating plasmonic nanostructures with good optical performances often requires lengthy and challenging patterning processes that can hardly be transferred to unconventional substrates, such as optical fiber tips or curved surfaces. Here we investigate the use of a single Ga focused ion beam process to fabricate 2D arrays of gold nanoplatelets for nanophotonic applications. While observing that focused ion beam milling of crossing tapered grooves inherently produces gaps below 20 nm, we provide experimental and theoretical evidence for the spectral features of grooves terminating with a sharp air gap. We show that transmission near 10% can be obtained via two-dimensional nano-focusing in a finite subset of 2D arrays of gold nanoplatelets. This enables the application of our nanostructure to detect variations in the refractive index of thin films using either reflected or transmitted light when a small number of elements are engaged.

Spherical-chain silica with super-hydrophobic surface and ultra-low refractive index for multi-functional broadband antireflective coatings

We present a new type of ultra-low refractive index antireflective (AR) coating based on spherical-chain silica particle with super-hydrophobic surface. This AR coating is fabricated using methyltriethoxysilane (MTES) and ethylsilicate (TEOS) as co-precursors to direct silica particles to form a spherical-chain structure. Then hexamethyldisilazane (HMDS) was further used to modify the surface of spherical-chain silica particle, which greatly decreases the refractive index of the silica thin film from 1.139 to 1.098. The formation mechanism of the ultralow refractive index thin film is proposed. The spherical-chain silica particle surface modification with HMDS significantly improves the hydrophobicity of the coated film; the water contact angle of the film increases from 42° to 168°. Ultimately, using this hydrophobic ultralow-index coating as a top-layer, a high-performance double-layer antireflective coating was fabricated with self-cleaning, environmental resistance and a high average transmittance of 99.64% in the wavelength range of 400–800 nm. This multi-functional broadband antireflective coating has potential value in the field of solar cells.