Refractive Index Of Films Research Articles

Combined experimental and DFT-TDDFT computational, structural and study effect of inter-diffusion Cu into CdTe thick film by annealing for optoelectronics

In the present study, thermal evaporation techniques were used to prepare Cadmium Telluride (CdTe) films with thickness 1 μm on a glass substrate (at constant temperature150 °C). By immersing these films in a solution Cu(NO3)2 (1g/1000ml) for 30 min, the prepared films were doped by ion exchange with Cu. Furthermore, the doped films were annealed in vacuum at different temperatures (25, 125, 250, 375, and 500 °C) for the diffusion of dopant Cu content, for 30 min. Using the method of Swanepoel, the film thickness as well as the refractive index of films was identified. The density functional theory (DFT-TDDFT) by DMol3 was used for the optimization of CdTe and Cu:CdTe as an isolated molecule in the gaseous phase. From using the DMol3/(GGA-PW91) method with DFT-TDDFT simulation, the HOMO and LUMO values for CdTe and Cu:CdTe isolated molecule are 2.41 eV and 1.66 eV, respectively. The MEP computations and Quantum-chemical calculations properties are computed and combined with the experimental study by using DMol3/(GGA-PW91) software. The possible transition in these as deposited and treated films are found to allow direct transition with reduction of the band gap from 1.50 to 1.37 eV with an increase of the temperature of the annealing. Dielectric constant, Energy loss functions (VELF and SELF) for CdTe as deposited and treated were addressed in terms of temperature rise in the annealing. The energy gap is also determined using photoluminescence (PL) and its values the corresponding wavelength peaks correspond roughly to the energy obtained through optical studies.

Point Defect Model Description of the Formation of Anodic Gold Oxide in H2SO4 Solution

An impedance-based Point Defect Model (PDM) was developed for the potentiostatic, anodic formation of gold oxide at potentials of 1.40–1.70 V vs SHE in H2SO4 (0.1 M and 0.5 M). Film thickness and refractive indices were determined at each oxide formation potential using spectroscopic ellipsometry. The thickness of the oxide increases linearly with increasing potential. Mott-Schottky analysis shows that the oxide exhibits both n-type and p-type character and the dominant defect density is calculated to be in the order of 1021−1022 (1 cm−3). The PDM was optimized upon experimental EIS data to extract values for model parameters and accounts well for the experimental observations in both the steady-state time and frequency domains.

Fabrication of TiO2-based broadband single-layer anti-reflection coating by collimated glancing angle deposition technique

Single-sided TiO2 thin films were prepared using a modified glancing angle deposition (GLAD) technique. An additional flux collimation plate was introduced into the GLAD arrangement to enhance the degree of collimation of depositing vapour flux. Enhancement in the ballistic growth of film on the substrate was observed with increasing distance from the vapour source. The substrate position near to the vapour source (i.e. bottom region) showed a high refractive index (RI, ∼1.336 @ 550 nm wavelength) and lower average film transmittance (∼94.5% in 400–900 nm wavelength range) compared to the others. In contrast, the TiO2 coating deposited at a distant position from the source (i.e. top region) showed a remarkably low RI (∼1.190 @ 550 nm wavelength) and excellent anti-reflection over a broad spectral region with a maximum average transmittance (∼95.3% in 400–900 nm wavelength) compared to the other substrate positions. The reduction in film RI was correlated qualitatively with the morphological alterations in the coating for different substrate positions. With a further increase in distance from the vapour source, an ultimate reduction in the RI of TiO2 to ∼1.101 was observed, which was ∼50% lower than the bulk TiO2 value (∼2.221 @ 550 nm wavelength). The present study reports the lowest RI of TiO2 together with fabrication of a TiO2-based broadband single-layer anti-reflection coating.

Study on Porosity in Zinc Oxide Ultrathin Films from Three-Step MLD Zn-Hybrid Polymers.

Deriving mesoporous ZnO from calcinated, molecular layer deposited (MLD) metal-organic hybrid thin films offers various advantages, e.g., tunable crystallinity and porosity, as well as great film conformality and thickness control. However, such methods have barely been investigated. In this contribution, zinc-organic hybrid layers were for the first time formed via a three-step MLD sequence, using diethylzinc, ethanolamine, and maleic anhydride. These zinc-organic hybrid films were then calcinated with the aim of enhancing the porosity of the obtained ZnO films. The saturation curves for the three-step MLD process were measured, showing a growth rate of 4.4 ± 0.2 Å/cycle. After initial degradation, the zinc-organic layers were found to be stable in ambient air. The transformation behavior of the zinc-organic layers, i.e., the evolution of the film thickness and refractive index as well as the pore formation upon heating to 400, 500, and 600 °C were investigated with the help of spectroscopic ellipsometry and ellipsometric porosimetry. The calculated pore size distribution showed open porosity values of 25%, for the sample calcinated at 400 °C. The corresponding expectation value for the pore radius obtained from this distribution was 2.8 nm.

The pivotal role of copper on the structural and optical parameters of ZnS thin films for optoelectronic applications

In this research, using chemical spray pyrolysis technology, Zn1-xCuxS doped (0.0, 0.02, 0.04, 0.06, 0.08 and 0.10 at.%) thin films were grown on a hot glass substrate with a substrate temperature of 275 °C, the thickness is about 110 nm. The spray solutions contain Zn(CH3COO)2•2H2O, SC(NH2)2 and CuCl2•2H2O with molar concentration 0.1 M/L. Energy Dispersion Analysis X-rays (EDAX) sets the initial processing components. The structure of the films was investigated by XRD pattern, and it was found that the films were polycrystalline with a cubic phase for Zn1-xCuxS at (x = 0, 0.02, 0.04 at.%) and mixed cubic and hexagonal phases for (x = 0.06, 0.08 and 0.10 at.%) with a small trace of (CuS). The micro-structural (lattice strain, e, and the crystallite's size, Dv) parameters for the pure and treated films were determined. The transmission spectrum envelope method is used to calculate the film thickness and refractive index. The estimated optical band gap of pure ZnS and ZnS:Cu is a direct transition, and decreases from 3.44 eV to 3.32 eV as the Cu concentration increases. The dielectric constants (ε1 and ε2), dispersion parameters (Eo, Ed), high-frequency dielectric constants, (ε∞), carrier concentration (N/m*) and plasma resonance frequency (ωp) were calculated. According to the changes of the microstructure parameters, the changes of all the optical parameters are discussed for applications in optoelectronics.

Investigation of thermal annealing effects on MoO3 thin film by atomic layer deposition

Molybdenum oxide (MoO3) thin films have been obtained by plasma-enhanced atomic layer deposition using precursors of Mo(CO)6 and O2 plasma at a reactor temperature of 160 °C. The MoO3 thin films deposited on p-type silicon substrates with thermally grown 300 nm thick SiO2 layer with different numbers of ALD growth cycles. Spectroscopic ellipsometer is used to characterize as-grown film thickness and refractive index. The as-grown films are treated at annealing temperatures at 300–600 °C. The structural properties of as-grown and annealed thin films have been characterized by optical microscopy, µRaman spectra, and atomic force microscopy.

Functional characterization of nano-porous silicate-polymer composite for bovine serum albumin immobilization

The paper dwells upon the elaboration of a simple and energy-efficient approach for the “bottom-up” fabrication of porous polymeric film, which possesses unique surface, structural and bulk properties, followed by its comprehensive study through various characterization techniques. The fabricated film is multi-layered methyl silsesquioxane and suitably modified with the help of several treatments making the film compatible for biosensing applications. Film characterization reports the self- organized topography of the film deposited over the substrate and confirms the successful bonding between the polymers. The influence of the concentration of polypropylene glycol, which itself acts as thermally labile dendrimer, is studied by observing its bond formation ensuring polymer mixing by using FTIR. Energy dispersive x-ray analysis has been performed for the confirmation of elements. In addition to this, the nanoporous film is also studied with the help of variable angle spectroscopic ellipsometry for the determination of film porosity and refractive index. In this analysis, Cauchy model and graded-index model were chosen for data analysis and the Bruggeman effective medium approximation method was used for evaluating the optical constant. The surface of the porous film has been treated with different silane surfaces, characterized with the help of FTIR, UV-VIS, and AFM and envisioned for protein immobilization.

A COMPREHENSIVE REVIEW ON THIN FILM DEPOSITIONS ON PECVD REACTORS

The deposition of thin films by Plasma Enhanced Chemical Vapor Deposition (PECVD) method is a critical process in the fabrication of MEMS or semiconductor devices. The current paper presents an comprehensive overview of PECVD process. After a short description of the PECVD reactors main layers and their application such as silicon oxide, TEOS, silicon nitride, silicon oxynitride, silicon carbide, amorphous silicon, diamond like carbon are presented. The influence of the process parameters such as: chamber pressure, substrate temperature, mass flow rate, RF Power and RF Power mode on deposition rate, film thickness uniformity, refractive index uniformity and film stress were analysed. The main challenge of thin films PECVD deposition for Microelectromechanical Systems (MEMS)and semiconductor devices is to optimize the deposition parameters for high deposition rate with low film stress which and if is possible at low deposition temperature.

Europium Doped Silicon Oxide Thin Films Using an Integrated PECVD and Sputtering System

Over the last decades, silicon-based materials have exhibited outstanding electronic properties and been used in photovoltaic and electrical devices such as transistors [1]. However, due to their indirect band gap nature and poor light emitting properties, they are not satisfying candidates when it comes to photonics. One way through which this poor performance is sorted out is doping of rare earth (RE) elements into the silicon nanostructure thin film to enhance the light emission. The reason for the use of RE elements in silicon-based materials is the fact that they showed well-defined emission peaks and 4f electron shielding making them independence of the host matrix [2].In this study, luminescence properties of Europium (Eu) doped oxygen rich silicon oxide (ORSO) materials using two fabrication techniques are discussed as well as controlling of the Eu concentration, argon partial pressure and sputtering power. In addition, the effect of different annealing atmospheres is observed as here pure nitrogen (N2) and forming gas (N2+5% H2) are tested at a variety of deposition temperatures ranging between 300 °C and 1350 °C. In particular, samples subjected to the higher annealing temperatures of 1200 °C and 1350 °C behave differently in comparison with lower annealing temperatures where their structural and photoluminescence (PL) properties are investigated in more details.The introducing of Eu into ORSO host matrix was performed by two different deposition methods with the first one being the conventional method of metal organic powders where RE elements are introduced using electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) system. The second method involves the use of a novel and custom-made integration of ECR-PECVD and magnetron sputtering [3]. The investigation of a variation of optical and structural properties of the samples made with similar deposition parameters using these two different techniques resulted in insignificant light emission of the ones fabricated with metal organic precursor and remarkable emission of the samples produced using the integrated ECR-PECVD and sputtering method.Variable angle spectroscopic ellipsometry (VASE) measurements are carried to comprehend the refractive index and thin films thicknesses, and their dependence on the deposition parameters such as the sputtering power. Rutherford backscattering spectrometry (RBS) measurements provide the film composition and verify a good control of the Eu concentration using the second deposition method (integrated ECR-PECVD and sputtering). X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) confirm the formation of nanostructures in the Eu-ORSO thin films following post-deposition annealing beyond 1200 °C. The PL studies are performed to study the light emission properties of Eu-ORSO thin films and the changes introduced by the hydrogen passivation. Figure 1 shows the influence of hydrogen passivation on one of the Eu-ORSO thin films containing 0.1 ± 0.01 at. % of Eu. The sample is annealed at 1200 °C and 1350 °C using N2 and N2+H2 atmospheres for 1 hour in the quartz tube furnace. The hydrogen passivation enhances the PL emission by one order of magnitude possibly due to the passivation of the defects and dangling bonds.

Synthesis, Crystallography, Microstructure, Crystal Defects, Optical and Optoelectronic Properties of ZnO:CeO2 Mixed Oxide Thin Films

We report the synthesis and characterization of pure ZnO, pure CeO2, and ZnO:CeO2 mixed oxide thin films dip-coated on glass substrates using a sol-gel technique. The structural properties of as-prepared thin film are investigated using the XRD technique. In particular, pure ZnO thin film is found to exhibit a hexagonal structure, while pure CeO2 thin film is found to exhibit a fluorite cubic structure. The diffraction patterns also show the formation of mixed oxide materials containing well-dispersed phases of semi-crystalline nature from both constituent oxides. Furthermore, optical properties of thin films are investigated by performing UV–Vis spectrophotometer measurements. In the visible region, transmittance of all investigated thin films attains values as high as 85%. Moreover, refractive index of pure ZnO film was found to exhibit values ranging between 1.57 and 1.85 while for CeO2 thin film, it exhibits values ranging between 1.73 and 2.25 as the wavelength of incident light decreases from 700 nm to 400 nm. Remarkably, refractive index of ZnO:CeO2 mixed oxide-thin films are tuned by controlling the concentration of CeO2 properly. Mixed oxide-thin films of controllable refractive indices constitute an important class of smart functional materials. We have also investigated the optoelectronic and dispersion properties of ZnO:CeO2 mixed oxide-thin films by employing well-established classical models. The melodramatic boost of optical and optoelectronic properties of ZnO:CeO2 mixed oxide thin films establish a strong ground to modify these properties in a skillful manner enabling their use as key potential candidates for the fabrication of scaled optoelectronic devices and thin film transistors.

Design of a Multimode Interferometer-Based Mid-Infrared Multispecies Gas Sensor

A $1\times 2$ multimode interferometer beam splitter based on mid-infrared emitting chalcogenides waveguides is designed. This device multiplexes mid-infrared light in two channels whose respective passbands overlap either CO2 or CO absorption bands, respectively between 4.20- $4.32~\mu \text{m}$ and 4.50- $4.86~\mu \text{m}$ . The proposed device offers a low-cost solution for monolithic combination of broadband on-chip mid-infrared light emission with dispersive spectroscopic element devoted to mid-IR multigas sensing applications. Based on restrictive interference mechanism in a $1\times 2$ multimode interferometer, the multimode section dimensions (width and length) are engineered to increase the imbalance between the two ports for the two passbands and consequently to increase the output contrast ratio. Tolerances to variations from the optimum device design resulting from processing conditions (materials fabrication and sputtering, photolithography and dry etching steps) are assessed. In particular, the $1\times 2$ multimode interferometer diplexer spectral transmission is investigated as a function of deposited film refractive index and multimode section dimensions (width and length) deviation from designed values. Input and output ports tapering is introduced to reduce the device insertion loss.

Development of highly reliable BiFeO3/HfO2/Silicon gate stacks for ferroelectric non-volatile memories in IoT applications

We have investigated the structural, electrical, and ferroelectric properties of metal–ferroelectric-high-k-silicon capacitors with BiFeO3 ferroelectric films deposited on the HfO2/Si substrate. BiFeO3, HfO2 films, and their stack were deposited on the silicon substrate using RF magnetron sputtering and plasma-enhanced atomic layer deposition (PEALD). Film crystal orientation, refractive index, and absorption constant parameters were extracted from X-ray diffraction and ellipsometric analysis. Electrical characterization of metal/ferroelectric/metal (MFM), metal/ferroelectric/silicon (MFS), metal/dielectric/silicon (MIS), and metal/ferroelectric/insulator/silicon (MFIS) capacitor structures provide memory window, leakage current density, hysteresis, fatigue, and data retention time. The metal/ferroelectric/silicon structure exhibits clockwise capacitance–voltage characteristics with the memory window of 5.04 V for the bias voltage of ± 10 V. The electrical and ferroelectric characteristics of MFIS structures were studied for different thicknesses of HfO2 layer, which shows that the introduction of high-k dielectric film between ferroelectric and silicon improves the interface quality. The memory window of the MFIS structure was found to significantly increase to 9.65 V with the introduction of a 10 nm HfO2 layer between the ferroelectric layer and the silicon substrate. Two-order reduction in the leakage current density was also observed in the MF(200 nm)I(10 nm)S structure as compared to the MF(200 nm)S structure. The fabricated MF(200 nm)I(10 nm)S gate stack shows fatigue resistance for read/write operations greater than 1012 cycles and data retention time for greater than 104 s. To the best of author’s knowledge, this is the first investigation to integrate pure BiFeO3 on PEALD-HfO2 dielectric for the gate stack of ferroelectric field effect transistors.

Effect of Co doping on optical parameters of SnO2 thin films

Abstract SnO2 thin films are deposited using spray pyrolysis technique on p-type silicon (Si) substrate by varying the Cobalt (Co) doping ratio from 3 to 5 at % in order to investigate the effect of the doping on the optical parameters of these films. Optical reflectance measurements are performed both for films and substrate. A simple analysis which is created as a combination of three different methods proposed earlier including the effect of the substrate is applied for the optical characterization of Co-doped SnO2 thin films. In addition to thickness, optical parameters such as refraction index and extinction coefficients are also obtained accurately, by applying this created procedure. The optical band gap and Urbach energy of the films are determined from the spectral dependence of the absorption coefficient. The refraction index and band gap energy of SnO2 films are found to be decreasing whereas Urbach energy is found to be increasing with increasing Co doping ratio. The roughness value of Co-doped SnO2 thin films on p-type Si is obtained with such a high precise only from reflectance spectrum.

Effect of SF6 flow ratio on microstructure and properties of MgF2 thin films prepared by magnetron sputtering

In order to suppress F- deficiency of MgF2 film prepared with magnetron sputtering, the effects of SF6: Ar gas flow ratio on the structure and properties of the film were investigated. F: Mg ratio increased rapidly first then decreased with the increase of SF6 flow ratio, got 2.13 at 7%, closest to the stoichiometric ratio 2:1; while the film's refractive index first decreased and then increased, got a minimum at 550 nm 1.409 at 7%. MgF2 film increased the glass substrate transmittance within 300–1100 nm to 94.24% from 93.2%, and improved photoelectric conversion efficiency of GaAs solar cell by 2.1%.

Hydrophobic polymer-incorporated hybrid 1D photonic crystals with brilliant structural colors via aqueous-based layer-by-layer dip-coating

Preparation and application of photonic crystal (PC) films with structural colors have received extensive attention in recent years. Aqueous-based layer-by-layer (LbL) dip-coating is an environmentally friendly and versatile method to prepare functional films. This work focuses on using the method to prepare a kind of hydrophobic polymer-containing 1D PCs with brilliant structural colors. High and low refractive index stacks are produced by electrostatic assembly of nano TiO2/poly (styrene sulfonate) (PSS) and poly (diallyldimethyl ammonium chloride) (PDAC)/nano poly (methyl methacrylate) (PMMA) multilayers, respectively. Hydrophobic PMMA was introduced for the first time in this aqueous-based electrostatically-assisted assembly for expanding the applicable materials. The zeta potential and particle size of the PMMA and TiO2 nanoparticles are measured under different pHs, and the effects of the bilayer number on both film thickness and refractive index are investigated. The structural colors of the heterostructure 1D PCs can be regulated in the visible range by variation of bilayer number, incident angle and stack number. This hydrophobic polymer incorporated 1D PCs can achieve colorful coatings on flat and curved glass substrates. In addition, upon exposure to organic solvent vapors, the PC film shows color change. Thereby, the obtained multilayered PCs exhibit potential applications in coating, decoration and sensing.

Single polymer-variable index for the design and fabrication of variable stop band distributed Bragg reflectors

Abstract Thin films of variable refractive index from a single polymer were developed by doping titanium dioxide (TiO2) in poly-vinyl alcohol (PVA) by solution processing. Refractive index as high as 1.80 was achieved by increasing the doping levels of TiO2 in PVA. Polymer distributed Bragg reflectors (DBRs) were fabricated by coating titania doped PVA polymer matrix composite (TPMC) and poly methyl methacrylate (PMMA) polymer as alternating high and low index layers respectively. The reflectivity of DBR was increased by increasing number of periods. The experimental results were in agreement with transfer matrix model (TMM) simulations. TMM simulation results showed that, to achieve reflectivity of more than 90%, 20 periods were required for an index contrast of 0.17 and periods reduced to 5 for an index contrast of 0.51. High index contrast of alternative layers will also benefit in having a relatively broad stop band. The present work suggests fabricating flexible polymer DBRs with any desired stop band by simply varying the concentration of TiO2 in PVA without altering any other thin film processing and DBR fabrication parameters.

Stress and Refractive Index Control of SiO2 Thin Films for Suspended Waveguides

Film stress and refractive index play an important role in the fabrication of suspended waveguides. SiO2 waveguides were successfully fabricated on multiple substrates including Si, Ge, and Al2O3 wafers; the waveguides were deposited using inductively coupled plasma chemical vapor deposition at 100 °C. The precursor gases were SiH4 and N2O at 1:3 and 1:9 ratios with variable flow rates. The occurrence of intrinsic stress was validated through the fabrication of suspended SiO2 bridges, where the curvature of the bridge corresponded to measured intrinsic stress, which measured less than 1 µm thick and up to 50 µm in length. The flow rates allow film stress tunability between 50 and −65 MPa, where a negative number indicates a compressive state of the SiO2. We also found that the gas ratios have a slight influence on the refractive index in the UV and visible range but do not affect the stress in the SiO2 bridges. To test if this method can be used to produce multi-layer devices, three layers of SiO2 bridges with air cladding between each bridge were fabricated on a silicon substrate. We concluded that a combination of low temperature deposition (100 °C) and photoresist as the sacrificial layer allows for versatile SiO2 bridge fabrication that is substrate and refractive index independent, providing a framework for future tunable waveguide fabrication.

Design of resonant cavity thin film structures with complex active layers

A systematic approach to designing resonant cavity distributed Bragg reflector (DBR) structures with complex-index active regions is developed in this paper. The technique is based on the effective reflectance index of multilayer thin films. While the design of DBR structures with real refractive index films is quite straightforward, the use of a complex refractive index in the cavity requires a different approach. In this paper, we show that a complex active region requires an asymmetric reflector geometry along with a separate phase compensator. This technique is illustrated using phase change materials and metals in the resonant cavity.

Design, preparation, and characterization of new high‐refractive index hybrid organic–inorganic polysiloxanes: Innovative coatings for optoelectronic applications

AbstractThe current demand for high‐refractive index materials is very high due to their importance in optoelectronic applications. Such materials already exist in the market, but they present many disadvantages. They might contain toxic metals; their preparation can be challenging or produce high quantity of waste. Consequently, there is an urgent need to produce new friendly coatings with high‐refractive index. Hybrid organic–inorganic polysiloxanes can offer a solution to this problem. They can be easily prepared from nontoxic alkoxy silanes using the sol–gel chemistry process. Herein, a series of new hybrid polysiloxanes are synthesized from the monomer 1–(2–(triethoxysilyl)ethyl)triphenylsilane and other silanes. The preparation of the macromolecules is optimized at both stages of the sol–gel process. The polymers are characterized by gel permeation chromatography and NMR spectroscopy. Spin coating of the materials on silicon wafers, followed by film thickness and refractive index measurements, indicates that the new polysiloxanes can have refractive indexes as high as 1.6 with thicknesses varying from 2200 to 3700 nm. Consequently, it is expected that the new materials described in this report are valuable for optoelectronic applications such as high‐dielectric constant (high‐k) gate oxides, interlayer high‐k dielectrics, or high‐refractive index abrasion resistant coatings.

Enhanced sensitivity of guided mode resonance sensor through super-mode excitation at near cut-off diffraction

This work theoretically and experimentally demonstrates sensitivity enhancement in dielectric guided mode resonance (GMR) sensor via controlling a super-mode resonance at nearly cut-off diffraction (or at Rayleigh wavelength.) A bulk refractive index sensitivity can reach the upper limit at the value linearly proportional to the grating’s periodicity. Super-mode excitation in the multilayer configuration of the 2D GMR sensor (a high refractive index film coated on a low refractive index imprinted grating) is demonstrated. This concept is verified using numerical calculations: Rigorous Coupled Wave Analysis (RCWA) and Homogeneous Waveguide Approximation (HWA). Modal allocation for each resonance in the GMR structure is performed using the approximated four-layer waveguide. The measured super-mode resonance has shown sensitivity enhancement almost three folds of that of the traditional guide mode resonance. Also, this realization occurs in a broad dynamic range through optimization of the structure’s parameters. This guarantees a usage in multiple sensing applications.