Ellipsometric Technique Research Articles

Engineering electrically tunable TiN/SiO2 epsilon-near-zero metamaterials

Electrically tunable TiN/SiO2/TiN epsilon-near-zero photonic structures with various parameters were fabricated using the reactive DC magnetron sputtering approach. Effective medium approximation was used to predict the optical permittivity of a multilayered TiN/SiO2 metamaterial and guide the design/fabrication. Experimental reflectance measurements for tunable TiN/SiO2/TiN structures were obtained using the ellipsometer technique in the visible and near-infrared spectral ranges. Results show that reflectance for biased (12 V) and un-biased bulk TiN/SiO2/TiN structure changes up to ∼ 2% with the spectral shift at the ENZ spectral point ∼ 10 nm for samples with an optimal SiO2 dielectric layer (thickness d=10 nm). Reflectance measurements for multilayered tunable TiN/SiO2/TiN structures show strong variation in reflectance change for s- polarized light at epsilon-near-zero wavelengths due to applied voltage (12 V). We expect that the results of this research study of the tunable TiN/SiO2/TiN epsilon-near-zero photonic structures will potentially be useful for the photonic density of states engineering, surface sensing, and metamaterial-based super-resolution imaging.

Optical functions of uniaxial zinc oxide (ZnO) revisited

The optical functions of uniaxial ZnO are determined from 200 to 850 nm (6.2–1.46 eV) using three different ellipsometric techniques: (1) standard spectroscopic two-modulator generalized ellipsometry (2-MGE), (2) transmission two-modulator generalized ellipsometry, and (3) near-normal incidence two modulator generalized ellipsometry microscopy (2-MGEM). The 2-MGE results in very accurate values of the dielectric functions and error estimates from 1.46 to 6.2 eV, while the transmission 2-MGE results in more accurate values of the birefringence and associated errors below the band edge where ZnO is transparent. The 2-MGEM also measures the diattenuation (which is related to the birefringence) and other parameters, but at near-normal incidence at a single wavelength (577 nm). The 2-MGEM is designed as a scanning instrument resulting in these parameters being measured over a surface.

Nanomechanical Spectroscopy of 2D Materials.

We introduce a nanomechanical platform for fast and sensitive measurements of the spectrally resolved optical dielectric function of 2D materials. At the heart of our approach is a suspended 2D material integrated into a high Q silicon nitride nanomechanical resonator illuminated by a wavelength-tunable laser source. From the heating-related frequency shift of the resonator as well as its optical reflection measured as a function of photon energy, we obtain the real and imaginary parts of the dielectric function. Our measurements are unaffected by substrate-related screening and do not require any assumptions on the underling optical constants. This fast (τrise ∼ 135 ns), sensitive (noise-equivalent power = ), and broadband (1.2-3.1 eV, extendable to UV-THz) method provides an attractive alternative to spectroscopic or ellipsometric characterization techniques.

Interferometric Imaging Ellipsometer for Characterizing the Physical Parameters of a Grown Oxide Layer

Interferometric and ellipsometric techniques are widely used in object characterization, investigation and testing. Both techniques are crucial for industrial sectors in manufacturing and production. In this work, an interferometric imaging ellipsometry method has been developed to measure the ellipsometric parameters Ψ, Δ and thickness t of native oxide layer formed on a copper thin film at wide angle of incidence 57.8–80.2º instantaneously. In this system, Michelson interferometer is illuminated with 45° polarized laser beam of 30 mm diameter. The produced fringes are split by a polarizing beam splitter (PBS) into p- and s- polarization fringes. The interferograms are captured separately by two CCD sensors at the reference and the measurement states without moving any parts in the optical system for each state. The detected p- and s- interferograms are analyzed using ImageJ software for mathematically calculating the values of Ψ, Δ and t of the oxide layer grown on copper thin film surface. The proposed method avoids the offset errors and the probable misalignment resulting from the beam and the optical components. In addition, it gathers the information of the interference pattern with the state of polarization of light for accurate, precise and real time contrast images. The oxide layer thickness is determined under controlled environment with high accuracy and low uncertainty. The results obtained by the proposed technique are consistent with the spectroscopic ellipsometer measurements.

Optical measurements on a budget: A 3D-printed ellipsometer

Ellipsometry is an optical analysis technique that is useful for characterizing the physical properties of a thin-film system. Light reflected from a sample surface undergoes a change in polarization due to phase delay and anisotropic reflection. This enables one to perform non-destructive measurements of film thickness, surface roughness, refractive index, and other optical constants. Ellipsometric techniques are particularly convenient for characterizing coatings or films in the semiconductor and optics industries. However, these techniques may be inaccessible to undergraduate students and educators due to the prohibitive cost of ellipsometers and similar instrumentation. In response to this roadblock, we describe the construction of a simple, inexpensive, manually operated, rotating analyzer ellipsometer (RAE). Required materials include a laser pointer, polarizing film, photometric detector, and a 3D-printed opto-mechanical framework, which are all readily accessible at most institutions. The instrument's performance was evaluated by comparing thickness measurements of tetraethyl orthosilicate films to those determined by a commercially available reflectometer. An average film thickness difference of 0.77% was measured using the two instruments.

Design and development of double-layer anti-reflection coating for HgCdTe based mid-wave infrared detector

A novel design and development of double-layer antireflection coating (ARC) is presented here for back side illuminated HgCdTe based mid- wave infrared (MWIR) detector. Reflectance of infrared radiation in the CdZnTe/HgCdTe structure is simulated to achieve optimum material and thickness of antireflection coating layers for mid- wavelength range. A polishing process for the surface qualification of CdZnTe material prior to deposition of layers has been developed using different chemical treatments and ellipsometric characterisation techniques. The desired ellipsometry parameters (i.e. 4.0<Ψ < 4.6 and 145<Δ<150) of CdZnTe surface is achieved with the polishing of Br2-metanol solution. The optimized ARC layers of YF3 and ZnS are deposited on the back side of CdZnTe surface and measured the reflectance by Fourier-Transform Infrared (FTIR) technique. The reflectance of below 2% is observed in the backside illuminated YF3/ZnS/CdZnTe/HgCdTe structure for mid-wave infrared range, which is similar with the simulated results. Thus, an improvements as well as new functionalities are implemented in infrared sensors by depositing optimum stack of thin film layers.

Influence of Deposition Conditions on Properties of Ta2O5 Films Deposited by Ion Beam Sputtering Coating Technique

Investigation of deposition conditions on structural, optical, and surface properties of Tantalum pentaoxide (Ta2O5) thin films deposited without assisted ion beam (Single Ion Beam Sputtering technique, SIBS) and with assisted ion beam (Dual Ion Beam Sputtering technique, DIBS) is carried out. For both SIBS and DIBS identical coating process conditions are applied for deposition of Ta2O5 films onto highly polished and clean, fused silica substrates. Estimation of deposition rates of Ta2O5 with identical beam energies and coating chamber conditions is done. Benefits of O2 assist beam on the behavior of structural, optical, and surface properties of thin films deposited are studied. The films are characterized with an ellipsometer, optical profilometer, XRD, FE-SEM, and XPS techniques to bring the merits films coated of Ion Beam Sputtering deposition with and without assist Ion Beam. Configuration of ion sources and targets in the coating chamber for DIBS of oxide targets is carried out in the present work are useful for multi-layer coatings for high reflectivity mirrors for electro-optical instruments like ring laser-based rotation sensors.

Correlation of electronic and vibrational properties with the chiro-optical activity of polyfluorene copolymers

The rationale of this paper is to shed some light on the origin of the optical response of two similar chiral fluorene copolymers in correlation with their vibrational modes, to understand how a chiral center placed in a ramification affects the optical properties of the main chain. Various spectroscopic ellipsometric techniques, in the scope of the Stokes theory were used to characterize the optical-vibrational behavior of the polyfluorenes: ellipsometry in emission (EE), transmission (TE), and Raman (ERS). The results showed that the optical activity and the emission of the circularly polarized light depends substantially on the interaction of the chiral carbon in the ramification and the main chain through specific optically active vibrational modes, for each sample. One interesting achievement was to find the absolute dextrorotatory configuration of the studied molecules, that could induce a helicoidal structure to the entire material.

In situ ellipsometric monitoring of composition and temperature of HgCdTe layers during their growth

An ellipsometric technique has been developed which makes it possible to observe changes in the composition and temperature of cadmium--mercury--tellurium layers during their growing by molecular beam epitaxy. The technique was tested for diagnostics the variations of the composition and the temperature during layer growth in the mode of constant power of the substrate heater and with its sharp change. It was found that the drop in power and a following decrease in the growth temperature were also accompanied by a monotonic decrease in the composition. In the case of a constant heater power, a slight increase in the sample temperature was observed with an almost unchanged composition of the growing layer. Keywords: ellipsometry, mercury--cadmium--telluride, in situ control, epitaxial growth, temperature.

Electronic states structure of Gd-=SUB=-5-=/SUB=-Sb-=SUB=-3-=/SUB=- and Gd-=SUB=-5-=/SUB=-Ge-=SUB=-2-=/SUB=-Sb compounds according to band calculations and optical spectroscopy

Results of investigations of the electronic structure and optical properties of Gd5Sb3 and Gd5Ge2Sb compounds are presented. Calculations of band spectra were carried out in frame of local density approximation with a correction for strong correlation effects in 4f shell of rare-earth ion (DFT + U + SO method). Optical constants of these materials were measured by ellipsometric technique in wide wavelength interval. Energy dependencies of a number of spectral parameters were determined. The nature of quantum light absorption is discussed on the base of comparative analysis of the experimental and calculated spectra of optical conductivity. Keywords: Gd5Sb3, Gd5Ge2Sb compounds, optical properties, electronic structure.

Структура электронных состояний соединений Gd-=SUB=-5-=/SUB=-Sb-=SUB=-3-=/SUB=- и Gd-=SUB=-5-=/SUB=-Ge-=SUB=-2-=/SUB=-Sb по данным зонных расчетов и оптической спектроскопии

Results of investigations of the electronic structure and optical properties of Gd5Sb3 and Gd5Ge2Sb compounds are presented. Calculations of band spectra were carried out in frame of local density approximation with a correction for strong correlation effects in 4f shell of rare-earth ion (DFT+U+SO method). Optical constants of these materials were measured by ellipsometric technique in wide wavelength interval. Energy dependencies of a number of spectral parameters were determined. The nature of quantum light absorption is discussed on the base of comparative analysis of the experimental and calculated spectra of optical conductivity.

Structural, optical and half-metallic properties of Mn and As co-implanted ZnO thin films

In this work, we use ion implantation to implant Mn ions and As ions into the ZnO films prepared by molecular beam epitaxy.The surface morphology and crystalline structure of ZnO thin films are investigated by X-ray diffraction, atomic force microscopy and Raman spectroscopy. First-principles calculations discover the half-metallic property of the ZnO films implanted with Mn ions. The effects of Mn ions and As ions implantation on the absorption edges, refractive index (n), extinction coefficient (k) and dielectric constant of ZnO films are studied by transmission spectra, absorption spectroscopy and spectroscopic ellipsometric technique. From the spectroscopic ellipsometry (SE), the n and k of the films have increased after ion implantation. Due to the half-metallic properties of the Mn-implanted ZnO film, the variation trend of the peaks of n and k with wavelength is much gentler than the peak of unimplanted ZnO film. The dielectric constant measured by SE and the results of photoluminescence spectra reveal that the electron transition of ZnO films is weakened by Mn ions implantation. The results provide a new direction for the design and optimization of optoelectronic devices based on ZnO thin films with semi-metallic properties.

Nanopatterned silicon exhibiting partial polarization and chirality

In this paper, we report a study on Si nanopatterns, fabricated as a one-dimensional (1D) Si nanograting with a sub-wavelength (≈200 nm) period. Unpolarized light normally incident on the nanopatterned Si becomes partially polarized and chiral over the entire visible range of 380–740 nm. The degree and the state of polarization of light were measured using polarimetric and ellipsometric techniques. The analysis showed that the reflected light is partially linearly polarized and at the same time a slight chirality (Ŝ3≠0) is observed. Although the polarization of the reflected light is related to the 1D nanograting anisotropy, the chiral transformation of the light could be related to a micrometer-scale chiral substructure on the Si nanopatterned surface. This structure results from the dynamic polarization rotation of the femtosecond laser pulses in their filaments in liquid carbon disulfide near the Si surface during the interferential plasmonic self-organization of the surface nanorelief. These results could underline a key enabling process for the fabrication of polarization-sensitive metasurface-based sensors or devices within the common complementary metal-oxide semiconductor (CMOS)-compatible technology.

Investigation of photoluminescence emission from β-Ga2O3: Ce thin films deposited by spray pyrolysis technique

Ce doped Ga2O3 thin films for different doping concentrations (3 at%, 4 at%, 5 at%, 6 at%, 7 at%, and 8 at%) were deposited by spray pyrolysis method. X-ray diffraction analysis confirmed the crystalline structure as that of monoclinic β-Ga2O3. The effect of doping on the band gap of the material was studied by UV-Visible spectroscopic method and the thickness of the film and refractive index were measured by ellipsometric technique. The photoluminescence excitation and emission spectra were recorded for pure and doped samples and the energy band scheme with possible radiative and nonradiative transitions were elucidated. Concentration quenching effect was observed, and the underlying mechanism responsible for quenching effect was studied based on Dexter theory.

Электронная структура и оптические спектры соединений GdFeAl и GdFeSi

Results of investigations of electronic structure and optical properties of GdFeAl and GdFeSi compounds are presented. Spin-plarized density of states and interband optical conductivity spectra were calculated in frame of DFT+U technique with a correction for strong correlation effects in 4f shell of Gd. Optical properties were measured by ellipsometric technique in wavelength interval of 0.22 – 16 μm. Nature of quantum light absorption is discussed on the base of comparative analysis of experimental and calculated spectra. It is shown that main features of frequency dependencies of the optical conductivity are interpret qualitatively by the calculated density of electronic states.

Benefits of pH-responsive polyelectrolyte coatings for carboxymethyl cellulose-based microparticles in the controlled release of esculin.

Moderate and prolonged payload release in response to a particular factor is highly demanded for efficient carriers of low-molecular-weight, chemically unstable phytopharmaceuticals. Thus, the objective of our contribution was to establish the effect of pH-responsive polyelectrolyte coatings on the release properties of carboxymethyl cellulose-based microparticles designed to deliver phytopharmaceuticals through the gastrointestinal tract. Microparticles were fabricated via extrusion coupled with external gelation and further coated with polyelectrolytes (PEs) (chitosan, gelatin, or PAH and PSS) involving electrostatic interactions. Successful deposition of PEs was confirmed by FTIR, and their thickness and viscosity were characterized in terms of QCM-D and ellipsometric techniques. The encapsulation efficiency of esculin, used as a model phytopharmaceutical, as proven by UV-Vis studies, was over 57%. SEM and fluorescence microscopy revealed a micrometric size, a mostly spherical shape and an altered topography of the investigated microcapsules. The physical stability of the microcapsules in media of various pH values was confirmed with CLSM and gravimetric studies. Studies on human gingival fibroblasts in vitro revealed that the obtained microparticles did not induce any cytotoxic effects. Payload release was monitored in situ by means of CLSM and ex situ under gastrointestinal conditions in vitro. Mathematical evaluation of the microparticle release profiles using classical models led to the establishment of a new hybrid model that revealed the mechanism behind esculin release. We demonstrated that the application of a polyelectrolyte shell onto CMC-based microspheres may provide controlled delivery of the payload, with its release triggered by the pH and ionic strength of the medium. These observations suggest that the release manner of small-molecule glycosides under gastrointestinal conditions can be tailored by careful selection of suitable materials to obtain biocompatible and functional hydrogel microparticles.

Investigation on structural, optical and electrical properties of Nd doped titania films and application of optical model

The effect of dopant concentration and temperature on the structural, optical and electrical properties of TiO2 (Titania) thin films deposited through sol-gel spin coating was investigated. The X-Ray Diffractometer was used for phase analysis, UV–Vis spectrometer and Ellipsometer techniques were used for the optical measurements and Hall effect was used for the electrical characterization. Annealing temperature and dopant concentration were chosen as the parameters in the present study. The optical band gap marginally increased from 3.40 eV to 3.43 eV with increase in dopant concentration for the films annealed at 350 ֯C. The increasing trend was also observed for the films annealed at 450 °C with the optical band gap in the range 3.34 eV–3.39 eV. Using ellipsometric measurement, thickness and optical constants were obtained and we compared the refractive index values with those obtained from PARAV software. For Nd doped films, a single oscillator model was tested by using the refractive index values from ellipsometric measurement. The carrier density and plasma frequency were calculated using the Wemple Di Domenico (W-D) model. The electrical properties indicate decreased resistivity from 103 Ωcm to 101 Ωcm and increased carrier density from 1015 cm-3 to 1017 cm-3 with increase in annealing temperature. Similarly, with increase in dopant concentration at a given annealing temperature, we have observed a decreased resistivity compared to the prestine samples. However, the carrier density increased marginally with increase in dopant concentration.

Highly sensitive electro-optic detection of terahertz waves in a prism-coupled thin LiNbO3 layer

Electro-optic sampling of pulsed terahertz radiation by femtosecond laser pulses in noncollinear geometry in a 40 μm thick layer of LiNbO3 attached to a Si prism is experimentally demonstrated. Terahertz radiation is prism-coupled into the layer through its surface and modulates the frequency and angular spectra of the optical radiation propagating along the layer as a fundamental mode of a dielectric slab waveguide. The modulation results in the optical intensity variations in the optical beam transmitted through the layer. By measuring the intensity variations, we achieved 38 and 216 times enhancement in the sensitivity of electro-optic detection as compared to the conventional collinear ellipsometric technique with 1 mm thick ZnTe and 0.2 mm thick GaP crystals, respectively.

Электронная структура соединения DyFe-=SUB=-2-=/SUB=-Si-=SUB=-2-=/SUB=-: зонный расчет и оптические исследования

Investigations of electronic structure and optical properties of DyFe2Si2 compound have been carried out. Calculations of the band structure were made with employing local electron density approximation with correction for strong electron correlation effects in the 4f-shells of rare earth metal (GGA+U method). Optical properties were studied by ellipsometric technique in wide wavelength interval. A number of spectral and electronic characteristics were determined. It is shown that the optical conductivity of the compound in interband transitions range is interpreted satisfactorily by means of the density of states calculations.

Электронная структура и оптические свойства соединения FeAl-=SUB=-2-=/SUB=-

Electronic structure and optical properties of the FeAl2 intermetallic compound are investigated. Spin-polarized calculations of the electronic structure were carried out, magnetic moments of the atoms were determined. Optical properties of the compound were measured by ellipsometric technique in spectral interval 0.22 – 15 μm. It is shown that the experimental optical conductivity is satisfactory interpreted on the base of the calculated density of electronic states.