Ellipsometry Study Research Articles

Ammonia-vapour-induced two-layer transformation of mesoporous silica coatings on various substrates

We prepared mesoporous silica layers by sol-gel dip-coating technique on various substrates (silicon, polycarbonate, microscope glass and quartz) with the aid of a pore-forming triblock copolymer (Pluronic PE10500). The freshly deposited layers were aged in an aqueous ammonia solution atmosphere. Two types of thermal curing were implemented depending on the substrates: a low-temperature heat treatment at 120 °C for 13 hours or a high-temperature heat treatment at 480 °C for 1 hour. We carried out the porogen extraction of the copolymer molecules from the low-temperature heat-treated samples in a water washing step.Optical spectroscopy measurements gave evidence of a significantly improved and long-lasting light transmission of coatings. The maximum light transmission was 98.3% on glass and 97.6% on polycarbonate after 4 years of storage. TEM investigations showed thin layers with distorted face centred cubic structure.Spectroscopic ellipsometry and ellipsometric porosimetry studies showed a “two-layer” structure. The applied synthesis technique promoted the formation of a double layer structure with relatively thick (10–25 nm) pore sizes. The pseudomorphic transformation rearranged the silica/copolymer structure in presence of ammonia. The transformation was incomplete and resulted in a low porosity (23–34%) upper-layer and a high porosity (40–76%) lower-layer.

Ellipsometry Study of CdSe Thin Films Deposited by PLD on ITO Coated Glass Substrates.

Cadmium selenide (CdSe) thin films were deposited on indium tin oxide (ITO) coated glass substrates using pulsed laser deposition (PLD) technique under different growth temperatures. Samples were investigated for their structural, morphological, and optical properties through X-ray diffraction (XRD), atomic force microscopy (AFM), and UV-Vis-NIR spectroscopy. AFM analysis revealed that the surface roughness of the as-grown CdSe thin films increased with the increase in deposition temperature. The optical constants and film thickness were obtained from spectroscopic ellipsometry analysis and are discussed in detail. The optical band gap of the as-grown CdSe thin films, calculated from the Tauc plot analysis, matched with the ellipsometry measurements, with a band gap of ~1.71 eV for a growth temperature range of 150 °C to 400 °C. The CdSe thin films were found to have a refractive index of ~3.0 and extinction coefficient of ~1.0, making it a suitable candidate for photovoltaics.

Structure and spectroscopic ellipsometry studies of nanocrystalline Dy2O3 thin films deposited on Al2O3 wafers by electron beam evaporation technique

This work investigates the effect of film thickness on the optical properties of dysprosium oxide (Dy2O3), fabricated onto sapphire (Al2O3) substrates using electron beam evaporation. The grazing incidence X-ray diffraction (GI-XRD) analysis showed that all films have a cubic crystalline structure. The average crystallite size was calculated using the Debye–Scherrer equation and was found to increase with the increasing film thickness. Similar behavior was observed in scanning electron microscopy and atomic force microscopy images. The optical properties of the grown layers such as the refractive index (n), extinction coefficient (k), and optical allowed f–f transitions of Dy3+were analyzed using spectroscopic ellipsometry (SE). The allowed f–f transitions of Dy3+was found to increase from 2.35 eV to 2.50 eV by decreasing the film thickness from 10 nm to 5 nm. UV–Vis spectrophotometry was used to examine the reflectance of Dy2O3 thin films. The results obtained in this study indicated that Dy2O3 with a 5 nm thickness is a better choice to grow an improved anti-reflective layer compared with the 10 nm layer.

Ellipsometry Study of Hexagonal Boron Nitride Using Synchrotron Radiation: Transparency Window in the Far‐UVC

The linear optical response of the ultrawide bandgap h‐BN is investigated by spectroscopic ellipsometry. The ordinary dielectric function of h‐BN is determined up to 25 eV on a high‐quality single‐crystal platelet. The direct bandgap and the high‐energy transitions are characterized with the aid of ab initio self‐consistent GW calculations and the optical properties are calculated using the Bethe–Salpeter equation. The dispersion of the ordinary refractive index in the visible and UV part of the spectrum below the bandgap is in excellent agreement with previous transmission experiments. A sharp excitonic peak at 6.1 eV associated with the direct bandgap dominates the absorption spectrum, and a second peak is observed at 6.8 eV. At higher energies, a strong absorption peak emerges at 15 eV associated with higher σ → σ* transitions. As a consequence of the unique electronic band structure of h‐BN, a transparency window is observed in the far‐UV region between 7 and 13 eV, where the light penetration depth reaches a value of 38 nm, as opposed to the value of 0.8 nm at the absorption peak of the fundamental bandgap.

Spectroscopic ellipsometry study of CsPbBr3 perovskite thin films prepared by vacuum evaporation

CsPbX 3 (X = Cl, Br, or I) perovskite thin films can be fabricated by vacuum evaporation (VE) with high reproducibility and good film-forming ability. To design optical devices based on CsPbX 3 thin films, precise optical constants are required. As only a few optical and dielectric properties of perovskites obtained by VE have been reported, we have comprehensively studied the complex reflective index and complex dielectric function of CsPbBr3 perovskite VE films. Spectroscopic ellipsometry combined with x-ray diffraction and scanning electron microscopy revealed that the three-oscillator model precisely describes the optical constants. Therefore, the wavelength-dependent optical constants of a material can be empirically determined. Time-resolved photoluminescence of a designed CsPbBr3-light-emitting device with a Fabry–Perot cavity and agreement of its dielectric properties with reported data confirmed the existence of a microcavity effect and accurately predicted the electric field intensity distribution and cavity length. This methodology also enables the composition of perovskite to be monitored, which contains a fraction that is desirable for optimizing the performance of optical electronics.

Spectroscopic Ellipsometry Characterization of As-Deposited and Annealed Non-Stoichiometric Indium Zinc Tin Oxide Thin Film.

A spectroscopic ellipsometry study on as-deposited and annealed non-stoichiometric indium zinc tin oxide thin films of four different compositions prepared by RF magnetron sputtering was conducted. Multi-sample analysis with two sets of samples sputtered onto glass slides and silicon wafers, together with the analysis of the samples onto each substrate separately, was utilized for as-deposited samples. Annealed samples onto the glass slides were also analyzed. Spectroscopic ellipsometry in a wide spectral range (0.2–6 eV) was used to determine optical constants (refractive index n and extinction coefficient k) of these films. Parameterized semiconductor oscillator function, together with Drude oscillator, was used as a model dielectric function. Geometrical parameters (layer thickness and surface roughness) and physical parameters (direct optical bandgap, free carrier concentration, mobility, and specific electrical resistivity) were determined from spectroscopic ellipsometry data modeling. Specific electrical resistivity determined from the Drude oscillator corresponds well with the results from electrical measurements. Change in the optical bandgap, visible especially for annealed samples, corresponds with the change of free carrier concentration (Moss–Burstein effect). Scanning electron microscope did not reveal any noticeable annealing-induced change in surface morphology.

Parameterization of the optical constants of polydopamine films for spectroscopic ellipsometry studies.

Bio-inspired polydopamine coatings offer vast possibilities for surface modification of materials. The thickness of such nanometric coatings is usually estimated based on ellipsometry measurements. However, the complex light-absorbing nature of polydopamine is often overlooked when analyzing such data, which can result in inaccurate estimations of the coating thickness as well as the optical properties. In this study, we prepared and characterized three polydopamine coatings where the film thickness and surface roughness are systematically varied. For each case, we developed suitable optical models and showed how an inappropriate optical model can provide inaccurate estimates of the coating properties. AFM height profiles were obtained from scratched areas of each sample to verify the thickness values estimated by ellipsometry. The results confirm that polydopamine coatings, depending on the oxidation conditions, can possess different structural and optical properties, and thus require unique optical models for the ellipsometry analysis.

Spectroscopic ellipsometry and morphological studies of nanocrystalline NiO and NiO/ITO thin films deposited by e-beams technique

The current article reported a new data on the structural, surface morphology and optical properties of multi-thickness nanocrystalline NiO/glass substrate and NiO/ITO/glass substrate semiconductor thin films prepared by electron beam deposition technique. Structural investigation shows that the as-deposited multi-thickness NiO films deposited on a glass substrate crystallize in the form of cubic NaCl type structure. However, ITO thin film has a cubic type structure. Besides, the increase in the crystallite size was observed with increasing the thickness of NiO film, this behavior was confirmed by AFM micrographs. In the spectral range 280 nm–1800 nm, the optical properties of the NiO/glass substrate and NiO/ITO/glass substrate thin films have been investigated using spectroscopic ellipsometry (SE) technique. For NiO/glass substrate sample, the SE results providing direct energy E g d i r ≈ 3.954 eV, indirect energy E g i n d i r ≈ 2.855eV and phonon energy of order 200 meV. In addition, the analysis of the refractive index dispersion gives the atomic number density to be N f i j = 2.213 x 10 22 c m − 3 . On the other hand, for the NiO (410 nm)/ITO (99 nm)/glass substrate thin film sample, a reduction in the direct transition energy to E g d i r ≈ 3.24eV and also in the factor N f i j to 1.6 x 10 22 c m − 3 was observed. Additionally, the values of the oscillator parameters were calculated for NiO/glass substrate and NiO/ITO/glass substrate thin films using the Wemple-DiDomenico single oscillator model (WDD). Finally, it was found that the values of Urbach energy for NiO/glass substrate and NiO (410 nm)/ITO (99 nm)/glass substrate are very small relative to the energy gap values which indicates that the region of localized sates is very narrow compared to the width of the energy gap. • The D/nm of NiO film increase from 16.86 to 22.75nm and for NiO/ITO from 15 to 26nm with increasing thickness from 75 to 410nm. • Good correlation between the increase in D/nm and reduction of dislocation density (δ) is found. • SE provides E g d i r ≈ 3.954 eV, E g i n d i r ≈ 2.855eV and E phon 200meV. For NiO/glass film a reduction in E g d i r to 3.24eV for the NiO(410nm)/ITO (99 nm)/glass. • The refractive index of NiO film is independent of the film thickness and atomic number density is found to be N f i j = 2.213 x 10 22 c m − 3 • The values of E o = 6.828eV, E d = 19.3eV for NiO film and E o = 4.56eV, E d = 15.1eV for (410 nm)/ITO (99nm)/glass substrate film are found.

Origin of area selective plasma enhanced chemical vapor deposition of microcrystalline silicon

Plasma-enhanced chemical vapor deposition of silicon from a SiF4/H2/Ar gas mixture is observed on a SiOxNy surface, while under the same plasma conditions, silicon films do not grow on AlOx or on Al surfaces. Transmission electron microscopy confirms that the silicon deposited on SiOxNy has a microcrystalline structure. After the plasma process, fluorine is detected in abundance on the AlOx surface by x-ray photoelectron spectroscopy and energy dispersive x-ray chemical analyses. This suggests that Al–F bonds are formed on this surface, blocking any deposition of silicon on it. In situ ellipsometry studies show that deposition can be initiated on AlOx surfaces by increasing the temperature of the electrodes or increasing the RF plasma power, leading to a loss of selectivity.

Structural and optical properties of multilayered un-doped and cobalt doped TiO2 thin films

The present investigation reports the effect of multilayers (1, 3 and 7 layers) and cobalt (Co) doping on structural and optical properties like transmittance, refractive index, extinction coefficient, etc. of TiO2 thin films prepared by a sol–gel spin coating technique. X-ray diffraction (XRD) and Raman spectroscopy were used to investigate the phase and structure of the prepared films which confirm the formation of single phase anatase TiO2 structure of the films. Morphology study by SEM indicate development of cracks with increase in number of layers at large scale but in the small (nano) scale the films are compact and smooth. Thickness study by cross sectional SEM shows increase in thickness with increase in number of layers. Energy Dispersive X-ray spectra were used to study the presence of cobalt in doped films. UV–Visible spectroscopy was used to study the transmittance of the films and spectroscopic ellipsometry was used to study the optical constants like refractive index and extinction coefficient which indicate the highest refractive index and the lowest extinction coefficient for single layered cobalt doped TiO2 thin films while 7 layered films show the lowest refractive index and the highest transmittance. Spectroscopic ellipsometry studies indicate increase in packing density of coated layers in Co-doped TiO2 films due to which refractive index as well as transmittance of these films are significantly more in comparison to undoped films. Photoluminescence spectra show increase in oxygen vacancies in Co-doped multilayered TiO2 films indicating increase in blue emission. Thus, the enhanced values of refractive index as well as transmittance and blue emission in Co-doped TiO2 multilayers films are promising for optical device applications.

Spectroscopic ellipsometry studies of an electrochemically synthesized molecularly imprinted polymer for the detection of an aviation biokerosene contaminant

The present work reports the use of spectroscopic ellipsometry to study the properties of molecularly imprinted poly(ortho-phenylenediamine) film. This polymer was electrosynthesized by cyclic voltammetry and applied for the detection of hexahydrofarnesol, which is the main contaminant of aviation biokerosene. Ellipsometry was used to obtain the thickness of the polymeric film and to investigate the optical and dielectric properties of this material. The results obtained showed that the optical properties and dielectric constants of the molecularly imprinted polymer were sensitive to the presence or absence of the hexahydrofarnesol molecule. Detection studies for this molecule showed that the modified electrode responds linearly in two distinct concentration ranges: 5.0 × 10−8 to 1.3 × 10−7 mol L−1 and 3.0 × 10−7 to 1.5 × 10−6 mol L−1, with the first linear range presenting a sensitivity 27.3 times higher than the second range. This is in line with the behavior of the optical properties (refractive index and extinction coefficient) of the polymeric film, which pointed to the presence of a larger number of imprinted cavities in the non-homogeneous part of the polymer. Essentially, this study proved that, apart from measuring film thickness, spectroscopic ellipsometry is a powerful tool for the characterization of molecularly imprinted polymers.

Sulphamic acid: potential single crystal for nonlinear optical applications

A bulk-sized single crystal of sulphamic acid (SA) was grown by the solution growth technique. The lattice dimensions and the plane’s identification of the grown crystal were confirmed with powder X-ray diffraction. High-resolution X-ray diffraction was employed to observe crystalline perfection that was found fairly good. The optical transmission studies reveal its suitability for optical applications in the complete UV–visible region of the electromagnetic spectrum. Bandgap calculations and other optical parameters like absorption and extinction coefficient were calculated to scrutinize its optical characteristics. The photoluminescence emission spectrum was recorded for the corresponding excitation wavelength to reveal the crystal behavior and energy gap transitions. The presence of the titled compound was examined through FTIR spectroscopy. Ellipsometry study was also carried out for the measurement of linear refractive index (n) and also for the extinction coefficient (K). Z-scan studies have been examined to reveal third-order nonlinear optical behavior and calculated the value of its nonlinear absorption coefficient (β). The Terahertz response of the grown crystal was analyzed by the terahertz time-domain spectroscopy. Observed results showed that SA crystal is a good aspirant for NLO applications.

DC sputter deposited TiO2 thin film on ITO/glass substrate for perovskite based solar cell application

A compact TiO2 (c-TiO2) thin film, which acts as electron transport layer (ETL) in perovskite type solar cell is deposited onto ITO coated glass substrate using DC sputtering at room temperature followed by post annealing treatment at 450 °C and 500 °C for 2 h. The films are deposited for 90 min. Ellipsometry studies showed that the thickness of deposited sample is about 57 nm. XRD pattern of TiO2 coated ITO bilayer revealed the anatase phase of TiO2 along with polycrystalline nature of cubic phase In2O3. Optical transmittance of TiO2/ITO bilayer exhibited an average of 80% transmission of light. Energy band gap of the TiO2 layer is found to be 3.2 eV. SEM images showed smooth, uniform and defect free thin film of TiO2 on ITO substrate. Band gap of deposited mesoporous TiO2 (m-TiO2), CH3NH3SnI3 and CuI thin layers are found to be 3.2 eV, 1.5 eV and 3.1 eV, respectively. Sn based perovskite solar cell is fabricated with a device structure of glass/ITO/c-TiO2/m-TiO2/CH3NH3SnI3/CuI/Au. Sn based perovskite solar cell is a promising candidate to overcome the toxic and high cost solar cells.

Spectroscopic ellipsometry study of non-hydrogenated fully amorphous silicon films deposited by room-temperature radio-frequency magnetron sputtering on glass: Influence of the argon pressure

The complex dielectric functions of unhydrogenated amorphous silicon (a-Si) thin films, grown by the radio-frequency magnetron-sputtering (RFMS) technique, at room temperature, upon glass substrates, have been accurately determined by using ex-situ variable-angle spectroscopic ellipsometry, in the photon energy range from 0.73 to 4.96 eV (i.e. 1700 to 250 nm). Mass density of sputter-deposited amorphous silicon films was changed by a simple argon-working-gas pressure control: higher Ar gas pressure results in reduced film mass density, or increased porosity. The optical response of the hydrogen-less amorphous silicon films under study can be successfully parameterized employing a single, Kramers-Kronig (K-K)-consistent Cody-Lorentz (CL) oscillator dispersion model; the Urbach absorption tail included in the CL model, is certainly needed in the present case of hydrogen-free sputtered a-Si films. It has been unambiguously demonstrated that the obtained values of CL-model parameters are reasonably correlated with the particular argon-gas sputtering pressure utilized for each deposition. The behavior of these best-fit CL-model parameters with varying argon pressure from 0.13Pa up to 4.4Pa, can be clearly understood in terms of the effect of the existing micro-voids, within the as-deposited a-Si film material.

Thermal Transitions in P3HT:PC60BM Films Based on Electrical Resistance Measurements.

In this paper, we present research on thermal transition temperature determination in poly (3-hexylthiophene-2,5-diyl) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM), and their blends, which are materials that are conventionally used in organic optoelectronics. Here, for the first time the results of electrical resistance measurements are explored to detect thermal transitions temperatures, such as glass transition Tg and cold crystallization Tcc of the film. To confirm these results, the variable-temperature spectroscopic ellipsometry studies of the same samples were performed. The thermal transitions temperatures obtained with electrical measurements are well suited to phase diagram, constructed on the basis of ellipsometry in our previous work. The data presented here prove that electrical resistance measurements alone are sufficient for qualitative thermal analysis, which lead to the identification of characteristic temperatures in P3HT:PC60BM films. Based on the carried studies, it can be expected that the determination of thermal transition temperatures by means of electrical resistance measurements will also apply to other semi-conducting polymer films.

Structure of DPPC Monolayers at the Air/Buffer Interface: A Neutron Reflectometry and Ellipsometry Study

Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine, known as DPPC, at the air/water interface are extensively used as model systems of biomembranes and pulmonary surfactant. The properties of these monolayers have been mainly investigated by surface pressure–area isotherms coupled with different complementary techniques such as Brewster angle microscopy, for example. Several attempts using neutron reflectometry (NR) or ellipsometry have also appeared in the literature. Here, we report structural information obtained by using NR and ellipsometry on DPPC monolayers in the liquid condensed phase. On one side, NR can resolve the thickness of the aliphatic tails and the degree of hydration of the polar headgroups. On the other side, ellipsometry gives information on the refractive index and, therefore, on the physical state of the monolayer. The thickness and surface excess obtained by multiple-angle-of-incidence ellipsometry (MAIE) is compared with the results from NR measurements yielding a good agreement. Besides, a novel approach is reported to calculate the optical anisotropy of the DPPC monolayer that depends on the orientation of the aliphatic chains. The results from both NR and ellipsometry are also discussed in the context of the existing results for DPPC monolayers at the air/water interface. The differences observed are rationalized by the presence of buffer molecules interacting with phospholipids.

Temperature-dependent infrared ellipsometry of Mo-doped VO2 thin films across the insulator to metal transition

We present a spectroscopic ellipsometry study of Mo-doped VO2 thin films deposited on silicon substrates for the mid-infrared range. The dielectric functions and conductivity were extracted from analytical fittings of Ψ and Δ ellipsometric angles showing a strong dependence on the dopant concentration and the temperature. Insulator-to-metal transition (IMT) temperature is found to decrease linearly with increasing doping level. A correction to the classical Drude model (termed Drude-Smith) has been shown to provide excellent fits to the experimental measurements of dielectric constants of doped/undoped films and the extracted parameters offer an adequate explanation for the IMT based on the carriers backscattering across the percolation transition. The smoother IMT observed in the hysteresis loops as the doping concentration is increased, is explained by charge density accumulation, which we quantify through the integral of optical conductivity. In addition, we describe the physics behind a localized Fano resonance that has not yet been demonstrated and explained in the literature for doped/undoped VO2 films.

Utilization of nanoporous biosilica of diatoms as a potential source material for fabrication of nanoelectronic device and their characterization

Biosilica obtained from frustules of diatoms have very delicate nanostructures similar to many micro- and nanofluidic devices. In the present investigation, a cheaper and ecofriendly metal-oxide-semiconductor (MOS) tool has been fabricated exploiting frustules of the diatom Halamphora subturgida. The structural, optical, and chemical characterizations of the cleaned frustules of cultured diatom were investigated through various techniques. Electron microscopic images revealed intricate morphology of the nanostructured silica with very minute pores making the frustules very hard but light material. UV-Vis spectroscopy showed maximum absorbance at 223 nm. The absorption maximum for photoluminescence was centered at 462 nm and that of cathodoluminescence was at 439.9 nm and 466.6 nm. Bulk of extracted silicon dioxide (SiO2) nano-powder from diatom frustules was used as a source material for preparing a high-quality crystalline film on P-type silicon (p-Si) by vapor-liquid-solid (VLS) method. The crystalline quality of the film was tested by X-ray diffraction (XRD) and the crystalline size obtained was 62 ± 2.4 nm. From scanning electron microscopic (SEM) investigation, the growth of a continuous film from diatom biosilica on p-Si substrate was revealed. The thickness of the as-grown SiO2 film was 22.2 ± 1.6 nm, obtained from spectroscopic ellipsometry (SE) study. The performances of fabricated Al/SiO2/Si metal-oxide-semiconductor capacitor were tested by measuring leakage current (~ 43 ± 8 × 10−11 A μm−2 at +2 V), capacitance-voltage, constant current (0.1 μA), and voltage stress (at − 2 V) for reliable gate dielectrics applications in MOS devices. Overall, the process was cost-effective and provides an alternative technique to design high-quality diatom-derived “Bio-SiO2 films” on p-Si substrate.

Spectroscopic Ellipsometry Based Biosensor on Gold Thin Film for Detection of Microalgae

The study of spectroscopic ellipsometry on gold thin film with different thicknesses (30, 50, and 70 nm) for biosensor application has been done. In this work, a rotating analyzer ellipsometer (RAE) has been used to characterize gold thin film and detect microalgae. The measurement was performed at different incidence angles (60°, 65°, 70°, and 75°) assuming the gold film as an isotropic material. The light absorptions of electron represented by the ellipsometer parameter (Δ) and the extinction coefficient (k) are due to the intraband transition of free electrons in the lower photon energy and interband transition of bounded electrons from 5d to 6sp in the higher photon energy. The light absorption increases with the decrease in the thickness of Au thin film. However, for the detection of microalgae, the light absorption of the electron increases with the increase in the thickness of Au thin film due to the dominant absorption by microalgae and PVA. We report that the use of Au thin film with the thickness of 70 nm provides the most sensitive detection of microalgae which is confirmed by the change in Δ (63.1°), at the photon energy of 2.11 eV and the incidence angle of 75°.

Crystal Growth and Structure–Property Optimization of Thermally Annealed Nanocrystalline Ga2O3 Films

The effects of thermal annealing on the crystal chemistry, crystallization process, index of refraction, mechanical properties, and electrical characteristics of nanocrystalline Ga2O3 films was evaluated. Ga2O3 thin films were sputtered onto Si(100) substrates at 500 °C utilizing a Ga2O3 ceramic target, while postdeposition thermal annealing was performed between a range of 500–900 °C. Both structural quality and packing density of the Ga2O3 films was improved by the thermal annealing as indicated by the X-ray diffraction and ellipsometry studies. The atomic force microscopy analysis indicates that the annealing temperature has a dramatic effect on surface roughness, especially when the annealing temperature exceeds 700 °C. Corroborating with structure and morphology changes, the high values of hardness and elastic modulus are noted for Ga2O3 films annealed at higher temperatures (800–900 °C). Index of refraction (n) and extinction coefficient (k) results, and their dispersion profiles indicate that the annealing temperature strongly influences the optical properties. The refractive index values vary in the range of 1.78–1.84 (632 nm) because of the gradual improvement of structural quality, texturing, and packing density upon thermal annealing. A correlation between annealing temperature, optical characteristics, and electrical characteristics in Ga2O3 films is established.