Spectroscopic Ellipsometry Study Research Articles

Spectroscopic ellipsometry study of linear and nonlinear optical properties of NaBi(Mo0.5W0.5O4)2 crystal

Spectroscopic ellipsometry study of linear and nonlinear optical properties of NaBi(Mo0.5W0.5O4)2 crystal

Native Oxidation of HgCdTe Compound Semiconductors and Its Impact on Infrared Detectors Performances

HgCdTe surface processing and exposition to the atmospheric environment promote the formation of surface oxides, which have been reported to influence the electrical behavior of devices. This work investigates the formation of HgCdTe of air native oxides on epitaxial Hg(1-x)Cd(x)Te layers after a standard wet etching procedure (x ≃ 0.2 to 0.7). Real-Time Spectroscopic Ellipsometry (RTSE) studies were performed to monitor initial native oxide formation in a clean-room environment and revealed a two-stage kinetic of oxide formation. X-ray Photoelectron Spectroscopy (XPS) was used to assess the evolution of the surface chemistry. After etching, the surfaces exhibited an excess of tellurium that oxidized during early oxide formation (< 45min). Longer air exposures resulted in oxide thicknesses correlated to the alloy composition, indicating a cadmium contribution to further oxidize the material. The combination of techniques allowed the investigation of the formation mechanisms surrounding the native oxide of wet-etched HgCdTe surfaces.

Optical behaviour of magnetron sputtered nano-hilled TiN coatings

Cylindrical magnetron sputtered TiN thin films have been grown on glass (G) and quartz (Q) substrates to examine optical properties under two flow conditions: increasing nitrogen flow rate (1 → 35 sccm): (I) and decreasing nitrogen flow rate (35 → 1 sccm): (D). The optical properties of the film are characterized using UV–Vis-NiR spectroscopy, spectroscopic ellipsometry, and photoluminescence studies. Films deposited under both parameters exhibited excellent UV-restriction properties. Nano-hilled topography of the film contributed to multiple reflections and scattering of incident light on both quartz and glass specimens. Clustering of nano-particles in G(D) specimen increases the light interaction and absorption within the film leading to higher absorbance and lower transmittance properties compared to G(I). TiN-Quartz specimen displayed better UV absorbing properties compared to TiN-Glass as confirmed through ellipsometry studies. lack of phonon-related transitions in Tauc's plot indicated the involvement of direct allowed transitions.

Fingerprints of Mott–Hubbard physics in optical spectra of antiferromagnetic LaTiO3

Magnetic properties of Mott–Hubbard insulators are determined by superexchange interactions mediated by the high-spin (HS) and low-spin (LS) intersite d–d charge excitations, which can be associated with the HS- and LS-Hubbard subbands in optical experiments. To explore the Mott–Hubbard physics in orthorhombic LaTiO3 crystal exhibiting the G-type antiferromagnetic order at the Néel temperature TN = 146 K, we present a comprehensive spectroscopic ellipsometry study in the spectral range 0.5–5.6 eV at temperatures 10 ⩽ T ⩽ 300 K. We found that the complex dielectric function spectra of LaTiO3 crystal are almost featureless, nearly isotropic, and weakly temperature dependent in the range of the intersite d–d optical transitions. Nonetheless, analyzing the difference spectra below the TN, we have identified the LS-state d1d1⇌d2d0 excitations at ∼3.7 and ∼5.15 eV and estimated values of the on-site Coulomb repulsion U ∼ 4.2 eV and Hund’s exchange constant JH ∼ 0.5 eV, which define the energy of the HS-state d1d1⇌d2d0 excitation at ∼2.7 eV. In addition, we discovered that the pronounced lowest-energy 1.3 eV optical band displays the critical intensity behavior and anomalous broadening with decreasing temperature below the TN. The discovered properties indicate that the 1.3 eV band in LaTiO3 can be associated with a Mott–Hubbard exciton.

Influence of microstructure on dielectric function and plasmonic properties of silver nanoparticles grown by solid state dewetting: a spectroscopic ellipsometry study

This work reports the microstructure influence on dielectric function and plasmonic properties of silver nanoparticles (Ag NPs). Ag NPs with varying microstructures were grown on corning glass substrate by solid-state dewetting (SSD) of sputtered silver thin films deposited by varying RF power. Dielectric function and plasmonic properties of Ag NPs were investigated from spectroscopic ellipsometry (SE) data using a quite unique model in terms of the combination of different oscillators. Drude–Lorentz model along with two Gauss oscillators was used to account for intraband, interband transitions and different modes of localized surface plasmon resonance (LSPR) of Ag NPs. It was observed that peak of imaginary part of pseudo dielectric function, which is due to LSPR of Ag NPs, shifted towards the lower energy at higher RF power due to increase in thickness of precursor films which subsequently resulted in to increase in particle size. A shift in the LSPR peak in absorbance spectra in UV–Vis-NIR spectroscopy was also observed. No LSPR peak is observed in SE or UV–Vis absorbance spectra for thick films deposited at high RF power due to the presence of continuous silver film even after annealing. This change in microstructure from nanoparticle formation to continuous films is also reflected in the values of void fraction and surface roughness calculated from SE using Bruggeman Effective Medium Approximation (BEMA). Field Emission Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and X-ray diffraction (XRD) were used to probe the microstructure of Ag NPs. Root mean square (RMS) roughness evaluated from AFM matched well with surface roughness measured from SE.

Formation of quaternary [formula omitted] epilayers driven by thermally induced interdiffusion between spinel [formula omitted] epilayer and [formula omitted] substrate

Zinc aluminogallate, Zn(AlxGa1−x)2O4 (ZAGO), a single-phase spinel structure, offers considerable potential for high-performance electronic devices due to its expansive compositional miscibility range between aluminum (Al) and gallium (Ga). Direct growth of high-quality ZAGO epilayers however remains problematic due to the high volatility of zinc (Zn). This work highlights a novel synthesis process for high-quality epitaxial quaternary ZAGO thin films on sapphire substrates, achieved through thermal annealing of a ZnGa2O4 (ZGO) epilayer on sapphire in an ambient air setting. In-situ annealing x-ray diffraction measurements show that the incorporation of Al in the ZGO epilayer commenced at 850 °C. The Al content (x) in ZAGO epilayer gradually increased up to around 0.45 as the annealing temperature was raised to 1100 °C, which was confirmed by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy. X-ray rocking curve measurement revealed a small full width at half maximum value of 0.72 °, indicating the crystal quality preservation of the ZAGO epilayer with a high Al content. However, an epitaxial intermediate β–(AlxGa1−x)2O3 layer (β - AGO) was formed between the ZAGO and sapphire substrate. This is believed to be a consequence of the interdiffusion of Al and Ga between the ZGO thin film and sapphire substrate. Using density functional theory, the substitution cost of Ga in sapphire was determined to be about 0.5 eV lower than substitution cost of Al in ZGO. Motivated by this energetically favorable substitution, a formation mechanism of the ZAGO and AGO layers was proposed. Spectroscopic ellipsometry studies revealed an increase in total thickness of the film from 105.07 nm (ZGO) to 147.97 nm (ZAGO/AGO) after annealing to 1100 °C, which were corroborated using TEM. Furthermore, an observed increase in the direct (indirect) optical bandgap from 5.06 eV (4.7 eV) to 5.72 eV (5.45 eV) with an increasing Al content in the ZAGO layer further underpins the formation of a quaternary ZAGO alloy with a tunable composition.

Structural and optical study of conducting polymer PEDOT:PSS and its composite with GO

Conducting polymers such as PEDOT:PSS have received tremendous attention as possible substitute for ITO as transparent and conductive material in flexible electronic devices. Due to its extraordinary electrical, physical, and chemical properties Graphene has sparked huge interest in many advanced technologies. To enhance the aggregate properties, conducting polymers have been reinforced with graphene, graphene oxide (GO), reduced graphene oxide (rGO) etc. In this study, thin films of PEDOT:PSS and GO composites were deposited on glass substrates by spin-coating technique. Dimethyl sulfoxide (DMSO) was added to PEDOT:PSS to enhance the conductivity. The films were characterized by four probe, XRD, Scanning electron microscopy (SEM) and Ellipsometry. Conductivity measurement by four probe technique shows highest conductivity of 1170 S/cm for 5% DMSO doped PEDOT:PSS films. XRD shows shift in peak position of PEDOT:PSS films due to addition of DMSO and GO. Spectroscopic ellipsometry study indicates an increase in refractive index due to addition of GO in PEDOT:PSS.

Atomic structure and annealing-induced reordering of ε-Ga2O3: A Rutherford backscattering/channeling and spectroscopic ellipsometry study

The crystallographic structure of thin Ga2O3 layers grown by metal–organic vapour phase epitaxy on Al2O3 substrate was analyzed by Rutherford Backscattering Spectrometry/Channeling (RBS/C) angular yield scans performed around the c-axis of as-grown Ga2O3. The measured widths and minimum yields of the scan curves for the Ga and O component were compared to calculations based on the continuum steering potential model. The results obtained are consistent with a crystal structure containing oxygen atoms arranged in a 4H hexagonal closely packed lattice and Ga atoms preferentially occupying octahedral interstitial sites in the 4H cells - a structure closely related to the ε-Ga2O3 polymorph. After high-temperature annealing remarkable structural transformation is detected via significant changes in the RBS/C spectra. This effect is related to the hexagonal-monoclinic, i.e., ε-β phase transformation of Ga2O3. Spectroscopic ellipsometry spectra of as-grown and annealed samples can be best fitted using a vertically graded single-layer B-spline model. Significant differences in the dielectric functions were found, showing bandgap reduction for long term annealing. These features are related to the ε-β polymorphic transformation, variation of the preferred crystallographic orientation upon annealing, and differences in residual strain and defect structure determined by the annealing conditions.

Review on High-Throughput Micro-Combinatorial Characterization of Binary and Ternary Layers towards Databases.

The novel, single-sample concept combinatorial method, the so-called micro-combinatory technique, has been shown to be suitable for the high-throughput and complex characterization of multicomponent thin films over an entire composition range. This review focuses on recent results regarding the characteristics of different binary and ternary films prepared by direct current (DC) and radiofrequency (RF) sputtering using the micro-combinatorial technique. In addition to the 3 mm diameter TEM grid used for microstructural analysis, by scaling up the substrate size to 10 × 25 mm, this novel approach has allowed for a comprehensive study of the properties of the materials as a function of their composition, which has been determined via transmission electron microscopy (TEM), scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), X-ray diffraction analysis (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry, and nanoindentation studies. Thanks to the micro-combinatory technique, the characterization of multicomponent layers can be studied in greater detail and efficiency than before, which is beneficial for both research and practical applications. In addition to new scientific advances, we will briefly explore the potential for innovation with respect to this new high-throughput concept, including the creation of two- and three-component thin film databases.

Aluminum nitride on insulator: Material and processing optimization for integrated photonic applications

Thin film aluminum nitride on insulator (AlNOI) has gained attention as a promising material platform for integrated photonic circuits (PICs) due to its ability to operate over a wide spectral range covering the ultra-violet to mid-infrared regions, while enabling a broad range of passive photonic functionalities. This study aims to optimize sputtered AlNOI films for PICs, with an emphasis on the spectroscopic ellipsometry study over a range from 0.19 µm to 25 µm. Furthermore, we discuss our approach for fabricating AlNOI PICs components, with a particular focus on optimizing the etching process to attain smooth sidewall waveguides.

Spectroscopic Ellipsometry Studies on Solution-Processed OLED Devices: Optical Properties and Interfacial Layers.

Τhe fabrication of organic light-emitting diodes (OLEDs) from solution involves the major problem of stack integrity, setting the determination of the composition and the characteristics of the resulting interfaces prerequisite for the optimization of the growth processes and the achievement of high devices' performance. In this work, a poly(9,9-dioctylfluorene) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) blend is used for the emissive layer (EML), poly-3,4-ethylene dioxythiophene; poly-styrene sulfonate (PEDOT:PSS) is used for a hole transport layer (HTL), and Poly(9,9-bis(3'-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluore-ne))dibromide (PFN-Br) for an electron transport layer (ETL) to produce the OLED device. All the layers are developed using the slot-die process, onto indium tin oxide (ITO)-coated polyethylene terephthalate (PET) flexible substrates, whereas Ag cathode was formed by ink-jet printing under ambient conditions. Spectroscopic ellipsometry measurements were performed upon completion of the successive films' growth, in sequential steps, for the multilayer OLED development. Ellipsometry analysis using different models demonstrate the degree of intermixing within the layers and provide information about the interfaces. These interfacial properties are correlated with the emission characteristics as well as the final performance of the OLED devices.

Spectroscopic ellipsometry study of Mn doped CeO2 thin films prepared by radio-frequency magnetron sputtering

Mn doped CeO2 (Ce1-xMnxO2, x=0, 0.03, 0.06) thin films were deposited on Si (100) substrates by radio-frequency magnetron sputtering. X-ray diffraction and Raman analysis indicates that the films are cubic fluorite crystal structure with a preferred orientation along (111), which is the same as that of pure CeO2. Atomic force microscopy reveals that the film surface morphology is dependent on the Mn doped content. The influence of Mn doped content on the optical properties was studied by spectroscopic ellipsometry (SE) in the UV-NIR region (210∼2500 nm). The energy dispersion optical constants (the refractive index n and the extinction coefficient k) of Ce1-xMnxO2 thin films were obtained by analyzing the SE spectra. Under the assumption of a direct band-to-band transition, the optical band gap energies Eg for these films were determined. The values of n, k and Eg are functions of the Mn doped contents. The results showed that the Eg values of the Ce1-xMnxO2 thin films are 3.22, 3.32 and 3.35 eV, and the n values at wavelength of 632 nm are about 2.29, 2.38 and 2.49 for Mn doped content x=0, 0.03 and 0.06, respectively. The values of n and Eg increases linearly with increasing Mn doped content.

Spectroscopic ellipsometry study of dielectric functions of Ag films and chemically deposited layers of Ag nanoparticles on silicon

The optical properties of thin films and layers of Ag nanoparticles on a c-Si substrate are modeled by calculating the complex pseudo-dielectric function <ε>. The evolution of the imaginary part <ε2> with an increase in the thickness of continuous layers from the dielectric function ε of the substrate to ε of bulk silver is studied, which demonstrates the appearance of optical characteristics of Ag and the suppression of c-Si features in the form of critical points. The data measured on the spectroscopic ellipsometer for Ag films produced by magnetron sputtering for several nominal thicknesses from 10 to 300 nm, and layers of Ag nanoparticles chemically deposited on a c-Si substrate, were interpreted using a pseudo-dielect ric function and by calculating the complex dielectric functions ε using the Drude-Lorentz model. Morphological parameters obtained by atomic force microscopy and scanning electron microscopy were also used in the calculations. Since the Ag layers and films were deposited on the c-Si substrate without any additional layers (except for the native layer), the determined pseudo-dielectric functions for thicknesses in the range of 7−50 nm turned out to be close to the calculations of the dielectric functions using the Drude-Lorentz model. It was found that in the calculated and experimental spectra in the imaginary part of ε2 and <ε2> a peak appears at E ∼ 3.9 eV, which is interpreted as a plasmon resonance in the longitudinal mode at oblique incidence of light. In the ε2 spectrum of a layer of disordered Ag nanoparticles produced by chemical deposition, there is a broader localized surface plasmon resonance peak at E ∼ 2.5 eV, in contrast to thin films. Whereas, in a layer of larger nanoparticles, the peak is absent, and its ε dependence is close to ε for bulk Ag.

Spectroscopic Ellipsometry Study on Tuning the Electrical and Optical Properties of Zr-Doped ZnO Thin Films Grown by Atomic Layer Deposition.

This work reports the ellipsometry analysis of atomic layer deposition (ALD) films of ZnO doped with Zr to determine parameters like free carrier concentration and mobility. Thin films of zinc oxide (ZnO) and Zr-doped ZnO of thickness ∼100 nm were prepared by atomic layer deposition on sapphire, SiO2/Si(100), and Si(100) substrates. Variable-angle spectroscopic ellipsometry was used to study their optical properties in the 0.5–3.5 eV spectral range. The optical constants were accurately obtained using a model that combines Drude and Tauc–Lorentz oscillators with Bruggeman effective medium approximations, allowing the inclusion of a roughness layer in the optical model. The effect of Zr doping (ca. 1.9–4.4 atom %) was then investigated in both as-prepared samples and samples annealed in the temperature range of 100–300 °C. All of the films exhibited good optical transparency (ca. 70–90% in the visible region). For doping levels below 2.7 atom %, the real part of the dielectric permittivity reveals a semiconductor-to-metal transition in the near-infrared (NIR) region, as the permittivity goes from positive to negative. Besides, the plasma energy increases with increasing Zr concentration, and both resistivity and carrier concentration exhibit slightly parabolic behaviors, with a minimum of ∼1.5 × 10–3 Ω cm and a maximum of 2.4 × 1020 cm–3, respectively, at the same critical Zr concentration (2.7 atom %). In contrast, the carrier mobility decreases rapidly from 76.0 to 19.2 cm2/(V s) with increasing Zr content, while conductivities and carrier mobilities worsen when the annealing temperature increases, probably due to the segregation of ZnO crystals. Finally, the optical band gap is very stable, revealing its interesting independence of substrate composition and annealing temperature, as it collapses to a single master curve when band gap energy is plotted versus free carrier concentration, following the Burstein–Moss effect. Overall, the Zr-doped ZnO films studied here would be a highly desirable system for developing thermally stable transparent conductive oxides (TCOs).

Investigation of structural aspect in terms of atypical phases within material deposited for a-Si:H solar cell fabrication

The structural investigation of the a-Si:H material, deposited at different pressures by PECVD process, has been carried out to analyze the signatures of diffused intermediate sort of crystalline phases within the amorphous silicon matrix. Raman characterization along with the Photoluminescence (PL) and spectroscopic ellipsometry studies were carried out to understand the microstructuree of these films. From Raman analysis the material was found to have indistinguishable crystalline phase, which can also be named as “intermediate amorphous phase” (a phase defined between amorphous and ultra nano-crystalline silicon) with crystalline volume fractions as 56 % and 62 % for 0.23 Torr and 0.53 Torr respectively. Here the contribution of ultra nano-crystallites results in higher crystalline fraction, which is not visibly revealed from the Raman spectra due to its sub nano-crystallite characteristics. For the film deposited at 0.53 Torr stable photo-conductance in conjunction with high photo-response under 10 hour light soaking has been observed, which is as expected due to high crystalline volume fraction. The presence of these phases might be the possible reason for the distinct device characteristics though having nearly the similar electrical properties (photo-response ~104). These studies will help to make improvement in the individual layer properties, other than the interface effect, in the fabrication of efficient p-i-n solar cells.

Hybrid Perovskite Degradation from an Optical Perspective: A Spectroscopic Ellipsometry Study from the Deep Ultraviolet to the Middle Infrared

AbstractA quantitative analysis of the thermally induced degradation of various device‐relevant multi‐cation hybrid perovskite films is performed using spectroscopic ellipsometry, for temperatures between 80 and 120 °C. The studied compositions are a triple cation perovskite Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3, a Rb‐containing variant Rb0.05Cs0.05(MA0.17FA0.83)0.90Pb(Br0.17I0.83)3, and a methylammonium‐free Rb0.05Cs0.10FA0.85PbI3 composition. A very wide combined spectral range of 200 nm to 25 μm is covered by combining the data from two separate instruments. The relative changes in organic cation concentrations are quantified from the middle infrared molecular absorption bands, leveraging the use of point‐by‐point fitting for increased sensitivity. Additionally, the formation of PbI2 and non‐perovskite δ‐CsPbI3 phases is evidenced from Bruggemann effective medium fits to the visible and ultraviolet complex refractive indices. Methylammonium is almost completely depleted from the relevant compositions within 100 to 285 min of thermal annealing. The MA‐free perovskite degrades faster at intermediate temperatures, which is attributed to phase instability due to the formation of δ‐CsPbI3 in addition to PbI2.

In Situ and Ex Situ diagnostics of ALD-Ultrathin Lithium-Ion Films

All solid-state ion layers has an ever-growing interest in order to accomplish on-chip energy storage devices. As such, lithium-ion synaptic transistor to build artificial neural networks, integrated area-enhanced capacitors and lithium-ion microbatteries for energy supply are suitable candidates fulfilling energy-efficient devices. Atomic layer deposition (ALD) is one of the most promising techniques for manufacturing ultrathin layers for lithium-ion devices with exceptional capabilities to enable conformal growth at atomic scale. In this area, in situ diagnostics has become of vital importance for the growth process understanding especially on view of the air-sensitivity character of lithium ultra-thin layers.The purpose of this work is to present an in situ spectroscopic ellipsometry (SE) study of ALD thin films used on the fabrication of lithium-ion devices. We will consider several aspects of ALD ultrathin films growth, such as film thickness, saturation curves and initial films nucleation. We shall compare in situ SE results with those of ex situ diagnostics such as XRR (x-ray reflectometry) and XPS (x-ray photoelectron spectroscopy).We focus on the characterization of 10-100 nm thin lithium phosphate electrolyte with and without nitrogen doping deposited at ALD temperature range 300-350°C using LiHMDS-TMPO and LiHMDS-DEPA precursors, respectively. On the other hand, the realization of silicon integrated lithium ionic devices requires the implementation of essential barrier films to prevent Li-ion into the Si substrate. We will explore here the ability of titanium nitride depositions to act as lithium-ion diffusion barriers. TiN deposition (10-20 nm thin) by ALD process (350°C-400°C) uses TiCl4 and NH3 precursors.First, we investigate the growth process of LiPO, LiPON and TiN intrinsic layers deposited using thermal ALD. Secondly, we apply in situ and ex situ diagnostics on exemplary LiPO/LiPON deposited on top of the 10 nm ALD TiN film (Figure 1: Monitoring of LiPON thickness vs deposition time using in-situ Ellipsometry). The film thickness deduced from in situ SE measurements was corroborated by thickness measurements with XRR technique (Figure 2: Evolution of LiPON thickness vs ALD cycles using Ellipsometry and SE characterization techniques). Ex situ SE was used most often for WiW uniformity evaluating (Figure 3: 8” Wafer thickness mapping of ALD LiPON layers (a: 10nm TiN film; b: 17nm LiPON film). The preliminary results underline the fact that ALD growth rate and nucleation of lithium electrolyte and titanium nitride obviously depends on the ALD process parameters (temperature, pulse and purge times, number of cycles) but on the substrate nature (silicon, thermal oxide, and metallic). In situ and ex situ diagnostics highlight that initial film growth of lithium electrolytes and TiN layers strongly depends on the precursors kind used in the ALD process and the substrate material employed. Figure 1

Highly Transparent and Conductive Indium‐Free Vanadates Crystallized at Reduced Temperature on Glass Using a 2D Transparent Nanosheet Seed Layer

AbstractIndium‐tin‐oxide (ITO) is a widely employed transparent conducting oxide (TCO), but the indium scarcity and price encourage developing some alternatives. The correlated metals CaVO3 and SrVO3 have been recently identified as new TCOs with functional properties being comparable to ITO. However, their technological potential is limited by the critical requirement of a perovskite structure of the film, impossible to achieve via direct growth on substrates commonly used for applications. In this article, the authors tackle this limitation by demonstrating the crystalline growth of vanadate TCOs on glass at temperatures below 600 °C, with the help of 2D nanosheets as transparent seed layers. The functional properties do not suffer from the textured structure of the films, as confirmed by an in‐depth spectroscopic ellipsometry study, allowing for an industrially viable approach to integrate vanadate TCOs on virtually any surface and to exploit their promising performances as a new generation TCO.

Unveiling a critical thickness in photocatalytic TiO2 thin films grown by plasma-enhanced chemical vapor deposition using real time in situ spectroscopic ellipsometry

TiO2 thin films of various thicknesses have been deposited on silicon at low-temperature by PECVD operating in continuous mode (T < 130 °C) and pulsed mode (T < 80 °C) using oxygen/titanium isopropoxide low-pressure inductively coupled plasma. The study of the crystallinity and microstructure of the films by atomic force microscopy, scanning electron microscopy and x-ray diffraction allowed showing that the roughness and amount of anatase are closely related to the film thickness. The coalescence of large polycrystalline columns emerging from an assembly of thin columns was found to happen at a critical thickness, at about 150 nm in the continuous mode and 250 nm in the pulsed mode. Real time in situ spectroscopic ellipsometry study allowed to monitor the growth and to determine this critical thickness for both plasma modes. The change of morphology type to large columnar structure is associated with an important increase in the photocatalytic activity. The determination of this coalescence thickness by ellipsometry may provide an interesting method to evaluate the impact of process parameters on TiO2 thin films characteristics.

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.