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The prototypical correlated metal ${\mathrm{Sr}}_{2}{\mathrm{RhO}}_{4}$ was studied using optical and photoemission spectroscopy. At low energies and temperatures, the optical data reveal a complex, multicomponent response that on the surface points to an unconventional metallic state in this material. Via a comparison with photoemission, the anomalous optical response may be attributed to an unexpectedly strong interband transition near 180 meV between spin-orbit coupled bands that are nearly parallel along $\mathrm{\ensuremath{\Gamma}}X$. This spin-orbit coupling effect is shown to occur in a number of related metallic ruthenates and explains the previously puzzling optical properties reported for these materials.

We report the effects of deposition temperature on the evolution of defect and second phases and on the ferroelectric properties of BiFeO3 thin films. We grew BiFeO3 thin films on (001) SrTiO3 substrates by using pulsed laser deposition at temperatures in the range of 570–600 °C at intervals of 10 °C. We found that defects and a resulting second phase appeared at temperatures greater than 590 °C. The second phase led to significant changes in the optical absorption and to the appearance of impurity peaks in the X-ray diffraction data. An analysis of the X-ray diffraction data indicated that the second phase was Fe2O3. Atomic force microscopy measurements showed that the appearance of defects accompanied an abrupt increase in the surface roughness. Furthermore, the presence of the second phase significantly affected the ferroelectric hysteresis. Our results suggest that the evolution of defects and resulting second phase in BiFeO3 thin films depends strongly on the deposition temperature.

Two kinds of anthracene derivative thin films, 2, 6-bis((4-hexylphenyl)ethynyl)-9, 10-bis(phenyl ethynyl)anthracene (B-ant-THB) and 9, 10-bis((4-hexyl phenyl)ethynyl)-2, 6-bis (phenyl ethynyl) anthracene (HB-ant-TB), were synthesized to investigate their optical properties. The difference between the two anthracene derivatives consisted of the position of the 1-ethynyl-4-hexylbenzene group substitution into an anthracene ring. We measured the optical properties of the anthracene derivatives by using photoluminescence (PL), transmittance spectroscopy, and spectroscopic ellipsometry. The dielectric functions of the two films were similar with respect to transition energies, but were different in terms of amplitudes. The optical band gap energies of the B-ant-THB and the HB-ant-TB film states were estimated to be 2.45 eV and 2.34 eV, respectively, whereas density functional theory (DFT) calculations of isolated molecular states showed the same value of 2.42 eV. The large bathochromic shift of the HB-ant-TB film state compared to the DFT calculation is attributed to strong intermolecular coupling between the HB-ant-TB molecules in the crystalline film because the HB-ant-TB film has higher crystallinity than the B-ant-THB film. The symmetric structures of the transmittance and PL spectra of the anthracene derivative films were observed as distinct peaks having similar vibrational energy levels for the singlet ground state and the first excited state.

Topotactic phase transformation enables structural transition without losing the crystalline symmetry of the parental phase and provides an effective platform for elucidating the redox reaction and oxygen diffusion within transition metal oxides. In addition, it enables tuning of the emergent physical properties of complex oxides, through strong interaction between the lattice and electronic degrees of freedom. In this communication, the electronic structure evolution of SrFeO

We grew Ge-SbTe films on glass substrates using RF sputtering deposition. We measured the dielectric function of the Ge-doped SbTe thin films in the infrared and visible spectral region. By applying linear extrapolation to the absorption coefficient, we obtained accurate band gap energy values, which decreased with increasing Te composition. Using the Drude model, we estimated their resistivity and mean scattering time. Compared to the Hall effect parameters of carrier concentration and mobility, we estimated the effective mass of holes for the Ge-SbTe thin films.

Rotatable retarders have been developed for applications in spectroscopic, full Mueller Matrix ellipsometry in the far-IR spectral range. Several materials, such as silicon, KRS-5, and a commercial polymer plastic (TOPAS) have been utilized to achieve a fully adjustable retardation between 0° and 90°. Experimental characteristics of the rotatable retarders that utilize three- and four-bounce designs are compared with calculations. We discuss the effect of light focusing on the performance of these rotatable retarders.

We report on GaN-based vertical cavities using crack-free 40.5 pair of AlGaN/GaN distributed Bragg reflectors (DBRs) by employing a selective growth method to avoid wafer cracking that has been commonly observed in conventional planar Al(Ga)N/GaN DBRs. An Al0.46Ga0.54N/GaN DBR with ∼98% reflectivity was selectively grown with square patterns of up to 150 × 150 μm2 in size, which were separated from each other by 10 μm wide SiO2 mask stripes. Vertical cavity structures employing InGaN multiple quantum wells were grown on these crack-free DBRs and capped with 8 pair dielectric SiO2/SiNx DBRs. Cavity mode centered at ∼400 nm was observed to have a quality factor of ∼100. The selective DBR and vertical cavity growth to eliminate crack formation appears very promising for the fabrication of nitride-based vertical-cavity surface emitting laser devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Barium bismuth oxide (BaBiO_{3}) is the end member of two families of high-T_{c} superconductors, i.e., BaPb_{1-x}Bi_{x}O_{3} and Ba_{1-x}K_{x}BiO_{3}. The undoped parent compound is an insulator, exhibiting a charge density wave that is strongly linked to a static breathing distortion in the oxygen sublattice of the perovskite structure. We report a comprehensive spectroscopic and x-ray diffraction study of BaBiO_{3} thin films, showing that the minimum film thickness required to stabilize the breathing distortion and charge density wave is ≈11 unit cells, and that both phenomena are suppressed in thinner films. Our results constitute the first experimental observation of charge density wave suppression in bismuthate compounds without intentionally introducing dopants.

Using variable-angle spectroscopic ellipsometry, we measure the pseudo-dielectric functions of as-deposited and annealed SiO2/SiOx multilayers. The SiO2(2 nm)/SiOx(2 nm) multilayers are prepared under various deposition temperatures by ion beam sputtering. Annealing at temperatures above 1100 °C leads to the formation of Si nanocrystals (nc-Si) in the SiOx layer of multilayers. Transmission electron microscopy images clearly demonstrate the existence of nc-Si. We assume a Tauc–Lorentz lineshape for the dielectric function of nc-Si, and use an effective medium approximation for SiO2/nc-Si multilayers as a mixture of nc-Si and SiO2. We successfully estimate the dielectric function of nc-Si and its volume fraction. We find that the volume fraction of nc-Si decreases after annealing, with increasing x in as-deposited SiOx layer. This result is compared to expected nc-Si volume fraction, which is estimated from the stoichiometry of SiOx.

We grew ZnO and Zn 1− x Mg x O thin films on (0001) sapphire substrate by metal-organic vapor phase epitaxy and measured the dielectric functions using variable angle spectroscopic ellipsometry. We analyzed the dielectric functions using a multi-layer model. We included non-uniform thickness of layers in the model. The dielectric functions were fitted using the Holden model dielectric function. We used anisotropic layer modeling for the ZnO thin film, whereas we adopted the approximation of isotropic layer modeling for Zn 1− x Mg x O alloys. We also discussed the Mg composition dependence of the band-gap and binding energy in Zn 1− x Mg x O alloys.

We have measured the dielectric function of poly 2-methoxy-5-hexyloxy phenylenevinylene and the alternating copolymers with N-hexylphenothiazine grown on glass using variable angle spectroscopic ellipsometry and Raman spectroscopy at room temperature. Using the parametric optical constant model, we estimated the dielectric function of each polymer and also determined the band gap parameters, such as threshold energy, broadening, and amplitude. We also determined the band gap parameters by performing lineshape curve-fitting on the second derivative of the fit dielectric function using standard critical point model, and compared to those of the parametric optical constant model. We discussed the shift of band gap parameters and phonon wave numbers in terms of the chemical structures.

We used spectroscopic ellipsometry to characterize four different microcrystalline silicon (μc-Si) films, which were fabricated by crystallizing a-Si:H films predeposited on glass substrates using solid phase crystallization (SPC), excimer laser annealing (ELA), Ni induced silicide-mediated crystallization (Ni-SMC), and field enhanced silicide-mediated crystallization (FESMC) method, respectively. A linear regression analysis, which took the effective dielectric function of μc-Si layer into account using effective medium approximation, showed that all these films were homogeneous throughout their thickness except the oxide overlayers, and completely crystallized regardless of the crystallization method. In our linear regression analysis, the complex dielectric function of silicon microcrystallites was represented by the Adachi model dielectric function (MDF) [T. Suzuki and S. Adachi, Jpn. J. Appl. Phys., Part1 32, 4900 (1993)], and the broadening parameters of the critical points (CPs) in MDF were allowed to vary. The dielectric function of silicon microcrystallites showed systematic broadening and shrinking of the peak features corresponding to the E1 and E2 CPs, from which we concluded that the average microcrystallite size increased in the order of SPC, ELA, Ni-SMC, and FESMC μc-Si. The Raman spectra and the transmission-electron-microscopy images of these films also supported the idea of systematic variation in the microcrystallite size.

The surface plasmon resonance (SPR) of Pt nanoparticles (NPs) in TiO2-SiO2 nanocomposite films, in which Pt NPs of about 5 nm are incorporated, is investigated by using spectroscopic ellipsometry. After obtaining the dielectric functions of Pt NPs from the Pt-SiO2 nanocomposite film, Pt-TiO2-SiO2 nanocomposite films are analyzed by applying a homogenous single layer model with an effective medium approximation. The effects of Pt NPs on the optical properties of the nanocomposite films are clearly revealed in the imaginary part of the dielectric functions, showing an increase in broadband absorption near the band gap of the films with the increasing volume fraction of Pt NPs in the films. Particularly, the maximum of extinction cross-section of Pt NPs in the films coincides with the broadband absorption, indicating that the localized SPR of Pt NPs is responsible for the enhanced light absorption at the visible-light wavelengths. This work emphasizes that, although SPR absorption of Pt NPs is not so distinc...

Topotactic phase transformation enables structural transition without losing the crystalline symmetry of the parental phase and provides an effective platform for elucidating the redox reaction and oxygen diffusion within transition metal oxides. In addition, it enables tuning of the emergent physical properties of complex oxides, through strong interaction between the lattice and electronic degrees of freedom. In this communication, the electronic structure evolution of SrFeOx epitaxial thin films is identified in real-time, during the progress of reversible topotactic phase transformation. Using real-time optical spectroscopy, the phase transition between the two structurally distinct phases (i.e., brownmillerite and perovskite) is quantitatively monitored, and a pressure–temperature phase diagram of the topotactic transformation is constructed for the first time. The transformation at relatively low temperatures is attributed to a markedly small difference in Gibbs free energy compared to the known similar class of materials to date. This study highlights the phase stability and reversibility of SrFeOx thin films, which is highly relevant for energy and environmental applications exploiting the redox reactions.

We report a high sensitivity to oxygen vacancy formation as well as the temperature dependence of anisotropic optical properties of a nanocrystalline ${\text{V}}_{2}$${\text{O}}_{5}$ thin film. Spectroscopic ellipsometry data show that the film has a uniaxial optical anisotropy due to a highly ordered nanocrystalline layer structure. The anisotropic optical properties of the film begin to change at \ensuremath{\sim}400 K in a high vacuum and can be linked to the changes in the electronic structure of the film upon reduction. An increase in the refractive indices, anisotropic changes of the optical conductivities, and a decrease in film thickness are observed after vacuum heating and are recovered to original values by heating in air up to 480 K. The experimental results are supported by the previous theoretical studies on the stability of reduced ${\text{V}}_{2}$${\text{O}}_{5}$ surface through the formation of oxygen vacancies. We discuss the formation of oxygen vacancies, vacancy-induced structural relaxations, and changes in the electronic structure of ${\text{V}}_{2}$${\text{O}}_{5}$ in conjunction with the experimental results.

We investigated the electronic structure of Na${}_{2}$IrO${}_{3}$ using optical spectroscopy, first-principles calculation, and x-ray absorption spectroscopy. We found that the electronic structure of Na${}_{2}$IrO${}_{3}$ is mainly determined by anisotropic hopping interactions and spin-orbit coupling. Due to the hopping interaction, the orbital character of the bands near the Fermi level deviates from the spin-orbit coupling-induced ${J}_{\mathrm{eff}}$ $=$ 1/2 states. Polarization-dependent O 1$s$ x-ray absorption spectroscopy showed that the ${J}_{\mathrm{eff}}$ $=$ 1/2 state of an Ir atom can be mixed with the ${J}_{\mathrm{eff}}$ $=$ 3/2 state of the neighboring Ir atom. This result implies that mixing between the ${J}_{\mathrm{eff}}$ $=$ 1/2 and 3/2 states in the valence state should be carefully considered in proposed exotic states of Na${}_{2}$IrO${}_{3}$, such as topological insulator and quantum spin liquid states.

The temperature ($T$) dependence of the optical conductivity spectra $\ensuremath{\sigma}(\ensuremath{\omega})$ of a single crystal ${\mathrm{SrRuO}}_{3}$ thin film is studied over a $T$ range from 5 to 450 K. We observed significant $T$ dependence of the spectral weights of the charge transfer and interband $d\mathrm{\text{\ensuremath{-}}}d$ transitions across the ferromagnetic Curie temperature (${T}_{c}\ensuremath{\sim}150\text{ }\text{ }\mathrm{K}$). Such $T$ dependence was attributed to the increase in the Ru spin moment, which is consistent with the results of density functional theory calculations. $T$ scans of $\ensuremath{\sigma}(\ensuremath{\Omega},T)$ at fixed frequencies $\ensuremath{\Omega}$ reveal a clear ${T}^{2}$ dependence below ${T}_{c}$, demonstrating that the Stoner mechanism is involved in the evolution of the electronic structure. In addition, $\ensuremath{\sigma}(\ensuremath{\Omega},T)$ continues to evolve at temperatures above ${T}_{c}$, indicating that the local spin moment persists in the paramagnetic state. This suggests that ${\mathrm{SrRuO}}_{3}$ is an intriguing oxide system with itinerant ferromagnetism.

Far-infrared spectra of ferrimagnetic Dy3Fe5O12 single crystals have been studied in the spectral range between 12 and 700 cm(-1) and in a wide temperature range between 5 K and 300 K using transmission spectroscopy and rotating analyzer ellipsometry. In the temperature range below T-C = 16 K for the magnetic ordering of Dy3+ spins, a number of ligand field and Kaplan-Kittel (KK) exchange resonance modes have been found. Temperature dependencies of their frequencies allowed us to estimate the ratio between the Fe-Dy and Dy-Dy exchange constants. We found that variation of the oscillator strength of the KK modes correlates with the magnetic-field-induced changes of magnetic permeability. The low-temperature peak in the static value of the dielectric function at T-C = 16 K may be related to the observed temperature-induced variation of the oscillator strength of the optical phonons.

We investigated the carrier responses of [(LaVO${}_{3}$)${}_{6n}$(SrVO${}_{3}$)${}_{n}$] (n = 1, 2, and 4) superlattices using spectroscopic ellipsometry. All the superlattice samples showed an unexpectedly large spectral response in the midinfrared region, which indicated geometrically confined doping near the LaVO${}_{3}$ and SrVO${}_{3}$ interfaces. The intensity of the midinfrared absorption systematically decreased as the superlattice periodicity n increased while the ratio of LaVO${}_{3}$ and SrVO${}_{3}$ layers was kept constant. In addition, we observed that the far-infrared spectral weight of the n = 1 superlattice was reduced by up to 30% with decreasing temperature, while the spectral weights of the n = 2 and n = 4 superlattices were almost temperature independent. This behavior was attributed to the carrier localization effects near the interfaces between LaVO${}_{3}$ and SrVO${}_{3}$.

Far-infrared spectra of magnetodielectric Dy3Fe5O12 garnet were studied using a combination of transmittance, reflectivity, and rotating analyzer ellipsometry. In addition to purely dielectric and magnetic modes, we observed several hybrid modes with a mixed magnetic and electric dipole activity. Using 4 x 4 matrix formalism for materials with mu(omega) 1, we modeled the experimental optical spectra and determined the far-infrared dielectric and magnetic permeability functions. The matching condition mu(omega_h)Se = epsilon(omega_h)Sm for the oscillator strengths Se/m explains the observed vanishing of certain hybrid modes at omega_h in reflectivity.

Forward models for the Mueller Matrix (MM) components of materials with relative magnetic permeability tensor {\mu} \neq 1 are studied. 4x4 matrix formalism is employed to produce general solutions for the complex reflection coefficients and MMs of dielectric-magnetic materials having arbitrary crystal symmetry and arbitrary laboratory orientation. For certain orientations of materials with simultaneously diagonalizable {\epsilon} and {\mu} tensors (with coincident principal axes), analytic solutions to the Berreman equation are available. For the single layer thin film configuration of these materials, analytic formulas for the complex reflection and transmission coefficients are derived for orthorhombic or higher crystal symmetry. The separation of the magnetic and dielectric contributions to the optical properties of a material are demonstrated using measurements of the MM at varying angles of incidence., Comment: presented at ICSE-V, May 2010, submitted to Thin Solid Films presented at the International Conference on Spectroscopic Ellipsometry (ICSE-V, May 2010), submitted to Thin Solid Films

The temperature dependence of the electronic response of BiFeO3 thin film grown on a SrTiO3 substrate is investigated using spectroscopic ellipsometry. By analyzing the pseudodielectric function, we identify two d-d crystal field transitions of Fe3+ ions in the energy region between 1 and 2 eV. The d-d transitions show abnormal temperature dependence that cannot be attributed to conventional electron-phonon interactions. The origin of the abnormal temperature dependence is discussed in terms of spin-charge coupling. The temperature dependence of the charge transfer transitions located above 2.5 eV is characterized by standard critical point model analysis of the 2nd derivatives of the dielectric function. This analysis provides detailed information of the critical point parameters for charge transfer transitions.

The growth of Pb(ZrxTi1-x)O3 (PZT) films by molecular beam epitaxy was demonstrated. Single-crystal, single-phase PZT films were grown on (001) SrTiO3 substrates at a growth temperature of 600°C. In situ monitoring of the growth process by reflection high-energy electron diffraction revealed two dimensional growth for the PZT constituent ternaries, namely, PbTiO3 and PbZrO3, and three-dimensional growth for PZT films of intermediate compositions. Layer-by-layer growth of PZT films, however, was achieved by using a PbTiO3 buffer layer between the SrTiO3 substrate and PZT films. Optical properties of the films of the end ternaries were investigated by spectroscopic ellipsometry. Refractive index at 633 nm was found to be 2.66 for PbTiO3 and 2.40 for PbZrO3. Band gap energies of PbTiO3 and PbZrO3 were determined as 3.81 and 3.86 eV, in good agreement with theoretically calculated values. The P-E hysteresis loop of a 70-nm-thick PZT film was well saturated and had a square shape. The remanent polarization and the coercive field were 83 μC/cm2 and 77 kV/cm, respectively, which are respectable.

Lead titanate (PbTiO3), a ferroelectric material with perovskite structure, has received a great deal of attention owing to a unique combination of its piezoelectric, pyroelectric, dielectric, electo- and acousto-optic properties [1–3]. PbTiO3 is a very attractive material for the use in a wide variety of fields, including ultrasonic sensors, infrared detectors, electro-optic modulators, and ferroelectric random access memories. To harness the intrinsic properties of PbTiO3 for device applications, however, high-quality epitaxial films are required. PbTiO3 thin films have been prepared by various methods such as chemical vapor deposition, rf magnetron sputtering, pulsed laser deposition, hydrothermal method, and sol-gel technique. Surprisingly, molecular beam epitaxy (MBE), with its precise control over composition, has not been widely applied, except of a few reports on MBE growth with the use of ozone as an oxidizing agent [4]. In the present work, high-quality single-crystal PbTiO3 layers were grown on (001) SrTiO3 substrates by MBE with the use of hydrogen peroxide as an oxidant [5]. Phase composition as well as structural and optical properties of the films were examined as a function of growth parameters by high-resolution x-ray diffractometry, spectroscopic ellipsometry, and photoluminescence. It was found that single-phase PbTiO3 films grew epitaxially at substrate temperatures above 600°C, whereas layers grown at lower temperature contained lead oxide inclusions. All the PbTiO3 layers were c-axis oriented with the epitaxial relationship PbTiO3(100)//SrTiO3(100) and PbTiO3[001]//SrTiO3[001]. No evidence of a-domains was found. Full width at half maximum of (001) rocking curves for 50–60 nm thick PbTiO3 layers are as low as 6–8 arcmin, indicating their good crystal quality. Pseudodielectric function of PbTiO3 was measured using variable angle spectroscopic ellipsometry at room temperature. Refractive index was found to be 2.605 at 633 nm (1.96 eV), which is consistent with the literature data. With the help of the standard critical point (SCP) lineshape analysis the band gap energy was calculated to be (3.778±0.005) eV.

Using variable-angle spectroscopic ellipsometry, we measure the pseudo-dielectric functions of as-deposited and annealed SiO2/SiOx multilayers (MLs). The SiO2(2nm)/SiOx(2nm) MLs have been prepared under various deposition temperature by ion beam sputtering. The annealing at temperatures ≥ 1100°C leads to the formation of Si nanocrystals (nc-Si) in the SiOx layer of MLs. Transmission electron microscopy images clearly demonstrate the existence of nc-Si. We assume a Tauc-Lorentzian lineshape for the dielectric function of nc-Si, and use an effective medium approximation for SiO2/nc-Si MLs as a mixture of nc-Si and SiO2. We successfully estimate the dielectric function of nc-Si and its volume fraction. We find that the volume fraction of nc-Si decreases after annealing, with increasing x in as-deposited SiOx layer. This result is compared to expected nc-Si volume fraction, which was estimated from stoichiometry of SiOx.

Today, most synchrotron facilities offer beamlines dedicated to infrared (IR) spectroscopy and IR microspectroscopy. The main advantage of synchrotron-based infrared spectroscopy is the brightness of the synchrotron radiation source which can provide a brightness two or three orders of magnitude higher than a thermal (black-body radiation) infrared source. Thus, synchrotron-based infrared spectroscopy allows a high spatial resolution (infrared microspectroscopy) and a high spectral resolution, especially for low-throughput technologies and far-infrared spectroscopy. In this article, a brief introduction to synchrotron-based infrared spectroscopy and its application will be given.

In this study, we investigated the structural and optical properties of Ge-doped SbTe Ge–ST thin films with three differing compositions: Ge0.06Sb0.77Te0.17 Ge–STH ,G e 0.05Sb0.70Te0.25 Ge–STM, and Ge0.05Sb0.64Te0.31 Ge–STL, grown on Si substrate by radio-frequency sputtering method. The films were annealed at 250°C for crystallization and their crystal structures were examined by X-ray diffraction. Compared to the X-ray diffraction spectra of the undoped SbTe, the Ge–ST thin films had a hexagonal structure with large stacking periods. Using Raman spectroscopy, we investigated the shift of the phonon mode frequencies A1g and Eg of the films with varying Sb:Te ratios. We compared the dependence of the phonon frequencies of Ge–ST on the Sb content to those of the corresponding undoped SbTe. The composition dependence of the A1g phonon frequency could be explained in terms of the linear extrapolation of Sb and Sb2Te3 crystals. By using spectroscopic ellipsometry, we measured the dielectric function of the thin films in the near-IR, visible, and ultraviolet spectral regions. The optical energy gaps and bandgaps of the amorphous and crystalline phases, respectively, were determined using linear extrapolation of the absorption coefficient. The optical gap energies of the amorphous Ge–ST films were determined to be about 0.5–0.6 eV, whereas the indirect bandgap energies of the crystalline films shrank substantially to about 0.15–0.2 eV.

Using spectroscopic ellipsometry electro-optic effect was studied in lead zirconate titanate (PZT) thin films grown epitaxially on Nb-doped SrTiO3(001) substrates by RF magnetron sputtering. A uniaxial multilayer model analysis was applied to extract the linear and quadratic electro-optic coefficients from the shifts in the ordinary and extraordinary refractive indices with electric field applied along the (001) direction. The effective linear and quadratic coefficients were measured as −134.6×10−12 m/V and 8.5×10−18 m2/V2, respectively, at a wavelength of 632.8 nm, while the individual linear electro-optic coefficients r33 and r13 were −157.1 and 22 pm/V, respectively. The existence of the linear electro-optic effect in unpoled PZT films was attributed to the presence of a built-in polarization and simultaneous poling during measurements.

The authors measure the dielectric functions of (GeTe, Sb2Te3) pseudobinary thin films by using spectroscopic ellipsometry. By using standard critical point model, they obtained the optical transition (critical point) energies of the amorphous (crystalline) thin films. The optical (indirect band) gap energies of the amorphous (crystalline) phase are estimated from the linear extrapolation of the absorption coefficients. The band structure calculations show that GeTe, Ge2Sb2Te5, and Ge1Sb2Te4 have indirect gap whereas Ge1Sb4Te7 and Sb2Te3 have direct gap. The measured indirect band gap energies match well with electronic band structure calculations.

Amorphous GaInZnO and polycrystalline ZnO thin films are grown by rf magnetron sputtering. Their optical properties are investigated by spectroscopic ellipsometry. The optical gap of the GaInZnO film increases with the increase of Ga content and by annealing. These are attributed to the large band-gap energy of Ga2O3 and the structural relaxation after annealing, respectively. The changes in optical properties show a strong correlation to the device characteristics of GaInZnO thin film transistors: The turn-on voltage increases as the optical gap increases with increasing Ga∕In ratio. This study shows that the GaInZnO thin films are as excellent as transparent oxide semiconductors.

Single crystalline PbTiO3, PbZrO3, and PbZr0.57Ti0.43O3 thin films on SrTiO3 (001) substrates were grown by a combination of molecular beam epitaxy and rf sputtering methods. The authors measured the dielectric functions of the thin films using spectroscopic ellipsometry and determined the interband critical point energies using standard critical point model. They compared the critical point energies to the band structure calculations in the literature. The data suggest that anticrossing behavior occurs between Ea and Eb near Zr=0.17. This phenomenon is attributed to a coupling between X1c and X3c bands caused by intrinsic alloy disorder.

The purpose of this work is to investigate the effect of corona poling on the optical functions of the nonlinear-optical (NLO) polymers. We measured the complex refractive indices of NLO polymers deposited on glasses before and after corona poling using spectroscopic ellipsometry at room temperature at various incidence angles. In addition, we observed the absorption spectral change using ultraviolet-visible spectroscopy after corona poling, which is attributed to the chromophore orientation. In order to make NLO polymers, we attached a NLO active dye and photocrosslinkable moieties as side chains of poly(4-hydroxystyrene), deposited the polymer thin films on glass substrates by spin-coating, and corona-poled it along the surface-normal direction to align the dipoles of the chromophores along the electric field direction. In detail, PSDR1-25 designates a poly(4-hydroxystyrene) where 25% of hydroxyl groups in the side chain are substituted by disperse red 1 (DR1) and PSDR1-50 means the same except for 50% ...

Using spectroscopic ellipsometry, we measure the dielectric functions of NiO and CoO single crystals, which are grown by using the Verneuil (flame fusion) process. Taking the 2nd derivative of the dielectric function, we identify several optical structures below and near the band gap. We fit the 2nd derivative of the dielectric function by using an exciton lineshape and the standard critical point (SCP) model. The band gap energies of NiO and CoO are estimated to be 3.87 eV and 5.43 eV, respectively. The optical structures below and near the band gaps are attributed to intra-atomic d-d transitions and are estimated to be 1.2, 1.3, 1.8, 2.6, 2.9, 3.2, 3.4, 3.7, and 4.2 eV for NiO and 1.61, 2.26, 2.72, and 3.6 eV for CoO. Both the band gap and the d-d transition energies of NiO and CoO are compared to the literature values. The derivative spectra show unambiguously the d-d transitions near and above the band gap and those below the band gap. The lineshape fitting using the SCP model provides accurate values for the band gap energy and the d-d transitions. In addition, the SCP analysis verifies the exciton nature of the band gap and the d-d transitions. We attribute this to the formation of Frenkel excitons in NiO and CoO transition metal oxides.

We grow Zn1−xMnxO∕Al2O3 (0⩽x⩽0.08) thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5eV. Using the model of Holden et al. [T. Holden et al., Phys. Rev. B 56, 4037 (1997)], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gap energy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large broadening of both the E0 band gap and its exciton partner E0x peaks even for less than 2% of optically determined Mn composition. In ellipsometric spectra, we also find Mn-related 3eV optical structure. In particular, optical absorption spectra with varying N2 gas flow rate show that the Mn-related peak intensity decreases with increasing N2 flux. The decrease of the 3eV Mn-r...

We measure pseudodielectric functions in the visible-deep ultraviolet spectral range of Pb(ZrxTi1−x)O3 (x=0.2,0.56,0.82) (PZT), Pb0.98Nb0.04(Zr0.2Ti0.8)0.96O3, Pb0.91La0.09(Zr0.65Ti0.35)0.98O3, and Pb0.85La0.15Ti0.96O3 films grown on platinized silicon substrates using a sol-gel method and on (0001) sapphire using a radio-frequency sputtering method. Using a parametric optical constant model, we estimate the dielectric functions (ϵ) of the perovskite oxide thin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical-point model, we determine the parameters of the critical points. In the second derivative spectra, the lowest band-gap energy peak near 4eV is fitted as a double peak for annealed PZTs due to the perovskite phase. As-grown PZTs have mainly pyrochlore phase and the lowest band-gap peak is fitted as a single peak. We also examine the effect of dopants La and Nb, which substitute at Pb and Zr (Ti) sites, respectively. We found three band gaps E...