Optical reflectivity of (SN)x-single crystals

The optical reflectivity of (SN)_x single crystals was measured in the visible region and the near infrared with light polarized parallel and perpendicular to the polymer chain axis. Whereas the reflectivity for light polarized perpendicular to the chain axis is approximately constant in this region, the reflectance for light polarized parallel to the chain axis exhibits a pronounced plasma edge at 2.72 eV. A simple Drude model was used to analyse the data. Differences between these results and those of previous film measurements are discussed.     

Energy bands in stannic oxide (SnO2)

The energy band structure of stannic oxide has been calculated by a self-consistent augmented plane wave (APW) method. The calculation predicts SnO₂ to be a semiconductor with an allowed direct band gap of 3·68 eV for light polarized perpendicular to the tetragonal axis, and of 4·07 eV for parallel polarized light; these values agree well with the measured values of 3·57 and 3·93 eV. The theory also predicts indirect and direct-forbidden optical transitions which are consistent with experiment.     

Evolution of molecular states studied in collisions of ions with laser excited atoms by a crossed beam experiment

Differential scattering cross sections in the energy rangeE _CM=25–50 eV have been measured in a crossed beam machine for the scattering of Na⁺ by laser excited Na(3² P _3/2). The superelastically scattered ions resulting from the collisional deexcitation process 3² P _3/2-² S _1/2 are sharply peaked at a constant reduced scattering angle of 180eV degrees. Through the choice of either linearly or circularly polarized light, one can selectively excite the magnetic sublevels of the Na atoms. This ability to align or orient the Na^* allows us to discuss in considerable detail both the transition from the space-fixed (atomic) to the body-fixed (molecular) system and the dynamics in the merging region of the two frames. We find that the symmetry axis of the excited electron charge cloud is locked to the internuclear axis and hence to the body-fixed reference frame at an internuclear separation of about 35 a.u. A pronounced asymmetry of the scattering from atoms excited with LHC or RHC polarized light is discussed in terms of simple models.     

Zeeman effect on the 4E level of Mn2+ in ZnS

The fine structure lines of the ⁴E level of Mn²⁺ in ZnS have been studied under a high magnetic field. Experiments were performed with the magnetic field parallel to the [111]_W crystallographic axis. The computed positions and intensities for polarized and non-polarized light are in agreement with the experiments.     

Green up-conversion of Er3+ in KGd(WO4)2 crystals. Effects of sample orientation and erbium concentration

Pumping with infrared light resonant to the energy position of ⁴ I _11/2 and ⁴ I _9/2 multiplets respectively has excited green up-conversion of Er³⁺ in KGd(WO₄)₂ single crystal. At room temperature the maximum green-emission intensity is achieved by pumping with light polarized parallel to the C₂ symmetry axis of the crystal (//p) at 981 and 801.5 nm, while pumping with light parallel to the principal m axis (//m) has maximum up-conversion at 978.2, 806 and 800 nm. The emission is weakly polarized. The maximum of the emission peaks at 547.8 nm if the light is analyzed parallel to the C₂ axis or at 552.4 nm for light perpendicular to it. The largest emission intensity was achieved with an erbium concentration about 3×10²⁰ cm^-3. A schematic model of the up-conversion process is suggested. Received: 4 July 2000 / Published online: 22 November 2000     

Optical properties of the semiconducting “metal-like” complex (NMe3H) (I) (TCNQ)

We present the results of a study of the room temperature polarized reflectance between 2.5 meV and 3.8 eV of (NMe₃H)(I)(TCNQ) single crystals. The reflectance found with the electric field parallel to the stacking axis is fit with a Drude-Lorentz model and analyzed using Kramers-Kronig transforms to give the response functions σ₁(ω) and ε₁(ω). The results confirm the model of semiconducting behavior despite a “metal-like” d.c. electrical conductivity at room temperature.     

Electrical properties of vapour grown ZrSe3 single crystals

Resistivity, Hall coefficient and thermoelectric power measurements of ZrSe₃ single crystals along the chain axis were carried out in the temperature range from 200 to 400 K. Experimental results are explained by the model of compensated semiconductors with two-dimensional characteristics. The activation energy of the donor level is determined to be 0.25 eV and the effective mass of the conduction band parallel to the layer is estimated to be 0.3m₀.     

Influence of the surface on the quantum P.E.M. effect in InP

The photoelectromagnetic effect of InP is studied in quantizing magnetic fields at 4·2 K in an energy range 1·4–1·5 eV for linearly polarized light. Depending on the sample surface condition two types of spectral oscillations may appear, those associated with interband transitions between Landau levels or the LO phonon type usually seen in photoconductivity. An analysis of the spectral oscillations gives: E₀ = 1·423±0·001 eV; Δ₀ = 0·102±0·006 eV; hω_L = 0·036 eV.     

Reflectance and thermoreflectance of gallium

Reflectance spectrum of a (001) single crystal face of gallium below 50 eV and thermoreflectance spectra with light polarized parallel to each crystallographic axis for energies between 1 and 5 eV are given. An interpretation of the optical properties is given in terms of critical points.     

Observation of OH angular momentum polarization produced by H+O2 at 2.6 eV collision energy

The OH rotational polarization produced by the reaction of fast H atoms from the polarized 193 nm photolysis of HBr with O₂ (2.6 eV collision energy) has been measured by laser-induced fluorescence using polarized analysis light. A strong rotational polarization parallel to the electric vector of the dissociation laser and perpendicular to the flight direction of the H atoms is observed. Implications for the H+O₂ reaction dynamics at high collision energies are discussed.     

Fundamental optical properties of Cd1-xMnxSe single crystals

The absorption near the fundamental edge of Cd_1-xMn_xSe was measured in the composition range 0<x<0.3 at room and liquid nitrogen temperature with the electric field of the radiation parallel and perpendicular to the hexagonal axis. An exponential dependence of the absorption coefficient versus photon energy was found, and a linear dependence of energy gap E₀ on composition was obtained. The room temperature reflectivity measurements in the energy range 2.5–5.2eV, for two polarization of light were performed, and a linear dependence of the interband transitions energies vs. alloy composition was found.     

Stress-induced stimulated emission from excitonic molecule in CdS

Stimulated emission has been observed at the M line (2.543 eV) in optically excited CdS crystals under an applied uniaxial stress perpendicular to the C axis at 4.2 K. This emission is strongly polarized with an electric vector parallel to the applied stress. The observed polarization characteristics are successfully accounted for by assuming a radiative annihilation of an excitonic molecule, providing an experimental evidence for ascribing this emission to the excitonic molecule in CdS.     

Special-angle-of-incidence ellipsometry for uniaxial crystals: Part 1. Negative crystals

We introduce a new method to determine, by ellipsometry, the ordinary N_o and extraordinary N_e refractive indices of a uniaxial crystal, with its optic axis parallel to the surface. First, the type of the crystal; negative or positive, is determined. Second, N_o and N_e are determined using very simple expressions. The only measurement required is a special angle of incidence $\text{ø}$, which we define in this paper as the largest angle of incidence at which linearly polarized light as reflected linearly polarized, at two orientation angles ω. A detailed error analysis is presented considering errors of $\text{ø}$, ω, and the effect of the ambient refractive index n. The results prove the high accuracy of the method.     

Temperature dependence of the reflectance spectrum of (TMTSF)2ClO4

The near-infrared and visible reflectance spectrum was measured on (TMTSF)₂ClO₄ single crystal at various temperatures in the range of 30K–290K. The reflectance spectrum polarized parallel to the stacking axis was analyzed by Drude model, giving the results that the band width 4t is about 1 eV and m¹_p/m is about 1.3. The band parameters obtained here were almost the same as those of (TMTSF)₂PF₆ reported by Jacobsen et al.     

The influence of light intensity on surface recombination in GaS single crystals

Gallium sulphide (GaS) is a layer structure semiconductor with relatively wide energy gap (E_g (295 K) = 2.5 eV and E_g (80 K) = 2.62 eV). It has potential applications in some areas of optoelectronics. This paper presents the investigations of the influence of light intensity on surface recombination velocity of charge carriers in GaS single crystals. To attain this purpose spectral dependences (between 420 and 550 nm) of absorption coefficients, reflectivity coefficients and photoconductivity were measured in vacuum. The investigations were performed for various light intensities in several temperatures from 80 to 333 K. The least square method was applied to fit the theoretical dependences of photoconductivity on wavelength and intensity of illumination at these temperatures. From the fittings the temperature and light intensity dependences of surface recombination velocity and bulk lifetime of charge carriers were obtained.     

Ultraviolet to far infrared optical properties of the one-dimensional conductor K2Pt(CN)4Br0·3. 3H2O

An experimental study of the optical properties of single crystals of the quasi-one-dimensional conductor K₂Pt(CN)₄Br_0·3, 3H₂O in the spectral range from 45,000 to 10 cm^?1 is presented.For light polarized perpendicular to the highly conducting direction the material behaves as a transparent dielectric, as evidenced by reflection and transmission spectra. The reflection spectrum measured with polarization parallel to the chain direction (E∥Z) shows, in addition to the previously reported ‘metal-like’ optical reflectance and plasma edge in the visible, deviations from free carrier type reflectance in the i.r. This was expected because the conductivity is thermally activated at low temperatures. The optical constants for E∥Z polarization have been determined by Kramers-Kronig analysis of the reflection spectrum and, at a few discrete wavelengths, from measurements of polarized reflectance under oblique incidence. The results are qualitatively consistent with various models of the electronic structure but do not distinguish between them.     

Magnetic linear dichroism in photoemission from an ultrathin iron silicide film

The effect of magnetic linear dichroism in photoemission of Fe 3p electrons was used to investigate the magnetic properties of the Si(100)2 × 1 surface on which iron films up to 10 monolayers thick were deposited at room temperature under ultrahigh vacuum. The experiments were performed with linearly polarized light (at a photon energy of 135 eV) incident at an angle of 30° to the surface. The photoelectron spectra were measured in a narrow solid angle oriented along the normal to the sample surface for two opposite magnetization directions which were parallel to the surface plane and perpendicular to the polarization vector of the light wave. An analysis of the data obtained showed that the effect has a threshold character and appears after deposition of eight Fe monolayers, when the ferromagnetic silicide Fe₃Si is formed on the surface.     

The blue bronze K0.3MoO3: A new one-dimensional conductor

The optical reflectivity of the blue bronze K_0.3MoO₃ has been measured on single crystals for photon energies between 0.03 and 12 eV at temperatures from 10 to 300 K using polarized light. The data are interpreted that this compound is a one-dimensional conductor for temperatures above 180 K and that the metal-semiconductor transition at 180 K is due to a Peierls type transition, leading to a gap of 0.15 eV in the density of states.     

The Properties of Strings Formed in the Homochiral Solutions of Trifluoroacetylated Amino Alcohols in Cyclohexane

The strings formed in the solutions of trifluoroacetylated amino alcohols in cyclohexane were studied. It was found that microscopic strings with the diameter d ～ 1 μm were woven from tightly coupled rigid submicroscopic strings with the diameter d ～ 0.1 μm in increments of >100 μm. Therefore, the compound strings are transparent, and they usually look like an unstructured cylinder. Microscopic strings can be tightly combined in strings to 60 μm in diameter. Submicroscopic strings are arranged almost parallel to the axis of a microscopic string. The microscopic string acts as a polarizer: it transmits light polarized across its axis and absorbs light polarized along the axis. The majority of these properties can be explained based on the assumption that a connection between the strings of all hierarchical levels in cyclohexane is stronger than that in solvents with different string morphology.     

Optical absorption in tin monoselenide single crystal

Optical absorption in single crystals of tin monoselenide has been measured at room temperature with plane polarized light near the fundamental absorption edge. The electric field of the incident light was oriented parallel to the a- and b-crystallographic axes in the plane of cleavage. Results have been analyzed on basis of two- and three-dimensional models. Absorption near the fundamental edge was found to be due to indirect forbidden transition with two phonons involved in the process. The energy gap and phonon energies were found to be 0.948 eV and 54 and 21 meV for the a-axis and 0.902 eV and 41 and 20meV for the b-axis. The two-dimensional model gave results similar to those obtained from the three-dimensional model and could thus be used to describe the main optical properties of SnSe single crystal.