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The properties of bulk contribution to sum-frequency generation reflected and transmitted by a finite layer in a multilayer system are described. The leading term is essentially due to the processes emitting in the transmission geometry, in particular for macroscopic layers. For such transmission processes, phase mismatch leads to the production of interference fringes when the layer thickness or a wavelength is tuned, which may be mistaken for resonant processes inside or at the surface of the material. Experimental evidence of such fringes measured from centrosymmetric bulks is provided for a diamond window in the far infrared and suggested for other materials in previously published data. The existence of a stationary point in the phase mismatch, related to the group velocity mismatch, is shown to be the source of another pseudo-resonant process in centrosymmetric calcium and barium fluorides, for which theoretical predictions reproduce the experimental observations. [ABSTRACT FROM AUTHOR]

Morphologies of adsorbed molecular films are of interest in a wide range of applications. To study the epitaxial growth of these systems in computer simulations requires access to long time and length scales, and one typically resorts to kinetic Monte Carlo (KMC) simulations. However, KMC simulations require as input transition rates and their dependence on external parameters (such as temperature). Experimental data allow only limited and indirect access to these rates, and models are often oversimplified. Here, we follow a bottom-up approach and aim at systematically constructing all relevant rates for an example system that has shown interesting properties in experiments, buckminsterfullerene on a calcium fluoride substrate. We develop classical force fields (both atomistic and coarse-grained) and perform molecular dynamics simulations of the elementary transitions in order to derive explicit expressions for the transition rates with a minimal number of free parameters. [ABSTRACT FROM AUTHOR]

We report on the development of an atomic layer deposition (ALD) process for calcium fluoride thin films using bis(N,N-di-i-propylformamidinato)calcium(II) and anhydrous HF as reactants. Deposition rates were observed to be linear versus the number of ALD cycles performed, varying between 0.4 and 0.3 Å/cycle at substrate temperatures ranging from 175 to 250 °C, respectively. The optical properties of the resulting nanocrystalline CaF2 films were characterized by spectroscopic ellipsometry and show good transparency down to a UV wavelength of 193 nm, and good agreement with reference refractive index parameters. One motivation for the development of this ALD process is for chemical barrier applications in fluorine-containing chemistries. The robustness of the coating was tested by reactive ion etching of CaF2 films deposited on silicon in an SF6 plasma, yielding an Si:CaF2 etch ratio of greater than 2000:1 at a plasma power of 300 W. [ABSTRACT FROM AUTHOR]

The capacitance-voltage (C-V) hysteresis in the bidirectional measurements of the p-GaN metal-insulator-semiconductor (MIS) capacitor is suppressed by using a CaF2 dielectric layer and a post annealing treatment. The density of trapped charge states at the CaF2/p-GaN interface is dramatically reduced from 1.3 × 1013 cm2 to 1.1 × 1011/cm2 compared to that of the Al2O3/p-GaN interface with a large C-V hysteresis. It is observed that the disordered oxidized interfacial layer can be avoided by using the CaF2 dielectric. The downward band bending of p-GaN is decreased from 1.51 to 0.85 eV as a result of the low-density oxides-related trap states. Our work indicates that the CaF2 can be used as a promising dielectric layer for the p-GaN MIS structures. [ABSTRACT FROM AUTHOR]

The interfacial chemical state and the band alignment of the sputtering-deposited CaF2/p-GaN hetero-structure were investigated by angle-resolved X-ray photoelectron spectroscopy. The dependence of Ga 3p core-level positions on the collection angles proves that the downward band bending of p-GaN is reduced from 1.51 to 0.85eV after the deposition of CaF2, which may be due to the reduction of Mg-Ga-O-related interface states by the oxygen-free deposition of CaF2. The band gap of sputtering-deposited CaF2 is estimated to be about 7.97eV with a potential gradient of 0.48eV obtained by the variation of the Ca 2p3/2 position on different collection angles. By taking into account the p-GaN surface band bending and potential gradient in the CaF2 layer, large valence and conduction band offsets of 2.66±0.20 and 1.92±0.20eV between CaF2 and p-GaN are obtained. These results indicate that CaF2 is a promising gate dielectric layer on the p-GaN for the application of metal-insulator-semiconductor devices. [ABSTRACT FROM AUTHOR]

Lattice based kinetic Monte Carlo simulations have been used to determine a functional form for the second order adsorption isotherms on two commonly investigated crystal surfaces: the (111) fluorite surface and the (100) perovskite surface which has the same geometric symmetry as the NaCl (100) surface. The functional form is generalized to be applicable to all values of the equilibrium constant by a shift along the pressure axis. Functions have been determined for estimating the pressure at which a desired coverage would be achieved and, conversely, for estimating the coverage at a certain pressure. The generalized form has been calculated by investigating the surface adsorbate coverage across a range of thermodynamic equilibrium constants that span the range 10-26 to 1013. The equations have been shown to be general for any value of the adsorption equilibrium constant. [ABSTRACT FROM AUTHOR]

The lattice thermal conductivity of CaF2 is accurately computed from a first-principles theoretical approach based on an iterative solution of the Boltzmann transport equation. The second- and third-order interatomic force constants are generated from a real-space finite-difference supercell approach. Then, the force constants for both the second- and third-order potential interactions are used to calculate the lattice thermal conductivity and related physical quantities of CaF2 at temperatures ranging from 30K to 1500 K. The obtained lattice thermal conductivity 8.6 W/(m·K) for CaF2 at room temperature agrees better with the experimental value than other theoretical data, demonstrating the promise of this parameter-free approach in providing precise descriptions of the lattice thermal conductivity of materials. The obtained dielectric parameters and phonon spectrum of CaF2 accord well with available data. Meanwhile, the temperature dependence curves of the lattice thermal conductivity, heat capacity, and phonon mean free path are presented. [ABSTRACT FROM AUTHOR]

In this paper, we report the existence of intervalence charge transfer (IVCT) luminescence in Ybdoped fluorite-type crystals associated with Yb2+-Yb3+ mixed valence pairs. By means of embedded cluster, wave function theory ab initio calculations, we show that the widely studied, very broad band, anomalous emission of Yb2+-doped CaF2 and SrF2, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb2+-Yb3+ mixed valence pairs. The IVCT luminescence is very efficiently excited by a two-photon upconversion mechanism where each photon provokes the same strong 4 ƒ14 - 1A1g → 4ƒ13(²F7/2)5deg-1T1u absorption in the Yb2+ part of the pair: the first one, from the pair ground state; the second one, from an excited state of the pair whose Yb3+ moiety is in the higher 4ƒ13(²F5/2) multiplet. The Yb2+-Yb3+ → Yb3+-Yb2+ IVCT emission consists of an Yb2+ 5deg → Yb3+ 4ƒ7/2 charge transfer accompanied by a 4ƒ7/2 → 4ƒ5/2 deexcitation within the Yb2+ 4ƒ13 subshell: [²F5/25deg, ²F7/2] → [²F7/2, 4ƒ4]. The IVCT vertical transition leaves the oxidized and reduced moieties of the pair after electron transfer very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are subtracted from the normal emission. The IVCT energy diagrams resulting from the quantum mechanical calculations explain the different luminescent properties of Yb-doped CaF2, SrF2, BaF2, and SrCl2: the presence of IVCT luminescence in Yb-doped CaF2 and SrF2; its coexistence with regular 5d-4ƒ emission in SrF2; its absence in BaF2 and SrCl2; the quenching of all emissions in BaF2 ; and the presence of additional 5d-4ƒ emissions in SrCl2 which are absent in SrF2. They also allow to interpret and reproduce recent experiments on transient photoluminescence enhancement in Yb2+-doped CaF2 and SrF2, the appearance of Yb² + 4ƒ-5d absorption bands in the excitation spectra of the IR Yb3+ emission in partly reduced CaF2:Yb3+ samples, and to identify the broadband observed in the excitation spectrum of the so far called anomalous emission of SrF2:Yb2+ as an IVCT absorption, which corresponds to an Yb2+ 4ƒ5/2 → Yb3+ 4ƒ7/2 electron transfer. [ABSTRACT FROM AUTHOR]

Calcium fluoride is a dielectric material with a wide bandgap (∼12.1 eV) and a relatively high dielectric constant (∼6.8) that forms a van der Waals interface with two-dimensional (2D) materials, meaning that it contains a very low amount of defects. Thin calcium fluoride films can be synthesized using multiple techniques that are scalable to the wafer level, including molecular beam epitaxy, atomic layer deposition, and chemical vapor deposition. However, the consolidation of calcium fluoride as dielectric for 2D electronics requires overcoming some fundamental challenges related to material quality and integration, as well as carrying out advanced characterization and computational studies to evaluate its real potential. Here, we review the status of calcium fluoride dielectric films in terms of material synthesis, fundamental electrical properties, and future applications; we also discuss the most important challenges of calcium fluoride integration in 2D materials–based, solid-state nano/micro-electronic devices, and propose several potential routes to overcome them. Our manuscript may serve as a useful guide for other scientists working on 2D electronics in general, and provides a clear pathway for calcium fluoride research in the future. [ABSTRACT FROM AUTHOR]

We report the synthesis of Nd1-xCaxFeAsO1-2xF2x superconductors using CaF2 as a binary dopant that provides both holes and electrons by simultaneous substitution of Ca2+ ions and F- ions at Nd3+ and O2- sites, respectively. The sample with x = 0.2 exhibits a maximum critical temperature (TC) of 52.3K and transport critical current density (JC) of 1240 A/cm² at 12K. An interesting feature observed for binary doped samples is the preferential alignment of (00l) planes and the refinement of microstructure both in terms of grain size and grain connectivity. NdFeAsO based superconductors are already known for their very high critical fields and field independent JC(H) performance. However, the development of the bulk superconductors with oriented large grains and good grain connectivity has not been reported so far and hence the present work will be definitely a step towards the progress in NdFeAsO based conductor development. [ABSTRACT FROM AUTHOR]

Understanding scintillation physics and nonproportionality is essential to accelerate materials discovery that has been restricted due to the difficulties inherent to large crystal growth and complex nature of gamma-solid interaction. Taking advantage of less restrictive growth and deposition techniques for smaller crystal sizes or thin films and better fundamental understanding of ion-solid interactions, a unique ion approach is demonstrated to effectively screen candidate scintillators with relatively small size and evaluate their nonlinear scintillation response. Response of CaF2:Eu and YAlO3:Ce scintillators to single ions of H+, He+, and O3+ are measured by the corresponding pulse height over a continuous energy range using a time-of-flight-scintillator-photoelectric multiplier tube apparatus. Nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering the energy partitioning process. In a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (Dexci) can be produced by energetic H+, He+ and O3+ ions, respectively, and significantly different impacts on the response characteristics of these two benchmark scintillators are observed. For CaF2:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO3:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response and the nonradiative quenching process under different excitation densities, which is also the main origin of the nonlinear response of the scintillators to irradiation. [ABSTRACT FROM AUTHOR]

The powder of CaF2 has been proposed as a practical reference for the quantitation of Ca and F in low energy ion scattering (LEIS) analysis. It is chemically inert, easy to clean, and inexpensive. LEIS is extremely surface sensitive. Thus, in contrast to surface analytic techniques such as x-ray photoelectron spectroscopy and secondary ion mass spectroscopy, the surface termination of a sample is clearly reflected in the LEIS results. It is, thus, unlikely that in LEIS, the F/Ca ratio for CaF2 is 2.0. This paper supports the reliability of the CaF2 powder reference by evaluating the calcium and fluorine atomic surface concentrations, roughness factor and shows that the surface termination of the powder is the same as that of CaF2(111). The CaF2 samples are treated by annealing at 725 K and measured at 625 K. The presented spectra are practically free of contamination. Ion scattering by LiF (001), an evaporated Ca layer, and a Cu foil are used as basic references for Ca and F. The atomic sensitivity factors and the relative sensitivity factors have been determined for F, Ca, and Cu (3 keV He+, 145°). The F/Ca atomic ratio is found to be the same (2.3 ± 0.1) for CaF2(111) and its powder. For the powder, the Ca and F signals are reduced by a factor of 0.77 ± 0.03 in comparison with those for the single crystal. [ABSTRACT FROM AUTHOR]

In the present article, we analyse the possibility of sensitizing the 3Pj levels of Pr3+ ion with Eu2+ ion in CaF2 thin film deposited by evaporation. Indeed, the forbidden nature of the 4f-4f transition of Pr3+ ion makes its absorption too weak for thin film applications, while materials doped with the Pr3+-Yb3+ couple are promising candidates for the achievement of efficient down-converter systems and could allow strong reduction of thermalization losses in silicon solar cells. [ABSTRACT FROM AUTHOR]

Information about the outermost atomic layer of a material is critically important for many processes and materials, including in catalysis, tribology, wetting, corrosion, and thin film growth. Low energy ion scattering (LEIS) is an extremely surface sensitive technique that can quantitatively analyze the outermost atomic layer of a material. Recent developments in LEIS have resulted in a particularly high sensitivity version of the technique known as high sensitivity LEIS (HS-LEIS). In LEIS and HS-LEIS, reference and/or standard materials allow straightforward quantitation of the spectra. In this submission, the authors show the HS-LEIS spectrum of a high purity calcium fluoride powder. CaF2 is a useful reference material for calcium in LEIS because it is relatively inexpensive, not hygroscopic, and available in high purity. Due to the applications/uses of calcium in different areas of science, including in catalysis, polymer light emitting diodes, organic photovoltaics, solid oxide fuel cells, and solar cells, these data may enable future work in these areas. A reference spectrum for gold is included with this submission. [ABSTRACT FROM AUTHOR]

Ab initio calculations, based on pseudopotentials and density functional theory, have been performed to investigate the atomic geometry and electronic structures of calcium fluoride (CaF2) on the Si(001) surface. We have considered the experimentally observed (2×1) and (3×1) reconstructions with different bonding configurations of the CaF2 molecule on the Si(001) surface. Our total energy calculations suggest that the (3×1) structure is slightly more preferable than the (2×1). The key structural parameters and electronic surface properties of their most stable structures have been discussed. In contrast to the experimental results, the most stable structures contain an appreciable bonding nature between the surface Si and F atoms, however, no real bonding between Si and Ca atoms is indicated. [ABSTRACT FROM AUTHOR]

Au/CaF2/nSi(111) structures with 4–5 monolayers of epitaxial fluoride are fabricated and electrically tested. The leakage current in these structures was substantially smaller than in similar samples reported previously. Simulations adopting a Franz-type dispersion relation with Franz mass of mF∼1.2m0 for carriers in the forbidden band of CaF2 reproduced the measured current-voltage curves quite satisfactorily. Roughly, these curves could also be reproduced using the parabolic dispersion law with the electron mass of me=1.0m0, which is a material constant rather than a fitting parameter. Experimental facts and their comparison to modeling results allow qualification of the crystalline quality of fabricated structures as sufficient for device applications. [ABSTRACT FROM AUTHOR]

Calcium difluoride crystals cleaved along the (111) direction are etched with the dislocation site selective etchants HNO3, HCl, H2SO4, and H3PO4 and their surfaces are inspected ex situ with scanning force microscopy (AFM). Force microscopy yields characteristic features of the etch pits at the nanometer scale such as terracing and ditrigonal patterns. The method enables direct quantitative measurements of etch pit structures to derive kinetic data revealing details of the dissolution mechanism. Orthophosphoric acid is found to yield the best scaleable etching figures at ambient and elevated temperatures, as for this etchant, the dissolution is reaction-rate controlled. The scanning tip can induce a precipitationlike process by adherent traces of sulfuric or phosphoric acid that can be removed by a treatment with nitric acid following the regular etching procedure. [ABSTRACT FROM AUTHOR]

The development of high-energy lasers requires optical windows capable of handling megajoule beam energies without compromising the system’s performance. Calcium fluoride (CaF2) has been identified as a prime candidate for windows operating at chemical laser wavelengths due to very low bulk absorption and exceptionally small thermal lensing coefficients; it is, however, vulnerable to structural failure owing to poor mechanical strength characteristics and a large thermal stress factor. It is, therefore, essential to properly assess the ultimate potential of this material, which we attempt to do here in the following manner: (a) We assemble reliable numbers for all pertinent properties of (111)-oriented CaF2 single crystals and polycrystalline isotropic aggregates (PIAs), such as fusion-cast CaF2, which requires addressing issues relating to the elastic properties, the stress-optic coefficients, and the flexural strength. (b) We provide correct analytical expressions for evaluating the impact of pressure- and beam-induced effects on wave-front phase distortions and mechanical failure modes, taking advantage of a previous investigation [J. Appl. Phys. 98, 043103 (2005)]. (c) We perform detailed calculations on “model” windows made of either (111)CaF2 or (PIA)CaF2 that transmit optimally truncated Gaussian beams at wavelengths of 1.15 and 3.39 μm, for run times such that lateral heat conduction and surface cooling can be ignored. Our main conlusions are as follows: (a) With CaF2 windows thermal lensing, as measured in terms of the Strehl ratio and on assuming coating absorptances of no more than 3×10-5, is of no consequence in the sense that catastrophic failure may occur at fluence levels way below the threshold for optical distortion. (b) Evidence of a poor Weibull shape factor (m≃3.5) degrades the design safety margins, which requires operating at peak intensities of no more than 100 kW/cm2 to achieve optimum on-target fluences. (c) Regarding the issue of (111)CaF2 vs (PIA)CaF2, we note that fusion-cast material outperforms single crystals based on the figure of merit for distortion, as well as fracture and yield strengths, but contrary to (111)-oriented material, it exhibits birefringence that may rule out its use if depolarization is of concern. [ABSTRACT FROM AUTHOR]

The performance of a laser-window material must be assessed not only in terms of its ability to transmit high-power beams without generating undue optical distortion but also in terms of the constraints imposed by stress-related failure modes. In operational use, the stress field images the superposition of stresses originating from the mechanical load created by the pressure differential and the thermal load created by the laser beam. Here, we provide the tools to carry out an analysis of both pressure- and beam-induced stresses, and illustrate the procedure in the context of assessing the performance of a “model” window made of fusion-cast CaF2. The analysis assumes (a) operation on a time scale such that lateral heat diffusion can be ignored, and (b) cylindrically symmetric Gaussian beam shapes, which permit straightforward calculations of stress distributions that should be representative of worst case situations. Pressure-induced stresses strongly depend on the window’s aspect ratio, which suggests increasing the thickness to minimize the stress, but considerations relating to the optical performance require minimum allowable thicknesses based on a Weibull statistical analysis of the fracture probability. Beam-induced stresses are best evaluated in terms of (a) thickness-averaged radial and azimuthal stresses, which increase linearly with exposure time and depend on radial distances through the truncation parameter, and (b) across-the-thickness stress deviations relative to the average stress, which are caused by surface absorption and reach steady-state configurations on a time scale much shorter than the characteristic time for lateral heat transport. The average stress is always compressive and equibiaxial in the central region of the window, but its azimuthal component turns tensile in the rim region, thus threatening the structural integrity through brittle fracture. In addition, the coating-induced stress results in on-axis surface compressions that may exceed the yield strength of the windowpane material. In this light we formulate a figure of merit for stress, which demonstrates that promising laser-window materials must combine a small stress factor (expansion coefficient times elastic modulus) with superior thermal properties in terms of the product of heat capacity and thermal conductivity; CaF2 and SrF2 are the only known candidates that exhibit outstanding optical features at chemical laser wavelengths together with acceptable thermomechanical properties. [ABSTRACT FROM AUTHOR]

The growth of MnF2 and ZnF2 layers on Si(001) and Si(111) substrates was studied by molecular-beam epitaxy. Calcium fluoride buffer layers with (001), (110), and (111) orientations were used to prevent chemical interaction of MnF2 and ZnF2 molecules with the Si substrate. The analysis of x-ray and reflection high-energy electron-diffraction (RHEED) patterns showed that MnF2 layers grow on all of these planes in the orthorhombic α-PbO2-type crystal phase observed earlier only at high pressures and temperatures. Atomic force microscopy revealed a strong dependence of the surface morphology on the buffer orientation and growth temperature. The best-ordered MnF2 growth occurred at 500 °C on a CaF2 (110) buffer layer. The diffraction analysis enabled us to find the epitaxial relations at the MnF2/CaF2 interface. A careful analysis of the RHEED patterns of the films grown on CaF2(001) showed a similarity in the structure and growth modes between MnF2 and ZnF2 layers, with ZnF2 tending to form multiphase layers. These findings are in agreement with the x-ray diffraction measurements. [ABSTRACT FROM AUTHOR]

Recording of gratings by interference of two pump pulses and diffraction of a third probe pulse is useful for investigating ultrafast material phenomena. We demonstrate, in theory and experiment, that the temporal resolution in such configurations does not degrade appreciably even for large angular separation between the pump pulses. Transient Kerr gratings are generated inside calcium fluoride (CaF2) crystals by two interfering femtosecond (pump) pulses at 388 nm and read out by a Bragg-matched probe pulse at 776 nm. The solution to the relevant coupled-mode equations is well corroborated by the experimental results, yielding a value of the Kerr coefficient of ≈4.4×10-7 cm2/GW for CaF2. [ABSTRACT FROM AUTHOR]

Presents a heteroepitaxy method of germanium films on calcium fluoride/silicon structures. Influence of electron beam exposure on the predeposited germanium layer; Measurement of the dependencies on electron dose and dose rate; Chemical bond dissociation of calcium fluoride surfaces.

Focuses on a study which examined optical absorption spectra for manganese in CaF[sub2]. Experimental procedures; Results; Discussion; Summary.

Discusses a study which investigated the heteroepitaxial growth of silicon on a calcium fluoride/silicon structure by molecular-beam epitaxy. Applications of calcium fluoride film; Crystalline quality of epitaxial silicon; Behavior of predeposited silicon layer.

Presents information on a study which measured the spectral dependence of the photoionization of Eu&sup2+;:CaF[sub2], Ce&sup3+;:YAG and Sm&sup2+;:CaF[sub2] systems. Calculation of photoionization thresholds; Experimental details; Results and discussion; Conclusions.

Presents a study that examined the epitaxial growth of calcium fluoride films on silicon substrates. Methodology; Characteristics of the calcium fluoride film grown on silicon substrates; Analysis of the Rutherford backscattering channeling measurements.

Simulations of the superionic conductor CaF[SUB2] have been undertaken, with a model for the interionic interactions derived directly from electronic structure calculations. The model includes such many-body effects as polarization and the adaptation of the size of the anion to its instantaneous environment ("compression"). Physical properties of CaF[SUB2] accurately reproduced include the phonon frequencies, the fluorite → α-PbCl[SUB2]-structure phase transition and the solid-state diffusion. Analysis shows that the compression effect is much less important for fluorides than oxides but, nevertheless, significantly affects the phase transition pressure. Polarization effects, particularly of the cations, play a crucial role in allowing the anion diffusion, and the importance of a short-range contribution to the cation polarization is highlighted. These findings are contrasted with previous work using empirically parametrized shell and pair potentials, which suggest that other interactions play the dominant role. [ABSTRACT FROM AUTHOR]

An ab initio calculation of the optical absorption spectrum of Mn2+-doped CaF2 is performed in which electrostatic and quantum embedding effects originated by a relaxed and polarized CaF2 lattice on the ligand field ground and excited states of a MnF86- cluster have been considered. The theoretical spectrum is calculated by means of the complete active space self-consistent-field (CASSCF) and average coupled pair funtional (ACPF) methods, correlating up to 23 electrons. An excellent overall agreement with the experiments is found and a detailed analysis of the results is presented. The initial assignment of the 4A1g(4G) and 4Eg(4G) states, lately reversed, is supported. The wrong assignment of the 4T1g(4P) state is shown to be responsible for a recently proposed change of the value of the crystal field splitting paramenter initially accepted, 10Dq=4250 cm-1, which is in turn supported here. Also, new assignments for the absorptions to the 4T1g(4F) and 4T2g(4F) excited states are suggested. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A Monte Carlo simulation of CaF2 in the canonical ensemble was carried out using the Metropolis algorithm and the Soft-Core and Born–Mayer–Huggins potentials. By studying the behavior of the mean square displacement and the specific heat, the existence of a transition to a superionic phase at about 1470 K was confirmed. A partial occupation of the interstitial sites in this superionic phase was also found. [ABSTRACT FROM AUTHOR]

Ground and excited state energies of CaCH3, CaNH2, CaOH, and CaF are obtained from electron propagator calculations of electron affinities of the corresponding cations at the optimized geometries of the neutral ground states. Feynman–Dyson amplitudes (FDA’s) describe the distribution of the least bound electron in various states. The ground states differ from the cations by the occupation of a one-electron state dominated by Ca s functions. The next two FDA’s have π pseudosymmetry and the corresponding states have unpaired electrons in orbitals which display mixing between Ca p and d functions. Above these lies a σ pseudosymmetry FDA with nearly equal contributions from Ca d and p functions. Next one finds two FDA’s with δ pseudosymmetry. Higher excited states are also discussed. [ABSTRACT FROM AUTHOR]

Deals with a study that determined the effect of neodymium (Nd&sup3+;) concentration on the emission spectra of calcium fluroide (CaF[sub2]):Nd layers grown by molecular-beam epitaxy. Growth condition and characterization and the sample; Spectroscopic characterization of Nd&sup3+; in CaF[sub2] layers; Effect of Nd concentration.

Presents a study which reported and discussed room-temperature measurements of linear and nonlinear photoconductivity in calcium fluoride containing trace amounts of yttrium, lanthanum and several rate earths. Experimental details; Composition information and measurement summary of the six calcium samples used in the investigation; Conclusions.

Focuses on a study which measured the velocities of the principal and higher-order elastic modes localized in calcium fluoride films grown epitaxially on Si (111) using Brillouin scattering. Materials and procedure; Evaluation of the effective elastic constants of the epilayers; Parameters used for deriving the fits to the measured dispersion.

Presents a study that investigated the epitaxial growth and characteristics of silicon on heteroepitaxial calcium fluoride/silicon semiconductors. Methodology; Effect of silicon predeposit on the epitaxial growth of silicon; Examination of the microstructure of the samples using transmission electron microscopy and x-ray diffraction.

The ArF laser induced absorption feature between 450 and 700 nm observed in the bulk of mono crystalline calcium fluoride (CaF2) upon prolonged 193 nm irradiation is shown to have two origins: The first band at 530 nm is revealed by a transient femtosecond (fs) laser transparency spectrum and attributed to Ca clusters (colloid). The second band at 600 nm originates from MNa centers as identified by their laser induced fluorescence excitation spectrum, emission wavelength, and fluorescence lifetime. The analysis of the absorption feature by fs pump-probe techniques benefits from the different lifetimes of the transient transparency (excited states of the Ca clusters) and the fluorescing MNa centers of about 5 ps and 22 ns, respectively. [ABSTRACT FROM AUTHOR]

Examines the aluminum-aluminum oxide-gold light emitting tunneling junctions deposited on the underlayers of calcium difluoride. Modes of surface plasmon polarization; Use of a vacuum deposition technique; Emission spectra of the junction with a gold film.

Microstructure of FeSe1-xTex thin films near the interface to CaF2 is investigated by means of transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX). TEM observation at the initial crystal-growth stage reveals that marked lattice compression occurs along the in-plane direction in the films with Se-rich composition, while the a-axis length of FeTe remains as its original value of bulk crystal. Subsequent EDX analysis demonstrates substantial diffusion of Se into the CaF2 substrate. Such diffusion is not prominent for Te. Thus, the formation of Se-deficient layer at the initial growth stage on CaF2 is concluded to be the main reason of the lattice compression in FeSe1-xTex thin films. [ABSTRACT FROM AUTHOR]

We demonstrate that a current can be induced and switched in a sub-femtosecond time-scale in an insulating calcium fluoride single crystal by an intense optical field. This measurement indicates that a sizable current can be generated and also controlled by an optical field in a dielectric medium, implying the capability of rapid current switching at a rate of optical frequency, PHz (1015 Hz), which is a couple of orders of magnitude higher than that of contemporary electronic signal processing. This demonstration may serve to facilitate the development of ultrafast devices in PHz frequency. [ABSTRACT FROM AUTHOR]

We fabricated a calcium fluoride (CaF2) whispering gallery mode (WGM) microcavity with a computer controlled ultra-precision cutting process. We observed a thermo-opto-mechanical (TOM) oscillation in the CaF2 WGM microcavity, which may influence the stability of the optical output when the cavity is employed for Kerr comb generation. We studied experimentally and numerically the mechanism of the TOM oscillation and showed that it is strongly dependent on cavity diameter. In addition, our numerical study suggests that a microcavity structure fabricated with a hybrid material (i.e. CaF2 and silicon), which is compatible with an ultra-high Q and high thermal conductivity, will allow us to reduce the TOM oscillation and stabilize the optical output. [ABSTRACT FROM AUTHOR]

YO1.5-substituted HfO2 thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO1.5 amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to highsymmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO1.5 amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polar structure. This means that the direct growth by vapor is of polar orthorhombic HfO2-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO1.5 amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO2-based film helps clarify the nature of ferroelectricity in HfO2-based films (186 words/200 words). [ABSTRACT FROM AUTHOR]