Spectral diffuse reflectance measurements of gadolinia, silica thin film systems using synchrotron radiation

Diffuse reflectance or optical scattering in thin films and multilayers can pose serious limiting factors to their desired or ultimate performances. Besides, such studies provide valuable information related to the buried microstructures and interfaces. Synchrotron radiation is the most appropriate source to record wavelength dependent polarized light scattering in thin films and multilayers. In the present experiment several gadolinia, silica thin films and multilayers were studied for their light scattering using the white light synchrotron beam. Various thin film layer geometries were selected to probe the results due to different types and combinations of interfaces. Due to phase coherent delay in certain optical non-wedged component used in the experimental setup very interesting spectral interference were noticed as the modulations in the diffuse reflectance signal. Appropriate modeling approach utilizing Gaussian function de-convolution technique is used to compute the pulse delay between the back reflected and forward propagating scattering signals that lead to such spectral interference. Alternatively inverse fast Fourier transform (IFFT) and analytical techniques were adopted to determine the group delays. The diffuse reflectance spectra were finally compared with their specular counter part and a shift both in the wavelength and phase were noticed. This may be explained on the basis of thin film roughness factors, different polarizations and incident geometries used in the measurements. However, all most all the spectral scattering signals exhibited the features resembling their specular reflection characteristic.     

Influence of film morphology on thin film ferromagnetism

Cobalt, nickel and their alloy, Co₁Ni₉, films were epitaxially grown on Cu(100) under different growth conditions and subsequent treatments and studied using surface magneto-optic Kerr effect (SMOKE) in an attempt to understand the effects of film morphology on the magnetic properties. CO contamination can significantly reduce the magnetization and Curie temperature. Thermal desorption spectroscopy (TDS) shows that CO desorbs at 422 K from Ni and 410 K from Co₁Ni₉ at a heating rate of 6 K per minute. Annealing the films below 450 K produces smooth and clean films with stable magnetic behavior. However, annealing at higher temperatures results in Cu segregation and island formation leading to the finite-size ferromagnetic or even superparamagnetic behavior.     

Nuclear resonant scattering of synchrotron radiation from thin films

Hyperfine Interactions - The optical properties of thin films containing Mössbauer isotopes undergo dramatic changes in the vicinity of a nuclear resonance. Remarkable phenomena are observed...     

Influence of surface and bulk layers on the crossover features for interaction parameters of a ferroelectric thin film

The phase diagram of a ferroelectric thin film is studied by using the usual mean-field approximation. The crossover features, from the ferroelectric-dominant phase diagram to the paraelectric-dominant phase diagram, for the physical parameters of the thin film are discussed. Special attention is devoted to the investigation of surface and bulk layers, and how to influence the crossover values of exchange interactions and transverse fields.     

Reversible magnetization of a thin superconducting film with radiation defects

The thermodynamic potential of a system of Peierls vortices in a thin superconducting film, containing radiation defects, in a perpendicular external magnetic field is calculated. The equilibrium temperature dependences of the densities of free vortices and vortices trapped by defects are found in the mean-field approximation for various magnitudes of the external field. It is shown that the equilibrium magnetization of a thin superconducting film exhibits the same features that were observed experimentally in the reversible magnetization of high-temperature superconductors. An asymptotic expression is obtained for the difference of the magnetizations of perfect and irradiated films. According to this expression, the difference depends on the pinning energy of a vortex on a defect and the density of defects.     

Basic features of coherent nuclear resonant scattering of synchrotron radiation

The time dependences of spatially coherent nuclear resonant scattering of synchrotron radiation show a wealth of characteristic features which originate from the interference of several radiation components and from dynamical nuclear scattering. These effects will be of importance for the future fields of time domain Mössbauer spectroscopy and of nuclear resonant -ray optics. The basic features are discussed and experimental evidence is reviewed.     

Influence of radiation on thin ZnS-Tb films

Changes in thin zinc-sulfide films under the action of the γ-radiation of Co⁶⁰ are studied by investigating electroluminescence spectra of terbium embedded in these films as a luminescent probe. It is shown that changes in the relation of the intensities of bands, a decrease in their halfwidth and the background component, and simplification of the spectrum are observed in a short-wave region of the Tb radiation spectrum that corresponds to⁵D₃→⁷F_j transitions. The same modification of the radiation spectrum is characteristic of ZnS films whose crystalline structure is ordered in the course of thermal annealing at a temperature of 350°C. Based on the analysis of the data obtained it is inferred that irradiating the ZnS films with small radiation doses of 10⁴–10⁵ rad leads to the ordering of their crystalline structure due to the elimination of one of the types of structural defects. Institute of Physics of Semiconductors, National Academy of Sciences of Ukraine, 45, Nauka Ave., Kiev-28, 252650. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 338–341, May–June, 1997.     

Kosterlitz-Thouless transition and radiation defects in a superconducting thin film

The thermodynamics of a system of Pearl vortices in a superconducting thin film containing radiation defects is studied. It is shown that three phase transition scenarios are possible, depending on the defect density. At low densities there is one stable state of the system. When the first critical density n _d 1 is reached, there appears a temperature interval in which the system can be in two stable states. If the density exceeds n _d 2, then the lower limit of stability of the metastable states shifts abruptly to zero. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 9, 643–648 (10 May 1999)     

Influence of interfactants on thin metal film growth

The growth of Pb on Si(1 1 1) with and without Ag as an interfactant is studied in the temperature range from 270 to 375 K by microscopy and spectroscopy. Whereas Pb grows on the Si(1 1 1)-7×7 surface in the Stranski–Krastanov (SK) mode, the growth mode on the Si(1 1 1)-√3×√3-R30°-Ag surface changes from layer-by-layer below 300 K to SK mode above 300 K. Spectroscopy shows that Ag remains at the interface between the substrate and the growing Pb film. The influence of the interfactant on the growth is attributed to the increase of the island density by an order of magnitude and to the changes of the growth kinetics resulting from this increase.     

Emission of radiation from a long Josephson junction in a thin film

Space-time nonlocal electrodynamic equations are derived for nonlinear vortex states of a Josephson junction in a film of thickness much smaller than the London penetration depth. The spectrum and damping of generalized Swihart waves propagating in such a junction are analyzed. The radiation damping constant associated with the possible emission of electromagnetic radiation is determined in the range of Swihart wave phase velocities exceeding the speed of light. The emission of radiation from nonlinear states having dimensions greater than the distance traversed by light in vacuum during the characteristic time of variation of the phase difference is investigated. It is shown that the flux density of radiation emitted by such states is localized in a plane orthogonal to the axis of the tunnel junction and depends weakly on the angle of observation in this plane. Zh. éksp. Teor. Fiz. 115, 1426–1449 (April 1999)     

Inelastic nuclear resonant absorption of synchrotron radiation in thin films and multilayers

Inelastic nuclear resonant absorption of synchrotron radiation is an efficient and unique method for the direct measurement of vibrational density of states (VDOS) of thin films and interfaces that contain Mössbauer isotopes. This is demonstrated for the ⁵⁷Fe nuclear resonance in the case of amorphous and crystalline Tb–Fe alloy thin films and buried Fe/Cr interfaces in epitaxial α-Fe(0 0 1)/Cr(0 0 1) superlattices.

     

Two-photon interaction of coherent radiation with a thin film of resonant atoms

The problem of the interaction of an ultrashort optical pulse and a thin film of resonant atoms under the conditions of two-photon absorption, third-harmonic generation, and the inverse effect of the latter on the pump pulse via Raman scattering is studied. The fact that the field acting on an atom differs from the macroscopic field in the film is also taken into consideration. It is shown that the polarization of the film undergoes dynamic relaxation even in the absence of irreversible relaxation, suppressing Rabi oscillations and establishing stationary values of the populations of the resonant energy levels and of the polarization of the film at the pump and the third-harmonic frequencies. Zh. éksp. Teor. Fiz. 115, 30–42 (January 1999)     

Thermodynamics of a vortex system in a thin superconducting film with radiation defects

The effect of radiation defects on the thermodynamics of a system of Pearl vortices in a thin superconducting film is examined. The scenario for a Kosterlitz-Thouless transition in this system is shown to depend on the defect concentration n _d . At low concentrations, the transition takes place continuously, while at high concentrations, a range of temperatures exists in which there are two metastable states. The concentrations of free vortices and of vortices captured by defects are calculated as functions of temperature for different defect concentrations n _d . A phase diagram is constructed for the vortex system in the n _d −T plane. Zh. éksp. Teor. Fiz. 116, 1081–1090 (September 1999)     

Nonequilibrium fluctuations of a thin metal diffuse film exposed to microwave radiation

Nonlinear fluctuations of the electron energy distribution function in a microwave-irradiated thin diffuse metal film are calculated in the nonlinear approximation for various energy relaxation models. The spectral density of the resulting nonequilibrium fluctuations is calculated as a function of the microwave-radiation power for various ratios between the electron-phonon and electron-electron relaxation rates.     

Physical features of the spectral distribution of circularly polarized synchrotron radiation intensity

An asymptotic formula is constructed for the dependence of the serial number of harmonic on the relativistic factor for circularly polarized synchrotron radiation in the upper half-plane. Numerical values of particle velocities at which the maximum of synchrotron radiation intensity is transferred from one harmonic to another are obtained.     

Study of the growth of fullerene-carbonized epitaxial SiC thin films by synchrotron radiation

 Thin SiC films have been deposited on silicon(0 0 1) substrates by fullerene-carbonization. Using synchrotron radiation X-ray diffraction pole figure measurements have been employed in order to study the texture of the layers. It is qualitatively shown that the films contain epitaxially aligned β-SiC crystallites with the same orientation as the underlying substrate and their twins of first and second order. The orientational spread of the epitaxial crystallites in terms of tilt against and rotation around the substrate normal is smaller than 3°. The formation of twins as a growth defect plays a major role which is even more pronounced at a higher substrate temperature. Furthermore, an additional preferred orientation has been identified which can only be explained by a non-cubic SiC phase. The portion of these crystallites in the film can be considerably reduced by an increase of the deposition temperature. Received: 18 April 1996/Accepted: 12 August 1996     

Highlights of synchrotron radiation

The applications of the electromagnetic radiation generated by relativistic electrons circulating in synchrotrons and storage rings have rapidly extended into many scientific disciplines. This article first briefly reviews the history of synchrotron radiation, and recapitulates its properties. The available sources are listed, and some aspects of the facilities that are required to make use of the radiation are discussed, with particular emphasis on the optical elements. Several noteworthy examples of scientific research conducted with synchrotron radiation are described. These are drawn principally from the X-ray region, and comprise X-ray fluorescence, small-angle scattering, powder profile refinement, extended X-ray absorption fine structure, topography, time-resolved spectroscopy, and VUV and photoelectron spectroscopy of solids. In conclusion, a few topics are mentioned relating to the future expansion and application of synchrotron radiation research facilities.     

Properties of synchrotron radiation

Muon capture on hydrogen gives a unique possibility for a measurement of the pseudo-scalar form factor g _p (q _c ² = -0.88 m _μ ² ) of the nucleonic weak current, thus providing a sensitive test of the QCD chiral symmetry perturbation theory which predicts the value of this form factor with a precision of Δg _p /g _p ≃ 2%. For adequate comparison with theory, the muon capture rate Λ_c should be measured with a precision of ΔΛ_c/Λ_c ≤ 1%, that is an order of magnitude better than the precision of the present world data. We report on the project of an experiment designed to provide the required precision. Also, we present the final result of our previous experiment on a high precision measurement of the μ³He capture rate and compare this result with the PCAC prediction. This revised version was published online in August 2006 with corrections to the Cover Date.