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Experiments on self-diffusion in amorphous silicon between 400 and 500 ℃ are presented, which were carried out by neutron reflectometry in combination with 29Si/natSi isotope multilayers. Short range diffusion is detected on a length scale of about 2nm, while long range diffusion is absent. Diffusivities are in the order of 10-19-10-20m²/s and decrease with increasing annealing time, reaching an undetectable low value for long annealing times. This behavior is strongly correlated to structural relaxation and can be explained as a result of point defect annihilation. Diffusivities for short annealing times of 60 s follow the Arrhenius law with an activation enthalpy of (0.74±0.21) eV, which is interpreted as the activation enthalpy of Si migration. [ABSTRACT FROM AUTHOR]

LixLaySrzMnO3 thin films of various compositions (x,y,z) have been grown using pulsed laser deposition. The compositions of the films have been studied as a function of deposition temperature, target-to-substrate distance and deposition pressure with respect to different cation ratios of the targets by inductively coupled plasma mass spectrometry. When growing multi-elemental oxide thin films containing lithium (with its large mass difference to other elements), lithium loss is most probably inevitable. But the desired thin film composition can be achieved by selecting specific growth conditions and different target compositions. The experiments also elucidate some of the mechanisms behind the incongruent lithium transfer from the targets to thin films. [ABSTRACT FROM AUTHOR]

The self-diffusion of iron and nitrogen is measured in nm range non-magnetic iron nitride thin films. Two non-magnetic iron nitrides, Fe2.23N and FeN, were studied using neutron reflectivity. Neutron reflectivity with a depth resolution in the sub-nm range has a different scattering cross section for isotopes, providing a unique opportunity to measure very small diffusivities. The isotope heterostructure in thin film multilayers [Fe-N/57Fe-N]10 and [Fe-N/Fe-15N]10 were prepared using magnetron sputtering. It was observed that nitrogen diffuses slower than iron although the atomic size of iron is larger than that of nitrogen. It was found that a significantly larger group of N atoms participates in the diffusion process than of Fe, making N diffusion slower than that of Fe. [ABSTRACT FROM AUTHOR]

Self-diffusion was studied in magnetron sputtered nitrogen-rich amorphous compounds of the system Si-C-N by using nitrogen as a model tracer. As shown by infra-red spectroscopy a transient metastable region exists, where the structure of the material can be visualized as silicon nitride tetrahedra which are connected by carbo-diimide (-N=C=N-) bonds to a three dimensional amorphous network. In this region diffusion studies are carried out by neutron reflectometry and isotope multilayers as a function of annealing time, temperature and chemical composition. Low diffusivities between 10-20 and 10-24 m2/s were found. In the metastable region, diffusion is faster than diffusion in amorphous silicon nitride by 1 to 2 orders of magnitude, while the activation enthalpies of diffusion between 3.1 and 3.4 eV are the same within error limits. This can be explained by the fact that the diffusion mechanism along SiN4 tetrahedra is identical to that in amorphous silicon nitride, however, the carbo-diimide bonds seem to widen the structure, allowing faster diffusion. A correlation between diffusivities and the number of carbo-diimid bonds present in the material is found, where the highest diffusivities are observed for materials with the highest number of carbo-diimid bonds, close to the composition Si2CN4. [ABSTRACT FROM AUTHOR]

Neutron reflectometry and isotope multilayers were used to investigate self-diffusion in covalent amorphous solids during isothermal annealing and its correlation to structural relaxation. Amorphous silicon nitride was chosen as a model system. Neutron reflectometry is a superior method to measure very low self-diffusivities, occurring in covalent solids, by applying only short time anneals. This allows one to determine time dependent changes of diffusivity over a broad temperature range before crystallization of the metastable solid occurs. The measured nitrogen diffusivities decrease by more than one order of magnitude during annealing between 950 and 1150 °C, while at the same time also a decrease of the atomic density is observed. We interpret this behavior as a structural relaxation of the amorphous network structure that is governed by annihilation of interstitial-like defects. [ABSTRACT FROM AUTHOR]

The self-diffusion of lithium in congruent LiNbO3 single crystals was investigated at low temperatures between 379 and 523 K by neutron reflectometry. From measurements on 6LiNbO3 (amorphous film)/natLiNbO3 (single crystal) samples, Li self-diffusivities were determined in single crystals down to extremely low values of 1 × 10−25 m2 s−1 on small length scales of 1–10 nm. The measured diffusivities are in excellent agreement with (extrapolated) literature data obtained by experiments based on Secondary Ion Mass Spectrometry and Impedance Spectroscopy. The tracer diffusivities can be described by a single Arrhenius line over ten orders of magnitude with an activation enthalpy of 1.33 eV, which corresponds to the migration energy of a single Li vacancy. A deviation from the Arrhenius behaviour at low temperatures, e.g., due to defect cluster formation is not observed. [ABSTRACT FROM AUTHOR]

Here we report on a feasibility study aiming to explore the potential of Polarized Neutron Reflectometry (PNR) for detecting the inverse proximity effect in a single superconducting/ferromagnetic bilayer. Experiments, conducted on the V (40 nm)/Fe (1 nm) S/F bilayer, have shown that experimental spin asymmetry measured at T = 0.5 T is shifted towards higher Q values compared to the curve measured at T = 1.5 T. Such a shift can be described by the appearance in superconducting vanadium of magnetic sublayer with a thickness of 7 nm and a magnetization of +0.8 kG. [ABSTRACT FROM AUTHOR]

In this work, we studied a correlation between spin-dependent scattering and interface roughness in Cu/Co multilayers. In Cu/Co multilayers, Cu-on-Co and Co-on-Cu interfaces are not identical because of significant difference in the surface free energy of Cu and Co. By adding Ag surfactant during the growth of multilayer structure, we found that the difference between the interface roughness of two interfaces can be minimized. By doing this we found that the strength of anti-ferromagnetic coupling increases significantly. A comparison between normalized magnetoresistance to antiferromagnetic fraction with interface roughness shows the variation of spin-dependent scattering at the interface in Cu/Co multilayers. [ABSTRACT FROM AUTHOR]

Grain boundary self-diffusion in Type-C regime was investigated in nano-crystalline bcc iron at low temperatures between 100 and 250 °C using neutron reflectometry in combination with [natFe(7 nm)/57Fe(3 nm)]10 isotope multilayers. The method allows to determine diffusivities in a stable nanostructure without concurrent grain growth. An activation enthalpy of diffusion of (0.9 ± 0.3) eV is found, comparable to the value of coarse-grained Fe. [ABSTRACT FROM AUTHOR]

Artificial multilayers offer unique opportunities for combining materials with antagonistic orders such as superconductivity and ferromagnetism. This in turn may allow one to study new quantum phenomena, which arise from the mutually exclusive ground-state properties of the building blocks [1]. Examples are the so-called π-junction effect, where the phase of the superconducting order parameter is modulated across the layers [2], or states with a spatial modulation of the amplitudes of the ferromagnetic and superconducting order parameters, such as spontaneous vortex phases or the Larkin-Ovchinikov-Fulde-Ferrel state. [ABSTRACT FROM AUTHOR]

Artificial multilayers offer unique opportunities for combining materials with antagonistic orders such as superconductivity and ferromagnetism and thus to realize novel quantum states. In particular, oxide multilayers enable the utilization of the high superconducting transition temperature of the cuprates and the versatile magnetic properties of the colossal-magnetoresistance manganites . However, apart from exploratory work, the in-depth investigation of their unusual properties has only just begun. Here we present neutron reflectometry measurements of a [Y0.6Pr0.4Ba2Cu3O7 (10 nm)/La2/3Ca1/3MnO3 (10 nm)]10 superlattice, which reveal a surprisingly large superconductivity-induced modulation of the vertical ferromagnetic magnetization profile. Most surprisingly, this modulation seems to involve the density rather than the orientation of the magnetization and is highly susceptible to the strain, which is transmitted from the SrTiO3 substrate. We outline a possible explanation of this unusual superconductivity-induced phenomenon in terms of a phase separation between ferromagnetic and non-ferromagnetic nanodomains in the La2/3Ca1/3MnO3 layers. [ABSTRACT FROM AUTHOR]

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Focuses on the experimental determination of electric-field-induced differences in structure-factor phases of the order of two percent. Electron density response of covalently bonded materials to an externally applied electric field; Predictions of a semi-empirical bond-charge model; Measured phase variation.

Reports on the completion of the current best sets of X-ray structure amplitudes and valence charge density for gallium arsenide (GaAs) by highly precise data. Weak reflections determined from the integral intensities as a function of the effective thickness from thick GaAs wafers; Expected charge accumulation between nearest neighbors that slightly shifted towards the arsenic site.

Polarized neutron reflectivity experiments have been performed to investigate polarizing multilayer monochromators. The neutron monochromators have been sputtered with Ti and Fe–Co–V as layer materials with a nominal period of 11 nm. For more than two layers per period, the bulk magnetization of 2.35μB is reduced to 1.6μB. With 22 layers per period and 15 periods the higher-order contributions are decreased to below 0.6% of the first-order Bragg peak intensity (reflectivity of 0.21) at qz=0.06 Å-1. The polarization efficiency for the final monochromator is 95.5%. [ABSTRACT FROM AUTHOR]

Monochromators used in neutron or x-ray experiments often have higher-order contributions, which have to be reduced by filters. Multilayer monochromators produced by dc-magnetron sputtering, with intentionally blurred interfaces, have reduced these higher-order contributions. The approach is to substitute the bilayer structure by several layers with individual thicknesses per period. A Ni/Ti monochromator was prepared where higher-order contributions were reduced below 0.1% of the first-order reflectivity of 93% (measured up to the seventh order). In order to determine the lifetime of such a structure, the interdiffusion of the constituents was measured with thermal annealing (interface diffusion activation energy: 0.16(1) eV). [ABSTRACT FROM AUTHOR]

In this work, we investigate the process of iron nitride (Fe-N) phase formation using 2 at. % Al or 2 at. % Ti as additives. The samples were prepared with a magnetron sputtering technique using different amount of nitrogen during the deposition process. The nitrogen partial pressure (RN2) was varied between 0% and 50% (rest argon) and the targets of pure Fe, [Fe + Ti] and [Fe + Al] were sputtered. The addition of small amount of Ti or Al results in improved soft-magnetic properties when sputtered using RN2≤ 10%. It was found that the thermal stability of soft-magnetic phase increases considerably when Al or Ti additives were used. When RN2 is increased to 50% non-magnetic Fe-N phases are formed. We found that iron mononitride (FeN) phases (N at. % ∼50) are formed with Al or Ti addition at RN2 = 50% whereas in the absence of such addition ε-Fe3-xN phases (N at. % ∼30) are formed. It was found that the overall nitrogen content can be increased significantly with Al or Ti additions. On the basis of obtained result, we propose a mechanism describing formation of Fe-N phases with Al and Ti additives. [ABSTRACT FROM AUTHOR]

We carried out experiments of self-diffusion in single crystalline silicon at a temperature of 900 °C by a method that is based on neutron reflectometry in combination with 29Si/28Si isotope multilayers. The experimental reflectivity pattern shows artificial Bragg peaks due to isotope periodicity and is fitted by the program Parratt32. Diffusivities are calculated from the roughness parameter of the isotope interfaces. The results are compared to that one obtained from a simple analytical expression on the reduction of the Bragg peak. The results exhibit that both methods deliver identical diffusivities within error limits. The diffusivity of 4 × 10−22 m2 · s−1 does not depend on annealing time for diffusion on a length scale of 1-6 nm and is in good accordance to literature data, ranging between 1 and 10 × 10−22 m2 · s−1. The results demonstrate that the neutron reflectometry method is well suited to determine self-diffusivities in single crystalline silicon at very short length scales. [ABSTRACT FROM AUTHOR]

In many areas of soft and hard matter research science, the amount of material to investigate is rather limited. Partly because the fabrication of larger samples is too expensive or not feasible, yet, partly because the interesting features depend on the size. The aim of this work is to develop a neutron reflectometer optimized for small samples and specular measurements. We present a new concept which is based on state-of-the-art neutron optical elements and which allows studies of samples 100 times smaller than with previous instrumentation. The concept is to use an elliptically focusing guide in the sample plane, and a converging beam geometry in the scattering plane. The latter allows for the simultaneous measurement of a wide angle-of-incidence range simultaneously. Here we report on the prototype setup and first measurements, where we reached a reduction of counting time by one order of magnitude. If a complete instrument is built based on the presented principle, another order of magnitude can be expected. [ABSTRACT FROM PUBLISHER]

In order to develop a neutron spin polarizer on the basis of magnetically remanent supermirrors, we produced a first Fe/Si supermirror (m = 2, q = 0.044 Å[sup -1]) giving polarizations of 96% to 98%. The addition of the reactive gases O[sub 2] and N[sub 2] to Si reduced the stress in the supermirror and improved the matching of Si and Fe for spin-down neutrons. [ABSTRACT FROM AUTHOR]

The phase transition from tetragonal to orthorhombic structure in the high-temperature superconductor La[sub 2-x]Sr[sub x]CuO[sub 4±δ] (La214) has been studied by means of elastic neutron scattering. Both underdoped (x = 0.09) and overdoped (x = 0.17) compounds have been investigated. From the temperature dependence of the superstructure peaks, we are able to estimate the critical exponent β, which is found to increase with increasing x. We also observe that the temperature interval over which the critical behaviour appears to be valid is unusually large and strongly dopingdependent. [ABSTRACT FROM AUTHOR]