NaCl Single Crystals Research Articles

Impedance measurements of the complex dielectric permittivity of sea ice at 50 MHz: pore microstructure and potential for salinity monitoring

AbstractWe report impedance measurements of the complex dielectric permittivity ε = ε′ − jε″ of sea ice and laboratory-grown NaCl single crystals using 50 MHz Stevens Water Monitoring Systems Hydra Probes. Temperature cycling of the single-crystal samples shows hydrohalite precipitation, and hysteresis in ε′ and ε″ qualitatively consistent with the expected evolution of brine-inclusion microstructure. Measurements parallel and perpendicular to intra-crystalline brine layers show weak (<10%) anisotropy in ε′ and a 20–40% difference in ε″ due to enhanced d.c. conductivity along the layers. Measurements in landfast, first-year ice near Barrow, Alaska, USA, indicate brine motion in warming ice as the brine volume fraction vb increases above 5%. Plots of vb derived from salinity profiles against ε′ and ε″ for these and previous measurements display too much variability between datasets for unguided inversion of vb. Contributing to this variability are intrinsic microstructural dependence, uncertainties in vb, and sub-representative sample volumes. A standard model of sea-ice permittivity is inverted to derive the apparent brine-inclusion aspect ratio and bulk d.c. conductivity at a spatial scale complementary to previous measurements. We assess Hydra Probe performance in high-salinity environments and conclude that they are not generally suited for autonomous sea-ice salinity measurements, partly due to the range of relevant brine pocket inclusion length scales.

Accumulation and relaxation of internal stresses in single crystals during high-temperature creep with hindered dislocation slip

The relationship between the kinetics of the initial high-temperature creep of KCl and NaCl single crystals and the internal stresses induced during deformation is examined. The influence of the external stresses and temperature on the internal stresses is established. The possible mechanisms of the accumulation and relaxation of internal stresses that govern deformation kinetics are experimentally established and analyzed.

Ultrathin epitaxially grown bismuth (111) membranes

An ex situ cleaning and etching technique was applied to NaCl single crystals to prepare atomically flat and clean NaCl surfaces. These were used as substrates for molecular beam epitaxial growth of ultrathin continuous Bi(111) films. The high film quality—as studied with low energy electron diffraction, atomic force microscopy, and transmission electron diffraction—is attributed to the commensurate 10:7 ratio of the lattice constants. Dissolving the NaCl substrates in water allows the fabrication of freestanding 20 nm thin Bi(111) membranes of centimeter size.

Feasibility Tests on Pressure-Transmitting Media for Single-Crystal Magnetic Neutron Diffraction under High Pressure

The hydrostaticity of pressure-transmitting media, such as graphite powder, a mixture of Fluorinert, Fomblin oil, silicone oil, Daphne7373 oil and glycerin, was investigated by high-pressure neutron diffraction experiments on the mosaic spread of NaCl single crystals. The width of the rocking curve of the NaCl single crystal in the medium other than glycerin increases rapidly with increasing pressure below 2.5 GPa, indicating that the medium solidifies below 2.5 GPa. On the other hand, glycerin transmits nearly hydrostatic pressure at least up to 7 GPa. The diffraction profiles of the media were also measured to evaluate the background intensities. Daphne7373 oil and glycerin generate low and flat diffraction profiles particularly at approximately 25°, where the principal magnetic diffraction signals are often present. Thus, glycerin is the most suitable pressure medium for single-crystal magnetic neutron scattering experiments beyond 3 GPa.

Volume expansion in heavily gamma irradiated NaCl and LiF single crystals

Linear expansion and stored energy measurements have been performed on NaCl and LiFsingle crystals gamma irradiated up to 150 MGy. The thermal recovery steps of theradiation-induced linear expansion upon heating coincide with the energy release peaks forboth materials. This, together with the amount of volume expansion measured afterirradiation, leads to the conclusion that this expansion is related to the formation ofdivacancies and divacancy clusters.

A New Preparation Pathway to Well-Defined In2O3 Nanoparticles at Low Substrate Temperatures

The structure and morphology of thin In2O3 films deposited on NaCl(001) single-crystal cleavage faces and thin sapphire sheets has been studied by transmission electron microscopy techniques and scanning electron microscopy. Both the substrate temperature and the nature of the substrate proved to be crucial for the formation of crystalline and well-defined In2O3 structures and morphologies. For In2O3 films grown on single-crystal NaCl(001) faces, a gradual transition from a quasi amorphous small-grain structure after deposition at 298 K to well-oriented In2O3 particles predominantly exhibiting pyramidal and octahedral shapes after deposition at 603 K has been observed. At the highest substrate temperatures, most particles were found to be oriented along a [001] zone axis and few particles in a [011] orientation. In contrast, depositing In2O3 on sapphire sheets under otherwise identical experimental conditions does not result in well-facetted In2O3 particles, but rather leads to rounded In2O3 agglomerates ...

Strain compensation by twinning in Au thin films: Experiment and model

Epitaxial Au thin films with thicknesses of 40–160 nm were grown on (1 0 0)-oriented single-crystal NaCl substrates at 300 °C by magnetron sputtering. Microstructural analyses revealed that all films possess orthogonal twin networks along the 〈0 1 1〉 directions. The experimentally observed relationship of an increase in twin density with decreasing film thickness is explained by kinematical and thermodynamical modeling. The developed twin model predicts a nanometer-sized width of the twins, in agreement with the experiment.

Microstructure of pulsed laser deposited FePd thin films on amorphous and crystalline substrates

Equiatomic FePd thin films have been deposited at room temperature by pulsed laser deposition (PLD) on amorphous, Si 3N 4 and SiO 2, and crystalline, (100)-NaCl, substrates. The resulting FePd film microstructures have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). We observed a complex orientation relationship between grains in nanocrystalline thin films of FCC FePd and the single crystal NaCl substrates. FePd films obtained under identical deposition conditions using the amorphous substrates also exhibited nanocrystalline morphology but with a fiber texture and consisted of a phase mixture of FCC FePd and the tetragonal ordered L1 0-FePd phase.

Optical and thermoluminescence properties of a NaCl single crystal doped with Cd2+, Mn2+ and exposed to gamma-rays

The thermoluminescense (TL) behavior of solid solutions of cadmium and manganese doped single crystals under γ-irradiation is reported. Various compositions of single crystals of NaCl doped with Cd2+ and Mn2+ have been irradiated with ionizing radiation. The increase in the glow curve was followed as a function of the F-centers produced by the dose. The analysis shows the potential use of these materials as dosimeters.

Stages of surface erosion under ion irradiation

Initial stages of surface erosion have been studied for NaCl and LiF single crystals bombarded by Ar + ions with 20 keV. For irradiation with doses D=10 10–10 11 ions/cm 2, exoelectron emission has been used, whereas for higher doses, we have used electron microscopy. Two stages of initial surface erosion have been identified; for small doses, there is slow development of atomic-scale roughening, which reaches its peak when areas damaged by closest incident ions start to overlap, and then, beginning with D=10 16 ions/cm 2, there is rapid etching, deep into the crystal, followed by the emergence of secondary microscopic structure, i.e. caverns, concentric closed steps and terraces. Ion-induced surface structure of alkali halide crystals has been shown to depend strongly on the presence of foreign particles on the surface, as well as on segregation. Topography of thin carbon films and some metals have been discussed.

The structure and composition of oxidized and reduced tungsten oxide thin films

The structure, morphology and composition of pure WO 3 thin films deposited onto vacuum-cleaved NaCl(001) single crystals have been studied at different substrate temperatures up to 580 K and under different oxidative and reductive treatments in the temperature range 373–873 K by Transmission Electron Microscopy, Selected-Area Electron Diffraction and X-ray Photoelectron Spectroscopy (XPS). A transition from an amorphous structure obtained after deposition at 298 K to a more porous structure with small crystallites at the highest substrate temperatures has been observed. XPS spectra reveal the presence of W 6+ irrespective of the preparation procedure. Significant changes in the film structure were only observed after an oxidative treatment in 1 bar O 2 at 673 K, which induces crystallization of a monoclinic WO 3 structure. After raising the oxidation temperature to 773 K, the film shows additional reconstruction and a hexagonal WO 3 structure becomes predominant. This hexagonal structure persists at least up to 873 K oxidation temperature. However, these structural transformations observed upon oxidation were almost completely suppressed by mixing the WO 3 thin film with a second oxide, e.g. Ga 2O 3. Reduction of the WO 3 films in 1 bar H 2 at 723–773 K eventually induced the formation of the β-W metal structure, as evidenced by electron diffraction and XPS.

Hygroscopic behavior of NaCl‐bearing natural aerosol particles using environmental transmission electron microscopy

We used conventional and environmental transmission electron microscopes to determine morphology, composition, and water uptake of individual natural inorganic aerosol particles collected from industrial pollution plumes and from clean and polluted marine environments. Five particle types are described in detail. They range from relatively insoluble mineral grains to internally mixed particles containing NaCl with other soluble or relatively insoluble material. We studied the hygroscopic behavior of these particles from 0 to 100% relative humidity (RH). Relatively insoluble materials do not take up water over the experimental RH range. Single crystals of NaCl from both natural and laboratory sources have a well‐defined deliquescence point of approximately 76% RH at 291 K. NaCl‐bearing aggregate particles appear to deliquesce between 74 and 76% RH (same RH within error) when NaCl is internally mixed with relatively insoluble phases, but the particles deliquesce at lower RH when aggregated with other soluble phases such as NaNO3. For all NaCl‐bearing particles studied, hygroscopic growth is pronounced above 76% RH, and water uptake by the particles is dominated by the soluble phase. Furthermore, the soluble phase initiating deliquescence controls the locus of further hygroscopic growth of the aggregate particle. Our results demonstrate that composition and mixing state affect water uptake of natural aerosol particles. Furthermore, internally mixed particles are confirmed to deliquesce at lower RH values than predicted from the individual components.

Bromine Enrichment in the Near-Surface Region of Br-Doped NaCl Single Crystals Diagnosed by Rutherford Backscattering Spectrometry

Bromine released from sea-salt aerosols and seawater ice is known for its high chemical reactivity. Previous studies have suggested that its availability to the gas-phase could be enhanced by segregation processes increasing Br concentration on the aerosol surface as compared to the bulk. However, little is known about the composition within the near-surface region, that is, the outermost approximately 100 monolayers. We used Rutherford backscattering spectrometry (RBS) to measure Br concentration profiles to a depth of about 750 nm of Br-doped NaCl single crystals to characterize the thermodynamics and kinetics of Br segregation to the near-surface region in moist air. These experiments were carried out on cleavage planes of melt-grown and of annealed solution-grown crystals at room temperature and relative humidities (RH) too low for formation of a stable liquid phase. Segregation of Br was below the detection limit on melt-grown crystals with Br/Cl = 0.01. In the case of annealed solution-grown crystals with Br/Cl = 0.002, average segregations of (0.24 +/- 0.11) x 10(15) and (0.42 +/- 0.12) x 10(15) Br atoms cm-2 were observed at 50% and 65% RH, respectively. No segregation was found at 20% RH. The observed Br segregation can be explained by the formation of an adsorbed liquid layer (depending on crystal surface properties and relative humidity) and preferential, diffusion-limited dissolution of Br into this layer according to the partition coefficient of Br between aqueous and solid NaCl. The thickness of the adsorbed liquid layer, which depends on crystal surface geometry and on relative humidity, can be estimated to range from 4 to at most 59 nm on the basis of measured Br concentrations and partition coefficients. Applying this concept of partitioning to natural sea salt suggests a Br/Cl molar ratio of up to 0.2 in adsorbed surface water of crystallized natural aerosol particles compared to about 0.0015 in seawater. This would have a major impact on heterogeneous reactions on sea-salt particles under dry conditions such as in the freeze-dried Arctic boundary layer.

Radiative and non-radiative processes ofAg− centres doped in NaCl single crystals

Luminescence properties including decay kinetics have been investigated forAg− centres doped in NaCl single crystals in the temperature range from 7 to 250 K. When theC absorption band peaking at 4.5 eV is photo-excited at low temperature, theA′ and C′ luminescence bands are observed at 2.85 and 4.12 eV, respectively. As the temperature increases, theA′ luminescence grows, with compensation for the decrease of the luminescence intensity of theC′ band, reflecting a thermally activated non-radiative process from the1T1u to3T1u states. With increasing temperature above 130 K, theA′ luminescence intensity also decreases. Since the decay time of theA′ luminescence is almostconstant at 10 µs above 80 K,the decrease of the A′ luminescence intensity is not attributed to a non-radiative process from the3T1u state but arises from the quenching of the non-radiative relaxation from the1T1u to3T1u states. The temperature dependence of the luminescence intensities of theA′ and C′ bands is discussed on the basis of a simple configuration coordinate model, which consists of the1T1u,3T1u and 1A1g adiabatic potential energy surfaces intersecting at each other.

Microstructural evolution and metastable phase formation in laser ablation-deposited films of Fe-rich Fe–Ge intermetallic compounds

Thin films of Fe-rich Fe–18 at% Ge and Fe–25 at% Ge were deposited by a pulsed laser ablation technique on single crystal NaCl substrates at room temperature to study phase evolution using transmission electron microscopy. As-deposited films contain nano-scale clusters embedded in a featureless matrix. Quadrupole mass spectrometric observations of the laser-ablated plume show the presence of charged clusters. During in situ heating of the films, the fine-scale clusters grow and profuse crystallization to a bcc FeGe solid solution occurs. For Fe–25 at% Ge thin film, crystallized bcc grains undergo two ordering transitions, viz. bcc → B2 → DO3, during subsequent cooling to room temperature. However, in the case of Fe–18 at% Ge thin film, crystallization leads to formation of the disordered bcc phase. Growth morphologies of the crystals formed during heat treatment indicate faceted growth form, which has been explained by using Jackson's interface model.

Coloration dependence in the thermoluminescence properties of the double doped NaCl single crystals under gamma irradiation

AbstractIn this work the behaviour of calcium manganese doped NaCl single crystals under gamma irradiation is reported. Various single crystals of NaCl doped with Ca and Mn have been irradiated at different doses with ionising radiation. The production of defects has been correlated to the increase in the intensity of the thermo luminescent glow curve as a function of doses. The glow curves intensity as a function of doses shows the potential use of these materials as dosimeters. Optical properties of such crystals after irradiation with gamma rays have also been studied; results have shown their potentiality as a good detector and optical store memory devices. Since the creations of colour centres by photons with energy less than the band gap energy has been detected also in ns2‐ion doped alkali halides. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Brillouin spectrometer interfaced with synchrotron radiation for simultaneous x-ray density and acoustic velocity measurements

We describe a new Brillouin spectrometer that has been installed on a synchrotron x-ray beamline for simultaneous measurements of sound velocities (by Brillouin scattering) and density (by x-ray diffraction). The spectrometer was installed at the 13-BM-D station (GSECARS) of the Advanced Photon Source. This unique facility has been tested in studies of transparent single crystal and polycrystalline materials at high pressure and temperature. The equation of state, acoustic velocities, and, hence, elastic moduli of materials as a function of pressure and temperature can now be determined without resort to a secondary pressure standard, such as the ruby fluorescence scale, or the equation of state of standard materials such as Au, Pt, or MgO, thus offering the potential to determine an absolute pressure scale. This article describes the design of the combined Brillouin-x-ray system and the first experimental results obtained. As a general-user facility, the system was designed to require minimal setup time and alignment of sensitive optics, run-time control and adjustments of optics from outside the experimental station, compatibility with powder and single crystal x-ray diffraction measurements, and no interference with other experimental techniques used on the beamline. To satisfy these requirements we adopted a novel optical design for the Brillouin system with a vertical scattering plane. Examples of measurements of acoustic velocities and elastic moduli on single crystal NaCl (B1) and polycrystalline NaCl (B2) at high pressure and single crystal velocities and elastic moduli of MgO at high temperature (to 600°C) and at high pressure are presented.

Study on ferromagnetic shape memory alloy Ni–Mn–Ga films

The Ferromagnetic Shape Memory Alloy (FSMA) Ni–Mn–Ga films have been prepared by ECR DC magnetron sputtering respectively on unheated NaCl single crystal, Cu, glass and Si wafer. It is found that the optimal parameters for Ni–Mn–Ga film formation are as follows: 22.5 W sputtering power, 60 mm between target and substrate, 0.1 Pa Ar 2 pressure. The films have been characterized by XRD, SEM, AFM and other techniques. There are a large number of fine grains on substrates which were formed by sputtering particles gathering. Ni–Mn–Ga film is typical nucleation growth and development. By comparison of morphology of films on different substrates, it indicates that the roughness of films is greatly affected by substrates. After heat treatment, most of the films are more uniform and compact. But the film on NaCl is broken up due to the different expansion coefficient of film and substrate. It did not occur on Cu and Si wafers. The result of X-ray diffraction indicates that the annealed films are crystalline and most orient to (022). The average crystalline grain size perpendicular to (022) lattice face crystal plane is about 8.503 nm, while its lattice deformation rate is about 1.36%. The strain of Ni–Mn–Ga film induced by magnetic field was tested. Negative 85 ppm was got when applying magnetic field about 13 koe paralleled to film surface. The standard indentation test was employed to Ni–Mn–Ga film with thickness about 400 nm. Elastic modulus of film is calculated as 3.79 GPa while hardness is 252.92 MPa.

Nanoscaled surface structures of ionic crystals by spinodal decomposition

Self-organised periodic surface structures are prepared by spinodal decomposition of AgCl–NaCl single crystals and subsequent ex-solution of the alkali-rich component. While the kinetics of decomposition was studied previously by time-resolved neutron scattering, in the present paper, the etching process is studied in some detail and the surface structures are characterised by atomic force microscopy. It is shown that the duration of both, the demixing process as well as the etching process, determines the characteristic length scale of the periodic pattern. Under well controlled conditions, relief structures with wavelengths of some 100 nm are obtained that are uniform over areas of some mm 2. These patterns can possibly be used as templates for the decoration with metals, macromolecules, etc.

Discountinuity of Plastic Flow Controlled by Magnetic Field in NaCl:Eu Crystals

An influence of a constant magnetic field (MF) with induction up to 15 T upon macroscopic plastic deformation of diamagnetic NaCl single crystals containing paramagnetic Eu impurity was observed. Effects of MF on instability of plastic flow (on the Portevin-Le Chatelier effect) in quenched NaCl:Eu crystals were found. The MF results in a decrease of the yield stress, a decrease of the probability of the instability appearance, and a decrease of the averaged magnitude of the deformation jumps, as well as in a chaotization of the distribution of the deformation jump magnitudes. The latter can be explained by partial plastic relaxation of internal stresses under MF that was confirmed by dislocations displacement induced by internal stresses in MF. The averaged amount of shear bands observed on the surface of the investigated crystals deformed under MF is half of that in reference specimens.