Ions Scatter Research Articles

Towards understanding groundwater quality using hydrochemical and statistical approaches: case of shallow aquifer of Mahdia-Ksour Essaf (Sahel of Tunisia).

Understanding the controlling factor of groundwater quality could certainly enhance the promotion of the sustainable development of groundwater resources. In fact, during the last decades, the coastal aquifer of Mahdia-Ksour Essef that belongs to the semi-arid region of Tunisia has been marked by an increase of groundwater extraction for irrigation and water for drinking. Moreover, the water quality shows deterioration due to the septic tanks and intensive agricultural activities especially in the coastal side of the aquifer. This study aimed to (1) assess the water quality using Piper Diagram, Box Plot, ions scatter diagrams, (2) understand the processes of mineralization acquisition in the aquifer, and (3) identify the chemical processes and their spatial distribution in the study area. To solve these objectives, the multivariate statistical analysis such as multiple correspondence analysis and hydrochemical analysis was performed. Accordingly, two types of groundwater are identified through the hydrochemical analysis as Na-Cl and Ca-SO4. According to multiple correspondence analysis, three water groups are determined (G1, G2, and G3). Indeed, the groundwater quality is controlled by the water-rock interactions and affected by the seawater intrusion and agricultural activities. The generated results would be helpful to provide a managing model highlighting the threatened locations. It could be considered as a basis for future monitoring programs that aspire to protect water resources.

Effect of Fe alloying on the thermoelectric performance of Cu2Te

Copper telluride belongs to the “Phonon Liquid Electron Crystal” (PLEC) class of materials owing to its mobile Cu ions which migrate easily inside the crystal lattice. The mobile copper ions scatter phonons and lead to low thermal conductivity making it a suitable choice as a thermoelectric material. However, the formation of copper vacancies results in high hole carrier concentration (∼1021 cm−3) leading to poor Seebeck coefficient and degrades its overall thermoelectric efficiency. In this work, we aim at improving the thermoelectric transport properties of Cu2Te by alloying with Fe. The alloys of Cu2-xFexTe (where x varies from 0 to 0.06) were synthesized via solid-state synthesis followed by compaction in an induction hot press system. The formation of the trigonal phase (space group P3m1) of Cu2Te and the solubility of Fe ∼ x = 0.05 in Cu2-xFexTe is confirmed by means of X-ray Diffraction and backscattered electron micrographs. The decrease in electrical conductivity and the Hall carrier concentration and increase in the Seebeck coefficient with increasing Fe content signifies the compensation of holes by the electrons contributed from the trivalent Fe. The specific heat capacities of the Fe substituted samples were higher than the Dulong Petit limit of 3NkB, which implies that “liquid-like” behaviour of the Cu ions has been suppressed. This is because the Fe atoms act as barriers to the Cu ion diffusion. Due to the maximum power factor (∼0.47 mW m−1 K−2) and minimum thermal conductivity (∼2.19 W m−1 K−1), the maximum figure of merit of ∼0.16 at 750 K was obtained for the sample Fe0.03. It is hypothesized that the substitution of Fe not only helped to control the high carrier concentration but also restricted the cationic diffusion in Cu2Te. Hence, the present study points to a possibility of synergistically improving the thermoelectric properties as well as suppressing the ionic diffusivity in PLEC materials.

Direct dioxygen evolution in collisions of carbon dioxide with surfaces

The intramolecular conversion of CO2 to molecular oxygen is an exotic reaction, rarely observed even with extreme optical or electronic excitation means. Here we show that this reaction occurs readily when CO2 ions scatter from solid surfaces in a two-step sequential collision process at hyperthermal incidence energies. The produced O2 is preferentially ionized by charge transfer from the surface over the predominant atomic oxygen product, leading to direct detection of both O2+ and O2−. First-principles simulations of the collisional dynamics reveal that O2 production proceeds via strongly-bent CO2 configurations, without visiting other intermediates. Bent CO2 provides dynamic access to the symmetric dissociation of CO2 to C+O2 with a calculated yield of 1 to 2% depending on molecular orientation. This unexpected collision-induced transformation of individual CO2 molecules provides an accessible pathway for generating O2 in astrophysical environments and may inspire plasma-driven electro- and photo-catalytic strategies for terrestrial CO2 reduction.

A hydrogeochemical approach to evaluate the occurrence and source of salinization in the shallow aquifers of the southeastern Imphal valley in the Indo-Myanmar range of Northeast India

The Imphal valley is an intramontane basin confined within an anticlinorium of several anticlines and synclines in the Disang Group of rocks of Tertiary age. This valley of more than 2 million people is occupied by fluvio-lacustrine deposits of Quaternary age and is located in the central part of the Indo-Myanmar range of Northeast India. The hydrogeochemical parameters of temperature, pH, ORP, TDS, Na, Cl, Br, Ba, B, Sr, Li, δ18O, HCO3, K, Mg, Ca, NO3, PO4, SO4 in 173 samples using ion-chromatograph, ICP (AES), ICP (OES), ICP (MS) and 37 dugwells were studied to understand the occurrence and origin of salinization process for the first time. The order of abundance of ions is identified as HCO3 > Na > Cl > Ca > Mg > K > NO3 > PO4 > Sr > Br > B>Ba > Li > SO4. Five hydrochemical facies (Na–Cl, Ca–Mg–HCO3, Na–HCO3, Ca–Mg–HCO3–Cl and Ca–Mg–Cl) represent the types of waters. The saline-dominated water types (Na–Cl and Na–HCO3) represent piedmont and the rest of the facies represent alluvial plain and flood plain groundwaters. Durov’s diagram reveales initial and intermediate stages of groundwater evolution. Isotope δ18O, Gibbs diagram and ions scatter plots suggest evaporation and crystallization processes leading to halite encrustation in the Disang shales. Negative Eh, low NO3 and the absence of SO4 indicates reduced condition coupled with rich dissolve organic matters leading to elevation of salts in soils around piedmont where the rock type is exclusively of the Disang shales. Trilinear plot, correlation matrix and water table flow analysis suggest salinization of groundwater originates in piedmont groundwater and disseminates towards alluvial plain and flood plain along the flow path.

Energy transfer in quasibinary and collective scattering events at a Ag(001) surface

We have measured the in-plane scattered distributions of ${\text{K}}^{+}$ ions incident on a Ag(001) surface with energies from 9 to 100 eV. Energy- and angle-resolved spectra of the scattered flux show multiple peaks distinctly separated in energy corresponding to specific ion trajectories at the surface. Using a calculated interaction potential combined with the classical scattering simulation SAFARI we are able to model these trajectories and detail their energy-loss characteristics. At energies below approximately $24\text{ }\text{eV}$ we find that the ions scatter with a larger energy than one would expect from quasibinary collisions. Our trajectory analysis reveals this is a transition from the quasibinary behavior to a collective surface response more commonly associated with thermal energy atom scattering.

A method for calculating the conductivity mobility spectrum using multi-carrier fitting

At low temperatures, ionized impurities are the dominant scattering mechanism limiting carrier mobilities in most semiconductors. Calculations of ionized impurity scattering have usually been based on the assumption that the ions scatter independently of one another. The purpose of this paper is to investigate the method of mobility calculation in which the carrier spectrum is found by solving the neutrality equation numerically. A development of the method, which allows calculation of the temperature dependent mobility spectrum of all carriers used in the neutrality equation for the GaAs/GaAs sample is presented. In order to explain the transport properties the following topics are discussed: Theoretical calculation of the n-type GaAs transport parameters. Comparison between measured and calculated values of the conductivity and Hall concentration, resistivity, conductivity and Hall mobility. The values of conductivity mobility for each carrier transport component. Application of the method for characterization of n-GaAs on SI GaAs MBE epi-layers. The new method allows for determination of the carrier mobility spectrum and is applied to GaAs/SI-GaAs layers in which the Hall voltage is magnetic field dependent.

A method for calculating the conductivity mobility spectrum using multi-carrier fitting

At low temperatures, ionized impurities are the dominant scattering mechanism limiting carrier mobilities in most semiconductors. Calculations of ionized impurity scattering have usually been based on the assumption that the ions scatter independently of one another. The purpose of this paper is to investigate the method of mobility calculation in which the carrier spectrum is found by solving the neutrality equation numerically. A development of the method, which allows calculation of the temperature dependent mobility spectrum of all carriers used in the neutrality equation for the GaAs/GaAs sample is presented. In order to explain the transport properties the following topics are discussed: • Theoretical calculation of the n-type GaAs transport parameters. • Comparison between measured and calculated values of the conductivity and Hall concentration, resistivity, conductivity and Hall mobility. • The values of conductivity mobility for each carrier transport component. • Application of the method for characterization of n-GaAs on SI GaAs MBE epi-layers. The new method allows for determination of the carrier mobility spectrum and is applied to GaAs/SI-GaAs layers in which the Hall voltage is magnetic field dependent.

Hyperthermal scattering of Cs+ from Pt(1 1 1): the effect of image charge on the ion–surface energy transfer

We have studied the energy exchange between hyperthermal (5–100 eV) Cs+ projectiles and a Pt(111) surface by measuring the kinetic energy of the scattered ions. The scattering geometry was chosen to be in-plane with specular scattering angles, and the energy of the scattered ions was analyzed as functions of incidence energy and angle. For low incidence energy (<40 eV), the energy transfer to the Pt surface is substantially enhanced due to the attractive image charge force between Cs+ and the surface. The image charge effects are highlighted by the different energy transfer on Pt(111) and Si(111) surfaces. Analysis of the experimental results using two- and three-dimensional theoretical models revealed a well depth of 1 eV for the image charge potential. Hyperthermal Cs+ ions scatter from Pt(111) predominantly via double collisions with Pt atoms, though the scattering phenomena are insensitive to the impact site at the surface.

Dynamics of Cr(CO)6+ collisions with hydrogenated surfaces

Classical trajectory simulations are used to study the activation of Cr(CO)6+ ions by 5–110 eV collisions with n-hexyl thiolate self-assembled monolayer (SAM) and the H-terminated diamond {111} surfaces. The transfer of the ion’s initial translational energy Ei to the ion’s internal degrees of freedom Eint, to the surface Esurf, and to final translational energy Ef depends on both Ei and the surface. At Ei=70 eV the percent energy transfers to Eint, Esurf, and Ef are 9, 81, and 10 for collision with the SAM and 17, 29, and 54 for collision with diamond. For collision with the SAM, the percent energy transfer to Eint is 8–10% and nearly independent of Ei, while it depends on Ei for collision with diamond. The percent transfer to Eint, for collision with the SAM, is in excellent agreement with experiment. For both surfaces, the percent energy transfer to Esurf and to Ef increase and decrease, respectively, as Ei is increased. For Ei of 30 and 70 eV the Cr(CO)n+, n=4–6, ions shatter as Cr(CO)6+ strikes the diamond surface. At 110 eV some of the n=1–3 ions also begin to shatter. Shattering is only observed for collision with the SAM at an Ei of 110 eV, for which the n=4–6 ions shatter. At lower Ei, the Cr(CO)6+ ions rebound off the SAM and dissociate via intramolecular vibrational energy redistribution, with lifetimes approximately the same as those of Rice–Ramsperger–Kassel–Marcus theory. Energy partitioning to the Cr(CO)n+→Cr(CO)n−1++CO, n=1–6, dissociation products is nonstatistical, with the partitioning to relative translation and CO vibrational and rotational energy, larger and smaller, respectively, than the prediction of phase space theory. There is negligible energy transfer to the CO vibration during the collision of Cr(CO)6+ with either surface or later as a result of intramolecular vibrational energy redistribution after the Cr(CO)n+ ions scatter off the surfaces.

Study of C3H5+ ion deposition on polystyrene and polyethylene surfaces using molecular dynamics simulations

Molecular dynamics simulations of ion deposition processes are used to study the deposition of C3H5+ ions on crystalline polystyrene (PS) and polyethylene (PE) surfaces at energies of 50 and 25 eV. For each system, 80 trajectories are carried out on pristine surfaces and the incident angle in every case is normal to the surface. The forces are determined using the reactive empirical bond order method developed by Tersoff and parametrized for hydrocarbons by Brenner, coupled to long-range Lennard–Jones potentials. The simulations predict that the ions deposited at 50 eV either dissociate and stick to the surface or remain on the surface intact in 98% of the trajectories on PS, and in 89% of the trajectories on PE. At 25 eV, the ions are deposited intact in 70% of the trajectories on PS and dissociate in only 3%. No dissociation of the incident ions is predicted to occur on PE at 25 eV. Rather, the ions scatter away in 90% of the trajectories. Consequently, ion deposition on PE at 25 eV is predicted to be very inefficient for thin-film growth. Many more ions or major ion fragments (such as C2Hn and CH2) remain near the surface on PS than PE at 50 eV. Thus, in general, polyatomic ion deposition for thin film growth is more efficient on PS than PE, and deposition at 50 eV is more efficient than deposition at 25 eV.

X-transport: A baseline nonambipolar transport in a diverted tokamak plasma edge

A new nonambipolar neoclassical transport (X-transport) mechanism has been identified which can be an irreducible baseline source of a strong radial electric field and edge pedestal formation immediately inside the separatrix in a diverted tokamak. Due to the vanishingly small poloidal magnetic field in the vicinity of a divertor X-point, there exists an ion velocity space hole at the thermal energy level. This becomes a source of a nonambipolar, collisional, convective radial transport of plasma ions, as the ions scatter into and out of the loss hole in the vicinity of an X-point. The widths of the Er and edge pedestal layers are somewhat smaller than the ion poloidal gyroradius, measured at the midplane. A simple estimate shows that the X-transport rate can be significant enough to influence a high mode transition and edge pedestal formation.

Study of angular influence of C3H5+ ion deposition on polystyrene surfaces using molecular dynamics simulations

The influence of incident angle on the interaction of polyatomic hydrocarbon ions (C3H5+) with polystyrene surfaces is examined using classical molecular dynamics simulations. The forces are determined using the reactive empirical bond order method developed by Tersoff and parametrized by Brenner. The total incident energy is 50 eV and the angles considered are 0° (normal to the surface), 15°, 45°, and 75°. At each angle, the outcomes of 80 trajectories are compiled and averaged. The results show that intact ions scatter from the surface in only 2% of the trajectories and that the ions dissociate in 61% of the trajectories at normal incidence. At 75°, intact ions scatter away in 56% and they dissociate in only 30% of the trajectories. The largest total amount of carbon is deposited at normal incident angles. However, more ions or ion fragments are predicted to remain near the surface (penetrate 3.5–5.5 Å) at 45°. This is because ion fragments tend to penetrate more deeply (6–7 Å) into the surface at smaller angles. Consequently, some inclined angles are found to be most efficient for the deposition of the precursors necessary for polymer thin-film growth.

Probing of magnetic surfaces with inherent monolayer sensitivity by ion scattering

When ions scatter off surfaces, some particles are neutralized into excited states that are subsequently de-excited by light emission. In case of magnetic surfaces the information about the spin of the captured electron might be accessed via the polarization of the emitted light. In the grazing incidence mode, the surface sensitivity is highest due to the fact that the particles do not penetrate into the target surface but are scattered well above the uppermost atomic layer. Thus the electrons that neutralize the incoming ion originate from the topmost layer. This implies that the method is very well suited to investigate the properties of magnetic surfaces and multilayer structures. We present data that show the inherent surface sensitivity of this method. By properly choosing the experimental parameters one also assures that the energy deposited by the projectiles in the surface is negligible as well as the number of sputtered particles. We also present the first hysteresis curves recorded with this method, thereby showing that the measured signal follows the magnetic state of the surface. In combination with its surface sensitivity this shows that ion beam scattering is very well suited to investigate not only the surfaces of magnetic materials but also (ultra-)thin films and multilayer systems.

Reactive scattering of Cs + from chemisorbed molecules on a Ni(100) surface. Secondary neutral mass spectrometry with a hyperthermal ion beam

Reactive scattering of hyperthermal Cs + ions is studied from a Ni(100) surface chemisorbed with CO, OH, and benzene. The products of reactive scattering, CsCO +, CSOH +, and CsC 6H 6 +, reflect molecular identity of the chemisorbed species. It is demonstrated that this method can be used to monitor adsorption kinetics of the adsorbates in real-time. The reaction dynamics is investigated through measurement of reaction yields as a function of adsorbate surface coverage, Cs + beam exposure, and beam incidence angle. Cs + collision induces desorption of CO from a CO-covered surface, with a desorption cross section of 2.4(± 1.4) × 10 −15 cm 2 molecule −1 for a 30 eV beam incident at 45°. The desorbing CO molecules are combined to the scattered Cs + ions with an association probability of 1.0(± 0.6) × 10 −3. This number indicates that a hyperthermal Cs + ion provides an efficient means of cationizing a collisionally desorbed neutral molecule. From angular dependence study, it is suggested that Cs + ions scatter from a Ni(100) surface to a specular direction with a sharp angular distribution. The desorbing CO molecules have an angular distribution that is peaked more probably toward a specular direction than the surface normal.

Surface Channeling Experiments at 20 MeV and Resonant Coherent Excitation ofN6+Ions

Surface channeling of 21.8 and 23 MeV ${\mathrm{N}}^{6+}$ ions of a Pt(110) surface is experimentally verified. At 21.8 MeV resonant coherent excitation is observed leading to enhanced ionization when the ions scatter along the $[1\overline{1}0]$ surface half channels.

Ion scattering from strong turbulence with long-range correlations

Colliding plasmas can excite strong Langmuir turbulence in which collective correlations affect the probability distribution P( E) of the electric microfield. This can be modeled by including long-range correlations but not dynamics over lengths ⪢ λ D. Earlier work yielded a characteristic distribution P( E) ∝ E d−1 exp (− E 2/〈 E 2〉), with d the dimensionality of the electric field and 〈 E 2〉 proportional to the square of the correlated particle density. Ions scatter from this localized strong turbulence at rates greatly exceeding classical collisions for solar coronal conditions, while laboratory ion beams have no appreciable scatter beyond the Coulomb rate.

High time resolution studies of upstream ions

Diffuse upstream ions at low energy (∼1.6 keV) fluctuate rapidly compared to higher energy ions and vary in intensity in a systematic way with ϕ, the angle between the interplanetary magnetic field BI and the earth‐sun direction. The 1.6 keV ion intensity is highest when ϕ is in the range 60° to 90°, and these ions may nearly disappear for values of ϕ near 0°. There is a rather narrow energy range in which the flux remains remarkably constant. At times this energy interval may be centered at an energy as high as 30 keV and at other times as low as 6 keV. This energy appears to vary systematically with the angle ϕ. We have also found that few ions scatter out of the foreshock onto less disturbed interplanetary field lines upstream from the foreshock boundary. Finally, we have found several events in which diffuse ions with energies at least as high as 60 keV are present on field lines that make angles up to 60° with respect to the earth‐sun direction. In these cases a first‐order Fermi process would have only about 3 minutes to increase the energy of the upstream ions. Energization at the bow shock may provide the required additional acceleration. Intermediate upstream ions of 60 keV energy appear even at ϕ angles up to 80°.

Observation of “zig-zag” collisions in scattering of Ar + from Mg(0001)

Three distinct peaks are observed in scattering of 4 keV Ar + from 〈0 1 1〉 rows on the Mg(0001) surface. Computer simulation work indicates that the central peak is due to “zig-zag” collision sequences, in which the ions scatter between neighbouring surface atomic rows. The implications of these observations for neutralization lifetime estimation are discussed.

Observation of “zig-zag” collisions in scattering of Ar + from Mg(0001)

Three distinct peaks are observed in scattering of 4 keV Ar + from 〈0 11〉 rows on the Mg(0001) surface. Computer simulation work indicates that the central peak is due to “zig-zag” collision sequences, in which the ions scatter between neighbouring surface atomic rows. The implications of these observations for neutralization lifetime estimation are discussed.

Solutions of salts in liquid sodium electrical resistivity of solutions of sodium hydride and of sodium monoxide, and the solubility of sodium hydride in sodium

The electrical resistivity of solutions of sodium hydride (between 340 and 430 °C) and of sodium monoxide (at 400 °C) in liquid sodium up to saturation concentrations has been determined. The resistivity increases linearly with increasing concentration of each salt but hydride ions scatter conduction electrons more effectively; unit resistivity increases are 4.5 × 10 −8 and 1.8 × 10 −8 Ω m (mol.%) −1 for H − and O 2−, respectively, which may reflect the difference in size of the solvated anions. The solubility of sodium hydride was determined from the change in resistivity which occurred on saturation. Values are combined with those derived from pressurecomposition isotherms to give the solubility equation: Iog 10 ( mol.% H) = 4.82 − 3600/ T 613 ⩽ T ⩽ 673 K