Effect of impurities in charge-exchange carbon foil on foil thickness reduction

Carbon thin foils are commonly used as a charge stripping material in particle accelerators. Depending on the original foil thickness, changes in thickness during beam irradiation vary: thin foils (∼10 μg/cm²) thicken by build-up, medium thickness foils (∼15 μg/cm²) remain unchanged, and thick foils (∼20 μg/cm²) become thinner. The thickness reduction differs even under identical manufacturing processes and conditions.The factor causing foil thinning is unknown. On the basis of the low sputtering rate of carbon, it can be said that impurities contained in the foil cause foil thinning.Carbon foils contain impurities such as water. These impurities dissociate and combine with carbon and then evaporate. Taking this into consideration, we examined the gas composition during beam irradiation, to determine which impurity causes foil thinning. As a result, we found that oxygen contained in the foil plays a role in foil thinning.     

Calibration factors for determination of relativistic particle induced fission rates in U, U, Th, Pb and Au foils

Calibration factors w, for determination of fission rate in metallic foils of ^natU, ²³⁵U, ²³²Th, ^natPb and ¹⁹⁷Au were determined for foils in contact with synthetic mica track detectors. Proton-induced fission at proton energies of 0.7 GeV and 1.5 GeV were used. Using our experimental results as well as those of the other authors, w for different foil-mica systems were determined. Two methods were used to calculate w, relative to the calibration factor for uranium-mica system, which has been obtained in a standard neutron field of energy 14.7 MeV. One of these methods requires the knowledge of the mean range of the fission fragments in the foils of interest and other method needs information on the values of the fission cross-sections at the required energies as well as the density of the tracks recorded in the track detectors in contact with the foil surfaces. The obtained w-values were compared with Monte Carlo calculations and good agreements were found. It is shown that a calibration factor obtained at low energy neutron induced fissions in uranium isotopes deviates only by less than 10% from those obtained at relativistic proton induced fissions.     

Copper nanowall array grown on bulk Fe-Co-Ni alloy substrate at room temperature as lithium-ion battery current collector

Large-scale copper nanowall array on the bulk Fe-Co-Ni alloy substrate has been prepared in aqueous solution at room temperature via an electroless deposition method. The thickness of the nanowalls is about 15 nm. A possible growth mechanism of the nanowalls was proposed. The effects of reaction temperature, reaction time and the amount of critical agent (Fe³⁺) on the morphology and crystalline phase of the nanowalls were investigated. Furthermore, the electrochemical performance of Sn film supported on the as-prepared copper nanowalls current collector is enhanced in comparison with that on the commercial copper foil when used as anode for Li-ion batteries with the operating voltage window of 0.01-2.0 V (vs. Li). After 20 cycles, the discharge capacity of Sn-Cu nanowalls anode still remained 365.9 mAh g^− 1, that is, 40% retention of the reversible capacity, while the initial charge capacity of Sn film cast on commercial Cu foil was 590 mAh g^− 1, dropping rapidly to 260 mAh g^− 1 only after 10 cycles.     

The impact of high-dose implantation into manganin on its thermo-resistance properties under high pressure

Using high-dose implantation into manganin of 253 MeV Kr ions (a surface dose of 2.5×10¹⁵ ion/cm²), as well as 250 keV Bi ions (a surface dose of 10¹⁷ ion/cm²) and 250 keV Kr ions (a surface dose of 10¹⁶ ion/cm²), the pressure and temperature sensitivities of manganin foil have been investigated. It was found that the pressure sensitivity of manganin increased (α=2.45×10⁻⁵ MPa⁻¹ before implantation and α_imp=4.60×10⁻⁵ MPa⁻¹ after complex implantation with 250 keV of Bi and Kr ions, the accuracy of estimation does not exceed 0.01×10⁻⁵ MPa⁻¹) and its temperature sensitivity remained appreciably reduced.     

Fabrication of Cu2S on Cu film electrode and its application in lithium ion battery

Cu₂S film electrode direct growth on Cu foil is prepared by a simple hydrothermal approach. The electrochemical properties of the as-prepared Cu₂S electrode are investigated via conventional discharge and charge tests. When applying a current density of 0.1 mA cm^− 2, the as-prepared Cu₂S electrode exhibits discharge and charge capacity of 0.27, 0.32, 0.35, 0.34 and 0.34 mAh cm^− 2 at the 100th, 200th, 300th, 400th and 500th cycle, respectively. Such good performance of the as-prepared Cu₂S electrode is attributed to the fine electric contact between Cu₂S and Cu foil and the possible hollow structure of Cu₂S film.     

Silicon oxide diffusion barrier coatings on polypropylene

In this study the influence of process conditions for the plasma-enhanced chemical vapor deposition of SiO_x diffusion barrier coatings on polypropylene (PP) is investigated and compared to results obtained on polyethylene terephthalate (PET). It was observed that the thermal load during deposition is much more crucial in the case of PP. If the thermal load is not the limiting factor, the composite parameter (CP) energy input per mass of precursor showed to be valuable to describe plasma conditions at constant oxygen to monomer ratio. Low oxygen transmission rates (OTRs) of 5.1 ± 3.6 and 0.3 ± 0.1 cm³/m²day/atm were achieved on PP and PET foil, respectively, for an optimal CP of 4.1 × 10⁵ J/g. Fourier transform infrared (FTIR) spectroscopy revealed that low carbon and silanol content is necessary for good barrier performance. Low RF power, necessary to reduce thermal load on PP, can be compensated by increasing the oxygen to monomer ratio.For favorable plasma conditions, the dependence of the OTR on the coating thickness follows a similar trend for both substrate materials with a critical thickness of approximately 12 nm. The residual permeation can be correlated to the defect density at each stage of film growth by means of a simple correlation. Further support for permeation through defects is found by the activated rate theory, since the apparent activation energy of oxygen permeation is below typical values of amorphous glasses and remains unchanged due to the deposition of SiO_x on both substrates.     

Electrochemical characterization of a Ge-based composite film fabricated as an anode material using magnetron sputtering for lithium ion batteries

Amorphous germanium and germanium-based films are sputter-deposited as anodes for lithium ion batteries. The structures of Ge and Ge-Mo composites are investigated using an X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The surface morphologies of the electrodes are observed using a field emission scanning electron microscope (FESEM). In order to determine the influence of inactive material in the anode, cell tests are carried out on half cells (Ge/Li metal and Ge_xMo_1 − x/Li metal) and full cells (Ge/LiCoO₂ and Ge_xMo_1 − x/LiCoO₂). The Ge film electrodes prepared on rough copper foil substrates showed stable capacities of 1000 mA h g⁻¹ over 50 cycles. The Ge_0.88Mo_0.12 composite film electrode showed reversible gravimetric capacities of up to 1000 mA h g⁻¹ with 77.9% capacity retention rates of the half-cell test after 100 cycles. Therefore, it may be possible to fabricate Ge-based anode materials with high capacity and improved capacity retention. The results of this study suggest that sputtered Ge-based electrodes are promising anode materials for next generation lithium ion batteries.     

Growth of well-aligned carbon nanotubes by RF-DC plasma chemical vapor deposition

Highly aligned carbon nanotubes (CNTs) were grown under high sheath electric field and gas pressure conditions by the radio frequency (RF) plasma-enhanced direct current (DC) plasma chemical vapor deposition (CVD) method due to a stabilized DC discharge. The uniform growth of highly aligned multi-walled CNTs was achieved over the entire surface area of a 50 × 50 mm² iron foil. The growth of multi-walled CNTs on a 75 × 75 mm² iron foil was also confirmed.     

The electron beam gun with thermionic hairpin-like cathode for welding and surface modifications

An axial thermionic electron beam emitter assembly with a special geometry of the cathode along with particular spacing of the electrodes has been used to produce a stable, sharp and high power density image at an acceleration voltage of 10 kV only. A hairpin-like tungsten wire, with diameter of 0.7 mm having semi-spherical emitting area at the crown with an angle of 45 degree at the vertex was used as a cathode. A direct heating method was used to heat the cathode. The emission current of the gun is in accordance with the Langmuir relation. An electromagnetic coil was used for focusing the beam at the target. A two dimensional programmable movement was applied to control the work site in the x-y direction. Focusing of the beam has been achieved up to 1 mm in diameter at an acceleration voltage of 10 kV.Thermionic efficiency of the gun is 4 mA W⁻¹ and the power density measured is ∼10⁵ W cm⁻².The gun was used for welding and surface modification of different materials including refractory metals.     

Structural transformation and magnetic properties of CaMn1 − xFexO3 − δ (0.0 ≤ x ≤ 0.5)

We have investigated the structural and magnetic properties of CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). Solid state method is used for the synthesis of these samples. Sintering of these compositions at 1300 °C stabilizes higher ionic radii Fe^+ 3 (0.645 Å) at Mn^+ 4 (0.53 Å) site in CaMn_1 − xFe_xO_3 − δ. Structural transformation from orthorhombic to tetragonal to pseudo cubic crystal system and the increase in lattice parameters have been observed with the substitution of Fe at Mn site in CaMn_1 − xFe_xO_3 − δ (0.0 ≤ x ≤ 0.5). The magnetization data show the transformation of G type of antiferromagnetic arrangement of Mn^+ 4 electrons spins in CaMnO₃ into paramagnetic spin type arrangement with the substitution of Fe at Mn site. The compositions x = 0.05, x = 0.1and x = 0.2 show a small kink ~ 100 K in the magnetization data, which resulted due to the competition between antiferromagnetic and paramagnetic states with the Fe substitution.     

In-situ monitoring of the time evolution of the effective thermal conductivity of snow

We report on a 3-month long time series of in-situ measurements of the effective thermal conductivity (k_eff) of snow at 6 heights in an Alpine snowpack in the Mont-Blanc mountain range, France, at an altitude of 2400 m. Measurements were carried out automatically every 2 days using heated-needle probes embedded in the snowpack. The experimental procedure used is presented in detail and demonstrates the applicability of single heated-needle probes for the evaluation of k_eff in snow, both for long-term measurements within the snowpack and occasional use in the field. Results based on 139 automatically collected data show k_eff values ranging between 0.04 and 0.35 W m^− 1 K^− 1, and a consistent pattern of effective thermal conductivity increase throughout the measurements campaign. The temporal rate of change of k_eff varies up to 0.01 W m⁻¹ K^− 1day^− 1, with maximum values just after snowfall.     

Magnetocaloric properties in Ln0.67Ba0.33Mn1 − xFexO3 (Ln = La or Pr) manganites

We have investigated the magnetocaloric properties of Ln_0.67Ba_0.33Mn_1 − xFe_xO₃ (Ln = La or Pr) manganites with x = 0 and 0.05. All compounds present a maximum and large magnetocaloric effect near the Curie temperature (T_C). The associated maximum value of the magnetic entropy change, at 5 T applied change in the magnetic field, is 4.37 J.kg^− 1.K^− 1 for Pr_0.67Ba_0.33MnO₃ manganite with a T_C value of 205 K. The corresponding relative cooling power (RCP) reaches 230 J.kg^− 1. All the samples present similar RCP values that are relatively high and are promising materials to be used in ecologically friendly magnetic refrigeration technology. Iron doping reduces both T_C and ΔS_M^max and spreads the temperature working range with an almost constant RCP and can then be used to tune the working conditions of a refrigerator device.     

Electrical properties of polycrystalline GaInAs thin films

Polycrystalline Ga_xIn_1 − xAs films with x ranging from 0 to 1 were deposited on glass substrates by molecular-beam deposition at 240 or 350 °C. Room temperature Hall-effect measurements showed that the Ga_xIn_1 − xAs films deposited at either temperature exhibit high electron concentrations in the range of 10¹⁸ cm^− 3 for x ≤ 0.21 while the electron concentration decreases with increasing Ga content for x ≥ 0.29 to be < 10¹⁵ cm^− 3 at x = 0.64. Even at the low deposition temperature of 240 °C, the electron mobility remains > 400 cm²/(V s) at x ~ 0.2 and then decreases with Ga content to be ~ 40 cm²/(V s) at x = 0.64. Temperature-varying Hall-effect measurements in the range of 100-390 K revealed that both the electron concentration and mobility of the samples with x ≤ 0.21 are almost independent of the measurement temperature, while those of the samples with x ≥ 0.30 decrease with decreasing measurement temperature. The concentrations and ionization energies of donor levels were deduced from the temperature dependence of the electron concentration with the non-parabolicity of the conduction band taken into account. The temperature dependences of electron mobility in the samples with x ≥ 0.30 are well explained in terms of thermionic electron emission across the grain-boundary barriers assuming fluctuation in potential barrier height, while the almost temperature-independent high electron mobilities in the samples with x ≤ 0.21 are attributed to the absence of potential barrier at the grain boundaries.     

High performance low temperature solution-processed zinc oxide thin film transistor

Amorphous zinc oxide thin films have been processed out of an aqueous solution applying a one step synthesis procedure. For this, zinc oxide containing crystalline water (ZnO⋅ × H₂O) is dissolved in aqueous ammonia (NH₃), making use of the higher solubility of ZnO⋅ × H₂O compared with the commonly used zinc oxide. Characteristically, as-produced layers have a thickness of below 10 nm. The films have been probed in standard thin film transistor devices, using silicon dioxide as dielectric layer. Keeping the maximum process temperature at 125 °C, a device mobility of 0.25 cm²V^− 1s^− 1 at an on/off ratio of 10⁶ was demonstrated. At an annealing temperature of 300 °C, the performance could be optimized up to a mobility of 0.8 cm²V^− 1s^− 1.     

Guided transmission of Ne ions through nanocapillaries in PET: dependence on the tilt angle

We measured the transmission of 3 keV Ne⁷⁺ ions through nanocapillaries of 100 nm diameter and 10 μm length in a PET polymer foil. The capillaries were produced before the transmission experiments by etching tracks of fast xenon ions. The foils were tilted up to 15° for which the incident ions are forced to approach the capillary surface. After a characteristic time the majority of Ne⁷⁺ ions were found to be transmitted in their initial charge state. The angular distributions of the transmitted Ne⁷⁺ projectiles reveals a propagation of the ions parallel to the capillary axis. This indicates that the ions are guided through the capillaries. The capillary guiding is the result of deposit of charges in a self-organizing process. A non-linear model is presented to interpret the experimental observation. The analysis exhibits a significant dependence of the ion transmission on the tilt angle.     

Synthesis, structure and dielectric properties of a rare earth double perovskite oxide Ba2CeTaO6

A rare earth double perovskite oxide barium cerium tantalate, Ba₂CeTaO₆ (BCT) is synthesized by solid-state reaction. The X-ray diffraction pattern of the sample at room temperature (25 °C) shows monoclinic structure, with the lattice parameters, a = 9.78 Å, b = 9.02 Å and c = 4.27 Å and β = 93.8°. A scanning electron micrograph shows the formation of grains with average size ∼ 2 μm. Impedance spectroscopy is applied to investigate the ac electrical properties of BCT in a temperature range from 303 to 673 K and in a frequency range from 100 Hz to 1 MHz. Complex-impedance-plane plots show grain contribution for BCT. The frequency-dependent electrical data are analyzed in the framework of the conductivity and modulus formalisms. The frequency-dependent conductivity spectra follow a power law. The conductivity at 110 Hz varies from 3.5 × 10⁻⁷ S m⁻¹ to 1.2 × 10⁻² S m⁻¹ with increasing temperature from 303 to 673 K, respectively. The scaling behaviour of M″ and Z″ suggest that the relaxation describes the same mechanism at various temperatures.     

Influence of Cr deficiency on sintering character and properties of SOFC interconnect material La0.7Ca0.3Cr1−xO3−δ

The SOFC interconnect materials La_0.7Ca_0.3Cr_1−xO_3−δ (x = 0-0.09) were prepared using an auto-ignition process and characterized. XRD analysis indicated that all the samples displayed a pure perovskite phase after sintered at 1400 °C for 4 h. The relative density increased from 67% (x = 0) to 95.8% (x = 0.02) and reached to about 97% (x > 0.02), as sintered at 1400 °C for 4 h. The electrical conductivity in air dramatically increased and then lowered slowly with x values. The sample with 0.03 Cr deficiency got a maximum conductivity of 61.7 S cm⁻¹ at 850 °C in air, which is about three times as high as that of the sample with no Cr deficiency (20.6 S cm⁻¹). The sample with 0.06 Cr deficiency exhibited the highest electrical conductivity of 3.9 S cm⁻¹ at 850 °C in pure H₂. The thermal expansion coefficient (TEC) were below 11.8 × 10⁻⁶ K⁻¹ for samples of x = 0.02-0.09, that was of well compatibility with other components in SOFCs. Results indicate that the materials with 0.02-0.06 Cr deficiency have high properties and are much suitable for SOFC interconnect.     

Rare-earth doped solid-state phosphor with temperature induced variable chromaticity

Temperature induced variable chromaticity lanthanide multidoped solid-state phosphors are presented. The phosphors are composed of ytterbium-sensitized multiple-doped (Tm, Er, Ho) PbGeO₃-PbF₂-CdF₂ glass excited at 1.064 µm. The temperature induced color variation exploits the heat enhanced effective absorption cross-section of the ytterbium sensitizer under quasi-resonance excitation. The temperature enhancement of the energy-transfer mechanism between the sensitizer and the appropriate active light emitter allows the selective intensity control of the RGB emissions due to distinct excitation routes. The suitable combination of active ions generated variable chromaticity light with CIE-1931 coordinates changing from CIE-X = 0.283; Y = 0.288 at 20 °C to CIE-X = 0.349;Y = 0.412 at 190 °C, and CIE-X = 0.285; Y = 0.361 at 25 °C to CIE-X = 0.367; Y = 0.434 at 180 °C in Yb³⁺/Tm³⁺/Ho³⁺ and Yb³⁺/Tm³⁺/Er³⁺ samples, respectively.     

Structural and transport properties of stoichiometric Mn-doped magnetite: Fe3−xMnxO4

The polycrystalline samples of Fe_3−xMn_xO₄ (0.10 ≤ x ≤ 0.50) were prepared by a solid-state route reaction method. X-ray diffraction pattern shows that Mn²⁺ doped magnetites are in single phase and possess cubic inverse spinel structure. The resistivity measurements (10 < T < 300 K) for x = 0.0 and 0.01 confirms the first order phase transition at the Verwey transition T_V = 123 K and 117 K, respectively. No first order phase transition was evidenced for Fe_3−xMn_xO₄ (0.10 ≤ x ≤ 0.50). Small polaron model has been used to fit the semiconducting resistivity behavior and the activation energy ?_a, for samples x = 0.10 and 0.50 is about 72.41 meV and 77.39 meV, respectively. The Raman spectra of Fe_3−xMn_xO₄ at room temperature reveal five phonons modes for Fe_3−xMn_xO₄ (0.01 ≤ x ≤ 0.50) as expected for the magnetite (Fe₃O₄). Increased Mn²⁺ doping at Fe site leads to a gradual changes in phonon modes. The Raman active mode for Fe_3−xMn_xO₄ (x = 0.50) at ≅641.5 cm⁻¹ is shifted as compared to parent Fe₃O₄ at ≅669.7 cm⁻¹, inferring that Mn⁺² ions are located mostly on the octahedral sites. The laser power is fixed to 5 mW causes the bands to broaden and to undergo a small shift to lower wave numbers as well as increase in the full width half maxima for A_1g phonon mode with the enhancement of Mn²⁺ doping. Mössbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields confirms that Mn⁺² ions are located mostly on the octahedral sites of the Fe_3−xMn_xO₄ spinel structure.     

Surface mound formation during epitaxial growth of CrN(001)

Single crystal CrN(001) layers, 10 to 160 nm thick, were grown on MgO(001) by reactive magnetron sputtering at growth temperatures T_s = 600 and 800 °C. Insitu scanning tunneling microscopy shows that all layer surfaces exhibit mounds with atomically smooth terraces that are separated by monolayer-high step edges aligned along ( 110) directions, indicating N-rich surface islands. For T_s = 600 °C, the root mean square surface roughness σ initially increases sharply from 0.7 ± 0.2 for a thickness t = 10 nm to 2.4 ± 0.5 nm for t = 20 nm, but then remains constant at σ = 2.43 ± 0.13 nm for t = 40, 80 and 160 nm. The mounds exhibit square shapes with edges along ( 110) directions for t ≤ 40 nm, but develop dendritic shapes at t = 80 nm which revert back to squares at t = 160 nm. This is associated with a lateral mound growth that is followed by coarsening, yielding a decrease in the mound density from 5700 to 700 µm⁻² and an initial increase in the lateral coherence length ξ from 7.2 ± 0.6 to 16.3 ± 0.8 to 24 ± 3 nm for t = 10, 20, and 40 nm, respectively, followed by a drop in ξ to 22 ± 2 and 16 ± 2 nm for t = 80 and 160 nm, respectively. Growth at T_s = 800 °C results in opposite trends: σ and ξ decrease by a factor of 2, from 2.0 ± 0.4 and 20 ± 4 nm for t = 10 nm to 0.92 ± 0.07 and 10.3 ± 0.4 nm for t = 20 nm, respectively, while the mound density remains approximately constant at 900 μm⁻². This unexpected trend is associated with mounds that elongate and join along ( 100) directions, yielding long chains of interconnected square mounds for t = 40 nm. However, coalescence during continued growth to t = 160 nm reduces the mound density to 100 µm⁻² and increases σ and ξ to 2.5 ± 0.1 and 40 ± 2 nm, respectively.