Pseudo spin-valve on plastic substrate as sensing elements of mechanical strain

Giant magnetoresistance and magnetostriction effects in a Co-based e-beam evaporated pseudo spin-valve (SV) with Au spacer were studied. Samples were deposited onto polyimide substrates. The effect of strain on samples was studied in bending configuration. The strain was changed in the interval of [−900 −× 10⁻⁵ + 1100× 10⁻⁵]. Resistance was measured in an external field of ±25 kA/m with current and field in the plane of the sample and angle between them from 0° to 90°. It was shown that the magnetoresistance ratio depends on the strain, changing from 2.5% at −900 × 10⁻⁵ to 2.9% at 1100 × 10⁻⁵ and crossing 2.7% at zero strain in a typical SV with parallel current and field configuration. With increasing angle between the current and the field the magnetoresistance value increases. The results are comparable with those obtained for similar structures deposited on Si substrates. Nevertheless, the plastic substrate represents a cheaper alternative to Si and the dynamic range of these sensors is increased due to the higher strain achieved.     

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.     

Magnetoresistance enhancement of amorphous CoNbZr-buffered magnetoresistive multilayers

Amorphous CoNbZr alloys are thermally stable and thus have been intensively studied as soft layers of a pseudo-spin-valve (PSV). By depositing a wedge-shaped Co inset layer (IL) between the CoNbZr and Cu layer, we were able to simultaneously fabricate CoNbZr(t_CNZ)/Co(0-3 nm)/Cu/Co PSVs with various CoNbZr and Co IL thicknesses. We have investigated the dependence of magnetic properties, giant magnetoresistance (GMR) effect, and microstructure on the thickness of the amorphous CoNbZr buffer layer. The GMR enhancement behaviour of the PSVs with different CoNbZr thickness was also studied along the inset Co wedge. By optimizing the thickness of CoNbZr and Co IL, a maximum GMR ratio of 7% was obtained in the stack of CoNbZr(4 nm)/Co(1.2 nm)/Cu(2.2 nm)/Co(4 nm).     

Thermal properties of TiO2 films grown by atomic layer deposition

We study the thermal properties of amorphous TiO₂ thin films of various thicknesses t, grown by atomic layer deposition. The thermo-optic coefficient dn/dT and the temperature coefficient dρ/dT of film density ρ are determined from ellipsometric data in wavelength range 380 < λ < 1800 nm with the Cauchy model and the Lorentz-Lorenz relation. It is found that dn/dT exhibits negative values for films with t < 150 nm and positive values for thicker films, while no significant changes in the two coefficients take place if t < 200 nm. A qualitative physical explanation based on porosity of the thin films is suggested. Films with t = 60 nm are illustrated in detail at λ = 640 nm: the room-temperature values of the coefficients are found to be dn/dT = − 3.1 × 10^− 5 °C^− 1 and dρ/dT = − 4.8 × 10^− 5g cm^− 3° C^− 1.     

Extrusion properties of a Zr-based bulk metallic glass

The extrusion behavior of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at temperatures higher than 395 °C. The metallic glasses were fully extruded without crystallization and failure within the range of T = 395-415 °C under strain rates from 5 × 10^− 3 s^− 1 to 5 × 10^− 2 s^− 1, and the deformation behavior of the metallic glasses during the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0.     

Hot deformation behavior of an extruded Mg-Li-Zn-RE alloy

A new Mg-7.8%Li-4.6%Zn-0.96%Ce-0.85%Y-0.30%Zr alloy has been developed. α phase, β phase and RE-containing intermetallics formed in the alloy. It is found that the alloy can easily be extruded at 260 °C with σ_0.2 = 256 MPa, σ_b = 260 MPa and δ = 14%. Hot deformation behavior of the extruded alloy was studied using the processing map technique. Compression tests were conducted in the temperature range of 250-450 °C and strain rate range of 0.001-10 s⁻¹ and the flow stress data obtained from the tests were used to develop the processing map. The different efficiency domains and flow instability region corresponding to various microstructural characteristics have been identified as follows: (1) Domain I occurs in the temperature range of 250-275 °C and strain rate range of 1-10 s⁻¹, with a peak efficiency of about 50% at 250 °C/10 s⁻¹. Incomplete DRX process has occurred in β phase and DRX process hardly occurs in α phase; (2) Domain II occurs in the temperature range of 250-275 ?C and strain rate range of 0.001-0.003 s⁻¹, with a peak efficiency of about 42% at 250 °C/0.001 s ⁻¹. Incomplete DRX process has occurred in β phase and α phase; (3) Domain III occurs in the temperature range of 400-450 °C and strain rate range of 1-10 s⁻¹, with a peak efficiency of about 42% at 450 °C/10 s⁻¹. Complete DRX process has occurred in β phase and α phase. No cracking, cavity and band of flow localization are observed in flow instability region. The optimum parameters for hot working of the alloy are 250 °C/10 s⁻¹ and 250 °C/0.001 s⁻¹, at which fine dynamic recrystallization microstructure will be achieved. RE-containing intermetallics and α phase accelerate the DRX process in β phase. The softer β phase reduces the driving force for DRX process in α phase, so DRX process in α phase is retarded.     

Constitutive modeling for the dynamic recrystallization evolution of AZ80 magnesium alloy based on stress-strain data

In order to improve the understanding of the dynamic recrystallization (DRX) behaviors of as-cast AZ80 magnesium alloy, a series of isothermal upsetting experiments with height reduction 60% were performed at the temperatures of 523 K, 573 K, 623 K and 673 K, and the strain rates of 0.01 s⁻¹, 0.1 s⁻¹, 1 s⁻¹ and 10 s⁻¹ on a Gleeble 1500 thermo-mechanical simulator. Dependence of the flow stress on temperature and strain rate is described by means of the conventional hyperbolic sine equation. By regression analysis, the activation energy of DRX in the whole range of deformation temperature was determined to be Q = 215.82 kJ mol⁻¹. Based on dσ/d? versus σ curves and their processing results, the ?ow stress curves for AZ80 magnesium alloy were evaluated that they have some characteristic points including the critical strain for DRX initiation (?_c), the strain for peak stress (?_p), and the strain for maximum softening rate (?*), which means that the evolution of DRX can be expressed by the process variables. In order to characterize the evolution of DRX volume fraction, the modified Avrami type equation including ?_c and ?* as a function of the dimensionless parameter controlling the stored energy, Z/A, was evaluated and the effect of deformation conditions was described in detail. Finally, the theoretical prediction on the relationships between the DRX volume fractions and the deformation conditions were validated by the microstructure graphs.     

Stress–strain relationships of polycarbonate over a wide range of strain rate,including a shock wave regime

Stress–strain relationships of polycarbonate (PC) are determined over a very wide range of strain rates, including a shock wave regime. Plate impact tests, drop-weight tests, and quasi-static tests using universal and Instron testing machines are used for the high strain rate (10⁷ s⁻¹), medium strain rate (10² s⁻¹) and low strain rate (10⁻⁴ s⁻¹) tests, respectively. A newly modified unsteady wave sensing system (NM-UWSS) for plate impact tests is developed to determine the stress–strain relationships of PC. The system consists of a powder gun for plate impact tests, three embedded polyvenyliden fluoride (PVDF) gauges, and NM-UWSS. As originally proposed, UWSS is aimed at obtaining experimental inputs for the Lagrangian analysis used in determining the dynamic behavior of materials. We revise this standard system (UWSS) twice to gain a higher time resolution. In the past, the conventional charge mode (Q₂ method) was used. The first modified system (M-UWSS) has been used to study two classes of materials: (1) metallic materials and (2) polymeric materials, where the Q₁ method coupled with a transient differential equation for the equivalent circuit of the measurement circuit for the PVDF stress gauge was used. The latest method (Q_t method) for gaining the highest time resolution of shock wavefront structure by considering the effects of a piezofilm's thickness is proposed for PC at particle velocities of up to 1 km/s. Here we show from basic equations of piezoelectricity that the charge density q, i.e., the charge release per unit area, of the active electrode is proportional to the ratio of the thickness of the shocked region to the total thickness of the piezofilm. It is demonstrated that the rise time of shock charge density q in the piezofilm induced by such shock in the Q₂, Q₁ and Q_t methods, in this order, is becoming much shorter. The latest Q_t method has the highest accuracy among these three methods. Power law relations between stress and strain rate are observed again with PC under conditions of uniaxial strain over a very wide range of strain rates, i.e., 10⁻⁴–10⁷ s⁻¹ including a shock wave regime. For the PC, the effects of strain rate on the stress–strain relationships are estimated using empirical formula.     

Ambient effect on damping peak of NiTi shape memory alloy

We report the effects of ambient condition and loading rate on the damping capacity of a superelastic nickel-titanium shape memory alloy during stress-induced martensitic phase transformation with release and absorption of latent heat. The damping capacity was measured via a tensile loading-unloading cycle in the strain-rate range of 10^− 5-10^− 1/s and three ambient conditions: still air and flowing air with velocities of 2 m/s and 17 m/s. It is found that, for each ambient condition, the maximum damping capacity (damping peak) is achieved at the strain rate whose loading time (t_T) is close to the characteristic heat-transfer time (t_h) of the ambient condition.     

Ohmic contacts and n-type doping on TixCr2 − xO3 films and the temperature dependence of their transport properties

A procedure to dope n-type Cr_2 − xTi_xO₃ thin films is proposed. Besides doping the material, at the same time the method forms ohmic contacts on Ti_xCr_2 − xO₃ films. It consists on the deposition of 10 nm Ti and 50 nm Au, followed by thermal annealing at 1000 °C for 20 min in N₂ atmosphere. Ohmic contacts were formed on three samples with different composition: x = 0.17, 0.41 and 1.07 in a van der Pauw geometry for Hall effect measurements. These measurements are done between 35 K and 373 K. All samples showed n-type nature, with a charge carrier density (n) on the order of 10²⁰ cm^− 3, decreasing as x increased. As a function of temperature, n shows a minimum around 150 K, while the mobilities have an almost constant value of 11, 28 and 7 cm²V^− 1 s^− 1 for x = 0.17, 0.41 and 1.07, respectively.     

Low power CW optical limiting properties of bis(2-aminopyridinium)-succinate-succinic acid (2APS) single crystal

The increase in the usage of low power CW lasers in various applications needs for the design of optical limiters with low thresholds. The optical limiting properties and nonlinear refractive index (n₂ = −2.4189 × 10⁻⁸ cm²/W) of transparent organic crystal bis(2-aminopyridinium)-succinate-succinic acid (2APS) single crystal using continuous wave He-Ne laser excitation following Z-scan method have been evaluated. The sample exhibited negative (defocusing) nonlinearity. This thermally induced defocusing nature of 2APS crystal can be used to design the low power optical limiters. As the origin for this nonlinearity is thermal, a complete thermal transport properties such as thermal diffusivity (α_s = 5.97 ± 0.03 × 10⁻³ cm²/s), thermal effusivity (e_s = 1.94 ± 0.02 × 10⁻² J/cm²-K-s^1/2), thermal conductivity (k_s = (4. 66 ± 0.04) × 10⁻³ W/cm-K)) and specific heat capacity (C_ps = (5.61 ± 0.05) × 10⁻¹ J/g-K) of the material were studied following the photopyro electric (PPE) technique.     

Analysis of ductility of nanostructured copper prepared by powder metallurgy

The strain rate sensitivity (m) was determined as a function of the strain rate using mechanical jump tests, on a nanostructured copper (grain size of 90 nm) prepared by powder metallurgy. The largest value is m = 0.050 ± 0.005, measured at 1 × 10⁻⁵ s⁻¹. Apparent activation volume was derived giving an insight of the micromechanisms involved in the plastic deformation. Nanostructured face centred cubic metals exhibit elongation due to their strain rate sensitivity and the related delay in the localisation of the deformation. The present analysis brings elements of the micromechanism involved in the plasticity, providing with the guide to design a relevant ultra-fine grained architecture with improved ductility.     

Adsorption of single Ag and Cu atoms on regular and defective MgO(0 0 1) substrates: an ab initio study

The DFT slab calculations were performed for Ag and Cu atoms adsorbed on both regular and defective MgO(0 0 1) substrates. Both metal atoms and surface O vacancies (F_s centers) were distributed uniformly with a concentration of one Ag, Cu or F_s per 2×2 surface supercell. Surface O²⁻ ions are energetically more preferable for metal-atom adsorption on a regular substrate as compared to Mg²⁺ ions. The nature of the interaction between Ag or Cu adatoms and a defectless MgO substrate is physisorption (despite the difference in the adsorption energies: 0.62 vs. 0.39 eV per Cu and Ag adatom, respectively). Above the F_s centers, metal atoms are bounded much stronger when compared with regular O²⁻ sites (2.4  vs. 2.1 eV per Cu and Ag adatoms, respectively). This is accompanied by a substantial charge transfer towards each adatom (Δq_Cu=0.41e and Δq_Ag=0.32e) as well as a formation of partly covalent Me-F_s bonds across the interface (Mulliken bond populations p_Cu-Fs=0.25e and p_Ag-Fs=0.33e).     

Synthesis of three dimensional photoluminescent [In10S20 − xSex] supertetrahedral clusters: (x < 0.3)

Two strong solid state luminescence peaks, centered at 457 nm and 538 nm, were observed from the newly synthesized ternary [In₁₀S_20 − xSe_x]¹⁰⁻ T3 clusters, under excitation by UV radiation (λ = 360 nm). The 457 nm peak is due to the porosity property of T3 clusters. Nevertheless, the 538 nm peak has not been reported for the T3 clusters before. In this letter, we demonstrate that the 538 nm peak is attributed to the trace Se atoms confined in the [In₁₀S_20 − xSe_x]¹⁰⁻ clusters. The luminescent output from the ternary [In₁₀S_20 − xSe_x]¹⁰⁻ T3 clusters is independent of temperature from 298 K until 77 K.     

Deformation and strain rate sensitivity of a Zr-Cu-Fe-Al metallic glass

The deformation behaviour of Zr₆₅Cu₂₀Fe₅Al₁₀ bulk metallic glass has been studied at room temperature under uniaxial compression conditions at the strain rate of 5 × 10⁻⁴ s⁻¹ and performing jump tests for the strain rates (SR) ranging between 5 × 10⁻⁶ s⁻¹ and 5 × 10⁻² s⁻¹. The alloy always shows the formation of shear bands and exhibits serrated flow. In the SR range of 5 × 10⁻⁶ to 5 × 10⁻³ s⁻¹ absence of strain rate sensitivity within the experimental error is observed. However, when the SR changes from 5 × 10⁻³ s⁻¹ to 5 × 10⁻² s⁻¹ the alloy exhibits a negative strain rate sensitivity of −0.0026. The number of shear bands on the side view appears to be correlated with the range of stress softening from the maximum stress to the stress at which the sample fails.     

Crystal structure, thermal expansion and electrical properties of a new compound Al0.33DyGe2

A new ternary compound Al_0.33DyGe₂ has been synthesized and studied from 298 K to773 K by means of X-ray powder diffraction technique. The crystal structural refinement of Al_0.33DyGe₂ has been performed by using the Rietveld method. The ternary compound Al_0.33DyGe₂ crystallizes in the orthorhombic of the defect CeNiSi₂-type structure (space group Cmcm, a = 0.41018(2)nm, b = 1.62323(6)nm, c = 0.39463(1)nm, Z = 4 and D_calc = 8.004 g/cm³). The average thermal expansion coefficients α_a, α_b and α_c of Al_0.33DyGe₂ are 1.96 × 10^− 5 K^− 1, 0.93 × 10^− 5 K^− 1 and 1.42 × 10^− 5 K^− 1, respectively. The bulk thermal expansion coefficient α_V is 4.31 × 10^− 5 K^− 1. The resistivity is observed to fall from 387 to 308 µΩ cm between room temperature and 25 K.     

Giant magnetostriction in magnetite nanoparticles

Typically the value of the magnetostrictive coefficient (λ) observed for bulk magnetic materials such as cubic ferrites is 10⁻⁶. However, giant magnetostriction (λ ≤ 10⁻³) is only observed in a few bulk intermetallic materials based on alloys of rare earth and iron such as TbFe, TbFe₂, DyFe₂ and Terefenol-D. While giant magnetostriction is known in nanostructured films, we show for the first time, this phenomenon occurs in magnetic nanoparticles. By using in-field small angle X-ray scattering (SAXS) as a tool, we demonstrate that a 4% relative change in dimension of the particle can be observed in 5.0 nm Fe₃O₄ nanoparticles at room temperature with 1 kG magnetic field. Also, we propose that the observed values are due to interaction effects and magnetoelastic coupling of particle magnetic moments and external magnetic field.     

Experiments on high excitation density, quenching, and radiative kinetics in CsI:Tl scintillator

Information on quenching as a function of electron-hole density through the range of 10¹⁹ to 2×10²⁰ e-h/cm³ typically deposited towards the end of an electron track has been acquired using 0.5 ps pulses of 5.9 eV light to excite in the band-to-band or high-exciton region of CsI and CsI:Tl. A streak camera records partially quenched luminescence from self-trapped excitons (STE) and excited activators (Tl^+?). Both the Tl^+? and STE luminescence exhibit decreasing light yield versus excitation density N_max, but it is only the 302 nm STE luminescence that exhibits decay time quenching dependent on N_max. Fitting the STE decay time data to a model of dipole-dipole quenching yields the time-dependent bimolecular rate constant for quenching of STEs (and Tl^+? light yield) in CsI at room temperature: k₂(t)=2.4×10⁻¹⁵ cm³ s^−1/2 (t^−1/2).     

Fabrication and properties of titanium–hydroxyapatite nanocomposites

Titanium–hydroxyapatite nanocomposites with different HA contents (3, 10, 20 vol%) were produced by the combination of mechanical alloying (MA) and powder metallurgical process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vickers microhardness as high as 1030 and 1500 HV_0.2, which is more than 4–6 times higher than that of a conventional microcrystalline titanium. Titanium nanocomposite with 10 vol% of HA was more corrosion resistant (i_C = 1.19 × 10⁻⁷ A cm⁻², E_C = −0.41 V vs. SCE) than microcrystalline titanium (i_C = 1.31 × 10⁻⁵ A cm⁻², E_C = −0.36 V vs. SCE). Additionally, the electrochemical treatment in phosphoric acid electrolyte results in porous surface, attractive for tissue fixing and growth. Mechanical alloying and powder metallurgy process for the fabrication of titanium–ceramic nanocomposites with a unique microstructure are developed.     

A study on stress affecting the microwave surface resistance of YBCO high temperature superconducting thin films

We calculate stress in YBa₂Cu₃O_7−x/MgO (YBCO/MgO) and YBa₂Cu₃O_7−x/LaAlO₃ (YBCO/LAO) by XRD of the sample, σ₁ = −1.2 GPa and σ₂ = −1.4 GPa, respectively, which shows that the stress in YBCO/LAO is stronger than that in YBCO/MgO. In addition, microwave response of the two pieces of thin films is also investigated by microstrip resonator technique. Surface resistance and penetration depth of the films are obtained by analyzing S₂₁ resonant curves of the microstrip resonator, the penetration depth λ₀ = 280 nm for YBCO/MgO and λ₀ = 265 nm for YBCO/LAO, and surface resistance R_s = 0.376 mΩ for YBCO/MgO and R_s = 2.660 mΩ for YBCO/LAO at 78 K, 10 GHz. The results show stronger stress in YBCO/LAO which lead to a larger microwave surface resistance than YBCO/MgO's. Some rational explanations are also analyzed and discussed in the paper.