Strain Effect on the Electrical and Magnetic Properties of La<Subscript>0.7</Subscript>Ba<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> Thin Films Grown by Metal-Organic Deposition

La_0.7Ba_0.3MnO₃ thin films have been epitaxially grown by metal-organic deposition on SrTiO₃ (STO) and LaAlO₃ (LAO) single-crystal substrates. Temperature dependence of magnetization M(T) and resistivity ρ(T) are used to characterize the Curie temperature (T _C) of the ferromagnetic transition. T _C is found to be extremely sensitive to the biaxial strain and film thickness. The T _C increases gradually by increasing the film thickness on both STO and LAO substrates, but does not reach the value of the bulk material. This behavior is interpreted in terms of lattice strain in the films and correlated to the microstructural properties.     

Strain-Induced First-Order Magnetic Phase Transition in Epitaxial Sm<Subscript>0.35</Subscript>Pr<Subscript>0.15</Subscript>Sr<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> Thin Film

Epitaxial Sm_0.35Pr_0.15Sr_0.5MnO₃ thin films were deposited on LaAlO₃ (LAO, (001)), SrTiO₃ (STO, (001)), and (La_0.18Sr_0.82)(Al_0.59Ta_0.41)O₃ (LSAT, (001)) single-crystalline substrates by using pulsed laser deposition technique. In order to examine the strain effect on electronic and magnetic properties, films were studied by X-ray diffraction, electrical resistivity, and dc magnetization measurements. The film grown on LAO substrate is under compressive strain, and it undergoes ferromagnetic → paramagnetic transition at Curie temperature (T _C) of ～ 165 K and metal → insulator transition at ～ 107 K. The films grown on STO and LSAT substrates are under tensile strain and have T _C of ～ 120 and 130 K, respectively, and show metal → insulator transition at ～ 145 and 137 K, respectively. At T < T _C, the zerofield and fieldcooled magnetization curves of all the films show a huge bifurcation. In the case of films on STO and LSAT substrates, hysteresis is also observed in fieldcooled cooling and warming magnetization vs. temperature measurement protocols at low magnetic field. All the signatures of the firstorder magnetic phase transition are absent in the case of film on LAO substrate. The occurrence and absence of firstorder magnetic phase transition in films on LAO, STO, and LSAT substrates, respectively, have been well explained through the substrateinduced film lattice strain.     

Spectroscopic study of Co-doped BaTiO3 thin films

Co-doped BaTiO₃ thin films with the perovskite structure were prepared by pyrolysis of metalorganic compounds. According to optical-absorption and luminescence data, the introduction of Co had an insignificant effect on the Curie temperatureT _C of the films (about 120δC), presumably because of the competitive effects of the Co dopant, reducingT _C , and the large compressive strain due to the thermal expansion mismatch, raisingT _C . An absorption band tentatively attributed to a small-radius polaron was observed in the near-infrared spectral region.     

The effect of strain on nonlinear temperature dependence of resistivity in SrMoO3 and SrMoO3−xNx films

Highly oriented SrMoO₃ thin films have been fabricated by pulsed laser deposition of SrMoO₄ in hydrogen. The films are found to grow along the (1 0 0) direction on LaAlO₃ (1 0 0) and SrTiO₃ (1 0 0) substrates. The method has been extended for the fabrication of oxynitride thin films, using ammonia as the reducing medium. The resistivity measurements show nonlinear temperature dependent (Tⁿ) behaviour in the temperature interval of 10-300 K. The conduction mechanism is largely affected by the strain due to the substrate lattice. A combination of T and T² dependence of resistivity on temperature is observed for films having lesser lattice mismatch with the substrate. The X-ray photoelectron spectroscopic studies confirm the formation of SrMoO₃ and SrMoO_3−xN_x films.     

Epitaxial growth and interface strain coupling effects in manganite film/piezoelectric-crystal multiferroic heterostructures

We constructed multiferroic structures by epitaxially growing colossal magnetoresistive La_0.7Sr_0.3MnO₃ (LSMO) thin films on piezoelectric single-crystal substrates of composition 0.67Pb(Mg_1/3Nb_2/3)O₃–0.33PbTiO₃ (PMN-PT). Due to the efficient elastic coupling at the interface, the electric-field-induced piezoelectric strain (?_piezo) in the PMN-PT substrate is effectively transferred to the LSMO film, giving rise to a remarkable modulation of the lattice strain, resistivity, and Curie temperature T_C of the LSMO film. Particularly, it was found that the magnetic field has an opposite effect on the strain-tunability of resistivity above and below T_C. Moreover, we found that the resistivity of the film is most sensitive to ?_piezo near T_C and becomes less sensitive to ?_piezo when the temperature is lower or higher than T_C. These, together with the well fitted resistivity data into a phenomenological model based on coexisting phases, demonstrate that the phase separation is crucial to understand the strain-mediated multiferroic properties in manganite film/PMN-PT structures.     

Competition Between the Superfluid Overlayer and the Mobile Solid Layer of 3He-4He Mixture Films on Porous Gold

In the previous quartz crystal microbalance measurements for ⁴He films adsorbed on porous gold, we have observed a competition between superfluidity and slippage: In low areal densities, the resonance frequency increases gradually below T _S due to the slippage of solid layer, while at high areal densities the slippage disappears and the superfluid onset of liquid overlayer is observed at T _C . In the crossover region, the slippage below T _S is suddenly suppressed at T _D , which is much lower than T _C . In the present work, we introduced a small amount of ³He onto ⁴He films, and studied the competition as a function of ³He areal density ρ ₃. As ρ ₃ is increased, T _C is monotonically lowered. In contrast, T _D increases up to a certain value of ρ ₃, and then turns over to decrease in parallel to T _C .     

Bandgap modifications by lattice deformations in β-FeSi2 epitaxial films

The modifications of direct transition energies by lattice deformations were investigated in β-FeSi₂ epitaxial films, polycrystal films and single crystal, systematically. The lattice deformations depending on thermal annealing temperature (T_a) were observed in β-FeSi₂ epitaxial films. In photoreflectance (PR) measurements, the direct transition energies of the epitaxial films shifted to lower energies as the T_a increased. The polycrystal films did not show the lattice deformation and the shift of direct transition energies. These results show that the direct bandgap is modified by the lattice deformation originating from the lattice mismatch at the hetero-interface of β-FeSi₂/Si.     

Lattice instability in the normal state of La2?xSrxCuO4

Novel softening has been found in the transverse elastic constant (C ₁₁–C ₁₂)/2 below 50 K in single-crystalline La_1.86Sr_0.14CuO₄ (LSCO) by high-precision ultrasonic measurements in magnetic fieldsH along thec axis. With decreasing temperature, this lattice softening persists down to the superconducting transition temperatureT _c(H), which is reduced to 14 K by applying fields up to 14 T. BelowT _c(H) the softening turns to rapid hardening. This behavior indicates the presence of lattice instability of the orthorhombic (Bmab) structure in the normal state of LSCO, which disappears in the superconducting state. This is evidence for the intimate interplay between high-T _c superconductivity and the lattice instability in LSCO.     

Lattice instability in the normal state of La2−x Sr x CuO4

Novel softening has been found in the transverse elastic constant (C ₁₁–C ₁₂)/2 below 50 K in single-crystalline La_1.86Sr_0.14CuO₄ (LSCO) by high-precision ultrasonic measurements in magnetic fieldsH along thec axis. With decreasing temperature, this lattice softening persists down to the superconducting transition temperatureT _c(H), which is reduced to 14 K by applying fields up to 14 T. BelowT _c(H) the softening turns to rapid hardening. This behavior indicates the presence of lattice instability of the orthorhombic (Bmab) structure in the normal state of LSCO, which disappears in the superconducting state. This is evidence for the intimate interplay between high-T _c superconductivity and the lattice instability in LSCO.     

Magnetic and transport polaron percolation in diluted GeMn films

Magnetic and electronic transport properties of Mn-doped Ge films have been studied as a function of Mn content. The films exhibit a long-range ferromagnetic behavior and a Mn dilution-dependent Curie temperature T_C. Resistivity shows an insulator-like character with two distinct activation energies below about 80 K, while the Hall coefficient evidences a strong contribution from the anomalous Hall effect, in a p-type material. At a characteristic temperature T_R, resistivity experiences a sudden reduction and the Hall coefficient reverses its sign from positive to negative. Moreover, around T_R, any residual remanence and coercivity disappear.The transport and magnetic results are deeply related and can be qualitatively explained by a percolation model based on bound magnetic polarons due to localized holes in the GeMn alloy lattice.     

Annealing effect on the characteristics of La0.67Sr0.33MnO3 polycrystalline thin films produced by the sol–gel dip-coating process

The effect of annealing temperature on selected characteristics of polycrystalline La_0.67Sr_0.33MnO₃ films, which have been produced on quartz substrates, was investigated. X-Ray powder diffraction patterns showed that the phase formation started at 873 K and all the films had perovskite structure. By increasing the annealing temperature, the lattice parameters were decreased. Scanning electron microscope indicated that the film thicknesses were approximately 3 μm and the average grain size of the samples varied between 30–100, 50–110, 70–120, and 100–150 nm for films annealed at 873, 973, 1,073, and 1,173 K, respectively. All the films showed a paramagnetic–ferromagnetic (T_C) and metal–insulator (T_IM) phase transition. The T_C indicated a small variation [from 131 K (S4) to 124 K (S1)] as a function of annealing temperature, whereas the T_IM went down from 212 K (S4) to 110 K (S1), a strong decrease of 102 K. A colossal magneto resistance with magneto resistance ratios of 130, 139, 156, and 163% were observed near T_C and at 6 T magnetic field.     

Strain effects and phase separation tendency in highly strained La0.7Ba0.3MnO3 thin films on LaAlO3 substrates

The magnetic and transport properties of epitaxial La_0.7Ba_0.3MnO₃ films on LaAlO₃ substrates have been investigated and compared with those on SrTiO₃ substrates. It is found that the ferromagnetic and metallic transition temperature of the highly compressive strained films on LaAlO₃ substrates decreases steadily with decreasing film thickness, while it changes little in the lightly strained films on SrTiO₃ substrates. The properties of the films on LaAlO₃ substrates are more sensitive to a post-annealing procedure. A tendency to phase separation, which induces a difference between the insulator-metal transition temperature T_MI and the Curie temperature T_C, is observed for the films with a medium oxygen annealing process. We argue that the phase separation is due to both the highly compressive strain and oxygen deficiency in the films.     

Local lattice anomalies in underdoped YBa2Cu3O7-Σ probed by X-ray absorption fine structure

Temperature-dependent local lattice anomalies in underdoped YBa₂Cu₃O_7-Σ are studied by extended X-ray absorption fine structure (EXAFS) in a fluorescence mode. The in-plane polarized Cu A^-EXAFS is measured on underdoped epitaxial YBa₂Cu₃O_7-Σ films (100-120 nm) prepared onto SrTiO₃ substrates using a pulsed laser ablation technique. The Fourier transform (FT) results for a sample withT _c = 55K (△T = 4K) shows an in-plane lattice anomaly atT* = 83 K (~ 1.5T _c ) below which the in-plane oxygen distribution consists of the two Cu-O peaks separated by 0.2-0.3 A. The contribution of the elongated Cu-O bond increases on loweringT, indicating either the in-plane rhombic distortion of the square-planar CuO₄ or the tilting of the CuO₅ pyramid. Contrary to the anomalies in spin susceptibility and transport measurements indicating the presence of a spin gap, the onset temperature of the in-plane lattice anomaly (T*) shifts to the lowerT _c on decreasing the carrier density. The results suggest that the in-plane local lattice anomaly is anextrinsic lattice effect which is not directly related to the spin-phonon interaction.     

Thickness dependent transport and magnetotransport in CSD grown La0.7Pb0.3MnO3 manganite films

We report the effect of film thickness on transport and magnetotransport in La_0.7Pb_0.3MnO₃ (LPMO) manganite films grown on single crystalline LaAlO₃ substrate using chemical solution deposition (CSD) technique. AFM measurements show the island type grain growth responsible for the strain at the film-substrate interface, while structural studies using XRD shows the presence of thickness dependent compressive strain in the films which modifies the transport and magnetotransport in LPMO/LAO films. The observation of low temperature resistivity minima behavior in all the LPMO films has been explained in the context of electron-electron scattering mechanism. The ZFC-FC magnetization measurements show the glassy state behavior below T_min.     

Growth and characterization of La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on different substrates

Colossal magnetoresistance La_5/8Sr_3/8MnO₃ (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was ?17.21 % for LSMO/MgO film followed by ?15.65 % for LSMO/Si and ?14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (T_P) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (T_C) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. T_C such as 363 and 352 K are the high T_C that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature.     

Specific heat of quench-condensed hydrogen films

The specific heatC(X, T) of quench-condensed films of H₂ has been measured as a function of ortho concentration X with 0.28–2 at temperatures between 0.4 and 3.0 K. The films were condensed on evaporated gold substrates held at several temperaturesT. _cond between 1.0 and 3.5 K. The observed specific heat is attributed to orientational ordering of the ortho-H₂ molecules. For the films withX = 0.74 condensed atT _cond>2.5 K, there is a peak which indicates a bulk-like ordering transition. At temperatures below the peak, there is a large contribution toC, which is not present in bulk H₂, and which we attribute to short-range ordering size effects. AsT _cond is decreased below 2.5 K, the shape of the specific heat curve changes, and the peak at 1.5 K is replaced by a gradual rise with a sharp drop above 2.6 K. Despite this strong dependence ofC onT _cond, the entropy per molecule at 3 K is only weakly dependent onT _cond and comparable to that for bulk H₂. Film annealing at 3.4 K produces a change in the specific heat curve, and a study of this effect is presented. The ortho-para conversion rate of the films condensed at the various temperatures is found to be same as in bulk, well-annealed H₂. As in bulk H₂, the transition temperature inferred from the location of the specific heat peak or anomaly decreases withX. Unlike in bulk H₂, there is no temperature hysteresis inC for any of the quench-condensed films. This implies that the ordering transitions are not accompanied by a martensitic transformation.     

Triple-Point Wetting of Molecular Hydrogen on Tailored Substrates

Triple-point wetting is a well-known phenomenon of many simple adsorbates on solid substrates. It implies that in the liquid phase above the triple-point temperature, T₃, complete wetting with the formation of arbitrarily thick films is observed, whereas below T₃ only a few monolayers of the solid phase are adsorbed at saturated vapour pressure. This effect is usually ascribed to substrate-induced strain in the solid film, which occurs due to lattice mismatch and/or the strong van der Waals pressure in the first monolayers. Molecular hydrogen is a suitable system to investigate this phenomenon, in particular by tailoring the adsorbate-substrate interaction by means of thin preplating layers of other adsorbates, and by introducing disorder into the system by using not only the pure systems H₂ and D₂, but also mixtures thereof. In particular the dependence of T₃ of the mixture on the mass ratio of its components is measured and deviations from the simple van der Waals law are discussed. The experiments show that triple-point wetting is a rather dominating effect, which in contrast to expectation persists even if the system parameters are widely varied, indicating that the present picture of this effect is incomplete.     

Selection and change in deformation mode to maintain continuity of strains and slip/twinning planes at lamellar boundaries in fatigued TiAl polysynthetically twinned crystals

Change in deformation mode in six types of γ domain (A_M–C_T) and α₂ plates in TiAl polysynthetically twinned (PST) crystals fatigued at a loading axis parallel to lamellar planes with stress amplitude (Δσ) of 420–450 MPa was examined by the transmission electron microscope focusing on continuity of macroscopic strains and slip/twinning planes at lamellar boundaries. At Δσ = 420 and 450 MPa, the strain continuity is always maintained at lamellar boundaries by activation of one of the symmetric twinning systems in A-type domain and selection of the dominant deformation mode between ordinary dislocations and twins in (B and C)-type γ domain. The (B and C)-type γ domains of B_M,B_T,C_M and C_T behave as two sets of (B_M,C_T) and (B_T,C_M) because each set selects either the deformation mode of ordinary dislocations or twins as a dominant system in order to keep macroscopic strain continuity. The set (B_T,C_M) which accounts for a larger volume fraction than the set (B_M,C_T) in TiAl-PST crystals used in this study selected a twinning system at Δσ = 450 MPa, while ordinary dislocations were selected at Δσ = 420 MPa. At Δσ = 450 MPa, twinning deformation prevented the further motion of ordinary dislocations with a Burgers vector parallel to lamellar boundaries, and rapid fatigue hardening occurred accompanied by reduction of the accumulative plastic strain energy. Anomalous change in strain energy during fatigue is infiuenced by the volume fraction of a set of (B and C)-type domain and the anomalous behavior in fatigued TiAl-PST crystals may disappear when each type of γ domain is equally distributed.     

Transparent,Flexible, and Conductive 2D Titanium Carbide (MXene) Films with High Volumetric Capacitance

2D transition‐metal carbides and nitrides, known as MXenes, have displayed promising properties in numerous applications, such as energy storage, electromagnetic interference shielding, and catalysis. Titanium carbide MXene (Ti₃C₂T_x ), in particular, has shown significant energy‐storage capability. However, previously, only micrometer‐thick, nontransparent films were studied. Here, highly transparent and conductive Ti₃C₂T_x films and their application as transparent, solid‐state supercapacitors are reported. Transparent films are fabricated via spin‐casting of Ti₃C₂T_x nanosheet colloidal solutions, followed by vacuum annealing at 200 °C. Films with transmittance of 93% (≈4 nm) and 29% (≈88 nm) demonstrate DC conductivity of ≈5736 and ≈9880 S cm^?1, respectively. Such highly transparent, conductive Ti₃C₂T_x films display impressive volumetric capacitance (676 F cm^?3) combined with fast response. Transparent solid‐state, asymmetric supercapacitors (72% transmittance) based on Ti₃C₂T_x and single‐walled carbon nanotube (SWCNT) films are also fabricated. These electrodes exhibit high capacitance (1.6 mF cm^?2) and energy density (0.05 µW h cm^?2), and long lifetime (no capacitance decay over 20 000 cycles), exceeding that of graphene or SWCNT‐based transparent supercapacitor devices. Collectively, the Ti₃C₂T_x films are among the state‐of‐the‐art for future transparent, conductive, capacitive electrodes, and translate into technologically viable devices for next‐generation wearable, portable electronics.     

Comparison of Flux Pinning Mechanism in Laser Ablated YBCO and YBCO:BaZrO3 Nanocomposite Thin Films

Thin films of YBCO and YBCO:BaZrO₃ (BZO) nanocomposite have been deposited using the pulsed laser deposition technique. Substantial increase in critical current density (J _C ) and pinning force density (F _p ) of the nanocomposite thin films was observed. The possible pinning mechanism in YBCO:BZO nanocomposite thin films has been explored and compared with the pinning mechanism in pure YBCO thin film by studying the variation of J _C with magnetic field (B) and temperature. In the intermediate field regime (0.1–1 T), J _C follows B ^−α with nearly similar values of α for YBCO and YBCO:BZO nanocomposite thin films indicating similar pinning mechanism in both thin films. The variation of J _C with reduced temperature (t=T/T _C ) has been studied for both the films and it was observed that the mechanism of pinning in both YBCO and YBCO:BZO thin films is similar (δT _C pinning). The observed enhanced values of J _C and F _p of the nanocomposite thin film is attributed to the presence of BZO nanoparticles, which induces more defects due to lattice mismatch between YBCO and BZO leading to improved flux pinning properties of the nanocomposite thin film.