Pb Thin Films Research Articles

Vortex microavalanches in superconducting Pb thin films

Local magnetization measurements on 100 nm type-II superconducting Pb thin films show that flux penetration changes qualitatively with temperature. Small flux jumps at the lowest temperatures gradually increase in size, then disappear near T = 0.7Tc. Comparison with other experiments suggests that the avalanches correspond to dendritic flux protrusions. Reproducibility of the first flux jumps in a decreasing magnetic field indicates a role for defect structure in determining avalanches. We also find a temperature-independent final magnetization after flux jumps, analogous to the angle of repose of a sandpile.

Guided vortex motion in superconductors with a square antidot array

We have measured the in-plane anisotropy of the vortex mobility in a thin Pb film with a square array of antidots. The Lorentz force, acting on the vortices, was rotated by adding two perpendicular currents and keeping the amplitude of the net current constant. One set of voltage probes was used to detect the vortex motion. We show that the pinning landscape provided by the square antidot lattice influences the vortex motion in two different ways. First, the modulus of the vortex velocity becomes angular dependent with a lower mobility along the diagonals of the pinning array. Second, the vortex displacement is preferentially parallel to the principal axes of the underlying pinning lattice, giving rise to a misalignment between the vortex velocity and the applied Lorentz force. We show that this anisotropic vortex motion is temperature dependent and progressively fades out when approaching the normal state.

Impact of microstructure on dielectric properties of Pb(Mg 1/3Nb 2/3)O 3–PbTiO 3 thin films

Relaxor thin films of Pb(Mg 1/3Nb 2/3)O 3–PbTiO 3 (PMN–PT) with different microstructures have been grown on platinum-coated silicon substrate using pulsed excimer laser ablation technique. The microstructure of the thin films was found to be strongly influenced by the substrate temperature and the substrate microstructure. An intermediate layer of La 0.5Sr 0.5CoO 3 (LSCO) was deposited on the platinum-coated silicon substrate prior to the deposition of the (PMN–PT) thin films. We found that the both the microstructure and perovskite phase in the PMN–PT thin films could be controlled by monitoring the substrate temperature along with the microstructure of the template layer. The dielectric properties of the films with different microstructure were studied as a function frequency over a wide range of temperatures. A direct impact of the microstructure on relaxor properties has been observed in the present case.

Microstructural investigation of the PZT films prepared from the suspension of nanocrystalline powders

PZT thin films of composition Pb(Zr 0.52Ti 0.48)O 3 were prepared by a novel method from the suspension of nanocrystalline PZT powders. The powders were obtained by mechanochemical synthesis. Films were deposited on silicon (1 0 0) and platinum covered silicon substrates (Pt (1 1 1) /Ti/SiO 2/Si) using spin-on technique. Substrate type has influence on films crystallinity, orientation and can react with the films changing its phase composition. Films microstructure strongly depends on thermal treatment conditions due to phase and compositional changes of the films.

The Influence of Various Upper Electrodes on Fatigue Properties of Perovskite Pb(Zr,Ti)O3 Thin Films

Ferroelectric thin films of Pb(Zr,Ti)O3 (PZT) were prepared by chemical solution deposition (CSD). The top electrodes of platinum (Pt), SrRuO3 (SRO), and IrO2 thin films are deposited on the PZT thin films by RF magnetron sputtering (RF) and the pulsed laser deposition (PLD) methods, respectively. The polarization fatigue of ferroelectric thin-film capacitors is investigated. As a result, the remanent polarization value of the PZT thin films of SRO/PZT/PT/Pt/TiOx/SiO2/Si and IrO2/PZT/PT/Pt/TiOx/SiO2/Si remains more than 1011 switching cycles at constant value and the value of the PZT thin films of Pt/PZT/PT/Pt/TiOx/SiO2/Si decreases to approximately 50% of its initial value at 108 cycles. It is confirmed that polarization fatigue is improved using SRO and IrO2 thin-film electrodes as top electrodes.

Vortex avalanches in a Pb film with a square antidot array

We have performed magnetization measurements on a Pb thin film perforated by a square array of antidots in a broad temperature range. For temperatures below 6 K, we observe magnetization jumps at low fields. In the film with the antidot lattice, the region in the field-temperature plane, where the jumps are observed, is substantially enlarged but the relative jump size is smaller compared to a reference film without any nanostructuring. Also, the width of the magnetization loops for the perforated film is much smaller than that for the plain film at very low temperatures. These results can be understood by taking into account the existence of a multiterrace critical state induced by the antidot array. The size distributions of the magnetization jumps do not follow the power-law decay expected in the case of self-organized criticality.

Effect of laser fluence on the ferroelectric properties of pulsed laser deposited (Pb 1− xLa x)Ti 1− x/4 O 3 thin films

Dielectric thin films of (Pb 0.72La 0.28)Ti 0.93O 3 (PLT) have been deposited on Pt/Ti/SiO 2/Si substrates in situ by laser ablation. We have systematically investigated the effect of laser energy density on the ferroelectric properties of PLT thin films and the variation of grain sizes depending on the process conditions of a single-step deposition process and a two-step deposition process. Two-step deposition process was verified to be useful to enlarge the grain size of the film and to reduce the leakage current characteristics. PLT thin films on p-type (1 0 0) Si substrate were fabricated by pulsed laser deposition technique using a Nd:YAG laser with different energy densities of 1.5, 2.5 and 3.5 J/cm 2. The average grain sizes of the PLT thin films were successfully controlled from 80 to 130 nm by changing processing parameters. Structural properties and electrical properties including dielectric constant, ferroelectric characteristics and leakage current of PLT thin films were shown to be strongly influenced by grain size and laser energy density.

Clustering in Pb thin films on bromine-passivated Si(1 1 1) surfaces

Thin Pb films, deposited on clean Si surfaces at room temperature (RT), show spectral broadening in ion backscattering spectra due to clustering of Pb, when annealed [Nucl. Instr. and Meth. B 190 (2002) 641]. In order to study the dynamics of clustering on bromine-passivated Si(1 1 1) substrates, Pb thin films (∼1–3 nm) were deposited from a Knudsen cell under ultrahigh vacuum conditions. Each film was deposited at RT and subsequently annealed at 100, 150 and 260 °C for about 4 h. Five Rutherford backscattering spectrometry (RBS) measurements were made at different time intervals for each annealing . Analysis of RBS spectra of as-deposited and annealed Pb films, does not show any significant spectral broadening in annealed Pb films. However, island formation has been confirmed by transmission electron microscopy on a 100 °C-annealed sample. Clustering has apparently occurred in the as-deposited film due to lower surface free energy of the passivated substrate and further detectable growth in cluster height has not occurred in annealing.

Structural, dielectric and pyroelectric studies of Pb 1− XCa XTiO 3 thin films

Thin films of Pb 1− x Ca x TiO 3 [ x=0.20, 0.24 and 0.28] have been prepared on ITO coated Corning glass substrates by sol gel technique. The perovskite phase of PCT films is formed at 650 °C with a polycrystalline tetragonal structure. The tetragonal factor ( c/ a) decreases with increasing Ca concentration. Dielectric, pyroelectric and ferroelectric studies have been carried out on these films. The effects of introduction of Ca ion in PbTiO 3 have also been discussed.

Image-potential resonances studied by selective electron scattering in thin Pb(1 1 1) films and clusters on Ge( [formula omitted

Image-potential resonance related peaks are observed in HREEL spectra by so-called selective electron scattering at the reciprocal lattice vector of a thin Pb(1 1 1) film. Upon a variation of the scattering conditions the spectral features change according to the electron scattering process and the effective masses, i.e. dispersion, of different orders are obtained. Image-potential resonances on the continuous film at 120 K and on lead islands at 300 K are equivalent. Electron scattering processes in the thin lead film can be distinguished from those in the substrate. In this way, the Stranski–Krastanov growth mode at room temperature is confirmed by separate electron scattering events on surface regions with different reciprocal lattice vectors. The appearance of an additional peak might be due to the presence of domain walls on the surface.

Characterization of sol-gel synthesized lead calcium titanate (PCT) thin films for pyro-sensors

Thin films of Pb 0.80Ca 0.20TiO 3 and Pb 0.76Ca 0.24TiO 3 are prepared using the sol-gel technique on ITO coated corning 7059 glass. X-ray diffraction studies on these films show perovskite structure with tetragonal phase. Dielectric, pyroelectric and ferroelectric studies are carried out on these films. Results suggest that PCT76/24 with pyrocoefficient (∼43 nC cm −2 K −1) and voltage responsivity (∼2340 V cm −2 J −1) is a promising pyrosensor material.

Field-dependent vortex pinning strength in a periodic array of antidots

We explore the dynamic response of vortex lines in a Pb thin film with a periodic array of antidots by means of ac-susceptibility measurements. For low drive field amplitudes, within the Campbell regime, vortex motion is of intra-valley type and the penetration depth is related to the curvature of the pinning potential well, $\alpha$. For dc-fields below the first matching field $H_1$, $\alpha$ reaches its highest value associated with a Mott Insulator-like phase where vortex lines are strongly localized at the pinning sites. For $H_1<H_{dc}<H_2$, the response is mainly due to the interstitial vortices and $\alpha$ drops to smaller values as expected for this metallic-like regime. Strikingly, for $H_2<H_{dc}<H_3$, we observe that $\alpha$ reduces further down. However, for $H_3<H_{dc}<H_4$, a reentrance in the pinning strength is observed, due to a specific configuration of the flux line lattice which strongly restricts the mobility of vortices. We present a possible explanation for the measured $\alpha(H_{dc})$ dependence based on the different flux line lattice configurations.

Persistence exponents for step edge diffusion

Time dependent STM was used to observe step fluctuations on Pb(1 1 1) and Ag(1 1 1) thin films just above room temperature. The previously reported step edge diffusion limited fluctuation kinetics was verified by measuring temporal correlation functions. The persistence probability for the step fluctuations was computed from the same data and found to agree with a numerical prediction of 7/8 for a solid-on-solid model of the edge diffusion process.

Electron Beam Induced Degradation of CaS:Pb Thin Film Phosphor Grown by Atomic Layer Deposition

The effects of electron (e)-beam irradiation on the luminescent and the materials properties of CaS:Pb films were investigated using structural and compositional analysis techniques. Continuous e-beam irradiation on CaS:Pb thin film for 180 min resulted in an approximately 60% decrease of cathodoluminescence (CL) intensity. Transmission electron microscopic analysis indicated that e-beam irradiation induced the precipitation of Pb. The decrease of CL intensity by e-beam irradiation was mostly caused by the decrease of Pb 2 + luminescent center ion concentration due to the precipitation of Pb. E-beam irradiation also resulted in heavy carbonaceous contamination on the surface. The thickness of the carbonaceous layer was approximately 10 nm.

High Pressure Deposition of Epitaxial PZT Thin Films on Sr(Nb)TiO3

ABSTRACTEpitaxial thin ferroelectric films of Pb(Zr0.53Ti0.47) (PZT) were successfully grown on Sr(Nb)TiO3(SNTO) single crystal substrates by high-pressure rf sputtering. Pure O2was used as working gas at a pressure above 1 Torr. Deposition temperature was varied from 550°C to 600°C. Under these conditions we were able to deposit films at a rate of 2.7 Å/min. Their crystalline properties, evaluated by Θ/2Θ, ω and φ scans, showed both in-plane and out of plane orientation. Film composition and film-substrate interface characteristics were studied by Rutherford Backscattering Spectroscopy (RBS). For RBS data the composition ratios for the films were calculated having obtained the expected values for a stoichiometric composition. A very thin diffusion layer of Pb at the film-substrate interface was also introduced. However, the deficiency in Pb, which is correlated to the presence of oxygen vacancies, is lower in our films produced at high O2 pressure than those reported for films produced by sputtering at lower pressures. The ferroelectric hysteresis loops measured in the Pt/PZT/SNTO heterostructures show good ferroelectric behavior with remanent polarizations of 12μ Ccm-2and coercive field of 50kVcm-1at 5V. The high-pressured technique representing a useful and capable method capable of obtainingin situepitaxial, fully oxygenated, pyrochlore-free ferroelectric thin film with high quality structural, compositional and dielectric properties, without post deposit treatment.

Ceramics and Thin Films of Some New Pb(B 3+ ,Nb)TiO 3 -PbTiO 3 Systems

The structure, dielectric, and electromechanical properties of (1 m x )Pb(B 3+ ,Nb)TiO 3 - x PbTiO 3 binary systems (B = Lu, Er, Tb, Ho) are reported. The crystallographic features at the morphotropic phase boundary (MPB) between tetragonal P4mm and pseudo-monoclinic M phases are discussed with respect to electro-mechanical properties. Doping effect (with La 3+ ) on the properties of ceramic samples of pseudobinary Pb(Lu 1/2 Nb 1/2 )O 3 -PbTiO 3 (PLuNT) system has been investigated. Pb(Mg 1/3 Nb 2/3 )-PbTiO 3 (PT) solid solutions were studied under different processing conditions for obtaining ceramics of 100% perovskite structure with sufficient high j T EC ∼ 1 K near room temperature. The PLuNT with composition near the MPB formed by in situ pulsed laser deposition onto LSCO/(100)MgO as well as PluN thin films exhibit ferroelectric behaviour at room temperature (in contrast to typical antiferroelectric features of PLuN ceramic).

Structure and Properties of Pb(LuNb)O3-PbTiO3 Ceramics and Thin Films

The crystallographic features of binary system Pb(LuNb)O3-PbTiO3 (PLuNT) including the morphotropic phase boundary (MPB) region between tetragonal P4mm and pseudo-monoclinic M phases are reported and discussed with respect to dielectric, polarization and electromechanical characteristics. Non-isovalent doping of PLuNT in the Pb sublattice according to 2Pb2+ → 2La3+ + □A either in both components or maintaining the PbTiO3 unmodified: (i) shifts the MPB to the pseudo-monoclinic side of the phase diagram; (ii) diminishes the distortion of the unit cell (c/a −1 = 0.009 at 2 mol.% of La); (iii) reduces the coercive field to 15.8 kV/cm in the first case and below 10 kV/cm in the latter case. Simultaneously high values of maximum polarization Pm = 50.3 μC/cm2 and remnant polarization Pr ≅ 40.3 μC/cm2 maintain. The films of PLuNT with composition near the MPB formed by in situ pulsed laser deposition (PLD) onto LSCO/(100)MgO exhibited ferroelectric (FE) behaviour with Pm ≅ 29 μC/cm2, Pr ≅ 14 μC/cm2, Ec ≅ 70 kV/cm. The zero-field dielectric permittivity ϵ = 300–450 at room temperature, and demonstrates a relaxor type broad peak around 350°C. Au/PLuN/LSCO thin film heterostructures exhibit FE behaviour as well in contrast to typical AFE features of PLuN ceramic; a diffuse peak of ϵ was observed around 100°C. The lower degree of structural ordering is considered to be the main factor in the different behaviour of thin films and bulk ceramic material.

Dynamic regimes in films with a periodic array of antidots

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility chi(T,H) measurements. At low enough ac drive amplitudes h, vortices moving inside the pinning potential give rise to a frequency- and h-independent response together with a scarce dissipation. For higher amplitudes, the average distance travelled by vortices surpasses the pinning range and a critical state develops. We found that the boundary h*(H,T) between these regimes smoothly decreases as T increases whereas a step-like behavior is observed as a function of field. We demonstrate that these steps in h*(H) arise from sharp changes in the pinning strength corresponding to different vortex configurations. For a wide set of data at several fields and temperatures in the critical state regime, we show that the scaling laws based on the simple Bean model are satisfied.

Theory of quantum size effects in thin Pb(111) films

We have carried out first-principles calculations of Pb (111) films up to 25 monolayers to study the oscillatory quantum size effects exhibited in the surface energy and work function. These oscillations are correlated with the thickness dependence of the energies of confined electrons, which can be properly modeled by an energy-dependent phase shift of the electronic wave function upon reflection at the interface. It is found that a quantitative description of these quantum size effects requires a full consideration of the crystal band structure.

Preparation of Lead Zirconate Titanate Thin Films Derived by Hybrid Processing: Sol‐Gel Method and Laser Ablation

Thin films of Pb(Zr0.52Ti0.48)O3 (PZT) were prepared by hybrid processing (sol‐gel and excimer laser ablation) on Pt/Ti/SiO2/Si substrates. Crystalline phases and microstructures of the PZT films were investigated by X‐ray diffraction analysis and scanning electron microscopy, respectively. Electrical properties of the films were evaluated by measuring their P‐E hysteresis loops and dielectric constants. The temperature of postdeposition annealing in hybrid processing was lower than that in the case of direct film deposition by laser ablation on a Pt/Ti/SiO2/Si substrate. The preferred orientation of the films derived by hybrid processing could be controlled using the seeding layer deposited by the sol‐gel process. The films fabricated by hybrid processing consisted of the perovskite phase with a (111) preferred orientation and had good ferroelectric properties.