Pb Thin Films Research Articles

Growth mechanism of Pb0.9Cd0.1Te: Pb thin films prepared by PVD technique

Abstract The complex surface morphology, defect subsystem and an ab initio model study of Pb1-xCdxTe thin films deposited on mica-muscovite substrates by PVD technology are presented in this paper. The thickness, growth mechanisms and uniformity of condensates dependence on deposition regimes were studied by scanning electron microscopy and energy-dispersive x-ray spectroscopy. The deposited films have a granular structure and sizes of crystallites depend on thickness and difference between substrate and condensate crystallographic parameters. The dominance of film growth by the Vollmer-Weber mechanism is demonstrate. Studies of film growth mechanisms allowed us to predict that the formation of grains and the dynamics of their size changes during film growth are caused by complex defects that are associated with Cd atoms in nodes and vacancies of chalcogens.

Twin boundary formation in Pb thin film under conditions of the quantum confinement effect

Twin boundary formation in Pb thin film under conditions of the quantum confinement effect

Electrochemical separation of fission element neodymium using plumbum electrode from molten LiCl–KCl based on spent fuel reprocessing

In order to investigate the application prospects for the extraction of fission products neodymium (Nd) by electrolytic refining at active plumbum (Pb) electrodes, the reduction mechanism of Nd(III)/Pb(II) at inert tungsten, and Nd(III) at Pb thin film electrodes was investigated. This work simultaneously presents the results of kinetic and thermodynamic parameter of Pb(II)/Nd(III). The composition of the Pb–Nd alloy compound formed on the activated Pb electrode was determined by X-ray diffraction analysis (XRD) and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), and the thermodynamic parameters of the formed Pb3Nd alloy were calculated: ΔHf0Pb3Nd=−219.92kJmol−1 and ΔSf0Pb3Nd=−47.48Jmol−1K−1. Nd(III) was extracted in the form of Pb–Nd alloy by constant potential electrolysis (PE) in LiCl–KCl melt. Based on the analysis of inductively coupled plasma-atomic emission spectrometry (ICP-AES) results, the average extraction rate of Nd(III) ions at the liquid Pb electrode could reach 99.03%.

Characterization of PbWO4 thin films formed by the pulsed laser welding technique

Herein thin films of PbWO4 were formed from bilayers of Pb/WO3 by the pulse laser welding technique (PLW) within couple of seconds in an argon atmosphere. Thin films of Pb (100 nm)/WO3 (500 nm) were deposited by the thermal evaporation technique under a vacuum pressure of 10−5 mbar. The films were then exposed to a pulse laser beam of fixed amplitude and variable pulse width (0.1–10 ms). The produced films were characterized by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and optical spectrophotometry techniques. An almost pure phase (∼90%) of tetragonal PbWO4 was achieved after the pulse width exceeds 5.0 ms. PbWO4 thin films produced by the PLW technique exhibited a direct and indirect energy band gaps of 2.27 eV and 3.52 eV, respectively. Energy band tails of widths of 1.35 eV were found dominant in these films. In addition fitting of the dielectric resonance spectra for Pb/WO3 and PbWO4 thin films indicated that the formation of PbWO4 was accompanied with a decrease in the high frequency dielectric constant, a decrease in the free hole concentration and an increase in the electronic friction in the films. The fast method of obtaining PbWO4 thin films and the formation of the direct band gap being 2.27 eV together with the nonlinear dielectric and optical properties make the PbWO4 films obtained by the PLW technique suitable for optoelectronic technology.

Magnetic flux penetration in nanoscale wedge-shaped superconducting thin films

Thickness uniformity is regarded as an important parameter in designing thin film devices. However, some applications based on films with non-uniform thickness have recently emerged, such as gas sensors and optimized materials based on the gradual change of film composition. This work deals with superconducting Pb thin films with a thickness gradient prepared with the aid of a diffuse stencil mask. Atomic Force Microscopy and Energy-Dispersive X-ray Spectroscopy show variations ranging from 90~nm to 154~nm. Quantitative magneto-optical images reveal interesting features during both the abrupt and the smooth penetration regimes of magnetic flux, as well as the thickness-dependent critical current density ($J_c$). In addition, we observe a gradual superconducting transition as the upper critical field is progressively reached for certain thicknesses. Furthermore, the hysteresis observed for triggering flux avalanches when increasing and decreasing magnetic fields is also accounted for by the $J_c$ profile evolution along the thickness gradient. Numerical simulations based on the Thermomagnetic Model are in fair agreement with the experimental data. These findings demonstrate that wedge-shaped films are a viable approach to investigate, in a continuous fashion, thickness-dependent properties of a superconducting materials.

Relaxation of photoexcited hot carriers beyond multitemperature models: General theory description verified by experiments on Pb/Si(111)

The equilibration of electronic carriers in metals after excitation by an ultra-short laser pulse provides an important class of non-equilibrium phenomena in metals and allows measuring the effective electron-phonon coupling parameter. Since the observed decay of the electronic distribution is governed by the interplay of both electron-electron and electron-phonon scattering, the interpretation of experimental data must rely on models that ideally should be easy to handle, yet accurate. In this work, an extended rate-equation model is proposed that explicitly includes non-thermal electronic carriers while at the same time incorporating data from first-principles calculations of the electron-phonon coupling via Eliashberg-Migdal theory. The model is verified against experimental data for thin Pb films grown on Si(111). Improved agreement between theory and experiment at short times (<0.3ps) due to non-thermal electron contributions is found. Moreover, the rate equations allow for widely different coupling strength to different phonon subsystems. Consequently, an indirect, electron-mediated energy transfer between strongly and weakly coupled groups of phonons can be observed in the simulations that leads to a retarded equilibration of the subsystems only after several picoseconds.

Method to extracting the penetration field in superconductors from DC magnetization data.

The lower critical field, Bc1, is one of the fundamental quantities of a superconductor that directly manifests the Cooper pair bulk density in the material. Although this field can be measured using several techniques, the most conventional method is to calculate this field from the experimentally measured DC penetration field, Bp, which is defined as the starting point of the deviation of the DC magnetization curve, M(Bappl), from a linear dependence. Surprisingly, we found no mathematical routine that describes how this starting point of deviation can be found. Here, we propose the extraction of Bp from the fit of the M(Bappl) dataset to the power law, where the threshold criterion Mc can be established by a convention. The advantage of this approach is that the procedure extracts one additional characteristic parameter: the power-law exponent. We demonstrated the applicability of this approach to polycrystalline ThIr3, WB4.2, BaTi2Bi2O, and Th4H15; thin films of Pb and MgB2; and Nb single crystal. In most reports, Bc1(T) analysis is limited by the extraction of the London penetration depth. We advanced the analysis to extract primary thermodynamic superconducting parameters [i.e., the ground state superconducting energy gap, Δ(0); the relative jump in electronic specific heat at transition temperature, ΔCγTc; and the gap-to-transition temperature ratio, 2Δ0kBTc] from Bc1(T) data. This extraction was performed for Nb, ThIr3, TaRh2B2, and NbRh2B2.

Dynamic response and roughening of ferroelectric domain walls driven at planar electrode edges

Understanding and controlling the motion, stability, and equilibrium configuration of ferroelectric domain walls is key for their integration into potential nanoelectronic applications, such as ferroelectric racetrack memories. Using piezoresponse force microscopy, we analyze the growth and roughness of ferroelectric domains in epitaxial thin film Pb(Zr0.2Ti0.8)O3, driven by the electric fields at straight edges of planar electrodes at two different temperatures. This device relevant geometry allows us to confirm that the domain walls are well described as one-dimensional monoaffine elastic interfaces driven in random-bond disorder. However, we observe a progressive increase in roughness as initially flat domain walls move through the disorder landscape, which could prove a significant limiting factor for racetrack-type memories using ferroelectrics.

Observation of Hidden Parts of Dislocation Loops in Thin Pb Films by Means of Scanning Tunneling Spectroscopy

Local electronic properties of quasi-two-dimensional Pb(111) islands with screw dislocations of different types on their surfaces were experimentally studied by means of low-temperature scanning tunneling microscopy and spectroscopy in the regime of constant current. A comparison of the topography map, the maps of tunneling current variation and the differential tunneling conductance acquired simultaneously allows one to visualize the hidden parts of the dislocation loops under the sample surface. We demonstrate that two closely-positioned screw dislocations with the opposite Burgers vectors can either (i) connect to each other by the sub-surface dislocation loop or (ii) generate independent hidden edge dislocation lines which run towards the perimeter of the Pb island. In addition, we found a screw dislocation, which does not produce outcoming sub-surface dislocation loops. Screw dislocations and the hidden dislocations lines are the source of the non-quantized variation of the local thickness of the Pb terraces, affecting the local electronic properties.

Fabrication and Resonance Characteristics of PZT Cantilevers

Thin films of lead zirconate titanate Pb(Zr0,52Ti0,48)O3 (PZT) with thickness of 1.4 μm were prepared on Si/SiO2/TiO2/Pt substrates by chemical solutions deposition. Based on the obtained films, the structures of PZT cantilevers were formed, with a length from 500 to 1000 /um and wide from 100 to 500 μm. Platinum (100 nm) as the bottom and top electrode, has been deposited by magnetron sputtering. PZT cantilevers werereleased by etching the sacrificial layer in SF6. The resonance characteristics of the PZT cantilevers were determined by the light lever method using a special optical measuring stand. Output characteristics of the PZT cantilevers, can be used in MEMS devices, specially, in MEMS resonators.

Design & Characterization of Pb Electrode for Sensing Trichloroethylene in Ionic Liquid/Acetonitrile Co-Solvents

Design & Characterization of Pb Electrode for Sensing Trichloroethylene in Ionic Liquid/Acetonitrile Co-Solvents

A system for probing Casimir energy corrections to the condensation energy

In this article, we present a nanoelectromechanical system (NEMS) designed to detect changes in the Casimir energy. The Casimir effect is a result of the appearance of quantum fluctuations in an electromagnetic vacuum. Previous experiments have used nano- or microscale parallel plate capacitors to detect the Casimir force by measuring the small attractive force these fluctuations exert between the two surfaces. In this new set of experiments, we aim to directly detect the shifts in the Casimir energy in a vacuum due to the presence of the metallic parallel plates, one of which is a superconductor. A change in the Casimir energy of this configuration is predicted to shift the superconducting transition temperature (Tc) because of the interaction between it and the superconducting condensation energy. In our experiment, we take a superconducting film, carefully measure its transition temperature, bring a conducting plate close to the film, create a Casimir cavity, and then measure the transition temperature again. The expected shifts are smaller than the normal shifts one sees in cycling superconducting films to cryogenic temperatures, so using a NEMS resonator in situ is the only practical way to obtain accurate, reproducible data. Using a thin Pb film and opposing Au surface, we observe no shift in Tc >12 µK down to a minimum spacing of ~70 nm at zero applied magnetic field.

Nanostructured Pb(S, O) Films: Synthesis, Mechanism of Deposition, and Optical Properties

Chemical deposition is used to obtain thin solid films of lead sulfide Pb(S, O) with oxygen contents of 0.2 to 30.7 at %, regulated by a variety of ligands. The oxygen effect on the mechanism of formation and optical properties of Pb(S, O) films is studied experimentally and through quantum-chemical modeling. A heterostructured nature of the synthesized Pb(S, O) compounds is shown for the first time, and a mechanism of their formation in an aqueous solution is proposed.

Critical role of parallel momentum in quantum well state couplings in multi-stacked nanofilms: An angle resolved photoemission study

We use angle resolved photoemission spectroscopy to investigate the coupling of electron quantum well states (QWSs) in epitaxial thin Pb and Ag films. More specifically, we investigate the Ag/Si, Pb/Si, and Pb/Ag/Si systems. We found that the parallel momentum plays a very profound role in determining how two adjacent quantum wells are coupled electronically across the interface. We revealed that in the Pb/Ag bimetallic system, there exist two distinctly different regimes in the energy vs momentum (E vs k) space. In one regime, the electronic states in Ag and Pb are strongly coupled, resulting in a new set of QWSs for the bi-metallic system. In the other regime, the electronic states in individual metallic layers are retained in their respective regions, as if they are totally decoupled. This result is corroborated by calculations using density functional theory. We further unravel the underlying mechanism associated with the electron refraction and total internal reflection across the interface.

A Chip-Scale, Low Cost PVD System

Standard physical vapor deposition systems are large, expensive, and slow. As part of an on-going effort to build a fab-on-a-chip, we have developed a chip-scale, low cost, fast physical vapor deposition system designed to be used with atomic calligraphy or dynamic stencil lithography to direct write nanostructures. The system comprises two MEMS devices: a chip-scale thermal evaporator and a mass sensor that serves as a film thickness monitor. Here, we demonstrate the functionality of both devices by depositing Pb thin-films. The thermal evaporator was made by fabless manufacturing using the SOIMUMPs processs (MEMSCAP, inc). It turns on in 1:46 s and reaches deposition rates as high as 7.2Å s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with ~1 mm separation from the target. The mass sensor is a re-purposed quartz oscillator (JTX210) that is commercially available for less than one dollar. Its resolution was measured to be 2.65 fg or 7.79E-5 monolayers of Pb.

Surface Phase Nucleation of Lead Monoatomic Layers on Si(111) Induced by Manganese Phthalocyanine Molecules

Hybrid interfaces where organic molecules are adsorbed on metallic substrates are very interesting to understand the fundamental interactions that might modify the chemical–physical properties of molecules or substrate. Here, we explore the adsorption of manganese phthalocyanines (MnPcs) on different structural phases of a Pb monatomic layer, namely, the √7 × √3-Pb and the striped incommensurate phase (SIC-Pb) phase, grown on Si(111). Surprisingly, the deposition of a minute amount of MnPc molecules (∼0.18 molecules/100 nm2) nucleates a macroscopic structural transition of the √7 × √3-Pb phase into the SIC-Pb phase. Our combined scanning tunneling microscopy, low-energy electron diffraction, and density functional theory study revealed that the mechanism behind this surface transformation is related to a strong and local molecule–substrate interaction. The structural phase transition is finally driven by the strained nature of the Pb phases and the energetic stability of the MnPc/SIC-Pb/Si(111) system with respect to the MnPc/√7 × √3-Pb/Si(111) one. The molecule–substrate interaction found in the present study is stronger than the one observed on Pb(111) bulk or thin films, highlighting the implication of the Pb/Si(111) interface in the interaction process. Hence, our results reveal that playing with the substrate dimensionality to tune the molecule–substrate coupling has strong impact on the electronic/magnetic properties of organic hybrid systems.

Effect of a thin (doped) PZT interfacial layer on the properties of epitaxial PMN-PT films

Pure perovskite phase, (001)-oriented, epitaxial thin films of (Pb(Mg1/3Nb2/3)O3)0.67-(PbTiO3)0.33 (PMN-PT) were fabricated on single crystal, (001)-oriented SrTiO3 substrates using a hard (Fe-doped) and soft doped (Nb-doped) PZT(52/48) interfacial layer. The effect of different interface layers on the structural and ferroelectric properties of the PMN-PT films was investigated in detail. A significant self-bias voltage in the PMN-PT films can be introduced by using an appropriate interfacial layer. There are significant differences in polarization for different types of doped and undoped interface layers and a doubling of the relative dielectric constant was observed for the Nb-doped interfacial layer. Device properties remain stable up to at least 108 cycles.

Improved Cu2ZnSnS4 thin film performance via Pb consumption layer

Abstract Adding a certain amount of Pb element into the perovskite solar cells can improve the devices' overall performance. However, there are few reports on the incorporation of Pb into Cu2ZnSnS4(CZTS) thin film solar cells. In this work, a novel absorber layer of CZTS:Pb thin film has been fabricated through sulfurization CZTS precursor with 15 nm Pb layer. XRD, Raman, and EDS characterizations exhibited that Pb was incorporated into CZTS and partially replaced Sn. Meanwhile, XPS measurement indicated that Pb was +4 valence and no distinct change of the CZTS chemical environment. SEM reveals that compact large grains almost span the whole thickness of the absorber when Pb is used as a consumption layer, while some fine grains and voids at the back contact exist in common CZTS films. The best efficiency of CZTS:Pb is 3.01% with the open-circuit voltage of 615.95 mV, the short-circuit current density of 14.74 mA/cm2 and the fill factor of 33.01%, which is mainly due to the Pb consumption layer improving the crystallinity of CZTS.

Quantum-well and modified image-potential states in thin Pb(111) films: an estimate for the local work function

Quantum-confined electronic states such as quantum-well states (QWS) inside thin Pb(111) films and modified image-potential states (IPS) above the Pb(111) films grown on Si(111) 7 × 7 substrate were studied by means of low-temperature scanning tunnelling microscopy (STM) and spectroscopy (STS) in the regime of constant current I. By plotting the position of the nth emission resonances Un versus n2/3 and extrapolating the linear fit for the dependence Un(n2/3) in the high-n limit towards n = 0, we estimate the local work function for the Pb(111) film: W ≃ 3.8 ± 0.1 eV. We experimentally demonstrate that modifications of the shape of the STM tip can change the number of the emission peaks associated with the resonant tunnelling via quantized IPS levels for the same Pb terrace; however it does not affect the estimate of the local work function for the flat Pb terraces. We observe that the maxima in the spectra of the differential tunnelling conductance dI/dU related to both the QWS and the modified IPS resonances are less pronounced if the STM tip becomes more blunt.

Study of the physical properties of quaternary Ge–As–Te–Pb thin films for technology applications

Study of the physical properties of quaternary Ge–As–Te–Pb thin films for technology applications