Films Of Pt Research Articles

Epitaxial growth of perovskite (111) 0.65PMN-0.35PT films directly on wurtzite GaN (0002) surface

PMN-PT films were deposited on GaN/sapphire substrates via pulsed laser deposition without any intermediate buffer layers, and epitaxial perovskite (111) 0.65PMN-0.35PT films on wurtzite GaN(0002) surfaces were obtained by adjusting the experimental parameters including substrates temperature and O $$_2$$ pressure. The microstructures and electrical properties of PMN-PT/GaN heterostructure were characterized by reflection high-energy electron diffraction, X-ray diffraction, atom force microscope, transmission electron microscope and polarization–electric field (P–E) measurements. The as-grown PMN-PT films exhibit highly (111) oriented perovskite crystal structure. The in-plane orientation relationship of PMN-PT film with respect to GaN is (111) $$\times$$ [11-2] PMN-PT//(0002) $$\times$$ [11-20] GaN. A domain matching epitaxy model is proposed to account for the epitaxial growth mechanism of PMN-PT on GaN. The P–E curves show typical ferroelectric characteristics, while the remnant polarization and coercive field are about 18.1 $$\upmu$$ C/cm $$^2$$ and 75 kV/cm, respectively. This work provides a good start point for the further development of advanced electronic devices based on the integration of ferroelectric PMN-PT with wide-gap GaN semiconductor.

Atomic Layer Deposition Using Self-Terminated Electrodeposition Reactions

Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and iron group metals and alloys thereof. Common to all these systems is the role of reaction intermediates, namely adsorbed H or OH-, in the quenching of metal deposition reactions. Further details on the mechanisms of self-terminated deposition reactions will be discussed. Likewise, the utility and relevance of the process to the synthesis of nanoparticles and thin films, and the study of bimetallic electrocatalysts, will be outlined.

Pulsed-Laser Deposited 35 Bi(Mg1/2Ti1/2)O3-65 PbTiO3 Thin Films-Part II: Influence of A-Site Deficiency and Thickness Scaling on Electric Properties.

35 Bi(Mg1/2Ti1/2)O3-65 PbTiO3 (35 BiMT-65 PT) thin films with varying levels of A-site deficiency were investigated as a potential candidate for high-temperature nonvolatile ferroelectric memories. PbTiO3 seed layers utilized to nucleate the perovskite phase in A-site deficient films induced a thickness dependence to the ferroelectric hysteresis and dielectric permittivity. Adjusting for this, the dielectric response of the 35 BiMT-65 PT films is $\approx 960$ . The maximum dielectric permittivity was 430 °C at 1 MHz for A-site deficient films. The transition temperature is independent of film thickness to 85 nm. Tan( $\delta$ ) remains less than 15% at 1 MHz regardless of film thickness and temperature up to 585 °C. High-temperature polarization-electric field hysteresis measurements show charge injection with increasing temperature, while positive-up-negative-down measurements show little temperature dependence of $P_{r}$ up to temperatures of 200 °C. Poole-Frenkel emission dominated the high field leakage behavior. The refractive index measured by ellipsometry is 2.58 at 633 nm. All samples show significant retention loss. As the stoichiometry improves, retention improves such that >40% of the initial $\Delta P$ is retained over $\approx 280$ min.

Pulsed-Laser Deposited 35 Bi(Mg1/2Ti1/2) O3-65 PbTiO3 Thin Films-Part I: Influence of Processing on Composition, Microstructure, and Ferroelectric Hysteresis.

35 Bi(Mg1/2Ti1/2)O3 - 65 PbTiO3 (35 BiMT-65 PT) is a potential candidate material for a high-temperature nonvolatile ferroelectric memory. For pulsed-laser deposited 35 BiMT-65 PT films with the perovskite structure, it was found that as the chamber pressure during deposition decreased, the Mg and Pb contents in as-deposited films drop, while the concentration of Bi increases. Concurrently with the change in composition, the remanent polarization $P_{r}$ increases 64% to $\approx 21~\mu \text{C}$ /cm2 and the polarization-electric field loops rotated counterclockwise as the deposition pressure increases. Decreasing the seed layer thickness from 36 to 16 nm led to a decrease in $P_{r}$ to $\approx 14~\mu \text{C}$ /cm2. Adjusting the target composition allowed the deposition of films which had near-stoichiometric Bi and Mg concentrations, but in all cases, the grown films were lead deficient. These films had remanent polarizations of 18- $20~\mu \text{C}$ /cm2. If the lead content of the target was increased too far, the remanent polarization decreased, possibly due to the need to evolve more PbO from defective growth layers. Finally, the deposition rate showed no substantial effect on the film composition, but did have a significant impact on the ferroelectric properties. As the deposition rate decreased, the $P_{r}$ increased to $\approx 22~\mu \text{C}$ /cm2 due to enhanced crystalline quality. At laser frequencies of 5 Hz, a Mg-rich pyrochlore phase begins to form and films showed a maximum $P_{r} \approx 22~\mu \text{C}$ /cm2. The processing-composition behavior is explained via preferential adsorption of Bi on the A-site, which results in lead vacancies.

Growth and electrical properties of epitaxial 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 thin film by pulsed laser deposition

(100)-oriented epitaxial relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) thin film was prepared on SrRuO3-buffered SrTiO3 single-crystal substrate by pulsed laser deposition. The phase and domain structure, ferroelectric and piezoelectric properties, and leakage current behavior were studied. Results indicated well saturated polarization-versus-electric field hysteresis loops with large remnant polarization of 30 µC/cm2 and coercive field of 11 kV/mm was obtained. The analysis on the leakage current behavior proposed that linear ohmic conduction and Fowler–Nordheim tunneling were the dominant mechanism for the electric field amplitude below and above 15 kV/mm, respectively. Furthermore, the epitaxial PMN-0.3PT thin film exhibited excellent local piezoelectric response and in situ electric-field-induced domain switching behavior. These results suggest the potential applications of the present epitaxial PMN-0.3PT film in integrated ferroelectric devices.

Paper-based device with a sputtered tin-film electrode for the voltammetric determination of Cd(II) and Zn(II)

This work describes a microfabricated electrochemical paper-based analytical device (ePAD) for the simultaneous voltammetric determination of Cd(II) and Zn(II) at trace levels. The ePAD integrates a wax-printed microfluidic channel and, on the reverse side of the paper, sputtered thin films of Sn, Pt and Ag serving as the working, counter and reference electrodes, respectively. The microfluidic channel ensures electrolytic contact between the electrodes with only 10 μL of working solution. The determination of Cd(II) and Zn(II) is performed at the 400 nm-thick sputtered Sn-film working electrode, in a pump-free and unstirred mode, by anodic stripping voltammetry. Under the selected conditions, the limits of detection were 0.9 μg L−1 Cd(II) and 1.1 μg L−1 Zn(II) and the between-sensor reproducibility was 5.7% for Cd(II) and 7.5% for Zn(II) at the 30 μg L−1 level (n = 5). The ePAD costs only 0.11$ and presents favorable fabrication and operational features, that make it suitable for simple, fast and on-site analysis.

Electrochemical Atomic Layer Deposition: Self-Terminated Electrodeposition Reactions

Development of a sustainable hydrogen economy based on water electrolysis and fuel cells is constrained by the performance, longevity and high cost of Pt group electrocatalysts. Important strategies for improving catalytic reactivity include alloying, forming bimetallic or alloyed surfaces, and engineering substrate–catalyst interactions. At the same time, significant effort is underway to minimize the loading of Pt group metals by examining new synthesis methods and electrode geometries. Of specific interest is atomic layer deposition (ALD) that can be used for growing ultrathin films to maximize utilization of rare, expensive metals and facilitate the exploration of bimetallic effects in electrocatalysis. Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and iron group metals and alloys thereof. The mechanism of self-terminated deposition reactions will be discussed and the utility of these films as bimetallic electrocatalysts will be demonstrated. For example, monolayer equivalent Pt and Ir films were found to match or exceed the best known specific HER/HOR activity for bulk polycrystalline Pt or Ir electrodes and thereby offer the promise of increasing the scalability of these important precious metals in energy conversion devices. The effectiveness of such reaction on a variety of different substrates will also be examined.

Interfaces Formed by ALD Metal Oxide Growth on Metal Layers

Oxidation of metal layer surfaces due to atomic layer deposition (ALD) of thin metal oxide films is studied. For this, dense and smooth metal films of Pt, Ta and Hf were grown by off-axis sputtering and were in-situ transferred into the ALD system. Oxide films like HfO2, TiO2 and Al2O3 with a thickness of about 2 to 3 nm were deposited between 250 and 300°C by means of plasma assisted ALD utilizing a remote oxygen plasma as oxygen source. The ‘built-in’ oxygen gradients formed at different metal/ALD metal oxide interfaces were analysed by angle resolved X-ray photoelectron spectroscopy. The Pt metal films show no evidence of oxidation due to the PE-ALD process, independent of the grown metal oxide. In contrast, the thickness of the metal oxide layers formed at the surfaces of the Hf and Ta metal films depends on the ALD surface reactions as well as on the differences in oxidation enthalpy of the substrate metal and the metal oxide. The results are important for the design of high-density memristor arrays based on OxRAM devices.

Influence of metal electrodes on c‐axis orientation of AlN thin films deposited by DC magnetron sputtering

Nanocrystalline aluminum nitride (AlN) thin films were deposited on two types of metallic seed layers on silicon substrates, (111) textured Pt and (110) Mo, by reactive DC magnetron sputtering at low temperature (200 °C). Both textured films of Pt and Mo promote nucleation, thereby improving the crystallinity and epitaxial growth condition for AlN thin films. The deposited films were examined by X‐ray diffraction, scanning electron microscopy and atomic force microscopy techniques. The results indicated that the preferred orientation of crystallites greatly depends upon the kinetic energy of the sputtered species (target power) and seed layers used. Furthermore, AlN thin films with c‐axis perpendicular to the substrate grew on both types of metal electrodes at all power levels larger than 100 W. By comparing the structural properties and compressive stresses at perfect c‐axis orientation conditions, it is evident that AlN films deposited on (110) oriented Mo substrates exhibited superior properties as compared with Pt/Ti seed layers. Furthermore, less values of compressive stresses (−3 GPa) as compared with Pt/Ti substrates (−7.08 GPa) make Mo preferentially better candidate to be employed in the field of suspended Micro/Nano ‐ electromechanical systems (MEMS/NEMS) for piezoelectric devices. Copyright © 2017 John Wiley & Sons, Ltd.

(Invited) Electrochemical Atomic Layer Deposition of Ultrathin Electrocatalytic Films

Development of a sustainable hydrogen economy based on water electrolysis and fuel cells is constrained by the performance, longevity and high cost of Pt group electrocatalysts. Important strategies for improving catalytic reactivity include alloying, forming bimetallic or alloyed surfaces, and engineering substrate–catalyst interactions. At the same time, significant effort is underway to minimize the loading of Pt group metals by examining new synthesis methods and electrode geometries. Of particular interest is atomic layer deposition (ALD) for growing ultrathin films that maximize utilization of rare, expensive metals and facilitate the exploration of bimetallic effects in electrocatalysis. Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and iron group metals and alloys thereof. The mechanism of self-terminated deposition reactions will be discussed and the utility of these films as bimetallic electrocatalysts will be demonstrated. For example, monolayer equivalent Pt and Ir films were found to match or exceed the best known specific HER/HOR activity for bulk polycrystalline Pt or Ir electrodes and thereby offer the promise of increasing the scalability of these important precious metals in energy conversion devices.

High recoverable energy storage density and large piezoelectric response in (Bi0.5Na0.5)TiO3-PbTiO3 thin films prepared by a sol-gel method

Low-lead-content (1-x)(Bi0.5Na0.5)TiO3-xPbTiO3 (x=0, 0.05, 0.10, 0.15, 0.25) (hereafter abbreviated as BNT-xPT) thin films were prepared by a sol-gel method, and their crystal structure, dielectric properties, recoverable energy-storage density and piezoelectric response were investigated as a function of PT concentration. Combining the XRD patterns and Raman spectroscopy indicate the phase structures go through rhombohedral (R) – rhombohedral+tetragonal (R+T) – tetragonal (T) evolution with increasing of PT content. A high recoverable energy storage density of 13.02±0.39J/cm3 was achieved in the BNT-0.10PT thin films due to the high field endurance and significantly enhanced polarizability. Moreover, a superior piezoelectric response (d33*=120±5pm/V) was also obtained in the 10% PT-modified BNT films, which can be attributed to easy polarization rotation due to low polarization anisotropy on the R-T phase boundary. These properties indicate that BNT-0.10PT films might be promising multifunctional materials for piezoelectric micro-actuator and energy storage embedded capacitor applications.

Enhanced Methanol Oxidation on Strained Pt Films

We report a systematic investigation into the effect of strain on the electrocatalytic activity of films of Pt. We use an electroless deposition process to deposit the Pt onto sputtered Au substrates and characterize their structural and electrochemical properties. We found a direct correlation between the rate of methanol oxidation and the fractional surface coverage of methanol on the compressively strained catalyst surfaces. The fractional methanol surface coverage, ΘM, varied on the Pt surfaces with values ranging from 20.5 to 61.7%, depending on the level of compressive strain. A compressive strain of about e = −0.110% resulted in a high fractional surface coverage of 61.7% with highest peak current density for methanol oxidation of 0.46 mA cm–2 and earliest peak potential of 0.67 V vs Ag/AgCl. As the absolute value of the compressive strain increased, the fractional surface coverage and peak current density for methanol oxidation decreased. Therefore, the adsorption of molecular methanol was control...

Supramolecular imprinted electrochemical sensor for the neonicotinoid insecticide imidacloprid based on double amplification by Pt-In catalytic nanoparticles and a Bromophenol blue doped molecularly imprinted film

The authors describe an electrochemical sensor for the neonicotinoid insecticide imidacloprid (IMI) based on Pt-In catalytic nanocomposite film and Bromophenol blue amplification. The Pt-In nanocomposite film was deposited on the surface of a modified glassy carbon electrode. The composite molecularly imprinted polymer (MIP) was prepared by electro-polymerization using bromophenol blue doped o-aminophenol as functional monomer and 4-tert-butylcalix[6]arene-IMI supramolecular inclusion complex as template molecule. The experimental results showed that the current intensity of IMI was clearly amplified in the potential range from −0.3 to −1.8 V, because of the double amplification, based on the Pt-In film and Bromophenol blue catalysis. Moreover, the double recognition ability of the sensor, which relied on the MIP and the vacuum structure of 4-tert-butylcalix[6]arene, effectively increased the specific recognition performance. The feasibility of its practical applications has been demonstrated by the analysis of vegetable samples.

Influence of the polarization anisotropy on the electrocaloric effect in epitaxial PMN-PT thin films

Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) compounds, which are typically used for high performance actuator applications due to their outstanding piezoelectric properties, show, in addition, a pronounced electrocaloric (EC) effect. The study of epitaxial films is a useful tool to analyze the correlation between the microstructure and EC properties in order to optimize the performance of these materials. Therefore, the 0.9PMN-0.1PT films were grown by a pulsed laser deposition on (001) as well as (111) oriented SrTiO3 single crystalline substrates using a La0.7Sr0.3CoO3 buffer as the bottom electrode and additional Au top electrodes. The structural properties determined by a high resolution X-ray and electron microscopy techniques indicated an undisturbed epitaxial growth. The anisotropy of the ferroelectric domain structure was investigated by a vertical and lateral piezoresponse force microscopy showing clear differences between the two orientations. A significant reduction of the thermal hysteresis was observed in the T-dependent polarization measurements for (111) oriented PMN-PT films, whereas the indirectly determined EC properties yield a maximum ΔT of around 15 K at 40 °C for a field of about 400 kV/cm for both film orientations.

Self-Terminated Electrodeposition Reactions for Electrocatalysis

Development of a sustainable hydrogen economy based on water electrolysis and fuel cells is constrained by the performance, longevity and high cost of Pt group electrocatalysts. Important strategies for improving catalytic reactivity include alloying, forming bimetallic or alloyed surfaces, and engineering substrate–catalyst interactions. At the same time, significant effort is underway to minimize the loading of Pt group metals by examining new synthesis methods and electrode geometries. Of particular interest is atomic layer deposition (ALD) for growing ultrathin films that maximize utilization of rare, expensive metals and facilitate the exploration of bimetallic effects in electrocatalysis. Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and Fe-group metals and alloys thereof. The mechanism of self-terminated deposition reactions will be discussed and the utility of these films as bimetallic electrocatalysts will be demonstrated. For example, monolayer equivalent Pt and Ir films were found to match or exceed the best known specific HER/HOR activity for bulk polycrystalline Pt or Ir electrodes and thereby offer the promise of increasing the scalability of these important precious metals in energy conversion devices.

Influence of Hydrogen Adsorption on Electrodeposition of Platinum from Chloro Complex Solution

Platinum (Pt) is widely used as insoluble and catalytic electrodes for electrolysis, automotive catalytic converters, and fuel cells. We have been investigating hydrogen incorporation in electrodeposited metal films and its influence on crystal structure of metals (1-3). It was reported that large amount of hydrogen (content in atomic ratio: x = H/Pt = 0.1) is incorporated in the Pt films electrodeposited from a solution including dinitrosulfatoplatinate(II) (H2Pt(NO2)2SO4, DNS) as a metal source. In this study, an electrochemical quartz crystal microbalance (EQCM) method (4) is used to examine influence of hydrogen adsorption on the electrodeposition and hydrogen incorporation into deposited films of Pt from a chloro complex solution. The current-potential and mass increase (Pt deposition rate)-potential curves in 0.024 mol dm-3 K2PtCl4solution adjusted at pH of 0.8 with HCl were measured using an EQCM system (Hokuto Denko, HQ-101D and HZ-5000). A quartz electrode coated with Au, an Ag/AgCl electrode, and a Pt wire were used as the working, reference, and counter electrodes, respectively. The hydrogen content of samples was measured by thermal desorption spectroscopy (TDS). Figure 1 shows the current density and mass increase rate versus electrode potential curves for the chloro complex solution. In the first forward potential sweep toward negative potentials of Fig. 1(a), the cathode current and deposition rate of Pt started increasing at +0.3 V vs. Ag/AgCl. Peaks for cathode current and deposition rate appeared at -0.19 V. The current efficiency was 74% at this peak. Then, as the potential was swept to lower potentials, the deposition rate and current efficiency decreased. This decrease in the current efficiency of Pt deposition is caused by hydrogen adsorption. In the return potential sweep (Fig.1 (b)), the cathode current and Pt deposition steeply increased by hydrogen desorption from the Pt surface, and the current efficiency was 113% at the potential of -0.25 V. The hydrogen content of Pt-electrodeposited Au foil (Pt: 1 μm and Au: 20 μm in thickness) increased as the deposition potential of Pt decreased from 0 to -0.3 V, and was much lower than that deposited from the DNS solution. Acknowledgements The present work was partly supported by JSPS KAKENHI (26289276). References N. Fukumuro, M. Yokota, S. Yae, H. Matsuda, Y. Fukai, J. Alloys Compd., 580, S55 (2013). N. Fukumuro, S. Kojima, M. Fujino, Y. Mizuta, T. Maruo, S. Yae, Y. Fukai, J. Alloys Compd., 645, S404 (2015). N. Hisanaga, N. Fukumuro, S. Yae, H. Matsuda, ECS Trans., 50, 77 (2013). T. Hagihara, K. Yaori, K. Iwakura, N, Fukumuro, S. Yae, Electrochim. Acta, 176, 65 (2015). Figure 1

Eigenstress model for electrochemistry of solid surfaces.

Thermodynamic analysis and molecular dynamics simulations were conducted to systematically study the size-dependent electrochemical response of solids. By combining the generalized Young-Laplace equation with the popular Butler-Volmer formulation, the direct influence of surface stress on solid film electrochemical reactions was isolated. A series of thermodynamic formulas were developed to describe the size-dependent electrochemical properties of the solid surface. These formulas include intrinsic surface elastic parameters, such as surface eigenstress and surface elastic modulus. Metallic films of Au, Pt, Ni, Cu and Fe were studied as examples. The anodic current density of the metal film increased, while the equilibrium potential decreased with increasing solid film thickness.

Optimized properties of xBiInO3−(1−x)PbTiO3 thin films deposited by an RF‐magnetron sputtering method

Ferroelectric xBiInO3−(1−x)PbTiO3 (x = 0.15, 0.20, 0.25, and 0.30) thin films are deposited on (101)SrRuO3/(100)Pt/(100)MgO substrates by an RF‐magnetron sputtering method. By adjusting the deposition conditions, the electric properties of the thin films are optimized. The ferroelectricities of the thin films show that the remnant polarizations (Pr) decrease from 43 to 34 µC cm−2 as x increases from 0.15 to 0.25, and the coercive fields (Ec) are about 177 kV cm−1. The Curie temperatures (Tc) increase from 580 to 650 °C on increasing x from 0.15 to 0.30. The results illustrate that the xBI−(1−x)PT films have high ferroelectricities, high coercive fields, and high Curie temperatures simultaneously, which may have wide potential applications in high‐temperature and ‐voltage environments.

Self-Terminated Electrodeposition Reactions for Electrocatalysis

Development of a sustainable hydrogen economy based on water electrolysis and fuel cells is constrained by the performance, longevity and high cost of Pt group electrocatalysts. Important strategies for improving catalytic reactivity include alloying, forming bimetallic or alloyed surfaces, and engineering substrate–catalyst interactions. At the same time, significant effort is underway to minimize the loading of Pt group metals by examining new synthesis methods and electrode geometries. Of particular interest is atomic layer deposition (ALD) for growing ultrathin films that maximize utilization of rare, expensive metals and facilitate the exploration of bimetallic effects in electrocatalysis. Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and iron group metals and alloys thereof. The mechanism of self-terminated deposition reactions will be discussed and the utility of these films as bimetallic electrocatalysts will be demonstrated. For example, monolayer equivalent Pt and Ir films were found to match or exceed the best known specific HER/HOR activity for bulk polycrystalline Pt or Ir electrodes and thereby offer the promise of increasing the scalability of these important precious metals in energy conversion devices.

Temperature dependent optical dispersion and electronic transitions of highly a-axis oriented 0.8Pb(Zn1/3Nb2/3)O3-0.2PbTiO3 films on SrTiO3 crystals: An ellipsometric evidence

The relaxor ferroelectric 0.8Pb(Zn1/3Nb2/3)O3-0.2PbTiO3 (0.8PZN-0.2PT) films have been fabricated on (100) SrTiO3 substrates by the sol–gel method. The structure, optical properties and electronic transitions have been investigated using X-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy and ellipsometric spectra. The pure perovskite phase with highly a-axis (100)-preferential orientation as well as low screw dislocation are extracted based on high resolution XRD. Moreover, the red-shift trend of the electronic transitions at about 3.01eV as a function of temperature follows the Bose-Einstein law induced by the electron–phonon interactions and lattice thermal expansion. Interestingly, the different optical behavior and structure variation can be observed at about 500K, which reveal tetragonal to cubic structural transformations for the 0.8PZN-0.2PT films. It indicates that the potential application of ellipsometric spectra in judging the phase transitions and symmetries of ferroelectric material.