PT Thin Films Research Articles

Effects of substrate shape, curvature and roughness on thin heteroepitaxial films of Pt on Au(111)

Abstract The growth of thin (1–10 nm) films of Pt on Au(1 1 1) was studied in order to understand and clarify differences in growth mode observed in ultra-high vacuum (UHV) studies and in electrochemical deposition studies. It was found that on flat Au(1 1 1), Pt grows in a layer-by-layer growth mode, but if the gold substrate is exposed to an acidic environment prior to Pt deposition, then the substrate becomes nanoscopically rough (islanded) and Pt growth follows a pseudo-Stranski–Krastanov (SK) growth mode in which an initially thin wetting layer becomes rougher with increasing film thickness. An analysis of curvature effects on epitaxial growth mode shows that thermodynamic curvature effects involving surface stress are negligible for the Pt/Au(1 1 1) system. Rather, the apparent SK growth is linked to kinetic effects associated with inhomogeneous in-plane elastic relaxation of Pt films on rough surfaces that drive Pt atoms from pits to the tops of islands in the early stages of growth. Implications for the control of epitaxial film roughness are discussed.

Effect of titanium dioxide (TiO 2) seed layer on the phase composition of 0.7Pb (Mg 1/3Nb 2/3)O 3–0.3PbTiO 3 film prepared by pulsed laser deposition

Lead–magnesium niobate–lead titanate (PMN–PT) thin films with and without the TiO 2 seed layer were deposited on Pt/Ti/SiO 2/Si substrates through pulsed laser deposition. The study aimed to characterize the effect of the TiO 2 seed layer on the phase composition and properties of PMN–PT film. Without the TiO 2 seed layer, the pure perovskite phase could be obtained in the thinner PMN–PT film while with the TiO 2 seed layer, the pure perovskite phase was formed in the thicker PMN–PT film. The ferroelectric properties of PMN–PT films with the TiO 2 seed layer were exhibited. As a result, the maximum amount of remnant polarization reached the amount of 32 μC/cm 2 for the PMN–PT thin film with the TiO 2 seed layer.

Self-assembled nanoparticle arrays as nanomasks for pattern transfer

Argon ion milling was used to transfer the pattern of sparse 12 nm iron oxide nanoparticles into underlying thin films of Pt and magnetic tunnel junction stacks and quantify their etching rates and morphological evolution. Under typical milling conditions, Pt milled at 10 nm min−1, while the isolated particles of iron oxide used for the mask milled at 5 nm min−1. Dilute dispersions of nanoparticles were used to produce the sparse nanomasks, and high resolution scanning electron microscopy (SEM) and atomic force microscopy were used to monitor the evolution of etched structures as a function of milling time. SEM measurements indicate an apparent 20% increase in feature diameter before the features began to diminish under additional milling, suggesting redeposition as a limiting feature in the milling of dense arrays. Simulations of the milling process in nanoparticle arrays that include redeposition are consistent with this observation. These simulations predict that an edge-to-edge spacing of 3 nm in a dense array is feasible, but that redeposition reduces the final structure aspect ratio from that of the masking array by as much as a factor of two.

Structural properties of 0.65Pb(Mg 1/3Nb 2/3)O 3–0.35PbTiO 3 relaxor ferroelectric thin films on SrRuO 3 conducting oxides

Coating of 0.65Pb(Mg 1/3Nb 2/3)O 3–0.35PbTiO 3 (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO 3 (SRO) metallic oxide electrodes on SrTiO 3 (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed.

Electrochemical reduction of oxygen on thin-film Pt electrodes in acid solutions

The electrochemical reduction of oxygen on thin-film platinum electrodes in 0.1 M HClO 4 and 0.05 M H 2SO 4 solutions has been investigated using the rotating disk electrode (RDE) method. Thin films of Pt (0.25–20 nm thick) were prepared by vacuum evaporation onto glassy carbon substrate. The surface morphology of Pt films was examined by transmission electron microscopy (TEM). The specific activity of O 2 reduction was higher in HClO 4 and decreased with decreasing film thickness. In H 2SO 4, the specific activity was lower and appeared to be independent of the Pt loading. The values of Tafel slopes close to −120 mV dec −1 in high current density range and −60 mV dec −1 in low current density range were obtained for all electrodes in both solutions, indicating that the mechanism of O 2 reduction is the same for thin-film electrodes as for bulk Pt. The number of electrons transferred per O 2 molecule was close to four for all thin Pt films studied.

Crystallographic Characteristics of Nanostructured Thin-Film Fuel Cell Electrocatalysts: A HRTEM Study

This paper reports a study of thin films of Pt and Pt-alloys deposited on oriented crystalline organic whiskers using high resolution transmission electron microscopy imaging. It is our opinion tha...

Characterization of FeS2-Based Thin Films as Model Catalysts for the Oxygen Reduction Reaction

FeS2 and (Fe,Co)S2 thin films prepared by magnetron sputtering have been investigated as model catalysts for the oxygen reduction reaction (ORR), and their activities were compared against that of a sputtered thin film of Pt. Scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and micro-Raman spectroscopy have been used, in parallel with electrochemical activity measurements using the thin film as a rotating disk electrode (RDE), to assess how the electrochemical performances of the sulfide films relate to chemical composition and structure. Comparisons were also made against a mineral FeS2 pyrite whose open circuit potential (OCP) was 0.62 V and much less than the values of 0.78 and 0.80 V found for the FeS2 and (Fe,Co)S2 thin films, respectively (all potentials are given vs the reversible hydrogen electrode). There are indications that the ORR activities for these films may be associated with the presence of some p...

Effects of LaNiO 3 buffer layers on preferential orientation growth and properties of PbTiO 3 thin films

(1 0 0)- and (1 0 1)-oriented PbTiO 3 (PT) thin films on conductive LaNiO 3 (LNO)-coated Si(1 1 1) substrates were prepared by a metal-organic decomposition method. It is found that the crystallization states of LNO thin films used as buffer layers have significantly effects on preferential orientation of PT thin films. PT thin films with (1 0 0) orientation could be obtained not only on the crystalline LNO (1 0 0) film, but also on the amorphous LNO thin film. The highly (1 0 0)-oriented PT films show high dielectric constant of 189.4 on LNO (1 0 0) films and 183.1 on amorphous LNO films. The PT capacitors fabricated on the LNO buffer layers display good P– E hysteresis loops. The remnant polarization ( P r) and coercive field ( E c) of PT films on amorphous, (1 0 0)- and (1 1 0)-oriented LNO films are 9.35 μC/cm 2 and 162.8 kV/cm, 10.03 μC/cm 2 and 163.3 kV/cm, 11.23 μC/cm 2 and 166.2 kV/cm, respectively.

Preparation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films Via a Polyvinylpyrrolidone‐Assisted Aqueous Sol–Gel Process and Dielectric Properties

Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) thin films were prepared by spin coating using aqueous solutions of metal salts containing polyvinylpyrrolidone, where niobium oxide layers and lead—magnesium–titanium oxide layers were laminated on Pt(111)/TiOx/SiO2/Si(100) substrates and fired at 750° or 800°C. 250 ± 20 nm thick 0.7PMN–0.3PT thin films of a single‐phase perovskite could be prepared, and the film fired at 750°C had dielectric constants and dielectric loss of 1900 ± 350 and 0.13 ± 0.03, respectively, exhibiting polarization‐electric field hysteresis with a remanent polarization of 5.1 μC/cm2 and a coercive field of 21 kV/cm.

PAMAM Dendrimers as Anchors for the Preparation of Electrocatalytically Active Ultrathin Metallic Films

This paper describes the formation of catalytically active thin films of Pt, Pt/Au, and Pt/Ru on gold substrates stabilized by amine-terminated polyamidoamine (PAMAM) dendrimers. A monolayer of dendrimer is initially self-assembled on the gold substrate, which serves as a template for the growth of catalytically active thin films. As dendrimers contain tens to hundreds of functional groups at the periphery, the aggregate strength of the multidentate interactions with the gold substrate leads to the formation of robust films. The films were found to exhibit high catalytic activity for the oxidation of small hydrocarbons such as methanol. Such films offer versatility and scope for the design of effective electrocatalysts, especially in the context of microfuel cells and "dendrichips"; hence, they could find applications in the fields of sensors, fuel cells, and waste-water treatment.

Atomic Layer Deposition of Titanium Disulfide Thin Films

AbstractTitanium disulfide thin films are grown by atomic layer deposition (ALD) at 400–500 °C using TiCl4 and H2S as precursors. Soda‐lime glass, silicon, and thin films of TiN, ZnS, Rh, Ir, Pd, Pt, and Ru are used as substrates. Hexagonal (001)‐oriented TiS2 is deposited on ZnS at 400 °C with growth rates of between 0.15 and 0.20 Å per cycle. Randomly oriented, hexagonal, platelike crystals are deposited on glass and TiN with a growth rate of 0.26 Å per cycle. Significant variations in surface morphologies were detected in TiS2 films on various noble metals. TiS2 was also grown on the pore walls of an alumina membrane.

Nanoimprinted electrodes for micro-fuel cell applications

Nanoimprint lithography (NIL) was used to fabricate electrodes with high specific Pt surface areas for use in micro-fuel cell devices. The Pt catalyst structures were characterized electrochemically using cyclic voltammetry and were found to have electrochemical active surface areas (EAS) ranging from 0.8 to 1.5 m 2 g −1 Pt. These NIL catalyst structures were tested in fuel cell membrane electrode assemblies (MEA) by directly embossing a Nafion 117 membrane. The features of the mold were successfully transferred to the Nafion and a 7.5 nm thin film of Pt was deposited at a wide angle to form the anode catalyst layer. The resulting MEA yielded a very high Pt utilization of 15,375 mW mg −1 Pt compared to conventionally prepared MEAs (820 mW mg −1 Pt). Embossing pattern transfer was also demonstrated for spin casted Nafion films which could be used for new applications.

Effect of photon irradiation on the process of recrystallization of thin metallic films

Recrystallization of thin polycrystalline films of Au, Pt, and Pd obtained by thermal evaporation and condensation in a vacuum on silicon plates that are not warmed up and are coated on both sides with silicon oxide has been studied by transmission electron microscopy. It has been established that the rate of normal grain growth in such films is higher upon photon treatment by the radiation of power xenon lamps (spectral region of 0.2–1.2 μm) than upon heat treatment. A quantitative estimate of the effect revealed indicates a change in the mechanism of the process that controls migration of grain boundaries. The effect is connected with the possible activation of hypersonic waves owing to the coexistence of phonon and electron excitations localized in nanosized regions of metallic films.

Thin film Pt/TiO 2 catalysts for the polymer electrolyte fuel cell

Thin film Pt/TiO 2 catalysts are evaluated in a polymer electrolyte electrochemical cell. Individual thin films of Pt and TiO 2, and bilayers of them, were deposited directly on Nafion membranes by thermal evaporation with varying deposition order and thickness (Pt loadings of 3–6 μg cm −2). Structural and chemical characterization was performed by transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Oxygen reduction reaction (ORR) polarization plots show that the presence of a thin TiO 2 layer between the platinum and the Nafion increases the performance compared to a Pt film deposited directly on Nafion. Based on the TEM analysis, we attribute this improvement to a better dispersion of Pt on TiO 2 compared to on Nafion and in addition, substantial proton conduction through the thin TiO 2 layer. It is also shown that deposition order and the film thickness affects the performance.

Shear Stress Effect on the Absorption Spectra of Organic Thin Films Under High Pressure

The effects of shear stress on the absorption spectra of a thin film of one-dimensional bis(diphenylglyoximato)platinum(II), Pt(dpg)2 have been studied under high pressure. The color of the thin film turns from red-brown at ambient pressure to green at 0.4 GPa. Then, one sapphire anvil is rotated by applied force in order to generate shear stress at 0.4 GPa. The color of the thin film at the outer part on the anvil changes remarkably from green to yellow, but the color at the center is green. The absorption spectra of Pt(dpg)2 have simultaneously been measured under shear deformation and non-hydrostatic conditions. The absorption intensity of the visible band decreases sharply at outer part, and this absorption peak abruptly shifts to the near-infrared region. The powder x-ray diffraction profiles of the thin film of Pt(dpg)2 at center and outer parts have been studied under shear deformation. The 110 and 200 lines at outer part markedly shift to the lower d-value region. In contrast, both diffraction lines at the center part are insensitive to shear stress. This behavior corresponds to the shift of the absorption band at outer part.

Structure and Properties of (1−x)PZN−xPT Thin Films with Perovskite Phase Promoted by Polyethylene Glycol

Perovskite ferroelectric (1−x)Pb(Zn1/3Nb2/3)O3−xPbTiO3 ((1−x)PZN−xPT) thin films were prepared on LaAlO3 (LAO) substrates with a polyethylene glycol (PEG)-modified sol−gel method. It was found that the introduction of the PEG in the precursor solutions dramatically promoted the formation of the perovskite phase while suppressing the pyrochlore phase. With the aid of PEG, (001)-oriented epitaxial perovskite (1−x)PZN−xPT thin films with x as low as 0.3 were successfully achieved without detectable pyrochlore phase. The perovskite phase was still dominant when x was reduced to 0.1 in which the composition is around the morphotropic phase boundary (MPB). The electric properties of our 0.7PZN−0.3PT films deposited on conductive LaNiO3-coated LAO substrates were characterized, and the films exhibited good dielectric, ferroelectric, and piezoelectric properties. An understanding on the mechanism of PEG promoting the perovskite phase and suppressing the pyrochlore phase has been developed through systematic inves...

Shear Stress Effect on Thin Films of Platinum Complex Pt(dpg)2 and Chromic Compounds

We have studied the effect of shear stress on thin films of Pt(dpg)2 and chromic compounds, spiropyrans, by using the sapphire-anvil cell. From Raman spectra under hydrostatic pressure and shear deformation, the shear stress effect on Pt(dpg)2 was quantitatively estimated. Then, it was observed that the color of spiropyran (1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitro-spiro [2H-1-benzopyran-2,2′-[2H]indole]) was changed by shear stress.

Dielectric behavior of ferroelectric thin films grown on orthorhombic substrates

Using Landau–Devonshire (LD)-type phenomenological model, we investigate the dielectric behaviors of single-domain PT thin films grown on orthorhombic substrates. Effects of in-plane misfit strains and external electric fields are combined on dielectric properties. In our calculation of permittivities, we take account of the susceptibility matrix. Basing on the assumption that in-plane misfit strains u m 1 = − u m 2 , we find that in-plane permittivities ε 11 and ε 22 are symmetrical about the line where in-plane misfit strains are zero. Same is out-plane permittivity ε 33 . Anisotropic in-plane misfit strains result in anomalies of permittivities at boundaries of phase transitions. Further calculation reveals that dielectric tunability reach to maximums at boundaries of phase transitions where the same direction polarization component appears or disappears. So the permittivities and tunabilities can be chosen to satisfy different demands by controlling applied fields and changing in-plane misfit strains.

Shear stress effect on thin films of platinum complex Pt(dpg)2 and chromic compounds

Shear stress effect on thin films of platinum complex Pt(dpg)2 and chromic compounds

Fabrication of Pb(Mg1/3Nb2/3)O3-PbTiO3 Relaxor Ferroelectric Thin Films on Si Using SrO Buffer Layer and SrRuO3 Electrode

0.9Pb(Mg 1/3 Nb 2/3 )O 3 – 0.1 PbTiO 3 (0.9 PMN-0.1 PT) thin films were deposited on Si substrates by pulsed laser deposition using SrO as buffer layer and a conducting perovskite SrRuO 3 electrode. For comparison, we have also grown 0.9 PMN-0.1 PT thin films on commercially available Pt/TiO 2 /SiO 2 /Si substrates. PMN-PT thin films grown on SrRuO 3 /SrO/Si are pure and oriented such as (001)film/(001)lower electrode/(001)substrate. However, 0.9 PMN-0.1 PT thin films grown on Pt/TiO 2 /SiO 2 /Si substrate show preferential (111) orientation of the perovskite phase with the presence of some (100) and (110) reflections. The lower electrode plays the crucial role to control the microstructure of the thin films. The sizes of the grains depend upon the nucleation density and the rate of growth onto the lower electrode used. The surface of the 0.9 PMN-0.1 PT thin films grown on SrRuO 3 (001) is quite different from that of the film on Pt (111). Well connecting granularly shaped grains are present at around 2 μm diameter on SrRuO 3 and the grain sizes in case of films grown on the Pt/TiO 2 /SiO 2 /Si substrate is in the range of .4 to .8 μm.