Comparison of Properties of Pt/PZT/Pt and Ru/PZT/Pt Ferroelectric Capacitors

Pb（Zr0.4Ti0.6）O3 film prepared by sol-gel spin coating on a Pt/Ti/SiO2/Si substrate is applied to ferroelectric capacitors with Pt or Ru as the top electrode. For the Pt/PZT/Pt and Ru/PZT/Pt ferroelectric capacitors, although with the same ferroelectric film, different top electrode materials incur different properties of PZT capacitors, such as fatigue, leakage, remanent and saturated polarization, except the similar crystal orientations of the PZT film. After 10^10 switch cycles, the remanent polarizations of the Ru/PZT/Pt and Pt/PZT/Pt capacitors decrease to 70% and 84%, respectively. The leakage current density of the latter increases obviously at positive bias after 108 switch cycles, compared with the former. Different materials for the top electrode bring different conditions at the PZT/top electrode interface. The influence of oxygen-vacancy concentration at the PZT/electrode interface and the influence of oxides of the electrode material at the PZT/electrode interface to charge injection can explain the difference of properties of the PZT capacitors with Pt or Ru as the top electrodes.     

Morphology and chemical state of PVP-protected Pt,Pt–Cu,and Pt–Ag nanoparticles prepared by alkaline polyol method

Well-dispersed, uniform monometallic Pt and bimetallic Pt–Cu, and Pt–Ag nanoparticles protected with PVP have been synthesized by a modified-protocol alkaline polyol method. The nanoparticles were characterized by various methods (TEM, XPS, and XRD) to elucidate the relationship between morphology and preparation variables. The average of monodispersed nanoparticles ranged between 4.1 and 4.9 nm. Core–shell structure was obtained in the case of bimetallic nanoparticles. The core of bimetallic nanoparticles was found to be rich in platinum, whereas the shell contained mostly copper or silver. The final structure of bimetallic nanoparticles was found to be determined by the morphology particles resulted in the first reduction step. Explanations are advanced on the light of experimental results.     

Effect of Pt on interdiffusion and mechanical properties of the γ and γ′ phases in the Ni–Pt–Al system

The effect of Pt on the growth kinetics of the γ′-[Ni(Pt)]₃Al ordered intermetallic phase and the γ-Ni(Pt, Al) solid solution diffusion rates of the species, hardness and elastic modulus was examined by employing the diffusion couple experimental technique. Experiments were conducted by using the β-Ni(Pt)Al phase and Ni(Pt) alloy couples, each of which had a fixed amount of Pt (5, 10 and 15 at. %) in both the end members so that the Pt content is more or less constant throughout the interdiffusion zone. The results suggest that the growth kinetics of both phases and the average effective interdiffusion coefficients of Ni and Al increase with the increase in Pt content. Nanoindentation studies across the compositional gradients show that the mechanical properties of the intermetallic phase in the superalloy are relatively insensitive to the presence of Pt but are more sensitive to the Ni/Al ratio. In contrast, the marked variation in the hardness of the γ phase were noted, increasing markedly with Al concentration in a given couple and also increasing with increasing Pt content. Possible causes for the observed variations are discussed.     

Morphology and structural stability of Pt–Pd bimetallic nanoparticles

The morphologies and structures of Pt–Pd bimetallic nanoparticles determine their chemical and physical properties.Therefore, a fundamental understanding of their morphologies and structural stabilities is of crucial importance to their applications. In this article, we have performed Monte Carlo simulations to systematically explore the structural stability and structural features of Pt–Pd alloy nanoparticles. Different Pt/Pd ratios, and particle sizes and shapes were considered.The simulated results reveal that the truncated octahedron, which has the remarkably lowest energy among all the considered shapes, exhibits the best structural stability while the tetrahedron has the worst invariably. Furthermore, all the structures of Pt–Pd alloy nanoparticles present Pd-rich in the outmost layer but Pt-rich in the sub-outmost layer. Especially, atomic distribution and chemical short-range order parameter were applied to further characterize the structural features of Pt–Pd alloy nanoparticles. This study provides a significant insight not only into the structural stability of Pt–Pd alloy nanoparticles with different compositions, and particle sizes and shapes but also to the design of bimetallic nanoparticles.     

Synthesis and characterization of highly textured Pt–Bi thin films

Pt–Bi films were synthesized on glass and thermally oxidized silicon substrates by e-beam evaporation and annealing. The structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) techniques. Single-phase PtBi was obtained at an annealing temperature of 300°C, whereas a higher annealing temperature of 400°C was required to obtain the highly textured γ-PtBi₂ phase. TEM/SAED analysis showed that the films annealed at 400°C contain a dominant γ-PtBi₂ phase with a small amount of β-PtBi₂ and α-PtBi₂ phases. Both the PtBi and γ-PtBi₂ phases are highly textured in these two kinds of film: the c-axis of the hexagonal PtBi phase is mostly in the film plane, whereas the c-axis of the trigonal γ-PtBi₂ phase is perpendicular to the film plane. The electrical resistivity of the film with the γ-PtBi₂ phase was smaller by one order of magnitude than that of the film with the PtBi phase.     

Tuning of size and shape of Au–Pt nanocatalysts for direct methanol fuel cells

In this article, we report the precise control of the size, shape, and surface morphology of Au–Pt nanocatalysts (cubes, blocks, octahedrons, and dogbones) synthesized via a seed-mediated approach. Gold “seeds” of different aspect ratios (1–4.2), grown by a silver-assisted approach, were used as templates for high-yield production of novel Au–Pt nanocatalysts at a low temperature (40 °C). Characterization by electron microscopy (SEM, TEM, HRTEM), energy dispersive X-ray analysis, UV–Vis spectroscopy, zeta-potential (surface charge), atomic force microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry were used to better understand their physico-chemical properties, preferred reactivities and underlying nanoparticle growth mechanism. A rotating disk electrode was employed to evaluate the Au–Pt nanocatalysts electrochemical performance in the oxygen reduction reaction (ORR) and the methanol oxidation reaction of direct methanol fuel cells. The results indicate the Au–Pt dogbones are partially and in some cases completely unaffected by methanol poisoning during the evaluation of the ORR. The ORR performance of the octahedron particles in the absence of MeOH is superior to that of the Au–Pt dogbones and Pt-black; however, its performance is affected by the presence of MeOH.     

Adsorption and interaction energy of π ethene on Pt(1 1 1) and Pt alloys: A detailed analysis of vibrational,energetic and electronic properties

We present a detailed analysis of the electronic and geometric bonding properties of the model alkene ethene on different mono- and bimetallic surfaces to establish the difference between adsorption energy and interaction energy and to elucidate the chemical character of a single platinum atom in different chemical environments. The adsorption of ethene on Pt(1 1 1) at 100 K leads to two adsorption states, which are commonly described as being of di-σ-type (bidentate, μ₂η²) and π-type (monodentate, μ₁η²). While the later is the minority species on Pt(1 1 1) it is of larger abundance on the platinum alloys. We have chosen π-bonded ethene for our study since it can be found on Pt(1 1 1), the Pt₃Sn and Pt₂Sn surface alloys, and Cu₃Pt(1 1 1). Density functional theory calculations of the adsorption structures, site and decomposed densities of states, as well as partial charge densities in conjunction with vibrational spectroscopy show that the bonding, i.e. the interaction energy, of the π ethene is only weakly influenced by alloying. Even in a copper matrix – as in the case of Cu₃Pt(1 1 1) – the bonding platinum atom essentially keeps its chemical identity and the interaction energy is reduced by only 14% compared to Pt(1 1 1). This observation suggests that bonding on surfaces is a strongly localized phenomenon. However, the adsorption energy decreases significantly due to alloying, which is attributed to the varying local relaxation of the different metal surfaces.     

Systematic study of rigid triaxiality in Ba–Pt nuclei and role of $$$$ subshell effect

A systematic variation of shape variables \(\beta \) and \(\gamma \) with N and \(N_\mathrm {p}N_\mathrm {n}\) is studied in the framework of an asymmetric rotor model of Davydov and Filippov for the \(Z=\) 50–82, \(N=\) 82–126 major shell space. The role of the \(Z=64\) subshell in producing smooth systematics has been discussed. The quadrupole moments are extracted after considering both axially symmetric and axially asymmetric nuclei. The correlation of \(\beta \) with \(\gamma \) together with the measured quadrupole moments indicates that \(\gamma \)-rigidity is better observed in nuclei with modest deformation.     

Structure and magnetic properties of the Co x Pt100−x nanowire arrays

The development of photocathodes materials has become an important task for X-ray free electron laser and new generation of particle accelerator. The choice of the optimum cathode type and its further improvement is a fundamental issue for the progress in radio-frequency photoinjectors. Metallic photocathodes offer several advantages over the semiconductor ones, e.g. long lifetime and prompt response time on the photoemission. This paper reviews the requirements and the current status of metallic photocathodes prepared by pulsed laser ablation deposition technique. Magnesium, yttrium and lead are proposed as good alternative to copper photocathode which is generally used in radio-frequency photoinjectors. Parametric studies of the irradiation conditions are demanded to optimize the metallic thin film deposition. The main achievements on the morphology and structure characterization as well as photoemission testing of metallic photocathodes are presented and discussed.     

Electrical,magnetic, and thermal properties of UCu5− x Pt x

We report measurements of the structural and electronic properties of UCu_{5??? x} Pt _x , a Pt-based analogue of the nFL system UCu_{5??? x} Pd _x , in the concentration range 0≤?x?≤?5. Forx?≤?2.5 and x?≥?4.5, the UCu_{5??? x} Pt _x system crystallizes in the AuBe₅ structure, but is mixed phase in the range 2.5?<?x?<?4.5. We observe a rapid suppression of long range antiferromagnetic order for small concentrations of Pt. The electrical resistivity, DC magnetic susceptibility, and specific heat of UCu_{5??? x} Pt _x in the concentration range 0.75?≤?x?≤?1 have temperature dependencies at low temperature (T?≤?10?K) consistent with the non-Fermi liquid behaviour found in UCu_{5??? x} Pd _x . Above x?=?1, there is a transition from non-Fermi liquid behaviour to Fermi liquid behaviour with no observation of any spin glass behaviour.     

Ab initio study of structural,electronic,thermo-elastic and optical properties of Pt3Zr intermetallic compound

Structural,elastic,electronic and optical properties of the Pt3Zr intermetallic compound are investigated using first principles calculations based on the density functional theory(DFT)within the generalized gradient approximation(GGA)and the local density approximation(LDA).The Pt3Zr compound is predicted to be of cubic L12 and hexagonal D024 structures.The calculated equilibrium ground-state properties(lattice parameters a and c,bulk modulus B and its pressure derivative B',formation enthalpy ΔH)of the Pt3Zr compound,for both cubic and hexagonal phases,show good agreement with the experimental results and other theoretical data.Elastic constants(C11,C12,C13,C33,C44,and C55)are calculated.The predicted elastic properties such as Young's modulus E and shear modulus GH,Poisson ratioν,anisotropic ratio A,Kleinman parameter ξ,Cauchy pressure(C12-C44),ratios B/C44 and B/G,and Vickers hardness Hv indicate the stiffness,hardness and ductility of the compound.Thermal characteristic parameters such as Debye temperature θD and melting temperature Tm are computed.Electronic properties such as density of states(DOS)and electronic specific heat γ are also reported.The calculated results reveal that the Fermi level is on the psedogap for the D024 structure and on the antibonding side for the L12 structure.The optical property functions(real partε1(ω)and imaginary part ε2(ω)of dielectric function),optical conductivity σ(ω),refraction index n(ω),reflectivity R(ω),absorption α(ω)and extinction coefficients k(ω)and loss function L(ω)are also investigated for the first time for Pt3Zr in a large gamme of energy from 0 to 70 eV.     

A study of melting of various types of Pt–Pd nanoparticles

The melting processes of various Pt–Pd nanoparticles (binary alloy, core–shell, D ≤ 4.0 nm) with different percent platinum atom content are investigated via the molecular dynamics using the embedded atom method potential in order to establish the thermal stability of simulated particle structure. In accordance with the data obtained, the most thermally stable are Pt–Pd nanoalloys with a diameter above 2.0 nm and core–shell Pd@Pt particles. As is shown, heating of binary Pt–Pd cluster alloys with the particle diameters less than 2.0 nm may cause the transition to pentagonal symmetry structures and core–shell-like complex formations.

     

Structural and Magnetic Properties of Ultrathin Fe Films on Pt（O01） Surface

Magnetic anisotropy evolution of ultrathin Fe films grown on Pt(001)single-crystal surface is investigated by UHV in situ surface magneto-optical Kerr effect (SMOKE)measurement.After annealing at～600K，the magnetic anisotropy of Fe film switches from in-plane to perpendicular at low coverage,leading to a spin reorientation transiton (SRT).Meanwhile,in the range of 3-4 monolayer (ML) thickness,the coercivity of the Fe polar hysteresis loop decreases dramatically.Further scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED) investigation correlates the magnetic properties with the film structures.We attribute this SRT to the formation of Fe-Pt ordered alloy.     

Synthesis of core–shell nanoparticles with a Pt nanoparticle core and a silica shell

A method to prepare a core–shell structure consisting of a Pt metal core coated with a silica shell (Pt(in)SiO₂) is described herein. A silica shell was grown on poly(vinylpyrrolidone) (PVP)-stabilized Pt nanoparticles 2–3 nm in size through hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) in a water/ethanol mixture with ammonia as a catalyst. This process requires precise control of the reaction conditions to avoid the formation of silica particles containing multiple Pt cores and core-free silica. The length of PVP molecules, water content, concentration of ammonia and Pt nanoparticles in solution were found to significantly influence the core–shell structure. By optimizing these parameters, it was possible to prepare core–shell particles each containing a single Pt nanoparticle with a silica layer coating approximately 10 nm thick.     

Effect of alloying on the stabilities and catalytic properties of Pt–Au bimetallic subnanoclusters: a theoretical investigation

Density functional theory (DFT) has been applied to study the geometrical and electronic structures and the catalytic properties for NO oxidation of pure Pt and PtAu clusters. The calculated results suggest that Pt₁₀ clusters shows the most stable structure among the pure Pt _n (n = 2–13) clusters with the local maximum Δ₂ E value. The doping of Au atoms reduces the stability of the clusters, and Pt₆Au₄ cluster has the most stable structure among Pt_10?n Au _n (n = 1–7) clusters, due to the closest band centers between Pt and Au atoms (0.83 eV) and the obvious s–p resonance peaks near the Fermi level. Pt₆Au₄ cluster displays the strongest activation of O₂ molecules among Pt_10?n Au _n (n = 0–7) clusters, owing to the clear overlap between O 2p and Pt 6 s and Au 6 s near the Fermi level, and the more positive d band center than the others. The interaction between NO and metals changes slightly in NO/Pt_10-nAu_n (n = 2–7) systems, which is weaker than that in NO/Pt₉Au system, as a result of the decreasing resonance peaks of sp hybridization near the Fermi level. Compared to pure Pt₁₀ cluster, the lower energy barriers and larger reaction energies on Pt₆Au₄ cluster suggest a higher catalytic activity of PtAu cluster for the O₂ dissociation and NO oxidation reactions. Our study provides atomic-scale insights into the nature of the interfacial effect that determines NO oxidation on PtAu cluster catalysts.     

γ-ray irradiation effect on hysteresis symmetry and data retention of Pt/SrBi2Ta2O9/Pt thin-film capacitors

The γ-ray irradiation effect on hysteresis symmetry and data retention of Pt/SrBi₂Ta₂O₉/Pt ferroelectric thin-film capacitors has been investigated as a function of irradiation dose. A horizontal shift of polarization–voltage curves along the voltage axis, known as imprint, was observed after the polarized capacitors had been irradiated. The voltage shift increased with increasing irradiation dose and increasing remanent polarization written before irradiation. After irradiation, severe data loss was observed after these capacitors had been written to the state opposite to the one stored during irradiation. Possible functional failure due to such a data loss was discussed. Received: 17 January 2001 / Revised version: 27 April 2001 / Published online: 20 June 2001     

Pressure–volume–temperature equations of state of Au and Pt up to 300 GPa and 3000 K: internally consistent pressure scales

By using a Mie–Grüneisen-type analysis method, the pressure–volume–temperature equations of state (P–V–T EOSs) of Au and Pt have been determined up to 300?GPa and 3000?K based on the experimental shock Hugoniot and thermodynamic data. The calculated results of Au and Pt show an excellent agreement with available experimental volume compression data over a wide range of pressures and temperatures. A comparison of our results with previous theoretical investigations has also been done. In addition, we have further examined the consistency of our results and the P–V–T EOS of MgO [K. Jin, X.Z. Li, Q. Wu, H.Y. Geng, L.C. Cai, X.M. Zhou, and F.Q. Jing, The pressure–volume–temperature equation of state of MgO derived from shock Hugoniot data and its application as a pressure scale, J. Appl. Phys. 107 (2010), pp. 113518] using simultaneous volume measurements of Au, Pt, and MgO at various temperatures. The good agreement among the P–V–T EOSs of Au, Pt, and MgO implies that these EOSs can be used as the reliable pressure scales in high pressure–temperature diamond anvil cell experiments.     

States and homomorphisms on the Pták sum

Summing of a Boolean algebra and a quantum logic has been defined by P. Pták and studied by, e.g., V. Jani, Z. Rieanová, O. Nánásiová, and C. A. Drossos. It was shown that there is a special case when this structure is a direct product. Drossos has studied the connection between this structure and a Boolean power. In this paper we investigate the conditions when the Pták sum is a free product and when the connection is between the center ofL and the structure of states onBL.