New Spectroscopic Information on 98Pd

Neutron deficient ⁹⁸Pd nuclei were produced in the ⁵⁰Cr(⁵⁸Ni,2p2α)⁹⁸Pd reaction at a beam energy of 261 MeV. A revision and extension of the level structure of ⁹⁸Pd is proposed. About 40 new transitions have been assigned to, and placed in the level scheme of this nucleus. A sequence of states are candidates for the negative parity 4—quasiparticle states built on the πg _9/2 ^?3 πp _1/2 ^?1 configuration predicted in the framework of the nuclear shell model.     

Two-quasiparticle and collective excitations in transitional 108,110 Pd nuclei

High-spin states in ^108,110Pd isotopes are studied by -ray spectroscopy of heavy-ion-induced fission. The Pd isotopes are produced in the fission channel of the ³¹P + ¹⁷⁶Yb reaction at beam energy 152 MeV. The prompt -rays are detected with the EUROBALL4 multidetector array. The yrast states of ^108,110Pd have been observed above the region of the first backbend. The level scheme of ¹⁰⁸Pd was extended with a new negative-parity band. The yrast sequence in ¹¹⁰Pd is observed up to spin I = 14 ⁺ and negative-parity bands have also been identified. The backbending in these even-mass Pd isotopes is associated with the alignment of the neutron (h _11/2)² pair. The negative-parity states arise from two neutron configurations and and they are interpreted in the frame of two-quasiparticle + rotor model as semidecoupled bands. The observed experimental staggering in the -bands of ^108,110Pd supports the theoretical predictions for -instability of their shapes.Received: 22 April 2003, Revised: 27 June 2003, Published online: 2 December 2003PACS: 21.60.-n Nuclear structure models and methods - 23.20.Lv transitions and level energies - 25.70.Jj Fusion and fusion-fission reactions - 27.60. + j      

Synthesis of Pd/Pt core/shell nanostructures with truncated-octahedral morphology toward formic acid oxidation

In this study, a simple one-pot method was adopted to synthetize Pd/Pt core/shell nanostructures with truncated-octahedral morphology. The morphology of the obtained Pd/Pt nanoparticles was characterized by transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). In addition, the composition was determined by energy-dispersive X-ray spectroscopy (EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the electric structures were studied by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Based on the above results, it could be noticed that Pd/Pt core/shell nanostructures with truncated-octahedral morphology were produced, where the core consisted of Pd atoms and the shell consisted of Pt atoms. In order to test the catalytic properties of the prepared Pd/Pt nanoparticles, cyclic voltammetry (CV) was carried out in 0.5 M H₂SO₄ and 0.5 M H₂SO₄ + 1 M HCOOH. Compared with commercial Pt black, the Pd/Pt core/shell nanostructures with truncated-octahedral morphology exhibited higher activity and stability toward formic acid oxidation.

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Graphical abstract Pd/Pt core/shell nanostructures which exhibit excellent activity and stability are synthesized by a simple one-pot method

     

Fractal Germanium Patterns: Annealing Strategies and Perspectives of Metal-Induced Crystallization

Semiconductor germanium (Ge) in contact with some metals, such as Al, Pd, and Au, etc., is a class of distinctive materials with non-integer dimensions (D) that differ from integer dimensional materials, such as nanoparticles (0D), nanowires/nanorods//nanotubes/nanoribbons (1D), and thin films (2D). In this article, we describe our efforts toward understanding the annealing strategies and perspectives of metal-induced crystallization for the amorphous Ge embedded in Al, Pd, and Au matrices prepared by high vacuum thermal evaporation techniques, highlighting contributions from our laboratory. First, we present the Al-induced crystallization of amorphous Ge and formation processes of fractal Ge patterns. In addition, the fractal Ge patterns induced by Pd nanoparticles with solid-state reactions will be summarized in detail. Temperature-dependent properties of resistance and fractal dimension in Pd/Ge bilayer films will be expounded. In particular, the nonlinear optical properties are discussed in detail. Finally, we will emphasize the in situ observations by transmission electron microscopy and multi-fractal analysis for the fractal Ge patterns induced by Au nanoparticles. Moreover, the polycondensation-type fractal Ge patterns with non-integer dimensions, thick branches and smooth edges, and metastable gamma-Au_0.6Ge_0.4 are further investigated. The computer simulation indicated that the experimental results are good agreement with the simulation patterns, which were carried out by a ripening mechanism of non uniform grains. This review may provide a novel insight to modulate their competent performance and promote rational design of micro/nanodevices.     

Preparation of metallic Pd nanoparticles using supercritical CO<Subscript>2</Subscript> deposition: An efficient catalyst for Suzuki cross-coupling reaction

Ligand-free palladium nanoparticles supported on multi-walled carbon nanotubes (Pd/MWCNT) were prepared by the supercritical carbon dioxide (scCO₂) deposition method using a novel scCO₂-soluble Pd organometallic complex as a precursor. The precursor with the perfluoroalkyl chain group was synthesized and identified by microanalytic methods. The deposition was carried out at the temperature of 363.15 K and pressure of 27.6 MPa CO₂. The prepared metallic nanoparticles were obtained with an average size of 2 nm. Pd/MWCNT was utilized as a heterogeneous catalyst in Suzuki cross-coupling reaction. The nanocatalyst was found very effective in Suzuki reaction and it could also be recovered easily from the reaction media and reused over several cycles without significant loss of catalytic activity under mild conditions.

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Graphical Abstract Pd/MWCNT was prepared by the scCO2 deposition method using a new synthesized perfluroalkylated vic-dioxime Pd complex as the precursor. The prepared nanoparticle was very effective as catalyst and reusable for Suzuki cross coupling reaction under mild conditions.

     

Intrinsic point defects in niobium: Trapping at100Pd and111In impurities observed by PAC

Radiation-induced lattice defects in high-purity niobium have been investigated in the temperature range of 30K to 540 K by means of - perturbed angular correlation (PAC) measurements using the radioactive probes¹⁰⁰Pd/¹⁰⁰Rh and¹¹¹In/¹¹¹Cd. Both probes were produced within the niobium samples by means of heavy-ion nuclear reactions. At the Pd impurities trapping of defects occurred during heavy-ion irradiation at about 30 K in two defined configurations: defect 1(Pd) withv _Q1=e ² qQ/h=42(±2) MHz, ₁=0 and defect 2 (Pd) withv _Q2=(±2) MHz, ₂=1. Two defects were observed at the In impurities in annealing stage III (around 250 K) after heavy-ion as well as electron irradiations: defect 1(In) withv _Q1=87(±1) MHz, ₁=0 and defect 2(In) withv _Q2=105(±2) MHz, ₂=0.65(±0.02). A third defect (defect 3(In):v _Q3=177(±2) MHz, ₃0.2) appeared above 260 K after heavy-ion irradiation only. The data are interpreted in terms of interstitial trapping at the Pd impurities and vacancy trapping at the In impurities. Information on the microscopic structure of defect 1(In) and 2(In) is obtained from a PAC-single-crystal experiment. For defect 1(In) axial 111-symmetry is found, which leads us to identify this defect with a monovacancy as nearest neighbor with respect to the In probe. Defect 2(In) is the trapped divacancy for which an orientation is found that is consistent with both vacancies being nearest neighbor to the probe but second nearest neighbors to each other.     

Diffusion of Al in ion-implanted Pd and Pt

The diffusion coefficients of aluminium have been measured in polycrystalline fcc Pd and Pt. The Al-implanted palladium and platinum samples were annealed at 400°–800 °C and 450°–900 °C, respectively. The aluminium profiles were probed using the nuclear resonance broadening (NRB) technique. Values of (1.41±0.09) and (1.38±0.09) eV for the activation energy and (1.5 _–1.0 ⁺⁵ )×10^–6 and (4 _–3 ⁺¹⁰ )×10^–7cm²/s for the frequency factor were obtained for Al in Pd and Pt, respectively. These anomalous results, compared to the normal impurity diffusion, were checked using also Al-evaporated samples.     

UV-activated gas sensing properties of ZnS nanorods functionalized with Pd

Pd-functionalized ZnS nanorods were prepared for use as gas sensors. Scanning electron microscopy revealed the diameters and lengths of the nanorods ranging from 30 to 80 nm and from 2 to 5 μm, respectively. The diameter of Pd nanoparticles ranged from 2 to 5 nm. Transmission electron microscopy revealed that ZnS nanorods and Pd nanoparticles were monocrystalline and amorphous, respectively. The responses of multiple networked ZnS nanorods sensors to 1–5 ppm NO₂ were increased substantially by a combination of Pd functionalization and UV irradiation. Pristine ZnS nanorod sensors at room temperature in the dark showed a response (∼100%) almost independent of NO₂ concentration in a NO₂ concentration range of 1–5 ppm. Pristine ZnS nanorod sensors showed enhanced responses of 214–603% to 1–5 ppm NO₂ at room temperature under UV illumination. Pd-functionalized ZnS nanorods sensors showed further enhanced responses of 355–1511% to 1–5 ppm NO₂ at room temperature under UV illumination. The NO₂ gas sensing mechanism of the Pd-functionalized ZnS nanorods sensors under UV illumination is discussed in depth.     

Optical and electrochemical properties of cyclometalated Pd(II) and Pt(II) complexes with a metal-metal chemical bond

Cyclometalated [M(C^N)(μ-(N-S))]₂ complexes ((M = Pd(II), Pt(II)), (C^N)^? are the deprotonated forms of 2-tolylpyridine and benzo[h]quinoline, and (N-S)^? are pyridine-2-thiolate and benzothiazole-2-thiolate ions) are studied by ¹H NMR, IR, electronic-absorption, and emission spectroscopy, as well as by voltammetry. It is shown that the formation of the metal-metal chemical bond and the σ _dz2 ^* orbital as a HOMO of complexes leads to the long-wavelength spin-allowed (410–512 nm) and spin-forbidden (595–673 nm) optical transitions σ _dz2 ^* ?π _(C^N) ^* in the absorption and phosphorescence spectra, as well as to the two-electron and successive one-electron oxidation with the formation of binuclear Pt(III) and Pd(III) complexes. The substitution of Pt(II) by Pd(II) is characterized by hypso- and bathochromic shifts of the spin-allowed and forbidden σ _dz2 ^* ?π _(C^N) ^* optical transitions in the absorption and phosphorescence spectra of complexes, by phosphorescence quenching of Pd(II) complexes in liquid solutions, and by an anodic shift of the oxidation potential of Pd(II) complexes compared with Pt(II) complexes.     

PAC Measurements on New Ferromagnetic Compound Pd2TiSn

Magnetic hyperfine field (mhf) acting on ¹⁸¹Ta at the Ti site has been investigated in the alloy Pd₂TiSn by Perturbed Angular Correlation (PAC) measurements using the (133–482) keV – cascade in ¹⁸¹Ta following the ^– decay of ¹⁸¹Hf. The magnetic hyperfine field was measured as a function of temperature in the range of 45–1000K. The magnetization measurements were carried out with a vibrating sample magnetometer. The interpretation of the experimental results is based on the assumption that the probe nuclei occupy both the regular Ti sites as well as the Ti atom sites randomly distributed on the Pd sublattice.     

Pd,Ge薄膜体系中的分形晶化行为

利用透射电子显微镜（ＴＥＭ）对有化合物生成（Ｐｄ₂Ｇｅ和ＰｄＧｅ等）的Ｐｄ，Ｇｅ薄膜体系中的分形晶化行为进行了系统研究实验结果和分析表明：在各种退火温度条件下，Ｐｄ－Ｇｅ共蒸膜都难以发生分形晶化，Ｐｄ／ａ－Ｇｅ双层膜较ａ－Ｇｅ／Ｐｄ双层膜更容易导致分形结构的产生Ｚ化合物Ｐｄ₂Ｇｅ和ＰｄＧｅ的形成对薄膜中的分形晶化有明显的抑制作用，体系中能否出现分形结构，取决于非晶Ｇｅ的成核生长和Ｐｄ，Ｇｅ化学反应两种过程的相互竟争． 关键词：     

Isomeric cross section ratio for110Pd(n,2n)109Pd reaction at 14.7 MeV

Reaction¹¹⁰Pd(n, 2n)¹⁰⁹Pd has been investigated at 14.7 MeV neutrons. Cross sections for the formation of^109m Pd and^109g Pd were measured. Experimental value of the isomeric cross section ratio has been compared with the theoretical calculation performed with the Huizenga and Vandenbosch method.     

Defect trapping by100Pd in fcc metals

Lattice defects in Al, Cu, Ag and Au were studied by the perturbed angular correlation technique (PAC) using the probe atom¹⁰⁰Pd/¹⁰⁰Rh. The comparison of data obtained on interstitial trapping in Cu and Au at different probe atoms (¹⁰⁰pd,¹¹¹In) allows defect characterisation less affected by the respective probe. The trapping efficiency of¹⁰⁰Pd for vacancy like defects is quite different to that of¹¹¹In atoms.     

Electric quadrupole interaction of181Ta in Pd and Zn

A strong electric field gradient (EFG) has been observed at¹⁸¹ Ta in Pd and Zn metals using DPAC technique. The value of the EFG in Pd is found to be 12.5(8)×10¹⁷ V/cm² with an asymmetry parameter () of 0.33(2). The value of the EFG in Zn has the same value as in the Pd metal, but the asymmetry parameter has the value 0.36(3). The variation of EFG in Pd with temperature has shown a weak dependence. The results are interpreted in terms of oxygen trapping at Hf atoms during the sample preparation.     

Novel urchin-like Pd nanostructures prepared by a simple replacement reaction and their catalytic properties

Novel urchin-like Pd nanostructures were firstly synthesized using a simple replacement reaction between Al and PdCl₂ aqueous solution at room temperature without the assistance of any surfactant or ligand. Their phase structure, morphology, specific surface area, and catalytic property were characterized by XRD, TEM, EDS, BET and DSC/TG. The results show numerous one-dimensional Pd nanorods radiate from the center of the aluminum templates to form an urchin-like shape with a diameter of ∼0.5-1.0 μm. The as-prepared urchin-like Pd nanostructures can serve as a promising additive to accelerate the thermal decomposition of ammonium perchlorate (AP), a key oxidizer in composite solid propellants.     

Hydrogen and ozone gas sensing using multiple ZnO nanorods

ZnO nanorods grown by site-selective molecular beam epitaxy show current–voltage characteristics that are sensitive to the presence of hydrogen or ozone in the measurement ambient for temperatures as low as 112 °C for H₂ or room temperature for O₃. The sensitivity to hydrogen increases sharply with temperature and multiple nanorods contacted at both ends by ohmic electrodes show currents of 10^-8 A at 200 °C and a differential current change of 18% when changing from a pure N₂ ambient to 10% H₂ in N₂. The nanorods are able to detect small concentrations (3%) of O₃ in O₂, with changes in current of 10^-7 A at 25 °C. The sensitivity was 21% for O₃ at room temperature. The nanorods also show a strong response to above-band-gap illumination with ultraviolet light. PACS 81.05.Dz; 73.61.Ga; 72.80.Ey     

Functionalized Pd/ZnO Nanowires for Nanosensors

A method for surface doping and functionalization of ZnO nanowires (NWs) with Pd (Pd/ZnO) in a one‐step process is presented. The main advantage of this method is to combine the simultaneous growth, surface doping, and functionalization of NWs by using electrochemical deposition (ECD) at relatively low temperatures (90 °C). Our approach essentially reduces the number of technological steps of nanomaterial synthesis and final nanodevices fabrication with enhanced performances. A series of nanosensor devices is fabricated based on single Pd/ZnO NWs with a radius of about 80 nm using a FIB/SEM system. The influence of Pd nominal composition in Pd/ZnO NW on the H₂ sensing response is studied in detail and a corresponding mechanism is proposed. The results demonstrate an ultra‐high response and selectivity of the synthesized nanosensors to hydrogen gas at room temperature. The optimal concentration of PdCl₂ in the electrolyte to achieve extremely sensitive nanodevices with a gas response (S_H2) ≈ 1.3 × 10⁴ (at 100 ppm H₂ concentration) and relatively high rapidity is 0.75 µM. Theoretical calculations on Pd/ZnO bulk and functionalized surface further validated the experimental hypothesis. Our results demonstrate the importance of noble metal presence on the surface due to doping and functionalization of nanostructures in the fabrication of highly‐sensitive and selective gas nanosensors operating at room temperature with reduced power consumption.     

Lattice dynamics of a Pd0.90Rh0.10 crystal

Using inelastic neutron scattering, the phonon dispersion relations along the [100], [110] and [111] directions of a single crystal of Pd_0.90Rh_0.10 have been measured at 296K. From these results and phonon data for Pd, the phonon frequency shifts,(q), and the self-energy function, _j (q, _j (q)), have been determined for all branches. The frequency changes exhibit large wave vector and polarization dependence and behave non linearly with the increase concentration of Rh. The seventh neighbour tensor Born-von Kármán model has been fitted to the experimental phonon dispersion curves, and the force constants and elastic constants calculated. Correlations between the phonon anomalies, displayed in the slope ofT ₁ [110] branch, and the structure of the generalized susceptibility function, ₀(q), for Pd were discussed. From which follows the influence of the electron-electron interaction on theT ₁ [110] branch in Pd and Pd-Rh alloys.     

Anomalous ferromagnetic behavior of CuO nanorods synthesized via hydrothermal method

Copper monoxide (CuO) nanorods of 30-40 nm in diameter and 100-200 nm in length were successfully synthesized using a hydrothermal reaction method in the presence of sodium citrate. On the basis of the morphology observation and X-ray diffraction patterns of the samples, a possible growth mechanism of the CuO nanorods was proposed. The magnetic properties of CuO nanorods were studied using a SQUID magnetometer and a vibrating sample magnetometer. It was interesting to note that the as-synthesized CuO nanorods showed an anomalous ferromagnetic behavior. The coercive force (H_c) for the CuO nanorods at and were estimated to be 331.39 and 175.88 Oe, respectively. The anomalous ferromagnetic behavior of the as-synthesized CuO nanorods was discussed in terms of the effect of the peculiar morphology.