Resistivity Of Pd Research Articles

Development of a Pd/Cu nanowires coated SAW hydrogen gas sensor with fast response and recovery

Employing palladium and copper nanowires (Pd/Cu NWs) as the sensitive interface, a new surface acoustic wave (SAW) sensor with fast response and recovery was developed successfully for hydrogen gas sensing. The adsorption in Pd/Cu NWs towards hydrogen molecules modulates the SAW propagation by the induced acoustoelectric coupling effect from the changes in the resistivity of Pd, and the corresponding shifts in oscillation frequency proportional to gas concentration was collected as the sensor signal. Larger surface-to-volume of the Pd/Cu NWs contributes to improve the response speed and sensitivity. A 150 MHz SAW device with delay line pattern was fabricated photolithographically on 128° YX LiNbO3 substrate, and the Pd/Cu NWs that synthesized by optimized electrochemical deposition were dissolved in ethanol and deposited onto the SAW device surface by dropping method to build the SAW hydrogen sensors. The prepared SAW sensors were characterized by using the differential oscillation loop experimentally, excellent repeatability, fast response and recovery within 4s, and a sensitivity of 1.5 kHz/%were achieved at room temperature (25°C). Additionally, the response mechanism in hydrogen sensing was investigated experimentally.

Growth of Pd4S, PdS and PdS2 films by controlled sulfurization of sputtered Pd on native oxide of Si

Thin films of different Pd–S phase, namely Pd4S, PdS and PdS2, have been reproducibly grown by the sulfurization of Pd films deposited on native oxide of (111) Si substrates by radio frequency sputtering method. In order to achieve controlled sulfurization, a three-stage sulfurization setup consisting of evaporation chamber, activation chamber and sulfurization chamber has been developed. The sulfurization of Pd films (kept at a constant temperature of 500°C) was carried out using sulfur vapors activated to different temperature between 550 and 700°C. The results of X-ray diffraction and X-ray photoelectron spectroscopy measurements show that formation of Pd4S, PdS and PdS2 phases takes place for the activation temperatures of 550, 600 and 700°C, respectively. The room temperature resistivity of Pd, Pd4S, PdS and PdS2 were found to be respectively 0.1, 15.9, 15,000 and 20,000μΩ cm. The temperature-dependent electrical resistivity measurements showed metallic conduction for Pd and Pd4S films. The Seebeck coefficient measured at 300K for these Pd–S phases showed their n-type conducting behavior.

The influence of nanoscale morphology on the resistivity of cluster-assembled nanostructured metallic thin films

We have studied in situ the evolution of the electrical resistivity of Fe, Pd, Nb, W and Mo cluster-assembled films during their growth by supersonic cluster beam deposition. We observed resistivity of cluster-assembled films several orders of magnitude larger than the bulk, as well as an increase in resistivity by increasing the film thickness in contrast to what was observed for atom-assembled metallic films. This suggests that the nanoscale morphological features typical of ballistic films growth, such as the minimal cluster–cluster interconnection and the evolution of surface roughness with thickness, are responsible for the observed behaviour.

Electrical resistivity, strain and permeability of Pd–Ag membrane tubes

A Pd–Ag (silver 25 wt.%) permeator tube has been tested in order to measure the electrical resistivity, the strain, and the hydrogen permeability under different hydrogenation conditions in the temperature range 50–400 °C. The permeator tube has been assembled into the membrane module in a finger-like configuration: pure hydrogen has been fed in the lumen side of the tube at a pressure of 100–400 kPa while the permeated hydrogen has been recovered in the shell side of the membrane via a nitrogen purge gas stream of 3.70 × 10 −4 mol s −1 at atmospheric pressure. The electrical resistivity increases with both the temperature and hydrogen pressure but a minimum of the resistivity is present at 100 °C. The strain of the hydrogenated material increases with the hydrogen pressure and reduces with the temperature. Moreover, the relationship between the strain and the hydrogen content has been investigated and a power law for isotherms in the temperature range 50–400 °C has been found out. Values of hydrogen permeability of 1–2 × 10 −8 mol m −1 s −1 Pa −0.5 have been measured in the temperature range 200–400 °C: the results showed a modest influence of the hydrogen pressure while the dependence from the temperature follows the Arrhenius’ law in agreement with literature.

Effect of exchange bias on the electrical resistivity of Pd doped NiMn thin films: Two-channel Kondo system

Electrical resistivity measurements have been carried out for both flash-evaporated reentrant spin glasses (RSGs) (Ni76−xPdx)Mn24 and Ni74.5Mn23.5Pd2, as well as Ni75Mn23Pd2, a pure SG. These measurements were carried out at temperatures down to 4K. We observed a very deep resistivity minimum at about 75K for Ni74Mn24Pd2. It was found previously [Öner et al., J. Appl. Phys. 89, 7044 (2001)] that this sample shows the largest coercivity and exchange unidirectional anisotropy among these films. In addition, magnetization measurements show that this takes place just on the border of the RSG such that it could be handled as a superparamagnetic sample. Previously it was assumed that the exchange bias created in the sample between the domains plays the dominant role in the resistivity minimum. On the other hand, in order to account for the temperature dependence of the resistivity below the minimum we have analyzed these data using the Kondo, two-channel Kondo, weak localization, and Cochrane models for structural disorder based on the Anderson mechanism. We have deduced that the two-channel Kondo model gives the best agreement with the data; a logarithmic temperature dependence Δρ(T)=βlog10(T∕TK), was observed at the temperatures below Tf accompanied by a resistivity behavior Δρ(T)=ρ0m(0)(1−αT1∕2), at lower temperatures. All parameters deduced from the fitting correlate consistently with the strength of the exchange anisotropy and coercivity in the RSG films, and thus provide a separate measure of the presence of antiferromagnetically coupled domains in these materials.

Thermal stability improvement by using Pd∕NiO∕Al∕Ti∕Au reflective ohmic contacts to p-GaN for flip-chip ultraviolet light-emitting diodes

The thermal stability, optical reflectivity, and contact resistivity of Pd∕NiO∕Al∕Ti∕Au ohmic contacts to p-type GaN were investigated. In contrast to Pd∕Ni∕Al∕Ti∕Au counterparts, the ohmic contacts Pd∕NiO∕Al∕Ti∕Au retained their specific contact resistivity (<3.3×10−2Ωcm2) and high reflectivity (>75% @ 370 nm) after a long thermal aging at 200 °C for 100 h in nitrogen ambient. According to the results of the secondary ion mass spectroscopy in-depth profiles study, it is found that the NiO layer is more transparent and a better diffusion barrier than Ni to prevent the penetration of upper metals into p-type GaN during thermal treatment.

High-reflectivity Pd∕Ni∕Al∕Ti∕Au ohmic contacts to p-type GaN for ultraviolet light-emitting diodes

Thermal stability, optical reflectivity, and contact resistivity of Pd∕Ni∕Al∕Ti∕Au ohmic contacts to p-type GaN were investigated. In contrast to its Pd∕Al∕Ti∕Au counterparts, Pd∕Ni∕Al∕Ti∕Au contacts retained their specific contact resistivity (<2×10−2Ωcm2) and reflectivity (>76%) after long-term annealing at 150 °C in nitrogen ambient. According to the results of the secondary ion mass spectroscopy study, it is suggested that the Ni layer prevents the penetration of Ti into GaN during thermal treatment.

Resistivity maximums due to growth of hydrogen-ordered domains in resistivity curves of Pd–H alloys during heating up with constant rates

The resistivity maximum in the isothermal annealing curve of Pd–H(D) alloys is caused by the nucleation and growth of ordered domains of hydrogen (deuterium) atoms as reported in a previous paper; the resistivity increases in the early stage of hydrogen (deuterium) ordering and decreases in the later stage. In order to determine whether a similar decrease of electrical resistivity is present in the heating-up curves during hydrogen ordering, the resistivity of Pd–H alloys is investigated for various hydrogen concentrations and various constant heating-up rates. Two resistivity maximums, or one maximum and hump are observed in the curves at low heating-up rates, i.e. the resistivity decrease due to the ordering different from the decrease due to the disordering is clearly separated as the first maximum. The heating-up rates observed in the above separation depend on the hydrogen concentration.

Piezoresistance and electrical resistivity of Pd, Au, and Cu films

Electrical resistivity and piezoresistance of some metal films, such as the Pd, Au, and Cu films, were measured. Surface features of a few characteristic films, used in this study, were revealed by using an atomic force microscope. The electrical resistivity ρ is plotted as a function of the film thickness t, and the strain gauge factor γ is plotted as a function of the sheet resistivity R sq. Two parameters are found useful: i.e. h/λ and 2 h/ t, where h is the amplitude of undulations of the surface roughness and λ is the electron mean free path at room temperature. By taking the Cu film as an example, the area-distribution function of island-like humps on the specimen surface is also analyzed. Two models, namely the surface roughness and the electron tunneling models, are employed to explain the electrical resistivity and piezoresistance data observed. It is found that (1) if h/λ⩽0.3 and 2 h/ t<0.5, the films are continuous, and the former model is effective, and (2) if 0.5<2 h/ t<1, the films are critically coalesced, and the latter model is important. Finally, from the area-distribution plot, we can show indirectly that if the film is at the coalescence stage, the average separation Δ d between two neighboring humps is wider than if the film is at the continuous stage.

Temperature Dependence of Magnetization and Electrical Resistivity of Weak Itinerant Ferromagnetic Pd in NiO/Pd Multilayers

The temperature dependence of magnetization and electrical resistivity of ferromagnetic Pd is investigated using NiO/Pd multilayers. The temperature dependence of the magnetization M ( T ) shows there is a fairly large region of T 2 dependence below the Curie temperature T C and M ( T )∝( T C 4/3 - T 4/3 ) 1/2 near T C . The resistivity is proportional to T 5/3 over a wide temperature range after T 2 dependence. These temperature dependences are well explained by spin fluctuation theory and it is experimentally supported that Pd in NiO/Pd multilayers is a weak itinerant ferromagnet.

Effect of surface treatment by (NH4)2Sx solution on the reduction of ohmic contact resistivity of p-type GaN

Surface treatment using aqua regia and (NH4)2Sx solution in sequence prior to Pd metal deposition was effective in reducing the contact resistivity of Pd to p-type GaN. The contact resistivity was drastically decreased from 3.6×10−1 to 2.9×10−4 Ω cm2 by the treatment. The surface oxides formed on p-type GaN during epitaxial growth were effectively removed using aqua regia, and the following (NH4)2Sx treatment protected the surface from the formation of oxides during air exposure. The reduction of the contact resistivity is due to the direct contact of Pd to the clean surface of p-type GaN, via shift of the Fermi level to an energy level near the valence band, resulting in the reduction of the barrier height for holes at the interface of Pd/p-type GaN.

Electrical conductivity of one-dimensional halogen-bridged metal complexes at high pressures

The resistivity of four one-dimensional halogen-bridged metal complexes, Pt 2(CH 3CS 2) 4I and M(chxn) 2X 3 (M = Ni, Pd, Pt; X = Br; I; chxn = 1R, 2R-cyclohexanediamine), has been studied up to 7 GPa under quasi-hydrostatic conditions. The resistivity of Pt 2(CH 3CS 2) 4I and Ni(chxn) 2Br 3 with regular chains monotonically decreased with increasing pressure. On the other hand, the resistivity of Pd(chxn) 2Br 3 and Pt(chxn) 2I 3 with alternating lienar chains rapidly decreased in the low pressure region. The activation energy of the four metal complexes was in the range 0.03–0.05 eV at 7 GPa. Metallic behavior was not observed even at high pressures. The electrical conduction of the complexes is discussed.

On the T2-dependence of the electrical resistivity of Pd and PdH films

By vapor-quenching onto liquid-helium cooled substrates, Pd and PdH films of different thicknesses (5 nm < D < 50 nm were prepared and the T 2-dependence of the electrical resistivity was studied in situ By stepwise annealing, the degree of disorder could be systematically changed and the corresponding influence of the T 2-dependence was investigated. For pure Pd-films a T 2-dependence is observed in the range between 35 and 50 K. The corresponding coefficient (400 × 10 −6 μΩ cm K −2) is found to be independent of disorder and film thickness, but by a factor of 1.33 larger than for Pd bulk samples. The PdH x-films also show a T 2-dependence in the same temperature range, but with a significantly smaller coefficient, the value depending on whether the hydrogen is incorporated by an equilibrium or a non-equilibrium technique.

Deviations of Matthiessen's rule in some PdAu alloys

The low temperature electrical resistivity of Pd 1−cAu c alloys ( c = 0.1, 0.22, 0.38, 0.69, 0.82 and 1.1 at.%) have been studied in detail between 1.5 and 300 K. Deviations from Matthiessen's rule (DMR) have been analysed on the basis of a two-band model, and the agreement is found to be reasonably good. The parameter λ was found to decrease monotonically with temperature, and no anomalous maximum was observed as with earlier studies of Pd Ti. The variation of β shows a weak temperature dependence. The limitations of the model are also discussed.

Effect of structural relaxation on the electrical resistivity of Pd 82−xV xSi 18 amorphous alloys

The dependence of the resistivity-temperature and resistivity-structural relaxation behavior of amorphous Pd 82−xV xSi 18 alloys on Vanadium content, 0≦ x≦6, was investigated. The temperature coefficient of resistivity at constant volume decreases with x, going from positive to negative at x≈4, while the resistivity change due to structural relaxation (π relaxed - π unrelaxed) increases with x, going from negative to positive at x≈2. This behavior is shown to be consistent with the Ziman theory.

Some muffin-tin calculations of electrical resistivity in molten palladium

Abstract Calculations of the electrical resistivity of liquid Pd are presented, based upon a number of muffin-tin potentials with the effect of neighbours and exchange-correlation treated in some approximations of current interest. The T-matrix extension of the Ziman theory is used and the electronic density of states is treated in the single-site approximation. Comparisons are then made with recent experimental work on liquid Pd.

The T3 Term in the Diffusion Thermopower, Applications to Pd, Pt, and Their Alloys

The free electron thermopower is derived to order T3. We also obtain a useful approximate expression relating the coefficient of T3 in the thermopower to the coefficient of T2 in the residual resistivity of Pd, Pt, and some of their alloys.

The electrical resistivity of liquid Fe, Co, Ni and Pd

The electrical resistivity of Fe, Co, Ni and Pd has been measired at high temperatures in the solid and liquid state. We discuss the results in the light of recent ideas on the Ziman theory and the spin-disorder scattering of liquid transition metals.

Electrical resistivity of PdH x: I. Residual resistivity

Results are presented for the electrical resistivity of PdH x alloys at several fixed temperatures. The residual resistivity goes through a maximum at x = 0.73 and then drops sharply as x approaches 1. From this we conclude that the residual resistivity for 0.8 < x < 1 is due primarily to vacancies in the hydrogen lattice and that the hydrogen atoms occupy only the octahedral sites of the Pd lattice. The absolute values of the residual resistivity are in reasonable agreement with theoretical expectations.

D resonance calculation of the resistivity and thermopower of liquid Ni and Pd

Calculations are given of the d resonant contribution to the resistivity and thermopower of liquid Ni and Pd, using the T matrix formulation of Evans et al. The d wave resonance energies and widths are taken from recent calculations in the literature and the parameters entering the model calculations are taken from recent experimental data. A comparison of results is given using the measured liquid structure factor of Ni and the theoretical hard sphere model results of Percus-Yevick. A comparison with other recent calculations and with existing experimental data is given.