Laser-assisted activation of dielectrics for electroless metal plating

2 O₃, SiC, diamond, ZrO₂, etc. are presented. The activation of the dielectric surface can be achieved in a wide range of laser wavelengths and is stable in time. This activation allows selective deposition of various metals (Cu, Ni, Pt, Pd, etc.) with lateral dimensions of several μm. The model of the activation process is discussed. This deals with the modification of the band gap of the dielectric, which involves the appearance of a non-zero density of electronic states in the vicinity of the potential of electroless metal reduction. These electronic states can arise either from the formation of point defects in the ablated surface (for example, F centers in Al₂O₃, CeO₂, or ZrO₂) or from the band bending of the dielectric caused by residual mechanical stresses left in the material after laser ablation (SiC or diamond). The data on the activation of dielectrics by mechanical indentation are qualitatively consistent with the model. Received: 5 January 1998/Accepted: 7 January 1998     

Improved electroluminescence performance of ZnS:Cu,Cl phosphors by ultrasonic treatment

ZnS:Cu,Cl electroluminescence (EL) phosphors were prepared by high-temperature (1150 °C) solid-state reaction, subsequent ultrasonic treatment (t=0-60 min) and final low-temperature annealing process at 750 °C. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), UV-vis absorbance spectra, electron probe microanalyzer (EPMA) and photoluminescence (PL) spectra. EL performance was investigated on an EL lamp fabricated by screen-printing at 100 V and 400 Hz. Ultrasound irradiation leads to intensity reductions and width increases of some XRD diffraction peaks, and results in a slight red-shift of UV-vis absorption edge. It also exhibits strong influences on PL and EL properties of the phosphors. Generally, PL performance monotonically declines with the increase of ultrasonic time, while EL performance benefits from the ultrasonic treatment and is superior to that of the commercial ones. The defects in the microstructure induced by the ultrasonic treatment are the fundamental reason for the change of PL and EL performances.     

Electrochemical formation of intermediate layer for Co/Pd multilayered media

Pd nanocluster seeds were formed on a soft magnetic underlayer (SUL) using an electrochemical substitution reaction, and were utilized as an intermediate layer for a Co/Pd multilayered ([Co/Pd]_n) perpendicular magnetic recording medium. A CoNiFeB film prepared with electroless deposition was used as SUL, which was immersed into a PdCl₂ solution for the formation of Pd seeds. The Pd seeds were found to effectively reduce the size of magnetic domains in the [Co/Pd]_n film deposited on them. The optimization of the concentration of the PdCl₂ solution and the use of the pretreatment process with a SnCl₂ solution were effective to obtain the smooth SUL surface with fine Pd seeds as small as 5 nm. The 20 nm-thick [Co/Pd]_n film deposited on the optimized Pd seeds/CoNiFeB SUL exhibited a high coercivity of 7.8 kOe and a small magnetic domain size of 69 nm. These results indicated that the combination of the Pd seeds and the electroless-deposited SUL was desirable in terms of the improvement not only in the magnetic properties of [Co/Pd]_n media but also in the mass productivity of the underlayer.     

Crystal structure and magnetic properties of RCu5−xPdx (R=Pr, Nd, Sm and Eu) alloys

We report the effect of replacing Cu by Pd in RCu₅ (R=Pr, Nd, Sm and Eu). The parent RCu₅ compounds crystallize in the hexagonal CaCu₅-type structure. The hexagonal symmetry is retained in PrCu₄Pd and EuCu_5−xPd_x (x=1 and 2) but the crystal structure changes to cubic AuBe₅-type in PrCu₃Pd₂, NdCu_5−xPd_x (x=1 and 2) and SmCu₄Pd. Substitution with Pd leads to lattice expansion and modifies the magnetic behavior. While PrCu₅ is known to be a van-Vleck paramagnet with a singlet ground state, PrCu₄Pd and PrCu₃Pd₂ show ferromagnetic-like behavior at low temperatures. SmCu₄Pd orders ferromagnetically near 28 K in contrast to the antiferromagnetic nature of the parent SmCu₅. The divalent nature of the Eu ions in EuCu₅ is retained in the ternary alloys, but the Curie temperature is reduced from 57 to 24.5 and 14.5 K in EuCu₄Pd and EuCu₃Pd₂, respectively, inferred from the location of peak in the heat capacity of these two compounds. The magnetic hyperfine field at the Eu nucleus measured with ¹⁵¹Eu Mössbauer spectroscopy in the ternary Eu-alloys is comparable to that in EuCu₅. The magnetic behavior of NdCu₄Pd is similar to that reported in NdCu₅. The zero-field-cooled, low-field magnetization of NdCu₃Pd₂ shows a region of diamagnetic behavior roughly between 21 and 4 K, but the field-cooled response is positive.     

Infrared reflection absorption study of carbon monoxide adsorption on Cu(1 0 0)-c(2 × 2)-Pd surfaces formed by palladium vacuum-depositions at various temperatures

Using infrared reflection absorption spectroscopy (IRRAS) and temperature programmed desorption (TPD), we investigated carbon monoxide (CO) adsorption and desorption behaviors on atomic checkerboard structures of Cu and Pd formed by Pd vacuum deposition at various temperatures of Cu(1 0 0). The 0.15-nm-thick Pd deposition onto a clean Cu(1 0 0) surface at room temperature (RT) showed a clear c(2 × 2) low-energy electron diffraction (LEED) pattern, i.e. Cu(1 0 0)-c(2 × 2)-Pd. The RT-CO exposure to the c(2 × 2) surfaces resulted in IRRAS absorption caused by CO adsorbed on the on-top sites of Pd. The LEED patterns of the Pd-deposited Cu(1 0 0) at higher substrate temperatures revealed less-contrasted c(2 × 2) patterns. The IRRAS intensities of the linearly bonded CO bands on 373-K-, 473-K-, and 673-K-deposited c(2 × 2) surfaces are, respectively, 25%, 22%, and 10% less intense than those on the RT-deposited surface, indicating that Pd coverages at the outermost c(2 × 2) surfaces decrease with increasing deposition temperature. In the initial stage of the 90-K-CO exposure to the RT surface, the band attributable to CO bonded to the Pd emerged at 2067 cm⁻¹ and shifted to higher frequencies with increasing CO exposure. At saturation coverage, the band was located at 2093 cm⁻¹. In contrast, two distinct bands around 2090 cm⁻¹ were apparent on the spectrum of the 473-K-deposited surface: the CO saturation spectrum was dominated by an apparent single absorption at 2090 cm⁻¹ for the 673-K-deposited surface. The TPD spectra of the surfaces showed peaks at around 200 and 300 K, which were ascribable respectively to Cu-CO and Pd-CO. Taking into account the TPD and IRRAS results, we discuss the adsorption-desorption behaviors of CO on the ordered checkerboard structures.     

Spin-wave resonance in multilayer FeNiP/Pd films

Ferromagnetic and spin wave resonances are studied in FeNiP/Pd multilayer films obtained via chemical vapor deposition. The partial exchange interaction constant of polarized Pd films is found to be A _Pd ≈ 1 × 10^?7 erg/cm.     

Effect of preparation method on the properties of deposited copper-palladium deep-oxidation catalysts

Activity of alumocopper-palladium catalysts (0.5 at.% Pd, 0.1–3.0 at.% Cu) which differ in preparation method in CO, C₂H₄ and CH₄ oxidation is studied. It is shown that preliminary modification of a carrier by copper leads to an enhancement of catalyst activity as compared with an alumopalladium one. With the methods of EDRS, TPR-TRS, and TPR of adsorbed CO and O₂, the Pd/Cu/Al₂O₃, Cu/Pd/Al₂O₃ and (Pd−Cu)/Al₂O₃, systems are studied. It is established that premodification of the carrier leads to a weakening of its interaction with the second metal while the combined deposition from one impregnating solution in subsequent thermal treatment is accompanied by a strong metal aggregation. Institute of Physicoorganic Chemistry, National Academy of Sciences of Belarus, 13, Surganov St., Minsk, 220072. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 114–120, January–February, 1998.     

A Simple Theoretical Method to Predict the Hardness of Pure Metal Crystals

Design of superhard bulk materials requires predicting their hardness, challenging current theories for material design. By introducing a concept of condensing force （CF）, it is shown via ab initio calculations for fcc （Ni, Cu, Al, Ir, Rh, Au, Ag, Pd） and hcp Re crystals that materials with larger CF can have greater hardness. Since the calculation of CF is easy, this method might prove a convenient way to evaluate the hardness of newly designed materials.     

Hydrogen adsorption on palladium and palladium hydride at 1 bar

The dissociative sticking probability for H₂ on Pd films supported on sputtered Highly Ordered Pyrolytic Graphite (HOPG) has been derived from measurements of the rate of the H–D exchange reaction at 1 bar. The sticking probability for H₂, S, is higher on Pd hydride than on Pd (a factor of 1.4 at 140 °C), but the apparent desorption energy derived from S is the same on Pd and Pd hydride within the uncertainty of the experiment. Density Functional Theory (DFT) calculations for the (1 1 1) surfaces of Pd and Pd hydride show that, at a surface H coverage of a full mono layer, H binds less strongly to Pd hydride than to Pd. The activation barrier for desorption at a H coverage of one mono layer is slightly lower on Pd hydride, whereas the activation energy for adsorption is similar on Pd and Pd hydride. It is concluded that the higher sticking probability on Pd hydride is most likely caused by a slightly lower equilibrium coverage of H, which is a consequence of the lower heat of adsorption for H on Pd hydride.     

Novel hydrophobic/hydrophilic patterning process by photocatalytic Ag nucleation on TiO2 thin film and electroless Cu deposition

A hydrophobic/super-hydrophilic pattern was prepared on a TiO₂ thin film by a new fabrication process. The process consists of five key steps: (1) photocatalytic reduction of Ag⁺ to Ag (nucleation), (2) electroless Cu deposition, (3) oxidation of Cu to CuO, (4) deposition of a self-assembled monolayer (SAM), and (5) photocatalytic decomposition of selected areas of the SAM. A hydrophobic/super-hydrophilic pattern with 500-μm² hydrophilic areas was obtained in this process. It is particularly noteworthy that a UV irradiation time of only 1 s was sufficient for the nucleation step in the patterning process.     

Generalized stacking fault energy in FCC metals with MEAM

The second nearest-neighbor modified embedded atom method (2NN-MEAM) is used to investigate the generalized stacking fault (GSF) energy surfaces of eight FCC metals Cu, Ag, Au, Ni, Pd, Pt, Al and Pb. An offset is observed in all the metals for the displacement δ_us of unstable stacking fault energy from the geometrically symmetric displacement point . The offset value is the greatest for Al and the smallest for Ag. By analyzing the stable stacking fault energy γ_sf and unstable stacking fault energy γ_usf, it can be predicted that stacking fault is more favorable in Cu, Ag, Au, and especially in Pd than the other metals, while it is most preferred to create partial dislocation for Ag and to create full dislocation for Al.     

Modeling of transient electroluminescence overshoot in bilayer organic light-emitting diodes using rate equations

When a voltage pulse is applied under forward biased condition to a spin-coated bilayer organic light-emitting diode (OLED), then initially the electroluminescence (EL) intensity appearing after a delay time, increases with time and later on it attains a saturation value. At the end of the voltage pulse, the EL intensity decreases with time, attains a minimum intensity and then it again increases with time, attains a peak value and later on it decreases with time. For the OLEDs, in which the lifetime of trapped carriers is less than the decay time of the EL occurring prior to the onset of overshoot, the EL overshoot begins just after the end of voltage pulse. The overshoot in spin-coated bilayer OLEDs is caused by the presence of an interfacial layer of finite thickness between hole and electron transporting layers in which both transport molecules coexist, whereby the interfacial energy barrier impedes both hole and electron passage. When a voltage pulse is applied to a bilayer OLED, positive and negative space charges are established at the opposite faces of the interfacial layer. Subsequently, the charge recombination occurs with the incoming flux of injected carriers of opposite polarity. When the voltage is turned off, the interfacial charges recombine under the action of their mutual electric field. Thus, after switching off the external voltage the electrons stored in the interface next to the anode cell compartment experience an electric field directed from cathode to anode, and therefore, the electrons move towards the cathode, that is, towards the positive space charge, whereby electron–hole recombination gives rise to luminescence. The EL prior to onset of overshoot is caused by the movement of electrons in the electron transporting states, however, the EL in the overshoot region is caused by the movement of detrapped electrons. On the basis of the rate equations for the detrapping and recombination of charge carriers accumulated at the interface expressions are derived for the transient EL intensity I, time t_m and intensity I_m corresponding to the peak of EL overshoot, total EL intensity I_t and decay of the intensity of EL overshoot. In fact, the decay prior to the onset of EL overshoot is the decay of number of electrons moving in the electron transporting states. The ratio I_m/I_s decreases with increasing value of the applied pulse voltage because I_m increases linearly with the amplitude of applied voltage pulse and I_s increases nonlinearly and rapidly with the increasing amplitude of applied voltage pulse. The lifetime τ_t of electrons at the interface decreases with increasing temperature whereby the dependence of τ_t on temperature follows Arrhenius plot. This fact indicates that the detrapping involves thermally-assisted tunneling of electrons. Using the EL overshoot in bilayer OLEDs, the lifetime of the charge carriers at the interface, recombination time of charge carriers, decay time of the EL prior to onset of overshoot, and the time delay between the voltage pulse and onset time of the EL overshoot can be determined. The intense EL overshoot of nanosecond or shorter time duration may be useful in digital communication, and moreover, the EL overshoot gives important information about the processes involving injection, transport and recombination of charge carriers. The criteria for appearance of EL overshoot in bilayer OLEDs are explored. A good agreement is found between the theoretical and experimental results.     

Influence of capacitance effect on alternating-current organic light-emitting diodes

The capacitance effect on ITO/poly[2-methoxy-5-[(2′-ethylhexyl)oxy]-p-phenylenevinylene] (MEH-PPV)/Al is studied by impedance spectroscopy technology, and the electroluminescence (EL) mechanism of this device driven by a sinusoidal alternating-current (AC) bias is suggested. By calculating the RC time constant of the device, we find that it is in good agreement with the lag-time between the EL and applied AC bias. Also, the influence of operating frequency on the EL intensity of the device is presented and it is concluded that a low operating frequency is good for a high device performance.     

Isotope effects in the kinetics of simultaneous H and D thermal desorption from Pd

The kinetics of simultaneous hydrogen and deuterium thermal desorption from PdH_xD_y has been investigated. A novel experimental approach for the study of the transition state (TS) characteristics of the surface recombination reaction is proposed based on the analysis of the H and D partitioning into H₂, HD and D₂ molecules. It has been found that the hydrogen molecular isotopes distribution is determined by the energy differences of the corresponding TS of the atom-atom recombination reactions. On the other hand, the mechanisms and activation energies of the desorption process have been obtained. At 420 K, the desorption reaction changes from a surface recombination limiting mechanism during desorption from β-PdH_xD_y to a reaction limited by the rate of β to α phase transformation during the two phase coexistence. Surface recombination reaction becomes again rate limiting above 480 K, due to a change in the catalytic properties of the Pd surface. TS energies obtained from the kinetic analysis of the thermal desorption spectra are in good accordance with those obtained from the analysis of the H₂, HD and D₂ distributions. Anomalous TS energies have been observed for the H-D recombination reaction, which may be related to the heteronuclear character of this molecule.     

Surface functionalization of porous ZrO2-TiO2 membranes using γ-aminopropyltriethoxysilane in palladium electroless deposition

A pre-treatment technique was developed to facilitate the electroless deposition of Pd layers onto ZrO₂-TiO₂ ceramic membrane surfaces in the preparation of novel multi-functional porous membranes. Surface functionalization using an aqueous solution of γ-aminopropyltriethoxysilane (γ-APTES) aided the surface immobilization of the Pd activation particles and the subsequent electroless deposition of metal layers onto the hydroxyl-rich membrane surface. The attractiveness of γ-APTES functionalization, in the electroless deposition of metal layers, was thus demonstrated. Characterization techniques employed in the structural study of the surface-modified membranes included SEM, EDS, dynamic analysis in micro-PIXE, and XRD. Special membrane techniques such as electrokinetic analysis and single-gas permeation measurements were also used in the study of surface modification. These membranes were developed for application in tasks associated with the hydrogen economy.     

Structure, thermally and optically induced effects in amorphous As2Se3 films prepared by pulsed laser deposition

Thin amorphous As-Se films were prepared by pulsed laser deposition (PLD) and by classical thermal evaporation techniques. Raman spectra and optical properties (optical gap, E_g^opt, index of refraction, n, third-order non-linear susceptibility, χ⁽³⁾) of prepared films and their photo- and thermally induced changes were studied. The structure of laser deposited films was close to the corresponding bulk glasses contrary to thermal evaporated films. The composition of PLD films was practically unchanged during the process of deposition. The optically and thermally induced changes of n and of E_g^opt in PLD films are different from the changes in thermally deposited films. The differences are discussed.     

New compounds in the Mn-X-Bi system where X = Ni, Cu, RhorPd

A new class of magnetic compounds has been discovered in the temary system Mn-X-Bi where X is Ni, Cu, Rh or Pd. The approximate compositions of these compounds are Mn₅Ni₂Bi₄, Mn₃Cu₄Bi₄, Mn₅Rh₂Bi₄, and Mn₅Pd₂Bi₄. The Bravais lattice is face-centered cubic, and the lattice constants are 12.16 Å (X = Ni), 12.18 Å (X = Cu), 12.31 Å (X = Rh) and 12.44 Å (X = Pd). These compounds are probably ferromagnetic and have Curie temperatures in the range -7°C to 183°C. A crystal structure is proposed for these compounds which contains 88 atoms/unit cell.     

Auger line shape changes in epitaxial (111)Pd/(111)Cu films

Epitaxial Pd films ranging in thickness from a few tenths of a monolayer up to many monolayers were formed on (111)Cu substrate films at room temperature under UHV conditions. The growth of these Pd films was monitored in situ by Auger electron spectroscopy. The line profiles of the Cu MMM (61 eV) and Pd MVV (329 eV) AES doublets varied significantly with the amount of Pd deposited. A new measure of the AES doublet line profile, called the R-factor, was defined. A graph R_pd versus Pd film thickness shows a sharp decline with increasing thickness. Superimposed on the major trend is a cyclical variation. A corresponding periodicity in R_cu was observed for the Cu MMM (61 eV) AES doublet. The results suggest that the R-factor provides a direct measure of changes in the electronic structures of the overgrowth and substrate films as the former thickens by a layer-growth mechanism.     

Ab initio calculations of generalized-stacking-fault energy surfaces and surface energies for FCC metals

The ab initio calculations have been used to study the generalized-stacking-fault energy (GSFE) surfaces and surface energies for the closed-packed (1 1 1) plane in FCC metals Cu, Ag, Au, Ni, Al, Rh, Ir, Pd, Pt, and Pb. The GSFE curves along (1 1 1) direction and (1 1 1) direction, and surface energies have been calculated from first principles. Based on the translational symmetry of the GSFE surfaces, the fitted expressions have been obtained from the Fourier series. Our results of the GSFEs and surface energies agree better with experimental results. The metals Al, Pd, and Pt have low γ_us/γ_I value, so full dislocation will be observed easily; while Cu, Ag, Au, and Ni have large γ_us/γ_I value, so it is preferred to create partial dislocation. From the calculations of surface energies, it is confirmed that the VIII column elements Ni, Rh, Ir, Pd, and Pt have higher surface energies than other metals.     

Charge carrier injection and transport in polymer blend films

The steady current-voltage characteristics of single layer organic devices based on MEH-PPV and N,N′-diphenyl-N,N′-bis(4′-[N,N-bis(naphth-1-yl)-amino]-biphenyl-4-yl)-benzidine (TPTE) blend with different TPTE concentrations was investigated. The thickness dependence of the current-voltage relationship clearly demonstrates that the current at low voltage and at high voltage are all space charge limited. The current density-electric field characteristic proves the blend polymer LEDs to operate in the tunneling-controlled model. The effective hole mobility is directly determined by space charge limited current at high voltage and increases with increasing TPTE content in the blend. The EL efficiency shows concentration dependence, which is attributed to the change of the transport of holes in the blend film.