Arc plasma deposition of Pd seeding for Cu electroless deposition

Arc plasma deposition (APD) has been used for surface treatment of glass and polyimide (PI) substrates for Cu electroless deposition (ELD). The thickness of Cu ELD films increased linearly with time up to 2,000 nm on glass and 3,400 nm on PI substrates. Resistivity of Cu ELD films on glass (1.4–3.4 μΩ cm) and on PI (4.1–5.8 μΩ cm) was lower than that reported for conventional ELD processes (5–10 μΩ cm). The adhesion strength of Cu ELD films produced by our process was as good as, or better than, that for conventional Cu ELD films. APD is an effective, simple, and dry method for deposition of the seed layer for ELD on the surfaces of insulating materials.     

Mechanistic investigations of the ethylene tetramerisation reaction

The unprecedented selective tetramerisation of ethylene to 1-octene was recently reported. In the present study various mechanistic aspects of this novel transformation were investigated. The unusually high 1-octene selectivity in chromium-catalyzed ethylene tetramerisation reactions is caused by the unique extended metallacyclic mechanism in operation. Both 1-octene and higher 1-alkenes are formed by further ethylene insertion into a metallacycloheptane intermediate, whereas 1-hexene is formed by elimination from this species as in other reported trimerisation reactions. This is supported by deuterium labeling studies, analysis of the molar distribution of 1-alkene products, and identification of secondary co-oligomerization reaction products. In addition, the formation of two C6 cyclic products, methylenecyclopentane and methylcyclopentane, is discussed, and a bimetallic disproportionation mechanism to account for the available data is proposed.     

Mechanistic investigations with Bromamine-T: Kinetics of oxidation of thiocyanate ion

The kinetics of oxidation of thiocyanate ion by Bromamine-T (BAT) has been investigated in alkaline medium. The rate of reaction is first order in [OH^–] and zero order in [NCS^–]. The pseudo-first order rate constants decrease with increase in [BAT]. Addition of the reaction products p-toluenesulfonamide, Br^– and neutral salts has no significant effect on the rate. The rate increases with either increase in ionic strength or decrease in dielectric constant of the medium. The activation parameters have been computed. A mechanism consistent with the experimental results has been proposed and the rate law derived. The rate constants predicted from the rate law for the variation of [BAT] are in excellent agreement with the observed rate constants.

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- (BAT) . [OH^–] [NCS^–]. [BAT]. -, Br^– . . . , , . , , [BAT]_o, .

     

Catalytic effect of Pd nanoparticles on electroless copper deposition

This study elucidates the application of Pd nanoparticles as catalysts of electroless copper deposition and their catalytic effect on the deposition kinetics and microstructure in an electroless copper bath. Quartz crystal microgravimetry (QCM) and high-resolution field emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray spectroscopy (EDX) demonstrated that the kinetic changes associated with electroless copper deposition (ECD) comprised two stages—the incubation period and the acceleration period. In the incubation period, small copper particles were deposited. In the acceleration period, the ECD rate increased rapidly and continuously conducting films with large grains were formed. Leaner sweep voltammetry (LSV) and mixed potential theory (MPT) were applied to examine the catalytic powers of the prepared Pd nanoparticles and the related electrochemical kinetics in the ECD bath.     

Substrate-enhanced electroless deposition of metal nanoparticles on carbon nanotubes

By simply supporting carbon nanotubes with a metal substrate of a redox potential lower than that of the metal ions to be reduced into nanoparticles, we have developed a facile yet versatile and effective substrate-enhanced electroless deposition (SEED) method for functionalizing nanotubes with a large variety of metal nanoparticles, including those otherwise impossible by more conventional electroless deposition methods, in the absence of any additional reducing agent. The nanotube-supported metal nanoparticles thus produced are electrochemically active, and the newly developed SEED process represents a significant advance in functionalization of carbon nanotubes with metal nanoparticles for a wide range of potential applications, including in advanced sensing and catalytic systems.     

Mechanistic investigations of PEG-directed assembly of one-dimensional ZnO nanostructures

Mechanistic investigation on spherical assembly of the unique one-dimensional ZnO nanorods, solid nanocones, or hollow prisms with the closed -c end, directed by poly ethylene glycol (PEG) with different molecular weights, has been carried out using spectroscopic methods. The single crystalline ZnO nanoprisms, hollow along the c axis but closed at the -c end, aggregate to urchin-type globules in the microscale when PEG 2000 is used as directing reagent, while spherical aggregates of single crystalline ZnO nanocones are obtained under the direction of PEG 200. Studies reveal that both the PEG molecules aggregate to globules by interacting with zinc species in suitable solvents and englobe the zinc species. By the short time of ultrasonic pretreatment on the solution, a kind of flagellum structure is induced around the globules, in long tubular shapes for PEG 2000 but as shorter wedges for PEG 200. The globules with flagellums are templates for the assembly of the ZnO nanotubes or ZnO nanocones in the hydrothermal treatment. The tiny ZnO crystallites, produced in the hydrothermal process, stack to the templates and amalgamate to single crystalline nanotubes or nanocones, similar to the oriented attachment mechanism. The PEG 2000 template is included in the ZnO cavity of nanotubes, while PEG 200 is excluded from the ZnO nanocones due to the different intertwist properties between the two PEG molecules. Both the urchin-type assemblies, possessing the same external crystalline plane, compose a isotropic powder and emit very strong yellow light, centered at approximately 2.1 eV, under the excitation of the He-Cd laser at 325 nm, which has been correlated to the specific crystal plane. The special powders will be easily coated onto any type of surface for the decoration of a large area of surfaces for future applications.     

Process analysis of electroless nickel deposition baths using optical spectroscopies

Summary The analytical techniques of Vis-spectrophotometry and FTIR spectroscopy have been applied to the quantitative determination of important plating bath constituents of an electroless nickel-phosphorus electrolyte under realistic bath operation conditions. In combination with multivariate calibration methods (partial-least squares (PLS)- and principal component (PCR) regression) Ni²⁺, the reducing agent H₂PO ₂ ^– and its oxidation product HPO ₃ ^– could be directly determined even in the presence of other bath constituents like malic, lactic and adipic acids. For Ni²⁺, absorbance spectra in the 500–900 nm wavelength range were used to develop a PLS calibration model that allows to compensate matrix influences on the Ni²⁺ spectrum. PLS regression was carried out in the concentration range 0.5–6 g l^–1 Ni²⁺ with independently varying bath parameters (concentration of other bath constituents, pH and temperature). Evaluation of the model by predicting the concentrations of test samples which had been drawn from real process solutions of a Ni plating bath yielded a root-mean-squared error of 0.06 g l^–1. The metal concentration of the nickel electrolyte in a compact electroplating unit was monitored in-line by measuring spectra by means of a Vis-spectrometer adapted to the process via quartz glass fiber optical cables of 50 m length. A comparison of the in-line data with potentiometric off-line reference analyses showed good agreement of both data sets with a root mean-squared error of 0.15 g l^–1. The potential of FTIR spectroscopy for process analysis of plating bath solutions could be demonstrated by measuring off-line the concentrations of H₂PO ₂ ^– and HPO ₃ ^– . For these two components calibration samples containing all other main bath constituents were used to set up a PCR calibration model with IR spectra measured in the range from 850 to 1800 cm^–1 with an ATR trough technique. The data showed — within the error of the method of about 10% — generally a good accordance with the stoichiometry of the Ni²⁺/H₂PO ₂ ^– reduction process. The correlation of both parameters which was confirmed in these experiments could allow effective bath control with minimum analytical instrumentation, e.g. only a Vis-spectrophotometer.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Mechanistic investigations of imine hydrogenation catalyzed by cationic iridium complexes

Complexes [IrH2(eta6-C6H6)(PiPr3)]BF4 (1) and [IrH2(NCMe)3(PiPr3)]BF4 (2) are catalyst precursors for homogeneous hydrogenation of N-benzylideneaniline under mild conditions. Precursor 1 generates the resting state [IrH2{eta5-(C6H5)NHCH2Ph}(PiPr3)]BF4 (3), while 2 gives rise to a mixture of [IrH{PhN=CH(C6H4)-kappaN,C}(NCMe)2(PiPr3)]BF4 (4) and [IrH{PhN=CH(C6H4)-kappaN,C}(NCMe)(NH2Ph)(PiPr3)]BF4 (5), in which the aniline ligand is derived from hydrolysis of the imine. The less hindered benzophenone imine forms the catalytically inactive, doubly cyclometalated compound [Ir{HN=CPh(C6H4)-kappaN,C}2(NH2CHPh2)(PiPr3)]BF4 (6). Hydrogenations with precursor 1 are fast and their reaction profiles are strongly dependent on solvent, concentrations, and temperature. Significant induction periods, minimized by addition of the amine hydrogenation product, are commonly observed. The catalytic rate law (THF) is rate = k[1][PhN=CHPh]p(H2). The results of selected stoichiometric reactions of potential catalytic intermediates exclude participation of the cyclometalated compounds [IrH{PhN=CH(C6H4)-kappaN,C}(S)2(PiPr3)]BF4 [S = acetonitrile (4), [D6]acetone (7), [D4]methanol (8)] in catalysis. Reactions between resting state 3 and D2 reveal a selective sequence of deuterium incorporation into the complex which is accelerated by the amine product. Hydrogen bonding among the components of the catalytic reaction was examined by MP2 calculations on model compounds. The calculations allow formulation of an ionic, outer-sphere, bifunctional hydrogenation mechanism comprising 1) amine-assisted oxidative addition of H2 to 3, the result of which is equivalent to heterolytic splitting of dihydrogen, 2) replacement of a hydrogen-bonded amine by imine, and 3) simultaneous H delta+/H delta- transfer to the imine substrate from the NH moiety of an arene-coordinated amine ligand and the metal, respectively.     

Mechanistic investigations of imine hydrogenation catalyzed by dinuclear iridium complexes

Treatment of [Ir2(mu-H)(mu-Pz)2H3(NCMe)(PiPr3)2] (1) with one equivalent of HBF4 or [PhNH=CHPh]BF4 affords efficient catalysts for the homogeneous hydrogenation of N-benzylideneaniline. The reaction of 1 with HBF4 leads to the trihydride-dihydrogen complex [Ir2(mu-H)(mu-Pz)2H2(eta2-H2)(NCMe)(PiPr3)2]BF4 (2), which has been characterized by NMR spectroscopy and DFT calculations on a model complex. Complex 2 reacts with imines such as tBuN=CHPh or PhN=CHPh to afford amine complexes [Ir2(mu-H)(mu-Pz)2H2(NCMe){L}(PiPr3)2]BF4 (L = NH(tBu)CH2Ph, 3; NH(Ph)CH2Ph, 4) through a sequence of proton- and hydride-transfer steps. Dihydrogen partially displaces the amine ligand of 4 to form 2; this complements a possible catalytic cycle for the N-benzylideneaniline hydrogenation in which the amine-by-dihydrogen substitution is the turnover-determining step. The rates of ligand substitution in 4 and its analogues with labile ligands other than amine are dependent upon the nature of the leaving ligand and independent on the incoming ligand concentration, in agreement with dissociative substitutions. Water complex [Ir2(mu-H)(mu-Pz)2H2(NCMe)(OH2)(PiPr3)2]BF4 (7) hydrolyzes N-benzylideneaniline, which eventually affords the poor hydrogenation catalyst [Ir2(mu-H)(mu-Pz)2H2(NCMe)(NH2Ph)(PiPr3)2]BF4 (11). The rate law for the catalytic hydrogenation in 1,2-dichloroethane with complex [Ir2(mu-H)(mu-Pz)2H2(OSO2CF3)(NCMe)(PiPr3)2] (8) as catalyst precursor is rate = k[8]{p(H2)}; this is in agreement with the catalytic cycle deduced from the stochiometric experiments. The hydrogenation reaction takes place at a single iridium center of the dinuclear catalyst, although ligand modifications at the neighboring iridium center provoke changes in the hydrogenation rate. Even though this catalyst system is also capable of effectively hydrogenating alkenes, N-benzylideneaniline can be selectively hydrogenated in the presence of simple alkenes.     

Thermophoretic deposition of palladium aerosol nanoparticles for electroless micropatterning of copper

A method for catalytic activation was introduced by producing palladium aerosol nanoparticles via spark generation and then thermophoretically depositing the particles onto a flexible polyimide substrate through a hole in pattern mask, resulting in a line (24 μm in width) and a square (136 μm × 136 μm) patterns. After annealing, the catalytically activated substrate was placed into a solution for electroless copper deposition. Finally, copper micropatterns of a line (35 μm in width) and a square (165 μm × 165 μm) were formed only on the activated regions of the substrate. Both patterns had the height of 1.6 μm.     

Mechanistic investigations on the densification behaviour of barium titanate ceramics

The processes occurring during the densification of La_0.002Ba_0.998TiO₃ powders with different SiO₂-containing additives (TiO₂+SiO₂), (CaO+TiO₂+SiO₂), (2BaO+TiO₂+2SiO₂) have been investigated using a step-like annealing of the compacts. The reactions taking place during isothermal dwelling and their effects on the shrinkage rates in the following heating period have been characterized. The samples dwelt for 30 minutes exhibited a higher shrinkage rate than the compacts dwelt for 120 minutes. X-ray diffraction measurements revealed that the differences between both dwelling times are caused by the differences in the structural activity of the powders, i.e. by the reaction-mediated formation and degradation of defects in the surface regions of the BaTiO₃ grains. The process of formation of the Ba₂TiSi₂O₈ phase which acts as a defect source is kinetically preferred to the formation of the Ba₄Ti₁₃O₃₀ phase which acts as a defect drain. Thus, during short dwelling times defect-rich surfaces of the BaTiO₃ grains and/or glass-like intermediates are created. These structures favour the sliding of whole grains and consequently result in high shrinkage rates. The gradual degradation of these thermodynamically unstable structures by the formation of the Ba₄Ti₁₃O₃₀ phase during prolonged dwelling times deteriorates the sliding properties of the grains and reduces the shrinkage rate.     

Selective electroless metal deposition using microcontact printing of phosphine-phosphonic acid inks

We report a low-cost approach to selectively deposit films of nickel and copper on glass substrates. Our approach uses microcontact printing of organic inks containing phosphonic acid groups to bind the ink to a glass substrate and phosphine groups to bind a colloidal catalyst that initiates electroless metallization. We demonstrate this procedure by fabricating patterned nickel and copper films with areas as large as 15 cm2 and minimum feature sizes of approximately 2 microm. We present studies on the use of two ink types, an oligomer and a bifunctional molecule, and demonstrate that pattern quality and adhesion of the metallized films depends on the molecular weight of the ink and the ratio of phosphine and phosphonic acid groups.     

Synthesis of nickel nanowires via electroless nanowire deposition on micropatterned substrates

Electroless nanowire deposition on micropatterned substrates (ENDOM) is a promising new technique by which to direct the synthesis and precise placement of metallic nanowires. ENDOM is generally applicable to the preparation of metallic, semiconducting, and even insulating nanowires on technologically relevant substrates, is inexpensive, and can achieve high growth rates. The deposited nanowires are ultralong (centimeters) and can be patterned in arbitrary shapes. We demonstrate ENDOM using the growth of nickel nanowires. By controlling the deposition time, the width of the nanowires can be varied from 200 to 1000 nm and the height can be varied from 7 to 20 nm.     

Effect of 3-S isothiuronium propyl sulfonate on electroless nickel deposition

The effects of organic additive, 3-S isothiuronium propyl sulfonate (UPS) on bath stability, deposition rate, reaction activation energy, and Ni-P coating composition in acidic electroless nickel (EN) plating were investigated. The study was performed by measuring the polarization curves and X-ray fluorescence spectrometer (XRF) in combination with X-ray photoelectron spectroscopy (XPS) analysis. The results show that UPS improves bath stability and increases the reaction activation energy. At lower concentration, UPS is an effective accelerator for EN deposition; whereas, at higher concentration, it decreases deposition rate. It also reveals that UPS inhibits the anodic oxidation of hypophosphite and accelerates the cathodic reduction. In addition, UPS decreases the phosphorus content in Ni-P deposit and can be adsorbed on the deposit surface and compound with Ni²⁺. On the basis of these results, the effect mechanism of UPS on electroless nickel deposition was deduced.     

Mechanistic investigations of cooperative catalysis in the enantioselective fluorination of epoxides

This report describes mechanistic studies of the (salen)Co- and amine-cocatalyzed enantioselective ring opening of epoxides by fluoride. The kinetics of the reaction, as determined by in situ (19)F NMR analysis, are characterized by apparent first-order dependence on (salen)Co. Substituent effects, nonlinear effects, and reactivity with a linked (salen)Co catalyst provide evidence for a rate-limiting, bimetallic ring-opening step. To account for these divergent data, we propose a mechanism wherein the active nucleophilic fluorine species is a cobalt fluoride that forms a resting-state dimer. Axial ligation of the amine cocatalyst to (salen)Co facilitates dimer dissociation and is the origin of the observed cooperativity. On the basis of these studies, we show that significant improvements in the rates, turnover numbers, and substrate scope of the fluoride ring-opening reactions can be realized through the use of a linked salen framework. Application of this catalyst system to a rapid (5 min) fluorination to generate the unlabeled analog of a known PET tracer, F-MISO, is reported.     

Investigation of the mechanism of nickel electroless deposition on functionalized self-assembled monolayers

We have investigated the seedless electroless deposition (ELD) of Ni on functionalized self-assembled monolayers (SAMs) using scanning electron and optical microscopies, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. For all SAMs studied, the Ni deposition rate is dependent on the bath pH, deposition temperature, and complexing agent. In contrast to the physical vapor deposition of Ni on SAMs, electrolessly deposited Ni does not penetrate through the SAM. This behavior indicates that ELD is a suitable technique for the deposition of low-to-moderate reactivity on organic thin films. We demonstrate that Ni can be selectively deposited on SAMs using two different methods. First, selectivity can be imparted by the formation of Ni(II)-surface complexes. As a demonstration, we selectively deposited Ni on the -COOH terminated SAM areas of patterned -COOH/-CH(3) or -COOH/-OH terminated SAMs. Here, Ni(2+) ions form Ni(2+)-carboxylate complexes with the -COOH terminal group, which comprise the nucleation sites for subsequent metal deposition. Second, we demonstrate that nickel is selectively deposited on the -CH(3) terminated SAM areas of a patterned -OH/-CH(3) terminated SAM. In this case, the Ni(2+) ion does not specifically interact with the -CH(3) terminal group. Rather, selectivity is imparted by the interaction of the reductant, dimethylamine borane (DMAB), with the -OH and -CH(3) terminal groups.