Metal Deposition Reaction Research Articles

Catalysis Chemistry of Dimethyl Ether Synthesis

Dimethyl ether (DME) is receiving great attention as a clean alternative fuel, owing to the increasing energy demand. Despite tremendous efforts, catalytic synthesis of DME via a high efficient route remains a great challenge. Catalyst design is at the heart of enhancing the catalytic efficiency of DME synthesis. In this paper, we pay close attention to recent advances on the evolution of catalysts for direct dehydration from methanol and for the tandem catalysis from synthesis gas (syngas). The progress in metal deposition mode, support modification, and reaction routes is encouraging in recent years. In addition, significant challenges and future research scope in DME synthesis are focused as well.

Frontispiece

The frontispiece shows a schematic representation of a technique that simultaneously combines electrochemical impedance spectroscopy and nanogravimetric measurements by using an electrochemical quartz crystal nanobalance. This approach allows in situ characterization and better understanding of concurrent processes (adsorption, absorption, metal deposition, and catalytic reactions) at different electrode potentials or as a function of time. A full account can be found in the Minireview by A. Bandarenka and co-workers on page 348 ff.,.

Selective Plating on Photopatterned Titanium Oxide Films

A method for direct formation of patterned metal film on glass without resist use or etching was investigated. Palladium, which functions as an initiation catalyst for auto-catalytic metal deposition reactions, was selectively adsorbed onto solution processed nano-porous titanium oxide films on glass from an ionic palladium solution. After selective palladium catalyst grafting onto the titanium oxide, exposure of the films to an electroless nickel, copper or gold plating solution resulted in metal deposition selectively on the titanium oxide surface. Photo-active titanium complex films were photo-patterned then pyrolyzed to give the respective pattern preserved titanium oxide films that could then be selectively plated. Correlations between titanium oxide film characteristic and palladium adsorption were analyzed by ellipsometry and inductively coupled plasma mass spectroscopy. Cross section observation of metalized glass showed penetration of palladium catalyst into and elucidated the structure of plated metal on the patterned titanium oxide films.

Modeling Extreme Bottom-Up Filling of Through Silicon Vias

Extreme bottom-up superfilling of through silicon vias (TSV) was recently described wherein deposition occurs on the bottom surface of the vias with negligible deposition on their sidewalls or the field around them. The process uses a deposition suppressing adsorbate subject to breakdown through the metal deposition reaction. Positive feedback associated with this suppressor disruption coupled with resistive electrolyte losses underlies the bottom-up feature filling dynamic by distributing the applied potential between the interface double layer and the bulk electrolyte in a time dependent manner. A simple pseudo steady state model that links suppressor disruption with the potential drop between the reference and working electrodes in resistive electrolytes is shown to capture essential aspects of the bottom-up filling process. Understanding the coupling of potential and additive concentration gradients provides a rational design strategy for bottom-up filling of recessed surface features that offers to minimize unneeded deposition on the substrate surface thereby substantially decreasing fill times and improving materials utilization.

Extreme Bottom-Up Superfilling of Through-Silicon-Vias by Damascene Processing: Suppressor Disruption, Positive Feedback and Turing Patterns

Extreme bottom-up copper superfilling of through-silicon-vias (TSV) is demonstrated using a CuSO4-H2SO4 electroplating bath containing chloride and a polyether suppressor. Via filling occurs almost exclusively by deposition on the bottom via surface. The differential between the incoming fluxes of hydrated metal cations and larger suppressor molecules is accentuated by the recessed via geometry and accounts for preferential metal deposition initiating and growing from the bottom surface. The bottom-up growth front eventually propagates beyond the via opening and a substantial overburden develops. Feature filling is enhanced in electrolytes with a high [Cu2+]/[H3O+] ratio where global coupling by migration helps sustain the flux of Cu2+ to actively growing surface sections. Bottom-up superfilling relies on positive feedback whereby inhibition provided by adsorption of the polyether additive on the chloride saturated surface is disrupted by the metal deposition reaction. Release of the water of hydration that accompanies reduction of the Cu2+ aquo complex contributes to the sustained disruption of suppressor activity at the growth front. The correlation between TSV superfilling and additive-generated voltammetric hysteresis on planar substrates, which also involves a negative-differential-resistance (S-NDR) coupled with the electrolyte resistance, provides a general framework for understanding and guiding optimization of the bottom-up growth mode in recessed surface features.

Stoichiometry of Pt Submonolayer Deposition via Surface-Limited Redox Replacement Reaction

The work exploring the stoichiometry of Pt deposition via surface-limited redox replacement of the underpotentially deposited (UPD) Cu monolayer on Au(111) is presented. The Cu UPD monolayer is formed from solution, whereas the Pt deposition via surface-limited redox replacement reaction is carried out in solution at open-circuit potential. Our results indicate that the Pt submonolayers have two-dimensional morphology and linear dependence of their coverage on the amount (coverage) of the replaced Cu UPD monolayers. Our analysis shows that the oxidation state of Cu during redox replacement reaction is , suggesting that four Cu UPD adatoms are replaced by each deposited Pt adatom. This work stresses the general importance of the anions, determining the stoichiometry of metal deposition reaction via surface-limited redox replacement of the UPD monolayers.

Simulation of the Two-Phase Flow Hydrodynamics in an IRDE Reactor

Many industrial processes deal with gas bubbles, e.g., the chlor-alkali processes or a side reaction in metal deposition reactions. It is therefore very important to describe the influence of gas bubbles on the fluid flow in a quantitative way. In the present paper, the two-phase flow is both experimentally characterized and numerically modeled in a reactor with a rotating flow field such as the inverted rotating disk electrode (IRDE). Polarization curves of the hydrogen evolution in 0.1 M at pH 2.5 are recorded at different rotation speeds. The bubble dispersion and size distribution of the hydrogen bubbles are determined by laser marked shadowgraphy and interferometric laser imaging for droplet sizing. Concerning the numerical investigations, in the first step the single-phase flow solution in the vicinity of the IRDE is compared to the analytical solution of the flow field, as proposed by Cochran [ Proc. Cambridge Philos. Soc. , 30 , 365 (1934) ]. In the following step, an Eulerian–Lagrangian two-phase flow model is used to track the bubbles. Two-way momentum coupling effects between bubbles and electrolyte flow are taken into account. The calculated two-phase flow field compares well against the experimental data of the two-phase flow field obtained from the optical imaging techniques.

Superconformal Electrodeposition of Co and Co–Fe Alloys Using 2-Mercapto-5-benzimidazolesulfonic Acid

Superconformal Co(Fe) filling of submicrometer trenches by electrodeposition is demonstrated in the presence of 2-mercapto-5-benzimidazolesulfonic acid (MBIS). MBIS inhibits the initiation of Co deposition. Inhibition breakdown is characterized by hysteretic voltammetry and rising chronoamperometric transients. The positive feedback process reflects the competition between MBIS adsorption and its desorption, and consumption, with the latter being closely coupled with proton reduction and the metal deposition reaction. Void-free Co trench filling proceeds by preferential metal deposition at the bottom corners leading to a V-notch interface shape that is followed by geometrical leveling. Void-free filling is also demonstrated for a via geometry. Almost identical superconformal trench filling is obtained for Co-rich Co–Fe alloys. Analytical transmission electron microscopy and energy dispersive X-ray analysis indicate that the Fe/Co ratio within the filled trenches is uniform. MBIS does not significantly perturb the magnetic properties of the Co or Co–Fe alloy deposits.

Electrodeposition of Cu in the PEI-PEG-Cl-SPS Additive System: Reduction of Overfill Bump Formation During Superfilling

The impact of branched polyethyleneimine (PEI) on Cu electrodeposition from an acidified cupric sulfate electtrolyte containing a combination of superfilling additives, specifically polyethylene glycol, bis(3-sulfopropyl)disulfide, and chloride , is examined. Electroanalytical measurements reveal that adsorption of cationic PEI leads to inhibition of the metal deposition reaction to an extent similar to that provided by adsorption. However, unlike the suppressor, PEI is shown to deactivate adsorbed SPS accelerator. As a result, addition of PEI quenches the hysteretic voltammetric response that is a signature of competitive adsorption in the additive system. Trench-filling experiments in a electrolyte demonstrate that the deactivating interaction between PEI adsorption and adsorbed SPS can be optimized to prevent overfill bump formation without substantial detrimental impact on bottom-up, void-free feature filling.

Selective high-resolution electrodeposition on semiconductor defect patterns.

We report a new principle and technique that allows one to electrodeposit material patterns of arbitrary shape down to the submicrometer scale. We demonstrate that an electrochemical metal deposition reaction can be initiated selectively at surface defects created in a p-type Si(100) substrate by Si (++) focused ion beam bombardment. The key principle is that, for cathodic electrochemical polarization of p-type material in the dark, breakdown of the blocking Schottky barrier at the semiconductor/electrolyte interface occurs at significantly lower voltages at implanted locations than for an unimplanted surface. This difference in the threshold voltages is exploited to achieve selective electrochemical deposition.

Formation of Catalytic Pd on ZnO Thin Films for Electroless Metal Deposition

The formation process of highly dispersed Pd on ZnO thin films as a catalyst for electroless metal deposition was studied in detail by means of adsorption experiments combined with X‐ray photoelectron spectroscopy measurements. The chemical state of the yellow‐brown species adsorbed on ZnO thin film during the catalyzation process in acidic solution (pH 2.5) was determined to be . It was found that the adsorption of Pd on the ZnO thin film is closely related to the partial dissolution of ZnO in acidic solution, which results in an increase of the pH in the vicinity of ZnO surface, while the pH of the overall solution remains essentially unchanged (∼2.5) within the period of the catalyzation treatment (<10 min). This pH increase results in partial hydrolysis of Pd‐containing ions, and thus is formed near the surface of the ZnO thin film. The thus produced is then efficiently adsorbed on the ZnO surface, which has been made highly porous by its partial dissolution in the acidic solution. In the subsequent electroless metal deposition step, is first reduced to by the reductant, e.g., HCHO, contained in the deposition bath, and then the Pd particles act as catalytic nuclei for the deposition reaction. The Pd catalyst prepared in this fashion was found to be highly dispersed and can initiate several types of electroless metal deposition reactions.

Polarographic methods of monitoring addition agents in the electroplating of Sn-Pb solders

The electrochemical techniques typically used to monitor organic addition agents in electroplating baths work poorly in Sn-Pb solder plating baths. These electrochemical monitoring methods are based on the principle that additives act through their effects on the kinetics of the metal-deposition reaction, and thus the reaction M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n+</sup> + ne <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> → M can be used as a probe to determine the additive concentration. The heavy metal ions in solder plating baths readily poison probe electrodes, however, and thus electrochemical methods on solid electrodes are irreproducible and unreliable in these systems. A polarographic technique, which uses a renewable Hg drop electrode, can be used for the quantitative analysis of addition agents in solder plating solutions, even though the chemical identity of these species may not be known to the user of the plating solution.

Electrowinning of Non‐Noble Metals with Simultaneous Hydrogen Evolution at Flow‐Through Porous Electrodes: I . Theoretical

A mathematical model, is developed to simulate the electrowinning of non‐noble metals (e.g., Zn, Cr) within flow‐through porous electrodes under the conditions of simultaneous evolution of hydrogen gas bubbles. The results of the model are presented as a function of several dimensionless groups representing kinetics, mass transfer, ohmic resistance, and gas bubbles. These coupled, nonlinear effects are investigated by examining the distributions of the metal reduction and hydrogen evolution currents, coulombic efficiency of the metal electrowinning reaction, and gas void fractions under a series of limiting conditions. The gas bubbles accentuate the nonuniform distribution of the potential and the currents of both reactions by increasing the effective resistance of the gas‐electrolyte dispersion filling the pore space. This results in the underutilization of the internal surface area of the porous electrode and accelerates preferential localized plugging of the pores with the reduced metal. It can also instigate localized mass‐transfer limitations, i.e., the polarization at some points within the pores becomes large enough to support the limiting current of the metal deposition reaction (i.e., it becomes mass‐transfer controlled) while at other points lower polarizations and hence smaller currents prevail. Consequently, the optimum current which maximizes the removal rate of the metal is shown to be well below the theoretical limiting current of the electrode. This optimum current is significantly influenced by the evolving hydrogen gas bubbles. Neglecting this phenomenon leads to erroneous design and operational considerations.

Metal deposition and dissolution monitored by In situ scanning tunneling microscopy

The possibilities of scanning tunnelling microscopy (STM) for the study of metal deposition and dissolution reactions under in situ electrochemical conditions will be described and illustrated by examples. The metal reaction being studied is copper deposition and dissolution on foreign substrates such as Au(111), or polycrystalline copper. Data on atomically-resolved copper adlayers and on bulk copper deposition on gold will be presented. In addition, time resolved in situ STM for the study of copper deposition and dissolution on polycrystalline copper will be shown as well. From the latter local reaction rates can be estimated. The necessity to consider a possible influence of the tip on the results will be emphasized and the reasons for such an interference of the tip will be briefly discussed.

Thermally induced epitaxial recrystallization of NiSi2 and CoSi2

Time-resolved reflectivity and Rutherford backscattering spectrometry combined with channeling have been used to measure the epitaxial recrystallization kinetics of amorphous NiSi2 and CoSi2 layers. Epitaxial metal silicide layers, fabricated on (111) Si substrates by metal deposition and thermal reaction, were implanted with low-energy Si ions to form amorphous surface layers. Such layers recrystallized epitaxially from the underlying crystalline metal silicide during thermal annealing at temperatures of 60–176 °C. Post-anneal disorder consisted of dislocation networks as observed with transmission electron microscopy. Reduced recrystallization rates were apparent in samples implanted with O and Ar ions. Activation energies of 1.09±0.03 and 1.17±0.03 eV were determined for the epitaxial recrystallization of amorphous NiSi2 and CoSi2 layers, respectively.

Cathodic reactions involving lead, cadmium and silver ions in NaNO 3-KNO 3 melts at 250°C

Cyclic voltammetric studies of Pb 2+ and Cd 2+ ions on Pt and Hg electrodes suggest that the cathodic deposition of the metal does not occur in NaNO 3-KNO 3 melts. The new cathodic wave produced by the addition of these metal ions to the melt is due to the irreversible reduction of the nitrato complex, ie (PbONO 2) + + 2 e − → PbO + No − 2. In contrast to metal deposition reactions, there is no oxidation state change for the metal ion since only the nitrate ligand is reduced. Irreversible cathodic waves were observed for Pb(NO 3) 2 additions to molten NaNO 3-KNO 3 over the concentration range of 2.0 × 10 −4 to 2.0 × 10 −1 m. Fast potential scan experiments from 1 to 1000 Vs −1 using a Pt microelectrode gave no indication of any Pb or Cd metal deposition. The exhaustive electrolysis of 0.10 m Pb(NO 3) 2 and 0.12 m Cd(NO 3) 2 in molten NaNO 3-KNO 3 followed by atomic absorbance analyses of the mercury cathodes showed that the amount of metal deposition is insignificant. An investigation of Cd 2+ ions in NaNO 2-KNO 3-NaNO 3 suggests a similar reduction of nitrato or nitrito complexes rather than metal deposition. Silver ions are unique in that the reversible metal deposition reaction readily occurs in nitrate melts. This is due to both the small electric field of this univalent cation and its favorable thermodynamics that places the reversible potential for the Ag +/Ag couple significantly more positive than the potentials required for the reduction of nitrate melts.

Plating on anodized aluminum—I. The mechanism of charge transfer across the barrier-layer oxide film on 1100 aluminum

The mechanism of plating on anodized aluminum was investigated. Porous anodic films were formed on 1100 aluminum and the electrochemical behaviour of a number of test reactions (Ag +/Ag, Cu 2+/Cu, [Fe(CN) 6] 4− /[Fe(CN) 6] 3− and QH 2/Q) was determined. Hydrogen evolution can damage the oxide film and enhance the rate of electrochemical reactions on the surface. It is not a prerequisite, however, for metal deposition and other electrode reactions. Under the experimental conditions studied, the activity of the pores was not uniform and metal was plated in only a fraction of the pores, even when the total charge passed exceeded that required to fill all the pores tenfold or more. Metal ions can penetrate the barrier layer at the bottom of the pores by migration or diffusion, to be discharged at the aluminum surface. The barrier layer may also act as a heavily doped semiconductor which allows passage of charges with no specificity for the reversible potential of the redox couple tested. Observation of the uniformity of deposition of metals into the pores at an early stage by SEM with electron microanalysis can serve as a powerful tool in determining the best conditions for uniformly filling the pores. This should lead to improvements in the quality of plating on anodized aluminum.

Analysis of the static mercury drop electrode below the limiting current

A model has been developed that describes the combined effects of electrochemical kinetics, ohmic potential drop, and mass transfer for a metal deposition reaction at a static mercury drop electrode. For a single drop, the system behavior is expressed in terms of three dimensionless parameters. Two additional parameters are needed to describe the characteristics of polarograms. Results are compared with experimental observations and with theoretical predictions for the dropping mercury electrode and the hanging mercury drop electrode.

Characteristics of the dropping mercury electrode below the limiting current: Part II. Drop time and scan rate effects

A mathematical model of the dropping mercury electrode that includes the effects of electrochemical kinetics, ohmic potential drop, and mass transfer is used to examine the influence of scan rate and drop time on the shape of the polarographic wave. The system behavior is described in terms of three characteristic dimensionless parameters. For certain parameter values, the half-wave potential predicted for a metal deposition reaction is dependent on the drop time and scan rate used to obtain the polarogram.

The Effect of Multiple Current Collectors on the Performance of Flow‐Through Porous Electrodes

A one‐dimensional model for flow‐through porous electrodes is used to predict the variation in electric driving force within the porous electrode and the effluent concentration for current collectors placed at the front and the back of the electrode. Results are obtained for upstream and downstream placement of the counterelectrode relative to the fluid inlet. Analytical expressions have been developed for an electrode operating under limiting current conditions. A computer model is used to predict electrode behavior above and below the limiting current of a metal deposition reaction. Results show that the variation in electric driving force within the electrode and the effluent reactant concentration can be minimized for any set value of the solution to matrix conductivity ratio (κ/σ) by varying the current passed at each current collector. For the limiting current case, conditions for the minimum electric driving force variation can be predicted analytically. For the above and below limiting current case, conditions for the minimum electric driving force variation and the effluent concentration have also been obtained.