New formation process of plating thin films on several substrates by means of self-assembled monolayer (SAM) process

This review describes our recent works on the preparation of Ni-alloy films deposited by electroless deposition as a diffusion barrier layer for ultra large-scale integration (ULSI) interconnects by using an all-wet process.In this process, we create a novel wet fabrication process including a self-assembled monolayer (SAM) as an attachment technique between diffusion barrier layer and a substrate. Our proposal process was applied to the substrates of SiO₂/Si and both organic (methyl silsesquioxane) and inorganic (hydrogen silsesquioxane) low-k dielectrics. The key technique of this proposed process is using SAM as a catalyst trapping layer. The Ni-alloy films such as NiB were deposited on catalyzed SiO₂ or low-k substrates. The electrolessly deposited NiB films were found to exhibit sufficient thermal stability and an acceptable barrier property for preventing Cu diffusion into the SiO₂ and low-k dielectrics.     

Synthesis of a stable and porous Co–B nanoparticle catalyst for selective hydrogenation of cinnamaldehyde to cinnamic alcohol

The Co–B nanoparticle catalyst supported on TiO₂ for the selective hydrogenation of cinnamaldehyde to cinnamic alcohol was prepared by a modified electroless plating method. The as-prepared catalyst was characterized by X-ray diffraction and transmission electron microscope. The results showed that porous Co–B nanoparticles were distributed narrowly (40–45 nm) over the support. Compared with the Co–B nanoparticles prepared by chemical reduction of Co²⁺ ions with borohydride, the as-resulted Co–B nanoparticles were stable to be stored in air, and exhibited higher activity and selectivity of cinnamic alcohol in cinnamaldehyde hydrogenation.     

All-wet fabrication process for ULSI interconnect technologies

“All-wet process” for fabrication of Cu wiring on a silicon chip was proposed as a novel ultra-large scale integration (ULSI) interconnect technology for integrated circuits (ICs) applications. Electroless-NiB film was deposited on SiO₂/Si substrate modified by self-assembled-monolayer (SAM) activated with PdCl₂. The NiB film formed by this method has highly uniform, with good adhesion to the substrate and with good diffusion barrier characteristics against Cu diffusion. Cu was electrodeposited directly on the electroless NiB film that acted as a seed layer. This was done without any conventional conductive or adhesive layer that is conventionally formed by physical vapor deposition (PDV). The thermal stability of electroless NiB layer as a barrier preventing copper from diffusing into the SiO₂/Si substrate was evaluated by secondary ion mass spectroscopy (SIMS) and sheet resistance measurement at several annealing temperatures. It was confirmed that the electroless NiB film blocked Cu diffusion and kept the layer integrity under annealing temperatures of up to 400 °C for 30 min. The same process of electroless NiB was used for the capping layer that was also formed by “wet process”, as the electroless NiB film deposited selectively onto a surface of Cu wiring was also applicable to a capping layer. We conclude that the proposed process is very promising for sub-100 nm technologies as it offers a variety of desirable properties: it has good step coverage while showing good barrier and seed layer properties.     

Electroless plating of rhenium–nickel alloys

In this study, rhenium–nickel (Re–Ni) films were formed by electroless deposition on conductive (Cu) and non-conductive (SiO₂) substrates. Different bath compositions were evaluated, aiming to achieve high Re-content. Both sodium hypophosphite and dimethylamine-borane were used as reducing agents. Films containing up to 75 at% Re were obtained. The influence of nickel concentration in the solution on alloy composition, deposition rate and surface morphology were determined. It is shown that Ni²⁺ acts as a catalyst for the in situ reduction of the perrhenate ion, in a manner similar to what was proposed for electroplating of the same alloy. The rate of electroless plating is similar to that found in electroplating at an applied current density of 50 mA cm⁻². While pure Re cannot be deposited from our electroless plating baths, the addition of even a very small amount of Ni²⁺ ions (0.25 mM) is enough to start the induced codeposition of Re. Proper selection of the bath composition can lead to fine control of the alloy thickness and its Re-content, thus making it potentially attractive for thin barrier layers.     

Preparation of Ni(Co)–W–B amorphous catalysts for cyclopentanone hydrodeoxygenation

Ni–Co–W–B, Ni–W–B and Co–W–B catalysts were prepared by chemical reduction method and showed high activity in the HDO of cyclopentanone. Co–W–B had higher thermal stability than Ni–Co–W–B and Ni–W–B catalyst. The conversion of cyclopentanone could be high to 96.6% with a cyclopentanol selectivity of 0.4% and a deoxygenation rate of 95.4%. The HDO activity of the catalyst was related to its thermal stability, surface area, hydrogen supplying ability and Brönsted acid sites.     

States of carbon nanotube supported Mo-based HDS catalysts

As HDS catalysts, the supported catalysts including oxide state Mo, Co–Mo and sulfide state Mo on carbon nanotube (CNT) were prepared, while the corresponding supported catalysts on γ-Al₂O₃ were prepared as comparison. Firstly, the dispersion of the active phase and loading capacity of Mo species on CNT was studied by XRD and the reducibility properties of Co–Mo catalysts in oxide state over CNTs were investigated by TPR while the sulfide Co–Mo/CNT catalysts were characterized by XRD and LRS techniques. Secondly, the activity and selectivity of hydrodesulfurization (HDS) of dibenzothiophene with Co–Mo/CNT and Co–Mo/γ-Al₂O₃ were studied. It has been found that the main active molybdenum species in the oxide state MoO₃/CNT catalysts were MoO₂, rather than MoO₃ as generally expected. The maximum loading before formation of the bulk phase was lower than 6%m (calculated in MoO₃). The TPR studies revealed that that active species in oxide state Co–Mo/CNT catalysts were more easily reduced at relatively lower temperatures in comparison to those in Co–Mo/γ-Al₂O₃, indicating that the CNT support promoted the reduction of active species. Among 0–1.0 Co/Mo atomic ratio on Co–Mo/CNT, 0.7 has the highest reducibility. It shows that the Co/Mo atomic ratio has a great effect on the reducibility of active species on CNT and their HDS activities and that the incorporation of cobalt improved the dispersion of molybdenum species on CNT and mobilization. It was also found that re-dispersion could occur during the sulfiding process, resulting in low valence state Mo₃S₄ and Co–MoS_2.17 active phases. The HDS of DBT showed that Co–Mo/CNT catalysts were more active than Co–Mo/γ-Al₂O₃ and the hydrogenolysis/hydrogenation selectivity of Co–Mo/CNT catalyst was also much higher than Co–Mo/γ-Al₂O₃. For the Co–Mo/CNT catalysis system, the catalyst with Co/Mo atomic ratio of 0.7 showed the highest activity, whereas, the catalyst with Co/Mo atomic ratio of 0.35 was of the highest selectivity.     

Selective Oxidation of Diphenylmethane Over Cobalt Doped Mesoporous Titania–Silica Catalyst with High Ti Content

Cobalt doped mesoporous titania–silica with Ti/Si molar ratio of 0.5 (Co–TiO₂–SiO₂) was synthesized for the oxidation of diphenylmethane in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Fast hot catalyst filtration experiment proved that the catalyst acted as a heterogeneous one. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. The effects of reaction time and reaction temperature on the performance of the catalyst were investigated. Moreover, cobalt doped mesoporous titania with a crystalline structure and cobalt doped mesoporous titania–silica with different molar ratio were also studied. It was found that Co–TiO₂–SiO₂ with Ti/Si molar ratio of 0.5 showed the highest activity.     

Adsorption and degradation of the cationic dyes over Co doped amorphous mesoporous titania–silica catalyst under UV and visible light irradiation

Cobalt doped amorphous mesoporous titania–silica with Ti/Si mass ratio of 0.8 (Co–TiO₂–SiO₂) was synthesized and used for the photodegradation of six cationic dyes (gentian violet, methyl violet, methylene blue, fuchsin basic, safranine T, and Rhdamine B) under UV and visible light illumination. The catalyst was characterized by a combination of various physicochemical techniques, such as N₂ physisorption, diffuse reflectance UV–vis, X-ray diffraction, and FT-IR.Co–TiO₂–SiO₂ exhibited activity under UV light and had better activity under visible light when compared with that of Degussa P25 TiO₂. The activity of Co–TiO₂–SiO₂ was also compared with that of Co-MCM-41, Co doped mesoporous titania with a crystalline framework (Co–MTiO₂) and titania-loaded Co doped MCM-41 (TiO₂/Co-MCM-41) for the degradation of gentian violet under visible light irradiation. It was also found that the degradation rates of Co–TiO₂–SiO₂ for gentian violet, methyl violet, methylene blue, fuchsin basic and safranine T were greater in alkaline media than in acid and neutral media, while it did not exhibit any significant activity for the photodegradation of Rhdamine B in alkaline media or in acid media under visible light irradiation.     

Cu/SiO2 catalyst prepared by electroless method

Cu/SiO₂ catalysts prepared by an electroless deposition method were investigated and compared with those by an impregnation method. Copper contents varied from 5% to 15% and SiO₂ was used as support. All catalysts were characterized by BET, DSC, SEM and TPR and tested by an n-butanol dehydrogenation reaction for activities and stabilities. BET analysis showed that the catalysts prepared by the two methods present larger average pore size and less surface area than those of the fresh SiO₂, indicating that smaller pores may get blocked during the course of preparation. This blockage is more severe in the impregnation method. SEM photos showed that the electroless method produces smaller copper crystals than the impregnated method. The reaction activity was found to be in the order of the calcined electroless copper catalyst>the fresh electroless copper catalyst>impregnated copper catalyst. © 1998 Society of Chemical Industry     

Fischer–Tropsch synthesis on mono- and bimetallic Co and Fe catalysts supported on carbon nanotubes

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNTs)-supported bimetallic cobalt/iron catalysts is reported. Up to 4 wt.% of iron is added to the 10 wt.% Co/CNT catalyst by co-impregnation. The physico-chemical properties, FTS activity and selectivity of the bimetallic catalysts were analyzed and compared with those of 10 wt.% monometallic cobalt and iron catalysts at similar operating conditions (H₂/CO = 2:1 molar ratio, P = 2 MPa and T = 220 °C). The metal particles were distributed inside the tubes and the rest on the outer surface of the CNTs. For iron loadings higher than 2 wt.%, Co–Fe alloy was revealed by X-ray diffraction (XRD) techniques. 0.5 wt.% of Fe enhanced the reducibility and dispersion of the cobalt catalyst by 19 and 32.8%, respectively. Among the catalysts studied, cobalt catalyst with 0.5% Fe showed the highest FTS reaction rate and percentage CO conversion. The monometallic iron catalyst showed the minimum FTS and maximum water–gas shift (WGS) rates. The monometallic cobalt catalyst exhibited high selectivity (85.1%) toward C₅+ liquid hydrocarbons, while addition of small amounts of iron did not significantly change the product selectivity. Monometallic iron catalyst showed the lowest selectivity for 46.7% to C₅+ hydrocarbons. The olefin to paraffin ratio in the FTS products increased with the addition of iron, and monometallic iron catalyst exhibited maximum olefin to paraffin ratio of 1.95. The bimetallic Co–Fe/CNT catalysts proved to be attractive in terms of alcohol formation. The introduction of 4 wt.% iron in the cobalt catalyst increased the alcohol selectivity from 2.3 to 26.3%. The Co–Fe alloys appear to be responsible for the high selectivity toward alcohol formation.     

Dissolution from electrodeposited copper–cobalt–copper sandwiches

The electrochemical behaviour of electrodeposited Co–Cu/Cu multilayers from citrate electrolytes was investigated using cyclic voltammetry and stripping techniques at a rotating ring disc electrode. Copper and cobalt–copper alloy sandwiches were deposited from an electrolyte containing 0.0125 M CuSO₄, 0.250 M CoSO₄ and 0.265 M trisodium citrate at two different pHs, 1.7 and 6.0. The Cu/Co–Cu/Cu sandwich is representative of a single layer in a Co–Cu/Cu multilayer deposit, which is known to exhibit unusual physical and magnetic properties. Results from cyclic voltammetry and detection of dissolving species at the ring showed that cobalt is stripped from a Cu/Co–Cu/Cu sandwich even when a copper layer as thick as 600 nm covers the Co–Cu alloy. Scanning electron microscopy showed that cobalt can dissolve from the deposit easily because the copper layer covering the Co–Cu alloy is porous. A separate series of experiments with Cu/Co–Ni–Cu/Cu sandwich showed that cobalt does not dissolve from these deposits because the addition of nickel stabilises cobalt in the Co–Ni–Cu alloy.     

Effect of boric oxide doping on the stability and activity of a Cu–SiO2 catalyst for vapor-phase hydrogenation of dimethyl oxalate to ethylene glycol

Stable and efficient B–Cu–SiO₂ catalysts for the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol were prepared through urea-assisted gelation followed by postimpregnation with boric acid. Auger electron spectroscopy and CO adsorption by in situ Fourier transform infrared spectroscopy revealed that the Cu⁺ species on the catalyst surface increased together with an increase in the amount of boric oxide dopant. X-ray diffraction and N₂O chemisorption indicated that a suitable amount of boric oxide doping tended to improve copper dispersion and retard the growth of copper particles during DMO hydrogenation. Catalytic stability was greatly enhanced in the B–Cu–SiO₂ catalyst with an optimized Cu/B atomic ratio of 6.6, because of the formation and preservation of appropriate distributions of Cu⁺ and Cu⁰ species on the catalyst surfaces. The effect of boric oxide was attributed to its relatively high affinity for electrons, which tended to lower the reducibility of the Cu⁺ species.     

Hydrogenation of dimethyl oxalate to ethylene glycol on a Cu/SiO2/cordierite monolithic catalyst: Enhanced internal mass transfer and stability

The design and application of a Cu/SiO₂‐based monolithic catalyst for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) is presented. The catalyst was dip‐coated on cordierite with highly dispersed Cu/SiO₂ slurry prepared by ammonia evaporation method. This structure guarantees high dispersion of copper species within the mesopores of silica matrix in the form of copper phyllosilicate. The catalyst is low cost, stable, and exhibits high activity in the reaction of hydrogenation of DMO, achieving a 100% conversion of DMO and more than 95% selectivity to EG. Notably, STY_EG over the monolith is significantly enhanced compared to the packed bed Cu/SiO₂ catalysts in both forms of pellet and cylinder. It is primarily due to the relatively short diffusive pathway of the thin wash‐coat layer and high efficiency of the active phase derived from the monolithic catalyst. Theoretical results indicated that the internal mass transfer is dominated on the catalysts of pellet and cylinders. Moreover, the monolithic catalyst possessed excellent thermal stability compared to the pellet catalyst, which is attributed to the regular channel structure, uniform distribution of flow. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effect of SiO2 content on iron-based catalysts for slurry Fischer–Tropsch synthesis

A study has been carried out to investigate the effects of binder SiO₂ content on catalytic behavior of spray-dried precipitated Fe/Cu/K/SiO₂ catalysts for Fischer–Tropsch synthesis (FTS). The catalysts were characterized by means of N₂ physisorption, H₂ temperature-programmed reduction (TPR), scanning electron microscopy (SEM), and Mössbauer effect spectroscopy (MES). The Fischer–Tropsch synthesis performances (activity, selectivity and stability) of the catalysts were studied in a slurry-phase continuously stirred tank reactor (CSTR). The results indicated that the increase of SiO₂ content stabilizes Fe₃O₄ phase and suppresses the further reduction and carburization of the catalysts in syngas. Long time on stream FTS performances showed that the catalyst with SiO₂ improves its reaction stability. The selectivities to light hydrocarbons (methane, C₂–C₄, C₅–C₁₁) are enhanced whereas those to heavy hydrocarbons (C₁₂⁺) are suppressed with increasing SiO₂ content. The results were explained to the interactions of Fe–SiO₂ and K–SiO₂. From the present study, it is found that a catalyst with composition of 100Fe/5Cu/4.2K/25SiO₂ on mass basis displays both better FTS performances and a good attrition resistance, which is suitable for the use in CSTRs or SBCRs (Slurry Bubble Column Reactors) for FTS reaction.     

Growth of vertically aligned bamboo-like carbon nanotubes from ammonia/methane precursors using a platinum catalyst

Vertically aligned multi-walled carbon nanotubes have been synthesized by microwave plasma enhanced chemical vapor deposition using ammonia/methane source gas mixtures and a platinum thin film catalyst on thermally oxidized silicon substrates. The SiO₂ layer served as a diffusion barrier to reduce PtSi formation and aide the formation of well dispersed catalytic nanoparticles. Nevertheless, some degree of substrate–catalyst interaction occurred even with this diffusion barrier present. Carbon nanotube growth using a relatively thick catalyst film was either inhibited or prevented altogether when increasing the duration of plasma pretreatment or by moving the substrate closer to the center of the plasma. This was primarily attributed to increased substrate–catalyst interactions resulting in catalyst poisoning. Decreasing the plasma pretreatment time or moving the substrate away from the center of the plasma improved the growth, increasing the length of the nanotubes. Varying the catalyst film thickness enabled control of the diameter and density of the carbon nanotubes. Transmission electron microscopy revealed a bamboo-like structure with the orientation of internal compartments consistent with a base-growth mode.     

Electronic nature of potassium promotion effect in Co–Mn–Al mixed oxide on the catalytic decomposition of N2O

A series of Co–Mn–Al mixed oxides was prepared by a thermal treatment of coprecipitated layered double hydroxide precursors modified with different amount of potassium (0–3 wt.%) and tested in N₂O catalytic decomposition. Chemical analysis, XRD, XPS, surface area measurements, SEM, and contact potential difference measurements were used for bulk and surface characterization of the catalysts. The Co–Mn–Al mixed oxide with 1.1–1.8 wt.% K exhibited the highest conversion of N₂O and minimum value of the catalyst surface work function. Direct correlation between the work function values and the activity of the catalysts demonstrates that N₂O decomposition over K-promoted Co–Mn–Al mixed oxides proceeds via the cationic redox mechanism and controlled modification of surface electronic properties provides the essential factor for catalyst optimization.     

Effect of Ag, Cu, and Au Incorporation on the Diesel Soot Oxidation Behavior of SiO2: Role of Metallic Ag

The catalytic behaviors of Ag, Cu, and Au loaded fumed SiO₂ have been investigated for diesel soot oxidation. The diesel soot generated by burning pure Mexican diesel in laboratory was oxidized under air flow in presence of catalyst inside a tubular quartz reactor in between 25 and 600 °C. UV–Vis optical spectroscopy was utilized to study the electronic states of Ag, Cu, and Au(M) in M/SiO₂ catalysts. The soot oxidation was seen to be strongly enhanced by the presence of metallic silver on 3 % Ag/SiO₂ surface, probably due to the formation of atomic oxygen species during the soot oxidation process. The catalyst is very stable due to the stability of Ag⁰ species on the catalyst surface and high thermal stability of SiO₂. Obtained results reveal that though the freshly prepared 3 % Cu/SiO₂ is active for soot oxidation, it gets deactivated at high temperatures in oxidizing conditions. On the other hand, 3 % Au/SiO₂ catalyst does not present activity for diesel soot oxidation in the conventional soot oxidation temperature range. The catalytic behaviors of the supported catalyst samples have been explained considering the electron donating ability of the metals to generate atomic oxygen species at their surface.     

Effect of the Ratio of Precipitated SiO2 to Binder SiO2 on Iron-based Catalysts for Fischer–Tropsch Synthesis

The effects of the ratio of precipitated SiO₂ to binder SiO₂ (Si(P)/Si(B)) on the reduction, carburization and catalytic behavior of precipitated Fe–Cu–K–SiO₂ catalysts for Fischer–Tropsch synthesis (FTS) were investigated by N₂ physisorption, temperature-programmed reduction/desorption (TPR/TPD) and Mössbauer effect spectroscopy (MES). FTS performances of the catalysts were tested in a continuous stirred tank reactor (CSTR). It is found that the increase of Si(P)/Si(B) ratio (Si(P)/Si(B) = 0/25 ～ 15/10) decreases the crystallite size of the catalysts, improves the surface basicity, enhances the reduction and carburization of the catalysts, and increases the activity of the catalyst. However, when Si(P)/Si(B) ratio is further increased (Si(P)/Si(B) = 25/0), the catalyst exhibits a restrained reduction and carburization behavior, which may be attributed to the stronger metal–support interaction. Based on the present work, a catalyst with a suitable ratio of Si(P)/Si(B), for example Si(15)/Si(10) displays an optimal FTS performances.     

Spinel CuFe2O4: a precursor for copper catalyst with high thermal stability and activity

Spinel CuFe₂O₄ has been studied as a precursor for copper catalyst. The spinel CuFe₂O₄ was effectively formed on the SiO₂ by calcination in air at 800 °C with the atomic ratio of Fe/Cu = 2. The spinel CuFe₂O₄ on the SiO₂ was reduced to fine dispersion of Cu and Fe₃O₄ particles by the H₂ reduction at 240 °C. After H₂ reduction at 600 °C, sintering of Cu particles over the CuFe₂O₄/SiO₂ (Fe/Cu = 2) was inhibited significantly, while fatal sintering of Cu particles over the Cu/SiO₂ (Fe/Cu = 0) occurred. The CuFe₂O₄/SiO₂ catalyst exhibited much higher activity and thermal stability for steam reforming of methanol (SRM), compared with the Cu/SiO₂ catalyst. The spinel CuFe₂O₄ on the SiO₂ can be regenerated after an intentional sintering treatment by calcination in air at 800 °C where the activity is also restored completely. Based on these findings, we propose that spinel CuFe₂O₄ is an effective precursor for a high performance copper catalyst in which the immiscible interaction between Cu and Fe (or Fe oxide) plays an important role in the stabilization of Cu particles.     

Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO₂ catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO₂ catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO₂ catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO₂ catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn₃O₄).