Formation Of Seed Layer Research Articles

Synthesis of isolated ZnO nanorods on introducing g-C3N4 for improved photoelectrocatalytic methanol production by CO2 reduction

The photoelectrocatalytic (PEC) CO2 reduction into fuels has been developed as a prospective approach to resolve the environmental and energy concerns. Herein, a composite catalyst comprising ZnO nanorods dispersed on the g-C3N4 surface (g-C3N4/ZnO) was successfully obtained by simple ZnO seed layer formation and then hydrothermal processes. The synthesized and characterized g-C3N4/ZnO catalytic composite showed 2.8 times enhanced photocurrent density at −1 V applied potential than the bare g-C3N4. The g-C3N4/ZnO catalyst exhibited 2.86 times enhanced the PEC CO2 reduction to methanol than the prepared bare ZnO catalyst. The catalyst’s enhanced PEC CO2 reduction performance was ascribed to the high surface area, and higher generation and lower recombination of e−/h+ pairs. For the first time, this study showed the enhanced methanol production by the PEC reduction of CO2 over the prepared g-C3N4/ZnO catalytic composite.

Comparison of vacuum ultraviolet irradiation and oxygen plasma treatment as pretreatment for copper seed layer on cycloolefin polymer

This study explores the factors governing the peel strength characteristics between a cycloolefin polymer (COP) film and a copper plating layer with a copper seed layer, for applying to antenna circuits in 6 G communications. The peel strength depended on the surface modification methods as pretreatment for copper seed layer formation: vacuum ultraviolet (VUV) irradiation and oxygen plasma treatment. VUV irradiation induced a modified layer with brittleness on the COP surface, leading to substrate failure. Conversely, oxygen plasma treatment formed a quite thin modified layer and facilitated Cu2O formation by bonding functional groups on the topmost COP surface with copper in the seed layer at the interface between the COP film and the copper plating layer, resulting in interface failure rather than substrate failure. Therefore, enhancing peel strength involves preventing the formation of a modified layer on the surface and generating a significant quantity of functional groups on the topmost surface.

Growth of highly aligned ZnO nanorod arrays on zinc plates: Morphological and structural characterization

In this work, uniform and highly aligned ZnO nanorod arrays were simply synthesized on zinc plates by hydrothermal method using zinc–ammonia complex solution. Effects of ZnO seed layer formation, Zn(NO3)2 concentration and NH3/Zn(NO3)2 mole ratio (R) in the reaction medium on the morphology and crystal structure of nanorods were investigated in detail. ZnO nanorods grown on zinc surfaces were highly crystalline and had a hexagonal wurtzite structure, as revealed by XRD analysis. In addition, the dominant crystal growth direction was in c-axis, indicating the verticality of the nanorods. SEM images showed that one-dimensional (1D) ZnO nanorods with high verticality and number density were synthesized on seeded plates whereas randomly oriented arrays were grown on non-seeded surfaces. Increase in the Zn2+ concentration changed the top ends of the rods from tapering to hexagonal ends; and also led to an increase in the average size and verticality of the nanorods. The increase in R value (or i.e., amount of NH3) caused the rods to misalign on the surface and decrease in size. The size of well-aligned nanorods can be adjusted from 50 to 260 nm in diameter and 0.11 to 6 m in length by changing the reaction parameters, implying their large potential to be used in photocatalytic and also in electronic applications.

Seed layer formation determines photocurrent response of hydrothermally-grown WO3 photoanodes

We reveal that the preparation conditions of seed layers by spin coating have a very strong effect on the resulting photoelectrochemical performance of hydrothermally-grown WO3 films for water splitting, thus their preparation conditions can be tailored for maximum photocurrents.

Area-Selective, In-Situ Growth of Pd-Modified ZnO Nanowires on MEMS Hydrogen Sensors.

Nanomaterials are widely utilized as sensing materials in semiconductor gas sensors. As sensor sizes continue to shrink, it becomes increasingly challenging to construct micro-scale sensing materials on a micro-sensor with good uniformity and stability. Therefore, in-situ growth with a desired pattern in the tiny sensing area of a microsensor is highly demanded. In this work, we combine area-selective seed layer formation and hydrothermal growth for the in-situ growth of ZnO nanowires (NWs) on Micro-electromechanical Systems (MEMS)-based micro-hotplate gas sensors. The results show that the ZnO NWs are densely grown in the sensing area. With Pd nano-particles’ modification of the ZnO NWs, the sensor is used for hydrogen (H2) detection. The sensors with Pd-ZnO NWs show good repeatability as well as a reversible and uniform response to 2.5 ppm–200 ppm H2. Our approach offers a technical route for designing various kinds of gas sensors.

Epitaxial Graphene on 4H-SiC (0001) as a Versatile Platform for Materials Growth: Mini-Review

Material growth on a dangling-bond-free interface such as graphene is a challenging technological task, which usually requires additional surface pre-treatment steps (functionalization, seed layer formation) to provide enough reactive sites. Being one of the most promising and adaptable graphene-family materials, epitaxial graphene on SiC, due to its internal features (substrate-induced n-doping, compressive strain, terrace-stepped morphology, bilayer graphene nano-inclusions), may provide pre-conditions for the enhanced binding affinity of environmental species, precursor molecules, and metal atoms on the topmost graphene layer. It makes it possible to use untreated pristine epitaxial graphene as a versatile platform for the deposition of metals and insulators. This mini-review encompasses relevant aspects of magnetron sputtering and electrodeposition of selected metals (Au, Ag, Pb, Hg, Cu, Li) and atomic layer deposition of insulating Al2O3 layers on epitaxial graphene on 4H-SiC, focusing on understanding growth mechanisms. Special deliberation has been given to the effect of the deposited materials on the epitaxial graphene quality. The generalization of the experimental and theoretical results presented here is hopefully an important step towards new electronic devices (chemiresistors, Schottky diodes, field-effect transistors) for environmental sensing, nano-plasmonics, and biomedical applications.

Rational Strategy for Space-Confined Seeded Growth of ZnO Nanowires in Meter-Long Microtubes

Seeded crystal growths of nanostructures within confined spaces offer an interesting approach to design chemical reaction spaces with tailored inner surface properties. However, such crystal growth within confined spaces tends to be inherently difficult as the length increases as a result of confinement effects. Here, we demonstrate a space-confined seeded growth of ZnO nanowires within meter-long microtubes of 100 μm inner diameter with the aspect ratio of up to 10 000, which had been unattainable to previous methods of seeded crystal growths. ZnO nanowires could be grown via seeded hydrothermal crystal growth for relatively short microtubes below the length of 40 mm, while any ZnO nanostructures were not observable at all for longer microtubes above 60 mm with the aspect ratio of 600. Microstructural and mass spectrometric analysis revealed that a conventional seed layer formation using zinc acetate is unfeasible within the confined space of long microtubes as a result of the formation of detrimental residual Zn complex compounds. To overcome this space-confined issue, a flow-assisted seed layer formation is proposed. This flow-assisted method enables growth of spatially uniform ZnO nanowires via removing residual compounds even for 1 m long microtubes with the aspect ratio of up to 10 000. Finally, the applicably of ZnO-nanowire-decorated long microtubes for liquid-phase separations was demonstrated.

Seed Layer Formation on Carbon Electrodes to Control Li2O2 Discharge Products for Practical Li–O2 Batteries with High Energy Density and Reversibility

The high theoretical energy densities of lithium-air batteries (LAB) make this technology an attractive energy storage system for future mobility applications. Li2O2 growth process on the cathode relies on the surrounding chemical environment of electrolytes. Low conductivity and strong reactivity of Li2O2 discharge products can cause overpotential and induce side reactions in LABs, respectively, eventually leading to poor cyclability. The capacity and reversibility of LABs are highly susceptible to the morphology of the Li2O2 discharge products. Here, we identify for the first time that a seed layer formed by the combination of a cathode and an electrolyte determines the morphology of Li2O2 discharge products. This seed layer led to its high reversibility with a large areal capacity (up to 10 mAh/cm2). Excellent OER (oxygen evolution reaction) was achieved by the formation of a favorable interface between the carbon electrode and electrolyte, minimizing the decomposition of the electrolyte. These remarkable improvements in LAB performance demonstrate critical progress toward advancing LAB into practical uses, which would exploit good reversibility of LABs in pouch-type cell arrangements with 1.34 Ah.

Powder Filling and Sintering of 3D In-chip Solenoid Coils with High Aspect Ratio Structure.

In this study, a 3D coil embedded in a silicon substrate including densely distributed through-silicon vias (TSVs) was fabricated via a rapid metal powder sintering process. The filling and sintering methods for microdevices were evaluated, and the effects of powder types were compared. The parameters influencing the properties and processing speed were analyzed. The results showed that the pre-alloyed powder exhibited the best uniformity and stability when the experiment used two or more types of powders to avoid the segregation effect. The smaller the particle diameter, the better the inductive performance will be. The entire structure can be sintered near the melting point of the alloy, and increasing the temperature increases strength, while resulting in low resistivity. Finally, an 800-µm-high coil was fabricated. This process does not need surface metallization and seed layer formation. The forming process involves only sintering instead of slowly growing copper with a tiny current. Therefore, this process has advantages, such as a process time of 7 h, corresponding to an 84% reduction compared to current electroplating processes (45 h), and a 543% efficiency improvement. Thus, this process is more efficient, controllable, stable, and suitable for mass production of devices with flexible dimensions.

On the effects of water exposure of as-synthesized LTA membranes on their structural properties and dehydration performances

LTA (Linde Type A) type zeolites have been manufactured in a form of a continuous membrane and widely used for pervaporation-based dehydration of organic solvents. Despite the extremely high dehydration performances, the effects of parameters related to seed layer formation and, more importantly, water exposure of the resulting LTA membrane on the final membrane properties and, concomitant dehydration performances have not been investigated intensively. In this study, we examined how the immersion of as-synthesized LTA membranes in water (considering duration of water immersion) affected the membrane properties and dehydration performances. In addition, we focused on how to handle a LTA seed suspension (dependent on duration of precipitation) for forming proper seed layers on α-alumina tubes. We found that optimal preparation methods were necessary for securing a proper seed suspension and forming a seed layer that allowed for manufacturing high performance LTA membranes. In particular, when the disc-supported and tube-supported LTA membranes were immersed in water for ~12 h, they could show high dehydration performances with the H2O/CH3OH separation factors of ~860 ± 260 and ~910 ± 420, respectively, at 50 °C. However, after a critical time (~100–200 h), the corresponding dehydration performance was dramatically decreased, apparently due to the dissolution of LTA zeolites. Along with regular structural investigation with scanning electron microscopy and X-ray diffraction analyses, fluorescence confocal optical microscopy clearly revealed that the immersion of the LTA membranes in water resulted in forming almost defect-free membranes, but after some time, damaging the corresponding membrane structure. Nevertheless, the LTA membrane that did not contain non-zeolitic defects could preserve its aforementioned high dehydration performance with respect to a water-containing feed (~10 wt% H2O) up to ~102 h.

A Study on Characterization of Light-Induced Electroless Plated Ni Seed Layer and Silicide Formation for Solar Cell Application

Light-induced electroless plating (LIEP) is an easy and inexpensive method that has been widely used for seed layer deposition of Nickel/Copper (Ni/Cu)-based metallization in the solar cell. In this study, material characterization aspects of the Ni seed layer and Ni silicide formation at different bath conditions and annealing temperatures on the n-side of a silicon diode structure have been examined to achieve the optimum cell contacts. The effects of morphology and chemical composition of Ni film on its electrical conductivity were evaluated and described by a quantum mechanical model. It has been found that correlation exists between the theoretical and experimental conductivity of Ni film. Residual stress and phase transformation of Ni silicide as a function of annealing temperature were evaluated using Raman and XRD techniques. Finally, transmission line measurement (TLM) technique was employed to determine the contact resistance of Ni/Si stack after thermal treatment and to understand its correlation with the chemical-structural properties. Results indicated that low electrical resistive mono-silicide (NiSi) phase as low as 5 mΩ.cm2 was obtained.

Influence of substrate surface energy and surfactant on crystalline morphology and surface defect density in hydrothermally-grown ZnO nanowires

We investigated the influence of substrate surface energy before seed layer formation on hydrothermally grown zinc oxide (ZnO) nanowires (NWs). The qualities of ZnO NWs prepared by the surface-enhanced growth method with ultraviolet ozone (UVO) treatment were analyzed in terms of crystalline morphology and surface defect density, and were compared with those of ZnO NWs prepared by the conventional bulk-enhanced growth method adopting polyethyleneimine (PEI) as the surfactant in an aqueous growth solution. In both cases, a positive effect on the morphological properties and crystallinity of ZnO NWs was observed; however, the surface-enhanced growth method was more efficient for obtaining hydrothermally grown ZnO NWs with higher aspect ratios and larger surface areas. The ZnO NW growth rate in the surface-enhanced growth method was two times faster than in the conventional bulk-enhanced growth method. Photoluminescence (PL) spectra and time-resolved PL (TR-PL) responses indicated that a high density of oxygen vacancies on ZnO NW surfaces was produced by the surface-enhanced growth method, because highly oriented ZnO NWs can be grown without surface passivation effect, on the contrary with the bulk-enhanced growth method.

Synthesis and characterization of ZnO nanorods by hydrothermal method

Hydrogen generation through solar-driven photoelectrolysis of water is a promising technology for clean power supply. Zinc oxide (ZnO) is often applied to a photoelectrochemical (PEC) cells for water splitting, because ZnO has a favorable band edge that straddles the redox potential of photoelectrolysis in water. In addition, formation of ZnO nanostructure is attracting much attention, since the efficiency of PEC cell largely depends on a surface area of contacts. Here we report a modified hydrothermal method to prepare ZnOnanorods, whose structures can be controlled by changing preparation parameters. Our method includes seeding process by simple dip-coating technique, followed by post annealing process and hydrothermal growth process of ZnO nanostructures. The morphology of the grown ZnO depended on the concentration of the solvent used to form the seed layer formation, post-annealing temperature, and growth temperature. At the seed layer solvent concentration of 0.2 M, the ZnOnanorods were needle-like. At 0.9 M, hexagonal ZnOnanorods were obtained. We have successfully prepared hexagonalZnOnanorods by varying seed layer concentration at 0.9M, annealed at 150 °C for 2 h and grown at 120 °C for 1 h.

Ultra-fine Cu Wiring Surrounded by Electroless-Plated Ni: Effective Structure for High Insulation Reliable Wiring Applicable to Panel Level Fabrication

Abstract Panel level packages such as 2.1D organic interposer and fan-out packages have been attracting the attention as a low cost substrate technology with high density fine wiring layers which interconnect multiple die set side by side. The Cu trench wirings for these packages are usually fabricated by fine and almost rectangular shaped pattern formation of insulation film followed by Ti/Cu sputtering as a seed layer formation, Cu electroplating and CMP. However, sputtering tends to be difficult to deposit on the side wall of almost rectangular shaped pattern. Another challenge is insulation reliability between ultra-fine wirings because electrochemical migration of Cu ion is one of the most serious problems for ultra-fine wirings. Here, instead of seed sputtering, we applied a Ni electroless plating because electroless plating is appropriate to panel process and Ni has high corrosion resistance. Ni seed was uniformly formed on both side wall and bottom of these rectangular patterns. After Cu electroplating, CMP and Ni selective electroless plating on Cu, Cu trench wiring fully surrounded by Ni in 1.5/1.5 μm of line and space was fabricated which has passed biased HAST over 200 h by suppressing corrosion of wiring.

Thin uniform nickel seed layer formation and its impact on Ni-Cu contact adhesion for c-Si solar cell applications

Abstract Poor contact adhesion is one of the major concerns in the low cost Ni-Cu front contact metallization for c-Si solar cells. It reduces the mechanical as well as electrical reliability of the solar cell. Thermal annealing of the Ni seed layer is generally considered as crucial step for contact adhesion and cell performance, however the deposition of Ni seed layer itself requires proper investigation. The objective of this work is to improve the contact adhesion by improving Ni seed layer characteristics. This has been achieved through detailed process optimization of electroless Ni deposition using Palladium (Pd) activation method and subsequent annealing. After optimizing the Pd activation process with respect to its nucleation and growth characteristics, a very thin (∼20 nm) conformal seed layer deposition has been obtained with excellent uniformity across textured solar cell substrate. In addition, no interfacial void formation is observed after seed layer annealing, even at 600 °C. This has resulted in significantly improved contact adhesion of 23 MPa.

Improving the mechanical properties of p‐aramid fabrics and composites by developing ZnO nanostructures

Zinc oxide (ZnO) nanostructures have been grown on p‐aramid (Kevlar) fabric to improve interfacial properties of reinforced composites. Whiskerization technique was adopted to develop ZnO nanostructures, like an array of whiskers, on the surface of Kevlar fabric. Hydrothermal process was used which involves three steps i.e. functionalization, seed layer formation and growth of nanorods. Hexamethylenetetramine and zinc nitrate were used to grow ZnO nanostructures. It was found that pressure controlled autoclave was the best method for generation of nanostructures. It was also observed that the material (fabric) to solution ratio (M:S) significantly affected the morphology and density of developed nanostructures. Incorporation of ZnO nanostructures on Kevlar fabric improved the tensile and impact properties of Kevlar fabric and its composites. The deposition of nanostructures improved the interfacial properties by causing fibers to interlock with matrix thus allowing the formation of a graded interface between the two phases. POLYM. COMPOS., 39:3300–3306, 2018. © 2017 Society of Plastics Engineers

Fabrication of oxide heterostructures for promising solar cells of a new generation

The prospects of the fabrication of solar cells based on metal oxides (ZnO formed by the hydrothermal method) with a bulk heterojunction are considered. The results of synthesizing zinc-oxide nanorods on different seed layers are presented. The important role of seed-layer formation is noted. It is shown that the structure of nanorod arrays can be controlled using a surfactant. Faceted nanorods are obtained, which are promising for designing new-generation solar cells.

Electroless Ru/Cu Deposition Without Pd Activation for the Formation of Continuous Cu Seed Layers in High-Aspect-Ratio Via-Holes

Electroless Ru/Cu Deposition Without Pd Activation for the Formation of Continuous Cu Seed Layers in High-Aspect-Ratio Via-Holes

Phosphorous doping in vertically aligned ZnO nanorods grown by wet-chemical method

The synthesis of well-aligned highly crystalline phosphorous (P) doped ZnO nanorods (ZnO:P) on glass substrates is demonstrated here. Vertically aligned ZnO nanorods are fabricated by a two-step method comprises of nanocrystalline ZnO seed layer formation by dc sputtering technique followed by solution growth of ZnO nanorods. To incorporate P, aligned ZnO nanorod films are exposed to P vapor in a vacuum chamber and then subjected to rapid thermal annealing in vacuum at an elevated temperature of 450 °C. Scanning electron microscopy and X-ray diffraction measurement confirm the growth of highly crystalline well aligned hexagonal ZnO nanorods that are perpendicular to the substrate surface. The optical band gap estimated from the transmittance spectra recorded by a UV–VIS–NIR spectrophotometer is 0.24 eV lower for ZnO:P compared to ZnO nanorods. Vibrational properties of ZnO:P nanorods are studied by FTIR and Raman spectra. Raman peak appeared at 355 cm−1 for ZnO:P is due to the Zn-site substituted by phosphorous. For ZnO nanorods, the room temperature photoluminescence (PL) spectra shows a sharp UV emission peak due to near band edge transition and a broad blue–green emission peak due to defect related transition. The observed red shift for the UV emission peak in the ZnO:P nanorods is associated with the shrinking band gap whereas the intense and broad blue–green emission peak is due to defects introduced with P doping.

Magnetic and optical properties of Mn-doped ZnO vertically aligned nanorods synthesized by hydrothermal technique

In this paper we have reported the synthesis of high quality vertically aligned undoped and Mn-doped ZnO single crystalline nanorods arrays on Si (100) substrates using two steps process, namely, initial slow seed layer formation followed by solution growth employing wet chemical hydrothermal method. The shapes of the as grown single crystalline nanorods are hexagonal. The diameter and length of the as grown undoped ZnO nanorods varies in the range of 80-150 nm and 1.0 - 1.4 μm, respectively. Along with the lattice parameters of the hexagonal crystal structure, the diameter and length of Mn doped ZnO nanorods are found to increase slightly as compared to the undoped ZnO nanorods. The X-ray photoelectron spectroscopy confirms the presence of Mn atoms in Mn2+ state in the single crystalline ZnO nanorods. The recorded photoluminescence spectrum contains two emissions peaks having UV exciton emissions along with a green-yellow emission. The green-yellow emissions provide the evidence of singly ionized oxygen vacancies. The magnetic field dependent magnetization measurements [M (H)] and zero field cooled (ZFC) and field cooled (FC) magnetization [M(T)] measurements have been carried out at different isothermal conditions in the temperature range of 5-300 K. The Mn doped ZnO nanorods clearly show room temperature ferromagnetic ordering near room temperature down to 5 K. The observed magnetization may be attributed to the long range ferromagnetic interaction between bound magnetic polarons led by singly charged oxygen vacancies.