Pure Copper Surface Research Articles

Condensation heat transfer enhancement by surface modification on a monolithic copper heat sink

In this study, the condensation heat transfer performance on a pure copper surface, as well as a superhydrophobic-modified copper surface were compared. Differing from other condensation heat transfer experimental designs, a monolithic copper heat sink was utilized in this study to prevent contact thermal resistance and/or thermal conduction limitation of the thermal paste applied between the modified condensation surface and heat sink plate. This approach has not yet been documented in the literature. The superhydrophobic copper heat sink surface was prepared using a hydrogen peroxide immersion and fluorosilane polymer (EGC-1720) spin-coating. Experimental results show that the condensation heat transfer performance on the superhydrophobic copper surface is superior to that of a pure copper surface. Additionally, durability tests of the pure and superhydrophobic coating copper surfaces in a harsh vapor environment are discussed in this study.

Solvent polarity effect on quality of n-octadecanethiol self-assembled monolayers on copper and oxidized copper

This article reports the effect of solvent polarity on the formation of n-octadecanethiol self-assembled monolayers (C18SH-SAMs) on pure copper surface and oxidized copper surface. The quality of SAMs prepared in different solvents (n-hexane, toluene, trichloroethylene, chloroform, acetone, acetonitrile, ethanol) was monitored by EIS, RAIRS and XPS. The results indicated that C18SH-SAMs formed in these solvents were in good barrier properties on pure copper surface and the structures of monolayers formed in high polarity solvents were more compact and orderly than that formed in low polarity solvents. For comparison, C18SH adsorbed on the surface of oxidized copper in these solvents were studied and the results indicated that C18SH could be adsorbed on oxidized copper surface after the reduction of copper oxide layer by thiols. Compared with high polarity solvents, a limited reduction process of oxidized copper by thiols led to the incompletely formation of monolayers in low polarity solvents. This can be interpreted that the generated water on solid–liquid interface and a smaller reaction force restrict the continuous reduction reaction in low polarity solvents

Electrochemical reduction of CO2 on electrodeposited Cu electrodes crystalline phase sensitivity on selectivity

The product distribution of electrochemical reduction of CO2 can be altered by modifying the surface of pure copper by deposition. In this study, chronoamperometric deposition of Cu on Cu (Cu/Cu) was carried out at two different CuSO4 bath concentrations, 0.25M (high) and 0.025M (low), termed as Cu/Cu-H and Cu/Cu-L respectively. These deposits were characterized by X-ray diffraction and they vary in their crystal orientation. Pure Cu and Cu/Cu were aligned towards (111) and (220) plane with a texture coefficient of 1.2 and 1.7, respectively. Electrodeposited electrodes were tested for the electrochemical reduction of CO2 in KCl electrolyte and the results were compared with that of pure Cu electrode. Electrochemical reduction of CO2 showed methane and ethane, with hydrogen as the byproduct. The product distribution varied with the crystal orientation of Cu electrodes. The maximum Faradaic efficiency of methane was 26% obtained on pure Cu electrode with (111) and (200) orientation, whereas Cu/Cu-L with dominating (220) orientation showed a maximum formation of ethane with Faradaic efficiency of 43%. A possible mechanism of product formation on Cu towards C1 and Cu/Cu towards C2 is also discussed.

Colorizing pure copper surface by ultrafast laser-induced near-subwavelength ripples.

We demonstrate that the colorizing effect of angle dependence can be efficiently and conveniently achieved on the rippled surface of pure copper processed by the femtosecond laser with an out-of-focus method, which greatly improves the machining speed. Such a laser-induced colorization can occur in a wide range of laser fluence, which determines the coverage and morphological characteristics of laser-induced ripples and thus can finely tune the colorizing effect. By inspecting the colors and corresponding spectra of treated areas at different angles, the relationship between the diffracted light central wavelength and the laser-induced near-subwavelength grating is analyzed quantitatively based on the fundamental grating equation with the experimental grating parameters. The spectrum analysis indicates that for the laser fluence increasing in a suitable range, the more clarity and regularity of formed ripples should bring out a more prominent grating effect, which becomes further matching of the grating equation in a larger inspecting angle for the elimination of the influence of the diffused reflection light. In short, the study confirms that the colorizing phenomenon mainly ascribes to the grating diffraction effect of the laser-induced periodic surface ripples, which would help to enable the flexible control of the colorizing effect induced by laser processing on pure copper.

Effects of Cu content and mechanical alloying parameters on the preparation of W–Cu composite coatings on copper substrate

Abstract A novel surface coating preparation technique utilizing high-energy mechanical alloying (MA) method was used to deposit tungsten–copper composite coatings on pure copper surface using a planetary ball mill. The microstructures and elemental and phase composition of mechanically alloyed coatings at different process parameters were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS). The effects of mechanical alloying parameters on the fabricating of tungsten–copper composite coatings had been investigated. Fully dense and uniform tungsten–copper composite coatings were metallurgically bonded on the copper substrate, with an average thickness of ∼65 μm under the optimized mechanical alloying parameters (i.e., rotation speed of 350 rpm, milling time of 9 h and powder ratio of W–30 wt.%Cu). Microhardness tests were carried out to examine the mechanical properties of the coatings. The results showed that the maximum microhardness of the coatings reached HV 0.1 193, showing a great improvement upon pure copper substrate. Mechanical alloying is a complex process and hence involves optimization of a number of variables to achieve the desired results. In this work, effects of the main parameters on the preparation of tungsten–copper composite coatings were properly presented.

Copper Protection by SAM and Low Temperature Bonding for 3Dimentional Integration

3Dimensional Integration can solve many challenges which are being faced by modern planer integration. The major bottleneck of 3D-Integration are contamination and Copper surface oxidation which is the cause of the requirement of high temperature while bonding. Reduction of this high bonding temperature is the key challenge of 3Dimensional Integration. In this research work we investigate and compare the Copper surface protection characteristic of Self-Assembled Monolayer (SAM) of Alkyl Thiol having different Carbon chains (C6,Hexanethiol and C12, Dodecanethiol). We also study the thermal desorption of these SAM layers. SAM can minimize the oxidation of the Copper which acts as a bonding medium. By thermal desorption the pure Copper surface is brought back and exposed. Finally Copper-Copper thermocompression bonding is performed in different conditions and compared.

Microstructures and formation mechanism of W–Cu composite coatings on copper substrate prepared by mechanical alloying method

In the present work, high-energy mechanical alloying (MA) method was applied to prepare tungsten–copper composite coatings on pure copper surface using a planetary ball mill. During mechanical alloying process, grains on the surface layer of substrate were refined and the substrate surface was activated as a result of repeated collisions by a large number of flying balls along with powder particles. The repeated ball-to-substrate collisions resulted in the deposition of coatings. The microstructures and elemental and phase composition of mechanically alloyed coatings at different milling durations during mechanical alloying process were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS). Microhardness tests were carried out to examine the mechanical properties of the coatings. The results showed that the coatings and the substrates were well bonded, and with the increase of the milling duration, multi-layered coatings with different structures were generated and the coatings became denser. The microhardness tests showed that the maximum microhardness of the coatings reached HV0.1 228, showing a threefold improvement upon the substrate. And the cross-sectional microhardness values of the processed sample changed gradually, which gave a proof for the cushioning and sustaining functions of the multi-layered coatings. A reasonable formation mechanism of coatings on bulk materials with metallic immiscible system by mechanical alloying method was presented.

Effect of Al on Zn-Al Filler Metal Wettability on Pure Copper Surface

Zn-Al filler metal wettability tests were performed. With the match of CsF-AlF3 flux, Zn-Al filler metal wettability is poor on pure copper surface. The Cu-Al-Zn intermetallic compound interface layer exits between Zn-Al filler metal and Cu base metal. When Al content is low in Zn-Al filler metal, the filler metal wettability is poor and the filler metal melting point is low. In the wettability test course, the time is long in which Cu base metal interacts with liquid Zn-Al filler metal. And the Cu-Al-Zn intermetallic compound interface layer grows thick between filler metal and base metal. With the increase of Al content in Zn-Al filler metal, the interaction strengthens between Zn-Al filler metal and Cu base metal. In the wettability test course, the time beocome short in which Cu base metal interacts with liquid Zn-Al filler metal. The Cu-Al-Zn intermetallic compound interface layer gets thin between filler metal and base metal. Meanwhile, Zn-Al filler metal wettability improves on pure copper surface. But the improvement is not remarkable. Its wettablility is still poor on pure copper surface.

Synthesis and Characterization of Micropores on Nanocrystalline Pure Copper Surface by High-Current Pulsed Electron Beam Irradiation

In this paper, we studied the formations of surface micropores in nanocrystalline pure copper under the action of high-current pulsed electron beam (HCPEB) surface irradiation. It was established that surface porous metal can be successfully fabricated using HCPEB technique. After HCPEB irradiation, a mass of rounded micropores are formed on the irradiated surface. The size and distribution of the micropores can be effectually controlled by adjusting HCPEB processing parameters. The number density of surface micropores decreased but their size increased with increasing HCPEB energy density. The present results indicate that HCPEB technique can provide a new approach for surface porous materials synthesis.

Forming Nanocrystalline Surface Layers in Copper Using Friction Stir Processing

In the present work, a nanostructured layer was formed on the surface of pure copper via friction stir processing (FSP). The surface nanostructuring can be of significant importance in terms of surface-dependent properties such as fatigue, wear, coating, and even corrosion. During FSP, the applied rotating and traverse speeds were 1600 rpm and 50 mm/min, respectively. The results show that a nanograin layer of about 90 µm thick, having the grain size of 50–200 nm, was formed on the surface of pure copper. The nanostructured layer was then characterized using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), as well as scanning electron microscopy (SEM). The microhardness of nanograin layer (175 Hv) was about three times that of the base material (60 Hv).

Internal Oxidation of Rare Earth Additive Accelerating Aluminized Layer on Copper Matrix

The aluminizing treatment on the surface of commercial pure copper with addition of rare earth compound CeCl3 was carried out. The followed internal oxidation of the aluminized copper was also carried out in the industrial nitrogen gas flow. The influences of the aluminizing and internal oxidization processing time on the thickness, hardness profile and microstructure were investigated. Results show that the addition of rare earth oxide CeCl3 has great accelerating effect on the aluminizing and internal oxidation processing. The hardness of the surface Al2O3 dispersion hardened copper composite layer by means of internal oxidation with addition of rare earth compound is higher than that of the without addition. The internal oxidation mechanism of the aluminized layer on copper matrix is comprehensive processes of the oxygen inner-toward diffusion and localized internal oxidation of the inner-toward diffusion of aluminum.

Bactericidal Performance of Flame-Sprayed Nanostructured Titania-Copper Composite Coatings

A large concern surrounding stainless steel surfaces is the ability of bacteria to grow and attach to them quite easily. One possible solution to destroy these pathogens is to coat surfaces with a biocidal agent. The photocatalytic effect of titanium dioxide (TiO2) is known to have a bactericidal effect. Coatings of TiO2 were prepared on 1010 low carbon steel substrates using an oxy-acetylene flame spray torch. TiO2 coatings containing 5 wt.% copper (Cu) were fabricated to increase the bactericidal effect of the coating. After deposition, the coatings were polished to an average roughness of 1 μm. Solutions of Pseudomonas aeruginosa (PAK) bacteria were placed onto the coating surface for periods of up to 3 h, and the amount of surviving bacteria were counted. Some samples were irradiated with white light and other samples were held in a dark chamber. In coatings of copper-free flame-sprayed TiO2, the high flame temperatures facilitated the conversion of the anatase phase to the rutile phase, which limited the photocatalytic destruction of the bacterial cells. However, TiO2-copper composite coatings showed a large bactericidal effect, killing approximately 75% of PAK bacterial cells after 3 h. Under the same conditions, the TiO2-copper composite coatings had the same bactericidal capabilities as pure copper surfaces, with the composite coatings showing improved bactericidal performance when exposed to light. It was proposed that increased concentrations of reactive oxide species produced due to TiO2 photocatalysis improved the performance of the irradiated TiO2-copper composite coatings.

Defect microstructures in polycrystalline pure copper induced by high-current pulsed electron beam——the vacancy defect clusters and surface micropores

In this paper, high-current pulsed electron beam (HCPEB) was used to irradiate the polycrystalline pure copper. The vacancy defect clusters of the irradiated surface layer have been investigated by using transmission electron microscopy. Very dense vacancy defect clusters involving square cells, vacancy dislocation loops and stacking fault tetrahedra were formed after HCPEB irradiation. It suggests that the very high stress and high strain rate induced by rapid heating and cooling due to HCPEB irradiation could cause the shifting of whole atomic planes synchronously, which is the probable mechanism of the formation of the vacancy defect clusters. Additionally, it was established by scanning electron microscopy investigations that dense, fine and dispersed micropores on the irradiated surface of pure copper can be successfully fabricated by using HCPEB irradiation. The dominating formation mechanism of surface micropores should be attributed to the formation of supersaturation vacancies within the near-surface introduced during HCPEB irradiation and vacancy migration along grain boundaries and (or) dislocations towards the irradiated surface. The present results indicate that HCPEB technique may become a new method for rapid synthesis of surface porous materials.

N-Octadecanethiol self-assembled monolayer coating with microscopic roughness for dropwise condensation of steam

Here we presented a novel technology to achieve a Super-hydrophobic coating with microscopic roughness on copper surface. First, make a layer of verdigris grow on the fresh pure copper surface. Gain it by exposing the copper to air and the mist of acetic acid solution. The green coating is a mixture of basic copper(II) carbonate and copper(II) acetate. Second heat the coating and make it decompose to CuO. Lastly, form an n-octadecanethiol self-assembled monolayers coating on the outermost surface. Contact angle test, scanning electron microscope analysis and electrochemical testing were carried out to characterize the surface, and a heat transfer experiment for dropwise condensation of steam was performed also. Results show that the modified surface bears a few Super-hydrophobic features, the static contact angle is higher than that in literatures, reaching 153.1±1.7°. The microscopic roughness can be seen in SEM images, differing much from H2O2 etched surface and bare copper surface. The condensation of steam on the surface is a typical form of dropwise condensation, in the measured range of temperature difference, under 0.1 MPa, the average convection heat transfer coefficients of the vertical surface are 1.7∼2.1 times for those of film condensation. At the same time, the inhibition efficiency of surface is improved to some extent comparing with the same kind of SAMs, which suggests that the lifetime of maintenance dropwise condensation would have the possibility to surpass the existing record.

Characterization on laser clad nickel based alloy coating on pure copper

Nickel based alloy coating has been successfully deposited onto pure copper surface by laser cladding with coaxial powder feeding. Coating with thickness in the region of 1.5 mm can be obtained by depositing two layers of overlapping laser clad tracks. The microstructure observation from optical microscopy and scanning electron microscopy indicated that the coating was free of cracks and pores, and soundly bonded with the substrate. The X-ray diffraction analysis results showed that the coating was mainly composed of γ-(Ni, Cr, Mo, W) solid solution, some carbides and silicides. The average hardness of the coating was about HV 0.1 360, which was about 5 times that of the pure copper. The dry sliding wear tests showed the wear resistance of copper was significantly improved after laser clad nickel based alloy coating.

A model system for the optimization of lamination parameters of PTFE-based dielectrics and metal surfaces

In microelectronic packaging, organic dielectric materials continue to displace ceramic materials because of cost, reduced weight, and performance advantages. Because thermosetting dielectric composites have long found widespread use in printed wiring board (PWB) fabrication, they have been the components of choice for many organic chip carriers. Conversely, thermoplastic dielectrics, such as fluoropolymer (FP), and in particular poly(tetrafluoroethylene)-based dielectric composites (PTFE composites) have seldom found use in multilayer wiring packages in spite of their attractive electrical properties due to their processing challenges. In this paper, we report the use of a model system comprising pure PTFE film and Cr-coated copper surfaces to optimize the bonding process through lamination conditions for a fluoropolymer composite and chromium-coated copper surfaces and to study both the interface mechanics and its chemistry as a function of processing parameters. The significant finding of the investigation was the linkage between the macroscopic mechanical properties of the interface and the observable chemical alteration of the same under some lamination conditions. The relationship of the interface properties and the processing conditions extend a conceptual framework for the thermodynamics of the metal-polymer interface and the reliability of these electronic packages in their practical designs.

Study of copper corrosion products formed during localized corrosion using field emission Auger electron spectroscopy

AbstractCorrosion of pure copper surfaces in chloride‐containing solutions leads to the combined local and global attack of the surface. To be able to identify both reactions, it is important to know the nature of the corrosion products formed in both processes. This was done by investigation of the corroded surface using field emission AES (FE‐AES). The spectra recorded from different locations on the surface were compared to reference spectra using target factor analysis (TFA). The study confirmed the porous nature of the general corrosion product layer. In this layer both Cu2O and CuO are present, the former in higher concentrations. In the local attack sites more CuO than Cu2O is detected and also more chlorides are present. Copyright © 2008 John Wiley & Sons, Ltd.

Application of multisine impedance spectroscopy, FE-AES and FE-SEM to study the early stages of copper corrosion

During the first 24 h of immersion of a pure copper surface in a NaCl containing solution, this surface is in constant evolution. The reactions going on the surface are still not known; discrepancies are found between different published studies. This study resolves these discrepancies using broadband impedance spectroscopy, field emission Auger spectroscopy and field emission electron microscopy. The surface evolution was studied using time series of impedance spectra. Also the experimental variables convection and electrolyte concentration were varied. Parameter evolutions were obtained by fitting the obtained impedance spectra to an equivalent circuit. Combining the calculated parameter values and their evolution with the spectroscopic data led to the identification or replacement of the elements present in the very general equivalent circuit found in the literature: a double layer, two circuit films in parallel and mass transfer.

Potential use of copper surfaces to reduce survival of epidemic meticillin-resistant Staphylococcus aureus in the healthcare environment

Epidemic meticillin-resistant Staphylococcus aureus (EMRSA) emerged in the early 1980s with EMRSA-15 and -16 being the most prevalent strains within the UK. MRSA transmission between patients is largely via the hands of healthcare workers, and contamination of the hospital environment may occur. The objective of this study was to evaluate the effectiveness of copper and brass to reduce the viability of air-dried deposits of three MRSA strains [MRSA (NCTC 10442), EMRSA-1 (NCTC 11939) and EMRSA-16 (NCTC 13143)] compared with stainless steel. MRSA and EMRSA [10(7)colony-forming units (CFU)] were inoculated on to coupons (1 cm x 1 cm) of copper, brass or stainless steel and incubated at either 22 degrees C or 4 degrees C for various time periods. Viability was determined by resuspending removed CFUs and plating out on tryptone soy agar plates in addition to staining with the respiratory indicator fluorochrome 5-cyano-2,3-ditolyl tetrazolium. On pure copper surfaces, 10(7) MRSA, EMRSA-1 and EMRSA-16 were completely killed after 45, 60 and 90 min, respectively, at 22 degrees C. In contrast, viable organisms for all three strains were detected on stainless steel (grade 304) after 72 h at 22 degrees C. At 4 degrees C, complete kill was achieved on copper for all three strains within 6 h. The results demonstrate an antimicrobial effect of copper on MRSA, EMRSA-1 and -16 in contrast to stainless steel. Consequently, the contemporary application of stainless steel in hospital environments for work surfaces and door furniture is not recommended.

Nanocrystalline Ni–B coating surface strengthening pure copper

An electroless deposition technique is used to synthesize nanocrystalline Ni–B coating in strengthening the surface of pure copper. The microstructure and some properties of Ni–B coating are studied. It is practicable to coat a uniform and continuous nanocrystalline Ni–B hardening layer on copper surface by this technique, Ni 2B and Ni 3B are formed in the Ni–B coated layer during heat treatment, and the average grain size of nanocrystalline Ni–B coating is about 42–65 nm and properties of the prepared copper alloys are also improved.