Bulk Copper Substrate Research Articles

Multilayers for efficient thermal energy conversion in high vacuum flat solar thermal panels

Multilayer absorbers based on Cr2O3 and Cr, designed to improve the solar-to-thermal conversion efficiency at mid temperatures in high vacuum flat thermal panel, are fabricated via sputtering deposition on bulk copper substrates and characterized by thermal and optical analysis. The refractive index of the single layers has been measured and used to estimate absorber thermal efficiency at the operating temperatures. Multilayers have been produced via sputtering deposition on bulk copper substrates. The absorber multilayers can be 10% more efficient than the commercial alternative at 250 °C operating temperatures, reaching 380 °C stagnation temperature without sun concentration. The thermal stability has been checked at temperature of 400 °C in vacuum for four hours. High vacuum flat thermal collectors, equipped with the produced selective solar absorbers can obtain unprecedented performances and can give important contribution to the energy transition from fossil fuels to renewable energy for efficient heat production.

Direct synthesis of carbon nanomaterials via surface activation of bulk copper

A facile and novel surface activation approach using a strong-base solution enables the synthesis of carbon nanomaterials (CNMs) directly from bulk copper substrates via chemical vapor deposition. Amorphous carbon nanofibers (CNFs) were grown at temperatures as low as 250 °C, whereas at 600 °C the nanofibers were observed to be turbostratic, and at 700 °C turbostratic CNFs were synthesized together with a new aerogel-like 3D porous turbostratic CNM. A mechanistic model for the observed growth of CNMs from surface activated bulk copper is proposed. Our process is shown to yield conformal CNF growth on various complex-shaped copper substrates, such as meshes and wires, as well as copper-coated materials including carbon fibers and polymer films.

Tribological Properties and Microstructure of the Metal-Polymer Composite thin Layer Deposited on a Copper Plate by Electrocontact Sintering

Abstract The properties of the electrocontact sintered metal-polymer composite materials are strongly determined by the heat flow taking place during sintering, which, in turn, is influenced by the amount and initial distribution of the polymer particles in the metal matrix. In case of the metal-polymer powder mixture in the form of a thin layer deposited on the bulk metal substrate, the influence of the latter is also taken into consideration. Thus, the model simulating the heating and sintering of the thin layer made of metal-polymer powder mixture on a metal plate is proposed. Based on mathematical calculations relating to the model describing the thermal state of the system, it is shown how heat flow fields are formed within the layer, depending on the polymer content and its distribution. These theoretical simulations seem to be useful in optimising the production of the antifriction metal-polymer layer on a bulk copper substrate by electrocontact sintering. The results of the tribological experiments and microstructural observations are in a good agreement with the theoretical model.

Bulk substrate porosity verification by applying Monte Carlo modeling and Castaing’s formula using energy-dispersive x-rays

The leadframe fabrication process normally involves additional thin-metal layer plating on the bulk copper substrate surface for wire bonding purposes. Silver, tin, and copper flakes are commonly adopted as plating materials. It is critical to assess the density of the plated metal layer, and in particular to look for porosity or voids underneath the layer, which may reduce the reliability during high-temperature stress. A fast, reliable inspection technique is needed to assess the porosity or void weakness. To this end, the characteristics of x-rays generated from bulk samples were examined using an energy-dispersive x-ray (EDX) detector to examine the porosity percentage. Monte Carlo modeling was integrated with Castaing’s formula to verify the integrity of the experimental data. Samples with different porosity percentages were considered to test the correlation between the intensity of the collected x-ray signal and the material density. To further verify the integrity of the model, conventional cross-sectional samples were also taken to observe the porosity percentage using Image J software measurement. A breakthrough in bulk substrate assessment was achieved by applying EDX for the first time to nonelemental analysis. The experimental data showed that the EDX features were not only useful for elemental analysis, but also applicable to thin-film metal layer thickness measurement and bulk material density determination. A detailed experiment was conducted using EDX to assess the plating metal layer and bulk material porosity.

Heterogeneous wetting surfaces with graphitic petal-decorated carbon nanotubes for enhanced flow boiling

Two-phase cooling is widely employed in temperature-sensitive devices for high heat flux dissipation owing to the benefits of latent heat exchange. The objective of this work is to elucidate the subcooled flow boiling characteristics of heterogeneous wetting surfaces using water as the working fluid. Heterogeneous wetting surfaces with alternating parallel stripes of superhydrophobic (SHo) and superhydrophilic (SHi) regions are fabricated with graphitic petal-decorated carbon nanotube (GPCNT) coatings. Graphitic petals are a carbon nanostructure comprising of stacks of graphene layers standing vertically on a substrate. GPCNTs are synthesized on bulk copper substrates by a two-step microwave plasma enhanced chemical vapor deposition technique. A combination of Teflon coating, shadow mask, and oxygen plasma treatment is utilized to create composite wetting surfaces with differing superhydrophilic area fractions and SHo to SHi channel width ratios. Boiling experiments reveal that heterogeneous wetting surfaces with higher superhydrophilic area fraction (0.66 and 0.85) exhibit significant reduction in surface superheat and higher heat transfer coefficients throughout the entire boiling regime as opposed to uniform SHo and SHi boiling surfaces. Flow visualization reveals enhanced active nucleation site density and preferential bubble nucleation in the superhydrophobic channels of composite wetting surfaces. Isolated near-spherical vapor morphologies on surfaces with higher superhydrophilic area fraction promote thin film evaporation and enhanced bubble ebullition cycles, thereby leading to improved two-phase thermal performance.

Cost-Effective Thermally-Managed 1.55-$\mu{\rm m}$ VECSEL With Hybrid Mirror on Copper Substrate

An electroplated copper substrate was evaluated for heat dissipation in 1.55-μ.m optically pumped vertical extended cavity surface emitting lasers (OP-VECSELs). It is a cost-effective and flexible solution compared with the previously proposed chemical vapor deposition diamond substrate assembled by metallic bonding. Continuous-wave (CW) lasing operation was demonstrated from a device (with copper electroplated substrate) under optical pumping with pump spot diameter of 100 μm and a maximum output power of 260 mW at 0°C; heatsink temperature was achieved. Room-temperature CW operation with an output power of 75 mW and an external quantum efficiency of 35% was achieved in an optimized plane-concave cavity. The thermal resistance and the maximum output power of VECSEL chips assembled with bonded bulk copper and electroplated copper substrates were measured and compared. A value of ~50 K/W was estimated for both devices, and a similar rollover point was observed, which indicates that the electroplated copper solution leads to similar thermal properties as a bonded bulk copper substrate.

Substrate considerations for graphene synthesis on thin copper films

Chemical vapor deposition on copper substrates is a primary technique for synthesis of high quality graphene films over large areas. While well-developed processes are in place for catalytic growth of graphene on bulk copper substrates, chemical vapor deposition of graphene on thin films could provide a means for simplified device processing through the elimination of the layer transfer process. Recently, it was demonstrated that transfer-free growth and processing is possible on SiO2. However, the Cu/SiO2/Si material system must be stable at high temperatures for high quality transfer-free graphene. This study identifies the presence of interdiffusion at the Cu/SiO2 interface and investigates the influence of metal (Ni, Cr, W) and insulating (Si3N4, Al2O3, HfO2) diffusion barrier layers on Cu–SiO2 interdiffusion, as well as graphene structural quality. Regardless of barrier choice, we find the presence of Cu diffusion into the silicon substrate as well as the presence of Cu–Si–O domains on the surface of the copper film. As a result, we investigate the choice of a sapphire substrate and present evidence that it is a robust substrate for synthesis and processing of high quality, transfer-free graphene.

Nickel Catalyst-Assisted Vertical Growth of Dense Carbon Nanotube Forests on Bulk Copper

Vertical growth of carbon nanotubes using thermal chemical vapor deposition (CVD) is demonstrated on bulk copper substrates by first sputtering a thin Ni film on the surface of copper. Vertical growth of carbon nanotubes occurred when the nickel film thickness was 20 nm and the carbon nanotubes were grown using a xylene source and additional ferrocene catalyst during CVD. These results show the effectiveness of this method in directly integrating carbon nanotubes with highly conductive substrates for applications where a conductive carbon nanotube network is desirable.

Synthesis of High-Quality Vertically Aligned Carbon Nanotubes on Bulk Copper Substrate for Thermal Management

Vertically aligned carbon nanotubes (VACNTs) grown on bulk copper substrate are of great importance for real-life commercial applications of carbon nanotubes (CNTs) as thermal interface materials in microelectronic packaging. However, their reproducible syntheses have been a great challenge so far. In this study, by introducing a well-controlled conformal Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> support layer on the bulk copper substrate by atomic layer deposition, we reproducibly synthesized VACNTs of good alignment and high quality on the copper substrate. The alignment and the quality were characterized by scanning electron microscope, transmission electron microscope, and Raman spectroscopy. The key roles of the conformal Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> support layer by atomic layer deposition are discussed. This progress may provide a real-life VACNT application for thermal management.

Fabrication of Copper Oxide Nanoboxes Containing a Platinum Nanocluster via an Optical and Galvanic Route

Copper oxide hollow nanoboxes containing a platinum nanocluster have been fabricated in mild conditions at room temperature by dropping a laser-irradiated aqueous platinum colloidal solution onto a copper substrate. The irradiation of laser pulses at 1064 nm induces the ejection of photoelectrons from platinum nanoclusters suspended in water. The aqueous colloidal solution containing photooxidized platinum nanoclusters was then dropped onto a bulk copper substrate to form hollow (CuO)0.75(Cu2O)0.25 nanoboxes having an average edge size of 195 nm and an average wall thickness of 26 nm, and the resulting platinum nanoclusters, produced by galvanic reduction, remained inside the newly formed copper oxide nanoboxes.

Growth of aligned multiwalled carbon nanotubes on bulk copper substrates by chemical vapor deposition

Successful growth of vertically aligned carbon nanotube (CNT) arrays on copper substrate by thermal chemical vapor deposition is reported in this paper. The effects of Ti, Ni, and Ni–Cr intermediate layers have been studied to eliminate cracking of the copper surface during the synthesis of CNTs. It was found that these intermediate layers play a critical role in achieving vertical alignment of CNTs on copper substrates. The effects of other reaction parameters such as flow rate of ethylene, concentration of water vapor, and deposition temperature have also been studied. Scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy were used to evaluate the quality and nature of the CNT formed.

Synthesis of Vertically Aligned Multi-Walled Carbon Nanotubes on Copper Substrates for Applications as Thermal Interface Materials

AbstractVertically aligned carbon nanotubes (VACNTs) grown on bulk copper substrate are of great importance for CNT real-life applications as thermal interface materials in microelectronic packaging. However, their reproducible synthesis has been a great challenge so far. In this study, by introducing a well-controlled conformal Al2O3 support layer on the bulk copper substrate by atomic layer deposition (ALD) prior to the deposition of the iron catalyst layer, we reproducibly synthesize VACNTs of good alignment and high quality on the copper substrate, using a conventional thermal chemical vapor deposition process. The alignment and the quality are characterized by scanning electronic microscopy and Raman spectroscopy, respectively. The roles of the conformal Al2O3 support layer are discussed. A kinetics-controlled growth mechanism is shown. This progress provides a viable VACNT commercial application for thermal management, on the basis of which, we show a recent progress on a state-of-art Si/VACNT/Cu assembling process, named “chemical anchoring”. The high quality of the VACNTs on the copper growth substrate and the covalent bonding formed between the VACNTs and the silicon mating substrate greatly reduces the thermal resistance of the VACNT-mediated thermal interface.

SIMS study of absorbates: II. Benzaldehyde and benzoic acid adsorption on copper

The oxidation of benzaldehyde on bulk copper substrates is investigated by XPS and static SIMS. The difficulties in interpreting the XPS data are discussed. Static SIMS gives information on the adsorbate molecular structure, though copper substrates give extensive cationization. Benzoate ion was a major feature in the negative SIMS spectrum, and gave direct evidence for the oxidation of the adsorbate. Restricting the amount of oxygen in the system produced minor changes in the SIMS spectrum of the adsorbate, in contrast to the marked effect noted previously for aluminium substrates.

Sims study of adsorbates: II. Benzaldehyde and benzoic acid adsorption on copper

Abstract The oxidation of benzaldehyde on bulk copper substrates is investigated by XPS and static SIMS. The difficulties in interpreting the XPS data are discussed. Static SIMS gives information on the adsorbate molecular structure, though copper substrates give extensive cationization. Benzoate ion was a major feature in the negative SIMS spectrum, and gave direct evidence for the oxidation of the adsorbate. Restricting the amount of oxygen in the system produced minor changes in the SIMS spectrum of the adsorbate, in contrast to the marked effect noted previously for aluminium substrates.

Ion Backscattering Analysis of Mixing in Au–Cu and Au–Al Thin Films

To illustrate the applications of ion backscattering technique to investigate the low temperature mixing of bimetallic thin films a few unreported experimental data for Au-Cu and Au-Al systems are presented as examples. In the copper gold thin film couples a fast initial interdiffusion has been detected. From time dependence of the concentration profiles different interdiffusion coefficients have been determined for different alloy compositions. A similar investigation in thin gold films evaporated on a bulk copper substrate shows a migration of copper through gold with an activation energy of about 1 eV. In the Au-Al system the initial fast mixing is absent and the backscattering spectra show the presence of the Au2Al and of the AuAl2 compounds for annealing temperatures of 140°C and 230°C respectively.