Microstructure and friction performance of copper film fabricated by ion implantation assisted electroless plating on PTFE

Abstract

The polytetrafluoroethylene (PTFE), which was implanted with Ni ion to different energy and doses, fabricated metallic structures by selective electroless copper plating. The characteristic and microstructure of the copper film were studied using SEM and X-ray diffraction. Friction performance of the interface between copper film and basal body of PTFE was tested with a CETR UMT-2 (CETR Co., Campbell, CA, USA) multifunction micromechanics instrument. The test loads were 10, 20 and 40 N, while the line velocity was 8 mm s^?1, and the frequency of data acquisition was 1 Hz. The Ni ion implantation replaces the complicated electroless plating surface pretreatment, and it is an assisted technique of electroless plating of copper on the surface of PTFE and plate Cu directly on its surface. Continuous, prepressing and uniformity plating was obtained with proper technique parameters and the dosage of Ni⁺. The frictional performance comprehensive property of copper film was remarkably influenced by different plating methods, annealing treatment and testing loads under unlubricated condition. The friction coefficients and wear rates changed with the varied load. Annealing treatment improves the tightness and uniformity of the copper film, while it decreases its cavity. Friction performance of copper film was thus increased. The mechanisms of friction and wear of copper film under different test conditions are also discussed.     

Synthesis and optical characterization of copper nanoparticles prepared by laser ablation

The remarkable size-tunable properties of nanoparticles (NPs) make them a hot research topic with applications in a wide range of fields. Hence, copper (Cu) colloidal NPs were prepared using laser ablation (Nd:YAG, 1064 nm, 7 ns, 10 Hz, 6000 pulses) of a copper metal plate at different laser fluences (LFs) in the range of 1–2.5 J cm^?2 in ethylene glycol (EG), at room temperature. Analysis of NPs was carried using different independent techniques such as ultraviolet–visible (UV–vis) spectroscopy; transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. TEM analysis showed that the NPs were spherical with a bimodal distribution and an average particle size of 5 and 16 nm influence of 1.2 J cms^?2, and 9 and 22 nm at 2 J cm^?2. The UV–vis spectra of colloidal NPs revealed the maximum absorbance at around 584 nm, indicating the formation of Cu NPs, which supported using FTIR spectra. Furthermore, the absorption spectra confirmed the metallic nature of Cu NPs. FTIR spectroscopy was utilized to verify information about the NPs surface state and chemical bonds constructed in the atom groups apparent on their surface.     

Experimental investigation of graphite explosive-emission cathodes operating in a periodic pulse regime

We have studied the electron emission from graphite cathodes under the action of voltage pulses with an amplitude of up to 300 kV, a pulse duration of 10^?9 s, and a pulse repetition frequency of 1–3.5 kHz. The magnetically insulated electron beam had a peak power of up to 600 MW at an average power of 1–3 kW. The dynamics of emission current delay was studied in relation to the charge transferred by the beam and to the state of the cathode surface (studied by scanning electron microscopy). It is established that smoothening of the microrelief leads to degradation of the cathode emissivity, which can be compensated by increasing the pulse repetition rate above a certain critical level.     

Degradation processes in the aluminum-silicon system induced by pulsed electric signals

Thermal conditions in a metallization layer deposited onto a single crystal silicon substrate were studied during the passage of single electric pulses with a current density of j=(1–8)×10¹⁰ A/m² and a duration of τ=50–800 μs. Mechanisms of the irreversible degradation in the aluminum-silicon contact under the pulsed current action are established. The degradation is manifested by the contact melting and the metallization layer fusion. Methods for the identification of these phenomena and determination of the critical current densities j _k are proposed. The critical current density depends on the current pulse duration as described by the relationship $j_k \sim 1/\sqrt[4]{\tau }$ . It is established that the passage of single current pulses with j≥5×10¹⁰ A/m² and τ≥200 μs leads to the formation of linear defects in the region of maximum temperature gradient in the test structure.     

Generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external noise

The generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external narrow-band noise microwave signal occurring outside the band of frequencies of the chaotic microwave signal was observed. Chaotic generation emerged due to the parametric instability of the magnetostatic surface wave in the ferromagnetic film, whereas formation of single chaotic microwave pulses was caused by the absence of complete suppression of chaos under the action of narrowband noise.     

Brittle intergranular fracture at elevated temperatures in low–alloy steel

Abstract

Recent studies of stress-relief cracking in low-alloy steels have focused attention on a novel mode of brittle intergranular fracture which occurs at elevated temperatures (300–650°C) in hard, coarse–grained heat–affected–zone microstructures. Fracture initiates at stress concentrators such as sharp cracks or inclusions, and can propagate under static loading at rates of 10^?11?10^?5 ms^?1 to produce intergranular facets with very little associated plastic deformation. The stress-intensity parameter K has been used to characterize crack growth, and three regimes of behaviour have been observed: (i) a threshold region at growth rates of 10^?11?10^?10 m S^?1, (ii)a plateau region, in which growth rates are independent of K between 10^?10 and 10^?8 m S^?1, and (iii) a region of highly K-sensitive crack growth between 10^?8 and ^?5 m S^?1. Independent Auger electron spectroscopy analyses have demonstrated that sulphur segregates locally to the high-temperature crack tip, giving rise to the embrittlement of a limited area of grain boundary. Together with other presegregated solutes, this enables brittle fracture to occur at high temperature, and the transfer of sulphur to the crack tip controls the rate of crack growth. Two models describing crack-tip sulphur segregation are currently proposed. In the first model, a quantitative analysis demonstrates that the crack-tip stress field will drive undersize solute atoms such as sulphur to the physical crack tip. In the second, the intergranular crack is modelled as a sharp cavity. Grain-boundary sulphides which are exposed by cavity formation become unstable and dissolve, saturating the cavity surface with sulphur, which is then drawn into the tip as part of the cavity growth process.

MSTj77     

Carbon coatings for fusion applications

The use of low atomic number material coatings in a fusion reactor plasma chamber may ease concern over maintaining plasma purity. A deposition process involving the discharge activated deposition of carbon coatings from methane at about 1 Pa pressure has been investigated. A coating of thickness 10 μm on copper has survived 1000 cycles of pulsed thermal heating at 37 MW m^-2 with only minor flaking. The surface damage of similar coatings on stainless steel surfaces has been investigated for irradiation with 20, 40, 60 and 120 keV D⁺ and He⁺ ions at ambient temperature. Scanning electron microscopy of irradiated surfaces revealed no significant surface damage for either D⁺ or He⁺ irradiation with energies of 40 and 60 keV for doses of 4 × 10²² and 8.1 × 10²² ions m^-2 respectively. For 120 keV D⁺ and He⁺ irradiations for a dose of 2.2 × 10²³ ions m^-2, surface damage in the form of ridges was observed. A comparison of the results for carbon coatings with those obtained for ATJ graphite reveals that this type of graphite shows surface damage for all irradiations performed, while the carbon coating appears to be more resistant to damage for many of these irradiations. These results reflect favorably on the possible use of these coatings on various components in the plasma chamber of a fusion reactor.     

Surface resistance of superconducting leads at 6.5 GHz

The quality factor (Q value) of a cylindrical TEO11 mode lead cavity has been measured at 6.5 GHz in the temperature range 1.4–4.2 K. Lead was electroplated on a copper substrate. The temperature dependence of the surface resistance derived from the Q measurements has been compared with the semi-empirical formula of Pippard and the microscopic formula of Abrikosov, Gorkov and Khalatnikov (AGK). The plot fit is better with AGK. In this way, the normalized residual resistance (5.0 ± 0.2) × 10^?4 and the energy gap Δ(0) = (4.30 ± 0.05)kT_c was obtained.     

Modeling and kinetics study of microwave heat drying of low grade manganese ore

During the industrial-scale smelting process of manganese ore, blast may occur due to the high moisture content of the ore, and drying pretreatment of the manganese ore is needed in the aspects of safety. In the present paper, microwave drying experiments were conducted under different particle size distributions and different microwave power conditions to explore the basic theory of microwave drying characteristics and kinetics of manganese ore, and the experimental data were fitted and analyzed by using thin-layer drying dynamics model. Results indicated that with the increase of the particle size and the microwave power of the manganese ore, the microwave drying rate increased, and accompanied with a promoting on the drying efficiency. For describing the microwave drying process of manganese ore, diffusion approach model was adopted among the commonly used thin-layer drying kinetic models. Based on Fick's second law, it can be seen that the surface diffusion coefficient increased from 4.27 × 10⁻¹³ m²/s to 8.24 × 10⁻⁸ m²/s with the increase of particle size from a particle size range of 0.012–0.095 mm to a particle size range of 4.2–5.0 mm. Clearly, the particle size has a significant influence on microwave drying efficiency.     

Influence of current pulses on the mobility and multiplication of dislocations in Zn

For the purpose of clarification of the mechanisms of the electron-plastic effect the influence of current pulses with a length of 2·10^–4 sec and a density of more than 20 MA/m² on the mobility of pyramidal dislocations in Zn single crystals in the area of thermally activated movement at 77 and 293 K and also on their multiplication was studied by the method of selective etching. It was shown that the increase in the rate of movement of dislocations under the action of current pulses is accompanied by multiplication of the dislocations with current densities of more, than 10² MA/m². The rules established are discussed taking into consideration the pondermotive forces, thermal effects, electron-dislocation interaction, and the work of the Frank-Reid effect under the action of the electron wind.S. Ordzhonikidze Siberian Metallurgical Institute, Novokuznetsk. Translated from Problemy Prochnosti, No. 10, pp. 48–53, October, 1989.     

Solid state spreading in the Cu/Cu system

Solid state spreading of copper particles on a copper polycrystalline substrate was analysed at 1050^°C. A specific procedure was settled to produce pure monocrystalline and nearly spherical copper particles. Spreading dynamics were analysed from SEM images and preferential particle/substrate orientations were identified by EBSD. The effect of a preferential orientation on the spreading kinetics is limited, if any. A general agreement is found between the kinetic results and numerical calculations of Mullins [1] for mass transport by surface diffusion under the action of surface curvature gradients. The experimental kinetics are however significantly more rapid, due to the contribution of other mechanisms like volume diffusion.     

Influence of nanocrystalline structure of surface on boron gettering from silicon

The boron gettering from nanocrystallites of porous silicon with rate significantly greater in comparison with planar structure has been for the first time observed. As a probe of gettering process, the EPR signal intensity of P_b center was used. It was established that strain effect during the surface oxidation stimulates strongly the boron gettering process from nanocrystallites bulk to SiO₂/Si interface of porous layer.Phenomenon of strong absorption of microwave radiation by porous layer after the sample was annealed in air at 400–500 °C was also detected at 37 GHz. This absorption is equivalent to high conductivity of layer (ρ = 10^− 2–10^− 3 Ω cm) and it is much higher (at least in 10⁴ times) than of c-Si substrate. Removal of porous layer (thickness of ∼ 20 μm) from 400-μm substrate leads to where Q-factor of cavity is restored completely. The high conductivity of the porous layer comes mainly from conduction along the nanocrystalline grains, while SiO₂ layer essentially insulates their interface. One possible effect explanation is that high concentration of positive charge states formed in SiO₂ layer can lead to the creation of high density of free electrons in the SiO₂/Si interface with formation of conductive channels along each nanocrystallite. On the other hand, appreciable microwave absorption is not detected on 9.4 GHz (X-band); therefore, we cannot exclude the existence of quasi-resonant microwave absorption that is related with nanocrystallites sizes, i.e. quantum confinement and electrons tunneling between grains.     

Fatigue behavior and failure mechanism of basalt FRP composites under long-term cyclic loads

This paper studies the fatigue behavior of basalt fiber reinforced epoxy polymer (BFRP) composites and reveals the degradation mechanism of BFRP under different stress levels of cyclic loadings. The BFRP composites were tested under tension–tension fatigue load with different stress levels by an advanced fatigue loading equipment combined with in-situ scanning electron microscopy (SEM). The specimens were under long-term cyclic loads up to 1 × 10⁷ cycles. The stiffness degradation, S–N curves and the residual strength of run-out specimens were recorded during the test. The fatigue strength was predicted with the testing results using reliability methods. Meanwhile, the damage propagation and fracture surface of all specimens were observed and tracked during fatigue loading by an in-situ SEM, based on which damage mechanism under different stress levels was studied. The results show the prediction of fatigue strength by fitting S–N data up to 2 × 10⁶ cycles is lower than that of the data by 1 × 10⁷ cycles. It reveals the fatigue strength perdition is highly associated with the long-term run-out cycles and traditional two million run-out cycles cannot accurately predict fatigue behavior. The SEM images reveal that under high level of stress, the critical fiber breaking failure is the dominant damage, while the matrix cracking and interfacial debonding are main damage patterns at the low and middle fatigue stress level for BFRP. Based on the above fatigue behavior and damage pattern, a three stage fracture mechanism model under fatigue loading is developed.     

Prediction model of lifetime for copper pillar bumps under coupling effects of current and thermal cycling

Considering the current induced voids flow will accelerate the creep strain rate and lower the strength of the solder, a current induced activation energy change, ΔQ_e is added in the Anand model. A lifetime prediction model was constructed based on linear damage rule for the current-thermal cycling coupling test. To verify the accuracy of the model, mean-time-to-failure (MTTF) of copper pillar has been experimentally and analytically investigated under the combination of thermal cycling with temperature range of ?40 to 125 °C and a superimposed electric current with current densities of 17.4–22.4 × 10⁴ A/cm². The experimental results reveal that the MTTF sharply decreases with the increasing current density. The acceleration factors are calculated, which is consistent well with the prediction model.     

Study of microwave components for an electron cyclotron resonance source: Simulations and performance

A high power (2 kW, CW) magnetron-based microwave system operating at 2.45 GHz has been designed, tested, characterized, and used to produce plasma. The system consists of a microwave source, an isolator, a directional coupler, a three-stub tuner, a high voltage break, a microwave vacuum window, and a microwave launcher. These microwave components were simulated using microwave studio software. The low power and full term characterization of the microwave system has been done using vector network analyzer. The system was tested for 2 kW continuous wave of microwave power using glass-water load. The microwave system has been developed to study the microwave interaction with plasma at different operation regimes (Gases: Nitrogen, argon and hydrogen; Gas pressure : 10^?5–10^?3 mbar; Microwave power : 300–1000 W; Magnetic field: 875–1000 G) and to extract the proton beam current with hydrogen produced plasma. A plasma density ～5 × 10¹¹ cm^?3 and average electron temperature of ～13 eV was obtained. This article describes various aspects of the microwave system including design, fabrication, characterization and performance studies of the microwave components.     

Characteristics of Cu/C films on polymer substrates prepared by ECR–MOCVD

Cu/C films were prepared at ambient temperature under a Cu(hfac)₂-Ar-H₂ atmosphere in order to obtain metallized polymer by using electron cyclotron resonance metal organic chemical vapor deposition(ECR-MOCVD) coupled with a direct current (DC) bias system. DC bias selectively attracts the positively charged copper ions and then makes them deposit on the polymer substrate. Structural analysis of the films by ECR showed that fine copper grains were embedded in an amorphous polymer matrix. The electrical properties of the films were closely related to the process parameters such as microwave power, magnet current, H₂/Ar mole ratio and periodic negative voltage. The increase in H₂ contents, microwave power, magnet current and the negative voltage brought on copper-rich film formation with low electrical resistance. On the other hand carbon-rich films with low sheet electrical resistance were prepared with lower values for process parameters described above. Formation of Cu/C films depends strongly on the periodic negative pattern of DC bias and the electrical sheet resistance of the films was controlled in the 10⁸–10⁰ ohm/sq range by process parameters of the ECR-MOCVD system.     

Ratcheting and fatigue behavior of a copper alloy under uniaxial cyclic loading with mean stress

Stress-control fatigue tests have been conducted on a copper alloy at room temperature with and without mean stress. Ratcheting strain was measured to failure under four sets of stress amplitude and mean stress. The ratcheting strain versus cycle curve is similar to the conventional creep curve under static load consisting of primary, steady-state and tertiary stages. The steady-state rate and ratcheting strain at failure increase with mean stress for a given stress amplitude and with stress amplitude for a given mean stress. Ratcheting strain increases as the stress rate decreases. The S–N curve approach and mean stress models of Smith–Watson–Topper and Walker yielded good correlation of fatigue lives in the life range of 10²–10⁵ cycles.     

GaAs MMIC reliability studies

Three types of GaAs monolithic microwave integrated circuits (MMICs) were RF high temperature accelerated life tested to determine the median time before failure (MTBF). Life testing was performed under the d.c. bias conditions and RF input power levels the MMICs would be expected to use under actual operating conditions. the accelleration condition was to raise the base-plate temperature high enough to result in degradation in approximately 1000 hours at the highest test temperature. Because the MMICs were designed for power applications, the input signal level was large enough to cause approximately 1 dB compression. Device failure was defined as a 20 per cent decrease in output power as measured at 125°C, or room temperature when the temperature control system was turned off. Under these conditions the MTBF extrapolated to a channel temperature of 125°C varied between 8 × 10³ hours and 2 × 10⁵ hours depending on the MMIC type. The primary failure mode appeared to be surface leakage currents under the passivation layer.     

Electron-stimulated reduction of the surface of graphite oxide

Auger-electron spectroscopy has been used to study in situ the initial stage of graphite oxide (GO) reduction under the action of a low-intensity electron beam that does not lead to heating of the irradiated region. It was found that this stage evolves at a rate that is tens of times the rate of the subsequent reduction. It was shown that the fast stage is associated with the removal of oxygen groups from the GO surface. The effective cross sections of the initial and subsequent stages of GO reduction by 1500 eV electrons were found to be σ_in ~ 0.5 × 10^–16 cm² and σ_av ~ 1.2 × 10^–18 cm², respectively.     

Heat treatment,surface roughness and corrosion effects on the damage mechanism of mechanical components in the very high cycle fatigue regime

Many engineering components are subjected to combined torsion and axial loading in their working conditions, and the cyclic combined loading can result in fatigue fracture after a very long life fatigue regime. The present investigation extends over a wider range of test conditions involving surface treatment and manufacturing effects such as machining, so as to understand the fatigue properties and damage mechanisms of the material beyond 10⁹ cycles.This work reviews the effect of surface conditions on the fatigue behaviour of mechanical components in the gigacycle regime. Evidently, surface conditions can be variable and are due to very different reasons such as manufacturing effects like machining or final surface processes on the parts, heat treatment before and after manufacturing or environmental conditions like corrosion. In fact, this is a detailed comparative study based on the results of experiments carried out by our research team working in this domain. For this reason, it reveals a continuous decrease of the fatigue strength in the VHCF domain for the investigated materials under different surface conditions as important information for design engineers.Experimental investigation on the test specimens was performed at a frequency of 20 kHz with different stress ratios varying between R = ?1 and R = 0.7 at room temperature. All of the fatigue tests were carried out up to 10¹⁰ cycles. The damage mechanism was evaluated by Scanning Electron Microscopy (SEM).