Diffusion Of Cu Research Articles

Elucidating the formation and active state of Cu co-catalysts for photocatalytic hydrogen evolution.

The design of active and selective co-catalysts constitutes one of the major challenges in developing heterogeneous photocatalysts for energy conversion applications. This work provides a comprehensive insight into thermally induced bottom-up generation and transformation of a series of promising Cu-based co-catalysts. We demonstrate that the volcano-type HER profile as a function of calcination temperature is independent of the type of the Cu precursor but is affected by changes in oxidation state and location of the copper species. Supported by DFT modeling, our data suggest that low temperature (<200 °C) treatments facilitate electronic communication between the Cu species and TiO2, which allows for a more efficient charge utilization and maximum HER rates. In contrast, higher temperatures (>200 °C) do not affect the Cu oxidation state, but induce a gradual, temperature-dependent surface-to-bulk diffusion of Cu, which results in interstitial, tetra-coordinated Cu+ species. The disappearance of Cu from the surface and the introduction of new defect states is associated with a drop in HER performance. This work examines electronic and structural effects that are in control of the photocatalytic activity and can be transferred to other systems for further advancing photocatalysis.

Phase field study of effect of Al on Cu-rich precipitates in Fe-Cu-Mn-Al alloys

Low carbon steel plays an important role in many applications due to its high strength. Its high strength comes from the strengthening effect of nano-Cu-rich phase precipitates. In order to effectively adjust the microstructure of Cu-rich phase precipitates and obtain Fe-Cu-based steel with the best properties by adding different alloying elements (Mn, Al), it is necessary to understand the precipitation process of Cu particles. In this paper, based on the Ginzburg-Landau theory, the previous phase field model is modified, and the continuous phase field method is used to simulate the precipitation mechanism of nanometer Cu-rich precipitates and the inhibiting of the effect of Al content on Cu-rich precipitates of Fe-15%Cu-3%Mn-&lt;i&gt;x&lt;/i&gt;Al (&lt;i&gt;x&lt;/i&gt; = 1%, 3%, 5% mass fraction) alloy at 873 K isothermal aging. Combining with the free energy derived from thermodynamics database, the microstructure evolution corresponds to the real alloy system. By calculating the composition field variables and structural order parameters, the evolution of phase separation and precipitated phase morphology in aging process are simulated. Moreover, the influence law of morphology, quantity density, average particle radius, growth and coarsening of Cu-rich precipitated phase are discussed. The results show that in the early stage of aging process, the nano-Cu-rich phase precipitates through the spinodal decomposition mechanism, and is randomly distributed in the iron matrix. Furthermore, due to the difference in atomic diffusion rate, the core-shell structure with Cu-rich phase as a core is formed. With the aging time extending, the structure of Cu-rich phase precipitates changes from bcc to fcc. Because of the synergistic effect between Al and Cu, the diffusion of Cu is slowed down. Besides, with the Al and Mn atoms precipitating, Al/Mn clusters are segregated around the Cu-rich precipitates, forming the Al/Mn intermetallic core-shell structure, and gradually wrapping the Cu-rich phase uniformly. During the evolution of the precipitation stage, the Al/Mn clusters are isolated around the Cu-rich precipitation phase, forming a gradually uniform Al/Mn intermetallic phase core shell structure covering the Cu-rich phase, which is to hinder the buffer layer from forming in the precipitation stage of the reservoir. In addition, with the Al content increasing, the Al/Mn intermetallic phase promotes the growth of the buffer layer and hinders the Cu-rich precipitate phase from growing and coarsening.

Improvement of thermal stability of Ta-N film in Cu metallization by a Zr-Si interlayer

Ta-N (10 nm)/Zr (20 nm) film was grown on n-type (100) silicon wafer at various substrate temperatures in a rf magnetron sputtering system, followed by in situ deposition of Cu. The Cu/Ta-N/Zr/Si samples were subjected to thermal annealing up to 800 ℃ under the protection of pure nitrogen gas. In order to investigate the effect of insertion of a thin Zr layer under Ta-N film on Ta-N diffusion barrier performance in Cu metallization, Cu/Ta-N/Zr/Si contact system was characterized by X-ray diffraction (XRD), four-point probe (FPP) measurement, scanning electron microscopy (SEM), and Auger electron spectroscopy (AES) depth profile. The results reveal that the microstructure of Ta-N films deposited on Zr is amorphous at different substrate temperatures. The barrier breakdown temperature of Ta-N/Zr film is about 100°C higher than that of Ta-N. It can effectively prevent the diffusion of Cu after annealed at 800°C. The improvement of diffusion barrier performance may be due to the production of Zr-Si layer with low contact resistivity after annealed at 800°C.

Atomic layer deposited Mo2N thin films using Mo(CO)6 and NH3 plasma as a Cu diffusion barrier

Thin films of molybdenum nitride (Mo2N) are prepared using sequential exposure of molybdenum hexacarbonyl [Mo(CO)6] and NH3 plasma in a plasma-enhanced atomic layer deposition (PEALD) reactor. Several process parameters such as the deposition temperature, plasma power, and post-annealing conditions are systematically investigated to achieve the best quality films. The superior growth kinetics is evident with a significantly higher growth per cycle (GPC) value with lower incubation period for this PEALD process (~1.1 Å, ~36 cycles) when compared to thermal ALD (~0.3 Å, ~63 cycles), both carried out at 200 °C. The growth rate of the Mo2N film reveals a significant jump above 215 °C, indicating a severe decomposition of Mo(CO)6, however, polycrystalline γ-Mo2N films with face-centered-cubic structure are evident within the deposition temperature range of 200–230 °C. The sharp decrease in the resistivity of the as-grown Mo2N films is observed with increasing deposition temperature, film thickness, and plasma power. The resistivity could be further lowered by a post-annealing process and the lowest resistivity of ~395 μΩ cm is achieved for the thin film deposited with 300 watt plasma power and annealed at 700 °C. Finally, the Cu-diffusion barrier capability of an extremely thin film (~7 nm) of as-deposited Mo2N is evaluated in Cu/PEALD-Mo2N/Si structure. The X-ray diffractometry analysis confirms that such a thin layer can successfully prevent the diffusion of Cu up to 500 °C and significant Cu3Si formation was observed only at 600 °C and above. The gradual failure of the diffusion barrier upon annealing is further investigated using electrical impedance (EI) analyses in two different modes. In-plane EI measurements directly indicate the change in the Cu layer at the top, and the formation of Cu3Si can be inferred from the through-plane mode. A comparison with PEALD and thermal-ALD-grown MoNx from EI analyses further reflects the superiority of plasma-enhanced process towards fabricating diffusion barrier layer.

Study on Metallurgically Prepared Copper-Coated Carbon Fibers Reinforced Aluminum Matrix Composites

Carbon materials, like carbon fiber, carbon nanotubes and graphene, were widely used as promising reinforcements to strengthen aluminum matrix composites (AMCs). The dispersion of reinforcement in matrix and interface wettability between matrix and reinforcing phase have been key factors affecting AMCs properties. In this study, electroless copper-coated carbon fibers reinforced aluminum (Cu-Cf/Al) composites were prepared by spark plasma sintering processing followed by heat treatment. Microstructure and mechanical properties were investigated. Microstructure observation indicated that fibers distributed uniformly in the composites containing up to 9 wt% copper-coated carbon fibers (Cu-Cf). In addition, an interfacial layer of 50 nm thickness was formed between the fiber and Al matrix due to mutual diffusion of Cu and Al atoms. Vickers hardness, tensile strength and bending strength of 9 wt% Cu-Cf/Al composite increased from 40 to 93 HV, 59 to 190 MPa and 110 to 326 MPa, respectively, compared to Al matrix. The improved mechanical properties are ascribed to the synergistic effect of dispersion, precipitation and solution strengthening. However, the elongation of composite decreased as compared to that of Al matrix. Moreover, Cu-Cf/Al composite exhibits superior corrosion resistance over uncoated carbon fiber/Al composite but less than Al matrix.

Effect of small amounts of chalcogen alloying elements on the oxidation resistance of copper

Abstract The effect of small amounts of chalcogen alloying elements (S, Se and Te) on the oxidation resistance (OR) of Cu has been investigated at 300–800 °C in 0.1 MPa oxygen atmospheres. Compared to pure copper, the addition of S, Se and Te could effectively improve the OR below 600 °C mainly owing to the chalcogen-element inclusions which hinder the diffusion of Cu. However, it becomes weak above 800 °C. In contrast, the failure at 800 °C is associated with the absence of those inclusions. The results are discussed in detail by the thermodynamic methods.

AlCoCrFeNi high entropy alloy reinforced Cu-based composite with high strength and ductility after hot extrusion

To improve the effectiveness of high entropy alloys (HEAs) as reinforcing agents in metal matrix composites, the 10 vol.% HEA/Cu composite was fabricated by spark plasma sintering, followed by different holding time at 850 °C and hot extrusion. The as-extruded composites were examined by microstructural characterization using scanning electron microscopy, electron probe microanalysis and transmission electron microscopy along with performance tests. The results show that the preheating at 850 °C promotes the diffusion of Al, Co, Cr Fe and Ni from the reinforcement to Cu matrix, along with the diffusion of Cu towards reinforcement, which give rise to the formation of core-shell structure at less than 6 h. However, such core-shell structure is invisible once the preheating time is above 6 h. At less than 6 h, the increased yield strength of the HEA/Cu composite can be ascribed to the solid solution strengthening of Cu matrix stemmed from element diffusion, whereas the improved plasticity is due to the increasing shell thickness in reinforcements with the preheating time. At above 6 h, the strengthening effect of reinforcements decreases significantly, giving rise to the decrease in the yield strength and the improvement in the plasticity.

A thin Cu interlayer-mediated control of phase evolution of Cu2ZnSnS4 thin films grown by RF magnetron sputtering of a single elementary target with high white light sensitivity

Although sputter deposition from a single target to prepare Cu2ZnSnS4 (CZTS) thin films appears attractive, it must suppress the growth of secondary phases that detrimentally affect performance of CZTS based thin film solar cells. Here we demonstrate a rational strategy for deposition of phase pure kesterite CZTS films by RF magnetron sputtering using a single target prepared from elemental powders via a thin Cu interlayer-mediated control of phase evolution. The films grown from a target of stoichiometric elemental proportion were Cu poor that determined the reaction pathway during sulfurization and resulted in growth of spurious phases despite a large variation in the sulfurization configuration. Inserting a 195 nm thick Cu interlayer between successively sputtered precursor layers provided improved compositional stability through thermally activated diffusion of Cu from the intermediate layer towards both the sides and resulted in the formation of kesterite CZTS even at a modest sulfurization temperature of 500 °C. The obtained phase-pure films have a bandgap of ~1.58 eV. The films show excellent photoresponse behavior characterized by increase in current by three orders of magnitude at a bias of 3 V upon white light illumination, typically that required for a potential absorber layer in thin film solar cells.

Dynamic disorder phonon scattering mediated by Cu atomic hopping and diffusion in Cu3SbSe3

Cu3SbSe3 that exhibits distinct liquid-like sublattice due to the heterogeneous bonding environment has emerged as a promising low cost superionic semiconductor with intrinsic ultralow thermal conductivity. However, the relationship between atomic dynamics resulting in liquid-like diffusion and anomalous phonon transport properties remains poorly understood. Herein, combing ab initio molecular dynamics with temperature-dependent Raman measurements, we have performed a thorough investigation on the lattice dynamics of Cu3SbSe3. Superionic transition is unveiled for both structurally inequivalent Cu atoms at elevated temperatures, while the Se-formed tetrahedral framework can simultaneously maintain. An intermediate state of Cu3SbSe3 through the mixture of quasi-1D/2D Cu nearest-neighbor vacancy hopping is discovered below the superionic transition temperature. Our results also manifest that phonons predominately involved with Cu contributions along diffusion channels have been strongly scattered during the superionic transition, whereas the liquid-like diffusion of Cu is too slow to completely breakdown the propagation of all transverse phonon modes. The insight provided by this work into the atomic dynamics and phonon scattering relationship may pave the way for further phonon engineering of Cu3SbSe3 and related superionic materials.

A novel strategy for hierarchical structure in multicomponent nano-precipitated steels by high magnetic field aging

The influence of high magnetic field (HMF) during aging on the precipitation behavior of co-precipitates consisted of Cu-rich precipitates and Ni(AlMn) precipitates in multicomponent nano-precipitated steels was carefully investigated. It was indicated that HMF promoted the construction of hierarchical structures of Cu-rich and Ni(AlMn) co-precipitates. It was thought that HMF increased nucleation rates of secondary co-precipitates during aging because of the thermodynamics change, thus refining the secondary precipitates. Meanwhile, HMF increased the Ostwald ripening rate of primary particles during the further aging after tempering because of increasing diffusion of Cu, thus accelerating the coarsening process.

Highly luminescent copper gallium selenium based multicomponent quantum dots: Formation process and tunable white-light emission

Single-phased and white-emissive quantum dots (QDs) with a broadband spectrum are highly desirable as color converter for white light-emitting diodes (WLEDs) and have been less researched up till now. In this work, a series of copper gallium selenium based multicomponent QDs including quaternary Cu-Zn-Ga-Se (CZGSe) and quinary Cu-Mn-Zn-Ga-Se (CMZGSe) QDs were synthesized. From the perspective of thermodynamics and kinetics, the comparison between PL spectra under increasing temperatures via one-pot and hot-injection methods indicated that the formation of CZGSe cores originated from the diffusion of Cu+ into Zn-Ga-Se nanoparticles. For wider spectra distribution, the incorporation of Mn2+ gave rise to Mn d-d emission around 590 nm. Together with Cu-related emission about 500 nm and intrinsic emission around 430 nm, white emission of CMZGSe QDs could be realized well-tuned by incremental ZnSe deposition, whose chromaticity coordinates shifted along with the Planckian locus. These results about multicomponent alloyed QDs enrich mechanistic insight for the formation kinetics and reveal the potential to fabricate better color rendering WLEDs.

Study on Dissolution of Al2Cu in Al-4.3Cu and A205 Cast Alloys

Evolution of microstructure in a binary Al-Cu system (Al-4.3Cu) and a commercially alloyed Al-Cu system (A205) during solution heat treatment was investigated using optical microscopy (OM), scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy (WDS), and differential scanning calorimetry (DSC). The diversified coarseness of the microstructure was initiated by controlling the solidification rate. Different solution treatment temperatures were applied to identify a proper solutioning temperature. The larger microstructural scale required an increased solutioning temperature and prolonged holding time to obtain homogenized solutes in the α-Al matrix. The diffusion of Cu primarily controlled the solution heat treatment process. A diffusion-based model was applied and calibrated to determine the dissolution rate of an Al2Cu particle in the matrix. The model operates on a similar time scale with the experimental results for the Al-4.3Cu and A205 alloys with various microstructural scales, different chemical compositions, and at different solution treatment temperatures. Three-dimensional (3D) reconstructed images from SEM images and energy dispersive spectroscopy (EDS) map of elements showed that TiB2 particles shield the Cu-rich phases in the boundaries of α-Al grains, presumably acting as a physical barrier to the diffusion of Cu solutes toward α-Al grains. The model also suggests that the effective diffusion coefficient of Cu in Al, in the presence of TiB2 particles, reduced by a factor of 2.0–2.5 in the A205 alloy compared with the binary Al-Cu alloy.

Formation of interfacial Al-Ce-Cu-W amorphous layers in aluminum matrix composite through thermally driven solid-state amorphization

Interfacial Al-Ce-Cu-W amorphous layers formed through thermally driven solid-state amorphization within the (W+CeO2)/2024Al composite were investigated. The elemental distributions and interfacial microstructures were examined with an electron probe microanalyzer and a high-resolution transmission electron microscope, respectively. The consolidation of composites consisted of two thermal processes: vacuum degassing (VD) and hot isostatic pressing (HIP). During consolidation, not only the three major elements (Al, W, and Ce) but also the alloying elements (Mg and Cu) in the Al matrix contributed to amorphization. At VD and HIP temperatures of 723 K and 763 K, interfacial amorphous layers were formed within the composite. Three diffusion processes were necessary for interfacial amorphization: (a) long-range diffusion of Mg from the Al matrix to the interfaces during VD; (b) long-range diffusion of Cu from the Al matrix to the interfaces during HIP; (c) short-range diffusion of W toward the Al matrix during HIP. The newly formed interfacial Al-Ce-Cu-W amorphous layers can be categorized under the Al-Ce-TM (TM: transition metals) amorphous system.

First-principles study on the effect of Sn doping in Cu2S—Acanthite phase as a substitute to low chalcocite for modeling complex doping

The major challenge in the application of Cu2S, as a solar absorber for photovoltaic, is its excessive Cu-vacancy formation tendency within the crystal structure that makes it a degenerate semiconductor. A recent study on Ag alloyed Cu2S acanthite phase has shown a reduced Cu-vacancy formation and a high Cu diffusion barrier. Though low chalcocite is the experimentally known ground state phase at room temperature, its low crystallinity makes it computationally expensive for complex doping modeling. In this work, we first establish the structural correspondence between a newly predicted acanthite and experimentally known low chalcocite phases of Cu2S. This study shows that the acanthite crystal structure of Cu2S can be used to model complex doping in the low chalcocite. The simulated pair distribution functions and diffusions of Cu at room temperature in acanthite and low chalcocite phases of Cu2S show that they have similar structural behavior. Pristine band structures and density of state plots of these two phases also show similarity. Next, we report density functional theory based first-principles investigations of Cu2−xSnxS systems for x = 0 to 0.31 in the acanthite phase for thermodynamic, electronic, and optical properties. We have found that Sn doping coupled with Cu vacancies creates charge-neutral defects and results in higher photoabsorption in the visible light spectra. It was found from these detailed studies that a low concentration of Sn doping is preferable. Then, Sn doping and Cu-vacancy related defects in low chalcocite Cu2S are also studied. Ab initio molecular dynamics simulations show that these compound defects in Cu2S do not negatively affect Cu diffusion inside the crystal. We propose a possible route to synthesize Sn doped acanthite like Cu2S.

Device Postannealing Enabling over 12% Efficient Solution-Processed Cu2 ZnSnS4 Solar Cells with Cd2+ Substitution.

Kesterite Cu2 ZnSnS4 is a promising photovoltaic material containing low-cost, earth-abundant, and stable semiconductor elements. However, the highest power conversion efficiency of thin-film solar cells based on Cu2 ZnSnS4 is only about 11% due to low open-circuit voltage and fill factor mainly caused by antisite defects and unfavorable heterojunction interface. In this work, a postannealing procedure is proposed to complete a Cd-alloyed Cu2 ZnSnS4 device. The postannealing to complete the device significantly enhances the performance of the indium tin oxide and promotes the moderate interdiffusion of elements between the layers in the device. As a result of the diffusion of Cu, Zn, In, and Sn, the interfacial electron and hole densities are improved, leading to the achievement of a suitable band alignment for carrier transport. The postannealing also reduces the interface traps and deep-level defects, contributing to decreased nonradiative recombination. Therefore, the open-circuit voltage and fill factor are both improved, and an efficiency over 12% for pure sulfide-based kesterite thin-film solar cells is obtained.

Application of artificial neural networks for rigid lattice kinetic Monte Carlo studies of Cu surface diffusion

Kinetic Monte Carlo (KMC) is a powerful method for simulation of diffusion processes in various systems. The accuracy of the method, however, relies on the extent of details used for the parameterization of the model. Migration barriers are often used to describe diffusion on atomic scale, but the full set of these barriers may become easily unmanageable in materials with increased chemical complexity or a large number of defects. This work is a feasibility study for applying a machine learning approach for Cu surface diffusion. We train an artificial neural network on a subset of the large set of 226 barriers needed to correctly describe the surface diffusion in Cu. Our KMC simulations using the obtained barrier predictor show sufficient accuracy in modelling processes on the low-index surfaces and display the correct thermodynamical stability of these surfaces.

Fabrication and characterization of Cu2O/Cu-WO3 bilayers for lateral programmable metallization cells

Lateral Programmable Metallization Cell (PMC) structures rely on metal electrodeposition in a long channel consisting of a solid electrolyte layer between an anode and a cathode. Integration of these devices with CMOS circuitry demands using materials such as copper and tungsten for the electrodes, and an oxide of tungsten (WO3) doped with Cu for the electrolyte. However, low diffusivity of Cu in WO3 and its high resistivity results in a slow electrodeposition process. Our solution to this problem involves the use of a Cu2O/Cu-WO3 bilayer, formed by oxidation of a thin Cu film on a WO3 layer and a simultaneous diffusion of Cu into the WO3 at moderate temperatures. This creates a Cu-WO3 solid electrolyte with a semiconducting Cu2O coating that brings electrons to where the ions are most abundant and thereby greatly increases the electrodeposition rate. In this paper, an investigation of thin film Cu oxidation is presented along with the diffusion kinetics of Cu in WO3. The Cu was oxidized in air to form Cu2O with an activation energy of 0.70 eV. The diffusion analysis showed activation energy of Cu diffusion in WO3 was 0.74 eV, which we believe is the first time this value has been reported.

Kinetics of Aqueous Cu(II) Biosorption onto Thevetia peruviana Leaf Powder.

Copper is an essential micronutrient; however, as a result of its increasing demand, subsequent mining followed by its direct discharge into the environment has led to the contamination of our ecosystem. Thevetia peruviana (TP) is an ornamental herb of medicinal interest and is extensively used as an antipyretic and anticancer agent due to the presence of cardiac glycosides. In this work, we have explored the TP leaf powder as a biosorbent for Cu(II) removal from aqueous media and observed that it yields better results in comparison to other reported biosorbents for the removal of Cu(II). This work also emphasizes on the biosorption kinetics along with its plausible mechanism of interactions. The leaf powder characterized by FT-IR spectroscopy confirmed the diverse surface functionalities including hydroxyl, carbonyl, glycosides, etc. The morphology and elemental composition of the plant material have been investigated using SEM-EDAX analysis that confirms the heterogeneity and porosity of the biosorbent surface. The encouraging results revealed that the TP leaf powder could be used as a cost-effective biosorbent with an adsorption capacity of 187.51 mg g–1 for Cu(II) in aqueous media at pH ∼ 5 and a temperature of 303 K. The complex functionality of the TP surface most likely played a significant role in attaining fast equilibrium within 60 min by following pseudo-second-order kinetics, having a rate constant of 2 × 103 mg g–1 min–1 that has been confirmed with statistical tools such as regression coefficient, chi-squared, and sum of error square tests. The adsorption mechanism is controlled by diffusion of Cu(II) from the liquid phase to the solid phase of the TP biosorbent followed by the chemical interaction between the biosorbent and the adsorbate with slow intraparticle diffusion on the biosorbent surface. The adsorption of Cu(II) on TP has been observed to rise from 59.29 to 197.63 mg g–1 with the rise in the pH of the medium from 2 to 7. The adsorption of Cu(II) has been found to increase from 176.80 to 191.33 mg g–1 with increasing temperature from 293–308 K, confirming the endothermic nature of the adsorption process. The thermodynamic study revealed the adsorption process to be spontaneous with negative ΔG (−10.43 to −13.74 kJ mol–1) and that it has an endothermic nature with positive ΔH (54.24 kJ mol–1). The isotherm study for Cu(II) on TP followed the Langmuir adsorption isotherm model with the maximum monolayer adsorption capacity of 303.03 mg g–1 rather than Freundlich and Temkin isotherm models, which confirmed the chemical interaction between the sorbent and sorbate. FT-IR and SEM-EDAX analyses have also been used to confirm the adsorption of Cu(II) onto the TP surface. The present study revealed 99.7% Cu(II) desorption using 0.8 N HCl as the desorbent accompanied by a 69.71% regeneration efficiency of the TP biosorbent. After desorption of Cu(II), the regenerated TP could be disposed of in soil. The encouraging results revealed that TP could be used as an alternative and low-cost biosorbent for the removal of heavy metals from aqueous solutions.

High pressure torsion of Cu–Ag and Cu–Sn alloys: Limits for solubility and dissolution

The high-pressure torsion (HPT) of binary copper alloys with 3, 5, 8, 10 wt. % Ag and 14 wt. % Sn has been studied at room temperature THPT. Before HPT, the Cu–Ag alloys have been annealed at 12 different temperatures between 320 and 800 °C and Cu–14 wt. % Sn has been annealed at 9 different temperatures between 310 and 500 °C. Thus, before HPT the Cu–Ag alloys consisted of Ag-particles in the Cu-based matrix with silver content cinit from almost zero to 8 wt.%. The Cu–14 wt. % Sn samples had Cu-based matrix with tin concentration cinit from almost zero to 14 wt.% Sn and precipitates of ε or δ Hume-Rothery intermetallic phases. After about 1.5 plunger rotations a certain steady-state concentration css of the alloying element is reached in the matrix. The measured css values were 5.5±0.1 wt. % Ag and 13.1±0.1 wt. % Sn. If the initial concentration cinit in Cu matrix was below css (cinit < css), it increased towards css during HPT. If cinit > css it decreased towards css. We observed that css did not depend on cinit in broad interval of cinit and was, therefore, equifinal. The equifinal css values corresponded to the certain equilibrium solubilities of silver and tin in Cu matrix and allowed to estimate the (elevated) effective temperature as Teff (Ag) = 700±10 °C and Teff (Sn) = 400±10 °C, respectively. The observed phenomena are discussed using the ideas of non-equilibrium thermodynamics of open systems. During HPT the decomposition of a solid solution competed with dissolution of precipitates. As a result, a dynamic equilibrium established between precipitation and dissolution at steady-state deformation stage. In this dynamic equilibrium a certain steady-state concentration css of the alloying element is reached in the matrix. In Cu-based alloys, the obtained Teff is always higher than THPT and correlates with activation enthalpy of dopant diffusion in Cu. Other HPT-driven phenomena such as accelerated mass transfer, intermetallic phase formation, grain boundary faceting and grain boundary segregation are taken into account to evaluate the effective temperature Teff.

(Invited) 2D Materials for Backend Technology

Cu is used as the interconnect material in IC chips because of its superior conductivity. However, the diffusion of Cu into the dielectric between two interconnects can cause shorting and create chip failures, while the diffusion to transistors can introduce deep-level traps to Si and affect the transistor performance. Ta/TaN bilayer stacks have been used as diffusion barrier/liner materials to isolate Cu from surrounding intra/inter-layer dielectrics. Along with the scaling of VLSI, the dimensions of interconnects and vias need to be scaled as well. To maximize Cu volume for lower line resistance and reduce the via resistance, the thickness of the barrier/liner bilayer should be scaled accordingly. However, these materials lose their capability of blocking Cu diffusion as their thickness is extremely reduced. In this talk, I will show that the diffusion barrier and liner properties of several 2D materials are investigated by various characterization methods. We observe that the lifetime of the dielectrics surrounding Cu electrodes can be significantly extended with the presence of the tested 2D barriers, providing strong evidence for promising alternative barrier/liner solutions.