Migration Of Atoms Research Articles

Atomic-Scale Investigation of Electromigration Behavior in Cu-to-Cu Joints at High Current Density

Three-dimensional integrated circuit (3D IC) packaging offers significant advantages, such as enhanced computational efficiency through greater integration and shorter interconnection distances. The effective interconnection of layers, particularly through redistribution layer (RDL) technology, is crucial for the successful operation of 3D ICs. While copper remains the preferred material for interconnections, often in conjunction with through-silicon via (TSV) technology for chip-to-chip links, the shrinking dimensions of components present challenges. In particular, the reduction in size may lead to elevated current densities in individual joints, giving rise to issues like electromigration (EM) and potential failure. EM-induced atomic migration may lead to the formation of voids in the interconnection. The accumulation of voids to a critical point may result in an open circuit in the joints, significantly impacting the conductor's reliability. This work delves into the micro-scale aspects of these challenges, complementing previous macroscopic investigations. We aim to elucidate the behavioral mechanisms through atomic-scale observations, employing an in-situ high-resolution transmission electron microscope (in-situ HRTEM) to observe atomic-scale images of EM. The insights gained from this work not only contribute to the academic understanding of industry challenges but hold potential applications in real-world manufacturing processes. Fig. 1. (a) Schematic diagram of TEM sample preparation. (b) Cross-sectional HRTEM image of copper bonding. (c, d) TEM images showing voids expansion at bonding interface. Figure 1

Unveiling the secrets of non-evaporable getter films: Activation temperature, activation time, and achievable activation degree

Non-evaporable getter films play an important role in the creating and maintaining of high or ultra-high vacuum environments in advanced scientific disciplines. Prior to application, thermal activation in a vacuum environment is essential. Despite numerous attempts to reduce the film activation temperature, uncertainty remains as to whether extending the activation time at a relatively lower activation temperature will ensure a fully-activated state of the film. To address this issue, the microstructure and activation performance of the film has been investigated. Techniques, such as scanning electron microscopy, grazing incidence X-ray diffraction, energy dispersive spectroscopy, and in-situ X-ray photoelectron spectroscopy were employed. Experimental investigations show that a fully-activated state of the film cannot be achieved at around 150°C, regardless of the activation time. Further analysis shows that, at activation temperatures below about 200°C, the migration trend of oxygen atoms within TiZrV/TiZrHfV films exhibits asynchronous features. This process was accompanied by boundary effects of foreign atom migration channels. In addition, the achievable activation degree of the film shows a step characteristic. These results improve the understanding of the relationship between activation temperature, activation time, and the achievable activation degree of the film.

Molecular dynamics simulation of alloying characteristics of Al–Mg nanoparticles under different process heating conditions

ABSTRACT The effect of thermal process parameters on the alloying of Al–10Mg (wt%) system has been studied in molecular dynamics approach. Five distinct values of heating rate have been considered for Al and Mg nanoparticles (NPs) to melt, coalesce followed by identical cooling. Detailed investigation of Al-Mg NPs alloying has been done in terms of alloying temperature, atomic migration, coalescence kinetics and mechanical characteristics for various heating rates were carried out. Prior to the alloying simulation, component melting simulations of Al and Mg single particles (SPs) were conducted to determine the melting temperature of NPs and to inspect their individual thermo-stability. From the change in potential energy, its evident that the melting temperature of the component NPs significantly depends on heating rates. Following the component melting, alloying simulations were conducted in three distinct phases: (i) heating, (ii) relaxation, and (iii) cooling and solidification. Following the solidification, uniaxial tensile test simulation was done on a block cut to characterise the mechanical behaviour in context to dislocation analysis, HCP evolution, stacking fault analysis and corresponding stress–strain relationship. Obtained results showed a substantial affiliation of heating rates and coalescence kinetics but showed minimal effect on mechanical properties.

Identifying the Origin of Thermal Modulation of Exchange Bias in MnPS3/Fe3GeTe2 van der Waals Heterostructures.

The exchange bias phenomenon, inherent in exchange-coupled ferromagnetic and antiferromagnetic systems, has intrigued researchers for decades. Van der Waals materials, with their layered structures, offer an ideal platform for exploring exchange bias. However, effectively manipulating exchange bias in van der Waals heterostructures remains challenging. This study investigates the origin of exchange bias in MnPS3/Fe3GeTe2 van der Waals heterostructures, demonstrating a method to modulate nearly 1000% variation in magnitude through simple thermal cycling. Despite the compensated interfacial spin configuration of MnPS3, a substantial 170 mT exchange bias is observed at 5 K, one of the largest observed in van der Waals heterostructures. This significant exchange bias is linked to anomalous weak ferromagnetic ordering in MnPS3 below 40 K. The tunability of exchange bias during thermal cycling is attributed to the amorphization and changes in the van der Waals gap during field cooling. The findings highlight a robust and adjustable exchange bias in van der Waals heterostructures, presenting a straightforward method to enhance other interface-related spintronic phenomena for practical applications. Detailed interface analysis reveals atom migration between layers, forming amorphous regions on either side of the van der Waals gap, emphasizing the importance of precise interface characterization in these heterostructures.

Research on Residual Gas Adsorption on Surface of Hexagonal Boron Nitride-Based Memristor.

As a promising nonvolatile memory device with two ends, the memristor has received extensive attention for its industrial manufacture. Density functional theory was used to analyze the adsorption properties of residual gas on hexagonal boron nitride (h-BN)-based memristor model surfaces with Stone-Wales-5577 grain boundary defects [h-BN(SW)]. First, by calculating the adsorption energy, geometric parameters, and charge transfer, we identified the most stable adsorption sites for hydrogen atoms (H-TB1) and H2 molecules (H2-TN2). We observed a tendency toward chemisorption for hydrogen atoms and physical adsorption for H2 molecules at these sites. Furthermore, two coadsorption configurations were formed by introducing H2 molecules and hydrogen atoms into single adsorption configurations: namely H-TB1_H2-TN1TN2 and H2-TN2_H-TB1TN1TN3. In the case of hydrogen-based configuration, there is weak dissociation of the H2 molecule, which does not facilitate hydrogen atom adsorption. However, adjacent hydrogen atoms tend to form stable dimers, while excess hydrogen atoms have a tendency to weakly chemisorb in the case of H2-based configuration. The pristine h-BN surface is more favorable for hydrogen atom migration compared to the h-BN(SW) surface due to its higher adsorption energy. On the h-BN(SW) surface, hydrogen atoms tend to migrate inward from the center of adjacent heptagonal boron nitride rings while coadsorption has a minimal impact on their vertical migration as well as that of H2 molecules. This work provides theoretical insights into the H/H2 trace gas interaction during h-BN wafer-level fabrication for memristor devices.

Grain boundary diffusion and segregation of Cr in Ni [formula omitted] bicrystals: Decoding the role of grain boundary defects

Grain boundary diffusion of Cr in a near Σ11(1̄13)[110] Ni bicrystal is measured over a temperature interval between 503 K and 1203 K using the radiotracer technique. The grain boundary diffusion coefficients, Dgb, and the triple products, P=s⋅δ⋅Dgb, are determined in the C- and B-type kinetics regimes, respectively, with s being the segregation factor and δ the grain boundary width. Opposite to expectations, two distinct contributions to short-circuit diffusion along the nominally single interface are distinguished and related to the existence of two macroscopic facets with distinct grain boundary inclinations and, as a result, distinct structures. The experimental results indicate that the segregation factor of Cr in Ni is about unity, which is fully supported by ab initio calculations. Using classical atomistic simulations, Ni grain boundary self-diffusion coefficients are calculated for the symmetric and asymmetric facets. The computational simulations reveal accelerated self-diffusion kinetics along the asymmetric facet, attributing this phenomenon to the presence of disconnection-like defects. This elucidates the experimentally observed diffusion dynamics of chromium atoms, thereby corroborating the heterogeneous mechanisms governing atomic migration across distinct facets.

Quantitative analysis of atomic migration in lithium-ion conducting oxide solid electrolytes

Direct observation of intrinsic atom migration inside bulk materials is crucial for understanding the ion-conducting property; however, microscopy experiments remain challenging. Here, intrinsic atom migration in bulk lithium-ion conductor La2/3–xLi3xTiO3 was investigated by using aberration-corrected transmission electron microscopy. The atomic migration was triggered by high-energy electron beam irradiation. Through quantitative analysis of high-angle annular dark-field image sequences and estimation of random errors using the 3σ criterion, the subtle contrast variation caused by single atom migration was extracted, in which the validity was further confirmed by image simulations. It provides a simple and feasible methodology for investigating the mechanism of atomic migration in bulk materials.

Ab initio simulation of the dynamic shock response of single crystal and lightweight multicomponent alloy

The dynamic response of shock wave impact on single crystal aluminium and lightweight multicomponent alloy Al-Cu-Li-Mg is simulated by using the combination of Ab initio Molecular Dynamics (AIMD) and Multi-Scale Shock Technique (MSST), with the analysis carried out at the atomic/electronic levels. The simulation is verified by comparing the particle velocity of single crystal obtained in this work with the data in literature. The shock compression process not only involves the migration of atoms, but also is related to electronic transition. Two stages could be found in the shock compression process: oscillatory compression of the crystal cell and oscillatory migration of the atoms. The crystal structure of the multicomponent alloy could be disordered even at low shock speed, due to the difference in the ability to migrate between different kinds of atoms. As the sample is shock-compressed, the contribution proportion of crystal orbitals shows a sharp decrease for D orbital, while it increases significantly for S orbital and P orbital. The electron structure shows a quicker response to the shock wave compression process than the crystal structure. The orbital contribution from P orbital of the crystal is mainly due to the P orbital of Al atoms, while the orbital contribution from D orbital of the crystal is mainly due to the D orbital of Cu atoms. Total Density of States (TDOS) is mainly contributed by the Projected Density of State (PDOS) of Cu atoms in the occupied state of energy levels, while it is close to the PDOS of Al atoms in the non-occupied state of energy levels.

Enhancing the dipole ring of hexagonal boron nitride nanomesh by surface alloying

Surface templating by electrostatic surface potentials is the least invasive way to design large-scale artificial nanostructures. However, generating sufficiently large potential gradients remains challenging. Here, we lay the groundwork for significantly enhancing local electrostatic fields by chemical modification of the surface. We consider the hexagonal boron nitride (h-BN) nanomesh on Rh(111), which already exhibits small surface potential gradients between its pore and wire regions. Using photoemission spectroscopy, we show that adding Au atoms to the Rh(111) surface layer leads to a local migration of Au atoms below the wire regions of the nanomesh. This significantly increases the local work function difference between the pore and wire regions that can be quantified experimentally by the changes in the h-BN valence band structure. Using density functional theory, we identify an electron transfer from Rh to Au as the microscopic origin for the local enhancement of potential gradients within the h-BN nanomesh.

Enabling long-distance hydrogen spillover in nonreducible metal-organic frameworks for catalytic reaction

Hydrogen spillover is an extraordinary effect in heterogeneous catalysis and hydrogen storage, which refers to the surface migration of metal particle-activated hydrogen atoms over the solid supports. Historical studies on this phenomenon have mostly been limited to reducible metal oxides where the long-distance proton-electron coupled migration mechanism has been established, yet the key question remains on how to surmount short-distance and defect-dependent hydrogen migration on nonreducible supports. By demerging hydrogen migration and hydrogenation reaction, here we demonstrate that the hydrogen spillover in nonreducible metal-organic frameworks (MOFs) can be finely modulated by the ligand functional groups or embedded water molecules, enabling significant long-distance (exceed 50 nm) movement of activated hydrogen. Furthermore, using sandwich nanostructured MOFs@Pt@MOFs as catalysts, we achieve highly selective hydrogenation of N-heteroarenes via controllable hydrogen spillover from Pt to MOFs-shell. We anticipate that this work will enhance the understanding of hydrogen spillover and shed light on de novo design of MOFs supported catalysts for many important reactions involving hydrogen.

Unveiling Metal Single Atom Migration Dynamics: Insights into Support-Induced Stability

Unveiling Metal Single Atom Migration Dynamics: Insights into Support-Induced Stability

Hydrogenation of hexene catalyzed by a ruthenium (II) complex with N‐heterocyclic carbene ligands

AbstractIn this study, we investigated the mechanism of the inactivated hexene hydrogenation reaction catalyzed by a ruthenium (II) complex containing “N‐heterocyclic carbene” (NHC) ligands, specifically SIMes and CBA, using DFT calculations. Our focus was on RuH(OSO2CF3)(CO)(SIMes)(CBA), which exhibits excellent catalytic behavior. We tested the B3LYP‐D3, cam‐B3LYP, and TPSSh functionals. The hydrogenation reaction is initiated by the release of SIMes rather than CBA due to the lower associated dissociation energy. Our findings indicate a reaction mechanism consisting of two consecutive steps, each involving one hydrogen atom migration. The first step, considered as the kinetically limiting transition state, exhibits a Gibbs free activation barrier of 12.9 kcal mol−1. This step involves two asynchronous processes. The first one describes the migration of the ruthenium hydride to the internal carbon of the olefine function, transitioning from π to σ coordination mode, which promotes the formation of a bond between ruthenium and the terminal olefinic carbon. The second process involves the oxidation of ruthenium from Ru(II) to Ru(IV). This oxidation is crucial as it enables the decomposition of the H2 molecule into two hydrogen atoms bonded to the ruthenium atom. The geometrical structures of the Hidden Reaction Intermediate Ru(II) complex and the quasi‐transition state of the second process have been determined by means of the RIRC technique. The second step entails the migration of one of the newly formed hydrides of the Ru(IV) complex to the terminal olefinic carbon, resulting in the release of hexane with a weak activation Gibbs free energy of .8 kcal mol−1. Lastly, we explored the use of dichloromethane as a solvent, considering the PCM model. The presence of the solvent significantly decreases the energy dissociation of SIMes from 17.9 to 9.0 kcal mol−1, providing notable benefits.

Engineering interfacial sulfur migration in transition-metal sulfide enables low overpotential for durable hydrogen evolution in seawater

Hydrogen production from seawater remains challenging due to the deactivation of the hydrogen evolution reaction (HER) electrode under high current density. To overcome the activity-stability trade-offs in transition-metal sulfides, we propose a strategy to engineer sulfur migration by constructing a nickel-cobalt sulfides heterostructure with nitrogen-doped carbon shell encapsulation (CN@NiCoS) electrocatalyst. State-of-the-art ex situ/in situ characterizations and density functional theory calculations reveal the restructuring of the CN@NiCoS interface, clearly identifying dynamic sulfur migration. The NiCoS heterostructure stimulates sulfur migration by creating sulfur vacancies at the Ni3S2-Co9S8 heterointerface, while the migrated sulfur atoms are subsequently captured by the CN shell via strong C-S bond, preventing sulfide dissolution into alkaline electrolyte. Remarkably, the dynamically formed sulfur-doped CN shell and sulfur vacancies pairing sites significantly enhances HER activity by altering the d-band center near Fermi level, resulting in a low overpotential of 4.6 and 8 mV at 10 mA cm−2 in alkaline freshwater and seawater media, and long-term stability up to 1000 h. This work thus provides a guidance for the design of high-performance HER electrocatalyst by engineering interfacial atomic migration.

Experimental and molecular dynamics multiscale study on sintering and interfacial reaction of Fe2O3/CaO particle system

High-temperature sintering and solid-state reaction within the intricate Fe2O3/CaO system are pivotal factors influencing material characteristics. The current work focused on the sintering and reaction behavior of Fe2O3/CaO particles at high temperatures with a multiscale study of in-situ high-temperature stage microscopy (HTSM) and molecular dynamics (MD). The laws governing atomic migration and the evolution of crystal structure during the sintering process were simulated at the nanoscale. The results elucidated that a heightened heating rate fosters particle shrinkage and concomitant reduction in surface area. The sintering activation energy (Esin) exhibited an increment proportional to the linear shrinkage of the particles. Furthermore, an augmented potential barrier in advanced stages impeded subsequent sintering behavior. Augmented temperature promoted the particle shrinkage and sintering neck formation, culminating in pore closure and a diminution in the free surface. However, this promotional effect attenuated with escalating temperatures. Particle shrinkage and sintering neck formation are contingent upon atomic migration and diffusion, with the growth of sintering necks primarily reliant on atom diffusion along the surface of the sintering necks. The atomic diffusion activation energy was determined to be 49.5 kJ/mol within the temperature range of 1073–1473 K. Within the Fe2O3/CaO system, the preferential generation of Ca2Fe2O5 (C2F) over CaFe2O4 (CF) was found, leading to a decrease in the atomic diffusion barrier and an enhancement of the diffusivity, with the latter dominating in later stages. The highest mobility of O2–, Fe3+, and Ca2+ was discerned in CF, and the sintering shrinkage of the particles predominantly hinges on the generation of CF.

Effect of binder content and sintering time on the microstructure and mechanical properties of gradient cemented carbides with Ni binder

Replacement of Co by alternative Ni binder in gradient cemented carbide is an effective way to reduce the health concerns associated with Co powders. In the present work, gradient cemented carbides with different Ni contents and gradient sintering times were prepared by traditional powder metallurgy with a two-step sintering method. The microstructure of cemented carbide including the gradient layer formation was analyzed by XRD, SEM, EDS, TEM, and EBSD. The thickness of the gradient layer is almost proportional to the square root of sintering time, indicating that the gradient layer formation is a diffusion-controlled process. The atomic migration can be accelerated to form a thicker gradient layer with the increase of the binder content. The coherent interface of the Ti(C, N) core-rim structure for the gradient cemented carbides with Ni binder was revealed. With the increase in binder content, the average grain size of the WC phase is increased. The hardness and fracture toughness of the cemented carbides were also studied and analyzed according to the crack propagation behavior and the distribution of dislocation and stress indicated by KAM and GND. The variation of the hardness and the fracture toughness with the sintering time is mainly related to the density and the grain size of hard phases, while the change of the mechanical properties along with the Ni content probably results from the local dislocation density and the stress in the cemented carbides. The cemented carbide can obtain a good combination of hardness and fracture toughness with 10 wt% Ni gradient sintered for 2h.

Surface atomic bidirectional migration modulated electrocatalytic activity in Co2MnO4 nanoparticles

Polymetallic cationic spinel-type oxides are increasingly being used as catalysts for oxygen reduction/oxygen evolution reactions (ORR/OER). Here, we have modified the anti-spinel Co2MnO4 using a quenching strategy (CMO-Q) and demonstrated that the bidirectional migration of Co and Mn cations at the tetrahedral/octahedral positions is the essential reason for enhancing the ORR/OER performance. Electrochemical test results show that CMO-Q is better than Co2MnO4, OER initial potential decreased by 100 mV, and ORR current density increased from 4.2 to 7.3 mA cm−2 at 1600 rpm, with more stable CMO-Q-based zinc–air battery performance. Meanwhile, density functional theory calculations confirm that the primary factor contributing to the reduction of distance from the d-band center of Co and Mn to the Fermi level is the conductivity enhancement. This study offers insight into regulating the surface atomic migration and catalytic performance of spinel without compromising its stable structure.

Influence of SiC particles on the microstructure and mechanical behaviors of AlMgScZr alloy processed by laser powder bed fusion

Laser powder bed fusion (LPBF) of AlMgScZr alloy has garnered significant attention as a high-strength aluminum alloy. However, its low modulus, Portevin-Le Chatelier (PLC) behavior, and weak strain hardening capability restrict its application in the aerospace sector. In this study, SiC/AlMgScZr composites with different SiC content have been successfully fabricated using LPBF. The inherent bimodal grain structure of AlMgScZr alloy was not completely altered by the addition of SiC particles. However, with increasing SiC content, heat accumulation increased, and the solidification cooling rate decreased. This led to an increase in the size of α-Al grains in the 5 wt% SiC/AlMgScZr composites. Meanwhile, movable dislocations can be efficiently preserved inside the grains, where they effectively accumulate and become entangled. Consequently, the strain hardening capability of the 5 wt% SiC/AlMgScZr composites improved by approximately 58 % compared to AlMgScZr alloy, with a strain hardening index (n) reaching 0.29. Additionally, the addition of SiC particles led to an increase in the elastic modulus (81.0 GPa). Furthermore, the reaction between Mg atoms and SiC particles resulted in the formation of Mg2Si, which altered the distribution of Mg elements and initiated the reactive precipitation of a Mg-rich phase. There is no competition between the diffusive migration of solute atoms and the motion of movable dislocations within the composites. The additional SiC particles effectively eliminated the PLC effect in the LPBF of AlMgScZr alloy. This work provides essential guidance for developing high-strength and high-stiffness aluminum matrix composites with excellent processing properties in LPBF technology.

Electron Beam-Induced Atomic Migration in the Formation of Nd(OH)3 Nanostructures

Electron Beam-Induced Atomic Migration in the Formation of Nd(OH)3 Nanostructures

Microstructural modifications induced by He implantation at elevated temperature in AlN

The elastic strain and damage build-ups induced by 50 keV He implantations at elevated temperature in (0001)AlN were studied using a combination of X-ray diffraction, transmission electron microscopy and elastic recoil detection analysis experiments. No long-range migration of He atoms occurs up to 700°C. The point defect recombination is found to be enhanced with the increase of implantation temperature. When He concentration exceeds a determined temperature-dependent threshold, the stabilization of vacancies through the formation of He-vacancy clusters of critical size strongly enhances the interstitial concentration and elastic strain in proportion with the local He concentration. Above this threshold, for a critical He concentration that decreases from several at% at room temperature to a few tenths of at% at 700°C, bubbles form and induce a strong increase of disorder. Specific features observed at 700°C, including the systematic superimposition of bubble clusters with basal stacking faults, suggest the triggering between 550 and 700°C of a mechanism promoting disorder, which is discussed.

Unraveling oxygen-driven surface segregation dynamics in platinum-gold alloys

In this study we use high-energy resolution and fast X-ray Photoelectron Spectroscopy (XPS) measurements combined with Density Functional Theory (DFT) calculations to investigate the interplay between surface segregation and bulk migration of Pt atoms on Au(111) in an oxygen environment. We demonstrate that the segregation of Pt atoms is significantly influenced by the oxygen partial pressure and identify a range of O2 pressure where PtAu surface alloy formation is inhibited while promoting the formation of Au oxide. These findings are essential to understand the compositional changes in the bimetallic surface alloy, which could potentially lead to modifying the catalytic properties of PtAu up to catalyst deactivation. Our results offer a strategy to control Pt surface coverage on Au(111), a quantity that is of paramount relevance given the applications of PtAu alloys as catalysts in reactions such as the oxygen reduction reaction or the oxidation of methanol and carbon monoxide. Additionally, our findings indicate a method for controlling the composition and properties of the surface of PtAu catalysts through adjustments made during the formation of the PtAu alloy.