As transistor integration accelerates and miniaturization progresses, improving the interfacial adhesion characteristics of complex metal interconnect has become a major issue in ensuring ...semiconductor device reliability. Therefore, it is becoming increasingly important to interpret the adhesive properties of metal interconnects at the atomic level, predict their adhesive strength and failure mode, and develop computational methods that can be universally applied regardless of interface properties. In this study, we propose a method for theoretically understanding adhesion characteristics through steering molecular dynamics simulations based on machine learning interatomic potentials. We utilized this method to investigate the adhesion characteristics of tungsten deposited on titanium nitride barrier metal (W/TiN) as a representative metal interconnect structure in devices. Pulling tests that pull two materials apart and sliding tests that pull them against each other in a shear direction were implemented to investigate the failure mode and adhesive strength depending on TiN facet orientation. We found that the W/TiN interface showed an adhesive failure where they separate from each other when tested with pulling force on Ti-rich (111) or (001) facets while cohesive failures occurred where W itself was destroyed on N-rich (111) facet. The adhesion strength was defined as the maximum force causing failure during the pulling test for consistent interpretation and the strengths of tungsten were predicted to be strongest when deposited onto N-rich (111) facet while weakest on Ti-rich (111) facet.
The recently developed narrow-band blue-emitting organoboron chromophores
based on the multiple-resonance (MR) effect have now become one of
the most important components for constructing efficient ...organic light
emitting diodes (OLEDs). While they basically emit through fluorescence,
they are also known for showing substantial thermally activated delayed
fluorescence (TADF) even with a relatively large singlet–triplet
gap (Δ
E
ST
). Indeed, understanding
the reverse intersystem crossing (RISC) dynamics behind this peculiar
TADF will allow judicious molecular designs toward achieving better
performing OLEDs. Explaining the underlying nonadiabatic spin-flip
mechanism, however, has often been equivocal, and how the sufficiently
fast RISC takes place even with the sizable Δ
E
ST
and vanishingly small spin–orbit coupling is
not well understood. Here, we show that a vibronic resonance, namely
the frequency matching condition between the vibration and the electronic
energy gap, orchestrates three electronic states together and this
effect plays a major role in enhancing RISC in a typical organoboron
emitter. Interestingly, the mediating upper electronic state is quite
high in energy to an extent that its thermal population is vanishingly
small. Through semiclassical quantum dynamics simulations, we further
show that the geometry dependent non-Condon coupling to the upper
triplet state that oscillates with the frequency Δ
E
ST
/
ℏ
is the main driving force
behind the peculiar resonance enhancement. The existence of an array
of vibrational modes with strong vibronic rate enhancements provides
the ability to sustain efficient RISC over a range of Δ
E
ST
in defiance of the energy gap law, which
can render the MR-emitters peculiar in comparison with more conventional
donor–acceptor type emitters. Our investigation may provide
a new guide for future blue emitting molecule developments.
Predicting photolithography performance in silico for a given materials combination is essential for developing better patterning processes. However, it is still an extremely daunting task because of ...the entangled chemistry with multiple reactions among many material components. Herein, we investigated the EUV-induced photochemical reaction mechanism of a model photoacid generator (PAG), triphenylsulfonium cation, using atomiC–Scale materials modeling to elucidate that the acid generation yield strongly depends on two main factors: the lowest unoccupied molecular orbital (LUMO) of PAG cation associated with the electron-trap efficiency ‘before C–S bond dissociation’ and the overall oxidation energy change of rearranged PAG associated with the proton-generation efficiency ‘after C–S bond dissociation’. Furthermore, by considering stepwise reactions accordingly, we developed a two-parameter-based prediction model predicting the exposure dose of the resist, which outperformed the traditional LUMO-based prediction model. Our model suggests that one should not focus only on the LUMO energies but also on the energy change during the rearrangement process of the activated triphenylsulfonium (TPS) species. We also believe that the model is well suited for computational materials screening and/or inverse design of novel PAG materials with high lithographic performances.
The focus of mainstream lithium-ion battery (LIB) research is on increasing the battery’s capacity and performance; however, more effort should be invested in LIB safety for widespread use. One ...aspect of major concern for LIB cells is the gas generation phenomenon. Following conventional battery engineering practices with electrolyte additives, we examined the potential usage of electrolyte additives to address this specific issue and found a feasible candidate in divinyl sulfone (DVSF). We manufactured four identical battery cells and employed an electrolyte mixture with four different DVSF concentrations (0%, 0.5%, 1.0%, and 2.0%). By measuring the generated gas volume from each battery cell, we demonstrated the potential of DVSF additives as an effective approach for reducing the gas generation in LIB cells. We found that a DVSF concentration of only 1% was necessary to reduce the gas generation by approximately 50% while simultaneously experiencing a negligible impact on the cycle life. To better understand this effect on a molecular level, we examined possible electrochemical reactions through ab initio molecular dynamics (AIMD) based on the density functional theory (DFT). From the electrolyte mixture’s exposure to either an electrochemically reductive or an oxidative environment, we determined the reaction pathways for the generation of CO2 gas and the mechanism by which DVSF additives effectively blocked the gas’s generation. The key reaction was merging DVSF with cyclic carbonates, such as FEC. Therefore, we concluded that DVSF additives could offer a relatively simplistic and effective approach for controlling the gas generation in lithium-ion batteries.
Abstract
We report a high-performance multi graphics processing unit (GPU) implementation of the Kohn–Sham time-dependent density functional theory (TDDFT) within the Tamm–Dancoff approximation. Our ...algorithm on massively parallel computing systems using multiple parallel models in tandem scales optimally with material size, considerably reducing the computational wall time. A benchmark TDDFT study was performed on a green fluorescent protein complex composed of 4353 atoms with 40,518 atomic orbitals represented by Gaussian-type functions, demonstrating the effect of distant protein residues on the excitation. As the largest molecule attempted to date to the best of our knowledge, the proposed strategy demonstrated reasonably high efficiencies up to 256 GPUs on a custom-built state-of-the-art GPU computing system with Nvidia A100 GPUs. We believe that our GPU-oriented algorithms, which empower first-principles simulation for very large-scale applications, may render deeper understanding of the molecular basis of material behaviors, eventually revealing new possibilities for breakthrough designs on new material systems.
The simulation of electron beam induced welding of crossed carbon nanotubes is considered with classical molecular dynamics simulations. Covalent junctions are predicted to form between various types ...of carbon nanotubes that contain many defects and are likely to be representative of experimentally welded nanotubes under highly nonequilibrium synthesis conditions. The effect of the junction structure and hydrogen termination of dangling bonds on the mechanical responses of the junctions is also considered.
•GPGPU acceleration method for Monte Carlo ion implantation simulation is proposed.•Our method avoids a branch divergence and is efficient for high energy implantation.•Particle control scheme ...mitigates inaccurate damage due to massive parallelization.•Our methodology shows remarkable speedup for realistic CIS device structure.
In this paper, we develop a GPGPU acceleration methodology for the Binary-Collision-Approximation based Monte Carlo ion implantation simulation (MCII). Our proposed method avoids the branch-divergence issue which comes from the difference of material crystallinity for the structure with multiple materials. We also introduce an efficient scheme to mitigate the side effect for damage accumulation due to massive parallelization of simulation. Our demonstration of high energy implantation into CIS structure shows almost 40x speed-up compared to CPU implementation of MCII. We conclude that GPU-MCII is effective for acceleration of Monte Carlo simulations with high energy implantation e.g. deep photodiode or well isolation formation.
An atomistic simulation flow for contact formation process was developed and integrated into logic transistor frontend process simulation. Existing atomistic kinetic lattice Monte Carlo model of ...epitaxy process was extended to silicidation. Metal and silicon diffusion and silicide formation reactions were taken into account at atomic level which allowed accurate simulation of silicide shape including faceting effects. This approach enables device performance prediction depending on design rules and parameters thus providing a way for TCAD-based technology optimization. As an implementation example a contact resistance prediciton depending on contact opening and recess depth for a 10-nm class logic device is demonstrated.
We examine the strain effect on the dielectric permittivity of cubic SrTiO3 (STO) with Self-Consistent Phonon (SCP) theory calculations. Despite the soft mode frequency overestimation with this ...theory scheme and workflow, our calculations predict the correct tendency of TO1 with respect to temperature and strain. We found that a uniform tensile strain leads to softer TO1 modes. In addition, the TO1 frequency drops suddenly to zero at a specific temperature in the presence of a ferroelectric transition. The square linear relation between TO1 and temperature is used to estimate the Curie Temperature (TC), and the STO dielectric permittivity calculated with the Lyddane-Sachs-Teller relation follows the Curie-Weiss (CW) law; which can also be used to determine another TC value. Results from both approaches are in good agreement with each other and show that TC increases significantly even when the applied tensile strain is only a few percent.
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•SCP theory enables the prediction of temperature-dependent dielectric constants.•The dielectric constant of SrTiO3 has strong temperature dependence.•The tensile strain increases the ferroelectric transition temperature of SrTiO3.
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