The foundry industry and academia are confronting the limits of Moore’s Law scaling for logic transistors. Silicon field‑effect transistors (FETs) now rely on gate‑all‑around structures and ultrathin channels, even at the cost of decreased carrier mobility and complex fabrication processes. Two‑dimensional (2D) semiconductors offer a promising alternative because they retain their crystalline quality at atomic thicknesses. Nonetheless, whether they truly exhibit higher performance than silicon remains questionable. Here, by implementing a dual‑gate structure on bilayer MoS2 FETs, we mitigate the fringing‑field barrier created by the elevated top contact and achieve high carrier densities without increasing fabrication complexity. Simulations and statistical analysis confirm that the dual‑gate compensates the fringe field, enabling a drain current of 1.55 mA µm−1 even with conventional gold contacts. Quantum‑transport simulation indicates that, with further gate‑length and equivalent‑oxide‑thickness scaling, the on-state current can reach levels comparable to silicon FETs at the 3-nm node, and monolithic 3D integration can extend the applicability of dual‑gate 2D transistors to future logic technologies. A dual-gate structure in bilayer MoS2 FETs is reported, allowing a high carrier density by compensating for the fringing field, which holds promise for 2D semiconductor logic applications.

Solid-state lithium diffusion dynamics are critical for the rate capability and longevity of Li-ion batteries. Conventionally, nanoscale lithium diffusion within individual battery particles has been simplified as being primarily driven by concentration gradients, despite the associated processes inducing local lattice expansion, contraction, and strain fields. Using operando scanning transmission soft X-ray microscopy with high spatial resolution and chemical sensitivity to track nanoscale intraparticle lithium transport, and post-cycling Bragg coherent diffraction X-ray imaging to directly reveal three-dimensional intraparticle strain fields, we uncover strain-associated lithium transport dynamics within single-crystalline LiNi1/3Mn1/3Co1/3O2 (scNMC) particles during cycling. Contrary to the expected thermodynamic solid-solution behavior of scNMC, our observations reveal near-uniform but fluctuating regions of lithium-dense and lithium-dilute areas during cycling. These fluctuations suggest that nanoscale lithium diffusion can proceed counter to concentration gradients. Additionally, we demonstrate that an increased presence of lithium-dilute regions near the surface enhances lithium surface insertion kinetics, emphasizing the importance of controlling surface lithium distribution to improve rate performance. Our study provides insights into nanoscale solid-state ion transport, with potential applications in batteries, solid-state fuel cells, and memristors.

The foundry industry and academia dedicated to advancing logic transistors are encountering significant challenges in extending Moore's Law. In the industry, silicon (Si)-based transistors are currently adopting gate-all-around (GAA) structures and reducing channel thickness, even at the cost of decreased mobility, for maximizing gate controllability. To compensate for the reduced mobility, multi-channel structures are essential, making the fabrication process extremely challenging. Meanwhile, two-dimensional (2D) semiconductors are emerging as strong alternatives for the channel material in logic transistors, thanks to their ability to maintain crystallinity even when extremely thin. In the case of 2D semiconductors, introducing a dual gate structure, which has a much lower fabrication complexity, can achieve effects similar to GAA. Through this research, we have identified the fringing field originating from the common structure of elevated top contact in 2D FETs results in a high charge injection barrier. Through simulation and statistical analysis with large-area FET arrays, we confirmed that introducing a dual-gate structure in bilayer MoS2 FETs effectively compensates for the fringing field. We have confirmed that this leads to a significant boost in on-current. Remarkably, even with conventional contacts and polycrystalline materials, we observed a record-high on-current of 1.55 mA/µm. Additional circuit simulations have confirmed the potential for dual gate bilayer FETs to surpass the performance of Si GAAFETs when possessing a gate length of 5 nm, achievable only with 2D materials. Therefore, here we propose that by using 2D materials, we can focus on extreme gate length scaling and monolithic 3D integration rather than the challenging GAA process for extending Moore’s Law.

Modern graphics processing units (GPUs) provide an unprecedented level of computing power. In this study, we present a high-performance, multi-GPU implementation of the analytical nuclear gradient for Kohn-Sham time-dependent density functional theory (TDDFT), employing the Tamm-Dancoff approximation (TDA) and Gaussian-type atomic orbitals as basis functions. We discuss GPU-efficient algorithms for the derivatives of electron repulsion integrals and exchange-correlation functionals within the range-separated scheme. As an illustrative example, we calculate the TDA-TDDFT gradient of the S1 state of a full-scale green fluorescent protein with explicit water solvent molecules, totaling 4353 atoms, at the ωB97X/def2-SVP level of theory. Our algorithm demonstrates favorable parallel efficiencies on a high-speed distributed system equipped with 256 Nvidia A100 GPUs, achieving >70% with up to 64 GPUs and 31% with 256 GPUs, effectively leveraging the capabilities of modern high-performance computing systems.

As the pitch size of Cu lines in the back-end-of-line (BEOL) is decreased below a few tens of nanometers, resistivity exponentially increases and electromigration (EM) causes device failure. Graphene has shown promise for both problems, but graphene grown at 400 degrees C for the BEOL-compatible process is far from its ideal honeycomb lattice. In this report, we successfully demonstrated that graphene grown at low temperatures improves Cu resistance by 5% and increased the EM lifetime by 78 times compared to Cu-only interconnect. We proved that the resistivity gain by graphene capping is due to the improvement of the Cu surface, excluding other effects of parallel resistivity and grain boundary scattering. First-principles calculation demonstrated that the graphene edge-Cu bond can inhibit the migration of Cu vacancies, thereby improving the EM lifetime. We manipulated the graphene nanostructure to have more edge contact with Cu, which enhanced the EM lifetime by 116 times compared to Cu-only interconnect. This work systematically investigated the causes for the decrease in resistance of graphene-capped Cu and discovered key factors that contribute the improvement of the interconnect reliability.

Negative differential capacitance in ferroelectrics, which can be stabilized using a dielectric, could be used to overcome the limitations of capacitive coupling in electronic devices. However, the use of negative differential capacitance in scaled silicon-based structures—such as those used in advanced low-power logic devices—remains challenging. Here we report the electrical performance enhancement due to negative differential capacitance in metal–oxide–semiconductor capacitors based on ferroelectric zirconium-doped hafnia (Hf 0.5 Zr 0.5 O 2 ) with a thickness down to 1 nm. The devices exhibit superior performance to physically thinner control devices without the ferroelectric zirconium-doped hafnia. An S-shaped polarization–electric field relation verifies the negative differential capacitance effect. The effect is also achieved in field-effect transistors in which high- κ hafnia is replaced with the ferroelectric zirconium-doped hafnia, leading to an increase in on current and decrease in off current along with negative drain-induced barrier lowering. The negative differential capacitance exhibits endurance over more than 10 15 cycles and can be tuned using doping that controls the interface charges.

Single layers of two-dimensional (2D) materials hold the promise for further miniaturization of semiconductor electronic devices. However, the metal-semiconductor contact resistance limits device performance. To mitigate this problem, we propose modulation doping, specifically a doping layer placed on the opposite side of a metal-semiconductor interface. Using first-principles calculations to obtain the band alignment, we show that the Schottky barrier height and, consequently, the contact resistance at the metal-semiconductor interface can be reduced by modulation doping. We demonstrate the feasibility of this approach for a single-layer tungsten diselenide (WSe2) channel and 2D MXene modulation doping layers, interfaced with several different metal contacts. Our results indicate that the Fermi level of the metal can be shifted across the entire band gap. This approach can be straight-forwardly generalized for other 2D semiconductors and a wide variety of doping layers.

Although solid-state phase transformations through chemical reaction with the surrounding environment are important in the field of materials science, the atomic-level dynamics at reacting surfaces have been difficult to observe directly. Herein, we found highly ordered arrays of 1D intermediate crystals with a unique atomic configuration during the thermal sulfidation of 3D-structured MoO2 to 2D layer-structured MoS2. These arrays reveal a dimension-breaking reconstruction process (3D -> 1D -> 2D) as well as a unique electronic structure evolution. Theoretical calculations show that the 1D crystals have a cross-sectional structure of four transition-metal atoms arranged in a diamond shape; these are critical to the atomic layer-by-layer formation of 2D transition-metal dichalcogenides. Furthermore, electronic structure analyses reveal that the 1D intermediate crystals alter the MoO2/MOS2 contact structure from p- to n-type with increases in the number of formed MoS2 layers.

Roughness-induced resistivity variation of thin metal films is conveniently described by the Fuchs–Sondheimer model, where the phenomenological parameter p is used to quantify the extent of specular scattering at surfaces. However, p is a lumped parameter and does not include microscopic information that characterizes roughness, viz., auto-correlation function, root-mean-square height, and correlation length. In this work, we extract these roughness parameters for Cu films of thickness ranging from 31 nm to 95 nm. We find that the roughness–roughness correlation function is an exponential with a characteristic correlation length that increases monotonically with the film thickness. Using this, we predict the roughness parameter-dependent specularity coefficient, which has an implicit thickness dependency. This alters the resistivity scaling compared to the prevailing model of resistivity scaling, where p is assumed to be a constant.

Atomic layer deposition (ALD) has scarcely been utilized in large-scale manufacturing and industrial processes due to its low productivity, even though it possesses several advantages for improving the device performance. The major cause of its low productivity is the slow growth rate, which is determined by the amount of chemisorbed precursor. The slow growth rate of ALD has become even more critical due to the introduction of heteroleptic-based precursors for achieving a higher thermal stability. In this study, we investigated the theoretical and experimental chemisorption characteristics of the Ti(CpMe5)(OMe)3 precursor during the ALD of TiO2. By density functional theory calculations, the relationship between the steric hindrance effect and the chemistry of a chemisorbed precursor was revealed. Based on the calculation result, a way for improving the growth per cycle by 50% was proposed and demonstrated, successfully.

HfO2-based ferroelectrics are highly expected to lead the new paradigm of nanoelectronic devices owing to their unexpected ability to enhance ferroelectricity in the ultimate thickness scaling limit (≤2 nm). However, an understanding of its physical origin remains uncertain because its direct microstructural and chemical characterization in such a thickness regime is extremely challenging. Herein, we solve the mystery for the continuous retention of high ferroelectricity in an ultrathin hafnium zirconium oxide (HZO) film (∼2 nm) by unveiling the evolution of microstructures and crystallographic orientations using a combination of state-of-the-art structural analysis techniques beyond analytical limits and theoretical approaches. We demonstrate that the enhancement of ferroelectricity in ultrathin HZO films originates from textured grains with a preferred orientation along an unusual out-of-plane direction of (112). In principle, (112)-oriented grains can exhibit 62% greater net polarization than the randomly oriented grains observed in thicker samples (>4 nm). Our first-principles calculations prove that the hydroxyl adsorption during the deposition process can significantly reduce the surface energy of (112)-oriented films, thereby stabilizing the high-index facet of (112). This work provides new insights into the ultimate scaling of HfO2-based ferroelectrics, which may facilitate the design of future extremely small-scale logic and memory devices.

Wafer-scale growth of transition metal dichalcogenides with precise control over the number of layers, and hence the electronic state is an essential technology for expanding the practical application of 2D materials. Herein, a new growth method, phase-transition-induced growth (PTG), is proposed for the precisely controlled growth of molybdenum disulfide (MoS2 ) films consisting of one to eleven layers with spatial uniformity on a 2 in. wafer. In this method, an energetically unstable amorphous MoSx Oy (a-MoSx Oy ) phase is effectively converted to a thermodynamically stable crystalline MoS2 film. The number of MoS2 layers is readily controlled layer-by-layer by controlling the amount of Mo atoms in a-MoSx Oy , which is also applicable for the growth of heteroatom-inserted MoS2 . The electronic states of intrinsic and Nb-inserted MoS2 with one and four layers grown by PTGare are analyzed based on their work functions. The work function of monolayer MoS2 effectively increases with the substitution of Nb for Mo. As the number of layers increases to four, charge screening becomes weaker, dopant ionization becomes easier, and ultimately the work function increases further. Thus, better electronic state modulation is achieved in a thicker layer, and in this respect, PTG has the advantage of enabling precise control over the film thickness.

Picket-fence-type substituents effectively suppress the π–π stacking interaction of flat aromatic molecules and enhance solid-state emission for application in organic light-emitting diodes.

For practical device applications, monolayer transition metal dichalcogenide (TMD) films must meet key industry needs for batch processing, including the high-throughput, large-scale production of high-quality, spatially uniform materials, and reliable integration into devices. Here, high-throughput growth, completed in 12 min, of 6-inch wafer-scale monolayer MoS2 and WS2 is reported, which is directly compatible with scalable batch processing and device integration. Specifically, a pulsed metal-organic chemical vapor deposition process is developed, where periodic interruption of the precursor supply drives vertical Ostwald ripening, which prevents secondary nucleation despite high precursor concentrations. The as-grown TMD films show excellent spatial homogeneity and well-stitched grain boundaries, enabling facile transfer to various target substrates without degradation. Using these films, batch fabrication of high-performance field-effect transistor (FET) arrays in wafer-scale is demonstrated, and the FETs show remarkable uniformity. The high-throughput production and wafer-scale automatable transfer will facilitate the integration of TMDs into Si-complementary metal-oxide-semiconductor platforms.

As the feature size of semiconductor devices decreases, the resist layer with high etch resistance is required to achieve fine pattern transfer during lithography. Conventional resists (e.g., amorphous carbon layers and polycyclic aromatic hydrocarbon films) have reached the limit of etch resistance. Here, we proposed graphene as an etch resist in lithographic process for future semiconductor device. First-principles simulation and experimental reactive ion etching (RIE) revealed that the etch resistance of single-layer graphene (SLG) with the sp(2) carbon fully connected hexagonal structure is superior to that of conventional carbon resist, with an etch selectivity against SiO2 reaching similar to 20. Furthermore, we experimentally confirmed that wafer-scale graphene films, prepared via complementary metal oxide semiconductor (CMOS)-compatible processes, show etch resistances several times higher than those of conventional resists and allow successful pattern transfer to the underlying substrate. This study demonstrates the potential of graphene as an advanced etch resist for future lithographic technologies.

We investigate using the Boltzmann transport equation the electrical resistivity of atomically smooth single-crystal Cu(111) and Cu(001) films with thickness 1-45 nm. Our transport calculations show that, in the absence of grain-boundary scattering and surface perturbations, the resistivity of Cu films of thickness comparable to the electron mean free path (40 nm for bulk copper) is close to the bulk resistivity. The resistivity increases trivially for sub-40-nm-thick films. These single-crystal Cu films show an intrinsic limit of resistivity. A steep increase in resistivity observed for ultrathin films is due to enhanced finite-size effects. We explain the cause of increase in resistivity by investigating the electronic structure at the Fermi level.

A low‐temperature one‐step growth method for few‐layer MoS2 using an atomic layer deposition scheme with MoCl5 and H2S precursors is systematically studied by introducing an ultrathin Al seed layer. First, to optimize the deposition conditions, the effects of the deposition (200–420 °C) and MoCl5 canister (100–160 °C) temperatures on the MoS2 growth behavior are investigated. On the SiO2 surface, increasing the deposition temperature reduces the growth rate while favoring more lateral growth. However, an increase in the MoCl5 sublimating temperature, which is beneficial to improve the film quality, sharply reduces the growth rate, probably owing to the pronounced self‐etching effect of MoCl5. To compensate for the reduced deposition rate while maintaining the MoS2 quality, an ultrathin Al seed layer (≈5 nm) is introduced, which promotes the surface adsorption of MoCl5 molecules at an early growth stage according to density functional theory calculations. Thus, a polycrystalline mono‐to‐bilayer MoS2 film with negligible amounts of residual contaminants (particularly Cl and Al) is successfully synthesized using the proposed Al seeding approach.

Intrinsic defects in graphitic materials, like vacancies and edges, have been expected to possess magnetic states from the many-body interaction of localized electrons. However, charge screening from graphite bulk carriers significantly reduces the localization effect and hinders the observation of those magnetic states. Here, we use an ultra-low-temperature scanning tunneling microscope with a high magnetic field to observe the magnetic states of atomic vacancies in graphite generated by ion sputtering. Scanning tunneling spectroscopy reveals localized states at the vacancies, which exhibit splitting at a certain magnetic field whose separation increases with the field strength. The transition is well described by the “Anderson model,” which describes the emergence of localized magnetic states inside the metallic reservoir through electron–electron interaction. The interaction strength is estimated to be between 1 meV and 3 meV, which is supported by the density functional theory calculation. The observation provides an important foundation for application of intrinsic defects to carbon-based spintronic devices.

Non-specular scattering of carriers, despite being one of the key contributors to metal film resistivity, is conveniently characterized by a single parameter p (referred to as specularity parameter) in the literature without providing a means to separate out relative contributions of surface defects to it. In this work, we report a theoretical formalism to predict contributions to (non-specular) reflection (scattering) of carriers from different types of chemical and structural defects on the film surface. Establishing specular reflection as a special case of the more generalized reflection from the surface, we show that elastic scatterings contribute to the non-specular reflections by randomizing the forward momentum along the transport direction. We predict density and angle-dependent specularity coefficient for various types of defects and show that large angle reflections tend to be non-specular in the presence of isotropic surface defects. Using this formalism, we predict the probability of specular reflection for technologically relevant metal–metal and metal–insulator interfaces. Calculated specularity coefficients are in agreement with values obtained from experimental measurements. Our methodology will help in designing next generation interconnects and engineering the interfaces with minimal diffuse reflection.