Han Wang

Tin–oxo clusters are promising candidates for extreme ultraviolet (EUV) photoresists owing to their high absorption cross sections and defined molecular structures. However, the influence of solvent environments on their photoionization behavior remains unclear. Here, density functional theory calculations combined with the solvation model based on density (SMD) were performed to systematically investigate solvent-dependent ionization energies of representative organotin clusters across 179 solvents. All solvents were found to reduce the vertical ionization potential (VIP) relative to vacuum, and 24 solvents were identified as particularly favorable. Correlation analysis shows that the dielectric constant exhibits a strong inverse relationship with VIP, whereas the molecular polarity index displays only moderate relevance. A hydrogen-like dielectric cavity model was further developed, yielding an analytical expression of the form VIP = a/ϵ_r + b, which quantitatively describes dielectric stabilization effects. These results provide a physically grounded solvent-selection criterion for enhancing EUV photoresist sensitivity.

We report on the observation of coherent molecular vibrations in the methyl radical, which is produced by 267 nm photodissociation of methyl iodide. The radical is excited to high levels in its ν 2 “umbrella” vibrational mode by the dissociation, and the ensuing coherent vibrational dynamics are observed by measuring ultrafast time-dependent changes in the x-ray transition energy from the C 1 s to the singly occupied valence orbital. Due to symmetry, the real-space vibrational motion appears predominantly in the x-ray energy shift at the difference frequencies of the ν 2 progression, although the fundamental frequencies of the ν 2 mode are also observed. By constructing a quantum-mechanical model of the dynamics, the coherent superposition is characterized and the real-space motion of the radicals is reconstructed. The retrieved trajectories are dominated by pronounced quantum beating governed by the high degree of coherent excitation and the strong negative anharmonicity of the ν 2 mode.

The surface thermodynamic properties of ruthenium (Ru) targets were systematically investigated under different laser energy fluences to elucidate the irradiation damage mechanisms of the grazing incidence mirror in x-ray free-electron laser (XFEL) facilities, by combining the two-temperature model and molecular dynamics method. Initially, the 50 nm Ru thin film was irradiated by a 20 fs laser pulse at an absorbed laser fluence of 40 mJ cm−2, and surface dynamic processes with rapid heating and homogeneous melting lasting picosecond-timescale were observed. However, the ultra-short laser-induced surface dynamic responses in 600 nm Ru thick film were lasting much longer time. With the increasing energy fluence of the laser pulse, the intensified irradiation effects characterized by the surface morphology changes were observed, followed by homogeneous melting of the Ru thick film. As the laser fluence approaches the damage threshold, an unconventional ablation effect was observed in the irradiated thick film, featuring the formation of point defects, voids, and subsequent nanometer-scale splitting in the front surface (approximately 5 nm). It indicates that, at laser fluences ranging from 20 to 320 mJ cm−2, the surface morphology undergoes expansion at angstrom to nanometer scales, accompanied by nanoscale splitting. The results provide valuable insights into the irradiation damage mechanism of the high-Z coating materials for x-ray optics in XFELs.

With the advancement of extreme ultraviolet (EUV) lithography technology, the demand for high-performance EUV photoresists has surged. Traditional photoresists struggle to meet the stringent requirements for increasingly smaller feature sizes in semiconductor manufacturing. Among emerging candidates, tin-based materials, particularly Sn₁₂-oxo photoresists, have shown promise due to their superior EUV light absorption properties. Modifying these clusters offers a potential pathway to tailoring their properties for specific lithographic applications. In this study, we investigate the relationship between the photosensitivity of experimentally synthesized Sn₁₂-oxo photoresists and their calculable parameters with quantum chemistry calculations. Key parameters such as bonding energies between metal atoms and organic ligands, molecular ionization potential, electrostatic potential, and HOMO-LUMO gap are identified as critical for predicting photosensitivity. While current research predominantly focuses on replacing counter-anions in Sn₁₂-oxo clusters, there is limited exploration of modifications through the replacement of organic ligands. We examined the effects of electron-withdrawing and electron-donating groups as ligands on the Sn₁₂-oxo cluster's ionization potential and Sn-ligand bonding energy. Our findings suggest a strategy for designing high-performance photoresists, thereby illuminating the path to discovering novel photoresist materials.

The surface properties of nickel-based alloys with different alloying compositions against aggressively corrosive species were systematically evaluated by using the segregated and non-segregated models designed through first-principles calculations. The presence of typical VIB alloying elements such as chromium (Cr), molybdenum (Mo), and tungsten (W) elements near the nickel surface was identified to significantly enhance the surface adsorption of water molecules (H2O) and their decomposed products (OH, O, and H). The doping patterns and surface electronic structures were found to determine the adsorption diversity of these substances. Consequently, adsorbates containing oxygen were likely to induce the segregation tendencies of these selected alloying elements from the deep area of nickel toward the top-most surface layer (TSL). The electrode potential shifts of the surface Ni atom in the designed alloying systems, compared to the bare Ni (111) surface, were further calculated to identify the beneficial electrochemical performance of alloy surfaces in the absence/presence of various adsorbates. In vacuum, the locations of these alloying elements in the near-surface layers would more increase the electrode potential shifts, thereby delaying the dissolution of Ni atoms from metal substrates. Nevertheless, the presence of adsorbates led to notably negative electrode potential shifts for the Ni (111) surface, among which the decomposed products (hydroxyl and oxygen) were of the most passive effects on corrosion behavior of nickel. The detrimental effects of these adsorbates on surface stability would be effectively alleviated with the aid of atomic VIB alloying elements of nickel-based alloys, especially W segregation to the TSL regardless of the pH in aqueous environments.

We simulated XAS with LR-TDDFT for Cu²⁺/Cu⁺ in MOF Cu^I-MFU-4l and revealed a larger 2p core-exciton binding energy for Cu²⁺, finding that corrections with self-consistent excited-state total energy differences provide accurate XAS peak alignment.

Understanding the dynamics of charge transfer at vertical heterostructures of transition metal dichalcogenide monolayers is fundamentally important for future technological applications, given the unique feature of van der Waals interactions at the interface. Here, we employ time-dependent density functional theory formalism combined with molecular dynamics to investigate photoexcited electrons and holes in the type-I MoS₂/PtSe₂ van der Waals heterobilayer. While type-I junctions have been traditionally viewed as being ineffective in photocarrier separation, we show that here a different mechanism from type-II is at play, which effectively separates photoelectrons from photoholes. The key is the phonon bottleneck, arising from the characteristically different dynamic band alignments in the valence and conduction bands, respectively, which only affects the transfer of holes but not electrons. The disparity between electron and hole transfer rates offers a new direction for effective control of charge separation at interfaces.

The photodissociation dynamics of alkyl iodides along the C–I bond are captured by attosecond extreme-ultraviolet (XUV) transient absorption spectroscopy employing resonant ∼20 fs UV pump pulses. The methodology of previous experiments on CH₃I [Chang et al., J. Chem. Phys. 154, 234301 (2021)] is extended to the investigation of a C–I bond-breaking reaction in the dissociative A-band of C₂H₅I, i-C₃H₇I, and t-C₄H₉I. Probing iodine 4d core-to-valence transitions in the XUV enables one to map wave packet bifurcation at a conical intersection in the A-band as well as coherent vibrations in the ground state of the parent molecules. Analysis of spectroscopic bifurcation signatures yields conical intersection crossing times of 15 ± 4 fs for CH₃I, 14 ± 5 fs for C₂H₅I, and 24 ± 4 fs for i-C₃H₇I and t-C₄H₉I, respectively. Observations of coherent vibrations, resulting from a projection of A-band structural dynamics onto the ground state by resonant impulsive stimulated Raman scattering, indirectly reveal multimode C–I stretch and CCI bend vibrations in the A-bands of C₂H₅I, i-C₃H₇I, and t-C₄H₉I.

Two-dimensional materials with excellent surface–volume ratios and massive reaction sites recently have been receiving attention for gas sensing. With first-principles calculations, we explored the performance of monolayer Sc₂CF₂ as a gas sensor. We investigated how molecule adsorption affects its electronic structure and optical properties. It is found that a large charge transfer quantity happens between Sc₂CF₂ and NO₂, which results from the fact that the lowest unoccupied molecular orbital (LUMO) of NO₂ is below the valence band maximum (VBM) of Sc₂CF₂. Moreover, the MD simulation shows that NO₂ can adsorb on the Sc₂CF₂ surface stably at room temperature. We explored the effect of biaxial strain on the adsorption energy and charge transfer quantity of each system, and the results show that the biaxial strain can enhance both the adsorption energy and charge transfer quantity of the NO₂ system and thus can improve the sensitivity of Sc₂CF₂ in detecting the NO₂ molecule. Furthermore, we investigated the adsorption behavior and charge transfer of polar polyatomic molecules at the Sc₂CF₂ surface with h-BN as a substrate, and the results demonstrate that the h-BN substrate can hardly modify the main results. Our result predicts that Sc₂CF₂ can be a promising selective and sensitive sensor to detect the NO₂ molecule, and could also give a theoretical guide for other terminated MXenes used for gas sensors or detectors.

Extreme ultraviolet (EUV)-induced radiation exposure chemistry in organotin–oxo systems, represented by the archetypal [(R–Sn)₁₂O₁₄(OH)₆](A)₂ cage, has been investigated with density functional theory. Upholding existing experimental evidence of Sn–C cleavage-dominant chemistry, computations have revealed that either electron attachment or ionization can single-handedly trigger tin–carbon bond cleavage, partially explaining the current EUV sensitivity advantage of metal oxide systems. We have revealed that tin atoms at different parts of the molecule react differently to ionization and electron attachment and have identified such selectivity as a result of local coordination chemistry instead of the macro geometry of the molecule. An ionization–deprotonation pathway has also been identified to explain the observed evolution of an anion conjugate acid upon exposure and anion mass dependence in resist sensitivity.