Noble Gas Clusters Research Articles

Two-dimensional few-atom noble gas clusters in a graphene sandwich.

The van der Waals atomic solids of noble gases on metals at cryogenic temperatures were the first experimental examples of two-dimensional systems. Recently, such structures have also been created on surfaces under encapsulation by graphene, allowing studies at elevated temperatures through scanning tunnelling microscopy. However, for this technique, the encapsulation layer often obscures the arrangement of the noble gas atoms. Here we create Kr and Xe clusters in between two suspended graphene layers, and uncover their atomic structure through transmission electron microscopy. We show that small crystals (N < 9) arrange on the basis of the simple non-directional van der Waals interaction. Larger crystals show some deviations, possibly enabled by deformations in the encapsulating graphene lattice. We further discuss the dynamics of the clusters within the graphene sandwich, and show that although all the Xe clusters with up to N ≈ 100 remain solid, Kr clusters with already N ≈ 16 turn occasionally fluid under our experimental conditions (under a pressure of ~0.3 GPa). This study opens a way for the so-far unexplored frontier of encapsulated two-dimensional van der Waals solids with exciting possibilities for fundamental condensed-matter physics research and possible applications in quantum information technology.

Size limits and fission channels of doubly charged noble gas clusters.

Small, highly charged liquid droplets are unstable with respect to spontaneous charge separation when their size drops below the Rayleigh limit or, in other words, their fissility parameter X exceeds the value 1. The absence of small doubly charged atomic cluster ions in mass spectra below an element-specific appearance size na has sometimes been attributed to the onset of barrierless fission at X = 1. However, more realistic models suggest that na marks the size below which the rate of fission surpasses that of competing dissociative channels, and the Rayleigh limit of doubly charged van der Waals clusters has remained unchartered. Here we explore a novel approach to form small dicationic clusters, namely by Penning ionization of singly charged noble gas (Ng) clusters that are embedded in helium nanodroplets; the dications are then gently extracted from the nanodroplets by low-energy collisions with helium gas. We observe Ngn2+ ions that are about 40% smaller than previously reported for xenon and krypton and about 20% for argon. These findings suggest that fission barriers have been underestimated in previous theoretical work. Furthermore, we measure the size distributions of fragment ions that are produced by collisional excitation of mass-selected dications. At lowest collision gas pressure, dicationic Kr and Xe clusters that are smaller than previously observed are found to evaporate an atom before they undergo highly symmetric fission. The distribution of fragments resulting from fission of small dicationic Ar clusters is bimodal.

Two-dimensional few-atom noble gas clusters in a graphene sandwich

Two-dimensional few-atom noble gas clusters in a graphene sandwich

Exploring the energy landscape of graphynes for noble gas adsorption using swarm intelligence

Gas adsorption on one-atom-thick membranes is a growing technology for separation applications owing to its excellent energy efficiency. Herein, we investigate the adsorption of the noble gases, Ne, Ar and Kr on graphynes (GYs), a novel class of one-atom-thick carbon membranes using a swarm intelligence technique, namely particle swarm optimization (PSO). Modeling the adsorption of noble gas clusters on two-dimensional substrates requires a thorough examination of the energy landscape. The high dimensionality of the problem makes it tricky to employ ab initio methods for such studies, necessitating the use of a metaheuristic global optimization technique such as PSO. We explored the adsorption of 1–30 atoms of Ne, Ar and Kr on α-, β-, γ- and rhombic-GYs to predict the most suitable form of GY for the adsorption of each of the gases. Employing the dispersion-corrected density functional theory (DFT-D) data for the adsorption of single gas atoms as the reference data, we parametrized two empirical pairwise potentials, namely, Lennard-Jones (LJ) and improved Lennard-Jones (ILJ) potentials. We then analyzed the growth pattern as well as the energetics of adsorption using the parametrized potentials, in combination with the PSO technique, which enabled us to predict the best possible membrane for the adsorption of the noble gases: α-GY for Ne and γ-GY for Ar and Kr. The accuracy of our modeling approach is further validated against DFT-D computations thereby establishing that PSO, when combined with the ILJ potential, can serve as a computationally feasible approach for modeling gas adsorption on GYs.

Meta-analysis of the effects of inert gases on cerebral ischemia–reperfusion injury

Recently, noble gas has become a hot spot within the medical field like respiratory organ cerebral anemia, acute urinary organ injury and transplantation. However, the shield performance in cerebral ischemia–reperfusion injury (CIRI) has not reached an accord. This study aims to evaluate existing evidence through meta-analysis to determine the effects of inert gases on the level of blood glucose, partial pressure of oxygen, and lactate levels in CIRI. We searched relevant articles within the following both Chinese and English databases: PubMed, Web of science, Embase, CNKI, Cochrane Library and Scopus. The search was conducted from the time of database establishment to the end of May 2023, and two researchers independently entered the data into Revman 5.3 and Stata 15.1. There were total 14 articles were enclosed within the search. The results showed that the amount of partial pressure of blood oxygen in the noble gas cluster was beyond that in the medicine gas cluster (P < 0.05), and the inert gas group had lower lactate acid and blood glucose levels than the medical gas group. The partial pressure of oxygen (SMD = 1.51, 95% CI 0.10 ~ 0.91 P = 0.04), the blood glucose level (SMD = − 0.59, 95% CI − 0.92 ~ − 0.27 P = 0.0004) and the lactic acid level (SMD = − 0.42, 95% CI − 0.80 ~ − 0.03 P = 0.03) (P < 0.05). These results are evaluated as medium-quality evidence. Inert gas can effectively regulate blood glucose level, partial pressure of oxygen and lactate level, and this regulatory function mainly plays a protective role in the small animal ischemia–reperfusion injury model. This finding provides an assessment and evidence of the effectiveness of inert gases for clinical practice, and provides the possibility for the application of noble gases in the treatment of CIRI. However, more operations are still needed before designing clinical trials, such as the analysis of the inhalation time, inhalation dose and efficacy of different inert gases, and the effective comparison of the effects in large-scale animal experiments.

Effect of gas cluster species on crater formation for fused silica

The interactions of the Ne, Ar, and Kr clusters with the fused silica surface were investigated by molecular dynamics simulations. The impacts of noble gas clusters with kinetic energies ranging from 25 to 110 eV per atom were compared. The characteristics of the formed craters were examined at cluster incidence angles of 0° and 60°. It was found that the crater diameter is almost the same for different gas species at normal incidence. However, at oblique incidence, the depths of craters formed by the Ne and Kr clusters differ insignificantly. Additionally, it has been shown that the ratio of crater length to depth is a function of the energy per cluster atom and can be the same for clusters with different energies and sizes. The dependencies of the crater volume on the scaled cluster energy and energy per unit area were studied. The cratering efficiency of different gas species was estimated, and the relationship between crater volume and sputtering yield was revealed. Moreover, it was shown that the ratio of sputtered volume to crater volume is power law related to the ratio of the sputtered atoms energy to the initial kinetic energy of clusters.

On the angular distributions of atoms sputtered by gas cluster ion beam

The angular distributions of atoms sputtered by the noble gas cluster ion beam from metal surfaces are studied. The experimental results on the angular distributions of Cu and W atoms sputtered by 10 keV Ar, Kr, and Xe GCIB are presented. The deviation from the conventional « lateral » angular distribution, found in previous works was studied in detail with new experimental data.The molecular dynamics simulations are performed for the detailed study of the mechanisms that affect the angular distributions. The simulation of consequent impacts considered the effects of the bombarding cluster ion fluence and cluster size distribution. The significant effect of energy per cluster atom on the angular distributions was revealed and explained. Both the cluster size distribution and the surface topography were found to affect the angular distributions of sputtered atoms. The mechanisms of these effects were analyzed.

Electron transfer in strong-field three-body fragmentation of ArKr2 trimers.

We experimentally studied the three-body fragmentation dynamics of a noble gas cluster (ArKr2) upon its multiple ionization by an intense femtosecond laser pulse. The three-dimensional momentum vectors of correlated fragmental ions were measured in coincidence for each fragmentation event. A novel comet-like structure was observed in the Newton diagram of the quadruple-ionization-induced breakup channel of ArKr2 4+→ Ar+ + Kr+ + Kr2+. The concentrated head part of the structure mainly originates from the direct Coulomb explosion process, while the broader tail part of the structure stems from a three-body fragmentation process involving electron transfer between the distant Kr+ and Kr2+ ion fragments. Due to the field-driven electron transfer, the Coulomb repulsive force of the Kr2+ and Kr+ ions with respect to the Ar+ ion undergoes exchange, leading to changes in the ion emission geometry in the Newton plot. An energy sharing among the separating Kr2+ and Kr+ entities was observed. Our study indicates a promising approach for investigating the strong-field-driven intersystem electron transfer dynamics by using the Coulomb explosion imaging of an isosceles triangle van der Waals cluster system.

Elucidation of Noble Gas Cluster Configurations Bound on Graphdiyne: A Metaheuristic Approach.

Graphynes are a class of all-carbon two-dimensional membranes that have been intensely researched for various membrane-based technologies on account of their unique pore architectures. Herein, we report an investigation of the mechanism and energetics of adsorption of noble gases (He, Ne and Ar) on graphdiyne (GDY), the most popular form of graphynes. Two global optimization techniques, namely particle swarm optimization (PSO) and differential evolution are employed to predict the putative global minima configurations of rare gas clusters in the size range 1-30 when adsorbed on GDY. We use the 12-6 Lennard-Jones potential to represent the pairwise non-covalent interactions between various interacting atoms. Initially, the gas atoms adsorb as monolayers on GDY at the centers of the triangular pores until all the triangular pores are filled. This is followed by a second layer formation on top of the hexagonal pore centers or on top of the C-C bonds. The findings from the empirical approach are further validated by performing density functional theory calculations on the predicted adsorbed cluster configurations. We have also looked into the adsorption of noble gas clusters on bilayer GDY systems and have found that the intercalation of gas atoms within the bilayers is feasible. Our study suggests that the stochastic nature of the swarm intelligence technique, PSO can assist in an effective search of the potential energy surfaces for the global minima, eventually enabling large-scale simulations.

Spectral Signatures of Protonated Noble Gas Clusters of Ne, Ar, Kr, and Xe: From Monomers to Trimers.

The structures and spectral features of protonated noble gas clusters are examined using a first principles approach. Protonated noble gas monomers (NgH+) and dimers (NgH+Ng) have a linear structure, while the protonated noble gas trimers (Ng3H+) can have a T-shaped or linear structure. Successive binding energies for these complexes are calculated at the CCSD(T)/CBS level of theory. Anharmonic simulations for the dimers and trimers unveil interesting spectral features. The symmetric NgH+Ng are charactized by a set of progression bands, which involves one quantum of the asymmetric Ng-H+ stretch with multiple quanta of the symmetric Ng-H+ stretch. Such a spectral signature is very robust and is predicted to be observed in both T-shaped and linear isomers of Ng3H+. Meanwhile, for selected asymmetric NgH+Ng’, a Fermi resonance interaction involving the first overtone of the proton bend with the proton stretch is predicted to occur in ArH+Kr and XeH+Kr.

Properties of radiative charge transfer in heterogeneous noble-gas clusters

Radiative charge transfer (RCT) from cationic to neutral atoms is a fundamental and frequently occurring process in ion-neutral collisions and in van der Waals clusters. In contrast to collisions with only two collision partners, RCT in clusters is more involved as it may depend on the cluster size, the cluster stoichiometry, and the local arrangement of atoms in the cluster. Here, we present a systematic investigation of an RCT photon spectrum as a function of cluster size, stoichometry, and local atom arrangement. For this purpose, we utilize RCT in heterogeneous NeKr and NeXe clusters after Ne $2p$ photoionization. Our results confirm that Ne dimer ions form prior to RCT if enough Ne is available and we observe that different features dominate the photon spectrum depending on the cluster production parameters. Additionally, we find that the lifetime of the radiative decay is sensitive to the cluster stoichiometry, which we explain and interpret by theoretical calculations on the RCT decay width for different local geometric structures of the involved atoms. We conclude that RCT properties such as photon spectrum and lifetime in turn exhibit information on the mean size and stoichiometry of a cluster jet and the arrangement of the involved atoms.

Directional terahertz beam generation under interaction of an intense femtosecond laser pulse with a cluster jet

A supersonic jet consisting of atomic clusters of noble gases under interaction with high-power femtosecond radiation allows control of the radiation pattern and efficiency of generation of terahertz (THz) radiation. The laser filament formed in this jet is spatially defined by the shape of the jet. The concentration, spatial distribution, and size of the clusters influence the propagation of the femtosecond laser pulse in it and the formation of a THz pulse. We show that a specially formed cluster jet allows the shaping of THz radiation with a high degree of directionality and increase its intensity by more than 10 times.

The cluster species effect on the noble gas cluster interaction with solid surfaces

The effect of noble gas cluster species on the cluster interaction with solid surfaces was investigated. Processes of Ar, Kr and Xe clusters interaction with Cu and Mo surfaces were studied using molecular dynamics simulations. It is shown that lighter cluster front atoms undergo more backscattering from surface atoms, causing more intense multiple collisions between cluster atoms. This affects cluster penetration, energy exchange between the cluster and surface atoms, and cluster thermalization. The influence of energy per cluster atom on these effects is discussed.

Swarm intelligence unravels the confinement effects for tiny noble gas clusters within carbon nanotubes

Inspired by the myriad manifestations of confinement effects for atoms and molecules encapsulated within carbon nanotubes (CNTs), herein, we explore the role of the physical dimensions of the CNTs in controlling the optimal configurations of confined noble gas clusters. We utilize the particle swarm optimization (PSO) technique together with the continuum approximation for CNTs to arrive at the minimum energy configurations of the encapsulated He, Ne and Ar clusters in the size range 2–10. The ease with which a global search technique such as PSO can track down the minima on complex potential energy surfaces within reasonable computational times enables probing a wide spectrum of CNTs covering nanotubes with lengths in the 10–50 A range and possessing radii of 3–6 A. Our findings indicate a strong correlation between the most stable cluster configuration and the physical dimensions of the CNT within which it is confined. Notably, the confined cluster geometries encompass linear, zigzag and spiral configurations, in striking contrast to their isolated geometries. Guided by the chemical intuition, we have further expanded the search space and examined the possibility of exohedral binding in necessary cases. The implementation of the PSO along with the continuum approximation can generate excellent starting geometries amenable for further analysis using highly accurate first-principles calculations.

Freestanding and Supported MoS2 Monolayers under Cluster Irradiation: Insights from Molecular Dynamics Simulations.

Two-dimensional (2D) materials with nanometer-size holes are promising systems for DNA sequencing, water purification, and molecule selection/separation. However, controllable creation of holes with uniform sizes and shapes is still a challenge, especially when the 2D material consists of several atomic layers as, e.g., MoS2, the archetypical transition metal dichalcogenide. We use analytical potential molecular dynamics simulations to study the response of 2D MoS2 to cluster irradiation. We model both freestanding and supported sheets and assess the amount of damage created in MoS2 by the impacts of noble gas clusters in a wide range of cluster energies and incident angles. We show that cluster irradiation can be used to produce uniform holes in 2D MoS2 with the diameter being dependent on cluster size and energy. Energetic clusters can also be used to displace sulfur atoms preferentially from either top or bottom layers of S atoms in MoS2 and also clean the surface of MoS2 sheets from adsorbents. Our results for MoS2, which should be relevant to other 2D transition metal dichalcogenides, suggest new routes toward cluster beam engineering of devices based on 2D inorganic materials.

Determination of Mean Cluster Sizes by Fluorescence Detection upon Site-Specific Photoexcitation

Electronic excitations in the valence shell of Ne clusters were studied by fluorescence spectroscopy. The measured fluorescence excitation functions contain information about the nature and number of excitonic states and the mean cluster size of the produced size distribution. Mean cluster sizes were determined by comparing surface and bulk contributions using a multidimensional fitting algorithm, with good agreement to commonly used scaling laws. The influence of different size distributions, which were not considered in previous investigations, on homogeneous noble gas cluster jets is implemented in the proposed model. The present work is the first approach using fluorescence spectroscopy for the determination of the mean size of Ne cluster jets created by supersonic expansion.

Ab initio study of He, Ne, Ar, Kr incorporation in zirconium carbide

Due to the potential utilization of ZrC in advanced nuclear reactors, it is important to understand the behavior of intrinsic defects and fission gas products. In this study, the energetics of intrinsic defects (i.e. monovacancy, self-interstitial, anti-site defect, Frenkel pair, Schottky defect and divacancy), the incorporation and migration of single noble gas atom (Ng = He, Ne, Ar and Kr), the atomic configuration of small noble gas clusters (Ngn) and Ngn-vacancies complexes have been systemically investigating by ab initio calculations. Carbon atoms escape from the lattice site easily and then form vacancy, interstitial or Frenkel pairs, while the formations of Zr vacancy and interstitial cost more energy and the presence of Zr vacancy would induce a new C vacancy along <100> direction. Due to the higher formation energy, anti-site defects are not expected to be the dominant defect in ZrC. The formation energy of Ng atom increases linearly with the atomic numbers (thus atomic radius) of Ng; meanwhile, the lattice distortion is also more pronounced. The lowest diffusion barrier of Ng atom is found on the path from one interstitial site to an adjacent one along <100> direction. The nearest distance and the corresponding binding energy between Ng-Ng pair gradually increase with the atomic radius, meaning that Ng atoms tend to aggregate in ZrC crystal. In addition, existence of the monovacany, divacancy and Schottky defect (especially Zr vacancy) considerably reduces the formation energies of Ngn clusters.

Construction of elementary reaction paths of pure and mixed Argon-Xenon clusters : a parallel tempering based study

The problem of studying structural transformation for going from one isomer to another through a transition state is one of considerable interest in chemistry. In this work, we would like to examine the efficiency of the replica exchange Monte Carlo strategy or parallel tempering to search potential energy surface describing the interaction between atoms in noble gas clusters. The systems chosen are both a pure noble gas cluster as well as those formed by two different noble gas entities. Location of minimal structures as well as transition state with the path connecting these three critical points has been carried out for different sizes. To understand the working principles of the parallel tempering method, distribution of structures found in different replicas has been analyzed and insights have been given as to how parallel tempering can be use effectively to handle this problem effectively.

Mixed cationic clusters of nitrogen and hydrogen.

The addition of small impurities, such as a single proton charge carrier, in noble gas clusters has recently been shown to have considerable effects on their geometries and stabilities. Here, we report on a mass spectrometric study of cationic clusters of N2 molecules and the effects that adding hydrogen, in the form of D2, has on the systems. Protonated nitrogen clusters formed by the breakup of D2 are shown to have similar behaviors as protonated rare gas clusters. For larger systems consisting of different mixtures of intact N2 and D2, different molecular species are found to be interchangeable sometimes with regard to magic numbers. This is especially true for the (N2)n(D2)mD+ systems with n + m = 17, which is particularly abundant for all measured combinations of n and m.

A swarm intelligence modeling approach reveals noble gas cluster configurations confined within carbon nanotubes.

Confinement of atoms and molecules brings forth fascinating properties to chemical systems that are otherwise not known in the bulk. Carbon nanotubes (CNTs) and fullerenes are excellent hosts for probing the confinement effects. Herein, we explore the potential energy surfaces of large noble gas clusters, Ngn (Ng = He, Ne and Ar; n = 10, 20, 30, 40, and 50), in the confines of CNTs of various lengths. Our implementation involves integrating the continuum approximation for CNTs with the well-known swarm intelligence technique, particle swarm optimization (PSO), followed by a deterministic local optimization. Global search techniques such as PSO have been increasingly utilized in recent times to track down minimum energy configurations on highly rugged potential energy surfaces. Aside from the position vectors of the noble gas atoms, we have considered the radius of the CNTs as a design variable. Such an approach enabled us to predict the optimal CNT radii for the encapsulation of each of the clusters. Confined cluster geometries ranging from linear, zig-zag, and double-helical to spiral configurations are obtained on encapsulation, in sharp contrast to their bare cluster geometries. On increasing the CNT length, our approach yielded quasi-linear geometries, suggesting that the length of the CNTs plays a crucial role in determining the stable cluster configurations on confinement.