- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
A study of surface diffusion of ternary (Cu-Ag-Zr) adatoms clusters for applications in thin film formation
摘要： This study presents the diffusion of heterogeneous ternary (Cu‐Ag‐Zr) adatoms clusters on Ag(111) using molecular dynamics techniques which could be important for the surface phenomena's and helpful for the ternary cluster's growth and formation of ternary alloy‐based thin films. The mechanism of nanoscale surface diffusion is investigated for 1Cu‐1Ag‐1Zr, 2Cu‐2Ag‐2Zr, 3Cu‐3Ag‐3Zr, and 4Cu‐4Ag‐4Zr clusters at temperatures 300, 500, and 700 K. The diffusion mechanism displays that the diffusion of trimer cluster exhibits hopping, sliding, and shearing at 300 K, whereas for hexamer, nonamer, and decamer, the diffusion rate is low; however, breathing, anchoring, and concentrated motion dominates. At 500 K, trimer and hexamer show the process of atomic exchange; however, the atomic exchange is not observed in the case of nonamer and decamer diffusion. The atomic exchange mechanism of Cu and Zr adatoms dominates at 700 K for all size clusters, except Ag adatoms, where Zr adatoms show a relatively more tendency. Separation and rejoining of the one and two adatoms (likely Zr adatom) are also witnessed at high temperature. The pop‐up of Ag adatoms also occurs in very short intervals over the remaining adatoms of clusters. Interestingly, during trimer diffusion, the adsorption of the Zr‐ or Cu‐adatom among the trimer cluster into the substitutional site is found. At 700 K, vacancy generation, filling of vacancies, and migration of vacancy, in the neighborhood of the adatoms cluster, also observed. Moreover, the rate of diffusion decreases with the size increase of the clusters and increases with the increase in temperature.
关键词： molecular dynamics,adatoms clusters,vacancy diffusion,surface diffusion
更新于2025-09-23 15:22:29
-
Do cluster properties affect the quenching rate?
摘要： The quenching rate is known to depend on galaxy stellar mass and environment, however, possible dependences on the hosting halo properties, such as mass, richness, and dynamical status, are still debated. The determination of these dependences is hampered by systematics, induced by noisy estimates of cluster mass or by the lack of control on galaxy stellar mass, which may mask existing trends or introduce fake trends. We studied a sample of local clusters (20 with 0.02 < z < 0.1 and log(M200/M(cid:3)) (cid:2) 14), selected independent of the galaxy properties under study, having homogeneous optical photometry and X-ray estimated properties. Using those top quality measurements of cluster mass, hence of cluster scale, richness, iron abundance, and cooling time/presence of a cool-core, we study the simultaneous dependence of quenching on these cluster properties on galaxy stellar mass M and normalised cluster-centric distance r/r200. We found that the quenching rate can be completely described by two variables only, galaxy stellar mass and normalised cluster-centric distance, and is independent of halo properties (mass, richness, iron abundance, and central cooling time/presence of a cool-core). These halo properties change, in most cases, by less than 3% the probability that a galaxy is quenched, once the mass-size (M200 – r200) scaling relation is accounted for through cluster-centric distance normalisation.
关键词： galaxies: star formation,galaxies: evolution,galaxies: clusters: general
更新于2025-09-23 15:22:29
-
Charge-state analysis of small barium-oxide clusters by X-ray absorption spectroscopy
摘要： Small barium-oxide clusters BamOn+ are studied by mass spectrometry and X-ray absorption spectroscopy to discuss stability of the clusters and oxidation state of constituent atoms. It is found that clusters with bulk composition, n = m, are stable, which can accommodate one or two excess oxygen atoms additionally as manifested by n = m + 1 and m + 2 species in the mass spectrum. XAS spectra of Ba2O2+ and Ba2O3+ reveal that the oxidation state of barium atoms stays at +2 (the bulk BaO value) even after binding excess oxygen, whereas spectral features originating from oxygen exhibit composition dependence. The present finding suggests that stoichiometric small barium-oxide clusters bind less-negatively-charged oxygen atoms without change in the charge state of barium.
关键词： X-ray absorption spectroscopy,charge state,barium-oxide clusters,oxidation number
更新于2025-09-23 15:22:29
-
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)
摘要： We study the role of the environment on galaxy evolution using a sample of 868 galaxies in the Virgo cluster and in its surrounding regions that are selected from the GALEX Ultraviolet Virgo Cluster Survey (GUViCS) with the purpose of understanding the origin of the red sequence in dense environments. The sample spans a wide range in morphological types (from dwarf ellipticals to Im and BCD) and stellar masses (107 (cid:2) Mstar (cid:2) 1011.5 M(cid:3)). We collected multifrequency data covering the whole electromagnetic spectrum for most of the galaxies, including UV, optical, mid- and far-infrared imaging data, as well as optical and HI spectroscopic data. We ?rst identify the di?erent dynamical substructures that compose the Virgo cluster, and we calculate the local density of galaxies using di?erent methods. We then study the distribution of galaxies belonging to the red sequence, the green valley, and the blue cloud within the di?erent cluster substructures or as a function of galaxy density. Our analysis indicates that all the most massive galaxies (Mstar (cid:3) 1011 M(cid:3)) are slow rotators and are the dominant galaxies of the di?erent cluster substructures, which are generally associated with a di?use X-ray emission. They are probably the result of major merging events that occurred at early epochs, as also indicated by their very old stellar populations. Slow rotators of lower stellar mass (108.5 (cid:2) Mstar (cid:2) 1011 M(cid:3)) are also preferentially located within the di?erent high-density substructures of the cluster. Their position in the velocity space indicates that they are virialised within the cluster; thus, they are Virgo members since its formation. They have been shaped by gravitational perturbations occurring within the infalling groups that later form the cluster (pre-processing). On the contrary, low-mass star-forming systems are extremely rare in the inner regions of the Virgo cluster A, where the density of the intergalactic medium is at its maximum. Our ram pressure stripping models consistently indicate that these star-forming systems can be rapidly deprived of their interstellar medium during their interaction with the intergalactic medium. The lack of gas quenches their star-formation activity transforming them into quiescent dwarf ellipticals. This mild transformation does not perturb the kinematic properties of these galaxies, which still have rotation curves typical of star-forming systems.
关键词： galaxies: interactions,galaxies: star formation,galaxies: clusters: general,galaxies: clusters: individual: Virgo,galaxies: ISM,galaxies: evolution
更新于2025-09-23 15:21:21
-
Weak lensing magnification of SpARCS galaxy clusters
摘要： Context. Measuring and calibrating relations between cluster observables is critical for resource-limited studies. The mass–richness relation of clusters offers an observationally inexpensive way of estimating masses. Its calibration is essential for cluster and cosmological studies, especially for high-redshift clusters. Weak gravitational lensing magnification is a promising and complementary method to shear studies, that can be applied at higher redshifts. Aims. We aim to employ the weak lensing magnification method to calibrate the mass–richness relation up to a redshift of 1.4. We used the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) galaxy cluster candidates (0.2 < z < 1.4) and optical data from the Canada France Hawaii Telescope (CFHT) to test whether magnification can be effectively used to constrain the mass of high-redshift clusters. Methods. Lyman-break galaxies (LBGs) selected using the u-band dropout technique and their colours were used as a background sample of sources. LBG positions were cross-correlated with the centres of the sample of SpARCS clusters to estimate the magnification signal, which was optimally-weighted using an externally-calibrated LBG luminosity function. The signal was measured for cluster sub-samples, binned in both redshift and richness. Results. We measured the cross-correlation between the positions of galaxy cluster candidates and LBGs and detected a weak lensing magnification signal for all bins at a detection significance of 2.6–5.5σ. In particular, the significance of the measurement for clusters with z > 1.0 is 4.1σ; for the entire cluster sample we obtained an average M200 of 1.28 +0.23 ?0.21 × 1014 M⊙. Conclusions. Our measurements demonstrated the feasibility of using weak lensing magnification as a viable tool for determining the average halo masses for samples of high redshift galaxy clusters. The results also established the success of using galaxy over-densities to select massive clusters at z > 1. Additional studies are necessary for further modelling of the various systematic effects we discussed.
关键词： galaxies: clusters: general,galaxies: clusters: individual: SpARCS,gravitational lensing: weak
更新于2025-09-23 15:21:21
-
A DNA-Encapsulated Silver Cluster and the Roles of Its Nucleobase Ligands
摘要： Silver clusters consisting of ~10 atoms are readily bound by and encapsulated within DNA strands to yield strong absorption and emission. The coordination environments, however, are poorly understood, so cluster adducts can only be empirically tuned. This work describes the C4AC4TC3G strand that templates a particular cluster adduct. Its sequence has three types of nucleobases with distinct roles – tracts of cytosines that collectively coordinate the cluster, thymine acting as a junction in the overall strand, and the adenine/guanine pair that exclusively forms the cluster. In relation to the native oligonucleotide, the DNA-silver cluster complex diffuses faster and is more compact, thus suggesting that the strands folds because of the cluster. The Ag10 6+ adduct emits with λex/λem = 490/540 nm, a 19% quantum yield, and a biexponential 1.1/2.1 ns lifetime. The electronic environment for the cluster is controlled by the heteroatoms in the adenine and guanine. Most significantly, the N7 and the N2 in the guanine change the fluorescence quantum yield by 60-fold and shift the fluorescence lifetime by ~3.8 ns. Thus, our studies discern distinct spectroscopic and structural roles for the nucleobase ligands in C4AC4TC3G, and these finding may help develop new DNA templates for other silver cluster adducts.
关键词： Nucleobase ligands,DNA,Silver clusters,Lifetime,Fluorescence,Quantum yield
更新于2025-09-23 15:21:21
-
The <i>Gaia</i> DR2 view of the Gamma Velorum cluster: resolving the 6D structure
摘要： Gaia-ESO Survey observations of the young Gamma Velorum cluster led to the discovery of two kinematically distinct populations, Gamma Vel A and B, respectively, with population B extended over several square degrees in the Vela OB2 association. Using the Gaia DR2 data for a sample of high-probability cluster members, we find that the two populations differ not only kinematically, but are also located at different distances along the line of sight, with the main cluster Gamma Vel A being closer. A combined fit of the two populations yields (cid:36)A = 2.895 0.011 mas 11.5 pc and 383.4+2.5+15.3 and 0.091 14.2 pc, respectively, showing that Gamma Vel A is closer than Gamma Vel B by 38 pc. We find that the two clusters are nearly coeval, and that Gamma Vel B is expanding. We suggest that Gamma Vel A and B are two independent clusters located along the same line of sight.
关键词： open clusters and associations: individual: Gamma Velorum,stars: late-type,stars: pre-main sequence,stars: distances,stars: kinematics and dynamics
更新于2025-09-23 15:21:21
-
Electron acceleration up to MeV level under nonlinear interaction of subterawatt femtosecond laser chirped pulses with Kr clusters
摘要： The acceleration of electrons to MeV energies from a Kr cluster jet irradiated by a relativistic (6 × 1018 W cm?2) femtosecond laser pulse is studied. For the first time, the action of transform-limited laser pulse effects on the generation of hot electrons with an effective temperature (Thot) of around 150 keV is experimentally demonstrated. The particles were accelerated in the plasma channel formed under self-focusing of the laser beam. Introducing a linear positive chirp together with pulse elongation from 50–~120 fs results in substantially enhanced hot electrons flux with a growth of Thot up to 300 keV and a maximal energy of over 2 MeV. The observed effect may be related to the strongly nonlinear propagation of the pulse through plasma, accompanied by more favorable conditions for efficient particles energy gain and pulse nonlinear compression.
关键词： femtosecond laser,nonlinear phenomena,krypton,clusters,laser-driven electron acceleration
更新于2025-09-23 15:21:01
-
An extended chiral surface coordination network based on Ag <sub/>7</sub> -clusters
摘要： We present an extended metal-coordinated structure obtained by deposition of trimesic acid (TMA) onto the Ag(111) surface under ultra-high vacuum conditions followed by annealing to 510 K. Scanning tunneling microscopy and density functional theory calculations reveal the structure to consist of metal clusters containing seven Ag atoms each, coordinated by six dehydrogenated TMA molecules. The molecules are asymmetrically arranged, resulting in a chiral structure. The calculations confirm that this structure has a lower free energy under the experimental conditions than the hydrogen-bonded structures observed after annealing at lower temperatures. We show that the formation of such large metal clusters is possible due to the low adatom formation energy on silver and the relatively strong Ag-O bond in combination with a good lattice match between the structure and the Ag surface.
关键词： Ag7-clusters,TMA molecules,metal-coordinated structure,density functional theory,chiral structure
更新于2025-09-23 15:21:01
-
Slow photoelectron velocity-map imaging of cold C7? and C9?
摘要： High-resolution anion photoelectron spectra of cryogenically cooled C7? and C9? clusters obtained using slow photoelectron velocity-map imaging are presented, providing insight into the vibronic structure of neutral C7 and C9. These spectra yield accurate measurements of vibrational frequencies for the neutral clusters as well as electron affinities of 3.3517(4) and 3.6766(14) eV for C7 and C9, respectively. In the C7? spectrum, transitions involving the previously unreported v1 and v2 symmetric stretching modes, as well as the v9, v10, and v11 asymmetric bending modes, are assigned. Spin–orbit splitting is observed for several transitions in this spectrum, giving an energy difference of 28(6) cm?1 between the 2Π1/2g and 2Π3/2g spin–orbit levels of the C7? anion. In the spectrum of C9?, transitions involving the previously unreported symmetric stretch v1 and the asymmetric bend v11 are observed. In both spectra, several features are assigned to Franck-Condon forbidden transitions involving the doubly degenerate v10 and v11 modes of C7 and the v13 and v14 modes of C9. The appearance of these transitions is attributed to Herzberg-Teller coupling between the electronic states of the neutral clusters. Additional FC-forbidden transitions to states previously observed in gas-phase infrared experiments are observed and attributed to vibronic coupling between the electronic states of the anion, resulting in non-totally symmetric character in the anion’s full vibrational ground state. Finally, consideration of the energy dependence of detachment cross sections and Dyson orbital analyses reveal that addition of more carbon atoms to the linear chain results in photodetachment from delocalized molecular orbitals with increasing nodal structure, leading to threshold photodetachment cross sections that differ considerably from simple symmetry considerations.
关键词： Herzberg-Teller coupling,Franck-Condon forbidden transitions,anion photoelectron spectroscopy,vibronic structure,carbon clusters,slow photoelectron velocity-map imaging
更新于2025-09-23 15:21:01