AuCu bimetallic nanocluster-modified titania nanotubes for photoelectrochemical water splitting: composition-dependent atomic arrangement and activity.

The photoelectrochemical (PEC) water splitting reaction of bimetallic AuCu ( = 1, 0.75, 0.5, 0.

Pathways of cluster growth: infra-red multi-photon dissociation spectroscopy of a series of Re-Si clusters, [ReSi], = 3-9.

Infra-red multiple-photon dissociation spectroscopy on Xe-tagged Re/Si clusters, [ReSi], = 3-9, reveals intense absorption features around 400 cm, along with, in some cases, additional bands in the 250-350 cm window. A survey of the potential energy surface using density functional theory in conjunction with particle swarm optimisation indicates a growth pattern based on a growing network of Si atoms wrapped around the Re centre: the Si units can be viewed as fragments of a putative 16-vertex Frank-Kasper polyhedron. The structural evolution for the [ReSi] series differs significantly from the iso-electronic Mn series studied previously, where the metal ion is typically bound externally to the surface of a growing 3-dimensional Si cluster, the differences reflecting the greater accessibility of 5d 3d electron density.

Direct probing of low-energy intra d-band transitions in gas-phase cobalt clusters.

The interplay between constituent localized and itinerant electrons of metal clusters defines their physical and chemical properties. In turn, the electronic and geometrical structures are strongly entwined and exhibit strong size-dependent variations. Current understanding of low-energy excited states of metal clusters relies on stand-alone theoretical investigations and few comparisons with measured properties, since direct identification of low-lying states is lacking hitherto.

Fragmentation channels of non-fullerene cationic carbon clusters.

The unimolecular fragmentation channels of highly excited small cationic carbon clusters have been measured with a time-of-flight mass spectrometer after photofragmentation. The dominant channel is loss of the neutral trimer, for all C = 10-27 clusters except for = 11, 12 which decay by monomer emission, and C which shows competing loss of C and C. The results permit to quantify the role of the rotational entropy in the competition between monomer and trimer decays with the help of energies calculated with density functional theory.

Pentagon, Hexagon, or Bridge? Identifying the Location of a Single Vanadium Cation on Buckminsterfullerene Surface.

Buckminsterfullerene C has received extensive research interest since its discovery. In addition to its interesting intrinsic properties of exceptional stability and electron-accepting ability, the broad chemical tunability by decoration or substitution on the C-fullerene surface makes it a fascinating molecule. However, to date, there is uncertainty about the binding location of such decorations on the C surface, even for a single adsorbed metal atom.

Small chromium-doped silicon clusters CrSi: structures, IR spectra, charge effect, magnetism and chirality.

A series of small chromium-doped silicon clusters with = 3-10 in the cationic, neutral and anionic charge states were investigated using quantum chemical methods. The CrSi cations with = 6-10 were produced in the gas phase and characterized by far-IR multiple photon dissociation (IR-MPD) spectroscopy. Good agreement between experimental spectra in the 200-600 cm frequency range and those determined for the lowest-energy isomers by density functional theory calculations (B3P86/6-311+G(d)) provide a strong support for the geometrical assignments.

Gas phase deposition of well-defined bimetallic gold-silver clusters for photocatalytic applications.

Cluster beam deposition is employed for fabricating well-defined bimetallic plasmonic photocatalysts to enhance their activity while facilitating a more fundamental understanding of their properties. AuAg clusters with compositions ( = 0, 0.1, 0.

Influence of oxidation on the magnetism of small Co oxide clusters probed by Stern-Gerlach deflection.

We report on the magnetic properties of small neutral suboxide CoO ( = 5-18 and = 0-10, ≤ ) clusters produced by laser vaporisation and gas aggregation. Their magnetism is probed experimentally by means of Stern-Gerlach magnetic deflection. The results imply that the cobalt atoms couple ferromagnetically not only in pure Co clusters, as known from previous investigations, but also in their oxidized counterparts.

Radiative cooling in silver and palladium doped gold clusters.

The emission of photons from a thermally populated electronic excited state, the process of recurrent fluorescence, has been recognized as a prominent cooling channel in hot molecules and small metal clusters. For the latter case, however, only monometallic species have been investigated to date. An active radiative cooling channel has a stabilizing effect and can favor the size and composition specific production of selected clusters.

Spin excitations of individual magnetic dopants in an ionic thin film.

Individual magnetic transition metal dopants in a solid host usually exhibit relatively small spin excitation energies of a few meV. Using scanning tunneling microscopy and inelastic electron tunneling spectroscopy (IETS) techniques, we have observed a high spin excitation energy around 36 meV for an individual Co substitutional dopant in ultrathin NaCl films. In contrast, the Cr dopant in the NaCl film shows much lower spin excitation energy around 2.

Evolution of Vibrational Spectra in the Manganese-Silicon Clusters MnSi, = 10, 12, and 13, and Cationic [MnSi].

A comparison of DFT-computed and measured infrared spectra reveals the ground state structures of a series of gas-phase silicon clusters containing a common Mn unit. MnSi and [MnSi] are both axially symmetric, allowing for a clean separation of the vibrational modes into parallel (a) and perpendicular (e) components. Information about the Mn-Mn and Mn-Si bonding can be extracted by tracing the evolution of these modes as the cluster increases in size.

The wavelength-dependent non-linear absorption and refraction of Au and Au monolayer-protected clusters.

In the past decade, the structural and electronic properties of monolayer-protected metal clusters, which can be produced size-selected in macroscopic amounts, have received a lot of attention. Their great potential for optical applications has been identified. In the high intensity regime, monolayer-protected metal clusters show pronounced nonlinear absorption and refraction.

Antimicrobial and Aging Properties of Ag-, Ag/Cu-, and Ag Cluster-Doped Amorphous Carbon Coatings Produced by Magnetron Sputtering for Space Applications.

Inside a spacecraft, the temperature and humidity, suitable for the human crew onboard, also creates an ideal breeding environment for the proliferation of bacteria and fungi; this can present a hazard to human health and create issues for the safe running of equipment. To address this issue, wear-resistant antimicrobial thin films prepared by magnetron sputtering were developed, with the aim to coat key internal components within spacecrafts. Silver and copper are among the most studied active bactericidal materials, thus this work investigated the antibacterial properties of amorphous carbon coatings, doped with either silver, silver and copper, or with silver clusters.

Impact of the gas dynamics on the cluster flux in a magnetron cluster-source: Influence of the chamber shape and gas-inlet position.

Although producing clusters by physical methods offers many benefits, low deposition rates have prevented cluster-beam deposition techniques from being adopted more widely. The influence of the gas aerodynamics inside the condensation chamber of a magnetron cluster-source on the cluster throughput is reported, leading to an improved understanding of the influence of gas aerodynamics on cluster transport. In the first part of this paper, the influence of the carrier gas's inlet position on the cluster flux is studied.

Enhanced Methanol Electro-Oxidation Activity of Nanoclustered Gold.

Size-selected 3 nm gas-phase Au clusters dispersed by cluster beam deposition (CBD) on a conducting fluorine-doped tin oxide template show strong enhancement in mass activity for the methanol electro-oxidation (MEO) reaction compared to previously reported nanostructured gold electrodes. Density functional theory-based modeling on the corresponding Au clusters guided by experiments attributes this high MEO activity to the high density of exposed under-coordinated Au atoms at their faceted surface. In the description of the activity trends, vertices and edges are the most active sites due to their favorable CO and OH adsorption energies.

Stability of cationic silver doped gold clusters and the subshell-closed electronic configuration of AgAu.

Silver doping is a valuable route to modulate the structural, electronic, and optical properties of gold clusters. We combine photofragmentation experiments with density functional theory calculations to investigate the relative stability of cationic Ag doped Au clusters, AgAu (N ≤ 40). The mass spectra of the clusters after photofragmentation reveal marked drops in the intensity of AgAu , AgAu , and AgAu , indicating a higher relative stability of these sizes.

Photofragmentation Patterns of Cobalt Oxide Cations CoO ( = 5-9, = 4-13): From Oxygen-Deficient to Oxygen-Rich Species.

Cobalt oxide clusters, CoO (5 ≤ ≤ 9 and 4 ≤ ≤ 13), are produced by laser vaporization and studied by time-of-flight mass spectrometry. Specific stoichiometries are mass separated and photofragmented using 355 nm laser light. The preferred fragmentation channels of = -1, = -2, and ≥ species are investigated.

A platinum-nickel bimetallic nanocluster ensemble-on-polyaniline nanofilm for enhanced electrocatalytic oxidation of dopamine.

We report a new approach to design flexible functional material platforms based on electropolymerized polyaniline (PANI) polymer nanofilms modified with bimetallic nanoclusters (NCs) for efficient electro-oxidation of small organic molecules. Composition defined ligand free PtNi NCs were synthesized in the gas phase using the Cluster Beam Deposition (CBD) technology and characterized using RToF, HAADF-STEM, XAFS and XPS. NCs were then directly deposited on PANI coated templates to construct electrodes.

Unraveling the atomic structure, ripening behavior, and electronic structure of supported Au clusters.

The free-standing Au cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The "magic" Au has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters.

Altering CO binding on gold cluster cations by Pd-doping.

The introduction of dopant atoms into metal nanoparticles is an effective way to control the interaction with adsorbate molecules and is important in many catalytic processes. In this work, experimental and theoretical evidence of the influence of Pd doping on the bonding between small cationic AuN+ clusters and CO is presented. The CO adsorption is studied by combining low-pressure collision cell reactivity and infrared multiple photon dissociation spectroscopy experiments with density functional theory calculations.

Tuning the Reactivity of Small Metal Clusters by Heteroatom Doping.

The reactivity of small metallic clusters, nanoparticles composed of a countable number of atoms (typically up to ∼100 atoms), has attracted much attention due to the fascinating properties these objects possess toward a variety of molecules. Cluster reactivity often is significantly different from the homologous bulk, with gold as prototypical example. Bulk gold is the noblest of all metals, whereas small gold clusters react with carbon monoxide, molecular oxygen, and hydrocarbons, among others.

Stability of small cationic platinum clusters.

The relative stability of small cationic platinum clusters is investigated by photofragmentation experiments. Mass spectra show a smooth intensity distribution except for a local intensity minimum at Pt5+, revealing enhanced stability of the platinum tetramer Pt4+. The possibility that radiative cooling competes with statistical fragmentation after photoexcitation is examined and it is shown that clusters in the N = 3-8 size range do not radiate on the time scale of the experiment.

Shaping the Optical Properties of Silver Clusters Inside Zeolite A via Guest-Host-Guest Interactions.

The appealing luminescent properties of Ag-zeolites have been shown to be dependent on the local environment of the confined silver clusters. Herein, we shed light on the properties of Ag clusters inside hydrated Linde-type A (LTA) zeolites and relate them to the nature of the host framework when expanded and compressed by the incorporation of Li cations and the Ag loading. Within this scenario, we measure a strong emission color shift in these materials, which we directly correlate with the fine structure details derived by optical luminescence-detected X-ray absorption in combination with deep UV-Raman spectroscopy and X-ray diffraction.

Origin of the bright photoluminescence of few-atom silver clusters confined in LTA zeolites.

Silver (Ag) clusters confined in matrices possess remarkable luminescence properties, but little is known about their structural and electronic properties. We characterized the bright green luminescence of Ag clusters confined in partially exchanged Ag-Linde Type A (LTA) zeolites by means of a combination of x-ray excited optical luminescence-extended x-ray absorption fine structure, time-dependent-density functional theory calculations, and time-resolved spectroscopy. A mixture of tetrahedral Ag(HO) ( = 2 and = 4) clusters occupies the center of a fraction of the sodalite cages.

Atomic scale reversible opto-structural switching of few atom luminescent silver clusters confined in LTA zeolites.

Luminescent silver clusters (AgCLs) stabilized inside partially Ag exchanged Na LTA zeolites show a remarkable reversible on-off switching of their green-yellowish luminescence that is easily tuned by a hydration and dehydration cycle, making them very promising materials for sensing applications. We have used a unique combination of photoluminescence (PL), UV-visible-NIR Diffuse Reflectance (DRS), X-ray absorption fine structure (XAFS), Fourier Transform-Infrared (FTIR) and electron spin resonance (ESR) spectroscopies to unravel the atomic-scale structural changes responsible for the reversible optical behavior of the confined AgCLs in LTA zeolites. Water coordinated, diamagnetic, tetrahedral AgCLs [Ag4(H2O)4]2+ with Ag atoms positioned along the axis of the sodalite six-membered rings are at the origin of the broad and intense green-yellowish luminescence in the hydrated sample.