Shallow implantation of "Size-Selected" Ag clusters into graphite

Utilizing ballistic nanoparticle impact to reconfigure the metal support interaction in Pt-TiN electrocatalysts

Tuning the metal support interaction (MSI) in heterogeneous catalysts is of utmost importance for various applications in different catalysis reactions. Pt-TiN systems are strong contenders for commercial catalysts, although the charge screening of Pt and non-involvement of N reduces their effective MSI and limits it to the Pt-Ti interface. Here, the bias driven landing of gas phase synthesized Pt nanoparticles (NPs) is used to change the nature of the MSI and enhance the charge transfer phenomenon. Bias driven landing of the Pt NPs translates their impact energies to the TiN surface, resulting in a weakening of the Ti-N bonds. This facilitates a new interaction between the Pt and N atoms, resulting in an electronic equilibration in the N-Pt-Ti triumvirate, nullifying the charge screening of Pt. This change in the nature of the MSI enables long range charge transfer throughout the catalyst surface and an increase in the electrocatalytic hydrogen evolution reaction (HER) activity of the Pt-TiN system.

Enhanced immobilization of gold nanoclusters on graphite

The immobilization of individual biological molecules by metal nanoparticles requires that the particles themselves be immobilized. We introduce a new technique for immobilization of gold clusters based on their binding to small tunnels in a graphite support, themselves created by the implantation of small clusters. These tunnels are shown to perform as more effective cluster immobilization sites than point defects on the surface of graphite. The method is tested with atomic force microscopy (AFM) (both contact and noncontact mode) scanning. Size-selected clusters with 923, 561, 309, and 147 atoms have been immobilized and imaged with high-resolution, noncontact AFM.

Size-dependent propagation of Au nanoclusters through few-layer graphene

We report the size-dependent propagation of gold nanoclusters through few-layer graphene (FLG). We employ aberration-corrected scanning transmission electron microscopy (STEM) to track the fate of Au55 and Au923 clusters that have been deposited, independently and isoenergetically, onto suspended FLG films using cluster beam deposition. We demonstrate that Au55 clusters penetrate through the FLG, whereas the monodisperse Au923 clusters reside at the surface. Our approach offers a route to the controlled incorporation of dopant nanoparticles and the generation of nanoscale defects in graphene.

How nanoscience translates into technology: the case of self-assembled monolayers, electron-beam writing, and carbon nanomembranes

One of the great quests in nanotechnology is to translate nanoprecision materials science into practical manufacturing processes. The paper by Angelova et al. in this issue of ACS Nano, which discusses the production of functional carbon-based membranes with a thickness of 0.5 to 3 nm, provides instructive insight into how researchers are pulling together complementary strands from a quarter century of nanoscience research to develop novel, hybrid processing schemes. In this Perspective, we reflect on the progress that is taking place in the two principal component technologies combined in this scheme, namely, (i) control of self-assembled monolayers, including their detailed atomic structures, and (ii) electron-induced manipulation and processing of molecular layers, as well as considering (iii) remaining challenges for thin membrane production in the future.

Laser ablation source for formation and deposition of size-selected metal clusters

This work describes construction of a source and optimisation of its parameters for production of cluster ion beams using material ablation by the second harmonic of a Nd:YAG laser (532 nm). The influence of different source parameters such as carrier gas pressure, laser power, delay time between gas, and laser pulses as well as nozzle configuration on the cluster formation are studied. For the current experiments the laser ablation cluster source was optimized for production of Con+ cluster ions. Clusters with n up to 150 atoms are registered by a time-of-flight mass spectrometer. Deposition of size-selected Co50+ clusters with kinetic energies in the interval of 250-4850 eV/cluster on highly ordered pyrolytic graphite is studied. At the highest impact energies the clusters are implanted. Craters and well-like structures can be seen by scanning tunneling microscopy at impact spots. A decrease in cluster kinetic energy leads to formation of bumplike structures which probably represent damaged graphite areas with incorporated Co atoms. Further decrease in the cluster impact energy to the level of 450-250 eV/cluster creates condition for so-called cluster pinning when the cluster constituents are intact but the energy transferred to the graphite is still enough to produce radiation defects to which the cluster is bound.

Decoration of surfaces with size-selected clusters and molecular manipulation at room temperature: precision and uncertainty in organizing atoms

The deposition onto surfaces of clusters of atoms, prepared and size-selected in the gas phase, is, like atomic or molecular manipulation with the scanning tunnelling microscope, an appealing (but parallel) route to the creation of nanoscale surface features. Both of these seemingly orthogonal approaches allow, in principle, a selected number of atoms to be organized, and both are strongly affected by the lateral thermal diffusion of the constituent atoms, molecules or clusters over the surface. In this sense, the room-temperature (as opposed to cryogenic-temperature) regime can be regarded as a hostile environment for organizing atoms. In this paper we review recent achievements in size-selected cluster deposition and molecular manipulation at room temperature and thus address the fundamental question: with what precision can we organize atoms at room temperature?

Deposition of size-selected metal clusters generated by magnetron sputtering and gas condensation: a progress review

This paper presents a topical review of the production and deposition of size-selected metal clusters generated by magnetron sputtering and gas condensation. Clusters with up to 75,000 atoms can be obtained by controlling the gas pressure in the sputtering source, prior to size selection with a novel (time-of-flight) mass filter. The clusters are deposited on the model graphite substrate to study the cluster-surface interaction. Two regimes for cluster deposition have been identified at elevated impact energies: (i) 'pinning' (ca. 10 eV per atom) and (ii) implantation (ca. 100 eV per atom). Of particular importance is the pinning regime, since this allows the fabrication of monodispersed cluster arrays, which are stable against diffusion at room temperature (and above). The deposition of size-selected metal clusters represents a novel method of preparing surface nanostructures, with potential applications including model catalyst studies and the immobilization of biological molecules.

Nanostructured surfaces from size-selected clusters

The deposition of ionized beams of size-selected atomic clusters onto well-defined substrates represents a new method of preparing nanostructured surfaces, with lateral feature sizes in the range 1-10 nm. 'Pinning' of the incident clusters prevents the diffusion of the clusters on the surface, and thus preserves the gas-phase cluster size, even at room temperature and above. At the same time, advances in diblock copolymer techniques allow the preparation of ordered two-dimensional arrays of clusters. Here we discuss the creation and applications of these nanostructured surfaces, ranging from the fabrication of semiconductor nanostructures to the immobilization of protein molecules.

Scaling relations for implantation of size-selected Au, Ag, and Si clusters into graphite

The deposition of size-selected clusters represents a new route to the fabrication of truly nanometer-scale surface architectures, e.g., nanopores. We report a systematic experimental study, coupled with molecular dynamics simulations, of the implantation depths of size-selected Au7, Ag7, and Si7 clusters in the model graphite substrate. For impact energies between 1.0 and 5.5 keV, we find that the implantation depth scales linearly with the momentum of the clusters for all three types of cluster. This "universal" behavior is consistent with a (viscous) retarding force proportional to the velocity of the cluster, akin to Stokes's law.

Minimizing boundary reflections in coupled-domain simulations

We propose a time-dependent boundary condition coupling an atomistic simulation system to linear surroundings such that reflection of elastic waves across the boundary is minimized. Interdomain interactions expressed in terms of memory kernel functions within linear-response theory are treated in a natural dynamical manner, albeit numerically. The approach is shown to give significantly reduced phonon reflections at the domain boundaries relative to existing coupling methods. In addition, we demonstrate that the framework is also effective in the context of static relaxation of displacement fields associated with embedded inhomogeneities.