Clusters have the potential to serve as building blocks of materials, enabling the tailoring of materials with novel electronic or magnetic properties. Historically, there has been a disconnect between magic clusters found in the gas phase and the synthetic assembly of cluster materials. We approach this challenge through a proposed protocol that combines gas-phase investigations to examine feasible units, theoretical investigations of energetic compositional diagrams and geometrical shapes to identify potential motifs, and synthetic chemical approaches to identify and characterize cluster assemblies in the solid state. Through this approach, we established As7(3-) as a potential stable species via gas-phase molecular beam experiments consistent with its known existence in molecular crystals with As to K ratios of 7:3. Our protocol also suggests another variant of this material. We report the synthesis of a cluster compound, As7K1.5(crypt222-K)1.5, composed of a lattice of As7 clusters stabilized by charge donation from cryptated K atoms and bound by sharing K atoms. The bond dimensions of this supercluster assembled material deduced by X-ray analysis are found to be in excellent agreement with the theoretical calculations. The new compound has a significantly larger band gap than the hitherto known solid. Thus, our approach allows the tuning of the electronic properties of solid cluster assemblies.

Detailed in the present investigation are results pertaining to the photoelectron spectroscopy of negatively charged atomic ions and their isoelectronic molecular counterparts. Experiments utilizing the photoelectron imaging technique are performed on the negative ions of the group 10 noble metal block (i.e. Ni − , Pd − , and Pt − ) of the periodic table at a photon energy of 2.33 eV (532 nm). The accessible electronic transitions, term energies, and orbital angular momentum components of the bound electronic states in the atom are then compared with photoelectron images collected for isoelectronic early transition metal heterogeneous diatomic molecules, M-X − (M ¼ Ti; Zr; W; X ¼ O or C). A superposition principle connecting the spectroscopy between the atomic and molecular species is observed, wherein the electronic structure of the diatomic is observed to mimic that present in the isoelectronic atom. The molecular ions studied in this work, TiO − , ZrO − , and WC − can then be interpreted as possessing superatomic electronic structures reminiscent of the isoelectronic elements appearing on the periodic table, thereby quantifying the superatom concept.cluster anions | photoelectron imaging | superatoms | angular distributions | transition metal A lchemy, the medieval practice that endeavored to transform mundane elements into the rarer, exotic variety has found many analogies in the modern physical sciences ranging from gas-phase clusters (1) to surface science (2). Particularly intriguing was a report (2) demonstrating that a tungsten carbide surface displayed similar chemical reactivity as the noble metal platinum, an element well established in its propensity for catalytically initiating a vast array of chemical transformations. By contrast, elemental tungsten alone did not exhibit comparable reactivity patterns. In order to provide insight to these findings, we have undertaken a comparative spectroscopic investigation between anionic group 10 elements ðNi − ; Pd − ; Pt − Þ and their complementary isoelectronic early transition metal molecular counterparts M-X − (M ¼ Ti; Zr; W and X ¼ O or C). We observe photoelectron signatures and angular distributions in the acquired images that exhibit very similar aspects between the respective atom and molecule. This observation suggests a correlation between the spectroscopy of an element and the isoelectronic molecular species. As a representative example, consider the formation of the diatomic molecule TiO from the united atom perceptive of molecular orbital theory (3). If only the 6 valence electrons of O ( ½He 2s 2 2p 4 ) are to be considered, subsequent combination with the 4 valence electrons of Ti ( ½Ar 3d 2 4s 2 ) creates a molecular entity with an isoelectronic configuration commensurate with the 10 valence electrons of elemental Ni ( ½Ar 3d 8 4s 2 ). In other words, the early transition metal Ti is positioned on the periodic table 6 elements removed from Ni and the intervening periodic span is traversed by the valency of atomic O. The diatomic molecule, TiO,...

In this Letter, we report on the efficient generation of electrons from metals using multiphoton photoemission by use of nanostructured plasmonic surfaces to trap, localize, and enhance optical fields. The plasmonic surface increases absorption over normal metals by more than an order of magnitude, and due to the localization of fields, this results in over 6 orders of magnitude increase in effective nonlinear quantum yield. We demonstrate that the achieved quantum yield is high enough for use in rf photoinjectors operating as electron sources for MHz repetition rate x-ray free electron lasers.

We present results of a combined two-photon photoemission and scanning electron microscopy investigation to determine the electromagnetic enhancement factors of silver-coated spherical nanoparticles deposited on an atomically flat mica substrate. Femtosecond laser excitation of the nanoparticles produces intense photoemission, attributed to near-resonant excitation of localized surface plasmons. Enhancement factors are determined by comparing the respective two-photon photoemission yields measured for single nanoparticles and the surrounding flat surface. For p-polarized, 400 nm (∼3.1 eV) femtosecond radiation, a distribution of enhancement factors is found with a large percentage (67%) of the nanoparticles falling within a median range. A correlated scanning electron microscopy analysis demonstrated that the nanoparticles typifying the median of the distribution are characterized by spherical shapes and relatively smooth silver film morphologies. In contrast, the largest enhancement factors were produced by a small percentage (7%) of particles that displayed silver coating defects that altered the overall particle structure. Comparisons are made between the experimentally measured enhancement factors and previously reported calculations of the localized near-field enhancement for isolated silver nanoparticles.