Intrinsic Visible Plasmonic Properties of Colloidal PtIn Intermetallic Nanoparticles.

Materials that intrinsically exhibit localized surface plasmon resonance (LSPR) in the visible region have been predominantly researched on nanoparticles (NPs) composed of coinage metals, namely Au, Ag, and Cu. Here, as a coinage metal-free intermetallic NPs, colloidal PtIn NPs with a C1 (CaF -type) crystal structure are synthesized by the liquid phase method, which evidently exhibit LSPR at wavelengths similar to face-centered cubic (fcc)-Au NPs. Computational simulations pointed out differences in the electronic structure and photo-excited electron dynamics between C1-PtIn and fcc-Au NPs; reduces interband transition and stronger screening with smaller number of bound d-electrons compare with fcc-Au are unique origins of the visible plasmonic nature of C1-PtIn NPs.

Unique Structural Relaxations and Molecular Conformations of Porphyra-334 at the Excited State.

Quantum chemistry based simulations were used to examine the excited state of porphyra-334, one of the fundamental mycosporine-like amino acids present in a wide variety of aqueous organisms. Our calculations reveal three characteristic aspects of porphyra-334 related to either its ground or excited state. Specifically, (i) the ground state (S) structure consists of a planar geometry in which three units can be identified, the central cyclohexene ring, the glycine branch, and the threonine branch, reflecting the π conjugation of the system; (ii) the first singlet excited state (S) shows a large oscillator strength and a typical ππ* excitation character; and (iii) upon relaxation at S, the originally ground state planar structure undergoes a relaxation to a nonplanar one, S, especially at the carbon-nitrogen (CN) groups linking the cyclohexene ring to the glycine or threonine arm.

Realization of red shift of absorption spectra using optical near-field effect.

In many applications such as CO reduction and water splitting, high-energy photons in the ultraviolet region are required to complete the chemical reactions. However, to realize sustainable development, the photon energies utilized must be lower than the absorption edge of the materials including the metal complex for CO reduction, the electrodes for water splitting, because of the huge amount of lower energy than the visible region received from the sun. In the previous works, we had demonstrated that optical near-fields (ONFs) could realize chemical reactions, by utilizing photon energies much lower than the absorption edge because of the spatial non-uniformity of the electric field.

Hydrogen storage mechanism and diffusion in metal-organic frameworks.

Diffusion and storage of hydrogen molecules in metal-organic frameworks are crucial for the development of next-generation energy storage devices. By resorting to the first principles modeling, we compute the diffusion coefficient of molecular hydrogen in these systems in a range of temperatures where MOF-based devices are expected to operate. The explicit inclusion of the electronic structure shows that diffusivities are one order of magnitude smaller than those reported by classical simulations, evidencing the insufficiency of the empirical force fields used so far.

A detailed insight into the catalytic reduction of NO operated by Cr-Cu nanostructures embedded in a CeO surface.

Replacing rare and expensive elements, such as Pt, Pd, and Rh, commonly used in catalytic devices with more abundant and less expensive ones is mandatory to realize efficient, sustainable and economically appealing three-way catalysts. In this context, the surface of a Cr-Cu/CeO2 system represents a versatile catalyst for the conversion of toxic NO into harmless N2. Yet, a clear picture of the underlying mechanism is still missing.

Angstrom-scale flatness using selective nanoscale etching.

The realization of flat surfaces on the angstrom scale is required in advanced devices to avoid loss due to carrier (electron and/or photon) scattering. In this work, we have developed a new surface flattening method that involves near-field etching, where optical near-fields (ONFs) act to dissociate the molecules. ONFs selectively generated at the apex of protrusions on the surface selectively etch the protrusions.

Evolution of Excited-State Dynamics in Periodic Au, Au, Au, and Au Nanoclusters.

Understanding the correlation between the atomic structure and optical properties of gold nanoclusters is essential for exploration of their functionalities and applications involving light harvesting and electron transfer. We report the femto-nanosecond excited state dynamics of a periodic series of face-centered cubic (FCC) gold nanoclusters (including Au, Au, Au, and Au), which exhibit a set of unique features compared with other similar sized clusters. Molecular-like ultrafast S → S internal conversions (i.

How seaweeds release the excess energy from sunlight to surrounding sea water.

We report an atomistic insight into the mechanism regulating the energy released by a porphyra-334 molecule, the ubiquitous photosensitive component of marine algae, in a liquid water environment upon an electron excitation. To quantify this rapidly occurring process, we resort to the Fourier analysis of the mass-weighted auto-correlation function, providing evidence for a remarkable dynamic change in the number of hydrogen bonds among water molecules and between the porphyra-334 and its surrounding hydrating water. Hydrogen bonds between the porphyra-334 and close by water molecules can act directly and rather easily to promote an efficient transfer of the excess kinetic energies of the porphyra-334 to the surrounding solvating water molecules via an activation of the collective modes identified as hydrogen-bond stretching modes in liquid water which eventually results in a disruption of the hydrogen bond network.

Development of theoretical approach for describing electronic properties of hetero-interface systems under applied bias voltage.

We have developed a theoretical approach for describing the electronic properties of hetero-interface systems under an applied electrode bias. The finite-temperature density functional theory is employed for controlling the chemical potential in their interfacial region, and thereby the electronic charge of the system is obtained. The electric field generated by the electronic charging is described as a saw-tooth-like electrostatic potential.

Atomically modified thin interface in metal-dielectric hetero-integrated systems: control of electronic properties.

We have performed first-principles studies of the electronic properties of Cu-diamond hetero-integrated systems, particularly placing emphasis on elucidating the effects of surface modification of diamond with H or O. It is found that the electronic properties crucially depend on the chemical compositions of the modified atomically thin interface region. The local density of states (LDOS) of the H-terminated diamond moiety near the Cu surface exhibits a clearly different distribution from that near the vacuum region, whereas the LDOS of the O-terminated diamond is almost independent of the Cu deposition.

An atomic-level insight into the basic mechanism responsible for the enhancement of the catalytic oxidation of carbon monoxide on a Cu/CeO surface.

The reaction mechanisms of CO molecules interacting with a Cu/CeO surface and related morphological modifications occurring upon removal of O atoms to generate CO are investigated by first-principles dynamical simulations complemented by a free-energy sampling technique. We show that the reactivity of oxygen atoms located in the first layer in the vicinity of the Cu site is remarkably high because of a reduction of the O coordination number. Moreover, we evidence that the doped Cu atoms are responsible for an enhancement of the exposure of other surrounding O atoms, even below the first surface layer, which can then easily react with CO and are gradually removed from the system in the oxidation process.

Tuning the electronic structure of thiolate-protected 25-atom clusters by co-substitution with metals having different preferential sites.

Trimetallic AuAgPd and tetrametallic AuAgCuPd clusters were synthesized by the subsequential metal exchange reactions of dodecanethiolate-protected AuPd clusters. EXAFS measurements revealed that Pd, Ag, and Cu dopants preferentially occupy the center and edge sites of the core, and staple sites, respectively. Spectroscopic and theoretical studies demonstrated that the synergistic effects of multiple substitutions on the electronic structures are additive in nature.

Simple but Efficient Method for Inhibiting Sintering and Aggregation of Catalytic Pt Nanoclusters on Metal-Oxide Supports.

A simple and efficient method to inhibit aggregation of Pt clusters supported on metal oxide was developed, preserving the accessible clusters surface where catalytically active sites are located even at relatively high temperatures up to 700 K. The key idea was the inclusion of transition metal atoms such as Ni into the Pt clusters, thus anchoring the clusters through formation of strong chemical bonds with oxygen atoms of the metal-oxide support. To elucidate the efficiency of the method, first-principles molecular dynamics enhanced with free-energy sampling methods were used.

The absence of a gap state and enhancement of the Mars-van Krevelen reaction on oxygen defective Cu/CeO2 surfaces.

We report a detailed first-principles analysis of the electronic structures of oxygen defective CeO2 and Cu/CeO2 surfaces aimed at elucidating the disappearance of the gap state of defective CeO2 when a Cu atom is added at the surface. The top of the valence band of Cu/CeO2 originates from the O 2p states around this Cu atom. We show that this redistribution of electronic states at the defective Cu/CeO2 surface enhances the reactivity of the surface O atoms.

Electric field effects on the electronic properties of the silicene-amine interface.

We performed first-principles studies of electric field (EF) effects on the electronic properties of silicene-amine (NH3 and NH2CH3) hetero-interface systems focusing on the electronic interactions at the interface. The band gaps of the systems increase with a positive applied EF but decrease with a negative EF; that is, the band gaps monotonically vary on changing the applied EF from negative to positive. The phenomenon of band gap variation with the sign of the applied EF is a characteristic feature of hetero-interface systems.

Optically controlled magnetic-field etching on the nano-scale.

Electric and magnetic fields play an important role in both chemical and physical reactions. However, since the coupling efficiency between magnetic fields and electrons is low in comparison with that between electric fields and electrons in the visible wavelength region, the magnetic field is negligible in photo-induced reactions. Here, we performed photo-etching of ZrO nano-stripe structures, and identified an etching-property polarisation dependence.

Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters.

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy.

Gold Quantum Boxes: On the Periodicities and the Quantum Confinement in the Au₂₈, Au₃₆, Au₄₄ , and Au₅₂ Magic Series.

Revealing the size-dependent periodicities (including formula, growth pattern, and property evolution) is an important task in metal nanocluster research. However, investigation on this major issue has been complicated, as the size change is often accompanied by a structural change. Herein, with the successful determination of the Au44(TBBT)28 structure, where TBBT = 4-tert-butylbenzenethiolate, the missing size in the family of Au28(TBBT)20, Au36(TBBT)24, and Au52(TBBT)32 nanoclusters is filled, and a neat "magic series" with a unified formula of Au8n+4(TBBT)4n+8 (n = 3-6) is identified.

Reducing the Cost and Preserving the Reactivity in Noble-Metal-Based Catalysts: Oxidation of CO by Pt and Al-Pt Alloy Clusters Supported on Graphene.

The oxidation mechanisms of CO to CO2 on graphene-supported Pt and Pt-Al alloy clusters are elucidated by reactive dynamical simulations. The general mechanism evidenced is a Langmuir-Hinshelwood (LH) pathway in which O2 is adsorbed on the cluster prior to the CO oxidation. The adsorbed O2 dissociates into two atomic oxygen atoms thus promoting the CO oxidation.

Gold tetrahedra coil up: Kekulé-like and double helical superstructures.

Magic-sized clusters, as the intermediate state between molecules and nanoparticles, exhibit critical transitions of structures and material properties. We report two unique structures of gold clusters solved by x-ray crystallography, including Au40 and Au52 protected by thiolates. The Au40 and Au52 clusters exhibit a high level of complexity, with the gold atoms in the cluster first segregated into four-atom tetrahedral units-which then coil up into a Kekulé-like ring in the Au40 cluster and a DNA-like double helix in Au52.

Observation of Body-Centered Cubic Gold Nanocluster.

The structure of nanoparticles plays a critical role in dictating their material properties. Gold is well known to adopt face-centered cubic (fcc) structure. Herein we report the first observation of a body-centered cubic (bcc) gold nanocluster composed of 38 gold atoms protected by 20 adamantanethiolate ligands and two sulfido atoms ([Au38S2(SR)20], where R=C10H15) as revealed by single-crystal X-ray crystallography.

Control of optical response of a supported cluster on different dielectric substrates.

We develop a computational method for optical response of a supported cluster on a dielectric substrate. The substrate is approximated by a dielectric continuum with a frequency-dependent dielectric function. The computational approach is based on our recently developed first-principles simulation method for photoinduced electron dynamics in real-time and real-space.

Effect of trimetallization in thiolate-protected Au(24-n)Cu(n)Pd clusters.

We synthesized a mixture of Au24-nCunPd(SC12H25)18 (n = 0-3) and Au25-nCun(SC12H25)18 (n = 0-7) and compared their stability. The results showed that, in a cluster containing one Cu atom, the presence of Pd is effective in improving the cluster stability. Conversely, the presence of Pd has different effects depending on the number of Cu atoms in the cluster: cluster formation was inhibited for clusters containing four or more Cu atoms.

Structure determination of [Au18(SR)14].

Unravelling the atomic structures of small gold clusters is the key to understanding the origin of metallic bonds and the nucleation of clusters from organometallic precursors. Herein we report the X-ray crystal structure of a charge-neutral [Au18(SC6H11)14] cluster. This structure exhibits an unprecedented bi-octahedral (or hexagonal close packing) Au9 kernel protected by staple-like motifs including one tetramer, one dimer, and three monomers.

First-principles computational visualization of localized surface plasmon resonance in gold nanoclusters.

Cluster-size dependence of localized surface plasmon resonance (LSPR) for Aun nanoclusters (n = 54, 146, 308, 560, 922, 1414) is investigated by using our recently developed computational program of first-principles calculations for photoinduced electron dynamics in nanostructures. The size of Au1414 (3.9 nm in diameter) is unprecedentedly large in comparison with those addressed in previous first-principles calculations of optical response in nanoclusters.