Self-assembly of isolated plasmonic dimers with sub-5 nm gaps on a metallic mirror.

Realizing plasmonic nanogaps with a refractive index ( = 1) environment in metallic nanoparticle (NP) structures is highly attractive for a wide range of applications. So far in self-assembly-based approaches, without surface functionalization of metallic NPs, achieving such extremely small nanogaps is challenging. Surface functionalization introduces changes in the refractive index at nanogaps, which in turn deteriorates the desired plasmonic properties.

Band alignment at InP/TiOinterfaces from density-functional theory.

The natural band alignments between indium phosphide and the main dioxides of titanium, i.e. rutile, anatase, and brookite as well as amorphous titania are calculated from the branch-point energies of the respective materials.

DFT-Assisted Investigation of the Electric Field and Charge Density Distribution of Pristine and Defective 2D WSe by Differential Phase Contrast Imaging.

Most properties of solid materials are defined by their internal electric field and charge density distributions which so far are difficult to measure with high spatial resolution. Especially for 2D materials, the atomic electric fields influence the optoelectronic properties. In this study, the atomic-scale electric field and charge density distribution of WSe bi- and trilayers are revealed using an emerging microscopy technique, differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM).

Unraveling Electron Dynamics in p-type Indium Phosphide (100): A Time-Resolved Two-Photon Photoemission Study.

Renewable ("green") hydrogen production through direct photoelectrochemical (PEC) water splitting is a potential key contributor to the sustainable energy mix of the future. We investigate the potential of indium phosphide (InP) as a reference material among III-V semiconductors for PEC and photovoltaic (PV) applications. The p(2 × 2)/c(4 × 2)-reconstructed phosphorus-terminated p-doped InP(100) (P-rich p-InP) surface is the focus of our investigation.

Defect-Assisted Exciton Transfer across the Tetracene-Si(111):H Interface.

Exciton transfers are ubiquitous and extremely important processes, but often poorly understood. A recent example is the triplet exciton transfer in tetracene sensitized silicon solar cells exploited for harvesting high-energy photons. The present ab initio molecular dynamics calculations for tetracene-Si(111):H interfaces show that Si dangling bonds, intuitively expected to hinder the exciton transfer, actually foster it.

P-Terminated InP (001) Surfaces: Surface Band Bending and Reactivity to Water.

Stable InP (001) surfaces are characterized by fully occupied and empty surface states close to the bulk valence and conduction band edges, respectively. The present photoemission data show, however, a surface Fermi level pinning only slightly below the midgap energy which gives rise to an appreciable surface band bending. By means of density functional theory calculations, it is shown that this apparent discrepancy is due to surface defects that form at finite temperature.

Water/InP(001) from Density Functional Theory.

The interface between water and the In-rich InP(001) surface is studied by density functional theory with water coverage ranging from single molecules to multiple overlayers. Single molecules attach preferably to three-fold coordinated surface In atoms. Water dissociation is energetically favorable but hindered by an energy barrier that decreases with increasing water coverage.

Electron-Nuclear Coherent Coupling and Nuclear Spin Readout through Optically Polarized V Spin States in hBN.

Coherent coupling of defect spins with surrounding nuclei along with the endowment to read out the latter are basic requirements for an application in quantum technologies. We show that negatively charged boron vacancies (V) in hexagonal boron nitride (hBN) meet these prerequisites. We demonstrate Hahn-echo coherence of the V spin with a characteristic decay time = 15 μs, close to the theoretically predicted limit of 18 μs for defects in hBN.

Reconstructions of the As-Terminated GaAs(001) Surface Exposed to Atomic Hydrogen.

We explore the atomic structures and electronic properties of the As-terminated GaAs(001) surface in the presence of hydrogen based on ab initio density functional theory. We calculate a phase diagram dependent on the chemical potentials of As and H, showing which surface reconstruction is the most stable for a given set of chemical potentials. The findings are supported by the calculation of energy landscapes of the surfaces, which indicate possible H bonding sites as well as the density of states, which show the effect of hydrogen adsorption on the states near the fundamental band gap.

Adatom mediated adsorption of N-heterocyclic carbenes on Cu(111) and Au(111).

The adsorption of N-heterocyclic carbenes (NHCs) on Cu(111) and Au(111) surfaces is studied with density-functional theory. The role of the molecular side groups as well as the surface morphology in determining the adsorption geometry are explored in detail. Flat-laying NHCs, as observed experimentally for NHC with relatively small side groups, result from the adsorption at adatoms and give rise to the so-called ballbot configurations, which are more stable than adsorption on flat surfaces and provide an efficient precursor for the formation of bis(NHC) dimers.

Spin Polarization, Electron-Phonon Coupling, and Zero-Phonon Line of the NV Center in 3-SiC.

The nitrogen-vacancy (NV) center in 3-SiC, the analog of the NV center in diamond, has recently emerged as a solid-state qubit with competitive properties and significant technological advantages. Combining first-principles calculations and magnetic resonance spectroscopy, we provide thorough insight into its magneto-optical properties. By applying resonantly excited electron paramagnetic resonance spectroscopy, we identified the zero-phonon absorption line of the → transition at 1289 nm (within the telecom O-band) and measured its phonon sideband, the analysis of which reveals a Huang-Rhys factor of = 2.

Controlled growth of ordered monolayers of N-heterocyclic carbenes on silicon.

N-Heterocyclic carbenes (NHCs) are promising modifiers and anchors for surface functionalization and offer some advantages over thiol-based systems. Because of their strong binding affinity and high electron donation, NHCs can dramatically change the properties of the surfaces to which they are bonded. Highly ordered NHC monolayers have so far been limited to metal surfaces.

InP and AlInP(001)(2 × 4) Surface Oxidation from Density Functional Theory.

The atomic structure and electronic properties of the InP and AlInP(001) surfaces at the initial stages of oxidation are investigated via density functional theory. Thereby, we focus on the mixed-dimer (2 × 4) surfaces stable for cation-rich preparation conditions. For InP, the top In-P dimer is the most favored adsorption site, while it is the second-layer Al-Al dimer for AlInP.

A photoredox catalysed Heck reaction hole transfer from a Ru(ii)-bis(terpyridine) complex to graphene oxide.

The attachment of homoleptic Ru bis-terpy complexes on graphene oxide significantly improved the photocatalytic activity of the complexes. These straightforward complexes were applied as photocatalysts in a Heck reaction. Due to covalent functionalization on graphene oxide, which functions as an electron reservoir, excellent yields were obtained.

Photochemical Ring Opening of Oxirane Modeled by Constrained Density Functional Theory.

A constrained density functional theory/classical trajectory surface hopping study of the photochemical dissociation of oxirane (CH)O is presented. The calculations confirm the Gomer-Noyes mechanism for the initial reaction and agree largely with experimental photolysis data including reaction yields. The calculated yields, however, depend both on temperature and its modeling.

Toward Efficient Toxic-Gas Detectors: Exploring Molecular Interactions of Sarin and Dimethyl Methylphosphonate with Metal-Centered Phthalocyanine Structures.

The rapid and reliable detection of lethal agents such as sarin is of increasing importance. Here, density-functional theory (DFT) is used to compare the interaction of sarin with single-metal-centered phthalocyanine (MPc) and MPc layer structures to a benign model system, i.e.

Photocatalytic properties of graphene-supported titania clusters from density-functional theory.

Density-functional theory calculations of (TiO ) clusters (n = 1-5) in the gas phase and adsorbed on pristine graphene as well as graphene quantum dots are presented. The cluster adsorption is found to be dominated by van der Waals forces. The electronic structure and in particular the excitation energies of the bare clusters and the TiO /graphene composites are found to vary largely in dependence on the size of the respective constituents.

Vibration-Driven Self-Doping of Dangling-Bond Wires on Si(553)-Au Surfaces.

Density-functional theory is used to explore the Si(553)-Au surface dynamics. Our study (i) reveals a complex two-stage order-disorder phase transition where with rising temperature first the ×3 order along the Si step edges and, subsequently, the ×2 order of the Au chains is lost, (ii) identifies the transient modification of the electron chemical potential during soft Au chain vibrations as instrumental for disorder at the step edge, and (iii) shows that the transition leads to a self-doping of the Si dangling-bond wire at the step edge. The calculations are corroborated by Raman measurements of surface phonon modes and explain previous electron diffraction, scanning tunneling microscopy, and surface transport data.

Electron paramagnetic resonance study of ferroelectric phase transition and dynamic effects in a Mn doped [NH][Zn(HCOO)] hybrid formate framework.

We present an X- and Q-band continuous wave (CW) and pulse electron paramagnetic resonance (EPR) study of a manganese doped [NH4][Zn(HCOO)3] hybrid framework, which exhibits a ferroelectric structural phase transition at 190 K. The CW EPR spectra obtained at different temperatures exhibit clear changes at the phase transition temperature. This suggests a successful substitution of the Zn2+ ions by the paramagnetic Mn2+ centers, which is further confirmed by the pulse EPR and 1H ENDOR experiments.

Water Splitting Reaction at Polar Lithium Niobate Surfaces.

Water splitting is a highly promising, environmentally friendly approach for hydrogen production. It is often discussed in the context of carbon dioxide free combustion and storage of electrical energy after conversion to chemical energy. Since the oxidation and reduction reactions are related to significant overpotentials, the search for suitable catalysts is of particular importance.

Oxygen and potassium vacancies in KTP calculated from first principles.

The atomic geometry and energetics of oxygen and potassium vacancies in potassium titanyl phosphate (KTP) as well as their electronic and optical properties are studied within density-functional theory in dependence of their charge state. Oxygen vacancies formed between Ti and P are characterized by a negative-U behavior. Their neutral charge state is favored for Fermi levels near the conduction band and gives rise to a defect level in the band gap, which leads to an additional optical absorption peak.

Beyond the molecular movie: Dynamics of bands and bonds during a photoinduced phase transition.

Ultrafast nonequilibrium dynamics offer a route to study the microscopic interactions that govern macroscopic behavior. In particular, photoinduced phase transitions (PIPTs) in solids provide a test case for how forces, and the resulting atomic motion along a reaction coordinate, originate from a nonequilibrium population of excited electronic states. Using femtosecond photoemission, we obtain access to the transient electronic structure during an ultrafast PIPT in a model system: indium nanowires on a silicon(111) surface.

Unraveling the Oxidation and Spin State of Mn-Corrole through X-ray Spectroscopy and Quantum Chemical Analysis.

The interplay between Mn ions and corrole ligands gives rise to complex scenarios regarding the metal centers' electronic properties expressing a range of high oxidation states and spin configurations. The resulting potential of Mn-corroles for applications such as catalysts or fuel cells has recently been demonstrated. However, despite being crucial for their functionality, the electronic structure of Mn-corroles is often hardly accessible with traditional techniques and thus is still under debate, especially under interfacial conditions.