Electronic Structure of an Organic/Metal Interface: Pentacene/Cu(110)

A detailed understanding of the organic molecule/substrate interface is of crucial importance for the design of organic semiconducting devices, as the interface determines the contact resistance and the charge injection. Generally, two different adsorption situations are considered: physisorption and chemisorption. For small molecular adsorbates like CO or N₂, the adsorption energy alone can be used as a criterion to classify the adsorption in chemisorption (adsorption energies larger than 1 eV) and physisorption (few tens of meV). This classification fails for complex π-conjugated organic molecules. Here we discuss on the basis of a pentacene/Cu(110) model system a different set of criteria to distinguish between chemisorption and physisorption beyond the total bond energy argument. We analyze the bonding situation on the basis of density functional theory (DFT) calculations and photoelectron spectroscopy. Theory predicts (i) a significant bending of the molecule after adsorption, (ii) a buckling of the top layer Cu atoms, (iii) the emergence of new hybrid states, and (iv) a substantial charge redistribution and accompanying charge transfer. Photoemission confirms the energies of the 3 topmost molecular orbitals with an almost “half-filled” lowest unoccupied molecular orbital (LUMO). The four criteria are used to qualify the adsorption mechanism in the pentacene/Cu(110) system as chemisorption. This set of criteria is indicative of chemisorption also in the case of other noncovalently coupled large adsorbates, far beyond the pentacene/Cu(110) case

An Endohedral Single-Molecule Magnet with Long Relaxation Times: DySc₂N@C₈₀

The magnetism of DySc₂N@C₈₀ endofullerene was studied with X-ray magnetic circular dichroism (XMCD) and a magnetometer with a superconducting quantum interference device (SQUID) down to temperatures of 2 K and in fields up to 7 T. XMCD shows hysteresis of the 4f spin and orbital moment in Dy^III ions. SQUID magnetometry indicates hysteresis below 6 K, while thermal and nonthermal relaxation is observed. Dilution of DySc₂N@C₈₀ samples with C₆₀ increases the zero-field 4f electron relaxation time at 2 K to several hours

Triangular Monometallic Cyanide Cluster Entrapped in Carbon Cage with Geometry-Dependent Molecular Magnetism

Clusterfullerenes are capable of entrapping a variety of metal clusters within carbon cage, for which the entrapped metal cluster generally keeps its geometric structure (e.g., bond distance and angle) upon changing the isomeric structure of fullerene cage, and whether the properties of the entrapped metal cluster is geometry-dependent remains unclear. Herein we report an unusual triangular monometallic cluster entrapped in fullerene cage by isolating several novel terbium cyanide clusterfullerenes (TbNC@C₈₂) with different cage isomeric structures. Upon varying the isomeric structure of C₈₂ cage from C₂(5) to C_s(6) and to C_2v(9), the entrapped triangular TbNC cluster exhibits significant distortions as evidenced by the changes of Tb–C­(N) and C–N bond distances and variation of the Tb–C­(N)–N­(C) angle by up to 20°, revealing that the geometric structure of the entrapped triangular TbNC cluster is variable. All three TbNC@C₈₂ molecules are found to be single-ion magnets, and the change of the geometric structure of TbNC cluster directly leads to the alternation of the magnetic relaxation time of the corresponding TbNC@C₈₂ clusterfullerene

Centimeter-Sized Single-Orientation Monolayer Hexagonal Boron Nitride With or Without Nanovoids

Large-area hexagonal boron nitride (<i>h</i>-BN) promises many new applications of two-dimensional materials, such as the protective packing of reactive surfaces or as membranes in liquids. However, scalable production beyond exfoliation from bulk single crystals remained a major challenge. Single-orientation monolayer <i>h</i>-BN nanomesh is grown on 4 in. wafer single crystalline rhodium films and transferred on arbitrary substrates such as SiO₂, germanium, or transmission electron microscopy grids. The transfer process involves application of tetraoctylammonium bromide before electrochemical hydrogen delamination. The material performance is demonstrated with two applications. First, protective sealing of <i>h</i>-BN is shown by preserving germanium from oxidation in air at high temperatures. Second, the membrane functionality of the single <i>h</i>-BN layer is demonstrated in aqueous solutions. Here, we employ a growth substrate intrinsic preparation scheme to create regular 2 nm holes that serve as ion channels in liquids