Kondo resonances are a very precise measure of spin-polarized transport through magnetic impurities. However, the Kondo temperature, indicating the thermal range of stability of the magnetic properties, is very low. By contrast, we find for iron phthalocyanine a Kondo temperature in spectroscopic measurements which is well above room temperature. It is also shown that the signal of the resonance depends strongly on the adsorption site of the molecule on a gold surface. Experimental data are verified by extensive numerical simulations, which establish that the coupling between iron states and states of the substrate depends strongly on the adsorption configuration.

Molecular rotors with a fixed off-center rotation axis have been observed for single tetra-tert-butyl zinc phthalocyanine molecules on an Au(111) surface by a scanning tunneling microscope at LN 2 temperature. Experiments and first-principles calculations reveal that we introduce gold adatoms at the surface as the stable contact of the molecule to the surface. An off-center rotation axis is formed by a chemical bonding between a nitrogen atom of the molecule and a gold adatom at the surface, which gives them a welldefined contact while the molecules can have rotation-favorable configurations. Furthermore, these singlemolecule rotors self-assemble into large scale ordered arrays on Au(111) surfaces. A fixed rotation axis off center is an important step towards the eventual fabrication of molecular motors or generators. DOI: 10.1103/PhysRevLett.101.197209 PACS numbers: 85.85.+j, 63.20.dk, 68.37.Ef, 82.37.Gk The motion of single atoms or molecules plays an important role in nanoscale engineering at the single atomic or molecular scale [1,2]. The controllability of molecular motion is critical for molecular motors [3], which may convert external energy into orchestrated motion at the molecular level [4,5]. For molecular rotors [6] a high level of control over the rotation axis and, equivalently, selfassembly on a very large scale, are the key ingredients for their integration into complex molecular machines. Previously, the reported molecular rotors on surfaces had no fixed axis on the surface [7][8][9][10]. In addition, the studies mainly focused on single molecules, while it is desirable, for eventual applications, that individual molecular rotors self-assemble into large scale ordered arrays while keeping their original functions. Here we show, using scanning tunneling microscopy (STM) [7][8][9][10][11][12], that single tetratert-butyl zinc phthalocyanine (ðt-BuÞ 4 -ZnPc) molecules on the reconstructed Au(111) surface possess a welldefined rotation axis fixed on the surface, and also, that these single-molecule rotors form large scale ordered arrays due to the reconstruction of the gold surface.Our experiments were conducted with an Omicron MBE-LTSTM system with a base pressure below 3:0 Â 10 À10 mbar. An atomically clean Au(111) surface was prepared by repeated cycles of Ar þ sputtering and subsequent annealing, and then dosed with a minute quantity of ðt-BuÞ 4 -ZnPc molecules. In our experiments, the STM tip is grounded, and the bias voltage refers to the sample voltage. All STM measurements in this study are conducted at 78 K if not specified. First-principles calculations were carried out based on density functional theory (DFT), a Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) for exchange-correlation energy [13], projector augmented waves (PAW) [14], and a plane wave basis set as implemented in the Vienna ab initio simulation package (VASP) [15]. A cð5 Â 8Þ supercell was employed to model the isolated molecule on the gold surface. Because of numerical limitations and the size of t...

Anisotropic triangular graphene monolayers grown on a Ru(0001) surface represent unique two-dimensional templates for creating ordered, large-scale assembly of functional molecules. Using scanning tunneling microscopy and spectroscopy, we demonstrate the selective adsorption and the formation of ordered molecular arrays of iron phthalocyanine and pentacene molecules of different structural symmetries on the graphene/Ru(0001) templates. With in-depth investigations of the molecular adsorption and assembly processes, we reveal the existence of site-specific, lateral electric dipoles (or lateral electric fields) in the epitaxial graphene monolayers and the capability of the dipoles in directing and driving the molecular adsorption and assembly. We show that the lateral dipoles originate from the inhomogeneous distribution of charge due to the epitaxial constraint of graphene on a Ru(0001) surface. The adsorption mechanism is rather general and applicable to similar molecular systems on graphene monolayers formed on other transition metal surfaces.

The development of methods for controlling the motion and arrangement of molecules adsorbed on a metal surface would provide a powerful tool for the design of molecular electronic devices. Recently, metal phthalocyanines (MPc) have been extensively considered for use in such devices. Here we show that applied electric fields can be used to turn off the diffusivity of iron phthalocyanine (FePc) on Au(111) at fixed temperature, demonstrating a practical and direct method for controlling and potentially patterning FePc layers. Using scanning tunneling microscopy, we show that the diffusivity of FePc on Au(111) is a strong function of temperature and that applied electric fields can be used to retard or enhance molecular diffusion at fixed temperature. Using spin-dependent density-functional calculations, we then explore the origin of this effect, showing that applied fields modify both the molecule-surface binding energies and the molecular diffusion barriers through an interaction with the dipolar Fe-Au adsorption bond. On the basis of these results FePc on Au(111) is a promising candidate system for the development of adaptive molecular device structures.

SnO x films were fabricated by reactive rf magnetron sputtering under various oxygen partial pressures (P O = 1.6%-50%) and then annealed in an air ambient. Four operating window regions of the SnO x films are demonstrated such as metallic Sn dominated films with n-type conduction, polycrystalline SnO dominated films with p-type conduction, SnO-SnO 2 composite films with high resistivity, and amorphous SnO 2 dominated films with n-type characteristics. TFT devices using the SnO dominated films as channels are investigated. The TFTs with the channels of a hole concentration over 10 18 cm −3 show depletion p-type characteristics. The hole concentration can be tunable by changing P O , the channel thickness, and the annealing durations. An ambipolar operating mode is obtained by modulating the hole concentration.

We report for the first time a new methodology to determine molecular configurations of a large molecular complex in a dynamical process on a metal surface by combining time-resolved tunneling spectroscopy (I-t) and density functional theory calculation (DFT). Two examples, ðt-BuÞ 4 -ZnPc and FePc, representing molecular rotation and lateral diffusion on Au(111) surfaces, respectively, were applied to demonstrate our method. Through analysis of statistical occupation time for each configuration, the molecular configuration numbers and energy differences between different configurations of these molecular systems could be unambiguously determined. These experimental results are further compared with DFT calculation to determine corresponding molecular configurations. Importantly, through the spatial I-t mapping, valuable insights of molecular surface diffusion paths are obtained.

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