Magnetic field dependence of rotationally resolved excitation spectra of the 1B3u 000 transition of jet-cooled pyrazine

We report rotationally resolved excitation spectra of the 1B3u 000 transition of jet-cooled pyrazine in magnetic fields up to 50 kG. The emission intensity of every rotational line is found to decrease by a factor of three for magnetic fields larger than about 300 G. For still larger magnetic fields up to 50 kG the total emission intensity remains constant. The effect of collisions on the threefold quenching of the emission is studied separately, and found to be of minor importance. It is concluded that the reduction of the quantum yield due to the magnetic field originates from an intramolecular process. The threefold decrease of the quantum yield is interpreted in terms of a nonradiative decay rate constant of the zero-order triplet states. The decay rate constant consists of both a magnetic field dependent part (about 0.3 MHz at zero field) and a magnetic insensitive part (about 0.7 MHz)

Fabrication of a Complex Two-Dimensional Adenine Perylene-3,4,9,10-tetracarboxylic Dianhydride Chiral Nanoarchitecture through Molecular Self-Assembly

International audienceThe two-dimensional self-assembly of a nonsymmetric adenine DNA base mixed with symmetric perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules is investigated using scanning tunneling microscopy (STM). We experimentally observe that these two building blocks form a complex close-packed chiral supramolecular network on Au(111). The unit cell of the adenine PTCDA nanoarchitecture is composed of 14 molecules. The high stability of this structure relies on PTCDA PTCDA and PTCDA adenine hydrogen bonding. Detailed theoretical analysis based on the density functional theory (DFT) calculations reveals that adenine molecules work as a "glue", providing additional strengthening to the PTCDA-based skeleton of this sophisticated multicomponent nanoarchitecture. At the same time, we find that orientation and chirality of adenine molecules across the monolayer is likely to vary, leading to a disorder in the atomistic structure of the entire assembly

Nanoscale Networks of Metal Oxides by Polymer Imprinting and Templating for Future Adaptable Electronics

While network formation is prevalent in nature, networks are generally not expected in inorganic structures. Exceptions are those cases in which surface states become important, such as nanoparticles. However, even in these cases, the morphology of these networks is difficult to control and they show a large degree of disorder. In this work, we show that highly ordered and interconnected nanoscale networks of functional metal oxides can be fabricated by a combination of polymer imprinting and polymer templating through solution processable methods. We report the fabrication of a number of functional oxide networks (i.e., BiFeO3, SrTiO3, La0.7Ca0.3MnO3, and HfO2) from solution, showing that all the oxide materials tried so far are able to follow the self-assembled network morphology dictated by the polymer structure. These networks were characterized for the overall structure by scanning electron microscopy and atomic force microscopy (AFM). Grazing incidence small angle X-ray scattering showed a good imprint quality on the mm2 scale for the combined networks, which is challenging given that multiple processing steps were involved during the fabrication. The material stoichiometries were investigated by X-ray photoemission spectroscopy and the crystal phases by grazing incidence wide angle X-ray scattering. When electronic functionality is anticipated, the networks behave as expected: conducting AFM on the La0.7Ca0.3MnO3 networks confirmed the conductive character of this composition; and piezoresponse force microscopy of the BiFeO3 network is consistent with the presence of ferroelectric behavior. These nanoscale networks show promise for future applications in adaptable electronics, such as neuromorphic computing or brain-inspired information processing.</p

Secondary Ion Mass Spectrometry:a Tool for Identification of Matrix-isolated Species

An argon matrix-isolated propane sample (1:150, 10 K) is used to demonstrate the applicability of secondary ion mass spectral analysis to the characterization of matrix-isolated species

Electronic spin transport and spin precession in single graphene layers at room temperature

The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport also supercurrent transport has already been observed. It has also been suggested that graphene might be a promising material for spintronics and related applications, such as the realization of spin qubits, due to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. As a first step in the direction of graphene spintronics and spin qubits we report the observation of spin transport, as well as Larmor spin precession over micrometer long distances using single graphene layer based field effect transistors. The non-local spin valve geometry was used, employing four terminal contact geometries with ferromagnetic cobalt electrodes, which make contact to the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals which reflect the magnetization direction of all 4 electrodes, indicating that spin coherence extends underneath all 4 contacts. No significant changes in the spin signals occur between 4.2K, 77K and room temperature. From Hanle type spin precession measurements we extract a spin relaxation length between 1.5 and 2 micron at room temperature, only weakly dependent on charge density, which is varied from n~0 at the Dirac neutrality point to n = 3.6 10^16/m^2. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around 10%

A Microscopic Model for the Second-Harmonic Generation from C60

We discuss the microscopic origin of the Second-Harmonic Generation (SHG) resonance at ħω=1.81 eV, based on spectroscopic and thickness dependent SHG measurements on C60 thin films. We assign the three-level diagram responsible for the observed SHG resonance, and show it to be of magnetic-dipole-induced origin. Furthermore we explain the absence of almost any surface contributions, and the narrow line width of the involved HOMO-LUMO (11Ag→11T1g) excitation at 1.81 eV