Engineering Negative Differential Conductance with the Cu(111) Surface State

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate electron tunneling from a C60-terminated tip into a Cu(111) surface. Tunneling between a C60 orbital and the Shockley surface states of copper is shown to produce negative differential conductance (NDC) contrary to conventional expectations. NDC can be tuned through barrier thickness or C60 orientation up to complete extinction. The orientation dependence of NDC is a result of a symmetry matching between the molecular tip and the surface states.Comment: 5 pages, 4 figures, 1 tabl

Conductance-Driven Kondo Effect in a Single Cobalt Atom

A low-temperature scanning tunneling microscope is employed to build a junction comprising a Co atom bridging a copper-coated tip and a Cu(100) surface. An Abrikosov-Suhl-Kondo resonance is evidenced in the differential conductance and its width is shown to vary exponentially with the ballistic conductance regardless of the tip structure. Using a theoretical description based on the Anderson model, we show that the Kondo effect and the conductance are related through the atomic relaxations affecting the environment of the Co atom.Comment: 5 pages, 4 figures, final versio

Size-dependent Surface States on Strained Cobalt Nanoislands on Cu(111)

Low-temperature scanning tunneling spectroscopy over Co nanoislands on Cu(111) showed that the surface states of the islands vary with their size. Occupied states exhibit a sizeable downward energy shift as the island size decreases. The position of the occupied states also significantly changes across the islands. Atomic-scale simulations and ab inito calculations demonstrate that the driving force for the observed shift is related to size-dependent mesoscopic relaxations in the nanoislands.Comment: 4 pages, 4 figure

Visualizing the spin of individual molecules

Low-temperature spin-polarized scanning tunneling microscopy is employed to study spin transport across single Cobalt-Phathalocyanine molecules adsorbed on well characterized magnetic nanoleads. A spin-polarized electronic resonance is identified over the center of the molecule and exploited to spatially resolve stationary spin states. These states reflect two molecular spin orientations and, as established by density functional calculations, originate from a ferromagnetic molecule-lead superexchange interaction mediated by the organic ligands

Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate

The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices

High-resolution manipulation of gold nanorods with an atomic force microscope

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Detection of Magnetic Force Fields at Macroscopic Distances with a Micromechanical Cantilever Oscillator

International audienceWe report a procedure for measuremingt magnetic field gradients generated by a macroscopic coil. A micromechanical cantilever oscillator covered with a magnetic material is used to detect variations of the magnetic force field at distances exceeding several times the coil diameter (4 mm). The detection is based on the phase of the first eigenmode of the cantilever while modulating the magnetic field at low frequencies. The nanoscale oscillation of the cantilever along with the high-quality resonance factor are responsible for a coherent oscillation allowing high sensitivity. A detection sensitivity, under ambient conditions, of the order of 10-13 T/nm 2 is estimated with the help of numerical calculations. The approach is useful for measuring the spatial variation of the magnetic field gradients generated by any source of magnetic field when the magnetic field can be modified at rates below the resonant frequency of the cantilever. These results can be useful for gradient fields monitoring in macro-and micro-scale magnetic resonance imaging, non-contact electric currents identification from stray magnetic fields, electrical power monitoring, 3D-magnetic fields mapping, or miniature orientation devices

Photothermal Plasmonic Actuation of Micromechanical Cantilever Beams

International audienceOscillations of charge carriers in plasmonic metal nanoparticles activated by resonant absorption of light are accompanied by local temperature increase due to non-radiative plasma damping. The control of this photothermal effect is considered essential for many applications ranging from photochemistry or nanomedicine to chemical/physical sensing. Here, we present a study on the conversion of visible light into mechanical energy via photothermal plasmonic and non-plasmonic effects. Using atomic force microscopy cantilevered sensors coated with various materials and excited in vacuum by a wavelength tunable laser, it is shown that light generates a resonant oscillation of the cantilever. The photoinduced oscillation amplitude depends on the wavelength of the incident light, allowing for an optimization of energy conversion based on absorption spectroscopy of the coating material. The effect of non-photonic forces acting on the cantilever is probed in the context of photoinduced force microscopy by placing the cantilever in interaction with a substrate surface at various distances. The findings are relevant for any technique utilizing an optical actuation of a mechanical system, and for photoinduced force detection methods in particular

Photoinduced Atomic Force Spectroscopy and Imaging of Two-Dimensional Materials

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