151 research outputs found
A scalable optical detection scheme for matter wave interferometry
Imaging of surface adsorbed molecules is investigated as a novel detection
method for matter wave interferometry with fluorescent particles. Mechanically
magnified fluorescence imaging turns out to be an excellent tool for recording
quantum interference patterns. It has a good sensitivity and yields patterns of
high visibility. The spatial resolution of this technique is only determined by
the Talbot gratings and can exceed the optical resolution limit by an order of
magnitude. A unique advantage of this approach is its scalability: for certain
classes of nano-sized objects, the detection sensitivity will even increase
significantly with increasing size of the particle.Comment: 10 pages, 4 figure
Decoherence in a Talbot Lau interferometer: the influence of molecular scattering
We study the interference of C70 fullerenes in a Talbot-Lau interferometer
with a large separation between the diffraction gratings. This permits the
observation of recurrences of the interference contrast both as a function of
the de Broglie wavelength and in dependence of the interaction with background
gases. We observe an exponential decrease of the fringe visibility with
increasing background pressure and find good quantitative agreement with the
predictions of decoherence theory. From this we extrapolate the limits of
matter wave interferometry and conclude that the influence of collisional
decoherence may be well under control in future experiments with proteins and
even larger objects.Comment: 8 pages, 5 figure
Adatom Bonding Sites in a Nickel-Fe<sub>3</sub>O<sub>4</sub>(001) Single-Atom Model Catalyst and O<sub>2</sub> Reactivity Unveiled by Surface Action Spectroscopy with Infrared Free-Electron Laser Light
Single-atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst’s performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe3O4. We reveal that Ni and Au adatoms selectively bind to surface oxygen ions which are octahedrally coordinated to Fe ions. In addition, we find that the Ni adatoms can activate O2 to superoxide in contrast to the bare surface and Ni in subsurface positions. Overall, we unveil the advantages of combining SAS and DFT for improving the understanding of single-atom catalysts
Quantum Theory Approach for Neutron Single and Double-Slit Diffraction
We provide a quantum approach description of neutron single and double-slit
diffraction, with specific attention to the cold neutron diffraction (\AA) carried out by Zeilinger et al. in 1988. We find the
theoretical results are good agreement with experimental data.Comment: 10 page
Adatom Bonding Sites in a Nickel-Fe<sub>3</sub>O<sub>4</sub>(001) Single-Atom Model Catalyst and O<sub>2</sub> Reactivity Unveiled by Surface Action Spectroscopy with Infrared Free-Electron Laser Light
Single-atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst’s performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe3O4. We reveal that Ni and Au adatoms selectively bind to surface oxygen ions which are octahedrally coordinated to Fe ions. In addition, we find that the Ni adatoms can activate O2 to superoxide in contrast to the bare surface and Ni in subsurface positions. Overall, we unveil the advantages of combining SAS and DFT for improving the understanding of single-atom catalysts
Surface oxygen Vacancies on Reduced Co<sub>3</sub>O<sub>4</sub>(100): Superoxide Formation and Ultra-Low-Temperature CO Oxidation
The activation of molecular oxygen is a fundamental step in almost all catalytic oxidation reactions.We have studied this topic and the role of surface vacancies for Co3O4(100) films with a synergistic combination of experimental and theoretical methods. We show that the as-prepared surface is Blayer terminated and that mild reduction produces oxygen single and double vacancies in this layer. Oxygen adsorption experiments clearly reveal different superoxide species below room temperature. The superoxide desorbs below ca. 120 K from a vacancy-free surface and is not active for CO oxidation while superoxide on a surface with oxygen vacancies is stable up to ca. 270 K and can oxidize CO already at the low temperature of 120 K. The vacancies are not refilled by oxygen from the superoxide, which makes them suitable for long-term operation. Our joint experimental/theoretical effort highlights the relevance of surface vacancies in catalytic oxidation reactions
Surface oxygen Vacancies on Reduced Co<sub>3</sub>O<sub>4</sub>(100): Superoxide Formation and Ultra-Low-Temperature CO Oxidation
The activation of molecular oxygen is a fundamental step in almost all catalytic oxidation reactions.We have studied this topic and the role of surface vacancies for Co3O4(100) films with a synergistic combination of experimental and theoretical methods. We show that the as-prepared surface is Blayer terminated and that mild reduction produces oxygen single and double vacancies in this layer. Oxygen adsorption experiments clearly reveal different superoxide species below room temperature. The superoxide desorbs below ca. 120 K from a vacancy-free surface and is not active for CO oxidation while superoxide on a surface with oxygen vacancies is stable up to ca. 270 K and can oxidize CO already at the low temperature of 120 K. The vacancies are not refilled by oxygen from the superoxide, which makes them suitable for long-term operation. Our joint experimental/theoretical effort highlights the relevance of surface vacancies in catalytic oxidation reactions
The wave nature of biomolecules and fluorofullerenes
We demonstrate quantum interference for tetraphenylporphyrin, the first
biomolecule exhibiting wave nature, and for the fluorofullerene C60F48 using a
near-field Talbot-Lau interferometer. For the porphyrins, which are
distinguished by their low symmetry and their abundant occurence in organic
systems, we find the theoretically expected maximal interference contrast and
its expected dependence on the de Broglie wavelength. For C60F48 the observed
fringe visibility is below the expected value, but the high contrast still
provides good evidence for the quantum character of the observed fringe
pattern. The fluorofullerenes therefore set the new mark in complexity and mass
(1632 amu) for de Broglie wave experiments, exceeding the previous mass record
by a factor of two.Comment: 5 pages, 4 figure
Lithium atom interferometer using laser diffraction : description and experiments
We have built and operated an atom interferometer of the Mach-Zehnder type.
The atomic wave is a supersonic beam of lithium seeded in argon and the mirrors
and beam-splitters for the atomic wave are based on elastic Bragg diffraction
on laser standing waves at 671 nm. We give here a detailed description of our
experimental setup and of the procedures used to align its components. We then
present experimental signals, exhibiting atomic interference effects with a
very high visibility, up to 84.5 %. We describe a series of experiments testing
the sensitivity of the fringe visibility to the main alignment defects and to
the magnetic field gradient.Comment: 8 avril 200
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