Silver
is the ideal material for plasmonics because of its low
loss at optical frequencies, though it is often replaced by a lossier
metal, gold. This is because of silver’s tendency to tarnish,
an effect which is enhanced at the nanoscale due to the large surface-to-volume
ratio. Despite chemical tarnishing of Ag nanoparticles (NPs) has been
extensively studied for decades, it has not been well understood whether
resulted by sulfidation or oxidation processes. This intriguing quest
is herein rationalized by studying the atmospheric corrosion of electron
beam lithography-fabricated Ag NPs, through nanoscale investigation
performed by high-resolution transmission electron microscopy (HRTEM)
combined with electron energy loss (EEL) and energy dispersive X-ray
(EDX) spectroscopies. We demonstrate that tarnishing of Ag NPs upon
exposure to indoor air of an environment located inside a rural site,
not particularly influenced by naturally and human-made sulfur sources,
is caused by chemisorbed sulfur-based contaminants rather than via
an oxidation process. Furthermore, we show that the sulfidation occurs
through the formation of crystalline Ag2S bumps onto Ag
surface in place of a homogeneous growth of a silver sulfide film.
From a single 2D Z-contrast scanning transmission electron microscopy
image, a method for 3D reconstruction of silver nanoparticles with
extremely high spatial resolution has been derived thus establishing
the preferential nucleation of Ag2S bumps in proximity
of lattice defects located on the NP surface. Finally, we also provide
a straightforward and low-cost solution to achieve stable Ag NPs by
passivating them with a self-assembled monolayer of hexanethiols.
The sulfidation mechanism inhibition allows to prevent the increased
material damping and scattering losses.
We discuss and demonstrate a prototype of superconducting transformer with a flux transfer function that can be varied in a wide range, by acting on a control parameter. The device is realized by inserting a small hysteretic superconducting quantum interference device (dc-SQUID) with unshunted junctions, working as a Josephson junction with flux-controlled critical current, parallel to a superconducting transformer; by varying the magnetic flux coupled to the dc-SQUID, the transfer function for the flux coupled to the transformer can be varied. This feature can prove particularly appealing in the field of quantum computing, where it could be exploited to achieve a controllable magnetic coupling among flux-based qubits. Measurements carried out on a prototype at 4.2?K show a reduction factor of about 30 between the “on” and the “off” states. We discuss the system characteristics and the experimental results
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