96 research outputs found
Identifying and abating copper foil impurities to optimize graphene growth
Copper foil impurities are hampering scalable production of high-quality
graphene by chemical vapor deposition (CVD). Here, we conduct a thorough study
on the origin of these unavoidable contaminations at the surface of copper
after the CVD process. We identify two distinct origins for the impurities. The
first type is intrinsic impurities, originating from the manufacturing process
of the copper foils, already present at the surface before any high-temperature
treatment, or buried into the bulk of copper foils. The buried impurities
diffuse towards the copper surface during high-temperature treatment and
precipitate. The second source is external: silica contamination arising from
the quartz tube that also precipitate on copper. The problem of the extrinsic
silica contamination is readily solved upon using an adequate confinement the
copper foil samples. The intrinsic impurities are much more difficult to remove
since they appear spread in the whole foil. Nevertheless, electropolishing
proves particularly efficient in drastically reducing the issue.Comment: 26 pages, 12 figure
Graphene-coated holey metal films: tunable molecular sensing by surface plasmon resonance
We report on the enhancement of surface plasmon resonances in a holey
bidimensional grating of subwavelength size, drilled in a gold thin film coated
by a graphene sheet. The enhancement originates from the coupling between
charge carriers in graphene and gold surface plasmons. The main plasmon
resonance peak is located around 1.5 microns. A lower constraint on the
gold-induced doping concentration of graphene is specified and the interest of
this architecture for molecular sensing is also highlighted.Comment: 5 pages, 4 figures, Final version. Published in Applied Physics
Letter
FOUCAULT, Michel, Histoire de la sexualité. Tome I. La volonté du savoir
The interest of using polyimide as a sacrificial and anchoring layer is demonstrated for post-processing surface micromachining and for the incorporation of metallic nanowires into microsystems. In addition to properties like a high planarization factor, a good resistance to most non-oxidizing acids and bases, and CMOS compatibility, polyimide can also be used as a mold for nanostructures after ion track-etching. Moreover, specific polyimide grades, such as PI-2611 from HD Microsystemsâą, involve a thermal expansion coefficient similar to silicon and low internal stress. The process developed in this study permits higher gaps compared to the state-of-the-art, limits stiction problems with the substrate and is adapted to various top-layer materials. Most metals, semiconductors or ceramics will not be affected by the oxygen plasma required for polyimide etching. Released structures with vertical gaps from one to several tens of ÎŒm have been obtained, possibly using multiple layers of polyimide. Furthermore, patterned freestanding nanowires have been synthesized with diameters from 20 to 60ânm and up to 3âÎŒm in length. These results have been applied to the fabrication of two specific devices: a generic nanomechanical testing lab-on-chip platform and a miniaturized ionization sensor
Toward an experimental proof of superhydrophobicity enhanced by quantum fluctuations freezing on a broadband-absorber metamaterial
Previous theoretical works suggested that superhydrophobicity could be
enhanced through partial inhibition of the quantum vacuum modes at the surface
of a broadband-absorber metamaterial which acts in the extreme ultraviolet
frequency domain. This effect would then compete with the classical
Cassie-Baxter interpretation of superhydrophobicity. In this article, we first
theoretically establish the expected phenomenological features related to such
a kind of "quantum" superhydrophobicity. Then, relying on this theoretical
framework, we experimentally study patterned silicon surfaces on which
organosilane molecules were grafted, all the coated surfaces having similar
characteristic pattern sizes but different profiles. Some of these surfaces can
indeed freeze quantum photon modes while others cannot. While the latter ones
allow hydrophobicity, only the former ones allow for superhydrophobicity. We
believe these results lay the groundwork for further complete assessment of
superhydrophobicity induced by quantum fluctuations freezing.Comment: 10 pages, 5 figures, final version, accepted for publication in
Journal of Applied Physic
Schottky barrier lowering with the formation of crystalline Er silicide on n-Si upon thermal annealing
The evolution of the Schottky barrier height (SBH) of Er silicide contacts to
n-Si is investigated as a function of the annealing temperature. The SBH is
found to drop substantially from 0.43 eV for the as-deposited sample to reach
0.28 eV, its lowest value, at 450 C. By x-ray diffraction, high resolution
transmission electron microscopy, and x-ray photoelectron spectroscopy, the
decrease in the SBH is shown to be associated with the progressive formation of
crystalline ErSi2-x
Enhanced LightâMatter Interactions in Graphene-Covered Gold Nanovoid Arrays
The combination of graphene with noble-metal nanostructures is currently
being explored for strong light-graphene interaction enhanced by plasmons. We
introduce a novel hybrid graphene-metal system for studying light-matter
interactions with gold-void nanostructures exhibiting resonances in the visible
range. Strong coupling of graphene layers to the plasmon modes of the nanovoid
arrays results in significant frequency shifts of the underlying plasmon
resonances, enabling more than 30% absolute light absorption in a single layer
of graphene and up to 700-fold enhancement of the Raman response of the
graphene. These new perspectives enable us to verify the presence of graphene
on gold-void arrays and the enhancement even allows us to accurately quantify
the number of layers. Experimental observations are further supported by
numerical simulations and perturbation-theory analysis. The graphene gold-void
platform is beneficial for sensing of molecules and placing R6G dye molecules
on top of the graphene, we observe a strong enhancement of the R6G Raman
fingerprints. These results pave the way toward advanced substrates for
surface-enhanced Raman scattering (SERS) with potential for unambiguous
single-molecule detection on the atomically well-defined layer of graphene.Comment: 17 pages including 5 figure
A dataset of acoustic measurements from soundscapes collected worldwide during the COVID-19 pandemic
Political responses to the COVID-19 pandemic led to changes in city soundscapes around the globe. From March to October 2020, a consortium of 261 contributors from 35 countries brought together by the Silent Cities project built a unique soundscape recordings collection to report on local acoustic changes in urban areas. We present this collection here, along with metadata including observational descriptions of the local areas from the contributors, open-source environmental data, open-source confinement levels and calculation of acoustic descriptors. We performed a technical validation of the dataset using statistical models run on a subset of manually annotated soundscapes. Results confirmed the large-scale usability of ecoacoustic indices and automatic sound event recognition in the Silent Cities soundscape collection. We expect this dataset to be useful for research in the multidisciplinary field of environmental sciences
Evidence from site-directed mutagenesis that the cytoplasmic domain of the beta3 subunit influences the conformational state of the alphaVbeta3 integrin ectodomain.
In order to explore the mechanisms leading to conformational changes of the vitronectin receptor alphavbeta3 following ligand or divalent cation binding, we have investigated the expression of epitopes known as ligand-induced binding sites (LIBS) on beta3 cytoplasmic tail mutants expressed in CHO cells. Truncation of the entire beta3 cytoplasmic domain induced constitutive LIBS exposure on alphavbeta3 and alphaIIbeta3. Deletion of the C-terminal NITY759 sequence or disruption of the NPLY747 motif by a Y747A substitution impaired extracellular conformational changes on alphavbeta3 following RGDS, echistatin or Mn2+ binding, whereas the substitutions Y747F, Y759A or Y759F allowed normal LIBS exposure. Furthermore, metabolic energy depletion totally prevented Mn2+-dependent LIBS exposure, but had only a minor effect on RGDS-induced conformational changes. Our results demonstrate that the structural integrity of the NPLY747 motif in the beta3 cytoplasmic domain, rather than potential phosphorylation of Tyr747 or Tyr759, is a prerequisite for conformational changes within the alphavbeta3 ectodomain, and suggest that two different mechanisms are responsible for RGDS- and Mn2+-dependent conformational changes
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