39 research outputs found
Understanding the interaction between energetic ions and freestanding graphene towards practical 2D perforation
We report experimentally and theoretically the behavior of freestanding
graphene subject to bombardment of energetic ions, investigating the ability of
large-scale patterning of freestanding graphene with nanometer sized features
by focused ion beam technology. A precise control over the He+ and Ga+
irradiation offered by focused ion beam techniques enables to investigate the
interaction of the energetic particles and graphene suspended with no support
and allows determining sputter yields of the 2D lattice. We find strong
dependency of the 2D sputter yield on the species and kinetic energy of the
incident ion beams. Freestanding graphene shows material semi-transparency to
He+ at high energies (10-30 keV) allowing the passage of >97% He+ particles
without creating destructive lattice vacancy. Large Ga+ ions (5-30 keV), in
contrast, collide far more often with the graphene lattice to impart
significantly higher sputter yield of ~50%. Binary collision theory applied to
monolayer and few-layer graphene can successfully elucidate this collision
mechanism, in great agreement with experiments. Raman spectroscopy analysis
corroborates the passage of a large fraction of He+ ions across graphene
without much damaging the lattice whereas several colliding ions create single
vacancy defects. Physical understanding of the interaction between energetic
particles and suspended graphene can practically lead to reproducible and
efficient pattern generation of unprecedentedly small features on 2D materials
by design, manifested by our perforation of sub-5-nm pore arrays. This
capability of nanometer scale precision patterning of freestanding 2D lattices
shows practical applicability of the focused ion beam technology to 2D material
processing for device fabrication and integration.Comment: 31 pages of main text (with 4 figures) plus 4 pages of supporting
information (with 2 figures). Original article submitted to a journal for
consideration for publicatio
Linear Relaxation Processes Governed by Fractional Symmetric Kinetic Equations
We get fractional symmetric Fokker - Planck and Einstein - Smoluchowski
kinetic equations, which describe evolution of the systems influenced by
stochastic forces distributed with stable probability laws. These equations
generalize known kinetic equations of the Brownian motion theory and contain
symmetric fractional derivatives over velocity and space, respectively. With
the help of these equations we study analytically the processes of linear
relaxation in a force - free case and for linear oscillator. For a weakly
damped oscillator we also get kinetic equation for the distribution in slow
variables. Linear relaxation processes are also studied numerically by solving
corresponding Langevin equations with the source which is a discrete - time
approximation to a white Levy noise. Numerical and analytical results agree
quantitatively.Comment: 30 pages, LaTeX, 13 figures PostScrip
Holder exponents of irregular signals and local fractional derivatives
It has been recognized recently that fractional calculus is useful for
handling scaling structures and processes. We begin this survey by pointing out
the relevance of the subject to physical situations. Then the essential
definitions and formulae from fractional calculus are summarized and their
immediate use in the study of scaling in physical systems is given. This is
followed by a brief summary of classical results. The main theme of the review
rests on the notion of local fractional derivatives. There is a direct
connection between local fractional differentiability properties and the
dimensions/ local Holder exponents of nowhere differentiable functions. It is
argued that local fractional derivatives provide a powerful tool to analyse the
pointwise behaviour of irregular signals and functions.Comment: 20 pages, Late
Incubating Isolated Mouse EDL Muscles with Creatine Improves Force Production and Twitch Kinetics in Fatigue Due to Reduction in Ionic Strength
Creatine supplementation can improve performance during high intensity exercise in humans and improve muscle strength in certain myopathies. In this present study, we investigated the direct effects of acute creatine incubation on isolated mouse fast-twitch EDL muscles, and examined how these effects change with fatigue. muscle from mice aged 12–14 weeks was isolated and stimulated with field electrodes to measure force characteristics in 3 different states: (i) before fatigue; (ii) immediately after a fatigue protocol; and (iii) after recovery. These served as the control measurements for the muscle. The muscle was then incubated in a creatine solution and washed. The measurement of force characteristics in the 3 different states was then repeated. In un-fatigued muscle, creatine incubation increased the maximal tetanic force. In fatigued muscle, creatine treatment increased the force produced at all frequencies of stimulation. Incubation also increased the rate of twitch relaxation and twitch contraction in fatigued muscle. During repetitive fatiguing stimulation, creatine-treated muscles took 55.1±9.5% longer than control muscles to lose half of their original force. Measurement of weight changes showed that creatine incubation increased EDL muscle mass by 7%. sensitivity of contractile proteins as a result of ionic strength decreases following creatine incubation
Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan
Understanding the interaction between energetic ions and freestanding graphene towards practical 2D perforation
We report experimentally and theoretically the behavior of freestanding graphene subject to bombardment of energetic ions, investigating the ability of large-scale patterning of freestanding graphene with nanometer sized features by focused ion beam technology. A precise control over the He+ and Ga+ irradiation offered by focused ion beam techniques enables to investigate the interaction of the energetic particles and graphene suspended with no support and allows determining sputter yields of the 2D lattice. We find strong dependency of the 2D sputter yield on the species and kinetic energy of the incident ion beams. Freestanding graphene shows material semi-transparency to He+ at high energies (10-30 keV) allowing the passage of >97% He+ particles without creating destructive lattice vacancy. Large Ga+ ions (5-30 keV), in contrast, collide far more often with the graphene lattice to impart significantly higher sputter yield of ~50%. Binary collision theory applied to monolayer and few-layer graphene can successfully elucidate this collision mechanism, in great agreement with experiments. Raman spectroscopy analysis corroborates the passage of a large fraction of He+ ions across graphene without much damaging the lattice whereas several colliding ions create single vacancy defects. Physical understanding of the interaction between energetic particles and suspended graphene can practically lead to reproducible and efficient pattern generation of unprecedentedly small features on 2D materials by design, manifested by our perforation of sub-5-nm pore arrays. This capability of nanometer scale precision patterning of freestanding 2D lattices shows practical applicability of the focused ion beam technology to 2D material processing for device fabrication and integration
Multifunctional wafer-scale graphene membranes for fast ultrafiltration and high permeation gas separation
Reliable and large-scale manufacturing routes for perforated graphene membranes in separation and filtration remain challenging. We introduce two manufacturing pathways for the fabrication of highly porous, perforated graphene membranes with sub–100-nm pores, suitable for ultrafiltration and as a two-dimensional (2D) scaffold for synthesizing ultrathin, gas-selective polymers. The two complementary processes—bottom up and top down—enable perforated graphene membranes with desired layer number and allow ultrafiltration applications with liquid permeances up to 5.55 × 10−8 m3 s−1 Pa−1 m−2. Moreover, thin-film polymers fabricated via vapor-liquid interfacial polymerization on these perforated graphene membranes constitute gas-selective polyimide graphene membranes as thin as 20 nm with superior permeances. The methods of controlled, simple, and reliable graphene perforation on wafer scale along with vapor-liquid polymerization allow the expansion of current 2D membrane technology to high-performance ultrafiltration and 2D material reinforced, gas-selective thin-film polymers.ISSN:2375-254
Freestanding and Permeable Nanoporous Gold Membranes for Surface-Enhanced Raman Scattering
Surface-enhanced Raman spectroscopy (SERS) demands reliable, high enhancement substrates in order to be used in different fields of application. Here, we introduce freestanding porous gold membranes (PAuM) as easy to produce, scalable, mechanically stable, and effective SERS substrates. We fabricate large-scale sub-30 thick PAuM, that form freestanding membranes with varying morphologies depending on the nominal gold thickness. These PAuM are mechanically stable for pressures up to >3 bar, and exhibit surface-enhanced Raman scattering with local enhancement factors of 104 to 105, which we demonstrate by wavelength-dependent and spatially resolved Raman measurements using graphene as a local Raman probe. Numerical simulations reveal that the enhancement arises from individual, nanoscale pores in the membrane acting as optical slot antennas. Our PAuM are mechanically stable, provide robust SERS enhancement for excitation power densities up to 106Wcm−2, and may find use as a building block in flow-through sensor applications based on SERS
Freestanding and Permeable Nanoporous Gold Membranes for Surface-Enhanced Raman Scattering
Surface-enhanced Raman spectroscopy (SERS) demands reliable, high enhancement substrates in order to be used in different fields of application. Here, we introduce freestanding porous gold membranes (PAuM) as easy to produce, scalable, mechanically stable, and effective SERS substrates. We fabricate large-scale sub-30 thick PAuM, that form freestanding membranes with varying morphologies depending on the nominal gold thickness. These PAuM are mechanically stable for pressures up to >3 bar, and exhibit surface-enhanced Raman scattering with local enhancement factors of 104 to 105, which we demonstrate by wavelength-dependent and spatially resolved Raman measurements using graphene as a local Raman probe. Numerical simulations reveal that the enhancement arises from individual, nanoscale pores in the membrane acting as optical slot antennas. Our PAuM are mechanically stable, provide robust SERS enhancement for excitation power densities up to 106Wcm−2, and may find use as a building block in flow-through sensor applications based on SERS
Freestanding and Permeable Nanoporous Gold Membranes for Surface-Enhanced Raman Scattering
Surface-enhanced Raman spectroscopy (SERS) demands reliable, high-enhancement substrates in order to be used in different fields of application. Here we introduce freestanding porous gold membranes (PAuM) as easy-to-produce, scalable, mechanically stable, and effective SERS substrates. We fabricate large-scale sub-30 nm thick PAuM that form freestanding membranes with varying morphologies depending on the nominal gold thickness. These PAuM are mechanically stable for pressures up to more than 3 bar and exhibit surface-enhanced Raman scattering with local enhancement factors from 104 to 105 , which we demonstrate by wavelength-dependent and spatially resolved Raman measurements using graphene as a local Raman probe. Numerical simulations reveal that the enhancement arises from individual, nanoscale pores in the membrane acting as optical slot antennas. Our PAuM are mechanically stable, provide robust SERS enhancement for excitation power densities up to 106 W cm−2 , and may find use as a building block in SERS-based sensing applications.ISSN:1944-8244ISSN:1944-825