54 research outputs found
On the diffraction pattern of C60 peapods
We present detailed calculations of the diffraction pattern of a powder of
bundles of C peapods. The influence of all pertinent structural
parameters of the bundles on the diffraction diagram is discussed, which should
lead to a better interpretation of X-ray and neutron diffraction diagrams. We
illustrate our formalism for X-ray scattering experiments performed on peapod
samples synthesized from 2 different technics, which present different
structural parameters. We propose and test different criteria to solve the
difficult problem of the filling rate determination.Comment: Sumitted 19 May 200
Anharmonicity in Raman-active phonon modes in atomically thin MoS
Phonon-phonon anharmonic effects have a strong influence on the phonon
spectrum; most prominent manifestation of these effects are the softening
(shift in frequency) and broadening (change in FWHM) of the phonon modes at
finite temperature. Using Raman spectroscopy, we studied the temperature
dependence of the FWHM and Raman shift of and
modes for single-layer and natural bilayer MoS over a
broad range of temperatures (T K). Both the Raman shift and FWHM
of these modes show linear temperature dependence for K, whereas they
become independent of temperature for K. Using first-principles
calculations, we show that three-phonon anharmonic effects intrinsic to the
material can account for the observed temperature-dependence of the line-width
of both the modes. It also plays an important role in determining the
temperature-dependence of the frequency of the Raman modes. The observed
evolution of the line-width of the A mode suggests that electron-phonon
processes are additionally involved. From the analysis of the
temperature-dependent Raman spectra of MoS on two different substrates --
SiO and hexagonal boron nitride, we disentangle the contributions of
external stress and internal impurities to these phonon-related processes. We
find that the renormalization of the phonon mode frequencies on different
substrates is governed by strain and intrinsic doping. Our work establishes the
role of intrinsic phonon anharmonic effects in deciding the Raman shift in
MoS irrespective of substrate and layer number
Local Optical Probe of Motion and Stress in a multilayer graphene NEMS
Nanoelectromechanical systems (NEMSs) are emerging nanoscale elements at the
crossroads between mechanics, optics and electronics, with significant
potential for actuation and sensing applications. The reduction of dimensions
compared to their micronic counterparts brings new effects including
sensitivity to very low mass, resonant frequencies in the radiofrequency range,
mechanical non-linearities and observation of quantum mechanical effects. An
important issue of NEMS is the understanding of fundamental physical properties
conditioning dissipation mechanisms, known to limit mechanical quality factors
and to induce aging due to material degradation. There is a need for detection
methods tailored for these systems which allow probing motion and stress at the
nanometer scale. Here, we show a non-invasive local optical probe for the
quantitative measurement of motion and stress within a multilayer graphene NEMS
provided by a combination of Fizeau interferences, Raman spectroscopy and
electrostatically actuated mirror. Interferometry provides a calibrated
measurement of the motion, resulting from an actuation ranging from a
quasi-static load up to the mechanical resonance while Raman spectroscopy
allows a purely spectral detection of mechanical resonance at the nanoscale.
Such spectroscopic detection reveals the coupling between a strained
nano-resonator and the energy of an inelastically scattered photon, and thus
offers a new approach for optomechanics
On the efficiency of bile salt for stable suspension and isolation of single-walled carbon nanotubes—spectroscopic and microscopic investigations
Volumetric Properties of the Mixture Chlorobenzene C6H5Cl + C6H12 Cyclohexane (LB2859, VMSD1212)
Volumetric Properties of the Mixture Chlorobenzene C6H5Cl + C6H12 Cyclohexane (LB2857, VMSD1111)
Volumetric Properties of the Mixture Heptane C7H16 + C8H18 2,2,4-Trimethylpentane (LB2861, VMSD1212)
Complexation of Pb(II) by Chloride Ions in Aqueous Solutions
Lead chloride formation constants at 25°C were derived from analysis of previous spectrophotometrically generated observations of lead speciation in a variety of aqueous solutions (HClO4–HCl and NaCl–NaClO4 mixtures, and solutions of MgCl2 and CaCl2). Specific interaction theory analysis of these formation constants produced coherent estimates of (a) PbCl+, PbCl20, and PbCl −3 formation constants at zero ionic strength, and (b) well-defined depictions of the dependence of these formation constants on ionic strength. Accompanying examination of a recent IUPAC critical assessment of lead formation constants, in conjunction with the spectrophotometrically generated formation constants presented in this study, revealed significant differences among various subsets of the IUPAC critically selected data. It was found that these differences could be substantially reduced through reanalysis of the formation constant data of one of the subsets. The resulting revised lead chloride formation constants are in good agreement with the formation constants derived from the earlier spectrophotometrically generated data. Combining these data sets provides an improved characterization of lead chloride complexation over a wide range of ionic strengths
Evolution of inter-layer coupling in artificially stacked bilayer MoS 2
International audienceIn this paper, we show experimentally that for van der Waals heterostructures (vdWh) of atomically-thin materials, the hybridization of bands of adjacent layers is possible only for ultra-clean interfaces. This we achieve through a detailed experimental study of the effect of interfacial separation and adsorbate content on the photoluminescence emission and Raman spectra of ultra-thin vdWh. For vdWh with atomically-clean interfaces, we find the emergence of novel vibrational Raman-active modes whose optical signatures differ significantly from that of the constituent layers. Additionally, we find for such systems a significant modification of the photoluminescence emission spectra with the appearance of peaks whose strength and intensity directly correlate with the inter-layer coupling strength. Our ability to control the intensity of the photoluminescence emission led to the observation of detailed optical features like indirect-band peaks. Our study establishes that it is possible to engineer atomically-thin van der Waals heterostructures with desired optical properties by controlling the inter-layer spacing, and consequently the inter-layer coupling between the constituent layers
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