3,283 research outputs found
Enhanced Raman and photoluminescence response in monolayer MoS due to laser healing of defects
Bound quasiparticles, negatively charged trions and neutral excitons, are
associated with the direct optical transitions at the K-points of the Brillouin
zone for monolayer MoS. The change in the carrier concentration,
surrounding dielectric constant and defect concentration can modulate the
photoluminescence and Raman spectra. Here we show that exposing the monolayer
MoS in air to a modest laser intensity for a brief period of time enhances
simultaneously the photoluminescence (PL) intensity associated with both trions
and excitons, together with 3 to 5 times increase of the Raman intensity
of first and second order modes. The simultaneous increase of PL from trions
and excitons cannot be understood based only on known-scenario of depletion of
electron concentration in MoS by adsorption of O and HO molecules.
This is explained by laser induced healing of defect states resulting in
reduction of non-radiative Auger processes. This laser healing is corroborated
by an observed increase of intensity of both the first order and second order
2LA(M) Raman modes by a factor of 3 to 5. The A mode hardens by
1.4 cm whereas the E mode softens by 1 cm.
The second order 2LA(M) Raman mode at 440 cm shows an increase in
wavenumber by 8 cm with laser exposure. These changes are a
combined effect of change in electron concentrations and oxygen-induced lattice
displacements.Comment: 15 pages, 5 figures, Journal of Raman Spectroscopy, 201
Structure of Carbon Nanotube-dendrimer composite
Using all atomistic molecular dynamics (MD) simulations we report the
microscopic picture of the nanotube-dendrimer complex for PAMAM dendrimer of
generation 2 to 4 and carbon nanotube of chirality (6,5). We find compact
wrapping conformations of dendrimer onto the nanotube surface for all the three
generations of PAMAM dendrimer. The degree of wrapping is more for
non-protonated dendrimer compared to the protonated dendrimer. For comparison
we also study the interaction of another dendrimer, poly(propyl ether imine)
(PETIM), with nanotube and show that PAMAM dendrimer interacts strongly as
compared to PETIM dendrimer as is evident from the distance of closest approach
as well as the number of close contacts between the nanotube and dendrimer. We
also calculate the binding energy between the nanotube and the dendrimer using
MM/PBSA methods and attribute the strong binding to the charge transfer between
them. Dendrimer wrapping on CNT will make it soluble and can act as an
efficient dispersing agent for nanotube
Pneumothorax and Pneumomediastinum in a Sputum Positive Tuberculosis Patient: The Continuous Diaphragm Sign
Secondary pneumothorax is a very common medical emergency. At times it is associated with pneumomediastinum, which could be fatal at times if not identified. We present a case of a 11 years old sputum positive child who presented with both these conditions and was diagnosed on chest x ray
Symmetry-dependent phonon renormalization in monolayer MoS2 transistor
Strong electron-phonon interaction which limits electronic mobility of
semiconductors can also have significant effects on phonon frequencies. The
latter is the key to the use of Raman spectroscopy for nondestructive
characterization of doping in graphene-based devices. Using in-situ Raman
scattering from single layer MoS electrochemically top-gated field effect
transistor (FET), we show softening and broadening of A phonon with
electron doping whereas the other Raman active E mode remains
essentially inert. Confirming these results with first-principles density
functional theory based calculations, we use group theoretical arguments to
explain why A mode specifically exhibits a strong sensitivity to
electron doping. Our work opens up the use of Raman spectroscopy in probing the
level of doping in single layer MoS-based FETs, which have a high on-off
ratio and are of enormous technological significance.Comment: 5 pages, 3 figure
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Radiation induced lichen planus - an uncommon side effect
Cutaneous lichen planus is classically characterized by violaceous, pruritic, planar papules and plaques, most commonly affecting the extremities. Lichen planus following radiation therapy is extremely rare and lichen planus following radiation therapy for prostate carcinoma has not been previously reported in the literature. We report a 66-year-old man who presented to the dermatology clinic with a symmetric pruritic eruption affecting the pelvic and gluteal region within two months of radiation therapy targeting the prostate and pelvic lymph nodes for prostate adenocarcinoma. The patient did not have a prior history of lichen planus. Physical examination demonstrated well demarcated, violaceous papules and plaques in a circumferential band-like distribution on the bilateral gluteal, lumbosacral, and pelvic region. In addition, he had a few discrete lesions on the calves and dorsal feet. Punch biopsy revealed an acanthotic epidermis with "saw-tooth" rete ridges and a lichenoid inflammatory infiltrate. A diagnosis of hypertrophic lichen planus was made, reinforcing the importance for clinicians to recognize radiation therapy as a risk factor for developing lichen planus despite no prior history of lichen planus
Sharp Raman Anomalies and Broken Adiabaticity at a Pressure Induced Transition from Band to Topological Insulator in Sb2Se3
The nontrivial electronic topology of a topological insulator is thus far
known to display signatures in a robust metallic state at the surface. Here, we
establish vibrational anomalies in Raman spectra of the bulk that signify
changes in electronic topology: an E2 g phonon softens unusually and its
linewidth exhibits an asymmetric peak at the pressure induced electronic
topological transition (ETT) in Sb2Se3 crystal. Our first-principles
calculations confirm the electronic transition from band to topological
insulating state with reversal of parity of electronic bands passing through a
metallic state at the ETT, but do not capture the phonon anomalies which
involve breakdown of adiabatic approximation due to strongly coupled dynamics
of phonons and electrons. Treating this within a four-band model of topological
insulators, we elucidate how nonadiabatic renormalization of phonons
constitutes readily measurable bulk signatures of an ETT, which will facilitate
efforts to develop topological insulators by modifying a band insulator
Ageusia associated to treatment with amitriptyline and terbinafine
Ageusia is a rare condition characterized by loss of taste functions of the tongue.A large number of conditions may be responsible for causing ageusia. Adverseeffects of drug therapy are the most common cause for the loss of taste. Ageusiacan have a significant effect on the quality of life of patients and can lead to lossof appetite, weight, and may require discontinuation of drug administration inalready compromised patients. We present two cases of ageusia one associated withamitriptyline in a patient with endogenous depression and the other with terbinafinein patient with tinea unguium
Raman anomalies as signatures of pressure induced electronic topological and structural transitions in black phosphorus: Experiments and Theory
We report high pressure Raman experiments of Black phosphorus up to 24 GPa.
The line widths of first order Raman modes A, B and A of the
orthorhombic phase show a minimum at 1.1 GPa. Our first-principles density
functional analysis reveals that this is associated with the anomalies in
electron-phonon coupling at the semiconductor to topological insulator
transition through inversion of valence and conduction bands marking a change
from trivial to nontrivial electronic topology. The frequencies of B and
A modes become anomalous in the rhombohedral phase at 7.4 GPa, and new
modes appearing in the rhombohedral phase show anomalous softening with
pressure. This is shown to originate from unusual structural evolution of black
phosphorous with pressure, based on first-principles theoretical analysis.Comment: 13pages, 12figure
Phonon Anomalies, Orbital-Ordering and Electronic Raman Scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: Temperature-dependent Raman Study
We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a
wide spectral range of 120-5200 cm-1 from 5K to 300K, covering the tetragonal
to orthorhombic structural transition as well as magnetic transition at Tsm ~
160K. The mode frequencies of two first-order Raman modes B1g and Eg, both
involving displacement of Fe atoms, show sharp increase below Tsm.
Concomitantly, the linewidths of all the first-order Raman modes show anomalous
broadening below Tsm, attributed to strong spin-phonon coupling. The high
frequency modes observed between 400-1200 cm-1 are attributed to the electronic
Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The
splitting between xz and yz d-orbital levels is shown to be ~ 25 meV which
increases as temperature decreases below Tsm. A broad Raman band observed at ~
3200 cm-1 is assigned to two-magnon excitation of the itinerant Fe 3d
antiferromagnet.Comment: Accepted for Publication in JPC
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