1,133 research outputs found
Intrinsic carrier mobility of multi-layered MoS field-effect transistors on SiO
By fabricating and characterizing multi-layered MoS-based field-effect
transistors (FETs) in a four terminal configuration, we demonstrate that the
two terminal-configurations tend to underestimate the carrier mobility
due to the Schottky barriers at the contacts. For a back-gated two-terminal
configuration we observe mobilities as high as 125 cmVs which
is considerably smaller than 306.5 cmVs as extracted from the
same device when using a four-terminal configuration. This indicates that the
intrinsic mobility of MoS on SiO is significantly larger than the
values previously reported, and provides a quantitative method to evaluate the
charge transport through the contacts.Comment: 8 pages, 5 figures, typos fixed, and references update
Frequency- and electric-field-dependent conductivity of single-walled carbon nanotube networks of varying density
We present measurements of the frequency and electric field dependent
conductivity of single walled carbon nanotube(SWCNT) networks of various
densities. The ac conductivity as a function of frequency is consistent with
the extended pair approximation model and increases with frequency above an
onset frequency which varies over seven decades with a range of film
thickness from sub-monolayer to 200 nm. The nonlinear electric field-dependent
DC conductivity shows strong dependence on film thickness as well. Measurement
of the electric field dependence of the resistance R(E) allows for the
determination of a length scale possibly characterizing the distance
between tube contacts, which is found to systematically decrease with
increasing film thickness. The onset frequency of ac conductivity
and the length scale of SWCNT networks are found to be correlated, and
a physically reasonable empirical formula relating them has been proposed. Such
studies will help the understanding of transport properties and benefit the
applications of this material system.Comment: 7 pages and 6 figure
A study on the effect of adenoidectomy with tonsillectomy in otitis media with effusion in children
Background: The aural symptoms attributed to adenoid hypertrophy are Eustachian tube block (ET) and otitis media with effusion (OME). It is thought that adenoid hypertrophy causes a block in air flow through the ET, thus creating a negative pressure in the middle ear leading to effusion which acts as a focus of infection. The role of hypertrophied tonsils in the aetiology of OME is controversial. Adenoid and tonsillar hypertrophy and associated inflammation continue to be a major problem in paediatric age group despite the advances in medicine. Otitis media with effusion is a treatable cause of deafness which may hamper the learning ability of a child. This study was undertaken to study the effect of adenoidectomy with tonsillectomy on established otitis media with effusion in children.Methods: 35 children presenting to the department of ENT, Government Medical College, Thrissur, Kerala, India over one and a half years with features suggestive of secretory otitis media, tonsillar and adenoid hypertrophy who underwent adenoidectomy with tonsillectomy in Government Medical College, Thrissur, Kerala, India were included in the study. A predesigned questionnaire was prepared which included details on clinical symptoms, relevant investigations and preoperative and postoperative evaluation of hearing after 6 weeks and 3 months. Data collected was analyzed using paired t-test and chi square test to determine the improvement in hearing after 6 weeks and 3 months following surgery.Results: Out of the 35 children included in the study, it was seen that 56% of cases, after 6 weeks showed complete resolution of OME which improved to 67% after 3 months. This was assessed by PTA and tympanometry. 33% showed partial improvement with Type C curve in tympanometry and improvement in PTA values.Conclusions: All cases of OME associated with adenoid and tonsillar hypertrophy responded to our treatment with 67% showing complete cure of the condition. It can be assumed that, in the 33% partial responders there may be other factors like allergy, anatomical deformities, immunological which prevented the complete resolution of symptoms in OME.
Submicrometer Dimple Array Based Interference Color Field Displays and Sensors
We report a technique for producing bright color fields over extended surfaces, via optical interference, with the capability of producing arbitrary visible colors in areas as small as 100 μm^2. Periodic arrays of submicrometer dimples are fabricated on reflective silicon surfaces, and diffraction-induced mutual interference of light reflected from the upper and lower levels of the dimpled surfaces generates color depending on wavelength scaled dimple depth and periodicity. Colors of the entire visible spectrum can be generated by dimple arrays with different dimple depths. The topological permeability of such an open surface readily allows infusion of liquids, with different refractive indices, for color switching and detection. These easy to fabricate, scalable, robust devices, on solid as well as flexible supports, could find a wide range of applications such as cheap high-resolution printable dye/pigment-free displays, reliable index-of-refraction sensors with color readout for liquids, and lab-on-chip liquid flow monitors
Spontaneous alloying in binary metal microclusters - A molecular dynamics study -
Microcanonical molecular dynamics study of the spontaneous alloying(SA),
which is a manifestation of fast atomic diffusion in a nano-sized metal
cluster, is done in terms of a simple two dimensional binary Morse model.
Important features observed by Yasuda and Mori are well reproduced in our
simulation. The temperature dependence and size dependence of the SA phenomena
are extensively explored by examining long time dynamics. The dominant role of
negative heat of solution in completing the SA is also discussed. We point out
that a presence of melting surface induces the diffusion of core atoms even if
they are solid-like. In other words, the {\it surface melting} at substantially
low temperature plays a key role in attaining the SA.Comment: 15 pages, 12 fgures, Submitted to Phys.Rev.
Identification of Electron Donor States in N-doped Carbon Nanotubes
Nitrogen doped carbon nanotubes have been synthesized using pyrolysis and
characterized by Scanning Tunneling Spectroscopy and transmission electron
microscopy. The doped nanotubes are all metallic and exhibit strong electron
donor states near the Fermi level. Using tight-binding and ab initio
calculations, we observe that pyridine-like N structures are responsible for
the metallic behavior and the prominent features near the Fermi level. These
electron rich structures are the first example of n-type nanotubes, which could
pave the way to real molecular hetero-junction devices.Comment: 5 pages, 4 figures, revtex, submitted to PR
Blue shifting of the A exciton peak in folded monolayer 1H-MoS2
The large family of layered transition-metal dichalcogenides is widely
believed to constitute a second family of two-dimensional (2D) semiconducting
materials that can be used to create novel devices that complement those based
on graphene. In many cases these materials have shown a transition from an
indirect bandgap in the bulk to a direct bandgap in monolayer systems. In this
work we experimentally show that folding a 1H molybdenum disulphide (MoS2)
layer results in a turbostratic stack with enhanced photoluminescence quantum
yield and a significant shift to the blue by 90 meV. This is in contrast to the
expected 2H-MoS2 band structure characteristics, which include an indirect gap
and quenched photoluminescence. We present a theoretical explanation to the
origin of this behavior in terms of exciton screening.Comment: 16 pages, 8 figure
Bundling up carbon nanotubes through Wigner defects
We show, using ab initio total energy density functional theory, that the
so-called Wigner defects, an interstitial carbon atom right besides a vacancy,
which are present in irradiated graphite can also exist in bundles of carbon
nanotubes. Due to the geometrical structure of a nanotube, however, this defect
has a rather low formation energy, lower than the vacancy itself, suggesting
that it may be one of the most important defects that are created after
electron or ion irradiation. Moreover, they form a strong link between the
nanotubes in bundles, increasing their shear modulus by a sizeable amount,
clearly indicating its importance for the mechanical properties of nanotube
bundles.Comment: 5 pages and 4 figure
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