Intrinsic carrier mobility of multi-layered MoS2_2 field-effect transistors on SiO2_2

By fabricating and characterizing multi-layered MoS$_2$-based field-effect transistors (FETs) in a four terminal configuration, we demonstrate that the two terminal-configurations tend to underestimate the carrier mobility $\mu$ due to the Schottky barriers at the contacts. For a back-gated two-terminal configuration we observe mobilities as high as 125 cm$^2$V$^{-1}$s$^{-1}$ which is considerably smaller than 306.5 cm$^2$V$^{-1}$s$^{-1}$ as extracted from the same device when using a four-terminal configuration. This indicates that the intrinsic mobility of MoS$_2$ on SiO$_2$ 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

Epley’s maneuver versus Semont’s maneuver in treatment of posterior canal benign positional paroxysmal vertigo

Background: Benign paroxysmal positional vertigo (BPPV) is characterized by brief but violent attacks of paroxysmal vertigo provoked by certain positions of the head. BPPV is the most common cause of vertigo, resulting from migration of otoconia into the semicircular canals. Majority of patients have posterior canal BPPV. Epley’s Canalith Repositioning and Semont Liberatory Maneuver have been shown to be highly efficacious in the successfultreatment of posterior canal BPPV. The main objective of this study was to compare the efficacy of Epley’s maneuver versus Semont’s maneuver in the management of benign paroxysmal positional vertigo.Methods: This study was conducted in the Department of Otorhinolaryngology of a rural Medical College in Kerala, for a period of one and half year, from January 2015 to June 2016. It was an observational prospective cohort study. 200 patients with posterior canal BPPV were enrolled in this study based on inclusion and exclusion criteria. Patients were allotted alternatively to Epley’s group and Semont’s group, 100 patients in each group based on the treatment maneuvers they underwent. Efficacy of maneuvers were assessed at the end of 1st week, 1st month and 3rd month on the basis of resolution of symptoms and Dix-Hallpike negativity.Results: Of the 100 cases managed by Epley’s maneuver 95 cases showed complete relief of symptoms after 3 months. Out of 100 cases managed by Semont’s maneuver, 94 cases showed complete recovery after 3 months. The results were compared by Chi square test, as the data was mainly qualitative in nature. The results of both the groups were compared at the end of 1st week, 1st month and 3rd month, which revealed that both the Semont’s and Epley’s maneuver are equally effective in the treatment of posterior canal BPPV.Conclusions: Both Epley’s and Semont’s maneuver are equally effective for treating the patients of posterior canal benign paroxysmal positional vertigo

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 $\omega_0$ 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 $L_{E}$ possibly characterizing the distance between tube contacts, which is found to systematically decrease with increasing film thickness. The onset frequency $\omega_0$ of ac conductivity and the length scale $L_{E}$ 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.

Square selenene and tellurene: novel group VI elemental 2D materials with nontrivial topological properties

With first principles calculations, we predict a novel stable 2D layered structure for group VI elements Se and Te that we call square selenene and square tellurene, respectively. They have chair-like buckled structures similar to other layered materials such as silicene and germanene but with a square unit cell rather than a hexagonal one. This special structure gives rise to anisotropic band dispersions near the Fermi level that can be described by a generalized semi-Dirac Hamiltonian. We show that the considerably large band gap (~0.1 eV) opened by spin-orbit coupling makes square selenene and tellurene topological insulators, hosting non-trivial edge states. Therefore, square selenene and tellurene are promising materials for novel electronic and spintronic applications. Finally, we show that this new type of 2D elemental materials can potentially be grown on proper substrates, such as a Au(1 0 0) surface

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

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

Fluorinated graphene oxide for enhanced S and X-band microwave absorption

Here we report the microwave absorbing properties of three graphene derivatives, namely, graphene oxide (GO), fluorinated GO (FGO, containing 5.6 at. % Fluorine (F)), and highly FGO (HFGO, containing 23 at. % F). FGO is known to be exhibiting improved electrochemical and electronic properties when compared to GO. Fluorination modifies the dielectric properties of GO and hence thought of as a good microwave absorber. The dielectric permittivities of GO, FGO, and HFGO were estimated in the S (2 GHz to 4 GHz) and X (8 GHz to 12 GHz) bands by employing cavity perturbation technique. For this, suspensions containing GO/FGO/HFGO were made in N-Methyl Pyrrolidone (NMP) and were subjected to cavity perturbation. The reflection loss was then estimated and it was found that −37 dB (at 3.2 GHz with 6.5 mm thickness) and −31 dB (at 2.8 GHz with 6 mm thickness) in the S band and a reflection loss of −18 dB (at 8.4 GHz with 2.5 mm thickness) and −10 dB (at 11 GHz with 2 mm thickness) in the X band were achieved for 0.01 wt. % of FGO and HFGO in NMP, respectively, suggesting that these materials can serve as efficient microwave absorbers even at low concentrations

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