Two-dimensional (2D) materials are a new type of materials under intense study because of their interesting physical properties and wide range of potential applications from nanoelectronics to sensing and photonics. Monolayers of semiconducting transition metal dichalcogenides MoS2 or WSe2 have been proposed as promising channel materials for field-effect transistors. Their high mechanical flexibility, stability, and quality coupled with potentially inexpensive production methods offer potential advantages compared to organic and crystalline bulk semiconductors. Due to quantum mechanical confinement, the band gap in monolayer MoS2 is direct in nature, leading to a strong interaction with light that can be exploited for building phototransistors and ultrasensitive photodetectors. Here, we report on the realization of light-emitting diodes based on vertical heterojunctions composed of n-type monolayer MoS2 and p-type silicon. Careful interface engineering allows us to realize diodes showing rectification and light emission from the entire surface of the heterojunction. Electroluminescence spectra show clear signs of direct excitons related to the optical transitions between the conduction and valence bands. Our p–n diodes can also operate as solar cells, with typical external quantum efficiency exceeding 4%. Our work opens up the way to more sophisticated optoelectronic devices such as lasers and heterostructure solar cells based on hybrids of 2D semiconductors and silicon.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-004565.pdf

Light Generation and Harvesting in a Van der Waals Heterostructure

Recent advances in eco-friendly and cost-effective materials towards sustainable dye-sensitized solar cells

The dissipated power and the directivity of antennas in a homogeneous, lossy
medium are systematically analyzed in this paper. The antennas are ideal
and located inside a lossless sphere. In the lossy space outside the sphere, the
electromagnetic ﬁelds are expanded in a complete set of vector wave functions.
The optimal values of the radiation eﬃciency, the directivity, as well as the
power gain are derived.

Physical limitations of antennas in a lossy medium

We investigate Atomic Layer Deposition (ALD) of metal oxide on pristine and functionalized graphene. On pristine graphene, ALD coating can only actively grow on edges and defect sites, where dangling bonds or surface groups react with ALD precursors. This affords a simple method to decorate and probe single defect sites in graphene planes. We used perylene tetracarboxylic acid (PTCA) to functionalize graphene surface and selectively introduced densely packed surface groups on graphene. Uniform ultrathin ALD coating on PTCA graphene was achieved over large area. The functionalization method could be used to integrate ultrathin high-k dielectrics in future graphene electronics.

Atomic Layer Deposition of Metal Oxides on Pristine and Functionalized Graphene

Nickel-manganese phosphate: An efficient battery-grade electrode for supercapattery devices

A theoretical study is presented for the feasibility of a microwave heating device that will raise the temperature of heavy oil and bitumen reservoir. The device is enclosed in a radome which is surrounded by a perforated metal pipe. Outside the pipe is occupied by a mixture of heavy oil and calcite. Various dielectric properties are assumed for the radome and the calcite region. Analytical and numerical results are presented for the temperature rise around the pipe.

Microwave heating of heavy oil and bitumen

Charge carrier modulation of graphene-based field effect transistors (GFETs) is the key factor to utilize and enhance its fascinating properties for technological applicability. Here, we have demonstrated the gate-dependent tweaking of electrical properties of graphene devices by application of honey as a top gate dielectric. Electrical characterization of dual-gated GFET is elucidated at different top and back-gate voltages. A charge neutrality point is fine-tuned by varying the top gate voltage (Vtg) from + 3 to − 4 V. The change in carrier density is clearly observed from 3.66 × 1012 to 2.15 × 1011 cm−2 at + 3 to − 4 Vtg. The charge carrier mobility of gel-gated GFET is increased significantly to 5376 cm2/V ⋅ sec by increasing top-gate voltages up to − 4 V. Result demonstrates a cost-effective, facile and rapid fabrication of top-gated devices and suggest natural dielectric materials as good candidate to replace conventionally available gate dielectrics in FET technology.

Charge carrier modulation in dual-gated graphene field effect transistor using honey as polar organic gate dielectric

A numerical study is presented for the compensation of mutual coupling in antenna arrays. A Matlab code based on method of moments is used to find the compensated far field radiation patterns for non-identical and/or staggered wire antenna arrays. The isolated patterns for some antenna arrays when applicable are found using the principle of pattern multiplication which are used to predict the compensated patterns.

Compensation for the mutual coupling in transmitting antenna arrays

This paper presents a numerical technique for the compensation of mutual coupling in transmitting arrays of thin wire antennas. The Method of Moments is used to compute the scattering parameters of the array. Using these parameters and the original excitations, a set of new excitation values are computed. The new excitation values compensate the effect of the mutual coupling. Computed results are given for linear, circular, and 3-Dimensional arrays. Uniform and binomial excitations are studied. Results obtained are compared with other available data and very good agreement is observed.

Mutual coupling compensation in transmitting arrays of thin wire antennas

Mutual coupling is compensated in a four element uniform linear receiving array using software defined radios. Direction of arrival (DoA) is estimated in real-time for the array with spacing $d=\lambda/4$ . The decoupling matrix was measured using a VNA for only one incident angle. After compensation the error in DoA estimation was reduced to 5%. Comparing the DoA results with $d=\lambda/2$ spaced Uniform Linear Array (ULA), 1.2% error was observed. Although, the experiment was performed indoors with a low SNR, the results show a substantial improvement in the estimated DoA after compensation.

Sana Khan

Papers

Microwave heating of heavy oil and bitumen

Charge carrier modulation in dual-gated graphene field effect transistor using honey as polar organic gate dielectric

Compensation for the mutual coupling in transmitting antenna arrays

Mutual coupling compensation in transmitting arrays of thin wire antennas

Mutual Coupling Compensation in Receiving Arrays and Its Implementation on Software Defined Radios