A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

/pdf/projector-augmented-wave-method-an-introduction-52mwdn0ndp.pdf

Projector-Augmented Wave Method: An introduction

Flexible broadband photodetectors based on 2D MoS2 have gained significant attention due to their superior light absorption and increased light sensitivity. However, pristine MoS2 has absorption only in visible and near IR spectrum. This paper reports a paper-based broadband photodetector having ZnS–MoS2 hybrids as active sensing material fabricated using a simple, cost effective two-step hydrothermal method wherein trilayer MoS2 is grown on cellulose paper followed by the growth of ZnS on MoS2. Optimization in terms of process parameters is done to yield uniform trilayer MoS2 on cellulose paper. UV sensing property of ZnS and broadband absorption of MoS2 in visible and IR, broadens the range from UV to near IR. ZnS plays the dual role for absorption in UV and in the generation of local electric fields, thereby increasing the sensitivity of the sensor. The fabricated photodetector exhibits a higher responsivity toward the visible light when compared to UV and IR light. Detailed studies in terms of energy band diagram are presented to understand the charge transport mechanism. This represents the first demonstration of a paper-based flexible broadband photodetector with excellent photoresponsivity and high bending capability that can be used for wearable electronics, flexible security, and surveillance systems, etc.

Large‐Area, Flexible Broadband Photodetector Based on ZnS–MoS2 Hybrid on Paper Substrate

The 2007 discovery of quantized conductance in HgTe quantum wells delivered the field of topological insulators (TIs) its first experimental confirmation. While many three-dimensional TIs have since been identified, HgTe remains the only known two-dimensional system in this class. Difficulty fabricating HgTe quantum wells has, moreover, hampered their widespread use. With the goal of breaking this logjam we provide a blueprint for stabilizing a robust TI state in a more readily available two-dimensional material---graphene. Using symmetry arguments, density functional theory, and tight-binding simulations, we predict that graphene endowed with certain heavy adatoms realizes a TI with substantial band gap. For indium and thallium, our most promising adatom candidates, a modest 6% coverage produces an estimated gap near 80K and 240K, respectively, which should be detectable in transport or spectroscopic measurements. Engineering such a robust topological phase in graphene could pave the way for a new generation of devices for spintronics, ultra-low-dissipation electronics and quantum information processing.

Engineering a robust quantum spin Hall state in graphene via adatom deposition

Two-dimensional transition metal dichalcogenides (2D TMDs) have attracted much attention in the field of optoelectronics due to their tunable bandgaps, strong interaction with light and tremendous capability for developing diverse van der Waals heterostructures (vdWHs) with other materials. Molybdenum disulfide (MoS2) atomic layers which exhibit high carrier mobility and optical transparency are very suitable for developing ultra-broadband photodetectors to be used from surveillance and healthcare to optical communication. This review provides a brief introduction to TMD-based photodetectors, exclusively focused on MoS2-based photodetectors. The current research advances show that the photoresponse of atomic layered MoS2 can be significantly improved by boosting its charge carrier mobility and incident light absorption via forming MoS2 based plasmonic nanostructures, halide perovskites–MoS2 heterostructures, 2D–0D MoS2/quantum dots (QDs) and 2D–2D MoS2 hybrid vdWHs, chemical doping, and surface functionalization of MoS2 atomic layers. By utilizing these different integration strategies, MoS2 hybrid heterostructure-based photodetectors exhibited remarkably high photoresponsivity raging from mA W−1 up to 1010 A W−1, detectivity from 107 to 1015 Jones and a photoresponse time from seconds (s) to nanoseconds (10−9 s), varying by several orders of magnitude from deep-ultraviolet (DUV) to the long-wavelength infrared (LWIR) region. The flexible photodetectors developed from MoS2-based hybrid heterostructures with graphene, carbon nanotubes (CNTs), TMDs, and ZnO are also discussed. In addition, strain-induced and self-powered MoS2 based photodetectors have also been summarized. The factors affecting the figure of merit of a very wide range of MoS2-based photodetectors have been analyzed in terms of their photoresponsivity, detectivity, response speed, and quantum efficiency along with their measurement wavelengths and incident laser power densities. Conclusions and the future direction are also outlined on the development of MoS2 and other 2D TMD-based photodetectors.

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A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

Influence of an Al2O3 interlayer in a directly grown graphene-silicon Schottky junction solar cell

Transition metal dichalcogenides (TMDs) have been attracting attention because of their applications in optoelectronics and photo-detection. A widely used TMD semiconductor is molybdenum disulfide (MoS2), which has tremendous applications because of its tunable bandgap and high luminescence quantum efficiency. This paper reports on high photo responsivity (Rλ ∼ 1913 A W−1) of MoS2 photodetector by decorating a thin layer of zinc oxide (ZnO) quantum dots (ZnO-QDs) on MoS2. Results show that Rλ increases dramatically to 2267 A W−1 at Vbg = 30 V. The high response of ZnO-QDs/MoS2 heterostructures is attributed to a number of factors, such as effective charge transfer between ZnO-QDs and MoS2 surface and re-absorption of light photon resulting in production of electron–hole pairs.

/pdf/enhanced-photoresponse-of-zno-quantum-dot-decorated-mos2-59kd1ucx4k.pdf

Enhanced photoresponse of ZnO quantum dot-decorated MoS2 thin films

Two-dimensional (2D) material based heterostructures have gained tremendous attention because of their capability and multi-functionality in electronic devices. In this work, high gate-modulated rectification in a van der Waals (vdW) heterostructure composed of p-type germanium selenide (p-GeSe) and n-type palladium diselenide (n-PdSe2) with pure ohmic contacts is introduced and examined. A large rectification ratio is extracted, up to 5.5 × 105, arising from the clean interface of p-GeSe and n-PdSe2 and low Schottky barriers. Further, the photovoltaic characteristics are measured under incident light with a wavelength λ = 532 nm and different power intensities (20–100 nW). The obtained results showed a high photoresponsivity of 1 × 103 A W−1 with an EQE of 47%. Fast rise (2 μs) and decay times (4.5 μs) are estimated. Furthermore, the heterostructure of p-GeSe/n-PdSe2 showed extraordinary performance in CMOS binary inverter and rectifier behavior. Such devices based on the TMD heterostructure may improve energy harvesting along with multifunctional logic switches.

Multifunctional and high-performance GeSe/PdSe2 heterostructure device with a fast photoresponse

Thickness-dependent efficiency of directly grown graphene based solar cells

A single nanoflake lateral p-n diode (in-plane) based on a two-dimensional (2D) material can facilitate electronic architecture miniaturization. Here, a novel lateral homojunction p-n diode of a si...

Imtisal Akhtar

Papers

Influence of an Al2O3 interlayer in a directly grown graphene-silicon Schottky junction solar cell

Enhanced photoresponse of ZnO quantum dot-decorated MoS2 thin films

Multifunctional and high-performance GeSe/PdSe2 heterostructure device with a fast photoresponse

Thickness-dependent efficiency of directly grown graphene based solar cells

WSe2 Homojunction p-n Diode Formed by Photoinduced Activation of Mid-Gap Defect States in Boron Nitride.