1,721,254 research outputs found
Fabrication and characterization of graphene/silicon heterojunctions
No full textThe graphene/silicon (Gr/Si) heterojunction is currently the subject of an intense research activity. It holds promises for a new generation of graphene-based devices such as photodetectors, solar cells and chemical-biological sensors, and offers the opportunity of studying new fundamental physics at the interface between a 2D semimetal and a 3D semiconductor [1].
A Schottky barrier is usually formed at the Gr/Si heterojunction, which consequently shows the typical rectifying behavior of a metal-semiconductor Schottky diode. The Schottky barrier height strongly depend on the fabrication method and on the quality of the interface. Compared to a metal-semiconductor diode, the Gr/Si heterojunction presents important new peculiarities. The vanishing density of states of graphene at the Dirac point enables energy Fermi tuning and hence Schottky barrier height modulation by a single anode-cathode bias [1,2]. Hence, the Gr/Si heterojunction can function as a two terminal barristor. Furthermore, graphene can be used as anti-reflecting and transparent layer, and can facilitate photo-charge separation and transport, thus enabling optoelectronic applications for the Gr/Si heterojunction [1,2].
Here we report extensive I-V and C-V characterization at different temperatures and the response to light of two types of Gr/Si devices, fabricated on nanotip terminated [3] and on flat [4] Si surfaces (device A and B of Fig. 1), respectively. We study several features of the Gr/Si heterojunction and extract relevant parameters such as Schottky barrier height, ideality factor, series resistance, etc. Both Gr/Si devices can be operated as high responsivity photodiodes (up to 3 A/W). We unveil the physical mechanism behind the quite surprisingly high photocurrent, which results in reverse current exceeding the forward on
Welcome to Nano Express
No full textScience at the nanoscale is multidisciplinary and intersects communities extending across physics, materials science, engineering, chemistry, biology, medicine and environmental science as well as industry. Nano Express reflects this situation as a cross-disciplinary open access journal that builds upon IOP Publishing's long-standing reputation of serving the whole nanoscience community
Sysal: a new fully automatic system for emulsion scanning
No full textA new system for automatic scanning of nuclear emulsions was developed in the last three years at Salerno University. An optical microscope, with a motorised stage, was equipped with a CCD camera and an image digitiser, and interfaced to a personal computer. New methods of two-dimensional image analysis and three-dimensional pattern recognition were applied in order to detect with high efficiency and to measure with high accuracy tracks of particles in nuclear emulsion pellicles. Further improvements are in progres
2D Materials and Van der Waals Heterostructures Physics and Applications
No full textThe advent of graphene, and more recently of two-dimensional (2D) layered materials, has opened new perspectives in electronics, optoelectronics, energy generation and sensing applications. 2D materials can be fabricated with relatively inexpensive production methods, integrated into existing semiconductor technologies, and offer new physical and chemical properties. Electrically, they can behave as insulators, semiconductors, metals or even superconductors. Layered materials consist of covalently bonded and dangling-bond-free layers that can be stuck on top of each other by van der Waals forces to form bulk structures. In general, the number of layers can be controlled to tailor specific properties. The possibility to accurately predict the physical properties of layered materials with the exact number of layers is a unique opportunity for directing the design and fabrication of new electronic and optoelectronic devices. Different types of 2D materials can form heterojunctions with each other or with bulk materials, without the need of a close lattice matching. In these heterojunctions, the weak van der Waals forces between the participant materials do not introduce significant changes at the atomic scale and usually maintain the original electronic structure of the materials. Hence, van der Waals heterojunctions offer the opportunity to combine layers with different properties as the building blocks to engineer new functional materials for high-performance electronic devices, chemical sensors or water-splitting photocatalysts. A great advantage is that the easy stacking of a variety of 2D materials allows a far greater number of combinations than any traditional growth method. A tremendous amount of work has been done thus far on the physical and chemical properties as well as on the synthesis and the characterization of 2D materials such as graphene, transition metal chalcogenides and dichalcogenides, hexagonal boron nitride, black phosphorus, organic perovskites, etc. Many of these materials have been used to fabricate stacked 2D-2D heterostructures, 2D/3D heterojunctions with common bulk semiconductors or even 0D-2D and 1D-2D hybrids. The underlying physics and the possible applications in photodetection, biochemical sensing, strain gauges, photovoltaic energy generation and photocatalytic water splitting have attracted the attention of both theorists and experimentalists. This article collection, reprint of the Special Issue “2D Materials and Van der Waals Heterostructures: Physics and Applications” published by Nanomaterials – MDPI, covers state-of-the-art experimental, simulation and theoretical research on 2D materials and on their van der Waals heterojunctions for applications in electronics, optoelectronics, energy generation and photocatalysis
Field emission from vertically aligned carbon nanotube array measured by non-contact AFM
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