Newsgroup: it.scienza.chimica
Titolo: Rectenna al MoS2

Premessa su cos'è una rectenna:
 
https://it.wikipedia.org/wiki/Rectenna
 
 
   Una rectenna è una speciale antenna utilizzata per convertire 
direttamente le microonde in corrente continua. Il nome è la contrazione 
di rectifying antenna e questa tipologia di antenne usualmente sono 
utilizzate in configurazione a griglia e quindi sono esteticamente molto 
diverse dalle classiche antenne.
 
   Una semplice rectenna è costituita da un diodo Schottky collegato tra 
i dipoli di un'antenna. Il diodo rettifica la corrente indotta 
sull'antenna dalle microonde, ad esempio tramite effetto pelle. Sono 
utilizzati diodi Schottky dato che hanno la minor tensione di soglia tra 
i diodi in commercio e quindi sono quelli che disperdono meno potenza.
 
   Le rectenne sono molto efficienti nel convertire le microonde in 
corrente. In laboratorio si riesce a raggiungere il 90% di efficienza. 
Sono state svolte delle sperimentazioni con una rectenna inversa per 
convertire corrente continua in microonde ma l'efficienza del sistema è 
stata molto bassa, dell'ordine dell'1%.
 
Ebbene, la molibdenite MoS2 non servirà più solo come lubrificante, ma 
anche per ricaricare e/o tenere in funzione smartphone e notebook con 
l'energia del campo Wi-Fi:
 
https://www.nature.com/articles/s41586-019-0892-1
 
 
   Letter | Published: 28 January 2019
 
   Two-dimensional MoS2-enabled flexible rectenna for Wi-Fi-band 
wireless energy harvesting
 
   Abstract
 
   The mechanical and electronic properties of two-dimensional materials 
make them promising for use in flexible electronics. Their atomic 
thickness and large-scale synthesis capability could enable the 
development of ‘smart skin’, which could transform ordinary objects into 
an intelligent distributed sensor network. However, although many 
important components of such a distributed electronic system have 
already been demonstrated (for example, transistors, sensors and memory 
devices based on two-dimensional materials), an efficient, flexible and 
always-on energy-harvesting solution, which is indispensable for 
self-powered systems, is still missing. Electromagnetic radiation from 
Wi-Fi systems operating at 2.4 and 5.9 gigahertz is becoming 
increasingly ubiquitous and would be ideal to harvest for powering 
future distributed electronics. However, the high frequencies used for 
Wi-Fi communications have remained elusive to radiofrequency harvesters 
(that is, rectennas) made of flexible semiconductors owing to their 
limited transport properties. Here we demonstrate an atomically thin and 
flexible rectenna based on a MoS2 semiconducting–metallic-phase 
heterojunction with a cutoff frequency of 10 gigahertz, which represents 
an improvement in speed of roughly one order of magnitude compared with 
current state-of-the-art flexible rectifiers. This flexible MoS2-based 
rectifier operates up to the X-band (8 to 12 gigahertz) and covers most 
of the unlicensed industrial, scientific and medical radio band, 
including the Wi-Fi channels. By integrating the ultrafast MoS2 
rectifier with a flexible Wi-Fi-band antenna, we fabricate a fully 
flexible and integrated rectenna that achieves wireless energy 
harvesting of electromagnetic radiation in the Wi-Fi band with zero 
external bias (battery-free). Moreover, our MoS2 rectifier acts as a 
flexible mixer, realizing frequency conversion beyond 10 gigahertz. This 
work provides a universal energy-harvesting building block that can be 
integrated with various flexible electronic systems.

 wireless energy harvesting
 
Chi sa leggere lo spagnolo trova qua un buon riassunto con le figure a 
colori tratte dall'articolo su Nature:
 
https://francis.naukas.com/2019/01/29/una-rectena-flexible-para-reciclar-la-energia-ambiental-del-wifi/
 
 
Comunque nell'articolo su Nature la didascalia dell'immagine:
 
https://media.springernature.com/m685/springer-static/image/art%3A10.1038%2Fs41586-019-0892-1/MediaObjects/41586_2019_892_Fig1_HTML.png
 
 
recita:
 
   Fig. 1 | Flexible rectenna based on a 2D self-aligned 
MoS2-heterostructure Schottky diode.  a, Schematic of a lateral Schottky 
diode based on a MoS2 semiconducting–metallic (2H–1T/1T′) phase 
junction. The gold layer forms an Ohmic contact with metallic (1T/1T′) 
MoS2, which also forms an Ohmic contact with semiconducting (2H) MoS2. 
The palladium layer forms a Schottky contact with semiconducting (2H) 
MoS2. The antenna converts electromagnetic radiation in the Wi-Fi band 
into an a.c. signal. The lateral MoS2 diode is fast enough to rectify 
the a.c. signal and generate a d.c. signal to power a load at its 
output. The blue and red arrows indicate a.c. and d.c. currents, 
respectively. Inset, scanning electron microscopy image of a MoS2 
Schottky rectifier. Channel width, 40 μm.  b, The d.c. I–V 
characteristics of the MoS2 Schottky diode in the logarithmic scale. 
Inset, band diagram of the MoS2 Schottky junction under forward bias V. 
Φbi is the built-in potential of the MoS2 Schottky diode, e is the 
electron charge and EF indicates the Fermi level of the semiconducting 
MoS2.  c, Current responsivity of the MoS2 Schottky diode at different 
external bias points.
 
Bye,
 
   *GB*