Xene Fabrication for a Two-Dimensional Nanotechnology Platform

Project Information

XFab

Grant agreement ID: 772261

DOI

10.3030/772261

Project closed

EC signature date 7 March 2018

Start date 1 April 2018

End date 31 March 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 998 785,00

EU contribution

€ 1 998 785,00

Coordinated by

CONSIGLIO NAZIONALE DELLE RICERCHE
Italy

Periodic Reporting for period 4 - XFab (Xene Fabrication for a Two-Dimensional Nanotechnology Platform)

Reporting period: 2022-10-01 to 2024-03-31

Summary of the context and overall objectives of the project

The XFab projects stems from the idea of exploiting the capability to grow two-dimensional (2D) Xenes and lift them to a higher technology level than the lab demonstration. Xenes are the last frontier of 2D materials made of a single element (like graphene) and displaying diverse electronic states (beyond graphene). Not all the Xene systems are suitable for this technology upgrade because they often suffer from scalability and stability issues, or they may be stacked in a configuration that is unfit to device integration. Often, Xenes currently remain confined to a niche research where the atomistic identification or the demonstration of specific, though important, physical properties are the main target. XFab is the first step to cast Xenes away from this academic perspective towards a more viable technology exploitation.

The societal challenges in the future technologies spanning from the digital agenda (e.g. 6G transition, internet of things, AI, etc.), green economy (renewable energy sources, etc.) as well ass long-standing background challenges such as the technology evolution of electronic devices and the emerging request for energy conversion and storage are in direct need of new materials that are able to more effectively boost the mainstream technology performance or to open new paradigms of operation. This was the case of graphene that just from its rise radically upset the current thinking of mainstream technologies opening up new paths in nanotechnologies. Xenes may expand the technology potential of graphene and then boost the existing technology background or pave the way to new directions.

Few examples may clarify the opportunity. Making silicene fit to electronic devices would ultimately downscale the device feature size and hence reduce the overall power consumption. Making stanene fit to a topological transistor may reset the energy dissipation by taking benefit from the unique predicted topological properties. Out of the nanoelectronics framework, silicene may also be adapted to work as functional layer for flexible electronics, or as an active materials in THz plasmonic grating with outstanding implications in the silicon photonics; epitaxial phosphorene can provide the very first one-atom thick 2D semiconductor available for nanoelectronics, optoelectronics, and sensors, and tellurene can be configured to address memristive applications targeting neuromorphic computational systems.
As overall objectives, here we want to select those Xenes that can have a true potential for device integration in nanotechnology taking the electronic device as prior vehicle in this direction but also considering other technology directions like photonics, energy, biomedical, etc. where the Xenes may play the role of game-changer materials. Therefore main objectives go through a) the selection of those Xenes that are reliable in making the technology step, b) the development of Xene integration schemes in operational devices (electronic devices like transistors and/or memristors, but also optical devices like plasmonic gratings, and more), and c) the proof of Xene device operation.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The workflow has been articulated according to the project implementation plan in the three declared work packages WP, WP1: Synthesis of Xene Systems, WP2: Stabilization and device integration, WP3: Physical Characterization. WP3 has paralleled all the WP1 steps by taking additional benefit from the acquisition of an in situ Raman spectroscopy tool inside the materials production system and of a maskless lithography system for device fabrication. In detail, specific aspects of the workflow are as follows.

WP1 has been carried out in a pre-existing (MBE) apparatus , and since October 2019 in the new MBE apparatus fully dedicated to the XFab purposes. Specific achievements are listed as follows:
- Silicene grown on sapphire substrates as single- and multi-layer; large-area silicene grown Ag substrate for further processing ( WP2); epitaxial phosphorene grown on Au substrates and stanene grown on Ag substrates;
- silicene-stanene and stanene-silicene heterostructures on Ag substrates;
- tellurene growth by vapour transfer deposition at low temperature.

WP2 has been carried out by extending previously developed stabilization schemes to new Xenes produced in WP1 and by developing new schemes for processing Xenes and transferring them from their native substrates to a second substrate. Specific achievements are listed as follows:
- universal encapsulation for Xeens;
- silicene transfer performed via wet and dry transfer methodologies;
- integration of Xenes in device platforms: transistors, piezoresistors, memristors, plasmonic gratings, Hall bars.

WP3 has been carried out by means of extensive in situ and ex situ probing of the produced Xene systems (major techniques used: XPS, STM, LEED-Auger, in situ and ex situ Raman spectroscopy ).


Main results are as follows:
- Epitaxy of silicene on sapphire substrates [Nano Lett. (2018) 18, 7124];
- Growth of epitaxial phosphorene on Au-based substrates [Nanosc. (2019) 11, 18232];
- Evidence of stanene multilayer in the tin epitaxy on sapphire and on InSb substrates [ACS Apple. Nano Mater. (2021) 4, 2351];
- Universality of Al2O3 encapsulation to Xenes-on-substrates [Faraday Discussion (2020) 227, 184] and all-around encapsulation of silicene [Nanoscale. Horiz. (2023) 8, 1428];
- New disassembling and transfer schemes for Xenes [Adv. Funct. Mater. (2020), 30, 2004546];
- Silicene epitaxy by interface engineering [Nanoscale (2023) 15, 11005];
- Epitaxial growth of Xene heterostructures [Adv. Funct. Mater. (2021) 31, 2102797];
- Production of bendable silicene membranes for flexible electronic devices [Adv. Mater. (2023) 35, 2211419];
- Production of tellurene for memristive applications [preprint at doi: 10.26434/chemrxiv-2024-l0q8c].

In parallel, a significant amount of work was devoted to analyse the current state of the art and give new perspectives about the Xenes [see Molle et al, Chem Soc Rev (2018) 47, 6370; Grazianetti et al, PSS-RRL (2019), 14, 1900439; Grazianetti et al, IEEE Trans. Mater. Electr. Dev. (2024) 1,1]

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The achievements of the XFab project beyond the state of the art include:
1- Prior demonstration of Xene (silicene and stanene) epitaxy on sapphire;
2- First demonstration of universal Al2O3 encapsulation of epitaxial Xenes: silicene, epitaxial phosphorene, stanene proven, extension to other Xenes possible;
3- First demonstration of two possible Xene disassembling schemes and transfer to a second arbitrary substrates: t-UXEDO (transfer universal Xene encapsulation, decoupling and operation) and s-SEDNE (seamless silicene encapsulated delamination with native electrode);
4- Prior demonstration of Xene heterostructures;
5- Single crystal growth (phase selection) of silicene by interface engineering;
5- Fabrication of operational electronic devices (namely field effect transistors, memristors, piezoresistors) based on transferred/encapsulated Xenes or Xene heterostructures or Xenes directly grown on substrates;
6- Prior demonstration of bendable silicene membranes with further developments for technology transfer;
7- Prio demonstration of tellurene nano sheets with memristive behaviour with further development of technology transfer.
8- Characterization of the topological Dirac state in alpha-Sn.

XFab cover image