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Extending the science perspectives of linear wires of carbon atoms from fundamental research to emerging materials

Periodic Reporting for period 2 - EspLORE (Extending the science perspectives of linear wires of carbon atoms from fundamental research to emerging materials)

Reporting period: 2018-11-01 to 2020-04-30

EspLORE aims at exploiting the potential of carbon atomic wires to fabricate emerging materials for advanced applications. Besides fullerenes, nanotubes and graphene which play a leading role in science and technology of new materials, carbon atomic wires represent peculiar nanostructures with appealing properties. As graphene is the ultimate 2-dimensional carbon system (1 atom thick), carbon atomic wires are the ultimate 1-dimensional structure made of carbon (1 atom diameter) with properties strongly dependent on length and on type of termination. The present knowledge of carbon wires opened new opportunities and challenges that need to be addressed for a realistic implementation of carbon atomic wires as a new class of materials for engineering applications.
The project wants to contribute to the foundations of the science and technology of carbon wire-based materials and their future implementation in advanced technological applications. Based on an experimental and theoretical approach, EspLORE sets up a multidisciplinary research merging different competencies from fundamental science to engineering. The developed materials, able to provide complementary properties to nanotubes and graphene, could synergistically contribute to open new perspectives for an innovative ‘all-carbon’ approach to present and future challenges in many fields of science and technology.
Period 1-30 months. At the mid-term reporting period, the implementation of the project is successful and substantially on time.

For pursuing the project goals new laboratories have been set up and are fully operational. They have been established from scratch at the Host Institution, with the following equipment:
- New system for carbon wires synthesis by submerged arc discharge in liquid (SADL) in fume hood.
- New system for pulsed laser ablation in liquid (PLAL) in fume hood.
- High performance liquid chromatography (HPLC) with diode array detector (DAD) and fraction collector.
- UV-vis spectrophotometer
- New system for in situ Raman spectroscopy equipped with two fiber optic remote probes for in situ analysis.
- Upgrade of the UHV scanning tunneling microscope with electronic control system and new sample holder, new molecular evaporator and new pumping system.
- New system for high performance computing (HPC) with 88 parallel processors, 1TB RAM.

Our achievements in the context of the activities conducted so far are reported below with respect to the main project objectives and related work package organization of the activity (WP).
The activity was focused on the synthesis of carbon atomic wires by means of physical techniques such as pulsed laser ablation and arc discharge. The main objective is the control of wire length and termination. We studied the length and termination of carbon wires produced by PLAL and by SADL investigating the process parameters affecting the formation process. Wires up to 22 carbon atoms have been observed and with different terminations induced by the choice of the solvent. Wires has been selected in size and collected as size-selected samples for wires with 6,8,10 carbon atoms. Careful investigation of the stability and degradation effects has been carried on identifying some procedure for sample storage. More work is needed to control suitable terminations on view of obtaining stable wires.
Structure-property relationship has been investigated outlining a structure-dependent charge transfer when carbon wires interact with metal nanoparticles.
Atomic scale studies of the structure of carbon wires have been conducted by depositing long sp-sp2 wires on a gold substrate in ultrahigh vacuum for scanning tunneling microscopy imaging at atomic/molecular resolution. For the first time, atomic scale imaging has been combined with vibrational spectroscopy (Raman) to investigate carbon wires. In parallel an experimental activity is going on to develop 2D materials to be used as substrates for or in combination with carbon wires. Pulsed laser deposition (PLD) and in situ STM have been used to develop the fabrication of 2D transition metal dicalcolgenides (TMDCs) such as MoS2 on metal substrates (Au(111)).
The experimental work has been supported by a computational-modeling activity with a twofold aim. On one side it is aimed at investigating the properties of carbon wire systems to suggest and guide possible future experimental work and on the other the activity is meant to support the interpretation of experimental results.
This activity is focused at investigating the fabrication of materials assembled from carbon wires. The main objective is to produce a solid-state material in the form of a film or a coating and to investigate how and to what extent its properties are affected and/or modulated by the properties of individual carbon wires employed in the material. We developed nanocomposites consisting in a polymer matrix embedding carbon wires. Carbon wires in such nanocomposites show prolonged stability in time, much higher than in liquid. Thanks to a collaboration the protocol for the fabrication of polymeric nanofibers embedding carbon wires has been developed. We investigated the vibrational and charge transfer properties of thin films of carbon wires. We outlined an electron donor or electron acceptor behavior of the wires depending on their structure.
This activity was planned to start and to be fully conducted in the second half of the project period. However, to identify the possible and most interesting aspects and to direct future activities, some preliminary studies have been done. This has led, for instance, to the ERC Proof-of-Concept (PoC) grant PROTECHT which will start in 2020 and will focus on exploration of technological solutions in the field of anti-counterfeiting. In parallel we started new collaborations to assess the electronic properties in view of device realization.
Carbon wires and carbon structures based on sp-hybridization of carbon atoms including carbyne have been considered elusive system or even impossible to obtain for stability limitations. This resulted in a large number of theoretical works focusing on these systems which is not counterbalanced at all by the few experimental results looking at potential applications. In this context, the activity of EspLORE, together with the recent advancements made by the scientific community, is contributing to put the foundations to consider carbon wires as appealing nanostructures in nanoscience and nanotechnology in Europe. The possibility to have carbon wires or carbon wires assemblies stable in ambient conditions opens the possibility to assess their functional properties and to evaluate the potential for future applications. The development of stable materials comprising carbon wires and the proof-of-concept demonstration of specific size-dependent functionalities could allow to make progress beyond the state of the art.
In many technological fields the availability of radically new materials could be a key step to develop new solutions in a revolutionary way. From electronic to energy conversion and storage devices new materials could overcome present limitations opening to new functionalities and enhanced performances.