Tracking carbon atomic wires growth with in situ resonant UV Raman
Carbon atomic wires are a form of the elusive 1D carbon allotrope carbyne, the ideal infinite chain made of sp-hybridized carbon bonds. Carbon atomic wires possess unique, structure-dependent properties valuable for materials science. While UV Raman spectroscopy offers precise characterization of these wires, the synthesis with pulsed laser ablation in liquid (PLAL) yields low wire quantities. Due to PLAL’s flexibility, scalability, and cost effectiveness, researchers are exploring ways to understand the growth mechanism and enhance production efficiency.
Our research team from Politecnico di Milano (Nanolab from the Department of Energy) developed and used for the first time synchrotron-based, in situ UV resonance Raman spectroscopy at the IUVS beamline of Elettra to monitor the real-time growth of carbon atomic wires during PLAL in various solvents (see Figure 1). This method enabled us to track individual carbon chains with high selectivity by tuning the synchrotron radiation to specific wavelengths, isolating signals based on the unique UV absorption and vibrational fingerprint of the wires, dependent on their structure. In situ monitoring is crucial as it captures the dynamic process of wire formation under actual operating conditions. By selecting different solvents with varying chemical properties, we explored how these properties impact the growth and stability of these wires during synthesis.
Figure 1: schematic representation of the in situ UV Raman setup coupled with our PLAL setup. The ablation cell was designed ad hoc to carry out this experiment.
A key challenge we encountered was self-absorption, a phenomenon where carbon atomic wires themselves absorb the UV Raman excitation light. This absorption not only reduces the Raman signals but also leads to a misleading saturation effect, which can obscure the true interpretation of wire growth dynamics. To address this issue, we developed an empirical model to correct and compensate for self-absorption, allowing us to obtain accurate data about wire growth.
Our study emphasizes that solvent choice significantly influences the synthesis yield of carbon atomic wires. We revealed that organic solvents like methanol, isopropanol, and acetonitrile were far more effective than water for producing carbon atomic wires. This was attributed to water’s inability to supply additional carbon atoms for wire formation, while organic solvents not only contributed carbon but also provided a more favorable environment for the chains to grow (see Figure 2).
Figure 2: growth dynamics of four different carbon atomic wires (HC8H, HC10H, HC12H, and HC14H) obtained through PLAL in different solvents, i.e, water (H2O), methanol (MeOH), isopropanol (i-PrOH), and acetonitrile (MeCN).
We identified formation-degradation dynamics during PLAL synthesis, primarily influenced by oxidation and crosslinking (i.e., degradation of wires via bonding) reactions. Water and alcohols can produce reactive oxygen species that destabilize carbon atomic wires, while solvents like acetonitrile do not dissociate into such species, leading to lower oxidative degradation. Moreover, the limited solubility of carbon atomic wires in water accelerates aggregation and crosslinking, resulting in quicker saturation at lower concentrations (Figure 2). In contrast, organic solvents allow for greater solubility and slower crosslinking, enabling longer growth periods (Figure 2).
Our findings suggest that while longer ablation times are generally expected to yield higher concentrations, degradation mechanisms such as crosslinking can limit this efficiency. Alternative approaches, such as increasing the liquid volume during ablation or employing continuous flow systems, may improve carbon atomic wires yields. Additionally, transferring carbon atomic wires to more stable environments could enhance their stability.
Our study provides valuable insights into how different solvents affect the production of carbon atomic wires, emphasizing the potential of organic solvents to enhance synthesis efficiency. Additionally, it underscores the importance of in situ characterization techniques, such as UV Raman spectroscopy, in elucidating carbon atomic wires growth and informing strategies for scaling up production. By understanding these dynamics, this research could lead to more effective methods for producing carbon-based nanomaterials applicable in nanotechnology and materials.
This research was conducted by the following research team:
P. Marabotti1, S. Peggiani1, S. Melesi1, B. Rossi2, A. Gessini2, A. Li Bassi1, V. Russo1, and C. S. Casari1
1 Micro and Nanostructured Materials Laboratory - NanoLab, Department of Energy, Politecnico di Milano via Ponzio 34/3, I-20133, Milano, Italy
2 Elettra - Sincrotrone Trieste S.C.p.A., Trieste, Italy.
The authors would like to thank Lia Tagliavini (Communications Manager, Department of Energy - Politecnico di Milano) for creating the graphic illustration that accompanies this work.
Reference
P. Marabotti, S. Peggiani, S. Melesi, B. Rossi, A. Gessini, A. Li Bassi, V. Russo and C. S. Casari, “Exploring the Growth Dynamics of Size-Selected Carbon Atomic Wires with In Situ UV Resonance Raman Spectroscopy", Small 2403054 (2024); DOI: 10.1002/smll.202403054 .