Laser induced nanojet functionalization of two-dimensional materials for sensing and energy harvesting applications

Project Information

LANAFUSEHA

Grant agreement ID: 101067553

DOI

10.3030/101067553

Project closed

EC signature date 7 November 2022

Start date 30 July 2023

End date 29 July 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 169 326,72

Coordinated by

ETHNIKO IDRYMA EREVNON
Greece

Periodic Reporting for period 1 - LANAFUSEHA (Laser induced nanojet functionalization of two-dimensional materials for sensing and energy harvesting applications)

Reporting period: 2023-07-30 to 2025-07-29

Summary of the context and overall objectives of the project

The development of modern green technologies using micro- and nanostructuring is inextricably linked to the search for new approaches for non-invasive manipulation of matter at the sub-micron and even nanoscale. One approach is the use of laser radiation as a unique methodology, developed by humankind and not found in living nature. Today, laser radiation is used everywhere, from supermarkets to laser surgery. However, a key limitation is the finite focusing dimensions of the radiation, which amount to hundreds of nanometers. Lanafuseha exploited near-field effects for laser processing of materials, using the photonic nanojet technology. This novel processing technology was applied to 2D materials, as they are emerging and highly promising materials for extremely high-demand technological fields such as medicine, solar energy, and sensing.
The implementation of the photonic nanojet technology is inextricably linked to the use of optical tweezers. Specifically, optical tweezers enable contactless capturing of microparticles, using only light as a “tweezer”, for subsequent use in super-focusing the processing laser radiation. This way, we are able to form the narrowest beams to date, for high-precision nanostructuring.
The development of modern green technologies using micro- and nanostructuring is inextricably linked to the search for new approaches for non-invasive manipulation of matter at the sub-micron and even nanoscale. One approach is the use of laser radiation as a unique methodology, developed by humankind and not found in living nature. Today, laser radiation is used everywhere, from supermarkets to laser surgery. However, a key limitation is the finite focusing dimensions of the radiation, which amount to hundreds of nanometers. Lanafuseha exploited near-field effects for laser processing of materials, using the photonic nanojet technology. This novel processing technology was applied to 2D materials, as they are emerging and highly promising materials for extremely high-demand technological fields such as medicine, solar energy, and sensing.
The implementation of the photonic nanojet technology is inextricably linked to the use of optical tweezers. Specifically, optical tweezers enable contactless capturing of microparticles, using only light as a “tweezer”, for subsequent use in super-focusing the processing laser radiation. This way, we are able to form the narrowest beams to date, for high-precision nanostructuring.

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 primary objective of the project was to establish the fundamental principles and key laws governing the operation of optical tweezers and the formation of photonic nanojets (PNJ) for subsequent application in sub-diffraction laser material processing. The theoretical part of the work was based on solving the classical Mie scattering problem. The work involved the systematical and precise solution of this problem, which enabled the creation of a reliable calculation model and specialized code for numerical simulations.
Analytical expressions were obtained for the components of the scattered electric field and the field inside the optically trapped microsphere, as well as for the scattering and extinction cross-sections. The calculations utilized Riccati-Bessel functions and recurrence relations for Legendre polynomials. The accuracy of the analytical calculations based on Mie theory was confirmed by comparing them with the results of finite element method (FEM) modeling. The analytical method was chosen as the primary one due to its efficiency, while FEM was used for modeling non-ideal cases, such as particle displacement from the beam axis.
A key achievement was the optimization of PNJ formation. Simulations showed that the jet characteristics (field enhancement, width, distance to the trapped microparticle) critically depend on the parameters of the incident laser beam. In particular, obtaining a narrow PNJ requires a wider incident beam. It was established that for silica microspheres with a diameter of 2 µm trapped in water, the optimal incident beam diameter is 5-6 µm.
Based on the modeling results, an experimental setup was developed and assembled, integrating an optical tweezer (1064 nm laser) for trapping dielectric microspheres and a pulsed laser (532 nm, nanosecond) for material processing. A method for precise positioning of the trapped particle relative to the material surface (with an accuracy of hundreds of nanometers) was developed and successfully applied by controlling the incident beam size in the objective aperture of the trapping setup.
A thin AuPd film was used as the test material. Experiments confirmed the field enhancement effect in the PNJ: the threshold for surface modification using the nanojet was significantly lower (< 5.6 nJ) than that for direct laser processing (~8 nJ). Sub-diffraction lithography was demonstrated: the width of the modified line on the AuPd film was 240 nm (≈ 0.45λ), which is below the diffraction limit of λ/2. Experiments also showed that the presence of the PNJ is a necessary condition for modification in this regime: removing the particle from the beam immediately stopped the process.
A comprehensive thermal analysis was conducted to determine the optimal processing regimes that exclude boiling of the surrounding water. A regime map was constructed, linking the film thickness and the threshold energy density for material modification to the onset of boiling. For a nominal film thickness of 6 nm, a safe operating range was determined.

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)

Sub-diffraction processing of 2D materials: The developed methodology was successfully applied for the precise functionalization of complex 2D materials – graphene and molybdenum disulfide (MoS2) monolayers.
Processing of MoS2: The possibility of creating defined patterns on MoS2 using a PNJ was shown. Material modification was confirmed by scanning electron microscopy (SEM) and Raman spectroscopy, which showed complete material removal in the track region. Successful chemical functionalization of the processed samples with lipoic acid was carried out, confirmed by Fourier-transform infrared (FTIR) spectroscopy.
Processing of graphene: It was established that processing graphene with a PNJ is fundamentally different from direct laser ablation. The modification threshold for graphene in the PNJ regime decreased to ~0.1 J/cm² (compared to ~0.7 J/cm² for direct irradiation), and the morphology of the modified regions indicated a different interaction mechanism. Subsequent functionalization of the processed areas with aryldiazonium salts showed a significant increase in efficiency compared to pristine graphene, manifested in the enhancement and shift of the D and G peaks in the Raman spectra. This paves the way for creating highly sensitive platforms for chemical sensing (e.g. SERS-type) based on functionalized graphene.
Scientific impact: A comprehensive theoretical and experimental platform for controlling light at the subwavelength scale using photonic nanojets was developed. The fundamental possibility of ultra-precise, sub-diffraction laser lithography without the use of resists and chemical etching was demonstrated.
Technological and industrial impact: The method has direct potential for applications in nanotechnology, particularly for creating nanoscale patterns on sensitive materials (e.g. 2D semiconductors), which is in demand in microelectronics and sensing.
Environmental aspect: The technology aligns with the principles of "green" chemistry and sustainable development, as it minimizes the use of chemical reagents and reduces energy consumption through localized exposure.

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