Financed scholarships:

• Optical properties of Nanoplastics
• Holographic dualities and non-perturbative methods in quantum field theory
• Infrared photothermal heterodyne imaging (IR-PHI): new detection limit and applications

Optical properties of Nanoplastics

Student: Mattia Andrini

Background and motivation

The pervasive distribution of nanoplastics (NPLs) with dimensions less than 1 micrometers in the environement prompted considerable scientific inquiry and public health concerns. Reliable detection of NPLs is essential for understanding their environmental and ecological impacts [1]. In contrast to engineered nanoparticles or larger microplastics, NPLs have been less widely studied, and effective separation, detection and quantification methods are still under development for environmental samples [2]. Since commercial NPLs (polystyrene) are not specifically designed as reference materials for environmental nanoplastics, test materials better mimicking environmental nanoplastics should be developed. Furthermore, heterogeneous NPLs samples present a characterization challenge, e.g. the determination of the refractive index of such mixed materials [3], and the sample evolution as a function of environmental characteristics optical properties are undergoing scrutiny for their applicability to heterogeneous NPLs samples to determine the refractive index of complex samples [4]

The main scope of the project is dual. A first step will investigate the optical properties of controlled NPLs through spatially averaged and spatially resolved optical techniques. A second step will translate initial findings into realistic NPLs models, refining and validating a new class of NPls models closely resembling their environmental counterparts. A particular care could be devoted to the NPLs photodegradation.

The major expected project results are: 1) development of novel tools tailored specifically for investigating NPLs optical properties. 2) Advancement in analytical techniques for characterizing heterogeneous nanoplastic samples.

References:
[1] Bank MS, et al. Nat Rev Earth Environ. 2022; 3:736-737. DOI: 10.1038/s43017-022-00365-x
[2] Nguyen B, et al. Acc. of Chem. Res. 2019; 52: 858-866. DOI: 10.1021/acs.accounts.8b00602
[3] K. Kniazev et al. Environ. Sci. Technol. 2021, 55, 15891−15899. https://doi.org/10.1021/acs.est.1c05181
[4] O. Nwachukwu et al. Environ. Sci. Technol. 2024, 58, 1312−1320. https://doi.org/10.1021/acs.est.3c06498

Supervisors

Prof. Luca Gavioli, UCSC, Italy, luca.gavioli@unicatt.it
Prof. Masaru Kuno, Univ. Notre Dame, US, mkuno@nd.edu
Dr. Stefania Federici, Università di Brescia, Italy, stefania.federici@unibs.it
 

Holographic dualities and non-perturbative methods in quantum field theory

Student: Lihan Guo

Background and motivation

The holographic principle, asserting that the physical properties of a gravitational system are encoded in its boundary, has garnered substantial support from the study of quantum information, including the study of entanglement, computational complexity, error correction and bulk reconstruction. In parallel, a great improvement in the understanding of Anti de-Sitter/Conformal Field Theory (AdS/CFT) correspondence has been achieved in recent years by focusing on certain applications of the duality, such as non-relativistic limits, defects and quenches. A further challenge is to extend holographic approaches to asymptotically dS spacetimes. The main goal of the project is to acquire a solid knowledge in theoretical physics and to conduct independent research within the following topics:

• Black holes and quantum information in AdS/CFT.
• Theories with defects or boundaries.
• Non-relativistic limits applied to AdS/CFT duality.
• Investigation of holography in de Sitter space.
• Solitons and instantons.

The candidate is also expected to carry out research projects in theoretical physics, interacting with the theory staff of UCSC and KU Leuven.

Supervisors

Prof. Roberto Auzzi, UCSC, Italy, roberto.auzzi@unicatt.it
Prof. Giuseppe Nardelli, UCSC, Italy, giuseppe.nardelli@unicatt.it
Prof. Thomas Van Riet, KU Leuven, Belgium, thomas.vanriet@kuleuven.be

Infrared photothermal heterodyne imaging (IR-PHI): new detection limit and applications

Student: Linda Biondelli

Background and motivation

The Infrared Photothermal Heterodyne Imaging (IR-PHI) is an advanced and ultrasensitive technique that leverages the photothermal effect to achieve high-contrast imaging at the nanoscale. This method employs an infrared laser in the spectral range of 1040 – 1840 cm^-1 to induce localized heating within the sample. This heating results in changes to the material physical properties, such as its refractive index. These changes are then probed using a visible laser, in this case a 515 nm laser, which allows for the detection of minute variations in the sample properties with exceptional sensitivity.

The primary goal of this project is reaching the detection limits of IR-PHI beyond the current threshold of 200 nm. By enhancing the spatial resolution and sensitivity, this technique can be applied to investigate complex phenomena that were previously inaccessible. One such application is the study of hybrid perovskites, materials that have garnered significant attention for their potential in low-cost, high-efficiency solar cells. Specifically, the project aims to explore the intrinsic instabilities of anions and cations in hybrid perovskites when exposed to light. These instabilities have been known to limit the efficiency and stability of perovskite-based devices, but their underlying mechanisms remain poorly understood.

Another promising avenue for IR-PHI is the investigation of nanoscale particles, which have become increasingly pervasive in various ecosystems, industries, and even in the food and healthcare sectors. The ability of IR-PHI to detect and characterize these particles at the nanoscale opens new possibilities for studying their impact and developing strategies to mitigate their presence in the environment.

At the core of IR-PHI is the concept of light-induced photothermal changes, which are used to detect infrared absorption in materials. When a sample absorbs mid-infrared (MIR) radiation, it experiences a localized temperature increase, typically on the order of 1-50 K. These changes are then detected using a probe laser (515 nm), which is focused on the same spatial region as the IR pump beam. By modulating the intensity of the IR pump, periodic changes in the sample properties can be induced, resulting in modulations of the probe beam intensity. These modulations enable lock-in detection, a technique that significantly enhances the sensitivity of the measurement by filtering out noise and isolating the signal corresponding to the infrared absorption.

Furthermore, by tuning the frequency of the pump laser, it is possible to acquire localized IR absorption spectra from specific regions of the sample. This capability provides detailed information about the chemical composition and structure of the sample, making IR-PHI a powerful tool for materials characterization.

In summary, IR-PHI is a cutting-edge technique that combines high sensitivity, sub-diffraction-limit resolution, and chemical specificity, making it an invaluable tool for advancing our understanding of complex materials and environmental issues. The ongoing efforts to improve its detection limits and expand its applications could lead to significant breakthroughs in fields ranging from renewable energy to environmental science.

Supervisors

Prof. Masaru Kuno, Univ. Notre Dame, US, mkuno@nd.edu
Prof. Luca Gavioli, UCSC, Italy, luca.gavioli@unicatt.it