Proton irradiation of lithium fluoride (LiF) crystals and thin films causes the formation of electronic defects, known as color centers, in the crystal lattice, some of which show photoluminescence in the visible range under blue-light excitation. With a suitable irradiation geometry, the energy density that protons deposit in the material can be recorded as a spatial distribution of these light-emitting color centers, from which a luminous replica of the proton Bragg curve can be thereafter extracted and analyzed in a fluorescence microscope. In this paper, the cases of two LiF thin films deposited on silicon substrates and of a LiF crystal, all of them transversally irradiated with a nominal 35 MeV proton beam, are considered. A comparison of the measured photoluminescent Bragg curves with Monte Carlo simulations demonstrates (i) that the Bragg peaks in the films are located at the very same positions that would be expected in the underlying silicon substrates rather than in LiF and (ii) that an even small grazing angle of the impinging proton beam is able to significantly modify the shape of the Bragg curve in the films. Both of these findings are ascribed to the effects of multiple Coulomb scattering in both the film and the substrate. The coincidence of the Bragg peak positions with those expected in the silicon substrates and the possibility of visualizing such peaks in the Bragg curves stored as latent fluorescence images in the LiF films allow one to regard them as information transducers for proton beam diagnostics and dosimetry.

Stimuli-responsive microgels have attracted great interest in recent years as building blocks for fabricating smart surfaces with many technological applications. In particular, PNIPAM microgels are promising candidates for creating thermo-responsive scaffolds to control cell growth and detachment via temperature stimuli. In this framework, understanding the influence of the solid substrate is critical for tailoring microgel coatings to specific applications. The surface modification of the substrate is a winning strategy used to manage microgel–substrate interactions. To control the spreading of microgel particles on a solid surface, glass substrates are coated with a PEI or an APTES layer to improve surface hydrophobicity and add positive charges on the interface. A systematic investigation of PNIPAM microgels spin-coated through a double-step deposition protocol on pristine glass and on functionalised glasses was performed by combining wettability measurements and Atomic Force Microscopy. The greater flattening of microgel particles on less hydrophilic substrates can be explained as a consequence of the reduced shielding of the water–substrate interactions that favors electrostatic interactions between microgels and the substrate. This approach allows the yielding of effective control on microgel coatings that will help to unlock new possibilities for their application in biomedical devices, sensors, or responsive surfaces.

Lithium fluoride (LiF) crystals and thin films are utilized as radiation detectors for energy diagnostics of proton beams. This is achieved by analyzing the Bragg curves in LiF obtained by imaging the radiophotoluminescence of color centers created by protons. In LiF crystals, the Bragg peak depth increases superlinearly with the particle energy. A previous study has shown that, when 35 MeV protons impinge at grazing incidence onto LiF films deposited on Si(100) substrates, the Bragg peak in the films is located at the depth where it would be found in Si rather than in LiF due to multiple Coulomb scattering. In this paper, Monte Carlo simulations of proton irradiations in the 1–8 MeV energy range are performed and compared to experimental Bragg curves in optically transparent LiF films on Si(100) substrates. Our study focuses on this energy range because, as energy increases, the Bragg peak gradually shifts from the depth in LiF to that in Si. The impact of grazing incidence angle, LiF packing density, and film thickness on shaping the Bragg curve in the film is examined. At energies higher than 8 MeV, all these quantities must be considered, although the effect of packing density plays a minor role.

Passive solid-state detectors based on the visible radiophotoluminescence (RPL) of stable aggregate F₂ and F₃ ⁺ color centers in lithium fluoride (LiF) are successfully used for X-ray imaging and advanced diagnostics of intense X-rays sources. Among their advantages, these detectors offer a wide dynamic range and simplicity of use. They can be read non-destructively using a fluorescence microscope, enabling high spatial resolution over a large field of view. Optically transparent LiF films, of three different increasing thicknesses, were grown by thermal evaporation on glass and silicon substrates and subsequently irradiated with monochromatic 7 keV X-rays at several doses from 1.3 × 10¹ to 4.5 × 10³ Gy at the SOLEIL synchrotron facility. For all the LiF films, the RPL response was found to depend linearly on the irradiation dose, with films grown on Si(100) substrates exhibiting up to a 50% higher response compared to those grown on glass. A minimum dose of 13 Gy was detected, despite the low thickness of the irradiated films. The limited thickness of the homogeneously colored LiF film allowed to obtain a spatial resolution of (0.44 ± 0.04) μm in edge-enhancement imaging experiments conducted by placing an Au mesh in front of the samples.

Lithium fluoride (LiF) film detectors for extreme ultraviolet radiation, soft and hard X-rays, based on the photoluminescence of radiation-induced electronic defects, have been proposed and are currently under further development and investigation. LiF film detectors are versatile and can be integrated in different experimental apparatus and imaging configurations. LiF can be grown in the form of polycrystalline thin films and it is compatible with several substrates. The radiation-induced color center (CCs) photoluminescence (PL) response can be enhanced through the appropriate choice of substrates and multilayer designs, and by tailoring the micro-structural properties of polycrystalline LiF films through the control of the growth conditions. In this work, we present the characterization, through fluorescence and Raman micro-spectroscopy, of LiF films, thermally evaporated on different substrates with thicknesses of up to 1 μm, irradiated with soft X-rays produced by a laser plasma source. The combination of these micro-spectroscopy techniques could represent an advanced method to investigate the role of the polycrystalline film structures in CC formation efficiency at the microscopic level, a fundamental aspect of the development of LiF film radiation-imaging detectors.