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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract In the last few years, the peculiar photoluminescence properties of radiation-induced color centers in lithium fluoride (LiF) films have been successfully used for advanced diagnostics of low-energy proton beams produced by the TOP-IMPLART linear accelerator for protontheraphy under development at ENEA C.R. Frascati. The two-dimensional spatial dose map of the transversal section of proton beams was fully reconstructed in a wide interval of doses. In this work the optical emission properties of LiF thin films, grown by thermal evaporation on glass and Si(100) substrates and subsequently irradiated by proton beams of nominal energy 3 MeV at doses higher than 105 Gy, were carefully investigated. Their structural and morphological analyses were performed by X-ray diffraction and atomic force microscopy. A careful comparison of the photoluminescence and photoluminescence-excitation spectra of F 2 and F 3 + electronic defects was performed. Substrate-enhanced photoluminescence intensity increase up to 100% was observed in colored LiF films grown on Si substrates with respect to glass ones. This behavior can be substantially ascribed to the reflective properties of the Si substrate at the emission wavelengths of F 2 and F 3 + CCs, although other complex effects due to the polycrystalline nature of the films cannot be excluded. Highlights • Photoluminescence of color centers in LiF thin films successfully used for advanced diagnostics of low-energy proton beam. • Color centers emission properties investigated in LiF thin films irradiated by 3 MeV proton beams at high doses. • Polycrystalline LiF thin films thermally-evaporated on glass and silicon substrates for low-energy proton beam detectors. • Morphological and structural analysis together with optical investigation by photoluminescence and photoexcitation spectra. • Substrate-enhanced PL up to 100% measured in colored LiF films grown on Si substrates with respect to glass ones. [ABSTRACT FROM AUTHOR]

In recent years, lithium fluoride (LiF) detectors based on the optical reading of photoluminescence emitted by radiation-induced F 2 and F 3 + colour centres have been successfully used for advanced diagnostics of proton beams. In this work, the visible photoluminescence response of LiF film-based radiation detectors of three different thicknesses, grown by thermal evaporation on glass and Si(100) substrates and irradiated with 27 MeV proton beams at doses in the range between 4.2 × 103 and 1.7 × 105 Gy, was carefully investigated by fluorescence optical microscopy. Before irradiation, the structural and morphological properties of LiF films were investigated by atomic force microscopy and X-ray diffraction techniques. Substrate-enhanced photoluminescence response up to 48% was observed in LiF film-based detectors grown on Si(100) substrates with respect to those deposited on glass in the same deposition run and irradiated in the same conditions. This photoluminescence enhancement can be mainly ascribed to the reflective properties of the Si substrate in the visible spectral range, where the emission bands of F 2 and F 3 + colour centres are located, combined with the proper choice of the film thickness. Other complex effects related to the polycrystalline nature of the LiF films cannot be excluded. • LiF thin films thermally-evaporated on glass and silicon as proton beam detectors. • Morphological and structural analysis performed by AFM and X-ray diffraction. • Radiophotoluminescence of colour centres investigated by fluorescence optical microscopy. • Substrate-enhanced photoluminescence response measured in LiF detectors grown on Si. • Enhanced photoluminescence response up to 48% depending on the LiF film thickness. [ABSTRACT FROM AUTHOR]

Thin films of poly(N-isopropylacrylamide) (PNIPAM) microgels have recently attracted significant attention as promising candidates for creating switchable interfaces in biomedical and biotechnological applications. In this study, microgel films are proposed as smart coatings for photoluminescent solid-state radiation detectors based on lithium fluoride (LiF). Understanding the impact of the solid substrate is crucial for customising and refining microgel coatings for specific applications. To investigate the effects of surface quality, microgel size, and particle concentration on the properties of microgel films, PNIPAM microgels were spin-coated onto LiF crystal surfaces and characterised through wettability measurements, UV-Vis-NIR spectrophotometry, and Atomic Force Microscopy. This approach enabled effective control over the optical and morphological properties of the films, paving the way for the development of hybrid and potentially biocompatible radiation detectors using PNIPAM microgel films. [Display omitted] [ABSTRACT FROM AUTHOR]

Smart surfaces and surface coatings have been attracting increasing interest in the last decades. In particular, thin films assembled from microgels offer good control of morphology, elasticity and hydrophobicity thanks to the high tunability of microgel mechanical properties and chemical composition. Among smart microgels, Poly(N-isopropylacrylamide) (PNIPAM) based microgels are the most used systems for theoretical and experimental studies and for nanotechnological applications. When used as building blocks to fabricate 2D assemblies, they exhibit new properties offering many advantages for additional applications in different fields. Here we report a systematic investigation of aqueous suspensions of soft PNIPAM microgels through Dynamic Light Scattering (DLS), Small Angle X-ray Scattering (SAXS) and rheometry. Starting from these suspensions, optical and morphological properties of PNIPAM microgel thin films deposited by spin-coating on a glass substrate at different weight concentrations and deposition conditions are investigated through UV-Vis-NIR spectroscopy and Atomic Force Microscopy (AFM). Homogeneous and smooth thin films of soft PNIPAM microgels were obtained with high transparency in the whole wavelength range from the visible to the near-infrared region. Moreover, their optical properties were correlated to microgel arrangement at the solid surface that can be opportunely tuned by changing the spin-coating deposition parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

In the last few years, the visible photoluminescence (PL) of radiation-induced laser-active F 2 and F 3 + aggregate color centers (CCs) in lithium fluoride, LiF, has been successfully used for advanced diagnostics of low-energy proton beams. A systematic study of the optical properties of LiF crystals and thin films exposed in different irradiation geometries to a proton beam of nominal energy 7 MeV is under way. The ionization induces the stable formation of primary and aggregate CCs in the crystalline lattice, among which the F 2 and F 3 + defects possess broad emission bands in the red and green spectral ranges, respectively, when optically pumped at wavelengths close to 450 nm. Their PL intensity has been found to be linearly proportional to the dose absorbed by the host material over at least three orders of magnitude, so that LiF solid-state dosimeters based on spectrally-integrated PL reading can be envisaged. A simple defect formation model that takes into account the energy released in the material, crystals and films, together with the saturation of CC concentration at high doses, allows obtaining both the full Bragg curve reconstruction with its dose distribution with depth and the accumulated bi-dimensional transversal dose-mapping from the visible fluorescence images latently stored in LiF crystals and thin films, respectively. Results obtained by using a fluorescence microscope are presented and discussed with the aim of highlighting some quantitative aspects of the PL behavior of CCs both in LiF crystals and films, which are relevant for low-energy proton-beam Bragg curve imaging and dose mapping in a wide interval of doses up to the ones at which strong CC saturation occurs. • Photoluminescence of color centers in LiF used for advanced diagnostics of low-energy proton beams. • Transversal beam intensity distribution and Bragg curve imaging obtained by fluorescence microscopy. • Defect formation model describes photoluminescence behavior vs dose in crystals and films up to saturation. • The model allows full reconstruction of the Bragg/dose curve in LiF crystals with depth at high doses. • The model allows proton-beam 2-D dose-mapping reconstruction in LiF films also at high doses. [ABSTRACT FROM AUTHOR]