Irradiation of a pure Sn wafer with a nanosecond pulsed Nd:YAG laser with different intensities from 2 GW/cm2 to 6 GW/cm2 and a wavelength of λ=1.06 μm leads to the formation of SnO thin films with different thicknesses and unique optical properties. Photoluminescence (PL) spectra, PL relaxation spectra, and Raman light backscattering spectra were used to study the optical properties, crystallinity, and phase composition of the films. Optical microscopy and UV photoluminescence were used to study the size, position, and visualization of the SnO film. Laser emission from a thin SnO film was first observed by excitation with a femtosecond laser with a wavelength of λexc=266 nm on the exciton band with λ=390 nm. The film was formed under the action of Nd:YAG laser with an intensity of 6 GW/cm2. Laser radiation is characterized by both the threshold excitation energy density - fluence Fthr=0.8 mJ/cm2, and the Purcell factor FP=50, measured during femtosecond laser excitation of photoluminescence with a femtosecond laser with a wavelength of λexc=266 nm.

We investigated the formation of graphite nanocrystals covered with graphite oxide for white light generation. The nanoparticles were formed using cost-efficient oxidation of a carbon-based dye pigment at different temperatures and verified using X-ray diffraction and Raman measurements. Formation of the graphite nanoparticles via thermal annealing was observed, while their light emission increased at higher oxidation temperatures. This was associated with a higher amount of oxygen defect groups. The time-resolved photoluminescence measurements showed linearly faster decays at shorter wavelengths and similar decays at different annealing temperatures. Broadband and linear vs. excitation emission spectra of the particles were found to be suitable for white-light-emitting devices and phosphor markers. The fast photoluminescence decay opens the possibility for the application of nanoparticles in optical wireless communication technology.

Resorption time is essential for bone substitution composite materials. In the best case, it has to coincide with the time of new bone formation. In this work, biphasic biomaterial consisting of natural hydroxyapatite (NHAp) and endodontic cement MTA Angelus (EC) is explored. In our experiment we have used three concentrations of the new composite material: first, EC40/NHAp60 volume %, second, EC50/NHAp50 volume %, and third, EC60/NHAp40 volume %. The main task was porosity exploration of each material and also determination of NHAp crystallite size in the material, both mentioned parameters are essential for the resorption process. Results indicate that the composite material EC40/NHAp60 has the highest porosity, at nearly 8%. We consider that such result is due to the higher content of NHAp in the specimens. In contrast, the lowest level of porosity is in the material EC60/NHAp40, at 5.2%. Porosity of the third material is between the two first mentioned composites. The size of NHAp crystallites in the biomaterial is approximately 20 nm. Consequently, it is possible to assert that the size of the crystallites is nearly the same as hydroxyapatite crystallites in natural bone, which is a prerequisite for biomaterial resorption. The study shows that material with the mentioned porosity and size of crystallites has potential to be used as bone substitute material.

A quantum prism, a new structure, consisting of many quantum wires with a diameter that gradually decreases from the base to the top, is the focus of our research. This distribution of quantum wires leads to a dispersive emitted spectrum. The red edge of the spectrum is determined by the band gap width of the bulk semiconductor, and the blue edge is determined by the quantum size of the excitons at the top of the prism. The PL spectrum of the silicon prismatic sample was excited by weak and strong light absorption. At weak absorption (hνex = 1.2 eV), the PL spectrum is located in the visible part of the spectrum, from 1.4 eV to 1.9 eV, with an energy higher than the band gap of the Si crystal. Such a “blue shift” of PL spectra by 0.7 eV is characteristic of the quantum confinement effect. It is a rainbow spectrum with an optical upconversion. The quantum prism is a new type of nano light source, as it replaces two elements in a conventional spectrometer: a light source and a dispersive element. These features enable to create a nano-spectrometer for measuring the absorption spectrum of individual molecules or viruses.

We study a quantum cone, a novel structure composed of multiple quantum dots with gradually decreasing diameters from the base to the top. The dot distribution leads to a dispersive radiated spectrum. The blue edge of the spectrum is determined by the quantum confinement of excitons on top of the cones, while the red edge is determined by the bandgap of a semiconductor. We observe the kinetics of photoluminescence by obeying the stretch-exponential law from quantum cones formed on the surface of diamond-like carbon (DLC). They are explained by an increase in the lifetime of excitons along the height of the cone from the top to the base of the cone and an increasing concentration of excitons at the base due to their drift in the quasi-built-in electric field of the quantum cone. The possible visualization of the quantum cone tops of DLC using irradiation by a UV light source is shown. A quantum cone is an innovative nano-source of light because it substitutes for two elements in a conventional spectrometer: a source of light and a dispersive element—an ultrafast monochromator. These features enable the building of a nano-spectrometer to measure the absorbance spectra of virus and molecule particles.

We elaborate a method for determining the 0D–1D nanostructure size by photoluminescence (PL) emission spectrum dependence on the nanostructure dimensions. As observed, the high number of diamond-like carbon nanocones shows a strongly blue-shifted PL spectrum compared to the bulk material, allowing for the calculation of their top dimensions of 2.0 nm. For the second structure model, we used a sharp atomic force microscope (AFM) tip, which showed green emission localized on its top, as determined by confocal microscopy. Using the PL spectrum, the calculation allowed us to determine the tip size of 1.5 nm, which correlated well with the SEM measurements. The time-resolved PL measurements shed light on the recombination process, providing stretched-exponent decay with a τ0 = 1 ns lifetime, indicating a gradual decrease in exciton lifetime along the height of the cone from the base to the top due to surface and radiative recombination. Therefore, the proposed method provides a simple optical procedure for determining an AFM tip or other nanocone structure sharpness without the need for sample preparation and special expensive equipment.

In this study, the light propagation in a structure consisting of SiOx on Si substrate with Al nanoparticles regularly placed in the SiOx layer is considered. Numerical modelling is performed by solving the Maxwell equations for the electromagnetic waves. In distinction from the well-known finite-difference time-domain (FDTD) simulation technique, we do not solve time-dependent wave equations here; rather, we propose a new numerical technique. This technique allows us to determine the stationary amplitudes of the electromagnetic oscillations directly from the linear algebraic equation system. The obtained results apply to silicon solar cells with an SiOx + Al top layer to maximise their efficiency. We found that 26 nm and 39 nm diameters of spherical Al nanoparticles are nearly optimal for a λ = 435.8 nm wavelength of the incident light. In addition, we evaluated the (nearly) optimal parameters of their placement in the SiOx layer. The results show the possibility of increasing the efficiency of solar cells by increasing the light absorption inside the active Si layer from ≈60% to ≈80%. Future perspectives on the proposed method and its possible applications are discussed.

Bulk niobium is currently the material of choice for superconducting radio frequency (SRF) cavities and is a well matured process. However, it is possible that SRF cavities could be further improved beyond bulk Nb by sputtering thin Nb films onto Cu cavities. Copper has a greater thermal conductivity than Nb and is also easier to machine, while sputtering films on the surface reduces the amount of Nb used to fabricate the whole cavity. However, sputtering Nb on Cu produces other issues, for example, the surface quality of the Cu affects the quality of the Nb deposited on the surface and therefore the superconducting parameters. As the Nb on the surface is not perfect, the magnetic field produced by the RF can enter the cavity earlier than expected, producing RF losses, which can in turn lead to a quench. One approach is to treat the Nb post deposition by irradiating the surface using a laser to polish the surface of the Nb and increase the surface magnetic field that the cavity can maintain while remaining in the Meissner state. A magnetic field penetration experiment designed and built at Daresbury Laboratory has been used to measure the field of full flux penetration to characterize the effect of the laser treatment on the superconducting properties of the Nb. Surface characterization and the response of the Nb in a dc magnetic field have also been performed to try and provide an explanation for the change in the superconducting properties. The results demonstrate that the laser treatment can lead to an increase in the magnetic field at which the flux penetrates from one side of the sample to the other, thus it could potentially improve the performance of Nb coated RF cavities.

In this work, we have investigated two series of Nb/Cu samples deposited by HiPIMS technique, and differing in Nb deposition conditions, Nb film thickness and Cu substrate polishing techniques. All the films were additionally irradiated by Nd:YAG laser to smooth their surfaces. The impact of the magnetic field enhancement at the surface defects on the premature start of magnetic field penetration into the superconducting film was studied, combining experiments and numerical calculations. Compared to previous study, improved numerical calculations by using the Finite Element Method (FEM) served to calculate the maximum field enhancement factor β m , reflecting impact of the most crucial surface defects found in the samples. Magnetization measurements at 4.2 K in DC magnetic field, oriented parallel to the film, were employed to determine the start of the field penetration H en . The SEM and AFM analyses served to investigate the Nb surface morphology. In some samples, deviations from the H en (β m ) dependence were observed. It was found that the magnetic field penetration could start from the Nb/Cu interface rather than from the free Nb surface due to visibly better quality of the free Nb surface observed by SEM analysis, and that could lead to the deterioration of H en (β m ) dependence.

In this study, the laser processing of thermally annealed TiO2 thin films at 420 ℃ in hydrogen atmosphere, utilizing an pulsed fourth-harmonic generation Nd: YAG laser employing different laser intensities in the atmosphere at room temperature, has been reported. Further, the surface morphology and crystalline structure have been investigated by means of atomic force microscopy [AFM], X-ray diffraction [XRD], Raman analysis. The AFM images obtained show that the film’s surface changes as the effect of the laser processes. Moreover, XRD and Raman analysis of the TiO2 thin films indicate at the threshold laser intensity, Ith = 66 MW/cm2 of the fourth-harmonic generation Nd: YAG laser phase transition from atanase-rutile to a crystalline 100

Superconducting radiofrequency (SRF) cavities are vital components of particle accelerators nowadays. In order to minimise the energy dissipation, a perfect inner surface of the cavity, hindering the penetration of magnetic field, is required. In this work, we investigated ten planar samples differing in the surface quality of Nb film deposited on Cu substrate, and as a consequence exhibiting various levels of the first entry field, H en, at which the magnetic field starts to enter the film. The observed surface defects are categorised as hills, pits and cracks. For a practical range of dimensions of these features, the factor β, characterising the local magnetic field enhancement, was calculated by the numerical finite-element simulations. It is expected that the local field enhancement causes a premature penetration of the magnetic field, thus lowering H en. Then, for each investigated sample, the range of β values characterising defect type that cause the highest field enhancement, is identified and compared with the H en fields. We have found that the H en of the samples that contain multiple types of the surface features is indeed limited by those defects that cause the highest field enhancement. The H en vs β dependence has shown a good match with linear fit for the set of investigated samples. Thus, the main result is that the local magnetic field enhancement, computed in a straightforward way for the most significant defects, is a strong indicator of the surface quality that is relevant for the superconducting film intended for SRF cavity application.

Photoluminescence of composites containing carbon nanostructures is critical for many modern applications. Of particular significance are metamaterials capable of generating white light photoluminescence within a single structure, as the white luminescence usually needs separate red-green-blue emitters. This work provides an insight into the photoluminescent properties of a promising family of hierarchical metamaterials made of carbon nanocones in a silicon oxide matrix in view of their use as efficient single-layer white light emitters. The composites were prepared using a facile plasma-enhanced technology, followed by a thermal treatment. ATR-FTIR, Raman, SEM, and AFM microscopy and profilometry characterization confirmed the presence of silica and carbon nanocones. The advanced comprehensive photoluminescence studies conducted using solid-state Yb:KGW laser revealed a significant difference in photoluminescent properties for the composites containing sharp nanocones of similar parameters. A comprehensive morphological analysis performed using several analytical techniques including the 2D fast Fourier transform spectra, Hough distributions, spectral density function, and Minkowski functionals revealed the Minkowski boundary functional, ordering, and connectivity to be the most important morphological descriptors for the photoluminescent response. This study suggests that these morphological parameters play a critical role in defining the key properties of advanced metamaterials via the overlap of Psi functions and may therefore be targeted for informed material design and intelligent fabrication.

A comparative analysis of the features of UV-stimulated emission (SE) of various disordered active materials based on ZnO crystallites for a random laser (RL) was carried out. The superlinear increase in the intensity of the UV photoluminescence (PL) band of polydisperse nano-micro-crystalline (PNMC) ZnO powder at a wavelength of λ = 387 nm and some narrowing of its halfwidth in the range of 20 ÷ 15 nm with increasing pump intensity indicates random lasing with incoherent feedback (FB). The properties of similar UV PL bands under the same conditions of a thin film containing hexagonal ZnO microdisks, as well as samples of monodisperse ZnO nanopowder with nanoparticle sizes of 100 nm, indicate stimulated radiation with coherent feedback. It is shown that, among the studied materials, PNMC ZnO powder with widely dispersed crystallites ranges in size from 50 nm to several microns, which in turn, consists of nanograins with dimensions of ~25 nm, is the most suitable for creating a random laser with incoherent feedback at room temperature. The dominant factor of UV SE in PNMC ZnO powder is radiation transitions under exciton–exciton scattering conditions. The possible mechanisms of this random emission with the continuous spectrum are discussed. The average optical gain coefficient αg at λ = 387 nm in this RL system is estimated as αg~150 cm−1.

The possibility of laser-induced structural transformation of amorphous SiOx thin layers into the SiOx -based nanocomposite layers with increased Si nanoparticles (NPs) has been studied. It was found that the average sizes of silicon NPs depend on the laser intensity (I-L) and wavelength (lambda). The NPs range of sizes d increase from 1 nm <= d <= 10 nm in initial films up to 1 nm <= d <= 35 nm with predominant of the single-crystalline Si NPs in modified SiOx after processing by pulses of the Nd+3: YAG laser (lambda = 532 nm) with a pulse duration t = 10 ns. The structural and topographic changes of SiOx films were studied using field emission scanning electron microscope (FESEM), Energy-Dispersive X-ray Spectroscopy (EDXS), and Raman spectroscopy. The high-frequency shift of the Raman band responsible for the crystalline phase of silicon NPs, caused by the quantum confinement effect, showed an increase in the average of the NPs size with the laser intensity (IL). This is correlated with a decrease of intensity Raman band with a maximum at a vibration frequency at 475 cm 1, which testifies for the decrease of the amorphous phase in the SiOx film with an IL increasing. The correlation between the increase of the average sizes of silicon NPs, the values growing of the stoichiometric index x in SiOx film, and the decrease of the percentage of amorphous silicon was established. The physical mechanisms that explain the growth process of Si NPs are based on the laser thermal shock effect with the following coalescence of Si atoms into NPs and recrystallization of a melted fraction of SiOx film into the NPs with changed sizes have been proposed.

Photo-detection in the near-infrared is commonly performed by Ge or InGaAs-based photodetectors. Further extension of the detection range to the midinfrared region can be performed by germanium-tin (GeSn) material which shows promising characteristics and is fully compatible with silicon electronics as can be directly grown on silicon substrates. In this study, we focused on the optoelectronic properties of the photodiodes prepared by using 200 nm thick Ge0.95Sn0.05 epitaxial layers on Ge/n-Si substrate with aluminium contacts. Photodiodes were formed on non-irradiated and Nd:YAG laser irradiated Ge0.95Sn0.05 layers. The samples were irradiated by pulsed Nd:YAG laser with 61.5-259.2 MW/cm2 intensity. The photodiodes were characterized by using short laser pulses with the wavelength in 2.0-2.6 m range. The laser-irradiated diode was found more sensitive in the long wavelength range due to laser induced Sn atoms redistribution providing formation of graded bandgap structure. Sub-millisecond photocurrent relaxation in the diodes revealed their suitability for image sensors. Our findings open the perspective for improving the photo-sensitivity of GeSn alloys in the mid-infrared by pulsed laser processing [1]. In Fig. 1 responsivity spectral dependencies of the photodiodes with different laser irradiation are provided. It is evident that the laser irradiation extends the photosensitivity to longer wavelengths by 250 nm, revealing a positive impact of laser irradiation at low intensities. Further increase of the laser annealing induces a strong Sn accumulation into a thin surface layer, and a drop of efficiency is observed at longer wavelengths, since Sn-enriched surface layer is suspected to have stronger non-radiative losses, as evidenced by faster photocurrent relaxation decay and faster recombination of carriers investigated by pumpprobe. XRD 2-theta peak broadening explains the Sn redistribution and arising relaxation, which increased the concentration of dislocation defects from 2×108 cm-2 to ~109 cm-2. Photocurrent dependencies on laser power showed a slight reduction of the photocurrent with laser irradiation. Rather low photo-responsivity is explained mainly by the weak absorption in the layer due to its indirect bandgap. Similar values of 33 mA/W [2] and 24 mA/W [3] at 2000 nm were obtained in conventional GeSn photodiodes.

Photo-detection in the near-infrared is commonly performed by Ge or InGaAs-based photodetectors. Further extension of the detection range to the mid-infrared region can be performed by germanium-tin (GeSn) material which shows promising characteristics and is fully compatible with silicon electronics as can be directly grown on silicon substrates. In this study, we focused on the optoelectronic properties of the photodiodes prepared by using 200 nm thick Ge0.95Sn0.05 epitaxial layers on Ge/n-Si substrate with aluminium contacts. Photodiodes were formed on non-irradiated and Nd:YAG laser irradiated Ge0.95Sn0.05 layers. The samples were irradiated by pulsed Nd:YAG laser with 61.5?259.2 MW/cm2 intensity. The photodiodes were characterized by using short laser pulses with the wavelength in 2.0?2.6 ?m range. The laser-irradiated diode was found more sensitive in the long wavelength range due to laser induced Sn atoms redistribution providing formation of graded bandgap structure. Sub-millisecond photocurrent relaxation in the diodes revealed their suitability for image sensors. Our findings open the perspective for improving the photo-sensitivity of GeSn alloys in the mid-infrared by pulsed laser processing.

A laser-induced oxidation method for the formation of a TiO2 layer on a Ti substrate was used. The TiO2 phase can be controlled by an Nd:YAG laser with fundamental frequency at an intensity I = 52.8 MW/cm2 and three different doses. Dose D1 = 3.1x1020 phot/cm2 forms a TiO2 layer in the anatase phase, which possesses the highest photocatalytic, antibacterial and adhesion properties. As the laser dose increases, the TiO2 layer thickness increases from 40 nm to 100 nm, but the photocatalytic decomposition reaction constant decreases. The observed super-linear increase of the TiO2 layer thickness with the laser dose is explained by the presence of positive feedback during the irradiation process. The temperature rises with increasing of the thickness due to the interference-caused decrease of the reflection coefficient. As the thickness increases, TiO2 on Ti structure adhesion decreases from 800 mN to 400 mN due to the formation of a layer with a mixture of phases. The colonization intensities of P. aeruginosa and S. epidermidis bacteria decrease more than tenfold after TiO2 formation. These results are explained by the partial transformation of the TiO2 layer, formed in the anatase phase at dose D1, into the rutile one at doses D2 and D3 due to a deficit of O atoms caused by the low diffusion of O atoms in Ti. According to our experiments and calculations, using the Wagner oxide model, the laser technology can be used to form crystalline structures with a monolayer precision.