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ZnO:Eu thin film fabricated by pulsed laser deposition was treated by pulsed UV laser. The effect of laser fluence from 70 to 125 mJ cm−2 on film properties was investigated. The results showed that the surface morphology was clearly modified and the film treated at laser fluence of 70 mJ cm−2 was more densified compared to the other annealed films. Laser treatment led to a reduction of carbon content and to a stoichiometric ZnO:Eu composition on the surface. Refractive index significantly decreased and extinction coefficient was blue shifted for higher laser fluences. Strong characteristic Eu3+ transitions were obtained using excitation at 266 nm. The highest photoluminescence intensity was observed for the annealed film at a laser fluence of 70 mJ cm−2. The influence of ambient composition (N2 and O2) and temperature (room temperature and 150 °C) to photoluminescence response was examined for optical gas sensor application. The laser-untreated film showed higher sensitivity to the presence of oxygen at both temperatures compared to the treated film. The stability of photoluminescence intensity at elevated temperature was improved for laser-treated areas.

The control and arguably the tailoring aspect of technologies like pulsed laser deposition (PLD) rises from understanding the chemistry hidden by the laser generated plasma. With the continuous transition towards thin films with complex structures and geometries, the comprehension of the fundamental processes during the film deposition becomes critical. During the PLD of Mo and Eu-doped Lu2O3, optical emission spectroscopy was implemented for in-situ plasma monitoring. The spatial distribution of individual elements revealed the structuring of a stoichiometric plasma while the formation of LuO molecule within the plasma plume is seen as being induced by the addition of a minimum 1 Pa of O2. The energy of the ejected particles was controlled through doping and O2 pressure. The effect of O2 pressure over the plasma energy revealed a transition from an atomic dominated region towards a molecular dominated one. The properties of the resulted films were analyzed by XRD, AFM, and photoluminescence techniques and show a strong correlation between the dynamical regime of the plasma and their structural properties.

International audience; Three different compounds, cubic Gd2O3, orthorhombic GdGaO3, and cubic Gd3Ga5O12 doped with Pr3+ ions were fabricated as waveguiding films by pulsed laser deposition from the same target material, Pr3+ doped Gd3Ga5O12 (Pr:GGG) single crystal. All of them were deposited at the same substrate temperature of 800 °C. The different crystalline phases obtained depend only on the ambient oxygen pressure and the substrate type (YAG or YAP single crystals). The structural and texture properties of the films were analyzed by x-ray diffraction. Pr3+ fluorescence properties were found to be similar to those of the bulk crystals. The refractive indices and waveguiding properties of the films were determined. The fluorescence properties of Pr3+ doping ions and the refractive index of the film are presented. The oriented crystalline Pr:GdGaO3 and Pr:GGG films show waveguiding propagation with attenuation around 2.5 and 1 dB/cm, respectively

Ultra-thin silver films of thicknesses of the order of 10 nm and less were prepared in different ambient conditions (vacuum, Ar, and N2) by pulsed laser deposition on glass and fused silica substrates. The in situ monitoring of electrical resistance of deposited films and optical emission spectroscopy of plasma were implemented as real-time analysis techniques. Change in the growth mechanism of the Ag layer in N2 ambient is expressed by an acceleration of the coalescence process, which shifts the percolation point toward lower mass thicknesses. The films prepared in vacuum and Ar ambient were found to be unstable for a final resistance in the range from 1 to 100 MΩ while the films deposited in N2 revealed stable electrical resistance. The percolation point was further lowered by introducing a sublayer of AgxOy for the film deposited in N2 gas. Based on data provided by AFM, SEM, and spectroscopic ellipsometry, different film formation mechanisms are discussed in relation to surface morphology and optical properties. Optical emission spectroscopy was used to monitor the deposition process and identify the species presented during the deposition process. The energy of the ejected particle is affected by the addition of ambient gas and depends on the properties of the working gas.

In this work, we deal with a study of the electron-transport behavior of zirconium nitride RF magnetron sputtered films using Zr target in reactive nitrogen ambient. The films were grown on silica-coated silicon substrates at a substrate temperature of 300°C. The growth process was monitored using an in-situ spectral ellipsometer in a spectral range from 245 to 1690 nm. The ellipsometric data were analyzed using a dispersion model based on Drude-Lorentz oscillators. We estimated electron-transport properties at each stage of the deposition process by analysis of the model parameters. The mechanism of the thickness-dependent electron-transport phenomenon of the ZrN films is discussed in this work.

In this work, a comparison of the microstructure of black and classic reflective aluminum films is provided. The N2 concentration during the magnetron sputtering deposition has a key impact on the growth process and final moth-eye-like morphology of black Al films. The study of films with thickness ~1.5 µm and ~8 µm and fully developed microstructure enabled us to clarify the origin of different optical properties of black and reflective Al. Atomic force microscopy measurements showed high roughnesses for both types of films leading to light scattering from their surface. In the case of black Al, the incident light is absorbed in a fractal-like nanoporous surface. Less than 3% of the intensity in the wavelength range from 190 nm to 1200 nm is reflected. Positronium formation in columnar nanopores with a diameter of 4 – 5 A was observed by positron annihilation lifetime spectroscopy. The nanoporosity rather than the roughness is the key feature of black films compared to reflective ones.

ZnO:Mo powders of nano- and microrods were fabricated by the hydrothermal growth method. ZnO:Mo thin films deposited on a fused silica glass substrate were synthesized for comparison as well. X-ray diffraction and fluorescence (XRD, XRF), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), photo- and radioluminescence (PL, RL) were applied to characterize these materials. The samples were also annealed in air at elevated temperatures to study the defects and luminescence modification. In particular, EPR spectra in the powder and thin film samples were composed of the signals originating from shallow donors before any treatment. The Mo5+ signal appeared after the annealing at 350 °C in the powder spectra. It existed prior to the treatment in the thin film samples. New EPR signal appears after X-ray irradiation in the powder samples. Red luminescence occurs in all powder samples. The intensity of this band demonstrated different dependences on the annealing temperatures in the samples with different Mo content. The exciton-related band at 380 nm never observed in the powder samples before the annealing, appears after the annealing at 350 °C. The strongest it was in the ZnO:Mo powder with low Mo content.

Four pairs of p–i–n structures based on polymorphous Si:H (pm-Si:H) are fabricated by the method of plasma-enhanced chemical vapor deposition. The structures in each pair are grown on the same substrate so that one of them does not contain Ge in the i-type layer while the other structure contains Ge deposited by molecular-beam epitaxy as a layer with a thickness of 10 nm. The pair differ from one another in terms of the substrate temperature during Ge deposition; these temperatures are 300, 350, 400, and 450°C. The data of electron microscopy show that the structures formed at 300°C contain Ge nanocrystals (nc-Ge) nucleated at nanocrystalline inclusions at the pm-Si:H surface. The nc-Ge concentration increases as the temperature is raised. The study of the current–voltage characteristics show that the presence of Ge in the i-type layer decreases the density of the short-circuit current in p–i–n structures when they are used as solar cells, whereas these layers give rise to an increase in current at a reverse bias under illumination. The obtained results are consistent with known data for structures with Ge clusters in Si; according to these data, Ge clusters increase the coefficient of light absorption but they also increase the rate of charge-carrier recombination.

It is important for electro-optical applications of nanocrystalline diamond (NCD) films to achieve high optical transparency with low electrical resistivity. However, currently fabrication of highly transparent NCD films with reasonable electrical conductivity remains a challenge – any increase in conductivity simultaneously reduces transparency. Here, we report on fabrication of highly conductive and yet highly transparent electrodes based on boron-doped nanocrystalline diamond (B-NCD) films and Ti grids. We studied B-NCD films with variable boron content and thickness to determine preferable electrical and optical characteristics. Composite electrodes with a sheet resistance of 200 Ω/sq and optical transparency of 80% have been obtained by the integration of a thin nanostructured Ti-grid, sandwiched between the glass substrate and B-NCD layer.

International audience; Eu doped ZnO thin films were deposited by pulsed laser deposition on fused silica substrate at room temperature and 300 °C in an oxygen ambient of pressure of 10 Pa. The films exhibited a wurtzite structure. The average transmittance exceeded 80% in the visible region confirming a good optical quality of the films. The characteristic emission of both Eu2+ and Eu3+ was observed when indirectly excited. The increase of substrate temperature to 300 °C led to higher crystallites size, lower efficiency of energy transfer from ZnO to Eu ions and lower resistivity of the film. XPS revealed the ratio of Eu divalent and trivalent states as 35%:65% and 27%:73% for sample deposited at room temperature and 300 °C, respectively. AFM showed higher RMS for the sample prepared at 300 °C.

The continuous increase of atmospheric carbon dioxide (CO2) concentration along with pollution of waters by organic wastes have led the scientific community to investigate novel strategies to address these worldwide environmental problem. Electrochemical methods are a promising approach to convert CO2 into a variety of useful chemicals and to remove contaminants from wastewater [1,2]. Nevertheless, it is necessary to develop inexpensive and chemically robust electrodes with long life-time in harsh electrochemical conditions for these processes to be efficient and economically viable. Boron-doped diamond (BDD) has been recently shown to be a promising material for electrochemical reduction of CO2 into formic acid and formaldehyde [3]. In contrast to thick microcrystalline BDD films, thin nanocrystalline BDD layers (thickness of 100 - 500 nm) provide a higher degree of flexibility in material properties, e.g. due to a variable diamond/non-diamond content, and allows efficient bottom-up nanostructuring, e.g. BDD growth on porous templates [4]. In this work, we investigate nanocrystalline boron-doped diamond and composite BDD/SiC electrodes synthesized via microwave plasma enhanced chemical vapor deposition (MW PE CVD) method at different deposition temperatures (250 - 750°C) towards electrochemical reduction of CO2 in water-based electrolytes [5]. Fabricated electrodes were characterized by a variety of techniques, including Raman spectroscopy, scanning electron microscopy imaging and electrical conductivity measurements. Electrochemical properties of nanocrystalline BDD electrodes of various thickness, boron content and electrical conductivity were studied. This work has been supported by the Grant Agency of the Czech Republic (GACR) contract 19-09784Y. [1] I. Sirés et al., Environ Sci Pollut Res (2014) 21: 8336. [2] A. Goeppert et al., Chem. Soc. Rev. (2014), 43, 7995-8048. [3] K. Nakata et al., Angew. Chem. Int. Ed. (2014), 53, 871 –874. [4] V Petrák et al., Carbon (2017), 114, 457. [5] A. Taylor et al., J. Alloys. Compd., (2019) 800, 327-333

In this work, current multiplication at high electric field in epitaxial boron-doped diamond with high acceptor concentration is analyzed, including self-heating effect and impurity impact ionization. Quasi-static current-voltage (I-V) characteristics were measured using a transmission-line pulse setup with 100 ns pulse duration on samples with two Ohmic titanium/gold electrodes. Unambiguous exponential and super-exponential behaviors are observed in the I-V curves along with, in some cases, negative differential resistance. The self-heating effect is analyzed using transient interferometric mapping of the thermal energy distribution between electrodes with an ns time scale. Measured I-V characteristics are modelled by finite element method and by considering boron acceptor ionization due to self-heating effect and impurity impact ionization. Simulated I-V characteristics, in particular the appearance of the negative differential resistance region attributed to self-heating, are in good agreement with experimental data.

Oxidation and hydrolysis are two spontaneous reactions occurring when scandium nitride (ScN) is exposed to air (oxygen and humidity). In order to evaluate the detrimental effect of the oxidation on functional properties of the material, ScN films were prepared under ultrahigh vacuum conditions at 700 °C onto two different substrates; crystalline MgO(0 0 1) and amorphous fused silica. X-ray Photoelectron Spectroscopy analysis was performed to study the oxidation reactions. The study also employed vacuum transferred pristine samples. Crystalline quality and oxidation resistance were found to be strongly correlated. Degradation of electrical and optical properties was observed for polycristalline films prepared on fused silica. On the other hand, highly ordered crystalline films grown on MgO(0 0 1) demonstrated surface passivation preventing further progress of the oxidation. Post-deposition exposure to air was found to be a principal source of the observed oxidation.

Black and smooth Al films were characterized by the variable energy positron annihilation spectroscopy (VEPAS). It was found that in smooth films positronium (Ps) is formed on the surface only while in black metal films, it is formed also in nanoscopic pores inside the film. The mean pore size increases from the substrate to the surface due to increasing film roughness.

International audience; TbxDy1 − xFe2 (Terfenol-D) thin films were grown in situ at 500 °C on Pt/TiO2/SiO2/Si substrate by multi-target sputtering. The thickness effect of the Terfenol-D layer on the microstructure and on the magnetic properties was investigated. Magnetic force microscopy was used to observe local domain patterns. Strong changes in the shape of magnetic domains were observed when the thickness of the Terfenol-D film was increased. Transmission Electron Microscopy observations showed that in situ elaboration at 500 °C gives rise to large diffusion of the platinum of the bottom electrode into the Terfenol-D film leading to different sub-layers. Saturation magnetization values increased from 500 to 840 kA/m, and coercive fields from 15 to 140 kA/m, respectively, when the thickness of the Terfenol-D film was varied from 100 to 1000 nm. Co-sputtering of Pt and Terfenol-D through the entire film thickness led to a similar saturation magnetization as well as an interesting strong decrease of the coercive field of these mixed films.

A black aluminum (B-Al) film was deposited onto the surface of a stack structure of platinum/Pb(ZrxTi1 − x)O3/platinum (Pt/PZT/Pt) to convert light into a heat variation and the heat variation into a polarization change. A comparison was performed between B-Al/Pt/PZT/Pt and conventional Pt/PZT/Pt structures. An absorbance higher than 95% was measured for the B-Al layer over a large range of wavelengths varying from 350 nm to 1000 nm. The theoretical model shows that heat diffusion was extremely fast through the layers, and the sample holder played a key role in the variation and stabilization of the system temperature. A doubled variation of the polarization was observed when the light was applied onto the surface of the stack structure with stable B-Al on the top. This behavior was interpreted by the larger temperature variations induced under the highly absorptive B-Al layers, in good correlation with the theoretical model prediction based on the heat fluxes in the structures. This result is very promising for possible pyroelectric energy harvesting applications.

Scandium nitride (ScN) is a rocksalt-structure semiconductor that has attracted attention for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices. ScN nanolayers of 30 nm thickness were deposited on MgO (001) substrate by reactive sputtering. Epitaxial growth of ScN(002) was observed with a mosaicity between grains around the {002} growth axis. Both direct band gaps theoretically predicted were measured at 2.59 eV and 4.25 eV for the energy gaps between the valence band and the conductance band at the X point and the Γ point respectively. Electrical and optical properties were observed to be strongly influenced by the crystalline order and the carrier concentration.

Методом плазмохимического осаждения сформированы четыре пары p-i-n-структур на основе pm-Si:H (полиморфного Si : H). Структуры в каждой паре выращивались на одной подложке так, что одна из них была без Ge в i-слое, а другая содержала Ge, который осаждался слоем толщиной 10 нм методом вакуумного напыления. Пары различались между собой температурой подложки при осаждении Ge, которая была 300, 350, 400 и 450 oC. Данные электронной микроскопии показали, что структуры, полученные при 300 oC, содержали нанокристаллы Ge (nc-Ge), центрами зарождения которых являлись нанокристаллические включения на поверхности pm-Si:H. Концентрация nc-Ge увеличивалась c возрастанием температуры. Исследование вольт-амперных характеристик показало, что наличие Ge в i-слое уменьшало плотность тока короткого замыкания в p-i-n-структурах, когда они использовались как солнечные элементы, тогда как наблюдалось увеличение тока под действием освещения при обратном смещении. Полученные результаты согласуются с известными данными для структур с кластерами Ge в Si, согласно которым кластеры Ge увеличивают коэффициент поглощения света, но также увеличивают и скорость рекомбинации носителей. DOI: 10.21883/FTP.2017.10.45024.8547

Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 (Terfenol-D/Pt/PZT) magnetoelectric (ME) thin films were deposited on Pt/TiO2/SiO2/Si substrate. Ferroelectric and magnetic properties were characterized at room temperature. At zero dc magnetic field and out of mechanical resonance, a variation of the voltage across the ferroelectric film was obtained when a small external ac magnetic field was applied to the device. The corresponding ME voltage coefficient was 1.27 V/cm Oe. On the same sample, local magnetic domain patterns were imaged by magnetic force microscopy. Reversible changes in magnetic domain patterns were observed when a dc electric field of 120 to 360 kV/cm was applied to the ferroelectric layer. These results confirm that both magnetic control of ferroelectric polarization and electric control of magnetization are achievable on ME thin films devices deposited on silicon substrates.

International audience; Heterostructures of piezoelectric Pb(Zr,Ti)O 3 and magnetostrictive Galfenol were fabricated by sputtering and pulsed laser deposition on platinized Si substrates with the aim to induce a magnetoelectric coupling between the layers of the two materials. In this study, no intermediate layer was introduced between Pb(Zr 0.56 Ti 0.44 )O 3 and Galfenol in contrast to most of the previous thin films studies. The obtained magnetoelectric coupling constant is in the range of 6-7 V/(cm Oe), indicating that an undisturbed piezoelectric-magnetostrictive interface can outbalance small deteriorations of the ferroic properties of the active materials. © 2015 AIP Publishing LLC.

International audience; Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 (Terfenol-D/Pt/PZT) magnetoelectric (ME) thin films were deposited on Pt/TiO2/SiO2/Si substrate. The ME voltage coefficient αH ME was determined at room temperature using a lock-in amplifier and by applying to the sample an alternating magnetic field of a few mT. Surprisingly, very similar responses were obtained from a simple commercial capacitor set in series with a small loop of wire. This allowed us first to accurately model and reproduce the frequency response of the ferroelectric PZT layer alone. We also observed that, at low frequency, the voltage across the ferroelectric capacitor and the current in the circuit did not decrease significantly when diminishing then removing, the area of the conductive loop. One major conclusion is that eddy currents in the lead wires, rather than the classical electromotive force across conductive loops, contribute significantly to the total voltage response, at least for thin film ME devices. A model taking into account eddy currents was then developed for the extraction of the true αH ME. A large αH ME of 4.6V/cm.Oe was thus obtained for the Terfenol-D/Pt/PZT thin film device, without DC magnetic field. © 2015 AIP Publishing LLC.

Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 (Terfenol-D/Pt/PZT) thin films were sputtered on Pt/TiO2/SiO2/Si substrate. PZT and Terfenol-D layers were chosen for their large piezoelectric and magnetostrictive coefficients, respectively. 4%–5% magnetocapacitance has been measured on a Terfenol-D/Pt/PZT stack at room temperature. A magnetoelectric (ME) voltage coefficient of 150 mV/cm Oe was obtained at low dc magnetic field out of mechanical resonance. This work demonstrates the possibility to achieve ME effect in integrated devices involving Terfenol-D and PZT thin films providing that the diffusion, which may occur between both active layers is reduced using an intermediate layer.