The pulsed laser deposition (PLD) method is widely used in the production of different thin films. PLD has several advantages: flexible adjustment of parameters and controllability of processes and ease of synthesis of materials. The deposition of zinc oxide droplets during the synthesis of zinc oxide thin films by PLD is considered and the temperature and initial speed of droplets, which can boil on the thin film surface, are determined. The study of the process of the deposition of droplets from a ZnO target was carried out during the growth of thin films according to the traditional scheme for the PLD method. The process of the deposition of ZnO droplets during the PLD of ZnO films under vacuum conditions is considered. For the first time, it has been revealed that ZnO drops are boiling on the thin ZnO film surface. For the first time, the temperature and speed of solid and liquid drops of ZnO, at which they can boil when they hit the substrate, have been calculated taking into account the processes of heat loss through radiation and the heat of phase transition. Thus, for the first time, it has been established experimentally and confirmed in calculations that at the moment of collision some drops of ZnO are boiling. The role of the heat of phase transition and heat loss due to radiation during the flight of droplets during the PLD of ZnO thin films in a vacuum has been clarified. The temperature of a ZnO drop after a collision with a substrate was calculated in a wide range of initial speed and temperature taking into account heat losses due to radiation and heating from impact.

NbOx thin films demonstrating the analog resistive switching characteristics in planar geometry were fabricated by the droplet-free pulsed laser deposition from Nb metal targets. The memristive properties of the films were controlled by tuning the oxygen pressure from 0.7 to 8 Pa and the wavelength of the ablative laser (lambda = 248 nm or lambda = 532 nm). The stoichiometry of the NbOx films was controlled by the X-ray photoelectron spectroscopy, optical and electrical investigations. Variation of the film thickness from 20 to 50 nm affects the resistive switching characteristics. The 20 nm NbO2 films obtained at the oxygen pressure of 1.3 Pa show a volatile memristive switching with a memory window of ON/OFF resistances similar to 10(1) after 500 direct current cycles at an operating voltage of 4.5 V. The 30 nm Nb2O5 films fabricated at the oxygen pressure of 4 Pa, showed a gradual increase in device conductivity with successive positive voltage sweeps with an amplitude of +5 V, which is characteristic of non-volatile memristive switching. Thus, the use of NbOx memristive films of different compositions and crystallinity degree will allow creating neuromorphic systems based on the same material by controlling the memristive behavior by the laser synthesis conditions.

Investigations of the dependence of the ferromagnetism of MnxSi1-x (x - 0.5) films on the energy spectrum of target plume particles are topical for spintronics. The time-of-flight (TOF) method using a Langmuir probe has been used to study the dynamics of a laser plume during ablation of a SiMn target in vacuum and in an atmosphere of He, Xe, Ar, N2 buffer gases in a wide pressure range from 10-6 to 4 & BULL;10- 1 mbar. The TOF curves of the probe signal have been obtained by ablation of the SiMn target by the second harmonic of the Q-switched Nd: YAG laser. A nonmonotonic dependence of the probe signal amplitude on the buffer gas pressure was established. A feature of the delay of the TOF curve signal from the moment of target ablation as a function of the N2 pressure in the chamber was revealed, which was explained by the resonant scattering of the Si + ion and the N2 nitrogen molecule. The most suitable gases for control of the ion velocity were selected based on the dynamics of the laser plume. The dependence of the electrical characteristics of MnxSi1-x (x - 0.5) films on the pressure of helium and argon has been established.

In this work, we investigate the possibility of controlled tuning the resistive switching of the Pt/TaOх/Ta2O5/Pt/c-Al2O3 memristors in crossbar geometry by changing the oxygen pressure from 0.5 to 50 mTorr during the low-temperature laser synthesis. The stochastic process of nanocrystallite formation significantly affects the spread of memristor parameters. X-ray diffraction studies of the TaOx films with high resolution made it possible to determine the conditions for obtaining the active region of the memristor with the formation of certain size nanocrystallites. The presence of the nanocrystallites in the amorphous matrix of the oxide region of the memristor based on tantalum oxides makes it possible to improve the uniformity and reliability of the resistive switching with an increase in the memory window performance by an order of magnitude. The memristor showed very reliable resistive switching performance over 100 I-V cycles with the memory window performance of RON/ROFF ~ 103 at RESET operating voltage of ~2.3 V.

Various materials that ensure the creation of volatile and nonvolatile memristor structures are under study in the development of elements of neuromorphic systems. TaOx thin films and memristor structures in the crossbar geometry based on them are synthesized by pulsed laser deposition in the droplet-free mode using mask technologies. TaOx thin films are obtained at different temperatures of the sapphire substrate (25 and 350°C), oxygen pressure in the vacuum chamber (from 0.5 to 80 mTorr), and wavelength of the ablation radiation (248 and 532 nm). High-resolution X-ray diffraction studies of films make it possible to determine the conditions for the preparation of films with the formation of nanocrystallites and the dependence of the size of nanocrystallites on the preparation conditions. The composition of the films and the degree of oxidation of tantalum are determined by X-ray photoelectron spectroscopy. The two-probe method is used to study the current–voltage characteristics (I—V characteristics) of the films at unipolar and bipolar voltage scanning. The nonvolatile memristive effect in Ta/TaOх/Ta/с-Аl2O3 thin-film structures is revealed during measurements of the I—V characteristics in the planar and crossbar geometry.

Amorphous NbOx (x < 2.5) thin films with the presence of nanocrystallites, which are promising for use as an active region of volatile memristors were fabricated on c-Al2O3 substrates by the laser synthesis. The films were obtained from targets of niobium metallic during ablation of laser with lambda = 248 nm or lambda = 532 nm in oxygen pressure range from 5 to 50 mTorr. The effect of the oxygen partial pressure and the wavelength of ablating laser on the chemical, structural, electrical, and optical properties of the films was studied. The optimal conditions for the formation of Nb2O5 and NbO2 stable phases in the films were determined. It was found that the amorphous NbOx phase, which was a source of defects associated with oxygen deficiency, required for the creation of memristors, appeared only at low oxygen pressures in the chamber (similar to 5 .10(-3) -10(-1) Ohm . cm) during the film synthesis by the laser with both lambda = 248 nm and lambda = 532 nm. Volatile memristors of Nb/NbO?/Nb2O5/Pt/c-Al2O3 (x <= 2.5) in cross-bar geometry were created demonstrating long-term stability of operation for 60 DC cycles with delta R-HRS/R-HRS < 8% at an operating switching voltage of similar to 0.5 V.

Thin films of MnxSi1 – x (x ≈ 0.5) alloy were synthesized by pulsed laser deposition in a droplet-free mode on sapphire substrates with different crystallographic cut-off plane orientations (c-Al2O3 and r-Al2O3) at various laser energy densities E at the polycrystalline target MnSi. X-ray structure properties, as well as static and resonance magnetic characteristics of the films depending on the value of E and substrate orientation were investigated. The presence of a ferromagnetic phase with an unusually high Curie temperature TC ~ 300 K which is untypical of MnSi single crystals (TC ~ 30 K) was revealed in films deposited using high laser energy densities E > 6 J/cm2 at the target. The magnetic moment of the films on c-Al2O3 substrates is somewhat larger than in the case of r-Al2O3 substrates. Moreover, the films deposited on c-Al2O3 substrates show significantly higher values of the effective magnetic anisotropy field 4πMeff, measured by ferromagnetic resonance. Obtained data show that the structure of the substrate has a remarkable influence on the formation process and magnetic properties of the high-temperature ferromagnetic phase in the MnxSi1 – x films.

Методом лазерного синтеза из металлических мишеней при абляции излучением 248 и 532 нм получены тонкие пленки NbOx и TaOx в атмосфере кислорода и мемристоры на их основе в кроссбар-геометрии. В качестве электродов служили пленки Pt, Au, Ag, Ta, Nb. Изучено поведение ВАХ-мемристоров, полученных при разных условиях.

Thin films of MnxSi1-x (x ≈ 0.5) alloy were synthesized by pulsed laser deposition in a droplet-free mode on sapphire substrates with different crystallographic orientations of the cut plane (c-Al2O3 and r-Al2O3) at various laser energy densities E at the polycrystalline MnSi target. The X-ray structural, as well as static and resonance magnetic properties of the films were studied depending on E and the orientation of the substrate. The films deposited at high E > 6 J/cm2 are found to demonstrate the presence of a ferromagnetic phase with anomalously high Curie temperature TC ~ 300 K which is not typical of MnSi single crystals (TC ≈ 30 K). In the case of the c-Al2O3 sub-strates, the magnetic moment of the films turns out to be somewhat higher than in the case of the r-Al2O3 substrates. Moreover, the films deposited on the c-Al2O3 substrates exhibit noticeably higher values of the effective surface anisotropy field 4πMeff measured by ferromagnetic resonance. The data obtained indicate a significant effect of the substrate structure on the formation and magnetic properties of the high-temperature ferromagnetic phase in the MnxSi1-x films.

The amorphous thin TaOx films (x <= 5) of different thicknesses with different levels of oxygen vacancy content, which are promising for use as an active region of non-volatile memristors, were fabricated by the pulsed laser deposition in a drop-free mode on the c-sapphire substrates. The films were obtained from tantalum metal targets at substrate temperatures of 25 degrees C and 350 degrees C in the oxygen pressure range from 0.5 to 50 mTorr. The relationship between the partial oxygen pressure and the optical, electrical, and chemical properties of the films was studied. It was found that the amorphous TaO x phase, which is a source of defects associated with oxygen deficiency, required for the creation of memristors, appears only at low oxygen pressures in the chamber (similar to 5 x10(-4) Torr), this leads to low values resistivity in the films (similar to 10(-3) Ohm . cm). Memristor structures Ag(Pt)/TaOx/TaOy /Ta/c-Al2O3 (x > y) in cross-bar geometry have been created that do not require electroforming, due to the choice of design and deposition conditions. Memristor using two mechanisms of resistive switching based on oxygen vacancies and silver cations showed very reliable RS performance with memory window performance R-ON/R-OFF similar to 10(3) and RESET operating voltage similar to 1 V. (C) 2020 Elsevier Ltd. All rights reserved.

Structural features of carbon nanotubes make them highly promising for nanoelectronics, nanosensors, electrodes for energy storage and harvesting devices, composites, and weaving yarns. Carbon nanotubes covered with amorphous carbon can be efficiently applied as field emitters with higher brightness and stability compared to the metal ones. Vertically aligned arrays of the CNTs covered with amorphous carbon were synthesized by modified CVD method in the tube flow reactor via catalytic pyrolysis of acetylene. Stepwise films of iron on single crystal silicon substrate (100) obtained by the pulsed laser deposition (PLD) method were used as catalyst for their growth. The height of the CNT arrays was found to be dependent on the thickness of iron films. The obtained arrays were formed by multiwalled carbon nanotubes covered with the amorphous carbon. Low thermal stability of acetylene and insufficient activity of iron catalysts at the reaction temperature enable the reproducible formation of vertically aligned amorphous carbon covered CNT arrays promising for electronic applications and carbon textile preparation.

Thin films of MnxSi1-x (x ~ 0.5) were obtained by pulsed laser deposition in droplet-free mode on c- and r-Al2O3 substrates at different laser energy densities E at the target. Their structural, electrical, and magnetic properties were studied depending on the value of E and the orientation of the substrate. The films are X-ray amorphous on the substrates of both types at E < 6.8 J/cm2, and only at E ≅ 6.8 J/cm2 the reflections of ε-MnSi crystallites with B20-type of structure begin to appear in the MnxSi1-x films on c-Al2O3 and at E ≅ 7.4 J/cm2 - on r-Al2O3 substrates. The X-ray diffraction data of the samples indicate the presence in the films of the ε-MnSi nanocrystallites of an optimal size for the manifestation of high-temperature ferromagnetism; the concentration of nanocrystallites is controlled by the type of substrate and the energy density at the target. It is found that at E > 5.5 J/cm2 the high-temperature ferromagnetic phase shows in the films, and at E ≅ 4 - 5 J/cm2, the low-temperature ferromagnetic phase predominates and there is no influence of the sapphire substrate orientation. The highest Curie temperature TC reached was 330 K at E ≅ 7.4 J/cm2 for the MnxSi1-x films obtained on c- and r-Al2O3. The correlated behavior of the magnetization and the signal of diffuse X-ray radiation scattering confirms the existence of ε-MnSi nanocrystallites.

Методом импульсного лазерного осаждения в бескапельном режиме при изменении давления кислорода от 0,5 до 50 мторр на подложках с-сапфира созданы и исследованы тонкие пленки оксидов тантала, а также энергонезависимые мемристорные структуры на их основе, не требующие процедуры электроформовки благодаря использованию двух механизмов резистивного переключения на основе кислородных вакансий и ионов серебра.

— Amorphous dielectric WO 3 films with a surface roughness from 4 to 5 nm have been grown by room-temperature pulsed laser deposition on quartz and c -sapphire substrates using metallic targets. We have examined the effect of the nature of the substrates and the oxygen pressure during the growth process on the transmission spectrum of the WO 3 films in the range from 400 to 2000 nm. The parameters of the films have been shown to depend on the oxygen pressure during the growth process. Raising the oxygen pressure from 20 to 60 mTorr during the film growth process increases the transmission of the WO 3 films from 40 to 75% in the visible and UV spectral regions and from 10 to 70% in the IR. With increasing oxygen pressure during film growth, the band gap of the WO 3 films increases from 3.01 to 3.34 eV in the case of sapphire substrates and from 2.95 to 3.42 eV in the case of quartz substrates, being only slightly dependent on the nature of the substrate. Using a WO 3 film grown at room temperature, we have fabricated the first thin-film liquid-electrolyte electrochromic cell. Its transmission in the spectral range from 300 to 900 nm drops by 30% at an applied voltage of 2.5 V, with a coloration time on the order of 2 min.

Magnetic properties of two-phase granular semiconductor–ferromagnet GaSb–MnSb films obtained by pulsed laser deposition as a function of growth temperature and postgrowth annealing were stu-died.

The magnetic properties of two-phase granular semiconductor-ferromagnet GaSb–MnSb films obtained by pulsed laser deposition, depending on the temperature conditions of growth and postgrowth annealing, are investigated.

MnxSi1 – x (x ≈ 0.5) thin films have been produced on c- and r-cut sapphire substrates by the droplet-free pulsed laser deposition method at various laser energy densities E on the target. Their magnetic, electric, and X-ray diffraction properties as a function of E and substrate orientation have been investigated. It has been established that the high-temperature ferromagnetic phase in the films at E ≥ 6 J cm–2 is more pronounced than that at E ≈ 4–5 J cm–2, when the low-temperature ferromagnetic phase dominates and there is no influence of the sapphire substrate orientation. The attained Curie temperature TC was 330 K at E ≈ 7.4 J cm–2 for the MnxSi1 – x films produced on c- and r-cut sapphire substrates. The magnetization of the MnxSi1 – x films produced at E ≥ 6 J cm–2 on c-cut sapphire is higher than that on r-cut sapphire and, conversely, lower when E ≤ 5.5 J cm–2. A change in the ratio of the diffuse signal amplitudes in the X-ray spectra for the films grown on different substrates is also observed under these conditions. Such a correlated behavior with magnetization is explained by the existence of ε-MnSi nanocrystallites of optimal sizes, which, on the one hand, are responsible for the emergence of a diffuse signal in the X-ray spectra and, on the other hand, determine the high-temperature ferromagnetism of the films. The concentration of such nanocrystallites and the distribution of defects in the films are controlled by the type of substrate and the energy density on the target.