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The formation process for planar solid electrolytes in the CeO2-Y2O3 system has been studied using efficient, high-performance, high-resolution microplotter printing technology, using functional ink based on nanopowders (the average size of crystallites was 12–15 nm) of a similar composition obtained by programmed coprecipitation of metal hydroxides. The dependence of the microstructure of the oxide nanoparticles obtained and their crystal structure on yttrium concentration has been studied using a wide range of methods. According to X-ray diffraction (XRD), the nanopowders and coatings produced are single-phase, with a cubic crystal structure of the fluorite type, and the electronic state and content of cerium and yttrium in the printed coatings have been determined using X-ray photoelectron spectroscopy (XPS). The results of scanning electron (SEM) and atomic force microscopy (AFM) have shown that the coatings produced are homogeneous, they do not contain defects in the form of fractures and the height difference over an area of 1 µm2 is 30–45 nm. The local electrophysical characteristics of the oxide coatings produced (the work function of the coating surface, capacitance values, maps of the surface potential and capacitive contrast distribution over the surface) have been studied using Kelvin-probe force microscopy (KPFM) and scanning capacitive microscopy (SCM). Using impedance spectroscopy, the dependence of the electrophysical characteristics of printed planar solid electrolytes in the CeO2-Y2O3 system on yttrium content has been determined and the prospects of the technology developed for the manufacture of modern, intermediate-temperature, solid oxide fuel cells have been demonstrated.

New opportunities in the development and commercialization of novel photonic and electronic devices can be opened following the development of technology-compatible arbitrary-shaped ferroelectrics encapsulated in a passive environment. Here, we report and experimentally demonstrate nanoscale tailoring of ferroelectricity by an arbitrary pattern within the nonferroelectric thin film. For inducing the ferroelectric nanoregions in the nonferroelectric surrounding, we developed a technology-compatible approach of local doping of a thin (10 nm) HfO

This work reports a radical-enhanced atomic layer deposition (REALD) process using WH2(Cp)2–O*–H* reaction cycles (Cp = cyclopentadienyl group) to grow WO3–x films with a wide range of tunable oxyg...

While the conductance of a first-order memristor is defined entirely by the external stimuli, in the second-order memristor it is governed by the both the external stimuli and its instant internal state. As a result, the dynamics of such devices allows to naturally emulate the temporal behavior of biological synapses, which encodes the spike timing information in synaptic weights. Here, we demonstrate a new type of second-order memristor functionality in the ferroelectric HfO2-based tunnel junction on silicon. The continuous change of conductance in the p+-Si/Hf0.5Zr0.5O2/TiN tunnel junction is achieved via the gradual switching of polarization in ferroelectric domains of polycrystalline Hf0.5Zr0.5O2 layer, whereas the combined dynamics of the built-in electric field and charge trapping/detrapping at the defect states at the bottom Si interface defines the temporal behavior of the memristor device, similar to synapses in biological systems. The implemented ferroelectric second-order memristor exhibits various synaptic functionalities, such as paired-pulse potentiation/depression and spike-rate-dependent plasticity, and can serve as a building block for the development of neuromorphic computing architectures.

The method of deposition from the gas phase is applied to the synthesis of thin films of molybdenum disulfide. It was established that varying the rate of temperature rise in the course of the synthesis affects the character of growth and the structure of the layers formed. With a decrease in the rate of temperature rise, a transition from standard two-dimensional to screw growth of MoS2 films is observed. MoS2 films produced as a result of screw growth have a high density of edge states, which makes them promising for use in catalysis.

The discovery of ferroelectricity in hafnium oxide has revived the interest in ferroelectric memories as a viable option for low power non-volatile memories. However, due to the high coercive field of ferroelectric hafnium oxide, instabilities in the field cycling process are commonly observed and explained by the defect movement, defect generation and field induced phase transitions. In this work, the optical and transport experiments are combined with ab-initio simulations and transport modeling to validate that the defects which act as charge traps in ferroelectric active layers are oxygen vacancies. A new oxygen vacancy generation leads to a fast growth of leakage currents and a consequent degradation of the ferroelectric response in Hf0.5Zr0.5O2 films. Two possible pathways of the Hf0.5Zr0.5O2 ferroelectric property degradation are discussed.

Graphene is a promising building block material for developing novel photonic and optoelectronic devices. Here, we report a comprehensive experimental study of chemical-vapor deposited (CVD) monolayer graphene’s optical properties on three different substrates for ultraviolet, visible, and near-infrared spectral ranges (from 240 to 1000 nm). Importantly, our ellipsometric measurements are free from the assumptions of additional nanometer-thick layers of water or other media. This issue is critical for practical applications since otherwise, these additional layers must be included in the design models of various graphene photonic, plasmonic, and optoelectronic devices. We observe a slight difference (not exceeding 5%) in the optical constants of graphene on different substrates. Further, the optical constants reported here are very close to those of graphite, which hints on their applicability to multilayer graphene structures. This work provides reliable data on monolayer graphene’s optical properties, which should be useful for modeling and designing photonic devices with graphene.

New interest in microscopic studies of ferroelectric materials with low piezoelectric coefficient, $d_{33}^\ast$, has emerged after the discovery of ferroelectric properties in HfO2 thin films, which are the main candidate for the next generation of nonvolatile ferroelectric memory. The study of the microscopic structure of ferroelectric HfO2 capacitors is crucial to get insights into the device behavior and performance. However, a small $d_{33}^\ast$ of ferroelectric HfO2 films leads to a low piezoresponse, especially in band excitation piezoresponse force microscopy (BE-PFM). In this work, we have implemented the BE-PFM technique with an increased scanning rate, thus improving this versatile tool for weak ferroelectrics. The acceleration of measurement was achieved by focusing excitation into a narrow frequency band and tuning the central frequency on-the-fly using an online real-time model estimation by fitting a complex BE response. The tracking of the contact resonance frequency was implemented using a pure mechanical cantilever response acquired in BE atomic force acoustic microscopy. To obtain optimal excitation parameters, we perform statistical analysis by minimizing estimator variance. The measurement precision of several PFM techniques was compared both by the simulation and experimentally using a Hf0.5Zr0.5O2-based ferroelectric capacitor.

We have applied spark ablation technology for producing nanoparticles from platinum ingots (purity of 99.97 wt. %) as a feed material by using air as a carrier gas. A maximum production rate of about 400 mg/h was achieved with an energy per pulse of 0.5 J and a pulse repetition rate of 250 Hz. The synthesized nanomaterial, composed of an amorphous platinum oxide PtO (83 wt. %) and a crystalline metallic platinum (17 wt. %), was used for formulating functional colloidal ink. Annealing of the deposited ink at 750 &deg, C resulted in the formation of a polycrystalline material comprising 99.7 wt. % of platinum. To demonstrate the possibility of application of the formulated ink in printed electronics, we have patterned conductive lines and microheaters on alumina substrates and 20 &mu, m thick low-temperature co-fired ceramic (LTCC) membranes with the use of aerosol jet printing technology. The power consumption of microheaters fabricated on LTCC membranes was found to be about 140 mW at a temperature of the hot part of 500 &deg, C, thus allowing one to consider these structures as promising micro-hotplates for metal oxide semiconductor (MOS) gas sensors. The catalytic activity of the synthesized nanoparticles was demonstrated by measuring the resistance transients of the non-sintered microheaters upon exposure to 2500 ppm of hydrogen.

The microstructures of amorphous and polycrystalline ferroelectric Hf0.5Zr0.5O2 films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO2 and ZrO2. After rapid thermal annealing, the mixed Hf0.5Zr0.5O2 oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands are formed in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO2 and ZrO2. The presence of the HfO2 and ZrO2 phases in the Hf0.5Zr0.5O2 films is also detected by ellipsometry.

Hf0.5Zr0.5O2 thin films are one of the most appealing HfO2-based ferroelectric thin films, which have been researched extensively for their applications in ferroelectric memory devices. In this work, a 1 mol % La-doped Hf0.5Zr0.5O2 thin film was grown by plasma-assisted atomic layer deposition and annealed at temperatures of 450 and 500 °C to crystallize the film into the desired orthorhombic phase. Despite the use of a lower temperature than that used in previous reports, the film showed highly promising ferroelectric properties—a remnant polarization of ∼30 μC/cm2 and switching cycle endurance up to 4 × 1010. The performance was much better than that of undoped Hf0.5Zr0.5O2 thin films, demonstrating the positive influence of La doping. Such improvements were mainly attributed to the decreased coercive field (by ∼30% compared to the undoped film), which allowed for the use of a lower applied field to drive the cycling tests while maintaining a high polarization value. La doping also decreased the leakage...

The growth per cycle saturation behaviors depending on the precursor pulse duration, reactant pulse duration, and reactant concentration were examined for hydrogen radical enhanced atomic layer deposition (REALD) of TaOx using tantalum-ethoxide as the precursor and plasma-activated hydrogen as the reactant. The chemical state of the TaOx film was dependent on the active hydrogen pulse duration and hydrogen volume fraction in the H2/Ar plasma mixture. The density of the electronic states in the dielectric band gap increased with the increase in the plasma exposure time (6–50 s) and hydrogen volume fraction (7–70%) whereas Ta4f core-level X-ray photoelectron spectroscopy indicated that the observed defects in the TaOx band gap are related to the oxygen deficiency. The ab initio calculations of oxygen deficiency concentrations and the energy spectrum satisfactorily correlated with the experimental data. The demonstrated combination of the growth saturation availability with the precise control of oxygen deficiency concentrations in the PEALD process could be highly useful in fields in which oxide dielectrics with adjustable oxygen deficiencies are required.

The clear substrate-dependent growth and delayed film continuity are essential challenges of Ru atomic layer deposition (ALD) demanding adequate and versatile approaches for their study. Here, we report on the application of in situ Angle Resolved X-ray Phototelectron Spectroscopy (ARXPS) for investigation of initial and steady-state ALD growth of Ru using Ru(EtCp) 2 and O 2 as precursors. Using ARXPS surface analysis technique we determine such parameters of Ru ALD initial growth as incubation period, fractional coverage and the thickness of islands/film depending on the substrate chemical state, governed by the presence/absence of NH 3 /Ar plasma pretreatment. It was demonstrated that NH 3 /Ar plasma pretreatment allows to obtain the lowest incubation period (∼7 ALD cycles) resulting in a continuous ultrathin (∼20 A) and smooth Ru films after 70 ALD cycles. In situ XPS at UHV was used at steady state Ru growth for analysis of half-cycle reactions that revealed formation of RuO x (x ≈ 2) layer with thickness of ∼8 A after O 2 pulse (first half-cycle). It was also shown that oxygen of RuO x layer combusts Ru(EtCp) 2 ligands in the second half-cycle reaction and the observed Ru growth of ∼0.34 A per cycle is in a good agreement with the amount of oxygen in the RuOx layer.

The plasma-enhanced atomic layer deposition (PEALD) process using Ta(OC2H5)5 as a Ta precursor and plasma-activated hydrogen as a reactant for the deposition of TaOx films with a controllable concentration of oxygen vacancies (VO) is reported herein. The VO concentration control was achieved by varying the hydrogen volume fraction of the hydrogen–argon mixture in the plasma, allowing the control of the leakage current density in the tantalum oxide films within the range of 5 orders of magnitude compared with the Ta2O5 film grown via thermal ALD using the identical Ta precursor and H2O. Temperature-dependent current–voltage measurements combined with Poole-Frenkel emission modeling demonstrated that the bulk trap depth decreases with the increasing hydrogen volume fraction, which could be attributed to the increase of the VO concentration. The possible chemical change in the PEALD TaOx films grown under different hydrogen volume fractions was confirmed by the in situ X-ray photoelectron spectroscopy (XPS) ...

For the decade, ferroelectric hafnium oxide films are attracting the interest as a promising functional material for nonvolatile ferroelectric random access memory due to full scalability and complementary metal-oxide-semiconductor integratability. Despite the significant progress in key performance parameters, particularly, the readout charge and voltage as well as the endurance, the developed devices can only be implemented by the electronics industry if they exhibit a standard retention time of 10 years. Material engineering modifies not only target ferroelectric properties, but also the retention time. To understand how to maintain the sufficient retention, the physical mechanism behind it should be clarified. For this purpose, we have fabricated the capacitor memory cell with a high rate of retention loss. Comparing the device performance with the results of capacitance transient spectroscopy, operando hard X-ray photoelectron spectroscopy and in situ piezoresponse force microscopy, we have concluded that the retention loss is caused by the accumulation of the positively charged oxygen vacancies at the interfaces with capacitor electrodes. The redistribution of charges during long-term storage of information is fully defined by the domain structure in memory cell.

TaO x films with controlled ratio of Ta4+ and Ta5+ atoms were prepared at different hydrogen concentrations in plasma. As shown by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, the chemical state of Ta4+ corresponds to oxygen vacancies in the TaO x film. Electrophysical studies of the metal–dielectric–metal structures revealed an increase in the leakage current by four orders of magnitude as the hydrogen concentration in the plasma was increased from 7 to 70%, which is due to an increase in the concentration of oxygen vacancies in TaO x . A test structure of a resistive memory cell was made on the basis of the nonstoichiometric TaO x obtained. It withstood more than 106 rewriting cycles. The suggested atomic layer deposition process shows promise for solving one of the main problems of resistive memory: extension of its working life.

The mechanism responsible for the charge transport in thin ferroelectric Hf0.5Zr0.5O2 films has been studied. It is shown that in these films the transport mechanism is phonon-assisted tunneling between the traps. The optimal thickness of dielectric film for TiN/Hf0.5Zr0.5O2/Pt structures is determined. As a result of comparing the experimental current–voltage (I–V) characteristics of TiN/Hf0.5Zr0.5O2/Pt structures with the calculated ones, the thermal and optical energies of the traps are determined and the concentration of the traps is estimated. A comparison between the transport properties of ferroelectric and amorphous Hf0.5Zr0.5O2 films is carried out. It is shown that the charge transport mechanism in this dielectric does not depend on its crystalline phase. A method for decreasing leakage currents in Hf0.5Zr0.5O2 is proposed. A study of the resource of repolarization cycles for TiN/Hf0.5Zr0.5O2/TiN metal-dielectric-metal (MDM) structures fully grown by atomic layer deposition (ALD) has been carried out.

The structural and electrical properties of materials based on hafnium oxide grown by atomic layer deposition (ALD) are analyzed. The possibility and prospects of the use of their nanoscale films in nonvolatile memory are considered. The possibility of scaling Ferroelectric random access memory (FRAM) to subμm dimensions while preserving the ferroelectric properties is shown.

Сombining the sol–gel method and pen plotter printing, using the hydrolytically active heteroligand complex [Co(C5H7O2)2-x(C4H9O)x] as a component of a new functional ink, Co3O4 thin films were produced on the surface of substrates of various types. The influence of synthesis conditions and print modes on the microstructure, optical, electrophysical and sensor properties of planar nanomaterials was comprehensively studied. The optical band gap energies associated with charge transfer for transitions O2-→Co3+ and O2-→Co2+ of the obtained thin films were evaluated. Using Kelvin probe force microscopy and impedance spectroscopy, the electrophysical characteristics (the electronic work function of the film surface, the temperature dependence of electrical conductivity, and the activation energy of electrical conductivity) of the obtained Co3O4 films were determined. The sensitivity of printed cobalt(II, III) oxide thin films with respect to various gases (Н2, СН4, СО and NO2) was studied. It was established that the obtained samples demonstrated the highest sensor response when detecting CO and NO2 in the operating temperature range of 150–200°С. The prospects of the proposed synthesis method and printing technology when forming Co3O4 thin-film nanostructures to create electrodes of supercapacitors and receptor components of resistive CO and NO2 gas sensors were shown.

The charge transport mechanism in thin amorphous and ferroelectric Hf0.5Zr0.5O2 films has been studied. It has been shown that the transport mechanism in studied materials does not depend on the crystal phase and is phonon-assisted tunneling between traps. The comparison of the experimental current–voltage characteristics of TiN/Hf0.5Zr0.5O2/Pt structures with the calculated ones provides the trap parameters: thermal energy of 1.25 eV and the optical energy of 2.5 eV. The trap concentration has been estimated as ~1019–1020 cm–3.

The crystalline structure and electrical response of La-doped HfO2-ZrO2 thin films of which processing temperature did not exceed 400 °C were examined, where the La-doping concentration was varied from zero to ≈2 mol. %. The film structure and associated properties were found to vary sensitively with the minute variation in the La-concentration, where the ferroelectric response at low La-concentration ( ≈1 mol. %, which was accompanied by a significant increase in dielectric permittivity. La-doping was found to be very effective in inhibiting the monoclinic phase formation and in decreasing the leakage current. Notably, the high coercive field, which was one of the most significant problems in this material system, could be decreased by ∼35% at the most promising La-concentration of 0.7 mol. %. As a result, a highly promising field cycling endurance up to 1011 cycles could be secured while maintaining a high remnant polarization value (≥25 μC/cm2). This is one of the best results in this field of the authors' knowledge.

The influence of La content on the ferroelectric properties of HfO2-ZrO2 thin films was examined for integrated electrostatic supercapacitor applications. A transition from ferroelectric to antiferroelectric-like behavior, accompanied by a significant increase of energy storage density value and efficiency, was observed with the increasing La concentration in La-doped HfO2-ZrO2-based capacitor structures, where the processing temperature remained below 400 °C. The combination of high energy storage density value (≈50 J/cm3) with high efficiency (70%) was obtained for the film with the highest La content (2.0 mol. %). The 2.0 mol. % La-doped HfO2-ZrO2-based capacitor structures were field cycled up to 109 times and were found to provide >40 J/cm3 energy storage density along with up to 80% efficiency. Moreover, the high thermal stability of such capacitors was confirmed. The founded property combination makes the La-doped HfO2-ZrO2 thin films suitable for integrated energy storage and pulse-power devices.The influence of La content on the ferroelectric properties of HfO2-ZrO2 thin films was examined for integrated electrostatic supercapacitor applications. A transition from ferroelectric to antiferroelectric-like behavior, accompanied by a significant increase of energy storage density value and efficiency, was observed with the increasing La concentration in La-doped HfO2-ZrO2-based capacitor structures, where the processing temperature remained below 400 °C. The combination of high energy storage density value (≈50 J/cm3) with high efficiency (70%) was obtained for the film with the highest La content (2.0 mol. %). The 2.0 mol. % La-doped HfO2-ZrO2-based capacitor structures were field cycled up to 109 times and were found to provide >40 J/cm3 energy storage density along with up to 80% efficiency. Moreover, the high thermal stability of such capacitors was confirmed. The founded property combination makes the La-doped HfO2-ZrO2 thin films suitable for integrated energy storage and pulse-power devices.

We report the possibility of employment of low temperature (≤330 °C) plasma-enhanced atomic layer deposition for the formation of both electrodes and hafnium-oxide based ferroelectric in the metal-insulator-metal structures. The structural and ferroelectric properties of La doped HfO2-based layers and its evolution with the change of both La content (2.1, 3.7 and 5.8 at. %) and the temperature of the rapid thermal processing (550–750 °C) were investigated in detail. Ferroelectric properties emerged only for 2.1 and 3.7 at. % of La due to the structural changes caused by the given doping levels. Ferroelectric properties were also found to depend strongly on annealing temperature, with the most robust ferroelectric response for lowest La concentration and intermediate 650 °C annealing temperature. The long term wake-up effect and such promising endurance characteristics as 3 × 108 switches by bipolar voltage cycles with 30 μs duration and ± 3 MV/cm amplitude without any decrease of remnant polarization value were demonstrated.