We have demonstrated the possibility of manufacturing thermocatalytic and chemoresistive gas sensors with functional layers fabricated by microplotter printing with colloidal inks formulated from palladium based (PdOx) and tin based (SnOx) nanoparticles synthesized by spark discharge. The microhotplate chips comprising 20–30 μm thick glass-ceramic membrane with patterned microheater and readout electrodes were used to implement sensors. For fabricating catalytic layers of thermocatalytic sensors, we used printing ink with inorganic (dispersed) phase containing 63 wt. % of PdOx and 37 wt. % of SnOx. The gas sensing layers of chemoresistive sensors were fabricated by using two types of inks with the following compositions of inorganic phase: i) 30 wt. % (PdOx), 70 wt. % (SnOx); ii) 40 wt. % (PdOx), 60 wt. % (SnOx). The thermocatalytic sensors demonstrated relatively high sensitivity to methane (51 mV per 1% of methane) and detection limit as low as 6 ppm at a power consumption of about 350 mW being comparable with that of commercial analogs. The achieved response (relative change of conductance) of chemoresistive sensors to 1% of methane is about 5.2 and detection limit is estimated at 45 ppm at a power consumption of about 140 mW.

Ultra-thin layers of TiO2 on MoS2 surface are used as part of source-to-drain contact stacks in field-effect transistors, for surface passivation, improvement of channel conductivity, etc. The growth kinetics of TiO2 obtained by atomic layer deposition from TDMAT and H2O precursors on the surface of monocrystalline and MoS2 films was investigated in this work. It is shown that irradiation of MoS2 by He (+) ions with kinetic energy of 500 eV leads to chemical activation (functionalization) of MoS2 surface and the beginning of TiO2 growth without incubation period, which allows to obtain continuous TiO2 layers of similar to 1 nm thickness. The formation of chemical states at interfaces in MoS2/Ru and MoS2/TiO2/Ru structures has been studied. TiO2 layer prevents the sulfur sputtering. The measurement results of the band alignment in the investigated structures confirm that a tunnel-thin TiO2 intermediate layer can be effectively utilized as a low-resistance buffer layer. It is shown that the absence of continuity of the TiO2 layer leads to a decrease in valence band offset and, consequently, an increase in conduction band offset. The obtained results can be used in the design of contact stacks with low resistance to MoS2 channels in field-effect transistors.

2D MoS2 is a promising material for electronics and optoelectronics. Currently, the most cost-effective and simple way of its synthesis on large-scale substrates is sulfurization, resulting in nanocrystalline films. These films are very specific objects, which deserve special attention. Making appropriate metallic contacts to nanocrystalline MoS2 is also assumed as another critical challenge. Therefore, in this work we synthesized nanocrystalline MoS2 films via the sulfurization technique and investigated the influence of their thickness on the structural and electrical properties. It was found that the 2.5 nm film contained significantly smaller crystalline grains compared to the 3.5 nm one, but with signs of in-plane orderliness. This film also showed a much higher modulation of ti2 x 104, which is mainly attributed to the achievement of the very low currents in the "Off" state, while the 3.5 nm thick MoS2 film essentially retained its conductivity. However, in both cases the FET performance in the "On" state was solely limited by the contact resistance (Rc). The Arrhenius measurements showed that the effective Schottky barrier height depended on the gate voltage, but generally it was ti2 times higher for a thinner film. Therefore, the contact engineering technique is not invariant to the film thickness.

HfO2 ferroelectrics, especially Hf0.5Zr0.5O2 (HZO) attract enormous attention as the basis of the non-volatile ferroelectric random-access memory. However, there is a problem with achieving practically acceptable reliability (including both high endurance and long retention) of the capacitors with HZO, which makes the production of HZO-based memory still elusive. According to recent investigations, the incorporation of the ultrathin TiO2 dielectric layers to HZO/TiN interfaces could be used for performance improvement. However, these studies either do not cover the impact of the TiO2 on the whole set of practically important properties (usually excluding retention ability because of the time-consuming experiments) or do not show if TiO2 inset can be used on both interfaces for the ultimate reliability improvement. In this work, employing the comprehensive analysis of all the aspects related to the reliability of the ferroelectric capacitors, we investigate how the location of the TiO2 inset (top, bottom, or both) impact the ferroelectric response and all the reliability properties of TiN/HZO/TiN capacitors. Our findings show that although both top and bottom TiO2 insets significantly improve imprint, which is the major origin of the retention loss, and do not contribute noticeably to the depolarization, the positive effect of the bottom inset is more pronounced than the one of the top TiO2. In addition, it has been demonstrated, that imprint behavior should be considered in combination with the shape of the ferroelectric hysteresis of a particular sample. The last one is exceptionally different for the top, bottom, and both insets, which leads to the unexpected difference in the impact of the inset location on the retention. Taking into account that it is bottom TiO2 that improves retention most significantly, enhances 2Pr, and does not deteriorate endurance as compared to the samples with top and both insets, we propose that implementation of bottom TiO2 remains the best solution for the reliability improvement of TiN/HZO/TiN capacitors.

Despite the great potential of the hafnium zirconium oxide (HZO)-based ferroelectrics for the emerging non-volatile ferroelectric memories, it provides also a material solution to the existing technological challenge arising for DRAM memory. In this work, we explore the possibility of using the La-doping of HZO to ensure low leakages along with high dielectric permittivity k and low equivalent oxide thickness (EOT) and the technological and operational approaches, including rapid thermal annealing and electric-field cycling, for their further improvement. We show that fully ALD grown TiN/La-HZO/TiN devices formed in the temperature budget not exceeding backend-of-line-compatible 400 °C easily provide the EOT value of 0.86 nm at the La-HZO thickness of 10 nm. The optimal cycling and annealing conditions (3–4 V@550 °C) provide the EOT as low as 0.46 nm. Considering also the rather low leakage currents, significantly less than 10−7 A/cm2, and moderate energy loss, this result makes the La-HZO films promising for the future DRAM technology.

The plasmonic sensors based on silver nanoparticles are limited in application due to their relatively fast degradation in the ambient atmosphere. The technology of ion-beam modification for the creation of monocrystalline silver nanoparticles (NPs) with stable plasmonic properties will expand the application of silver nanostructures. In the present study, highly-stable monocrystalline NPs were formed on the basis of a thin silver film by low-energy ion irradiation. Combined with lithography, this technique allows the creation of nanoparticle ensembles in variant forms. The characterization of the nanoparticles formed by ion-beam modification showed long-term outstanding for Ag nanoparticles stability of their plasmonic properties due to their monocrystalline structure. According to optical spectroscopy data, the reliable plasmonic properties in the ambient atmosphere are preserved for up to 39 days. The mapping of crystal violet dye via surface-enhanced Raman spectroscopy (SERS) revealed a strong amplification factor sustaining at least thrice as long as the one of similarly sized polycrystalline silver NPs formed by annealing. The plasmonic properties sustain more than a month of storage in the ambient atmosphere. Thus, ion-beam modification of silver film makes it possible to fabricate NPs with stable plasmonic properties and form clusters of NPs for sensor technology and SERS applications.

van der Waals topological insulators, characterized by their high-index dielectric response, offer a promising materials platform for nanophotonics. Among these materials, Bi2Te3 has one of the highest refractive indices and extinction coefficients. However, the precise determination of Bi2Te3 optical properties remains challenging owing to its complicated physical model, which includes an oxide layer, topological conducting states, and optical anisotropy. Here, we resolve this problem and develop an accurate optical model for Bi2Te3 in a broad (450-1500 nm) spectral range. Our study shows that an oxide layer plays a major role in optical model for these wavelengths, while the influence of topological conducting states and optical anisotropy is minimal. Our model allows us to obtain accurate Bi2Te3 optical constants and demonstrate their use in biosensors, thermal theranostics, and topological phase singularities. Moreover, we observe a polarization transition of topological phase singularity for Bi2Se3, which opens a new direction for the development of topological phase effects. Therefore, our results open new avenues for photonic applications of Bi2Te3 optical properties.

In the presented work, the method of metal-organic chemical vapor deposition (MOCVD) using Mo(CO)6 and H2S assisted by oxidative etching with water vapor, was employed for the synthesis of MoS2. This study was aimed at detailed investigation of the films' properties obtained via this method and identifying methods for elimination of such disadvantages as the carbon impurities and the small size of crystalline domains in the films. It was found that in the temperature range from 850 degrees C to 950 degrees C, the effect of water vapor on the morphology of MoS2 is significantly different. The study of the chemical states of molybdenum and sulfur made it possible to associate the size of the crystal domains formed with the efficiency of removing the oxidized states of Mo6+ and S6+. It is assumed that the increase in the domains' size is due to rapid lateral growth, resulting from the complete removal of the oxidized states at the edges, as well as a decrease in the density of nucleation centers due to the etching of less stable seeds on the substrate surface.

In the presented work, the method of metal–organic chemical vapour deposition (MOCVD) using Mo(CO)6 and H2S assisted by oxidative etching with water vapor, was employed for the synthesis of MoS2. This study was aimed at detailed investigation of the films’ properties obtained via this method and identifying methods for elimination of such disadvantages as the carbon impurities and the small size of crystalline domains in the films. It was found that in the temperature range from 850oC to 950oC, the effect of water vapor on the morphology of MoS2 is significantly different. The study of the chemical states of molybdenum and sulfur made it possible to associate the size of the crystal domains formed with the efficiency of removing the oxidized states of Mo6+ and S6+. It is assumed that the increase in the domains’ size is due to rapid lateral growth, resulting from the complete removal of the oxidized states at the edges, as well as a decrease in the density of nucleation centers due to the etching of less stable seeds on the substrate surface.

Correction for ‘Tunable optical properties of transition metal dichalcogenide nanoparticles synthesized by femtosecond laser ablation and fragmentation’ by Anton S. Chernikov et al., J. Mater. Chem. C, 2023, 11, 3493–3503, https://doi.org/10.1039/D2TC05235K.

Recently, the extensive study of the platinum group metal oxide electrodes for TiN replacement in Hf0.5Zr0.5O2 (HZO)-based ferroelectric memory stacks began. In this work, we use high sensitivity of x-ray photoelectron spectroscopy to the interface chemical and electronic states to investigate the chemistry and band alignment between HZO and RuO2, which is one of the most suitable noble metal oxide electrodes. We report that RuO2 is easily reduced to metallic Ru during the atomic layer deposition (ALD) of HZO because of the chemical reaction between the oxygen stored in RuO2 and metallic precursors used for HZO deposition. This process makes it impossible to use RuO2 as a bottom electrode, when HZO is grown by the conventional thermal ALD process (with H2O as a reactant). At the same time, RuO2 may be effectively conserved if one uses more active oxygen reactants for the HZO growth because of the re-oxidation of the newly formed Ru. RuO2 is also effectively conserved at the top interface, at least within the thermal budget of the growth of all functional layers. We also report the detailed investigation of the band alignment between RuO2 and HZO in both type of stacks (with reduced and conserved RuO2) and both interfaces with HZO (top and bottom), which may be useful for the understanding of the ferroelectric properties of the related stacks in the future. In addition, the potential of RuO2 utilization for the reliability improvement of HZO-based stacks is discussed.

Metal-Organic CVD method (MOCVD) allows for deposition of ultrathin 2D transition metal dichalcogenides (TMD) films of electronic quality onto wafer-scale substrates. In this work, the effect of temperature on structure, chemical states, and electronic qualities of the MOCVD MoS2 films were investigated. The results demonstrate that the temperature increase in the range of 650 °C to 950 °C results in non-monotonic average crystallite size variation. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman spectroscopy investigation has established the film crystal structure improvement with temperature increase in this range. At the same time, X-Ray photoelectron spectroscopy (XPS) method allowed to reveal non-stoichiometric phase fraction increase, corresponding to increased sulfur vacancies (VS) concentration from approximately 0.9 at.% to 3.6 at.%. Established dependency between the crystallite domains size and VS concentration suggests that these vacancies are form predominantly at the grain boundaries. The results suggest that an increased Vs concentration and enhanced charge carriers scattering at the grains’ boundaries should be the primary reasons of films’ resistivity increase from 4 kΩ·cm to 39 kΩ·cm.

Neuromorphic capabilities of a self-aligned complementary metal-oxide-semiconductor compatible W/WOx/HfO2/Ru cell in a 3D vertical memristive structure were investigated. We show that the device exhibits nonfilamentary forming-free multilevel resistive switching with gradual resistance change. In addition, the poor retention of a low resistance state allows integration of these structures in architectures that require short-term memory characteristics such as reservoir computing systems. The ability of the device to rely on the temporal sequence of the stream was tested with the digit recognition task. Since a WOx layer was obtained by thermal oxidization and HfO2 and Ru layers were grown by atomic layer deposition methods, the device is suitable for high-density systems with high connectivity within a neural network.

ABSTRACT. The plasmonic sensors based on silver nanoparticles are limited in application due to their relatively fast degradation in the ambient atmosphere. The technology of ion-beam modification for the creation of monocrystalline silver nanoparticles (NPs) with stable plasmonic properties will expand the application of silver nanostructures. In the present study, highly-stable monocrystalline NPs were formed on the basis of a thin silver film by low-energy ion irradiation. Combined with lithography, this technique allows the creation of nanoparticle ensembles in variant forms. The characterization of the nanopar- ticles formed by ion-beam modification showed long-term outstanding for Ag nanoparticles stability of their plasmonic properties due to their monocrystalline structure. According to optical spectroscopy data, the reliable plasmonic properties in the ambient atmosphere are preserved for up to 39 days. The mapping of crystal violet dye via surface-enhanced Raman spectroscopy (SERS) revealed a strong amplification factor sustaining at least thrice as long as the one of similarly sized polycrystalline silver NPs formed by annealing. The plasmonic properties sustain more than a month of storage in the ambient atmosphere. Thus, ion-beam modification of silver film makes it possible to fabricate NPs with stable plasmonic properties and form clusters of NPs for sensor technology and SERS applications.

Heterogeneous nanostructures composed of metastable tetragonal 1T-MoS2 and stable hexagonal 2H-MoS2 phases are highly promising for a wide range of applications, including catalysis and ion batteries, due to the high electrical conductivity and catalytic activity of the 1T phase. However, a controllable synthesis of stabilized 1T-MoS2 films over the wafer-scale area is challenging. In this work, a metal-organic chemical vapor deposition process allowing us to obtain ultrathin MoS2 films containing both 1T and 2H phases and control their ratio through rhenium doping was suggested. As a result, Mo1-xRexS2 films with a 1T-MoS2 fraction up to ≈30% were obtained, which were relatively stable under normal conditions for a long time. X-ray photoelectron spectroscopy and Raman spectroscopy also indicated that the 1T-MoS2 phase fraction increased with rhenium concentration increase saturating at Re concentrations above 5 at. %. Also, its concentration was found to significantly affect the film resistivity. Thus, the resistivity of the film containing approximately 30% of the 1T phase was about 130 times lower than that of the film without the 1T phase.

Control of the chemical composition and optical properties of molybdenum disulfide nanoparticles by laser ablation and fragmentation is demonstrated.

Ultrathin ( 10 nm) functional layers of a high-k dielectric, Hf0.5Zr0.5O2 (HZO), precision-doped with lanthanum, were prepared by molecular layering (atomic layer deposition), and capacitor structures based on them were formed. Such doping suppresses the formation of the equilibrium monoclinic phase in HZO and leads to the formation of metastable tetragonal/orthorhombic phases. Electrophysical measurements demonstrate signs of the formation of a morphotropic boundary between these phases and abnormally high, for dielectrics based on HfO2/ZrO2, relative dielectric permittivity (k 58). This quantity consists of the structure post-treatment conditions, namely, on the rapid thermal anneal (RTA) temperature. The maximal dielectric permittivity is reached at the RTA temperature of 550°С, with low leakage currents, <10–7 A cm–2, being preserved. Owing to such combination of properties, the functional layers synthesized show promise as high-k dielectrics in logic device transistors and in random-access memory cells.

This paper reports on the hysteresis and frequency tuning (electrical and magnetic) of the Bragg resonance in the spectrum of spin waves in a multiferroic structure based on YIG (100 nm thick) and HZO (10 nm thick) with a periodic modulation of parameters. The resonance can be tuned in a wide frequency range of 1-4 GHz by a magnetic field H and in a narrow frequency range of similar to 3 MHz by an electric field E. Electrical tuning was carried out due to a combination of the magnetostriction of the ferromagnetic layer and the piezoelectric effect in the ferroelectric due to mechanical coupling between the layers. The direction of the resonance shift caused by the electric field changed at the coercive field, and the alteration characteristic is of "butterfly" type.

The nanosecond speed of information writing and reading is recognized as one of the main advantages of next-generation non-volatile ferroelectric memory based on hafnium oxide thin films. However, the kinetics of polarization switching in this material have a complex nature, and despite the high speed of internal switching, the real speed can deteriorate significantly due to various external reasons. In this work, we reveal that the domain structure and the dielectric layer formed at the electrode interface contribute significantly to the polarization switching speed of 10 nm thick Hf0.5Zr0.5O2 (HZO) film. The mechanism of speed degradation is related to the generation of charged defects in the film which accompany the formation of the interfacial dielectric layer during oxidization of the electrode. Such defects are pinning centers that prevent domain propagation upon polarization switching. To clarify this issue, we fabricate two types of similar W/HZO/TiN capacitor structures, differing only in the thickness of the electrode interlayer, and compare their ferroelectric (including local ferroelectric), dielectric, structural (including microstructural), chemical, and morphological properties, which are comprehensively investigated using several advanced techniques, in particular, hard X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and electron beam induced current technique.

Atomically thin molybdenum disulfide(MoS2) is a promisingsemiconducting material for next-generation electronics and photonics.These applications often require its pairing with ultrathin AtomicLayer Deposited (ALD) high-k dielectrics, which maynot only improve the performance of fabricated field-effect transistors(FET) but also protect against harmful interactions with the ambientenvironment. However, because ALD on the pristine MoS2 surfacesuffers from prolonged nucleation, resulting in ultrathin continuousfilm growth difficulty, its preliminary functionalization becomesa necessary aspect. To date, the most reliable way of MoS2 functionalization is ion beam exposure, which enables to producepoint defects, the presence of which should improve the precursorchemisorption during the following ALD growth. In this work, we demonstratedthe possibility of the sulfur vacancy (V (S)) concentration tuning both at the sub-surface level of a bulk crystaland in few-layer films by controlling the He+ ion energyand the irradiation dose. Based on X-ray photoelectron spectroscopy(XPS) analysis, the bulk crystal was prone to significant sulfur losseven under 500 eV He+ irradiation, which is governed byphysical sputtering selectivity. In contrast to the bulk crystal,for the case of few-layer MoS2 films, just the Frenkel V (S) formation was observed, as indicated by Ramanspectroscopy, since no stoichiometry changes were detected. Generatedsulfur vacancies are readily passivated through Mo-OH species duringsubsequent water vapor exposure in the ALD reactor, which resultedin a significantly enhanced ALD HfO2 growth. As a result,the possibility of the ultrathin (<3 nm) and continuous film growthon the irradiated bulk MoS2 surface was demonstrated, andfor the monolayer MoS2 film, an increase in the surfacedensity of ALD active sites by a factor of & AP;2 was observed.