Crystallinity as a factor of SERS stability of silver nanoparticles formed by Ar irradiation.

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.

Effect of Domain Structure and Dielectric Interlayer on Switching Speed of Ferroelectric HfZrO Film.

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 HfZrO (HZO) film.

Temperature-Dependent Structural and Electrical Properties of Metal-Organic CVD MoS Films.

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 MoS 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.

Stabilization of the Nano-Sized 1T Phase through Rhenium Doping in the Metal-Organic CVD MoS Films.

Heterogeneous nanostructures composed of metastable tetragonal 1T-MoS and stable hexagonal 2H-MoS 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-MoS films over the wafer-scale area is challenging. In this work, a metal-organic chemical vapor deposition process allowing us to obtain ultrathin MoS films containing both 1T and 2H phases and control their ratio through rhenium doping was suggested.

Synthesis of Titanium Nitride Nanoparticles by Pulsed Laser Ablation in Different Aqueous and Organic Solutions.

Owing to a strong photothermal response in the near-IR spectral range and very low toxicity, titanium nitride (TiN) nanoparticles (NPs) synthesized by pulsed laser ablation in liquids (PLAL) present a novel appealing object for photo-induced therapy of cancer, but the properties of these NPs still require detailed investigation. Here, we have elaborated methods of femtosecond laser ablation from the TiN target in a variety of liquid solutions, including acetonitrile, dimethylformamide, acetone, water, and HO, to synthesize TiN NPs and clarify the effect of liquid type on the composition and properties of the formed NPs. The ablation in all solvents led to the formation of spherical NPs with a mean size depending on the liquid type, while the composition of the NPs ranged from partly oxidized TiN to almost pure TiO, which conditioned variations of plasmonic peak in the region of relative tissue transparency (670-700 nm).

Topological phase singularities in atomically thin high-refractive-index materials.

Atomically thin transition metal dichalcogenides (TMDCs) present a promising platform for numerous photonic applications due to excitonic spectral features, possibility to tune their constants by external gating, doping, or light, and mechanical stability. Utilization of such materials for sensing or optical modulation purposes would require a clever optical design, as by itself the 2D materials can offer only a small optical phase delay - consequence of the atomic thickness. To address this issue, we combine films of 2D semiconductors which exhibit excitonic lines with the Fabry-Perot resonators of the standard commercial SiO/Si substrate, in order to realize topological phase singularities in reflection.

Broadband Optical Properties of Atomically Thin PtS and PtSe.

Noble transition metal dichalcogenides (TMDCs) such as PtS and PtSe show significant potential in a wide range of optoelectronic and photonic applications. Noble TMDCs, unlike standard TMDCs such as MoS and WS, operate in the ultrawide spectral range from ultraviolet to mid-infrared wavelengths; however, their properties remain largely unexplored. Here, we measured the broadband (245-3300 nm) optical constants of ultrathin PtS and PtSe films to eliminate this gap and provide a foundation for optoelectronic device simulation.

Optical Constants and Structural Properties of Epitaxial MoS Monolayers.

Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality flakes with a size limited to a few micrometers, the latter gives large-area layers but with a nonuniform surface resulting from multiple defects and randomly oriented domains.

Optical Constants of Chemical Vapor Deposited Graphene for Photonic Applications.

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.

Band Excitation Piezoresponse Force Microscopy Adapted for Weak Ferroelectrics: On-the-Fly Tuning of the Central Band Frequency.

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).

Microplotter printing of planar solid electrolytes in the CeO-YO system.

The formation process for planar solid electrolytes in the CeO-YO 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).

Nanoscale Tailoring of Ferroelectricity in a Thin Dielectric Film.

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 film by Ga ions right in the thin-film capacitor device focused ion beam implantation.

Temperature controlled Ru and RuO growth via O radical-enhanced atomic layer deposition with Ru(EtCp).

This work demonstrates by in vacuo X-ray photoelectron spectroscopy and grazing-incidence X-ray diffraction that Ru(EtCp) and O radical-enhanced atomic layer deposition, where EtCp means the ethylcyclopentadienyl group, provides the growth of either RuO or Ru thin films depending on the deposition temperature (T), while different mechanisms are responsible for the growth of RuO and Ru. The thin films deposited at temperatures ranging from 200 to 260 °C consisted of polycrystalline rutile RuO phase revealing, according to atomic force microscopy and the four-point probe method, a low roughness (∼1.7 nm at 15 nm film thickness) and a resistivity of ≈83 µΩ cm.

Ferroelectric Second-Order Memristor.

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 HfO-based tunnel junction on silicon.

In Situ Control of Oxygen Vacancies in TaO Thin Films via Plasma-Enhanced Atomic Layer Deposition for Resistive Switching Memory Applications.

The plasma-enhanced atomic layer deposition (PEALD) process using Ta(OCH) as a Ta precursor and plasma-activated hydrogen as a reactant for the deposition of TaO films with a controllable concentration of oxygen vacancies (V) is reported herein. The V 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 TaO film grown via thermal ALD using the identical Ta precursor and HO. 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 V concentration.