Performance Improvement by Ozone Treatment of 2D PdSe2.

Atomic-scale defects in two-dimensional transition metal dichalcogenides (TMDs) often dominate their physical and chemical properties. Introducing defects in a controllable manner can tailor properties of TMDs. For example, chalcogen atom defects in TMDs were reported to trigger phase transition, induce ferromagnetism, and drive superconductivity. However, reported strategies to induce chalcogen atom defects including postgrowth annealing, laser irradiation, or plasma usually require high temperature (such as 500 °C) or cause unwanted structural damage. Here, we demonstrate low-temperature (60 °C) partial surface oxidation in 2D PdSe2 with low disorder and good stability. The combination of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations provide evidence of atomic-scale partial oxidation with both atomic resolution and chemical sensitivity. We also experimentally demonstrate that this controllable oxygen incorporation effectively tailors the electronic, optoelectronic, and catalytic activity of PdSe2. This work provides a pathway toward fine-tuning the physical and chemical properties of 2D TMDs and their applications in nanoelectronics, optoelectronics, and electrocatalysis.

EEG Analysis in Structural Focal Epilepsy Using the Methods of Nonlinear Dynamics (Lyapunov Exponents, Lempel-Ziv Complexity, and Multiscale Entropy).

This paper analyzes a case with the patient having focal structural epilepsy by processing electroencephalogram (EEG) fragments containing the "sharp wave" pattern of brain activity. EEG signals were recorded using 21 channels. Based on the fact that EEG signals are time series, an approach has been developed for their analysis using nonlinear dynamics tools: calculating the Lyapunov exponent's spectrum, multiscale entropy, and Lempel-Ziv complexity. The calculation of the first Lyapunov exponent is carried out by three methods: Wolf, Rosenstein, and Sano-Sawada, to obtain reliable results. The seven Lyapunov exponent spectra are calculated by the Sano-Sawada method. For the observed patient, studies showed that with medical treatment, his condition did not improve, and as a result, it was recommended to switch from conservative treatment to surgical. The obtained results of the patient's EEG study using the indicated nonlinear dynamics methods are in good agreement with the medical report and MRI data. The approach developed for the analysis of EEG signals by nonlinear dynamics methods can be applied for early detection of structural changes.

Unveiling structural, chemical and magnetic interfacial peculiarities in ε-Fe2O3/GaN (0001) epitaxial films.

The metastable ε-Fe2O3 is known to be the most intriguing ferrimagnetic and multiferroic iron oxide phase exhibiting a bunch of exciting physical properties both below and above room temperature. The present paper unveils the structural and magnetic peculiarities of a few nm thick interface layer discovered in these films by a number of techniques. The polarized neutron reflectometry data suggests that the interface layer resembles GaFeO3 in composition and density and is magnetically softer than the rest of the ε-Fe2O3 film. While the in-depth density variation is in agreement with the transmission electron microscopy measurements, the layer-resolved magnetization profiles are qualitatively consistent with the unusual wasp-waist magnetization curves observed by superconducting quantum interference device magnetometry. Interestingly a noticeable Ga diffusion into the ε-Fe2O3 films has been detected by secondary ion mass spectroscopy providing a clue to the mechanisms guiding the nucleation of exotic metastable epsilon ferrite phase on GaN at high growth temperature and influencing the interfacial properties of the studied films.

In situ insights into the nanoscale deposition of 5,6-dihydroxyindole-based coatings and the implications on the underwater adhesion mechanism of polydopamine coatings.

The biomimetic coating polydopamine (PDA) has emerged as a promising coating material for various applications. However, the mechanism of PDA deposition onto surfaces is not fully understood, and the coating components of PDA and its relation to the putative intermediate 5,6-dihydroxyindole (DHI) are still controversial. This investigation discloses the deposition mechanisms of dopamine (DA)-based coatings and DHI-based coatings onto silicon surfaces by monitoring the nanoscale deposition of both coatings in situ using high-precision ellipsometry. We posit that the rapid and instantaneous nano-deposition of PDA coatings onto silicon surface in the initial stages critically involves the oxidation of DHI and/or its related oligomers. Our studies also show that the slow conversion of DA to DHI in PDA solution and the coupling between DA and DHI-derived precursors could be crucial for subsequent PDA coating growth. These findings elucidate the critical role of DHI, acting as an 'initiator' and a 'cross linker', in the PDA coating formation. Overall, our study provides important information on the early stage nano-deposition behavior in the construction of PDA coatings and DHI-based coatings.

Protein-tannic acid multilayer films: A multifunctional material for microencapsulation of food-derived bioactives.

The benefits of various functional foods are often negated by stomach digestion and poor targeting to the lower gastrointestinal tract. Layer-by-Layer assembled protein-tannic acid (TA) films are suggested as a prospective material for microencapsulation of food-derived bioactive compounds. Bovine serum albumin (BSA)-TA and pepsin-TA films demonstrate linear growth of 2.8±0.1 and 4.2±0.1nm per bi-layer, correspondingly, as shown by ellipsometry. Both multilayer films are stable in simulated gastric fluid but degrade in simulated intestinal fluid. Their corresponding degradation constants are 0.026±0.006 and 0.347±0.005nm-1min-1. Milk proteins possessing enhanced adhesion to human intestinal surface, Immunoglobulin G (IgG) and ß-Lactoglobulin (BLG), are explored to tailor targeting function to BSA-TA multilayer film. BLG does not adsorb onto the multilayer while IgG is successfully incorporated. Microcapsules prepared from the multilayer demonstrate 2.7 and 6.3 times higher adhesion to Caco-2 cells when IgG is introduced as an intermediate and the terminal layer, correspondingly. This developed material has a great potential for oral delivery of numerous active food-derived ingredients.

Origin and Quenching of Novel ultraviolet and blue emission in NdGaO3: Concept of Super-Hydrogenic Dopants.

In this study we report the existence of novel ultraviolet (UV) and blue emission in rare-earth based perovskite NdGaO3 (NGO) and the systematic quench of the NGO photoluminescence (PL) by Ce doping. Study of room temperature PL was performed in both single-crystal and polycrystalline NGO (substrates and pellets) respectively. Several NGO pellets were prepared with varying Ce concentration and their room temperature PL was studied using 325 nm laser. It was found that the PL intensity shows a systematic quench with increasing Ce concentration. XPS measurements indicated that nearly 50% of Ce atoms are in the 4+ state. The PL quench was attributed to the novel concept of super hydrogenic dopant (SHD)", where each Ce4+ ion contributes an electron which forms a super hydrogenic atom with an enhanced Bohr radius, due to the large dielectric constant of the host. Based on the critical Ce concentration for complete quenching this SHD radius was estimated to be within a range of 0.85 nm and 1.15 nm whereas the predicted theoretical value of SHD radius for NdGaO3 is ~1.01 nm.

Electron Doping of Ultrathin Black Phosphorus with Cu Adatoms.

Few-layer black phosphorus is a monatomic two-dimensional crystal with a direct band gap that has high carrier mobility for both holes and electrons. Similarly to other layered atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is sensitive to surface impurities, adsorbates, and adatoms. Here we study the effect of Cu adatoms onto few-layer black phosphorus by characterizing few-layer black phosphorus field effect devices and by performing first-principles calculations. We find that the addition of Cu adatoms can be used to controllably n-dope few layer black phosphorus, thereby lowering the threshold voltage for n-type conduction without degrading the transport properties. We demonstrate a scalable 2D material-based complementary inverter which utilizes a boron nitride gate dielectric, a graphite gate, and a single bP crystal for both the p- and n-channels. The inverter operates at matched input and output voltages, exhibits a gain of 46, and does not require different contact metals or local electrostatic gating.

Large Area Directed Self-Assembly of Sub-10 nm Particles with Single Particle Positioning Resolution.

Directed self-assembly of nanoparticles (DSA-n) holds great potential for device miniaturization in providing patterning resolution and throughput that exceed existing lithographic capabilities. Although nanoparticles excel at assembling into regular close-packed arrays, actual devices on the other hand are often laid out in sparse and complex configurations. Hence, the deterministic positioning of single or few particles at specific positions with low defect density is imperative. Here, we report an approach of DSA-n that satisfies these requirements with less than 1% defect density over micrometer-scale areas and at technologically relevant sub-10 nm dimensions. This technique involves a simple and robust process where a solvent film containing sub-10 nm gold nanoparticles climbs against gravity to coat a prepatterned template. Particles are placed individually into nanoscale cavities, or between nanoposts arranged in varying degrees of geometric complexity. Brownian dynamics simulations suggest a mechanism in which the particles are pushed into the template by a nanomeniscus at the drying front. This process enables particle-based self-assembly to access the sub-10 nm dimension, and for device fabrication to benefit from the wealth of chemically synthesized nanoparticles with unique material properties.

Naturally inspired polyelectrolyte multilayer composite films synthesised through layer-by-layer assembly and chemically infiltrated with CaCO3.

Naturally occurring composite structures like antler bone and nacre have a highly ordered structural design at the nanoscale. Nature's successful architecture has attracted widespread interest in mimicking such systems artificially, the goal being to design tough composite materials with adaptable mechanical properties. Here we report results on synthesis pathways towards fabricating such materials, including a chemical infiltration route where calcium carbonate particles nucleate and grow inside polyelectrolyte multilayers assembled via a layer-by-layer route. SEM analysis demonstrates a considerable change in the morphology of thin films upon chemical infiltration. The depth of mineralisation within the multilayer is confirmed by TOF-SIMS studies of both mineralised and non-mineralised thin films. TGA was used to calculate the overall content of CaCO3 within multilayer films. Infiltrated multilayers have shown up to 60% w/w of calcium carbonate which is comparable to structures like bones. X-ray diffraction to characterise the crystallographic structure and micromechanical testing involving nano-indentation have also been conducted. The Young's modulus of mineralised multilayer thin films significantly increased up to 10 GPa after infiltration in comparison to the non-mineralised multilayers with a modulus of only 3.8 GPa, while the increase in hardness is almost 50-fold. Thus, the synthetic composites can be compared with natural biomineralised tissues like nacre, ultimately replicating the natural strength of biomimetic materials on the nanoscale.

Bias induced transition from an ohmic to a non-ohmic interface in supramolecular tunneling junctions with Ga2O3/EGaIn top electrodes.

This study describes that the current rectification ratio, R ≡ |J|(-2.0 V)/|J|(+2.0 V) for supramolecular tunneling junctions with a top-electrode of eutectic gallium indium (EGaIn) that contains a conductive thin (0.7 nm) supporting outer oxide layer (Ga2O3), increases by up to four orders of magnitude under an applied bias of >+1.0 V up to +2.5 V; these junctions did not change their electrical characteristics when biased in the voltage range of ±1.0 V. The increase in R is caused by the presence of water and ions in the supramolecular assemblies which react with the Ga2O3/EGaIn layer and increase the thickness of the Ga2O3 layer. This increase in the oxide thickness from 0.7 nm to ∼2.0 nm changed the nature of the monolayer-top-electrode contact from an ohmic to a non-ohmic contact. These results unambiguously expose the experimental conditions that allow for a safe bias window of ±1.0 V (the range of biases studies of charge transport using this technique are normally conducted) to investigate molecular effects in molecular electronic junctions with Ga2O3/EGaIn top-electrodes where electrochemical reactions are not significant. Our findings also show that the interpretation of data in studies involving applied biases of >1.0 V may be complicated by electrochemical side reactions which can be recognized by changes of the electrical characteristics as a function voltage cycling or in current retention experiments.

A facile approach for screening isolated nanomagnetic behavior for bit-patterned media.

Bit-patterned media (BPM) fabricated by the direct deposition of magnetic material onto prepatterned arrays of nanopillars is a promising approach for increasing magnetic recording of areal density. One of the key challenges of this approach is to identify and control the magnetic interaction between the bits (on top of the nanopillars) and the trench material between the pillars. Using independent techniques, including magnetic force microscopy, the variable-angle magneto-optic Kerr effect, and remanence curves, we were able to determine the presence and relative intensities of exchange and dipolar interactions in Co-Pd multilayer-based BPM fabricated by direct deposition. We found that for pitches of 30 nm or less, there were negligible exchange interactions, and the bits were found to be magnetically isolated. As we move to higher densities, the absence of exchange interactions indicates that direct deposition is a promising approach to BPM fabrication.

Magnetocaloric effect of a series of remarkably isostructural intermetallic [Ni(II)3Ln(III)] cubane aggregates.

A new series of remarkably isostructural 3d-4f compounds, [Ni3Ln(hmp)4(OAc)5]·H2O·CH2Cl2 (Ln = Gd (1), Tb (2), Dy (3), Ho (4), Y (5)) were synthesized based on a simple one-pot self-assembly method. Magnetic measurements demonstrated the ferromagnetic property of the [Ni3Ln] cores and the heterometallic influence on the magnetocaloric properties. This study suggested that robust and discrete intermetallic cubanes can be an alternative to other magnetically active materials such as high-nuclearity aggregates or clusters whose structures are not generally controlled by common synthetic methodological designs.

General one-step self-assembly of isostructural intermetallic Co(II)(3)Ln(III) cubane aggregates.

A new family of Co/rare-earth intermetallic cubane aggregates [Co3Ln(hmp)4(OAc)5H2O] (Ln = Dy, Ho, Er, Tm, Yb, Y) have been synthesized by self-assembly. Single-crystal X-ray diffraction analysis revealed that they are remarkably isostructural in showing a common [Co3Ln] core. Magnetic studies showed that the Dy, Er, Tm, Yb, and Y complexes are ferromagnetic. The Dy complex exhibits the largest magnetocaloric effect (-ΔSm = 12.58 J kg(-1) K(-1)), which can be attributed to the large magnetic density of Dy(III).

Direct adsorption and monolayer self-assembly of acetyl-protected dithiols.

The alpha,omega-dithiols, with sulfur-containing groups at both ends of the molecules, can be used to bridge a metallic gap. Functional self-assembled monolayers (SAMs) of these dithiols must "stand up" on the surface and expose one thiol group for further reaction. However, both parallel and upright surface orientations and multilayer formation can occur for alpha,omega-dithiols. We find SAMs deposited directly from acetyl protected dithiols (i.e., with no de-protection step) overcome these problems. We present a systematic study of adsorption kinetics from in situ surface plasmon resonance spectroscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy of alkane- and oligo(phenylene ethylnylene)-based alpha,omega-dithioacetates on gold.