In the realm of two-dimensional material frameworks, single-element graphene-like lattices, known as Xenes, pose several issues concerning their environmental stability, with implications for their use in technology transfer to a device layout. In this Discussion, we scrutinize the chemical reactivity of epitaxial silicene, taken as a case in point, in oxygen-rich environments. The oxidation of silicene is detailed by means of a photoemission spectroscopy study upon carefully dosing molecular oxygen under vacuum and subsequent exposure to ambient conditions, showing different chemical reactivity. We therefore propose a sequential Al2O3 encapsulation of silicene as a solution to face degradation, proving its effectiveness by virtue of the interaction between silicene and a silver substrate. Based on this method, we generalize our encapsulation scheme to a large number of metal-supported Xenes by taking into account the case of epitaxial phosphorene-on-gold.

A cost effective method to tailor the optical response of large-area nanosheets of 2D materials is described. A reduced effective metalayer model is introduced to capture the key-role of the out-of-plane component of the dielectric tensor. Such a model indicates that the optical extinction of 2D materials can be strongly altered by controlling the geometry at the local (i.e., subwavelength) scale. In particular, a giant linear optical dichroism at normal incidence is demonstrated, with major features around the excitonic peaks, that can be tailored by acting on the average curvature and slope of the nanosheets. The approach is experimentally demonstrated in few-layer MoS2 grown by chemical vapor deposition on cm-scale anisotropic nanopatterned substrates prepared by a self-assembling technique, based on defocused ion beam sputtering. Major variations in the photoluminescence spectrum as a function of the average curvature and slope are also revealed. A full-vectorial numerical study beyond the effective metalayer model and comprising strain effects induced by the geometry turns out to be consistent with such a complex scenario. The results demonstrate that the extrinsic geometrical engineering definitely opens viable way to tailor the optical properties and modulate bandgap of low dimensional materials.

Synthetic two-dimensional (2D) mono-elemental crystals, namely X-enes, have recently emerged as a new frontier for atomically thin nanomaterials with on-demand properties. Among X-enes, antimonene, the ?-phase allotrope of antimony, is formed by atoms arranged in buckled hexagonal rings bearing a comparatively higher environmental stability with respect to other players of this kind. However, the exploitation of monolayer or few-layer antimonene and other 2D materials in novel opto-electronic devices is still hurdled by the lack of scalable processes. Here, we demonstrated the viability of a bottom-up process for the epitaxial growth of antimonene-like nanocrystals (ANCs), based on a Metal-Organic Chemical Vapor Deposition (MOCVD) process, assisted by gold nanoparticles (Au NPs) on commensurate (1 1 1)-terminated Ge surfaces. The growth mechanism was investigated by large- and local-area microstructural analysis, revealing that the etching of germanium, catalyzed by the Au NPs, led to the ANCs growth on the exposed Ge (1 1 1) planes. As a supportive picture, ab-initio calculations rationalized this epitaxial relationship in terms of compressively strained ?-phase ANCs. Our process could pave the way to the realization of large-area antimonene layers by a deposition process compatible with the current semiconductor manufacturing technology.

Flat optics nanoarrays based on few-layer MoS2 are homogeneously fabricated over large-area (cm(2)) transparent templates, demonstrating effective tailoring of the photon absorption in two-dimensional (2D) transition-metal dichalcogenide (TMD) layers. The subwavelength subtractive re-shaping of the few-layer MoS2 film into a one-dimensional (1D) nanostripe array results in a pronounced photonic anomaly, tunable in a broadband spectral range by simply changing the illumination conditions (or the lattice periodicity). This scheme promotes efficient coupling of light to the 2D TMD layers via resonant interaction between the MoS2 excitons and the photonic lattice, with subsequent enhancement of absorption exceeding 400% relative to the flat layer. In parallel, an ultra-broadband absorption amplification in the whole visible spectrum is achieved, thanks to the non-resonant excitation of substrate guided modes promoted by MoS2 nanoarrays. These results highlight the potential of nanoscale re-shaped 2D TMD layers for large-area photon harvesting in layered nanophotonics, quantum technologies and new-generation photovoltaics.

Hybrid plasmonic-semiconductor assemblies are receiving considerable attention due to the possibility to achieve hot-carrier-based photodetection. In this context, 2D transition metal dichalcogenides (TMDs) coupled to metal nanostructures are very promising. However, the plasmon-to-TMD carrier injection process is extremely challenging to achieve and even to reveal in a clear-cut way. Herein, a report of multiple transient absorption ultrafast measurements, with tunable pump excitation, enabling quantitative comparison between the ultrafast behavior of metal nanostructures, TMDs, and their assembly is shown. This allows to provide the evidence of plasmon-enhanced charge injection from Au nanostripes to a rippled-shaped molybdenum disulfide (MoS2) few-layer nanosheet. Finite element method numerical simulations and modeling of the transient optical response corroborate the charge transfer mechanism, showing that the experimental data cannot be described in terms of the thermomodulational nonlinearity of gold nanostripes or by simple superposition of metal and semiconductor responses. The sample is obtained by a self-organization process on a large area; this demonstrates that plasmon-enhanced photon harvesting exploiting hot-electron injection can be achieved on a large area (approximately cm(2)) surface and provides a substantial advancement toward scalable ultrathin photodetection devices based on hot-electrons technology.

When coupled with ferromagnetic layers (FM), topological insulators (TI) are expected to boost the charge-to-spin conversion efficiency across the FM/TI interface. In this context, a thorough control and optimization of the FM/TI interface quality are requested. Here, the evolution of the chemical, structural, and magnetic properties of the Fe/Sb(2)Te(3)heterostructure is presented as a function of a rapid mild thermal annealing conducted on the Sb2Te3-TI (up to 200 degrees C). While the bilayer is not subjected to any thermal treatment upon Fe deposition, the annealing of Sb(2)Te(3)markedly improves its crystalline quality, leading to an increase in the fraction of ferromagnetic Fe atoms at the buried Fe/Sb(2)Te(3)interface and a slight lowering of the magnetic coercivity of the Fe layer. The method is an efficient tool to clean up the Fe/Sb(2)Te(3)interface, which may be extended to different FM/TI heterostructures. Simultaneously to the interface reconstruction, a constant approximate to 20% fraction of FeTe develops at the interface. Since FeTe can display superconductivity, the Fe/Sb(2)Te(3)system could have potentialities for exploiting phenomena at the edge of magnetism, superconductivity and topology.

Large area molybdenum disulfide (MoS2) monolayers are typically obtained by using perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt (PTAS) as organic seeding promoter in chemical vapor deposition (CVD). However, the influence of the seeding promoter and the involvement of the functional groups attached to the seed molecules on the physical properties of the MoS(2)monolayer are rarely taken into account. Here, it is shown that MoS(2)monolayers exhibit remarkable differences in terms of the electronic polarizability by using two representative cases of seeding promoter, namely, the commercial PTAS and a home-made perylene-based molecule,N,N-bis-(5-guanidil-1-pentanoic acid)-perylene-3,4,9,10-tetracarboxylic acid diimide (PTARG). By thermogravimetric analysis, it is verified that the thermal degradation of the promoters occurs differently at the CVD working condition: with a single detachment of the functional groups for PTAS and with multiple thermal events for PTARG. As a consequence, the promoter-dependent electronic polarizability, derived by free charges trapped in the monolayer, impacts on the photoluminescence emission, as well as on the electrical performances of the monolayer channel in back-gated field-effect transistors. These findings suggest that the modification of the electronic polarizability, by varying the molecular promoter in a pre-growth stage, is a path to engineer the MoS(2)opto-electronic properties.

In the 2D material framework, molybdenum disulfide (MoS2) was originally studied as an archetypical transition metal dichalcogenide (TMD) material. The controlled synthesis of large-area and high-crystalline MoS2 remains a challenge for distinct practical applications from electronics to electrocatalysis. Among the proposed methods, chemical vapor deposition (CVD) is a promising way for synthesizing high-quality MoS2 from isolated domains to a continuous film because of its high flexibility. Herein, we report on a systematic study of the effects of growth pressure, temperature, time, and vertical height between the molybdenum trioxide (MoO3) source and the substrate during the CVD process that influence the morphology, domain size, and uniformity of thickness with controlled parameters over a large scale. The substrate was pretreated with perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt (PTAS) seed molecule that promoted the layer growth of MoS2. Further, we characterized the as-grown MoS2 morphologies, layer quality, and physical properties by employing scanning electron microscopy (SEM), Raman spectroscopy, and photoluminescence (PL). Our experimental findings demonstrate the effectiveness and versatility of the CVD approach to synthesize MoS2 for various target applications.

Colloidal semiconductor nanocrystals (NCs) and, recently, nanoplatelets (NPLs), owing to their efficient and narrow-band luminescence, are considered as frontier materials for light-emitting diode (LED) technology. NC-LEDs typically incorporate interfacial layers as charge regulators to ensure charge balancing and high performance. In this Letter, we show the prolongation of the lifetime of multilayer solution-processed NC-LEDs by combining a self-doped conductive conjugated polyelectrolyte and exfoliated molybdenum disulfide (MoS2) flakes as an alternative to PEDOT:PSS. The ink features a neutral pH and a tunable hydrophobicity that mainly results in a remarkable stability of LEDs, using CdSe/CdZnS NPLs.

Systems based on the combination of ferromagnetic (FM) thin films and two-dimensional (2D) transition metal dichalcogenides are currently of high interest in the context of spintronic devices. Here, we report on the fabrication of MoS2/(Fe3O4, Fe) heterojunctions by using chemical-based methods. FM thin films have been initially synthesized on top of Si/SiO2 substrates by chemical vapour deposition. The 2D-MoS2 nanosheets have been grown on top of the FM layers by following the sulfurization of a solid film precursor of molybdenum oxide evaporated at the FMs surface. A comprehensive structural, chemical, morphological and magnetic characterization has been carried out at each step of the process. Several bottlenecks in the fabrication of MoS2 /(Fe3O4, Fe) systems have been evidenced, the most critical being the sulfurization process, in which we detect a pronounced tendency of S to react with the underlying FM layers. Our results could explain the limited functionalities often observed so far in spintronic devices based on 2D transition metal dichalcogenides, prompting some limits for their inclusion into practical devices.

Antimony telluride (Sb2Te3) thin films were prepared by a room temperature Metal-Organic Chemical Vapor Deposition (MOCVD) process using antimony chloride (SbCl3) and bis(trimethylsilyl)telluride (Te(SiMe3)2) as precursors. Pre-growth and post-growth treatments were found to be pivotal in favoring out-of-plane and in-plane alignment of the crystallites composing the films. A comprehensive suite of characterization techniques were used to evaluate their composition, surface roughness, as well as to assess their morphology, crystallinity, and structural features, revealing that a quick post-growth annealing triggers the formation of epitaxial-quality Sb2Te3 films on Si(111).

Exploiting first-principles simulations and x-ray absorption near edge spectroscopy (XANES) in high magnetic fields, we investigated the magnetic properties of thin films of zirconia doped with Fe impurities. In our Zr1-xFexO2-y samples, grown by atomic layer deposition (ALD), the Fe dopants are uniformly distributed, ranging from diluted (x=2-3%) up to high (x=25%) atomic concentration. By x-ray magnetic circular dichroism (XMCD), we carefully analyzed, for samples having different Fe concentration, the magnetic moments as a function of temperature, in the range from 5 K up to 150 K, studying the best dopant concentration range maximizing the magnetic signal. Surprisingly, the iron magnetic moment measured for diluted concentrations degrades as the concentration of magnetic dopant increases. On the basis of ab initio simulations, we propose that the microscopic mechanisms responsible for the peculiar magnetic properties of this compound can be explained by oxygen-mediated superexchange mechanism between the Fe dopants producing, at high dopant concentration, an antiferromagnetic coupling between two Fe atoms. We identify and discuss the role of O vacancies to control such microscopic mechanisms.

Capacitors are the most critical passive components of future in-package and on-chip electronic systems with augmented energy-storage capabilities for consumer and wearable applications. Although an impressive increase of both capacitance and energy densities has been achieved over the last years for supercapacitors (SCs), electronic applications of SCs have been hindered by their intrinsic low operation voltage (a few Volts), poor frequency range (a few Hz to hundreds of Hertz), and difficult integration with integrated circuit (IC) processes. On the other hand, integrated dielectric capacitors (DCs) able to operate at higher voltage (tens of Volts) and higher frequencies (hundreds of kHz to MHz) suffer from significantly lower capacitance and energy densities.

The controlled growth of chalcogenide nanoscaled phase change material structures can be important to facilitate integration and to enable complex architectures for phase change memory and other microelectronic applications. Here, the growth of Sb-Te and In-Ge-Te alloys by metal-organic chemical vapour deposition (MOCVD) on patterned substrates featured with an array of recesses (~130 nm features width) was investigated. High selectivity, with preferential growth on a CoSi2 metallic layer at the recess bottom with respect to the surrounding SiO2 masking layer, was obtained, leading to a single-step fabrication of arrays of high-aspect-ratio chalcogenide nanostructures. The growth selectivity, as well as the morphology, composition and microstructure of the grown nanostructures, as a function of the different MOCVD process parameters, were investigated by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy and Fourier transformed infrared spectroscopy. Thanks to the chosen substrates, the synthesized nanostructures were also directly electrically accessible, as proved by conductive-atomic force microscopy.

The interfacial Dzyaloshinskii-Moriya interaction (DMI) plays a crucial role in chiral domain wall (DW) motion, favoring fast DW velocities. We explore the effect of interface disorder on DMI and DW dynamics in perpendicular magnetized Ta/CoFeB/MgO thin films. Light He+ irradiation has been used to gently engineer interface intermixing on a scale of 0.1 nm. We demonstrate that a slight modification of the Ta/CoFeB interface leads to an increase of the DMI value accompanied by an enhancement of DW velocity in the flow regime. Using micromagnetic simulations based on granular structures, we show that the enhancement of DW velocity is mainly related to an increase in the distribution of magnetic parameters related to the interface. We further infer that the DMI modulation is related to the asymmetric disorder induced by irradiation leading to alloying with the Ta buffer layer. Understanding the role of disorder is therefore crucial for the design of future devices where post-growth interface alloying can be used to finely tune the DMI.

The possibility of tuning the Dzyaloshinskii-Moriya interaction (DMI) by electric (E)-field gating in ultrathin magnetic materials has opened up new perspectives in terms of controlling the stabilization of chiral spin structures. The most recent efforts have used voltage-induced charge redistribution at the interface between a metal and an oxide to modulate the DMI. This approach is attractive for active devices but tends to be volatile, making it energy-demanding, and it is limited by Coulomb screening in the metal. Here we demonstrate nonvolatile E-field manipulation of the DMI by ionic-liquid gating of Pt/Co/HfO2 ultrathin films. The E-field effect on the DMI scales with the E-field exposure time, and we propose that it is linked to the migration of oxygen species from the HfO2 layer into the Co and Pt layers and subsequent anchoring. This effect permanently changes the properties of the material, showing that E fields can be used not only for local gating in devices but also as a highly scalable materials design tool for postgrowth tuning of the DMI.

In this paper we report the development of a new method for the evaluation of thin films mass thickness and composition based on the Energy Dispersive X-Ray Spectroscopy (EDS). The method exploits the theoretical calculation of the in-depth characteristic X-ray generation distribution function (phi(rho z)) in multilayer samples, where (phi(rho z)) is obtained by the numerical solution of the electron transport equation. Once the substrate composition in known, this method gives reliable measurements without the need of a reference sample and/or multiple voltage acquisitions.

This paper focuses on the impact of annealing on the current conduction and trap states of metal-insulator-metal capacitors with CeO2/La2O3 dielectrics. Capacitance-frequency measurements identify two main trap levels (T-1 and T-2), characterized by an activation energy of 0.2 and 0.3 eV, respectively, and by a time constant of 1 ms and 20 mu s at room temperature. The current conduction is found to be ruled by a Poole-Frenkel effect and space charge limited current under positive and negative bias, respectively. Selective annealing of CeO2 and La2O3 layers clarifies the nature of the aforementioned traps. Although providing no change in the activation energy, an additional annealing of the CeO2 and La2O3 layer is found to significantly change the trap amplitude of T-1 and T-2, respectively. The corresponding change of the current conduction in the region where trap assisted mechanisms play a major role is discussed. Published by the AVS.

Within the class of two-dimensional materials, transition metal dichalcogenides (TMDs), are extremely appealing for a variety of technological applications. Moreover, the manipulation of the layered morphology at the nanoscale is a knob for further tailoring their physical and chemical properties towards target applications. Here, the combination of atomic layer deposition (ALD) and chemical vapour deposition (CVD) is presented as a general approach for the fabrication of TMD layers arranged in arbitrary geometry at the nanoscale. Indeed, following such all-chemical based approach, high-resolution electron microscopy shows the conformal growth of MoS2 to nano-trench pattern obtained in SiO2 substrates on large area. Growth is uniform not only in the flat region of the pattern but also at the hinges and throughout vertical faces, without rupture, all along the rectangular shape profile of the trenches. Furthermore, MoS2 bending dramatically affects the electron-phonon coupling as demonstrated by resonant Raman scattering. The proposed approach opens the door to the on-demand manipulation of the TMDs properties by large-scale substrate pattern design.

Low resistivity n-type epsilon-Ga2O3 epilayers were obtained for the first time either by adding silane to the gas phase during the metal organic vapour phase epitaxy deposition or by diffusing Sn in nominally undopeci, layers after the growth. The highest doping concentrations were few 10(18) cm(-3) and about 10(17) cm(-3) for Si and Sn doping, with corresponding resistivity below 1 and 10 Omega cm, respectively. Temperature dependent transport investigation in the range of 10-600 K shows a resistivity behavior consistent with the Mott law, suggesting that conduction through localized states dominates the electrical properties of Si- and Sn-doped samples. For both types of dopants, two different mechanisms of conduction through impurity band states seem to be preserit, each of them determining the transport behavior at the lower and higher temperatures of the measurement range.