Dopant Segregation Research Articles

(Invited) Mesoscale Reaction Kinetics Modulated By Structural and Compositional Heterogeneity in Battery Cathode Materials

Doping, coating, and particle engineering for cathode materials are broadly adopted by both academia and industry to improve the battery performance. The lack of an in-depth understanding for the underlying mechanism, however, makes it a largely try-and-error process with unsatisfactory efficiency and effectiveness. This is particularly true for the electrochemical reaction kinetics that is heterogeneous over a broad range of length scales and is determined collectively by the cathode’s electronic structure, lattice configuration, and micro-morphology.In this presentation, I will talk about the use of advanced synchrotron techniques for imaging the cathode particles with structural, chemical and compositional sensitivities. We will talk about the mutual modulation between the surface chemistry and the bulk charge distribution and mechanical cracking. As an example, we will discuss how a facet-dependent dopant segregation in Zr-modified single-crystal LiNi0.6Co0.2Mn0.2O2 cathode would modulate its mesoscale reaction kinetics. This study suggests that a delicately controlled dopant distribution is a viable strategy for designing the next-generation battery cathode with superior structural and chemical robustness.

Study of variability induced by random dopant fluctuation in Fe DS-SBTFET

This paper explores the affectability of random dopant fluctuation (RDF) on the performance of Ferroelectric Dopant Segregated Schottky Barrier (Fe DS-SB) TFET by utilizing 3-D TCAD simulation. The simulation technique involves the device bifurcation into rectangular coordinates where the doping charges are placed randomly as individual and discrete dopants. Threshold voltage varies significantly due to variation in source-channel dopant concentration. The dependency of threshold voltage standard deviation on various source doping concentration has been studied. Doping variability within the channel and drain regions mainly leads to alteration in ON state current. Moreover, the impact of temperature (300 K–500 K) on switching characteristics of the proposed device has been investigated.

Binary dopant segregation enables hematite-based heterostructures for highly efficient solar H2O2 synthesis

Dopant segregation, frequently observed in ionic oxides, is useful for engineering materials and devices. However, due to the poor driving force for ion migration and/or the presence of substantial grain boundaries, dopants are mostly confined within a nanoscale region. Herein, we demonstrate that core–shell heterostructures are formed by oriented self-segregation using one-step thermal annealing of metal-doped hematite mesocrystals at relatively low temperatures in air. The sintering of highly ordered interfaces between the nanocrystal subunits inside the mesocrystal eliminates grain boundaries, leaving numerous oxygen vacancies in the bulk. This results in the efficient segregation of dopants (~90%) on the external surface, which forms their oxide overlayers. The optimized photoanode based on hematite mesocrystals with oxide overlayers containing Sn and Ti dopants realises high activity (~0.8 μmol min−1 cm−2) and selectivity (~90%) for photoelectrochemical H2O2 production, which provides a wide range of application for the proposed concept.

Understanding δ-Bi2O3 fluorite degradation mechanism and related solutions for promising applications in distributed multigeneration

Oxygen selective membrane on the base of cermet δ-Bi 2 O 3 /Ag with an interpenetrating structure has the maximum potential efficiency of air separation. However, the degradation processes, including the phase degradation of fluorite δ-Bi 2 O 3 , do not make it possible to create a membrane with the required perfection and durability. In this work, the ordering of oxygen vacancies with the transformation of fluorite into the rhombohedral phase (S.G. R -3) was studied by powder HT XRD in situ at 600 °C on dense Bi 0.78 Er 0.2 Hf 0.02 O 1.51 ceramics. Fast regeneration of disordered fluorite occurs at T = 640–700 °C. The phase degradation of fluorite due to the segregation of dopants at the second stage leads into stable phases - sillenite, tetragonal or rhombohedral phase (S.G. R -3 m ), depending on the composition of δ-Bi 2 O 3 . Fast regeneration of fluorite occurs when heated to 820 °C, which is unacceptable for membranes. Analysis of all available data allows us to propose approaches to optimize the composition of δ-Bi 2 O 3 and technical solutions for creating durable oxygen selective membranes with promising use in distributed multigeneration. As a result of the analysis, a new solid electrolyte with better parameters was obtained. • Cubic disordered fluorite δ-Bi 2 O 3 with aging at 600 °C degrades in two stages. • Fast heating up to 700°С regenerates fluorite after 1 st stage of aging. • Degradation of fluorites on the 2 nd stage leads to three stable phases. • Composition of durable fluorite is determined by the choice of operation mode. • The stated limitations were validated and resulted in a better solid electrolyte.

Tuning the oxygen vacancy concentration in a heterostructured electrode for high chemical and electrochemical stabilities

Thermally driven chemical instability at the perovskite electrode is one of the biggest challenges to overcome in the development of sustainable solid oxide fuel cells. At elevated temperatures, the A-site dopant (typically Sr) segregation toward the surface of the perovskite electrode induces the substantially nonstoichiometric surface with the formation of insulating Sr-rich phases by the electrostatic interactions between oxygen vacancies (Vo∙∙) and doped Sr (SrLa'), deteriorating the oxygen reduction reaction kinetics. Herein, we report the precise tuning of the oxygen vacancy concentration at the perovskite surface in a Gd0.1Ce0.9O2−δ (GDC)/La0.6Sr0.4CoO3−δ (LSC) heterostructured electrode by rearranging the oxygen vacancies near the interface, resulting in an ∼15-fold increase in the surface exchange coefficient after long-term operation at 650 °C for 100 h. The depth profiles of the charged defects obtained by X-ray photoelectron spectroscopy revealed that the oxygen vacancy concentration at the perovskite surface can be controlled by the amount of vacancy acceptable sites in the GDC layer. This strongly affects the chemical and electrochemical stabilities after long-term operations. Our results demonstrate the potential of tuning the defect concentration in heterostructured electrodes to achieve highly sustainable electrodes for the long-term operations at elevated temperatures.

Characterization of fully silicided source/drain SOI UTBB nMOSFETs at cryogenic temperatures

• SOI UTBB nMOSFETs are operated at cryogenic temperature with different gate lengths. • The impact of the back-gate on the device performance is systematically studied. • A good performance of devices is obtained at cryogenic temperature by back-gate. • Short channel effects are investigated at cryogenic temperature. In this paper we present an experimental study of SOI UTBB n-MOSFETs at cryogenic temperatures. The device employs fully silicided source/drain with dopant segregation formed by “Implantation Into Silicide” (IIS) process. The impact of the back-gate (V back ) on the device performance is systematically investigated. The results demonstrate that V back is essential to tune the threshold voltage V th. And optimization of V back values can improve the subthreshold swing (SS), Drain-Induced Barrier Lowering (DIBL), transconductance G m and mobility at cryogenic temperatures, providing a potential to fulfill the ultra-low power requirement for quantum computing application.

Improvement of Fermi-Level Pinning and Contact Resistivity in Ti/Ge Contact Using Carbon Implantation.

Effects of carbon implantation (C-imp) on the contact characteristics of Ti/Ge contact were investigated. The C-imp into Ti/Ge system was developed to reduce severe Fermi-level pinning (FLP) and to improve the thermal stability of Ti/Ge contact. The current density (J)-voltage (V) characteristics showed that the rectifying behavior of Ti/Ge contact into an Ohmic-like behavior with C-imp. The lowering of Schottky barrier height (SBH) indicated that the C-imp could mitigate FLP. In addition, it allows a lower specific contact resistivity (ρc) at the rapid thermal annealing (RTA) temperatures in a range of 450–600 °C. A secondary ion mass spectrometry (SIMS) showed that C-imp facilitates the dopant segregation at the interface. In addition, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) mapping showed that after RTA at 600 °C, C-imp enhances the diffusion of Ge atoms into Ti layer at the interface of Ti/Ge. Thus, carbon implantation into Ge substrate can effectively reduce FLP and improve contact characteristics.

Spin Polarization-Assisted Dopant Segregation at a Coherent Phase Boundary.

Coherent phase boundaries are widely expected as segregation-free boundaries due to their low interfacial energies and lack of trapping sites for impurities. Here, we report an equilibrium segregation of W atoms at fully coherent terraces of a Fe3O4 (111)/Fe2O3 (0001) phase boundary that was never expected previously. Through comparison of pristine and W-doped Fe3O4/Fe2O3 phase boundaries, it is revealed that the spin polarization of O atoms at the interface plays an important role in the periodic segregation of W atoms. Unusual spin-polarized O atoms with large magnetic moments are periodically arranged in the interfacial O plane of the pristine phase boundary. After doping of W at this boundary, W atoms will selectively substitute the Fe atoms of Fe2O3 that directly bond with three spin-polarized O atoms, thereby resulting in the complete neutralization of the magnetic moments of the spin-polarized O atoms. These findings reveal that coherent phase boundaries are able to trap impurities and local spin polarization is one of the driving forces for dopant segregation, suggesting that elemental doping is an efficient way for tailoring the physical properties of boundaries in magnetic materials and devices.

Doping of tantalum, niobium, and hafnium in a translucent ZrO2-SiO2 nanocrystalline glass-ceramic

• The ternary dopants enhanced the transformability of tetragonal ZrO 2 . • Lamella nanotwins were formed within many ZrO 2 nanocrystallites. • No obvious segregation of dopants was detected at ZrO 2 grain boundaries. • The dopants imparted a yellowish- or dark-brown color to the glass-ceramics. • Tetragonal and monoclinic ZrO 2 were metastable in the thermal treatments. The addition of dopant(s) is an effective strategy to regulate the microstructure and properties of ZrO 2 -based ceramics. In this study, we investigated the effects of ternary element alloying, namely tantalum (Ta), niobium (Nb), and hafnium (Hf) elements, on the microstructure and transformability of ZrO 2 nanocrystallites in a ZrO 2 -SiO 2 nanocrystalline glass-ceramic (NCGC) during sintering and thermal treatments. The ternary dopants enhanced the transformability of tetragonal ZrO 2 (t-ZrO 2 ) nanocrystallites during sintering, i.e., the dopants acted as t-ZrO 2 destabilizer. The Ta, Nb and Hf elements dissolved in ZrO 2 nanocrystallites, forming ZrO 2 solid solution. Meanwhile, lamella nanotwins were formed within many ZrO 2 nanocrystallites. No obvious segregation of dopants was detected at ZrO 2 grain boundaries. t-ZrO 2 and monoclinic (m) ZrO 2 nanocrystallites were metastable in thermal treatments process, with “t” to “m” and the reverse “m” to “t” polymorphic transformation occurred simultaneously. Meanwhile, t-ZrO 2 and m-ZrO 2 nanocrystallites had a great tendency to grow larger during thermal treatments.

On the relevance of understanding and controlling the locations of dopants in hematite photoanodes for low-cost water splitting

Successful large-scale implementation of solar fuel technologies relies on cost, performance, and reliability of materials, devices, and infrastructures. Earth-abundant, low-cost, easily recyclable, and environmentally benign light absorbers are desired for renewable fuel generation technologies, such as solar photoelectrochemical (PEC) water splitting. Hematite is considered an ideal material for PEC oxygen evolution reaction, which is a critical component in the overall water splitting process for hydrogen fuel generation. However, intrinsic and operational limitations have prevented hematite-based PEC devices from reaching their highest theoretical solar-to-hydrogen efficiency of 15%–17%. Literature clearly shows that no single approach can eliminate these limitations. An overall fundamental understanding of the effect of dopant addition as well as their physical locations and functions within the photoelectrode, in both as-synthesized form and under operating conditions, is of critical importance to unleash the tremendous potentials of hematite-based PEC systems. In this short perspective, the concept of effective doping (i.e., increase of charge carrier density) up to the limit of dopant segregation at the grain boundaries to lower the charge recombination is discussed. Based on relevant theoretical and experimental data from the literature on the effects of surface-to-bulk doping as well as dopant segregation at the grain boundaries on hematite photoelectrode performance, we discuss here the views on the necessity of understanding these processes and their individual and synergistic effects to unravel a simple yet powerful approach to design and develop highly efficient hematite photoanodes for clean hydrogen generation using water and sunlight.

Photodarkening and dopant segregation in Cu-doped β-Ga2O3 Czochralski single crystals

• Cu-doped β-Ga 2 O 3 was grown via Czochralski and vertical gradient freeze methods. • Crystals displayed novel photodarkening with UV excitation, stable at room temp. • Photodarkening is reversible back to as-grown state with an anneal at 400 °C. • Dopant segregation was shown via laser ablation inductively coupled mass spec. β-Ga 2 O 3 has demonstrated insulating properties with Mg, Fe, and Zn acceptor doping. Here we investigate Cu doping (0.25 at.%) in bulk Czochralski (CZ) and vertical gradient freeze (VGF) β-Ga 2 O 3 , with significant Cu incorporation, even with the expected Cu evaporation. Representative crystals were assessed for orientation, purity, optical, and electrical properties. The solubility and electronic behavior of Cu dopants are consistent with measured concentrations of 1 × 10 18 –1 × 10 19 atoms/cm 3 and electrical measurements that show high resistivities of 10 9 –10 10 Ω∙cm. Segregation and precipitation of Cu species in part of the VGF material was determined to be Cu 2 O by analysis with Raman spectroscopy, photoluminescence microscopy, energy-dispersive X-ray spectroscopy, and laser ablation inductively coupled plasma mass spectrometry. With sufficient Cu concentration, β-Ga 2 O 3 crystals excited with deep ultraviolet light photodarken rapidly and exhibit decreased resistivity. This darkened state remains at room temperature for several days before decaying.

Surface strain and co-doping effect on Sm and Y co-doped BaCeO3 in proton conducting solid oxide fuel cells

• Surface strain effect on BaCeO 3 -proton-conductor was calculated for the first time. • Dopant segregation trend is reduced as the surface strain increase from −2% to 2% • E vac surf and E binding do not change monotonously with surface strain. • 1% tensile strain is the most favorable for surface hydration and proton transport. • Proton stability under different strains may mainly affected by electrons interaction. Although promising, regulating the surface strain is still immature for enhance the performance of proton-conducting materials and no clear law has been found. In this work, surface strain and co-doping effect on dopant segregation, hydration reaction and proton transport of Sm and Y co-doped BaCeO 3 (BCYS) in proton-conducting solid oxide fuel cells (P-SOFC) was investigated. We found that although the dopant segregation trend is reduced as the surface strain increase from −2% to 2%, which means that a large tensile strain is beneficial to enhance structural stability, oxygen vacancy formation energy and proton binding energy near the BCYS surface do not change monotonously with the surface strain. We found that the fewer electrons around the oxygen atoms before hydrogen adsorption, the more stable the proton. It is worth noting that 1% tensile strain is most favorable for enhancing the degree of surface hydration and proton transport in our calculation results, which helps to weaken the negative effects of the space charge layer formed by the accumulation of positive charges on the surface. The collocation of Sm and Y has a synergistic effect, which means Sm facilitates oxygen vacancy formation, while Y promotes hydration reaction. Moreover, the introduction of Sm and Y can hardly change the electronic conductivity of BCYS, which is conducive to the open circuit voltage of P-SOFC.

Room temperature ferroic orders in Zr and (Zr, Ni) doped SrTiO3

• Undoped SrTiO 3 , Zr doped Sr 1−x Zr x TiO 3 and (Zr, Ni) co-doped Sr 1−x Zr x Ti 1−y Ni y O 3 samples were synthesized. • Cubic Pm-3 m phase in Sr 1−x Zr x TiO 3 up to x = 0.04. • Room temperature soft ferromagnetic order in undoped SrTiO 3 . • Dielectric constant enhancement in Zr doped Sr 1−x Zr x TiO 3 sample for x = 0.04. • Simultaneous room temperature ferroelectric and ferromagnetic orders in (Zr, Ni) co-doped Sr 0.96 Zr 0.04 Ti 0.90 Ni 0.10 O 3 . We synthesized strontium titanate SrTiO 3 (STO), Zr doped Sr 1−x Zr x TiO 3 and (Zr, Ni) co-doped Sr 1−x Zr x Ti 1−y Ni y O 3 samples using solid state reaction technique to report their structural, electrical and magnetic properties. The cubic Pm -3 m phase of the synthesized samples has been confirmed using Rietveld analysis of the powder X-ray diffraction pattern. The grain size of the synthesized materials was reduced significantly due to Zr doping as well as (Zr, Ni) co-doping in STO. The chemical species of the samples were identified using energy-dispersive X-ray spectroscopy (EDX). The Zr and Ni dopants’ homogeneity were confirmed from EDX mapping to negate spurious ferroic order due to dopant segregation. We observed forbidden first order Raman scattering at 148, 547 and 797 cm −1 which may indicate nominal loss of inversion symmetry in cubic STO. The absence of absorption at 500 cm −1 and within 600–700 cm −1 band in Fourier Transform Infrared spectra corroborates Zr and Ni as substitutional dopants in our samples. Due to 4% Zr doping in Sr 0.96 Zr 0.04 TiO 3 sample dielectric constant, remnant electric polarization, remnant magnetization and coercivity were increased. Notably, in the case of 4% Zr and 10% Ni co-doping we have observed clearly the existence of both FE and FM hysteresis loops in Sr 0.96 Zr 0.04 Ti 0.90 Ni 0.10 O 3 sample. In this co-doped sample, the remnant magnetization and coercivity were increased by ∼1 and ∼2 orders of magnitude respectively as compared to those of undoped STO. The coexistence of FE and FM orders in (Zr, Ni) co-doped STO might have the potential for interesting multiferroic applications.

Planar and three-dimensional damage-free etching of β-Ga2O3 using atomic gallium flux

In situ etching using Ga flux in an ultra-high vacuum environment like molecular beam epitaxy is introduced as a method to make high aspect ratio three-dimensional (3D) structures in β-Ga2O3. Etching of β-Ga2O3 due to excess Ga adatoms on the epilayer surface had been viewed as non-ideal for epitaxial growth especially since it results in plateauing and lowering of the growth rate. In this study, we use this well-known reaction from epitaxial growth to intentionally etch β-Ga2O3. We demonstrate etch rate ranging from 2.9 to 30 nm/min with the highest reported etch rate being only limited by the highest Ga flux used. Patterned in situ etching is also demonstrated and used to study the effect of fin orientation on the sidewall profiles and dopant (Si) segregation on the etched surface. Using in situ Ga etching, we also demonstrate 150 nm wide fins and 200 nm wide nanopillars with high aspect ratio. This etching method could enable future development of highly scaled vertical and lateral 3D devices in β-Ga2O3.

Gate-First Negative Capacitance Field-Effect Transistor With Self-Aligned Nickel-Silicide Source and Drain

In this brief, we demonstrate the gate-first HfZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (HZO) fully depleted silicon-on-insulator (FDSOI) negative capacitance field-effect transistor (NCFET) with self-aligned nickel-silicide (NiSi) source and drain (S/D). Although the gate-first process has advantages in terms of fabrication simplicity, the dopants of S/D cannot be fully activated since the polarization of ferroelectric HZO film is seriously degraded at high temperatures. To improve the S/D resistance without the polarization degradation, self-aligned S/D nickel silicidation, which induces dopant activation and dopant segregation at relatively low temperature, was simultaneously performed during ferroelectric post metal annealing (PMA). It is experimentally confirmed that 1) high concentrated dopants (As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) can be fully activated during silicidation through diode measurements and 2) S/D resistance can be reduced by NiSi silicidation through resistance measurements. Furthermore, it is verified that the electrical characteristic of NCFET with NiSi S/D exhibits superior current drivability without subthreshold swing (SS) degradation compared with that of NCFET without NiSi.

Dopant-defect interactions in Mg-doped GaN via atom probe tomography

In this work, an in-depth analysis of atomic level dopant-defect interactions in N-polar GaN:Mg was performed using atom probe tomography (APT). The 3D visualization of ion distribution revealed the formation of spherical Mg-rich clusters and the segregation of Mg dopant toward dislocations in MOCVD-grown GaN:Mg. Impurities, such as oxygen and hydrogen, were identified and detected adjacent to Mg-rich dislocations. Crystal stoichiometry around the defect regions was investigated to understand how the defects can influence dopant diffusion. Non-stoichiometric regions of N:Ga were found adjacent to Mg-rich dislocations and overlapping with some Mg-rich clusters, indicating dopant-defect interplay. Variations in N:Ga were not proportional to the Mg content, suggesting that the micro-features (clusters and dislocations) interact differently with local chemistry. Techniques for defining the quality of an APT experiment through invalidation of artifacts are also demonstrated. Mg-rich defects and variations in N:Ga were found to be independent of artifacts related to the evaporation field in APT.

The improved inverted AlGaAs/GaAs interface: its relevance for high-mobility quantum wells and hybrid systems

Two dimensional electron gases (2DEGs) realized at GaAs/AlGaAs single interfaces by molecular-beam epitaxy (MBE) reach mobilities of about 15 million cm2 V s−1 if the AlGaAs alloy is grown after the GaAs. Surprisingly, the mobilities may drop to a few millions for the identical but inverted AlGaAs/GaAs interface, i.e. reversed layering. Here we report on a series of inverted heterostructures with varying growth parameters including temperature, doping, and composition. Minimizing the segregation of both dopants and background impurities leads to mobilities of 13 million cm2 V s−1 for inverted structures. The dependence of the mobility on electron density tuned by a gate or by illumination is found to be the identical if no doping layers exist between the 2DEG and the respective gate. Otherwise, it differs significantly compared to normal interface structures. Reducing the distance of the 2DEG to the surface down to 50 nm requires an additional doping layer between 2DEG and surface in order to compensate for the surface-Schottky barrier. The suitability of such shallow inverted structures for future semiconductor-superconductor hybrid systems is discussed. Lastly, our understanding of the improved inverted interface enables us to produce optimized double-sided doped quantum wells exhibiting an electron mobility of 40 million cm2 V s−1 at 1 K.

Robust ferromagnetism in Mn and Co doped 2D-MoS2 nanosheets: Dopant and phase segregation effects

• Mn substitution in MoS 2 nanosheets is ineffective and results in weak ferromagnetism . • Robust ferromagnetism in Co doped MoS 2 nanosheets shows three distinct regions. • Bound magnetic polaron interactions induce ferromagnetism at x < 0.025 in Mo 1- x Co x S 2. • Ferromagnetic and antiferromagnetic interactions coexist with MoS 2 for 0.025 < x ≤ 0.05. • Co 9 S 8 phase segregates beyond x > 0.075 leading to large magnetization. We investigate the structural and ferromagnetic properties of Mo 1- x Mn x S 2 and Mo 1- x Co x S 2 ( x = 0, 0.025, 0.05, 0.075, 0.1 and 0.25) nanosheets synthesized by a wet chemical process. X-ray diffraction (XRD) patterns confirm the 2H polytype of MoS 2 for both pristine and doped nanosheets. From X-ray absorption near-edge spectral (XANES) studies, Mn doping in MoS 2 is found to be very ineffective even for x up to 0.25 and is found to be in Mn 4+ oxidation state. Cobalt doping in MoS 2 is very effective and found in a mixed oxidation state of 2 + /3 + . For x > 0.05, Co 9 S 8 secondary phase is discerned in XRD. XANES and extended X-ray absorption fine structure study further confirm the absence of Co, Mn clusters. All the MoS 2 nanosheets are multi-layered (~10 to 20 layers) as discerned from Raman and high-resolution transmission electron microscopy (HRTEM) studies. HRTEM images also show the presence of planar and edge defects in MoS 2 nanosheets. These defects arise from the bends, tears, folds and edges of the nanosheets. In addition to these defects, sulphur vacancy point defects are predominant as evidenced from electron paramagnetic resonance signal at g = 2.03. Pristine MoS 2 nanosheets exhibit weak ferromagnetism [magnetization (M S ) = 19 × 10 −3 emu/g and 1.3 × 10 −3 emu/g at T = 5 K and 300 K] mostly arising from the planar defects. While the magnetization increases roughly 6 (3) times higher for Mn-doped MoS 2 compared to the pristine MoS 2 nanosheets at 300 K (5 K). For Co-doped MoS 2 nanosheets 7 times increase in M S is found at 300 K, however, the changes are minimal at 5 K. A small change in M S for Mo 1- x Mn x S 2 nanosheets is due to ineffective Mn substitution at Mo sites. On the contrary, Co doped samples exhibit strong paramagnetic contribution at 5 K. Despite effective substitution of Co in MoS 2 , the saturation magnetization values obtained after subtracting the paramagnetic component are slightly less compared to Mn doped samples. This is most probably due to the dominant antiferromagnetic interaction and the Co 9 S 8 phase segregation. Thus, our experiments show that controlled Mn and Co doping in the low concentration ( x < 0.05) is a promising candidate for enabling ferromagnetism in MoS 2 nanosheets for spintronics and sensor applications.

Local damage in grain boundary stabilized nanocrystalline aluminum

The excess free volume in grain boundaries of pure nanocrystalline aluminum leads to the grain coarsening, which degrades their desirable mechanical properties. The preferential segregation of dopants to the grain boundaries has been proposed to enhance the stability of the nanostructure. To shed light on the stabilization mechanisms, we present results from virtual mechanical tests on nanocrystalline aluminum samples with similar grain sizes but different magnesium dopant contents. The segregation of magnesium decreases the excess free volume within the grain boundaries and prohibits the nucleation and growth of intergranular cracks.

Interfacial segregation in Cl−-doped nano-ZnO polycrystalline semiconductors and its effect on electrical properties

In this study, interfacial segregation in Cl−-doped ZnO (0.0, 1.0, 3.0, 4.0, and 6.0 mol%) was explored as a strategy to compensate the space charge layer to decrease the electric potential barrier height at the grain boundaries and increase the overall electrical conductivity of the system. The focus of this work was to evaluate the dopant segregation and provide the first insights into the influence of interfacial segregation on the electrical properties. By using a systematic lixiviation method, we demonstrated that in addition to the bulk solubility, the Cl− anions segregated at both the surface and grain boundaries. Impedance spectroscopy measurements showed a four orders of magnitude reduction in the total electrical resistivity in the Cl−-doped ZnO samples compared to that of undoped ZnO. The calculated value of the electric potential barrier height decreased, as well as the activation energy for conduction, which decreased from 853 meV for undoped ZnO to 168 meV for 1.2 mol% Cl−-doped ZnO.