Emergent,Non-Aging,Extendable, and Rechargeable Exchange Bias in 2D Fe3GeTe2 Homostructures Induced by Moderate Pressuring

As a crucial concept in magnetism and spintronics, exchange bias (ExB) measures the asymmetry in the hysteresis loop of a pinned ferromagnet (FM)/antiferromagnet (AFM) interface. Previous studies are mainly focused on FM/AFM heterostructures composed of conventional bulk materials, whose complex interfaces prohibit precise control and full understanding of the phenomenon. Here, the enabling power of 2D magnets is exploited to demonstrate the emergence, non-aging, extendability, and rechargeability of ExB in van der Waals Fe₃GeTe₂ homostructures, upon moderate pressuring. The emergence of the ExB is attributed to a local stress-induced FM-to-AFM transition, as validated using first-principles calculations, and confirmed in magneto-optical Kerr effect and second harmonic generation measurements. It is also observed that, negligible ExB aging before the training effect suddenly takes place through avalanching, pronounced delay of the avalanche via timed pressure repetition (extendability), ExB recovery in the post-training sample upon refreshed pressuring (rechargeability), and demonstrate its versatile tunability. These striking findings offer unprecedented insights into the underlying principles of ExB and its training, with immense technological applications in sight.     

Photoinduced Contact Evolution and Junction Rearrangement in Two-Dimensional van der Waals Heterostructure

Devices based on 2DMs van der Waals (vdW) heterostructures always compose of multiple contacts. Due to the instability of nanoscale 2DMs and interfaces, these contacts can be affected by the operation-induced photo or thermal effect. They can trigger the evolution of junctions and rearrange the junctions across a device, which are detrimental for applications. Herein, vdW heterostructure of indium selenide (InSe) and black phosphorus (BP) on Au electrodes are investigated to reveal the contact evolution and its relation to device performance. During operation, light irradiation changes the I–V characteristics from symmetry to strong rectification. Photocurrent mapping and Kelvin-probe force microscopy (KPFM) reveal triple junctions in this heterostructure, i.e., Au-InSe junction, InSe homojunction, and InSe-BP heterojunction. The variation of I–V characteristics of vdW heterostructure is ascribed to the evolution of Au-InSe junction from quasi-ohmic junction with a near-zero work function difference (Δφ) to a strong Schottky junction (Δφ = ≈0.27 eV). The stabilized device demonstrates distinguished time-domain response at individual junctions and overall device, indicating the evolution of contacts and the consequent opposite junction directions degrade the overall device performance. This research emphasizes the importance of dealing with heterogeneous contacts and junction directions in designing vdW heterostructure photodetectors.     

新型范德华绝缘体封装的MoS2晶体管性能研究

以MoS₂为代表的二维半导体材料是下一代延续摩尔定律的潜在电子学新材料之一。然而,二维特性使得MoS₂中电子的输运行为对环境条件高度敏感。采用范德华绝缘体材料进行封装包覆,是目前消除二维半导体器件环境敏感性的有效方案之一。文章采用化学气相传输法制备新型范德华绝缘体材料CrOCl,并以少层CrOCl为介电层和封装材料,设计并制备了基于MoS₂的场效应晶体管。以CrOCl为底栅介电层及封装材料的MoS₂晶体管的室温场效应迁移率约为60 cm²·V^-1·s^-1,2 K下进一步增大至100 cm²·V^-1·s^-1。此外,相比于无封装MoS₂晶体管高达20 V的回滞窗口,CrOCl的包覆有效消除了晶体管转移特性的回滞现象,证明其在二维材料电子学中的应用潜力。     

COMMENTS CONCERNING A SIMPLE EQUATION OF STATE OF THE VAN DER WAALS FORM

When the Carnahan-Starling equation of state for hard spheres is combined with a simple attractive term, the molecular size parameter b for argon (as obtained from critical data) is much closer to the “correct” value than that obtained from the empirical Redlich-Kwong equation

For the critical isotherm for argon, the best simple form of the attractive term lies between the two common forms, proposed by van der Waals and by Redlich. At constant temperature, the attractive contribution to the compressibility factor is proportional to (v + 0.2b)^?1 where v is the molar volume. This proportionality is in agreement with results for a square-well fluid recently reported by Sandier.     

铯原子与无缺陷金属表面间的范德瓦尔斯（vdw）作用势：特定量子态C3的数值计算

根据电偶极跃迁几率的定义和Wigner-Eckart定理,建立了计算铯原子与无缺陷金属表面间范德瓦尔斯（vdw）作用势的特定量子态的理论模型,并计算了铯原子基态、激发态各特定量子态C3的数值。     

Pulmonary dispersion formulations: The impact of dispersed powder properties on pressurized metered dose inhaler stability

Suspension-type metered dose inhaler formulations characteristically have a high degree of dispersion instability. This may occur as the result of any of a large number of formulation issues including phase separation, particle growth, agglomeration/flocculation, moisture ingress, and particle interactions with both the canister material and other particles. Many of these undesirable instabilities may arise as a result of the physical and chemical properties of the dispersed powder in the liquid propellant system. As such, this review provides a detailed understanding of the characteristics of the dispersed phase in the liquid propellant system necessary to ensure stability of the final formulation.     

How imidazolium-based ionic liquids solubilize the poorly soluble ibuprofen? A theoretical study

Molecular dynamics simulations were performed to study combinations of [AcO]⁻, [TfO]⁻, [BF₄]⁻, and [PF₆]⁻ anions paired with imidazolium cations of increasing alkyl chain length to elucidate the roles of anions and cations in solvating ibuprofen. Our simulation results revealed that ionic liquids (ILs) with strong ibuprofen solvation capacity should possess strong van der Waals force from cations and strong hydrogen bond (HB) from anions. Accordingly, it was found that ILs containing anions with strong HB acceptability, such as [AcO]⁻ anion, were the best effective solvent for ibuprofen solvation, while the longer alkyl chain in the imidazolium cations decrease the polarity, thus increasing the affinity with ibuprofen. Therefore, it was suggested that the heterocyclic structure of imidazolium cation with moderate polarity and longer alkyl chain is a promising cation candidate, whereas the anions which have a strong HB acceptability and substituents without electron withdrawing groups are beneficial. The obtained results can provide useful information for rational design and selection of new ILs to dissolve insoluble drugs.     

Numerical studies of the effects of fines on fluidization

Euler‐Lagrange simulations of fluidized beds of Geldart Group A particles containing different levels of fines are performed in periodic domains with various domain‐averaged solid volume fractions. Bubble‐like voids readily form when no fines are added. Introducing fines does not reduce bubble sizes if van der Waals force between particles is not accounted for. In contrast, the addition of van der Waals force produces significant changes. With no fines, bubbles are found to be suppressed at sufficiently high solid volume fractions, corresponding to the expanded bed regime for Group A particles. With the addition of fines, bubbles can be suppressed at lower solid volume fractions. With more fines added, bubbles can be suppressed at even lower solid volume fractions. When bubbles are suppressed, the system is found to be in a stable solid‐like regime. In this regime, forces on each particle are balanced, and the particle velocity fluctuations are dampened. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2271–2281, 2016     

The Effect of Relative Humidity on Particle Adhesion and Removal

The removal of small particles is vital for contamination-free manufacturing. In humid environments liquid can condense between the particle and substrate and give rise to a very large capillary force, which increases the total force of adhesion. The removal and adhesion forces of polystyrene latex (PSL) particles and pigmented coating chips were measured on silicon, polyethylene terephthalate, metallized and polyester coating substrates as a function of humidity. The results indicate that the capillary force is significant at a relative humidity above 50% and dominates at a relative humidity above 70%. At relative humidity below 45%, the electrostatic force becomes significant. The adhesion forces varied depending on the particles and substrates used, but the trend of high adhesion at high and low relative humidity was observed for all PSL particles/substrate systems. The pigmented coating chips/substrate system however, exhibited high adhesion at high relative humidity and low adhesion at low relative humidity.     

Design of the spherical agglomerate size in crystallization by developing a two-step bridging mechanism and the model

Spherical agglomeration technology can produce high-performance spherical particles in a single crystallization unit, although it is still challenging to control the particle size and shape. To solve this issue, a two-step bridging (TSB) mechanism containing a preconditioning period, size period, and shape period is proposed. The dynamic balance among the forces of adhesion, dispersion, and capillary action in the multi-liquid phases plays a key role. This is fully considered to establish the TSB-based thermodynamic size model and particle design framework by weighting the force action regions in multi-liquid phases with dynamic composition. The spherical agglomerates of benzoic acid, celecoxib, and salicylic acid with narrow particle size distributions and tunable particle size ranges of 2000–5000, 800–3500, and 1500–4500 μm, respectively, were designed and prepared successfully, showing good correlation with the calculation, which is superior to the reported methods and indicates that the mechanism has certain universality and guiding significance.