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Two-dimensional vortex quantum droplets
摘要： It was recently found that the Lee-Huang-Yang (LHY) correction to the mean-field Hamiltonian of binary atomic boson condensates suppresses the collapse and creates stable localized modes (two-component quantum droplets, QDs) in two and three dimensions (2D and 3D). In particular, the LHY effect modifies the effective Gross-Pitaevskii equation (GPE) in 2D by adding a logarithmic factor to the usual cubic term. In the framework of the accordingly modified two-component GPE system, we construct 2D self-trapped modes in the form of QDs with vorticity S embedded into each component. Because of the effect of the logarithmic factor, the QDs feature a flat-top shape, which expands with the increase of S and norm N. An essential finding, produced by a systematic numerical investigation and analytical estimates, is that the vortical QDs are stable (which is a critical issue for vortex solitons in nonlinear models) up to S = 5, for N exceeding a certain threshold value, which is predicted to scale as Nth ～ S4 for large S (for three-dimensional QDs, the scaling is Nth ～ S6). The prediction is corroborated by numerical findings. Pivots of QDs with S (cid:2) 2 are subject to structural instability, as specially selected perturbations can split the single pivot in a set of S or S + 2 pivots corresponding to unitary vortices; however, the structural instability remains virtually invisible, as it occurs in a broad central "hole" of the vortex soliton, where values of fields are very small, and it does not cause any dynamical instability. In the condensate of 39K atoms, in which QDs with S = 0 and a quasi-2D shape were created recently, the vortical droplets may have radial size (cid:2)30 μm, with the number of atoms in the range of 104–105. The role of three-body losses is considered too, demonstrating that they do not prevent the creation of the vortex droplets but may produce a noteworthy effect, leading to sudden splitting of "light" droplets. In addition, hidden-vorticity (HV) states in QDs, with topological charges S+ = ?S? = 1 in their components, which are prone to strong instability in other settings, have their stability region too. Unstable HV states tend to spontaneously merge into zero-vorticity solitons. Collisions of QDs, which may lead to their merger, and dynamics of elliptically deformed QDs (which form rotating elongated patterns or ones with oscillations of the eccentricity) are briefly considered too.
关键词： hidden-vorticity states,Gross-Pitaevskii equation,Lee-Huang-Yang correction,quantum droplets,vorticity,three-body losses,stability
更新于2025-09-09 09:28:46
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Effects of Strategically Placed Water Droplets on Monolayer Growth of Molybdenum Disulfide
摘要： Two-dimensional (2D) molybdenum disulfide (MoS2) films with a tunable bandgap hold great promise for next-generation electronic and optoelectronic devices. Synthesis of large areas of high-quality MoS2 monolayers lacks experimental reproducibility. Moreover, the outcome of MoS2 growth by chemical vapor deposition is dependent on several interconnected growth parameters. In this study, we present results of MoS2 monolayer growth by strategically placing water droplets on the growth substrate and/or in the source prior to its loading in the growth chamber. The volume and distribution of water on the growth substrate and in the source had a direct impact on the morphology of the as-grown MoS2. Characterized by scanning electron microscopy (SEM), Raman microscopy, and atomic force microscopy (AFM), the number and size of MoS2 layers as well as its distribution on the growth substrate were found to have a strong dependence on the positioning of the water droplet. This study on MoS2 monolayer growth using water droplets as a promoter provides a simple and reproducible experimental technique enabling growth with high reliability.
关键词： molybdenum disulfide,water droplets,Raman microscopy,scanning electron microscopy,chemical vapor deposition,atomic force microscopy,monolayer growth
更新于2025-09-09 09:28:46
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Liquid crystalline droplets in aqueous environments: electrostatic effects
摘要： We demonstrate the strong impact of electrostatic properties on radial–bipolar structural transitions in nematic liquid crystal (LC) droplets dispersed in different aqueous environments. In the experimental part of the study, we systematically changed the electrostatic properties of both LC droplets and aqueous solutions. Mixtures of nematics were studied by combining LC materials with negative (azoxybenzene compounds) and strongly positive (cyanobiphenyl) dielectric anisotropy. The aqueous solutions were manipulated by introducing either polyvinyl alcohol, glycerol, electrolyte or amphiphilic anionic surfactant SDS into water. In the supporting theoretical study, we identified the key parameters influencing the dielectric constant and the electric field strength of aqueous solutions. We also estimated the impact of different electrolytes on the Debye length at the LC–aqueous interface. The obtained results are further analysed for chemical and biological sensing applications.
关键词： electrostatic effects,aqueous environments,nematic droplets,liquid crystals,structural transitions
更新于2025-09-09 09:28:46
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Light-actuated droplets coalescence and ion detection on the CAHTs-assisted superhydrophobic surface
摘要： Coalescence and mixing of the complex chemical reagents on the droplet-based open micro?uidics are considered to be critical steps for the sample processing and the follow-up reactions and chromogenic/?uorescence analyses. Recently, using the light to actuate the droplets coalescence has been demonstrated to be able to create the ?exible, precise and high-throughput optical droplet-based reaction/analysis platforms. Particularly, the photothermal e?ect, which is one of the ?uid-light interactions, is promising in the droplets coalescence by the light-induced phase change. In present study, a contact angle hypothesis traps (CAHTs)-assisted optical droplet-based reaction/analysis platform was developed. With the triple-phase contact line extension caused by the light-heating induced wetting transition, the coalescence of two neighboring droplets on the CAHTs was induced to facilitate the rapid mixing and detection. It was also con?rmed that with the o?-center light heating, the orientable extension of the irradiated droplet was realized, which could increase the critical CAHTs gap required for the occurrence of the droplets coalescence. With the developed platform, an ion detection by processing a chromogenic reaction was presented as a proof of concept. It is believed that this concept has the signi?cant potential in many applications, including biomedicine, pharmacy, clinical diagnosis and chemosynthesis.
关键词： Ion detection,Superhydrophobic surface,Contact angle hypothesis traps,Photothermal e?ect,Droplets coalescence,Orientable extension
更新于2025-09-04 15:30:14