薄膜中经典去湿不稳定性的流体动力学是一个非线性过程。然而，在特征长度和时间尺度方面的不稳定性的物理表现可以通过薄膜动力学的初始条件的线性化形式来描述。或者，基于将自由能降低速率等同于粘性耗散的热力学方法[de Gennes，C. R. Acad. [298]可以提供类似的信息。在这里，我们已经评估了去湿的存在下所产生的薄膜厚度（h）依赖于温度的热毛细作用力。这种情况可以在脉冲激光熔化金属薄膜的过程中发现，其中纳米级效应导致局部h依赖性温度。热力学方法提供了一个分析描述这种热毛细去湿。只要使自由能的减小率等于粘性耗散的最小值，这种方法的结果与线性理论和实验观察的结果是一致的。产生这种最小粘性耗散的流动边界条件是当膜-基底切向应力为零时。这一发现的物理含义是，自发脱湿不稳定遵循的路径的能量损失率最小。
英文摘要：
The fluid dynamics of the classical dewetting instability in ultrathin films is a non-linear process. However, the physical manifestation of the instability in terms of characteristic length and time scales can be described by a linearized form of the initial conditions of the films's dynamics. Alternately, the thermodynamic approach based on equating the rate of free energy decrease to the viscous dissipation [de Gennes, C. R. Acad. Paris.v298, 1984] can give similar information. Here we have evaluated dewetting in the presence of thermocapillary forces arising from a film-thickness (h) dependent temperature. Such a situation can be found during pulsed laser melting of ultrathin metal films where nanoscale effects lead to a local h-dependent temperature. The thermodynamic approach provides an analytical description of this thermocapillary dewetting. The results of this approach agree with those from linear theory and experimental observations provided the minimum value of viscous dissipation is equated to the rate of free energy decrease. The flow boundary condition that produces this minimum viscous dissipation is when the film-substrate tangential stress is zero. The physical implication of this finding is that the spontaneous dewetting instability follows the path of minimum rate of energy loss.
Practical applications of nanocrystalline metallic thin films are often limited by instabilities. In addition to grain growth, the thin film itself can become unstable and collapse into islands through solid-state dewetting. Selective alloying can improve nanocrystalline stability, but the impact of this approach on dewetting is not clear. In this study, two alloys that exhibit nanocrystalline thermal stability as ball milled powders are evaluated as thin films. While both alloys demonstrated dewetting behavior following annealing, the severity decreased in more dilute compositions. Ultimately…
Everyday experience confirms the tendency of adhesive films to detach from spheroidal regions of rigid substrates -- what is a petty frustration when placing a sticky bandage onto an elbow or knee is a more serious matter in the coating and painting industries. Irrespective of their resistance to bending, a key driver of such phenomena is Gauss' \textit{Theorema Egregium}, which implies that naturally flat sheets cannot conform to doubly-curved surfaces without developing a strain whose magnitude grows sharply with the curved area. Previous attempts to characterize the onset of curvature-induc…
Stability of thin lubricating fluid coated slippery surfaces depends on the surface energy of the underlying solid surface. High energy solid surfaces, coated with thin lubricating oil, lead to the dewetting of the oil films upon depositing aqueous drops on it. The total surface energy, which is due to the long range and short range interactions, also predict the instability of thin lubricating films under the given condition. In this article, we present experimental study of dewetting of thin lubricating oil films sandwiched between hydrophilic solid surface and aqueous drops. Fluorescence im…
We propose a sharp interface model for simulating solid-state dewetting where the surface energy is (weakly) anisotropic. The morphology evolution of thin films is governed by surface diffusion and contact line migration. The mathematical model is based on an energy variational approach. Anisotropic surface energies lead to multiple solutions of the contact angle equation at contact points. Introduction of a finite contact point mobility is both physically based and leads to robust, unambiguous determination of the contact angles. We implement the mathematical model in an explicit finite diffe…
The instability of ferroelectric ordering in ultra-thin films is one of the most important fundamental issues pertaining realization of a number of electronic devices with enhanced functionality, such as ferroelectric and multiferroic tunnel junctions or ferroelectric field effect transistors. In this paper, we investigate the polarization state of archetypal ultrathin (several nanometres) ferroelectric heterostructures: epitaxial single-crystalline BaTiO$_3$ films sandwiched between the most habitual perovskite electrodes, SrRuO$_3$, on top of the most used perovskite substrate, SrTiO$_3$. We…
Through ${in~situ}$ photoemission spectroscopy, we investigated the change in the electronic and crystal structures of dimensionality-controlled VO$_2$ films coherently grown on TiO$_2$(001) substrates. In the nanostructured films, the balance between the instabilities of a bandlike Peierls transition and a Mott transition is controlled as a function of thickness. The characteristic spectral change associated with temperature-driven metal-insulator transition in VO$_2$ thick films holds down to 1.5 nm (roughly corresponding to five V atoms along the [001] direction), whereas VO$_2$ films of le…
Morphological instability of a planar surface ([111], [011], or [001]) of an ultra-thin metal film is studied in a parameter space formed by three major effects (the quantum size effect, the surface energy anisotropy and the surface stress) that influence a film dewetting. The analysis is based on the extended Mullins equation, where the effects are cast as functions of the film thickness. The formulation of the quantum size effect (Z. Zhang et al., PRL 80, 5381 (1998)) includes the oscillation of the surface energy with thickness caused by electrons confinement. By systematically comparing th…
The molecular dynamics method is used to study the process of development of dynamic instability of a thin film, leading to its destruction. The calculations are performed for a thin (5 atomic layers) $fcc$ aluminum film using the interatomic interaction potential tested by comparing the numerical results with the analytical ones obtained in the framework of elasticity theory. For this purpose, an original approach is developed, which allows one to calculate the dispersion law of long-wave phonons in ultrathin films using the molecular dynamics method. The temperatures ($< 600 K$) at which the…
