The variegated family of two-dimensional (2D) crystals has developed rapidly since the isolation of its forerunner: Graphene. Their plane-confined nature is typically associated with exceptional and peculiar electronic, optical, magnetic, and mechanical properties, heightening the interest of fundamental science and showing promise for applications. Methods for tuning their properties on demand have been pursued, among which the application of mechanical stresses, allowed by the incredible mechanical robustness and flexibility of these atomically thin materials. Great experimental and theoretical efforts have been focused on the development of straining protocols and on the evaluation of their impact on the peculiar properties of 2D crystals, revealing a novel, alluring physics. The relevance held by strain for 2D materials is introduced in Sec. I. Sections II and III present the multiplicity of methods developed to induce strain, highlighting the peculiarities, effectiveness, and drawbacks of each technique. Strain has largely widened the 2D material phase space in a quasi-seamless manner, leading to new and rich scenarios, which are discussed in Secs. IV–VI of this work. The effects of strain on the electronic, optical, vibrational, and mechanical properties of 2D crystals are discussed, as well as the possibility to exploit strain gradients for single-photon emission, non-linear optics, or valley/spintronics. Quantitative surveys of the relevant parameters governing these phenomena are provided. This review seeks to provide a comprehensive state-of-the-art overview of the straining methods and strain-induced effects, and to shed light on possible future paths. The aims and developments, the tools and strategies, and the achievements and challenges of this research field are widely presented and discussed.

中文翻译：

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二维晶体的电子、光学和振动特性的应变调谐

自从分离出其先驱石墨烯以来，二维 (2D) 晶体的杂色家族发展迅速。它们的平面限制性质通常与特殊和奇特的电子、光学、磁性和机械性能有关，从而提高了基础科学的兴趣并显示出应用前景。人们一直在寻求根据需要调整其性能的方法，其中包括施加机械应力，这得益于这些原子级薄材料令人难以置信的机械强度和灵活性。大量的实验和理论工作都集中在应变协议的开发和评估它们对 2D 晶体的特殊性质的影响上，揭示了一种新颖的、诱人的物理学。应变对二维材料的相关性在第二节中介绍。一世。第二节和第三节介绍了为诱导应变而开发的多种方法，突出了每种技术的特点、有效性和缺点。应变以准无缝的方式在很大程度上拓宽了 2D 材料相空间，导致了新的和丰富的场景，这将在第 2 节中讨论。这项工作的 IV-VI。讨论了应变对二维晶体的电子、光学、振动和机械性能的影响，以及利用应变梯度用于单光子发射、非线性光学或谷/自旋电子学的可能性。提供了对控制这些现象的相关参数的定量调查。本综述旨在对应变方法和应变引起的影响提供全面的最新概述，并阐明未来可能的路径。目标和发展，