Title: Substrate interference and strain in the second harmonic generation from MoSe$_2$ monolayers Show Chinese title

Title: 基底干扰和二次谐波生成中的应变来自MoSe$_2$单层

Abstract: Nonlinear optical materials of atomic thickness--such as non-centrosymmetric 2H transition metal dichalcogenide monolayers--have a second order nonlinear susceptibility ($\chi^{(2)}$) whose intensity can be tuned by strain. However, whether $\chi^{(2)}$ is enhanced or reduced by tensile strain is a subject of conflicting reports. Here, we grow high-quality MoSe$_2$ monolayers under controlled biaxial strain created by two different substrates, and study their linear and non-linear optical responses with a combination of experimental and theoretical approaches. A 15-fold overall enhancement in second harmonic generation (SHG) intensity is observed on MoSe$_2$ monolayers grown on SiO$_2$ when compared to its value when on a Si$_3$N$_4$ substrate. A seven-fold enhancement was ascertained to substrate interference, and a factor of two to the enhancement of $\chi^{(2)}$ arising from biaxial strain: substrate interference and strain are independent handles to engineer the SHG strength of non-centrosymmetric 2D materials. Show Chinese abstract

Abstract: 具有原子厚度的非线性光学材料——如非中心对称的2H过渡金属二硫属化物单层——具有二级非线性极化率($\chi^{(2)}$)，其强度可以通过应变进行调节。 然而，$\chi^{(2)}$是否因拉伸应变而增强或减弱是一个存在矛盾报告的问题。 在这里，我们在由两种不同基底产生的受控双轴应变下生长高质量的MoSe$_2$单层，并通过实验和理论方法结合研究它们的线性和非线性光学响应。 与在Si$_3$N$_4$基底上的值相比，在SiO$_2$上生长的MoSe$_2$单层中观察到二次谐波生成(SHG)强度整体增强了15倍。 通过确定基底干扰带来了七倍的增强，并且由于双轴应变导致的$\chi^{(2)}$增强因素为二：基底干扰和应变是独立的调控手段，用于工程非中心对称二维材料的SHG强度。