Brekhov Kirill, Bilyk Vladislav, Ovchinnikov Andrey, Chefonov Oleg, Mukhortov Vladimir, Mishina Elena
Department of Nanoelectronics, MIREA-Russian Technological University, Moscow 119454, Russia.
Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, The Netherlands.
Nanomaterials (Basel). 2023 Jun 28;13(13):1961. doi: 10.3390/nano13131961.
This study investigates the impact of narrow-band terahertz pulses on the ferroelectric order parameter in BaSrTiO films on various substrates. THz radiation in the range of 1-2 THz with the pulse width of about 0.15 THz was separated from a broadband pulse with the interference technique. The 375 nm thick BST film on a MgO (001) substrate exhibits enhanced THz-induced second harmonic generation when excited by THz pulses with a central frequency of 1.6 THz, due to the resonant excitation of the soft phonon mode. Conversely, the BST film on a Si (001) substrate shows no enhancement, due to its polycrystalline state. The 800 nm thick BST film on a MgO (111) substrate demonstrates the maximum of a second harmonic generation signal when excited by THz pulses at 1.8 THz, which is close to the soft mode frequency for the (111) orientation. Notably, the frequency spectrum of the BST/MgO (111) film reveals peaks at both the fundamental and doubled frequencies, and their intensities depend, respectively, linearly and quadratically on the THz pulse electric field strength.
本研究调查了窄带太赫兹脉冲对各种衬底上的BaSrTiO薄膜中铁电序参量的影响。利用干涉技术从宽带脉冲中分离出频率范围为1 - 2太赫兹、脉冲宽度约为0.15太赫兹的太赫兹辐射。由于软声子模式的共振激发，在MgO(001)衬底上的375纳米厚的BST薄膜在由中心频率为1.6太赫兹的太赫兹脉冲激发时，表现出增强的太赫兹诱导二次谐波产生。相反，由于其多晶状态，在Si(001)衬底上的BST薄膜没有增强。在MgO(111)衬底上的800纳米厚的BST薄膜在由1.8太赫兹的太赫兹脉冲激发时，展示出二次谐波产生信号的最大值，该频率接近(111)取向的软模式频率。值得注意的是，BST/MgO(111)薄膜的频谱在基频和倍频处均显示出峰值，并且它们的强度分别线性和二次方地依赖于太赫兹脉冲电场强度。
