Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes (¹⁰B and ¹¹B) compared to those with the natural distribution of boron (20 at% ¹⁰B and 80 at% ¹¹B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in ¹⁰BN than in ¹¹BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

六方氮化硼是一种典型的层状化合物，其中弱的，非局部的范德华相互作用确保了由牢固结合的硼和氮原子构成的二维蜂窝晶格的垂直堆叠。我们通过合成具有几乎纯的硼同位素（¹⁰ B和¹¹ B）的六方氮化硼晶体（与具有自然分布的硼（20 at％¹⁰ B和80 at％¹¹）的那些相比）来研究层状化合物的同位素工程B）。一方面，与标准半导体一样，声子能量和电子带隙都随硼同位素质量而变化，后者是归因于零点重新归一化的量子效应。另一方面，着重于相邻层的剪切运动和呼吸运动的依赖温度的实验揭示了层状材料中同位素工程的特殊性，同时对同位素纯化后的范德华相互作用进行了改进。与¹¹ BN晶体相比，在¹⁰ BN中相邻层之间的电子密度分布更加分散。我们的结果为理解和控制分层材料中的范德华键合开辟了前景。