The quasiparticle spectra of atomically thin semiconducting transition metal dichalcogenides (TMDCs) and their response to an ultrafast optical excitation critically depend on interactions with the underlying substrate. Here, we present a comparative time- and angle-resolved photoemission spectroscopy (TR-ARPES) study of the transient electronic structure and ultrafast carrier dynamics in the single- and bilayer TMDCs MoS₂ and WS₂ on three different substrates: Au(111), Ag(111) and graphene/SiC. The photoexcited quasiparticle bandgaps are observed to vary over the range of 1.9–2.5 eV between our systems. The transient conduction band signals decay on a sub-50 fs timescale on the metals, signifying an efficient removal of photoinduced carriers into the bulk metallic states. On graphene, we instead observe a fast timescale on the order of 170 fs, followed by a slow dynamics for the conduction band decay in MoS${}_2$. These timescales are explained by Auger recombination involving MoS${}_2$ and in-gap defect states. In bilayer TMDCs on metals we observe a complex redistribution of excited holes along the valence band that is substantially affected by interactions with the continuum of bulk metallic states.

原子级薄半导体过渡金属二硫属元素化物 (TMDC) 的准粒子光谱及其对超快光激发的响应严重依赖于与底层基板的相互作用。在这里，我们展示了单层和双层 TMDC MoS ₂和 WS _{2 中}瞬态电子结构和超快载流子动力学的比较时间和角度分辨光电子能谱 (TR-ARPES) 研究在三种不同的基材上：Au(111)、Ag(111) 和石墨烯/SiC。观察到光激发准粒子带隙在我们的系统之间在 1.9-2.5 eV 的范围内变化。瞬态导带信号在金属上以低于 50 fs 的时间尺度衰减，表明光致载流子有效去除到块体金属状态。在石墨烯上，我们观察到 170 fs 量级的快速时间尺度，然后是 MoS 中导带衰减的缓慢动力学${}_2$. 这些时间尺度由涉及 MoS 的俄歇重组解释${}_2$和间隙缺陷状态。在金属上的双层 TMDC 中，我们观察到激发空穴沿价带的复杂重新分布，这在很大程度上受到与块状金属状态连续体的相互作用的影响。