Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, ${\mathrm{MoSe}}_2$)] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in $\mathrm{graphene}/{\mathrm{MoSe}}_2$ is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps) room-temperature ${\mathrm{MoSe}}_2$ exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and ${\mathrm{MoSe}}_2$ Raman modes, which reveals net photoinduced electron transfer from ${\mathrm{MoSe}}_2$ to graphene and hole accumulation in ${\mathrm{MoSe}}_2$. Remarkably, the steady-state Fermi energy of graphene saturates at $290\pm 15\mathrm{meV}$ above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets) and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in $\mathrm{graphene}/{\mathrm{MoSe}}_2$. This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron exchange or dipole-dipole interaction) is the dominant interlayer coupling mechanism between atomically thin TMDs and graphene.

中文翻译：

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原子薄石墨烯-过渡金属二硫属化物范德华结构中的电荷与能量转移

范德华异质结构由二维材料堆叠制成，展现出独特的光-质相互作用，并有望用于新型光电器件。这种设备的性能由通过例如层间电荷和/或能量转移的近场耦合来控制。需要新的概念和实验方法来正确描述二维异质接口。在这里，我们报告了对原子薄金属半导体中层间电荷和能量转移的原始研究[即，石墨烯-过渡金属二硫化碳（TMD，在此为二硒化钼，${\mathrm{硒化钼}}_{\mathrm{2个}}$）]结合使用微光致发光和拉曼散射光谱学的异质结构。发光强度$\mathrm{石墨烯}/{\mathrm{硒化钼}}_{\mathrm{2个}}$ 被淬灭超过2个数量级，并随入射光子通量线性增加，表明室温大大缩短（约1 ps） ${\mathrm{硒化钼}}_{\mathrm{2个}}$激子寿命。通过对石墨烯和${\mathrm{硒化钼}}_{\mathrm{2个}}$ 拉曼模式，揭示了来自 ${\mathrm{硒化钼}}_{\mathrm{2个}}$ 石墨烯和空穴积累 ${\mathrm{硒化钼}}_{\mathrm{2个}}$。值得注意的是，石墨烯的稳态费米能在$290\pm 15\mathrm{病毒}$高于狄拉克点。在环境空气和真空中都可以观察到这种可重现的行为，并根据内在因素（即，带偏移）和环境影响进行了讨论。在这种饱和状态下，平衡的光诱导电子和空穴流可以转移到石墨烯，这种机制有效地导致了能量转移。使用各种各样的入射光子通量和不同的环境条件，我们发现净光诱导的电荷转移的存在对近统一的光致发光猝灭效率没有可测量的影响。$\mathrm{石墨烯}/{\mathrm{硒化钼}}_{\mathrm{2个}}$。这种相关性的缺乏强烈表明，转移至石墨烯的能量（以电子交换或偶极-偶极相互作用的形式）是原子薄TMD和石墨烯之间的主要层间耦合机制。