Copper chalcogenides and pnictogenides often behave as heavily doped p-type semiconductors, because of the presence of a high density of Cu vacancies, with corresponding hole carriers in the valence band. If the free-carrier concentration is high enough, localized surface plasmon resonances can be sustained in nanocrystals of these materials, with frequencies that are typically observed in the infrared region of the spectrum (<1 eV), differently from the typical resonances featured in the visible range by metallic nanoparticles. Here, we demonstrate that Cu vacancies in hexagonal Cu_3–xP nanocrystals can be directly quantified by scanning transmission electron microscopy (STEM) analysis. We also report, for the first time, the spatial localization of the plasmon resonances in individual Cu_3–xP nanocrystals by means of STEM energy loss spectroscopy (EELS), which is an achievement that, to date, had been possible only on nanoparticles of noble metals. Two plasmon modes can be seen from STEM-EELS, which are in agreement with the resonances calculated from the vacancy concentration obtained from the STEM analysis.

中文翻译：

---

铜空位的直接定量和磷化铜纳米晶体中表面等离振子共振的空间定位

由于存在高密度的Cu空位，并且在价带中具有相应的空穴载流子，所以硫属铜和硫属铜化物通常表现为重掺杂的p型半导体。如果自由载流子浓度足够高，则可以在这些材料的纳米晶体中维持局部表面等离振子共振，其频率通常在光谱的红外区域（<1 eV）内观察到，与典型的共振频率不同。金属纳米粒子的可见范围。在这里，我们证明六角形Cu _{3– x中的}Cu空位P纳米晶体可以通过扫描透射电子显微镜（STEM）分析直接定量。我们还首次通过STEM能量损失谱（EELS）报告了单个Cu _{3– x} P纳米晶体中的等离振子共振的空间定位，这是迄今为止仅在纳米颗粒上才有的成就。贵金属。从STEM-EELS可以看到两种等离激元模式，这与从STEM分析获得的空位浓度计算出的共振一致。