Tailoring of photon-matter interaction in solid material is critical for surface plasmon resonance-based sensing. This can be achieved from suitable material with interface engineering. The modified plasma oscillations in metal-metal interfaces are highly sought-after phenomena in plasmonics; however, such a localized nature of this oscillation has never been reported. Here we present the first evidence of localized interface plasmons from CoAg bimetallic nanoparticles by employing scanning transmission electron microscopy-electron energy-loss spectroscopy. We found that the localized interface plasmons oscillate with a frequency in between in-plane dipole localized surface plasmon resonance (LSPR) mode and quasiplanar mode. Moreover, we observed that the localized interface plasmon resonance is stronger than in-plane dipole LSPR which was characterized by comparing the quality factor of the energy-loss peaks. Such interface plasmon resonance was not distinctly observed from ensembles of CoAg nanoparticles by optical excitation incident normally; however, a broader in-plane dipole mode was observed compared to similar pure Ag nanoparticles. This direct detection of plasmons confined to the interface region could drive to future engineering of bimetallic interfaces with improved plasmonic activity.

调整固体材料中的光子-物质相互作用对于基于表面等离振子共振的传感至关重要。这可以通过使用界面工程的合适材料来实现。在金属-金属界面中经过修改的等离子振荡是等离激元学中非常受欢迎的现象。但是，这种振荡的这种局部性质从未被报道过。在这里，我们通过扫描透射电子显微镜-电子能量损失谱，从CoAg双金属纳米颗粒中呈现局部界面等离子体激元的第一个证据。我们发现，局部界面等离子体激元以平面内偶极局部表面等离子体激元共振（LSPR）模式和准平面模式之间的频率振荡。此外，我们观察到局部界面等离子体激元共振比平面内偶极子LSPR强，这是通过比较能量损失峰的品质因数来表征的。通过正常入射的光激发，没有从CoAg纳米颗粒的集合中清楚地观察到这种界面等离子体共振。然而，与类似的纯银纳米粒子相比，观察到了更宽的面内偶极子模式。对局限于界面区域的等离激元的这种直接检测可以推动未来具有改善的等离激元活性的双金属界面的工程化。与类似的纯银纳米粒子相比，观察到了更宽的面内偶极子模式。对局限于界面区域的等离激元的这种直接检测可以推动未来具有改善的等离激元活性的双金属界面的工程化。与类似的纯银纳米粒子相比，观察到了更宽的面内偶极子模式。对局限于界面区域的等离激元的这种直接检测可以推动未来具有改善的等离激元活性的双金属界面的工程化。