标题： 纳米显微镜揭示金属黑色磷 显示英文标题

标题： Nanoscopy Reveals Metallic Black Phosphorus

摘要： 层状和二维（2D）材料，如石墨烯、氮化硼、过渡金属二硫属化物（TMDCs）和黑磷（BP），具有引人入胜的基本物理特性，并在电子学和光学领域展现出许多重要应用的前景。其中，BP是一种新型的二维材料，理论上预测当高度掺杂时，在约0.4 eV以下的频率下可以表现出等离激元行为。BP的电子特性因其各向异性结构而独特，这可能强烈影响集体电子激发。作为纳米电子学和纳米光学材料，BP的优势在于与金属不同，其自由载流子密度可以通过静电门控动态控制，这一点已通过其在场效应晶体管中的应用得到证实。尽管BP引起了广泛关注，但其近场和等离激元特性尚未被实验研究。在这里，我们报告了BP纳米尺度近场特性的首次观察。我们发现，纳米薄膜BP的外部明亮条纹近场图案和高表面极化率与其中红外（中红外）频率下的表面金属、等离激元行为一致。这种行为具有高度的频率色散性，在频率{\omega }=1070 cm-1 以上消失，这使我们能够估算等离子体频率和载流子密度。我们还在其他二维半导体如TMDCs中观察到类似行为，但在二维绝缘体如氮化硼中未观察到。这种新现象归因于半导体纳米薄膜的表面电荷。这一发现开辟了纳米等离激元和光电子学的新研究领域和潜在应用。 显示英文摘要

摘要： Layered and two-dimensional (2D) materials such as graphene, boron nitride, transition metal dichalcogenides(TMDCs), and black phosphorus (BP) have intriguing fundamental physical properties and bear promise of numerous important applications in electronics and optics. Of them, BP is a novel 2D material that has been theoretically predicted to acquire plasmonic behavior for frequencies below ~0.4 eV when highly doped. The electronic properties of BP are unique due to an anisotropic structure, which could strongly influence collective electronic excitations. Advantages of BP as a material for nanoelectronics and nanooptics are due to the fact that, in contrast to metals, the free carrier density in it can be dynamically controlled by electrostatic gating, which has been demonstrated by its use in field-effect transistors. Despite all the interest that BP attracts, near-field and plasmonic properties of BP have not yet been investigated experimentally. Here we report the first observation of nanoscopic near-field properties of BP. We have discovered near field patterns of outside bright fringes and high surface polarizability of nanofilm BP consistent with its surface-metallic, plasmonic behavior at mid-infrared (mid-IR) frequencies. This behavior is highly frequency-dispersive, disappearing above frequency, {\omega} =1070 cm-1, which allowed us to estimate the plasma frequency and carrier density. We have also observed similar behavior in other 2D semiconductors such as TMDCs but not in 2D insulators such as boron nitride. This new phenomenon is attributed to surface charging of the semiconductor nanofilms. This discovery opens up a new field of research and potential applications in nanoplasmonics and optoelectronics.