SGER: Controlling the Dispersion of Newly Discovered Acoustic Surface Plasmons

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*****NON-TECHNICAL ABSTRACT****Recently a startling discovery was made, electrons on beryllium (a metal) surfaces behave very much like waves on the surface of a lake. This observation contradicts established physics, which states that electrons on metal surfaces can only become collectively excited, or form a wave, if their energy lies above a certain value, generally of a few electron volts (eV). In the light of the newly discovered phenomenon, electrons can be collectively excited over a broader range starting at a much lower energy, a few 1/1000 of an eV, and continuing up to many eV. This novel excitation is called Acoustic Surface Plasmon (ASP). This Small Grant for Exploratory Research (SGER) supports a project that will (i) test the generality of this new phenomenon on technologically important surfaces such as copper and silver using sophisticated methods. (ii) It will also test our understanding of the new Physics presented by this phenomenon by inducing controlled surface modifications at the atomic level and measuring their effects on the ASP. The experiments are time-urgent since the results on beryllium have attracted worldwide attention and there is a need to confirm the generality of the original results. The research is expected to have a deep impact on the fundamental understanding of chemical reactions on surfaces, nano-optics, and plasmon resonant microscopy, with potential applications such as the direct integration of optical and electronic devices on a single circuit. The collaborative nature of this project introduces students and post-docs to various international research labs, experimental techniques and theoretical approaches.*****TECHNICAL ABSTRACT****This SGER supports research seeking to provide substantial insight into the new physics governing the recently discovered acoustic surface plasmon (ASP) on Be(0001), a low-energy collective excitation of the electrons bond to a metallic surface. Its intellectual merit lies in the fact that it challenges our basic understanding of collective surface excitations. The first part of the project will attempt a direct observation of the ASP on Cu(111) and Ag(111); thus showing the general character of this new phenomenon. To this effect, electron energy loss spectroscopy measurements will be performed at collaborative facilities that provide the best conditions for these measurements. The second part of the project will look at the influence of surface modifications on the ASP dispersion. According to developing understanding, the ASP exists because of the non-local screening of surface electrons by the underlying bulk electrons. Thus a modification of the surface state dispersion via standard surface science techniques is expected to alter the ASP itself. With this in mind, the ASP dispersion on the two known hydrogen induced reconstructions of the Be(0001) surface will be measured and compared with first-principles calculations. The experiments are time-urgent since the results on beryllium have attracted worldwide attention and there is a need to confirm the generality of the original results. The research is expected to have a deep impact on the fundamental understanding of chemical reactions on surfaces, nano-optics, and plasmon resonant microscopy, with potential applications such as the direct integration of optical and electronic devices on a single circuit. The collaborative nature of this project introduces students and post-docs to various international research labs, experimental techniques and theoretical approaches.