Direct observation of standing wave formation at surface steps using scanning tunneling spectroscopy

Atomic-Scale Dynamics of a Two-Dimensional Gas-Solid Interface

The interface between a two-dimensional (2D) molecular gas and a 2D molecular solid has been imaged with a low-temperature, ultrahigh-vacuum scanning tunneling microscope. The solid consists of benzene molecules strongly bound to step edges on a Cu{111} surface. Benzene molecules on the Cu{111} terraces move freely as a 2D gas at 77 kelvin. Benzene molecules transiently occupy well-defined adsorption sites at the 1D edge of the 2D solid. Diffusion of molecules between these sites and exchange between the two phases at the interface are observed. On raised terraces of the copper surface, the 2D gas is held in a cage of the solid as in a 2D nanometer-scale gas bulb.

Observation of Quantum-Size Effects at Room Temperature on Metal Surfaces With STM

Surface steps act as confining barriers for electrons in metal-surface states. Thus, narrow terraces and small single-atom-high metal islands act as low-dimensional, electron-confining structures. In sufficiently small structures, quantum-size effects are observable even at room temperature. Scanning tunneling spectroscopy is used to image the probability amplitude distributions and discrete spectra of the confined states. Examination of the electronic structure of the steps provides evidence for electron-density smoothing and the formation of step-edge states. Estimates of the electron-confining barriers are obtained.

Confinement of Electrons to Quantum Corrals on a Metal Surface

A method for confining electrons to artificial structures at the nanometer lengthscale is presented. Surface state electrons on a copper(111) surface were confined to closed structures (corrals) defined by barriers built from iron adatoms. The barriers were assembled by individually positioning iron adatoms with the tip of a 4-kelvin scanning tunneling microscope (STM). A circular corral of radius 71.3 A was constructed in this way out of 48 iron adatoms. Tunneling spectroscopy performed inside of the corral revealed a series of discrete resonances, providing evidence for size quantization. STM images show that the corral's interior local density of states is dominated by the eigenstate density expected for an electron trapped in a round two-dimensional box.