For the first time, a team of physicists has recently demonstrated that the electron cloud distribution of a silicon crystal surface can be smoother than the spatial distribution of the atoms.
At the atomic scale, the most polished surfaces are not flat. However, the study of some metals show that their surfaces have atoms located at irregular heights while they appears very flat when one observe the irregularities of the electronic clouds associated to the atoms. These irregularities, called electronic corrugation, rule several important physical properties such as the surface reactivity or the interaction with electromagnetic waves. By measuring the electronic corrugation of the silicon surface sample, physicist from the Institut des Sciences Moléculaires d’Orsay – ISMO (CNRS/ Univ. Paris Sud) and from the department of chemistry at Jackson State University (Jackson USA) have demonstrated for the first time that a semiconductor can show electronic corrugation being much lower than the corrugation of the atoms. In these conditions, the electronic properties of the surface arise from a mix between the electronic properties of the bulk and the surface. The researchers could confirm their results by using the density functional theory. This work has been published in the Journal of Physics :Condensed matter.
For this work, researchers have measured the electronic corrugation of the (100) surface of a silicon sample with a scanning tunneling microscope (STM). After checking carefully that the tip of the STM don’t modify the structure of the surface they could do their measurement at low temperature (9K) to fix the atomic position of the silicon surface. In such conditions, the silicon atoms bonds in dimer to form rows that are separated by deeper grooves made of a single line of silicon located two layers of silicon deeper than the surface. By tuning the bias applied between the STM tip and the surface, the physicists could picture the 2D structure of the electronic cloud and show that they correspond to various electronic states. In particular, they could observe that within two thin energy windows, the electronic cloud spread on top of the valley to show a very flat electronic surface. These results have been confirmed by means of state of the art numerical STM image simulations which originality resides in the use of hybrids functional. These allow a better accuracy in the estimation of the unoccupied states energies, the ones that are observed for their experimental findings. These results have been correlated with optical properties of the semiconductor for which some singularities in the density of state distribution are involved.
Atomic scale study of corrugating and anticorrugating states on the bare Si(100) surface
M. Yengui1, H. P. Pinto2, J. Leszczynski2 and D. Riedel1 Journal of Physics : Condensed Matter (2015)
Damien Riedel, chargé de recherche CNRS