Scanning tunneling microscopy of cyclic unsaturated organic molecules on Si(001)

Abstract

Scanning tunneling microscopy and optical spectroscopy techniques have been utilized to investigate the formation of ordered organic monolayer films on the (001) face of silicon. While norbornadiene produces only disordered films, cyclopentene and 1,5-cyclooctadiene both produce monolayer films that are ordered translationally and rotationally. The rotational orientations of the molecules arise from the directional interaction of the π orbitals of the starting alkene with the π orbital of the dimers comprising the reconstructed Si(001) surface, with the Si(001) surface acting as a template for determining the directionality of molecules in the subsequent organic film. Using single-domain Si(001) samples, it is shown that the molecular films also exhibit anisotropy in optical properties when measured on centimeter length scales.Chemisorption of organic molecules on Si(001) surfaces typically involves fragmentation of the molecule. In the specific case of unsaturated organic molecules, however, another mode of bonding is possible. As depicted in Fig. 1, alkenes Fig. 1. Schematic depiction of cycloaddition reaction between Si=Si dimers or Si(001) surface and an unsaturated alkene, cyclopentene * Corresponding author (molecules having one or more double bonds) can bond to the Si(001) surface by breaking the π bonds of the alkene and the Si(001) dimers and forming two new sigma (σ) bonds. This mode of bonding is interesting and unique because it does not involve fragmentation of the organic molecule and therefore provides better control of the atomic-level structure than dissociative reactions would. Previous studies have shown that this mode of bonding is utilized in the bonding of ethylene and acetylene to the Si(001) surface [1][2][3][4][5][6][7][8]. We have recently shown that this mode of bonding can be utilized with larger organic molecules, leading to the formation of ordered organic monolayer films at room temperature [9][10][11][12][13][14].

First‐principles studies of the electronic structure of cyclopentene on Si(001): density functional theory and GW calculations

“…Several recent experimental studies have reported the fabrication and characterization of ordered, self-assembled monolayers of organics on Si(001) [5][6][7]. The homogeneous structure of these monolayer-thin organic films, as well as their ability to form strong covalent bonds with the underlying Si substrate, make them extremely promising for integration with silicon microelectronics technology.…”

Adsorption and thermal treatments of 1-dodecene on Si(100) investigated by STM

“…The mechanism and products of this reaction have been the subjects of a number of experimental [8][9][10][11] and theoretical studies [15][16][17]. After …”

“…Despite the great technological importance of organic-based devices, there has been little work attempting to understand well-defined 1-dodecene films at the nanometre-scale. The surface chemistry of organic molecules on Si(100) has been widely studied for alkenes C n H 2n using scanning tunnelling microscopy (STM) [8][9][10][11][12], but not for the long-chain molecules (C n H 2n , n ≥ 8) [13].…”

QM/QM study of the coverage effects on the adsorption of amino‐cyclopentene at the Si(100) surface

“…32,33 This means that cyclopentene adsorbs roughly on a 0.5ML (half monolayer) surface coverage. It has also been shown previously that the C-adsorbed forms of ACP are very similar to the adsorbed cyclopentene.…”

“…Indeed, STM images already showed that the typical cyclopentene functionalized Si(100) surface is mostly filled with molecules at a distance that is around double the distance seen between the silicon dimers. 32,33 We clearly see that forming the 0.5ML surface seems straightforward and that each molecule adsorbs as if the surface was completely clean. However, over 0.5ML, the situation gets more complicated due to the molecules proximity and the adsorption energies become less favorable.…”