Characterization of self-assembled alkanethiol monolayers using a low-current scanning tunneling microscope

Abstract

Articles you may be interested inCommunication: Scanning tunneling microscopy study of the reaction of octanethiolate self-assembled monolayers with atomic chlorine Insertion process and electrical conduction of conjugated molecules in n-alkanethiol self-assembled monolayers on Au(111) A low-current scanning tunneling microscope ͑STM͒ was used to image ordered alkanethiol self-assembled monolayers ͑SAMs͒ on Au ͑111͒ surface. The effects of the tunneling current on the STM images of both decanethiol and dodecanethiol SAMs were studied. At low current, with the tip above the sample surface, domain boundaries and ordered alkanethiol molecules can be seen clearly. When the tunneling current was increased, destructive STM images of decanethiol and dodecanethiol SAMs were observed. However, when the tunneling current was reduced back to the original low values, the ordered structures of alkanethiol molecules reappeared. This reversible process suggests that there is no rearrangement in the sulfur head groups under different tunneling current conditions. In this article, we present a model which supports the important role of the alkyl chain in the STM imaging of SAMs. In our model, the medium conductance is a key factor.

Work‐Function Modification of Au and Ag Surfaces upon Deposition of Self‐Assembled Monolayers: Influence of the Choice of the Theoretical Approach and the Thiol Decomposition Scheme

“…The latter were allowed to fully relax together with the topmost two layers of the metal surface during the geometry optimizations performed both with SIESTA and VASP. The unit cell used in this study corresponds to a particular arrangement based on the ${\left( {\sqrt 3 \times \sqrt 3 } \right)}$ R30° symmetry experimentally reported for alkanethiolated SAMs on a gold surface 53–55. However, it should be noted that alkanethiol molecules on silver are preferably adsorbed following a ${\left( {\sqrt 7 \times \sqrt 7 } \right)}$ R10.9° symmetry 54.…”

Tip-enhanced Raman spectroscopic imaging shows segregation within binary self-assembled thiol monolayers at ambient conditions

“…Some research groups have attempted to use conventional scanning probe microscopy (scanning tunneling microscopy, STM, or atomic force microscopy, AFM) to distinguish domains but failed to discern different chemisorbed molecules based on their height [12,15], although friction force AFM did reveal contrast [12]. Characterizing the molecular structure of SAMs is possible with high-resolution STM imaging at ambient conditions [16]; however, even in a pure SAM, many packing patterns could be observed [17], which means that the height measured by SPM can hardly identify the compounds in a mixed SAM. Additionally, the tunneling current in STM reflects not only the tip-sample distance but also the local electronic structure of the surface, which will require further complex data processing to reveal the domains [18].…”

Tunneling Current-Distance Characteristic of Scanning Vibrating Probe / 1-Alkanethiol Self-Assembled Monolayer (SAM) / Au (111) Structure

“…It should be noted that a SAM can be used as tunneling barrier that directly corresponds to R 2 . When a nanoparticle is placed on the alkanethiol SAM, the tunneling resistance R 2 can be controlled by choosing alkyl chain length of alkanethiol SAM [5][6][7][8][9]. It should be noted that if the nanomechanical single electron devices want to be used even at room temperature, operation voltage should be larger than 1V to overcome the thermal fluctuation.…”