AVS 56th International Symposium & Exhibition
    Applied Surface Science Tuesday Sessions
       Session AS-TuP

Paper AS-TuP15
Kelvin Probe Force Microscopy on Phase-Separated Self-Assembled Monolayers of Alkanethiol and Amide-Containing Alkanethiol

Tuesday, November 10, 2009, 6:00 pm, Room Hall 3

Session: Applied Surface Science Poster Session
Presenter: S. Ikebukuro, Kyoto University, Japan
Correspondent: Click to Email
Frequency modulation atomic force microscopy (FM-AFM) is a very powerful tool for investigating various materials including organic samples. Since the chemical interaction and the van der Waals interaction between the tip and the sample are the main origin of the FM-AFM contrast, it can be applied for chemical identification of surface functional groups as well as structural analysis of organic ultrathin films[1, 2]. However, the decay-length of those interaction is less than 1 nm, the FM-AFM contrast only provides the chemical information of the sample surface and the subsurface information is difficult to be obtained. On the other hand, Kelvin probe force microscopy (KFM) is a method to investigate surface potential (SP) distribution on the nanometer scale. Since the electrostatic force, which is the origin of KFM contrast, is a long-range interaction, it is expected that we can obtain the subsurface information and discriminate two separated areas that have same surface profile while subsurface structures differ from each other using KFM.

In this study, to evaluate transitions of SP caused by the difference of subsurface structures, we investigated a phase-separated self-assembled monolayer (SAM) formed from a binary mixture of nearly isometric adsorbates, n-alkanethiol (n-dodecanethiol : DDT) and amide-containing alkanethiol (3-mercapto-N-octylpropionamide : 1ATC8), on a Au(111) substrate using FM-AFM/KFM. The SAMs were prepared by the coadsorption from an equimolar solution of DDT and 1ATC8 (1 μM in total thiol) and two separated regions were discriminated in the FM-AFM/KFM images. The same experiments were also performed on a DT/1ATC8 phase separated SAMs. We compared these results and concluded that the SP of the 1ATC8 areas was lower by 240 mV compared to the DDT areas. Considering the differences of molecular properties between DDT and 1ATC8, these SP images present reasonable contrast and suggest that the difference of the subsurface structures was detected using FM-AFM/KFM.

References

[1] T. Ichii et al., Jpn. J. Appl. Phys. 43, 4545 (2004)

[2] T. Ichii et al., Jpn. J. Appl. Phys. 44, 5378 (2005)