Organic Molecular Films
The degree of miniaturization in microelectronics has been steadily increasing over the past few years. The characteristic size of present-day devices is already on a submicron-scale and a simple extrapolation gives a size of 50 nm by the year 2011. Conse
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Organic Molecular Films
Hirofumi Yamada
The degree of miniaturization in microelectronics has been steadily increasing over the past few years. The characteristic size of present-day devices is already on a submicron-scale and a simple extrapolation gives a size of 50 nm by the year 2011. Consequently, there has been growing interest in singlemolecule electronics, where each individual molecule can be an electronic or optical device as an independent functional unit. One of the remarkable features of organic molecules is that each molecule shows characteristic electrical and/or optical properties which are extremely sensitive to its molecular structure and conformation. This allows us to design a wide variety of functional devices. However, it is essential to have direct access to the single molecule and to be able to measure its properties if we are to establish molecular electronics. Developments in scanning probe microscopy (SPM), including atomic force microscopy (AFM), have brought great advances in molecular technology, since even atoms or molecules can be imaged, manipulated and/or controlled by SPM [1-4]. In addition, local surface properties can be investigated on an atomic or molecular scale. There have been several studies demonstrating the possibility of imaging organic materials on a molecular scale by atomic force microscopy (AFM) in contact mode, especially in a liquid environment [5,6]. However, one often finds that the contact mode scanning process modifies or damages organic samples, most of which are formed by weak van der Waals interactions. It is essential to reduce the forces between the tip and sample for molecular-scale imaging of organic films. Recent progress in dynamic force microscopy (DFM) including non-contact atomic force microscopy (NC-AFM) has demonstrated the possibility of overcoming these difficulties [7]. It has already produced a large number of successful results including atomically resolved images of semiconductor surfaces [8,9], alkali halides [10,11], metals [12,13] and metal oxides [14,15]. Furthermore, NC-AFM imaging of organic molecules has also been successful [16-22]. However, the number of molecular species reported so far has been very limited and there are still some technical issues for the high-resolution imaging of organic molecules. Application of NC-AFM to a wide range of the samples is extremely important not only for the further development of molecular technology, but also for a comprehensive understanding of the contrast mechanisms in NC-AFM.
S. Morita et al. (eds.), Noncontact Atomic Force Microscopy © Springer-Verlag Berlin Heidelberg 2002
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Hirofumi Yamada
This chapter describes applications of NC-AFM to organic molecular films. Imaging of fullerene (C 60 ) thin films on the Si(111)7x7 reconstructed surface and self-assembled mono layers (SAMs) of alkanethiol molecules deposited on Au(111) are discussed first. Since both samples have been intensively studied by STM and are well understood, they are suitable for NC-AFM applications as model samp
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