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Über dieses Buch

Michael Lepper presents a detailed room temperature scanning tunneling microscopy study of Nickel-tetraphenyltetrabenzoporphyrin on Cu(111), a prototype system for the fabrication of functional molecular architectures. The peculiar adsorption behavior, in particular the observation of three different coexisting supramolecular arrangements and the identification of two different intramolecular conformations within one arrangement, yield valuable insights into the specific molecular interactions and the self-assembly process in general.



1. Introduction

In modern technology there is an increasing demand for miniaturization of functional building blocks. Therefore engineering of systems on a molecular level by ‘bottom up’ approaches is desirable in contrast to classical ‘top down’ approaches like UV-lithography in semiconductor industry. One promising way to realize the fabrication of functional structures from molecules is through self-assembly on well-defined surfaces. In order to control the arrangement of the corresponding molecular building blocks on the surface it is essential to characterize and understand the adsorbate- adsorbate as well as the adsorbate-substrate interactions which determine the assembly processes. In this regard scanning tunneling microscopy (STM) has proven to be a very suitable method to determine the adsorption behavior of large organic molecules on solid surfaces and partially also their intramolecular conformation.
Michael Lepper

2. Fundamentals

In the first part of the chapter fundamental theoretical and technical fundamentals of the used analytical instruments will be described.
In the second part of this chapter the substrate and the investigated organic molecules are introduced.
Michael Lepper

3. Experimental

All experiments in the thesis at hand were performed in a two chamber UHV system with a base pressure in the low 10-10 mbar regime. The system is divided in two main chambers: the STM chamber and the preparation chamber. Within the STM chamber the scanning tunneling microscope (RHK UHV VT RTM 300) is housed for the actual measurements. In the other chamber various sample preparation, characterization and manipulation tools are situated. The two chambers are linked by a VAT gate valve (CF150) which is usually only opened for transferring the sample. The sample transfer between the chambers is realized by a linear transfer rod and wobble sticks. Furthermore a fast entry lock is attached to the STM chamber enabling a quick sample exchange.
Michael Lepper

4. Adsorption behavior of Ni-TPBP on Cu(111)

In order to design self-assembled supramolecular architectures with specific functional properties it is important to understand the adsorption behavior of molecular building blocks on well-defined substrates. One very versatile class of adsorbates in this regard are porphyrins which offer not only a rigid molecular framework but also ligand functionality to bind metals.
Michael Lepper

5. Conclusion and Outlook

In the following the adsorption behavior of Ni-TPBP on Cu(111) investigated with STM under UHV at RT will be summarized briefly.
Starting with low coverage individual stationary molecules are only found arranged in chains agglomerated at the step edges of the surface. While on the terraces Ni-TPBP molecules are probably freely diffusing on the surface and cannot be imaged as individual entities.
Michael Lepper


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