Molecular adlayers

Equation (4.4) stresses that the surface plasma wave propagates within the aluminium substrate whose frequency is modified by the dielectric response of the molecular adlayer. From the measurements reported, with hcog = 8.5 eV and hcob = 15 eV, one obtains e = 2.1 for CuPc, a value in agreement with those measured for other planar organic molecules, with an extended delocalization of 7T-electrons (Alonso et al, 2003). 

For STM investigations, the substrates need to have atomically flat terraces of the size of some hundred molecules. Several ways to deposit molecules on these substrates are briefly discussed here. These methods not only strongly differ in their technical realization, but also in the properties of the resulting molecular adlayers. As will be discussed below, some methods are only suitable for particular classes of molecules. 

Nanoscopies supplemented with conventional techniques will allow the rational handling of the catalyst/reactive system based on its knowledge at the atoniic/molecular level. The application of nanoscopies in surface chemistry offers the possibility for determining the nanostructure of solid surfaces, surface reconstruction phenomena, to identify the structure of ionic and molecular adlayers, to study the dynamics of these adlayers in their adsorption and desorption at the submonolayer and monolayer (ML) level. Likewise, they are important tools to follow reactions at sohd surfaces in real time in different environments. The reader can get acquainted with the state of the art on these topics in Refs [5-12]. 

The macroscopic electrochemical experiments as well as the structural studies with molecular adlayers were performed on single crystal metal electrodes, such as Au hkl), Ag(hkl) and Cu(hkl). To describe our experimen-... 

The adsorption of organic molecules with different functional groups on Cu(lll) in a 0.1 M HCIO4 solution was investigated in situ by cyclic voltammetry. The molecules of CYA and cyanuric chloride (CC) adsorb on the Cu(lll) electrode surface and form well-defined adlayers with (3 x 3) structure in the double-layer potential region. The results were compared with those obtained on aromatic and heterocyclic molecular adlayers <2002PCB11272>. 

Impressive atomic- and molecular-scale details of steady state properties of 2D phase changes in ionic and molecular adlayers, and substrate surfaces have been obtained, mostly based on in situ STM, IR- and SXS-studies. Clear evidence was presented of the effect of crystallographic orientation, the coadsorption of ions of the supporting electrolyte and of the solvent... 

For the preparation of molecular adlayers on solid substrate surfaces, a variety of different methods exists. This is not surprising since several million organic compounds are known with a corresponding wide variety of molecular properties and, hence, not every preparation method will be suitable for every compound. The most common preparation methods can be divided into solution (Figure 3a and b) and gas-phase deposition (Figure 3c and d). Solution... 

Figure 3 Overview of various preparation methods for the adsorption of molecular adlayers on solid surfaces. See text for more information.

An advantage in connection with the investigation of molecular adlayers is the fact that light atoms with de-Broglie wavelengths in the 0.1 nm regime have incident energies whieh are so small that... 

However, it has been demonstrated that the FEM-method is capable of monitoring adsorbate motion or diffusion on a substrate via fluctuations in the electron emission. In fact, the method has become one of the most important tools for measuring the diffusion coefficient of adsorbates on metal surfaces [90GOM]. In one experiment the temporal variation of the emitted electrons has been studied on the picosecond time-scale, thus allowing the observation of the motion of a single adsorbed atom [93HEI]. Recently the method has been extended to study fluctuations in the course of a surface chemical reaction in adsorbed molecular adlayers on a Pt-substrate [99SUC]. 

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