Hydrogen on HOPG is an interesting system because it forms a variety of different structures on the substrate: individual, dimers, quasi one dimensional chains or rather more complex structures. The aim of our work is to determine the electronic structure properties of a quasi one dimensional chain as a function of the number of atoms found in particular chains.
In this work we used Scanning Tunneling Microscopy (STM) and STS to investigate individual, dimers and structures of atomic hydrogen deposited on Highly Oriented Pyrolitic Graphite (HOPG) (0001). Hydrogen is ideal for a model system due to the calculation simplicity of the s orbital and it is the smallest atom. The choice of the substrate was important as well, the lattice parameters have to be comparable to the intramolecular distance for having electron wavefunctions overlap and equally important, the local density of states (LDOS) is rather featureless. Atomic hydrogen deposition is done using a RF plasma discharge. Before the measurements each sample is annealed in UHV at 400 K. We performed the measurement in UHV (5X10-11 mbar) and at different temperatures, from 4 K up to room temperature. We succeeded in identifying by STM imaging previously reported hydrogen dimers1, in addition being able to investigate individual hydrogen atoms and slightly more complex hydrogen structures. We will present STS data on individual, dimers and different structures of hydrogen that are found on the substrate and furthermore, we will compare our experimental findings with LDA calculations made for our specific systems. Even more interesting, the STS data was obtained for different temperatures indicating a change in electron interactions, possibly showing a many-body behavior at low temperatures.
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