AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP22
Adsorption of Hydrogen on CNT Surfaces and Surface Chemistry on HOPG

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: J. Nakamura, University of Tsukuba, Japan
Authors: J. Nakamura, University of Tsukuba, Japan
E. Yoo, University of Tsukuba, Japan
M. Ishihara, University of Tsukuba, Japan
T. Habe, University of Tsukuba, Japan
N. Yagai, University of Tsukuba, Japan
E. Matsuyama, University of Tsukuba, Japan
T. Matsumoto, University of Tsukuba, Japan
Correspondent: Click to Email
Hydrogen storage by carbon nanotubes, graphite and the other carbon materials have been studied from the viewpoints of chemisorption of hydrogen at atmospheric pressure. We find that deposited Pd nanopraticles and formation of defects produced by oxidation increased the chemisorption of H atoms (2 - 4 wt%) on CNT surfaces. IR spectra showed peaks assigned to CH@sub 2@ . Desorption of hydrogen was observed around 700 K. In order to study the site of hydrogen on carbon surfaces with scanning tunneling microscopy (STM), we used highly oriented pyrolytic graphite (HOPG) surfaces as a model surface. The hydrogen adsorption is not observed on a clean HOPG surface by STM after dosing H2 or atomic H at 300 K. Temperature programmed desorption (TPD) experiment gives no desorption peak and small desorption peak of H@sub 2@ (m/e=2) at ~570 K assignable to H atoms adsorbed at step edges. Defects are produced on HOPG by Ar ion sputtering and annealing at 1173 K. Bright hillocks are observed by STM, and are assigned to pits in graphene sheets due to high local density of states of sp3-like dangling bonds produced by removing adjacent carbon atoms. After dosing atomic H on the defective HOPG at 300 K, the STM topographs show dark lines on the bright hillocks. The average height of the hillock also decreases from 0.71 nm to 0.32 nm. The average height of the hillocks is recovered to 0.69 nm by heating the sample to 873 K where H desorbed fully from the HOPG surface on a TPD spectrum. These results indicate that the atomic H adsorbed on the defect sites at 300 K, and the local density of states was lowered around the pits.