Diamond oxygen-terminated

Reproducible electrochemical analysis of phenolic compounds by high-pressure liquid chromatography with oxygen-terminated diamond sensor... 

ELECTROCHEMICAL PROPERTIES OF OXYGEN-TERMINATED DIAMOND ELECTRODES... 

Diamond surfaces after anodic oxidation treatment involve oxygen-containing surface functional groups. The electron-transfer kinetics for ions and polar molecules are expected to be quite different. Fe(CN)l /4 was highly sensitive to the surface termination of diamond. For an anionic reactant, there was an inhibition of the electron transfer for the oxygen-terminated diamond electrodes compared with the hydrogen-terminated diamond electrodes, and there was also an acceleration of the electron transfer for oxygen-terminated diamond for some cationic reactants such as Ru(NH3) +/3+ and Fe2+/3+. These results can be explained by electrostatic effects, which interact between the ionic... 

Figure D.l. Possible reconstructed structures of diamond (100) surface, (a) unrelaxed surface with the dangling bonds being terminated by H atoms, (b) hydrogen-terminated 2 X 1 structure, (c) oxygen-terminated 2 x 1 structure, (d) single oxygen-terminated 2 x 1 structure, and (e) rt-bonded 2 x 1 structure [139],...

In practice, these solid-vacuum interfacial energies are not likely to be seen, since the diamond surface and the graphite prism-face surfaces will reconstruct or react with adatoms such as hydrogen and oxygen to reduce their surface energy. Under atmospheric conditions, diamond is terminated by a range of hydride and oxide... 

Kloss FR, Gassner R, Preiner J, Ebner A, Larsson K, Hachl O, et al. The role of oxygen termination of nanocrystaUine diamond on immobUisation of BMP-2 and subseqnent bone formation. Biomaterials 2008 29 2433-42. 

Polycrystalline boron-doped diamond (pBDD) is inherently heterogeneous due to variations in dopant density across different facets. Figure 19.5a shows an example of an SECCM reactivity map of oxygen-terminated pBDD for a complex multistage reaction, the oxidation of the neurotransmitter serotonin (5-hydroxytryptamine) in aqueous solution. The advantage of a confined electrochemical... 

Concerning oxygen termination, neither experimental nor theoretical data for the diamond (110) surface are available to date. 

When considering surface states in the band gap one should distinguish occupied (donorlike) and unoccupied (acceptorlike) states. Those of the latter type were not directly accessible experimentally so far, but in fact found in band structure calculations of all the surfaces discussed above. Quahtative confirmation of their existence within the band gap was for the (100) and the (111) surfaces obtained from NEXAFS in form of clear surface core exciton resonances. The unoccupied surface states are not electronically active for p-type material, but are expected to become important for n-type diamond. Occupied surface states in the band gap are found only for the clean diamond (111) surface, but can be removed by hydrogen or oxygen termination. All diamond surfaces are semiconducting. In the case of the clean C(lll)2xl and C(110)lxl surfaces, which show symmetric and unbuckled 7T-bonded rows of surface atoms, many-body effects are responsible for the opening of a surface band gap, which caimot be modeled theoretically on the DFT level. Table 10.2 summarizes the reconstructions and surface state distributions of the diamond surfaces discussed above. 

By use of Auger electron spectroscopy, the amount of oxygen on the diamond surface was found to have increased after the modification [51]. This indicates that the diamond surface scanned with high positive bias voltage has been oxidized, i.e., has become oxygen-terminated. Furthermore, the AFM modification method requires moderate atmospheric humidity (e.g. 55%), and thus the modification should be due to a surface anodic reaction involving water condensing on the AFM tip as an electrolyte. The idea that condensed water exists between an AFM tip and a sample under ambient humidity conditions is well accepted. 

This type of treatment can convert the hydrogen termination to oxygen termination. An additional benefit is that possible nondiamond carbon impurities, as well as metallic impurities, can be removed from the surface in this way. The chemical oxidation of diamond is closely related to electrochemical oxidation, discussed later, and which is also discussed in Chapters 8 and 10. 

In many cases, chemical oxidation has been used as a standard preparation technique for certain types of experimental measurements, particularly those that involve semiconducting properties, because it removes hydrogen from the surfe.ce and/or subsurface, which can impart metallic conductivity [13]. There have been several reports in which the electronic properties of hydrogen-terminated vs. oxygen-terminated diamond have been compared [l, 3]. 

As a separate topic, we now discuss metals and metal oxides deposited on diamond surfaces. The topic of metals on diamond has been studied for a number of years from the standpoint of semiconductor devices [3, 88 105]. Many of these papers discuss the effect of hydrogen vs. oxygen termination and the resulting surface dipoles. As mentioned above, this work has received attention over the years due to the great interest in electron emission. 

Fig. 10.7. Termination structure of oxygen-terminated diamond for the (100) and (ill) faces.

---