Anodic oxides luminescence

To understand the electrochemical behavior of silicon, however, the formation and the properties of anodic oxides are important The formation of an anodic oxide on silicon electrodes in HF and HF-free electrolytes will therefore be discussed in detail in this chapter. The formation of native and chemical oxides is closely related to the electrochemical formation process and will be reviewed briefly. The anodic oxidation of porous silicon layers is closely related to the morphology and the luminescent properties of this material and is therefore discussed in Section 7.6. 

In this section the properties of chemically and thermally oxidized and nitridized PS will be discussed. Wet anodic oxidation of PS is commonly accompanied by luminescence and is therefore discussed in Section 7.4. 

Partially functionalized cyclopolysilanes recently attracted attention as model substances for siloxene and luminescent silicon. The yellow luminescent silicon is formed by the anodic oxidation of elemental silicon in HF-containing solutions and may be used for the development of silicon-based materials for light-emitting structures which could be integrated into optoelectronic devices77. Because the visible photoluminescence of... 

Silicon oxide nanostruaures are prepared by local anodic oxidation on dodecyl-terminated silicon. Cationic dye molecules (Rhodamin 6G) bound electrostatically to the generated nanostructures are investigated by optical methods. Quenching of luminescence due to the interaction of the excited states with silicon can be found. The luminescence signal is attributed to monomeric Rh6G molecules with a slight blue shift of the emission due to the changed chemical environment... 

The attachment of a redox center to a calkarene-substituted PPy has been achieved by the anodic oxidation of pyrrole-substituted trisbipyridylruthenium(II)-Iinked calixarenes [307]. However, only thin films with a low amount of immobilized [Ru(bpy)3] (bpy = 2,2 -bipyridine) were obtained by homopolymerization. Thicker films could be grown from copolymerization with iV-methylpyrrole. Even if the sensory properties of these polymers have not been investigated yet, it can be predicted that the electrochemical and/or luminescent responses of the ruthenium complex could be changed upon the complexation of a guest cation by the immobilized host calixarene. It must be pointed out that such a recognition event had been already observed with a polypyrrole film N-substituted by an aza crown ether-linked bipyridine ruthenimn (II) complex [271]. 

An IR study of electro-oxidized PS showed a decrease in the OH signal and an increase in the SiO signal with anodization time. This can be interpreted as oxide formation on the PS surface and a removal of electrolyte from the pores. Furthermore a correlation in intensity of localized carrier IR absorption and luminescence indicates that localized states are involved in the red EL [Du4]. 

The first observation of luminescence associated with a charge recombination process came in the early part of the 20th century in experiments involving oxidative electrolysis of aqueous halide solution at mercury anodes [1]. The report describes the observation of colored flames from the mercury pool surface following formation of a coating of mercury halide on the electrode surface during electrolysis and the authors relate this to flame emission of mercury halides. 

Electroluminescence is observed to occur during anodization on both n- and p-type materials. The luminescence onp type is uniform on the sample surface, whereas that on n type is highly nonuniform.It occurs only when the oxide reaches a certain thickness as shown in Fig. 3.14. ° No light emission is observed below a thickness of 15 nm. For Si02 greater than 25 nm thick, the intensity of emitted light increases exponentially, the exponential factor being lOnm as shown in Fig. 3.14. 

Another interesting phenomenon is producing luminescence from electrochemical reactions. This can be achieved by doping crystalline metal oxides and related materials or anodic metal oxide layers (Meulenkamo et al., 1993) or depositing organic molecules onto nanostructured porous materials such silicon (Martin et al., 2006). 

Meulenkamo, E.A., Nelly, J.J., and Blasse, G. 1993. Electrochemically induced characteristic luminescence of metal ions at anodic valve metal oxides. Journal of the Electrochemical Society 140, 84-91. 

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