Modification of silicon surface with redox molecules derived from ferrocene

Abstract

Este estudo apresenta um método novo para ligar moléculas redox ativas derivadas de ferroceno à superfície de silicone monocristalino. O procedimento consiste na reação de silicone hidrogenado com brometo de alila ativado com luz branca e sua reação subseqüente com monolítio ferroceno para criar uma união covalente entre a molécula redox e a superficie do semicondutor. As camadas formadas são eletroquimicamente ativas e apresentam um processo electroquímico quasi-reversível, atribuído às moléculas de ferroceno ligadas à superfície de silicone. A análise por espectroscopia fotoeletrônica de raios-X (XPS) confirma a presença de moléculas de ferroceno na superficie de silicone.This study presents a new method to bind active redox molecules derived of ferrocene to the surface of single crystal silicon. The procedure consists in the reaction of hydrogenated silicon with allyl bromide activated with white light and its subsequent reaction with monolithio ferrocene in order to create a covalent union between the redox molecule and the semiconductor surface. The layers formed are electrochemically active and present a quasireversible electrochemical process which is attributed to the ferrocene molecules which are bound to the silicon surface. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of ferrocene molecules on the silicon surface.Keyword: silicon, ferrocene, surface modification, characterization IntroductionAlthough molecular electronics appears as a new alternative in the development of nanometric electronic devices, 1 the production of transistors and other electronic devices is still dominated by silicon technology. Contributions to the transition between both technologies centered in the development of hybrid semiconductormolecule materials are therefore of paramount importance. 2In this field, there are several studies referring to the preparation and redox property studies of self-assembled monolayers (SAMs) on silicon surfaces. The formation of SAMs on oxidized silicon surfaces has been well documented.3-5 However, the Si-O bond is in general unfavorable for electronic applications because of a generally poor molecule-electrode electron transfer. Much better results are obtained in absence of the oxide layer through a direct Si-C union linkage. 6The formation of the Si-C bond has been usually performed by ultra high vacuum (UHV) techniques, 7-9 or by radicalary processes.3,9 The latter have been studied more thoroughly due to the relatively low operation cost. The general mechanism of these reactions involves the double bond addition to the Si-H surface, 9 where double bond homolytic cleavage is achieved by reaction with peroxides, 10 by UV irradiation, 11 by thermal activation, 12 by electrochemical processes, 13,14 or more recently, by white light irradiation. [15][16][17][18] The union of electroactive molecules on the silicon surface opens a new route for the making of hybrid devices, in which the properties of current silicon technology are combined with those of the molecules own...

Ferrocene Molecular Architectures Grafted on Si(111): A Theoretical Calculation of the Standard Oxidation Potentials and Electron Transfer Rate Constant

“…Comparison with the experimental results of similar molecular architectures shows an encouraging agreement concerning the Si M –Me –FC system (experimentally, values are found in the 4 to 160 range [ 34 , 35 , 36 , 39 ]). On the contrary, for the Si M –UA –FC system, large differences are evident ( experimental values are found in the 30 to 50 range [ 38 , 39 ]), suggesting that some physics underlying the ET process is missing in the Marcus model. Indeed, the experimental results indicate a much faster charge transfer process than expected on the basis of the results calculated using the Marcus theory.…”

“…Remarkably, a semi-quantitative agreement between the experimental and theoretical values is found for the “short spacer” Si M –Me–FC system: our value is comparable to experimental results obtained for quite similar molecular interfacial architectures: Dalchiele and Roth reported and values, respectively [ 19 , 34 ]. An unsatisfactory agreement is instead found with the values reported by Riveros and Decker, and values, respectively [ 35 , 39 ]. In the case of the Si M –UA–FC long spacer, the difference between theoretical and experimental values is striking.…”

“…CDFT calculations allow us to evaluate the energy and electronic structure of molecular systems featuring a discrete net charge localization on suitably selected moieties [ 32 , 33 ]. Theoretical calculations are then discussed in the view of the available experimental results [ 10 , 12 , 19 , 34 , 35 , 36 , 37 , 38 , 39 ]. It is important to note that the theoretical calculation of ET rate constants are rarely reported in the literature [ 40 , 41 ].…”

Electron Transfer Rates of Alkyl-Ferrocene Molecules Forming Incomplete Monolayer on Silicon Electrodes

“…In this case, following a reaction sequence on the silicon surface, the latter is modified with an alkyl chain which is latter functionalized with a ferrocene molecule. In the same manner, we have achieved a new route which will enable to modify the silicon surface with ferrocene molecules 28 . The procedure includes a hydrosilylation reaction (activated by white light) between an alkenyl halide and the hydride-terminated silicon surface, and the following reaction of this modified surface with monolithio-ferrocene (figure 1).…”

“…Thus, this new, simple, and versatile synthesis method for the silicon modification with different ferrocene molecules can help to carry out new investigation in this field. However, the main problem of this procedure is that incomplete monolayers are obtained, showing that this method must be improved in some aspect, like quality of dry-box and source of light 28 .…”