Greffage de molécules à la surface du silicium par voie électrochimique

Abstract

La surface hydrogenee du silicium possede des proprietes remarquables, mais une stabilite a I'oxydation insuffisante. Pour y remedier, plusieurs groupes organiques ont ete substitues a I'hydrogene de surface. Ces greffages peuvent se fairc chimiquement en plusieurs etapes, mais la voie electrochimique permet des reactions directes a partir de la surface hydrogenee. On peut ainsi methoxyler partiellement la surface du silicium poreux par dissolution anodique controlec, mais surtout methyler sa surface de maniere non destructive, avec un rendement de 80% limite seulement par I'encombrernent sterique. La surface methylee du silicium poreux possede une stabilite accrue d'un ordre de grandeur.The hydrogentated surface of silicon exhibits remarkable properties, but poor resistance to oxidation. To improve its stability, surface hydrogen has been replaced by several organic groups. Such grafting can be carried out chemically by a multi-step reaction scheme. However, an electrochemical approach allows direct reaction with the hydrogenated surface. The porous-silicon surface has been partially methoxylated by a controlled anodic dissolution. If has also been methylated using a non-destructive anodic process, with a yield of 80%, limited only by steric hindrance. The methylated surface of porous silicon exhibits a stability against oxidation increased by an order of magnitude.Mots cles: silicium, silicium poreux, greffage, greffage electrochimique, chimie de surface.1 y a plus de 20 ans, Harrick et Beckmann (1974) ont I demontre que l'on pouvait, par simple rinqage dans I'acide fluorhydrique, preparer des surfaces de silicium vierges d'oxydes et passivees par une monocouche de liaisons Si-H. Cette monocouche de liaisons Si-H est relativement stable a l'echelle de quelques heures. Elle confere a la surface des proprietes electroniques remarquables, en particulier une vitesse de recombinaison de surface extr2me-ment faible (Yablonovitch et al., 1986).Le silicium peut 6tre rendu poreux par dissolution anodique dans l'acide fluorhydrique. Lorsque la porosite du materiau est suffisamment elevee, le silicium poreux acquiert des proprietes optiques etonnantes. En particulier, il devient luminescent a temperature ambiante, avec un rendement eleve (Canham, 1990). Le matkriau possede une surface specifique tres importante cjusqu'a 1000 m2/cm3), sa porosite est ajustable, en fonction des conditions d'electrolyse, entre 30 et 90%, et l'epaisseur des couches poreuses peut atteindre plusieurs centaines de microns (Bomchil et al., 1989). Toutes ces proprietes font du silicium poreux un materiau attractif pour differents types d'application.Au niveau moleculaire, apres fabrication, la surface du silicium poreux est couverte de liaisons Si-H, ce qui n'est pas surprenant puisque le materiau a ete obtenu par un traitement dans l'acide fluorhydrique. La passivation de la surface associee a ce recouvrement par l'hydrogene est cmciale pour les proprietes de luminescence. En effet, si on introduit quelques defauts de surface, ceux-ci se comporte...

Lewis Acid Mediated Hydrosilylation on Porous Silicon Surfaces

“…The nanoscale architecture of porous silicon is inherently fragile, and thus rapid and efficient syntheses under room-temperature conditions are preferable. Previous approaches taken toward Si−C bond formation on porous silicon include reactions with methyl Grignard under electrochemical conditions, alkyl and aryllithium and Grignard reagents in the absence of electronic bias, and thermal hydrosilylation of alkynes and alkenes . We have found that hydrosilylation of unsaturated carbon−carbon bonds on the native hydride-terminated porous silicon can be induced by the Lewis acid EtAlCl 2 or white light illumination (on photoluminescent samples) at room temperature in a matter of minutes or hours, depending upon the organic fragment, as outlined in Scheme .…”

Chemical routes to fine tuning the redox potential of monolayers covalently attached on H–Si(100)

“…Chazalviel and co-workers [27][28][29] were the first to propose the use of Grignard salts on both porous and flat silicon, under electrochemical conditions [30]. Bansal et al [31] showed that it is possible to chlorinate the H-Si(1 1 1) surface in a benzene solution of PCl 5 , which in principle allows to further react the obtained chlorinated surface with organic Grignard reagents.…”

Controlled Functionalization and Multistep Chemical Manipulation of Covalently Modified Si(111) Surfaces1

“…11,12 Similar reactions have been reported for modification of porous silicon. [13][14][15][16][17] In addition, covalently modified surfaces also may be prepared from the reaction of alkyl Grignard or alkyllithium reagents with the halogenated Si(111) surface. [18][19][20][21] In many of these examples the reactions lead to organic films that are terminated with a methyl group.…”

“…While this is useful for passivation and chemical stabilization, the low reactivity of the terminal methyl group makes further manipulation of the surface physical or chemical properties difficult. Other workers have demonstrated the possibility of creating a functionalized organic film on a single crystal 4,[11][12][13][14]22 surface, but only in a few cases have the sequential reactions of the organic film been investigated. 2,3,6 To incorporate more complex organic or bioorganic structures at the interface new strategies to increase the chemical functionality of the surface must be devised.…”