Cathodic Electrografting of Versatile Ligands on Si(100) as a Low‐Impact Approach for Establishing a SiC Bond: A Surface‐Coordination Study of Substituted 2,2′‐Bipyridines with Cu^I Ions

Abstract

Three distinct wet chemistry recipes were applied to hydrogen-terminated n- and p-Si(100) surfaces in a comparative study of the covalent grafting of two differently substituted 2,2'-bipyridines. The applied reactions require the use of heat, or visible light under a controlled atmosphere, or a suitable potential in an electrochemical cell. In this last case, hydrogen-terminated silicon is the working electrode in a cathodic electrografting (CEG) reaction, in which it is kept under reduction conditions. The resulting Si--C bound hybrids were characterized by a combination of AFM, dynamic contact-angle, and XPS analysis, with the help of theoretical calculations. The three distinct approaches were found to be suitable for obtaining ligand-functionalized Si surfaces. CEG resulted in the most satisfactory anchoring procedure, because of its better correlation between high coverage and preservation of the Si surface from both oxidation and contamination. The corresponding Si-bipyridine hybrid was reacted in a solution of CH3CN containing CuI ions coordinatively bound to the anchored ligands, as evidenced from the XPS binding-energy shift of the N atom donor functions. The reaction gave a 1:2 Cu-bipyridine surface complex, in which two ligands couple to a single CuI ion. The surface complex was characterized by the Cu Auger parameter and Cu/N XPS atomic-ratio values coincident with those for pure, unsupported CuI complex with the same 2,2'-bipyridine. Further support for such a specific metal-ligand interaction at the functionalized Si surface came from the distinct values of Cu2p binding energy and the Cu Auger parameter, which were obtained for the species resulting from CuI ion uptake on hydrogen-terminated Si(100).

Electrografting: a powerful method for surface modification

“…Furthermore, 5-bromomethyl-2,2 0 -bipyridine has been electrografted and photografted on SiH. 711 Precious (Au) and industrial metals (Fe, Cu, TiN (a barrier to the diffusion of Cu into Si in microelectronics)) as well as glassy carbon have also been electrografted (by chronoamperometry at the foot of the voltammetric reduction wave to prevent, as much as possible, the reduction of the radical to anion) by IC 6 H 13 (for example À2.3 V /SCE for 30 min in 0.1 M solution) and I-(CH 2 ) 2 -C 8 F 17 . 712 The modified surfaces were characterized by: (i) water contact angle-the layers are hydrophobic, as could be expected, (ii) by ellipsometry-the thickness varies from 6 to 10 nm indicating the formation of multilayers, (iii) by IR-the characteristic signals of the chains are observed and the chains appear to be disordered, (iv) the electrografting of ICH 2 CH 2 C 8 F 17 on highly resistive TiN was demonstrated by the presence of a F1s peak at 689 eV corresponding to the CF 2 groups, (v) ToF-SIMS, which indicates the presence of chain fragments, but also of fragments such as Cu(CH 2 ) 4 , that testify to the attachment of the chains to the copper surface.…”

Selective Assembling of Calixarenes and Pseudorotaxanes on Si(100) and Polycrystalline Copper

“…We first report on the behavior of calix [6]arene-SH (1) and NO 2 -calix [6]arene-C C (2) on polycrystalline Cu and Si(100), respectively. Each compound possesses three anchoring arms, each with functional groups suitable for chemisorption on the respective surface: a thiol (-SH) or C C termination, respectively for Cu or Si(100) (Scheme 1).…”

Assembly of Gold Nanoparticles on Functionalized Si(100) Surfaces through Pseudorotaxane Formation

“…The method adopted for the surface anchoring requires visible‐light activation (see the Supporting Information) 10. 11, 22–24 This extra‐mild approach preserves the integrity of the molecular species and effectively limits the surface oxidation of the silicon substrate.…”

“…6 Several reports on organic monolayers formed through a covalent SiC bond have been published so far by several research groups,7–9 including ours 10. 11…”