Influence of Surface Hydroxylation on 3-Aminopropyltriethoxysilane Growth Mode during Chemical Functionalization of GaN Surfaces: An Angle-Resolved X-ray Photoelectron Spectroscopy Study

Abstract

A comparative study of the chemical functionalization of undoped, n- and p-type GaN layers grown on sapphire substrates by metal-organic chemical vapor deposition was carried out. Both types of samples were chemically functionalized with 3-aminopropyltriethoxysilane (APTES) using a well-established silane-based approach for functionalizing hydroxylated surfaces. The untreated surfaces as well as those modified by hydroxylation and APTES deposition were analyzed using angle-resolved X-ray photoelectron spectroscopy. Strong differences were found between the APTES growth modes on n- and p-GaN surfaces that can be associated with the number of available hydroxyl groups on the GaN surface of each sample. Depending on the density of surface hydroxyl groups, different mechanisms of APTES attachment to the GaN surface take place in such a way that the APTES growth mode changes from a monolayer to a multilayer growth mode when the number of surface hydroxyl groups is decreased. Specifically, a monolayer growth mode with a surface coverage of approximately 78% was found on p-GaN, whereas the formation of a dense film, approximately 3 monolayers thick, was observed on n-GaN.

Optimized monolayer grafting of 3-aminopropyltriethoxysilane onto amorphous, anatase and rutile TiO2

“…After APTES grafting on the surface, two clear N 1s peaks are detected, which can be assigned to the different attachment modes of APTES (desired silane coupling or non-desired reverse (amino) coupling). Several sources [16,39,40] report that hydroxyl groups on the TiO 2 surface can either react with the Si end of APTES to form a silanized surface or with the amine groups. If silane coupling occurs, the free NH 2 termination is observed at 399.4 eV.…”

“…Among different functional groups used on TiO 2 for anchoring (phosphonates, carboxylates, silanes), especially silane coupling, is frequently used to attach molecules with a second terminal functionality -often amine -for further modification. A most typical agent is aminopropyl(triethoxy)silane (APTES) that can be used on titania but also on other oxide semiconductors [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. APTES has for example been used as a coupling agent [17][18][19][20], to link proteins [21][22][23] or to promote cell adhesion [24] on TiO 2 surfaces.…”

“…Most surface analytical studies such as Youngblood find clear evidence of TiAOASi bonds [32][33][34]. Most of the more detailed studies on the kinetics and mechanism for APTES immobilization on surfaces are based on investigations on the silanization of silicon and other semiconductors [14,16,25,32,33]. Vandenberg et al investigated the APTES grafting onto silicon oxide under various conditions to obtain the controllable thickness and morphology of APTES layers during immobilization process [25].…”

UV-stable paper coated with APTES-modified P25 TiO2 nanoparticles

“…Since the contribution of the peak at 399.18 eV is 60.42 % and much higher than that of the peaks at 400.61 eV (24.92 eV) and 401.61 (14.67 eV), APTES appears to be mainly attached by silanized bonding with free terminal NH2 projecting away from the nanoparticle surface, which would be similar to similar to previously reported behaviour. (Pasternack, Amy, & Chabal, 2008;Arranz, Palacio, Garcia-Fresnadillo, Orellana, Navarro, & Munoz, 2008;25 Vandenberg, Bertilsson, Liedberg, Uvdal, Erlandsson, Elwing, & Lundstrom, 1991) The active surface area of the APTES-modified P25 TiO2 nanoparticles as determined using absorption experiments and BET analysis is 47.5 m 2 /g, which is marginally lower (2.5 m 2 /g) than that of the untreated P25 TiO2 nanoparticles (50.0 m 2 /g), due to the coating of APTES on the surface of P25 TiO2 nanoparticle powder. The photocatalytic activity of the P25 TiO2 and APTES modified TiO2 powder was tested by adding samples of the untreated and 5 treated P25 TiO2 nanoparticles to a Rhodamine solution followed by UV-irradiation at 365 nm for 30 min.…”

Biofunctionalization of Si nanowires using a solution based technique

“…The N 1s peak can be de-convoluted into two, NH 3 + (401.5 eV) and NH 2 (399.8 eV), peaks. 11,12 The NH 3 + peak may also represent a hydrogen bonded NH 2 group (NH 2 ---H). 11,12 The terminal amino group on the NW surface may exist in protonated or de-protonated forms (see Figure 2) at the pH utilized in this study and was also observed by XPS in our previous work utilizing the same pH (pH= 7.4).…”