The effect of covalently bonded aryl layers on the band bending and electron density of SnO₂ surfaces probed by synchrotron X-ray photoelectron spectroscopy

Abstract

A downward to upward surface band bending change can be induced by grafted 4-(trifluoromethyl)phenyl groups on SnO2.

Bidirectional Control of the Band Bending at the (2̅01) and (010) Surfaces of β-Ga2O3 Using Aryldiazonium Ion and Phosphonic Acid Grafting

“…This large emission peak is similar to those previously observed for NP-modified ZnO, Si(111), and indium tin oxide (ITO) and is attributed to the NO 2 group of the NP modifier. It is likely that this emission also contains contributions from (i) unreacted surface OH groups and (ii) the Ga–O–C bonds anchoring the NP groups to the β-Ga 2 O 3 surface, although these cannot be separately resolved from the NO 2 -related emission. , The low-intensity signal at ∼536 eV is due to π–π* transitions within the NO 2 group …”

“…This additional upward shift is Δ V bb = +0.35 and +0.20 eV for the (2̅01) and (010) β-Ga 2 O 3 samples, respectively. This indicates that NO 2 reduction results in additional negative charge transfer from the surface to the aryl modifier, possibly due to electrons or hydrogen from the β-Ga 2 O 3 substrate participating in the reduction . Consequently, the reduction of the grafted NP films yielded (2̅01) and (010) β-Ga 2 O 3 surfaces with the largest upward band bending with V bb = +0.96 and +0.63 eV, respectively.…”

“…To fully exploit the potential of β-Ga 2 O 3 , strategies are required for tuning its surface band bending. One approach that has been successful in other TSOs is the covalent grafting of electron-withdrawing and -donating molecules. − In previous work, we showed that the downward band bending at ZnO(0001̅) surfaces could be removed by the electrochemical grafting of 4-nitrophenyl (NP) layers, while it could be enhanced by the spontaneous grafting of octadecylphosphonic acid (ODPA). , The electrochemical grafting of 4-(trifluoromethyl)­phenyl groups was also found to decrease the downward band bending at SnO 2 (101) surfaces . However, it is not certain that a similar approach will be successful in modifying the unusual upward band bending and electron depletion present at β-Ga 2 O 3 surfaces.…”

Grafting of Diazonium Salts on Surfaces: Application to Biosensors

“…For example, a diazonium salt bearing an Iniferter initiator (a group acting as initiator, transfer, and terminator agent of controlled free radical polymerization) was grafted on isolating silica particles in basic medium to give a silica core@poly(acrylic acid) shell [12]. Trifluoromethylphenyl layers were grafted by immersing SnO 2 plates in an aqueous solution of trifluoromethylbenzenediazonium for 8 h, in the dark [13].…”

Electrografting of Carbon Surfaces with Aliphatic Chains and its Effect on the Rectification of Ferrocene as Redox Probe in Solution

“…This feature of the electrografting processes allows the covalent attachment of thin organic films on electrode surfaces, which are potentially attractive for many applications [7–11] . The characterization of these films has been mainly performed using different spectroscopic [12–14] and microscopic techniques, [15–17] however, when the grafted film bears electrochemically active groups, its chemical identity can be directly inferred from cyclic voltammetry experiments in solutions containing only the solvent and the supporting electrolyte [3,18] . An alternative approach to obtain information about the properties of the grafted films requires the use of redox probes in solution, for example, quinones, [19] ferrocene derivatives, [20] potassium hexacyanoferrate, [21] TEMPO [22] and other compounds that show a well‐defined behavior.…”