Simplified Approach to Work Function Modulation in Polyelectrolyte Multilayers

Abstract

The layer-by-layer (LbL) method is based on sequential deposition of polycations and polyanions. Many of the properties of polyelectrolyte thin films deposited via this method depend on the nature of the topmost layer. Thus, these properties show odd-even oscillations during multilayer growth as the topmost layer alternates from polycations to polyanions. The work function of a (semi)conductive substrate modified with an LbL polyelectrolyte multilayer also displays an oscillatory behavior independent of film thickness. The topmost layer modulates the work function of a substrate buried well below the film. In agreement with previous observations, in this work, we show that the work function of a gold substrate changes periodically with the number of adsorbed layers, as different combinations of polycations and polyanions are deposited using the LbL method. For the first time, we rationalize this behavior in terms of formation of a dipole layer between the excess charge at the topmost layer and the charge of the metal substrate, and we put forward a semiquantitative model based on a continuum description of the electrostatics of the system that reproduces the experimental observations.

Interface Engineering of Hematite with Nacre-like Catalytic Multilayers for Solar Water Oxidation

“…After the deposition of the base layer, interestingly, the shift of onset potential was comparable to that of the flat band potential (∼200 mV), while the charge injection efficiency was considerably improved (Figure c inset), supporting our hypothesis that the local dipole moment formed by the deposition of a polymeric base layer improved the charge separation and injection efficiency. Our finding is consistent with recent reports on the fabrication of a low work-function electrode by the deposition of polyelectrolytes. − Further study is currently underway to disclose its underling mechanism more clearly. This study is noteworthy in that GO, Co-POM, and polymeric base layers are rationally assembled on hematite considering the energy level of each material and effective charge transfer.…”

Modulating Charge Separation Efficiency of Water Oxidation Photoanodes with Polyelectrolyte‐Assembled Interfacial Dipole Layers

“…The structure and properties of the LbL‐assembled polyelectrolyte multilayers can be explained by the three Zone model: Zone I is denoted as the first polyelectrolyte layer interfacing with the underlying substrate, Zone II as an intermediate charge‐compensation region with free mobile ions, and Zone III as the outermost layer. An important feature of the polyelectrolyte multilayers is that their overall thickness and the type of polyelectrolytes in Zone III could be controlled precisely, thereby enabling precise manipulation of the direction and magnitude of the interfacial dipole moment.…”

Electronic Structure of a Self-Assembled Monolayer with Two Surface Anchors: 6-Mercaptopurine on Au(111)

“…Thus, 6MP molecules form a dipole layer with negative charges at the SAM/metal interface and positive at the vacuum/SAM interface. 36,37 We…”

“…Thus, 6MP molecules form a dipole layer with negative charges at the SAM/metal interface and positive charges at the vacuum/SAM interface. 36,37 We estimated a component of the molecular dipole perpendicular to the surface 38 equal to 1.05 D from the work function change, using a surface density of 3.47 nm −2 and a relative dielectric constant of the SAM equal to 1.5. 39 When the 6MP monolayer is present on the Au(111) surface, the Au 5d and 6s bands decrease in intensity as the adsorbate attenuates the photoelectrons.…”

“…The secondary electron cutoff shift observed in Figure a implies that formation of the 6MP SAM decreases the work function of Au(111) by −0.9 eV in agreement with the DFT calculations discussed below. Thus, 6MP molecules form a dipole layer with negative charges at the SAM/metal interface and positive charges at the vacuum/SAM interface. , We estimated a component of the molecular dipole perpendicular to the surface equal to 1.05 D from the work function change, using a surface density of 3.47 nm –2 and a relative dielectric constant of the SAM equal to 1.5 …”