Work Function Control of Germanium through Carborane-Carboxylic Acid Surface Passivation

Abstract

Self-assembled monolayers (SAMs) of carborane isomers with different dipole moments passivate germanium to modulate surface work function while maintaining chemical environment and surface energy. To identify head groups capable of monolayer formation on germanium surfaces, we studied thiol-, hydroxyl-, and carboxyl-terminated carboranes. These films were successfully formed with carboxylic acid head groups instead of the archetypal thiol, suggesting that the carborane cluster significantly affects headgroup reactivity. Film characterization included X-ray and ultraviolet photoelectron spectroscopies as well as contact angle goniometry. Using these carboranes, the germanium surface work function was tailored over 0.4 eV without significant changes to wetting properties.

Computational Approaches to Photoelectrode Design through Molecular Functionalization for Enhanced Photoelectrochemical Water Splitting

“…If one is interested in only relative band‐edge positions or surface dipoles (relative to a reference surface such as hydrogen‐terminated Si(111)), DFT/PBE simulations can be used instead of MBPT. Since relative surface dipoles and band‐edge shifts were proven to be extremely predictive, this is a reasonable approximation. However, comparative studies are needed to establish a rigorous connection between computed surface dipoles and band‐edge positions, especially in the presence of an electrolyte.…”

“…Similar surface dipole calculations were performed on other photoelectrode materials such as functionalized TiO 2 , Ge, Si, and ZnO . Because computational investigations of the surface dipole are often combined with experimental X‐ray (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurements, theoretical trends have been widely validated by experiments . All these studies suggest that the surface dipole is primarily determined by the dipole moment of the isolated organic molecule and the bond dipole between the functional group and the semiconductor surface atoms, enabling easy screening of candidate functional groups.…”

“…Current surface dipole calculations are performed for photoelectrode surfaces in vacuum . Extending these calculations to include electrolyte effects using first‐principles MD simulations or implicit solvation models might resolve discrepancies between theoretical and experimental surface dipoles, allowing more accurate predictions of barrier‐height shifts.…”

Off-Cycle Processes in Pd-Catalyzed Cross-Coupling of Carboranes

“…The electronic diversity among carborane regioisomers has enabled tuning of their hydrophobicity, pharmacological properties, photoluminescence, and surface chemistry. 32 Among the presently available boron vertex functionalization methods, metal-catalyzed transformations enable the installation of the broadest class of chemical groups. These metalcatalyzed methods can be loosely grouped into (1) directed B−H activation and (2) cross-coupling at B−X bonds (X = Br, I).…”

Enhancement of Luminescence Efficiencies by Thermal Rearrangement from ortho‐ to meta‐Carborane in Bis‐Carborane‐Substituted Acenes

“…More recently, o ‐carborane has attracted attention as a key unit for optically functional materials . o ‐Carborane is known to act as an electron acceptor because of the electron‐deficient nature of the three‐center two‐electron bonds when an electron donor is bonded to a carbon,, and bright emission from the induced charge‐transfer (ICT) state can be obtained upon combination with electron‐donating units . It should be mentioned that bright emission from this ICT state has often been observed even in the solid state by suppressing aggregation‐caused quenching (ACQ) .…”