Quantitative surface structure determination
File(s)
Author(s)
Ryan, Paul
Type
Thesis
Abstract
In this thesis work, normal incidence X-ray standing waves (NIXSW) and energy scanned photoelectron diffraction (PhD)
were utilised to determine the surface structures of a number of adsorbate/ surface systems. The systems
under study can be separated into two subject areas: those concerning the study of adsorbates on the
magnetite (001) facet (Fe3O4(001)) and those that comprise the adsorption of 2,3,5,6-tetra
uro-7,7,8,8-
tetracyanoquinodimethane (F4-TCNQ) on coinage metals which is proposed to form charge transfer
salts.
Formic acid dissociatively adsorbs on the (001) facet of magnetite (Fe3O4(001)) producing an
adsorbed formate and a surface hydroxyl. The NIXSW results of this thesis corroborate with prior
studies which place the formate bidentate bonding on the surface to the surface Fe cations. An additional
structural study, using PhD, was uniquely able to determine the location of the surface hydroxyl as
being at a surface interstitial site. It has been proposed that deposited Ni metal sits at the adatom site
on the Fe3O4(001) surface as well in the subsurface cation vacancies of the subsurface cation vacancy
termination. NIXSW results presented in this thesis unequivocally determine this to be the case. The
vertical height of the subsurface Ni, as determined by NIXSW, likely shows that it sits in subsurface sites
and not at the surface. Finally, the NIXSW technique was used to determine the effect CO adsorption has
on the structure of Ag adatoms on the Fe3O4(001) surface. The NIXSW results find that the CO pulls
the Ag adatom away from the surface and these results have been used to benchmark computationally
affordable approaches to calculating the adatom adsorption heights and other properties of the system.
Prior NIXSW studies of 7,7,8,8-tetracyanoquinodimethane (H4-TCNQ) on the coinage metals show
that it does not adsorb on coinage metals in a planar geometry. It has been determined that the molecule
twists and bends on the surface and incorporates substrate adatoms into a charge transfer salt. The
NIXSW results of this thesis show that F4-TCNQ also adsorbs on many of the coinage metals, not in
a planar geometry, but twisted at either end. Such twisting of the molecule is analogous to that of H4-
TCNQ and could potentially indicate that F4-TCNQ also forms charge transfer salts on coinage metals.
This would corroborate with ARPES, STM and LEED results from prior investigations. These results
provide a benchmark for future theoretical calculations investigating the various electronic properties of
these adsorbate/ metal surface systems.
were utilised to determine the surface structures of a number of adsorbate/ surface systems. The systems
under study can be separated into two subject areas: those concerning the study of adsorbates on the
magnetite (001) facet (Fe3O4(001)) and those that comprise the adsorption of 2,3,5,6-tetra
uro-7,7,8,8-
tetracyanoquinodimethane (F4-TCNQ) on coinage metals which is proposed to form charge transfer
salts.
Formic acid dissociatively adsorbs on the (001) facet of magnetite (Fe3O4(001)) producing an
adsorbed formate and a surface hydroxyl. The NIXSW results of this thesis corroborate with prior
studies which place the formate bidentate bonding on the surface to the surface Fe cations. An additional
structural study, using PhD, was uniquely able to determine the location of the surface hydroxyl as
being at a surface interstitial site. It has been proposed that deposited Ni metal sits at the adatom site
on the Fe3O4(001) surface as well in the subsurface cation vacancies of the subsurface cation vacancy
termination. NIXSW results presented in this thesis unequivocally determine this to be the case. The
vertical height of the subsurface Ni, as determined by NIXSW, likely shows that it sits in subsurface sites
and not at the surface. Finally, the NIXSW technique was used to determine the effect CO adsorption has
on the structure of Ag adatoms on the Fe3O4(001) surface. The NIXSW results find that the CO pulls
the Ag adatom away from the surface and these results have been used to benchmark computationally
affordable approaches to calculating the adatom adsorption heights and other properties of the system.
Prior NIXSW studies of 7,7,8,8-tetracyanoquinodimethane (H4-TCNQ) on the coinage metals show
that it does not adsorb on coinage metals in a planar geometry. It has been determined that the molecule
twists and bends on the surface and incorporates substrate adatoms into a charge transfer salt. The
NIXSW results of this thesis show that F4-TCNQ also adsorbs on many of the coinage metals, not in
a planar geometry, but twisted at either end. Such twisting of the molecule is analogous to that of H4-
TCNQ and could potentially indicate that F4-TCNQ also forms charge transfer salts on coinage metals.
This would corroborate with ARPES, STM and LEED results from prior investigations. These results
provide a benchmark for future theoretical calculations investigating the various electronic properties of
these adsorbate/ metal surface systems.
Version
Open Access
Date Issued
2020-10
Date Awarded
2021-04
Copyright Statement
Creative Commons Attribution Non-Commercial Licence
License URL
Advisor
Payne, David
Sponsor
Diamond Light Source (Firm)
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)