I09-Surface and Interface Structural Analysis
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Jack E. N.
Swallow
,
Benjamin A. D.
Williamson
,
Max
Birkett
,
Alex
Abbott
,
Mark
Farnworth
,
Thomas J.
Featherstone
,
Nianhua
Peng
,
J.
Kieran Cheetham
,
Paul
Warren
,
Anna
Regoutz
,
David A.
Duncan
,
Tien-lin
Lee
,
David O.
Scanlon
,
R.
Vin Dhanak
,
Tim D.
Veal
Abstract: Fluorine-doped tin oxide (FTO) is a commercially successful transparent conducting oxide with very good electrical (resistivities < 1 × 10 3 Ω⋅ cm) and optical properties (transmittance >85%). These properties coupled with cheap and large-scale deposition on float-glass lines means FTO has found commercial use in, for example, low emissivity windows and solar cells. However, despite its widespread application, a detailed understanding is lacking of the doping and defects in FTO. Recent work [1] has suggested that the fluorine interstitial plays a major role in limiting the conductivity of FTO. Here we present synchrotron radiation high energy x-ray photoemission spectroscopy (XPS) of the fluorine 1s core level of FTO films without in situ surface preparation. This probes deeper than standard XPS and shows that the fluorine interstitial is present not just at the surface of the films and is not an artefact of argon ion sputtering for surface preparation.
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Nov 2018
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[8436]
Abstract: The interaction of oxalic acid with the Cu(110) surface has been investigated by a combination of scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), soft X-ray photoelectron spectroscopy (SXPS), near-edge X-ray absorption fine structure (NEXAFS) and scanned-energy mode photoelectron diffraction (PhD), and density functional theory (DFT). O 1s SXPS and O K-edge NEXAFS show that at high coverages a singly deprotonated monooxalate is formed with its molecular plane perpendicular to the surface and lying in the
[11¯0]
azimuth, while at low coverage a doubly-deprotonated dioxalate is formed with its molecular plane parallel to the surface. STM, LEED and SXPS show the dioxalate to form a (3 × 2) ordered phase with a coverage of 1/6 ML. O 1s PhD modulation spectra for the monooxalate phase are found to be simulated by a geometry in which the carboxylate O atoms occupy near-atop sites on nearest-neighbour surface Cu atoms in
[11¯0]
rows, with a Cu-O bondlength of 2.00±0.04 Å. STM images of the (3 × 2) phase show some centred molecules attributed to adsorption on second-layer Cu atoms below missing [001] rows of surface Cu atoms, while DFT calculations show adsorption on a (3 × 2) missing row surface (with every third [001] Cu surface row removed) is favoured over adsorption on the unreconstructed surface. O 1s PhD data from dioxalate is best fitted by a structure similar to that found by DFT to have the lowest energy, although there are some significant differences in intramolecular bondlengths.
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Oct 2017
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Open Access
Abstract: Diamond Light Source's Surface and Interface Structural Analysis beamline (I09) is the first in the world designed to deliver both hard and soft X-rays with optimized, independent sources and optics. With the extended energy range, we offer a wide variety of X-ray techniques that are based primarily on X-ray photoelectron and absorption spectroscopies, which can be combined to maximize the information one can extract from a visit to the beamline. For photoelectron spectroscopy, this energy range corresponds to an information depth from 0.5 to more than 20 nm, providing the bulk as well as surface sensitivity for depth-profiling of heterostructures and buried interfaces.
This unique combination has allowed I09 to develop, since becoming operational in 2013, a user community that is interested in two interconnected research areas. One concentrates on surface chemistry and structures, in particular adsorption of organic molecules on solid surfaces and epitaxial growth of two-dimensional materials. The other area of research deals with the electronic structures of oxide heterointerfaces, electron correlations and metal-insulator transitions, energy research, functionalized materials, and material design. The vast majority of these studies, particularly those on surface structures and lithium ion batteries, have benefited from the use of both soft and hard X-rays at I09. In the following sections, we outline the design, science cases, and future plans of the beamline.
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Jul 2018
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I09-Surface and Interface Structural Analysis
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Abstract: Proton-conducting perovskite oxides form a class of solid electrolytes for novel electrochemical devices operating at moderate temperatures. Here, we use hard X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and density functional theory calculations to investigate the structure and elucidate the origin of the fast proton transport properties of strained ultrathin films of Y-doped BaZrO3 grown by pulsed lased deposition on NdGaO3. Our study shows that our BaZr0.8Y0.2O3 films incorporate a significant amount of Y dopants, and to a lesser extent also Zr ions, substituting for Ba2+, and that these substitutional defects agglomerate forming columnar regions crossing vertically from the surface to the interface the entire film. Our calculations also show that, in regions rich in Y substitutions for both Zr and Ba, the proton transfer process involves nearly zero-energy barriers, indicating that A-site cation substitutions by Y lead to fast transport pathways and hence are responsible for the previously observed enhanced values of the proton conductivity of these perovskite oxide films.
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Mar 2016
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I09-Surface and Interface Structural Analysis
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Martin
Schwarz
,
Manuela
Garnica
,
David A.
Duncan
,
Alejandro
Pérez Paz
,
Jacob
Ducke
,
Peter S.
Deimel
,
Pardeep K.
Thakur
,
Tien-lin
Lee
,
Angel
Rubio
,
Johannes V.
Barth
,
Francesco
Allegretti
,
Willi
Auwärter
Diamond Proposal Number(s):
[14624]
Abstract: The tetrapyrrole macrocycle of porphine is the common core of all porphyrin molecules, an interesting class of π-conjugated molecules with relevance in natural and artificial systems. The functionality of porphines on a solid surface can be tailored by the central metal atom and its interaction with the substrate. In this study, we present a local adsorption geometry determination for cobalt porphine on Cu(111) by means of complementary scanning tunneling microscopy, high-resolution X-ray photoelectron spectroscopy and X-ray standing wave measurements, and density functional theory calculations. Specifically, the Co center was determined to be at an adsorption height of 2.25 ± 0.04 Å occupying a bridge site. The macrocycle adopts a moderate asymmetric saddle-shape conformation, with the two pyrrole groups that are aligned perpendicular to the densely packed direction of the Cu(111) surface tilted away from the surface plane.
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Feb 2018
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I09-Surface and Interface Structural Analysis
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Benjamin
Stadtmuller
,
Sonja
Schroder
,
Francois
Bocquet
,
Caroline
Henneke
,
Christoph
Kleimann
,
Serguei
Soubatch
,
Martin
Willenbockel
,
Blanka
Detlefs
,
Jorg
Zegenhagen
,
Tien-lin
Lee
,
Stefan
Tautz
,
Christian
Kumpf
Diamond Proposal Number(s):
[8449, 9231]
Abstract: The formation of metalorganic hybrid interfaces is determined by the fine balance between molecule-substrate and molecule-molecule interactions at the interface. Here, we report on a systematic investigation of interfaces between a metal surface and organic monolayer films that consist of two different molecular species, one donor and one acceptor of electronic charge. Our x-ray standing wave data show that in heteromolecular structures, the molecules tend to align themselves to an adsorption height between those observed in the respective homomolecular structures. We attribute this alignment effect to a substrate-mediated charge transfer between the molecules, which causes a mutual enhancement of their respective donor and acceptor characters. We argue that this effect is of general validity for π-conjugated molecules adsorbing on noble metal surfaces.
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Apr 2014
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I09-Surface and Interface Structural Analysis
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Phil J.
Blowey
,
Billal
Sohail
,
Luke A.
Rochford
,
Timothy
Lafosse
,
David A.
Duncan
,
Paul
Ryan
,
Daniel Andrew
Warr
,
Tien-lin
Lee
,
Giovanni
Costantini
,
Reinhard J.
Maurer
,
David Phillip
Woodruff
Diamond Proposal Number(s):
[15899, 18191]
Abstract: Efficient charge transfer across metal–organic interfaces is a key physical process in modern organic electronics devices, and characterization of the energy level alignment at the interface is crucial to enable a rational device design. We show that the insertion of alkali atoms can significantly change the structure and electronic properties of a metal–organic interface. Coadsorption of tetracyanoquinodimethane (TCNQ) and potassium on a Ag(111) surface leads to the formation of a two-dimensional charge transfer salt, with properties quite different from those of the two-dimensional Ag adatom TCNQ metal–organic framework formed in the absence of K doping. We establish a highly accurate structural model by combination of quantitative X-ray standing wave measurements, scanning tunnelling microscopy, and density-functional theory (DFT) calculations. Full agreement between the experimental data and the computational prediction of the structure is only achieved by inclusion of a charge-transfer-scaled dispersion correction in the DFT, which correctly accounts for the effects of strong charge transfer on the atomic polarizability of potassium. The commensurate surface layer formed by TCNQ and K is dominated by strong charge transfer and ionic bonding and is accompanied by a structural and electronic decoupling from the underlying metal substrate. The consequence is a significant change in energy level alignment and work function compared to TCNQ on Ag(111). Possible implications of charge-transfer salt formation at metal–organic interfaces for organic thin-film devices are discussed.
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May 2020
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I09-Surface and Interface Structural Analysis
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J.
Sforzini
,
L.
Nemec
,
T.
Denig
,
B.
Stadtmüller
,
T. L
Lee
,
C.
Kumpf
,
S.
Soubatch
,
U.
Starke
,
P.
Rinke
,
V.
Blum
,
Francois
Bocquet
,
Stefan
Tautz
Diamond Proposal Number(s):
[8449, 10271]
Open Access
Abstract: We measure the adsorption height of hydrogen-intercalated quasifreestanding monolayer graphene on the
(0001) face of 6H silicon carbide by the normal incidence x-ray standing wave technique. A density
functional calculation for the full ð6
ffiffiffi
3 p × 6
ffiffiffi
3 p Þ-R30° unit cell, based on a van derWaals corrected exchange
correlation functional, finds a purely physisorptive adsorption height in excellent agreement with experiments,
a very low buckling of the graphene layer, a very homogeneous electron density at the interface, and
the lowest known adsorption energy per atom for graphene on any substrate.Astructural comparison to other
graphenes suggests that hydrogen-intercalated graphene on 6H-SiCð0001Þ approaches ideal graphene.
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Mar 2015
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I09-Surface and Interface Structural Analysis
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Peter
Knecht
,
Bodong
Zhang
,
Joachim
Reichert
,
David A.
Duncan
,
Martin
Schwarz
,
Felix
Haag
,
Paul
Ryan
,
Tien-lin
Lee
,
Peter S.
Deimel
,
Peter
Feulner
,
Francesco
Allegretti
,
Willi
Auwärter
,
Guillaume
Médard
,
Ari Paavo
Seitsonen
,
Johannes V.
Barth
,
Anthoula C.
Papageorgiou
Diamond Proposal Number(s):
[24320]
Abstract: The controlled arrangement of N-heterocyclic carbenes (NHCs) on solid surfaces is a current challenge of surface functionalization. We introduce a strategy of using Ru porphyrins in order to control both the orientation and lateral arrangement of NHCs on a planar surface. The coupling of the NHC to the Ru porphyrin is a facile process which takes place on the interface: we apply NHCs as functional, robust pillars on well-defined, preassembled Ru porphyrin monolayers on silver and characterize these interfaces with atomic precision via a battery of experimental techniques and theoretical considerations. The NHCs assemble at room temperature modularly and reversibly on the Ru porphyrin arrays. We demonstrate a selective and complete functionalization of the Ru centers. With its binding, the NHC modifies the interaction of the Ru porphyrin with the Ag surface, displacing the Ru atom by 1 Å away from the surface. This arrangement of NHCs allows us to address individual ligands by controlled manipulation with the tip of a scanning tunneling microscope, creating patterned structures on the nanometer scale.
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Mar 2021
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[16005]
Abstract: Zn
M
I
I
I
2
O
4
(
M
I
I
I
=
Co
, Rh, Ir) spinels have been recently identified as promising
p
-type semiconductors for transparent electronics. However, discrepancies exist in the literature regarding their fundamental optoelectronic properties. In this paper, the electronic structures of these spinels are directly investigated using soft/hard x-ray photoelectron and x-ray absorption spectroscopies in conjunction with density functional theory calculations. In contrast to previous results,
ZnCo
2
O
4
is found to have a small electronic band gap with forbidden optical transitions between the true band edges, allowing for both bipolar doping and high optical transparency. Furthermore, increased
d
−
d
splitting combined with a concomitant lowering of Zn
s
/
p
conduction states is found to result in a
ZnCo
2
O
4
(
ZCO
)
<
ZnRh
2
O
4
(
ZRO
)
≈
ZnIr
2
O
4
(
ZIO
)
band gap trend, finally resolving long-standing discrepancies in the literature.
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Aug 2019
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