I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[29451]
Open Access
Abstract: Interdiffusion phenomena between adjacent materials are highly prevalent in semiconductor device architectures and can present a major reliability challenge for the industry. To fully capture these phenomena, experimental approaches must go beyond static and post-mortem studies to include in situ and in-operando setups. Here, soft and hard X-ray photoelectron spectroscopy (SXPS and HAXPES) is used to monitor diffusion in real-time across a proxy device. The device consists of a Si/SiO2/TixW1−x(300 nm)/Cu(25 nm) thin film material stack, with the TixW1−x film (x = 0.054, 0.115, 0.148) acting as a diffusion barrier between Si and Cu. The interdiffusion is monitored through the continuous collection of spectra whilst in situ annealing to 673 K. Ti within the TiW is found to be highly mobile during annealing, diffusing out of the barrier and accumulating at the Cu surface. Increasing the Ti concentration within the TixW1−x film increases the quantity of accumulated Ti, and Ti is first detected at the Cu surface at temperatures as low as 550 K. Surprisingly, at low Ti concentrations (x = 0.054), W is also mobile and diffuses alongside Ti. By monitoring the Ti 1s core level with HAXPES, the surface-accumulated Ti was observed to undergo oxidation even under ultra-high vacuum conditions, highlighting the reactivity of Ti in this system. These results provide crucial evidence for the importance of diffusion barrier composition on their efficacy during device application, delivering insights into the mechanisms underlying their effectiveness and limitations.
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May 2023
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I09-Surface and Interface Structural Analysis
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Maria
Basso
,
Elena
Colusso
,
Chiara
Carraro
,
Curran
Kalha
,
Aysha A.
Riaz
,
Giada
Bombardelli
,
Enrico
Napolitani
,
Yu
Chen
,
Jacek
Jasieniak
,
Laura E.
Ratcliff
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Anna
Regoutz
,
Alessandro
Martucci
Diamond Proposal Number(s):
[29451]
Abstract: The thermochromic properties of vanadium dioxide (VO2) offer great advantages for energy-saving smart windows, memory devices, and transistors. However, the crystallization of solution-based thin films at temperatures lower than 400°C remains a challenge. Photonic annealing has recently been exploited to crystallize metal oxides, with minimal thermal damage to the substrate and reduced manufacturing time. Here, VO2 thin films, obtained via a green sol-gel process, were crystallized by pulsed excimer laser annealing. The influence of increasing laser fluence and pulse number on the film properties was systematically studied through optical, structural, morphological, and chemical characterizations. From temperature profile simulations, the temperature rise was confirmed to be confined within the film during the laser pulses, with negligible substrate heating. Threshold laser parameters to induce VO2 crystallization without surface melting were found. With respect to furnace annealing, both the crystallization temperature and the annealing time were substantially reduced, with VO2 crystallization being achieved within only 60 s of laser exposure. The laser processing was performed at room temperature in air, without the need of a controlled atmosphere. The thermochromic properties of the lasered thin films were comparable with the reference furnace-treated samples.
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May 2023
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I09-Surface and Interface Structural Analysis
I21-Resonant Inelastic X-ray Scattering (RIXS)
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A. S.
Menon
,
B. J.
Johnston
,
S. G.
Booth
,
L.
Zhang
,
K.
Kress
,
B. E.
Murdock
,
G.
Paez Fajardo
,
N. N.
Anthonisamy
,
N.
Tapia-Ruiz
,
S.
Agrestini
,
M.
Garcia-Fernandez
,
K.
Zhou
,
P. K.
Thakur
,
T. L.
Lee
,
A. J.
Nedoma
,
S. A.
Cussen
,
L. F. J.
Piper
Diamond Proposal Number(s):
[29104, 29113]
Open Access
Abstract: The desire to increase the energy density of stoichiometric layered
Li
TM
O
2
(TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true
O
-redox, as observed in
Li
-excess cathodes. Through a high-resolution
O
K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the
Mn
-free
Ni
-rich layered oxide
Li
Ni
0.98
W
0.02
O
2
, we demonstrate that the same oxidized oxygen environment exists in both
Li
-excess and non-
Li
-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
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Mar 2023
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[21897]
Open Access
Abstract: Preparing aqueous silicon slurries in presence of a low-pH buffer improves the cycle life of silicon electrodes considerably because of higher reversibility of the alloying process and higher resilience towards volume changes during (de)alloying. While the positive effects of processing at low pH have been demonstrated repeatedly, there are gaps in understanding of the buffer's role during the slurry preparation and the effect of buffer residues within the electrode during cycling. This study uses a combination of soft and hard X-ray photoelectron spectroscopy (SOXPES/HAXPES) to investigate the silicon particle interface after aqueous processing in both pH-neutral and citrate-buffered environments. Further, silicon electrodes are investigated after ten cycles in half-cells to identify the processing-dependant differences in the surface layer composition. By tuning the excitation energy between 100 eV and 7080 eV, a wide range of XPS probing depths were sampled to vertically map the electrode surface from top to bulk. The results demonstrate that the citrate-buffer becomes an integral part of the surface layer on Si particles and is, together with the electrode binder, part of an artificial solid-electrolyte interphase that is created during the electrode preparation and drying.
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Feb 2023
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I09-Surface and Interface Structural Analysis
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Leanne A. H.
Jones
,
Zongda
Xing
,
Jack E. N.
Swallow
,
Huw
Shiel
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Nicole
Fleck
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Laurence J.
Hardwick
,
David O.
Scanlon
,
Anna
Regoutz
,
Tim D.
Veal
,
Vinod R.
Dhanak
Diamond Proposal Number(s):
[25980]
Open Access
Abstract: A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS2, MoSe2, and MoTe2 are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX2 series as 5.86, 5.40, and 5.00 eV for MoSe2, MoSe2, and MoTe2, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.
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Dec 2022
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I09-Surface and Interface Structural Analysis
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[29451]
Abstract: Topochemical reduction of the cation-disordered
perovskite oxides LaCo0.5Rh0.5O3 and LaNi0.5Rh0.5O3 with Zr yields
the partially anion-vacancy ordered phases LaCo0.5Rh0.5O2.25 and
LaNi0.5Rh0.5O2.25, respectively. Neutron diffraction and Hard X-ray
photoelectron spectroscopy (HAXPES) measurements reveal that
the anion-deficient phases contain Co1+/Ni1+ and a 1:1 mixture of
Rh1+ and Rh3+ cations within a disordered array of apex-linked
MO4 square-planar and MO5 square-based pyramidal coordination
sites. Neutron diffraction data indicate that LaCo0.5Rh0.5O2.25
adopts a complex antiferromagnetic ground state, which is the
sum of a C-type ordering (mM5
+) of the xy-components of the Co
spins and a G-type ordering (mΓ1
+) of the z-components of the Co
spins. On warming above 75 K, the magnitude of the mΓ1
+
component declines, attaining a zero value by 125 K, with the magnitude of the mM5
+ component remaining unchanged up to
175 K. This magnetic behavior is rationalized on the basis of the differing d-orbital fillings of the Co1+ cations in MO4 square-planar
and MO5 square-based pyramidal coordination sites. LaNi0.5Rh0.5O2.25 shows no sign of long-range magnetic order at 2 K − behavior
that can also be explained on the basis of the d-orbital occupation of the Ni1+ centers.
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Sep 2022
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I09-Surface and Interface Structural Analysis
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Theodore D. C.
Hobson
,
Huw
Shiel
,
Christopher N.
Savory
,
Jack E. N.
Swallow
,
Leanne A. H.
Jones
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Bhaskar
Das
,
Chris
Leighton
,
Guillaume
Zoppi
,
Vin R.
Dhanak
,
David O.
Scanlon
,
Tim D.
Veal
,
Ken
Durose
,
Jonathan D.
Major
Diamond Proposal Number(s):
[23160]
Open Access
Abstract: Antimony selenide (Sb2Se3) is a promising absorber material for thin-film
photovoltaics. However, certain areas of fundamental understanding of this material
remain incomplete and this presents a barrier to further efficiency gains. In particular,
recent studies have highlighted the role of majority carrier type and extrinsic doping
in drastically changing the performance of high efficiency devices [1]. Herein, Sndoped
Sb2Se3 bulk crystals are shown to exhibit p-type conductivity using Hall effect
and hot-probe measurements. The measured conductivities are higher than those
achieved through native defects alone, but with a carrier density (up to 7.4 × 1014
cm−3) several orders of magnitude smaller than the quantity of Sn included in the
source material. Additionally, a combination of ultraviolet, X-ray and hard X-ray
photoemission spectroscopies are employed to obtain a non-destructive depth profile of
the valence band maximum, confirming p-type conductivity and indicating a majority
carrier type inversion layer at the surface. Finally, these results are supported by
density functional theory calculations of the defect formation energies in Sn-doped
Sb2Se3, showing a possible limit on the carrier concentration achievable with Sn as
a dopant. This study sheds light on the effectiveness of Sn as a p-type dopant in
Sb2Se3 and highlights avenues for further optimisation of doped Sb2Se3 for solar energy
devices.
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Sep 2022
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I09-Surface and Interface Structural Analysis
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Laura E.
Ratcliff
,
Takayoshi
Oshima
,
Felix
Nippert
,
Benjamin M.
Janzen
,
Elias
Kluth
,
Rüdiger
Goldhahn
,
Martin
Feneberg
,
Piero
Mazzolini
,
Oliver
Bierwagen
,
Charlotte
Wouters
,
Musbah
Nofal
,
Martin
Albrecht
,
Jack E. N.
Swallow
,
Leanne A. H.
Jones
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Curran
Kalha
,
Christoph
Schlueter
,
Tim D.
Veal
,
Joel B.
Varley
,
Markus R.
Wagner
,
Anna
Regoutz
Diamond Proposal Number(s):
[21430, 24670]
Open Access
Abstract: Ga2O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga2O3 presents a particular challenge across synthesis, characterisation, and theory due to its inherent disorder and resulting complex structure – electronic structure relationship. Here, density functional theory is used in combination with a machine learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the γ-phase. Theoretical results are compared with surface and bulk sensitive soft and hard X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of γ-Ga2O3. The first onset of strong absorption at room temperature is found at 5.1 eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17 eV obtained by PLE spectroscopy, where the latter shifts to 5.33 eV at 5 K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step towards exploring how their electronic structure can be understood in terms of local coordination and overall structure.
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Jul 2022
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I09-Surface and Interface Structural Analysis
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Luke
Thomas
,
Theo D. C.
Hobson
,
Laurie J.
Phillips
,
Kieran J.
Cheetham
,
Neil
Tarbuck
,
Leanne A. H.
Jones
,
Matthew J.
Smiles
,
Chris H.
Don
,
Pardeep K.
Thakur
,
Mark
Isaacs
,
Huw
Shiel
,
Stephen
Campbell
,
Vincent
Barrioz
,
Vin
Dhanak
,
Tim
Veal
,
Jonathan D.
Major
,
Ken
Durose
Diamond Proposal Number(s):
[28268]
Open Access
Abstract: This paper is motivated by the potential advantages of higher doping and lower contact barriers in CdTe photovoltaic devices that may be realized by using n- type rather than the conventional p-type solar absorber layers. We present post-growth doping trials for indium in thin polycrystalline CdTe films using diffusion of indium metal and with indium chloride. Chemical concentrations of indium up to 1019 cm-3 were achieved and the films were verified as n-type by hard x-ray photoemission. Post growth chlorine treatment (or InCl3) was found to compensate the n-doping. Trial structures comprising CdS/CdTe:In verified that the doped absorber structures performed as expected both before and after chloride treatment, but it is recognized that this is not an optimum combination. Hence in order to identify how the advantages of n-type absorbers might be fully realized in future work, we also report simulations of a range of p-n junction combinations with n-CdTe, a number of which have the potential for high Voc.
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Jun 2022
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I09-Surface and Interface Structural Analysis
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Matthew J.
Smiles
,
Thomas
Shalvey
,
Luke
Thomas
,
Theodore D. C.
Hobson
,
Leanne A. H.
Jones
,
Laurie
Phillips
,
Christopher
Don
,
Thomas
Beesley
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Ken
Durose
,
Jonathan D.
Major
,
Tim
Veal
Diamond Proposal Number(s):
[31170]
Open Access
Abstract: Germanium selenide (GeSe) bulk crystals, thin films and solar cells are investigated with a focus on acceptor-doping with silver (Ag) and the use of an Sb2Se3 interfacial layer. The Ag-doping of GeSe occurred by a stoichiometric melt growth technique that created Ag-doped GeSe bulk crystals. A combination of capacitance voltage measurements, synchrotron radiation photoemission spectroscopy and surface space-charge calculations indicate Ag-doping increases the hole density from 5.2×1015 cm-3 to 1.9×1016 cm-3. The melt-grown material is used as the source for thermally evaporated GeSe films within solar cells. The cell structure with the highest efficiency of 0.260% is FTO/CdS/Sb2Se3/undoped-GeSe/Au compared with solar cells without the Sb2Se3 interfacial layer or with the Ag-doped GeSe.
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Apr 2022
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