I09-Surface and Interface Structural Analysis
|
N.
Yang
,
E.
Strelcov
,
A.
Belianinov
,
A.
Tebano
,
V.
Foglietti
,
C.
Schlueter
,
T.-L.
Lee
,
S.
Jesse
,
S. V.
Kalinin
,
G.
Balestrino
,
C.
Aruta
Abstract: Water adsorption, splitting, and proton liberation were investigated on Sm0.1Ce0.9O2-δ thin films by scanning probe microscopy. An irreversible volume expansion was observed by applying a positive bias with increased temperature. The volume expansion is also linearly dependent on the relative humidity. A reversible water adsorption process and its effect on the conductivity were also investigated by electrochemical strain microscopy and first order reversal curve under a number of experiment conditions. The presence of a Ce3+ along with OH groups, detected by hard x-ray photoemission spectroscopy established a clear correlation between the water incorporation and the valence state of Ce.
|
Oct 2015
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[15716]
Open Access
Abstract: We use 9 nm and 15 nm thin membranes for determining the effective attenuation length of photoelectrons in silicon. One side of silicon membranes was covered with a thin film of aluminium and exposed to X-rays with energies from 3 to 8 keV. We recorded Al 1s and 2s photoelectrons that were (a) emitted from the Al film directly and (b) transmitted through the membranes. With the help of the ratio of both yields, we obtained values for the effective attenuation length (EAL) of electrons with kinetic energies up to 7.9 keV in silicon. The experimentally determined EAL values are smaller than obtained from different predictive equations. Using a power law fit View the MathML sourceEAL(k,p)=kEkinp to the experimental and predicted EAL values we find that mainly different is the pre-factor of the power law, k, while the exponent, i.e. the dependence on kinetic energy Ekin is represented well. Our study underlines the feasibility of using membranes for investigating surfaces under (near) ambient pressure conditions by photoelectron spectroscopy and points out the advantages of employing hard X-rays.
|
Mar 2018
|
|
I09-Surface and Interface Structural Analysis
|
Judith Veronika
Berens
,
Sebastian
Bichelmaier
,
Nathalie K.
Fernando
,
Pardeep Kumar
Thakur
,
Tien-Lin
Lee
,
Manfred
Mascheck
,
Tomas
Wiell
,
Susanna K.
Eriksson
,
J. Matthias
Kahk
,
Johannes
Lischner
,
Manesh
Mistry
,
Thomas
Aichinger
,
Gregor
Pobegen
,
Anna
Regoutz
Diamond Proposal Number(s):
[19885]
Open Access
Abstract: SiC is set to enable a new era in power electronics impacting a wide range of energy technologies, from electric vehicles to renewable energy. Its physical characteristics outperform silicon in many aspects, including band gap, breakdown field, and thermal conductivity. The main challenge for further development of SiC-based power semiconductor devices is the quality of the interface between SiC and its native dielectric SiO2. High temperature nitridation processes can improve the interface quality and ultimately the device performance immensely, but the underlying chemical processes are still poorly understood. Here, we present an energy-dependent hard X-ray photoelectron spectroscopy (HAXPES) study probing non-destructively SiC and SiO2 and their interface in device stacks treated in varying atmospheres. We successfully combine laboratory- and synchrotron-based HAXPES to provide unique insights into the chemistry of interface defects and their passivation through nitridation processes.
|
Apr 2020
|
|
I09-Surface and Interface Structural Analysis
|
Zachary W.
Lebens-Higgins
,
Nicholas
Faenza
,
Pinaki
Mukherjee
,
Shawn
Sallis
,
Fadwa
Badway
,
Nathalie
Pereira
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
Frederic
Cosandey
,
Glenn
Amatucci
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[12764, 16005]
Abstract: For layered oxide cathodes, aluminum doping has widely been shown to improve performance, particularly at high degrees of delithiation. While this has led to increased interest in Al-doped systems, including LiNi0.8Co0.15Al0.05O2 (NCA), the aluminum surface environment has not been thoroughly investigated. Using hard x-ray photoelectron spectroscopy measurements of the Al 1s core region for NCA electrodes, we examined the evolution of the surface aluminum environment under electrochemical and thermal stress. By correlating the aluminum environment to transition metal reduction and electrolyte decomposition, we provide further insight into the cathode-electrolyte interface layer. A remarkable finding is that Al-O coatings in LiPF6 electrolyte mimic the evolution observed for the aluminum surface environment in doped layered oxides.
|
Dec 2017
|
|
I09-Surface and Interface Structural Analysis
|
Jia-Ye
Zhang
,
Weiwei
Li
,
Robert L. Z.
Hoye
,
Judith
Macmanus-Driscoll
,
Melanie
Budde
,
Oliver
Bierwagen
,
Le
Wang
,
Yingge
Du
,
Matthew
Wahila
,
Louis F. J.
Piper
,
Tien-Lin
Lee
,
Holly
Edwards
,
Vinod R.
Dhanak
,
Hongliang
Zhang
Diamond Proposal Number(s):
[16005]
Abstract: NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. Understanding and improving its optical and transport properties have been of considerable interest. In this work, we have investigated the effect of Li doping on the electronic, optical and transport properties of NiO epitaxial thin films grown by pulsed laser deposition. We show that Li doping significantly increases the p-type conductivity of NiO, but all the films have relatively low room-temperature mobilities (< 0.05 cm2 V−1s−1). The conduction mechanism is better described by small-polaron hoping model in the temperature range of 200 K < T <330 K, and variable range hopping at T <200 K. A combination of x-ray photoemission and O K-edge x-ray absorption spectroscopic investigations reveal that the Fermi level gradually shifts toward the valence band maximum (VBM) and a new hole state develops with Li doping. Both the VBM and hole states are composed of primarily Zhang-Rice bound states, which accounts for the small polaron character (low mobility) of hole conduction. Our work provides guidelines for the search for p-type oxide materials and device optimization.
|
Jan 2018
|
|
I09-Surface and Interface Structural Analysis
|
X. C.
Huang
,
J. Y.
Zhang
,
M.
Wu
,
S.
Zhang
,
H. Y.
Xiao
,
W. Q.
Han
,
T.-L.
Lee
,
A.
Tadich
,
D.-C.
Qi
,
L.
Qiao
,
L.
Chen
,
K. H. L.
Zhang
Diamond Proposal Number(s):
[21432]
Abstract: This work reports a fundamental study on the electronic structure, optical properties, and defect chemistry of a series of Co-based spinel oxide (
Co
3
O
4
,
ZnCo
2
O
4
, and
CoAl
2
O
4
) epitaxial thin films using x-ray photoemission and absorption spectroscopies, optical spectroscopy, transport measurements, and density functional theory. We demonstrate that
ZnCo
2
O
4
has a fundamental bandgap of 1.3 eV, much smaller than the generally accepted values, which range from 2.26 to 2.8 eV. The valence band edge mainly consists of occupied
Co
3
d
t
6
2
g
with some hybridization with O
2
p
/Zn
3
d
, and the conduction band edge of unoccupied
e
∗
g
state. However, optical transition between the two band edges is dipole forbidden. Strong absorption occurs at photon energies above 2.6 eV, explaining the reasonable transparency of
ZnCo
2
O
4
. A detailed defect chemistry study indicates that Zn vacancies formed at high oxygen pressure are the origin of a high
p
-type conductivity of
ZnCo
2
O
4
, and the hole conduction mechanism is described by small-polaron hoping model. The high
p
-type conductivity, reasonable transparency, and large work function make
ZnCo
2
O
4
a desirable
p
-type transparent semiconductor for various optoelectronic applications. Using the same method, the bandgap of
Co
3
O
4
is further proved to be ∼0.8 eV arising from the tetrahedrally coordinated
Co
2
+
cations. Our work advances the fundamental understanding of these materials and provides significant guidance for their use in catalysis, electronic, and solar applications.
|
Sep 2019
|
|
|
|
Arian
Arab
,
Xiaoran
Liu
,
Okan
Koksal
,
Weibing
Yang
,
Ravini U.
Chandrasena
,
Srimanta
Middey
,
Mikhail
Kareev
,
Siddharth
Kumar
,
Marius-Adrian
Husanu
,
Zhenzhong
Yang
,
Lin
Gu
,
Vladimir N.
Strocov
,
Tien-Lin
Lee
,
Jan
Minar
,
Rossitza
Pentcheva
,
Jak
Chakhalian
,
Alexander X.
Gray
Abstract: Artificial complex-oxide heterostructures containing ultrathin buried layers grown along the pseudocubic [111] direction have been predicted to host a plethora of exotic quantum states arising from the graphene-like lattice geometry and the interplay between strong electronic correlations and band topology. To date, however, electronic-structural investigations of such atomic layers remain an immense challenge due to the shortcomings of conventional surface-sensitive probes, with typical information depths of a few Ångstroms. Here, we use a combination of bulk-sensitive soft x-ray angle-resolved photoelectron spectroscopy (SX-ARPES), hard x-ray photoelectron spectroscopy (HAXPES) and state-of-the-art first-principles calculations to demonstrate a direct and robust method for extracting momentum-resolved and angle-integrated valence-band electronic structure of an ultrathin buckled graphene-like layer of NdNiO3 confined between two 4-unit cell-thick layers of insulating LaAlO3. The momentum-resolved dispersion of the buried Ni d states near the Fermi level obtained via SX-ARPES is in excellent agreement with the first-principles calculations and establishes the realization of an antiferro-orbital order in this artificial lattice. The HAXPES measurements reveal the presence of a valence-band (VB) bandgap of 265 meV. Our findings open a promising avenue for designing and investigating quantum states of matter with exotic order and topology in a few buried layers.
|
Oct 2019
|
|
I09-Surface and Interface Structural Analysis
|
Paul C.
Rogge
,
Ravini U.
Chandrasena
,
Antonio
Cammarata
,
Robert J.
Green
,
Padraic
Shafer
,
Benjamin M.
Lefler
,
Amanda
Huon
,
Arian
Arab
,
Elke
Arenholz
,
Ho Nyung
Lee
,
Tien-Lin
Lee
,
Slavomir
Nemsak
,
James M.
Rondinelli
,
Alexander
Gray
,
Steven J.
May
Diamond Proposal Number(s):
[17824]
Abstract: We investigated the metal-insulator transition for epitaxial thin films of the perovskite CaFeO3, a material with a significant oxygen ligand hole contribution to its electronic structure. We find that biaxial tensile and compressive strain suppress the metal-insulator transition temperature. By combining hard x-ray photoelectron spectroscopy, soft x-ray absorption spectroscopy, and density functional calculations, we resolve the element-specific changes to the electronic structure across the metal-insulator transition. We demonstrate that the Fe sites undergo no observable spectroscopic change between the metallic and insulating states, whereas the O electronic configuration undergoes significant changes. This strongly supports the bond-disproportionation model of the metal-insulator transition for CaFeO3 and highlights the importance of ligand holes in its electronic structure. By sensitively measuring the ligand hole density, however, we find that it increases by ∼5–10% in the insulating state, which we ascribe to a further localization of electron charge on the Fe sites. These results provide detailed insight into the metal-insulator transition of negative charge transfer compounds and should prove instructive for understanding metal-insulator transitions in other late transition metal compounds such as the nickelates.
|
Jan 2018
|
|
I05-ARPES
I09-Surface and Interface Structural Analysis
|
Shyama V.
Ramankutty
,
Jans
Henke
,
Adriaan
Schiphorst
,
Rajah
Nutakki
,
Stephan
Bron
,
Georgios
Araizi-Kanoutas
,
Shrawan K.
Mishra
,
Lei
Li
,
Yingkai
Huang
,
Timur
Kim
,
Moritz
Hoesch
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
Anne
De Visser
,
Zhicheng
Zhong
,
Jasper
Van Wezel
,
Erik
Van Heumen
,
Mark
Golden
Diamond Proposal Number(s):
[15189, 16433, 18410]
Open Access
Abstract: SrMnSb2 is suggested to be a magnetic topological semimetal. It contains square, 2D Sb planes with non-symmorphic crystal symmetries that could protect band crossings, offering the possibility of a quasi-2D, robust Dirac semi-metal in the form of a stable, bulk (3D) crystal. Here, we report a combined and comprehensive experimental and theoretical investigation of the electronic structure of SrMnSb2, including the first ARPES data on this compound. SrMnSb2 possesses a small Fermi surface originating from highly 2D, sharp and linearly dispersing bands (the Y-states) around the (0,π/a)-point in k-space. The ARPES Fermi surface agrees perfectly with that from bulk-sensitive Shubnikov de Haas data from the same crystals, proving the Y−states to be responsible for electrical conductivity in SrMnSb2. DFT and tight binding (TB) methods are used to model the electronic states, and both show good agreement with the ARPES data. Despite the great promise of the latter, both theory approaches show the Y-states to be gapped above EF, suggesting trivial topology. Subsequent analysis within both theory approaches shows the Berry phase to be zero, indicating the non-topological character of the transport in SrMnSb2, a conclusion backed up by the analysis of the quantum oscillation data from our crystals.
|
Feb 2018
|
|
I09-Surface and Interface Structural Analysis
|
Slavomir
Nemsak
,
Mathias
Gehlmann
,
Cheng-Tai
Kuo
,
Shih-Chieh
Lin
,
Christoph
Schlueter
,
Ewa
Mlynczak
,
Tien-Lin
Lee
,
Lukasz
Plucinski
,
Hubert
Ebert
,
Igor
Di Marco
,
Ján
Minár
,
Claus M.
Schneider
,
Charles S.
Fadley
Diamond Proposal Number(s):
[11516, 12032]
Open Access
Abstract: The dilute magnetic semiconductors have promise in spin-based electronics applications due to their potential for ferromagnetic order at room temperature, and various unique switching and spin-dependent conductivity properties. However, the precise mechanism by which the transition-metal doping produces ferromagnetism has been controversial. Here we have studied a dilute magnetic semiconductor (5% manganese-doped gallium arsenide) with Bragg-reflection standing-wave hard X-ray angle-resolved photoemission spectroscopy, and resolved its electronic structure into element- and momentum- resolved components. The measured valence band intensities have been projected into element-resolved components using analogous energy scans of Ga 3d, Mn 2p, and As 3d core levels, with results in excellent agreement with element-projected Bloch spectral functions and clarification of the electronic structure of this prototypical material. This technique should be broadly applicable to other multi-element materials.
|
Aug 2018
|
|
