5 research outputs found
Visible Surface Plasmon Modes in Single Bi<sub>2</sub>Te<sub>3</sub> Nanoplate
Searching for new plasmonic building
blocks which offer tunability
and design flexibility beyond noble metals is crucial for advancing
the field of plasmonics. Herein, we report that solution-synthesized
hexagonal Bi<sub>2</sub>Te<sub>3</sub> nanoplates, in the absence
of grating configurations, can exhibit multiple plasmon modes covering
the entire visible range, as observed by transmission electron microscopy
(TEM)-based electron energy-loss spectroscopy (EELS) and cathodoluminescence
(CL) spectroscopy. Moreover, different plasmon modes are observed
in the center and edge of the single Bi<sub>2</sub>Te<sub>3</sub> nanoplate
and a breathing mode is discovered for the first time in a non-noble
metal. Theoretical calculations show that the plasmons observed in
the visible range are mainly due to strong spin–orbit coupling
induced metallic surface states of Bi<sub>2</sub>Te<sub>3</sub>. The
versatility of shape- and size-engineered Bi<sub>2</sub>Te<sub>3</sub> nanocrystals suggests exciting possibilities in plasmonics-enabled
technology
Molecular Alignment and Electronic Structure of <i>N</i>,<i>N</i>′‑Dibutyl-3,4,9,10-perylene-tetracarboxylic-diimide Molecules on MoS<sub>2</sub> Surfaces
The
molecular orientation of organic semiconductors on a solid
surface could be an indispensable factor to determine the electrical
performance of organic-based devices. Despite its fundamental prominence,
a clear description of the emergent two-dimensional layered material–organic
interface is not fully understood yet. In this study, we reveal the
molecular alignment and electronic structure of thermally deposited <i>N</i>,<i>N</i>′-dibutyl-3,4,9,10-perylene-dicarboximide
(PTCDI-C4) molecules on natural molybdenum disulfide (MoS<sub>2</sub>) using near-edge X-ray absorption fine structure spectroscopy (NEXAFS).
The average tilt angle determination reveals that the anisotropy in
the π* symmetry transition of the carbon <i>K</i>-edge
(284–288 eV range) is present at the sub-monolayer regime.
Supported by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron
spectroscopy (XPS), and resonant photoemission spectroscopy (RPES)
measurements, we find that our spectroscopic measurements indicate
a weak charge transfer established at the PTCDI-C4/MoS<sub>2</sub> interface. Sterical hindrance due to the C4 alkyl chain caused tilting
of the molecular plane at the initial thin film deposition. Our result
shows a tunable interfacial alignment of organic molecules on transition
metal dichalcogenide surfaces effectively enhancing the electronic
properties of hybrid organic–inorganic heterostructure devices
Direct Observation of Room-Temperature Stable Magnetism in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> Heterostructures
Along with an unexpected conducting interface between nonmagnetic insulating perovskites LaAlO<sub>3</sub> and SrTiO<sub>3</sub> (LaAlO<sub>3</sub>/SrTiO<sub>3</sub>), striking
interfacial magnetisms have been observed in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures. Interestingly, the strength of the interfacial
magnetic moment is found to be dependent on oxygen partial pressures
during the growth process. This raises an important, fundamental question
on the origin of these remarkable interfacial magnetic orderings.
Here, we report a direct evidence of room-temperature stable magnetism
in a LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructure prepared
at high oxygen partial pressure by using element-specific soft X-ray
magnetic circular dichroism at both Ti L<sub>3,2</sub> and O K edges.
By combining X-ray absorption spectroscopy at both Ti L<sub>3,2</sub> and O K edges and first-principles calculations, we qualitatively
ascribe that this strong magnetic ordering with dominant interfacial
Ti<sup>3+</sup> character is due to the coexistence of LaAlO<sub>3</sub> surface oxygen vacancies and interfacial (Ti<sub>Al</sub>–Al<sub>Ti</sub>) antisite defects. On the basis of this new understanding,
we revisit the origin of the weak magnetism in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures prepared at low oxygen partial pressures.
Our calculations show that LaAlO<sub>3</sub> surface oxygen vacancies
are responsible for the weak magnetism at the interface. Our result
provides direct evidence on the presence of room-temperature stable magnetism and a novel perspective
to understand magnetic and electronic reconstructions at such strategic
oxide interfaces
Tailoring the Optical and Electronic Properties of 2D Hybrid Dion–Jacobson Copper Chloride Perovskites
The upsurge of low-dimensional Dion–Jacobson (DJ)
phase
perovskites has brought significant interest in view of their appealing
stability against harsh environmental conditions as well as their
promising performance in optoelectronic applications. Few reports
to date have concentrated on the fundamental relationship of fine-tuning
the control of diamine-based perovskite single crystals toward their
electronic properties and optical behaviors. Here, we demonstrate
that cationic control is proposed to regulate the role of hydrogen
bonding of organic ligands with the edge-sharing [CuCl6]4– octahedral layers, leading to strong differences
in the material excitonic profile and tunability of their electronic
properties. Interestingly, we observe a significant reduction of photoluminescence
intensity upon controlling the Cu2+/Cu+ proportion
in this hybrid system. According to the photoemission measurements,
variation in the oxidation states of Cu cations plays a crucial role
in stabilizing the diammonium-based perovskite geometric structure.
Interestingly, we find that the electronic signatures of the singlet
spin-state and high-energy region transition are not influenced by
the thermal effect, as probed by temperature-dependent X-ray absorption
spectroscopy (XAS) at elevated temperature. Density functional calculations
suggest that such an electronic difference originates from the hydrogen
bonding reduction that altered the magnitude of the octahedral distortion
within the DJ layered structure. As a result, the 3+NHC4H9NH3+ conformation
produces a non-negligible interaction toward tuning the optical and
electronic properties of DJ copper-based perovskites
The Mechanism of Electrolyte Gating on High‑<i>T</i><sub><i>c</i></sub> Cuprates: The Role of Oxygen Migration and Electrostatics
Electrolyte
gating is widely used to induce large carrier density
modulation on solid surfaces to explore various properties. Most of
past works have attributed the charge modulation to electrostatic
field effect. However, some recent reports have argued that the electrolyte
gating effect in VO<sub>2</sub>, TiO<sub>2</sub>, and SrTiO<sub>3</sub> originated from field-induced oxygen vacancy formation. This gives
rise to a controversy about the gating mechanism, and it is therefore
vital to reveal the relationship between the role of electrolyte gating
and the intrinsic properties of materials. Here, we report entirely
different mechanisms of electrolyte gating on two high-<i>T</i><sub><i>c</i></sub> cuprates, NdBa<sub>2</sub>Cu<sub>3</sub>O<sub>7−δ</sub> (NBCO) and Pr<sub>2–<i>x</i></sub>Ce<sub><i>x</i></sub>CuO<sub>4</sub> (PCCO), with
different crystal structures. We show that field-induced oxygen vacancy
formation in CuO chains of NBCO plays the dominant role, while it
is mainly an electrostatic field effect in the case of PCCO. The possible
reason is that NBCO has mobile oxygen in CuO chains, while PCCO does
not. Our study helps clarify the controversy relating to the mechanism
of electrolyte gating, leading to a better understanding of the role
of oxygen electro migration which is very material specific