16 research outputs found
Electron-Beam-Induced ElasticâPlastic Transition in Si Nanowires
It is generally accepted that silicon nanowires (Si NWs)
exhibit
linear elastic behavior until fracture without any appreciable plastic
deformation. However, the plasticity of Si NWs can be triggered under
low strain rate inside the transmission electron microscope (TEM).
In this report, two in situ TEM experiments were conducted to investigate
the electron-beam (e-beam) effect on the plasticity of Si NWs. An
e-beam illuminating with a low current intensity would result in the
bond re-forming processes, achieving the plastic deformation with
a bent strain over 40% in Si NWs near the room temperature. In addition,
an effective method was proposed to shape the Si NWs, where an e-beam-induced
elasticâplastic (EâP) transition took place
Electron-Beam-Induced ElasticâPlastic Transition in Si Nanowires
It is generally accepted that silicon nanowires (Si NWs)
exhibit
linear elastic behavior until fracture without any appreciable plastic
deformation. However, the plasticity of Si NWs can be triggered under
low strain rate inside the transmission electron microscope (TEM).
In this report, two in situ TEM experiments were conducted to investigate
the electron-beam (e-beam) effect on the plasticity of Si NWs. An
e-beam illuminating with a low current intensity would result in the
bond re-forming processes, achieving the plastic deformation with
a bent strain over 40% in Si NWs near the room temperature. In addition,
an effective method was proposed to shape the Si NWs, where an e-beam-induced
elasticâplastic (EâP) transition took place
Electron-Beam-Induced ElasticâPlastic Transition in Si Nanowires
It is generally accepted that silicon nanowires (Si NWs)
exhibit
linear elastic behavior until fracture without any appreciable plastic
deformation. However, the plasticity of Si NWs can be triggered under
low strain rate inside the transmission electron microscope (TEM).
In this report, two in situ TEM experiments were conducted to investigate
the electron-beam (e-beam) effect on the plasticity of Si NWs. An
e-beam illuminating with a low current intensity would result in the
bond re-forming processes, achieving the plastic deformation with
a bent strain over 40% in Si NWs near the room temperature. In addition,
an effective method was proposed to shape the Si NWs, where an e-beam-induced
elasticâplastic (EâP) transition took place
Hyperdislocations in van der Waals Layered Materials
Dislocations
are one-dimensional line defects in three-dimensional crystals or
periodic structures. It is common that the dislocation networks made
of interactive dislocations be generated during plastic deformation.
In van der Waals layered materials, the highly anisotropic nature
facilitates the formation of such dislocation networks, which is critical
for the friction or exfoliation behavior for these materials. By transmission
electron microscopy analysis, we found the topological defects in
such dislocation networks can be perfectly rationalized in the framework
of traditional dislocation theory, which we applied the name âhyperdislocationsâ.
Due to the strong pinning effect of hyperdislocations, the state of
exfoliation can be easily triggered by 1° twisting between two
layers, which also explains the origin of disregistry and frictionlessness
for all of the superlubricants that are widely used for friction reduction
and wear protection
Elastic Properties of GaN Nanowires: Revealing the Influence of Planar Defects on Youngâs Modulus at Nanoscale
The elastic properties of gallium nitride (GaN) nanowires
with different structures were investigated by in situ electron microscopy
in this work. The electric-field-induced resonance method was utilized
to reveal that the single crystalline GaN nanowires, along [120] direction,
had the similar Youngâs modulus as the bulk value at the diameter
ranging 92â110 nm. Meanwhile, the elastic behavior of the obtuse-angle
twin (OT) GaN nanowires was disclosed both by the in situ SEM resonance
technique and in situ transmission electron microscopy tensile test
for the first time. Our results showed that the average Youngâs
modulus of these OT nanowires was greatly decreased to about 66 GPa
and indicated no size dependence at the diameter ranging 98â171
nm. A quantitative explanation for this phenomenon is proposed based
on the rules of mixtures in classical mechanics. It is revealed that
the elastic modulus of one-dimensional nanomaterials is dependent
on the relative orientations and the volume fractions of the planar
defects
Elastic Properties of GaN Nanowires: Revealing the Influence of Planar Defects on Youngâs Modulus at Nanoscale
The elastic properties of gallium nitride (GaN) nanowires
with different structures were investigated by in situ electron microscopy
in this work. The electric-field-induced resonance method was utilized
to reveal that the single crystalline GaN nanowires, along [120] direction,
had the similar Youngâs modulus as the bulk value at the diameter
ranging 92â110 nm. Meanwhile, the elastic behavior of the obtuse-angle
twin (OT) GaN nanowires was disclosed both by the in situ SEM resonance
technique and in situ transmission electron microscopy tensile test
for the first time. Our results showed that the average Youngâs
modulus of these OT nanowires was greatly decreased to about 66 GPa
and indicated no size dependence at the diameter ranging 98â171
nm. A quantitative explanation for this phenomenon is proposed based
on the rules of mixtures in classical mechanics. It is revealed that
the elastic modulus of one-dimensional nanomaterials is dependent
on the relative orientations and the volume fractions of the planar
defects
Impact of Polar Edge Terminations of the Transition Metal Dichalcogenide Monolayers during Vapor Growth
The
polar edges of two-dimensional monolayer transition metal dichalcogenides
(TMD) and their alloys are examined by combined theoretical (density
functional theory) and experimental approaches. For these polar edges,
the growth reaction energies between different edge terminations are
considered instead of the surface free energies. Due to different
energy evolutions during growth on the zigzag edges between MoS<sub>2</sub> and WS<sub>2</sub>, the S-ZZ edges in the WS<sub>2</sub> monolayer
flakes more easily decompose into sawtooth-like edges in M-ZZ type
as compared to the MoS<sub>2</sub> monolayer; thus, the hexagonal
morphology can be seen more often in WS<sub>2</sub>. Moreover, the
observed anisotropic short-range order in the MoS<sub>2</sub>/WS<sub>2</sub> alloys is originated from the freezed edge configurations
during growth, explainable by the growth kinetics and thermodynamics
of the Mo-ZZ-edges. The determination of the growing edge terminations
is of great importance for the controllable synthesis of the emergent
two-dimensional TMD materials
Charge Transport in MoS<sub>2</sub>/WSe<sub>2</sub> van der Waals Heterostructure with Tunable Inversion Layer
Despite numerous
studies on two-dimensional van der Waals heterostructures,
a full understanding of the charge transport and photoinduced current
mechanisms in these structures, in particular, associated with charge
depletion/inversion layers at the interface remains elusive. Here,
we investigate transport properties of a prototype multilayer MoS<sub>2</sub>/WSe<sub>2</sub> heterojunction <i>via</i> a tunable
charge inversion/depletion layer. A charge inversion layer was constructed
at the surface of WSe<sub>2</sub> due to its relatively low doping
concentration compared to that of MoS<sub>2</sub>, which can be tuned
by the back-gate bias. The depletion region was limited within a few
nanometers in the MoS<sub>2</sub> side, while charges are fully depleted
on the whole WSe<sub>2</sub> side, which are determined by Raman spectroscopy
and transport measurements. Charge transport through the heterojunction
was influenced by the presence of the inversion layer and involves
two regimes of tunneling and recombination. Furthermore, photocurrent
measurements clearly revealed recombination and space-charge-limited
behaviors, similar to those of the heterostructures built from organic
semiconductors. This contributes to research of various other types
of heterostructures and can be further applied for electronic and
optoelectronic devices
Novel Selective Estrogen Receptor Downregulators (SERDs) Developed against Treatment-Resistant Breast Cancer
Resistance to the
selective estrogen receptor modulator tamoxifen
and to aromatase inhibitors that lower circulating estradiol occurs
in up to 50% of patients, generally leading to an endocrine-independent
ER+ phenotype. Selective ER downregulators (SERDs) are able to ablate
ER and thus, theoretically, to prevent survival of both endocrine-dependent
and -independent ER+ tumors. The clinical SERD fulvestrant is hampered
by intramuscular administration and undesirable pharmacokinetics.
Novel SERDs were designed using the 6-OH-benzothiophene (BT) scaffold
common to arzoxifene and raloxifene. Treatment-resistant (TR) ER+
cell lines (MCF-7:5C and MCF-7:TAM1) were used for optimization, followed
by validation in the parent endocrine-dependent cell line (MCF-7:WS8),
in 2D and 3D cultures, using ERα in-cell westerns, ERE-luciferase,
and cell viability assays, with <b>2</b> (GDC-0810/ARN-810)
used for comparison. Two BT SERDs with superior in vitro activity
to <b>2</b> were studied for bioavailability and shown to cause
regression of a TR, endocrine-independent ER+ xenograft superior to
that with <b>2</b>
<i>In Situ</i> Observations of Free-Standing Graphene-like Mono- and Bilayer ZnO Membranes
ZnO in its many forms, such as bulk, thin films, nanorods, nanobelts, and quantum dots, attracts significant attention because of its exciting optical, electronic, and magnetic properties. For very thin ZnO films, predictions were made that the bulk wurtzite ZnO structure would transit to a layered graphene-like structure. Graphene-like ZnO layers were later confirmed when supported over a metal substrate. However, the existence of free-standing graphene-like ZnO has, to the best of our knowledge, not been demonstrated. In this work, we show experimental evidence for the <i>in situ</i> formation of free-standing graphene-like ZnO mono- and bilayer ZnO membranes suspended in graphene pores. Local electron energy loss spectroscopy confirms the membranes comprise only Zn and O. Image simulations and supporting analysis confirm that the membranes are graphene-like ZnO. Graphene-like ZnO layers are predicted to have a wide band gap and different and exciting properties as compared to other ZnO structures