398 research outputs found
Fabrication of nanofluidic chip for liquid TEM cell using parylene and silicon nitride direct bonding
No full textFor fabrication of a liquid cell for transmission electron microscope (TEM), it is important to achieve bonding of nanochannels with nanoscale thickness of adhesive layers, which requires extremely high flatness and clean interfaces. We fabricated a nanofluidic chip for liquid TEM using parylene-to-SiN direct bonding. A-few-hundred nanometer thick parylene layer was deposited on a SiN wafer and etched to pattern nanochannel and then was directly bonded to another silicon nitride wafer by surface activation and thermal bonding
Structural and quantum-state phase transitions in van der Waals layered materials
No full textVan der Waals layered transition metal dichalcogenides can exist in many different atomic and electronic phases. Such diverse polymorphisms not only provide a route for investigating novel topological states, such as quantum spin Hall insulators, superconductors and Weyl semimetals, but may also have applications in fields ranging from electronic and optical/ quantum devices to electrochemical catalysis. And the methods for triggering robust phase transitions between polymorphs are evolving and diversifying-several growth processes, high-pressure/strain methods, and optical, electronic and chemical treatments have been developed. Here, we discuss recent progress on phase transitions and the related physics in layered materials, and demonstrate unique features compared with conventional solid-state materials.
Regioselective Introduction of Heteroatoms at the C-8 Position of Quinoline N-Oxides: Remote C-H Activation Using N-Oxide as a Stepping Stone
No full textReported herein is the metal-catalyzed regioselective C-H functionalization of quinoline N-oxides at the 8-position: direct iodination and amidation were developed using rhodium and iridium catalytic systems, respectively. Mechanistic study of the amidation revealed that the unique regioselectivity is achieved through the smooth formation of N-oxide-chelated iridacycle and that an acid additive plays a key role in the rate-determining protodemetalation step. While this approach of remote C H activation using N-oxide as a directing group could readily be applied to a wide range of heterocyclic substrates under mild conditions with high functional group tolerance, an efficient synthesis of zinquin ester (a fluorescent zinc indicator) was demonstrated.11711741sciescopu
Topological magnon-polarons in honeycomb antiferromagnets with spin-flop transition
No full textWe theoretically investigate the thermal Hall transport of magnon-polarons in
a two-dimensional honeycomb antiferromagnetic insulator under the influence of
a perpendicular magnetic field, varying in strength. The application of a
perpendicular magnetic field induces a magnetic phase transition from the
collinear antiferromagnetic phase to the spin-flop phase, leading to a
significant alteration in Hall transport across the transition point. In this
paper, our focus is on the intrinsic contribution to thermal Hall transport
arising from the magnetoelastic interaction. To facilitate experimental
verification of our theoretical results, we present the dependence of thermal
Hall conductivity on magnetic field strength and temperature.Comment: 10 pages, 6 figure
Modified gap states in Fe/MgO/SrTiO3 interfaces studied with scanning tunneling microscopy
No full textThe geometric and electronic structures of Fe islands on MgO film layers were studied with scanning tunneling microscopy and spectroscopy. The MgO layers were grown on a Nb-doped single crystal SrTiO3 (100) surface. Deposited Fe atoms aggregate into islands, the height and diameter of which are about 2.5 and 9.4 nm respectively. Fe islands modify the electronic structure of MgO surface; a ring type depression in the scanning tunneling microscope topography appears by lowered local electron density of states around Fe islands. We find that adsorbed Fe atoms reduce the gap states of MgO layers around Fe islands, which is attributed to the reason for the depletion of the electronic density of states.close1
Phase Engineering of 2D Materials
No full textPolymorphic2D materials allow structural and electronic phaseengineering, which can be used to realize energy-efficient, cost-effective,and scalable device applications. The phase engineering covers notonly conventional structural and metal-insulator transitionsbut also magnetic states, strongly correlated band structures, andtopological phases in rich 2D materials. The methods used for thelocal phase engineering of 2D materials include various optical, geometrical,and chemical processes as well as traditional thermodynamic approaches.In this Review, we survey the precise manipulation of local phasesand phase patterning of 2D materials, particularly with ideal andversatile phase interfaces for electronic and energy device applications.Polymorphic 2D materials and diverse quantum materials with theirlayered, vertical, and lateral geometries are discussed with an emphasison the role and use of their phase interfaces. Various phase interfaceshave demonstrated superior and unique performance in electronic andenergy devices. The phase patterning leads to novel homo- and heterojunctionstructures of 2D materials with low-dimensional phase boundaries,which highlights their potential for technological breakthroughs infuture electronic, quantum, and energy devices. Accordingly, we encourageresearchers to investigate and exploit phase patterning in emerging2D materials.
Tunable Out-of-Plane Piezoelectricity in Thin-Layered MoTe2 by Surface Corrugation-Mediated Flexoelectricity
No full textPiezoelectricity crystallographically exists only in the in-plane direction in two-dimensional transition metal dichalcogenides. Here, we demonstrated flexoelectricity-tunable out-of-plane piezoelectricity in semiconducting 2H-MoTe2 flakes by creating surface corrugation. In particular, the strong out-of plane piezoelectricity and its spatial variation depending on local flexoelectricity was observed even though crystallographically there exists only in-plane piezoelectricity. Surface corrugation mediated flexoelectricity tuning can be applied to other two-dimensional or thin-layered materials and, furthermore, the results could provide useful information on the interweaving nature between mechanical stimulus and electric dipole in low-dimensional materials.
Post-patterning of an electronic homojunction in atomically thin monoclinic MoTe2
No full textMonoclinic group 6 transition metal dichalcogenides (TMDs) have been extensively studied for their intriguing 2D physics (e.g. spin Hall insulator) as well as for ohmic homojunction contacts in 2D device applications. A critical prerequisite for those applications is thickness control of the monoclinic 2D materials, which allows subtle engineering of the topological states or electronic bandgaps. Local thickness control enables the realization of clean homojunctions between different electronic states, and novel device operation in a single material. However, conventional fabrication processes, including chemical methods, typically produce non-homogeneous and relatively thick monoclinic TMDs, due to their distorted octahedral structures. Here, we report on a post-patterning technique using laser-irradiation to fabricate homojunctions between two different thickness areas in monoclinic MoTe2. A thickness-dependent electronic change from a metallic to semiconducting state, resulting in an electronic homojunction, was realized by the optical patterning of pristine MoTe2 flakes, and a pre-patterned device channel of monoclinic MoTe2 with a thickness-resolution of 5 nm. Our work provides insight on an optical post-process method for controlling thickness, as a promising approach for fabricating impurity-free 2D TMDs homojunction devices. © 2017 IOP Publishing Ltd3711sciescopu
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