Nanowerk April 11, 2024 The exact role of h-BN encapsulation in relation to the internal defects of 2D semiconductors in hexagonal boron nitride (h-BN) remains unclear. An international team of researchers (South Korea, Japan) reported that h-BN encapsulation greatly removes the defect-related gap states by stabilizing the chemisorbed oxygen molecules onto the defects of monolayer tungsten disulfide (WS2) crystals. Studies showed that h-BN encapsulation prevented the desorption of oxygen molecules over various excitation and ambient conditions, resulting in a greatly lowered and stabilized free electron density in monolayer WS2 crystals. This suppressed the exciton annihilation processes by two orders of […]
Tag Archives: 2D materials
Researchers control quantum properties of 2D materials with tailored light
Phys.org April 15, 2024 The stacking and twisting of atom-thin structures with matching crystal symmetry has provided a unique way to create new superlattice structures in which new properties emerge. An international team of researchers (Germany, Spain, USA – SLAC National Accelerator Laboratory, Stanford University) demonstrated a tailored light-wave-driven analogue to twisted layer stacking. Tailoring the spatial symmetry of the light waveform to that of the lattice of a hexagonal boron nitride monolayer and then twisting this waveform resulted in optical control of time-reversal symmetry breaking and the realization of the topological Haldane model in a laser-dressed two-dimensional insulating crystal. […]
New method enables synthesis of hundreds of new 2D materials
Phys.org March 14, 2024 MXenes are a family of 2D materials typically formed by etching the A element from a parent MAX phase. Computational screening for other 3D precursors suitable for such exfoliation is challenging because of the intricate chemical processes involved. Researchers in Sweden proposed a theoretical approach for predicting 2D materials formed through chemical exfoliation under acidic conditions by identifying 3D materials amenable for selective etching. From a dataset of 66,643 3D materials, they identified 119 potentially exfoliable candidates, within several materials families. To corroborate the method, they chose a material distinctly different from MAX phases, in terms […]
New class of 2D material displays stable charge density wave at room temperature
Phys.org March 1, 2024 Charge density waves are emergent quantum states that spontaneously reduce crystal symmetry, drive metal-insulator transitions, and precede superconductivity. In low-dimensions, distinct quantum states arise, however, thermal fluctuations and external disorder destroy long-range order. A team of researchers in the US (University of Michigan, Harvard University) has stabilized ordered 2D charge density waves through endotaxial synthesis of confined monolayers of 1T-TaS2. Specifically, an ordered incommensurate charge density wave (oIC-CDW) was realized in 2D with dramatically enhanced amplitude and resistivity. By enhancing CDW order, the hexatic nature of charge density waves became observable. Upon heating via in-situ TEM, […]
New adhesive tape picks up and sticks down 2D materials as easily as child’s play
Science Daily February 9, 2024 The use of graphene and other 2D materials to create electronic and optoelectronic devices has been limited by the lack of effective large-area transfer processes. An international team of researchers (South Korea, Japan) has developed a method that uses functional tapes with adhesive forces controlled by ultraviolet light. The adhesion of the tape was optimized for the transfer of monolayer graphene, providing a yield of over 99%. Once detached from the growth substrate, the graphene/tape stack enables easy transfer of graphene to the desired target substrate. The method could be used to transfer other 2D […]
From a five-layer graphene sandwich, a rare electronic state emerges
Science Daily October 18, 2023 Multiferroics have multifunctional electrical and magnetic device applications. Two-dimensional materials with honeycomb lattices offer opportunities to engineer unconventional multiferroicity. Orbital multiferroics could offer strong valley–magnetic couplings and large responses to external fields—enabling device applications such as multiple-state memory elements and electric control of the valley and magnetic states. An international team of researchers (USA – MIT, Harvard University, Japan) has shown orbital multiferroicity in Penta layer rhombohedral graphene. They observed anomalous Hall signals Rxy with an exceptionally large Hall angle and orbital magnetic hysteresis at hole doping. There were four such states with different valley […]
Nanosheet technology developed to boost energy storage dielectric capacitors
Science Daily July 4, 2023 Dielectric capacitors can become ideal, safe energy storage devices. However, they yield rather low energy densities compared with other energy storage devices such as batteries and supercapacitors. Researchers in Japan designed ultrahigh energy storage capacitors using two-dimensional (2D) high-κ dielectric perovskites (Ca2Nam–3NbmO3m+1; m = 3–6). Individual Ca2Nam–3NbmO3m+1 nanosheets exhibited an ultrahigh dielectric strength even in the monolayer form, which exceeded those of conventional dielectric materials. Multilayer stacked nanosheet capacitors exhibited ultrahigh energy densities, high efficiencies (>90%), excellent reliability (>107 cycles), and temperature stability (−50–300 °C); the maximum energy density was much higher than those of […]
Blocking radio waves and electromagnetic interference with the flip of a switch
Phys.org January 16, 2023 Foam materials can adjust the reflection and absorption of microwaves, enabling a tunable electromagnetic interference shielding capability. But their thickness of several millimetres hinders their application in integrated electronics. Researchers at Drexel University have developed a method for modulating the reflection and absorption of incident electromagnetic waves using various submicrometre-thick MXene thin films. The reversible tunability of electromagnetic interference shielding effectiveness was realized by electrochemically driven ion intercalation and de-intercalation; this resulted in charge transfer efficiency with different electrolytes, accompanied by expansion and shrinkage of the MXene layer spacing. They demonstrated an irreversible electromagnetic interference shielding […]
Unexpected speed-dependent friction with graphene
Nanowerk, December 6, 2022 Graphene is being examined with a view to potential use as a lubricating layer. If it is applied to a platinum surface, it has a significant impact on the measurable friction forces. An international team of researchers (Israel, Switzerland) has reported that, in this instance, the friction depends on the speed at which the tip of an atomic force microscope (AFM) is moved across the surface. In conjunction with the platinum substrate, graphene no longer forms only the hexagonal honeycomb pattern of carbon atoms and instead forms Moiré superlattices. The surface is then no longer completely […]
The answer is in the sheets: 2D nanosheets as anodes in Li-ion batteries
Phys.org October 31, 2022 2D nanostructures based on transition-metal diborides (TMDs) are theoretically predicted to possess an exceptionally high rate and long cycling stability for Li-ion storage owing to the intrinsic presence of boron honeycomb planes and multivalent transition-metal atoms. An international team of researchers (Japan, India) investigated the Li-ion storage potential of the TMD-based nanostructure–titanium diboride (TiB2)-based hierarchical nanosheets (THNS). They demonstrated that THNS can be utilized as a high-rate anode material for Li-ion battery (LIB) and that a high discharge capacity can be obtained at a current rate of 0.025 A g1– galvanostatic charge/discharge. They demonstrated that the […]