Jiuxiang Dai

Nature Electronics, Published online: 27 December 2021; doi:10.1038/s41928-021-00687-6

An integrated circuit fabricated using industry-standard 40 nm complementary metal–oxide–semiconductor technology can combine silicon quantum devices, digital addressing and analogue multiplexed dispersive readout electronics.

A new efficient method to fabricate high-quality and large-area suspended two-dimensional (2D) materials is developed. The superior properties of suspended samples over supported ones are proved by Raman spectra, photoluminescence spectra, second harmonic generation, low energy electron microscopy as well as mobility characterization. This work could facilitate the studies of the intrinsic properties of 2D materials and the applications of active 2D nano devices.

Abstract

Two-dimensional (2D) materials are highly sensitive to substrates, interfaces, and the surrounding environments. Suspended 2D materials are free from substrate-induced effects, thus an ideal approach to study their intrinsic properties. However, it is very challenging to prepare large-area suspended 2D materials with high efficiency. Here we report a universal method, based on pretreatments of densely patterned hole array substrates with either oxygen-plasma or gold film deposition, to prepare large-area suspended mono- and few-layer 2D materials. Multiple structural, optical, and electrical characterization tools were used to fully evaluate the improved performance of various suspended 2D layers. Some of these observations reported in this study are: (1) Observation of a new Raman low frequency mode for the suspended MoS₂; (2) Significantly stronger photoluminescence (PL) and second harmonic generation (SHG) signals of suspended WSe₂, which enables the study of new optical transition processes; (3) The low energy electron diffraction pattern on suspended MoS₂ also exhibits much sharper spots than that on the supported area; and (4) The mobility of suspended graphene device approaches 300 000 cm² V⁻¹ s⁻¹, which is desirable to explore the intrinsic properties of graphene. This work provides an innovative and efficient route for fabricating suspended 2D materials, and we expect that it can be broadly used for studying intrinsic properties of 2D materials and in applications of hybrid active nanophotonic and electronic devices.

Publication date: 15 March 2022

Source: Journal of Hazardous Materials, Volume 426

Author(s): Xuezheng Guo, Yanqiao Ding, Xi Yang, Bingsheng Du, Chengjiu Zhao, Chengyao Liang, Yi Ou, Delin Kuang, Zhilin Wu, Yong He

Nature Chemistry, Published online: 23 December 2021; doi:10.1038/s41557-021-00868-y

Bilayer borophene, predicted to be stabilized by interlayer linkages, has now been grown by molecular beam epitaxy on copper and silver surfaces in two independent studies. The growth substrate and temperature are found to influence the lattice structures formed.

Nature Materials, Published online: 23 December 2021; doi:10.1038/s41563-021-01184-z

Ferrimagnets and topological insulators offer new platforms for utilizing the spin of electrons in functional materials.

Nature Materials, Published online: 23 December 2021; doi:10.1038/s41563-021-01112-1

Heterogeneous microscale contacts between molybdenum disulfide and graphene or hexagonal boron nitride layers demonstrate ultralow friction independent of their relative orientation with residual drag that originates from edge effects.

Nature Materials, Published online: 23 December 2021; doi:10.1038/s41563-021-01171-4

Integration of memristors in a chain of nano-constriction spintronic oscillators allows for individual control of oscillation frequencies and emerging synchronization patterns. The control of such synchronization could enable learning through association like neurons in the brain.

Nature Electronics, Published online: 23 December 2021; doi:10.1038/s41928-021-00685-8

Sulfur vacancies in monolayer molybdenum disulfide can be passivated using an oxygen-incorporated chemical vapour deposition technique, which results in less n-type doping, enhanced photoluminescence and decreased contact resistance compared with growth without oxygen.

2D van der Waals nanosheets from molecular intercalation-assisted electrochemical exfoliation are assembled to form building blocks for wafer-scale electronics. By using graphene, MoS₂ and single-walled carbon nanotube, and oxidized HfS₂ as metallic, n-type and p-type semiconducting, and insulating building blocks, various devices are realized including field-effect transistors, photodetectors, p–n diodes, and complementary logic gates.

Abstract

2D van der Waals (vdW) materials have been considered as potential building blocks for use in fundamental elements of electronic and optoelectronic devices, such as electrodes, channels, and dielectrics, because of their diverse and remarkable electrical properties. Furthermore, two or more building blocks of different electronic types can be stacked vertically to generate vdW heterostructures with desired electrical behaviors. However, such fundamental approaches cannot directly be applied practically because of issues such as precise alignment/positioning and large-quantity material production. Here, these limitations are overcome and wafer-scale vdW heterostructures are demonstrated by exploiting the lateral and vertical assembly of solution-processed 2D vdW materials. The high exfoliation yield of the molecular intercalation-assisted approach enables the production of micrometer-sized nanosheets in large quantities and its lateral assembly in a wafer-scale via vdW interactions. Subsequently, the laterally assembled vdW thin-films are vertically assembled to demonstrate various electronic device applications, such as transistors and photodetectors. Furthermore, multidimensional vdW heterostructures are demonstrated by integrating 1D carbon nanotubes as a p-type semiconductor to fabricate p–n diodes and complementary logic gates. Finally, electronic devices are fabricated via inkjet printing as a lithography-free manner based on the stable nanomaterial dispersions.

The optimized two-dimensional material (2DM) static random-access memory designed with state-of-the-art contact resistance leads to excellent stability and operation speed at the 1-nm node. Applying the nanosheet gate-all-around structure to 2DMs further improves speed and area density, showing the feasible scaling path beyond the Si technology. The process challenges of 2DM nanosheet field-effect transistors are also discussed.

Abstract

2D transition-metal dichalcogenide semiconductors, such as MoS₂ and WSe₂, with adequate bandgaps are promising channel materials for ultrascaled logic transistors. This scalability study of 2D material (2DM)-based field-effect transistor (FET) and static random-access memory (SRAM) cells analyzing the impact of layer thickness reveals that the monolayer 2DM FET with superior electrostatics is beneficial for its ability to mitigate the read–write conflict in an SRAM cell at scaled technology nodes (1–2.1 nm). Moreover, the monolayer 2DM SRAM exhibits lower cell read access time and write time than the bilayer and trilayer 2DM SRAM cells at fixed leakage power. This simulation predicts that the optimization of 2DM SRAM designed with state-of-the-art contact resistance, mobility, and equivalent oxide thickness leads to excellent stability and operation speed at the 1-nm node. Applying the nanosheet (NS) gate-all-around (GAA) structure to 2DM further reduces cell read access time and write time and improves the area density of the SRAM cells, demonstrating a feasible scaling path beyond Si technology using 2DM NSFETs. In addition to the device design, the process challenges for 2DM NSFETs, including the cost-effective stacking of 2DM layers, formation of electrical contacts, suspended 2DM channels, and GAA structures, are also discussed.

Publication date: April 2022

Source: Materials Today, Volume 54

Author(s): Hussein O. Badr, Tarek El-Melegy, Michael Carey, Varun Natu, Mary Q. Hassig, Craig Johnson, Qian Qian, Christopher Y. Li, Kateryna Kushnir, Erika Colin-Ulloa, Lyubov V. Titova, Julia L. Martin, Ronald L. Grimm, Rahul Pai, Vibha Kalra, Avishek Karmakar, Anthony Ruffino, Stefan Masiuk, Kun Liang, Michael Naguib

We report the fabrication and the electrical characterization of back-gated field effect transistors with a black phosphorus (BP) channel. We show that the hysteresis of the transfer characteristic, due to intrinsic defects, can be exploited to realize non-volatile memories. We demonstrate that gate voltage pulses allow to trap and store charge inside the defect states, which enable memory devices with endurance over 200 cycles and retention longer than 30 min. We show that the use of a protective poly(methyl methacrylate) layer, positioned on top of the BP channel, does not affect the electrical properties of the device but avoids the degradation caused by the exposure to air.

Quantum-entangled magnetic excitons develop in a triangular multiferroic NiI₂ when it goes through a second phase transition at low temperatures. In this graph of optical absorption data, the bright regions indicate where two exciton-related peaks appear below the second magnetic phase transition as indicated by the dashed line. The many-body calculations show that this exciton arises from a transition between two quantum-entangled states of Zhang–Rice triplet and Zhang–Rice singlet states.

Abstract

Matter–light interaction is at the center of diverse research fields from quantum optics to condensed matter physics, opening new fields like laser physics. A magnetic exciton is one such rare example found in magnetic insulators. However, it is relatively rare to observe that external variables control matter-light interaction. Here, it is reported that the broken inversion symmetry of multiferroicity can act as an external knob enabling magnetic excitons in the van der Waals antiferromagnet NiI₂. It is further discovered that this magnetic exciton arises from a transition between Zhang–Rice-triplet and Zhang–Rice-singlet fundamentally quantum-entangled states. This quantum entanglement produces an ultrasharp optical exciton peak at 1.384 eV with a 5 meV linewidth. The work demonstrates that NiI₂ is 2D magnetically ordered with an intrinsically quantum-entangled ground state.

A new high-T _c superconducting state emerges in 2H-TaS₂ under high pressure. The T _c enhances rapidly and reaches a maximum of ≈16.4 K at ≈157.4 GPa, which sets a new record for transition metal dichalcogenides (TMDs). It is the first time this remarkable superconducting state has been found in TMDs. The result brings a new broad perspective on layered materials.

Abstract

Pressure has always been an effective method for uncovering novel phenomena and properties in condensed matter physics. Here, an electrical transport study is carried on 2H-TaS₂ up to ≈208 GPa, and an unexpected superconducting state (SC-II) emerging around 86.1 GPa with an initial critical temperature (T _c) of 9.6 K is found. As pressure increases, the T _c enhances rapidly and reaches a maximum of 16.4 K at 157.4 GPa, which sets a new record for transition metal dichalcogenides (TMDs). The original superconducting state (SC-I) is found to be re-enhanced above 100 GPa after the recession around 10 GPa, and coexists with SC-II to the highest pressure applied in this work. In situ high-pressure X-ray diffraction and Hall effect measurements reveal that the occurrence of SC-II is accompanied by a structural modification and a concurrent enhancement of hole carrier density. The new high-T _c superconducting state in 2H-TaS₂ can be attributed to the change of the electronic states near the Fermi surface, owing to pressure-induced interlayer modulation. It is the first time finding this remarkable superconducting state in TMDs, which not only brings a new broad of perspective on layered materials but also expands the field of pressure-modified superconductivity.

In this study, flexible n-type Bi₂Te₃-based thin-films are successfully prepared through facile thermal diffusion method and further induce Te/Bi₂Te₃ heterojunctions and energy filtering effect at the Te/Bi₂Te₃ interfaces to optimize the thermoelectric performance through tuning the diffusion temperature.

Abstract

Flexible Bi₂Te₃-based thermoelectric devices can function as power generators for powering wearable electronics or chip-sensors for internet-of-things. However, the unsatisfied performance of n-type Bi₂Te₃ flexible thin films significantly limits their wide application. In this study, a novel thermal diffusion method is employed to fabricate n-type Te-embedded Bi₂Te₃ flexible thin films on flexible polyimide substrates, where Te embeddings can be achieved by tuning the thermal diffusion temperature and correspondingly result in an energy filtering effect at the Bi₂Te₃/Te interfaces. The energy filtering effect can lead to a high Seebeck coefficient ≈160 µV K⁻¹ as well as high carrier mobility of ≈200 cm² V⁻¹ s⁻¹ at room-temperature. Consequently, an ultrahigh room-temperature power factor of 14.65 µW cm⁻¹ K⁻² can be observed in the Te-embedded Bi₂Te₃ flexible thin films prepared at the diffusion temperature of 623 K. A thermoelectric sensor is also assembled through integrating the n-type Bi₂Te₃ flexible thin films with p-type Sb₂Te₃ counterparts, which can fast reflect finger-touch status and demonstrate the applicability of as-prepared Te-embedded Bi₂Te₃ flexible thin films. This study indicates that the thermal diffusion method is an effective way to fabricate high-performance and applicable flexible Te-embedded Bi₂Te₃-based thin films.

Nature Electronics, Published online: 21 December 2021; doi:10.1038/s41928-021-00684-9

Measurements of inkjet-printed thin-film devices made from titanium carbide MXene (metal), molybdenum disulfide (semiconductor) and few-layer graphene (semimetal) clarify the charge transport mechanisms of the devices and highlight the role of inter-flake and intra-flake processes.