Jiuxiang Dai

A feasible strategy to construct high-performance and low-power chemical vapor deposition-grown polycrystalline molybdenum ditelluride thin film transistors with solution-processed ternary Hf_0.5Zr_0.5O₂/HfAlO₂ high-k dielectric is demonstrated.

Abstract

Besides the widely investigated potential as alternative to silicon in microelectronics, semiconducting 2D transition metal dichalcogenides (TMDs) also show appealing prospects in thin film transistors (TFTs)-based applications, while still suffer from insufficient demonstration. Herein, the authors systematically report high-performance and low-power chemical vapor deposition-grown polycrystalline molybdenum ditelluride (MoTe₂) TFTs with solution-processed ternary Hf_0.5Zr_0.5O₂/HfAlO₂ high-k dielectric. Benefitting from the optimized high quality HfAlO₂ film synthesis and proper postannealing treatment, the constructed MoTe₂ TFTs exhibit a high mobility ≈27.24 cm² V⁻¹ S⁻¹, a current on/off ratio ≈6.43 × 10⁵, threshold voltage ≈−3.27 V, and subthreshold swing (SS) value ≈152.4 mV dec⁻¹, respectively. Moreover, by supplementing another solution-processed layer of ferroelectric Hf_0.5Zr_0.5O₂ to form double layer of HfAlO₂/Hf_0.5Zr_0.5O₂ dielectric, the device performance can be further improved with an ignorable hysteresis, increased mobility of ≈55.53 cm² V⁻¹ S⁻¹, and significantly reduced SS value of ≈110.16 mV dec⁻¹, respectively. The current investigation offers a feasible strategy to fabricate high-performance and low-power MoTe₂ TFTs for potential TMDs-based TFTs applications.

Abstract

Supported bilayer α-borophene (BL-α borophene) on Ag(111) substrate has been synthesized in recent experiments. Based on the experimentally observed quasi-planar C_6v B₃₆ (1), its monolayer assembly α⁺-borophene B₁₁ (P6/mmm) (2), and extensive global minimum searches augmented with density functional theory calculations, we predict herein freestanding BL-α⁺ borophenes B₂₂ (Cmmm) (3) and B₂₂ (C2/m) (4) which, as the most stable BL borophenes reported to date, are composed of interwoven boron triple chains as boron analogs of monolayer graphene (5) consisting of interwoven carbon single chains. The nearly degenerate eclipsed B₂₂ (3) and staggered B₂₂ (4) with the hexagonal hole density of η = 1/12 and interlayer bonding density of u = 1/4 appear to be two-dimensional semiconductors with the indirect band gaps of 0.952 and 1.144 eV, respectively. Detailed bonding analyses reveal one delocalized 12c-2e π bond over each hexagonal hole in both the B₂₂ (3) and B₂₂ (4), similar to the situation in monolayer graphene which contains one delocalized 6c-2e π bond over each C₆ hexagon. Furthermore, these BL-α⁺ borophenes appear to remain highly stable on Ag(111) substrate, presenting the possibility to form supported BL-α⁺ borophenes.

Schottky-contacted high-performance GaSb nanowires photodetectors are achieved by the surface decoration of lead-free all-inorganic perovskites. Benefiting from the expected Schottky barrier, the dark current is reduced to 2 pA, the I _light/I _dark ratio is improved to 10³ and the response time is reduced by more than 15 times under the illumination of a 1550 nm laser.

Abstract

The surface Fermi level pinning effect promotes the formation of metal-independent Ohmic contacts for the high-speed GaSb nanowires (NWs) electronic devices, however, it limits next-generation optoelectronic devices. In this work, lead-free all-inorganic perovskites with broad bandgaps and low work functions are adopted to decorate the surfaces of GaSb NWs, demonstrating the success in the construction of Schottky-contacts by surface engineering. Benefiting from the expected Schottky barrier, the dark current is reduced to 2 pA, the I _light/I _dark ratio is improved to 10³ and the response time is reduced by more than 15 times. Furthermore, a Schottky-contacted parallel array GaSb NWs photodetector is also fabricated by the contact printing technology, showing a higher photocurrent and a low dark current of 15 pA, along with the good infrared photodetection ability for a concealed target. All results guide the construction of Schottky-contacts by surface decorations for next-generation high-performance III–V NWs optoelectronics devices.

Intertube Excitonic Coupling

In article number 2104969, James Lloyd-Hughes and co-workers demonstrate strong intertube excitonic coupling in 1D van der Waals heterostructures comprising C/BN/MoS₂ core/shell/skin nanotubes. Remarkably, infrared excitation of excitons in the carbon nanotube core creates a prominent excitonic response in the visible range from the MoS₂ skin. Via classic analogies and a quantum model of the light–matter interaction these findings are assigned to intertube excitonic correlations.

Carbon Nanotubes

In article number 2108541, Chang Liu, Hui-Ming Cheng, and co-workers show that floating catalyst chemical vapor deposition (FCCVD) is an efficient technique that produces high-quality carbon nanotubes in tunable forms of powders, fibers, films, and vertically aligned arrays with intriguing physiochemical properties.

Nature Electronics, Published online: 09 March 2022; doi:10.1038/s41928-022-00734-w

Publication date: March 2022

Source: Materials Today, Volume 53

Author(s): Laurie Donaldson

Nature, Published online: 09 March 2022; doi:10.1038/s41586-021-04360-y

Nature, Published online: 09 March 2022; doi:10.1038/s41586-021-04323-3

Light: Science & Applications, Published online: 10 March 2022; doi:10.1038/s41377-022-00741-8

Although the research of 2D photocatalysts has made great progress in the past decades, there are still many challenges in understanding the deep relationship between the surface state and the reaction mechanism. The surface modification strategies and reaction mechanisms of 2D photocatalysts are reviewed, and some useful views are put forward for future research in this field.

Abstract

2D materials show many particular properties, such as high surface-to-volume ratio, high anisotropic degree, and adjustable chemical functionality. These unique properties in 2D materials have sparked immense interest due to their applications in photocatalytic systems, resulting in significantly enhanced light capture, charge-transfer kinetics, and surface reaction. Herein, the research progress in 2D photocatalysts based on varied compositions and functions, followed by specific surface modification strategies, is introduced. Fundamental principles focusing on light harvesting, charge separation, and molecular adsorption/activation in the 2D-material-based photocatalytic system are systemically explored. The examples described here detail the use of 2D materials in various photocatalytic energy-conversion systems, including water splitting, carbon dioxide reduction, nitrogen fixation, hydrogen peroxide production, and organic synthesis. Finally, by elaborating the challenges and possible solutions for developing these 2D materials, the review is expected to provide some inspiration for the future research of 2D materials used on efficient photocatalytic energy conversions.

Multiferroic Materials

In article number 2109144, Jae Hoon Kim, Je-Geun Park, and co-workers report a new exciton in multiferroic NiI₂, consisting of a 2D triangular lattice. This newly discovered exciton is not only magnetic but also quantum entangled. When an electron and hole combine via a transition between two quantum-entangled states, it produces a bright reddish light of 1.384 eV.

Biosensors

In article number 2108607, Miaomiao Yuan, Hossam Haick, and co-workers report an innovative, stretchable, skin-conformal, fast-response, microneedle, extended-gate field-effect transistor biosensor for real-time detection of sodium in interstitial fluids for minimally invasive health monitoring. High sensitivity, low limit of detection, excellent biocompatibility, and on-body mechanical stability are demonstrated. This platform can be integrated with a wireless-data transmitter and the Internet-of-Things cloud for real-time monitoring and long-term analysis.

Thin Films

When thinning down silicon films toward nanometer thickness, their thermal conductivity decreases dramatically. In article number 2108352, Klaas-Jan Tielrooij and co-workers report a combined experimental–theoretical study that shows that this is not the case for the layered semiconductor MoSe₂. For the thinnest MoSe₂ films, the decreasing thermal conductivity is compensated by low-energy, long-mean-free-path heat-carrying modes. These thin films furthermore exhibit efficient heat dissipation to air molecules.

Nature Nanotechnology, Published online: 10 March 2022; doi:10.1038/s41565-022-01076-6

npj 2D Materials and Applications, Published online: 08 March 2022; doi:10.1038/s41699-022-00297-6

A controllable Fe doping strategy is developed in centimeter-sized monolayer MoS₂ films with ultralow contact resistance. Excellent device performance featured with ultrahigh electron mobility and on/off current ratio is achieved, thanks to the ultralow electron effective mass. Unidirectional Fe-MoS₂ domains are prepared on 2 in. commercial c-plane sapphire, suggesting the feasibility of synthesizing wafer-scale single-crystal semiconductors with outstanding device performance.

Abstract

2D semiconductors are emerging as plausible candidates for next-generation “More-than-Moore” nanoelectronics to tackle the scaling challenge of transistors. Wafer-scale 2D semiconductors, such as MoS₂ and WS₂, have been successfully synthesized recently; nevertheless, the absence of effective doping technology fundamentally results in energy barriers and high contact resistances at the metal–semiconductor interfaces, and thus restrict their practical applications. Herein, a controllable doping strategy in centimeter-sized monolayer MoS₂ films is developed to address this critical issue and boost the device performance. The ultralow contact resistance and perfect Ohmic contact with metal electrodes are uncovered in monolayer Fe-doped MoS₂, which deliver excellent device performance featured with ultrahigh electron mobility and outstanding on/off current ratio. Impurity scattering is suppressed significantly thanks to the ultralow electron effective mass and appropriate doping site. Particularly, unidirectionally aligned monolayer Fe-doped MoS₂ domains are prepared on 2 in. commercial c-plane sapphire, suggesting the feasibility of synthesizing wafer-scale 2D single-crystal semiconductors with outstanding device performance. This work presents the potential of high-performance monolayer transistors and enables further device downscaling and extension of Moore's law.

Synergistic heavy hole doping and thermal conductivity reduction are demonstrated in polycrystalline SnSe by nonequilibrium isovalent Te ion substitution. The weak SnTe bonds formed in layered Sn(Se_{1− x} Te _x ) doped with large-size Te ions not only increases the hole-donating Sn vacancies but also enhances the phonon scattering, resulting in the degenerate hole conduction and ultra-low lattice thermal conductivity of SnSe.

Abstract

Tin mono-selenide (SnSe) exhibits the world record of thermoelectric conversion efficiency ZT in the single crystal form, but the performance of polycrystalline SnSe is restricted by low electronic conductivity (σ) and high thermal conductivity (κ), compared to those of the single crystal. Here an effective strategy to achieve high σ and low κ simultaneously is reported on p-type polycrystalline SnSe with isovalent Te ion substitution. The nonequilibrium Sn(Se_{1− x} Te _x ) solid solution bulks with x up to 0.4 are synthesized by the two-step process composed of high-temperature solid-state reaction and rapid thermal quenching. The Te ion substitution in SnSe realizes high σ due to the 10³-times increase in hole carrier concentration and effectively reduced lattice κ less than one-third at room temperature. The large-size Te ion in Sn(Se_{1− x} Te _x ) forms weak SnTe bonds, leading to the high-density formation of hole-donating Sn vacancies and the reduced phonon frequency and enhanced phonon scattering. This result—doping of large-size ions beyond the equilibrium limit—proposes a new idea for carrier doping and controlling thermal properties to enhance the ZT of polycrystalline SnSe.