Chen Luo

Zeeman splitting and dynamical mass generation in Dirac semimetal ZrTe5

Dirac semimetals have attracted extensive attentions in recent years. It has been theoretically suggested that many-body interactions may drive exotic phase transitions, spontaneously generating a Dirac mass for the nominally massless Dirac electrons. So far, signature of interaction-driven transition has been lacking. In this work, we report high-magnetic-field transport measurements of the Dirac semimetal candidate ZrTe5. Owing to the large g factor in ZrTe5, the Zeeman splitting can be observed at magnetic field as low as 3u2009T. Most prominently, high pulsed magnetic field up to 60u2009T drives the system into the ultra-quantum limit, where we observe abrupt changes in the magnetoresistance, indicating field-induced phase transitions. This is interpreted as an interaction-induced spontaneous mass generation of the Dirac fermions, which bears resemblance to the dynamical mass generation of nucleons in high-energy physics. Our work establishes Dirac semimetals as ideal platforms for investigating emerging correlation effects in topological matters.

Ultrafast Dynamic Pressure Sensors Based on Graphene Hybrid Structure

Mechanical flexible electronic skin has been focused on sensing various physical parameters, such as pressure and temperature. The studies of material design and array-accessible devices are the building blocks of strain sensors for subtle pressure sensing. Here, we report a new and facile preparation of a graphene hybrid structure with an ultrafast dynamic pressure response. Graphene oxide nanosheets are used as a surfactant to prevent graphene restacking in aqueous solution. This graphene hybrid structure exhibits a frequency-independent pressure resistive sensing property. Exceeding natural skin, such pressure sensors, can provide transient responses from static up to 10u202f000 Hz dynamic frequencies. Integrated by the controlling system, the array-accessible sensors can manipulate a robot arm and self-rectify the temperature of a heating blanket. This may pave a path toward the future application of graphene-based wearable electronics.

In Situ Transmission Electron Microscopy Characterization and Manipulation of Two‐Dimensional Layered Materials beyond Graphene

Two-dimensional (2D) ultra-thin materials beyond graphene with rich physical properties and unique layered structures are promising for applications in electronics, chemistry, energy, and bioscience, etc. The interaction mechanisms among the structures, chemical compositions and physical properties of 2D layered materials are critical for fundamental nanosciences and the practical fabrication of next-generation nanodevices. Transmission electron microscopy (TEM), with its high spatial resolution and versatile external fields, is undoubtedly a powerful tool for the static characterization and dynamic manipulation of nanomaterials and nanodevices at the atomic scale. The rapid development of thin-film and precision microelectromechanical systems (MEMS) techniques allows 2D layered materials and nanodevices to be probed and engineered inside TEM under external stimuli such as thermal, electrical, mechanical, liquid/gas environmental, optical, and magnetic fields at the nanoscale. Such advanced technologies leverage the traditional static TEM characterization into an in situ and interactive manipulation of 2D layered materials without sacrificing the resolution or the high vacuum chamber environment, facilitating exploration of the intrinsic structure-property relationship of 2D layered materials. In this Review, the dynamic properties tailored and observed by the most advanced and unprecedented in situ TEM technology are introduced. The challenges in spatial, time and energy resolution are discussed also.

Metallic few-layered VSe2 nanosheets: high two-dimensional conductivity for flexible in-plane solid-state supercapacitors

Metallic two-dimensional (2D) 1T-VSe2 with high conductivity and a large specific surface area is a promising electrode material for supercapacitors. Here, we use a facile chemical vapor deposition (CVD) method to prepare thin VSe2 nanosheets. A flexible in-plane solid-state supercapacitor is fabricated using the high-quality VSe2 nanosheets as the electrode material. The prepared supercapacitor presents an electrical double-layer capacitive behavior, and it has a high power density that is comparable with that of advanced graphene-based supercapacitors. The flexible supercapacitor also shows good mechanical stability to both bending and fatigue tests up to 10u2006000 cycles. This work provides a novel method for the fabrication of high-performance thin-film power sources, and paves the way for their application in soft thin-geometry devices.

Probing and Manipulating the Interfacial Defects of InGaAs Dual‐Layer Metal Oxides at the Atomic Scale

The interface between III-V and metal-oxide-semiconductor materials plays a central role in the operation of high-speed electronic devices, such as transistors and light-emitting diodes. The design of high-performance devices requires a detailed understanding of the electronic structure at the interface. However, the relation between the interface state charges to the electrical failure, such as breakdown of the oxide in the transistor remains unknown. Herein, the defect-driven interfacial electron structure of the Ti/ZrO2/Al2O3/InGaAs system are probed and manipulated using a specifically designed in situ transmission electron microscopy experimental method. The interfacial defects induced by oxygen-atom missing is found the main reason for the device failure. This study unearths the fundamental defect-driven interfacial electric structure of III-V semiconductor materials and paves the way to future high-speed and high-reliability devices.

High-Performance Wafer-Scale MoS2 Transistors toward Practical Application

Atomic thin transition-metal dichalcogenides (TMDs) are considered as an emerging platform to build next-generation semiconductor devices. However, to date most devices are still based on exfoliated TMD sheets on a micrometer scale. Here, a novel chemical vapor deposition synthesis strategy by introducing multilayer (ML) MoS2 islands to improve device performance is proposed. A four-probe method is applied to confirm that the contact resistance decreases by one order of magnitude, which can be attributed to a conformal contact by the extra amount of exposed edges from the ML-MoS2 islands. Based on such continuous MoS2 films synthesized on a 2 in. insulating substrate, a top-gated field effect transistor (FET) array is fabricated to explore key metrics such as threshold voltage (V T ) and field effect mobility (μFE ) for hundreds of MoS2 FETs. The statistical results exhibit a surprisingly low variability of these parameters. An average effective μFE of 70 cm2 V-1 s-1 and subthreshold swing of about 150 mV dec-1 are extracted from these MoS2 FETs, which are comparable to the best top-gated MoS2 FETs achieved by mechanical exfoliation. The result is a key step toward scaling 2D-TMDs into functional systems and paves the way for the future development of 2D-TMDs integrated circuits.