Mechanical and electromechanical properties of 2D materials studied microscopy techniques.

Two-dimensional (2D) materials with van der Waals stacking have been reported to have extraordinary mechanical and electromechanical properties, which give them revolutionary potential in various fields. However, due to the atomic-scale thickness of these 2D materials, their fascinating properties cannot be effectively characterized in many cases using conventional measurement techniques. Based on typical microscopy techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), a range of microscopy techniques have been developed to systematically quantify the mechanical and electromechanical properties of 2D materials.

Large and Pressure-Dependent Axis Piezoresistivity of Highly Oriented Pyrolytic Graphite near Zero Pressure.

The axis piezoresistivity is a fundamental and important parameter of graphite, but its value near zero pressure has not been well determined. Herein, a new method for studying the axis piezoresistivity of van der Waals materials near zero pressure is developed on the basis of scanning electron microscopy and finite element simulation. The axis piezoresistivity of microscale highly oriented pyrolytic graphite (HOPG) is found to show a large value of 5.

An On-Chip Microscale Vacuum Chamber with High Sealing Performance Using Graphene as Lateral Feedthrough.

On-chip microscale vacuum chambers with high sealing performance and electrical feedthroughs are highly desired for microscale vacuum electronic devices and other MEMS devices. In this paper, we report an on-chip microscale vacuum chamber which achieves a high sealing performance by using monolayer graphene as lateral electrical feedthrough. A vacuum chamber with the dimensions of π × 2 mm × 2 mm × 0.

Pull-to-Peel of Two-Dimensional Materials for the Simultaneous Determination of Elasticity and Adhesion.

The flexible and clinging nature of ultrathin films requires an understanding of their elastic and adhesive properties in a wide range of circumstances from fabrications to applications. Simultaneously measuring both properties, however, is extremely difficult as the film thickness diminishes to the nanoscale. Here we address such difficulties through peeling by pulling thin films off from the substrates (we thus refer to it as "pull-to-peel").

Efficient and Dense Electron Emission from a SiO Tunneling Diode with Low Poisoning Sensitivity.

We report a tunneling diode enabling efficient and dense electron emission from SiO with low poisoning sensitivity. Benefiting from the shallow SiO channel exposed to vacuum and the low electron affinity of SiO (0.9 eV), hot electrons tunneling into the SiO channel from the cathode of the diode are efficiently emitted into vacuum with much less restriction in both space and energy than those in previous tunneling electron sources.

Controlling the Facet of ZnO during Wet Chemical Etching Its (000 ) O-Terminated Surface.

Special surface plays a crucial role in nature as well as in industry. Here, the surface morphology evolution of ZnO during wet etching is studied by in situ liquid cell transmission electron microscopy and ex situ wet chemical etching. Many hillocks are observed on the (000 ) O-terminated surface of ZnO nano/micro belts during in situ etching.

Configurable multifunctional integrated circuits based on carbon nanotube dual-material gate devices.

Nanoelectronic devices with specifically designed structures for performance promotion or function expansion are of great interest, aiming for diversified advanced nanoelectronic systems. In this work, we report a dual-material gate (DMG) carbon nanotube (CNT) device with multiple functions, which can be configured either as a high-performance p-type field-effect transistor (FET) or a diode by changing the input manners of the device. When operating as a FET, the device exhibits a large current on/off ratio of more than 108 and a drain-induced barrier lowering of 97.

Constant-rate dissolution of InAs nanowires in radiolytic water observed by in situ liquid cell TEM.

Understanding the dissolution process and mechanism of materials in a liquid at the nanoscale is very important for both science and technology in many fields. Although the dissolution process of nanoparticles has been studied by many groups, the dissolution of one-dimensional (1D) nanomaterials with a high aspect ratio has seldom been directly observed with a high spatial resolution. In this paper, the dissolution process of 1D nanowires (NWs), InAs NWs as an example, in radiolytic water is studied by in situ liquid cell transmission electron microscopy.

Interlayer electrical resistivity of rotated graphene layers studied by in-situ scanning electron microscopy.

Interlayer electrical transport between two-dimensional atomic crystals can be strongly modulated by the rotational misalignment between them. However, the experimental study on the interlayer electrical transport between rotated two-dimensional atomic crystals with variable rotation angles is challenging. Here, an in-situ scanning electron microscopy method is developed to study the interlayer electrical transport between rotated graphene layers.

1D Piezoelectric Material Based Nanogenerators: Methods, Materials and Property Optimization.

Due to the enhanced piezoelectric properties, excellent mechanical properties and tunable electric properties, one-dimensional (1D) piezoelectric materials have shown their promising applications in nanogenerators (NG), sensors, actuators, electronic devices etc. To present a clear view about 1D piezoelectric materials, this review mainly focuses on the characterization and optimization of the piezoelectric properties of 1D nanomaterials, including semiconducting nanowires (NWs) with wurtzite and/or zinc blend phases, perovskite NWs and 1D polymers. Specifically, the piezoelectric coefficients, performance of single NW-based NG and structure-dependent electromechanical properties of 1D nanostructured materials can be respectively investigated through piezoresponse force microscopy, atomic force microscopy and the in-situ scanning/transmission electron microcopy.

Deterministic Line-Shape Programming of Silicon Nanowires for Extremely Stretchable Springs and Electronics.

Line-shape engineering is a key strategy to endow extra stretchability to 1D silicon nanowires (SiNWs) grown with self-assembly processes. We here demonstrate a deterministic line-shape programming of in-plane SiNWs into extremely stretchable springs or arbitrary 2D patterns with the aid of indium droplets that absorb amorphous Si precursor thin film to produce ultralong c-Si NWs along programmed step edges. A reliable and faithful single run growth of c-SiNWs over turning tracks with different local curvatures has been established, while high resolution transmission electron microscopy analysis reveals a high quality monolike crystallinity in the line-shaped engineered SiNW springs.

Single-walled carbon nanotube thermionic electron emitters with dense, efficient and reproducible electron emission.

Thermionic electron emitters have recently been scaled down to the microscale using microfabrication technologies and graphene as the filament. While possessing several advantages over field emitters, graphene-based thermionic micro-emitters still exhibit low emission current density and efficiency. Here, we report nanoscale thermionic electron emitters (NTEEs) fabricated using microfabrication technologies and single-walled carbon nanotubes (SWCNTs), the thinnest conducting filament we can use.

Superlubricity between MoS Monolayers.

The ultralow friction between atomic layers of hexagonal MoS , an important solid lubricant and additive of lubricating oil, is thought to be responsible for its excellent lubricating performances. However, the quantitative frictional properties between MoS atomic layers have not been directly tested in experiments due to the lack of conventional tools to characterize the frictional properties between 2D atomic layers. Herein, a versatile method for studying the frictional properties between atomic-layered materials is developed by combining the in situ scanning electron microscope technique with a Si nanowire force sensor, and the friction tests on the sliding between atomic-layered materials down to monolayers are reported.

Influence of water vapor on the electronic property of MoS field effect transistors.

The influence of water vapor on the electronic property of MoS field effect transistors (FETs) is studied through controlled experiments. We fabricate supported and suspended FETs on the same piece of MoS to figure out the role of SiO substrate on the water sensing property of MoS. The two kinds of devices show similar response to water vapor and to different treatments, such as pumping in the vacuum, annealing at 500 K and current annealing, indicating the substrate does not play an important role in the MoS water sensor.

Direct Observation of the Layer-by-Layer Growth of ZnO Nanopillar by In situ High Resolution Transmission Electron Microscopy.

Catalyst-free methods are important for the fabrication of pure nanowires (NWs). However, the growth mechanism remains elusive due to the lack of crucial information on the growth dynamics at atomic level. Here, the noncatalytic growth process of ZnO NWs is studied through in situ high resolution transmission electron microscopy.

Whole-journey nanomaterial research in an electron microscope: from material synthesis, composition characterization, property measurements to device construction and tests.

The whole-journey nanomaterial research from material synthesis, composition and structure characterizations, property measurements to device construction and tests in one equipment chamber provides a quick and unambiguous way of establishing the relationships between synthesis conditions, composition and structures, physical properties and nanodevice performances of nanomaterials; however, it still proves challenging. Herein, we report the whole-journey research of tungsten oxide nanowires in an environmental scanning electron microscope (ESEM) equipped with an x-ray energy dispersive spectrometer (EDS) and a multifunctional nanoprobe system. Tungsten oxide nanowires are synthesized by irradiating a tungsten filament using a high-energy laser in O atmosphere with the dynamic growth processes of nanowires being directly visualized under ESEM observation.

Tunable graphene micro-emitters with fast temporal response and controllable electron emission.

Microfabricated electron emitters have been studied for half a century for their promising applications in vacuum electronics. However, tunable microfabricated electron emitters with fast temporal response and controllable electron emission still proves challenging. Here, we report the scaling down of thermionic emitters to the microscale using microfabrication technologies and a Joule-heated microscale graphene film as the filament.

Remarkable influence of slack on the vibration of a single-walled carbon nanotube resonator.

We for the first time quantitatively investigate experimentally the remarkable influence of slack on the vibration of a single-walled carbon nanotube (SWCNT) resonator with a changeable channel length fabricated in situ inside a scanning electron microscope, compare the experimental results with the theoretical predictions calculated from the measured geometric and mechanical parameters of the same SWCNT, and find the following novel points. We demonstrate experimentally that as the slack s is increased from about zero to 1.8%, the detected vibration transforms from single-mode to multimode vibration, and the gate-tuning ability gradually attenuates for all the vibration modes.

Crystal Phase- and Orientation-Dependent Electrical Transport Properties of InAs Nanowires.

We report a systematic study on the correlation of the electrical transport properties with the crystal phase and orientation of single-crystal InAs nanowires (NWs) grown by molecular-beam epitaxy. A new method is developed to allow the same InAs NW to be used for both the electrical measurements and transmission electron microscopy characterization. We find both the crystal phase, wurtzite (WZ) or zinc-blende (ZB), and the orientation of the InAs NWs remarkably affect the electronic properties of the field-effect transistors based on these NWs, such as the threshold voltage (VT), ON-OFF ratio, subthreshold swing (SS) and effective barrier height at the off-state (ΦOFF).

The intrinsic origin of hysteresis in MoS2 field effect transistors.

We investigate the hysteresis and gate voltage stress effect in MoS2 field effect transistors (FETs). We observe that both the suspended and the SiO2-supported FETs have large hysteresis in their transfer curves under vacuum which cannot be attributed to the traps at the interface between the MoS2 and the SiO2 or in the SiO2 substrate or the gas adsorption/desorption effect. Our findings indicate that the hysteresis we observe comes from the MoS2 itself, revealing an intrinsic origin of the hysteresis besides some extrinsic factors.

One-step DGC assembly and structural characterization of a hairy particle zeolite-like organic-inorganic hybrid as an efficient modifiable catalytic material.

Organic-inorganic hybrid microporous crystalline molecular sieves, extending the application of conventional zeolites in the fields of selective catalysis and adsorption, have aroused great interest in chemists. However, the complicated and difficult synthesis of organic-inorganic hybrid microporous molecular sieves by using a conventional hydrothermal method has hindered the rapid development of this field. The present work describes the recent progress in the synthesis of a hairy particle zeolite-like organic-inorganic hybrid with the high organic group content by one-step dry-gel conversion (DGC) assembly of organic Si, inorganic Si and other inorganic species without any organic template, which is proven to be efficient, economical, simple, and controllable.

Directly correlating the strain-induced electronic property change to the chirality of individual single-walled and few-walled carbon nanotubes.

We fabricate carbon nanotube (CNT)-field effect transistors (FETs) with a changeable channel length and investigate the electron transport properties of single-walled, double-walled and triple-walled CNTs under uniaxial strain. In particular, we characterize the atomic structure of the same CNTs in the devices by transmission electron microscopy and correlate the strain-induced electronic property change to the chirality of the CNTs. Both the off-state resistance and on-state resistance are observed to change with the axial strain following an exponential function.

Amorphization and Directional Crystallization of Metals Confined in Carbon Nanotubes Investigated by in Situ Transmission Electron Microscopy.

The hollow core of a carbon nanotube (CNT) provides a unique opportunity to explore the physics, chemistry, biology, and metallurgy of different materials confined in such nanospace. Here, we investigate the nonequilibrium metallurgical processes taking place inside CNTs by in situ transmission electron microscopy using CNTs as nanoscale resistively heated crucibles having encapsulated metal nanowires/crystals in their channels. Because of nanometer size of the system and intimate contact between the CNTs and confined metals, an efficient heat transfer and high cooling rates (∼10(13) K/s) were achieved as a result of a flash bias pulse followed by system natural quenching, leading to the formation of disordered amorphous-like structures in iron, cobalt, and gold.