Yagang Yao

Large-scale production of two-dimensional nanosheets

Two-dimensional (2D) nanomaterials such as graphene, boron nitride (BN), and molybdenum disulfide (MoS2) have been attracting increasing research interest in the past few years due to their unique material properties. However, the lack of a reliable large-scale production method is an inhibiting issue for their practical applications. Here we report a facile, efficient, and scalable method for the fabrication of monolayer and few-layer BN, MoS2, and graphene using combined low-energy ball milling and sonication. Ball milling generates two forces on layered materials, shear force and compression force, which can cleave layered materials into 2D nanosheets from the top/bottom surfaces, and the edge of layered materials. Subsequent sonication would further break larger crystallites into smaller crystallites. These fabricated 2D nanosheets can be well dispersed in aqueous solutions at high concentrations, 1.2 mg mL−1 for BN, 0.8 mg mL−1 for MoS2, and 0.9 mg mL−1 for graphene, which are highly advantageous over other methods. These advantages render great potential in the construction of high-performance 2D material-based devices at low cost. For example, a prototype gas sensor is demonstrated in our study using graphene and MoS2, respectively, which can detect several ppm of ammonia gas.

Aligned, ultralong single-walled carbon nanotubes: from synthesis, sorting, to electronic devices.

Aligned, ultralong single-walled carbon nanotubes (SWNTs) represent attractive building blocks for nanoelectronics. The structural uniformity along their tube axis and well-ordered two-dimensional architectures on wafer surfaces may provide a straightforward platform for fabricating high-performance SWNT-based integrated circuits. On the way towards future nanoelectronic devices, many challenges for such a specific system also exist. This Review summarizes the recent advances in the synthesis, identification and sorting, transfer printing and manipulation, device fabrication and integration of aligned, ultralong SWNTs in detail together with discussion on their major challenges and opportunities for their practical application.

Ultrafast, dry microwave synthesis of graphene sheets

Through direct absorption of microwave irradiation by GO film, we developed a rapid, dry approach to synthesize reduced graphene.

Chirality-Dependent Transport Properties of Double-Walled Nanotubes Measured in Situ on Their Field-Effect Transistors

Double-walled carbon nanotubes (DWNT), consisting of two coaxial tubes, is an ideal structure for chemical and physical applications. It is of essential importance to probe the one-to-one relationship between electrical transport and chiral structure of DWNTs. Here, the chirality-dependent transport properties of DWNTs have been systematically investigated in situ on their field-effect transistors, through building DWNT-based field-effect transistors into a transmission electron microscope. The transport characteristics of DWNTs can be directly correlated with their chiral indices, and the probe of inner tubes has also been achieved in situ.

The use of polyimide-modified aluminum nitride fillers in AlN@PI/Epoxy composites with enhanced thermal conductivity for electronic encapsulation

Polymer modified fillers in composites has attracted the attention of numerous researchers. These fillers are composed of core-shell structures that exhibit enhanced physical and chemical properties that are associated with shell surface control and encapsulated core materials. In this study, we have described an apt method to prepare polyimide (PI)-modified aluminum nitride (AlN) fillers, AlN@PI. These fillers are used for electronic encapsulation in high performance polymer composites. Compared with that of untreated AlN composite, these AlN@PI/epoxy composites exhibit better thermal and dielectric properties. At 40 wt% of filler loading, the highest thermal conductivity of AlN@PI/epoxy composite reached 2.03 W/mK. In this way, the thermal conductivity is approximately enhanced by 10.6 times than that of the used epoxy matrix. The experimental results exhibiting the thermal conductivity of AlN@PI/epoxy composites were in good agreement with the values calculated from the parallel conduction model. This research work describes an effective pathway that modifies the surface of fillers with polymer coating. Furthermore, this novel technique improves the thermal and dielectric properties of fillers and these can be used extensively for electronic packaging applications.

One step synthesis of fluorescent smart thermo-responsive copper clusters: a potential nanothermometer in living cells

Temperature measurement in biology and medical diagnostics, along with sensitive temperature probing in living cells, is of great importance; however, it still faces significant challenges. Metal nanoclusters (NCs) with attractive luminescent properties may be promising candidates to overcome such challenges. Here, a novel one-step synthetic method is presented to prepare highly fluorescent copper NCs (CuNCs) in ambient conditions by using glutathione (GSH) as both the reducing agent and the protective layer preventing the aggregation of the as-formed NCs. The resultant CuNCs, with an average diameter of 2.3 nm, contain 1–3 atoms and exhibit red fluorescence (λem = 610 nm) with high quantum yields (QYs, up to 5.0%). Interestingly, the fluorescence signal of the CuNCs is reversibly responsive to the environmental temperature in the range of 15–80 °C. Furthermore, as the CuNCs exhibit good biocompatibility, they can pervade the MC3T3-E1 cells and enable measurements over the physiological temperature range of 15–45 °C with the use of the confocal fluorescence imaging method. In view of the facile synthesis method and attractive fluorescence properties, the as-prepared CuNCs may be used as photoluminescence thermometers and biosensors.

Wrapping Aligned Carbon Nanotube Composite Sheets around Vanadium Nitride Nanowire Arrays for Asymmetric Coaxial Fiber-Shaped Supercapacitors with Ultrahigh Energy Density

The emergence of fiber-shaped supercapacitors (FSSs) has led to a revolution in portable and wearable electronic devices. However, obtaining high energy density FSSs for practical applications is still a key challenge. This article exhibits a facile and effective approach to directly grow well-aligned three-dimensional vanadium nitride (VN) nanowire arrays (NWAs) on carbon nanotube (CNT) fiber with an ultrahigh specific capacitance of 715 mF/cm2 in a three-electrode system. Benefiting from their intriguing structural features, we successfully fabricated a prototype asymmetric coaxial FSS (ACFSS) with a maximum operating voltage of 1.8 V. From core to shell, this ACFSS consists of a CNT fiber core coated with VN@C NWAs as the negative electrode, Na2SO4 poly(vinyl alcohol) (PVA) as the solid electrolyte, and MnO2/conducting polymer/CNT sheets as the positive electrode. The novel coaxial architecture not only fully enables utilization of the effective surface area and decreases the contact resistance between the two electrodes but also, more importantly, provides a short pathway for the ultrafast transport of axial electrons and ions. The electrochemical results show that the optimized ACFSS exhibits a remarkable specific capacitance of 213.5 mF/cm2 and an exceptional energy density of 96.07 μWh/cm2, the highest areal capacitance and areal energy density yet reported in FSSs. Furthermore, the device possesses excellent flexibility in that its capacitance retention reaches 96.8% after bending 5000 times, which further allows it to be woven into flexible electronic clothes with conventional weaving techniques. Therefore, the asymmetric coaxial architectural design allows new opportunities to fabricate high-performance flexible FSSs for future portable and wearable electronic devices.

An all-solid-state, lightweight, and flexible asymmetric supercapacitor based on cabbage-like ZnCo2O4 and porous VN nanowires electrode materials

A series of high-performance all-solid-state, lightweight, and flexible asymmetric supercapacitors (ASC) were prepared using cabbage-like ZnCo2O4 as the positive electrode material, porous VN nanowires as the negative electrode material, and flexible carbon nanotube film (CNTF) as the collector. Excellent electrochemical performance was achieved with an areal capacitance of 789.11 mF cm−2 for the positive electrode and 400 mF cm−2 for the negative electrode. The assembled all-solid-state flexible ASC device possessed a specific capacitance of 196.43 mF cm−2, large voltage window of 1.6 V, and a volume energy density of 64.76 mW h cm−3. Moreover, the assembled device exhibited good cycling stability with 87.9% initial capacitance retention after 4000 cycles with the coulombic efficiency remaining close to 100%. In addition, the capacitance retention reached 95.7% after 2000 bending cycles, indicating its good flexible and mechanical stability.

Crack-Free and Scalable Transfer of Carbon Nanotube Arrays into Flexible and Highly Thermal Conductive Composite Film

Carbon nanotube (CNT) arrays show great promise in developing anisotropic thermal conductive composites for efficiently dissipating heat from high-power devices along thickness direction. However, CNT arrays are always grown on some substrates and liable to be deformed and broken into pieces during transfer and solution treatment. In the present study, we intentionally synthesized well-crystallized and large-diameter (~80 nm) multiwalled CNT (MWCNT) arrays by floating catalyst chemical vapor deposition (FCCVD) method. Such arrays provided high packing density and robust structure from collapse and crack formation during post solution treatment and therefore favored to maintain original thermal and electrical conductive paths. Under optimized condition, the CNT arrays can be transferred into flexible composite films. Furthermore, the composite film also exhibited excellent thermal conductivity at 8.2 W/(m·K) along thickness direction. Such robust, flexible, and highly thermal conductive composite film may enable some prospective applications in advanced thermal management.

Gold nanoclusters decorated with magnetic iron oxide nanoparticles for potential multimodal optical/magnetic resonance imaging

Efficient nanoprobes for fluorescent and magnetic resonance multimodal imaging (MRI/FI) are in high demand in bioimaging. Herein, a nanoprobe with fluorescent gold nanoclusters (NCs) and magnetic iron oxide composite materials (Fe3O4@AuNCs) was prepared for dual bioimaging. The AuNCs were synthesized using the glutathione (GSH) template. The hydrophobic Fe3O4 magnetic nanoparticles (MNPs) were capped with cetyltrimethyl ammonium bromide (CTAB) to obtain hydrophilic Fe3O4 MNPs. Subsequently, the Fe3O4@AuNCs were prepared by the adsorption of Fe3O4–CTAB on the GSH–AuNCs through electrostatic attraction. The resultant Fe3O4@AuNCs, having an average size of 13.5 nm, can be readily dispersed in water, which displayed a strong red fluorescence (λEm = 650 nm) with a quantum yield of 4.3%. Confocal laser scanning microscopy studies proved that the Fe3O4@AuNCs have good photostability and low cytotoxicity to 293T cells. The magnetic properties of Fe3O4@AuNCs showed that this material was a T2-based contrast agent for MRI with a transverse relaxivity r2 of 20.4 mM−1 S−1. Furthermore, the signal intensity of the T2-weighted MRI decreased with an increase in the concentration. The dual optical and magnetic properties of the synthesized Fe3O4@AuNCs were applicable to dual fluorescence and MR-based imaging.