Qiuchen Zhao

Morphological effects on the field emission of ZnO nanorod arrays

The field-emission properties of ordered ZnO nanorod arrays with different morphologies were investigated in detail. After comparison of three different morphologies, it was found that the morphology of the ZnO nanorods has considerable effect on their field emission properties, especially the turn-on field and the emission current density. Among them, the ZnO nanoneedle arrays have the lowest turn-on field, highest current density, and the largest emission efficiency, which is ascribed to the small emitter radius on the nanoscale. On the other hand, high nanorod density remarkably reduces the local field at the emitters owing to the screening effect, which is related to the density of the emitters. The analysis results could be valuable for the application of field-emission-based devices using ZnO nanorod arrays as cathode materials.

Enhanced field emission from ZnO nanorods via thermal annealing in oxygen

To optimize the field emission behavior of the ZnO nanorods, postthermal annealing in different ambience was conducted. The field emission properties of the ZnO nanorods are considerably improved after annealing in oxygen and getting worse when annealing in air or ammonia. Photoluminescence and Raman spectroscopy were employed to elucidate the reason for such a significant improvement of the field emission when annealing in oxygen. Those detailed analyses suggested that oxygen annealing can reduce the oxygen vacancy concentration, improve the crystal quality, lower the work function, and increase the conductivity of the ZnO nanorods. Our work is important for applications of ZnO nanorods as a promising candidate in flat panel displays and high brightness electron sources.

Field-emission from long SnO2 nanobelt arrays

We report on field emission from SnO2 nanobelt arrays with the length of about 90 μm grown on silicon substrates. The turn-on field of the nanobelt arrays at the current density of 1μA∕cm2, is 4.5, 3.0, 2.4, and 2.3V∕μm as the distance between anode and cathode (d) is 0.1, 0.2, 0.35, and 0.5 mm, respectively. The current density rapidly reaches 2.1mA∕cm2 at the electrical field of 4.4V∕μm at d=0.35mm. The current density is higher than or comparable to those of the carbon nanotubes and other one-dimensional nanostructured materials. We also discuss the mechanism of high current densities and estimate the enhancement factor according to both the Fowler–Nordheim law and the reported model on micrometer-long of carbon nanotubes.

Field emission from AlN nanoneedle arrays

AlN nanoneedles with an average tip dimension of ∼15nm were synthesized via a simple vapor deposition method. The AlN nanoneedles exhibit excellent field-emission properties with a low turn-on field of 3.1V∕μm and a high current density of 4.7mA∕cm2 at the field of 9.9V∕μm. The field enhancement factor for a single nanoneedle is estimated to be as high as 30 000 due to its small tip radius. These features make the AlN nanoneedles a competitive candidate for field-emission-based displays.

CMP Aerogels: Ultrahigh‐Surface‐Area Carbon‐Based Monolithic Materials with Superb Sorption Performance

Monolithic conjugated microporous polymer (CMP) aerogels are obtained in an extremely facile way by selection of adequate reaction conditions and a freeze-drying technique. The aerogels possess an ultrahigh specific surface area and hierarchical interconnected pores, exhibiting superb gas/oil adsorption performance compared with all microporous organic polymers to date.

Growth of high-density horizontally aligned SWNT arrays using Trojan catalysts

Single-walled carbon nanotube (SWNT)-based electronics have been regarded as one of the most promising candidate technologies to replace or supplement silicon-based electronics in the future. These applications require high-density horizontally aligned SWNT arrays. During the past decade, significant efforts have been directed towards growth of high-density SWNT arrays. However, obtaining SWNT arrays with suitable density and quality still remains a big challenge. Herein, we develop a rational approach to grow SWNT arrays with ultra-high density using Trojan catalysts. The density can be as high as 130 SWNTs μm(-1). Field-effect transistors fabricated with our SWNT arrays exhibit a record drive current density of -467.09 μA μm(-1) and an on-conductance of 233.55 μS μm(-1). Radio frequency transistors fabricated on these samples exhibit high intrinsic fT and fMAX of 6.94 and 14.01 GHz, respectively. These results confirm our high-density SWNT arrays are strong candidates for applications in electronics.

State of the Art of Single‐Walled Carbon Nanotube Synthesis on Surfaces

Single-walled carbon nanotubes (SWNTs) directly synthesized on surfaces are promising building blocks for nanoelectronics. The structures and the arrangement of the SWNTs on surfaces determine the quality and density of the fabricated nanoelectronics, implying the importance of structure controlled growth of SWNTs on surfaces. This review summarizes the recent research status in controlling the orientation, length, density, diameter, metallicity, and chirality of SWNTs directly synthesized on surfaces by chemical vapor deposition, together with a session presenting the characterization method of the chirality of SWNTs. Finally, the remaining major challenges are discussed and future research directions are proposed.

Microscopic Dimensions Engineering: Stepwise Manipulation of the Surface Wettability on 3D Substrates for Oil/Water Separation.

Microscopic dimensions engineering is proposed to devise a series of 3D superhydrophobic substrates with microstructures of different dimensions. Combined theoretical modeling and experiments give the relationship of surface roughness and superhydrophobic properties, important for guiding the design of superior superwettable materials for water remediation and other uses.

Macroscopic Carbon Nanotube‐based 3D Monoliths

Carbon nanotubes (CNTs) are one of the most promising carbon allotropes with incredible diverse physicochemical properties, thereby enjoying continuous worldwide attention since their discovery about two decades ago. From the point of view of practical applications, assembling individual CNTs into macroscopic functional and high-performance materials is of paramount importance. For example, multiscaled CNT-based assemblies including 1D fibers, 2D films, and 3D monoliths have been developed. Among all of these, monolithic 3D CNT architectures with porous structures have attracted increasing interest in the last few years. In this form, theoretically all individual CNTs are well connected and fully expose their surfaces. These 3D architectures have huge specific surface areas, hierarchical pores, and interconnected conductive networks, resulting in enhanced mass/electron transport and countless accessible active sites for diverse applications (e.g. catalysis, capacitors, and sorption). More importantly, the monolithic form of 3D CNT assemblies can impart additional application potentials to materials, such as free-standing electrodes, sensors, and recyclable sorbents. However, scaling the properties of individual CNTs to 3D assemblies, improving use of the diverse, structure-dependent properties of CNTs, and increasing the performance-to-cost ratio are great unsolved challenges for their real commercialization. This review aims to provide a comprehensive introduction of this young and energetic field, i.e., CNT-based 3D monoliths, with a focus on the preparation principles, current synthetic methods, and typical applications. Opportunities and challenges in this field are also presented.

Growth of Close-Packed Semiconducting Single-Walled Carbon Nanotube Arrays Using Oxygen-Deficient TiO2 Nanoparticles as Catalysts

For the application of single-walled carbon nanotubes (SWNTs) in nanoelectronic devices, techniques to obtain horizontally aligned semiconducting SWNTs (s-SWNTs) with higher densities are still in their infancy. We reported herein a rational approach for the preferential growth of densely packed and well-aligned s-SWNTs arrays using oxygen-deficient TiO2 nanoparticles as catalysts. Using this approach, a suitable concentration of oxygen vacancies in TiO2 nanoparticles could form by optimizing the flow rate of hydrogen and carbon sources during the process of SWNT growth, and then horizontally aligned SWNTs with the density of ∼ 10 tubes/μm and the s-SWNT percentage above 95% were successfully obtained on ST-cut quartz substrates. Theoretical calculations indicated that TiO2 nanoparticles with a certain concentration of oxygen vacancies have a lower formation energy between s-SWNT than metallic SWNT (m-SWNT), thus realizing the preferential growth of s-SWNT arrays. Furthermore, this method can also be extended to other semiconductor oxide nanoparticles (i.e., ZnO, ZrO2 and Cr2O3) for the selective growth of s-SWNTs, showing clear potential to the future applications in nanoelectronics.