Peng Liu

Measuring the Work Function of Carbon Nanotubes with Thermionic Method

The work function of carbon nanotubes might depend on their diameters and the number of walls, and be different for their tips and sidewalls. Here we report the work function measurement of single-walled, double-walled, and multiwalled carbon nanotubes by investigating the thermionic emission from the middle of their bundles. It is found that the sidewall work functions of the three kinds of carbon nanotubes are all around 4.7-4.9 eV; the diameter and the numbers of walls have no obvious influence on their work functions. For the carbon nanotube bundle with some tips appearing in the middle, the measured work function is smaller than without tips, indicating that the work function of tips is smaller than that of the sidewalls. This tip effect also results in a difference in the thermionic emission characteristic, implying non-uniform work function distribution along the bundle.

New-type planar field emission display with superaligned carbon nanotube yarn emitter.

With the superaligned carbon nanotube yarn as emitter, we have fabricated a 16 × 16 pixel field emission display prototype by adopting screen printing and laser cutting technologies. A planar diode field emission structure has been adopted. A very sharp carbon nanotube yarn tip emitter can be formed by laser cutting. Low voltage phosphor was coated on the anode electrodes also by screen printing. With a specially designed circuit, we have demonstrated the dynamic character display with the field emission display prototype. The emitter material and fabrication technologies in this paper are both easy to scale up to large areas.

Reversibility of Noble Metal-Catalyzed Aprotic Li-O2 Batteries

The aprotic Li-O2 battery has attracted a great deal of interest because, theoretically, it can store far more energy than todays batteries. Toward unlocking the energy capabilities of this neotype energy storage system, noble metal-catalyzed high surface area carbon materials have been widely used as the O2 cathodes, and some of them exhibit excellent electrochemical performances in terms of round-trip efficiency and cycle life. However, whether these outstanding electrochemical performances are backed by the reversible formation/decomposition of Li2O2, i.e., the desired Li-O2 electrochemistry, remains unclear due to a lack of quantitative assays for the Li-O2 cells. Here, noble metal (Ru and Pd)-catalyzed carbon nanotube (CNT) fabrics, prepared by magnetron sputtering, have been used as the O2 cathode in aprotic Li-O2 batteries. The catalyzed Li-O2 cells exhibited considerably high round-trip efficiency and prolonged cycle life, which could match or even surpass some of the best literature results. However, a combined analysis using differential electrochemical mass spectrometry and Fourier transform infrared spectroscopy, revealed that these catalyzed Li-O2 cells (particularly those based on Pd-CNT cathodes) did not work according to the desired Li-O2 electrochemistry. Instead the presence of noble metal catalysts impaired the cells reversibility, as evidenced by the decreased O2 recovery efficiency (the ratio of the amount of O2 evolved during recharge/that consumed in the preceding discharge) coupled with increased CO2 evolution during charging. The results reported here provide new insights into the O2 electrochemistry in the aprotic Li-O2 batteries containing noble metal catalysts and exemplified the importance of the quantitative assays for the Li-O2 reactions in the course of pursuing truly rechargeable Li-O2 batteries.

Carbon‐Nanotube‐Film Microheater on a Polyethylene Terephthalate Substrate and Its Application in Thermochromic Displays

Carbon nanotubes (CNTs) show many fascinating properties and are regarded as one of the most promising nanomaterials that can be used in many kinds of application. It has been reported that CNTs can fi nd broad applications in electronics [ 1 ] and photonics. [ 2 ] Recently, their application in sensors for gases [ 3 ] and biological materials, [ 4,5 ] electrodes for fl exible electronics [ 6 ] and solar cells, [ 7 ] fi llers for polymers, [ 8 ]

Development of an ultra-thin film comprised of a graphene membrane and carbon nanotube vein support

Graphene, exhibiting superior mechanical, thermal, optical and electronic properties, has attracted great interest. Considering it being one-atom-thick, and the reduced mechanical strength at grain boundaries, the fabrication of large-area suspended chemical vapour deposition graphene remains a challenge. Here we report the fabrication of an ultra-thin free-standing carbon nanotube/graphene hybrid film, inspired by the vein-membrane structure found in nature. Such a square-centimetre-sized hybrid film can realize the overlaying of large-area single-layer chemical vapour deposition graphene on to a porous vein-like carbon nanotube network. The vein-membrane-like hybrid film, with graphene suspended on the carbon nanotube meshes, possesses excellent mechanical performance, optical transparency and good electrical conductivity. The ultra-thin hybrid film features an electron transparency close to 90%, which makes it an ideal gate electrode in vacuum electronics and a high-performance sample support in transmission electron microscopy.

Thermoacoustic Chips with Carbon Nanotube Thin Yarn Arrays

Aligned carbon nanotube (CNT) films drawn from CNT arrays have shown the potential as thermoacoustic loudspeakers. CNT thermoacoustic chips with robust structures are proposed to promote the applications. The silicon-based chips can play sound and fascinating rhythms by feeding alternating currents and audio signal to the suspending CNT thin yarn arrays across grooves in them. In additional to the thin yarns, experiments further revealed more essential elements of the chips, the groove depth and the interdigital electrodes. The sound pressure depends on the depth of the grooves, and the thermal wavelength can be introduced to define the influence-free depth. The interdigital fingers can effectively reduce the driving voltage, making the chips safe and easy to use. The chips were successfully assembled into earphones and have been working stably for about one year. The thermoacoustic chips can find many applications in consumer electronics and possibly improve the audiovisual experience.

High frequency response of carbon nanotube thin film speaker in gases

The thermoacoustic response of carbon nanotube (CNT) thin films at frequencies ranging from 300 Hz up to 100 kHz has been studied in a variety of gaseous mediums. Theoretical derivations show that the sound pressure generated by CNT thin films is approximately proportional to the inverse of the heat capacity of the gas within the audible frequency range of human hearing, which is consistent with the experimental results in argon, air, and helium. For large size CNT films, a decrease in sound pressure is observed within a higher frequency range in air, which is attributed to the destructive interference of sound waves in the near field zone according to the theoretical calculations.

LaB6 tip-modified multiwalled carbon nanotube as high quality field emission electron source

An effective field emitter has been developed by modifying an individual multiwalled carbon nanotube (MWCNT) tip with LaB6. The modified emitter possesses the merits of both the MWCNT and LaB6, which presents a significant low turn-on voltage, good emission properties, and long lifetime. As a result, a total current of 70μA has been reached at a very low electric field of only 1.2V∕μm for an individual modified MWCNT emitter, which is also expected to have advantages of high brightness and coherence, clearly indicating great promise for practical applications such as electron guns or cathodes for field emission flat panel display.

Cold linear cathodes with carbon nanotube emitters and their application in luminescent tubes

We introduce an efficient method of fabricating cold, linear cathodes with carbon nanotube (CNT) emitters. A nickel wire was painted first with silver paste, then with CNT paste. After sintering under nitrogen and activation by adhesive tape, the cathode wire provided a stable and homogeneous emission density of 200xa0mAxa0cm−2 at 6.2xa0Vxa0µm−1. As an application, luminescent tubes were constructed using this CNT wire as the cathode and a transparent CNT film as the anode. These cold cathodes can replace conventional hot cathodes, which are widely used in vacuum electronic devices. The novel two-layer structure can be applied to any substrate, and is simple and inexpensive to fabricate.

Heating graphene to incandescence and the measurement of its work function by the thermionic emission method

The work function (WF) of graphene is an essential parameter in graphene electronics. We have derived the WF of graphene by the thermionic emission method. Chemical vapor deposition (CVD)-grown single-layered polycrystalline graphene on copper foil is transferred to a cross-stacked carbon nanotube (CNT) film drawn from a super-aligned multiwalled CNT array. By decreasing the pore size of the CNT film, the as-prepared CNT-graphene film (CGF) can be Joule heated to a temperature as high as 1,800 K in vacuum without obvious destruction in the graphene structure. By studying the thermionic emission, we derive the WF of graphene, ranging from 4.7 to 4.8 eV with the average value being 4.74 eV. Because the substrate influence can be minimized by virtue of the porous nature of the CNT film and the influence of adsorbents can be excluded due to the high temperature during the thermionic emission, the measured WF of graphene can be regarded as intrinsic.