Shaozhi Deng

Polymerized carbon nanobells and their field-emission properties

Aligned nitrogen-containing carbon nanofibers consisting of polymerized “nanobells” have been grown on a large scale using microwave plasma-assisted chemical-vapor deposition with a mixture of methane and nitrogen. A greater part of the fiber surface consists of open ends of the graphitic sheets. A side-emission mechanism is proposed. A low-threshold field of 1.0 V/μm and a high-emission current density of 200 mA/cm2 for an applied field of 5–6 V/μm were achieved, implying that the materials have a high potential for future application as electron field emitters, especially in flat-panel displays.

Electrical and Photosensitive Characteristics of a-IGZO TFTs Related to Oxygen Vacancy

The electrical and photosensitive characteristics of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) related to the oxygen vacancies V̈_O are discussed. With the filling of V̈_O of ratio from 14 to 8, the electron density of the a-IGZO channel decreases from 7.5 to 3.8 ( ×10¹⁶ cm^-3); the saturation mobility of the TFT decreases from 3.1 to 1.4 cm^-2/(V · s); the threshold voltage increases from 7 to 11 V for the TFT with a lower on-current; and the subthreshold slope increases from 2.4 to 4.4 V/dec for the TFT with a higher interface defect density of 4.9 × 10¹¹ cm^-2, the worst electrical stability of V_th ~ 10 V, and a hysteresis-voltage decrease from 3.5 to 2 V. The photoreaction properties of a-IGZO TFTs are also sensitive to the oxygen-content-related absorption of the a-IGZO channel. With the lowest content of oxygen in the channel, the TFT has the largest photocurrent gain of 50 μA (V_g = 30 V; V_d = 10 V) and decrease in V_th ( V_th V) at a high light intensity. The light-induced change of TFT characteristics is totally reversible with the time constant for recovery of about 2.5 h.

Correlation between resistance and field emission performance of individual ZnO one-dimensional nanostructures.

Both electrical and field emission measurements were carried out to study the correlation between resistance and field emission performance of individual one-dimensional (1D) ZnO nanostructures. Three types of 1D ZnO nanostructures were investigated (i.e., agave-like shape, pencil-like shape, and hierarchical structure) and were prepared by thermal chemical vapor transport and condensation without using any catalyst. The 1D ZnO nanostructures have obvious differences in resistance and thus conductivity from type to type. In addition, in the same type of 1D ZnO nanostructure, each individual emitter may also have variation in resistance and thus in conductivity. The field emission performance of the ZnO emitters was found to be strongly correlated with the resistance of each individual ZnO nanostructure: (i) a ZnO emitter with low resistance will have better emission; (ii) a high resistance region in a ZnO nanostructure is liable to the initiation of a vacuum breakdown event. The results indicate that, besides the uniformity in the geometrical structure, the uniformity in conductivity of the emitters in an array should be ensured, in order to meet the requirement of device application.

Field Electron Emission Characteristics and Physical Mechanism of Individual Single-Layer Graphene

Due to its difficulty, experimental measurement of field emission from a single-layer graphene has not been reported, although field emission from a two-dimensional (2D) regime has been an attractive topic. The open surface and sharp edge of graphene are beneficial for field electron emission. A 2D geometrical effect, such as massless Dirac fermion, can lead to new mechanisms in field emission. Here, we report our findings from in situ field electron emission characterization on an individual singe-layer graphene and the understanding of the related mechanism. The measurement of field emission from the edges was done using a microanode probe equipped in a scanning electron microscope. We show that repeatable stable field emission current can be obtained after a careful conditioning process. This enables us to examine experimentally the typical features of the field emission from a 2D regime. We plot current versus applied field data, respectively, in ln(I/E(3/2)) ∼ 1/E and ln(I/E(3)) ∼ 1/E(2) coordinates, which have recently been proposed for field emission from graphene in high- and low-field regimes. It is observed that the plots all exhibit an upward bending feature, revealing that the field emission processes undergo from a low- to high-field transition. We discuss with theoretical analysis the physical mechanism responsible for the new phenomena.

Controlled Synthesis of Large‐Scale, Uniform, Vertically Standing Graphene for High‐Performance Field Emitters

Large-scale, uniform, vertically standing graphene with atomically thin edges are controllably synthesized on copper foil using a microwave-plasma chemical vapor deposition system. A growth mechanism for this system is proposed. This film shows excellent field-emission properties, with low turn-on field of 1.3 V μm(-1) , low threshold field of 3.0 V μm(-1) and a large field-enhancement factor more than 10 000.

Extended vapor–liquid–solid growth and field emission properties of aluminium nitride nanowires

Hexagonal AlN (h-AlN) nanowires with an average diameter of around 15 nm have been prepared by an extended vapor–liquid–solid growth technique and characterized by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy and field emission measurements. This preparation is a rather simple route for bulk fabrication of h-AlN nanowires. The promising field emission property observed for h-AlN nanowires points to the important application potential of this material.

Metal-like single crystalline boron nanotubes: synthesis and in situ study on electric transport and field emission properties

Boron nanotubes (BNTs) have been theoretically proposed to have metallic properties whether they are in armchair or zigzag structure, so they have attracted much interest from researchers. However, their real properties have been not understood until now because they are hard to synthesize. In this paper, we have successfully fabricated a large quantity of boron nanotubes, which may provide a way to master their electric and field emission (FE) properties. Study on individual boron nanotubes shows that BNTs have metallic properties with an averaged conductivity of 40 Ω−1cm−1. Moreover, individual BNTs can sustain a high current of about 80 μA and their current density can reach 2.04 × 1011 A m−2, which is very close to those of CNTs. They are also incorporated into prototype luminescent tube devices for the first time and exhibit high luminescent efficiency and stability, which suggests that BNTs have a promising future in the FE area.

Water-evaporation-induced electricity with nanostructured carbon materials

Water evaporation is a ubiquitous natural process that harvests thermal energy from the ambient environment. It has previously been utilized in a number of applications including the synthesis of nanostructures and the creation of energy-harvesting devices. Here, we show that water evaporation from the surface of a variety of nanostructured carbon materials can be used to generate electricity. We find that evaporation from centimetre-sized carbon black sheets can reliably generate sustained voltages of up to 1 V under ambient conditions. The interaction between the water molecules and the carbon layers and moreover evaporation-induced water flow within the porous carbon sheets are thought to be key to the voltage generation. This approach to electricity generation is related to the traditional streaming potential, which relies on driving ionic solutions through narrow gaps, and the recently reported method of moving ionic solutions across graphene surfaces, but as it exploits the natural process of evaporation and uses cheap carbon black it could offer advantages in the development of practical devices.

Optimize the field emission character of a vertical few-layer graphene sheet by manipulating the morphology

Vertical few-layer graphene (FLG) sheets have been fabricated by using microwave-plasma-enhanced chemical vapour deposition. Their shape was manipulated through adjusting the growth time and hydrocarbon gas ratio. The growth mechanism during different growth stages is discussed. The field emission characteristics for different FLG shapes were tested and found to be strongly influenced by the tip shape, the height and the amorphous carbon content. The optimal shape of vertical FLG for field emission had fewer layers, sharp corners, large height and was free of amorphous carbon. The best field emission properties with the optimal shape were observed with a turn-on field of 1:8 V μm(-1) and maximum current density of 7 mA cm(-2).

Facile synthesis of a new class of aggregation-induced emission materials derived from triphenylethylene

A series of new aggregation-induced emission compounds with strong blue light-emitting properties derived from triphenylethylene were facilely synthesized by a Wittig–Horner reaction of bis(4-bromophenyl)methanone with diethyl 4-bromobenzylphosphonate, followed by a Suzuki reaction with arylboronic acids. Their maximum fluorescence emission wavelengths were 452–462 nm. The glass transition temperatures ranged from 70–145 °C, and the decomposition temperatures were 360–508 °C. The unoptimized device fabricated with benzofuranyl substituted compound as emitter turned on at ∼6 V, and the maximum luminance was ∼1500 cd m−2.