THE IMPROVEMENT OF ELECTRON FIELD EMISSION FROM AMORPHOUS CARBON FILMS DUE TO HYDROGEN PLASMA CHEMICAL ANNEALING EFFECT

Hydrogenated amorphous carbon films were fabricated by using layer-by-layer deposition method and hydrogen dilution method in a small d.c.-assisted plasma enhanced chemical vapor deposition system. It was found that the hydrogen plasma treatment could change the sp2/sp3 ratio to some extent by chemical etching. The improvements of field emission characteristics were observed compared with that from conventionally deposited a-C films, which can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters and the reduction of the surface emission barrier due to the hydrogen termination.

Controlled growth and field emission of vertically aligned A1N nanostructures with different morphologies

The controllable growth of three different morphologies of AlN nanostructures （nanorod, nanotip and nanocrater） arrays are successfully realized by using chemical vapour deposition （CVD） technology. All three nanostructures are of single crystal h-AlN with a growth orientation of [001]. Their growth is attributed to the vapour-liquid-solid （VLS） mechanism. To investigate the factors affecting field emission （FE） properties of AlN nanostructures, we compare their FE behaviours in several aspects. Experimental results show that AIN nanocrater arrays possess the best FE properties, such as a threshold field of 7.2 V/μm and an emission current fluctuation lower than 4%. Moreover, the three AlN nanostructures all have good field emission properties compared with a number of other excellent cathode nanomaterials, which suggests that they are future promising FE nanomaterials.

Simple method to rapidly fabricate chain-like carbon nanotube films and its field emission properties

A simple process to fabricate chain-like carbon nanotube （CNT） films by microwave plasma-enhanced chemical vapor deposition （MPCVD） was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were ground with Fe-doped SiO2 powder. The nano-structure of the deposited films was analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and Raman spectroscopy. The field electron emission characteristics of the chain-like carbon nanotube films were measured under the vacuum of 10-5 Pa. The low turn-on field of 0.80 V/μm and the emission current density of 8.5 mA/cm2 at the electric field of 3.0 V/μm are obtained. Based on the above results, chain-like carbon nanotube films probably have important applications in cold cathode materials and electrode materials.

Electron field emission characteristics of nano-catkin carbon films deposited by electron cyclotron resonance microwave plasma chemical vapour deposition

This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface morphology and the structure of the fabricated films were characterized by using scanning electron microscopes and Raman spectroscopy, respectively. The stable field emission properties with a low threshold field of 5V/μm corresponding to a current density of about 1μA/cm^2 and a current density of 3.2mA/cm^2 at an electric field of 10V/μm were obtained from the carbon film deposited at CH4 concentration of 8%. The mechanism that the threshold field decreased with the increase of the CH4 concentration and the high emission current appeared at the high CH4 concentration was explained by using the Fowler-Nordheim theory.

Enhanced field emission characteristics of thin-Au-coated nano-sheet carbon films

This paper reports that the nano-sheet carbon films （NSCFs） were fabricated on Si wafer chips with hydrogen- methane gas mixture by means of quartz-tube-type microwave plasma chemical vapour deposition （MWPCVD）. In order to further improve the field emission （FE） characteristics, a 5-nm Au film was prepared on the samples by using electron beam evaporation. The FE properties were obviously improved due to depositing Au thin film on NSCFs. The FE current density at a macroscopic electric field, E, of 9 V/μm was increased from 12.4 mA/cm2 to 27.2 mA/cm2 and the threshold field was decreased from 2.6 V/μm to 2.0 V/μm for Au-coated carbon films. A modified F-N model considering statistic effects of FE tip structures in the low E region and a space-chavge-limited-current effect in the high E region were applied successfully to explain the FE data of the Au-coated NSCF.

Field emission properties of capped carbon nanotubes doped by alkali metals:a theoretical investigation

The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation.The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable.In addition,the adsorption energies increase with the introduction of the electric field.The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function.Furthermore,the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.

Electrophoretic Carbon Nanotube Field Emission Layer for Plasma Display Panels

A carbon-nanotube(CNT) electrophoretic deposition(EPD) process has been developed to prepare a field emission layer in plasma display panels(PDP) for discharge voltage reduction. The CNT layer as a source of discharge priming electrons has been fabricated on the PDP front panel. The balling grinding,mix-acid treatment and EPD parameters have been investigated in order to obtain good uniformity and excellent field emission capability of CNT layer, in order to meet the specifications of CNTs in PDP cell. The measured turn-on field was around 1.1 V/μm in the field emission testing while the minimum sustaining voltage was decreased by 30~40 V with the use of CNT layer in the discharge testing.

Effect of nitrogen on deposition and field emission properties of boron-doped micro-and nano-crystalline diamond films

In this paper,we report the effect of nitrogen on the deposition and properties of boron doped diamond films synthesized by hot filament chemical vapor deposition.The diamond films consisting of micro-grains(nano-grains) were realized with low(high) boron source flow rate during the growth processes.The transition of micro-grains to nano-grains is speculated to be strongly(weekly) related with the boron(nitrogen) flow rate.The grain size and Raman spectral feature vary insignificantly as a function of the nitrogen introduction at a certain boron flow rate.The variation of electron field emission characteristics dependent on nitrogen is different between microcrystalline and nanocrystalline boron doped diamond samples,which are related to the combined phase composition,boron doping level and texture structure.There is an optimum nitrogen proportion to improve the field emission properties of the boron-doped films.

Field emission characteristics of nano-sheet carbon films deposited by quartz-tube microwave plasma chemical vapour deposition

Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition （MPCVD） in a gas mixture of hydrogen and methane. The structure of the fabricated films is investigated by using field emission scanning electron microscope （FESEM） and Raman spectroscopy. These nano^carbon films are possessed of good field emission （FE） characteristics with a low threshold field of 2.6 V/μm and a high current density of 12.6 mA/cm^2 at an electric field of 9 V/μm. As the FE currents tend to be saturated in a high E region, no simple Fowler-Nordheim （F-N） model is applicable. A modified F N model considering statistic effects of FE tip structures and a space-charge-limited-current （SCLC） effect is applied successfully to explaining the FE data observed at low and high electric fields, respectively.

Phase Transformation and Enhancing Electron Field Emission Properties in Microcrystalline Diamond Films Induced by Cu Ion Implantation and Rapid Annealing

Cu ion implantation and subsequent rapid annealing at 500℃ in N2 result in low surface resistivity of 1.611 ohm/sq with high mobility of 290 cm2 V-1S-1 for microcrystalline diamond （MCD） films. Its electrical field emission behavior can be turned on at Eo = 2.6 V/μm, attaining a current density of 19.5μA/cm2 at an applied field of 3.5 V/#m. Field emission scanning electron microscopy combined with Raman and x-ray photoelectron mi- croscopy reveal that the formation of Cu nanoparticles in MCD films can catalytically convert the less conducting disorder/a-C phases into graphitic phases and can provoke the formation of nanographite in the films, forming conduction channels for electron transportation.

ZnO nanorod arrays with tunable size and field emission properties on an ITO substrate achieved by an electrodeposition method

In the present work, vertically aligned ZnO nanorod arrays with tunable size are successfully synthesized on nonseeded ITO glass substrates by a simple electrodeposition method. The effect of growth conditions on the phase, morphology, and orientation of the products are studied in detail by X-ray diffraction （XRD）, scanning electron mi-croscopy （SEM）, and transmission electron microscopy （TEM）. It is observed that the as-prepared nanostructures exhibit a preferred orientation along c axis, and the size and density of the ZnO nanorod can be controlled by changing the concentration of ZnC12. Field emission properties of the as-synthesized samples with different diameters are also studied, and the results show that the nanorod arrays with a smaller diameter and appropriate rod density exhibit better emission properties. The ZnO nanorod arrays show a potential application in field emitters.

A comparison of the field emission characteristics of vertically aligned graphene sheets grown on different SiC substrates

The field emission （FE） properties of vertically aligned graphene sheets （VAGSs） grown on different SiC substrates are reported. The VAGSs grown on nonpolar SiC （10-10） substrate show an ordered alignment with the graphene basal plane-parallel to each other, and show better FE features, with a lower turn-on field and a larger field enhancement factor. The VAGSs grown on polar SiC （000-1 ） substrate reveal a random petaloid-shaped arrangement and stable current emission over 8 hours with a maximum emission current fluctuation of only 4%. The reasons behind the differing FE characteristics of the VAGSs on different SiC substrates are analyzed and discussed.

Field Emission of SiCN Thin Films Bombarded by Ar^+ Ions

SiCN thin films were synthesized by a radio frequency chemical vapor deposition (RFCVD) system on P\|type Si (1 0 0) wafers using C 2 H 4 , SiH 4 and N 2 as raw materials. In order to get rid of the oxygen absorbed on the surface and improve the characteristics of electron field emission, Ar + ions of low energy were used to bombard the samples. The field emission characteristics of SiCN thin films before and after Ar + bombardment were studied in the super vacuum environment of 10 -6 Pa. It was showed that the turn\|on field (defined as the point where the current\|voltage curve shows a sharp increase in the current density) decreased from 38 V/μm before bombardment to 25 V/μm after bombardment. And the maximum emission current density increased from 159.2 to 267.4 μA/cm 2 . The composition before and after Ar + bombardment was compared using X\|ray photoelectron spectroscopy (XPS). Our results illustrated that the field emission characteristics were improved after the bombardment of Ar + .

Field emissions of graphene films deposited on different substrates by CVD system

Graphene films are deposited on copper （Cu） and aluminum （Al） substrates, respectively, by using a microwave plasma chemical vapour deposition technique. Furthermore, these graphene films are characterized by a field emission type scanning electron microscope （FE-SEM）, Raman spectra, and field emission （FE） I-V measurements. It is found that the surface morphologies of the films deposited on Cu and Al substrates are different： the field emission property of graphene film deposited on the Cu substrate is better than that on the Al substrate, and the lowest turn-on field of 2.4 V/p-m is obtained for graphene film deposited on the Cu substrate. The macroscopic areas of the graphene samples are all above 400 mm2.

An easy way to controllably synthesize one-dimensional Sm B_6 topological insulator nanostructures and exploration of their field emission applications

A convenient fabrication technique for samarium hexaboride（SmB6） nanostructures（nanowires and nanopencils） is developed, combining magnetron-sputtering and chemical vapor deposition. Both nanostructures are proven to be single crystals with cubic structure, and they both grow along the [001] direction. Formation of both nanostructures is attributed to the vapor-liquid-solid（VLS） mechanism, and the content of boron vapor is proposed to be the reason for their different morphologies at various evaporation distances. Field emission（FE） measurements show that the maximum current density of both the as-grown nanowires and nanopencils can be several hundred μA/cm^2, and their FN plots deviate only slightly from a straight line. Moreover, we prefer the generalized Schottky-Nordheim（SN） model to comprehend the difference in FE properties between the nanowires and nanopencils. The results reveal that the nonlinearity of FN plots is attributable to the effect of image potential on the FE process, which is almost independent of the morphology of the nanostructures.All the research results suggest that the SmB6 nanostructures would have a more promising future in the FE area if their surface oxide layer was eliminated in advance.

Low-Frequency Noise in Gate Tunable Topological Insulator Nanowire Field Emission Transistor near the Dirac Point

Low-frequency flicker noise is usually associated with material defects or imperfection of fabrication procedure. Up to now, there is only very limited knowledge about flicker noise of the topological insulator, whose topologically protected conducting surface is theoretically immune to back scattering. To suppress the bulk conductivity we synthesize antimony doped Bi2Se3 nanowires and conduct transport measurements at cryogenic temperatures. The low-frequency current noise measurement shows that the noise amplitude at the high-drain current regime can be described by Hooge＇s empirical relationship, while the noise level is significantly lower than that predicted by Hooge＇s model near the Dirac point. Furthermore, different frequency responses of noise power spectrum density for specific drain currents at the low drain current regime indicate the complex origin of noise sources of topological insulator.

In situ mitigation strategies for field emission-induced cavity faults using low-level radiofrequency system

In the Chinese ADS front-end demo superconducting radiofrequency linac(CAFe)at the Institute of Modern Physics,a burst-noise signal-triggered cavity fault frequently appears during beam commissioning.These events are characterized by a rapid burst noise in the cavity pick-up,which may lead to an unexpected low-level radiofrequency(LLRF)response that eventually causes a cavity fault.To eliminate the undesirable reaction of the LLRF control loop,we propose a method that uses a burstnoise detection and processing algorithm integrated into the LLRF feedback controller.This algorithm can prevent undesired regulations in LLRF systems.Data analysis revealed that some burst-noise events did not exhibit measurable energy loss.In contrast,the other events were accompanied by a rapid loss of cavity stored energy and exhibited similarities to the‘‘E-quench’’phenomena reported in other laboratories.A particle-in-cell simulation indicated that the suspected E-quench phenomenon may be related to a plasma formation process inside the cavity.Fortunately,the LLRF algorithm is robust to the two different types of burst-noise events and can significantly mitigate the corresponding cavity faults in CAFe beam commissioning.

Residual gas properties in a field emission device with ZnO emitters

In this paper, a vacuum system is employed to compare the emission stabilities of the same ZnO cathode in a sealed field emission （FE） device and under ultrahigh vacuum （UHV） conditions. It is observed that the emission current is more stable under the UHV level than in the device. When all conditions except the ambient gases are kept unchanged, the emission current degradation is mainly caused by the residual gases in the sealed device. The quadrupole mass spectrometer （QMS） equipped on the vacuum system is used to investigate the residual gas components. Based on the obtained QMS data, the following conclusions can be drawn： the residual gases in ZnO-FE devices are H2, CH4, CO, Ar, and CO2. These residual gases can change the work function at the surface through adsorption or ion bombardment, thereby degrading the emission current of the cathode.

Electrodeposition of aligned ZnO sheet array on ITO substrate and their field emission characteristics

ZnO sheet array was fabricated by a simple electrodeposition method on the transparent ITO substrate at a temperature of about 60℃. The field emission properties of the ZnO sheet array were investigated. The fluctuation of the field emission current is less than 5% over several hours. The Fowler Nordheim curves with a roughly linear characteristic were obtained by analysing the current density and the intensity of the electrical field. The results prove that such a simple electrochemical method can potentially meet the demands on the production of cold cathodes for field emission display.

The influence of electronic transport across interface junction between Si substrate and the root of ZnO micro-prism on field emission performance

ZnO micro-prisms are prepared on the p-type and n-type Si substrates, separately. The Ⅰ-Ⅴ curves analysed by AFM show that the interface junctions between the ZnO micro-prisms and the p-type substrate and between the ZnO micro-prisms and the n-type Si substrate exhibit p-n junction behaviour and ohmic contuct behuviour, respectively. The formation of the p-n heterojunction and ohmic contact is ascribed to the intrinsic n-type conduction of ZnO material. Better field emission performance （lower onset voltage and larger emission current） is observed from an individual ZnO micro-prism grown on the n-type Si substrate. It is suggested that the n-Si/n-ZnO interracial ohmic contact benefits the electron emission; while the p-Si/n-ZnO interface heterojunction deteriorates the electron emission.