Zhanling Lu

The field emission properties of graphene aggregates films deposited on Fe-Cr-Ni alloy substrates

The graphene aggregates films were fabricated directly on Fe-Cr-Ni alloy substrates by microwave plasma chemical vapor deposition system (MPCVD). The source gas was a mixture of H2 and CH4 with flow rates of 100 sccm and 12 sccm, respectively. The micro- and nanostructures of the samples were characterized by Raman scattering spectroscopy, field emission scanning electron microscopy (SEM), and transparent electron microscopy (TEM). The field emission properties of the films weremeasured using a diode structure in a vacuum chamber. The turn-on field was about 1.0 V/µm. The current density of 2.1 mA/cm2 at electric field of 2.4 V/µm was obtained.

Growth and field electron emission properties of nanostructured white carbon films

Nano-structured white carbon films were synthesized by microwave plasma chemical vapor deposition. The X-ray diffraction line at 2thetas=21.6deg (d=0.4107 nm) corresponds to the (110) facet of beta modifications of white carbon. The peak position at 283.46 eV in X-ray photoelectron spectrum represents binding energy of C 1s core level of sp1-hybridization of carbon. Field electron emission characteristics of the film were tested

Study on the field-emission characteristics of a-C:H films

Hydrogen contained nano-amorphous carbon films (a-C:H) were deposited on Si substrates by using microwave plasma chemical vapor deposition(MPCVD). A low turn-on field of 2.77 V//spl mu/m was obtained. The current density of 0.28 mA/cm/sup 2/ was obtained at electric field of 4.8 V//spl mu/m. When the electric field was increased to 6.85 V//spl mu/m, the current density was dramatically decreased to 0.067 mA/cm/sup 2/. It was found that the surface bonding ratio sp/sup 2//sp/sup 3/ of 1.25 was decreased to 0.53. It was revealed that some of the sp/sup 2/ phase changed to sp/sup 3/ due to arc-discharging, and sp/sup 2/ phase played a important role in field emission for a-C:H films. Field emission measurements from local emission sites of a-C:H films were carried out by using STM, and explained by DG model.

Preparation of nano-structure amorphous carbon film and its field emission properties

Nano-structure amorphous carbons films were fabricated on n-Si(111) substrates coated with titanium by microwave plasma chemical vapor deposition (MPCVD) system. The source gas was a mixture of H/sub 2/ and CH/sub 4/ with the flow rates of 100 sccm and 16 sccm, respectively. During the deposition, the total pressure of 6.0 KPa, substrates temperature of 830/spl deg/C and microwave power of 1700W which were kept for 4 hours. The surface morphology and the nano-structure of the films were tested by field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman scattering spectroscopy and X-ray photoelectron spectroscopy (XPS). The results show that the film consists of carbon grain size of no more than 100 nm and the main component was amorphous carbon with the mixture of sp/sup 2/ and sp/sup 3/ bond. Field emission of as-deposited film was then measured at a vacuum of below 5/spl times/10/sup -5/Pa. It was found that the initial turn-on field was very low, which was about 0.6 V//spl mu/m; the current density of 2.5mA/cm/sup 2/ was obtained under an electric field of 3.7 V//spl mu/m. The emission sites density was estimated to be more than 10/sup 4//cm/sup 2/ at electric field of 3.7V//spl mu/m. All these characteristics indicate that such deposited nano-structure amorphous carbon film is an efficient cold cathode material.

The effect of surface sp2/sp3 bonding ratios of carbon films on the field emission property

Summary form only given. Amorphous carbon films were deposited on Si substrates by using microwave plasma chemical vapor deposition (MPCVD). It is often noted that a conditioning of carbon film is required before the onset of reproducible field emission. It involves the cycling of the voltage up and down over several cycles etc, which may be accompanied by surface damage and phase changing. The exact nature of this conditioning step and the role of the damage-induced surface structure is not fully understood. In this paper, the change of surface bonding structure by cycling of the voltage up and down, and the effect of sp2/sp3 bonding ratios of the carbon films on field emission are investigated. The surface microstructure and sp2/sp3 bonding ratios were analyzed by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Field emission measurements of the films were carried out in a vacuum chamber with a base pressure of below 5/spl times/10-5Pa. The surface bonding structure of the as-deposited film was mainly sp2 component before doing field emission measurement. After emission conditioning treatment by cycling of the voltage up and down over several cycles, the surface sp2/sp3 bonding ratio of 1.25 was got, and the I-V characteristic of the field emission was getting reproducible and stable. The current density of 0.28 mA/cm/sup 2/ was obtained at electric field of 4.8 V//spl mu/m. When the electric field was increased to 6.85 V//spl mu/m, the current density was dramatically decreased to 0.067 mA/cm/sup 2/, and the surface sp2/sp3 bonding ratio was decreased to 0.53. It was revealed that surface sp2 phase in amorphous carbon films may be the main factor in obtaining low turn-on field and high current density.

The growth process and field emission characteristics of globe-like polycrystalline diamond films

This paper presents the growth process and field-emission(FE) characteristics of globe-like polycrystalline diamond films grown on titanium coated Si substrates by microwave plasma chemical vapor deposition. Scanning electron microscopy (SEM) and Raman scattering spectroscopy are utilized to characterize the morphology and microstructure. The macroscopic FE current-voltage(I-V) curve is measured by diode structure. Microscopic characteristics and local FE measurements are studied by scanning tunneling microscope (STM) in a vacuum of below 10-8 Pa. The turn-on field of the film deposited at 2h is 0.92V/μm and the current density is 0.62mA/cm at the electric field of 2V/μm.

The controllable growth of graphene and CNTs through change of the structure of Fe-Cr-Ni catalyst

In this paper, the controllable growth of graphene and carbon nanotubes were studied. Graphene and CNTs were deposited by microwave plasma chemical vapor deposition (MPCVD) using FeNiCr catalyst. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the morphology and microstructure of the materials.

Study on the field emission characteristics of a-C:H films

Hydrogen contained nano-amorphous carbon films (a-C:H) were deposited on Si substrates by using microwave plasma chemical vapor deposition(MPCVD). A low turn-on field of 2.77 V//spl mu/m was obtained. The current density of 0.28 mA/cm/sup 2/ was obtained at electric field of 4.8 V//spl mu/m. When the electric field was increased to 6.85 V//spl mu/m, the current density was dramatically decreased to 0.067 mA/cm/sup 2/. It was found that the surface bonding ratio sp/sup 2//sp/sup 3/ of 1.25 was decreased to 0.53. It was revealed that some of the sp/sup 2/ phase changed to sp/sup 3/ due to arc-discharging, and sp/sup 2/ phase played a important role in field emission for a-C:H films. Field emission measurements from local emission sites of a-C:H films were carried out by using STM, and explained by DG model.

Field emission characteristics of mixture films of nano-structure amorphous graphite and carbon nanotubes

The mixture film of nano-structure graphite and carbon nanotubes was fabricated on titanium coated ceramic substrate by microwave plasma chemical vapor deposition system (MPCVD). The source gas was a mixture of H/sub 2/ and CH/sub 4/ with flow rates of 100 sccm and 12 sccm, respectively. During the deposition, the total pressure of 6.0 KPa, substrate temperature of 850/spl deg/C and microwave power of 1500W were kept for 2 hours. The surface morphology and the nano-structure of the film were examined using field emission scanning electron microscopy, X-ray diffraction, Raman scattering spectroscopy and X-ray photoelectron spectroscopy. Field emission of the film were carried out in a vacuum chamber with base pressure of below 5/spl times/10/sup -5/Pa. The initial turn-on field was 0.6V//spl mu/m and 1.7 mA/cm/sup 2/ of current density at 1.7 V//spl mu/m was obtained. The stability of the emission was tested by maintaining the electric field at 1.8 V//spl mu/m. The experiments indicate that the film is an efficient and stable cathode material at low electric field.

Field electron emission of nano-structure carbon based thin films

Nano-crystalline fullerene-like film, nano-crystalline graphitic film and nano structure amorphous carbon film were prepared by microwave plasma chemical vapor deposition (MPCVD). The nano-structure and surface morphology of the deposited films were identified by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering and scanning electron microscope (SEM). The field electron emission characteristics of the films were studied by a testing method of diode structure in a vacuum chamber. The deposited nano-structure carbon based thin films and phosphor coated indium tin oxide (ITO) film were used to be cathode and anode, respectively. At the initial measurement, a very low turn-on field of 0.6V//spl mu/m was obtained for the three kinds of nano-structure carbon based materials. After cycling of voltage up and down several times, the turn-on field went up to more than 1.0 V//spl mu/m, and the current density decreased. In this paper, we suggest a theoretical model to discuss the field electron emission mechanism for the nano-structure carbon based thin films, and explain the emission characteristics. The surface local states, the bond dangling of carbon atoms and adsorbates on the surface of the films were considered in the theoretical model.