类球状微米金刚石聚晶的场发射

Growth and Field Emission Properties of Globe-like Diamond Microcrystalline-aggregate

在覆盖金属钛层的陶瓷上,采用微波等离子体化学气相沉积(MPCVD)法制备出类球状微米金刚石聚晶薄膜。利用扫描电子显微镜、拉曼光谱,X射线衍射,分析了薄膜的结构和表面形貌。测试了类球状微米金刚石聚晶膜的场致电子发射特性。开启电场仅为0.55V/μm,在2.18V/μm的电场下,其场发射电流密度高达11mA/cm2。仔细分析了膜的发射过程,发现类球状微米金刚石聚晶的结构对发射有很大影响,并对其发射机理进行了研究。

Carbon based materials with a low or negative electron affinity, such as diamond, diamond-like carbon （DLC）, amorphous carbon （a-C）, were widely used as cold cathode. Diamond films were generally deposited on the substrates by using chemical vapor deposition （CVD）, introducing a hydrocarbon gas diluted with an amount of hydrogen gas. There were a limited number of reports dealing with the field emission characteristics of the globe-like diamond microcrystalline aggregates. The globe-like diamond microcrystalline-aggregates were fabricated by microwave plasma chemical vapor deposition （MPCVD） method in the high methane concentration of H2/CH4 = 100/10 sccm using a microwave plasma CVD system in our laboratory. The ceramic with a Ti mental layer was used as substrate. The fabricated diamond aggregates were evaluated by Raman scattering spectroscopy, scanning electron microscopy （SEM）, X-ray diffraction （XRD）. It concluded that the globe-like diamond microcrystalline-aggregates are composed of diamond. The field emission properties were tested by using a diode structure in a vacuum chamber. A phosphorcoated indium tin oxide （ITO） anode was used for observing and characterizing the field emission. It was found that the globe-like diamond microcrystalline-aggregate exhibited good electron emission properties. The turn-on field was only 0.55 V/μm, and emission current density as high as 11 mA/cm^2 was obtained under an applied field of 2.18 V/μm. At the successive operation circles, the turn-on field tends to stabilize at 1.6 V/ μm and the current density of 1.1 mA/cm^2 is obtained at an electric field of 2.9 V/μm. The Fowler-Nordheim （F-N） plots of the field emission are almost straight line, which indicates that the mechanism of the electron emission from the diamond microcrystalline-aggregate is linked to field emission by tunnel effect. The growth mechanism and field emission properties of the globe-like diamond microcrystalline-aggregates are discussed relating to microstructure and electrical conductivity. We think that the good emission properties of the diamond aggregates are considered to be combined results from the lots of the grain boundaries in the diamonds microcrystalline-aggregates and the emission enhance factor is very high as β = 1 328.2.