Department of Physics, Tamkang University, Tamsui 251, Taiwan, ROC.
ACS Appl Mater Interfaces. 2011 Oct;3(10):4007-13. doi: 10.1021/am200867c. Epub 2011 Oct 6.
Freestanding ultrananocrystalline diamond (UNCD) films with homojunction insulating layer in situ grown on a conducting layer showed superior electron field emission (EFE) properties. The insulating layer of the films contains large dendrite type grains (400-600 nm in size), whereas the conducting layer contains nanosize equi-axed grains (5-20 nm in size) separated by grain boundaries of about 0.5-1 nm in width. The conducting layer possesses n-type (or semimetallic) conductivity of about 5.6 × 10(-3) (Ω cm)(-1), with sheet carrier concentration of about 1.4 × 10(12) cm(-2), which is ascribed to in situ doping of Li-species from LiNbO(3) substrates during growth of the films. The conducting layer intimately contacts the bottom electrodes (Cu-foil) by without forming the Schottky barrier, form homojunction with the insulating layer that facilitates injection of electrons into conduction band of diamond, and readily field emitted at low applied field. The EFE of freestanding UNCD films could be turned on at a low field of E(0) = 10.0 V/μm, attaining EFE current density of 0.2 mA/cm(2) at an applied field of 18.0 V/μm, which is superior to the EFE properties of UNCD films grown on Si substrates with the same chemical vapor deposition (CVD) process. Such an observation reveals the importance in the formation of homojunction on enhancing the EFE properties of materials. The large grain granular structure of the freestanding UNCD films is more robust against harsh environment and shows high potential toward diamond based electronic applications.
独立的纳米晶金刚石（UNCD）薄膜具有同结绝缘层，在导电层上原位生长，表现出优异的电子场发射（EFE）性能。该薄膜的绝缘层含有大的树枝状晶粒（尺寸为 400-600nm），而导电层含有纳米级等轴晶粒（尺寸为 5-20nm），由约 0.5-1nm 宽的晶界隔开。导电层具有 n 型（或半金属）导电性，约为 5.6×10^(-3)（Ω cm）^(-1)，载流子浓度约为 1.4×10^（12）cm^(-2)，这归因于在薄膜生长过程中来自 LiNbO3 衬底的 Li 物种的原位掺杂。导电层通过不形成肖特基势垒而与底部电极（Cu 箔）紧密接触，与绝缘层形成同结，有利于电子注入金刚石导带，并在低外加电场下容易场发射。独立的 UNCD 薄膜的 EFE 可以在低场 E(0)=10.0V/μm 下开启，在外加电场为 18.0V/μm 时达到 EFE 电流密度为 0.2mA/cm^2，优于相同化学气相沉积（CVD）工艺下在 Si 衬底上生长的 UNCD 薄膜的 EFE 性能。这种观察结果表明，在增强材料的 EFE 性能方面，同结的形成非常重要。独立的 UNCD 薄膜的大晶粒颗粒结构更能抵抗恶劣环境，在基于金刚石的电子应用方面具有很高的潜力。
