High-Performance Electron Field Emitters and Microplasma Cathodes Based on Conductive Hybrid Granular Structured Diamond Materials

High-performance diamond electron field emitters (EFEs) with extremely low turn-on field (<i>E</i>₀ = 1.72 V/μm) and high current density (1.70 mA/cm² at an applied field of 3.86 V/μm) were successfully synthesized by using a modified two-step microwave plasma chemical deposition process. Such emitters possess EFE properties comparable with most of carbon- or semiconductor-based EFE materials, but with markedly better lifetime stability. The superb EFE behavior of these materials was achieved owing to the reduction in the diamond-to-Si interfacial resistance and the increase in the conductivity of the bulk diamond films (HBD_–400 V) via the applications of high bias voltage during the preparation of the ultrananocrystalline diamond (UNCD) primary layer and the subsequent plasma post-treatment (PPT) process, respectively. The superior EFE properties along with enhanced robustness of HBD_–400 V films compared with the existing diamond-based EFE materials rendered these materials of greater potential for applications in high brightness display and multifunctional microplasma

Tribological Properties of Ultrananocrystalline Diamond Films in Inert and Reactive Tribo-Atmospheres: XPS Depth-Resolved Chemical Analysis

Tribological properties of diamond films are sensitive to the chemically reactive and inert tribo-atmospheric media, and therefore, it is difficult to understand the underlying tribological mechanisms. In the present work, tribological properties of surface-modified ultrananocrystalline diamond (UNCD) thin films were investigated in four distinct tribo-environmental conditions of ambient humid-atmosphere, nitrogen (N₂), argon (Ar), and methane (CH₄) gases. The in situ depth-resolved X-ray photoelectron spectroscopy (XPS) showed the desorption of oxygen and oxy-functional additives and sputtering of weakly bonded amorphous carbon species from the UNCD film surface after the Ar⁺-ion sputtering process. After desorption of these chemical entities, friction and wear were decreased and run-in regime cycles became shorter in UNCD films. Friction in the ambient humid-atmosphere was higher compared to other tribo-environmental conditions, and it was explained by the oxidation mechanism of the sliding interfaces and the formation of the oxidized carbon transferfilm. However, low friction and wear in the N₂ atmosphere was associated with the adsorption of N₂ species, forming nitrogen-terminated carbon bonds at the sliding interfaces. This was directly investigated by XPS and energy dispersive X-ray spectroscopy techniques. Furthermore, low friction in the Ar atmosphere was explained by the physical adsorption of Ar gaseous species, which tend to avoid the covalent carbon bond formation across the sliding interfaces. Moreover, ultralow friction in the CH₄ atmosphere was governed by the passivation of dangling carbon bonds by dissociative CH₄ complexes, which creates hydrogen-terminated repulsive sliding interfaces. More importantly, a shorter run-in regime with low friction and wear in Ar⁺-ion-sputtered UNCD films were explained by desorption of the oxygen and oxy-functional groups, which are inherently present in the UNCD films

Heterogranular-Structured Diamond–Gold Nanohybrids: A New Long-Life Electronic Display Cathode

In the age of hand-held portable electronics, the need for robust, stable and long-life cathode materials has become increasingly important. Herein, a novel heterogranular-structured diamond–gold nanohybrids (HDG) as a long-term stable cathode material for field-emission (FE) display and plasma display devices is experimentally demonstrated. These hybrid materials are electrically conductive that perform as an excellent field emitters, viz. low turn-on field of 2.62 V/μm with high FE current density of 4.57 mA/cm² (corresponding to a applied field of 6.43 V/μm) and prominently high lifetime stability lasting for 1092 min revealing their superiority on comparison with the other commonly used field emitters such as carbon nanotubes, graphene, and zinc oxide nanorods. The process of fabrication of these HDG materials is direct and easy thereby paving way for the advancement in next generation cathode materials for high-brightness FE and plasma-based display devices

Investigations on Diamond Nanostructuring of Different Morphologies by the Reactive-Ion Etching Process and Their Potential Applications

We report the systematic studies on the fabrication of aligned, uniform, and highly dense diamond nanostructures from diamond films of various granular structures. Self-assembled Au nanodots are used as a mask in the self-biased reactive-ion etching (RIE) process, using an O₂/CF₄ process plasma. The morphology of diamond nanostructures is a close function of the initial phase composition of diamond. Cone-shaped and tip-shaped diamond nanostructures result for microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films, whereas pillarlike and grasslike diamond nanostructures are obtained for Ar-plasma-based and N₂-plasma-based ultrananocrystalline diamond (UNCD) films, respectively. While the nitrogen-incorporated UNCD (N-UNCD) nanograss shows the most-superior electron-field-emission properties, the NCD nanotips exhibit the best photoluminescence properties, viz, different applications need different morphology of diamond nanostructures to optimize the respective characteristics. The optimum diamond nanostructure can be achieved by proper choice of granular structure of the initial diamond film. The etching mechanism is explained by in situ observation of optical emission spectrum of RIE plasma. The preferential etching of sp²-bonded carbon contained in the diamond films is the prime factor, which forms the unique diamond nanostructures from each type of diamond films. However, the excited oxygen atoms (O*) are the main etching species of diamond film

Enhanced Electron Field Emission Properties of Conducting Ultrananocrystalline Diamond Films after Cu and Au Ion Implantation

The effects of Cu and Au ion implantation on the structural and electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were investigated. High electrical conductivity of 186 (Ω•cm)^‑1 and enhanced EFE properties with low turn-on field of 4.5 V/μm and high EFE current density of 6.70 mA/cm² have been detected for Au-ion implanted UNCD (Au-UNCD) films that are superior to those of Cu-ion implanted UNCD (Cu-UNCD) ones. Transmission electron microscopic investigations revealed that Au-ion implantation induced a larger proportion of nanographitic phases at the grain boundaries for the Au-UNCD films in addition to the formation of uniformly distributed spherically shaped Au nanoparticles. In contrast, for Cu-UNCD films, plate-like Cu nanoparticles arranged in the row-like pattern were formed, and only a smaller proportion of nanographite phases along the grain boundaries was induced. From current imaging tunneling spectroscopy and local current–voltage curves of scanning tunneling spectroscopic measurements, it is observed that the electrons are dominantly emitted from the grain boundaries. Consequently, the presence of nanosized Au particles and the induction of abundant nanographitic phases in the grain boundaries of Au-UNCD films are believed to be the authentic factors, ensuing in high electrical conductivity and outstanding EFE properties of the films

Role of Carbon Nanotube Interlayer in Enhancing the Electron Field Emission Behavior of Ultrananocrystalline Diamond Coated Si-Tip Arrays

We improved the electron field emission properties of ultrananocrystalline diamond (UNCD) films grown on Si-tip arrays by using the carbon nanotubes (CNTs) as interlayer and post-treating the films in CH₄/Ar/H₂ plasma. The use of CNTs interlayer effectively suppresses the presence of amorphous carbon in the diamond-to-Si interface that enhances the transport of electrons from Si, across the interface, to diamond. The post-treatment process results in hybrid-granular-structured diamond (HiD) films via the induction of the coalescence of the ultrasmall grains in these films that enhanced the conductivity of the films. All these factors contribute toward the enhancement of the electron field emission (EFE) process for the HiD_CNT/Si‑tip emitters, with low turn-on field of <i>E</i>₀ = 2.98 V/μm and a large current density of 1.68 mA/cm² at an applied field of 5.0 V/μm. The EFE lifetime stability under an operation current of 6.5 μA was improved substantially to τ_{HiD/CNT/Si‑tip} = 365 min. Interestingly, these HiD_CNT/Si‑tip materials also show enhanced plasma illumination behavior, as well as improved robustness against plasma ion bombardment when they are used as the cathode for microplasma devices. The study concludes that the use of CNT interlayers not only increase the potential of these materials as good EFE emitters, but also prove themselves to be good microplasma devices with improved performance

Preferentially Grown Ultranano c‑Diamond and n‑Diamond Grains on Silicon Nanoneedles from Energetic Species with Enhanced Field-Emission Properties

The design and fabrication of well-defined nanostructures have great importance in nanoelectronics. Here we report the precise growth of sub-2 nm (c-diamond) and above 5 nm (n-diamond) size diamond grains from energetic species (chemical vapor deposition process) at low growth temperature of about 460 °C. We demonstrate that a pre-nucleation induced interface can be accounted for the growth of c-diamond or n-diamond grains on Si-nanoneedles (Si-NN). These preferentially grown allotropic forms of diamond on Si-NN have shown high electron field-emission properties and signify their high potential towards diamond-based electronic applications