I.-Nan Lin

On the enhancement of field emission performance of ultrananocrystalline diamond coated nanoemitters

Ultrananocrystalline diamond (UNCD) nanoemitters were synthesized by a microwave plasma enhanced chemical vapor deposition process using silicon nanowires (SiNWs) as the template. Preseeding markedly enhances the nucleation of diamond on the SiNW templates, resulting in UNCD grains of smaller size and uniform distribution, which leads to significantly improved electron field emission (EFE) properties. The EFE for UNCD nanoemitters can be turned on at (E0)UNCD-NE=4.4V∕μm, achieving large EFE current density, (Je)UNCD-NE=13.9mA∕cm2 at an applied field of 12V∕μm, which is comparable with that of carbon nanotubes, but with much better processing reliability.

Catalytically induced nanographitic phase by a platinum-ion implantation/annealing process to improve the field electron emission properties of ultrananocrystalline diamond films

We report a Pt-ion implantation/annealing process for enhancing the electrical conductivity and the field electron emission (FEE) properties of ultrananocrystalline diamond (UNCD) films. Platinum ion implantation was performed on UNCD films at room temperature with the implantation energy of 500 keV and the ion dosages were varied from 1 × 1015 to 1 × 1017 ions per cm2 at an ion flux of 1.035 × 1012 ions per cm2 per s. The UNCD films, which were Pt-ion implanted with 1 × 1017 ions per cm2 and annealed at 600 °C possess the high electrical conductivity of 94.0 ohm−1 cm−1 and low turn-on field of 4.17 V μm−1 with the high FEE current density of 5.08 mA cm−2 (at 7.2 V μm−1). Current imaging tunneling spectroscopy and the local current–voltage curves of the scanning tunneling spectroscopic measurements illustrate that electrons are predominantly emitted from the grain boundaries. Transmission electron microscopy examinations reveal that the implanted Pt-ions first formed Pt nanoparticles in the UNCD films and then catalytically induced the formation of a nanographitic phase at the grain boundaries during the annealing process. Consequently, the formation of Pt nanoparticles induced abundant nanographitic phases in the Pt-ion implanted/annealed UNCD films, which is believed to be the genuine factor that results in the high electrical conductivity and excellent FEE properties of the films.

Direct observation of enhanced emission sites in nitrogen implanted hybrid structured ultrananocrystalline diamond films

A hybrid-structured ultrananocrystalline diamond (h-UNCD) film, synthesized on Si-substrates by a two-step microwave plasma enhanced chemical vapour deposition (MPECVD) process, contains duplex structure with large diamond aggregates evenly dispersed in a matrix of ultra-small grains (∼5 nm). The two-step plasma synthesized h-UNCD films exhibit superior electron field emission (EFE) properties than the one-step MPECVD deposited UNCD films. Nitrogen-ion implantation/post-annealing processes further improve the EFE properties of these films. Current imaging tunnelling spectroscopy in scanning tunnelling spectroscopy mode directly shows increased density of emission sites in N implanted/post-annealed h-UNCD films than as-prepared one. X-ray photoelectron spectroscopy measurements show increased sp2 phase content and C–N bonding fraction in N ion implanted/post-annealed films. Transmission electron microscopic analysis reveals that the N implantation/post-annealing processes induce the formation of defects in...

Growth, structural and plasma illumination properties of nanocrystalline diamond-decorated graphene nanoflakes

The improvement of the plasma illumination (PI) properties of a microplasma device due to the application of nanocrystalline diamond-decorated graphene nanoflakes (NCD-GNFs) as a cathode is investigated. The improved plasma illumination (PI) behavior is closely related to the enhanced field electron emission (FEE) properties of the NCD-GNFs. The NCD-GNFs possess better FEE characteristics with a low turn-on field of 9.36 V μm−1 to induce the field emission, a high FEE current density of 2.57 mA cm−2 and a large field enhancement factor of 2380. The plasma can be triggered at a low voltage of 380 V, attaining a large plasma current density of 3.8 mA cm−2 at an applied voltage of 570 V. In addition, the NCD-GNF cathode shows enhanced lifetime stability of more than 21 min at an applied voltage of 430 V without showing any sign of degradation, whereas the bare GNFs can last only 4 min. The superior FEE and PI properties of the NCD-GNFs are ascribed to the unique combination of diamond and graphene. Transmission electron microscopic studies reveal that the NCD-GNFs contain nano-sized diamond films evenly decorated on the GNFs. Nanographitic phases in the grain boundaries of the diamond grains form electron transport networks that lead to improvement in the FEE characteristics of the NCD-GNFs.

Microwave plasma-assisted photoluminescence enhancement in nitrogen-doped ultrananocrystalline diamond film

Optical properties and conductivity of nitrogen-doped ultrananocrystal diamond(UNCD) films were investigated following treatment with low energy microwaveplasma at room temperature. The plasma also generated vacancies in UNCD films and provided heat for mobilizing the vacancies to combine with the impurities, which formed the nitrogen-vacancy defect centers. The generated color centers were distributed uniformly in the samples. The conductivity of nitrogen-doped UNCD films treated by microwaveplasma was found to decrease slightly due to the reduced grain boundaries. The photoluminescence emitted by the plasmatreated nitrogen-doped UNCD films was enhanced significantly compared to the untreated films.

Nanoscale investigation of enhanced electron field emission for silver ion implanted/post-annealed ultrananocrystalline diamond films

Silver (Ag) ions are implanted in ultrananocrystalline diamond (UNCD) films to enhance the electron field emission (EFE) properties, resulting in low turn-on field of 8.5 V/μm with high EFE current density of 6.2 mA/cm2 (at an applied field of 20.5 V/μm). Detailed nanoscale investigation by atomic force microscopy based peak force-controlled tunneling atomic force microscopy (PF-TUNA) and ultra-high vacuum scanning tunneling microscopy (STM) based current imaging tunneling spectroscopy (CITS) reveal that the UNCD grain boundaries are the preferred electron emission sites. The two scanning probe microscopic results supplement each other well. However, the PF-TUNA measurement is found to be better for explaining the local electron emission behavior than the STM-based CITS technique. The formation of Ag nanoparticles induced abundant sp2 nanographitic phases along the grain boundaries facilitate the easy transport of electrons and is believed to be a prime factor in enhancing the conductivity/EFE properties of UNCD films. The nanoscale understanding on the origin of electron emission sites in Ag-ion implanted/annealed UNCD films using the scanning probe microscopic techniques will certainly help in developing high-brightness electron sources for flat-panel displays applications.

Effect of milling process on the microwave dielectric properties of Ba2Ti9O20 materials

The effects of the milling process on the characteristics of Ba2Ti9O20 materials were investigated. The chemical analyses using transmission electron microscopy (EDAX in TEM) revealed that the SiO2 species incorporated into the Ba2Ti9O20 materials were expelled by the Ba2Ti9O20 grains. It induced the dissociation of the Ba2Ti9O20 materials near the grain boundaries and degraded the microwave dielectric properties of the materials. The same phenomenon was assumed to be the procedure by which the high-energy-milling (HEM) process using Si3N4 grinding media (Si3N4-HEM) deleteriously influenced the microwave dielectric properties for the Ba2Ti9O20 materials. Utilizing the three-dimensional-milling (3DM) process in place of the Si3N4-HEM one markedly improved the characteristics of the Ba2Ti9O20 materials. The 3DM-processed samples own the same crystallinity as the HEM-processed ones but possess a pronouncedly more uniform microstructure and, therefore, exhibit a superior quality factor [(Q ? f)3DM = 28?500?GHz and (Q ? f)HEM = 21,900?GHz] with the same large dielectric constant (K = 38?39), when sintered at the same conditions (1350??C/4?h). Such a phenomenon is ascribed to the fact that the 3DM process can pulverize the powders efficiently but induce no SiO2-contamination.