Divinah Manoharan

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/cm(2) (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.

High Stability Electron Field Emitters Synthesized via the Combination of Carbon Nanotubes and N2-Plasma Grown Ultrananocrystalline Diamond Films

An electron field emitter with superior electron field emission (EFE) properties and improved lifetime stability is being demonstrated via the combination of carbon nanotubes and the CH4/N2 plasma grown ultrananocrystalline diamond (N-UNCD) films. The resistance of the carbon nanotubes to plasma ion bombardment is improved by the formation of carbon nanocones on the side walls of the carbon nanotubes, thus forming strengthened carbon nanotubes (s-CNTs). The N-UNCD films can thus be grown on s-CNTs, forming N-UNCD/s-CNTs carbon nanocomposite materials. The N-UNCD/s-CNTs films possess good conductivity of σ = 237 S/cm and marvelous EFE properties, such as low turn-on field of (E0) = 3.58 V/μm with large EFE current density of (J(e)) = 1.86 mA/cm(2) at an applied field of 6.0 V/μm. Moreover, the EFE emitters can be operated under 0.19 mA/cm(2) for more than 350 min without showing any sign of degradation. Such a superior EFE property along with high robustness characteristic of these combination of materials are not attainable with neither N-UNCD films nor s-CNTs films alone. Transmission electron microscopic investigations indicated that the N-UNCD films contain needle-like diamond grains encased in a few layers of nanographitic phase, which enhanced markedly the transport of electrons in the N-UNCD films. Moreover, the needle-like diamond grains were nucleated from the s-CNTs without the necessity of forming the interlayer that facilitate the transport of electrons crossing the diamond-to-Si interface. Both these factors contributed to the enhanced EFE behavior of the N-UNCD/s-CNTs films.

Multienergy gold ion implantation for enhancing the field electron emission characteristics of heterogranular structured diamond films grown on Au-coated Si substrates

Multienergy Au-ion implantation enhanced the electrical conductivity of heterogranular structured diamond films grown on Au-coated Si substrates to a high level of 5076.0 (Ω cm)−1 and improved the field electron emission (FEE) characteristics of the films to low turn-on field of 1.6 V/μm, high current density of 5.4 mA/cm2 (@ 2.65 V/μm), and high lifetime stability of 1825 min. The catalytic induction of nanographitic phases in the films due to Au-ion implantation and the formation of diamond-to-Si eutectic interface layer due to Au-coating on Si together encouraged the efficient conducting channels for electron transport, thereby improved the FEE characteristics of the films.

Microstructural Evolution of Nanocrystalline Diamond Films Due to CH4/Ar/H2 Plasma Post-Treatment Process

Plasma post-treatment process was observed to markedly enhance the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films. TEM examinations reveal that the prime factor which improves the EFE properties of these films is the coalescence of ultrasmall diamond grains (∼5 nm) forming large diamond grains about hundreds of nanometers accompanied by the formation of nanographitic clusters along the grain boundaries due to the plasma post-treatment process. OES studies reveal the presence of large proportion of atomic hydrogen and C2 (or CH) species, which are the main ingredients that altered the granular structure of the UNCD films. In the post-treatment process, the plasma interacts with the diamond films by a diffusion process. The recrystallization of diamond grains started at the surface region of the material, and the interaction zone increased with the post-treatment period. The entire diamond film can be converted into a nanocrystalline granular structure when post-treated for a sufficient length of time.

Improvement of electron field emission properties of nanocrystalline diamond films by a plasma post-treatment process for cathode application in microplasma devices

The electron field emission (EFE) properties of nanocrystalline diamond (NCD) films were markedly enhanced when prepared with a plasma post-treatment on the ultra-small-grain granular-structured diamond films, as compared with conventional NCD films directly grown on Si using CH4/Ar/H2 plasma. Transmission electron microscopy reveals that the primary influence for the improvement of the EFE properties of these films was owing to an induction of the nanographitic phase in the films, while the ultrasmall diamond grains (∼5 nm) coalesced to form large diamond grains (∼hundreds of nanometers) during the plasma post-treatment process. This modification of the granular structure of the NCD films was greatly enhanced when a negative bias voltage (−300 V) was applied during the plasma post-treatment process. Moreover, three-electrode microplasma devices performed overwhelmingly better than two‐electrode devices, exhibiting a higher plasma current density with a longer lifetime stability. These microplasma devices...

Engineered design and fabrication of long lifetime multifunctional devices based on electrically conductive diamond ultrananowire multifinger integrated cathodes

Multi-functional vacuum electron field emission (VEFE) devices were developed using a laterally arranged multi-finger configuration with negative biased ultrananocrystalline-diamond graphite (NBG-UNDG) cathode/anode materials. The NBG-UNDG based multifinger lateral electron field emitter (ML-EFE) devices were fabricated using micropatterning and a simple lift-off process. The fabrication process of ML-EFE devices is observed to markedly enhance the electron field emission (EFE) properties of NBG-UNDG materials. The EFE investigations of ML-EFE devices revealed a low turn-on field for EFE at a voltage as low as 2.02 V μm−1 with a high current density of 1.51 mA at an electric field of 2.6 V μm−1. The presence of multi-layer nanographite (ng) in NBG-UNDG diamond nanowires and a Au interlayer at the film-to-substrate interface are presumed to be the main factors, which result in superior EFE properties for NBG-UNDG ML-EFE devices. The enhanced properties of NBG-UNDG based multifinger integrated cathodes have noteworthy potential for the generation of new display panel applications. Using NBG-UNDG ML-EFE devices as cathodes, a microplasma device was fabricated that can generate plasma at a low voltage of 260 V. Also, a photodetector, which provides an excellent photoresponsivity of 1.7 A W−1, was demonstrated using NBG-UNDG ML-EFE devices as sensing materials. Moreover, a NBG-UNDG based self-aligned cathode and gate VEFE transistor was fabricated, which exhibits enhanced transistor characteristics with a low turn-on gate voltage of 320 V. The fabrication of these NBG-UNDG devices, which can be operated at high power and under various vacuum conditions with long lifetime, demonstrates a practical approach in diamond based vacuum microelectronics and integrated circuits.

Synthesis of ultra-nano-carbon composite materials with extremely high conductivity by plasma post-treatment process of ultrananocrystalline diamond films

Needle-like diamond grains encased in nano-graphitic layers are an ideal granular structure of diamond films to achieve high conductivity and superior electron field emission (EFE) properties. This paper describes the plasma post-treatment (ppt) of ultrananocrystalline diamond (UNCD) films at low substrate temperature to achieve such a unique granular structure. The CH4/N2 plasma ppt-processed films exhibit high conductivity of σ = 1099 S/cm as well as excellent EFE properties with turn-on field of E0 = 2.48 V/μm (Je = 1.0 mA/cm2 at 6.5 V/μm). The ppt of UNCD film is simple and robust process that is especially useful for device applications.

The enhancement of the electron field emission behavior of diamond/CNTs materials via the plasma post-treatment process for the applications in triode-type vacuum field emission transistor

Plasma post-treatment (ppt) process for enhancing the electron field emission (EFE) properties of diamond/CNTs films for the applications in triode vacuum field emission (VFE) transistors is being reported. The EFE properties of UNCD/CNTs films were markedly improved by modifying the granular structure by ppt-process. The factor which resulted in enhanced EFE properties is due to the formation of nano-graphitic layers, while the nano-sized diamond grains coalesced. The triode VFE transistors performance was also significantly enhanced due to the utilization of DGC/CNTs (or HiD/CNTs) films as cathode that renders the triode VFE transistors possessing great potential for applications in vacuum microelectronics.

Synthesis of SiV-diamond particulates via the microwave plasma chemical deposition of ultrananocrystalline diamond on soda-lime glass fibers

We report the synthesis of silicon-vacancy (SiV) incorporated spherical shaped ultrananocrystalline diamond (SiV-UNCD) particulates (size ~1 μm) with bright luminescence at 738 nm. For this purpose, different granular structured polycrystalline diamond films and particulates were synthesized by using three different kinds of growth plasma conditions on the three types of substrate materials in the microwave plasma enhanced CVD process. The grain size dependent photoluminescence properties of nitrogen vacancy (NV) and SiV color centers have been investigated for different granular structured diamond samples. The luminescence of NV center and the associated phonon sidebands, which are usually observed in microcrystalline diamond and nanocrystalline diamond films, were effectively suppressed in UNCD films and UNCD particulates. Micron sized SiV-UNCD particulates with bright SiV emission has been attained by transfer of SiV-UNCD clusters on soda-lime glass fibers to inverted pyramidal cavities fabricated on Si substrates by the simple crushing of UNCD/soda-lime glass fibers in deionized water and ultrasonication. Such a plasma enhanced CVD process for synthesizing SiV-UNCD particulates with suppressed NV emission is simple and robust to attain the bright SiV-UNCD particulates to employ in practical applications.

Enhancement of plasma illumination characteristics via typical engineering of diamond–graphite nanocomposite films

Microstructural engineering of a diamond–graphite nanocomposite (DGC) with requisite properties in order to enhance the plasma illumination characteristics is being established via bias enhanced nucleation and growth of the nanocomposite material on silicon substrates using a microwave plasma (CH4/N2/H2) enhanced chemical vapor deposition method. Inspired by the concept of structure–property relationship, the microstructure of the DGC films is altered via varying the %H2 gas inclusion in the plasma. Consequently, the electrical conductivity, field emission (FE) properties and the plasma illumination characteristics of the DGC films are optimized depending upon their microstructure as well as morphological characteristics. The films grown using the optimum level of H2 (0.01%) encompass a diamond core with a needle-like morphology encased in layers of an sp2-bonded graphitic phase exhibiting an onion-like hierarchical structure forming a continuous network throughout the film and act as a matrix. The nano-sized diamond grains with needle-like morphology encased in graphitic layers is an exclusive choice of cathode material for plasma device applications as the Ar plasma of the DGC device can be triggered by a voltage as low as 310 V and possesses a better lifetime (14 h). The underlying mechanism of the microstructural engineering of the diamond–graphite nanocomposite is being proposed.