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

Nitrogen-Incorporated Boron-Doped Nanocrystalline Diamond Nanowires for Microplasma Illumination

The origin of nitrogen-incorporated boron-doped nanocrystalline diamond (NB-NCD) nanowires as a function of substrate temperature (T_s) in H₂/CH₄/B₂H₆/N₂ reactant gases is systematically addressed. Because of T_s, there is a drastic modification in the dimensional structure and microstructure and hence in the several properties of the NB-NCD films. The NB-NCD films grown at low T_s (400 °C) contain faceted diamond grains. The morphology changes to nanosized diamond grains for NB-NCD films grown at 550 °C (or 700 °C). Interestingly, the NB-NCD films grown at 850 °C possess one-dimensional nanowire-like morphological grains. These nanowire-like NB-NCD films possess the co-existence of the sp³-diamond phase and the sp²-graphitic phase, where diamond nanowires are surrounded by sp²-graphitic phases at grain boundaries. The optical emission spectroscopy studies stated that the CN, BH, and C₂ species in the plasma are the main factors for the origin of nanowire-like conducting diamond grains and the materialization of graphitic phases at the grain boundaries. Moreover, conductive atomic force microscopy studies reveal that the NB-NCD films grown at 850 °C show a large number of emission sites from the grains and the grain boundaries. While boron doping improved the electrical conductivity of the NCD grains, the nitrogen incorporation eased the generation of graphitic phases at the grain boundaries that afford conducting channels for the electrons, thus achieving a high electrical conductivity for the NB-NCD films grown at 850 °C. The microplasma devices using these nanowire-like NB-NCD films as cathodes display superior plasma illumination properties with a threshold field of 3300 V/μm and plasma current density of 1.04 mA/cm² with a supplied voltage of 520 V and a lifetime stability of 520 min. The outstanding plasma illumination characteristics of these conducting nanowire-like NB-NCD films make them appropriate as cathodes and pave the way for the utilization of these materials in various microplasma device applications.

Enhancement of UV Photodetection Properties of Hierarchical Core-Shell Heterostructures of a Natural Sericin Biopolymer with the Addition of ZnO Fabricated on Ultra-Nanocrystalline Diamond Layers

A novel self-assembled hierarchical heterostructure is derived from cocoon-derived sericin biopolymer (CSP) biowaste with ZnO deposited on ultra-nanocrystalline diamond (UNCD) substrates using a scalable chemical deposition technique. Then, high-performance long-life UV photodetectors are fabricated using this hybrid sericin, diamond, and ZnO (SDZ) nanostructure. The microstructural analysis reveals a several nanometer-thick CSP shell coated with a highly uniform ZnO nanorod (ZNR) array grown on the UNCD substrate. The CSP shell also contains columnar nanograins on top of the ZNR as well as vertical sidewalls with unique alignments. The hierarchical core-shell SDZ heterostructures reveal superior UV diode performance, with an ultrahigh UV switching ratio of 1.1 × 10⁵ at 5 V, an increase of up to 49 900% greater than that of as-grown ZNRs (220). High UV responsivity is observed around 3.6 A W^-1 under 365 nm UV light illumination. The perfect distribution of the sericin in the ZNRs on the UNCD substrates resulted in the ultrafast electron-hole recombination. The sericin dopants and the UNCD interlayer enabled the device to reach new energy levels in the conduction band, with the reduced barrier height allowing for improved charge carrier transportation during UV light illumination. It is believed that the sericin dopants and the UNCD layer increased the UV adsorptivity and the amount of conducting carbon dopants within the ZNRs was sufficient for s0tability. These noteworthy features make the SDZ heterostructures promising candidates for the fabrication of cost-efficient biopolymers and UNCD hybrid-based UV photodetectors.

Origin of Conductive Nanocrystalline Diamond Nanoneedles for Optoelectronic Applications

Microstructural evolution of nanocrystalline diamond (NCD) nanoneedles owing to the addition of methane and nitrogen in the reactant gases is systematically addressed. It has been determined that varying the concentration of CH₄ in the CH₄/H₂/N₂ plasma is significant to tailor the morphology and microstructure of NCD films. While NCD films grown with 1% CH₄ in a CH₄/H₂/N₂ (3%) plasma contain large diamond grains, the microstructure changed considerably for NCD films grown using 5% (or 10%) CH₄, ensuing in nanosized diamond grains. For 15% CH₄-grown NCD films, a well-defined nanoneedle structure evolves. These NCD nanoneedle films contain sp³ phase diamond, sheathed with sp²-bonded graphitic phases, achieving a low resistivity of 90 Ω cm and enhanced field electron emission (FEE) properties, namely, a low turn-on field of 4.3 V/μm with a high FEE current density of 3.3 mA/cm² (at an applied field of 8.6 V/μm) and a significant field enhancement factor of 3865. Furthermore, a microplasma device utilizing NCD nanoneedle films as cathodes can trigger a gas breakdown at a low threshold field of 3600 V/cm attaining a high plasma illumination current density of 1.14 mA/cm² at an applied voltage of 500 V, and a high plasma lifetime stability of 881 min is evidenced. The optical emission spectroscopy studies suggest that the C₂, CN, and CH species in the growing plasma are the major causes for the observed microstructural evolution in the NCD films. However, the increase in substrate temperature to ∼780 °C due to the incorporation of 15% CH₄ in the CH₄/H₂/N₂ plasma is the key driver resulting in the origin of nanoneedles in NCD films. The outstanding optoelectronic characteristics of these nanoneedle films make them suitable as cathodes in high-brightness display panels.

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 (E₀ = 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.

Structural and morphological peculiarities of hybrid Au/nanodiamond engineered nanostructures

Nanostructured Au nano-platelets have been synthesized from an Au(III) complex by growth process triggered by nanodiamond (ND). An electroless synthetic route has been used to obtain 2D Au/ND architectures, where individual nanodiamond particles are intimately embedded into face-centered cubic Au platelets. The combined use of high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED), was able to reveal the unusual organization of these hybrid nanoparticles, ascertaining the existence of preferential crystallographic orientations for both nanocrystalline species and highlighting their mutual locations. Detailed information on the sample microstructure have been gathered by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) of HR-TEM images, allowing us to figure out the role of Au defects, able to anchor ND crystallites and to provide specific sites for heteroepitaxial Au growth. Aggregates constituted by coupled ND and Au, represent interesting systems conjugating the best optoelectronics and plasmonics properties of the two different materials. In order to promote realistically the applications of such outstanding Au/ND materials, the cooperative mechanisms at the basis of material synthesis and their influence on the details of the hybrid nanostructures have to be deeply understood.