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In the present work, Au-Si eutectic layer was used to enhance the electrical conductivity/electron field emission (EFE) properties of Au-ion implanted ultrananocrystalline diamond (Au-UNCD) films grown on Si substrates. The electrical conductivity was improved to a value of 230 (Ω cm)-1, and the EFE properties was enhanced reporting a low turn-on field of 2.1 V/μm with high EFE current density of 5.3 mA/cm2 (at an applied field of 4.9 V/μm) for the Au-UNCD films. The formation of SiC phase circumvents the formation of amorphous carbon prior to the nucleation of diamond on Si substrates. Consequently, the electron transport efficiency of the UNCD-to-Si interface increases, thereby improving the conductivity as well as the EFE properties. Moreover, the salient feature of these processes is that the sputtering deposition of Au-coating for preparing the Au-Si interlayer, the microwave plasma enhanced chemical vapor deposition process for growing the UNCD films, and the Au-ion implantation process for inducing the nanographitic phases are standard thin film preparation techniques, which are simple, robust, and easily scalable. The availability of these highly conducting UNCD films with superior EFE characteristics may open up a pathway for the development of high-definition flat panel displays and plasma devices. [ABSTRACT FROM AUTHOR]

Electron field emission (EFE) properties of nanocrystalline diamond (NCD) films synthesized by the bias-enhanced growth (beg) process under different bias voltages were investigated. The induction of the nanographitic phases is presumed to be the prime factor in enhancing the EFE properties of negative biased NCD films. Transmission electron microscopic investigations reveal that a negative bias voltage of -300V increases the rate of growth for NCD films with the size of the grains changing from nano to ultranano size. This effect also is accompanied by the induction of nanographitic filaments in the grain boundaries of the films. The turn-on field (E0) for the EFE process then effectively gets reduced. The EFE process of the beg-NCD-300V films can be turned on at E0=3.86 V/μm, and the EFE current density achieved is 1.49 mA/cm2 at an applied field of 7.85 V/μm. On the other hand, though a positive-bias beg process (+200 V) results in the reduction of grain size, it does not induce sufficient nanographitic phases to lower the E0 value of the EFE process. Moreover, the optical emission spectroscopic investigation indicates that one of the primary causes that changes the granular structure of the NCD films is the increase in the proportion of C2 and CH species induced in the growing plasma. The polarity of the bias voltage is of less importance in the microstructural evolution of the films. [ABSTRACT FROM AUTHOR]

The influence of N2 concentration in CH4/H2/N2 plasma on microstructural evolution and electrical properties of diamond films is systematically investigated. While the diamond films grown in CH4/N2plasma contain large diamond grains, for the diamond films grown using CH4/H2/(4%)N2 plasma, the microstructure drastically changed, resulting in ultra-nanosized diamond grains with Fd3m structure and a0=0.356 nm, along with the formation of n-diamond (n-D), a metastable form of diamond with space group Fm3m and a0=0.356 nm, and i-carbon (i-C) clusters, the bcc structured carbon with a0=0.432 nm. In addition, these films contain wide grain boundaries containing amorphous carbon (a-C). The electron field emission (EFE) studies show the best EFE behavior for 4% N2 films among the CH4/H2/N2 grown diamond films. They possess the lowest turn-on field value of 14.3 V/μm and the highest EFE current density value of 0.37 mA/cm2 at an applied field of 25.4 V/μm. The optical emission spectroscopy studies confirm that CN species are the major criterion to judge the changes in the microstructure of the films. It seems that the grain boundaries can provide electron conduction networks to transport efficiently the electrons to emission sites for field emission, as long as they have sufficient thickness. Whether the matrix nano-sized grains are 3C-diamond, n-D or i-C is immaterial. [ABSTRACT FROM AUTHOR]

Microstructural evolution of bias-enhanced grown (BEG) ultrananocrystalline diamond (UNCD) films has been investigated using microwave plasma enhanced chemical vapor deposition in gas mixtures of CH4 and Ar under different negative bias voltages ranging from -50 to -200 V. Scanning electron microscopy and Raman spectroscopy were used to characterize the morphology, growth rate, and chemical bonding of the synthesized films. Transmission electron microscopic investigation reveals that the application of bias voltage induced the formation of the nanographitic filaments in the grain boundaries of the films, in addition to the reduction of the size of diamond grains to ultra-nanosized granular structured grains. For BEG-UNCD films under -200 V, the electron field emission (EFE) process can be turned on at a field as small as 4.08 V/μm, attaining a EFE current density as large as 3.19 mA/cm2 at an applied field of 8.64 V/μm. But the films grown without bias (0 V) have mostly amorphous carbon phases in the grain boundaries, possessing poorer EFE than those of the films grown using bias. Consequently, the induction of nanographitic filaments in grain boundaries of UNCD films grown in CH4/Ar plasma due to large applied bias voltage of -200V is the prime factor, which possibly forms interconnected paths for facilitating the transport of electrons that markedly enhance the EFE properties. [ABSTRACT FROM AUTHOR]

Copper ion implantation and subsequent annealing at 600 °C achieved high electrical conductivity of 95.0 (Ωcm)-1 for ultrananocrystalline diamond (UNCD) films with carrier concentration of 2.8 x 1018 cm-2 and mobility of 6.8 x 10² cm²/V s. Transmission electron microscopy examinations reveal that the implanted Cu ions first formed Cu nanoclusters in UNCD films, which induced the formation of nanographitic grain boundary phases during annealing process. 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 nanographitic phases presence in the grain boundaries formed conduction channels for efficient electron transport, ensuing in excellent electron field emission (EFE) properties for copper ion implanted/annealed UNCD films with low turn-on field of 4.80 V/μm and high EFE current density of 3.60 mA/cm2 at an applied field of 8.0 V/μm. [ABSTRACT FROM AUTHOR]

Microstructural evolution of ultrananocrystalline diamond (UNCD) films as a function of substrate temperature (TS) and/or by introducing H2 in Ar/CH4 plasma is investigated. Variation of the sp2 and sp3 carbon content is analyzed using UV-Raman and near-edge X-ray absorption fine structure spectra. Morphological and microstructural studies confirm that films deposited using Ar/CH4 plasma at low TS consist of a random distribution of spherically shaped ultra-nano diamond grains with distinct sp2-bonded grain boundaries, which are attributed to the adherence of CH radicals to the nano-sized diamond clusters. By increasing TS, adhering efficiency of CH radicals to the diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nano-sized diamond grains break, whereas the addition of 1.5% H2 in Ar/CH4 plasma at low TS induces atomic hydrogen that preferentially etches out the t-PA attached to ultra-nano diamond grains. Both cases make the sp3-diamond phase less passivated. This leads to C2 radicals attaching to the diamond lattice promoting elongated clustered grains along with a complicated defect structure. Such a grain growth model is highly correlated to explain the technologically important functional property, namely, plasma illumination (PI) of UNCD films. Superior PI properties, viz. low threshold field of 0.21 V/μm with a high PI current density of 4.10 mA/cm2 (at an applied field of 0.25 V/μm) and high γ-coefficient (0.2604) are observed for the UNCD films possessing ultra-nano grains with a large fraction of grain boundary phases. The grain boundary component consists of a large amount of sp2-carbon phases that possibly form interconnected paths for facilitating the transport of electrons and the electron field emission process that markedly enhance PI properties. [ABSTRACT FROM AUTHOR]