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Low-temperature growth of diamond films using the chemical vapor deposition (CVD) method is not so widely reported and its initial periods of nucleation and growth phenomenon are of particular interest to the researchers. Four sets of substrates were selected for growing diamond films using linear antenna microwave plasma-enhanced CVD (LA-MPCVD). Among them, silicon and sapphire substrates were pre-treated with detonation nanodiamond (DND) seeds before diamond growth, for enhancement of its nucleation. Carbon nanotube (CNT) films on Si substrates were also used as another template for LA-MPCVD diamond growth. To enhance diamond nucleation during CVD growth, some of the CNT films were again pre-treated by the electrophoretic deposition (EPD) of diamond nanoparticles. All these substrates were then put inside the LA-MPCVD chamber to grow diamond films under variable processing conditions. Microwave input powers (1100–2800 W), input power modes (pulse or continuous), antenna-to-stage distances (5–6.5 cm), process gas recipes (with or without CO2), methane gas percentages (3%–5%), and deposition times (11–120 min) were altered to investigate their effect on the growth of diamond film on the pre-treated substrates. The substrate temperatures were found to vary from as low as 170 °C to a maximum of 307 °C during the alteration of the different processing parameters. Contrary to the conventional MPCVD, it was observed that during the first hour of LA-MPCVD diamond growth, DND seeds and the nucleating structures do not coalesce together to make a continuous film. Deposition time was the most critical factor in fully covering the substrate surfaces with diamond film, since the substrate temperature could not become stable during the first hour of LA-MPCVD. CNTs were found to be oxidized rapidly under LA-MPCVD plasma conditions; therefore, a CO2-free process gas recipe was used to reduce CNT burning. Moreover, EPD-coated CNTs were found to be less oxidized by the LACVD plasma during diamond growth. [ABSTRACT FROM AUTHOR]

In this work, a diamond/Ti/diamond multilayer structure has been fabricated by successively following thin-film CVD and PVD routes. It has been found that a combined pre-treatment of the silicon base substrate, via argon plasma etching for creating surface roughness and, thereafter, detonation nanodiamond (DND) seeding, helps in the nucleation and growth of well-adherent CVD diamond films with a well-defined Raman signal at 1332 cm−1, showing the crystalline nature of the film. Ti sputtering on such a CVD-grown diamond surface leads to an imprinted bead-like microstructure of the titanium film, generated from the underlying diamond layer. The cross-sectional thickness of the titanium layer can be found to vary by as much as 0.5 µm across the length of the surface, which was caused by a subsequent hydrogen plasma etching process step of the composite film conducted after Ti sputtering. The hydrogen plasma etching of the Ti–diamond composite film was found to be essential for smoothening the uneven as-grown texture of the films, which was developed due to the unequal growth of the microcrystalline diamond columns. Such hydrogen plasma surface treatment helped further the nucleation and growth of a nanocrystalline diamond film as the top layer, which was deposited following a similar CVD route to that used in depositing the bottom diamond layer, albeit with different process parameters. For the latter, a hydrogen gas diluted with PH3 precursor recipe produced smaller nanocrystalline diamond crystals for the top layer. The titanium layer in between the two diamond layers possesses a very-fine-grained microstructure. Transmission electron microscopy (TEM) results show evidence of intermixing between the titanium and diamond layers at their respective interfaces. The thin films in the composite multilayer follow the contour of the plasma-etched silicon substrate and are thus useful in producing continuous protective coatings on 3D objects—a requirement for many engineering applications. [ABSTRACT FROM AUTHOR]

Perovskite-type ferroelectric film can be utilized in ultra-high capacity dynamic random access memories, infrared detectors, surface acoustic waves devices and optical waveguide device applications. This ferroelectric film is effective in these applications because of its dielectric, ferroelectric, pyroelectric, piezoelectric, electro-optic and acousto-optic properties. The ferroelectric film also features a surface acoustic waves characteristic which is useful in the integration of various devices in the similar substrate.

The electron field emission (EFE) properties of microcrystalline diamond (MCD) films are significantly enhanced due to the Fe coating and post-annealing processes. The 900 °C post-annealed Fe coated diamond films exhibit the best EFE properties, with a turn on field (E0) of 3.42 V/μm and attain EFE current density (Je) of 170 μA/cm2 at 7.5 V/μm. Scanning tunnelling spectroscopy (STS) in current imaging tunnelling spectroscopy mode clearly shows the increased number density of emission sites in Fe-coated and post-annealed MCD films than the as-prepared ones. Emission is seen from the boundaries of the Fe (or Fe3C) nanoparticles formed during the annealing process. In STS measurement, the normalized conductance dI/dVI/V versus V curves indicate nearly metallic band gap, at the boundaries of Fe (or Fe3C) nanoparticles. Microstructural analysis indicates that the mechanism for improved EFE properties is due to the formation of nanographite that surrounds the Fe (or Fe3C) nanoparticles. [ABSTRACT FROM AUTHOR]

The electron field emission (EFE) process for diamond films was tremendously enhanced by Fe-coating and post-annealing processes. Microstructural analysis indicates that the mechanism for the improvement in the EFE process is the formation of nanographites with good crystallinity that surround the Fe (or Fe3C) nanoclusters. Presumably the nanographites were formed via the reaction of Fe clusters with diamond films, viz. by the dissolution of carbons into Fe (or Fe3C) clusters and the reprecipitation of carbon species to the surface of the clusters, a process similar to the growth of carbon nanotubes via Fe clusters as catalyst. Not only is a sufficiently high post-annealing temperature (900°C) required but also a highly active reducing atmosphere (NH3) is needed to give a proper microstructure for enhancing the EFE process. The best EFE properties are obtained by post-annealing the Fe-coated diamond films at 900°C in an NH3 environment for 5 min. The EFE behavior of the films can be turned on at E0 = 1.9 V/μm, attaining a large EFE current density of 315 μA/cm2 at an applied field of 8.8 V/μm (extrapolation using the Fowler-Nordheim model leads to Je = 40.7 mA/cm2 at a 20 V/μm applied field). [ABSTRACT FROM AUTHOR]

ZnO films with c-axis (0002) orientation have been successfully grown by radio frequency magnetron sputtering on glass substrates. The alumina films were deposited on interdigital transducers/ZnO/glass substrates by electron beam evaporation to enhance the performance of the ZnO thin film surface acoustic wave (SAW) devices. The crystalline structure and surface roughness of the films were investigated by X-ray diffraction and atomic force microscopy, respectively. The phase velocity and coupling coefficient of SAW device were apparently increased when we increased the thickness of alumina film. The experimental result is beneficial to improve the characteristics of the ZnO thin film SAW devices on cheap glass substrates. [ABSTRACT FROM AUTHOR]

Highly c-axis oriented AlN films were successfully deposited on SiO2/Si and sapphire substrates by RF magnetron sputtering. The optimum deposition conditions are nitrogen gas ratio (N2/Ar + N2) of 40%, RF power of 400 W, deposition pressure of 4 mTorr, and substrate temperature of 200°C. The full width at half maximum intensity of AlN(002) peak of AlN films on SiO2/Si and sapphire substrates sputtered at the optimum deposition conditions were about 0.26° and 0.2°, respectively. The phase velocity of the fabricated SAW device with AlN/SiO2/Si and AlN/sapphire layered structure was estimated to be about 4996 and 5589 m/s, respectively. [ABSTRACT FROM AUTHOR]

A two-mask fabrication process of a four-level Fresnel lens was used to evaluate its characteristics through investigating the effect of SU-8 photoresist on the profile of the focusing lens. A two-step deposition of ZnO films was applied to develop a feasible fabrication of a piezoelectric transducer with the structure Al/ZnO/Pt/Ti/SiO2/Si under reasonable conditions, which include deposition pressure of 0.7 Pa and 1.3 Pa, RF power of 100 W and 178 W, and sputtering gas ratio Ar:O2= 1:3 and 1:1 for first and second step deposition, respectively. Highly c-axis textured ZnO films were successfully obtained through two-step deposition process. [ABSTRACT FROM AUTHOR]

Abstract: Highly C-axis textured LiNbO3 thin films were grown on SiO2/Si substrates with a ZnO buffer layer by XeCl excimer pulsed laser deposition technique. We fixed the target–substrate spacing at 40mm, oxygen flow rate of 20sccm and the repetition rate of 5Hz, and then changed the substrate temperature, energy density and oxygen pressure to obtain the optimum deposition conditions. The effect of post-annealing process on improving the structural properties of the as-deposited LiNbO3 thin films was also studied. The ZnO buffer layers and LiNbO3 films were characterized by X-ray diffraction (XRD), atomic force microscopy and scanning electron microscopy to analyze their crystalline structure, surface roughness and surface morphology, respectively. For the optimum deposition parameters such as substrate temperature of 700°C, energy density of 4.6J/cm2 and oxygen pressure of 150Pa, the full width at half maximum intensity (FWHM) of LiNbO3(006) peak was 0.22°. The FWHM of LiNbO3(006) peak was further reduced to 0.19° via. in-situ post-treatment at 750°C for 30min. The results could be useful for integrating the surface acoustic wave device, optical waveguide and semiconductor device on the same Si substrate. [Copyright &y& Elsevier]

Abstract: Highly c-axis textured SrTiO3 (STO) thin films were directly grown on Si(100) substrates by XeCl excimer pulsed laser deposition technique without the utilization of buffer layer. Among the important deposition parameters, the substrate temperature, oxygen pressure, and target-to-substrate distance imposed most significant effect on the c-axis preferred orientation characteristics of the STO thin films. For the optimum deposition parameters such as substrate temperature of 700°C, oxygen pressure of 6.67×10−2 mbar and target-to-substrate distance of 35mm, the full width at half maximum intensity (FWHM) of STO(002) XRD peak was 0.42°. The FWHM of STO(002) peak was further reduced to 0.35° and 0.32° via. post-treatment with rapid thermal annealing (RTA at 800°C for 30s) and furnace annealing process (at 1000°C for 1.5h), respectively. The STO/Si films thus obtained are suitable for the synthesis of perovskite ferroelectric thin films. [Copyright &y& Elsevier]

Abstract: ZnO films with c-axis (0002) orientation have been grown on SiO2/Si substrates with an Al2O3 buffer layer by radio frequency magnetron sputtering. Crystalline structures of the films were investigated by X-ray diffraction, atomic force microscopy and scanning electron microscopy. The center frequency of the surface acoustic wave (SAW) device with a 4.8 μm thick Al2O3 buffer layer was measured to be about 408 MHz, which was much higher than that (265 MHz) of ZnO/SiO2/Si structure and approaches that (435 MHz) of ZnO/sapphire. It is a possible way as an alternative for the sapphire substrate for the high frequency SAW device applications, and is also useful to integrate the semiconductor and high frequency SAW devices on the same Si substrate. [Copyright &y& Elsevier]

Abstract: The propagation characteristics of surface acoustic wave for the ZnO piezoelectric films and nanocrystalline diamond (NCD) films multilayer SAW devices on Si substrates were investigated. High surface acoustic wave velocity is achieved for a ZnO/NCD/Si multilayer structure excited by a bottom-electroded device configuration. The NCD films deposited on Si substrates (NCD/Si) not only possess smooth surface, but also show good compatibility with ZnO materials, such that [002] textured ZnO films can be directly grown on NCD/Si substrates without the necessity of using buffer layer. The surface acoustic wave velocity increased with the thickness of the NCD films. For the thickness of the ZnO and NCD films investigated, the 0th mode surface acoustic velocity in IDT/ZnO/NCD/Si structure achieves 5100 m/s, whereas the 1st mode SAW in the ZnO/IDT/NCD/Si structure reaches 8500 m/s. [Copyright &y& Elsevier]

The interaction between Fe-coatings and ultrananocrystalline diamond (UNCD) films during annealing was investigated in detail using transmission electron microscopy. The thin Fe-coating first formed nanosized Fe-clusters and then catalytically dissociated the diamond, re-precipitating carbon to form nanosized graphite clusters. These clusters formed conducting networks that facilitated electron transport and greatly improved the electron field emission (EFE) properties of the UNCD films. The extent of enhancement varied markedly with annealing temperature and atmosphere. For H2-annealed films, EFE behavior was optimized by annealing at 900 °C. EFE was turned on at (E0)H2 = 1.2 V/μm, attaining EFE current density of (Je)H2 = 772.0 μA/cm2 at an applied field of 8.8 V/mm. These characteristics were superior to those of UNCD films NH3-annealed at 850 °C. The inferior EFE properties for the NH3-annealed samples were attributed to reaction of NH3 with the hydrocarbon phase that encapsulated the nanosized diamond grains, hindering Fe-diamond interaction. [ABSTRACT FROM AUTHOR]

Transparent p–n junctions composed of zinc oxide and magnesium-doped copper–chromium oxide thin films were prepared using radio-frequency (RF) magnetron sputtering deposition on indium–tin oxide glass substrates. The temperature of the substrate during deposition was varied to examine differences in the diode characteristics of the current–voltage response effect. The crystalline structure of the diode films was verified using X-ray diffraction (XRD) analysis. The ratio of the forward current to the reverse current reached 85.9 in the range of +4 to -4 V at a deposition temperature of 450 °C. The p–n junction diode film had an optical transparency above 75% for wavelengths in the visible range. [ABSTRACT FROM AUTHOR]

Enhanced electron field emission (EFE) properties in microcrystalline diamond (MCD) films that have been Fe-coated and postannealed are observed. Additionally, improved microplasma characteristics are also observed when these materials are used as cathodes. The turn-on field for inducing the EFE process decreases from 4.7 V/μm for pristine MCD films to 2.2 V/μm for the Fe-coated/postannealed ones, whereas the EFE current density at an applied field of 8.8 V/μm increases from 36.5 to 5327.1 μA/cm2. Transmission electron microscopy, in conjunction with high-angle annular dark field and 3D-tomography studies, reveals that enhanced EFE in the Fe-coated/postannealed MCD films is due to the graphite-like phase on the surface of diamond films. The authors infer that the Fe-coating interacts with the diamond in the postannealing process to dissolve carbons and reprecipitate them in nanographite networks. This process is similar to the formation of carbon nanotubes by the dissolution and reprecipitation of carbon species at the presence of nanosized Fe catalysts. The utilization of high EFE diamond films as cathode materials enhances the microplasma, as the ignition field for initiating the plasma is lowered and a high plasma current density is attainable. [ABSTRACT FROM AUTHOR]

In this study, we grew a microcrystalline diamond film on a textured Si substrate (MCD/textured Si) and demonstrated the improved electron field emission (EFE) properties of the film. We used a simple wet chemical etching method to fabricate the textured Si substrate and then grew the MCD film by microwave plasma enhanced chemical vapor deposition. Although the Raman spectroscopy profile of the MCD film was essentially unchanged, the surface morphology of the MCD film was altered markedly owing to the utilization of the textured substrate as a template. Hillocks of nanodiamond aggregates, rather than large grain granular structures, were formed for the MCD/textured Si films. The turn-on field for the EFE of the MCD/textured Si film was as small as 3.2 V/µm, with a current density as large as 751 µA/cm2 (at an applied field of 8.8 V/µm). The enhanced EFE properties of the thus-obtained MCD/textured Si film, along with the simplicity and cost-effectivity of the substrate texturing process, renders the MCD/textured Si film a good candidate for application as an electron field emitter. [ABSTRACT FROM AUTHOR]

Alumina films have been successfully deposited on ST-cut quartz and 128° Y–X LiNbO3 substrates by electron beam evaporation without any interlayer between them to ensure good adhesion of the alumina films to quartz and LiNbO3 substrates. The alumina films markedly increase the surface acoustic wave (SAW) velocity and coupling coefficient, and they can be used to improve the performance of SAW devices. The increase in SAW velocity with increasing thickness of the alumina film results from the the high stiffness of the alumina layer. The temperature coefficient of frequency (TCF) value of the alumina film is positive, and it can be used to compensate the negative TCF value of the LiNbO3 substrate. More temperature-stable SAW devices on LiNbO3 substrates with a higher phase velocity and coupling coefficient could be obtained by depositing the alumina overlayer. [ABSTRACT FROM AUTHOR]

The electron field emission (EFE) properties of diamond films were markedly improved by Fe-coating and postannealing processes. Transmission electron microscopy examination indicated that the possible mechanism of enhancing the EFE behavior is the reaction of the Fe layer with diamond and the reprecipitation of the dissolved carbon species to form nanographite. Scanning electron micrographs showed that the Fe coating first formed Fe particles at 700 °C and then reacted with diamond, forming iron carbide (Fe3C) at 800 °C. The dissolution and reprecipitation processes occurred simultaneously during the postannealing process at higher temperatures (800–950 °C), which leads to the formation of amorphous carbon when the postannealing temperature is low (800–850 °C) and to that of nanographite when the postannealing temperature is high (900–950 °C). The 900 °C-postannealed diamond films exhibit the best EFE properties, which can be turned on at a field of E0=2.8 V/µm, and attain an EFE current density of Je=21.4 µA/cm2 at 8 V/µm. [ABSTRACT FROM AUTHOR]

A four-level Fresnel lens and piezoelectric transducer were fabricated as an ejector using focused ultrasonic energy. The influence of the fabrication parameters on the profile of the focusing lens was investigated. Highly c-axis (002)-oriented ZnO films were successfully deposited on Pt (annealed)/Ti/SiO2/Si substrates under reasonable conditions, such as RF power of 178 W, substrate temperature of 380 °C, deposition pressure of 10 mTorr, and Ar:O2 gas flow ratio of 50%. These conditions were applied and confirmed through investigating the influence of deposition parameters on the properties of ZnO films. [ABSTRACT FROM AUTHOR]

ZnO films with c-axis (0002) orientation have been successfully grown by RF magnetron sputtering on Al2O3/SiO2/Si substrates. The alumina films were deposited on SiO2/Si substrates by electron beam evaporation. Crystalline structures of the films were investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The phase velocity of the surface acoustic wave (SAW) device with a 8-µm-thick alumina film was measured to be about 4733 m/s, which is much higher than that (4069 m/s) of the ZnO/SiO2/Si structure and approaches (89.6%) that (5283 m/s) of ZnO/sapphire. The coupling coefficient and temperature coefficient of the frequency of the ZnO/Al2O3/SiO2/Si structure with 8-µm-thick alumina film were close to those of the ZnO/sapphire structure. The experimental result is beneficial to the replacement of the expensive single-crystalline sapphire substrate with alumina film at lower cost for high-frequency SAW devices, and is also useful for integrating the semiconductor and high-frequency SAW devices on the same Si substrate. [ABSTRACT FROM AUTHOR]

The growth, structure and field emission properties of the two-dimensional carbon nanoflakes (CNFs) produced by radio-frequency (RF) sputtering without any catalyst or special substrate treatment have been investigated. The effects of deposition parameters (such as deposition time, sputtering gas composition, substrate temperature and RF power) on the structure and properties of the CNFs were also studied. Possible growth mechanism of the CNFs has been discussed with time evolution of surface microstructure. These films contain nanosized diamonds and allotropic phases (i-carbons and graphites) embedded in amorphous carbon films. The electron field emission (EFE) process can be turned on at E0=2.8 V/µm, achieving an EFE current density of Je = 1 mA/cm2 at a 5 V/µm applied field. The low turn-on field of 2.8 V/µm for electron field emission suggests that the CNFs could be used as a potential edge emitter. [ABSTRACT FROM AUTHOR]

ZnO films with a c-axis (0002) orientation have been successfully grown by RF magnetron sputtering on interdigital transducer (IDT)/Al2O3/SiO2/Si substrates. Al2O3 films were deposited on SiO2/Si substrates by electron beam evaporation. The crystalline structure and surface roughness of the films were investigated by X-ray diffraction and atomic force microscopy, respectively. The second-order phase velocity of a surface acoustic wave (SAW) device with a 7.5-µm-thick Al2O3 film was measured to be about 5432 m/s, which approaches (93%) that (5840 m/s) of ZnO/IDT/sapphire. This experimental result indicates that a low-cost Al2O3 film can be used to replace an expensive single-crystalline sapphire substrate for the fabrication of high-frequency SAW devices and is also useful in the integration of semiconductor and high-frequency SAW devices on the same Si substrate. [ABSTRACT FROM AUTHOR]

Carbon films with flakelike geometry, exhibiting excellent electron field emission (EFE) properties were synthesized by a modified RF sputtering process, which used an Ar:CH4:H2 gas mixture, instead of a conventional Ar:H2 mixture. These films contain nanosized diamonds and allotropic phases (i-carbons and graphites) embedded in amorphous carbon films. The EFE process can be turned on at E0 = 4.83 V/µm, achieving an EFE current density of Je = 280 µA/cm2 at an 8 V/µm applied field. The EFE properties of these flakelike carbon films essentially do not change with processing parameters, indicating that these carbon films are more process-reliable and hence have better potential for application as electron field emitters. [ABSTRACT FROM AUTHOR]

Aluminum oxide (Al2O3) films have been successfully deposited on stable temperature (ST)-cut quartz substrates by electron beam evaporation without any interlayer to ensure a good adhesion of the Al2O3 films to the quartz substrates. The Al2O3 thin films increase the surface acoustic wave (SAW) velocity sufficiently, and can be used to improve the performance of SAW devices. Both the theoretical and experimental results show that the SAW phase velocity in the Al2O3/quartz structure was increased with the insertion of an Al2O3 film. The increase in SAW velocity with increasing thickness of the Al2O3 film results from the stiffening effect of the Al2O3 layer. The velocity change ratio predicted by the theoretical analysis of the Al2O3 (1.45 µm)/quartz sample was about 4.38% which is slightly larger than the experimental result of 3.28%. These results are better than those published in the literature for a diamond-like carbon/SiC buffer layer/quartz structure with a velocity change ratio of 2.3%. [ABSTRACT FROM AUTHOR]

Highly (002)- or (200)-oriented BaTiO3 thin films were successfully grown on a Si substrate with a MgO buffer layer by RF magnetron sputtering. The deposition parameters need to be stringently controlled in order to grow BaTiO3 films with good crystallinity. The sputtering parameters such as substrate temperature, RF power, gas flow ratio, and deposition pressure were varied to obtain the optimum deposition conditions for the BaTiO3 films. The as-deposited films were characterized by X-ray diffraction analysis and atomic force microscopy to analyze their crystalline structure and surface morphology. The full width at half maximum intensity of the BaTiO3 (002) or (200) peak of the sample fabricated under the optimum deposition parameters was only 0.28°. The surface roughness of the BaTiO3 films was about 3.2 nm. The results could be useful in the integration of ferroelectric and semiconductor devices on the same Si substrate. [ABSTRACT FROM AUTHOR]

Highly c-axis-oriented LiNbO3(006) thin films were successfully grown on SiO2/Si substrates with a ZnO buffer layer by XeCl excimer pulsed laser deposition (PLD). The as-deposited films were characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy to analyze their crystalline structure and surface morphology. The results show that the highly c-axis-oriented LiNbO3 thin films of 2.5 µm thickness were successfully grown on SiO2/Si substrates with a ZnO buffer layer by PLD. The full width at half maximum intensity of the LiNbO3(006) peak of the sample fabricated under the optimum deposition conditions is only 0.18°. The center frequency of the LiNbO3/ZnO/SiO2/Si substrate with line width of 4 µm is 188 MHz, and the phase velocity is 3010 m/s, which is slightly lower than that of the 36° Y–X LiNbO3 substrate. [ABSTRACT FROM AUTHOR]

Abstract: Incorporation of H2 species into Ar plasma was observed to markedly alter the microstructure of diamond films. TEM examinations indicate that, while the Ar/CH4 plasma produced the ultrananocrystalline diamond films with equi-axed grains (~5nm), the addition of 20% H2 in Ar resulted in grains with dendrite geometry and the incorporation of 80% H2 in Ar led to micro-crystalline diamond with faceted grains (~800nm). Optical emission spectroscopy suggests that small percentage of H2-species (<20%) in the plasma leads to partially etching of hydrocarbons adhered onto the diamond clusters, such that the C2-species attach to diamond surface anisotropically, forming diamond flakes, which evolve into dendrite geometry. In contrast, high percentage of H2-species in the plasma (80%) can efficiently etch away the hydrocarbons adhered onto the diamond clusters, such that the C2-species can attach to diamond surface isotropically, resulting in large diamond grains with faceted geometry. The field needed to turn on the electron field emission for diamond films increases from E 0 =22.1V/μm (J e =0.48mA/cm2 at 50V/μm applied field) for 0% H2 samples to E 0 =78.2V/μm (J e <0.01mA/cm2 at 210V/μm applied field) for 80% H2 samples, as the grains grow, decreasing the proportion of grain boundaries. [Copyright &y& Elsevier]

Abstract: The effect of the N2 and H2 addition in Ar plasma on the characteristics of the UNCD films was systematically investigated. It is found that, while the N2/Ar plasma results in UNCD films with ultra-small grains (~5nm), incorporation of H2 into the N2/Ar plasma increased monotonously the size of the grains. Moreover, the diamond grains synthesized in H2 free plasma are of equi-axed geometry and those grown in H2-containing plasma are of plate-like one. The optical emission spectroscopic investigation indicated that the increase in electron temperature due to the addition of H2 into Ar plasma is the main cause, altering the microstructure of the UNCD films. As the H2 content increases, the spherical diamond grains first agglomerated to form elongated grains, which coalesce to form dendrite clusters. The proportion of grain boundaries is thus decreased that increased the turn-on field necessary for inducing the electron field emission process. [Copyright &y& Elsevier]