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

[[abstract]]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 the diamond grains, which decreases the band gap and increases the density of states within the band gap of diamond. Moreover, the formation of nanographitic phase surrounding the small diamond grains enhanced the conductivity at the diamond grain boundaries. Both of the phenomena enhance the EFE properties.[[booktype]]紙本[[booktype]]電子

Direct observation and mechanism of increased emission sites in Fe-coated microcrystalline diamond films

[[abstract]]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.[[booktype]]電子

The induction of nanographitic phase on Fe coated diamond films for the enhancement in electron field emission properties

[[abstract]]A thin layer of iron coating and subsequent post-annealing (Fe-coating/post-annealing) is seen to significantly enhance the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films. The best EFE properties, with a turn on field (E0) of 1.98 V/μm and current density (Je) of 705 μA/cm2 at 7.5 V/μm, are obtained for the films, which were Fe-coated/post-annealed at 900 °C in H2 atmosphere. The mechanism behind the enhanced EFE properties of Fe coated/post-annealed UNCD films are explained by the microstructural analysis which shows formation of nanographitic phase surrounding the Fe (or Fe3C) nanoparticles. The role of the nanographitic phase in improving the emission sites of Fe coated/post-annealed UNCD films is clearly revealed by the current imaging tunneling spectroscopy (CITS) images. The CITS images clearly show significant increase in emission sites in Fe-coated/post-annealed UNCD films than the as-deposited one. Enhanced emission sites are mostly seen around the boundaries of the Fe (or Fe3C) nanoparticles which were formed due to the Fe-coating/post-annealing processes. Moreover, the Fe-coating/post-annealing processes enhance the EFE properties of UNCD films more than that on the microcrystalline diamond films. The authentic factor, resulting in such a phenomenon, is attributed to the unique granular structure of the UNCD films. The nano-sized and uniformly distributed grains of UNCD films, resulted in markedly smaller and densely populated Fe-clusters, which, in turn, induced more finer and higher populated nano-graphite clusters.[[booktype]]紙

Tribochemistry of TaN, TiAlN and TaAlN coatings under ambient atmosphere and high-vacuum sliding conditions

© 2019 Elsevier B.V.Tribochemical analysis of monolithic TaN, TiAlN, and TaAlN coatings deposited by reactive magnetron sputtering onto 316LN stainless steel (SS) substrates are described. Tribology experiments were carried out in ambient atmospheric and high-vacuum sliding conditions to investigate the tribo-atmospheric dependent friction and wear characteristics of these coatings. The lower friction coefficient and improved wear-resistant properties were observed for TaN and TiAlN coatings in the humid atmosphere than in high-vacuum testing condition. Interestingly, lower friction and wear resistance properties of TaAlN coated SS are significantly enhanced in atmospheric as well as high-vacuum sliding conditions because of their highly dense and fine-grained microstructure with stable cubic B1 TaAlN phase. Energy dispersive X-ray spectroscopy elemental mapping and micro-focused X-ray photoelectron spectroscopy were carried out on the wear tracks to explore the comprehensive tribo-environment dependent tribochemistry. Formations of alumina (Al2O3) rich tribolayer reduced the friction and enhanced the wear resistance of TaAlN/SS sample tested in atmospheric condition; whereas this coating is highly stable in the high-vacuum condition with higher wear resistance11sciescopu

Microwave cavity perturbation of nitrogen doped nano-crystalline diamond films

Non-contact and non-destructive electrical conductivity measurements of nitrogen doped nano-crystalline diamond films have been demonstrated using a microwave cavity perturbation system. The conductivity of the films was controlled by simply varying the CH4 gas concentration during microwave plasma assisted chemical vapour deposition, thereby promoting the formation of sp2 carbon at the grain boundaries. The presence of sp2 carbon is verified through Raman spectroscopy, x-ray photoelectron spectroscopy and electron energy loss spectroscopy, while scanning electron microscopy confirms an increasing surface area for sp2 to form. The microwave cavity perturbation results show that the measured cavity quality factor varies with CH4 concentration. The extraction of conductivity is achieved through a depolarisation model, which must be considered when the sample is smaller than the cavity and through both electric and magnetic field perturbations. The microwave measurements are comparable to contacting and damaging measurements when the film conductivity is greater than the substrate, thus demonstrating an invaluable method for determining conductivity without the need for depositing any electrodes on the film

Effect of N+ ion implantation on micro/nano tribological properties of nanocrystalline diamond films

[[abstract]]Nanocrystalline diamond (NCD) films are prospective materials for micro/nanoelectromechanical systems (M/NEMS), due to their unique mechanical and tribological properties. In the present study, we report N+ ion implantation on NCD films, which exhibit superhydrophobic properties and ultra low friction coefficient contrary to as-deposited films. Interestingly, in microtribo-test, super low friction coefficient is observed due to the formation of carbonaceous transferlayer on the ball counter body. However, in nanotribo-test, high friction coefficient is obtained which is caused by severe deformation of ball due to the absence of stable transfer layer.[[journaltype]]國外[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]GB

Direct Observation and Mechanism for Enhanced Electron Emission in Hydrogen Plasma-Treated Diamond Nanowire Films

[[abstract]]The effect of hydrogen plasma treatment on the electrical conductivity and electron field emission (EFE) properties for diamond nanowire (DNW) films were systematically investigated. The DNW films were deposited on silicon substrate by N2-based microwave plasma-enhanced chemical vapor deposition process. Transmission electron microscopy depicted that DNW films mainly consist of wirelike diamond nanocrystals encased in a nanographitic sheath, which formed conduction channels for efficient electron transport and hence lead to excellent electrical conductivity and EFE properties for these films. Hydrogen plasma treatment initially enhanced the electrical conductivity and EFE properties of DNW films and then degraded with an increase in treatment time. Scanning tunneling spectroscopy in current imaging tunneling spectroscopy mode clearly shows significant increase in local emission sites in 10 min hydrogen plasma treated diamond nanowire (DNW10) films as compared to the pristine films that is ascribed to the formation of graphitic phase around the DNWs due to the hydrogen plasma treatment process. The degradation in EFE properties of extended (15 min) hydrogen plasma-treated DNW films was explained by the removal of nanographitic phase surrounding the DNWs. The EFE process of DNW10 films can be turned on at a low field of 4.2 V/μm and achieved a high EFE current density of 5.1 mA/cm2 at an applied field of 8.5 V/μm. Moreover, DNW10 films with high electrical conductivity of 216 (Ω cm)−1 overwhelm that of other kinds of UNCD films and will create a remarkable impact to diamond-based electronics.[[journaltype]]國外[[booktype]]紙本[[countrycodes]]US

Tribological properties of ultrananocrystalline diamond and diamond nanorod films

[[abstract]]Tribological properties of ultra nanocrystalline diamond (UNCD) and diamond nanorod (DNR) films are studied in ambient and nitrogen test atmospheres. Friction coefficient of UNCD films is found to be low in nitrogen and high in ambient test atmospheres using steel (100Cr6) and alumina (Al2O3) counter bodies. However, DNR films exhibit a high friction coefficient in nitrogen and a low value in ambient atmospheric conditions. Interestingly, in low humid conditions, the friction coefficient of UNCD decreases whereas it increases for the DNR films. Remarkable change in high/low friction coefficients of the UNCD and DNR films depending on test atmospheres is found to relate with the modification of internal chemical structures of these films. The distinct effect of the test atmospheres on the internal structure and chemistry of these films dominantly influence the interacting forces during the sliding interfaces. Internal characteristics of these film phase fractions such as sp3/sp2, nanocrystalline graphitic content and formation of carbonitrile phase are found to be the basic factors that influence the friction behaviors. Understanding the environmental dependent tribological properties of these films will be useful in the implementation of reliable micro- and nanoelectromechanical systems (MEMS/NEMS) in different test atmospheric conditions.[[journaltype]]國外[[ispeerreviewed]]Y[[booktype]]紙本[[booktype]]電子版[[countrycodes]]CH

Tribological properties of N+ ion implanted ultrananocrystalline diamond films

[[abstract]]Tribological properties of ultra nanocrystalline diamond (UNCD) films have chemically been modified by N+ ion implantation and subsequent annealing processes. Friction coefficient is found to be 0.15 in as-prepared film comparing to 0.09 and 0.05 in N+ ion implanted and post-annealed films, respectively. Such a modification of friction coefficient is a characteristic of the transformation of sp3 to graphitized/amorphized sp2 bonded carbon network. Transformation of sp3 to sp2 carbon network causes conversion of higher surface energy state (hydrophilic) to lower (hydrophobic) one which results in ultra low friction coefficient. Graphitization/amorphization in wear track observed by micro Raman spectroscopy is found to be the prominent mechanism for the reduction in friction coefficient.[[booktype]]紙本[[booktype]]電子

Enhanced charge storage properties of ultrananocrystalline diamond films by contact electrification-induced hydrogenation

© The Royal Society of Chemistry 2020. We report the enhanced charge storage characteristics of ultrananocrystalline diamond (UNCD) by contact electrification-induced hydrogenation. The non-catalytic hydrogenation of UNCD films was achieved by using platinum as an electron donor and sulfuric acid as a hydrogen proton donor, confirmed by Raman spectroscopy and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Chemical treatment with only a H2SO4 solution is responsible for the surface oxidation. The oxidation of UNCD resulted in an increase in the quantity and duration of the tribocharges. After non-catalytic hydrogenation, the generation of friction-induced tribocharges was enhanced and remained for three hours and more. We show that the hydrogen incorporation on grain boundaries is responsible for the improvement of charge storage capability, because the doped hydrogen acts as a trap site for the tribocharges. This lab-scale and succinct method can be utilized to control charge trap capability in nanoscale memory electronics11sciescopu