Ultrananocrystalline Diamond Films Research Articles

Lubricious behavior in CVD diamond/iron friction system at 25–700 ˚C

In this paper, we focus on the comparison of the friction for the microcrystalline and ultrananocrystalline diamond films against steel and found the differences between the compositions of the formed lubricious layers. We have found that for the microcrystalline diamond Fe catalyzes a graphite-based lubricious layer while for the ultrananocrystalline diamond the lubricious layer is an amorphous carbon-based. Minimum value of the friction coefficient µ = 0.37 was found for microcrystalline film at 575 ± 25 ˚C.

Growth and characterization of multilayer hot-filament chemical vapor deposition diamond coatings on WC–Co substrates

The diamond coating of tungsten carbide (WC)–cobalt (Co) hard metals has been the focus of various research activities mainly due to growing interest in diamond-coated tools for industrial machining of different materials. In this work, multilayered diamond coatings have been grown on pretreated tungsten carbide–cobalt substrates by hot-filament chemical vapor deposition. Two types of multilayer coatings have been prepared: (a) three-layer (alternating nanocrystalline diamond and microcrystalline diamond films) and (b) five-layer (alternating ultrananocrystalline and microcrystalline diamond films). The morphology, roughness, structure, thickness, adhesion of these coatings have been investigated using atomic force microscopy, field emission gun scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, nanoindentantion and Rockwell C indentation tests at 600 N load. Raman spectra of the two types of samples exhibited sharp characteristic bands of nanocrystalline diamond and a centered peak at 1340 cm−1. The displacement of this peak in relation to the natural diamond peak (1332 cm−1) can be attributed to graphitic inclusions in diamond grain boundaries and the thermal coefficient mismatch of the multilayer coating–substrate system. Roughness surface measurements showed very smooth surfaces for both samples. Although the substrate has a high binder content, the results show that well-adhered chemical vapor deposition diamond multilayer coatings were produced.

Antimicrobial propensity of ultrananocrystalline diamond films with embedded silver nanodroplets

Ultrananocrystalline diamond (UNCD) layers exhibit excellent mechanical properties and combine chemical inertness with good biological compatibility. Therefore, UNCD is considered a promising material for coating of implants. In this work we present the preparation of thin UNCD films with embedded silver nanodroplets that provide antimicrobial property, addressing another important topic concerning implant surgery, namely the risk of a life threatening bacterial infection. UNCD layers were prepared by microwave plasma-assisted chemical vapor deposition on a silicon substrate. Afterwards, a thin film of silver was deposited on top and treated by rapid thermal annealing (RTA) leading to dewetting and formation of silver nanodroplets on the surface. A second UNCD deposition with a short duration between 5 and 30 min was applied for capping the silver nanodroplets with a thin layer. The sample surfaces were characterized after each step by atomic force microscopy and scanning electron microscopy. The composition of the final samples, including the depth of the incorporated Ag nanodroplets, was analyzed by Auger electron spectroscopy. The impact of the silver layer thickness and the RTA temperature on the nanodroplet morphology was investigated. It was found that after 10 min of capping deposition the silver particles were completely covered with UNCD. In order to study the release of silver ions, the UNCD/Ag/UNCD samples were submerged in deionized water for 7 days at 37 °C, followed by detection of the silver concentration in the aqueous samples by inductively coupled plasma mass spectrometry. The determined concentration was strongly dependent on the thickness of the capping UNCD layer, exhibiting the highest silver content for the sample with the thinnest capping layer. Thus, the UNCD layer thickness can be utilized to control the amount of Ag ions released into the surrounding environment. The antibacterial properties were investigated with bacterial assays of the Gram-negative Escherichia coli and Gram-positive Bacillus subtilis bacteria that were exposed to the samples. All silver containing samples showed significant antimicrobial propensity, whereas the different capping thicknesses affected the time-course dependent antibacterial efficiency. Prime noveltyThin UNCD films were provided with supreme antibacterial propensity by embedding of silver nanodroplets. The thickness of the UNCD capping layer was varied and its influence on the release of silver in water was investigated. The UNCD/Ag/UNCD samples showed significant and controlled by the capping thicknesses time-dependent antibacterial efficiency against Gram-negative E. coli and Gram-positive B. subtilis bacteria.

Oxygen ion implanted grains dominantly contributed electron field emission of nanocrystalline diamond films

We have performed O ion implantation and annealing on nanocrystalline diamond (NCD) films with novel microstructure consisted of nanocrystalline diamond grains and intergranular interfaces instead of amorphous carbon grain boundaries. With annealing temperature increasing from 500 to 900 °C, a turn-on field of NCD films decreases from 4.5 to 5.9 V/μm to 3.6 V/μm, and its current density dramatically increases to 216 μA/cm2 at 8.0 V/μm. X-ray photoelectron spectroscopy results show that the content of sp3 carbon increases with lower C-O and C=O contents on the film surface, suggesting that fewer diamond grains are oxidized in the case of 900 °C annealing, dramatically improving the EFE properties. This reveals that O-doped diamond grains make main contribution to the enhanced EFE properties, which is further proved by the fact that EFE properties are not observed in C ion implanted and 900 °C annealed NCD film with the same structure. This is different from the typical NCD and ultrananocrystalline diamond (UNCD) films that the EFE properties were enhanced by the formation of nanographtic phase.

Nanoscale investigation of improved triboelectric properties of UV-irradiated ultrananocrystalline diamond films.

We report improved the triboelectric properties of ultraviolet (UV)-irradiated ultrananocrystalline diamond (UNCD) films that were measured using atomic force microscopy (AFM). Fabricated using the chemical vapor deposition (CVD) method, UNCD is an artificial diamond film with mechanical properties similar to single-crystal diamond. Surface modification by means of UV irradiation is a simple method to modify the surface properties of carbon-based and oxide materials. While the physical properties (e.g., roughness, adhesion, and friction) of these UNCD films did not exhibit any significant change following the UV treatment, we found that the UV-irradiated UNCD surface was oxidized and became graphitic, as confirmed using X-ray photoelectron spectroscopy, work function measurements using Kelvin probe force microscopy, and ultraviolet photoelectron spectroscopy. The work function of the samples increased with increasing UV exposure time, which is associated with the reduction of carbon atoms on the surface and oxygen-rich surfaces. Tribocharges were generated by scratching the surface of the UNCD films with a diamond-coated AFM tip. The duration of the tribocharges increased because of reactive radicals and the insulating property resulting from the UV/ozone treatment. The radicals were responsible for trapping charges; the UV-irradiated UNCD films preserved the charges for more than 5 h, which is five times longer than that on bare UNCD. This study demonstrated that UNCD is a promising material for generating triboelectricity and that UNCD can be used as a charge-trapping layer in charge-trap flash memory devices.

Phase transitions and critical phenomena of tiny grains carbon films synthesized in microwave‐based vapor deposition system

Different peak trends of tiny grains carbon film have been observed under the investigations of the Raman spectroscopy and energy loss spectroscopy. Carbon films known in nanocrystalline and ultrananocrystalline diamond films are synthesized by employing microwave‐based vapor deposition system. Carbon atoms exhibit several state behaviors depending on the incurred positions of their electrons. Different morphology of tiny grains under different chamber pressure is related to different rate of arriving typical energies at/near substrate surface. Those tiny grains of carbon film, which evolved in graphitic state atoms are converted to structure of smooth elements where elongation of atoms of one‐dimensional arrays is as per exerting surface format forces along opposite poles from their centers. Such tiny grains in the film are the cause of v1 peak under the investigation of the Raman spectrum because of the enhanced propagation of input laser signals through channelized inter‐state electron gaps of elongated graphitic state atoms. Those tiny grains of carbon film, which evolved in fullerene state are the cause of v2 peak. The tiny grains related to v1 peak possess a low intensity as compared with the ones which comprised atoms having state behaviors known in their exceptional hardness. Tiny grains representing v1 peak in the Raman spectrum are also the cause of field emission characteristic of a carbon film. Different peak recordings were made for the Raman at defined positions indicating a different state of carbon atoms for a different phase of deposited tiny grains, which is in line to their energy loss spectroscopy.

Nanostructured modified ultrananocrystalline diamond surfaces as immobilization support for lipases

Ultrananocrystalline diamond (UNCD) is a promising and - so far - relatively unexploited material for biocatalytic applications. In this study, UNCD films, deposited on silicon wafers by microwave plasma-assisted chemical vapor deposition, were investigated as supports for immobilization of the enzyme lipase B from Candida antarctica (CalB). The motivation for this work was the potential of utilization of the resulting biomaterials for the fabrication of flow bioreactors, harnessing both the benefits of the UNCD and the biocatalysts. Prior to immobilization, the UNCD surfaces were structured by reactive ion etching with a randomly distributed gold nanodroplet mask that was applied on top of the UNCD films, in order to increase the area for interaction with the enzyme. Furthermore, structured UNCD films were subjected to modification by UV/ozone treatment or trifluoromethane plasma which rendered the surfaces oxygen-terminated and hydrophilic or fluorine-terminated and hydrophobic, respectively. Two established coupling strategies, based on carbodiimide and oxalyl chloride chemistry, were investigated for covalent immobilization of CalB on structured oxygen-terminated surfaces. However, non-covalent immobilization on fluorine- and as-grown hydrogen-terminated surfaces, mediated by physical adsorption of the enzyme, appeared to be more efficient. Moreover, the data strongly suggested that the chemical nature of the termination and the hydrophobicity of the surface influence the substrate selectivity of the enzyme. Non-covalently immobilized CalB on strongly hydrophobic fluorine-terminated surfaces showed a ~5.5-fold higher preference for the short-chain substrate p-nitrophenyl butyrate over the medium-chain ester p-nitrophenyl laurate, whereas on hydrophilic O-terminated surfaces this selectivity was only ~1.9-fold. Moderately hydrophobic H-terminated surfaces conferred a selectivity ratio of ~3.5, which is in between the two former values and therefore in line with the hypothesized dependence of the substrate selectivity on the hydrophobicity of the surface material. These primary results can help on the optimization of the design of immobilized biocatalysts on UNCD surfaces to produce columns for flow bioreactors. Prime noveltyNanostructured modified ultrananocrystalline diamond (UNCD) surfaces were studied as immobilization support for lipases. The physical adsorption of lipase CalB was more efficient on hydrophobic F- or H-terminated surfaces than the two covalent coupling approaches on hydrophilic O-terminated UNCD. Furthermore, the chemical nature of the surface termination had an impact on the substrate selectivity by catalyzed hydrolysis.

Nitrogen ion implanted ultrananocrystalline diamond films: A better electrostatic charge storage medium

Atomic force microscopy (AFM) is used to induce electrostatically charged areas on nitrogen-ion-implanted ultrananocrystalline diamond (UNCD) films by applying a bias voltage to the AFM tip during the tapping mode scan. For local and intentional electrostatic charging, both positive and negative charges can be stored on pristine as well as nitrogen-ion-implanted UNCD films, as detected by Kelvin probe force microscopy. Interestingly, the charge storage capacity of pristine UNCD increases with the N-ion implantation dose. The potential amplitude and spatial distribution of the trapped charges can be controlled by the bias and load applied to the tip. The enhanced charge storage properties with doping are attributed to the formation of impurities, various defects, and the induction of an enhanced graphitic sp2 phase because of the high N-ion implantation dose, where all act as trapping centres for extra charge. The formation of various defect states and conducting sp2 nanographitic phases facilitate enhanced charge storage in N-ion-implanted UNCD films. This study underscores the potential importance of doping-dependent charge storage and the role of defects and nanographitic phases as a strategy for enhancing the electrostatic charge storage capability of diamond-based charge storage devices.

Nitrogen-Incorporated Ultrananocrystalline Diamond Electrodes for Dopamine Determination.

In this paper, nitrogen incorporated ultrananocrystalline diamond (NUNCD) films were fabricated for use as electrodes to detect dopamine. The NUNCD electrodes achieved high sensitivity, great selectivity, and excellent detection limits for dopamine sensing. The NUNCD electrode, fabricated as a potential sensitive biosensor for dopamine without any catalyst or mediators, demonstrated good activity for the direct detection of dopamine by simply putting the bare NUNCD electrode into a dopamine solution. Furthermore, the marked selectivity of the NUNCD electrode is very favorable for the determination of dopamine (DA) concentration (0.32 μM) in the presence of ascorbic acid (AA) and uric acid (UA). Considering dopamine detection in real biological fluid samples, the NUNCD electrode performed excellently with a detection limit of 0.39 μM and a high recovery ranging from 90-120%, revealing that NUNCD electrodes have promising use in the sensing of dopamine.

Boron doping of ultrananocrystalline diamond films by thermal diffusion process

Abstract

Structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond films**Project supported by the National Natural Science Foundation of China (Grant Nos. 50972129 and 50602039), the International Science Technology Cooperation Program of China (Grant No. 2014DFR51160), the National Key Research and Development Program of China (Grant No. 2016YFE0133200), European Unio’s Horizon 2020 Research and Innovation Staff Exchange (RISE) Scheme (Grant No. 734578),

We investigate the structural and electrical properties of carbon-ion-implanted ultrananocrystalline diamond (UNCD) films. Impedance spectroscopy measurements show that the impedance of diamond grains is relatively stable, while that of grain boundaries (GBs) (Rb) significantly increases after the C+ implantation, and decreases with the increase in the annealing temperature (Ta) from 650 °C to 1000 °C. This implies that the C+ implantation has a more significant impact on the conductivity of GBs. Conductive atomic force microscopy demonstrates that the number of conductive sites increases in GB regions at Ta above 900 °C, owing to the formation of a nanographitic phase confirmed by high-resolution transmission electronic microscopy. Visible-light Raman spectra show that resistive trans-polyacetylene oligomers desorb from GBs at Ta above 900 °C, which leads to lower Rb of samples annealed at 900 and 1000 °C. With the increase in Ta to 1000 °C, diamond grains become smaller with longer GBs modified by a more ordered nanographitic phase, supplying more conductive sites and leading to a lower Rb.

Evolution of Granular Structure and the Enhancement of Electron Field Emission Properties of Nanocrystalline and Ultrananocrystalline Diamond Films Due to Plasma Treatment Process.

The present work reports the plasma post treatment (ppt) process that instigates the evolution of granular structure of nanocrystalline diamond (NCD), consequently conducing the enhancement of the electron field emission (EFE) properties. The NCD films contain uniform and nanosized diamond grains (∼20 nm) with negligible thickness for grain boundaries that is distinctly different from the microstructure of ultrananocrystalline (UNCD) films with uniformly sized ultrananodiamond grains (∼5 nm) having relatively thick grain boundaries (∼0.1 nm). The turn-on of the electron field emission (EFE) process occurs at ( E0)NCD = 24.1 V/μm and ( E0)UNCD = 18.6 V/μm for the pristine NCD and UNCD materials, respectively. The granular structure of the starting diamond films largely influenced the microstructure evolution behavior and EFE properties of the materials subject to plasma annealing. The CH4/(Ar-H2) ppt-process leads to formation of a hybrid granular structured diamond (HiDNCD and HiDUNCD) via isotropic conjoining of nanosized diamond grains, whereas the CH4/N2 ppt-process leads to the formation of acicular granular structured diamond films (NNCD and NUNCD) via inducing aeolotropic growth of nanodiamond grains. While both of the HiDNCD and HiDUNCD films contain hybrid granular structure, the HiDUNCD films contain a larger proportion of nanographite phase and result in improved EFE properties, viz. ( E0)HiD-UNCD = 7.7 V/μm and ( E0)HiD-NCD = 12.3 V/μm. In contrast, when the films were CH4/N2 ppt-processed, the acicular diamond grains were formed for NUNCD and NNCD films; however, carbon nanoclusters attached to the diamond grains of NNCD films and the nanographitic layers encasing diamond cores are not crystallized very well, as compared with NUNCD films. Therefore, the NNCD films exhibit slightly inferior EFE properties than the NUNCD films, viz. ( E0)N-UNCD = 5.3 V/μm and ( E0)N-NCD = 11.8 V/μm. The difference in EFE properties for ppt-processed NCD and UNCD films corresponds to the dissimilar granular structure evolution behavior in these films that is, in turn, due to the distinct different microstructure of the pristine NCD and UNCD films.

Tailoring of polycrystalline diamond surfaces from hydrophilic to superhydrophobic via synergistic chemical plus micro-structuring processes

The wettability properties of the surfaces of polycrystalline diamond films, grown by Hot Filament Chemical Vapor Deposition, with different grain sizes, ranging from microcrystalline diamond (MCD), to nanocrystalline diamond (NCD), to ultrananocrystalline diamond (UNCD), were successfully tailored from as-grown flat semi-hydrophobic to hydrophilic surfaces, via oxygen (O2) plasma treatment, to highly-hydrophobic by carbon tetrafluoride (CF4) plasma treatment, and to super-hydrophobic diamond surface, via synergistic tailoring of surface chemistry and 3-D texturing. Raman spectroscopy analysis and secondary electron microscopy revealed the Hydrogen-surface termination and increased grain size, respectively, of the diamond films. Atomic Force Microscopy imaging of the plasma-treated UNCD films revealed no significant change in the surface roughness after either O2 or CF4 treatments. Nevertheless, a surface-chemistry alteration was confirmed by X-ray Photoelectron Spectroscopy. Finally, the synergistic combination of 3-D surface structuring and plasma-induced fluorine atoms surface termination of UNCD films produced a superhydrophobic state as revealed by a Water Contact Angle (WCA) close to ∼174°, thus producing the highest superhydrophobic surface of diamond material demonstrated today. The metastable Cassie-Baxter state, for the superhydrophobic 3-D UNCD surface, was demonstrated via a close correlation between the mathematical calculation based on the Cassie-Baxter Model and the experimental measurement of the WCA.

Microstructural modification of diamond-graphite nanohybrid films via adjusting deposition temperatures for enhanced electron field emission

To achieve enhanced electron field emission, diamond-graphite nanohybrid films are deposited on Si substrates by means of a microwave plasma chemical vapor deposition (MPCVD) reactor. Liquid diethylamine is used as a sole reactive source. An increase of deposition temperature from 730 °C to 830 °C leads to remarkable changes of morphology and microstructure of diamond-graphite nanohybrid films, namely from a typical planar ultrananocrystalline diamond (UNCD) film at 730 °C to a novel nanocrystalline diamond/graphene nanowall (ND/GNW) film at 830 °C. The electrical conductivity of a ND/GNW film is measured to be 762.4 Ω−1·cm−1, while for a UNCD film it is 18.0 Ω−1·cm−1. Moreover, the electron field emission is significantly enhanced on a ND/GNW film. With an applied electrical field of 9.9 V μm−1 its emission current density is 1.6 mA cm−2, 8-time larger than that for a UNCD film. The possible electron emission mechanism is then discussed based on the Fowler-Nordheim theory. This work offers a simple way to alter effectively the microstructures of sp2/sp3 nanohybrid films that benefit greatly to develop carbon-based field emission cold cathodes featuring high performance.

Addressing the Properties of Ultranano- and Microcrystalline CVD Diamond Films Grown on 4H-SiC Substrates

The growth of diamond films on different substrates has been studied extensively to support the emerging technologies ranging from mechanical to nano/microelectronics. It is known that the performance of these applications is affected by diamond film properties, such as structure and morphology. Using chemical vapor deposition (CVD) technique, we have deposited ultrananocrystalline diamond (UNCD) and microcrystalline diamond (MCD) films on 4H-SiC substrates and investigated their basic material properties. The understanding and exploitation of the material properties are fundamental to evaluate the potential of UNCD-on-SiC and MCD-on-SiC structures for fabrication of electronic devices and sensors.

An all-diamond X-ray position and flux monitor using nitrogen-incorporated ultra-nanocrystalline diamond contacts.

Diamond X-ray detectors with conducting nitrogen-incorporated ultra-nanocrystalline diamond (N-UNCD) films as electrodes were fabricated to measure X-ray beam flux and position. Structural characterization and functionality tests were performed for these devices. The N-UNCD films grown on unseeded diamond substrates were compared with N-UNCD films grown on a seeded silicon substrate. The feasibility of the N-UNCD films acting as electrodes for X-ray detectors was confirmed by the stable performance in a monochromatic X-ray beam. The fabrication process is able to change the surface status which may influence the signal uniformity under low bias, but this effect can be neglected under full collection bias.

Effective thermal and mechanical properties of polycrystalline diamond films

Polycrystalline diamond films were demonstrated as good candidates for electron field emitters, and their mechanical/thermal properties should thus be considered for real devices. We utilized ultrafast optical techniques to investigate the phonon dynamics of several polycrystalline diamond films, prepared by microwave plasma enhanced chemical vapor deposition. The mechanical properties (longitudinal acoustic velocity) and thermal conductivities of diamond films were evaluated from the coherent and incoherent phonon dynamics, respectively. Ultrananocrystalline diamond films were grown using a CH4 (2%)/Ar plasma, while microcrystalline diamond films were grown using a CH4 (2%)/H2 plasma. The ultrananocrystalline diamond film (with a grain size of several nanometers) possesses low acoustic velocity (14.5 nm/ps) and low thermal conductivity (3.17 W/m K) compared with other kinds of diamond films. The acoustic velocity of diamond films increased abruptly to nearly the same as that of natural diamond and remained there when the rod-shaped diamond grains were induced due to the incorporation of H2 in the growth plasma (CH4/Ar). The thermal conductivities of the materials increased monotonously with increasing incorporation of H2 in the growth plasma (CH4/Ar). The thermal conductivity of 25.6 W/m K was attained for nanocrystalline diamond films containing spherical diamond grains (with a size of several tens of nanometers). Compared with single crystalline diamond, the low thermal conductivity of polycrystalline films results from phonon scattering at the interfaces of grains and amorphous carbon in the boundary phases.

Ultrananocrystalline diamond-coated nanoporous membranes support SK-N-SH neuroblastoma epithelial [corrected] cell attachment.

Ultrananocrystalline diamond (UNCD) has been demonstrated to have attractive features for biomedical applications and can be combined with nanoporous membranes for applications in drug delivery systems, biosensing, immunoisolation and single molecule analysis. In this study, free-standing nanoporous UNCD membranes with pore sizes of 100 or 400 nm were fabricated by directly depositing ultrathin UNCD films on nanoporous silicon nitride membranes and then etching away silicon nitride using reactive ion etching. Successful deposition of UNCD on the substrate with a novel process was confirmed with Raman spectroscopy, X-ray photoelectron spectroscopy, cross-section scanning electron microscopy (SEM) and transmission electron microscopy. Both sample types exhibited uniform geometry and maintained a clear hexagonal pore arrangement. Cellular attachment of SK-N-SH neuroblastoma endothelial cells was examined using confocal microscopy and SEM. Attachment of SK-N-SH cells onto UNCD membranes on both porous regions and solid surfaces was shown, indicating the potential use of UNCD membranes in biomedical applications such as biosensors and tissue engineering scaffolds.

Afterglow, thermoluminescence and optically stimulated luminescence characterization of micro-, nano- and ultrananocrystalline diamond films grown on silicon by HFCVD

The exceptional combined properties of diamond such as, high hardness, corrosion resistant, high thermal conductivity, chemical inertness, non-toxicity and biocompatibility makes it a good candidate for applications in a new generation of optoelectronics, electronics, and biomedical devices. This paper focuses on describing systematic studies on the synthesis of polycrystalline diamond films and characterization of their optoelectronic properties. The studies focused on characterizing the relations among the structure, surface morphology and grain size of the polycrystalline diamond films investigated and the afterglow (AG) and thermoluminescence (TL) and optically stimulated luminescence (OSL) of the diamond films. Three different types of polycrystalline diamond films were investigated, namely: microcrystalline diamond (MCD, ≥1 μm grain size), nanocrystalline diamond (NCD, ≥10–100s nm grain size) and ultrananocrystalline diamond (UNCD, 2–10 nm grain size) grown on Si (111) substrate by hot filament chemical vapor deposition (HFCVD). The MCD films were grown for 8 h. and the NCD films were grown for 4 h. on substrates surfaces heated to ~800 °C, using a mixture of CH4 (3 sccm flow) and H2 (200 sccm flow) gases flown into an evacuated chamber to a total pressure of 10 Torr. UNCD films were grow for 2 h. on substrate surfaces at ~600 °C, using a mixture of CH4 (1 sccm flow), H2 (5 sccm flow), and Ar (45 sccm flow) gases flown into an evacuated chamber to a total pressure of 10 Torr and. The MCD and NCD films showed the typical Raman spectra (using visible 532 nm laser wavelength) for diamond with a well-defined peak at 1332 cm−1 indicating good quality of the diamond structure. The Raman of the UNCD film showed the characteristic D (~1344 cm−1) and G (~1389 cm−1) bands noticeable in visible Raman (532 nm laser wavelength). After beta irradiation, all films exhibited pronounced AG, TL and OSL signals with similar glow and decay curves, with intensities depending on diamond film structure.

Tribological Properties of Ultrananocrystalline Diamond Films in Inert and Reactive Tribo-Atmospheres: XPS Depth-Resolved Chemical Analysis

Tribological properties of diamond films are sensitive to the chemically reactive and inert tribo-atmospheric media, and therefore, it is difficult to understand the underlying tribological mechanisms. In the present work, tribological properties of surface-modified ultrananocrystalline diamond (UNCD) thin films were investigated in four distinct tribo-environmental conditions of ambient humid-atmosphere, nitrogen (N2), argon (Ar), and methane (CH4) gases. The in situ depth-resolved X-ray photoelectron spectroscopy (XPS) showed the desorption of oxygen and oxy-functional additives and sputtering of weakly bonded amorphous carbon species from the UNCD film surface after the Ar+-ion sputtering process. After desorption of these chemical entities, friction and wear were decreased and run-in regime cycles became shorter in UNCD films. Friction in the ambient humid-atmosphere was higher compared to other tribo-environmental conditions, and it was explained by the oxidation mechanism of the sliding interfaces a...