Contact angle goniometry is conducted for epitaxial graphene on SiC. Although only a single layer of epitaxial graphene exists on SiC, the contact angle drastically changes from 69 degrees on SiC substrates to 92 degrees on graphene. It is found that there is no thickness dependence of the contact angle from the measurements of single-, bi-, and multilayer graphene and highly ordered pyrolytic graphite (HOPG). After graphene is treated with oxygen plasma, the level of damage is investigated by Raman spectroscopy and the correlation between the level of disorder and wettability is reported. By using a low-power oxygen plasma treatment, the wettability of graphene is improved without additional damage, which can solve the adhesion issues involved in the fabrication of graphene devices.

In this work, we demonstrate that thermal atomic layer deposited (ALD) titanium oxide (TiOx) films are able to provide a—up to now unprecedented—level of surface passivation on undiffused low-resistivity crystalline silicon (c-Si). The surface passivation provided by the ALD TiOx films is activated by a post-deposition anneal and subsequent light soaking treatment. Ultralow effective surface recombination velocities down to 2.8 cm/s and 8.3 cm/s, respectively, are achieved on n-type and p-type float-zone c-Si wafers. Detailed analysis confirms that the TiOx films are nearly stoichiometric, have no significant level of contaminants, and are of amorphous nature. The passivation is found to be stable after storage in the dark for eight months. These results demonstrate that TiOx films are also capable of providing excellent passivation of undiffused c-Si surfaces on a comparable level to thermal silicon oxide, silicon nitride, and aluminum oxide. In addition, it is well known that TiOx has an optimal refractive index of 2.4 in the visible range for glass encapsulated solar cells, as well as a low extinction coefficient. Thus, the results presented in this work could facilitate the re-emergence of TiOx in the field of high-efficiency silicon wafer solar cells.

The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic-arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy ͑EELS͒, and cross-sectional transmission electron microscopy. EELS analysis shows that the highest sp 3 contents ͑85%͒ and densities ͑3.00 g/cm 3 ͒ are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp 3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ϳ20 nm surface layer which is structurally different and softer than the bulk. © 1996 American Institute of Physics. ͓S0003-6951͑96͒01105-6͔A cathodic-arc plasma source equipped with a magnetic macroparticle filter is an efficient tool for depositing highquality thin films of metals, alloys, and compounds. To date, the technique has been employed primarily in laboratory settings, but recent advances have led to large units capable of full-scale commercial production. 1 One material which has received a great deal of attention in cathodic-arc processing is amorphous carbon ͑a-C͒. In addition to being chemically inert, electrically insulating, transparent, and having a low coefficient of friction, cathodic-arc carbon is of interest because of its potential as thin coating material with very high hardness. Amorphous carbon has been deposited from a cathodic arc by various groups. [2][3][4][5][6][7][8] Hardness values ranging from 26 GPa to over 60 GPa have been measured by nanoindentation methods. The difficulties of deriving hardness values for such hard, thin films on softer substrates are well recognized. 9 Nevertheless, the high values reported suggest that a-C with very high hardness can be achieved by cathodic-arc deposition.The key to producing high hardness in amorphous carbon films appears to be in promoting high sp 3 bond content through careful control of the energy of incident ions during deposition. 6,10-14 For cathodic-arc deposition, one way to achieve this is by substrate pulse biasing. 15 Pulse biasing has an important advantage compared to dc bias in that, whereas with dc bias electrical breakdown can result with pulsed biasing the applied voltage can be arbitrarily high ͑the voltage is switched off before the high voltage plasma sheath expands to dangerous distances͒.We have investigated the properties of cathodic-arc carbon as a function of biasing conditions and have found a set of conditions which produces very hard films. Here, we report the hardness and elastic modulus of these films measured by nanoindentation methods and the structure of the films determined by transmission electron microscopy ͑TEM͒ and electron energy loss spectroscopy ͑EELS͒.The carbon films were deposited on silicon substrates using a cathodic-arc plasma source combined with a 90°bent magnetic macroparticle filter. The source and f...

To determine the friction coefficient of graphene, micro-scale scratch tests are conducted on exfoliated and epitaxial graphene at ambient conditions. The experimental results show that the monolayer, bilayer, and trilayer graphene all yield friction coefficients of approximately 0.03. The friction coefficient of pristine graphene is less than that of disordered graphene, which is treated by oxygen plasma. Ramping force scratch tests are performed on graphene with various numbers of layers to determine the normal load required for the probe to penetrate graphene. A very low friction coefficient and also its high pressure resistance make graphene a promising material for antiwear coatings.Graphene, a one-atom-thick planar sheet of carbon atoms, has been studied intensively in the last few years due to its unique characteristics. However, only a few studies investigate its mechanical properties [1, 2]. In particular, micro-scale friction coefficient of graphene has never been investigated despite its promising potential for low-friction antiwear coatings. In this report, scratch tests are conducted to determine the friction coefficient of mechanically exfoliated graphene on SiO 2 and epitaxial graphene on SiC under ambient conditions. Although the electrical properties of graphene are sensitive to the number of layers, no thickness dependence of friction coefficient is observed. The friction coefficient measurements on disordered graphene treated by oxygen plasma show that disorder in graphene increases the friction coefficient. Ramping force scratch tests are performed on graphene samples with different numbers of layers to determine the normal load required for the probe to penetrate through the graphene, inducing failure of the film. This load is referred to here the critical load. Single-, bi-, and tri-layer exfoliated graphene samples are identified by Raman spectra as shown in Fig (d) show error signal and topographical in-situ scanning probe microscopy (SPM) images after scratch tests, respectively. Although the magnitude of the error signal depends on the feedback parameters of the scan, the error signal image, the difference between the actual force and the set point at any given moment, is useful because it often shows more contrast than the accompanying topography image. Deformed parts of graphene after scratch tests are marked by red circles. . The difference from our data can be attributed to measurement environments [6]. First of all, our experiment is conducted at ambient conditions and their experiment is under ultra high vacuum conditions. It is well known that the existence of water can influence the friction coefficient, therefore it is reasonable to have a different 3 friction coefficient depending on the measurement conditions [6]. The different value could be also attributed to the difference in the size of probes; Filleter used an atomic force microscopy (AFM) based system, whereas we used a larger diamond probe with a 1 µm radius. This is in line with a previous study, where a lar...

A novel scheme of pre-surface modification of media using mixed argon-nitrogen plasma is proposed to improve the protection performance of 1.5 nm carbon overcoats (COC) on media produced by a facile pulsed DC sputtering technique. We observe stable and lower friction, higher wear resistance, higher oxidation resistance, and lower surface polarity for the media sample modified in 70%Ar + 30%N2 plasma and possessing 1.5 nm COC as compared to samples prepared using gaseous compositions of 100%Ar and 50%Ar + 50%N2 with 1.5 nm COC. Raman and X-ray photoelectron spectroscopy results suggest that the surface modification process does not affect the microstructure of the grown COC. Instead, the improved tribological, corrosion-resistant and oxidation-resistant characteristics after 70%Ar + 30%N2 plasma-assisted modification can be attributed to, firstly, the enrichment in surface and interfacial bonding, leading to interfacial strength, and secondly, more effective removal of ambient oxygen from the media surface, leading to stronger adhesion of the COC with media, reduction of media corrosion and oxidation, and surface polarity. Moreover, the tribological, corrosion and surface properties of mixed Ar + N2 plasma treated media with 1.5 nm COCs are found to be comparable or better than ~2.7 nm thick conventional COC in commercial media.