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Title: Top-surface characterization of a near-frictionless carbon film.

Abstract

A detailed study of the top surface ({approx}2 nm) of a near frictionless carbon film has revealed new information with respect to the sp{sup 3} fraction. Previous work on near frictionless carbon films made at Argonne had shown a large fraction of sp{sup 2}-hybridized carbon in the bulk of the film. However, in this study of the surface, the majority of the carbon was found to be sp{sup 3}. In addition we compared and contrasted the behavior of the films after mechanical abrasion and Ar{sup +} etching. The study also revealed that oxygen on untreated samples was rapidly reduced by etching or heating or mechanical abrasion; this finding was corroborated by an angle-resolved study, where different depths of the sample were probed. It was also found that the fraction of sp{sup 3} carbon decreased linearly with depth, falling in one film from {approx}90% sp{sup 3} to {approx}80% sp{sup 3} in the top 2 nm.

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
935626
Report Number(s):
ANL/ET/JA-56617
TRN: US200816%%636
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Diamond Related Mater.; Journal Volume: 16; Journal Issue: 2 ; Feb. 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; FILMS; SURFACE PROPERTIES; ABRASION; CARBON; FRICTION; ETCHING; HEATING

Citation Formats

Johnson, J. A., Holland, D., Woodford, J. B., Zinovev, A., Gee, I. A., Eryilmaz, O. L., Erdemir, A., Univ. of Warwick, and Sheffield Hallam Univ. Top-surface characterization of a near-frictionless carbon film.. United States: N. p., 2007. Web. doi:10.1016/j.diamond.2006.05.005.
Johnson, J. A., Holland, D., Woodford, J. B., Zinovev, A., Gee, I. A., Eryilmaz, O. L., Erdemir, A., Univ. of Warwick, & Sheffield Hallam Univ. Top-surface characterization of a near-frictionless carbon film.. United States. doi:10.1016/j.diamond.2006.05.005.
Johnson, J. A., Holland, D., Woodford, J. B., Zinovev, A., Gee, I. A., Eryilmaz, O. L., Erdemir, A., Univ. of Warwick, and Sheffield Hallam Univ. Thu . "Top-surface characterization of a near-frictionless carbon film.". United States. doi:10.1016/j.diamond.2006.05.005.
@article{osti_935626,
title = {Top-surface characterization of a near-frictionless carbon film.},
author = {Johnson, J. A. and Holland, D. and Woodford, J. B. and Zinovev, A. and Gee, I. A. and Eryilmaz, O. L. and Erdemir, A. and Univ. of Warwick and Sheffield Hallam Univ.},
abstractNote = {A detailed study of the top surface ({approx}2 nm) of a near frictionless carbon film has revealed new information with respect to the sp{sup 3} fraction. Previous work on near frictionless carbon films made at Argonne had shown a large fraction of sp{sup 2}-hybridized carbon in the bulk of the film. However, in this study of the surface, the majority of the carbon was found to be sp{sup 3}. In addition we compared and contrasted the behavior of the films after mechanical abrasion and Ar{sup +} etching. The study also revealed that oxygen on untreated samples was rapidly reduced by etching or heating or mechanical abrasion; this finding was corroborated by an angle-resolved study, where different depths of the sample were probed. It was also found that the fraction of sp{sup 3} carbon decreased linearly with depth, falling in one film from {approx}90% sp{sup 3} to {approx}80% sp{sup 3} in the top 2 nm.},
doi = {10.1016/j.diamond.2006.05.005},
journal = {Diamond Related Mater.},
number = 2 ; Feb. 2007,
volume = 16,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • The uniquely low friction behavior of near frictionless carbon (NFC) as compared to conventional diamond-like carbon (DLC) is determined by the bonding within the film. Inelastic neutron scattering (INS) and Fourier Transform Infrared (FTIR) spectroscopy were used to probe the bonding environment of carbon and hydrogen; both INS and FTIR can probe the whole sample. Previous work has focused on surface studies; the present results show that in the film as a whole the majority of the hydrogen is adjacent to sp3-bonded carbon. In addition this work has determined the absence of any molecular hydrogen in NFC.
  • The uniquely low friction behavior of near-frictionless carbon (NFC) as compared to conventional diamondlike carbon (DLC) is determined by the bonding within the film. Inelastic neutron scattering (INS) and Fourier transform infrared (FTIR) spectroscopy were used to probe the bonding environment of carbon and hydrogen; both INS and FTIR can probe the whole sample. Previous work has focused on surface studies; the present results show that in the film as a whole the majority of the hydrogen is adjacent to sp{sup 3}-bonded carbon. In addition this work has determined the absence of any molecular hydrogen in NFC.
  • Using imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS), we investigated the initial and steady-state sliding behavior of a nearly frictionless carbon (NFC) film. Specifically, TOF-SIMS images (both 2-D and 3-D) of these surfaces were constructed to highlight the spatial distributions of ionized and molecular species that were present on as-received and friction-tested NFC surfaces and as a function of depth. As a complementary technique, we used X-ray photoelectron spectroscopy (XPS) to gain further insight into the chemical nature of the sliding surfaces. The NFC films were produced on Si wafers and steel substrates in a gas discharge plasma that consistedmore » of 25 vol.% methane and 75 vol.% hydrogen using a plasma-enhanced chemical vapor deposition (PECVD) system. They were then subjected to sliding friction and wear experiments in a pin-on-disk machine under 5- and 10-N loads and at sliding velocities of 0.2-0.5 m/s in dry nitrogen. The initial friction coefficients of the NFC films were in the range of 0.05-0.1, but decreased rapidly to values less than 0.01 at steady state. Positive and negative TOF-SIMS spectra and 2- and 3-D images reconstructed from selected masses revealed that the elemental distribution of certain chemical species differs substantially between undisturbed and tribo-tested areas of the NFC films. Specifically, the tribo-tested areas are essentially made up of carbon and hydrogen, while undisturbed or as-received areas are covered by a layer that is rich in oxygen and other species. These findings correlate well with the initial and steady-state friction coefficients of these films and help further explain their superlubricity in inert test environments.« less
  • ''Near-frictionless carbon,'' a form of amorphous hydrogenated diamondlike carbon developed at Argonne National Laboratory, has been investigated by neutron and x-ray reflectivity under ambient conditions, in vacuum, and at elevated temperature. A series of films was made with different ratios of hydrogen to carbon in the plasma; the deuterated counterparts were also synthesized. The details of scattering length density profiles, thickness, and surface and interfacial roughness of the films were obtained from neutron and x-ray reflectivity profiles. This allowed us to calculate the mass density and hydrogen composition of the bulk carbon film, leading to insight into the frictional properties.more » From the analysis we found that the magnitude of the scattering length density of the top surface layer was greatly affected by the experimental atmosphere in which the films were contained although the trend with hydrogen in the plasma remained the same. All samples were fitted with a three-layer model in addition to the substrate.« less
  • A series of hydrogenated diamondlike carbon films grown using plasma-enhanced chemical-vapor deposition is systematically studied as a function of source gas composition using transmission electron microscopy. The structure of the films is examined at three distinct length scales. Both plan-view and cross-sectional studies are undertaken to reveal any large-scale inhomogeneities or anisotropy in the films. The degree of medium-range order in the films is measured by performing fluctuation electron microscopy on the plan-view and cross-sectional specimens. Electron-energy-loss spectroscopy is employed to measure the mass density and sp{sup 2}:sp{sup 3} carbon bonding ratios of the samples. Thus, inhomogeneity as a functionmore » of depth in the film is revealed by the measurements of the short- and medium-range orders in the two different sample geometries. Soft, low-density diamondlike carbon films with low coefficients of friction are found to be more homogeneous as a function of depth in the film and possess reduced medium-range order in the surface layer. We find that these properties are promoted by employing a high hydrogen content methane and hydrogen admixture as the growth ambient. In contrast, harder, denser films with higher coefficients of friction possess a distinct surface layer with a relatively elevated level of carbon sp{sup 3} bonding and a higher degree of medium-range order. The structure of the films is examined in the light of the energetics of the growth process. It appears that a high flux of penetrating hydrogen ions modifies the surface layer containing the remnant damage from the carbon ions, homogenizing it and contributing to a lowering of the coefficient of friction.« less