Nanotribological Characteristics Research Articles

Nanotribological properties of perfluoropolyether-coated magnetic disk evaluated by vertical and lateral vibration wear tests

Perfluoropolyether (PFPE) lubricants are generally used in order to obtain good tribological properties of magnetic disks. This is performed to protect the magnetic elements from corrosion and wear and to provide interface durability. In this paper, we present the results of the nanotribological characteristics of two perfluoropolyether-coated (PFPE) magnetic diamondlike carbon (DLC) film disks with and without thermal curing. Lateral oscillation wear experiments were performed using the lateral modulation friction force microscopy (LM-FFM) mode in the load range of 2280 nN, at a scanning speed of 3 Hz and a vibration frequency of 1 kHz, using a diamond tip of approximately 26 nm radius. The surface topography of the PFPE-coated disks with and without thermal curing was examined by atomic force microscopy (AFM). The result shows that the PFPE-coated disk without curing has a good wear resistance property, compared with that of the PFPE-coated disk with curing due to the supply of free lubricant by tip sliding. Corresponding to this, using viscoelasticity AFM (VE-AFM) in the vertical force mode, the vertical oscillation wear experiments were performed under the same conditions and the result shows that the viscoelasticity of the PFPE-coated disk without curing increased, which provides the evidence of the supply of free lubricant on the PFPE film without curing.

Surface Damage Characteristics of Self-Assembled Monolayers of Alkanethiols on Metal Surfaces

The effect of metal oxide layer on the nano-tribological characteristics of single chain alkanethiol (CH3(CH2) n SH) self-assembled monolayers (SAMs) on various metal surfaces (gold, silver, copper) was investigated. In order to correlate the surface structures with the tribological characteristics, various surface analysis techniques such as Scanning Probe Microscopy, X-ray Photoelectron Spectroscopy, Secondary Ion Mass Spectrometry and Spectroscopic Ellipsometry were used. Results of surface analyses showed that thiols on a metal surface were susceptible to forming multilayers if the metal surface was oxidized before the thiol assembly process. From the friction and wear tests conducted using an Atomic Force Microscope and a Lateral Force Microscope, it was found that thiols on copper oxide surface could be easily removed even under a few nano-Newton normal load. On the other hand, thiols on gold and copper fresh surfaces (the surface which was made by minimizing oxide formation) could endure up to micro-Newton level loads. Based on these findings, it could be concluded that the nano-tribological characteristics of alkanethiol SAMs on various metal surfaces were largely dependent on the oxide layer that already formed on the metal surface before the thiol adsorption process.

Micro/nano-tribological characteristics of self-assembled monolayer and its application in nano-structure fabrication

The fundamental tribological characteristics of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS), octadecyltrichlorosilane (OTS), and single chain alkanethiol self-assembled monolayers (SAMs) with various chain lengths were investigated in order to identify the mechanical scribing condition for micro-machining applications. The concept of the novel surface micro-machining explored in this work is to mechanical scribe away the SAM resist coated on the workpiece surface where, pattern formation by subsequent chemical etching is desired. From the experimental results, it was found that the FDTS surface was damaged about 20% more rapidly than the OTS surface due to higher friction, even though the surface energy of FDTS was lower than that of OTS. Also, it was found that thiol on a copper surface could be removed even under a few nN normal load. The nano-tribological characteristics of alkanethiol SAM on various metals were largely dependent on the native oxide layer of metals. Based on these findings, FDTS and 1-hexadecanethiol (HDT) were chosen as the resists for silicon and metal surfaces, respectively. By using the mechano-chemical process with a diamond-coated tip, nano-patterns with sub-micrometer width and depth on surfaces of Au, Ag, Cu and Si could be fabricated.

The Effect of Topography on Water Wetting and Micro/Nano Tribological Characteristics of Polymeric Surfaces

The effect of surface topography on the water-wetting nature and micro/nano tribological characteristics of polymer surfaces was experimentally studied. A plasma-treated thin polymer film and ion-beam-treated PTFE (polytetrafluoroethylene) were used as flat specimens. Thin polymer films were deposited on Si-wafer (100) by the parallel-plate plasma technique. The ion-beam-roughening treatment was performed to change the PTFE surface topography using a hollow cathode ion gun under different argon-ion dose conditions in a vacuum chamber. Micro and nano tribological characteristics, water-wetting angles and roughness were measured with a micro-tribotester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. The plasma-treated thin polymer film and ion-beam-treated PTFE surfaces were rendered increasingly hydrophobic as a function of the treatment time. The wetting characteristics were strongly dependent on the micro-roughness and the sharpness of the asperities. The tribological characteristics on the nano-scale showed different results from those on the micro-scale. It was noted that the contact-size ratio, especially the ratio of the tip or ball to the average surface roughness at a standard cut-off length, should be considered for evaluating the micro- and nano-scale tribological test results.

Adhesion force and Nanotribological Characteristics of Chemical Vapor Deposited Fluorocarbon Films

ABSTRACTIn this study, Adhesion force and Nanotribological Characteristics of fluorocarbon (FC) films on Al deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) were evaluated. The contact angle of FC thin films on Al was measured to be around 110°. The surface energy was calculated to be 15 dynes/cm from the measurements of contact angles of polar and nonpolar solutions on surfaces. The contact angle hysteresis, which is an indicator for the surface heterogeneity, was lower than 30°. The friction force of FC films coated surfaces was three times lower than bare Al. The adhesion force of bare Al was measured to be around 9.6nN. The presence of FC films on Al reduced it to below 4nN. Fourier transform infra-red (FTIR) spectra showed the presence of fluorocarbon groups such as –CFn- and =CF=CF2.

Effects of substrate bias on nanotribologyof a-C:H films deposited by ECR-MPCVD

Nanotribological characterization of amorphous hydrogenated carbon (a-C:H) films is performed by scanning probe microscopy. The a-C:H films are produced on silicon substrate by electron cyclotron resonance microwave plasma chemical vapor deposition. The influence of substrate bias voltage on nanotribological characteristics is investigated. Scanning probe nanotribological tests, including the nano-friction, nano-wear and nano-scratch, are carried out. Large quantitative variations in friction coefficient and wear depth are found for different substrate biases. Results indicate that higher bias is beneficial to wear and deposition rate, and produces a larger friction coefficient. It also shows that substrate bias plays an important role in the tribological characteristics of a-C:H films.

Nanotribology of amorphous hydrogenated carbon films using scanning probe microscopy

Nanotribological characterization of amorphous hydrogenated carbon (a-C:H) films is performed by scanning probe microscopy. The a-C:H films are produced on silicon substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD). The influences of different percentages of hydrogen (H 2) and methane (CH 4) in the gas-discharge plasmas on the nanotribological characteristics are investigated. Scanning probe nanotribological tests, including the nano-friction, nano-wear and nano-scratch, are carried out. Large quantitative variations of the friction coefficient as well as the wear depth are found for different H 2 content percentages in source gas. The results indicate that a higher H 2 content in the source gas is beneficial to wear and scratch resistance, and produces a lower friction coefficient and that source gas H 2 content plays an important role in the tribological characteristics of diamond-like films.

Nano-Scale Mechanical Characterization of Plasma Treated Polymer Surfaces

AbstractRecent advances in atomic force microscopy (AFM) allow one to perform complex analysis of materials surfaces and near-surface regions with a nanometer scale resolution; this includes the imaging of surface topography and the measurements of stiffness, elasticity, hardness and nano-tribological characteristics. Understanding of the complex AFM response is still in its early stage, and it frequently requires the use of multiple complementary techniques. In the present work we have applied AFM for the study of the surface and nearsurface mechanical properties of plasma-treated polycarbonate. The results from AFM analysis, such as the stiffness and the relative Young modulus, were compared with the hardness values obtained by depth-sensing indentation and by the micro-scratch technique. The characteristics of the observed hardened surface layer are discussed with respect to the role of the “interphase” in adhesion en1hancement of plasma-deposited films on polymers.