Fomblin Zdol Research Articles

Atmospheric vapor phase deposition of nanometer-thick anti-stiction fluoropolymer coatings for silicon surfaces

Anti-stiction coatings for silicon surfaces are a key technology to prevent the failure of nanoelectromechanical systems (NEMS) during operation and improve the forming accuracy in nanoimprint technology. In this study, we propose an atmospheric vapor phase deposition method to coat a silicon surface with fluoropolymers such as the perfluoropolyethers Fomblin Zdol 2000 and Zdol 4000. Thickness distributions, surface energies, coverages, and stiction forces for the deposited films were evaluated experimentally. The proposed method resulted in over 90% coverage with a film thickness of about 1 nm. The film thickness uniformity was around 0.1 nm over an area of 5 × 5 mm2. This coating effectively reduced the stiction forces by half compared with a bare silicon surface.

シリコン表面に気相蒸着したナノ厚さフッ素系潤滑膜の耐凝着性能の評価

Anti-stiction coating must be one of the key technologies to ensure reliability of NEMS devices and to improve accuracy in a nanoimprint lithography. Typically, polymer films were coated on a silicon surface for anti-stiction. In this study, we proposed vapor-phase deposition technique to form fluoropolymer film on silicon surfaces. Fluoropolymer used in this study was perfluoropolyether (PFPE) Fomblin Zdol (molecular weight of 2000 amu). As a substrate to coat the Zdol, we used a silicon wafer. Anti-stiction properties were verified by measuring surface energies by a contact angle measurement and also by measuring stiction forces using an atomic force microscope (AFM). As a result, it was revealed that the films thicker than 0.5 nm effectively reduced the adhesion forces down to approximately a half of that of the bare silicon surface.

Novel Ionic Lubricants for Magnetic Thin Film Media

New protic ionic liquids (PILs) have been developed. The kinetic friction coefficients of ammonium salts of the alcolate, the carboxylate, and the sulfonate were from 0.23, 0.17, and 0.15, respectively, and 0.26 for Fomblin Z-DOL. PILs have better friction and wear properties compared to Z-DOL. The ammonium salts as a hydrophilic group have a lower frictional coefficient, which enhanced the abrasion resistance. The friction and the thermal degradation decreases with the increasing between the Broensted acid and the Broensted amine. The material based on an ammonium sulfonate has higher , and does not decompose even at 300 , making it more thermally stable than Z-DOL.

Reversed Micelle Structures in PFPE Lubricant Thin Films on Magnetic Disk Surface Observed by Non-Contact AFM

PFPE lubricants (Fomblin Z-dol) for hard disk surface lubrication have two hydroxyl groups, one at each end of the molecules, and form stable insoluble monolayers at the water surface. In this study, molecular weight-fractionated PFPE lubricant monolayers were transferred from the water surface to solid substrates such as a hydrophilized silicon wafer, gold-sputtered mica, and a hard disk after adjusting the two-dimensional density of the lubricant molecules. The molecular structures of the PFPE lubricant molecules at the solid surfaces were observed by the cryogenic non-contact AFM under ultra-high vacuum. At the hydrophilic silicon wafer surface we could observe a single lubricant molecule in a random coil sphere shape. However, at the non-polar gold surface we confirmed the formation of reversed micelle structures. At the hard disk surface we detected various sizes of reversed micelles of PFPE lubricant in a flat oval shape.

Effects of Lubricants and Their Treatments on Tribological Characteristics of Thin-Film Disks

We used a transparent pin-on-disk seek wear test to evaluate the effectiveness at reducing disk drive head wear of several perfluoropolyether lubricants with different end-groups, under various heat and UV irradiation conditions. The extent of Pin wear decreased as bonding ratio increased, with a wear minimum between 30 and 40% bonding ratio on UV irradiated Fomblin Z-dol or Phospharol A20H lubricants. A further wear minimum occurred at higher bonding ratios on both lubricants. Pin wear amounts on disks with heat treated lubricants were different from those on disks with UV irradiated lubricants. Disk failure occurred on disks with UV irradiated Fombrin Z-dol lubricant of high bonding ratio. Sliding conditions during wear tests were also recorded and investigated, showing changes in the lubricant picked-up on pin surfaces - at low bonding ratio disks, this was liquid-like whereas at medium to high bonding ratio disks it became gel-like. On UV irradiated high bonding ratio disks, black powdery debris were found. The mimima in wear found on UV irradiated Z-dol and A-20H lubricated disk seemed to be affected by the amount of debris under the pins. Changes in lubricant rheological properties by UV irradiation or heat treatment should be studied further.

Microfluidic behaviour of perfluoropolyether fluids in poly(dimethylsiloxane) micro-channels

Two different perfluoropolyether-based fluids, namely the unfunctionalized GALDEN SV90 ® and the dihydroxy derivative FOMBLIN Z-DOL ® 2000 were employed as liquid samples in a poly(dimethylsiloxane) (PDMS) microfluidic setup, fabricated by soft-lithography techniques. The results of our investigation were compared with the behaviour of the low viscosity and high-fragility polyurethane structural adhesive (NOA72 ®), that is well known as an excellent material for the fabrication of sub-micrometer structures by soft-lithography techniques, and whose structural elastic properties inside restricted geometric systems have been recently investigated.

Electron stimulated decomposition of fluorocarbons on amorphous hydrogenated carbon (a-CHx) overcoats used in data storage media

The electron-induced surface chemistry of perfluoropolyalkylether (PFPE) lubricants on a-CHx films has been probed by studying the impact of free electrons on perfluorodiethylether, (CF3CF2)2O, and 2,2,2-trifluoroethanol, CF3CH2OH, as models of the chemical functionality of PFPE lubricants such as Fomblin Zdol. Electron-stimulated decomposition of (CF3CF2)2O and CF3CH2OH on fresh and oxidized a-CHx is observed when the sample is unbiased and in the presence of 70 eV free electrons. Electron-induced decomposition is indicated by the deposition of fluorine onto the surface of the a-CHx film following desorption of molecular (CF3CF2)2O and CF3CH2OH by heating in front of a mass spectrometer. Biasing the sample to −80 V successfully eliminates the decomposition by preventing the impingement of electrons onto the surface. The electron-stimulated decomposition of PFPE lubricants may contribute to lubricant decomposition during normal drive operation.

Adsorption of Fluorinated Ethers and Alcohols on Fresh and Oxidized Carbon Overcoats for Magnetic Data Storage

Temperature programmed desorption has been used to study the desorption kinetics and desorption energies of perfluorodiethylether, (CF3CF2)2O, and 2,2,2-trifluoroethanol, CF3CH2OH, adsorbed on fresh and oxidized hydrogenated amorphous carbon (a-CHx) films. (CF3CF2)2O and CF3CH2OH serve as models for the ether backbone and hydroxyl end-groups of Fomblin Zdol, the lubricant most commonly used to lubricate the surfaces of amorphous carbon overcoats on magnetic data storage hard disks. Our measurements clearly reveal, for the first time, the effects of surface oxidation on the adsorption of fluorocarbon lubricants such as Fomblin Zdol on a-CHx films. Oxidation of the a-CHx surface increases the desorption energy of CF3CH2OH but has no observable impact on the desorption energy of (CF3CF2)2O. These results support the suggestion that the alcohols interact with the surface via hydrogen bonding. From a practical perspective, these results imply that the oxidation of the fresh a-CHx film may serve as a means to control or tailor the a-CHx surface to optimize the properties of the lubricant-overcoat interface in hard disks.

Lubrication of MEMS under vacuum

The concept of replenishing lubrication provided by a pair of bound/mobile hydrocarbon-based lubricants has been extended to silicon-based MEMS in vacuum (∼1.3×10−4 Pa). Several bound/mobile pairs of lubricants were evaluated to study the effects of bound phase end-group and mobile phase chemical functionality towards performance. The bound species studied were derived from 1-decanol and 1,7-heptanediol. Mobile phases investigated were, a pentaerythritol ester, a multiply alkylated cyclopentane, Pennzane®, and a polysilane developed for spacecraft application. Lubricant performance was compared with data generated in dry air earlier, and also with fresh Fomblin Zdol® under identical conditions of vacuum. The best performance from among those studied was provided by a mixture of bound 1,7-heptanediol and the pentaerythritol ester. An explanation for its superior performance is advanced based on intermolecular hydrogen bonding.

MEMS lubricants based on bound and mobile phases of hydrocarbon compounds: film deposition and performance evaluation

The concept of a thin layer of mobile hydrocarbon-based lubricant providing protection by replenishment to a surface already protected by a chemically bound material has been explored for the first time, for application to silicon-based microelectromechanical (MEMS) systems. Several bound/mobile pairs of lubricants were evaluated to study the effects of bound phase end group and mobile phase chemical functionality on wettability and performance. The bound species studied were derived from 1-decanol and 1,7-heptanediol. Mobile phases investigated were, a pentaerythritol ester, a multiply alkylated cyclopentane, Pennzane, and a polysilane developed for spacecraft application. Hydrocarbon lubricant performance was evaluated using electrostatic motors run in dry air, and was compared with that provided by Fomblin Zdol under identical conditions. Motors with hydrocarbon coatings showed substantial improvement in performance over uncoated motors, and for some bound/mobile pairs, was equal to Zdol within experimental error. We believe that for silicon-based devices, hydrocarbon coatings will be preferable at least for some applications, as the degradation observed due to aging of a fluorinated lubricant in direct contact with a silicon surface is absent.

Kinetics of laser induced desorption and decomposition of Fomblin Zdol on carbon overcoats

Heat assisted magnetic recording (HAMR) on magnetic hard disks is being explored as a means of increasing the areal density of stored data beyond the limits of current technologies. HAMR will subject the magnetic media, the overcoat, and the lubricant on its surface to temperatures in the range 400–650 °C for periods of a few nanoseconds per pass of the read-write head. During such rapid heating events the lubricant is prone to decomposition and desorption from the surface, either of which lead to degradation of the lubricant film, jeopardizing the integrity of the stored data. Rapid laser annealing is known to bias the reactions of small molecules adsorbed on surfaces to favor desorption over decomposition. Analysis of the desorption and decomposition kinetics of perfluoropolyalkylether lubricants such as Fomblin Zdol shows that rapid heating to high temperatures favors desorption over decomposition for molecules with molecular weights of less than 3000. For higher molecular weight Fomblins decomposition is favored at the temperatures to be used for HAMR.

Aging of a fluorinated lubricant on bare and DLC-coated silicon-based MEMS

The aging of Fomblin Zdol® on a silicon-based MEMS device was investigated. The MEMS device used was an electrostatic lateral output motor. Devices freshly coated with Zdol performed exceedingly well compared to uncoated devices, but their performance deteriorated on storage in air. This is apparently due to the decomposition of the fluorinated lubricant in contact with the polysilicon surface for an extended period. XPS and AFM studies show that the composition and morphology of the Zdol-coated polysilicon surface change on aging. A stable, cohesive barrier layer deposited to prevent direct contact of the fluorinated lubricant with polysilicon enhanced the stability of the lubricant. As widely used in hard disk lubrication, a thin film of diamond-like carbon (DLC) acted as an excellent barrier layer extending the life of unlubricated devices and preventing degradation of those lubricated by Zdol.

Poly(caprolactone-co-lactide)/perfluoropolyether block copolymers: Synthesis, thermal, and surface characterization

Poly[(caprolactone-co-lactide)-6-perfluoropolyether-b-(caprolactone-co-lactide)] copolymers (TXCLLA) were prepared by ring-opening polymerization of D,L-dilactide (LA2) and caprolactone (CL) in the presence of α,ω-hydroxy terminated perfluoropolyether (Fomblin Z-DOL TX) as macroinitiator and tin(II) 2-ethylexanoate as catalyst. 1 H NMR analysis showed that LA2 is initially incorporated into the copolymer preferentially with respect to CL. A blocky structure of the polyester segment was also indicated by the sequence distribution analysis of the monomeric units. Differential scanning calorimetry analysis showed the compatibility between poly(lactide) (PLA) and poly(caprolactone) (PCL) blocks inside the amorphous phase with glass-transition temperature values increasing from -60 to -15 °C by increasing the PLA content. Copolymers with high average length of CL blocks were semicrystalline with a melting temperature ranging from +35 to +47 °C. Surface analysis showed a high surface activity of TXCLLA copolymers with values of surface tension independent from the PLA/PCL content and very close to those of pure TX.

Effects of End Groups on the Tribochemical Reactions of Lubricants at Head-Disk Interface

Mass spectrometry was used to monitor in-situ gaseous species that were generated at the head-disk interface (HDI) in a high vacuum. It was found that the end groups of the lubricants significantly affected the wear durability at the HDI; piperonyl (–CH2-phe = (O)2 = CH2) terminated Fomblin AM3001 lubricant exhibited longer life than hydroxyl (–OH) terminated Fomblin ZDOL lubricant. The continuous removal of the lubricants resulted in a continuously increasing friction coefficient. Further, the characteristics of tribochemical reactions of the lubricants (Fomblin Z series) with different end groups was investigated in details using Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) just after the sliding tests. It was found that the decomposition of the end groups was more significant than that of the backbone. The lubricants terminated with the following groups showed the following order of increasing decomposition: –CH2O-CH2-phe = (O)2 = CH2 (AM3001), –CH2OH (ZDOL) < –CH2OCH2CH(OH)CH2OH (Z Tetraol) < –CH2(OCH2CH2)nOH (ZDOL-TX), –COOH (Z Diac). The decomposition of the lubricants appeared to start from the end groups.

TOF-SIMS characterization of lubricants used in magnetic recording media

In this study, TOF-SIMS was used to characterize lubricants used in magnetic recording media. Films of lubricants, perfluoropolyether (PFPE) Fomblin Z-DOL, Z-TETRAOL, AM3001, and cyclo triphosphazene X-1P were deposited on carbon overcoats of the magnetic disks from solutions. TOF-SIMS results showed that each thin film lubricant produces characteristic ions that are closely related to its chemical structure. Ratios of characteristic ions from the Z-DOL and carbon overcoat can be used to monitor the thickness and molecular weights of the lubricant. Molecular or molecule related ions have been observed for Z-DOL and X-1P. It was also found that the average mass of molecular ions correlates very well with the number average molecular weight determined by nuclear magnetic resonance (NMR) for Z-DOL.

Investigation of fomblin Z-Dol end-groups on the magnetic recording disks by ToF-SIMS

On magnetic recording disks, a surface lubricant film has been widely used in order to reduce friction and wear. It is very important to analyze the lubricant film on the disk directly. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a suitable technique for direct analysis of lubricant films because of its high surface sensitivity for the information about organic chemical structure. In this study, we investigated the effect of thickness and molecular weight of Z-Dol lubricants on the intensity of the Z-Dol end-group ion. ToF-SIMS results revealed that the calculated intensities of Z-Dol end-group ions from free lubricant films are proportional to free lubricant thickness, and decrease with the increase in molecular weight. By investigating the calculated intensities of Z-Dol end-group ions from free lubricant films, we concluded that it is possible to compare molecular weights of lubricant films on the disks.

TOF-SIMS characterization of lubricants used in magnetic recording media

In this study, TOF-SIMS was used to characterize lubricants used in magnetic recording media. Films of lubricants, perfluoropolyether (PFPE) Fomblin Z-DOL, Z-TETRAOL, AM3001, and cyclo triphosphazene X-1P were deposited on carbon overcoats of the magnetic disks from solutions. TOF-SIMS results showed that each thin film lubricant produces characteristic ions that are closely related to its chemical structure. Ratios of characteristic ions from the Z-DOL and carbon overcoat can be used to monitor the thickness and molecular weights of the lubricant. Molecular or molecule related ions have been observed for Z-DOL and X-1P. It was also found that the average mass of molecular ions correlates very well with the number average molecular weight determined by nuclear magnetic resonance (NMR) for Z-DOL.

Investigation of fomblin Z-Dol end-groups on the magnetic recording disks by ToF-SIMS

On magnetic recording disks, a surface lubricant film has been widely used in order to reduce friction and wear. It is very important to analyze the lubricant film on the disk directly. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a suitable technique for direct analysis of lubricant films because of its high surface sensitivity for the information about organic chemical structure. In this study, we investigated the effect of thickness and molecular weight of Z-Dol lubricants on the intensity of the Z-Dol end-group ion. ToF-SIMS results revealed that the calculated intensities of Z-Dol end-group ions from free lubricant films are proportional to free lubricant thickness, and decrease with the increase in molecular weight. By investigating the calculated intensities of Z-Dol end-group ions from free lubricant films, we concluded that it is possible to compare molecular weights of lubricant films on the disks.

Frictional properties of bilayered mixed lubricant films on an amorphous carbon surface: effect of alkyl chain length and SAM/PFPE portion

Twenty-Å-thick mixed lubricants with bilayered structures, which consist of alkylsilane monolayers (C6, C8, and C10) and mobile perfluoropolyether (PFPE) lubricants, were deposited on a hydrogenated amorphous carbon surface. The friction and durability properties of the mixed lubricants on the carbon surface were measured using an atomic force microscope and a micro-scratch tester, which were compared with 20 Å-thick perfluoropolyether lubricant coated carbon surfaces. The friction and durability properties of the mixed lubricant on a carbon surface were mainly dependent on the silane monolayers, that is, the friction force became low and the critical load was enhanced by increasing the alkylsilane chain length although the amount of the mobile lubricant decreased. On the other hand, the mixed lubricants on the carbon surfaces showed a higher friction force compared to that of the Fomblin Zdol lubricant that has a satisfactory molecular flexibility, whereas it showed a higher durability due to a higher surface coverage of the chemisorbed molecules and the rigid nature of the silane monolayers. The frictional properties of the perfluoropolyether lubricants on a carbon surface are related to the radius of gyration, R g, of the molecule. The excess mobile molecules contribute to the high friction due to the capillary effect, that is, an optimum thickness of the mobile lubricant exists for a lower friction, which is comparable to R g.

Catalytic decomposition of perfluoropolyether lubricants

With the ongoing decrease in magnetic spacing, the chemical durability of the lubricant film on magnetic recording media becomes a major factor in the reliability of the head-disk interface. There are several reports in the literature that have attributed deterioration of lubricant film to catalytic decomposition, and a reaction mechanism has been proposed by Kasai involving chain scission of the lubricant main chain promoted by Lewis acids. In this work, an alternative mechanism is proposed, wherein perfluoropolyether (PFPE) lubricants are catalytically decomposed via a free radical degradation loop. The catalytic decomposition of Fomblin Zdol in the presence of the Lewis acid Al/sub 2/O/sub 3/ was studied using thermogravimetric analysis (TGA). We show that various types of antioxidants can retard PFPE catalytic decomposition to different degrees, which we attribute to their different roles in breaking the free radical degradation loop. These data provide useful guidance in the development of new lubricants that are resistant to free radical initiated decomposition.