Optical Surface Analyzer Research Articles

A variable-speed drag test for characterizing wear of ultra-thin carbon films

A drag test with a speed alternating between two levels was developed to create wear tracks on disk surfaces. This approach reduces the uncertainty involved in the contact start/stop (CSS) test of thin carbon overcoats. The wear tracks were identified with an optical surface analyzer as regions with higher values of the absorption ratio calculated from reflectivity data of both P- and S-polarized lights. Calibrated with scanning micro-ellipsometry, the absorption ratio was converted to a wear depth. The amount of wear in a drag test increased with time, and a low-flying head resulted in more wear than a high-flying head. The 45-angstrom nitrogenated carbon film sputtered at a lower temperature exhibited a smaller wear depth. The higher wear resistance of the low-temperature sputtered film is supported by less wear in a nanowear test, a lower Raman G-peak position, and less frequent crashes in CSS tests.

Non-destructive defect detection scheme using Kerr-channel optical surface analyzer

Magnetic defects on the surface of magnetic disks, unlike normal topological defects, are difficult to detect because they are solely due to magnetic signal loss as seen by the MR element and often do not have any obvious topological features. Defects without any topological features usually render conventional defect finding techniques such as visual inspection, optical microscopy, and SEM useless. In the past, the painstaking way of locating the defect was to index the drive with a strobe light and followed with ferrofluid decoration of the surface to determine the location of the defect. The disadvantage is that the magnetic particles in the decoration technique can often confound the origin of the defect. Furthermore, the old technique does not have high enough resolution to locate defect with a size on the order of a micrometer. In this work, we describe how a magnetic marking technique (MMT) is utilized to circumscribe the magnetic defects. The markers are written in such a way that both the defect and the magnetic markers are easily detected using a Kerr-channel optical surface analyzer and magnetic force microscope. Typically, the accuracy of locating the defect using the MMT is within a track-pitch radially and within one data sector circumferentially. The new scheme provides at least one order of magnitude improvement in detection resolution over the old technique.

The lubricant migration rate on the hard disk surface

The optical surface analyzer (OSA) was found to be an excellent tool to examine the lubricant migration rate on thin film disks. Using the OSA it was found that the rate of lubricant migration increased as molecular weight decreased. An AM type perfluoropolyether with an aromatic end group and Z-Dol were also observed to have different migration rates for the same molecular weight. The migration rate of AM lubricant was increased significantly by the presence of X-1P as an additive in the lubricant system.

Formation of lubricant “moguls” at the head/disk interface

In a typical head/disk interface of a rigid disk drive, the motion and redistribution of a 14 A thick lubricant film on the disk under a flying slider is analyzed with an optical surface analyzer. At short times (∼seconds to a few minutes), the film is rearranged in an isotropic manner, creating a pattern of “moguls”1 of ∼100 μm in lateral size and a few angstroms in height. A strong correlation is demonstrated between the resulting distribution of the lubricant film and the underlying substrate topography. Surprisingly, lubricant becomes thicker on the peaks of the micro-waviness, and thinner in the valleys. Possible mechanisms for this unexpected behavior will be discussed, as well as its tribological implications. At longer times, the lubricant film is pushed away from underneath the slider, creating the previously reported circumferentially depleted tracks beneath the slider rails. In the timeframe of our experiment, no significant net lubricant loss was observed.

Progress in temporal speckle modulation

Summary Time sequential speckle pattern analysis can be very useful for quantitative and quasi absolute shape and deformation analysis of optical and technical surfaces. Speckle methods for measuring deformation can be greatly enhanced with respect to range and resolution by using temporal evaluation of the speckle modulation. It will be shown that vibration analysis can occur with a very simple optical setup.

High fly-stiction as a result of grease contamination

Fly-stiction is a special kind of stiction that occurs at the interface between a hard drive head and the hard disk. It can have very high values and has caused serious problems for the computer industry in the past. It is defined as that taken after a certain number of CSS cycles in the landing zone of a disk, followed by an extended period of time of sweep or track dwell in the data zone and finally an extended period of park time in the landing zone. This paper has studied the nature, mechanism and solutions of the high fly-stiction phenomenon. CSS testers, optical microscopes, an optical surface analyzer and a Fourier transform infrared spectrometer were used to measure fly-stiction values and analyze the test surfaces of heads and disks. The results obtained indicate that the fly-stiction value is much higher than the corresponding park-stiction value. The fly-stiction value does not change with increasing number of CSS cycles, and may decrease slightly with increasing lubricant thickness. In addition, a high fly-stiction value may be caused by a contamination of spindle grease. Finally, a high fly-stiction value can be reduced by avoiding contamination or increasing the resistance to contamination of a disk. For instance, an ion-beam carbon overcoat can reduce the fly-stiction to half the value obtained with a sputter carbon overcoat.

Imaging performance of telescope mirrors for far-ultraviolet astronomy

We describe image testing, surface metrology, and modeling of telescope mirrors (0.5 m in diameter, f/4.3) for the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Laboratory image testing of wavelengths in the visible, vacuum, and midultraviolet validated a theoretical analysis by use of the Optical Surface Analysis Code (OSAC). Our modeling is based on surface metrology, including measurements of figure, midfrequency error, and microroughness. This combination of metrology, out-of-band performance testing, and modeling verified that the mirrors would meet mission requirements. We use OSAC to predict the FUSE telescope's far-ultraviolet (90-120-nm) point-spread function and assess its effect on instrument efficiency. The mirrors have a 90% encircled energy diameter of 1.5 arc sec at lambda = 100 nm. Including the effects of spacecraft pointing error, the mirrors have a predicted average slit transmission at lambda = 100 nm of approximately 87% and 96% for the 1.25- and 4-arc sec-wide spectrograph slits, respectively, where the required transmissions are 50% and 95%.

In-Situ Wear Monitoring of Slider and Disk Using Acoustic Emission

The methodology has been developed for both the evaluation and analysis of slider/disk interface phenomena. We have been studying the direct relationships between the acoustic emission (AE) signal and wear of materials. The power in the AE signal is directly related to the power required for material removal in the wear process. This technique has been successfully applied to monitoring the wear of the tri-pad contact slider and the disk. The AE transducers were directly mounted onto both the arm with the slider and the disk in order to measure the slider/disk contact behavior. The AE transducer output from the disk was transmitted by the slip ring and the brush. The predicted wear of the slider and the disk based on the AE signals were computed from the relationship mentioned above. The measured wear of the slider and the disk were obtained by atomic force microscopy (AFM) and an optical surface analyzer (OSA) respectively. According to the experimental results, the predicted wear of both the slider and the disk using AE signals agreed with the wear which was measured. Therefore, wear can be estimated and monitored indirectly in-situ using the AE signals without direct measurements of the wear volume.

Disk wear as a result of low frequency HDI resonance

Spinstand level testing has demonstrated a failure mechanism that may go undetected using standard strain gage and acoustic emission methods of data capture. Since normally static friction is higher than dynamic friction, dynamic friction measurements are often ignored, filtered, or sampled at a much lower data rate than static friction measurements. In this study, dynamic friction peak values significantly higher than the static friction were recorded during take-off of Pico heads on laser-textured media. Furthermore, data collected using an optical surface analyzer (OSA) showed a greater degree of wear on disks exhibiting high dynamic friction. FFT was employed to analyze the signal modulation of the high dynamic friction event. Resonance at a frequency of approximately 1050 Hz was found to be associated with the high dynamic friction. Experiments were designed to reveal factors that influence this resonance occurrence. The factors identified that contribute to this resonance were natural frequency of the head load arm, disk bump pitch, and lubricant thickness. The head/disk interface system is believed to be excited by an improper bump pitch if the lubricant layer is not thick enough to reduce the friction value.

Effect of the additive X-1P on the tribological performance and migration behavior of PFPE lubricant at the head-disk interface

We study the effect of X-1P as an additive in PFPE lubricants using an ultra-high vacuum (UHV) tribochamber equipped with a mass spectrometer. The studies consist of drag tests in the UHV tribochamber. Two decomposition processes of ZDOL under sliding friction conditions are studied-one is with a carbon film coated slider, and another is with an uncoated Al/sub 2/O/sub 3/-TiC slider. An optical surface analyzer (OSA) is also used to observe the lube migration behavior. We observe that X-1P passivates the head and prevents the catalytic reaction of the PFPE when used as an additive. In addition, X-1P also increases PFPE's mobility and, hence, improves the tribological performance at the head-disk interface.

In situ quantitative analysis of nano-scale lubricant migration at the slider–disk interface

A thin layer of lubricant is a critical element of the head/disk interface needed to improve its tribological durability and to prevent media corrosion. Local thinning of lubricant with its subsequent breakdown often leads to the immediate failure of the interface. This paper is devoted to the in situ quantitative analysis of nano-scale lubricant migration on the surface of a thin-film disk using the Optical Surface Analyzer (OSA). The calibration procedure, which enables quantitative measurements, is discussed and the technique's capabilities are demonstrated using specially prepared samples. Two cases of slider/disk interaction are analyzed: low-speed, when the slider is dragged over the disk surface, and high-speed, when the slider is flown over the same track for several days. Lubricant migration phenomena, such as depletion and pooling, are investigated quantitatively to analyze the origination of carbon wear and the mechanisms of interfacial failure. A model of high-speed slider/disk interaction involving the dynamic formation of a liquid bridge at the interface is proposed.

A novel drag test for observing lubricant redistribution due to head-disk interactions

The redistribution of a thin perfluoropolyether lubricant film on magnetic rigid disks after sliding was studied by mapping the surface reflectivity under polarized light using an optical surface analyzer. Both lubricated and nonlubricated regions were created on the disks with a special dip-coating process, and a drag test was conducted with the head placed in the smooth data zone. Due to sliding, a portion of the lubricant film in the initially lubricated regions was displaced into the nonlubricated regions. A numerical procedure was developed to determine lubricant thickness profiles from the surface reflectivity data calibrated by FTIR. The displaced lubricant volume increases with increasing sliding time, increasing initial lubricant thickness, or decreasing sliding speed. Local removal of a lubricant film was observed after long-term parking of the head, and surface diffusion was examined for the diminishing displaced lubricant band.

Optical surface analysis of graded index coatings on glass

A method for the determination of the refractive index close to an interface, valid for inhomogeneous films, is presented as an extension of the Abelès—Hacskaylo technique used for homogeneous films. Consistent refractive index values, with precision in the third decimal place, are determined for Ag + (1.550 ± 0.001) and K + (1.522 ± 0.002) ion-exchange films on glass, as well as for bare glass substrates (1.509 ± 0.002), in the neighborhood of their interface with air. The validity of the method is discussed in simple fundamental terms, which, along with the experimental evidences, indicates applicability to any graded index film, provided an index discontinuity is present at one of its extremes.

Acoustic emission study of lubricant effect on proximity contact recording

Pseudo-impact contact at the interface between proximity sliders and magnetic rigid disks were investigated by acoustic emission (AE) technique. Under a hot/wet condition of 60/spl deg/C/80%RH and an operation speed of 19.15 m/s., AE responses were collected in real-time to monitor interaction events at the head/disk interface (HDI). The profile of AE responses shows various events at the HDI which can be correlated to the micro-wear of the carbon overcoat and lubricant degradation. These events were also detected by optical surface analysis (OSA). These wear and degradation events indicate the need for choosing the proper lubricant and demonstrate that AE is a suitable tool to detect these events at the head/disk interface.

Evaluation of head/disk pseudo-impact contact byacoustic emission technique

Pseudo-impact contact at the interface between proximity slidersand magnetic rigid disks were investigated by acoustic emission(AE) technique. Under a hot/wet condition of 60°C/80% RH andan operation speed of 19.15 m/s, AE responses were collected inreal time to monitor interaction events at the head/diskinterface (HDI). The profile of AE responses shows various eventsat the HDI which could be correlated to the micro-wear of thecarbon overcoat andlubricant degradation. These events were also detected by opticalsurface analysis (OSA). These wear and degradation eventsindicate the need for choosing the proper lubricant anddemonstrate that AE is a suitable tool to detect these events atthe head/disk interface.

96/04493 Characterization of coal injection chars by thermogravimetric analysis, scanning electron and optical microscopies and surface analysis

96/04493 Characterization of coal injection chars by thermogravimetric analysis, scanning electron and optical microscopies and surface analysis

Analysis of optical surfaces by means of surface plasmon spectroscopy

The sensitivity to material parameters of surface plasmon oscillations is explored for the design of a prototype system operating at a wavelength of 670 nm, for the simultaneous determination of thickness, complex permittivity and surface roughness of metal films. The apparatus was employed for characterization of gold and silver films with thicknesses within the 10-100 nm range. Thickness data measured with the prototype system were well correlated with those measured on a conventional surface profilometer. The Fourier spectrum of surface irregularities extracted from scattered light, enhanced by surface plasmon oscillations, was used to determine surface roughness parameters for the distinct samples. Those parameters were shown to be representative of typical surface structures observed with the atomic force microscope.

Performance of ion-figured silicon carbide SUMER telescope mirror in the vacuum ultraviolet

Measured and theoretical encircled energy and small-angle scatter of the telescope mirror (SST) of the solar ultraviolet measurements of emitted radiation (SUMER) instrument are compared at the wavelength of 123.6 nm. Mirror performance modeling was accomplished with the Optical Surface Analysis Code software package. The modeling is based on measured mirror-surface figure error data and roughness characteristics covering all important spatial frequencies that affect imaging in the vacuum ultraviolet wavelength region. Mirror-surface errors were measured with a Zygo Mark IV interferometer, Bauer Model 200 Profiler, and WYKO Topo 2-D (two-dimensional) interferometer. Performance of the SST mirror, including encircled energy and small-angle scatter, was also directly measured. A good agreement is found between measured and theoretical encircled energy within 6 arcsec and small-angle scatter up to ~50 arcmin from the peak. The 80% encircled energy diameter of the SST mirror is ~1.9 arcsec, and the amount of scattered light drops to approximately 1.0 × 10(-10) of peak irradiance (normalized to 1 arcsec(2) in the focal plane) 50 arcmin from the peak. Vacuum ultraviolet performance of the mirror is degraded primarily by midfrequency errors.

Optical Surface Analysis of the Head-Disk-Interface of Thin Film Disks

This paper describes the design, operation, theory, and data interpretation of an Optical Surface Analyzer (OSA). The OSA can measure carbon wear, lubricant depletion/accumulation, surface roughness, and lubricant alteration on carbon coated thin film disks. This device can measure an Angstrom of carbon wear or lubricant depletion/accumulation. The OSA can also measure debris generation and lubricant degradation through a measurement of optical index change. The lateral resolution of the OSA is approximately 5 by 10 microns and the bandwidth of the device is 2 MHz. The small device size allows it to be used within a test stand environment.

The effect of hydrogen in carbon overcoats on the tribology of the head-disk interface

The effect of hydrogen in the carbon overcoat on the CSS durability of thin film media lubricated with perfluoropolyether (PFPE) is reported. A strain-gauge force transducer and optical surface analyzer (OSA) were employed to investigate the failure mechanism. The OSA provided in-situ monitoring of lubricant migration and modification as well as carbon wear. Durability improved with increasing hydrogen content over the range from 12 to 36 at% of H. The improvement is attributed to changes in lubricant bonding and mobility as a function of hydrogen content.