Anton V. Goldade

Measurements and analysis of surface potential change during wear of single-crystal silicon (100) at ultralow loads using Kelvin probe microscopy

The change in surface potential resulting from wear at ultralow loads using Kelvin probe microscopy is studied. Samples studied include single-crystal silicon (100), single-crystal silicon (100) lubricated with fully bonded Z-DOL (a perfluoropolyether). The effects of relative humidity (RH) as well as that of load and number of cycles during wear on the change in surface potential have been investigated. It is believed that the removal of either contaminant layer, natural oxide layer or lubricant during few wear cycles gives rise to the initial change in surface potential. As the number of cycles and/or load increases, the material is removed from the silicon surface by subsurface fatigue wear and stresses beneath the silicon surface resulting in subsurface structural changes which are responsible for further change in the surface potential.

Measurements of elastic properties of ultra-thin diamond-like carbon coatings using atomic force acoustic microscopy

We present a comparative study of the elastic stiffness of ultra-thin (5, 20 and 100 nm thick) diamond-like carbon coatings with a sampling depth less than or comparable to the thickness of the coating. The experiments were conducted using atomic force acoustic microscopy, which is a dynamic operation mode of the atomic force microscope that permits the measurement of elastic properties with high spatial resolution. The method is based on the evaluation of the shift of the cantilever resonance frequencies caused by the contact stiffness between the sensor tip and the sample surface. Two sets of measurements are reported: one in which the silicon sensor tips were employed; and another set in which diamond-coated tips were used. The silicon tips showed considerable wear during data acquisition. Using the diamond-coated tips, however, the wear could be avoided and qualitative measurements of high stability could be performed, thereby permitting the comparison of coatings obtained by different deposition techniques. It is also shown how the obtained results can lead to future quantitative measurements on stiff coatings.

On the nanoscale measurement of friction using atomic-force microscope cantilever torsional resonances

We studied friction and stick-slip phenomena on bare and lubricated silicon samples by measuring the torsional contact resonances of atomic force microscope cantilevers. A piezoelectric transducer placed below the sample generates in-plane sample surface vibrations which excite torsional vibrations of the cantilever. The resonance frequencies of the vibrating beam depend on the tip-sample forces. At low lateral surface amplitudes the cantilever behaves like a linear oscillator with viscous damping. Above a critical surface amplitude, typically 0.2 nm, the amplitude maximum of the resonance curves does not increase any more and the shape of the resonance curves changes, indicating the onset of sliding friction. The critical amplitude increases with increasing static cantilever load. For a bare silicon sample it is higher than for the lubricated silicon. Microslip known from macroscopic contacts causes energy dissipation in the atomic force microscope tip-contact before sliding friction sets in.

Measurement and Origin of Tape Edge Damage in a Linear Tape Drive

Integrity of the magnetic tape edge is the key to maintaining high performance of modern tape drives. Damage to the tape edge under normal drive operation results in the change in tape dimensions and debris generation, both leading to degradation in the reproduction of the recorded signal. The objective of the present study is to develop a methodology for evaluation of tape edge quality and to apply the methodology to monitor tape edge degradation under normal drive operation. Optical microscopy, atomic force microscopy and scanning electron microscopy are employed to study and quantify the quality of the tape edge. AFM measure-ments were made on both individual tape layers and the tape reel. An edge quality measurement technique is used to quantify the damage to tape edge. A technique for the tape lateral motion measurement is used to study the effect of continuous sliding on tape guiding. A lateral force measurement technique is developed to measure the force exerted by the tape edge on the guide flange. The effect of normal drive operation on tape edge quality and on tape guiding in a linear tape drive is studied. It is shown that two edges of a factory-slit tape are imperfect and different, with cracking of the magnetic coating occurring at one edge. Under normal drive operation, one edge experiences more wear with larger amount of debris produced. This larger debris generation occurs on the edge with cracks developed during manufacturing. A possible mechanism of tape edge wear under normal drive operation is proposed.

Effect of Particulate Contamination on Pole Tip Recession in a Linear Tape Drive

Three-body abrasion is the cause of differential wear in magnetic tape heads resulting in recession of the magnetic poles with respect to the head substrate; this is called pole tip recession (PTR). The increasing head--tape spacing caused by PTR results in a lower write density, so the recession must be minimized. The three-body particles that may interact with the head--tape interface can originate from the operating environment (contaminant particles) and from the interface itself (debris particles). The effect of airborne particulate contaminants trapped at the head--tape interface (particle concentration, size, and hardness), which results in three-body abrasion, on PTR growth is studied experimentally. PTR increases with increases in any of the following: particle concentration, size, and hardness. Analytical modeling supports the experimental results. Possible mechanisms responsible for the observed behavior are discussed.

Effect of operating environment on failure mechanism of a head-tape interface in a linear tape drive with a belt-driven cartridge

Abstract The effect of the operating environment on the failure mechanism of a head-tape interface in a linear tape drive with a belt-driven cartridge was studied. A modified commercial drive with magnetoresistive head and metal particle tape were used. Durability tests for the full tape length were performed at ambient and extreme environmental conditions. Head output, coefficient of friction and number of dropouts per minute were measured during the test. Optical and atomic force microscopy and Auger electron spectroscopy were used to evaluate changes at the head-tape interface at the end of the tests. Magnetic and tribological performance of head-tape interface is the best at low temperatures and low relative humidities. Increases in both temperature and relative humidity result in performance degradation, with the worst performance at the highest temperature. At ambient conditions, sporadic variations in the coefficient of friction and the number of dropouts per minute are observed, associated with a cycle of stain formation and removal. Possible mechanisms responsible for the observed tribological behaviour of the interface at various environmental conditions are discussed.

Investigating ultra-thin lubricant layers using lateral atomic force acoustic microscopy

The ultrasonic friction mode of an atomic force microscope is a scanning probe technique allowing one to analyze the load and velocity dependence of friction. The technique is based on the evaluation of the resonance behavior of an AFM cantilever when in contact with a vibrating sample surface. The effect of load and lateral displacement of the sample surface on the shape of the torsional resonance spectra of the AFM cantilever is evaluated under dry and lubricated sliding conditions. A characteristic flattening of the torsional resonance curve has been observed at large surface displacements, resulting from the onset of sliding friction in the contact of the AFM cantilever tip with the sample surface. This is confirmed by an analytical model describing torsional cantilever vibrations in case of a Hertzian, i.e. purely elastic, contact and by numerical simulations of the cantilever vibrations.