Bhushan B. Nanotribology and Nanomechanics: An Introduction

Подождите немного. Документ загружается.

1132 B. Bhushan

35. Glassmaker NJ, Jagota A, and Hui CY (2005), Adhesion enhancement in a biomimetic

ﬁbrillar interface, Acta Biomaterialia 1, 367–375

36. Gorb S (2001), Attachment Devices of Insect Cuticles, Kluwer, Dordrecht, Netherlands

37. Gorb S, Varenberg M, Peressadko A, and Tuma J (2007), Biomimetic mushroom-

shaped ﬁbrillar adhesive microstructures, J. Royal Soc. Interf. 4, 271–275

38. Hamaker HC (1937), London van der Waals attraction between spherical bodies, Phys-

ica, 4, 1058

39. Han D, Zhou K, and Bauer AM (2004), Phylogenetic relationships among gekkotan

lizards inferred from C-mos nuclear DNA sequences and a new classiﬁcation of the

Gekkota, Biol. J. Linn. Soc. 83, 353–368

40. Hanna G and Barnes WJP (1991), Adhesion and detachment of the toe pads of tree

frogs, J. Exper. Biol. 155, 103–125

41. Hansen WR and Autumn K (2005), Evidence for self-cleaning in gecko setae, Proc.

Natl. Acad. Sci. USA 102, 385–389

42. Hiller U (1968), Untersuchungen zum Feinbau und zur Funktion der Haftborsten von

Reptilien, Z. Morphol. Tiere, 62, 307–362

43. Hinds WC (1982), Aerosol Technology: Properties, Behavior, and Measurement of Air-

borne Particles, Wiley, New York

44. Hora SL (1923), The adhesive apparatus on the toes of certain geckos and tree frogs,

J. Asiat. Soc. Beng. 9, 137–145

45. Houwink R and Salomon G (1967), Eﬀect of contamination on the adhesion of metallic

couples in ultra high vacuum, J. Appl. Phys. 38, 1896–1904

46. Huber G, Gorb SN, Spolenak R, and Arzt E (2005), Resolving the nanoscale adhesion

of individual gecko spatulae by atomic force microscopy. Biol. Lett. 1, 2–4

47. Huber G, Mantz H, Spolenak R, Mecke K, Jacobs K, Gorb SN, and Arzt E (2005), Ev-

idence for capillarity contributions to gecko adhesion from single spatula and nanome-

chanical measurements, Proc. Natl. Acad. Sci. USA 102, 16293–16296

48. Irschick DJ, Austin CC, Petren K, Fisher RN, Losos JB, and Ellers O (1996), A com-

parative analysis of clinging ability among pad-bearing lizards, Biol. J. Linn. Soc. 59,

21–35

49. Israelachvili JN and Tabor D (1972), The measurement of Van der Waals dispersion

forces in the range of 1.5 to 130 nm, Proc. R. Soc. Lond. A. 331, 19–38

50. Israelachvili JN (1992), Intermolecular and Surface Forces, 2nd edition, Academic,

San Diego

51. Jaenicke R (1998) Atmospheric aerosol size distribution, Atmospheric Particles,

RM Harrison and R van Grieken, eds., Wiley, New York, 1–29

52. Jagota A and Bennison SJ (2002), Mechanics of adhesion through a ﬁbrillar microstruc-

ture, Integr. Comp. Biol. 42, 1140–1145

53. Johnson KL, Kendall K, and Roberts AD (1971), Surface energy and the contact of

elastic solids, Proc. R. Soc. Lond. A. 324, 301–313

54. Kesel AB, Martin A, and Seidl T (2003), Adhesion measurements on the attachment

devices of the jumping spider Evarcha arcuata

, J. Exp. Biol. 206, 2733–2738

55. Kim TW and Bhushan B (2007), The adhesion analysis of multi-level hierarchical at-

tachment system contacting with a rough surface, J. Adhesion Sci. Technol. 21, 1–20

56. Kim TW and Bhushan B (2007), Eﬀect of stiﬀness of multi-level hierarchical attach-

ment system on adhesion enhancement, Ultramicroscopy 107 902–912

57. Kim TW and Bhushan B (2007), Optimization of biomimetic attachment system con-

tacting with a rough surface, J. Vac. Sci. Technol. A 25, 1003–1012

58. Kim TW and Bhushan B (2008), The adhesion model considering capillarity for gecko

attachment system, J. Royal Soc. Interf. 5, 319–327

20 Gecko Feet: Natural Hairy Attachment Systems for Smart Adhesion 1133

59. Kluge AG (2001), Gekkotan lizard taxonomy, Hamadryad 26, 1–209

60. Losos JB (1990), Thermal sensitivity of sprinting and clinging performance in the

Tokaygecko(Gekko gecko), Asiat. Herp. Res. 3, 54–59

61. Maderson PFA (1964), Keratinized epidermal derivatives as an aid to climbing in

gekkonid lizards, Nature 2003, 780–781

62. Maschmann MR, Franklin AD, Amama PB, Zakharov DN, Stach EA, Sands TD, and

Fisher TS (2006), Vertical single- and double-walled carbon nanotubes grown from

modiﬁed porous anodic alumina templates, Nanotechnology, 17, 3925–3929

63. Menon C, Murphy M, and Sitti M (2004) Gecko inspired surface climbing robots, IEEE

Int. Conf. on Robotics and Biomimetics, August 22-26, 431–436

64. Northen MT and Turner KL (2005), A batch fabricated biomimetic dry adhesive, Nano-

technology, 16, 1159–1166

65. Northen MT and Turner KL (2006), Meso-scale adhesion testing of integrated micro-

and nano-scale structures, Sensors and Actuators A, 130–131, 583–587

66. Orr FM, Scriven LE, and Rivas AP (1975), Pendular rings between solids: meniscus

properties and capillary forces, J. Fluid. Mech. 67, 723–742

67. Pan B, Gao F, Ao L, Tian H, He R, and Cui D (2005), Controlled self-assembly of thiol-

terminated poly(amidoamine) dendrimer and gold nanoparticles, Colloids and Surfaces

A, 259, 89–94

68. Peressadko Aand Gorb SN (2004), When less is more: experimental evidence fortenac-

ity enhancement by division of contact area, J. Adhesion, 80, 247–261

69. Persson BNJ (2003), On the mechanism of adhesion in biological systems, J. Chem.

Phys. 118, 7614–7621

70. Persson BNJ and Gorb S (2003), The eﬀect of surface roughness on the adhesion of

elastic plates with application to biological systems, J. Chem. Phys. 119, 11437–11444

71. Phipps PB and Rice DW (1979), Role of water in atmospheric corrosion, ACS Sympo-

sium Series 89

72. Rizzo N, Gardner K, Walls D, Keiper-Hrynko N, and Hallahan D (2006), Characteri-

zation of the structure and composition of gecko adhesive setae, J. Royal Soc. Interf. 3,

441–451

73. Ruibal R and Ernst V (1965), The structure of the digital setae of lizards, J. Morphol.

117, 271–294

74. Russell AP (1975), Acontribution to the functional morphology of the foot of the tokay,

Gekko gecko, J. Zool. Lond. 176, 437–476

75. Russell AP (1986), The morphological basis of weight-bearing in the scansors of the

tokay gecko, Can. J. Zool. 64, 948–955

76. Schäﬀer E, Thurn-Albrecht T, Russell TP, and Steiner U (2000) Electrically induced

structure formation and pattern transfer, Nature, 403, 874–877

77. S

chleich HH and Kästle W (1986), Ultrastrukturen an Gecko-Zehen, Amphibia Rep-

tilia, 7, 141–166

78. Schmidt HR (1904), Zur Anatomie und Physiologie der Geckopfote, Jena. Z. Natur-

wissen 39, 551

79. Shah GJ and Sitti M (2004), Modeling and design of biomimetic adhesives inspired by

gecko foot-hairs, IEEE Int. Conf. on Robotics and Biomimetics, 873–878

80. Simmermacher G (1884), Untersuchungen über Haftapparate an Tarsalgliedern von In-

sekten, Zeitschr. Wissen Zool. 40, 481–556

81. Sitti M (2003) High aspect ratio polymer micro/nano-structure manufacturing using

nanoembossing, nanomolding and directed self-assembly, Proc. IEEE/ASMEAdvanced

Mechatronics Conf. 2, 886–890

1134 B. Bhushan

82. Sitti M and Fearing RS (2003) Synthetic gecko foot-hair for micro/nano structures as

dry adhesives, J. Adhesion Sci. Technol. 17, 1055–1073

83. Sitti M and Fearing RS (2003) Synthetic gecko foot-hair for micro/nano structures

for future wall-climbing robots, Proc. IEEE Int. Conf. on Robotics and Automation

1, 1164–1170

84. Spolenak R, Gorb S, and Arzt E (2005), Adhesion design maps for bio-inspired attach-

ment systems, Acta Biomaterialia 1, 5–13

85. Stork NE (1980), Experimental analysis of adhesion of Chrysolina polita on a variety

of surfaces, J. Exp. Biol. 88, 91–107

86. Stork NE (1983), J. Nat. Hist., 17, 829–835

87. Tian Y, Pesika N, Zeng H, Rosenberg K, Zhao B, McGuiggan P, Autumn K, and Is-

raelachvili J (2006), Adhesion and friction in gecko toe attachment and detachment,

Proc. Nat. Acad. Sci. U. S. A. 103, 19320–19325

88. Tinkle DW (1992), Gecko, Encylcopedia Americana, Grolier, U.K., 12, 359

89. Van der Kloot WG (1992), Molting, Encylcopedia Americana, Grolier, U.K., 19, 336–

337

90. Wagler J (1830), Naturliches System der Amphibien, JG Gotta’schen Buchhandlung,

Munich

91. Wan KT, Smith DT, and Lawn BR (1992), Fracture and contact adhesion energies of

mica-mica, silica-silica, and mica-silica interfaces in dry and moist atmospheres, J. Am.

Ceram. Soc. 75, 667–676

92. Wenzel RN (1936), Resistance of solid surfaces to wetting by water, Ind. Eng. Chem.

28, 988–994

93. Williams EE and Peterson JA (1982), Convergent and alternative designs in the digital

adhesive pads of scincid lizards, Science 215, 1509–1511

94. Yao H and Gao H (2006), Mechanics of robust and releasable adhesion in biology:

bottom-up designed hierarchical structures of gecko, J. Mech. Phys. Solids, 54, 1120–

1146

95. Young WC and Budynas R (2001) Roark’s Formulas for Stress and Strain,7thed.

McGraw Hill, New York

96. Yurdumakan B, Raravikar NR, Ajayan PM, and Dhinojwala A (2005), Synthetic gecko

foot-hairs from multiwalled carbon nanotubes, Chem. Comm., 3799–3801

97. Zhao Y, Tong T, Delzeit L, Kashani A, Meyyappan M, and Majumdar A (2006), Inter-

facial energy and strength of multiwalled-carbon-nanotube-based dry adhesive, J. Vac.

Sci. Technol. B, 24, 331–335

98. Zimon AD (1969), Adhesion of Dust and Powder, translated from Russian by M. Corn,

Plenum, New York

99. Zisman WA (1963), Inﬂuence of constitution on adhesion, Ind. Eng. Chem. 55(10),

18–38

Part V

Applications

Micro/Nanotribology and Micro/Nanomechanics

of Magnetic Storage Devices

Bharat Bhushan

Summary. A magnetic recording process involves relative motion between a magnetic

medium (tape or disk) against a stationary or rotating read/write magnetic head. For ever-

increasing, high areal recording density, the linear ﬂux density (number of ﬂux reversals

per unit distance) and the track density (number of tracks per unit distance) should be as

high as possible. The size of a single bit dimension for current devices is typically less than

1000 nm

. This dimension places stringent restrictions on the defect size present on the head

and medium surfaces.

Reproduced (read-back) magnetic signal amplitude decreases with a decrease in the

recording wavelength and/or the track width. The signal loss results from the magnetic coat-

ing thickness, read gap length, and head-to-medium spacing (clearance or ﬂying height). It is

known that the signal loss as a result of spacing can be reduced exponentially by reducing the

separation between the head and the medium. The need for increasingly higher recording den-

sities requires that surfaces be as smooth as possible and the ﬂying height (physical separation

or clearance between a head and a medium) be as low as possible. The ultimate objective is to

run two surfaces in contact (with practically zero physical separation) if the tribological issues

can be resolved. Smooth surfaces in near contact lead to an increase in adhesion, friction, and

interface temperatures, and closer ﬂying heights lead to occasional rubbing of high asperities

and increased wear. Friction and wear issues are resolved by appropriate selection ofinterface

materials and lubricants, by controlling the dynamics of the head and medium, and the en-

vironment. A fundamental understanding of the tribology (friction, wear, and lubrication) of

the magnetic head/medium interface, both on macro- and micro/nanoscales, becomes crucial

for the continued growth of this more than $ 60 billion a year magnetic storage industry.

In this chapter, initially, the general operation of drives and the construction and materials

used in magnetic head and medium components are described. Then the micro/nanotribo-

logical and micro/nanomechanics studies including surface roughness, friction, adhesion,

scratching, wear, indentation, and lubrication relevant to magnetic storage devices are pre-

sented.

1138 Bharat Bhushan

21.1 Introduction

21.1.1 Magnetic Storage Devices

Magnetic storage devices used for storage and retrieval are tape, ﬂexible (ﬂoppy)

disk and rigid disk drives. These devices are used for audio, video and data-

storage applications. Magnetic storage industry is some $ 60 billion a year indus-

try with $ 20 billion for audio and video recording (almost all tape drives/media)

and $ 40 billion for data storage. In the data-storage industry, magnetic rigid

disk drives/media, tape drives/media, ﬂexible disk drives/media, and optical disk

drive/mediaaccount for about$ 25B, $ 6B, $ 3B, and $ 6B, respectively. Magnetic

recording and playback involves the relative motion between a magnetic medium

(tape or disk) against a read-write magnetic head. Heads are designed so that they

develop a (load-carrying) hydrodynamic air ﬁlm under steady operating conditions

to minimize head-medium contact. However, physical contact between the medium

and head occurs during starts and stops, referred to as contact-start-stops (CSS)

technology [1–4]. In the modern magnetic storage devices, the ﬂying heights (head-

to-medium separation) are on the order of 5 to 20nm and roughnesses of head and

medium surfaces are on the order of 1–2 nm RMS. The need for ever-increasing

recording densities requires that surfaces be as smooth as possible and the ﬂying

heights be as low as possible. Smooth surfaces lead to an increase in adhesion, fric-

tion, and interfacetemperatures, and closer ﬂying heightslead to occasional rubbing

of high asperities and increased wear. High stiction (static friction) and wear are the

limiting technology to future of this industry. Head load/unload (L/UL) technology

has recently been used as an alternative to CSS technology in rigid disk drives that

eliminates stiction and wear failure mode associated with CSS. In an L/UL drive,

a lift tab extending from the suspension load beam engages a ramp or cam structure

as the actuator movesbeyondthe outerradius of the disk. The ramplifts (or unloads)

the head stack from the disk surfaces as the actuator moves to the parking position.

Starting and stopping the disk only occur with the head in the unloaded state. Sev-

eral contact or near contact recording devices are at various stages of development.

High stiction and wear are the major impediments to the commercialization of the

contact recording [1–7].

Magnetic media fall into two categories: particulate media, where magnetic par-

ticles (γ-Fe

,Co–γFe

,CrO

, Fe or metal (MP), or barium ferrite) are dis-

persed in a polymeric matrix and coated onto a polymeric substrate for ﬂexible me-

dia (tape and ﬂexible disks); thin-ﬁlm media, where continuous ﬁlms of magnetic

materials are deposited by vacuum deposition techniques onto a polymer substrate

for ﬂexible media or onto a rigid substrate (typically aluminium and more recently

glass or glass ceramic)for rigid disks. The most commonly used thin magneticﬁlms

for tapes are evaporated Co

−

Ni (82–18at. %) or Co

−

O dual layer. Typical mag-

netic ﬁlms for rigid disks are metal ﬁlms of cobalt-based alloys (such as sputtered

−

Ni, Co

−

Ni, Co

−

Cr, Co

−

Cr and Co

−

NiCr). For high recording densities,

trends have been to use thin-ﬁlm media. Magnetic heads used to date are either con-

ventional thin-ﬁlm inductive, magnetoresistive (MR) and giant MR (GMR) heads.

21 Micro/Nanotribology and Micro/Nanomechanics of Magnetic Storage Devices 1139

The air-bearing surfaces (ABS) of tape heads are generally cylindrical in shape.

For dual-sided ﬂexible-disk heads, two heads are either spherically contoured and

slightly oﬀset (to reduce normal pressure) or are ﬂat and loaded against each other.

The rigid-disk heads are supported by a leaf spring (ﬂexure) suspension. The ABS

of heads are almost made of Mn

−

Zn ferrite, Ni

−

Zn ferrite, Al

−

TiC and calcium

titanate. The ABS of some conventional heads are made of plasma sprayed coatings

of hard materials such as Al

−

TiO

and ZrO

[2–4].

Figure 21.1 shows the schematic illustrating the tape path with details of tape

guides in a data-processing linear tape drive (IBM LTO Gen1) which uses a rect-

angular tape cartridge. Figure 21.2a shows the sectional views of particulate and

thin-ﬁlm magnetic tapes. Almost exclusively, the base ﬁlm is made of semicrys-

talline biaxially-oriented poly (ethylene terephthalate) (or PET) or poly (ethylene

2,6 naphthalate) (or PEN) or Aramid. The particulate coating formulation consists

of binder (typically polyester polyurethane), submicron accicular shaped magnetic

particles (about 50nm long with an aspect ratio of about 5), submicron head clean-

ing agents (typically alumina) and lubricant (typically fatty acid ester). For protec-

tion against wear and corrosion and low friction/stiction, the thin-ﬁlm tape is ﬁrst

coated with a diamondlike carbon (DLC) overcoat deposited by plasma enhanced

chemical vapor deposition, topically lubricated with primarily a perﬂuoropolyether

lubricant.Figure21.2b shows theschematic of an 8-track (alongwith 2 servo tracks)

thin-ﬁlm read-write head with MR read and inductive write. The head steps up and

down to provide 384 total data tracks across the width of the tape. The ABS is made

of Al

−

TiC. A tape tension of about 1 N over a 12.7mmwidetape(normalpres-

sure ≈ 14kPa) is used during use. The RMS roughnesses of ABS of the heads and

tape surfaces typically are 1–1.5nm and 5–8nm, respectively.

Figure 21.3 shows the schematic of a data processing rigid disk drive with 21.6-,

27.4-,48-,63.5-, 75-, and 95-mm form factor. Nonremovablestack ofmultiple disks

mounted on a ball bearing or hydrodynamic spindle, are rotated by an electric mo-

tor at constant angular speed ranging from about 5000 to in excess of 15,000RPM,

dependent upon the disk size. Head slider-suspension assembly (allowing one slider

Cartridge reel Take-up reel Rewind

Wind

Read/write

head

Flanged roller with tension transducer

Fig. 21.1. Schematic of tape

path in an IBM Linear Tape

Open (LTO) tape drive

1140 Bharat Bhushan

Fig. 21.2. (a) Sectional views of particulate and thin-ﬁlm magnetic tapes, and (b) schematic

of a magnetic thin-ﬁlm read/write head for an IBM LTO Gen 1 tape drive

21 Micro/Nanotribology and Micro/Nanomechanics of Magnetic Storage Devices 1141

Fig. 21.3. Schematic of

a data-processing magnetic

rigid disk drive

for each disk surface) is actuated by a stepper motor or a voice coil motor using

a rotary actuator. Figure 21.4a shows the sectional views of a thin-ﬁlm rigid disk.

The substrate forrigid disksis generallya non heat-treatablealuminium-magnesium

alloy 5086, glass or glass ceramic. The protective overcoat commonlyused forthin-

ﬁlm disks is sputtered DLC, topically lubricated with perﬂuoropolyether type of

lubricants. Lubricants with polar-end groups are generally used for thin-ﬁlm disks

in order to provide partial chemical bonding to the overcoat surface. The disks used

for CSS technology are laser textured in the landing zone. Figure 21.4b shows the

schematic of two thin-ﬁlm head picosliders with a step at the leading edge, and

Fig. 21.4. (a) Sectional views

of a thin-ﬁlm magnetic rigid

disk, and (b) schematic of

two picosliders - load/unload

picoslider and padded pi-

coslider used for CSS

1142 Bharat Bhushan

GMR read and inductive write. “Pico” refers to the small sizes of 1.25mm×1mm.

These sliders use Al

−

TiC (70–30wt %) as the substrate material with multi-

layered thin-ﬁlm head structure coated and with about 3.5nm thick DLC coating

to prevent the thin ﬁlm structure from electrostatic discharge. The seven pads on

the padded slider are made of DLC and are about 40µm in diameter and 50nm in

height. A normal load of about 3g is applied during use.

21.1.2 Micro/Nanotribology and Micro/Nanomechanics

and Their Applications

The micro/nanotribological studies are needed to develop fundamental understand-

ing of interfacial phenomena on a small scale and to study interfacial phenomena

in [8–12]. Magnetic storage devices operate under low load and encounter isolated

asperity interactions. These use multilayered thin ﬁlm structure and are generally lu-

bricated with molecularly-thin ﬁlms. Micro/nanotribologicaland micro/nanomech-

anical techniques are ideal to study the friction and wear processes of micro/nano-

scale and molecularly thick ﬁlms. These studies are also valuable in fundamental

understanding of interfacial phenomena in macrostructures to provide a bridge be-

tween science and engineering. At interfaces of technological applications, contact

occurs at multiple asperity contacts. A sharp tip of tip-based microscopes (atomic

force/friction force microscopes or AFM/FFM) sliding on a surface simulates a sin-

gle asperity contact, thus allowing high-resolutionmeasurements of surface interac-

tions at a single asperity contacts. AFMs/FFMs are now commonly used for tribo-

logical studies.

In thischapter,we presentstate-of-the-artofmicro/nanotribologyand micro/nano-

mechanics of magnetic storage devices including surface roughness, friction, adhe-

sion, scratching, wear, indentation, and lubrication.

21.2 Experimental

21.2.1 Description of AFM/FFM

AFM/FFMs used in the tribological studies have been described in several pa-

pers [10,12,13]. Brieﬂy, in one of the commercial designs, the sample is mounted

on a PZT tube scanner to scan the sample in the x-y-planeandtomovethesample

in the vertical (z) direction (Fig. 21.5). A sharp tip at the end of a ﬂexible can-

tilever is brought in contact with the sample and the sample is scanned in a raster

pattern (Fig. 21.6). Normal and frictional forces being applied at the tip–sample

interfaceare simultaneously measuredusing a laser beam deﬂection technique.Sur-

face roughnessis measured either in the contact mode or the so-calledtapping mode

(intermittent contactmode). For surfaceroughness and friction measurements, a mi-

crofabricated square pyramidal Si

tip with a tip radius of about 30 nm attached

to a cantilever beam (with a normal beam stiﬀness of about 0.5N/m) for contact