AFM Probe-Based Data Recording Technology · AFM Probe-Based Data Recording Technology Prof. Bharat...

AFM Probe-Based Data Recording Technology

Prof. Bharat Bhushanbh h 2@ [email protected]

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

1Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Outline• Introduction

• Objectives and Approach

• ExperimentalTip shape characterizationTip shape characterizationFriction and wear measurementsMechanical properties measurementsExperimental samplesExperimental samples

• ResultsPt-coated tipsOther noble metal-coated tipsOther noble metal-coated tips

Nanotribological characterizationNanomechanical characterizationRole of lubricants, scanning velocity, operating environment, g y, p g

Surface treated tipsNanotribological characterizationNanomechanical characterization


Electrical and surface characterization• Conclusions

2

Introduction BackgroundBackground• Magnetic and optical recording technologies are used for nonvolatile

data storage. These technologies are reaching limit of data recording g g g gdensity of 500 Gb/in2 and 100 Gb/in2, respectively.

• Battle: Flash vs. hard drives B th fl h i d i di k d i h b t l hBoth flash memories and micro-disk drives have begun to replace each other mostly in portable but also in some fixed drives which require low storage capacity.

• Probe-based recording technologyProbe based recording technologyIt has the potential of extremely areal recording density of several Tb/in2

or higher.Based on thermomechanical recording, IBM has developed a technology which uses an array of 1024 silicon cantilevers (Millipede).Phase-change memory (PCM) uses chalcogenide alloys.A third technique is ferroelectric memory with typically lead zirconate titanate (PZT) medium

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 3

titanate (PZT) medium.

• Intergrated tip heaters consist of tips of nanoscale pdimension.

• Thermomechanical recording is performed on an about 40-

thi k l dinm thick polymer medium on Si substrate.

• Heated tip to about 400 oC contacts with the medium forcontacts with the medium for recording.

• Wear of the heated tip is an issue.

(http://www ibm com)32 x 32 tip array


Probe-based NEMS data storage based on thermomechanical recording

4

(http://www.ibm.com)

• In phase change media electric current• In phase-change media, electric current of different magnitudes are passed to a chalcogenide material (Ge2Sb2Te3) using a conducting Pt-coated AFM probe

Local joule heating is used to change the structure.

• Binary recording: generating difference levels of high and low resistance onlevels of high and low resistance on chalcogenide medium

High current (through electrode probe) heating of medium to more than 630oC cooling to amorphous state high resistance (“1”)Low current (through electrode probe) heating of medium to less than 630oC gcooling to crystalline state low resistance (“0”)

• Wear of the tip and medium at 630oC is an issue.Schematic of the electrical probe storage system

using phase change media (Wright et al 2006)


Probe-based NEMS data storage based on phase change memory

5

using phase-change media (Wright et al., 2006).

B. Bhushan and K. Kwak, Nanotechnol. 18, 345504 (2007)

• Ferroelectric material, typically lead zirconate titanate (PZT)zirconate titanate (PZT)

• Electrical current switches between two different polarization states by applying short voltage pulses (~10 V, ~100 μs), g p ( , μ ),resulting in recording. Temperature rise on the order of 80oC is expected.

• Piezoresponse force can be read out by applying an AC voltage of 1 V.

• Wear of the tip and medium at 80oC is an issue, but to a lesser degree.

• Furthermore, the tip does not need to be in contact with medium during readback.


Probe-based NEMS data storage based on ferroelectric recording

6

B. Bhushan and K. Kwak, J. Phys.: Condens. Matter 20, 225013 (2008)

I

• For fast data rate, the cantilever array needs to be moved at high velocities on the order of 100 mm/s Wear of the tip and medium is

Issues

velocities on the order of 100 mm/s. Wear of the tip and medium is an issue.

• In order to achieve high wear resistance and long lifetime, a high surface hardness of metal-coated tip with high electrical conductivity is essential.

• Durability is a concern for soft metals such as pure Au An alloyDurability is a concern for soft metals such as pure Au. An alloy such as AuNi5 of a hard contact material, used in relays, is of interest.

• Lubricant coating on substrate surface should be optimized for friction and wear protection.

• Tip wear mechanism in nanoscale region is not well-understood,


Tip wear mechanism in nanoscale region is not well understood, especially with various top metal layers on the probe tip.

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ObjectivesObjectives and Approach

• For comprehensive investigation of friction and wear of the tip sliding against PZT film, perform a wear study at a range of loads, distances and temperature to compare wear resistance of metal-coated top layers with

j

p p p yvarious noble metals and their alloys.

• Evaluate tribological performance of lubricants applied on PZT

• Evaluate mechanical properties of noble metal coatings and PZT• Evaluate mechanical properties of noble metal coatings and PZT

Approach• Use silicon grating and software to deconvolute tip shape in order to

characterize the change in the tip shape and evaluate the tip radius and its wear volume.

• Adhesive force and coefficient of friction measurement to evaluate lubricant tribological performance.

• Surface potential and resistance mapping after wear test on PZT.

• Nanoindentation and nanoscratch to evaluate hardness elastic modulus


B. Bhushan and K. Kwak, J. Phys.: Condens. Matter 20, 225013 (2008); M. Palacio and B. Bhushan, Nanotechnology, 19, 105705 (2008).

• Nanoindentation and nanoscratch to evaluate hardness, elastic modulus, creep and scratch resistance.

Tip shape characterizationExperimental

p p

• (a) A schematic of grating (with array of sharp tips) on silicon wafer surface, (b) illustration of tip characterization and calculation of tip radius and (c) illustration of


illustration of tip characterization and calculation of tip radius, and (c) illustration of calculation of the wear volume.

9

B. Bhushan and K. Kwak, Nanotechnol. 18, 345504 (2007); Ibid., J. Phys.: Condens. Matter 20, 225013 (2008)

• Schematics and photographs of a triangular V shaped and rectangular cantilevers


• Schematics and photographs of a triangular V-shaped and rectangular cantilevers with metal-coated layer

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Friction and wear measurements• The friction force experiments were carried out by scanning the sample along an axis

perpendicular to the long axis of the cantilever, at a scan velocity of 1 μm/s using a scan rate of 0.5 Hz at 1 to 80 nN normal loads .

• The measured friction force was plotted as a function of normal load. The data could be fitted with a straight line which suggests that friction force is proportional to normal load. The coefficient of friction was obtained by calculating the slope of the line.

• For Pt wear experiments the tip was slid on a PZT film sample for 1 m at a normal• For Pt wear experiments, the tip was slid on a PZT film sample for 1 m at a normal load of 50 nN, followed by 1 m at 100 nN in contact mode at velocities ranging from 0.1 to 100 mm/s. Scan direction was parallel to the long axis of the cantilever beam.

• In order to obtain the tip profile to calculate wear volume the tip was scanned beforeIn order to obtain the tip profile to calculate wear volume, the tip was scanned before sliding and after wear test on the grating sample in tapping mode and in a direction perpendicular to the long axis of cantilever beam. Scanning was performed on 2 x 2 μm2 scan area with a velocity of 1 μm/s.

• For other noble metal-coated tips, the tip profiles were obtained before and after 1, 10 and 100 m sliding at 10 mm/s, and 300 m sliding at 100 mm/s and at 100 nN.

• To evaluate the effect of lubrication on PZT wear, a diamond tip was used to create a


B. Bhushan and K. Kwak, J. Phys.: Condens. Matter 20, 225013 (2008); M. Palacio and B. Bhushan, J. Vac. Sci. Technol. A, in press (2008).

5 x 5 μm2 wear scar. Afterwards, the surface potential and contact resistance image of the worn surface was imaged with a conducting AFM tip.

Mechanical properties measurements

• Hardness and elastic modulus were evaluated using a NanoIndenter II (MTS) in the continuous stiffness mode (CSM) equipped with a diamond

p p

( ) ( ) q ppBerkovich tip. The maximum indentation displacement was controlled to 250 nm for Pt, Pt-Ni and Au-Ni, and 50 nm for Pt, Pt-Si and PZT.

• Creep experiments were performed using CSM with the diamond BerkovichCreep experiments were performed using CSM with the diamond Berkovich indenter tip penetrating the coatings at a rate of 100 μN/s. The tip was held for 600 s at the maximum load.

• Scratch experiments were carried out using a conical diamond indenter tip• Scratch experiments were carried out using a conical diamond indenter tip with 1 μm radius of curvature and 90o included angle. Scratches made were 500 μm long, and the scratch-induced damage was evaluated by scanning electron microscopy (SEM).


Experimental samplesp pDetails of noble metal-coated probes

Tipp

PZT flat sampleNoble metal

Stiffness (N/m) and initial 2-D tip radius (nm)

Thickness of metal films (nm)

Pt ~2 N/m, 74 nm(CSC21, MikroMasch)

185 nm/15 nm Pt/Cr(Sputter deposition)

-15 nm/50 nm PbZr0.2Ti0.8O3/SrRuO3

film on 0.5 mm c-axis SrTiO3

(P l l d iti )(Pulse laser deposition)Au-Ni ~2.8 N/m, 65 nm

Au-Ni (PPP-FM, Nanosensors)

65 nm/10 nm Au-Ni/Cr(Sputter deposition with Au-Ni alloy, and sputtering with Cr target, respectively)

Pt-Ir ~2.8 N/m, 53 nmPt-Ir (PPP-EFM, Nanosensors)

25 nm/3 nm Pt-Ir/Cr(Sputter deposition)

Pt-Ni ~2.8 N/m, 61 nmPt-Ni

95 nm/10 nm Pt-Ni/Ni(Co-sputtering with

(PPP-FM, Nanosensors) separate Pt and Ni targets, and sputtering with Ni target, respectively)


Ph i l ti f t i l d i b tiPhysical properties of materials used in probe tipsMaterial Crystal

structureDensity(g/cm3)

Melting point(oC)

Electricalresistivity

at 0oC (mΩcm)

Coeff. of linear

thermalexpansion( 10 6 oC 1)

Tensilestrength(MPa)

Elongationin 50 mm

(%)

Hardness(GPa)

Elastic modulus(GPa)

Poisson’s ratio

(x10-6 oC-1)Noble metals

Pt fcca 21.45a 1769a 9.85a 9.1a 207-241 (as-worked)a

124-165 (annealed)

1-3 (as-worked)a

30-40 (annealed)

0.91 (as-worked)a

0.36 (annealed)0.42 (as-cast)

171a 0.39a

Au fcca 19.32a 1064a 2.06a 14.2a 207-221 (as- 4 (as-worked)a 0.56 (as- 77a 0.42aAu fcc 19.32 1064 2.06 14.2 207 221 (asworked)a

124-138 (annealed)

4 (as worked)39-45

(annealed)

0.56 (asworked)a


77 0.42

Ir fcca 22.65a 2447a 4.71a 6.8a 2070-2480 (hot-worked)a

1103-1241

15-18 (hot-worked)a

20-22

6.4 (as-worked)a


517a 0.26a

(annealed) (annealed)Noble metal alloys

Pt-Ni fccb - - - - - - - - -Au-Ni (sp.) fccb - - - - - - 7c 130c -

Other materials

aDavis (1998) eKabo et al. (2004)bHultgren et al. (1963) fDavila et al. (2007)cBaker and Nix (1994) sp. - sputtered

materialsNi fcca 8.90a 1445a 6.8a 13.3a 462 (annealed)e 47e 0.45 (annealed)e 204a 0.31e

Si(100) diamonde

2.33d 1420d - 42d 130e - 13f 180f 0.28e


dBhushan and Gupta (1991)

Alloys of noble metals have increased hardness and elastic modulus relative to pure noble metals.

Physical, thermal and electrical properties of BMIM-PF6 and Z-TETRAOL1-Butyl-

3-methylimidazolium hexafluorophosphate (BMIM-PF )

Z-TETRAOL

hexafluorophosphate (BMIM-PF6)Cation C8H15N2

+ -Anion PF6

- -Molecular weight (g/mol) 284a 2300b

Tmelting (oC) 10c -Tdecomposition (oC) 300c ~320b

Density (g/cm3) 1 37a 1 75bDensity (g/cm3) 1.37a 1.75b

Kinematic viscosity (mm2/s) 281a (20oC)78.7d (40 oC)

2000b (20 oC)

Pour point (oC) <-50e -67b

Specific heat (J/g K) 1.44f (25oC) ~0.20b(50oC)

Thermal conductivity at 25oC (W/ K)

0.15g ~0.09b

(W/m-K)Dielectric strength at 25oC

(kV/mm)- ~30b

Volume resistivity (Ω cm)

714 ~1013 b

Vapor pressure at 20oC (Torr) <10-9 ~10-12 b

Wettability on Si moderatec -Water contact angle 95o h 102o h

Miscibility with isopropanol Totala -

Miscibility with water - -


aMerck Ionic Liquids Database, Darmstadt, Germany eKabo et al. (2004)bZ-TETRAOL Data Sheet, Solvay Solexis Inc., Thorofare, NJ fKabo et al. (2004)cKinzig and Sutor (2005) gFrez et al. (2006)dReich et al. (2003) hPalacio and Bhushan (2008); For comparison,

the contact angle of PZT is 88o.

Selected physical and thermal properties of bulk PZT and polycrystalline diamond

PZT Poly. diamondPhysical Elastic modulus, E (GPa) 200 1140a

Hardness, H (GPa) 13 80a,b

Poisson’s ratio, ν 0.25c 0.07a

Density (kg/m3) 7.8x103 -Thermal Thermal conductivity, k (W/m K) 1.60d (@ 227oC) 400a

Thermal diffusivity, κ (m2/s) 0.60x10-6,d (@ 227oC) -Specific heat at constant 0 34d (@ 227oC) 0 52a (@ 27oC)

aField (1992)bBhushan and Gupta (1991)

Specific heat at constant pressure, cp (kJ/kg K)

0.34d (@ 227oC) 0.52a (@ 27oC)

bBhushan and Gupta (1991)cassumeddMorimoto et al. (2003)

A polycrystalline diamond tip was used to create wear scars on the PZT surface.


A polycrystalline diamond tip was used to create wear scars on the PZT surface.

ResultsPt-coated tipsEffect of tip coating

p

• The wear volume increases with an increase of velocity typical of• The wear volume increases with an increase of velocity, typical of adhesive and abrasive wear modes. At higher velocities, wear could be caused by the adhesive wear and periodical high velocity impact on the PZT film surface. • The wear volume increases as the logarithm of velocity up to

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 17K. Kwak and B. Bhushan, J. Vac. Sci. Technol. A 26, 783 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

between 0.1 and 1 mm/s and then levels off. This wear behavior at lower sliding velocities is associated with thermally activated atomic-scale stick-slip.

• From SEM images, significant wear is observed in the case of the higher sliding velocity as compared to those of the lower velocities. The mechanism for tip wear is adhesive and abrasive wear.

• At higher velocity impact wear could be caused by periodic high velocity impact of


• At higher velocity, impact wear could be caused by periodic high velocity impact of asperities on the PZT film.

18

K. Kwak and B. Bhushan, J. Vac. Sci. Technol. A 26, 783 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

• At 0.1 mm/s sliding velocity, wear scars are observed on the PZT film. Black arrows are used to identify wear scars and white arrows indicate significant damage. The line profile shows wear depth in the range of 1.5-2.2 nm after sliding at 100 nN.

• At a velocity of 100 mm/s wear scars are not observed on the PZT film Here the sliding cycles are


At a velocity of 100 mm/s, wear scars are not observed on the PZT film. Here, the sliding cycles are calculated to be 500 cycles lower than that at lower velocities. Wear scar on the PZT film is not distinguishable due to this small number of the sliding cycles.

19K. Kwak and B. Bhushan, J. Vac. Sci. Technol. A 26, 783 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

• At both loads of 50 nN and 100 nN, the wear volume is higher at 80 oC than at 20 oC after sliding on the unlubricated sample. The increase is associated with the degradation of the mechanical


properties of the Pt coating.

20

K. Kwak and B. Bhushan, J. Vac. Sci. Technol. A 26, 783 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

Other noble metal-coated tipsOther noble metal coated tipsNanotribological characterization

• A normal load of 100 nN can be used with measurable wear and was selected from the baseline experiment. This

d d f t t th bl t l t dprocedure was used for tests on other noble metal-coated tips.

• Reduction in height indicates tip blunting resulting from wear and is seen in all cases.


B. Bhushan and K. Kwak, J. Phys.: Condens. Matter 20, 225013 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

• The wear of Pt-coated tip is higher than other metal-coated tips. The Pt-coated tip surface is significantly softer than the PZT film surface.

• The other noble metal-coated tips are harder so they exhibit less wear compared to the Pt-coated tip.

• Pt-Ir-coated tip shows highest wear resistance and will be used for further


studies on lubrication of PZT.


• SEM images show plastic deformation of the tip, which is indicative of adhesive wear.

• Brittle Pt-coated silicon asperities can fracture when sliding against the film surface and produce particles. These particles stay between the contacting surfaces and could accelerate the abrasive wear.

f f


• At high velocities, wear is caused by periodic impact of asperities on the PZT surface in all cases .

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Nanomechanical characterization

• PZT has H and E of about 13 and 200 GPa, respectively.• Scratch deformation of PZT is a combination of plastic and brittle modes.


M. Palacio and B. Bhushan, J. Vac. Sci. Technol. A, 26, 768 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

• The alloying of Pt has a significant effect on improving its modulus and hardness.


M. Palacio and B. Bhushan, Nanotechnology, 19, 105705 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

• The noble metal coatings creep at the nanoscale.• Alloyed coatings exhibit less creep compared to Pt• Alloyed coatings exhibit less creep compared to Pt.



• Deformation of the noble metal coatings from scratch is mainly plastic, and the Pt alloys exhibit less damage compared to Pt film.



Role of lubricants, scanning velocity, operating environment

• The increase in the tip radius after psliding leads to a larger contact area leading to higher adhesion, which increases the friction force and the measured value of coefficient of frictionmeasured value of coefficient of friction.

• Adhesion, friction and wear data for the Pt-Ir tips against the Z-TETRAOL-lubricated PZT film are the lowest, followed by the BMIM-PF6-lubricated PZT film. This shows that lubricants provide wear protection on both Pt-Ir and PZT surfaces.

• Z-TETRAOL-lubricated film exhibited the best performance and was used for velocity, temperature and relative humidity studies

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 28B. Bhushan and K. Kwak, J. Phys.: Condens. Matter, 20, 325240 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

humidity studies

• The exposed underlayer of the Si part is observed in the tip against the unlubricated film. The tip is plastically deformed during wear; therefore, the mechanism for tip wear is adhesive


mechanism for tip wear is adhesive.

• This shows that both lubricants provide wear protection on Pt-Ir.

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B. Bhushan and K. Kwak, J. Phys.: Condens. Matter, 20, 325240 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

Effect of velocity

• Wear volume initially increases as a logarithm of sliding velocity at two loads, and then it increases with sliding velocity at a slower rate with a velocity exponent in the range of 0.06–0.11.

• The initial logarithm dependence for both• The initial logarithm dependence for both friction and wear is based on the thermally-activated stick-slip mechanism.

• At higher velocity, impact wear could be


caused by periodic high velocity impact of asperities on the PZT film.

30


Effect of temperature

• At higher test temperatures, wear f fand friction increase for both

unlubricated and lubricated PZT because of the degradation of the mechanical properties of PZTmechanical properties of PZT.

• Lubricant reduces friction and wear at a given temperature.



Effect of humidity

• Surface water molecules aggregate with mobile lubricant fractions of Z-TETRAOL and form a large meniscus.

• Increase of meniscus force results in increase in wear volume and friction at 80% RH.



• Surface water molecules are expected to form a large meniscus.• Increase in meniscus thickness results in an increase of meniscus force and an



increase in wear volume and friction at 80% RH.

Role of lubricants on PZTAdhesion and friction of PZTRole of lubricants on PZT

Adh i f d ffi i f• Adhesive force and coefficient of friction decreased upon application of Z-TETRAOL and BMIM-PF6.

• After 100 cycles, lubricated surfaces exhibit a small change in coefficient of friction, i.e., low surface wear, in contrast to PZTcontrast to PZT.



Surface potential of PZT

• The change in surface potential is most distinct on the PZT surface because it experienced the most wear from sliding with a diamond tip. Built-up charges during the sliding did not get dissipated and remained on the PZTremained on the PZT.

• For lubricated surfaces, change in surface potential is minimal, as Z-TETRAOL and BMIM PF id d dBMIM-PF6 provided adequate wear protection.



Contact resistance of PZT

• PZT did not show resistance change, indicating that the tip did not penetrate the entire thickness of the film duringthe entire thickness of the film during the wear test.

• Both lubricated surfaces did not show b bl i t hany observable resistance change,

indicating that some lubricant may still be present on the surface and the substrate is not fully exposed.y p



Surface-treated tipsNanotribological characterization

• Formation of silicide in the Pt-Si interface results inSi interface results in decrease in the wear volume and the coefficient of friction .


B. Bhushan, et al., Acta Mater., 56, 4233 (2008); B. Bhushan et al., J. Phys. Condens. Matter 20, 365207 (2008).

• Mechanism for tip wear is adhesive because the tip is plastically deformed. Blunting of the Pt-Si tip occurred to a lesser extent as


observed earlier.

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Nanomechanical characterization

• The increase in the H and E of the thermally-treated film indicates elemental composition changes such as formation of silicide.

• Pt film exhibits plastic deformation, while Pt-Si film exhibits brittle failure, which accounts for higher load to failure for the latter.



Electrical and surface characterizationElectrical resistivity

Measured resistivity of the thermally-treated film using four-point probe is in good agreement with reported resistivity values for platinum silicide.



Auger electron spectroscopy

• Surface elemental composition as a function of sputter time indicates that Si is diffusing through the Pt film, which may lead to formation of platinum silicide.

• AES data confirm results from electrical resistivity measurements.



Conclusions

• Wear rate increases with load when Pt-coated tips are slid over the PZT film at the velocity range of 0.1 to 100 mm/s.

• Wear of noble metal-coated tips is primarily adhesive and abrasive wear ith i twith some impact wear.

• Wear and friction increase as a logarithm of sliding velocity in lower velocity range, which is due to a thermally-activated stick slip mechanism.

• At higher test temperatures, wear and friction increase for both unlubricated and lubricated PZT because of the degradation of the mechanical properties of PZT.

• The PZT film exhibits considerable scratch resistance and exhibits plastic• The PZT film exhibits considerable scratch resistance and exhibits plastic and brittle deformation modes.

• Alloyed noble metal coatings have better hardness, elastic modulus and creep resistance, with Pt-Ir exhibiting the best characteristics. Their primary scratch deformation mode is plastic. Scratch results show comparable tends with wear experiments.


• Silicide formation was accomplished by thermal treatment of a Pt film on a Si AFM probe, and confirmed by electrical resistivity measurements and Auger electron spectroscopy. This Pt-Si film has better hardness and elastic modulus and exhibits brittle deformation during scratch testingmodulus, and exhibits brittle deformation during scratch testing.

• The thermal treatment makes the Pt-Si probes more wear resistant, electrically conducting, and therefore suitable for probe-based data storage.


References• Bhushan, B. and Kwak, K. J. (2007), “Platinum coated probes sliding at up to 100 mm/s against silicon wafers

for AFM probe based recording technology ” Nanotechnol 18 345504for AFM probe-based recording technology, Nanotechnol. 18, 345504.• Bhushan, B. and Kwak, K. J. (2007), “Velocity dependence of nanoscale wear in atomic force microscopy,”

Appl. Phys. Lett. 91, 163113.• Bhushan, B. and Kwak, K. J. (2008), “Effect of temperature on nanowear of platinum-coated probes sliding

against coated silicon wafers for probe based recording technology ” Acta Mater 56 380 386against coated silicon wafers for probe-based recording technology,” Acta Mater. 56, 380-386.• Bhushan, B. and Kwak, K. J. (2008), “Noble metal-coated probes sliding at up to 100 mm/s against PZT films

for AFM probe-based ferroelectric recording technology,” J. Phys. Cond. Matter, 20, 225013. • Kwak, K. J. and Bhushan, B. (2008), “Platinum-coated probes sliding at up to 100 mm/s against lead zirconate

tit t fil f t i f i b b d f l t i di t h l ” J V S i T h ltitanate films for atomic force microscopy probe-based ferroelectric recording technology,” J. Vac. Sci. Technol. A, 26, 783-793.

• Palacio, M. and Bhushan, B. (2008), “Nanotribological and nanomechanical properties of lubricated PZT thin films for ferroelectric data storage applications,” J. Vac. Sci. Technol. A, 26, 768-776.

• Palacio, M. and Bhushan, B. (2008), “Nanomechanical and nanotribological characterization of noble metal-coated AFM tips for probe-based ferroelectric data recording,” Nanotechnol. 19, 105705.

• Bhushan, B. and Kwak, K. J. (2008), “The Role of Lubricants, Scanning Velocity, and Environment on Adhesion, Friction and Wear of Pt-Ir coated Probes for Atomic Force Microscope Probe-based Ferroelectric Recording Technolog ” J Ph s Condens Matter 20 325240Recording Technology,” J. Phys.: Condens. Matter, 20, 325240.

• Bhushan, B., Palacio, M. and Kwak, K. J. (2008), “Thermally-treated Pt-Coated Silicon AFM tips for Wear Resistance in Ferroelectric Data Storage,” Acta Mater., 56, 4233-4241.

• Bhushan, B., Kwak, K. J. and Palacio, M. (2008), “Nanotribology and nanomechanics of AFM probe-based data di t h l ” J Ph C d M tt 20 365207


recording technology,” J. Phys. Condens. Matter 20, 365207.

http://www.mecheng.osu.edu/nlbb/

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