INTERPLAY OF ION BOMBARDMENT, SURFACE...

Leibniz-Institut für Oberflächenmodifizierung

INTERPLAY OF ION BOMBARDMENT,

SURFACE ORIENTATION AND DIFFUSION

DURING NITRIDING OF ALUMINIUM

D. Manova, S. Mändl, B. Rauschenbach


MotivationMotivation

• Wide applications of Al and its alloys

• Low hardness, high wear, low chemical and thermal stability

� Surface modification is necessary


ContentsContents

• Motivation

• Formation of Aluminium Nitride

• Surface Orientation & Sputter Yield

• Diffusion & Temperature

• Conclusion


Bulk DiffusionBulk Diffusion

• Methods: ion implantation, plasma nitriding, low energy implan-tation, plasma immersion ion implantation, ...

• Large scatter in diffusivity

1,4 1,6 1,810-17

10-16

10-15

10-14

10-13

10-12

10-11

Detection Limit

PIII, 30 kV LEI, 1 keV LEI, 1 keV (contaminated) LEI, 1 keV + Anneal II, 100 keV + Anneal

Diff

usio

n co

effic

ient

(cm

2 /s)

1/Temperature (1000/K)

500 450 400 350 300 250

Temperature (°C)


Surface EffectsSurface Effects

• Native oxide layer as barrier against nitrogen insertion

• Sufficient oxygen partial pressure blocks nitrogen supply

• Competition of surface adsorption and sputter removal

AlN ≡ Nitriding of Steel??

Data from T.Fitz, PhD Thesis


Surface EffectsSurface Effects

• Sputtering in Ar/H2 mixture, 410 °C

• Almost uniform surface with regularly arranged features

• Possible explanations:

i) self organisation

ii) selective redeposition of sputtered oxide layer

But: polycrystalline substrate: orientation dependence?

M.Quast et al., Surf. Coat. Technol. (2001),


Sputtering with CsSputtering with Cs++: EBSD: EBSD

• Sputtering of Al with 5 keV Cs+ ions

• For different grains-different sputter yield and different patterns

• Structure related with grain orientation and not with plane of incident ions

• Relation supported by EBSD patterns and inverse pole figure

60°

EBSD

IPFSEM12 3


Surface Structure: PIIISurface Structure: PIII

• Sputtering independent of process (SIMS, PIII) • Different surface morphology for different grain orientation after

sputtering • Competing processes: sputtering + adsorption + diffusion

� Surface structure determined by orientation of base material


Temperature and Surface StructureTemperature and Surface Structure

• Nitrogen PII implantation in Al at medium temperature

• Strongly inhomogeneous surface

• Grain boundary diffusion dominates over bulk diffusion at medium temperatures

• Surface determined by grain boundary diffusion


High Temperature DiffusionHigh Temperature Diffusion

• Nitrogen PII implantation in Al at high temperatures

• Very rough surface as a result of competition between sputtering and diffusion

• Uniform surface morphology due to dominance of bulk diffusion


Summary & ConclusionsSummary & Conclusions

• Nitriding of Al different from nitriding of steel.

• Important role of surface orientation

– different sputter yield, diffusion rate, surface morphology

• Grain boundary diffusion starts to dominate over surface diffusion at medium temperatures.

• Bulk diffusion dominates at high temperatures, smoothing differences between grains. But: highly corrugated surface due to simultaneous sputtering.

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AcknowledgementsAcknowledgements

Dr. M. Schreck, Universität Augsburg

Dr. J. W. Gerlach, IOM Leipzig

G. Thorwarth, Universität Augsburg

INTERPLAY OF ION BOMBARDMENT, SURFACE...

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