Tài liệu Handbook of Micro and Nano Tribology P3 pptx

Ferrante, J. et. al. “Surface Physics in Tribology”

Handbook of Micro/Nanotribology.

Ed. Bharat Bhushan

Boca Raton: CRC Press LLC, 1999

© 1999 by CRC Press LLC

© 1999 by CRC Press LLC

3

Surface Physics

in Tribology

John Ferrante and Phillip B. Abel

3.1 Introduction

3.2 Geometry of Surfaces

3.3 Theoretical Considerations

Surface Theory • Friction Fundamentals

3.4 Experimental Determinations of Surface Structure Low-Energy Electron Diffraction • High-Resolution Electron

Microscopy • Field Ion Microscopy

3.5 Chemical Analysis of Surfaces Auger Electron Spectroscopy • X-Ray Photoelectron

Spectroscopy • Secondary Ion Mass Spectroscopy • Infrared

Spectroscopy • Thermal Desorption

3.6 Surface Effects in Tribology

Monolayer Effects in Adhesion and Friction • Atomic Effects

Due to Adsorption of Hydrocarbons • Atomic Effects in

Metal–Insulator Contacts

3.7 Concluding Remarks

References

3.1 Introduction

Tribology, the study of the interaction between surfaces in contact, spans many disciplines from physics

and chemistry to mechanical engineering and material science. Besides the many opportunities for

interesting research, it is of extreme technological importance. The key word in this chapter is surface.

The chapter will be rather ambitious in scope in that we will attempt to cover the range from microscopic

considerations to the macroscopic experiments used to examine the surface interactions. We will approach

this problem in steps, first considering the fundamental idea of a surface and next recognizing its atomic

character and the expectations of a ball model of the atomic structures present, viewed as a terminated

bulk. We will then consider a more realistic description of a relaxed surface and then consider how the

class of surface, i.e., metal, semiconductor, or insulator affects these considerations. Finally, we will present

what is expected when a pure material is alloyed, as well as the effects of adsorbates.

Following these more fundamental descriptions, we will give brief descriptions of some of the exper￾imental techniques used to determine surface properties and their limitations. The primary objective

here will be to provide a source for more thorough examination by the interested reader.

© 1999 by CRC Press LLC

Finally, we will examine the relationship of tribological experiments to these more fundamental

atomistic considerations. The primary goals of this section will be to again provide sources for further

study of tribological experiments and to raise critical issues concerning the relationship between basic

surface properties with regard to tribology and the ability of certain classes of experiments to reveal the

underlying interactions. We will attempt to avoid overlapping the material that we present with that

presented by other authors in this publication. This chapter cannot be a complete treatment of the physics

of surfaces due to space limitations. We recommend an excellent text by Zangwill (1988) for a more

thorough treatment. Instead, we concentrate on techniques and issues of importance to tribology on the

nanoscale.

3.2 Geometry of Surfaces

We will now discuss simply from a geometric standpoint what occurs when you create two surfaces by

dividing a solid along a given plane. We limit the discussion to single crystals, since the same arguments

apply to polycrystalline samples except for the existence of many grains, each of which could be described

by a corresponding argument. This discussion will start by introducing the standard notation for describ￾ing crystals given in many solid-state texts (Ashcroft and Mermin, 1976; Kittel, 1986). It is meant to be

didactic in nature and because of length limitations will not attempt to be comprehensive. To establish

notation and concepts we will limit our discussion to two of the possible Bravais lattices, face-centered

cubic (fcc) and body-centered cubic (bcc), which are the structures often found in metals. The unit cells,

i.e., the structures which most easily display the symmetries of the crystals, are shown in Figure 3.1. The

other descriptions that are frequently used are the primitive cells, which show the simplest structures

that can be repeated to create a given structure. In Figure 3.1 we also show the primitive cell basis vectors,

which can be used to generate the entire structure by the relation

(3.1)

where n1, n2, and n3 are integers, and →

a1, →

a2, and →

a3 are the unit basis vectors.

Since we are interested in describing surface properties, we want to present the standard nomenclature

for specifying a surface. The algebraic description of a surface is usually given in terms of a vector normal

to the surface. This is conveniently accomplished in terms of vectors that arise naturally in solids, namely,

the reciprocal lattice vectors of the Bravais lattice (Ashcroft and Mermin, 1976; Kittel, 1986). This is

FIGURE 3.1 (a) Unit cube of fcc crystal structure with primative cell basis vectors indicated. (b) Unit cube of bcc

crystal structure, with primative cell basis vectors indicated.

r rr r R =+ + n a n a n a 1 22 33

© 1999 by CRC Press LLC

convenient since these vectors are used to describe the band structure and diffraction effects in the solid.

They are usually given in the form

(3.2)

where h, k, and l are integers. The reciprocal lattice vectors are related to the basis vectors of the direct

lattice by

(3.3)

where a cyclic permutation of i, j, k are used in the definition. Typically, parentheses are used in the

definition of the plane, e.g., (h,k,l). The (100) planes for fcc and bcc lattices are shown in Figure 3.2

where dots are used to show the location of the atoms in the next plane down.

This provides the simplest description of the surface in terms of terminating the bulk. There is a rather

nice NASA publication by Bacigalupi (1964) which gives diagrams of many surfaces and subsurface

structures for fcc, bcc, and diamond lattices, in addition to a great deal of other useful information such

FIGURE 3.2 Projection of cubic face (100) plane for (a) fcc and (b) bcc crystal structures. In both cases, smaller

dots represent atomic positions in the next layer below the surface.

r rrr K hb kb lb =++ 1 23

r r r

rr r b

a a

aa a i

j k = π

×

( ) ×

2

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