Book chapter 6

Introduction to Surface and Thin Film Processes

John A. Venables

Cambridge University Press (2000)

Supplementary notes by John A. Venables

© Arizona Board of Regents for Arizona State University and John A. Venables


Chapter 6: Electronic structure and emission processes at metallic surfaces

Corrections, comments and updates


6.1 The electron gas: work function, surface structure and energy

In section 6.1.1 on page 188-9, quantum corrals are discussed and shown in figure 6.4. Pictures in color, false of course but very pretty, can be found either through my Experimental group STM pages, or directly at Don Eigler's IBM web site. On pages 188-9, I am making introductory points about free electron models, not worrying about explanation of the fine details of these images. However, that topic has been researched, and can be understood in terms of s- and d- electrons, and their mutual interaction. This topic is discussed in the context of magnetism in section 6.3.4; details of the application to Fe/Cu corrals are given by Heller et al. (1994).

In the problems section on page 225, problem 6.1(e) concerns the ripples inside 'quantum corrals' such as those in figure 6.4, with a reference to Petersen et al. (1998) for quantitative understanding. This work has been developed further into Fourier transform STM (Petersen et al., 2000) as a means of determining the surface Fermi contour, the surface analogue of the bulk Fermi surface. This special issue (volume 109) of the Journal of Electron Spectroscopy contains several articles updating STM results on metals, including that on atomic-scale structures by Crommie (2000).

In section 6.1.2 on page 193, reference is made to a Danish site from which EMT programs can be obtained. This site can be accessed via my Surface theory and simulation pages, or directly at Per Stoltze's web site (his email address and other details are here). If you wish to persue this topic, you should definitely contact Per by email, and ask his permission and advice. This is not something to be undertaken 'blind'.

In section 6.1.3 on page 195, there is some confusion about the units of work function. This quantity can be considered either as an energy or a voltage, but one ought to be consistent. The general convention in surface science is that it is an energy, expressed in electron volts (eV), and this has been followed in the chapter up to page 195. However, here I slip into volts (V) in two values on lines 1 and 3. Formula 6.6 is correct as stated, with DV in volts, but previously DV has been quoted as an energy in eV.

In practice the units V and eV are used interchangeably, but you may need to know which is meant on any one occasion. As Ralph Waldo Emerson has it: "A foolish consistency is the the hobgoblin of little minds, adored by little statesmen and philosophers and divines. With consistency a great soul has nothing to do..." (This was one of my father's favorite quotations, in case you want to make 2 + 2 = 5).

New references for section 6.1

6.2 Electron emission processes

In section 6.2.2 on pages 202-3, there is again some potential confusion about units, in relation to equations 6.8 and 6.9, though with care it should all be clear. The units of the current density, J in equation 6.8, are A/m2 in MKS, or A/cm2 as often quoted. So the units of the constant A in equation 6.9 depend on the units used for the terms in equation 6.9 and the units used for the field strength F, in this case (V/cm) as stated on page 203. The field strength F is usually given in (V/Angstrom) or (V/nm), as otherwise the numbers are just too large for comfort.

The argument of the exponential in equation 6.8 has to be dimensionless, and the value of B corresponds to a work function f expressed in volts. If f is to be expressed in eV for consistency, then the units of B are V/[cm.(eV)3/2], for F in (V/cm), with the same value of B. If F in expressed in (V/m), then the units of B are obviously V/[m.(eV)3/2], but the value of B is changed to 6.83x109. You get the point about consistency: it's a pain, but sometimes it matters. I am grateful to Michael Isaacson for spotting these points, to Richard Forbes for pointing me in the right direction, and to Yong Jiang for working through problem 1.6 in Spring 2002, which was set in response to Michael and Richard's input. If you really are working on this topic, and want to get to get to the bottom of all the historical twists and turns, you should consider contacting Richard (email: R.Forbes@surrey.ac.uk) to get a copy of a thorough tutorial he has written on the topic, for the 4th Moscow International (ITEP) School of Physics.

New references for section 6.2

6.3 Magnetism at surfaces and in thin films

I acknowledged on pages 210 and 224 that to make progress in magnetism, one needs a lot of background information, and suggested that a good strategy might be to go first to the major reviews in international conference proceedings. Other articles along the same lines are those contained in landmark volumes of particular journals, such as volume 299/300 of Surface Science (Duke, 1994), which has been liberally referenced throughout the book.

In the case of the Journal of Magnetism and Magnetic Materials, the 200th volume more or less coincided with the millenium, so the editors, Art Freeman and Sam Bader, had a double reason to celebrate the progress that has been made, and to chart the problems that need to be addressed. This special issue (Freeman & Bader, 1999) is available in both journal and book formats, and should be added to the reading list for this section; many of the authors quoted in my book have updates of their topics in this volume. There is also now a new celebratory volume 500 of Surface Science (Duke and Plummer, 2002), marking Charles Duke's retirement from the editorship of the journal; this contains many articles of interest including two specifically on magnetism, by Sam Bader, and by Jürgen Kirschner.

In a similar vein, in chapter 8 on pages 285-7, there is a discussion of magneto-resistance measurements in various geometries, with especial reference to the work of Shinjo et al. in Japan. An update can be obtained from a special issue of J. Phys. D. in honour of Professor T. Shinjo, to mark his retirement from Kyoto University, containing selected papers from the 17th International Colloquium on Magnetic Films and Surfaces (Maekawa and Chapman, 2002).

There is a more recent update on Magnetic materials for magnetic data storage edited by Coufal et al. (2006). These updates include a wide range of topics in magnetic thin films, and techniques sensitive to magnetism, including many of the authors referenced in this section and in section 8.3.

New references for section 6.3


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Latest version 27 August 2006.