What is What in the Nanoworld - Victor E. Borisenko - E-Book

What is What in the Nanoworld E-Book

Victor E. Borisenko

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Beschreibung

The third, partly revised and enlarged edition of this introductory reference summarizes the terms and definitions, most important phenomena, and regulations occurring in the physics, chemistry, technology, and application of nanostructures. A representative collection of fundamental terms and definitions from quantum physics and chemistry, special mathematics, organic and inorganic chemistry, solid state physics, material science and technology accompanies recommended secondary sources for an extended study of any given subject. Each of the more than 2,200 entries, from a few sentences to a page in length, interprets the term or definition in question and briefly presents the main features of the phenomena behind it. Additional information in the form of notes ("First described in", "Recognition", "More details in") supplements the entries and gives a historical perspective of the subject with reference to further sources. Ideal for answering questions related to unknown terms and definitions among undergraduate and PhD students studying the physics of low-dimensional structures, nanoelectronics, and nanotechnology.

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Table of Contents

Related Titles

Title Page

Copyright

Preface to the Third Edition

Sources of Information

Chapter A: From Abbe's Principle to Azbel'–Kaner Cyclotron Resonance

Chapter B: From B92 Protocol to Burstein–Moss shift

Chapter C: From C-AFM (Conductive Atomic Force Microscopy) to Cyclotron Resonance

Chapter D: From D'Alembert Equation to Dzyaloshinskii-Moriya Interaction

Chapter E: From (e,2e) Reaction to Eyring Equation

Chapter F: From Fabry–Pérot resonator to FWHM (full width at half maximum)

Chapter G: From Gain-Guided Laser to Gyromagnetic Frequency

Chapter H: From Habit Plane to Hyperelastic Scattering

Chapter I: From IBID (Ion-Beam-Induced Deposition) to Isotropy (of Matter)

Chapter J: From Jahn–Teller Effect to Joule's Law of Electric Heating

Chapter K: From Kadowaki–Woods Ratio to Kuhn–Thomas–Reiche Sum Rule

Chapter L: From Lab-on-a-Chip to Lyman Series

Chapter M: From Mach–Zender Interferometer to Murrell–Mottram Potential

Chapter N: From NAA (Neutron Activation Analysis) to Nyquist–Shannon Sampling Theorem

Chapter O: From Octet Rule to Oxide

Chapter P: From PALM (Photoactivable Localization Microscopy) to Pyrrole

Chapter Q: From Q-Control to Qubit

Chapter R: From Rabi Flopping to Rydberg Gas

Chapter S: From Sabatier Principle to Synergetics

Chapter T: From Talbot's Law to Type II Superconductors

Chapter U: From Ultraviolet-Assisted Nanoimprint Lithography (UV-NIL) to Urbach Rule

Chapter V: From Vacancy to Von Neumann Machine

Chapter W: From Waidner–Burgess Standard to Wyckoff Notation

Chapter X: From XMCD (X-Ray Magnetic Circular Dichroism) to XRD (X-Ray Diffraction)

Chapter Y: From Yasukawa Potential to Yukawa Potential

Chapter Z: From Zeeman Effect to Zundel Ion

Appendix

A List and a Presentation of Scientific Journals which Contain the Stem Nano in their Title

Abbreviations for the Scientific Journals which Appear as Sources in the Text

Appendix — Main Properties of Intrinsic (or Lightly Doped) Semiconductors

Related Titles

Ostrikov, K.

Plasma Nanoscience

Basic Concepts and Applications of Deterministic Nanofabrication

2008

ISBN: 978-3-527-40740-8

Schmid, G. (ed.)

Nanotechnology

Volume 1: Principles and Fundamentals

2008

ISBN: 978-3-527-31732-5

Balzani, V., Credi, A., Venturi, M.

Molecular Devices and Machines

Concepts and Perspectives for the Nanoworld

2008

ISBN: 978-3-527-31800-1

Rao, C. N. R., Müller, A., Cheetham, A. K. (eds.)

Nanomaterials Chemistry

Recent Developments and New Directions

2007

ISBN: 978-3-527-31664-9

Vedmedenko, E.

Competing Interactions and Patterns in Nanoworld

2007

ISBN: 978-3-527-40484-1

Waser, R. (ed.)

Nanoelectronics and Information Technology

Advanced Electronic Materials and Novel Devices

2012

ISBN: 978-3-527-40927-3

The Authors

Dr. Victor E. Borisenko

University of Informatics

and Radioelectronics

Minsk, Belarus

[email protected]

Prof. Stefano Ossicini

Uni. di Modena e Reggio Emilia

Sc. e Metodi dell'Ingegneria

Reggio Emilia, Italia

[email protected]

Cover

Scanning Electron Microscope image of Gallium Arsenide nanowires grown using gold as catalyst.

Experiment: Faustino Martelli, Silvia Rubini, TASC, Trieste.

Artwork: Lucia Covi, from “Blow-up. Images from the Nanoworld” Copyright S3, 2007.

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available in the Internet at <http://dnb.d-nb.de>.

© 2012 Wiley-VCH Verlag & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978-3-527-41141-2

ePDF ISBN: 978-3-527-64839-9

ePub ISBN: 978-3-527-64838-2

mobi ISBN: 978-3-527-64837-5

oBook ISBN: 978-3-527-64836-8

Preface to the Third Edition

This is the third, enlarged, and updated edition of our book. From about 1400 entries in the first edition we have now reached to more than 2300 terms and definitions. Moreover, a large number of the previous entries have been improved or extended. The gallery of illustrations has been enriched by new figures, and new tables are added throughout the book. The presented terms, phenomena, regulations, and experimental and theoretical tools are very easy to consult since they are arranged in alphabetical order, with a chapter for each letter. The great majority of the terms have additional information in the form of notes such as “First described in: …”, “More details in …”, and “Recognition: …”, thus giving a historical retrospective of the subject with references to further sources of extended information, which can be pioneering papers, books, review papers, or web sites.

In particular, in this third edition, following the advices of friends and readers, we have tried, for the overwhelming majority of the entries, to find out the most authoritative and/or most recent work to be inserted in the voice “More details in …”, we consider all these additional notes to be quite useful. Moreover, a particular attention has been paid to augmenting the number of entries dedicated to experimental techniques recently developed within nanoscience. Only eight years separate this third edition from the first one. Nevertheless, we have seen not only a true explosion of research in nanoscience and developments of nanotechnologies but also an avalanche increase in the number of new journals that contain the stem “nano” in their title. A list of more than 100 “nano” journals is presented at the end of this book. A large majority appeared in the last few years.

The last decade has witnessed also the digital revolution. We have seen an incredible diffusion of the use of Internet, especially of web sites such as Wikipedia or similar, yet is legitimate to question whether it still makes sense to rely on books and manuals/handbooks in particular. Our answer is clearly yes.

The reason is twofold. First of all, as suggested by two bibliophiles, the Italian critic and writer Umberto Eco and the French screenwriter and playwright Jean-Claude Carriere, in their “playdoyer” This is Not the End of the Book, appeared in 2011, “… A book is like spoons, hammers, wheels, and scissors. Once you've invented them, there's nothing left to improve them”. Second, in the short story On Rigor in Science (the original Spanish-language novel Del rigor en la ciencia appeared in 1946), the Argentine writers Jorge Luis Borges and Adolf Bioy Casares described the inability to construct a map as big as the territory it represents, the mythical map 1:1, which, overlapping and corresponding well to the physical space it represents, results useless and unnecessary. With it, the two writers have given us a reflection not only on the difficult and problematic nature of any summary but also on the true necessity to take responsibility and to perform a synthesis, a selection. We hope that our map regarding the Nanoworld will be useful to the readers, independently of their experience in “nano,” if they are motivated with a goal to know more and more about the Nanoworld.

Minsk

Victor E. Borisenko

Modena-Reggio Emilia

Stefano Ossicini

January 2012

Sources of Information

Besides their personal knowledge and experience and the scientific journals and books cited in the text, the authors also used the following sources of information:

Encyclopedias and Dictionaries

1. Encyclopedic Dictionary of Physics, edited by J. Thewlis, R. G. Glass, D. J. Hughes, A. R. Meetham (Pergamon Press, Oxford 1961).
2. McGraw–Hill Dictionary of Physics and Mathematics, edited by D. N. Lapedes (McGraw–Hill Book Company, New York 1978).
3. Landolt-Bornstein. Numerical Data and Functional Relationships in Science and Technology, v. 17, edited by O. Madelung, M. Schultz, H. Weiss (Springer, Berlin 1982).
4. McGraw–Hill Encyclopedia of Electronics and Computers, edited by C. Hammer (McGraw–Hill Book Company, New York 1984).
5. Encyclopedia of Semiconductor Technology, edited by M. Grayson (John Wiley & Sons, New York 1984).
6. Encyclopedia of Physics, edited by R. G. Lerner, G. L. Trigg (VCH Publishers, New York 1991).
7. Physics Encyclopedia, edited by A. M. Prokhorov, vols. 1–5 (Bolshaya Rossijskaya Encyklopediya, Moscow 1998) — in Russian.
8. Encyclopedia of Applied Physics, Vols. 1–25, edited by G. L. Trigg (Wiley VCH, Weinheim 1992–2000).
9. Encyclopedia of Physical Science and Technology, Vols. 1–18, edited by R. A. Meyers (Academic Press, San Diego 2002).
10. Handbook of Nanotechnology, edited by B. Bhushan (Springer, Berlin 2004).

Books

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4. C. Bai, Scanning Tunneling Microscopy and Its Applications (Springer, Heidelberg, 2010).
5. V. Balzani, M. Venturi, A. Credi, Molecular Devices and Machines: A Journey into the Nanoworld (Wiley–VCH, Weinheim,

2003).

6. F. Bassani, G. Pastori Parravicini, Electronic and Optical Properties of Solids (Pergamon Press, London, 1975).
7. F. Bechstedt, Principles of Surface Physics (Spriger, Berlin, 2003).
8. D. Bimberg, M. Grundman, N. N. Ledentsov, Quantum Dot Heterostructures (John Wiley & Sons, London, 1999).
9. W. Borchardt-Ott, Crystallography, Second edition (Springer, Berlin, 1995).
10. V. E. Borisenko, S. Ossicini, What is What in the Nanoworld (Wiley–VCH, Weinheim, 2004 and 2008).
11. M. Born, E. Wolf, Principles of Optics, Seventh (expanded) edition (Cambridge University Press, Cambridge, 1999).
12. J. H. Davies, The Physics of Low-Dimensional Semiconductors (Cambridge University Press, Cambridge, 1995).
13. DNA based Computers edited by R. Lipton, E. Baum (Am. Math. Soc., Providence, 1995).
14. M. S. Dresselhaus, G. Dresselhaus, P. Eklund, Science of Fullerenes and Carbon Nanotubes (Academic Press, San Diego, 1996).
15. D. K. Ferry, S. M. Goodnick, Transport in Nanostructures (Cambridge University Press, Cambridge, 1997).
16. Frontiers in Surface Nanophotonics, edited by D. L. Andrews and Z. Gaburro (Springer, Berlin, 2007).
17. S. V. Gaponenko, Optical Properties of Semiconductor Nanocrystals (Cambridge University Press, Cambridge, 1998).
18. S. V. Gaponenko, Introduction to Nanophotonics (Cambridge University Press, Cambridge, 2009).
19. W. A. Harrison, Electronic Structure and the Properties of Solids (W. H. Freeman & Company, San Francisco, 1980).
20. H. Haug, S. W. Koch, Quantum Theory of the Optical and Electronic Properties of Semiconductors (World Scientific, Singapore, 1994).
21. S. Hüfner, Photoelectron Spectroscopy (Springer, Berlin, 1995).
22. Y. Imri, Introduction to Mesoscopic Physics (Oxford University Press, Oxford, 2002).
23. L. E. Ivchenko, G. Pikus, Superlattices and Other Heterostructures: Symmetry and other Optical Phenomena (Springer, Berlin, 1995).
24. C. Kittel, Elementary Solid State Physics (John Wiley & Sons, New York, 1962).
25. C. Kittel, Quantum Theory of Solids (John Wiley & Sons, New York, 1963).
26. C. Kittel, Introduction to Solid State Physics, seventh edition (John Wiley & Sons, New York, 1996).
27. L. Landau, E. Lifshitz, Quantum Mechanics (Addison–Wesley, London, 1958).
28. O. Madelung, Semiconductors: Data Handbook (Springer, Berlin, 2004).
29. G. Mahler, V. A. Weberrus, Quantum Networks: Dynamics of Open Nanostructures (Springer, New York, 1998).
30. L. Mandel, E. Wolf, Optical Coherence and Quantum Optics (Cambridge University Press, Cambridge, 1995).
31. Molecular Electronics: Science and Technology, edited by A. Aviram, M. Ratner (Academy of Sciences, New York, 1998).
32. Nanobiotechnology. Concepts, Applications and Perspectives, edited by C. M. Niemeyer and C. A. Mirkin (Wiley–VCH, Weinheim, 2004).
33. Nanoelectronics and Information Technology, edited by R. Waser (Wiley–VCH, Weinheim, 2003).
34. Nanostructured Materials and Nanotechnology, edited by H. S. Nalwa (Academic Press, London, 2002).
35. R. C. O'Handley, Modern Magnetic Materials: Principles and Applications (Wiley & Sons, New York, 1999).
36. S. Ossicini, L. Pavesi, F. Priolo, Light Emitting Silicon for Microphotonics, Springer Tracts on Modern Physics 194 (Springer, Berlin, 2003).
37. K. Oura, V. G. Lifshits, A. A. Saranin, A. V. Zotov, M. Katayama, Surface Science (Springer, Berlin, 2003).
38. J. Pankove, Optical Processes in Semiconductors (Dover, New York, 1971).
39. N. Peyghambarian, S. W. Koch, A. Mysyrowicz, Introduction to Semiconductor Optics (Prentice Hall, Englewood Cliffs, New Jersey, 1993).
40. C. P. Poole, F. J. Owens, Introduction to Nanotechnology (Wiley–VCH, Weinheim, 2003).
41. P. N. Prasad Nanophotonics (Wiley–VCH, Weinheim, 2004).
42. C. N. Rao, P. J. Thomas, G. U. Kulkarni, Nanocrystals: Synthesis, Properties and Applications (Springer, Berlin, 2007).
43. S. Reich, C. Thomsen, J. Maultzsch, Carbon Nanotubes (Wiley–VCH, Weinheim, 2004).
44. E. Rietman, Molecular Engineering of Nanosystems (Springer, New York, 2000).
45. Roadmap of Scanning Probe Microscopy, edited by S. Morita (Springer, Berlin, 2007).
46. K. Sakoda, Optical Properties of Photonic Crystals (Springer, Berlin, 2001).
47. H.-E. Schaefer, Nanoscience. The Science of the Small in Physics, Engineering, Chemistry, Biology and Medicine (Springer, Berlin, 2010).
48. Silicon Photonics, edited by L. Pavesi and D. J. Lockwood (Springer, Berlin, 2004).
49. S. Sugano, H. Koizumi, Microcluster Physics (Springer, Berlin, 1998).
50. The Chemistry of Nanomaterials. Synthesis, Properties and Applications, edited by C. N. Rao, A. Müller, A. K. Cheetham (Wiley–VCH, Weinheim, 2004).
51. L. Theodore, R. G. Kunz, Nanotechnology. Environmental Implications and Solutions (Wiley–VCH, Weinheim, 2005).
52. J. D. Watson, M. Gilman, J. Witkowski, M. Zoller, Recombinant DNA (Scientific American Books, New York, 1992).
53. E. L. Wolf, Nanophysics and Nanotechnology — Second Edition (Wiley–VCH, Weinheim, 2006).
54. E. L. Wolf, Quantum Nanoelectronics. An Introduction to Electronic Nanotechnology and Quantum Computing (Wiley-VCH, Weinheim, 2009).
55. S. N. Yanushkevich, V. P. Shmerko, S. E. Lyshevski, Logic Design of NanoICs (CRC Press, Boca Raton, 2004).
56. P. Y. Yu, M. Cardona, Fundamentals of Semiconductors (Springer, Berlin, 1996).

Web sites

http://www.britannica.com

Encyclopedia Britannica

http://www.Google.com

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Science world. World of

physics and mathematics.

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Physics

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PHOTONICS DIRECTORY

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The Nobel Prize Laureates

http://www-history.mcs.st-and.ac.uk/history/

MATHEMATICS ARCHIVE

http://www.chem.yorku.ca/NAMED/

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http://www.hyperdictionary.com/

HYPERDICTIONARY

http://www.wordreference.com/index.htm

http://WordReference.com

. French,

German, Italian and Spanish

Dictionary with Collins

Dictionaries

http://web.mit.edu/redingtn/www/netadv/

The Net Advance of Physics.

Review Articles and Tutorials

in an Encyclopedic Format

Fundamental Constants Used in Formulas

A

From Abbe's Principle to Azbel'–Kaner Cyclotron Resonance

The diffraction limit of light was first surpassed by the use of scanning near-field optical microscopes; by positioning a sharp optical probe only a few nanometers away from the object, the regime of far-field wave physics is circumvented, and the resolution is determined by the probe–sample distance and by the size of the probe which is scanned over the sample.

Also, fluorescence light microscopy based techniques have been developed in order to break the diffraction barrier, as in the case of fluorescence nanoscopy.

First described in: E. Abbe, Beiträge zur Theorie des Mikroskops und der mikroskopischen Wahrnehmung, Schultzes Archiv für mikroskopische Anatomie 9, 413–668 (1873).

Abbe's resolution limit → Abbe's principle.

More details in: R. Leach, Fundamental Principles of Engineering Nanometrology (Elsevier, London, 2010).

aberration — any image defect revealed as distortion or blurring in optics. This deviation from perfect image formation can be produced by optical lenses, mirrors and electron lens systems. Examples are astigmatism, chromatic or lateral aberration, coma, curvature of field, distortion, and spherical aberration.

In astronomy, it is an apparent angular displacement in the direction of motion of the observer of any celestial object due to the combination of the velocity of light and of the velocity of the observer.

ab initio(approach, theory, calculations) — Latin meaning “from the beginning”. It supposes that primary postulates, also called first principles, form the background of the referred theory, approach or calculations. The primary postulates are not so directly obvious from experiment, but owe their acceptance to the fact that conclusions drawn from them, often by long chains of reasoning, agree with experiment in all of the tests which have been made. For example, calculations based on the Schrödinger wave equation, as well as on the basis of Newton equations of motion or any other fundamental equations, are considered to be ab initio calculations.

Abney's law states that the shift in apparent hue of spectral color that is desaturated by addition of white light is toward the red end of the spectrum if the wavelength is below 570 nm and toward the blue if it is above.

First described in: W. Abney, E. R. Festing, Colour photometry, Phil. Trans. Roy. Soc. London 177, 423–456 (1886).

More details in: W. Abney, Researches in colour vision (Longmans & Green, London, 1913).

Abrikosov vortex — a specific arrangement of lines of a magnetic field in a type II superconductor.

First described in: A. A. Abrikosov, An influence of the size on the critical field for type II superconductors, Doklady Akademii Nauk SSSR 86(3), 489–492 (1952) — in Russian.

Recognition: in 2003 A. A. Abrikosov, V. L. Ginzburg, A. J. Leggett received the Nobel Prize in Physics for pioneering contributions to the theory of superconductors and superfluids.

See also www.nobel.se/physics/laureates/2003/index.html.

More details in: A. A. Abrikosov, Nobel Lecture: Type-II superconductors and the vortex lattice, Rev. Mod. Phys. 76(3), 975–979 (2004).

acceptor (atom) — an impurity atom, typically in semiconductors, which accepts electron(s). Acceptor atoms usually form electron energy levels slightly higher than the uppermost field energy band, which is the valence band in semiconductors and dielectrics. An electron from this band is readily excited into the acceptor level. The consequent deficiency in the previously filled band contributes to the hole conduction.

achiral → chirality.

acoustic phonon — a quantum of excitation related to an acoustic mode of atomic vibrations in solids → phonon.

actinic — pertaining to electromagnetic radiation capable of initiating photochemical reactions, as in photography or the fading of pigments.

actinodielectric — a dielectric exhibiting an increase in electrical conductivity when electromagnetic radiation is incident upon it.

activation energy — an energy in excess over a ground state, which must be added to a system to allow a particular process to take place.

adatom — an atom adsorbed on a solid surface.

adduct — a chemical compound that forms from the addition of two or more substances. The term comes from Latin meaning “drawn toward”. An adduct is a product of the direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components, with formation of two chemical bonds and a net reduction in bond multiplicity in at least one of the reactants. The resultant is considered a distinct molecular species. In general, the term is often used specifically for products of addition reactions.

adiabatic approximation is used to solve the Schrödinger equation for electrons in solids. It assumes that a change in the coordinates of a nucleus passes no energy to electrons, that is the electrons respond adiabatically, which then allows the decoupling of the motion of the nuclei and electrons → Born-Oppenheimer approximation.

adhesion — the property of a solid to cling to another solid controlled by intermolecular forces at their interface.

adiabatic principle — perturbations produced in a system by altering slowly external conditions resulting, in general, in a change in the energy distribution in it, but leaving the phase integrals unchanged.

adiabatic process — a thermodynamic procedure which take place in a system without an exchange of heat with surroundings.

adjacent charge rule states that it is possible to write formal electronic structures for some molecules where adjacent atoms have formal charges of the same sign. In the Pauling formulation (1939), it states that such structures will not be important owing to instability resulting from the charge distribution.

adjoint operator — an operator B such that the inner products (Ax,y) and (x,By) are equal for a given operator A and for all elements x and y of the Hilbert space. It is also known as associate operator and Hermitian conjugate operator.

adjoint wave functions — functions in the Dirac electron theory which are formed by applying the Dirac matrix to the adjoint operators of the original wave functions.

admittance — a measure of how readily alternating current will flow in an electric circuit. It is the reciprocal of impedance. The term was introduced by Heaviside (1878).

adsorption — a type of absorption, in which only the surface of a matter acts as the absorbing medium. Physisorption and chemisorption are distinguished as adsorption mechanisms.

Term coined by: H. Kayser Über die Verdichtung von Gasen an Oberflächen in ihrer Abhängigkeit von Druck und Temperatur, Ann. Phys. 12, 526–547 (1880).

AES — an acronym for Auger electron spectroscopy.

affinity → electron affinity.

AFM — an acronym for atomic force microscopy.

Aharonov–Bohm effect — the total amplitude of electron waves at a certain point oscillates periodically with respect to the magnetic flux enclosed by the two paths due to the interference effect. The design of the interferometer appropriate for experimental observation of this effect is shown in Figure A.1. Electron waves come from the waveguide to left terminal, split into two equal amplitudes going around the two halves of the ring, meet each other and interfere in the right part of the ring, and leave it through the right terminal. A small solenoid carrying magnetic flux Φ is positioned entirely inside the ring so that its magnetic field passes through the annulus of the ring. It is preferable to have the waveguide sufficiently small in order to restrict a number of possible coming electron modes to one or a few.

Figure A.1 Schematic layout of the interferometer for observation of the Aharonov–Bohm effect. Small solenoid inside the ring produces the magnetic field of the flux Φ enclosed between the two arms and characterized by the vector potential A.

First described in: Y. Aharonov, D. Bohm, Significance of electromagnetic potentials in the quantum theory, Phys. Rev. 115(3), 485–491 (1959).

More details in: A. Batelaan, A. Tonomura, The Aharonov–Bohm effects: Variations on a subtle theme. Phys. Today 62(9), 38–43 (2009).

Aharonov–Casher effect supposes that a beam of neutral particles with magnetic dipole moments passing around opposite sides of a line charge will undergo a relative quantum phase shift. The effect has a “duality” with the Aharonov–Bohm effect, where charged particles passing around a magnetic solenoid experience a phase shift despite, it is claimed, experiencing no classical force. It is pointed out that a magnetic dipole particle passing a line charge does indeed experience a classical electromagnetic force in the usual electric-current model for a magnetic dipole. This force will produce a relative lag between dipoles passing on opposite sides of the line charge, and the classical lag then leads to a quantum phase shift. Thus, the effect has a transparent explanation as a classical lag effect.

First described in: Y. Aharonov, A. Casher, Topological quantum effects for neutral particles, Phys. Rev. Lett. 53(4), 319–321 (1984).

More details in: D. Rohrlich, The Aharonov-Casher effect, in: Compendium of Quantum Physics: Concepts, Experiments, History and Philosophy, edited by F. Weinert, K. Hentschel, D. Greenberger, B. Falkenburg (Springer, Berlin, 2009).

First described in: G. B. Airy, Trans. Camb. Phil. Soc. 6, 379 (1838); G. B. Airy, An Elementary Treatise on Partial Differential Equations (1866).

Airy functions — solutions of the Airy equation. The equation has two linearly independent solutions, conventionally taken as the Airy integral functions Ai(x) and Bi(x). They are plotted in Figure A.2. There are no simple expressions for them in terms of elementary functions, while for large absolute values of x: Ai(x) ∼ π−1/2x−1/4exp[−(2/3)x3/2], Ai(−x) ∼ (1/2)π−1/2x−1/4cos[−(2/3)x3/2 − π/4]. Airy functions arise in solutions of the Schrödinger equation for some particular cases.

Figure A.2 Airy functions.

First described in: G. B. Airy, An Elementary Treatise on Partial Differential Equations (1866).

Airy spirals — spiral interference patterns formed by quartz cut perpendicularly to the axis in convergent circularly polarized light.

Recognition: in 1831 G. B. Airy received the Copley Medal of the Royal Society for their studies on optical subjects.

ALD –an acronym for atomic layer deposition.

aldehydes — organic compounds that have at least one hydrogen atom bonded to the carbonyl group (>C—O). These may be RCHO or ArCHO compounds with R representing an alkyl group (– CnH2n + 1) and Ar representing an aromatic ring.

algorithm — a set of well-defined rules for the solution of a problem in a finite number of steps.

aliphatic compound — an organic compound in which carbon atoms are joined together in straight or branched chains. The simplest aliphatic compound is methane (CH4). Most aliphatic compounds provide exothermic combustion reactions, thus allowing their use as a fuel.

alkanes → hydrocarbons.

alkenes → hydrocarbons.

alkyl groups → hydrocarbons.

allotropy — the property of a chemical element to exist in two or more different structural modifications in the solid state. The term polymorphism is used for compounds.

alternating current Josephson effect → Josephson effects.

Al'tshuler–Aronov–Spivak effect — occurs when the resistance of the conductor in the shape of a hollow cylinder oscillates as a function of the magnetic flux threading through the hollow with a period of hc/2e. This effect was predicted for the diffusive regime of the charge transport where the mean free path of the electrons is much smaller than the sample size. The conductance amplitude of the oscillations is of the order of e2/h and depends on the phase coherence length over which an electron maintains its phase coherence. Coherent backscattering of an electron when there is interference in a pair of backscattered spatial waves with time-reversal symmetry causes the oscillations.

First described in: B. L. Al'tshuler, A. G. Aronov, B. Z. Spivak, Aharonov–Bohm effect in non-ordered conductors, Pis'ma Zh. Eksp. Teor. Fiz. 33(2), 101–103 (1981) — in Russian.

More details in: K. Nakamura, T. Harayama, Quantum Chaos and Quantum Dots (Oxford University Press, Oxford, 2004).

amides — organic compounds that are nitrogen derivates of carboxylic acids. The carbon atom of a carbonyl group (>C—O) is bonded directly to a nitrogen atom of an –NH2, –NHR or –NR2 group, where R represents an alkyl group (–CnH2n + 1). The general formula of amides is RCONH2.

amines—organic compounds that are ammonia molecules with hydrogen substituted by alkyl groups (–CnH2n + 1) or aromatic rings. These can be RNH2, R2NH, or R3N, where R is an alkyl or aromatic group.

amino acid — an organic compound containing an amino group (NH2), a carboxylic acid group (COOH), and any of various side groups that are linked together by peptide bonds. The basic formula is NH2CHRCOOH. Amino acids are building blocks of proteins.

There are twenty standard amino acids used in protein biosynthesis. These are presented in Figure A.3.

Figure A.3 Amino acids found in proteins. Their symbols are shown in parentheses.

Just as the letters of the alphabet can be combined to form an almost endless variety of words, amino acids can be linked in varying sequences to form a huge variety of proteins.

More details in: en.wikipedia.org/wiki/Amino_acid.

Amontons' law currently supposes the statement that the friction force between two bodies is directly proportional to the applied load (normal), with a constant of proportionality that is the friction coefficient. This force is constant and independent of the contact area, the surface roughness and the sliding velocity.

In fact, this statement is a combination of a few laws: the law of Euler and Amontons stating that friction is proportional to the loading force, the law of Coulomb → Coulomb law (mechanics) stating that friction is independent of the velocity, and the law of Leonardo da Vinci stating that friction is independent of the area of contact. In particular, Leonardo da Vinci arrived (1500) at the result that on an inclined plane a slider would move if the ratio between the tangential and normal components of the gravitational force exceeded one-fourth.

First described in: G. Amontons, De la résistance causée dans les machines, Mem. Acad. Roy. Sci. A, 206–222 (1699).

More details in: R. Schnurmann, Amontons' law, “traces” of frictional contact, and experiments on adhesion, J. Appl. Phys. 13(4), 235 (1942).

amorphous solid — a solid with no long-range atomic order.

Ampère currents — molecular-ring currents postulated to explain the phenomenon of magnetism as well as the apparent nonexistence of isolated magnetic poles.

First described in: A. M. Ampère, Mémoire sur les effets du courant électrique, Annales de chimie et de physique 15, 59–118 (1820).

More details in: André-Marie Ampère, Exposé méthodique des phénomènes électro-dynamiques et des lois de ces phénomènes (Plasson, Paris, 1822).

Ampère's rule states that the direction of the magnetic field surrounding a conductor will be clockwise when viewed from the conductor if the direction of current flow is away from the observer.

First described in: A. M. Ampère, Mémoire sur les effets du courant électrique, Annales de chimie et de physique 15, 59–118 (1820).

More details in: André-Marie Ampère, Exposé méthodique des phénomènes électro-dynamiques et des lois de ces phénomènes (Plasson, Paris, 1822).

Ampère's theorem states that an electric current flowing in a circuit produces a magnetic field at external points equivalent to that due to a magnetic shell whose bounding edge is the the conductor and whose strength is equal to the strength of the current.

First described in: A. M. Ampère, Mémoire sur les effets du courant électrique, Annales de chimie et de physique 15, 59–118 (1820).

More details in: André-Marie Ampère, Exposé méthodique des phénomènes électro-dynamiques et des lois de ces phénomènes (Plasson, Paris, 1822).

amphichiral → chirality.

AND operator → logic operator.

Anderson insulator — a solid state material with insulating properties defined by the interaction of electrons with impurities and other lattice imperfections. The material is characterized by a robust energy gap, which is a gap for charge excitations between the Fermi energy and spatially extended states. Any related metal-to-insulator transition is a type of quantum phase transitions in which the energy gap is formed.

More details in: F. Gebhard, The Mott Metal-Insulator Transition: Models and Methods (Springer, Heidelberg, 2010).

Andersen-Nose algorithm — a method used in molecular dynamics simulation for numerical integration of ordinary differential equation systems based on a quadratic presentation of time-dependent atom displacement.

First described in: S. Nose, F. Yonezawa, Isothermal–isobaric computer simulations of melting and crystallization of a Lennard–Jones system, J. Chem. Phys. 84(3), 1803–1812 (1986).

First described in: P. W. Anderson, Absence of diffusion in certain random lattices, Phys. Rev. 109(5), 1492–1505 (1958).

Recognition: in 1977 P. W. Anderson, N. F. Mott and J. H. van Vleck received the Nobel Prize in Physics for their fundamental theoretical investigations of the electronic structure of magnetic and disordered systems.

See also www.nobel.se/physics/laureates/1977/index.html.

Anderson rule, which is also called the electron affinity rule, states that vacuum levels of two materials forming a heterojunction should be lined up. It is used for construction of energy band diagrams of heterojunctions and quantum wells.

The electron affinity χ of the materials is used for the lining up procedure. This material parameter is nearly independent of the position of the Fermi level, unlike the work function, which is measured from the Fermi level and therefore depends strongly on doping.

Figure A.4 Alignment of the bands at a heterojunction according to Anderson's rule.

The validity of the rule was discussed by H. Kroemer in his paper Problems in the theory heterojunction discontinuities CRC Crit. Rev. Solid State Sci. 5(4), 555–564 (1975). The hidden assumption about the relation between the properties of the interface between two semiconductors and those of the much more drastic vacuum-to-semiconductor interface is a weak point of the rule.

First described in: R. L. Anderson, Germanium-gallium arsenide heterojunction, IBM J. Res. Dev. 4(3), 283–287 (1960).

Andreev process — reflection of a quasiparticle from the potential barrier formed by normal conductor and superconductor when the barrier height is less than the particle energy. It results in the temperature leap at the barrier if a heat flow takes place there. The conductor part of the structure can be made of a metal, semimetal or degenerate semiconductor.

The basic concept of the process is schematically illustrated in Figure A.5 for an electron crossing the interface between a conductor and superconductor.

Figure A.5 Andreev reflection process.

There is a superconducting energy gap opened up for a single electron on the superconductor side. Thus, an electron approaching the barrier from the metal side with the energy above the Fermi level, but still within the gap, cannot be accommodated in the superconductor as a single particle. It can only form a Cooper pair there that needs an additional electron from the metal side with the energy below the Fermi level to come. This removed electron leaves behind a hole in the Fermi sea. If the incident electron had a momentum k, the generated hole has the momentum −k. It traces the same path as the electron, but in the opposite direction. Describing the phenomenon one says that the incident electron is reflected as a hole.

First described in: A. F. Andreev, Thermal conductivity of the intermediate state of superconductors, Zh. Exp. Teor. Fiz. 46(5), 1823–1928 (1964) — in Russian.

More details in: C. W. J. Beenakker, Colloquium: Andreev reflection and Klein tunneling in graphene, Rev. Mod. Phys. 80(4), 1337–1354 (2008).

Å ngstrom — a metric unit of length measurements that corresponds to 10−10 m. The atomic diameters are in the range of 1–2 . It is named in honor of the nineteenth-century physicist Anders Jonas Å ngstrom, one of the founders of modern spectroscopy.

anisodesmic structure — a structure of an ionic crystal in which bound groups of ions tend to be formed → mesodesmic and isodesmic structures.

anisotropy (of matter) — different physical properties of a medium in different directions. The alternative is isotropy.

anisotropic magnetic resistance — the difference in magnetoresistance when the resistance of a conductor is measured by the current passing either parallel or perpendicular to the material → giant magnetoresistance effect.

First described in: W. Thomson (Lord Kelvin), On the electro-dynamic qualities of metals: effects of magnetization on the electric conductivity of nickel and of iron, Proc. R. Soc. London 8, 546–550 (1856).

anomalous Hall effect — an additional voltage proportional to the magnetization arising in Hall effect measurements in ferromagnetic materials. Unlike the ordinary Hall effect, this contribution is strongly temperature dependent.

In general, the anomalous Hall effect occurs in solids with broken time- reversal symmetry, typically in a ferromagnetic phase, as a consequence of spin–orbit coupling.

First described in: E. H. Hall, On the new action of magnetism on a permanet electric current, Philos. Mag. 10, 301–329 (1880); E. H. Hall, On the possibility of transverse currents in ferromagnets, Philos. Mag. 12, 157–160 (1881).

More details in: N. Nagaosa, J. Sinova, S. Onoda, A. H. MacDonald, N. P. Ong, Anomalous Hall effect, Rev. Mod. Phys. 82(2), 1539–1592 (2010).

See also www.lakeshore.com/pdf-files/systems/Hall-Data-Sheets/Anomalous-Hall1.pdf.

anomalous Zeeman effect → Zeeman effect.

antibody — an inducible immunoglobulin protein produced by B lymphocytes of the immune system, in humans and other higher animals, which recognizes and binds to a specific antigen molecule of a foreign substance introduced into the organism. When antibodies bind to corresponding antigens they set in motion a process to eliminate the antigens.

antibonding orbital — the orbital which, if occupied, raises the energy of a molecule relative to the separated atoms. The corresponding wave function is orthogonal to that of the bonding state → bonding orbital.

antiferroelectric — a dielectric of high permittivity, which undergoes a change in crystal structure at a certain transition temperature, usually called the antiferroelectric Curie temperature. The antiferroelectric state in contrast to a ferroelectric state possesses no net spontaneous polarization below the Curie temperature. No hysteresis effects are therefore exhibited by this type of materials. Examples: BaTiO3, PbZrO3, NaNbO3.

antiferromagnetic → magnetism.

antigen — any foreign substance, such as virus, bacterium, or protein, which, after introduction into an organism (humans and higher animals), elicits an immune response by stimulating the production of specific antibodies. It also can be any large molecule, which binds specifically to an antibody.

anti-Stokes line → Raman effect.

anti-dot — a quantum dot made of wider band gap semiconductor in/on a smaller band gap semiconductor, for example Si dot in/on Ge substrate. It repels charge carriers rather than attracting them.

anti-wires — the quantum wires made of wider band gap semiconductor in/on a smaller band gap semiconductor. They repel charge carriers rather than attracting them.

APCVD — an acronym for atmospheric pressure chemical vapor deposition.

APFIM an acronym for atom probe field ion microscopy.

a priori Latin meaning before the day. It usually indicates some postulates or facts known logically prior to the referred proposition. It pertains to deductive reasoning from assumed axioms or self-evident principles.

approximate self-consistent molecular orbital method the Hartree-Fock theory as it stands is too time consuming for use in large systems. However, it can be used in a parametrized form, and this is the basis of many of the semi-empirical codes used like Complete Neglect of Differential Overlap (CNDO) and Intermediate Neglect of Differential Overlap (INDO).

In the CNDO method all integrals involving different atomic orbitals are ignored. Thus, the overlap matrix becomes the unit matrix. Moreover, all the two-center electron integrals between a pair of atoms are set equal and the resonance integrals are set proportional to the overlap matrix. A minimum basis set of valence orbital is chosen using Slater type orbitals. These approximations strongly simplify the Fock equation.

In the INDO method the constraint present in CNDO that the monocentric two-electron integrals are set equal is removed. Since INDO and CNDO execute on a computer at about the same speed and INDO contains some important integrals neglected in CNDO, INDO performs much better than CNDO especially in prediction of molecular spectral properties.

It is interesting to note that the first papers dealing with the CNDO method appear in a supplementary issue of the Journal of Chemical Physics that contains the proceedings of the International Symposium on Atomic and Molecular Quantum theory dedicated to R. S. Mulliken Hund Mulliken theory, held in USA on 18–23 January 1965.

First described in: J. A. Pople, D. P. Santry, G. A. Segal, Approximate self-consistent molecular orbital theory. I. Invariant procedures, J. Chem. Phys. 43(10), S129–S135 (1965); J. A. Pople, D. P. Santry, G. A. Segal, Approximate self-consistent molecular orbital theory. II. Calculations with complete neglect of differential overlap, J. Chem. Phys. 43(10), S136–S151 (1965); J. A. Pople, D. P. Santry, G. A. Segal, Approximate self consistent molecular orbital theory. III. CNDO results for AB2 and AB3 systems, J. Chem. Phys. 44(9), 3289–3296 (1965).

More details in: J. A. Pople, Quantum chemical models, Rev. Mod. Phys., 71 (5), 1267–1274 (1999).

Recognition: in 1998 J. A. Pople shared with W. Kohn the Nobel Prize in Chemistry for his development of computational methods in quantum chemistry.

See also www.nobel.se/chemistry/laureates/1998/index.html.

APW — an acronym for an augmented plane wave.

archaea — are single-celled organisms thriving in a variety of habitats. Most of the archaea prefer extreme environments. Archaea form together with bacteria and eucarya the three domains in life.

argon laser — a type of ion laser with ionized argon as the active medium. It generates light in the blue and green visible light spectrum, with two energy peaks: at 488 and 514 nm.

armchair structure → carbon nanotube.

aromatic compounds → hydrocarbons.

aromatic ring → hydrocarbons.

First described by J. H. van't Hoff in 1884; in 1889, S. Arrhenius provided a justification and interpretation for it. See S. A. Arrhenius, Über die Reaktiongeschwindigkeit der Inversion vor Rohrzucker durch Säuren, Z. Phys. Chem. 4, 226 (1889).

Recognition: in 1901 J. H. van't Hoff received the Nobel Prize in Chemistry in recognition of the extraordinary services he has rendered by the discovery of the laws of chemical dynamics and osmotic pressure in solutions. In 1903 S. Arrhenius received the Nobel Prize in Chemistry in recognition of the extraordinary services he had rendered to the advancement of chemistry by his electrolytic theory of dissociation.

See also www.nobel.se/chemistry/laureates/1901/index.html.

See also www.nobel.se/chemistry/laureates/1903/index.html.

artificial atom(s) → quantum confinement.

Asaro–Tiller–Grinfeld instability arises in a growing stressed film, that is, the surface of the stressed film is unstable against perturbations with wavelengths longer than the critical wavelength,

where γ is the surface tension, ε is the misfit strain of the growing layer with respect to the substrate, ν is the Poisson ratio of the material, and G is its shear modulus.

First described in: R. J. Asaro, W. A. Tiller, Surface morphology development during stress corrosion cracking: Part I: via surface diffusion, Metall. Trans. 3, 1789–1796 (1972); M. A. Grinfeld, Instability of the separation boundary between a nonhydrostatically stressed elastic body and a melt, Sov. Phys. Dokl. 31, 831–835 (1986).

More details in: M. A. Grinfeld, Thermodynamic Methods in the Theory of Heterogeneous Systems (Longman, New York, 1991).

associate operator → adjoint operator.

atmospheric pressure chemical vapor deposition (APCVD) → chemical vapor deposition.

atomic engineering — a set of techniques used to built atomic-size structures. Atoms and molecules may be manipulated in a variety of ways by using the interaction present in the tunnel junction of scanning tunneling microscope (STM). In a sense, there is a possibility to use the proximal probe in order to extend our touch to a realm where our hands are simply too big.

Two formal classes of atomic manipulation processes are distinguished: parallel processes and perpendicular processes. In the class of parallel processes an adsorbed atom or molecule is forced to move along the substrate surface. In the class of perpendicular processes the atom or molecular is transferred from the surface to the STM tip or vice versa. In both processes the goal is the purposeful rearrangement of matter on the atomic scale. One may view the act of rearrangement as a series of steps that results in the selective modification or breaking of chemical bonds between atoms and subsequent creation of new ones. It is equivalent to a procedure that causes a configuration of atoms to evolve along some time-dependent potential energy hyper-surface from an initial to a final configuration. Both points of view are useful in understanding physical mechanisms by which atoms may be manipulated with a proximal probe.

In the class of parallel processes, the bond between the manipulated atom and the underlying surface is never broken. This means that the adsorbate always lies within the absorption potential well. The relevant energy scale for these processes is the energy of the barrier to diffusion across the surface. This energy is typically in the range of 1/10 to 1/3 of the adsorption energy and thus varies from about 0.01 eV for weakly bound physisorbed atoms on a close-packed metal surface to 1 eV for strongly bound chemisorbed atoms. There are two parallel processes tested for atomic manipulation: field-assisted diffusion and sliding process.

The field-assisted diffusion is initiated by interaction of the spatially inhomogeneous electric field of an STM tip with the dipole moment of an adsorbed atom. The inhomogeneous electric field leads to a potential energy gradient at the surface resulting in a field-assisted directional diffusion motion of the adatom. In terms of the potential energy the process can be presented as follows.

An atom in an electric field E(r) is polarized with a dipole moment , where μ is the static dipole moment, the induced dipole moment, and the polarizability tensor. The related spatially dependent energy of the atom is given by . This potential energy is added to the periodic potential at the substrate surface. Weak periodic corrugation of the energy occurs. The resulting potential reliefs are shown in Figure A.6. A broad or sharp potential well is formed under the STM tip depending on the particular interaction between the tip, adatom and substrate atoms. The interaction of the electric field with the adsorbate dipole moment gives rise to a broad potential well. The potential energy gradient causes the adatom to diffuse toward the potential minimum under the tip. When there is a strong attraction of the adsorbate to the tip by chemical binding, it leads to a rather steep potential well located directly below the tip apex. The adsorbate remains trapped in the well as the tip is moved laterally.

Figure A.6 Schematic of the potential energy of an adsorbed atom as a function of its lateral position on a surface above which there is located the STM tip.

Realization of field-assisted diffusion needs the substrate to be positively biased. At a negative substrate polarity the static and induced dipole terms being opposite in sign compensate each other. In this case no potential well and related stimulating energy gradient for diffusion are produced.

The sliding process supposes pulling of an adsorbate across the surface by the tip of a proximal probe. The tip always exerts a force on an adsorbate bound to the surface. One component of this force is due to the interatomic potential, that is, the chemical binding force, between the adsorbate and the outermost tip atoms. By adjusting the position of the tip one may tune the magnitude and the direction of the force exerted on the adsorbate, thus forcing it to move across the surface.

The main steps of atomic manipulation via the sliding process are depicted in Figure A.7. The adsorbate to be moved is first located with the STM in its imaging mode and then the tip is placed near the adsorbate (position “a”). The tip–adsorbate interaction is subsequently increased by lowering the tip toward the adsorbate (position “b”). This is achieved by changing the required tunnel current to a higher value and letting the feedback loop move the tip to a height which yields the higher demanded current. The adsorbate–tip attractive force must be sufficient to keep the adsorbate located beneath the tip. The tip is then moved laterally across the surface under constant current conditions (path “c”) to the desired destination (position “d”), pulling the adsorbate along with it. The process is terminated by reverting to the imaging mode (position “e”), which leaves the adsorbate bound to the surface at the desired location.

Figure A.7 Schematic of the sliding process: a and e–imaging, b–connecting, c–sliding, d–disconnecting.

In order for the adsorbate to follow the lateral motion of the tip, the tip must exert enough force on the adsorbate to overcome the lateral forces between the adsorbate and the surface. Roughly speaking, the force necessary to move an adsorbate from site to site across the surface is given by the ratio of the corrugation energy to the separation between atoms of the underlying surface. However, the presence of the tip may also cause the adsorbate to be displayed normal to the surface relative to its unperturbed position. The displaced adsorbate would have an altered in-plane interaction with the underlying surface. If the tip pulls the adsorbate away from the surface causing a reduction of this in-plane interaction, then we would expect our estimate to be an upper bound for the force necessary to move the adsorbate across the surface.

The manipulation of an adsorbate with the sliding process may be characterized by a threshold tip height. Above this height the adsorbate-tip interaction is too weak to allow manipulation. At the threshold this interaction is just strong enough to allow the tip to pull the adatom along the surface. The absolute height of the STM tip above the surface is not directly measured. But resistance of the tunnel junction strongly correlated to the tip–surface separation is accurately controlled. An increasing resistance corresponds to greater tip–surface separation, and hence to their weaker interaction. The threshold resistance to slide an adsorbate depends on the particular arrangement of atoms at the apex of the tip. But for that reason it can vary by not more than a factor of 4. The resistance is more sensitive to the chemical nature of the adatom and surface atoms ranging from tens kΩ to a few MΩ. The ordering of the threshold resistances is consistent with the simple notion that the corrugation energy scales with the binding energy and thus greater force must be applied to move adatoms that are more strongly bound to the surface.

In perpendicular processes an atom, molecule or group of atoms is transferred from the tip to the surface or initially from the surface to the tip and then back to a new site on the surface. In order to illustrate the main regularities of these processes we discuss transferring an adsorbed atom from the surface to the tip. The relevant energy for such process is the height of the potential barrier that the adsorbate should come through to go from the tip to the surface. The height of this barrier depends on the separation of the tip from the surface. It approaches the adsorption energy in the limit of large tip–surface separation and goes to zero when the tip is located close enough to the adsorbate. By adjusting the height of the tip one may tune the magnitude of this barrier. Electrical biasing of the tip with respect to the substrate, as it is usually performed in STM, controls the transfer process. Three approaches distinguished by the physical mechanisms employed have been proposed for perpendicular manipulations of atoms. These are transfer on- or near-contact, field evaporation and electromigration.

The transfer on- or near-contact is conceptually the simplest among the atomic manipulation processes. It supposes the tip to be moved toward the adsorbate until the adsorption well on the tip and surface sides of the junction coalesce. That is, the energy barrier separating the two wells is gone and the adsorbate can be considered simultaneously bound to the tip and the surface. The tip is then withdrawn, carrying the adsorbate with it. For the process to be successful the adsorbate's bond to the surface must be broken when the tip is moved out. One might expect that the adsorbate would “choose” to remain bound to the side of the junction on which it has the greatest binding energy. However, the “moment of choice” comes when the adsorbate has strong interactions with both tip and surface, so the binding energy argument may be too simple. It does not account for the simultaneous interaction of the adsorbate with the tip and the surface.

At a slightly increased separation between the tip and sample surface, the adsorption well of the tip and surface atom are close enough to significantly reduce the intermediate barrier but have it still remain finite, such that thermal activation is sufficient for atom transfer. It is called transfer-near-contact. This process has a rate proportional to νexp(−Ea/kBT), where ν is the frequency factor, and Ea the reduced energy barrier between the tip and the sample. The transfer rate exhibits an anisotropy if the depth of the adsorption well is not the same on each side of the barrier. It is important to distinguish this transfer-near-contact mechanism from field evaporation, which requires an intermediate ionic state.

In its simplest form, the transfer on- or near-contact process occurs in the complete absence of any electric field, potential difference, or flow of current between the tip and the sample. Nevertheless, in some circumstances it should be possible to set the direction of transfer by biasing the junction during contact.

The field evaporation uses the ability of ions to drift in the electric field produced by an STM probe. It is a thermally activated process in which atoms at the tip or at the sample surface are ionized by the electric field and thermally evaporated. Drifting in this field they come more easily through the potential Schottky-type barrier separating the tip and the surface because this barrier appears to be decreased by the electric field applied. Such favorable conditions are simply realized for positively charged ions by the use of a pulse voltage applied to the tip separated from a sample surface by about 0.4 nm or smaller. Field evaporation of negative ions meets difficulties associated with the competing effect of field electron emission, which would melt the tip or surface at the fields necessary for negative ion formation.

The electromigration in the gap separating an STM tip and sample has much in common with the electromigration process in solids. There are two components of the force driving electromigration. The first is determined by the electrostatic interaction of the charged adsorbates with the electric field driving the electron current through the gap. The second, which is called the “wind” force, is induced by direct scattering of electrons at the atomic particles. These forces are most strongly felt by the atoms in the immediate vicinity of the tunnel junction formed by the tip of a proximal probe and sample surface. The highest electric field and current density are here. Within the electromigration mechanism the manipulated atoms always move in the same direction as the tunneling electrons. Moreover, “heating” of adsorbates by tunnel current stimulates electromigration as soon as a “hot” particle may more easily jump to a neighboring site. Atomic electromigration is a reversible process.

Summarizing the above-presented physical mechanisms used for manipulation of individual atoms with proximal probes one should remember that there is no universal approach among them. Applicability of each particular mechanism is mainly determined by the physical and chemical nature of the atoms supposed to be manipulated, by the substrate and to some extent by the probe material. An appropriate choice of the adsorbate/substrate systems still remains a state-of-art point.

More details in: Handbook of Nanotechnology, edited by B. Bhushan (Springer Verlag, Berlin Heidelberg, 2004).

atomic force microscope — an apparatus used for atomic force microscopy.

atomic force microscopy (AFM) originated from scanning tunneling microscopy (STM)