Nanophysics and Nanotechnology

An Introduction to Modern Concepts in Nanoscience

Edward L. Wolf

• Publisher: Wiley-VCH
• Year: 2015
• ISBN:
  9783527684168
• Edition: 3
• Topic: Tecnologia e ingegneria
• Subtopic: Microelettronica

Long awaited new edition of this highly successful textbook, provides once more a unique introduction to the concepts, techniques and applications of nanoscale systems by covering its entire spectrum up to recent findings on graphene.

Chapter 1
Introduction

Technology has to do with the application of scientific knowledge to the economic (profitable) production of goods and services. This textbook is concerned with the size or scale of working machines and devices in different forms of technology. It is particularly concerned with the smallest devices that are possible, and equally with the appropriate laws of nanometer-scale physics: “nanophysics,” which are available to accurately predict behavior of matter on this invisible scale. Physical behavior at the nanometer scale is predicted accurately by quantum mechanics, represented by Schrodinger's equation. Schrodinger's equation provides a quantitative understanding of the structure and properties of atoms. Chemical matter, molecules, and even the cells of biology, being made of atoms, are therefore, in principle, accurately described (given enough computing power) by this well-tested formulation of nanophysics.

There are often advantages in making devices smaller, as in modern semiconductor electronics. What are the limits to miniaturization and how small a device can be made? Any device must be composed of atoms, whose sizes are of the order of 0.1 nm. Here, the term “nanotechnology” will be associated with human-designed working devices in which some essential element(s), produced in a controlled fashion, have sizes of 0.1 nm to thousands of nanometers, or, 1 Å to 1 µm. There is thus an overlap with “microtechnology” at the micrometer-size scale. Microelectronics is the most advanced present technology, apart from biology, whose complex operating units are on a scale as small as micrometers.

Even though the literature of nanotechnology may refer to nanoscale machines, even “self-replicating machines built at the atomic level” [1], it is admitted that an “assembler breakthrough” [2] will be required for this to happen, and no nanoscale machines presently exist. In fact, scarcely any micrometer-scale machines exist either, and it seems that the smallest mechanical machines readily available in a wide variety of forms are really on the millimeter scale, as in conventional wristwatches. (To avoid confusion, note that the prefix “micro” is sometimes applied, but never in this textbook, to larger scale techniques guided by optical microscopy, such as “microsurgery.”)

The reader may correctly infer that nanotechnology is presently more concept than fact, although it is certainly a media and funding reality. The fact that the concept has great potential for technology is the message to read from the funding and media attention to this topic.

The idea of the limiting size scale of a miniaturized technology is fundamentally interesting for several reasons. As sizes approach the atomic scale, the relevant physical laws change from classical to quantum-mechanical laws of nanophysics. The changes in behavior from classical, to “mesoscopic,” to atomic scale, are broadly understood in contemporary physics, but the details in specific cases are complex and need to be worked out. While the changes from classical physics to nanophysics may mean that some existing devices will fail, the same changes open up possibilities for the invention of new devices.

A primary interest in the concept of nanotechnology comes from its connections with biology. The smallest forms of life, bacteria, cells, and the active components of living cells of biology, have sizes in the nanometer range. In fact, it may turn out that the only possibility for a viable complex nanotechnology is that represented by biology. Certainly, the present understanding of molecular biology has been seen as an existence proof for “nanotechnology” by its pioneers and enthusiasts. In molecular biology, the “self-replicating machines at the atomic level” are guided by DNA, replicated by RNA, specific molecules are “assembled” by enzymes, and cells are replete with molecular-scale motors, of which kinesin is one example. Ion channels, which allow (or block) specific ions (e.g., potassium or calcium) to enter a cell through its lipid wall, seem to be exquisitely engineered molecular-scale devices where distinct conformations of protein molecules define an open channel versus a closed channel.

Biological sensors, such as the rods and cones of the retina and the nanoscale magnets found in magnetotactic bacteria, appear to operate at the quantum limit of sensitivity. Understanding the operation of these sensors doubtlessly requires application of nanophysics. One might say that Darwinian evolution, a matter of odds of survival, has mastered the laws of quantum nanophysics, which are famously probabilistic in their nature. Understanding the role of quantum nanophysics entailed in the molecular building blocks of nature may inform the design of artificial sensors, motors, and perhaps much more, with expected advances in experimental and engineering techniques for nanotechnology.

In the improbable event that engineering, in the traditional sense, of molecular-scale machines becomes possible, the most optimistic observers note that these invisible machines could be engineered to match the size or scale of the molecules of biology. Medical nanomachines might then be possible, which could be directed to correct defects in cells, to kill dangerous cells, such as cancer cells, or even, most fancifully, to repair cell damage present after thawing of biological tissue, frozen as a means of preservation [3].

This textbook is intended to provide a guide to the ideas and physical concepts that allow an understanding of the changes that occur as the size scale shrinks toward the atomic scale. Our point of view is that a general introduction to the concepts of nanophysics will add greatly to the ability of students and professionals whose undergraduate training has been in engineering or applied science, to contribute in the various areas of nanotechnology. The broadly applicable concepts of nanophysics are worth study, as they do not become obsolete with inevitable changes in the forefront of technology.

1.1 Nanometers, Micrometers, and Millimeters

A nanometer, 10⁻⁹ m, is about 10 times the size of the smallest atoms, such as hydrogen and carbon, while a micron is barely larger tha...