CK-12 21st Century Physics: A Compilation of Contemporary and Emerging Technologies
Page 17
Figure 7.12
Table 2. Technology at a different scale.
What Happens to Materials at the Nanoscale?
At the nanoscale, property and functionality of materials are either changed or enhanced significantly more than their bulk forms. For example, gold is a yellowish orange color when its dimension is more than . The color changes to green when particle size is and to red/ruby at . Similarly, silver is yellow at , but blue at . These changes in color are due to confinement of electrons in smaller areas.
Changes in properties of nanomaterials are due to greater surface area per unit mass compared with their bulk form or larger particle size. That means most of the constituent atoms are at the surface, and hence, the nanomaterials are chemically more reactive. Additionally, at the molecular scale quantum effects begin to play a vital role—affecting their optical, electrical, thermal, and magnetic behaviors.
Why Nanoscience and Nanotechnology are Important to Us
Nanotechnology is not just the miniaturization of the electronic gadgets we use today. This century technology will provide a better understanding of nature's science and technology. For example, we have a deeper understanding of the underlying features at the molecular level regarding how viruses take control of normal cells within the body and spread in different conditions. For many diseases, early detection is the single most important determinant in faster and successful treatments. Besides early stage determination, we will be able to target and destroy or completely stop reactivity of molecules responsible for different diseases, including cancer, as they begin to spread in the body. A present treatment of cancer, chemotherapy, causes severe side effects as a bulk quantity of medicine is injected into the body. Nanotechnology will enable us to deliver drugs more efficiently to the exact location of cancer cells, reducing side-effects significantly. The concentration of a small molecule found in urine could reveal how advanced a patient's prostate cancer is. This recent (Jan. 2009) discovery could lead to simple, noninvasive tests for men who have the disease and might help avoid the need for biopsies. These are a few examples of nanotechnology's impact on health care.
The other aspects of nanoscience and nanotechnology are man-made nanomaterials. Over the years, scientists and technologists have developed and fabricated new materials for wider applications. The following image depicts the comparison of natural and man-made things at different sizes. Technological development at the nanoscale enables us to see and understand the underlying features of Mother Nature's science more closely.
Figure 7.13
Nature and Man-made Things in Different Scales.
The following sites have summarized some basic and pertinent information.
An Introduction to Nanotechnology: http://www.nanowerk.com/nanotechnology/introduction/introduction_to_nanotechnology_1.html
How Stuff Works: http://science.howstuffworks.com/nanotechnology.htm
A Brief History of Nanotechnology's Rapid Emergence
Dec 29, 1959
Richard P. Feynman, a Nobel laureate physicist, made a speech (at an APS meeting at Caltech) envisioning the manipulation of materials on the nanoscale.
"The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom."
"Why cannot we write the entire volumes of the Encyclopedia Britannica on the head of a pin?"
Feynman's Lecture: http://www.zyvex.com/nanotech/feynman.html
Figure 7.14
Richard P. Feynman
1974
The term nanotechnology was coined by Tokyo Science University Professor Norio Taniguchi to describe the precision manufacturing of materials with nanometer tolerances http://en.wikipedia.org/wiki/Norio_Taniguchi
Why did it take so long to implement nanotechnology? Because there was no tool to see and work on such a small scale.
1981
Gerd Binnig and Heinrich Rohrer invented the scanning tunneling microscope (STM), which can image atomic-sized objects. Electron microscopes help technology to move from micro-to nanoscale.
Figure 7.15
Heinrich Rohrer
Figure 7.16
Gerd Binnig
1985
C60 fullerene (also known a “buckminsterfullerenes” or “bucky balls”), a new form of carbon, was discovered by Robert F. Curl, Jr., Sir Harold W. Kroto, and Richard E. Smalley.
Figure 7.17
Fullerene, diameter . A soccer ball is a model of buckyball, but times larger.
1986
K. Eric Drexler, in his 1986 book Engines of Creation: The Coming Era of Nanotechnology, proposed the idea of a nanoscale "assembler," which would be able to build a copy of itself.
For more information about K. Eric Drexler: http://en.wikipedia.org/wiki/K._Eric_Drexler
1991
Sumio Iijima, a researcher at NEC in Japan, discovered the carbon nanotube; he went on to produce an advanced, single-walled version in 1993.
Figure 7.18
Sumio Iijima
Figure 7.19
Different forms of single-wall carbon nanotubes. These are hollow tubes made from carbon atoms and their diameters vary from 0.5 to 3 nm. The longest tube synthesized so far is a few millimeters long. The discovery of fullerenes and nanotubes helped to expedite nanotechnology.
Changes in Man-Made Technology Over the Years
The Computer
Let us see how these metric units (mm, , and ) are related to technology by considering the computer as an example. The first digital computer ENIAC (dimension: , weight: about , total space: about or meter) contained vacuum tubes (acts like an on-off switch), crystal diodes (blocks electricity at certain conditions and allows it to pass when those conditions change), resistors (limits the flow of electricity), capacitors (collects electricity and releases it all in one quick burst), and around million hand-soldered joints.
Figure 7.20
First Digital Computer ENIAC
The size of the vacuum tube, which is a key component of the computer and other electronic devices (such as the telephone, radio, and TV), is about millimeter .
Figure 7.21
Vacum tubes
The vacuum tube (invented in 1941) was replaced by much smaller millimeter scale transistors in 1955. In 1971, Intel introduced the first microprocessor, which contained about transistors for use in a calculator. In the following year, Intel doubled the number of transistors in an bit microprocessor designed to run computer terminals. The number of transistors in current processors, such as in the Pentium is more than a few million, and the size ranges between to each. Presently, Intel's Duo-core chips contain million transistors in square millimeter area, and the Quad-core Itanium chip (launched in Feb. 2008) packs more than billion transistors in nanometers is almost the same size as the chip. The size of the transistor is further decreased by Taiwanese Chipmaker TSMC to , and recently IBM developed a chip.
Figure 7.22
Figure 7.23
A microprocessor incorporates most or all of the functions of a central processing unit (CPU) on a single integrated circuit (IC) or chip.
Over the last 40 years, the size of the transistor, which is a key component of almost all electronic gadgets used today, was reduced in size from a millimeter to a micrometer to a nanometer. The mid-'80s to 2006 - 07 marked the period when technological development was based on micro (one-millionth of a meter) size components, and hence, termed microtechnology. Similarly, the current use of nanometer sized components (size less than ) deem calling it nanotechnology. In the future, we will use single molecule transistors of sizes less than .
Figure 7.24
Single molecule transistor
View animation of single molecule transistor: http://stm.phys.ualberta.ca/wolkow/molecular/WebMidRezAudio.mov
Examples of Computer Hard Disks
In 1956, IBM invented the first computer disk storage system that could store . It had fifty inch diameter disks. The following are some images of hard disks an
d drives developed between 1960–1980. The weight of this hard drive is more than , and the diameter of the disk is foot. Technicians had to manually replace the disks and drives from time to time depending on usage.
Figure 7.25
Hard disk drive and hard disk
Microtechnology
In 1980, Seagate Technology introduced the first hard disk drive for personal computers. It was " drive and held .
Figure 7.26
The large drive is a " full-height drive. The smaller drive is a " IDE drive. These drives also contained the disk. Currently, a drive is able to hold more than worth of data.
Nanotechnology
Atoms will be used in future drives and about million worth of data may be stored in one square cm area.
Figure 7.27
Future Hard Drive
In summary, miniaturization of man-made devices significantly improves efficiency, capacity, and functionality of all electronic gadgets, and at the same time saves lots of electrical energy.
Introduction to Electron Microscopes
Electron microscopes are the most important tools to enable us to see, manipulate, and characterize objects at the nanoscale. An electron microscope uses electrons (instead of light) to “illuminate” an object. Electron microscopes have an electron gun that emits electrons, which then strike the specimen. Conventional lenses used in optical microscopes to focus visible light do not work with electrons. Magnetic fields are used to create “lenses” that direct and focus the electrons. Because electrons are easily scattered by air molecules, the interior of an electron microscope must be sealed at a very high vacuum.
Human vision spans from in the red wavelengths of light to in the blue-violet wavelengths. The human eye cannot see electron wavelengths; therefore, we need a television-type screen or special photographic film to make electron microscope images visible to human eyes. Electrons have a much smaller wavelength than light and thus resolve much smaller objects. The wavelength of electrons used in electron microscopes is usually to .
There are two types of electron microscopes—the Scanning Electron Microscope (SEM) and the Transmission Electron Microscope (TEM). The SEM is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons. The electrons interact with the atoms that make up the sample, producing signals that contain information about the sample's surface topography, composition, and other properties such as electrical conductivity.
The TEM beam of electrons is transmitted through an ultra–thin specimen, interacting with the specimen as they pass through and then scatter providing a 2-D image of the specimen. The Scanning Transmission Electron Microscope (STEM) is a combination of SEM and TEM.
Figure 7.28
Scanning Electron Microscope
The other kind of electron microscope uses a probe that scans the surface of objects providing 3-D images of atomic networks at the surface. Extremely sharp metal points that can be as narrow as a single atom at the tip is used in scanning probe microscopes. The Scanning Tunneling Microscope (STM) is an example of this type of microscope.
Figure 7.29
How the Scanning Tunneling Microscope works.
Another type of scanning probe microscope is the Atomic Force Microscope (AFM). As the probe in an AFM moves along the surface of a sample, the electrons in the metal probe are repelled by the electron clouds of the atoms in the specimen. As the probe moves along the object, the AFM adjusts the height of the probe to keep the force on the probe constant. A sensor records the up-and-down movements of the probe, and feeds the data into a computer to construct a image of the surface of the sample.
Figure 7.30
Atomic Force Microscope
Figure 7.31
Block Diagram of Atomic Force Microscope (AFM)
AFM and STM enable us to work on atoms and design molecules the way we want by placing atoms by atoms. An excellent example is placing iron atoms (step-by-step) to form a quantum coral (see image at the bottom right-hand corner of Figure 11 and check out this Web site http://www.almaden.ibm.com/vis/stm/corral.html.
Here are some additional links to electron microscope images:
http://www.mos.org/sln/sem/sem.html
http://www5.pbrc.hawaii.edu/microangela/
http://www.denniskunkel.com/
http://www.ou.edu/research/electron/www-vl/image.shtml
Applications of Atomic Force Microscope (AFM):
http://www.pacificnanotech.com/application_part.html
How Are Nanomaterials Made?
There are two approaches to make nanomaterials: “Top-down” and “bottom-up.” Top-down technique is as old as the Stone Age—that is cut, process, and design tools for practical purposes from large pieces of materials. This fabrication method is used to manufacture electronic circuits on the surface of silicon by etching. The most common top-down approach to fabrication of circuits involves lithographic patterning techniques using optical sources and high-energy electron beams for etching. Top-down approaches work well at the microscale, but it becomes increasingly difficult to use for nanoscale fabrication.
http://www.wisegeek.com/what-is-a-lithograph.htm
Further reading: http://en.wikipedia.org/wiki/Lithography
Building atom-by-atom and molecule-by-molecule is the philosophy of the “bottom-up” approach. This concept of a self-assembly technique comes from biological systems, where nature has harnessed chemical forces to create essentially all the structures needed for life. Different self-assembly methods have been developed for producing nanoscale materials, such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). The basic concept of these methods is to create atoms from suitable precursors and allow them to deposit layer by layer on a substance in vacuum. In this approach highly pure nanomaterials without defects in structure can be made. Also SEM tip can be used to design and create nanostructures by placing atom by atom. This process is tedious and time consuming and is not useful for industrial purposes.
Magic of Carbon
Carbon is one of the most abundant elements. It is not only the key element in all known life forms, but it is also present in several common materials that we use in our daily life. For example, coal, gasoline, pencil, pitch, and aromatic compounds are all carbon based. Carbon has a unique capacity to form bonds with itself and many other elements making possible to form millions of compounds.
Graphite and Diamond
Graphite and diamond are two compounds of carbon and they have different properties. Diamond, in which each carbon is bonded to four other carbon atoms to form a three-dimensional network, is the hardest known natural material. Graphite, in which each carbon is bonded to three neighbors, is one of the softest materials. Diamond is an insulator but graphite is a good conductor of electricity. Even though graphite and diamond are the same chemically, their structures are significantly different to produce very different properties.
Figure 7.32
Diamond (left) and graphite (right) are two allotropes of carbon: pure forms of the same element that differ in structure.
Fullerenes
Fullerenes (also know as buckyballs) and carbon nanotubes are new forms of carbons that were discovered in the late 1980s. The first fullerene reported was a hollow ball that contained sixty carbon atoms. There are pentagons and hexagons in and each pentagon is surrounded by hexagons and each hexagon is surrounded by alternating hexagons and pentagons. At present, several other cage structured fullerenes containing to carbon atoms are available. Traces of fullerene are available in nature and several chemical methods are developed to synthesize pure (%) fullerenes. Carbon nanotubes are synthesized in laboratories.
Figure 7.33
Different forms of Carbon (allotropes of carbon) : a) Diamond, b) Graphite, c) Lonsdaleite, d) (Buckminsterfullerene or buckyball), e) , f) , g) Amorphous carbon, and h) single-walled carbon nanotube or buckytube.
Because of their unique structure and properties (semiconduc
ting and electron acceptor), fullerenes can be used in different technologically based areas, such as the solar cell, trapping active molecules inside the cage, drug delivery, and bio-sensors.
Carbon Nanotubes
Carbon nanotubes can have different forms depending on how a single hexagonal graphitic sheet is rolled to form the nanotube. Depending on their structures, carbon nanotubes can be either metallic or semiconductors. Figure 7.34 is an illustration of single-wall carbon nanotubes (SWCNT). Double-wall and multi-wall (MWCNT) nanotubes are also synthesized in the laboratory. However, synthesis results in a mixture of all kinds of nanotubes and it is hard to separate them. This has hindered some applications of individual carbon nanotubes, and current research is progressing to separate them.