Nanoelectromechanical systems (NEMS) are devices integrating electrical and mechanical functionality on the nanoscale. NEMS form the logical next miniaturization step from so-called microelectromechanical systems, or MEMS devices. NEMS typically integrate transistor-like nanoelectronics with mechanical actuators, pumps, or motors, and may thereby form physical, biological, and chemical sensors. The name derives from typical device dimensions in the nanometer range, leading to low mass, high mechanical resonance frequencies, potentially large quantum mechanical effects such as zero point motion, and a high surface-to-volume ratio useful for surface-based sensing mechanisms. Uses include accelerometers, or detectors of chemical substances in the air.
Because of the scale on which they can function, NEMS are expected to significantly impact many areas of technology and science and eventually replace MEMS. As noted by Richard Feynman in his famous talk in 1959, "There's Plenty of Room at the Bottom," there are a lot of potential applications of machines at smaller and smaller sizes; by building and controlling devices at smaller scales, all technology benefits. Among the expected benefits include greater efficiencies and reduced size, decreased power consumption and lower costs of production in electromechanical systems.
In 2000, the first very-large-scale integration (VLSI) NEMS device was demonstrated by researchers from IBM. Its premise was an array of AFM tips which can heat/sense a deformable substrate in order to function as a memory device. In 2007, the International Technical Roadmap for Semiconductors (ITRS) contains NEMS Memory as a new entry for the Emerging Research Devices section.
A key application of NEMS is atomic force microscope tips. The increased sensitivity achieved by NEMS leads to smaller and more efficient sensors to detect stresses, vibrations, forces at the atomic level, and chemical signals. AFM tips and other detection at the nanoscale rely heavily on NEMS. If implementation of better scanning devices becomes available, all of nanoscience could benefit from AFM tips.
Two complementary approaches to fabrication of NEMS systems can be found. The top-down approach uses the traditional microfabrication methods, i.e. optical and electron beam lithography, to manufacture devices. While being limited by the resolution of these methods, it allows a large degree of control over the resulting structures. Typically, devices are fabricated from metallic thin films or etched semiconductor layers.
Bottom-up approaches, in contrast, use the chemical properties of single molecules to cause single-molecule components to (a) self-organize or self-assemble into some useful conformation, or (b) rely on positional assembly. These approaches utilize the concepts of molecular self-assembly and/or molecular recognition. This allows fabrication of much smaller structures, albeit often at the cost of limited control of the fabrication process.
A combination of these approaches may also be used, in which nanoscale molecules are integrated into a top-down framework. One such example is the carbon Nanotube nanomotor.
Many of the commonly used materials for NEMS technology have been carbon based, specifically diamond, carbon nanotubes and graphene. This is mainly because of the useful properties of carbon based materials which directly meet the needs of NEMS. The mechanical properties of carbon (such as large Young's modulus) are fundamental to the stability of NEMS while the metallic and semiconductor conductivities of carbon based materials allow them to function as transistors.
Both graphene and diamond exhibit high Young's modulus, low density, low friction, excessively low mechanical dissipation, and large surface area. The low friction of CNTs, allow practically frictionless bearings and has thus been a huge motivation towards practical applications of CNTs as constitutive elements in NEMS, such as nanomotors, switches, and high-frequency oscillators Carbon nanotubes and graphene's physical strength allows carbon based materials to meet higher stress demands, when common materials would normally fail and thus further support their use as a major materials in NEMS technological development.
Along with the mechanical benefits of carbon based materials, the electrical properties of carbon nanotubes and graphene allow it to be used in many electrical components of NEMS. Nanotransistors have been developed for both carbon nanotubes as well as graphene. Transistors are one of the basic building blocks for all electronic devices, so by effectively developing usable transistors, carbon nanotubes and graphene are both very crucial to NEMS.
Metallic carbon nanotubes have also been proposed for nanoelectronic interconnects since they can carry high current densities. This is a very useful property as wires to transfer current are another basic building block of any electrical system. Carbon nanotubes have specifically found so much use in NEMS that methods have already been discovered to connect suspended carbon nanotubes to other nanostructures. This allows carbon nanotubes to be structurally set up to make complicated nanoelectric systems. Because carbon based products can be properly controlled and act as interconnects as well as transistors, they serve as a fundamental material in the electrical components of NEMS.
Despite all of the useful properties of carbon nanotubes and graphene for NEMS technology, both of these products face several hindrances to their implementation. One of the main problems is carbon’s response to real life environments. Carbon nanotubes exhibit a large change in electronic properties when exposed to oxygen. Similarly, other changes to the electronic and mechanical attributes of carbon based materials must fully be explored before their implementation, especially because of their high surface area which can easily react with surrounding environments.
TASKS
1. Read the title of the passage to know what it deals with.
2. Read the passage carefully to know its content in more detail.
3. Name the paragraphs dealing with predictions of very-large-scale integration.
4. Name the paragraphs that describe the optical and electron beam lithography.
5. Find the conclusive paragraph in which nanotubes in NEMS are accounted for.
6. Find the paragraph concerned with the complementary approaches to fabrication of NEMS systems.
7. Thoroughly read paragraph 1 and define its main point. Summarize paragraph 1 in no more than two sentences. Begin with: The paper reports on...
8. Thoroughly read paragraphs 2, 3, 4 and condense their content. Compress paragraphs 2, 3 and 4 into a statement using the phrases: A careful account is given to... It is reported that... The paper claims that...
9. Thoroughly read paragraphs 5, 6 and condense their content. Compress paragraphs 5 and 6 into a statement using the phrases: Much attention is given to... It is claimed that... The paper points out that...
10. Summarize the content of the passage using the phrases: The paper provides information on... The paper defines the phenomenon of... An attempt is made to... The paper points out... The paper claims that...
TEXT 2 Nanocircuitry
Nanocircuits are electrical circuits operating on the nanometer scale. This is well into the quantum realm, where quantum mechanical effects become very important. One nanometer is equal to 10−9 meters or a row of 10 hydrogen atoms. With such progressively smaller circuits, more can be fitted on a computer chip. This allows faster and more complex functions using less power. Nanocircuits are composed of three different fundamental components. These are transistors, interconnections, and architecture, all fabricated on the nanometer scale.
One of the most fundamental concepts to understanding nanocircuits is the formulation of Moore’s Law. This concept arose when Intel co-founder Gordon Moore became interested in the cost of transistors and trying to fit more onto one chip. It relates that the number of transistors that can be fabricated on a silicon integrated circuit—and therefore the computing abilities of such a circuit—is doubling every 18 to 24 months. The more transistors one can fit on a circuit, the more computational abilities the computer will have. This is why scientists and engineers are working together to produce these nanocircuits so millions and perhaps even billions of transistors will be able to fit onto a chip. Despite how good this may sound, there are many problems that arise when so many transistors are packed together. With circuits being so tiny, they tend to have more problems than larger circuits, more particularly heat - the amount of power applied over a smaller surface area makes heat dissipation difficult, this excess heat will cause errors and can destroy the chip. Nanoscale circuits are more sensitive to temperature changes, cosmic rays and electromagnetic interference than today's circuits. As more transistors are packed onto a chip, phenomena such as stray signals on the chip, the need to dissipate the heat from so many closely packed devices, tunneling across insulation barriers due to the small scale, and fabrication difficulties will halt or severely slow progress. Many believe the market for nanocircuits will reach equilibrium around 2015. At this time they believe the cost of a fabrication facility may be as much as $200 billion. There will be a time when the cost of making circuits even smaller will be too much, and the speed of computers will reach a maximum. For this reason, many scientists believe that Moore’s Law will not hold forever and will soon reach a peak, since Moore's law is largely predicated on computational gains caused by improvements in micro-lithographic etching technologies.
In producing these nanocircuits, there are many aspects involved. The first part of their organization begins with transistors. As of right now, most electronics are using silicon-based transistors. Transistors are an integral part of circuits as they control the flow of electricity and transform weak electrical signals to strong ones. They also control electric current as they can turn it on off, or even amplify signals. Circuits now use silicon as a transistor because it can easily be switched between conducting and nonconducting states. However, in nanoelectronics, transistors might be organic molecules or nanoscale inorganic structures. Semiconductors, which are part of transistors, are also being made of organic molecules in the nano state.
The second aspect of nanocircuit organization is interconnection. This involves logical and mathematical operations and the wires linking the transistors together that make this possible. In nanocircuits, nanotubes and other wires as narrow as one nanometer are used to link transistors together. Nanowires have been made from carbon nanotubes for a few years. Until a few years ago, transistors and nanowires were put together to produce the circuit. However, scientists have been able to produce a nanowire with transistors in it. In 2004, Harvard University nanotech pioneer Charles Lieber and his team have made a nanowire—10,000 times thinner than a sheet of paper—that contains a string of transistors. Essentially, transistors and nanowires are already pre-wired so as to eliminate the difficult task of trying to connect transistors together with nanowires.
The last part of nanocircuit organization is architecture. This has been explained as the overall way the transistors are interconnected, so that the circuit can plug into a computer or other system and operate independently of the lower-level details. With nanocircuits being so small, they are destined for error and defects. Scientists have devised a way to get around this. Their architecture combines circuits that have redundant logic gates and interconnections with the ability to reconfigure structures at several levels on a chip. The redundancy lets the circuit identify problems and reconfigure itself so the circuit can avoid more problems. It also allows for errors within the logic gate and still have it work properly without giving a wrong result.
Scientists in India have recently developed the world’s smallest transistor which will be used for nanocircuits. The transistor is made entirely from carbon nanotubes. Nanotubes are rolled up sheets of carbon atoms and are more than a thousand times thinner than human hair. Normally circuits use silicon-based transistors, but these will soon replace those. The transistor has two different branches that meet at a single point, hence giving it a Y shape. Current can flow throughout both branches and is controlled by a third branch that turns the voltage on or off. This new breakthrough can now allow for nanocircuits to hold completely to their name as they can be made entirely from nanotubes. Before this discovery, logic circuits used nanotubes, but needed metal gates to be able to control the flow of electrical current.
TASKS
1. Read the title of the passage to know what it deals with.
2. Read the passage carefully to know its content in more detail.
3. Name the paragraphs dealing with predictions of aspects of nanocircuit.
4. Name the paragraphs that describe the semiconductors, nanowires and nanotubes.
5. Find the conclusive paragraph in which architecture as a part of nanocircuit organization is accounted for.
6. Find the paragraph concerned with the Moore’s Low.
7. Thoroughly read paragraph 1 and define its main point. Summarize paragraph 1 in no more than two sentences. Begin with: The paper reports on...
8. Thoroughly read paragraphs 2, 3, 4 and condense their content. Compress paragraphs 2, 3 and 4 into a statement using the phrases: A careful account is given to... It is reported that... The paper claims that...
9. Thoroughly read paragraphs 5, 6 and condense their content. Compress paragraphs 5 and 6 into a statement using the phrases: Much attention is given to... It is claimed that... The paper points out that...
10. Summarize the content of the passage using the phrases: The paper provides information on... The paper defines the phenomenon of... An attempt is made to... The paper points out... The paper claims that...
UNIT IX SPECIAL TEXTS
TEXT 1Carbon nanotube
Carbon nanotube — a hollow cylindrical structure with diameter varying from fractions of a nanometer to several dozen nanometers and length ranging from one micron to several hundred microns or more; carbon nanotube consists of carbon atoms and is a rolled-up graphene sheet.
Carbon nanotubes (CNT) were first systematically described by Sumio Iijima of NEC, who discovered them in 1991 as a by-product of C60 fullerene synthesis, and almost simultaneously by a group of researchers led by L.A. Chernozatonsky. The existence of extraordinary forms of carbon with similar morphology had been mentioned before, but those research efforts remained unnoticed.
A graphene sheet may be wrapped into a regular cylinder along different directions, which gives rise to a broad family of nanotubes. Single walled carbon nanotubes (SWCNTs) are characterised by the chiral vector (n,m), which links pairs of atoms that coincide upon this imaginary process of wrapping, where n and m (n ≥ m) are coordinates of this vector in the basis of lattice vectors of a graphene sheet. Depending on the values of n and m, nanotubes may exhibit totally different properties: nanotubes with n – m divisible by 3 are metallic (or narrow-gap semiconductors) while the rest of the nanotubes are semiconductors, although their band gap approaches zero with the increase of the diameter. The values of n and m uniquely define the diameter and band structure of nanotubes, which is broadly used for their characterisation using electron (absorption and fluorescence) and vibrational Raman spectroscopy.
There are “zigzag” nanotubes, also known as (n, 0) nanotubes and “armchair” (n,n) nanotubes. These two classes of nanotubes are optically inactive while all other nanotubes are chiral. Besides SWCNTs, there are multi-walled carbon nanotubes (MWCNTs) made up of several single-walled nanotubes inserted one into another. Another distinction lies between open and capped nanotubes. In capped nanotubes, the ends are closed with dome-shaped carbon caps that include six pentagonal faces and constitute halves of certain fullerene molecules. With the higher curvature of these caps causing them to be more reactive than the cylindrical walls, capped nanotubes may be transformed into the open by controlled oxidation. The latter approach, combined with ultrasonic treatment, is also an approach to cut long nanotubes into shorter fragments.
There are several techniques of manufacturing nanotubes. Originally, they were produced using the arc discharge technique, similarly to fullerene synthesis, that yielded mixtures of SWCNTs and MWCNTs. Later, a technique based on laser ablation (see pulsed laser deposition) of graphite in the presence of metal particles (cobalt, nickel) acting as catalysts was proposed. This technique made it possible to produce primarily single-walled nanotubes with controllable diameters and good yields.
Lately, techniques based on vapour deposition have been gaining popularity as the most commercially viable methods. These techniques are based on the thermal decomposition of carbon-containing gases (carbon monoxide, lower hydrocarbons and alcohols, or more complex molecules) on catalytic nanoparticles of metals, which results in the growth of nanotubes from their catalyst-bound end.
In the plasma enhanced deposition technique, the direction of nanotubes’ growth can be controlled via manipulating the electric field. Vapour deposition techniques are used to produce dense linear nanotube arrays with thickness (array height) of up to several millimetres and make it possible to control the type of nanotubes formed.
Separation of nanotubes is an important issue since particular applications may require nanotubes of a certain type (e.g., metallic or semiconductor nanotubes) in a non-aggregated state, whereas as-synthesised nanotubes may be quite firmly bonded into strands due to Van der Waals interactions. Existing separation methods employ centrifugation, electrophoresis, chromatography, etc. Single nanotubes can be obtained using different surfactants and even nanotube-DNA systems. Perhaps researchers will be able to address many present challenges in the field when they master more advanced techniques for the directed catalytic synthesis of nanotubes of desired types.
Nanotubes may find application in a wide range of industries due to their unique electrical, magnetic, optical and mechanical properties. For example, CNTs are an order of magnitude stronger than steel; the Young modulus of SWCNT reaches the order of 1–5 TPa. The latter fact has triggered interest in modulating the strength of materials via the addition of nanotubes. Nanotubes can be used in organic diodes and field effect transistors, and current density in metallic nanotubes may be several orders greater than in metals. Molecular electronics can considerably benefit from the use of defective nanotubes where local defects may bind nanotubes of different types and may even create triplex (branched) contacts.
Scientists are studying potential applications of nanotubes in innovative ultra-strong and ultralight composite materials. Nanotubes are used as needles in scanning tunneling and atomic force microscopy, as well as in the development of semiconductor heterostructures. Prototypes of thin flat displays based on CNT matrices have been designed and tested. In this respect, of importance is the essential difference between nanotubes and many conventional materials: the anisotropy of their properties. While nanotubes show extremely high electric and thermal conductivity along the tube axis, in the lateral directions they act as insulators.
TASKS
1. Read the title of the passage to know what it deals with.
2. Read the passage carefully to know its content in more detail.
3. Name the paragraphs dealing with the application of carbon nanotubes.
4. Name the paragraphs that describe multi-walled carbon nanotubes.
5. Find the conclusive paragraph about the several techniques of manufacturing nanotubes.
6. Find the paragraph concerned with single walled carbon nanotubes.
7. Thoroughly read paragraph 1 and define its main point. Summarize paragraph 1 in no more than two sentences. Begin with: The paper reports on...
8. Thoroughly read paragraphs 2, 3, 4 and condense their content. Compress paragraphs 2, 3 and 4 into a statement using the phrases: A careful account is given to... It is reported that... The paper claims that...
9. Thoroughly read paragraphs 5, 6 and condense their content. Compress paragraphs 5 and 6 into a statement using the phrases: Much attention is given to... It is claimed that... The paper points out that...
10. Summarize the content of the passage using the phrases: The paper provides information on... The paper defines the phenomenon of... An attempt is made to... The paper points out... The paper claims that...
TEXT 2 Quantum computer
A quantum computer is a computer design which uses the principles of quantum physics to increase the computational power beyond what is attainable by a traditional computer. Quantum computers have been built on the small scale and work continues to upgrade them to more practical models.
Computers function by storing data in a binary number format, which result in a series of 1s and 0s retained in electronic components such as transistors. Each component of computer memory is called a bit and can be manipulated through the steps of Boolean logic so that the bits change, based upon the algorithms applied by the computer program, between the 1 and 0 modes (sometimes referred to as "on" and "off").
A quantum computer, on the other hand, would store information as either a 1, 0, or a quantum superposition of the two states. Such a "quantum bit," called a qubit, allows for far greater flexibility than the binary system.
Specifically, a quantum computer would be able to perform calculations on a far greater order of magnitude than traditional computers a concept which has serious concerns and applications in the realm of cryptography and encryption. Some fear that a successful and practical quantum computer would devastate the world's financial system by ripping through their computer security encryptions, which are based on factoring large numbers that literally cannot be cracked by traditional computers within the life span of the universe. A quantum computer, on the other hand, could factor the numbers in a reasonable period of time.
To understand how this speeds things up, consider this example. If the qubit is in a superposition of the 1 state and the 0 state, and it performed an calculation with another qubit in the same superposition, then one calculation actually obtains 4 results: a 1/1 result, a 1/0 result, a 0/1 result, and a 0/0 result. This is a result of the mathematics applied to a quantum system when in a state of decoherence, which lasts while it is in a superposition of states until it collapses down into one state. The ability of a quantum computer to perform multiple computations simultaneously (or in parallel, in computer terms) is called quantum parallelism.
The exact physical mechanism at work within the quantum computer is somewhat theoretically complex and intuitively disturbing. Generally, it is explained in terms of the multi-world interpretation of quantum physics, wherein the computer performs calculations not only in our universe but also in other universes simultaneously, while the various qubits are in a state of quantum decoherence.
Quantum computing tends to trace its roots back to a 1959 speech by Richard P. Feynman in which he spoke about the effects of miniaturization, including the idea of exploiting quantum effects to create more powerful computers. (This speech is also generally considered the starting point of nanotechnology.)
Of course, before the quantum effects of computing could be realized, scientists and engineers had to more fully develop the technology of traditional computers. This is why, for many years, there was little direct progress, nor even interest, in the idea of making Feynman's suggestions into reality.
In 1985, the idea of "quantum logic gates" was put forth by University of Oxford's David Deutsch, as a means of harnessing the quantum realm inside a computer. In fact, Deutsch's paper on the subject showed that any physical process could be modeled by a quantum computer.
Nearly a decade later, in 1994, AT&T's Peter Shor devised an algorith that could use only 6 qubits to perform some basic factorizations more cubits the more complex the numbers requiring factorization became, of course.
A handful of quantum computers have been built. The first, a 2-qubit quantum computer in 1998, could perform trivial calculations before losing decoherence after a few nanoseconds. In 2000, teams successfully built both a 4-qubit and a 7-qubit quantum computer. Research on the subject is still very active, although some physicists and engineers express concerns over the difficulties involved in upscaling these experiments to full-scale computing systems. Still, the success of these initial steps do show that the fundamental theory is sound.
The quantum computer's main drawback is the same as its strength: quantum decoherence. The qubit calculations are performed while the quantum wave function is in a state of superposition between states, which is what allows it to perform the calculations using both 1 and 0 states simultaneously.
However, when a measurement of any type is made to a quantum system, decoherence breaks down and the wave function collapses into a single state. Therefore, the computer has to somehow continue making these calculations without having any measurements made until the proper time, when it can then drop out of the quantum state, have a measurement taken to read its result, which then gets passed on to the rest of the system.
The physical requirements of manipulating a system on this scale are considerable, touching on the realms of superconductors, nanotechnology, and quantum electronics, as well as others.
TASKS
1. Read the title of the passage to know what it deals with.
2. Read the passage carefully to know its content in more detail.
3. Name the paragraphs dealing with the characteristics of quantum computers.
4. Name the paragraphs that describe the application of quantum computers.
5. Find the conclusive paragraph in which the quantum computer's main drawback is accounted for.
6. Find the paragraph concerned with quantum parallelism.
7. Thoroughly read paragraph 1 and define its main point. Summarize paragraph 1 in no more than two sentences. Begin with: The paper reports on...
8. Thoroughly read paragraphs 2, 3, 4 and condense their content. Compress paragraphs 2, 3 and 4 into a statement using the phrases: A careful account is given to... It is reported that... The paper claims that...
9. Thoroughly read paragraphs 5, 6 and condense their content. Compress paragraphs 5 and 6 into a statement using the phrases: Much attention is given to... It is claimed that... The paper points out that...
10. Summarize the content of the passage using the phrases: The paper provides information on... The paper defines the phenomenon of... An attempt is made to... The paper points out... The paper claims that...
