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Biology 代写:An Introduction To Nanoscience And Nanotechnology

1.3.1 Moore’s Law

The top-down approach to microelectronics seems to be governed by exponential time dependence. In 1965, Gordon E. Moore, Director of Fairchild Semiconductor Division, was the first to note this exponential behaviour in his famous paper “Cramming more components onto integrated circuits”. He made the astounding prediction that the number of transistors in a given area on a chip would double every two years for the next ten years. It has been observed that the transistor count in integrated circuits double in every two years as shown in figure 1.3. His prediction is popularly known as Moore’s law. This trend has not only continued so far but it has crossed the limit of the prediction. There has been a corresponding decrease in the size of individual electronic elements, going from millimeters in the 60’s to tens of nanometers (~ 25 nm) in modern circuitry. Moore’s law plot of number of transistors on an integrated circuit versus year is illustrated in figure 1.3.

Moore’s Law Equation:

Computer processing power in future years, Pn = Po x 2n,

where Po = computer processing power in the beginning year,

n = number of years to develop a new microprocessor divided by 2.

.

Fig. 1.3: Moore’s law plot of number of transistor on an IC/CPU versus year

In the last century, the transition from one technology to another has occurred several times in information industry. For example, the mechanical relay was replaced by the vacuum tube, which was then substituted by the transistor. Subsequently, the transistor gave way to the current integrated circuit.

1.4 Applications

The enhanced abilities to understand and manipulate matter at the molecular and atomic levels promise a wave of significant new technologies over the next few decades. Dramatic breakthroughs will occur in diverse areas such as medicine, communications, computing, energy, and robotics. These changes will generate large amounts of wealth and force wrenching changes in existing markets and institutions. The aim of this section is to give an overview of the significant foreseeable applications of nanotechnology. A detailed discussion of the various potential applications of nanotechnology is given in chapter 7.

1.4.1 Medicine

Nanomaterials are one of the most interesting bio-sensing materials because of their unique size and shape dependent optical properties, high surface energy and surface-to-volume ratio, and tunable surface properties. A wide variety of nanomaterials have found very useful applications in many kinds of biosensors for the diagnosis and monitoring of diseases, drug discovery, proteomics, environmental detection of biological agents and so on. Since disease is the result of physical disorder of misarranged molecules and cells, medicine at this level should be able to cure most diseases. Hence, nanotechnology has wide scope in medicine. Nanostructures such as particles and polymeric dendrimers could be designed as drug delivery systems. Assembler-based manufacturing will provide new tools for medicine, making possible molecular-scale surgery to repair and rearrange cells. Mutations in DNA could be repaired, and cancer cells, toxic chemicals, and viruses could be destroyed through use of medical nanomachines, including cell repair machines. Nanotechnology will improve health care, help to extend the life span, improve its quality, and extend human physical capabilities. Medicinal fluids containing nano robots are programmed to attack and reconstruct the molecular structure of cancer cells and viruses to make them harmless. Nanorobots could also be programmed to perform delicate surgeries. Nanotechnology will create biocompatible joint replacements that will last for entire life of the patient.

Fig. 1.4: Biosensors for detecting biomarkers of cancer: (a) Nanoscale cantilevers,

(b) Nanowire sensors.

With faster and cheaper diagnostic equipments, better diagnostic tests will be conducted. For example, DNA mapping of the newborn children may help to point out future potential problems and thereby prevent disease before it takes hold. Today most harmful side effects of treatments such as chemotherapy are a result of drug delivery methods that cannot pinpoint their intended target cells accurately. Researchers at Harvard University have been able to attach special RNA strands, measuring about 10 nm in diameter, to nanoparticles and fill the nanoparticles with a chemotherapy drug. These RNA strands are attracted to cancer cells. When the nanoparticle encounters a cancer cell it adheres to it and releases the drug into the cancer cell. This directed method of drug delivery has great potential for treating cancer patients while producing less side harmful effects than those produced by conventional chemotherapy. Figure 1.4 shows biosensors, such as nanoscale cantilevers and nanowires, for detecting biomarkers of cancer.

1.4.2 Nanoelectronics

Nanoelectronics can be used to build computer memory, using individual molecules or nanotubes to store bits of information. It has potential applications in molecular switches, molecular or nanotube transistors, nanotube flat-panel displays, nanotube integrated circuits, fast logic gates, switches, nanoscopic lasers and nanotubes as electrodes in fuel cells.

1.4.3 Batteries

With the tremendous growth in portable electronic equipments such as mobile phones, navigation devices, laptop computers, remote sensors, there is a great demand for lightweight and high-energy density batteries. Nanomaterials synthesized by sol-gel techniques are candidates for separator plates in batteries because of their aerogel structure, which can hold considerably more energy than conventional ones. Nickel-metal hydride batteries made of nanocrystalline nickel and metal hydrides are envisioned to require less frequent recharging and to last longer because of their large surface area.