Molecular Electronics
The prospects of using organic materials in electronics and optoelectronics applications have attracted scientists and technologists since the 1970s. This field has become known as molecular electronics. Some successes have already been achieved, for exam
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Molecular Ele 53. Molecular Electronics
53.1
Electrically Conductive Organic Compounds ......................................... 1220 53.1.1 Orbitals and Chemical Bonding ... 1220 53.1.2 Band Theory ............................. 1221 53.1.3 Electrical Conductivity ................ 1222 53.2 Materials ............................................ 1223 53.3 Plastic Electronics ................................ 1225 53.3.1 Diodes and Transistors ............... 1225 53.3.2 Organic Light-Emitting Structures 1226 53.3.3 Photovoltaic Devices .................. 1227 53.3.4 Chemical Sensors ...................... 1228 53.4 Molecular-Scale Electronics .................. 1229 53.4.1 Moore’s Laws ............................ 1229 53.4.2 Nanoscale Organic Films............. 1230 53.4.3 Patterning Technologies............. 1232 53.4.4 Molecular Device Architectures .... 1233 53.5 DNA Electronics.................................... 1235 53.6 Conclusions ......................................... 1236 References .................................................. 1237
Molecular electronics is concerned with the exploitation of organic and biological materials in electronics and optoelectronics [53.1–3]. The subject, as it has matured over the last 30 years, can broadly be divided into two themes. The first area, molecular materials for electronics, has its origins in materials science and concerns the development of devices that utilise the unique macroscopic properties of organic compounds. The most successful commercial product to date is the liquid-crystal display. However, following many years of research, devices such as organic light-emitting displays, pyroelectric detectors for infrared imaging, and chemical and biochemical sensors are beginning to make a technological impact. The Nobel prize in Chemistry for 2000 was awarded to three scientists working in this area: Alan Heeger, Alan MacDiarmid and Hideki Shirakawa, who have made significant contributions to the development of electrically conductive polymers. More challenging is molecular-scale electronics. Here, the focus is on the behaviour of individual organic molecules or groups of molecules. Topics such as molecular switches [53.3–9], molecular memories [53.10–13], mo-
lecular rectifiers [53.14], negative differential-resistance junctions [53.15], deoxyribonucleic acid (DNA) electronics [53.16] and molecular manufacturing [53.17,18] have all been described in the literature. It is much too early to say which, if any, of these could find their way into the commercial arena. This chapter provides an introduction to the interdisciplinary world of molecular electronics. In the first instance, the physics background to semiconductive organic compounds is outlined. A review of the available materials is presented and some of the possible device applications are described. There are currently a limited number of ways in which organic molecules can be deposited and manipulated on surfaces to form solid films, which can then be used in device structures. The most popular me
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