1 Overview
The development of electronic devices has reduced the computer from several houses to small notebooks that can be loaded into pockets, which makes people's computers Development is highly expected. The high performance and small volume of the computer depends mainly depending on the electronic device constituting it. In recent years, the development of nano-molecular devices has been greatly concerned, and the nano-molecular device has a high intensive advantage. One finger is capped to integrate one million billion Molecular electronic components, the improvement of computer integration helps operational speed increases. Nano molecular devices can also be synthesized in large quantities, which will significantly reduce production costs, thereby more competitive advantage. Therefore, nano-molecular devices are becoming an important direction for future electronic devices development.
Molecular Electronics Concept
The concept of molecular electronics is different from the organic micro-transistor or electronics in the previous period and the transmission and "body" effect in the "body" material. Organic devices. Molecular electronics also referred to as "molecular internal electronics", which is composed of a covalent bond molecular structure that is electrically isolated from the "body" substrate, or molecular wires and molecules that consist of a superstructured molecule and a super-molecular structure of the nanometer level. The switch is connected. From the perspective of the preparation process, molecular electronics is more likely to produce less cost of hundreds of millions of almost complete equivalent nano-magnitude-based structures than solid nano-electronic devices. This is mainly due to the emergence of nano-machining and nano-operation, that is, mechanical synthesis and chemical synthesis techniques of nano-magnitude structures. Mechanical synthesis is to control the molecule for controlling the scanning tunneling microscope (STM), atomic force microscope (AFM), and new microelectromechanical systems. Chemical synthesis includes chemical self-assembly growth of nanostructures, borrowed from biochemical and molecular genetics, and the like. The method of chemical synthesis can be combined into a molecular electronic device in an organic molecule.
Molecular electronic device is to construct various components in electronic circuits, such as molecular wires, molecular switches, molecular diode, molecular field effect transistors, molecular storage devices, etc., measurement and analysis of molecular wires, molecular switches, molecular storage devices, etc. The electrical properties of these molecular scale components. Its goal is to use a single molecule, a super-molecular or molecular cluster instead of solid electronic components such as silicon-based semiconductor transistors, and even assembled intact molecular computers.
2 molecular electronic device material
Organic electromechanical material
It is conducive to molecular clipping organic compounds to molecular crystals in solid state, due to no current in molecular crystals Sub electronic or holes) and molecular spacing are large (it is difficult to migrate) and is often an insulator. To make organic solid conductive, there is a carrier in the crystal and a passage for transported transport. The mechanism of the two conditions can be divided into two major categories. One type is a polymerization molecule having a common choice of π system, which is partially oxidized or reduced to produce an unparalleled electron, thereby forming a conductor in the chain direction. The room temperature conductivity of polyacetylene has reached 8 x 10scm, which can be compared to metal copper. The other is based on electron donor (D) and receptor (A) molecules formed charge transfer composite salts. General D and A at least There is one part to a flat-shaken molecule, and the two are arranged in the crystals. When the molecular spacing of the column is small to make the π track overlap each other to form a band (channel), there is an incomplete charge transfer to form a mixed price belt. The supplied carriers can be passed along the column direction.
Organic light discoloration and electrochromic material
The compound is in light, such as obey, geometric The phenomenon of structural, dimerization, molecular internal proton metastasis, bond breakage, and charge transfer, resulting in photoloration. It is possible to develop as light discoloration. When variation is reversible and the two states are sufficiently stable, it is possible to develop The optical switch, the optical recording element. For example, a colored zerogenic ion is generated after the heating atom, the bond is broken, and the heating or another wave of long light can be recovered to the original state. Electrochromic material is An reversible oxidation reaction occurs under external electric fields. When the difference between the oxidation state and the reducing protocol on the light absorption, different colors are present in the visible optical zone. For example, TTF loses an electron with an electric field, from the reduction The state changes to the oxidation state, and the color changes from yellow to blue purple. The metal organic coordination compound containing D electrons and doped conductive polymers can also be used as electroslastic materials.
Piezoelectric, thermoelectric and ferroelectric material
as molecules of piezoelectric, thermoelectric and ferroelectric materials should also be polar or polarized molecules. External pressure, heating Next, the molecular orientation in the molecular crystal is rearranged, so that the vector dipole moment in a certain direction in the crystal is not equal to zero, thereby exhibiting piezoelectric, thermoelectric and ferroelectric properties in this direction. In addition to the small molecule, some low molecular weight polymerization The object also has piezoelectric, thermoelectric and ferroelectric properties. Typical is polyfluoride. Develop a switch, memory element, and is not easy to implement due to low switching speed, but its film is in signal transmission. And sensing is desirable to develop practical devices such as ultrasonic transmission, underwater transmission and full plastic motors.LCD material
Usually molecules in liquid state are disorderly. However, Some compounds have an alignment structure similar to crystals in a liquid state, which is liquid crystal. The liquid crystal molecules are more than a rod-shaped molecule having a self-assembly function and an aromatic ring. The liquid crystal is mainly used as an electro-optical property as an electronic display material: in the current or electric field. Under the action, the refractive index, the dielectric constant and the orientive elasticity of the index, the color change occurs due to the molecular interaction, and the color changes are collected. From this sense, the liquid crystal belongs to the electrosa material. High capacity, wide view, high contrast, fast response, Low energy consumption, low drive voltage, high reliability and rich color is a common requirement for electron display liquid crystal materials. The ferroelectric liquid crystal material is the most important object in liquid crystal research. Since it has microsecond response speed and large capacity information The storage function can be used as light storage, optical recording, and display materials.
3 molecular electronic device classification
molecular wire
Currently, people study molecular wire system Mainly focused on the following 4 categories: linear hydrocarbon conjugate low polymer molecular systems, porphyrin oligomer molecular systems, carbon nanotube systems, and DNA biomolecular systems. Carbon atomlines are the simplest carbon hydrogen molecular wires. All carbon atoms in the carbon atom wire use SP to hybrid, thereby having an alternating single triple bond structure. Gladysz et al. Synthesized from 20 carbon atoms with carbon atom lines of the end group.
Carbon nanotubes in the future molecular electronic device and potential applications in the circuit have also been received in recent years. People's widespread concern. It can be seen as a tubular structure having a spiral cycle by a hexagonal graphite sheet. Carbon nanotubes have good electrical properties and rigid structures. It is an ideal molecular wire that modulates its conductivity by changing the diameter size and roll angle.
molecular diode
< P> As early as 1974 Aviram, the idea of molecular diode is proposed, which can be said that this is the origin of molecular electronics. They describe the molecular structure formed by the bridge bridge of the organic donor and receptor, which can display I-V rectifier characteristics similar to P-N feature. Model molecular structure of this molecular diode. The donor is a tetraviorene (TTF), and the receptor is 7,7,8,8-tolytanopanocyanobenzoquinone (TCNQ). The intermediate is three methylene bridges, the purpose is to make the molecules have a certain rigidity that is not easily deformed, so that the donor and receptor have a physical distance to avoid mutual charge transfer to form a charge transfer complex.Initially, the study of molecular diode is mainly focused on model molecular systems proposed in Aviram and Ratner. Due to the small dipole of the study, it has not made a big progress in the lack of effective experimental means. With the continuous development of langmuir-blodgett (lb) film, molecular self-assembly (SA) and scanning probe microscope (SPM), people have developed rapidly from the study of molecular devices, and the research on molecular diode is also from the original The Aviram and Ratner model molecular systems expand to other conjugated molecular systems. DHiraai et al. Used STM to study single-layer film in gold and silver, discovered that the rectification of molecules is also enhanced as the conjugate chain increases. Liu Yunxia, the Chemistry of the Chinese Academy of Sciences, synthesized a series of asymmetric phthalocyanine containing electron donors (-NH2) and electronic receptors (-NO2, -CN, etc.), assembled into LB films, and using STM technology to measure their IV curves confirmed that the single monthalocyanine molecule also has rectifier characteristics. Recently, Chicago University Yu Luping is synthesized with a type of new type of diode molecule, which consists of an electron-rich thiophene (C4S) and a deficient thiazole (C3NS) 2 part. They successfully put this molecules between the two gold electrodes by mercapto, and using the STM method to demonstrate that this rectification behavior is indeed derived from the self-characteristics of the molecule, rather than because the asymmetric coupled or molecular electrode of the molecule and the electrode. Interface factors caused by.
Molecular switch and molecular memory device
The switch is the basic control element of all electronic devices, and is also an important part of molecular storage and logic devices. Rotaxanes and Catenanes are currently studied more double steady-state molecules. The wheel is composed of one annular portion and 1 rod-like portion, and the ring can be rotated or slid in the direction of the rod, and the two ends of the rod have a larger having a larger having a larger resistance. . If two different sites are introduced on the rod, when the ring is left in these two different sites, it corresponds to two different states. Electrochemical or chemical environment-induced rancane molecules have already reported. The soil is composed of 2 sets together, and there can be rotation between 2 rings. Different sites are introduced into one ring in the pestine, which can also constitute a dual steady-state molecular switch.
Molecular Field Effect Transistor
As the device size is reduced, the substantially amplified unit will become a triode transistor into a triode monodisone (SET). The working principle of SET is that the quantum tunneling is mainly a tunneling effect between metal-insulator-metal. When the barrier of the metal electrode is sufficiently narrow, the electron at the Fermi level can be tunneled through the insulating layer to form a tunneling current.
In the development of the moisture range, people initially utilize the carbon nanotubes (CNT) to obtain a breakthrough, forming a field effect tube composed of a single carbon nanotube. With the development of nanotechnology, people have also made a field effect tube composed of a single C60 molecule. In addition to CNT and C60, the study of other materials in recent years has also made great progress. PARK et al. Connect the complex molecule of 1 central ion as CO to constitute a field effect between two gold electrodes. The experimental results show that as the gate pressure changes, the current can be greatly regulated between the source and the drain; in addition, the current-voltage curve is not a conventional smooth curve, but the stepped, presenting a carrier transmission. Quantum characteristics. Robert et al. Proposed and designed a new concept of single molecular field effect transistor, in which the transmission behavior of electrons is regulated by a certain single atomic charge near the molecule, by changing the molecule A single atom's charge state can control molecular current conducting or disconnect. In the past, in the past, in order to measure the change in molecular conductance, it must be performed under the condition of absolute zero, and the field effect of this new concept of molecular transistors can be observed at room temperature; this new concept Another feature of the molecular field effect transistor is that only one electron from the atom can realize the conduction or disconnection of the molecule, while the conventional field effect tube requires millions of electrons to achieve this switch.
Quantum Effect Molecular Electronic Device
The representative of the quantum effector electronic device is the molecular resonance tunneling diode, referred to as molecular RTD. It has a barrier structure and the same working principle similar to the barrier of the solid RTD.
Molecular RTD consists of four parts: (1) The emitter and collector of the main molecular wire molecule RTD are composed of a polyphenylene molecular chain. This aromatic organic molecule has a conjugated π-electronic track. One or more of this long-filled or partially filled π track can provide a channel. When there is a bias in both ends of the molecule, the electronic can move from one end of the molecule to the other end. It is estimated that each second can be passed through 2 * 10 electrons per second, and this molecular wire is often referred to as Tour molecular wire; (2) "island" or potential well composed of a single fat ring has a lower energy, The size is approximately 1 nanometer, which is smaller than the solid RTD well scale; (3) constitutes two barriers by two fatty nail moions, which is to insert the two sides of the insulating properties into the "island" side, with Between the left and right molecular wires, two barriers to the molecular RTD; ($) the end lead of the molecular electronic device, the two ends of the molecular device often paste on the gold (Au) electrode by thiol (-SH), as it is introduced End, such a "crocodile clip" (-SH) tightly attached to the metal (-SH) is known as its molecular device. The working principle of the molecular RTD is basically the same as the solid RTD. When the electron is limited to a very narrow potential well, its energy generates quantization formation, and the energy level and the emitter are not electronically filled in the middle of the well trap. The molecular orbit energy is not aligned, and the resonance tunneling does not occur, the device is not turned on. When the bias is added, the medium level of the well is aligned with the orbital energy of the electronic filled, and the energy level and the collector empty energy state are also aligned, the resonance tunneling effect occurs, and there is a tunneling current through the device, RTD In the on state.
Electrical Machine Electronic Equipment
Atomic relay
Atomic relay is similar to a molecular gate switch. In the atomic relay, a movable atom is not fixedly attached to the substrate, but is movable between the two electrodes, forward or backward. Two atomic conductors are connected to a relay with a movable switch atom. If the switch atom is located in place, the entire device can conduct electricity; if the switch atom is separated from the original position, the causing void suddenly reduces the current flowing through the atomic wire, so that the entire device becomes broken. The third atomic wire of the switching atom constitutes the gate of the atomic relay, placing a small negative charge on the gate wire, so that the switch atom is removed from its original