Electronics

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One of the elementary particles

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Electron is the earliest discovered Elementary particle , commonly expressed by the symbol e, with negative electricity, the electricity quantity is 1.602176634 × 10 -19 Coulomb, yes Electricity The smallest unit of 9.10956 × 10 -31 Kg. It was studied by British physicist Joseph John Thomson in 1897 Cathode ray Found when.

All atoms are composed of a positively charged nucleus and a number of electrons moving around it. charge Formation of directional movement of electric current , such as the current in the metal wire. utilize electric field and magnetic field , can control the movement of electrons as required (in solid and vacuum), thus producing various Electronic instrument And components, such as various Electronic tube 、 electron microscope Etc. The fluctuation of electrons was changed from Crystal diffraction The experiment is confirmed.^[1]

Chinese name: Electronics
Foreign name: Electron
Applicable fields: Science and technology
Discipline: Physics
Applied discipline: Chemistry 、 Physics

Charge: -1.602176634×10 -19 C
Quality: 9.10956✕10 -31 kg
Symbol: e
Essence: Fermion
Discoverer: Joseph John Thomson

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brief introduction

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Electrons are negatively charged subatomic particles. It can be free (not belonging to any atom) or bound by the nucleus. Electrons in atoms exist in spherical shells of various radii and energy levels. The larger the spherical shell, the higher the energy contained in the electron.

In an electric conductor, current is generated by the independent movement of electrons between atoms, and usually flows from the cathode reach anode 。 stay semiconductor In materials, electric current is also generated by moving electrons. But sometimes it is more instructive to think of the current as the movement of electron deficiency from atom to atom. The electron deficient atoms in semiconductors are called hole （hole）。 Typically, the hole "moves" from the positive pole of the electrode to the negative pole.

Electronics belong to Subatomic particle Leptons in. Lepton Considered to constitute matter Elementary particle one of. It has 1/2 spin, which is another Fermion (According to Fermi Dirac statistics). The charge of the electron is e=- 1.6 × 10 -19 C (coulomb), mass 9.11 × 10 -31 kg（0.51MeV/c two ）, the energy is 5.11 × 10 five eV， It is usually expressed as e ⁻. Electronic Antiparticle yes positron It has the same mass, energy, spin and equivalent positive charge (The charge of the positive electron is+1, and the charge of the negative electron is - 1).

The basic constituent unit of matter—— atom The electronic neutron and proton The three are composed together. Neutrons are uncharged, protons are positively charged, and atoms are not apparent. Relative to the composition of neutrons and protons Nucleus The mass of the electron is very small. The mass of the proton is about 1840 times that of the electron.

When electrons are free to move away from the nucleus in other atoms, the net flow phenomenon generated is called current.

Various atoms have different ability to bind electrons, so they become Positive ion , get electrons and become anion 。

static electricity It refers to the situation when the electron carried by the object is more or less than the electric quantity of the atomic nucleus, resulting in the imbalance of positive and negative electric quantity. When there are excess electrons, it is called body band negative electricity ； When there are not enough electrons, it is called object belt positive electricity 。 When the positive and negative electric quantities are balanced, the object is called Electroneutrality Of. There are many applications of static electricity in our daily life, including Laser printer 。^[2]

Encyclopedia x Knowledgeable: Illustration of Particles

Research History

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The electron was created in 1897 by University of Cambridge Cavendish Laboratory Of Joseph John Thomson Studying Cathode ray Was discovered at. Joseph John Thomson proposed Jujube cake model 。^[3]

In 1897 Joseph John Thomson The Hertz experiment was redone. Use higher vacuum Vacuum tube And stronger electric field He observed the deflection of negative ray and calculated the mass charge ratio of negative ray particles (electrons), so he obtained The nobel prize in physics 。 Thomson called this particle electron, which was named by George Stony in 1891. So far, electron was discovered by Thomson as the first subatomic particle discovered by mankind and the door to open the atomic world.

More than 100 years ago, when Robert Millikan, an American physicist, first measured through experiments that the charge of electrons was 1.602 × 10 -19 After C, this charge value is widely regarded as the basic unit of charge. However, if we regard electrons as "whole" or "basic" particles according to the classical theory, we will be extremely confused about the behavior of electrons in some physical situations, such as the non integral quantum Hall effect when electrons are placed in a strong magnetic field.

University of Cambridge Researchers and University of Birmingham A study was completed in collaboration with peers of. According to the bulletin, electronics are generally considered indivisible. Cambridge University researchers placed the extremely thin "quantum metal wire" on a metal plate, controlled the distance between them to be about 30 atoms wide, and placed them in an ultra-low temperature environment near absolute zero, then changed the external magnetic field , found that the electrons on the metal plate are passing through Quantum tunnelling effect It splits when it jumps onto the wire spinon And acupoints.

In order to solve this problem, in 1980, American physicist Robert Laughlin proposed a new theory to solve this puzzle, which also explained the complex interaction between electrons very concisely. However, to accept this theory is to make the physics community pay a "price": the strange inference derived from this theory shows that the current actually consists of 1/3 Electronic charge Composed of.

But in 1981, some physicists proposed that under certain special conditions, electrons can be split into magnetic spinon And charged Caviton 。

On November 16, 2018, the International Metrology Conference passed a resolution that when the basic charge e is expressed in unit C (i.e. A · s), its fixed value is taken as 1.602176634 × 10 −19 To define.^{[5 ]}

Characteristics

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Electrons are attributed to Subatomic In particles Lepton Class. Leptons are a class of basic particles that matter is divided into. Electronic belt 1/2 spin , satisfied Fermion Conditions (according to Fermi -Dirac statistics). The charge of the electron is about - 1.6 × 10 -19 Coulomb, mass 9.10956 × 10 -31 kg（0.51MeV/c two ）。 It is usually expressed as e ⁻. A particle whose electrical property is opposite to that of an electron is called a positron, which has the same mass, spin, and positive charge 。 The more energy the electron moves around the nucleus in the atom Large distance The farther the trajectory of nuclear motion is, the space where there are electrons is called Electronic layer The first layer can have up to 2 electrons. The second layer can have 8 at most, and the n-layer can hold 2n at most two The outermost layer can hold up to 8 electrons. The number of electrons in the last layer determines the chemical property Active or not, 1, 2 and 3 electrons are metallic element , 4, 5, 6, 7 are non-metallic elements, 8 are non-metallic elements Noble gas Element.

The electrons of matter can be lost or obtained, and the nature of matter that has electrons is called Oxidizability , the substance is an oxidant; Matter has the property of losing electrons called Reducibility , the substance is reducing agent 。 The oxidizability or reducibility of a substance is determined by the difficulty of gaining or losing electrons, and has nothing to do with the number of electrons gained or lost.

Electronic layer

By electronic and neutron 、 proton Composed of atom , is physical Basic unit 。 Relative to the composition of neutrons and protons Nucleus The mass of the electron is very small. The mass of the proton is about 1842 times that of the electron. When the number of electrons in an atom is different from the number of protons, the atom will be charged, and the atom is called an ion. When an atom gets extra electrons, it is negatively charged, called anion When the electron is lost, it has positive charge, called cation 。 If the electron carried by an object is more or less than the electric quantity of the atomic nucleus, which leads to the imbalance of positive and negative electric quantity, the object is said to have static electricity 。 When the positive and negative electric quantities are balanced, the electrical property of the object is called Electroneutrality 。 Static electricity has many uses in daily life, for example, electrostatic paint system can Enamel paint (English: enamel paint) or Polyurethane paint , spray evenly on the surface of the object.

Attraction between electron and proton Coulomb force , so that the electron is bound to the atom, which is called Bound electron 。 More than two atoms will exchange or share their bound electrons. This is Chemical bond The main cause of formation. When an electron can move freely without being bound by the nucleus, it is called free electron 。 The net flow of many free electrons moving together is called current. In many physical phenomenon Inside, like Electric conduction , magnetic or heat conduction Electronics have played an important role. Moving electrons will produce magnetic field , will also be deflected by the external magnetic field. Electrons in accelerated motion will emit electromagnetic radiation 。

The ultimate carrier of charge is the tiny electrons that make up atoms. In a moving atom, each electron moving around the nucleus carries a unit negative charge, while the proton in the nucleus carries a unit positive charge. Under normal circumstances, the number of electrons and protons in the matter is equal, the charge they carry is balanced, and the matter is neutral. After friction, matter will either lose electrons, leaving more positive charges (protons are more than electrons). Either increase the number of electrons to obtain more negative charges (more electrons than protons). This process is called Triboelectricity 。

Arrangement rule

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Electronic cloud image

1. The electron is Nucleus The outer nuclei are arranged in layers on different electron layers from near to far and from low to high energy.

2. The maximum number of electrons per layer is 2n two (n represents the number of electronic layers).

3. The number of electrons in the outermost layer shall not exceed 8 (the first layer shall not exceed 2), the number of electrons in the secondary layer shall not exceed 18, and the number of electrons in the penultimate layer shall not exceed 32.

4. Electrons are always ranked first in the lowest energy Electronic layer In other words, first row the first floor, then row the second floor when the first floor is full, and then row the third floor when the second floor is full.

Electronic cloud It's electrons in space outside the nucleus probability density The image description of the distribution shows that electrons appear in a certain area of the outer space of the atomic nucleus, as if a cloud with negative charges is shrouded around the atomic nucleus. People call it the "electron cloud". In 1926, the Austrian scholar Schr ö dinger, on the basis of the Debroy relation, made a proper mathematical treatment of the motion of the electron and proposed the famous Schr ö dinger equation of the second order partial differential. The solution of this equation, if expressed graphically in three-dimensional coordinates, is an electron cloud.

Atomic theory

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In different times, people have had different speculations about the existence of electrons in atoms.

The earliest atomic model was Thomson's Plum pudding model 。 Published in 1904, Thomson believed that electrons are evenly arranged in atoms, just like negatively charged plums in positively charged pudding. In 1909, the famous Rutherford scattering experiment completely overturned this model.

Rutherford designed Rutherford model in 1911 according to his experimental results. In this model, most of the mass of the atom is concentrated in the small nucleus, and most of the atom is vacuum 。 Electrons, on the other hand, revolve around atomic nuclei like planets around the sun. This model has had a great impact on later generations. Until now, many high-tech organizations and units still use electronics to surround Nucleus To represent ourselves.

Under the framework of classical mechanics, the planetary orbit model has a serious problem that cannot be explained: electrons moving in acceleration will produce electromagnetic wave , and the generation of electromagnetic waves will consume energy; Eventually, the depleted electrons will head into the atomic nucleus (just like the depleted satellite will eventually enter the Earth's atmosphere). In 1913, Niels Bohr Proposed Bohr model 。 In this model, electrons move in a specific orbital region outside the nucleus. The farther away from the atomic nucleus, the higher the orbital energy. Electron transition When reaching the orbital region closer to the atomic nucleus, energy will be released in the form of photons. On the contrary, energy will be absorbed from low energy level orbit to high energy level orbit. With these quantized orbital domains, Bohr correctly calculated Atomic hydrogen spectroscopy 。 However, the Bohr model cannot explain the relative intensity of spectral lines, nor can it calculate the spectra of more complex atoms. These problems are yet to be solved quantum mechanics Interpretation of.

In 1916, Gilbert Lewis, an American physical chemist, successfully explained the interaction between atoms. He suggested that a pair of shared electrons between two atoms form covalent bond 。 In 1923, Walter Heitler and Fritz London applied the theory of quantum mechanics to completely explain the production and Chemical bond Cause of formation. In 1919, Owen Langmuir Louis' cubic atom model. It is suggested that all electrons should be distributed in concentric (near concentric) spherical shells of equal thickness. He divided the spherical shells into several parts, each of which contains a pair of electrons. Using this model, he can explain the periodic chemical properties of each element in the periodic table.

In 1924, the Austrian physicist Wolfgang Pauli used a set of parameters to explain the shell structure of atoms. The four parameters of this group determine the quantum state 。 Each quantum state can only allow one electron to occupy. (This rule, which prohibits more than one electron from occupying the same quantum state, is called Pauli exclusion principle ）。 The first three parameters of this group are Principal quantum number 、 Angular quantum number and Magnetic quantum number 。 The fourth parameter can have two different values. In 1925, the Dutch physicists Samuel Abraham Goudsmit and George Ulenbeck proposed the physical mechanism represented by the fourth parameter. They believe that the electron, in addition to the angular momentum in the moving orbital domain, may have an internal angular momentum, called spin, which can be used to explain the mysterious spectral line splitting observed by high-resolution spectrometers in previous experiments. This phenomenon is called fine structure splitting.

Quality measurement

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The mass of electron appears in many basic laws in the field of subatomic, but because the mass of particle is very small, it is very difficult to measure directly. A team of physicists overcame these challenges and came up with the most accurate electronic mass measurement to date.

An electron is bound in a hollow carbon nucleus, and the synthetic atom is put into a uniform electromagnetic field called Penning ion trap. In the Penning ion trap, the atom began to oscillate at a stable frequency. The research team used microwave to shoot the trapped atom, causing electron spin Flip up and down. By comparing the frequency of atomic rotation with the frequency of spin flipped microwave, the researchers used Quantum electrodynamics The mass of the electron is obtained from the equation.

Positron antielectron

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Among many theories explaining the early evolution of the universe, the Big Bang theory is a scientific theory that can be widely accepted by the physics community. In the first few seconds of the Big Bang, the temperature was much higher than 10 billion K. At that time, the average energy of photons was much more than 1.022 MeV, and there was enough energy to create electron and positron pairs.

Theory of Electronic Astronomy

At the same time, antielectron and positron pairs are also annihilating each other and emitting High energy photons 。 In this brief stage of cosmic evolution, electrons, positrons and photons strive to maintain a delicate balance. However, because the universe is expanding rapidly and the temperature continues to cool, the temperature has dropped to 3 billion K in 10 seconds, which is 10 billion K below the temperature threshold of the electron positron creation process. Therefore, photon There is no longer enough energy to create electron and positron pairs, and the large-scale electron positron creation event will no longer occur. However, antielectrons and positrons continue to annihilate each other and emit high-energy photons. Due to some undetermined factors Lepton In the process of creation (English: leptogenesis (physics)), more positrons are created than Antielectron 。 Otherwise, if the number of electrons is equal to the number of positrons, there will be no electrons. About one positron in every billion electrons will survive the annihilation process. Not only that, but also because of the Baryon asymmetry The number of protons is also more than antiprotons. Coincidentally, the number of positrons is exactly equal to the number of protons more than antiprotons. Therefore, the universe Net charge The quantity is zero Electroneutrality 。

application area

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There are many applications of electronics, such as Electron beam welding 、 crt 、 electron microscope 、 Radiotherapy , laser and Particle accelerator wait. In the laboratory, sophisticated instruments like Quadrupole ion trap The electron can be constrained for a long time for observation and measurement. large Tokamak Facilities like International thermonuclear experimental reactor By restraining electrons and ions Plasma , to implement Controlled nuclear fusion 。 Radio telescope Can be used to detect electrons in outer space plasma Body.^[4]

At one time NASA Of Wind tunnel test Medium, electron beam A mini model shot at the space shuttle to simulate the free gas around the space shuttle when it returns to the atmosphere.

Astronomical observation

The remote observation of various electron phenomena mainly depends on the detection of electrons Radiant energy 。 For example, in a high-energy environment such as a star's corona, free electrons will form a plasma that radiates energy by braking radiation. Electron gas Plasma oscillation. Is a kind of fluctuation, which is caused by electron density A wave produced by rapid oscillations. This fluctuation will cause energy emission. Astronomers can use radio telescopes to detect this energy.

Welding application

Electron beam technology, applied to welding, is called electron beam welding. This welding technology can deliver up to 107W · cm two The heat energy of energy density is focused on the small area with a diameter of 0.3~1.3 mm. Using this technology, technicians can weld deeper objects, limiting most of the heat energy to narrow areas without changing the material of nearby materials. In order to avoid the possibility of oxidation of materials, electron beam welding must be carried out in vacuum. For conductive materials that are not suitable for welding by ordinary methods, electron beam welding can be considered. In nuclear engineering and aerospace engineering, some high-value welding workpieces cannot tolerate any defects. At this time, engineers often choose to use electron beam welding to complete the task.

printed circuit

Electron beam lithography is a method of etching semiconductors with a resolution of less than one millimeter. The disadvantages of this technology are high cost, slow process, and must be operated in vacuum. In addition, the electron beam will disperse quickly in the solid, and it is difficult to maintain the focus. Finally, this disadvantage limits the resolution to no less than 10nm. Therefore, electron beam lithography is mainly used to prepare a small number of special integrated circuits.

Radiotherapy

Technology uses an electron beam to illuminate matter. In this way, the physical properties of the substance can be changed or the microorganisms contained in medical articles and food can be eliminated. As Radiation One kind of therapy, linear accelerator. The prepared electron beam is used to irradiate superficial tumors. Since the electron beam can only penetrate a limited depth before absorption (the electron beam with energy of 5~20MeV can usually penetrate 5cm organisms), electron beam therapy can be used for medical image substrate Cellular carcinoma A kind of skin disease. Electron beam therapy can also assist in the treatment of areas that have been irradiated by X-rays.

Particle accelerators use electric fields to increase the energy of electrons or positrons, so that these particles have high energy. When these particles pass through a magnetic field, they emit synchrotron radiation. Because the intensity of radiation is related to spin, the polarization of electron beam is caused. This process is called the Soklov Tenov effect. Many experiments need to use polarized electron beams as particle sources. Synchrotron radiation can also be used to reduce the temperature of the electron beam and the momentum deviation of particles. When the particles reach the required energy, the electron beam and the positron beam collide and annihilate each other, which will cause high-energy radiation emission. By detecting the distribution of these energies, physicists can study the physical behavior of electron positron collision and annihilation.

Imaging technology

Low energy electron diffraction (LEED) irradiates a collimated electron beam onto a crystalline material, and then infers the structure of the material according to the observed diffraction patterns. The electron energy used in this technique is usually between 20 and 200 eV. Reflection high-energy electron diffraction (RHEED) technology irradiates the collimated electron beam on the crystal material at a low angle, and then collects reflection patterns to infer the data of the crystal surface. The energy of the electrons used in this technique is between 8 and 20 keV, and the incidence angle is 1 to 4 °.

The electron microscope incident the focused electron beam on the sample. Due to the interaction between the electron beam and the sample, the properties of the electron will change, such as the moving direction, relative phase and energy. Carefully analyzing these data, we can get sample images with atomic resolution. Use blue light, ordinary optical microscope The resolution is about 200nm due to diffraction limitation; Compare with each other, electron microscope The resolution of De Broglie wavelength For electrons with energy of 100keV, the resolution is about 0.0037nm. Aberration corrected penetrating electron microscope. The resolution can be reduced to less than 0.05 nm, which is enough to clearly observe individual atoms. This capability makes the electron microscope an indispensable instrument for high-resolution imaging in the laboratory. However, electron microscopes are expensive and difficult to maintain; Moreover, due to the need to maintain a vacuum in the sample environment during operation, scientists cannot observe living organisms.

Electron microscope is mainly divided into two types: penetrating type and scanning type. The operating principle of the penetrating electron microscope is similar to that of the overhead projector. The electron beam is aimed at the sample slice for emission, and the penetrating electron is projected onto the negative film or Charge coupled element 。 scanning electron microscope Scanning the sample with a focused electron beam is like a raster scanning in a display machine. The magnification of these two electron microscopes can range from 100 times to 1000000 times or more. Applying quantum tunneling effect, Scanning tunneling microscope Tunneling electrons from a sharp metal tip to the sample surface. In order to maintain a stable current, the tip will move with the height of the sample surface, so that the sample surface image with atomic resolution can be obtained.

Free laser

Free electron lasers pass a relativistic electron beam through a pair of undulators. Each undulator is composed of a row of alternating magnetic fields Magnetic dipole moment form. Because of these magnetic fields, electrons will emit synchrotron radiation ； And this radiation will interact with the electron coherently. When the frequency matches the resonant frequency, the radiation field will be strongly amplified. Free electron lasers can emit coherent high emissivity electromagnetic radiation , and the frequency domain is quite wide, from microwave to soft X-ray. In the near future, this instrument can be used in manufacturing, communications and various medical purposes, such as soft tissue surgery.

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