The electrons irradiated by the light beam will absorb the energy of photons, but the mechanism follows the all-or-nothing standard. All the energy of photons must be absorbed to overcome the work function, otherwise this energy will be released. If the energy absorbed by the electron can overcome the work function and there is residual energy, this residual energy will become the kinetic energy of the electron after being emitted.
Work function w is the minimum energy required to emit photoelectrons from a metal surface. From the point of view of frequency conversion, the frequency of photons must be greater than the limit frequency of metal features in order to give electrons enough energy to overcome the work function. The relationship between work function and limit frequency v0 is
W=h*v0
Where h is Planck constant, which is the energy of photons with optical frequency h*v0.
After overcoming the work function, the maximum kinetic energy Kmax of photoelectrons is
Kmax=hv-W=h(v-v0)
Where hv is the energy carried by photons with optical frequency V and absorbed by electrons.
Actual physics requires that the kinetic energy must be positive, so the optical frequency must be greater than or equal to the limit frequency before the photoelectric effect can occur. An enlightening view on the generation and transformation of light.
[Name] Albert Einstein (Jewish theoretical physicist)
1March 905
There are profound formal differences between physicists' theoretical ideas about the formation of gases or other heavy objects and Maxwell's theory about the so-called electromagnetic process in vacuum space. That is, we think that the state of an object is completely determined by the coordinates and speeds of a large number of atoms and electrons; On the contrary, in order to determine the electromagnetic state of a space, we need to use a continuous space function. Therefore, if we want to completely determine the electromagnetic state of a space, we can't think that a finite number of physical quantities is enough. According to Maxwell's theory, for all pure electromagnetic phenomena and the resulting light, energy should be regarded as a continuous spatial function, while according to physicists, the energy of a heavy object should be expressed by the sum of the energy of atoms and electrons. The energy of a heavy object cannot be divided into any number of small parts, but according to Maxwell's theory of light (or, more generally, according to any wave theory), the energy of a light beam emitted by a point light source is continuously distributed in an increasing volume.
The wave theory of light operated by continuous space function has proved to be very excellent in describing pure optical phenomena, and it seems difficult to replace it with any other theory. However, don't forget that optical observation is related to the average value of time, not to the instantaneous value, and although the theories of diffraction, reflection, refraction and dispersion are completely confirmed by experiments, it is still conceivable that when people apply the theory of light operated by continuous space function to the phenomenon of light generation and conversion, this theory will lead to contradictions with experience.
Indeed, in my opinion, the observation of blackbody radiation, photoluminescence, cathode rays produced by ultraviolet light and other phenomena related to the generation and transformation of light seems to be better understood if it is explained by the assumption that the energy of light is not continuously distributed in space. According to the assumption here, the energy of the light beam emitted by a point light source is not continuously distributed in an increasingly large space, but is composed of a limited number of energy photons limited at various points in the space. These energy photons can move, but cannot be divided, and can only be absorbed or generated as a whole.
Next, I will describe my thinking process and list some facts that led me to this path. I hope that the viewpoints to be expounded here may be helpful to some researchers.
A difficult point in the theory of "blackbody radiation" 1
Let's first use Maxwell's theory and electronic theory to examine the following situation. In the space surrounded by the completely reflecting wall, there are a certain number of gas molecules and electrons, which can move freely. When they are very close to each other, they will exert a conservative force on each other, that is, they can collide with each other like gas molecules in the gas [molecular] motion theory. In addition, suppose that a certain number of electrons are bound to a distant point in this space by a certain force, and the direction of the force points to these points, and the magnitude of the force is proportional to the distance between the electrons and each point. When free [gas] molecules and electrons are very close to these [bound] electrons, there should also be conservative [force] interactions between these electrons and free molecules and electrons. We call these electrons bound to space points "oscillators"; They emit electromagnetic waves with a certain period and also absorb electromagnetic waves with the same period.
According to the modern viewpoint about the generation of light, the radiation in the dynamic equilibrium according to Maxwell's theory should be completely equivalent to "blackbody radiation"-at least when we regard all oscillators with frequencies that should be considered as existing.
Let's not consider the radiation emitted and absorbed by the oscillator for the time being, but discuss the dynamic equilibrium conditions compatible with the interaction (or collision) between molecules and electrons. The theory of gas [molecular] motion puts forward the condition of dynamic equilibrium that the average kinetic energy of electron oscillator must be equal to the average kinetic energy of gas molecule translation. If we decompose the motion of the electronic oscillator into three perpendicular [minute] vibrations, then we get the average value of the energy of such a linear [minute] vibration as follows.
Where r is the absolute gas constant, n is the gram equivalent number of "actual molecules" and t is the absolute temperature. Since the average of the kinetic energy and potential energy of the oscillator is equal to time, the energy is equal to the kinetic energy of the free monoatomic gas molecule. If, for whatever reason-in our case, due to the radiation process-the energy of the oscillator is greater than or less than the time average, then its collision with free electrons and molecules will cause the gas to gain or lose energy with an average not equal to zero. Therefore, in our case, dynamic balance is possible only when each oscillator has average energy.
We further consider the interaction between oscillators and radiation, which also exist in space. Planck once assumed that radiation can be considered as the most disorderly process imaginable. Under this assumption, he deduced the dynamic equilibrium conditions in this case. He found that:
Here is the average energy of the oscillator (each vibration component) with the intrinsic frequency ν, C is the speed of light, ν is the frequency, and it is the energy radiated by the part with the frequency between ν and ν in unit volume.
For radiation with frequency ν, if its energy is neither continuously increased nor continuously decreased, then the following formula is given.
Must be established.
The relationship found as a dynamic equilibrium condition is not only inconsistent with experience, but also shows that it is impossible to talk about any definite energy distribution between ether and matter in our picture. Because the wider the vibration number range of the selected oscillator, the greater the radiation energy in space will become. In the limit case, we get:
2. Determination of Planck's Basic Constant
Next, we will point out that the determination of the basic constant made by Mr. Planck has nothing to do with the blackbody radiation theory he founded to some extent.
So far, all experiences can satisfy Planck's formula:
Among them,
For large values, that is, for large wavelengths and radiation densities, in the limit case, the formula becomes the following form:
People see that this formula is consistent with Maxwell's theory and electronic theory in L. By making the coefficients of these two formulas equal, we get:
or
That is to say, the weight of a hydrogen atom is100g. This is exactly the value obtained by Mr. Planck, which is in satisfactory agreement with the values obtained by other methods about this quantity.
Therefore, we come to the conclusion that the greater the energy density and wavelength of radiation, the more applicable the theoretical basis we use; But for small wavelength and small radiation density, our theoretical basis is completely inapplicable. (1) abnormal photovoltaic effect:
Photovoltaic effect
Generally, the photovoltaic voltage will not exceed Vg=Eg/e, but the photovoltaic voltage of some thin-film semiconductors will be much higher than Vg under strong white light irradiation, which is the so-called abnormal photovoltaic effect. (A photovoltaic voltage of 5000 volts has been observed)
In the 1970s, it was found that the abnormal photovoltaic effect (APV) of photoferroelectrics can generate voltages of 65,438+000 V to 65,438+0,00000 V, and it only appears in the direction of spontaneous polarization of crystals.
Photovoltage: V=(Jc/(σD+△σl))l
Becquerel effect:
When two identical electrodes are immersed in electrolyte, and one of them is irradiated by light, there will be a potential difference between the two electrodes, which is called becquerel effect.
It is possible to make high-efficiency solar cells by imitating photosynthesis.
(3) Photon traction effect:
When the energy of a photon is not enough to cause the electron-hole laser to irradiate the sample, a potential difference VL can be established at both ends of the sample along the beam direction, and its magnitude is proportional to the optical power, which is called photon traction effect.
(d) Auger effect (1925 French Auger)
Electrons are knocked out from the inner layer of atoms by high-energy photons or electrons, and at the same time, electrons with certain energy (Auger electrons) are generated, so the phenomenon that atoms and molecules are called higher-order ions is called Auger effect.
Application: Auger electron spectrometer is used for surface analysis, which can distinguish the "fingerprints" of different molecules.
photoeffect
(5) photocurrent effect (1927 Pan Ning)
The light-induced voltage (current) change between two discharge tubes is called photocurrent effect.
(1): low-pressure gas (inert gas of about 100Pa) can be discharged.
(2): space charge effect and glow discharge;
There are seven different areas in the discharge tube from cathode to anode:
1: Aston dark area: a thin dark area near the cathode. Reason: The kinetic energy of cathode positive ions bombarding secondary electrons is too small to excite atoms to emit light.
2. Cathode luminous area: a thin luminous layer behind Aston dark area.
3. Dark area of cathode: When electrons reach this area from the cathode, they gain more and more energy, which exceeds the ionization energy of atoms, causing a lot of collision ionization, and the avalanche ionization process takes place here. After ionization, electrons quickly leave, forming strong positive space charges here, causing electric field distribution distortion, and most of the pipe pressure between here and the cathode drops.
The above three areas are cathode potential drop areas.
4. Negative luminous area: it is the area with the strongest luminous intensity. Electrons generate many excitation collisions in the negative glow region, and emit bright glow.
5. Faraday dark region: electrons lose energy in the negative glow region, and there is not enough energy to generate excitation when entering this region.
6. Positive column region: In this region, the electron density is equal to the positive ion density and the net space charge is zero, so it is also called plasma region.
7. Anode area: anode dark area and anode glow area can be seen. Uses: gas discharge devices, such as gas discharge lamps (fluorescent lamps, neon lamps, atomic spectrum lamps, neon lamps), voltage regulators, cold cathode thyratron, etc. Particle beam inversion is realized by using positive column area in laser, cold cathode ion source in particle beam device, plasma etching, thin film sputtering deposition and plasma chemical deposition in semiconductor technology.
Photocurrent effect mechanism: Metastable atoms (with lifetimes of about 10 (-4) s to 10 (-2) s) are easier to ionize than neutral atoms, and more excited atoms, especially metastable atoms, may change the carrier concentration in the discharge tube.
Application of photocurrent spectrum technology: photocurrent spectrum can produce photocurrent effects from ultraviolet, visible, infrared to microwave without the optical system of conventional spectrometer. The photocurrent spectrum has a dynamic range of 8 orders of magnitude, which is an ultra-sensitive spectrum technology with high sensitivity and low noise. (1976 Green et al. confirmed the photocurrent spectrum with laser)
Jiaoxi effect: When the gas capacitor with air or insulating gas as the medium is continuously irradiated by visible light, the low-frequency current flowing through the capacitor will change, which is called Jiaoxi effect.
Malta effect: when there is a metal oxide film on the cathode surface of the discharge tube and positive ions bombard the surface, the secondary electron emission is enhanced, which is called Malta effect.