The properties of the thin film are determined by the manufacturing method, and different methods have their own advantages and disadvantages. Commonly used preparation processes include magnetron sputtering, chemical vapor deposition, vacuum evaporation, pulsed laser deposition, etc. Among them, magnetron sputtering deposition technology has been widely researched and applied due to its high film formation rate and good uniformity.
Magnetron Sputtering
The basic principle of the method is that under the action of electric and magnetic fields, the accelerated high-energy particles (A, +) bombard the surface of the target, and after the energy is exchanged, the atoms on the surface of the target escape from the original lattice, and finally, the sputtering particles are deposited on the surface of the substrate and react with oxygen atoms to form an oxide film. The magnetron sputtering process is characterized by excellent optical and electrical properties of the film deposited at low temperatures. In addition, it has the advantages of a high deposition rate, low substrate temperature, good film adhesion, easy to control, and large-area film formation. Therefore, it has become the most researched and widely used film-forming technology in industrial production today as well as a research hotspot in ITO film preparation technology.
Chemical Vapor Deposition
The chemical vapor deposition method is a process in which a gaseous reactant (including a gaseous reactant that becomes a vaporized condensed matter after evaporation) is chemically reacted on the surface of the substrate to deposit a film. This chemical reaction occurring on the surface of the substrate is usually the thermal decomposition and in-situ oxidation of the source material. The reaction system selected by the CVD method must satisfy:
(1) At the deposition temperature, the reactant must have a sufficiently high vapor pressure;
(2) The chemical reaction product must be in a gaseous state except for the solid matter deposited on the substrate;
(3) The vapor pressure of the deposit should be low enough to ensure good adsorption on a substrate having a certain temperature.
Vacuum Evaporation
The vacuum evaporation method is a method in which a raw material of a to-be-formed film in an evaporation vessel is vaporized from a surface to form a vapor stream, and is incident on a surface of the substrate to react with a gas to form a film in a vacuum chamber. A high-quality ITO film can be prepared by the electron beam evaporation deposition method, in which the evaporation substance is In2O3 doped with SnO2, and the mass percentage of SnO2 is 10%. Under suitable process conditions, the deposited film has a minimum resistivity of 4×10-4 Ω•cm and an average transmittance in the visible range of more than 90%.
Pulsed Laser Deposition
The pulsed laser deposition (PLD) process is a very competitive new vacuum physical deposition process developed in recent years. Compared with other processes, it has the advantages of precise control of stoichiometry, synthesis, and deposition, and no requirement for the shape and surface quality of the target, so the surface of the solid material can be processed without affecting the material body.
Stanford Advanced Materials(SAM) is a global sputtering targets manufacturer which supplies high-quality and consistent products to meet our customers’ R&D and production needs. Please visit https://www.sputtertargets.net/ for more information.
For most people who could not afford a pure gold watch, a gold coating may be a good choice for them. However, since it is a thin film coating, it is inevitable that the gold color would fade out. So the primary consideration in choosing the coating material/method is durability. If you want to give your watch a durable coat, you really should think about PVD coating.
What is PVD coating?
PVD coating, or Physical Vapor Deposition, refers to a variety of vacuum deposition techniques where solid metal is vaporized to produce thin films and coating. The main methods of physical vapor deposition include vacuum evaporation, sputtering deposition, arc plasma plating, ion plating, etc. PVD film has fast deposition speed as well as strong adhesion, good diffraction, and a wide application range.
Maybe you will find it not easy to understand it since PVD is a physical terminology. But actually, as a watch lover, you should just know that PVD coating can provide a metal coat to your watch, making it more beautiful and durable.
Why should you choose PVD coating?
PVD coating has high hardness, high wear resistance, low friction coefficient, good corrosion resistance, and chemical stability. So PVD coating would definitely have a longer lifetime than other traditional coatings. Apart from durability, PVD coating provides multiple kinds of metallic colors, such as gold(TiN), rose gold(TiAlN), silver(Cr2N), brass(ZrN), light grey(TiC), and so on. You will always find the one you like.
More tips
If you are going to give your watch a PVD coating after reading this blog, I’d like to help you save time in choosing the coating materials. Please consider Stanford Advanced Materials (SAM), which is a global supplier of various technical-grade coating materials as well as high-purity chemicals (up to 99.99999%). All of the coating materials we talked about above can be found on SAM’s website. We ensure that you can get your watch the most durable coat here.
At present, reactive sputtering deposition is a well-established sputter coating technology and is widely used for industrial coating deposition to produce thin layers for high-added value products, such as flat panel displays, solar cells, optical components, and decorative finishes.
Definition
In the process of reactive sputtering, a target material is sputtered in the presence of a gas or a mixture of gasses that will react with the target material to prepare a compound film of a predetermined chemical ratio. Reactive sputtering is most often practiced using one or more magnetron sputtering cathodes. Therefore, it is also called reactive magnetron sputtering.
Sputtering Target
Sputtering targets can be divided into metal targets, alloy targets, ceramic targets, etc. Metal sputtering targets can be used to produce compound materials. For example, a titanium sputtering target can be used to produce coatings such as TiO2, TiN, and Ti-O-N. Apart from it, titanium targets can also be used to produce any of the aforementioned different compositions as well as boride and carbide films. Compared with the compound target, the metal target has the advantage of longer service life.
Reactive gases
In most cases, Argon is the main gas used in reactive sputtering as well as other sputter coating methods. It has to be mentioned that the amount of a reactive gas introduced into a process chamber should be strictly controlled in order to either achieve a certain amount of doping or to produce a fully reacted compound. Here is a list of other gasses used in reactive sputtering).
Gasses
Uses
Oxygen (O2)
deposition of oxide films (e.g. Al2O3, SiO2, TiO2, HfO2, ZrO2, Nb2O5, AZO, ITO)
Nitrogen (N2)
deposition of nitride films (e.g. TiN, ZrN, CrN, AlN, Si3N4, AlCrN, TiAlN)
Carbon dioxide (CO2)
deposition of oxide coatings
Acetylene (C2H2)
deposition of metal-DLC, hydrogenated carbide, carbo-nitride films
Methane (CH4)
similar applications as for C2H2
Several reactive gasses can be mixed in order to deposit a multi-component functional thin film. Additional reactive gas is sometimes used to enhance a certain deposition process (e.g. addition of N2 in the SiO2 reactive sputtering process).
Application
Coatings and films produced by Reactive Magnetron Sputtering can be used in a large variety of products such as OLED devices, optical antireflective coatings, and decorative coatings.
Sputtering targets are materials that are indispensable during the sputtering process in the coating industry. Uniformity is an indicator used to value the quality of the coated film. Usually, there are two factors that determine the coating uniformity: the length of the targets and the distance between the target and the substrate.
Length of the sputtering targets
The length of the target is an important factor in producing a coating with good uniformity, because it decides which construction method to be used. It’s better you consider the length of certain monolithic targets during the process requirements planning phase in order to achieve good uniformity.
Suitable target length depends on the orientation of the sputtering target materials and how much weight the target flanges can support without plastically deforming or breaking which can occur for brittle materials. For example, ceramic targets are usually brittle and usually need to be bonded with a backing tube, so the length of ceramic targets cannot be too long, otherwise, they will easily break into pieces. In addition, people usually joined small ceramic targets together to produce the large-area ceramic thin film in the case.
Distance between the target and Substrate
The other factor to define the achievable uniformity of the obtained film is the distance between the sputtering target and the substrate. The larger the distance is, the poorer the uniformity is achieved on the substrate. To be noted, the distance is not stable during the process: it keeps increasing as the target materials keep being consumed and eroding. Therefore, generally speaking, the density of the coating is not uniform, and the worst process uniformity occurs when the sputtering ends.
In general, the distance between the target and the substrate is measured before the start of sputtering, so that the uniformity we calculated is theoretically the best, or the most achievable. But in fact, at the end of the sputtering, the initial uniformity specification could not be reached due to the increase in the distance. The specific difference depends on the initial target thickness.
Magnetic field influences inversely the sputtering voltage. In other words, when the magnetic field on the surface of thesputtering target increases, the operating voltage of magnetron sputtering will decrease. It happens because the sputter-etched surface of the target gets closer to the strong magnetic field of the permanent magnet behind the target. To be noted, when the magnetic field strength increases above 0.1T, its effect on the sputtering voltage is no longer obvious.
In order to reduce the influence of this factor, the thickness of the sputtered material is not arbitrary, but limited. In general, thicker non-magnetic targets can be used in stronger magnetic fields.
Material Type
Different target materials also affect the sputtering voltage. Here are examples of ITO, copper, aluminum, titanium, manganese, and chromium target.
Sputtering Target
Sputtering Voltage
Indium Tin Oxide (ITO)
≈200V
Copper (Cu)
Aluminum (Al)
Titanium (Ti)
400~600V
Manganese (Mn)
Chromium (Cr)
>700V
Gas Pressure
Working gas pressure
Under the condition that various parameters (such as environmental conditions, power control panel parameters, etc.) remain unchanged, the increase of the working gas pressure will reduce the magnetic sputtering voltage.
Reactive gas pressure
On contrary, under the determined environment and constant power source, the increase of reactive gas pressure will result in the increase of magnetic sputtering voltage.
Distance Between Cathode & Anode
The distance between the cathode and anode in vacuum gas discharge can have a certain effect on the sputtering voltage. If the distance is too large, the internal resistance of the equivalent gas discharge is mainly determined by the plasma equivalent internal resistance. Conversely, if the distance is too small, the internal resistance of the plasma discharge will be small.
When the magnetron target ignited and enters the normal sputtering, if the distance between the cathode and anode is too small, although the sputtering current has reached the process setting value, the target sputtering voltage is still low.
Most modern buildings have begun to use large areas of glass for lighting, and its biggest advantage is that it can bring us brighter light and a wider view. However, since the heat energy transmitted through the glass is much higher than the surrounding walls, the energy consumption of the entire building increases significantly. In order to solve this problem, people have begun to study and apply large-area Low-E glass.
Low-E glass is commonly used in building construction because of its ability to save energy, control light, and for aesthetics. The sputtering target material is one of the essential components for making low-e glass, so this article will introduce 3 factors of target quality that influence large-area coating of low-E glass.
The shape of the target materials
For large-area coating, commonly used targets include planar targets and rotatory targets according to their shapes. The shape of the target affects the stability and film properties of the magnetron sputtering coating, as well as the utilization rate of the target. Therefore, the coating quality and production efficiency can be improved by changing the shape design of the target, and the cost can be saved.
Planar targets and rotatory targets
Relative density & porosity of the target
The relative density of the target is the ratio of the actual density to the theoretical density. The theoretical density of a single-component target is the crystal density, and the theoretical density of an alloy or compound target is calculated from the theoretical density of each component and its proportion in the alloy or mixture.
If the target material is loose and porous, it will absorb more impurities and moisture, which are the main pollution sources in the coating process. These impurities will hinder the rapid acquisition of high vacuum, easily lead to electrical discharge during the sputtering process, and even burn out the target. Find high-quality target material here: https://www.sputtertargets.net/
Target grain size and crystallographic direction
For targets of the same composition, the one with the smaller grain size has a faster deposition rate. This is mainly due to the fact that grain boundaries are more vulnerable to attack during the sputtering process, and the more grain boundaries, the faster the film formation.
In addition, the grain size also affects the quality of the film formation. For example, in the production process of Low-E glass, NiCr thin-film is used as the protective layer of the infrared reflection layer Ag, and its quality has a great influence on the coating products. Since the extinction coefficient of the NiCr film is relatively large, it is generally plated very thinly (about 3nm). If the grain size is too large and the sputtering time is short, the compactness of the film will be poor, the protective effect of the Ag layer will be reduced, and the coating product will be oxidized and removed.
Conclusion
The shape of the target mainly affects the utilization rate of the target material, and a reasonable size design can improve the utilization rate of the target material and save costs. The smaller the grain size, the faster the coating rate and the better the uniformity. The higher the purity and density, the lower the porosity, the better the quality of the film formation, and the lower the probability of slag removal by discharge.
Electron beam deposition is a form of physical vapor deposition (PVD) in which the target anode material is bombarded with a stream of electrons generated by a tungsten filament. Electron beam thin film deposition techniques are widely used in R&D as well as in mass production applications.
Electron beam deposition is performed in a vacuum, typically starting the process at levels below 10-5 Torr. Once a suitable vacuum is reached, a tungsten filament in the electron beam source emits a stream of electrons. This electron beam can be generated in various ways, including thermionic emission, field electron emission, or ion arc source, depending on the design of the source and associated power supply.
In all cases, the negatively charged electrons are attracted to the positively charged anode material. The generated electron beam is accelerated to high kinetic energy and directed towards the material to be deposited on the substrate. This energy is converted into heat by interacting with the atoms of the evaporated material.
The purpose of generating a stream of electrons in an electron beam source is to heat the deposited material to a temperature above a vapor pressure threshold at a given background pressure. The vapor stream is then condensed onto the surface of the substrate.
Schematic representation of electron beam evaporation system depicting various parts.. Mohanty, P. & Kabiraj, Debdulal & Mandal, R.K. & Kulriya, Pawan Kumar & Sinha, Ask & Rath, Chandana. (2014). Evidence of room temperature ferromagnetism in argon/oxygen annealed TiO2 thin films deposited by electron beam evaporation technique. Journal of Magnetism and Magnetic Materials. 355. 240–245. 10.1016/j.jmmm.2013.12.025.
Deposition Rate
As with all thermal evaporation systems, the electron beam deposition rate depends on the temperature of the material being deposited and the vapor pressure (physical constant) of that material. For elemental materials, there is a fixed vapor pressure for any particular background pressure (vacuum) and material temperature. However, for alloys or composites, there may be different partial pressures associated with each component.
Compared with Sputter Coating
Unlike sputter deposition, where individual atoms arrive at the substrate surface with very high velocity and momentum, the thermally generated vapor stream arrives at the substrate surface at a considerably lower velocity, but a much greater velocity. In other words, e-beam deposition rates can be orders of magnitude greater than sputter deposition rates, making e-beam coatings very beneficial for high volume production or thick film requirements. One disadvantage, however, is that the material tends to condense directly on the substrate surface due to the different kinetic energy of the arriving species during electron beam evaporation than that of the sputtered species. In contrast, atoms of sputtered materials tend to penetrate several atomic layers (or more) to the substrate surface before losing momentum and then establishing cohesive bonds in nucleation structures and film growth. Thus sputtered films tend to provide better adhesion properties than thermally evaporated materials.
Molybdenum target inspection is a new digital imaging technology that combines traditional radiology technology with modern computer technology. It finally transforms the ordinary X-ray image into a digital image that can be quantized. The traditional X-ray film technology and the qualitative quality of image quality make it easier for radiologists to find suspicious malignant lesions in mammography, which is considered to be a method to improve the early detection rate of breast cancer.
Advantages
The mammography system has the characteristics of clear imaging, convenient and quick inspection operation, and small radiation dose. The instrument can accurately detect the shape, size, density, and nature of breast hyperplasia, lesions, masses, and calcifications. It can accurately judge and identify calcifications of breast lesions that cannot be identified by color Doppler ultrasound, and is known as the “gold standard” for international breast disease examination.
As a non-invasive method of examination, mammary gland Molybdenum target X-Ray inspection has a relatively small pain in the examination of the breast. The images retained are available for comparison before and after, regardless of the limit of age or body shape. Mammography has now become a routine breast disease examination with a sensitivity of 82% to 89% for breast cancer and a specificity of 87% to 94%.
Molybdenum target mammograms of a patient. (a) and (b) are molybdenum target mammograms of the patient’s left breast from the craniocaudal (CC) and mediolateral oblique (MLO) views, respectively, while (c) and (d) are molybdenum target mammograms of the patient’s right breast from the CC and MLO views, respectively. Sun, Lilei & Jie, Wen & Wang, Junqian & Zhao, Yong & Zhang, Bob & Wu, Jian & xu, Yong. (2022). Two‐view attention‐guided convolutional neural network for mammographic image classification. CAAI Transactions on Intelligence Technology. n/a-n/a. 10.1049/cit2.12096.
Unique value
1 It can be used as a relatively non-invasive method of examination, and it can fully and accurately reflect the structure of the entire breast.
2 Molybdenum target inspection can be used to observe the effects of various physiological factors (such as menstrual cycle, pregnancy, lactation, economic status and endocrine changes) on the mammary gland structure, and can be used for dynamic observation.
3 Benign lesions and malignant tumors of the breast are relatively reliably identified.
4 Breast cancer can be detected early, and even occult breast cancer that is not clinically detectable can be detected.
5 According to the Molybdenum target inspection, some precancerous lesions can be found and can be followed up for observation.
Conclusion
In conclusion, Mammary gland Molybdenum target X-Ray inspection is currently the first choice and the easiest and most reliable non-invasive detection method to diagnose breast diseases. It is relatively less painful, easy to operate, and has high resolution.
Stanford Advanced Materials (SAM) Corporation is a global supplier of various sputtering targets such as metals, alloys, oxides, and ceramic materials which are widely used in the medical industry. We will regularly update knowledge and interesting stories of sputtering targets on our website. If you are interested, please visit https://www.sputtertargets.net/ for more information.
Thermal evaporation, or vacuum evaporation, refers to the vaporization of evaporation materials. By heating evaporation materials to a certain temperature, the vapor pressure becomes appreciable, and the surface or molecules are lost from the surface in the vacuum. Vaporization can come from the surface of a liquid or from the surface of a solid. The equilibrium vapor pressure (EVP) is 10-2 Torr. Some evaporation materials have a vapor pressure so that they can sublime or evaporate (e.g., titanium) at temperatures near their melting points. Some composites sublime and some evaporate.
Studies about thermal evaporation in vacuum began in the late 19th century. In the 1880s, H. Hertz and S. Stefan determined the equilibrium vapor pressure, but they did not consider using of vapor to form thin films.In 1884, Thomas Edison applied for a patent covering the vacuum evaporation of “heating to incandescence” and film deposition. However, his patent makes no mention of the evaporation of molten materials, and many materials do not evaporate at an appreciable rate until they reach or exceed their melting point. Edison did not use the process in any application, presumably because radiant heating from the source was detrimental to the vacuum materials available at the time.
In 1887, Nahrwold reported the formation of platinum thin films by subliming platinum evaporation materials in a vacuum. Therefore, some believe that he was the first to use thermal evaporation to form thin films in a vacuum.
In 1907, Soddy proposed that it would be possible to evaporate solid calcium onto the surface to reduce the residual pressure in the sealed tube. This is believed to be the first “reactive deposition” process in history.
In 1909, Knudsen proposed the “Knudsen Cosine Distribution Law” for vapor from a point source. After 6 years, he refined the free surface evaporation rate as a function of equilibrium vapor pressure and ambient pressure. The resulting equation is called the Hertz-Knudsen surface equation for free-surface vaporization. Honig summarized the equilibrium vapor pressure data for 1957.
Various Types of Evaporation Pellets
From the early 1900s to the mid-1900s
In 1912, von Pohl and Pringsheim reported the formation of thin films by evaporating solid materials in a vacuum using a magnesia crucible as a container. Their experiments are sometimes considered the first thin-film deposition by thermal evaporation in a vacuum.
In 1931, Ritschl reported thermal evaporation of silver from a tungsten wire basket to form half-silvered mirrors. And he is often credited with being the first to use evaporation from a filament to form a film in a vacuum.
Evaporating Aluminum Thin-Film
Cartwright and Strong reported on the evaporation of metals from tungsten wire baskets in the same year. However, their attempts to vaporize aluminum failed, because molten aluminum would wet with the tungsten filament to form an alloy, which causes it to “burn out” when there is a relatively large volume of molten aluminum.
Aluminum thin films were not successfully produced by vacuum evaporation until 1933, when John Strong used large gauge tungsten filaments wetted by molten aluminum. John has done extensive development work for astronomical mirror coatings using the aluminothermic evaporation of multiple tungsten wires. Strong, with the help of designer Bruce Rule, used multiple filaments and a 19-foot diameter vacuum chamber to aluminize the 200-inch Palomar telescope mirror in 1947.
AR Coating
In 1933 A.H. Pfund vacuum-deposited the first single-layer (AR) coating (ZnS) while reporting on making beamsplitters and Bauer mentioned AR coatings in his work on the properties of alkali halides.
The Germans deposited CaF2 a nd MgF2 AR coatings during WWII. Plasma cleaning of glass surfaces is reported to have been used by Bauer at the Zeiss Company in 1934. The Schott Company (Germany) was also reported to have deposited three-layer AR coatings by flame-pyrolysis CVD during WWII.
In 1935, based on Bauer’s observation, A. Smakula of the Zeiss Company developed and patented AR coatings on camera lenses. The patent was immediately classified as a military secret and was not revealed until 1940.
In1936, Strong reported depositing AR coatings on glass.
In 1939, Cartwright and Turner deposited the first two-layer AR coatings.
One of the first major uses of coated lenses was on the projection lenses for the movie Gone With the Wind, which opened in December 1939. The AR-coated lenses gained importance in WWII for their light-gathering ability in such instruments as rangefinders and the Norden Bombsight.
The AR coated lenses gained importance in WWII for their light-gathering ability in such instruments as rangefinders and the Norden Bombsight. During WWII, baking of MgF2 films to increase their durability was developed by D.A. Lyon of the U.S. Naval Gun Factory. The baking step required that the lens makers coat the lens elements prior to assembly into compound lenses.
In 1943, the U.S. Army sponsored a conference on “Application of Metallic Fluoride Reflection Reducing Films to Optical Elements.” The proceedings of this conference are probably the first extensive publication on coating optical elements.
In 1958, the U.S. military formally approved the use of “vacuum cadmium plating” (VacCad) for application as corrosion protecmium. In recent years Physical Vapor Deposition (PVD) methods have been used to replace electroplating in a number of applications to avoid the water pollution associated with electroplating.
From the mid-1900s to the late 1900s
E-beam Evaporation Development
In 1949, Pierce described the “long-focus” electron beam gun for melting and evaporation in a vacuum. The long focus gun suffers from shorting due to the deposition of evaporated material on the filament insulators that are in the line of sight of the evaporating material. Deposition rates as high as 50 µm/s have been reported using e-beam evaporation. To avoid exposure of the filament to the vapor flux, bent-beam electron evaporators were developed.
In 1951, L. Holland patented the use of accelerated electrons to melt and evaporate the tip of a wire (“pendant drop”), which involved no filament or crucible.
In 1968, Hanks filed a patent on a 270° bent beam electron beam evaporation source that has become the most widely used design. Mastering the electron beam allows the energy of the electron beam to be distributed over the surface.
In 1970, Kurz was using an electron-beam system to evaporate gold for web coating. In electron beam evaporation a high negative “self-bias” can be generated on the surface of an insulating material or on an electrically isolated fixture. This bias can result in high-energy ion bombardment of the self-biased surface.
In 1971, Chambers and Carmichael avoided that problem by having the beam pass through a small hole in a thin sheet in a section of a plate that separated the deposition chamber from the chamber where the filament was located. This allowed a plasma to be formed in the deposition chamber while the filament chamber was kept under a good vacuum. The plasma in the deposition chamber allowed ion bombardment of the depositing film material as well as “activation” of reactive gas.
In 1972, the use of a hollow cathode electron emitter for e-beam evaporation was reported by J.R. Morley and H. Smith.
In 1978 H.R. Smith described a unique horizontally emitting electron beam (EB) vapor source. The source used a rotating crucible to retain the molten material, and its function was to coat large vertical glass plates. A number of thermoelectron-emitter e-beam source designs followed, including rod-fed sources and “multi-pocket” sources. The high voltage on the filament prevented the source from being used in a plasma where ions accelerated to the cathodic filament; this caused rapid sputter-erosion of the filament.
Crucible material Development
In 1951 Picard and Joy described the use of evaporation of materials from an RF-heated crucible. In 1966 Ames, Kaplan, and Roland reported the development of an electrically conductive TiB/BN composite ceramic (Union Carbide Co., UCAR™) crucible material that was compatible with molten aluminum.
Directed Deposition Development
The directed deposition is confining the vapor flux to one axis by eliminating off-axis components of the flux. Directed deposition can be attained by the collimation of the vaporized material. This was done in evaporation by Hibi (1952), who positioned a tube between the source and the substrate. Collimation was also attained by H. Fuchs and H. Gleiter in their studies of the effects of atom velocity on film formation using a rotating, spiral-groove, velocity selector.
In 1983, Ney described a source that emitted a gold atom beam with a 2° divergence. Recently, “directed deposition” has been obtained using a flux of thermal evaporated material projected into a directed gas flow.
Thermally Evaporating Development
When thermally evaporating alloys, the material is vaporized with a composition in accordance with Raoult’s Law (1887). This means that the deposited film will have a continuously varying composition unless very strict conditions are met as to the volume of the molten pool using a replenishing source. One way of avoiding the problem is by “flash evaporation” of small volumes of material.
In 1948, L. Harris and B.M. Siegel reported flash evaporation by dropping small amounts of material on a very hot surface so that all of the material was vaporized before the next material arrived on the hot surface.
In 1964, Smith and Hunt described a method for depositing continuous strips of alloy foils by evaporation. Other free-standing thin-film structures are also deposited, such as beryllium Xray windows and nuclear targets.
To learn more about the history of thermal evaporation, please follow our website. We will update articles about evaporation pellets every week, so stay tuned. If you want to buy high-quality evaporating pellets, please visit our official website for coating materials at https://www.sputtertargets.net/.
In recent years, the rapid economic development and the continuous improvement of people’s living standards have led to the continuous emergence of high-tech thin-film products, especially in the field of electronic materials and components. Vacuum coating technology has also gained significant application in this field.
At present, the common film-forming methods include vapor-phase film-forming method, oxidation method, ion implantation method, diffusion method, electroplating method, coating method, liquid-phase growth method, etc. The vapor generation method can be further subdivided into physical vapor deposition, chemical vapor deposition, and discharge polymerization.
Principle
The experiments listed in this article are related to physical vapor deposition coatings. This method is basically carried out under vacuum, so it is called vacuum coating technology.
Vacuum evaporation, sputter coating, and ion plating are commonly referred to as basic physical vapor deposition thin film preparation techniques. The vacuum evaporation coating method is a method in which the evaporation material of a film to be formed in a vaporization chamber is heated in a vacuum chamber, and atoms or molecules are vaporized from the surface to form a vapor stream, which is incident on the surface of the substrate and condensed to form a solid film.
Purposes
To familiarize yourself with the operating procedures and methods obtained by vacuum;
In order to understand the principle and method of evaporation coating;
To learn how to use evaporation coating technology.
Results
(1) Vacuum conditions during evaporation
When the average free path of the vapor molecules in the vacuum vessel is greater than the distance between the evaporation source and the substrate (called the steaming distance), sufficient vacuum conditions are obtained. For this reason, it is necessary to increase the mean free path of the residual gas to reduce the collision probability of the vapor molecules with the residual gas molecules, and to evacuate the vacuum chamber to a high vacuum.
(2) How to choose evaporation source selection
1 It should have good thermal stability, chemical inactivity; the vapor pressure of the heater itself is sufficient to reach the evaporation temperature.
2 Its melting point should be higher than the evaporation temperature of the evaporated material. The heater should have a large enough heat capacity.
3 The mutual melting of the evaporated material and the evaporation source material must be very low, and it is difficult to form an alloy.
4 The material used for the coil-shaped evaporation source is required to have a good wetting with the evaporation material and a large surface tension.
5 For a case where it is difficult to form a filament, or when the surface tension of the evaporation material and the filament evaporation source is small, a boat-shaped evaporation source can be used.
(3) Main physical processes of thermal evaporation coating
1 Using various forms of thermal energy conversion to vaporize or sublimate the coating material into gaseous particles (atoms, molecules or atomic groups) with certain energy (0.1~0.3eV);
2 Gaseous particles are transported to the substrate by a substantially collision-free linear motion;
3 Particles are deposited on the surface of the substrate and agglomerated into a film.
(4) Factors affecting the quality and thickness of vacuum coating
There are many factors affecting the quality and thickness of the vacuum coating, including the degree of vacuum, the shape of the evaporation source, the position of the substrate, and the temperature of the evaporation source. The solid matter has very low evaporation at normal temperature and normal pressure. The higher the degree of vacuum, the easier it is for the molecules of the evaporation source material to scatter away from the surface of the material. The fewer molecules in the vacuum chamber, the lower the probability that the evaporating molecules will collide with the gas molecules, so that the surface of the substrate can be reached unobstructed straight.
