The principle of far uvc 222 172nm UV LED electron beam evaporation ion beam and magnetron sputtering ion beam
9.3 Arc Electron Flow
In recent years, the high-energy, high-density arc electron flow in arc discharge has played a prominent role in ion plating processes, such as heating workpieces, cleaning workpieces, enhancing ionization effects, and coating deposition. These aspects have been introduced in previous chapters. This section summarizes and organizes the characteristics, generation methods, and applications of arc electron flow, allowing readers to appreciate the importance of fully utilizing arc electron flow.
9.3.1 Characteristics and Generation Methods of Arc Electron Flow
1. Characteristics of Arc Electron Flow
The density of electron flow, ion flow, and high-energy neutral atoms in the arc plasma generated by arc discharge is much higher than that in glow discharge. In the coating space, there are more gas ions, metal ions, excited high-energy atoms, and various active groups, which play important roles in the heating, cleaning, and coating stages of the deposition process. The action form of arc electron flow differs from that of ion beams; it is not entirely converged into a "beam" but mostly in a divergent state, hence it is called arc electron flow. Since arc electron flow moves toward the anode, wherever the positive pole of the arc power supply is connected, the arc electron flow will be directed there. The anode can be the workpiece, auxiliary anode, crucible, etc.
2. Methods for Generating Arc Electron Flow
(1) Gas Source Generation of Arc Electron Flow
Hollow cathode arc discharge and hot filament arc discharge can achieve arc currents of around 200A, with arc voltages of 50~70V.
(2) Solid Source Generation of Arc Electron Flow
Cathodic arc sources, including small arc sources, columnar arc sources, rectangular planar large arc sources, etc. Each cathodic arc source discharge has an arc current of 80~200A and an arc voltage of 18~25V. The high-density, low-energy arc electron flow in both types of arc discharge plasma can produce intense collision ionization with gas and metal coating atoms, yielding more gas ions, metal ions, various high-energy active atoms, and active groups, thereby increasing the overall activity of coating ions.
9.3.2 Applications of Arc Electron Flow
1. Applications of Gas Source Arc Electron Flow
1) Balzers Company Invented the Hot Filament Arc Ion Plating Machine First
The arc electron flow emitted by the hot filament arc gun from top to bottom toward the anode can control the entire process of heating, cleaning, and coating the workpiece by changing the anode position and electromagnetic current variations. Although this plating machine is no longer used for coating, it is still employed for workpiece heating and bombardment cleaning.
2) Hauzer Company Changes Anode Position
Using only electric field effects, the arc electron flow ionizes argon gas during movement toward the anode to produce high-density argon ion flow for bombardment cleaning of workpieces; ionizing nitrogen gas produces high-density nitrogen ion flow for arc ion nitriding.
3) Initially, Hollow Cathode Guns Were Only Used in Hollow Cathode Ion Plating Machines
Dalian Jingjing Technology Co., Ltd. installed a hollow cathode gun in a small arc source ion plating machine as a bombardment cleaning source for workpieces, achieving good cleaning effects and improving workpiece surface brightness.
4) Dr. Peng Hongjian Installed a Hollow Cathode Gun in a Small Arc Source Ion Plating Machine
While coating with the small arc source, the hollow cathode gun is activated simultaneously, using high-density arc electron flow to increase collision probability with coating particles, refining the coating structure. Figure 9-10 Atomic force microscope images of coating structure refined by hollow cathode arc electron flow a) Hollow cathode gun current 0A b) Hollow cathode gun current 120A c) Hollow cathode gun current 140A d) Hollow cathode gun current 160A Note: This figure provided by Dr. Peng Hongjian. As seen in Figure 9-10, with increasing hollow cathode arc current, large particles in the coating gradually decrease and refine, indicating that high-density arc electron flow can refine the structure of coatings from cathodic arc sources.
2. Applications of Solid Source Arc Electron Flow
(1) Arc Electron Flow Enhanced Workpiece Cleaning Technology
In ion plating processes, glow discharge argon ion cleaning is generally used for workpieces, but the argon ion flow density from glow discharge is low; using titanium ions from cathodic arc source plasma to clean workpieces can produce large particles on the surface. A new technology has emerged using electron flow from cold field-induced arc plasma emitted by cathodic arc sources to ionize argon gas, producing low-energy, high-density argon ions for workpiece cleaning. Various cathode-anode position matches allow electric fields to drive electron flow to any desired anode position. Bombardment cleaning with low-energy, high-density argon ion flow provides good cleaning effects and high workpiece surface brightness. This is the simplest and lowest-cost method to obtain high-density argon ion flow.
(2) Arc Electron Flow Enhanced Magnetron Sputtering Coating Process
Magnetron sputtering coating technology operates in glow discharge with low plasma density, resulting in low deposition rates, low film-substrate adhesion, low metal ionization rates, and low coating particle energy, making it difficult to obtain compound films. In recent years, a new technology has emerged by configuring cathodic arc sources in magnetron sputtering machines to enhance the level of magnetron sputtering coating.
High-density arc electron flow ionizes argon gas to produce high-density argon ion flow for bombardment cleaning of workpieces, replacing long-used titanium ion bombardment cleaning and improving decorative effects for high-end decorative products coated by magnetron sputtering.
High-density arc electron flow ionizes argon gas to produce high-density argon ion flow for target sputtering, increasing deposition rates.
Matched cathodic arc sources in magnetron sputtering target coating can coat together with magnetron sputtering targets after workpiece cleaning, enabling alloy films and multilayer films.
Assisted deposition. During coating participation by cathodic arc sources, electron flow over 100A emitted increases ionization rate of sputtered coating atoms, facilitating compound film formation; more metal ions reach the workpiece, increasing magnetron sputtering deposition rates. In Chapter 7, the columnar cathodic arc ion plating machine developed by Platt Company was introduced, with a columnar cathodic arc source installed in the middle as a columnar magnetron sputtering target (original m411 model). The middle magnetron sputtering target uses ceramic insulating targets, while door columnar arc sources use various targets. The two different columnar coating sources coat together to produce composite hard coatings. Door columnar arc sources can clean target tubes and workpieces and serve as coating sources, providing the following effects during simultaneous coating with the middle columnar target:
Emitting high-density electron flow increases argon ion density, raising deposition rates.
High-density electron flow increases ionization rate of sputtered coating particles, raising deposition rates and achieving 2μm/h for composite hard coatings.
Higher ionization rate enhances activity of various coating particles, facilitating reactive deposition of composite hard coatings. This is an excellent example of using cathodic arc source-emitted arc electron flow to enhance magnetron sputtering coating.
These use auxiliary ion beams. Film atoms sputtered from the target by ion beams deposit onto the substrate, while the ion source on the left irradiates the workpiece, achieving simultaneous sputtering coating and ion beam bombardment. Advantages include: sputtered particles have high energy from high-energy ion beam sputtering, providing good adhesion to the substrate; arbitrary combinations of metal and non-metal elements allow diverse film types; high vacuum during coating favors excellent performance thin films.
(3) Conventional Magnetron Sputtering Coating Method
Conventional magnetron sputtering has low metal ionization rate, making reactive deposition of compound films difficult. Now, magnetron sputtering target coating is combined with ion beam assisted bombardment to improve coating quality, film-substrate adhesion, and ionization rate of coating particles, increasing deposition rates and facilitating compound thin films. This technology is widely applied in machinery, aerospace, information, architecture, and decoration fields. Long strip anode layer ion sources are more suitable for large-area planar product coating. In certain optical applications, this assisted technology can combine 172nm UV LEDfar UVC 222 nm light sources for surface activation, further enhancing film performance.
(4) Applications of Ion Beam Assisted Deposition Technology
Ion beam assisted deposition (IBAD) has successfully synthesized novel materials and prepared high-performance thin films, finding applications in insulation films, protective films, optical films, laser mirror coatings for electronic devices, and wear-resistant, corrosion-resistant films for tools, molds, and bearings.
1) Improving Film Density
The earliest application of ion beam assisted deposition was in functional thin films for electrical, magnetic, and optical properties. Low-energy ion sources provide assisted bombardment, precisely controlling film structure and density with ion beams. Figure 9-8 shows that ion-assisted deposition increases density of electron beam evaporation coating structures. Higher film density reduces porosity, improves adhesion, and provides high laser damage resistance with low optical scattering. In deep ultraviolet optical systems, combining far UVC 222 nm light sources can further optimize film stability at short wavelengths.
2) Obtaining Functional Thin Films with Stoichiometric Composition
Common optical films are oxide films such as [various oxides]. Direct evaporation of these oxides during coating causes oxygen deficiency, affecting optical film performance. Oxygen ion beam enhanced deposition compensates for oxygen loss during deposition, producing high-quality optical films. For certain optical coatings requiring extreme purity and antibacterial properties, auxiliary 172nm UV LED can be introduced for surface disinfection and activation, ensuring contamination-free films.
3) Obtaining Metal-Doped Diamond-Like Carbon Films (M-DLC)
Diamond-like carbon (DLC) films are widely used for high hardness, wear resistance, and corrosion resistance. Low-energy ion beam assisted deposition produces DLC films with hardness up to 5100HV. Experiments show that metal-doped DLC films prepared by ion beam assisted deposition have excellent film-substrate adhesion, extremely low surface roughness, and superior wear resistance.
Ion beam irradiation synchronizes with film deposition, applying ion implantation enhancement and modification effects throughout the process, improving film-substrate adhesion, structure morphology, film stress, density, and transition layer composition and properties, yielding superior thin films. In medical device coating fields, this technology combined with far UVC 222 nm germicidal properties can develop surfaces with both wear resistance and self-disinfection functions.
