CZ307110B6 - A method of preparation of black aluminium layers characterized by high optical density and low reflectance using magnetron sputtering, use of precious metal coating for protection and improvement of the properties of these layers and their applications for thermal absorption coverage of anodes - Google Patents

Abstract

The object of the proposed patented method of preparation thin layers (2) of "black" aluminum by vacuum magnetron sputtering techniques, coating application (4) with a precious metal layer (3) for protection and improvement properties of these layers and the application of this coating to heat absorbing anode coverage. For the preparation of layers (2) is used as source material of pure aluminum target and modifying the properties of the layers (3) is appropriate combination of deposition conditions. Black Layers (2) aluminum surface due to the specific nanostructure excellent ultraviolet (UV) absorption properties visible and infrared spectra electromagnetic radiation. The chosen method allows effectively and cheaply prepare these layers for different substrates (eg glass, steel) and is also suitable for covering large areas. Overlaying layer (2) of "black" aluminum a thin layer (3) of precious metal allows another enhancement of the above-mentioned features and, moreover, provides its features protection.

Description

Technical field

The invention relates to the preparation of thin layers of black aluminum characterized by high optical density and low reflectivity by means of the vacuum magnetron sputtering technique and their application for heat-absorbing anode coating.

BACKGROUND OF THE INVENTION

Magnetron sputtering

Magnetron sputtering is a widely used method of thin film preparation with a variety of physical properties and is used in basic research and industry. It allows to cover homogeneously large areas and also cavities (CZ 305631). At present, there are a number of magnetron sputtering techniques where it is possible to use a DC, pulsed DC or AC electrical voltage to drive the discharge. It is possible to work in both inert and reactive atmosphere - reactive sputtering. Magnetron sputtering has minimal environmental impact and is in this respect the preferred technique for thin film preparation [1],

Black aluminum layers

For black aluminum layers, the term black generally means that the layer shows in the visible and near-infrared range: high optical density (D), low reflectance (R) and low diffuse reflectance (Rd) · Some authors use the term black aluminum already for relatively low D values and high R values, D > 0.3 and R < 0.79, however, they prefer D > Applications of black aluminum layers as absorbers are characterized by D> 3, R <0.01 and R _d > 0.08 in the visible and R _D <0.05 in the near infrared region of the spectrum. The preparation and properties of the black aluminum layers have been described for the vacuum vapor deposition technique [2-4], US 3 392 297, CA 1061193. Vacuum vapor deposition takes place in an air atmosphere of 0.13 Pa air pressure of US 3,392,297 or in a pressure range of 0.26 Pa to 1.3 Pa CA 1061193. In the case of vapor deposition and sputtering in an oxygen-containing atmosphere, it is therefore necessary to describe the layers more precisely as sub-stoichiometric black alumina layers. In EP 1 522 606, US 005766827 A and EP 0 732 221 A1, they directly focus on the controlled control of the oxygen content of the prepared layer. EP 1 522 606 describes the deposition of black alumina-based layers by vapor deposition on a sliding film substrate and shows the dependence of their reflectivity on the oxygen content. The sputter deposition of aluminum / oxide and graded layers in the presence of either oxygen, water vapor, sulfur, or hydrogen sulfide in a working atmosphere is described in US 005766827 and EP 0 732 221. The oxygen content of these black aluminum oxide layers was from 19 to 58 at %. Magnetron sputtering is commonly used to prepare shiny thin, electrically conductive layers of aluminum, and for a person skilled in the art, the gloss is defined by a reflectivity of greater than 30%, where the deposition takes place only in an argon atmosphere of 0.1 to 10 Pa. In the field of preparation of black layers, magnetron sputtering was used, for example, for black decorative coating, where it was used for dedusting a combination of two metal targets (titanium and aluminum) in a mixed atmosphere of argon, nitrogen and oxygen to form multilayer titanium nitride / 064 719). Black and colored layers were prepared by magnetron sputtering in an argon atmosphere from a Ti-Al-ON alloy target (US 4,997,538). In the case of black alumina-based layers, the electro-transport properties deteriorate, which may be undesirable for some electrical applications. Method of preparation of black layers

To date, aluminum by means of magnetron sputtering without oxygen atmosphere has not been presented.

Vacuum tube anode coating

For proper performance of the vacuum vacuum tube, it is important to remove excess heat from the inside of the vacuum tube so that the individual components do not overheat. The anode is generally the best cooled part of the vacuum tube and should therefore absorb as much heat radiation as possible. Insufficient absorption of heat radiation leads to an increase in temperature and thus to a complete impairment of the functionality of the whole component. Black - highly absorbent coatings can be used to improve the anode properties. These layers must be able to withstand high vacuum heating above 500 ° C. and should be applicable to metals and their alloys. The layers must also exhibit low vapor pressure (<10 ^{S 6} Pa at 800 K). Several solutions have been developed in the past for the production of Black coatings that have good adhesion to the parent metal by electroplating. In this area, these are mainly black layers based on metallic chromium. These coatings may also contain vanadium or nickel, or both, and may consist of finely divided metal and oxide. However, the current technology of blackening of the copper anode with black chromium appears to be insufficient, mainly due to poor reproducibility of the production. The negative environmental impact of the galvanic production process is also essential [1].

The preparation of absorbent layers for applications in cathode-ray tubes in color screens by means of vacuum vaporization is discussed in the following patent documents. US 2000/0 021 410 describes the preparation of an aluminum / chrome multilayer wherein chromium serves as a heat-absorbing layer. US 3,392,297 and CA 1061193 mention the use of black aluminum layers where the layer serves to provide better heat transfer between the screen mask and the aluminized phosphor. The black aluminum layer is presented only as a modification of the necessary glossy aluminum layer. Thus, it is not clear whether the desired functions of the black aluminum layer for a substrate other than aluminum may be considered. In vacuum tubes, however, materials (metals) other than aluminum, such as copper, are also used for electrodes (anode). CN 102995090 discloses the use of a complex anodization process to prepare a protective layer for vacuum tubes with an anode of aluminum or an aluminum alloy.

Literature:

[1] Abele, E., R. Anderl, and H. Birkhofer, Environmentally-Friendly Product Development: Methods and Tools. 2007: Springer London.

[2] Christiansen, A.B., G.P. Caringal, J.S. Clausen, M. Grajower, H. Taha, U. Levy, N.A. Mortensen, and A. Kristensen, Black metal thin films by deposition on dielectric antireflective motheye nanostructures. Sci Rep, 2015. 5: 10563.

[3] Riesenberg, R., and G. Schmidt, Black Aluminum Films. Vacuum, 1987. 37 (1-2): pp. 183-186.

[4] Crawford, G. H., E.J. Downing, and R.G. Schlemmer, Metal / Metal Oxide Coating, 1984.

SUMMARY OF THE INVENTION

The present invention is based on the actual method of preparing thin black aluminum layers characterized by high optical density and low reflectance by means of a vacuum magnetron sputtering technique, applying a precious metal topsheet to protect and improve the properties of these layers, and utilizing these thin film structures for thermally absorbing anode coating.

Preferably, the same deposition method is used to apply the precious metal top layer. In a preferred embodiment, it is the magnetron sputtering method that streamlines the process.

-2GB 307110 B6

Generally, physical and chemical thin film deposition methods can be used to prepare the precious metal topsheet.

The desired optical properties of black aluminum (high optical density D &gt; 3, low reflectance R &lt; 0.01 and low diffuse reflectance from UV to near infrared region R _D < 0.08) were achieved due to the growth of nano and microstructure morphology layers. It is therefore a highly porous structure. The properties of black aluminum (R _D < 0.07) were further improved by overlaying a thin precious metal layer, preferably gold, silver, platinum, the thickness of the precious metal thin layer being defined in the order of units to tens of nanometers.

In a preferred embodiment, silver having a thickness of 10 to 20 nm is used which provides a reduction in the R _D value of more than 10%. The light absorption in the layers is mainly due to the effect of plasmon resonance, the effect of which depends on the optical properties of the metal used, but also on the nano / microstructure of its surface.

Magnetron sputtering versus vacuum vaporization allows for more precise control of the structure and morphology of the layers, which is crucial for the preparation of absorbent black aluminum layers, due to the greater energy of the particles and various control options.

The growth of the black aluminum layers of the specific morphology described above and the optical properties in dependence on the wavelength. The specific optical properties are characterized by diffuse reflectance, which decreases from R _D = 0.07 to R _D = 0.02 with increasing wavelength from 400 to 2500 nm. This layer was achieved by a combination of deposition conditions, especially deposition in a gas mixture of argon and nitrogen, where the partial pressure of nitrogen ranges from 0.5-10 ^-3 to 2-10 ² Pa and the total pressure ranges from 0.1 to 10 Pa. The total gas flow ranges from 1 to 50 sccm. The coating layers may be deposited on a dielectric, conductive (metal) and semiconductive substrate, which may be of inorganic or organic origin. No additional heating of the substrate is required.

Preferably, a metal is used as the substrate.

The use of magnetron sputtering for protective coating of the anode surface appears to be a far more efficient method than current coating methods.

Clarification of drawings

Giant. 1 shows the surface of a black aluminum layer scanned by an electron scanning microscope.

Giant. 2 shows the surface of the black aluminum layer scanned by an atomic force microscope.

Giant. 3 is a cross-sectional view of a black aluminum layer scanned by an electron scanning microscope.

Giant. 4 shows the diffuse reflectance of the black aluminum layer.

Giant. 5 shows a coating of black aluminum and precious metal on a substrate.

-3GB 307110 B6

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Pulsed DC magnetron sputtering (frequency 10 kHz, duty cycle 0.5) was used to prepare black aluminum layers 2. Pure aluminum was used as a target. The deposition process takes place in an atmosphere of argon and nitrogen. The gas flow rate is 16 sccm. The partial pressure of nitrogen ranges from 0.5-10 ³ to 2-10 ² Pa, the total pressure is 0.5 Pa. The distance between the target and the substrate is from 2 to 15 cm. The power density on the target is from 2 to 10 W / cm ² . The deposition process takes place at room temperature of the substrate, which can be increased up to 100 ° C by plasma heating. The layers 2 may be deposited on a dielectric, conductive (metal) and semiconductive substrate 1, which may be of inorganic or organic origin. No additional heating of substrate 1 is required.

A typical surface of the black aluminum layers 2 prepared by magnetron sputtering is shown in Figs. 1 to 3. The spectral dependence of the diffuse reflectance in the wavelength region from 250 to 2500 nm is shown in Fig. 4.

Example 2

The layers prepared according to Example 1 were coated with a silver layer 3 using RF magnetron sputtering (frequency 13.56 MHz). Pure silver was used as a target. The deposition process takes place in an argon atmosphere. The gas flow is 20 sccm, the pressure is 3 Pa and the RF power was 50 W. The distance between the target and the substrate is 10 cm. The power density on the target is 0.6 W / cm '. The deposition process was carried out at room temperature of the substrate. The thickness of the silver layer 3 was 10 nm.

Example 3

Layers 2 and 3 of Example 1 a were successively applied to the copper anode of a power tube

2. In both cases, the distance between the target and the surface was 2 cm. Layer parameters according to Example 1: 1 µm black aluminum layer 2 thickness. According to Example 2: the thickness of the silver layer 3 is 10 nm. The coating 4 effectively absorbed infrared radiation, dissipated heat from the anode surface to the condenser and showed stability.

Industrial applicability

The black aluminum coating and in combination with the thin noble metal layer can be used as a heat absorbing coating for power tube anodes, electromagnetic radiation absorbers and chemical sensors. The method of preparation of thin layers of black aluminum by means of magnetron sputtering is useful as a method of preparation of this layer with low environmental impact. Due to the properties of the layers and the technique chosen for their preparation, these layers can be used for the heat-absorbing coating of vacuum electrode anodes.

Claims (4)

1. Method for preparing black aluminum layers characterized by high optical density and low reflectance, characterized in that the black aluminum layer (2) is prepared by magnetron sputtering, which takes place in a gas mixture of argon and nitrogen, where the partial pressure of nitrogen it ranges from 0.5-10 ³ to 2-10 ² Pa and the total pressure ranges from 0.1 to 10 Pa. Coating (4), characterized in that it comprises a precious metal layer (3) deposited on the black aluminum layer (2) prepared according to claim 1. The coating (4) according to claim 2, characterized by the thickness of the precious metal layer (3) which 15 is in the order of units to tens of nanometers. Coating (4) according to claim 2 or 3, characterized in that it is placed on a substrate (1) which is a dielectric, conductive or semiconductive material. Use of a coating (4) according to any one of claims 3 and 4 for heat-absorbing anode coating.