A transparent, hydrophobic, and Anti-corrosive gallium nitride coatings and method to fabricate gallium nitride on glass thin films

Abstract

ABSTRACT A TRANSPARENT, HYDROPHOBIC, AND ANTI-CORROSIVE GALLIUM NITRIDE COATINGS AND METHOD TO FABRICATE GALLIUM NITRIDE ON GLASS THIN FILMS The present invention relates to a transparent, hydrophobic, and anti-corrosive gallium nitride coatings and method to fabricate gallium nitride on glass (GaN@glass) thin films. Gallium nitride films are prepared using RF magnetron sputtering on glass substrates (GaN@glass). The deposited thin films were analysed for their structural properties using X-ray diffraction (XRD) technique. Optical transmittance measurements were implemented by UV-Visible spectroscopy and the fabricated thin films observed a transmittance of more than 72%. The water contact angle of ~1200, indicating the highly hydrophobic (?WCA= 90o-150o) nature of the thin film. Corrosion properties were studied using Tafel plot in saline water and corrosion rate is 0.0044 µm / yr. Published with Figure 1

Description

FIELD OF INVENTION:

[001] The present invention relates to the field of anti-corrosive hydrophobic transparent coatings. The present invention in particular relates to a transparent, hydrophobic, and anti-corrosive gallium nitride coatings and method to fabricate gallium nitride on glass (GaN@glass) thin films.DESCRIPTION OF THE RELATED ART:

[002] In recent times, hydrophobic transparent thin films have gained significant attention among researchers due to their versatile applications. These films find utility in various fields, including solar cells, lenses for traffic and security cameras, glasses, and windows in buildings. However, there are several challenges that need to be addressed, including developing an easy methodology, achieving hydrophobicity, and ensuring optical transparency with low corrosion rate.

[003] Reference may be made to the following:

[004] Publication no. CN105655238B relates to the growing gallium nitride with silicon graphene using magnetron sputtering of aluminum nitride involves using chemical vapor deposition method and growing graphene on metal substrate, obtained product is placing in mixed solution.

[005] Publication no AU2020103598A4 relates to the method for preparing gallium nitride based photoelectric detector, involves magnetron sputtering aluminum nitride film on sapphire substrate and growing single layer of graphene on copper substrate by chemical vapor deposition.

[006] Publication no CN115595032A relates to the preparation and application of transparent and stretchable super-hydrophobic coating.

[007] Publication no US20230182434A1 relates to a self-cleaning transparent conductive surface includes a hydrophobic film and a metal nano-web coupled to the hydrophobic film. The metal nanoweb imparts conductive properties to the surface of the film and texturing formed by either the hydrophobic film, substrate or metal nano-web create a super-hydrophobic surface. This superhydrophobic and conductive surface may be created by etching and layering a metal nano-web over the surface of a hydrophobic film or a rigid substrate, the metal grid may the hydrophobic film or substrate may also be etched in a moth's eye pattern. Both the hydrophobic film or substrate and metal nano-web may be coated in a layer of hydrophobic material to further increase the hydrophobic effect.

[008] Publication no WO2023161595A1 relates to glazing comprising a transparent substrate, characterized in that it comprises, at the periphery of the substrate, at least one emitter of hydrophobic compounds by a gaseous process; said at least one emitter being arranged to enable the release of said hydrophobic compounds, and a fraction of said released hydrophobic compounds being able to be deposited on the surface of said transparent substrate. The present invention also relates to the use of this glazing as described above as rain-proof glazing, said rain-proof glazing being able to be used as glazing in buildings, land-, air- or water-based vehicles, or urban furniture, preferably as aircraft cockpit glazing. The present invention also relates to a method for hydrophobising glazing as described above.

[009] Hence there needed a cost effective, transparent, hydrophobic, and anti-corrosive gallium nitride coatings which can be fabricated on glass thin film.

[010] In order to overcome above listed prior art, the present invention aims to provide a transparent, hydrophobic, and anticorrosive gallium nitride coatings and method to fabricate gallium nitride on glass (GaN@glass) thin films.OBJECTS OF THE INVENTION:

[011] The principal object of the present invention is to provide a transparent, hydrophobic, and anti-corrosive gallium nitridecoatings and its method fabrication.

[012] Another object of the present invention is to provide gallium nitride coatings and method to fabricate gallium nitride on glass (GaN@glass) thin films.

[013] Yet another object of the present invention is to provide a durable hydrophobic and transparent coating with integrated anti corrosion properties.

[014] Still another objective of the present invention is to provide a rapid, cost effective, accurate, and highly reproducible coatings to integrate it with currently available glasses.SUMMARY OF THE INVENTION:

[015] The present invention relates to a transparent, hydrophobic, and anti-corrosive gallium nitride coatings and method to fabricate gallium nitride on glass (GaN@glass) thin films. Gallium nitride films are prepared using RF magnetron sputtering on glass substrates (GaN@glass). The deposited thin films were analysed for their structural properties using X-ray diffraction (XRD) technique.Optical transmittance measurements were implemented by UV-Visible spectroscopy and the fabricated thin films observed a transmittance of more than 72%. The water contact angle is of -120°, indicating the highly hydrophobic (θwca= 90°-150°) nature of the thin film. The corrosion rate is 0.0044 pm / yr. Thus GaN@glass is a promising material for future hydrophobic transparent devices with integrated anti-corrosion properties.BREIF DESCRIPTION OF THE INVENTION

[016] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments.

[017] Figure 1 shows schematics for sputtering chamber.

[018] Figure 2 shows X-ray diffraction pattern for GaN@glass.

[019] Figure 3 shows water contact angle for GaN@glass at various substrate temperature.

[020] Figure 4 shows water contact angle for (a) uncoated glass and (b) GaN coated glass with real time picture of droplets.

[021] Figure 5 shows UV-visible spectrum for glass and GaN coated glass.

[022] Figure 6 shows Tafel curves for GaN@glass coatings.DETAILED DESCRIPTION OF THE INVENTION:

[023] The present invention provides a transparent, hydrophobic, and anti-corrosive gallium nitride coatings and its method fabrication. Transparent and hydrophobic Gallium nitride films are prepared using RF magnetron sputtering on glass substrates. XRD reveals that the sputtering thin films are with preferred (002) orientation. Also, the water contact angle of 121.1° makes it suitable for water repellent and self-cleaning applications. Also, GaN@glass have an optical transmittance of 74% w.r.t. air in visible region. Combined hydrophobic and transparent glass coated with GaN have high potential for practical applications. The corrosion properties in highly corrosive saline environment (3.5% NaCl) were analyzed using Tafel plot analysis. The results obtained from these measurements indicates extremely low corrosion rate (-0.0044 pm / yr). Therefore, the coating with the excellent and stable anti-corrosion properties may be a potential candidate for corrosion resistant application at industry scale.

[024] GaN thin films were fabricated on transparent glass substrate using radio frequency (RF, 13.5 MHz) magnetron sputtering Figure 1. Prior to sputtering, the surface of glass substrate was cleaned using acetone and DI water by keeping it in ultrasonic bath for 20 mins. Before deposition, the chamber was vacated to the base pressure of ~ 3 * 10-6 Torr by turbomolecular pump followed by rotary pump to achieve an environment with low impurities.

[025] Sputtering, which is a physical vapor deposition (PVD) technology utilizes the erosive action of accelerated ions at the surface of a target material as source of the formed coating. These ions have enough energy to remove, i.e., to sputter particles at a target surface. Here, the 99.9% pure GaN target, available commercially, was used for sputtering process. Under high vacuum an electrical field is generated in a sputtering apparatus with a deposition chamber between an anode and the target (cathode). Argon (Ar) is ionized by means of electrical voltage generating a glow discharge. Positive Ar+ ions are accelerated towards the target and sputter the atoms on its surface. In magnetron sputtering, magnets are placed in the proximate to the target to keep the - density of the sputtering ions very high further increasing the 5 sputtering efficiency. In reactive magnetron sputtering, there is further a reactive gas present reacting with the atoms sputtered from the target during the coating deposition on the substrate, i.e., the sputtered atoms or particles undergo a chemical reaction with the reactive gas before deposited on the substrate. The deposited 10 coating is therefore different from the target.

[026] As used herein, the term "coating" means at least one deposited layer applied to at least a part or all an exposed surface of the substrate. The coating can be formed by one or more than one layer.

[027] GaN, coating which is also referenced as "Gallium Nitride coating" means a coating comprising and in particular essentially consisting of Nitrides of Gallium.

[028] The reactive magnetron sputtering is preferably carried out with a sputtering pressure, i.e., a deposition chamber pressure, of about 5 mTorr to about 15 mTorr for obtaining a sustainable plasma in the deposition chamber. The substrate temperature during the reactive magnetron sputtering is preferably kept at a temperature in the range of about 27°C. to about 500°C. The distance between the GaN target and the surface of the substrate onto which the GaN coating is to be deposited in the deposition chamber can be between about 5 cm to 7cm. the applied power to the GaN target is in the range 40 to 80W. As the deposition rate is very low for GaN so, the deposition has been taken for 2.5 hrs. The working gas is preferably argon, in particular high purity argon, and the reactive gas preferably comprises and more preferably is nitrogen, in particular high purity nitrogen. By adjusting the gas flow ratio of argon and Nitrogen in the ratio (Ar:N) of 27:3 seem, the stoichiometry of the GaN, coating can be controlled. Argon and Nitrogen used are preferably of high purity, which means herein a gas purity of at least about 99.9% and in particular at least about 99.99%, i.e., this means that impurities are present in an amount of at most about 0.1% and further preferred of at most about 0.01%. The reactive magnetron sputtering is carried out at a temperature between about 20°C. and about 500°C., preferably at 400°C., without external heating to the substrate.

[029] All the sputtering parameters are tabulated in Table 1.Table 1: Sputtering parameters for GaN@Glass

[030] Structural properties: for Confirmation of prepared GaN film

[031] The crystal phase and structure of GaN@glass was studied using X-ray Diffractometer (Rigaku smart lab), with Cu Ka radiation with wavelength (A= 0.154 nm). The X-ray diffraction (XRD) findings of GaN@glass thin film are illustrated in Figure 2. The XRD scans reveal the presence of GaN (JCPDS card no. 50-0792) with a pronounced preferential growth orientation along the (002) direction. The intensity of the XRD peak in the diffractogram directly reflects the crystallinity of the film.

[032] Wettability

[033] The water droplet contact angle was measured using contact angle goniometry (Kruss DSA 30E). The wettability of GaN@glass thin films was examined using the sessile drop method. The water contact angle (Gwca) presented in this study represents the average value of five measurements taken on each sample. The degree of hydrophobicity is determined by the measured water contact angle: 9wca below 90° indicates hydrophilicity or high wettability, while a Gwca above 90° indicates hydrophobicity. The Figure 3 illustrates the change in water contact angle as a function of substrate temperature in the range of Room temperature to 500°C. The coated samples exhibited a highly hydrophobic nature in the range of 110° to 122° at all the substrate temperature. Figure 4 shows the water contact angle of coated and uncoated glass with their respective real time images. Herein, the uncoated bare glass demonstrated hydrophilic behaviour with a contact angle of 45.4° and GaN coated glass shows the hydrophobic nature with WCA of 121.1°.

[034] UV- Visible Spectroscopy

[035] Optical measurements of thin films were carried out over the ultra-violet-visible range i.e., 300nm to 800nm by UV-vis spectrometer. Figure 5 shows the transmittance spectrum of the GaN thin films recorded as a function of wavelength (A). The Number of oscillations observed in the spectrum are due to interference effect. Uncoated glass shows the average transmittance of 78% followed by 74% of GaN@glass which is nearly 95% relative to glass substrate. This much high transparency is useful for application in windows, camera lens, windshields and glasses used in marine related equipment.

[036] Corrosion analysis

[037] The electrochemical corrosion characteristics for GaN@glass were examined by Tafel plot method. Before taking the electrochemical measurements, samples were kept in aqueous solution of 3.5% NaCl (Saline Water) for 8 hrs, to achieve stable open circuit potential (OCP). When immersion or exposure time 10 was increased, the OCP began to decline in the corrosive solution and eventually reached a steady value. The decreased OCP is probably related to the chemical attack that activates the surface, the following dissolving of the metal in the alloy, and the consequent generation of corrosion products.

[038] Figure 6 shows the polarization curves obtained after reaching the stable OCP, when analysed samples were exposed in saline environment for 8h. The crucial corrosion factors obtained from the polarization curves are listed in

[039] Table 2. The lower Icon- and high Ecorr values emphasize a lower corrosion dynamic 20 rate. Herein,

[039] Table 2 indicates the lower corrosion current density after coating the sample. The lower Icorr (0.31 nA / cm2) is responsible for lower corrosion rate (corrosion velocity (C.R.) ~ 0.0044 (um / yr). This lower value of C.R. indicates the higher time of protection, resulting better layer passivity. The better layer 25 passivity of the coating may be due to the low surface energy of the molecules, which contain chemical interfacial force between the substrate and molecules, resulting excellent corrosion resistance in saline corrosive media. The substrate corrosion resistance is determined in terms of polarization resistance (Rp). The Rp is inversely proportional to the C.R., which is an indication of layer passivity. A large value of Rp signifies a highly corrosion-resistant material. Therefore, the GaN coating showed promising results and withstand as a tough barrier against corrosion.

[039] Table 2 Corrosion parameters of the GaN@glass coatingsCorrosion Parameters GaN@GlassEcorr (mV) -229.03Icon- (pA / cm2) 0.00031C.R. (pm / yr) 0.0044Rp (Q / cm2) 1.10 x 1Q8

[040] Thus the films are highly transparent and hydrophobic GaN coatings are advantageous for optical, and material protecting applications and can become a potential candidate in practical applications especially for self-cleaning windows, anti-reflective 10 coatings etc.

[041] Numerous modifications and adaptations of the system of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the true spirit and scope of this invention.

Claims

1. A method of fabricating transparent, hydrophobic, and anticorrosive gallium nitride on glass (GaN@glass) thin films includes following steps- a) Clean surface of glass substrate using acetone and DI water by keeping it in ultrasonic bath for 20 mins. b) Before deposition, chamber was vacated to the base pressure of ~ 3 x 10"6 Torr to achieve an environment with low impurities. c) Fabricating GaN thin films were fabricated on transparent glass substrate using radio frequency (RF, 13.5 MHz) magnetron sputtering wherein Sputtering power was optimized to 80W and substrate temperature to 400 °C. As the deposition rate is very low for GaN so, the deposition has been taken for 2.5 hrs with the constant gas flow of Ar:N in ratio 27:3 seem using mass flow controller (MFC).

2. The method of fabricating transparent, hydrophobic, and anticorrosive gallium nitride coatings, as claimed in claim 1, wherein the 99.9% pure gallium nitride is used for sputtering process.

3. The method of fabricating transparent, hydrophobic, and anticorrosive gallium nitride coatings, as claimed in claim 1, wherein the temperature is 500°C, power 40-100 W, Working Pressure 2-10 mTorr, thickness of film in the range of 0.05 to 1.2 pm.

4. The method of fabricating transparent, hydrophobic, and anticorrosive gallium nitride coatings, as claimed in claim 1, wherein the light transmission of transparent coating of GaN on glass substrate is of 72%.

5. The method of fabricating gallium nitride coatings on glass thin films, as claimed in claim 1, wherein hydrophobic coating exhibits water contact angles greater than 90°.

6. The method of fabricating transparent, hydrophobic, and anticorrosive gallium nitride coatings, as claimed in claim 1, wherein highly hydrophobic coating is with water contact angle 110°- 122°C in substrate temperature range Room temperature to 500°C.

7. The method of fabricating transparent, hydrophobic, and anticorrosive gallium nitride coatings, as claimed in claim 1, wherein the anti-corrosive coating is with corrosion rate of 0.0044 gm / yr.