Description:Field of Invention

The present invention relates to the improvement of photoelectric characteristics of TiO2 by adjusting its bandgap, absorption coefficient, charge carrier concentration, and Hall mobility by the addition of Copper (Cu) dopant.

The objectives of this invention

The purpose of this invention is to design the compositional modification of Copper (Cu) doped Titanium Oxide (TiO2) thin film in order to optimize its optical, structural, and electrical characteristics for a variety of optoelectronic device applications.

Background of the invention

Titanium dioxide (TiO2) is a very attractive material for researchers studying device applications. This is mostly owing to its excellent photoelectric activity, as well as its high levels of chemical and biological stability, and its non-toxic nature [Bensouici, F., et al., "Optical, structural and photocatalysis properties of Cu-doped TiO2 thin films", Applied Surface Science 395 (2017): 110-116]. It undergoes oxidation reactions with both organic and inorganic molecules present in water and air, leading to the decomposition of organic components via redox mechanisms. Moreover, TiO2 has superior oxidizing capability against organic pollutants compared to other photocatalysts. Additionally, it is non-toxic, highly hydrophilic, chemically stable, and possesses a high energy conversion efficiency [Wang, S., et al., "Superhydrophilic Cu-doped TiO2 thin film for solar-driven photocatalysis", Ceramics International 40.4 (2014): 5107-5110]. TiO2 has two primary disadvantages: a high recombination rate of photogenerated electron-hole pairs and moderate absorbance in the visible range [Heiba, Zein K., Mohamed Bakr Mohamed, and Ali Badawi, "Structural and Optical Characteristic of Cu-Doped TiO2 Thin Film", Journal of Inorganic and Organometallic Polymers and Materials 32.8 (2022): 2853-2862]. Typically, the recombination seen in TiO2 occurs either via defects or impurities. Thin film TiO2 is extensively used as a photocatalyst due to its ability to destroy pollutants using photoelectric potential [Torres, CE Rodríguez, et al., "Magnetic and structural study of Cu-doped TiO2 thin films”, Applied surface science 254.1 (2007): 365-367]. Anatase and rutile are the two main phases of TiO2. The TiO2 anatase phase has a bandgap energy of 3.2?eV, corresponding to a wavelength of less than 388?nm. The rutile phase, on the other hand, has a bandgap energy of 3.0?eV, corresponding to a wavelength of less than 410?nm. Therefore, it will only absorb ultraviolet light from the solar spectrum, which constitutes a mere 3% of the whole range of wavelengths. The photoexcitation of electrons in a photocatalyst is determined by the location of the bandgap and the redox potential when exposed to light. In order to facilitate the transfer of electrons from the acceptor to the photocatalyst, it is necessary for the photocatalyst to have a conduction band with a higher positive potential compared to the acceptor's potential. Similarly, the photocatalyst should have a valence band with a higher negative potential compared to the donor level in order to receive the electron [Alotaibi, Abdullah M., et al., "Enhanced photocatalytic and antibacterial ability of Cu-doped anatase TiO2 thin films: theory and experiment", ACS applied materials & interfaces 12.13 (2020): 15348-15361]. In order to enhance the photoelectric activity of TiO2, metal ions are introduced into the TiO2 structure by a process known as doping. This doping reduces the bandgap energy of TiO2 and causes a shift in the absorption edge of TiO2 towards the visible area .
Furthermore, metal has the ability to induce a modest level of electron trapping and electron-hole recombination. Choi et al. documented the impact of doping transition metal ions on thin film TiO2 and its subpar photoelectric performance [Xu, Ying, et al., "Preparation and characterization of Cu-doped TiO2 thin films and effects on platelet adhesion", Surface and Coatings Technology 261 (2015): 436-441]. The presence of the transition metal ion dopant serves as a location where recombination occurs, leading to a significant rise in the recombination rate as the concentration of the dopant grows. Consequently, this drop in photoelectric activity is seen. Alkaline metal dopants alter the bandgap of TiO2, hence enhancing its electronic characteristics and promoting photoelectric activity. This phenomenon occurs because when an alkaline metal is doped with TiO2, it creates lattice defects such as oxygen vacancies. This leads to an improvement in the generation of reactive oxygen species, which in turn inhibits the recombination of electrons and holes. As a result, the photoelectric activity of the TiO2 thin film is enhanced [Çelik, Erdal, et al., "Processing, characterization and photocatalytic properties of Cu doped TiO2 thin films on glass substrate by sol–gel technique" , Materials Science and Engineering: B 132.3 (2006): 258-265]. The addition of TiO2 to copper, known as doping, is very advantageous for industrial use since it is cost-effective, simple to prepare, and non-toxic. The manufacture of TiO2 thin film involves several processes such as sol-gel, wet chemical, chemical vapor deposition, sonochemical, solvothermal, and hydrothermal, direct oxidation, electrodeposition, and microwave approaches [19]. The present study involves the fabrication of Cu-doped TiO2 thin films using the RF sputtering technique, using varying concentrations of Cu. The findings demonstrated the enhanced photoelectric performance of a thin layer of Titanium Dioxide (TiO2) doped with Copper (Cu).

Detailed of Prior Art
Considerable efforts have been undertaken to reduce the bandgap of TiO2 in order to augment the photoelectric performance within the visible light spectrum by introducing metal or non-metal elements into the compound (US7632761B2). The practical applicability of TiO2 is often limited due to its large bandgap, which makes it susceptible to absorption of UV light by water and glass. When photons are irradiated, the dopants in TiO2 may generate shallow donor or acceptor states for ionization. This, in turn, leads to a longer diffusion length of carriers before recombination occurs, resulting in a high level of photoelectric activity (US7994602B2). Although doping causes a red shift in the absorption band edge, the photoelectric activity of some materials does not improve. This is because the introduction of defect states by doping creates recombination sites for carriers when they transition from the interior to the surface. The atomic radii of the Cu anion and the Ti cation were similar, allowing for Cu doping into the TiO2 lattice without causing any harm to its crystal structure. Copper (Cu) is a readily accessible and cost-effective metal dopant that may enhance the photoelectric activity and modify the bandgap and electrical properties of titanium dioxide (TiO2). The reason for this is that when an alkaline metal is infused with TiO2, it creates lattice defects such oxygen vacancies, which enhances the production of reactive oxygen species. This, in turn, hinders the recombination of electrons and holes, leading to an increase in the photoelectric activity of TiO2. Titanium dioxide (TiO2) doped with copper (Cu) has shown enhanced photoelectric performance. The use of copper and other alkaline earth metals for doping TiO2 is very advantageous in terms of its affordability, simplicity of manufacturing, and non-toxic nature. This technique proves to be especially valuable for addressing environmental contamination and fulfilling industrial needs.
Summary of Invention
This patent explores the practicality of using the electron-beam evaporation deposition process. In this work, the researchers carefully evaluate the optical and morphological features of a thin film made of TiO2 doped with Cu (copper), aiming to increase the qualities of both the layer and the interface. The addition of Cu to TiO2 was found to greatly enhance the morphology of the TiO2 thin film, creating a favorable surface for the formation of the absorber layer. Optoelectronic investigations indicated that the band gap was significantly decreased by the use of Cu, resulting in an improved absorption range. The electrical investigation revealed that the TiO2 thin film doped with Cu exhibited improved conduction and superior light absorption in comparison to the films without doping.
Detailed description of the invention
The RF sputtering technique was employed to deposit thin films of Cu-doped TiO2. Sputtering at radio frequencies, often known as RF (radio frequency) sputtering, is a process that involves alternating the electrical potential in a setting that is vacuum. Additionally, this inhibits charge accumulation on specific sputtering target materials, which would otherwise lead to arcing into the plasma if it were not prevented. The arcing that occurs can cause droplets to be released, which can lead to problems with quality control on the thin films. Additionally, it has the potential to entirely halt the sputtering process by preventing the ejection of atoms.
In radio frequency (RF) sputtering, an energetic wave is employed to ionize an inert gas that is contained within a vacuum chamber. The substrate is subjected to a barrage of high-energy ions, which cause the target material, which will eventually form the thin film coating, to spit atoms onto the substrate in a fine spray. R.F. Sputtering using magnetrons is an improvement on this technique since it makes use of magnets that are located behind the negative cathode. These magnets are used to trap electrons over the negatively charged target material. This prevents the electrons from blasting the substrate, which in turn enables quicker deposition rates. Positive ions build up on the target face over time, which results in the target face acquiring a positive charge. If this charge accumulates to a significant degree, it has the potential to completely halt the sputtering process. This problem is solved by radiofrequency sputtering, which involves changing the electrical potential. This "cleans" the surface of the target material by removing any charge that has accumulated with each cycle. In the course of the positive cycle, electrons are drawn to the substance of interest, which results in the material having a negative bias. Ion bombardment of the target continues during the negative cycle, which takes place at a radio frequency of 13.56 MHz from the beginning to the end.
Sputtering using radio frequency (RF) offers a number of benefits, depending on the application in question. As opposed to DC sputtering, which involves the plasmas concentrating around the target material, radio frequency (RF) plasmas have a tendency to disperse over the whole chamber. This makes it possible for radiofrequency sputtering to maintain a plasma across the chamber at lower pressures. As a consequence, there are fewer collisions between ionized gases, and the coating material may be deposited more effectively in a line-of-sight manner. Arcing is less likely to occur while using RF Sputtering since the process "cleans" the material that is being sputtered on with each cycle. Arcing is characterized by a concentrated and localized discharge from the target material into the plasma, which results in the formation of droplets and the deposition of a film that is not uniform. RF sputtering reduces the amount of charge that accumulates on the surface of the target material, which in turn reduces the number of sparks and the quality control problems that are connected with them.
RF sputtering also reduces the amount of "racetrack erosion" that occurs on the surface of the target material. Magnetron sputtering is a technique that involves the etching of a circular pattern onto the target material. This is accomplished by utilizing a circular magnetic field to concentrate charged plasma particles in close proximity to the surface. In contrast, radiofrequency sputtering, which is characterized by its alternating current (AC) nature and less restricted electrons, distributes the plasma more uniformly, resulting in a racetrack that is broader, wider, and shallower. Through this process, the exploitation of target coating materials is improved, made more consistent, and made more efficient, all without the need for deep etching. RF sputtering has a number of major advantages, one of which is that it does not occur with the vanishing anode effect. Through the use of AC modulation, radio frequency sputtering is able to prevent considerable charge accumulation on the material that is going to be coated, therefore preserving the deposition process. Efficiency is further improved with the use of RF magnetron sputtering. Within the vicinity of the target surface, the magnetic field creates a barrier "tunnel" that traps electrons, hence enhancing the generation of gas ions and the containment of plasma discharge. Through this, a higher current may be achieved at a lower gas pressure, which ultimately results in a higher deposition rate.
Initially, the substrates made of quartz glass were subjected to a comprehensive cleaning procedure. Ultrasonic cleaning with acetone and isopropanol was performed on them first in order to eliminate any organic impurities that could have been present. After this step, the substrates were washed several times with deionized water in order to remove any residues that were still present. Following cleaning, the substrates were subjected to a nitrogen cannon drying process in order to guarantee that they were devoid of any moisture. Following the completion of the cleaning process, the substrates were brought into the RF sputtering chamber and carefully positioned within the substrate holder. There was a two-step pumping method that was utilized in order to accomplish the requisite vacuum conditions for sputtering. Through the utilization of roughing pumps, the pressure was initially lowered, and then a high vacuum pump, especially a Turbo Molecular Pump, was activated.
This was done in order to accomplish the desired result. In order to guarantee that the base pressure within the chamber reached roughly 2×10-6 mbar, the high vacuum pump carried out its operation for a considerable amount of time. After the base pressure was brought up to the necessary level, argon gas was injected into the RF sputtering chamber at a flow rate of thirty standard cubic centimeters per minute (sccm). One of the most important aspects of the sputtering process is the establishment of a working pressure of 5×10-4 mbar within the chamber, which was achieved by the injection of argon gas. Through the use of a co-sputtering technique, the deposition of TiO2 thin films that were doped with copper at concentrations of 1%, 5%, and 10% was accomplished. In order to do this, copper and titanium dioxide targets, each of which had a purity of 99.99%, were sputtered simultaneously. When it came to copper, the sputtering power that was applied was somewhere in the region of 60 to 90 watts, whereas for titanium dioxide, it was 120 watts. For the purpose of ensuring that the films have the appropriate adhesion and crystalline quality, the entire deposition process was carried out at a substrate temperature of 400 0C. A precise doping of titanium dioxide (TiO2) with copper was accomplished by the utilization of this radiofrequency (RF) sputtering technology.
This enabled a comprehensive investigation into the impact that varying concentrations of copper had on the characteristics of the thin films that were produced. The selection of parameters, which included the substrate cleaning procedure, vacuum conditions, argon flow rate, and sputtering powers, was of utmost importance in order to guarantee the effective deposition of high-quality Cu-doped TiO2 thin films.
Brief description of Drawing
Figure 1 Absorption spectra of 1%, 5% and 10 % Cu doped TiO2 thin film on glass substrate.
Figure 2 Bandgap extraction of Cu doped TiO2 thin film using Tauc plot.

Detailed description of the drawing
Figure 1 displays the absorption spectra of TiO2 thin films that have been doped with 1%, 5%, and 10% Cu on glass substrates. The absorption coefficient is positively correlated with increasing amounts of Cu doping. The level of absorption rises in proportion to the increase of Cu doping. The absorption is maximized at a Cu doping level of 10%, whereas the bandgap is minimized at a Cu doping level of 1%.Copper doping allows for the tuning of light absorption in titanium dioxide through the absorption of light.
Figure 2 depicts the process of extracting the bandgap of Cu-doped TiO2 using a Tauc plot. As the concentration of Cu doping increases, the bandgap lowers. The bandgap is at its lowest when the copper doping level is 10%, and at its maximum when the copper doping level is 1%.Copper doping can be used to adjust the bandgap. , Claims:The scope of the invention is defined by the following claims:

Claims:
1. A method for the growth of Cu doped TiO2 thin film comprises of following steps:
(a) The RF sputtering deposition carried out at 400°C for the formation Cu doped TiO2 thin film.
(b) The fabricated samples of Cu doped TiO2 shows n type nature, different absorbance and bandgap.
(c) The deposition of Copper (Cu) has been carried out at 60 Watt -90 Watt.

2. The method as claimed in claim 1, wherein tunable opto-electronic properties includes absorption coefficient and bandgap.
3. The method as claimed in claim 1, wherein room temperature denotes 400 0C inside the RF sputtering chamber. The flow rate of argon (Ar) maintained at 30 sccm inside the RF sputtering chamber and the deposition of TiO2 has been carried out at 100 Watt.