The thin-film quality from the PLD depends on the various parameters such as wavelength of the laser, energy, ambient gas pressure, pulsed duration, and the distance of the target to the substrate [ 19 ]. The ablation process during the deposition may control and monitor by using laser-induced fluorescence [ 20 ], laser ablation molecular isotopic spectroscopy [ 21 ], and optical emission spectroscopy [ 22 ].
The morphology of the deposited thin films is also affected by the substrate temperature.
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PLD has some advantages over other physical deposition systems because of its fast deposition time and its compatibility to oxygen and other inert gases. Sputtering technique is mostly used for depositing metal and oxide films by controlling the crystalline structure and surface roughness [ 11 , 25 ]. The simple form of the sputtering system consists of an evacuated chamber containing metallic anode and cathode [ 25 ] in order to obtain a glow discharge in the residual gas in the chamber. Also, an applied voltage in the order of several KeV with pressure more than 0.
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The sputtering process depends on the bombardment of the ions released from the discharge to the molecules in the cathode leading to the liberation of the molecules from the cathode with higher kinetic energy. The atomic weight of the bombarding ions should be nearly to that of the target material in order to maximize the momentum transfer. These molecules move in straight lines and strike on the anode or on the substrate to form a dense thin film [ 25 ].
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The process of sputtering has several advantages. High-melting point materials can be easily formed by sputtering. The deposited films have composition similar to the composition of the starting materials. Sputtering technique is available to use for ultrahigh vacuum applications. The sputtering sources are compatible with reactive gases such as oxygen.
There are two common types of sputtering process: direct current DC and radio frequency RF sputtering. The first one depends on DC power, which is generally used with electrically conductive target materials. It is easy to control with low-cost option. The RF sputtering uses RF power for most dielectric materials. A common example for sputtered films is aluminum nitride films. These films were prepared by both DC- and RF-sputtering technique, and their structure and optical properties were compared [ 26 , 27 ].
Although the production of thin films via physical methods as previously described gives good quality and functionalizes properties, it is highly expensive and perhaps requires a large amount of material target. Since the need to produce good-quality thin films with low economical cost is necessary, chemical deposition techniques are widely used globally.
These techniques are cheap producing good-quality films. Most of them do not require expensive equipment. The chemical deposition is strongly dependent on the chemistry of solutions, pH value, viscosity, and so on. The most common chemical deposition has been obtained via sol-gel route, chemical bath deposition, electrodeposition, chemical vapor deposition CVD , and spray pyrolysis technique.
This section is concerned only on sol-gel and chemical bath deposition techniques because they can form good film quality with low equipment requirement. The sol-gel technique is broadly used for the synthesis of oxide materials [ 28 ]. Sol-gel process is one of the famous wet-chemical methods. It works under lower-temperature processing and gives better homogeneity for multicomponent materials.
Two routes are used to prepare transition metal oxides TMOs as follows:. It can be synthesized via the reaction of metal salt chloride, acetate, nitrate, etc. Hydrolysis: this step is aimed to form reactive M-OH groups [ 30 ]:. Condensation : condensation is the second step after hydrolysis leading to the departure of a water molecule. The process of condensation can be either olation process or oxolation process. Oxolation: oxolation is a reaction in which an oxo bridge —O— is created between two metal centers.
The previous description provides the preparation of the precursor solution. In order to make thin film from the precursor solution, there are two processes for the production of the films, that is, dip-coating and spin-coating techniques. Dip-coating technique is almost used to fabricate transparent layers of oxides on a transparent substrate with a high degree of planarity and surface quality [ 32 ]. Other substrates are also possible to use. Several additive layers can be superimposed.
Scriven [ 33 ] described the dip-coating process in five stages: immersion, start-up, deposition, drainage, and evaporation.
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The fluorescence switching device was made of two layers, the highly-fluorescent polymer and a conducting medium, sandwiched between two transparent indium tin oxide ITO electrodes. During the research, the quantum yields of these fluorescent polymers under varying conditions were calculated by using spectral data collected by the AvaSpec-ULSL-USB2 spectrometer. This work with electrochemical fluorescence will contribute to advances in graphic displays and telecommunications devices. Titanium dioxide has enjoyed wide use in many applications such as environmental purification, gas sensing, and most recently, solar energy.
The recent innovation of dye sensitized solar cells DSSCs are finding prevalent application in the solar energy industry due to their power conversion properties, low cost and ease of fabrication. Dye-sensitized solar cells consist of a porous layer of titanium- dioxide nanoparticles impregnated with a molecular dye that absorbs sunlight. The molecular dye is arranged in a 3D lattice formed by the semiconductor material which is responsible for transporting the charge generated by exciting electrons in the dye which then flow into the titanium dioxide nanoparticles. Researchers from the University of Malaysia published a novel method for the preparation of Titanium Oxide thin films on an indium tin oxide substrate.
They followed fabrication by aerosol-assisted chemical deposition with a hydrogen chloride post treatment and gold particle deposition.
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This removed sodium ions detrimental to photoactivity. The end result was a Dye Sensitized Solar Cell which boasted a fivefold increase in photocurrent density and sevenfold increase in DSSC conversion efficiency. The bio-compatibility of medical implants is a crucial concern in a surgical setting. Metallic implants are subject to corrosion and wear and it can be difficult to achieve a strong bond between the implant and the surround tissue.
In these cases, biocompatible coatings, such as calcium phosphate, improve the likelihood of the implant adhering and reduces the chances of rejection or complications. For implants made with titanium or nickel alloys the coating will also prevent the release of heavy metal ions into host tissue from the surface of the substrate. Biocompatible coatings should be dense, pore free, and adhere strongly to the substrate, qualities that calcium phosphate offer. The rf-magnetron sputtering deposition process, however, produces coatings of variable composition, resulting in either an amorphous or stoichiometric crystalline structure.
Researchers at the Tomsk Polytechnic University in Tomsk Russia carried out experiments to understand the film growth mechanisms that determine coating composition. To define the mechanisms of film growth, the researchers investigated parameters related to rf-magnetron sputtering deposition such as the rf-power, the working gas atmosphere, deposition time, substrate position, and plasma composition. The chemical composition of the plasma was analyzed using Optical Emission Spectroscopy OES in the nm wavelength range using an Avantes AvaSpec-ULS spectrometer , and found to greatly affect the composition of the resultant coatings.
The content of calcium and phosphorous in the coating was dependent on molecular ions in the plasma. Ultimately, this work sought to control the crystallinity and composition of the calcium phosphate coating through varying deposition parameters. Mass spectrometers for vacuum, gas, plasma and surface science. Skip to content Home Products for Thin Films, Plasma and Surface Engineering HPR A residual gas analyser for vacuum process analysis Measures the vacuum process gas composition, contamination and leak detection View full description.
EQP Series For the analysis of positive and negative ions, neutrals, and radicals from plasma processes Measures mass spectra and energy distributions of ions, neutrals and radicals in plasma View full description.