Characterization of SnO2 Film with Al-Zn Doping Using Sol-Gel Dip Coating Techniques

Sn1-2x AlxZnxO2 film has been developed using sol-gel dip coating technique. The materials SnCl2.2H2O, AlCl3 and ZnCl2 dissolved in water and ethanol with 5:95 volume ratio. Variations dopant concentration x = 0.000, 0.005, 0.0025, and 0.050. The film was grown with sol concentration 0.4 M, the withdrawal speed of 12 cm/min and sintering at 600 °C for 30 minutes. The characteristics Sn1-2x AlxZnxO2 films with various doping concentration phase were characterized by XRD. The morphological characteristics and the composition of the constituent elements of the film were characterized by SEM-EDX. The characteristics of the shape, structure, and size of the particles were characterized by TEM. The XRD results show that all films have a tetragonal SnO2 rutile phase without any secondary phase with an average particle size in the range 5.14 – 2.09 nm. The SEM results show that the film grown has a smooth morphology with a striped texture (x = 0.00), and there is a crack (x = 0.050). The EDX results show that the composition and distribution of the constituent elements of the film are uniformly distributed. TEM results show that the particle films has tetragonal rutile structure, orthorhombic and amorphous with a spherical shape.


Introduction
The tin oxide (SnO 2 ) is one n-type transparent semiconductor material with a wide energy band gap (~ 3.6 eV), combines high optical transparency and low resistivity that makes this material applied to solar cells, Liquid Crystal Display and other optoelectronic devices. In addition, SnO 2 is very sensitive to the presence of surrounding gas which makes it is applied as gas sensors [1]. Due to its nature and application, the study of SnO 2 engineering is very intensive. The preparation and growth of SnO 2 film can be done with various techniques such as Chemical Vapor Deposition (CVD) [2], DC and RF Sputtering [3], Pulsed Laser Deposition [4], Chemical Bath Deposition [5], and Sol-Gel Spray Pyrolysis [6], Sol-Gel Spin Coating [7], and Sol-Gel Dip Coating [8]. Of all these methods, Sol-Gel Dip Coating is a very good technique, because it is the simplest one that can grow the film on various forms of the substrate, ease in controlling particle growth and doping, and economical addition. The characteristics of SnO 2 films are known to be enhanced by the addition of doping. Dopants generally have larger or smaller valence electrons with Sn + , and have a similar ionic radius. Dopants may be of a single element such as Sb, F, Zn, Al, Mn or double-shaped elements such as Sb-F, Zn-Co, and others that depend on the application of SnO 2 itself. The SnO 2 films doped with Zn 2 + and Al 3 + ions are known to affect SnO 2 properties themselves, including stabilizing SnO 2 particles and changing energy band gaps, increasing optical transmittance and electrical conductivity, altering structural, increasing responsiveness, selectivity and stability in sensor gas. However, it is not yet known how the effect of these two dopants 2 1234567890 ''"" combined on the characteristics of the SnO 2 film. So it is necessary to further investigate the effect of these two dopants on the characteristics of the SnO 2 film. Therefore, in this study the growth of the SnO 2 thin film with combined doping of Zn 2 + and Al 3 + was done using Dip Coating Sol-Gel.

Materials and Methods
The basic ingredients used as the films in this study were as follows Tin (II) chloride dihydrate (SnCl 2 • 2H 2 O) with molar mass 225.63gr/mol, 98% purity, Merck). The solvent used was Ethanol (C 2 H 5 OH) with a molar mass of 46.07gr/mol (98% purity, Merck) and Aquades. The dopant material used was Zinc dichloride (ZnCl 2 ) with molar mass 136.30 g/mol (98% purity, Merck) and Aluminum Chloride (AlCl 3 ) with molar mass 133.34 g/mol (98% purity, Merck). The substrate film used is glass preparations with dimensions of 2.54 mm x 76.2 mm x 1 mm. While the material for washing the substrate is Hydrochloride (HCl 1.0 M) and ceramic detergent. The procedure of Sn 1-2x Zn x Al x O 2 sol preparation is a modification of the sol-gel preparation of SnCl 2 .2H 2 O. The ZnCl 2 and AlCl 3 , dissolved in 5 ml of distilled water using a magnetic stirrer for 30 minutes at 80 ° C until the mass composition ratio SnCl 2 .2H 2 O, ZnCl 2 , AlCl 3 with varying concentrations x (m/m) = 0.000, 0.005, 0.025, 0.050. Then 45 ml of ethanol (C 2 H 5 OH) was added in the mixture solution to obtain a constant solubility concentration of 0.4 mol / L. The solution was then stirred at 80 °C for two hours and kept for two days. The glass substrate before the deposition was washed using detergent followed by substrate soaking for one day in a mixed solution of 100 ml of HCl 1M with 300 ml of distilled water for one day. Then the substrate was washed with flowing distilled water. The substrate is then dried using an oven at 100 °C for one hour [7,9]. Thin layer deposition is done using an instrument with a dip coater pull Speed (Withdrawal Speed) at 12 cm/minute, long soaking 5 seconds, in sintering the electric furnace at a temperature of 600 °C for 30 minutes. This step is done as much as 5 times repetition. The Characterization of Sn 1-2x Zn x Al x O 2 film sample structure was done using XRD Rigaku Smartlab type with Cu Kα radiation. The XRD operating conditions are set at 40.0 kV 30 mA, and the XRD spacer angle range is set at the angle range (2θ) 5°-90°. The morphological characteristics and sample composition are characterized using SEM paired with EDX. In this study, the samples were characterized by samples with doping composition x = 0,000 and 0.050. The regional characterization, size, and regularity of samples were observed using JEOL JEM 1400 TEM. The samples characterized by TEM were samples with dopant composition x = 0.050. Where D is the average size of the crystal, K is a constant associated with the crystal form and has a value of 0.9, λ is the X-ray wavelength used (nm), and β represents the peak width at half the maximum diffraction peak (FWHM) (radians). The lattice parameter data and thin film particle size estimation on dopant concentration variations are shown in Table 1.

Characteristics of Morphological
The characteristic Film surface morphology is characterized using Scanning Electron Microscope (SEM). FIG. 2 (a) shows the Sn 1-2x Zn x Al x O 2 film image at dopant concentration x = 0,000 textured lines, whereas for dopant concentration x = 0.050 (Fig. 2 (b)) has a smooth surface with two crack types Size 3.27 μm and 0.80 μm and the presence of crater (cater). A crack with a size of 3.27 μm is applied to the previous coating which has been covered by other coatings, whereas a crack with a size of 0.80 μm was observed on the final coating. This crack is due to the high sol high concentration [13] and the high rate of heating at the time of sintering by the electric furnace [14]. Figure 2 (c) shows the transverse incision image of SEM. The films grown have varying thicknesses with a range of 4.37 -5.00 μm. This thickness is categorized as a thin film [15].

Characteristics of Composition
Distribution characteristics and composition of the embedded film material were characterized using the Energy Dispersive X-Ray Spectroscopy (EDX) coupled with the SEM test apparatus. The composition of the film sampling elements for x = 0.000 is indicated by the presence of the energy peaks shown in Fig. 3 (a). The peak at 3.44 and 3.68 eV energy emission from Sn and peak at 0.52 eV represents the energy emission of element O. The pattern of element distribution for a film with x = 0.050 by Fig. 3(b).

Characteristics of Shape and Particle Size
The characteristics of particle shape and size were characterized using TEM. The samples characterized by TEM are samples with doping concentration x = 0.050. The particles are grown spherical with a size range of 3.72 -6.16 nm. This result differs from the result of particle size estimation with Scherer formula on XRD with particle size range 1.01-3.69 nm ( figure 4(a)). TEM can also be used to determine the particle structure through electrons diffraction future in the selected area (Selected Area Diffraction Electron -SAED). Figure 4(b) shows an irregular pattern of electron diffraction that indicates that some particles have polycrystalline structures with a tetragonal rutile phase with various orientations. This diffraction pattern results in spot irregularities in electron diffraction indicating a lattice disturbance by the Al-Zn dopant corresponding to the XRD results [16]. Figure 4(c) shows that some particles also have polycrystalline structures with orthorhombic phases. The electron diffraction pattern is similar to that of Cd Doped SnO 2 diffraction film grown by Chemical Bath Deposition (CBD) method. The existence of an orthorhombic structure is caused by a lattice distortion caused by a substituted Zn doping ion replacing the SnO 2 lattice, while image 4(d) shows the particles are amorphous. This is due to the nucleation and Growth of imperfect film crystals due to the shortness of sintering time [17].

Conclusion
Results and data analysis can be concluded that the addition of Al-Zn doping does not change the phase SnO 2 . The SEM results show that the grown film has a smooth morphology with a striped texture (x = 0,000) and there is a crack (x = 0.050). EDX results show that the constituent elements of the film are spread evenly with the composition according to the calculation. The TEM results show that the film particles have three tetragonal, orthorhombic and amorphous, polycrystalline rutile structures