Preparation study of the Structural, Morphological and Optical properties of pure Tin Oxide Nanoparticle doped with Cu

: In this study, pure SnO 2 Nanoparticles doped with Cu were synthesized by a chemical precipitation method. Using SnCl 2 .2H 2 O, CuCl 2 .2H 2 O as raw materials, the materials were annealed at 550°C for 3 hours in order to improve crystallization. The XRD results showed that the samples crystallized in the tetragonal rutile type SnO 2 stage. As the average SnO 2 crystal size is pure 9nm and varies with the change of Cu doping (0.5%, 1%, 1.5%, 2%, 2.5%, 3%),( 8.35, 8.36, 8.67, 9 ,7, 8.86)nm respectively an increase in crystal size to 2.5% decreases at this rate and that the crystal of SnO 2 does not change with the introduction of Cu, and SEM results of the pure and doped confirmed that the particle size is within the range (25-56)nm within the nanosize. UV-Vis studies of reflection spectroscopy revealed that energy of band gap increased with increasing doping ratios (4.33,4.18 ,4.21, 4.21 4.23,4.35) ev For pure and doped with Cu (0.5%, 1%, 1.5%, 2%, 2.5%, 3%) respectively. Results of AFM show roughness rate, SPM and grain size of pure samples doped with Cu where the roughness rate of SnO 2 is (3.04, 25,27,16,41.8,23.6,25.2) nm and average diameter is (98.9, 72.56 ,92.91, 88.38, 76.79, 70.94, 71.21) nm for pure and doped with Copper (0.5%, 1%, 1.5%, 2%, 2.5%, 3%) respectively.


Introduction:
In recent years, nanotechnology has become one of the most priority areas in chemistry, physics and biology .The basis of nanotechnology is that the particle size is less than 100nm and thus we will get a new behavior that depends on the size, it has been observed that the conductivity melting temperature , mechanical and electrical properties ̒ change when the particles become smaller than Critical size 1 .Thus, stronger, lighter, and stiffer materials will be produced due to two important factors: Increased surface area , Quantum effect.
The impetus that caused this technology to advance so rapidly is the development of devices such as the Scanning electron microscope; the Transmission electron microscope; the Atomic force microscope and other devices 2 . The physical and chemical properties of nanomaterials differ compared to bulk in these materials, as the presence of atoms or impurities to modify the electronic, optical and magnetic properties of bulk semiconductors 3 . The researchers have been interested in metal oxide semiconductors due to their unique physical and chemical properties, these properties are increased and improved by doping other ingredients [4][5][6] . It is like these oxides:( (ZnO, TiO 2 , WO 3 , CeO 3 and SnO 2 etc 7,8 Tin oxide is an important material because it has a high degree of transparency in the visible spectrum. It has a strong chemical and physical interaction with absorbent species. It also has a low operating temperature. Strongly thermally stable in the air up to 500°C 9 , Tin has two types of oxides; stannous oxide (SnOromarchite) and stannic oxide (SnO 2 cassiterite) 10 .
Tin oxide (SnO 2 ) is one of the (n-type) metallic semiconductors that has a wide gap (3.6ev) in room temperature, and its excellent properties make it a suitable material for many applications, in transparent electrodes, solar cells, gas-sensing photocatalysts, photoelectric devices 11,12 Open Access Baghdad Science Journal One of the influences that affect the performance of the sensors is the increase in the surface area , as attention has been paid to preparing crystalline materials with a large surface area where the properties of crystalline materials are very sensitive on the surface of atomic structures, especially applications such as solar cells and gas sensors [13][14][15] . Oxide nanoparticles can be prepared by both Physical and Chemical methods. Chemical methods are better because they are easy to use and inexpensive Therefore, nanoparticles were synthesized by chemical methods 16 .
One of the inexpensive chemical methods that aims to create high-quality nanoparticles at low temperatures and not the need for a special atmosphere is the method of chemical precipitation, as in this study the pure and doped nanoparticles of tin oxide were synthesized and manufactured by this method 17 .
There are many processes for creating SnO 2 nanoparticles such as hydrothermal methods, chemical vapor deposition, Sol -gel method 18,19 ; However, in this study, SnO 2 pure nanoparticles were synthesized by the chemical precipitation method as well as the doped copper element .
Copper is a reddish-colored metal whose color and properties change when it unites with other elements in the form of different compounds that exist in several forms, single or combined such as oxides and it is a soft malleable substance that interacts chemically or physically with the external source, which is the atmosphere that creates rust. It has high electrical and thermal conductivity. The metal is the most electric and thermal conductor after silver 20,21 .
This study aims to prepare the nanomaterial from pure SnO 2 doped with Cu by the method of chemical precipitation, as this nanomaterial has wide applications including sensitizing gases such as (CO 2 , NH 3 ), data storage, in solar cells, antibacterial applications.

Preparation of pure Tin Oxide Nanoparticle and doped with Cu
Pure SnO 2 and doped with Cu nanoparticle were prepared by chemical precipitation method. 2g of tin chloride (SnCl 2 .2H 2 O) was used and dissolved in 100ml deionized water to make a 0.1M solution where molarity is given by relation 1 22 : The volume of deionized water , W: the weight , . : Molecular weight The resulting solution was placed on the stirring device (1500 rpm) for homogenization for 30 minutes, then a surfactant (Triton X-100) was added. We notice that the solution changed its color to white, then we add ammonia by distillation to the resulting solution while it is on the stirring device until it reaches the pH = 8, the color of the final product became milky. Then the solution was filtered and washed more than once in a centrifuge to separate unwanted materials, the product was left at room temperature for two days to dry out. After drying, the product was collected which was reddish-brown and annealed at 550 °C for 3 hours, and the final product was yellow in color after annealing. SnO 2 doped with Cu was prepared in the same way but by adding (0.5, 1, 1.5,2, 2.5, and 3) %wt of CuCl 2 .2H 2 O into SnCl 2 .2H 2 O and that is through the following relationship 2 23 : %dopants= The molar concentration doped CuCl 2 .2H 2 O(X) , % dopants : doped concentrations (0.5, 1, 1.5,2, 2.5, and 3) %wt , 2.2 2 : 0.1 M The color of the solution changed to green, the intensity of the color changed with the concentration, annealing the concentrations at 550°C for 3 hours in the presence of air.

Characterization
The X-ray diffraction (XRD) pattern of pure SnO 2 and doped with Cu nanoparticles were recorded by a system Siemens model D500 using CuKα,λ=0.154 nm. The particle morphology and size were examined by scanning electron microscopy (SEM) ZEISS model SigmaVP with a magnification of 50.00KX and (EDX) Oxford instruments UK. Optical properties were analyzed by means of ultraviolet diffusion. The Reflection Spectroscopy with UV-VIS (Shimadzu) was done within the wavelength range of 280 nm-900nm. The AFM showed the morphology of the SnO 2 NPs, and the average grain size was found by the cumulative distribution plot. Results and Discussion: XRD analysis Fig1 shows the XRD pattern of pure SnO 2 and doped with Cu nanoparticles with concentrations of (0.5%, 1%, 1.5%, 2%, 2.5% and 3%)w% respectively and annealing at 550°C for 3 hours. All samples were identified as tetragonal rutile, and the results are in agreement with JCPDS standard card No. (96-900-9083) where the diffraction peaks coincide with the standard data from (110), (101), (211) and the most obvious peak is (110). There are no identical peaks for Cu .The results match those of the researchers Sagadevan et al. 24 . and this leads to the conclusion that there are two types of doped SnO 2 with Cu: substitutive and interstitial. In this case, some ions are replaced by Sn + with a Cu + ion based on similar radius Cu, Sn d : is the mean crystalline size, κ is the constant 0.89, λ is the wavelength of the incident beam (λ=1.5418Å) Cukα, β is the full width at half maximum,θ is the Bragg diffraction angle (in degrees). The crystal size of pure SnO 2 is 9.9nm, but when doped with Cu, it becomes less than 8.35nm. The reason for this is the quantum confinement effect. When increasing the doping led to an increase in the crystal size because the radius of Cu greater than Sn increased the G.S, but at 2.5% the size decreased. The reason for this is that there were defects in the system that led to the deflected of the diffraction angle of 2θ so the distance between the atomic levels decreased (d) according to Bragg's law (nλ=2d sinθ) 27 as a result of which increased FWHM( ) according to Scherrer eq.3 at 2.5% the crystal size decreases ,Tab. 2 shows the lattice constants for pure SnO 2 nanoparticles and doped with Cu , which can be calculated using the eq. 4 :    Fig.2 shows the SEM images of the pure SnO 2 and doped with Cu nanoparticles at proportions (0.5%, 1%, 1.5%, 2%, 2.5%, 3%) respectively prepared by chemical precipitation method.
Since the SEM images give clarity about the surface morphology and the average particle size shown in this figure ranges from 25nm to 56nm, these nanoparticles contain spherical shapes with sizes smaller than 100 nm (Sarmah et al.) 28 . The particles were agglomerated, and the reason for this was due to the adhesion of particles to each other by the forces of Vander Waals, and the reason was due to the formation of covalent or metallic bonds that could not be separated easily 29 . Its reason is that during the process of initial contact of water molecules with SnO2, these agglomerations occur and lead to the trapping of water between the particles. Also, the electric charges between the particles affect the agglomeration of the particles. The mutual electrostatic repulsion force is produced between the neighboring particles 30 It can be noted that crystallite size ≤ grain size ≤ and particle size (i.e. Particles made up with grains and grains made up with crystallites) Crystal size measured in XRD and grain size and particle size in, SEM AFM. The crystal size does not exceed 10 nm. And the size of the grains did not exceed 60 nm, but the size of the particles was less than 100 nm 31,32

Optical studies
In order to better understand the effect of copper doping on the optical properties of SnO 2 nanoparticles at different concentrations. This UV-VIS Spectroscopy analysis was performed. Fig.4 shows the variation in absorbance with wavelength within the range of 280 nm-900 nm(The energy gap was within this range) for the pure SnO 2 samples and doped with Cu ions where the band gap is calculated using the Planck eq.4 33 : The energy gap for pure SnO 2 nanoparticles doped with concentrations (0.5, 1, 1.5, 2, 2.5, and 3)  Table 4. which shows how the energy gap value increases with increasing concentration Cu and decreases with increasing wavelength.The results match those of the researchers Saikia et al. 34 due to blue shifts as a result of the quantum confinement effect Sharma et al. 35 , Vayssieres et al. 36 . It can be seen from Tab.4 below that the bandgap in pure is 4.33 ev and when copper doped decreased to 4.18 ev. The reason is due to the fact that the radius of the Cu +2 impurity ion is equal to 0.73Å when compared with the radius of the material Sn + 4 approaches 0.69A°, and this leads to the entry of copper impurities into the crystal of SnO2 in the form of an alternating impurity. When doping Cu by 0.5%, we notice that the energy gap decreased to 4.18 ev due to the formation of localized levels, but with the increase of doping, the band gap increased because the doping system is destroyed and works to destroy the lattice levels and thus increase the band gap and lead to an increase in oxygen vacancies and reduce the concentration of free electrons. The confinement of electrons and holes increases the band gap. and it all depends on where the Fermi level of doping is located, which causes tape tails to appear. As a result, the band gap effectively decreases or increases 37 SnO 2 n-type. after doping, band gap will increase because of rise number of majority carriers  Fig.5 shows an atomic force microscope image of the pure SnO 2 sample surface and doped with Cu at different concentrations and annealed at 550 ° C, in 2D and 3D directions, to calculate the average surface roughness and average particle size as shown in Tab.5 below , i.e. the increase and decrease in the roughness rate and the average size pure SnO 2 nanoparticles and doped with Cu , From the Table 5, it can be noticed that the roughness is not related to the size of the grains, but from Fig. 5. the cumulative report explains this, as when the difference between the particle sizes is large, the roughness is greater, as is evident at 2%, although the average size was less, but higher roughness. Crystalline size is smaller than grain or particle size. inside a grain or particle, we have many crystals of identical orientation. Particle size and grain size are not same. one particle can have several grains 38 From Tab.5, we note that the best roughness is at the concentration of copper 2%, and this indicates that this percentage is the best in medical applications.

Conclusion:
In this paper, pure tin oxide nanoparticles have been synthesized and doped with copper by chemical precipitation method, this method is simple and effective to form Tin oxide nanoparticles. The compositions of the pure tin oxide nanoparticles and doped with different concentration of Cu are characterized by XRD, SEM, AFM and UV -VIS Spectrometer. The XRD pattern shows that the Tin oxide nanoparticles formed from this synthesis are tetragonal polycrystalline and that the crystal size is (9.97,8.35,8.36,8.67, 9,7, and8.86) nm for pure samples and doped with (0.5,1,1.5,2,2.5, and 3) wt% of Cu. The results of the AFM show that the grain size within the nanoscale, are spherical in shape with different sizes ranging from (98.9 ,72.5, 92.9 ,88.3 ,76.7 ,70.9,71.2) nm. The higher roughness is 41.8 nm for sample doped with 2%Cu. The roughness of pure samples is 3.04 nm. The uvvis spectroscopy results show that the energy gap increases with increasing doping. From the results obtained, it is evident that the prepared samples can be used in various electronic applications, such as using them as a gas sensor as well as in various medical applications such as cancer.