Nano Materials Synthesis, Properties, Nano Materials Synthesis, Properties, Applications, etc. Applications, etc. Zinc Oxide ( ZnO )Zinc Oxide ( ZnO )

WAQI AHMED NAJAMWAQI AHMED NAJAM31159991183115999118 Master Of Electronics And Information Master Of Electronics And Information Engineering (MEIE)Engineering (MEIE)Email: Email: waqinajam@qq.comTel: 18629489487Tel: 18629489487

Date Of Presentation : November 19Date Of Presentation : November 19thth 2015 2015

Characteristics of crystal lattice:Each constituent particle is represented by one point in a crystal lattice. These points are known as lattice point or lattice site.Lattice points in a crystal lattice are joined together by straight lines. By joining the lattice points with straight lines the geometry of the crystal lattice is formed.Unit Cell – The smallest portion of a crystal lattice is called Unit Cell. By repeating in different directions unit cell generates the entire lattice.There are three types of Centered Unit Cell.(a) Body Centered Unit Cells: – If one constituent particle lies at the centre of the body of a unit cell in addition to the particles lying at the corners, it is called Body-Centered Unit Cell.(b) Face-Centered Unit Cells: – If one constituent particle lies at the centre of each face besides the particles lying at the corner, it is known as Face-Centered Unit Cells.(c) End-Centered Unit Cell: – If one constituent particle lies at the centre of any two opposite faces besides the particles lying at the corners, it is known as End-Centered Unit Cell. It is also known as base-centered unit cell.

Orthorhombic Cubic Lattice Cubic Lattice

 The lattice constants are a = 3.25 Å and c = 5.2 Å; their ratio c/a ~ 1.60 is close to the ideal value for hexagonal cell c/a= 1.633. Wurtzite Structure

Wurtzite Structure

In this chemical route, we used the inc Acetate [Zn(CH3CO2)2.2H2O] precursor as a inc ion source. In this typical synthesis process of ZnO nanocrystals, the inc Acetate was dissolved in NaOH with a molar ratio of 1:85. The solution was strongly stirred with reflux at a constant temperature of 80°C for 3 hour. Finally, white precipitate was formed within the solution. The solution was filtered by a Whatman filter paper of precise porosity. The precipitate was washed repeatedly many times by ethanol to eliminate impurities. The washed precipitate was annealed at a temperature of 100°C in an oven for 2 hour and ground into fine powders. The fine powders were characterized using XRD, SEM, UV–vis, and photoluminescence spectroscopy. The absorbance spectrum of the annealed powders was obtained in the range of 200 to 900 nm using JASCO UV–VIS-NIR spectrometers (Model-V570, Jasco Analytical Instruments, Easton, MD, USA).

The X-ray diffraction studies indicated the development of hexagonal structure of the chemically synthesized ZnO nanocrystals.

The different peak orientations were observedalong the (100), (002), (101), (102), and (110) planes.

The typical hexagonal wurtzite structure of the synthesized ZnO nano particles is inferred from the XRD pattern, which is in good agreement with the intrinsic fundamental structure of ZnO as reported in the literature.

The crystallite size (D) of the synthesized ZnO nanocrystals was calculated using the Debye-Scherrer formula as given below. D= kλ / β2θcosθWhere k is a constant taken to be 0.94,λ is the wavelength of the X-ray used (λ=1.54 Å),β2θis the full width at halfmaxima of the (002) peak of the X-ray diffraction pattern,and 2θis the Bragg angle around 34.44°. Finally, the calcu-lated average value of grain size is found to be 25 nm.

The photoluminescence spectroscopy is an excellent intensive technique for the investigation of the exact band edge transition levels of a material.

A well-defined photoluminescence spectrum of the synthesized ZnO nano crystals is depicted in Figure 5.

The ZnO nano crystal PL spectrum showed a very strong and intenseemission peak at 365 nm, exactly near the band edge emission, while showing no trap-related emission.

From the PL study, the optical band gap of the synthesized ZnO nano particles was estimated to be 3.5 eV.

A broad green-yellow illumination peak is observed over 450 to 600 nmwhich is attributed to the amount of non stoichiometry.

Chemical impurities may also cause a surrounding of structural defects by distorting the lattice as well as the surface of a crystal.

The absorbance spectrum of the synthesized ZnO nano-crystals is shown in Figure 3.

From Figure 3, it is evident that the ZnO nanocrystals showed high absorbance in the wavelength range of 200 to 270 nm in the absorbancespectrum.

The absorbance decreases abruptly near the band edge around 365 nm, after which it turns to the transmittance region.

Optical band gap of the synthesized ZnO nanocrystals was critically examined by the following equation.

αhν=A(hν-Egm)2 where A is the characteristic parameter (independent of photon energy) for this transition , h is Plank's constant, and ν is the frequency of the light. Eg is the band gap, and m is the parameter which characterizes the transition process involved.

(1/μ=1/me+1/mh), where mass of electron(me) =0.19 and mass of hole(mh)=0.8.

In this study, ZnO nano crystalline powders were synthesized successfully with hexagonal phase through the novel chemical route using inc Acetate as organic precursors. The optical band gap value of the synthesized ZnO nanocrystals is found to be 3.50 eV from the absorption spectroscopy, while the photoluminescence spectrum reveals a strong emission at 365 nm along with a broad green-yellow emission. In this investigation, a blue shift observed in both of the absorbance optical studies and PL spectroscopy on the ZnO nano particles indicates quantum confinement of carriers, which confirms the effective particle size reduction of the synthesized ZnO powders.