Optical Properties of ZnO

Properties of ZnO

            Novel mechanical, electrical, chemical and optical properties introduce due to size reduction, and are believed to be due to improved crystal quality, surface and quantum confinement effects. Nano-scale structures of ZnO may enhance the compactness and efficiency of photonic and electronic devices including sensors, optical waveguides and LEDs. The structural, mechanical, chemical, electrical and optical properties of such kind of devices have already been enhanced by the small size of ZnO nanostructures. Although, ZnO has many applications in industry due to its bandgap in the near UV range and piezoelectric properties, but its utilization in optoelectronic devices still has not been successful because of the unavailability of reliable and proper p-type ZnO epitaxial layer. So in the absence of p-ZnO layer, hetero-epitaxy of ZnO with other p-type materials is being used to utilize its advantages. A p-n hetero-structure of n-type ZnO can be realized by employing a p type material, while still using ZnO as an active layer. Much progress has been made in such kind of n-p devices. For example, n-ZnO/p-AlGaN heterojunction is successfully made to produce high-intensity UV emission in which ZnO served as the active layer. Another potential application of ZnO is in homo-epitaxial devices. Among the various ZnO nanostructures, Nanorods or nanowires-like structures have higher potential for use in high performance devices and may be key material morphologies for future nanotechnology devices (Ozgur et al., 2005).

1.3.2. Optical Properties of ZnO

            Many properties of Zinc oxide have been under study from many decades which include optical properties as wll as refaractive index. The effective radiative recomination , large energy gape and high exicitaon energy has fanned the many applications of ZnO nnstructures in optoelctronic devices. Due to the strong excitaion energy which is high for ZnO and is a grater value as compared to other semiconductors oxide nanomaterials and high thermal energy makes it an efficient materail for the high excitation emission enables it to cause luminiscence at room temperature. These above properties makes it a valuable material to be become a photo materail at blue to the Uv region wavelenghts (Yang et al., 2009).

1.3.3. Electrical properties of ZnO

It is difficult to raise the electrical properties of ZnO for their potential applications in electronics and optoelectronics. However in this oredr the ZnO nanorods and nanowires are made to undergo electrical transport measurements. The ZnO nanowires are configured as the field effect tansistors wth numerious tricks and properties. The nanowires suspension has been done by using disperserd isopropanal alchohal solution. These nanowires are then posted on the SiO2 or Si substrate. The contact electrode rane is charactrized by using photolithology and back electrode rang is generated which is functioned by Si doped substrate. These nanowires are reported to become the n-type semiconductors due to oxygen vacancy and presence of interstitial zinc (Parihar et al., 2018).

1.3.4. Mechanical properties of ZnO

            It is very much a challanging task today to directly measure the mechanical properties of ZnO nanstructures because the traditional measurement methods are not applicable. The electric field induced resonance method is used uin this prospect sing TEM. In this technique a unique holder of TEM is made and two electrodes are utilized in between a oscillating electric field is applied. At a particular frequency this electric field generates the resonance in between the nonobelts shaken by the field. The bendin modulus is calculated based on the elasticity theory. These nanobelts show the most important prospects of being a promising material in form of nanoresonater and nanocontiliver. these cantiliver show the imoportant properties as compared to the products prepared by conventional icrotechnology (Wang et al., 2003). 

1.4. Applications of ZnO NPs

            Zinx oxide plays a vital and effective role in central nervous suystem (CNS) and even durin the process of disease developments via meditating neuron excitability and discharge of nurotransmitters. It has been revealed that ZnO is effective too much in the function of many tissues and cells, natural enggineering of cells and biocompatibilty (Osmond et al., 2010).

1.5. Nickle oxide and its properties

            Nickel is a chemical element with the chemical symbol Ni and atomic number 28. The unit cell of nickel is a face centered cube with the lattice parameter of 0.352 nm giving an atomic radius of 0.124 nm. Nickel belongs to the transition metals and is hard, malleable, ductile, lustrous, silvery white, ferromagnetic metallic element in Group VIII of periodic table. Nickel is one of three noteworthy elements in the transition metals family (iron, cobalt, and nickel) that are known to produce a magnetic field. The electronic structure of Ni is 1s22s22p63s23p63d84s2. Its outer electrons shell has a 4s23d8 configuration. While nickel can exist in oxidation states 0, +1, +2, +3, and +4, its only important oxidation state is 2 under normal environmental conditions. Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are magnetic at or near room temperature. Its Curie temperature is 627K. That is, nickel is non-magnetic above this temperature (Maiti et al., 2007).    

                  Figure 1.3: Crystal structure of nickel oxide

1.5.1. Uses of Nickle oxide

            Nickel is used in many industrial and consumer products, including stainless steel, magnets, coinage, rechargeable batteries, electric guitar strings, microphone capsules, and special alloys. It is also used for plating and as a green tint in glass.  Nickel is pre-eminently an alloy metal, and its chief use is in the nickel steels and nickel cast irons, of which there are many varieties. It is also widely used in many other alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminium, lead, cobalt, silver, and gold (Maiti et al., 2007).    

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