Enhanced Optical Conductivity Nonlinear Optical Free Essay Example

Abstract

Mg1-xCuxO /PMMA nanocomposite films (where x = 0.05, 0.1, 0.15 and 0.2) samples were prepared using solid-state reaction technique. The values of both of dispersion energy (Ed) and oscillating energy (Eo) were determined optically, and these values decreased with increasing Cu content. The calculated values of free carrier concentration/effective mass) (N/m*) decreased with increasing Cu content. On the other hand, the values of first order of moment (M-1), the third order of moment (M-3) and static refractive index (no), were determined.  The determined values of real part of optical conductivity (?1) and imaginary part of optical conductivity (?2) increase with Cu content.

The Linear optical susceptibility increases with for all samples. The nonlinear optical parameters such as, nonlinear refractive index (n2), the third-order nonlinear optical susceptibility (, non-linear absorption coefficient, were determined theoretically. Both of The electrical susceptibility and relative permittivity increase with (h?). The semiconducting results such as, density of conduction band/electron effective mass ( Nc/ m*e (cm-3)), density of valence band/ hole effective mass (Nv/m*h (cm-3)) were calculated.

 Introduction

A nanocomposite is a composite material, in which one of the components has at least one dimension that is nano size . Inorganic/organic composite materials had attracted attention because of their excellent properties, such as high mechanical strength, magnetic and thermal flexibility, dielectric, ductility and processibility . These composite is a promising materials as a result of their applications. Such as super capacitors, rechargeable batteries, and antistatic textiles [10-12]. Poly (methyl methacrylate) (PMMA) is an imperative material which achieve excellent optical, electrical properties and high thermal stability.

Many scientists concentrate their attention to synthesis of the nanoparticles of transition conducting metal oxides (TCMOs). TCMOs were synthesized using different technique such as :Direct mixing of nanoparticles in the polymer, Sol gel methods, in-situ techniques and deposition method.The II VI semiconductor nanocrystals achieve an excellent physico-chemical properties to get a new optoelectronics and nano-electronics .

Synthesis and characterization of CuO MgO nanocrystal was studied by different techniques. The influence of doping on optical properties of PMMA had been studied by many authors. It was found that, the fluorescence branch ratios for is evaluated. For Nd(DBM)3Phen-doped PMMA, that absorption in PMMA films with Nd dopant is due to intratransition within the 4f shell of the Nd3+ ion, The energy band decreases with access of CdS in PMMA matrix[34], ZnO dopant decreased energy gap in PMMA/PVDF-ZnO nano composites[35]. While the nonlinear optical properties of doped PMMA were studied, it was noticed that, nonlinear absorption decreased with increase the filler PMMA doped with Ag enhanced a negative nonlinear refractive index[39], On the other hand The structure and optical properties of Mg1-xCuxO/PMMA nanocomposite films were studied in pervious work, it was found that, the energy gap decreased with increasing Cu content.

In this paper we study the influence of Cu content on the optical conductivity, linear optical susceptibility, nonlinear optical results and density of both valence and conduction states, for the Mg1-xCuxO /PMMA nanocomposite films.

Results and Discussion

Optical conductivity, VEL/SEL, linear optical susceptibility results. The influence of Cu content on optical transmittance (T) and reflectance (R) for these samples were measured and discussed in previous work. The single oscillator theory was expressed by the Wemple DiDomenico relationship. Where n is the refractive index values of these samples which is determined in previous work, E is the photon energy . The values of Eo and Ed with different Cu content values are shown in table 1. The ratio values of carrier concentration /effective mass (N/m*) using the following equation  where  is the lattice dielectric constant, ?o is the permittivity of free space, e is the charge of electron, n, k are the linear refractive index and the absorption index of these films respectively, which were determined in previous work [40] N is the free carrier concentration for these films and c is the speed of light, so the values of (N/m*) are determined by plotting (n2) vs. (wave length)2 (?2) as shown in Fig.1. It is known that the refractive index depends on the density of the material so when an additive increases in material then the refractive index increases, but in figure 1, we can observe that the refractive index of Mg1-xCuxO /PMMA composites decreases and then increases. The reason of this behavior can be explained depending on Ewald-Oseen extinction theorem [43] when an electromagnetic wave incident on the material, the atoms and electrons excited, so they will oscillate and emit electromagnetic waves in the same frequency of the original electromagnetic wave but with different phase which interface with the original wave, because of that the phase velocity of the new electromagnetic will change. The values of (N/m*) is shown in table 1. From this table it was noticed that (N/m*) increases with Cu content as a result of increasing carrier concentration with Cu.

The values of the ( f ) are shown in table 1. Another important parameter depending on both of Eo and Ed is that, static refractive index (no) which was determined as follow [44]:

The values of no for all these samples are shown in table 1. It is noticed that no increases as Cu content increases, this may be attributed to the difference in covalent radius of Mg (130Pm) and Cu (138Pm). The dependence of (n2-1)-1 on (h?) is shown in Fig.2. It is shown that the refractive index depends on the Cu content.

Figs 4(a,b) show, the both of and dependence on (h?) for these films. The increasing of the optical conductivity ?1 and ?2 at high photon energies may be arising from the electron excited by photon energy and also may be attributed to the high absorbance of sample thin films. The behavior of both (?1) and (?2) for all these studied films is the same with (h?), and also (?1) and (?2) increase with Cu content as a result of increasing free carrier concentration with Cu, which leads to increase of electron mobility and finally increase of both (?1) and (?2).

The values of the Volume Energy Loss Function (VELF) and Surface Energy Loss Function (SELF) for these films were determined optically.

The relation between VELF/SELF for these thin films is shown in Fig. 5. Linear optical susceptibility (?(1)) describes the response of the material to an optical wavelength, (?(1)) was determined using the following relation.

The relation between (?(1)) and (h?) for these investigates samples is shown in Fig.6, from this Fig. it was seen that, the (?(1)) increased with (h?), this means that, there is a possibility of wide change in optical properties with change doping, while the values of (?(1)) increase with Cu content due to the increase of free carrier concentration with Cu, which give the high possibility for a large number of electron to absorb light and go up to upper energy level for these samples.

 Nonlinear optical properties

An important parameter of the non-linear optical parameters is that the nonlinear refractive index (n2), which can be explained as, when light with high intensity propagates through a medium, this causes nonlinear effects[48], n2 was determined from the following simple equation.

Nearly the same for all materials =1.7 x 10-10 e.s.u. It was noticed that, the behavior  is the same for all the studied samples, the values of .increses with Cu content, this is due to, when Cu content creases this leads to increase of both of carrier concentration and also the mobility of electrons which caused decrease of defliction of the incident ligth.

On the other hand, another important nonlinear parameter such was non-lnear absorption coefficient.

Fig.  shows the electrical susceptibility (?(e)) dependence on (h?) of these investigated samples. From this figure it is clear that, the values of (?(e)) increase with (h?), and also the(?(e)) increase with increase of Cu content this is due to, the electron mobility increases with Cu ratio.

The relative permittivity ?r was calculated using the following relation.

The relation between relative permittivity (?r) and (?) studied samples is shown in Fig. 11. It is clear that, the values of (?r) increase with (h?) for all these samples; this could be attributed to, the electron mobility increases with (h?).

Semiconducting and electronic results

The density of states (DOS) of a system describes the number of states per interval of energy at each energy level available to be occupied. The Nv and Nc play very important rule of examination the linear optical transition and non-linear optical properties. Where Nv and Nc were the density of states for both valence and conduction bands respectively.

Conclusion

The effect of Cu content on optical conductivity, nonlinear optical results and semiconductiong results of Mg1-xCuxO /PMMA nanocomposite films with (0.05? x? 0.2) were studied. The values of (Eo) and (Ed) increased slightly with Cu ratio in these studied samples, and also the determined values of both (M-1), (M-3) and (f ) increased with Cu content, this is duo the increase of free electrons number and also electrons mobility’s with increasing Cu ratio, which affected also on the both values of (?) and (?). (?(1)) slightly increases with (h?) for all samples, this means that, the optical response of these films to increase with (h?), while (?(3)) increased with Cu content, this means Cu content increase the ability for changing optical properties, also the values of (n2) increase with increasing Cu content of these studied samples. The non-linear absorption coefficient (?c) increased with Cu ratio, also both of the (?(e)) and (?r) increase with Cu content, as a result of increasing the free carrier concentration and also the electron mobility’s, which leads to the values of both of (?(e)) and (?r). The Cu ratio had affected on the values density of conduction band/electron effective on both of ( Nc/ m*e (cm-3)) and (Nv/m*h (cm-3)).

Table 1: The influence of Cu content on the determined values of PMMA/Mg1-x CuxO thin films such as ?L, Eo, Ed, M-1, M-3, (f), (no), (N/m*e) and ( Nc/ m*e (cm-3)) and (Nv/m*h (cm-3)).

NV//m*h NC/m*e N/m* no Field strength (f) (eV)2 M-3 (eV) M-1 (eV) Dispersion energy Ed (eV) Oscillation energy Eo (eV) lattice dielectric constant ?L Sample

9.5E+20 9.2E+20 1.3E+49 1.43 91.14 3.13 9.55 9.80 9.30 1.50 PMMA

9.5E+20 9.2E+20 2.5E+49 1.44 81.78 3.07 9.04 9.40 8.70 1.20 PMMA/Mg0.95 Cu0.05O

9.5E+20 9.2E+20 5.2E+49 1.44 79.12 3.03 8.89 9.20 8.60 1.90 PMMA/Mg0.90 Cu0.10O

9.5E+20 9.2E+20 8.5E+49 1.44 75.60 3.00 8.69 9.00 8.40 1.30 PMMA/Mg0.85 Cu0.15O

9.5E+20 9.2E+20 1.1E+50 1.45 72.09 2.98 8.49 8.90 8.10 1.95 PMMA/Mg0.80 Cu0.20O