Chapter one 1-1 Introduction

Chapter one 1-1 Introduction: Nanotechnology speaks to the plan, creation and use of materials at atomic, molecular and macromolecular level, keeping in mind the end goal to deliver new nano - sized materials [ 1]. As

of late, the

meeting of nanometer size scale advancements and biological techniques has paved way for the new field of Nano biotechnology. It is generally centered around the creation, control, and utilization of materials at the nanometer scale for cutting edge biotechnology [ 2]. The studies has been expression "nano" originates from the Greek word "nanos" which means dwarf and signifies an estimation on one (109) of a meter in size. It

billionth

envelops rameworks whose size is

above sub-atomic measurements and beneath naturally visible ones (i.e. > 1 nm and < 100 nm) [ 3].

Nanotechnology deals with

structures so tinny and undetected to the natural eye, so it provides the capability to synthesis materials and systems with essentially new functions and properties[ 4]. It has effects for almost every type of builtup process and result so that promise of nanotechnology is enormous. Its claims in the next few generations could give huge increases in different fields of medicines and industries [ 5]. The term “Nanoparticle” is referring to particle where all the three dimensions are nanometer in scale;

contain small enough

number of constituent atoms or molecules that they differ from the properties inherent in their bulk counterparts, exist in diverse shapes such as spherical, triangular, cubical, pentagonal, rod-shaped, shells, ellipsoidal and so forth [ 6 ]. Synthesis of nanoparticles in matrixes such as polymer films is of major interest in several optical, nonlinear

optical and sensor applications. Silver nanoparticles are an increasingly important material in many technologies [7] 1-2 Synthesis of Nanoparticles Synthesis techniques to generate metal nanoparticles depend on isolation of small amounts of a material. There are two general strategies mechanism to obtain materials on the nanoscale;

first: The top- down

method (dispersion method) is where material is removed from the bulk material, leaving only the desired nanostructures. Second: The bottom –up method (reduction method) is one where the atoms produced from reduction of ions, are assembled to generate nanostructures [8].this explain in fig(1-1)

Figure (1-1) Methods of nanoparticle production [10] 1-2-1 Dispersion Methods (Top down method) The Top- down method typically starting from bulk involves laser ablation arc discharge [9], etc... Nucleation takes place starting from the plume and continues till a solid substrate comes in its way. Control of particle size is achieved by tuning the fluence, wavelength irradiation time ...etc. The

above crude method may be modified by altering the

design of the cluster. Top- down techniques suffer from the need to remove large amounts of material [ 10]. One of the methods used: 2

1-Milling method: It is a mechanical method that produces nanoparticles in powder form where the material is placed under very high energy and is crushed by steel balls that move either planetary, vibrational or vertical and can be made of (3 to 25) nm powder[11 ]. Shown fig (1-2)

Fig (1-2)

Move crunching balls [11]

2- Etching method :This method was used by Professor Munir Naifah to produce

nanoparticles, either

in

chemical

or

electrochemical ways. The chemical method is taken with very thin silicon filaments and placed in HF materials and other materials), which scans the silicon slices and then exits chemical molecules such as silicon. They are placed on the surface and then placed in any solution you want, such as tetrahydrofuran, methanol, or..... Once placed in the solution you want, Ultrasound so that silicon particles fall into the solution and are attached to the solution [10]. 3- Electrochemical method: Where the silicon chip is placed in the positive electrode and the polycarbonate chip in the negative electrode and subjected to an electric current. This is after placing it in a chemical solution composed of chemicals that helps the process of spinning out the silicon nanoparticles [11].

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4- Laser ablation method: A high-energy pulse laser centered on a solid object is used in a vacuum chamber or liquid. The laser beam reactes to the target. The particles fly to form plasma and are deposited on the base. This method was first used in 1960 using sapphire laser but the thin films produced were contaminated and with research this method was improved [12]. 5- Sputtering method: Fig (1-3), it is used to make thin films where the material is placed under very low pressure discharged from the air and a cool base exposed to a magnetic field all these factors lead to the molecules are extracted from the material (or tails) to be deposited at the baseTo be thin film and must be placed gas to prevent aggregations.[10]

Fig (1-3) Image device Sputtering [13] 1-2-2 Reduction Methods (bottom up method) The

bottom - up

chemical electrochemical , photochemical

method

starting

from

sono - chemical

atoms, , thermal

reduction [7],...etc, have been used

include and

to generate

nanoparticles. Bottom- up synthesis techniques usually employ an agent to stop growth of the particle at the nanoscale. Capping materials, such as a surfactant or polymer are used to prevent

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aggregation and

precipitation of the metal nanoparticles out of

solution[10]. One of the methods used: 1-(sol_ gel) method: It passes through the two phases of the fluid phase and then after a period of the material evaporates into the gel phase and this is called the sol-gel method [11]. 2- Aerosol method: This is the same method of sol gas but it starts with the gas phase and ends with the phase of the liquid [11].

1-3 Laser ablation Pulsed laser ablation (PLA) was first developed in the 1960s, shortly after the invention of the pulsed ruby laser. Since then, laser ablation in a vacuum or dilute gas has been studied by many researchers. By using different target materials and background gases, and varying parameters such as the laser wavelength, fluence, and pulse duration, it is possible to produce a wide variety of thin films [14].The thin films have a variety of applications, for example semiconductor devices, electrodes, and wear-resistant coatings [15]. The introduction of pulsed laser ablation at the solid-liquid interface was first reported by Patil and co-workers in 1987, which used a pulsed laser to ablate a pure iron target in water to form iron oxides with metastable phases [16]. This method is known as Liquid Phase Pulsed Laser Ablation (LP-PLA), in which a solid target is immersed in a liquid medium and the laser beam is focused through the liquid on to the target surface [17]. The initial process of laser ablation is the interaction of light with the solid target surface which causes vaporization of the solid target and a small amount of surrounding liquid. Chemical reactions between the ablated species and molecules in the liquid can subsequently occur as

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the ejected species are highly excited

[18]. The prolonged interaction

with the laser radiation may occur, leading to reaction products are typically NPs composed of atoms from both the target and the liquid, which form a suspension in the liquid. Due to the accumulation of these NPs in the surrounding liquid,

forming

colloidal solution further

changes in the NPs composition, size or morphology [19]. Laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave laser beam if the laser intensity is high enough [20]. Show fig (1-4)

Fig (1_4) Preparation of nanoparticles by Laser in Solution [20]

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1-4 Colloids Thomas Graham (1861) studied the ability of dissolved substances to diffuse into water across a permeable membrane. He observed that crystalline substances such as sugar, urea, and sodium chloride passed through the membrane, while others like glue, gelatin and gum arabic did not. Graham thought that the difference in the behavior of „crystalloids‟ and „colloids‟ was due to the particle size. Later it was realised that any substance, regardless of its nature, could be converted into a colloid by subdividing it into particles of colloidal size [21].look to fig (1-5)

Fig (1-5) Types of solutions [21] The colloidal solutions or colloidal dispersions are intermediate between true solutions and suspensions. In other words, the diameter of the dispersed particles in a colloidal dispersion is more than that of the solute particles in a true solution and smaller than that of a suspension [22]. A true solution is a homogeneous solution in which the solute particles have diameters lesser than 1 nm i.e., the solute particles are of molecular dimensions [11].

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A colloid is a suspension of particles in range from 1 nm to 1 μm in size. Many colloidal particles can, however, be detected by the way the scatter light, such as dust particles in air. This particles are in state of constant random movement (Brownian motion) arising from collisions with solvent molecules, which themselves are in motion. Particles are kept in suspension by repulsive electrostatic forces between them [7]. Suspensions are heterogeneous systems. They stay only for a limited period i.e. these are not stable as the particles have a tendency to settle down under the influence of gravity. The particles of a suspension can neither pass through ordinary filter paper nor through animal membranes, e.g. sand in water, oil in water [12].

1-5 Historical Review In (2000), Reji Philip , and et.al.[23] used Monolayer-protected Au, Ag . The particle-size distribution is narrow with an average core size of (3–4) nm. Optical nonlinearity induced by 35 ps pulses at 532 nm has been investigated in these samples using the Z-scan technique. It is found that in general, they behave either as saturable absorbers or reverse saturable absorbers depending on the intensity of excitation. In (2001), R A Ganeev, and et.al.[24] The investigations of the nonlinear optical parameters of Ag colloidal solutions using the Z-scan method. The nonlinear refractive indices, nonlinear absorption coefficients of these solutions on the wavelengths of nanosecond Nd:YAG laser radiation (λ = 1064 nm) and its second harmonic (λ = 532 nm) have been measured. Shown that Cu, Ag and Pt colloidal solutions have a nonlinear refractive index with a positive value (for λ = 1064 nm). In (2001) A. V .Simakin ,et al [ 25] used laser ablation of Au and Ag targets in water by a Cu vapor laser generates Au and Ag sols. The 8

metal nanoparticles obtained after evaporation are disk-shaped (diameter in the (20-60) nm range, thickness of few nanometers). Their formation is observed at laser fluence between 10 and 20 J/cm2 . Both aqueous sols are characterized by well-resolved plasmon bands around 400nm (Ag) and 520 nm (Au). In (2002) Chang Hyun, et.al. [26] Used silver nanoparticles were synthesized by laser Nd : YAG, ʎ =1064 nm ) ablation of a silver target immersed in various concentrations of NaCl Solutions as well as in neat water. The concentration dependence of the surface plasmon absorption at around 400 nm was examined by analyzing the absorbance and peak shape. In (2003) Tsuji et al. [27] studied the preparation of Ag NP by laser ablation in water with femtosecond laser pulses at 800 nm. The formation efficiency for femtosecond pulses was significantly lower than nanoseconds pulse. In 2005, Pyatenko et al [28] prepared silver nanoparticles with 8 nm, by irradiating a silver colloid, prepared via the citric reduction method, using 532 nm Nd:YAG laser, with laser fluence more than about 0.2 J/cm2. In (2006) Zhao et al. [29] synthesized of Ag NP by laser ablation in water with excitation of 532 nm and 248 nm. It is proved that all of them are effective SERS-active substrates. In (2006) E. V . Zavedeev, et al [30]. The formation of a dense array of nanospikes is studied upon ablation of a silver target immersed into water or ethanol by 350-ps pulses from a neodymium laser. The irradiated surface is studied by using reflection spectroscopy in the 200–600-nm range and an atomic force microscope. The Plasmon resonance of

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nanospikes is observed at 380 nm and shifts to the visible region upon oxidation in air. In (2007) S.Porel ,et al [31]. A simple methodology is developed for the fabrication of freestanding polymer films with embedded silver nanoparticles grown in situ. Strong nonlinear absorption, positive nonlinear refraction, and efficient optical limiting in the femtosecond regime are demonstrated with these films. In (2007) Stephan Barcikowski, et al [32]. Fabrication of silver nanoparticle colloids using ultrashort pulse laser ablation in water is studied. Femtosecond laser ablation in water is 20% more efficient than picosecond laser ablation, but due to higher picosecond laser power (higher repetition rate), the nanoparticle productivity at the same pulse fluence is three times higher for picosecond laser ablation. In (2007) Phuoc et al.[33] fabricated the multi-pulse Nd-YAG lasers operating at 1064 nm laser ablation of silver in deionized water, arranged in a cross-beam configuration. It‟s found that the cross-beam ablation can increase the ablation rate and promote reduction of the particle sizes and particle size distribution. In ( 2008), Werner et al.[34] studied the formation of silver nanoparticles by nanosecond pulsed-laser irradiation (1064 and 532 nm, at 1 J/cm2) of silver flakes in alcohols such as methanol and ethanol, the NPs are extremely unstable and easily settled down to form precipitates. In ( 2008) Siskova et al.[ 35] synthesized Ag nanoparticles by laser ablation of a Ag target immersed in water and in aqueous electrolyte solutions (HCl, NaCl, NaOH) as stabilization of the resulting Ag nanoparticles.

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In ( 2008), Tsuji et al.[36] prepared silver nanoparticles by laser ablation of a silver plate in PVP aqueous solutions. Secondary laser irradiation onto the prepared colloidal solutions was also carried out. It was found that the formation efficiency was increased by addition of PVP as well as the stability of nanoparticles with fine particles no more than 4 nm. In (2009), M. Esposito, and et. al. [37] showed that the ion dynamics of silver ablated by Nd:YAG pulsed laser irradiation in vacuum by using (PLD). The kinetic energies of the ablated silver ions were measured to be between 5 and 40 eV depending on the laser fluence.

In (2009), Alonso, and et. al. [38] report the deposition of thin films of silver (Ag) nanoparticles by pulsed laser ablation in vacuum using Nd:YAG laser.The presence of Ag nanoparticles in the films was also evidenced from the appearance of a strong optical absorption band associated with surface plasmon resonance. This band was widened and its peak shift increased as the number of laser pulses was increased. In (2010), Xiaoqiang Zhang,et al [39]. The nonlinear-optical properties of metal Ag colloidal solutions, which were prepared by the reduction of silver nitrate, were investigated using Z-scan method. The data fitting result of optical limiting (OL) response of metal Ag colloidal solution indicated that the nonlinear absorption was attributed to twophoton absorption effect at 532 nm.

In (2010) H. Aleali, et al [40] In this study, the nonlinear optical properties and optical limiting performance of the silver nanoparticles (Ag NPs) in distilled water are investigated. The nonlinear absorption coefficient of the colloid is measured by the Z-scan technique. The optical

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limiting behavior of the Ag NP suspension is investigated under exposure to nanosecond laser pulses at 532 nm. The results show that nonlinear scattering can increase the performance of the optical limiting .

In (2010), Esmaeil . SH,et al [41] The nonlinear optical characteristics of silver nanofluid synthesized by γ-radiation technique The measurements were performed by a single Z-scan method using CW laser beam excitation wavelength of( λ = 532 nm). It is shown that the nonlinear refraction of the samples caused by the thermal effect increased nonlinearly with particle size.

In (2010), Karimzadeh et al.[42] synthesized silver nanoparticles by nanosecond pulsed laser ablation of silver plate in distilled water. The results showed narrow size distribution of the nanoparticles with radius centered at about 9 nm with a standard deviation of 3 nm.

In (2011), Anwar Latif [43] explored changes in structural, morphological, electrical and optical parameters for four transition metals, platinum (Pt), gold (Au), silver (Ag) and copper (Cu). Samples are exposed to Nd:YAG laser (1064nm,( 9-14)ns, 10mJ) for different number of shots (25, 50, 75, 100) in air as well as under vacuum (10 -3 torr and 10-6 torr). In Au and Ag, the decrease is in accordance with Boltzmann function.

In (2011), Khalaf et al [ 44] Silver nanoparticles were synthesized by pulsed laser ablation (Q-switched Nd:YAG, λ=1064nm, 10 ns pulse duration and E=100-900 mJ) of pure Ag metal plate immersed in double distilled and deionised water DDDW. UV-VIS absorption spectra of produced solution show a sharp peak around 400 nm, indicating the

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produced Ag nanoparticles with a narrow size ranging from 5 to 50 nm with almost spherical shape.

In (2011) Esmaeil. SH, et al [45] the non-linear refractive index of Ag nano-fluids prepared by γ-radiation method was investigated using a single beam z-scan technique. Under CW 532 nm laser excitation with power output of 40 mW, the Ag nano-fluids showed a large thermalinduced non-linear refractive index.

In (2011) Rawaa A.Faris, et al [46] In the present work, silver nanoparticles were prepared. Nonlinear optical properties and optical limiting of silver nanoparticles were investigated .Standard chemical synthesis . Z-Scan experiments were performed using 30 ns Q-switched Nd:YAG laser at 1064 nm and 532 nm at different intensities. The results showed that the nonlinear refractive index is directly proportional to the input intensities, which caused by the self-focusing of the material.In addition, the optical limiting behavior has been studied. The results showed that the sample could be used as an optical limiter device for a wide range of the input energies.

In (2012) Fan Guang -Hua. et al [47] Silver (Ag) nanoparticles with different average sizes are prepared, and the nonlinear absorption and refraction.The smallest Ag nanoparticles show insignificant nonlinear absorption, whereas the larger ones show saturable absorption. The nonlinear absorptions of Ag nanoparticles are found to be size-dependent. The nonlinear refraction is attributed to the effect of hot electrons arising from the intraband transition in the s–p conduction band of Ag nanoparticles.

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In (2013) Mohammed J. Haider et al [48] this work, silver nanoparticles has been prepared via ablation of pure Ag metal target in distilled water was accomplished using Q-switched Nd:YAG laser at (1.06 μm) laser wavelength , with different laser energy and number of laser pulses. The effect of these parameters on the optical and surface morphology have been studied , UV-Visible show a red shift in the absorption spectra related to the shift in the energy gap due to increment of the grain of prepared particles size is increased as laser energy. Grain size of the obtained NPs is found to increase with laser energy with rang (20112) nm. In (2013) Yu Ben-Hai et al [49]. The optical nonlinearities of an Ag

nanoparticle

array

are

investigated

by

performing

Z-scan

measurements at the selected wavelengths (400, 600, 650, and 800) nm . The nonlinear refraction index in the resonant region (around 400 nm) exhibits a significant enhancement by two orders compared with that in the off-resonant region (around 800 nm)), and exhibits an sign alternation of the resonant nonlinear absorption, which results in a negligible nonlinear absorption at a certain excitation intensity. Moreover, a low degree of nonlinear absorption was measured at the edges of the resonant region (600 and 650 nm), which is attributed to the competition of the saturated absorption and the two-photon absorption processes

In (2014) Amenah Ali [50 ] Noble metal silver NPs was synthesized by pulsed (Q-switched, 1064 nm Nd :YAG) laser ablation of silver metal plates immersed in double distilled and deionized water DDDW.The formation efficiency of PLAL process was quantified in term of the surface Plasmon extinction SPE peaks. The SPE spectra show a sharp and single peak around 400 nm, indicating the production of pure and spherical Ag.UV-Visible absorption results confirmed formation of

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silver particles prepared and atomic force microscope (AFM) indicates the size in nanometer (nm) range.

In (2014) Author: Raul [51] Solutions of silver nanoparticles are obtained by laser ablation method. The laser used was a Nd:YAG with 1064 nm of wavelength. The average diameter of the produced nanoparticles increases, from 9 to 22 nm, as the laser pulse energy increases from 9 to13 mJ. It is observed that the peak absorbance of each sample is directly related with the concentration and the size of silver nanoparticles.

In (2014) Bassam C.Rasheed [52] used Q-switched Nd:YAG laser has

been

ernployed

to

prepare

colloidal

solutions

of

silver

nanoparticles.Those nanoparticles were exhibited antibacterial activity on some bacteria which live in human body. It found that the most sensitive bacteria for silver nanoparticles was Proteus.

In (2014) Dr.Abdul Qader and et al [53] Silver and gold nanoparticles were prepared by using nanosecond pulsed laser ablation. Ablation of pure metal targets (Ag and Au) for nanoparticle colloidal production was studied in de-ionized water. The size and shape of nanoparticles was investigated by Transmission Electron Microscope (TEM). Also absorption peak intensities increase with increasing laser time ablation (30 min.> 15 min.> 5min.)

In (2014) R. Gamernyk et al.

[54] In this paper, the experimental

data on nonlinear refraction of silver nanoparticle composites using a standard Z-scan technique are presented. It was found that the colloids of silver nanoparticles of various size possess a defocusing ability.

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In (2015) A. Alesenkov et al [55]. In this report we present results of linear and nonlinear optical properties of colloidal material consisting of triangle silver nanoparticles in distilled water. The nonlinear optical properties of the material were investigated by a Z-scan technique using femtosecond laser pulses with tunable wavelength. Nanoparticle suspension showed distinct spectra with absorption lines, emerging due to the plasmonic properties of the silver nanoparticles. Surface plasmon resonance peak change over a wide range of wavelengths from 400 to almost 1100 nm was observed when the size of silver nanoparticles varied from 20 to 150 nm.

In(2015) Esmaeil Shahriari

et al [56] In this research, Ag

nanoparticles were prepared by using -radiation at concentration of 5.18×10-3 M and irradiated at different doses. A green laser was employed as excited source for measuring nonlinear refractive index and absorption coefficient. The measurements were done by z-scan method for both, closed and open aperture at temperature room. We deduced that with growth of size of Ag nanoparticles, nonlinear refractive index increased while absorption coefficient of samples decreased.

In(2015) Zainab et al [57] Q-switched Nd-YAG laser of wavelengths (1060, 532 and 322 nm) with energy in the range 200 to 1000 mJ and 1 Hz repetition rate was employed to synthesis silver nanoparticles using pulse laser ablation in liquid. Effect of laser wavelength has been studied for the fundamental, second and third harmonic generation. The experimental UV-Vis absorbance data were fitted with theoretical MieGans model. It is found that the smaller silver nanoparticle of 12 nm capable to terminate both Staphylococcus and Streptococcus bacteria. 16

In (2016)

Sadeq [58] In the present work, a Z-scan technique

was used to study the nonlinear optical properties, represented by the nonlinear refractive index and nonlinear absorption coefficients of the Ag nanoparticles. In this technique, a pulsed second harmonic Nd :YAG laser at wavelength 532 nm was used. The results show that the nonlinear refractive index and nonlinear absorption coefficients of the Ag nanoparticles are found to be dependent on the size these nanoparticles.

In (2016) Mohammed J. Haider [59] In this present study, Pulsed Laser Ablation in Liquid (PLAL) experiment setup for synthesis colloidal solution of silver-NPs. The laser system was used in this study, a (NdYAG) nanosecond laser system with optimal pulse duration of 10 ns and repetition rate 1-6 Hz. From morphology results for colloidal silver nanoparticles images were spherical shape and average size of the particles is 55-60 nm at wavelength (λ=1064 nm), average size of the particles is 35-40 nm at (λ =532 nm) and average size of the particles is 28 nm at (λ =355 nm).

In (2017) Salloom [60] study, silver colloidal nanoparticles have been prepared by chemical reduction of silver nitrate by trisodium citrate as a reduction agent. The resulting silver nanoparticles were characterized by UV-VIS absorption spectroscopy. The non-linear refractive index and absorption coefficient of silver nanoparticles were investigated using a single beam z-scan technique; nonlinear refractive index of silver nanoparticles is found to be negative and as high.

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1-6 Aim of the work  Preparation nanoparticles metal from (Ag) by using laser ablation.  Study the effect of changing the number of pulses on the shape and size of the resulting nanoparticles  Study Linear Optical Properties& Non Linear Optical Properties of Silver Nanoparticles.  Study Linear Optical Properties& Non Linear Optical Properties of Silver Nanoparticles doped PVA.

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Chapter two 2-1 Introduction: This chapter will review the mechanism of laser ablation in liquid for metal Ag NPs synthesis, and the important properties of NPs such as optical, structural and morphological properties. Also this chapter includes the theoretical concepts of the linear optics properties, the basic Concepts of Nonlinear Optics, explains the Z-scan technique Pas well as the optical limiter application.

2-2: Laser Ablation Synthesis In solution (LASIS) One of alternative methods to chemical reduction is the method of laser ablation in liquid phase. Laser ablation in gas phase was very well known method which used successfully for many years. The idea of applying this technique for liquid phase was proposed by two groups of researchers, Cotton-Chumanov group and Henglein group in 1993. Naonosecond Nd:YAG laser were used in both these experiments as well as in most of experiments accomplished up to day[60] . For production of silver nanoparticles, surface of the metal plate immobilized in water solution is irradiated by pulsed laser beam with different parameters (wavelength, pulse duration and pulse energy, pulse repetition rate). Lens is used for the beam focusing on the metal surface. Electron microscopy indicates the presence of some amount of large particles and particle agglomerates which can be removed from colloid by centrifugation. When liquid was changed from water to methanol or acetone, the amount of large particle and agglomerates into a colloid were increased. Such colloids became unstable and precipitated completely overnight at room tem perature [61]. The shape of NPs is prevalently spherical or slightly spheroidal, although particles aggregation can occur

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during or after the synthesis when the colloidal system is not sufficiently stable [62]. LP-PLA involves focusing a high power laser beam onto the surface of a solid target, which is submerged beneath a liquid. The interaction of the laser with the target causes the surface to vaporize in the form of an ablation plume, which contains species such as atoms, ions, and clusters, travelling with high kinetic energy. The species in the plume collide react with molecules of the surrounding liquid, producing new compounds containing atoms from both the original target and the liquid. Due the intensity of the laser and the nanosecond timescales, the instantaneous temperatures and pressures within the reaction volume can be extreme [63]. Such high temperature, high pressure, and high density conditions provide a "brute force" method of synthesizing novel materials that have hither to be inaccessible using milder, more conventional techniques is shown in Fig (.2-1)[64].

Fig (2-1): Sequential steps for NPs generation using nanosecond laser in water: a-laser absorption (fs-ps interval), b-vaporization(less than ns), cplasma formation (ns), d-plasma expansion and cavitation bubble(μs) and e- NPs formation (up to ms). [65] 20

2-3 Noble metal nanoparticles Noble metal nanoparticles such as Ag and Au NPs have been a source of great interest due to their novel electrical, optical, physical, chemical and magnetic properties. Gold and silver nanoparticles are chemically stable and typically exhibit surface enhanced Raman scattering SERS in the visible wavelength range, where they may cause a tremendous increase in various optical cross-sections [12]. Noble metal nanoparticles (NMNPs) can be prepared by both “top– down” and “bottom–up” approaches. For “top–down” procedures, a bulk

state metal is systematically broken down to generate metal

nanoparticles of desired dimensions. In this case, particle assembly and formation is controlled by a pattern or matrix. However, the “top–down” method is limited concerning the control of the size and shape of particles [7]. In contrast, in the “bottom– up” strategy, the formation of nanoparticles originates from individual molecules (atoms), because it involves a chemical or biological reduction [66]. Noble metal nanoparticles show brilliant colors due to the surface plasmon resonance absorption. The color of metal nanoparticles is found to depend on the shape and size of the nanoparticle and dielectric constant of the surrounding medium, leading to many studies on their synthesis and applications. Studies seek to identify the characteristics of nanoparticles, contributing to the basic science in a manner that creates the ability to use nanoparticles for many applications.[67]

2-4 Polymers A polymer is a large molecule built up from numerous smaller molecules. Polymers are substances of very high molecular weight, which may be nature or synthetic in origin. A polymer is a large molecule built up from numerous smaller molecules. These large molecules may be

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linear, slightly branched, or highly interconnected. The small molecules used as the basic building blocks for these large molecules are known as monomer [68]. Some polymeric materials which are in accessible by conventional polymerization may be prepared by chemical modification of other polymers. A good example of this type is poly (vinyl alcohol). Vinyl alcohol has no independent existence since it is the tautomer form of acetaldehyde the polymer, however, is readily prepared by the alcoholysis of poly (vinyl acetate) by ethanol or methanol with acidic or basic catalysts [69]

2.4.1 Polyvinyl Alcohol (PVA) Polyvinyl Alcohols (PVA) are synthetic polymers used in a wide range of industrial. It has the ability to dissolve in water which is resistant to solvents, oils, and has an exceptional ability to adhesive materials cellulosic so industries in membranes of industry resistance to oxygen in the coating as well as in high-voltage applications to possess high tensile strength in a high storage capacity. Figure (2-2) demonstrates the Structure of polyvinyl Alcohol [70].

Figure (2-2): The structure of polyvinyl alcohol (PVA) [70].

Poly (vinyl chloride) is made from the monomer vinyl chloride. The repeat unit in the polymer usually corresponds to the monomer from which the polymer was made .Vinyl alcohol has no independent existence since it

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is the tautomer form of acetaldehyde the polymer, however, is readily prepared by the alcoholysis of poly (vinyl acetate) by ethanol or methanol with acidic or basic catalysts[68].

2.5 Linear Optical Properties When light interacts with matter the optical processes observed in solid state materials can be classified as reflection, refraction, absorption, and transmission [71]. The intensity IO of the beam incident to the surface of the solid medium must equal the sum of the intensities of the transmitted, absorbed, and reflected beams, denoted as IT, IA, and IR, respectively [72] . …..

IO = IT + IA + IR T+A+R=1

(2 -1)

……

(2-2)

2-5-1-Transmittance Transmittance is defined as the ratio between the intensity of the transmitted beam from the matter to intensity incident beam, and can be expressed as [73][70]:

. … (2-3)

T=It /I◦ 2-5-2 Absorption

Is the ratio between the intensity-absorbed beam with absorbed by the matter to the original intensity incident beam on it, and gives the ratio [73].

A=IA / I◦

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……. (2-4)

2-5-3 Reflection Is defined as the ratio between intensity reflective light on the matter to intensity incident beam on it, and gives in the following relationship [73]: R=IR / I◦

…. (2-5)

2-5-4 Optical Energy gap calculation The value of the Absorption coefficient and optical energy gap (Eg) are given to the relationship: [74] α hν = Á ( hυ – Eg ) r

……… (2-6)

Where Á is constant dependent on effective mass and medium density, h is Plank constant and υ is the frequency of the incident photon. r: constant it takes values (3, 2, 2/3, 1/2) depending on the type of electronic transitions responsible for the optical absorption as: r = 1/2 for direct allowed transitions. r = 2/3 for direct forbidden transitions. r = 2 for indirect allowed transitions. r = 3 for forbidden indirect transitions. The absorption edge can be divided into three main regions, as shown in figure (2-3) [75]. (A) High Absorption Region: A region extended between the transition levels of valence band and conduction band, and the value of the absorption coefficient (α ≥ 104 cm-1). (B) Exponential Region: A region transition between localized levels at the edges of the band, where the absorption coefficient (1