Synthesis of Oxide Nano

particles

Report submitted by:

Asma Ashfaq

In partial fulfillment for the award of degree of

MASTER OF SCIENCS

IN

PHYSICS & NANO-TECHNOLOGY

UNDER THE ESTEEMATED GUIDENCE OF

Dr.Naeem Ahmad(HEC Approved Supervisor)

DEPARTMENT OF PHYSICS

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INTERNATIONAL ISLAMIC UNIVERSITY, ISLAMABAD

PAKISTAN

List of contents

• Synthesis-Nanostructures

• Nanoscale synthesis

• Nanoparticles Synthesis

• Synthesis-Different methods

• Oxides Nanoparitcles

• Introduction-ZnO Nanoparticles

• Why ZnO?

• How ZnO Nano-particles can be synthesised?

• Characterization

• Doping in ZnO

• PROPERTIES OF NANOPARTICULATED OXIDES

• Magnetic properties

• Applications

• Motivation

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ACKNOWLEDGMENT

Apart from the efforts of me, the success of any project depends largely on the

encouragement and guidelines of many others. I take this opportunity to express

my gratitude to the people who have been instrumental in the successful

completion of this project.

I would like to show my greatest appreciation to Dr. NAEEM AHMAD. I can’t say

thank you enough for his tremendous support and help. I feel motivated and

encouraged every time. Without his encouragement and guidance this project

would not have materialized.

The guidance and support received from all the members who contributed and

who are contributing to this project, was vital for the success of the project. I am

grateful for their constant support and help.

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INTRODUCTION:

Nanostructures (1nm = 10-9 m)

Zero-Dimension: Confined in all three spatial direction

Examples: Quantum dots, Nanoparticles

One-Dimension: Confined in two spatial directions

Examples: Nanorods, Nanowires, Nanotubes, DNA, Nanorings,

Nanobelts

Two-Dimension: Confined in one direction

Examples: Thinfilms, Interfaces, Membranes, Multi-layers,

Quantum- well

NANOSCALE SYNTHESIS

Nanoscale synthesis of metal oxides.Two Broad categories.TOP DOWN

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BOTTOM UP

• Top-down methodsbegin with a pattern generated on a largerscale, then reduced to nanoscale.–By nature, aren’t cheap and quick tomanufacture- Slow and not suitable for large scaleproduction.

• Bottom-up methodsstart with atoms or molecules and build up tonanostructures–Fabrication is much less expensive.

NANOPARTICLES SYNTHESIS

Gaseous phase methods

Liquid phase methods

GASEOUS PHASE TECHNIQUEPrincipal: Gas – phase precursors interactwith a liquid– or solid- phase materialGas state condensationChemical vapor deposition

LIQUID PHASE TECHNIQUE

Molecular self-assemblySol-gel processesElectrodeposition / electroplatingAnodizingHere we use for the synthesis of oxide nanoparticles THE SOLGEL METHOD.

SOL GEL METHOD

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Sol-gel process consists in the chemicaltransformation of a liquid (the sol) intoa gel state and with subsequent post-

treatment and transition into solidoxide material.

WHAT ARE OXIDE NANO-

PARTICLES?

THE WORLD OF OXIDE NANOMATERIALSMetal oxides play a very important role in many areas of chemistry, physics andmaterials science. The metal elements are able to form a large diversity of oxidecompounds. These can adopt a vast number of structural geometries with an electronic structure that can exhibit metallic, semiconductor or insulator character. In technological applications, oxides are used in the fabrication of microelectronic circuits, sensors, piezoelectric devices, fuel cells, coatings for the passivation of surfaces against corrosion, and as catalysts. In the emerging field of nanotechnology, a goal is to make nanostructures or nanoarrays with special properties with respect to those of bulk or single particle species. Oxide nanoparticles can exhibit unique physical and chemical properties due to their limited size and a high density of corner or edge surface sites. Particle size is expected to influence three important groups of basic properties:a:Structural characteristics.

b:Electronic Properties.

c:Size In Simple characteristics.

Bulk oxides are usually robust and stable systems with well-defined crystallographic structures. However, the growing importance of surface free energy and stress with decreasing particle size must be considered: changes inthermodynamic stability associate with size can induce modification of cell parametersand/or structural transformations and in extreme cases the nanoparticle candisappear due to interactions with its surrounding environment and a high surface freeenergy. In order to display mechanical or structural stability, a nanoparticle must have a

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low surface free energy. As a consequence of this requirement, phases that have a lowstability in bulk materials can become very stable in nanostructures. This structuralphenomenon has been detected in

e.g; TiO2, VOx, Al2O3 or MoOx oxides.

We choose ZnO for synthesis….

WHY ZnO?

REASONS…

Wide-Bandgap semiconductor.

Large exiton binding energy.

Radiation hard material

Enviornment friendly

Electronic material

Piezoelectric material

INTRODUCTION

Zinc oxide is an inorganic compound with the formula ZnO. It usually appears as a white powder, nearly insoluble in water. The powder is widely used as an

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additive into numerous materials and products including plastics, ceramics, glass, cement, rubber (e.g. car tyres), lubricants, paints, ointments, adhesives, sealants, pigments, foods (source of Zn nutrient), batteries, ferrites, fire retardants, etc. ZnO is present in the Earth crust as a mineral zincite; however, most ZnO used commercially is produced synthetically. In materials science, ZnO is often called a II-VI semiconductor because zinc and oxygen belong to the 2nd and 6th groups of the periodic table, respectively. This semiconductor has several favorable properties: good transparency, high electron mobility, wide bandgap, strong room- temperature luminescence, etc. Those properties are already used in emerging applications for transparent electrodes in liquid crystal displays and in energy-saving or heat-protecting windows, and electronic applications of ZnO as thin-film transistor and light-emitting diode are forthcoming as of 2009.

CRYSTAL STRUCTURESZinc oxide crystallizes in three forms:

• hexagonal wurtzite,• cubic zincblende,• and the rarelyobserved cubic rocksalt. The wurtzite structure is most stable and thus most common at ambient

conditions. The zincblende form can be stabilized by growing ZnO on substrates with cubiclattice structure. In both cases, the zinc and oxide are tetrahedral. The rocksalt NaCl-typestructure is only observed at relatively high pressures - ~10 GPa.3The hexagonal and zincblende ZnO lattices have no inversion symmetry (reflection of a crystalrelatively any given point does not transform it into itself). This and other lattice symmetryproperties result in piezoelectricity of the hexagonal and zinc blende ZnO, and in pyro-electricityof hexagonal ZnO.The hexagonal structure has a point group 6 mm (Hermann-Mauguin notation) or C6v

(Schoenflies notation), and the space group is P63mc or C6v. The lattice constants are a = 3.25 Åand c = 5.2 Å; their ratio c/a ~ 1.60 is close to the ideal value for hexagonal cell c/a = 1.633. Asin most II-VI materials, the bonding in ZnO is largely ionic, which explains its strong

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piezoelectricity. Due to this ionicity, zinc and oxygen planes bear electric charge (positive andnegative, respectively). Therefore, to maintain electrical neutrality, those planes reconstruct atatomic level in most relative materials, but not in ZnO - its surfaces are atomically flat, stableand exhibit no reconstruction. This anomaly of ZnO is not fully explained yet.

Wurtzite structure

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Zinc blende structure

Synthesis of Zinc Oxide Nano

Particles:

Zinc oxide quantum dot nano particles absorb UV light but are optically transparent making them useful as the active ingredient of sunscreens. The absorption wavelength is a function of particle size when the particles are small. This synthesis involves particle growth at 65°C; samples removed at longer times give larger particles. The cut-off wavelength from the absorption spectra can be used to estimate the particle size. Nanoparticles

Equipment:

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• 1L beakers for hot water bath and ice bath• thermometer to measure 65°C• Stirbars and stirring hotplate• 50 and 250 mL Erlenmeyer flasks• 25 mL graduated cylinder• 0.01 g balance • UV spectrometer

Chemical Required

• Zn(CH3CO2)2.H2O (0.10g per batch)• (CH3)2CHOH (165mL per batch). Isopropanol vapors irritate the

respiratory tract and eyes. Wear eye protection and use in a fume hood. Avoid skin contact.

• Ice• Stock NaOH Solution for 6 batches:

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Procedure:

ssDissolve 0.20 g NaOH in 100 mL isopropanol with heating. (Quickly weight out about 2 pellets of the hygroscopic NaOH and immediately transfer to the waiting solvent.)

Begin heating a large beaker of water to 65°C.

.

Meanwhile, dissolve 0.10 g Zn(CH3CO2)2.H2O in 25 mL isopropanol with heating in a fume hood

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Meanwhile, prepare an ice bath by adding water to ice. Place 125 mL isopropanol in a flask and chill the flask in the ice bath.

When the zinc acetate solid has all dissolved, add that solution to the 125 mL of chilled isopropanol.

Also obtain 15 mL of 0.050 M NaOH in isopropanol and chill the solution. (A stock solution may already be chilled.)

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Slowly transfer the chilled NaOH solution to the chilled and rapidly stirring zinc acetate solution using a pasteur pipet.

Place the flask with the mixed solution in the 65°C water bath and start taking samples .

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Calculations:Eg = hc /λh =6.626x10-34 Jsc =2.998x108 m/se =1.602x10-19 Cε0 =8.854x10-12 C2/N/m2

m0 = 9.110x10-31 kg

e.g;

For ZnO:

λbulk =365nmε=8.66me*=0.24mh* = 0.59The x-intercept of the linear portion of the absorbance as a function of wavelength graph is a measure of Eg.

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The effectivemassmodel suggests

where r is the radius of the nanoparticle. The second term is the particle-in-a-box confinement energy for an electron-hole pair in a spherical quantum dot and the third term is the Coulomb attraction between an electron and hole modified by the screening of charges by the crystal.After multiplying by r2, rearranging, and using the quadratic formula,

Precautions:• Isopropanol vapors irritate the respiratory tract and eyes. • Wear eye protection and use in a fume hood. Avoid skin contact.

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Doping:

In semiconductor production, doping intentionally introduces impurities into an extremely pure (also referred to as intrinsic) semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic. A semiconductor doped to such high levels that it acts more like aconductor than a semiconductor is referred to as degenerate.

N-type Doping or Donor:In semiconductor physics, a donor is a dopant atom that, when added to a semiconductor, can form a n-type region.For example, when silicon (Si), having four valence electrons, needs to be doped as an n-type semiconductor, elements from group V like phosphorus (P) or arsenic (As) can be used because they have five valence electrons. A dopant with five valence electrons is also called a pentavalent impurity. Other pentavalent dopants are antimony (Sb) and bismuth (Bi).When substituting a Si atom in the crystal lattice, four of the valence electrons of phosphorus form covalent bonds with the neighbouring Si atoms but the fifth one remains weakly bonded. At room temperature, all the fifth electrons are liberated, can move around the Si crystal and can carry a current and thus act as charge carriers. The initially neutral donor becomes positively charged (ionized).

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P-type Doping or Acceptor:

A p-type semiconductor (p for Positive) is obtained by carrying out a process of doping by adding a certain type of atoms (acceptors) to the semiconductor in order to increase the number of freecharge carriers (in this case positive holes).When the doping material is added, it takes away (accepts) weakly bound outer electrons from the semiconductor atoms. This type of doping agent is also known as an acceptor material and the vacancy left behind by the electron is known as a hole.The purpose of p-type doping is to create an abundance of holes. In the case of silicon, a trivalent atom (typically from Group 13 of the periodic table, such as boron or aluminium) is substituted into the crystal lattice. The result is that one electron is missing from one of the four covalent bonds normal for the silicon lattice. Thus the dopant atom can accept an electron from a neighboring atom's covalent bond to complete the fourth bond. This is why such dopants are called acceptors. The dopant atom accepts an electron, causing the loss of half of one bond from the neighboring atom and resulting in the formation of a "hole". Each hole is associated with a nearby negatively charged dopant ion, and the semiconductor remains electrically neutral as a whole. However, once each hole has wandered away into the lattice, one proton in the atom at the hole's location will be "exposed" and no longer cancelled by an electron. This atom will have 3 electrons and 1 hole surrounding a particular nucleus with 4 protons. For this

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reason a hole behaves as a positive charge. When a sufficiently large number of acceptor atoms are added, the holes greatly outnumber thermal excited electrons. Thus, holes are the majority carriers, while electrons become minority carriers in p-type materials.

Techniques of Doping and synthesis:The synthesis of n-type semiconductors may involve the use of vapor-phase epitaxy. In vapor-phase epitaxy, a gas containing the negative dopant is passed over the substrate wafer. In the case of n-type Gas doping, hydrogen sulfide is passed over the gallium arsenide, and sulfur is incorporated into the structure This process is characterized by a constant concentration of sulfur on the surface. In the case of semiconductors in general, only a very thin layer of the wafer needs to be doped in order to obtain the desired electronic properties The reaction conditions typically range from 600 to 800 °C for the n-doping with group VI elements and the time is typically 6–12 hours depending on the temperature.

Process:Some dopants are added as the (usually silicon) boule is grown, giving each wafer an almost uniform initial doping To define circuit elements, selected areas — typically controlled byphotolithography[8] — are further doped by such processes as diffusion and ion implantation, the latter method being more popular in large production runs because of increased controllability.Small numbers of dopant atoms can change the ability of a semiconductor to conduct electricity. When on the order of one dopant atom is added per 100 million atoms, the doping is said to be low orlight. When many more dopant atoms are added, on the order of one per ten thousand atoms, the doping is referred to as heavy or high. This is often shown as n+ for n-type doping or p+ for p-typedoping.

Doping in ZnO:Doping in ZnO play an important role to tailor the properties of nanostructures. There are four types of doping elements. Doping is expected to induce some changes in the morphology, optical, electrical, and magnetic properties of the nanostructures

• Doping with donor impurities to achieve high n-type conductivity, such as Al, Sn, In, Pb etc.

• Doping with acceptor impurities to achieve p-type conductivity, such as N, As, P etc.

• Doping with rare-earth elements such as Tb, Ce, Eu, and Dy to achieve

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desired optical properties.• Doping with transition metals such as Mn. Co, and Ni etc. to achieve

desired magnetic properties.

Aligned In-ZnO

NWs

Curves using different techniques;

Room-

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temperature PL spectra of different nanostructures: 1) Tetrapods, 2) needles, 3) nanorods, 4) shells, 5) highly faceted rods, 6) ribbons/combs

PROPERTIES OF

NANOPARTICULATED OXIDESCHEMICAL PROPERTIESZnO occurs as white powder commonly known as zinc white or as the mineral zincite. The mineral usually contains a certain amount of manganese and other elements and is of yellow to red color. Crystalline zinc oxide is thermo-chromic, changing from white to yellow when heated and in air reverting to white on cooling. This is caused by a very small loss of oxygen at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 °C, x= 0.00007.Zinc oxide is an amphoteric oxide. It is nearly insoluble in water and alcohol, but it is soluble in (degraded by) most acids, such as hydrochloric acid:ZnO + 2 HCl → ZnCl2 + H2OBases also degrade the solid to give soluble zincates:ZnO + 2NaOH + H2O → Na2(Zn(OH)4)

ZnO reacts slowly with fatty acids in oils to produce the corresponding carboxylates, such as oleate or stearate. ZnO forms cement-like products when mixed with a strong aqueous solution of zinc chloride and these are best described as zinc hydroxy chlorides. This cement was used in dentistry.ZnO also forms cement-like products when reacted with phosphoric acid, and this forms the basis of zinc phosphate cements used in dentistry. A major component of zinc phosphate cement produced by this reaction is hopeite, Zn3

(PO4)2·4H2O.ZnO decomposes into zinc vapor and oxygen only at around 1975 °C, reflecting its considerable stability. Heating with carbon converts the oxide into zinc vapor:ZnO + C → Zn + COZinc oxide reacts violently with aluminum and magnesium powders, with chlorinated rubber and linseed oil on heating causing fire and explosion hazard.It reacts with hydrogen sulfide to give the sulfide: this reaction is used commercially in removing H2S using ZnO powder (e.g., as deodorant). ZnO + H2S → ZnS + H2OWhen ointments containing ZnO and water are melted and exposed to ultraviolet light, hydrogen peroxide is produced. Metal oxides ar1e used for both their redox and acid/base properties in the context of Absorption and Catalysis. The three key features essential for their application as absorbents or catalysts are

• the coordination environment of surface atoms,• the redox properties,• the oxidation state at surface layers. Both redox and

acid/base properties are interrelated and may attempts can be found in the literature to establish correlations of

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both properties.105,106 In a simple classification, oxides having only s or p electrons in their valence orbitals tend to be more effective for acid/base catalysis, while those having d or f outer electrons find a wider range of uses.

The solid in a given reaction conditions that undergoes reduction and reoxidationSimultaneously by giving out surface lattice oxyen anions and taking oxygen from the gas phase is called a redox catalyst. This process necessarily demands microscopyreversibility and implies dynamic operation. The commonly accepted mechanism wasdeveloped by Mars van Krevelen and essentially implies that redox systems require highelectronic conduction cations to manage electrons and high oxygen-lattice mobility.Based on modern isotopic exchange experiments, the redox mechanism of chemicalreactions can be more specifically divided in (i) extrafacial oxygen in which adsorbed (oxygen) species react (electrophilic reaction), (ii) interfacial oxygen where lattice oxygen vacancies are created (nucleophilic reaction). There are enormous evidence that nucleophilic oxygen is capable of carrying out selective oxidations while it seems that electrophilic species seems to exclusively work on non-selective ones. Latter, it was shown that hydrocarbon selective oxidation starts with H-abstraction steps and that the filling of oxygen vacancies require the cooperation of a significant number of cations.105 So, typically, an oxidation reaction demands to optimize three important steps: the activation of the C-H bond and molecular oxygen, and the desorption of products (to limit over-oxidation). The effect of size on these key steps is unknown but can be speculated to be related to the oxidation state of surface cations and their ability to manage electrons and the influence of non-stoichiometry on the gas-phase oxygen species handling and activation.Many oxides also display acid/base properties. Oxide materials can contain Bronsted and Lewis acid/base sites. Bronsted acid (A) and base (B) interactions consist of an the exchange of protons as HA + B = A- + HB+. Lewis proposed a different approachto measure acid-base interaction as depicted by (B:) + A = d-B � Bd+. Latter, Petterson introduced the concepts of hard and soft acid and base but, usually, acid/base properties of solid are rationalized in terms of Bronsted and Lewis definitions. In any solid, two independent variables, the acid/base strength and amount (density per surface unit) need to be addressed to give a complete picture of its acid/base characteristics. Such characteristics are basically linked to the nature (valence/cation size) of the element present in the oxide and general views of the behavior of Bronsted/Lewis acidity as a function of solid state variables have been published.106 Essentially, Lewis acidity is characeristic of ionic oxides and practically absent (unless very aggressive outgassing treatments) in covalent oxides. The strongest Lewis acid oxides are Al2O3 and

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Ga2O3. As a general rule, the stronger the Lewis acid, the few available sites (amount) due to the higher level of surface hydroxylation. As mentioned, because Lewis acidity is mostly associated to oxides with ionic character, Lewis basicity is mostly associated with them. This means that the stronger the Lewis acid sites, the weaker the basic sites and vice versa. On the contrary, most of the ionic metal oxides do not carry sufficiently strong Bronsted acidity to protonate pyridine or ammonia at room temperature although the more acid of them can do it at higher temperatures. In spite of this, the surface OH groups of most ionic oxides have a basic more than acid character. Covalent low-valent nonmetal oxides (SiO2, GeOx, BOx) also show quite weak Bronsted acid properties. Finally, strong Bronsted acidity appears in oxides of elements with formal valence five or higher (WO3, MoO3, N2O5, V2O5, and S-containing oxides).

Electronic Properties;ZnO has a relatively large direct band gap of ~3.3 eV at room temperature; therefore, pure ZnO is colorless and transparent. Advantages associated with a large band gap include higher breakdown voltages, ability to sustain large electric fields, lower electronic noise, and high temperature and high-power operation. The bandgap of ZnO can further be tuned from ~3–4 eV by its alloying with magnesium oxide or cadmium oxide.Most ZnO has n-type character, even in the absence of intentional doping. Native defects such as oxygen vacancies or zinc interstitials are often assumed to be the origin of this, but the subject remains controversial. An alternative explanation has been proposed, based on theoretical calculations, that unintentional substitutional hydrogen impurities are responsible. Controllable n-type doping is easily achieved by substituting Zn with group-III elements Al, Ga, In or by substituting oxygen with group-VII elements chlorine or iodine. Reliable p-type doping of ZnO remains difficult. This problem originates from low solubility of p-type dopants and their compensation by abundant n-type impurities, and it is pertinent not only to ZnO, but also to similar compounds GaN and ZnSe. Measurement of p-type in "intrinsically" n-type material is also not easy because inhomogeneity results in spurious signals.Current absence of p-type ZnO does limit its electronic and optoelectronic applications which usually require junctions of n-type and p-type material. Known p-type dopants include group-I elements Li, Na, K; group-V elements N, P and As; as well as copper and silver. However, many of these form deep acceptors and do not produce significant p-type conduction at room temperature. Electron mobility of ZnO strongly varies with temperature and has a maximum of ~2000 cm2/(V·s) at ~80 Kelvin.[21] Data on hole mobility are scarce with values in the range 5-30 cm2/(V·s).

Optical properties.The optical conductivity is one of the fundamental properties of metal oxides and can be experimentally obtained from reflectivity and absorption measurements. While reflectivity is clearly size-dependent as scattering can display drastic

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changes when the oxide characteristic size (primary/secondary particle size) is in/out the range of photon wavelength,62 absorption features typically command main absorption behavior of solids. Due to quantum-size confinement, absorption of light becomes both discrete-like and size-dependent. For nano-crystalline semiconductors, both linear (one exciton per particle) and non-linear optical (multiple excitons) properties arise as a result of transitions between electron and hole discrete or quantized electronic levels. In the first case, depending on the relationship between the radius of the Nanoparticle (R) and the Bohr radius of the bulk exciton (RB = ε ħ2/µe2; µ exciton reduced mass and ε dielectric constant of the semiconductor), the quantum confinement effect can be divided into three regimes; weak, intermediate and strong confinement regimes, which correspond to R >> RB, R ≈ RB, and R << RB, respectively.63 The effective mass theory (EMA) is the most elegant and general theory to explain the size dependence of the optical properties of nano-meter semiconductors, although other theories as the free exciton collision model (FECM)64 or those based in the bond length – strength correlation65 have been developed to account for several deficiencies of the EMA theory.For the onset of light absorption, e.g. the optical band gap, as well as for all other electronic transitions present in the optical absorption spectrum, the EMA theory predicts a r-2 dependence, with a main r-1 correction term in the strong confinement regime, while FECM gives a exp(1/r) behavior. It can be thus concluded that metal oxide semiconductors would present, as a first rough approximation, an optical band gap energy with an inverse squared dependence of the primary particle size if quantum confinement dominates the energy behavior of the band gap. Shows that this happens to be the case for (direct band gap) Fe2O3 or (indirect band gap) CdO but not for Cu2O, CeO2,, ZnO, and TiO2. Limited deviations from the R-2 behavior, as observed for ZnO70 in or SnO2,74 can be based in the known fact that the theory overestimates the blue shift and can be justified with a proper calculation of electronic states by using simple quantum mechanical methods, while marked deviations are usually based in several chemical/physical phenomena not accounted for in the previous discussion. In the case of Cu2O68 or CeO2 it appears to be directly related with the presence of Cu2+ (remarkably for very low particle size) and Ce3+ ions at the surface of the nano structured materials. At the moment it is not clear if the presence of these oxidation states are intrinsic to the nanostructure or result from the specific procedure of preparation. The case of WO3 share also some of the difficulties pointed out above. Kubo et al. were able to show that the band gap of this oxide decrease with size from ca. 3.0 to 2.8 eV as a function of R but the presence of a variable number of oxygen defects, reduced W redox states and mid-gap electronic states with size makes this an open question. TiO2 is the other example included in having a band gap energy behavior with marked differences from that expected r-2 behavior. While bulk TiO2 is an indirect semiconductor, nano structured TiO2 materials are likely direct ones.72,78 This may be a general result. As discussed in ref. 79, the confinement of charge carriers in a limited space causes their wave functions to spread out in momentum space, in turn increasing the like hood of radiative transitions for bulk

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indirect semiconductors. This may also be the case of NiO. The indirect nature of the absorption onset would complicate the analysis of the optical band gap energy due to the above mentioned step structure of the absorption onset (which includes phonon-related absorption/emission features). In spite of this, the steady behavior shown in can not be accounted for by small variations in the absorption onset and should be grounded in other physical phenomena. Other optical excitations which showed quantum-size confinement effects concern the excitation of optical phonons of oxides. The effects of size on the phonon spectra of oxide materials have been well established by using Raman scattering experiments on nano crystals, in combination with the theoretical phonon confinementModels essentially, the theoretical background for the study of nano crystalline materials is provided by the phonon confinement model. This factor is the main responsible for the changes observed in the Raman spectrum which are caused by the size effect. Nevertheless, other factors have been described which can contribute to Raman spectrum modification as the non-stoichiometry or the internal stress/surface tension. The phonon confinement model links q vector selection rule for the excitation of Raman active optical phonons with long-range order and crystallite size In an amorphous material, owing to the lack of long-range order, the q-vector selection rule breaks downand the Raman spectrum resembles the phonon density of states. Nanocrystals represent an intermediate behavior. For a nanocrystal of average diameter L, the strict “infinite” crystal selection rule is replaced by a relaxed version, with the result that a range of q vectors is accessible due to the uncertainty principle, The q vector relaxation model can be used for the purpose of comparing experimental data with theoretically predicted phonon confinement. According to this model, for finite sized crystals, the Raman intensity can be expressed using the equation 1:The ρ (L) represents the particle size distribution, q is expressed in units of a L π (being

aL the unit cell parameter), ω( q ) is the phonon dispersion, and 0 Γ is the intrinsic linewidth of the bulk crystal. A spherically symmetric phonon dispersion curve is assumed and approximated by a simple linear chain model.84 For a given phonon mode, the slope of dispersion away from the BZ center determines the nature of the modification in the Raman line shape as a function of crystallite size: a negative slope, towards lower frequency, would produce a downshifted (red-shifted) Raman peak, whilea positive slope would result in an up-shifted (blue-shifted) Raman peak, in addition to an asymmetric peak broadening, as the crystallite size reduces. Usually is chosen for this kind of analysis the most intense Raman mode for the solid studied. Some examples of application of the confinement model for qualitative interpretation of Raman results in series of nano structured oxides like anatase ZnO, TiO2, CuO, Cr2O3, ZrTiO4, CeO2 or manganese oxides can be found elsewhere. In all cases, optical absorption features of nano sized oxides are additionally influenced by “non-stoichiometry” size-dependent defect effects.

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Typical point defects innano structured oxides concern oxygen or cation vacancies and/or the presence of aliens species, like Cu2+ and Ce3+. Vacancy defects introduce gap states in proportion to the defect number; in fact, a random distribution of (equal) vacancy defects introduce agaussian-like density of states which may produce mid-gap states and/or be localized near the valence and conduction bands depending on the electronic nature (donor/acceptor) of the defect and giving characteristic “localized” features in the UV-visible spectrum. Such point defects mainly contribute to the Raman spectra by producing a broadening of the peaks. Alien cations display specific features, like the localized d-d or f-f transitions of Cu/Ce. Besides electronic modifications, point defects but particularly alien ions, like Cu2+ and Ce3+ above, induce strain effects and concomitant structural differences in atomic positions with respect to bulk positions. The influence of strain in the optical absorption spectrum has been nicely demonstrated in the work of Ong et al. for ZnO, showing the splitting of the first exciton peak for large values of compressive strain. Strain effects (including parameter variations measured in optical phonons with the help of the Gruneisen parameter) are inherent to nano structured materials and may be comprised in the general, ambiguous term of “surface” effects usually claimed to account for significant deviations the confinement theories. Surface effects and, particularly, non stoichiometry related to the preparation method are critically important for very low particle size and produce characteristic features in the UV-visible spectrum for certain oxides, as SnO2 or ZrO2.

Transport properties. Oxide materials can present ionic or mixedionic/electronic conductivity and it is experimentally well established than both can be influenced by the nanostructure of the solid. The number of electronic charge carriers in a metal oxide is a function of the band gap energy according to the Boltzmann statistics. The electronic conduction is referred to as n- or p-hopping-type depending on whether the principal charge carrier are, respectively, electrons or holes. The number of “free” electron/holes of an oxide can be enhanced by introducing non-stoichiometry and, in such case, are balanced by the much less mobile oxygen/cation vacancies. In an analogous manner to hoping-type conduction, ionic conduction takes place when ions can hop from site to site within a crystal lattice as a result of thermal activation, and is typically interpreted on the basis of a modified Fick´s second law. Four mechanism types have been observed for ionic conduction: direct interstitial, interstitialcy, vacancy, and grotthus. As charge species (defects; impurities) in polycrystalline oxides typically segregate to particle boundaries to minimize strain and electrostatic potential contributions to the total energy, there is a contribution to the conductivity parallel to the surface which becomes important at the nanoscale regime. The charge carrier (defect) distribution also suffers strong modification from bulk materials as there is presence of charge carries through the whole material as a consequence of the shielded electrostatic potential depletion at surface layers of nanosized

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materials. As a result of these nanoscale derived effects, it is well known that CeO2 exhibits an improved n-type conductivity which may be four order of magnitude greater than the corresponding to bulk/micro-crystalline ceria, and is ascribed to a significant enhancement of the electronic contribution. Alteration of the transport properties is also observed in ZrO2 but the physical ground is still far from being understood. The strong size-dependence observed for the electrical conductance in the context of gas-sensing devices has been recently reviewed for the SnO2, WO3, and In2O3 oxides. In proton conductors, like SrCeYb O3-d, enhanced conduction and faster kinetics under H-atmospheres are observed in nanosized samples as these phenomena are largely determined by boundary/interfacial effects. Interesting to stress here is that some of the most dramatic effects of he nanostructure on ionic transport in oxides are observed in the field of Li+-ion batteries. An outstanding enhancement of Li+-ion vacancy conductivity have been achieved using Li-infiltrated nanoporous Al2O3.

Mechanical properties.Main mechanical properties concerns low (yield stress and hardness) and high (superpasticity) temperature observables. Information on oxide nanomaterials is scarce and mainly devoted to analyze sinterability, ductibility, and superpasticity. In particular, an important number of works have showed significant improvement in sintering with up to 600 K lower temperatures with respect to bluk counterparts. In conventional/bulk materials the yield stress (σ) and harness (H) follow the Hall-Petch (H-P) equation:/ H / H k d-1/2 (2) σ = σ 0 0 + where the initial constants describe friction stress and hardness, d is the primary particle/grain size and k the corresponding slope. The H-P effect in bulk materials is attributed to the particle/grain boundaries acting as efficient obstacles for slip transfer (stress) or dislocations (hardness). Typically by decrease the particle/grain size down to the order of a few tens nanometers the H-P slope, which is positive, gets smaller values. However, below such critical point it appears that conventional dislocation mechamisn(s) cease(s) to operate and a d-n (│n│> ½) behavior or a “reversal” H-P mechanism wouldbecome progressively dominant.101,102,103 On top of this, these mechanical properties are also found to be strain-rate dependent; an enhanced strain rate sensitivity at room temperature is observed for TiO2 and ZrO2 with decreasing primary particle/grain size. In spite of such facts, it is clear that oxide materials (like Al2O3, ZrO2, CeO2, and TiO2) sintered under vacuum or using the spark plasma technique display enhanced yield strength and hardness with respect to conventional/bulk ceramic materials and have the additional properties of being transparent (films), being potential materials for the aerospatial industry.Superplasticity refers to the capacity of oxide materials to undergo extensivetensile deformation without necking or fracture. The phenomenological relationship for superplasticity is defined as: where ε is the strain rate, D is the adequate diffusion coefficient, G is the shear modulus, b is the Burger´s vector, σ is the applied yield strength, and p/n the particle size and yield strength exponents. implies that reduction of the particle size leads to an increase of the

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super plasticity strain rate at constant temperature, or to a reduction in the super plasticity temperature as a constant strain rate, but very studies have been reported having oxides as the subject of the work. Essentially, policrystalline tetragonal ZrO2 appears as the most celebrated example of a superpacticity ceramic, and together with TiO2 are the only nano-oxides subjected to studies. At room temperature, nanocrystalline oxides may have a small amount of ductibility beyond that exhibited by bulk materials but they are not superplastics. Al high temperatures, they seem to exhibit significant compressive ductility and strain rate sensitivities that are indicate of superplasticity.

Magnetic propertiesIt is possible to induce room-temperature ferromagnetic-like behavior in ZnO nanoparticles without doping withmagnetic impurities but simply inducing an alteration of their electronic configuration. Capping ZnO nanoparticles (_10 nm size) with differentorganic molecules produces an alteration of their electronic configuration that depends on the particular molecule, as evidenced byphotoluminescence and X-ray absorption spectroscopies and altering their magnetic properties that varies from diamagnetic to ferromagneticlikebehaviorMagnetic properties can be induced by

• • • • Dopping

• • • • Capping

DoppingAlready described above.

Surface-capping of ZnO nanoparticlesA series of ormosils were prepared by varying the mole ratio of TEOS to DEDMS and then used for surface-capping of ZnO nanoparticles. the abbreviations for various surface-capped ZnO nanoparticle samples. As a typical example, 6.5 g of ZnO was mixed with 50 ml of absolute ethanol and 150 ml of deionized water by shearing at 4000 rpm for 5 min (BME100LX high-speed shearing machine, Weiyu Machinery & Electronics Company Limited, Shanghai, China), followed by ultrasonication (SK3200H, Shanghai Kudos Ultrasonic Instrument Company Limited, China) for 20 min. The resulting ZnO suspension was then slowly transferred to a 500-ml three-necked flask, followed by the addition of 0.5 ml of ammonia solution as the catalyst, generating a mixed suspension. Into the mixed suspension were added a proper amount of premixed TEOS and DEDMS and 25 ml of absolute ethanol. The resulting mixed reactants were vigorously stirred at 60 °C for 6 h, allowing the surface-capping of ZnO nanoparticles by ormosils. Upon completion of the surface-capping process, the mixed products were washed with ethanol and filtered, and the solid residue was collected as the as-prepared surface-capped ZnO nanoparticles. As-prepared ZnO nanoparticles

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were dried at 100 °C in air for 12 h, generating the final samples for characterization. The same process for preparing surface-capped sample ZT1D2 was also performed in the absence of ZnO nanoparticles generating sample T1D2 as a control sample.

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Scientific research;The last years,following the proposal by

Ohno; The research on these magnetic semiconductors has been mainly focused on theso-called Diluted magnetic semiconductors (DMS):semiconductors containing a small amount of magnetic impurities.The main challenge for this kind of materials is to preserve their magnetic character at room temperature (RT), that is,Curie temperature (TC) above 300 K, in order to be useful for technological applications. Despite some initial promising results on Mn:ZnO, it is not clear if DMS can exhibit this required high-temperature magnetism. For most of the experimental results, doubts arose about the real origin of magnetism. For some cases it was demonstrated that themagnetism was due to segregation of metallic clusters

The most recent and outstanding works on this field showed that the magnetic properties are not exclusively related to the presence of the magnetic ions but strongly determined by the defects.

Kittisltved et al. showed that Mn:ZnO nanoparticles and thin films only show RT ferromagnetism when capped with molecules that introduce n-type defects, while other capping that introduce p-type defects leads to no RT ferromagnetism. On the contrary, for Co: ZnO films the n-type defects favor the appearance of RT ferromagnetism while p-type defects yield to no RT ferromagnetism.

Rubi et al also found that magnetic properties of Co- and Mn-doped ZnO powder samples are modified by thermal annealing in different atmospheres that favor the presence of p- or n-type defects

Coey et al. insulating HfO2 the effect appears even without doping.1

Experimental observation of Capping of ZnO

NPs• Capping ZnO NPs with a variety of organic molecules modifies its

electronic structure• ZnO NPs were prepared by sol-gel

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• Subsequently capped with 3 different organic molecules:• Tryoctylphosphine (TOPO),• Dodecylamine (AMINE), and • Dodecanethiol (THIOL)• Bond to the particle surface through an O, N, and S atom,respectively.

Amine

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Figure 1. (a) X-ray diffraction patterns of the AMINE, THIOL, and TOPO samples. Diffraction

maxima of a ZnO wurtzite type unit cell.

(b) Low-magnification image of the AMINE sample, showing the size distribution. (c) HREM image along

Conclusions• The magnetic properties strongly depend on the preparation method.• slight modifications in the preparation conditions and size of thiol-capped

Zn NPs lead to important variations in their magnetic properties.• Absorption of certain organic molecules onto ZnO nanoparticles modifies

its electronic structure and gives rise to a ferromagnetic-like behavior at room temperature even in the absence of magnetic ions

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Application

During the battle of human being fighting against bacteria and viruses, organic medicine has become ever indispensable in daily life. Excessive usage of these medicines, however, will transform bacteria into other forms which are much more difficult to conquer. Moreover, as the entire human being is growing even more conscious of the importance of healthy life and good living habits, people use antibacterial products to create a hygienic environment to ensure the ultimate protection of healthy life style.

Because of Nano ZnO's unique antibacterial characteristics and excellent physical stability, it can serve as an effective antibacterial agent. Besides, Nano ZnO does not discolor, nor does it require ultra-violet to get activated. These properties make Nano ZnO a superior non-organic antibacterial agent versus other materials used nowadays, such as photo-catalyst, which needs ultra-violet light to be activated, and Silver Ion, which will discolor over the course of time.

Furthermore, ZnO is a multi-functional semi-conductive material. In the rapidly-growing electronic industries, ZnO may be used as a functional material in plastics, pigments and fibers in various kinds of products, offering immense benefits such as anti-static, electromagnetic-shielding and UV-blocking. Therefore, Nano ZnO powder will be further used in many different industries to deliver exceptional features and to enhance product performance not reached by those made of traditional ZnO.

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Medicine Application Nano ZnO Specification

ZnO is generally regarded as safe food additives under the condition of superb manufacturing process and feeding process. Element Zinc is the biggest micro metal that universally exists in live body, and is also the biggest micro metal among human body. All creatures need zinc as it composes of cells as the cofactor of fundamental enzyme system. Daily-recommended intake for adult is 15mg, and 25mg for breast-feeding mother. ZnO features mild wound astringent, inflammation reduction/relief, and anti-microbial functions, also serves as a remedy for dermatitis and infection diseases, such as eczema, impetigo, ringworm, slack abscess, itch and psoriasis. The diameter of a nano ZnO measures approximately 10 ~ 20nm. Most of them are fiber structure observed under microscope, with the features of fine grains, exceptional purity, and extraordinary whiteness.

Cosmetics,Sunscreen Application Nano Zno

Specification1. Nano ZnO shows excellent ability in resisting UVA and UVB. It also displays

excellent grain subtlety, high purity, and extremely low harmful content. It is also suitable for the use in sunscreen products to block the UV away from human body. ZnO is both safe and mild to body, approved by Food and Drug Administration (FDA) as one of two sunscreen ingredients of the first category skin-care products. Physical sunscreen ingredients are neither being absorbed nor be reduced by human body. It is proven that TiO2 has its flaws in blocking UVA (wave length ranging between 340 ~ 400nm), and that only ZnO can completely screen both UVA and UVB.

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2. Traditional ZnO normally appears unnaturally white when applied on the skin. Lifesavers, frequent users have a dislike for its white appearance. So the ordinary ZnO is not widely used for UV blocking. However, nano ZnO improves the above shortcoming and the test result was approved by CSIRO (Australian commonwealth scientific & industrialresearch organization). They found that nano ZnO block blocks double UV that ordinary ZnO does. Nano-infinity Nanotech Co., Ltd. produces high purity ZnO whose grain size is smaller than light wave yet the color being pure white. When ZnO is used as ingredient of UV blocking cream or lotion, it is silky and transparent and without color after applied onto humanskin. Therefore, Nano ZnO is the best ingredient to make cosmetics.

Industrial Application Nano Zno Specification1. Nano ZnO is not only fabulous in its performance but also tends to replace ordinary

ZnO. In many new fields, it shows unrivaled effects over ordinary ZnO. The excellent performance of nano ZnO makes itself perfect replacement for traditional micronized ZnO.

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2. Industrial Applications as Below:

Animal Feedstuffs and Drugs: The feedstuffs that contain nano ZnO deliver much better effect than those with micronized ZnO do, along with other benefits, such as higher absorption rate and less required dosage.Rubber Industry: Nano ZnO is the most effective inorganic surfactant and

sulfurizing accelerator, featuring faster sulfurizing and wider temperature ranges, which will lead to faster transformation into zinc sulfide and thus more efficient production of anti-abrasion rubber.Ceramics Industry: Ceramic industry is widely using ZnO as white dyestuff. With

nano ZnO, ceramic ware sintering temperature can lower to 400 ~ 600oC, yet surface is burned as polishing as a mirror.Textile Industry and Commodity Chemical Industry: Producing deodorant,

antibacterial, FIR and UV-blocking fiber.Painting Industry: Nano ZnO is a new-type of anti-static agent. Putting semi-

conductive nano ZnO into resin can result in better static shielding.

e.g;

ZnO nanostructures based Nanodevices

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MotivationMajor unresolved issues in ZnO material for its direct use in potential applications:

• P-type material• Band gap tailoring toward visible range • Establishment of ferromagnetism with high Tc

• Definite picture regarding the actual mechanism of ferromagnetic ordering• Practical use of these prepared nanostructures

REFERENCES

• A research paper on SYNTHESIS AND CHARACTERIZATION OF

ZnO

NANO-PARTICLES by Jayanta Kumar Behera

• • • • A research paper on Magnetic Properties of ZnO Nanoparticles by M.

A. Garcia,*,†,‡ J. M. Merino,†,§ E. Ferna´nde Pinel,†,‡

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• • • • A research paper on Metal Oxide Nanoparticles by Marcos

Fernánde Garci a, José A. Rodriguez

• • • • Dr. Shumaila Sajjad assistant professor IIUI

• • • • Dr. Khasif Nadeem assistant professor IIUI

6. Dr. Javed Iqbal assistant professor IIUI

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