Synthesis and characterisation of k doped zno 1

Thin film technology has been developed primarily for the need of the integrated circuit industry.

Thin films cannot exist by itself; it needs substrate to adhere to.

Thin film can be treated as two dimensional specimens because the third dimension namely the thickness is very small .

Thin film is created through atomic/molecular processes

Chemical Deposition In CVD process the substrate is exposed to one or more volatile precursors, which react or decompose on the substrate surface to produce the desired deposit. Physical Deposition Physical deposition uses mechanical or thermodynamic means to produce a thin film of solid.

Structural Properties The most convenient and powerful

tool for the structural study is electron diffraction and diffraction effect provides information regarding the nature of these films, their crystal structures, lattice parameters, grain size etc.

Electrical Properties Electrical conductivity of a film is

many orders of magnitude smaller than that of bulk material and is generally characterized by a negative temperature coefficient of resistivity

Optical Properties of Thin Film: Optical measurements constitute the

most important means of determining the band structures of semiconductors.

Optical measurements can also be used to study lattice vibrations.

Thin Film Drug Delivery Optical Coatings Thin Film Transistor Dye Sensitized Solar Cell Applications in Metallurgical Coatings

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

Crystal structure of ZnO

At ambient pressure and temperature, ZnO crystallizes in the wurtzite structure, hexagonal lattice.

ZnO bond also possesses very strong ionic character, and thus ZnO lies on the borderline of ionic and covalent compound.

Rubber manufacture Concrete industry Medical: Cigarette filters Food additive Pigment Coating Zinc oxide nanorod sensors Piezoelectricity

Objectives

Synthesis of K- doped ZnO thin film by double dip technique. Structural analysis by XRD. Particle size determination Determination of cell parameters. Measurement of thin film surface resistivity.Optical analysis by photoluminescence

The well cleaned substrate was first immersed in the sodium zincate bath for 10 sec (first dip) and then dipped in hot water for the same duration (second dip).

ZnSO4+4NaOH→Na2ZnO2+Na2SO4+2H2O

Na2ZnO2+H2O→ZnO+2NaOH

In order to improve the gas sensing properties, metal ions can be doped onto ZnO thin films.

The doped thin films have the following advantages:

Working temperature can be decreased. Response time for sensing can be decreased. Sensitivity can be increased. The sensitivity for low concentration gas can be

enhanced

The structural properties of film were studied by X-ray diffraction analysis using powder diffract meter

XRD is non- destructive method that reveals detailed information about the chemical deposition, crystallographic and microstructure of all types of natural and manufactured materials.

The constructive interference can take place when the Bragg law is satisfied:

2dhkl sinθ = nλ θ is the glancing angle of incident x-rays. λ is the incident wavelength. dhkl is the interplanar distance. n is any integer corresponding to spectral

order. For wurtzite structure, 1/d2

hkl = [4/3((h2 + hk + k2)/a2)] + (l/c)2

Photoluminescence describes the phenomenon of light emission from any form of matter after the absorption of photons (electromagnetic radiation).

In a typical PL experiment, a semiconductor is excited with a light-source that provides photons with energy larger than the band gap energy.

It is a measure of materials surface inherent resistance to current to flow.

This electrical resistance is proportional to the samples length and the resistivity and inversely proportional to the samples cross sectional area.

R = ρl/Awhere R = Resistivity A= cross – sectional area L = length

The resistance of ZnO thin film is measured using Keithley 2100 6 ½ Digital Multimeter which can measure mega ohm range.

X – ray powder diffraction may be used to measure the average crystal size in a powdered sample.

FWHM is the full width of the peak at the half of maximum value of intensity. For full width half maximum (FWHM), β = x2 – x1 .Debye Sherrer formula is used to calculate the grain size of the crystal, grain size D is given by

D = 0.9λ/ βcosθWhere: β = value of full width in radians λ =incident wavelength θ = diffraction angle at which peak occurs.

Al 7

Operations: Smooth 0.150 | Background 4.571,0.000 | Import

2)1)File: SAIFXR110824B-05(Al7).raw - Step: 0.020 ° - Step time: 31.2 s - WL1: 1.5406 - kA2 Ratio: 0.5 - Generator kV: 40 kV - Generator mA: 35 mA -

Obs. Max: 36.495 ° - FWHM: 0.454 ° - Raw Area: 15.33 Cps x deg. - Net Area: 13.79 Cps x deg. Obs. Max: 34.694 ° - FWHM: 0.325 ° - Raw Area: 52.36 Cps x deg. - Net Area: 50.45 Cps x deg.

Lin

(C

ou

nts

)

0

1000

2000

3000

4000

5000

2-Theta - Scale

3 10 20 30 40 50 60 70 80

2th=

8.10

6 °,

d=10

.899

01

2th=

32.0

02 °

,d=

2.79

448

2th=

34.6

85 °

,d=

2.58

418

2th=

36.4

97 °

,d=

2.45

990

2th=

47.8

41 °

,d=

1.89

978

2th=

63.2

31 °

,d=

1.46

943

  2θ

d values(A0)

Relative Intensity

 31.737

2.81717 56.9

 34.379

2.61562 41.5

 36.215

2.4784 100

 47.484

1.91322 21.2

 62.777

1.48414 26.5

1. Standard values of 2θ and d

2θ 

d values(A0) Relative Intensity

32.002 

2.79448 45.9

34.685 

2.58418 39.2

36.497 

2.45990 100

47.841 

1.89978 22.2

63.231 

1.46943 16.2

2. Observed values of 2θ and d

sample β D(nm) 5% 0.313 26.85 3% 0.4737 17.48

D=k/ cosθ k=0.9 =1.542A0

Cell parameter Standard cell

parameter value

(Ao)

Observed cell

parameter value

(Ao)

a

b

c

3.25

3.25

5.21

3.23

3.23

5.17

Sample 

Average particle size (nm)

Resistance at room temp (MΩ)

PURE 15.12 10.2

3% 

17.48 5

5% 

26.85 2

1. Samples of K- doped ZnO thin films were synthesized by double dip technique.

2. Phase determination of sample was done by XRD technique. From XRD analysis the sample was found to be phase pure.

3. Average particle size of thin film is calculated. It was found that as the doping percentage increases particle size also increases.

4. Cell parameters of the film were determined and it is in agreement with the standard values.

5. Resistance of the samples is measured. As doping concentration increases resistance was found to be decreased.

6. Optical analysis is done by photoluminescence studies and it was found that intensity of visible light emission peak was significantly enhanced with increasing K concentration.

7. By doping particle size of the sample was found to be increased significantly.