Thin film formation

2. Under the Guidance of
Dr. ANGEL SUSAN
CHERIAN
DEPARTMENT OF
PHYSICS
MAR THOMA
COLLEGE
THIRUVALLA,KERALA
2013-2015
A PROJECTON
THIHFILM FORMATIONUSINGCHEMICALBATH DEPOSITION
Presented by
RANI RAJAN
DEPARTMENT OF PHYSICS
MAR THOMA COLLEGE
THIRUVALLA,KERALA

3. AIM
 To deposit PbS thin film using chemical
bath deposition (CBD) technique.
 To study the effect of different precursor
solution in the formation of thin film.
 To study the structural characterization
of the film by using X-ray diffraction
(XRD) method
 To study the effect on conductivity of the
film with the variation on lead content

4. THIN FILM
• Any solid or liquid object with one of its dimensions very
much less than that of the other two may be called a “thin
film”.
• A thin film is a layer of material ranging from fractions of a
nanometer (monolayer) to several micrometers in thickness.
• Electronic semiconductor devices and optical coatings are the
main applications benefiting from thin-film construction.
• The most commonly observed phenomenon associated with
thin film is the fascinating colours on it. e g. a thin layer of oil
floating on the surface of water.

5. •Thin films can be classified into three types based on
the range of their thickness
Ultra thin(50-100 A0 )
Thin(or very thin)(100-1000 A0 )
Comparatively thicker(greater than 1000 A0 )

6. APPLICATIONS OF THIN FILM
• A familiar application of thin films is the
household mirror, which typically has a thin
metal coating on the back of a sheet of glass to
form a reflective interface.
•Work is being done with thin films for use as
computer memory.
•It is also being applied to pharmaceuticals, via
thin-film drug delivery.
•Thin films are used to produce thin-film
batteries.
•Thin films are also used in dye-sensitized solar
cells.

7. DEPOSITION
The act of applying a thin film to a surface is
thin-film deposition or any technique for
depositing a thin film of material on to a
substrate or on to previously deposited layers

8. DEPOSITION TECHNIQUES
Deposition techniques can be broadly classified into
two:
1) Physical :uses mechanical, electromechanical or
thermodynamic means to produce a thin film of solid.
2) Chemical: Here, a fluid precursor undergoes a
chemical change on a solid surface, leaving a solid
layer

9. PHYSICAL DEPOSITION TECHNIQUES
• Thermal evaporation
• Electron beam evaporator
• Molecular beam epitaxy
• Sputtering
• Pulsed laser deposition
• Cathodic arc deposition
• Electrohydrodynamic deposition

10. • Plating
• Chemical bath deposition
• Spin coating or spin casting
• Chemical vapour deposition
• Plasma enhanced CVD
• Atomic layer deposition

11.  The Chemical bath deposition (CBD) method is one of
the cheapest methods to deposit thin films and nano
materials, as it does not depend on expensive
equipment and is a scalable technique that can be
employed for large area batch processing or continuous
deposition.
 The chemical bath deposition (CBD) method uses a
controlled chemical reaction to effect the deposition of
a thin film by precipitation.
 Substrates are immersed in a chemical bath containing
precursor solution

12. Advantages
It requires only solution containers and substrate
mounting devices.
Among various deposition techniques, chemical bath
deposition yields stable, adherent, uniform and hard
films.
It is one of the suitable methods for preparing highly
efficient thin films in a simple manner.
Disadvantages
 Wastage of solution after every deposition.
Proper substrate cleaning is a very important factor in
obtaining good adherent films

13. LEAD SULPHIDE(PbS)

14. Molecular formula = PbS
Molar mass = 239.30 g/mol
Density = 7.60 g/cm3
Melting point = 1,118 °C (2,044 °F; 1,391 K)
Boiling point = 1,281 °C (2,338 °F; 1,554 K)
Band gap energy = 0.4eV
DESCRIPTION OF PbS

15. APPLICATIONS OF PBS
 PbS was once used as a black pigment, but
current applications exploit its semiconductor
properties .
 As an infrared detector due to its narrow
band gap

16. EXPERIMENTAL PROCEDURE

17. • The reactive substances used to obtain the
PbS thin film were lead acetate/lead nitrate
(Pb(CH3COO)2)/ (Pb(NO3)2), sodium hydroxide
(NaOH) and thiourea(SC(NH2)2) and H2O for
different concentration at constant room
temperature.

18. PREPARATION OF PbS USING LEAD NITRATE
(PRECURSOR SOLUTION)
 The first step was to prepare 1M solution of Thiourea
(SC(NH2)2),Lead nitrate (Pb(NO3)2 ), and Sodium hydroxide
(NaOH),.
 The second step is to prepare chemical bath using this
solutions
 The third step is to immerse the substrate on the precursor
solution

19. • First the complexing agent NaOH was added to lead
nitrate and after some time Thiourea was added.
• A white precipitated solution was formed which
turned into a blackish colour after some time which
indicates the presence of PbS.
• NaOH fixes the alkalinity of lead nitrate solution.
The reaction of lead nitrate and NaOH resulted in
the production of Pb 2+ ions.
• Then thiourea was added which resulted in the
formation of PbS. Water was added only after mixing
the reactants.
IMPORTANCEOF ORDEROF MIXING0F REACTANTS

20. PREPARATION OF PbS USING LEAD ACETATE
(PRECURSOR SOLUTION)
• The first step in preparation of PbS using lead acetate is
preparation of 1 molar solution of lead acetate,thiourea,sodium
hydroxide
• The second step is to prepare precursor soluion using this
solution
• The third step is to immerse the substrate on the precursor
solution
• Order of mixing is important in this case also

21. OPTIMUM CONDITION
DIPPING TIME:65 MIN
At this condition thickness~200nm
When dipping time less than 65 min ,the films are not uniform
MOLARITY OF NaOH=0.55M
MOLARITY OF THIOUREA=0.1M
MOLARITY OF LEAD ACETATE/LEAD NITRATE=0.1M
AT ROOM TEMPERATURE

22. COMPARISON OF FILMS
 We observed that uniformly deposited film is obtained
when we use lead acetate precursor solution. This film
was found to be more adhesive and pinhole free.
 Lead nitrate precursor solution precipitated faster
than lead acetate solution. It is reported that slow
precipitation yielded better films.

24. THE HOT-PROBE METHOD
 The "hot-probe" experiment provides a very simple
way to distinguish between n-type and p-type
semiconductors using a standard multimeter.
 The experiment is performed by heating the
positive terminal of the standard multimeter.The
heated probe is hot probe and the other one is cold
probe. The two terminals are placed on the film,the
experimental setup is as shown in the figure

25. When applying the probes to n-type material one obtains a positive
current reading on the multimeter, while p-type material yields a
negative current.A . PbS thin film is observed to be p-type material.

26. STRUCTURAL CHRACTERISATION
X-ray crystallography is a tool used for identifying the atomic and
molecular structure of a crystal, in which the crystalline atoms cause a
beam of incident X-rays to diffract into many specific directions.
By measuring the angles and intensities of these diffracted beams, a
three-dimensional picture of the density of electrons within the crystal can
be produced.
Using this electron density, the mean positions of the atoms in the
crystal can be determined, as well as their chemical bonds, their disorder
and various other information.
 The method also revealed the structure and function of many biological
molecules, including vitamins, drugs, proteins and nucleic acids such as
DNA.
X-ray crystallography is still the chief method for characterizing the
atomic structure of new materials and in discerning materials that appear
similar by other experiments

27.  Crystals are regular arrays of atoms, and X-rays can be considered waves of
electromagnetic radiation. Atoms scatter X-ray waves, primarily through the atoms'
electrons.waves cancel one another out in most directions through destructive
interference, they add constructively in a few specific directions, determined by Bragg's
law:
Here d is the spacing between diffracting planes,
θ is the incident angle, n is any integer, and
λ is the wavelength of the beam.

28. THE DIAMETER OF THE CRYSTALLITES
we use the Debye-Scherrer formula to find the
diameter of the crystal.
Debye-Scherrer formula
D = 0.9λ/ β cosθ
Where,
D is the diameter of the crystallites forming the
film,
λ is the wavelength,
β is the FWHM (Full Width at Half Maximum) in
radians and
θ is the Bragg angle

29. Bragg Condition
2dsin θ= nλ
Where,
d is the interplanar distance,
n is the order of diffraction,
θ is the Bragg angle and
λ is the wavelength.

30. XRD of Sample of lead nitrate
20 30 40 50 60
0
50
100
150
200
250
300
350
INTENSITY[inarbitaryunits]
in degrees]
2θ(in
degrees)
(h k l)values
26.7 (1 1 1)
30.8 (2 0 0)
43.8 (2 2 0)
Inferences from XRD
• Thin films formed are
lead sulphide cubic
crystal and no other
phases are present.
• Using debye-scherrer
formula grain size is
calculated and is of the
order 41.9nm
• Using braggs condition
inter planar distance is
also calculated is equal
to 29nm
conc.of Pb(NO3)2 = 0.1M, conc.of SC(NH2)2 = 0.1M , conc.of NaoH=0.55M

31. 20 30 40 50 60
0
100
200
300
INTENSITY[inarbitaryunits]
[in degrees]
XRD of Sample of lead acetate
2θ(in
degrees)
(h k l)values
26.7 (1 1 1)
30.8 (2 0 0)
43.8 (2 2 0)
Inferences from XRD
•Thin films formed are
lead sulphide cubic crystal
and no other phases are
present.
•Using debye-scherrer
formula grain size is
calculated and is of the
order 45.44nm
•Using braggs condition
inter planar distance is
also calculated and equal
to28nm
•It is observed that
crystallinity is slightly
higher for lead acetate
conc.of Pb(CH3COO)2 = 0.1M,conc.of SC(NH2)2 =0.1M, conc.of NaoH =0.55M

32. EFFECT ON THE VARIATION OF LEAD CONCENTRATION ON
LEAD ACETATE PRECURSOR SOLUTION
For this the concentration of NaOH is fixed at 0.55M and that of thiourea at 0.1M and
the concentration of leadnitrate is varied from 0.1 to 0.22M
Sample name Molarity of NaOH(M) Molarity ofThiourea(M) Molarity of lead
acetate(M)
A 0.55 0.1 0.1
B 0.55 0.1 0.1
C 0.55 0.1 0.14
D 0.55 0.1 0.16
E 0.55 0.1 0.18
F 0.55 0.1 0.2
G 0.55 0.1 0.22
The best film was obtained at 0.1M concentration of lead acetate.Structural
characterization were done using x ray diffraction technique and electrical properties
are studied.

33. 20 30 40 50 60
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340
INTENSITY[inarbitaryunits]
[in degrees]
20 30 40 50 60
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340
INTENSITY[inarbitaryunits]
in degrees]
Here crystallinity was observed to be decreasing on increasing the Pb concentration in PbS
films.Decreases in crstallinity may be due to the removal of Pb2+ ions from the surface of
films.S.Seghaier et al reported that decrease in crystallinity in lead sulphide was due to the
depletion of Pb2+ ions resulting lower rate of deposition.Optimum lead content may be
reached even at 0.1M concentration of lead acetate (Reference : S. Seghaier, N. KamouN, R.
Brini, A.B. Amara, Materials Chemistry Physics 97 (2006) 71–80.)
STRUCTURAL ANALYSIS ON THE VARIATION OF LEAD
conc.of Pb(CH3COO)2 = 0.22M,conc.of SC(NH2)2 =0.1M,
conc.of NaoH =0.55M
conc.of Pb(CH3COO)2 =0.18M,conc.of SC(NH2)2 =
0.1M,conc.of NaoH =0.55M

34. Electrical contacts was given using silver paint of 5mm length in the form
of two end contacts having a distance of 5mm between them. Then
readings are taken by multimeters. Multimeters readings show that lead
sulphide films are conductive.
Resistivity and conductivity
Resistance, R = ρA
l
Therefore, Resistivity ρ = R x t x d
l
Where l is the length of the silver paint
d is the distance between two electrical contacts
t is the thickness of the film
here d and l are same
therefore ρ = R x t
here t,thickness of the film ~ 200nm
ρ = R x 200nm
ELECTRIAL CHARACTERISATION

35. Sample Resistance(MΩ) Resistivity( 10-3 Ωm) Conductivity(Ω-1m-1)
A
6.3 1260
0.79
C 5.2 1040 0.96
E 3.1 620 1.612
G 0.9 180 5.5
[lead concentration of samples:A = 0.1M, C = 0.14M , E = 0.18M , G = 0.22M ]
RESISTIVITY AND CONDUCTIVITY OF THE SAMPLES ON
VARYING THE LEAD CONCENTRATION IN LEAD ACETATE

36. MOLARITY OF LEAD VS CONDUCTIVITY
0
1
2
3
4
5
6
0 0.05 0.1 0.15 0.2 0.25
conductivity(ohm-1m-1)
concentration of lead (M)
From the graph we can understand that when concentration of lead increases
,there is a sharp increase in electrical conductivity which may be due to the greater
metal content.

37. • It was proved that films are PbS from the crystalline peaks of XRD and
there were three peaks corresponding to (1 1 1), (2 0 0) and (2 2 0)
orientations
• It was found out that the PbS films produced are p-type in nature
by hot probe method
• The resistance values of all PbS films can be measured using multimeter
and it means that our films are conductive. We have calculated resistivity
and conductivity of the films
• A clear increase in conductivity was observed on increasing the lead
concentration in PbS films,which may be due to the increase in metal
content
INFERENCES FROM THE PROJECT
• It is observed that the PbS films formed from lead acetate
precursor is more adherent than from lead nitrate

38.  CBD is a cost effective method for the formation of
thin films.
 The method does not involve heating or stirring.
 The order of adding the reactants of the precursor
solution is important.
 The films formed are conductive and crystalline in
nature.
 The selection of precursor solutions also play a great
role in the formation of films.