Lead thin film by physical vapor deposition and CdSe Optical
properties
Mohammad th. Almsri
Department of Physics, Arab-American University, Jenin, West Bank, Palestine
This work divides to two parts, at the first part we prepared a thin film of lead (Pb) by using
physical vapor deposition technique (PVD). The lead has a thickness equal 101.6 nm. At the
second part we examined the optical properties of a thin film of cadmium selenide.
Keyword: lead, Pb, cadmium selenide, CdSe, reflectance, transmittance, physical vapor
deposition, PVD.
1. Introduction
Physical vapor deposition describes a variety
of vacuum deposition methods which can be
used to produce thin films and coatings. PVD
is characterized by a process in which the
material goes from a condensed phase to a
vapor phase and then back to a thin film
condensed phase. The most common PVD
processes are sputtering and evaporation.[1]
Lead is an element with the symbol Pb and
atomic number 82. It is a heavy metal that is
denser than most common materials. Lead is
soft and malleable, and also has a relatively
low melting point. used for pipes, pewter
and paint since Roman times. It has also
been used in lead glazes for pottery and, in
this century, insecticides, hair dyes and as an
anti-knocking additive for petrol. All these
uses have now been banned, replaced or
discouraged as lead is known to be
detrimental to health, particularly that of
children.[2] cadmium selenide is an inorganic
compound with the formula CdSe. It is a
black to red-black solid that is classified as a
II-VI semiconductor of the n-type. Much of
the current research on this salt is focused
on its nanoparticles. Three crystalline forms
of CdSe are known which follow the
structures: wurtzite (hexagonal), sphalerite
(cubic) and rock-salt (cubic). The sphalerite
CdSe structure is unstable and converts to
the wurtzite form upon moderate heating.
The transition starts at about 130 °C, and at
700 °C it completes within a day. The rocksalt structure is only observed under high
pressure. CdSe quantum dots have been
implemented in a wide range of applications
including solar cells, light emitting diodes,
and biofluorescent tagging. CdSe-based
materials also have potential uses in
biomedical imaging. Human tissue is
permeable to near infra-red light. By
injecting appropriately prepared CdSe
nanoparticles into injured tissue, it may be
possible to image the tissue in those injured
areas.[3]
In our work we will use physical vapor
deposition to make two thin films. The first
one made from lead. Second one made from
cadmium selenide. After that we will
examinate the optical properties of
cadmium
selenide
as
reflectance,
transmittance and absorption coefficient.
2.Experimental:
At the first part of this work, we will use
evaporation machine that show in fig 1 to
make the thin film of the two substance we
need.
Figure 1. evaporation machine works with PVD technique
We add Pb powder in the boat of the
machine after cleaning it carefully. After that
we put the cover of the machine and using
the air compressor to make the pressure
equal 1.6 ∗ 10−5 tour. This process takes 4
to 5 hours. After that we gives the boat
current pass through it to make the lead
vaporizing and tern into a gas directly
without pass through liquid phase of the
substance. After this process we open the
barrier which block the vapor of lead to
arrive to the substrate and make
composition on the surface. After 24 hours,
we open the cover of the machine and take
the thin film of lead which was made inside
before. The same processes applied on
cadmium selenide to make thin film of it.
After that we toke the thin film of lead to
measure the thickness of it. The thickness
was measured by using Thickness Gauges.
For the second part we toke the thin film of
cadmium selenide to machine called Thermo
Scientific Evolution 300 UV-VIS-NIR
Spectrophotometer as show in figure 2 to
measure the transmittance and reflectance
of cadmium selenide thin film.
Figure 2. Thermo
Spectrophotometer
Scientific
Evolution
300
UV-VIS-NIR
3.Result and discussion:
We will start with graph of transmittance as
function of wavelength shown in figure 3.
Figure 3. transmittance versus wavelength
The transmittance percent rise very fast
between 300nm to 650nm of wavelength
that means the thin film of CdSe can be use
as a filter of the electromagnetic waves
below 300nm because the transmittance
percent equal to zero on this region is
ultraviolet range of wavelengths.
Now we will analysis the reflectance percent
graph as function of wavelength as shown in
figure 4.
Figure 5. Energy versus absorption coefficient
As we see in figure 5, the most sharpness line
is appearing. That means we have an energy
gap on this material & this energy gap is
equal to 1.74 eV.
4.conclution
Figure 4. percent of reflectance versus wavelength
As we see in figure 4 the high percent of
reflectance start between 800nm to 1100nm
that means 33% of wave have wavelength
between 800nm to 1100nm reflected. This
region is near-infrared range.
Now we will show the relation between
energy & absorption coefficient on figure 5.
On this work, we obtain good method to
make a thin film with homogeneous
distribution on the surface of the substrate,
the first substrate thin film made from lead.
The second one was made from CdSe. On the
second part of this work, we measure the
reflectance, transmittance and energy gap
by using spectrometer. CdSe is good barrier
for ultraviolet waves & and have 33% of
reflectance for near-infrared rays. The
energy gap of CdSe is equal to 1.74 eV.
5.Reference:
1. The preparation of thin films by physical
vapor deposition methods. panelK.Reichelt,
X.Jiang. KFA Jülich, Postfach 1913, D-5170
Jülich F.R.G.
2. Theodore Low De Vinne (1899). Century
Company. pp. 9–36.
3. Nanotechnology Structures – Quantum
Confinement