Download Scott Lascelle Bill Davis Nanomaterials Workshop University of

Scott Lascelle
Bill Davis
Nanomaterials Workshop
University of Tulsa
July 12-23,2004
The Nanomaterials workshop was provided by the University of Tulsa,
and was presented by Dr. Saibal Mitra, Associate Professor of Physics,
by Dr. Winton Cornell, Senior Research Associate of Geosciences, by
Dr. Richard Portman of the Biological Sciences department, and by Dr. Peter
Zhang. Also providing help and service were Suchitra Mutlur, and Vanessa
Russo.
Eight teachers from various high schools and science disciplines participated in the workshop.
Our first two days were filled with orientation, introduction to
materials, various lectures, and demonstrations of equipment in the field
of nanotechnology.
Materials and objects at the nano scale are so small (one-thousandth
of a micron) that special tools are needed for handling, manufacturing, and
examining manomaterials.
EQUIPMENT
Our main thrust in our lab experiments was twofold: first, we sought
to deposit pure Nickel as a substrate on materials to act as nucleation sites;
Second, was the attempt to grow nanotubes of carbon on the Nickel sites.
The following is a list of equipment we used in the deposition of Nickel, the
growth of the carbon nanotubes, and also the examination of our results.
PVD (sputtering)- Physical Vapor Deposition- In this process, heat is used to
move atoms from a source (known as a “target”) toward the object to be
coated. This process is especially useful in SEM, as it provides a conductive
surface for the electron
beam.
HWCVD-Hot Wire Chemical
Vapor Deposition- Jokingly
referred to as a
“glorified light bulb”, this
device uses a hot tungsten
filament as its heat source
for the coating of substrates.
Inside a low-pressure bell jar, the filament is hated, and a mixture of
gases is then introduced, providing the atoms needed for the coatings. We
did not use this method in our research.
CHARACTERIZING
After these processes had been completed, careful analysis was
needed to confirm or deny our success. Several methods were employed,
each contributing its own special data.
AFM- Atomic Force Microscope- This device employs a
small cantilever arm, known as a cantilever, which has a
tiny tip (probe). A piezo crystal is used to help guide the
probe as it scans the surface of the material. A laser
beam is carefully focused on the end of the arm. The
interactions of atom forces between the tip and the
substrate deflect the arm, causing the laser beam to also
deflect. These changes are picked up by a Photodiode
that sends the data to a computer, that then generates
an image. (This image is of gold deposited on a
substrate.)
XRD- X-ray Defractometer- X-rays
produced by this device penetrate a
sample and will be reinforced and
reflected back to a sensor only if the
diffraction angles are at certain angles
to the original beam. By careful
measurement and comparison to known
values, the composition of the material
can be found.
ED(Electro-deposition) – This is a method of electro plating using a computer
to precisely control the rate and degree of deposition on the substrate
(steel). We used a solution of nickel sulfate, which contributed the nickel
ions to the steel substrate. Varying the time will affect the rate of
deposition.
CVD(Microwave Plasma Chemical Vapor Deposition) – A plasma is generated
by submitting hydrogen gas to a high microwave electrical energy. Then
methane is introduced into the chamber where the plasma strips the
hydrogen from the methane molecule, leaving only the carbon atoms. This
then allows the carbon to be deposited on the substrate in the form of
carbon nanotubes.
SEM(Scanning Electron Microscope) – The development of the electron
microscope was a natural evolution in the search for ways to see smaller and
smaller units, with the ultimate goal to be able to visualize an individual
atom.
This was something that normal light prevented, as visible light wavelengths are
too large for applications of this type. As knowledge about X-Rays, electron
beams, and other related phenomena was discovered and perfected, it was
inevitable that someone would eventually figure out a way to use a stream of
electrons as a substitute for a light beam in a microscope. In doing so, the
electron microscope was born.
Today’s SEMs utilize the following:
A: Backscatter electron detector – identifies atoms on the surface of the
sample.
B. Secondary electron detector – detects low energy electrons
C. EDX (Energy Dispersal X-Ray detector – detects X-Rays emitted by the
target.
TEM (Transmission Electron Microscope) - TEM involves the manipulation of
an electron beam which passes through a specially prepared ultrathin section
of a specimen to obtain a greatly enlarged, high-resolution picture of the
specimen's internal structures.
LAB EXPERMENTS AND RESULTS
As the lab procedures were being carried out, our two main concerns
were the deposition of thin-film coatings, and the growth of carbon
nanotubes on those substrates. The following is a short discussion of our
group’s findings.
Electrodeposition- Here is a results table for all the groups:
experiment type
substr
ate
time
(s)
Electrodepostion
Steel
500
0.1 molar NiS04 with 1 drop of HCl in 100 mL
2.5
-1500 mV
Electrodepostion
Steel
750
0.1 molar NiS04 with 1 drop of HCl in 100 mL
2.5
-1500 mV
Ni not detected
Electrodepostion
Steel
1000
0.1 molar NiS04 with 1 drop of HCl in 100 mL
2.5
-1500 mV
Ni detected
Electrodepostion
Steel
1000
0.5 molar NiS04 with 1 drop of HCl in 50 mL
2.5
-1500 mV
Ni detected
Electrodepostion
Steel
1500
0.1 molar NiS04 with 1 drop of HCl in 200 mL
2.5
-1500 mV
Ni detected
Electrodepostion
Steel
2000
0.1 molar NiS04 with 1 drop of HCl in 50 mL
2.5
-1500 mV
Ni detected
Electrodepostion
Steel
2000
0.5 molar NiS04 with 1 drop of HCl in 100 mL
2.5
-1500 mV
Ni detected
Electrodepostion
Steel
3600
0.1 molar NiS04 with 1 drop of HCl in 200 mL
2.5
-1500 mV
Ni detected
solution used
pH
conditions
comments
Please notice that our lab team found no results in time intervals less than
750seconds.
MPCVD- Photos of results
thickness
(nm)
Gas type 1
and flow
rate
(sccm)
Gas
type2
Gas type 3
and flow rate
(sccm)
Time for
CH4
(mins)
Time for
H2
(mins)
Experiment
Type
Sample
Name
substrate
CVD
071504A1
20
CH4 - 10
H2 - 40
4
10
CVD
071504A2
20
CH4 - 10
H2 - 40
4
10
CVD
071504A3
alumina
silicon (Ni face
down)
silicon (Ni face
up)
20
CH4 - 10
H2 - 40
4
10
CVD
071504B1
20
CH4 - 10
H2 - 30
4
10
CVD
071504B2
20
CH4 - 10
H2 - 30
4
10
CVD
071504B3
alumina
silicon (Ni face
down)
silicon (Ni face
up)
20
CH4 - 10
H2 - 30
4
10
CVD
071604C1
alumina
20
CH4 - 10
H2 - 30
N2 - 10
2.5
10
CVD
071604C2
silicon
20
CH4 - 10
H2 - 30
N2 - 10
2.5
10
CVD
071604C3
20
CH4 - 10
H2 - 30
N2 - 10
2.5
10
CVD
071904D
alumina
silicon (Ni face
up)
40
CH4 - 2.5
H2 - 250
120
5
Note: Our final run for CVD deposition used different gas combination for
much longer time as we were trying to deposit diamond, rather than carbon
nanotubes. (See SEM photos)
PVD (Sputtering)- The PVD apparatus was not operational, so no data was
collected.
AFMData which can be collected from the
Atomic Force Microscope (AFM), can
also be gathered from the SEM more
quickly and accurately. So, no data was
obtained from the AFM. AFM devices
bridge the gap between
opticalmicroscopes and electron
microscopes. The cost is also between
the two- and may well be within the
reach of some schools’ budgets.
SEM/TEM – The SEM uses a narrow beam of electrons to scan an object’s
surface. The TEM uses an electron beam to observe the specimen by
passing the beam through said specimen. Two types of electrons are
emitted to scan the surface, backscattered and secondary. The
backscattered travels in straight lines, while the secondary move in curved
paths. The secondary electrons give the fine detailing. The images produced
by the SEM are three-dimensional.
The substrate used was silicon. A mixture of 1% methane and 99% hydrogen
was used to produce the product. A time of 120 minutes was selected for
the time period of growth. At the end of that time, the product was
examined with a SEM.
Figure 1
Upon examination of the photo, one can see “square” features which could
indicate alignment with the silicon substrate. Evidently the larger structure
on the squares could be either diamond or possibly nickel. Evidence of
nanotube growth can be seen in the photos.
Figure 2
Figure 3
This photo was the most intriguing of all. Starting in the middle of the
picture, a total of five(5) deposits can be seen exhibiting a diamond-like
structure. A product was achieved that was unusual and unique to the
experiment.
XRD – This machine utilizes a high energy X-Ray beam to analyze a specimen.
The beam is projected onto the specimen at a specified angle and reflected
onto a receiving target. Bragg’s Law is used in determining the spacing
values used to identify the specimen in question.
The specimen used was nickel deposited on a steel substrate. Upon
examination, it was determined that the substrate was of nickel-steel
composition and therefore interfered with the collection of accurate data.
CLASSROOM ACTIVITIES
After some brainstorming- our group decided on four main “doable”
activities that could well be integrated into our curriculums.
-AFM model (very large) to show concepts of measuring with the AFM
with its subsequent plotting and imaging.
-A section of teaching involving Quantum nanodots and their applications for CAT and PET scans.
-Field trips to TU for brief sessions with the SEM and TEM.
-A section of teaching involving electrodeposition and field trip
to TU to examine results with the XRD and SEM/EDX.