Electrical Properties of Thin Carbon Films
Oxana Petritchenko
Rochester Institute of Technology
Principal Investigators:
Professor Richard Nelson
Electrical Engineering and Computer Science
Professor John LaRue
Associate Dean for Student Affairs
The Henry Samueli School of Engineering
University of California, Irvine
I. ABSTRACT
Exciting technological applications of carbon thin films lie within the realm of
microelectromechanical systems (MEMS), fabrication of which are based mostly on
photolithography techniques. Traditionally, silicon is used; however, recent advances in research on
carbon microelectromechanical systems (C-MEMS) showed that carbon films, pyrolyzed from
common positive and negative photoresist used in photolithography, can be used as structural
materials in fabricating 3-D micro- and nanostructures. These carbon films have the advantage of
controllable electrical resistivity and low Young’s modulus. Characterizing the electrical properties
of thin carbon films will provide the engineering data to enable C-MEMS applications. Several types
of carbon films of pre-pyrolysis thickness of 3 m and 15 m were prepared from variations of SU-8
negative photoresists. The relationship between resistance and ambient temperature of these films
was determined using two techniques: the four point probe method and a two point contact test
fixture, previously designed and fabricated for measuring electrical resistivity as a function of
ambient temperature. It was found that sheet resistance of carbon film was approximately linearly
proportional or exhibited a behavior of a curve that can be modeled with a polynomial function with
respect to the temperature of the carbon film. Also, studies observing the effects of humidity and
nitrogen gas on carbon film resistance were performed. Exposure to water resulted in inconsistent
carbon resistance versus ambient temperature curves during heating and cooling, while exposure to
nitrogen gas for several days resulted in more consistent resistance data. Exposure to nitrogen gas
also caused a decrease in the resistance of the carbon film. Additionally, a scanning electron
microscope (SEM) was used to observe the surface topology of the carbon films.
II. KEY TERMS
Carbon properties; carbon surface topology; C-MEMS (Carbon-MicroElectroMechanical Systems);
four point probe; resistivity; scanning electron microscopy; thin carbon films.
1
III. INTRODUCTION
Positive and negative photoresists can be spin coated to thin layers on Si/SiO 2 wafers and
pyrolyzed at different temperatures in different ambient gasses to form even thinner amorphous
carbon films, which can be used as structural material in micro-electro-mechanical systems
(MEMS). This generally new material possesses interesting electrical and mechanical properties that
can be characterized and used for maximum performance and new applications in MEMS.
Previously, electrical resistance of carbon films with respect to pyrolysis temperature was studied;
however, no studies have been done on carbon resistance in various ambient environments. The
purpose of this research was to determine the relationship between carbon sheet resistance and
ambient temperature, to assess potential humidity effects and to quantify changes upon submersion
in de-ionized H2O and introduction of N2 gas to amorphous carbon films, and to observe any
porosity in the carbon films. Resistance of carbon films can be determined in two ways: first, to pass
a current through a strip of carbon film and measure current and voltage drop on two opposite sides
of the carbon strip and, using Ohm’s Law, obtain total resistance; and second, to use a four point
probe, where its four probe tips contact the surface of the carbon film from above, measuring voltage
drop between the two middle probe tips and current between the two farthest probe tips. In the
second method, an introduction of two correction factors is required, and their values can be
obtained from tabulated data in literature on four point probe techniques. The results of this research
will be used in the future to further understand the behaviors of carbonaceous structural and
electrical interconnect materials in device applications.
2
IV. METHODS AND MATERIALS
1. Carbon Film Preparation
For production of thin amorphous carbon films, both positive and negative photoresists may
be used. In this study, the carbon films were obtained from SU-8 photoresist, which is a high
contrast, epoxy based negative photoresist designed for micromachining and other microelectronic
applications. Different parameters of procedures, shown in Table 1, were used to fabricate the films
required for the research samples. All the silicon wafers were cleaned with isopropyl alcohol (IPA)
and baked at 200 C for 5 minutes for complete dehydration. Next, they were cut into four equal
quarter-wafers with a glasscutter. Then, SU-8 photoresist was deposited on quarter-wafers at various
rotational velocities to attain certain layer thickness, and the samples were soft baked for a number
of minutes as shown in Table 1. After the soft bake, 3-x series of samples were exposed to near UV
light (350-400 nm) with a mask of three 1.5 x 1.5 cm squares and one 1 x 1 cm square. The 1.5 x 1.5
cm squares were labeled N1, N2, and N3, while the 1 x 1 cm square was labeled Ns. Samples 3 and
5 were patterned to make two thin strips of carbon. Exposure was performed using Karl Zeuss MJB3
contact aligner. Series 1-x and 2-x were not patterned. Next, the samples were hard baked (Post
Exposure Bake (PEB)) for a given time, as seen in Table 1, and then developed with MicroChem's
SU-8 Developer, which removed the unexposed area of photoresist. Following development, the
samples were rinsed briefly with isopropyl alcohol (IPA), then dried with a gentle stream of
nitrogen.
3
Table 1. Carbon Film Preparation Parameters
Sample
Photoresist
#
Thickness
(m)
Spin
Speed
(rpm)
SU-8 2
3-1, 3-2
5
1000
PreSoft
Exposure
Bake @ Bake @
Energy
65C
95C
(mJ/cm2)
(min)
(min)
1
3
150
SU-8 25
3-3, 3-4
15
1-1, 1-2,
5
1-3, 1-4
2-1, 2-2,
15
2-3, 2-4
3000
2
5
1000
1
3000
3, 5
1000
SU-8 2
SU-8 25
SU-8 2
5
PEB 1 PEB 2
@ 65C @ 95C
(min)
(min)
1
1
200
1
2
3
—
1
1
2
5
—
1
2
5
5
150
5
5
“—“ Represents no patterning of the SU-8 photoresists was done.
After the initial preparation of the samples, a two-step pyrolysis process followed. The
samples were placed in a quartz-tube furnace, which was set to heat to 300 C in an N2 atmosphere
for 40 minutes, and the samples were allowed to sit at that temperature for 60 more minutes. Then
the samples were heated to 900 C for 60 minutes, and forming gas [H2(5%)/N2(95%] was
introduced for another 60 minutes. At this point, the furnace and the forming gas were turned off and
the samples in the furnace were allowed to cool to room temperature for about 9 hours in an N 2
environment. Only samples 3 and 5 were taken to have a rectangular thin titanium layer deposited,
followed by a rectangular thin gold layer, making up the contacts on each side of the carbon strips.
The design of the series of samples can be seen in Pictures 1-3.
Picture 1: Sample Series 3-x
Picture 2: Sample Series 1-x
and 2-x
4
Picture 3: Samples 3 and 5
2. Two Point Contact Measurement Technique
To obtain resistance measurements of
carbon film samples 3 and 5, each individual
sample was placed inside aluminum housing and
covered with a Teflon/Aluminum block, as shown
in Picture 4. Copper probes attached to the
Teflon/Aluminum block interfaced with the Ti/Au
contacts on opposite sides of the carbon resistors.
Picture 4. Two Point Contact Measurement Method
The copper probes were connected to a digital ohmmeter, so that resistance measurements could be
observed and recorded instantaneously. Temperature was increased or decreased using a hot plate
under the aluminum housing, and Type K thermocouple was placed inside the housing to make
accurate temperature measurements. A layer of cooking foil was placed on top of the
Teflon/Aluminum block to prevent air drift, and a Teflon top was used to cover the entire aluminum
housing. The Teflon/Aluminum construction allowed measurements to be made up to 250 C. The
hot plate was turned on and the resistance measurements were taken at intervals of 1 C from a room
temperature of about 24 C to 81 C.
3. Four-Point Probe Measurement Technique
The four-point probe method was used to
determine sheet resistivity measurements of 3-x series
of samples. The SP4 Four-Point Probe Head, which is
designed for measurement of thin films and materials,
was ordered form Lucas Labs, a Division of
Lucas/Signatone
Picture 5. Four Point Probe Method
5
Corporation.
The
configuration
parameters of the probe head are specified in
Table 2. The probe head was attached to a micromanipulator, which, in turn, was attached to an
aluminum plate using ceramic stands and screws.
Table 2. Configuration parameters of SP4 Probe
Spacing between tips
0.1 cm
Pressure on each probe tip
45 grams
Tip Radius
Probe tip material
Compression for good contact
0.0254 cm
Osmium
50 - 60 %
The aluminum plate was set on a hot plate. The samples were placed beneath the probe head
and taped to the aluminum plate. The Type K thermocouple was taped directly to the silicon wafer
for accurate temperature measurements. The four probe tips were set to contact the surface of the
carbon film exactly in the middle of each carbon film square. The entire structure was then covered
completely with cooking foil to prevent drift of resistance values due to variable convective cooling.
Also, the exact pressure of the probe tips onto the film sample was always followed because
resistance of the carbon film is affected by the pressure of the four-point probe tips.
Figure 1 shows the schematic of how the four point probe was connected to the power supply
and current and voltage measurements were acquired. The HP Triple Output DC Power Supply was
set to output 6V, which was connected to a 3.3 k
resistor. Before, during and after the hot plate was turned
on the current and voltage measurements were taken at
intervals of 1 C from a room temperature of about 24 C
to 81-87 C. The current through this circuit was
measured with a Keithley 177 Microvolt DMM and
Picture 6. Schematic of Four Point Probe
voltage
was
Multimeter.
6
measured
with
BKPrecision
5491A
The current and voltage readings acquired during the experiments were then used in the
equation R = (V/I)*C.F.1*C.F.2, where R is resistance, V is voltage potential, and I is current. C.F.1
is the correction factor, which depends on the geometry of the thin film and the spacing between
probes, and was obtained from Table 1 in Measurement of Sheet Resistivities with the Four-Point
Probe by F. M. SMITS1. Correction factor C.F.2 depends on the spacing between probes and the
thickness of the film; this value was obtained from Four Point Resistivity and Conductivity Type
Measurements by Ziyi Dai2.
4. Carbon Surface Topology Studies
Sample series 1-x and 2-x were used for the Scanning Electron Microscopy (SEM) studies.
The surface was observed on a nanometer scale with a voltage difference of about 1 kV to 0.8 kV,
which controls the speed of the electron beam, and a working distance of 3 mm, which controls the
magnification and focus of the lens. These images were obtained using the primary sensor of SEM;
even though the secondary sensor was also used, no clear images could be obtained using just the
secondary sensor or a combination of the primary and the secondary sensors. More technical details
are recorded and can be seen below each SEM image (Pictures 7-10) in the Results section of this
report.
7
V. RESULTS
1. Carbon Film Thickness Measurements
Thickness measurements of each carbon film sample before and after pyrolysis were found
using a profilometer. The average of these measurements was found and recorded in Table 3.
Uncertainties in thickness measurements for sample series 1-x and 2-x, and samples 3-3 and 3-4
were 0.02 m; for samples 3-1 and 3-2 they were 0.2 m.
Table 3. Thickness Measurements of all carbon film samples using profilometer.
Sample
Before
Pyrolysis
Thickness
(m)
After
Pyrolysis
Thickness
(m)
1-1
1-2
1-3
1-4
2-1
2-2
2-3
2-4
4.00
3.20
4.35
4.00
15.60
16.00
18.60
17.60
0.90
1.00
1.00
1.25
2.80
5.00
4.00
5.00
Sample
Before
Pyrolysis
Thickness
(m)
After
Pyrolysis
Thickness
(m)
3-1 N1
3-1 N2
3-1 N3
3-1 Ns
3-2 N1
3-2 N2
3-2 N3
3-2 Ns
3.20
3.25
3.25
3.20
3.31
3.22
3.22
3.31
0.59
0.59
0.59
0.59
0.59
0.59
0.59
0.59
8
Sample
Before
Pyrolysis
Thickness
(m)
After
Pyrolysis
Thickness
(m)
3-3 N1
3-3 N2
3-3 N3
3-3 Ns
3-4 N1
3-4 N2
3-4 N3
3-4 Ns
13.90
13.90
13.85
13.85
14.42
14.71
14.71
14.42
2.52
2.53
2.53
2.53
2.48
2.59
2.52
2.56
2. Temperature dependency of the resistance of thin carbon films
Graph 1. Sample 3-1. Stored in N2 gas. Four-Point Probe Method.
200.0
N1
195.0
N2
Resistance (ohms/sq.)
N3
190.0
185.0
180.0
175.0
20.0
30.0
40.0
50.0
60.0
Temperature (C)
9
70.0
80.0
90.0
Graph 2. Sample 3-2. Not stored in N2 gas. Four-Point Probe Method.
190.0
185.0
Ns
Resistance (ohms)
N2
180.0
175.0
170.0
165.0
20.0
30.0
40.0
50.0
Temperature (C)
10
60.0
70.0
80.0
Graph 3. Sample 3-3. Stored in N2 gas for four days and heated to 135 C for 12 minutes.
Four-Point Probe Method.
43.0
42.5
3-3 Ns (1st run)
3-3 N3 (2nd run)
42.0
Resistance (ohms/sq.)
3-3 N1 (3rd run)
3-3 N2 (4th run)
41.5
41.0
40.5
40.0
39.5
39.0
38.5
20.0
30.0
40.0
50.0
60.0
Temperature (C)
11
70.0
80.0
90.0
Graph 4. Sample 3-4. Stored in N2 gas. Four-Point Probe Method.
47.0
N1
N2
46.0
N3
Ns
Resistance (ohms/sq.)
45.0
44.0
43.0
42.0
41.0
40.0
20.0
30.0
40.0
50.0
Temperature (C)
12
60.0
70.0
80.0
Table 4. Sample Series 3-x linear regression fit.
Sample
N1
3-1
N2
N3
N2
3-2
Ns
N1
N2
3-3
N3
Ns
N1
N2
3-4
N3
Ns
Slope (/1C)
0.2844
0.2596
0.2589
0.2788
0.2678
0.0464
0.0458
0.0521
0.0404
0.0573
0.0606
0.0572
0.0532
R2
0.9928
0.9973
0.9741
0.9882
0.9760
0.9865
0.9844
0.9673
0.9650
0.9911
0.9955
0.9943
0.9989
Table 5. Sample Series 3-x linear regression fit: Slope Averages.
3-1
3-2
3-3
3-4
Slope Averages
(/1C)
0.2676
0.2733
0.0462
0.0571
13
3. Humidity Study: Water Submergence and drying by N2 gas
Graph 5. Sample 5. S1:Carbon Strip 1 and S2: Carbon Strip 2. Stored in N2 gas for one week.
Two Point Contact Method.
1.60
1.58
1.56
Resistance (kohms)
1.54
1.52
1.50
1.48
1.46
S1: No Nitrogen
S1: After Nitrogen Exposure
1.44
1.42
1.40
20.0
S2: No Nitrogen
S2: After Nitrogen Exposure
30.0
40.0
50.0
Temperature (C)
14
60.0
70.0
80.0
Graph 6. Sample 3. Stored in N2 gas for five nights. Two Point Contact Method.
1.66
1.64
1.62
No nitrogen
Resistance (kohms)
1.60
After
Nitrogen
Exposure
1.58
1.56
1.54
1.52
1.50
1.48
1.46
20
24
28
32
36
40
44
48
52
56
Temperature (C)
15
60
64
68
72
76
80
84
Graph 7. Sample 3-4 Ns. Sample submerged in H2O for 24 hrs, then dried in N2 gas for three
nights and tested twice. Four-Point Probe Method.
45.0
44.5
Original
44.0
Wet:1 Night in H2O
Dry: 3 Nights in N2, Trial 1
Resistance (ohms/sq.)
43.5
Dry: 3 Nights in N2, Trial 2
43.0
42.5
42.0
41.5
41.0
40.5
40.0
20.0
30.0
40.0
50.0
60.0
Tem perature (C)
16
70.0
80.0
90.0
Graph 8. Sample 3-3 N1 and N2. Before and after storage in N2 gas and heating to 135 C for
12 minutes. Four-Point Probe Method.
44.0
N1 Original
43.0
N1 after N2 and Heating
N2 Original
Resistance (ohms/sq.)
N2 after N2 and Heating
42.0
41.0
40.0
39.0
38.0
20.0
30.0
40.0
50.0
60.0
Temperature (C)
17
70.0
80.0
90.0
4. Effect of Nitrogen Gas and Heating
Graph 9. Sample 3-3. Effect of N2 gas and heating to 135 C for 12 minutes. Four-Point Probe
Method.
45.0
N1 Original
N2 Original
44.0
N3 (1 Night in N2)
Ns (after N2 and heating)
N3 (after N2 and heating)
Resistance (ohms/sq.)
43.0
N1 (after N2 and heating)
N2 (after N2 and heating)
42.0
41.0
40.0
39.0
38.0
20.0
30.0
40.0
50.0
60.0
Tem perature (C)
18
70.0
80.0
90.0
5. Temperature Coefficient of Resistance Analysis of the Sample Series 3-x
Table 6. Sample 3-1  Summary
3-1 R. vs. T. Slopes
N1 Total -0.2844
N2 Total -0.2596
N3 Total -0.2589
R @ 27C
199.4931
198.0683
192.3127
Average:
St. Dev.:
Table 9. Sample 3-3  Summary

-0.00143
-0.00131
-0.00135
-0.00136
0.00006
3-4 R. vs. T. Slopes R @ 27C
44.2907
N1 Total -0.0573
46.6560
N2 Total -0.0606
44.8495
N3 Total -0.0572
-0.0532
43.2015
Ns Total
Average:
St. Dev.:
Table 7. Sample 3-2  Summary
3-2 R. vs. T. Slopes R @ 27C
N1 Total -0.2735
189.5173
N2 Total -0.2901
185.2470
Ns Total -0.2697
180.8808
Average:
St. Dev.:

-0.00144
-0.00157
-0.00149
-0.00150
0.00006
Table 10. Sample Series 3-x  Average
Summary
Samples
3-1
3-2
3-3
3-4
St. Dev.
Table 8. Sample 3-3  Summary
3-3 R. vs. T. Slopes R @ 27C
N1 Total
-0.0464
41.8591
N2 Total
-0.0458
41.3178
N3 Total
-0.0521
42.3131
Ns Total
-0.0404
41.5810
Average:
St. Dev.:

-0.00129
-0.00130
-0.00128
-0.00123
-0.00127
0.00003

-0.00111
-0.00111
-0.00123
-0.00097
-0.00110
0.00011
19

Average
-0.0014
-0.0015
-0.0011
-0.0013
0.0002
6. Carbon Surface Topology Studies
Several images of the surface of the thin carbon films were obtained using the Zeuss Scanning
Electron Microscope. These images, Pictures 7 –10, are shown below. More details about each
image can be seen right below each image.
Picture 7. SEM Carbon Film
Surface
Picture 8. SEM Carbon Film
Surface
20
Picture 9. SEM Carbon Film
Surface
Picture 10. SEM Carbon Film
Surface
21
VI. DISCUSSION
1. Carbon Film Thickness Measurements
The goal of sample series 1-x and samples 3-1 and 3-2 was a pre-pyrolysis thickness of 5
m, and for sample series 2-x and samples 3-3 and 3-4, a thickness of 15 m. The standard
procedure listed in the Nano SU-8 Negative Tone Photoresist Formulation3 article was followed to
achieve these thicknesses. The deviation in film thickness was most likely due to imprecision of a
spin-coating machine. In general, the pre-pyrolysis thickness values were acceptable for continuation
of the experiments. Several abnormalities were observed during profilometer measurements of postpyrolysis thicknesses in samples 3-1 and 3-2. The silicon wafer, ideally possessing a generally flat
surface, which is used as a reference point for film thickness measurements, was observed to have
surface variation in the range of 20 m, yet the carbon film surface remained relatively even. As a
result, the uncertainty for the post-pyrolysis film thickness measurements in samples 3-1 and 3-2
were 0.2 m, much higher than uncertainties in other samples. The carbon film thickness
information is essential in further computations of carbon film resistivity.
2. Temperature dependency of the resistance of thin carbon films
For sample 3-1, only N1, N2 and partially N3 carbon film sample resistance data and, for
sample 3-2, only N2 and Ns carbon film resistance data were obtained, due to the fact that voltage
and current values were not stable throughout the experiment; therefore, no complete accurate
resistance data was obtained. This variability in data acquisition for these samples can be attributed
to unstable four-point probe tip to carbon contact. Some micro-movement could have occurred
during testing, easily resulting in scratching of the carbon film, the thickness of which is only 0.59
m. Also, carbon film sample N3 of sample 3-2 was damaged during fabrication and could not be
tested for accurate results.
22
Solid contact was achieved in thicker films of samples 3-3 and 3-4 (~3.5 m), and therefore,
resistance data could easily be obtained at each temperature reading. Stored in nitrogen gas and
heated for dehydration, the samples provided fairly consistent sheet resistance readings at given
temperatures in the 70 – 80 C range upon heating and cooling processes, but the readings deviated
at lower temperatures. This deviation can be attributed to delay in temperature readings or
microscopic movement of probe tips causing mechanical damage to the carbon films. It is highly
improbable that the carbon film chemical structure changes during each heating process because
sample 3-4, as shown in Graph 4, exhibited no or very minimal difference in resistance readings at
given temperatures during the heating and cooling processes for all four carbon film samples.
Therefore, composition and structure of the carbon film is not changing, and the inconsistency in
data in samples 3-1, 3-2, and 3-3 has to be explained by some other variable factor.
Even though sample 3-4 sheet resistance readings were very consistent, the actual sheet
resistance varied for each carbon film sample. Such general resistance variation can be explained by
several factors. First of all, possible variation in the horizontal and vertical position of the four-point
probe tip cannot be ignored. Ideally, the probe tips had to be exactly in the center of the film
undergoing the testing; however, since position was set by eye, the probe tips were most likely
slightly off center. Second, variation in pressure of the probe tips upon the carbon film surface also
has an effect on resistance values. Several studies were preformed to show that sheet resistance of
the carbon changed in the range of 2 from point of contact to the point of bordering carbon film
damage. Standard deviation was found to be 0.95 of this data. As a result of this study, a set
vertical distance was defined, which in turn set a standard pressure for the carbon film, for all
experiments. Yet, possible slight variations in probe tip pressure could have occurred to vary the
data. Third, variation in carbon film thickness also cannot be ignored.
23
Linear regression fit was obtained for each curve data collected and the slope was recorded in
Table 4. The slope averages were found and presented in Table 5. For samples of similar thickness,
the slope values, which represent average resistance decrease in ohms for every 1 C increase, are
only different by 0.0057 /C and 0.0109 /C, for samples 3-1, 3-2 and samples 3-3, 3-4,
respectively. These differences are within 3% error and 20% error of the total slope values,
respectively.
As a result of these studies, few conclusions can be made. It is recommended that this
experiment be repeated with more samples.
3. Humidity Study: Water Submergence and drying by N2 gas
The two point contact method was used to test sample 5 before and after the sample’s
exposure to nitrogen gas. Resistance versus temperature heating and cooling data curves of both
carbon film strips became more consistent after exposure to nitrogen gas, as demonstrated in Graph
5. The same method was used to test sample 3, which was tested originally as manufactured and then
exposed to nitrogen gas and tested after one night, two nights, five nights, and one more week in
nitrogen gas. The most change in resistance versus temperature curves, where the heating and
cooling curves became more consistent at a given temperature, occurred after a period of one night.
As the time in nitrogen gas progressed, there were very slight changes in resistance versus
temperature data: with each test the data curves evened out and became the most consistent by the
fifth night; therefore, only the resistance versus temperature data after five nights is displayed in
Graph 6.
The carbon film sample 3-4 Ns presented in Graph 7 was studied for H2O and nitrogen gas
effects. It was noticed that after sample 3-4 Ns was submerged in H2O for 24 hrs, the heating
resistance versus temperature curve exhibited an inversely parabolic behavior, and upon sample
24
cooling, the resistance versus temperature curve straightened out and seemed to follow a linear
pattern. Also, when the sample 3-4 Ns was dried by nitrogen gas the cooling and heating data curves
became more consistent. The best results were achieved on the second trial during which neither the
probe head nor the sample were moved or touched. The second trial was performed right after the
cooling of the system to approximately room temperature, and the experiment was repeated for the
second time under exactly the same conditions. For further reference, after the sample was
submerged in de-ionized water, and even after it was kept in nitrogen gas for three days, the sheet
resistance increased approximately by 1. This could be a result of incomplete dehydration of the
carbon film or possible damage to the film in the water after the first test. It is recommended that this
experiment be repeated with more samples.
4. Effect of Nitrogen Gas and Heating
Analyzing Graph 9, it can be observed that nitrogen gas and/or heating of the sample
decreases the general resistance values at set temperatures. This decrease is attributed to the
humidity of the carbon film and water evaporation during heating and drying by nitrogen gas. It is
recommended that this experiment be repeated with more samples.
5. Temperature Coefficient of Resistance Analysis
Temperature coefficient of resistance, , which is defined as the change in resistance of a
material for a given change in temperature, was found for each sample in series 3-x and summarized
in Tables 6-10. Alpha values were found using R(T) = R0*[1 + *(T-T0)], where R0 means
resistance at a given initial temperature, and T0 stands for the initial temperature. The negative value
of  indicates that resistance decreases as temperature goes up. Alpha values were only within
0.0002 standard deviations among each other, which means the material produced was under exactly
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the same conditions, and little variation in carbon film composition is present from one sample to
another.
6. Carbon Surface Topology Studies
The surface of the carbon film seemed to posses an even texture with some observable
roughness. Some foreign particles were present on the surface of the film, and no porosity of the film
was observed on a micrometer or a nanometer scale.
VII. ACKNOWLEDGEMENTS
The work of Ph.D. student Chang-hsui Chang, George Horansky and Allen Kine, and the
mentorship of Professor Richard Nelson and Professor John LaRue are gratefully acknowledged.
This work was supported by Said M. Shokair, Director of the Undergraduate Research Opportunities
Program (UROP), Division of Undergraduate Education in University of California, Irvine and
funded by the National Science Foundation.
VIII. WORKS CITED
1. Smits, F. M.. “Measurement of Sheet Resistivities with the Four-Point Probe.: The Bell
System Technical Journal. May 1958: 711-718.
2. Four Point Resistivity and Conductivity Type Measurements. Ziyi Dai. Thomas Mooney. 28
October 1997. <http://www.mems.louisville.edu/lutz/resources/sops/sop45.html>
3. Microchem. Nano SU-8 Negative Tone Photoresist Formulation. 2-25.
<http://www.microchem.com/products/pdf/SU8_2-25.pdf>
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