A STUDY IN ATMOSPHERIC DIELECTRIC BARRIER DISCHARGE PLASMA

ELECTRODE CATALYTIC EFFECT USING OXYGEN AND NITROGEN

by

Alex J. Gemsheim

APPROVED BY SUPERVISORY COMMITTEE:

Dr. Lawrence J. Overzet, Co-Chair

Dr. Matthew J. Goeckner, Co-Chair

Dr. Gil S. Lee Copyright 2018

Alex J. Gemsheim

All Rights Reserved This thesis is dedicated to Emma. Without whom I could not have accomplished so much. A STUDY IN ATMOSPHERIC DIELECTRIC BARRIER DISCHARGE PLASMA

ELECTRODE CATALYTIC EFFECT USING OXYGEN AND NITROGEN

by

ALEX J. GEMSHEIM, BS

THESIS

Presented to the Faculty of

The University of Texas at Dallas

in Partial Fulfillment

of the Requirements

for the Degree of

MASTER OF SCIENCE IN

ELECTRICAL ENGINEERING

THE UNIVERSITY OF TEXAS AT DALLAS

May 2018 ACKNOWLEDGMENTS

The author thanks family and friends. Prof. Overzet, Prof. Goeckner, Prof. Lee who have guided me. I thank my lab partner Shivam Patel, who worked cooperatively with me to make this research possible. I thank Keith Hernandez and Alex Press who aided in my education.

April 2018

v A STUDY IN ATMOSPHERIC DIELECTRIC BARRIER DISCHARGE PLASMA

ELECTRODE CATALYTIC EFFECT USING OXYGEN AND NITROGEN

Alex J. Gemsheim, MS The University of Texas at Dallas, 2018

Supervising Professors: Dr. Lawrence J. Overzet, Co-Chair Dr. Matthew J. Goeckner, Co-Chair

Atmospheric dielectric barrier discharge (DBD) plasma creates a gaseous environment con- ducive to the generation of reactive species. DBD plasmas have a variety of applications in the clinical and industrial fields. During this experiment, an DBD plasma was ignited in controlled gas environments using alumina as a dielectric barrier with gold, copper, or nickel electrodes. The gas environment was formed by varying ratios of oxygen, O2, and nitrogen,

N2, with trace amounts of water and carbon dioxide. The plasma transformed these diatomic molecules into reactive species, primarily ozone, O3, and nitric acid, HNO3. A higher initial percentage of oxygen will result in a higher ozone concentration. The selected electrode material also alters the concentrations of ozone and nitric acid. Additionally, the electrode material can modulate the ratio of ozone to nitric acid, providing a specific selectivity be- tween reactive species. The electrode material generating the highest ozone concentration was gold, then copper and nickel. The electrode material with the highest ratio of ozone to nitric acid was nickel at 4:1; then gold at 2:1; and copper at 1.5:1. Utilizing these parameters allows for the generation of reactive species to desired concentrations and specific selectivity.

vi TABLE OF CONTENTS

ACKNOWLEDGMENTS ...... v

ABSTRACT ...... vi

LIST OF FIGURES ...... ix

LIST OF TABLES ...... xiii

CHAPTER 1 INTRODUCTION ...... 1

CHAPTER 2 THEORY ...... 11

2.1 Atmospheric Dielectric Barrier Discharge Plasma ...... 11

2.2 Gas Chemistry ...... 17

2.3 Fourier Transform Infrared Spectroscopy ...... 20

2.4 Optical Emission Spectroscopy ...... 29

CHAPTER 3 HIGH RESOLUTION FTIR EXPERIMENT ...... 30

3.1 General Experimental Procedure ...... 30

3.2 High Resolution FTIR Measurements ...... 32

3.3 High Resolution FTIR Results ...... 33

3.4 Ozone FTIR Data ...... 33

3.5 Nitric Acid FTIR Data ...... 39

3.6 Carbon Dioxide FTIR Data ...... 48

CHAPTER 4 TIME RESOLVED FTIR EXPERIMENT ...... 52

4.1 Time Resolved FTIR Measurement ...... 52

vii 4.2 Time Resolved FTIR Results ...... 53

CHAPTER 5 CONCLUSION ...... 60

REFERENCES ...... 63

BIOGRAPHICAL SKETCH ...... 69

CURRICULUM VITAE

viii LIST OF FIGURES

1.1 Siemens Experimental Setup ...... 1

1.2 Ellasson Experimental Setup ...... 2

1.3 Chen Experimental Setup ...... 4

1.4 Boonduang Experimental Setup ...... 5

1.5 Wang Experimental Setup ...... 6

1.6 Abdelaziz Experimental Setup ...... 7

1.7 Hsiao Experimental Setup ...... 10

2.1 Capacitively Coupled Electrodes ...... 12

2.2 Breakdown Regimes ...... 15

2.3 Electron Avalanche Effect in atmospheric DBD Plasma: Dielectric panel with

two electrodes in gold, electrons in blue, neutral species in gray, positive ions in

red, and the direction and relative magnitude of the electric field is shown by

green arrows...... 16

2.4 Vibrational and Rotational Energy Levels ...... 24

2.5 Michelson Interferometer ...... 26

2.6 Background Comparison Between Vacuum and Air ...... 27

2.7 Transitions of a carbon dioxide molecule, captured by a FTIR ...... 29

3.1 Plasma Panel Dimensions in Inches ...... 31

3.2 GEC Plasma Chamber and Accessories ...... 32

ix −1 3.3 Experimental Results: O3 from 980 to 1080 [cm ] ...... 34

−1 3.4 HITRAN Results: O3 from 980 to 1080 [cm ] [50] ...... 34

3.5 Ozone ν3 bend ...... 35

3.6 Ozone ν1 bend ...... 35

−1 3.7 Experimental Results: O3 from 1060 to 1220 [cm ] ...... 36

−1 3.8 HITRAN Results: O3 from 1060 to 1220 [cm ] [50] ...... 36

−1 3.9 Experimental Results: O3 from 2030 to 2140 [cm ] ...... 37

−1 3.10 HITRAN Results: O3 from 2030 to 2140 [cm ] [50] ...... 37

−1 3.11 Experimental Results: O3 from 600 to 850 [cm ] ...... 38

−1 3.12 HITRAN Results: O3 from 600 to 850 [cm ] [50] ...... 38

3.13 Ozone ν2 bend ...... 38

3.14 Nitric Acid ν1 -OH stretching ...... 39

−1 3.15 Experimental Results: HNO3 from 3500-3600 [cm ] ...... 40

−1 3.16 Experimental Results: HNO3 from 2000-3500 [cm ] ...... 41

−1 3.17 Experimental Results: HNO3 from 1640-1800 [cm ] ...... 42

−1 3.18 HITRAN Results: HNO3 from 1640-1800 [cm ] [50] ...... 42

3.19 Nitric Acid ν2 NO2 asymmetric stretch ...... 43

3.20 Nitric Acid ν3 NO2 symmetric stretch ...... 43

3.21 Nitric Acid ν4 H − O − N bend ...... 43

x −1 3.22 Experimental Results: HNO3 from 1260-1380 [cm ] ...... 44

−1 3.23 HITRAN Results: HNO3 from 1260-1380 [cm ] [50] ...... 44

−1 3.24 Experimental Results: HNO3 from 900-1250 [cm ] ...... 45

−1 3.25 HITRAN Results: HNO3 from 900-1250 [cm ] [50] ...... 45

−1 3.26 Experimental Results: HNO3 from 700-950 [cm ] ...... 46

−1 3.27 HITRAN Results: HNO3 from 700-950 [cm ][50] ...... 46

3.28 Nitric Acid ν5 O − NO2 in-plane bend ...... 47

3.29 Nitric Acid ν8 NO2 out-of-plane bend ...... 47

−1 3.30 Experimental Results: CO2 from 2300-2400 [cm ] ...... 49

−1 3.31 HITRAN Results: CO2 from 2300-2400 [cm ][50] ...... 49

3.32 Carbon Dioxide ν3 asymmetric stretch ...... 49

−1 3.33 Experimental Results: CO2 from 2230-2310 [cm ] ...... 50

−1 3.34 HITRAN Results: CO2 from 2230-2310 [cm ][50] ...... 50

−1 3.35 Experimental Results: CO2 from 620-720 [cm ]...... 51

−1 3.36 HITRAN Results: CO2 from 620-720 [cm ][50] ...... 51

3.37 Carbon Dioxide ν2 bend ...... 51

4.1 Atmospheric DBD Generation, Diffusion, Decay ...... 53

4.2 Ozone FTIR Time Resolved Integrated Intensity Data ...... 56

4.3 Nitric Acid FTIR Time Resolved Integrated Intensity Data ...... 57

xi 4.4 Ratio O3/HNO3 FTIR Time Resolved Integrated Intensity Data ...... 58

4.5 Carbon Dioxide FTIR Time Resolved Integrated Intensity Data ...... 59

5.1 Plasma Panel Lithography Mask [cm]...... 62

xii LIST OF TABLES

2.1 Reactions and Rate Constants. These values were compiled by [12] ...... 18

3.1 Nitric Acid Vibrational Modes ...... 39

xiii CHAPTER 1

INTRODUCTION

The field of atmospheric dielectric barrier discharge (DBD) plasmas have been widely studied because of their potential applications[1][2]. The DBD plasma creates an environment of reactive species, which was used in the first ozone generator[3]. The reactive gas chemistry can also be employed for equipment and wound sterilization[4][5][6][7][8][9][10][11]. If a DBD were placed in contact with, or submerged in water, the resulting reactions form an acidic solution[12]. This process can be used in water treatment facilities. NASA has proven DBD plasmas can be utilized on an airfoil to reduce turbulence [13]. Plasma forces the surrounding air in a particular direction, acting as an actuator to create laminar flow around the airfoil. Siemens first studied the gas chemistry of DBD plasmas in 1857, for the production of ozone [3]. In his experiment, he used concentric glass tubes to allow the flow of oxygen between the tubes, as seen in Figure 1.1. Glass is a solid dielectric. Here it formed a barrier between the electrodes, and corresponds to the dielectric barrier of a DBD. Tin electrodes

Figure 1.1. Siemens Experimental Setup covered the outside of the outer tube and the inside of the inner tube. When the electrodes were connected to a spark generator the oxygen broke down forming a DBD plasma. This was a new plasma discharge structure, and it ignited decades of research to discover the nature of the DBD plasma and the resulting reactive gas chemistry. The first detailed study of the structure of DBD plasma was by Buss in 1932[14]. With the use of Lichtenberg figures, he described the filamentary nature of the micro-discharge.

1 The discharge was not uniform in space, but consisted of a large number of microscopic dis- charges forming and terminating rapidly. From this, a series of models, Homogeneous[15][16], Avalanche[5], and Numerical[17][18] were developed to attempt to capture one or multiple attributes of the discharge. These attributes include energy distribution[19], particle motion, discharge structure, plasma formation and termination, and chemical species reactions. How- ever, models considering only ground state atoms and molecules failed to properly predict all of the reactive oxygen species observed in DBD plasmas. In 1986, Ellasson, Hirth, and Kogelschatz expanded upon the knowledge of both plasma structure and gas chemistry, which propelled previous DBD models to near current stan- dards. They implemented a cylindrical micro-discharge structure and excited atomic and molecular states, which greatly altered the model of generated species [20]. The experimen- tal configuration confined the discharge between two concentric tubes, shown in Figure 1.2. To achieve this, the interior of a 1.8 [mm] thick Pyrex tube was coated with aluminum to

Figure 1.2. Ellasson Experimental Setup form an electrode. The second electrode was formed by placing the Pyrex tube interior to a stainless steel tube. This created a 0.1 [mm] gap between the stainless steel and Pyrex in which oxygen could flow. Additionally, the stainless steel electrode was water cooled to a steady temperature. The discharge was powered by a high voltage transformer capable of 50-5000 [Hz] at 10-30 [kV ]. As part of thier studies, Ellasson, Hirth, and Kogelschatz controlled experimental param- eters and monitored DBD and gas chemistry responses. An experimental control was the

2 discharge structure. The discharge structures examined were constructed with cylindrical and flat surfaces. The dielectric and electrode materials were chosen, and fixed to the struc- ture in different inner and outer surface combinations. The gas species were chosen. The gas pressure and flow rate were controlled. Power, voltage, and frequency were controlled to ignite a plasma. The responses to adjusting these controls were measured. Gas measure- ments were taken spectroscopically and monitored species: concentration, generation, and recombination. Changes in gas temperature, electron temperature, and electrode/dielectric temperature were reported.

Particularly important in Ellasson, Hirth, and Kogelschatz’s (E, H, & A) work is their measured experimental response for a pure oxygen DBD. Here, the generated gas species were measured spectroscopically, allowing measurements of the concentration of ground and excited states of atomic-oxygen (O), oxygen (O2), and ozone (O3) with respect to discharge electric field intensity to gas density ratio [E/n] and time. The ratio of electric field to gas density is often expressed in units of Townsend, where 1[T d] = 10−17[V cm2]. The most efficient ozone generation was achieved [20] at approximately 120 [T d]. Using this potential value, at atmospheric pressure, across a 1 [mm] gap, shows that a 3 [kV ] potential needed to be applied to maximize ozone production. This provided a reference for voltage and power supplied, while other results provided a time scale reference. The current was monitored by a shielded fast current probe. When the plasma was ignited, the resulting current pulse had the fastest time scale of 2 [ns]. This is the time scale that oxygen dissociates to form atomic oxygen[20]. Whereas, ozone formation [20] is much longer at a time scale of 3 [µs], and

finally ozone diffuses [20] into the gas volume over a longer time constant of 1.6 [ms]. After diffusing into the gas volume, ozone is stable. Because early simulated ozone concentrations were significantly higher than the experimental results, E, H, & A needed to add additional dissociation and recombination terms due to surface interactions into the chemical reaction processes[20]. The cumulation of this research improved the performance of ozone generators

3 and delved into the importance of excited states for ozone generation, providing key findings that drove future research.

In later studies, experimental parameters from the work of Ellasson, Hirth, and Ko- gelschatz were varied while monitoring the effect. The parameters to be varied can be separated into three categories: discharge structure, power, and gas parameters. To change the discharge structure the size, shape, gap, and material for electrodes and dielectrics can be altered. Aspects of the power changed are the voltage, current, and frequency. Finally the gas parameters controlled include the gas species or ratio of species, flow rate, and pressure.

The DBD studies to follow controlled these parameters and monitored how the DBD and gas environment is affected.

While many previous DBD plasma studies used pure oxygen, in 2010, H. L. Chen, H. M. Lee, S. H. Chen, T. C. Wei, and M. B. Chang showed that mixing in argon influenced plasma parameters[21]. For that work, they performed an experiment that flowed a ratio of argon and oxygen using similar concentric tubes. Contrary to the previously described setup, this one consisted of an inner tube with a metallic surface instead of a dielectric (Figure 1.3). The inner tube was made from a stainless steel rod, which was placed interior to the outer

Figure 1.3. Chen Experimental Setup glass tube, creating a gap size of 5 [mm]. The outer surface of the glass tube was wrapped with a stainless steel mesh forming the second electrode. Voltage was applied to the system at potentials of 8.16-21.2 [kV ] at 100 [Hz]. Oxygen with 0%, 10%, 30%, 50%, and 80%

4 argon was flowed at 0.5 [L/min]. When the plasma was ignited with additional argon, the average electron energy increased with increasing argon to oxygen ratio[21]. Despite the higher electron energy, the ozone production decreased, even though the higher electron energy aids in the dissociation of oxygen, leading to the formation of ozone[21]. In more recent work, it has been shown that DBD plasma parameters can be controlled by gas mixtures [21] and the gas constants of pressure and flow rate[22]. In 2012, Boonduang, Limsuwan, Kongsri, and Limsuwan created a DBD with the dielectric on the surface of the inner tube (Figure 1.4). The discharge apparatus consisted of an aluminum outer tube that

Figure 1.4. Boonduang Experimental Setup confined Pyrex and stainless steel tubes. The applied voltage and frequency ranges were 1-10 [kV ] and 0-10 [kHz]. The oxygen pressure and flow rate were controlled by a pressure regulator and mass flow controller, respectively. The pressure was then confirmed with an additional pressure monitor. Pressures were tested from 1.11e5-1.93e5 [P a], at a constant flow rate, showing that plasma operated at the lowest pressure generated the largest ozone concentration across all flow rates 0-20 [L/min][22]. Experimenting with total flow rates spanning 0-20 [L/min] at a constant pressure resulted in varying concentrations of ozone. The authors of [22] found that ozone generation increased quickly as the oxygen flow rate was raised from 0 [L/min] until reaching the maximum of 80 [g/m3] at 2 [L/min]. It then decreased quickly to 30 [g/m3] at 6 [L/min], and continued slowly decreasing reaching 13 [g/m3] at 20 [L/min][22]. Combined data resulted in a maximum ozone concentration at 2 [L/min] and a maximum yield at 12 [L/min], both at a pressure of 1.11e5 [P a][22]. Thus,

5 controlling the pressure and flow rate are vital when designing an ozone generator, as well as controlling the applied frequency and power.

The final known controls are the frequency and power supplied to the electrodes. This can alter aspects of the plasma, which alter aspects of the gas chemistry. Wang, Li, and

Wen created a 0-D simulation of an experimental setup that differed from the previous cylindrical tubes, and instead modeled two parallel brass discs (Figure 1.5)[23]. One of the brass electrodes was covered with a glass plate forming the dielectric barrier. This created a

Figure 1.5. Wang Experimental Setup gap in which argon was flowed at 2 [L/min]. The simulation varied the gap size and relative dielectric constant. The voltage applied across the plates was 0-20 [kV ] at frequencies of 1

[kHz] to 100 [MHz]. Over the range of 1-5 [kHz], the electron temperature rises from 20

[eV ] to 23 [eV ] before falling to a minimum of 11.2 [eV ] at 50 [kHz], and finally rising to a maximum of 82.2 [eV ] at 10 [MHz][23]. The chemical processes of DBD plasmas are initiated by electron dissociation, which is electron temperature dependent. The total power absorbed by the plasma increases linearly with applied frequency from 20 [µW ] at 1 [kHz] to 0.1 [W ] at

100 [MHz][23]. Results also show that electron density increases with increasing frequency.

With the ability to change the electron density and temperature, the frequency can aid in the generation of the desired species dependent on the required chemical rates. Higher electron density and electron temperature can be achieved by using a dielectric material with a higher relative permittivity and/or by using a thinner dielectric[23]. The best material for a DBD is the thinnest and strongest dielectric, however, when decreasing the thickness this increases the power being absorbed into the dielectric. This causes heating, which decreases ozone

6 generation[24]. The increase in electrons are sourced from the ionizations in the gas and

secondary electron emission from the electrodes.

Controlling the voltage and frequency, while substituting oxygen for air, results in dif-

ferent species production rates[25]. Abdelaziz, Ishijima, Seto, Osawa, Wedaa, and Otani

studied this effect using a surface DBD. Their DBD was formed with two stainless steel elec-

trodes affixed to the flat surface of a 0.14 [mm] thick mica sheet on opposite sides. The width

of the top electrode was smaller, at 0.1 [mm], compared to the bottom grounded electrode’s width of 0.5 [mm] (Figure 1.6). This created an offset between the electrodes on the surface

Figure 1.6. Abdelaziz Experimental Setup

of the mica in which the plasma was formed. The entire assembly was contained in a glass

tube forming a small chamber, and allowed gas to flow. Dry air was flowed into the chamber

at a rate of 2.05 [L/min] giving the gas 2.9 [s] to react in the chamber. Various data were

collected using an optical emission spectrometer, Fourier transform infrared spectrometer,

ozone analyzer, fiber optic thermometer, high voltage probe, and an additional voltage probe

connected across a known resistor to measure current. Both voltage probes were connected

to an oscilloscope. The plasma was operated at frequency values of 1, 5, and 10 [kHz], with applied potentials incremented from 1-5 [kV ]. When igniting a plasma using 1 [kHz] and 10 [kHz] waveforms at a constant 6 [kV ], the plasma consisted of a larger number of

current spikes at the higher applied frequency[17]. A higher applied frequency also created a larger energy density at a constant voltage. When holding frequency constant, and varying voltage, the higher applied voltage resulted in a larger energy density [25]. This effect can

7 be combined to form the largest energy density at the highest frequency and highest applied

voltage. The energy density values were then correlated with ozone production. For energy

densities 0-10 [J/L] ozone production was independent of frequency. All frequencies resulted

in the same linear increase in ozone concentration, reaching 50 [ppm] at 10 [J/L]. Above 10

[J/L], the higher frequencies produced slightly less ozone at the same energy density value.

While the largest concentration of ozone of 350 [ppm] occurred at the highest applied energy

density of 85 [J/L], the most efficient ozone production occurred at an energy density of 10

[J/L], see Ref. [25]. Nitrogen species were also recorded. There were high concentrations of nitrous oxide (N2O) and dinitrogen pentoxide (N2O5), and low concentrations of nitric

oxide (NO) and nitrogen dioxide (NO2). Nitrogen dioxide appears to be uncorrelated with energy density and frequency[25]. Whereas nitrous oxide increases linearly with energy den-

sity across all frequencies achieving 7 [ppm] at 85 [J/L], Ref. [25]. Now frequency and power

can be used to optimize the species of electron, oxygen, and nitrogen. If hydrogen or water

was added to the system then acidic species could be produced.

The addition of water in direct or remote contact with an air DBD plasma modifies the

surrounding aqueous and gas production rates. The authors of [12] created a 0-D model

for atmospheric direct current discharge using a water cathode and air. The simulation

was run with 0.2%, 2.3%, and 5% water concentrations[12]. The plasma dissociates water

molecules, which permits hydrogen or hydroxyls (OH) to interact with other species. This

can create new species such as nitric acid (HNO3) and hydrogen peroxide (H2O2). The simulation involved varying the discharge current while measuring species concentrations.

When applying a discharge current greater than 26 [mA], the lowest water concentration

created the lowest ozone concentration and the largest nitric acid concentration. The inverse

was also true over current ranging from 26-50[mA], both 2.3% and 5% water concentrations

produced the largest ozone concentration and lowest nitric acid concentration[12]. Water

concentrations therefore have an impact on the selectivity of species generated.

8 The applied voltage, gas composition, and electrode material all contribute to producing

electrons which modifies the species production rates. Electrons are accelerated due to the

applied potential, creating ionizing collisions. The ions then travel towards the surface of

the metal electrode. Upon collision, an electron escapes to neutralize the ion, and has a

probability of emitting a second electron into the gas volume. This is governed by the work

function, or the amount of energy required to remove an electron from the surface. Of the

work functions for the three metals used in this research, gold has the highest at 5.25 [eV ], then nickel at 5.15 [eV ], and lastly copper at 4.51 [eV ][26]. Ref [27] has shown that the maximum secondary electron emission (SEE) was found for electron incident energies less than 800 [eV ]. Gold had the highest secondary electron of 1.92 at 800 [eV ], then copper

+ at 1.42 at 590 [eV ], and finally nickel at 1.03 at 430 [eV ] [27]. When comparing ion (N2 ) induced SEE, the gold produced a slightly higher SEE yield[28]. If the process was left

static for a period long enough to allow all ions to neutralize, then the recombination of

atomic nitrogen (N) on gold electrodes produced 50 times more secondary electrons[28].

This was explained by copper absorbing more atomic nitrogen. If air replace nitrogen, this

data demonstrates a possible selectivity to generate nitrogen species dependent on electrode

material.

The authors of [24] focused research on electrode materials and discovered a catalytic

effect on species generation for DBD plasmas. A cylindrical DBD apparatus was constructed

with an outer cylindrical metal electrode interfacing with a quartz tube (Figure 1.7). The

inner electrode was spaced 1 [mm] away from the larger quartz tube. This gap allowed

oxygen to flow at 3 [L/min], and water to flow through the interior of the hollow electrode in order to control the temperature. The materials of the inner electrode was copper, carbon, and stainless steel. Hollow tubes made of copper and stainless steel were used as electrodes.

The carbon electrode was crafted by applying conductive carbon tape around a stainless steel tube. When the temperature of the electrode was not controlled, but instead allowed

9 Figure 1.7. Hsiao Experimental Setup to increase freely, all electrode materials increase ozone production with increasing voltage before reaching a maximum of 14 [g/m3]. Despite the voltage increasing further the ozone concentration decreases. When the temperature is controlled, ozone production continues to increase, but differs in quantity between the different materials. At an applied 5 [kV ], copper produced the largest ozone concentration of 16.5 [g/m3], then carbon with 6 [g/m3], and lastly stainless steel with 4.5 [g/m3][24]. Similarly in order to produce 20 [g/m3] of ozone requires the lowest voltage of 5.3 [kV ] on copper, then 5.7 [kV ] on carbon, and lastly 6.4 [kV ] on stainless steel[24]. The primary focus of my research is to increase the sample size of electrode materials, as well as monitor the resulting gas chemistry formed from different ratios of oxygen and nitrogen, with trace amounts of water and carbon dioxide. This study used a planar DBD discharge with gold, copper, and nickel electrodes on an alumina dielectric. These materials increase the sample size for planar structure DBDs. While the ratio of nitrogen to oxygen was previously only 80/20, I used ratios of 90/10, 80/20, 70/30, and 60/40 with no flow rate. The use of a DBD plasma allows nitrogen and oxygen, which are not initially reactive, to form reactive species such as ozone and nitric acid. Understanding these concepts will contribute to a wide variety of applications.

10 CHAPTER 2

THEORY

2.1 Atmospheric Dielectric Barrier Discharge Plasma

It is important to discuss the mechanism for forming an atmospheric dielectric barrier dis-

charge plasma. Standard temperature and pressure (STP) is defined as 1.01e5 [P a] at 273.15

[◦K]. The distribution of kinetic energy of molecules in a gas volume can be described by the Maxwell-Boltzmann distribution, Eq. 2.1.

3   2 2 m − mv f(v) = n e 2kbT (2.1) 2πkbT

When calculated at STP, the thermal energy is not sufficient to create enough ionizing

collisions to sustain a plasma. Thus to ignite a plasma, energy must be added to the system

in order to overcome the ionization energy threshold. To further explain this phenomenon,

consider a scenario with two parallel plates separated by an electrode gap distance, d. The gas between the electrodes consists of Nitrogen (N2), at STP. The concentration of free electrons in a gas at thermal equilibrium is determined by the Saha equation[29],

3/2 ni T ≈ 2.4 ∗ 1021 e−Ui/kbT (2.2) nn ni

At STP, this estimates negligible amounts of ionization to occur, where Eq. 2.2 gives an ion-

−122 ization ratio of ni/nn ≈ 10 [29]. There are cosmic rays impacting the Earth’s atmosphere creating high energy particles resulting in background ionization and an initial concentration of free electrons, ne0, in the gas volume. When a potential is applied across the electrodes this introduces a Coulombic force upon the electrons, Eq. 2.3, accelerating the electrons.

F~ = eE~ (2.3)

11 Figure 2.1. Capacitively Coupled Electrodes

To demonstrate the formation of a DBD plasma, Figure 2.1 depicts the gas volume

between two electrodes. Taking a small region of space with distance, dx, from x = x0 to

x = x1. There is some initial concentration of electrons, ne = ne0, at the entrance of the

region x = x0. The electrons are forced in the opposite direction of the electric field towards

x = x1. During their travel across dx there is some probability of releasing another free electron though an ionizing collision with one of the nitrogen molecules. This creates an increase in electron density. Determining the concentration of electrons exiting the region can be found by adding the initial concentration to the change in concentration that occurred across dx, resulting in ne = ne0 +dne. To derive an equation for electron density as a function of distance the probability for an ionization collision must be determined.

12 The number of ionizing collisions per unit length, is the increase in the electron density as a function of distance, and described by the parameter α. The change in electron con- centration is determined by the initial electrons, the probability they will create an ionizing collision per distance traveled, and the distance they travel.

dne = ne(x)αdx (2.4)

By dividing the left hand side of Eq. 2.4 by a factor of ne, an integral can now be taken as shown in Eq. 2.5. Solving the integration yields the concentration of electrons as a function of location, seen in Eq. 2.6. Finally, the equation for current across parallel plate electrodes, x1 − x0 = d, with uniformly applied potential can be seen in Eq. 2.7, Ref. [30].

Z dn Z x1 e = αdx (2.5) ne(x) x0

α(x1−x0) ne(x) = ne0e (2.6)

αd i = i0e (2.7)

The number of ionizing collisions per distance can now be described by dividing the probability of an ionizing collision by the average distance between collisions.

εi 1 − ~ α = e eEλmfp (2.8) λmfp

Substituting 1 = Ap into Eq. 2.8 results in Eq. 2.9. Where A is the saturation ionization λmfp constant and p is the pressure.

α − Aεip = Ae eE~ (2.9) p

Further simplifications result in Eq. 2.10, by substituting the inelastic barrier constant

Aεi B = e , Ref. [31].

α − Bp = Ae E~ (2.10) p

13 Eq 2.10 is the probability to produce an ionizing collision per length traveled, and α is defined as the First Townsend Ionization Coefficient. To complete the equation for total current, ion induced secondary electrons must be included. After an ionizing collision has occurred, the newly formed ion has a force acting upon it by the electric field. The ion then accelerates in the direction of the electric field where it will collide with the cathode. During the collision the ion is neutralized, in doing so, there is a chance of a secondary electron being emitted from the metal surface. Energy must be conserved, and when an electron drops in energy to neutralize the molecule, energy is given to another electron. If the energy is enough to overcome the metal’s work function then there might be a SEE. This processes is known as the Auger process. The electron emitted due to ion induced SEE is denoted ne+, and alters the initial concentration of electrons.

αd ne = (ne0 + ne+)e (2.11)

Here the ion induced electron concentration is given by, Ref. [30],

ne+ = γ(ne − (ne0 + ne+)) (2.12)

Where γ is the probability an ion will release a secondary electron. Using substitutionary elimination on Eq. 2.11 and Eq. 2.12 yields,

eαd n = n (2.13) e e0 1 − γ(eαd − 1) eαd i = i (2.14) 0 1 − γ(eαd − 1)

The total electron current, including SEE, is seen in Eq. 2.14, and if γ = 0 the equation reverts to Eq. 2.7. Due to the denominator, the case that would cause i → ∞ is given by,

1 = γ(eαd − 1) (2.15)

This is known as the Breakdown Criteria. It occurs when every initial electron creates enough ions by ionization to produce a SEE that replaces the initial electron when it recombines.

14 Figure 2.2. Breakdown Regimes

Figure 2.2 contains the derived relation and depicts the current-voltage relation across the townsend regime. The townsend regime is also called the dark discharge regime because light emission is very low. Once the discharge reaches reaches a corona discharge, where ionizing collisions occur, it becomes much brighter. Background radiation occurs in the red box suppling an initial concentration of electrons. Energy is then supplied to the electrons and if the energy is not great enough to overcome the ionization energy, the electrons drift across the gap without increasing the current. Once the ionization energy is overcome, additional electrons are generated and the current begins to crest upwards. As the elec- tron multiplication by ionization rises, the current slopes nearly vertical and tends towards breakdown. To prevent the current from tending towards infinity and causing the plasma to break- down, a dielectric is placed over one of the electrode surfaces. Now the electrons will build

15 up on the surface of the dielectric. If allowed, the electrons will continue to accumulate on the dielectric surface and will eventually equalize the potential of the anode in accordance with Poisson’s equation, Eq. 2.16.

ρ −∇2φ = (2.16) 

This will diminish the electric field, reducing the electrons’ kinetic energy, halting ionizing collisions and the avalanche effect. These effects combined stop the flow of current, quenching the plasma. The species created interact and diffuse throughout the plasma chamber.

Figure 2.3. Electron Avalanche Effect in atmospheric DBD Plasma: Dielectric panel with two electrodes in gold, electrons in blue, neutral species in gray, positive ions in red, and the direction and relative magnitude of the electric field is shown by green arrows.

16 If radio frequency (RF) voltage is applied to a surface DBD plasma panel the process continues, shown schematically in Figure 2.3. Electrons are accelerated producing ioniz- ing collisions in step 1. Step 2, the electrons create an avalanche effect, which deposited electrons onto the dielectric surface. The ionizing collisions continue until the electric field is diminished to a point where electrons are no longer gaining enough energy to overcome the ionization threshold, step 3. The plasma then self extinguishes. When the potential is reversed. Steps 4 and 5 show ions being attracted to the surface of the dielectric where they neutralize with the electrons left there previously. While this is happening, on the opposite side of the panel, electrons are being accelerated to generate an avalanche. Step 6, the neutrals diffuse into the gas volume, and the process is ready to repeat.

2.2 Gas Chemistry

Electron with sufficient energy to cause ionizing collisions also have sufficient energy to excite and dissociate oxygen and nitrogen molecules. These reactive species then diffuse into the surrounding neutral gas volume and interact dependent on their corresponding reaction rates. The reaction rates depend upon the concentrations of various species. The reaction rates of Table 2.1 were compiled by the authors of [12] and contains reaction rates studied by many authors. R1, in Table 2.1, shows ground state oxygen being excited to the

1 − 1 − a ∆ state via electron impact, O2(X) + e ⇒ O2(a ∆) + e . The reaction rates describe how a species density evolves in time, R = d[A]/dt. The reaction rates are dependent on

− the concentrations of colliding species, which are [O2(X)] and [e ] for R1. Examining the

1 reaction rate for product, [O2(a ∆)], with reaction rate constant, k(T ), gives,

− R = k(T )[O2(X)][e ] (2.17)

17 Table 2.1. Reactions and Rate Constants. These values were compiled by [12] Reaction Reactants Products Rate Constant Ref Number [cm3s−1], [cm6s−1] − 1 − R1 O2(X) + e O2(a ∆) + e f(E/n) [12] − 1 − R2 O2(X) + e O2(b Σ) + e f(E/n) [12] − 3 − R3 O2(X) + e O2(A Σ) + e f(E/n) [12] − 3 3 − R4 O2(X) + e O( P ) + O( P ) + e f(E/n) [12] − 3 1 − R5 O2(X) + e O( P ) + O( D) + e f(E/n) [12] − 3 3 − R6 O2(X) + e O(3p P ) + O( P ) + e f(E/n) [12] − 3 3 − R7 O2(X) + e O(3s S) + O( P ) + e f(E/n) [12] − − R8 N2(X) + e N2(A) + e f(E/n) [12] − − R9 N2(X) + e N2(B) + e f(E/n) [12] − − R10 N2(X) + e N2(a) + e f(E/n) [12] − 4 − R11 N2(X,V ) + e 2N( S) + e f(E/n) [12] − 1 − −10 R12 O + O2(a ∆) O3 + e 3.0 ∗ 10 [32] − 3 − −10 R13 O2 + O( P ) O3 + e 1.5 ∗ 10 [32] 510 3 −34 T R14 O( P ) + O2(X) + H2O O3 + H2O 9.9 ∗ 10 e g [33] 663 3 −35 T R15 O( P ) + O2(X) + O2(X) O3 + O2(X) 6.4 ∗ 10 e g [34] + − 3 3 −7 R16 O2( ) + O2( ) O( P ) + O( P ) + O2(X) 4.2 ∗ 10 [35] + − 3 −7 R17 O2( ) + O( ) 3O( P ) 1.2 ∗ 10 [36] − − −15 R18 O( ) + O2(X) O3 + e 5.25 ∗ 10 [37] R19 O(3P ) + N(2P ) NO+ + e− 1.0 ∗ 10−12 [38] R20 O− + N(4S) NO(X) + e− 2.6 ∗ 10−10 [39] − − −10 R21 O + NO(X) NO2 + e 2.6 ∗ 10 [39] 3 −10 R22 N2(B) + O2(X) N2(X) + 2O( P ) 3.0 ∗ 10 [40] 3 −11 R23 N2(a) + O2(X) N2(X) + 2O( P ) 2.8 ∗ 10 [41] 1560 −12 − T R24 NO(X) + O3 O2(X) + NO2 4.3 ∗ 10 e g [12] 2450 −13 − T R25 NO2 + O3 O2(X) + NO3 1.2 ∗ 10 e g [12] 3 −14 R26 N2(A) + O2(X) N2O + O( P ) 7.8 ∗ 10 [42] −30 Tg −2.9 R27 NO2 + OH(X) + N2(X) HNO3 + N2(X) 1.6 ∗ 10 ( 298 ) [12] 550 3 − −11 − T R28 H2O + O( P ) OH(X) + OH(X) + e 1 ∗ 10 e g [33] − 1 − R29 H2O + e H( S) + OH(X) + e f(E/n) [12] −11 −0.4 R30 OH(X) + OH(X) H2O2 1.5 ∗ 10 Tg [43] − 3 − R31 O3 + e O( P ) + O2(X) + e f(E/n) [44] 1 3 −11 R32 O2(b Σ) + O3 O( P ) + 2O2(X) 1.8 ∗ 10 [45] 1 1 3 −10 R33 O( S) + O3 O( D) + O( P ) + O2(X) 2.9 ∗ 10 [12] 1 −10 R34 O( S) + O3 2O2(X) 2.9 ∗ 10 [12] 2300 3 −11 − T R35 O( P ) + O3 O2(X) + O2(X) 1.8 ∗ 10 e g [34] − − −10 R36 O + O3 + e O2(X) + O2(X) 3.31 ∗ 10 [37]

18 The full list of reactions that can occur in a humid air DBD plasma cannot be reproduced

here, but several reactions of interest are noted in Table 2.1. The experiment was simulated

with a water cathode, instead of a metal electrode. This significantly reduces the resulting

ozone concentration generated, when compared to DBDs with metal electrodes[12]. For

demonstrative purposes, this trades the under estimation ozone generation for the inclusion

of water reactions (R14,R27 − R30) from Table 2.1. The inclusion of water allows the production of acidic molecules, which is important for this study.

Excited or disassociated oxygen and nitrogen further interact to produce other species such as ozone. Electrons impact oxygen (O2) and nitrogen (N2) species to excite (R1-

R3,R8-R10) or dissociate (R4-R7,R11) the molecule. The excited and atomic species are

key participants in numerous reactions. Their importance in many reactions classifies them

as reactive oxygen and nitrogen species (RONS). A DBD plasma is a prime environment

for producing these reactive species. It can be seen from R16 and R17, that after oxygen

has been activated, the reactive oxygen works quickly to dissociate ground state oxygen

producing the highest reaction rate constants. The RONS interact through R12-R15, R18 to

form ozone, while R31-R35 act to dissociate ozone. RONS also produce various compounds

of oxygen and nitrogen. The products include nitric oxide (NO), nitrogen dioxide (NO2),

nitrate (NO3), nitrous oxide (N2O), and dinitrogen pentaoxide (N2O5). When the products

interact with hydrogen they form an acid. Hydrogen is supplied by dissociating water. Water

is dissociated by RONS reaction (R28) and electron impact dissociation (R29). The reaction

with RONS contributes larger amounts of hydrogen, in the form of hydroxyls. The hydroxyls

can create nitric acid (HNO3) through R27, or hydrogen peroxide (H2O2) R30. All of these

species absorb in the infrared, and as a result can be monitored with Fourier Transform

Infrared Spectroscopy.

19 2.3 Fourier Transform Infrared Spectroscopy

Studying the various vibrational and rotational modes possible for a molecule is essential to understanding the absorption spectrum obtained from Fourier Transform Infrared Spec- troscopy (FTIR). Firstly, the rigid rotator model consist of two masses that are connected by a massless rigid rod (vibrations will be added later). Starting with the time independent Schr¨odingerequation (Eq. 2.18), the Hamiltonian is determined by Eq. 2.19.

Hˆ Ψ(θ, φ) = EΨ(θ, φ) (2.18) 2 Hˆ = − ~ ∇2 + V (2.19) 2m The Laplacian of the Hamiltonian is taken with respect to spherical coordinates, ! ! 1 δ 1 δ2 1 δ δ ∇2 = r2 + + sin(φ) (2.20) r2 δr r2sin(φ) δθ2 r2sin(φ) δφ δφ The wave function is separated into functions that only depend on one variable,

Ψ = Θ(θ)Φ(φ) (2.21)

The Schr¨odingerequation now becomes, " ! !# 2 1 δ 1 δ2 1 δ δ − ~ r2 + + sin(φ) Θ(θ)Φ(φ) = EΘ(θ)Φ(φ) 2m r2 δr r2sin(φ) δθ2 r2sin(φ) δφ δφ

(2.22)

The moment of inertia, I, is given by,

I = µr2 (2.23) m m µ = 1 2 (2.24) m1 + m2 Where r is the bond length and µ is the reduced mass given in Eq. 2.24. In a rigid rotator r is constant, not a variable, so Eq. 2.22 reduces to, " !# 2 1 δ2 1 δ2 δ − ~ + sin(φ) Θ(θ)Φ(φ) = EΘ(θ)Φ(φ) (2.25) 2I sin(φ) δθ2 sin2(φ) δφ2 δφ

20 A substitutional variable is defined as,

2IE λ = (2.26) ~2 When Eq. 2.25 is algebraically separated to contain all θ terms on the left hand side (LHS) and all φ terms on the right hand side (RHS) it results in, " # 1 δ  δ  1 δ2 sin(θ) sin(θ) Θ(θ) + (λsin2(θ)Θ(θ) = − Φ(φ) (2.27) Θ(θ) δθ δθ Φ(φ) δφ2

The LHS and RHS of Eq. 2.27 are equal, and only dependent upon θ and φ respectively. Therefore the differential equations on each side must be equal to a constant. The solution becomes,

λ = J(J + 1) (2.28)

Equating Eq. 2.26 and 2.28 gives the energy value solutions,

2 E = ~ J(J + 1) (2.29) 2I

Dividing the rotational energy value solution (Eq.2.29) of the time independent Schr¨odinger equation (Eq. 2.18) by hc results in the rotational term, F (J), Eq. 2.32. F (J) is quantized and depends upon the rotational quantum number J. B is the rotational constant given in Eq 2.33.

E F (J) = (2.30) hc h F (J) = J(J + 1) (2.31) 8πcI F (J) = BJ(J + 1) (2.32) h B = (2.33) 8π2cI

This concept becomes important during transitions because a photon is absorbed with a specific wavenumber [cm−1]. Given the characteristics of different molecules, these transitions

21 can be utilized to determine the species and concentrations through their individual spectra. The wavenumber corresponding to the radiation emitted from a rotational transition can be determined from Eq. 2.37, Ref. [46]. h ν = pJ(J + 1) (2.34) rot 4π2I p νrot = c2B J(J + 1) (2.35)

ν = F (J 0) − F (J 00) (2.36)

ν = BJ 0(J 0 + 1) − BJ 00(J 00 + 1) (2.37)

If the rotator is allowed to be non-rigid and vibrate, r from Eq. 2.22 cannot be ignored. The energy value solution must add a centrifugal distortion term,

E(J) = BJ(J + 1) − DJ 2(J + 1)2 (2.38) h3 D = (2.39) 32π4I2r2kc The energy now has a centrifugal distortion term, DJ 2(J + 1)2, and D is the centrifugal constant. This addition means that Eq. 2.38 will no longer be linear, causing spectral lines that are no longer equidistantly spaced[46].

ν = F (J + 1) − F (J) (2.40)

ν = 2B(J + 1) − 4D(J + 1)3 (2.41)

To account for the vibrations of a molecule, the simple harmonic oscillator model is used. The vibrations act like a mass oscillating on a spring, where the natural frequency of the oscillations are given by, r 1 k ν = (2.42) osc. 2π m Where k, is the spring constant of the system. The potential energy of the oscillator is given by, 1 V = kr2 (2.43) 2

22 Implementing the potential energy into the Hamiltonian (Eq. 2.19) and applying it to the Schr¨odingerequation gives,

2 1 − ~ ∇2Ψ(r) + kr2Ψ(r) = EΨ(r) (2.44) 2m 2

Rearranging the differential equation,

2m 1 Ψ(r)00 + (E − kr2)Ψ(r) = 0 (2.45) ~2 2 The energy value solutions to this equation is found by,

1 E(v) = hν (v + ) (2.46) osc. 2

Where v is zero, or a positive integer. When the Schr¨odingerequation is solved once again, the energy is divided by hc to yield the vibration term, G(v),

E(v) G(v) = (2.47) hc ν 1 G(v) = osc. (v + ) (2.48) c 2 1 G(v) = ω(v + ) (2.49) 2

The frequency of a vibrational transition,

f = G(v0) − G(v00) (2.50)

When v0 − v00 = ±1, Eq. 2.50 becomes,

f = G(v + 1) − G(v) (2.51)

This demonstrates that the frequency of the emitted photon is simply the frequency of the harmonic oscillator[46].

f = G(v + 1) − G(v) = ω (2.52)

νosc. = cω (2.53)

23 This culminates in a molecular model with both rotation and vibration. Each electronic

state has its own vibrational and rotational energy levels, denoted by v(n),J (n). In Figure 2.4,

the vibrational energy levels are colored blue for v0 = 0 and red for v0 = 1. Each vibrational level contains smaller energy steps, J = 0 − n, represent the n rotational energy levels. The

various vibrational modes include: symmetric or antisymmetric radial stretching, latitudinal

scissoring and rocking, and longitudinal wagging and twisting[47].

Figure 2.4. Vibrational and Rotational Energy Levels

In Figure 2.4, the vertical lines represent transitions which occur in or between electronic

states for various rotational and vibrational energy levels. The transitions are characterized

into P, Q, and R branches. The R-branch is a ∆J = +1 transition, whereas the P-branch

relates to a ∆J = −1 transition. There is one spectral line missing at the center, it is known

as the zero line or null line. Due to the conservation of energy, there is a forbidden transition

24 state between the rotationless states J 0 = 0 and J 00 = 0. This is the Q-branch, and the frequency at which this occurs is ν = ν0. The frequency, ν0, is known as the band origin. Combining the band origin, rotational, and vibrational properties culminates in the equa- tion for determining the frequency of the emitted radiation, Eq. 2.54. Where Bv is the

vibrational constant, Dv is the rotational constant, m = J + 1 or values 1, 2, 3, ... for the R branch, and m = −J or values of −1, −2, −3, ... for the P branch. Declaring m this way

0 00 allows m = 0 to be defined as the band origin where ν0 = G(v ) − G(v ), Ref. [46].

0 00 0 00 0 00 2 0 00 3 0 00 4 ν = ν0 + (Bv + Bv )m + (Bv − Bv − Dv + Dv )m − 2(Dv + Dv )m − (Dv − Dv )m (2.54)

This concept is used in FTIR spectroscopy by exposing a sample to radiation with a wide range of IR frequencies. If there is an allowable transition possible, the molecule will absorb radiation at that frequency. Therefore, when the transmitted radiation is monitored, the resulting spectrum allows the determination of species. Understanding the workings of the

FTIR will be of notable interest to complete the section.

To fully grasp the workings of a FTIR spectrometer requires understanding the operation of a Michelson type interferometer. The FTIR source, a glowing filament emitting black body radiation, is passed to a Michelson type interferometer. The interferometer operates by utilizing a beam splitter to divide the incoming radiation, Io, among two paths, Ipath1,

Ipath2. Figure 2.5, demonstrates the paths taken. The first path reflects upon the beam splitter, RBS, and is directed to a fixed mirror, where it is then reflected, RFM , back through the beam splitter, TBS, towards the sample. Giving intensity,

Ipath1 = IoRBSRFM TBS (2.55)

The other is transmitted through the beam splitter, and is then diverted to a movable mirror.

This mirror’s distance can be adjusted, inducing a difference in beam path, before reflecting

25 Figure 2.5. Michelson Interferometer

the radiation, RVM back to the beam splitter where it reflects towards the sample. Giving intensity,

Ipath2 = IoRVM TBSRBS (2.56)

Provided the reflection coefficient of the moving and fixed mirrors are the same, the intensity of the two beams will be the same, with a phase difference set by the difference in path length. Thus, the two original beams recombine with constructive and destructive interference with the detector monitoring the resulting net radiation. When plotted as net intensity vs. path length, one obtains a Fourier transform of the blackbody emission vs. frequency changed to the blackbody emission vs. mirror position. This is known as the interferogram. One can then use a computer to do an inverse Fourier transform on the interferogram the from mirror distance (x) back to frequency (ν) domain, resulting in the IR spectrum.

26 Figure 2.6. Background Comparison Between Vacuum and Air

If all of the radiation is transmitted, with no absorption, this as known and the back-

ground spectrum. The top spectrum of Figure 2.6 is a background taken under vacuum, with

a pressure of ≈ 30[mT orr]. There is minor absorbance from a small amount of water water at wavenumber around 1750 [cm−1], and carbon dioxide at 2400 [cm−1]. The large peaks

at 1400 [cm−1] and 2950 [cm−1] are from nitric acid reacting with the potassium bromide,

KBr, windows to form potassium nitrate, KNO3. If a sample is placed in the beam path,

part of the radiation is absorbed. The bottom spectrum was obtained when the chamber

was filled with a sample, here atmospheric pressure air. There are large amounts of water

and carbon dioxide in air, resulting a significant change in the measured spectrum.

27 With a background and sample spectra, the radiation absorbed by the sample can be calculated. The absorption is given by the absorbed intensity over the background intensity,

I (ν) I (ν) − I (ν) A(ν) = A = o T (2.57) Io(ν) Io(ν) Which is equal to,

A(ν) = 1 − e−α(ν)xni (2.58)

Where α is the absorptivity, or absorption cross section, x is the beam path length, and ni is the concentration. Taking the Taylor series expansion of the exponential, and ignoring higher order terms, gives the linear region of absorption.

A(ν) ≈ α(ν)xni (2.59)

Notice the absorbance and concentration are linearly related. The FTIR takes the data in either decadian or napian. The decadian calculation uses, ! IA(ν) A(ν) ≈ log10 = αd(ν)xni (2.60) Io(ν) While napian uses, ! IA(ν) A(ν) ≈ ln = α(ν)xni (2.61) Io(ν) Knowing that,

elog10(x) = ln(x) (2.62)

There are two definitions of absorptivity, where the decadian absorptivity, αd, is scaled by a factor of e−1. FTIRs that use napian are typically more expensive, and the FTIR used in this study used decadian. An example of an experimental FTIR spectrum shows the theory discussed. The spec- trum, of Figure 2.7, is of carbon dioxide. Transitions between rotationless states are forbid- den, creating zero absorbance, at the band origin, where the Q-branch would be located.

28 The P-branch is seen at wavenumber below ν0, where individual peaks indicate transitions of ∆J = −1. Similarly, the R-branch is seen at wavenumber higher than ν = 0, and the peaks indicate transitions of ∆J = +1.

Figure 2.7. Transitions of a carbon dioxide molecule, captured by a FTIR

2.4 Optical Emission Spectroscopy

An atom consists of a nucleus surrounded by electrons in discrete energy levels. An electron can develop into an excited state due to collisions in the plasma. After, there is a probability that this electron will spontaneously experience a magnetic dipole transition. Due to the transition, the electron will drop in energy level and emit electromagnetic radiation. Utilizing the uniqueness of the energy levels for individual atoms and Einstein’s equations, it is possible to calculate the frequency of the light being emitted. Further details can be found in [48], but shall not be covered here because OES was not used during this study.

29 CHAPTER 3

HIGH RESOLUTION FTIR EXPERIMENT

The experimental setup consists of vacuum system, plasma production systems, and mea- surement apparatus. The vacuum system consists of a reference chamber, the Gaseous Elec- tronics Conference (GEC), recreated schematically in Figure 3.2. It is a cylindrical vacuum chamber with dimensions of 25.1 cm in diameter and 22.2 cm in height. The plasma panel consists of an alumina substrate with copper tape electrodes. The geometry in Figure 3.1 depicts the panel dimensions. Power was applied to the panel, providing the top and bottom electrodes with positive and negative voltage. This was done utilizing an ENI EGR2300 followed by a step up transformer to achieve 6 kVpp at 9 kHz. Spectra were monitored in the infrared and visible to near-ultraviolet frequency ranges by a Nicolet 870 FTIR and a Verity

SD1024D Optical Emission Spectrometer (OES).

3.1 General Experimental Procedure

The general experimental procedure explains the process of sample loading, gas filling and evacuation, and data collection for both both high resolution and time resolved data. The plasma panel is loaded into the GEC and placed upright with a 45◦ turn in the front left quadrant, demonstrated in Figure 3.2. Once the plasma panel is loaded into the GEC chamber, the gas is then evacuated using a rough pump and turbo pump down to 10−6

[T orr]. The low pressures are verified using a hot cathode ionization gauge and 0.1 Torr

Baratron. The chamber is then isolated and refilled using bottled oxygen, O2, to a desired pressure measured by a 1-1000 Torr Baratron. The remainder is filled with bottled nitrogen,

N2, to achieve atmospheric pressure of 760 [T orr]. With the panel loaded and chamber filled, the FTIR then captures a background spectrum. High resolution or time resolved data can then be collected. Data collection allows for one full spectrum to complete prior to plasma

30 Figure 3.1. Plasma Panel Dimensions in Inches ignition. The plasma is then ignited and spectra are collected sequentially for 6 minutes.

After the plasma is extinguished spectra are obtained for up to another 30 minutes. The 6 minute plasma exposure time was selected to allow the longest exposure time with maximum species generation while remaining in the linear region of the FTIR. After 6 minutes, the plasma was shut off while continuing spectra collection. During this period there is no plasma or gas flow, allowing the species generated to diffuse and recombine. Post-plasma collection times varied in length depending on the experiment. Once data collection was terminated, the remaining reactive species were evacuated. The chamber was then refilled with nitrogen and evacuated a second time to further purge the system. This was proven to be sufficient

31 Figure 3.2. GEC Plasma Chamber and Accessories

isolation from previous experiments utilizing FTIR spectral measurements. The chamber environment was then reset for further experimental runs. When varying oxygen to nitrogen gas ratios the experiments were run in random order to prevent correlation. A pure nitrogen plasma exposure was initially being used to ”clean” the panel between runs, however it did not show any significant impact on the results, and therefore was not utilized.

3.2 High Resolution FTIR Measurements

In order to accurately determine the active species in the gas volume, high resolution spectra were taken and compared with the PNNL [49] and HITRAN [50] databases. At a resolution of

0.125 [cm−1] and 64 scans, individual peaks were resolved for the various species allowing for species identification. The sequential spectra demonstrated increasing species concentration

32 versus time. For more detailed concentration versus time data, see Chapter 4 ”Time Resolved

FTIR Measurements”. The data was taken sequentially and required 6 minutes per spectra.

The plasma exposure time ranged from 6 to 30 minutes and the post plasma collection was

taken for up to 60 minutes after plasma termination, although one set of data was taken

after 24 hours.

3.3 High Resolution FTIR Results

The IR spectra from PNNL and HITRAN databases and experimental data were compared

in order to identify the individual vibrational modes and confirm the presence of the species.

The corresponding atomic diagram representing the vibrational mode is demonstrated with

CPK coloring, where white is hydrogen, black is carbon, sky blue is nitrogen, and red is

oxygen.

3.4 Ozone FTIR Data

−1 Ozone has three vibrational modes: symmetric stretching, seen at ν1 = 1103.157 [cm ],

−1 −1 bend at ν2 = 701.42 [cm ], and antisymmetric stretch at ν3 = 1042.096 [cm ] [50]. The antisymmetric stretch is the strongest having the largest absorbance. The combination of

−1 symmetric and antisymmetric stretching results in ν1 + ν3 = 2111 [cm ]. Figure 3.3 shows the dominant absorption band of ozone. It was also the largest ab- sorption band in the measured spectrum. The band origin at 1042.096 [cm−1] corresponds to ν3, the third vibrational mode of ozone[50]. The P-branch is seen from 980 − 1042.096 [cm−1]. The Q-branch is forbidden, resulting in an absorbance of zero at the band origin,

− −1 ν3 = 1042.096 [cm 1]. The R-branch consists of values 1042.096 − 1080 [cm ]. The res- olution, 0.125 [cm−1], is not small enough to completely resolve the individual vibrational-

rotational transitions. HITRAN uses a much finer resolution of 0.015 [cm−1], and fully

33 −1 Figure 3.3. Experimental Results: O3 from 980 to 1080 [cm ]

−1 Figure 3.4. HITRAN Results: O3 from 980 to 1080 [cm ] [50]

resolves individual peaks in Figure 3.4. While the experimental absorbance spectrum is not fully resolved, it matches the HITRAN spectrum quite well.

34 Figure 3.5. Ozone ν3 bend

Figure 3.6. Ozone ν1 bend

The first vibrational mode of ozone, ν1, is symmetric stretching, meaning the two oxygen atoms oscillate symmetrically, seen in Figure 3.6. Figure 3.7 contains the first vibrational

−1 mode, and is located at frequency ν1 = 1103.157 [cm ]. The first vibrational mode is a minor peak, and is much smaller in absorbence when compared to ν3. The minor peak matched with the known HITRAN spectrum, Figure 3.8, further verifying the species as ozone. Figure 3.9, is the absorbance spectrum due to the combination of two vibrational modes.

The first vibrational mode, ν1, is symmetric stretching, and the third vibrational mode, ν3 is antisymmetric stretching. The band origin and spectral shape of Figure 3.9, match the known HITRAN spectrum, Figure 3.10.

The second vibrational, ν2, is shown in Figure 3.11. Due to the resolution the exper- imental spectrum appears as a small hill at 701.42 [cm−1], whereas the full detail can be seen in the HITRAN spectrum, Figure 3.12. The second vibrational mode is a bend shown schematically in Figure 3.13. All of the major and minor are verified with a known spectrum, proving the presence of ozone.

35 −1 Figure 3.7. Experimental Results: O3 from 1060 to 1220 [cm ]

−1 Figure 3.8. HITRAN Results: O3 from 1060 to 1220 [cm ] [50]

36 −1 Figure 3.9. Experimental Results: O3 from 2030 to 2140 [cm ]

−1 Figure 3.10. HITRAN Results: O3 from 2030 to 2140 [cm ] [50]

37 −1 Figure 3.11. Experimental Results: O3 from 600 to 850 [cm ]

−1 Figure 3.12. HITRAN Results: O3 from 600 to 850 [cm ] [50]

Figure 3.13. Ozone ν2 bend

38 3.5 Nitric Acid FTIR Data

Nitric acid, HNO3 is the second predominant peak of the spectrum, and coincided well with

known HITRAN spectra. Nitric acid and nitrate, NO3, only differ by one hydrogen. With a resolution of 0.125 [cm−1], the differences between the species band origins and transitions are resolved, allowing differentiation between species. Nitric acid has 9 vibrational modes.

Vibrational modes ν1, ν2, ν3, ν4, ν5, and ν8 were seen in experimental data, and vibrational modes ν6, ν7, and ν9 are out of the recommended operating frequency range of the FTIR. Table 3.1 provides a reference to each vibrational mode, the frequency of the band origin, and the Figure where it can be found and is discussed.

Table 3.1. Nitric Acid Vibrational Modes Vibrational Frequency Type Figure Ref Mode [cm−1] ν1 3550.7 OH stretch 3.15 [49] ν2 1709.5 NO2 asymmetric stretch 3.17 [49] ν3 1326.2 NO2 symmetric stretch 3.22 [50] ν4 1301.1 H − O − N bend 3.22 [50] ν5 879.1 O − NO2 in-plane bend 3.26 [50] ν6 646.8 O − NO2 stretch N/A [50] ν7 580.3 O − NO2 bend N/A [50] ν8 763.2 NO2 out-of-plane bend 3.26 [50] ν9 458.2 OH torsion N/A [50]

Figure 3.14. Nitric Acid ν1 -OH stretching

39 −1 Figure 3.15. Experimental Results: HNO3 from 3500-3600 [cm ]

The first nitric acid vibrational mode is hydroxyl stretching. The shape of nitric acid is more complicated than ozone, and has a more complicated absorbance spectrum. The shape of the spectral line can no longer be explained by simple diatomic models. Nitric acid is

flat, with all atoms in the same plane while in equilibrium. Stretching the bond between

−1 hydrogen and oxygen, Figure 3.14, creates a spectrum centered at at ν1 = 3550.7 [cm ],

Figure 3.15.

Figure 3.16 matches with known nitric acid PNNL spectrum. The data wasn’t available for reproduction, but can be verified with spectra in reference [49].

The second vibrational mode is an asymmetric stretching of nitrogen dioxide. One oxygen compresses while the other stretches shown in Figure 3.19. Both experimental and HITRAN data have the same origin, and have shapes that appear slightly different due to the difference in resolution. PNNL data, [49], used a resolution of 0.125 [cm−1] and has matching spectral line shape.

40 −1 Figure 3.16. Experimental Results: HNO3 from 2000-3500 [cm ]

The third and forth vibrational modes are within the frequency range 1260-1360 [cm−1].

−1 The third vibrational mode is nitrogen dioxide stretching at ν3 = 1326.2 [cm ]. The two oxygen compress and stretch together, shown in Figure 3.20. The forth vibrational mode is a bend between hydroxyl and nitrogen seen in Figure 3.21. Experimental data provided

−1 a ν3 peak at exactly 1326.2 [cm ], seen in Figure 3.22, which was confirmed by a known spectrum of nitric acid from HITRAN, seen in Figure 3.23.

Figure 3.24 contains the spectral lines for nitric acid and ozone because the plasma gen- erates both species. The ozone spectral lines are vacant from Figure 3.25 because HITRAN experimented with pure nitric acid.

Figure 3.26 contains the fifth and eighth vibrational modes. The fifth vibrational mode has a dominant peak at 879.1 [cm−1] and 3 additional peaks confirmed by known spectrum,

Figure 3.27. ν5 is the result of an in-plane bend between the oxygen of the hydroxyl and the nitrogen dioxide, Figure 3.28. The eighth vibrational mode is a similar bend between

41 −1 Figure 3.17. Experimental Results: HNO3 from 1640-1800 [cm ]

−1 Figure 3.18. HITRAN Results: HNO3 from 1640-1800 [cm ] [50] the oxygen of the hydroxyl and the nitrogen dioxide, but twists out of the page with an out-of-plane bend, Figure 3.29.

42 Figure 3.19. Nitric Acid ν2 NO2 asymmetric stretch

Figure 3.20. Nitric Acid ν3 NO2 symmetric stretch

Figure 3.21. Nitric Acid ν4 H − O − N bend

43 −1 Figure 3.22. Experimental Results: HNO3 from 1260-1380 [cm ]

−1 Figure 3.23. HITRAN Results: HNO3 from 1260-1380 [cm ] [50]

44 −1 Figure 3.24. Experimental Results: HNO3 from 900-1250 [cm ]

−1 Figure 3.25. HITRAN Results: HNO3 from 900-1250 [cm ] [50]

45 −1 Figure 3.26. Experimental Results: HNO3 from 700-950 [cm ]

−1 Figure 3.27. HITRAN Results: HNO3 from 700-950 [cm ][50]

46 Figure 3.28. Nitric Acid ν5 O − NO2 in-plane bend

Figure 3.29. Nitric Acid ν8 NO2 out-of-plane bend

47 3.6 Carbon Dioxide FTIR Data

Carbon dioxide has three vibrational modes. The first vibrational mode is Raman active and not viewable with IR spectroscopy. Figure 3.30 is the third vibrational mode, centered at

−1 ν3 = 2349[cm ], and is the dominant peak of carbon dioxide. This spectrum originates from the asymmetric stretching between carbon and oxygen in the straight structure of carbon dioxide, Figure 3.32. Figure 3.33 is a minor peak of carbon dioxide. The minor peak is present in both experimental data and HITRAN results. This further indicates carbon dioxide as the species present. Figure 3.35 is the second vibrational mode of carbon dioxide. The experimental results are truncated to the lower recommended operating frequency of 650[cm−1], however the primary peak and surrounding structure match with known Figure 3.36. This spectrum is created by a bending motion shown schematically in Figure 3.37.

48 −1 Figure 3.30. Experimental Results: CO2 from 2300-2400 [cm ]

−1 Figure 3.31. HITRAN Results: CO2 from 2300-2400 [cm ][50]

Figure 3.32. Carbon Dioxide ν3 asymmetric stretch

49 −1 Figure 3.33. Experimental Results: CO2 from 2230-2310 [cm ]

−1 Figure 3.34. HITRAN Results: CO2 from 2230-2310 [cm ][50]

50 −1 Figure 3.35. Experimental Results: CO2 from 620-720 [cm ]

−1 Figure 3.36. HITRAN Results: CO2 from 620-720 [cm ][50]

Figure 3.37. Carbon Dioxide ν2 bend

51 CHAPTER 4

TIME RESOLVED FTIR EXPERIMENT

To further understand the species versus time correlation for plasma panels fabricated with

copper, nickel, or gold electrodes, spectra were taken every 15 seconds, providing much

better time resolution. The copper and nickel were both metal tape, and were cut to the

same dimensions used previously. The gold was fabricated using a hand cut Kapton tape

mask applied to the alumina panel. The panel was then put in a plasma sputtering chamber

in order to deposit gold. There were significant inconsistencies with the work being done

by hand. The electrodes could be uneven and/or crooked, yet still resulted in significant

findings. Future studies will be conducted to remove this error by using a lithographic

process, see Chapter 5 for more detail.

4.1 Time Resolved FTIR Measurement

Spectra were taken rapidly in time to monitor species generation and recombination. High

resolution spectra confirmed the presence of known species at known frequency ranges. Be-

cause the species had already been determined, the finer details of the spectral structure

were sacrificed to monitor how concentration evolved in time. The decrease in resolution

allowed spectra to be taken in rapid succession, and calculated using a base line corrected

integrated intensity. The time resolved spectra collection used a resolution of 2 [cm−1] and

32 scans, resulting in it taking 15 seconds to capture the spectrum. The plasma was turned on for 6 minutes and then left off for 9 minutes, completing a 15 minute recording time. The same procedure was used for loading samples as in the ”General Experimental Procedure” section.

52 4.2 Time Resolved FTIR Results

Analysis of species concentration versus time data found three different regimes, ”genera- tion”, ”diffusion”, and ”recombination”. All species concentration versus time data had the corresponding shape, seen in Figure 4.1. The plasma was initially off for 15 [s], which cre- ated an initially flat region of zero concentration. After plasma ignition, the concentrations began to increase until the plasma was turned off. The rate at which a species increased was determined by DBD plasma parameters and chemical reaction rates covered in Ch. 2.1 and

Ch. 2.2. The sharp decrease after the plasma is turned off correlates to the diffusion phase.

This is due to the peristaltic plasma wave formed around the atmospheric DBD plasma [51].

This wave forces the surrounding gas in the direction of the discharge. The authors of [7]

Figure 4.1. Atmospheric DBD Generation, Diffusion, Decay

53 determined the location of ozone concentration inside their chamber, and found that ozone

was pushed to one side of the chamber, while the plasma was turned on. When the plasma is

turned off it removes the peristaltic wave effect, allowing the gas to freely diffuse throughout

the volume. Lastly, the reactive species decay back into the non-reactive diatomic nitrogen

and oxygen, but the reactive species were found to be surprisingly stable.

Figure 4.2 shows the ozone intensity versus time for gold, copper, and nickel panels.

These electrode materials were used to ignite a DBD plasma with nitrogen to oxygen ratios

of 90/10 in blue, 80/20 in orange, 70/30 in yellow, and 60/40 in purple. For gold and

copper electrodes, when a larger oxygen concentration was supplied, it resulted in a larger

ozone concentration. The gold electrodes created the most ozone for every N2/O2 ratio, then copper, and lastly nickel. For gold electrodes, the amount of ozone intensity increase

between N2/O2 ratios increases as the oxygen concentration increases. This can be seen at

15 minutes, the separation between intensity lines increases as O2 increases. The opposite trend can be seen for copper electrodes. The separation between the lines decreases. The

intensity results were not expected for nickel electrodes. The intensity was lower than both

gold and copper, and the ozone concentration increased with decreasing supplied oxygen

concentration. While decreasing the separation between the lines decreased at 15 minutes.

Figure 4.3 contains the nitric acid intensity versus time data. The data shows gold and

copper produced comparable nitric acid concentrations with gold producing slightly more.

The nitric acid concentration increased with increasing oxygen supplied for gold and copper.

Nickel produced the same nitric acid concentration for all ratios except 90/10, where the

concentration was less. For gold and copper the separation between ratios increased from

90/10 to 80/20 then decreased between 80/20 to 70/30 and then increased from 70/30 to

60/40.

The intensity values for ozone and nitric acid were divided to find the ratio, O3/HNO3, seen in Figure 4.4. For all electrode materials the concentrations of ozone and nitric acid

54 increase until the plasma is turned off at 6 minutes. For gold and copper electrodes the

O3/HNO3 ratio increases until reaching a maximum around 1 minute before falling to a minimum at 6 minutes. After, the ratio slowly increases until 15 minutes. For nickel elec- trodes the ratio increases quickly for 1 minute and then continues to slowly increases until 15 minutes. All ratios of nitrogen to oxygen produce similar ratios of ozone to nitric acid. Examining the ratio of ozone to nitric acid at 15 minutes, found that the electrode material with the highest ratio was nickel at 4:1; then gold at 2:1; and copper at 1.5:1. Figure 4.5 shows carbon dioxide versus time data. The intensity of carbon dioxide is similar for all electrode materials and is roughly 2 orders of magnitude less than oxygen or nitric acid. The intensity increases until the plasma is shut off at 6 minutes and continues to increase slowly until 15 minutes. The carbon dioxide was not intensionally supplied in the oxygen and nitrogen gas mixture.

55 Figure 4.2. Ozone FTIR Time Resolved Integrated Intensity Data 56 Figure 4.3. Nitric Acid FTIR Time Resolved Integrated Intensity Data 57 Figure 4.4. Ratio O3/HNO3 FTIR Time Resolved Integrated Intensity Data 58 Figure 4.5. Carbon Dioxide FTIR Time Resolved Integrated Intensity Data 59 CHAPTER 5

CONCLUSION

Through high resolution and time resolved spectral analysis correlations between electrode material and species production can be made. High resolution data confirmed the production of known species. With species confirmation, this allowed spectra to be taken with finner time resolution. Time resolved spectral data, in Figure 4.2 & 4.3, found that supplying a larger oxygen concentration produced more ozone and nitric acid for gold and copper electrodes. The same data showed that the highest concentration of ozone and nitric acid were produced using gold electrodes, at the largest oxygen concentration supplied (60% nitrogen/40% oxygen). If one desired to produce a larger ozone concentration with limited nitric acid, nickel electrode could be utilized, because nickel demonstrated the highest ratio of 3 ozone to 1 nitric acid produced, see Figure 4.4. If an application requires similar concentrations of ozone and nitric acid, copper electrodes could be utilized. With copper electrodes, for every 3 ozone molecules produced, 2 nitric acid molecules were produced. Future work will improve the experimental setup and produce results with more convic- tion. The two experimental parameters that require attention are the discharge structure and initial gas species concentrations. Uncontrolled levels of hydrogen is a key source of errors that must be removed in order to correlate plasma parameters to the resulting nitric acid concentration. Hydrogen was created through dissociation of water molecules. The supply of water was minimized by evacuating the chamber to 10−6 [T orr], so the amount of water intentionally supplied was negligible. Spectra were taken and confirmed that water was no longer present while the chamber was under vacuum. Pure bottled nitrogen and oxygen ideally shouldn’t supply any water to the system. While the gas supply lines were previously evacuated, after filling the chamber small traces of water entered the system. The unknown supply of water was from either the bottles, supply gas lines, or water coming off the walls of the chamber. To remove the uncertainty, water will be added in known

60 concentrations. The addition of a bubbler controls the supplied water concentration and furthermore the hydrogen concentration. With a controlled hydrogen supply the resulting nitric acid correlation will be credible.

Inconsistencies in the discharge structure occurred during fabrication of the plasma pan- els. The copper and aluminum tape used different types of adhesive. When the plasma was ignited the adhesive compound vaporized adding unwanted organic compounds to the results. The gold panel, which was sputtered onto the substrate, removed this source of error. All three were constructed by hand, and lacked the required precision for electrode size, pattern, rotation, and backside alignment. Construction by hand will be replaced by a lithographic fabrication process in order to create repeatable results.

The lithographic fabrication process of the plasma panels eliminates inconsistencies in the discharge structure. The plasma panels will be fabricated in a clean room allowing precision of 100µm or less tolerances. I have begun some initial tests for feasibility. In those tests, alumina, Al2O3, panels of 96% purity were used as the substrate. SPR 220-7, a thick positive resist, was spun onto the panel using a resist spinner at 1500 rpm with 500 rpm/s acceleration and then baked. The lithography mask, Figure 5.1, was used to expose the panel. The edges of the alumina panel were aligned between the vertical red lines on each side. The horizontal lines at the top are spaced 1 [mm] apart and were used to control the electrode gap distance. The study will have a constant 1 [mm] gap distance, however future work can expand the gap distance up to 7 [mm]. The panel was aligned and exposed with a dose of 470 [mJ/cm2] using a Karl Suss mask aligner. The resist was developed in MF-26 for 6 mins, which created a patterned panel ready for deposition. The variety of electrode materials will be expanded to cover more elements of the periodic table, with a wider range of elemental groups and valence levels. The electrodes could include titanium, chromium, nickel, copper, molybdenum, silver, tungsten, and gold. These various electrode metals will be deposited using an AJA sputter deposition tool. The selected electrode material was

61 deposited at 150W Ar 20 sccm for 45 mins. After the deposition has completed liftoff was achieved by placing in an Acetone bath and an agitator until complete. The lithography process was then repeated for the back side along with the desired electrode gap distance. The deposition and liftoff repeated again with the same parameters resulting in a uniform plasma panel.

Figure 5.1. Plasma Panel Lithography Mask [cm]

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68 BIOGRAPHICAL SKETCH

Alex Gemsheim began the undergraduate electrical engineering program at the University of Texas at Dallas. In the Spring of 2015, he started working in the Plasma Science and Applications Laboratory under Professors Lawrence J. Overzet and Matthew J. Goeckner. In December of 2015, he achieved his bachelor’s degree in electrical engineering, and was accepted into the master’s of science in electrical engineering program. After his first semester he started working as a teaching assistant, and continued into the doctor of philosophy in electrical engineering program. Passing the qualifying exam, he looks forward to furthering his education and research in the field of atmospheric plasma science and applications.

69 CURRICULUM VITAE

Alex J. Gemsheim

May 10, 2018

Contact Information:

Department of Electrical Engineering Email: [email protected]

The University of Texas at Dallas

800 W. Campbell Rd.

Richardson, TX 75080-3021, U.S.A. Educational History:

B.S., Electrical Engineering, University of Texas at Dallas, 2015

M.S., Electrical Engineering, University of Texas at Dallas, 2018

Ph.D., Electrical Engineering (in progress), University of Texas at Dallas, c. 2019

Employment History:

Teaching Assistant, The University of Texas at Dallas, August 2016 – present

Technical Skills:

Plasma Science and Technology RF Laboratory Experience

Vacuum Systems Analog Laboratory Experience

FTIR Spectroscopy Digital Laboratory Experience

MATLAB LabVIEW