Understanding that life on this planet may have originated under extreme circumstances, such as high temperatures and acidic conditions, it would be extremely beneficial to study how simple biological molecules, like amino acids, behave under these scenarios. Importantly, this is possible through the use of electrochemical scanning tunneling microscopy, which can be used to both image and electrochemically manipulate the model systems under consideration. Earlier reports have examined the similarities between studies conducted at ultrahigh vacuum or low temperature and electrochemical conditions with both finding that amino acid molecules trap diffusing metal atoms on surfaces to form 2D ad-islands. Critically, all of the past work was conducted at room temperature. In this report, it has been found that as the temperature of the Au(111) surface was increased, the islands grew by 14% at 300 K and 40% at 305 K, relative to room temperature. Additionally, the increased surface temperature allowed for the formation of islands that were one atomic step higher than those observed at room temperature. Higher surface temperatures not only allowed for the observation of larger immobilized adatom islands, but they also demonstrated how temperature can be used as another method to control surface modification and molecular assembly. Not only is this work critical for a basic understanding of the role between temperature and surface diffusion, but it also begins to mimic how surfaces may have behaved during the emergence of life on Earth.
When considering the ability to construct nanoarchitectures out of organic and biological molecules for applications in molecular recognition, catalysis, sensors, solar cells, and optoelectronics, it is critical to understand the fundamental interactions and binding mechanisms at the molecule–surface interface.1–4 The rapidly growing industry of nanodevices has driven the field of surface science to largely focus on the detailed investigation of the interactions between organic molecules and metallic substrates.5–7 Specifically, the adsorption of proteins and peptides on metallic substrates can be used to study the geometry of associated nanoarchitectures and is largely dependent upon the molecule–substrate interactions, intermolecular forces, chirality, polarity, and molecular footprint.8–13 Although the multifaceted interactions between proteins and metallic substrates are of great interest, understanding the adsorption mechanisms of simple amino acids to metal surfaces can give insight into the molecular interactions in their simplest form, as amino acids are the building blocks of all proteins. The interactions are also of great importance in the ongoing effort to better comprehend biological processes occurring in nature.
Due to the complexity and precision necessary to both control and investigate molecular modifications made to metallic substrates, various instrumentation and methodologies have emerged to conduct research at this size domain. A powerful technique that is commonly used, scanning tunneling microscopy (STM), has developed into a very advantageous and versatile method of investigating metals and semiconductors in the realm of surface science and nanotechnology. Most STM studies involving amino acids and other organic molecules are regularly conducted under ultrahigh vacuum (UHV) and at low temperatures (LTs). Although these studies allow for the intricate analysis of molecular orientation and lattice perturbation, experimentation under these pristine conditions fails to simulate interactions that may occur in an archetypal biological environment.14–17 Recent studies have made various modifications to these pristine systems in order to better simulate molecular interactions at ambient conditions.8,9,18 A modified version of STM, electrochemical scanning tunneling microscopy (EC-STM), allows for the investigation and observation of molecules of interest, which have been solvated within an electrolyte and their interactions with a metallic surface. Importantly, the molecular species can be electrochemically controlled via redox reactions occurring on the surface itself, which can often be used to force an interaction of the molecule with the surface which may otherwise be difficult at room or elevated temperatures.8,9 Not only does this technique allow for the fine EC control of atoms and molecules at the surface, but it also permits the simultaneous imaging of the system, allowing for modifications of the surface typography to be observed in real time. Furthermore, EC-STM serves as an ideal method to investigate molecular interactions and binding mechanisms at the solid–liquid interface.8,9,19–23
As a model surface, Au(111) was recently used in a comparative in situ EC-STM study in order to ascertain the validity and reproducibility of the LT-UHV-STM observation of 2D nanoarchitectures formed by the interaction of amino acids with the substrate.8,9 Both LT-UHV-STM and EC-STM investigations reported the formation of 2D metal islands or clusters when the metallic substrates were dosed with amino acids.8–10 It was determined that the formation of these islands was contingent upon the molecular interactions between the amino acids and the interactions occurring at the substrate interface between the amino acids and diffusing metal adatoms.
It is well understood that when a metallic substrate is supplied with thermal energy, atoms and molecules can diffuse across the surface of that material. At room temperature, metals are supplied with enough thermal energy for a 2D layer of gaseous adatoms to diffuse across the surface–vacuum interface.24,25 Although this type of diffusion is perhaps the most well understood, it is not limited to the solid–vacuum interface. Studies investigating the solid–liquid interface have reported an increase in adatom mobility and species adsorption relative to the solid–vacuum interface due to modified thermodynamic properties and metallic bond weakening.26,27 There are many facets that affect surface diffusion such as crystallinity, material, phase, and temperature.26,28,29 By modifying any of these handles, the reactivity of a surface can be greatly altered. Crystallinity and lattice planes may be the most costly facet to control, but their effects on diffusion behavior are rather significant. When investigating face centered cubic metals, it was discovered that the (111) plane showed apparent adatom surface diffusion at cryogenic temperatures approaching ≈55 K, while adatom motion on the (100) plane did not occur until ≈300 K.29–31 The (111) planes of various metals displayed a drastically lower activation energy to adatom diffusion, which subsequently increased in the other planes as the surface roughness was enhanced.30 Temperature is the simplest, yet easily the most effective variable to alter in order to observe a variance in adatom surface diffusion. Many extensive studies focusing on the effect of temperature on surface diffusion found that increasing the temperature of the material drastically increased the concentration of free adatoms on the surface, as well as the rate of surface diffusion.28,32,33 Taking advantage of these variables of surface diffusion can allow for enhanced modifications of various materials and opens the door to investigations on surface diffusion as functions of these various effects. Furthermore, switching investigations from LT-UHV-STM to EC-STM not only provides a more biologically relevant environment for experiments involving biological molecules, but it also allows for increased interactions at the solid–liquid interface as controlled by an applied external potential.9,26,28 Because these increased interactions have been shown in the past to be dependent upon the diffusion of adatoms, it becomes relevant to question how interactions at the interface will be altered with increasing surface temperature.
Over the years, the biological conditions in which life originated have been widely debated.34–38 The realization that several bacterial and archaeal species exist under extreme biological conditions, including high temperature, UV light, or negligible nutrient levels, brings forth the suggestion that extremophiles, organisms that are able to survive in extreme environmental conditions, may be models of the earliest independent life forms.39 The early existence of extremophiles further suggests that the environment may have also been highly acidic.40 Simulating these conditions in a liquid environment and in the presence of simple organic molecules could allow for a better understanding of the theorized interactions that lead to the development of life on this planet.
In this paper, EC-STM imaging performed at elevated temperatures in the presence of amino acids was used to directly demonstrate how an increase in adatom number and diffusion led to the formation of larger adatom islands as compared to room temperature. Upon increasing the temperature of the Au(111) surface, the average island size that was initially 20.9 nm2 at room temperature increased to 23.9 nm2 at 300 K and further increased to 29.3 nm2 at 305 K. These adatom islands were formed through an interaction of amino acid (AA) molecules, specifically l-valine, and the underlying Au(111) surface on which the amino acid immobilized diffusing metal adatoms. As the temperature of the surface was increased, the islands grew by 14% at 300 K and 40% at 305 K, relative to room temperature. At these elevated temperatures, valine’s interaction with the underlying Au surface mimicked that of a much larger amino acid. Additionally, at elevated temperatures, the heights of the islands often grew by one atomic step, suggesting a Volmer–Weber growth mode for the islands.41,42 These findings indicate that temperature is a critical handle to alter the reactivity of a surface and that, in many ways, it is an even stronger handle than polarity or molecular footprint. Not only is this work critical for a basic understanding of the role between temperature and surface diffusion, but it also begins to mimic how surfaces may have behaved during the emergence of life on this planet, which may have occurred at elevated temperatures.
II. MATERIALS AND METHODS
All experiments were conducted under ambient conditions using in situ STM. Data was collected using an Agilent/Keysight PicoScan 5500 scanning probe microscope. This scanning probe was equipped with an internal bipotentiostat that allowed for the application of external potentials and the capability of performing electrochemistry in situ. A sample plate modified with a fluid cell made it possible to use a three-electrode system under a liquid layer to perform electrochemistry. An Au(111) crystal (Princeton Science Corp.), with a surface roughness of <0.01 μm and 99.999% purity, served as the working electrode. The counter electrode was a Pt0.8Ir0.2 wire (Nanoscience Instruments), and a Pt wire (Alfa Aesar, ≥99.997%) acted as the pseudoreference electrode. The Pt wire is understood to be a pseudoreference electrode and was ultimately referenced to an Ag/AgCl electrode in saturated KCl, obtaining an open circuit potential of +0.63 V versus Ag/AgCl. All potentials reported in this paper will be expressed versus Ag/AgCl. Keysight Technologies N9802A, Apiezon wax coated Pt0.8Ir0.2 wire tips were used for all imaging. The Apiezon coating allowed less than 70 pA of leakage current into the system, preventing the scanning tip from acting as an additional electrode within the fluid cell. A Lakeshore 325 Temperature Controller was used to increase and monitor the temperature of the crystal. Once data was collected, it was processed with Gwyddion version 2.49 (Czech Metrology Institute, Department of Nanometrology).
The use of electrolytic cells as a simulation for naturally occurring redox events has allowed for a better understanding of these multistep reactions as a whole and has allowed for the evaluation of the energy present in various biological systems.43 When simulating these reactions, a three-electrode setup is typically used, with the working electrode being the substrate of interest.43–46 The incorporation of a three-electrode system in EC-STM allows for EC techniques to be used as an additional tool for surface analysis. Cyclic voltammetry (CV) is a potentiostatic technique that involves cycling the potential of the working electrode and measuring the output current that develops at the surface. By monitoring the fluctuation in current, the energy or potential required for the redox species to undergo a transformation at the electrode surface can be determined. Applying this potential to the working electrode affords electrochemical control of the adsorbing species. In work involving molecules, like amino acids, this potential can be used to force the amino acids to adsorb to the surface of the working electrode, which may otherwise be difficult at elevated temperatures. Because EC-STM is an in situ technique, the entire surface modification process can be monitored and imaged in real time and under a liquid layer.
B. Crystal preparation
The extreme chemical sensitivity inherent to EC-STM required that all components of the fluid cell, including the Au(111) crystal, undergo an extensive and rigorous cleaning procedure. All components of the fluid cell underwent a daily soaking in a freshly made piranha solution [1:3 H2O2 (30%):H2SO4] prior to and upon the conclusion of the experiments in order to remove all organic material and other contaminants. After the piranha soak, the crystal was removed from the solution and rinsed eight times with 18.2 MΩ high purity water (HPW). The crystal was then placed on a quartz plate and flame annealed under a high purity 1000 K hydrogen flame for 10 min. This process ensured that the surface was clean and flat. The crystal was then placed on the sample plate and quenched with a drop of HPW while the other components were removed from the piranha solution and rinsed with HPW, and the fluid cell was constructed. The fluid cell was then filled with a 0.1M HClO4 (Fisher Scientific, ACS Optima Grade) electrolyte, which in addition to being a well understood electrolyte also provided an acidic environment to better simulate conditions of early Earth.13,47–49 The sample plate was connected to the potentiostat and a 0.73 V potential was applied for 2 h to flatten the surface of the crystal. This flattening process electrochemically lifted the , or herringbone, surface reconstruction innate to bare Au(111). This reconstruction occurs due to ∼4.4% extra Au atoms present on the surface relative to the bulk crystal underneath. The lifting of the reconstruction is a very well understood process and prevents possible templating effects upon molecular adsorption.48,50 After the flattening process was complete, CVs were taken and the surface was imaged in order to confirm the cleanliness of the substrate (see Fig. 1). Because the electrochemical interaction between HClO4 and Au(111) is well understood and is accompanied by a well-defined electrochemical signature, CVs can be used to determine the cleanliness of the Au(111) surface.48–51 Once the Au(111) surface was determined to be flat and free of contamination via imaging and CVs, experimentation proceeded with the adsorption of l-valine.
C. Statistical measurements
In this study, thorough statistical measurements of the adatom island areas and heights were taken. In order to account for any thermal drift or drift associated with the instrument itself, island areas were averaged using both up and down scans. By doing so, the elongation or contraction of imaged features was accounted for and canceled out. Over 200 islands at each temperature were analyzed for statistical measurements. In order to improve the accuracy of the height measurements, the system was calibrated to the height of a single gold step. Any error associated with the height profiles was accounted for through this calibration and the application of a correction factor.
III. RESULTS AND DISCUSSION
A. Examination of the bare Au(111) surface
After the flattening process, as described in the experimental section, and prior to the addition of the AA, the bare Au(111) surface was imaged to ensure the surface was clean and devoid of contaminants. CVs were also taken as another means to determine the cleanliness of the sample, as clean Au(111) has a well-defined and understood electrochemical signature in HClO4.48–51 Figure 1(a) shows an image of the Au surface at 297 K, absent of any major structures or features like islands or etch pits that would indicate contamination. It is also clear that the herringbone reconstruction has been lifted, resulting in a flat Au(111) surface.48 The large scale CV, Fig. 1(b), displays only the innate faradaic peaks known to manifest in the presence of HClO4 on bare Au(111). Figure 1(c) shows a CV taken in a decreased scan window in order to specifically analyze the region in which amino acids are known to adsorb.8 As expected with bare Au, there were no faradaic peaks present, indicating no redox chemistry occurred in this region in the absence of amino acids. Furthermore, imaging of bare Au also took place at an elevated temperature (300 K) in order to ensure that the increase in temperature did not affect the surface structure, Fig. 2.
B. Adsorption of l-valine to the Au(111) surface
Prior to the addition of l-valine to the electrochemical cell, the solution was sparged with UHP (ultrahigh purity) N2 (g) for 15 min. This typical electrochemical procedure allowed for O2 (g), which has the tendency to manifest in cyclic voltammograms, to be removed from the solution along with other possible contaminants. Once the amino acid solution was sparged, it was then added to the fluid cell by pipetting ∼50 μl into the cell. Upon the addition of the solution, a CV was taken in order to determine the potential at which l-valine adsorbed to the Au(111) surface. As can be seen in Fig. 3, the adsorption potential for l-valine was ∼0.45 V in agreement with previous reports.8 For experiments occurring at room temperature, once this potential was determined, it was applied to the surface and the STM tip was approached for imaging. For experiments occurring at elevated temperatures, the surface temperature was first increased at a ramp rate of 0.2 K/min until it reached the desired temperature, and then a CV was taken. Importantly, the potential was not applied to the working electrode until the desired elevated temperature was reached in order to ensure that the observed island formation could only be attributed to the Au surface diffusion at the elevated temperature rather than any intermediate temperatures. Once the potential was applied, the system was allowed ample time (∼20 min) to thermally equilibrate before imaging occurred. Furthermore, STM imaging occurred at the elevated temperatures in order to keep the environment consistent and demonstrate the stability and utility of the ambient instrument.
The CV taken in the presence of l-valine prior to imaging showed a reduction peak at ∼0.45 V as seen in Fig. 3.8 Importantly, the peak in the CV is small due to a variety of well-known factors including small electrolyte volumes, small areas of the electrodes, and a low concentration of amino acid molecules. Once the potential was applied, the surface was imaged, and adatom islands were immediately observed (Fig. 3). The ad-island formation was understood from previous reports to be promoted by AA assembly and the application of an external potential that drew the molecules to the surface and forced an interaction.8 The exact bonding mechanism between AAs and the surface is not yet understood for the aqueous environment, but under LT and UHV conditions, it is known that the molecules formed a tilted tridentate bond with the diffusing metal adatoms to immobilize them on the surface and ultimately form islands.8–10 The tridentate bond consists of the nitrogen of the amino group and the oxygen of the carboxylic acid group binding to a diffusing metal adatom.8,10 Upon this amino acid–adatom interaction, the amino acids further interacted with each other via van der Waals forces and hydrogen bonding, forming a corral around the immobilized adatoms.10,52,53 The size of these corrals or ad-islands was found to depend on various factors including polarity, molecular footprint, and, in this report, surface temperature.8 Another important attribute of the surface in Fig. 3 are the scalloped and kinked step edges, which indicate that the diffusing metal ad-atoms were immobilized by the presence of the adsorbed molecules on the surface. These molecules withdrew electron density from the step edges and prohibited the diffusing atoms from reaching the edges to provide the necessary material to straighten them.54–56
C. Area distribution of islands as a function of surface temperature
In order to investigate the role that temperature plays in the formation of these islands, a single amino acid (l-valine) was investigated, keeping the polarity and molecular footprint consistent while only changing one variable, surface temperature. For this study, it is important to note that 297 K was considered room temperature as that was the temperature consistently measured by the thermocouple attached to the sample plate prior to the start of the experiments. This part of the investigation started with observing l-valine, one of the smallest and simplest amino acids [see the molecular structure in Fig. 3(b)], at room temperature. Figure 3 shows the ad-islands formed on the Au(111) surface through the adsorption of l-valine and details the island distribution at room temperature. Due to the small size of l-valine (117.15 g/mol) and a previous investigation, it was expected that valine would form relatively small islands.8 Nearly 95% of the islands formed in the presence of valine were <35 nm2 in area, with more than 70% of the islands formed at <15 nm2. Specifically, valine had the highest affinity for forming islands with areas between 10 and 15 nm2. Therefore, it consequently had the lowest affinity for forming larger islands on the surface with 5% being larger than 35 nm2 and only 3% having an area of >60 nm2. At room temperature, the average area of the islands produced in the presence of valine was 20.9 nm2.
Interestingly, increasing the temperature of the Au surface by even a small amount to 300 K caused a rather dramatic shift in the area distribution of the islands. As seen in Fig. 4, there was a drastic decrease in the number of islands with areas <15 nm2 from 70% at room temperature to 36% at 300 K. Surprisingly at 300 K, not only was there an increase in island area, but there was also an increase in island area variation. At room temperature, valine seemed to have a terminating area between 10–15 nm2 with over 70% of the islands formed near this range, yet when the surface temperature was increased, the terminating area doubled to 30–35 nm2. Roughly, 19% of the islands formed were over 35 nm2, nearly four times the area at room temperature. The average island area at 300 K was ∼23.9 nm2, yielding a 14% increase in island area from room temperature.
As previously mentioned, it was determined that both polarity and molecular footprint played a larger role in the area of the islands formed in the presence of AAs.8 Threonine, valine’s polar counterpart, was found to have an enhanced interaction with the Au(111) surface, which can be attributed to both its increased molecular weight, by ∼2 g/mol, and a hydroxyl group substitution at the β-carbon position.8 When comparing valine at 300 K and threonine at room temperature, the increased surface temperature seems to have a much more drastic effect on the island area than that of polarity and molecular footprint combined. Threonine, a polar amino acid with a molecular weight of 119.12 g/mol, formed 92% of its islands at <35 nm2 and no islands >60 nm2 in area.8 Yet, by simply increasing the surface temperature of Au(111) by 3 K in the presence of valine, the island area began to rival that of isoleucine, a more complex amino acid with an increased molecular footprint. Isoleucine, with a molecular weight of 131.17 g/mol, formed 19% of its islands with an area of >35 nm2, the same percentage formed by valine at 300 K, further exemplifying the radical effect that temperature has on island formation and area.8
Importantly, further increasing the surface temperature from 300 to 305 K in the presence of l-valine shifted the area distribution of the islands even further to the right, indicating a higher propensity to form larger islands at elevated temperatures. Figure 4(c) shows the distribution of islands formed after the adsorption of valine to the surface at 305 K. At this temperature, the average island area was ∼29.3 nm2, a 40% increase from the average island size at room temperature and a 23% increase from 300 K. Furthermore, at 305 K, islands formed with an area of >35 nm2 rose to 31%, a sixfold increase from the island area at room temperature. With only ∼2% of islands at <5 nm2 and over 10% formed at >60 nm2, the preferential formation of larger islands at 305 K is quite clear. When directly comparing island formation at >60 nm2 at 300 and 305 K, the percentage more than tripled from 3% to 10%. Once again, due to elevated surface temperatures and the subsequent increase in surface diffusion of the metal adatoms, island formation in the presence of valine, the smallest essential amino acid, began to resemble that of a much larger and more complex amino acid. Valine at 305 K displayed an enhanced interaction with the Au(111) surface in a very similar fashion to isoleucine ethyl ester, a modified version of the essential amino acid isoleucine. Isoleucine ethyl ester, with a molecular weight of 195.69 g/mol, at room temperature formed 39% of its islands with areas of >35 nm2, only ∼8% greater than that formed by valine at 305 K, an amino acid that is 78.54 g/mol lighter.8 EC-STM images taken at all of the experimental temperatures can be seen in Fig. 5. Importantly, it is possible to observe some thermal drift in Fig. 5(c). This is due to the surface being imaged at 305 K, which resulted in an increased amount of thermal drift within the image. Errors associated with drift were compensated by taking all island measurements from both up and down scans, which are affected in equal and opposite ways by thermal drift, essentially cancelling out its effect. To clarify the statistical data relating to the islands formed in the presence of valine at three different temperatures, Table I is provided above. A clear trend in increasing island area as a function of temperature is demonstrated.
|Amino acid .||Temperature (K) .||Average area (nm2) .||Area <35 nm2 (%) .||Area >35 nm2 (%) .||Molecular weight (g/mol) .|
|Amino acid .||Temperature (K) .||Average area (nm2) .||Area <35 nm2 (%) .||Area >35 nm2 (%) .||Molecular weight (g/mol) .|
D. Ad-Island height determination
Although the areas of the observed islands varied, the heights of the islands were consistent among each temperature group. Figure 5 shows the height profiles of multiple islands at various temperatures. The blue dotted-line represents the average height from hundreds of islands analyzed, and the gold dotted-line represents the height of a single gold step. Islands formed at room temperature and most islands formed at the elevated temperatures in the presence of l-valine were determined to be approximately one atomic step in height, indicating that the islands were comprised of a single layer of immobilized Au adatoms and further verifying the findings in past LT-UHV-STM and EC-STM studies.8–10
Although a majority of the islands were found to be approximately one atomic step in height, increasing the surface temperature promoted the growth of islands with an observable change in height. Various islands at 300 and 305 K appeared to have an additional layer of immobilized Au adatoms (Fig. 6). Height profiles confirmed that the second layer is the approximate height of an atomic Au step, as seen in Fig. 6. The emergence of the additional adatom layer gives insight into the possible growth mode of the amino acid immobilized Au islands and speaks to the increased thermal motion of the Au adatoms. The 3D growth of the islands is indicative of the Volmer–Weber growth mode, which is characterized by adatom–adatom interactions being stronger than the adatom interaction with the surface, resulting in the 3D growth of adatom clusters.41,42 Furthermore, the scalloped step edges observed in Figs. 3, 5, and 6 indicate that the amino acids immobilized diffusing adatoms, hindering those atoms from migrating and filling in the step edges. Not only does this phenomenon hold true in both LT-UHV-STM and EC-STM, but it also reveals the strength of the molecule–substrate interaction, prohibiting the surface from reverting back to its natural state. The drift in Fig. 6(b) is due to the fact that the image was taken at 305 K; importantly, all statistical measurements of the island heights were derived from both up and down images as a correction for thermal drift.
In an attempt to more accurately reflect the conditions under which life may have emerged on this planet, an EC-STM study was conducted looking at the interaction of amino acids with metal surfaces as a function of temperature. Through this study, it was possible to directly demonstrate how elevated temperatures led to increased surface diffusion of metal adatoms and how that increased diffusion manifested in the formation of larger adatom islands in the presence of AAs relative to room temperature. These diffusing adatoms were immobilized by the presence of amino acid molecules on the surface, in particular l-valine. As the temperature of the surface was increased, the islands grew by 14% at 300 K and 40% at 305 K, relative to room temperature. Importantly, the islands at room temperature were one atomic step in height, which had been observed previously in both LT-UHV-STM and EC-STM studies. Furthermore, increasing the surface temperature followed by the adsorption of amino acids allowed for the 3D growth of the adatom islands, resembling the Volmer–Weber growth mode. The islands always grew by a factor of one atomic step with some of the islands at increased temperatures displaying a height of two atomic layers. This is the first EC-STM study to examine how these molecular interactions changed as the surface temperature was increased.
Increasing the surface temperature not only allowed for the observation of larger immobilized adatom islands, but it also demonstrated that temperature can be used as another handle to control surface modification and molecular assembly. This study also provides clear evidence of how increased thermal energy can lead to a larger concentration of metal adatoms in the 2D gas on metal surfaces, which can subsequently interact with adsorbed molecules. As for the implications on the emergence of early life, it is now clear how great an effect temperature has on biomolecule–substrate interactions. A mere change of less than 10 K began to alter the growth mode of the metal islands on the surface. This indicates that studies examining the formation of early biotic molecules may need to focus on how those molecules both form and propagate in systems at higher temperatures. It is also significant to point out that substrates should not be considered static and may, in fact, have a considerable role in how biological molecules come together and template, possibly affecting their secondary structures. Future investigations will include the observation of various amino acids with differing chirality, polarities, and molecular footprints at elevated temperatures. These studies will also include higher temperatures than those of the current study to further investigate how temperature affects the formation of these ad-islands and whether that effect is linear or displayed in a more complicated fashion. Additionally, theoretical studies will take place to clearly identify the bonding mechanism between AAs and the metal adatoms.
The authors gratefully acknowledge financial support from The University of Tulsa. Additional support for this work was provided by the National Science Foundation under Award No. OIA-1833019. K.P.S.B. and J.A.P. were supported in part through the Graduate Research Grant Program through the Office of Research and Sponsored Programs at The University of Tulsa. M.A.P., K.K.E., and E.A.C. were supported through both the Chemistry Summer Undergraduate Research Program and the Tulsa Undergraduate Research Challenge offered through The University of Tulsa.
Kennedy Boyd is a Master’s student at the University of Tulsa, where she also received her undergraduate degree. She was first introduced to EC-STM as an undergraduate when she joined the Iski Research Group in 2017. Her research focuses on surface modification through the electrochemical control of silver halides and organic molecules. Upon completing her master’s degree, she hopes to pursue her Ph.D.
Jesse Phillips is a research scientist with over 5 years of experience working in surface modification and materials development. He completed his Ph.D. at the University of Tulsa under the direction of Dr. Erin V. Iski. Currently, Dr. Phillips is the Assistant Director of Research and Development for the Tulsa based company, Xcaliber International Ltd., L.L.C. focusing on bringing product from concept to creation. He specializes in project management and experimental design, working closely with his team to foster inquiry while still delivering results.
Maria Paszkowiak is a third year, undergraduate student at the University of Tulsa. She is majoring in Biological Science with a premedical track and is obtaining minors in Chemistry, Psychology, and Anthropology. Maria began working with the Iski Research Group in Spring 2019 which led her to pursue her minor in Chemistry. By working with amino acids and electrochemistry, she has been able to study both of her major academic interests. In the future, Maria will be applying to medical school and intends to continue performing research beyond her undergraduate degree.
Kassidy Everett is a junior chemistry major at the University of Tulsa and is from Greenbrier, AR. After she finishes her bachelor’s degree, she hopes to become a researcher and possibly go to graduate school to complete a master’s degree in Chemistry. In her free time, she enjoys playing a few different instruments including French horn and bass guitar. She is also the treasurer of the Sigma Gamma chapter of SAI, a women’s music fraternity.
Emily Cook is currently a sophomore at the University of Tulsa studying Biochemistry and Mathematics. After completing her undergraduate degree, she plans to attend graduate school and pursue a career doing research. She initially became interested in research in high school and has continued her interest in research while in the Iski Lab. In her free time, she enjoys organizing and participating in STEM outreach events, especially ones aimed at promoting women in STEM, and baking.
Erin Iski is an Assistant Professor of Chemistry at the University of Tulsa. She received her B.S. degree in Chemistry from the University of Tulsa in 2005 and Ph.D. from Tufts University in 2011 under the direction of Prof. Charles Sykes. While at Tufts, her research focused on the surface chemistry of large molecules on metal surfaces through the use of scanning tunneling microscopy (STM). Utilizing the STM in the Sykes Lab that was capable of low temperature scanning and ultrahigh vacuum conditions, Dr. Iski successfully published over 15 peer-reviewed publications. After working as a Postdoctoral Fellow at Argonne National Lab with Dr. Nathan Guisinger in the Center for Nanoscale Materials, Dr. Iski joined the University of Tulsa in 2013. At TU, the Iski Group focuses on the use of Electrochemical STM (EC-STM) to study thermally stable nanoalloys of Ag on Au(111) and the assembly and interaction of amino acids on metal surfaces, which was recently awarded a grant from the National Science Foundation. In addition to research, Dr. Iski is committed to educational outreach within the Tulsa community and was recognized in 2016 with the Women of Distinction Award from the Tulsa Business & Legal News. She is a member of ACS, serving as the local ACS secretary for 2 years, the Executive Committee of the Surface Science Division of AVS, and the AAUW (American Association of University Women).
What would you tell your 16 year old self?—Like many young women, when I was 16, I was constantly second guessing myself and dealing with severe imposter syndrome. While those feelings never go away completely, I wish I had been a little more accepting of my intuition and desires. Along with that, I would also tell myself to not put so much pressure on perfect grades, friends, etc. Finally, I would encourage myself to pursue all passions, even those outside of science. Being well-rounded is a great attribute later in life!