Organic Chemistry is considered by many to be the quintessential “weeder course”, widely identified in the premed and STEM persistence literature as a gatekeeper to students interested in STEM or health fields (Barr, Gonzalez, & Wanat, 2008; Lovecchio & Dundes, 2002). There has therefore been considerable interest in determining ways to improve students’ outcomes in organic chemistry courses. While redesigning curriculum and developing interventions is an important step in this process, it is also important to better understand what helps students to do well in organic chemistry.

In this dissertation I utilize a mixed-methods study design to explore how students’ study behaviors and problem-solving strategies are associated with student performance in a second-semester organic chemistry course for non-majors, Organic Chemistry 2. This dissertation begins by exploring how study behaviors are associated with overall performance but then interrogates differences in the relationships between different types of questions (mechanism and predict-the-product) and between questions with different relationships to the curriculum (problem-type and exercise-type questions). It finally conducts a more detailed exploration on the differences between student problem-solving strategies on problem-type and exercise-type questions. In order to explore these issues, the goal of data collection was to provide a comprehensive understanding of the entire course. A survey based on the resources available in Organic Chemistry 2 and students’ study behaviors associated with them was developed and utilized. In-class observations, student exams, course materials, and exam scores were also collected. A subset of students was also interviewed using a think-aloud protocol based on questions from their exams.

Survey results were analyzed using hierarchical linear modeling and multiple linear regression. Results showed that students’ overall exams scores were positively associated with studying more than 10 hours, active note-taking, and testing their understanding when working on practice problems. Exam scores were negatively associated with passive engagement in group-work. However subsequent analyses showed that different categories of questions (mechanism and predict-the-product) are associated with very different strategies from each other and overall exam scores. Notable differences were also seen between problem-type and exercise-type questions even within the same category of question. All these results indicate that determining what study behaviors are associated with higher scores in Organic Chemistry is more complicated than might be initially expected and that advice to students on how to study should consider the type of questions that students are struggling with. It also indicates that instructors should think critically about more than just the content being tested when designing exam questions.

Interviews were analyzed using thematic coding centered on student decision making and reasoning strategies. Results from initial thematic coding were finalized into activity logs which were then tabulated to better compare the reasoning strategies used in the problem-type and exercise-type questions and their outcomes. Results showed that problem-type and exercise-type questions are associated with different approaches and reasoning strategies. In particular the use of chemical reasoning seems to be important for performance on problem-type questions but other reasoning strategies can be just as effective in exercises. This chapter then discusses how chemical reasoning is undervalued by students and how exercise-type questions may not measure students understanding of chemical concepts.

Abstract

The Electrodeposition of PbTe Nanowires for Thermoelectric Applications

by

Peter Hillman

Doctor of Philosophy in Chemistry

University of California, Berkeley

Professor Angelica Stacy, Chair

The electrodeposition of PbTe nanowires for thermoelectric applications is presented in this thesis. The Pb-Te electrochemical system was investigated to determine the optimal conditions for deposition. It was found that citric acid complexed tellurium in solution shifting its reduction potential cathodically. The shift in reduction potential led to the deposition of pure PbTe without any observable excess tellurium.

Nanowires of PbTe were doped p-type and n-type through the addition of thallium and indium to the plating solution. Indium-doped nanowire arrays showed a linear relation between lattice parameter and atomic percent indium confirming successful incorporation. The lattice parameter trend in thallium-doped nanowire arrays was linear only after annealing. In the case of thallium doping, thallium tellurides were formed, which upon annealing formed a solid solution with PbTe.

The results of the thallium doping study led to the investigation of the Tl-Te electrochemical system. Cyclic voltammagrams were used to determine the deposition mechanism of TlTe and Tl5Te3. Thin films and nanowire arrays of these compounds were deposited. This was the first study of the electrochemical Tl-Te system and the first report of the electrodeposition of TlTe and Tl5Te3.

Thermoelectric measurements were conducted on thin films and nanowire arrays of PbTe. The Seebeck coefficient and resistivity of PbTe thin film were measured. Results from thin films were complicated by the Pt substrate on which PbTe was deposited. Subtracting the effects of the Pt layer suggested PbTe thin films could have a large zT, however further work is needed to confirm this result. Resistivity measurements on nanowire arrays were also conducted. Despite efforts to minimize the oxidation of PbTe nanowires, good electrical contacts could not be created. The resistivity of nanowire arrays were orders of magnitude higher than expected. As a result of their low conductivity, the thermoelectric efficiency of PbTe nanowires were negliglable.

Nanotube arrays of conductive polyaniline were synthesized through the electrochemical deposition into porous anodic alumina. PbTe nanowires were deposited into these nanotubes to create a PbTe/polyaniline core-shell structure. PbTe/polyaniline hybrids should have a lower thermal conductivity than pure PbTe. Measurements of PbTe/polyaniline core-shell nanowires are still needed to confirm the predicted lower thermal conductivity.

While there is consensus that conceptual change is surprisingly difficult, many competing theories of conceptual change co-exist in the literature. This dissertation argues that this discord is partly the result of an inadequate account of the unwritten rules of human social interaction that underlie the field's preferred methodology--semi structured interviewing.

To better understand the contributions of interaction during explanations, I analyze eight undergraduate general chemistry students as they attempt to explain to various people, for various reasons, why phenomena involving chemical phase equilibrium occur. Using the methods of interaction analysis, I characterize the unwritten, but systematic, rules that these participants follow as they explain.

The result is a description of the contributions of interaction to explaining. Each step in each explanation is a jointly performed expression of a subject-predicate relation, an interactive accomplishment I call an information performance (in-form, for short). Unlike clauses, in-forms need not have a coherent grammatical structure. Unlike speaker turns, in-forms have the clear function of expressing information. Unlike both clauses and speaker turns, in-forms are a co-construction, jointly performed by both the primary speaker and the other interlocutor. The other interlocutor strongly affects the form and content of each explanation by giving or withholding feedback at the end of each in-form, moments I call feedback-relevant places.

While in-forms are the bricks out of which the explanation is constructed, they are secured by a series of inferential links I call an illative sequence. Illative sequences are forward-searching, starting with a remembered fact or observation and following a chain of inferences in the hope it leads to the target phenomenon. The participants treat an explanation as a success if the illative sequence generates an in-form that describes the phenomenon. If the illative sequence does not, it is partly or entirely scrubbed, a new in-form is introduced as a starting point, and the illative sequence begins anew.

Knowledge of these interactional contributions to the production of explanations could allow researchers to better characterize conceptual understanding, be in a stronger position to support particular theories of conceptual change over others, improve assessments of conceptual understanding, and improve interviewing practices.

This dissertation explores how student beliefs about the nature of science learning, beliefs in their academic ability, perceptions of the classroom environment, perceptions of external support, and use of resources contribute to success in introductory chemistry as measured by midterm and final exam scores. These factors were selected for study because they are susceptible to instructional intervention. A beliefs and perceptions survey and use of resources framework were developed, tested, and utilized to find predictors for student grades.

To measure beliefs and perceptions the Chemistry Beliefs and Perceptions Survey was developed and tested. A total of 428 introductory chemistry students responded to the survey measuring their beliefs and perceptions during Fall 2009. Factor analysis of student responses yielded four categories of beliefs and perceptions: nature of science learning, academic ability, classroom environment, and external support. A hierarchical linear model estimated the influence of student beliefs and perceptions on exam scores. There was a positive relationship between exam scores and (a) belief in academic ability and (b) belief that learning science involves understanding dynamic processes. There was a negative relationship between exam scores and perception of external support. Perceptions of the classroom environment were not strongly related to exam scores. These results were replicated with survey responses collected from students taking the course the following Fall (N=597).

To characterize student use of resources, a subset of survey participants (N=61) were interviewed at three time-points spanning the Fall 2009 semester. Interview responses were used to create a Use of Resources Framework. This framework described students as memorizers, procedural thinkers, critical thinkers, or researchers. Students characterized as memorizers or procedural thinkers view outside sources of information as the "authority," while critical thinkers and researchers evaluate information for themselves and generate explanations in their own words by using multiple relevant ideas. The four use of resource levels were shown to predict exam performance. There was a positive relationship between use of resources and exam performance.

Survey and interview measures were combined for the subset of 61 students to explore the joint contribution of use of resources along with beliefs and perceptions on exam performance. The influence of student beliefs in their academic ability on exam performance was found to be mediated by use of resources. That is, there was a positive relationship between belief in academic ability and use of resources. There was also a positive relationship between overall use of resources and exam performance.

To illustrate these relationships, three case studies are described. The case studies demonstrate the strong relationship between use of resources (for example the textbook, solving problems, interactions with peers) and understanding of chemistry as revealed on the exams. The cases illustrate how students use resources to understand the course material. Memorizers and procedural thinkers explain the idea of boiling based on connection of recalled information with little evaluation of these ideas. Critical thinkers and researchers explain their understanding in their own words, including evaluation of multiple explanations on the topic. These results suggest that it might be valuable to instruct students in productive ways to use resources so they can succeed in chemistry. This may be done by modeling effective strategies to become a more independent learner such as (a) evaluation or critique of information before accepting its accuracy, (b) translate information to create their own understanding, (c) work out problems on their own before confirming answers with others, (d) opportunities to exchange and evaluate ideas with others. Instructional interventions that improve student use of resources in chemistry could lead to better overall student performance.

This dissertation aims to explore how students think about atomic absorption and emission of light in the area of introductory quantum chemistry. In particular, the impact of classical ideas of electron position and energy on student understanding of spectra is studied. The analysis was undertaken to discover how student learning can be characterized along different dimensions of competence, and to determine the strength of the correlations between these dimensions.

The research in this dissertation study comes from a set of semi-structured clinical interviews after a unit on quantum chemistry using a stratified random sample. Open-ended questions were asked on the topic of atomic spectra to a representative sample (N=65) of students from a large introductory chemistry class. Data was examined using elements of grounded theory. Three dimensions were found, Continuous to Discrete, Interpreting Spectra, and Energy/Force, that explain how student thinking about atomic spectra can be characterized. A fourth dimension, Deterministic to Probabilistic, had been discussed in the research before.

Students who exhibited a mastery of discrete energy absorption predominantly were skilled with a difference reasoning, an understanding that the energy values of the spectral lines correlate to differences of energy levels. Students who successfully interpreted spectra did not necessarily have a probabilistic view of electron position, signaling that those two concepts, as least as they were assessed, do not strongly impact each other.

Using grounded methods on ten student interviews, four main types of representation use and conceptual understanding in the topic of atomic spectra were discovered: Literal Reasoning, Threshold Reasoning, Exact Difference Reasoning, and Meta-Reasoning. Threshold reasoning was indicative of an influence of classical ideas of energy absorption, while Exact-Difference reasoning consisted of a full appreciation of the all or nothing discrete absorption process. Advanced students recognized the stark difference of the quantum behavior from their classical understandings. While some classical ideas, such as threshold reasoning, hindered students from fully understanding the quantum nature of bound electrons, other more productive classical ideas, such as energy conservation, Coulombic attraction of the electron to the nucleus, and the spatial model of the atom, strengthened student understanding.

In an exploratory study, data was analyzed from two students who initially struggled with interpreting spectra. Their interaction with a representation designed to scaffold their understanding of spectra was studied, and their successes and obstacles were explored. One student transitioned from a literal type of thinking to an exact difference type of thinking through interaction with the representation. The second student remained holding onto a threshold type of thinking, despite the representation, signaling possible limitations of such curricular tools.

This dissertation highlights the deeply rooted and persistent nature of students' classical ideas as they learn about quantum concepts. Understanding the impact of classical ideas on the learning of atomic energy absorption will help instructors better understand the issues students face and will assist in developing better curriculum to address and challenge students' classical notions.

This dissertation explores student perceptions of the instructional chemistry laboratory and the approaches students take when learning in the laboratory environment.

To measure student perceptions of the chemistry laboratory, a survey instrument was developed. 413 students responded to the survey during the Fall 2011 semester. Students’ perception of the usefulness of the laboratory in helping them learn chemistry in high school was related to several factors regarding their experiences in high school chemistry. Students’ perception of the usefulness of the laboratory in helping them learn chemistry in college was also measured. Reasons students provided for the usefulness of the laboratory were categorized.

To characterize approaches to learning in the laboratory, students were interviewed midway through semester (N=18). The interviews were used to create a framework describing learning approaches that students use in the laboratory environment. Students were categorized into three levels: students who view the laboratory as a requirement, students who believe that the laboratory augments their understanding, and students who view the laboratory as an important part of science. These categories describe the types of strategies students used when conducting experiments.

To further explore the relationship between students’ perception of the laboratory and their approaches to learning, two case studies are described. These case studies involve interviews in the beginning and end of the semester. In the interviews, students reflect on what they have learned in the laboratory and describe their perceptions of the laboratory environment.

In order to encourage students to adopt higher-level approaches to learning in the laboratory, a metacognitive intervention was created. The intervention involved supplementary questions that students would answer while completing laboratory experiments. The questions were designed to encourage students to think critically about the laboratory procedures. In order to test the effects of the intervention, an experimental group (N=87) completed these supplementary questions during two laboratory experiments while a control group (N=84) performed the same experiments without these additional questions. The effects of the intervention on laboratory exam performance were measured. Students in the experimental group had a higher average on the laboratory exam than students in the control group.

There is a strong interest in thermoelectric materials for energy production and savings. The properties which are integral to thermoelectric performance are typically linked, typically changing one of these properties for the better will change another for the worse. The intertwined nature of these properties has limited bulk thermoelectrics to low efficiencies, which has curbed their use to only niche applications. There has been theoretical and experimental work which has shown that limiting these materials in one or more dimensions will result in deconvolution of properties. Nanowires of well established thermoelectrics should show impressively high performance.

Tellurium is attractive in many fields, including thermoelectrics. Nanowires of tellurium have been grown, but with limited success and with out the ability to dope the tellurium. Working on previous work with other systems, tellurium was studied in dimethyl sulfoxide

(DMSO). The electrochemical system of tellurium was found to be quite dierent from its aqueous analog, but through comprehensive cyclic voltammetric study, all events were identified and explained. The binary antimony-tellurium system was also studied, as doping

of tellurium is integral for many applications. Cyclic voltammograms of this system were studied, and the insight from these studies was used to grow nanowire arrays. Arrays of tellurium were grown and analysis showed that by using DMSO, antimony doped tellurium

nanowire arrays could be grown. Furthermore, analysis showed that the antimony doped tellurium interstitially, resulting in a n-type material.

Measurements were also performed on arrays and individual wires. Arrays of 1.15% antimony showed ZT of 0.092, with the low ZT attributed to poor contact methods. Although contacting was an obstacle towards measuring whole arrays, single wire measurements were also performed. Single wire measurements were done by a novel method which allows for easy, reproducible measurements of wire properties. So far, this method has only been used to measure the properties of bismuth telluride, but can easily be adapted to any type of nanowire. Bismuth telluride nanowires were found to have electrical resistivities matching that of bulk (1.4*10^{-5<\super>&Omega-m), and thermal conductivities lower than bulk (<1 W/m-K).}

Scholars have called for the design of alternative educational spaces that counter dominant narratives about who is capable of learning science (Nasir et al., 2013) and what it means to be “good” at science (Carlone et al., 2011). This design-based research study examines possibilities for learning and identity in CHEM 101B, an undergraduate general chemistry course re-designed to dismantle racialized, gendered, and classed hierarchies of competence in chemistry and provide broad access to rich chemistry learning and identities of competence for students. Specifically, this study sought to understand: 1) shifts in students’ conceptions of chemistry, chemical competence, and themselves; 2) shifts in students’ participation in chemistry learning; and 3) how course design was organized to support these shifts. Classroom video, fieldnotes, student artifacts, and written course reflections were collected and interviews were conducted with students. Analysis was carried out through close examination of students’ participation in groups, and through analyzing students’ meaning making about competent participation in chemistry learning and their chemical identities.

Findings indicate that developing more authentic conceptions of chemistry as a social practice supported students to reject the notion that being good at chemistry requires innate intelligence. Giving students opportunities to participate in ways aligned with notions of authentic chemical practice supported students to both develop identities as competent participants in chemical thinking and learning, and engage in rich and rigorous chemistry learning.

This study found that supporting rich and authentic participation in and conceptions of chemistry learning required a significant restructuring of the classroom systems around: (1) coherent content connected to core ideas, (2) engagement in collective investigation of big scientific ideas and relationships, (3) opportunities for students to be scientists as themselves and connect science to their lives, and (4) reflection that creates awareness of tensions between common sense notions and new conceptions of science. This dissertation has implications for institutions of higher education, course designers and instructors committed to constructing learning settings that deconstruct and disrupt hegemonic narratives in science and build more productive counter narratives in their place.

Much like a practiced linguist, expert chemists utilize the power and elegance of chemical symbols to understand what is happening at the atomic level and to manipulate atoms and molecules to effect an observable change at the macroscopic level. Unfortunately, beginning chemistry is often taught in a way that emphasizes memorizing the symbolic representations of equations and reactions without much opportunity to meaningfully connect the observable macroscopic phenomena with an understanding of the chemistry taking place at the atomic level. The compartmentalized manner of chemistry instruction in most chemistry classrooms further nullifies the efficacy of the triplet relationship to connect between macroscopic observations, symbolic representations, and atomic scale views. If symbolic representations are presented as the goal of instruction, rather than as the means to gain understanding, then students will be impaired in developing a coherent understanding of chemical principles.

This dissertation describes the development and implementation of an interview study to examine how undergraduate students interpreted multiple representations of a chemical equilibrium. To establish a baseline of ideas, students first were coached to verbally generate successive representations. They were then cued to think about the chemistry occurring between atoms and ions at the molecular level. Next, an experiment involving a change in states of matter and color was performed which paralleled the symbolic representations. Through self-explanations and verbalizing of conjectures, students were encouraged to explore, interpret, and refine their understanding of the observations related to the chemical symbols presented to them. Finally, with the goal of fostering a deeper understanding of the process of equilibrium, a dynamic visualization of the molecular level was introduced as a tool for helping students connect these multiple representations.

This study revealed that one way in which students develop conceptual understanding and resolve conflicts between different representations of the same phenomena is by verbalizing their ideas as a conjecture (as a verbal explanation to advance towards a hypothesis). Thus, it is proposed that symbolic representations are most effective viewed not as an end goal but as a bridge for connecting macroscopic, visible phenomena with what is occurring at the molecular, invisible level. When the focus on merely memorizing chemical equations and symbols is removed, students can gain a coherent understanding of the meaning available when multiple representations are viewed together.

Representations, such as figures and drawings, are aspects of biology that are key to learning, teaching, and communicating scientific ideas. While many studies have investigated undergraduate students’ abilities to interpret representations generated by science experts, much remains to be understood about how student-generated representations (i.e., drawings) can support learning. Prior research suggests that theoretical mechanisms to explain how drawing aids learning may parallel those that explain how self-explanation aids learning, an area of educational research that has been extensively studied. As such, this research draws from the self-explanation literature to explore the similarities and differences between the use of drawing and self-explaining as independent study strategies for learning about the cardiovascular system (CVS) from text.

We found that students who were asked to draw as they studied the CVS text performed better than students asked to self-explain on multiple learning measures. Their mental models, as interpreted from their drawings of the system, were significantly more accurate, and their responses to questions about structures and pathways within the system were more accurate. Further analyses of self-explanations and drawings revealed that the number of goal-oriented self-explanations a student generated was a significant predictor of their assessment scores, especially on questions about functions. Meanwhile, the number of passage-specific images a learner generated in their drawing was predictive of assessment scores, especially on questions about structures. Finally, findings from case studies identified attributes of self-explanations and drawings that may make them more meaningful for learning, such as self-explaining for the purposes of understanding how parts of the system connect together, and drawing to highlight the main ideas of the text. Findings from this study suggest that drawing is generally more effective than self-explanation for learning about the CVS, and should be promoted as a useful strategy for learning biology from text.