Publications

    E. Mazur. 2009. “Farewell, Lecture?” Science, 323, Pp. 50–51. Publisher's VersionAbstract
    Discussions of education are generally predicated on the assumption that we know what education is. I hope to convince you otherwise by recounting some of my own experiences. Download a podcast of this article narrated by Samuel Smith of the Center for Teaching and Learning at Brigham Young University.
    S. H. Chung and E. Mazur. 2009. “Femtosecond laser ablation of neurons in C. elegans for behavioral studies.” Appl. Phys. A, 96, Pp. 335–341. Publisher's VersionAbstract
    Femtosecond laser ablation selectively dissects subcellular components of the C. elegans neuronal circuit with submicrometer precision for studying the neuronal origins of behavior. We describe the theoretical basis for the high precision of femtosecond laser ablation in the target bulk. Next, we present the experimental setup and a worm rotation technique to facilitate imaging and surgery. We describe the damage caused by different pulse energies on cell bodies and neuronal fibers. Finally, we discuss the regrowth of neuronal fibers after surgery and its impact on behavioral study.
    M. Shinoda, R. R. Gattass, and E. Mazur. 2009. “Femtosecond laser-induced formation of nanometer-width grooves on synthetic single-crystal diamond surfaces.” J. Appl. Phys., 10, Pp. 053102-1–053102-4. Publisher's VersionAbstract
    We form periodic linear grooves in synthetic single-crystal diamond with femtosecond pulses at 800 nm. The grooves are 40 nm wide, 500 nm deep, up to 0.3 mm long, and have an average spacing of 146 7 nm. The grooves are perpendicular to the direction of the laser polarization and are formed below the ablation threshold. The submicrometer periodicity is caused by interference between a laser-induced plasma and the incident laser beam, which locally enhances the field at the surface so the ablation threshold is exceeded. Using Raman spectroscopy we find that the structures retain the original diamond composition.
    T. Voss, G. Thomas Svacha, E. Mazur, S. Müller, and C. Ronning. 2009. “The influence of local heating by nonlinear pulsed laser excitation on the transmission characteristics of a ZnO nanowire waveguide.” Nanotechnology, 20, Pp. 095702–095707. Publisher's VersionAbstract
    We perform a transmission experiment on a ZnO nanowire waveguide to study its transmission characteristics under nonlinear femtosecond-pulse excitation. We find that both the second harmonic and the photoluminescence couple into low-order waveguide modes of the nanowires but with distinctly different efficiencies. We measure the transmission spectrum of a single ZnO nanowire waveguide for near-UV light generated by interband recombination processes. The transmission spectrum allows us to determine the absorption edge of the excited nanowire and to study the temperature profile of the nanowire under femtosecond-pulse excitation.
    B. R. Tull, M. T. Winkler, and E. Mazur. 2009. “The role of diffusion in broadband infrared absorption in chalcogen-doped silicon.” Appl. Phys. A. Publisher's VersionAbstract
    Sulfur doping of silicon beyond the solubility limit by femtosecond laser irradiation leads to near-unity broadband absorption of visible and infrared light and the realization of silicon-based infrared photodetectors. The nature of the infrared absorption is not yet well understood. Here we present a study on the reduction of infrared absorptance after various anneals of different temperatures and durations for three chalcogens (sulfur, selenium, and tellurium) dissolved into silicon by femtosecond laser irradiation. For sulfur doping, we irradiate silicon in SF6 gas; for selenium and tellurium, we evaporate a film onto the silicon and irradiate in N2 gas; lastly, as a control, we irradiated untreated silicon in N2 gas. Our analysis shows that the deactivation of infrared absorption after thermal annealing is likely caused by dopant diffusion. We observe that a characteristic diffusion lengthcommon to all three dopantsleads to the reduction of infrared absorption. Using diffusion theory, we suggest a model in which grain size of the re-solidified surface layer can account for this characteristic diffusion length, indicating that deactivation of infrared absorptance may be caused by precipitation of the dopant at the grain boundaries.
    M. T. Winkler. 2009. “Non-Equilbrium Chalcogen Concentrations in Silicon: Physical Structure, Electronic Transport, and Photovoltaic Potential”. Publisher's VersionAbstract
    This thesis explores the structure and properties of silicon doped with chalcogens beyond the equilibrium solubility limit, with a focus on the potential presence of an impurity band and its relevance to photovoltaics. The investigations that we report here shed new light on the electronic role of sulfur dopants in particular, and also provide new evidence of a semiconductor-to-metal transition consistent with the formation of an electron-conducting impurity band. The thesis is divided into three primary studies. First, we describe doping silicon with a single fs-laser pulse. We find that irradiation above the melting threshold is sufficient for doping a thin layer of silicon to non-equilibrium sulfur concentrations. Next, we explore the interaction of many fs-laser pulses with a silicon substrate. Temperature-dependent electronic transport measurements indicate metallic conduction, while a form of Fermi level spectroscopy and optical absorption data indicate the presence of an impurity band located 200 − 300 meV below the conduction band edge. Third, we investigate silicon doped to non- equilibrium concentrations using a different technique: ion-implantation followed by pulsed laser melting and crystal regrowth. We determine one of the sulfur states present at low sulfur dose. Additional transport measurements point to the presence of a semiconductor-to- metal transition at sulfur doses corresponding to implanted sulfur concentrations just above 10^20 cm−3 . Finally, in the appendices of this thesis, we describe methods to laser-dope silicon while avoiding the development of significant surface roughness that typically characterizes such samples. Additionally, we present the status of investigations into laser-doping silicon with selenium to non- equilibrium concentrations.
    E. D. Diebold, N. H. Mack, S. K. Doorn, and E. Mazur. 2009. “Femtosecond laser-nanostructured substrates for surface-enhanced Raman scattering.” Langmuir, 25, Pp. 1790–1794. Publisher's VersionAbstract
    We present a new type of surface-enhanced Raman scattering (SERS) substrate that exhibits extremely large and uniform cross-section enhancements over a macroscopic (greater than 25 mm2) area. The substrates are fabricated using a femtosecond laser nanostructuring process, followed by thermal deposition of silver. SERS signals from adsorbed molecules show a spatially uniform enhancement factor of approximately 107. Spectroscopic characterization of these substrates suggests their potential for use in few or single-molecule Raman spectroscopy.
    S. H. Chung and E. Mazur. 2009. “Surgical applications of femtosecond lasers.” J. Biophoton., 2, Pp. 557–572. Publisher's VersionAbstract
    Femtosecond laser ablation permits non-invasive surgeries in the bulk of a sample with submicrometer resolution. We briefly review the history of optical surgery techniques and the experimental background of femtosecond laser ablation. Next, we present several clinical applications, including dental surgery and eye surgery. We then summarize research applications, encompassing cell and tissue studies, research on C. elegans, and studies in zebrafish. We conclude by discussing future trends of femtosecond laser systems and some possible application directions.
    C. R. Mendonca, D. S. Correa, F. Marlow, T. Voss, P. Tayalia, and E. Mazur. 2009. “Three-dimensional fabrication of optically active microstructures containing an electroluminescent polymer.” Appl. Phys. Lett., 95, Pp. 113309–113311. Publisher's VersionAbstract
    Microfabrication via two-photon absorption polymerization is a technique to design complex microstructures in a simple and fast way. The applications of such structures range from mechanics to photonics to biology, depending on the dopant material and its specific properties. In this paper, we use two-photon absorption polymerization to fabricate optically active microstructures containing the conductive and luminescent polymer poly(2-methoxy-5-(2'-ethylhexyloxy)- 1,4-phenylenevinylene) (MEH-PPV). We verify that MEH-PPV retains its optical activity and is distributed throughout the microstructure after fabrication. The microstructures retain the emission characteristics of MEH-PPV and allow waveguiding of locally excited fluorescence when fabricated on top of low refractive index substrates
    N. Lasry, N. Finkelstein, and E. Mazur. 2009. “Are most people too dumb for physics?” Physics Teacher, 47, Pp. 418–422. Publisher's VersionAbstract
    In a recent article in The Physics Teacher, Michael Sobel claims (as do many teachers) that physics is in a "special category of hard" and is usually taken only by a "certain sort of very bright student." The appealing, yet suspiciously conceited, notion that physics is only for smart or industrious people is questionable. We offer this response as a means to initiate a dialogue on how we engage with students in our physics courses.
    D. S. Correa, P. Tayalia, G. Cosendey, D. S. Dos Santos, R. F. Aroca, E. Mazur, and C. R. Mendonca. 2009. “Two-Photon Polymerization for Fabricating Structures Containing the Biopolymer Chitosan.” Journal of Nanoscience and Nanotechnology, 9, Pp. 5845–5849. Publisher's VersionAbstract
    Two-photon polymerization is a powerful tool for fabricating three-dimensional micro/nano structures for applications ranging from nanophotonics to biology. To tailor such structure for specific purposes it is often important to dope them. In this paper we report on the fabrication of structures, with nanometric surface features (resolution of approximately 700 nm), using two-photon polymerization of an acrylic resin doped with the biocompatible polymer chitosan using a guest-host scheme. The fluorescence background in the Raman spectrum indicates the presence of chitosan throughout the structure. Mechanical characterization reveals that chitosan does not affect the mechanical properties of the host acrylic resin and, consequently, the structures exhibit excellent integrity. The approach presented in this work can be used in the fabrication of micro- and nanostructures containing biopolymers for biomedical applications.
    C. R. Mendonca, M. Kandyla, T. Shih, R. F. Aroca, C. J.L. Constantino, and E. Mazur. 2009. “Ultrafast dynamics of bis (n-butylimido) perylene thin films excited by two-photon absorption.” Appl. Phys. A, 86, Pp. 369–372. Publisher's VersionAbstract
    We report a pump-probe study of the two-photon induced reflectivity changes in bis (n-butylimido) perylene thin films. To enhance the two-photon excitation we deposited bis (n-butylimido) perylene films on top of gold nano-islands. The observed transient response in the reflectivity spectrum of bis (n-butylimido) perylene is due to a depletion of the molecule�s ground state and excited state absorption.
    E. D. Diebold, P. Peng, and E. Mazur. 2009. “Isolating surface-enhanced Raman scattering hot spots using multiphoton lithography.” J. Am. Chem. Soc., 131, Pp. 16356–16357. Publisher's VersionAbstract
    We present a method for improving femtomole-level trace detection (10^9 molecules) using large-area surface-enhanced Raman scattering (SERS) substrates. Using multiphoton-induced exposure of a commercial photoresist, we physically limit the available molecular adsorption sites to only the electromagnetic hot spots on the substrate. This process prevents molecules from adsorbing to sites of weak SERS enhancement, while permitting adsorption to sites of extraordinary SERS enhancement. For a randomly adsorbed submonolayer of benzenethiol molecules the average Raman scattering cross section of the processed sample is 27 times larger than that of an unprocessed SERS substrate.
    J. Schell. 2009. “Venturing toward better teaching: STEM professors' efforts to improve their introductory undergraduate pedagogy at major research universities*.” Teachers College, Columbia University, Doctoral Dissertation.Abstract
    This study explored 20 tenured professors' teaching improvement efforts in introductory undergraduate science, technology, engineering and mathematics (STEM) classrooms at two major American research universities (MRUS). It identified the mechanisms central to these professors' efforts to improve their undergraduate teaching and the influences and resources shaping those efforts. Despite the billions of federal dollars invested in STEM educational enhancement, STEM professors' teaching improvement efforts are little understood. This research examined this problem through analysis of 40 in-depth interviews (two per participating professor), 36 observations of professors' classroom teaching, and hundreds of documents representing professors' instructional efforts and career progression. The following propositions summarize key study findings: First, contrary to prevailing views, some STEM professors in MRUs do engage in efforts to improve their introductory teaching. Second, some of these professors employ creative, strategic, and systematic designs in so doing. Third, STEM professors' teaching improvement efforts are contextualized by internal and external forces that may facilitate or stymie their teaching improvement endeavors. Finally, STEM professors may be aware of institutional and external resources available to them as supports toward introductory STEM teaching improvement. Taken together, the data suggest that some university STEM professors do engage in efforts to improve their teaching and that such effort may be more common than popular opinion holds. The study revealed the inaccuracy of common beliefs and policy assumptions that the large majority of MRU-based STEM professors neglect their introductory teaching, do not care about it, lack knowledge about students and pedagogy, and prefer use of (and consistently rely on) conventional teaching approaches. To the contrary, all 20 participating professors were found to devote extensive energy toward improving their introductory teaching. Further, all 20 participants indicated extensive knowledge of introductory STEM subject matter, students, and pedagogies. The study also identified over 30 innovative pedagogies that participating STEM professors employed in their classrooms. Drawing on these findings, the study calls for public and policy-level reconsiderations of what it means to be a research-active STEM professor, including revision of extant ideas about how these professors invest their energies and time, and what they care about.
    J. Watkins and E. Mazur. 2009. “Using JiTT with Peer Instruction.” In Just in Time Teaching Across the Disciplines, edited by Scott Simkins and Mark Maier, Pp. 39–62. Stylus Publishing. Publisher's VersionAbstract
    eer Instruction (PI) is an interactive teaching technique that promotes classroom interaction to engage students and address difficult aspects of the material (Crouch, Watkins, Fagen, & Mazur, 2007; Crouch & Mazur, 2001; Mazur, 1997). By providing opportunities for students to discuss concepts in class, PI allows students to learn from each other. However, for this method to be most effective, students need to come to class with some basic understand- ing of the material. Just-in-Time Teaching (JiTT) is an ideal complement to PI, as JiTT structures students' reading before class and provides feedback so the instructor can tailor the PI questions to target student difficulties. Separately, both JiTT and PI provide students with valuable feedback on their learning at different times in the process – JiTT works asynchronously out of class, and PI gives real-time feedback. Together, these methods help students and instructors monitor learning as it happens, strengthening the benefits of this feedback. As this chapter details, the combination of these methods is useful for improving student learning and skill development.
    L. Tong and E. Mazur. 2008. “Nanophotonics and nanofibers.” In Handbook for Fiber Optic Data Communications: A Practical Guide to Optical Networking, edited by Casimer DeCusatis, Pp. 713–728. Academic Press. Publisher's VersionAbstract
    Nanophotonics is a fusion of photonics and nanotechnology, and is defined as nanoscale optical science and technology that includes nanoscale confinement of radiation, nanoscale confinement of matter, and nanoscale photoprocesses for nanofabrication [1.], [2.] and [3.]. While photonics has been widely used for fiber-optic data communication for decades, the application of nanotechnology for optical communication is an emerging technology. The basic motivation for incorporating photonics with nanotechnology is spurred by the requirement of increased integration of photonic devices for a variety of applications such as higher data transmission rates, faster response, lower energy consumption, and denser data storage [2]. For example, to reach an optical data transmission rate as high as 10Tb/s, the size of photonic matrix switching devices should be reduced to 100-nm scale [4].
    L. Tong and E. Mazur. 2008. “Glass nanofibers for micro- and nano-scale photonic devices.” J. Non-Crystalline Solids, 354, Pp. 1240–1244. Publisher's VersionAbstract
    Subwavelength- and nanometer-diameter glass nanofibers have been fabricated using a high-temperature taper-drawing process. As-drawn nanofibers show extraordinary uniformities in terms of diameter variation and surface roughness and are suitable for single-mode optical wave guiding. Measured optical losses of these nanofibers are typically below 0.1 dB/mm. Photonic devices such as linear waveguides, optical couplers and microrings assembled with nanofibers are also demonstrated. Our results show that taper-drawn glass nanofibers are promising building blocks for micro- and nano-scale photonic devices.
    M. Zhang, S. H. Chung, C. Fang-Yen, C. Craig, R. A. Kerr, H. Suzuki, A. D. T. Samuel, E. Mazur, and W. R. Schafer. 2008. “A self-regulating feed-forward circuit controlling C. elegans egg- laying behavior.” Curr. Biol., 18, Pp. 1445–1455. Publisher's VersionAbstract
    Background Egg laying in Caenorhabditis elegans has been well studied at the genetic and behavioral levels. However, the neural basis of egg-laying behavior is still not well understood; in particular, the roles of specific neurons and the functional nature of the synaptic connections in the egg- laying circuit remain uncharacterized. Results We have used in vivo neuroimaging and laser surgery to address these questions in intact, behaving animals. We have found that the HSN neurons play a central role in driving egg-laying behavior through direct excitation of the vulval muscles and VC motor neurons. The VC neurons play a dual role in the egg-laying circuit, exciting the vulval muscles while feedback-inhibiting the HSNs. Interestingly, the HSNs are active in the absence of synaptic input, suggesting that egg laying may be controlled through modulation of autonomous HSN activity. Indeed, body touch appears to inhibit egg laying, in part by interfering with HSN calcium oscillations. Conclusions The egg-laying motor circuit comprises a simple three-component system combining feed-forward excitation and feedback inhibition. This microcircuit motif is common in the C. elegans nervous system, as well as in the mammalian cortex; thus, understanding its functional properties in C. elegans may provide insight into its computational role in more complex brains.

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