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Teaching engineering students how to effectively communicate using the language, representations, and tools specific to their discipline is important to their development as practitioners in their respective fields. This article describes a literature review of learning activities intended to teach crystal structure and crystallography and explores the extent to which educators implement elements of disciplinary literacy. We categorized the purpose of the paper, what the students are asked to do, the representations used in the activities, and the learner roles that the activities support. We observe that a majority of the papers engage students in disciplinary practices and support many, but not all aspects of disciplinary literacy. Instructors use a variety of representations in presenting concepts and ask students to interact with the learning activities to recount information or interpret results. However, we find that the activities rarely ask students to synthesize new information or evaluate their information in any wider context. We suggest that instructors should aim to implement the entire range of learning roles, and employ more critical socio-cultural approaches when designing learning activities to make the sciences accessible to a more diverse population of learners.

In large lecture courses, it can be challenging for instructors to address student misconceptions, supplement background knowledge, and identify ways to motivate the various interests of all students during the allotted class time. Instructors can harness instructional technology such as screencasts, recordings that capture audio narration along with computer screen images, to supplement the lecture with content that addresses the diversity in student academic backgrounds, motivations, and interests, to extend the classroom experience, and reach the individualized needs of students. This study documents the strategic use of screencasts in a large introductory Materials Science and Engineering (MSE) course, and examines their impact on student usage and course performance. To assess the efficacy of screencasts, students were surveyed to determine how they used screencasts and whether they perceived these resources to be helpful. In addition, we correlated student usage based on website hits with student performance (e.g. final grade) to determine statistical significance. Since the course is comprised of students from different academic and social backgrounds, we also analyzed usage and performance patterns for particular student subgroups. The results indicate that students perceive the screencasts to be helpful and tend to use the resources as a study supplement. Overall, usage of screencasting in its various forms is positively and significantly correlated with course performance as indicated by the final grade. The most substantial gains were found for students with the least amount of prior exposure to concepts in the course material. These results indicate a potential for screencasts to address the various academic needs of students in a large lecture environment.

We have investigated the structure and shape of GaN-based nanowires grown on (001) Si substrates for optoelectronic device applications. The nanowire heterostructures contained InN disks and InGaN barrier layers in the active region. The resulting nanowire array comprised two differently shaped nanowires: shorter pencil-like nanowires and longer bead-like nanowires. The two different nanowire shapes evolve due to a variation in the In incorporation rate, which was faster for the bead-like nanowires. Both types of nanowires exhibited evidence of significant migration of both Ga and In during growth. Ga tended to diffuse away and down along the sidewalls, resulting in a Ga-rich shell for all nanowires. Despite the complex structure and great variability in the In composition, the optical properties of the nanowire arrays were very good, with strong luminescence peaking at ∼ 1.63 μm. [ABSTRACT FROM AUTHOR]

This work studies the spontaneous self-assembly of Ge QDs on AlAs, GaAs and AlGaAs by high-temperature in␣situ annealing using molecular beam epitaxy (MBE). The morphology of Ge dots formed on AlAs were observed by atom probe tomography, which revealed nearly spherical QDs with diameters approaching 10 nm and confirmed the complete absence of a wetting layer. Reflection high-energy electron diffraction and atomic force microscopy of Ge annealed under similar conditions on GaAs and AlGaAs surfaces revealed the gradual suppression of QD formation with decreasing Al-content of the buffer. To investigate the prospects of using encapsulated Ge dots for upconverting photovoltaics, in which photocurrent can still be generated from photons with energy less than the host bandgap, Ge QDs were embedded into the active region of III-V PIN diodes by MBE. It was observed that orders of magnitude higher short-circuit current is obtained at photon energies below the GaAs bandgap compared with a reference PIN diode without Ge QDs. These results demonstrate the promise of Ge QDs for upconverting solar cells and the realization of device-quality integration of group IV and III-V semiconductors. [ABSTRACT FROM AUTHOR]

We have investigated the properties of In0.51Ga0.49N/GaN disk-in-nanowire light emitting diodes (LEDs) epitaxially grown on silicon substrates by plasma-assisted molecular beam epitaxy. The radiative efficiency of the nanowire ensemble, obtained from the temperature-dependent photoluminescence measurements, under optimized growth conditions is 43%, which increases to 55% after parylene passivation. From high resolution transmission electron microscopy, it is evident that there is significant coalescence between nanowires when the areal density approaches 1011 cm-2. We have identified and characterized deep level electron and hole traps in the GaN nanowires and it is found that the trap densities increase with nanowire density, or with the degree of coalescence. It is therefore believed that the deep levels originate from dislocations and stacking faults arising from nanowire coalescence. The best output characteristics are measured in a LED having a nanowire density of 2 × 1010 cm-2, which exhibits a maximum internal quantum efficiency of ~55% at an injection level of 10 A/cm2. It is seen that the maximum efficiency would increase to 60% in the absence of deep level traps. [ABSTRACT FROM AUTHOR]