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Student socialisation into the norms and environment of their institution is a crucial process during their college experience. During the COVID-19 pandemic, these processes were disrupted, and little published research exists exploring comparisons of these student socialisation processes before and during the pandemic. Accordingly, we report on a quantitative study conducted at a large mid-western university in the United States, which compared survey data from 2018 to data collected in 2021. We operationalised student socialisation processes using Ashford and Black's proactive behaviours scale to explore how these behaviours and relevant socialisation outcomes changed from before to during the pandemic. The primary socialisation outcomes of interest were engineering identity and social capital. During the COVID pandemic, students reported lower levels of social capital. However, we simultaneously observed higher ratings of students' engineering identity. Next, using multivariate linear regression, we examined which proactive behaviours best predicted socialisation outcomes in both datasets. We found all proactive behaviours were significant predictors of social capital. Proactive behaviours did not influence student's sense of engineering identity. This study contributes to the growing literature on the pandemic's impact on engineering undergraduate students and how proactive behaviours are related to their socialisation outcomes. [ABSTRACT FROM AUTHOR]

There is a nationwide effort to increase the representation and engagement of minoritized students in computer science education. Discourse about the barriers to diversity among computer science majors is often characterized by student pathologies and does not consider the impacts of classroom culture and instructor pedagogies. Amid the push for strategies to recruit and retain minoritized students in computer science, little has been done to transform curriculum and analyze faculty perspectives on curriculum and pedagogy as methods to increase students' access to the computer science major. This paper presents an example of curriculum redesign for an undergraduate introductory computer science course (ICS) that sought to address issues of inequitable representation by centering student identities and redistributing power in favor of students. The authors draw upon critical sociocultural and the 4Es heuristic for disciplinary literacy to reimagine the ICS course as a space that centers on the important roles of identity and power in solving for diversity in computer science education. We highlight for researchers and practitioners how our work may be used to disrupt meritocratic practices that alienate minoritized and economically disadvantaged students and to expand definitions of mastery and expertise in computer science education. [ABSTRACT FROM AUTHOR]

The interaction between Sb and As is investigated by scanning tunneling microscopy of InAs (001) surfaces. Sb roughens the surface by increasing the coverage of divots (vacancy clusters) and two dimensional islands, which both possess a c(4×4) reconstruction. ab initio total energy calculations predict that the As-terminated b2(2×4) transforms into In-Sb heterodimer terminated c(4×4) configurations with increasing Sb chemical potential, which causes the roughening by pulling atoms from the terrace. Thus we propose an alternative model for interfacial broadening by intermixing rather than by surface segregation. [ABSTRACT FROM AUTHOR]

Droplet epitaxy (DE) has emerged as an alternative to Stranski-Krastanov (SK) as a method for epitaxial nanostructure formation. We find significant structural differences of similar sized nanostructures embedded in GaAs between the two methods. Atomic force microscopy and atom probe tomography measurements reveal that uncapped and capped SK structures resemble each other. However, the DE nanostructures appear as rings topographically but are quantum dots compositionally. A GaSb wetting layer is present regardless of the growth method and shares a nearly identical Sb concentration profile. DE nanostructures are shown to have a lower Sb concentration, and transmission electron microscopy measurements reveal that they produce less strain on the capping layer. Despite significant structural differences, SK and DE nanostructures exhibit the same photoluminescence response, suggesting that the emission is from a shared feature such as the wetting layer, rather than the nanostructures. [ABSTRACT FROM AUTHOR]

GaAsBi is of great interest for applications in high efficiency optoelectronic devices due to its highly tunable bandgap. However, the experimental growth of high Bi content films has proven difficult. Here, we model GaAsBi film growth using a kinetic Monte Carlo simulation that explicitly takes cation and anion reactions into account. The unique behavior of Bi droplets is explored, and a sharp decrease in Bi content upon Bi droplet formation is demonstrated. The high mobility of simulated Bi droplets on GaAsBi surfaces is shown to produce phase separated Ga-Bi droplets as well as depressions on the film surface. A phase diagram for a range of growth rates that predicts both Bi content and droplet formation is presented to guide the experimental growth of high Bi content GaAsBi films. [ABSTRACT FROM AUTHOR]

Bi incorporation in GaAs and GaSb has exhibited some promising properties allowing for potential new materials operating in the infrared regime. The growth of these materials has proven difficult, often leading to surfaces covered in droplets or nonuniformity in the composition. We propose a new kinetic model to capture the dynamics of incorporation and droplet formation in the growth of these alloys. The model accurately predicts trends found experimentally. Furthermore, the model shows that compositional nonuniformity arises due to a reduction in the incorporation rate of Bi caused by the nucleation of droplets. [ABSTRACT FROM AUTHOR]

The phase diagram of the Bi/GaSb surface reconstructions has been established using density functional theory and cluster expansion computational methods. The predominant reconstructions in the alloy system are the same as those found for pure GaSb. That is, the (4 ×3) family of reconstructions dominate the phase diagram. However, at low Sb and Bi chemical potentials, the calculations predict a (2 × 1) structure for both GaSb and Bi/GaSb. It is found that Bi does not stabilize any additional structures, and Bi does not readily incorporate into the surface in the presence of Sb. [ABSTRACT FROM AUTHOR]

The influence of using a Bi surfactant during the growth of InAsSb on the composition was examined, and it was found that increasing Bi flux on the surface during growth inhibits the incorporation of Sb. Analysis of the data via a kinetic model of anion incorporation shows that surface Bi acts as a catalyst for InAs formation, thus inhibiting Sb incorporation. [ABSTRACT FROM AUTHOR]

We present a kinetic model predicting anion incorporation in InAsSb. Included are the effects of As desorption, Sb segregation, and Sb displacement by As, any of which may be limited by the In flux if it is comparatively larger. The model captures experimental data over a range of growth conditions for the InAsSb system using activation energies for desorption and Sb segregation found in literature. The activation energy for Sb displacement found in this work is 1.3 eV. This model is general and should be valid for other mixed anion systems, or, appropriately modified, mixed cation systems and mixed anion/cation systems such as AlInAsSb. [ABSTRACT FROM AUTHOR]

Background: Demographic characteristics are known to influence participation in cocurricular activities. Less studied are the effects of other background characteristics. Purpose We hypothesize that considering college knowledge and students' proactive behaviors in tandem with demographics provides better models for predicting such participation. Method: We developed a questionnaire and administered it to 3,618 domestic third‐ and fourth‐year undergraduate engineering students at a large public R1 Midwestern university, yielding 860 responses. Logistic regression models predicting five types of cocurricular participation were constructed with demographic characteristics, college knowledge, and proactive behaviors in all combinations as predictors. Results: Four of five types of cocurricular participation were better modeled using factors beyond demographics. Two were better modeled using only proactive behavior as predictors and two were better modeled using demographics in combination with either college knowledge or proactive behavior. Only one type of participation could be best predicted by demographics alone. Conclusions: These findings contribute quantitative evidence establishing relationships between participation in engineering cocurricular activities and a wider range of factors than previously reported. Furthermore, they provide guidance for creating intervention programs because, unlike demographics, college knowledge and proactive behavior can be shaped by either the individual or the institution. [ABSTRACT FROM AUTHOR]

Thin GaAs films grown on lattice-matched In0.53Ga0.47As/InP(001) have been imaged by in vacuo scanning tunneling microscopy. We observe that the morphological evolution of these strained films depends on the deposition and diffusion of group III adatoms and the incorporation of As from the vapor, in addition to Asaro–Tiller–Grinfeld instabilities. We compare step edge densities to a model for the Ga adatom density and find that the absolute magnitude of the group V and group III fluxes has a strong effect on the number of adatoms on the surface and, thus, the morphology of the films. [ABSTRACT FROM AUTHOR]

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]

A feasible optical interconnect on a silicon complementary metal-oxide-semiconductor chip demands epitaxial growth and monolithic integration of diode lasers and optical detectors with guided wave components on a (001) Si wafer, with all the components preferably operating in the wavelength range of 1.3–1.55 \mu \textm at room temperature. It is also desirable for the fabrication technique to be relatively simple and reproducible. Techniques demonstrated in the past for having optically and electrically pumped GaAs- and InP-based lasers on silicon include wafer bonding, selective area epitaxy, epitaxy on tilted substrates, and use of quantum dot or planar buffer layers. Here, we present a novel monolithic optical interconnect on a (001) Si substrate consisting of a III-nitride dot-in-nanowire array edge emitting diode laser and guided wave photodiode, with a planar SiO2/Si3N4 dielectric waveguide in between. The active devices are realized with the same nanowire heterostructure by one-step epitaxy. The electronic properties of the InN dot-like nanostructures and mode confinement and propagation in the nanowire waveguides have been modeled. The laser, emitting at the desired wavelength of 1.3~\mu \textm , with threshold current ~350 mA for a device of dimension 50~\mu \mathrm m\times 2 mm, has been characterized in detail. The detector exhibits a responsivity ~0.1 A/W at 1.3 \mu \textm . Operation of the entire optical interconnect via the dielectric waveguide is demonstrated. [ABSTRACT FROM AUTHOR]

Compositional inhomogeneities in III-V alloys heavily influence the device performance. This work presents evidence for Ga droplets inducing inhomogeneities in the Bi composition, which we propose is due to a variation in the Ga flux across the surface. These inhomogeneities may be manipulated through the use of growth interrupts, which eliminate the buildup of Ga at the growth front. [ABSTRACT FROM AUTHOR]

The III-nitride nanowire heterostructure arrays with multiple InN disk light absorbing regions have been grown by plasma-assisted molecular beam epitaxy on (001)Si substrates, and guided wave photodiodes have been fabricated and characterized. The spectral photocurrent of the devices has been measured under reverse bias, and the data exhibit distinct shoulders in the range of 0.69-3.2 eV (0.39-1.8 μm). The estimated responsivity at a wavelength of 1.3 μm is 0.2 A/W. The nanowire photodiode response was also measured with an excitation at one facet provided by an edge-emitting laser fabricated with the same nanowire array and emitting at 1.3 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]

The small signal modulation characteristics of an InGaN/GaN nanowire array edge-emitting laser on (001) silicon are reported. The emission wavelength is 610 nm. Lattice matched InAlN cladding layers were incorporated in the laser heterostructure for better mode confinement. The suitability of the nanowire lasers for use in plastic fiber communication systems with direct modulation is demonstrated through their modulation bandwidth of f-3dB,max=3.1 GHz, very low values of chirp (0.8Å) and α-parameter, and large differential gain (3.1╳10-17 cm²). [ABSTRACT FROM AUTHOR]

The small signal modulation characteristics of an InGaN/GaN nanowire array edge-emitting laser on (001) silicon are reported. The emission wavelength is 610 nm. Lattice matched InAlN cladding layers were incorporated in the laser heterostructure for better mode confinement. The suitability of the nanowire lasers for use in plastic fiber communication systems with direct modulation is demonstrated through their modulation bandwidth of f_3dB,max = 3.1 GHz, very low values of chirp (0.8 A) and α-parameter, and large differential gain (3.1 x 10-17 cm²). [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]

Atom probe tomography and cross-sectional scanning tunneling microscopy show that GaSb/GaAs quantum dots disintegrate into ring-like clusters of islands upon capping. Band transition energies calculated using an 8-band k.p model of the capped dots with the observed dimensions are consistent with emission energies observed in photoluminescence data. These results emphasize the need for full three-dimensional characterization to develop an accurate understanding of the structure, and thus the optical properties, of buried quantum dots. [ABSTRACT FROM AUTHOR]

We experimentally investigate the nucleation behavior of metallic gallium droplets deposited on gallium arsenide substrates and calculate the critical cluster size for various growth conditions and substrate templating. We find that the critical cluster size for liquid Ga on GaAs is approximately six atoms. Deposition on substrates templated with arrays of holes does not result in significant ordering of the droplets at the array dimensions studied here, but does result in an apparent reduction of the critical cluster size due to heterogeneous nucleation. [ABSTRACT FROM AUTHOR]

BACKGROUND Prior research on the instructional use of screencasts (video of a computer screen output with realtime audio commentary) suggests that this technology is perceived by students as beneficial and results in improved course performance. PURPOSE This study explores how and why students use screencasts, as well as why some students choose not to use them. The study also investigates whether the perception that screencasts are helpful aligns with the reality of students' course performance. DESIGN/METHOD A quantitative study was conducted throughout two semesters in an undergraduate engineering survey course at a large public university. The investigation used a student perceptions survey and case study analysis to explore the connection between screencast use, the perception of having gained a deeper understanding of the course material based on this use, and actual course performance. RESULTS Findings indicate that students' preferred strategies for using screencasts are related to the frequency of use and the degree of understanding. Students who use the screencasts more and perceive them to have increased their understanding demonstrate increased competence on particular exam questions. Only those students who actively chose not to use screencasts (compared to those who forgot or ran out of time) show no detrimental effects on their performance. CONCLUSION Our findings highlight both the perceived and actual value of screencasting to students and the ways this technology is used. This research suggests that screencasting may promote self-efficacy among undergraduate engineering students. [ABSTRACT FROM AUTHOR]

Multilayer and single layer GaSb/GaAs(001) quantum dot structures were grown on an Sb-terminated (2 × 8) surface reconstruction and compared to those grown on an As-terminated (2 × 4) surface reconstruction. Uncapped quantum dots grown on the (2 × 8) surface were approximately 25% smaller in diameter and had a larger width/height aspect ratio. Quantum dots grown on both surfaces were defect free at the quantum dot/spacer layer interface. The dots did not appear to be fully compact when imaged by transmission electron microscopy, which may be due to dissolution and/or quantum ring formation. The quantum dot photoluminescence peak for dots grown on the (2 × 8) surface was brighter but at the same energy as that of dots grown on the (2 × 4) surface. This was likely the result of a higher areal density of dots on the (2 × 8) surface and a lower tendency for them to intermix during capping, resulting in dots of similar size for both samples after capping. Quantum dots grown on the (2 × 8) surface also displayed greater morphological stability when quenched in the absence of Sb. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Thin films of In0.81Ga0.19As/InP, grown by molecular beam epitaxy and imaged by in vacuo scanning tunneling microscopy, are observed to possess surfaces that consist of multiple reconstruction domains; small anisotropic regions of β2(2×4) in a matrix of a disordered (n×3) reconstruction. The shape and size distribution of these domains is consistent with anisotropic elastic relaxation at the domain boundaries. The boundary energy anisotropy varies with the growth temperature, indicating that the configurational entropy along the [110] direction is higher than for the [110]. [ABSTRACT FROM AUTHOR]

The effects of lattice mismatch strain and atomic size mismatch strain on surface reconstructions are analyzed using density functional theory. These calculations demonstrate the importance of an explicit treatment of alloying when calculating the energies of alloyed surface reconstructions. Lattice mismatch strain has little impact on surface dimer ordering for the α2(2×4) reconstruction of GaAs alloyed with In. However, atomic size mismatch strain induces the surface In atoms to preferentially alternate position, which, in turn, induces an alternating configuration of the surface anion dimers. These results agree well with experimental data for α2(2×4) domains in InGaAs/GaAs surfaces. [ABSTRACT FROM AUTHOR]

The electronic structure and thermal carrier capture and escape mechanisms are studied for GaSb/GaAs quantum dots with a type-II band alignment using admittance spectroscopy. Clear signatures are observed corresponding to confined quantum dot states with extracted activation energy of 0.337 eV and the thermal capture cross section in the range from 2.10 × 10-16 to 1.19 × 10-13 cm2. The thermal emission rates in the GaSb/GaAs quantum dots are significantly lower than prior reports for type-I systems, where optical emission is predicted to be the dominant process in an intermediate band solar cells under solar concentration. [ABSTRACT FROM AUTHOR]

In[sub 0.25]Ga[sub 0.75]As epilayers were grown on GaAs (001) substrates (1.8% misfit strain) by molecular beam epitaxy to investigate the two-dimensional to three-dimensional transition as a function of thickness (t≤30 MLs). Tapping-mode atomic force micrographs show the evolution of the morphology as a function of thickness. As the film is deposited, the nucleation of 3D islands followed by cooperative nucleation of pits is observed. As the thickness increases, both islands and pits continue to nucleate and grow until they coalesce, resulting in a fully formed ripple morphology running along the [11¯0]. The ripples also exhibit a secondary alignment roughly along the <310> which is attributed to the nucleation of islands with {136} faces. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Different modes of intermixing are observed in GaSb/GaAs layers via atom probe tomography. The intermixing length scale for quantum wells of varying thickness is on the order of a monolayer, but three times longer for the wetting layer of a quantum dot structure. The former arises from segregation of Sb and/or surface-induced intermixing via detachment from step edges. The latter is dominated by surface-induced intermixing due to disintegration of the GaSb dots upon capping. [ABSTRACT FROM AUTHOR]

Atomic force microscopy was used to investigate the effects of templating parameters on focused ion beam patterned single-, two-, and three-layer InAs/GaAs(001) quantum dot structures. The number of layers, focused ion beam dwell time, and pattern spacing affected the fidelity of the quantum dots. The highest single dot fidelities were found in regions with 1 and 3 ms dwell times and 1 and 2 μm pattern spacings. A two-layer region patterned with 1 ms dwell time and 1 μm spacing was found to have 100% single quantum dot fidelity with no off-site dot nucleation in a 20 × 20 μm2 scan. Holes that were milled with 6 and 9 ms dwell times and 0.25 μm spacing became faceted, that is, deep, tightly packed, and rhombic, by the third layer. Autocorrelation of the images was used to analyze the periodicity and size of the features. [ABSTRACT FROM AUTHOR]