Graphitization of a polymer layer provides a convenient route to synthesize nanocrystalline graphene on dielectric surfaces. The transparent and conducting wafer scale material is of interest as a membrane and a coating, and for the generation and detection of light, or strain sensing. In this work, we study the formation of nanocrystalline graphene on germanium, a surface which promotes the CVD synthesis of monocrystalline graphene. The surprising result that we obtained through graphitization is the formation of cavities in germanium, over which nanocrystalline graphene is suspended. Depending on the crystallographic orientation of the germanium surface, either trenches in (110)-Ge or pits in (111)-Ge are formed, and their dimensions depend on the graphitization temperature. Using Raman spatial imaging, we can show that nanocrystalline graphene is formed across the entire wafer in spite of the cavity formation. Interestingly, the Raman intensity is suppressed when the material is supported by germanium and is enhanced when the material is suspended. Through simulations, we can show that these effects are induced by the high refractive index of germanium and by interferences of the light field depending on the spacing between graphene and germanium. Using atomic force and scanning electron microscopy, we determined that ripples in the suspended material are induced by the mismatch of thermal expansion coefficients. Our results provide a new route to lithography-free fabrication of suspended membranes.
In this study, to elucidate origin of inductance and its relation to the phenomenon of hysteresis in hybrid perovskite solar cells (PSCs), two electron transport layer (ETL) structures are utilized:...
Chemicals and materials with essential and functional
uses are
central to economic and social well-being. However, the development
and application of such items may be challenged when sustainability
factors are considered. These are further challenged by disciplinary
gaps and concerns over reproducible and responsible research. Here,
we detail a checklist for early career researchers on how “to
do” research on chemicals, materials, processes, and products
in a manner that is safe and sustainable by design. The checklist
contains 20 items that are organized into five interconnected sections:
(1) think broad and big, (2) set a clear research foundation, (3)
focus on quality and reproducibility, (4) flag safe and sustainability
issues, and (5) communicate, listen, and learn. Each item can be self-scored
on 0–3 scale. This checklist is meant to be a fast tool to
help researchers better “think and do” things so that
outcomes and outputs may help address societal grand challenges.
Ever since their dawn in 2009 1, hybrid organic–inorganic perovskite materials have been experiencing an ever increase in research investment to finally emerge as a strong alternative for high power conversion efficiency (PCE) photovoltaic devices at low costs. One of the main challenges that is currently impeding the upscaling of these solar cells is the phenomenon of hysteresis on their j–V response that has been correlated with slow ion migration which, in turn, affects their photovoltaic properties. Although hysteresis has been described to some extent of detail, the precise role of the external contacts remains under debate. Furthermore, there has been a great deal of focus on materials and interface design while less attention has been given to optical aspects of these cells. Our work highlights the role of electron transport layer (ETL) of different compositions and synthesized through various routes on the hysteresis response of these systems. We show that there’s a clear correlation between thickness, morphology and composition of the ETL on the photovoltaic response these systems. To better elucidate such a response, we have utilized photoluminescence, electroluminescence, absorption and kelvin probe force microscopy to get a substantial grasp of the optoelectronic phenomena occurring at the interfaces in perovskite solar cells.
Acknowledgments: This research was supported by a Hydro-Quebec/NSERC CRD grant and the McGill Sustainability Systems Initiative (MSSI).
1- Kojima, A., Teshima, K., Shirai, Y. and Miyasaka, T., 2009. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. Journal of the American Chemical Society, 131(17), pp.6050-6051.
The role of reflection and self-regulation in academic performance was tested using the "Exam Wrapper" strategy with a writing assignment for a technical elective course. The technical writing assignment involved the creation of a detailed outline for a technical report. This outline was submitted for grading and feedback before a subsequent extended technical report assignment. The outline was graded by the course teaching assistant, following a detailed grading rubric.
After receiving the grade and feedback, students could resubmit a revised outline for re-grading, and include a reflection on the circumstances of their performance. Using the grading rubric, the resubmission was graded by the course instructor. A second graduate student evaluated the student reflection quality, and the resubmission quality.
The effect of the self-reflection quality on re-submitted assignment improvement was assessed. The average grade improvement for students who resubmitted a reflection was +15.1 % (n=16), and for students who resubmitted without a reflection was +6.3 % (n=3). The difference between the average resubmitted and first submission grades positively correlated with reflection quality. These results suggest that a reflection exercise associated with a resubmission has potential to improve student technical writing quality.
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