FES Funded ProjectsOutputs
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Terahertz photoconductivity of germanium inverse opal structuresT12-Z01 | Activity | 2018-06-21 | Mary Narreto, Frank Hegmann, "Giebel, M.", "Fassler, T.", "Amer, N." | Photoluminescence dynamics of functionalized two-dimensional silicon nanosheetsT12-Z01 | Activity | 2018-06-21 | Mary Narreto, "Lyuleeva, A.", "Helbich, T.", Jonathan G C Veinot, "Rieger, R.", Frank Hegmann | Time-resolved Terahertz Spectroscopy of Inverse Opal Ge FilmsT12-Z01 | Activity | 2018-05-28 | Mary Narreto, "Giebel, M.", "Amer, N.", "Fassler, T.", Frank Hegmann | Topology-Based Prediction of Pathway Dysregulation Induced by Intense Terahertz Pulses in Human Skin Tissue ModelsT12-Z01 | Publication | 2018-06-01 | David Purschke, C M Hough,, "Huang, C.", L V Titova,, "Kovalchuk, O.", B J Warkentin,, Frank Hegmann | Modulated Photoluminescence of Germanium via Intense Terahertz Electric Fields T12-Z01 | Activity | 2018-06-01 | Mary Narreto, "Huang, C.", David Purschke, Frank Hegmann | Ultrafast photoconductivity and terahertz vibrational dynamics in double helix SnIP nanowiresT06-Z01, T12-Z01 | Publication | 2021-03-10 | David Purschke, M R Pielmeier, "E. Uzer", "C. Ott", "A. Vogel", Charles Jensen, "A. Degg", "N. Amer", "T. Nilges", Frank Hegmann | Photocatalytic mechanism control and study of carrier dynamics in CdS@C3N5 core-shell nanowiresWe present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low bandgap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, FDTD simulations, time-resolved terahertz spectroscopy (TRTS) and photoconductivity measurements. TRTS indicated high carrier mobilities > 450 cm2Vs-1 and carrier relaxation times > 60 ps for CdS-MHP while CdS-MHPINS exhibited much lower mobilities < 150 cm2Vs-1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J-V characteristics of CdS NWs disappeared in CdS-MHP confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low bandgap can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core-shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis. T12-P02, T12-P03, T06-Z01, T12-Z01 University of Alberta | Publication | 2021-04-30 | Kazi Alam, Charles Jensen, Pawan Kumar, Riley Hooper, Guy Bernard, "A. Patidar ", Ajay Manuel, "N. Amer ", "A. Palmgren ", Narendra Chaulagain, David Purschke, John Garcia, "P. Kirwin ", "L. Shoute ", "K. Cui ", "S. Gusarov ", "A. Kobryn ", Vladimir K Michaelis, Frank Hegmann, Shankar, K. | Intense terahertz pulses inhibit ras signaling and other cancer-associated signaling pathways in human skin tissue modelsT06-Z01, T12-Z01 | Publication | 2021-03-30 | C M Hough, David Purschke, "C. Huang", "L.V.Titova", "O. Kovalchuk", "B.J.Warkentin", Frank Hegmann | Picosecond Photoconductivity and Vibrational Mode Screening in Double-Helix SnIPT12-Z01 | Activity | 2020-11-12 | David Purschke, M R Pielmeier, "E. Uzer", "C. Ott", "A. Vogel", Charles Jensen, "A. Degg", "N. Amer", "T. Nilges", Frank Hegmann | Ultrafast Carrier Dynamics of CdS Nanowires Wrapped In C3N5 NanosheetsT12-P02, T06-Z01, T12-Z01 University of Alberta | Activity | 2020-11-13 | Charles Jensen, Kazi Alam, "A. Palmgren ", David Purschke, "N. Amer ", Shankar, K., Frank Hegmann | Genomic Signature of Membrane Permeation Induced By Intense THz PulseszT12-Z01 | Activity | 2020-11-13 | C M Hough, David Purschke, "C. Huang", L V Titova, "O. Kovalchuck", B J Warkentin, Frank Hegmann | Characterization of THz-Induces Bias Voltage Modulation In An STMT12-Z01 | Activity | 2020-11-12 | Howe Simpson, Frank Hegmann, "Y. Luo", "J.M.Calzada", "G.Chen", "P. Nguyen", "V.Jelic", "R.Liu", "D. Mildenberger" | C3N4 and C3N5 Nanosheets As Passivation Layers and Carrier Extractors for Inorganic Semiconductor Nanowires and Quantum DotsInorganic semiconductor nanowires and quantum dots made of chalcogenides, III-V semiconductors and halide perovskites offer exciting potential for optoelectronic devices. The orthogonalization possible in nanowires between the normally competing processes of charge generation and charge separation have been used to project very high operating performance exceeding that of thin films and single crystals in light harvesting devices such as solar cells, photodetectors, photocatalysts and photoelectrolyzers. Likewise, inorganic quantum dots with size-tunable absorption and emission spectra are excellent candidates for light emitting devices as well as light harvesting devices. However, the practical performance of inorganic nanowire based optoelectronic devices has significantly lagged theoretical predictions. A major reason for the discrepancy between theory and experiment is the presence of surface traps and defects in nanowires and quantum dots, which exhibit a large surface area to volume ratio. Several chemical treatments and annealing regimens have been employed to heal surface defects in nanowires and quantum dots. One popular strategy involves wrapping nanowires and/or quantum dots with a thin coating of a molecular monolayer (e.g. alkanethiols) or an atomic layer deposited conformal oxide. While such core-shell architectures are frequently effective in reducing surface defects, the surface passivation is invariably accompanied by a deterioration in optoelectronic properties due to the difficulty experienced by charge carriers in tunneling through the thin shell layer. The resulting trade-off between surface passivation and carrier extraction limits performance improvements in light harvesting devices. Thus there is a strong need for passivating layers that do not negatively impact carrier extraction.
Herein, we show that graphitic carbon nitride coatings are highly effective in passivating the surfaces of inorganic nanowires and quantum dots while preserving excellent carrier transport and extraction. Three illustrative examples are provided together with in-depth spectroscopic and electrical characterization:
(1) Cesium lead bromide (CsPbBr3) quantum dots passivated by g-C3N4 nanosheets and performing spectacularly as CO2 photoreduction catalysts and water-splitting photoanodes
(2) The double helical ternary semiconductor SnIP passivated by g-C3N4 nanosheets which experienced a remarkable improvement in photoelectrochemical performance
(3) Cadmium sulfide (CdS) nanowires passivated by C3N5 nanosheets resulting in a superior photocatalytic performanceT12-P02 University of Alberta | Activity | 2022-07-01 | Kazi Alam, Pawan Kumar, Devika Laishram, Charles Jensen, Annabelle Degg, Narendra Chaulagain, Frank Hegmann, Tom Nilges, Rakesh Sharma, Shankar, K. |
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