Dynamics of Carriers and Photoinjected Currents in Carbon Nanotubes and Graphene
Bibliographic record
Abstract
This thesis reports results from the investigation of optically-induced carrier dynamics in graphite and graphitic carbon nanostructures. In this first set of experiments, the dynamics of photo-excited carriers in exfoliated graphene and thin graphitic films are studied by optical pump-probe spectroscopy. Samples ranging in thickness from 1 to 260 carbon layers are deposited onto an oxidized silicon substrate. Time-resolved reflectivity and transmissivity are measured at 1300 nm, following excitation by 150 fs, 800 nm pump pulses at room temperature. Two time scales are identified over which the extracted transient dielectric function returns to its quiescent value. A fast decay time of ~200 fs in graphene is associated with hot phonon emission and increases to ~300 fs for thicknesses greater than only a few carbon layers. The slow decay time, associated with hot phonon interaction and/or carrier recombination, increases more gradually, from ~2.5 to 5 ps over ~30 layers. A simple model suggests the thickness dependence of the slow decay time is likely a result of thermal diffusion into the substrate. In the second set of experiments, coherently-controlled two-colour injection photocurrents are generated via quantum interference of single- and two-photon absorption in bulk graphite and a variety of single-walled carbon nanotube samples, such as a CVD-grown aligned forest of nanotubes (tube diameter dt = 2.5 ± 1.5 nm), and both arc discharge (dt = 1.44 ± 0.15 nm) and HiPco (dt = 0.96 ± 0.14 nm) nanotube films separated by electronic type (metallic vs. semiconducting). At pump wavelengths of 1500 and 750 nm, the emitted terahertz radiation is used to estimate a peak current density of ~12 kA/cm² in graphite and a peak current of ~8 nA per nanotube. From the dependence of the injected current on pump polarization, the relative values of the current injection tensor elements are measured, and information is gained on the alignment and birefringence of the nanotube samples. The dependence of the injected current on pump wavelength implies that the currents are likely based on band-band electronic transitions and not on excitonic effects, which govern most linear optical processes.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".