RESUMO
In the emerging two-dimensional organic-inorganic hybrid perovskites, the electronic structures and carrier behaviors are strongly impacted by intrinsic electron-phonon interactions, which have received inadequate attention. In this study, we report an intriguing phenomenon of negative carrier diffusion induced by electron-phonon coupling in (2T)2PbI4. Theoretical calculations reveal that the electron-phonon coupling drives the band alignment in (2T)2PbI4 to alternate between type I and type II heterostructures. As a consequence, photoexcited holes undergo transitions between the organic ligands and inorganic layers, resulting in abnormal carrier transport behavior compared to other two-dimensional hybrid perovskites. These findings provide valuable insights into the role of electron-phonon coupling in shaping the band alignments and carrier behaviors in two-dimensional hybrid perovskites. They also open up exciting avenues for designing and fabricating functional semiconductor heterostructures with tailored properties.
RESUMO
The exceptional semiconducting properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) have made them highly promising for the development of future electronic and optoelectronic devices. Extensive studies of TMDs are partly associated with their ability to generate 2D-confined hot carriers above the conduction band edges, enabling potential applications that rely on such transient excited states. In this work, room-temperature spatiotemporal hot carrier dynamics in monolayer MoS2 is studied by transient absorption microscopy (TAM), featuring an initial ultrafast expansion followed by a rapid negative diffusion, and ultimately a slow long-term expansion of the band edge C-excitons. We provide direct experimental evidence to identify the abnormal negative diffusion process as a spatial contraction of the hot carriers resulting from spatial variation in the hot phonon bottleneck effect due to the Gaussian intensity distribution of the pump laser beam.
RESUMO
STUDY OBJECTIVE: Stroke mimics may be difficult distinguish from acute ischemic strokes and are often treated with alteplase though not by intent. We report the characteristics, frequency, and outcomes of stroke mimics treated at our institution. Using our data, we then explore how the inclusion of stroke mimics in stroke outcomes research may be an important source of bias. METHODS: We retrospectively identified all patients treated with alteplase in our emergency department from August 2013 to December 2017 for suspected acute ischemic stroke. We collected the following variables: gender, age, risk factors (hypertension, diabetes, and atrial fibrillation), admission glucose, admission National Institute of Health Stroke Scale, admission mean arterial pressure, onset-to-treatment time, adverse events, discharge diagnosis, length of stay, discharge NIHSS, discharge destination, and 3 month modified Rankin score. RESULTS: One hundred and eighteen patients were treated with alteplase for suspected acute ischemic stroke of which 33 (27.9%) were stroke mimics. Compared to ischemic strokes, stroke mimics were younger (median age 53 versus 69; P < .0003); were less likely to have vascular risk factors (hypertension [51.5% versus 78.8%; P < .005] diabetes (9.1% versus 32.9%; P < .007), and atrial fibrillation (3.0% versus 23.5%; P < .006). The most common stroke mimic was transient ischemic attack (33.3%). Stroke mimics were significantly more likely to be discharged home (75.8% versus 41.2%; P < .002). Outcomes unadjusted for stroke mimics led to artificial inflation of a favorable discharge destination. CONCLUSIONS: Inclusion of stroke mimics led to an artificial inflation of a favorable discharge destination for our entire cohort. Our study highlights the potential for bias in reporting favorable outcomes if appropriate adjustment accounting for stroke mimics does not occur.