Low electron-polar optical phonon scattering as a fundamental aspect of carrier mobility in methylammonium lead halide CH3NH3PbI3 perovskites.

High carrier mobility is often invoked to justify the exceptionally long diffusion length in CH3NH3PbI3 perovskites. Using a combination of an ab initio band structure and scattering models, we present clear evidence that large electrical and Hall mobilities are crucially related to the low scattering rate of carriers with polar optical phonons, which represents the dominant mobility-limiting mechanism at room temperature. With a charge-injection regime at room temperature, we obtained carrier relaxation times (τrel) of ∼10 fs, which are typical of polar inorganic semiconductors, and electrical mobilities (µ) as high as ∼60 cm(2) V(-1) s(-1) and 40 cm(2) V(-1) s(-1) for electrons and holes, respectively, which were robustly independent on the injected carrier density in the range of n ∼ 10(14) cm(-3) to 10(20) cm(-3). In the absence of a significant concentration of trapping centers, these mobilities foster diffusion lengths of ∼10 µm for the low injection density regime (n ∼ 10(15) cm(-3)), which are in agreement with recent measurements for highly pure single-crystal perovskites.

Temperature Evolution of Methylammonium Trihalide Vibrations at the Atomic Scale.

The temperature evolution of vibrations of CH3NH3PbI3 (MAPI) is studied by combining first principles and classical molecular dynamics and compared to available experimental data. The work has a fundamental character showing that it is possible to reproduce the key features of the vibrational spectrum by the simple physical quantities included in the classical model, namely the ionic-dispersive hybrid interactions and the mass difference between organic and inorganic components. The dynamics reveals a sizable temperature evolution of the MAPI spectrum along with the orthorhombic-to-tetragonal-to-cubic transformation and a strong dependence on molecular confinement and order. The thermally induced weakening of the H-I interactions and the anharmonic mixing of modes give two vibrational peaks at 200-250 cm(-1) that are not present at zero temperature and are expected to have detectable infrared activity. The infrared inactive vibrational peak at ∼140 cm(-1) due to molecular spinning disappears abruptly at the orthorhombic-to-tetragonal transition and forms a broad molecular band red-shifting progressively with temperature. This trend is correlated to the reduced confinement of the rotating cations due to thermal expansion of the lattice.

The study of polythiophene/water interfaces by sum-frequency generation spectroscopy and molecular dynamics simulations.

Semiconducting polymer/water interfaces are gaining increasing attention due to a variety of promising applications in the fields of biology and electrochemistry, such as electrochemically-gated transistors and photodetectors, which have been used for biosensing and neuroscience applications. However, a detailed characterization of the polymer surface in the presence of an aqueous environment is still lacking. In this work, we employed sum-frequency generation vibrational spectroscopy, a surface-specific technique compatible with electrochemical/biological conditions, to demonstrate that the surface of thin films of regio-regular poly-3-hexylthiophene (rr-P3HT) undergoes a molecular reorientation when exposed to aqueous electrolytes, with respect to their surface structure in air. Experimental results are corroborated by molecular dynamics simulations. Since surface molecular orientation is believed to play a fundamental role in electrochemical and environmental stability of conjugated polymers, the reported findings not only contribute to the fundamental understanding of conjugated polymer/water interfaces, but they may also have implications in the design of conjugated polymers for enhancing their performance in electrolytic environments.

A pelvic retroperitoneal Schwannoma presenting as an adnexal mass.

Solitary nerve sheath tumors such as benign schwannomas arising in the pelvic retroperitoneum are infrequently reported. We report a case of a benign retroperitoneal pelvic schwannoma that presented with pelvic pain and an adnexal mass. Complete surgical excision was achieved only after transection of the S1 nerve root on the left side. The adjacent vascular and urinary channels sustained no injuries and the patient had minimal neurologic deficit.

Missile injuries to the brain treated by simple wound closure: results of a protocol during the Lebanese conflict.

This is a prospective study of the treatment of penetrating missile injuries to the brain without intracranial surgery carried out at the American University of Beirut Medical Center between 1981 and 1988. Of 600 patients treated for missile injuries to the head, 32 satisfied the study criteria. There were 27 shrapnel and 5 bullet injuries. The mean patient age was 23 years (range, 3-51 years). Twenty patients had intracranial indriven bone fragments. Six patients had exposed brain tissue. The mean follow-up was 3.5 years (range, 1-7.5 years). The superficial entry wound was debrided and closed without drainage in the Emergency Room within a mean of 3 hours (range, 0.5-6 hours), and the patient received methicillin for 14 days. All patients survived and had no or improved neurological deficits. No leakage of the cerebrospinal fluid, infection, or seizures occurred in 31 patients. One patient with indriven bone fragments had leakage of the cerebrospinal fluid and developed seizures and a brain abscess 20 days after the injury. The management of penetrating missile injuries to the brain without intracranial surgery in a select patient population is a reasonable option. This treatment becomes important for a surgeon facing large numbers of casualties, or when operative personnel or resources are limited or unavailable.

Intensive care of head-injured patients.

The intensive care and monitoring of patients with head injury is essentially the same among patients with mass lesions requiring surgery and those with no mass lesions. The surgical procedure should be looked upon as an adjuvant therapy to lower a rising intracranial pressure due to an expanding hematoma, macerated or infarcted brain. Apart form this all patients will have the same medical management and ICP recording will determine the extent of such therapy.