Melt-Processed Halide Perovskite Thin Films from a Two-Dimensional Ruddlesden-Popper Phase Precursor.

While halide perovskite thin films have enormous potential for photovoltaics and other optoelectronics, the use of environmentally hazardous solvents during their deposition and processing poses a barrier to their commercialization. In this work, we demonstrated the deposition of melt-processable precursors and subsequent transformation into halide perovskite thin films without using environmentally hazardous solvents. We melted the wide-bandgap layered perovskites [(C6H5CH(CH3)CH2NH3)2PbI4:ß-Me-PEA2PbI4] at ∼210 °C and blade coated them into films. The ß-Me-PEA2PbI4 films were subsequently transformed to perovskite-phase methylammonium or formamidinium lead iodide films using a cation-exchange process in an alcohol-based solvent. Lastly, we demonstrate the potential and limitations of a completely solvent-free approach that uses solid-state transformation of a ß-Me-PEA2PbI4 film. This work represents a substantial step toward eliminating environmentally hazardous solvents and enables inexpensive industrial-scale liquid-phase deposition processes that do not require expensive systems for handling and disposing of environmentally hazardous solvents.

Transport Properties of Methyl-Terminated Germanane Microcrystallites.

Germanane is a two-dimensional material consisting of stacks of atomically thin germanium sheets. It's easy and low-cost synthesis holds promise for the development of atomic-scale devices. However, to become an electronic-grade material, high-quality layered crystals with good chemical purity and stability are needed. To this end, we studied the electrical transport of annealed methyl-terminated germanane microcrystallites in both high vacuum and ultrahigh vacuum. Scanning electron microscopy of crystallites revealed two types of behavior which arise from the difference in the crystallite chemistry. While some crystallites are hydrated and oxidized, preventing the formation of good electrical contact, the four-point resistance of oxygen-free crystallites was measured with multiple tips scanning tunneling microscopy, yielding a bulk transport with resistivity smaller than 1 Ω·cm. When normalized by the crystallite thickness, the resistance compares well with the resistance of hydrogen-passivated germanane flakes found in the literature. Along with the high purity of the crystallites, a thermal stability of the resistance at 280 °C makes methyl-terminated germanane suitable for complementary metal oxide semiconductor back-end-of-line processes.

Anisotropic Disorder and Thermal Stability of Silicane.

Atomically thin silicon nanosheets (SiNSs), such as silicane, have potential for next-generation computing paradigms, such as integrated photonics, owing to their efficient photoluminescence emission and complementary-metal-oxide-semiconductor (CMOS) compatibility. To be considered as a viable material for next-generation photonics, the SiNSs must retain their structural and optical properties at operating temperatures. However, the intersheet disorder of SiNSs and their nanoscale structure makes structural characterization difficult. Here, we use synchrotron X-ray diffraction and atomic pair distribution function (PDF) analysis to characterize the anisotropic disorder within SiNSs, demonstrating they exhibit disorder within the intersheet spacing, but have little translational or rotational disorder among adjacent SiNSs. Furthermore, we identify changes in their structural, chemical, and optical properties after being heated in an inert atmosphere up to 475 °C. We characterized changes of the annealed SiNSs using synchrotron-based total X-ray scattering, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, electron paramagnetic resonance, absorbance, photoluminescence, and excited-state lifetime. We find that the silicon framework is robust, with an onset of amorphization at ∼300 °C, which is well above the required operating temperatures of photonic devices. Above ∼300 °C, we demonstrate that the SiNSs begin to coalesce while keeping their translational alignment to yield amorphous silicon nanosheets. In addition, our DFT results provide information on the structure, energetics, band structures, and vibrational properties of 11 distinct oxygen-containing SiNSs. Overall, these results provide critical information for the implementation of atomically thin silicon nanosheets in next-generation CMOS-compatible integrated photonic devices.

Synthesis of germanium nanocrystals from solid-state disproportionation of a chloride-derived germania glass.

Germanium nanocrystals (Ge NCs) have potential to be used in several optoelectronic applications such as photodetectors and light-emitting diodes. Here, we report a solid-state route to synthesizing Ge NCs through thermal disproportionation of a germania (GeOX) glass, which was synthesized by hydrolyzing a GeCl2·dioxane complex. The GeOX glass synthesized in this manner was found to have residual Cl content. The process of nanocrystal nucleation and growth was monitored using powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Compared to existing solid-state routes for synthesizing colloidal Ge NCs, this approach requires fewer steps and is amenable to scaling to large-scale reactions.

Solution-Processed Bismuth Halide Perovskite Thin Films: Influence of Deposition Conditions and A-Site Alloying on Morphology and Optical Properties.

Bismuth-based halide perovskites have been proposed as a potential nontoxic alternative to lead halide perovskites; however, they have not realized suitable performance. Their poor performance has been attributed to substandard film morphologies and too wide of a band gap for many applications. Herein we used a two-step deposition procedure to convert BiI3 thin films into A3Bi2I9 (A = FA+, MA+, Cs+, or Rb+), which resulted in a substantial improvement in film morphology, a larger band gap, and greater compositional tunability compared toresults when using aconventional single-step deposition technique. Additionally, we attempted to reduce the undesirably wide band gap in Rb3Bi2I9 thin films by inducing chemical pressures through cation-size mismatch, with an underlying hypothesis that cation-size mismatch could induce compressive strain within the 2D Rb3Bi2I9 lattice. However, we found that all A xRb3- xBi2I9 compositions with x > 0 adopted the 0D structure, and no changes to the band gap were observed with alloy. These results imply that the band gap of A xRb3- xBi2I9 is insensitive to A-site alloying.

Laparoscopic procurement model for living donor liver transplantation.

BACKGROUND/AIMS: Noting the contribution to renal transplantation by the introduction of the laparoscopic approach to donor nephrectomy, we investigated the possibility of performing a laparoscopic hepatic lobe procurement with the goal of performing a live donor liver transplantation. We describe our technique and determine its feasibility for such a goal. METHODS: The surgical technique was developed over a series of 12 adult female pigs and adapted in two human cadavers. The technique included pneumoperitoneum with CO2, mobilization of the liver, and transection of the parenchyma into right and left lobes with a laparoscopic cavitron ultrasonic aspirator. The vascular inflow and outflow structures (hepatic artery, portal vein, hepatic veins) of the anatomical specimen being procured were preserved undisturbed during the hepatic transection. No temporary vascular occlusion techniques were utilized. The vascular structures were stapled and sectioned just prior to removal of the specimen. RESULTS: Hepatic lobectomies were successfully performed laparoscopically. Vascular and biliary structures were preserved to allow for subsequent transplantation. Operative time from establishment of pneumoperitoneum to lobe procurement was under 4 h. CONCLUSIONS: This study demonstrates the feasibility of laparoscopic living donor procurement for liver transplantation, from both a technical and a physiological perspective.