Direct Observation of Node-to-Node Communication in Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks (ZIFs) with open-shell transition metal nodes represent a promising class of highly ordered light harvesting antennas for photoenergy applications. However, their charge transport properties within the framework, the key criterion to achieve efficient photoenergy conversion, are not yet explored. Herein, we report the first direct evidence of a charge transport pathway through node-to-node communication in both ground state and excited state ZIFs using the combination of paramagnetic susceptibility measurements and time-resolved optical and X-ray absorption spectroscopy. These findings provide unprecedented new insights into the photoactivity and charge transport nature of ZIF frameworks, paving the way for their novel application as light harvesting arrays in diverse photoenergy conversion devices

Design and Fabrication of a Self-Calibrating Germanium Photodiode for Radiometric Applications

This work is concerned with the design and fabrication of an absolute radiometric detector operated over the 0.7 to 1.5 μm wavelength range. This application requires a semiconductor photodiode with high internal quantum efficiency and long term stability. Of many possible materials, germanium is chosen because high quality material is available, the fabrication processes are relatively straight forward, and a high quantum efficiency is achievable. The fabrication procedures for a germanium cell were developed. Two types of germanium photodiodes were fabricated and tested. In both photodiodes, a channel stop has been employed to reduce the lateral current due to surface inversion. Ion implantation is used to form the n+-p junction, the channel stop and the back surface field. To reduce the surface recombination, CVD Si02 was deposited for surface passivation. A Ti/Pd/Ag metal layer was then sputtered to make the interconnections. With this process, dark current as low as 0.35 mA/cm2 has been observed on a 2 Ω -cm substrate. The n+pp+ photodiodes had a considerably low quantum efficiency than the induced junction photodiodes. It is shown by computer simulation that the internal quantum efficiency, η, of an n+pp+ diode is strongly affected by the carrier lifetime, r, in the emitter and the surface recombination velocity, S, at the SiO2-Ge surface. The high quantum efficiency in the induced junction diodes can be attributed to the absence of implantation induced damage in the emitter, and an electric field near the surface, induced by the fixed charges of the SiO2 layer. With the induced junction structure, we have observed an internal quantum efficiency of 98.8% at 0.7 μm and of 97% at 1.5 μm

Robust Scaling of Strength and Elastic Constants and Universal Cooperativity in Disordered Colloidal Micropillars

We study the uniaxial compressive behavior of disordered colloidal free-standing micropillars composed of a bidisperse mixture of 3- and 6-μm polystyrene particles. Mechanical annealing of confined pillars enables variation of the packing fraction across the phase space of colloidal glasses. The measured normalized strengths and elastic moduli of the annealed freestanding micropillars span almost three orders of magnitude despite similar plastic morphology governed by shear banding. We measure a robust correlation between ultimate strengths and elastic constants that is invariant to relative humidity, implying a critical strain of ∼0.01 that is strikingly similar to that observed in metallic glasses (MGs) [Johnson WL, Samwer K (2005) Phys Rev Lett 95:195501] and suggestive of a universal mode of cooperative plastic deformation. We estimate the characteristic strain of the underlying cooperative plastic event by considering the energy necessary to create an Eshelby-like ellipsoidal inclusion in an elastic matrix. We find that the characteristic strain is similar to that found in experiments and simulations of other disordered solids with distinct bonding and particle sizes, suggesting a universal criterion for the elastic to plastic transition in glassy materials with the capacity for finite plastic flow

EUS-guided portal pressure gradient measurement with a simple novel device: a human pilot study.

Background and aimsPortal hypertension is a serious adverse event of liver cirrhosis. Recently, we developed a simple novel technique for EUS-guided portal pressure gradient (PPG) measurement (PPGM). Our animal studies showed excellent correlation between EUS-PPGM and interventional radiology-acquired PPGM. In this video we demonstrate the results of the first human pilot study of EUS-PPGM in patients with liver disease.MethodsEUS-PPGM was performed by experienced endosonographers using a linear echoendoscope, a 25-gauge FNA needle, and a novel compact manometer. The portal vein and hepatic vein (or inferior vena cava) were targeted by use of a transgastric or transduodenal approach. Feasibility was defined as successful PPGM in each patient. Safety was based on adverse events captured in a postprocedural interview.ResultsTwenty-eight patients underwent EUS-PPGM with 100% technical success and no adverse events. PPG ranged from 1.5 to 19 mm Hg and had excellent correlation with clinical parameters of portal hypertension, including the presence of varices (P = .0002), PH gastropathy (P = .007), and thrombocytopenia (P = .036).ConclusionThis novel technique of EUS-PPGM using a 25-gauge needle and compact manometer is feasible and appears safe. Given the availability of EUS and the simplicity of the manometry setup, EUS-guided PPG may represent a promising breakthrough for procuring indispensable information in the management of patients with liver disease