Role of Hydrogen Bonding on Transport of Coadsorbed Gases in Metal-Organic Frameworks Materials.

Coadsorption of multicomponents in metal-organic framework (MOF) materials can lead to a number of cooperative effects, such as modification of adsorption sites or during transport. In this work, we explore the incorporation of NH3 and H2O into MOFs preloaded with small molecules such as CO, CO2, and SO2. We find that NH3 (or H2O) first displaces a certain amount of preadsorbed molecules in the outer portion of MOF crystallites, and then substantially hinders diffusion. Combining in situ spectroscopy with first-principles calculations, we show that hydrogen bonding between NH3 (or H2O) is responsible for an increase of a factor of 7 and 8 in diffusion barrier of CO and CO2 through the MOF channels. Understanding such cooperative effects is important for designing new strategies to enhance adsorption in nanoporous materials.

Efficacy and safety of memantine in children with autism spectrum disorder: Results from three phase 2 multicenter studies.

Three phase 2 trials were conducted to assess the efficacy and long-term safety of weight-based memantine extended release (ER) treatment in children with autism spectrum disorder. MEM-MD-91, a 50-week open-label trial, identified memantine extended-release treatment responders for enrollment into MEM-MD-68, a 12-week randomized, double-blind, placebo-controlled withdrawal trial. MEM-MD-69 was an open-label extension trial in which participants from MEM-MD-68, MEM-MD-91, and open-label trial MEM-MD-67 were treated ⩽48 weeks with memantine extended release. In MEM-MD-91, 517 (59.6%) participants were confirmed Social Responsiveness Scale responders at week 12; mean Social Responsiveness Scale total raw scores improved two to three times a minimal clinically important difference of 10 points. In MEM-MD-68, there was no difference between memantine and placebo on the primary efficacy parameter, the proportion of patients with a loss of therapeutic response (defined as ⩾10-point increase from baseline in Social Responsiveness Scale total raw score). MEM-MD-69 exploratory analyses revealed mean standard deviation improvement in Social Responsiveness Scale total raw score of 32.4 (26.4) from baseline of the first lead-in study. No new safety concerns were evident. While the a priori-defined efficacy results of the double-blind trial were not achieved, the considerable improvements in mean Social Responsiveness Scale scores from baseline in the open-label trials were presumed to be clinically important.

Selective Growth of Interface Layers from Reactions of Sc(MeCp)2(Me2pz) with Oxide Substrates.

The transformation of an oxide substrate by its reaction with a chemical precursor during atomic layer deposition (ALD) has not attracted much attention, as films are typically deposited on top of the oxide substrate. However, any modification to the substrate surface can impact the electrical and optical properties of the device. We demonstrate herein the ability of a precursor to react deep within an oxide substrate to form an interfacial layer that is distinct from both the substrate and deposited film. This phenomenon is studied using a scandium precursor, Sc(MeCp)2(Me2pz) (1, MeCp = methylcyclopentadienyl, Me2pz = 3,5-dimethylpyrazolate), and five oxide substrates (SiO2, ZnO, Al2O3, TiO2, and HfO2). In situ Fourier transform infrared (FTIR) spectroscopy shows that at moderate temperatures (∼150 °C) the pyrazolate group of 1 reacts with the surface hydroxyl groups of OH-terminated SiO2 substrates. However, at slightly higher temperatures (≥225 °C) typically used for the ALD of Sc2O3, there is a direct reaction between 1 and the SiO2 layer, in addition to chemisorption at the surface hydroxyl groups. This reaction is sustained by sequential exposures of 1 until an ∼2 nm thick passivating interface layer is formed, indicating that 1 reacts with oxygen derived from SiO2. A shift of the Si 2p core level position, measured by ex situ X-ray photoelectron spectroscopy, is consistent with the formation of a ScSi xO y layer. Similar observations are made following the exposure of a ZnO substrate to 1 at 275 °C. In contrast, Al2O3, TiO2, and HfO2 substrates remain resistant to reaction with 1 under similar conditions, except for a surface reaction occurring in the case of TiO2. These striking observations are attributed to the differences in the electrochemical potentials of the elements comprising the oxide substrates to that of scandium. Precursor 1 can react with SiO2 or ZnO substrates, since the constituent elements of these oxides have less-negative electrochemical potentials than do aluminum, titanium, and hafnium. Additionally, Sc2O3 and surface carbonates are deposited on all substrates by gas-phase reactions between 1 and residual water vapor in the reactor. The extent of gas-phase reactions contributing to film growth is governed by the relative pressure of water vapor in the presence of 1. These results suggest caution when using very reactive, oxophilic precursors such as 1 to avoid misinterpreting unconventional film deposition as that resulting from a standard ALD process.

Thermal Atomic Layer Etching of Silica and Alumina Thin Films Using Trimethylaluminum with Hydrogen Fluoride or Fluoroform.

Thermal atomic layer etching (ALE) is an emerging technique that involves the sequential removal of monolayers of a film by alternating self-limiting reactions, some of which generate volatile products. Although traditional ALE processes rely on the use of plasma, several thermal ALE processes have recently been developed using hydrogen fluoride (HF) with precursors such as trimethylaluminum (TMA) or tin acetylacetonate. While HF is currently the most effective reagent for ALE, its potential hazards and corrosive nature have motivated searches for alternative chemicals. Herein, we investigate the feasibility of using fluoroform (CHF3) with TMA for the thermal ALE of SiO2 and Al2O3 surfaces and compare it to the established TMA/HF process. A fundamental mechanistic understanding is derived by combining in situ Fourier transform infrared spectroscopy, ex situ X-ray photoemission spectroscopy, ex situ low-energy ion scattering, and ex situ spectroscopic ellipsometry. Specifically, we determine the role of TMA, the dependence of the etch rate on precursor gas pressure, and the formation of a residual fluoride layer. Although CHF3 reacts with TMA-treated oxide surfaces, etching is hindered by the concurrent deposition of a fluorine-containing layer, which makes it unfavorable for etching. Moreover, since fluorine contamination can be deleterious to device performance and its presence in thin films is an inherent problem for established ALE processes using HF, we present a novel method to remove the residual fluorine accumulated during the ALE process by exposure to water vapor. XPS analysis herein reveals that an Al2O3 film etched using TMA/HF at 325 °C contains 25.4 at. % fluorine in the surface region. In situ exposure of this film to water vapor at 325 °C results in ∼90% removal of the fluorine. This simple approach for fluorine removal can easily be applied to ALE-treated films to mitigate contamination and retain surface stoichiometry.

Energy transfer from colloidal nanocrystals to strongly absorbing perovskites.

Integration of colloidal nanocrystal quantum dots (NQDs) with strongly absorbing semiconductors offers the possibility of developing optoelectronic and photonic devices with new functionalities. We examine the process of energy transfer (ET) from photoactive CdSe/ZnS core/shell NQDs into lead-halide perovskite polycrystalline films as a function of distance from the perovskite surface using time-resolved photoluminescence (TRPL) spectroscopy. We demonstrate near-field electromagnetic coupling between vastly dissimilar excitation in two materials that can reach an efficiency of 99% at room temperature. Our experimental results, combined with electrodynamics modeling, reveal the leading role of non-radiative ET at close distances, augmented by the waveguide emission coupling and light reabsorption at separations >10 nm. These results open the way to combining materials with different dimensionalities to achieve novel nanoscale architectures with improved photovoltaic and light emitting functionalities.

A system for measuring complex dielectric properties of thin films at submillimeter wavelengths using an open hemispherical cavity and a vector network analyzer.

Quasi-optical (QO) methods of dielectric spectroscopy are well established in the millimeter and submillimeter frequency bands. These methods exploit standing wave structure in the sample produced by a transmitted Gaussian beam to achieve accurate, low-noise measurement of the complex permittivity of the sample [e.g., J. A. Scales and M. Batzle, Appl. Phys. Lett. 88, 062906 (2006); R. N. Clarke and C. B. Rosenberg, J. Phys. E 15, 9 (1982); T. M. Hirovnen, P. Vainikainen, A. Lozowski, and A. V. Raisanen, IEEE Trans. Instrum. Meas. 45, 780 (1996)]. In effect the sample itself becomes a low-Q cavity. On the other hand, for optically thin samples (films of thickness much less than a wavelength) or extremely low loss samples (loss tangents below 10(-5)) the QO approach tends to break down due to loss of signal. In such a case it is useful to put the sample in a high-Q cavity and measure the perturbation of the cavity modes. Provided that the average mode frequency divided by the shift in mode frequency is less than the Q (quality factor) of the mode, then the perturbation should be resolvable. Cavity perturbation techniques are not new, but there are technological difficulties in working in the millimeter/submillimeter wave region. In this paper we will show applications of cavity perturbation to the dielectric characterization of semi-conductor thin films of the type used in the manufacture of photovoltaics in the 100 and 350 GHz range. We measured the complex optical constants of hot-wire chemical deposition grown 1-µm thick amorphous silicon (a-Si:H) film on borosilicate glass substrate. The real part of the refractive index and dielectric constant of the glass-substrate varies from frequency-independent to linearly frequency-dependent. We also see power-law behavior of the frequency-dependent optical conductivity from 316 GHz (9.48 cm(-1)) down to 104 GHz (3.12 cm(-1)).

Serum complements and heart fatty acid binding protein in Bangladeshi patients with acute myocardial infarction.

The complement system is activated following acute myocardial infarction (AMI). Heart fatty acid binding protein (H-FABP) is a sensitive early biomarker of myocardial necrosis that can be used to confirm or exclude a diagnosis of AMI and to monitor recurrent infarction. This study was designed to detect changes in C3, C4 and H-FABP after AMI. Forty patients with AMI and a control group of 40 apparently healthy people were included. Selections were based on inclusion and exclusion criteria. The baseline characteristics were not significantly different between the groups. Patients' blood samples were collected within 12 h of admission. Significant increases in C3 (AMI group 1.4260+0.04, healthy group 1.26040+0.04; p<0.05), C4 (AMI group 0.29305±0.013, healthy group 0.20860±0.012; p<0.05) and H-FABP (AMI group 12.3±1.69, healthy group 0.16±0.057; p<0.001) were seen in patients with AMI. The correlation between serum C3 and body mass index (BMI, r=0.33; p<0.05), serum C4 and BMI(r=0.313; p<0.05), serum C3 and total cholesterol high density lipoprotein (HDL, r=0.32; p<0.05), serum C4 and HbA1C (r=0.335; p<0.05) and serum C3 and troponin I (r= 0.325p<0.05) was found to be significant. But the correlation between serum C3 and waist:hip ratio (p=0.56), serum C4 and waist:hip ratio (p=0.83), serum C4 and total cholesterol HDL (p=0.993), serum C3 and HbA1C (p=0.440), serum C3 and random blood sugar (p=0.563), serum C4 and random blood sugar (p=0.828) and serum C4 and troponin I (p=0.373) was not significant. The significant complement activation detected in the plasma of patients with AMI indicated that complement plays a part in the pathogenesis of myocardial infarction. A significant increase of H-FABP improves the diagnosis of AMI.