AlGaN-based high-performance metal–semiconductor–metal photodetectors

Design, structure growth, fabrication, and characterization of high performance AlGaN-based metal–semiconductor–metal (MSM) photodetectors (PD) are reported. By incorporating AlN nucleation and buffer layers, the leakage current density of GaN MSM PD was reduced to 1.96 × 10⁻¹⁰ A/cm² at a 50 V bias, which is four orders of magnitude lower compared to control devices. A 229 nm cut-off wavelength, a peak responsivity of 0.53 A/W at 222 nm, and seven orders of magnitude visible rejection was obtained from Al_0.75Ga_0.25N MSM PD. Two-color monolithic AlGaN MSM PD with excellent dark current characteristics were demonstrated, where both detectors reject the other detector spectral band with more than three orders of magnitude. High-speed measurements of Al_0.38Ga_0.62N MSM PD resulted in fast responses with greater than gigahertz bandwidths, where the fastest devices had a 3-dB bandwidth of 5.4 GHz.     

Measurement of mass attenuation coefficients in some Cr,Co and Fe compounds around the absorption edge and the validity of the mixture rule

The total mass attenuation coefficients for elements Cr, Co and Fe and compounds CrCl₂, CrCl₃, Cr₂(SO₄)₃K₂SO₄·24H₂O, CoO, CoCl₂, Co(CH₃COO)₂, FePO₄, FeCl₃·6H₂O, Fe(SO₄)₂NH₄·12H₂O were measured at different energies between 4.508 and 14.142 keV using secondary excitation method. Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr were chosen as secondary exciters. 59.5 keV γ-rays emitted from a ²⁴¹Am annular source were used to excite a secondary exciter and K_α(K-L₃, L₂) lines emitted by the secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. It was observed that mixture rule method is not a suitable method for determination of the mass attenuation coefficients of compounds, especially at an energy that is near the absorption edge. The obtained values were compared with theoretical values.      

Diffuse optical measurement of blood flow, blood oxygenation, and metabolism in a human brain during sensorimotor cortex activation

We combine diffuse optical and correlation spectroscopies to simultaneously measure the oxyhemoglobin and deoxyhemoglobin concentration and blood flow in an adult human brain during sensorimotor stimulation. The observations permit calculation of the relative cerebral metabolic rate of oxygen in the human brain, for the first time to our knowledge, by use of all-optical methods. The feasibility for noninvasive optical measurement of blood flow through the skull of an adult brain is thus demonstrated, and the clinical potential of this hybrid, all-optical noninvasive, methodology can now be explored.     

Free energy simulations of single and double ion occupancy in gramicidin A

Simultaneous occupancy of the two binding sites in gramicidin A by monovalent cations is a well known property of this channel, but the energetic feasibility of this process in molecular dynamics simulations has not been established so far. Here the authors study the energetics of single and double ion occupancy in gramicidin A by constructing the potential of mean force for single and pair of cations. As representatives of small and large ions, they consider both Na+ and K+ ions in the calculations. Binding constants of ions are estimated from the free energy profiles. Comparisons with the experimental results indicate 3-4 kT discrepancy in the binding energies. They also study the coordination of the ions in their respective binding sites and the dynamic behavior of the channel water during the double ion binding process.     

Synthesis of new 1,3-disubstituted-2,3-dihydro-1H-naphth[1,2e][1,3]oxazines

1,3-Disubstituted-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines were prepared through the ring-closure reactions of the aminobenzylnaphthols with substituted aryl- and heteroarylaldehydes.     

Hybrid reinforcement in nitrile rubber composites

Nitril rubber‐PVC composites having carbon black and mica fillers in different compositions as hybrid reinforcements have been studied. The degree of replacement on static‐dynamic mechanical, swelling behavior of resultant composites were all discussed. Results showed that increase in mica in total filler resulted in increase in toughness values, decrease in swelling in organic solvents together with increase in vibrational damping capacity of the resultant composites.     

High‐molecular‐weight polyisobutylenes (PIBs) and PIB networks from liquid PIBs by thiol‐ene clicking

We report the synthesis of high‐molecular‐weight linear polyisobutylenes (PIBs) and PIB networks from low‐molecular‐weight PIB by thiol‐ene click chemistry. Thus, liquid allyl‐telechelic PIB was reacted with small di‐ and tri‐thiols, and the thiolated intermediates chain‐extended by UV‐ or thermally induced free radical initiation to linear and crosslinked products. PIB networks were also prepared by crosslinking SH‐telechelic PIB with a small triallyl compound. Linear products were characterized by ¹H NMR spectroscopy and GPC, and networks by FTIR spectroscopy, extractables, swelling, and permanent set. The effect of reaction conditions (nature of thiol chain extender, concentration of photo‐ and thermal initiators, UV radiation time, and reagent concentrations) on chain extension and crosslinking was investigated. Under well‐defined conditions high‐molecular‐weight PIBs and tight PIB networks were prepared. Thiol‐ene click chemistry provides novel thiolated PIB derivatives and is a useful strategy for the convenient preparation of high‐molecular‐weight rubbery PIBs and tight PIB networks from low‐molecular‐weight PIB precursors. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019     

Synthesis of nonperipherally tetra-[5-(diethylamino)-2-formylphenoxy] substituted metallophthalocyanines and their electrochemistry

3-[5-(diethylamino)-2-formylphenoxy]phthalonitrile ( n-TY-CN ), metallophthalocyanines n-TY-Co , n-TY-Cu , and n-TY-Mn bearing [5-(diethylamino)-2-formylphenoxy] groups at nonperipheral positions were prepared for the first time. These compounds were characterized with IR, NMR (only for n-TY-CN ), mass and UV-vis (except n-TY-CN ) spectroscopy. Voltammetric characterizations of n-TY-Co , n-TY-Cu , and n-TY-Mn revealed that while n-TY-Co , n-TY-Cu , and n-TY-Mn showed characteristic Pc ring and/or metal-based reduction reaction, n-TY-Co , n-TY-Cu , and n-TY-Mn were coated on the working electrode during the oxidation processes owing to the cationic electropolymerizations of the [5-(diethylamino)-2-formylphenoxy] substituents.