An easily-prepared impedance matched Josephson parametric amplifier

An impedance matched parametric amplifier(IMPA)with Josephson junctions is fabricated and characterized.A hybrid structure containing coplanar and strip structures is implemented to realize an impedance taper line and a plate capacitor in an LC nonlinear resonator based on Josephson junctions.The upper plate of the capacitor is isolated with SiNx without grounding as well as the strips.Such easily-prepared designs greatly reduce the requirements for lithography alignment and precision,which makes the fabrication process more reliable.The experimental results show that in such IMPA a gain higher than 25 dB with a bandwidth of about 100 MHz can be obtained.This broadband amplifier operates close to the quantum limit.By adjusting the working point,a higher bandwidth of about 400 MHz can be obtained with a gain of about 17 dB.

High-loading single cobalt atoms on ultrathin MOF nanosheets for efficient photocatalytic CO_(2) reduction

Based on suitable scaffolds,constructing high-loading single-atom catalysts is a promising strategy to achieve highly efficient catalysis.Herein,using ultrathin metal-organic framework(MOF)nanosheets(2.4±0.5 nm)as the support,single-atom catalysts with high cobalt loading(6.0 wt%)were constructed(denoted as Co-MNSs)by a simple bottom-up synthetic strategy.The catalytic system of Co-MNSs exhibited an outstanding photocatalytic CO_(2)-to-CO evolution rate of 7,041μmol g^(-1)h^(-1)and a selectivity of 86%in aqueous media under visible-light irradiation,which has reached the top level of the reported MOF-based photocatalysts.The control experiments and theoretical calculation revealed that the Co-N_(4)moiety in the MOF nanosheets acted as the active site for the photocatalytic CO_(2)-to-CO conversion.The boosted photocatalytic performance could be ascribed to the high aspect-ratio of layered Co-MNSs providing abundant accessible active sites on their surfaces,which reduced the energy barrier,improved the charge separation efficiency,and also facilitated the adsorption of CO_(2)to form the reactive radicals of*COOH.Our study provides an appealing strategy for constructing high-loading single-atom catalysts and demonstrates the significance of 2D ultrathin MOF nanosheets as the support in boosting CO_(2)photoreduction efficiency.

Single-Metal-Atom Polymeric Unimolecular Micelles for Switchable Photocatalytic H_(2) Evolution

Developing“green”catalytic systems with desirable performance such as good water solubility,recyclability,and switchability is a great challenge.Here,to address this challenge,we extend the concept of polymeric unimolecular micelles(a typical selfassembled structure)to the construction of a stimuli-responsive and recoverable molecular catalyst with single-metal atoms that exhibits switchable photocatalytic activity for water splitting.