编译 | 未玖
Science, 17 FEB 2023, VOL 379, ISSUE 6633
《科学》2023年2月17日，第379卷，6633期
物理学Physics
Imaging the breaking of electrostatic dams in graphene for ballistic and viscous fluids
弹道和粘性流体的石墨烯静电势垒破裂成像
▲ 作者：ZACHARY J. KREBS, WYATT A. BEHN, SONGCI LI, KEENAN J. SMITH, KENJI WATANABE, TAKASHI TANIGUCHI, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.abm6073
▲ 摘要：
在特殊情况下，材料中的载流子可以表现为粘性流体。在这项工作中，研究组使用扫描隧道电位测量法来研究这种行为，以探测石墨烯中电子流体在通过由光滑且可调谐面内p-n结势垒限定通道时的纳米尺度流动。
实验观察到，随着样品温度和通道宽度的增加，电子流体流动经历了从弹道到粘性态的Knudsen-to-Gurzhi转变，其特征是通道电导超过弹道极限，并抑制了对势垒的电荷积聚。
该结果通过二维粘性电流流动的有限元模拟实现精确建模，还解释了费米液体流动如何随着载流子密度、通道宽度和温度而演变。
▲ Abstract：
The charge carriers in a material can, under special circumstances, behave as a viscous fluid. In this work, we investigated such behavior by using scanning tunneling potentiometry to probe the nanometer-scale flow of electron fluids in graphene as they pass through channels defined by smooth and tunable in-plane p-n junction barriers. We observed that as the sample temperature and channel widths are increased, the electron fluid flow undergoes a Knudsen-to-Gurzhi transition from the ballistic to the viscous regime characterized by a channel conductance that exceeds the ballistic limit, as well as suppressed charge accumulation against the barriers. Our results are well modeled by finite element simulations of two-dimensional viscous current flow, and they illustrate how Fermi liquid flow evolves with carrier density, channel width, and temperature.
材料科学Materials Science
Reducing nonradiative recombination in perovskite solar cells with a porous insulator contact
多孔绝缘体接触降低钙钛矿太阳能电池的非辐射重组
▲ 作者：WEI PENG, KAITIAN MAO, FENGCHUN CAI, HONGGUANG MENG, ZHENGJIE ZHU, TIEQIANG LI, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.ade3126
▲ 摘要：
在吸收层和传输层之间插入超薄的低导电性夹层已成为减少最佳钙钛矿太阳能电池表面重组的重要策略。然而，这种方法的挑战之一是开路电压（Voc）和填充因子（FF）之间的权衡。
研究组通过引入具有随机纳米级开口的厚（约100纳米）绝缘体层来克服这一挑战，对具有这种多孔绝缘体接触（PIC）的电池进行了漂移扩散模拟，通过控制氧化铝纳米片的生长方式，使用溶液工艺来实现。
利用接触面积减少约25%的PIC，研究组在p-i-n器件中实现了高达25.5%的效率（认证稳态效率为24.7%）。Voc×FF的乘积为Shockley-Queisser极限的87.9%。p型接触的表面重组速度从64.2 cm/s降低至9.2 cm/s。
由于钙钛矿结晶度的提高，体复合寿命从1.2 μs增加到6.0 μs。钙钛矿前驱体溶液润湿性改善使研究组实现了效率高达23.3%的1 cm2 p-i-n电池。该研究结果证明了该PIC电池对不同p型接触和钙钛矿组成的广泛适用性。
▲ Abstract：
Inserting an ultrathin low-conductivity interlayer between the absorber and transport layer has emerged as an important strategy for reducing surface recombination in the best perovskite solar cells. However, a challenge with this approach is a trade-off between the open-circuit voltage (Voc) and the fill factor (FF). Here, we overcame this challenge by introducing a thick (about 100 nanometers) insulator layer with random nanoscale openings. We performed drift-diffusion simulations for cells with this porous insulator contact (PIC) and realized it using a solution process by controlling the growth mode of alumina nanoplates. Leveraging a PIC with an approximately 25% reduced contact area, we achieved an efficiency of up to 25.5% (certified steady-state efficiency 24.7%) in p-i-n devices. The product of Voc × FF was 87.9% of the Shockley-Queisser limit. The surface recombination velocity at the p-type contact was reduced from 64.2 to 9.2 centimeters per second. The bulk recombination lifetime was increased from 1.2 to 6.0 microseconds because of improvements in the perovskite crystallinity. The improved wettability of the perovskite precursor solution allowed us to demonstrate a 23.3% efficient 1-square-centimeter p-i-n cell. We demonstrate here its broad applicability for different p-type contacts and perovskite compositions.
Rational design of Lewis base molecules for stable and efficient inverted perovskite solar cells
稳定高效倒置钙钛矿太阳能电池路易斯碱分子的合理设计
▲ 作者：CHONGWEN LI, XIAOMING WANG, ENBING BI, FANGYUAN JIANG, SO MIN PARK, YOU LI, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.ade3970
▲ 摘要：
已知在界面和晶界（GBs）结合未配位铅原子的路易斯碱分子可提高金属卤化物钙钛矿太阳能电池（PSCs）的耐久性。
利用密度泛函理论计算，研究组发现在现今研究的路易斯碱分子库成员中，含磷化氢的分子具有最强的结合能。
实验中发现，在模拟AM1.5光照、最大功率点和约40℃下连续运行>3500小时后，经1,3-双（二苯基膦基）丙烷（DPPP）（一种钝化、结合和桥接界面和GBs的二膦-路易斯碱）处理的最佳倒置PSC的功率转换效率（PCE）略高于约23%的初始PCE。在85℃开路条件下，DPPP处理器件保持>1500小时后，PCE也出现类似的增加。
▲ Abstract：
Lewis base molecules that bind undercoordinated lead atoms at interfaces and grain boundaries (GBs) are known to enhance the durability of metal halide perovskite solar cells (PSCs). Using density functional theory calculations, we found that phosphine-containing molecules have the strongest binding energy among members of a library of Lewis base molecules studied herein. Experimentally, we found that the best inverted PSC treated with 1,3-bis(diphenylphosphino)propane (DPPP), a diphosphine Lewis base that passivates, binds, and bridges interfaces and GBs, retained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after continuous operation under simulated AM1.5 illumination at the maximum power point and at ~40°C for >3500 hours. DPPP-treated devices showed a similar increase in PCE after being kept under open-circuit conditions at 85°C for >1500 hours.
化学Chemistry
Dynamic kinetic asymmetric arylation and alkenylation of ketones
酮的不对称芳基化和烯基化动态动力学
▲ 作者：LIN-XIN RUAN, BO SUN, JIA-MING LIU, AND SHI-LIANG SHI
▲ 链接：
https://www.science.org/doi/10.1126/science.ade0760
▲ 摘要：
尽管富对映体醇在药物化学、全合成和材料科学中具有重要意义，但高效和选择性地构建具有两个相邻立体中心的富对映体叔醇仍颇具挑战。
研究组报道了一个制备富对映体叔醇的平台，通过对映汇聚、镍催化加成有机硼酸酯至外消旋、非活化酮来实现。他们通过芳基和烯基亲核试剂的动态动力学不对称加成，一步合成了几类重要的α、β手性叔醇，具有很高的非对映选择性和对映选择性。
应用这一方案来修饰几种洛芬药物，可快速合成生物学相关分子。研究组希冀这种镍催化的无碱酮外消旋工艺能成为一种广泛应用于动态动力学工艺发展的策略。
▲ Abstract：
Despite the importance of enantioenriched alcohols in medicinal chemistry, total synthesis, and materials science, the efficient and selective construction of enantioenriched tertiary alcohols bearing two contiguous stereocenters has remained a substantial challenge. We report a platform for their preparation through the enantioconvergent, nickel-catalyzed addition of organoboronates to racemic, nonactivated ketones. We prepared several important classes of α,β-chiral tertiary alcohols in a single step with high levels of diastereo- and enantioselectivity through a dynamic kinetic asymmetric addition of aryl and alkenyl nucleophiles. We applied this protocol to modify several profen drugs and to rapidly synthesize biologically relevant molecules. We expect this nickel-catalyzed, base-free ketone racemization process to be a widely applicable strategy for the development of dynamic kinetic processes.
Continuous-flow electrosynthesis of ammonia by nitrogen reduction and hydrogen oxidation
氮还原-氢氧化连续流电化学合成氨
▲ 作者：XIANBIAO FU, JAKOB B. PEDERSEN, YUANYUAN ZHOU, MATTIA SACCOCCIO, SHAOFENG LI, ROKAS SAINAS, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.adf4403
▲ 摘要：
氨是制备化肥、药品和精细化学品的关键成分，是理想的无碳燃料。近年来，锂介导的氮还原已被证明是在环境条件下电化学合成氨的一条颇有前景的途径。
在这项工作中，研究组报道了一个配备25 cm2有效面积的气体扩散电极的连续流电解槽，其中氮还原与氢氧化耦合。他们还发现，经典催化剂铂对有机电解质中氢氧化不稳定，但铂-金合金降低了阳极电位，避免了有机电解质的递减分解。
在最佳操作条件下，在1 bar、电流密度为-6 mA/cm2时，研究组实现了高达61±1%的氨生产法拉第效率和13±1%的能源效率。
▲ Abstract：
Ammonia is a critical component in fertilizers, pharmaceuticals, and fine chemicals and is an ideal, carbon-free fuel. Recently, lithium-mediated nitrogen reduction has proven to be a promising route for electrochemical ammonia synthesis at ambient conditions. In this work, we report a continuous-flow electrolyzer equipped with 25–square centimeter–effective area gas diffusion electrodes wherein nitrogen reduction is coupled with hydrogen oxidation. We show that the classical catalyst platinum is not stable for hydrogen oxidation in the organic electrolyte, but a platinum-gold alloy lowers the anode potential and avoids the decremental decomposition of the organic electrolyte. At optimal operating conditions, we achieve, at 1 bar, a faradaic efficiency for ammonia production of up to 61 ± 1% and an energy efficiency of 13 ± 1% at a current density of 6 milliamperes per square centimeter.
地球科学Earth Science
Ultralow frictional healing explains recurring slow slip events
超低摩擦愈合解释了反复发生的慢滑事件
▲ 作者：SRISHARAN SHREEDHARAN, DEMIAN SAFFER, LAURA M. WALLACE AND CHARLES WILLIAMS
▲ 链接：
https://www.science.org/doi/10.1126/science.adf4930
▲ 摘要：
浅层俯冲巨型冲断层上的板块运动由一系列构造滑动模式决定。然而，维持这些不同滑移行为的摩擦特性和条件仍然是谜。摩擦愈合就是这种性质，它描述了地震之间断层再强化的程度。
研究发现，在新西兰Hikurangi海沟北部边缘（该区域经常反复发生浅层慢滑事件[SSEs]）沿巨型冲断层夹带物质的摩擦愈合率几乎为零（每十年<0.0001）。这些低愈合率为Hikurangi海沟和其他俯冲边缘浅SSE的低应力下降（<50 kPa）和短重复时间（1至2年）提供了一种机制。
研究组认为，与俯冲带中常见弱层状硅酸盐相关且接近于零的摩擦愈合速率可能会促进海沟附近频繁、小应力下降、缓慢的破裂。
▲ Abstract：
Plate motion on shallow subduction megathrusts is accommodated by a spectrum of tectonic slip modes. However, the frictional properties and conditions that sustain these diverse slip behaviors remain enigmatic. Frictional healing is one such property, which describes the degree of fault restrengthening between earthquakes. We show that the frictional healing rate of materials entrained along the megathrust at the northern Hikurangi margin, which hosts well-characterized recurring shallow slow slip events (SSEs), is nearly zero (<0.0001 per decade). These low healing rates provide a mechanism for the low stress drops (<50 kilopascals) and short recurrence times (1 to 2 years) characteristic of shallow SSEs at Hikurangi and other subduction margins. We suggest that near-zero frictional healing rates, associated with weak phyllosilicates that are common in subduction zones, may promote frequent, small-stress-drop, slow ruptures near the trench.
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