New approach to fabricate nanoporous gold film

A simple preparation of ultrathin nanoporous gold film was described. Copper and gold were used to fabricate Cu-Au alloy films through vacuum deposition. The formation of nanoporous gold films from the alloy films involved thermal process and chemical etch by hydrochloric acid or by nitric acid. The free-standing nanoporous gold films have been analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectrometer （XPS） and surface-enhanced Raman scattering （SELLS）. R was noted that the nanoporous gold film etched by hydrochloric acid is uniform with a cover of fog-like moieties.

Atomic scale visualizations of low-angle grain boundary mediated plasticity by coupled dislocation climb and glide in nanoporous gold

Grain boundaries(GBs),as a prevalent structural characteristic,play a crucial role in the deformation of nanoporous metals with nanosized grains and ligaments.However,the fundamental understanding of GB-mediated deformation is still lacking because the plastic behavior of discrete ligaments involving GBs remains to be unknown.Here,we report atomic scale visualizations of coupled GB dislocation climb and glide in nanoporous gold ligaments with low-angle GBs via in situ tensile straining inside a Cs-corrected transmission electron microscope.The zig-zag motion paths of GB dislocations are precisely determined by real-time tracking of the movements of dislocation cores.The concurrent climb and glide of the dislocation arrays are confined to a narrow GB region,greatly enhancing GB diffusion in the bicrystal ligament.Our findings of coupled dislocation climb and glide shine a light on the room-temperature deformation of nanoporous metals and provide a time-dependent atomic-level physical image for GB engineering.

Achieving a sub-10 nm nanopore array in silicon by metal-assisted chemical etching and machine learning

Solid-state nanopores with controllable pore size and morphology have huge application potential.However,it has been very challenging to process sub-10 nm silicon nanopore arrays with high efficiency and high quality at low cost.In this study,a method combining metal-assisted chemical etching and machine learning is proposed to fabricate sub-10 nm nanopore arrays on silicon wafers with various dopant types and concentrations.Through a SVM algorithm,the relationship between the nanopore structures and the fabrication conditions,including the etching solution,etching time,dopant type,and concentration,was modeled and experimentally verified.Based on this,a processing parameter window for generating regular nanopore arrays on silicon wafers with variable doping types and concentrations was obtained.The proposed machine-learning-assisted etching method will provide a feasible and economical way to process high-quality silicon nanopores,nanostructures,and devices.

Self-supporting nanoporous gold-palladium overlayer bifunctional catalysts toward oxygen reduction and evolution reactions

The oxygen reduction reaction （ORR） and oxygen evolution reaction （OER） are crucial processes for energy conversion/storage systems, such as fuel cells, metal-air batteries, and water splitting. However, both reactions are severely restricted by their sluggish kinetics, thus requiring highly active, cost-effective, and durable electrocatalysts. Herein, we develop novel bifunctional nanocatalysts through surface nanoengineering of dealloying-driven nanoporous gold （NPG）. Pd overlayers were precisely deposited onto the NPG ligament surface by epitaxial layer-by-layer growth. More importantly, the obtained NPG-Pd overlayer nanocatalysts exhibit remarkably enhanced electrocatalytic activities toward both the ORR and OER in alkaline media, benchmarked against a state- of-the-art Pt/C catalyst. The improved electrocatalytic performance is rationalized by the unique three-dimensional nanoarchitecture of NPG, enhanced Pd utilization efficiency from precise control of the Pd overlayers, and change in electronic structure, as revealed by density functional theory calculations.

Electrochemical synthesis of silver nanoparticles-coated gold nanoporous film electrode and its application to amperometric detection for trace Cr(VI)

A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high potential of 5 V, and then reduced to obtain gold nanoporous film (AuNF) by freshly prepared ascorbic acid. The Ag nanoparticles (AgNPs) were grown on the AuNF electrode by potential-step electrodeposition. The resulting AgGNF composites electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and cyclic voltammetry (CV). As-prepared AgGNF electrode was used as a kind of superior sensor for Cr(VI) detection, which exhibited better electrocatalytic behavior than those of AuNF and SGE under identical conditions. Such a designed AgGNF nanocomposites electrode showed outstanding sensitivity (about 0.15 nA/ppb) and favorable reproducibility for Cr(VI) detection. The dependence of reduction current on Cr(VI) concentration is linear from 2 to 370 ppb with a low detection limit of 0.65 ppb. Interferences from other heavy metals ions (Cr3+, Cu2+, Pb2+, As3+ and Hg2+) associated with Cr(VI) analysis could be effectively diminished. The present method proves to be rapid, reliable, sensitive and low-cost.

Highly coordinated Pd overlayers on nanoporous gold for efficient formic acid electro-oxidation

Design and fabrication of highly efficient and stable electrocatalysts remain key challenges in green energy technologies such as low-temperature direct liquid fuel cells.Based on in-depth theoretical calculations,here we demonstrate that surface Pd atoms with high coordination numbers(HCNs)can effectively modulate their adsorption energies for CO and OH,and thus achieve very high performance for formic acid electro-oxidation reaction(FAOR).Based on epitaxial coating Pd atomic layers onto nanoporous gold(NPG)thin membranes and a slight further decoration of Au clusters on top,the resulted core-shell structured NPG-Pd-Au electrocatalyst can demonstrate Pd intrinsic and mass activities of 8.62 mA·cm^(-2)and 27.25 A·mg^(-1)respectively at the peak potential around 0.33 V versus saturated calomel electrode toward FAOR,which are far better than those of commercial Pd/C catalysts(1.09 mA·cm^(-2)and 0.32 A·mg^(-1))tested under the same conditions.Moreover,the membrane electrode assemblies based on these low precious metal loading electrodes can achieve an anode Pd power efficiency over 10 W·mg^(-1)in a direct formic acid fuel cell,which is two orders of magnitude higher than that of the commercial Pd/C.These results provide new inspirations for the development of revolutionary electrodes for energy technologies in a rational manner.

Slice Thickness Optimization for the Focused Ion Beam-Scanning Electron Microscopy 3D Tomography of Hierarchical Nanoporous Gold

The combination of focused ion beam (FIB) with scanning electron microscopy (SEM), also known as FIB-SEM tomography, has become a powerful 3D imaging technique at the nanometer scale. This method uses an ion beam to mill away a thin slice of material, which is then block-face imaged using an electron beam. With consecutive slicing along the z-axis and subsequent imaging, a volume of interest can be reconstructed from the images and further analyzed. Hierarchical nanoporous gold (HNPG) exhibits unique structural properties and has a ligament size of 15–110 nm and pore size of 5–20 nm. Accurate reconstruction of its image is crucial in determining its mechanical and other properties. Slice thickness is one of the most critical and uncertain parameters in FIB-SEM tomography. For HNPG, the slice thickness should be at least half as thin as the pore size and, in our approach, should not exceed 10 nm. Variations in slice thickness are caused by various microscope and sample parameters, e.g., converged ion milling beam shape, charging effects, beam drift, or sample surface roughness. Determining and optimizing the actual slice thickness variation appear challenging. In this work, we examine the influence of ion beam scan resolution and the dwell time on the mean and standard deviation of slice thickness. After optimizing the resolution and dwell time to achieve the target slice thickness and lowest possible standard deviation, we apply these parameters to analyze an actual HNPG sample. Our approach can determine the thickness of each slice along the z-axis and estimate the deviation of the milling process along the y-axis (slow imaging axis). For this function, we create a multi-ruler structure integrated with the HNPG sample.

原位透射电镜在纳米多孔金原子尺度变形研究中的应用

纳米多孔金(NPG)具有高曲率、高比表面积的结构特征,且比强度较高,作为一种结构功能一体化材料受到广泛关注。然而,影响NPG实际应用的最大障碍之一是其在拉伸作用下内部单根韧带失效导致的塑性失稳。过去的研究主要集中在宏观力学实验的研究,无法直接观察单根韧带的塑性变形行为。随着原位透射电子显微镜(transmission electron microscopy,TEM)的发展,已具备从原子尺度研究NPG中单根韧带塑性变形过程的能力,这对理解NPG变形机理进而合理设计制备高塑性纳米多孔结构金属具有重要意义。本文主要以近几年利用球差校正透射电子显微镜(Cs⁃corrected TEM)原位原子尺度研究NPG塑性变形的系列工作为例,简要综述了NPG单根韧带在塑性变形过程中位错运动(攀移和滑移)和表面原子扩散行为的最新进展,并对纳米结构金属材料的未来研究进行了展望。

Electrically tunable pore morphology in nanoporous gold thin films

Nanoporous gold （np-Au） is an emerging nanostructured material that exhibits many desirable properties, including high electrical and thermal conductivity, high surface area-to-volume ratio, tunable pore morphology well-established surface-binding chemistry, and compatibility with microfabrication. These features make np-Au a popular material for use in fuel cells, optical and electrical biosensors, drug delivery vehicles, neural electrode coatings, and as a model system for nanoscale mechanics. In each of its many applications, np-Au morphology plays an essential role in the overall device operation. Therefore, precise morphological control is necessary to attain optimal device performance. Traditionally thermal treatment by furnaces and hot plates is used to obtain np-Au with self-similar but coarser morphologies. However, this approach lacks the ability to create different morphologies on a single substrate and requires high temperatures （〉 250 ℃） incompatible with most plastic substrates. Herein, we report electro-annealing as a novel method that permits control of the extent and location of pore coarsening on a single substrate in one fast treatment step. The electro-annealing entails much lower temperatures （〈 150 ℃） than traditional thermal treatment, putatively due to electrically assisted phenomena contributing to the thermally activated surface diffusion of gold atoms, responsible for coarsening. Overall, this approach is easily scaled to display multiple pore morphologies on a single chip, therefore enabling high-throughput screening of optimal nanostructures for specific applications.

Mechanical properties of nanocrystalline nanoporous gold complicated by variation of grain and ligament: A molecular dynamics simulation

A series of large-scale molecular dynamics(MD) simulations has been performed to study the effects of grain size and ligament diameter on the mechanical properties of nanocrystalline nanoporous gold. Such simulations indicate that the principal deformation mechanism is a combination of grain boundary sliding, grain rotation and dislocation movement. The results of uniaxial tensile tests reveal the presence of a reverse Hall-Petch relation between strength and nominal grain size, rather than the conventional Hall-Petch relationship in the present range of nominal grain size(7.9–52.7 nm). An increase of flow stress may possibly attribute to the lower total proportion of grain boundary sliding and grain rotation in the deformation of samples with larger grain size. The Young's modulus shows a linear relation with the reciprocal of nominal grain size, which depends largely on the volume fraction of grain boundaries and thus decreasing grain size leads to relatively lower Young's modulus. MD simulations on samples with ligament diameter ranging from 4.07 to 8.10 nm are also carried out and results show that the increasing ligament diameter resulted in decreased flow stress and increased Young's modulus.

纳米孔金膜电极:合金化/去合金化法制备及电化学性能

采用合金化/去合金化法在金电极表面制备出一层具有纳米孔结构的金膜,其孔径约为15nm。该方法首先在金电极表面电沉积一层锌,再通过热处理形成合金层,最后利用化学去合金化法去除合金中的锌。X射线衍射(XRD)结果表明在合金化过程中,锌扩散进入金基体并形成了金-锌合金层。利用场发射扫描电子显微镜(FESEM)对去合金化得到的纳米孔金膜进行了形貌的表征,结果表明合金化条件对样品的纳米结构有明显的影响。电化学测试结果表明,经合金化/去合金化处理的金电极,其表面粗糙度有明显的提高。这种金电极对甲醇具有较高的催化氧化活性,在0.3mol·L-1甲醇的KOH溶液中,甲醇的氧化峰电流密度高达2.02mA·cm-2。

纳米多孔金薄膜的电催化氧化水合肼性能研究

通过脱合金方法对金银合金薄膜进行选择性腐蚀得到了具有三维双连通结构的纳米多孔金(NPG)。将NPG作为三电极测试体系中的工作电极,利用循环伏安法表征了其在碱性条件下对10 mmol/L的水合肼溶液的电催化性能。结果表明,纳米多孔金对水合肼的电催化氧化不仅峰电流强度比纯金电极高一个数量级以上,而且起峰电位很低,表现出很高的电催化氧化性能,这种优越的电催化性能和它的高比表面积以及多孔结构紧密相关。

金修饰纳米多孔Pd催化剂对甲酸氧化的电催化活性

以水热法制备出纳米多孔网状钯催化剂(nanoPd),采用电位扫描在其上沉积金,制成金修饰纳米钯电极(Au/nanoPd),运用循环伏安法(CV)、线性扫描(LSV)和交流阻抗谱(EIS)比较nanoPd和Au/nanoPd电极对甲酸氧化反应的电催化活性。CV和LSV结果表明:金在nanoPd表面的沉积促进钯对甲酸氧化的电催化活性,起始电位提前,电流密度更高。EIS研究结果也表明:在Au/nanoPd电极上,甲酸氧化反应的电荷传递电阻更低。结果表明:金修饰纳米钯电极(Au/nanoPd)对甲酸氧化具有较高的电催化活性。

退火温度对纳米多孔金微米线热导率的影响(英文)

采用T形探针法测量了纳米多孔金微米线的热导率.实验结果表明,热导率随着退火温度的升高而减小.如果只考虑孔隙率及金孔壁宽度的影响,根据已有模型计算得到的热导率将大于实验结果.纳米多孔金结构的形态学分析显示,随着退火温度的升高,纳米多孔金的孔壁宽度增大,从而可能导致孔壁内部的拉应力增加.内部拉应力将引入纳米结构缺陷,进而使得电子与缺陷之间的散射增强,最终降低了纳米多孔材料的热导率.

纳米多孔金薄膜显微结构分析

采用亚硫酸金钠为主盐,在阳极氧化铝模板上进行了化学镀和电镀金实验研究。通过扫描电子显微镜和X射线衍射分析测试表明:采用以上两种方法均能制备出纳米多孔金薄膜。两种方法制备的多孔金薄膜微观结构存在较大的差异。化学镀制备的多孔金薄膜微观上是枝晶状的,电镀制备的多孔金薄膜微观上由纳米线构成。

纳米多孔金薄膜的表面等离子体共振传感特性

对淀积在玻璃衬底上厚度约60nm的金银合金溅射薄膜进行硝酸腐蚀脱银处理,得到纳米多孔金薄膜.利用自建的波长检测型表面等离子体共振(SPR)传感装置研究了腐蚀时间对纳米多孔金薄膜SPR特性的影响,结果发现纳米多孔金薄膜与水溶液接触后在400-900nm光谱范围内不具有SPR效应,而当薄膜置于空气中时会产生明显的传播等离子体共振吸收峰,其共振波长随腐蚀时间增加逐渐红移.纳米多孔金薄膜在空气气氛中的SPR效应使其能够用于原位监测气相分子在孔内的吸附,还可对在液相中吸附的生化分子进行离位测试.本文对L-谷胱甘肽、L-半胱氨酸、2-氨基乙硫醇三种含巯基的生化小分子在纳米多孔金薄膜内的吸附进行了离位分析,结果表明与传统的致密金薄膜SPR芯片比较,纳米多孔金薄膜对这些分子显示出更高的灵敏度和更低的检测下限,这归功于多孔金的大比表面积使其能够吸附大量的生化小分子.实验还对乙醇蒸气在纳米多孔金薄膜内的吸附进行了原位监测,发现吸附平衡所用时间较长,约为160min.

距离调控纳米多孔金表面增强荧光特性

通过调控纳米多孔金(NPG)基底与荧光分子之间的距离,系统研究了其表面增强荧光特性.利用物理气相沉积方法在NPG表面沉积二氧化硅薄膜,通过调整二氧化硅的厚度来控制NPG与荧光分子之间的距离,系统研究了NPG孔径尺寸以及与荧光分子之间距离对其表面增强荧光(SEF)特性的影响.由于多孔金具有纳米级多孔结构,其表面等离子体能够通过分子附近局域电场的增强使分子的激发光场得到增强,从而提高分子的激发强度和效率;当荧光分子与多孔金表面存在一定距离时,通过与光子之间的共振耦合作用,表面等离子体能够增强多孔金周围电磁场,实现荧光增强.通过研究发现,NPG孔径为36nm、表面二氧化硅厚度为20nm时,表面组装的罗丹明6G荧光分子的荧光强度得到最大增强.

高效铂-纳米多孔金催化剂的设计和制备

使用去合金法制备了孔径和孔壁均匀的纳米多孔金(NPG)电极.研究发现NPG对甲酸、甲醛的氧化具有很高的电催化活性.如在NPG基体再沉积微量的铂,不仅明显改善了NPG的结构稳定性,而且由于Pt、Au两组分之间的协同效应而使该催化剂对有机小分子的电催化氧化具有比纯铂更高的催化活性和更强的抗催化毒物能力.

自支撑纳米多孔金薄膜制备研究

采用磁控溅射镀金银膜,长时间热处理合金化制备前驱体合金,以渐进浓度的硝酸自由腐蚀去合金化成功制备出具有自支撑结构的纳米多孔金薄膜。采用扫描电镜和X射线能谱仪对去合金腐蚀前后样品的形貌和成分进行了分析,结果表明：400℃,36h的热处理使得薄膜样品完全合金化,获得了结晶致密的Au42Ag58合金膜;渐进浓度的自由腐蚀避免了薄膜的完全开裂,获得了样品尺寸大于15mm×15mm、厚度400~500nm、孔隙率约56%、具有自支撑结构的纳米多孔金薄膜,其微观结构为连续的三维多孔结构,系带尺寸40~140nm,80~100nm的系带达58%。

纳米多孔金薄膜及其微电极结构的制备

结合磁控溅射、lift-off工艺和脱合金法制备了纳米多孔金薄膜及其微电极结构。首先利用磁控溅射法和lift-off技术制备了金银合金叉指型微薄膜电极结构,然后采用浓硝酸通过脱合金方法进一步制备出纳米多孔金薄膜微电极结构。本文系统研究了腐蚀时间对磁控溅射金银合金薄膜去合金化所制备的纳米多孔金薄膜形貌、组分和结构的影响。利用X射线衍射、场发射扫描电子显微镜和透射电子显微镜表征了纳米多孔金薄膜微电极的结构和形貌。结果表明纳米多孔金主要呈现(111)晶面,且脱合金时间对纳米多孔结构形成与演化有明显的影响。随着腐蚀时间增加,纳米多孔金薄膜孔隙度增加,金韧带分布更加均匀,逐渐形成均匀的具有高表面积的开放式多孔结构。