One-step large-scale synthesis of micrometer-sized silver nanosheets by a template-free electrochemical method

High-performance grating-like SERS substrate based on machine learning for ultrasensitive detection of Zexie-Baizhu decoction

Rapid, universal and accurate identification of chemical composition changes in multi-component traditional Chinese medicine (TCM) decoction is a necessary condition for elucidating the effectiveness and mechanism of pharmacodynamic substances in TCM. In this paper, SERS technology, combined with grating-like SERS substrate and machine learning method, was used to establish an efficient and sensitive method for the detection of TCM decoction. Firstly, the grating-like substrate prepared by magnetron sputtering technology was served as a reliable SERS sensor for the identification of TCM decoction. The enhancement factor (EF) of 4-ATP probe molecules was as high as 1.90 × 107 and the limit of detection (LOD) was as low as 1 × 10-10 M. Then, SERS technology combined with support vector machine (SVM), decision tree (DT), Naive Bayes (NB) and other machine learning algorithms were used to classify and identify the three TCM decoctions, and the classification accuracy rate was as high as 97.78 %. In summary, it is expected that the proposed method combining SERS and machine learning method will have a high development in the practical application of multi-component analytes in TCM.

Two-Dimensional Metal Nanostructures: From Theoretical Understanding to Experiment

This paper reviews recent studies on the preparation of two-dimensional (2D) metal nanostructures, particularly nanosheets. As metal often exists in the high-symmetry crystal phase, such as face centered cubic structures, reducing the symmetry is often needed for the formation of low-dimensional nanostructures. Recent advances in characterization and theory allow for a deeper understanding of the formation of 2D nanostructures. This Review firstly describes the relevant theoretical framework to help the experimentalists understand chemical driving forces for the synthesis of 2D metal nanostructures, followed by examples on the shape control of different metals. Recent applications of 2D metal nanostructures, including catalysis, bioimaging, plasmonics, and sensing, are discussed. We end the Review with a summary and outlook of the challenges and opportunities in the design, synthesis, and application of 2D metal nanostructures.

First principles study of thermoelectric performance in pristine and binary alloyed monolayers of noble metals

In search of novel thermoelectric materials, we have investigated the thermoelectric performance of freestanding pristine and binary alloyed monolayers of noble metals (viz. Au, Ag, Cu, Pt) in honeycomb morphology using first principles methods based on density functional theory (DFT) and the non-equilibrium Green's function (NEGF) approach. The requisite electron transmission function is calculated using the TranSIESTA code - a module of the SIESTA package, while its phonon counterpart is obtained using the Phonons module of the python package along with the NEGF utility - PHtrans. Transport is explored along both the armchair (ac) and zigzag (zz) directions. Due to greater transverse length of the unit cell, electron and phonon transport is found to be more in the zz-direction. Among the pristine monolayers, Pt is found to exhibit ferromagnetism as well as the highest thermoelectric efficiency ZT ∼ 8 with an external bias of μ = 0.795 eV. However, alloying brings in a characteristic energy gap in the phononic transmission function, which diminishes the (room-temperature) relative phononic conductance to less than 5% in Pt-containing alloys. Also, monolayers of AuAg and AuCu turn semiconducting, with the former yielding a high Seebeck coefficient of 1264.96 μV K^-1 at μ ∼ -0.055 eV. Moreover, they exhibit an enhanced ZT near the edges of the band gap, with ZT_max as high as 3.74 and 3.05, respectively. Interestingly, the Pt-containing alloyed monolayers also show a ferromagnetic character and hence, a spin-dependent Seebeck effect. In the CuPt monolayer, the bias μ can be tuned to attain an appreciable charge figure of merit Z_cT = 4.80 at μ = 0.58 eV, while a decent spin figure of merit Z_sT = 1.43 at μ = 0.56 eV. Instead, the pristine Pt monolayer shows a much better Z_sT = 5.45 for a bias of μ = 0.785 eV. Nevertheless, the predicted ZT remains smaller than the corresponding alloyed atomic chains in double zigzag topology.

A Review of Sintering-Bonding Technology Using Ag Nanoparticles for Electronic Packaging

Metal nanoparticles (NPs) have attracted growing attention in recent years for electronic packaging applications. Ag NPs have emerged as a promising low-temperature bonding material owing to their unique characteristics. In this study, we mainly review our research progress on the interconnection of using polyol-based Ag NPs for electronic packaging. The synthesis, sintering-bonding process, bonding mechanism, and high-temperature joint properties of Ag NP pastes are investigated. The paste containing a high concentration of Ag NPs was prepared based on the polyol method and concentration. A nanoscale layer of organic components coated on the NPs prevents the coalescence of Ag NPs. The effects of organic components on the bondability of the Ag NP paste were studied. Compared to the aqueous-based Ag NP paste, the polyol-based Ag NP with the reduction of organic component can improve the bondability, and the coffee ring effect was successfully depressed due to the increased Marangoni flow. The sintering behaviors of Ag NPs during the bonding process were investigated using the classical sphere-to-sphere approach. The mechanical property of joints using this Ag paste was better than that using Pb₉₅Sn₅ solders after storage at high temperatures. The sintering–bonding technology using polyol-based Ag NPs was helpful to the low-temperature interconnection for electronic packaging applications.

Morphology-Controlled Fabrication of Large-Scale Dendritic Silver Nanostructures for Catalysis and SERS Applications

Highly branched metallic nanostructures, which possess a large amount of catalyst active sites and surface-enhanced Raman scattering (SERS) hot spots owing to their large surface areas, multi-level branches, corners, and edges, have shown potential in various applications including catalysis and SERS. In this study, well-defined dendritic silver (Ag) nanostructures were prepared by a facile and controllable electrochemical deposition strategy. The morphology of Ag nanostructures is controlled by regulating electrodeposition time and concentration of AgNO₃ in the electrolyte solution. Compared to conventional Ag nanoparticle films, dendritic Ag nanostructures exhibited larger SERS enhancement ascribed to the numerous hot spots exist in the nanogaps of parallel and vertically stacked multilayer Ag dendrites. In addition, the prepared dendritic Ag nanostructures show 3.2-fold higher catalytic activity towards the reduction of 4-nitrophenol (4-NP) by NaBH₄ than the Ag nanoparticle films. The results indicate that the dendritic Ag nanostructures represent a unique bifunctional nanostructure that serves as both efficient catalysts and excellent SERS substrates, which may be further employed as a nanoreactor for in situ investigation and real-time monitoring of catalytic reactions by SERS technique.

Recent Progress in Rapid Sintering of Nanosilver for Electronics Applications

Recently, nanosilver pastes have emerged as one of the most promising high temperature bonding materials for high frequency and high power applications, which provide an effective lead-free electronic packaging solution instead of high-lead and gold-based solders. Although nanosilver pastes can be sintered at lower temperature compared to bulk silver, applications of nanosilver pastes are limited by long-term sintering time (20⁻30 min), relative high sintering temperature (>250 °C), and applied external pressure, which may damage chips and electronic components. Therefore, low temperature rapid sintering processes that can obtain excellent nanosilver joints are anticipated. In this regard, we present a review of recent progress in the rapid sintering of nanosilver pastes. Preparation of nanosilver particles and pastes, mechanisms of nanopastes sintering, and different rapid sintering processes are discussed. Emphasis is placed on the properties of sintered joints obtained by different sintering processes such as electric current assisted sintering, spark plasma sintering, and laser sintering, etc. Although the research on rapid sintering processes for nanosilver pastes has made a great breakthrough over the past few decades, investigations on mechanisms of rapid sintering, and the performance of joints fabricated by pastes with different compositions and morphologies are still far from enough.

Elemental two-dimensional nanosheets beyond graphene

The recent progress of elemental two-dimensional nanosheets, beyond graphene, has been summarized with the focus on their preparation and applications.

Observation of the formation of anisotropic silver microstructures by evanescent wave and electron microscopy

Using a well-known galvanic displacement reaction, ∼25-40 μm long silver ribbons grown after mixing ∼50 nm copper particles with AgNO3 solution were observed as a function of Ag(+) concentration and their growth was characterized in real-time and in situ by evanescent wave (EW) microscopy. At low Ag(+) concentration, chain-like structures consisting of both Ag and Cu were observed. When the sequence of mixing these two reactants was reversed, different Ag microstructures (platelets and dendrites) were formed and were also characterized by EW microscopy. Dependence of the morphology of all these microstructures on silver ion concentration was determined by EW microscopy in conjunction with scanning and transmission electron microscopy.

One-Step Preparation of Silver Hexagonal Microsheets as Electrically Conductive Adhesive Fillers for Printed Electronics

A facile one-step solution-phase chemical reduction method has been developed to synthesize Ag microsheets at room temperature. The morphology of Ag sheets is a regular hexagon more than 1 μm in size and about 200 nm in thickness. The hexagonal Ag microsheets possess a smoother and straighter surface compared with that of the commercial Ag micrometer-sized flakes prepared by ball milling for electrically conductive adhesives (ECAs). The function of the reagents and the formation mechanism of Ag hexagonal microsheets are also investigated. For the polyvinylpyrrolidone (PVP) and citrate facet-selective capping, the Ag atoms freshly reduced by N2H4 would orientationally grow alone on the {111} facet of Ag seeds, with the synergistically selective etching of irregular and small Ag particles by H2O2, to form Ag hexagonal microsheets. The hexagonal Ag microsheet-filled epoxy adhesives, as electrically conductive materials, can be easily printed on various substrates such as polyethylene terephthalate (PET), epoxy, glass, and flexible papers. The hexagonal Ag microsheet filled ECAs demonstrate lower bulk resistivity (approximately 8 × 10(-5) Ω cm) than that of the traditional Ag micrometer-sized-flake-filled ECAs with the same Ag content of 80 wt % (approximately 1.2 × 10(-4) Ω cm).