Au-Sn Alloy Research Articles

Aqueous Synthesis of Plasmonic Gold-Tin Alloy Nanoparticles.

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have potential applications in catalysis, optoelectronics, imaging, and drug delivery. Previously, methods for producing alloy nanoparticles have been time-consuming, require complex reaction conditions, and can have inconsistent results. The outlined protocol first describes the synthesis of approximately 13 nm Au nanoparticle seeds using the Turkevich method. The protocol next describes the reduction of Sn and its incorporation into the Au seeds to generate Au-Sn alloy nanoparticles. The optical and structural characterization of these nanoparticles is described. Optically, prominent localized surface plasmon resonances (LSPRs) are apparent using UV-visible spectroscopy. Structurally, powder X-ray diffraction (XRD) reflects all particles to be less than 20 nm and shows patterns for Au, Sn, and multiple Au-Sn intermetallic phases. Spherical morphology and size distribution are obtained from transmission electron microscopy (TEM) imaging. TEM reveals that after Sn incorporation, the nanoparticles grow to approximately 15 nm in diameter.

Dual-cluster interpretation of Au–Sn binary eutectics and solders

Au–Sn alloy is an important high-temperature solder, but it has some disadvantages such as high cost and brittleness. Multicomponent alloying is often performed to improve performance and reduce their cost. However, due to the absence of an atomic structure model, there has been a lack of effective theory to guide their composition design. Since Au–Sn solders are typically eutectic-based, understanding the Au–Sn eutectic at the atomic level is of great significance for clarifying the composition origin of Au–Sn solders and the subsequent multi-component composition design. In the present work, the short-range order of Au–Sn eutectics is characterized using a dual-cluster model. In the dual-cluster formulism, the two eutectics Au69.6Sn30.3 and Sn94.6Au5.4 at. % are interpreted in terms of the hypoeutectic [SnAu12]Sn2Au3 + [Au–Au2Sn6]Au3 = Au70.0Sn30.0 and [Au–Sn8]Au1 + 2{[Sn–Sn10]Sn5} = Sn95.2Au4.8 alloys, respectively. The compositions of Au–Sn solders are then analyzed based on the interpreted dual-cluster formulas, which indicate that the number of atoms of the alloying elements that replace the atoms in the dual-cluster formulas is always an integer. The present method provides a quantitative approach toward developing a practical composition interpretation and design tool for Au–Sn-based solders.

A Cu Pillar Bump Bonding Method Using Au-Sn Alloy Cap as the Interconnection Layer

A Cu Pillar Bump Bonding Method Using Au-Sn Alloy Cap as the Interconnection Layer

Thermomechanical Stresses in Silicon Chips for Optoelectronic Devices

The growing interest in improving optoelectronic devices requires continuous research of the materials and processes involved in manufacturing. From a chemical point of view, the study of this sector is crucial to optimize existing manufacturing processes or create new ones. This work focusses on the experimental evaluation of residual stresses on samples that are intended to simulate part of the structure of an optoelectronic device. It represents an important starting point for the development of optoelectronic devices with characteristics suitable for future industrial production. Silicon chips, with a thickness of 120 μm, were soldered onto copper and alumina substrates, using different assembly parameters in terms of temperature and pressure. Using Raman spectroscopy, the stress evaluation was estimated in a wide temperature range, from −50 to 180 °C. Silicon chips soldered with AuSn alloy on copper substrates demonstrated at 22 °C a compressive stress, developed in the center of the assembly with a maximum value of −600 MPa, which reached −1 GPa at low temperatures. They present a stress distribution with a symmetric profile with respect to the central area of the chip. The silicon chip assembled on a ceramic substrate without pressure turned out to be extremely interesting. Even in the absence of pressure, the sample did not show a large shift in the Raman position, indicating a low stress.

Epitaxial Growth of SnS2 Ribbons on a Au-Sn Alloy Seed Film Surface.

Two-dimensional metal chalcogenide film has attracted considerable interest for its use as an emerging device material for nanoelectronics. The film has been synthesized by various methods such as chemical vapor deposition, molecular beam epitaxy, and thermal vapor sulfurization. In this study, we took a new approach to synthesize tin disulfide (SnS2) by using Au-Sn alloy film as a metal seed deposited on a sapphire substrate. Multilayer SnS2 films were formed in a ribbon shape on (111)-oriented Au film and were aligned in the directions of threefold rotational symmetry. Furthermore, the SnS2 was found to have an epitaxial relationship relative to the Au film and the sapphire substrate as follows: SnS2[2̅110] || Au[101̅] || Al2O3[011̅0]. The segregation of grains consisting of a Sn-rich phase on the Au film surface and the subsequent sulfurization of these grains can be the key to the epitaxial SnS2 ribbon formation.

Laser-induced alloy nanoparticles on Au-Sn thin layers

The paper analyses the process of Au-Sn alloy nanoparticles (ANPs) formation by laser-induced dewetting of thin intermetallic layers for the first time. Tests were carried out for several samples with different Au-Sn atomic ratios and different total layer thicknesses (7.5 and 15 nm). The initial parameters of the samples were verified by spectroscopic ellipsometry (SE). To develop the experiment, a nanosecond ytterbium fiber laser (Yb:glass) with a wavelength of 1064 nm was used. The study was carried out both with the use of single laser pulses as well as raster scanning of the given surface. The use of two modes allowed to determine the impact of key process parameters (including pulse energy, degree of pulse overlap and laser fluency) on the formation, evolution, morphology, distribution and chemical composition of the obtained structures. The optimal conditions for the formation of Au-Sn ANPs were established.The samples were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The chemical composition was analysed by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The optical properties of the obtained ANPs were determined by spectroscopic ellipsometry and the morphology and chemical composition were examined by transmission electron microscopy (TEM).

2430% Superplastic strain in a eutectic Au-Sn alloy with micrometer-sized grains maintained by spinodal-like decomposition

Polycrystalline metals with fine grains are highly possible to possess superplasticity via grain boundaries sliding (GBS). However, the mechanism of stabilizing the fine grains and releasing grain boundary strain incompatibilities to maintain GBS has puzzled the researchers for several decades. Here, a classic example is represented by the Au-Sn eutectic (ζ-Au5Sn + δ-AuSn) alloy with micrometer-sized equiaxed grains, which achieved 2430% tensile strain at 473 K. Characterization at nanoscale reveals, unexpectedly, the universal occurrence of spinodal-like decomposition in one of the eutectic phases (δ-AuSn phase) in the Au-Sn alloy. The occurrence of the spinodal-like decomposition is energetically favorable. Therefore, the system's free energy was minimized by the spinodal-like decomposition rather than grain growth. Micrometer-sized grains were thus maintained at relatively high temperatures for maintaining GBS. In addition, the stacking faults (SFs) were generated in the spinodal-like decomposed substructures during deformation. SFs coordinated the strain incompatibilities during GBS and contributed to the plastic flow during superplasticity. In the present Au-Sn alloy, the spinodal-like decomposition is the root cause to stabilize the fine grains, eventually leading to outstanding superplasticity. This study enriches our fundamental understanding of the relation between spinodal-like decomposition and mechanical performance. It also provides new insights into the design of polycrystalline metals to achieve superplasticity.

Improved contact resistance and solderability of electrodeposited Au-Sn alloy layer with high thermal stability for electronic contacts

We investigated the effect of thermal aging on the contact resistance and solderability of Au-Sn and Au-Co alloy films. The Au-Sn alloy exhibited lower contact resistance and better solderability compared to the conventional Au-Co alloy. In the Au-Sn alloy, an Au-Sn–Ni intermetallic compound layer was formed at the interface between the electroplated Ni and Au-Sn layers during the thermal aging process. The resulting Au-Sn–Ni layer effectively blocked the diffusion of underlying nickel to the surface, leading to improved solderability and enhanced thermal stability of the contact resistance. Meanwhile, the results revealed that a significant amount of nickel diffused to the surface of the Au-Co alloy during the thermal treatment, and the nickel atoms on the surface were oxidized to NiO or Ni2O3, which increased the contact resistance and deteriorated solderability by acting as a barrier layer.

Direct Observation of Crystal Facet Transformation During Gold-Tin Alloy Electroplating

Gold-Tin alloys are commonly used as solder materials in semiconductor industries. In this work, Au-Sn alloys have been electroplated with different bath conditions. For the first time, Au-Sn alloy single crystals have been observed. There are two kinds of single crystals were grown with the compositions of Au4Sn and Au2Sn, different from literature-stated Au5Sn and AuSn. The effects of bath composition and plating factors on crsytal facet development of Au-Sn deposits have been investigated. SEM/EDX analysis showed that only Au4Sn and Au2Sn phases are single crystals among all plated deposits. The growth of either Au4Sn or Au2Sn phases showed preferred orientation with plating conditions. We report on quantitative SEM/EDX characterizations used to study the facet transformation behavior of Au-Sn alloy at the nanometer scale. We have obtained direct evidence that the single crystals and crystal facet transformation of Au4Sn and Au2Sn does exist in Au-Sn alloy, and high Sn content enhanced the crystal growth through a spiral-like growth mechanism.

Thermomechanical stress in GaN‐LEDs soldered onto Cu substrates studied using finite element method and Raman spectroscopy

AbstractLocal thermomechanical stress can cause failures in semiconductor packages during long‐time operation under harsh environmental conditions. This study helps to explain the packaging‐induced stress in blue GaN‐LEDs soldered onto copper substrates using AuSn alloy as lead‐free interconnect material. Based on the finite element method, a virtual prototype is developed to simulate the thermomechanical behavior and stress in the LED and in the complete LED/AuSn/Cu assembly considering plastic and viscoplastic strain. The investigations were performed by varying the temperature between −50°C and 180°C. To validate the model, the simulation results are compared to experimental data collected with Raman spectroscopy. Studies of the phonon mode of GaN semiconductor are elaborated to understand the induced thermomechanical stress. The model enables evaluation of the stress in the interfaces of the assembly, which otherwise cannot be accessed by measurements. It serves to predict how assemblies would perform, before committing resources to build a physical prototype.

Electronic structure and morphology of thin surface alloy layers formed by deposition of Sn on Au(1 1 1)

We demonstrate formation of thin AuSn and Au2Sn surface alloy layers at room and elevated substrate temperatures (TS = 413–493 K), respectively by the deposition of Sn on Au(1 1 1) using core-level X-ray photoelectron spectroscopy and scanning tunneling microscopy. Low energy electron diffraction patterns show different surface structures: p(3 × 3) R15° at room temperature for AuSn, 2113 at TS = 413 K and (3×3) R30° at TS = 493 K for Au2Sn. Angle resolved photoemission spectroscopy reveals evolution of bands from an electron-like surface state to appearance of a hole-like band structure corresponding to AuSn and Au2Sn. The 2113 phase of Au2Sn, which has a unit cell of oblique symmetry, exhibits an interesting linear band that meets at the Fermi level in the zone-center and have Fermi velocity comparable to graphene. Thus, our study establishes that Au-Sn bimetallic surface alloys have interesting electronic properties with potential for future applications.

Electrochemical preparation of Pt nanoparticles modified nanoporous gold electrode with highly rough surface for efficient determination of hydrazine

A highly sensitive electrochemical sensing platform for hydrazine was developed based on a highly surface-roughened nanoporous gold electrode decorated with Pt nanoparticles (Pt/HNPG). The self-supporting composite electrode is binder-free, which was fabricated via anodization of a commercial AuSn alloy in HCl electrolyte and subsequent electrodeposition of H2PtCl6 precursor in aqueous solution. The morphology and composition of Pt/HNPG electrode were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of Pt/HNPG towards electrooxidation of hydrazine was examined. It is found that both Pt nanoparticles loadings and solution pH have strong influence on the electrocatalytic activity. At the potential of –0.1 V (vs. SCE), the fabricated composite electrode showed excellent sensing performance for hydrazine with a wide linear range of 5 μM to 6.105 mM, a low detection limit of 1.03 μM (signal-to-noise ratio (S/N) of 3) and a high sensitivity of 3449.68 μA mM−1 cm−2. Moreover, the sensor exhibited good selectivity, repeatability and stability. It was also successfully applied for the highly sensitive determination of hydrazine in real water samples with satisfactory results.

Plasmon-enhanced photoluminescence from SnO2 nanostructures decorated with Au nanoparticles

We report significantly enhanced photoluminescence from hybrid nanostructured Au/SnO2 thin films due to surface plasmons excited in Au nanoparticles decorating SnO2 nanostructured thin film. Nanostructured thin films with Au nanoparticles decorated SnO2 nanostructures were prepared by sputter deposition of ultrathin Au films following thermal evaporation of SnO2 film. The effects of deposition of ultrathin film of Au nanoparticles on the morphology, structure and optical response of nanostructured SnO2 film were investigated. Nanocrystalline SnO2, Au, Sn and Au-Sn alloy were revealed by XRD analysis. PL studies revealed that Au nanoparticle decoration of nanostructured SnO2 film led to highly enhanced UV emission. The mechanism of strong enhancement of PL from nanostructured SnO2 film is tentatively proposed. The coupling of excitonic emission from SnO2 nanostructures and excited surface plasmons in Au nanoparticles led to the observed strong PL enhancement. The hybrid nanostructured Au/SnO2 thin films with strong UV emission are promising for designing efficient optical and photoelectrical devices.

Au-Sn Catalyzed Growth of Ge1-xSnx Nanowires: Growth Direction, Crystallinity, and Sn Incorporation.

Ge1-xSnx nanowires (NWs) have been a focus of research attention for their potential in realizing next-generation Si-compatible electronic and optoelectronic devices. To control the growth of NWs and increase their Sn content, the growth mechanism needs to be understood. The use of Au-Sn alloy catalysts instead of Au catalysts allows an easier understanding of Ge1-xSnx NW growth, and the effects of Sn at different concentrations in catalysts on growth direction, Sn incorporation, and crystallinity of Ge1-xSnx NWs can be clarified. High Sn content in Au-Sn alloy catalysts favors ⟨110⟩-oriented NW growth and high Sn incorporation in NWs. The higher Sn content in Au-Sn alloy catalysts also improves the crystallinity of NWs.

Ionic liquid assisted combustion synthesis of ZnO and its modification by Au[sbnd]Sn bimetallic nanoparticles: An efficient photocatalyst for degradation of organic contaminants

AuSn/ZnO nanocatalyst was synthesized by a two-step synthetic approach in which AuSn alloy bimetallic nanoparticles (NPs) were incorporated into presynthesized ZnO in 1-butyl 3-methylimidazolium (BMIMBF4) ionic liquid (IL) via combustion route. The structure, morphology, and optical properties of the above synthesized material were analysed by using various analytical techniques, including X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive Spectroscopy Mapping (EDS), UV–vis Spectroscopy, Photoluminescence, Nitrogen Adsorption–Desorption, photoelectrochemical measurements and X-Ray Photoelectron Spectroscopy (XPS). The average particle size and the homogeneous distribution of AuSn nanoparticle over the surface of ZnO was analyzed by using TEM. XPS analysis provides information regarding the elemental structure of individual species as well as the possible electronic interaction between the nanoparticles. The photocatalytic activity of the nanocatalyst was studied towards the degradation of organic contaminants such as rhodamine B dye, 2-chlorophenol, phenol, 2,4- dichlorophenol and 2,4-dinitrophenol. After 90 min the complete degradation of Rhodamine B (95%) and phenol (94%) and its derivatives was achieved under visible irradiation. The high photoactivity of 3Au1Sn/ZnO can be attributed to the combined effect of enhanced light absorption intensity, longer lifetime of electron-hole pair, lower electron-hole recombination rate, increased stability, higher surface area and the synergistic effect between the metal nanoparticles and support material. It is expected that our current work could open promising prospects for the utilization of Sn-based bimetallic system as a potential visible light photocatalyst for environmental applications.

Realization of Strained Stanene by Interface Engineering.

Stanene, the tin analogue of graphene, has been predicted to be a two-dimensional topological insulator, providing an ideal platform for the realization of the quantum spin Hall effect even at room temperature. Here, continuous stanene has been successfully formed on the Au(111) substrate, and its crystalline structure, phonon properties, and electronic structures are investigated by scanning tunneling microscopy and in situ Raman spectroscopy combined with first-principles calculations. The surface Sn-Au alloy with a coverage-dependent structural evolution is first identified. At coverage above a critical value, the Au-Sn alloy is gradually converted into epitaxial stanene with a √3 × √7 superstructure. Distinctive vibrational phonon modes are discovered in √3 × √7 stanene through in situ Raman spectroscopy, which are correlated with the tensile strain evoked by its singular buckled structure. Our results present clear evidence for the existence of epitaxial stanene and provide a platform for exploration of the exotic properties of this strained two-dimensional material.

A Review of Developments in Au-Sn Eutectic Alloy Electrodeposition

Background: The problems in the electrochemical synthesis of Au-Sn alloy from aqueous and non-aqueous solutions concerning Au : Sn ratio and phase composition control, as well as the stability of the solutions and mechanisms of the alloying are discussed. The information is presented on the methods of Au-Sn eutectic synthesis by layer-by-layer gold and tin deposition and by simultaneous metals electrochemical reduction. The importance of this alloy synthesis is stipulated by its unique properties determining application as a solder in electronics and instrumentation. Method: The analysis is performed on the effect of tin and gold compounds composition and concentration in the solutions for electrochemical gold, tin and Au-Sn alloy deposition, the nature of a solvent, the value of pH in aqueous solutions, the availability of different additives on the stability of electrolytes, current efficiency, the rate of coatings deposition, and their chemical and phase composition. Results: The reasons for the instability of aqueous electrolytes such as Sn(II, IV) compounds hydrolysis, and Au(I, III) compounds reduction in the solution together with the causes of small tin content in the alloys which is largely stipulated by a great difference between gold and tin electrode potentials, are analyzed. The known methods of these drawbacks of diminution are described. Conclusion: The conceptions about mechanisms of electrochemical simultaneous reduction of Sn(II, IV) and Au(I, III) from aqueous and non-aqueous electrolytes are considered. The advantages and weak aspects of the usage of non-aqueous electrolytes based on glycols, mixtures of choline chloride with urea and/or glycols are shown.

Hierarchical bi-continuous Pt decorated nanoporous Au-Sn alloy on carbon fiber paper for ascorbic acid, dopamine and uric acid simultaneous sensing

In this work, Pt nanoparticles modified nanoporous AuSn(Pt@NP-AuSn) alloy on Ni buffered flexible carbon fiber paper (CFP) is fabricated by a simple replacement reaction in which NP-AuSn is fabricated by controllable dealloy of electrodeposited Au-Sn alloy films. The as prepared Pt@NP-AuSn/Ni/CFP possesses hierarchical pore structure, high specific surface area and excellent catalytic activity. Due to the bi-functions of both the large surface area of nanoporous metal and macroporous of carbon fiber paper facilitating mass transfer, the Pt@NP-AuSn/Ni/CFP shows high sensitivity of detecting ascorbic acid (AA), dopamine (DA) and uric acid (UA), with sensitivities of 0.14 μA μM−1 cm−2, 15.23 μA μM−1 cm−2, 0.28 μA μM−1 cm−2 under the concentration ranging from 200 to 2000 μM, 1–10 μM, and 25–800 μM for AA, DA and UA, respectively. Further, the Pt@NP-AuSn/Ni/CFP possesses long-term stability of sensing AA, DA and UA and presents great anti-interference towards a variety of common compounds in body fluid. All of these results manifest the Pt@NP-AuSn/Ni/CFP can be a promising candidate for the application of the electrochemical sensor for simultaneous detection of AA, DA and UA.

Ultra-rapid fabrication of highly surface-roughened nanoporous gold film from AuSn alloy with improved performance for nonenzymatic glucose sensing

Using one-step anodization strategy, a nanoporous gold film (HNPG) with large surface area was rapidly fabricated on Au80Sn20 (wt%) alloy in just 80 s. The formation of highly surface-roughened nanoporous structures results from a complex process of electrochemical dealloying of Sn component from AuSn alloy, anodic electrodissolution, disproportion and deposition of Au component, and spontaneous redox reaction between electrodissolved Sn2+ and AuCl4－species at the applied anodic potential. As-prepared HNPG/AuSn shows enhanced electrochemical performance for glucose oxidation in alkaline electrolyte. At a low potential of 0.1 V (vs. SCE), it offers a short response time of 4 s, a wide linear detection range of 2 μM to 8.11 mM, an ultralow detection limit of 0.36 μM (S/N = 3), an ultrahigh sensitivity of 4374.6 μA cm−2 mM−1, and satisfactory selectivity and reproducibility. Specifically, after 6 weeks, no obvious loss of glucose amperometric signal was observed on HNPG/AuSn. The facile preparation and excellent sensing performance of HNPG/AuSn electrode make sure that it is a promising candidate for advanced enzyme-free glucose sensors.

Hermetic packaging for implantable microsystems: Effectiveness of sequentially electroplated AuSn alloy.

With modern microtechnology, there is an aggressive miniaturization of smart devices, despite an increasing level of integration and overall complexity. It is therefore becoming increasingly important to be achieve reliable, compact packaging. For implantable medical devices (IMDs), the package must additionally provide a high quality hermetic environment to protect the device from the human body. For chip-scale devices, AuSn eutectic bonding offers the possibility of forming compact seals that achieve ultra-low permeability. A key feature is this can be achieved at process temperatures of below 350315°C, therefore allowing for the integration of sensors and microsystems with CMOS electronics within a single package. Issues however such as solder wetting, void formation and controlling composition make formation of high-quality repeatable seals highly challenging. Towards this aim, this paper presents our experimental work characterizing the eutectic stack deposition. We detail our designmethods and process flow, share our experiences in controlling electrochemical deposition of AuSn alloy and finally discuss usability of sequential electroplating process for the formation of hermetic eutectic bonds.