Two-Dimensional Conjugated Metal-Organic Framework/Graphene π–π Stacked Heterostructures for Ultrafast Photonics

2D conjugated metal-organic frameworks (MOFs) with high in-plane-π-conjugation are attracting significant attention in various fields owing to their outstanding electrical transport property, substantial specific surface areas, and tunable structures. However, their potential in ultrafast photonics has not been extensively explored. Herein, 2D conjugated Ni₃(HITP)₂ metal-organic framework (MOF) and graphene (GR) π–π stacked vertical heterostructures (NG-VHS) are synthesized using an ultrasound-assisted method. Based on theoretical simulations and characterization analyses, the results suggest that the fast interface charge transfer and the extension of the π-conjugated electron cloud will significantly enhance the electrical conductivity and the nonlinear optical properties, which is attributed to the π–π stacking interactions between Ni₃(HITP)₂ and GR. The charge transfer rate of NG-VHS is given by 6.9 × 10¹¹ s⁻¹. Noticeably, NG-VHS can serve as an excellent saturable absorber (SA) that can achieve fundamental mode-locking with a pulse width of 451 fs, harmonic mode-locking with repetition frequencies up to 1.205 GHz, and tunable dual-wavelength mode-locking. These results indicate the potential of NG-VHS as a promising nonlinear optical material for ultrafast optical applications and a new platform for the design of advanced optoelectronic devices based on 2D conjugated MOFs.     

Nanotribological Characteristics of Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript>, Cu<Subscript>3</Subscript>Sn,and Ni<Subscript>3</Subscript>Sn<Subscript>4</Subscript> Intermetallic Compounds

Nanotribological characteristics, including the coefficient of friction, wear coefficient, and wear resistance, of Cu₆Sn₅, Cu₃Sn, and Ni₃Sn₄ intermetallic compounds developed by the annealing of Sn–Cu or Sn–Ni diffusion couples were investigated in this work. The scratch test conditions combined a constant normal load of 10 mN, 20 mN, or 30 mN and a scratch rate of 0.1 μm/s, 1 μm/s, or 10 μm/s. Experimental results indicated that, as the normal load increases, the pile-up grows taller and the scratch deepens, leading to a greater coefficient of friction and wear coefficient, and reduced wear resistance. Moreover, the scratch rate does not have a significant effect on the nanotribological characteristics except for those of Cu₆Sn₅ and Cu₃Sn under a normal load of 10 mN. Though the hardness of Cu₆Sn₅, Cu₃Sn, and Ni₃Sn₄ is similar, Ni₃Sn₄ appears to be more prone to wear damage.     

Electromigration-Induced Interfacial Reactions in Cu/Sn/Electroless Ni-P Solder Interconnects

The effect of electromigration (EM) on the interfacial reaction in a line-type Cu/Sn/Ni-P/Al/Ni-P/Sn/Cu interconnect was investigated at 150°C under 5.0 × 10³ A/cm². When Cu atoms were under downwind diffusion, EM enhanced the cross-solder diffusion of Cu atoms to the opposite Ni-P/Sn (anode) interface compared with the aging case, resulting in the transformation of interfacial intermetallic compound (IMC) from Ni₃Sn₄ into (Cu,Ni)₆Sn₅. However, at the Sn/Cu (cathode) interface, the interfacial IMCs remained as Cu₆Sn₅ (containing less than 0.2 wt.% Ni) and Cu₃Sn. When Ni atoms were under downwind diffusion, only a very small quantity of Ni atoms diffused to the opposite Cu/Sn (anode) interface and the interfacial IMCs remained as Cu₆Sn₅ (containing less than 0.6 wt.% Ni) and Cu₃Sn. EM significantly accelerated the dissolution of Ni atoms from the Ni-P and the interfacial Ni₃Sn₄ compared with the aging case, resulting in fast growth of Ni₃P and Ni₂SnP, disappearance of interfacial Ni₃Sn₄, and congregation of large (Ni,Cu)₃Sn₄ particles in the Sn solder matrix. The growth kinetics of Ni₃P and Ni₂SnP were significantly accelerated after the interfacial Ni₃Sn₄ IMC completely dissolved into the solder, but still followed the t ^1/2 law.     

Ni Interdiffusion Coefficient and Activation Energy in Cu6Sn5

Ni diffusion in Cu₆Sn₅ intermetallic compound was investigated. First, we successfully fabricated preferred-orientation Cu₆Sn₅ crystal by liquid-phase electroepitaxy (LPEE). Then, Ni/Cu₆Sn₅ diffusion couples were produced by sputtering from a Ni thin film onto the Cu₆Sn₅ crystal. Ni/Cu₆Sn₅ diffusion couples were annealed at different temperatures of 120°C, 160°C, 200°C, 255°C, 290°C, and 320°C for 2 h in a vacuum. The Ni atomic profile across the Ni/Cu₆Sn₅ interface was obtained by electron spectroscopy for chemical analysis (ESCA). From the Ni atomic profiles, the Matano method was used to evaluate the Ni interdiffusion coefficients ([(D)\tilde]_Ni \tilde{D}_{\rm{Ni}} ) in the Cu₆Sn₅ crystal obtained with different annealing temperatures, which then yields the activation energy for Ni diffusion in the Cu₆Sn₅ crystal at a particular Ni content. We found that, as Ni diffuses in the ternary Cu_6−x Ni _x Sn₅ compound phase, the activation energy of Ni interdiffusion decreases with the Ni content.     

Effect of Cu concentration on the reactions between Sn-Ag-Cu solders and Ni

The reaction between the Sn-Ag-Cu solders and Ni at 250°C for 10 min and 25 h was studied. Nine different Sn-Ag-Cu solders, with the Ag concentration fixed at 3.9 wt.% and Cu concentrations varied between 0.0–3.0 wt.%, were used. When the reaction time was 10 min, the reactions strongly depended on the Cu concentration. At low-Cu concentrations (≦0.2 wt.%), only a continuous (Ni_1−xCu_x)₃Sn₄ layer formed at the interface. When the Cu concentration increased to 0.4 wt.%, a continuous (Ni_1−xCu_x)₃Sn₄ layer and a small amount of discontinuous (Cu_1−yNi_y)₆Sn₅ particles formed at the interface. When the Cu concentration increased to 0.5 wt.%, the amount of (Cu_1−yNi_y)₆Sn₅ increased and (Cu_1−yNi₆)₆Sn₅ became a continuous layer. Beneath this (Cu_1−yNi_y)₆Sn₅ layer was a very thin but continuous layer of (Ni_1−xCu_x)₃Sn₄. At higher Cu concentrations (0.6–3.0 wt.%), (Ni_1−xCu_x)₃Sn₄ disappeared, and only (Cu_1−yNi_y)₆Sn₅ was present. The reactions at 25 h also depended strongly on the Cu concentration, proving that the strong concentration dependence was not a transient phenomenon limited to a short reaction time. The findings of this study were rationalized using the Cu-Ni-Sn isotherm. This study shows that precise control over the Cu concentration in solders is needed to produce consistent results.     

Proton Turnover Dominated Cascade Route for CO2 Photoreduction

Photoreduction carbon dioxide (CO₂) and water (H₂O) into valuable chemicals is a huge potential to mitigate immoderate CO₂ emissions and energy crisis. To date, tremendous attention is concentrated on the improvement of independent CO₂ reduction or H₂O oxidation behaviors. However, the simultaneous control of efficient electron and hole utilization is still a huge challenge due to the complex cascade redox reactions. Here, a proton turnover exists in the whole CO₂ photoreduction process is discovered, which is defined as the pivot to concatenate the hole and electron behaviors. As a demonstration of the concept, the efficient activated hydrogen (*H) production centers of copper (Cu) and rapid hydrogenation centers of nickel (Ni) are coupled by an alloying strategy, and the proton turnover behaviors could be directly determined by adjustment of the molar ratios of Cu_xNi_y. Moreover, Cu₃Ni₁–TiO₂ exhibits the highest electron selectivity of 93.7% for methane (CH₄) production with a rate of 175.9 µmol g⁻¹ h⁻¹, while Cu₁Ni₅–TiO₂ reaches up to the highest carbon monoxide (CO) electron selectivity and generation rate at 84.4% and 164.6 µmol g⁻¹ h⁻¹, respectively. Consequently, the experimental and theoretical analysis all clarify the predominate proton turnover effect during the overall CO₂ photoreduction process, which directly determines the categories and generated efficiency of C-based products by regulating variable reaction pathways. Therefore, the revelation of the proton turnover pivot could broaden the new sights by bidirectional optimization of dynamics during the overall CO₂ photoreduction system, which favors the efficient, selective, and stable photocatalytic CO₂ reduction with H₂O.     

Reflow and burn-in of a Sn-20In-0.8Cu ball grid array package with a Au/Ni/Cu pad

The intermetallic compounds formed after reflow and burn-in testing of a Sn-20In-0.8Cu solder ball grid array (BGA) package are investigated. Along with the formation of the Cu₆(Sn_0.78In_0.22)₅ precipitates (IM1) in the solder matrix, scallop-shaped intermetallic compounds (IM2) with a compositional mixture of Cu₆(Sn_0.87In_0.13)₅ and Ni₃(Sn_0.87In_0.13)₄ appear at the interfaces between the solder balls and Au/Ni/Cu pads. A significant number of intermetallic particles (IM3), with a composition of (Au_0.80Cu_0.20)(In_0.33Sn_0.67)₂, can also be found in the solder matrix. After aging at 115°C for 750 h, an additional intermetallic compound layer (IM4) with a composition of (Ni_0.91Cu_0.09)₃(Sn_0.77In_0.23)₂ is formed at the interface between IM2 and the Ni layer. The ball shear strength of the Sn-20In-0.8Cu BGA solder after reflow is 4.5 N and will rise to maximum values after aging at 75°C and 115°C for 100 h. With a further increase of the aging time at both temperatures, the joint strengths exhibit a tendency to decline linearly at about 1.7×10⁻³ N/h.     

Effects of Electromigration on Interfacial Reactions in the Ni/Sn-Zn/Cu Solder Interconnect

Electromigration in the Ni/Sn-Zn/Cu solder interconnect was studied with an average current density of 3.51 × 10⁴ A/cm² for 168.5 h at 150°C. When the electrons flowed from the Ni side to the Cu side, uniform layers of Ni₅Zn₂₁ and Cu₅Zn₈ were formed at the Ni/Sn-Zn and Cu/Sn-Zn interfaces. However, upon reversing the current direction, where electron flow was from the Cu side to the Ni side, a thicker Cu₆Sn₅ phase replaced the Ni₅Zn₂₁ phase at the Ni/Sn-Zn interface, whereas at the Cu/Sn-Zn interface, a thicker β-CuZn phase replaced the Cu₅Zn₈ phase.     

Confinement-Induced Phonon Softening and Hardening in Sb2Te3 Thin Films

Scaling effects in Sesqui-chalcogenides are of major interest to understand and optimize their performance in heavily scaled applications, including topological insulators and phase-change devices. A combined experimental and theoretical study is presented for molecular beam epitaxy-grown films of antimony-telluride  (Sb₂Te₃). Structural,vibrational, optical, and bonding properties upon varying confinement are studied for thicknesses ranging from 1.3 to 56 nm. In ultrathin films, the low-frequency coherent phonons of A_1g¹ symmetry are softened compared to the bulk (64.5 cm⁻¹ at 1.3 nm compared to 68 cm⁻¹ at 55.8 nm). A concomitant increase of the high-frequency A_1g² Raman mode is seen. X-ray diffraction analyses unravel an accompanying out of plane stretch by 5%, mainly stemming from an increase in the Te-Te gap. This conclusion is supported by density functional theory slab models, which reveal a significant dependency of chemical bonding on film thickness. Changes in atomic arrangement, vibrational frequencies, and bonding extend over a thickness range much larger than observed for other material classes. The finding of these unexpectedly pronounced thickness-dependent effects in quasi-2D material Sb₂Te₃ allows tuning of the film properties with thickness. The results are discussed in the context of a novel bond-type, characterized by a competition between electron localization and delocalization.     

Intermetallic Reactions in Sn-0.4Co-0.7Cu Solder BGA Packages with an ENIG Surface Finish

As-cast Sn-0.4Co-0.7Cu solder contains both (Cu_0.98Co_0.02)₆Sn₅ and (Co_0.85Cu_0.15) Sn₃ intermetallic phases in the matrix. After reflowing, the Au thin film in the electroless Ni/immersion Au (ENIG) surface-finished Sn-0.4Co-0.7Cu solder ball grid array (BGA) packages dissolved rapidly into the solder matrix to form AuSn₄ intermetallics, and a thin layer of (Cu_0.57Ni_0.35Au_0.08)₆Sn₅ intermetallic compound appeared at the solder/pad interface, growing very slowly during aging at 100°C. Increasing the aging temperature to 150°C caused the formation of a new intermetallic layer, (Ni_0.79Cu_0.21)₃Sn₄, at the (Cu_0.57Ni_0.35Au_0.08)₆Sn₅/Ni interface. The reflowed Sn-0.4Co-0.7Cu BGA packages have a ball shear strength of 6.8 N, which decreases to about 5.7 N and 5.5 N after aging at 100°C and 150°C, respectively. The reflowed and aged solder joints fractured across the solder balls with ductile characteristics in ball shear tests.     

Nanoporous PdNi Bimetallic Catalyst with Enhanced Electrocatalytic Performances for Electro‐oxidation and Oxygen Reduction Reactions

A nanoporous PdNi (np‐PdNi) bimetallic catalyst fabricated by electrochemically dealloying a Pd₂₀Ni₈₀ alloy in an acid solution is reported. Residual Ni in the nanoporous alloy can be controlled by tuning dealloying potentials and the electrocatalysis of the np‐PdNi shows evident dependence on Ni concentrations. With ～9 at.% Ni, the np‐PdNi bimetallic catalyst presents superior electrocatalytic performances in methanol and formic acid electro‐oxidation as well as oxygen reduction in comparison with commercial Pd/C and nanoporous Pd (np‐Pd). The excellent electrocatalytic properties of the dealloyed np‐PdNi bimetallic catalyst appear to arise from the combined effect of unique bicontinuous nanoporosity and bimetallic synergistic action.     

A wide-range VCO with an automatic frequency,amplitude and gain calibration loop

This paper presents a wide tuning range VCO with an automatic frequency, amplitude and gain calibration loop. To cover the wide tuning range, the automatic frequency calibration (AFC) loop is used. In addition, to provide the optimum Negative-Gm to the LC tank in a wide frequency range, the number of active Negative-Gm circuits is designed to be switched digitally based on the target frequency. Also, the VCO gain should be calibrated digitally to compensate for the gain variation. The VCO tuning range is 2.6 GHz, from 1.7 to 4.3 GHz, and the power consumption is 2–4 mA from a 1.8 V supply. The measured VCO phase noise is −120 dBc/Hz at 1 MHz offset.     

The effect of intermetallic compound morphology on Cu diffusion in Sn-Ag and Sn-Pb solder bump on the Ni/Cu Under-bump metallization

The eutectic Sn-Ag solder alloy is one of the candidates for the Pb-free solder, and Sn-Pb solder alloys are still widely used in today’s electronic packages. In this tudy, the interfacial reaction in the eutectic Sn-Ag and Sn-Pb solder joints was investigated with an assembly of a solder/Ni/Cu/Ti/Si₃N₄/Si multilayer structures. In the Sn-3.5Ag solder joints reflowed at 260°C, only the (Ni_1−x,Cu_x)₃Sn₄ intermetallic compound (IMC) formed at the solder/Ni interface. For the Sn-37Pb solder reflowed at 225°C for one to ten cycles, only the (Ni_1−x,Cu_x)₃Sn₄ IMC formed between the solder and the Ni/Cu under-bump metallization (UBM). Nevertheless, the (Cu_1−y,Ni_y)₆Sn₅ IMC was observed in joints reflowed at 245°C after five cycles and at 265°C after three cycles. With the aid of microstructure evolution, quantitative analysis, and elemental distribution between the solder and Ni/Cu UBM, it was revealed that Cu content in the solder near the solder/IMC interface played an important role in the formation of the (Cu_1−y,Ni_y)₆Sn₅ IMC. In addition, the diffusion behavior of Cu in eutectic Sn-Ag and Sn-Pb solders with the Ni/Cu UBM were probed and discussed. The atomic flux of Cu diffused through Ni was evaluated by detailed quantitative analysis in an electron probe microanalyzer (EPMA). During reflow, the atomic flux of Cu was on the order of 10¹⁶−10¹⁷ atoms/cm²sec in both the eutectic Sn-Ag and Sn-Pb systems.     

A 84% tuning range, 4.3-GHz VCO with two-step negative-G<Subscript>m</Subscript> tuning and amplitude calibration loop

This paper presents wideband, low voltage CMOS LC-VCO with automatic two-step amplitude calibration loop to compensate the PVT variation. To cover the wide tuning range, digital automatic negative-G_m tuning loop and analog automatic amplitude calibration loop are proposed. The power consumption is 2–6 mA from a 1.2 V supply. The VCO tuning range is 3.4 GHz, from 2.35 to 5.75 GHz. The measured phase noise is −117 dBc/Hz at the 1 MHz offset when the center frequency is 4.313 GHz.     

Interfacial reactions and compound formation in the edge of PbSn flip-chip solder bumps on Ni/Cu under-bump metallization

Flip-chip technology with the layout of ball grid array has been widely used in today’s microelectronics industry. The elemental distribution in the edge of the solder bump is crucial for its correlation with the bump strength. In this study, Ni/Cu under-bump metallization (UBM) was used to evaluate the intermetallic compound (IMC) formation in the edge of the solder bump between the UBM and eutectic Sn-Pb solder in the 63Sn-37Pb/Ni/Cu/Ti/Si₃N₄/Si multilayer structure. During reflows, layered-type (Ni_1−xCu_x)₃Sn₄ and island-like (Cu_1−yNi_y)₆Sn₅ IMCs formed in the interface between the solder and UMB, while only the (Cu_1−yNi_y)₆Sn₅ IMC was observed in the sideway of the Ni/Cu UBM. After high-temperature storage (HTS) at 150°C for 1,000 h, both (Cu_1−yNi_y)₆Sn₅ and (Cu_1−zNi_z)₃Sn were found in the sideway of the Ni/Cu UBM. Two other IMCs, (Ni_1−xCu_x)₃Sn₄ and (Cu_1−yNi_y)₆Sn₅, formed in the interface between the solder and UBM. The growth of the (Cu_1−yNi_y)₆Sn₅ IMC was relatively fast during HTS.     

The Effects of Solid-State Aging on the Intermetallic Compounds of Sn-Ag-Bi-In Solders on Cu Substrates

The growth behavior of the intermetallic compounds that formed at the interfaces between Sn-Ag-Bi-In solders and Cu substrates during solid-state aging is investigated. The compositions of the intermetallic compounds are Cu₃(Sn,In) near the Cu substrates and Cu₆(Sn,In)₅ near the solders; very little Bi or Ag was dissolved in the compounds. The aging temperatures were 120°C, 150°C, and 180°C for 5 days, 10 days, 20 days, and 40 days. The change in the morphology of Cu₆(Sn,In)₅ from scallop type to layer type was prominent at the aging temperature of 180°C. The thickness of the compound layers did not vary much at the lower aging temperatures but followed the diffusion- controlled mechanism at 180°C. Massive Kirkendall voids were observed in Cu₃(Sn,In) layers at the aging temperature of 180°C.     

Interfacial Reactions of Sn-9Zn-<Emphasis Type="Italic">x</Emphasis>Cu (<Emphasis Type="Italic">x</Emphasis> = 1, 4, 7, 10) Solders with Ni Substrates

This study investigates the effects of various reaction times and Cu contents on the interfacial reactions between Sn-9Zn-xCu alloys and Ni substrates. After aging at 255°C for 1 h to 3 h, the Ni₅Zn₂₁ and Cu₅Zn₈ phases formed at the interface of Sn-9Zn/Ni and Sn-9Zn-1wt.%Cu/Ni couples, respectively. The (Ni,Zn)₃Sn₄ phase was found in the Sn-9Zn-4wt.%Cu/Ni couple, and the (Cu,Ni)₆Sn₅ and Cu₆Sn₅ phases formed, respectively, in the Sn-9Zn-7wt.%Cu/Ni and Sn-9Zn-10wt.%Cu/Ni couples. As the reaction time was increased from 5 h to 24 h, the (Cu₅Zn₈ + Ni₅Zn₂₁) phases replaced the Cu₅Zn₈ phase to form in the Sn-9Zn-1wt.%Cu/Ni couple; the (Ni,Zn)₃Sn₄ phase formed in the Sn-9Zn-4wt.%Cu/Ni couple, and (CuZn + Cu₆Sn₅) formed in the Sn-9Zn-10wt.%Cu alloys. Experimental results indicate that intermetallic compound (IMC) formation in Sn-9Zn-xCu/Ni couples changes dramatically with reaction time and Cu content. The Sn-Zn-Ni, Sn-Cu-Ni, and Sn-Zn-Cu ternary isothermal sections greatly help us to understand the IMC evolutions in the Sn-9Zn-xCu/Ni couples.     

Symbiotically Reinforced Bimetallic Photocatalysis in Conjugated Metal−Organic Framework Nanosheets

Compared to monometallic counterparts, bimetallic two-dimensional conjugated metal-organic framework (2D c-MOF) nanosheets possess preferable metal tunability and synergistic effect for performance optimization, yet rarely developed in photocatalytic hydrogen evolution to date. In this study, a feasible post-synthetic strategy of second metal installation (SMI) is proposed and applied to construct a crystalline bimetallic 2D c-MOF nanosheet, HTHATN-Ni-Pt-NS. HTHATN-Ni-Pt-NS exhibits high electrical conductivity and efficient hydrogen evolution with the rate of 47.2 mmol g⁻¹ h⁻¹, which is 13.5-fold higher than that of pristine HTHATN-Ni-NS without Pt^II decoration under visible light irradiation. Experimental and theoretical analysis reveal that introduction of low amount of Pt^II provides catalytically active metal sites and optimizes the ΔG_H* value of Ni^II centers, thus resulting in the enhanced performance of proton reduction. This study represents the first example of symbiotic bimetallic centers in MOF nanosheets highlighting SMI strategy as an efficient approach to construct photocatalysts.     

Effect of intermetallic compound formation on electrical properties of Cu/Sn interface during thermal treatment

Cu₆Sn₅ and Cu₃Sn intermetallic compounds are commonly found in the Sn-Cu bimetallic system. Due to the distinct resistivity of these two compounds, the electrical properties of Cu/Sn interfaces, e.g., solder joints on Cu metallization, may be impacted by the formation of Cu-Sn compounds. In this study, the kinetics of Sn-Cu compound formation was investigated by in-situ resistivity measurement, x-ray diffraction, and scanning electron microscopy (SEM). The interfacial reaction of the Cu-Sn bimetallic thin film specimen was monitored by the resistivity change of the specimen during thermal treatment. The activation energy of formation of Cu-Sn compounds was determined to be 0.97±0.07 eV. It is proposed that the Cu₆Sn₅ compound first forms at Sn/Cu interfaces and then reacts with Cu, forming the Cu₃Sn compound at elevated temperatures during the thermal ramping process. The effect of thin film thickness on the sequential formation of Sn-Cu compounds is also discussed.     

Interactions between solder and metallization during long-term aging of advanced microelectronic packages

The reactions between the eutectic PbSn solder and the Au/Ni/Cu tri-layer metallization in advanced microelectronic packages were studied. In this investigation, reflowed packages were subjected to aging at 160°C for times as long as 4000 h. Immediately after the reflow, all the Au had left the Au/Ni/Cu metallization, forming many (Au_1−xNi_x)Sn₄ particles distributed throughout the whole solderjoint. In addition, there was a thin layer of Ni₃Sn₄ (1.4 μm) at the interface. After 500 h of aging, most of the (Au_1−xNi_x)Sn₄ particles regrouped at the interface as a continuous (Au_0.45Ni_0.55)Sn₄, layer over the Ni₃Sn₄ layer. After 2500 h of aging, nearly all the Ni layer had been consumed. A 15 μm layer of (Au_0.45Ni_0.55) Sn₄ and a 20 μm Ni₃Sn₄ were found over the remaining Ni. At 3000 h, the Cu had started to react with both Ni₃Sn₄ and (Au_1−xNi_x)Sn₄, forming a layer of (Cu_1−p−pAu_pNi_q)₆Sn₅, a layer of (Cu_1−r−sAu₁Ni_s)₆Sn₅, and a layer of Cu₃Sn over the Cu layer. A small amount of Cu (2.7–5.7 at.%) was found to dissolve in this Ni₃Sn₄, forming a ternary compound (Ni_1−yCu_y)₃Sn₄. It was revealed that Au diffused up-hill during the reaction. After aging for 4000 h, all the (Au_1−xNi_x)Sn₄ had disappeared and Au atoms had diffused into the (Cu_1−p−qAu_pNi_q)₆Sn₅ and (Cu_1−r−sAu_rNi_s)₆Sn₅ phases. The practical implications for the above findings were pointed out in this paper.