In Vivo Subcutaneous Thermal Video Recording by Supersensitive Infrared Nanothermometers

Some of the old and unrealizable dreams of biomedicine have become possible thanks to the appearance of novel advanced materials such as luminescent nanothermometers, nanoparticles capable of providing a contactless thermal reading through their light emission properties. Luminescent nanothermometers have already been demonstrated to be capable of in vivo subcutaneous punctual thermal reading but their real application as diagnosis tools still requires demonstrating their actual capacity for the acquisition of in vivo, time‐resolved subcutaneous thermal images. The transfer from 1D to 2D subcutaneous thermal sensing is blocked in the last years mainly due to the lack of high sensitivity luminescent nanothermometers operating in the infrared biological windows. This work demonstrates how core/shell engineering, in combination with selective rare earth doping, can be used to develop supersensitive infrared luminescent nanothermometers. Erbium, thulium, and ytterbium core–shell LaF₃ nanoparticles, operating within the biological windows, provide thermal sensitivities as large as 5% °C^?1. This “record” sensitivity has allowed for the final acquisition of subcutaneous thermal videos of a living animal. Subsequent analysis of thermal videos allows for an unequivocal determination of intrinsic properties of subcutaneous tissues, opening the venue to the development of novel thermal imaging‐based diagnosis tools.     

AgIn2/Ag2In transformations in an In-49Sn/Ag soldered joint under thermal aging

The interfacial reaction between liquid In-49Sn solders and Ag substrates results in the formation of a thicker Ag₂In intermetallic compound accompanied with the development of a thin AgIn₂ layer. Through further aging of the In-49Sn/Ag soldered specimens at various temperatures ranging from room to 100°C, solid/solid trnasitions between Ag₂In and AgIn₂ intermetallic compounds can be observed. When the temperature drops below 75°C, Ag₂In will react with the In-49Sn solder to form the dominant AgIn₂ phase. Conversely, AgIn₂ is consumed at a higher temperature (e.g., 100°C) when reacting with the Ag substrate to create a now dominant Ag₂In phase. Lastly, the different mechanical, electrical, magnetic, and corrosion behaviors of both intermetallic compounds are respectively made known through direct measurements of the material properties of the individual Ag₂In and AgIn₂ bulk samples.     

Controlled Synthesis of Ag2S,Ag2Se,and Ag Nanofibers by Using a General Sacrificial Template and Their Application in Electronic Device Fabrication

Nanofiber bundles of Ag₂S, Ag₂Se, and Ag have been successfully synthesized by making use of Ag₂C₂O₄ template nanofiber bundles, utilizing both anion‐exchange and redox reactions. The obtained bundles were polycrystalline nanofibers composed of nanoparticles in which the precursor morphology was well‐preserved, indicating that Ag₂C₂O₄ nanofiber bundles acted as a general sacrificial template for the synthesis of silver‐based semiconductor and metal nanofibers. Dispersing media and transforming reactants were found to be key factors influencing the chemical transformation in the system. In particular, separate single‐crystalline Ag nanofibers were obtained via a nontemplate route when ascorbic acid was used as a relatively weak reductant. An electrical transfer and switching device was built with the obtained Ag₂S and Ag nanofiber bundles, utilizing the unique ion‐conductor nature of Ag₂S and revealing their potential applications in electronics.     

Phosphorescent Cationic Au4Ag2 Alkynyl Cluster Complexes for Efficient Solution‐Processed Organic Light‐Emitting Diodes

Cationic Au₄Ag₂ heterohexanuclear aromatic acetylides cluster complexes supported by bis(2‐diphenylphosphinoethyl)phenylphosphine (dpep) are prepared. The Au₄Ag₂ cluster structure originating from the combination of one anionic [Au(C≡CR)₂]^? with one cationic [Au₃Ag₂(dpep)₂(C≡CR)₂]³⁺ through the formation of Ag?acetylide η²‐bonds is highly stabilized by Au–Ag and Au–Au contacts. The Au₄Ag₂ alkynyl cluster complexes are moderately phosphorescent in the fluid CH₂Cl₂ solution, but exhibit highly intense phosphorescent emission in solid state and film. As revealed by theoretical computational studies, the phosphorescence is ascribable to significant ³[π (aromatic acetylide) → s/p (Au)] ³LMCT parentage with a noticeable Au₄Ag₂ cluster centered ³[d → s/p] triplet state. Taking advantage of mCP and OXD‐7 as a mixed host with 20 wt% dopant of phosphorescent Au₄Ag₂ cluster complex in the emitting layer, solution‐processed organic light‐emitting diodes (OLEDs) exhibit highly efficient electrophosphorescence with the maximum current, power, and external quantum efficiencies of 24.1 cd A^?1, 11.6 lm W^?1, and 7.0%, respectively. Introducing copper(I) thiocyanate (CuSCN) as a hole‐transporting layer onto the PEDOT:PSS hole‐injecting layer through the orthogonal solution process induces an obvious improvement of the device performance with lower turn‐on voltage and higher electroluminescent efficiency.     

Electric current effects on Sn/Ag interfacial reactions

The effect of electric current on the Sn/Ag interfacial reaction was studied at 140°C and 200°C, by examining the growth of phase (ε-Ag₃Sn) in the Sn/Ag reaction couples with a constant current density. Only at 140°C was the growth of phase affected by the passage of electric current. The growth rate was enhanced when diffusion of Sn and electron flow were in the same direction, and retarded when they were in the opposite direction. It was found that the diffusion coefficient of Sn through Ag₃Sn was 3.37 μm²/h and the apparent effective charge for Sn in Ag₃Sn was −90, at 140°C.     

On the thermal properties of Ag2Te and Ag2Se in the region of the phase transition

A setup is developed for measuring the thermal properties of Ag₂Te and Ag₂Se near the main phase transition and in the region of it in high vacuum. The samples are of stoichiometric composition with an excess of Ag, Te, and Se. Differential thermal analysis is performed and the temperature differences across and along the samples are measured by the pulsed light method. Using data on the thermal diffusivity a(T), the temperature dependence of the thermal conductivity K = apc is determined, where p is the density and c is the specific heat. The measurement technique used allows us to establish that the main phase transitions are accompanied by intense heat release. New phase transitions before and after the main structural phase transition with heat absorption are found. According to the DTA data, in the Ag₂Te sample with an excess of Ag (0.25 at.%, cn = 1.2 × 10¹⁹ cm^?3) the phase transition at 365 K is also accompanied by heat absorption. Thus, it is established that all of the phase transitions in Ag₂Te and Ag₂Se are first-order.     

Mechanisms for interfacial reactions between liquid Sn-3.5Ag solders and cu substrates

Intermetallic compounds formed during the soldering reactions between Sn-3.5Ag and Cu at temperatures ranging from 250°C to 375°C are investigated. The results indicate that scallop-shaped η-Cu₆(Sn_0.933 Ag_0.007)₅ intermetallics grow from the Sn-3.5Ag/Cu interface toward the solder matrix accompanied by Cu dissolution. Following prolonged or higher temperature reactions, ɛ-Cu₃ (Sn_0.996 Ag_0.004) intermetallic layers appear behind the Cu₆(Sn_0.933 Ag_0.007)₅ scallops. The growth of these interfacial intermetallics is governed by a kinetic relation: ΔX=tⁿ, where the n values for η and ɛ intermetallics are 0.75 and 0.96, respectively. The mechanisms for such nonparabolic growth of interfacial intermetallics during the liquid/solid reactions between Sn-3.5Ag solders and Cu substrates are probed.     

Interfacial reactions between In 10Ag solders and Ag substrates

The morphology and growth kinetics of intermetallic compounds formed during the reaction of liquid In 10Ag on Ag substrates in the temperature range between 250°C and 375°C are studied. The results indicate that the Ag₂In intermetallic compounds that appear at the interface are in the columnar shape, enveloped by thin AgIn₂ shells. The growth kinetics of intermetallic compounds are parabolic, indicating that the reaction is diffusion-controlled. The Arrhenius reaction activation energy was found to be 44.9 kJ/mol. Also, the wetting behavior of the In10Ag on Ag substrates was studied. The results show that there exists a transient plateau of the contact angle variation. Such a phenomenon can be explained by the intermetallic compound precursor halo formation preceding the edge of the solder drop.     

Soldering reactions between In49Sn and Ag thick films

The interfacial reactions between In49Sn solders and Ag thick films at temperatures ranging from 200°C to 350°C have been studied. The intermetallic compound formed at the Ag/In49Sn interface is Ag₂In enveloped in a thin layer of AgIn₂. Through the measurement of the thickness decrease of Ag thick films, it has been determined that the reaction kinetics of Ag₂In has a linear relation to reaction time. Morphology observations indicated that the linear reaction of Ag₂In was caused by the floating of Ag₂In into the In49Sn solder as a result of the In49Sn solder penetrating into the porous Ag thick film. A sound joint can be obtained when a sufficient thickness of the Ag thick film (over 19.5 μm) reacts with the In49Sn solder. In this case, the tensile tested specimens fracture in the In49Sn matrix.     

Regeneration of novel visible-light-driven Ag/Ag3PO4@C3N4 hybrid materials and their high photocatalytic stability

Novel visible-light-driven Ag₃PO₄@C₃N₄PO₄ loaded with metal Ag were synthesised via an anion-exchange precipitation method and regenerated by H₂O₂ and NaNH₃HPO₄. The obtained Ag/Ag₃PO₄@C₃N₄ and regenerated Ag/Ag₃PO₄@C₃N₄ were characterised by XRD, XPS, SEM and UV–vis. The XRD and UV–vis results revealed that the crystal structure and light adsorption property of Ag/Ag₃PO₄@C₃N₄ were similar to that of regenerated Ag/Ag₃PO₄@C₃N₄. The XPS result showed that the metallic Ag⁰ deposited on the surface of Ag/Ag₃PO₄@C₃N₄ and regenerated Ag/Ag₃PO₄@C₃N₄. The Ag/Ag₃PO₄@C₃N₄ hybrids displayed remarkable photocatalytic activity and stability after regeneration. Compared with pure Ag₃PO₄ or C₃N₄, the Ag/Ag₃PO₄@C₃N₄ and regenerated Ag/Ag₃PO₄@C₃N₄ enhancement in the photodegradation rate towards methyl orange is observed over under visible light irradiation. The enhanced photocatalytic performance was attributed to the synergistic effect between Ag₃PO₄ and C₃N₄ and a small amount of Ag⁰ which suppresses the charge recombination during photocatalytic process. This work could provide new insights into the fabrication of high stability visible photocatalysts and facilitate their practical application in environment issues.     

Microstructural evaluation and failure analysis of Ag wire bonded to Al pads

We found the failure mechanisms in Ag wire bonded to Al pads during the high-temperature-storage lifetime test (HTST) and the unbiased highly-accelerated temperature and humidity storage test (uHAST). The native oxide layer on the Al pads caused a ball lift. The moisture and the thermal energy during uHAST along with the Cl⁻ ion in epoxy molding compounds (EMCs) induced repetitive oxidation and reduction reactions of the Ag–Al intermetallic compounds (IMCs) with the Al pads. These repetitive reactions formed H₂ gas as a by-product causing the formation of a micro-crack. In addition, the alumina layer acted as a resistive layer in the Ag–Al IMCs. The phases of the Ag–Al IMCs were identified as Ag₂Al and Ag₃Al, and the growth rates of those IMCs were measured at 150 and 175 °C for 2000 h.     

Electrodeposited and characterization of Ag–Sn–S semiconductor thin films

Thin film of silver tin sulfides (Ag–Sn–S) has been deposited on indium tin oxide coated glass (ITO) substrates using potentiostatic cathodic electrodeposition technique. New procedure for the growth of Ag–Sn–S film is presented. An electrolyte solution containing Silver Nitrate (AgNO₃), Tin(II) Chloride (SnCl₂) and Sodium Thiosulfate (Na₂S₂O₃)in acidic solution (pH ~2) and at temperature of the bath 55 °C were used for the growth of Ag–Sn–S thin film. Prior to the deposition, a cyclic voltammetry technique was performed in binary (Ag–S, Sn–S) and ternary (Ag–Sn–S) systems. This study was carried out to examine the behavior of electroactive species at the electrode surface. Based on these results, the cathodic applied potential was fixed at −1000 mV versus Ag/AgCl to obtain a uniform and good adhesion of ternary thin film. After that, structural, morphological and optical performances of films have been investigated. The X-ray diffraction patterns of the samples demonstrate the presence of the orthorhombic phase of Ag₈SnS₆ at applied potential of −1000 mV versus Ag/AgCl. Based on the scanning electron microscopy (SEM), it was found that the surface morphology and grain size were strongly influenced by the presence of Sn and/or Ag in the electrolyte bath. The band gaps of binaries and ternary compound are evaluated from optical absorption measurements. Band gap of Ag₈SnS₆ determined from transmittance spectra is in the range 1.56 eV. Flat-band potential and free carrier concentration have been determined from Mott–Schottky plot and are estimated to be around 0.18 V and 2.21×10¹⁴ cm⁻³ respectively. The photoelectrochemical test of Ag₈SnS₆ was studied and the experimental observations are discussed in detail.     

Lanthanide–Organic Framework Nanothermometers Prepared by Spray‐Drying

Accurate, noninvasive, and self‐referenced temperature measurements at the submicrometer scale are of great interest, prompted by the ever‐growing demands in the fields of nanotechnology and nanomedicine. The thermal dependence of the phosphor's luminescence provides high detection sensitivity and spatial resolution with short acquisition times in, e.g., biological fluids, strong electromagnetic fields, and fast‐moving objects. Here, it is shown that nanoparticles of [(Tb_0.914Eu_0.086)₂(PDA)₃(H₂O)]·2H₂O (PDA = 1,4‐phenylenediacetic acid), the first lanthanide–organic framework prepared by the spray‐drying method, are excellent nanothermometers operating in the solid state in the 10–325 K range (quantum yield of 0.25 at 370 nm, at room temperature). Intriguingly, this system is the most sensitive cryogenic nanothermometer reported so far, combining high sensitivity (up to 5.96 ± 0.04% K^?1 at 25 K), reproducibility (in excess of 99%), and low‐temperature uncertainty (0.02 K at 25 K).     

Anisotropic Ag2S–Au Triangular Nanoprisms with Desired Configuration for Plasmonic Photocatalytic Hydrogen Generation in Visible/Near‐Infrared Region

Anisotropic Ag₂S‐edged Au‐triangular nanoprisms (TNPs) are constructed by controlling preferential overgrowth of Ag₂S as plasmonic photocatalysts for hydrogen generation. Under visible and near‐infrared light irradiation, Ag₂S‐edged Au‐TNPs exhibit almost fourfold higher efficiency (796 µmol h⁻¹ g⁻¹) than those of Ag₂S‐covered Au‐TNPs (216 µmol h⁻¹ g⁻¹) and pure Au‐TNPs in hydrogen generation. A single‐particle photoluminescence study demonstrates that the plasmon‐induced hot electrons transfer from Au‐TNPs to Ag₂S for hydrogen generation. Finite‐difference‐time‐domain simulations verify that the corners/edges of Au‐TNPs are high‐curvature sites with maximum electric field distributions facilitating hot electron generation and transfer. Therefore, Ag₂S‐edged Au‐TNPs are efficient plasmonic photocatalyst with the desired configurations for charge separation boosting hydrogen generation.     

Specific Contact Resistance Measurement of Screen-Printed Ag Metal Contacts Formed on Heavily Doped Emitter Region in Multicrystalline Silicon Solar Cells

Multicrystalline silicon (mc-Si) wafers are widely used to develop low-cost high-efficiency screen-printed solar cells. In this study, the electrical properties of screen-printed Ag metal contacts formed on heavily doped emitter region in mc-Si solar cells have been investigated. Sintering of the screen-printed metal contacts was performed by a co-firing step at 725°C in air ambient followed by low-temperature annealing at 450°C for 15 min. Measurement of the specific contact resistance (ρ _c) of the Ag contacts was performed by the three-point probe method, showing a best value of ρ _c = 1.02 × 10^?4 Ω cm² obtained for the Ag contacts. This value is considered as a good figure of merit for screen-printed Ag electrodes formed on a doped mc-Si surface. The plot of ρ _c versus the inverse of the square root of the surface doping level (N _s ^?½ ) follows a linear relationship for impurity doping levels N _s ≥ 10¹⁹ atoms/cm³. The power losses due to current traveling through various resistive components of finished solar cells were calculated by using standard expressions. Cross-sectional scanning electron microscopy (SEM) views of the Ag metal and doped mc-Si region show that the Ag metal is firmly coalesced with the doped mc-Si surface upon sintering at an optimum firing temperature of 725°C.     

Brookite Formation in TiO2?Ag Nanocomposites and Visible‐Light‐Induced Templated Growth of Ag Nanostructures in TiO2

TiO₂? Ag‐nanocomposites exhibit various desirable properties that make them suitable for a variety of applications, for example in photocatalysis and as bactericidal coatings. In this work, a new method for processing TiO₂? Ag nanocomposites is presented. The nanocomposite films are fabricated from one precursor solution with high silver loading of up to 50%. The resulting films exhibit a microstructure consisting of TiO₂? Ag_xO nanocomposites with a largely XRD‐amorphous TiO₂ matrix containing brookite nanocrystals. This specific microstructure absorbs in the visible range so that photoreduction of Ag ions can be accomplished by using visible light. The thin films can be patterned using simple shadow masks. The illuminated areas show a high density of self‐organized nanoparticles (SNPs) and nanorods (SNRs), which are templated by the TiO₂ porous network. The particle size can be tuned by varying the irradiation time. Most of the SNPs and SNRs form faceted crystals, which are mostly a combination of {111} and {110}. The application of these films as substrates for surface‐enhanced Raman scattering is shown. Enhancement factors as high as 4.6 × 10⁶ could be obtained using rhodamine 6G dye molecules. More applications should involve photocatalytic water purification using visible light.     

Stabilization of PbS Nanocrystals by Bovine Serum Albumin in its Native and Denatured States

PbS nanocrystals (NCs) are synthesized in aqueous phase within a temperature range of 40–80 °C in the presence of native and denatured states of bovine serum albumen (BSA) as the capping/stabilizing agent. The NCs are characterized with the help of field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray analysis. At 40 °C, large ball‐shaped NCs (145 ± 37 nm) with small surface protrusions are formed when 1 × 10^?4 g mL^?1 BSA is used. As the reaction temperature is increased towards 80 °C, the size of NCs decreases and they acquire somewhat cubic geometries (49.1 ± 7.0 nm) due to a change in the capping behavior of BSA between its native and denatured states. The native and denatured states of BSA are simultaneously studied by fluorescence spectroscopy using tryptophan emission, and pH measurements with respect to time and temperature. Gel electrophoresis is used to determine the polarity of the BSA capped NCs. Only the small sized NCs conjugated with relatively larger amounts of BSA show a displacement towards the positively charged electrode in comparison to larger NCs with lower amounts of BSA capping. It was concluded that the denatured state of BSA is more effective in controlling the crystal growth of PbS than its native state especially in the low concentration range.     

Interfacial Microstructure Evolution Between Sn-Zn Solders and Ag Substrate During Solid-State Annealing

In this study, solid-state interfacial reactions between Ag and Sn-Zn alloys with varying Zn content (0.1 wt.% to 9 wt.%) were investigated at 170°C. The reaction couples were prepared by electroplating Ag on the Sn-Zn alloy to avoid dissolution of Ag into the molten solder during soldering. The Zn content greatly influenced the reaction products and the interfacial microstructures. When the Zn content was less than 4 wt.%, Ag₃Sn and AgZn layers were simultaneously formed. Notably, Zn could actively diffuse through the Ag₃Sn layer and react with Ag to form the AgZn phase. With the proceeding reaction, small α-Ag particulates were produced within the AgZn phase. With 9 wt.% Zn, the dominant reactions formed Ag₅Zn₈ and AgZn layers. The interfacial microstructure evolved significantly with reaction time. Interface instability due to Zn depletion in the solder resulted in massive spalling of the Ag₅Zn₈ layer. The Ag₃Sn phase was then produced next to the AgZn layer. Moreover, another reaction couple, Sn-9 wt.%Zn/Sn(15 μm)/Ag, was prepared, in which fast interdiffusion between Zn and Ag across the Sn layer was demonstrated due to the strong chemical affinity of Zn.     

Interfacial reaction between multicomponent lead-free solders and Ag,Cu, Ni,and Pd substrates

The interfacial reaction between two prototype multicomponent lead-free solders, Sn-3.4Ag-1Bi-0.7Cu-4In and Sn-3.4Ag-3Bi-0.7Cu-4In (mass%), and Ag, Cu, Ni, and Pd substrates are studied at 250°C and 150°C. The microstructural characterization of the solder bumps is carried out by scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis. Ambient temperature, isotropic elastic properties (bulk, shear, and Young’s moduli and Poisson’s ratio) of these solders along with eutectic Sn-Ag, Sn-Bi, and Sn-Zn solders are measured. The isotropic elastic moduli of multicomponent solders are very similar to the eutectic Sn-Ag solder. The measured solubility of the base metal in liquid solders at 250°C agrees very well with the solubility limits reported in assessed Sn-X (X=Ag, Cu, Ni, Pd) phase diagrams. The measured contact angles were generally less than 15° on Cu and Pd substrates, while they were between 25° and 30° on Ag and Ni substrates. The observed intermediate phases in Ag/solder couples were Ag₃Sn after reflow at 250°C and Ag₃Sn and ζ (Ag-Sn) after solid-state aging at 150°C. In Cu/solder and Ni/solder couples, the interfacial phases were Cu₆Sn₅ and (Cu,Ni)₆Sn₅, respectively. In Pd/solder couples, only PdSn₄ after 60-sec reflow, while both PdSn₄ and PdSn₃ after 300-sec reflow, were observed.     

Imidazolium Polyesters: Structure–Property Relationships in Thermal Behavior,Ionic Conductivity,and Morphology

New bis(ω‐hydroxyalkyl)imidazolium and 1,2‐bis[N‐(ω‐hydroxyalkyl)imidazolium]ethane salts are synthesized and characterized; most of the salts are room temperature ionic liquids. These hydroxyl end‐functionalized ionic liquids are polymerized with diacid chlorides, yielding polyesters containing imidazolium cations embedded in the main chain. By X‐ray scattering, four polyesters are found to be semicrystalline at room temperature: mono‐imidazolium‐C₁₁‐sebacate‐C₆ ( 4e ), mono‐imidazolium‐C₁₁‐sebacate‐C₁₁ ( 4c ), bis(imidazolium)ethane‐C₆‐sebacate‐C₆ ( 5a ), and bis(imidazolium)ethane‐C₁₁‐sebacate‐C₁₁ ( 5c ), all with hexafluorophosphate counterions. The other imidazolium polyesters, including all those with bis(trifluoromethanesulfonyl)imide (TFSI^?) counterions, are amorphous at room temperature. Room temperature ionic conductivities of the mono‐imidazolium polyesters (4 × 10^?6 to 3 × 10^?5 S cm^?1) are higher than those of the corresponding bis‐imidazolium polyesters (4 × 10^?9 to 8 × 10^?6 S cm^?1), even though the bis‐imidazolium polyesters have higher ion concentrations. Counterions affect ionic conduction significantly; all polymers with TFSI^? counterions have higher ionic conductivities than the hexafluorophosphate analogs. Interestingly, the hexafluorophosphate polyester, 1,2‐bis(imidazolium)ethane‐C₁₁‐sebacate‐C₁₁ ( 5c ), displays almost 400‐fold higher room temperature ionic conductivity (1.6 × 10^?6 S cm^?1) than the 1,2‐bis(imidazolium)ethane‐C₆‐sebacate‐C₆ analog ( 5a , 4.3 × 10^?9 S cm^?1), attributable to the differences in the semicrystalline structure in 5c as compared to 5a . These results indicate that semicrystalline polymers may result in high ionic conductivity in a soft (low glass tranition temperature, T_g) amorphous phase and good mechanical properties of the crystalline phase.