Douglas G. Ivey

Solid state interfacial reactions in electrodeposited Cu/Sn couples

Abstract Cu/Sn couples, prepared by sequentially electroplating Cu and Sn layers on metallized Si wafers, were employed to study the microstructures, phases and the growth kinetics of Cu-Sn intermediate phases, when electroplated Cu/Sn couples were aged at room temperature or annealed at temperatures from 373 K to 498 K for various time. Only Cu6Sn5 formed in aged couples or couples annealed at temperature below 398 K. The Cu6Sn5 layer was continuous, but not uniform, with protrusions extending into the Sn matrix. When Cu/Sn couples were annealed at temperatures from 423 K to 498 K, two continuous and uniform Cn6Sn5/Cu3Sn layers formed within the reaction region between Sn and Cu. There were many voids near the Cu3Sn/Cu interface and within the Cu3Sn layer. Cu6Sn5 and Cu3Sn formations both follow parabolic growth kinetics with activation energies of 41.4 kJ/mol for Cu6Sn5 and 90.4 kJ/mol for Cu3Sn, respectively.

Microstructural characterization of Au/Sn solder for packaging in optoelectronic applications

Abstract Preliminary results on the feasibility of using co-evaporation of eutectic Au/Sn solder for semiconductor packaging are presented. Gold is electron beam evaporated, while Sn is thermally evaporated, onto Ti/Pt/Au metallized InP substrates. Electron microscopy is utilized to determine the composition and uniformity of the solder and to characterize interfacial reactions between the solder and the semiconductor metallization. Eutectic Au/Sn solder, several microns thick, can be deposited with intermittent substrate cooling. Heating of the solder during simulated reflow experiments results in dissolution of Au and Pt into the solder, with Pt going into substitutional solid solution in AuSn. Part of the Ti layer is consumed as well, forming Au4Ti containing Sn. Bonding tests, reveal solder joints with a uniform distribution of small pores, significantly less than 1 μm in size.

A Li-rich Layered@Spinel@Carbon heterostructured cathode material for high capacity and high rate lithium-ion batteries fabricated via an in situ synchronous carbonization-reduction method

A novel Layered@Spinel@Carbon heterostructure is successfully fabricated via an in situ synchronous carbonization-reduction process based on a bio-inspired coating method, which comprises a core of Li-rich layered (Rm) oxide, a spinel phase (Fdm) interlayer and a carbon nano-coating. This unique structure, which combines the advantages of the high capacity Li-rich layered structure, 3D fast Li+ diffusion channels of the spinel structure and the high conductivity of the carbon coating, shows extremely high discharge capacity (as high as 334.5 mA h g−1) and superior rate capability. This strategy may provide some new insights into the design and synthesis of various electrode materials for high performance energy storage devices.

Low temperature reactions of thin layers of Mn with Si

Reactions between manganese thin films and silicon substrates, annealed at relatively low temperatures ( 3 Si, Mn 5 Si 3 , and MnSi, were formed through a layered growth process. The formation sequence for these silicides was Mn 3 Si, MnSi, and then Mn 5 Si 3 . The unusual phenomena of coexistence of these three phases and simultaneous growth of two phases (MnSi and Mn 5 Si 3 ) were also observed. A model has been proposed to explain the growth behavior. The formation sequence of Mn 3 Si, MnSi, and then Mn 5 Si 3 , and simultaneous growth of MnSi and Mn 5 Si 3 , can be explained by considering both thermodynamic and kinetic effects. Only those reactions that are thermodynamically allowed and kinetically preferred can take place. Kinetic preference is determined by the composition in the reaction region, which is controlled by the diffusion flux of the moving reactant. The proposed model is also compared with existing models.

Electron microscopy of heavy metal waste in cement matrices

Ordinary Portland cements mixed with various amounts of chromium metal in the form of nitrates (Cr(NO3)3), to simulate industrial waste, have been studied by electron microscopy techniques, i.e. scanning electron and scanning transmission electron microscopy. Trivalent chromium was found to be chemically incorporated in all hydrated cement phases, and appeared to substitute for silicon in calcium silicate hydrate (C-S-H), which is the major product of hydration. Chromium was also concentrated in polycrystalline Ca-Cr-rich phases.

Reactions between Pd thin films and InP

The reactions between Pd thin films and (001) oriented InP have been studied in detail. Palladium was deposited on InP by electron beam evaporation to a thickness of 60 nm. Specimens were then annealed in vacuum at temperatures up to 500° C for as long as several days. An amorphous ternary phase (Pd≈3InP) formed during deposition. During annealing, several crystalline ternary phases were detected. Pd2InP and Pd5InP were detected at lower annealing temperatures,i.e. from 225–275° C. Pd2InP grew first, exhibiting an epitaxial relationship with InP, followed by preferred growth of Pd5InP within the Pd2InP layer. Both phases later decomposed (≈400° C) producing Pd2InP(II), which also grew epitaxially on InP. At temperatures greater than 400° C, Pd2InP(II) decomposed to Pdln and PdP2, which were thermodynamically stable in contact with InP.

Hierarchical Nanocomposite of Hollow N-Doped Carbon Spheres Decorated with Ultrathin WS2 Nanosheets for High-Performance Lithium-Ion Battery Anode

Hierarchical nanocomposite of ultrathin WS2 nanosheets uniformly attached on the surface of hollow nitrogen-doped carbon spheres (WS2@HNCSs) were successfully fabricated via a facile synthesis strategy. When evaluated as an anode material for LIBs, the hierarchical WS2@HNCSs exhibit a high specific capacity of 801.4 mA h g(-1) at 0.1 A g(-1), excellent rate capability (545.6 mA h g(-1) at a high current density of 2 A g(-1)), and great cycling stability with a capacity retention of 95.8% after 150 cycles at 0.5 A g(-1). The Li-ion storage properties of our WS2@HNCSs nanocomposite are much better than those of the previously most reported WS2-based anode materials. The impressive electrochemical performance is attributed to the robust nanostructure and the favorable synergistic effect between the ultrathin (3-5 layers) WS2 nanosheets and the highly conductive hollow N-doped carbon spheres. The hierarchical hybrid can simultaneously facilitate fast electron/ion transfer, effectively accommodate mechanical stress from cycling, restrain agglomeration, and enable full utilization of the active materials. These characteristics make WS2@HNCSs a promising anode material for high-performance LIBs.

Electrochemical Oxidation of Mn/MnO Films: Mechanism of Porous Film Growth

1M Na2SO4. The capacitance was estimated from the current vs time curve that is part of the CV data set. Integrating the area underneath the current vs time curve between 0 and 0.9 V gave an estimate of the total charge capacity of the film. This was then divided by the change in voltage, 0.9 V, to give an estimate of the capacitance of the film. The samples were imaged in a JEOL field emission scanning electron microscope FESEM at 5 kV without any conductive coating. Surface analysis of various films was carried out by X-ray photoelectron spectroscopy XPS using a Kratos AXIS 165 X-ray photoelectron spectrometer. A monochromatic Al source was used, operating at 210 W, giving a pass energy of 20 eV and a step size of 0.1 eV. The XPS analysis was carried out according to a procedure developed by Chigane and Ishikawa. 12,13 The Mn 3s peaks were used to approximate the valence using 3s peak-splitting widths from Chigane and Ishikawa. 12,13 These values are tabulated in Table I. The high-resolution scan makes it possible to measure the peaksplitting width to within 0.01 eV. The quantity of hydration in the samples can be determined from the deconvolution of the O 1s spectrum into three different spectra representing three different types of bonding: pure oxide bonding Mn‐O‐Mn, hydroxide bonding Mn‐O‐H, and free water bonding H‐O‐H. The area beneath each individual curve gives a semiquantitative analysis of the amount of that bond present. The hydration of the film is given by the quantity of the Mn‐O‐H bonds. The standards are listed in Table II.

Microstructure and preferred orientation of Au–Sn alloy plated deposits

Abstract In single metal electroplating, the microstructure produced is related to the current density or polarization. At low current densities, the growth of existing grains is favored, while at high current densities the formation of new grains is favored. The microstructures formed from alloy plating solutions have not been studied as thoroughly. In this study, pulsed current electrodeposits were formed using a gold–tin alloy plating solution based on ammonium citrate, KAuCl4, SnCl2-2H2O, sodium sulfite and l -ascorbic acid. A series of electroplating tests at average current densities ranging from 1.2 to 3.6 mA cm−2 were performed in order to study the effects of current density on the microstructure and preferred orientation. The types of microstructures produced from the plating solution described follow the trend of microstructures, which have been proposed for single metal electroplating. The preferred orientation in the deposits relates not only to the microstructure produced, but also to the phase or phases, which are present in the deposit.

Enhancing the Redox Tolerance of Anode-Supported SOFC by Microstructural Modification

The most commonly used solid oxide fuel cell (SOFC) anode material is a two-phase, nickel- and yttria-stabilized zirconia (Ni/YSZ) cermet. During fuel cell operation, this material is exposed to a reducing environment and thus remains a cermet; however, the metallic component of the anode may reoxidize in a commercial SOFC system. Following an initial study of the redox kinetics and dimensional changes after reduction and oxidation, as well as a baseline characterization of the electrochemical performance degradation and microstructural changes after redox cycling, two modifications to the anode microstructure were made in order to enhance cell redox tolerance: the anode functional layer was functionally graded and an oxidation barrier layer was added to the bottom of the cell in order to restrict the ability of oxygen to flow into the anode. Both types of microstructural modification significantly improved the cell redox tolerance compared with standard baseline redox tests.