K. C. Hewitt

The electrochemical reaction of Li with amorphous Si-Sn alloys

Si12x Snx samples for 0 , x , 0.5 were prepared by magnetron sputtering using a combinatorial materials science approach. The room-temperature resistivity and X-ray diffraction ~XRD! patterns of the samples were used to select materials having both an amorphous structure and good conductivity for further study. The reaction of lithium with amorphous Si0.66Sn0.34 was then studied by electrochemical methods and by in situ XRD. The electrode material apparently remains amorphous throughout all portions of the charge and discharge profile, in the range 0 , x , 4.4 in LixSi0.66Sn0.34 . No crystalline phases are formed, unlike the situation when lithium reacts with tin. Using the Debye scattering formalism, we show that the XRD patterns of the a-Si0.66Sn0.34 starting material and a-Li4.4Si0.66Sn0.34 can be explained by the same local atomic arrangements as found in crystalline Si and Li4.4 Si or Li4.4 Sn, respectively. In fact, the in situ XRD patterns of a-LixSi0.66Sn0.34 , for any x, can be well approximated by a linear combination of the patterns for x 5 0 and x 5 4.4. This suggests that predominantly only two local environments for Si and Sn are found at any value of x in a-LixSi0.66Sn0.44 . However, based on differential capacity vs. potential results for Li/a-Si 0.66Sn0.34 there is no evidence for two-phase regions during the charge and discharge profile. Thus, the two local environments must appear at random throughout the particles. We speculate that the charge-discharge hysteresis in the voltage-capacity profile of Li/ a-LixSi0.66Sn0.34 cells is caused by the energy dissipated during the changes in the local atomic environment around the host atoms.

Electrochemistry of InSb as a Li insertion host problems and prospects

Ballmilling of In and Sb has been used to produce InSb for use in electrochemical and in situ X-ray diffraction studies (XRD) of Li/l MLiPF 6 ethylene carbonate:diethyl carbonate/InSb cells. The cell capacity decays rapidly when cycled between 0 and 1.3 V, while the capacity reduction is less pronounced when cycling is restricted to the 0.65-1.4 V range. In situ XRD studies reveal that Li 3 Sb and in are termed during the tirst plateau labove 0.65 V). according to the reaction 3Li 4 InSb - Li 3 Sb + In. The indium product subsequendy reacts with Li forming the InLi x phases InLi and In 4 Li 7 in sequence. When cells are cycle in the absence of InLi x formation) capacity retention improves significantly, remaining relatively constant near 250 mAh/g. Detailed in situ XRD studies of these cells suggest that 0.27 Li atoms per InSb may be intercalated during a sharp drop in the cell potential, acconling to the reaction xLi + InSb. LiInSb (v max - 0.27). This intercalation accounts for only a small (about. 30 mAh/g) fraction of the overall capacity of 680 mAh/g. Consequently, it appears that the reactivity of In and Sb with Li. not the structure type, detemines the reaction path. Therefore. InSb is not an attractive intercalation host for Li, in contrast to the claims made in the literature.

Effect of Heat Treatment on Si Electrodes Using Polyvinylidene Fluoride Binder

The electrochemical performance of Si electrodes using polyvinylidene fluoride binder heated at different temperatures ranging from 150 to 350°C was investigated. Compared to unheated electrodes that have no capacity after the first formation cycle, the heat-treated electrodes show an increasingly improved cycling performance as the heating temperature increases from 150 to 300°C. In particular, Si electrodes heated at 300°C retain a specific capacity of ∼600 mAh/g for 50 cycles with a lower cutoff potential of 0.170 V vs Li/Li + . The reasons for such improvements are considered based on results from thermal analysis, optical microscopy, and adhesion tests. It is suggested that heat-treatment improves the binder distribution, the adhesion to the Si particles and to the substrate, thereby leading to a better cycling performance.

Anomalous, High-Voltage Irreversible Capacity in Tin Electrodes for Lithium Batteries

Anomalous, high-voltage irreversible capacity is observed in electrodeposited and sputtered Sn films when used as working electrodes in electrochemical lithium cells. Sn electrodes can function as expected in Li/Sn cells provided the upper cutoff potential, while removing lithium from the Sn electrode, is kept below about 1.4 V. However, when the upper cutoff potential is increased to about 1.5 V and above, an anomalous irreversible high-voltage plateau in the voltage-capacity curve is often observed during subsequent lithiation. We discuss the relationship between the recharge cutoff voltage and the presence of anomalous high-voltage irreversible capacity. The dependence of the amount of anomalous, high-voltage irreversible capacity vs. discharge rate of the cell is investigated. A model is proposed to explain the anomalous high-voltage irreversible capacity, including strategies to avoid it. One of the strategies is to alloy Sn with Cu.

Surface-sensitive Raman spectroscopy of collagen I fibrils.

Collagen fibrils are the main constituent of the extracellular matrix surrounding eukaryotic cells. Although the assembly and structure of collagen fibrils is well characterized, very little appears to be known about one of the key determinants of their biological function-namely, the physico-chemical properties of their surface. One way to obtain surface-sensitive structural and chemical data is to take advantage of the near-field nature of surface- and tip-enhanced Raman spectroscopy. Using Ag and Au nanoparticles bound to Collagen type-I fibrils, as well as tips coated with a thin layer of Ag, we obtained Raman spectra characteristic to the first layer of collagen molecules at the surface of the fibrils. The most frequent Raman peaks were attributed to aromatic residues such as phenylalanine and tyrosine. In several instances, we also observed Amide I bands with a full width at half-maximum of 10-30 cm(-1). The assignment of these Amide I band positions suggests the presence of 3(10)-helices as well as α- and β-sheets at the fibrils surface.

The amorphous range in sputtered Si–Al–Sn films

Abstract A magnetron sputtering system modified to produce ternary films has been used to map large portions of the ternary phase diagram for the Si–Al–Sn system. The system is unconventional because the stoichiometries of the elements sputtered on the substrates vary linearly with position and in an orthogonal manner. Variations in the composition and structure vs. position were obtained by electron microprobe analysis and X-ray diffraction, respectively. We found that the amorphous range spans all compositions with over 60 at.% silicon. Compositions containing less than 50 at.% silicon were mixtures of the amorphous phase and Sn and/or Al. No intermetallic phases were observed. A ternary non-equilibrium ‘phase diagram’ showing the phases produced in the sputtered films was constructed.

Electrochemical and in situ XRD studies of the Li reaction with combinatorially sputtered Mo1-xSnx (0 ≤ x ≤ 0.50) thin films

b3M Company, 3M Center, St. Paul, Minnesota, 55144, USA Detailed electrochemical studies of the reaction of Li with combinatorially sputter-deposited BCC ( x 0.4) Mo12xSnx thin films are reported for 0.05 0.4), the appearance and growth of new dq/dV peaks after the first cycle is consistent with the aggregation of Sn clusters and the formation of Li-Sn phases. Inclusion of about 20% oxygen in nanostructured films seems to prevent Sn aggregation and improve the cycling performance markedly. The best materials give specific capacities near 350 mAh/g, have densities near 9 g/cc and cycle well. This could be the first report of true topotactic Li insertion into a metal host.

Synthesis and characterization of gold nanostructured Chorin e6 for Photodynamic Therapy

Photodynamic therapy is an alternative treatment for cancer based on cellular uptake of a photosensitizer, illuminated with an appropriate wavelength in the presence of oxygen. A cascade of reactions generates reactive oxygen species leading to cell death. Using carbodiimide chemistry, chlorin e6 (Ce6) was covalently bonded to thiourea, and (via the sulphur end group) to gold nanoparticles (AuNPs), forming the Ce6-AuNP complex. Ce6 absorbs in the range 650-680nm, where the coefficient of biological tissue absorption is low (part of the therapeutic window), which is ideal for biological application. Transmission Electron Microscopy, UV-vis spectroscopy, Fourier transform Infrared Spectroscopy and Zeta potential measurements were completed to characterize the Ce6-AuNP complex. The bare AuNPs have an average diameter of 18±4nm. A line of human breast carcinoma cells (MDA-MB-468) was used to determine whether Ce6 functionalization to AuNPs potentiate its activity. Trypan blue assays were used to assess cell viability. In the absence of light, Ce6 either alone or bounded to AuNPs was not cytotoxic. When irradiated at 660nm, the cytotoxicity of Ce6-AuNP was higher than Ce6 alone for MDA-MB-468 cells using 4h incubation. AuNPs without Ce6 showed no cytotoxic.

High-throughput resistivity apparatus for thin-film combinatorial libraries

An apparatus, capable of measuring the dc resistance versus temperature of a 49-member library prepared by thin-film deposition techniques was designed and tested. The library is deposited by dc magnetron sputtering onto 10.16cm×10.16cm alumina substrates on which are placed aluminum masks consisting of 8mm diam holes cut on a 7×7 grid, the center-to-center spacing being 10.15mm. Electrical contact to the library is made in a standard van der Pauw geometry using 196 spring-loaded, gold-coated pins, four pins for each member of the library. The temperature is controlled using a helium refrigerator in combination with a liquid-nitrogen radiation shield that greatly reduces radiative heating of the sample stage. With the radiation shield, the cold finger is able to sustain a minimum temperature of 7K and the sample stage a minimum temperature of 27K. The temperature (27–291K) dependent dc resistivity of a thin-film silver library of varying thickness (48–639nm) is presented to highlight the capabilities of t...

Combinatorial synthesis and rapid characterization of Mo1−xSnx (0⩽x⩽1) thin films

Thin films of Mo1−xSnx, continuously and linearly mapped for 0<x<1, have been prepared by d.c. magnetron sputter deposition under various growth conditions. X-ray diffraction results indicate that as x in high-pressure deposited Mo1−xSnx increases from 0 to approximately 0.45, the bcc lattice expands and no new phases are formed. At low deposition pressures, Mo3Sn, a β-tungsten structured phase, is formed along with the bcc Mo–Sn solid solution for 0.1<x<0.3. The variation of the lattice parameter for this intermetallic phase also indicates that solid solutions, possibly of the form Mo3+ySn, are being formed. These materials are of special interest as anode candidates in lithium-ion batteries.