Carlos Beauchamp

In situ measurements of stress evolution for nanotwin formation during pulse electrodeposition of copper

In situ stress measurements were performed during high frequency pulse electrodeposition of nanotwinned Cu thin films. Periodic stress changes during pulse-on and pulse-off periods were observed. The stress profile showed an abrupt increase in tensile stress to about 400 MPa during the pulse-on period and a stress relaxation during the pulse-off period. First-principles calculations predict that a complete relaxation of the tensile stress allows the formation of nanotwins separated by 28 nm or more. This is in good agreement with the results obtained from microstructural analysis of the Cu films fabricated during in situ stress measurements.

Three Dimensionally Structured CdTe Thin-Film Photovoltaic Devices with Self-Aligned Back-Contacts: Electrodeposition on Interdigitated Electrodes

Cadmium telluride is a commercially viable material for thin-film photovoltaic cells and is amenable to low cost electrochemical deposition. The majority-carrier type can be controlled by deposition conditions. We have produced back-contact thin-film solar cells by a self-aligned electrochemical deposition process onto two interdigitated electrodes. We report preliminary performance as a function of electrode geometry. The process and structure are readily amenable to optimization and should facilitate quantitative measurement and modeling of any candidate material that can be electrodeposited.

In Situ Stress Measurements during Electrodeposition of Au–Ni Alloys

We investigate the stress evolution in situ during the potentiostatic electrodeposition of metastable, nanostructured Au-Ni alloy films and develop a correlation between alloy composition, deposition rate, growth mode, and the observed stress state. We find that the internal stresses during Au-Ni deposition can be explained, at least for Ni-rich films, assuming a three-dimensional Volmer-Weber growth mode, where the stress is initially compressive, then transitions to tension, and finally remains tensile over longer times. The observed trends in maximum compressive stress, compressive-to-tensile transition thickness, and net steady-state tensile stress (SSTS) with alloy composition can all be related to the observed decrease in grain size with increasing Ni content. In particular, the SSTS is hypothesized to be the result of a dynamic competition between the stresses generated from nanoscale roughening and adatom insertion into grain boundaries. The Au-rich films, however, do not follow the above trends, suggesting that other stress mechanisms may be operative in this compositional range.

400-fold reduction in saturation field by interlayering

The buildup of stress with increasing thickness of magnetic thin films is a common phenomenon that often induces undesirable anisotropies that can convert an otherwise magnetically soft film into a magnetically hard one. We found that by interlayering such a magnetic thin film with films that are either not lattice matched or have a different crystal structure, reductions in the saturation field as large as 400-fold can be achieved. Differences in grain size appear to be responsible.

High performance dental resin composites with hydrolytically stable monomers

OBJECTIVE The objectives of this project were to: 1) develop strong and durable dental resin composites by employing new monomers that are hydrolytically stable, and 2) demonstrate that resin composites based on these monomers perform superiorly to the traditional bisphenol A glycidyl dimethacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) composites under testing conditions relevant to clinical applications. METHODS New resins comprising hydrolytically stable, ether-based monomer, i.e., triethylene glycol divinylbenzyl ether (TEG-DVBE), and urethane dimethacrylate (UDMA) were produced via composition-controlled photo-polymerization. Their composites contained 67.5wt% of micro and 7.5wt% of nano-sized filler. The performances of both copolymers and composites were evaluated by a battery of clinically-relevant assessments: degree of vinyl conversion (DC: FTIR and NIR spectroscopy); refractive index (n: optical microscopy); elastic modulus (E), flexural strength (F) and fracture toughness (KIC) (universal mechanical testing); Knoop hardness (HK; indentation); water sorption (Wsp) and solubility (Wsu) (gravimetry); polymerization shrinkage (Sv; mercury dilatometry) and polymerization stress (tensometer). The experimental UDMA/TEG-DVBE composites were compared with the Bis-GMA/TEGDMA composites containing the identical filler contents, and with the commercial micro hybrid flowable composite. RESULTS UDMA/TEG-DBVE composites exhibited n, E, Wsp, Wsu and Sv equivalent to the controls. They outperformed the controls with respect to F (up to 26.8% increase), KIC (up to 27.7% increase), modulus recovery upon water sorption (full recovery vs. 91.9% recovery), and stress formation (up to 52.7% reduction). In addition, new composites showed up to 27.7% increase in attainable DC compared to the traditional composites. Bis-GMA/TEGDMA controls exceeded the experimental composites with respect to only one property, the composite hardness. Significantly, up to 18.1% lower HK values in the experimental series (0.458GPa) were still above the clinically required threshold of approx. 0.4GPa. SIGNIFICANCE Hydrolytic stability, composition-controlled polymerization and the overall enhancement in clinically-relevant properties of the new resin composites make them viable candidates to replace traditional resin composites as a new generation of strong and durable dental restoratives.

Cariogenic potential of sweet flavors in electronic-cigarette liquids

Background Most electronic-cigarette liquids contain propylene glycol, glycerin, nicotine and a wide variety of flavors of which many are sweet. Sweet flavors are classified as saccharides, esters, acids or aldehydes. This study investigates changes in cariogenic potential when tooth surfaces are exposed to e-cigarette aerosols generated from well-characterized reference e-liquids with sweet flavors. Methods Reference e-liquids were prepared by combining 20/80 propylene glycol/glycerin (by volume fraction), 10 mg/mL nicotine, and flavors. Aerosols were generated by a Universal Electronic-Cigarette Testing Device (49.2 W, 0.2 Ω). Streptococcus mutans (UA159) were exposed to aerosols on tooth enamel and the biological and physiochemical parameters were measured. Results E-cigarette aerosols produced four-fold increase in microbial adhesion to enamel. Exposure to flavored aerosols led to two-fold increase in biofilm formation and up to a 27% decrease in enamel hardness compared to unflavored controls. Esters (ethyl butyrate, hexyl acetate, and triacetin) in e-liquids were associated with consistent bacteria-initiated enamel demineralization, whereas sugar alcohol (ethyl maltol) inhibited S. mutans growth and adhesion. The viscosity of the e-liquid allowed S. mutans to adhere to pits and fissures. Aerosols contained five metals (mean ± standard deviation): calcium (0.409 ± 0.002) mg/L, copper (0.011 ± 0.001) mg/L, iron (0.0051 ± 0.0003) mg/L, magnesium (0.017 ± 0.002) mg/L, and silicon (0.166 ± 0.005) mg/L. Conclusions This study systematically evaluated e-cigarette aerosols and found that the aerosols have similar physio-chemical properties as high-sucrose, gelatinous candies and acidic drinks. Our data suggest that the combination of the viscosity of e-liquids and some classes of chemicals in sweet flavors may increase the risk of cariogenic potential. Clinical investigation is warranted to confirm the data shown here.