Entity

Time filter

Source Type


Singh V.,University of Kansas | Misra A.,University of Kansas | Parthasarathy R.,University of Kansas | Ye Q.,University of Kansas | And 2 more authors.
Journal of Biomedical Materials Research - Part B Applied Biomaterials | Year: 2013

The aim of this study is to investigate the mechanical behavior of model methacrylate-based dentin adhesives under conditions that simulate the wet oral environment. A series of monotonic and creep experiments were performed on rectangular beam samples of dentin adhesive in three-point bending configuration under different moisture conditions. The monotonic test results show a significant effect of loading rate on the failure strength and the linear limit (yield point) of the stress-strain response. In addition, these tests show that the failure strength is low, and the failure occurs at a smaller deformation when the test is performed under continuously changing moisture conditions. The creep test results show that under constant moisture conditions, the model dentin adhesives can have a viscoelastic response under certain low loading levels. However, when the moisture conditions vary under the same low loading levels, the dentin adhesives have an anomalous creep response accompanied by large secondary creep and high strain accumulation. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 101B: 1437-1443, 2013. Copyright © 2013 Wiley Periodicals, Inc. Source


Canovas E.,FOM Institute for Atomic and Molecular Physics | Moll P.,FOM Institute for Atomic and Molecular Physics | Jensen S.A.,FOM Institute for Atomic and Molecular Physics | Gao Y.,Technical University of Delft | And 5 more authors.
Nano Letters | Year: 2011

We report the direct and unambiguous determination of electron transfer rates and efficiencies from PbSe quantum dots (QDs) to mesoporous SnO 2 films. We monitor the time-dependent electron density within the oxide with picosecond time resolution using Terahertz spectroscopy, following optical excitation of the QDs using a femtosecond laser pulse. QD-oxide electron transfer occurs with efficiencies of ∼2% in our samples under 800 nm pumping with a marked dependence on QD size, ranging from ∼100 ps injection times for the smallest, ∼2 nm diameter QDs, to ∼1 ns time scale for ∼7 nm QDs. The size-dependent electron transfer rates are modeled within the framework of Marcus theory and the implications of the results for device design are discussed. © 2011 American Chemical Society. Source


Aerts M.,Technical University of Delft | Suchand Sandeep C.S.,Technical University of Delft | Gao Y.,Technical University of Delft | Savenije T.J.,Technical University of Delft | And 4 more authors.
Nano Letters | Year: 2011

We show that in films of strongly coupled PbSe quantum dots multiple electron-hole pairs can be efficiently produced by absorption of a single photon (carrier multiplication). Moreover, in these films carrier multiplication leads to the generation of free, highly mobile charge carriers rather than excitons. Using the time-resolved microwave conductivity technique, we observed the production of more than three electron-hole pairs upon absorption of a single highly energetic photon (5.7Eg). Free charge carriers produced via carrier multiplication are readily available for use in optoelectronic devices even without employing any complex donor/acceptor architecture or electric fields. © 2011 American Chemical Society. Source


Wang H.,Max Planck Institute for Polymer Research | Wang H.,University of Mainz | McNellis E.R.,Max Planck Institute for Polymer Research | Kinge S.,Materials Research and Development | And 3 more authors.
Nano Letters | Year: 2013

Photoinduced electron transfer processes from semiconductor quantum dots (QDs) molecularly bridged to a mesoporous oxide phase are quantitatively surveyed using optical pump-terahertz probe spectroscopy. We control electron transfer rates in donor-bridge-acceptor systems by tuning the electronic coupling strength through the use of n-methylene (SH-[CH2] n-COOH) and n-phenylene (SH-[C6H4] n-COOH) molecular bridges. Our results show that electron transfer occurs as a nonresonant quantum tunneling process with characteristic decay rates of βn = 0.94 ± 0.08 and βn = 1.25 per methylene and phenylene group, respectively, in quantitative agreement with reported conductance measurements through single molecules and self-assembled monolayers. For a given QD donor-oxide acceptor separation distance, the aromatic n-phenylene based bridges allow faster electron transfer processes when compared with n-methylene based ones. Implications of these results for QD sensitized solar cell design are discussed. © 2013 American Chemical Society. Source


Ten Cate S.,Technical University of Delft | Liu Y.,University of California at Irvine | Suchand Sandeep C.S.,Technical University of Delft | Kinge S.,Materials Research and Development | And 5 more authors.
Journal of Physical Chemistry Letters | Year: 2013

Carrier multiplication - the generation of multiple electron-hole pairs by a single photon - is currently of great interest for the development of highly efficient photovoltaics. We study the effects of infilling PbSe quantum-dot solids with metal oxides by atomic layer deposition on carrier multiplication. Using time-resolved microwave conductivity measurements, we find, for the first time, that carrier multiplication occurs in 1,2-ethanedithiol-linked PbSe quantum-dot solids infilled with Al2O3 or Al 2O3/ZnO, while it is negligible or absent in noninfilled films. The carrier-multiplication efficiency of the infilled quantum-dot solids is close to that of solution-dispersed PbSe quantum dots, and not significantly limited by Auger recombination. © 2013 American Chemical Society. Source

Discover hidden collaborations