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1.
J Phys Chem B ; 114(31): 10200-8, 2010 Aug 12.
Article in English | MEDLINE | ID: mdl-20684644

ABSTRACT

Coherent anti-Stokes Raman scattering (CARS) microscopy is combined with spontaneous Raman scattering microspectroscopy and second harmonic generation (SHG) microscopy to interrogate the molecular alignment in dry and hydrated cellulose fibers. Two types of cellulose were investigated: natural cellulose I in cotton fibers and regenerated cellulose II in rayon fibers. On the basis of the orientation of the methylene symmetric stretching vibration, the molecular alignment of cellulose microfibrils is found to be conserved on the micrometer scale. Whereas the molecular orientation in cotton shows modest variability along the fiber, the alignment of the cellulose units in rayon is highly consistent throughout the fiber. The ordered alignment is retained upon fiber hydration. Upon hydration of the cellulose fibers, an anisotropic electronic contribution is observed, which indicates an ordered incorporation of water molecules into the fiber structure. The third-order and second-order electronic polarizability of cellulose I are directed along the axis of the polyglucan chain. No second-order optical response is observed in cellulose II, supporting the antiparallel arrangement of the polyglucan chains in regenerated cellulose.


Subject(s)
Cellulose/chemistry , Microscopy/methods , Spectrum Analysis, Raman/methods , Water/chemistry , Cotton Fiber , Electrons
3.
J Biomed Opt ; 14(4): 044019, 2009.
Article in English | MEDLINE | ID: mdl-19725730

ABSTRACT

Coherent anti-Stokes Raman scattering (CARS) microscopy is used to determine the distribution and concentration of selected compounds in intact human hair. By generating images based on ratiometric CARS contrast, quantitative concentration maps of both water and externally applied d-glycine are produced in the cortex of human hair fibers. Both water and d-glycine are found to homogeneously distribute throughout the cortical regions of the hair. The ability to selectively detect molecular agents in hair fibers is of direct relevance to understanding the chemical and physical mechanisms that underlie the performance of hair-care products.


Subject(s)
Algorithms , Body Water/chemistry , Hair/chemistry , Microscopy/methods , Skin Tests/methods , Spectrum Analysis, Raman/methods , Humans
4.
Nano Lett ; 9(2): 860-3, 2009 Feb.
Article in English | MEDLINE | ID: mdl-19161261

ABSTRACT

We demonstrate a bilayer photovoltaic device consisting of a heterojunction between colloidal cadmium selenide (CdSe) quantum dots (QDs) and a wide band gap organic hole-transporting thin film of N,N'-diphenyl-N,N'-bis(3-methylphenyl)[1,1'-biphenyl]-4,4'-diamine (TPD) molecules. The active light-absorbing film of QDs is nondestructively printed onto TPD using microcontact stamping. Indium-tin-oxide (ITO) provides the top contact. The resulting device structure can accommodate different size QDs, produces an exceptionally large open circuit voltage (0.8 V) for an architecture with symmetric electrodes, and yields an internal quantum efficiency of 10% at the first QD absorption peak.

5.
J Am Chem Soc ; 128(40): 13032-3, 2006 Oct 11.
Article in English | MEDLINE | ID: mdl-17017765

ABSTRACT

On the basis of evidence from 31P NMR spectroscopy, and using PbSe as a model, we propose two simultaneous mechanisms through which "monomers" are formed in preparations of lead chalcogenide nanocrystals (NCs). In one mechanism, selenium is delivered as a Se2- species, whereas in the other, Se0 reacts with metal already reduced by the organophosphine. This latter mechanism helps explain the sensitivity of NC preparations to the purity of organophosphines and allows the rational modification of batch NC reactions to increase yield.

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