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Continuous and patterned deposition of functional block copolymer thin films using electrospray
Hu, Hanqiong,Toth, Kristof,Kim, Myungwoong,Gopalan, Padma,Osuji, Chinedum O. Cambridge University Press (Materials Research Soc 2015 MRS Communications Vol.5 No.2
<▼1><B>Abstract</B><P/></▼1><▼2><P>We report the use of electrospray to continuously deposit thin films, including patterned films, of a block copolymer (BCP). High substrate temperatures led to vertically oriented cylindrical microdomains at the film surface independent of the solvent composition and deposition rates utilized. Conversely, low substrate temperatures resulted in morphologies that were more sensitive to these parameters, with poorly ordered films of globular structures observed at the lowest temperatures considered. The deposition pattern is defined by spatially varying the electric field at the substrate using an underlying charged grid. These results open up new possibilities for patterned deposition of BCP films with morphological control.</P></▼2>
Effect of Dipolar Molecule Structure on the Mechanism of Graphene-Enhanced Raman Scattering
Joo, Yongho,Kim, Myungwoong,Kanimozhi, Catherine,Huang, Peishen,Wong, Bryan M.,Singha Roy, Susmit,Arnold, Michael S.,Gopalan, Padma American Chemical Society 2016 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.120 No.25
<P>Graphene-enhanced Raman scattering (GERS) is a promising characterization technique which uses a single layer of graphene. As the electronic coupling of adsorbates with graphene leads to enhancement in the Raman signal, it is of immense interest to explore the factors that affect the coupling of the adsorbates with graphene. To probe this effect we have designed and synthesized a series of dipolar molecules with the general structure, N-ethyl-N-(2-ethyl(1-pyrenebutyrate)-4-(4-R-phenylazo)aniline) where the R-groups are varied from methoxy (-OCH3), methyl (-CH3), hydrogen (-H), nitrile (-CN), nitro (-NO2) to tricyanofuran (TCF) groups. This systematically changes the dipole moments and electronic/optical band gap of the molecules. By noncovalently interfacing these molecules on graphene, the Raman signal is enhanced by a factor of 40-90 at the excitation wavelength of 532 nm. Measurements of the Raman enhancement factor and Raman cross section are complemented with DFT calculations to correlate the dipole moment and the energy level of the hybrid to the Raman scattering efficiency. These studies highlight the relevance of the dipolar nature of chromophores, which determines their dipole moment and the band gap, and the resulting electronic coupling to graphene which simultaneously alters the energy level of the orbitals in the molecule and the Fermi level in graphene, resulting in efficient Raman excitations and GERS.</P>