Transfer of Graphene with Protective Oxide Layers

Transfer of graphene, grown by Chemical Vapor Deposition (CVD), to a substrate of choice, typically involves deposition of a polymeric layer (typically, poly(methyl methacrylate, PMMA or polydimethylsiloxane, PDMS). These polymers are quite hard to remove without leaving some residues behind. Here we study a transfer of graphene with a protective thin oxide layer. The thin oxide layer is grown by Atomic Deposition Layer (ALD) on the graphene right after the growth stage on Cu foils. One can further aid the oxide-graphene transfer by depositing a very thin polymer layer on top of the composite (much thinner than the usual thickness) following by a more aggressive polymeric removal methods, thus leaving the graphene intact. We report on the nucleation growth process of alumina and hafnia films on the graphene, their resulting strain and on their optical transmission. We suggest that hafnia is a better oxide to coat the graphene than alumina in terms of uniformity and defects.Comment: 13 pgs, 13 figure

Elucidating the Ultrafast Dynamics of Photoinduced Charge Separation in Metalloporphyrin-Fullerene Dyads Across the Electromagnetic Spectrum

Metalloporphyrins are prominent building blocks in the synthetic toolbox of advanced photodriven molecular devices. When the central ion is paramagnetic, the relaxation pathways within the manifold of excited states are highly intricate so that unravelling the intramolecular energy and electron transfer processes is usually a very complex task. This fact is critically hampering the development of applications based on the enhanced coupling offered by the electronic exchange interaction. In this work, the dynamics of charge separation in a copper porphyrin-fullerene are studied with several complementary spectroscopic tools across the electromagnetic spectrum (from near-infrared to X-ray wavelengths), each of them providing specific diagnostics. Correlating the various rates clearly demonstrates that the lifetime of the photoinduced charge-separated state exceeds by about 10-fold that of the isolated photoexcited CuII porphyrin. As revealed by the spectral modifications in the XANES region, this stabilization is accompanied by a transient change in covalency around the CuII center, which is induced by an enhanced interaction with the C60 moiety. This experimental finding is further confirmed by state-of-the art calculations using DFT and TD-DFT including dispersion effects that explain the electrostatic and structural origins of this interaction, as the CuIIP cation becomes ruffled and approaches closer to the fullerene in the charge-separated state. From a methodological point of view, these results exemplify the potential of multielectron excitation features in transient X-ray spectra as future diagnostics of subfemtosecond electronic dynamics. From a practical point of view, this work is paving the way for elucidating out-of-equilibrium electron transfer events coupled to magnetic interaction processes on their intrinsic time-scales

Dialkylimidazolium chloroaluminates: Ab initio calculations, Raman and neutron scattering measurements

The Raman and neutron scattering spectra of 46 mol% AlCl[sub 3] -54 mol% 1-ethyl-3-methyl imidazolium chloride (EMIC) and 67 mol% AlCl[sub 3] - 33 mol% EMIC melts are presented. Ab initio molecular orbital calculations have been carried out on structures of chloroaluminate anion and EMI cation and the interaction between anion and cation

Effects of chemical modifications on photophysics and exciton dynamics of π -conjugation attenuated and metal-chelated photoconducting polymers.

Abstract Effects of two types of chemical modifications on photoconducting polymers consisting of polyphenylenevinylene (PPV) derivatives are studied by static and ultrafast transient optical spectroscopy as well as semi-empirical ZINDO calculations. The first type of modification inserts 2,2'-bipyridyl-5 -vinylene units (bpyV) in the PPV backbone, and the second type involves metal -chelation with the bpy sites. Photohuninescence and exciton dynamics of polymers 1 and 2 with PV:bpyV ratios of 1 and 3 were examined in solution, and compared to those of the homopolymer, poly(2,5-bis(2' -ethylhexyloxy)-l ,4-phenylenevinylene) (BEH-PPV), Similar studies were carried out for several metal-chelated polymers. These results can be explained by changes in n-conjugation throughout the polymer backbone. The attenuation in n-conjugation by the chemical modifications transforms a conducting polymer from one-dimensional semiconductor to molecular aggregates. Keywords poly(phenylene vinylene) derivatives, molecular aggregates, x-conjugation, time-resolved fast spectroscopy, chemical synthesis, semi-empirical and model calculations. Introduction In order to expand applications for conducting polymers, chemical modifications have been carried out by researchers l-s. These modifications may occur at the backbone or at the side groups of the polymers5'7-'0. In this study, the photophysics of two poly(phenylene vinylene) (PPV) derivatives which are chemically modified at the backbon

Dialkylimidazolium Chloroaluminates: Ab Initio Calculations, Raman and Neutron Scattering Measurements

The Raman and neutron scattering spectra of 46 mol% AlCl{sub 3} -54 mol% 1-ethyl-3-methyl imidazolium chloride (EMIC) and 67 mol% AlCl{sub 3} - 33 mol% EMIC melts are presented. Ab initio molecular orbital calculations have been carried out on structures of chloroaluminate anion and EMI cation and the interaction between anion and cation