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Understanding the Unique Electronic Properties of Nano Structures Using Photoemission Theory.

ABSTRACT: Newly emerging experimental techniques such as nano-ARPES are expected to provide an opportunity to measure the electronic properties of nano-materials directly. However, the interpretation of the spectra is not simple because it must consider quantum mechanical effects related to the measurement process itself. Here, we demonstrate a novel approach that can overcome this problem by using an adequate simulation to corroborate the experimental results. Ab initio calculation on arbitrarily-shaped or chemically ornamented nano-structures is elaborately correlated to photoemission theory. This correlation can be directly exploited to interpret the experimental results. To test this method, a direct comparison was made between the calculation results and experimental results on highly-oriented pyrolytic graphite (HOPG). As a general extension, the unique electronic structures of nano-sized graphene oxide and features from the experimental result of black phosphorous (BP) are disclosed for the first time as supportive evidence of the usefulness of this method. This work pioneers an approach to intuitive and practical understanding of the electronic properties of nano-materials.

SUBMITTER: Kwon S

PROVIDER: S-EPMC4669468 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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Understanding the Unique Electronic Properties of Nano Structures Using Photoemission Theory.

Kwon Soonnam S Choi Won Kook WK

Scientific reports 20151204

Newly emerging experimental techniques such as nano-ARPES are expected to provide an opportunity to measure the electronic properties of nano-materials directly. However, the interpretation of the spectra is not simple because it must consider quantum mechanical effects related to the measurement process itself. Here, we demonstrate a novel approach that can overcome this problem by using an adequate simulation to corroborate the experimental results. Ab initio calculation on arbitrarily-shaped ...[more]

PMID: 26634647

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Project description:In order to develop new organic materials for optoelectronic applications, a fundamental understanding of the electronic properties of specific chromophore combinations must be realized. To that end, we report "model" acceptor (A)-acceptor' (A')-acceptor (A) triads in which the pendants (A') we selected are well-known components of organic optoelectronic applications. Our pendants are sandwiched between two dialkoxyphenazine (A) through an alkyne bond. The A' was systematically increased in electron-deficiency from benzothiadiazole (BTD-P) to naphthalene diimide with octyl (NDI-O-P) or ethylhexyl groups (NDI-EH-P) to perylene diimide with ethylhexyl (PTCDI-EH-P) to assess changes in the electronic properties of the resultant molecules. Characterizations were performed using both experimental and theoretical methods. From optical and cyclic voltammetry, we found that the electron deficiency of each pendant was directly correlated to the energy level of the lowest unoccupied molecular orbital (E LUMO). When examining the simple molecular orbital diagrams produced at the B3LYP/6-31G* level of theory, the LUMOs were, as expected, primarily localized on the more electron-deficient pendants. In terms of the energy level of the highest occupied molecular orbital (E HOMO), the numerical values obtained experimentally also correlated with values obtained computationally. Attempting to construct a simplified model that would explain these correlated values was not as readily apparent, given the disparate physical characteristics of these compounds. For example, BTD-P and NDI-O-P/NDI-EH-P achieved planarity when computationally optimized, but PTCDI-EH-P adapted a "buckled" geometry on the central PTCDI, consequently forcing the attached phenazines out-of-plane. The title compounds showed solvent polarity-dependent fluorescence, which is indicative of intramolecular charge transfer. In conjunction with our theoretical study, the current system can be viewed as an extension of donor-acceptor-donor systems. Thermal properties characterized by differential scanning calorimetry revealed that reversible phase transitions were only observed for BTD-P. In addition, BTD-P was found to be an efficient gelator in 1,1,1-trichloroethane and toluene. The other compounds in this study did not form gels in any of the solvents tested, which may have been a result of the alkyl groups on the pendants hampering the fibrillation process.

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Understanding the Unique Electronic Properties of Nano Structures Using Photoemission Theory.

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Understanding the Unique Electronic Properties of Nano Structures Using Photoemission Theory.

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