In situ functionalization of gallium nitride powder with a porphyrin dye
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Matthew S. Rahn Department of Materials Science and Engineering, Pennsylvania State University, State College, Pennsylvania 16801, USA
Albena Ivanisevica) Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA (Received 6 February 2015; accepted 1 May 2015)
This work focused on the modification of milled GaN powder. Successful attachment of a porphyrin derivative to a GaN powder was performed via in situ functionalization in the presence of phosphoric acid. The GaN powder was imaged using scanning electron microscopy and was found to be heterogeneous in nature, adopting no consistent geometry in the aggregates. The aqueous stability of the porphyrin used was observed in deionized water and a solution of phosphoric acid using ultraviolet–visible spectroscopy. Surface chemistry was characterized with x-ray photoelectron spectroscopy and infrared spectroscopy, which identified evidence of successful functionalization through the presence of characteristic peaks. The interface stability of the covalent bond between GaN and porphyrin was evaluated using fluorescence spectroscopy and demonstrated no leaching of dye in water solutions for 20 days.
I. INTRODUCTION
Contributing Editor: Joan Redwing a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.152
to other III–V semiconductors. Recent work has shown that wet etching gallium nitride with phosphoric acid in the presence of adsorbates alters the surface morphology as well as the surface chemical composition.17 This combined process opens up the ability to change the semiconductor surface, which introduces opportunities for the development of functional interfaces as well as biosensing applications. The attachment of dye molecules to semiconductor interfaces is beneficial for applications, such as dyesensitized solar cells (DSSCs) and optical sensors.18 In DSSCs, the dye is crucial as it allows a wider bandwidth of light to be absorbed. Previous research has documented evidence that the porphyrin sensitizers provide high photonto-electron conversion efficiency.19 The most studied semiconductor in DSSCs so far is TiO2. Due to a low-electron mobility of TiO2 (less than 1 cm2/V s),20 there is a focused effort in identifying alternative wide band gap materials. One alternative to TiO2 that has been investigated is ZnO21; however, the instability of the surface interaction between the dye and semiconductor is cited for the recorded lowconversion efficiency. Recent use of GaN for DSSC applications has shown promise compared to transition metal oxides.22 Incorporating GaN into DSSCs provides a semiconductor with higher electron mobility than traditional TiO2. Additionally, the high-chemical stability of GaN under different environmental conditions and various solvents is beneficial for future solar cell devices.23
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Ó Materials Research Society 2015
Research efforts in the solution-based surface functionalization of inorganic materials have sought to expand the knowledge
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