Excited state charge transfer promoted Raman enhancement of copper phthalocyanine by twisted bilayer graphenes

• Published in: Carbon (New York) Vol. 188; pp. 305 - 314
• Main Authors: Cheon, Younghoon, Kim, Youngsam, Park, Minsuk, Oh, Jehyun, Koo, Eunhye, Sim, Eunji, Ju, Sang-Yong
• Format: Journal Article
• Language: English
• Published: New York Elsevier Ltd 01.03.2022; Elsevier BV
• Subjects: Bilayers; Charge transfer; Chemical mechanism; Copper; Copper phthalocyanine; Graphene; Metal phthalocyanines; Monolayers; Raman enhancement; Raman spectra; Raman spectroscopy; Spectrum analysis; Substrates; Twisted bilayer graphene; van Hove singularity; van Hove singularity; Chemical mechanism; Twisted bilayer graphene; Copper phthalocyanine; Raman enhancement; Charge transfer
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2021.11.070

Few atom thick, twisted bilayer graphene (tBLG) possesses a rotation angle (θ) dependent van Hove singularity (vHs). Fine-tuning vHs serves a potential method to enhance charge transfer (CT) in surface enhanced Raman spectroscopy. This study shows that tBLG having a specific θ promotes as high as a 1.7 times enhancement of the Raman signals of copper phthalocyanine (CuPc) as compared to that caused by single layer graphene (SLG). The results of a combination of reflection imaging spectroscopy and widefield Raman provide spatial and spectral information about both tBLG with θ ranging from 10.9 to 13.7° and the corresponding vHs. Comparison of Raman spectra of CuPc in presence and absence of tBLG demonstrates that a significant enhancement of certain CuPc vibrational modes occurs when the underlying tBLG possesses a θ = 12.2°, showing as high as 6.8 and 1.7 times enhancements of certain vibrational mode as compared to those of CuPc on bare and SLG substrates, respectively. Theoretical calculations indicate that a match between the energies of vHs of tBLG with those of frontier orbitals of CuPc facilitates CT from the distant SLG to CuPc. [Display omitted]