Trion formation resolves observed peak shifts in the optical spectra of transition metal dichalcogenides

Monolayer transition metal dichalcogenides (TMDs) have the potential to unlock novel photonic and chemical technologies if their optoelectronic properties can be understood and controlled. Yet, recent work has offered contradictory explanations for how TMD absorption spectra change with carrier concentration, fluence, and time. Here, we test our hypothesis that the large broadening and shifting of the strong band-edge features observed in optical spectra arise from the formation of negative trions. We do this by fitting an ab initio based, many-body model to our experimental electrochemical data. Our approach provides an excellent, global description of the potential-dependent linear absorption data. We further leverage our model to demonstrate that trion formation explains the non-monotonic potential dependence of the transient absorption spectra, including through photoinduced derivative lineshapes for the trion peak. Our results motivate the continued development of theoretical methods to describe cutting-edge experiments in a physically transparent way.Comment: 5 pages, 5 figures main text. 4 pages, 6 figures, several passages of pseudocode SI, 66 reference

Breaking Barriers in Ultrafast Spectroscopy and Imaging Using 100 kHz Amplified Yb-Laser Systems

Ultrafast spectroscopy and imaging have become tools utilized by a broad range of scientists involved in materials, energy, biological, and chemical sciences. Commercialization of ultrafast spectrometers including transient absorption spectrometers, vibrational sum frequency generation spectrometers, and even multidimensional spectrometers have put these advanced spectroscopy measurements into the hands of practitioners originally outside the field of ultrafast spectroscopy. There is a technology shift occurring in ultrafast spectroscopy, made possible by new Yb-based lasers, that is opening exciting new experiments in the chemical and physical sciences. Amplified Yb-based lasers operate at many times the repetition rate of the previous generation of Ti:Sapphire amplifier technology, enabling improvements to long-standing techniques, new experiments, and the transformation of spectroscopies to microscopies. The impact of this technology will be felt across a great swath of the scientific communities. This review focuses on amplified Yb-based laser systems used in conjunction with 100 kHz spectrometers operating with shot-to-shot pulse shaping and detection. The shift to 100 kHz lasers is a transformative step in nonlinear spectroscopy and imaging, much like the dramatic expansion that occurred with the commercialization of Ti:Sapphire laser systems in the 1990s

Site-specific vibrational dynamics of the CD3 zeta membrane peptide using heterodyned two-dimensional infrared photon echo spectroscopy

Heterodyned two-dimensional infrared (2D IR) spectroscopy has been used to study the amide I vibrational dynamics of a 27-residue peptide in lipid vesicles that encompasses the transmembrane domain of the T-cell receptor CD3zeta. Using 1-C-13=O-18 isotope labeling, the amide I mode of the 49-Leucine residue was spectroscopically isolated and the homogeneous and inhomogeneous linewidths of this mode were measured by fitting the 2D IR spectrum collected with a photon echo pulse sequence. The pure dephasing and inhomogeneous linewidths are 2 and 32 cm(-1), respectively. The population relaxation time of the amide I band was measured with a transient grating, and it contributes 9 cm-1 to the linewidth. Comparison of the 49-Leucine amide I mode and the amide I band of the entire CD3zeta peptide reveals that the vibrational dynamics are not uniform along the length of the peptide. Possible origins for the large amount of inhomogeneity present at the 49-Leucine site are discussed. (C) 2004 American Institute of Physics

Characterizing Anharmonic Vibrational Modes of Quinones with Two-Dimensional Infrared Spectroscopy

Two-dimensional infrared (2D IR) spectroscopy was used to study the vibrational modes of three quinonesbenzoquinone, naphthoquinone, and anthraquinone. The vibrations of interest were in the spectral range of 1560–1710 cm^–1, corresponding to the in-plane carbonyl and ring stretching vibrations. Coupling between the vibrational modes is indicated by the cross peaks in the 2D IR spectra. The diagonal and off-diagonal anharmonicities range from 4.6 to 17.4 cm^–1 for the quinone series. In addition, there is significant vibrational coupling between the in-plane carbonyl and ring stretching vibrations. The diagonal anharmonicity, off-diagonal anharmonicity, and vibrational coupling constants are reported for benzoquinone, naphthoquinone, and anthraquinone

Direct Measurement of the Absolute Orientation of N3 Dye at Gold and Titanium Dioxide Surfaces with Heterodyne-Detected Vibrational SFG Spectroscopy

Light-harvesting dyes in dye-sensitized solar cells (DSSCs) must be designed not only to effectively harvest visible light but also to maintain an adsorption geometry at the solvent/TiO₂ interface that encourages electron injection. Electron injection is encouraged when the dye is adsorbed to the TiO₂ surface such that the LUMO of the dye is spatially near the surface. Furthermore, deleterious recombination pathways between the surface and dye are suppressed if the HOMO of the dye is spatially well-separated from the surface. Thus, measuring the configuration of dyes at these interfaces is important for understanding why some dyes perform better than others as well as providing insight into designing more ideal dyes. We investigate the adsorption geometry of N3 dye on gold and TiO₂ using heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). Incorporating heterodyne detection into our VSFG experiment provides both enhanced SFG signal and phase sensitivity, which enables the measurement of the absolute orientation of molecules at interfaces. On gold, we find that N3 adsorbs to the surface by binding through one of its isothiocyanate ligands at a 36° tilt angle from the surface normal. The other isothiocyanate ligand exhibits a tilt angle of 82° and thus does not interact with the interface as strongly. Conversely, on TiO₂, we find that N3 adsorbs to the surface through three carboxylic acid groups with both isothiocyanate ligands facing away from the surface at a 180° tilt angle from the surface normal. This adsorption geometry of N3 on the TiO₂ is arranged such that its LUMO, which resides primarily on the bipyridine ligands, is positioned near the surface while the HOMO, which resides primarily on the isothiocyanate ligands, is oriented far away from the surface. This study presents the first HD-VSFG spectra of N3 on nanoparticulate TiO₂ and on gold