Interface-Specific Two-Dimensional Electronic Sum Frequency Generation Spectroscopy

Abstract

High even-order surface/interface specific spectroscopy has the potential to provide more structural and dynamical information about surfaces and interfaces. In this work, we developed a novel fourth-order interface-specific two-dimensional electronic sum frequency generation (2D-ESFG) for structures and dynamics at surfaces and interfaces. A translating wedge-based identical pulses encoding system (TWINs) was introduced to generate phase-locked pulse pairs for coherent pump beams in 2D-ESFG. As a proof-of-principle experiment, fourth-order 2D-ESFG spectroscopy was used to demonstrate couplings of surface states for both n-type and p-type GaAs (100). We found surface dark state within the bandgap of the GaAs in 2D-ESFG spectra, which could not be observed in one-dimensional ESFG spectra. To our best knowledge, this is a first demonstration of interface-specific two-dimensional electronic spectroscopy. The development of the 2D-ESFG spectroscopy will provide new structural probes of spectral diffusion, conformational dynamics, energy transfer, and charge transfer for surfaces and interfaces.

Using Electronic Sum-Frequency Generation to Analyze the Interfacial Structure of Singlet Fission-Capable Perylenediimide Thin Films

“…Electronic sum-frequency generation (ESFG) is a measurement technique that selectively interrogates the electronic density of states and structural organization of molecular junctions and has been used to study liquid surfaces, − semiconductor surfaces, − and buried organic:inorganic junctions. − In an ESFG measurement, two pulses of light simultaneously impinge on a sample. One of these pules is a spectrally broad white light (WL) continuum that overlaps with different electronic resonances within the sample.…”

In Situ Spectroscopic Probing of Polarity and Molecular Configuration at Aerosol Particle Surfaces

“…Only a few techniques are available for investigating liquid surfaces, − not to mention the surfaces of liquid droplets. Second harmonic generation (SHG) and sum frequency generation (SFG) are two of the proven surface-sensitive methods to investigate liquid surfaces. ,− As a spectroscopic technique, SFG is anticipated to provide vibrational structures, ,− ,− as well as electronic characters, ,− both of which are essential to understanding chemical and physical properties of surfaces. Several groups demonstrated the applications of the SHG and SFG techniques in atmospheric science. ,− These pioneering works have shown cases of the powerful surface-specific techniques.…”

“…Several groups demonstrated the applications of the SHG and SFG techniques in atmospheric science. ,− These pioneering works have shown cases of the powerful surface-specific techniques. More than two decades ago, second harmonic scattering (SHS) was developed to extend the applications of the second-order nonlinear optical techniques from planar surfaces to curved surfaces. − Later, vibrationally sum frequency scattering (VSFS) was further developed to characterize vibrational chemical structures of micrometer to a few nanometer particle surfaces suspended in liquids. ,,− On the other hand, the development of electronic SFG and SHG spectroscopies has been left behind, even with tremendous effort. ,− For example, Shen et al showed interfacial electronic structure of molecules by tuning laser wavelengths . Eisenthal et al measured surface polarity at the air/water interface and interfacial electronic transition of a dye on TiO 2 surfaces .…”

In Situ Spectroscopic Probes for Structures and Processes at the Surface of Noble Metallic Nanoparticles

“…[185] Deng et al used 2D electronic sum-frequency generation (ESFG) to study the couplings of surface states for GaAs (111) and observed the surface dark state, which may not be revealed from conventional (1D) ESFG spectra. [186] Bian et al demonstrated that molecular structure and surface dynamics may be revealed by 2D-IR spectroscopy. [96] The effect of the interaction between metallic NPs and the surrounding materials on the ultrafast plasmon dynamics of Au NPs has also been discussed by Chen et al [187] However, applications of these studies to metallic NPs, especially those in colloids, are still rare.…”

“…used 2D electronic sum‐frequency generation (ESFG) to study the couplings of surface states for GaAs (111) and observed the surface dark state, which may not be revealed from conventional (1D) ESFG spectra. [ 186 ] Bian et al. demonstrated that molecular structure and surface dynamics may be revealed by 2D‐IR spectroscopy.…”