Investigation of the Electronic Structure of CdS Nanoparticles with Sum Frequency Generation and Photoluminescence Spectroscopy

2019 ◽  
Vol 123 (45) ◽  
pp. 27712-27716 ◽  
Author(s):  
Jingjing Wang ◽  
Xuejiao Wu ◽  
Yuhan He ◽  
Wei Guo ◽  
Qinghong Zhang ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Sum Frequency Generation ◽  
Photoluminescence Spectroscopy ◽  
Cds Nanoparticles ◽  
Sum Frequency ◽  
Frequency Generation

Energetics at the Edge: Direct Optical Mapping of Bulk and Interfacial Electronic Structure in CdSe Quantum Dots using Broadband Electronic Sum Frequency Generation Microspectroscopy

2019 ◽  
Author(s):  
Brianna R. Watson ◽  
Benjamin Doughty ◽  
Tessa Calhoun
Keyword(s):  
Quantum Dots ◽  
Electronic Structure ◽  
Sum Frequency Generation ◽  
Cdse Quantum Dots ◽  
Trap States ◽  
Sum Frequency ◽  
Interfacial Electronic Structure ◽  
Wide Range ◽  
Frequency Generation ◽  
Gap States

Understanding and controlling the electronic structure of nanomaterials is the key to tailoring their use in a wide range of practical applications. Despite this need, many important electronic states are invisible to conventional optical measurements and are typically identified indirectly based on their inferred impact on luminescence properties. This is especially common and important in the study of nanomaterial surfaces and their associated defects. Surface trap states play a crucial role in photophysical processes yet remain remarkably poorly understood. Here we demonstrate for the first time that broadband electronic sum frequency generation (eSFG) microspectroscopy can directly map the optically bright and dark states of nanoparticles, including the elusive below gap states. This new approach is applied to model cadmium selenide (CdSe) quantum dots (QDs), where the energies of interfacial trap states have eluded direct optical characterization for decades. Our eSFG measurements show clear signatures of electronic transitions both above the band gap, which we assign to previously reported one- and two-photon transitions associated with the CdSe core, as well as broad spectral signatures below the bandgap that are attributed to interfacial trap states. In addition to the core states, this analysis reveals two distinct distributions of below gap states providing the first direct optical measurement of both shallow and deep trapping sites on this system. Finally, chemical modification of the surfaces via oxidation results in the relative increase in the signals originating from the interfacial trap states. Overall, our eSFG experiments provide an avenue to directly map the entirety of QD bulk and interfacial electronic structure, which is expected to open up opportunities to study how these materials are grown <i>in situ</i> and how surface states can be controlled to tune functionality.

Energetics at the Edge: Direct Optical Mapping of Bulk and Interfacial Electronic Structure in CdSe Quantum Dots using Broadband Electronic Sum Frequency Generation Microspectroscopy

2019 ◽  
Author(s):  
Brianna R. Watson ◽  
Benjamin Doughty ◽  
Tessa Calhoun
Keyword(s):  
Quantum Dots ◽  
Electronic Structure ◽  
Sum Frequency Generation ◽  
Cdse Quantum Dots ◽  
Trap States ◽  
Sum Frequency ◽  
Interfacial Electronic Structure ◽  
Wide Range ◽  
Frequency Generation ◽  
Gap States

Understanding and controlling the electronic structure of nanomaterials is the key to tailoring their use in a wide range of practical applications. Despite this need, many important electronic states are invisible to conventional optical measurements and are typically identified indirectly based on their inferred impact on luminescence properties. This is especially common and important in the study of nanomaterial surfaces and their associated defects. Surface trap states play a crucial role in photophysical processes yet remain remarkably poorly understood. Here we demonstrate for the first time that broadband electronic sum frequency generation (eSFG) microspectroscopy can directly map the optically bright and dark states of nanoparticles, including the elusive below gap states. This new approach is applied to model cadmium selenide (CdSe) quantum dots (QDs), where the energies of interfacial trap states have eluded direct optical characterization for decades. Our eSFG measurements show clear signatures of electronic transitions both above the band gap, which we assign to previously reported one- and two-photon transitions associated with the CdSe core, as well as broad spectral signatures below the bandgap that are attributed to interfacial trap states. In addition to the core states, this analysis reveals two distinct distributions of below gap states providing the first direct optical measurement of both shallow and deep trapping sites on this system. Finally, chemical modification of the surfaces via oxidation results in the relative increase in the signals originating from the interfacial trap states. Overall, our eSFG experiments provide an avenue to directly map the entirety of QD bulk and interfacial electronic structure, which is expected to open up opportunities to study how these materials are grown <i>in situ</i> and how surface states can be controlled to tune functionality.

Using Heterodyne-Detected Electronic Sum Frequency Generation To Probe the Electronic Structure of Buried Interfaces

2017 ◽  
Vol 121 (34) ◽  
pp. 18653-18664 ◽  
Author(s):  
Aaron P. Moon ◽  
Ravindra Pandey ◽  
Jon A. Bender ◽  
Daniel E. Cotton ◽  
Benny A. Renard ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Sum Frequency Generation ◽  
Sum Frequency ◽  
Buried Interfaces ◽  
Frequency Generation

Temperature Dependence of the Air/Water Interface Revealed by Polarization Sensitive Sum-Frequency Generation Spectroscopy

2018 ◽  
Author(s):  
Daniel R. Moberg ◽  
Shelby C. Straight ◽  
Francesco Paesani
Keyword(s):  
Temperature Dependence ◽  
Low Frequency ◽  
Potential Energy Function ◽  
Md Simulations ◽  
Sum Frequency Generation ◽  
Water Molecules ◽  
Water Interface ◽  
Sum Frequency ◽  
Air Water Interface ◽  
Frequency Generation

<div> <div> <div> <p>The temperature dependence of the vibrational sum-frequency generation (vSFG) spectra of the the air/water interface is investigated using many-body molecular dynamics (MB-MD) simulations performed with the MB-pol potential energy function. The total vSFG spectra calculated for different polarization combinations are then analyzed in terms of molecular auto-correlation and cross-correlation contributions. To provide molecular-level insights into interfacial hydrogen-bonding topologies, which give rise to specific spectroscopic features, the vSFG spectra are further investigated by separating contributions associated with water molecules donating 0, 1, or 2 hydrogen bonds to neighboring water molecules. This analysis suggests that the low frequency shoulder of the free OH peak which appears at ∼3600 cm−1 is primarily due to intermolecular couplings between both singly and doubly hydrogen-bonded molecules. </p> </div> </div> </div>

Bulk Contributions Modulate the Sum-Frequency Generation Spectra of Interfacial Water on Model Sea-Spray Aerosols

2018 ◽  
Author(s):  
Sandeep K. Reddy ◽  
Raphael Thiraux ◽  
Bethany A. Wellen Rudd ◽  
Lu Lin ◽  
Tehseen Adel ◽  
...  
Keyword(s):  
Single Layer ◽  
Sum Frequency Generation ◽  
Second Order ◽  
Interfacial Structure ◽  
Sea Spray ◽  
Third Order ◽  
Systematic Analysis ◽  
Sum Frequency ◽  
Structure Of Water ◽  
Frequency Generation

Vibrational sum-frequency generation (vSFG) spectroscopy is used to determine the molecular structure of water at the interface of palmitic acid monolayers. Both measured and calculated spectra display speci c features due to third-order contributions to the vSFG response which are associated with nite interfacial electric potentials. We demonstrate that theoretical modeling enables to separate the third-order contributions, thus allowing for a systematic analysis of the strictly surface-sensitive, second-order component of the vSFG response. This study provides fundamental, molecular-level insights into the interfacial structure of water in a neutral surfactant system with relevance to single layer bio-membranes and environmentally relevant sea-spray aerosols. These results emphasize the key role that computer simulations can play in interpreting vSFG spectra and revealing microscopic details of water at complex interfaces, which can be difficult to extract from experiments due to the mixing of second-order, surface-sensitive and third-order, bulk-dependent contributions to the vSFG response.

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